U.S. patent application number 12/346670 was filed with the patent office on 2010-07-01 for high-yield paper and methods of making same.
This patent application is currently assigned to North Pacific Paper Corporation (NORPAC). Invention is credited to Brian S. Delgardno, Michael J. Dougherty, Amar N. Neogi, David W. Park.
Application Number | 20100163195 12/346670 |
Document ID | / |
Family ID | 42283463 |
Filed Date | 2010-07-01 |
United States Patent
Application |
20100163195 |
Kind Code |
A1 |
Dougherty; Michael J. ; et
al. |
July 1, 2010 |
High-Yield Paper and Methods of Making Same
Abstract
A high-yield paper sheet generally includes at least about 50
weight percent mechanical pulp, wherein the basis weight of the
sheet is in the range of about 24 to about 60 pounds, and a surface
layer on the sheet including nPCC pigment.
Inventors: |
Dougherty; Michael J.; (Roy,
WA) ; Neogi; Amar N.; (Kenmore, WA) ; Park;
David W.; (Puyallup, WA) ; Delgardno; Brian S.;
(Longview, WA) |
Correspondence
Address: |
WEYERHAEUSER COMPANY;INTELLECTUAL PROPERTY DEPT., CH 1J27
P.O. BOX 9777
FEDERAL WAY
WA
98063
US
|
Assignee: |
North Pacific Paper Corporation
(NORPAC)
Longview
WA
|
Family ID: |
42283463 |
Appl. No.: |
12/346670 |
Filed: |
December 30, 2008 |
Current U.S.
Class: |
162/135 |
Current CPC
Class: |
D21H 11/08 20130101;
D21H 19/385 20130101 |
Class at
Publication: |
162/135 |
International
Class: |
D21H 19/00 20060101
D21H019/00 |
Claims
1. A high-yield paper sheet, comprising: (a) at least about 50
weight percent mechanical pulp, wherein the basis weight of the
sheet is in the range of about 24 to about 60 pounds; and (b) a
surface layer on the sheet including nPCC pigment.
2. The high-yield paper sheet of claim 1, wherein the surface layer
on the sheet includes about 0.5 to about 10 gsm nPCC.
3. The high-yield paper sheet of claim 1, wherein the surface layer
on the sheet includes about 1 to about 6 gsm nPCC.
4. The high-yield paper sheet of claim 1, wherein the surface layer
on the sheet further includes about 0.1 to about 3 gsm binder.
5. The high-yield paper sheet of claim 4, wherein the binder is
selected from the group consisting of a binder component selected
from the group consisting starch, latex, polyvinyl alcohol,
carboxymethyl cellulose, glucomannan, protein, and other known
binders, and any combination thereof.
6. The high-yield paper sheet of claim 1, wherein the particle size
of the nPCC is selected from the group consisting of less than
about 200 nanometers, less than about 100 nanometers, and about 15
to about 40 nanometers.
7. The high-yield paper sheet of claim 1, wherein the nPCC
comprises substantially non-agglomerated particles.
8. The high-yield paper sheet of claim 1, wherein the nPCC has a
substantially needle-shaped morphology.
9. The high-yield paper sheet of claim 8, wherein the needle-shaped
nPCC has a diameter in the range of about 15 to about 200
nanometers.
10. The high-yield paper sheet of claim 8, wherein the
needle-shaped nPCC has a length of greater than 1 microns.
11. The high-yield paper sheet of claim 8, wherein the
needle-shaped nPCC has a length of about 4 to about 6 microns.
12. The high-yield paper sheet of claim 1, wherein the surface
layer on the sheet further includes other pigments selected from
the group consisting of GCC, calcined clay, delaminated clay,
plastic pigments, silicates, mica, kaolin, bentonite, alumina
trihydrate, phyllosilicant, talc, and any combination thereof.
13. A high-yield paper sheet, comprising: (a) at least about 50
weight percent mechanical pulp, wherein the basis weight of the
sheet is in the range of about 35 to about 55 pounds; and (b) a
surface layer on the sheet including nPCC pigment.
14. The high-yield paper sheet of claim 13, wherein the surface
layer on the sheet includes about 0.5 to about 10 gsm nPCC.
15. The high-yield paper sheet of claim 13, wherein the surface
layer further includes starch binder.
16. A high-yield paper sheet, comprising: (a) at least about 50
weight percent mechanical pulp, wherein the basis weight of the
sheet is less than about 45 pounds; and (b) a surface layer on the
sheet including nPCC pigment and binder.
17. The high-yield paper sheet of claim 16, wherein the surface
layer on the sheet includes about 0.5 to about 10 gsm nPCC.
18. The high-yield paper sheet of claim 16, wherein the surface
layer further includes starch binder.
Description
[0001] Related patent applications include U.S. patent application
Ser. No. ______ (WEYE Ref. 26548), filed Dec. 30, 2008, and U.S.
patent application Ser. No. ______ (WEYE Ref. 26549), filed Dec.
30, 2008.
BACKGROUND
[0002] High-speed ink jet printing is a newly developed form of
printing that currently is the highest speed of printing available
for variable information printing. Due to the speed, the cost per
page is relatively low compared to other forms of variable
information printing. High-speed ink jet markets generally include
high volume variable data applications, such as bills, statements,
promotional and direct mail, as well as other transactional
communications. A low basis weight paper, similar to a newsprint
basis weight is desirable for these high-speed ink jet applications
to reduce costs associated with the paper and the postage, as well
as to reduce paper waste.
[0003] Past low basis weight paper grades have not been suitable
for high-speed ink jet printing applications. For example,
newsprint grade paper has a desirable basis weight; however, it is
not fit for high-speed ink jet applications as a result of the ink
and newsprint paper interactions, such as bleeding, cockling, etc.
In addition, the image quality for newsprint, which is directly
proportional to the specialty treatment of the paper, is poor.
[0004] Therefore, there exists a need for a high-yield paper,
particularly designed to have desirable basis weight and porosity
values, as well as other desirable qualities particular for
high-speed ink jet printing applications.
SUMMARY
[0005] This summary is provided to introduce a selection of
concepts in a simplified form that are further described below in
the Detailed Description. This summary is not intended to identify
key features of the claimed subject matter, nor is it intended to
be used as an aid in determining the scope of the claimed subject
matter.
