JPH0118956B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a thickener that also imparts excellent water retention to a material to be thickened. More specifically, a monomer containing a high concentration of methacrylic acid and having two or more polymerizable double bonds is added to the polymerizable double bond of the monomer for one carboxyl group in all monomers. A monomer mixture containing a specific amount of The present invention relates to a method for producing a thickener that prevents the formation of "floating water". Water-soluble polymers, such as sodium (meth)acrylate, acrylamide homopolymers and copolymers, polyethylene oxide, and polyvinyl alcohol, are supplied as powders or aqueous solutions, and can be used as thickeners for emulsions and aqueous dispersions. It is widely prized as Each thickener is selected and used depending on the desired fluidity and spinnability. The biggest drawback of these water-soluble polymer thickeners is that the obtained thickeners do not have sufficient water-retention properties, and during storage, "floating water" occurs in the upper layer.
This phenomenon is especially true for clay, calcium carbonate,
This is often observed in emulsions, latexes (hereinafter referred to as compounds), and paints containing inorganic fillers such as aluminum hydroxide, and is a major problem, but no solution has been found. Also, in Japanese Patent Publication No. 34-992, thickeners (thickeners)
as a copolymer of 25 to 50% methacrylic acid and 75 to 50% of at least one neutral comonomer, the copolymer containing at least 10% of acrylic esters of lower alcohols and an emulsifier. describes aqueous dispersions of water-insoluble emulsifying copolymers dispersed by the method of the present invention, and also states that said copolymers can incorporate 0.1 to 0.8% of crosslinking agent. However, the concentration of methacrylic acid in this composition is
It is low at less than 50%, and although it can be used as a thickener, the resulting thickened product does not have sufficient water retention. Furthermore, there is a cross-linked emulsion type thickener containing a high concentration of methacrylic acid as a commercial product, but similar products that have been neutralized with alkali have no thickening effect as shown in Comparative Examples 4 and 5. It is low and has poor water retention. The same applies when used in emulsion. As a result of extensive research into thickeners for obtaining thickeners that do not produce "floating water" and have excellent water retention, the inventors of the present invention found that they contain thickeners with high concentrations of methacrylic acid.
The present invention was completed by discovering that the object can be achieved with a thickener made of a partially three-dimensional emulsion or an aqueous solution of its alkali neutralized salt. That is, the present invention uses 53 to 75% by weight of methacrylic acid, 25 to 47% by weight of alkyl acrylate having an alkyl group having 1 to 4 carbon atoms, and 1 to 4 carbon atoms, based on the total amount of monovinyl monomers. A monomer containing 0 to 20% by weight of a monomer selected from alkyl methacrylate having ~4 alkyl groups and styrene and having two or more polymerizable double bonds is added to the polymerizable double bond. It is characterized by emulsion polymerization of a monomer mixture containing a bonding ratio of 0.001 to 0.005 per carboxyl group in all monomers, or by further neutralizing with alkali after emulsion polymerization. This is a method for producing a thickener with excellent water retention. One of the characteristics of the present invention is that it contains a high concentration of carboxyl groups, and methacrylic acid is used for this purpose. Other unsaturated carboxylic acids, such as acrylic acid, are highly water-soluble and it is impossible to introduce carboxyl groups in high concentrations in emulsion polymerization. Furthermore, maleic acid, itaconic acid, crotonic acid, etc. have low copolymerizability, and it is difficult to achieve the high degree of polymerization required as a thickener. It is necessary for the purpose of the present invention to contain methacrylic acid in an amount of 53 to 75% based on the total amount of monovinyl monomers, and if it is less than 53%, water retention is poor (Comparative Examples 1, 7, 8 and 9) 75%
If it exceeds this amount, the hydrophilicity of the monomer mixture increases and stable emulsion polymerization cannot be carried out efficiently. Particularly preferred copolymerization ratio of methacrylic acid is 55 to 70%
It is. Copolymerized with methacrylic acid, having 1 to 4 carbon atoms
