U.S. patent application number 13/747566 was filed with the patent office on 2013-07-25 for separated treatment of paper substrate with multivalent metal salts and obas.
This patent application is currently assigned to INTERNATIONAL PAPER COMPANY. The applicant listed for this patent is BRIAN W. BROLLIER, BENNY J. SKAGGS. Invention is credited to BRIAN W. BROLLIER, BENNY J. SKAGGS.
Application Number | 20130189457 13/747566 |
Document ID | / |
Family ID | 47714547 |
Filed Date | 2013-07-25 |
United States Patent
Application |
20130189457 |
Kind Code |
A1 |
SKAGGS; BENNY J. ; et
al. |
July 25, 2013 |
SEPARATED TREATMENT OF PAPER SUBSTRATE WITH MULTIVALENT METAL SALTS
AND OBAs
Abstract
A process for providing printable substrates by separately
treating one or both surfaces of a paper substrate with an optical
brightening agent (OBA) and a multivalent metal salt drying agent,
where one or both surfaces of the paper substrate is treated with
one of these two agents at the size press, and where the surface(s)
is treated with the other of these two agents before or after the
size press.
Inventors: |
SKAGGS; BENNY J.;
(Springboro, OH) ; BROLLIER; BRIAN W.;
(Cincinnati, OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
SKAGGS; BENNY J.
BROLLIER; BRIAN W. |
Springboro
Cincinnati |
OH
OH |
US
US |
|
|
Assignee: |
INTERNATIONAL PAPER COMPANY
Memphis
TN
|
Family ID: |
47714547 |
Appl. No.: |
13/747566 |
Filed: |
January 23, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61589513 |
Jan 23, 2012 |
|
|
|
Current U.S.
Class: |
428/32.21 ;
427/158 |
Current CPC
Class: |
B05D 3/12 20130101; D21H
21/28 20130101; D21H 19/38 20130101; D21H 11/08 20130101; B05D 1/38
20130101; B05D 2203/22 20130101; D21H 23/22 20130101; B05D 5/06
20130101; D21H 17/66 20130101; B05D 1/02 20130101; D21H 19/10
20130101; D21H 11/14 20130101; D21H 21/30 20130101; D21H 23/56
20130101; D21H 21/14 20130101 |
Class at
Publication: |
428/32.21 ;
427/158 |
International
Class: |
D21H 23/22 20060101
D21H023/22 |
Claims
1. A process comprising the following steps: (a) for a paper
substrate about 10% or less by weight mechanical pulp fibers and
having a first surface and a second surface, treating at least one
of the first and second surfaces at a size press with one of the
following two agents: (1) an optical brightening agent or; (2) a
multivalent metal salt drying agent, to provide a treated paper
substrate having one of the two agents; and (b) before or after the
size press, treating the at least one surface of the paper
substrate of step (a) with the other of the two agents to provide a
printable substrate; (c) wherein the least one surface after steps
(a) and (b) comprises the multivalent metal salt drying agent in an
amount such that the at least one surface has a percent ink
transferred ("IT %") value equal to or less than about 65% and a
black print density value of at least about 1.15; (d) wherein the
optical brightening agent is present after steps (a) and (b) in an
amount sufficient to impart to the at least one surface an ISO
brightness value of at least about 75.
2. The process of claim 1, wherein steps (a) and (b) are carried
out on both the first and second surfaces.
3. The process of claim 2, wherein the first and second surfaces
are treated with the multivalent metal salt drying agent at a
pickup of from about 0.15 to about 3% by weight of the multivalent
metal salt drying agent per ton of paper substrate.
4. The process of claim 3, wherein the first and second surfaces
are treated with the multivalent metal salt drying agent at a
pickup of from about 0.35 to about 1.3% by weight of the
multivalent metal salt drying agent per ton of paper substrate.
5. The process of claim 2, wherein the first and second surfaces
are treated with the optical brightening agent at a pickup 0.25 to
about 3% by weight of the optical brightening agent per ton of
paper substrate.
6. The process of claim 5, wherein the first and second surfaces
are treated with the optical brightening agent at a pickup of from
about 1 to about 2% by weight of the optical brightening agent per
ton of paper substrate.
7. The process of claim 1, wherein the multivalent metal salt
drying agent comprises one or more of: a calcium salt or a
magnesium salt.
8. The process of claim 7, wherein the multivalent metal salt
drying agent comprises a calcium salt.
9. The process of claim 8, wherein the calcium salt comprises
calcium chloride.
10. The process of claim 1, wherein the multivalent metal salt
drying agent is present on the at least one of the first and second
surfaces in an amount sufficient to provide an IT % value equal to
or less than about 50%.
11. The process of claim 10, wherein the multivalent metal salt
drying agent is present on the at least one of the first and second
surfaces in an amount sufficient to provide a IT % value equal to
or less than about 40%.
12. The process of claim 1, wherein the multivalent metal salt
drying agent is present on the at least one of the first and second
surfaces to provide a black print density value of at least about
1.25.
13. The process of claim 12, wherein the multivalent metal salt
drying agent is present on the at least one of the first and second
surfaces to provide a black print density value of at least about
1.45.
14. The article of claim 1, wherein the multivalent metal salt
drying agent present on the at least one of the first and second
surfaces to provide an edge acuity (EA) value of less than about
15.
15. The process of claim 14, wherein the multivalent metal salt
drying agent is present on the at least one of the first and second
surfaces to provide an edge acuity (EA) value of less than about
10.
16. The process of claim 1, wherein the optical brightening agent
is present in an amount sufficient to impart an ISO Brightness
value of at least about 85.
17. The process of claim 16, wherein the optical brightening agent
is present in an amount sufficient to impart an ISO Brightness
value of at least about 90.
18. The process of claim 1, wherein the optical brightening agents
comprises one or more of:
4,4'-bis-(triazinylamino)-stilbene-2,2'-disulfonic acids,
4,4'-bis-(triazol-2-yl)stilbene-2,2'-disulfonic acids,
4,4'-dibenzofuranyl-biphenyls, 4,4'-(diphenyl)-stilbenes,
4,4'-distyryl-biphenyls, 4-phenyl-4'-benzoxazolyl-stilbenes,
stilbenzyl-naphthotriazoles, 4-styryl-stilbenes,
bis-(benzoxazol-2-yl) derivatives, bis-(benzimidazol-2-yl)
derivatives, coumarins, pyrazolines, naphthalimides,
triazinyl-pyrenes, 2-styryl-benzoxazole or -naphthoxazoles, or
benzimidazole-benzofurans or oxanilides.
19. The process of claim 18, wherein the optical brightening agent
comprises one or more stilbene-based sulfonates.
20. The process of claim 19, wherein these one or more
stilbene-based sulfonates comprise derivatives of
4,4'-diaminostilbene-2,2'-disulphonic acid,
4,4-bis(triazine-2-ylamino)stilbene-2,2'-disulphonic acid, disodium
salts of distyrlbiphenyl disulfonic acid, or disodium salts of
4,4'-di-triazinylamino-2,2'-di-sulfostilbene.
21. The process of claim 1, wherein the optical brightening agent
is present on the at least one of the first and second surfaces in
an amount sufficient to impart a CIE Whiteness value of at least
about 115.
22. The process of claim 21, wherein the optical brightening agent
is present on the at least one of the first and second surfaces in
an amount sufficient to impart a CIE Whiteness value of at least
about 125.
23. The process of claim 22, wherein the optical brightening agent
is present on the at least one of the first and second surfaces in
an amount sufficient to impart a CIE Whiteness value of at least
about 145.
24. The process of claim 1, wherein step (b) is carried out before
step (a).
25. The process of claim 1, wherein step (b) is carried out after
step (a).
26. The process of claim 1, wherein step (b) is carried out by
spraying the other of the two agents onto the at least one surface
of the paper substrate of step (a).
27. The process of claim 1, wherein step (a) is carried out by
treating the at least one of the first and second surfaces of the
paper substrate with the optical brightening agent, and wherein
step (b) is carried out by treating the at least one surface of the
paper substrate of step (a) with the multivalent metal salt drying
agent.
28. The process of claim 1, wherein step (a) is carried out by
treating the at least one of the first and second surfaces of the
paper substrate with the multivalent metal salt drying agent, and
wherein step (b) is carried out by treating the at least one
surface of the paper substrate of step (a) with the optical
brightening agent.
29. The process of claim 1, wherein the paper substrate comprises
less than about 5% by weight mechanical pulp fibers.
30. The process of claim 29, wherein the paper substrate comprises
less than about 1% by weight mechanical pulp fibers.
31. A process comprising the following steps: (a) for a paper
substrate comprising greater than about 10% by weight mechanical
pulp fibers and having a first surface and a second surface,
treating at least one of the first and second surfaces at a size
press with one of the following two agents: (1) an optical
brightening agent or; (2) a multivalent metal salt drying agent, to
provide a treated paper substrate having one of the two agents; and
(b) before or after the size press, treating the at least one
surface of the paper substrate of step (a) with the other of the
two agents to provide a printable substrate; (c) wherein the least
one surface after steps (a) and (b) comprises the multivalent metal
salt drying agent in an amount such that the at least one surface
has a percent ink transferred ("IT %") value equal to or less than
about 65% and a black print density value of at least about 1.15;
(d) wherein the optical brightening agent is present after steps
(a) and (b) in an amount sufficient to impart to the at least one
surface an ISO brightness value of at least about 75.
32. The process of claim 31, wherein steps (a) and (b) are carried
out on both the first and second surfaces.
33. The process of claim 32, wherein the first and second surfaces
are treated with the multivalent metal salt drying agent at a
pickup of from about 0.15 to about 3% by weight of the multivalent
metal salt drying agent per ton of paper substrate.
34. The process of claim 33, wherein the first and second surfaces
are treated with the multivalent metal salt drying agent at a
pickup of from about 0.35 to about 1.3% by weight of the
multivalent metal salt drying agent per ton of paper substrate.
35. The process of claim 32, wherein the first and second surfaces
are treated with the optical brightening agent at a pickup 0.25 to
about 3% by weight of the optical brightening agent per ton of
paper substrate.
36. The process of claim 35, wherein the first and second surfaces
are treated with the optical brightening agent at a pickup of from
about 1 to about 2% by weight of the optical brightening agent per
ton of paper substrate.
37. The process of claim 31, wherein the multivalent metal salt
drying agent comprises one or more of: a calcium salt or a
magnesium salt.
38. The process of claim 37, wherein the multivalent metal salt
drying agent comprises a calcium salt.
39. The process of claim 38, wherein the calcium salt comprises
calcium chloride.
