JP2006057019A - Aqueous acrylic copolymer emulsion, redispersible acrylic copolymer emulsion powder and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aqueous acrylic copolymer emulsion of protective colloid-type having excellent polymerization stability and produced by scarcely using a modified polyvinyl alcohol and a chain transfer agent. <P>SOLUTION: The aqueous acrylic copolymer emulsion is produced by carrying out high-temperature redox emulsion polymerization of a polyvinyl alcohol having a saponification degree of ≥95 mol% and an average polymerization degree of 100-1,000 and a hydrophobic ethylenic unsaturated monomer having a water-solubility of ≤1.0 wt.% in an aqueous medium in the presence of a reducing agent at 75-90°C, adding a monomer component at least containing an acrylic monomer and carrying out emulsion polymerization of the components. The emulsion composition has excellent polymerization stability. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

Background of the Invention

The present invention relates to a protective colloid acrylic copolymer emulsion having excellent polymerization stability and a method for producing the same. The present invention also relates to a redispersible acrylic copolymer emulsion powder obtained by spray drying an acrylic copolymer emulsion.

BACKGROUND ART Conventionally, anionic or nonionic surfactants have been used as emulsifiers in the emulsion polymerization of hydrophobic monomers such as acrylic monomers and styrene monomers.
However, many aqueous emulsions produced using a surfactant have poor mechanical stability. In recent years, for the purpose of saving labor, pumping of an emulsion polymer or the like is becoming common. At this time, if the mechanical stability of the emulsion is poor, agglomerates may be generated to reduce the efficiency of pumping. Moreover, since the emulsion manufactured using surfactant generally has low viscosity, it is necessary to add a thickener except for some uses, and the handling is complicated. Furthermore, an emulsion produced using a surfactant has poor mixing stability with an electrolyte, and when added to a cementitious material, the fluidity of the cement composition may be reduced.

  Therefore, polyvinyl alcohol (hereinafter sometimes referred to as PVA) is used as a protective colloid (emulsifier) instead of a surfactant. For example, it is known that when PVA is used as a protective colloid in emulsion polymerization of vinyl acetate, an emulsion having excellent polymerization stability and excellent standing stability and mechanical stability can be obtained.

  However, when emulsion polymerization is performed on hydrophobic monomers such as acrylic monomers, when PVA is used as a protective colloid, the resulting emulsion has poor polymerization stability and it is difficult to obtain a good synthetic resin emulsion. It is.

  Therefore, it has been proposed to use modified PVA such as PVA containing a sulfone group or PVA introduced with a mercapto group at the end as PVA as a protective colloid for the purpose of improving the polymerization stability of the emulsion. Yes. Further, in the polymerization process, a method using a completely saponified PVA having a low degree of polymerization and a chain transfer agent (Japanese Patent Laid-Open No. 10-60055 (Patent Document 1)) and a method using a partially saponified PVA (Japanese Patent Laid-Open No. 2001). -220409 (patent document 2)) and the like have been proposed. However, for example, when a chain transfer agent is used to such an extent that the polymerization can proceed stably, the degree of polymerization of the acrylic polymer itself may be lowered, and the expected water resistance, durability, etc. may not be ensured. Therefore, even emulsions produced by these methods have room for further improvement in polymerization stability and storage stability.

On the other hand, many of the known synthetic resin emulsion powders that can be re-dispersed in water use a water-soluble polymer such as PVA as a protective colloid (emulsifier) because of the need to re-disperse. It is obtained by emulsion polymerization using a vinyl ester monomer (for example, JP-A-5-140325 (Patent Document 3), JP-A-5-179008 (Patent Document 4)).
Japanese Patent Laid-Open No. 10-60055 JP 2001-220409 A Japanese Patent Laid-Open No. 5-140325 Japanese Patent Laid-Open No. 5-179008

Summary of the Invention

The present inventors have now devised the emulsion production process to obtain a protective colloid-based aqueous acrylic copolymer emulsion having excellent polymerization stability without using almost any modified polyvinyl alcohol or chain transfer agent. Successful. Moreover, the redispersible acrylic copolymer emulsion powder was also able to be obtained by spray-drying the obtained emulsion. The present invention is based on these findings.
Therefore, an object of the present invention is to provide a protective colloid-based aqueous acrylic copolymer emulsion excellent in polymerization stability without using almost any modified polyvinyl alcohol or chain transfer agent.

  The aqueous acrylic copolymer emulsion composition according to the present invention has a water solubility of 1.0% by weight in polyvinyl alcohol (PVA) having a saponification degree of 95 mol% or more and an average polymerization degree of 100 to 1000 in an aqueous medium. The following hydrophobic ethylenically unsaturated monomer is subjected to high-temperature redox emulsion polymerization at 75 to 90 ° C. in the presence of a reducing agent, and then further added with a monomer component containing at least an acrylic monomer for emulsion polymerization. Can be obtained.

