JP2002371248A - Self-curing coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a self-curing coating composition which, when cured with a curing agent comprising a carbodiimide-group-containing compound, exhibits an excellent curability and can form a coating film excellent in properties, especially smoothness. SOLUTION: This coating composition contains a carboxy-group-containing resin modified with a carbodiimide-group-containing compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a self-curing coating composition having excellent curability.

[0002]

2. Description of the Related Art Paints containing epoxy resin, acrylic resin, polyester resin or the like as a main binder and, if necessary, a curing agent such as a polyvalent carboxylic acid or a blocked isocyanate are widely known. It is used in many fields such as automobiles and building materials. inside that,
Coatings mainly composed of thermosetting resin compositions require baking conditions at a certain temperature or higher, usually at a high temperature of 180 ° C. or higher. However, such high-temperature baking requires a large amount of energy and generates a lot of volatile components, so that it is not environmentally preferable.

On the other hand, as a paint using a carbodiimide group-containing compound as a curing agent, JP-A-10-31689 discloses a paint.
No. 3 discloses a polycarbodiimide-based resin, a binder resin,
A heat resistant powder coating containing a curing agent and a colorant is disclosed.

JP-A-11-35850 discloses a carbodiimide compound having isocyanate groups at both ends,
Alternatively, a hardening agent for powder coatings mainly comprising a monoisocyanate compound and a carbodiimide compound blocked with an alcohol or the like is disclosed. This utilizes the high reactivity of the carbodiimide compound and has the advantage that the baking temperature during coating is low.

As the water-based paint, JP-A-2001-111
No. 51 and JP-A-2001-11152,
A carbodiimide compound having at least two isocyanate groups in the molecule is reacted with a polyol at a specific ratio, and then a hydrophilizing modified polycarbodiimide compound obtained by reacting a hydrophilizing agent, and a carboxyl group-containing resin. An aqueous coating composition is disclosed.
This is a one-part, room temperature-curable coating composition that can achieve both curability and storage stability.

However, when a carbodiimide group-containing compound is used as a coating material in combination with a binder resin such as a polyester resin, which is generally used, the carbodiimide group-containing compound is inferior in compatibility due to a difference in skeleton between the carbodiimide group-containing compound and the binder resin. In some cases, the curability was reduced or the resulting coating film was poor in smoothness.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a coating film having excellent curability and performance of the resulting coating film, particularly smoothness, when a carbodiimide group-containing compound is used as a curing agent. An object of the present invention is to provide a self-curable coating composition that can be obtained.

[0008]

Means for Solving the Problems The present inventors have improved the compatibility between a carbodiimide group-containing compound and a binder resin by introducing a carbodiimide group-containing compound into the binder resin skeleton, and have achieved excellent curability. The present invention was completed by constructing a one-component curing system that can be obtained.

That is, the present invention is a self-curing coating composition containing a carboxyl group-containing resin modified with a carbodiimide group-containing compound. Hereinafter, the present invention will be described in detail.

The self-curing coating composition of the present invention contains a carboxyl group-containing resin modified with a carbodiimide group-containing compound. In the present specification, a self-curing coating composition means that the binder resin in the coating composition can also serve as a curing agent, and can be cured under heating without separately adding a curing agent. Means a paint composition that can be used. The carbodiimide group-containing compound is not particularly limited as long as it has at least two functional groups in order to form a crosslinked structure by reacting under heating, but preferably has two isocyanate groups in the molecule ( 1) and (2) having at least two carbodiimide groups in the molecule.

The compound having two isocyanate groups in the molecule (1) is represented by the following formula OCN-R ^1- (NC
NR ¹ ) n-NCO (wherein R ¹ is the same or different and is a residue obtained by removing an isocyanate group from an organic diisocyanate, and n is an integer of 1 or more and represents the number of repeating carbodiimide groups). What is represented can be mentioned.

The above-mentioned compound having two isocyanate groups in the molecule (1) includes those produced by a method well known to those skilled in the art, for example, utilizing a condensation reaction of an organic diisocyanate accompanied by decarbonation. Thus, a product having isocyanate groups at both terminals can be obtained.

