JPH0621240B2 - Electrodeposition coating composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an acrylic electrodeposition coating composition that is used for coating metal products and metal parts such as aluminum sashes and steel furniture. The electrodeposition coating composition can be baked at a low temperature.

[Background of the Invention]

As this type of electrodeposition coating composition, many are mainly provided with a mixture of an anionic synthetic resin and a curing agent, and such an electrodeposition coating composition is used as an electrodeposition target for electrodeposition. The composition is coated, the composition is deposited on the surface of the article to be coated, and then the composition is heated and cured.

[Conventional technology]

Conventional Example 1: As the anodic deposition type electrodeposition coating composition, a mixture of an acrylic copolymer having a carbanion or an alkyd resin and a melamine resin or a phenol resin as a curing agent is widely used. As the melamine resin used as a curing agent, an alkyl etherified methylol melamine is particularly preferable from the viewpoints of stability of a coating material and accelerating property with a carbanion-containing synthetic resin (Japanese Patent Publication Nos. 45-28116 and 47-47). -1533, Japanese Patent Publication No. 48-29295, Japanese Patent Publication No. 52-32368, Japanese Patent Publication No. 52-32371, Japanese Patent Publication No. 52-32372, and Japanese Patent Publication No. 55-14105).

Conventional Example 2: As described above, this kind of electrodeposition coating is one which is cured by heating (baking) after electrodeposition. Therefore, Conventional Example 1
As a means for accelerating the curing of the electrodeposition coating composition, the uncured coating film after electrodeposition is dipped in an aqueous solution of boric acid, phosphoric acid or the like or an alcohol solution and then baked (Japanese Patent Publication No. 46-22351).
No.), or a method of copolymerizing an organic sulfonic acid or a salt thereof with a vinyl monomer (Japanese Patent Publication No. 49-48330).
Is proposed.

[Problems to be solved by the invention]

In Conventional Example 1, the alkyl etherified methylol melamine has good stability, but the temperature required for baking is high and it is not preferable from the viewpoint of resource saving and energy saving.

Therefore, in Conventional Example 2, measures are taken to reduce the baking temperature, but there are problems that it is difficult to obtain a uniform coating surface, and the effect of decreasing the baking temperature cannot be expected so much. Furthermore, the method of using a low molecular weight organic sulfonic acid or salt such as paratoluene sulfonic acid or naphthalene sulfonic acid as a curing catalyst is commonly used in general paints, but when used in electrodeposition paints, it lowers the baking temperature. However, in the case of industrial coating, the electrodeposition coating is refined with an anion exchange resin, and at this time, the above organic sulfonic acid or salt is removed and re-addition is required, which is not economically preferable. Ultrafiltration (UF) and reverse osmosis filtration are also commonly used in place of purification with anion exchange resin. However, in this case also, the above organic sulfonic acid or salt may be removed, so that the electrodeposition bath There are problems such as the balance of the amount of curing catalyst in the washing tank and the adverse effect on the finish of the coating surface by the curing catalyst in the washing tank.

[Means for solving problems]

The present invention, as a means for solving the above conventional problems, an alkali-neutralized salt of an acrylic copolymer (I) containing a carboxyl group and a hydroxyl group and / or an alkoxyalkyl group bonded to a nitrogen atom, and an amino group. Provided is an electrocoating composition comprising a plast resin (II) as a main component and 0.1 to 10% by weight of a sulfonic acid group-containing polymer (III) with respect to the resin content of the electrocoating composition. To do.

The present invention will be described in detail below.