40. The process of claim 31, wherein the multivalent metal salt
drying agent is present on the at least one of the first and second
surfaces in an amount sufficient to provide an IT % value equal to
or less than about 50%.
41. The process of claim 40, wherein the multivalent metal salt
drying agent is present on the at least one of the first and second
surfaces in an amount sufficient to provide a IT % value equal to
or less than about 40%.
42. The process of claim 31, wherein the multivalent metal salt
drying agent is present on the at least one of the first and second
surfaces to provide a black print density value of at least about
1.25.
43. The process of claim 42, wherein the multivalent metal salt
drying agent is present on the at least one of the first and second
surfaces to provide a black print density value of at least about
1.45.
44. The article of claim 41, wherein the multivalent metal salt
drying agent present on the at least one of the first and second
surfaces to provide an edge acuity (EA) value of less than about
15.
45. The process of claim 44, wherein the multivalent metal salt
drying agent is present on the at least one of the first and second
surfaces to provide an edge acuity (EA) value of less than about
10.
46. The process of claim 41, wherein the optical brightening agent
is present in an amount sufficient to impart an ISO Brightness
value of at least about 85.
47. The process of claim 46, wherein the optical brightening agent
is present in an amount sufficient to impart an ISO Brightness
value of at least about 90.
48. The process of claim 41, wherein the optical brightening agents
comprises one or more of:
4,4'-bis-(triazinylamino)-stilbene-2,2'-disulfonic acids,
4,4'-bis-(triazol-2-yl)stilbene-2,2'-disulfonic acids,
4,4'-dibenzofuranyl-biphenyls, 4,4'-(diphenyl)-stilbenes,
4,4'-distyryl-biphenyls, 4-phenyl-4'-benzoxazolyl-stilbenes,
stilbenzyl-naphthotriazoles, 4-styryl-stilbenes,
bis-(benzoxazol-2-yl) derivatives, bis-(benzimidazol-2-yl)
derivatives, coumarins, pyrazolines, naphthalimides,
triazinyl-pyrenes, 2-styryl-benzoxazole or -naphthoxazoles, or
benzimidazole-benzofurans or oxanilides.
49. The process of claim 48, wherein the optical brightening agent
comprises one or more stilbene-based sulfonates.
50. The process of claim 49, wherein these one or more
stilbene-based sulfonates comprise derivatives of
4,4'-diaminostilbene-2,2'-disulphonic acid,
4,4-bis(triazine-2-ylamino)stilbene-2,2'-disulphonic acid, disodium
salts of distyrlbiphenyl disulfonic acid, or disodium salts of
4,4'-di-triazinylamino-2,2'-di-sulfostilbene.
51. The process of claim 31, wherein the optical brightening agent
is present on the at least one of the first and second surfaces in
an amount sufficient to impart a CIE Whiteness value of at least
about 100.
52. The process of claim 50, wherein the optical brightening agent
is present on the at least one of the first and second surfaces in
an amount sufficient to impart a CIE Whiteness value of at least
about 105.
53. The process of claim 52, wherein the optical brightening agent
is present on the at least one of the first and second surfaces in
an amount sufficient to impart a CIE Whiteness value of at least
about 115.
54. The process of claim 31, wherein step (b) is carried out before
step (a).
55. The process of claim 31, wherein step (b) is carried out after
step (a).
56. The process of claim 51, wherein step (b) is carried out by
spraying the other of the two agents onto the at least one surface
of the paper substrate of step (a).
57. The process of claim 51, wherein step (a) is carried out by
treating the at least one of the first and second surfaces of the
paper substrate with the optical brightening agent, and wherein
step (b) is carried out by treating the at least one surface of the
paper substrate of step (a) with the multivalent metal salt drying
agent.
58. The process of claim 51, wherein step (a) is carried out by
treating the at least one of the first and second surfaces of the
paper substrate with the multivalent metal salt drying agent, and
wherein step (b) is carried out by treating the at least one
surface of the paper substrate of step (a) with the optical
brightening agent.
59. The process of claim 31, wherein the paper substrate comprises
from about 15 to 100% by weight mechanical pulp fibers.
60. The process of claim 59, wherein the paper substrate comprises
from about 50 to 95% by weight mechanical pulp fibers.
Description
FIELD OF THE INVENTION
[0001] The present invention broadly relates to a process for
providing printable substrates by separately treating one or both
surfaces of a paper substrate with an optical brightening agent
(OBA) (to impart improved brightness) and a multivalent metal salt
drying agent (to impart improved dry time), wherein one or both
surfaces of the paper substrate is treated with one of these two
agents at the size press, and wherein the surface(s) is treated
with the other of these two agents before or after the size
press.
BACKGROUND
[0002] The brightness and whiteness of printable paper may be
improved, for example, by treating the surface of the paper
substrate with optical brightening agents (OBAs). OBAs are
fluorescent materials which increase the brightness (e.g., white
appearance) of paper substrate surfaces by absorbing the invisible
portion of the light spectrum (e.g., from about 340 to about 370
nm) and converting this energy into the longer-wavelength visible
portion of the light spectrum (e.g., from about 400 to about 500
nm). In other words, the OBAs convert invisible ultraviolet light
and re-emits that converted light in the blue to blue-violet light
region through fluorescence.
[0003] In improving the brightness or whiteness of paper
substrates, OBAs often operate by compensating for a yellow tint or
cast which may be present in paper substrates prepared from paper
pulps which have, for example, been bleached to moderate levels.
This yellow tint or cast is caused by the absorption of
short-wavelength light (violet-to-blue) by the paper substrate. By
treating the paper substrates with OBAs, this short-wavelength
light causing the yellow tint or cast may be partially replaced,
thus improving the brightness and whiteness of the paper
substrate.
[0004] The use of OBAs in improving the brightness or whiteness of
paper substrates is not without problems. These OBAs may interact
or react with other chemicals used in papermaking. For example,
many OBAs used in papermaking are anionic. Illustrative of these
anionic OBAs are the stilbene-based sulfonates. By contrast, some
of the chemicals used in papermaking are cationic, or have cationic
moieties. These cationic chemicals used in papermaking may interact
or react with these anionic OBAs such as the stilbene-based
sulfonates. Such interactions or reactions may reduce the ability
of these OBAs to optically brighten and whiten the paper
substrate.
SUMMARY
[0005] According to a first broad aspect of the present invention,
there is provided a process comprising the following steps: [0006]
(a) for a paper substrate comprising about 10% or less by weight
mechanical pulp fibers and having a first surface and a second
surface, treating at least one of the first and second surfaces at
a size press with one of the following two agents: (1) an optical
brightening agent or; (2) a multivalent metal salt drying agent, to
provide a treated paper substrate having one of the two agents; and
[0007] (b) before or after the size press, treating the at least
one surface of the paper substrate of step (a) with the other of
the two agents to provide a printable substrate; [0008] (c) wherein
the least one surface after steps (a) and (b) comprises the
multivalent metal salt drying agent in an amount such that the at
least one surface has a percent ink transferred ("IT %") value
equal to or less than about 65% and a black print density value of
at least about 1.15; [0009] (d) wherein the optical brightening
agent is present after steps (a) and (b) in an amount sufficient to
impart to the at least one surface an ISO brightness value of at
least about 90.
[0010] According to a second broad aspect of the present invention,
there is provided a process comprising the following steps: [0011]
(a) for a paper substrate comprising greater than about 10% by
weight mechanical pulp fibers and having a first surface and a
second surface, treating at least one of the first and second
surfaces at a size press with one of the following two agents: (1)
an optical brightening agent or; (2) a multivalent metal salt
drying agent, to provide a treated paper substrate having one of
the two agents; and [0012] (b) before or after the size press,
treating the at least one surface of the paper substrate of step
(a) with the other of the two agents to provide a printable
substrate; [0013] (c) wherein the least one surface after steps (a)
and (b) comprises the multivalent metal salt drying agent in an
amount such that the at least one surface has a percent ink
transferred ("IT %") value equal to or less than about 65% and a
black print density value of at least about 1.15; [0014] (d)
wherein the optical brightening agent is present after steps (a)
and (b) in an amount sufficient to impart to the at least one
surface an ISO brightness value of at least about 75.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The invention will be described in conjunction with the
accompanying drawings, in which:
[0016] FIG. 1 is a schematic diagram of a system for carrying out
an embodiment of a process for treating one or both surfaces of a
paper substrate by first using a size press station, followed by
using a spray station, wherein one of the multivalent salt metal
drying agent or optical brightening agent is applied by a size
press station, and wherein the other of these agents is applied by
a spray station;
[0017] FIG. 2 is a schematic diagram of a system for carrying out
another embodiment of a process for treating one or both surfaces
of a paper substrate separately with the multivalent salt metal
drying agent and the optical brightening agent, but wherein the
order of treatment is reversed, i.e., by first using spray station
to apply one of the two agents, followed by using a size press
station to apply the other of the two agents;
[0018] FIG. 3 is a graphical plot of the CIE values versus actual
calcium chloride dosage (in lbs per ton of paper substrate) of
eight runs (R-1 through R-8) involving applying separate
compositions comprising either a multivalent metal salt drying
agent or an optical brightening agent (OBA), or applying a
composition comprising a mixture of the multivalent metal salt
drying agent and OBA;
[0019] FIG. 4 is a graphical plot of the ISO values versus actual
calcium chloride dosage (in lbs per ton of paper substrate) of
eight runs (R-1 through R-8) involving applying separate
compositions comprising either a multivalent metal salt drying
agent or an OBA, or applying a composition comprising a mixture of
the multivalent metal salt drying agent and OBA;
[0020] FIG. 5 is a graphical plot of the a* values versus actual
calcium chloride dosage (in lbs per ton of paper substrate) of
eight runs (R-1 through R-8) involving applying separate
compositions comprising either a multivalent metal salt drying
agent or an OBA, or applying a composition comprising a mixture of
the multivalent metal salt drying agent and OBA; and
[0021] FIG. 6 is a graphical plot of the optical density (OD)
values versus actual calcium chloride dosage (in lbs per ton of
paper substrate) of eight runs (R-1 through R-8) involving applying
separate compositions comprising either a multivalent metal salt
drying agent or an OBA, or applying a composition comprising a
mixture of the multivalent metal salt drying agent and OBA.
DETAILED DESCRIPTION
[0022] It is advantageous to define several terms before describing
the invention. It should be appreciated that the following
definitions are used throughout this application.
DEFINITIONS
[0023] Where the definition of terms departs from the commonly used
meaning of the term, applicant intends to utilize the definitions
provided below, unless specifically indicated.
