JPH0134272B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a dispersant for Sachin White. More specifically, the present invention relates to a dispersant that provides a satin white aqueous dispersion with excellent dispersibility and stability and low viscosity even at high concentrations. Sachin white is a white pigment in the form of needle-like crystals, and is generally obtained by adding and reacting an aqueous solution of aluminum sulfate to a suspension of calcium hydroxide.
It is _calcium sulfomate represented by the chemical formula _{Al2O3.3CaSO4.31 ~ 32H2O} . Usually 70~
Supplied as a hard cake-like sachin white paste containing 75% water by weight, it has been found to be one of the most difficult pigments to disperse. Traditionally, Sachin White has been used as a distinctive coating pigment along with kaolin clay, calcium carbonate, etc. For example, coated paper obtained using Sachin White has excellent whiteness, gloss, printability, etc. However, in this case, it is strongly required that the pigment particles have extremely fine particle diameters and excellent dispersibility. In particular, when coating at high speeds like the current one, if the dispersibility of the pigment is poor, the apparent viscosity of the coating solution will increase and the fluidity will deteriorate, making it difficult to achieve good coating. Physical properties deteriorate. Sodium pyrophosphate, sodium hexametaphosphate, sodium polyacrylate, and the like are conventionally known as dispersants for Sachin White. However, these dispersants require a large amount to be added in order to give the Sachin White aqueous dispersion sufficient fluidity, and they also have drawbacks such as extremely poor fluidity at high shear conditions. In order to overcome these drawbacks, a method using an inorganic fluorine compound as a dispersant has been proposed (Japanese Patent Application Laid-Open No. 117825/1982).
This is not preferable because a large amount of an inorganic fluorine compound, which is a readily water-soluble salt, is added. In addition, as dispersants, a copolymer of acrylic acid and itaconic acid (Japanese Patent Publication No. 47-33055) and a saponified product of polyacrylic acid ester (Japanese Patent Publication No. 47-45411) have been disclosed. However, all of these methods only demonstrate the dispersion effect at a low concentration of Sachin White of 20%. In view of the current situation, the present inventors have conducted extensive research and have discovered a water-soluble polymer that has excellent effects as a dispersant for Sachin White and solves the above problems. The invention was completed. Therefore, an object of the present invention is to provide a dispersant that is suitable for paper coating and that can easily produce a sachin white aqueous dispersion with high concentration, low viscosity, and excellent dispersion stability by adding a small amount. It is something to do. That is, the dispersant for Sachin White of the present invention has the general formula: (However, in the formula, m and n are 0 or positive integers, and m+n
= 1 to 100, and (-C ₂ H ₄ O)- unit and (-C ₃ H ₆ O)-
Units may be combined in any order. )
Polyalkylene glycol monoallyl ether () represented by, and general formula (However, in the formula, R ₁ represents hydrogen or a methyl group,
X represents hydrogen, a monovalent metal, a divalent metal, an ammonium group or an organic amine group. ) (meta)
Copolymerizing the acrylic acid monomer () using a polymerization initiator at a ratio such that () is 0.1% by weight or more and less than 5.0% by weight with respect to the total of () and (),
It consists of a water-soluble polymer obtained by further neutralizing with an alkaline substance if necessary. The polyalkylene glycol monoallyl ether () used in the present invention is represented by the above general formula, and has an added mole number m+n of 1 to 100 of alkylene oxide. Number of moles added m
If +n is 0, the resulting copolymer will not have sufficient performance as a dispersant for Sachin White, and if it exceeds 100, the copolymerization reactivity of such polyalkylene glycol monoallyl ether will be low, and the present invention A polymer that is effective as a dispersant cannot be obtained. Polyalkylene glycol monoallyl ether () is produced by converting ethylene oxide and/or allyl alcohol into allyl alcohol using an alkali such as KOH or NaOH as a catalyst.
