JPH0519473B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention is a coated paper for inkjet recording used in image printers, print printers, etc. that use water-based ink, and has a strong coating layer and can be used and written on in the same way as ordinary high-quality paper. The present invention relates to an inkjet recording sheet that has a high absorption speed and absorption capacity for ink adhering to the sheet surface, and provides sharp images and prints with bright ink colors. [Conventional technology] The technology of inkjet color printers, which create color hard copies at high speed using an inkjet recording method, has advanced.In order to obtain high-quality recorded images, water-based ink adhered to the recording sheet is removed from the surface. A number of proposals have been made in the past regarding sheets provided with a coating layer consisting mainly of pigment and adhesive so that the sheet is quickly absorbed in the thickness direction without spreading upward. For example, JP-A-55-51583 discloses a coating layer consisting of non-silica silica (particle size 0.1 to 10 μm) and a polymer binder; Coating layer with a pigment that adsorbs (many pigments such as zeolite are examples)
However, JP-A No. 56-145856 discloses that a receiving layer consisting of fine particles of silicic acid and a non-aqueous solvent-soluble resin, or consisting of fine particles of silicic acid, other inorganic pigment particles, and a non-aqueous solvent-soluble resin is provided on a substrate. are disclosed respectively. However, in these proposed sheets, the surface strength of the coating layer is weak, and the coating layer peels off under normal paper usage conditions, causing powder to fall off, poor pencil writing, and cracks in the coating layer. There is a problem that this occurs. Pencil writability can be improved to some extent by selecting a pigment such as finely powdered silica, and the problem of cracking can be improved to some extent by controlling drying conditions. However, it has been difficult to improve the strength of the coating layer. The reason for this is that in order to improve ink absorption and resolution, the blending ratio of fine powder silica in the paint must be increased to 30 to 88% by weight of the paint solids, and a high coating amount must be applied.
Sufficient improvement could not be obtained due to restrictions on the adhesive surface. For example, attempts have been made to dramatically increase the amount of adhesive to increase strength, but such paper suffers from noticeable bleeding of water-based ink, reduced image quality, and is unable to achieve the required resolution or reproduction of neutral colors. It's becoming difficult. Attempts have also been made to improve adhesive strength by using hydrophobic adhesives such as latex. Additionally, cationic polymers have recently been added to improve the clarity and water resistance of inkjet printed images. However, since cationic polymers are generally not compatible with latex emulsions of anionic hydrophobic polymers, strength cannot be improved by adding these latexes. As a result, it has been impossible to provide paper that can be used in the same way as high-quality paper, which is ordinary business paper, while taking full advantage of the full-color performance of inkjet printers. [Problems to be Solved by the Invention] The present invention has a high absorption speed and absorption capacity for aqueous ink attached to the surface of a recording sheet, the color of the ink is bright, the ink dots have little bleeding, and the ink dots are circular and sharp. This is a sheet for inkjet printers that provides high-resolution images and enables high-speed color printing of high-resolution prints and images.It also has a coating layer with a high surface strength comparable to that of ordinary high-quality paper. It is an object of the present invention to provide an inkjet recording sheet that does not cause powder to fall off, has good writing properties, and has an excellent image and water resistance, and can eliminate the above-mentioned drawbacks. [Means for Solving the Problems] The present invention provides pigments containing finely powdered silica in an amount of 30 to 88% by weight of the total paint solids on a sheet support made of natural pulp paper, plastic film sheet, or ordinary synthetic paper. and polyvinyl alcohol copolymer containing silanol groups in an amount of 5-40% by weight of the total paint solids.
The present invention relates to an inkjet recording sheet characterized in that it is provided with a coating layer containing as main components an adhesive containing the present invention and 2 to 10% by weight of a cationic polymer. As a result of various studies to solve the above-mentioned drawbacks of the prior art, the inventor of the present invention has discovered that the total paint solids content is 30%.
-Using pigments containing 88% by weight of finely powdered silica,
A polyvinyl alcohol copolymer having a silanol group is contained in an amount of 5 to 40% by weight of the total paint solids, and more preferably, an adhesive containing polyvinyl alcohol with a degree of polymerization of 1000 or less is used as another adhesive, and a pigment mainly composed of fine particle silica is used. It has been found that when used together with a cationic polymer as an adhesive, an inkjet recording sheet with excellent surface strength can be obtained without impairing the effects of the particulate silica and the cationic polymer. By using polyvinyl alcohol copolymer, which has excellent adhesion specifically to silica, as a binder for the coating layer, a unique synergistic effect with the fine particle silica and cationic polymer, which are the main components of the pigment, can be obtained.