As the organic diisocyanate, for example, aromatic diisocyanate, aliphatic diisocyanate, alicyclic diisocyanate, and a mixture thereof can be used. Specifically, 1,5-naphthylene diisocyanate, 4-diphenylmethane diisocyanate, 4,4-diphenyldimethylmethane diisocyanate, 1,3-phenylene diisocyanate, 1,4
-Phenylene diisocyanate, 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate,
Mixture of 2,4-tolylene diisocyanate and 2,6-tolylene diisocyanate, hexamethylene diisocyanate, cyclohexane-1,4-diisocyanate, xylylene diisocyanate, isophorone diisocyanate, dicyclohexylmethane-4,4-diisocyanate, methylcyclohexane diisocyanate And tetramethylxylylene diisocyanate.

In the above condensation reaction, a carbodiimidization catalyst is usually used. Phosphorene oxide can be used as the carbodiimidization catalyst. By using the above-mentioned phosphorene oxide as a catalyst, carbodiimidization can be performed within a range where temperature control is easy.

As the above-mentioned phosphorene oxide, 1-
Phenyl-3-methyl-3-phospholene-1-oxide, 1-methyl-3-methyl-3-phospholene-1-oxide, 1-ethyl-3-methyl-3-phospholene-
1-oxide, 1-butyl-3-methyl-3-phospholene-1-oxide, 1- (N-piperidinyl) -3
-Methyl-3-phospholene-1-oxide, 1-morpholino-3-methyl-3-phospholene-1-oxide, 1-phenyl-3-methyl-2-phospholene-1-
Oxide, 1-methyl-3-methyl-2-phospholene-1-oxide, 1-ethyl-3-methyl-2-phospholene-1-oxide, 1-butyl-3-methyl-2
-Phospholene-1-oxide, 1-phenoxy-3-
Methyl-2-phospholene-1-oxide, 1-phenyl-3-phospholene-1-oxide, 1-methyl-3
-Phospholene-1-oxide, 1-ethyl-3-phospholene-1-oxide, 1-phenyl-2-phospholene-1-oxide, 1-methyl-2-phospholene-1
-Oxide, 1-ethyl-2-phospholene-1-oxide, 1-phenyl-3-methyl-3-phospholene-
1-sulfide and the like. Among them, 1-phenyl-3-methyl-3-phospholene-1-oxide, 1-phenyl-3-methyl-2-phospholene-1-oxide
Oxide, 1-phenyl-3-phospholene-1-oxide, 1-phenyl-2-phospholene-1-oxide and the like are preferred.

The amount of the above-mentioned phosphorene oxide is preferably from 1 to 30 ppm based on the raw material organic diisocyanate. If the amount is less than 1 ppm, carbodiimidization does not sufficiently proceed, and if the amount exceeds 30 ppm, an effect corresponding to the added amount cannot be obtained.

The carbodiimidization is preferably carried out at 120 to 170 ° C. using the above-mentioned phosphorene oxide as a catalyst in order to promote the reaction efficiently. 1
If the temperature is lower than 20 ° C., the carbodiimidization may not proceed sufficiently and the desired compound may not be obtained. When the temperature exceeds 170 ° C., a side reaction may proceed, and a target compound may not be obtained.

In the carbodiimidization, a solvent that is inert to isocyanate and dissolves the isocyanate compound can be used, but the reaction is usually performed without a solvent. The carbodiimidization can be confirmed by the generation of a carbodiimide group peak at 2100 cm ^{−1 in} the IR spectrum.

The carbodiimide group-containing compound (1) having two isocyanate groups in the molecule obtained as described above preferably has 1 to 30 carbodiimide groups in the molecule. If it exceeds 30, the melting point and the viscosity become high, and it may be difficult to disperse and mix the resin. More preferably, the number is 1 to 15.

In the present invention, in the carbodiimide group-containing compound (1) having two isocyanate groups in the molecule, one of the two isocyanate groups is a free isocyanate group and the other is a free isocyanate group. It may be blocked. When all two isocyanate groups are free, there is a possibility of gelling in a reaction with a binder resin described later. However, a carbodiimide group-containing compound in which all two isocyanate groups are free can be included as long as the compound does not gel.

