JPH11286503A - Production of water-based polymer emulsion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production process for water-based polymer emulsions that can use a usual polymerizer with operation simplified and gives a polymer emulsion having excellent storage stability and physical properties of its coating layer. SOLUTION: A solution comprising a monomer mixture containing >=50 wt.% of a (meth)acrylic ester and an oil-soluble radical polymerization initiator is dispersed in water in the presence of an emulsifier to prepare an aqueous emulsion. Then, the monomer mixture is polymerized by adding the aqueous emulsion to a hot aqueous medium under the agitation conditions of 2.5 m/sec. peripheral speed of stirring blades.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an aqueous polymer emulsion, and the aqueous polymer emulsion obtained by the present invention has excellent coating film performance and storage stability. It can be used for a wide range of uses such as agents, and can be awarded in the technical field utilizing these.

[0002]

2. Description of the Related Art Conventionally, a curable copolymer having a hydrolyzable silyl group represented by an alkoxysilyl group (hereinafter referred to as a silane polymer) has been used for applications such as adhesives, sealing materials, paints and coating agents. It is widely used. In recent years, in these application fields, in order to avoid harm to the human body and environmental pollution due to volatilization of the organic solvent, an aqueous material that does not use an organic solvent has been demanded. The need is increasing.

However, since the silane polymer has a property of being crosslinked while being hydrolyzed, it is not easy to obtain a stable aqueous emulsion. For this reason, various attempts have been made to obtain an aqueous emulsion having excellent storage stability. For example, JP-A-3-227
No. 312 discloses an aqueous emulsion polymerization of a monomer having an alkyl (meth) acrylate and an alkoxysilyl group.
For the purpose of stabilizing the obtained curable copolymer, a specific water-soluble monomer such as acrylamide, acrylic acid or styrenesulfonic acid is used in an amount of about 0.1 to 5% by weight in addition to the above monomers. A method of copolymerizing has been proposed.
JP-A-5-25354 discloses that after a monomer having a hydrolyzable silyl group is copolymerized with a monomer having an amine imide group in an alcohol solvent, water is added to emulsify and further emulsify. Have been proposed. In addition, JP-A-59-152972 discloses a silane polymer emulsion composition having excellent water resistance, obtained by emulsion-polymerizing vinylsilane and an acrylic monomer using a polymerizable emulsifier, and obtaining a glass transition. A composition in which a specific amount of colloidal silica is blended with a copolymer emulsion having a temperature of 70 ° C. or lower is disclosed. However,
The aqueous emulsion of a silane polymer according to the prior art has a storage stability and physical properties of a coating film, and a high-quality curable emulsion is required.

[0004]

SUMMARY OF THE INVENTION The present inventors have disclosed in Japanese Patent Application Laid-Open No. 149840/1995 an aqueous emulsion in which a solution of a monomer in which an oil-soluble initiator is dissolved is dispersed to solve the above-mentioned problem. However, it has been found that a silane polymer emulsion having excellent stability and curability can be obtained by a method of supplying the mixture to an aqueous medium heated under stirring and polymerizing the mixture, that is, a so-called microsuspension polymerization method. However, in the method for producing the polymer, an aqueous emulsion to be used needs to prepare an emulsion having a small particle size of the monomer mixture. ,
If a special dispersing device with high shear force is required,
There is a problem that the operation becomes complicated. The present inventors are able to use a usual polymerization apparatus, the operation is simple, and furthermore, the obtained polymer emulsion has been studied diligently to find a method for producing an aqueous polymer emulsion having excellent storage stability and coating film properties. I went.