This is thought to be due to the formation of a unique interaction within the coating layer of the inkjet paper. The polyvinyl alcohol copolymer containing silanol groups used as the adhesive of the present invention is produced by copolymerizing a silicon-containing vinyl compound and vinyl acetate and then saponifying the copolymer, so that the vinyl acetate unit becomes vinyl alcohol and silicon It is obtained by converting each monomer unit contained into a silanol group. (Refer to Japanese Patent Application Laid-Open No. 58-59208). The silicon-containing monomer may be copolymerized in a very small amount of about 0.1-1.0 mol%. Since the polyvinyl alcohol copolymer containing silanol groups specifically and strongly bonds with silica, sufficient coating film strength can be achieved with a small amount that does not interfere with color development or resolution. The amount of polyvinyl alcohol copolymer containing silanol groups is from 5 to 40% by weight. Even if it is used in an amount of 40% by weight or more, the strength does not increase, and on the contrary, the silica ratio decreases and the image deteriorates, which is not preferable. If the amount is less than 5% by weight, sufficient effects cannot be obtained. In the present invention, polyvinyl alcohol having a degree of polymerization of 1000 or less can be used together with a polyvinyl alcohol copolymer containing a silanol group. Polyvinyl alcohol with a degree of polymerization of 1000 or less is often preferable to be added because it has excellent compatibility and dispersibility. It was necessary to blend a large amount of polyvinyl alcohol with a high polymerization degree of 1100 to 2000, which has poor properties, with respect to silica. However, in the present invention, there is no such need, and 5-20% by weight of polyvinyl alcohol having a degree of polymerization of 1000 or less can be contained. In addition, starch and starch derivatives as adhesives,
Among natural or processed adhesives such as cellulose derivatives, acrylic copolymers, etc., those having good compatibility with the cationic polymer can be selected and used in combination, thereby further improving adhesive strength. In order to achieve high image resolution, the amount of adhesive, including the amount of polyvinyl alcohol copolymer having silanol groups, is 10-40% by weight, preferably 10-30% by weight of the solid content of the paint. In the present invention, a cationic polymer is added to make the image waterproof. Suitable cationic polymers for polyethyleneimine include quaternary ammonium salt derivatives, acrylic containing quaternary ammonium groups as a copolymerized monomer, or methacrylic acid ester copolymers, within a range of 2-10% by weight. Make it exist. If it is less than 2% by weight, a sufficient effect cannot be obtained, and if it is more than 10% by weight, the effect is saturated and no further improvement is seen. The pigment used in the present invention is a color-developing white pigment with high oil absorption and high specific surface area, which is known to give clear images when used in inkjet paper. Fine particle silica, which is mainly composed of particles, is the best. Suitably, the finely divided silica is used in an amount of 30-88% by weight of the total paint solids. In terms of image quality, the more the better. Other white pigments can be used or used together depending on the purpose of use of the outer paper and the requirements of the printer, and the total amount of pigments is 50-88% by weight. Other white pigments that can be used include, for example, zeolite, calcium carbonate, diatomaceous earth, kaolin clay, talc, aluminum hydroxide, organic pigments (plastic pigments), and other pigments commonly used in paper coating. The sheet-like support used in the present invention may be any of ordinary natural pulp paper, plastic film sheets of polypropylene, polyethylene, polyester, etc., synthetic fibers, synthetic pulp, and so-called synthetic paper obtained by imitating synthetic resin films. The thickness of the sheet support is 10 to 200 μm, and the basis weight is 10 to 200 μm.
