JPH0546317B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to an inkjet recording sheet, and in particular, an inkjet recording sheet that has excellent ink absorption and color properties, small ink spreading on the sheet surface, and excellent pigment binding strength. This relates to sheets for use. [Prior Art] The inkjet recording method is widely applied to facsimile machines, printers, computer terminals, etc. because it produces less noise, can increase speed, provide multiple colors, and can be made compact. In general, the characteristics required for inkjet recording sheets are: (1) fast ink absorption, (2) small spread of ink on the sheet surface, (3) high recording density, and (4) sheet quality. It is important that the ink spreads on the surface in a nearly perfect circle, and it is also required to have water resistance so that the image will not run off even if the recorded matter gets wet with water. In addition, as basic characteristics of a recording sheet, if the sheet is paper, it is desired that there be little paper dust, especially that there is little paper dust that can clog the inkjet nozzle, and that the sheet has high surface strength. There is. In such an inkjet recording apparatus, a coating layer consisting of an ink-absorbing pigment and a binder for retaining the pigment is formed on a water-insoluble support such as paper or polyester. In general, pigments for high-resolution color inkjet sheets are used in Japanese Patent Application Laid-Open No. 59-185690 or No.
Silica having a large specific surface area and high oil absorption, as shown in Japanese Patent No. 230787, is used as a pigment. Such pigments are generally porous, and primary particles usually aggregate with each other to form secondary particles. [Problems to be Solved by the Invention] However, in conventional inkjet recording sheets, the binder is a water-soluble polymer such as polyvinyl alcohol, starch, or sodium polyacrylate; In the suspension, the binder molecules enter the pores of the pigment and absorb the ink.
This results in a significant reduction in the proportion of pores that adsorb dyes. As a result, the ink absorbency of the obtained inkjet recording sheet deteriorates, the spread and circularity of the ink on the sheet surface deteriorates, and furthermore, the dye adsorption power of the pigment decreases, resulting in a decrease in dye density. There was a problem. In addition, as the binder is absorbed into the pores of the pigment, the ability to bind the pigments to each other is reduced, so during cutting or fan folding, the pigment coating layer may peel off as powder, or this powder may This has caused problems such as clogging of ink nozzles. On the other hand, it has been considered to increase the amount of binder in order to increase the binding force, but this would result in the binder further covering the active sites of pigments such as silica, reducing color development, and further pores in the particles. This became a problem to the extent that the ink absorption capacity was significantly reduced due to the filling of the ink. Furthermore, commonly used binders such as polyvinyl alcohol (PVA) and starch have the disadvantage that it is difficult to make the pigment coating layer waterproof. [Means for Solving the Problems] In order to solve the above problems, the present invention provides an inkjet recording sheet in which a coating layer containing a binder and a pigment is provided on at least one surface of a support. contains a polymer obtained by reacting polyvinyl alcohol, methyl methacrylate, and acrylic acid, the polymer is present as particles of the polymer in water, and the acrylic acid is added in an amount of 3 to 20% by weight of the polymer particles. %. [Effects of the Invention] By configuring the present invention as described above, the binder can be used in the paint for forming the pigment layer.
Since the binder is suspended as polymer particles with a diameter larger than the pores of the pigment, the binder does not enter the pores of the pigment and can reliably bind the pigment particles with a small amount, improving ink absorption and color development. It has excellent properties, the spread of ink spots on the sheet surface is small, and it is excellent in roundness.Furthermore, there is virtually no peeling of pigment, so excellent effects such as no clogging of ink nozzles can be obtained. be. In addition, since acrylic acid is inserted into the binder polymer, the water resistance of the binder is improved, and cationic acid is added to improve the water resistance of polyamide polyamine epichlorohydrin resin, which is a water resistance agent, and other dyes. Since it causes soft aggregation with substances and makes the pigment layer more porous, ink absorbency, color development, etc. are further improved. The present invention will be explained in more detail below. The support used in the present invention is usually made of paper, such as non-sized paper, weak-sized paper, strong-sized paper such as high-quality paper, etc., but it can also be made of cloth, nonwoven fabric, synthetic paper, plastic film, etc. It's okay. Pigments used in the present invention include known pigments, such as synthetic silica, synthetic calcium silicate, synthetic aluminum silicate, synthetic magnesium silicate, and other synthetic silicates, zeolite, magnesium hydroxide, potassium aluminate, Sodium aluminate, synthetic hydrotalcite, magnesium hydroxide, magnesium oxide, alumina, satin white, zinc oxide, diatomaceous earth, magnesium sulfate, clay, titanium oxide, barium sulfate, calcium sulfate, magnesium carbonate, heavy calcium carbonate, light Examples include white inorganic pigments such as calcium carbonate, talc, and aluminum hydroxide, and white organic pigments such as ion exchange resin powder, urea resin powder, and polystyrene resin powder. Pigments that exist in the form of secondary particles are preferred because they tend to exhibit the excellent properties of the binder described in detail below, but it is also possible to use them satisfactorily even in the form of primary particles. In the present invention, the binder used in combination with the pigment is polyvinyl alcohol (PVA).