[0005]

The present inventors have conducted various studies and found that, when producing a polymer emulsion by microsuspension polymerization, the stirring during the polymerization reaction was controlled under specific conditions to preserve the polymer emulsion. The present inventors have found that a polymer emulsion having a fine particle diameter which is excellent in stability and physical properties of a coating film can be obtained, thereby completing the present invention. Hereinafter, the present invention will be described in detail.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION Monomer Mixture The monomer mixture used in the present invention contains (meth) acrylic acid ester in an amount of 50% by weight or more. (Meta)
Examples of the acrylate include methyl (meth) acrylate, ethyl (meth) acrylate, and n- (meth) acrylate.
Butyl, cyclohexyl (meth) acrylate, (meth)
(Meth) such as 2-ethylhexyl acrylate, lauryl (meth) acrylate and stearyl (meth) acrylate
Hydroxyalkyl (meth) acrylates such as alkyl acrylate, 2-hydroxyethyl (meth) acrylate and 2-hydroxypropyl (meth) acrylate, perfluoroalkyl (meth) acrylate, glycidyl (meth) acrylate and (meth) ) N, N-diethylaminoethyl acrylate and the like.

In the monomer mixture, a compound having an ethylenically unsaturated group copolymerizable therewith can be used in addition to the (meth) acrylic acid ester, if necessary. As the compound having an ethylenically unsaturated group, various compounds can be used, and a vinyl monomer having a hydrolyzable alkoxysilyl group; ethylenically unsaturated such as (meth) acrylic acid, itaconic acid and maleic acid. Compounds having a group and a carboxyl group; vinyl carboxylate such as vinyl acetate and vinyl propionate; and aromatic compounds containing an ethylenically unsaturated group such as styrene and α-methylstyrene.

In the present invention, it is preferable to use a vinyl monomer having a hydrolyzable alkoxysilyl group (hereinafter referred to as a silyl monomer) in combination, since a crosslinkability can be imparted to the obtained polymer emulsion. . As the silyl-based monomer, a compound represented by the following general formula (1) is preferable.

[0009]

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(Wherein, R ¹ is a monovalent hydrocarbon group selected from an alkyl group having 1 to 10 carbon atoms, an aryl group and an aralkyl group, R ² is a radical polymerizable group, X is an alkoxy group or a halogen atom, a is an integer from 0 to 2. Si
When each of X and R ¹ bonded to is two or more, they may be the same or different groups. In R ¹ , the aryl group includes a phenyl group, and the aralkyl group includes a benzyl group. R ¹ is preferably an alkyl group having 1 to 10 carbon atoms. As the radical polymerizable group for R ² , an ethylenically unsaturated group is preferable, and a functional group having high radical polymerizability such as a (meth) acryloyl group, a styryl group, a vinyl ester group, and a vinyl ether group is more preferable. In X, the alkoxy group includes a methoxy group, an ethoxy group, a propoxy group, a butoxy group, a pentanoxy group and a hexanoxy group, and the halogen atom is F, Cl, Br or the like.
And I. From the balance between reactivity and stability,
X is preferably an alkoxy group having 4 or less carbon atoms.

Preferred examples of the silyl monomer include vinyltrimethoxysilane, vinylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, vinyltriethoxysilane, vinylmethyl Diethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-methacryloxypropylmethyldiethoxysilane, vinyltripropoxysilane, vinylmethyldipropoxysilane, γ-methacryloxypropyltripropoxysilane, γ-methacryloxypropylmethyldi Examples include propoxysilane and vinyltris (β-methoxyethoxy) silane. The monomers may be used in combination of two or more.

When a silyl monomer is used in combination with a monomer mixture and a polymer having a silanol group is produced as a polymer, in addition to the essential component (meth) acrylate, (meth) acrylic acid Also, monomers having a carboxyl group such as, itaconic acid and maleic acid can be used. On the other hand, when producing a polymer having an alkoxysilyl group and having almost no silanol group as the polymer, it is desirable not to use a monomer having the carboxyl group that promotes hydrolysis of the alkoxyl group. .

When a silyl monomer is used as the monomer mixture, the (meth) acrylate used in combination with the silyl monomer may be an alkyl (meth) acrylate having an alkyl group having 1 to 8 carbon atoms. Preferred is a composition from which a hydroxyalkyl (meth) acrylate having an alkylene group having 2 to 3 carbon atoms is obtained, since the coating film properties are excellent. Further, as other monomers copolymerizable with these,
Styrene, (meth) acrylic acid, and glycidyl methacrylate are preferred in terms of copolymerizability, physical properties of the coating film, and the like. In the present invention, 5 (meth) acrylic acid esters are contained in the monomer mixture.
Since it is contained in an amount of 0% by weight or more, the weather resistance, strength, heat resistance and the like of the obtained coating film can be maintained at a high level.