[0024] For the purposes of the present invention, directional terms
such as "outer," "inner," "upper," "lower," "top", "bottom",
"side," "front," "frontal," "forward," "rear," "rearward," "back,"
"trailing," "above," "below," "left," "right," "horizontal,"
"vertical," "upward," "downward," etc. are merely used for
convenience in describing the various embodiments of the present
invention. For example, the embodiments of the present invention
illustrated in FIGS. 1-2, may be oriented in various ways.
[0025] For the purposes of the present invention, the term
"printable substrate" refers to any paper substrate which may be
printed on. Printable substrates may include webs, sheets, strips,
etc., may be in the form of a continuous roll, a discrete sheet,
etc.
[0026] For the purposes of the present invention, the term "paper
substrate" refers to a fibrous web that may be formed, created,
produced, etc., from a mixture, furnish, etc., comprising paper
pulp fibers, internal paper sizing agents, etc., plus any other
optional papermaking additives such as, for example, fillers,
wet-strength agents, optical brightening agents (or fluorescent
whitening agent), etc. The paper substrate may be in the form of a
continuous roll, a discrete sheet, etc.
[0027] For the purposes of the present invention, the term
"groundwood paper substrate" refers to a paper substrate comprising
greater than about 10% by weight mechanical pulp fibers, for
example, from about 15 to 100% by weight mechanical pulp fibers,
such as from about 50 to about 95% by weight mechanical pulp
fibers.
[0028] For the purposes of the present invention, the term "free
paper substrate" refers to a paper substrate comprising about 10%
or less by weight mechanical pulp fibers, for example, less than
about 5% by weight mechanical pulp fibers, such as less than about
1% by weight mechanical pulp fibers.
[0029] For the purposes of the present invention, the term
"mechanical pulp fibers" refers to pulp fibers which have been
subjected to mechanical treatment such as beating, grinding,
shredding, refining, etc., including mechanical pulp subjected to
thermal pretreatment, chemical pretreatment, combination of thermal
and chemical pretreatment, etc. Mechanical pulp fibers may include
one or more of: stone groundwood (SGW) pulp fibers, pressurized
groundwood (PGW) pulp fibers, refined mechanical pulp (RMP) fibers,
thermo-refiner mechanical pulp (TRMP) fibers, pressure-refiner
thermomechanical pulp (TMP) fibers, pressure/pressure
thermomechanical pulp (PPTMP) fibers, chemomechanical pulp (CMP)
fibers, including High Yield Sulfite (HYS) and High Yield Kraft
(HYK) pulp fibers, chemi-refiner mechanical pulp (CRMP) fibers,
chemi-thermo-mechanical pulp (CTMP) fibers, thermo-chemi-mechanical
pulp (TCMP) fibers, thermo-mechanical-chemi pulp (TMCP) fibers,
long fiber chemi-mechanical pulp/chemically treated long fiber
(LFCMP/CTLF) pulp fibers, bleached chemi-thermo mechanical pulp
(BCTMP) fibers, neutral sulfite semi chemical-pulp (NSSC) fibers,
alkaline peroxide mechanical pulp (APMP/AAP) fibers, etc. See G. A.
Smook, Handbook for Pulp and Paper Technologists (2.sup.nd Edition,
1992), pages 38-41, 45 (including Table 4-7), and 46-65, the entire
contents and disclosure of which is herein incorporated by
reference, for a general description of mechanical pulp, mechanical
pulping, and mechanical pulp nomenclature and terminology,
including semichemical pulping.
[0030] For the purposes of the present invention, the term "paper
filler" refers commonly to mineral products (e.g., calcium
carbonate, kaolin clay, etc.) which may be used in paper making to
reduce materials cost per unit mass of the paper, increase opacity,
increase smoothness, etc. These mineral products may be finely
divided, for example, the size range of from about 0.5 to about 5
microns.
[0031] For the purposes of the present invention, the term
"uncoated paper substrate" refers to a paper substrate which has 0
or substantially 0 paper surface loading of a coating composition
present on one or both sides or surfaces of the paper
substrate.
[0032] For the purposes of the present invention, the term
"single-side coated paper substrate" refers to a paper substrate
which has a surface loading of a coating composition present on
one, but not both, sides or surfaces of the paper substrate.
[0033] For the purposes of the present invention, the term
"double-side coated paper substrate" refers to a paper substrate
which has a surface loading of a coating composition present on
both sides or surfaces of the paper substrate.
[0034] For the purposes of the present invention, the term
"calendered paper" refers to a paper substrate which has been
subjected to calendering to, for example, smooth out the material
for enabling printing on the material, to increase the gloss on the
material surface, etc. For example, calendering may involve a
process of using pressure (and optionally temperature and moisture)
for embossing a smooth surface on the still rough material surface.
Calendering may be carried out on a calender which may comprise a
series of calender rolls at the end of, for example, a papermaking
machine (on-line), or separate from the papermaking machine
(off-line). Calendering may include supercalendering, hot-soft
calendering, moisture-gradient calendering, extended nip
calendering, belt calendering, etc. See G. A. Smook, Handbook for
Pulp and Paper Technologists (2.sup.nd Edition, 1992), pages
273-78, the entire contents and disclosure of which is herein
incorporated by reference, for a general description of
calendering, as well as devices for carrying out calendering, that
may be useful herein.
[0035] For the purposes of the present invention, the term "coating
composition" refers to those compositions, which comprise, at
minimum, one or more multivalent metal salt drying agents, or one
or more optical brightening agents (OBAs). These coating
compositions may also include other optional additives, such as,
for example, a calcium carbonate pigment component, plastic
pigments, substrate pigment binders, sizing agents, cationic dye
fixing agents, solvents, diluents, anti-scratch and mar resistance
agents, etc. The coating composition may be formulated as an
aqueous solution, an aqueous slurry, a colloidal suspension, a
liquid mixture, a thixotropic mixture, etc.
[0036] For the purposes of the present invention, the term "solids
basis" refers to the weight percentage of each of the respective
solid materials (e.g., multivalent metal salt drying agent(s);
optical brightener agent(s) (OBAs); calcium carbonate pigment
component; a cationic dye fixing agent; plastic pigment, sizing
agent, etc.) present in the coating composition, coating, etc., in
the absence of any liquids (e.g., water). Unless otherwise
specified, all percentages given herein for the solid materials are
on a solids basis.
[0037] For the purposes of the present invention, the term "solids
content" refers to the percentage of non-volatile, non-liquid
components (by weight) that are present in the composition,
etc.
[0038] For the purposes of the present invention, the term
"substrate pigment" refers to a material (e.g., a finely divided
particulate matter) which may be used or may be intended to be used
to affect optical properties of a printable substrate.
[0039] For the purposes of the present invention, the term "calcium
carbonate" refers various calcium carbonates which may be used as
substrate pigments, such as precipitated calcium carbonate (PCC),
ground calcium carbonate (GCC), modified PCC and/or GCC, etc.
[0040] For the purposes of the present invention, the term
"precipitated calcium carbonate (PCC)" refers to a calcium
carbonate which may be manufactured by a precipitation reaction and
which may used as a substrate pigment. PCC may comprise almost
entirely of the calcite crystal form of CaCO.sub.3. The calcite
crystal may have several different macroscopic shapes depending on
the conditions of production. Precipitated calcium carbonates may
be prepared by the carbonation, with carbon dioxide (CO.sub.2) gas,
of an aqueous slurry of calcium hydroxide ("milk of lime"). The
starting material for obtaining PCC may comprise limestone, but may
also be calcined (i.e., heated to drive off CO.sub.2), thus
producing burnt lime, CaO. Water may added to "slake" the lime,
with the resulting "milk of lime," a suspension of Ca(OH).sub.2,
being then exposed to bubbles of CO.sub.2 gas. Cool temperatures
during addition of the CO.sub.2 tend to produce rhombohedral
(blocky) PCC particles. Warmer temperatures during addition of the
CO.sub.2 tend to produce scalenohedral (rosette-shaped) PCC
particles. In either case, the end the reaction occurs at an
optimum pH where the milk of lime has been effectively converted to
CaCO.sub.3, and before the concentration of CO.sub.2 becomes high
enough to acidify the suspension and cause some of it to
redissolve. In cases where the PCC is not continuously agitated or
stored for many days, it may be necessary to add more than a trace
of such anionic dispersants as polyphosphates. Wet PCC may have a
weak cationic colloidal charge. By contrast, dried PCC may be
similar to most ground CaCO.sub.3 products in having a negative
charge, depending on whether dispersants have been used. The
calcium carbonate may be precipitated from an aqueous solution in
three different crystal forms: the vaterite form which is
thermodynamically unstable, the calcite form which is the most
stable and the most abundant in nature, and the aragonite form
which is metastable under normal ambient conditions of temperature
and pressure, but which may convert to calcite at elevated
temperatures. The aragonite form has an orthorhombic shape that
crystallizes as long, thin needles that may be either aggregated or
unaggregated. The calcite form may exist in several different
shapes of which the most commonly found are the rhombohedral shape
having crystals that may be either aggregated or unaggregated and
the scalenohedral shape having crystals that are generally
unaggregated.
[0041] For the purposes of the present invention, the term
"substrate pigment binder" refers to a binder agent for paper
substrates which may be used to improve the substrate pigment
binding strength of the coating composition, coating, etc.
Substrate pigment binders may be hydrophilic. Suitable substrate
pigment binders may include synthetic or naturally occurring
polymers (or a combination of different polymers), for example, a
polyvinyl alcohol (PVOH), starch binders, proteinaceous adhesives
such as, for example, casein or soy proteins, etc.; polymer latexes
such as styrene butadiene rubber latexes, acrylic polymer latexes,
polyvinyl acetate latexes, styrene acrylic copolymer latexes, etc.,
or a combination thereof.
[0042] For the purposes of the present invention, the term
"substantially free" refers to a coating composition, coating,
etc., having less than about 0.1% of a particular component by
weight of the coating composition, coating, etc.
[0043] For the purposes of the present invention, the term "starch
binder" refers to a binder agent for substrate pigments and/or
paper substrates which comprises starch, a starch derivative, etc.,
or a combination thereof. Suitable starch binders may be derived
from a natural starch, e.g., natural starch obtained from a known
plant source, for example, wheat, maize, potato, tapioca, etc. The
starch binder may be modified (i.e., a modified starch) by one or
more chemical treatments known in the paper starch binder art, for
example, by oxidation to convert some of OH groups to --COOH
groups, etc. In some cases the starch binder may have a small
proportion of acetyl groups. Alternatively, the starch binder may
be chemically treated to render it cationic (i.e., a cationic
starch) or amphoteric (i.e., an amphoteric starch), i.e., with both
cationic and anionic charges. The starch binder may also be a
starch converted to a starch ether, or a hydroxyalkylated starch by
replacing some --OH groups with, for example, --OCH.sub.2CH.sub.2OH
groups, --OCH.sub.2CH.sub.3 groups, --OCH.sub.2CH.sub.2CH.sub.2OH
groups, etc. A further class of chemically treated starch binders
which may be used are known as the starch phosphates.