As described above, when one of the two isocyanate groups is previously blocked, the blocking agent may be a phenolic compound such as phenol, cresol, xylenol, chlorophenol and ethylphenol; ε-caprolactam , Δ-valerolactam,
Lactams such as γ-butyrolactam and β-propiolactam; active methylenes such as ethyl acetoacetate and acetylacetone; methanol, ethanol, propanol, isopropanol, n-butanol, isobutanol, t-butanol, amyl alcohol, ethylene glycol monomethyl Ether, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether, ethylene glycol mono 2-ethylhexyl ether, propylene glycol monomethyl ether, methyl glycolate, butyl glycolate, diacetone alcohol, methyl lactate and ethyl lactate, furfuryl alcohol, etc. Alcohols; formaldoxime, acetoaldoxime, acetoxime, methyl ethyl ketoxime,
Oximes such as diacetyl monooxime and cyclohexane oxime; mercaptans such as butyl mercaptan, hexyl mercaptan, t-butyl mercaptan, thiophenol, methylthiophenol and ethylthiophenol; acid amides such as acetate amide and benzamide; succinimide and Imides such as maleic imide; imidazoles such as imidazole and 2-ethylimidazole;
Secondary amines such as dimethylamine, diethylamine and dibutylamine can be exemplified. In the present invention, from the viewpoint of ensuring low-temperature curability of the paint, methanol,
Alkyl alcohols such as ethanol, propanol and isopropanol are preferred.

The blocking agent is a carbodiimide group-containing compound (1) having two isocyanate groups in the molecule.
It is preferable to react at a ratio of 0.4 to 0.6 equivalent to the isocyanate group therein. If it is less than 0.4 equivalent, the ratio of free isocyanate groups becomes too large, and gelation may occur when a modified carboxyl group-containing resin is obtained. If it exceeds 0.6 equivalents, the yield of the modified carboxyl group-containing resin decreases. Furthermore, if one isocyanate group in the carbodiimide group-containing compound (1) is blocked by performing the reaction within the above range, the other isocyanate group is less likely to be blocked due to steric hindrance. A carbodiimide group-containing compound in which one is a free isocyanate group and one is a blocked isocyanate group can be easily obtained. The blocking method is well known to those skilled in the art and can be performed, for example, by heating at room temperature to about 80 ° C. for about 10 minutes to 2 hours.

At least two carbodiyl groups in the molecule
Carbodiimide containing carbodiimide group having amide group
As (2), the following formula R²-NCN-R¹− (NCN-R¹) M-NCN-R
²  (Where R¹Are the same or different and are organic diisocyanates
A residue obtained by removing an isocyanate group from²Are the same or
Differently from monoisocyanate compounds to isocyanate
And m is an integer of 0 or 1 or more,
Indicates the number of repetitions of the bodiimide group. )
Can be mentioned.

The compound represented by the above formula can be obtained by reacting a monoisocyanate compound with the carbodiimide group-containing compound (1) having two isocyanate groups in the molecule or the organic diisocyanate exemplified above. it can. Examples of the monoisocyanate compound include aliphatic isocyanates such as butyl isocyanate; alicyclic isocyanates such as cyclohexyl isocyanate; and one or a mixture of two or more aromatic isocyanates such as phenyl isocyanate and 2,6-diisopropylphenyl isocyanate. Examples can be given. In the above formula, m is preferably from 0 to 30, more preferably from 0 to 15. The compound (2) having at least two carbodiimide groups in the molecule can be produced in the same manner as in the method described in the above block.

As the resin to be modified, for the carbodiimide group-containing compound (1) having two isocyanate groups in the molecule, a resin having a hydroxyl group and a carboxyl group is used. As the carbodiimide group-containing compound (2) having two carbodiimide groups, a resin having a carboxyl group can be used. The reaction between a part of the carbodiimide and the carboxyl group causes the remaining carbodiimide to contribute to curing. This utilizes the property that isocyanate groups easily react with hydroxyl groups and carbodiimide groups easily react with carboxyl groups.

The resin to be modified is not particularly limited as long as it is a resin that can be modified with the above-mentioned carbodiimide group-containing compound, and examples thereof include polyester resins, acrylic resins, polyurethane resins, Examples thereof include a polyether resin, a polycarbonate resin, an epoxy resin, and a polyolefin resin.

The method for the modification is not particularly limited.
For example, the carbodiimide group-containing compound and the resin to be modified, under a solvent-free temperature at a temperature at which the resin is dissolved, or an organic solvent that does not react with the carbodiimide group or the isocyanate group, for example, an organic solvent such as methyl ethyl ketone or xylene. The reaction can be carried out in a solvent at a temperature of about room temperature to about 80 ° C. for about 5 minutes to 2 hours. The carbodiimide group-containing compound and the resin to be modified may be used alone or in combination of two or more.

