JP4013160B2 - Alkoxysilyl group-containing acrylic emulsion - Google Patents

Description

  The present invention is an acrylic emulsion having a hydrolyzable alkoxysilyl group, which has good long-term storage stability and excellent durability of a film formed from the emulsion, for paints, sealants, coatings, etc. The present invention relates to an acrylic emulsion that is useful as a base emulsion.

  Acrylic polymers have been used for coating materials such as paints. By the way, coating agents such as paints are required to have durability and weather resistance such as water resistance, acid resistance, alkali resistance and moisture resistance. One of the countermeasures is silyl having a solution type hydrolyzable group. It is well known to use a room temperature curable copolymer containing a group (a silyl group having a hydrolyzable group between the silicon atom and the same hereinafter). As this copolymer, a copolymer by solution polymerization having a number average molecular weight of 300 to 30,000 in which a silyl group having at least two hydrolyzable groups is introduced in one molecule is disclosed in Patent Document 1. can give. However, in recent years, from the viewpoint of low pollution, resource saving, and health and safety, these coating agents are also required to be emulsion types that are aqueous, but silyl groups having hydrolyzable groups are hydrolyzed and condensed in aqueous systems. It was difficult to produce an emulsion type that was easy and had good storage stability.

  Patent Document 2 proposes a reactive resin emulsion containing a resin having at least one silyl group having a hydrolyzable group and an amine imide group in each molecule for the purpose of improving storage stability. The method of polymerizing solution in an organic solvent and then topping the solution to emulsify the remaining resin, or the method of topping after emulsifying by adding water in the solution, the process is complicated and economical The disadvantages cannot be overcome. Furthermore, the condensation reaction of silyl groups having hydrolyzable groups during storage cannot be sufficiently prevented, and when stored for a long period of time, the gelation of the emulsion is not observed, but the silyl group having hydrolyzable groups in the emulsion particles. Intra-particle cross-linking due to group condensation proceeds, and the film-forming property of the emulsion deteriorates, making it difficult to form a good film.

Japanese Patent Publication No. 63-60046 Japanese Patent Laid-Open No. 5-25354

  From the situation as described above, the present invention is an alkoxysilyl group having excellent long-term storage stability and film-forming property and excellent durability of the formed film by remarkably reducing intra-particle crosslinking by alkoxysilyl groups. It was made in an attempt to provide an acrylic emulsion containing.

  As a result of intensive studies to solve the above problems, the present inventors have an acrylic group or a methacryl group, and among the alkoxysilyl groups, a trimethoxysilyl group having a high hydrolyzability of an alkoxyl-silicon atom bond. A combination of an alkoxysilane having an acryl group or a methacryl group and an alkoxysilane having a low hydrolyzability, such as a dimethoxysilyl group, a diethoxysilyl group or a triethoxysilyl group; By making the number average molecular weight of the polymer 50,000 or more and using a reactive surfactant during polymerization, a film having excellent storage stability of the acrylic emulsion over a long period of time and an excellent characteristic can be obtained. As a result, the present invention was completed by further study.

The alkoxysilyl group-containing acrylic emulsion of the present invention solves the above-mentioned problems, and is selected from (1) (meth) acrylic acid alkyl esters having 1 to 18 carbon atoms and monoalkenylbenzene. 80-99% by weight of monomer and (2) (a) a silane selected from γ- (meth) acryloxypropyltrimethoxysilane and (b) γ- (meth) acryloxypropylmethyldiethoxysilane, γ -A silane selected from (meth) acryloxypropyltriethoxysilane and γ- (meth) acryloxypropylmethyldimethoxysilane [where the weight ratio of (a) component silane / (b) component silane is 60/40 ~ 10/90] in total 1-20% by weight
The resulting copolymer is an emulsion having a number average molecular weight of 50,000 or more obtained by emulsion polymerization of a mixture of a monomer and a silane using a reactive surfactant. In addition, in this-application specification, a number average molecular weight means the number average molecular weight by GPC.

