JPH02158671A - Urethane baking paint composition for coating metal - Google Patents

Abstract

PURPOSE:To obtain the title composition composed of hydroxyl group-containing polyester resin, blocked isocyanate, organotin compound, organic solvents and coating additives having excellent hardness, folding processability, chemical resistance and weather resistance. CONSTITUTION:The subject composition is composed of (A) a hydroxyl group- containing polyester resin, preferably the hydroxyl value is 40 to 120mgKOH/g, (B) a blocked isocyanate compound (preferably prepared from an alicyclic isocyanate using an acetoxime as a blocking agent, (C) an organotin compound such as dibutyltin oxide, (D) organic solvents and (E) coating additives.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a urethane baking paint composition for coating metals, and more specifically, it relates to a urethane baking paint composition for coating metals with excellent hardness, bending workability, chemical resistance, and weather resistance. The present invention relates to a urethane baking paint composition for coating.

[Conventional technology]

Regarding the coating of metal materials such as aluminum plates, steel plates, and galvanized steel plates, there is a coil coating method as a method for supplying economical and high-quality pre-coated metal products.

Metal materials coated with this coil coating method are
After being painted, it is cut, bent, etc., and used for construction materials such as side wall materials, roof materials, shutters, and curtain walls, home appliances such as refrigerator cases, TV and audio equipment cabinets, and the protection of the undercarriage of automobiles. It is used in many fields such as rusted steel plates, blackboards, steel furniture, and signs.

The paint composition used for coil coating is
It is classified into general grade and high grade depending on the usage as mentioned above.

General grades are used for side wall materials and roofing materials, and thermosetting acrylic resin paints or oil-free alkyd resin paints are generally widely used.

High-grade grades are used for the exterior of refrigerators, home appliances such as TV and audio equipment cabinets, and rust-proof steel plates for the underside of automobiles, such as high molecular weight linear polyester resin paint, epoxy resin paint, silicone-modified polyester resin paint, There are fluorine resin paints, and in addition to chemical resistance, solvent resistance, water resistance, stain resistance, etc. ■High hardness and excellent workability ■Excellent corrosion resistance ■Excellent long-term weather resistance Performance that exceeds that required is required.

Particularly in recent years, the characteristics (■) have been mainly required.

However, since hardness and workability are contradictory properties, it is very difficult to strike a balance, but workability can be improved using high molecular weight linear polyester resin/methylated melamine tl)J resin type paint. In order to achieve this, a method has been taken that takes advantage of the flexibility of polyester resin and further increases its hardness by crosslinking it with melamine.

[Problem to be solved by the invention]

As described above, in the conventional thermosetting coil coating paint, a methylated melamine resin is blended into -m, and the hardness of the coating film is developed by the thermal condensation reaction of this melamine resin.

However, as mentioned above, in the future, coil coating paints will be required to have the following properties: 1) High hardness and excellent workability, 2) Excellent corrosion resistance, and 2) Excellent long-term weather resistance. Therefore, it can be said that there are various problems with melamine-curing paints. For example, although high-molecular-weight linear polyester resins with good processability have a very low content of hydroxyl groups that serve as crosslinking points, methylated melamine resins generally contain a large excess of droxyl groups. There is.

In other words, the processability, which is a characteristic of high molecular weight linear polyester resin/methylated melamine resin type paint, takes advantage of the flexibility of polyester resin, and not only crosslinks melamine, but also self-condenses most of the melamine resin to form a coating film. It can be assumed that the hardness of the material is increased.

Therefore, even if the paint film has high hardness and excellent workability, it is estimated that it is difficult to expect long-term weather resistance because the paint film contains self-condensed melamine resin. .

Furthermore, since the degree of crosslinking of the coating film is extremely low, it is thought that not only the stain resistance but also the corrosion resistance of the coating film will not be improved.

Furthermore, when melamine resin is self-condensed, it is necessary to carefully consider the baking conditions and the amount of curing catalyst. Otherwise, it can be easily assumed that not only will the coating film become brittle due to excessive baking and good workability will not be obtained, but also cracks generated in the processed portion will cause corrosion of the metal material.

Therefore, the authors made the following assumptions in order to obtain a coil coating film with high hardness and excellent workability.

In order to increase the hardness of the paint film, it is possible to add structurally hard components to the paint.9On the other hand, to improve processability, at the same time imparting flexible properties to the paint resin, it is possible to add structurally hard components to the paint. In order to prevent cracking, etc., it is considered necessary to make the firm and flexible parts of the paint film uniform.

In addition, in order to improve processability, it is considered that a resin having an ester bond is more suitable as a coating resin than a resin having a main chain consisting of a C--C bond such as an acrylic resin.

Furthermore, by applying intermolecular attraction, such as hydrogen bonds, between the molecules in the coating film, it may be possible to form a tough coating film. I surmised that it could be made into something.

[Means to solve the problem]

Based on the above estimations, the inventors of the present invention conducted extensive studies, and found that the processability and weather resistance of hydroxyl group-containing polyester resin, blocked isocyanate compound, organic tin compound, organic solvent, and paint additives It is now our turn to invent and present an excellent metal-coated urethane baking paint composition.

Next, the present invention will be explained in detail.

