U.S. patent application number 10/945306 was filed with the patent office on 2006-03-23 for method to reduce back trap offset print mottle.
This patent application is currently assigned to International Paper Company. Invention is credited to Abdu Yohance Bunch, Ronald Earl Hostetler, Svante Roding, Don Voas.
Application Number | 20060060317 10/945306 |
Document ID | / |
Family ID | 35840526 |
Filed Date | 2006-03-23 |
United States Patent
Application |
20060060317 |
Kind Code |
A1 |
Roding; Svante ; et
al. |
March 23, 2006 |
Method to reduce back trap offset print mottle
Abstract
A paper and paperboard material comprising a paper or paperboard
substrate, a basecoat layer on at least one surface of substrate
and topcoat on a surface of the basecoat, said topcoat comprising
one or more pigments dispersed in one or more binders and said
basecoat comprising low density thermoplastic particles dispersed
in one or more binders. The basecoat is compressible which reduces
back trap print mottle in offset printed images.
Inventors: |
Roding; Svante; (Highland
Mills, NY) ; Bunch; Abdu Yohance; (Harriman, NY)
; Voas; Don; (Loveland, OH) ; Hostetler; Ronald
Earl; (Rock Hill, SC) |
Correspondence
Address: |
INTERNATIONAL PAPER COMPANY
6285 TRI-RIDGE BOULEVARD
LOVELAND
OH
45140
US
|
Assignee: |
International Paper Company
Stamford
CT
|
Family ID: |
35840526 |
Appl. No.: |
10/945306 |
Filed: |
September 20, 2004 |
Current U.S.
Class: |
162/135 ;
427/391; 428/32.34; 428/32.35 |
Current CPC
Class: |
D21H 19/82 20130101 |
Class at
Publication: |
162/135 ;
428/032.35; 428/032.34; 427/391 |
International
Class: |
D21H 19/36 20060101
D21H019/36 |
Claims
1. A paper and paperboard material comprising a paper or paperboard
substrate, a basecoat layer on at least one surface of substrate
and topcoat on a surface of the basecoat, said topcoat comprising
one or more pigments dispersed in one or more binders and said
basecoat comprising low density thermoplastic particles dispersed
in one or more binders.
2. The material of claim 1, wherein the low density thermoplastic
particles are hollow particles or binders having a particle size
that is at least about 175 nm.
3. The material of claim 1, wherein the low density thermoplastic
particles are binders having a particle size that at least about
175 nm.
4. The material of claim 2, wherein the low density thermoplastic
particles are hollow polymer plastic pigments.
5. The material of claim 1, wherein the low density thermoplastic
particles are present in an amount from about 3 to about 30% by
weight of the basecoat composition.
6. The material of claim 3, wherein the low density thermoplastic
particles are present in an amount from about 3 to about 20% by
weight of the basecoat composition.
7. The material of claim 6, wherein the low density thermoplastic
particles are present in an amount from about 3 to about 15% by
weight of the basecoat composition.
8. The material of claim 7, wherein the low density thermoplastic
particles are present in an amount from about 4 to about 7% by
weight of the basecoat composition.
9. The material of claim 3, wherein the binder has a particle size
that is at least about 175 nm.
10. The material of claim 1, wherein the binder has a particle size
from about 175 to about 300 nm.
11. The material of claim 1, wherein the binder has a particle size
that is from about 185 nm to about 300 nm.
12. The material of claim 2, wherein the low density thermoplastic
particles are present in an amount from about 3 to about 30% by
weight of the basecoat composition.
13. The material of claim 10, wherein the low density thermoplastic
particles are present in an amount from about 3 to about 20% by
weight of the basecoat composition.
14. The material of claim 11, wherein the low density thermoplastic
particles are present in an amount from about 3 to about 15% by
weight of the basecoat composition.
15. The material of claim 12, wherein the low density thermoplastic
particles are present in an amount from about 4 to about 7% by
weight of the basecoat composition.
16. The material of claim 1, wherein the basecoat further comprises
an inorganic pigment having a rosette structure.
17. The material of claim 12, wherein the low density thermoplastic
particles are present in an amount from about 3 to about 30% by
weight of the basecoat composition, and the inorganic pigment is
present in an amount from about 5 to about 50% by weight of the
basecoat composition.
18. The material of claim 12, wherein the binder has a particle
size that is at least 175 nm.
19. The material of claim 1 having 2.sup.nd cyan scanner mottle
which is about 20% less than the 2.sup.nd cyan scanner mottle of a
similar material having the same characteristics except for the
presence of low density thermoplastic particles in the
basecoat.
