U.S. patent application number 14/340224 was filed with the patent office on 2014-11-13 for paper with improved stiffness and bulk and method for making same.
The applicant listed for this patent is INTERNATIONAL PAPER COMPANY. Invention is credited to LADISLAV BEDNARIK, MICHAEL C. HERMAN, PETER F. LEE, JAY C. SONG, AGNE SWERIN, SEN YANG.
Application Number | 20140335333 14/340224 |
Document ID | / |
Family ID | 31994177 |
Filed Date | 2014-11-13 |
United States Patent
Application |
20140335333 |
Kind Code |
A1 |
SWERIN; AGNE ; et
al. |
November 13, 2014 |
PAPER WITH IMPROVED STIFFNESS AND BULK AND METHOD FOR MAKING
SAME
Abstract
The invention provides a three layered reprographic paper having
improved strength, stiffness and curl resistance properties, and a
method for making same. The paper has a central core layer made
largely of cellulose and bulked with a bulking agent such as a
diamide salt. A starch-based metered size press coating is pressed
on both sides of the core layer, wherein the starch has a high
solid content. The coating forms a three layered paper having an
I-beam arrangement with high strength outer layers surrounding a
low density core.
Inventors: |
SWERIN; AGNE; (BANDHAGEN,
SE) ; SONG; JAY C.; (HIGHLAND MILLS, NY) ;
BEDNARIK; LADISLAV; (LOVELAND, OH) ; LEE; PETER
F.; (AUCKLAND, NZ) ; HERMAN; MICHAEL C.;
(MONROE, NY) ; YANG; SEN; (HIGHLAND MILLS,
NY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
INTERNATIONAL PAPER COMPANY |
Memphis |
TN |
US |
|
|
Family ID: |
31994177 |
Appl. No.: |
14/340224 |
Filed: |
July 24, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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13906864 |
May 31, 2013 |
8790494 |
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14340224 |
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12215686 |
Jun 27, 2008 |
8460512 |
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13906864 |
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10662699 |
Sep 15, 2003 |
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12215686 |
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60410666 |
Sep 13, 2002 |
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Current U.S.
Class: |
428/212 ;
427/209; 428/327; 428/535 |
Current CPC
Class: |
D21H 21/22 20130101;
Y10T 428/31982 20150401; Y10T 428/254 20150115; D21H 19/34
20130101; D21H 19/12 20130101; Y10T 428/31971 20150401; Y10T
428/24942 20150115; D21H 21/16 20130101; D21H 19/84 20130101; Y10T
428/2987 20150115; D21H 19/54 20130101; D21H 23/56 20130101; D21H
17/07 20130101; Y10T 428/2982 20150115 |
Class at
Publication: |
428/212 ;
428/535; 428/327; 427/209 |
International
Class: |
D21H 19/84 20060101
D21H019/84; D21H 19/34 20060101 D21H019/34; D21H 17/07 20060101
D21H017/07; D21H 21/16 20060101 D21H021/16; D21H 23/56 20060101
D21H023/56 |
Claims
1. A paper or paperboard having improved bulk and stiffness
comprising: a three layered single-ply I-beam structure having a
top layer, a central layer and a bottom layer, wherein the central
layer is a cellulosic core layer, and the top and bottom layers are
starch based, size-press applied coating layers that cover an upper
and low surface of the central layer with minimal penetration into
the central layer, and a bulking agent interpenetrated within the
central layer.
2. The paper or paperboard of claim 1, wherein the ratio of the
thickness of the central layer compared to the thickness of the
paper or paperboard is between 1:50 and 1:1.1.
3. The paper or paperboard of claim 1, wherein the basis weight of
the paper is between 59 g/m.sup.2 and 410 g/m.sup.2 the basis
weight of each of the top and bottom coating layers are between 2
and 10 g/m.sup.2.
4. The paper or paperboards of claim 1, wherein the top and bottom
layers have starch application controlled with a metered size
press.
5. The paper or paperboards of claim 1, wherein the top and bottom
layers are formed from an starch coating solution having starch
solids between 6% and 20% weight.
6. The paper or paperboard of claim 1, wherein the bulking agent is
diamide salt based product.
