JPH0242867B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a resin composition for coatings having a high solid content concentration, and more particularly to a resin composition comprising a specific acrylic copolymer and an amino resin or an isocyanate compound as main components. be. In recent years, there has been a strong demand for resin compositions for coatings with high solid content concentrations in order to reduce the amount of solvents used in response to solvent regulations or resource conservation. By the way, in order to obtain a coating resin composition with a high solid content concentration, it is usually necessary to lower the molecular weight of the acrylic copolymer, and by doing so, the dilutability of the copolymer to a solvent can be reduced. Since the viscosity of the copolymer solution is improved, the viscosity of the copolymer solution is further reduced, and as a result, the amount of solvent used in preparing the paint can be reduced, and a resin composition for paint having a high solids concentration can be obtained. . The method for manufacturing such low-molecular-weight acrylic copolymers usually involves solution polymerization under the reflux temperature of the solvent, that is, at a temperature of 80 to 120°C.
Although it is relatively easy to obtain an acrylic copolymer with a molecular weight of 5,000 to 10,000, it is extremely difficult to obtain an acrylic copolymer with a lower molecular weight of 500 to 3,000. Conventional acrylic copolymers of 500 to 3000, which were obtained with care, have too few hydroxyl groups and poor curability, so they can be obtained by crosslinking with amino resins or isocyanate compounds. It has been impossible to obtain a practical copolymer because the coating film has poor solvent resistance, stain resistance, weather resistance, etc. However, based on the technical background as described above, the present inventors used an acrylic copolymer having a number average molecular weight of 500 to 3000 and a solid content concentration of 50% by weight or more at the time of coating. As a result of intensive studies on the performance of cured coatings obtained by crosslinking reactions between copolymers and amino resins or isocyanate compounds, we found that (A) in the presence of a solvent and an initiator having a radical generation period, (a-1) Styrene 10 to 80 parts by weight, (a-2) Acrylic acid ester or methacrylic acid ester 0 to 65 parts by weight, (a-3) Hydroxyl group-containing vinyl monomer
5 to 40 parts by weight, (a-4) 0 to 10 parts by weight of acid group-containing vinyl monomer, and (a-5) 2-mercaptoethanol
consisting of 3 to 20 parts by weight, and the number average molecular weight obtained by copolymerizing these components to a total of 100 parts by weight is 500 to 3000, and the number of hydroxyl groups in one molecule is 2.3 or more The main components are an acrylic copolymer and (B) an amino resin (b-1) or an isocyanate compound (b-2), the former copolymer (A) component and the latter resin (b-1) component. The mixing weight ratio of is 40/
60 to 95/5, or the ratio of the number of hydroxyl groups in the former component to the number of isocyanate groups in the latter component in the former copolymer (A) component and the latter compound (b-2) component is 1/0.5 to 1/1.5 and the solid content concentration at the time of coating is 50% by weight or more, when using a resin composition for a high solids coating, the above copolymer (A) and the above resin (b- 1) or the copolymer (A) and the above-mentioned compound (b-2), the cured coating film obtained by the crosslinking reaction with the above compound (b-2) has significantly improved solvent resistance and stain resistance. The present invention was completed based on the discovery that the reactivity of the crosslinking reaction accompanying the reduction in molecular weight is also significantly improved. The present invention will be described in more detail. First, the acrylic copolymer (A) is prepared by adding the above-mentioned (a-1) and (a-
3) and (a-5), (a-1), (a-2), (a
-3) and (a-5), or (a-1), (a
-2), (a-3), (a-4) and (a-5) in the quantitative ranges described above (however, the total amount in each combination is 100 parts by weight),
It is obtained by solution polymerization at a temperature of 80 to 120°C, in which only a solvent or a mixture of a solvent and a monomer is present in a reaction vessel equipped with a reflux condenser and a stirrer. Next, a method can be adopted in which an initiator having a radical generating group and a mixture of the various combinations described above are continuously supplied, and the copolymer (A) can be stably obtained by such a method. As described above, the copolymer (A) is obtained by ordinary radical polymerization, but the molecular weight of the copolymer (A) is reduced due to the chain transfer effect of the 2-mercaptoethanol (a-5). can be arbitrarily adjusted within the range of 500 to 3000, and one hydroxyl group based on 2-mercaptoethanol can always be introduced at the end of the copolymer (A). Thus, the hydroxyl value in the copolymer (A) is 2-
