JPH06207135A - Copolymer latex for cold-and chipping-resistant water-based coating and coating composition - Google Patents

Abstract

PURPOSE:To obtain a copolymer latex for water-based coating, excellent in cold and chipping resistance and useful for coating the undersurface, etc., of an automotive floor, etc., by specifying the amount of an acid in a copolymer latex prepared by carrying out the emulsion copolymerization of specific monomers. CONSTITUTION:The latex is obtained by specifying the total detected amount of an acid of a copolymer latex prepared by carrying out the emulsion copolymerization of a monomer such as a conjugated diene-based, an aromatic vinylic or an ethylenically unsaturated carboxylic acid monomer with a monoolefinic monomer to 15-50 mequiv. measured by the conductometric titration and (1/0.2) to (1/1) partition ratio (A)/(B) of the acid between (A) the latex surface and (B) the aqueous layer part. A composition containing a filler, a cross-linking agent, etc., in an amount of 0.2-25 pts.wt. based on 100 pts.wt. objective latex is preferred for coating use.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to coating metal surfaces,
It relates to a cold- and chipping-resistant water-borne copolymer latex and a coating composition for protecting the metal products from chipping, especially in cold weather. More specifically, the present invention relates to a coating composition used for coating a surface of a portion where stones are likely to hit during traveling, such as an underfloor portion of a vehicle body of an automobile or the like.

[0002]

2. Description of the Related Art In recent years, bituminous protective materials have traditionally been used for automobile floors, side seals, fail tanks, front aprons, and tire housings because they have rust-preventive properties and are inexpensive. Although widely used, pebbles and flying stones that are rolled up while the vehicle is running, and salt and rock salt whose amount of spraying has been rapidly increasing in recent years cause cracks and impact scratches on the coating, especially during cold weather, resulting in damage. Corrosion generated from the part is a problem. In order to prevent such defects, so-called chipping resistant paints have been developed and put into use. As such chipping-resistant paints, emulsion-based paints, vinyl chloride resin plastisols, urethane or polyester paints, and improved bitumen-based paints have been developed (JP-A-63-10678).
No. 64-29472).

On the other hand, in recent years, in the field of paints and adhesives, there has been a shift from the so-called solvent system to water system due to pollution problems such as environmental pollution in the atmosphere, fire danger, hygiene problems during work, energy saving, and resource problems. This tendency is no exception in chipping resistant paints used for undercoating of automobiles.

Such a chipping-resistant water-based coating material requires a thicker coating film in order to maintain the elasticity of the coating film.
It is painted to about 800 μm. Further, a thicker coating film is required to improve the chipping resistance in cold weather.

However, in general, in the case of coating with a large film thickness, a coating material containing a water-based water-soluble resin, resin emulsion, latex, etc. as a vehicle is liable to cause blistering in the coating film, and immediately after being wet with water. The deterioration of the coating film characteristics such as the reduction of the adhesion (water resistance) of the coating film to the sheet metal part is observed. Therefore, in these water-based paints, the improvement of the balance between chipping resistance and coating property obtained by thickening the coating film is a serious problem.

[0006] Further, when painting with a spray gun or the like, if pressure is applied to the spray gun and pressure-fed, the viscosity rises, coagulation occurs, clogging, etc., and the paint is not stably discharged from the spray gun. Problems occur (this is generally referred to as poor mechanical stability of the paint)
Therefore, it is impossible to make the film thickness uniform and to apply the coating stably.

In order to solve these problems, for example, in JP-A-59-75954, JP-A-2-28269, and JP-A-4-202262, a styrene-butadiene copolymer latex is blended in a paint. Proposed to be used. However, it is hard to say that any of these can sufficiently overcome the above-mentioned problem of improving the balance between chipping resistance obtained by increasing the film thickness, especially chipping resistance in cold weather and coating film properties. .