  The redispersible acrylic copolymer emulsion powder according to the present invention is obtained by spray-drying the aqueous acrylic copolymer emulsion composition according to the present invention.

  In addition, the method for producing an aqueous acrylic copolymer emulsion composition according to the present invention has a water solubility of 1.0% by weight in polyvinyl alcohol having a saponification degree of 95 mol% or more and an average polymerization degree of 100 to 1000 in an aqueous medium. % Of a hydrophobic ethylenically unsaturated monomer at a high temperature redox emulsion polymerization at 75 to 90 ° C. in the presence of a reducing agent, and further comprising at least an acrylic monomer. In addition, emulsion polymerization is included.

  The method for producing a redispersible acrylic copolymer emulsion powder according to the present invention comprises spray-drying an aqueous acrylic copolymer emulsion composition obtained by the production method.

  Furthermore, the inorganic hydraulic composition according to the present invention comprises the redispersible acrylic copolymer emulsion powder according to the present invention and an inorganic hydraulic material.

    The aqueous acrylic copolymer emulsion composition according to the present invention requires little or no use of modified polyvinyl alcohol or chain transfer agent in its production. That is, according to the present invention, since it is not necessary to use the modified PVA, it is easier to obtain the raw material than in the case of using the modified PVA as in the conventional case, and it is advantageous from the viewpoint of cost. It is. Further, chain transfer agents generally tend to lower the degree of polymerization of acrylic polymers, and it can be said that their use is undesirable in terms of various physical properties of acrylic synthetic resin emulsions. According to the present invention, since it is not necessary to use a chain transfer agent in the production of an emulsion, problems associated with the use of such a chain transfer agent can be avoided. The aqueous acrylic copolymer emulsion composition according to the present invention is excellent in polymerization stability.

Detailed description of the invention

Aqueous Acrylic Copolymer Emulsion Composition As described above, the aqueous acrylic copolymer emulsion composition according to the present invention contains a specific hydrophobic ethylenically unsaturated monomer as a reducing agent in a specific polyvinyl alcohol in an aqueous medium. After high-temperature redox emulsion polymerization at 75 to 90 ° C. in the presence, a monomer component containing at least an acrylic monomer is further added and emulsion polymerization can be performed. That is, the emulsion composition according to the present invention is a so-called acrylic synthetic resin emulsion.

(1) Polyvinyl alcohol In the present invention, as the emulsifier (or protective colloid) for emulsion polymerization, polyvinyl alcohol having a saponification degree and an average polymerization degree within specific ranges is used.
The saponification degree of polyvinyl alcohol in the present invention is 95 mol% or more, preferably 98 mol% or more. If the degree of saponification is less than 95%, the polymerization does not easily proceed stably, and gelation may fail to obtain a good emulsion.
In the present specification, the saponification degree can be measured and determined by a conventional method. For example, it can be determined according to the saponification degree calculation method described in JIS K6726.

The average degree of polymerization of the polyvinyl alcohol in the present invention is 100 to 1000, preferably 200 to 500. When the average degree of polymerization of PVA is less than 100, the protective colloid ability at the time of emulsion polymerization may not be sufficient, and the polymerization may not proceed stably. On the other hand, if the average degree of polymerization exceeds 1000, polymerization may not proceed stably and gelation may fail to obtain a good emulsion.
In the present specification, the average degree of polymerization can be measured and determined by a conventional method. For example, it can be determined according to the method for calculating the average degree of polymerization described in JIS K6726.

  In this invention, it is preferable that the usage-amount of polyvinyl alcohol is 3 to 15 weight% with respect to the total amount of monomers used for manufacture of an emulsion composition, More preferably, it is 5 to 10 weight%. If the amount of PVA used is less than 3% by weight, the amount of emulsifier during emulsion polymerization may be insufficient, resulting in poor polymerization stability. On the other hand, when the amount of PVA used is more than 15% by weight, the polymerization is difficult to proceed stably, and gelation may not be performed to obtain a good emulsion. Moreover, in this case, the water resistance in the application use may be lowered.

In the present invention, polyvinyl alcohol is usually made into an aqueous solution using an aqueous medium, and this is used in the process of emulsion polymerization. The amount of polyvinyl alcohol (in terms of non-volatile content) in this aqueous solution is not particularly limited, but is preferably 5 to 30% by weight from the viewpoint of ease of handling. When the amount of PVA in the aqueous solution is 5% by weight or less, the non-volatile content of the polymerized synthetic resin emulsion may be too low, and when it is higher than 30% by weight, the viscosity of the aqueous solution becomes high and the aging increases. It may become difficult to handle due to stickiness.
In this specification, the aqueous medium refers to water or an alcoholic solvent mainly composed of water, preferably water.