, acrylic acid, and methyl methacrylate. The molecular weight of this PVA is generally 200 to 2000
and the degree of saponification is 40-90%, preferably 80-90
%. The ratio of PVA to methyl methacrylate is 95:5 to 10:90, preferably 90:10 to 20:
80, particularly preferably 70:30 to 30:70. If the amount of methyl methacrylate is less than the above-mentioned lower limit, the coloring effect will be reduced, while if it is more than the upper limit, the binding force will be reduced. Also,
Acrylic acid is used in an amount of 3 to 20% by weight based on the total weight of the binder polymer particles. If it is less than 3% by weight, the effect of imparting water resistance disappears, while if it is more than 20% by weight, the reaction between the cation, which is a waterproofing agent for the dye in the ink, and the chemical that causes a crosslinking reaction with acrylic acid becomes faster. The pot life may be reduced and the fluidity of the paint may be reduced. The polymer used as this binder is
When suspended in water, the pigment is suspended in water as particles having a diameter larger than the pore diameter of the pigment. Usually, the diameter is about 0.1 to 1 μm. A polymerization method for obtaining such particles includes, for example, mixing predetermined amounts of PVA, methyl methacrylate, and acrylic acid;
Stir and maintain preferably at 70 to 90°C, and use a polymerization initiator such as ammonium persulfate or potassium persulfate in an amount of generally 0.05 to 5% based on the weight of the monomer.
%, preferably 0.2%, continue stirring for about 2 to 10 hours to polymerize, and then adjust the pH to 3 to 9 to obtain a polymer. If there is a lot of heat generated during polymerization, monomers may be added dropwise one after another, and the pH may be adjusted in advance before polymerization. The binder polymer produced in this way is
In water, they generally exist as particles consisting of a core part mainly composed of a copolymerized part of acrylic acid and methyl methacrylate, and a shell part mainly composed of a PVA part surrounding it. It is thought to act as a protective colloid. A paint for forming a pigment layer on a support is generally prepared by suspending and dispersing a pigment such as silica in water.
Prepared by mixing a polymer as a binder. In this case, the binder may be used alone or in combination with other binders. Such other binders include known binders such as polyvinyl alcohol, polyvinyl alcohol derivatives such as acetoacetylated polyvinyl alcohol, starch derivatives such as starch, oxidized starch, and cationic starch, methylcellulose, carboxymethylcellulose, hydroxyethylcellulose, etc. Cellulose derivatives, casein, gelatin, proteins such as soybean protein, maleic anhydride resin,
Styrene-butadiene copolymer, melamine resin,
Synthetic resin adhesives such as urea resin, vinyl acetate resin, acrylic resin, etc. are used. Among them, when used in combination with a binder that works to increase the dot diameter, such as acetoacetylated polyvinyl alcohol, polyvinyl alcohol, or polyvinyl alcohol-acrylamide-acrylic acid copolymer, it becomes possible to control the dot diameter to a desired value. Further, in order to improve water resistance, a water resistant agent such as polyamide polyamine epchlorohydrin resin may be added to the paint. The ratio of the binder to the binder is 1:10 or more, preferably 3:10 or more. Furthermore, the coating material may contain a dye fixing agent, an antifoaming agent, a fluidity improver, a water retention agent, a fluorescent dye, a preservative, a surfactant, and the like. Furthermore, the above-mentioned coating material can be applied to the support by various commonly used coating methods, such as bar, rod, air knife,
Coaters include blades, rolls, curtains, gravure coaters, spray coaters, etc. The amount of paint to be applied is 2 to 30 g/ ^m2 in terms of solid content, preferably 4 to 15 g/m2.
g/ ^m2 . The coating layer thus obtained is dried and, if necessary, subjected to a calender treatment or the like. EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples. Note that parts and percentages shown in Examples are based on weight. [Example] Production examples 1 to 10 Polymer made of PVA, methyl methacrylate (MM), and acrylic acid (Aa) used as a binder (PVA/MM/Aa polymer)
were mixed in the proportions shown in Table 1 below, maintained under stirring at 80°C, added 0.2% ammonium persulfate as a polymerization initiator, polymerized by continuing stirring for about 4 hours, and then adjusted to pH 7. I synthesized it. Here, the molecular weight of PVA used was 600, its degree of saponification was 88%, and PVA was used in a 20% solution. PVA/MM/ thus obtained
Aa polymer was used as the binder for polymer numbers 1-10. Note that Table 1 also shows the size of the diameter of suspended particles of PVA/MM/Aa polymer in water.

