Paper making and fiber liberation – Processes and products – With coating after drying
Reexamination Certificate
2001-04-04
2003-04-15
Griffin, Steven P. (Department: 1731)
Paper making and fiber liberation
Processes and products
With coating after drying
C162S136000, C162S158000, C162S181100, C428S211100, C428S342000
Reexamination Certificate
active
06547929
ABSTRACT:
The present invention relates to a paper having the improved print quality of a heightened delta gloss and a method of producing the same.
Japanese Laid-Open Patent Application Publication No. 5-230795 discloses a paper coating composition containing pigment and adhesive as major components in which the pigment includes a plastic pigment having a vinyl aromatic monomer and an olefinic monomer as major components, the plastic pigment being present in an amount of 2-10 parts by weight per 100 parts by weight of total pigment, the plastic pigment having an average particle size of 30-100 nm. The coating composition is coated on a paper substrate to produce a matte coated paper having a low probability of regenerating gloss after coating while having excellent smoothness and strength. The paper substrate may be a top quality paper, an intermediate quality paper, paper sheets having a weight of 40-300 g/m
2
or a coated paper obtained by previously applying a coating composition on one or both surfaces, drying the coating and then calendering the coated, dried paper. The inventive coating composition, as shown in the working examples, is prepared as a dispersion in water having a solids content of 60% by weight and is applied at a coating rate of 15 g/m
2
dry weight.
European Published Patent Application No. 0 842 992 A2 discloses a low gloss coating composition, providing a coated paper having a sheet gloss of 50% or less, which is useful for improving the print quality of inks applied to a paper coated therewith, particularly, delta gloss, i.e., the difference in gloss between the substrate coated with the inventive composition and the ink applied to the so-coated substrate. The low gloss coating composition comprises one or more polymer particles and one or more pigments; wherein the polymer particles comprise at least one polymer core phase containing at least one void, at least one polymer shell phase at least partially surrounding the core and at least one channel connecting the void in the core to the exterior of the particle; and wherein the coating composition comprises 1.0 to 50 parts by weight of the polymer particles per 100 parts by weight of the pigment. The coating composition preferably contains water, solvent or combinations thereof. The water or solvent is preferably added in an amount to produce a solids content of 40 to 80 weight percent. The coating composition can be applied to a substrate in an amount of 0.15 to 45 g/m
2
. Suitable substrates include, for example, paper; paper board; paper products used for newspapers, advertisements, posters, books or magazines; and building substrates such as wall paper, wall board or ceiling tile. In the working examples, typical North American freesheet base stock paper sheets, having a weight of about 61 g/m
2
, were coated with the inventive composition having a solids content of between 52 and 58% by weight at a coating rate of 14.8 g/m
2
.
U.S. Pat. No. 5,922,457 and European Published Patent Application No. 0 825 296 A1 both disclose a matte-finished coated paper comprising a paper web provided with a surface coating on at least one side containing polyolefin resin particles, an adhesive and a pigment. The pigment includes porous particles of organic pigment material and calcium carbonate particles. The porous particles of organic pigment material have an oil absorbency of 80 to 400 ml/100 g when measured pursuant to JIS K5101; each calcium carbonate particle has an average particle diameter of 1.0 to 10 microns; and each polyolefin resin particle has an average diameter of 8 to 30 microns. However, the surface coating of the matte-finished coated paper must be finished to satisfy the following three conditions: (i) a degree of gloss in the range of 1-10% (measurement condition: 75°) when measured pursuant to JIS P 8142; (ii) a smoothness in the range of 1-25 seconds when measured pursuant to JIS P8119; and (iii) a surface roughness R
a
in the range of 2.0 to 6.0 microns when measured pursuant to JIS B0601.
U.S. Pat. No. 4,751,111 discloses a method for producing low sheet gloss coated paper wherein the synthetic polymer latex binder that is used to coat the papers is a carboxylated latex which swells substantially during the preparation of the aqueous coating composition and subsequently shrinks during the drying of the coated paper, whereby a microscopic surface roughness is obtained to yield a low gloss coated paper while retaining high ink gloss.
Published International Patent Application No. WO 99/31320 discloses a dull cast-coated paper and a method for manufacturing the same. The coating has a topographical surface profile in which the average peak-to-valley height R
a
is from 0.1 to 0.5 micron, the maximum peak-to-valley height R
t
is from 1.0 to 4.5 microns and the wave height W
t
is less than 5.0 microns. In the process for production of the cast-coated paper, an aqueous coating composition, which contains pigment(s) and binder, is applied to at least one surface of a base paper, the coated surface is brought into contact with the surface of a heated cylinder, the coating is dried in contact with the cylinder and the dried paper is removed from the cylinder surface. The cylinder surface has a topographical surface profile in which the average peak-to-valley height R
a
is from 0.1 to 0.6 micron and the maximum peak-to-valley height R
t
is from 1.0 to 5.0 microns. The aqueous coating composition is applied to the base paper in an amount such that the coating weight after drying is from 10 to 30 g/m
2
.
It has been desired to obtain high print gloss and high print quality on low gloss substrates since such a combination provides an easy-to-read, low glare background combined with high gloss, high quality, eye-catching images and text. However, it has been very difficult to achieve an adequate balance between the two. The difference in gloss between the printed and non-printed areas of a coated substrate, referred to as “delta gloss” (or “snap”), is the most important parameter used to quantitatively assess the print quality of low gloss substrates. The demand for larger delta gloss is high. Other challenges in printing on low gloss substrates are to obtain uniform ink density and ink holdout. The fundamental difficulty for all of the above is probably due to the fact that low gloss substrates tend to be rough. Low gloss coated substrates have a 75° sheet gloss of 50% or less. In the paper industry, the low gloss coated substrates are referred to as silk, matte or dull grades for sheet gloss.
Two major techniques have been utilized to improve the print quality on low gloss coated substrates. One is by blending specialty pigments such as talc or alumina, or specialty binders such as highly carboxylated styrene/butadiene latexes, into the matte coating composition. The other is to use special calendering techniques. The improvement achieved by these techniques has tended to be less than desired.
It has now been found that the delta gloss of coated substrates can be significantly improved by the application of a low solids content, light-weight top coat composition.
In a first aspect of the present invention, there is provided a paper having an improved print quality, comprising:
(i) a paper substrate, said paper substrate having a front and a back, and a surface on at least one of said front and said back of said paper substrate, said surface having a surface roughness of less than 6 microns and a surface gloss of 5 to 80%; and
(ii) a top coat disposed over said surface, said top coat comprising a rheology modifier/binder component and at least one pigment, said rheology modifier/binder component being present in an amount of 5-200 parts by weight for each 100 parts by weight of said at least one pigment, said at least one pigment having an average particle diameter of 200 to 2000 nm, said top coat being a partial monolayer of particles of said at least one pigment or clusters of said particles of said at least one pigment.
In a second aspect of the present invention, there is provided a process of making
Bobsein Barrett Richard
Brown James Tinney
Fu Zhenwen
Windisch Janet Drobits
Griffin Steven P.
Hug Eric
Rohm and Haas Company
Stauss Karl
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