U.S. patent application number 17/466556 was filed with the patent office on 2022-03-17 for filler compositions comprising microfibrillated cellulose and microporous inorganic particulate material composites for paper and paperboard applications with improved mechanical properties.
This patent application is currently assigned to FIBERLEAN TECHNOLOGIES LIMITED. The applicant listed for this patent is FIBERLEAN TECHNOLOGIES LIMITED. Invention is credited to Jonathan PHIPPS, Thomas REEVE-LARSON, David R. SKUSE.
Application Number | 20220081839 17/466556 |
Document ID | / |
Family ID | |
Filed Date | 2022-03-17 |
United States Patent
Application |
20220081839 |
Kind Code |
A1 |
REEVE-LARSON; Thomas ; et
al. |
March 17, 2022 |
FILLER COMPOSITIONS COMPRISING MICROFIBRILLATED CELLULOSE AND
MICROPOROUS INORGANIC PARTICULATE MATERIAL COMPOSITES FOR PAPER AND
PAPERBOARD APPLICATIONS WITH IMPROVED MECHANICAL PROPERTIES
Abstract
Method of making a filler composition comprising
microfibrillated cellulose and one or more microporous inorganic
particulate material and methods of making papermaking furnishes
and paper products comprising microfibrillated cellulose and one or
more microporous inorganic particulate material.
Inventors: |
REEVE-LARSON; Thomas; (St.
Austell, GB) ; PHIPPS; Jonathan; (Gorran Haven
Cornwall, GB) ; SKUSE; David R.; (Truro Cornwall,
GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
FIBERLEAN TECHNOLOGIES LIMITED |
Par |
|
GB |
|
|
Assignee: |
FIBERLEAN TECHNOLOGIES
LIMITED
Par
GB
|
Appl. No.: |
17/466556 |
Filed: |
September 3, 2021 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
PCT/US2021/049034 |
Sep 3, 2021 |
|
|
|
17466556 |
|
|
|
|
63077167 |
Sep 11, 2020 |
|
|
|
International
Class: |
D21H 11/18 20060101
D21H011/18; D21H 11/12 20060101 D21H011/12; D21H 17/68 20060101
D21H017/68; D21H 17/67 20060101 D21H017/67; D21H 17/37 20060101
D21H017/37; D21H 17/00 20060101 D21H017/00; D21H 21/08 20060101
D21H021/08 |
Claims
1-120. (canceled)
121. A paper or paperboard filler composition comprising
microfibrillated cellulose (MFC) and one or more microporous
inorganic particulate material for addition to a papermaking
furnish for the manufacture of paper or paperboard, wherein the MFC
and the one or more microporous inorganic particulate material
impart mechanical properties to the paper or paperboard that are
improved compared to paper and paperboard products made from an
identical papermaking furnish not containing MFC and the one or
more microporous inorganic particulate material.
122. The filler composition according to claim 121, wherein the one
or more microporous inorganic particulate material is selected from
the group consisting of: calcined clay, kaolin, kaolinite,
amorphous aluminum silicates, Scalenohedral precipitated calcium
carbonate, aragonite precipitated calcium carbonate, chemically
aggregated filler materials, diatomaceous earth, and milled
expanded perlite.
123. The filler composition according to claim 121, wherein the
microporous inorganic material comprises calcined clay.
124. The filler composition according to claim 121, wherein the
microporous inorganic material comprises kaolin.
125. The filler composition according to claim 121, wherein the
microporous inorganic material comprises kaolinite.
126. The filler composition according to claim 121, wherein the
microporous inorganic material comprises calcined clay.
127. The filler composition according to claim 121, wherein the
microporous inorganic material comprises amorphous aluminum
silicates.
128. The filler composition according to claim 121, wherein the
microporous inorganic material comprises Scalenohedral precipitated
calcium carbonate.
129. The filler composition according to claim 121, wherein the
microporous inorganic particulate material comprises at least two
microporous inorganic particulate material selected from the group
consisting of: calcined clay, kaolin, kaolinite, amorphous aluminum
silicates, Scalenohedral precipitated calcium chloride, aragonite
precipitated calcium carbonate, chemically aggregated filler
materials, diatomaceous earth, and milled expanded perlite.
130. The filler composition according to claim 121, wherein the
papermaking furnish comprises one or more pulp selected from
softwood pulps.
131. The filler composition according to claim 130, wherein the
softwood pulp is selected from the group consisting of: spruce,
pine, fir, larch and hemlock and mixed softwood pulps.
132. The filler composition according to claim 121, wherein the
papermaking furnish comprises one or more pulp selected from
hardwood pulps.
133. The filler composition according to claim 132, wherein the
hardwood pulp is selected from the group consisting of: eucalyptus,
aspen and birch, and mixed hardwood pulps.
134. The filler composition according to claim 121, wherein the
pulp source for the papermaking furnish is selected from the group
consisting of: eucalyptus pulp, spruce pulp, pine pulp, beech pulp,
hemp pulp, acacia, cotton pulp, and mixtures thereof.
135. The filler composition according to claim 121, wherein the
pulp source for the papermaking furnish is selected from the group
consisting of: Nordic Pine, Black Spruce, Radiata Pine, Southern
Pine, Enzyme-Treated Nordic Pine, Douglas Fir, Dissolving Pulp,
Birch, Eucalyptus, Acacia, Mixed European Hardwood, Mixed Thai
Hardwood, Tissue Dust, Cotton, Abaca, Sisal, Bagasse, Kenaf,
Miscanthus, Sorghum, Giant Reed and Flax.
136. The filler composition of claim 121, wherein the mechanical
property is selected from one or more of Tensile Strength, Tensile
Elongation, Bulk, Tensile Stiffness, Bending Stiffness, Porosity,
Burst and Tear Strength, and Tensile Strength in the `Z`
direction.
137. The filler composition according to claim 121, wherein the
microfibrillated cellulose has a modal fibre particle size ranging
from about 0.1 .mu.m-500 .mu.m.
138. The method according to claim 121, wherein the one or more
microporous inorganic particulate material has a median particle
size (d.sub.50) ranging from about 3 .mu.m to about 50 .mu.m.
139. The method according to claim 121, wherein the one or more
microporous inorganic particulate material has a median particle
size (d.sub.50) ranging from about 3 .mu.m to about 6 .mu.m.
140. The filler composition according to claim 121, wherein the one
or more microporous inorganic particulate material and
microfibrillated cellulose composite may be associated with one or
more dispersing agents selected from the group consisting of:
homopolymers or copolymers of polycarboxylic acids and/or their
salts or derivatives, esters based on, acrylic acid, methacrylic
acid, maleic acid, fumaric acid, itaconic acid; acryl amide or
acrylic esters, methylmethacrylate, or mixtures thereof; alkali
polyphosphates, phosphonic-, citric- and tartaric acids and the
salts or esters thereof, and mixtures thereof.
141. The filler composition according to claim 121, wherein the one
or more microporous inorganic particulate material and
microfibrillated cellulose composite is provided in the form of a
powder.
142. The filler composition according to claim 121, wherein the one
or more microporous inorganic particulate material and
microfibrillated cellulose composite is provided in the form of a
suspension.
143. The filler composition according to claim 142, wherein the
suspension is an aqueous suspension.
144. The filler composition according to claim 143, wherein the
aqueous suspension is a pumpable liquid.
145. The filler composition according to claim 121, wherein the one
or more microporous inorganic particulate material comprises a
blend of a first and second microporous inorganic particulate
material, wherein the ratio of the first microporous inorganic
particulate material to the second microporous inorganic
particulate material may range from about 10:90 to about 90:10 by
weight.
146. The filler composition according to claim 121, wherein the one
or more microporous inorganic particulate material comprises a
blend of a first and second microporous inorganic particulate
material, wherein the ratio of the first microporous inorganic
particulate material to the second microporous inorganic
particulate material may range from about 20:80 to about 80:20 by
weight.
147. The filler composition according to claim 121, wherein the one
or more microporous inorganic particulate material comprises a
blend of a first and second microporous inorganic particulate
material, wherein the ratio of the first microporous inorganic
particulate material to the second microporous inorganic
particulate material may range from about 25:75 to about 75:25 by
weight.
148. The filler composition according to claim 121, wherein the one
or more microporous inorganic particulate material comprises a
blend of a first and second microporous inorganic particulate
material, wherein the ratio of the first microporous inorganic
particulate material to the second microporous inorganic
particulate material may range from about 40:60 to about 60:40 by
weight.
149. The filler composition according to claim 121, wherein the one
or more microporous inorganic particulate material, comprises a
blend of a first and second microporous inorganic particulate
material, wherein the ratio of the first inorganic particulate
material to the second inorganic particulate material is about
50:50 by weight.
150. The filler composition according to claim 121, further
comprising a binder.
151. The filler composition according to claim 150, wherein the
binder is an inorganic or organic binder.
152. The filler composition according to claim 151, wherein the
binder is an alkali metal silicate.
153. The filler composition according to claim 152, wherein the
alkali metal silicate is sodium silicate.
154. The filler composition according to claim 152, wherein the
alkali metal silicate is potassium silicate.
155. The filler composition according to claim 121, wherein the
weight ratio of microfibrillated cellulose to the one or more
microporous inorganic particulate material on a dry weight basis is
from about 1:5 to about 5:1.
156. The filler composition according to claim 121, wherein the
total content of the one or more microporous inorganic particulate
material is present in an amount of from about 10 wt-% to about 95
wt-% on a dry weight basis of the filler composition.
157. A method of making a paper or paperboard with improved
mechanical properties, the method comprising the steps of:
preparing a papermaking furnish for production of paper or
paperboard; adding one or more microporous inorganic particulate
material to the papermaking furnish; adding microfibrillated
cellulose (MFC) to the papermaking furnish; wherein the MFC and the
one or more microporous inorganic particulate material are added
separately to the papermaking furnish or as a filler composition
comprising the MFC and the one or more microporous inorganic
particulate material; manufacturing the paper or paperboard from
the papermaking furnish by dewatering and drying the papermaking
furnish; wherein the MFC and the one or more microporous inorganic
particulate materials impart mechanical properties to the paper or
paperboard that are improved compared to paper and paperboard
products made from an identical papermaking furnish not containing
MFC and microporous inorganic particulate material.
158. The method according to claim 157, wherein the one or more
microporous inorganic particulate material is selected from the
group consisting of: calcined clay, kaolin, kaolinite, amorphous
aluminum silicates, Scalenohedral precipitated calcium chloride,
aragonite precipitated calcium carbonate, chemically aggregated
filler materials, diatomaceous earth, milled expanded perlite, and
mixtures thereof.
159. The method according to claim 157, wherein the microporous
inorganic material comprises calcined clay.
160. The method according to claim 157, wherein the microporous
inorganic material comprises kaolin.
161. The method according to claim 157, wherein the microporous
inorganic material comprises kaolinite.
162. The method according to claim 157, wherein the microporous
inorganic material comprises calcined clay.
163. The method according to claim 157, wherein the microporous
inorganic material comprises amorphous aluminum silicates.
164. The method according to claim 157, wherein the microporous
inorganic material comprises Scalenohedral precipitated calcium
carbonate.
165. The method according to claim 157, wherein the microporous
inorganic particulate material comprises at least two of calcined
clay, kaolin, kaolinite, amorphous aluminum silicates,
Scalenohedral precipitated calcium chloride, aragonite precipitated
calcium carbonate, chemically aggregated filler materials,
diatomaceous earth, milled expanded perlite and mixtures
thereof.
166. The method according to claim 157, wherein the papermaking
furnish comprises one or more pulp selected from softwood
pulps.
167. The method according to claim 166, wherein the softwood pulp
is selected from the group consisting of: spruce, pine, fir, larch
and hemlock and mixed softwood pulps.
168. The method according to claim 157, wherein the papermaking
furnish comprises one or more pulp selected from hardwood
pulps.
169. The method according to claim 168, wherein the hardwood pulp
is selected from the group consisting of: eucalyptus, aspen and
birch, and mixed hardwood pulps.
170. The method according claim 157, wherein the pulp source for
the papermaking furnish is selected from the group consisting of:
eucalyptus pulp, spruce pulp, pine pulp, beech pulp, hemp pulp,
acacia, cotton pulp, and mixtures thereof.
171. The method according to claim 157, wherein the pulp source for
the papermaking furnish is selected from the group consisting of:
Nordic Pine, Black Spruce, Radiata Pine, Southern Pine,
Enzyme-Treated Nordic Pine, Douglas Fir, Dissolving Pulp, Birch,
Eucalyptus, Acacia, Mixed European Hardwood, Mixed Thai Hardwood,
Tissue Dust, Cotton, Abaca, Sisal, Bagasse, Kenaf, Miscanthus,
Sorghum, Giant Reed, Flax, and mixtures thereof.
172. The method according to claim 157, wherein the mechanical
property is selected from one or more of Tensile Strength, Tensile
Elongation, Bulk, Tensile Stiffness, Bending Stiffness, Porosity,
Burst and Tear Strength, and Tensile Strength in the `Z`
direction.
173. The method according to claim 157, wherein the
microfibrillated cellulose has a modal fibre particle size ranging
from about 0.1 .mu.m-500 .mu.m.
174. The method according to claim 157, wherein microfibrillated
cellulose has a modal fibre particle size of at least about 0.5
.mu.m.
175. The method according to claim 157, wherein the one or more
microporous inorganic particulate material has a median particle
size (d.sub.50) ranging from about 3 .mu.m to about 50 .mu.m.
56. The method according to claim 157, wherein the one or more
microporous inorganic particulate material has a median particle
size (d.sub.50) ranging from about 3 .mu.m to about 6 .mu.m.
177. The method according to claim 157, wherein the one or more
microporous inorganic particulate material and microfibrillated
cellulose composite may be associated with one or more dispersing
agents selected from the group consisting of: homopolymers or
copolymers of polycarboxylic acids and/or their salts or
derivatives, esters based on, acrylic acid, methacrylic acid,
maleic acid, fumaric acid, itaconic acid; acryl amide or acrylic
esters, methylmethacrylate, or mixtures thereof, alkali
polyphosphates, phosphonic-, citric- and tartaric acids and the
salts or esters thereof; and mixtures thereof.
178. The method according to claim 157, wherein the one or more
microporous inorganic particulate material and microfibrillated
cellulose composite is provided in the form of a powder.
179. The method according to claim 157, wherein the one or more
microporous inorganic particulate material and microfibrillated
cellulose composite is provided in the form of a suspension.
180. The method according to claim 179, wherein the suspension is
an aqueous suspension.
181. The method according to claim 180, wherein the aqueous
suspension is a pumpable liquid.
182. The method according to claim 157, wherein the one or more
microporous inorganic particulate material comprises a blend of a
first and second microporous inorganic particulate material,
wherein the ratio of the first microporous inorganic particulate
material to the second microporous inorganic particulate material
may range from about 10:90 to about 90:10 by weight.
183. The method according to claim 157, further comprising a
binder.
184. The method according to claim 183, wherein the binder is an
inorganic or organic binder.
185. The method according to claim 183, wherein the binder is an
alkali metal silicate.
186. The method according to claim 183, wherein the alkali metal
silicate is sodium silicate.
187. The method according to claim 183, wherein the alkali metal
silicate is potassium silicate.
188. The method according to claim 157, wherein the weight ratio of
microfibrillated cellulose to the one or more microporous inorganic
particulate material on a dry weight basis is from about 1:5 to
about 5:1.
189. The method according to claim 157, wherein the total content
of the one or more microporous inorganic particulate material is
present in an amount of from about 10 wt-% to about 95 wt-% on a
dry weight basis of the filler composition.
190. The method according to claim 157, wherein the total content
of the one or more microporous inorganic particulate material is
present in an amount of from about 15 wt-% to about 90 wt-% on a
dry weight basis of the filler composition.
191. The method according to claim 157, wherein the total content
of the one or more microporous inorganic particulate material is
present in an amount of from about 20 to about 75 wt-% on a dry
weight basis of the filler composition.
192. The method according to claim 157, wherein the total content
of the one or more microporous inorganic particulate material is
present in an amount of from about 25 wt-% to about 67 wt-% on a
dry weight basis of the filler composition.
193. The method according to claim 157, wherein the total content
of the one or more microporous inorganic particulate material is
present in an amount of from about 33 to about 50 wt.-% on a dry
weight basis of the filler composition.
194. A method of making a papermaking furnish comprising
microfibrillated cellulose (MFC) and one or more microporous
inorganic particulate material, the method comprising the steps of:
adding the one or more microporous inorganic particulate material
to the papermaking furnish; adding the MFC to the papermaking
furnish; wherein the MFC and the one or more microporous inorganic
particulate material are added separately to the papermaking
furnish or as a filler composition comprising the MFC and the one
or more microporous inorganic particulate material; wherein the MFC
and the one or more microporous inorganic particulate material
impart mechanical properties to the paper or paperboard that are
improved compared to paper and paperboard products made from an
identical papermaking furnish not containing the microfibrillated
cellulose and the one or more microporous inorganic particulate
material.
Description
BACKGROUND
Field of Invention
[0001] The present invention relates to methods of manufacturing
paper comprising microfibrillated cellulose ("MFC") and bulky
microporous inorganic particulate material with improved mechanical
properties through selection of bulky microporous inorganic
particulate materials having optimal particle sizes and particle
size distributions.
Background of the Invention
[0002] Inorganic particulate material is commonly used in graphic
papers to enhance optical and printing properties. Because
inorganic particulate material (also referred to herein as
"minerals and "filler") is substantially less expensive than pulp
fibres, use of inorganic particulate material also allows the
papermaker to save costs. The amount of inorganic particulate
material that can be used is limited because of the effect the
inorganic particulate material has on the strength properties of
paper, both in the wet state during manufacture and after
drying.
[0003] During manufacture, the most important property which limits
the inorganic particulate material content is the tensile strength
of the wet paper after pressing. On most paper machines the paper
is passed unsupported from the press to the dryer section and thus
is held in tension whilst still at a relatively high-water content
of up to 60%.
[0004] After drying, many paper grades require a minimum tensile,
burst and tear strength, as well as tensile strength in the `Z`
direction (perpendicular to the plane of the paper) in order to
resist damage during printing and converting processes. Other
important sheet properties include resistance to bending and sheet
bulk or thickness.
[0005] The addition of microfibrillated cellulose (MFC) has been
established as a cost-effective way to increase many of the
important strength properties of paper, including wet strength
during manufacture, and thus enable higher inorganic particulate
material content to be used and to save costs. However, the
addition of MFC and the increase in inorganic particulate material
content typically both have the effect of densifying the paper,
leading to a reduction in sheet thickness.
[0006] Conventional filler compositions used in papermaking, such
as ground calcium carbonate (GCC) and kaolin can give a slight
increase in the thickness of paper per unit mass of fibre, since
some inorganic particulate material particles occupy areas between
overlapping fibres which would otherwise be tightly bonded together
and increase the spacing between the fibres. However, the majority
of particles are located in the void spaces in the fibre network
that would otherwise be empty, and given their higher density
compared with fibres the net effect of replacing fibre with filler
is to densify the paper.