Further, when a styrene-butadiene copolymer latex is blended in a paint and coated, the mechanical stability is inferior, the film thickness cannot be made uniform and stable, and the coating is dried and then cracked. In addition, since the coating film is brittle and weak, the coating film is easily broken by a stone splash, which causes a problem that rust is easily generated.

[0009]

[Means for Solving the Problems] In view of the above-mentioned circumstances, the inventors of the present invention have made diligent studies to solve the current problems, and as a result, detected all of the carboxylic acids in the styrene-butadiene copolymer latex. It has been found that by combining the acid amount and the distribution ratio of the detected acid amount in specific ranges, respectively, a copolymer latex having excellent cold and chipping resistance, coating film characteristics and mechanical stability of the paint can be obtained. Has been completed.

That is, according to the present invention, a conjugated diene-based monomer, an aromatic vinyl-based monomer, an ethylenically unsaturated carboxylic acid monomer and a mono-olefin-based monomer copolymerizable therewith are emulsion-polymerized. The resulting copolymer latex has a total detectable acid amount of 15 meq to 50 meq by conductivity titration of the copolymer latex, and a) the latex surface of the detected acid amount and b) the aqueous layer portion. Distribution ratio to a) / b) is in the range of 1 / 0.2 to 1/1, a cold-resistant chipping-resistant water-borne copolymer latex, further the latex and a filler, and further The present invention provides a coating composition having a crosslinking agent and / or a vulcanizing agent.

The present invention will be described in detail below.

As the conjugated diene-based monomer in the present invention, 1,3-butadiene, 2-methyl-1,3-butadiene, 2,3-dimethyl-1,3-butadiene and 2-chloro-1,3 are used. -Butadiene, substituted linear conjugated pentadienes, substituted and side chain conjugated hexadienes, and the like, and one kind or two or more kinds can be used. Especially 1,
3-Butadiene is preferred.

Aromatic vinyl monomers include styrene, α-methylstyrene, methyl α-methylstyrene,
Vinyltoluene and divinylbenzene and the like,
One kind or two or more kinds can be used. Particularly preferred is styrene.

Examples of the ethylenically unsaturated carboxylic acid monomer include mono- or dicarboxylic acids (anhydrides) such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid and itaconic acid.

Other monomers copolymerizable with the above-mentioned conjugated diene monomer, aromatic vinyl monomer and ethylenically unsaturated carboxylic acid monomer include unsaturated carboxylic acid alkyl ester monomers. Unsaturated monomers containing a hydroxyalkyl group, vinyl cyanide monomers, unsaturated carboxylic acid amide monomers and the like.

Examples of the unsaturated carboxylic acid alkyl ester monomer include methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate, glycidyl methacrylate, dimethyl fumarate, diethyl fumarate, dimethyl maleate, diethyl maleate, dimethyl. Itaconate, monomethyl fumarate, monoethyl fumarate, 2-ethylhexyl acrylate and the like can be mentioned, and one kind or two or more kinds can be used. Methyl methacrylate is particularly preferable.

Examples of unsaturated monomers containing a hydroxyalkyl group include β-hydroxyethyl acrylate and β-hydroxyethyl acrylate.
-Hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate,
Hydroxybutyl acrylate, hydroxybutyl methacrylate, 3-chloro-2-hydroxypropyl methacrylate, di- (ethylene glycol) maleate,
Di- (ethylene glycol) itaconate, 2-hydroxyethyl maleate, bis (2-hydroxyethyl)
Maleate, 2-hydroxyethylmethyl fumarate, etc. are mentioned, and 1 type (s) or 2 or more types can be used. Particularly, β-hydroxyethyl acrylate is preferable.

Examples of vinyl cyanide monomers include acrylonitrile, methacrylonitrile, α-chloroacrylonitrile and α-ethylacrylonitrile.
One kind or two or more kinds can be used. Acrylonitrile is particularly preferable.

