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Publication numberUS20060060317 A1
Publication typeApplication
Application numberUS 10/945,306
Publication dateMar 23, 2006
Filing dateSep 20, 2004
Priority dateSep 20, 2004
Also published asCA2581113A1, CN101048550A, EP1802805A1, WO2006033952A1
Publication number10945306, 945306, US 2006/0060317 A1, US 2006/060317 A1, US 20060060317 A1, US 20060060317A1, US 2006060317 A1, US 2006060317A1, US-A1-20060060317, US-A1-2006060317, US2006/0060317A1, US2006/060317A1, US20060060317 A1, US20060060317A1, US2006060317 A1, US2006060317A1
InventorsSvante Roding, Abdu Bunch, Don Voas, Ronald Hostetler
Original AssigneeInternational Paper Company
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Method to reduce back trap offset print mottle
US 20060060317 A1
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.
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Claims(28)
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 2nd cyan scanner mottle which is about 20% less than the 2nd 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 2nd cyan scanner mottle which is about 40% less than the 2nd 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 2nd cyan scanner mottle which is about 60% less than the 2nd 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 2nd Cyan Tobias mottle which is about 5% less than the 2nd 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 2nd Cyan Tobias mottle which is about 10% less than the 2nd 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 2nd Cyan Tobias mottle which is about 15% less than the 2nd 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

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 “¾-tones” or any ink density range in between or transition points within an image.

SUMMARY OF THE INVENTION

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.

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 2nd 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

The above and other aspects and advantages of the invention will now be further described in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic representation of an embodiment of the paper or paperboard of this invention.

FIG. 2 is a graph of 2nd Cyan Tobias mottle versus basecoat solids for various preferred paper or paperboard materials of this invention.

FIG. 3 is a graph of 2nd Cyan Tobias mottle versus parts of plastic pigment added to the basecoats for various preferred paper or paperboard materials of this invention.

FIG. 4 is a graph of 2nd Cyan Tobias mottle versus 2nd Cyan scanner mottle.

DETAILED DESCRIPTION

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.

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 2nd 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.

In these preferred embodiments, the 2nd 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 2nd cyan scanner mottle is preferably 20% lower and the 2nd Cyan Tobias mottle is preferably 5% lower, the 2nd cyan scanner mottle is more preferably 40% lower and the 2nd Cyan Tobias mottle is more preferably 10% lower and the 2nd cyan scanner mottle is most preferably 60% lower and the 2nd 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.

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.

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.

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”, 2nd 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.

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.

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 2nd 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.

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).

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® 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.

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.

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® 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® 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.

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.

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 μm 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 μm and more preferably from about 3.2 to about 6.8 μm. 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/m2, 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.

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.

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 μm 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 μm and more preferably from about 3.2 to about 6.8 μm 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.

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.

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%.

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.

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° C. The preferable range is 130° C. to 185° C. with nip loads between 20 kN/m and 300 kN/m.

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.

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:

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.

Controls were made using the same basecoat and topcoat formulations, except that there was no hollow pigment in the basecoat.

The coating formulations are set forth in the following Table 1.

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

The identity and source of the materials listed in Table 1 are set forth in the following Table 2.

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:

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° C.; nip load was varied, but sufficient to reach 60% sheet gloss (TAPPI Method, T480, 75° 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.

The combinations of topcoat and base coat of the coated paperboard substrates are set forth in the following Table 3.

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

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.

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

Using the procedure of Example 1, coating formulations were prepared. The coating formulations used are set forth in the following Table 4.

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

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 5
Substrate 8 Substrate 9
Basecoat 8 Top coat 4 Basecoat 9 Topcoat 4

The coated substrates identified in Table 5 were evaluated to determine their 2 cyan solid print gloss at 60° from a 6-color offset printing press as measured by the procedure of TAPPI test method T480, sheet gloss at 75° 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 6
Property Substrate 8 Substrate 9
Sheffield Smoothness 20 11
Parker Print Surface 1.76 1.35
Sheet Gloss (75°) 56 64
2nd Cyan Print Gloss (60°) 38 49

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.

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Classifications
U.S. Classification162/135, 427/391, 428/32.34, 428/32.35
International ClassificationD21H19/36
Cooperative ClassificationD21H19/82
European ClassificationD21H19/82
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