20. The material of claim 17 having 2.sup.nd cyan scanner mottle
which is about 40% less than the 2.sup.nd cyan scanner mottle of a
similar material having the same characteristics except for the
presence of low density thermoplastic particles in the
basecoat.
21. The material of claim 18 having 2.sup.nd cyan scanner mottle
which is about 60% less than the 2.sup.nd cyan scanner mottle of a
similar material having the same characteristics except for the
presence of low density thermoplastic particles in the
basecoat.
22. The material of claim 1 having 2.sup.nd Cyan Tobias mottle
which is about 5% less than the 2.sup.nd Cyan Tobias mottle of a
similar material having the same characteristics except for the
presence of low density thermoplastic particles in the
basecoat.
23. The material of claim 20 having 2.sup.nd Cyan Tobias mottle
which is about 10% less than the 2.sup.nd Cyan Tobias mottle of a
similar material having the same characteristics except for the
presence of low density thermoplastic particles in the
basecoat.
24. The material of claim 21 having 2.sup.nd Cyan Tobias mottle
which is about 15% less than the 2.sup.nd Cyan Tobias mottle of a
similar material having the same characteristics except for the
presence of low density thermoplastic particles in the
basecoat.
25. The material of claim 1 having Parker print Surface which is
about 10% less than the Parker Print Surface of a similar material
having the same characteristics except for the presence of low
density thermoplastic particles in the basecoat.
26. The material of claim 23 having Parker print Surface which is
about 20% less than the Parker Print Surface of a similar material
having the same characteristics except for the presence of low
density thermoplastic particles in the basecoat.
27. The material of claim 24 having Parker print Surface which is
about 30% less than the Parker Print Surface of a similar material
having the same characteristics except for the presence of low
density thermoplastic particles in the basecoat.
28. A method comprising: a) applying a basecoat composition to a
paper substrate, wherein the basecoat comprises a binder and low
density thermoplastic particles, and b) applying a topcoat
composition comprising one or more pigments dispersed in one or
more binders over the basecoat.
Description
BACKGROUND OF THE INVENTION
[0001] In offset printing, paper is run through from one to ten or
more printing nips. Typically, the heatset web offset (HSWOS)
process used for weekly national magazines has four process colors
and at least one Pantone, high-light or special color such as the
dark blue color on the cover of "Newsweek" magazine, which makes a
series of five printing units or offset print nips. Higher quality
sheet offset litho printing normally has at least six or more
printing units in series. The offset printing process, especially
in perfecting presses, has the capability of simultaneously
printing both sides of a paper web at speeds as high as 3000 fpm
(ft./min.). The "offset printing process" gets its name from the
fact that "images" are formed on lithography plates then
transferred (offset) to a rubberized printing blanket stretched
around a cylinder. The inked part of the lithography plate that is
also stretched around a cylinder forms the image that gets
transferred to the offset blanket then in turn to the paper. The
non-image areas of the lithographic plate are hydrophilic and are
protected against ink adherence by fountain solution (water, gum
arabic, surfactant, and acid). On perfecting offset presses, the
image is offset from the top lithography plate to the paper by the
offset blanket. To get sufficient pressure for transfer of the ink
from the top offset blanket, an identical unit "perfects" or
contacts the moving paper web from the bottom thus printing both
sides simultaneously. At the successive perfecting offset blanket
nips (unit 2, 3, 4, etc), ink is transferred to the web or
wet-trapped onto the paper either to previous inked image areas or
to non-image areas. This is called wet trap in that non-image areas
of the offset blanket transfer a very thin layer of fountain
solution to the paper along with ink in the image areas. The ink
forming the image on the paper from the previous printing station
(unit) has the possibility to re-split or "back trap" from the
paper to the next offset printing blanket and so on. This
phenomenon is known as back trap mottle (BTM). Back trap mottle is
an undesired result from offset printing because a non-uniform
print image is created. Printers desire to reduce or eliminate back
trap mottle so uniform ink densities result whether they are
"solids", "quarter tones", "half-tone" or "3/4-tones" or any ink
density range in between or transition points within an image.
SUMMARY OF THE INVENTION
[0002] The invention relates to a paper and paperboard material
comprising a paper or paperboard substrate, a basecoat layer on at
least one surface of substrate and topcoat on a surface of the
basecoat, said topcoat comprising one or more pigments dispersed in
one or more binders and said basecoat comprising low density
thermoplastic particles low density thermoplastic particles
dispersed in one or more binders. This invention also relates to a
method of preparing the material of this invention comprising:
applying a basecoat composition comprising low density
thermoplastic particles dispersed in one or more binders to a paper
or paperboard substrate and applying a topcoat composition
comprising one or more pigments dispersed in one or more binders
over the basecoat.