As the unsaturated carboxylic acid amide monomer,
Acrylamide, methacrylamide, N-methylol acrylamide, N-methylol methacrylamide, N,
N-dimethylacrylamide and the like can be mentioned, and one kind or two or more kinds can be used. Particularly preferred is acrylamide.

Further, in addition to the above monomers, fatty acid vinyl esters such as vinyl acetate and vinyl propionate,
It is possible to use basic monomers such as aminoethyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, 2-vinylpyridine and 4-vinylpyridine, vinyl chloride, vinylidene chloride and the like. it can.

The above monomer composition is not particularly limited,
30-80% by weight of aliphatic conjugated diene-based monomer, 10-69.5% by weight of aromatic vinyl-based monomer, 0.5-10% by weight of ethylenically unsaturated carboxylic acid monomer, and copolymerizable with these The content of the other monomer is preferably 0 to 59.5% by weight.

The method of adding various components in the present invention is not particularly limited, and any of a batch addition method, a divided addition method and a continuous addition method can be adopted. The emulsion polymerization method is also not particularly limited, and any one-step polymerization, two-step polymerization or multi-step polymerization can be adopted. Furthermore, in emulsion polymerization, a conventional chain transfer agent, an emulsifier, a polymerization initiator, an electrolyte, a polymerization accelerator,
A chelating agent or the like can be used.

The chain transfer agent used in the present invention includes
Alkyl mercaptans such as n-hexyl mercaptan, n-octyl mercaptan, t-octyl mercaptan, n-dodecyl mercaptan, t-dodecyl mercaptan, n-stearyl mercaptan, xanthogen compounds such as dimethylxanthogen disulfide, diisopropylxanthogen disulfide, α- Methylstyrene dimer, terpinolene, tetramethylthiuram disulfide, tetraethylthiuram disulfide,
Thiuram-based compounds such as tetramethylthiuram monosulfide, 2,6-di-t-butyl-4-methylphenol, phenol-based compounds such as styrenated phenol, allyl compounds such as allyl alcohol, dichloromethane, dibromomethane and carbon tetrachloride. , Halogenated hydrocarbon compounds such as carbon tetrabromide, α-benzyloxystyrene, α-benzyloxyacrylonitrile, vinyl ethers such as α-benzyloxyacrylamide, triphenylethane, pentaphenylethane, acrolein, methacrolein, thioglycolic acid , Thiomalic acid, 2-ethylhexyl thioglycolate and the like, and one or more of them can be used.

The amount of the chain transfer agent used is not particularly limited and can be appropriately adjusted according to the performance required for the copolymer latex, but preferably 0.05 to 100 parts by weight of the monomer mixture. 10 parts by weight.

As the emulsifier, anionic surfactant such as sulfuric acid ester salt of higher alcohol, alkylbenzene sulfonate, aliphatic sulfonate, aliphatic carboxylate, sulfuric acid ester salt of nonionic surfactant, or polyethylene glycol. One or more nonionic surfactants such as alkyl ester type, alkyl phenyl ether type, and alkyl ether type are used.

As the initiator, a water-soluble initiator such as potassium persulfate, ammonium persulfate or sodium persulfate, a redox initiator or an oil-soluble initiator such as benzoyl peroxide can be used.

In the emulsion polymerization, cyclopentene, cyclohexene, cycloheptene, 4-
Cyclic unsaturated hydrocarbon having one unsaturated bond in the ring such as methylcyclohexene and 1-methylcyclohexene,
You may add benzene, toluene, cyclohexane, etc. The amount of the compound used is 0.1 to 30 parts by weight based on 100 parts by weight of the monomer.

The copolymer latex used in the present invention has a total detectable acid amount of 15 meq to 50 meq by conductivity titration of the copolymer latex. b) It is essential that the distribution ratio to the water layer part is in the range of a) / b) = 1 / 0.2 to 1/1. If the total detected acid amount of the copolymer latex is less than 15 meq, the mechanical stability of the coating composition is lowered, which is not preferable, and if it is 50 meq or more, cold and chipping resistance are poor, which is not preferable. Further, the distribution ratio of the detected acid amount to a) the latex surface and b) the water layer part is a) / b) = 1.
/0.2 or more lowers the coating physical properties such as the mechanical stability and water resistance of the coating, and if a) / b) is less than 1/1, the coating will have blisters. Is not preferable.