7. The paper or paperboard of claim 1, wherein the bulking agent is
made from a polymeric material in form of microspheres selected
from the group consisting of methyl methacrylate,
ortho-chlorostyrene, polyortho-chlorostyrene, polyvinylbenzyl
chloride, acrylonitrile, vinylidene chloride, para-tert butyl
styrene, vinyl acetate, butyl acrylate, styrene, methacrylic acid,
vinylbenzyl chloride and combinations of two or more of the
foregoing.
8. The paper or paperboard of claim 7, wherein the central layer
further comprises a retention agent.
9. The paper or paperboard of claim 1, wherein the central layer
further comprises an additive selected from the group consisting of
fillers, surfactants, sizing agents, or a combination thereof.
10. The paper or paperboard of claim 1, wherein the starch is
selected from the group consisting of hydroxy ethylated starch,
oxidized starch, cationically modified or enzymatically converted
starch from any regularly used starch source, such as from potato,
corn, wheat, rice or tapioca.
11. The paper or paperboard of claim 1, wherein the top and bottom
layers further comprise a cross linking agent.
12. The paper or paperboard of claim 1, wherein the top and bottom
layers further comprise a viscosity modifier.
13. The paper or paperboards of claim 1, wherein the top and bottom
layers further comprise a pigment.
14. The paper or paperboard of claim 1, further comprising
additives selected from the group consisting of polyvinyl alcohols,
ammonium zirconium carbonate, borate chemicals, glyoxal, melamine
formaldehyde, ground and precipitated calcium carbonates, clays,
talc, TiO.sub.2, and silica, or a combination thereof.
15. A paper or paperboard having improved bulk and stiffness
comprising: a three layered single-ply I-beam structure having a
top layer, a central layer and a bottom layer, wherein the central
layer is a cellulosic core layer, and the top and bottom layers are
starch based, size-press applied coating layers that cover an upper
and lower surface of the central layer, a starch coat weights of
each of the top and bottom coating layers being between 2 and 10
g/m.sup.2, and a bulking agent interpenetrated within the
cellulosic core layer
16. A method for making a paper or paperboard comprising the steps
of: a) providing a furnish including cellulosic fibers bulking
agent, b) forming as fibrous web from the papermaking furnish, c)
drying the fibrous web to form a dried web, d) size-press treating
the dried web with a high strength starch based size-press solution
to form top and bottom coating layers on a top and bottom side of
the fibrous web, and e) drying the fibrous web after the size-press
treatment to form a three layered single-ply having an I-beam
structure.
17. The method of claim 16, wherein the ratio of the thickness of
the fibrous web compared to the thickness of the paper or
paperboard is between 1:50 and 1:1.1.
18. The method of claim 16, wherein the basis weight of the paper
is between 59 gsm and 410 gsm and the basis weight of each of the
top and bottom coating layers are between 2 and 10 gsm.
19. The method of claim 16, wherein no substantial levels of starch
from the top and bottom coating layers are in the fibrous web.
20. The method of claim 16, wherein the top and bottom coating
layers have starch solids less than 20% weight.
21. The method of claim 16, wherein the size-press treatment uses a
metered size-press.
22. The method of claim 16, wherein the bulking agent is a diamide
salt based product.
23. The method of claim 16, wherein the furnish further contains an
additive selected from the group consisting of: fillers,
surfactants, or a combination thereof.
24. The method of claim 17, wherein the starch is chosen from a
group comprising of: hydroxy ethylated starch, oxidized starch,
cationically modified or enzymatically converted starch from any
regularly used starch source, such from potato, corn, wheat, rice
or tapioca.
25. The method of claim 16, wherein the size-press solution further
contains an additive selected from the group consisting of:
polyvinyl alcohols, ammonium zirconium carbonate, borate chemicals,
glyoxal, melamine formaldehyde, ground and precipitated calcium
carbonates, clays, talc, TiO.sub.2, and silica, or a combination
thereof.
26. The method of claim 17, wherein a starch solution of the high
strength starch based size-press solution is pre-cooked with a
borate chemical prior to the size-press treatment.
Description
RELATED APPLICATION
[0001] This application claims the benefit of U.S. Provisional
Application Ser. No. 60/410,666, filed Sep. 13, 2002.