Acrylic Copolymer (I) The acrylic copolymer (I) used in the present invention contains a carboxyl group and a hydroxyl group and / or an alkoxyalkyl group bonded to a nitrogen atom. To introduce a carboxyl group into the acrylic copolymer (I), acrylic acid, methacrylic acid, maleic acid, maleic acid monoester, itaconic acid, itaconic acid monoester, crotonic acid, citraconic acid vinyl polymerizable By copolymerizing one or more α-β unsaturated fatty acids.
To introduce a hydroxyl group and / or an alkoxyalkyl group bonded to a nitrogen atom into the acrylic copolymer (I), β-hydroxyethyl acrylate or methacrylate, β-hydroxypropyl acrylate or methacrylate, N-methylol acrylamide, N- Methanol, ethanol, isopropanol, n-butanol, one or more kinds of hydroxyl group-containing monomers such as methylol methacrylamide and allyl alcohol, and the hydroxyalkyl group in the hydroxyalkyl group-containing monomer bonded to the nitrogen atom, 1 of alkoxyalkyl group-containing monomer modified with alcohol such as isobutanol
By copolymerizing one species or two or more species. The alcohol modification may be performed after copolymerizing the hydroxyl group-containing monomer. The acrylic copolymer (I) further contains, as an acrylic component, methyl acrylate or methacrylate, ethyl acrylate or methacrylate, isopropyl acrylate or methacrylate, normal butyl acrylate or methacrylate, isobutyl acrylate or methacrylate, 2-ethylhexyl acrylate or methacrylate, cyclohexyl. One or more kinds of acrylic ester and / or methacrylic ester such as acrylate or methacrylate, lauryl acrylate or methacrylate are copolymerized. In addition to the acrylic ester and / or methacrylic ester, the above α-β unsaturated fatty acid, hydroxyl group Containing monomer, other monomer copolymerizable with monomer containing alkoxyalkyl group bonded to nitrogen atom It is also possible to copolymerize styrene, α-methylstyrene, vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile, vinyl fluoride, vinylidene fluoride and the like which are monomers. In the above acrylic copolymer (I), the carboxyl group may be contained in an amount sufficient for the copolymer (I) to obtain water dilutability, usually in an acid value of about 30 to 100. Desirably, the monomer containing an alkoxyalkyl group bonded to a hydroxyl group and / or a nitrogen atom is usually contained in the acrylic copolymer (II) in an amount of 1 to 30.
It can be copolymerized in an amount of about wt%. The above acrylic copolymer
(I) can be polymerized by known methods such as solution polymerization, emulsion polymerization and suspension polymerization, but methanol, ethanol, isopropanol, methyl cellosolve, ethyl cellosolve, normal butyl cellosolve, ethylene glycol,
Solution polymerization using a water-miscible solvent such as propylene glycol, trimethylolpropane or glycerin is desirable.

The acrylic copolymer (I) thus obtained contains a carboxyl group containing an inorganic base such as ammonia, caustic soda, and caustical acid, an alkali base such as triethylamine, diisopropylamine, triethanolamine, and cisisopropanolamine. It imparts water dilutability by neutralizing all or part of it.

Aminoplast resin (II) The aminoplast resin used in the present invention is melamine,
Condensation product of amino compounds such as urea and benzoguanamine with aldehyde compounds such as formaldehyde and acetaldehyde, or a condensate modified product obtained by further modifying the condensation product with alcohol such as methanol, ethanol, isopropanol, n-butanol, etc. Preferably methanol, ethanol,
Isopropanol, methyl cellosolve, ethyl cellosolve, normal butyl cellosolve, ethylene glycol,
It is provided as a solution using a water-miscible solvent such as propylene glycol, trimethylolpropane, or glycerin. Particularly preferred aminoplast resin (II) is an alcohol-modified melamine-formaldehyde condensate, and in particular, the total of imino groups and methylol groups in the condensate is not more than 2 per triazine ring of melamine and the rest is all modified by alcohol. And an alkyl group in the alkyl ether is more preferably methyl, ethyl, isopropyl, normal propyl, normal butyl, isobutyl,
It is a single alkyl group or a mixed alkyl group of two or more selected from lower alkyl groups having 4 or less carbon atoms such as tert-butyl.

The acrylic copolymer (I) and the aminoplast resin
The preferable mixing ratio with (II) is 9% by weight as the resin component.
0:10 to 50:50, but acrylic copolymer
The mixing ratio can be changed according to the content of the functional group in (I) and the desired coating film performance.