[0003] This invention provides one or more advantages that are
believed to result from inclusion of the low density thermoplastic
particles in the basecoat. These advantages include reduced
2.sup.nd cyan mottle, enhanced sheet gloss and print gloss and/or
enhanced Sheffield and Parker Print smoothness as compared to a
similar material having the same characteristics except for the
presence of low density thermoplastic particles in the
basecoat.
BRIEF DESCRIPTION OF FIGURES
[0004] The above and other aspects and advantages of the invention
will now be further described in conjunction with the accompanying
drawings in which:
[0005] FIG. 1 is a schematic representation of an embodiment of the
paper or paperboard of this invention.
[0006] FIG. 2 is a graph of 2.sup.nd Cyan Tobias mottle versus
basecoat solids for various preferred paper or paperboard materials
of this invention.
[0007] FIG. 3 is a graph of 2.sup.nd Cyan Tobias mottle versus
parts of plastic pigment added to the basecoats for various
preferred paper or paperboard materials of this invention.
[0008] FIG. 4 is a graph of 2.sup.nd Cyan Tobias mottle versus
2.sup.nd Cyan scanner mottle.
DETAILED DESCRIPTION
[0009] As used throughout, ranges are used as a short hand for
describing each and every value that is within the range. Any value
within the range can be selected as the terminus of the range. As
depicted in FIG. 1, one aspect of this invention relates to coated
paper or paperboard material 10. Material 10 comprises a paper or
paperboard substrate 12, basecoat 14 and topcoat 16. Base coat 14
comprises low density thermoplastic particles dispersed in a
polymeric matrix.
[0010] In the preferred embodiments of this invention, the material
exhibits superior 2nd Cyan scanner mottle. Scanner mottle is
determined using the following procedure: Representative samples
are selected from pigment coated paper or paperboard printed under
controlled conditions typical of commercial offset litho production
with the cyan process ink at a reflection density of 1.35.+-.0.05.
A 100 percent solid cyan print reflective image is digitally
scanned and transformed through a neural network model to produce a
print mottle index number between zero (perfectly uniform ink lay
with no mottle) to ten (visually noticeable, objectionable and
likely rejectable because of print mottle, a random non-uniformity
in the visual reflective density or color of the printed area).
Data from this 2.sup.nd Cyan scanner mottle system can be
correlated to subjective visual perception (using the zero-to-ten
guideline) or can be transformed into equivalent mottle values as
measured with a Tobias mottle tester from Tobias Associates using
the following equation: Tobias=Scanner Mottle*8.8+188 that was
determined from the graph in FIG. 4. The data used in FIG. 4 was
obtained by measuring mottle of representative substrates using the
scanner mottle systems and the Tobias mottle test and plotting the
data to provide a means for converting mottle data between these
two systems.
[0011] In these preferred embodiments, the 2.sup.nd cyan scanner
mottle is less than about 6, preferably less than about 5, more
preferably less than about 4 and most preferably from about 2 to
about 3. In these preferred embodiments, the 2.sup.nd cyan scanner
mottle is preferably 20% lower and the 2.sup.nd Cyan Tobias mottle
is preferably 5% lower, the 2.sup.nd cyan scanner mottle is more
preferably 40% lower and the 2.sup.nd Cyan Tobias mottle is more
preferably 10% lower and the 2.sup.nd cyan scanner mottle is most
preferably 60% lower and the 2.sup.nd Cyan Tobias mottle is most
preferably 15% lower than that of a similar material having the
same characteristics except for the presence of the low density
thermoplastic particles in the basecoat.
[0012] Coated material 10 preferably has a smoothness of less than
2 as measured using TAPPI test method for Parker Print Surface: T
555 om-99. In the preferred embodiments of this invention, the
coated paper has Parker Print Surface preferably less than about
1.5. The Parker Print Surface is more preferably less than about
1.3 and most preferably less than about 1.2. In the embodiments of
choice, the Parker Print Surface is more preferably less than about
1. In these preferred embodiments, the Parker Print Surface is
preferably 10% lower, more preferably 20% lower and most preferably
30% lower than the Parker Print Surface of a similar material
having the same characteristics except for the presence of the low
density thermoplastic particles in the basecoat.