[0007] MFC bonds strongly to the fibres and draws them together,
which also reduces paper bulk and thickness. Since the bending
stiffness of a sheet of paper is very sensitive to its thickness,
the use of MFC to increase inorganic particulate material content
can also have a detrimental effect on this property. As a result,
the increase in inorganic particulate material content achievable
with the addition of MFC is often limited by the bulk and stiffness
of the paper rather than its strength
Microporous Inorganic Particulate Materials
[0008] Some types of filler, such as calcined clays and
scalenohedral and aragonite precipitated calcium carbonates (PCC),
consist of aggregates of particles with open porous structures
(i.e., these are examples of microporous inorganic particulate
materials). Calcined clays are described in U.S. Pat. No.
3,586,523, which is hereby incorporated herein by reference in its
entirety. Such calcined kaolin clays are substantially anhydrous,
amorphous aluminum silicates which are obtained by calcining a
specific type of kaolin clay, for example, hard sedimentary kaolin
clay.
[0009] Precipitated calcium carbonate (PCC) in clustered form is
known in the art as disclosed in U.S. Pat. No. 5,695,733, which is
hereby incorporated by reference in its entirety. The PCC is
produced in a unique clustered form having a substantial proportion
of particles having a prismatic morphology. By controlling the
solution environment utilized to produce PCC, i.e., the slaking of
lime (calcium oxide), temperature of carbonation and the rate of
introduction of carbon dioxide, either calcite, aragonite, or
vaterite are produced. Again, depending upon the process conditions
calcite may have either prismatic, scalenohedral or rhombohedral
crystal forms.
[0010] Other examples of microporous inorganic particulate
materials include chemically aggregated filler materials. Examples
of such chemically aggregated fillers may be found in U.S. Pat. No.
4,072,537, which is hereby incorporated herein in its entirety.
Such microporous inorganic particulate materials comprise a
composite silicate material comprising a clay component and a metal
silicate component. The clay component is typically kaolin clay or
kaolinite and the metal silicate material is typically a
water-soluble alkali metal silicate, for example sodium
silicate.
[0011] As described in the '537 patent, preferred methods for
preparing the composite pigment comprise the steps of, (a) forming
an aqueous suspension of a clay pigment, (b) blending into the clay
slurry a quantity of a salt such as calcium chloride, (c) metering
into the slurry of clay and salt at high shear a quantity of a
silicate component such as sodium silicate, and, optionally, (d)
adjusting the pH of the slurry with the addition of alum to a pH no
lower than pH 4, before (e) filtering and washing the precipitated
product to remove any soluble salts. Such microporous composite
silicate material is either used directly in a papermaking process
or dried and used later. Additional microporous inorganic
particulate material includes materials such as diatomaceous earth
and expanded perlite.
[0012] All of foregoing materials microporous inorganic particulate
materials consist of particles which contain rigid internal void
spaces that persist through paper pressing and drying, and should
also remain largely intact after calendering.
[0013] Scalenohedral PCC, calcined clays and chemically aggregated
fillers achieve this structure by forming open aggregates of
smaller particles and bonding the particles strongly where they
contact each other. Diatomaceous earth consists of particles which
naturally contain pores. Milled expanded perlite consists of
fragments of micron-sized glass bubbles. Thus, microporous
inorganic particulate materials comprise discrete particles or
aggregates of particles with outer dimensions of several microns,
which contain void spaces within the volume defined by the outer
dimensions which are several times smaller than said outer
dimensions. Collectively, the foregoing inorganic particulate
material are designated herein as "microporous inorganic
particulate materials" for the purpose of the present
invention.
[0014] When used in paper, these microporous inorganic particulate
materials have a much larger effect, per unit mass of added
particulate material, on the spacing of the fibres than solid
filler particles. This makes them more detrimental to paper
strength, but generates increased light scattering which is
beneficial to optical properties.
[0015] Another effect of inorganic particulate materials is always
to increase sheet porosity (air permeability), which is a
significant disadvantage in printing and converting processes. The
effective density of the microporous inorganic particulate
materials is also lower than that of solid fillers, and the
combination of these effects can lead to an increase in sheet bulk
and thickness as fibre is substituted for filler.
[0016] For scalenohedral PCC (an example of microporous inorganic
particulate material), the effect of agglomeration on strength can
be offset somewhat by controlling the particle size distribution to
a narrow range (thus eliminating ultrafine particles which are very
detrimental to paper strength) and using a larger median particle
size than is optimum for light scattering. However, if the particle
or agglomerate size is too large, then light scattering efficiency
is lost.
Microfibrillated Cellulose
[0017] Various methods of producing microfibrillated cellulose
("MFC") are known in the art. Certain methods and compositions
comprising microfibrillated cellulose are produced by grinding
procedures are described in WO-A-2010/131016. Husband, J. C.,
Svending, P., Skuse, D. R., Motsi, T., Likitalo, M., Coles, A.,
FiberLean Technologies Ltd., 2015, "Paper filler composition," PCT
International Application No. WO-A-2010/131016, the contents of
which is hereby incorporated by reference in its entirety. MFC
produced by the described grinding processes may include the
co-grinding of cellulose-containing fibres with inorganic
particulate material. Alternatively, MFC may be produced by
grinding cellulose fibres in the presence of grinding media other
than inorganic particulate material. Paper products comprising such
microfibrillated cellulose have been shown to exhibit excellent
paper properties, such as paper burst and tensile strength. The
methods described in WO-A-2010/131016 also enable the production of
microfibrillated cellulose economically.
[0018] WO2010/131016 describes a grinding procedure for the
production of microfibrillated cellulose with or without inorganic
particulate material. Such a grinding procedure is described below.
In an embodiment of the process set forth in WO-A-2010/131016, the
process utilizes mechanical disintegration of cellulose fibres to
produce microfibrillated cellulose ("MFC") cost-effectively and at
large scale, without requiring cellulose pre-treatment. An
embodiment of the method uses stirred media detritor grinding
technology, which disintegrates fibres into MFC by agitating
grinding media beads. In this process, a mineral such as calcium
carbonate or kaolin is added as a grinding aid, greatly reducing
the energy required. Husband, J. C., Svending, P., Skuse, D. R.,
Motsi, T., Likitalo, M., Coles, A., FiberLean Technologies Ltd.,
2015, "Paper filler composition," U.S. Pat. No. 9,127,405B2, which
is hereby incorporated herein by reference.
[0019] Notwithstanding the foregoing advances, there remains a need
to optimize paper filler compositions comprising MFC and inorganic
particulate material through judicious selection and control of
inorganic particulate material particles sizes and particle size
distributions to maintain sufficiently low porosity, high
brightness and opacity and both wet and dry strength properties,
including, minimum tensile, burst and tear strength, as well as
tensile strength in the `Z` direction (perpendicular to the plane
of the paper) of paper and paperboard and to resist damage during
printing and converting processes while optimizing resistance to
bending and sheet bulk or thickness.
SUMMARY OF THE INVENTION
[0020] In accordance with the description, Figures, Examples and
claims of the present specification, the inventors have discovered
processes for the manufacture of paper and paperboard having
improved mechanical properties through preparation and use of MFC
and one or more microporous inorganic particulate material based on
the particle size and particle size distribution of the one or more
microporous inorganic particulate material.
[0021] The present invention is based on the use of
microfibrillated cellulose and microporous inorganic particulate
material, which are added to a papermaking furnish to produce paper
and paperboard having enhanced mechanical properties that are not
substantially degraded or are maintained or even improved when the
compositions of MFC and microporous inorganic particulate material
are utilized in lieu of MFC and conventional inorganic particulate
material alone. The microfibrillated cellulose and microporous
inorganic particulate material can be added to a papermaking
furnish separately mish or as a filler composition comprising the
MFC and the one or more microporous inorganic particulate
material.
[0022] The present inventors have surprisingly found that the use
of MFC in combination with one or more microporous inorganic
particulate material, i.e., inorganic particulate material with a
coarser (larger) than conventional particle and agglomerate size,
can allow a substantial increase in the inorganic particulate
material content of graphic papers whilst maintaining the required
strength, bulk, stiffness and porosity properties. Losses in bulk
and stiffness resulting from the use of MFC are offset by the high
bulk contribution from the one or more microporous inorganic
particulate material, and losses in strength from the use of a high
content of microporous inorganic particulate material is offset by
the use of the MFC. The MFC also offsets the typical increase in
porosity associated with microporous inorganic particulate
materials and the increased content of MFC and microporous
inorganic particulate material offsets the loss of light scattering
efficiency associated with using a microporous inorganic
particulate material with a coarser than optimum particle size.
[0023] In accordance with the various aspects and embodiments of
the present disclosure the one or more microporous inorganic
particulate material comprises coarse particle size inorganic
particulate material and agglomerates of coarse particle size
microporous inorganic particulate material having a median particle
size (d.sub.50) ranging from about 3 .mu.m to about 50 .mu.m, such
as, for example, from about 5 .mu.m to about 30 .mu.m, from about
10 .mu.m to about 30 .mu.m, from about 15 .mu.m to about 25 .mu.m,
from about 20 .mu.m to about 30 .mu.m, from about 3 .mu.m to about
15 .mu.m, from about 5 .mu.m to about 15 .mu.m, from about 5 .mu.m
to about 10 .mu.m, from about 2 .mu.m to about 6 .mu.m, and,
particularly preferred between 3 .mu.m and 6 .mu.m, as measured by
sedimentation methods described herein and as known in the art.
[0024] Also in accordance with the various aspects and embodiments
of the present disclosure, the term mechanical properties comprises
one or more of Tensile Elongation, Tensile Stiffness, Bulk, and
Bending Stiffness. The foregoing properties may be measured by
methods described herein and as well known in the art of making
paper and paperboard.
[0025] In an aspect of the present disclosure, there is disclosed a
paper or paperboard filler composition comprising microfibrillated
cellulose (MFC) and one or more microporous inorganic particulate
material for addition to a papermaking furnish for the manufacture
of paper or paperboard, wherein the MFC and the one or more
microporous inorganic particulate material impart mechanical
properties to the paper or paperboard that are improved compared to
paper and paperboard products made from an identical papermaking
furnish not containing MFC and the one or more microporous
inorganic particulate material.
[0026] In another aspect of the present disclosure, there is
disclosed a paper or paperboard filler composition comprising
microfibrillated cellulose (MFC) and one or more microporous
inorganic particulate material for use in a method for making a
papermaking furnish for the manufacture of paper or paperboard,
wherein the MFC and the one or more microporous inorganic
particulate material impart mechanical properties to the paper or
paperboard that are improved compared to paper and paperboard
products made from an identical papermaking furnish not containing
MFC and the one or more microporous inorganic particulate
material
[0027] In another aspect of the present disclosure, there is
disclosed a paper or paperboard filler composition comprising
microfibrillated cellulose (MFC) and one or more microporous
inorganic particulate material for addition to a papermaking
furnish for the manufacture of paper or paperboard, wherein the MFC
is obtained by a co-grinding process using the same or different
microporous inorganic particulate material and/or a conventional
non-agglomerated inorganic particulate material and a fibrous
substrate containing cellulose; and wherein the MFC and the one or
more microporous inorganic particulate material impart mechanical
properties to said paper or paperboard that are improved compared
to paper and paperboard products made from an identical papermaking
furnish not containing MFC and the one or more microporous
inorganic particulate material.
[0028] In an embodiment of the foregoing aspects and embodiments of
the present disclosure, the one or more microporous inorganic
particulate material comprises (or is selected from the group
consisting of) calcined clay, kaolin, kaolinite, amorphous aluminum
silicates, Scalenohedral precipitated calcium chloride, aragonite
precipitated calcium carbonate, chemically aggregated filler
materials, diatomaceous earth, and milled expanded perlite.
[0029] In an embodiment of the foregoing aspects and embodiments of
the present disclosure, the one or more microporous inorganic
particulate material comprises (or consists essentially of or
consists of) calcined clay.
[0030] In an embodiment of the foregoing aspects and embodiments of
the present disclosure, the one or more microporous inorganic
particulate material comprises (or consists essentially of or
consists of) kaolin.
[0031] In an embodiment of the foregoing aspects and embodiments of
the present disclosure, the one or more microporous inorganic
particulate material comprises (or consists essentially of or
consists of) kaolinite.
[0032] In an embodiment of the foregoing aspects and embodiments of
the present disclosure, the one or more microporous inorganic
particulate material comprises (or consists essentially of or
consists of) amorphous aluminum silicates.
[0033] In an embodiment of the foregoing aspects and embodiments of
the present disclosure, the one or more microporous inorganic
particulate material comprises (or consists essentially of or
consists of) Scalenohedral precipitated calcium carbonate.
[0034] In an embodiment of the foregoing aspects and embodiments of
the present disclosure, the one or more microporous inorganic
particulate material comprises (or consists essentially of or
consists of) aragonite precipitated calcium carbonate.
[0035] In an embodiment of the foregoing aspects and embodiments of
the present disclosure, the one or more microporous inorganic
particulate material comprises (or consists essentially of or
consists of) chemically aggregated filler materials.
[0036] In an embodiment of the foregoing aspects and embodiments of
the present disclosure, the one or more microporous inorganic
particulate material comprises (or consists essentially of or
consists of) diatomaceous earth.
[0037] In an embodiment of the foregoing aspects and embodiments of
the present disclosure, the one or more microporous inorganic
particulate material comprises (or consists essentially of or
consists of) milled expanded perlite.
[0038] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the MFC and the one or more
microporous inorganic particulate material may be added separately
or may be added together as a filler composition to the papermaking
furnish.
[0039] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the papermaking furnish
comprises one or more pulp selected from softwood pulps.
[0040] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the softwood pulp is
selected from (or selected from the group consisting of) spruce,
pine, fir, larch and hemlock and mixed softwood pulps.
[0041] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the papermaking furnish
comprises one or more pulp selected from (or selected from the
group consisting of) hardwood pulps
[0042] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the hardwood pulp is
selected from (or selected from the group consisting of)
eucalyptus, aspen and birch, and mixed hardwood pulps.
[0043] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the pulp source for the
papermaking furnish is selected from (or consists essentially of or
consists of) eucalyptus pulp, spruce pulp, pine pulp, beech pulp,
hemp pulp, cotton pulp, acacia and mixtures thereof
[0044] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the pulp source for the
papermaking furnish is selected from (or consists essentially of or
consists of) Nordic Pine, Black Spruce, Radiata Pine, Southern
Pine, Enzyme-Treated Nordic Pine, Douglas Fir, Dissolving Pulp,
Birch (including Birch #1, Birch #2 set forth herein), Eucalyptus,
Acacia, Mixed European Hardwood, Mixed Thai Hardwood, Recycled
Paper, Cotton, Abaca, Acacia, Sisal, Bagasse, Kenaf, Miscanthus,
Sorghum, Giant Reed and Flax.
[0045] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the mechanical property is
selected from one or more of Tensile Strength, Tensile Elongation,
Bulk, Tensile Stiffness, Bending Stiffness, Porosity, Burst, Tear
Strength, and Tensile Strength in the `Z` direction.
[0046] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the mechanical property is
Tensile Strength.
[0047] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the mechanical property is
Tensile Elongation.
[0048] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the mechanical property is
Bulk.
[0049] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the mechanical property is
Tensile Stiffness.
[0050] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the mechanical property is
Bending Stiffness.
[0051] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the mechanical property is
Porosity.
[0052] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the mechanical property is
Burst.
[0053] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the mechanical property is
Tear Strength.
[0054] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the mechanical property is
Tensile Strength in the `Z` direction.
[0055] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the microfibrillated
cellulose has a modal fibre particle size ranging from about 0.1
.mu.m-500 .mu.m.
[0056] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, microfibrillated cellulose
has a modal fibre particle size of at least about 0.5 .mu.m, at
least about 10 .mu.m, at least about 50 .mu.m, at least about 100
.mu.m at least about 150 .mu.m, at least about 200 .mu.m, at least
about 300 .mu.m, or at least about 400 .mu.m.
[0057] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the one or more microporous
inorganic particulate material has a median particle size
(d.sub.50) ranging from about 3 .mu.m to about 50 .mu.m, from about
5 .mu.m to about 30 .mu.m, from about 10 .mu.m to about 30 .mu.m,
from about 15 .mu.m to about 25 .mu.m, from about 20 .mu.m to about
30 .mu.m, from about 3 .mu.m to about 15 .mu.m, from about 5 .mu.m
to about 15 .mu.m, from about 5 .mu.m to about 10 .mu.m, from about
3 .mu.m to about 6 .mu.m, or from about 3 to about 5 .mu.m, as
measured by laser light scattering.
[0058] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the one or more microporous
inorganic particulate material and microfibrillated cellulose
composite may be associated with one or more dispersing agents such
as those selected from the group comprising (or elected from the
group consisting of) homopolymers or copolymers of polycarboxylic
acids and/or their salts or derivatives, esters based on, acrylic
acid, methacrylic acid, maleic acid, fumaric acid, itaconic acid;
acryl amide or acrylic esters, methylmethacrylate, or mixtures
thereof; alkali polyphosphates, phosphonic-, citric- and tartaric
acids and the salts or esters thereof, and mixtures thereof.
[0059] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the one or more microporous
inorganic particulate material and microfibrillated cellulose
composite is provided in the form of a powder.
[0060] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the one or more microporous
inorganic particulate material and microfibrillated cellulose
composite is provided in the form of a suspension, or an aqueous
suspension and in alternative embodiments the aqueous suspension is
a pumpable liquid.
[0061] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, wherein the one or more
microporous inorganic particulate material comprises a blend of a
first and second microporous inorganic particulate material,
wherein the ratio of the first microporous inorganic particulate
material to the second microporous inorganic particulate material
may range from about 10:90 to about 90:10 by weight, or from about
20:80 to about 80:20 by weight, or from about 25:75 to about 75:25
by weight, or from about 40:60 to about 60:40 by weight, or from
about 50:50 by weight.
[0062] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the binder composition
further comprises a binder and in an embodiment may be an inorganic
or organic binder. In other embodiments, the binder may be an
alkali metal silicate, such as sodium silicate or potassium
silicate.
[0063] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the binder composition has a
weight ratio of microfibrillated cellulose to the one or more
microporous inorganic particulate material on a dry weight basis is
from 1:5 to 5:1, or from 1:3 to 3:1, or from 1:2 to 2:1, or from
1:1.5 to 1.5 to 1, or from 1:1.
[0064] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the total content of the one
or more microporous inorganic particulate material is present in an
amount of from 10 wt. % to 95 wt. % on a dry weight basis of the
filler composition, or from 15 wt. % to 90 wt. %, or from 20 to 75
wt. %, or from 25 wt. % to 67 wt. %, or from 33 to 50 wt. % on a
dry weight basis of the filler composition.