  In the present invention, an emulsion composition according to the present invention can be obtained without using a modified polyvinyl alcohol modified with a functional group as the polyvinyl alcohol to be used, but this denies the combined use of the modified polyvinyl alcohol. Not what you want. Therefore, in the present invention, if necessary, in addition to the specific polyvinyl alcohol described above, for example, polyvinyl alcohol modified with a functional group such as an acetoacetyl group, a mercapto group, a carboxyl group, a sulfonic acid group, or an alkoxysilyl group. May also be used in combination to obtain an emulsion composition.

(2) Hydrophobic ethylenically unsaturated monomer In the present invention, first, the above-described PVA is emulsion-polymerized with a hydrophobic ethylenically unsaturated monomer under conditions that facilitate graft polymerization. In the present invention, the hydrophobic ethylenically unsaturated monomer has a water solubility of 1.0% by weight or less. Such hydrophobic ethylenically unsaturated monomers are not particularly limited as long as they are well known to those skilled in the art, and include lauryl methacrylate, cyclohexyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, Examples include stearyl methacrylate, ethyl acetoacetate, 2-ethylhexyl methacrylate, tridecyl methacrylate, 2-ethylhexyl acrylate, and butyl acrylate.
According to a preferred embodiment of the present invention, the hydrophobic ethylenically unsaturated monomer is one or more selected from the group consisting of the above-mentioned examples.

(3) Monomer Component In the present invention, after the emulsion polymerization that promotes the graft polymerization, the monomer component is supplied to the polymerization site to advance the emulsion polymerization. The monomer component used here includes at least an acrylic monomer, and may further include a functional monomer, a copolymerizable monomer, and the like as necessary. When the monomer component comprises at least an acrylic monomer, the water resistance and durability of the resulting emulsion polymer can be improved.

(i) Acrylic monomer The acrylic monomer that can be used in the present invention is not particularly limited as long as it is well known to those skilled in the art as an acrylic monomer. For example, (meth) acrylic acid alkyl esters (here, The alkyl group is an alkyl group having 1 to 18 carbon atoms), (meth) acrylonitrile, (meth) acrylamide, and (meth) acrylic acid hydroxyalkyl esters (wherein the alkyl group is an alkyl group having 1 to 12 carbon atoms). There is a typical example. Here, “(meth) acryl” means acrylic or methacrylic.

  Specific examples of acrylic monomers include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, methacryl Examples include (meth) acrylic acid alkyl esters such as cyclohexyl acid, octyl methacrylate, and stearyl methacrylate. Further, acrylonitrile, methacrylonitrile, acrylamide, methacrylamide, hydroxyethyl acrylate, hydroxyethyl methacrylate, and the like can be given as specific examples of the acrylic monomer.

  According to a preferred embodiment of the present invention, the acrylic monomer is selected from (meth) acrylic acid alkyl esters in which the alkyl group has 1 to 8 carbon atoms. More preferably, the acrylic monomer is methyl methacrylate, butyl acrylate, or 2-ethylhexyl acrylate.

  In the present invention, it is preferable to use a combination of two or more acrylic monomers. Specific examples include a combination of methyl methacrylate / butyl acrylate, methyl methacrylate / 2-ethylhexyl acrylate, methyl methacrylate / butyl acrylate / 2-ethylhexyl acrylate, and the like.

  In the present invention, the acrylic monomer is a main component constituting the polymer, and the use amount thereof is preferably 50% by weight or more, more preferably 80% by weight with respect to the total monomers. It is. If the amount used is less than 50% by weight, the desired water resistance and weather resistance may be insufficient.

(ii) Functional monomer In the present invention, the monomer component may further comprise a functional monomer. According to one preferred embodiment of the present invention, the monomer component further comprises a functional monomer in addition to the acrylic monomer. Here, the functional monomer is a monomer that can be subjected to emulsion polymerization together with an acrylic monomer, and is not particularly limited as long as it contains a functional group. For example, a monomer having a glycidyl group, an acetoacetyl group Monomer having an allyl group, monomer having a silyl group, monomer having a hydroxyl group, monomer having a carboxyl group, monomer having a carbonyl group, and having two or more radical polymerizable unsaturated bonds in the molecular structure Monomer.

Specific examples of the monomer having a glycidyl group include glycidyl (meth) acrylate, glycidyl (meth) allyl ether, 3,4-epoxycyclohexyl (meth) acrylate, and the like.
Specific examples of the monomer having an acetoacetyl group include acetoacetoxyethyl (meth) acrylate.
Specific examples of the monomer having an allyl group include allyl acetate and allyl chloride.
Specific examples of the monomer having a silyl group include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane, vinylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, and γ-methacryloxypropylmethyl. Examples include dimethoxysilane, γ-acryloxypropyltrimethoxysilane, γ-acryloxypropylmethyldimethoxysilane, γ-methacryloxypropyltriethoxysilane, and γ-methacryloxypropylmethyldiethoxysilane.