Alternatively, it can be synthesized by a known method of directly adding propylene oxide. The (meth)acrylic acid monomer () is represented by the above general formula, and specifically includes acrylic acid, methacrylic acid, and their monovalent metal salts,
Mention may be made of divalent metal salts, ammonium salts and organic amine salts. and one or two of these
More than one species can be used. To produce the water-soluble polymer used as the dispersant of the present invention by copolymerizing polyalkylene glycol monoallyl ether () and (meth)acrylic acid monomer () using a polymerization initiator, a solvent This can be carried out by a method such as polymerization in a vacuum or bulk polymerization. Polymerization in a solvent can be carried out either batchwise or continuously, and the solvents used in this case include water,
Examples include lower alcohols, mixed solvents of water and lower alcohols, aromatic hydrocarbons, aliphatic hydrocarbons, ketone compounds, and ethyl acetate. Depending on the solvent used, various water-soluble polymerization initiators, peroxides,
Hydroperoxides, combinations of these with polymerization accelerators, azo compounds, etc. are used. The polymerization temperature is appropriately determined depending on the solvent and polymerization initiator used, but it is usually carried out within the range of 0 to 120°C. When water is used as a solvent, sodium hydrogen sulfite-oxygen may be used as a polymerization catalyst. In this case, the polymerization is carried out by blowing oxygen gas or a mixed gas of oxygen and an inert gas into the solvent while adding sodium hydrogen sulfite to the solvent containing the raw material monomer.
This can be carried out by proceeding the polymerization reaction within a temperature range of ~80°C. Bulk polymerization uses peroxide as a polymerization initiator,
It is carried out using hydroperoxide or an azo compound, etc., within a temperature range of 50 to 150°C. When producing a water-soluble polymer in this way, the charging ratio of polyalkylene glycol monoallyl ether () and (meth)acrylic acid monomer (), the amount of polymerization initiator used, the polymerization temperature,
In the case of polymerization in a solvent, the molecular weight of the resulting water-soluble polymer can be adjusted as appropriate by adjusting the type and amount of the solvent. The molecular weight of the water-soluble polymer used as the dispersant for Sachin White of the present invention is particularly effective in the range of 500 to 100,000, preferably 1,000 to 20,000. The water-soluble polymer thus obtained can be used as it is as the dispersant for Sachin White of the present invention, but it may be further neutralized with an alkaline substance if necessary. Preferred examples of such alkaline substances include hydroxides, chlorides, and carbonates of monovalent metals and divalent metals, ammonia, and organic amines. In order to obtain an aqueous dispersion of Sachin White using the dispersant for Sachin White of the present invention, Sachin White may be dispersed in water in the presence of the dispersant. The amount of the dispersant used is 0.1 to 5 parts by weight, preferably 0.5 to 3 parts by weight, based on 100 parts by weight of Sachin White. Examples of methods for dispersing Sachin White include adding Sachin White Paste to an aqueous solution containing a dispersant and stirring and mixing, or adding a dispersant and water to Sachin White Paste and stirring and mixing. By these methods, a sachin white aqueous dispersion can be easily obtained with good workability. As a method for stirring and mixing, commonly used stirring devices such as a ribbon mixer, kneader, and high-speed disper can be used. However, the scope of the present invention is not limited by such methods of adding and stirring the dispersant and Sachin White. The Sachin White aqueous dispersion thus obtained using the dispersant of the present invention exhibits low viscosity at a high solids concentration of 25% by weight with a small amount added compared to conventional dispersants. In addition, it has excellent dispersion stability and is extremely easy to handle. The present invention will be explained in more detail below using Examples and Comparative Examples, but it goes without saying that the present invention is not limited to these Examples. Furthermore, parts and percentages in the examples represent parts by weight and percentages by weight unless otherwise specified. In addition, the viscosity of the dispersant aqueous solution and the viscosity of the Sachin White aqueous dispersion in the examples were all measured using a Bismethron viscometer manufactured by Seiki Kogyo Research Institute at 25°C.