[0006] In accordance with one embodiment of the present disclosure,
a high-yield paper sheet is provided. The high-yield paper sheet
generally includes at least about 50 weight percent mechanical
pulp, wherein the basis weight of the sheet is in the range of
about 24 to about 60 pounds, and a surface layer on the sheet
including nPCC pigment.
[0007] In accordance with one embodiment of the present disclosure,
a high-yield paper sheet is provided. The high-yield paper sheet
generally includes at least about 50 weight percent mechanical
pulp, wherein the basis weight of the sheet is in the range of
about 35 to about 55 pounds, and a surface layer on the sheet
including nPCC pigment.
[0008] In accordance with one embodiment of the present disclosure,
a high-yield paper sheet is provided. The high-yield paper sheet
generally includes at least about 50 weight percent mechanical
pulp, wherein the basis weight of the sheet is less than about 45
pounds, and a surface layer on the sheet including nPCC pigment and
binder.
DESCRIPTION OF THE DRAWINGS
[0009] The foregoing aspects and many of the attendant advantages
of this disclosure will become more readily appreciated by
reference to the following detailed description, when taken in
conjunction with the accompanying drawings, wherein:
[0010] FIG. 1 is a schematic diagram of a paper machine process for
uncoated paper in accordance with one embodiment of the present
disclosure;
[0011] FIG. 2 is a schematic diagram of a paper machine process for
coated paper in accordance with another embodiment of the present
disclosure;
[0012] FIG. 3 is a photomicrograph of long needle nano precipitated
calcium carbonate (nPCC) at 2.00 K magnification; and
[0013] FIG. 4 is a photomicrograph of long needle nano precipitated
calcium carbonate (nPCC) at 10.00 K magnification.
DETAILED DESCRIPTION
[0014] Embodiments of the present disclosure are generally directed
to high-yield paper and methods of making the same. In accordance
with embodiments of the present disclosure, the high-yield paper is
suitable for high-speed ink jet printing applications using
suitable inks, including, but not limited to water based inks,
solvent based inks, and soy based inks, and resulting in good ink
and paper interactions.
[0015] Yield is the percentage of the wood raw material that is in
the final product. A high-yield paper is one that has a high
percentage of the original wood raw material in the final paper
product. Mechanical pulping is considered to be a high-yield
pulping process in comparison to a chemical pulping process. A
mechanical pulping process can have as high as 90 to 95% of the
original wood raw material in the pulp.
[0016] In order to meet the needs of high-speed ink jet printing,
embodiments of the present disclosure include high-yield papers
made from a high percentage of mechanical pulp, and having a low
porosity and a low basis weight. For example, in accordance with
one embodiment, the high-yield paper is made from at least 50%
mechanical pulp, and has a basis weight in the range of about 24 to
about 60 pounds and Sheffield porosity in the range of about 40 to
about 100, with a decreasing number meaning less porous (or a
Gurley porosity in the range of about 30 to about 70, with an
increasing number meaning less porous). Other desirable properties
for the high-yield paper may include, but are not limited to,
stiffness, brightness, opacity, optical density, and total color
hexagon, as described in greater detail below.
[0017] High-yield paper in accordance with embodiments of the
present disclosure is made using specific furnish components, using
suitable formulations for the application of surface layers to the
paper at the size press, and under specific machine conditions,
each described in greater detail below.
Paper Making Process
[0018] Prior to describing the furnish, surface layers, and machine
conditions, a brief description of the paper making process is
provided. Referring to FIGS. 1 and 2, methods of making the
high-yield paper will now be described. FIG. 1 is a schematic
drawing of a paper machine. Wood pulp fiber furnish and wet end
chemicals are mixed with water in a headbox 10 to form a slurry.
The slurry exits the headbox through a slice 12 onto a wire 14,
wherein the water in the slurry drains from the wire. A vacuum
chest 16 is also used to draw water from the slurry to form a wet
paper web. The web is carried through press rolls 18 and a drier 20
that remove additional water.
[0019] Size press chemicals or materials, described herein as a
surface layer, are placed on the wet paper web at the size press
22. The size press may be a horizontal type with the rolls
horizontally aligned, or a vertical type with the rolls vertically
aligned. The materials may be placed on the web from the rolls or
from a puddle between the rolls. In some instances, materials may
be placed on the web by a spraying apparatus 24. The materials
described in the various embodiments in the present disclosure
would also be applied at the size press 22 or the spraying
apparatus 24.
[0020] The paper web then passes through a drying section 26. The
drying is usually performed by steam heated drier cans through
which the paper web is threaded. The paper is then calendered by
calender rolls 28 and rolled into paper rolls at the winder 30. The
resulting product is known as uncoated paper even though there are
some materials added to the surface of the paper at the size press.
The terminology in the paper industry states that this is uncoated
paper because the materials on the surface of the paper were placed
on the surface at the size press, prior to the dryer. The uncoated
sheet may be coated in another application of one or more coating
layers placed on the sheet in an off-line coating operation. After
the uncoated sheet passes through an off-machine coating station
and a second drying station, this resultant paper sheet is referred
to as a coated paper sheet. In general, uncoated or coated printing
paper has a basis weight in the range of about 16 to about 180
pounds per 3300 square feet of paper, depending on the application
for the paper.
[0021] Now referring to FIG. 2, a schematic diagram for a paper
machine for making coated paper will be described in greater
detail. It should be appreciated that the following assembly is
substantially identical in operation as the previously described
embodiment shown in FIG. 1, except for differences regarding an
additional off-machine coating operation to provide coated paper.
For clarity in the ensuing descriptions, numeral references of like
elements in the paper machine are similar, but are in the 100
series for the illustrated embodiment of FIG. 2.
[0022] As seen in FIG. 2, the web goes from the dryer 126 to the
off-machine coating operation and passes through a coating station
132. Coating station 132 is shown as rolls but any type of coating
equipment may be used. The web may then pass through a dryer 134
and calender rolls 136. In some installations there are calender
rolls before and after the coating station 132. The paper web is
then wound into rolls 138.
Slurry
[0023] The components of the slurry including the wood fiber
furnish and the wet end chemicals used in accordance with
embodiments and methods of the present disclosure will now be
described in detail. The furnish includes mechanical pulp in a
sufficient amount such that the high-yield paper includes at least
about 50 weight percent mechanical pulp. Mechanical pulp is
recovered through mechanical production processes that can be
divided into two categories: ground wood pulp production and the
thermo-mechanical process (TMP), the latter in some cases with
chemical support (CTMP). Mechanical pulp is typically used in
newsprint grade paper, and it is desirable pulp for use in
high-yield paper because of the design parameters specific
high-yield paper and the desirable opacity, caliper, print yield,
and cost factors that mechanical pulp provide.