Sulfonic acid group-containing polymer (III) The sulfonic acid group-containing polymer (III) used in the present invention is vinyl sulfonic acid, styrene sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, sulfoalkyl acrylate, sulfoalkyl methacrylate, Sulfosuccinic acid alkyl alkenyl ester, sulfonic acid group-containing monomers such as acrylamidoalkyl sulfonic acid, or homopolymers of salts thereof with potassium, sodium, ammonium, amine or the like, or copolymers of two or more kinds of these monomers, Or, these monomers alone or in combination with two or more kinds, methyl acrylate or methacrylate, ethyl acrylate or methacrylate, isopropyl acrylate or methacrylate, normal butyl acrylate or methacrylate, 2-ethylhexyl. Le acrylate or methacrylate, cyclohexyl acrylate or methacrylate, lauryl acrylate or methacrylate, styrene, alpha-methyl styrene,
Of vinyl acetate, vinyl propionate, vinyl chloride, vinylidene chloride, acrylonitrile, methacrylonitrile, vinyl fluoride, vinylidene fluoride, etc. It is a homopolymer or a copolymer with two or more kinds. When the other monomer is copolymerized, the content of the other monomer is 30% by weight so that the concentration of sulfonic acid group in the copolymer does not decrease and the low temperature baking effect is not impaired. It is desirable to stay within.

The sulfonic acid group-containing polymer (III) is aqueous solution polymerized by a conventional method, or water miscible with methanol, ethanol, isopropanol, methyl cellosolve, ethyl cellosolve, normal butyl cellosolve, ethylene glycol, propylene glycol, trimethylolpropane, glycerin, acetone and the like. Produced by polymerizing a solvent having a single property, or a mixed solvent of two or more kinds thereof, and the weight average molecular weight measured by the liquid chromatography method of the polymer (III) is usually about 500 to 100,000,
It is preferably about 1,000 to 50,000.

In the polymerization of the sulfonic acid group-containing polymer (III), the sulfonic acid group-containing monomer may be used in the acid form or may be used in the salt form, but if used in the acid form, after polymerization Water-diluting property is imparted by neutralizing all or part with alkali. However, it is desirable that the sulfonic acid group-containing monomer is used in a salt form, and what is needed is to use the salt type sulfonic acid group-containing monomer in the case where the solid content concentration or the degree of polymerization during aqueous solution polymerization is used. This is because it can be easily adjusted.

The addition ratio of the sulfonic acid group-containing polymer (III) to the mixture of the acrylic copolymer (I) and the aminoplast resin (II) is usually 0.1 to 10% by weight with respect to the mixture, and 0.1% by weight. If the addition amount is less than the following, the low-temperature baking effect is not sufficient. On the contrary, if the addition amount is 10% by weight or more, there is a possibility that the current efficiency may decrease during electrodeposition coating, the stability of the coating may be poor, or the coating may be uneven. is there. If the added amount is 3% by weight or more, the gloss of the coating film may be lost in some cases. Therefore, when the coating film needs high gloss, the addition amount of 0.1 to 3% by weight is preferable. 0.1 if not required
An addition amount of up to 5% by weight is more desirable.

The electrodeposition coating composition of the present invention can also be applied to coatings containing various extender pigments and coloring pigments, or coatings containing disinfectants and other additives.

[Action]

 The operation of the present invention is as follows.

Generally, low-molecular-weight sulfonic acids or salts thereof have a high electrophoretic speed during electrodeposition coating, but are unlikely to be deposited on the surface of the object to be coated. On the other hand, the sulfonic acid group-containing polymer (III) in the electrodeposition coating composition of the present invention is easily deposited on the surface to be coated, and the sulfonic acid group-containing polymer (II) deposited on the surface to be coated (II
It exerts a low temperature baking effect due to the strong acidity of the sulfonic acid group of I). When the sulfonic acid group of the sulfonic acid group-containing polymer (III) is in the salt form, according to the ordinary coating method, it functions as a curing catalyst unless the alkali is vaporized and the sulfonic acid group is exposed. However, in the case of electrodeposition coating, the sulfonic acid group contained in the sulfonic acid group-containing polymer (III) that is deposited on the surface of the object to be coated by electrolysis is exposed. Therefore, in the case of the present invention, the sulfonic acid group-containing polymer (III)
Even if the sulfonic acid group of is in a salt form, it functions as a curing catalyst. Further, the sulfonic acid group-containing polymer (III) of the present invention is not removed by a treatment such as anion exchange treatment, ultrafiltration, reverse osmosis filtration or the like.

〔The invention's effect〕

Therefore, in the present invention, even if the electrodeposition coating composition is refined, the low temperature bakeability is maintained and it is not necessary to add the curing catalyst again. The stability of the electrodeposition coating composition of the present invention is good, and the baking temperature does not include the sulfonic acid group-containing polymer (III).
It was possible to lower the temperature by ℃, and the energy during electrodeposition coating was greatly saved.