FIELD OF THE INVENTION
[0002] The invention relates to the papermaking arts and, in
particular, to the manufacture of paper substrates. This invention
also relates to articles manufactured from the substrates of this
invention such as printing paper and paperboard articles.
BACKGROUND OF THE INVENTION
[0003] The contemporary work and home offices use multitude of
paper products including, but not limited to reprographic paper
grades and paperboard, such as writing papers, printing paper, copy
paper, and forms paper. Unfortunately, such paper and paperboard
products exhibit one or more disadvantages. For example, some of
these products have relatively low basis weights or are not
sufficiently stiff in bending or durable to sustain a fill run
through a copy machine. Thus, within the industry there is a
constant aim to produce reprographic papers at lower basis weights,
but at equal stiffness properties, in order to save raw materials
and to be able to increase productivity. Other important properties
of reprographic papers are curl, i.e. out-of-plane movement, and
hygroexpansivity, i.e. expansion and contraction of the paper with
varying relative humidities. A low curl is required during stacking
of paper in copier machines and for correct feeling. A low
hygroexpansivity is required because curl is a function of the
hygroexpansivity, and of the material distribution in the sheet
(see e.g. Carlsson, L.: A Study of the Bending Properties of Paper
and their Relation to the Layered Structure, Doctoral thesis,
Chalmers University of Technology, Department of Polymeric
Materials, Gothenburg, Sweden, 1980, ISBN 91-7032-003-9). The
hygroexpansivity and cur also a function of the papermaking
process, especially during drying of a fibrous web (see e.g.
Handbook of Physical Testing of Paper, 2.sup.nd Edition, Vol. 1,
Chapter 3, page 115-117, ISBN 0-8247-0498-3 by T. Uesaka:
Dimensional Stability and Environmental Effects on Paper
Properties). The bending stiffness S.sub.b of paper is a function
of he elastic modulus E and the thickness t, such that S.sub.b is
proportional to Et.sup.3. This means that the most effective means
to increase the bending stiffness is by increasing the paper
thickness. However, the thickness normally must be retained within
specifications. An even more efficient way to increase bending
stiffness is to create an I-beam effect, i.e. strong dense outer
layers and a lower density core. Mathematical expressions of a
three-layered structure show that the I-beam effect creates
considerably higher bending stiffness compared to a homogeneous
structure if all other parameters are kept constant (see e.g.
Handbook of Physical Testing of Paper, 2.sup.nd Edition, Vol. 1,
Chapter 5, page 233-256, ISBN 0-8247-0498-3 by C. Fellers and L. A.
Carlsson: Bending Stiffness, with Special Reference to Paperboard).
This knowledge has been reduced to practice in multi-ply paperboard
as well as for low basis weight printing papers, such as
reprographic papers (see e.g. Haggblom-Ahnger, U., 1998, Three-ply
office paper, Doctoral thesis, .ANG.bo Akademi University, Turku,
Finland, 1998).
[0004] Modern size-press units of paper machines produce
reprographic paper grades commonly having metered size-presses.
These units enable the application of size-press starch (and/or
other strengthening components) to other layers of the sheet. This
technology has been demonstrated in the published literature (see
e.g. Lipponen, J. et al.: Surface Sizing with Starch Solutions at
High Solids Contents, 2002 Tappi Metered Size Press Forum, Orlando,
Fla., May 1-4, 2002, Tappi Press 2002, ISBN 1-930657-91-9). The
authors concluded a significant bending stiffness improvement
running the starch solution at the size-press at 18% solids
compared to lower solids (8, 12 and 15%).
[0005] There are also flooded-nip (also called pond or puddle)
size-press units in common use. In this instance the potential for
application of starch solutions to the outer layers is not the same
as for metered size-press units due to inherent deeper penetration
into the sheet in the flooded-nip. However, results in the
literature suggest that an increase in starch solids can also cause
less penetration with potential for improved bending stiffness (see
e.g. Bergh, N.-O.: Surface Treatment on Paper with Starch from the
Viewpoint of Production Increase, XXI EUCEPA International
Conference, Vol. 2, Conferencias nos. 23 a 43, Torremolinos, Spain,
page 547-, 1984). There is, however, room for considerable
improvement in bending stiffness over the results reported in the
literature and to receive other benefits such as stated above.