[0065] In another aspect of the present disclosure there is
disclosed a method of making a papermaking furnish comprising
microfibrillated cellulose (MFC) and one or more microporous
inorganic particulate material, the method comprising the steps of:
adding the one or more microporous inorganic particulate material
to the papermaking furnish; adding the MFC to the papermaking
furnish; wherein the MFC and the one or more microporous inorganic
particulate material impart mechanical properties to the paper or
paperboard that are improved compared to paper and paperboard
products made from an identical papermaking furnish not containing
the microfibrillated cellulose and the one or more microporous
inorganic particulate material.
[0066] In another aspect of the present disclosure there is
disclosed a method of making a papermaking furnish comprising
microfibrillated cellulose (MFC) and one or more microporous
inorganic particulate material, the method comprising the steps of:
adding the one or more microporous inorganic particulate material
to the papermaking furnish; adding the MFC to the papermaking
furnish; wherein the MFC is obtained by a co-grinding process using
the same or different microporous inorganic particulate material
and/or a conventional non-agglomerated inorganic particulate
material and a fibrous substrate comprising cellulose; and wherein
the MFC and the one or more microporous inorganic particulate
material impart mechanical properties to said paper or paperboard
that are improved compared to paper and paperboard products made
from an identical papermaking furnish not containing the
microfibrillated cellulose and the one or more microporous
inorganic particulate material.
[0067] In another aspect of the present disclosure there is
disclosed a method of making a papermaking furnish comprising
microfibrillated cellulose (MFC) and one or more microporous
inorganic particulate material, the method comprising the steps of
adding a filler composition comprising MFC and the one or more
microporous inorganic particulate material to the papermaking
furnish; wherein the MFC and the one or more microporous inorganic
particulate material impart mechanical properties to the paper or
paperboard that are improved compared to paper and paperboard
products made from an identical papermaking furnish not containing
the microfibrillated cellulose and the one or more microporous
inorganic particulate material.
[0068] In another aspect of the present disclosure there is
disclosed a papermaking furnish comprising microfibrillated
cellulose (MFC) and one or more microporous inorganic particulate
material, the method comprising the steps of: adding a filler
composition comprising MFC and the one or more microporous
inorganic particulate material to the papermaking furnish; wherein
the MFC is obtained by a co-grinding process using the same or
different microporous inorganic particulate material and/or a
conventional non-agglomerated inorganic particulate material and a
fibrous substrate comprising cellulose; and wherein the MFC and the
one or more microporous inorganic particulate material impart
mechanical properties to said paper or paperboard that are improved
compared to paper and paperboard products made from an identical
papermaking furnish not containing the microfibrillated cellulose
and the one or more microporous inorganic particulate material.
[0069] In another aspect of the present disclosure there is
disclosed a paper or paperboard made from a papermaking furnish
comprising microfibrillated cellulose (MFC) and one or more
microporous inorganic particulate material, the method comprising
the steps of: adding a filler composition comprising MFC and the
one or more microporous inorganic particulate material to the
papermaking furnish; wherein the filler composition imparts
mechanical properties to said paper or paperboard that are improved
compared to paper and paperboard products made from an identical
papermaking furnish not containing the MFC and the one or more
microporous inorganic particulate material.
[0070] A method of making a paper or paperboard with improved
mechanical properties, the method comprising the steps of:
preparing a papermaking furnish for production of paper or
paperboard; adding one or more microporous inorganic particulate
material to the papermaking furnish; adding microfibrillated
cellulose (MFC) to the papermaking furnish; wherein the MFC and the
one or more microporous inorganic particulate material are added
separately to the papermaking furnish or as a filler composition
comprising the MFC and the one or more microporous inorganic
particulate material; manufacturing the paper or paperboard from
the papermaking furnish by dewatering and drying the papermaking
furnish; wherein the MFC and the one or more microporous inorganic
particulate materials impart mechanical properties to the paper or
paperboard that are improved compared to paper and paperboard
products made from an identical papermaking furnish not containing
MFC and microporous inorganic particulate material.
[0071] In another aspect of the present disclosure, there is a
method of making method of making a paper or paperboard from a
papermaking furnish comprising microfibrillated cellulose (MFC) and
one or more microporous inorganic particulate materials, the method
comprising the steps of:
adding a filler composition comprising MFC and the one or more
microporous inorganic particulate material to the papermaking
furnish; wherein the MFC is obtained by a co-grinding process using
the same or different microporous inorganic particulate material
and/or a conventional non-agglomerated inorganic particulate
material and a fibrous substrate comprising cellulose; and wherein
the filler composition imparts mechanical properties to said paper
or paperboard that are improved compared to paper and paperboard
products made from an identical papermaking furnish not containing
the MFC and one or microporous inorganic particulate material. In
an embodiment, the MFC and the one or more microporous inorganic
particulate material are added separately to the papermaking
furnish or as a filler composition comprising the MFC and the one
or more microporous inorganic particulate material.
[0072] In another aspect of the present disclosure, there is method
of making a paper or paperboard from a papermaking furnish
comprising microfibrillated cellulose (MFC) and one or more
microporous inorganic particulate materials, the method comprising
the steps of:
adding the one or more microporous inorganic particulate material
to the papermaking furnish; adding MFC to the papermaking furnish;
wherein the MFC and the one or more microporous inorganic
particulate material imparts mechanical properties to said paper or
paperboard that are improved compared to paper and paperboard
products made from an identical papermaking furnish not containing
the microfibrillated cellulose and the one or more microporous
inorganic particulate material. In an embodiment, the MFC and the
one or more microporous inorganic particulate material are added
separately to the papermaking furnish or as a filler composition
comprising the MFC and the one or more microporous inorganic
particulate material.
[0073] In another aspect of the present disclosure, there is a
method of making a paper or paperboard from a papermaking furnish
comprising microfibrillated cellulose (MFC) and one or more
microporous inorganic particulate materials, the method comprising
the steps of:
adding the one or more microporous inorganic particulate material
to the papermaking furnish; adding the MFC to the papermaking
furnish; wherein the MFC is obtained by a co-grinding process using
the same or different microporous inorganic particulate material
and/or a conventional non-agglomerated inorganic particulate
material and a fibrous substrate comprising cellulose; and wherein
the MFC and the one or more microporous inorganic particulate
material imparts mechanical properties to said paper or paperboard
that are improved compared to paper and paperboard products made
from an identical papermaking furnish not containing the MFC and
the one or microporous inorganic particulate material. In an
embodiment, the MFC and the one or more microporous inorganic
particulate material are added separately to the papermaking
furnish or as a filler composition comprising the MFC and the one
or more microporous inorganic particulate material.
[0074] In another aspect of the present disclosure, there is a
method of making a paper or paperboard with improved mechanical
properties, the method comprising the steps of:
preparing a papermaking furnish for production of paper or
paperboard; preparing a filler composition comprising
microfibrillated cellulose (MFC) and one or more microporous
inorganic particulate material; adding the filler composition to
the papermaking furnish; manufacturing a paper or paperboard from
the papermaking furnish by dewatering and drying the papermaking
furnish; wherein the filler composition imparts mechanical
properties to said paper or paperboard that are improved compared
to paper and paperboard products made from an identical papermaking
furnish not containing MFC and microporous inorganic particulate
material. In an embodiment, the MFC and the one or more microporous
inorganic particulate material are added separately to the
papermaking furnish or as a filler composition comprising the MFC
and the one or more microporous inorganic particulate material.
[0075] In another aspect of the present disclosure, there is a
method of making a paper or paperboard with improved mechanical
properties, the method comprising the steps of:
preparing a papermaking furnish for production of paper or
paperboard; preparing a filler composition comprising
microfibrillated cellulose (MFC) and one or more microporous
inorganic particulate material; adding the filler composition to
the papermaking furnish; manufacturing a paper or paperboard from
the papermaking furnish by dewatering and drying the papermaking
furnish; wherein the MFC is obtained by a co-grinding process using
the same or different microporous inorganic particulate material
and/or a conventional non-agglomerated inorganic particulate
material and a fibrous substrate comprising cellulose; and wherein
the filler composition imparts mechanical properties to said paper
or paperboard that are improved compared to paper and paperboard
products made from an identical papermaking furnish not MFC and the
one or more microporous inorganic particulate material. In an
embodiment, the MFC and the one or more microporous inorganic
particulate material are added separately to the papermaking
furnish or as a filler composition comprising the MFC and the one
or more microporous inorganic particulate material.
[0076] In another aspect of the present disclosure, there is a
method of making a paper or paperboard with improved mechanical
properties, the improvement comprising: preparing a papermaking
furnish for production of paper or paperboard; adding one or more
microporous inorganic particulate material to the papermaking
furnish; adding microfibrillated cellulose (MFC) to the papermaking
furnish; manufacturing a paper or paperboard from the papermaking
furnish by dewatering and drying the papermaking furnish; wherein
the MFC and the one or more microporous inorganic particulate
materials impart mechanical properties to said paper or paperboard
that are improved compared to paper and paperboard products made
from an identical papermaking furnish not containing MFC and
microporous inorganic particulate material. In an embodiment, the
MFC and the one or more microporous inorganic particulate material
are added separately to the papermaking furnish or as a filler
composition comprising the MFC and the one or more microporous
inorganic particulate material.
[0077] In another aspect of the present disclosure, there is a
method of making a paper or paperboard with improved mechanical
properties, the improvement comprising: preparing a papermaking
furnish for production of paper or paperboard; adding one or more
microporous inorganic particulate material to the papermaking
furnish; adding microfibrillated cellulose (MFC) to the papermaking
furnish; manufacturing a paper or paperboard from the papermaking
furnish by dewatering and drying the papermaking furnish; wherein
the MFC is obtained by a co-grinding process using the same or
different microporous inorganic particulate materials and/or a
conventional non-agglomerated inorganic particulate material and a
fibrous substrate comprising cellulose; and wherein the MFC and the
one or more microporous inorganic particulate materials impart
mechanical properties to said paper or paperboard that are improved
compared to paper and paperboard products made from an identical
papermaking furnish not containing MFC and the one or more
microporous inorganic particulate material. In an embodiment, the
MFC and the one or more microporous inorganic particulate material
are added separately to the papermaking furnish or as a filler
composition comprising the MFC and the one or more microporous
inorganic particulate material.
[0078] In additional embodiments of the foregoing aspects and
embodiments of the present disclosure, the one or more microporous
inorganic particulate material is selected from the group
comprising (or selected from the group consisting of) calcined
clay, kaolin, kaolinite, amorphous aluminum silicates,
Scalenohedral precipitated calcium chloride, aragonite precipitated
calcium carbonate, chemically aggregated filler materials,
diatomaceous earth, or milled expanded perlite.
[0079] In an embodiment, the one or more microporous inorganic
particulate material comprises or is calcined clay.
[0080] In an embodiment, the one or more microporous inorganic
particulate material comprises or is kaolin.
[0081] In an embodiment, the one or more microporous inorganic
particulate material comprises or is kaolinite.
[0082] In an embodiment, the one or more microporous inorganic
particulate material comprises or is amorphous aluminum
silicate.
[0083] In an embodiment, the one or more microporous inorganic
particulate material comprises or is Scalenohedral precipitated
calcium carbonate.
[0084] In an embodiment, the one or more microporous inorganic
particulate material comprises or is aragonite precipitated calcium
carbonate.
[0085] In an embodiment, the one or more microporous inorganic
particulate material comprises or is chemically aggregated filler
materials.
[0086] In an embodiment, the one or more microporous inorganic
particulate material comprises or is diatomaceous earth.
[0087] In an embodiment, the one or more microporous inorganic
particulate material comprises or is milled expanded perlite.
[0088] In an embodiment of the aspects of the present disclosure
the papermaking furnish comprises one or more pulp selected from
softwood pulps.
[0089] In an embodiment of the aspects of the present disclosure
the softwood pulp is selected from (or is selected from the group
consisting of) spruce, pine, fir, larch and hemlock or mixed
softwood pulps.
[0090] In an embodiment of the aspects of the present disclosure
the papermaking furnish comprises one or more pulp selected from
hardwood pulp.
[0091] In an embodiment of the aspects of the present disclosure
the hardwood pulp is selected from (or is selected from the group
consisting of) eucalyptus, aspen and birch, or mixed hardwood
pulps.
[0092] In an embodiment of the aspects of the present disclosure
the pulp source for the papermaking furnish is selected from (or is
selected from the group consisting of) eucalyptus pulp, spruce
pulp, pine pulp, beech pulp, hemp pulp, acacia, cotton pulp, and
mixtures thereof.
[0093] In an embodiment of the aspects of the present disclosure
the pulp source for the papermaking furnish is selected from (or is
selected from the group consisting of) Nordic Pine, Black Spruce,
Radiata Pine, Southern Pine, Enzyme-Treated Nordic Pine, Douglas
Fir, Dissolving Pulp, (Birch (including Birch #1, Birch #2 set
forth herein), Eucalyptus, Acacia, Mixed European Hardwood, Mixed
Thai Hardwood, Recycled Paper, Cotton, Abaca, Sisal, Bagasse,
Kenaf, Miscanthus, Sorghum, Giant Reed and Flax.
[0094] In an embodiment of the aspects of the present disclosure
the microfibrillated cellulose is prepared by a co-grinding process
with one or more non-agglomerated inorganic particulate material
utilized in preparation of the microfibrillated cellulose and one
or more microporous inorganic particulate material composite.
[0095] In an embodiment of the aspects of the present disclosure
the microfibrillated cellulose has a fibre steepness of about 20 to
about 50.
[0096] In an embodiment of the aspects of the present disclosure
the microfibrillated cellulose has a d.sub.50 ranging from about 5
to about 500 .mu.m, as measured by laser light scattering.
[0097] In an embodiment of the aspects of the present disclosure
the microfibrillated cellulose has a d.sub.50 of equal to or less
than about 400 .mu.m, as measured by laser light scattering.
[0098] In an embodiment of the aspects of the present disclosure
the microfibrillated cellulose has a d.sub.50 of equal to or less
than about 200 .mu.m, as measured by laser light scattering.
[0099] In an embodiment of the aspects of the present disclosure
the microfibrillated cellulose has a d.sub.50 of equal to or less
than about 200 .mu.m, as measured by laser light scattering.
[0100] In an embodiment of the aspects of the present disclosure
the microfibrillated cellulose has a d.sub.50 of equal to or less
than about 150 .mu.m, as measured by laser light scattering. [0101]
and
[0102] In an embodiment of the aspects of the present disclosure,
the one or more microporous inorganic particulate material and
microfibrillated cellulose composite is provided in the form of a
powder.
[0103] In an embodiment of the aspects of the present disclosure,
the one or more microporous inorganic particulate material and
microfibrillated cellulose composite is provided in the form of a
suspension. In another embodiment, the suspension may be an aqueous
suspension. In a further embodiment, the aqueous suspension is a
pumpable liquid.
[0104] In an embodiment of the aspects of the present disclosure,
the one or more microporous inorganic particulate material
comprises a blend of a first and second microporous inorganic
particulate material, wherein the ratio of the first microporous
inorganic particulate material to the second microporous inorganic
particulate material may range from about 10:90 to about 90:10 by
weight, from about 20:80 to about 80:20 by weight, or from about
25:75 to about 75:25 by weight, or from about 40:60 to about 60:40
by weight, or from about 50:50 by weight.
[0105] In an embodiment of the aspects of the present disclosure,
the method further comprises a binder. In another embodiment, the
binder is an organic or inorganic binder. In a further embodiment,
the binder is an alkali metal silicate, such as sodium silicate or
potassium silicate.
[0106] In further embodiments of the aspects of the present
disclosure, the weight ratio of microfibrillated cellulose to the
one or more microporous inorganic particulate material on a dry
weight basis is from 1:5 to 5:1, or 1:3 to 3:1, or 1:2 to 2:1, or
1:1.5 to 1.5 to 1, or about 1:1.
[0107] In further embodiments of the aspects of the present
disclosure, the total content of the one or more microporous
inorganic particulate material is present in an amount of from 10
wt-% to 95 wt-% on a dry weight basis of the filler composition,
from 15 wt. % to 90 wt. %, or from 20 to 75 wt. %, or from 25 wt. %
to 67 wt. %, or from 33 to 50 wt.-% on a dry weight basis of the
filler composition.
[0108] Unless otherwise stated, particle size properties referred
to herein for the inorganic particulate materials are as measured
in a well-known manner by sedimentation of the particulate material
in a fully dispersed condition in an aqueous medium using a
Sedigraph 5100 machine as supplied by Micromeritics Instruments
Corporation, Norcross, Ga., USA (telephone: +1 770 662 3620;
web-site: www.micromeritics.com), referred to herein as a
"Micromeritics Sedigraph 5100 unit". Such a machine provides
measurements and a plot of the cumulative percentage by weight of
particles having a size, referred to in the art as the `equivalent
spherical diameter` (e.s.d), less than given e.s.d values. The mean
particle size d.sub.50 is the value determined in this way of the
particle e.s.d at which there are 50% by weight of the particles
which have an equivalent spherical diameter less than that d.sub.50
value.
[0109] In an embodiment of the aspects of the present disclosure
the blend of the first and second inorganic particulate materials
and the binder solution may be mixed with sufficient agitation to
at least substantially uniformly distribute the binder composition
(slurry or suspension) among the agglomeration points of contact of
the blend of first and second inorganic particulate materials
without damaging the structure of the first or second inorganic
particulate materials.
[0110] In an embodiment of the aspects of the present disclosure
the contacting is performed in a low-shear mixing apparatus.
[0111] In an embodiment of the aspects of the present disclosure
the mixing may occur at about room temperature (i.e., from about
20.degree. C. to about 23.degree. C.).
[0112] In an embodiment of the aspects of the present disclosure
the mixing may occur at about room temperature (i.e., from about
20.degree. C. to about 50.degree. C.)
[0113] In an embodiment of the aspects of the present disclosure
the mixing may occur at about room temperature (i.e., from about
30.degree. C. to about 45.degree. C.)
[0114] In an embodiment of the aspects of the present disclosure
the mixing may occur at about room temperature (i.e., from about
35.degree. C. to about 45.degree. C.)
[0115] In an embodiment of the aspects of the present disclosure
the contacting may include spraying the blend of first and/or first
and second inorganic particulate materials with a binder
composition (slurry or suspension).
[0116] In an embodiment of the aspects of the present disclosure
the contacting is intermittent.
[0117] In an embodiment of the aspects of the present disclosure
the contacting is continuous.
[0118] In an embodiment of the aspects of the present disclosure
the binder may be present in a binder composition (slurry or
suspension) in an amount less than about 40% by weight, relative to
the weight of the binder solution. In some embodiments, the binder
may range from about 1% to about 10% by weight.