In the case of the carbodiimide group-containing compound (1) having two isocyanate groups in the molecule, the reaction ratio between the carbodiimide group-containing compound and the target to be modified is as follows. The amount is preferably 0.8 to 1.2 equivalents to the amount. In the case of the carbodiimide group-containing compound (2) having at least two carbodiimide groups in the molecule, the carbodiimide group-containing compound (0.4)
Preferably, it is ０．６0.6 equivalent. Outside of these ranges, the effect of improving the curability may not be obtained, or the desired properties of the coating film may not be obtained.

In the case of the carbodiimide group-containing compound (1) having two isocyanate groups in the molecule, the hydroxyl group in the resin to be modified reacts with the isocyanate group in the carbodiimide group-containing compound (1). Thus, a modified carboxyl group-containing resin can be obtained.
In the case of the carbodiimide group-containing compound (2) having at least two carbodiimide groups in the molecule, a part of the carboxyl group in the resin to be modified and the carbodiimide in the carbodiimide group-containing compound (2) The groups react with each other to obtain a modified resin containing a carboxyl group.

The modified carboxyl group-containing resin may contain a functional group such as a hydroxyl group in addition to the carboxyl group. If the carboxyl group-containing resin contains the carboxyl group and the hydroxyl group at the time of baking, the hydroxyl group reacts with the carbodiimide group derived from the carbodiimide group-containing compound. This reaction occurs between molecules or intramolecularly, and does not cause a decrease in compatibility due to a difference in skeleton between the resin and the curing agent as in the related art, and can provide excellent curability, and There is no decrease in smoothness due to a decrease in compatibility. Further, a high-temperature curing system can be realized by utilizing the high reactivity between the carbodiimide group and the carboxyl group. Further, the modified carboxyl group-containing resin used in the present invention is because the carbodiimide group-containing compound is incorporated in the resin,
One-component curing systems can be constructed.

In the present invention, for the purpose of controlling the reaction rate of the carboxyl group in the modified carboxyl group-containing resin, some of the carboxyl groups in the modified carboxyl group-containing resin are tertiary carboxyl groups. Is preferred. By the modified carboxyl group-containing resin having the tertiary carboxyl group, the reaction rate is appropriately controlled, and a coating film with excellent smoothness can be obtained.

The coating form of the self-curing coating composition of the present invention containing the modified carboxyl group-containing resin is not particularly limited, and examples thereof include a powder type, an aqueous type and a solvent type. Preferably, it is used as a powder coating. The self-curing coating composition of the present invention may contain various additives such as a surface conditioner, a plasticizer, an ultraviolet absorber, an antioxidant, and an anti-bake agent, if necessary. Further, in the case of a powder coating, an additive such as a charge controlling agent can be included.

In the case of a powder coating, as the above-mentioned surface conditioner, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, A number average molecular weight obtained from alkyl esters of (meth) acrylic acid such as 2-ethylhexyl (meth) acrylate and lauryl (meth) acrylate as a raw material is 300 to 50,000, preferably 1,000 to 30,000, and a glass transition temperature. Is preferably an acrylic polymer having a temperature of less than 20 ° C., preferably 0 ° C. or less. If the number average molecular weight is outside the above range, sufficient surface adjustability cannot be imparted, and insufficient appearance prevention such as dents will be insufficient. Further, when the glass transition temperature is 20 ° C. or more, there is a possibility that the surface adjustability cannot be sufficiently imparted.

The above surface conditioner is preferably incorporated in the self-curing coating composition in an amount of from 0.01 to 5% by weight, more preferably from 0.05 to 3% by weight, more preferably from 0.05 to 3% by weight in terms of solids. Is 0.1 to 2% by weight. When the content is less than 0.01% by weight, the surface adjustability cannot be sufficiently imparted, and the probability of poor appearance increases. When the content exceeds 5% by weight,
There is a possibility that the blocking property of the paint may be reduced. Commercially available surface conditioners include, for example, Acronal 4F
(Manufactured by BASF), Polyflow S (manufactured by Kyoeisha Chemical), Resiflow LV (manufactured by ESTRON CHEMICAL)
And acrylic polymers such as silica carrier, for example, Modaflow III (manufactured by Monsanto), Resiflow P67
(ESTRON CHEMICAL) etc. are preferably used.

