JPH0448350B2 - - Google Patents

Description

[Detailed description of the invention]

B. Object of the invention [Field of industrial application] The present invention relates to a coating composition for pressure-sensitive copying paper. More specifically, the present invention relates to a coating composition that provides a colored paper for pressure-sensitive copying paper that has excellent color development, light fastness, and moisture resistance, and also exhibits excellent surface strength and desensitizing ink drying properties and has excellent printability. It is something. Generally, pressure-sensitive copying paper contains an upper paper coated with fine capsules containing an electron-donating colorless or light-colored leuco dye dissolved in an organic solvent (capsule oil) on the back side, and an electron-accepting color developer. It consists of a bottom paper with a color developing layer on the surface, and by placing these two coated surfaces facing each other and applying pressure with a ballpoint pen or typewriter, the capsule in the pressurized area is destroyed. ,
Capsule oil containing a leuco dye is transferred to the color developing layer and a coloring reaction is performed, thereby making it possible to obtain printed records. The colored paper for pressure-sensitive copying paper expressed in the present invention includes, in addition to the bottom paper provided with a color developer layer as described above, an inner paper provided with a color developer layer on the front surface and a capsule coating layer on the back surface. include. Another form of coloring paper for pressure-sensitive copying paper includes what is called a single recording sheet or single coloring paper in which both the capsules and the color developer are coated on the same surface of the substrate. In recent years, demand for pressure-sensitive copying paper has shown remarkable growth due to the rationalization of office work, the development of the information industry, and the spread of computers, and its uses have also diversified. is required. For example, in addition to obtaining clear and high-density colored images during copying, the stability of colored images over time, especially sunlight fastness (lightfastness)
and excellent humidity fastness (moisture resistance),
Furthermore, it is required that the color developing performance of the color developing agent decreases little over time. In addition, in general ruled line character printing and desensitizing printing, it is also required that there is no piling trouble and that the desensitizing ink has good drying properties in order to withstand high-speed printing. [Prior Art] In order to satisfy the performance requirements of pressure-sensitive copying paper, attempts have been made to improve it from various aspects, including coating compositions consisting of color developers, pigments, binders, and the like. Regarding the binder, a carboxy-modified styrene-butadiene copolymer latex has been used as a binder, and various studies have been conducted because the properties of the latex are effective in improving the above-mentioned properties. For example, Japanese Patent Publication No. 57-52236 discloses a carboxy-modified styrene-butadiene copolymer latex containing unsaturated nitrile; Modified styrene-butadiene copolymer latex, JP-A-59-196289 discloses a combination of carboxy-modified styrene-butadiene copolymer latex with high gel content and low gel content; A carboxy-modified copolymer latex whose swelling property of Tux film is below a certain level is used in JP-A-60-24992, a carboxy-modified styrene-butadiene copolymer latex containing a large amount of unsaturated carboxylic acid is used. Things have been proposed. However, even if the specific carboxy-modified styrene-butadiene copolymer latex mentioned above is used as a binder, the performance required for pressure-sensitive copying paper, namely color development, light fastness and moisture resistance, surface strength, and desensitizing ink The actual situation is that it is not effective enough to satisfy all printability such as drying properties at the same time, and further improvements are desired to meet market needs. On the other hand, with regard to pigments, Japanese Patent Application Laid-Open No. 55-28857 proposes the use of calcium carbonate having a particle size distribution of 2 μ or less and 55% or more for the purpose of improving the color development and the erosion resistance of the color image. However, when such a pigment with a fine particle size is used, the specific surface area of the pigment naturally increases, and as a result, the amount of binder used increases. Therefore,