Examples of alkyl acrylates having 2 alkyl groups include methyl acrylate, ethyl acrylate, n-butyl acrylate, and iso-butyl acrylate, and the amount used is 25 to 47% by weight based on the total amount of monovinyl monomers. %. If it is less than 25% by weight, it is difficult to carry out stable emulsion polymerization, while if it exceeds 47% by weight, the amount of methacrylic acid used will be relatively small and the resulting thickener will have poor water retention. Furthermore, in the present invention, a monomer selected from alkyl methacrylates having an alkyl group having 1 to 4 carbon atoms and styrene is contained in an amount of 0 to 20% by weight based on the total amount of monovinyl monomers. May be used within. Furthermore, unsaturated mono- and dicarboxylic acids such as acrylic acid, maleic acid, and itaconic acid can also be used as copolymerization components within the range that does not impair the stability of the monomer mixture. In these monomer mixtures, even if a carboxyl group is simply contained at a high concentration, a thickening agent with excellent water retention cannot be obtained, and it is necessary to make the mixture three-dimensional with an appropriate molecular structure. Monomers having two or more polymerizable double bonds are copolymerized in order to partially make the polymer three-dimensional within or between the molecules. By setting the copolymerization ratio of the monomer having two or more polymerizable double bonds and methacrylic acid, etc. having a carboxyl group within an extremely limited range, optimal three-dimensionalization according to the purpose is achieved. It can be done. That is, the range is
The ratio of polymerizable double bonds in monomers having two or more polymerizable double bonds to one carboxyl group in all monomers is 0.001 to 0.005. If the copolymerization ratio is less than 0.001, the water retention property will not be improved much.
If it exceeds 0.005, the three-dimensional density will be too high and the thickening effect will be low when used in emulsion, and even if neutralized with alkali, the micelles will only swell.
It is unsuitable because it does not form a completely homogeneous aqueous solution and has low viscosity. A particularly preferable copolymerization ratio is
It is 0.0015-0.003. Although various monomers having two or more polymerizable double bonds can be used, specific examples are shown below. The difunctional ones include allyl acrylate, 1,3-butylene diacrylate, diallyl phthalate, ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, triethylene glycol di(meth)acrylate, etc. Functional ones include trimethylolethane tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, and tetrafunctional ones such as tetraallyloxyethane and pentaerythritol tetra(meth)acrylate. Considering economical aspects, allyl acrylate, diallyl phthalate, and ethylene glycol di(meth)acrylate are particularly preferred. Polymerization of these monomer mixtures is carried out by emulsion polymerization. In the aqueous solution polymerization method, there are few water-soluble monomers having two or more polymerizable double bonds;
Further, even if the copolymerization ratio of the present invention is used for polymerization, the desired thickener cannot be obtained because three-dimensionalization does not occur at all or gelation occurs during the polymerization. Emulsion polymerization can be carried out by any of the monomer batch charging method, divided charging method, and continuous charging method by using conventional techniques. Any monomer charging method can be used up to about 55% methacrylic acid, but if the amount is higher than that, it is preferable to adopt the batch charging method in order to allow the polymerization to proceed stably without forming coagulum. As the emulsifier used to emulsify the monomer mixture, either an anionic emulsifier or a nonionic emulsifier can be used. Examples of anionic emulsifiers include higher fatty acid salts, alkyl sulfate ester salts, alkylbenzene sulfonates, alkyl phosphate ester salts, and polyoxyethylene alkyl sulfate ester salts. Nonionic emulsifiers include polyoxyethylene alkyl ether and polyoxyethylene alkyl ester salts. Examples include phenol ether and polyoxyethylene fatty acid ester, which can be used alone or in combination. Among these, it is most preferable to use polyoxyethylene alkyl sulfate. Polymerization initiators include persulfates such as potassium persulfate, sodium persulfate, and ammonium persulfate, peroxides such as t-butyl hydroperoxide and hydrogen peroxide, and redox catalysts using peroxides/reducing agents.