Specific examples of the monomer having a hydroxyl group include 2-hydroxyethyl methacrylate and 2-hydroxyethyl acrylate.
Specific examples of the monomer having a carboxyl group include acrylic acid, methacrylic acid, maleic acid, crotonic acid, itaconic acid and the like.
Specific examples of the monomer having a carbonyl group include diacetone acrylamide and acetoacetoxyethyl methacrylate.
Specific examples of the monomer having two or more radically polymerizable unsaturated bonds in the molecular structure include divinylbenzene and ethylene glycol dimethacrylate.

  The amount of the functional monomer used is preferably 0.05 to 5% by weight, more preferably 0.1 to 1% by weight, based on the total weight. If the amount used is less than 0.1% by weight, the improvement in water resistance and wet adhesion may be insufficient. On the other hand, when the amount used is more than 10% by weight, the polymerization may be poor or the redispersibility may be lowered.

According to one preferred embodiment of the present invention, the monomer component may further comprise a curing agent capable of reacting with the functional monomer in addition to the functional monomer. Here, the curing agent capable of reacting with the functional monomer refers to a compound that can react with the functional group of the functional monomer to form a network structure.
Examples of such curing agents include isocyanate compounds, hydrazine compounds, aziridine compounds, epoxy group-containing compounds, and metal salts. Preferably, the curing agent is an isocyanate compound or a hydrazine compound.
The amount of the curing agent that can react with the possibility monomer can be used according to the molar equivalent of the functional group in the functional monomer.

(iii) Copolymerizable monomer In the present invention, the monomer component subjected to emulsion polymerization may further contain a copolymerizable monomer in addition to the acrylic monomer or the acrylic monomer and the functional monomer. .

  Such a copolymerizable monomer is not particularly limited as long as it is generally usable in emulsion polymerization. For example, olefinic monomers such as ethylene; vinyl acetate, vinyl propionate, vinyl versatate And carboxylic acid vinyl esters such as vinyl laurate and vinyl stearyl; and vinyl chloride and vinylidene chloride.

  When a copolymerizable monomer is used, the amount used is preferably less than 50% by weight, more preferably 20% by weight or less, based on the total amount of monomers.

(4) Other components In the aqueous acrylic copolymer emulsion composition according to the present invention, in addition to the above-described monomer components such as PVA, hydrophobic ethylenically unsaturated monomer, and acrylic monomer, other components may be used as necessary. Ingredients can be further used. Such other components are not particularly limited as long as the properties of the emulsion composition are not deteriorated, and can be appropriately selected according to the purpose. Examples of such other components include a polymerization initiator, a reducing agent, a polymerization regulator, and an auxiliary emulsifier.

The polymerization initiator can be used without particular limitation as long as it can be used for ordinary emulsion polymerization, such as inorganic peroxides such as potassium persulfate, sodium persulfate, ammonium persulfate; organic peroxides, And peroxides such as hydrogen peroxide and butyl peroxide. Two or more of these may be used in combination. In the present invention, among these, ammonium persulfate is preferable because it does not adversely affect film properties and strength enhancement and is easy to polymerize.

Reducing Agent In order to obtain the aqueous acrylic copolymer emulsion composition according to the present invention, emulsion polymerization is performed in a redox system in which a reducing agent is combined with an initiator in order to promote graft polymerization.
In the present invention, the reducing agent is preferably a reducing organic compound (for example, L-ascorbic acid, tartaric acid, citric acid, glucose, formaldehyde sulfoxylate metal salt, etc.) or a reducing inorganic compound (for example, sodium thiosulfate). Sodium sulfite, acidic sodium sulfite, sodium metabisulfite and the like. More preferably, the reducing agent is selected from the group consisting of L-ascorbic acid, tartaric acid, citric acid, glucose, formaldehyde sulfoxylate metal salt, sodium thiosulfate, sodium sulfite, sodium acid sulfite, sodium metabisulfite 1 More than a seed. More preferably, the reducing agent is acidic sodium sulfite.
The amount of the reducing agent used is preferably 0.001 to 0.3% by weight based on the total amount of monomers. When the amount used is outside the range of 0.001 to 0.3% by weight, the graft polymerization does not proceed during the emulsion polymerization and the polymerization stability becomes poor.

Polymerization regulator There is no restriction | limiting in particular as a polymerization regulator, It can select suitably from well-known things. Examples of such a polymerization regulator include a chain transfer agent and a buffer.

Here, examples of the chain transfer agent include alcohols such as methanol, ethanol, propanol, and butanol; And mercaptans such as dodecyl mercaptan, lauryl mercaptan, normal mercaptan, thioglycolic acid, octyl thioglycolate, and thioglycerol. Two or more of these may be used in combination.
Although the use of a chain transfer agent is effective in terms of stabilizing the polymerization, it reduces the degree of polymerization of the acrylic polymer, thus hindering the improvement of water resistance and durability in the application application of the resulting emulsion. Sometimes. For this reason, in the present invention, it is desirable to avoid the use of a chain transfer agent or to keep the amount used as low as possible even when it is used.