If the binder is used in a normal amount, the surface strength decreases and the workability during printing (picking trouble occurs frequently) deteriorates. In order to improve this problem, if the amount of binder used is increased more than usual, the coloring property and the fading property of the colored image will decrease, and the effect that can be achieved by using a pigment with a specific particle size distribution will not be fully exhibited. There is. Therefore, it can be said that with this method, it is difficult to simultaneously satisfy the above-mentioned performances required of pressure-sensitive copying paper. Furthermore, as a countermeasure against the deterioration of surface strength and workability, Japanese Patent Application Laid-Open No. 133093/1983 uses calcium carbonate of 0.6μ or less as a pigment and calcium carbonate as a binder.
It is proposed to use a styrene-butadiene copolymer latex with an extremely fine particle size of 0.08μ or less. However, when latex with such a fine particle size is used, the number of latex particles naturally increases and its effectiveness as a binder for adhering fine calcium carbonate is improved, but on the other hand, the total surface area of latex particles increases. The fading of the colored image (lightfastness,
At present, the moisture resistance (humidity resistance) deteriorates, and satisfactory performance is not necessarily achieved. Furthermore, latex with a fine particle size has a very high viscosity at a normal latex concentration, and there remain problems in handling. [Problems to be Solved by the Present Invention] The purpose of the present invention is to improve the various problems detailed in the prior art section, that is, to achieve excellent color development, light fastness, and moisture fastness, and at the same time to achieve high speed printing. Another object of the present invention is to provide a coating composition for pressure-sensitive copying paper, which can provide a colored paper for pressure-sensitive copying paper that does not cause any problems in surface strength, desensitized ink drying properties, printability, and workability. B. Structure of the Invention [Means for Solving the Problems] The present inventors have completed the present invention as a result of intensive research in order to achieve the above object. That is, the present invention uses an organic color developer, light calcium carbonate, 25 to 65% by weight of an aliphatic conjugated diolefin monomer as a binder, 0.2 to 10% by weight of an ethylenically unsaturated carboxylic acid amide monomer, and these. The present invention provides a coating composition for pressure-sensitive copying paper characterized by comprising a copolymer latex containing 25 to 74.8% by weight of other copolymerizable monomers. The present invention will be explained in more detail below. As the organic color developer used in the present invention, for example, Japanese Patent Publication No. 49-10856, Japanese Patent Publication No. 51-1986,
Benzoic acid, P-tert-butyl-benzoic acid, 4-methyl-3-nitrobenzoic acid, salicylic acid, 3-phenyl salicylic acid, 3- Cyclohexylsalicylic acid, 3-tert-butyl-5-methylsalicylic acid, 3,5-di-tert-butylsalicylic acid, 3-methyl-5-benzylsalicylic acid, 3-
Phenyl-5-(α,α-dimethylbenzyl)salicylic acid, 3-cyclohexyl-5-(α,α-
dimethylbenzyl)salicylic acid, 3-(α,α-
dimethylbenzyl)-5-methylsalicylic acid, 3,
5-di-cyclohexyl) salicylic acid, 3,5-
Di-(α-methylbenzyl)salicylic acid, 3,5
-di-(α,α-dimethylbenzylsalicylic acid),
3-(α-Methylbenzyl)-5-(α,α-dimethylbenzyl)salicylic acid, 4-methyl-5-cyclohexylsalicylic acid, 2-hydroxy-1-
Benzyl-3-naphthoic acid, 1-benzoyl-2
- Various aromatic carboxylic acids such as hydroxy-3-naphthoic acid and 3-hydroxy-5-cyclohexyl-2-naphthoic acid, and these, such as zinc, aluminum, magnesium, calcium,
Salts with polyvalent metals such as cobalt: Special Publication No. 40-9309
Phenol compounds such as 6,6'-methylenebis(4-chloro-m-cresol) as described in Japanese Patent Publication No. 42-20144, JP-A-48-14409, etc.: P-phenylphenol- Phenol resins such as phenol-aldehyde resins such as formalin resin, phenol-acetylene resins such as P-tertiary butylphenol-acetylene resin, and polyvalent metal salts thereof: maleic acid-rosin resin,
Acidic polymers such as copolymers of styrene, ethylene or vinyl methyl ether and maleic anhydride: as described in Japanese Patent Publication No. 48-8215, Japanese Patent Publication No. 8216-1982, Japanese Patent Publication No. 1326-1972, etc. Examples include polymers of aromatic carboxylic acids and aldehydes or acetylene, and polyvalent metal salts thereof. Among these organic color developers, aromatic carboxylic acids and their polyvalent metal salts, phenolic resins and their polyvalent metal salts, copolymers of aromatic carboxylic acids and aldehydes or acetylene, and their polyvalent metal salts are particularly useful. Preferably used. In addition, activated clay, acid clay, attapulgite,