[Table] Examples 1 to 9 Fine powder silica (manufactured by Tokuyama Soda Co., Ltd.) Pore diameter 0.005 to
0.04μ, average particle size 4.5μ) was dispersed in 400 parts of water, 257 parts of a 15% solution of acetoacetylated PVA (manufactured by Nippon Gosei Co., Ltd.), and 193 parts of each binder of polymer numbers 1 to 9 in Table 1. After adding 77 parts of 30% polyamide polyamine epichlorohydrin resin (manufactured by Showa Denko) and stirring, 8 parts of cationic dye fixing agent (manufactured by Nippon Shokubai Kagaku) was added to the pigment, and the pigment/binder (P/ B) Prepare a paint with a ratio of 50/50 and a solid content of 19.5%, apply it to sizeless paper with a Mayer bar and dry it to a solid content of 5 g/m ² , then lightly pass it through a super calender and apply it to an inkjet recording sheet. Formed and used PVA/MM/Aa
Examples 1--corresponding to the polymer number of the polymer.
It was set as 9. The pore size of the pigment was measured by mercury intrusion method using Carlo Erba model 220, and the average particle size was measured using a Coulter counter model TA (Coulter counter model TA).
Electronics). Example 10 An inkjet recording sheet was prepared in the same manner as in Example 4, except that acetoacetylated PVA was not used. Examples 11-13 In Example 1, polymer No. 4 binder, PVA (Example 11), cationized starch (Example
Example 1 was repeated to prepare an inkjet recording sheet, except that oxidized starch (Example 12) or oxidized starch (Example 13) was used. Comparative Example 1 Example 1 except that the PVA/MM/Aa polymer of the invention is not used and only 15% acetoacetylated PVA is used (pigment/binder (P/B) ratio = 50/50) An inkjet recording sheet was prepared according to the following. Comparative Example 2 PVA117 (manufactured by Kuraray Co., Ltd.) (polymerization degree 1700, saponification degree 99%, in aqueous solution) and PVA105 (manufactured by Kuraray Co., Ltd.) were used without using the PVA/MM/Aa polymer of the present invention.
Example 1 was repeated, except that 1:3 (polymerization degree: 500, saponification degree: 99%) was used. Comparative Example 3 Example 1 was repeated, except that the PVA/MM/Aa polymer of the invention was not used, but cationized starch (in aqueous solution) was used (P/B=50/50). Comparative Example 4 Example 1 was repeated, except that the PVA/MM/Aa polymer of the invention was not used, but oxidized starch (in aqueous solution) was used (P/B=50/50). Comparative Example 5 Example 1 was repeated except that the PVA/MM/Aa polymer of the invention was not used and a vinyl acetate emulsion was used (P/B=50/50). Comparative Example 6 Using PVA/MM/Aa polymer (acrylic acid 25%) of polymer number 10 without using the PVA/MM/Aa polymer of the present invention (acetoacetylated PVA/polymer number 10 = 50/50 ) Example 1 was repeated except for the following. Test Methods The inkjet recording sheets obtained in the above Examples or Comparative Examples were subjected to the following tests. Test method 1 Dot diameter: Printed with black ink from a Canon inkjet printer A-1210 and measured at 100x magnification. 2 Dot density: Regarding dots printed with black ink of Canon Inkjet Printer A-1210, Sakura Microdensitometer PDM-
Measure the concentration of each dot using Type 5. 3 Coating layer strength: Measured according to JISK-5400 (pencil scratch test described in 6.14). 4 Color: Sanyo inkjet printer
Yellow (Y), magenta (M), cyan (C), and black (B) were printed solidly using CJ-5700 (12 dots/mm) and measured using a Macbeth densitometer RD-918 model. 5. Water resistance of coating layer: When soaked in water and rubbed with fingers, the coating layer was rated ○ if it did not peel off, △ if it peeled off slightly, and × if it peeled off. 6 Ink absorption: Sharp inkjet printer IO-700 yellow, magenta, cyan,
Spray black ink at the same place at the same time,
After 1 second, the paper was rubbed with a paper pressing plate, and those with no stains on the white paper by ink were rated as ○, and those with slight stains were rated as △. Results The results of the above tests performed on the inkjet recording sheets obtained in Examples 1 to 13 and Comparative Examples 1 to 6 are listed in Table 2 below.