Alternatively, raw starch may be hydrolyzed by means of a dilute
acid, an enzyme, etc., to produce a starch binder in the form of a
gum of the dextrin type.
[0044] For the purposes of the present invention, the term "metal
salt drying agent" refers to those metal salts which may improve
the dry time of inks deposited or printed on printable substrates
by ink jet printing processes. These metal drying salt agents
comprise one or more multivalent metal drying salts, and may
optionally further comprise one or more monovalent metal drying
salts. The counter anions for these metal salts may include, for
example, chloride, bromide, acetate, bicarbonate, sulfate, sulfite,
nitrate, hydroxide, silicate, chlorohydrate, etc. The metal drying
salt may be provided as an aqueous solution comprising, for
example, from about 1 to about 60% (e.g., from about 10 to about
40%) of the multivalent metal drying salt.
[0045] For the purposes of the present invention, the term
"multivalent metal salt drying agent" refers to those metal drying
salts wherein the cationic moiety has a positive charge of two or
more (e.g., a calcium cation, a magnesium cation, an aluminum
cation, etc.) such as calcium salts, magnesium salts, aluminum
salts, etc., and which are water soluble. Suitable multivalent
metal drying salts (e.g., divalent salts, trivalent salts, etc.)
may include one or more of: calcium chloride, calcium acetate,
calcium hydroxide, calcium nitrate, calcium sulfate, calcium
sulfite, magnesium chloride, magnesium acetate, magnesium nitrate,
magnesium sulfate, magnesium sulfite, aluminum chloride, aluminum
nitrate, aluminum sulfate, aluminum chlorohydrate, sodium aluminum
sulfate, vanadium chloride, etc.
[0046] For the purposes of the present invention, the term
"monovalent metal salt drying agent" refers to those metal drying
salts wherein the cationic moiety is a monovalent cation having a
positive charge of one (e.g., a sodium cation, a potassium cation,
a lithium cation, etc.) such as sodium salts, potassium salts,
lithium salts, etc. Suitable monovalent metal drying salts may
include one or more of: sodium chloride, sodium acetate, sodium
carbonate, sodium bicarbonate, sodium hydroxide, sodium silicates,
sodium sulfate, sodium sulfite, sodium nitrate, sodium bromide,
potassium chloride, potassium acetate, potassium carbonate,
potassium bicarbonate, potassium hydroxide, potassium silicates,
potassium sulfate, potassium sulfite, potassium nitrate, potassium
bromide, lithium chloride, lithium acetate, lithium carbonate,
lithium bicarbonate, lithium hydroxide, lithium silicates, lithium
sulfate, lithium sulfite, lithium nitrate, lithium bromide,
etc.
[0047] For the purposes of the present invention, the term
"cationic dye fixing agent" refers to those cationic compounds
(e.g., nitrogen-containing compounds) or mixtures of such compounds
which may aid in fixing, trapping, etc, inks printed by inkjet
printing processes, and which may provide other properties,
including water fastness. These cationic dye fixing agents may
include compounds, oligomers and polymers which contain one or more
quaternary ammonium functional groups, and may include cationic
water-soluble polymers that are capable of forming a complex with
anionic dyes. Such functional groups may vary widely and may
include substituted and unsubstituted amines, imines, amides,
urethanes, quaternary ammonium groups, dicyandiamides, guanadines,
biguanides, etc. Illustrative of such compounds are polyamines,
polyethyleneimines, polymers or copolymers of diallyldimethyl
ammonium chloride (DADMAC), copolymers of vinyl pyrrolidone (VP)
with quaternized diethylaminoethylmethacrylate (DEAMEMA),
polyamides, polyhexamethylene biguanide (PHMB), cationic
polyurethane latexes, cationic polyvinyl alcohols, polyalkylamines
dicyandiamid copolymers, amine glycidyl addition polymers,
poly[oxyethylene (dimethyliminio) ethylene (dimethyliminio)
ethylene]dichlorides, etc., or combinations thereof. These cationic
dye fixing agents may include low to medium molecular weight
cationic polymers and oligomers having a molecular equal to or less
than 100,000, for example, equal to or less than about 50,000,
e.g., from about 10,000 to about 50,000. Illustrative of such
materials are polyalkylamine dicyandiamide copolymers,
poly[oxyethylene(dimethyliminio ethylene(dimethyliminio
ethylene]dichlorides and polyamines having molecular weights within
the desired range. Cationic dye fixing agents suitable herein may
include low molecular weight cationic polymers such as
polyalkylamine dicyandiamid copolymer,
poly[oxyethylene(dimethyliminio)ethylene(dimethyliminio)ethylene]dichlori-
de, for example, low molecular weight polyalkylamine dicyandiamid
copolymers. See U.S. Pat. No. 6,764,726 (Yang et al.), issued Jul.
20, 2004, the entire disclosure and contents of which is hereby
incorporated by reference.
[0048] For the purposes of the present invention, the term
"opacity" refers to the ability of a paper to hide things such as
print images on subsequent sheets or printed on the back, e.g., to
minimize, prevent, etc., show-through, etc. As used herein, opacity
of the paper substrate may be measured by, for example, in terms of
TAPPI opacity and show-through. TAPPI opacity may be measured by
T425 om-91.
[0049] For the purposes of the present invention, the term "print
quality" refers to those factors, features, characteristics, etc.,
that may influence, affect, control, etc., the appearance, look,
form, etc., of a printed image on the printable substrate. Print
quality of a paper substrate may be measured in terms of, for
example, one or more of: (1) print density; (2) print contrast; (3)
dry times); (4) edge acuity; (5) color gamut; (6) color richness;
(7) print gloss; (8) print mottle; and (9) color-to-color bleed.
For the purposes of the present invention, print quality of the
paper substrate is primarily determined herein by measuring the
print density, dry time, and edge acuity of the paper
substrate.
[0050] For the purposes of the present invention, the term "print
density" refers to the optical density ("OD") measured by using a
reflectance densitometer (X-Rite, Macbeth. Etc.) which measures the
light absorbing property of an image printed on a paper sheet. For
example, the higher the print density, the darker the print image
may appear. Higher print densities also provide a higher contrast,
a sharper image for viewing, etc. Print density is measured herein
in terms of the black print density (i.e., the print density of
images which are black in color). The method for measuring black
print density involves printing a solid block of black color on a
paper sheet, and then measuring the optical density. The printer
used to print the solid block of black color on the paper sheet is
an HP Deskjet 6122, manufactured by Hewlett-Packard, (or its
equivalent) which uses a #45 (HP product number 51645A) black ink
jet cartridge (or its equivalent). The default setting of Plain
Paper type and Fast Normal print quality print mode is used in
printing the solid block of black color on the paper sheet. An
X-Rite model 528 spectrodensitometer with a 6 mm aperture may be
used to measure the optical density of the solid block of black
color printed on the paper sheet to provide black print density
values. The black print density measurement settings used are
Visual color, status T, and absolute density mode. In general,
acceptable black print density ("OD.sub.O") values for black
pigment are at least about 1.15 when using a standard (plain paper,
normal) print mode for the HP desktop ink jet printer and when
using the most common black pigment ink (equivalent to the #45 ink
jet cartridge). Some embodiments of the paper substrates of the
present invention may exhibit black print density (OD.sub.O) values
of at least about 1.25, for example, at least about 1.45. See also
commonly assigned U.S. Pat. Appln. No. 2007/0087134 (Koenig et
al.), published Apr. 19, 2007, the entire disclosure and contents
of which is herein incorporated by reference, which describes how
to carry out this black print density test.
[0051] For the purposes of the present invention, the term "print
contrast" refers to the difference in print density between printed
and unprinted areas.
[0052] For the purposes of the present invention, the term "dry
time" refers to the time it takes for deposited ink to dry on the
surface of a printable substrate. If the deposited ink does not dry
quickly enough, this deposited ink may transfer to other printable
substrate sheets, which is undesirable. The percentage of ink
transferred ("IT %") is recorded as a measure of the dry time. The
higher the amount of the percentage of ink transferred, the slower
(worse) the dry time. Conversely, the lower the amount of the
percentage of ink transferred, faster (better) the dry time. In
general, embodiments of the paper substrates of the present
invention provide a percent ink transferred ("IT %") value equal to
or less than about 65%. In some embodiments of the paper substrates
of the present invention, the IT % value may be equal to or less
than about 50%, for example, equal to or less than about 40% (e.g.,
equal to or less than about 30%.
[0053] For the purposes of the present invention, the term "ink
transfer" refers to a test for determining the dry time of a
printable substrate, for example, printable paper sheets. "Ink
transfer" is defined herein as the amount of optical density
transferred after rolling with a roller, and is expressed as a
percentage of the optical density transferred to the unprinted
portion of the printable substrate (e.g., paper sheet) after
rolling with a roller. The method involves printing solid colored
blocks on paper having a basis weight of 20 lbs/1300 ft..sup.2,
waiting for a fixed amount of time, 5 seconds after printing, and
then folding in half so that the printed portion contacts an
unprinted portion of the paper sheet, and rolling with a 4.5 lb
hand roller as for example roller item number HR-100 from Chem
Instruments, Inc., Mentor, Ohio, USA. The optical density is read
on the transferred (OD.sub.T), the non-transferred (OD.sub.O)
portions of the block, and an un-imaged area (OD.sub.B) by a
reflectance densitometer (X-Rite, Macbeth. Etc.). The percent
transferred ("IT %") is defined as IT
%=[(OD.sub.T-OD.sub.B)/(OD.sub.O-OD.sub.B)].times.100. See also
commonly assigned U.S. Pat. Appln. No. 2007/0087134 (Koenig et
al.), published Apr. 19, 2007, the entire disclosure and contents
of which is herein incorporated by reference, which describes how
to carry out the ink transfer test.
