JPH1121305A - Manufacture of curable emulsion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a curable emulsion which comprises a polymer containing a hydrolyzable silyl group and shows excellent storage stability and crosslinking ability of films obtained therefrom. SOLUTION: Fine particles having a diameter of 0.05-1.0 μm of a monomer mixture of (a) 0.1-30% by weight of a vinyl monomer having a hydrolyzable alkoxysilyl group and (b) 99.9-70 % by weight of a monomer which can copolymerize therewith based on the total amount of all monomers and an oil soluble initiator for radical polymerization are dispersed in water in the presence of an emulsifying agent (preferably a surface active agent having a radically polymerizable group) and the monomer mixture is made to polymerize under pH of the aqueous dispersion maintained at not more than 7.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a method for producing a curable emulsion comprising a polymer having a silanol group. The curable emulsion obtained by the present invention can be used for various applications including paints, coating agents, pressure-sensitive adhesives and the like.

[0002]

2. Description of the Related Art Curable polymers having a hydrolyzable alkoxysilyl group are widely used in applications such as adhesives, sealing materials, paints and coatings, but in these fields of application, organic solvents are used. In order to avoid harm to the human body and environmental pollution due to volatilization of water, an aqueous material is required. The necessity of aqueous emulsification is also increasing for curable copolymers having an alkoxysilyl group. With respect to an aqueous emulsion comprising a curable copolymer having an alkoxysilyl group, it is necessary to solve the problem that the stability of the emulsion is likely to be impaired by hydrolysis of the alkoxysilyl group. It has been done.

[0003] That is, JP-A-3-227312 discloses that when a monomer having an alkyl (meth) acrylate and an alkoxysilyl group is subjected to aqueous emulsion polymerization, the resulting curable copolymer is stabilized. For the purpose, there has been proposed a method in which 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-mentioned monomer to carry out copolymerization. JP-A-7-149840 discloses that when a monomer having a hydrolyzable silyl group and a copolymerizable monomer are copolymerized in an aqueous medium, a pH buffer and a specific HLB are used.
It is disclosed to use a surfactant having ing.

According to the method described in the above publication, a curable emulsion having satisfactory stability in an aqueous medium can be obtained. However, the cured film obtained from the emulsion disclosed in the above-mentioned publication has one step in mechanical strength, adhesion to a substrate, and the like due to insufficient crosslinking. An object of the present invention is to provide a method for producing a curable emulsion having both excellent crosslinkability and storage stability.

[0005]

Means for Solving the Problems The present inventors have made intensive studies to solve the above-mentioned problems, and as a result, have found that a vinyl monomer having a hydrolyzable alkoxysilyl group and a monomer copolymerizable therewith. When copolymerizing is carried out, by adopting a specific polymerization method, without impairing the storage stability, the alkoxysilyl group is hydrolyzed during the polymerization and converted into a silanol group, resulting in a polymer emulsion having a large amount of the group. Was found, and it was found that a film excellent in mechanical properties and the like was obtained according to the emulsion, and the present invention was completed. That is, according to the present invention, based on the total amount of all the monomers, the ratio of (a) the vinyl monomer having a hydrolyzable alkoxysilyl group is 0.1 to 30% by weight and (b) Possible monomer ratio is 99.9-7
0% by weight of a monomer mixture and an oil-soluble radical polymerization initiator.
A method for producing a curable emulsion, comprising polymerizing the monomer mixture while maintaining the pH of an aqueous dispersion dispersed in water in the presence of an emulsifier at 7 or less. Hereinafter, the present invention will be described in more detail.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION As described above, the monomer to be polymerized in the present invention is a vinyl monomer having a hydrolyzable alkoxysilyl group (hereinafter referred to as a silyl monomer) and a monomer having the same. It is a copolymerizable monomer. Examples of the silyl-based monomer include a compound having a group —Si (X) _n (where X is an alkoxy group and n is an integer of 1 to 3) and a vinyl group as an essential unit. , Vinylmethyldimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane, γ-methacryloxypropyltrimethoxysilane, γ-methacryloxypropylmethyldimethoxysilane, γ-methacryloxypropyltriethoxysilane Examples include silane, γ-methacryloxypropylmethyldiethoxysilane, γ-acryloxypropyltrimethoxysilane, and γ-acryloxypropylmethyldimethoxysilane.