The self-curing coating composition of the present invention can obtain a transparent coating film without adding a pigment, or can add a pigment. The pigment is not particularly limited, and specifically, coloring pigments such as titanium dioxide, red iron oxide, yellow iron oxide, carbon black, phthalocyanine blue, phthalocyanine green, quinacridone pigments, and azo pigments; And pearl pigments of each color, metal powders and those subjected to surface treatment; extenders such as talc, silica, calcium carbonate, and precipitated barium sulfate. Also, to reduce the gloss, talc, silica, calcium carbonate, barium sulfate, feldspar, inorganic matting agents such as wollastonite,
It is preferable to include an organic matting agent composed of organic fine particles. The matting agent preferably has a volume average particle size of 3 to 30 μm. The production of the self-curing coating composition of the present invention can be carried out using a production method well-known in the field of coatings.

The self-curing coating composition of the present invention can be applied to an object to be coated and then heated to obtain a coating film. The object to be coated is not particularly limited, and specific examples include an iron plate, a steel plate, an aluminum plate, and the like, and those obtained by surface-treating them. Although a single layer of the self-curing coating composition of the present invention has a good protective function, a coating layer may be formed on the object to be coated. In this case, the self-curing coating composition of the present invention is directly applied to the object to be coated as an undercoat, that is, as a primer, to form an undercoat, and then apply an intermediate coating or a topcoat thereon. Good. In addition, the object to be coated may be already undercoated or the like, and the self-curing coating composition of the present invention may be applied as an intermediate coating or a top coating on the undercoat film. In this case, as the undercoat paint for forming the undercoat, a known paint such as an electrodeposition paint or a primer can be used.

The method for applying the self-curing coating composition of the present invention is not particularly limited, and a coating method suitable for the form of the coating can be used. The coating film thickness when applying the self-curing coating composition of the present invention can also be set according to the application and required performance.
00 μm.

The conditions for heating after application of the self-curing coating composition of the present invention vary depending on the amount of functional groups involved in curing and the like. For example, the heating temperature is 100 to 23.
0 ° C, preferably 140-200 ° C. In the case of a coating object that is weak to heat, a good cured coating film can be obtained even with heating at about 140 to 160 ° C. The heating time can be appropriately set according to the heating temperature. The self-curing coating composition of the present invention can be suitably used even for automobile parts such as aluminum wheels and plastic members that cannot be baked and hardened at high temperatures.

[0039]

According to the self-curing coating composition of the present invention, a carbodiimide group-containing compound is introduced into a binder resin skeleton. A coating film having excellent physical properties such as curability and smoothness can be obtained.
Further, a high-temperature curing system can be realized by utilizing the high reactivity between the carbodiimide group and the carboxyl group. Further, the modified carboxyl group-containing resin used in the present invention has a carbodiimide group-containing compound as a curing agent incorporated in the resin, so that a one-component curing system can be constructed. In addition, by using a modified carboxyl group-containing resin (A) containing a tertiary carboxyl group, it is possible to obtain an even more excellent coating film appearance.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Yasunori Minato 19-17 Ikedanakacho, Neyagawa-shi, Osaka Japan Paint Co., Ltd. (72) Inventor Tetsuro Kashino 19-17 Ikedananakacho, Neyagawa-shi, Osaka Japan Inside Paint Co., Ltd. (72) Inventor Masahiko Harada 19-17 Ikedanakamachi, Neyagawa-shi, Osaka F-term in Japan Paint Co., Ltd. (reference) 4J038 CB001 CG001 DB001 DD001 DE001 DF001 GA06 GA09 PC02 PC08

Claims (6)

[Claims] 1. A self-curing coating composition comprising a carboxyl group-containing resin modified with a carbodiimide group-containing compound. 2. The carbodiimide group-containing compound has two isocyanate groups in the molecule.
The self-curing coating composition according to the above. 3. The self-curing coating composition according to claim 2, wherein one of the two isocyanate groups is blocked in advance. 4. The self-curable coating composition according to claim 1, wherein the carbodiimide group-containing compound has at least two carbodiimide groups in a molecule. 5. The modified carboxyl group-containing resin,
4. The composition according to claim 1, wherein the tertiary carboxyl group is contained.
Or the self-curing coating composition according to 4. 6. The self-curable coating composition according to claim 1, wherein the coating composition is in the form of a powder.