[0054] For the purposes of the present invention, the term "edge
acuity (EA)" refers to the degree of sharpness (or raggedness) of
the edge of a printed image (e.g., a printed line). Edge acuity
(EA) may be measured by an instrument such as the QEA Personal
Image Analysis System (Quality Engineering Associates, Burlington,
Mass.), the QEA ScannerIAS, or the ImageXpert KDY camera-based
system. All of these instruments collect a magnified digital image
of the sample and calculate an EA value by image analysis. The EA
value (also known as "edge raggedness") is defined in ISO method
13660. This method involves printing a solid line 1.27 mm or more
in length, and sampling at a resolution of at least 600 dpi. The
instrument calculates the location of the edge based on the
darkness of each pixel near the line edges. The edge threshold may
be defined as the point of 60% transition from the substrate
reflectance factor (light area, R.sub.max) to the image reflectance
factor (dark area, R.sub.max) using the equation
R.sub.60=R.sub.max-60% (R.sub.max-R.sub.min). The edge raggedness
may then be defined as the standard deviation of the residuals from
a line fitted to the edge threshold of the line, calculated
perpendicular to the fitted line. For embodiments of paper
substrates of the present invention, the EA value may be less than
about 15, for example, less than about 12, such as less than about
10 (e.g., less than about 8). See also commonly assigned U.S. Pat.
Appln. No. 2007/0087134 (Koenig et al.), published Apr. 19, 2007,
the entire disclosure and contents of which is herein incorporated
by reference, which describes how to measure edge acuity (EA)
values.
[0055] For the purposes of the present invention, the term "color
gamut" refers to the total collection of possible colors in any
color reproduction system and may be defined by a complete subset
colors. A higher color gamut value indicates a more vivid color
print quality. Color gamut may be obtained by measuring the CIE L*,
a*, b* of a series of color blocks, including white (unprinted
area), cyan, magenta, yellow, red, green, blue and black, and from
these measured values, calculating a suitable color gamut. The CIE
L* represents the whiteness. The value of L* may range from zero
(representing black) to 100 (representing white or a perfectly
reflecting diffuser). The value of a* represents the degree of
green/red. A positive a* is red, while a negative a* is green. A
positive b* is yellow, while a negative b* is blue. The CIE L*, a*
and b* values may be measured by X-Rite 528 (or similar
spectrophotometer) using a D65 light source and a 10-degree viewing
angle.
[0056] For the purposes of the present invention, the term "color
richness" refers to a more vivid or vibrant color print with high
print density and high color gamut values.
[0057] For the purposes of the present invention, the term "gloss"
refers to the ability of paper to reflect some portion of the
incident light at the mirror angle. Gloss may be based on a
measurement of the quantity of light specularly reflected from the
surface of a paper specimen at a set angle, for example, at 75
degrees, such as in the case of 75 degree gloss (and as measured by
TAPPI test method T 480 om-92).
[0058] For the purposes of the present invention, the term "print
gloss" refers to a gloss measurement made on a printed paper
substrate.
[0059] For the purposes of the present invention, the term "print
mottle" refers to non-uniformity in the print image which may be
due to unevenness in ink lay, non-uniform ink absorption, etc.,
across the printable substrate surface. Print mottle may be
measured using a scanner based mottle tester such as the C3PATX03
Formation and Mottle Test with an Agfa Model DUOSCAN scanner. The
printable substrate (e.g., paper sheet) sample to be tested is
first printed on a test ink jet printer. The test pattern must
include a block of solid black (100%) image. The color block is a
square of about 20-50 mm by 20-50 mm. After 20 minutes of waiting
time, or when the printed image is fully dried, the printed sample
is positioned on the scanner with printed face down. The scanner is
set at a resolution of 500 ppi (pixel per inch). A Verity software
(Verity IA LLC, 2114 Sunrise Drive, Appleton, Wis. 54914) may be
used to analyze the test data from the scanner. An appropriate
dimension for testing based on the color block dimension is set.
Two mottle indices may be measured: Micro Mottle Index and Macro
Mottle Index. The Micro Mottle Index measures density variations
within an area of 0.1 in.sup.2; while the macro mottle index
measures the density variations of the averaged density values of
each square of 0.1 in.sup.2. The lower the mottle index value, the
better the print quality.
[0060] For the purposes of the present invention, the term
"color-to-color bleed" refers to the spreading of one color ink
into another color ink on paper which may reduce the resolution of
the colored text and lines on a colored background. For example
blue and black bars may be printed over a yellow color background.
Green and black bars may be printed over magenta color background,
and red and black bars may be printed over cyan color background.
The smallest distance in microns between two color bars without
bridging (or color intruding more than half way to the neighboring
color bar) is recorded as the color-to-color bleed index. In other
words, the smaller the value of color-to-color bleed, the better
the print quality. Distances which may be tested include 50
microns, 100 microns, 150 microns, 300 microns, etc. In some
embodiments of the present invention, the tested distance may reach
150 microns or less before bridging (bleed) occurs, which may be
considered a "good" color-to-color bleed property.
[0061] For the purposes of the present invention, the term "digital
printing" refers to reproducing, forming, creating, providing,
etc., digital images on a printable substrate, for example, paper.
Digital printing may include laser printing, ink jet printing,
etc.
[0062] For the purposes of the present invention, the term "laser
printing" refers to a digital printing technology, method, device,
etc., that may use a laser beam to create, form produce, etc., a
latent image on, for example, photoconductor drum. The light of
laser beam may later create charge on the drum which may then pick
up toner which carries an opposite charge. This toner may then be
transferred to the paper and the resulting print image created,
formed, produced, etc., fused to the printable substrate through,
for example, a fuser.
[0063] For the purposes of the present invention, the term
"electrophotographic recording process" refers to a process which
records images on a printable substrate, such as paper, by
xerography or electrophotography. In an electrophotographic
process, the image is often formed on of the c by toner particles
which are deposited one surface or side of the printable substrate,
and are then thermally fixed and/or fused to that one surface or
side of the printable substrate, for example, by heating. In
electrophotographic recording, the printable substrate may have two
relatively smooth or flat sides or surfaces, or may have one side
or surface which is textured, uneven or nonsmooth/nonflat, while
the other side or surface is relatively smooth or flat.
[0064] For the purposes of the present invention, the term "ink jet
printing" refers to a digital printing technology, method, device,
etc., that may form images on a printable substrate, such as paper,
by spraying, jetting, etc., tiny droplets of liquid inks onto the
printable substrate through the printer nozzles. The size (e.g.,
smaller size), precise placement, etc., of the ink droplets may be
provide higher quality inkjet prints. Ink jet printing may include
continuous ink jet printing, drop-on-demand ink jet printing,
etc.
[0065] For the purposes of the present invention, the term "liquid"
refers to a non-gaseous fluid composition, compound, material,
etc., which may be readily flowable at the temperature of use
(e.g., room temperature) with little or no tendency to disperse and
with a relatively high compressibility.
[0066] For the purposes of the present invention, the term
"viscosity," with reference to coating compositions, sizing
compositions, etc., refers to Brookfield viscosity. The Brookfield
viscosity may be measured by a Brookfield viscometer at 150.degree.
F., using a #5 spindle at 100 rpm.
[0067] For the purpose of the present invention, the term "printer"
refers to any device which prints an image on a printable
substrate, such as a paper sheet, including laser printers, inkjet
printers, electrophotographic recording devices (e.g., copiers),
scanners, fax machines, etc.
[0068] For the purpose of the present invention, the term "printer
pigment" may refer to either ink (as used by, for example, an
inkjet printer, etc.) or toner (as used by, for example, a laser
printer, electrographic recording device, etc.).
[0069] For the purpose of the present invention, the term "ink"
refers printer pigment as used by ink jet printers. The term ink
may include dye-based inks and/or pigment-based inks Dye-based inks
comprise a dye which may be an organic molecule which is soluble in
the ink medium. Dye-based inks may be classified by their usage,
such as acid dyes, basic dyes, or direct dyes, or by their chemical
structure, such as azo dyes, which are based on the based on an
--N.dbd.N-- azo structure; diazonium dyes, based on diazonium
salts; quinone-imine dyes, which are derivates of quinine, etc.
Pigment-based dyes comprise a pigment, which is a solid colored
particle suspended in the ink medium. The particle may comprise a
colored mineral, a precipitated dye, a precipitated dye which is
attached to a carrier particle, etc Inks are often dispensed,
deposited, sprayed, etc., on a printable medium in the form of
droplets which then dry on the printable medium to form the print
image(s).
[0070] For the purpose of the present invention, the term "toner"
refers printer pigment as used by laser printers. Toner is often
dispensed, deposited, etc., on the printable medium in the form of
particles, with the particles then being fused on the printable
medium to form the image.
[0071] For the purpose of the present invention, the term
"treating," with reference to multivalent metal drying salt agents,
optical brightening agents (OBAs), coating compositions comprising
such agents, etc., may include, for example, adding, depositing,
applying, spraying, coating, daubing, spreading, wiping, dabbing,
dipping, etc., the multivalent metal drying salt agents, optical
brightening agents (OBAs), coating compositions comprising such
agents, etc., to the surface(s) of the paper substrate.
[0072] For the purposes of the present invention, the term
"applicator" refers to a device, equipment, machine, etc., which
may be used to treat, apply, coat, spray, etc., for example,
multivalent metal drying salt agents, optical brightening agents
(OBAs), coating compositions comprising such agents, etc., to one
or more sides or surfaces of a paper substrate. Applicators may
include air-knife coaters, rod coaters, blade coaters, size
presses, sprayers, etc. See G. A. Smook, Handbook for Pulp and
Paper Technologists (2.sup.nd Edition, 1992), pages 289-92, the
entire contents and disclosure of which is herein incorporated by
reference, for a general description of applicators that may be
useful herein. Size presses may include a puddle size press, a
metering size press, etc. See G. A. Smook, Handbook for Pulp and
Paper Technologists (2.sup.nd Edition, 1992), pages 283-85, the
entire contents and disclosure of which is herein incorporated by
reference, for a general description of size presses that may be
useful herein.
[0073] For the purposes of the present invention, the term "flooded
nip size press" refers to a size press having a flooded nip (pond),
also referred to as a "puddle size press." Flooded nip size presses
may include vertical size presses, horizontal size presses,
etc.
[0074] For the purposes of the present invention, the term
"metering size press" refers to a size press that includes a
component for spreading, metering, etc., deposited, applied, etc.,
coating composition or coating on a paper substrate side or
surface. Metering size presses may include a rod metering size
press, a gated roll metering size press, a doctor blade metering
size press, etc.
[0075] For the purposes of the present invention, the term "rod
metering size press" refers to metering size press that uses a rod
to spread, meter, etc., the coating composition or coating on the
paper substrate surface. The rod may be stationary or movable
relative to the paper substrate.