For example, common radical polymerization initiators such as potassium persulfate/sodium sulfite and hydrogen peroxide/ferrous salt can be used. By carrying out emulsion polymerization under such conditions, the desired emulsion can be obtained. The desired aqueous thickener can also be obtained by neutralizing this emulsion with an alkali. Alkali include sodium hydroxide, potassium hydroxide, sodium carbonate, ammonia, n
-Propylamine, dimethylamine, monoethanolamine, diethanolamine, morpholine, etc., can all be used as long as they can be made water-soluble by neutralizing carboxyl groups. From the viewpoint of odor and economy, sodium hydroxide and ammonia are generally preferred. The degree of neutralization is not particularly limited to the pH range as long as it can be water-solubilized, but a pH of 7 to 11 (measured at 25°C) is preferred from the viewpoint of storage stability of the obtained aqueous thickener. PH
When the pH is low, the thickener tends to gel over time, and the PH
If is too high, the thickening property decreases, which is not preferable. In the case of an aqueous alkali-neutralized salt solution, the thickener obtained in this way has a viscosity (hereinafter referred to as BV
) 5000 to 50000 cps (measured using a BM type viscometer at 25°C and rotor No. 4 at 12 rpm). In order to make the aqueous alkali neutralized salt solution have such properties, polymerization conditions are usually set to suppress the degree of polymerization. Regarding the thickener of the present invention, showing the quantitative relationship:
The outline of the manufacturing method is shown below. The monomer mixture is charged in whole or in part at the beginning of polymerization to start polymerization, and the remaining monomers are added in portions or continuously. The monomer concentration for the whole system is 20
~50%. Emulsifier: 0.5 to total monomer
Preferably, it is used in a proportion of ~6%. The polymerization temperature is usually 50 to 100°C, preferably 50 to 70°C for redox systems, and 80 to 90°C for persulfates. The amount added is about 0.1 to 1% based on the total monomers. After the completion of polymerization, the emulsion is neutralized with an aqueous alkaline solution to make it water-solubilized at a temperature of about 40 to 60° C., which is advantageous for quick neutralization and uniformity. The thickener obtained in this way has high viscosity and excellent water retention, and especially when used in compounds and paints, it prevents the formation of so-called "floating water," and its industrial value is said to be extremely large. I can say that. EXAMPLES The present invention will be explained in more detail by giving Examples and Comparative Examples below. In addition, "part" in each example
and "%" are based on weight. In addition, the emulsion polymerization method (formulation, A and B) used in each example, the manufacturing method of an aqueous alkali neutralized salt solution (formulation A and
and B), compound preparation method (SBR compound and rosin compound) and evaluation of water retention properties were conducted using the following methods. 1 Emulsion polymerization method Prescription A Monomer mixture 500g, polyoxyethylene alkyl phenol ether sulfate sodium 15
g and 500 g of water were placed in a beaker and a preliminary emulsion was prepared using a homomixer. 965 g of water in a glass flask equipped with a stirrer;
100g of preliminary emulsion was added and the temperature was raised to 85°C.
After adjusting the temperature, 10 g of a 5% aqueous solution of ammonium persulfate was added to initiate polymerization. Subsequently, 915 g of the remaining preliminary emulsion and 40 g of a 5% aqueous solution of ammonium persulfate were continuously added dropwise over 2 hours. The internal temperature was maintained at 85±1°C during the polymerization. 30 minutes and 1 hour after the completion of the dropwise addition, 5 g each of 5% aqueous ammonium persulfate solution was added, and the mixture was aged for a total of 2 hours to consume unreacted monomers. This emulsion polymer was subjected to neutralization. Recipe B: 1435 ml of water in a glass flask equipped with a stirrer.
g, polyoxyethylene alkyl phenol ether sodium sulfate 15 g, monomer mixture 500
g and the temperature was adjusted to 65°C. After controlling the temperature, add 5% aqueous solutions of ammonium persulfate and sodium sulfite to each
20g was added. After the polymerization starts, when the internal temperature reaches the maximum temperature,
The flask was cooled and the internal temperature was again brought to 65°C. The same amount of polymerization initiator was added again, and the mixture was aged for 1 hour to consume unreacted monomers. This emulsion polymer was subjected to neutralization. 2. Method for producing aqueous alkali neutralized salt solution Prescription A (sodium salt) Put a predetermined amount of emulsion polymer and an amount of water calculated in advance to give a predetermined product concentration into a flask,
The temperature is raised to 50±5°C while stirring. After adjusting the temperature, add a 20% aqueous sodium hydroxide solution equivalent to neutralization and stir for 1 hour. After 1 hour, measure the pH at 25°C. If the pH is outside the range of 8 to 10, use a small amount of emulsion polymer or 20% aqueous sodium hydroxide solution to adjust the pH to 8 to 10.