[0119] The foregoing has outlined rather broadly the features and
technical advantages of the present invention in order that the
detailed description of the invention that follows may be better
understood. Additional features and advantages of the invention
will be described herein, which form the subject of the claims of
the invention. It should be appreciated by those skilled in the art
that any conception and specific embodiment disclosed herein may be
readily utilized as a basis for modifying or designing other means
for carrying out the same purposes of the present invention. It
should also be realized by those skilled in the art that such
equivalent means do not depart from the spirit and scope of the
invention as set forth in the appended claims. The novel features
which are believed to be characteristic of the invention, both as
to its organization and method of operation, together with further
objects and advantages will be better understood from the following
description when considered in connection with the accompanying
figures. It is to be expressly understood, however, that any
description, figure, example, etc. is provided for the purpose of
illustration and description only and is by no means intended to
define the limits the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0120] For a more complete understanding of the principles
disclosed herein, and the advantages thereof, reference is made to
the following descriptions taken in conjunction with the
accompanying drawings, in which:
[0121] FIG. 1 is a plot of Scott Bond, Bending Stiffness, Tensile
Index, Bulk and Light Scattering properties for compositions
comprising ground calcium carbonate (GCC) compositions at 20% and
30% levels with and without MFC compared to precipitated calcium
carbonate (PCC) compositions at 20% and 30% levels with and without
MFC.
[0122] FIG. 2 is a graph of Bending Stiffness in mNm versus
percentage filler proportion comprising PCC (remainder is GCC).
[0123] FIG. 3 is a graph of Light Scattering Coefficient (F10) in
cm.sup.2g.sup.-1 versus percentage filler proportion comprising PCC
(remainder is GCC).
[0124] FIG. 4 is a graph of Tensile Index in Nm/g versus percentage
filler proportion comprising PCC (remainder is GCC).
[0125] FIG. 5 is a graph of Scott Bond in J/m.sup.2 versus
percentage filler proportion comprising PCC (remainder is GCC).
[0126] FIG. 6 is a graph of Tensile Index in Nm/g versus Sheet
Filler Content in percentage PCC content.
[0127] FIG. 7 is a graph of Light Scattering (F10 S) versus Sheet
Filler Content in percentage PCC content.
[0128] FIG. 8 is a graph of Bending Stiffness in mN versus Sheet
Filler Content in percentage PCC content.
DETAILED DESCRIPTION OF THE INVENTION
[0129] The titles, headings and subheadings provided herein should
not be interpreted as limiting the various aspects of the
disclosure. Accordingly, the terms defined below are more fully
defined by reference to the specification in its entirety. All
references cited herein are incorporated by reference in their
entirety.
[0130] The present invention relates to filler composition
comprising MFC and one or more microporous inorganic particulate
material composite to be utilized in papermaking furnishes for the
production of paper and paperboard with improved mechanical
properties compared to paper and paperboard produced without MFC
and one or more microporous inorganic particulate material.
Definitions and Headings
[0131] The titles, headings and subheadings provided herein should
not be interpreted as limiting the various aspects of the
disclosure. Accordingly, the terms defined below are more fully
defined by reference to the specification in its entirety. All
references cited herein are incorporated by reference in their
entirety.
[0132] Unless otherwise defined, scientific and technical terms
used herein shall have the meanings that are commonly understood by
those of ordinary skill in the art. Further, unless otherwise
required by context, singular terms shall include pluralities and
plural terms shall include the singular.
[0133] In this application, the use of "or" means "and/or" unless
stated otherwise. In the context of a multiple dependent claim, the
use of "or" refers back to more than one preceding independent or
dependent claim in the alternative only.
[0134] The use of the word "a" or "an" when used in conjunction
with the term "comprising" may mean "one," but it is also
consistent with the meaning of "one or more," "at least one," and
"one or more than one." The use of the term "or" is used to mean
"and/or" unless explicitly indicated to refer to alternatives only
if the alternatives are mutually exclusive, although the disclosure
supports a definition that refers to only alternatives and
"and/or." Throughout this application, the term "about" is used to
indicate that a value includes the inherent variation of error for
the quantifying device, the method being employed to determine the
value, or the variation that exists among the study subjects. For
example, but not by way of limitation, when the term "about" is
utilized, the designated value may vary by plus or minus twelve
percent, or eleven percent, or ten percent, or nine percent, or
eight percent, or seven percent, or six percent, or five percent,
or four percent, or three percent, or two percent, or one percent.
The use of the term "at least one" will be understood to include
one as well as any quantity more than one, including but not
limited to, 1, 2, 3, 4, 5, 10, 15, 20, 30, 40, 50, 100, etc. The
term "at least one" may extend up to 100 or 1000 or more depending
on the term to which it is attached. In addition, the quantities of
100/1000 are not to be considered limiting as lower or higher
limits may also produce satisfactory results. In addition, the use
of the term "at least one of X, Y, and Z" will be understood to
include X alone, Y alone, and Z alone, as well as any combination
of X, Y, and Z.
[0135] The use of ordinal number terminology (i.e., "first",
"second", "third", "fourth", etc.) is solely for the purpose of
differentiating between two or more items and, unless otherwise
stated, is not meant to imply any sequence or order or importance
to one item over another or any order of addition.
[0136] As used herein, the term one or more microporous inorganic
particulate material comprises coarse particle size inorganic
particulate material and agglomerates of coarse particle size
inorganic particulate material having a median particle size
(d.sub.50) ranging from about 3 .mu.m to about 50 .mu.m, such as,
for example, from about 5 .mu.m to about 30 .mu.m, from about 10
.mu.m to about 30 .mu.m, from about 15 .mu.m to about 25 .mu.m,
from about 20 .mu.m to about 30 .mu.m, from about 3 .mu.m to about
15 .mu.m, from about 5 .mu.m to about 15 .mu.m, from about 5 .mu.m
to about 10 .mu.m, from about 2 .mu.m to about 6 .mu.m, and,
particularly preferred between 3 .mu.m and 6 .mu.m, as measured by
sedimentation methods described herein and as known in the art.
[0137] As used herein, the terms "comprising" (and any form of
comprising, such as "comprise", "comprises", and "comprised"),
"having" (and any form of having, such as "have" and "has"),
"including" (and any form of including, such as "includes" and
"include"), or "containing" (and any form of containing, such as
"contains" and "contain"), are inclusive or open-ended and do not
exclude additional, unrecited elements or method steps.
Additionally, a term that is used in conjunction with the term
"comprising" is also understood to be able to be used in
conjunction with the term "consisting of` or "consisting
essentially of." Similarly, the phrase "selected from" and words of
like import may also include the phrase "selected from the group
consisting of."
[0138] As used herein, the term "include" and its grammatical
variants are intended to be non-limiting, such that recitation of
items in a list is not to the exclusion of other like items that
can be substituted or added to the listed items.
[0139] The fibrous substrate comprising cellulose (variously
referred to herein as "fibrous substrate comprising cellulose,"
"cellulose fibres," "fibrous cellulose feedstock," "cellulose
feedstock" and "cellulose-containing fibres (or fibrous," etc.) may
be derived from virgin or recycled pulp or a papermill broke and/or
industrial waste, or a paper streams rich in mineral fillers and
cellulosic materials from a papermill.
[0140] As used herein, mechanical properties comprise one or more
of the following properties: Tensile Strength, Tensile Elongation,
Bulk, Tensile Stiffness, Bending Stiffness, Porosity, Tensile,
Burst, Tear Strength, and Tensile Strength in the `Z`
direction.
[0141] As used herein, the term "substantially" means that the
subsequently described event or circumstance completely occurs or
that the subsequently described event or circumstance occurs to a
great extent or degree. For example, when associated with a
particular event or circumstance, the term "substantially" means
that the subsequently described event or circumstance occurs at
least 80% of the time, or at least 85% of the time, or at least 90%
of the time, or at least 95% of the time. Conversely, when used to
signify that the mechanical properties, such as tensile strength
and/or bending stiffness are "not substantially degraded" or
similar language, the degradation of tensile strength and/or
bending stiffness are not diminished by more than 15%, or more than
10% or more than 5% from the properties of the control.
[0142] As used herein, the phrase "integer from X to Y" means any
integer that includes the endpoints. For example, the phrase
"integer from 1 to 5" means 1, 2, 3, 4, or 5.
Microfibrillated Cellulose
[0143] Microfibrillated cellulose (MFC), although well-known and
described in the art, for purposes of the presently disclosed
and/or claimed inventive concept(s), microfibrillated cellulose is
defined as cellulose consisting of microfibrils in the form of
either isolated cellulose microfibrils and/or microfibril bundles
of cellulose, both of which are derived from a cellulose raw
material. Thus, microfibrillated cellulose is to be understood to
comprise partly or totally fibrillated cellulose or lignocellulose
fibers, which may be achieved by a variety of processes known in
the art.
[0144] As used herein, "microfibrillated cellulose" can be used
interchangeably with "microfibrillar cellulose," "nanofibrillated
cellulose," "nanofibril cellulose," "nanofibers of cellulose,"
"nanoscale fibrillated cellulose," "microfibrils of cellulose,"
and/or simply as "MFC." Additionally, as used herein, the terms
listed above that are interchangeable with "microfibrillated
cellulose" may refer to cellulose that has been completely
microfibrillated or cellulose that has been substantially
microfibrillated but still contains an amount of
non-microfibrillated cellulose at levels that do not interfere with
the benefits of the microfibrillated cellulose as described and/or
claimed herein
[0145] By "microfibrillating" is meant a process in which
microfibrils of cellulose are liberated or partially liberated as
individual species or as small aggregates as compared to the fibres
of the pre-microfibrillated pulp. Typical cellulose fibres (i.e.,
pre-microfibrillated pulp) suitable for use in papermaking include
larger aggregates of hundreds or thousands of individual cellulose
fibrils
[0146] Microfibrillated cellulose comprises cellulose, which is a
naturally occurring polymer comprising repeated glucose units. The
term "microfibrillated cellulose", also denoted MFC, as used in
this specification, includes microfibrillated/microfibrillar
cellulose and nano-fibrillated/nanofibrillar cellulose (NFC), which
materials are also called nanocellulose.
[0147] Microfibrillated cellulose is prepared by stripping away the
outer layers of cellulose fibers that may have been exposed through
mechanical shearing, with or without prior enzymatic or chemical
treatment. There are numerous methods of preparing microfibrillated
cellulose that are known in the art.
[0148] In a non-limiting example, the term microfibrillated
cellulose is used to describe fibrillated cellulose comprising
nanoscale cellulose particle fibers or fibrils frequently having at
least one dimension less than 100 nm. When liberated from cellulose
fibres, fibrils typically have a diameter less than 100 nm. The
actual diameter of cellulose fibrils depends on the source and the
manufacturing methods.
[0149] The particle size distribution and/or aspect ratio
(length/width) of the cellulose microfibrils attached to the
fibrillated cellulose fiber or as a liberated microfibril depends
on the source and the manufacturing methods employed in the
microfibrillation process.
[0150] In a non-limiting example, the aspect ratio of microfibrils
is typically high and the length of individual microfibrils may be
more than one micrometer and the diameter may be within a range of
about 5 to 60 nm with a number-average diameter typically less than
20 nm. The diameter of microfibril bundles may be larger than 1
micron, however, it is usually less than one
[0151] In a non-limiting example, the smallest fibril is
conventionally referred to as an elementary fibril, which generally
has a diameter of approximately 2-4 nm. It is also common for
elementary fibrils to aggregate, which may also be considered as
microfibrils.
[0152] In a non-limiting example, the microfibrillated cellulose
may at least partially comprise nanocellulose. The nanocellulose
may comprise mainly nano-sized fibrils having a diameter that is
less than 100 nm and a length that may be in the micron-range or
lower. The smallest microfibrils are similar to the so-called
elemental fibrils, the diameter of which is typically 2 to 4 nm. Of
course, the dimensions and structures of microfibrils and
microfibril bundles depend on the raw materials used in addition to
the methods of producing the microfibrillated cellulose.
Nonetheless, it is expected that a person of ordinary skill in the
art would understand the meaning of "microfibrillated cellulose" in
the context of the presently disclosed and/or claimed inventive
concept(s)
[0153] Depending on the source of the cellulose fibers and the
manufacturing process employed to microfibrillate the cellulose
fibres, the length of the fibrils can vary, frequently from about 1
to greater than 10 micrometers.
[0154] A coarse MFC grade might contain a substantial fraction of
fibrillated fibers, i.e. protruding fibrils from the tracheid
(cellulose fiber), and with a certain amount of fibrils liberated
from the tracheid (cellulose fiber).
[0155] In an embodiment, the microfibrillated cellulose may also be
prepared from recycled pulp or a papermill broke and/or industrial
waste, or a paper streams rich in mineral fillers and cellulosic
materials from a papermill.
[0156] The fibrous substrate comprising cellulose may be added to a
grinding vessel fibrous substrate comprising cellulose in a dry
state. For example, a dry paper broke may be added directly to the
grinder vessel. The aqueous environment in the grinder vessel will
then facilitate the formation of a pulp.
Co-Grinding Process of Microfibrillated Cellulose and Inorganic
Particulate Material
[0157] In an embodiment, the present invention is related to
modifications, for example, improvements, to the methods and
compositions described in WO-A-2010/131016, the entire contents of
which are hereby incorporated by reference.
[0158] WO-A-2010/131016 discloses a process for preparing
microfibrillated cellulose comprising microfibrillating, e.g., by
grinding, a fibrous material comprising cellulose, optionally in
the presence of grinding medium and inorganic particulate material.
When used as a filler in paper, for example, as a replacement or
partial replacement for a conventional mineral filler, the
microfibrillated cellulose obtained by said process, optionally in
combination with inorganic particulate material, was unexpectedly
found to improve the burst strength properties of the paper. That
is, relative to a paper filled with exclusively mineral filler,
paper filled with the microfibrillated cellulose was found to have
improved burst strength. In other words, the microfibrillated
cellulose filler was found to have paper burst strength enhancing
attributes. In one particularly advantageous embodiment of that
invention, the fibrous material comprising cellulose was ground in
the presence of a grinding medium, optionally in combination with
inorganic particulate material, to obtain microfibrillated
cellulose having a fibre steepness of from 20 to about 50.
Co-Processing of a Fibrous Substrate Comprising Cellulose and at
Least One Inorganic Particulate Material
[0159] As used herein, the terms "co-grinding (or "co-ground")
composite of microfibrillated cellulose and inorganic particulate
material" refers to a composite obtained by a "co-grinding
microfibrillation process," wherein a fibrous substrate comprising
cellulose is microfibrillated in an aqueous environment in a
grinding apparatus in the presence of the at least one inorganic
particulate material, and optionally a grinding medium other than
the at least one inorganic particulate material (or stated
differently by "co-processing" a fibrous substrate comprising
cellulose in the presence of the at least one inorganic particulate
material in a wet grinding apparatus and optionally in the presence
of a grinding medium other than the at least one inorganic
particulate material, which is removed after grinding, to produce
microfibrillated cellulose). See the description below of an
exemplary microfibrillation process and wet-grinding process.
[0160] After co-processing to form a co-processed microfibrillated
cellulose and inorganic particulate material composite, additional
inorganic particulate material may be added (e.g., by blending or
mixing) to reduce the microfibrillated cellulose content of the
co-processed microfibrillated cellulose and inorganic particulate
material composite.
[0161] In an embodiment, the MFC may be manufactured using a tower
mill or a screened grinding mill such as a stirred media
detritor.
[0162] A stirred media mill consists of a rotating impeller that
transfers kinetic energy to small grinding media beads, which grind
down the charge via a combination of shear, compressive, and impact
forces. A variety of grinding apparatus may be used to produce MFC
by the disclosed methods herein, including, for example, a tower
mill, a screened grinding mill, or a stirred media detritor.
The Microfibrillating Process
[0163] In accordance with a further aspect and embodiments of the
present disclosure, there is provided a method of microfibrillating
a fibrous substrate comprising cellulose in the presence of at
least one inorganic particulate material. According to particular
embodiments of the present methods, the microfibrillating step is
conducted in the presence of an inorganic particulate material
which acts as a microfibrillating agent. In accordance with another
embodiment the microfibrillating step is conducted in the presence
of an inorganic particulate material and a grinding medium other
than the at least one inorganic particulate material, which is
removed after grinding.
[0164] The microfibrillated cellulose utilized in the present
invention is, however, not limited to a single manufacturing
method. Such microfibrillation processes are presented for
illustrative purposes.
[0165] By "microfibrillating" is meant a process in which
microfibrils of cellulose are liberated or partially liberated as
individual species or as smaller aggregates as compared to the
fibres of the pre-microfibrillated cellulose-containing pulp.
Typical cellulose fibres (i.e., pre-microfibrillated
cellulose-containing pulp) suitable for use in papermaking include
larger aggregates of hundreds or thousands of individual cellulose
microfibrils. By microfibrillating the cellulose, particular
characteristics and properties, including but not limited to the
characteristic and properties described herein, are imparted to the
microfibrillated cellulose and the compositions including
microfibrillated cellulose and at least one inorganic particulate
material.
[0166] The step of microfibrillating may be carried out in any
suitable apparatus. In one embodiment, the microfibrillating step
is conducted in a grinding vessel under wet-grinding conditions. In
another embodiment, the microfibrillating step is carried out in a
homogenizer. Each of these embodiments is described in greater
detail below.
Wet-Grinding Microfibrillation Process
[0167] The grinding may be an attrition grinding process in the
presence of a grinding medium, or may be an autogenous grinding
process, i.e., one performed in the absence of a grinding medium.
By grinding medium is meant a medium other than the at least one
inorganic particulate material which is co-ground with the fibrous
substrate comprising cellulose.
[0168] The grinding medium, when present, may be of a natural or a
synthetic material. The grinding medium may, for example, comprise
balls, beads or pellets of any hard mineral, ceramic or metallic
material. Such materials may include, for example, alumina,
zirconia, zirconium silicate, aluminum silicate or the mullite-rich
material which is produced by calcining kaolinitic clay at a
temperature in the range of from about 1300.degree. C. to about
1800.degree. C. For example, in some embodiments a Carbolite.RTM.
grinding medium is used. Alternatively, particles of natural sand
of a suitable particle size may be used.
[0169] Generally, the type of and particle size of grinding medium
to be selected for use in the invention may be dependent on the
properties, such as, e.g., the particle size of, and the chemical
composition of, the feed suspension of material to be ground.
Preferably, the particulate grinding medium comprises particles
having an average diameter in the range of from about 0.1 mm to
about 6.0 mm and, more preferably, in the range of from about 0.2
mm to about 4.0 mm. The grinding medium (or media) may be present
in an amount up to about 70% by volume of the charge. The grinding
media may be present in amount of at least about 10% by volume of
the charge, for example, at least about 20% by volume of the
charge, or at least about 30% by volume of the charge, or at least
about 40% by volume of the charge, or at least about 50% by volume
of the charge, or at least about 60% by volume of the charge.
