JPS6228690B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a dispersant for pigments for coated paper, and more specifically, the present invention relates to a dispersant for pigments for coated paper, and more specifically, the present invention relates to 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 dispersant that can be obtained in large quantities. Traditionally, kaolin, calcium carbonate, clay,
It is well known that coated papers are made using pigments such as satin white, aluminum hydroxide, titanium oxide, and the like. In other words, coated paper is generally made by adding a certain kind of dispersant to the above-mentioned pigments, dispersing them in water, and then adding casein, starch, vinyl synthetic latex, etc. alone or in combination as a pigment binder. However, the coating liquid thus obtained is applied to a base paper, then dried, and then subjected to mechanical treatment such as supercalendering. Today, in the production of these coated papers, various considerations are taken into consideration in order to obtain the best printability effects and to obtain these effects under the manufacturing conditions of relatively inexpensive coating liquids. is being paid. That is, when preparing the pigment dispersion,
There is a tendency for a variety of different pigments to be used as a mixture rather than just one type of pigment, and it has become desirable to prepare highly concentrated pigment dispersions with low water content. , and the coating process is changing from the conventional coating method to coating machines such as ultra-high-speed blade coaters, so today's requirements for pigment dispersants for coated paper are as follows: 1. Those that exhibit an effective dispersion effect for a wide variety of pigments 2. Those that enable the preparation of highly concentrated pigment dispersions with a smaller amount of use in terms of economy and coated paper quality 3. Pigments It is mentioned that the viscosity of the dispersion liquid has excellent temporal and thermal stability. Particularly when applying at high speeds, such as when using a high-speed coating machine, if a coating liquid with poor pigment dispersion is used, the viscosity will increase and the fluidity will decrease, making it difficult to perform a good coating. Not only is the coated paper not suitable for printing, the print quality of the obtained coated paper is poor and the purpose cannot be achieved. This poor dispersion state is caused by the poor functionality of the dispersant used, that is, the viscosity immediately after blending is high, or even if the viscosity immediately after blending is low enough to be applied to coating operations. Even if one is obtained, this is due to the fact that the viscosity increases over time. Conventionally, suitable dispersants for pigments for coated papers include sodium hexametaphosphate and some known surfactants, such as certain nonionic surfactants,
and naphthalene condensates are used,
In addition, as an organic polymer dispersant, for example, alkali metal salts of polyacrylic acid such as sodium polyacrylate are widely known as good dispersants, but as mentioned above, pigment dispersions for coated paper are currently available. The conditions required for the drug are still unsatisfactory. The present inventors have further investigated the dispersants for pigments for coated paper, and have found that calcium carbonate, aluminum hydroxide, satin white,
The present inventors have discovered a dispersant that does not have the above-mentioned drawbacks and has more suitable dispersibility for many types of pigments such as kaolin and clay, and has completed the present invention. Although the dispersant according to the present invention is effective for various pigments,
Among them, it is particularly effective against calcium carbonate. That is, the present invention provides α,β unsaturated monocarboxylic acids 35
A copolymer consisting of ~95 parts by weight (hereinafter simply referred to as parts), 5 to 65 parts of α,β unsaturated dicarboxylic acid (total of 100 parts of both), and 0.5 to 180 parts of sodium styrene sulfonate per 100 parts of these in total. a salt of the combination and at least one alkali compound selected from alkali metal-containing compounds and ammonia, or the copolymer and at least one compound selected from calcium-containing compounds, magnesium-containing compounds, zinc-containing compounds, and aluminum-containing compounds. This is a dispersing agent for pigments for coated paper, which is made of a salt of the above-mentioned compound and the above-mentioned alkali compound. The dispersant of the present invention is characterized in that the essential components of the copolymer are limited to the above-mentioned three specific components, that is, structurally speaking, it is completely different from α,β unsaturated carboxylic acids such as those in sodium polyacrylate. Using a heterogeneous sulfonic acid monomer as a constituent weight body,
Furthermore, among the various conventionally known sulfonic acid monomers, it is particularly characterized by having sodium styrene sulfonate as an essential component for the reasons described below, and its copolymerization ratio is also extremely unique. It has the following. Examples of α,β unsaturated monocarboxylic acids that can constitute the copolymer in the dispersant of the present invention include acrylic acid, methacrylic acid, crotonic acid, etc.; examples of α,β unsaturated dicarboxylic acids include itaconic acid. , fumaric acid, maleic acid, etc., but other generally known acids can also be used. The copolymerization ratio of these carboxylic acid monomers is
If the total amount of both is 100 parts, the α,β unsaturated monocarboxylic acid should be 35 to 95 parts and the α,β unsaturated dicarboxylic acid should be 5 to 65 parts. The reason is α, β
When the amount of unsaturated monocarboxylic acid is less than 35 parts (or when the amount of α, β unsaturated dicarboxylic acid exceeds 65 parts), the ability to reduce the viscosity of the pigment dispersion system is poor, and a large amount of dispersant is used, while α, β This is because if the amount of unsaturated monocarboxylic acid exceeds 95 parts (or if the amount of α,β unsaturated dicarboxylic acid is less than 5 parts), problems such as poor stability of the pigment dispersion over time will occur. The dispersant of the present invention requires the presence of a sodium styrene sulfonate unit in addition to the α,β unsaturated mono- and dicarboxylic acids, but the sodium styrene sulfonate may contain other existing sulfonic acid monomers, such as Unlike vinyl sulfonic acid, methallyl sulfonic acid, etc., it has good polymerization (reactivity) properties due to the inducing effect of the sulfonic group at the para position, and therefore has a low content of unpolymerized substances such as other sulfonic acid monomers. Not only does it eliminate the lack of dispersibility caused by a large amount of polycarbonate, it also increases the copolymerization reactivity of α,β-unsaturated dicarboxylic acids, which are generally considered to have poor polymerization reactivity. In order to exhibit these excellent properties, the α,β unsaturated dicarboxylic acid is used to further improve the stability over time of the pigment dispersion system, which is the intended use of the α,β unsaturated dicarboxylic acid. Furthermore, the dispersant of the present invention does not have the hydrolyzability found in other sulfonic acid monomers, such as acrylamide methylpropane sulfonic acid, and therefore, compared to the case where these are used, the dispersant of the present invention improves the thermal stability of the pigment dispersion system. is excellent. The copolymerization ratio of sodium styrene sulfonate is
The copolymerization ratio needs to be 0.5 to 180 parts per 100 parts of the total of the α,β unsaturated monocarboxylic acid and the α,β unsaturated dicarboxylic acid, and the more preferable copolymerization ratio is 2 to 180 parts. If the copolymerization ratio is less than 0.5 parts or exceeds 180 parts, the reactivity of the α,β unsaturated dicarboxylic acid and the pigment dispersion may deteriorate over time.