[0007] Monomers copolymerizable with the above-mentioned silyl-based monomers (hereinafter sometimes referred to as comonomer) include methyl (meth) acrylate, ethyl (meth) acrylate,
Alkyl (meth) acrylates such as n-butyl (meth) acrylate, cyclohexyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, lauryl (meth) acrylate, stearyl (meth) acrylate; (meth)
2-hydroxyethyl acrylate, 2-hydroxypropyl (meth) acrylate, (meth) acrylamide, N
-(Meth) acrylates such as methylolacrylamide, perfluoroalkyl (meth) acrylate, N, N-dimethylaminoethyl (meth) acrylate, N, N-diethylaminoethyl (meth) acrylate; vinyl acetate; Examples thereof include vinyl propionate, styrene, α-methylstyrene, (meth) acrylic acid, maleic acid, itaconic acid and 2-acrylamido-2-methylpropanesulfonic acid. Among the above, alkyl (meth) acrylate having an alkyl group having 1 to 8 carbon atoms, 2 carbon atoms
2-Hydroxyalkyl (meth) acrylates having -3 to 3 alkylene groups, styrene, glycidyl methacrylate and (meth) acrylic acid are preferred. In order to enhance the weather resistance, strength, heat resistance, etc. of the film, the proportion of the (meth) acrylic acid ester in the monomer used as a copolymer monomer with the silyl-based monomer is 50% by weight. % Is preferable.

The preferred proportions of the silyl monomer and the copolymer monomer are 0.5 to 30% by weight of the silyl monomer and the copolymer monomer based on the total amount of all the monomers. 99.5
To 70% by weight, more preferably 1 to 20% by weight of a silyl monomer and 99 to 80% by weight of a comonomer.
It is. If the proportion of the silyl-based monomer is less than 0.1% by weight, the curability of the coating film will decrease, while if it exceeds 30% by weight, the adhesion of the coating film to the substrate will decrease.

The polymerization initiator in the present invention is an oil-soluble polymerization initiator, and specifically, preferably has a solubility in water at 20 ° C. of 10% by weight or less. , 2'-azobisisobutyronitrile, 2,2'-azobis-2,4-dimethylvaleronitrile, 1-azobis-1-cyclohexanecarbonitrile and dimethyl-2,2'-azobisisobutyrate Azo initiators, and lauroyl peroxide, benzoyl peroxide, dicumyl peroxide,
Organic peroxides such as cyclohexanone peroxide, di-n-propylperoxydicarbonate and t-butylperoxypivalate. The amount of the polymerization initiator to be used is preferably 0.1 to 10% by weight, more preferably 0.5 to 5% by weight, based on the total amount of the monomers used. In the present invention, the polymerization initiator is dissolved in a monomer mixture composed of a silyl monomer and a copolymerizable monomer, and is aqueously emulsified together with the monomer.

As an emulsifier for aqueous emulsification of the above-mentioned monomer and polymerization initiator, various surfactants such as anionic, nonionic and cationic surfactants used as emulsifiers in general emulsion polymerization and the like can be used. In the present invention, a surfactant having a radically polymerizable group is preferable in that a high water resistance and weather resistance can be imparted to a film made of the curable emulsion. Further preferred surfactants are radically polymerizable surfactants represented by the following chemical formula. Chemical formula; Z- (AO) n-Y (wherein, Z is a structural unit having a radical polymerizable double bond, AO is an oxyalkylene group, n is an integer of 2 or more, Y
Represents an ion dissociable group) In the above chemical formula, preferred Z is an aromatic hydrocarbon group,
It is a structural unit consisting of a radically polymerizable double bond and a hydrophobic group such as an alkyl-substituted aromatic hydrocarbon group, a higher alkyl group or an alicyclic hydrocarbon group. ) Allyl, propenyl or butenyl are preferred. 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 Y _{are, -SO 3 Na, -SO 3 NH} 4, -COONa, -
COONH _4, -PO ₃ Na ₂ and -PO ₃ (NH _{4)
And the} like.

Specific examples of the above-mentioned surfactant include, for example, compounds represented by the following chemical formulas 1, 2 and 3. As R in Chemical Formulas 1 and 2, a linear or branched alkyl group having 6 to 18 carbon atoms is preferable. R2 in Chemical Formula 3
Is preferably an alkyl group having 8 to 24 carbon atoms.
1 is a hydrogen atom or a methyl group. Y in Chemical Formulas 1 to 3
Is as described above. A preferred amount of the surfactant is 0.5 to 100 parts by weight of the monomer.
20 parts by weight, more preferably 1 to 5 parts by weight.