[0170] The grinding may be carried out in one or more stages. For
example, a coarse inorganic particulate material may be ground in
the grinder vessel to a predetermined particle size distribution,
after which the fibrous material comprising cellulose is added and
the grinding continued until the desired level of microfibrillation
has been obtained. The coarse inorganic particulate material used
in accordance with an first aspect of this invention initially may
have a particle size distribution in which less than about 20% by
weight of the particles have an essential spherical diameter
(e.s.d) of less than 2 .mu.m, for example, less than about 15% by
weight, or less than about 10% by weight of the particles have an
e.s.d. of less than 2 .mu.m. In another embodiment, the coarse
inorganic particulate material used in accordance with the first
aspect of this invention initially may have a particle size
distribution, as measured using a Malvern Mastersizer S machine, in
which less than about 20% by volume of the particles have an e.s.d
of less than 2 .mu.m, for example, less than about 15% by volume,
or less than about 10% by volume of the particles have an e.s.d. of
less than 2 .mu.m.
[0171] The coarse inorganic particulate material may be wet or dry
ground in the absence or presence of a grinding medium. In the case
of a wet grinding stage, the coarse inorganic particulate material
is preferably ground in an aqueous suspension in the presence of a
grinding medium. In such a suspension, the coarse inorganic
particulate material may preferably be present in an amount of from
about 5% to about 85% by weight of the suspension; more preferably
in an amount of from about 20% to about 80% by weight of the
suspension. Most preferably, the coarse inorganic particulate
material may be present in an amount of about 30% to about 75% by
weight of the suspension. As described above, the coarse inorganic
particulate material may be ground to a particle size distribution
such that at least about 10% by weight of the particles have an
e.s.d of less than 2 .mu.m, for example, at least about 20% by
weight, or at least about 30% by weight, or at least about 40% by
weight, or at least about 50% by weight, or at least about 60% by
weight, or at least about 70% by weight, or at least about 80% by
weight, or at least about 90% by weight, or at least about 95% by
weight, or about 100% by weight of the particles, have an e.s.d of
less than 2 .mu.m, after which the cellulose pulp is added and the
two components are co-ground to microfibrillate the fibres of the
cellulose pulp.
[0172] In another embodiment, the coarse inorganic particulate
material is ground to a particle size distribution, as measured
using a Malvern Mastersizer S machine such that at least about 10%
by volume of the particles have an e.s.d of less than 2 .mu.m, for
example, at least about 20% by volume, or at least about 30% by
volume or at least about 40% by volume, or at least about 50% by
volume, or at least about 60% by volume, or at least about 70% by
volume, or at least about 80% by volume, or at least about 90% by
volume, or at least about 95% by volume, or about 100% by volume of
the particles, have an e.s.d of less than 2 .mu.m, after which the
cellulose pulp is added and the two components are co-ground to
microfibrillate the fibres of the cellulose pulp.
[0173] In one embodiment, the mean particle size (d.sub.50) of the
inorganic particulate material is reduced during the co-grinding
process. For example, the d.sub.50 of the inorganic particulate
material may be reduced by at least about 10% (as measured by a
Malvern Mastersizer S machine), for example, the d.sub.50 of the
inorganic particulate material may be reduced by at least about
20%, or reduced by at least about 30%, or reduced by at least about
50%, or reduced by at least about 50%, or reduced by at least about
60%, or reduced by at least about 70%, or reduced by at least about
80%, or reduced by at least about 90%. For example, an inorganic
particulate material having a d.sub.50 of 2.5 .mu.m prior to
co-grinding and a d.sub.50 of 1.5 .mu.m post co-grinding will have
been subject to a 40% reduction in particle size. In certain
embodiments, the mean particle size of the inorganic particulate
material is not significantly reduced during the co-grinding
process. By `not significantly reduced` is meant that the d.sub.50
of the inorganic particulate material is reduced by less than about
10%, for example, the d.sub.50 of the inorganic particulate
material is reduced by less than about 5%.
[0174] The fibrous substrate comprising cellulose may be
microfibrillated in the presence of at least one inorganic
particulate material to obtain microfibrillated cellulose having a
d.sub.50 ranging from about 5 .mu.m to about 500 .mu.m, as measured
by laser light scattering. The fibrous substrate comprising
cellulose may be microfibrillated in the presence of an inorganic
particulate material to obtain microfibrillated cellulose having a
d.sub.50 of equal to or less than about 400 .mu.m, for example
equal to or less than about 300 .mu.m, or equal to or less than
about 200 .mu.m or equal to or less than about 150 .mu.m, or equal
to or less than about 125 .mu.m, or equal to or less than about 100
.mu.m, or equal to or less than about 90 .mu.m, or equal to or less
than about 80 .mu.m, or equal to or less than about 70 .mu.m, or
equal to or less than about 60 .mu.m, or equal to or less than
about 50 .mu.m, or equal to or less than about 40 .mu.m, or equal
to or less than about 30 .mu.m, or equal to or less than about 20
.mu.m, or equal to or less than about 10 .mu.m.
[0175] The fibrous substrate comprising cellulose may be
microfibrillated in the presence of an inorganic particulate
material to obtain microfibrillated cellulose having a modal fibre
particle size ranging from about 0.1-500 .mu.m and a modal
inorganic particulate material particle size ranging from 0.25-20
.mu.m. The fibrous substrate comprising cellulose may be
microfibrillated in the presence of an inorganic particulate
material to obtain microfibrillated cellulose having a modal fibre
particle size of at least about 0.5 .mu.m, for example at least
about 10 .mu.m, or at least about 50 .mu.m, or at least about 100
.mu.m, or at least about 150 .mu.m, or at least about 200 .mu.m, or
at least about 300 .mu.m, or at least about 400 .mu.m.
[0176] The fibrous substrate comprising cellulose may be
microfibrillated in the presence of an inorganic particulate
material to obtain microfibrillated cellulose having a fibre
steepness equal to or greater than about 10, as measured by
Malvern. Fibre steepness (i.e., the steepness of the particle size
distribution of the fibres) is determined by the following
formula:
Steepness=100.times.(d.sub.30/d.sub.70).
[0177] The microfibrillated cellulose may have a fibre steepness
equal to or less than about 100. The microfibrillated cellulose may
have a fibre steepness equal to or less than about 75, or equal to
or less than about 50, or equal to or less than about 40, or equal
to or less than about 30. The microfibrillated cellulose may have a
fibre steepness from about 20 to about 50, or from about 25 to
about 40, or from about 25 to about 35, or from about 30 to about
40.
[0178] The grinding is suitably performed in a grinding vessel,
such as a tumbling mill (e.g., rod, ball and autogenous), a stirred
mill (e.g., SAM or IsaMill), a tower mill, a stirred media detritor
(SMD), or a grinding vessel comprising rotating parallel grinding
plates between which the feed to be ground is fed.
[0179] In one embodiment, the grinding vessel is a tower mill. The
tower mill may comprise a quiescent zone above one or more grinding
zones. A quiescent zone is a region located towards the top of the
interior of tower mill in which minimal or no grinding takes place
and comprises microfibrillated cellulose and inorganic particulate
material. The quiescent zone is a region in which particles of the
grinding medium sediment down into the one or more grinding zones
of the tower mill.
[0180] The tower mill may comprise a classifier above one or more
grinding zones. In an embodiment, the classifier is top mounted and
located adjacent to a quiescent zone. The classifier may be a
hydrocyclone.
[0181] The tower mill may comprise a screen above one or more
grinding zones. In an embodiment, a screen is located adjacent to a
quiescent zone and/or a classifier. The screen may be sized to
separate grinding media from the product aqueous suspension
comprising microfibrillated cellulose and inorganic particulate
material and to enhance grinding media sedimentation.
[0182] In an embodiment, the grinding is performed under plug flow
conditions. Under plug flow conditions the flow through the tower
is such that there is limited mixing of the grinding materials
through the tower. This means that at different points along the
length of the tower mill the viscosity of the aqueous environment
will vary as the fineness of the microfibrillated cellulose
increases. Thus, in effect, the grinding region in the tower mill
can be considered to comprise one or more grinding zones which have
a characteristic viscosity. A skilled person in the art will
understand that there is no sharp boundary between adjacent
grinding zones with respect to viscosity.
[0183] In an embodiment, water is added at the top of the mill
proximate to the quiescent zone or the classifier or the screen
above one or more grinding zones to reduce the viscosity of the
aqueous suspension comprising microfibrillated cellulose and
inorganic particulate material at those zones in the mill. By
diluting the product microfibrillated cellulose and inorganic
particulate material composite at this point in the mill it has
been found that the prevention of grinding media carry over to the
quiescent zone and/or the classifier and/or the screen is improved.
Further, the limited mixing through the tower allows for processing
at higher solids lower down the tower and dilute at the top with
limited backflow of the dilution water back down the tower into the
one or more grinding zones. Any suitable amount of water which is
effective to dilute the viscosity of the product aqueous suspension
comprising microfibrillated cellulose and inorganic particulate
material may be added. The water may be added continuously during
the grinding process, or at regular intervals, or at irregular
intervals.
[0184] In another embodiment, water may be added to one or more
grinding zones via one or more water injection points positioned
along the length of the tower mill, or each water injection point
being located at a position which corresponds to the one or more
grinding zones. Advantageously, the ability to add water at various
points along the tower allows for further adjustment of the
grinding conditions at any or all positions along the mill.
[0185] The tower mill may comprise a vertical impeller shaft
equipped with a series of impeller rotor disks throughout its
length. The action of the impeller rotor disks creates a series of
discrete grinding zones throughout the mill.
[0186] In another embodiment, the grinding is performed in a
screened grinder, preferably a stirred media detritor. The screened
grinder may comprise one or more screen(s) having a nominal
aperture size of at least about 250 .mu.m, for example, the one or
more screens may have a nominal aperture size of at least about 300
.mu.m, or at least about 350 .mu.m, or at least about 400 .mu.m, or
at least about 450 .mu.m, or at least about 500 .mu.m, or at least
about 550 .mu.m, or at least about 600 .mu.m, or at least about 650
.mu.m, or at least about 700 .mu.m, or at least about 750 .mu.m, or
at least about 800 .mu.m, or at least about 850 .mu.m, or at or
least about 900 .mu.m, or at least about 1000 .mu.m.
[0187] The screen sizes noted immediately above are applicable to
the tower mill embodiments described above.
[0188] As noted above, the grinding may be performed in the
presence of a grinding medium. In an embodiment, the grinding
medium is a coarse media comprising particles having an average
diameter in the range of from about 1 mm to about 6 mm, for example
about 2 mm, or about 3 mm, or about 4 mm, or about 5 mm.
[0189] In another embodiment, the grinding media has a specific
gravity of at least about 2.5, for example, at least about 3, or at
least about 3.5, or at least about 4.0, or at least about 4.5, or
least about 5.0, or at least about 5.5, or at least about 6.0.
[0190] In another embodiment, the grinding media comprises
particles having an average diameter in the range of from about 1
mm to about 6 mm and has a specific gravity of at least about
2.5.
[0191] As described above, the grinding medium (or media) may
present in an amount up to about 70% by volume of the charge. The
grinding media may be present in amount of at least about 10% by
volume of the charge, for example, at least about 20% by volume of
the charge, or at least about 30% by volume of the charge, or at
least about 40% by volume of the charge, or at least about 50% by
volume of the charge, or at least about 60% by volume of the
charge.
[0192] In one embodiment, the grinding medium is present in amount
of about 50% by volume of the charge.
[0193] By `charge` is meant the composition which is the feed fed
to the grinder vessel. The charge includes of water, grinding
media, fibrous substrate comprising cellulose and inorganic
particulate material, and any other optional additives as described
herein. The use of a relatively coarse and/or dense media has the
advantage of improved (i.e., faster) sediment rates and reduced
media carry over through the quiescent zone and/or classifier
and/or screen(s).
[0194] A further advantage in using relatively coarse grinding
media is that the mean particle size (d.sub.50) of the inorganic
particulate material may not be significantly reduced during the
grinding process such that the energy imparted to the grinding
system is primarily expended in microfibrillating the fibrous
substrate comprising cellulose.
[0195] A further advantage in using relatively coarse screens is
that a relatively coarse or dense grinding media can be used in the
microfibrillating step. In addition, the use of relatively coarse
screens (i.e., having a nominal aperture of least about 250 .mu.m)
allows a relatively high solids product to be processed and removed
from the grinder, which allows a relatively high solids feed
(comprising fibrous substrate comprising cellulose and inorganic
particulate material) to be processed in an economically viable
process. As discussed below, it has been found that a feed having a
high initial solids content is desirable in terms of energy
sufficiency. Further, it has also been found that product produced
(at a given energy) at lower solids has a coarser particle size
distribution.
[0196] Thus, in accordance with one embodiment, the fibrous
substrate comprising cellulose and inorganic particulate material
are present in the aqueous environment at an initial solids content
of at least about 4 wt. %, of which at least about 2% by weight is
fibrous substrate comprising cellulose. The initial solids content
may be at least about 10 wt. %, or at least about 20 wt. %, or at
least about 30 wt. %, or at least about at least 40 wt. %. At least
about 5% by weight of the initial solids content may be fibrous
substrate comprising cellulose, for example, at least about 10%, or
at least about 15%, or at least about 20% by weight of the initial
solids content may be fibrous substrate comprising cellulose.
[0197] In another embodiment, the grinding is performed in a
cascade of grinding vessels, one or more of which may comprise one
or more grinding zones. For example, the fibrous substrate
comprising cellulose and the inorganic particulate material may be
ground in a cascade of two or more grinding vessels, for example, a
cascade of three or more grinding vessels, or a cascade of four or
more grinding vessels, or a cascade of five or more grinding
vessels, or a cascade of six or more grinding vessels, or a cascade
of seven or more grinding vessels, or a cascade of eight or more
grinding vessels, or a cascade of nine or more grinding vessels in
series, or a cascade comprising up to ten grinding vessels. The
cascade of grinding vessels may be operatively linked in series or
parallel or a combination of series and parallel. The output from
and/or the input to one or more of the grinding vessels in the
cascade may be subjected to one or more screening steps and/or one
or more classification steps.
[0198] The total energy expended in a microfibrillation process may
be apportioned equally across each of the grinding vessels in the
cascade. Alternatively, the energy input may vary between some or
all of the grinding vessels in the cascade.
[0199] A person skilled in the art will understand that the energy
expended per vessel may vary between vessels in the cascade
depending on the amount of fibrous substrate being microfibrillated
in each vessel, and optionally the speed of grind in each vessel,
the duration of grind in each vessel, the type of grinding media in
each vessel and the type and amount of inorganic particulate
material. The grinding conditions may be varied in each vessel in
the cascade in order to control the particle size distribution of
both the microfibrillated cellulose and the inorganic particulate
material. For example, the grinding media size may be varied
between successive vessels in the cascade in order to reduce
grinding of the inorganic particulate material and to target
grinding of the fibrous substrate comprising cellulose.
[0200] In an embodiment the grinding is performed in a closed
circuit. In another embodiment, the grinding is performed in an
open circuit. The grinding may be performed in batch mode. The
grinding may be performed in a re-circulating batch mode. In
another embodiment, the grinding may be performed in a continuous
mode, as described elsewhere in this specification.
[0201] As described above, the grinding circuit may include a
pre-grinding step in which coarse inorganic particulate ground in a
grinder vessel to a predetermined particle size distribution, after
which fibrous material comprising cellulose is combined with the
pre-ground inorganic particulate material and the grinding
continued in the same or different grinding vessel until the
desired level of microfibrillation has been obtained.
[0202] As the suspension of material to be ground may be of a
relatively high viscosity, a suitable dispersing agent may
preferably be added to the suspension prior to grinding. The
dispersing agent may be, for example, a water soluble condensed
phosphate, polysilicic acid or a salt thereof, or a
polyelectrolyte, for example a water soluble salt of a poly(acrylic
acid) or of a poly(methacrylic acid) having a number average
molecular weight not greater than 80,000. The amount of the
dispersing agent used would generally be in the range of from 0.1
to 2.0% by weight, based on the weight of the dry inorganic
particulate solid material. The suspension may suitably be ground
at a temperature in the range of from 4.degree. C. to 100.degree.
C.
[0203] Other additives which may be included during the
microfibrillation step include: carboxymethyl cellulose, amphoteric
carboxymethyl cellulose, oxidising agents,
2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO), TEMPO derivatives,
and wood degrading enzymes.
[0204] The pH of the suspension of material to be ground may be
about 7 or greater than about 7 (i.e., basic), for example, the pH
of the suspension may be about 8, or about 9, or about 10, or about
11. The pH of the suspension of material to be ground may be less
than about 7 (i.e., acidic), for example, the pH of the suspension
may be about 6, or about 5, or about 4, or about 3. The pH of the
suspension of material to be ground may be adjusted by addition of
an appropriate amount of acid or base. Suitable bases included
alkali metal hydroxides, such as, for example NaOH. Other suitable
bases are sodium carbonate and ammonia. Suitable acids included
inorganic acids, such as hydrochloric and sulphuric acid, or
organic acids. An exemplary acid is orthophosphoric acid.
[0205] The amount of inorganic particulate material and cellulose
pulp in the mixture to be co-ground may vary in a ratio of from
about 99.5:0.5 to about 0.5:99.5, based on the dry weight of
inorganic particulate material and the amount of dry fibre in the
pulp, for example, a ratio of from about 99.5:0.5 to about 50:50
based on the dry weight of inorganic particulate material and the
amount of dry fibre in the pulp. For example, the ratio of the
amount of inorganic particulate material and dry fibre may be from
about 99.5:0.5 to about 70:30. In an embodiment, the ratio of
inorganic particulate material to dry fibre is about 80:20, or for
example, about 85:15, or about 90:10, or about 91:9, or about 92:8,
or about 93:7, or about 94:6, or about 95:5, or about 96:4, or
about 97:3, or about 98:2, or about 99:1. In a preferred
embodiment, the weight ratio of inorganic particulate material to
dry fibre is about 95:5. In another preferred embodiment, the
weight ratio of inorganic particulate material to dry fibre is
about 90:10. In another preferred embodiment, the weight ratio of
inorganic particulate material to dry fibre is about 85:15. In
another preferred embodiment, the weight ratio of inorganic
particulate material to dry fibre is about 80:20.
[0206] The total energy input in a typical grinding process to
obtain the desired aqueous suspension composition may typically be
between about 100 and 1500 kWht.sup.-1 based on the total dry
weight of the inorganic particulate filler. The total energy input
may be less than about 1000 kWht.sup.-1, for example, less than
about 800 kWht.sup.-1, less than about 600 kWht.sup.-1, less than
about 500 kWht.sup.-1, less than about kWht.sup.-1, less than about
300 kWht.sup.-1, or less than about 200 kWht.sup.-1. As such, the
present inventors have surprisingly found that a cellulose pulp can
be microfibrillated at relatively low energy input when it is
co-ground in the presence of an inorganic particulate material. As
will be apparent, the total energy input per tonne of dry fibre in
the fibrous substrate comprising cellulose will be less than about
10,000 kWht.sup.-1, for example, less than about 9000 kWht.sup.-1,
or less than about 8000 kWht.sup.-1, or less than about 7000
kWht.sup.-1, or less than about 6000 kWht.sup.-1, or less than
about 5000 kWht.sup.-1, for example less than about 4000
kWht.sup.-1, less than about 3000 kWht.sup.-1, less than about 2000
kWht.sup.-1, less than about 1500 kWht.sup.-1, less than about 1200
kWht.sup.-1, less than about 1000 kWht.sup.-1, or less than about
800 kWht.sup.-1. The total energy input varies depending on the
amount of dry fibre in the fibrous substrate being
microfibrillated, and optionally the speed of grind and the
duration of grind.