[0006] Accordingly, there exists a need for improved paper and
paperboard products that reduce or eliminate one or more of these
disadvantages while being able to produce paperboard and
reprographic paper grades at considerably lower basis weights, at
higher production rates, and, consequently, at lower manufacturing
costs. Such an improvement would benefit from increased bulk of the
paper web before the size-press application (n.b. the large
influence of paper thickness on bending stiffness) in combination
with high solids starch solutions including viscosity modifiers
and/or crosslinkers to increase the strength of the size-press
coating and to increase hold-out attachment of the surface to the
applied layer. Further, it is the object of this invention to
provide these benefits within a single-ply paper, thereby
eliminating the costa associated with the additional machinery
required for paper having multiple cellulosic layers.
SUMMARY OF THE INVENTION
[0007] Accordingly, it is an object of this invention to provide a
paper or paperboard having improved bulk and stiffness having a
three layered single-ply I-beam structure with a top layer, a
central layer and a bottom layer, wherein the central layer is a
cellulosic core layer, and the top and bottom layers are starch
based, size-press applied coating layers that cover an upper and
lower surface of the central layer with minimal penetration into
the central layer, and a bulking agent interpenetrated within the
cellulosic core layer.
[0008] It is a further object of the invention to provide a paper
or paperboard having improved bulk and stiffness having a three
layered single-ply I-beam structure having a top layer, a central
layer and a bottom layer, wherein the central layer is a cellulosic
layer, and the top and bottom layers are starch based, size-press
applied coating layers that cover an upper and lower surface of the
central layer, the top and bottom layer have starch coat weights in
the range of 2-10 gram per square meter, and a bulking agent
interpenetrated within the cellulosic core layer.
[0009] It is an additional object of the invention to provide a
method for making paper or paperboard comprising the steps of
providing a furnish including cellulosic fibers and a bulking
agent, forming a fibrous web from the papermaking furnish, drying
the fibrous web to form a dried web, size-press treating the dried
web with a high strength starch based size-press solution to form
top and bottom coating layers on a top and bottom side of the
fibrous web, and drying the fibrous web after the size-press
treatment to form a three layered single-ply having an I-beam
structure.
[0010] Other objects, embodiments, features and advantages of the
present invention will be apparent when the description of a
preferred embodiment of the invention is considered in conjunction
with the annexed drawings, which should be construed in an
illustrative and not limiting sense.
BRIEF DESCRIPTION OF THE FIGURES/DRAWINGS
[0011] FIG. 1 is a schematic illustration of the three layered
paper of the invention, achieved by bulking the base sheet and
using high solids starch including viscosity
modifiers/fillers/cross-linkers.
[0012] FIG. 2 is a schematic illustration of a paper machine
process.
DETAILED DESCRIPTION
[0013] A paper 10 in accordance with one embodiment of the
invention is shown in FIG. 1, wherein the term "paper", used
herein, includes not only paper and the production thereof, but
also other web-like products, such as board and paperboard and the
production thereof. A flat, bulked cellulosic core layer 12 is
coated on both sides by a high starch based size-press coating 14.
The cellulosic fibers are formed from a chemical pulp furnish
having a mixture of hardwood and softwood fibers with addition
fillers such as precipitated calcium carbonate or other fillers
known in the art. The fibers may also be interspersed with
surfactants, retention agents or other additives typically added to
paper products. The precise ratio of softwood to hardwood fibers
can vary within the scope of the invention. Ideally, the ratio of
hardwood to softwood fibers varies between 3:1 and 10:1. However,
other hardwood/softwood ratios or other types of fibers can be
used, such as fibers from chemical pulp such as sulphate, and
sulphite pulps, wood-containing or mechanical pulp such as
thermomechanical pulp, chemo-thermomechanical pulp, refiner pulp
and groundwood pulp. The fibers can also be based on recycled
fibers, optionally from de-inked pulps, and mixtures thereof.