When a (meth) acrylate and a silyl-based monomer are used in combination, a preferable ratio of these monomers is based on the total amount of all the monomers. Is 50 to 95% by weight, the vinyl monomer having a hydrolyzable alkoxysilyl group is 0.1 to 30% by weight, more preferably 1 to 20% by weight, and the monomer copolymerizable with these monomers is 0 to 30% by weight. If the proportion of the silyl monomer is less than 0.5% by weight, the curability of the resulting polymer emulsion coating film may decrease,
On the other hand, if it exceeds 30% by weight, the adhesion of the coating film to the substrate may decrease.

Oil-soluble radical polymerization initiator As the polymerization initiator of the present invention, various oil-soluble polymerization initiators can be used. Those which are soluble in the monomer mixture at the reaction temperature are preferred.
Specific examples of the polymerization initiator include 2,2′-azobisisobutyronitrile, 2,2′-azobis-2,4-dimethylvaleronitrile, 1-azobis-1-cyclohexanecarbonitrile, and dimethyl-2,2 Azo initiators such as' -azobisisobutyrate, and lauroyl peroxide, benzoyl peroxide, dicumyl peroxide, cyclohexanone peroxide, di-n-propylperoxydicarbonate and t-butylperoxypivalate Organic peroxides. The amount of the polymerization initiator used is 0.1 to 10% by weight based on the monomer mixture.
Is preferable, and 0.5 to 5% by weight is more preferable. In the present invention, the polymerization initiator is used after being dissolved in a monomer mixture.

Emulsifier As an emulsifier for dispersing a solution comprising the monomer mixture and the polymerization initiator in water, various kinds of interfaces such as anionic, nonionic and cationic, which are widely used in ordinary emulsion polymerization, are used. Activators can be used. In the present invention, a radical polymerizable surfactant is preferable in that the resulting polymer emulsion film has excellent water resistance and weather resistance.

As the radical polymerizable surfactant, a compound having a radical polymerizable unsaturated double bond and a hydrophilic site in the molecule is preferable, and a polyoxyalkylene group represented by the following general formula (2) and an ion Those containing a dissociable group are preferred.

[0018]

Embedded image Z- (AO) nY (2)

Wherein Z is an organic group having a radical polymerizable double bond copolymerizable with the monomer mixture, AO is an oxyalkylene group, n is an integer of 2 or more, and Y is an ion-dissociable group. The preferred Z in the general formula (2) is a hydrophobic group such as an aromatic hydrocarbon group, an alkyl-substituted aromatic hydrocarbon group, a higher alkyl group or an alicyclic hydrocarbon group, and a radical polymerizable double bond. Is a structural unit in which Furthermore, Z
As the organic group having a radical polymerizable double bond in the above, a (meth) allyl group, a propenyl group, a butenyl group, or the like is preferable.

The preferred ionicity of the radically polymerizable surfactant is an anion, and therefore, as Y, a group (AO)
A salt which can be bonded to n by an anionic group and in which a cation is ionically bonded to the anionic group is preferable. Specific examples of the preferred _{Y, -SO 3 Na, -SO 3} N
_{H 4, -COONa, -COONH 4,} -PO 3 Na 2
And -PO ₃ (NH _{4) 2} and the like, more preferably from -SO ₃ Na or -SO ₃ NH _4. Group (A
O) n in n is an integer of 2 or more. When n is 1, when a silyl-based monomer is used as the monomer, the alkoxysilyl group becomes unstable and easily decomposes. Preferred n is 300 or less, more preferably 5 to 50. When n is less than 5, when a silyl-based monomer is used as a monomer, the stability of the alkoxysilyl group tends to be insufficient. On the other hand, when n exceeds 300, a polymer emulsion obtained is obtained. May show a tendency for the physical properties of the coating film formed from to decrease. The unit A in the group (AO) n, that is, the alkylene group, is preferably an ethylene group or a propylene group.