[0207] In another embodiment, the grinding media comprises
particles having an average diameter of about 3 mm and specific
gravity of about 2.7.
[0208] In another embodiment, the MFC is manufactured in accordance
with the method described in WO-A-2010/131016, which comprises a
step of microfibrillating a fibrous substrate comprising cellulose
by grinding in the presence of a particulate grinding medium which
is to be removed after the completion of grinding. By
"microfibrillating" is meant a process in which microfibrils of
cellulose are liberated or partially liberated as individual
species or as small aggregates as compared to the fibres of the
pre-microfibrillated pulp. Typical cellulose fibres (i.e.,
pre-microfibrillated pulp) suitable for use in papermaking include
larger aggregates of hundreds or thousands of individual cellulose
fibrils. By microfibrillating the cellulose, particular
characteristics and properties, including the characteristics and
properties described herein, are imparted to the MFC and the
compositions comprising the MFC.
[0209] The fibrous substrate comprising cellulose (variously
referred to herein as "fibrous substrate comprising cellulose,"
"cellulose fibres," "fibrous cellulose feedstock," "cellulose
feedstock" and "cellulose-containing fibres (or fibrous," etc.) may
be derived from recycled pulp or a papermill broke and/or
industrial waste, or a paper streams rich in mineral fillers and
cellulosic materials from a papermill.
[0210] The cellulose pulp may be beaten (for example in a Valley
beater) and/or otherwise refined (for example, processing in a
conical or plate refiner) to any predetermined freeness, reported
in the art as Canadian standard freeness (CSF) in cm.sup.3. CSF
means a value for the freeness or drainage rate of pulp measured by
the rate that a suspension of pulp may be drained, and this test is
carried out according to the T 227 cm-09 TAPPI standard. For
example, the cellulose pulp may have a Canadian standard freeness
of about 10 cm.sup.3 or greater prior to being microfibrillated.
The cellulose pulp may have a CSF of about 700 cm.sup.3 or less,
for example, equal to or less than about 650 cm.sup.3, or equal to
or less than about 600 cm.sup.3, or equal to or less than about 550
cm.sup.3, or equal to or less than about 500 cm.sup.3, or equal to
or less than about 450 cm.sup.3, or equal to or less than about 400
cm.sup.3, or equal to or less than about 350 cm.sup.3, or equal to
or less than about 300 cm.sup.3, or equal to or less than about 250
cm.sup.3, or equal to or less than about 200 cm.sup.3, or equal to
or less than about 150 cm.sup.3, or equal to or less than about 100
cm.sup.3, or equal to or less than about 50 cm.sup.3. The cellulose
pulp may have a CSF of about 20 to about 700. The cellulose pulp
may then be dewatered by methods well known in the art, for
example, the pulp may be filtered through a screen in order to
obtain a wet sheet comprising at least about 10% solids, for
example at least about 15% solids, or at least about 20% solids, or
at least about 30% solids, or at least about 40% solids or at least
50% solids. The pulp may be utilized in an unrefined state, that is
to say, without being beaten or dewatered, or otherwise
refined.
[0211] In another embodiment, the microfibrillated cellulose is
prepared in accordance with a method comprising a step of
microfibrillating a fibrous substrate comprising cellulose in an
aqueous environment by grinding in the presence of a grinding
medium which is to be removed after the completion of grinding,
wherein the grinding is performed in a tower mill or a screened
grinder, and wherein the grinding is carried out in the absence of
grindable inorganic particulate material.
[0212] A grindable inorganic particulate material is a material
which would be ground in the presence of the grinding medium.
[0213] The particulate grinding medium may be of a natural or a
synthetic material. The grinding medium may, for example, comprise
balls, beads or pellets of any hard mineral, ceramic or metallic
material. Such materials may include, for example, alumina,
zirconia, zirconium silicate, aluminium silicate or the
mullite-rich material which is produced by calcining kaolinitic
clay at a temperature in the range of from about 1300.degree. C. to
about 1800.degree. C. For example, in some embodiments a
Carbolite.RTM. grinding media is preferred. Alternatively,
particles of natural sand of a suitable particle size may be
used.
[0214] Generally, the type of and particle size of grinding medium
to be selected for use in the invention may be dependent on the
properties, such as, e.g., the particle size of, and the chemical
composition of, the feed suspension of material to be ground.
Preferably, the particulate grinding medium comprises particles
having an average diameter in the range of from about 0.5 mm to
about 6 mm. In one embodiment, the particles have an average
diameter of at least about 3 mm.
[0215] The grinding medium may comprise particles having a specific
gravity of at least about 2.5. The grinding medium may comprise
particles have a specific gravity of at least about 3, or least
about 4, or least about 5, or at least about 6.
[0216] The grinding medium (or media) may be present in an amount
up to about 70% by volume of the charge. The grinding media may be
present in amount of at least about 10% by volume of the charge,
for example, at least about 20% by volume of the charge, or at
least about 30% by volume of the charge, or at least about 40% by
volume of the charge, or at least about 50% by volume of the
charge, or at least about 60% by volume of the charge.
[0217] The fibrous substrate comprising cellulose may be
microfibrillated to obtain microfibrillated cellulose having a
d.sub.50 ranging from about 5 to .mu.m about 500 .mu.m, as measured
by laser light scattering. The fibrous substrate comprising
cellulose may be microfibrillated to obtain microfibrillated
cellulose having a d.sub.50 of equal to or less than about 400
.mu.m, for example equal to or less than about 300 .mu.m, or equal
to or less than about 200 .mu.m, or equal to or less than about 150
.mu.m, or equal to or less than about 125 .mu.m, or equal to or
less than about 100 .mu.m, or equal to or less than about 90 .mu.m,
or equal to or less than about 80 .mu.m, or equal to or less than
about 70 .mu.m, or equal to or less than about 60 .mu.m, or equal
to or less than about 50 .mu.m, or equal to or less than about 40
.mu.m, or equal to or less than about 30 min, or equal to or less
than about 20 .mu.m, or equal to or less than about 10 .mu.m.
[0218] The fibrous substrate comprising cellulose may be
microfibrillated to obtain microfibrillated cellulose having a
modal fibre particle size ranging from about 0.1-500 min. The
fibrous substrate comprising cellulose may be microfibrillated in
the presence to obtain microfibrillated cellulose having a modal
fibre particle size of at least about 0.5 .mu.m, for example at
least about 10 .mu.m, or at least about 50 .mu.m, or at least about
100 .mu.m, or at least about 150 pan, or at least about 200 .mu.m,
or at least about 300 .mu.m, or at least about 400 .mu.m.
[0219] The fibrous substrate comprising cellulose may be
microfibrillated to obtain microfibrillated cellulose having a
fibre steepness equal to or greater than about 10, as measured by
Malvern. Fibre steepness (i.e., the steepness of the particle size
distribution of the fibres) is determined by the following
formula:
Steepness=100.times.(d.sub.30/d.sub.70)
[0220] The microfibrillated cellulose may have a fibre steepness
equal to or less than about 100. The microfibrillated cellulose may
have a fibre steepness equal to or less than about 75, or equal to
or less than about 50, or equal to or less than about 40, or equal
to or less than about 30. The microfibrillated cellulose may have a
fibre steepness from about 20 to about 50, or from about 25 to
about 40, or from about 25 to about 35, or from about 30 to about
40. In an embodiment, a preferred steepness range is about 20 to
about 50.
[0221] Calculation of fibre steepness of MFC fibres and inorganic
particulate material is well known in the art. For example, a
sample of co-ground slurry sufficient to give 5 g dry material is
weighed into a beaker, diluted to 60 g with deionised water, and
mixed with 5 cm3 of a solution of 1.0 wt % sodium carbonate and 0.5
wt % sodium hexametaphosphate. Further deionised water is added
with stirring to a final slurry weight of 80 g. The slurry is then
added in 1 cm.sup.3 aliquots to water in the sample preparation
unit attached to the Mastersizer S (or Mastersizer Insitec or other
comparable apparatus) until the optimum level of obscuration is
displayed (normally 10-15%). The light scattering analysis
procedure is then carried out. The instrument range selected was
300RF: 0.05-900, and the beam length set to 2.4 mm. For co-ground
samples containing calcium carbonate and fibre the refractive index
for calcium carbonate (1.596) is used. For co-ground samples of
kaolin and fibre the RI for kaolin (1.5295) is used. The particle
size distribution is calculated from Mie theory and gives the
output as a differential volume based distribution. The presence of
two distinct peaks is interpreted as arising from the mineral
(finer peak) and fibre (coarser peak).
[0222] The finer mineral peak is fitted to the measured data points
and subtracted mathematically from the distribution to leave the
fibre peak, which is converted to a cumulative distribution.
Similarly, the fibre peak is subtracted mathematically from the
original distribution to leave the mineral peak, which is also
converted to a cumulative distribution. Both these cumulative
curves may then be used to calculate the mean particle size
(d.sub.50) and the steepness of the distribution
(d30/d.sub.70.times.100). The differential curve may be used to
find the modal particle size for both the mineral and fibre
fractions
[0223] In one embodiment, the grinding vessel is a tower mill. The
tower mill may comprise a quiescent zone above one or more grinding
zones. A quiescent zone is a region located towards the top of the
interior of a tower miii in which minimal or no grinding takes
place and comprises microfibrillated cellulose and inorganic
particulate material. The quiescent zone is a region in which
particles of the grinding medium sediment down into the one or more
grinding zones of the tower mill.
[0224] The tower mill may comprise a classifier above one or more
grinding zones. In an embodiment, the classifier is top mounted and
located adjacent to a quiescent zone. The classifier may be a
hydrocyclone.
[0225] The tower mill may comprise a screen above one or more grind
zones. In an embodiment, a screen is located adjacent to a
quiescent zone and/or a classifier. The screen may be sized to
separate grinding media from the product aqueous suspension
comprising microfibrillated cellulose and to enhance grinding media
sedimentation.
[0226] In an embodiment, the grinding is performed under plug flow
conditions. Under plug flow conditions the flow through the tower
is such that there is limited mixing of the grinding materials
through the tower. This means that at different points along the
length of the tower mill the viscosity of the aqueous environment
will vary as the fineness of the microfibrillated cellulose
increases. Thus, in effect, the grinding region in the tower mill
can be considered to comprise one or more grinding zones which have
a characteristic viscosity. A skilled person in the art will
understand that there is no sharp boundary between adjacent
grinding zones with respect to viscosity.
[0227] In an embodiment, water is added at the top of the mill
proximate to the quiescent zone or the classifier or the screen
above one or more grinding zones to reduce the viscosity of the
aqueous suspension comprising microfibrillated cellulose at those
zones in the mill. By diluting the product microfibrillated
cellulose at this point in the mill it has been found that the
prevention of grinding media carry over to the quiescent zone
and/or the classifier and/or the screen is improved. Further, the
limited mixing through the tower allows for processing at higher
solids lower down the tower and dilute at the top with limited
backflow of the dilution water back down the tower into the one or
more grinding zones. Any suitable amount of water which is
effective to dilute the viscosity of the product aqueous suspension
comprising microfibrillated cellulose may be added. The water may
be added continuously during the grinding process, or at regular
intervals, or at irregular intervals.
[0228] In another embodiment, water may be added to one or more
grinding zones via one or more water injection points positioned
along the length of the tower mill, the or each water injection
point being located at a position which corresponds to the one or
more grinding zones. Advantageously, the ability to add water at
various points along the tower allows for further adjustment of the
grinding conditions at any or all positions along the mill.
[0229] The tower mill may comprise a vertical impeller shaft
equipped with a series of impeller rotor disks throughout its
length. The action of the impeller rotor disks creates a series of
discrete grinding zones throughout the mill.
[0230] In another embodiment, the grinding is performed in a
screened grinder, preferably a stirred media detritor. The screened
grinder may comprise one or more screen(s) having a nominal
aperture size of at least about 250 .mu.m, for example, the one or
more screens may have a nominal aperture size of at least about 300
.mu.m, or at least about 350 .mu.m, or at least about 400 .mu.m, or
at least about 450 .mu.m, or at least about 500 .mu.m, or at least
about 550 .mu.m, or at least about 600 .mu.m, or at least about 650
.mu.m, or at least about 700 .mu.m, or at least about 750 .mu.m, or
at least about 800 .mu.m, or at least about 850 .mu.m, or at or
least about 900 .mu.m, or at least about 1000 .mu.m, or at least
about 1,250 .mu.m or at least about 1,500 .mu.m.
[0231] The screen sizes noted immediately above are applicable to
the tower mill embodiments described above.
[0232] As noted above, the grinding is performed in the presence of
a grinding medium. In an embodiment, the grinding medium is a
coarse media comprising particles having an average diameter in the
range of from about 1 mm to about 6 mm, for example about 2 mm, or
about 3 mm, or about 4 mm, or about 5 mm.
[0233] In another embodiment, the grinding media has a specific
gravity of at least about 2.5, for example, at least about 3, or at
least about 3.5, or at least about 4.0, or at least about 4.5, or
least about 5.0, or at least about 5.5, or at least about 6.0.
[0234] As described above, the grinding medium (or media) may be in
an amount up to about 70% by volume of the charge. The grinding
media may be present in amount of at least about 10% by volume of
the charge, for example, at least about 20% by volume of the
charge, or at least about 30% by volume of the charge, or at least
about 40% by volume of the charge, or at least about 50% by volume
of the charge, or at least about 60% by volume of the charge.
[0235] In one embodiment, the grinding medium is present in amount
of about 50% by volume of the charge.
[0236] By `charge` is meant the composition which is the feed fed
to the grinder vessel. The charge includes water, grinding media,
the fibrous substrate comprising cellulose and any other optional
additives (other than as described herein).
[0237] The use of a relatively coarse and/or dense media has the
advantage of improved (i.e., faster) sediment rates and reduced
media carry over through the quiescent zone and/or classifier
and/or screen(s).
[0238] A further advantage in using relatively coarse screens is
that a relatively coarse or dense grinding media can be used in the
microfibrillating step. In addition, the use of relatively coarse
screens (i.e., having a nominal aperture of least about 250 urn)
allows a relatively high solids product to be processed and removed
from the grinder, which allows a relatively high solids feed
(comprising fibrous substrate comprising cellulose and inorganic
particulate material) to be processed in an economically viable
process. As discussed below, it has been found that a feed having a
high initial solids content is desirable in terms of energy
sufficiency. Further, it has also been found that product produced
(at a given energy) at lower solids has a coarser particle size
distribution.
[0239] In accordance with one embodiment, the fibrous substrate
comprising cellulose is present in the aqueous environment at an
initial solids content of at least about 1 wt. %. The fibrous
substrate comprising cellulose may be present in the aqueous
environment at an initial solids content of at least about 2 wt. %,
for example at least about 3 wt. %, or at least about at least 4
wt. %. Typically the initial solids content will be no more than
about 10 wt. %.
[0240] In another embodiment, the grinding is performed in a
cascade of grinding vessels, one or more of which may comprise one
or more grinding zones. For example, the fibrous substrate
comprising cellulose may be ground in a cascade of two or more
grinding vessels, for example, a cascade of three or more grinding
vessels, or a cascade of four or more grinding vessels, or a
cascade of five or more grinding vessels, or a cascade of six or
more grinding vessels, or a cascade of seven or more grinding
vessels, or a cascade of eight or more grinding vessels, or a
cascade of nine or more grinding vessels in series, or a cascade
comprising up to ten grinding vessels. The cascade of grinding
vessels may be operatively inked in series or parallel or a
combination of series and parallel. The output from and/or the
input to one or more of the grinding vessels in the cascade may be
subjected to one or more screening steps and/or one or more
classification steps.
[0241] The total energy expended in a microfibrillation process may
be apportioned equally across each of the grinding vessels in the
cascade. Alternatively, the energy input may vary between some or
all of the grinding vessels in the cascade.
[0242] A person skilled in the art will understand that the energy
expended per vessel may vary between vessels in the cascade
depending on the amount of fibrous substrate being microfibrillated
in each vessel, and optionally the speed of grind in each vessel,
the duration of grind in each vessel and the type of grinding media
in each vessel. The grinding conditions may be varied in each
vessel in the cascade in order to control the particle size
distribution of the microfibrillated cellulose.
[0243] In an embodiment the grinding is performed in a closed
circuit. In another embodiment, the grinding is performed in an
open circuit.
[0244] As the suspension of material to be ground may be of a
relatively high viscosity, a suitable dispersing agent may
preferably be added to the suspension prior to grinding. The
dispersing agent may be, for example, a water soluble condensed
phosphate, polysilicic acid or a salt thereof, or a poly
electrolyte, for example a water soluble salt of a poly(acrylic
acid) or of a poly(methacrylic acid) having a number average
molecular weight not greater than 80,000. The amount of the
dispersing agent used would generally be in the range of from 0.1
to 2.0% by weight, based on the weight of the dry inorganic
particulate solid material. The suspension may suitably be ground
at a temperature in the range of from 4.degree. C. to 100.degree.
C.
[0245] Other additives which may be included during the
microfibrillation step include: carboxymethylcellulose, amphoteric
carboxymethylcellulose, oxidising agents,
2,2,6,6-Tetramethylpiperidine-1-oxyl (TEMPO). TEMPO derivatives,
and wood degrading enzymes.
[0246] The pH of the suspension of material to be ground may be
about 7 or greater than about 7 (i.e., basic), for example, the pH
of the suspension may be about 8, or about 9, or about 10, or about
11. The pH of the suspension of material to be ground may be less
than about 7 (i.e., acidic), for example, the pH of the suspension
may be about 6, or about 5, or about 4, or about 3. The pH of the
suspension of material to be ground may be adjusted by addition of
an appropriate amount of acid or base. Suitable bases included
alkali metal hydroxides, such as, for example NaOH. Other suitable
bases are sodium carbonate and ammonia. Suitable acids included
inorganic acids, such as hydrochloric and sulphuric acid, or
organic acids. An exemplary acid is orthophosphoric acid.