[0024] As mentioned above, in one embodiment of the present
disclosure, the furnish includes sufficient mechanical pulp content
such that the high-yield paper includes at least about 50 weight
percent mechanical pulp fiber. The balance of the pulp content may
be chemical pulp. In another embodiment, the furnish includes
sufficient mechanical pulp content such that the high-yield paper
includes at least about 70 weight percent mechanical pulp fiber. In
yet another embodiment, the furnish includes sufficient mechanical
pulp content such that the high-yield paper includes at least about
85 weight percent mechanical pulp fiber.
[0025] The high-yield furnish may include an amount of kraft fiber
content to improve the strength and brightness of the high-yield
paper over typical newsprint grade paper. In one embodiment of the
present disclosure, the furnish includes sufficient kraft fiber
content such that the high-yield paper includes about 0 to about 50
weight percent kraft fiber. In a more preferable embodiment of the
present disclosure, the furnish includes sufficient kraft fiber
content such that the high-yield paper includes at least about 10
weight percent kraft fiber. In other embodiments, the furnish
includes sufficient kraft fiber content such that the high-yield
paper includes kraft fiber in the following ranges: about 10 to
about 50 weight percent kraft fiber, about 10 to about 30 weight
percent kraft fiber, and about 15 to about 25 weight percent kraft
fiber.
[0026] Wet end chemicals in the slurry may include fillers, such as
calcium carbonate and clay. In one embodiment, the slurry includes
sufficient precipitated calcium carbonate (PCC) ash such that the
high-yield paper includes at least about 8 weight percent internal
PCC ash. In another embodiment, the slurry includes sufficient PCC
content such that the high-yield paper includes about 8 to about 24
weight percent PCC ash. In another embodiment, the slurry includes
sufficient PCC content such that the high-yield paper includes
about 12 to about 24 weight percent PCC ash. The PCC ash can be
added to the furnish at the blend chest pump section (to the
machine chest). Notably, this is amount of PCC ash is about 2 to 4
times the amount of PCC ash normally used in newsprint grade paper.
Other wet end chemicals may include internal sizing, opacifiers,
brighteners, and dyes.
[0027] In addition to internal PCC ash and kraft fibers, the slurry
for high-yield paper in accordance with embodiments of the present
disclosure generally has increased TMP freeness and increased TMP
brightness over typical newsprint slurry. Increased TMP freeness is
achieved through a combination of increasing throughput and
decreasing refiner energy. In one embodiment of the present
disclosure, the TMP freeness range for the high-yield furnish is in
the range of about 60 to about 150 CSF. In another embodiment, the
TMP freeness range for the high-yield furnish is in the range of
about 100 to about 150 CSF. In another embodiment, the TMP freeness
range for the high-yield furnish is about 120 CSF to about 150 CSF.
Increased TMP freeness results in increased caliper and increased
stiffness over typical caliper and stiffness values for newsprint
grade paper. Typical freeness values for TMP newsprint furnish are
less than about 100 CSF.
[0028] Increased TMP brightness is achieved through increased
peroxide dosage, changed residence times and flows, and using trim
peroxide for residual control after thickening and dilution. In one
embodiment, the brightness of high-yield TMP furnish is in the
range of about 65 to about 80 TAPPI. Typical brightness values for
TMP newsprint furnish are about 52 to about 62.
Surface Layer
[0029] As mentioned above, additional size press chemicals or
materials are placed on the wet paper web at the size press 22 to
form a surface layer on the paper web. In accordance with
embodiments of the present disclosure, a surface layer including
pigment, binder, and/or additional surface modifying chemicals may
be added to the surface of the sheet at the size press. The surface
layer materials that can be placed on the web at the size press
must have a viscosity which allows for the transfer of the material
onto the web. In addition, some of the surface layer materials may
enter into the web if the pressure of the nip at the size press is
high enough. Moreover, the surface layer materials can also be
sprayed on the web prior to the dryer. The majority of surface
layer materials that are sprayed on the web will remain on the
surface of the web.
[0030] As mentioned above, a surface layer is provided to improve
the desirable qualities of the high-yield paper, for example, to
improve the ink and paper interactions for high-speed ink jet
printing that are not present in standard newsprint grade paper. As
mentioned above, the surface layer includes pigment. In accordance
with embodiments of the present disclosure, the pigment includes
nano precipitated calcium carbonate (nPCC) to improve color gamut,
color densities, ink bleed properties, show thru, and sheet
stiffness. In one embodiment, the nPCC may be present in the
surface layer in an amount in the range of about 1.25% to about 15%
of the weight of the base paper. In another embodiment, the nPCC
may be present in the surface layer in an amount in the range of
about 1 to about 6 gsm.
[0031] "Nano" precipitated calcium carbonate refers to calcium
carbonate having a mean particle size across the particle of less
than about 200 nm. In one embodiment, nPCC having a mean particle
size across the particle of less than about 200 nanometers is
applied to the surface of a paper product. In another embodiment,
nPCC having a mean particle size across the particle of less than
about 100 nanometers is applied to the surface of a paper product.
In another embodiment, nPCC having a mean particle size across the
particle of about 15 nanometers to about 50 nanometers is applied
to the surface of a paper product. In another embodiment, the nPCC
having a mean particle size across the particle of less than about
40 nanometers is applied to the surface of a paper product.
[0032] The nPCC is preferably substantially non-agglomerated
particles. For example, the nPCC may be formed using a high gravity
reactive precipitation (HGRP) reactor to avoid particle
agglomeration. A suitable nPCC is available from NanoMaterials
Technology Pte Ltd (NMT).
[0033] In accordance with embodiments of the present disclosure,
the nPCC surface layer may include other pigment components,
including but not limited to ground calcium carbonate (GCC),
calcined clay, delaminated clay, plastic pigments, silicates, mica,
kaolin, bentonite, alumina trihydrate, phyllosilicant, talc, and
other known pigments, as well as mixtures thereof. Ground calcium
carbonate (GCC) generally has a particle size of 0.75 microns (750
nanometers).