Measurement was performed at 60 rpm. Furthermore, the molecular weight was measured using gel permation chromatography (Model 244, manufactured by Waters). Example 1 Polyethylene glycol monoallyl ether (containing an average of 5 ethylene oxide units per molecule) was placed in a glass reaction vessel equipped with a thermometer, a stirrer, a dropping funnel, a gas inlet tube, and a reflux condenser.
7.5 parts and 389.9 parts of water were charged, and the inside of the reaction vessel was purged with nitrogen while stirring, and heated to 95°C in a nitrogen atmosphere. Then, 38% sodium acrylate aqueous solution
506.6 parts and 80 parts of a 5% ammonium persulfate aqueous solution were each added over 120 minutes. After addition, further
16 parts of 5% ammonium persulfate aqueous solution was added over 20 minutes. 120 minutes after completion of addition of monomer aqueous solution
The temperature was maintained at 95°C to complete the polymerization reaction, and a water-soluble polymer (1) was obtained. A 40% aqueous solution of this water-soluble polymer (1) obtained by concentrating under reduced pressure has a pH of 7.3 and a viscosity of
It was 267cps. Further, the molecular weight of this water-soluble polymer (1) was 4,100. Using the above water-soluble polymer (1) as a dispersant, the dispersibility for Sachin White (manufactured by Shiraishi Kogyo Co., Ltd.) was evaluated according to the following procedure. i.e. deionized water,
Sachin White and an aqueous solution of the water-soluble polymer (1) in the amount shown in Table 1 were placed in a stainless steel beaker with an internal volume of 1, and stirred for 20 minutes using a Labo Dice Bar (manufactured by Tokushu Kika Kogyo Co., Ltd., Model MR-L). 25%
A sachin white slurry was prepared and the viscosity of each slurry was measured. The results were as shown in Table 1. As shown in Table 1, the dispersant of the present invention has excellent dispersion ability even when added in a small amount compared to the low molecular weight sodium polyacrylate (molecular weight 5000) conventionally used in this field. There is. Example 2 In the same reaction vessel as in Example 1, 9.8 parts of polyethylene glycol monoallyl ether (containing an average of 10 ethylene oxide units per molecule) and water were added.
After charging 441.7 parts, the inside of the reaction vessel was purged with nitrogen while stirring, and heated to the boiling point in a nitrogen atmosphere. after that
500.5 parts of 38% sodium acrylate aqueous solution and 5%
40 parts of ammonium persulfate aqueous solution and 120 parts each
After the addition was complete, 8 parts of a 5% aqueous ammonium persulfate solution was added over 20 minutes. After the addition of the monomers was completed, the temperature was maintained at the boiling point for 120 minutes to complete the polymerization reaction, yielding a water-soluble polymer (2). A 40% aqueous solution of this water-soluble polymer (2) has a pH of 7.5 and a viscosity of
It was 348cps. Also, the molecular weight of the water-soluble polymer (2) is
It was 4700. The dispersibility of Sachin White was evaluated in the same manner as in Example 1 using the above water-soluble polymer (2) as a dispersant. The results were as shown in Table 1. Example 3 In the same reaction vessel as in Example 1, 1 part of polypropylene glycol monoallyl ether (containing on average 2 propylene oxide units per molecule),
Charge 495.5 parts of an azeotropic composition of isopropyl alcohol (hereinafter referred to as IPA) and water (IPA/water = 87.4/12.6 (weight ratio)), replace the inside of the reaction vessel with nitrogen while stirring, and heat to the boiling point. did. Then 199 parts of acrylic acid, 6 parts of benzoyl peroxide and IPA
- A mixture of 298.5 parts of water azeotrope was added in 120 minutes. After the addition was complete, the temperature was maintained at the boiling point for 120 minutes to complete the polymerization reaction. Thereafter, neutralization was performed with 276.2 parts of a 40% caustic soda aqueous solution, and IPA was distilled off to obtain a water-soluble polymer (3). This water-soluble polymer (3)
The 45% aqueous solution had a pH of 8.5 and a viscosity of 830 cps.