[0013] Coated material 10 preferably has a Sheffield smoothness of
less than about 25 as measured by the procedure of TAPPI test
method T5380m-1. In the preferred embodiments of this invention,
the coated paper has Sheffield smoothness preferably less than
about 20. The Sheffield smoothness is more preferably less than
about 15 and most preferably less than about 12. In these preferred
embodiments, the Sheffield smoothness is preferably 10% lower, more
preferably 20% lower and most preferably 30% lower than the
Sheffield smoothness of a similar material having the same
characteristics except for the presence of the low density
thermoplastic particles in the basecoat.
[0014] As one essential component material 10 comprises a paper or
paperboard substrate 12. Any conventional paper or paperboard web
having a wide variety of porosities, basis weights, densities,
calipers and the like can be used to make substrate 12. Such webs
and methods and apparatus for their manufacture are well known in
the art. See for example "Handbook For Pulp & Paper
Technologies", 2.sup.nd Edition, G. A. Smook, Angus Wilde
Publications (1992) and references cited therein. For example, the
paper and paperboard substrate can be made from pulp fibers derived
from hardwood trees, softwood trees, or a combination of hardwood
and softwood trees prepared for use in a papermaking furnish by any
known suitable digestion, refining, and bleaching operations as for
example known mechanical, thermo mechanical, chemical and semi
chemical, etc., pulping and other well known pulping processes. In
certain embodiments, at least a portion of the pulp fibers may be
provided from non-woody herbaceous plants including, but not
limited to, kenaf, hemp, jute, flax, sisal, or abaca although legal
restrictions and other considerations may make the utilization of
hemp and other fiber sources impractical or impossible. Either
bleached or unbleached pulp fiber may be utilized in the process of
this invention. Recycled pulp fibers are also suitable for use.
[0015] The substrate may also include other conventional additives
such as, for example, starch, mineral and polymeric fillers, sizing
agents, retention aids, and strengthening polymers. Among the
fillers that may be used are organic and inorganic pigments such
as, by way of example, minerals such as calcium carbonate, kaolin,
and talc and expanded and expandable microspheres. Other
conventional additives include, but are not restricted to, wet
strength resins, internal sizes, dry strength resins, alum,
fillers, pigments and dyes.
[0016] As another essential component, material 10 comprises a
basecoat 14 on a surface of substrate 12. Basecoat 14 comprises low
density thermoplastic particles dispersed in a polymeric binder. As
used herein, "low density thermoplastic particles" are particles
formed from thermoplastic or elastic polymers having a density of
less than 1.2 Kg/Liter in a dry state including the void air
volume. The density is preferably less than 0.8 Kg/Liter, more
preferably less than 0.6 Kg/Liter and most preferably from about
0.3 Kg/Liter to about 0.6 Kg/Liter. The low density thermoplastic
particles preferably are not expandable and more preferably have a
diameter less than about 3 microns, more preferably less than about
2 micron and most preferably from about 0.6 to about 1.5 microns.
While we do not wish to be bound to any theory, it is believed that
inclusion of the low density thermoplastic particles makes the
basecoat more compressible and enhances the beneficial properties
of the material 10. Improved properties include reduced 2.sup.nd
cyan scanner mottle, enhanced sheet and print gloss and/or enhanced
Sheffield and Parker Print smoothness as compared a similar
material having the same characteristics except for the presences
of the low density thermoplastic particles in the basecoat.
[0017] While we do not wish to be bound by any theory, it is also
believe that the amount of coating thickness and compressibility
(range of compaction) load versus decrease in coating height needed
to reduce back trap offset print mottle is directly proportional to
the Z-direction non-uniformity of the base paper board's formation
at offset printing pressures. For example, offset printing
pressures are typically in the range of about 10 kg/sq cm that has
been standardized as R (rubber) 10 kg/sq cm of Parker Print Surface
roughness (PPS, microns). If these load range is employed, the
compressibility of basecoat at the employed load range should
"float or cushion" the Z-direction hard fiber to fiber cross-over
points to prevent or reduce point to point printing pressure
variations. Where present, these variations lead to further
variations in ink film transfer initially and in subsequent print
units thus unevenly back trapping part of the ink film to
subsequent offset blankets (impression cylinder).
[0018] Low density thermoplastic particles that can be used may
vary widely and include, but are not limited to, hollow polymer
plastic pigments and binders having a particle size that is at
least about 175 nm. Examples of these are ROPAQUE.RTM. HP1055 and
AF1353 from Rohm and Haas and the HS 2000NA and HS 3000NA plastic
pigments from Dow Chemical Company. The amount of low density
thermoplastic particles present in the basecoat may vary widely but
is preferably in an amount less than about 30% by weight of the
basecoat composition. More preferably, they are present in an
amount from about 1 to about 15% by weight of the basecoat
composition most preferably in amount from about 2 to about 10% by
weight of the basecoat composition and in amount from about 3 to
about 7% by weight of the basecoat composition in the embodiments
of choice.