[0034] While nPCC has self-binding capabilities, the surface layer
may further include a binder to help improve the properties of the
surface layer. Suitable binders include but are not limited to
starch, latex, polyvinyl alcohol, carboxymethyl cellulose,
glucomannan, protein, and other known binders, as well as mixtures
thereof. In one embodiment of the present disclosure, the surface
layer of the high-yield paper includes about 0.1 to about 3 gsm
binder. In another embodiment, the binder in the surface layer is
present in an amount in the range of about 6% to about 12% of the
weight of the base paper. In one non-limiting example, starch
binder in the surface layer improves the surface integrity of the
high-yield paper sheet for improved ink and paper interactions for
high-speed ink jet printing. For comparative information, starch
content on newsprint grade paper is generally about 0.15 gsm, and
about 0.8 gsm on publication grade paper (i.e., book paper).
[0035] The nPCC surface layer may further include surface modifying
chemicals, such as surface sizing, salts such as nitrate salt,
charge modifiers, film formers, optical brighteners, latex,
cross-linkers for starch-based formulations such as glyoxal, as
well as other additives.
[0036] As shown in the data collected in EXAMPLES 7 and 8 and
TABLES 3 and 4 below, high-yield paper having a surface layer
including nPCC generally increases in desired properties for
increased amounts of nPCC content in the surface layer. For
example, the data in EXAMPLE 7 and corresponding TABLE 3 shows
improved stiffness, porosity, and ink density characteristics with
increased nPCC to starch ratios in the surface layer, and in
comparison to the GCC sample. The data in EXAMPLE 8 and
corresponding TABLE 4 shows improved stiffness, porosity, and color
parameters with increasing nPCC content in the surface layer.
NPCC Morphology
[0037] The morphology of the nPCC in the nPCC surface layer may
also vary to further improve the properties of the high-yield
paper. In that regard, nPCC is commonly available having a
cubic-shaped morphology. However, nPCC having a needle-shaped
morphology is also within the scope of the present disclosure. As
described in greater detail below, a paper sheet that includes long
needle nPCC in the surface layer has many enhanced attributes
compared to a sheet that has only cubic nPCC on its surface. The
long needle nPCC may be about 15 to about 200 nm in diameter, and
more preferably about 15 to about 50 nm in diameter, and about 4 to
about 6 microns (about 4000 to about 6000 nanometers) in length.
These dimensions compare to short needle nPCC having a length of
about 1 to about 3 microns (about 1000 to about 3000 nanometers).
FIGS. 3 and 4 are photomicrographs of the long needle nPCC. It can
be seen that a majority of the needles are long needle nPCC;
however, there are some short needles and debris associated with
the long needle nPCC.
[0038] Long needle nPCC may be made using the high gravity reactive
precipitation (HGRP) reactor and may be obtained, for example, from
NanoMaterials Technology Pte Ltd (NMT). In addition, a long needle
or long cigar nPCC having a length of about 4 to about 6 microns
may be available from Solvay S.A. Solvay, which makes a
needle-shaped aragonite nPCC Socal 90A, NZ and P2A and a
cigar-shaped calcite nPCC Solvay P1V, P2, P2V, P3E, 93V, 94V, NP,
N2, N2R, or P2PHV. The discussion of long needle nPCC throughout
the specification includes long cigar shaped nPCC.
[0039] As a result of the morphology, use of long needle nPCC in
the surface layer increases the stiffness of paper, as compared to
a paper sheet that does not have long needle nPCC applied to its
surface. Improved paper stiffness allows a sheet to be used where
paper stiffness is required for post printing and conversion
operations. Machine direction and cross direction Gurley stiffness
and machine direction and cross direction Taber stiffness were used
to determine the stiffness of paper. The machine direction and
cross direction Gurley stiffness of a paper sheet is determined
using TAPPI test method T-543. The machine direction and cross
direction Taber stiffness of a paper sheet is determined using
TAPPI test method T-489. In both methods the bending resistance of
paper is determined by measuring the force required to bend a
sample under controlled conditions.
[0040] The long needle nPCC may be combined with other materials
normally added at the size press. In one embodiment, the surface
layer materials include both the long needle nPCC and starch or
ethylated starch. In one embodiment of the present disclosure, the
amount of long needle nPCC may be in present in the surface layer
of the paper in an amount in the range of about 1.25% to about 15%
of the weight of the base paper. In another embodiment of the
present disclosure, the amount of starch (such as ethylated starch)
may be present in the surface layer in an amount in the range of
about 6% to about 12% of the weight of the base paper.
[0041] The long needle nPCC may also be combined with cubic or
short needle nPCC. In one embodiment of present disclosure, long
needle nPCC may be combined with an amount of cubic or short needle
nPCC, such that total nPCC is in the range of from about 1.25% to
about 15% of the weight of the base paper. In addition, the long
needle, short needle, and/or cubic nPCC may be combined with other
pigment additives.
[0042] As shown in the data collected in EXAMPLES 1-6 and TABLES 1
and 2 below, paper having a surface layer including long needle
nPCC generally has a greater machine direction and cross direction
Gurley stiffness and machine direction and cross direction Taber
stiffness than paper having a surface layer including standard size
press additives only, such as starch or ethylated starch, or with
cubic or short needle nPCC alone. However, paper having a surface
layer including long needle nPCC and cubic nPCC also shows greater
machine direction and cross direction Gurley stiffness and machine
direction and cross direction Taber stiffness than paper having a
surface layer including standard size press additives only, such as
ethylated starch, or with cubic or short needle nPCC alone.
[0043] In some embodiments of the present disclosure, the inventors
have found that paper having a surface layer including long needle
nPCC may have an increase in both machine direction and cross
direction Gurley stiffness of 15 to 20% when compared with paper
having a surface layer including standard size press additives,
such as starch and cubic or short needle nPCC. Paper having a
surface layer including long needle nPCC may have an increase in
both machine direction and cross direction Gurley stiffness of 5 to
10% when compared to paper having a surface layer including cubic
nPCC. Paper having a surface layer including long needle nPCC may
have an increase in machine direction Gurley stiffness of 7 to 12%
and an increase in cross direction Gurley stiffness of 20 to 25%
when compared to paper having a surface layer including short
needle nPCC.