EXAMPLES Examples are described below to more specifically describe the present invention. All composition ratios in the examples are weight ratios.
Indicates parts by weight, and parts indicates parts by weight.

[Production of acrylic copolymer (I)]

The acrylic copolymer (I) having the composition shown in Table 1 was produced as follows.

The solvent is charged into 3 reactors equipped with a stirrer, a condenser and a thermometer and heated to 80 ° C. and stirred. Then, stirring was continued, and a mixture of the monomer and azobisisobutyronitrile as a polymerization initiator was continuously added dropwise over 6 hours, and after the addition, the reaction was continued at 80 ° C. for another 2 hours. After completion of the reaction, the reaction mixture was cooled and neutralized with an amine, and then diluted with water to obtain a water-soluble acrylic copolymer (I) having a solid content of 50%.

Example 1 Acrylic copolymer (I) A 280 parts, melamine resin (Nikalac MW-40 manufactured by Sanwa Chemical Co., Ltd.) as aminoplast resin (II) 60 parts, and water 1660 parts were mixed, and a solid content of 10% was obtained. An electrodeposition paint was prepared. To this was added 0.5% (solid content to solid content) of polystyrene sulfonate sodium (Toyo Soda Ultraite PS-5) as the sulfonic acid group-containing polymer (III) to the above clear electrodeposition coating composition.

Example 2 In Example 1, the addition amount of sodium polystyrene sulfonate is set to 3% (solid content to solid content).

Example 3 In Example 1, the addition amount of sodium polystyrene sulfonate is set to 10% (solid content to solid content).

Comparative Example 1 In Example 1, the addition of polystyrene sulfonic acid was omitted.

[Electrodeposition coating test]

The paints prepared in Examples 1, 2, 3 and Comparative Example 1 were placed in a second electrodeposition tank at a temperature of 25 ° C. and a distance between the electrodes of 15 cm.
.mu.) was applied as an article to be coated at the voltage / current-carrying time shown in Table 2 and then baked and dried at 150.degree. C. for 30 minutes.

The coating film performance thus obtained is shown in Table 2. Second
It can be seen from the table that Examples 1, 2, and 3 can obtain sufficiently cured coating films even when the baking temperature is lowered by 30 ° C. as compared with Comparative Example 1.

Further, in order to remove the anions accumulated as a result of using the paints of Examples 1, 2, and 3, the respective electrodeposition paints were sent to the resin-packed tower of Amberlite IRA-410 for anion exchange treatment. As a result, the performance of the coating was sufficiently maintained, unlike the above-mentioned prior art which uses a low molecular weight organic sulfonic acid or a salt thereof.

Example 4 240 parts of acrylic copolymer (I) B, melamine resin (II)
80 parts of (Nikalac MW-40) and 1680 parts of water were blended to prepare an electrodeposition paint having a solid content of 10%. 20 parts of an aqueous polymer having a solid content of 20% obtained by polymerizing an aqueous solution of sodium salt of 2-sulfoethyl methacrylate as the sulfonic acid group-containing polymer (III) using ammonium persulfate as a polymerization initiator (acrylic copolymer 2% (solid content / solid content) based on the total amount of the combination (I) and the melamine resin (II))
Was added.

Comparative Example 2 In Example 4, the addition amount of the aqueous solution polymer of sodium salt of 2-sulfoethyl methacrylate was 0.5 part (based on the total amount of the acrylic copolymer (I) and the melamine resin (II).
0.05% (solid content / solid content)).

Comparative Example 3 In Example 4, the addition amount of the aqueous solution polymer of sodium salt of 2-sulfoethyl methacrylate was 120 parts (12% (based on the total amount of the acrylic copolymer (I) and the melamine resin (II) ( Solid content / solid content)).

[Electrodeposition coating test]

Regarding Example 4 and Comparative Examples 2 and 3, Examples 1, 2, and 3
The results of the same electrodeposition coating test as in Comparative Example 1 are shown in Table 3. Referring to Table 3, Comparative Example 2 is inferior in low-temperature baking effect, and Comparative Example 3 has the same low-temperature baking effect as in Example 4, but the gloss is reduced and gloss is uneven. Further, the coating material of Example 4 was subjected to anion exchange treatment (Amberlite IRA-41
After carrying out 0), an electrodeposition coating test was conducted under the same conditions, and the same coating performance was exhibited except that the film thickness was slightly reduced.