Adjust to. The contents were filtered through a 100 mesh cloth to obtain the desired aqueous thickener. Prescription B (Ammonium salt) The same procedure as Prescription A (sodium salt) was carried out except that 25% aqueous ammonia was used in place of the 20% aqueous sodium hydroxide solution. 3 Compound preparation method SBR compound SBR (product name JSR0593 manufactured by Japan Synthetic Rubber Co., Ltd.)
100g, 3% sodium pyrophosphate aqueous solution 10g, water
35g was placed in a beaker and stirred. Next, 175 g of heavy calcium carbonate was added and stirred for 5 minutes. (The solid content of this dispersion is 70%.) Finally, an aqueous thickener is added and the BV15000±
500cps (using a BM type viscometer at 25℃)
No. 4 rotor, measured at 12 rpm). Rosin compound Rosin emulsion (product name manufactured by Arakawa Chemical Co., Ltd.)
SE-50) 150g, acrylic-vinyl acetate emulsion (manufactured by Hoechst Synthesis Co., Ltd., trade name: Movinyl)
771H) and 35 g of water were placed in a beaker and stirred. Next, 50 g of heavy calcium carbonate was added and stirred for 5 minutes. (The solid content of this dispersion is 38%.) Finally, an aqueous thickener is added to achieve a BV5000±
The viscosity was increased to 500 PS (measurement method was the same as above). 4. Water retention evaluation: Place the compound in a 5cm diameter polyethylene container with a lid.
Pour 150 cc into the bottle, seal it tightly, and store it in a 40°C constant temperature bath. After 2 months, the upper “floating water” layer (mm) and BV
was measured. Examples 1 to 9 Table 1 shows examples of aqueous thickeners made of aqueous solutions of alkali neutralized salts of emulsions according to the present invention. There was no occurrence of "floating water" at all, showing excellent water retention. Comparative Examples 1 to 8 Table 2 shows examples of aqueous thickeners made of aqueous solutions of alkali neutralized salts of emulsions not according to the present invention. After two months at 40°C, the obtained compounds all had floating water in the upper layer, and had poor water retention properties.

[Table] Ntaerythritol tetraacrylate
2) Thickener solid content/total amount of compound

[Table] Examples 10, 11 and Comparative Example 9 Examples of emulsion type thickeners of the present invention (Example
10, 11) and examples of emulsion type thickeners outside the scope of the present invention (Comparative Example 9) are shown in Table 3. table-
As can be seen from 3, the emulsion type thickener of the present invention has high thickening properties and excellent water retention, whereas the emulsion type thickener outside the scope of the present invention has a 40%
After storage at ℃ for 2 months, floating water was formed, indicating poor water retention.

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Claims (1)

[Claims] 1 Based on the total amount of monovinyl monomers, 53 to 75% by weight of methacrylic acid, 25 to 47% by weight of alkyl acrylate having an alkyl group having 1 to 4 carbon atoms, and 25 to 47% by weight of alkyl acrylate having an alkyl group having 1 to 4 carbon atoms. A monomer containing 0 to 20% by weight of a monomer selected from alkyl methacrylates having an alkyl group and styrene and having two or more polymerizable double bonds, the proportion of the polymerizable double bonds being Carboxyl group 1 in all monomers
1. A method for producing a thickener with excellent water retention, which comprises emulsion polymerizing a monomer mixture containing a monomer mixture in an amount of 0.001 to 0.005, or further neutralizing with alkali after emulsion polymerization.