200 g/m ² is preferable, and one with good surface smoothness is preferable. Generally speaking, the coating weight on the support base paper is from 2 to 50 g/m ² , preferably from 5 to 30 g/m ² . Hereinafter, the present invention will be explained in more detail with reference to Examples. In the examples, parts indicate parts by weight as solid content. Example 1 Paint-1 Pigment Fine particle silicic acid containing 70% or more of secondary particle diameters of 2 to 5μ (Fine Seal Tokuyama Soda)
100 parts (68% by weight) Polyvinyl alcohol copolymer containing silanol groups (R-1130 Kuraray) (degree of polymerization 1700)
30 parts (20%) Polyvinyl alcohol (PVA-105 Kuraray)
10 parts (7%) Polyethyleneimine quaternary ammonium salt
5 parts (3%) Dispersant Sodium polyacrylate 1.5 parts (2%) Paint-1 with a concentration of 12% by weight was prepared from the above ingredients, and the solid content was ^20g /m2 on 65g/ ^m2 high-quality paper. It was coated and dried to obtain an inkjet sheet. Example 2 Paint-2 Pigment Fine particle silicic acid (Fine Seal Tokuyama Soda)
80 parts (61% by weight) Diatomaceous earth 20 parts (15%) Vinyl alcohol copolymer containing silanol groups (R-2105 clar) (degree of polymerization 500) 20 parts (15%) Acrylic copolymer containing quaternary ammonium salt Polymer emulsion (Tg-10℃, quaternary salt 25mol%)
10 parts (8%) Dispersant Sodium polyacrylate 1.5 parts (1%) Paint containing the above components at a concentration of 18% by weight.
2 was coated at a solid content of 20 g/m ² on a 65 g/m ² high-quality paper and dried to obtain an inkjet sheet. Comparative example 1 Paint-3 Pigment Fine particle silicic acid (Fine Seal Tokuyama Soda)
100 parts (71% by weight) Dispersant Sodium polyacrylate 1.5 parts (1%) Vinyl alcohol copolymer containing silanol groups (R-2105 Kuraray) (degree of polymerization 800) 50 parts (28%) Consists of the above components Paint with a concentration of 18% by weight
3 was coated at a solid content of 20 g/m ² on a 65 g/m ² high-quality paper and dried to obtain an inkjet sheet. Comparative Example 2 Paint-4 Pigment Fine particle silicic acid (Fine Seal Tokuyama Soda)
100 parts (62% by weight) Polyvinyl alcohol (GH-17 Nippon Gosei) (degree of polymerization 1700) 50 parts (31%) Emulsion of acrylic copolymer containing quaternary ammonium salt (Tg -10℃, 25 mol of quaternary salt) %)
10 parts (6%) Dispersing agent Sodium polyacrylate 1.5 parts (1%) Coating-4 consisting of the above components at a concentration of 8% by weight was coated on high quality paper at a solid content of 20g/ ^m2 on 65g/m2 ^. The mixture was processed and dried to obtain an inkjet sheet. Comparative Example 3 Paint-5 Pigment Fine particle silicic acid (Fine Seal Tokuyama Soda)
100 parts (71% by weight) Oxidized starch (Ace C Oji Cornstarch)
40 parts (28%) Dispersant Sodium polyacrylate 1.5 parts (1%) Paint with a concentration of 15% by weight consisting of the above components -
5 was coated at a solid content of 20 g/m ² on a 65 g/m ² high-quality paper and dried to obtain an inkjet sheet. The evaluation results of these inkjet recording sheets are shown in the table. The inkjet recording properties were evaluated using a commercially available inkjet printer, and the ink absorbency and color clarity were evaluated, and the strength of the coating layer was evaluated using a Scotch tape test and pencil writability. Ink absorption evaluation was performed by measuring the time taken for the ink to dry. The vividness of color development was visually evaluated by the color development of the yellow, magenta, and cyan color inks and the color development of the heavy colors of green, blue, and red. Pencil writability was sensually judged based on the difficulty of writing with an H pencil. The surface strength was determined by sensory evaluation of the degree to which the coating layer was removed by peeling off the cellophane tape. Water resistance was determined by immersing the image in running water for 5 minutes and then drying it to see if the image remained. ○ indicates excellent performance, △ indicates general quality, and × indicates defects that may cause problems in use.

[Table] Effects of the Invention The inkjet recording sheet of the present invention has a strong surface, can be easily written with a pencil, and has excellent ink absorption and
This makes it possible to create a high-resolution, high-speed, general-purpose inkjet color printer that eliminates the drawbacks of conventional methods, with excellent color vividness.

Claims (1)

[Claims] 1. On a sheet-like support made of natural pulp paper, plastic film sheet, or ordinary synthetic paper,
A pigment containing 30-88% by weight of total paint solids of finely powdered silica, an adhesive containing 5-40% by weight of total paint solids of a polyvinyl alcohol copolymer containing silanol groups, and 2-10% by weight of cations. 1. An inkjet recording sheet characterized by having a coating layer containing a polymer as a main component. 2. The inkjet recording sheet according to claim 1, which contains 5 to 20% by weight of polyvinyl alcohol having a degree of polymerization of 1000 or less as another adhesive.