The total amount of detected acid and the distribution ratio may be adjusted by a method of adjusting at the time of polymerization, for example, the kind of acid, the amount of acid used and the addition method thereof, the amount of chain transfer agent used, and the like. it can. Moreover, you may adjust by adding sodium polyacrylate etc. to the obtained copolymer latex.

In the present invention, the total detected acid amount and the distribution ratio of the detected acid amount of the copolymer latex are the values measured and determined by the following.

Total detection acid amount measuring method The solid content of the synthetic copolymer latex to be measured is adjusted to 5%, and then adjusted to pH 2.5 to 2.8 with 0.1 N sulfuric acid,
Conductivity titration was performed with 1N sodium hydroxide. Then, the total detected acid amount was obtained from the conductivity titration chart.

Detected acid amount a) latex surface, b) water layer
Method for measuring the distribution ratio a) / b) to the parts The solid content of the synthetic copolymer latex to be measured is made 5%, carbon tetrachloride and 0.1 N sodium hydroxide are added thereto, and centrifugation is carried out. Collect the precipitate part of. Then, the precipitated portion was dispersed with pure water, and the conductivity titration was carried out in the same manner as in the method of measuring the total amount of detected acid to determine the amount of detected acid. This acid amount was used as a) the latex surface, and b) the acid amount in the water layer portion was determined by subtracting the acid amount in a) from the total detected acid amount.

On the other hand, the present invention includes, as another embodiment, a coating composition obtained by adding a crosslinking agent and / or a vulcanizing agent to the above coating composition. By combining the cross-linking agent and / or the vulcanizing agent with the copolymer latex of the present invention, the balance between the cold chipping resistance and the coating film physical properties such as blistering in the coating film is improved.

Examples of the cross-linking agent or vulcanizing agent used in the present invention include zinc white, compounds having an epoxy group, blocked isocyanate compounds, ethylene urea compounds, melamine resins, urea resins, sulfur and peroxides. These can be used alone or in combination of two or more. Such a crosslinking agent or a vulcanizing agent may be used as the copolymer latex 100.
It is used at 0.2 to 25 parts by weight with respect to parts by weight (solid content). If the amount of the cross-linking agent or the vulcanizing agent is less than 0.2 parts by weight relative to 100 parts by weight (solid content) of the copolymer latex, the coating film will have blisters and the physical properties of the coating film will be deteriorated.
If it is 5 parts by weight or more, the cold and chipping resistance tends to decrease, which is not preferable.

As the filler used in the present invention, those generally used conventionally can be used. For example, powdery materials such as talc, calcium carbonate, diatomaceous earth, mica, kaolin, barium sulfate, graphite, alumina, iron oxide, titanium oxide and silica are used. Also, other fibrous materials can be used as the filler.

In addition to the above-mentioned copolymer latex and filler, the coating composition of the present invention includes pigments such as carbon black, organic pigments, metal salts of chromate, metal salts of phosphoric acid and metal salts of metaborate, Further, a dispersant, a thickener, an organic solvent, an antiaging agent, an ultraviolet absorber, an antistatic agent and the like can be added.

To coat the surface of the metal product with the coating composition of the present invention, the surface of the metal product is coated by airless coating, air spray coating or the like. After that, for example, 80-180 ℃
A coating is obtained by drying and curing at the temperature of 10 to 30 minutes.

[0038]

EXAMPLES In order to clearly show the excellent effects of the present invention, the present invention will be described in more detail below with reference to Examples and Comparative Examples. However, as long as the present invention does not exceed the gist thereof, these It is not limited in any way by the embodiment. In addition,
Parts and% shown in Examples and Comparative Examples are based on weight unless otherwise specified.