[0019] As another essential component basecoat 14 includes one or
more polymeric binders. Illustrative of useful are those which are
conventionally used in coated papers as for example styrene
butadiene rubber latex, styrene acrylate, polyvinyl alcohol and
copolymers, polyvinyl acetates and copolymers, vinyl acetate
copolymers, carboxylated SBR latex, styrene acrylate copolymers,
styrene/butadiene/acrylonitrile,
styrene/butadiene/acrylate/acrylonitrile polyvinyl pyrrolidone and
copolymers, polyethylene oxide, poly (2-ethyl-2-oxazoline,
polyester resins, gelatins, casein, alginate, cellulose
derivatives, acrylic vinyl polymers, soy protein polymer,
hydroxymethyl cellulose, hydroxypropyl cellulose, starches,
ethoxylated, oxidized and enzyme converted starches, cationic
starches, water soluble gums, mixtures of water soluble and
water-insoluble resins or polymer latexes, and the like may be
used. Preferred polymeric binders are carboxylated SBR latexes,
polyvinyl alcohol, polyvinyl acetate, styrene/acrylonitrile
copolymer, styrene/butadiene copolymer, styrene/acrylate copolymer,
and vinyl acetate polymers and copolymers.
[0020] Binder latex particles having a sufficient particle size
also provide an initial bulking when included with inorganic or
organic bulking pigments. Latex particles in general have a
particle size from about 100 to about 300 nm for paper coating
applications. Latex particles having sufficient size to provide
compressibility generally have a particle size that is at least 175
nm. The size of the latex that provides compressibility is directly
proportional to the average size of the inorganic and organic
pigments used in basecoats. Typically, a source of ground calcium
carbonate (GCC) used in paperboard basecoats is HYDROCARB.RTM. 60
(from OMYA). This ground calcium carbonate is a wet ball milled
product having 60% of its particles less than 2 microns.
Conversely, 40% of the particles are equal to or larger than about
2 microns. Preferably, the latex particle size is at least 175 nm
for basecoats composed mainly of HYDROCARB.RTM. 60 calcium
carbonate or similar products. More preferably, the latex particle
size is at least 185 nm, and even more preferably, the latex
particle size is at least 190 nm.
[0021] In the more preferred embodiments of the invention,
additional pigment or fillers are employed to improve the
properties of the coated paper and paperboard. These additional
pigments may vary widely and include those inorganic pigments
typically used in the coated paper and paperboard such as silica,
clay, calcium sulfate, calcium silicate, activated clay,
diatomaceous earth, magnesium silicate, magnesium oxide, magnesium
carbonate and aluminum hydroxide. To add additional initial coating
bulk, inorganic particles such as precipitated calcium carbonate
having bulky structures such as a rosette crystal can also be
included. In the most preferred embodiments of the invention,
inorganic pigments having a rosette or other bulky structure can be
included in the basecoat to make the basecoat have greater initial
bulk or thickness. The rosette structure provides greater coating
thickness, thus improved coating coverage for a given coat weight.
This allows for the dried coating to more easily move in the
Z-direction when compressed by the hot soft gloss calenders on
coated SBS paperboard machines, and thus to form a level coated
surface with a reduced number of low spots. Preferred inorganic
pigments include, but are not limited to, precipitated calcium
carbonate, mechanically or chemically engineered clays, calcined
clays, and other pigment types that function to lower the average
density of the coating when dry. These pigments do not provide
compressibility to dried basecoats. They synergistically lower
average coating density and, raise average coating thickness at a
given coat weight so compressible materials, such as larger size
binders and hollow plastic spheres, become more efficient in
cushioning the Z-direction non-uniformity of the base paperboard's
formation from creating point to point variations in printing
pressure in the offset printing nip.
[0022] Coat weight of the basecoat can vary widely and any
conventional coat can be used. Basecoats are generally applied to
paper substrates in an amount from about 4 to about 20 gms. The
coat weight of the basecoat is preferably from about 6 to about 18
gms and more preferably from about 7 to about 15 gms. The thickness
of the basecoat can vary widely and any thickness can be used.