The effect on thermal stability imparting, viscosity lowering ability, etc. is insufficient. As described above, the dispersant of the present invention is a salt of a copolymer of monomers consisting of α,β unsaturated monocarboxylic acid/α,β unsaturated dicarboxylic acid/sodium styrene sulfonate and an ammonium and/or metal-containing compound. Among metal-containing compounds, representative examples of alkali metal-containing compounds include hydroxides of generally known alkali metals such as sodium, potassium, and lithium. Other metal-containing compounds are compounds containing metals selected from calcium, aluminum, zinc, and magnesium (hereinafter referred to as specific metal compounds), and specifically include oxides of these metals, water It is used in the form of oxides, halides, carboxylates, oxyacids, etc. Particularly representative and specific examples thereof include calcium acetate, magnesium acetate, zinc acetate, aluminum acetate, calcium chloride, aluminum hydroxide, zinc lactate,
Examples include zinc tartrate, 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 unsaturated monocarboxylic acid, α, β unsaturated dicarboxylic acid) up to 70
It is desirable to react up to 100% of the total amount. If the amount of the specific metal compound exceeds 70 parts, the stability as a dispersant may be poor, or the dispersibility may not be significantly improved, 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 not only the salts with the contained compounds and/or ammonia, but also the salts when these are used in combination with specific metal compounds, 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. Here, an example of a method for obtaining the dispersant of the present invention is as follows. First, the copolymer component in the dispersant can be easily produced by a commonly known method. For example, α,β unsaturated monocarboxylic acid/α,β
A monomer consisting of unsaturated dicarboxylic acid/sodium styrene sulfonate is mixed with a common polymerization initiator such as persulfate or azobisisobutyronitrile, for example, about 0.1 to 10% by weight based on the monomer. Polymerization is performed in a solvent such as water or alcohol at approximately 50 to 150°C for about 1 to 10 hours, and if necessary, part or all of the solvent is distilled off to achieve a predetermined concentration. A copolymer is obtained. Polymerization rate is 90%
It is preferably 95% or more, and more preferably 95% or more. Further, as described above, an aqueous solution of an alkali metal-containing compound such as caustic soda and/or ammonia is added to the above-obtained aqueous polymer solution to neutralize a predetermined amount of unsaturated carboxylic acid units in the copolymer. By adjusting the pH, a salt of the copolymer and an alkali metal-containing compound and/or ammonia can be easily obtained. The reaction between the copolymer and the alkali metal-containing compound and/or ammonia is generally carried out after the copolymer is formed as described above.
This is also possible by a method in which β-unsaturated carboxylic acids (monocarboxylic acids and/or dicarboxylic acids) are 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 salt of the copolymer and an alkali metal-containing compound and/or ammonia, and reacting the same. Adding a mixed solution 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,
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 pigments 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. However, in the case of the copolymer salt in the present invention, the performance is not significantly affected by the 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 solution 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 exhibits excellent dispersibility that cannot be obtained with conventional dispersants even when used in a smaller amount, making it possible to disperse pigments with higher solid content concentrations. , and exhibits an excellent effect on the stability of the dispersion. 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 The specified water and dispersant shown in Table 1 were added to heavy calcium carbonate having a specific surface area of about 20,000 (cm ² /g), and the mixture was stirred for 15 minutes using a kneader. The viscosity of the dispersion slurry was measured immediately and after 5 days to examine its stability over time, and the results are shown in Table 1.
As seen in the results, the heavy calcium carbonate slurry prepared using samples Nos. 1 to 5 of Example 1 as a dispersant was clearly used in a smaller amount than the slurry using the sample of Comparative Example 1 as a dispersant. It exhibited low viscosity and also had excellent viscosity stability over time. 【table】

Claims (1)

[Claims] 1 35 to 95 parts by weight of α,β unsaturated monocarboxylic acid and 5 to 65 parts by weight of α,β unsaturated dicarboxylic acid (the total amount of both is 100 parts by weight), and the total of these
Sodium styrene sulfonate 0.5 to 100 parts by weight
A salt of a copolymer consisting of 180 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 an aluminum-containing compound A dispersant for pigments for coated paper, comprising a salt of at least one compound selected from the following and the alkali compound.