Specific examples of the surfactant include, for example, compounds represented by the following formulas (3) to (5). In the formulas (3) and (4), R ³ is preferably a linear or branched alkyl group having 6 to 18 carbon atoms.
In the formula (5), R ⁵ is preferably an alkyl group having 8 to 24 carbon atoms, and R ⁴ is a hydrogen atom or a methyl group. Further, specific examples of Y in the expressions (3) to (5) are as described above.

[0022]

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[0023]

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[0024]

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The preferred amount of the surfactant to be used is 0.5 to 20 parts by weight, more preferably 1 to 5 parts by weight, based on 100 parts by weight of the monomer mixture.

Production Method According to the present invention, an aqueous emulsion is produced by dispersing a solution comprising a monomer mixture and an oil-soluble radical polymerization initiator in water in the presence of an emulsifier. This is a method for producing an aqueous polymer emulsion in which the aqueous emulsion is added to a heated aqueous medium under stirring conditions of 5 m / sec or more to polymerize the monomer mixture. In the present invention, a so-called microsuspension polymerization in which a monomer mixture in which an oil-soluble polymerization initiator is dissolved is emulsified into fine particles in water to form an aqueous emulsion, and the aqueous emulsion is polymerized using the aqueous emulsion. To produce a weight part emulsion. Microsuspension polymerization is
Since the polymerization proceeds by the same mechanism as the suspension polymerization method except that the particle size is small (usually 0.05 to 1 μm), the polymer particles grow from the emulsifier micelle using a water-soluble polymerization initiator. This is completely different from general emulsion polymerization.

In the present invention, first, a solution comprising a monomer mixture and an oil-soluble radical polymerization initiator is dispersed in water in the presence of an emulsifier to produce an aqueous emulsion. When a solution consisting of a monomer mixture and an oil-soluble radical polymerization initiator is supplied directly to an aqueous medium and polymerized, a large stirring shear force is required to make the monomer mixture particles fine, so a special stirrer is installed. A new reactor is required. The average particle size of the solution comprising the monomer mixture and the oil-soluble radical polymerization initiator in the aqueous emulsion is preferably 10 μm or less. If the average particle size exceeds 10 μm, the stirring shear force required for making the particles fine during the polymerization reaction is large, and a reactor equipped with a special stirrer may be required.

When a silyl monomer is used as the monomer mixture to produce a polymer having an alkoxysilyl group, hydrolysis of the alkoxysilyl group in the silyl monomer during polymerization is prevented. It is preferred to use a pH buffer for the purpose. pH buffers include organic acids, inorganic acids,
Bases and salts thereof are exemplified. Among these, salts of inorganic acids are preferably used, and specific examples thereof include sodium hydrogen carbonate, sodium carbonate, ammonium carbonate, sodium borate and the like. On the other hand, when producing a polymer having a silanol group, it is not necessary to use a pH buffer. The polymer may become a polymer having a silanol group by hydrolysis of an alkoxysilyl group during polymerization.

The aqueous emulsion is mixed with a stirring blade at a peripheral speed of 2.
The monomer mixture is polymerized by adding it to an aqueous medium heated under stirring conditions of 5 m / sec or more. As a method of adding the aqueous emulsion, it is preferable to adopt a method of supplying the aqueous emulsion continuously or intermittently, and to employ a means of gradually dropping from a dropping device. At this time, a preferable amount of the aqueous medium to be charged into the polymerization reactor is 10 to 10 parts by weight of the monomer mixture.
The range is 200 parts by weight. The aqueous medium to be charged into the polymerization reactor contains at least 80% by weight of water, and may contain a water-compatible solvent or an additive such as alcohol, if necessary. For the purpose of improving the emulsion stability during polymerization, the surfactant used for preparing the aqueous emulsion may be charged into an aqueous medium. In this case, the amount of the surfactant used is preferably 20 parts by weight or less based on 100 parts by weight of the monomer mixture. If this amount exceeds 20 parts by weight, the water resistance of the coating film may decrease.