Generally, the thickness of the basecoat is from about 1.8 to about
9.0 .mu.m at a minimum, which is figured on the average density and
weight ratio of each component in a coating. The thickness of the
basecoat is preferably from about 2.7 to about 8.1 .mu.m and more
preferably from about 3.2 to about 6.8 .mu.m. When packing factors
to dissimilar shapes are taken into account, the average thickness
when applied to an impervious surface would be significantly
greater than the theoretical values given here. However, because of
the rough nature of paperboard in general and the application and
metering system used to apply and meter basecoats at an average
coat weight of 12 g/m.sup.2, the coating thickness at the rough
high spots in the paper may be as low as 2-3 microns while valleys
between large surface fiber may have coating thickness as great as
10+ microns. Stiff blade metering of the basecoat attempts to
provide a level surface to which a very uniform topcoat is
applied.
[0023] As depicted in FIG. 1, the third essential component of
material 12 is topcoat 16. Topcoat 16 comprises one or more
inorganic pigments dispersed in one or more polymeric binders.
Polymeric binders and inorganic pigments are those typically used
in coatings of coated paper and paperboard. Illustrative of useful
pigments and binders are those used in basecoat 14.
[0024] Coat weight of topcoat 16 can vary widely and any
conventional coat can be used. Topcoat 16 is generally applied to
paper substrates in amount from about 4 to about 20 gms. The coat
weight of the basecoat is preferably from about 6 to about 18 gms
and more preferably from about 7 to about 15 gms. The thickness of
topcoat 16 can vary widely and any thickness can be used.
Generally, the thickness of the basecoat is from about 1.8 to about
9.0 .mu.m at a minimum, which is figured on the average density and
weight ratio of each component in a coating. The thickness of the
basecoat is preferably from about 2.7 to about 8.1 .mu.m and more
preferably from about 3.2 to about 6.8 .mu.m at a minimum, which is
figured on the average density and weight ratio of each component
in a coating. The point at which the void volume is filled by
binder and additives among all pigments is referred to as the
"critical void volume". In the paint industry this point is
referred to as the transition from matte to gloss paints.
[0025] The paper or paperboard of this invention can be prepared
using known conventional techniques. Methods and apparatuses for
forming and applying a coating formulation to a paper substrate are
well known in the paper and paperboard art. See for example, G. A.
Smook referenced above and references cited therein all of which is
hereby incorporated by reference. All such known methods can be
used in the practice of this invention and will not be described in
detail. For example, the mixture of essential pigments, polymeric
or copolymeric binders and optional components can be dissolved or
dispersed in an appropriate liquid medium, preferably water.
[0026] The percent solids of the top and basecoat coating
formulation can vary widely and conventional percent solids are
used. The percent solids of the basecoat coating formulation is
preferably from about 46% to 69% because within range excellent
scanner mottle characteristics are exhibited by the material with
increased drying demands. The percent solids in the basecoat
coating formulation is more preferably from about 57 to 69% and is
most preferably from about 60% to about 68%. The percent solids in
the basecoat coating formulation in the embodiments of choice is
from about 63% to 67%.
[0027] The coating formulation can be applied to the substrate by
any suitable technique, such as cast coating, Blade coating, air
knife coating, rod coating, roll coating, gravure coating, slot-die
coating, spray coating, dip coating, Meyer rod coating, reverse
roll coating, extrusion coating or the like. In addition, the
coating compositions can also be applied at the size press of a
paper machine using rod metering or other metering techniques. In
the preferred embodiments of the invention, the basecoat coating
formulation is applied using blade coaters and the topcoat coating
formulation is applied using a blade coater or air knife coater. In
the most preferred embodiments the basecoat is applied using a
stiff blade coater and the topcoat is applied using a bent blade
coater or an air knife coater.
[0028] The coated paper or paperboard substrate is dried after
treatment with the coating composition. Methods and apparatuses for
drying paper or paperboard webs treated with a coating composition
are well known in the paper and paperboard art. See for example G.
A. Smook referenced above and references cited therein. Any
conventional drying method and apparatus can be used. Consequently,
these methods and apparatuses will not be described herein in any
great detail. Preferably after drying the paper or paperboard web
will have moisture content equal to or less than about 10% by
weight. The amount of moisture in the dried paper or paperboard web
is more preferably from about 5 to about 10% by weight. After
drying the paper or paperboard substrate may be subjected to one or
more post drying steps as for example those described in G. A.
Smook referenced above and references cited therein. For example,
the paper or paperboard web may be calendered to improve the
smoothness and other properties of the paper as for example by
passing the coated paper through a nip formed by a calender. Gloss
calenders (chromed steel against a rubber roll) or hot soft gloss
calenders (chromed steel against a composite polymeric surface) are
used to impart gloss to the top coated paper or paperboard surface.