  Here, examples of the buffer include sodium acetate, ammonium acetate, and dibasic sodium phosphate. Two or more of these may be used in combination.

The coemulsifier coemulsifier, if known to those skilled in the art as those that can be used in emulsion polymerization can also be used in any of those. Therefore, the auxiliary emulsifier is appropriately selected from known ones such as anionic, cationic, and nonionic surfactants, water-soluble polymers having protective colloid ability other than PVA, and water-soluble oligomers. Can do.

  Preferred specific examples of the surfactant include anionic surfactants such as sodium lauryl sulfate and sodium dodecylbenzenesulfonate, and nonionic properties such as those having a pluronic type structure and those having a polyoxyethylene type structure. Surfactant is mentioned. A reactive surfactant having a radical polymerizable unsaturated bond in the structure can also be used as the surfactant. However, if many of these surfactants are used as emulsifiers, the particles may adhere when the emulsion composition is dried, and the redispersibility may be reduced. For this reason, when using a surfactant, it is desirable that the amount used is an auxiliary amount to PVA, that is, as small as possible.

  Examples of the water-soluble polymer having protective colloid ability other than PVA include hydroxyethyl cellulose, polyvinyl pyrrolidone, and methyl cellulose. These are effective in changing the viscosity when the emulsion composition is spray-dried and used as a redispersible emulsion powder. However, depending on the amount used, the redispersibility of the redispersible emulsion powder may be reduced. Therefore, when used, the redispersible emulsion powder may be used in an amount that does not reduce the redispersibility. desirable.

  As the water-soluble oligomer, for example, a polymer or copolymer having a hydrophilic group such as a sulfonic acid group, a carboxyl group, a hydroxyl group, and an alkylene glycol group and having a degree of polymerization of about 10 to 500 is preferably exemplified. Specific examples of water-soluble oligomers include amide copolymers such as 2-methacrylamide-2-methylpropanesulfonic acid copolymer, sodium methacrylate-4-styrenesulfonate copolymer, styrene / maleic acid copolymer. , Melamine sulfonic acid formaldehyde condensate, poly (meth) acrylate, and the like. Furthermore, specific examples include a monomer having a sulfonic acid group, a carboxyl group, a hydroxyl group, an alkylene glycol group, and a water-soluble oligomer obtained by copolymerizing a radical polymerizable reactive emulsifier alone or in advance with another monomer. It is done. Among these, in the present invention, 2-methacrylamide-2-methylpropanesulfonic acid copolymer, sodium methacrylate-4-styrenesulfonate are preferred in view of imparting redispersibility and mixing stability with inorganic hydraulic components. A copolymer is preferred. As the water-soluble oligomer, those previously polymerized before starting the emulsion polymerization may be used, or commercially available products may be used. Two or more of these may be used in combination.

  The amount of these other components used is not particularly limited as long as the object of the present invention is not impaired, and can be appropriately selected according to the object.

Production of Aqueous Acrylic Copolymer Emulsion Composition As described above, the aqueous acrylic copolymer emulsion composition according to the present invention is further subjected to emulsion polymerization on fully saponified polyvinyl alcohol under conditions that facilitate graft polymerization. It can be produced by adding a monomer component comprising at least an acrylic monomer and emulsion polymerization.

  Here, “emulsion polymerization under conditions where graft polymerization is likely to proceed” corresponds to performing high-temperature redox emulsion polymerization at 75 to 90 ° C. Here, high temperature redox emulsion polymerization refers to redox emulsion polymerization under a temperature condition of 75 to 90 ° C. (preferably 78 to 82 ° C.), and uses a persulfate and a small amount of acidic sulfite. Can bring the system to redox conditions. In addition, the present inventors can promote graft polymerization with fully saponified PVA (saponification degree of 95 mol% or more) and perform stable polymerization by performing emulsion polymerization under such conditions. I think it will be.

Emulsion polymerization The emulsion polymerization method is not particularly limited. For example, a batch emulsion polymerization method in which all of water, an emulsifier, and a monomer are charged into a polymerization can, and the temperature is raised, and a polymerization initiator is appropriately added to advance the polymerization. A monomer dropping type emulsion polymerization method in which water and an emulsifier are charged into a polymerization can, and the temperature is increased to drop the monomer; and an emulsion monomer dropping method in which the dropping monomer is pre-emulsified with an emulsifier and water and then dropped. Examples thereof include an emulsion polymerization method.
The monomer and other components used for the polymerization can be appropriately selected from the monomers and / or components described above. Usually, the emulsion polymerization is carried out using other components such as a polymerization initiator, a polymerization regulator, an auxiliary emulsifier and the like as required in addition to the emulsifier and the monomer component. The polymerization reaction conditions are not particularly limited and can be appropriately selected depending on the type and purpose of the copolymerization component.