[0044] Paper having a surface layer including long needle nPCC may
have an increase in both machine direction and cross direction
Taber stiffness of 13 to 20% when compared with paper having a
surface layer including standard size press additives. Paper having
a surface layer including long needle nPCC may have an increase in
both machine direction and cross direction Taber stiffness of 5 to
12% when compared to paper having a surface layer including cubic
nPCC. Paper having a surface layer including long needle nPCC may
have an increase in machine direction Taber stiffness of 12 to 17%
and in cross direction Gurley stiffness of 25 to 30% when compared
to paper having a surface layer including short needle nPCC.
[0045] Paper having a surface layer including a combination of the
long needle nPCC and cubic or short needle nPCC may also have a
greater machine direction and cross direction Gurley stiffness and
machine direction and cross direction Taber stiffness than paper
having a surface layer including standard size press additives
only, or with cubic or short needle nPCC, on in some cases long
needle nPCC only.
[0046] Paper having a surface layer including a combination of long
needle nPCC and cubic or short needle nPCC may have an increase in
both machine direction and cross direction Gurley stiffness of 20
to 25% when compared with paper having a surface layer including
standard size press additives. Paper having a surface layer
including a combination of long needle nPCC and cubic or short
needle nPCC may have an increase in both machine direction and
cross direction Gurley stiffness of 10 to 15% when compared to
paper having a surface layer including cubic nPCC. Paper having a
surface layer including a combination of long needle nPCC and cubic
or short needle nPCC may have an increase in machine direction
Gurley stiffness of 10 to 15% and in cross direction Gurley
stiffness of 25 to 30% when compared to paper having a surface
layer including short needle nPCC.
[0047] Paper having a surface layer including a combination of long
needle nPCC and cubic or short needle nPCC may have an increase in
machine direction Taber stiffness of 15 to 20% and in cross
direction Taber stiffness of 20 to 25% when compared with paper
having a surface layer including standard size press additives.
Paper having a surface layer including a combination of long needle
nPCC and cubic or short needle nPCC may have an increase in both
machine direction Taber stiffness of 7 to 12% and in cross
direction Taber stiffness of 14 to 20% when compared to paper
having a surface layer including cubic nPCC. Paper having a surface
layer including a combination of long needle nPCC and cubic or
short needle nPCC may have an increase in machine direction Taber
stiffness of 15 to 20% and an increase in cross direction Gurley
stiffness of 30 to 40% when compared to paper having a surface
layer including short needle nPCC.
Machine Conditions
[0048] The preferred machine conditions for high-yield paper will
now be described in greater detail. It should be appreciated that
the properties of the high-yield paper described herein are a
result in part of machine conditions that move toward paper machine
conditions that are used for fine paper, rather than machine
conditions that are used for typical newsprint grade paper.
[0049] In one embodiment of the present disclosure, the orientation
of the sheet is squared up to improved curl properties and
stiffness. Generally, typical newsprint paper is very oriented in
the machine direction (MD). Therefore, squaring up the orientation
of the sheet, helps lessen the orientation of the sheet in the MD
direction. The sheet is squared up by running the stock jet into
the former at a speed that is close to the forming wire speed, as
opposed to being slower or faster than the forming wire speed.
[0050] In another embodiment, the drying conditions are altered to
be more similar to those for a fine paper sheet rather than a
typical newsprint sheet to improve moisture profiles and lower
sheet dryness. For example, the machine may be run at about 4% to
about 12% moisture into the size press and about 4% to about 10%
moisture at the reel with after-dryer section steam generally
greater than about 50 psig, as compared to about 10 to about 12%
moisture into the size press and about 9.5% moisture at the reel
with after-dryer section steam generally less than about 50 psig
for newsprint grade paper.
Characteristics of High-Yield Paper
[0051] Preferred characteristics of the high-yield paper will now
be described in greater detail. Such characteristics are the result
of the paper furnish and chemical additives to the slurry, surface
layer materials, and paper making machine conditions.
[0052] In accordance with embodiments of the present disclosure,
the high-yield paper is a low basis weight paper. "Basis weight"
was analyzed according to TAPPI test method T-410. The area of
paper or paperboard is determined from linear measurements and mass
is determined by weighing. The grammage is calculated from the
ratio of the mass to the area. In one embodiment, the high-yield
paper has a basis weight of less than about 55 pounds. In another
embodiment, the high-yield paper has a basis weight of less than
about 45 pounds. In yet another embodiment, the high-yield paper
has a basis weight in the range of about 35 to about 55 pounds.
[0053] In addition to low basis weight, the high-yield paper also
has a low porosity. Low porosity is achieved by the nPCC surface
layer because less air is able to permeate the sheet of paper with
the nPCC surface layer on the paper. Two types of instruments are
generally used to measure porosity--Gurley and Sheffield. The
Gurley Instrument measures "Gurley porosity" according to TAPPI
test methods T-460 and T-536, which are the seconds required for
given volume of air to pass through a single sheet of and is
generally used for porous papers. A high reading indicates a less
porous (or more dense) paper. Sheffield porosity measures the low
rate of air through a single sheet and is generally used for
non-porous or dense sheets. A high Sheffield porosity reading
indicates a more open paper, and a low reading indicates a less
porous (or more dense) paper. Sheffield porosity is measured
according to TAPPI test method T-547.
[0054] In one embodiment of the present disclosure, the high-yield
paper has a Sheffield porosity in the range of about 40 to about
100, with a decreasing number meaning less porous (or a Gurley
porosity in the range of about 30 to about 70, with an increasing
number meaning less porous).
[0055] In accordance with other embodiments of the present
disclosure, the high-yield paper has a Taber MD stiffness of
greater than about 2.3. In accordance with other embodiments of the
present disclosure, the high-yield paper has a Taber CD stiffness
in the range of greater than about 0.7, more preferably about 0.7
to about 0.9.
[0056] In accordance with other embodiments of the present
disclosure, the high-yield paper has a caliper in the range of
about 3.5 to about 6.5 mils. In some cases, the paper machine may
have caliper limitations that fall below this range, for example in
the range of about 3.5 to about 5.0 mils.
[0057] In accordance with other embodiments of the present
disclosure, the high-yield paper has a brightness in the range of
about 70 to about 85 TAPPI at the reel, preferably 70 to about 90
TAPPI at the reel, and more preferably 70 to about 100 TAPPI at the
reel. Brightness may be achieved through the use of kraft pulp in
the furnish having a high TMP brightness, internal fillers,
opacifying agents, pigmentation, and other components. Brightness
is measured by TAPPI test method T-452.
