JPH0156827B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a dispersant for pigments for coated paper, and more specifically, it is a dispersant for pigments for coated paper that is highly concentrated, has a low viscosity, and is stable over time. The present invention provides a dispersing agent that is highly effective. Traditionally, kaolin, calcium carbonate, clay,
It is well known that coated papers are made using various pigments such as satin white, aluminum hydroxide, titanium oxide, and the like. That is, coated processed paper is generally made by adding a certain kind of dispersant to the above-mentioned pigment to disperse it in water, and then adding casein, starch, vinyl synthetic latex, etc. alone or as a mixture as a pigment binder. is added, the thus obtained coating liquid is applied to base paper, then dried, and further subjected to mechanical treatment such as supercalendering. In the production of these coated papers, various points are now being paid attention to in order to obtain the best printability effects and to obtain these effects under relatively inexpensive coating liquid manufacturing conditions. consideration is given. In other words, when preparing a pigment dispersion liquid, there is a tendency for a variety of different pigments to be used as a mixture rather than just one type of pigment. As the preparation of dispersions has become desirable, and the coating process has shifted from conventional coating methods to coating machines such as high-speed blade coaters, the coating methods required today have become more desirable. The following points are listed as conditions that are widely required as a pigment dispersant for paper. (1) Those that exhibit effective dispersion effects on a wide variety of pigments. (2) In terms of economy and coated paper quality, it is possible to prepare a highly concentrated pigment dispersion using a smaller amount. (3) The pigment dispersion has excellent viscosity stability over time and thermal stability. Particularly during high-speed coating, such as when using a high-speed coating machine, even if a coating liquid with poor pigment dispersion is used, good coating can be achieved due to increased viscosity and decreased fluidity. Not only is this not possible, but the printability of the resulting coated paper is so poor that it cannot serve its purpose. Such poor dispersion state is due to poor functionality of the dispersant used, that is,
This is due to the fact that the viscosity is high immediately after blending, or even if a viscosity that is almost applicable to coating work is obtained immediately after blending, the viscosity increases over time. Conventionally, it has been used as a dispersant suitable for pigments for coated paper.
Sodium hexametaphosphate and some known surfactants, such as certain nonionic surfactants and naphthalene condensates, are used, and as organic polymer dispersants, for example, sodium polyacrylate. Although alkali metal salts of polyacrylic acid such as the above-mentioned polyacrylic acid salts are widely known as good dispersants, they are still unsatisfactory as dispersants for pigments for coated paper, which are required today as described above. The present inventors have already worked to improve the dispersion of sodium polyacrylate, which is a known dispersant for pigments for coated paper, and have used certain vinyl-based dispersants such as αβ unsaturated carboxylic acids and acrylic acid tester. It has been discovered that an alkali metal salt or annium salt copolymerized with a monomer in a specific proportion is effective for dispersing aluminum hydroxide (Japanese Patent Publication No. 50-23850, Patent No.
811068). As a result of continuing and further investigating the peripheral technology of the above-mentioned Japanese Patent Publication No. 50-23850, the inventors of the present invention have discovered that not only the dispersibility of aluminum hydroxide but also Sachin White,
The present invention has been completed by finding a dispersant that does not have the above-mentioned drawbacks and has suitable dispersibility for a wide variety of pigments such as kaolin, clay, and calcium carbonate. The dispersant according to the present invention is effective for various pigments, but among them, especially Sachin White,
Effective against calcium carbonate. That is, the present invention provides a vinyl-based compound selected from acrylic esters or methacrylic esters having an alkyl group having 1 to 4 carbon atoms per 100 parts by weight (hereinafter abbreviated as "parts") of αβ-unsaturated carboxylic acid, styrene, and vinyl acetate. A salt of a copolymer consisting of 5 to 185 parts of a monomer and 0.5 to 233 parts of a sulfonic acid monomer and at least one alkali compound selected from alkali metal-containing compounds and ammonia, or the above copolymer This is a dispersant for pigments for coated paper, which is made of a salt of the alkali compound and at least one compound selected from calcium-containing compounds, magnesium-containing compounds, zinc-containing compounds, and aluminum-containing compounds. Regarding the dispersant of the present invention, the types of essential constituent components of the copolymer are limited to the above three components, that is, α, β unsaturated carboxylic acids such as acrylic acid and maleic acid, and vinyl monomers. In addition, it is characterized by having a sulfonic acid monomer, which is structurally completely different from these, as a constituent monomer.