  The polymerization process in the present invention will be described with specific examples as follows. First, polyvinyl alcohol as a protective colloid component and other components as necessary are charged in a reaction can, and after heating this (for example, 75 to 90 ° C.), a hydrophobic ethylenic monomer, a polymerization initiator, A reducing agent is added here and emulsion polymerization is performed under conditions where graft polymerization is likely to proceed. Next, the monomer components are added all at once or dropwise, and emulsion polymerization is allowed to proceed while adding a polymerization initiator if necessary. When it is determined that the polymerization reaction is completed, the reaction can is cooled, and the target emulsion composition can be taken out.

  The emulsion composition according to the present invention is typically milky white and has an average particle size of 0.05 to 2.0 μm (preferably 0.3 to 1.5 μm). Here, the average particle size of the emulsion can be measured by a conventional method, for example, a laser analysis / scattering particle size distribution measuring apparatus LA-910 (manufactured by Horiba, Ltd.).

  In this invention, you may further add an additive to the synthetic resin emulsion composition after superposition | polymerization as needed. Examples of such additives include organic pigments, inorganic pigments, water-soluble additives, pH adjusters, preservatives, and antioxidants.

  The water-soluble additive is added for the purpose of improving the redispersibility of water in the redispersible emulsion powder obtained by spray drying the synthetic resin emulsion composition according to the present invention. When a water-soluble additive is used, the water-soluble additive is usually added to the emulsion composition after emulsion polymerization and before drying. The amount of the water-soluble additive used is preferably 5 to 50% by weight based on the solid content of the aqueous emulsion before drying. If the amount used exceeds 50% by weight, the water resistance of the redispersible emulsion powder may be insufficient, and if it is less than 5% by weight, the redispersibility may not be sufficiently improved.

  Examples of water-soluble additives include polyvinyl alcohol, hydroxyethyl cellulose, methyl cellulose, starch derivatives, polyvinyl pyrrolidone, polyethylene oxide, water-soluble alkyd resins, water-soluble phenol resins, water-soluble urea resins, water-soluble melamine resins, and water-soluble guanamine resins. Water-soluble naphthalene sulfonic acid resin, water-soluble amino resin, water-soluble polyamide resin, water-soluble acrylic resin, water-soluble polycarboxylic acid resin, water-soluble polyester resin, water-soluble polyurethane resin, water-soluble polyol resin, and water-soluble epoxy Resin etc. are mentioned. Two or more of these may be used in combination.

  Among these, polyvinyl alcohol is effective for improving redispersion. The polyvinyl alcohol to be used may be the same as that used as an emulsifier in the polymerization process, or may be different. Polyvinyl alcohol having a high degree of polymerization cannot be used during the polymerization because of its polymerization stability, but such a polyvinyl alcohol can be used without any problem as long as it is added after polymerization. However, those having low solubility in water may adversely affect redispersibility, so it is desirable to use them after confirming the solubility in water in advance.

In the present invention, the obtained aqueous acrylic copolymer emulsion composition is dried to obtain a redispersible acrylic copolymer emulsion powder.
The drying method is not particularly limited, and examples thereof include spray drying, freeze drying, and hot air drying after coagulation. Among these, spray drying is preferable from the viewpoint of production cost, energy saving, and re-emulsification of the obtained powder.

In the case of spray-drying, the spraying form is not particularly limited, and for example, it can be carried out by a disk type, a nozzle type or the like. Examples of the heat source for spray drying include hot air and heated steam. The conditions for spray drying can be appropriately selected according to the size and type of the spray drying group, the concentration of the emulsion, the viscosity, the flow rate, and the like. The temperature of spray drying is typically about 80 to 150 ° C.
The spray drying process will be further explained with specific examples. First, the non-volatile content in the synthetic resin emulsion is adjusted, and this is continuously supplied from the nozzle of the spray dryer, and the mist is pulverized with warm air. Let

  In the present invention, the anti-blocking agent can be used in combination by spray-drying and mixing with the emulsion powder, or spraying from a different nozzle from the synthetic resin emulsion during spray-drying. As the anti-blocking agent, known inert inorganic or organic powders such as calcium carbonate, talc, clay, anhydrous silicic acid, aluminum silicate, white carbon, alumina white and the like can be used. Among these, anhydrous silicic acid, aluminum silicate, calcium carbonate and the like having an average particle size of about 0.01 to 0.5 μm are preferable. It is preferable that the usage-amount of an antiblocking agent is about 2 to 30 weight% with respect to the redispersible emulsion powder obtained.

Applications The aqueous acrylic copolymer emulsion composition according to the present invention is excellent in polymerization stability and also in stability in actual applications such as mechanical stability, freezing stability, and high temperature storage stability. For this reason, the emulsion composition according to the present invention comprises a cement / mortar admixture, a cement / mortar coating agent, a civil engineering material, a paint, an adhesive, a pressure-sensitive adhesive (pressure-sensitive adhesive), a fiber processing agent, a paper processing material, and an inorganic substance. It can be suitably used for binders, resin modifiers such as vinyl chloride, solidifying stabilizers for viscous soils such as sludge and industrial waste, releasable coating materials for surface protection, and cosmetic applications.