The present invention will be described in more detail below.
The component (1) in the present invention is a main component monomer for forming the skeleton of the acrylic copolymer, and the alkyl group is a (meth) acrylic acid alkyl ester having 1 to 18 carbon atoms, that is, having a carbon number. Those selected from acrylic esters of alcohols having 1 to 18 alkyl groups, methacrylic esters of alcohols having 1 to 18 carbon atoms and monoalkenylbenzenes are used.
Specific examples of the alkyl group having 1 to 18 carbon atoms in the (meth) acrylic acid alkyl ester include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, an octyl group, a 2-ethylhexyl group, and a lauryl group. And stearyl groups, and examples of the monoalkenylbenzene include styrene, α-methylstyrene, vinyltoluene, and the like.
(1) As a component, the 1 type (s) or 2 or more types chosen from the group which consists of these (meth) acrylic-acid alkylesters and monoalkenylbenzene can be used. Monoalkenylbenzene generally raises the film-forming temperature of the emulsion, so it is usually used in combination with (meth) acrylic acid alkyl ester.
The amount of component (1) used is 80 to 99% by weight of the total amount of monomers [total amount of component (1) and component (2)] in order to exhibit the properties of the acrylic copolymer. Is preferably 85 to 95% by weight.

(2) The component is selected from γ-acryloxypropyltrimethoxysilane and γ-methacryloxypropyltrimethoxysilane (a), γ-acryloxypropylmethyldiethoxysilane, γ-methacryloxypropylmethyldiethoxy Comprising a combination of components (b) selected from silane, γ-acryloxypropyltriethoxysilane, γ-methacryloxypropyltriethoxysilane, γ-acryloxypropylmethyldimethoxysilane and γ-methacryloxypropylmethyldimethoxysilane; Introduced into the copolymer as a crosslinking component of the acrylic copolymer.
Among these, the component (a) alone has a high hydrolysis rate and condensation rate, and the crosslinking within the copolymer particles or between particles easily proceeds in the state of the emulsion. Hereinafter, it is abbreviated as MFT), and it becomes difficult to form a good coating film, resulting in poor storage stability. Conversely, the component (b) alone has a low hydrolysis rate and a low condensation rate, and it is difficult for crosslinking within the copolymer particles or between the particles to proceed, and there is little change in MFT and excellent storage stability, but the degree of crosslinking is low. The durability will be inferior.

When the weight ratio of component (a) / component (b) is 60/40 to 10/90, there is little increase in MFT during storage as an emulsion or paint, and a good coating is formed and the degree of crosslinking of the coating is An emulsion that is high and satisfies both storage stability and durability of the coating film is obtained. When the weight ratio of the component (a) / component (b) exceeds 60/40, the storage stability is inferior. When the component is less than 10/90, the durability of the coating film is inferior and both cannot be satisfied. .
(A), (b) Each component can be used alone or in combination of two or more of the above-mentioned silanes, but the total amount used as the component (2) is the total amount of monomers. It is 1 to 20 weight% of [the total amount of (1) component and (2) component], Preferably it is 5 to 10 weight%. (2) If the amount of the component is less than 1% by weight of the total amount of the monomers, the degree of cross-linking of the formed film is low and the durability is insufficient. After storage, the MFT becomes high and a good coating film cannot be formed, and both the storage stability and the durability of the coating film become insufficient.
Vinylmethyldimethoxysilane, vinylmethyldiethoxysilane, vinyltriethoxysilane, etc. can be used as component (b), but radical polymerization is much lower than that of (meth) acrylic acid alkyl ester, so that the polymerization efficiency is poor and preferable. Absent.