The polymerization temperature varies depending on the type of polymerization initiator used, but is preferably in the range of 40 to 100 ° C, more preferably in the range of 60 to 90 ° C. When the polymerization temperature is lower than 40 ° C., the polymerization rate is low, and the residual amount of the monomer in the produced polymer emulsion may increase.

As a polymerization apparatus used in the present invention, an apparatus used in ordinary emulsion polymerization may be applied. In the stirring device, various shapes can be used as the stirring blade, for example, a propeller type, a flat blade type, a Faudler type, and the like, and may have two or more stirring blades.
Further, a baffle plate may be provided in the polymerization apparatus. In the present invention,
As the stirring conditions in the polymerization of the monomer mixture, that is, at the time of adding the aqueous emulsion and the subsequent aging reaction, the peripheral speed of the stirring blade needs to be 2.5 m / sec or more, and 2.8.
It is preferably at least m / sec. The peripheral speed of the stirring blade is 2.
If the speed is lower than 5 m / sec, the polymer particles having a large particle size are mixed in the final product and are likely to settle during storage, and the gloss of the coating film of the polymer emulsion is reduced.

Applications and Methods of Use The aqueous polymer emulsion obtained in the present invention is suitable as a coating agent, and applicable substrates include glass, slate, metal, wood, plastic and the like.
Further, the use of the coating material is more specifically described as a paint for civil engineering / architecture, a paint for acid rain resistance, an antifouling paint, a water repellent for inorganic building materials, a moisture-proof coating agent for electric / electronic parts, and a magnetic tape. A back coat agent and the like can be mentioned. Other uses include sealing agents and adhesives.

In the emulsion obtained according to the present invention,
When a silyl-based monomer is used, a film can be obtained by coating on various substrates and evaporating water at room temperature or under heating. This film is crosslinked and cured by a condensation reaction of alkoxysilyl groups and / or silanol groups. The crosslinking reaction proceeds rapidly even at room temperature, but when further promoting crosslinking,
A curing catalyst can be included. As a curing catalyst,
For example, organic titanate compounds such as isopropyl triisostearoyl titanate and isopropyl tri (dioctyl pyrophosphate) titanate, tin dioctylate,
Examples thereof include organic tin compounds such as dibutyltin dilaurate and dibutyltin malate, and organic acid catalysts such as paratoluenesulfonic acid.

The emulsion obtained according to the present invention may contain pigments and fillers such as clay, talc, calcium carbonate, titanium white and colloidal silica, depending on the purpose.
Film-forming aids such as butyl cellosolve, butyl carbitol and butyl carbitol acetate; plasticizers such as dibutyl phthalate and dioctyl phthalate; tackifiers such as rosin, terpene phenol and petroleum resins; Various additives such as various surfactants, thickeners, thixotropic agents and antifreezing agents used for the purpose can be further added.

[0035]

The present invention will be described more specifically below with reference to examples and comparative examples. In addition, all the parts of the components in each example are parts by weight, and% is% by weight.

Example 1 (1) Production process of an aqueous emulsion A monomer mixture, a radical polymerizable surfactant, an oil-soluble radical initiator and water at the weights shown in Table 1 were mixed in a mixing tank for 1 hour. The mixture was mixed to prepare an aqueous emulsion. The average particle diameter of the obtained aqueous emulsion was 1.7 μm. The surfactant “AQUALON HS20” (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) is a compound represented by the following formula (6).

[0037]

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[0038]

[Table 1]

(2) Polymerization Step A polymerization reactor having a capacity of 1 m ³ was charged with 120 kg of deionized water as an aqueous medium, the liquid temperature was raised to 85 ° C., and the peripheral speed of the stirring blade was set to 2.8 m / sec. The aqueous emulsion was supplied over 3 hours under the above stirring, and after the completion of the supply, the polymerization was completed by maintaining the temperature at 85 ° C. for 2 hours under the same stirring conditions. During the polymerization, no liquid separation or blocking occurred, and the polymerization proceeded stably. The average particle size of the obtained polymer particles was 0.30 μm, and no large particles having a particle size of 1 μm or more were contained. This polymer emulsion had no sediment even after long-term storage, and had good storage stability. Further, a white pigment was blended into the obtained polymer emulsion to form a coating. The paint was applied on a zinc steel plate, and a dry coating film having a thickness of 60 μm was prepared using a doctor blade. When the gloss of the coating film was measured, the 60 ° gloss value was 85.

