Paper making and fiber liberation – Processes and products – Non-fiber additive
Reexamination Certificate
2000-03-13
2003-12-30
Mullis, Jeffrey (Department: 1711)
Paper making and fiber liberation
Processes and products
Non-fiber additive
C162S164600, C162S168100, C162S169000, C525S056000, C525S059000, C525S279000, C525S293000, C525S313000, C525S330300
Reexamination Certificate
active
06669815
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a treating agent for a sheet surface and a paper for ink jet printing which is applied with the treating agent.
BACKGROUND ART
Ink jet printing is a non-contact printing method that offers numerous advantages including high-speed printing, printing at low noise levels, ease of performing color printing, or the like, and consequently has been rapidly popularized for use in printers and plotters. Ink jet printing allows printing on ordinary printing paper, coated paper, PPC paper (paper for plain paper copy), medium-quality paper and even plastic film.
As a paper for use in ink jet printing, there is a coated paper for obtaining a high image quality, which has a coating layer containing synthetic silica or the like. In contrast, as low-priced common-use paper, one obtained by penetrate-treating paper with starch or the like by means of a size press is used. Common-use paper has the major problem of the occurrence of so-called feathering when it is printed with an aqueous ink which is used in the ink jet printing.
Since the ink used for the ink jet printing is both aqueous and anionic, a cationic waterproofing agent is applied to the surface of the paper. Although it is effective to coat or penetrate-treat paper with a cationic polymer to improve water resistance, this results in the occurrence of the problem of decreased color density during printing.
Various methods have been proposed to inhibit this decrease in color density, examples of which include a method wherein nonionic resin fine particles are combined with nonionic, anionic or cationic water-soluble polymer and coated (Japanese Patent Laid-Open Publication No. 9-1925), a method wherein emulsion particles are coated which are synthesized by copolymerization of acrylonitrile and acrylic esters to increase printing density (Japanese Patent Laid-Open Publication No. 8-50366), a method wherein cationic emulsion particles of acrylic esters are coated (Japanese Patent Laid-Open Publication No. 9-99632), and a method wherein colloidal silica and a water-soluble polymer are coated for the purpose of improving dye color development and printing density (Japanese Patent Laid-Open Publication No. 9-109544).
However, since all of these methods use water-insoluble fine particles, they bond weakly with the ink dye for ink jet printing, and the water-soluble cationic polymer that is used in combination with them does not demonstrate adequate water resistance.
In addition, the use of a mixture of polymer having vinylalcohol units such as polyvinyl alcohol and a cationic polymer for ink jet printing paper is known. Polyvinyl alcohol has a good film-forming ability, and has the effect of inhibiting decreases in color density. On the other hand, cationic polymers have the effect of increasing water resistance.
However, polyvinyl alcohol and cationic polymer have poor miscibility, and it is difficult to apply their mixture uniformly in the microscopic state. Consequently, these substances have shortcomings that include large decreases in color density, thereby requiring further improvement.
The use of a copolymer comprising a polymer moiety having vinyl alcohol units and a polymer moiety having cationic monomer units for ink jet printing paper as being useful in the present invention has heretofore been unknown.
Moreover, due to the considerable increase in viscosity that occurs when a conventional cationic polymer or the like is mixed into a coating color, it is necessary to dilute with water at the time of application. Thus, the polymer concentration is unable to be increased, and the coated amount of the polymer ends up being low, which had previously presented a problem. A surface treating agent that is able to effectively solve the problems of decreased quality, namely decreased color density, feathering and insufficient water resistance as mentioned above has yet to be developed. In addition, the light resistance of printed ink images or characters is also insufficient.
DISCLOSURE OF THE INVENTION
An object of the present invention is to provide a treating agent for a sheet surface that improves water resistance and light resistance without decreasing color density during printing when printing with an aqueous ink, for example, one used in ink jet printing.
Another object of the present invention is to provide a treating agent for a sheet surface that prevents the problem of feathering that particularly occurs with common-use paper for ink jet printing.
A further object of the present invention is to provide a treating agent for a sheet surface that prevents the occurrence of the considerable increase in viscosity when mixed with coating colors and can be applied in a sufficient polymer concentration.
A still further object of the present invention is to provide a coated paper for ink jet printing that improves water resistance and light resistance without decreasing color density during printing. A still further object of the present invention is to provide a common-use paper for ink jet printing that prevents feathering without decreasing color density during printing, and improves water resistance and light resistance.
As a result of earnest studies to solve the above-mentioned problems, the inventors of the present invention found that miscibility between polyvinyl alcohol and cationic polymers, which had presented a problem in the prior art, is improved by using a copolymer comprising a polymer moiety having vinyl alcohol units and a polymer moiety having cationic groups, especially a graft copolymer containing vinyl alcohol units for either a back bone polymer or branch polymers while the other has cationic groups, and that by treating sheet surface such as paper, offering an excellent printing without decreasing color density as well as better water resistance and light resistance than current commercially available paper, thereby leading to completion of the present invention. Furthermore, the occurrence of feathering can be prevented thereby.
In the preferred embodiments, the copolymer has the polymer moieties which are a back bone polymer and a branch polymer, and is a graft copolymer composed of the back bone polymer and branch polymer, either of which is a polymer having vinyl alcohol units, and the other of which is a polymer having cationic groups.
Furthermore, the present invention is to provide the above described treating agent for a sheet surface, in which the back bone polymer of the graft copolymer is composed of water-soluble polymer having vinyl alcohol units, and the branch polymer is composed of at least one repeating unit selected from the group consisting of a repeating unit represented by the following formula (1), a repeating unit represented by the following formula (2), a repeating unit represented by the following formula (3) and a repeating unit represented by the following formula (4):
(wherein, R
1
and R
2
represent H or CH
3
, R
3
and R
4
represent hydrogen, alkyl groups having 1~4 carbon atoms or benzyl groups, and X
−
represents a counter ion);
(wherein, A represents O or NH, B represents C
2
H
4
, C
3
H
6
or C
3
H
5
OH, R
5
represents H or CH
3
, R
6
and R
7
represent alkyl groups having 1~4 carbon atoms, R
8
represents hydrogen, an alkyl group having 1~4 carbon atoms or a benzyl group, and X
−
represents a counter ion);
(wherein, R
9
represents H or CH
3
, and X
−
represents a counter ion); and
(wherein, R
10
and R
11
represent H or CH
3
, and X
−
represents a counter ion).
In the preferred embodiments, the branch polymer comprises at least one repeating unit selected from the group consisting of the repeating unit represented by the formula (1) and the repeating unit represented by the formula (2). Furthermore, in the preferred embodiments the branch polymer comprises the repeating unit represented by the formula (1) and the repeating unit represented by the formula (3) and/or the repeating unit represented by the formula (4).
In addition, in the preferred embodiments, the graft copolymer can be obtai
Kamada Osamu
Ono Motosuke
Sugiyama Toshiaki
Hymo Corporation
Mullis Jeffrey
Ostrolenk Faber Gerb & Soffen, LLP
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