Stock material or miscellaneous articles – Structurally defined web or sheet – Discontinuous or differential coating – impregnation or bond
Reexamination Certificate
1998-08-21
2002-10-15
Hess, Bruce H. (Department: 1774)
Stock material or miscellaneous articles
Structurally defined web or sheet
Discontinuous or differential coating, impregnation or bond
C428S500000
Reexamination Certificate
active
06465078
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a recording sheet and a method for its manufacture and more particularly to recording sheet which is excellent in ink absorption and water-resistance and, hence, of use in an ink jet recording system and a method for its manufacture.
BACKGROUND ART
The ink jet recording system is rapidly prevailing these days, because the system is well adaptable to full-color image reproduction, less noisy, and superior in the quality of prints. From the standpoint of safety and recordability, water-based inks are mostly employed for ink jet recording in which droplets of an ink are ejected from a nozzle against a recording sheet for image recording. Therefore, the recording sheet is required to absorb the ink quickly. Thus, when a recording sheet of low ink absorption is used, the ink remains long on the surface of the recording sheet after completion of recording so that the record is easily smeared on contact with the equipment, with the operator, or with recorded sheets piled on one another. Moreover, in the high-density image area, the ink supplied in a large quantity is not well absorbed but flows out to cause a blurred image.
Japanese Patent Application Laid-open No.36692/1982 (JP-A-57-36692) discloses an ink jet recording sheet coated with a basic latex polymer for improved water resistance and better image resolution. It is mentioned in this literature that a water-soluble polymer and a pigment, among others, can be incorporated. Japanese Patent Application Laid-open No. 115780/1988 (JP-A-63-115780) discloses an ink jet recording sheet comprising a support and a coating layer composed of a quaternary ammonium salt-containing polymer and teaches the concomitant use of synthetic silica and, as a binder, polyvinyl alcohol or the like. Japanese Patent Application Laid-open No. 61113/1995 (JP-A-7-61113) discloses an ink jet recording medium having an ink receiving layer composed of a polyvinylacetal resin and a cationic compound. Japanese Patent Application Laid-open No. 227114/1994 (JP-A-6-227114) discloses an ink jet recording sheet having an ink receiving layer composed of a pigment, such as microfine silica powder and an ampho-ion or zwitterion latex.
In these recording sheets, ink fixation and water resistance have been improved in certain degrees. However, a conflicting relation holds between ink fixation/water resistance and ink absorption. Namely, any improvement in water resistance is inevitably accompanied by a decrease in ink absorption. Thus, high water resistance and high ink absorption can hardly be reconciled at the same time.
Japanese Patent Application Laid-open No. 174484/1989 (JP-A-1-174484) discloses an ink jet recording sheet comprising a substrate sheet and, as disposed thereon, a coating layer comprising a pigment and a copolymer of a fatty acid vinyl ester, e.g. vinyl acetate, with a cationic monomer. This literature also teaches that the cationic copolymer may be a copolymer containing a nonionic monomer unit or a polyvinyl alcohol graft copolymer, and may further contain a water-soluble polymer binder. Japanese Patent Application Laid-open No. 83178/1987 (JP-A-62-83178) proposes an ink jet recording sheet having a coating layer comprising finely divided silicic acid and a cationic polymer emulsion. This literature further mentions that it is preferable to use a self-crosslinkable acrylic emulsion having a glass transition temperature of not higher than 0° C. as an adhesive.
These recording sheets feature improved water resistance. However, the attained water resistance is not high enough so that when the sheet comes into contact with waterdrops, for instance, the character or picture image bleeds out and, in extreme cases, disappears locally to drastically reduce the quality of the record. Thus, it is difficult to improve water resistance and ink absorption in sufficient measures while insuring an improved quality of the print at the same time.
It is, therefore, an object of the present invention to provide a recording sheet greatly improved in both water resistance and ink absorption and a method of producing the recording sheet.
It is another object of the invention to provide a recording sheet by which the two conflicting characteristics of water resistance and ink absorption are reconciled with each other and a method of producing the same sheet.
DISCLOSURE OF THE INVENTION
The inventors of the present invention did much research for accomplishing the above objects and discovered that the combined use of a cationic polymer having at least crosslinking or crosslinkable groups and a hydrophilic polymer (macromolecular compound) results in improvements in water resistance and ink absorption and that the combined use of a cationic polymer and a hydrophilic polymer (macromolecular compound) which are mutually reactive leads to still greater improvements in both water resistance and ink absorption. The present invention has been developed on the basis of the above findings.
The recording sheet according to the present invention, therefore, comprises a substrate (support sheet) and, as disposed on at least one side thereof, an ink absorbing layer made of a cationic polymer having crosslinking or crosslinkable groups and a hydrophilic polymer (macromolecular compound). In this recording sheet, the cationic polymer may comprise an acrylic polymer emulsion. The cationic polymer can comprise (1) a copolymer of a cationic monomer and a crosslinking monomer or (2) a copolymer of a cationic monomer, a crosslinking monomer, and a hydrophilic monomer. The crosslinking monomer may have hydrolyzable condensing groups (hydrolytically condensing groups) such as alkoxysilyl groups. The hydrophilic monomer may have a polyoxyalkylene unit. The recording sheet of the present invention may be a recording sheet comprising a substrate (support sheet) and, as disposed on at least one side thereof, an ink absorbing layer comprising a cationic polymer containing at least a crosslinking monomer as a comonomer unit, for example (1) a cationic polymer containing a crosslinking monomer as a comonomer unit or (2) a cationic polymer comprising a crosslinking monomer and a hydrophilic monomer as comonomer units.
The present invention is further directed to a method of producing a recording sheet which comprises forming an ink absorbing layer comprising a cationic polymer containing crosslinking groups and a hydrophilic polymer on at least one side of a substrate or support.
The term “hydrophilic polymer” is used in this specification to mean any of various high molecular weight substances (macromolecular compounds) having an affinity for water, thus including water-absorbing polymers and water-soluble polymers.
BEST MODE FOR CARRYING OUT THE INVENTION
The recording sheet of the present invention comprises a substrate or support and an ink absorbing layer, and the ink absorbing layer comprises at least a cationic polymer having crosslinking or crosslinkable groups. This recording sheet is of great value as a recording sheet for ink jet recording in which flying droplets of ink are used to form a record.
[Substrate]
The substrate may be opaque, translucent, or transparent depending on the intended application. For the use as an overhead projector (OHP), the substrate is usually transparent.
There is no particular limitation on the kind of substrate. Thus, the substrate or support includes but is not limited to paper, coated paper, nonwoven cloth, and plastic film. Plastic film is preferred among these substrates.
As the polymers for constituting the plastic film, there may be mentioned polyolefins such as polyethylene and polypropylene, ethylene-vinyl acetate copolymer, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, poly(meth)acrylic acid esters, polystyrene, polyvinyl alcohol, ethylene-vinyl alcohol copolymer, cellulose derivatives such as cellulose acetate, polyesters (e.g. polyalkylene terephthalates such as polyethylene terephthalate and polybutylene terephthlate, polyalkylene naphthalates such as polyethylene naphthalate
Fujiwa Takaaki
Inokami Kiyotaka
Izuka Akihiro
Kawai Ken-ichi
Mizumoto Kiyoharu
Daicel Chemical Industries Ltd.
Grendzynski Michael E
Hess Bruce H.
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