The amount of heat and pressure needed in these calenders depends
on the speed of the web entering the nip, the roll sizes, roll
composition and hardness, specific load, the topcoat and basecoat
weights, the roughness of the under lying rough paperboard, the
binder strength of the coatings, and the roughness of the pigments
present in the coating. In general, topcoats contain very fine
particle size clays and ground or precipitate calcium carbonate,
binder, rheology aids, and other additives. Typically hot soft
calenders are 1 m and greater in diameter and are heated internally
with very hot heat transfer fluids. The diameter of the heated
steel roll is directly dependent on the width of the paper machine.
In general, a wider paper machine of 400'' as compared to 300'' or
250'' wide machines requires much larger diameter rolls so that the
weight of the roll does not cause sagging of the roll in the
center. Hydraulically, internally loaded, heated rolls that are
crown compensating are used. Surface temperatures typically used
range from 100 to 200.degree. C. The preferable range is
130.degree. C. to 185.degree. C. with nip loads between 20 kN/m and
300 kN/m.
[0029] The coated paper or paperboard of the present invention can
be used for conventional purposes. For example, specific uses of
the paper and paperboard include, but are not limited to use in the
formation of Bristol, folding carton, aseptic paperboard, double
coated free sheet, and any other type of product made from coated
paper or paper board.
[0030] The invention is further described in the following
examples. In the example, all amounts are parts per one hundred
parts of pigment except as expressly indicated otherwise. The
examples are merely illustrative and do not in any way limit the
scope of the invention as described and claimed.
EXAMPLE 1
A. Preparation of Coating Formulations:
[0031] Preformed aqueous slurries of the pigments and low density
thermoplastic particles are added to a high shear mixer. Then
dispersant, binder and viscosity modifier are added to the slurry
under shear to form a coating formulation having the desired
Brookfield viscosity. The viscosity of the basecoat coating
formulation is about 1000 centipoises (cps) spindle 4 at 100
revolutions per minute. The viscosity of the topcoat coating
formulation is about 700 to 800 centipoises (cps) spindle 4 at 100
revolutions per minute. After final mixing, the coatings are ready
for casting.
[0032] Controls were made using the same basecoat and topcoat
formulations, except that there was no hollow pigment in the
basecoat.
[0033] The coating formulations are set forth in the following
Table 1. TABLE-US-00001 TABLE 1 Top- Top- Top- Basecoat 1 Basecoat
2 Basecoat 3 Basecoat 4 Basecoat 5 Basecoat 6 Basecoat 7 coat 1
coat 2 coat 3 Hydrocarb 60 100.0 85.0 60.0 100.0 100.0 100.0 95.0
Ropaque HP-1055 15.0 30.0 5.0 Hydragloss 91 40.0 40.0 40.0
Hydrocarb 90 60.0 60.0 60.0 Capim NP 10.0 Acronal S-866 14.0 14.0
14.0 14.0 15.0 14.5 Acronal S-728 14.0 14.0 14.0 15.0 Dispex N-40
0.2 0.2 0.2 0.4 0.4 0.2 0.4 Sterocol FD 0.3 0.5 1.0 0.3 0.3 0.35
0.5 Acumer 9300 0.09 0.09 0.38 L-229 0.43 0.43 0.09 Calcium Sterate
1.0 1.0 2.0 Solids % 68.5 57.0 46.0 68.5 56.0 68.5 64.8 64.0 63.0
66.2
[0034] The identity and source of the materials listed in Table 1
are set forth in the following Table 2. TABLE-US-00002 TABLE 2
Coating Component Description Manufacturer Hydrocarb 60 Fine Ground
Calcium Carbonate Omya Ropaque HP-1055 Hollow Sphere Plastic
Pigment Rohm and Haas Hydragloss 91 Number 1 Glossing Clay Huber
Hydrocarb 90 Ultrafine Ground Calcium Omya Carbonate Capim NP
Engineered Clay Imerys Dispex N-40 Dispersant Allied Colloids
Acumer 9300 Polyacrylic Dispersant Rohm and Haas Acronal S-866
Styrene Acrylic Acrolonitrile BASF binder Acronal S-728 Styrene
Acrylic binder BASF Sterocoll FD Acrylic Viscosity Modifier BASF
Alcogum L-229 Acrylate Viscosity Modifier ALCO Chemical Sunkote 450
Calcium Stearate Lubricant Omnova
B. Preparation of Coated Paper:
[0035] The paperboard substrate having a basis weight of 255 gsm
was coated using a flooded nip blade coater to first form the
basecoat followed by coating to form the topcoat. A bent blade was
used to coat the topcoat and a stiff blade was used to form the
basecoat. The coat weight of the topcoat was 8 gsm and the coat
weight of the basecoat was 10 gsm. Controls were made using the
control basecoat and topcoat formulations that did not include
hollow pigment in the basecoat. At the line speed of the coater
applying the topcoat, a single hot soft calender nip was used to
impart gloss. The operating temperature of the metal roll surface
was 185.degree. C.; nip load was varied, but sufficient to reach
60% sheet gloss (TAPPI Method, T480, 75.degree. angle meter).