[0076] For the purposes of the present invention, the term "gated
roll metering size press" refers to a metering size press that may
use a gated roll, transfer roll, soft applicator roll, etc. The
gated roll, transfer roll, soft applicator roll, etc., may be
stationery relative to the paper substrate, may rotate relative to
the paper substrate, etc.
[0077] For the purposes of the present invention, the term "doctor
blade metering size press" refers to a metering press which may use
a doctor blade to spread, meter, etc., the coating composition or
coating on the paper substrate surface.
[0078] For the purposes of the present invention, the term "room
temperature" refers to the commonly accepted meaning of room
temperature, i.e., an ambient temperature of 20.degree. to
25.degree. C.
[0079] For the purposes of the present invention, the term "paper
substrate surface coverage" refers to amount of the multivalent
metal drying salt agents, optical brightening agents (OBAs),
coating comprising such agents, etc., present on a given side or
surface of the paper substrate being treated. Paper substrate
surface coverage may be defined in terms of grams of composition
per square meter of paper substrate (hereinafter referred to as
"gsm").
[0080] For the purposes of the present invention, the term "level
of paper sizing" refers to the paper sizing level present in and/or
on the paper substrate, and may comprise internal sizing, surface
sizing, or both internal sizing and surface sizing.
[0081] For the purposes of the present invention, the term
"internal sizing" refers to paper sizing present in the paper
substrate due to internal paper sizing agents which are included,
added, etc., during the papermaking process before a fibrous paper
substrate is formed. Internal paper sizing agents generally resist
penetration of water or other liquids into the paper substrate by
reacting with the paper substrate to make the paper substrate more
hydrophobic. Illustrative internal paper sizing agents may include,
for example, alkyl ketene dimers, alkenyl succinic anhydrides,
etc.
[0082] For the purposes of the present invention, the term "surface
sizing" refers to paper sizing present in the paper substrate due
to surface paper sizing agents which are applied on, added to,
etc., the surface of the formed fibrous paper substrate. Surface
paper sizing agents generally resist penetration of water or other
liquids into the paper substrate by covering the paper substrate
with a more hydrophobic film. Illustrative surface paper sizing
agents may include, for example, starch, modified starch, styrene
maleic anhydride copolymers, styrene acrylates, etc.
[0083] For the purposes of the present invention, the term "optical
brightener agent (OBA)" refers to certain fluorescent materials
which may increase the brightness (e.g., white appearance) of paper
substrate surfaces by absorbing the invisible portion of the light
spectrum (e.g., from about 340 to about 370 nm) and converting this
energy into the longer-wavelength visible portion of the light
spectrum (e.g., from about 400 to about 500 nm). In other words,
the OBA converts invisible ultraviolet light and re-emits that
converted light into blue to blue-violet light region through
fluorescence. OBAs may also be referred to interchangeably as
fluorescent whitening agents (FWAs) or fluorescent brightening
agents (FBAs). The use of OBAs is often for the purpose of
compensating for a yellow tint or cast of paper pulps which have,
for example, been bleached to moderate levels. This yellow tint or
cast is produced by the absorption of short-wavelength light
(violet-to-blue) by the paper substrate. With the use of OBAs, this
short-wavelength light that causes the yellow tint or cast is
partially replaced, thus improving the brightness and whiteness of
the paper substrate. OBAs are desirably optically colorless when
present on the paper substrate surface, and do not absorb light in
the visible part of the spectrum. These OBAs are anionic and may
include one or more of:
4,4'-bis-(triazinylamino)-stilbene-2,2'-disulfonic acids,
4,4'-bis-(triazol-2-yl)stilbene-2,2'-disulfonic acids,
4,4'-dibenzofuranyl-biphenyls, 4,4'-(diphenyl)-stilbenes,
4,4'-distyryl-biphenyls, 4-phenyl-4'-benzoxazolyl-stilbenes,
stilbenzyl-naphthotriazoles, 4-styryl-stilbenes,
bis-(benzoxazol-2-yl) derivatives, bis-(benzimidazol-2-yl)
derivatives, coumarins, pyrazolines, naphthalimides,
triazinyl-pyrenes, 2-styryl-benzoxazole or -naphthoxazoles,
benzimidazole-benzofurans or oxanilides, etc. See, for example,
commonly assigned U.S. Pat. No. 7,381,300 (Skaggs et al.), issued
Jun. 3, 2008; U.S. Pat. No. 7,622,022 (Skaggs et al.), issued Nov.
24, 2009; U.S. Pat. No. 7,972,477 (Skaggs et al.), issued Jul. 5,
2011; U.S. Pat. Appln. No. 20090317549 (Tan et al.), published Dec.
24, 2009; and, U.S. Pat. Appln. No. 20100129553 (Jackson et al.),
published May 27, 2010, the entire contents and disclosures of
which are herein incorporated by reference, which discloses OBAs
which may be suitable in embodiments of the process of the present
invention. In particular, these OBAs may comprise, for example, one
or more stilbene-based sulfonates (e.g., disulfonates,
tetrasulfonates, or hexasulfonates) which may comprise one or two
stilbene residues. Illustrative examples of such anionic
stilbene-based sulfonates may include 1,3,5-triazinyl derivatives
of 4,4'-diaminostilbene-2,2'-disulphonic acid (including salts
thereof), and in particular the bistriazinyl derivatives (e.g.,
4,4-bis(triazine-2-ylamino)stilbene-2,2'-disulphonic acid), the
disodium salt of distyrlbiphenyl disulfonic acid, the disodium salt
of 4,4'-di-triazinylamino-2,2'-di-sulfostilbene, etc. Commercially
available disulfonate, tetrasulfonate and hexasulfonate
stilbene-based OBAs may also be obtained, for example, from BASF
under the trademark TINOPAL.RTM., from Clariant under the trademark
LEUCOPHOR.RTM., from Blankophor under the trademark
BLANKOPHOR.RTM., and from 3V under the trademark
OPTIBLANC.RTM..
[0084] For the purposes of the present invention, the term
"brightness" refers to the diffuse reflectivity of paper, for
example, at a mean wavelength of light of 457 nm As used herein,
brightness of the paper substrate may be measured in terms of ISO
Brightness which measures brightness using, for example, an ELREPHO
Datacolor 450 spectrophotometer, according to test method ISO
2470-1, using a C illuminant with UV included. For embodiments of
ground paper substrates of the present invention, an ISO Brightness
value of at least about 75 is considered an acceptable degree of
brightness. In some embodiments of groundwood paper substrates of
the present invention, the ISO Brightness value may be at least
about 85, for example, at least about 90. For embodiments of ground
paper substrates of the present invention, an ISO Brightness value
of at least about 90 is considered an acceptable degree of
brightness. In some embodiments of free paper substrates of the
present invention, the ISO Brightness value may be at least about
94, for example, at least about 96. (Brightness may also be
measured in terms of TAPPI Brightness, for example, TAPPI Test
Method T452.)
[0085] For the purposes of the present invention, the term
"whiteness" refers to the white impression of paper, normally
favoring a bluish cast or tint. As used herein, whiteness of the
paper substrate may be measured in terms of CIE Whiteness which
measures whiteness using, for example, an ELREPHO Datacolor 450
spectrophotometer, according to test method ISO 11475, using a D65
outdoor illuminant. For embodiments of groundwood paper substrates
of the present invention, a CIE Whiteness value of at least about
100 is considered an acceptable degree of brightness. In some
embodiments of ground paper substrates of the present invention,
the CIE Whiteness value may be at least about 105, for example, at
least about 115. For embodiments of free paper substrates of the
present invention, a CIE Whiteness value of at least about 115 is
considered an acceptable degree of brightness. In some embodiments
of free paper substrates of the present invention, the CIE
Whiteness value may be at least about 125, for example, at least
about 145.
[0086] For the purposes of the present invention, the term
"quenching" refers to the diminishing, decreasing, reducing,
extinguishing, etc., of the fluorescence of OBAs by other cationic
molecules, compounds, etc. Cationic molecules which may cause
quenching of the fluorescence of OBAs include multivalent metal
drying salts, such as calcium chloride.
Description
[0087] Embodiments of the process of the present invention provide
printable substrates which solve the problem of diminished,
decreased, reduced, etc., paper brightening obtained with, for
example, stilbene-based optical brightening agents (OBAs) when
multivalent metal salts, such as calcium chloride, are added with
such OBAs simultaneously, concurrently, etc., for example, at a
size press. Multivalent metal salt drying agents, such as calcium
chloride, may be used as the metal salt drying agent to improve the
ink dry time and print density of paper substrates. But, because
OBAs have an anionic (negative) charge, these anionic molecules are
electrostatically attracted to multivalent cationic (positively
charged) molecules, such as the divalent calcium ion of calcium
chloride. This attraction of, and interaction between, anionic OBAs
and multivalent cationic metal ions, such as divalent cationic
metal ions (e.g., the calcium ions of calcium chloride), may
interfere with the fluorescence of the OBAs. Such interference
often occurs in such a way that the fluorescence of the OBAs may be
partially or completely quenched, and thus the OBAs may lose their
ability to impart an optical brightening effect to the paper
substrate surface. As a result, the optical brightening of the OBA
may be significantly diminished, decreased, etc., by the concurrent
or simultaneous addition with multivalent metal salt drying agents,
such as calcium chloride, including to the point that the OBAs may
impart insufficient optical brightness to the paper substrate
surface.
[0088] Inclusion of these multivalent metal salts to these size
press coating composition may have not only a quenching effect on
the OBAs, but may also increase the "greening" effect (i.e.,
increase in the amount of green tint) imparted to a paper sheet by
such sizing compositions containing comparable amounts of OBAs.
Previously, these quenching and "greening" effects might be
compensated for by adding more OBA(s) and tinting dyes. But
increasing the amount of added OBA(s) may also cause an undesired a
"green over" effect if an excess of OBA(s) is present, thus
necessitating compensation through addition of tinting dyes which
then reduce the achievable brightness/whiteness for the paper
sheet. This "green over" effect is due to the "yellow" color of the
excess OBA(s) optically blending with the blue/violet light
reflected by the OBA(s) (in fluorescing) to thus impart a
"greenish" tint, shade, hue, etc., to the paper substrate
surface.