Example 2 Except that the peripheral speed of the stirring blade during polymerization was set to 3.4 m / sec,
A polymer emulsion was produced in exactly the same manner as in Example 1. The average particle size of the obtained polymer particles is 0.29 μm
No large particles having a particle diameter of 1 μ or more were contained. This polymer emulsion has no sediment even after long-term storage,
The storage stability was good. A paint was prepared in the same manner as in Example 1, and the paint was evaluated under the same conditions as in Example 1. As a result, the 60 ° gloss value of the coating film was 86.

Example 3 Except that the peripheral speed of the stirring blade during the polymerization was set at 4.3 m / sec,
A polymer emulsion was produced in exactly the same manner as in Example 1. The average particle size of the obtained polymer particles is 0.28 μm
No large particles having a particle diameter of 1 μ or more were contained. This polymer emulsion has no sediment even after long-term storage,
The storage stability was good. A paint was prepared in the same manner as in Example 1, and the paint was evaluated under the same conditions as in Example 1. As a result, the 60 ° gloss value of the coating film was 85.

Comparative Example 1 Except that the peripheral speed of the stirring blade during polymerization was 0.6 m / sec,
A polymer emulsion was produced in exactly the same manner as in Example 1. The average particle size of the obtained polymer particles is 0.33 μm
And 6.7% of large particles having a particle size of 1 μ or more were contained. When this polymer emulsion was left for one week, a sedimentary layer was formed at the bottom of the container, and storage stability was poor.
A paint was prepared in the same manner as in Example 1, and the paint was evaluated under the same conditions as in Example 1. As a result, the 60 ° gloss value of the coating film was 68.

Comparative Example 2 Except that the peripheral speed of the stirring blade during polymerization was 2.1 m / sec,
A polymer emulsion was produced in exactly the same manner as in Example 1. The average particle size of the obtained polymer particles is 0.30 μm
And 3.0% of large particles having a particle diameter of 1 μ or more were contained. When this polymer emulsion was left for one week, a sedimentary layer was formed at the bottom of the container, and storage stability was poor.
A paint was prepared in the same manner as in Example 1, and the paint was evaluated under the same conditions as in Example 1. As a result, the 60 ° gloss value of the coating film was 80.

[0044]

According to the present invention, an aqueous polymer emulsion having excellent storage stability and giving high coating film properties can be easily produced by a simple production apparatus. It can be used for various applications such as adhesives, sealing agents, removable pressure-sensitive adhesives, masking agents and surface protection tapes, and has great industrial value.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Hiroyuki Kamimura 1 Toagosei Co., Ltd., Nagoya Research Institute, 1 Minami-ku, Minato-ku, Nagoya-shi, Aichi (72) Inventor Nobuhiro Ishikawa Funami-cho, Minato-ku, Nagoya-shi, Aichi 1st Toagosei Co., Ltd. Nagoya Research Laboratory

Claims (3)

[Claims] (1) 50% by weight of (meth) acrylic acid ester
A solution comprising the monomer mixture and the oil-soluble radical polymerization initiator contained above is dispersed in water in the presence of an emulsifier to produce an aqueous emulsion, and stirring is performed so that the peripheral speed of the stirring blade becomes 2.5 m / sec or more. A method for producing an aqueous polymer emulsion, comprising adding the aqueous emulsion to a heated aqueous medium under conditions to polymerize the monomer mixture. 2. The method for producing an aqueous polymer emulsion according to claim 1, wherein the emulsifier is a radically polymerizable surfactant. 3. A monomer mixture comprising 50 to 95% by weight of a (meth) acrylate, 0.1 to 30% by weight of a vinyl monomer having a hydrolyzable alkoxysilyl group, and copolymerized with these monomers. 3. The process for producing an aqueous polymer emulsion according to claim 1, which is a mixture comprising 0 to 30% by weight of possible monomers.