bentonite, zeolite, silicate talc,
The use of one or more inorganic color developers such as kaolin in combination with an organic color developer can be effectively carried out as long as it does not impede the effects of the present invention. The particle size and usage amount of light calcium carbonate used in the present invention are not particularly limited, but it is particularly preferable that the average particle size is 0.4μ or less and the total solid content of the coating composition is 50% by weight or more. used. The copolymer latex as a binder used in the present invention will be explained in detail below. The aliphatic conjugated diolefin monomer used in the present invention is selected from those having 4 to 10 carbon atoms, and specifically, 1,3-butadiene, 2-methyl-1,3-butadiene, ,2,3-
Examples include dimethyl-1,3-butadiene, halogen-substituted butadienes, substituted linear conjugated pentadienes, and conjugated hexadienes having a linear or side chain. The aliphatic conjugated diolefin monomer is
It is used in a monomer composition of 25-65% by weight. If this proportion is less than 25% by weight, the adhesive strength will be poor, and if it exceeds 65% by weight, the light resistance will decrease, which is not preferable. Examples of the ethylenically unsaturated carboxylic acid amide monomer used in the present invention include acrylamide, methacrylamide, N-methylolacrylamide, diacetone acrylamide, and the like. The ethylenically unsaturated carboxylic acid amide monomers can be used alone or in combination of two or more, and are used in a monomer composition of 0.2 to 10% by weight. If this proportion is less than 0.2% by weight, the effect of the present invention is not observed, and if it exceeds 10% by weight, adhesive strength, especially wet pick, tends to decrease, which is not preferred. Other monomers copolymerizable with the aliphatic conjugated diolefin monomer and ethylenically unsaturated carboxylic acid amide monomer used in the present invention include:
Aromatic vinyl monomers such as styrene, α-methylstyrene, vinyltoluene, dimethylstyrene; methyl acrylate, ethyl acrylate,
Acrylate monomers such as butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate; methyl methacrylate, ethyl methacrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, glycidyl methacrylate methacrylate monomers such as acrylonitrile, unsaturated nitrile monomers such as methacrylnitrile; Examples include crosslinkable monomers that form molecular crosslinked structures. These can be used alone or in combination of two or more, and are used in a monomer composition of 25 to 74.8% by weight. This ratio is 25
If it is less than 74.8% by weight, the light resistance will decrease.
Exceeding this is not preferable because the adhesive strength decreases. The gel content of the copolymer latex used in the present invention is not particularly limited, but is preferably in the range of 80 to 100% by weight, more preferably in the range of 95 to 100% by weight. Also,
There are no particular restrictions on the particle size of the copolymer latex, but in consideration of the viscosity of the copolymer latex, it is preferable to use a copolymer latex having an average particle size of 0.1 μm or more. Furthermore, regarding the method for producing copolymer latex,
For example, known emulsion polymerization methods such as continuous emulsion polymerization, bulk emulsion polymerization, and two-stage emulsion polymerization can be employed, and in this case, various known emulsifiers, chain transfer agents, polymerization initiators,
Additives and auxiliaries used in general emulsion polymerization, such as electrolytes and chelating agents, can be used, and the polymerization temperature can be selected from either high or low temperatures. In the present invention, when preparing a color developer-containing coating composition, the copolymer latex is mixed in a color developer dispersion system, and the dispersion medium at this time is water and/or copolymer latex. In this dispersion system, various auxiliary agents such as dispersants, antifoaming agents, and surfactants, which are conventionally used in the production of pressure-sensitive copying paper, can be used.