[0089] Embodiments of the process of the process of the present
invention provide printable substrates having improved brightness
(by using OBAs) in combination with improved dry time (by using
multivalent metal drying salt agents), but without incurring
adverse effects caused by simultaneously or concurrently adding
such agents, such as partial or complete quenching of the OBA(s),
increasing the amount of OBA(s) to the extent of creating "green
over" effects, etc. These benefits may be achieved in embodiments
of the present invention by treating one or both surfaces of a
paper substrate at the size press with either an optical
brightening agent or a multivalent metal salt drying agent, but not
both of these two agents. Instead, before or after the surface(s)
of the paper substrate is treated with one of these two agents, the
surface(s) is treated with the other of these two agents to provide
the printable substrate wherein: (1) the multivalent metal salt
drying agent in an amount such that the at least one surface has a
percent ink transferred ("IT %") value equal to or less than about
65% and a black print density value of at least about 1.15; and (2)
the optical brightening agent is present in an amount sufficient to
impart to the at least one surface an ISO brightness value of at
least about 90 (for "free" paper substrates comprising about 10% or
less by weight mechanical pulp fibers), or an ISO brightness value
of at least about 75 (for "groundwood" paper substrates" comprising
greater than about 10% by weight mechanical pulp fibers).
[0090] By treating the surface(s) of the paper substrate with each
of these two agents at separate and different points (i.e., one
agent added at the size press, the other agent added at a point
before or after the size press), embodiments of the process of the
present invention minimize, reduce, inhibit, avoid, eliminate,
prevent, etc., the undesired interactions between the OBAs and the
multivalent metal salt drying agents. In some embodiments, the OBAs
may be added to the surface(s) of the paper substrate at the size
press, while the multivalent metal drying salt agent(s) are added
to the paper substrate (e.g., by spraying) before or after the size
press. In such embodiments, a higher concentration of multivalent
metal drying salt agent (compared to the OBA) may be used, thus
permitting a lower overall amount of such multivalent metal salt
drying agent(s) to be applied to the surface(s) of the paper
substrate, and thus potentially decreasing the amount of drying
required of the treated paper substrate. In such embodiments,
applying such multivalent metal salt drying agent(s) to the
surface(s) of the paper substrate at, for example, before the size
press may also avoid certain dryer requirements if the OBAs were
applied separately as relatively dilute solutions from the size
press formulation. In addition, by adding multivalent metal salt
drying agent(s) (such as calcium chloride) to the paper substrate
at other than at the size press in such embodiments, the tendency
of such drying agents to make salts with fatty acids present in
starch (which may be present in the sizing composition applied at
the size press) which may precipitate and fall out of solution
(thus potentially causing undesired contamination of the paper
substrate and/or clogging of machines and/or apparatuses
responsible for delivering the calcium chloride, starch, and
optical brightening agent(s) to the paper substrate) may also be
avoided.
[0091] In other embodiments, the multivalent metal drying salt
agent(s) may be added to the surface(s) of the paper substrate at
the size press, while the OBAs are added to the paper substrate
(e.g., by spraying) before or after the size press. In such
embodiments where the OBAs are applied after the size press, the
OBAs would form an outer coating, layer, etc., of the treated
surface(s) of the paper substrate, thus protecting that treated
surface(s) from yellowing. Adding the OBA(s) to the surface(s) of
the paper substrate other than at the size press may also provide
more efficient brightening for the paper substrate.
[0092] The OBAs or multivalent metal salt drying agent(s) may be
applied before or after the size press by various techniques,
methods, etc. For example, in some embodiments, the OBAs or
multivalent metal salt drying agent(s) may be applied before or
after the size press by spraying. In such embodiments, spraying may
be carried out by airless spraying, atomized spraying, high
vacuum/low pressure (HVLP) spraying, air assisted airless spraying,
rotary spraying, etc. In one such embodiment, the calcium chloride
as the multivalent metal salt drying agent may be sprayed onto the
surface(s) of the paper substrate before the size press, with the
OBA(s) being applied at the size press. In another such embodiment,
the calcium chloride may be sprayed onto the surface(s) of the
paper substrate after the size press, with the OBA(s) being applied
at the size press. In yet another such embodiment, the calcium
chloride may be applied at the size press, with the OBA(s) being
sprayed after the size press to provide an outer coating, layer,
etc., which may be more resistant, protective against, etc.,
yellowing of the surface(s).
[0093] When treated with the OBA(s), the OBA pickup on one or both
paper substrate surfaces is in amount sufficient to impart an ISO
Brightness value of at least about 75 (e.g., at least about 85,
such as at least 90). For example, a pickup of from about 0.25 to
about 3 wt % of the OBA(s) (such as the stilbene-based sulfonates)
per ton of paper substrate (e.g., from about 1 to about 2 wt % of
the OBA(s) per ton of paper substrate) on each surface of the paper
substrate is sufficient to impart these ISO Brightness values. In
addition to imparting an ISO Brightness value of at least about 90
(for "free" paper substrates), or at least about 75 (for
"groundwood" paper substrates), these coverages with the OBA(s) may
also impart a CIE Whiteness value to the paper substrate surfaces
of at least about 115 (for "free" paper substrates), or at least
about 100 for "groundwood" paper substrates). When treated with the
multivalent metal salt drying agent(s), the pickup may be from
about 0.15 to about 3% by weight per ton of paper substrate, such
as, from about 0.35 to about 1.3% by weight per ton of paper
substrate.
[0094] One embodiment of a process of the present invention for
treating one or both surfaces of the paper substrate two separate
coating compositions, one comprising the multivalent metal salt
drying agent(s), the other comprising the OBAs (plus any other
optional ingredients, such as starch, other surface sizing agents,
surfactant, latex, coating fillers, defoamers, etc.) is further
illustrated in FIG. 1. Referring to FIG. 1, an embodiment of a
system for carrying out such an embodiment of the process of the
present invention is indicated generally as 100. System 100 may be
used to apply separately apply a coating composition comprising a
multivalent metal salt drying agent(s) and coating composition
comprising an OBA(s) to a paper substrate, indicated generally as
104. Substrate 104 moves in the direction indicated by arrow 106,
and which has a pair of opposed sides or surfaces, indicated,
respectively, as 108 and 112.
[0095] System 100 includes a size press station (which is
illustrated in FIG. 1, for example, as being metering rod size
press), which is indicated generally as 114. Size press station 116
includes a lower first assembly, indicated generally as 116, for
applying the coating composition to surface 108. Assembly 116
includes a first reservoir, indicated generally as 120, provided
with a supply of a first coating composition, indicated generally
as 124. A first take up roll, indicated generally as 128 which may
rotate in a counterclockwise direction, as indicated by curved
arrow 132, picks up an amount of a first coating composition from
supply 124. This amount of first coating composition 124 that is
picked up by rotating roll 128 may then be transferred to a first
applicator roll, indicated generally as 136, which rotates in the
opposite and clockwise direction, as indicated by curved arrow 140.
(The positioning of first take up roll 128 shown in FIG. 1 is
simply illustrative and roll 128 may be positioned in various ways
relative to first applicator roll 136 such that first coating
composition 124 is transferred to the surface of first applicator
roll 136.) The amount of the first coating composition that is
transferred to first applicator roll 136 may be controlled by a
first metering rod 144 which spreads the transferred first coating
composition on the surface of first applicator roll 136, thus
providing relatively uniform and consistent thickness of a first
surface coating, indicated as 148, of first coating composition 124
when applied onto the first surface 108 of substrate 104 by first
applicator roll 136.
[0096] As shown in FIG. 1, size press 114 may also be provided with
an upper second assembly indicated generally as 152, for applying
the first coating composition to surface 112. Assembly 152 includes
a second reservoir, a second supply of the first coating
composition, and a second take up roll (similar to reservoir 120,
supply 124, and take up roll 132) which is indicated generally by
the dashed-line box and arrow 156. As shown in FIG. 1, the amount
of the first coating composition that is transferred from second
supply reservoir/second take-up roll 156 to second applicator roll
160 (which rotates in a clockwise direction, as indicated by curved
arrow 164) may be controlled by a second metering rod 168 which
spreads the transferred first coating composition on the surface of
applicator roll 160, thus providing relatively uniform and
consistent thickness of a second surface coating of the first
coating composition, indicated as 172, when applied onto second
surface 112 of substrate 104 by second applicator roll 164.
[0097] As further shown in FIG. 1, system 100 is also provided with
a spray station, indicated generally as 176 which is positioned
after size press station 116. Spray station 176 comprises a lower
first sprayer 180 and an upper second sprayer 184. First sprayer
180 applies (sprays) a second coating composition onto first
surface coating 148, thus providing a first outer coating 188 of
the second coating composition over surface 108. Second sprayer 184
also applies (sprays) the second coating composition onto second
surface coating 148, thus providing a second outer coating 192 of
the second coating composition over surface 112.
[0098] In system 100, surface coatings 148 and 172 applied by size
press station 114 may be one of the multivalent metal salt drying
agent(s) or the OBA(s), while outer coatings 188 and 192 applied by
spray station 176 may the other of the multivalent metal salt
drying agent(s) or the OBA(s). For example, in one embodiment,
surface coatings 148 and 172 applied by size press station 114 may
comprise the multivalent metal salt drying agent(s), while outer
coatings 188 and 192 applied by spray station 176 may comprise the
OBA(s). Alternatively, in another embodiment, first coatings 148
and 172 applied by size press station 114 may comprise the OBA(s),
while outer coatings 188 and 192 applied by spray station 176 may
comprise the multivalent metal salt drying agent(s).
[0099] Another embodiment of a process of the present invention for
treating one or both surfaces of the paper substrate with the two
separate coating compositions, is illustrated in FIG. 2. Referring
to FIG. 2, an embodiment of a system for carrying out such an
alternative embodiment of the process of the present invention is
indicated generally as 200. System 200 may also be used to apply
separately apply a coating composition comprising a multivalent
metal salt drying agent(s) and coating composition comprising an
OBA(s) to a paper substrate, indicated generally as 204. Substrate
204 moves in the direction indicated by arrow 206, and which has a
pair of opposed sides or surfaces, indicated, respectively, as 208
and 212.
[0100] System 200 also includes a size press station (which is
again illustrated in FIG. 2, for example, as being metering rod
size press), which indicated generally as 214. But unlike system
100, system 200 has a spray station 220 which is positioned before
size press station 216. Like spray station 176 of system 100, spray
station 220 comprises a lower first sprayer 224 and an upper second
sprayer 228. First sprayer 224 applies (sprays) a first coating
composition onto surface 208, thus providing a first surface
coating 232 of the first coating composition on surface 208. Second
sprayer 228 also applies (sprays) the first coating composition
onto the second surface 212, thus providing a second surface
coating 236 of the first coating composition on surface 212.