[0247] The total energy input in a typical grinding process to
obtain the desired aqueous suspension composition may typically be
between about 100 and 1500 kWht.sup.1 based on the total dry weight
of the inorganic particulate filler. The total energy input may be
less than about 1000 kWht.sup.-1, for example, less than about 800
kWht.sup.-1, less than about 600 kWht.sup.-1, less than about 500
kWht.sup.-1, less than about 400 kWht.sup.-1, less than about 300
kWht.sup.-1, or less than about 200 kWht.sup.-1. As such, the
present inventors have surprisingly found that a cellulose pulp can
be microfibrillated at relatively low energy input when it is
co-ground in the presence of an inorganic particulate material. As
will be apparent, the total energy input per tonne of dry fibre in
the fibrous substrate comprising cellulose will be less than about
10,000 kWht.sup.-1, for example, less than about 9000 kWht.sup.-1,
or less than about 8000 kWht.sup.-1, or less than about 7000
kWht.sup.-1, or less than about 6000 kWht.sup.-1, or less than
about 5000 kWht.sup.-1 for example less than about 4000
kWht.sup.-1, less than about 3000 kWht.sup.-1, less than about
2,000 kWht.sup.-1, less than about 1500 kWht.sup.-1, less than
about 1200 kWht.sup.-1, less than about 1000 kWht.sup.-1, or less
than about 800 kWht.sup.-1. The total energy input varies depending
on the amount of dry fibre in the fibrous substrate being
microfibrillated, and optionally the speed of grind and the
duration of grind.
[0248] Various aspects of the invention are described in further
detail in the following subsections. The use of subsections is not
meant to limit the invention. Each subsection may apply to any
aspect of the invention. In this application, the use of "or" means
"and/or" unless stated otherwise.
[0249] MFC may be produced in a continuous or batch mode. MFC is an
aqueous suspension mixture of microfibrillated cellulose and
inorganic particulate material. In an embodiment, MFC is prepared
by co-grinding a low solids aqueous suspension of cellulose wood
pulp in the presence of inorganic particulate material particles in
a wet vertically stirred media mill. The mineral particles act as
grinding aids and facilitate the cost-effective fibrillation of
pulp fibers to microfibrils in a process analogous to pulp
refining.
[0250] The inorganic particulate material used is a standard paper
filler, often calcium carbonate or kaolin. Most processes will use
kaolin, ground calcium carbonate or precipitated calcium carbonate.
The inorganic particulate material will be in aqueous slurry
form.
[0251] The cellulose used is typically unrefined Kraft or sulphite
pulp from a paper mill's pulp source (>99% cellulose) or
recycled pulp from paper and board recycling activities. The pulp
is received from the paper mill as an aqueous slurry usually at
approximately 4-5 wt. % solids. The water used will be from the
mill's process streams or in some cases council (city) water. The
ceramic grinding media are typically 3 mm diameter beads made from
calcined kaolin. In some cases when recycled pulp is used, the pulp
will already contain some inorganic particulate material.
[0252] In an illustrative recipe: Kraft pulp at approximately 4%
solids and hydrous kaolin at approximately 66% solids or calcium
carbonate slurry at approximately 75% solids and water are added to
the grinder continuously. The grinder is loaded with 3 mm diameter
mullite grinding media such that approximately 50% of the total
charge volume is occupied by the media (total charge volume=volume
occupied by mullite+pulp+kaolin+water). The throughput is
controlled such that the pulp and mineral mixture is co-ground for
an optimised period. Typically, this optimum period corresponds to
the development of maximum viscosity and tensile properties.
Typically, between approximately 1500-5000 kWhr/dry tonne of MFC is
applied. The temperature in the grinder reaches about 65 degrees
centigrade during the grind. The MFC product is in aqueous slurry
form.
[0253] In some cases, rather than running continuously, the same
process is operated batchwise. In this case, the ingredients are
added at the start of a batch, then the grinders are run for an
allocated time such that 1500-5000 kWhr/dry tonne of MFC is applied
and then at the end of the batch further water is added and the
product is discharged before the process being repeated.
[0254] In some cases, where inorganic particulate material cannot
be tolerated in an end use application, the above processes are
conducted without any added inorganic particulate material.
[0255] The above MFC product which results from the grinding and
screening process contains agglomerates which reduce performance
and can cause blockages if subjected to very fine screening. These
agglomerates may be reduced by the use of a homogeniser.
[0256] In some cases some of the water associated with the MFC
product is removed to lower transportation costs. This is achieved
by use of dewatering via a belt press and/or drying using a hot air
dryer or by other means known in the art. When dewatered and dried
products are prepared, a biocide is sometimes added to increase
shelf life and protect the product from decomposition. The biocide
is mixed into the MFC, for example, using a plough shear mixer. The
dewatered and partially dried products are usually shipped in bulk
bags.
[0257] The biocides used are DBNPA
(2,2-dibromo-3-nitrilopropionamide), and CMIT/MIT
(5-chloro-2-methyl-2H-isothiazol-3-one/2-methyl-2H isothiazol-3-one
(CMIT/MIT) or for the partially dried product and OIT
(2-octyl-2H-isothiazol-3-one).
[0258] The continuous production process is a pass-through process
with cellulose, inorganic particulate material and water being
sourced from the mill and returned to the mill after
processing.
[0259] Parameters that may be used to control production are
product d.sub.50, as measured by laser light scattering and either
viscosity or tensile properties, for example, the FLT tensile index
described elsewhere in this specification.
[0260] Various aspects of the invention are described in further
detail in the following subsections. The use of subsections is not
meant to limit the invention. Each subsection may apply to any
aspect of the invention. In this application, the use of "or" means
"and/or" unless stated otherwise.
Microporous Inorganic Particulate Material Composites
[0261] Some types of filler, such as calcined clays and
scalenohedral and aragonite precipitated calcium carbonates (PCC),
consist of aggregates of particles with open porous structures
(i.e., these are examples of microporous inorganic particulate
materials). Calcined clays are described in U.S. Pat. No.
3,586,523, which is hereby incorporated in by reference in its
entirety. Such calcined kaolin clays are substantially anhydrous,
amorphous aluminum silicates which are obtained by calcining a
specific type of kaolin clay, for example, hard sedimentary kaolin
clay.
[0262] Precipitated calcium carbonate (PCC) in clustered form is
known in the art as disclosed in U.S. Pat. No. 5,695,733, which is
hereby incorporated by reference in its entirety. The PCC is
produced in a unique clustered form having a substantial proportion
of particles having a prismatic morphology. By controlling the
solution environment utilized to produce PCC, i.e., the slaking of
lime (calcium oxide), temperature of carbonation and the rate of
introduction of carbon dioxide, either calcite, aragonite, or
vaterite are produced. Again, depending upon the process conditions
calcite may have either prismatic, scalenohedral or rhombohedral
crystal forms.
[0263] Other examples of microporous inorganic particulate
materials include chemically aggregated filler materials. Examples
of such chemically aggregated fillers may be found in U.S. Pat. No.
4,072,537, which is incorporated herein in its entirety. Such
microporous inorganic particulate materials comprise a composite
silicate material comprising a clay component and a metal silicate
component. The clay component is typically kaolin clay or kaolinite
and the metal silicate material is typically a water soluble alkali
metal silicate, for example sodium silicate.
[0264] As described in the '537 patent, preferred method for
preparing the composite pigment comprises the steps of, (a) forming
an aqueous suspension of a clay pigment, (b) blending into the clay
slurry a quantity of a salt such as calcium chloride, (c) metering
into the slurry of clay and salt at high shear a quantity of a
silicate component such as sodium silicate, and, optionally, (d)
adjusting the pH of the slurry with the addition of alum to a pH no
lower than pH 4, before (e) filtering and washing the precipitated
product to remove any soluble salts. Such microporous composite
silicate material is either used directly in a papermaking process
or dried and used later. Additional microporous inorganic
particulate material include materials such as diatomaceous earth
and expanded perlite.
[0265] All of foregoing materials consist of particles which
contain rigid internal void spaces that persist through paper
pressing and drying, and should also remain largely intact after
calendering.
[0266] Scalenohedral PCC, calcined clays and chemically aggregated
fillers achieve this structure by forming open aggregates of
smaller particles and bonding the particles strongly where they
contact each other. Diatomaceous earth consists of particles which
naturally contain pores. Milled expanded perlite consists of
fragments of micron-sized glass bubbles. Thus, microporous
inorganic particulate materials comprise discrete particles or
aggregates of particles with outer dimensions of several microns,
which contain void spaces within the volume defined by the outer
dimensions and which are several time smaller than said outer
dimensions. Collectively, the foregoing inorganic particulate
material are designated herein as "microporous inorganic
particulate materials" for the purpose of the present
invention.
[0267] When used in paper, these microporous inorganic particulate
materials have a much larger effect per unit mass of filler on the
spacing of the fibres than solid filler particles. This makes them
more detrimental to paper strength, but generates increased light
scattering which is beneficial to optical properties.
[0268] Another effect of inorganic particulate materials is always
to increase sheet porosity (air permeability), which is a
significant disadvantage in printing and converting processes. The
effective density of the microporous inorganic particulate
materials is also lower than that of solid fillers, and the
combination of these effects can lead to an increase in sheet bulk
and thickness as fibre is substituted for filler.
[0269] For scalenohedral PCC (an example of microporous inorganic
particulate material), the effect of agglomeration on strength can
be offset somewhat by controlling the particle size distribution to
a narrow range (thus eliminating ultrafine particles which are very
detrimental to paper strength) and using a larger median particle
size than is optimum for light scattering. However, if the particle
or agglomerate size is too large, then light scattering efficiency
is lost.
[0270] In an aspect of the present disclosure, the microporous
inorganic particulate material composite has a median particle size
(d.sub.50) less than about 10 .mu.m and greater than about 3 .mu.m,
or from about 3 .mu.m to about 6 .mu.m.
In an aspect of the present disclosure, the microporous inorganic
particulate material composite, the d.sub.50 of the microporous
mineral composites is substantially larger compared to the d.sub.50
of an unagglomerated mixture of the same constituents used to form
the microporous mineral composites.
[0271] The microporous inorganic particulate material and
microfibrillated cellulose composite can be provided in the form of
a powder, although they are preferably added in the form of a
suspension, such as an aqueous suspension. In this case, the solids
content of the suspension is not critical as long as it is a
pumpable liquid.
[0272] For the determination of the weight median particle size
d.sub.50, for particles having a d.sub.50 greater than 0.5 .mu.m, a
Sedigraph 5100 device from the company Micromeritics, USA may be
used. The measurement may be performed in an aqueous solution of
0.1 wt-% Na.sub.4P.sub.2O.sub.7. The samples may be dispersed using
a high-speed stirrer and ultrasound. For the determination of the
volume median particle size for particles having a
d.sub.50.ltoreq.500 nm, a Malvern Mastersizer from the company
Malvern, UK may be used. The measurement may be performed in an
aqueous solution of 0.1 wt % Na.sub.4P.sub.2O.sub.7. The samples
may be dispersed using a high-speed stirrer and ultrasound. The
Sedigraph 5100 provides measurements and a plot of the cumulative
percentage by weight of particles having a size, referred to in the
art as the "equivalent spherical diameter," or "esd."
Alternatively, the particle size characteristics of microporous
mineral composites may be measured by a Malvern Mastersizer or
Microtrac laser particle size distribution analyzer utilizing the
suppliers instructions.
[0273] In an aspect of the present disclosure, the ratio of the
first inorganic particulate material to the second inorganic
particulate material may range from about 10:90 to about 90:10 by
weight, for example, from about 20:80 to about 80:20 by weight,
about 25:75 to 75:25 by weight, about 40:60 to about 60:40 by
weight, or about 50:50 by weight.
Binders
[0274] In an aspect of the present disclosure, a binder may be used
to facilitate agglomeration of the second microporous inorganic
particulate material to the first microporous inorganic particulate
material, and/or to the microfibrillated cellulose. For example, in
some embodiments, the binder may be an alkali silica binder.
[0275] In an embodiment of the foregoing aspects and embodiments of
the present disclosure, the binder may include at least one of an
inorganic binder or an organic binder. The binder may also improve
the adhesion and mechanical strength between components of the
microporous mineral composites.
[0276] In an embodiment of the foregoing aspects and embodiments of
the present disclosure, the binder may include an inorganic binder,
such as an alkali metal silicate.
[0277] In an embodiment of the foregoing aspects and embodiments of
the present disclosure, a blend of inorganic particulate materials
may be contacted with a binder solution by mixing the binder
solution with the blend of inorganic particulate materials.
[0278] In an embodiment of the foregoing aspects and embodiments of
the present disclosure, the mixing may include agitation.
[0279] In an embodiment of the foregoing aspects and embodiments of
the present disclosure, the blend of the first and second
microporous inorganic particulate materials and the binder solution
is mixed sufficiently to at least substantially uniformly
distribute the binder solution among the agglomeration points of
contact of the first and/or first and second inorganic particulate
materials.
[0280] In an embodiment of the foregoing aspects and embodiments of
the present disclosure, a blend of the first and second microporous
inorganic particulate materials and the binder solution may be
mixed with sufficient agitation to at least substantially uniformly
distribute the binder solution among the agglomeration points of
contact of the blend of first and second inorganic particulate
materials without damaging the structure of the first or second
inorganic particulate materials.
[0281] In an embodiment of the foregoing aspects and embodiments of
the present disclosure, the contacting may include low-shear
mixing.
[0282] In an embodiment of the foregoing aspects and embodiments of
the present disclosure, mixing may occur at about room temperature
(i.e., from about 20.degree. C. to about 23.degree. C.). In other
embodiments, mixing may occur at a temperature ranging from about
20.degree. C. to about 50.degree. C. In further embodiments, mixing
may occur at a temperature ranging from about 30.degree. C. to
about 45.degree. C. In still other embodiments, mixing may occur at
a temperature of from about 35.degree. C. to about 40.degree.
C.
[0283] In an embodiment of the foregoing aspects and embodiments of
the present disclosure, contacting may include spraying the blend
of first and/or first and second microporous inorganic particulate
materials with a binder solution. In some embodiments, the spraying
may be intermittent. In other embodiments, the spraying may be
continuous. In further embodiments, spraying includes mixing the
blend of the first and second microporous inorganic particulate
materials while spraying with a binder solution, for example, to
expose different agglomeration points of contacts to the spray. In
some embodiments, such mixing may be intermittent. In other
embodiments, such mixing may be continuous.
[0284] In an embodiment of the foregoing aspects and embodiments of
the present disclosure, the binder may be present in the binder
solution in an amount less than about 40% by weight, relative to
the weight of the binder solution. In some embodiments, the binder
may range from about 1% to about 10% by weight. In further
embodiments, the binder may range from about 1% to about 5% by
weight.
[0285] In an embodiment of the foregoing aspects and embodiments of
the present disclosure, the binder facilitates agglomeration of the
second microporous inorganic particulate material to the first
microporous inorganic particulate material. According to some
embodiments, the second microporous inorganic particulate material
has a smaller diameter than the first microporous inorganic
particulate material.
[0286] In an aspect of the present disclosure, the microporous
inorganic particulate material and microfibrillated cellulose
composite may be associated with dispersing agents such as those
selected from the group comprising homopolymers or copolymers of
polycarboxylic acids and/or their salts or derivatives such as
esters based on, e.g., acrylic acid, methacrylic acid, maleic acid,
fumaric acid, itaconic acid; e.g. acryl amide or acrylic esters
such as methylmethacrylate, or mixtures thereof; alkali
polyphosphates, phosphonic-, citric- and tartaric acids and the
salts or esters thereof; or mixtures thereof.
[0287] In an aspect of the present disclosure, the combination of
microfibrillated cellulose and microporous inorganic particulate
material can be carried out by adding the microporous inorganic
particulate material to the MFC in one or several steps.
[0288] In an aspect of the present disclosure, the combination of
microporous inorganic particulate material can be added to the MFC
in one or several steps. The microfibrillated cellulose and
microporous inorganic particulate material can be added entirely or
in portions after the fibrillating step.
[0289] In an aspect of the present disclosure, the weight ratio of
MFC to microporous inorganic particulate material on a dry weight
basis is from 1:33 to 10:1, more preferably 1:10 to 7:1, even more
preferably 1:5 to 5:1, typically 1:3 to 3:1, especially 1:2 to 2:1
and most preferably 1:1.5 to 1.5:1, e.g. 1:1.
[0290] In an aspect of the present disclosure, the total content of
microporous inorganic particulate material is present in an amount
of from 10 wt-% to 95 wt-%, preferably from 15 wt-% to 90 wt-%,
more preferably from 20 to 75 wt-%, even more preferably from 25
wt-% to 67 wt-%, especially from 33 to 50 wt.-% on a dry weight
basis of the composite material.
Precipitated Calcium Carbonate
[0291] Precipitated calcium carbonate (PCC) may be used as the
source of particulate calcium carbonate in the present invention,
and may be produced by any of the known methods available in the
art. TAPPI Monograph Series No 30, `Paper Coating Pigments", pages
34-35 describes the three main commercial processes for preparing
precipitated calcium carbonate which is suitable for use in
preparing products for use in the paper industry, but may also be
used in the practice of the present invention. In all three
processes, a calcium carbonate feed material, such as limestone, is
first calcined to produce quicklime, and the quicklime is then
slaked in water to yield calcium hydroxide or milk of lime. In the
first process, the milk of lime is directly carbonated with carbon
dioxide gas. This process has the advantage that no by-product is
formed, and it is relatively easy to control the properties and
purity of the calcium carbonate product. In the second process the
milk of lime is contacted with soda ash to produce, by double
decomposition, a precipitate of calcium carbonate and a solution of
sodium hydroxide. The sodium hydroxide may be substantially
completely separated from the calcium carbonate if this process is
used commercially. In the third main commercial process the milk of
lime is first contacted with ammonium chloride to give a calcium
chloride solution and ammonia gas. The calcium chloride solution is
then contacted with soda ash to produce by double decomposition
precipitated calcium carbonate and a solution of sodium chloride.
The crystals can be produced in a variety of different shapes and
sizes, depending on the specific reaction process that is used. The
three main forms of PCC crystals are aragonite, rhombohedral and
scalenohedral, all of which are suitable for use in the present
invention, including mixtures thereof.
[0292] In certain embodiments, the PCC may be formed during the
process of producing microfibrillated cellulose.
[0293] Wet grinding of calcium carbonate involves the formation of
an aqueous suspension of the calcium carbonate which may then be
ground, optionally in the presence of a suitable dispersing agent.
Reference may be made to, for example, EP-A-614948 (the contents of
which are incorporated by reference in their entirety) for more
information regarding the wet grinding of calcium carbonate.
[0294] In some circumstances, minor additions of other minerals may
be included, for example, one or more of kaolin, calcined kaolin,
wollastonite, bauxite, talc or mica, could also be present.
EXAMPLES
Example 1. Use of Coarse Scalenohedral PCC and FiberLean MFC for
Maintaining Bulk and Stiffness when Increasing the Filler
Content
[0295] The furnish was prepared from 70% hardwood (Eucalyptus, ex.
UPM Uruguay) and 30% softwood (BOTNIA RMA90 Pine, ex. Metsa)
co-refined to 450 CSF (28.5.degree. S.R.).