In addition, if necessary, the components (1) and (2) are added to provide the mechanical stability of the emulsion, the water resistance of the formed film, the glossiness, and other functionality within the range not impairing the object of the present invention. A copolymerizable monomer can be used.
Specific examples of such a monomer include carboxyl groups such as acrylic acid, methacrylic acid, and maleic anhydride, or monomers having anhydride groups thereof, 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meta ) Hydroxyl group-containing monomers such as acrylate, (meth) acrylamide, N-methylol (meth) acrylamide, N-methoxymethyl (meth) acrylamide, N-butoxymethyl (meth) acrylamide, diacetone (meth) acrylamide, etc. Amide group-containing monomer, alkoxyl group-containing monomer such as methoxyethyl (meth) acrylate, ethoxyethyl (meth) acrylate, glycidyl group-containing monomer such as glycidyl (meth) acrylate, glycidyl allyl ether, divinylbenzene, Allyl (meth) acrylate Monomers such as ethylene glycol di (meth) acrylate, diethylene glycol di (meth) acrylate, trimethylolpropane tri (meth) acrylate and the like having two or more radically polymerizable unsaturated groups, vinyl acetate, vinyl propionate And vinyl ester monomers such as acrylonitrile and methacrylonitrile, and vinyl halide monomers such as vinyl chloride and vinyl bromide. The above is selected and used, and the amount used is 10% by weight or less of the total amount of monomers [total amount of (1) component and (2) component].

  In order to remarkably improve the durability of the film formed from the emulsion of the present invention, such as water resistance, and to obtain performance close to that of a solution polymerization product, a reactive surfactant is used as a surfactant (emulsifier). I found it good. Examples of this reactive surfactant include:

And nonionic reactive surfactants such as quaternary ammonium salts and tertiary amine salts and cationic reactive surfactants containing a polymerizable group.
This reactive surfactant may be used alone or in combination of two or more, but if the amount is too small, a lot of coagulum will be generated in the produced emulsion, and the resulting film will also be It will not show good physical properties. If the amount is too large, the particle size of the emulsion particles becomes fine, the viscosity of the emulsion increases too much, and the water resistance of the film also deteriorates. Therefore, the amount of the reactive surfactant used is preferably 0.5 to 15% by weight, particularly 1 to 7% by weight based on the total monomers.

Further, as long as the object of the present invention is not impaired, it is possible to use a non-reactive surfactant used in ordinary emulsion polymerization in combination with this reactive surfactant, and the total amount of the surfactant is 30% by weight. 1 type or 2 types or more may be used together in the range of% or less.
These non-reactive surfactants include anionic surfactants such as alkyl or alkyl allyl sulfate, alkyl or alkyl allyl sulfonate, and dialkyl sulfosuccinate, and cationic such as alkyl trimethyl ammonium chloride and alkyl benzyl ammonium chloride. Examples of the surfactant include nonionic surfactants such as polyoxyethylene alkylphenyl ether, polyoxyethylene alkyl ether, and polyoxyethylene carboxylic acid ester.

  As the radical polymerization initiator used in the present invention, water-soluble types such as persulfates such as potassium persulfate and ammonium persulfate, hydrogen peroxide, t-butyl hydroperoxide, and hydrochloride of azobisamidinopropane, Examples thereof include oil-soluble types such as benzoyl peroxide, cumene hydroperoxide, dibutyl peroxide, diisopropyl peroxydicarbonate, cumyl peroxyneodecanoate, cumyl peroxyoctoate, and azobisisobutyronitrile. Furthermore, if necessary, a redox system using a reducing agent such as acidic sodium sulfite, Rongalite, L-ascorbic acid and the like can also be used. The amount of the polymerization initiator used is usually 0.1 to 10% by weight, more preferably 0.5 to 5% by weight, based on the total amount of monomers.

  In producing the alkoxysilyl group-containing acrylic emulsion of the present invention, it is preferable to control the pH during polymerization to 6.5 to 7.5 in order to suppress hydrolysis and condensation of alkoxysilyl groups. The polymerization is usually performed at a temperature of 10 to 90 ° C. At the end of the emulsion polymerization, a basic substance may be added to adjust the pH to 7 to 8 in order to prevent undesirable crosslinking reaction of the resulting polymer and further improve the storage stability, which is one of the objects of the present invention. Preferably, these substances include ammonia, amines, alkanolamines, sodium carbonate, caustic alkali and the like.