The amount of copolymer latex to be added is mainly taken into consideration from the viewpoint of adhesive strength and economical efficiency, and it can usually be added in an amount of 3 to 50 parts by weight per 100 parts by weight of the coating composition (solid content). In addition, in order to sufficiently retain these color developers on the substrate surface, starches, casein, gelatin, gum arabic, albumin, trakhaganth gum, methylcellulose, ethylcellulose, carboxymethylcellulose, carboxyethylcellulose, hydroxyethylcellulose, polyvinyl are usually used. It can be applied to the substrate surface together with a binder such as alcohol, carboxy-modified styrene-butadiene copolymer, vinyl acetate copolymer, or acrylic copolymer, but of course, the combination of these conventionally used binders mentioned above is not recommended. It can be carried out effectively as long as it does not impede the effects of the invention. [Examples] The present invention will be specifically explained below with reference to Examples, but the present invention is not limited to the Examples in any way. It should be noted that all parts and percentages used herein mean parts by weight and percentages by weight unless otherwise specified. On the other hand, the test methods for various measurement items are as follows. (a) Color-forming property A commercially available microcapsule-coated paper with a coated surface provided with a color-developing layer in color-forming paper for pressure-sensitive copying paper and microcapsules containing microdroplets of alkylnaphthalene containing crystal violet lactone. The surface coated with microcapsules was superimposed and colored under a load of 100 kg/cm, left in a dark place for 1 hour, and the density of the colored area was measured using a Macbeth color densitometer. (Hereinafter, the measured value is also referred to as the initial concentration.)
The larger the value, the better the color development. (b) Light resistance The colored paper developed under the conditions of (a) above was further exposed to direct sunlight for two days, and the color density of the colored area was measured.
Determine the light resistance according to the following formula. Note that the larger the value, the better the light resistance. Lightfastness (%) = Color density after irradiation with direct sunlight / initial density x 100 (c) Humidity resistance The colored paper developed under the conditions of (a) above was
After leaving it in a 90% atmosphere for 2 days, measure the color density of the colored area and determine the moisture resistance according to the following formula. Note that the larger the value, the better the moisture resistance. Humidity resistance (%) = Color density after being left at high humidity/initial density x 100 (d) Desensitizing ink drying property Desensitizing ink is printed solidly on colored paper using an RI printing machine. Next, the desensitizing ink is transferred to black paper (replica) at regular intervals, and the amount of desensitizing ink transferred to the replica is visually judged on a five-point scale. The smaller the amount of desensitized ink transferred, the faster the desensitized ink dries, and the better the drying properties of the desensitized ink become. The outline of the five-level evaluation is as follows: 5.0 (fast drying) to 1.0 (slow drying) (e) Surface strength Dry pick: Measure the surface strength of colored paper using an RI printing machine. Printed three times with commercially available offset ink, and evaluated the paper on a five-point scale based on the state of paper peeling with the naked eye as shown below. 5.0 (excellent) to 1.0 (poor) Wet Pick: Measure the surface strength of colored paper in a wet state using an RI printing machine. After moistening the surface of the colored paper with a Molton roll, it was printed once with a commercially available offset ink.
From the state of the paper at that time, the following is seen with the naked eye5
Perform graded evaluation. 5.0 (excellent) to 1.0 (poor) Γ Example 1 (Preparation of copolymer latex) In an autoclave that had been purged with nitrogen in advance, the monomer mixture and chain transfer agent shown in Table 1, 1.0 part of sodium alkylbenzenesulfonate, 0.5 parts of sodium hydrogen carbonate, 1.5 parts of potassium persulfate and 100 parts of pure water were added, and polymerization was carried out at 70°C for 16 hours to obtain copolymer latexes I~. (Preparation of coating composition) To 15 parts of zinc 3-phenyl-5-(α,α-dimethylbenzyl)salicylate, 85 parts of various calcium carbonates and kaolin having different average particle sizes listed in Table 2 were added, and sodium polyacrylate was added. Disperse in water using 0.6 parts to prepare a slurry with a concentration of 50%. Next, 3 parts of oxidized starch and 14 parts of the copolymer latex (solid content) shown in Table 2 were added to obtain coating compositions 1 to 12 with a solid content of 33%. (Preparation of colored paper and performance evaluation) Using the obtained coating compositions 1 to 12, 52 g/m ²
A dry coating amount of 5 g/m ² was applied to one side of high-quality paper to create colored paper. The performance of each colored paper obtained was evaluated and the results are shown in Table 2.