[0014] Cellulosic core layer 12 is a low density core bulked up by
a bulking agent, thus achieving increased thickness. The preferred
embodiment uses a diamide salt based bulking agent such as mono-
and distearamides of animoethylethalonalamine, commercially known
as Reactopaque 100, (Omnova Solutions Inc., Performance Chemicals,
1476 J.A. Cochran By-Pass, Chester, S.C. 29706, USA and marketed
and sold by Ondeo Nalco Co., with headquarters at Ondeo Nalco
Center, Naperville, Ill. 60563, USA) in about 0.025 to about 0.25
wt % by weight dry basis. However, various chemical bulking agents
known in art can be used, such as quaternized imidazoline or
microspheres, wherein the microspheres are made from a polymeric
material selected from the group consisting of methyl methacrylate,
ortho-chlorostyrene, polyortho-chlorostyrene, polyvinylbenzyl
chloride, acrylonitrile, vinylidene chloride, para-tert-butyl
styrene, vinyl acetate, butyl acrylate, styrene, methacrylic acid,
vinylbenzyl chloride and combinations of two or more of the
foregoing. Core layer 12 may contain other materials, such as
surfactants, retention agents and fillers known in the art. The use
of retention agents are generally preferred if microspheres are
utilized as the bulking agent. In the preferred embodiment
utilizing diamide salt, no retention agents are required.
[0015] In the preferred embodiment, starch based coating layers 14
cover both surfaces of the core layer. The high density coatings
cover an upper and lower surface of the lower density bulked
cellulose core, creating an I-beam effect that is a three-layered
single-ply paper product. In other embodiments, only one side of
the cellulosic core layer may be coated with a starch size press
coating. The high strength coatings are formed from starch based
solutions in a solids range of 6-20%, but preferably more starch
strength than a typical paper yet low enough to prevent excessive
penetration of the coatings into the core layers. Commercial
embodiments of the present invention generally use solid content of
about 6-12%. However, in other preferred embodiments, high
stiffness can be achieved with starch solids of about 18%.
[0016] The coating penetrates the cellulose core layer minimally or
not at all. As a result, starch can be substantially absent from
the cellulose core. The control of the penetration is ideally
achieved with metered size press coating, such that the thickness
of the outer film can be closely monitored. In preferred
embodiments, the ratio of the film thicknesses of the starch
coating layers to the paper as a whole is between 1:50 and 1:1.1.
The porosity levels of the paper also effects coating penetration.
Controlling the thickness and penetration is key to create three
separate adjacent layers that form the I-beam structure having high
strength outer coatings around a lower density core.
[0017] The starches used in the coating can be any starch typically
used in a coating, preferably a hydroxy ethylated starch, oxidized
starch, cationically modified or enzymatically converted starch
from any regularly used starch source, such as from potato, corn,
wheat, rice or tapioca. The coating may further contain viscosity
modifiers, cross-linkers and pigments such as polyvinyl alcohols,
ammonium zirconium carbonate, borate chemicals, glyoxal, melamine
formaldehyde, ground and precipitated calcium carbonates, clays,
talc, TiO.sub.2, and silica.
[0018] As completed, the basis weight of paper 10 is generally in
the range of 59-410 g/m.sup.2 and the coating has a basis weight
between 2 and 10 g/m.sup.2
[0019] FIG. 2 depicts a schematic that is one embodiment of a
method used for formulating the paper of FIG. 1. Numerous types of
papermaking machines are known, many with variants of a typical
wet-end/dry end type machine. Thus, the present invention is not
limited to a specific type of paper making machine such as the one
represented in the schematic of FIG. 2.
[0020] A bulking agent 20 is added to a furnish during the wet-end
of the paper making machine, wherein the furnish may further
comprise additives including fillers, retention aids, surfactants,
and other substances typically added to wet end paper furnished
that are known in the art. In the present embodiment, the preferred
bulking agent is a diamide salt based product (Reactopaque 100).
However, other bulking agents may be used within the spirit of the
invention.
[0021] The wet-end further comprises a refiner 22 for mechanical
treatment of the pulp, a machine chest 32, a headbox 24 that
discharges a wide jet of the furnish onto a wire section to form a
fibrous paper web, a wire section 26 having a moving screen of
extremely fine mesh, a press section 28, and a dryer section 34
comprising a plurality of support rolls that dries the fibrous web
and conveys it to the size press.