Further, the molecular weight of the water-soluble polymer (3) was 2,800. The dispersibility of Sachin White was evaluated in the same manner as in Example 1 using the above water-soluble polymer (3) as a dispersant. The results were as shown in Table 1. Example 4 285 parts of isopropyl alcohol (hereinafter abbreviated as IPA) was charged into the same reaction vessel as in Example 1, the inside of the reaction vessel was replaced with nitrogen while stirring, and the mixture was heated to the boiling point in a nitrogen atmosphere. Thereafter, a mixture of 4.5 parts of polyalkylene glycol monoallyl ether (containing an average of 18 ethylene oxide units and 2 propylene oxide units per molecule), 295.5 parts of acrylic acid, 3 parts of benzoyl peroxide, and 300 parts of IPA was added over 120 minutes. After the addition was completed, 0.6 parts of benzoyl peroxide dispersed in 11.4 parts of IPA was added in two portions every 30 minutes. After the addition of the monomer mixture was completed, the temperature was maintained at the boiling point for 120 minutes to complete the polymerization reaction. Thereafter, it was neutralized with 410.1 parts of a 40% caustic soda aqueous solution. Next, IPA was distilled off to obtain a water-soluble polymer (4). A 45% aqueous solution of this water-soluble polymer (4) had a pH of 8.5 and a viscosity of 1920 cps. Furthermore, the molecular weight of the water-soluble polymer (4) was 3,000. The dispersibility of Sachin White was evaluated in the same manner as in Example 1 using the above water-soluble polymer (4) as a dispersant. The results were as shown in Table 1. Example 5 438.8 parts of water was charged into the same reaction vessel as in Example 1,
While stirring, the inside of the reaction vessel was purged with nitrogen and heated to 95°C. Thereafter, 63 parts of a 10% aqueous solution of polyethylene glycol monoallyl ether (containing an average of 30 ethylene oxide units per molecule) and 38% of partially neutralized sodium acrylate (80 mol% neutralization) were added.
378.2 parts of an aqueous solution and 120 parts of a 5% ammonium persulfate aqueous solution were each added over 120 minutes. After the addition was complete, the temperature was maintained at 95° C. for 120 minutes to complete the polymerization reaction. Thereafter, it was completely neutralized with a caustic soda aqueous solution to obtain a water-soluble polymer (5). A 40% aqueous solution of this water-soluble polymer (5) had a pH of 9.0 and a viscosity of 403 cps. Further, the molecular weight of the water-soluble polymer (5) was 4,800. The dispersibility of Sachin White was evaluated in the same manner as in Example 1 using the above water-soluble polymer (5) as a dispersant. The results were as shown in Table 1. Comparative Example 1 Sachin white slurry was prepared in the same manner as in Example 1 except that a commercially available low molecular weight sodium polyacrylate (molecular weight 5000) was used as a dispersant, and the viscosity was measured. The results were as shown in Table 1.

[Table] As shown in Table 1, when the dispersant of the present invention is used, excellent dispersion ability is exhibited even when a small amount is used.
Also, compared to the conventionally used low molecular weight sodium polyacrylate, a sachin white slurry with a lower viscosity can be obtained by adding a small amount.

Claims (1)

[Claims] 1. General formula (However, in the formula, m and n are 0 or positive integers, and m+n=
1 to 100, and the (-C ₂ H ₄ O)- and (-C ₃ H ₆ O)- units may be bonded in any order. )
Polyalkylene glycol monoallyl ether () represented by and the general formula (However, in the formula, R ₁ represents hydrogen or a methyl group,
X represents hydrogen, a monovalent metal, a divalent metal, an ammonium group or an organic amine group. ) (meta)
Copolymerizing the acrylic acid monomer () using a polymerization initiator at a ratio such that () is 0.1% by weight or more and less than 5.0% by weight with respect to the total of () and (),
A dispersant for Sachin White made of a water-soluble polymer obtained by further neutralizing with an alkaline substance if necessary.