The blending ratio of monomers required for such polymerization is also extremely characteristic. To explain the dispersant of the present invention in more detail, the α,β unsaturated carboxylic acids that can constitute the copolymer in the dispersant of the present invention include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, fumaric acid, and maleic acid. are typical examples, but other commonly known materials can be used. Examples of vinyl monomers include acrylic acid alkyl esters or methacrylic acid alkyl esters in which the alkyl group has 1 to 4 carbon atoms, such as methyl acrylate, ethyl, propyl, butyl, isobutyl esters, or methacrylic esters thereof;
Styrene and vinyl acetate are used. These vinyl monomers are resistant to polyvalent metal ions, such as satin white, and therefore have poor dispersion stability in pigment systems containing significant concentrations of these ions. Improve your sexuality. In addition, the sulfonic acid monomer is a polymerizable monomer having a sulfonic group, such as styrene sulfonic acid, vinyl sulfonic acid, methallyl sulfonic acid,
Typical examples include -acrylamido-2-methylpropanesulfonic acid, allylsulfonic acid, and methacrylate ethylsulfonic acid, but other generally known substances can be used. Furthermore, polymerizable monomers having a sulfo group such as salts of the various sulfonic acids mentioned above can also be used. These sulfonic acid monomers are effective when used in conjunction with the vinyl monomers described above, and
Its characteristics include α,β unsaturated carboxylic acids, especially
It is extremely useful for improving the polymerization reactivity of α,β-unsaturated dicarboxylic acids. That is, even when a vinyl monomer and a sulfonic acid monomer are used alone in copolymerization with an α,β-unsaturated dicarboxylic acid, the polymerization reactivity of the α,β-unsaturated dicarboxylic acid is improved. Although a certain degree of contributing effect is recognized, it is still insufficient, and on the other hand, the effect when used in combination is
The effects of using the vinyl monomer are extremely significant, namely the resistance to metal ions and α, β.
- The synergistic effect of the ability to reduce the viscosity of the pigment dispersion system and the stability over time, which are the characteristics of unsaturated dicarboxylic acids, is exhibited, and the improvement effect is remarkable compared to conventionally known dispersants. Moreover, these effects can be sufficiently exhibited even when widely applied to various pigments. As described above, the dispersant of the present invention is a copolymer of monomers consisting of α,β-unsaturated carboxylic acid/specific vinyl monomer/sulfonic acid monomer and ammonium and/or metal-containing compound. Typical examples of alkali metal-containing compounds among metal-containing compounds include hydroxides of generally known alkali metals such as sodium, potassium, and lithium. Other metal-containing compounds include calcium, aluminum, zinc,
Compounds containing metals selected from magnesium (hereinafter referred to as specific metal compounds), specifically in the form of oxides, hydroxides, halides, carboxylates, oxyacids, etc. of these metals. used. Particularly representative and specific examples thereof include calcium acetate, magnesium acetate, zinc acetate, aluminum acetate, calcium chloride, aluminum hydroxide, zinc lactate, zinc tartrate, etc., and these are preferably used. When the copolymer consisting of the monomer is made into a salt with both an alkali compound selected from the group consisting of an alkali metal-containing compound and ammonia and a specific metal compound, the specific metal compound is a salt of the copolymer before reacting with the alkali. It is possible to react with either the polymer or the copolymer after reacting with the alkali, and it is also possible to react the specific metal compound with the alkali at the same time. The specific metal compound is 100 parts of copolymer (if the copolymer forms a reaction product with an alkali, the copolymer before reaction, i.e. α, β
It is desirable to react up to a maximum of 70 parts (based on the amount calculated as a copolymer consisting of an unsaturated carboxylic acid, a vinyl monomer, and a sulfonic acid monomer). If the amount of the specific metal compound exceeds 70 parts, the stability as a dispersant will be poor, or there will be no significant improvement in the dispersant, and on the contrary, the dispersibility may deteriorate. In order for the dispersant according to the present invention to fully exhibit its ability, it is suitable that the PH value of the dispersant itself is 4 or more and 11 or less, preferably 5 or more and 11 or less, and the copolymer and alkali metal It is desirable that the pH of the containing compound and/or the reactant with ammonia, as well as the salt when these are used in combination with a specific metal compound, is within the above range. When the pH of the salt is low, it is desirable to adjust the pH to a predetermined value by further adding an alkali metal-containing compound and/or ammonia. In the present invention, when an acrylic acid alkyl ester or methacrylic acid alkyl ester having more than 4 carbon atoms is used as a copolymer composition, the dispersibility of the pigment is poor and this is not preferred. Also, the vinyl monomer is α,
It is necessary to use 5 to 185 parts per 100 parts of β-unsaturated carboxylic acid, and the more desirable copolymerization ratio is
10 to 140 copies. When the copolymerization ratio is less than 5 parts or more than 185 parts, no significant improvement in dispersibility is observed compared to conventionally used dispersants. In addition, the copolymerization ratio of the sulfonic acid monomer is 0.5 to 100 parts of α, β unsaturated carboxylic acid.
