Patent Grant
7625607
This invention relates to printing papers and methods for making the same, and in particular to low glare and high print gloss printing papers and methods for making the same.
There is market demand for papers having comparatively low sheet gloss with high print gloss. Lower sheet gloss provides easy readability of printed text in high glare situations such as those encountered on air planes and with bed side lamps. High print gloss is desirable for effective advertising. In papers with high delta gloss (difference between paper sheet and printed gloss), the printed images appear to jump out of the page attracting more “looks” from the readers thus enhancing the value for the advertisers and publishers.
It is well known that print gloss may be enhanced by improving the smoothness of the sheet. Use of clay pigments and calendering improves sheet smoothness and gloss. However, increases in print gloss typically also result in increases in sheet gloss, with little or no change in delta gloss. Similarly, efforts to reduce sheet gloss, to provide a low glare paper, result in corresponding decreases in print gloss, with little or no change in delta gloss.
Various proposals have been made to provide a paper with low sheet gloss, and high print gloss. See, U.S. Pat. No. 4,751,111 to Lee et al.; U.S. Pat. No. 5,283,129 to Renk et al.; U.S. Pat. No. 5,922,457 to Yanagisawa; and U.S. Pat. No. 6,547,929 to Bobsein, et al, which are hereby incorporated by reference. However, demand exists for low glare papers with increased delta gloss.
The coating formulation and subsequent finishing operations of the invention yield lower paper gloss for easy readability of printed text in high glare situations while maintaining high print gloss for effective advertising. Exceptional delta gloss is achieved.
A most basic embodiment of the product of the invention is a low glare, high print gloss coated paper comprising a substrate, a coating on said substrate, the coating having at least one binder and plural pigments, 50-90 parts per 100 parts dry weigh of the pigments comprising coarse delaminated clay. The surface is mechanically treated to have a Parker Print-Surf roughness no greater than about 2.2, a sheet gloss level no greater than about 30, and an ink tack rate no greater than about 0.04. When 4-color printed the sheet has a print gloss of at least about 65 and a delta gloss of at least about 38.
The coating more preferably comprises in units of dry parts by weight per 100 parts of pigments, 50-90 parts delaminated clay having an average particle size of 8-12 microns, 10-20 parts calcium carbonate having an average particle size of 0.7-1.1 microns, 5-12 parts starch, and 5-12 parts latex.
A method of producing the low glare, high print gloss paper of the invention comprises the steps of providing a paper substrate, coating the substrate with an aqueous coating composition having, as a dry parts by weight per 100 parts of pigment, 50-90 parts coarse delaminated clay pigment having a particle size of 8-12 microns and 10-20 parts calcium carbonate having a particle size of between 0.7 and 1.1 microns, drying the coating; and supercalendering the coated substrate with at least two passes per side with rolls having a surface roughness of 90-130 Ra. The step of supercalendering imparts a Parker Print-Surf roughness of about 1.7-2.2 and a sheet gloss of about 25-30. Four color printing produces a print gloss of 65-70 and a delta gloss of at least 38.
Referring now to the drawings, it is known that standard grades of paper 10 made with a smooth surface 12 provide a uniform specular reflection of light, shown by arrows 14, that results in high sheet gloss as shown in
It has been discovered that low paper gloss and high print gloss are achieved by manufacturing the paper surface with micro roughness and macro smoothness.
In accordance with the present invention, micro roughness and macro smoothness of a paper surface is achieved by providing a coating formulation designed to provide macro smoothness, and subsequent finishing operations that improve macro smoothness and impart micro roughness.
A coating composition of the invention comprises one or more pigments, one or more binders and optional additives. Coarse delaminated clay offers large platy pigment particles to cover the macro roughness of the cellulose fibers. The delaminated clay has an average particle size of 8-12 microns, most preferably about 9.5 micron (measured on Horiba particle size analyzer). A suitable delaminated clay is Kaoroto SP™ manufactured by Thiele Kaolin Corp.
Preferably, the coating composition includes coarse ground calcium carbonate, which helps the rheology of the coating formulation, improves pigment spacing and also reduces the paper gloss due to its coarseness. Coarse precipitated calcium carbonate could be used in place of ground calcium carbonate. The calcium carbonate has an average particle size of 0.7 to 1.1 microns, preferably about 0.9 microns (measured on Horiba particle size analyzer). A suitable source for coarse calcium carbonate is Omyapaque™ form Omya Inc. In place of coarse carbonate, other clay pigments may be used that inhibit gloss development while filling the voids created by coarse delaminated clay for macro smoothness.
Other pigments such as calcined clay, talc, TiO2 and plastic pigments could be used to achieve brightness and opacity targets as needed.
One or more binders are required to bind the pigments to the surface of the substrate. Natural and synthetic binders can be used to impart sufficient surface strength while maintaining desired levels of opacity, brightness and surface smoothness. Suitable binders may include, but are not limited to, starch, protein and latex. Above about 10 parts of starch per 100 parts of pigment should be used the high level of starch can adversely affect print gloss.
Other additives such as lubricants may be added to the composition, but are not strictly required.
The operative ranges, preferred ranges and most preferred quantities of coating composition constituents are shown in the below table. The numeric data is expressed in units of parts by weight per 100 parts pigment.
The coating composition can be applied to a wide variety of substrates. The specific composition of the substrate is not important. However, in papers made with an acidic paper furnish, it is preferably to use no more than 20 parts calcium carbonate. The coating composition may be applied at a wide range of coat weights. Preferably the coat weight is 3 or more pounds per 3,300 square foot ream on conventional paper substrates, and more preferably 4-8 pounds per 3,300 square foot ream.