In addition to mercaptoethanol (a-5), it is also supplied by the hydroxyl group-containing vinyl monomer (a-3), and therefore the amount of the monomer (a-3) is
Since the hydroxyl value can be adjusted arbitrarily by changing the amount within the range of ~40 parts by weight,
By appropriately changing the supply amount (supply ratio) of both (a-3) and (a-5),
The hydroxyl value and number average molecular weight of the copolymer (A) can be adjusted at the same time. This is because conventional hydroxyl group-containing acrylic copolymers are made only from this type of hydroxyl group-containing vinyl monomer, and therefore the hydroxyl value is controlled only by such monomers, whereas the composition of the present invention In the case of the copolymer (A) constituting the product, in addition to the hydroxyl group-containing vinyl monomer, 2-mercaptoethanol adds one hydroxyl group to the end of the polymer, resulting in a low molecular weight copolymer. Even though the number of hydroxyl functional groups is obtained, the number of hydroxyl functional groups does not decrease, and a high hydroxyl value can always be provided, so that the control range of the hydroxyl value can be widened, as described above. Therefore, the hydroxyl group-containing acrylic copolymer (A) used in the present invention has a hydroxyl functional group number of 2.3 or more in one molecule, and for this reason, the amino resin (b-1) or isocyanate By crosslinking with compound (b-2), a cured coating film having a gel fraction of 85% or more can be provided. When the number of hydroxyl groups is less than 2.3, the gel fraction of the composition of the present invention decreases, resulting in a brittle film, which is not preferred. In addition, the hydroxyl group bonded to the end of the polymer has a higher crosslinkability with amino resins and isocyanate compounds than the hydroxyl group introduced into the backbone polymer, and for this reason, the acrylic copolymer (A) is better than conventional ones. It is noteworthy that despite the lower molecular weight, it compensates for the decrease in crosslinking reaction rate and maintains the same level of crosslinking properties as conventional acrylic copolymers with a molecular weight range of 5,000 to 10,000. It is worth it. Furthermore, this copolymer (A) used in the present invention has styrene as an essential component, which increases the glass transition point of the polymer, and as a result,
The hardness, solvent resistance and stain resistance of the composition of the present invention are extremely good. Typical initiators having the above-mentioned radical generating group used to obtain the copolymer (A) include benzoyl peroxide, di-t-butyl peroxide, cumene hydroperoxide, and t-butyl peroxide. -butyl hydroperoxide, t-butyl perbenzoate or azobisisobutyronitrile. Typical solvents used to obtain the copolymer (A) include aromatic solvents such as xylene or toluene; alcoholic solvents such as i-propanol, n-butanol, and i-butanol. ; ester systems such as ethyl acetate, isopropyl acetate or butyl acetate; ketone systems such as methyl ethyl ketone, methyl isobutyl ketone or cyclohexanone; or solvents such as methyl cellosolve, ethyl cellosolve or butyl cellosolve systems, which may be used as a single solvent or in combination. It can also be used as a mixed solvent of more than one species. Further, typical examples of the acrylic ester or methacrylic ester (a-2) used in obtaining the copolymer (A) include methyl (meth)acrylate, ethyl (meth)acrylate, Examples include butyl (meth)acrylate, t-butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, lauryl (meth)acrylate, tridecyl (meth)acrylate, and cyclohexyl (meth)acrylate. Representative examples of the hydroxyl group-containing vinyl monomer (a-3) include β.
-Hydroxyethyl (meth)acrylate, β-
hydroxy n-propyl (meth)acrylate,
Examples include β-hydroxyisopropyl (meth)acrylate and β-hydroxybutyl (meth)acrylate, and typical examples of the acid group-containing vinyl monomer (a-4) include (meth)acrylic acid and fumaric acid. acids, such as maleic acid or itaconic acid. On the other hand, the acrylic copolymer thus obtained
The amino resin (b-1) that participates in the crosslinking reaction with (A)
refers to a compound containing an amino group such as melamine, urea or guanamine, which is methylolated with formalin, and then at least two of the methylol groups are etherified with a lower aliphatic alcohol. Commercially available products include “Betsucomin P-138” and “Super Betsucomin J”.
-820, G-821, L-105-60, L-117-60"
(A product of Dainippon Ink & Chemicals Co., Ltd.) or Cymel 300 (a product of American Cyanamid Co., Ltd.)