[0058] Opacity is the lack of transparency that allows a sheet to
conceal print on its reverse side. Opacity is greatly influenced by
basis weight, brightness, type of fiber and filler. In testing,
reflectance of paper is measured when backed successfully by a
white body and a black body. The ratio of these two measurements
determines the opacity reading. In accordance with other
embodiments of the present disclosure, the high-yield paper has an
opacity in the range of about 90% to about 100%. Such an opacity
range may be achieved through the use of mechanical pulp in the
furnish, internal fillers, opacifying agents, pigmentation, as well
as other factors.
[0059] Optical properties of the high-yield paper will now be
described in greater detail. "Optical density" was analyzed by a
densitometer that measures darkness in terms of "optical density",
defined as the negative logarithm of the reflectance of the sample.
For example, a dark gray printed area that reflects 10% percent of
the incident light has an optical density of -log(0.10)=1.00
density units (D.U.). By taking the negative logarithm of
reflectance, the resulting density measurement gives a better match
with the visual impression of darkness.
[0060] A light source, usually white (a mix of all the visible
colors), illuminates the sample measurement area at a 45-degree
angle. Light reflected perpendicularly from the sample strikes the
light detector. The detector signal is logarithmically converted
and processed for display in optical density units on the readout.
A black-and-white densitometer uses a white light source and a
detector sensitive over the entire visible color spectrum. When the
overall densitometer spectral response is comparable to human
vision, the resulting measurement is called "visual" density. A
color densitometer measures in red, green, and blue wavelength
bands appropriate for cyan, magenta, and yellow colorants,
respectively. Except for neutral gray and black samples, the
reflectance and density of a given sample depend on the wavelength
or color of the incident light. Red, green, and blue filters in the
optical path are commonly used for separating the color bands.
[0061] Optical properties may also be measured in total color
hexagon, black, cyan, magenta, and yellow color densities, as
measured compared to a color control chart. Total color hexagon is
a trilinear plotting system for printed ink films. Adapted for the
printing industry by GATF, the method was originally developed by
Eastman Kodak. A color is located by moving in three directions (at
120 degree angles) on the diagram by amounts corresponding to the
densities of the printed ink film. The diagram is generally used as
a color control chart, particularly for detecting changes in the
hue of two-color overprints. In accordance with embodiments of the
present disclosure, the high-yield paper has a total color hexagon
of the sheet is greater than about 0.65, and more preferably
greater than 0.70.
[0062] "Show thru" or "backside color bleed" is a measure of
optical density on the opposite side of a printed paper, also
measured in total color hexagon, black, cyan, magenta, and yellow
color densities. This measurement helps determine the ability of a
substrate to hold the ink on the printed surface and not allow the
ink to "bleed" through the substrate. In accordance with
embodiments of the present disclosure, the high-yield paper has a
backside total color bleed value in the range of about 0.01 to
about 0.07.
EXAMPLES
[0063] EXAMPLES 1-5 and associated TABLE 1 include data relating to
pigment morphology and provide stiffness values for five different
surface layer formulations: ethylated starch (EXAMPLE 1), cubic
nPCC (EXAMPLE 2), short needle nPCC (EXAMPLE 3), long needle nPCC
(EXAMPLE 4), and a mixture of the long needle and cubic nPCC
(EXAMPLE 5). From the results of EXAMPLES 1-5, it can be seen that
the surface layers including long needle nPCC (EXAMPLE 4) and a
mixture of the long needle and cubic nPCC (EXAMPLE 5) provide
greater stiffness in both machine direction and cross direction
than standard materials (e.g., ethylated starch), cubic nPCC, and
short needle nPCC, as discussed in greater detail below.
[0064] EXAMPLE 6 and associated TABLE 2 include data relating to
pigment morphology and provide stiffness and brightness values for
four different surface layer formulations: Sample A has a surface
layer including control starch; Sample B has a surface layer
include cubic nPCC; Sample C has a surface layer include short
needle nPCC; and Sample D has a surface layer include long needle
nPCC. The data shows that Gurley and Taber stiffness values in both
the MD and the CD increase significantly for samples having a
surface layer including 4 micron long needle nPCC. In addition,
brightness values increased for samples having a surface layer
including cubic, 2 micron short needle nPCC, and 4 micron long
needle nPCC.
[0065] EXAMPLE 7 and associated TABLE 3 include data relating to
increasing ratios of cubic nPCC compared to starch in high-yield
paper samples having the following nPCC and starch surface layers:
Sample A includes a surface layer having control starch; Sample B
includes a surface layer having nPCC and starch in a ratio of 0.43
to 1; Sample C includes a surface layer having nPCC and starch in a
ratio of 0.80 to 1; Sample D includes a surface layer having nPCC
and starch in a ratio of 1.20 to 1; and Sample E includes a surface
layer having GCC and starch in a ratio of 1.20 to 1. The data shows
improved stiffness, porosity, and ink density characteristics over
control starch and GCC with increased nPCC to starch ratios in the
surface layer.
[0066] EXAMPLE 8 and associated TABLE 4 include data relating to
increasing amounts of cubic nPCC while maintaining similar starch
content in high-yield paper samples having the following nPCC and
starch surface layers: Sample 1 includes a control starch surface
layer; Sample 2 includes a GCC surface layer; Sample 3-6 include
nPCC surface layers, with similar starch contents and increasing
amounts of nPCC in the surface layer. Samples 1 and 2 relating to
starch control and GCC surface layers were included for comparison.
The data shows improved stiffness, porosity, and color parameters
with increasing nPCC content in the surface layer.
Example 1
Starch Surface Layer
[0067] Seven 81/2.times.11 sheets of 45 pound per ream newsprint
were coated with ethylated starch (Penford Gum 280). The following
is an average for the seven samples. The average total solids were
8% of the weight of the paper substrates. The average coated weight
of the samples was 6.41 grams. The average coat weight was 2.3
grams or 58.2 pounds per ton. The ambient viscosity was 62/2. The
samples were dried. The average dry weight of the samples was 4.7
grams. The samples were tested for machine direction (MD) and cross
direction (CD) Gurley stiffness and machine direction and cross
direction Taber stiffness. The average MD Gurley stiffness was
172.08, the average CD Gurley stiffness was 56.43, the average MD
Taber stiffness was 2.18 and the average CD Taber stiffness was
0.76.