Substrate 1 identified in Table 3 below required 75 kN/m to obtain
a 60% sheet gloss while Substrate 2 identified in Table 3 below
only required 65 kN/m to reach 60% sheet gloss. Substrate 6
required a calendering pressure of 50 kN/m to obtain a 60% sheet
gloss while Substrate 7 required a calendering pressure of 41 kN/m
to reach 60% sheet gloss.
[0036] The combinations of topcoat and base coat of the coated
paperboard substrates are set forth in the following Table 3.
TABLE-US-00003 TABLE 3 Substrate 1 Substrate 2 Substrate 3
Substrate 4 Substrate 5 Substrate 6 Substrate 7 Base Top Base Top
Base Top Base Top Base Top Base Top Base Top Coat 1 Coat 1 Coat 2
Coat 1 Coat 3 Coat 1 Coat 4 Coat 2 Coat 5 Coat 2 Coat 6 Coat 3 Coat
7 Coat 3
C. Testing of the Coated Paper
[0037] The coated substrates identified in Table 3 were evaluated
to determine their scanner mottle using a unit 2 cyan solid print
from a 6-color offset press. The scanner mottle results were
transformed into equivalent mottle values as measured with a Tobias
mottle tester from Tobias Associates using the following equation:
Tobias=Scanner Mottle*8.8+188 that was determined from the graph in
FIG. 4. The data used in FIG. 4 was obtained by measuring mottle of
representative substrates using the scanner mottle test and the
Tobias mottle test and plotting the data to provide a means for
converting mottle data between these two systems. Lower 2nd cyan
scanner and Tobias mottle values indicate a more uniform print. The
results are set forth in FIGS. 2 and 3.
[0038] Substrate 1 and Substrate 2 were tested for mottle on a
mottle tester from Tobias Associates, Inc using a unit 2 cyan solid
print from a 6-color offset press. Substrate 1 had a rating of 246,
and the Substrate 2 had a rating of 208.
EXAMPLE 2
[0039] Using the procedure of Example 1, coating formulations were
prepared. The coating formulations used are set forth in the
following Table 4. TABLE-US-00004 TABLE 4 Properties/Components
Basecoat 8 Basecoat 9 Topcoat 4 Hydrocarb 60 100 95 -- Ropaque
AF-1353 -- 5.0 -- Hydragloss 91 -- -- 40 Hydrocarb 90 -- -- 60
Acronal S-866 14.0 14.0 15.0 Acumer 9300 0.09 0.09 0.38 L-229 0.43
0.4.3 0.09 Calcium Stearate -- -- 2.0 Solids (%) 68.5 64.5 64.0
[0040] Using the procedure of Example 1, Substrate 8 and Substrate
9 coated substrates were prepared. Substrate 8 identified in Table
5 was calendered at 185 C and with sufficient load to achieve 60%
gloss measured at 75 and Substrate 9 was calendered under the same
calendering conditions as Substrate 8. TABLE-US-00005 TABLE 5
Substrate 8 Substrate 9 Basecoat 8 Top coat 4 Basecoat 9 Topcoat
4
[0041] The coated substrates identified in Table 5 were evaluated
to determine their 2 cyan solid print gloss at 60.degree. from a
6-color offset printing press as measured by the procedure of TAPPI
test method T480, sheet gloss at 75.degree. as measured by the
procedure of TAPPI test method T480, sheet gloss Parker Print
Surface as measured by the procedure of TAPPI test method: T555 and
Sheffield smoothness as measured by the procedure of TAPPI test
method T538. The results are set forth in the following Table 6.
TABLE-US-00006 TABLE 6 Property Substrate 8 Substrate 9 Sheffield
Smoothness 20 11 Parker Print Surface 1.76 1.35 Sheet Gloss
(75.degree.) 56 64 2nd Cyan Print Gloss (60.degree.) 38 49
[0042] It should be appreciated that the present invention is not
limited to the specific embodiments described above, but includes
variations, modifications and equivalent embodiments defined by the
following claims.
* * * * *