【table】

[Table] Γ Example 2 (Preparation of copolymer latex) In an autoclave that had been purged with nitrogen in advance, the monomer mixture and chain transfer agent shown in Table 3, 0.9 parts of sodium alkylbenzenesulfonate, 0.6 parts of sodium hydrogen carbonate, 1.0 part of potassium persulfate and 100 parts of pure water were added, and polymerization was carried out at 68°C for 18 hours to obtain copolymer latexes a to j. (Preparation of coating composition) Using the obtained copolymer latexes a to j,
Coating compositions 21 to 30 were prepared according to the following formulations. 3-phenyl-5-(α,α-dimethylbenzyl)zinc salicylate 15 parts activated clay 15 parts light calcium carbonate (average particle size 0.15μ) 60 parts sodium polyacrylate 0.6 parts starch oxide 3 parts copolymer latex (solid) ) 14 parts Desired water required to prepare solids content 33% (coloring paper preparation and performance evaluation) Using the obtained coating compositions 21 to 30, 65 g/m ²
A dry coating amount of 5 g/m ² was applied to one side of high-quality paper to obtain colored paper. The performance of each colored paper obtained was evaluated and the results are shown in Table 4.

【table】

[Table] Γ Example 3 Copolymer latex a obtained in Example-2
Using ~j, paint composition 31 according to the following formulations, respectively.
~40 were prepared. Colored paper was prepared and evaluated in the same manner as in Example-2. The results are shown in Table-5. p-phenylphenol aldehyde polycondensate 15 parts activated clay 15 parts light calcium carbonate (average particle size 0.35μ) 70 parts sodium hexametaphosphate 1 part sodium hydroxide 0.8 parts oxidized starch 7 parts copolymer latex (solid content) 15 parts desired water needed to prepare 30% solids

[Table] Γ Example 4 (Preparation of copolymer latex) Monomers and chain transfer agents used in the first stage polymerization shown in Table 6, 0.6 part of sodium alkylbenzenesulfonate, 0.6 part of sodium hydrogen carbonate,
1 part of potassium persulfate and 100 parts of pure water were charged into an autoclave which had been purged with nitrogen in advance, and polymerization was carried out at 65°C until the polymerization conversion reached 70% or more. Next, in order to carry out the second stage polymerization, the monomers used in the second stage polymerization shown in Table 6 were added to the same autoclave, and the polymerization was completed at 68°C to form copolymer latexes A to G. I got it. The final polymerization conversion rate was 98% or more in all cases. (Preparation of coating composition) Using the obtained copolymer latexes A to G,
Coating compositions 41 to 41 were prepared in the same manner as in Example-2.
Got 47. (Preparation of colored paper and performance evaluation) Using the obtained coating compositions 41 to 47, colored papers were prepared and evaluated in the same manner as in Example-2. The results are shown in Table-7.

【table】

【table】

[Effects of the present invention]

If the coating composition for pressure-sensitive copying paper of the present invention is used,
For use in high-quality pressure-sensitive copying paper that has excellent color development, light fastness, and moisture resistance, and at the same time does not cause any problems in printability and workability such as surface strength and desensitized ink drying properties even during high-speed printing. Colored paper can be obtained.

Claims (1)

[Claims] 1 Organic color developer, light calcium carbonate, 25 to 65% by weight of aliphatic conjugated diolefin monomer as a binder, and ethylenically unsaturated carboxylic acid amide monomer
A copolymer latex comprising 0.2 to 10% by weight and 25 to 74.8% by weight of other monomers copolymerizable with these (excluding ethylenically unsaturated carboxylic acids). Coating composition for pressure copying paper.