Example 2
Cubic NPCC Surface Layer
[0068] Seven 81/2.times.11 sheets of 45 pound per ream newsprint
were coated with ethylated starch (Penford Gum 280) and cubic nano
precipitated calcium carbonate (nPCC-111). The following is an
average for the seven samples. The average total solids were 16% of
the weight of the paper substrates, 8% Penford Gum 280 and 8% cubic
nPCC. The average coated weight of the samples was 6.46 grams. The
average coat weight was 4.7 grams or 120.8 pounds per ton. The
ambient viscosity was 355/2. The samples were dried. The average
dry weight of the samples was 4.69 grams. The samples were tested
for machine direction (MD) and cross direction (CD) Gurley
stiffness and machine direction and cross direction Taber
stiffness. The average MD Gurley stiffness was 189.04, the average
CD Gurley stiffness was 61.3, the average MD Taber stiffness was
2.33 and the average CD Taber stiffness was 0.81.
Example 3
Short Needle NPCC Surface Layer
[0069] Seven 81/2.times.11 sheets of 45 pound per ream newsprint
were coated with ethylated starch (Penford Gum 280) and short
needle nPCC (length 1-3 microns). The following is an average for
the seven samples. The average total solids were 16% of the weight
of the paper substrates, 8% Penford Gum 280 and 8% small needle
nPCC. The average coated weight of the samples was 6.35 grams. The
average coat weight was 4.5 grams or 117.9 pounds per ton. The
ambient viscosity was 344/2. The samples were dried. The average
dry weight of the samples was 4.64 grams. The samples were tested
for machine direction (MD) and cross direction (CD) Gurley
stiffness and machine direction and cross direction Taber
stiffness. The average MD Gurley stiffness was 185.7, the average
CD Gurley stiffness was 53.89, the average MD Taber stiffness was
2.17 and the average CD Taber stiffness was 0.70.
Example 4
Long Needle NPCC Surface Layer
[0070] Seven 81/2.times.11 sheets of 45 pound per ream newsprint
were coated with ethylated starch (Penford Gum 280) and long needle
nPCC. The following is an average for the seven samples. The
average total solids were 16% of the weight of the paper
substrates, 8% Penford Gum 280 and 8% long needle nPCC. The average
coated weight of the samples was 6.54 grams. The average coat
weight was 4.9 grams or 127.2 pounds per ton. The ambient viscosity
was 356/2. The samples were dried. The average dry weight of the
samples was 4.68 grams. The samples were tested for machine
direction (MD) and cross direction (CD) Gurley stiffness and
machine direction and cross direction Taber stiffness. The average
MD Gurley stiffness was 202.94, the average CD Gurley stiffness was
66.46, the average MD Taber stiffness was 2.48 and the average CD
Taber stiffness was 0.89.
[0071] The MD Gurley stiffness of the long needle nPCC sample
(EXAMPLE 4) was 18% greater than the ethylated starch sample
(EXAMPLE 1), 7% greater than the cubic nPCC sample (EXAMPLE 2), and
9% greater than the short needle nPCC sample (EXAMPLE 3).
[0072] The CD Gurley stiffness of the long needle nPCC sample
(EXAMPLE 4) was 18% greater than the ethylated starch sample
(EXAMPLE 1), 8% greater than the cubic nPCC sample (EXAMPLE 2), and
23% greater than the short needle nPCC sample (EXAMPLE 3).
[0073] The MD Taber stiffness of the long needle nPCC sample
(EXAMPLE 4) was 14% greater than the ethylated starch sample
(EXAMPLE 1), 6% greater than the cubic nPCC sample (EXAMPLE 2), and
14% greater than the short needle nPCC sample (EXAMPLE 3).
[0074] The CD Taber stiffness of the long needle nPCC sample
(EXAMPLE 4) was 17% greater than the ethylated starch sample
(EXAMPLE 1), 10% greater than the cubic nPCC sample (EXAMPLE 2),
and 27% greater than the short needle nPCC sample (EXAMPLE 3).
Example 5
Long Needle and Cubic NPCC Surface Layer
[0075] Seven 81/2.times.11 sheets of 45 pound per ream newsprint
were coated with ethylated starch (Penford Gum 280), long needle
nPCC and cubic nPCC. The following is an average for the seven
samples. The average total solids were 16% of the weight of the
paper substrates, 8% Penford Gum 280, 4% long needle nPCC and 4%
cubic nPCC. The average coated weight of the samples was 6.49
grams. The average coat weight was 4.6 grams or 116.3 pounds per
ton. The ambient viscosity was 290/2. The samples were dried. The
average dry weight of the samples was 4.76 grams. The samples were
tested for machine direction (MD) and cross direction (CD) Gurley
stiffness and machine direction and cross direction Taber
stiffness. The average MD Gurley stiffness was 209.61, the average
CD Gurley stiffness was 68.82, the average MD Taber stiffness was
2.56 and the average CD Taber stiffness was 0.94.
[0076] The MD Gurley stiffness of the long needle and cubic nPCC
sample (EXAMPLE 5) was 22% greater than the ethylated starch sample
(EXAMPLE 1), 11% greater than the cubic nPCC sample (EXAMPLE 2),
and 13% greater than the short needle nPCC sample (EXAMPLE 3).
[0077] The CD Gurley stiffness of the long needle and cubic nPCC
sample (EXAMPLE 5) was 22% greater than the ethylated starch sample
(EXAMPLE 1), 12% greater than the cubic nPCC sample (EXAMPLE 2),
and 28% greater than the short needle nPCC sample (EXAMPLE 3).
[0078] The MD Taber stiffness of the long needle and cubic nPCC
sample (EXAMPLE 5) was 17% greater than the ethylated starch sample
(EXAMPLE 1), 10% greater than the cubic nPCC sample (EXAMPLE 2),
and 28% greater than the short needle nPCC sample (EXAMPLE 3).
[0079] The CD Taber stiffness of the long needle and cubic nPCC
sample (EXAMPLE 5) was 24% greater than the ethylated starch sample
(EXAMPLE 1), 16% greater than the cubic nPCC sample (EXAMPLE 2),
and 34% greater than the short needle nPCC sample (EXAMPLE 3).
[0080] TABLE 1 below summerizes the data from EXAMPLES 1-5.