【table】

[Table] From Table 2, the dot diameters of Examples 1 to 13 are 230 to 240μ, while in Comparative Examples 1 to 4.
The dot diameter is 250 to 270μ, and in the case of the present invention, the dot diameter is small. In addition, the strength of the coating layer, color property,
Overall, the ink absorbency, dot density, water resistance, etc. were superior to Comparative Examples 1 to 4. Regarding water resistance, Examples 3, 7 and 8
Although the evaluation was △, there was no particular problem in practical use. In addition, when vinyl acetate was used as the binder (Comparative Example 5) and when PVA/MM/Aa polymer containing 25% acrylic acid was used (Comparative Example 6), polyamide polyamine epichlorohydrin resin and cationic dye fixing agents were used. The paint agglomerated at the point where it entered, making it difficult to apply. On the other hand, from Examples 1, 2, and 4, PVA:
The ratio of MM is preferably 80:10, more preferably
It can be seen that the color properties and dot density are improved with more MM than 70:30. Example 14 Finely powdered silica with a smaller particle size than the pigment used in Example 4 (manufactured by Tokuyama Sota Co., Ltd., pore size 0.005~
Example 4 was repeated except that 0.04 μm, average particle size 2.3 μm) was used. The inkjet recording sheet obtained in Example 14 was subjected to each of the above tests, and the results are shown in Table 3 below.

[Table] Compared to Example 4, the dot diameter was further reduced to 220μ, providing an inkjet recording paper with excellent coating layer water resistance, ink absorbency, and coating layer strength. Example 15 Synthetic aluminum silicate (manufactured by Kyowa Chemical Industry Co., Ltd.)
100 parts and 5 parts of polyvinyl alcohol (Gosenal T-350 manufactured by Nippon Gosei Kagaku Kogyo Co., Ltd.) as a dispersant to make an aqueous thriller with a solid content concentration of 40%.
Two parts of heavy magnesium carbonate was used as a coagulation aid, and the average particle size was adjusted to 5 μm using a sand grinder. (Average pore size 0.01-0.3 μm). To this slurry, Polymer No. 4 was added as a binder, polyamide polyamine epichlordoline resin as a water resistant agent was added in an amount of 30% of the weight of the PVA/MM/Aa polymer, and the pigment/binder ( P/B) = 8/2, coated on high-quality paper with a sizing degree of 15 seconds at a solid content of 15 g/m ² and dried, passed through a super calendar to obtain an inkjet recording sheet; It was subjected to each of the above tests. The results are shown in Table 4 below. Comparative Examples 7 to 10 In Example 15, Polymer No. 4 PVA/
Instead of the MM/Aa polymer, oxidized starch (manufactured by Oji National Co., Ltd., Oji Ace A) was used (Comparative Example 7), cationic starch was used (Comparative Example 8), and PVA117 and PVA105 were mixed at 1:3. Example 15 was repeated, except that a mixture containing acetoacetylated PVA was used (Comparative Example 9) and acetoacetylated PVA was used (Comparative Example 10). The inkjet recording sheet obtained here was subjected to each of the above tests. The results are also listed in Table 4 below. All of the oxidized starches used here were used in the form of aqueous solutions.