  In the alkoxysilyl group-containing acrylic emulsion of the present invention, the number average molecular weight of the copolymer is 50,000 or more. If it is less than 50,000, the flexibility and elasticity of the copolymer become insufficient. For example, when coated, it becomes impossible to follow the expansion and contraction of the base material, causing cracks, and the adhesiveness of the coating becomes strong and contaminates. Defects such as being easy to occur. The upper limit of the number average molecular weight is not particularly limited as long as the emulsion has film-forming properties. A number average molecular weight of 50,000 or more can usually be achieved by adjusting the amount of radical polymerization initiator and the polymerization temperature.

When the emulsion of the present invention is used for coatings, etc., in the alkoxysilyl group introduced into the copolymer side chain in the emulsion particles, condensation gradually occurs together with film formation to form a crosslinked film. A reaction catalyst can be added to promote the crosslinking reaction. The condensation at the alkoxysilyl group is dehydration condensation or dealcoholization condensation, whereby a siloxane bond is formed and crosslinking occurs.
Condensation reaction catalysts include organic titanate compounds such as isopropyltriisostearoyl titanate and isopropyltri (dioctylpyrophosphate) titanate, organoaluminum compounds such as acetoalkoxyaluminum diisopropylate, dibutyltin dilaurate, dibutyltin malate, dioctylic acid Carboxylic acid-type tin compounds such as tin, dialkyltin compounds such as dibutyltin oxide and dioctyltin oxide, carboxylic acid metal salts such as lead octylate and cobalt naphthenate, acidic phosphates, carboxylic acids and their anhydrides, triethylamine And amines such as dibutylamine-2-hexoate and salts thereof.
These catalysts may be added as they are if they are water-soluble, but oil-soluble ones are preferably added in the form of an aqueous dispersion, and the addition amount is preferably 0.01 to 10% by weight based on the emulsion of the present invention. .

When the emulsion of the present invention is used as a base emulsion for outdoor paints, it is necessary to form a good film at the temperature at the time of coating, and a copolymer that can form a film at a temperature lower than the coating temperature is used. MFT can be lowered from the coating temperature by adding a necessary amount of film forming aid to the emulsion having a high MFT to the emulsion. Preferable film forming aids include butyl carbitol acetate, butyl carbitol, butyl cellosolve acetate, benzyl acetate, 2,2,4-trimethyl-1,3-pentanediol monoisobutyrate and the like. Species or two or more are used.
Also, in the case of paints to be painted on the factory line, forced drying is possible, so a hard coating film is formed by using a high MFT emulsion within the range that can form a good film at the drying temperature and time, A product excellent in blocking resistance and stain resistance is obtained. In this case, a film forming aid may be used if necessary.

  The effect of the present invention is to combine an alkoxysilyl group [(a) component] having a high hydrolysis rate and a high condensation rate with an alkoxysilyl group [(b) component] having a low rate, by combining them at an appropriate ratio. It is thought that it was able to express by the synergistic effect of both.

  Since the alkoxysilyl group-containing acrylic emulsion of the present invention has good long-term storage stability and excellent durability of the resulting coating film, it is practically used as a base emulsion for paints, sealants, coating agents, etc. Useful.