TABLE-US-00001 TABLE 1 Sample Example 1 Example 3 Example 4 Example
5 Ethylated Example 2 Short Needle Long Needle Long and Starch
Cubic nPCC nPCC nPCC Cubic nPCC Total solids 8% EStarch 16% Total
16% Total 16% Total 16% Total 8% EStarch 8% EStarch 8% EStarch 8%
EStarch 8% CnPCC 8% SNnPCC 8% LNnPCC 4% CnPCC 4% LNnPCC Coated wt.
of 6.41 6.46 6.35 6.54 6.49 sample (g) Coat Wt. (g) 2.3 4.7 4.5 4.9
4.6 Coating ambient 62/2 355/2 344/2 356/2 290/2 viscosity Dry wt.
of 4.7 4.69 4.64 4.68 4.76 sample (g) Gurley Stiffness 172.08
189.04 185.7 202.94 209.61 MD Gurley Stiffness 56.43 61.3 53.89
66.46 68.82 CD Taber Stiffness 2.18 2.33 2.17 2.48 2.56 MD Taber
Stiffness 0.76 0.81 0.70 0.89 0.94 CD
Example 6
Comparative Morphology
[0081] Four different paper samples were tested for stiffness and
brightness. Sample A has a surface layer including control starch,
without pigmentation. Sample B has a surface layer including cubic
nPCC. Sample C has a surface layer including about 2 micron short
needle nPCC. Sample D has a surface layer including about 4 micron
long needle nPCC. The data in TABLE 2 below shows that Gurley and
Taber stiffness values in both the MD and the CD increase
significantly for samples having a surface layer including 4 micron
long needle nPCC. In addition, brightness values increased for
samples having a surface layer including cubic, 2 micron short
needle nPCC, and 4 micron long needle nPCC.
TABLE-US-00002 TABLE 2 Sample A C D Control B 2 micron Short 4
micron Long Starch Cubic nPCC Needle nPCC Needle nPCC Gurley 82.14
85.8 83.3 96.35 Stiffness MD Gurley 31.58 31.58 31.9 38.15
Stiffness CD Brightness 76.14 76.7 76.9 77.18 Taber Stiffness 1.160
1.150 1.060 1.210 MD Taber Stiffness 0.388 0.440 0.466 0.440 CD
Example 7
Lab Data
[0082] Paper characteristics were determined for four comparative
samples having four different surface layers: Sample A includes a
surface layer having control starch; Sample B includes a surface
layer having nPCC and starch in a ratio of 0.43 to 1; Sample C
includes a surface layer having nPCC and starch in a ratio of 0.80
to 1; and Sample D includes a surface layer having nPCC and starch
in a ratio of 1.20 to 1; and Sample E includes a surface layer
having GCC and starch in a ratio of 1.20 to 1. All nPCC samples
used cubic nPCC.
[0083] The data in TABLE 3 below shows improved stiffness,
porosity, and ink density characteristics with increased nPCC to
starch ratios in the surface layer. Moreover, comparing the results
for the GCC sample (Sample E) with the nPCC samples (Samples B, C,
and D), GCC does not achieve the stiffness, porosity, and ink
density characteristics achieved by the lowest ratio nPCC sample
(SAMPLE B), and even does not perform as well as starch alone.
(Sample A).
TABLE-US-00003 TABLE 3 Sample A B C D E Control nPCC:Starch
nPCC:Starch nPCC:Starch GCC:Starch Starch 0.43:1 0.80:1 1.20:1
1.20:1 Gurley 39.68 41.12 49.84 45.12 39.7 Stiffness MD Gurley
10.68 11.68 11.67 12.98 11.14 Stiffness CD Taber Stiffness 0.506
0.502 0.564 0.701 0.501 MD Taber Stiffness CD 0.212 0.200 0.211
0.232 0.211 Hagerty 70.5 71.7 67.6 68.8 70.9 Roughness Gurley 88.2
110.5 122.9 137.4 99.7 Porosity (sec/100 mL) Opacity % 92.833
93.283 92.887 94.741 92.9 total color 0.699 0.778 0.696 hexagon
Black ink 1.00 0.99 0.89 density Cyan ink 1.02 1.09 0.97 density
Magenta ink 0.96 0.98 0.93 density Yellow ink 0.72 0.71 0.65
density Backside 0.09 0.08 Black ink density Backside 0.03 0.02
Cyan ink density Backside 0.03 0.02 Magenta ink density Backside
0.03 0.01 Yellow ink density
Example 8
Commercial Data
[0084] Paper characteristics are shown for five comparative samples
having five different surface layers: Sample 1 includes a control
starch surface layer; Samples 2-5 include nPCC surface layers, with
similar starch contents and increasing amounts of nPCC in the
surface layer. Sample 1 relating to starch control was included for
comparison. All samples used cubic nPCC. The data was normalized
for a constant base ash of 15% to provide accurate backside color
bleed values.
[0085] The data in TABLE 4 below shows improved stiffness,
porosity, and color parameters with increasing nPCC content in the
surface layer.
TABLE-US-00004 TABLE 4 Sample 1 2 3 4 5 Starch nPCC nPCC nPCC nPCC
Basis Weight # 45 45 45 45 45 Starch (gsm) 0.991 1.285 0.872 0.973
0.877 nPCC (gsm) 0 1.324 2.437 3.280 5.373 total surface 1.307
2.609 3.309 4.253 6.250 layer (gsm) base ash % 14.90 15.00 15.00
15.00 15.00 surface layer 0.43 1.81 3.33 4.48 7.34 ash % total ash
% 15.33 16.81 18.33 19.48 22.34 Taber Stiffness 2.203 2.663 2.368
2.654 2.451 MD Taber Stiffness 0.688 0.769 0.755 0.752 0.743 CD
Gurley porosity 29 35 62 40 57 Sheffield 108 92 58 80 61 porosity
Total color 0.65 0.66 0.78 0.71 0.79 hexagon Black ink 1.00 0.98
0.98 0.99 0.99 density Cyan ink 0.95 0.95 1.08 0.99 1.07 density
Magenta ink 0.95 0.94 1.03 0.98 1.03 density Yellow ink 0.72 0.72
0.75 0.74 0.75 density Backside color 0.08 0.065 0.065 0.055 0.05
bleed-total color hexagon
[0086] Although the subject matter has been described in language
specific to structural features and/or methodological acts, it is
to be understood that the subject matter defined in the appended
claims is not necessarily limited to the specific features or acts
described above. Rather, the specific features and acts described
above are disclosed as example forms of implementing the claims.
While illustrative embodiments have been illustrated and described,
it will be appreciated that various changes can be made therein
without departing from the spirit and scope of the disclosure.
* * * * *