Preparation of copolymer latex In 10 liters of autoclave, 100 parts of water, 0.3 part of sodium dodecylbenzenesulfonate, 0.2 part of sodium hydrogen carbonate, 1.0 part of potassium persulfate, t -Dodecyl mercaptan (1.0 part) and the monomers shown in Tables 1 and 2 were charged, sufficiently stirred and then polymerized at 65 ° C.
Next, these copolymer latexes were adjusted to pH 8 with an aqueous solution of caustic soda, and unreacted monomers and the like were removed by steam distillation to obtain a copolymer latex.

Preparation of coating composition For 100 parts (solid content) of the above-mentioned copolymer latex,
70 parts of calcium carbonate, 50 parts of talc, 3 parts of carbon black and 5 parts of barium metaborate, 5 parts by weight of dispersant, 150 parts by weight of water, and coating compositions 6, 7, 12 to 1
For No. 5, ethylene urea resin was further mixed as a cross-linking agent to obtain coating compositions 1 to 15.

Conditions for coating film formation On the turn-sheet plate obtained by subjecting a steel plate to lead-tin plating, the above coating composition was airlessly coated and set at room temperature for 10 minutes, then at 80 ° C. for 10 minutes and 120 ° C. It was dried for 20 minutes. The coating film characteristics of the obtained coating film were measured by the following methods.

Blistering limit film thickness of coating film In the airless coating, coating is performed by changing the thickness of the dried coating film, and the maximum film thickness which does not cause blistering during drying is measured,
The blister limit film thickness was used.

Cold-proofing and chipping resistance A test piece obtained by coating so as to have a dry film thickness of 300 μ was fixed at an angle of 60 ° with respect to a horizontal plane, and a nut (M-6) was attached to the coated surface of this test piece. It was continuously dropped from a height of 2 m, and the total weight of the dropped nuts when the base material of the turn sheet steel plate was exposed was evaluated. The atmosphere temperature during the test was -30 ° C.

Water resistance According to JIS K5400, the state after immersion in water at room temperature for 7 days was examined. ◎ No abnormality ○ Slight chalking is observed △ Coating is soft and chalking is severe × Softening and chalking is remarkable and the coating peels off

Mechanical Stability 100 g of the paint was taken and placed in a Maron type mechanical stability tester for 10 minutes, after which the amount of residue remaining on 100 mesh was measured. The evaluation results are shown in Tables 1 and 2.

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

As described above, by using the specific copolymer latex of the present invention and further using the crosslinking agent or the vulcanizing agent in combination, it is possible to obtain the anti-cold resistance against cold and the swelling and water resistance of the coating film. It is possible to obtain a coating composition for an aqueous coating composition, which can remarkably improve the balance between the film characteristics and the mechanical stability.

Claims (3)

[Claims] 1. A copolymer obtained by emulsion polymerization of a conjugated diene monomer, an aromatic vinyl monomer, an ethylene-unsaturated carboxylic acid monomer, and a monoolefin monomer copolymerizable therewith. A polymer latex having a total detectable acid amount of 15 meq to 50 by conductivity titration of the copolymer latex.
meq, and the distribution ratio of these detected amounts of acid to a) the latex surface and b) the aqueous layer is a) / b) = 1 /
A copolymer latex for cold-resistant and chipping-resistant water-borne coatings, which is in the range of 0.2 to 1/1. 2. A coating composition for cold-resistant and chipping-resistant water-based paint, which comprises the copolymer latex according to claim 1 and a filler. 3. The copolymer latex according to claim 1 and a filler and a crosslinking agent and / or a vulcanizing agent are contained, and the amount of the crosslinking agent and / or the vulcanizing agent is 100 parts by weight of the copolymer latex ( 0.2 to 25 parts by weight based on the solid content) A coating composition for cold-resistant and chipping-resistant water-based paint.