Next, embodiments of the present invention will be described by way of examples. In addition, the part and% in an example show a weight part and weight%, respectively. Moreover, about the obtained emulsion, the characteristic and the molecular weight of the copolymer were measured by the following method.
a. Minimum film forming temperature (MFT)
The minimum temperature at which film formation was possible was measured with a minimum film formation temperature measuring machine manufactured by Rigaku Corporation.
b. Durability of the coating film For evaluating the durability of the coating film, the gel fraction and water resistance of the coating film, which are highly important, were measured by the following methods.
1) Gel fraction of the coating film Emulsion was applied to the aluminum foil so that the dry film thickness was about 25 μm, and the coating film obtained by curing for 7 days under the condition of 23 ° C. × 68% RH was shredded, This was subjected to Soxhlet extraction for 3 hours using methyl ethyl ketone, and the gel fraction was calculated from the unextracted amount.
2) Water resistance of coating film An emulsion was applied to a glass plate so that the dry film thickness was about 25 μm, and the film was cured for 7 days under the condition of 23 ° C. × 68% RH, and immersed in warm water at 50 ° C. for 5 days. The subsequent surface condition was observed and indicated by:
◯: No abnormality, Δ: Slightly whitened, ×: Whitening, blister generation c. Adhesion of the coating film Emulsion was applied to a glass plate so that the dry film thickness was about 25μm, and after curing for 7 days under the condition of 25 ° C x 68% RH Judged.
d. Average molecular weight of copolymer The emulsion immediately after polymerization was frozen and gelled, and the gel-like product was thoroughly washed with methanol to remove water, and dissolved in tetrahydrofuran. The number average molecular weight was measured by GPC.

Example 1
A polymerization vessel equipped with a stirrer, condenser, thermometer and nitrogen gas inlet was charged with 100 parts of deionized water and 0.03 part of sodium carbonate and 0.3 part of boric acid as a pH buffer, and the temperature was raised to 60 ° C. while stirring. After that, nitrogen substitution was performed. To this was added Longarit 0.15 parts, 1% aqueous solution of disodium ethylenediaminetetraacetate 0.03 parts of 1% aqueous solution of ferrous sulfate, 37 parts of methyl methacrylate, 43 parts of butyl acrylate, 10 parts of styrene, γ -2 parts methacryloxypropyltrimethoxysilane, 8 parts γ-methacryloxypropylmethyldiethoxysilane, 3.2 parts reactive surfactant Aqualon RN-20 (trade name, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) represented by the following structural formula, Aqualon HS-10 (Daiichi Kogyo Seiyaku Co., Ltd., trade name) 1.4 parts and t-butyl hydroperoxide (69% pure) 0.3 parts mixed solution 104.9 parts under stirring while maintaining the internal temperature at 60 ° C. The polymerization was completed by adding uniformly over time and further reacting at 60 ° C. for 1 hour. The solid content concentration of the obtained emulsion was 50.6% and pH 7.2.

上記で得られたエマルジョン及び塗膜の特性は表２に示すとおりであった。

The properties of the emulsion and coating film obtained above were as shown in Table 2.

Example 2
Polymerization was carried out in the same manner as in Example 1 with the monomers and surfactants shown in Table 1 and the amount (parts) thereof to obtain an emulsion having a solid content concentration of 50.5% and pH 6.9. The properties of the obtained emulsion and coating film were as shown in Table 2.

Example 3
A polymerization vessel equipped with a stirrer, condenser, thermometer and nitrogen gas inlet was charged with 50 parts of deionized water and 0.03 part of sodium carbonate and 0.3 part of boric acid as a pH buffer, and the temperature was raised to 60 ° C. while stirring. After that, nitrogen substitution was performed. To this, 0.15 parts of Rongalite, 0.09 part of 1% aqueous solution of ethylenediaminetetraacetate and 0.03 part of 1% aqueous solution of ferrous sulfate were added. At the same time, 39 parts of methyl methacrylate, 46 parts of butyl acrylate, and 10 parts of styrene , 1 part of γ-acryloxypropyltrimethoxysilane, 4 parts of γ-methacryloxypropyltriethoxysilane and 0.3 part of t-butyl hydroperoxide (69% pure) as a reactive surfactant Aqualon RN-20 ( Add 7.7 parts of the emulsion into 154.9 parts of the emulsified solution that was put into a solution of 3.2 parts, Aqualon HS-10 (above) 1.4 parts and 50 parts of deionized water and emulsified with a homomixer. After the polymerization reaction under stirring and the exotherm has subsided, the remaining emulsion is uniformly added over 2.5 hours with stirring while maintaining the internal temperature at 60 ° C, and further reacted at 60 ° C for 1 hour. To obtain an emulsion.
The resulting emulsion had a solid content concentration of 50.8% and pH 7.1. Further, the properties of the obtained emulsion and coating film were as shown in Table 2.