Redispersible acrylic copolymer emulsion powder The redispersible acrylic copolymer emulsion powder according to the present invention can be obtained by spray-drying the aqueous acrylic copolymer emulsion composition according to the present invention. Here, “redispersibility” refers to a powder that can produce an emulsion when the emulsion powder is redispersed in an aqueous medium (for example, water).

  The redispersible emulsion powder according to the present invention can be used for various applications such as additives to hydraulic materials, powder paints, adhesives and the like. Preferably, it can be used as an additive to hydraulic materials such as various cements and gypsum.

  The redispersible emulsion powder according to the present invention can be mixed with an inorganic hydraulic material as it is, and can be used by adding other materials and mixing water on site as a single powder product. When the redispersible emulsion powder according to the present invention is added to a hydraulic material, not only the normal adhesive strength but also the wet adhesive strength can be improved. For this reason, the utilization range of one-piece products can be further expanded.

Therefore, according to the present invention, there is provided an inorganic hydraulic composition comprising the redispersible acrylic copolymer emulsion powder according to the present invention and an inorganic hydraulic material. Here, examples of the inorganic hydraulic material include various cement-based materials such as Portland cement, early-strength cement, and fast-curing cement, various gypsum-based materials such as anhydrous gypsum, hemihydrate gypsum, and calcined gypsum, and blast furnace slag. Can be mentioned.
The inorganic hydraulic composition according to the present invention may further contain other materials. Examples of such other materials include silica sand, fly ash, limestone powder, calcium hydroxide, slaked lime, and calcium carbonate.

  The content of the redispersible acrylic copolymer emulsion powder according to the present invention in the inorganic hydraulic composition is preferably about 1 to 30 parts by weight, more preferably 100 parts by weight of the inorganic hydraulic material. Is 5 to 20 parts by weight. If the amount is less than 1 part by weight, the adhesive strength may not be sufficiently improved. If the amount is more than 30 parts by weight, the original performance of the hydraulic material may not be exhibited.

  Examples of the present invention will be described below, but the present invention is not limited to these examples. In the examples, “parts” and “%” mean “parts by weight” and “% by weight”, respectively.

Production of aqueous acrylic copolymer emulsion composition
Emulsion composition 1:
In a separable flask (reaction can) equipped with a stirrer, a thermometer, a condenser, and a dropping funnel, 110 parts by weight of water, polyvinyl alcohol having an average polymerization degree of 300 and a saponification degree of 98.0 to 99.0% ( (Product name: PVA103, manufactured by Kuraray Co., Ltd.) 10 parts by weight, and the reaction can was heated to 80 ° C. to dissolve polyvinyl alcohol in water. Next, the temperature of the reaction vessel is kept at 80 ° C., and 5 parts by weight of butyl acrylate and 5 parts of methyl methacrylate are added to the reaction vessel as hydrophobic ethylenically unsaturated monomers, and the polymerization initiator is used as a polymerization initiator. The emulsion polymerization reaction was carried out for 1 hour using ammonium sulfate and acidic sodium sulfite as the reducing agent. Subsequently, 45 parts by weight of butyl acrylate and 45 parts by weight of methyl methacrylate were dropped into the reaction can over about 4 hours as monomer components, and the dropping polymerization reaction was allowed to proceed while further adding ammonium persulfate as a polymerization initiator. After completion of dropping, the mixture was aged and cooled to complete the reaction. As a result, an aqueous acrylic copolymer emulsion composition (emulsion composition 1) having a solid concentration of about 50% was obtained.

Emulsion composition 2:
Except for changing the polyvinyl alcohol to polyvinyl alcohol having an average polymerization degree of 500 and a saponification degree of 98.0 to 99.0% (trade name: PVA105, manufactured by Kuraray Co., Ltd.), in the same manner as the emulsion composition 1, Emulsion composition 2 was prepared.

Emulsion composition 3:
Except for changing polyvinyl alcohol to polyvinyl alcohol (trade name: PVA102, manufactured by Kuraray Co., Ltd.) having an average polymerization degree of 200 and a saponification degree of 98.0 to 99.0%, Emulsion composition 3 was prepared.

Emulsion composition 4 (comparative example):
Except for changing polyvinyl alcohol to polyvinyl alcohol (trade name: PVA117, manufactured by Kuraray Co., Ltd.) having an average polymerization degree of 1700 and a saponification degree of 98.0 to 99.0%, Emulsion polymerization was performed. However, it gelled during the polymerization and an emulsion composition could not be obtained.

Emulsion composition 5 (comparative example):
Except for changing the polyvinyl alcohol to polyvinyl alcohol having an average polymerization degree of 500 and a saponification degree of 87.0 to 89.0% (trade name: PVA205, manufactured by Kuraray Co., Ltd.), the same as the emulsion composition 1, Emulsion polymerization was performed. However, it gelled during the polymerization and an emulsion composition could not be obtained.