Example 5 300 parts of acrylic copolymer (I) C, melamine resin (II)
An electrodeposition coating having a solid content of 10% was prepared by mixing 50 parts of (Nikalac MW-40) and 1650 parts of water. To this, 10 parts of an aqueous solution having a solid content of 20% obtained by polymerizing an aqueous solution of sodium acrylamido-2-methylpropanesulfonate as a sulfonic acid group-containing polymer (III) with potassium persulfate as a polymerization initiator was added, and bronze-colored anodized aluminum The plate and Bondellite # 144 treated steel plate were electrodeposited as in Example 1 under the conditions shown in Table 4.

Referring to Table 4, the coating material of Example 5 exhibits an excellent low-temperature baking effect on both aluminum plate and steel plate, but those having no added sulfonic acid group-containing polymer (III) have hardness of 2H and M.
The EK rubbing was 30 to 40 times.

The paint of Example 4 was anion exchange treated (Amberlite I
The coating performance after RA-410) was equivalent to that before treatment.

Example 6 Into three reaction vessels equipped with a stirrer, a condenser and a thermometer, 616 parts of an amine of acrylic copolymer (I) A, an unneutralized resin (solid content 65%) before addition of water, and isopropanol 526 A portion is charged and the mixture is heated and stirred at 80 ° C. Then 8
While maintaining heating and stirring at 0 ° C, 134 parts of glycidyl methacrylate, 66 parts of acrylic acid, and 4 parts of azobisisobutyronitrile were added. Procedure Glycidyl methacrylate 13
A mixture of 4 parts, 66 parts of acrylic acid, 4 parts of azobisisobutyronitrile, 466 parts of IPA and 3 parts of triethylamine was continuously added over 2 hours. Then add 3 parts of azobisisobutyronitrile 3 times every 1 hour,
The reaction was continued for 1 hour while maintaining heating and stirring at 80 ° C, and then cooled to room temperature.

The obtained cloudy particle dispersion was crushed for 60 minutes by a batch type sand mill. Obtained dispersion (solid content 40%) 150
Part, acrylic copolymer (I) A 254 parts, melamine resin (Nikalac MW-40) 13 parts, triethylamine 3
Parts and 1463 parts of water were mixed to prepare a barley electrodeposition coating composition having a solid content of 10%. This electrodeposition coating has a sulfonic acid group-containing polymer (I
As a II), 4.8 parts of sodium polystyrene sulfonate (Ultraite PS-5: solid content 21%) was added, and Example 1 was added.
In the same manner as above, electricity was applied to a bronze-colored anodized aluminum plate at 120 V for 2 minutes, followed by baking and drying at 140 ° C. for 30 minutes and 160 ° C. for 30 minutes. In the same manner as Comparative Example 4, the one to which Ultraite PS-5 was not added was similarly electrodeposited. The results of testing the performance of the coating film obtained by the above electrodeposition coating are shown in Table 5.

As seen from Table 5, Example 6 shows an excellent low temperature baking effect as compared with Comparative Example 4. And the coating film performance does not change after the anion exchange treatment (Amberlite IRA-410).

Electrodeposited paint after anion exchange treatment should be sealed at room temperature in 34
After standing for a period of time, the mixture was thoroughly stirred to re-disperse the precipitate, which was again subjected to anion exchange treatment and then electrodeposition coated. As shown in Table 6, the results of testing the performance of the coating film obtained by the above electrodeposition coating are:
It shows that good low temperature baking coating can be carried out even after 3 months.

Claims (1)

[Claims] 1. An acrylic copolymer (I) containing a carboxyl group and a hydroxyl group and / or an alkoxyalkyl group bonded to a nitrogen atom, and an aminoplast resin (II).
And a sulfonic acid group-containing polymer (III) contained in an amount of 0.1 to 10% by weight based on the total amount of the acrylic copolymer (I) and the aminoplast resin (II), and the acrylic resin Copolymer (I) and the sulfonic acid group-containing polymer (II
I) is an electrodeposition coating composition characterized by being neutralized with an alkali