and so on. Further, the isocyanate compound (b-2) is a diisocyanate such as tolylene diisocyanate or hexamethylene diisocyanate; an adduct of these diisocyanates with a polyhydric alcohol such as ethylene glycol, glycerin or trimethylolpropane; or 1 mol of water. A reaction product of 3 moles of diisocyanate and the like is typical, but any known and commonly used products can be used. Typical commercially available products are "Bernock D-750, DN-950"
(product of Dainippon Ink & Chemicals Co., Ltd.) or "Desmodeur N" (product of Bayer). The amount of these crosslinking agent (B) components used is preferably in a range such that the mixing weight ratio of the acrylic copolymer (A) component and amino resin (b-1) is 40/60 to 95/5. On the other hand, the mixing ratio of the copolymer (A) component and the isocyanate compound (b-2) is regulated by the number of functional groups in each, and is determined by the number of hydroxyl groups in the former copolymer (A) and the latter compound ( The ratio to the number of isocyanate groups in b-2) is preferably in a range of 1/0.5 to 1/1.5. Thus, the mixture enamelled using the acrylic copolymer (A), the amino resin (b-1), and the pigment is baked at a temperature of 120 to 160° C. for 15 to 30 minutes. As a result, it provides a cured coating film with excellent stain resistance and solvent resistance, as well as good hardness. Narushi, and also the acrylic copolymer
The mixture enamelled using (A), the isocyanate compound (b-2), and furthermore, the pigment can be dried naturally at room temperature or dried at most from room temperature.
It forms a tough film even when forced drying up to 80°C, and provides a cured film with excellent solvent resistance and stain resistance, as well as good hardness. The resin composition for coatings has a high concentration of 50% by weight or more. Therefore, the composition of the present invention has various advantages as mentioned above, and can be used as a top coat for automobiles.
It is widely used as a building material or for light electrical equipment. Next, the present invention will be specifically explained with reference to Examples and Comparative Examples. In the following, all parts and percentages are based on weight unless otherwise specified. Example 1 38.5 parts of styrene and 28 parts of n-butyl methacrylate were added to a reactor equipped with a stirrer and a reflux condenser.
parts, 25 parts of β-hydroxyethyl methacrylate,
2 parts acrylic acid, 6.5 parts 2-mercaptoethanol
1 part, 33.3 parts of xylene, 4 parts of azobisisobutyronitrile, and 1 part of di-t-butyl peroxide, and proceeded with the polymerization reaction at 125°C for 12 hours.
The monomer was supplied by dropwise addition over a period of 4 hours. The acrylic copolymer thus obtained had a number average molecular weight of 1200, a solid content hydroxyl value of 150, a number of hydroxyl groups of 3.3, and was obtained as a resin solution with a high solid content concentration of 75.4%. Hereinafter, this will be abbreviated as resin A-1. Preparation of paint (1) For 100 parts of resin A-1, 50 parts of "Super Betsucomin L-117-60" and "Taipeku R-
820'' (manufactured by Ishihara Sangyo Co., Ltd.) and dispersed the pigment using a sand mill, the mixture was spray-painted onto a mild steel plate and then baked at 140°C for 20 minutes. As shown in Table 2, the cured coating film obtained here had improved hardness, stain resistance, acid resistance, gasoline resistance, etc. The solid content concentration during spray painting was 68%. Preparation of paint (2) Add ``Tiepeke R-820'' to 100 parts of resin A-1.
After blending 100 parts of pigment and dispersing it with a sand mill, add 100 parts of "Bernok DN-950".
The viscosity of the coating was adjusted by diluting it with thinner, followed by spray coating and forced drying at a temperature of 80° C. for 20 minutes. As shown in Table 2, the thus obtained cured coating film had improved stain resistance, acid resistance, alkali resistance, etc., and the solid content concentration at the time of spray coating was 60%. Examples 2 to 5 and Comparative Examples 1 and 2 Except for changing the formulation as shown in Table 1,
The same operations as in Example 1 were repeated, and the results shown in Table 2 were obtained.

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Claims (1)

[Scope of Claims] 1 (A) In the presence of a solvent and an initiator having a radical generating group, (a-1) 10 to 80 parts by weight of styrene, (a-2) 0 to 80 parts by weight of acrylic ester or methacrylic ester 65 parts by weight, (a-3) hydroxyl group-containing vinyl monomer
5 to 40 parts by weight, (a-4) 0 to 10 parts by weight of acid group-containing vinyl monomer, and (a-5) 2-mercaptoethanol
3 to 20 parts by weight, and the total of each of these monomers is 100 parts by weight.
An acrylic copolymer having a number average molecular weight of 500 to 3000 and the number of hydroxyl groups in one molecule being 2.3 or more and (B) (b-1) an amino resin obtained by copolymerizing the parts by weight. or (b-2) a resin composition for a high solids coating, comprising as a main component an isocyanate compound. 2. The composition according to claim 1, characterized in that the mixing weight ratio of the acrylic copolymer (A) and the amino resin (b-1) is 40/60 to 95/5. thing. 3 In the acrylic copolymer (A) and the isocyanate compound (b-2), the ratio of the number of hydroxyl groups in the former copolymer (A) to the number of isocyanate groups in the latter compound (b-2) is 1/0.5. 2. A composition according to claim 1, characterized in that it is .about.1.5 times smaller.