[0022] A starch based coating is mixed in a mix-tank 30. The starch
used is preferably a hydroxy ethylated starch, oxidized starch,
cationically modified or enzymatically converted starch from any
regularly used starch source, such as from potato, corn, wheat,
rice or tapioca. In the present embodiment, starch is cooked and
added to the mix-tank with viscosity modifiers, cross-linkers and
fillers such one or more of the following: polyvinyl alcohols,
ammonium zirconium carbonate, borate chemicals, glyoxal, melamine
formaldehyde, ground and precipitated calcium carbonates, clays,
talc, TiO.sub.2, and silica. The starch may be cooked with a borate
chemical in a starch cooker 38 prior to entry into the mix-tank.
The mixed coating is conveyed to a size press tank and then size
pressed onto the paper web, coating one or both sides of the web.
The starched based coating preferably has starch solids in the
range of 6-20% by weight. The coating layers may be added
simultaneously or in series in accordance with one of two
techniques typically used in the industry. The paper's thickness,
weight, stiffness and curl resistance are largely the same with
either technique.
[0023] The size press-treatment used is preferably a metered
size-press application. Due to the nature of the metered size
press, application of starch solids can be controlled and
normalized. As a result, penetration of the starch coating into the
cellulosic core layer is minimal, maintaining the I-beam effect of
the three-layer single ply structure. Even so, other size-presses
known in the art, such as a flooded-nip size-press application, may
be used. In this instance the potential for application of starch
solutions to the outer layers not the same as for metered
size-press units due to inherent deeper penetration into the sheet
in the flood-nip.
[0024] The coated paper web is then conveyed to the size-press
treatment in the dry end 36 of the paper making machine, wherein
the dry end typically comprises a multiplicity of steam heated,
rotating cylinders under a heat confining hood structure in
proximity to the paper web traveling route to further dry the paper
after size press application.
[0025] The resultant paper substrate exhibits one or more enhanced
properties as compared to substrates that do not include the
bulking additive and/or the high solids starch size-press in
combination with viscosity modifiers and/or cross-linkers. For
example, for some embodiments of this invention, the substrate
exhibits improved Sheffield Smoothness (TAPPI 538om-88)) on both
wire side and felt side of the substrate in contrast to the same
substrate without the above mentioned ingredients, thus enabling
less calendering with retained bulk.
[0026] Further, the paper exhibits improved curl resistance, a
property of greatest importance for end-user performance of
reprographic grades, improved hygroexpansivity, and enhanced
Lorentzon & Wettre Bending Resistance. Other benefits of the
invention include a more closed sheet and/or an enhanced
possibility to target a certain porosity of the paper, resulting in
higher Gurley numbers (TAPPI T460 om-96). This is beneficial as
reprographic papers are usually fed through copier machines using
vacuum suction to lift the sheets.
[0027] The flowing non-limiting examples illustrate various
additional aspects of the invention. Unless otherwise indicated,
temperatures are in degrees Celsius, paper basis weight is in grams
per square meter and the percent of any pulp additive or moisture
is based on the oven-dry weight of the total amount of
material.
EXAMPLE 1
[0028] A series of trials were made on a paper machine equipped
with a flooded-nip size-press. Paper was made from a mixture of
about 9 parts hardwood and 1 part softwood and containing 19%
filler (precipitated calcium carbonate). A standard AKD size was
added as internal size and a standard surface size was added to the
size-press together with the starch solution. The trail commenced
with addition of Reactopaque 100 to the hardwood pulp chest before
refining. The addition rate was ramped up to 0.15% and the
size-press coating having enzymatically converted corn starch was
changed to contain starch at higher solids (10% instead of the
standard 8%) in combination with 5 parts based on starch of glyoxal
(Sequarez 755, Omnova Solutions Inc., SC, USA) and 25 parts based
on starch of ground calcium carbonate, (Omyafil OG, Omya, Inc.,
Alpharetta, Ga., USA). One condition was run at these settings,
then the size-press coating was switched back to starch without
glyoxal and filler while maintaining the higher solids. The last
condition maintained these settings but decreasing the paper basis
weight in order to evaluate the impact of bending stiffness. Table
1 gives the results in Lorentzon & Wettre bending resistance
(bending stiffness), paper caliper and Bendtsen porosity as
compared to a control without a bulking agent and standard starch
solids. Condition 2 shows an increase over the control in caliper
and in bending stiffness and a decrease in the porosity number.