[0012]

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[0013]

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[0014]

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In the present invention, the monomer and the polymerization initiator are emulsified and dispersed in an aqueous medium. At this time, the monomer and the polymerization initiator (hereinafter, these may be collectively referred to as oil-soluble components) are used. The particle size of the fine particles becomes 0.05 to 1.
0 μ, preferably 0.05 to 0.5 μ. It is preferable that the particle size of the dispersed particles composed of the oil-soluble component is as fine as possible. If it exceeds 1.0 μm, a stable aqueous emulsion cannot be obtained. The aqueous dispersion can be produced, for example, by the following method. After dispersing a mixture obtained by dissolving the oil-soluble polymerization initiator in a monomer in an aqueous medium in which an emulsifier has been previously dissolved, a high-pressure emulsifying disperser or a turbine-type mixer generally called a homogenizer It can be manufactured by further reducing the size using a dispersing device having high shear energy. At that time, a preferable ratio of the oil-soluble component to the aqueous medium is 20 to 150 parts by weight of the aqueous medium per 100 parts by weight of the oil-soluble component.

The polymerization is carried out using the aqueous dispersion, that is, the monomer emulsion, obtained by the above operation. In the present invention, it is necessary to maintain the pH of the reaction solution during the polymerization at 7 or less. During the latter half of the polymerization, that is, during the polymerization period after about 40% of the polymerization time has elapsed, p
H is more preferably 5 or less. Since the pH of the reaction solution during the polymerization period is on the acidic side, hydrolysis of the alkoxysilyl group in the silyl monomer occurs during polymerization, and the resulting silanol group forms the curable emulsion of the present invention. The crosslink density in the coating increases. The above-mentioned prior art JP-A-7-149840.
In the invention described in the above-mentioned publication, the pH of the reaction solution is maintained in the range of 6 to 9 during the period from the start to the end of the polymerization by using a pH buffer when performing the same polymerization as in the present invention. The technical means that is adopted. Such technical means are:
It is effective for suppressing the hydrolysis of the alkoxysilyl group in the silyl-based monomer, and since the publication of the above-mentioned patent publication, the silyl-based monomer and the monomer copolymerizable therewith in an aqueous medium. In the case of polymerization, it has been adopted as a conventional means.

On the other hand, in the present invention, as described above, it is necessary to maintain the pH of the reaction solution during polymerization at 7 or less. Such requirements include: silyl monomers; 0.1-30% by weight and monomers copolymerizable therewith; 99.9-70.
Polymerizing at a temperature of 50 to 100 ° C. in a state in which a monomer mixture having a weight percent composition and an oil-soluble radical polymerization initiator are dispersed as fine particles having a particle size of 0.05 to 1.0 μ in an aqueous medium. Can be realized. In short, by performing polymerization without using a pH buffering agent conventionally used by those skilled in the art as a usual means, the pH of the reaction solution is increased by the silanol group generated by hydrolysis of the silyl monomer during polymerization. The pH of the reaction solution after the polymerization has progressed to some extent becomes 2.5 to 5. In the present invention, if necessary, an inorganic acid or an organic acid may be added to the polymerization system to control the pH of the reaction solution, and the copolymerized monomer may be an unsaturated monomer such as (meth) acrylic acid. It is also preferred to use carboxylic acids. In any case, it is preferable that the pH of the reaction solution does not become 2 or less.

In the polymer emulsion obtained by the above polymerization, it is known by quantitative analysis of the alcohol produced by the hydrolysis that most of the alkoxysilyl groups in the polymer are hydrolyzed.
The hydrolysis rate of alkoxysilyl groups in the polymer is usually 7
0% or more, but a film with a high degree of crosslinking can be obtained.
The decomposition rate is more preferably 80% or more.

If the curable emulsion obtained by the present invention is applied and water is volatilized at normal temperature or under heating, a film can be obtained. This film is crosslinked and cured by a condensation reaction of silanol groups derived from silyl monomers. The crosslinking reaction proceeds rapidly even at room temperature, but if it is desired to further promote crosslinking, as a curing catalyst, for example, an organic titanate compound such as isopropyl triisostearoyl titanate or isopropyl tri (dioctyl pyrophosphate) titanate, or tin dioctylate or dibutyl tin Gilaurate,
An organic tin compound such as dibutyltin malate or an organic acid catalyst such as paratoluenesulfonic acid may be used.

The curable emulsion of the present invention is suitable as a coating agent, and is used as a coating material for building materials made of glass, slate, metal, wood, plastic, or the like, an acid rain-resistant coating material, an antifouling coating material, and an inorganic building material. It can be used as a liquid agent, a moisture-proof coating agent for electric and electronic parts, a back coating agent for magnetic tape, a sealing agent, an adhesive, and the like. When used as an adhesive, it has excellent heat resistance, so that it does not creep or peel even when used at high temperatures, and has a feature of maintaining stable adhesive strength for a long time. Since it has excellent removability at high temperatures, it can be used as a masking tape or surface protection tape. The curable emulsion obtained according to the present invention may be, depending on the application, a filler such as clay, talc, calcium carbonate, and titanium white, a film-forming aid such as butyl cellosolve, butyl carbitol, and butyl carbitol acetate; Phthalate, plasticizers such as dioctyl phthalate, rosin, terpene phenol, tackifiers such as petroleum resin, wetting, dispersion,
Various additives such as various surfactants used for defoaming, thickeners, thixotropic agents, antifreezing agents and the like may be added and used.