Example 4
Polymerization was carried out in the same manner as in Example 1 with the monomers and surfactant types and amounts (parts) shown in Table 1 to obtain an emulsion having a solid content concentration of 50.5%, pH 7.1 and MFT of 44 ° C. Table 2 shows the characteristics of the emulsion and coating film prepared by adding 10 parts of butyl carbitol acetate as a film forming aid to 100 parts of the solid content of the obtained emulsion.
In addition, an MFT 44 ° C. emulsion without adding a film forming aid was applied to a glass plate so that the dry film thickness was about 25 μm and dried at 105 ° C. for 30 minutes to form a coating film without cracks. When this was immersed in 50 ° C. warm water for 5 days to observe the surface condition and evaluated for water resistance, there was no abnormality. Furthermore, apply the aluminum foil to a dry film thickness of about 25μm, chop the coating film dried at 105 ℃ for 30 minutes, extract it with methyl ethyl ketone for 3 hours, and extract the gel fraction from the unextracted amount. The calculated value was as high as 96%, which proved useful as a base emulsion for paints for line painting.

Comparative Examples 1-3
In the same manner as in Example 1, polymerization was carried out with the monomers and surfactant types and amounts (parts) shown in Table 1 to obtain emulsions. The properties of the obtained emulsion and coating film were as shown in Table 2. Each emulsion was as follows.
Comparative Example 1: Solid content concentration 50.5%, pH 7.1
Comparative Example 2: Solid content concentration 50.6%, pH 7.1
Comparative Example 3: Solid content concentration 50.4%, pH 7.0

Comparative Example 4
A polymerization vessel equipped with a stirrer, condenser, thermometer and nitrogen gas inlet was charged with 100 parts of deionized water and 0.03 part of sodium carbonate and 0.3 part of boric acid as a pH buffer, and the temperature was raised to 60 ° C. while stirring. After that, nitrogen substitution was performed. After further raising the internal temperature to 80 ° C., 0.15 part of Rongalite, 0.09 part of 1% aqueous solution of disodium ethylenediaminetetraacetate and 0.03 part of 1% aqueous solution of ferrous sulfate were added to this, and at the same time, methyl methacrylate 39 Parts, 46 parts of butyl acrylate, 10 parts of styrene, 1 part of γ-acryloxypropyltrimethoxysilane, 4 parts of γ-methacryloxypropyltriethoxysilane, 3.2 parts of reactive surfactant Aqualon RN-20 (supra), Aqualon HS-10 (supra) 1.4 parts, t-butyl hydroperoxide (pure content 69%) 0.3 parts and dodecyl mercaptan 1 part mixed liquid 105.9 parts with stirring at 3 hours for 3 hours The mixture was then uniformly added and further reacted at 80 ° C. for 1 hour to complete the polymerization. The resulting emulsion had a solid content concentration of 50.2% and a pH of 6.9. Further, the properties of the obtained emulsion and coating film were as shown in Table 2.

ADEKA rear soap SE-10N and ADEKA rear soap NE-10 (both trade names manufactured by Asahi Denka Co., Ltd.) in Table 1 are represented by the following structural formulas.

Claims (1)

(1) 80 to 99% by weight of a monomer selected from (meth) acrylic acid alkyl ester having 1 to 18 carbon atoms and monoalkenylbenzene and (2) (a) γ- (meth) acryloxy Silane selected from propyltrimethoxysilane and (b) γ- (meth) acryloxypropylmethyldiethoxysilane, γ- (meth) acryloxypropyltriethoxysilane and γ- (meth) acryloxypropylmethyldimethoxysilane Only 1 to 20% by weight in total of selected silanes (however, the weight ratio of (a) component silane / (b) component silane is 60/40 to 10/90))
An alkoxysilyl group-containing acrylic emulsion having a number average molecular weight of 50,000 or more, which is obtained by emulsion polymerization of a mixture of a monomer and a silane using a reactive surfactant.