Condition 2 also showed a smoother surface as determined from the
Bendtsen smoothness number, which decreased from 225/210 ml/min
(wire/felt side) to 205/195 ml/min (wire/felt side). This and the
decreased porosity for condition 2 can be attributed to the filler
closing the surface and creating a smoother surface. The most
important finding is when comparing Condition 2, 3 and 4 with
Condition 1 (control). The caliper increases with addition of
Reactopaque and the bending stiffness goes up as a result of the
increased caliper in combination with increased starch located to
the surface layers. The overall starch content in the sheet also
increased as a result of the more open sheet (higher Bendtsen
porosity number). Condition 4 compared to Condition 1 is especially
important as it shows that the increased bending stiffness allows
for the basis weight to be decreased while maintaining almost the
same stiffness as the control.
TABLE-US-00001 TABLE 1 Bending Basis stiffness, Bendtsen Condi-
weight Caliper mN porosity tion Treatment gram/m.sup.2 micron MD/CD
ml/min 1 Control 80.3 99.4 104/62 880 2 Reactopaque 80.3 102.3
117/57 715 Increased starch solids with glyoxal and GCC 3
Reactopaque 79.8 102.5 121/55 980 Increased starch solids 4
Reactopaque 78.3 100.1 107/58 1000 Increased starch solids Reduced
basis weight
EXAMPLE 2
[0029] A series of papers were evaluated in metered size-press
trials. A test base paper was produced at 90 gram per square meter
without Reactopaque 100. Control C1 using this base paper was given
a size press coating of 2 g/m.sup.2, control C2 was given a size
press coating of 5 g/m.sup.2, and control C3 was given a size press
coating of 8 g/m.sup.2. The controls were run in side-by-side
comparisons on a metered size-press unit with a series of test
papers produced with 88 gram per square meter with 0.18%
Reactopaque 100 added before hardwood refining. The test base
papers were given a size-press coating containing hydroxy ethylated
corn starch (Ethylex 2035 from A.E. Staley Manufacturing Co.,
Decatur, Ill., USA) at higher solids (18% instead of the standard
8%) in combination with glyoxal and a filler (ground calcium
carbonate). The size-pressed coated papers were tested for bending
stiffness, smoothness and porosity. In order to summarize the
results, bending stiffness was plotted as a function of smoothness
and results evaluated at a Sheffield smoothness of 120 after steel
to steel calendering. Gurley porosity and Sheffield smoothness
numbers are given for the un-calendared papers. The coefficient of
hygroexpansion was evaluated on paper strips in machine and
cross-machine direction using a Varidim hygroexpansivity tester
(Techpap, Grenoble France). Hygroexpansion was measured between 15
and 90% relative humidity from which the coefficient of
hygroexpansion was calculated.
[0030] Different additives for the starch solutions were selected
from the list below: [0031] Sodium tetraborate pentahydrate, borax
(Neobor from US Borax, CA, USA) added in 0.25% on starch before the
starch was cooked. [0032] Glyoxal (Sequarez 755, Omnova Solutions
Inc., SC, USA) added in 5% on starch in combination with
precipitated calcium carbonate added in 50% based on starch
(Megafil 2000, Specialty Minerals, PA, USA) [0033] Polvinyl alcohol
(Celvol 325 from Celenese Chemicals, TX USA) added in 5% on starch.
Table 2 shows the results. The combination of high starch solids
and viscosity modifier/filler/cross-linker increases bending
stiffness by over 20% over the control. High starch solids alone
also give some benefit but the surprising result is the overall
impact on several important paper properties by the bulking and
size-press application. The size-press application gives a more
closed sheet as seen from the increasing Gurley porosity numbers,
the base paper containing the bulking additive is smoother and the
coefficient of hygroexpansion is significantly lower for the
conditions with the combination of high starch solids and viscosity
modifier/filler/cross-linker.