The copolymerization ratio is required to be 233 parts, and a more desirable copolymerization ratio is 2 to 180 parts. If the copolymerization ratio is less than 0.5 parts or more than 233 parts, the effect on the temporal and thermal stability of the pigment dispersion system will be insufficient. An example of a method for obtaining the dispersant of the present invention is as follows. That is, first, the copolymer component in the dispersant can be easily produced by a commonly known method. For example, a monomer consisting of a polymerizable αβ-unsaturated carboxylic acid/vinyl monomer/sulfonic acid monomer is used with a common polymerization initiator, such as persulfate or azobisisobutylisobutyronitrile. is used in a range of, for example, 0.1 to 10% by weight based on the monomer, and approximately
Polymerization is carried out at 50 to 150°C for about 1 to 10 hours, and if necessary, part or all of the solvent is distilled off to obtain a polymer having a predetermined concentration. The polymerization rate is preferably 90% or more, more preferably 95% or more. or,
As described above, an aqueous solution of an alkali metal-containing compound such as caustic soda and/or ammonia is added to the aqueous solution of the above-mentioned polymer obtained in this way, so that a predetermined amount of unsaturated carboxylic acid and sulfonic acid units in the copolymer is added. A salt of the copolymer and an alkali metal-containing compound and/or ammonia can be easily obtained by performing a sum reaction and adjusting the pH. The reaction between the copolymer and the alkali metal-containing compound and/or ammonia is generally carried out after the formation of the copolymer as described above. It is also possible to use a method in which carboxylic acid is reacted in advance and then copolymerized, and the present invention also includes such an embodiment. Next, as a method for obtaining a salt of a copolymer using a specific metal compound, there is a conventional method as already described in JP-A-54-82416. For example, it can be produced by adding and mixing an aqueous solution of the specific metal compound to an aqueous solution of a reaction product of a copolymer and an alkali metal-containing compound and/or ammonia, and reacting the same. , by adding a mixture of an alkali metal-containing compound and/or ammonia aqueous solution and the specific metal compound aqueous solution to the copolymer aqueous solution obtained by the method described above, and causing the mixture to react. However, the dispersants of the present invention are not limited to those obtained by these manufacturing methods. The reaction between the copolymer and an alkali metal-containing compound or ammonia is a so-called neutralization reaction, and the reaction with a specific metal compound is similar to this, and the reaction conditions are already known. Here, regarding the relationship between the dispersion effect of the pigment and the molecular weight of the polymer, for example, in the case of conventional polymers such as sodium polyacrylate, it is essential that the molecular weight be relatively low. Surprisingly, in the case of the copolymer salt in the present invention, the performance is not significantly affected by molecular weight, and when obtained as an aqueous resin, the viscosity of a solution of the copolymer salt at a concentration of 20% is
A good dispersion effect can be obtained even with a relatively high molecular weight such as 500 cps, and an even better dispersion effect can be obtained with a solution having a solution viscosity of 500 cps or less. Compared to conventional dispersants, the dispersant of the present invention can provide a pigment dispersion with high concentration, low viscosity, and stability over time with a smaller amount of use. EXAMPLES The present invention will be described in more detail below with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples. Example 1 and Comparative Example 1 Commercially available Sachin White Paste (solid content 25%)
After adding the specified amount of water and dispersant shown in Table 1 (adjusted so that the solid content of Sachin White is 20%) and stirring in a kneader for 20 minutes, the viscosity of the resulting dispersion slurry immediately after and its Table 1 shows the viscosity when it was left at room temperature for 24 hours and when it was further heated to 60°C. As seen in the results, the sample of Example 1 (Sample No.
1, 2, 3, 4, 5) as a dispersant, the sample of Comparative Example 1 (sample
Compared to slurry using No. 10, 11, 12) as a dispersant,
Obviously, the stability of the dispersion viscosity over time and the thermal stability were excellent. Example 2 and Comparative Example 2 A predetermined amount of water and a dispersant shown in Table 1 were added to commercially available aluminum hydroxide (adjusted so that the solid content of aluminum hydroxide was 70%), and the mixture was stirred for 15 minutes using a kneader. Table 1 shows the viscosity of the obtained dispersion slurry immediately after and the viscosity when it was left at room temperature for 24 hours. As seen in the results, the sample of Example 2 (Sample No.
6, 7, 8, 9) as a dispersant, the aluminum hydroxide slurry prepared using the samples of Comparative Example 2 (sample No. 13,
Compared to the slurry using 14, 15) as a dispersant, the slurry viscosity was clearly lower and the stability over time was excellent.

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Claims (1)

[Claims] 1 per 100 parts by weight of α,β-unsaturated carboxylic acid,
Acrylic acid alkyl ester or methacrylic acid alkyl ester in which the alkyl group has 1 to 4 carbon atoms,
5 to 185 parts by weight of a vinyl monomer selected from styrene and vinyl acetate and a sulfonic acid monomer
A salt of a copolymer consisting of 0.5 to 233 parts by weight and at least one alkali compound selected from alkali metal-containing compounds and ammonia, or a salt of the copolymer and a calcium-containing compound, a magnesium-containing compound, a zinc-containing compound, and aluminum. A dispersing agent for pigments for coated paper, comprising a salt of at least one compound selected from the contained compounds and the above-mentioned alkali compound.