The coated paper is preferably supercalendered to improve macro smoothness of the sheet and to impart micro roughness. Although supercalendering is preferred, it may be possible to impart micro roughness to the sheet by other means.
Referring to
The rough surface rolls 36 preferably have a surface roughness of 90 to 130 microns Ra. The rolls may be made in any manner known in the art, e.g., by sand blasting or spraying steel rolls with liquid metal to achieve the required roughness. Steel rolls with a tungsten carbide coating have been successfully used.
The temperature of the calender stack can be varied between ambient temperature and 180 F depending on the paper gloss required. For low levels of gloss, ambient temperature is preferred.
Macro smoothness is measured using TAPPI Test Method T 555 “Roughness of paper and paperboard” (Parker Print-Surf method). Paper made in accordance with the invention has a Parker Print-Surf roughness of 1.7-2.2 microns before printing.
Print gloss is affected by the rate at which ink develops its tack. Generally, papers that cause faster ink tack have lower print gloss due to ink split pattern. A slower rate of ink tack allows ink to fill the microscopic hills and valleys on the surface of the paper, level the ink surface, and thereby provide a smooth printed surface with increased print gloss. Ink tack rate can be improved by slowing the rate at which ink solvent is absorbed into the sheet. In the present invention the coating of the invention comprised of coarse delaminated clay in combination with other pigments such as calcium carbonate, creates a tortuous void structure that slows solvent absorption, improves ink hold out, and desirably reduces the ink tack rate. A comparatively high starch content, e.g., about 9 parts starch per 100 parts of pigment, also contributes to slow ink solvent absorption.
Ink tack rate can be quantified in units of force over time by known test methods and apparatus, e.g., Prufbau Deltack laboratory equipment. Papers made in accordance with the invention have a tack rate in the range of 0.02-0.04 N/sec. using a common printing ink (Flint Ink FXK 268, Aeroweb Process Black) and Prufbau Deltack equipment. This rate is exceptionally slow for a low gloss paper and thus provides excellent print gloss.
Papers made in accordance with the invention have sheet gloss in the range of 25-30, print gloss of 65-70, and delta gloss equal to or more than 38. As used herein, gloss levels are determined using TAPPI Test Method T 480. AF&PA categorizes the grades of gloss as:
A low glossing coating formulation was made, coated to a paper substrate, and subsequently supercalendered using specially treated tungsten carbide rolls. The coating formulation comprise of the following ingredients:
The coating was applied using short dwell type applicator at a coat weight of 4 pounds per side. After application, the coated samples were finished using a calender stack consisting of tungsten carbide coated rolls at surface roughness of 90 to 130 Ra. The paper is finished through multiple nips as shown in
Samples of the resulting paper were printed on a conventional offset printing press and tested for gloss. Samples of a standard gloss paper were also tested for comparative purposes. The results were as follows:
Comparative laboratory tests were conducted on a standard base paper coated with a preferred coating composition of the invention (sample 1255) and four variations from the preferred coating composition. All test samples were subject to the same laboratory calendering to simulate rough roll calendering as described above. The test data is set forth in table below shows improved delta gloss for the preferred composition (sample 1255) with a pigment comprised of 80 parts of coarse delaminated clay with a particle size of 8.6 microns and 20 parts coarse calcium carbonate.
While specific embodiments and examples of the products and methods of invention have been shown and described, it will be appreciated by those skilled in the art that changes and modifications may be made thereto without departing from the invention in its broader aspects and as set forth in the following claims.
This application claims the benefits of U.S. Provisional Application No. 60/489,161, filed Jul. 22, 2003.
| Number | Name | Date | Kind |
|---|---|---|---|
| 4241142 | Kaliski et al. | Dec 1980 | A |
| 4751111 | Lee et al. | Jun 1988 | A |
| 5283129 | Renk et al. | Feb 1994 | A |
| 5302437 | Idei et al. | Apr 1994 | A |
| 5922457 | Yanagisawa et al. | Jul 1999 | A |
| 6254725 | Lau et al. | Jul 2001 | B1 |
| 6547929 | Bobsein et al. | Apr 2003 | B2 |
| 6613419 | Ohbayashi et al. | Sep 2003 | B2 |
| 6696697 | Enomoto | Feb 2004 | B2 |
| 6808258 | Kaga et al. | Oct 2004 | B2 |
| 6983694 | Vermeersch et al. | Jan 2006 | B2 |
| 20020014318 | Bobsein et al. | Feb 2002 | A1 |
| 20020096277 | Lau et al. | Jul 2002 | A1 |
| 20030059546 | Johnson | Mar 2003 | A1 |
| 20030178165 | Bobsein et al. | Sep 2003 | A1 |
| 20040146726 | Heckes et al. | Jul 2004 | A1 |
| 20040208999 | Wang et al. | Oct 2004 | A1 |
| 20050191441 | Yamamoto et al. | Sep 2005 | A1 |
| Number | Date | Country |
|---|---|---|
| 0842992 | May 2003 | EP |
| 60239596 | Nov 1985 | JP |
| 4119192 | Apr 1992 | JP |
| 07119086 | Sep 1993 | JP |
| 5279984 | Oct 1993 | JP |
| WO 02072359 | Sep 2002 | WO |
| 02078978 | Oct 2002 | WO |
| 03000993 | Jan 2003 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 60489161 | Jul 2003 | US |