[Table] In Example 15, the dot diameter of the inkjet recording sheet was small, and the dot density, water resistance of the coating layer,
The surface strength was superior to that of the comparative example. Example 16 Fine powder silica (manufactured by Mizusawa Chemical Co., Ltd., pore size 0.005~
0.04μ, average particle size 3.8μ) dispersed in 400 parts of water, 226 parts of 15% acetoacetylated PVA, polymer
Add 170 parts of No. 4 PVA/MM/Aa polymer and 40 parts of 30% polyamide polyamine epichlorohydrin resin, and after stirring, add 8 parts of cationic dye fixing agent (manufactured by Nippon Shokubai Kagaku Co., Ltd.) to the pigment and 80 parts of water. A slurry having a solid content of 18% and a P/B ratio of 55/45 was obtained. This slurry was coated on high-quality paper with a size degree of 15 seconds at a solid content of 6.5 g/m ² and dried, and then lightly passed through a supercalender to obtain inkjet recording paper, which was used in each of the above tests. The results are shown in Table 5 below. Examples 17-19 In Example 16, 15% acetoacetylation
Polymer No. 5 PVA/MM/Aa instead of PVA and Polymer No. 4 PVA/MM/Aa polymer
Polymer alone was used (Example 17), PVA was used as Polymer No. 5 PVA/MM/Aa polymer (Example 18), and oxidized starch and Polymer No. 5 PVA/MM/Aa polymer were used. Example 16 was repeated with the exception that (Example 19) an inkjet recording paper was obtained which was subjected to the above test and the results are shown in Table 5 below. Comparative Examples 11-14 In Example 16, Polymer No. 4 PVA/
When only acetoacetylated PVA was used without using MM/Aa polymer (Comparative Example 11), acetoacetylated PVA and Polymer No. 4 PVA/
When oxidized starch was used instead of MM/Aa polymer (Comparative Example 12), when cationized starch was used (Comparative Example 13), PVA117 and PVA105 were mixed at 1:3.
(Comparative Example 14)
Example 16 was repeated except that: The inkjet recording papers obtained in these comparative examples were subjected to each of the above tests, and the results are shown in Table 5 below. Note that all other binders used here, such as acetoacetylated PVA, were used in the form of aqueous solutions.

【table】

〔Effect of the invention〕

According to the present invention having the above configuration, an inkjet recording sheet can be obtained which is excellent in ink absorption, color development, and water resistance, as well as excellent ink spotting properties and roundness on the recording sheet.

Claims (1)

[Scope of Claims] 1. An inkjet recording sheet in which a coating layer containing a binder and a pigment is provided on at least one surface of a support, wherein the binder is made by reacting polyvinyl alcohol, methyl methacrylate, and acrylic acid. An inkjet recording sheet comprising the obtained polymer, wherein the polymer exists as particles of the polymer in water, and the acrylic acid is contained in an amount of 3 to 20% by weight of the polymer particles. 2. The inkjet recording sheet according to claim 1, wherein the ratio of the polyvinyl alcohol to the methyl methacrylate is 95:5 to 10:90. 3. The inkjet recording sheet according to claim 2, which contains a polyamide polyamine epichlorohydrin resin as a waterproofing agent for the acrylic acid.