[0101] Like size press station 114, size press station 214 includes
a lower first assembly, indicated generally as 240, for applying
the coating composition onto first surface coating 232. Assembly
240 includes a first reservoir, indicated generally as 244,
provided with a supply of a second coating composition, indicated
generally as 248. A first take up roll, indicated generally as 252
which may rotate in a counterclockwise direction, as indicated by
curved arrow 256, picks up an amount of a second coating
composition from supply 248. This amount of second coating
composition 248 that is picked up by rotating roll 252 may then be
transferred to a first applicator roll, indicated generally as 260,
which rotates in the opposite and clockwise direction, as indicated
by curved arrow 264. (The positioning of first take up roll 252
shown in FIG. 2 is again simply illustrative and roll 252 may be
positioned in various ways relative to first applicator roll 260
such that the second coating composition is transferred to the
surface of first applicator roll 260.) The amount of second coating
composition 248 that is transferred to first applicator roll 260
may be controlled by first metering rod 268 which spreads the
transferred second coating composition on the surface of applicator
roll 260, thus providing relatively uniform and consistent
thickness of a first outer coating of the second coating
composition, indicated as 272, when applied by applicator roll 260
onto first surface coating 232.
[0102] As shown in FIG. 2, size press 214 may also be provided with
an upper second assembly indicated generally as 276, for applying
the second coating composition onto first coating 232. Assembly 276
includes a second reservoir, a second supply of the second coating
composition, and a second take up roll (similar to reservoir 244,
supply 248, and take up roll 256) which is indicated generally by
the dashed-line box and arrow 280. As shown in FIG. 2, the amount
of the second coating composition that is transferred from second
supply reservoir/second take-up roll 280 to second applicator roll
284 (which rotates in a clockwise direction, as indicated by curved
arrow 288) may be controlled by a second metering rod 292 which
spreads the transferred second coating composition on the surface
of second applicator roll 284, thus providing relatively uniform
and consistent thickness of a second outer coating of the second
coating composition, indicated as 296, when applied by second
applicator roll 284 onto second surface coating 236.
[0103] In system 200, surface coatings 232 and 236 applied by spray
station 220 may be one of the multivalent metal salt drying
agent(s) or the OBA(s), while outer coatings 272 and 296 applied by
size press station 214 may the other of the multivalent metal salt
drying agent(s) or the OBA(s). For example, in one embodiment,
surface coatings 232 and 236 applied by spray station 220 may
comprise the multivalent metal salt drying agent(s), while outer
coatings 272 and 296 applied by size press station 214 may comprise
the OBA(s). Alternatively, in another embodiment, surface coatings
232 and 236 applied by spray station 220 may comprise the OBA(s),
while outer coatings 272 and 296 applied by spray station 214 may
comprise the multivalent metal salt drying agent(s).
EXAMPLES
[0104] Compositions comprising calcium chloride as the multivalent
metal salt drying agent (CaCl.sub.2 Composition), a stilbene-based
hexasulfonate (Leucophor SUS hexasulphonated from Clariant) as the
OBA (OBA Composition), or a mixture of the calcium chloride and the
OBA (Mixed Composition) are prepared.
[0105] Eight runs are carried out (R1 through R8) using a free
paper substrate, i.e., less than about 1% by weight mechanical pulp
fibers. Runs R1 through R3 involve treating the paper substrate
with the Mixed Composition at the size press. Run R4 is the control
run where the paper substrate is treated solely with the OBA
Composition at the size press (i.e., no application of calcium
chloride). For runs R5 through R8, the paper substrate is treated
with the OBA Composition at the size press, and is then sprayed on
one side of the paper substrate with varying levels of the
CaCl.sub.2 Composition.
[0106] The Mixed Compositions used in runs R1 through R3 are
formulated with starch (74.6 wt % total solids basis), water, OBA
(22.4 wt % total solids basis) and varying levels of CaCl.sub.2
(approximately 3.0 wt %, 6.0 wt % and 9.0 wt % total solids basis,
respectively, see Table 1 below for runs R1, R2, and R3). All of
the components of the Mixed Compositions are added together in a
mix tank, and then delivered to the size press.
[0107] For runs R4 through R8, the OBA Composition is formulated
with starch (76.9 wt % total solids basis) and OBA (23.1 wt % total
solids basis), and then delivered to the size press. The CaCl.sub.2
Composition used in runs R5 through R8 is formulated as a dilute
solution of calcium chloride at approximately 5 wt % (solids basis
in the solution) for spray application, and then applied at a range
of liquid flows through a spray nozzle to provide various pickup
coverage amounts up to 8.4 pounds per ton of paper (see R5 through
R8 in Table 1 below) on a moving web of paper substrate.
[0108] For each of runs R1 through R8, the batch temperature for
the Mixed and OBA Compositions is maintained at 160.degree. F.
before delivery to the size press (i.e., a flooded nip size press,
which is illustrative). For runs R5 through R8, the spray solution
is applied (after the size press nip) to one side of the paper
substrate using an atomized spray nozzle with a flowmeter to
monitor and control dosage rates.
[0109] The OBA dosage (OBA Dose), calcium chloride dosage
(CaCl.sub.2 Dose) and the point where calcium chloride is added
(CaCl.sub.2 Addition Point) to the paper substrate for each of runs
R1 through R8 are shown in Table 1 below:
TABLE-US-00001 TABLE 1 OBA CaCl.sub.2 Addition Run Dose.sup.1
CaCl.sub.2 Dose.sup.2 Point R1 30 2.5 Size Press R2 30 5.1 Size
Press R3 30 10 Size Press R4 30 0.0 No Spray R5 30 0.1 Spray R6 30
2.7 Spray R7 30 6.8 Spray R8 30 8.4 Spray .sup.1Lbs. of OBA per ton
of paper substrate .sup.2Lbs. of CaCl.sub.2 per ton of paper
substrate
[0110] As test paper sheets for runs R1 through R8 are completed,
those test sheets are cut from the machine roll and measured using
a color spectrophotometer to gauge impact of various
application/dosing methods on optical parameters and print density,
as recorded in Table 2 below. Dosages of OBA and calcium chloride
applied in each of runs R-1 through R-8, as well as the color
values (L*, a*, and b*), CIE Whiteness (CIE), ISO Brightness (ISO),
and optical density (OD) which are obtained, are shown in Table 2
below:
TABLE-US-00002 TABLE 2 OBA CaCl.sub.2 Run L* a* b* CIE ISO OD
Dosage.sup.1 Dosage.sup.2 R-1 94.84 -0.19 -0.09 118.83 91.67 1.04
30 2.5 R-2 94.93 -0.19 0.06 118.20 91.75 1.27 30 5.1 R-3 94.92
-0.24 0.08 118.54 91.77 1.37 30 10 R-4 94.84 -0.01 0.14 117.28
91.15 0.84 30 0 R-5 94.84 -0.09 0.22 116.41 91.20 0.94 30 0.1 R-6
94.88 -0.11 0.11 117.62 91.53 1.25 30 2.7 R-7 94.92 -0.22 0.03
120.04 92.04 1.41 30 6.8 R-8 94.92 -0.27 -0.01 120.12 92.07 1.42 30
8.4 .sup.1Lbs. of OBA per ton of paper substrate .sup.2Lbs of
calcium chloride per ton of paper substrate
[0111] The CIE, ISO, a*, and OD values from Table 2 above for each
of runs R-1 through R-8 are graphically plotted, as shown in FIGS.
3-6. FIG. 3 is a graphical plot, indicated generally as 300, of the
CIE Whiteness values versus the actual calcium chloride dosage (in
lbs per ton of paper substrate). The CIE Whiteness values for runs
R-1 through R-3 are plotted as curve 304, while the CIE Whiteness
values for runs R-4 through R-8 are plotted as curve 308. Graphical
plot 300 shows that calcium chloride applied by spray separate from
the OBA (i.e., runs R5 through R8) continues to increase visual
appeal of the treated paper substrate (i.e., CIE Whiteness) over
size press applications containing combined OBA and calcium
chloride. This increase in visual appeal is applicable to calcium
chloride dosages above 4 pounds per ton of paper substrate (i.e.,
compare runs R7 and R8 to runs R2 and R3 in FIG. 3).
[0112] FIG. 4 is a graphical plot, indicated generally as 400, of
the ISO values versus the actual calcium chloride dosage (in lbs
per ton of paper substrate). The ISO values for runs R-1 through
R-3 are plotted as curve 404, while the ISO values for runs R-4
through R-8 are plotted as curve 408. Much like CIE Whiteness,
graphical plot 400 shows the visual appeal of the treated paper
substrate is increased by spray application of calcium chloride
separate from the OBA. Graphical plot 400 also shows that ISO
Brightness continues to increase at calcium chloride dosages above
4 pounds per ton of paper substrate with spray application of the
calcium chloride separate from the OBA (compare runs R7 and R8 to
runs R2 and R3 in FIG. 4).
[0113] FIG. 5 is a graphical plot, indicated generally as 500, of
the a* values versus the actual calcium chloride dosage (in lbs per
ton of paper substrate). The a* values for runs R-1 through R-3 are
plotted as curve 504, while the a* values for runs R-4 through R-8
are plotted as curve 508. These a* values (red when positive and
green when negative) represent an uncorrected color measurement of
the treated paper substrate after application of the calcium
chloride. As shown by graphical plot 500, spray application of
calcium chloride separate from the OBA shows a lower tendency for
the treated paper substrate to move towards a greener shade, thus
no longer requiring color correction in the paper manufacturing
process. (If dyes are added for color correction, the treated paper
substrate may darken, thus reducing overall visual appeal.) This
lower tendency to shift to greener shades is reflected in the CIE
Whiteness and ISO Brightness measured values of FIGS. 3 and 4, as
shown in graphical plots 300 and 400, respectively.
[0114] FIG. 6 is a graphical plot, indicated generally as 600, of
the OD values versus the actual calcium chloride dosage (in lbs per
ton of paper substrate). The OD values for R-1 through R-3 are
plotted as curve 604, while the OD values for R-4 through R-8 are
plotted as curve 608. Dashed horizontal line 612 indicates at least
a minimally acceptable OD value (i.e., about 1.15 or greater). The
OD values may be used to illustrate the improvement in print
density performance caused by treatment of the paper substrate with
calcium chloride. At every comparable dosage level, graphical plot
600 shows that the sprayed application of calcium chloride separate
from the OBA provides better print density performance relative to
inclusion of calcium chloride with the OBA (i.e., Mixed
Compositions) at the size press.
[0115] All documents, patents, journal articles and other materials
cited in the present application are hereby incorporated by
reference.
[0116] Although the present invention has been fully described in
conjunction with several embodiments thereof with reference to the
accompanying drawings, it is to be understood that various changes
and modifications may be apparent to those skilled in the art. Such
changes and modifications are to be understood as included within
the scope of the present invention as defined by the appended
claims, unless they depart therefrom.
* * * * *