Emulsion composition 6 (comparative example):
Polymerization was carried out in the same manner as the emulsion composition 1 except that acidic sodium sulfite was not used as the reducing agent. However, the progress of the polymerization reaction was slow and gelation occurred during the polymerization, and an emulsion composition could not be obtained.

Production of redispersible synthetic resin emulsion powder
Redispersible emulsion powders 1-3:
50 parts by weight of a 10% solution of polyvinyl alcohol (trade name: AH-17, manufactured by Nippon Synthetic Chemical Industry) was mixed with 100 parts by weight of the emulsion composition 1, and this was mixed with an anti-caking agent (trade name: Hydro The emulsion powder (redispersible emulsion powder 1) was obtained by spray drying in the presence of Calve, PLUSS-STAUFER (Switzerland) (calcium carbonate).
Redispersible emulsion powders 2 and 3 were obtained in the same manner as in the above procedure except that the emulsion composition 1 was changed to the emulsion composition 2 or 3.
In addition, about the emulsion compositions 4-6, since the emulsion composition was not obtained, manufacture of an emulsion powder was not able to be performed.

Evaluation test
Test 1: Polymerization stability Each emulsion composition was checked for gelation during the polymerization. When it did not gel, it was determined that the polymerization stability was “good”.
The results were as shown in Table 1.

Test 2: Redispersibility 100 parts by weight of the obtained redispersible emulsion powder was added to 100 parts by weight of deionized water with stirring using a stirrer to obtain a redispersed liquid. This redispersion was placed in a glass tube and allowed to stand at room temperature. The redispersibility at this time was evaluated according to the following criteria. In addition, this evaluation test was implemented about all the emulsion powders 1-3.
Judgment criteria:
A: A uniform re-dispersed liquid is obtained and only a slight sedimentation of the emulsion powder is observed. B: The re-dispersed liquid is phase-separated and a clear liquid phase and a precipitated emulsion powder phase are observed. : When emulsion powder could not be produced The results were as shown in Table 1.

Claims (11)

  Hydrophobic ethylenically unsaturated monomer having a water solubility of 1.0% by weight or less in polyvinyl alcohol (PVA) having an saponification degree of 95 mol% or more and an average polymerization degree of 100 to 1000 in an aqueous medium Aqueous acrylic copolymer emulsion obtainable by subjecting to a high-temperature redox emulsion polymerization at 75 to 90 ° C. in the presence of a reducing agent, and then emulsion polymerization by adding a monomer component containing at least an acrylic monomer. Composition.   Hydrophobic ethylenically unsaturated monomers are lauryl methacrylate, cyclohexyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, stearyl methacrylate, ethyl acetoacetate, 2-ethylhexyl methacrylate, tridecyl methacrylate, 2 The aqueous acrylic copolymer emulsion composition according to claim 1, which is one or more selected from the group consisting of -ethylhexyl acrylate and butyl acrylate.   The aqueous acrylic copolymer emulsion composition according to claim 1 or 2, wherein the acrylic monomer is a (meth) acrylic acid alkyl ester having 1 to 8 carbon atoms in the alkyl group.   The aqueous acrylic copolymer emulsion composition according to any one of claims 1 to 3, wherein the amount of the reducing agent used is 0.001 to 0.3% by weight based on the total amount of monomers.   The reducing agent is one or more selected from the group consisting of L-ascorbic acid, tartaric acid, citric acid, glucose, formaldehyde sulfoxylate metal salt, sodium thiosulfate, sodium sulfite, sodium acid sulfite, and sodium metabisulfite The aqueous acrylic copolymer emulsion composition according to any one of claims 1 to 4, wherein   The aqueous acrylic copolymer emulsion composition according to any one of claims 1 to 5, wherein the monomer component further comprises a functional monomer.   The aqueous acrylic copolymer emulsion composition according to claim 6, wherein the monomer component further comprises a curing agent capable of reacting with the functional monomer.   Redispersible acrylic copolymer emulsion powder obtained by spray-drying the aqueous acrylic copolymer emulsion composition according to any one of claims 1 to 7.   Hydrophobic ethylenically unsaturated monomer having a water solubility of 1.0% by weight or less in polyvinyl alcohol (PVA) having an saponification degree of 95 mol% or more and an average polymerization degree of 100 to 1000 in an aqueous medium Aqueous acrylic, comprising high-temperature redox emulsion polymerization at 75 to 90 ° C. in the presence of a reducing agent, and further emulsion polymerization by adding a monomer component at least including an acrylic monomer. A method for producing a copolymer emulsion composition.   A method for producing a redispersible acrylic copolymer emulsion powder comprising spray-drying an aqueous acrylic copolymer emulsion composition obtained by the production method according to claim 9.   An inorganic hydraulic composition comprising the redispersible acrylic copolymer emulsion powder according to claim 8 and an inorganic hydraulic material.