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples. In addition, all the parts of the component blend in each example are parts by weight. Among the surfactants used, “AQUALON HS10” (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) is a compound represented by the following chemical formula 4.

[0022]

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[0023]

Example 1 (1) Production of monomer emulsion Monomer (a) and monomer (b), oil-soluble radical initiator,
Using a radical polymerizable surfactant and an aqueous medium at the ratios shown in Table 1, a monomer emulsion having an average particle size of dispersed particles of 0.15 μm was produced using a homomixer.

[0024]

[Table 1]

(2) Polymerization Step A flask equipped with a stirrer, a thermometer and a cooler was charged with 2 parts of deionized water 70 and Aqualon HS10 as an aqueous medium, and the liquid temperature was raised to 85 ° C., followed by stirring. The above pre-emulsion was added dropwise over 3 hours. After completion of the dropwise addition, the temperature of the internal solution was raised to 90 ° C., and the temperature was further maintained for 1 hour to complete the polymerization.
The pH of the reaction solution during the polymerization was around 3. During the polymerization, liquid separation and blocking did not occur, and the polymerization was performed stably. The average particle size of the polymer particles was 0.15 μm, and the pH was 2.9. The ethanol content in the emulsion was 2.45%, and the hydrolysis rate was 99.9%.
The emulsion was dried and heat-treated at 80 ° C., and the coating film was extracted with acetone (23 ° C. for 15 hours) to measure the extraction ratio. The results are shown in Table 2. The emulsion did not show any change in properties even after standing at room temperature for one month, and showed good storage stability.

[0026]

Example 2 A curable emulsion was obtained in exactly the same manner as in Example 1, except that 5 parts of γ-methacryloxypropyltriethoxysilane and 20 parts of n-butyl acrylate were used. The average particle size of the polymer particles is 0.17 μm
And the pH was 2.7. The ethanol content in the emulsion was 1.0%, and the hydrolysis rate was 99.4%. The emulsion was stable after standing at room temperature for one month.

Example 3 2.5 parts of γ-methacryloxypropyltriethoxysilane and 22.5 parts of n-butyl acrylate
A curable emulsion was obtained in exactly the same manner as in Example 1, except for using part. The average particle size of the polymer particles is 0.1.
At 18 μm, the pH was 2.7. The ethanol content in the emulsion was 0.44%, and the hydrolysis rate was 8%.
It was 4.5%. The emulsion was stable after standing at room temperature for one month.

[0027]

Comparative Example 1 A resin emulsion was synthesized in exactly the same manner as in Example 1 except that the pH was maintained at 8 to 10 by adding sodium bicarbonate. The average particle size of the polymer particles is 0.2
At 0 μm, the pH was 9.2. The ethanol content in the emulsion was 0.07%, and the hydrolysis rate was 2.
9%. The emulsion was stable after standing at room temperature for one month.

[0028]

[Table 2]

[0029]

Example 4 A curable emulsion was produced in the same manner as in Example 1 except that γ-methacryloxypropyltrimethoxysilane was used instead of γ-methacryloxypropyltriethoxysilane, and the following components were used. γ-methacryloxypropyltrimethoxysilane 10 parts Cyclohexyl methacrylate 50 parts n-butyl acrylate 50 parts Acrylic acid 1 part The average particle size of the polymer particles is 0.10 μm, and the pH is 3.4.
Met. The physical properties of the film obtained from the curable emulsion obtained in this example were measured as follows. Table 3 shows the measurement results.

The curable emulsion was applied to a release paper and dried at room temperature for 10 days to form a coating film having a thickness of about 1 mm. The water resistance is as follows.
The transparency (○: transparency maintained, Δ: slightly whitened, ×: completely whitened) after immersion for a period of time and the water absorption were evaluated. The solvent resistance was measured by immersing the dried coating film in normal-temperature acetone for 24 hours. The change in the shape of the sample piece and the size of the sample piece after immersion were measured and evaluated as a ratio [swelling rate (%)] to the initial size.