[0296] The study design targeted 80 g/m.sup.2 UWF paper with a
starting filler content of 19% arising from GCC (60%<2 .mu.m)
addition.
[0297] The MFC product used was 50% POP MFCslurry comprised of NBSK
Botnia RMA90 and GCC mineral (60%<2 .mu.m).
[0298] A retention aid was added at 0.12% based on dry sheet
weight. The retention aid was cationic polyacrylamide (Percol
292NS, ex. BASF). The white water was re-circulated during
sheet-forming (in that the white-water from each sheet was used to
form the subsequent sheets in the trial point series to ensure
retention equilibrium was reached with each formulation). Further
details on the sheet forming methodology are shown in the
Appendix
[0299] The results of Example 1 are summarized in Table 1.
TABLE-US-00001 TABLE 1 Summary of results when using PCC with MFC
to restore Bulk and Stiffness when increasing the filler content.
L&W Actual Actual Opacity PPS Bending Calculated MFC Basis
Total Bright- at 80 Roughness Bendtsen Burst Scott Tensile
Stiffness Stiffness Dose Weight Filler Bulk ness g/m.sup.2 F10 S
(1000 kPa) Porosity Index bond Index MD @ 80 gsm Condition %
g/m.sup.2 % Cm.sup.3/g % % Cm.sup.2/g .mu.m ml/min kN/g J/m.sup.2 N
m/g mN mN/m GCC 20% 0 79.4 19.3 1.62 88.7 87.1 544 5.55 2730 1.57
95 27.7 0.446 0.449 No MFC GCC 30% 0 77.6 29.7 1.63 89.6 88.8 624
5.39 3240 1.03 66.9 20.3 0.321 0.37 No MFC GCC 30% 3 77.9 31.3 1.58
88.8 89.8 648 5.27 1650 1.33 83.9 25.9 0.378 0.393 3% MFC PCC 20% 0
78.8 19.1 1.88 89.0 87.3 572 5.46 4900 1.54 92.3 26.3 0.6 0.539 No
MFC PCC 30% 0 78.4 28.7 1.93 90.1 88.7 651 5.38 5900 1.03 69.5 19.9
0.403 0.466 No MFC PCC 30% 4 78.5 30.3 1.85 89.5 89.7 679 5.15 3210
1.32 98.6 23.9 0.422 0.434 4% MFC
[0300] N.B.: The furnish (70% Eucalyptus/30% Pine) represent 100%
of the pulp furnish, which was then replaced in the proportions
shown by filler and MFC in terms of overall mass per sheet.
[0301] These results indicate:
[0302] Increase of filler content from 20% to 30% using standard
GCC (IC60, median size 1.6 .mu.m) with 3% MFC gives minor reduction
in strength but significant loss of Bulk and Stiffness.
[0303] Increased MFC dose would result in greater Bulk loss.
Increase of filler content from 20% to 30% using coarse PCC (median
size 3.1 .mu.m) gives very high Porosity and low strength.
[0304] Combination of 30% PCC and 4% MFC gives high Bulk,
acceptable Porosity and strength and comparable Stiffness with 20%
GCC filled paper
[0305] Taken together the Examples demonstrate that:
[0306] MFC addition improves mechanical properties, Opacity,
Porosity and Roughness. In exchange for these improvements, several
possibilities are presented:
[0307] Furnish adjustments: Reduced long fibre or increased CTMP
contents (adjusting short fibre content proportionately).
[0308] Change of filler type used and increasing the filler
content.
[0309] Both possibilities present potential cost savings.
[0310] The use of MFC also reduces the Bulk, which in turn leads to
a detriment to Stiffness. Furthermore, using MFC to increase the
filler level can lead to a greater detriment to Stiffness.
[0311] These Bulk/Stiffness losses can be offset by:
[0312] Switching to a coarser/bulkier filler.
[0313] Reducing the long fibre content in the furnish.
[0314] Increasing the mechanical pulp content in the furnish.
[0315] Optimisation of these various levers when using MFC can
maximise cost savings and overall paper properties
[0316] All paper tests were conducted in accordance with the
following TAPPI standards:
[0317] Internal bond strength (Scott Bond): T 569
[0318] Tensile Properties: T494
[0319] Bendtsen Porosity: T460
[0320] Thickness (Caliper for Bulk calculations): T411
[0321] Basis weight: T410
[0322] Opacity: T425
[0323] Ash content: T413 and T211
[0324] Tensile Strength
[0325] Burst Strength: T403
[0326] Tear strength
[0327] Tensile strength in the `Z` direction (perpendicular to the
plane of the paper)
[0328] Bending Stiffness: T535
[0329] Bulk or thickness.
[0330] Roughness: T555
[0331] Sheet Preparation
[0332] All handsheets were prepared on a Rapid Kothen sheetformer
according to TAPPI standard T205. In order to ensure very high
overall retention of all components of the furnishes used to make
the sheets, whitewater was recirculated after the formation of each
sheet and used in the dilution of the furnish used to make the next
sheet. The first 5 sheets of each composition were discarded to
allow build-up of unretained material in the recirculating water to
a steady state, after which a further 7 sheets were formed, pressed
and dried for testing. Target filler loadings were achieved within
2 percentage points in all cases. A cationic retention aid (Percol
292NS, BASF) was added to each furnish at a level of 0.12% based on
the total solids in the furnish. Paper properties were measured
according to the relevant TAPPI standards. Filler contents were
calculated from residual ash weights measured after placing sheets
in a furnace at 450.degree. C. for 2 hours. At this temperature, no
loss on ignition occurs for the calcium carbonate fillers used.
Example 2
[0333] Handsheets were made from a blend of bleached Kraft pulps,
comprising 70% hardwood (Eucalyptus, UPM Uruguay) and 30% softwood
(Pine, Metsa Botnia RMA90). These were co-refined in a laboratory
Valley beater to a freeness of 450 ml CSF (28.5.degree. S.R.). Each
sheet was made to a target substance of 80 gsm, with target filler
contents of either 20% or 30% by weight.
[0334] MFC was produced by co-grinding Botnia RMA90 bleached Kraft
Pine pulp with a standard filler grade ground calcium carbonate
(GCC, Intracarb 60, 60%<2 .mu.m by weight, d50 1.4 .mu.m,
Imerys), at a 50/50 ratio by weight, using a stirred media detritor
mill.
[0335] Either GCC (Intracarb 60) or scalenohedral PCC (Syncarb
S350, Omya, 3.5 .mu.m d.sub.50), were added to the furnish for each
sheet so that its total filler content, including the filler added
with the co-ground MFC, would match the target value for the final
sheets.
[0336] Paper properties of the formed handsheets are shown in
Error! Reference source not found. below.
TABLE-US-00002 TABLE 2 Opacity Light PPS L&W MFC Filler Bright-
at 80 scattering Roughness Bendtsen Burst Scott Tensile Bending
Dose Substance content Bulk ness g/m.sup.2 coeffiecient (F10) (1000
kPa) Porosity Index bond Index Stiffness Composition % g/m.sup.2 %
cm.sup.3/g % % cm.sup.2/g .mu.m ml/min kN/g J/m.sup.2 N m/g mNm GCC
20% 0 79.4 19.3 1.62 88.7 87.1 544 5.55 2730 1.57 95 27.7 0.446 no
mfc GCC 30% 0 77.6 29.7 1.63 89.6 88.8 624 5.39 3240 1.03 66.9 20.3
0.321 no mfc GCC 30% 3 77.9 31.3 1.58 88.8 89.8 648 5.27 1650 1.33
83.9 25.9 0.378 3% mfc PCC 20% 0 78.8 19.1 1.88 89.0 87.3 572 5.46
4900 1.54 92.3 26.3 0.6 no mfc PCC 30% 0 78.4 28.7 1.93 90.1 88.7
651 5.38 5900 1.03 69.5 19.9 0.403 no mfc PCC 30% 4 78.5 30.3 1.85
89.5 89.7 679 5.15 3210 1.32 98.6 23.9 0.422 4% mfc
[0337] Table 3 below and FIG. 1 show the relative change in key
properties of each composition compared with the reference sheets
filled with 20% GCC. Increase of filler content to 30% with GCC
causes a significant loss of mechanical properties, which are
partially restored by the addition of 3% MFC. Switching from GCC to
the coarse PCC at 20% loading causes a significant increase in bulk
and stiffness at the expense of tensile index and Scott Bond, and
further increase to 30% PCC reduces the latter to below the level
of the GCC, whilst also reducing stiffness to below the reference.
The addition of 4% MFC restores the stiffness to within 5% of its
original value, whilst providing improvements in bulk, Scott Bond
and light scattering over the reference.
TABLE-US-00003 TABLE 3 Relative Relative Relative Relative Scott
tensile bending Relative light Composition Bond index stiffness
bulk scattering GCC 20% no 1.00 1.00 1.00 1.00 1.00 mfc GCC 30% no
0.70 0.73 0.72 1.01 1.15 mfc GCC 30% 3% 0.88 0.94 0.85 0.98 1.19
mfc PCC 20% no 0.97 0.95 1.35 1.16 1.05 mfc PCC 30% no 0.73 0.72
0.90 1.19 1.20 mfc PCC 30% 4% 1.04 0.86 0.95 1.14 1.25 mfc
Example 3
[0338] Handsheets were made from a blend of 95% bleached Eucalyptus
Kraft pulp and 5% bleached chemi-thermomechanical pulp (BCTMP). The
Kraft pulp was refined in a laboratory Valley beater to a freeness
of 330 ml CSF (37.5.degree. S.R.). Each sheet was made to a target
substance of 75 gsm, with target filler contents of either 25% or
35% by weight.
[0339] MFC was produced by co-grinding bleached Eucalyptus Kraft
pulp with a standard filler grade ground calcium carbonate (GCC,
Hydrocarb 60, 60%<2 .mu.m by weight, d50 1.4 .mu.m, Omya), at a
50/50 ratio by weight, using a stirred media detritor mill.
[0340] The reference sheet contained 25% GCC. For all the other
sheets, 2% MFC was added, and a blend of GCC (Hydrocarb 60) and
scalenohedral PCC (3.1 .mu.m d50, obtained from a satellite PCC
plant at a paper mill) was added to the furnish for each sheet so
that its total filler content, including the filler added with the
co-ground MFC, would be 35%, and the proportion of PCC filler in
the blend would be a fixed value between 0 and 100%.
[0341] Paper properties of the formed handsheets are shown in 4
below.
TABLE-US-00004 TABLE 4 % PCC Opacity PPS L&W in MFC Filler
Bright- at 75 Roughness Bendtsen Burst Scott Tensile Bending blend
Dose Substance content Bulk ness g/m.sup.2 F10 S (1000 kPa)
Porosity Index bond Index Stiffness 0 0 75.8 24.4 1.56 88.3 87.8
618 5.40 2562 1.235 113 28.5 0.38 0 2 75.5 34.2 1.50 88.9 89.0 688
5.32 2035 0.992 85 23.5 0.29 10 2 76.2 34.6 1.42 88.9 89.2 697 5.3
2245 0.997 92 23.2 0.30 20 2 74.9 34.2 1.50 89.2 89.2 704 5.1 2656
0.951 81 23.6 0.29 30 2 75.0 33.9 1.55 89.4 89.3 715 5.1 2838 0.911
84 23.2 0.32 40 2 76.1 35.1 1.57 89.5 89.4 729 5.0 3158 0.877 82
21.9 0.34 60 2 75.9 34.6 1.70 89.8 89.3 728 5.0 3509 0.876 80 21.4
0.36 80 2 76.2 34.1 1.63 90.3 89.5 754 5.1 3555 0.907 82 21.6 0.37
100 2 75.9 33.9 1.72 90.6 89.5 772 4.9 3658 1.128 77 24.0 0.38
[0342] The effect of changing from GCC to coarse PCC is shown in
Error! Reference source not found. to Error! Reference source not
found. below. Error! Reference source not found. shows that
increase of GCC filler from 25% to 35% causes a substantial drop in
bending stiffness, even with addition of 2% MFC, but substitution
of the added GCC with the coarse PCC restores it to the reference
value. Error! Reference source not found. shows that substitution
of GCC with PCC increases the light scattering coefficient of the
paper beyond that already achieved by the increase in filler
content. Error! Reference source not found. and Error! Reference
source not found. show that, despite the addition of 2% MFC, in
this highly refined furnish there is a slight drop in tensile index
and Scott Bond with the filler increase, but the substitution of
GCC with PCC does not affect this substantially.
Example 4
[0343] Handsheets were made from a blend of bleached Kraft pulps,
comprising 70% eucalyptus and 30% pine. These were co-refined in a
laboratory Valley beater to a freeness of 350 ml CSF (36.degree.
S.R.). Each sheet was made to a target substance of 80 gsm, with
target filler contents ranging between 16% and 35% by weight.
[0344] Either a standard filler grade scalenohedral PCC (2.3 .mu.m
d50, obtained from a satellite PCC plant at a paper mill) or a
coarse grade scalenohedral PCC (Syncarb S300, Omya, 3.0 .mu.m d50),
were added to the furnish for each sheet so that its total filler
content, including the filler added with the co-ground MFC, would
match the target value for the final sheets.
[0345] Paper properties of the formed handsheets are shown in 5
below.
TABLE-US-00005 TABLE 5 Opacity PPS L&W MFC Filler Bright- at 80
Roughness Bendtsen Scott Tensile Bending Added Dose Substance
content Bulk ness g/m.sup.2 F10 S 1000 kPa Porosity Burst Bond
Index Stiffness Filler % g/m.sup.2 % cm.sup.3/g % % cm.sup.2/g
.mu.m ml/min kPa J/m.sup.2 N m/g mNm 2.3 .mu.m 0 80.9 16.7 1.61
89.7 87.6 586 5.5 2847 149 145 33.9 0.58 satellite 0 80.2 20.6 1.67
89.6 89.3 642 5.4 3188 122 110 31.2 0.55 plant 0 79.6 25.1 1.68
89.1 90.9 687 5.3 3649 108 92 26.6 0.46 scaleno- 0 79.6 29.1 1.72
90.7 90.1 730 5.3 4045 90 86 23.4 0.43 hedral 0 78.1 34.2 1.73 91.5
90.3 773 5.1 4528 69 73 18.0 0.29 PCC 1 81.5 16.7 1.55 89.2 87.8
595 5.3 2188 179 160 39.2 0.60 1 81.7 20.7 1.56 89.8 88.6 640 5.3
2585 153 132 35.2 0.61 1 80.8 24.8 1.59 90.3 89.3 686 5.3 2977 134
103 30.7 0.53 1 80.7 28.8 1.61 90.7 89.8 728 5.0 3138 113 91 27.3
0.54 1 80.1 34.1 1.64 91.1 90.5 778 4.8 3357 94 78 23.4 0.45
Syncarb 0 82.8 16.0 1.60 90.8 86.2 572 5.6 2461 174 189 39.7 0.63
S300 0 82.8 20.2 1.64 91.3 87.2 621 5.5 2823 149 152 35.2 0.59 3.0
.mu.m 0 81.9 24.2 1.62 91.5 87.9 657 5.2 3214 136 137 31.5 0.65
Scaleno- 0 81.6 28.2 1.62 91.8 88.6 694 5.0 3451 118 118 29.4 0.59
hedral 0 81.4 33.0 1.63 92.2 89.3 745 4.8 3698 98 106 25.4 0.45 PCC
1 81.9 16.5 1.57 90.3 86.7 574 5.2 1984 201 187 41.0 0.68 1 81.6
20.9 1.59 90.7 87.5 617 5.0 2312 165 165 36.8 0.62 1 81.7 24.8 1.62
91.2 88.2 660 4.9 2649 142 142 31.7 0.62 1 81.7 28.7 1.62 91.4 88.9
702 4.9 2831 130 131 29.7 0.58 1 81.1 33.5 1.65 91.9 89.6 749 4.9
3259 106 112 24.6 0.48
[0346] Error! Reference source not found. shows that for a constant
tensile index, the addition of 100 MFC allows an increase in filler
content of 3.5% with the standard PCC, but 6% with the coarser
PCC.
[0347] Error! Reference source not found. shows that light
scattering increases by 100 cm.sup.2 g.sup.-1 for a 3.5% increase
in the standard 2.3 .mu.m filler, and by 80 cm.sup.2 g.sup.-1 for a
6% increase in the coarse 3.0 .mu.m filler.
[0348] Error! Reference source not found. shows that these
increases give equivalent stiffness for the 2.3 .mu.m filler, but
an increase of 0.04 mN m (7%) for the coarse 3.0 .mu.m
filler.cc
[0349] Those skilled in the art will recognize, or be able to
ascertain using no more than routine experimentation, many
equivalents to the specific embodiments of the invention described
herein. The scope of the present invention is not intended to be
limited to the above Description, but rather is as set forth in the
following claims.
[0350] Use of ordinal terms such as "first," "second," "third,"
etc., in the claims to modify a claim element does not by itself
connote any priority, precedence, or order of one claim element
over another or the temporal order in which acts of a method are
performed, but are used merely as labels to distinguish one claim
element having a certain name from another element having a same
name (but for use of the ordinal term) to distinguish the claim
elements.
[0351] The articles "a" and "an" as used herein in the
specification and in the claims, unless clearly indicated to the
contrary, should be understood to include the plural referents.
Claims or descriptions that include "or" between one or more
members of a group are considered satisfied if one, more than one,
or all of the group members are present in, employed in, or
otherwise relevant to a given product or process unless indicated
to the contrary or otherwise evident from the context. The
invention includes embodiments in which exactly one member of the
group is present in, employed in, or otherwise relevant to a given
product or process. The invention also includes embodiments in
which more than one, or the entire group members are present in,
employed in, or otherwise relevant to a given product or process.
Furthermore, it is to be understood that the invention encompasses
all variations, combinations, and permutations in which one or more
limitations, elements, clauses, descriptive terms, etc., from one
or more of the listed claims is introduced into another claim
dependent on the same base claim (or, as relevant, any other claim)
unless otherwise indicated or unless it would be evident to one of
ordinary skill in the art that a contradiction or inconsistency
would arise. Where elements are presented as lists, (e.g., in
Markush group or similar format) it is to be understood that each
subgroup of the elements is also disclosed, and any element(s) can
be removed from the group. It should be understood that, in
general, where the invention, or aspects of the invention, is/are
referred to as comprising particular elements, features, etc.,
certain embodiments of the invention or aspects of the invention
consist, or consist essentially of, such elements, features, etc.
For purposes of simplicity those embodiments have not in every case
been specifically set forth in so many words herein. It should also
be understood that any embodiment or aspect of the invention can be
explicitly excluded from the claims, regardless of whether the
specific exclusion is recited in the specification. The
publications, websites and other reference materials referenced
herein to describe the background of the invention and to provide
additional detail regarding its practice are hereby incorporated by
reference.
* * * * *
References