TABLE-US-00002 [0033] TABLE 2 Coat weight of size- press Bending
Percent coating, stiffness stiffness gram per mN, increase Porosity
Coefficient square MD+ relative Gurley Smoothness of Condition
Treatment meter CD to control seconds Sheffield hygroexpansion C1
Base paper 90 g/m.sup.2 2 164 0% 13 Starch 10% solids C2 Base paper
90 g/m.sup.2 5 191 0% 17 180 0.01 Starch 10% solids C3 Base paper
90 g/m.sup.2 8 210 0% 23 Starch 10% solids 4 Bulked base 2 185 13%
30 paper 88 g/m.sup.2 compared Starch 18% to C1 solids 5 Bulked
base 5 200 5% 35 paper 88 g/m.sup.2 compared Starch 18% to C2
solids 6 Bulked base 8 215 2% 34 148 0.01 paper 88 g/m.sup.2
compared Starch 18% to C3 solids 7 Bulked base 2 193 18% 34 paper
88 g/m.sup.2 compared Starch 18% to C1 solids 0.25 parts of borax
on starch added before starch cook 8 Bulked base 5 216 13% 35 paper
88 g/m.sup.2 compared Starch 18% to C2 solids 0.25 parts of borax
on starch added before starch cook 9 Bulked base 8 223 6% 34 157
0.009 paper 88 g/m.sup.2 compared Starch 18% to C3 solids 0.25
parts of borax on starch added before starch cook 10 Bulked base 2
200 22% 30 paper 88 g/m.sup.2 compared Starch 18% to C1 solids 5
parts glyoxal on starch and 25 parts PCC on starch added to starch
coating 11 Bulked base 5 212 11% 32 paper 88 g/m.sup.2 compared
Starch 18% to C2 solids 5 parts glyoxal on starch and 25 parts PCC
on starch added to starch coating 12 Bulked base 8 226 8% 37 158
0.009 paper 88 g/m.sup.2 compared Starch 18% to C3 solids 5 parts
glyoxal on starch and 25 parts PCC on starch added to starch
coating 13 Bulked base 2 192 17% 31 paper 88 g/m.sup.2 compared
Starch 18% to C1 solids 5 parts polyvinyl alcohol on starch added
to starch coating 14 Bulked base 5 213 12% 43 paper 88 g/m.sup.2
compared Starch 18% to C2 solids 5 parts polyvinyl alcohol on
starch added to starch coating 14 Bulked base 8 222 6% 52 160 0.009
paper 88 g/m.sup.2 compared Starch 18% to C3 solids 5 parts
polyvinyl alcohol on starch added to starch coating
EXAMPLE 3
[0034] A series of papers were formed from a mixture of 8 parts
Northern hardwood pulp and 2 parts Northern softwood pulp and
having 20% filler, precipitated calcium carbonate (Megafill 2000)
from Specialty Minerals. The pulps were refined together and having
a Canadian Standard Freeness of about 450 ml. A standard AKD size
(Hercon 70) from Hercules was added in the wet-end to give the base
sheet a Hercules size test number of 50-100 seconds. Reactopaque
100 at 0.17 wt %) was added before refining at a temperature of the
pulp of 54 C (130 F) to achieve the bulking effect. The papers were
tested for heated curl with a proprietary instrument developed for
such measurements at assignee's International Paper's research
center. The results are given in Table 3. It is shown that the
addition of Reactopaque 100 to the base sheet gives a significant
reduction in the curl number (a difference in 5 units is considered
to be a significant difference.)
TABLE-US-00003 TABLE 3 Heated curl, Paper sample Treatment
millimeter 1 75 gram per square meter 42 No Reactopaque 100 2 80
gram per square meter 32 No Reactopaque 100 3 75 gram per square
meter 25 Reactopaque 100 added 4 80 gram per square meter 20
Reactopaque 100 added
[0035] Although the invention has been described with reference to
preferred embodiments, it will be appreciated by one of ordinary
skill in the art that numerous modifications are possible in light
of the above disclosure. For example, the optimum amount of bulking
agent used with different types and ratios of cellulosic fibers may
vary. All such variations and modifications are intended to be
within the scope and spirit of the invention as defined in the
claims appended hereto.
* * * * *