[0031]

Comparative Example 2 A resin emulsion was synthesized in exactly the same manner as in Example 4 except that the pH was maintained at 8 to 10 by adding sodium bicarbonate. Its pH was 9.2. The film properties were measured in the same manner as in Example 4. Table 3 shows the results.

[0032]

[Table 3]

As is clear from the comparison between the cured films obtained in Example 4 and Comparative Example 2, the film formed from the emulsion synthesized by the method of the present invention did not whiten even when immersed in water. The water absorption after immersion for 2 to 3 hours.
5%. The test piece did not change even after immersion in acetone for 24 hours, and only swelled to 110 to 120% before immersion. In comparison with this, the emulsion coating film obtained by adjusting the pH of the polymerization reaction solution to around 9 with a buffering agent was whitened by immersion in water, and showed a high water absorption of 7.6%. Was. In addition, when immersed in acetone, although the sample piece does not change,
% Swelled.

Next, an example in which the curable emulsion obtained by the present invention is used as a pressure-sensitive adhesive will be described. 5 as holder
Using a 0 μPET film, a test piece was prepared by applying a 20 μm film thickness with a doctor blade. The evaluation of the emulsion and the evaluation of the pressure-sensitive adhesive performance were performed according to the following methods. (1) Amount of grit──Amount of unreached material when the curable emulsion was filtered through a 200-mesh net was defined as a grid content. (2) Adhesion strength 180 in accordance with JIS Z-0237
゜ Peeling adhesion was measured and indicated in grams per 25 mm width.
Measured after 0 minutes).

(3) Removability: Stainless steel plate for adherend
After applying for 20 minutes after pasting,
And cooled to room temperature after 1 hour. Specimen is room
After the temperature has dropped to the temperature,
The removability was evaluated. ○ ─ Cleanly peeled without glue residue. △ ─ Some adhesive residue was confirmed. × ─ All the adhesive was transferred to the adherend. (4) Heat resistance ─── Dynamic viscoelasticity measurement (used equipment: Rheomet
Rix Far East Co., Ltd., RDS-II)
The temperature dependence of the modulus was observed. Frequency 1 Hz, heating rate 3 ° C / min (temperature range 0 to 300
° C). ○ ─ Storage elastic modulus is 10 5-10 8dyn / cm Within 2
× ─ Storage elastic modulus is 10 5-10 8dyn / cm Range 2
Deviating from

[0036]

Example 5 49.6 parts of n-butyl acrylate, 49.6 parts of 2-ethylhexyl acrylate, 0.6 part of acrylic acid
Part, γ-methacryloxypropyltrimethoxysilane 0.5 part, 2,2′-azobisisobutyronitrile
0 parts, Aqualon HS-100.6 parts and deionized water 120 parts were mixed and emulsified and dispersed with a homomixer to prepare a monomer emulsion having an average particle size of 0.09μ. Polymerization was performed in the same manner. By this polymerization operation, a curable emulsion having a solid content of 40% by weight, an average particle size of the polymer particles of 0.09 μm, and a pH of 3.6 was obtained. The adhesive properties and the like of this emulsion are as shown in Table 4.

Example 6 A curable emulsion was prepared in the same manner as in Example 5 except that the amount of γ-methacryloxypropyltrimethoxysilane used in Example 5 was changed to 1.0 part, and all other components and polymerization procedures were the same as in Example 5. The adhesive properties of the obtained curable emulsion are as shown in Table 4.

[0037]

[Table 4]

[0038]

Comparative Example 3 A curable emulsion was produced in the same manner as in Example 5 except that γ-methacryloxypropyltrimethoxysilane was not used and the other components and polymerization operations were all the same.
The physical properties of the obtained curable emulsion are as shown in Table 4 above.

[0039]

According to the present invention, a curable aqueous emulsion having excellent storage stability and high coating film properties can be obtained.
The emulsion can be suitably used as a coating agent and an adhesive. Since the curable emulsion according to the present invention is further excellent in heat resistance, it is also useful as a heat-resistant removable adhesive.

Claims (2)

[Claims] (1) based on the total amount of all monomers,
A monomer mixture in which the proportion of a vinyl monomer having a hydrolyzable alkoxysilyl group is 0.1 to 30% by weight and (b) the proportion of a monomer copolymerizable therewith is 99.9 to 70% by weight And a particle size of oil-soluble radical polymerization initiator of 0.0
While maintaining the pH of an aqueous dispersion of 5 to 1.0 μm fine particles dispersed in water in the presence of an emulsifier at 7 or less,
A method for producing a curable emulsion, comprising polymerizing the monomer mixture. 2. The method according to claim 1, wherein a surfactant having a radical polymerizable group is used as the emulsifier.