The blocked isocyanate compound used in the present invention is an isocyanate compound, and when heated above a predetermined temperature, the blocking agent dissociates and the isocyanate group is regenerated.

The isocyanate compound described in the present invention has a straightforward structure, and in order to have heat resistance and improve weather resistance, alicyclic isocyanates are suitable, such as 4.4'-methylenebis(cyclohexyl isocyanate), methyl Cyclohexane 2.4(2,6) diisocyanate, 1.
3-(isocyanatomethyl)cyclohexane, 3-isocyanato-methyl-3,5,5-trimethylcyclohexyl isocyanate (isophorone diisocyanate) = I
PDI) and polyisocyanates having incyanurate bonds, uretdione bonds, biuret bonds, allophanate bonds using one or more of these, or these isocyanates and polyhydric alcohols, polyether polyols, polyester polyols, etc. Examples include adduct bodies.

Among them, 3-incyanato-methyl-3,5,5-trimethylcyclohexyl isocyanate has excellent weather resistance, and especially the isocyanurate form has excellent heat resistance.

Blocking agents that block the isocyanate groups of the above isocyanate compounds include acetoxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, acetylacetone, methyl acetoacetate, ethyl acetoacetate, etc., and one or more of these may be used. to block isocyanate groups.

Next, the method for synthesizing the blocked isocyanate compound will be explained in detail.

The isocyanate compound is dissolved under a nitrogen atmosphere in a solvent consisting of a compound having no active hydrogen that reacts with isocyanate groups, such as aromatic hydrocarbons, ketones, ethers, acetic esters, and the like.

At this time, in order to promote dissolution of the isocyanate compound, the contents are stirred while being heated at 40 to 80°C.

Next, the blocking agent in an amount equivalent to the isocyanate group is gradually introduced into the solution of the isocyanate compound either alone or diluted with a solvent.

The blocking agent reacts with the isocyanate group immediately after addition and generates heat, but the charging rate of the blocking agent may be adjusted so that the reaction temperature is within the range of 40 to 120°C, or the reactant may be cooled using a refrigerant or the like. Remove heat.

After the blocking agent has been charged, the reaction temperature is further increased to 40 to 1
The reaction product is aged at 20° C., and the reaction is completed when the content of NGO groups becomes 0.1% by weight or less.

The hydroxyl group-containing polyester resin used in the present invention is composed of a divalent or trivalent or higher polyhydric alcohol compound, a dibasic acid, and ε-caprolactone, and has a hydroxyl value of 20 to 140 mgKOH/g based on the solid content of the resin. Those having a droxyl group, particularly those having 40 to 120 mgKOH/g of a droxyl group, are excellent.

For polyester resins with a hydroxyl value of less than 20 mgKOH/g based on the solid content of the resin, the coating film obtained by baking and curing with a blocked isocyanate compound has a very low crosslinking density, resulting in insufficient hardness of the coating film. , and the chemical durability of the coating film, such as solvent resistance, decreases.

In addition, for polyester resins with a hydroxyl value higher than 140 mgKOH/g, the coating film obtained by baking and curing with a blocked isocyanate compound will have too high a crosslinking density, which improves the hardness and durability of the coating film, but this is contradictory. As a result, workability is significantly reduced.

Moreover, the hydroxyl group-containing polyester resin has 10 to 6
The hydroxyl group-containing polyester resin has excellent processability when modified with 0 parts by weight of ε-caprolactone, and the hydroxyl group-containing polyester resin is particularly suitable for modification in an amount of 20 to 50 parts by weight.

If the polyester resin has a modified amount of ε-caprolactone of less than 10 parts by weight, the coating film obtained by baking and curing with a blocked isocyanate compound will not have sufficient processability because the amount of soft segments will be insufficient. , defects such as cracks and peeling will occur in the processed part.

On the other hand, for polyester resins in which the amount of modification of ε-caprolactone is greater than 60 parts by weight, the amount of modification of ε-caprolactone is too high compared to the crosslinking density, so the hardness and durability of the coating film obtained by baking hardening are Significantly decreased.

Furthermore, if only a polyester resin that has not been modified with ε-caprolactone or contains a droxyl group is mixed with a polycaprolactone diol or/or triol, even if sufficient crosslinking is achieved, the same degree of modification with caprolactone and the same hydroxyl value will be obtained. Compared to the case of the hydroxyl group-containing polyester resin of the present invention, the coating film becomes too soft and the hardness is significantly reduced.

Next, the polyhydric alcohol which is one component of the hydroxyl group-containing polyester resin will be explained in detail.

Examples of the polyhydric alcohol used in the present invention include ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, 1,4-butanediol, 1,3-butanediol, neopentyl glycol, hexanediol, and 1,6-hexane. Diols, dihydric alcohols such as 2.2.4- and 2.4.4-trimethylhexanediol, glycerin, trimethylolethane, trimethylolpropane, pentaerythritol, etc., and one or more of these are used. do.

Next, the other component of the hydroxyl group-containing polyester resin, the dibasic acid, will be explained in detail.

Examples of dibasic acids used in the present invention include polymethylene dicarboxylic acids (succinic acid, adipic acid, azelaic acid, sebacic acid, etc.), aromatic dicarboxylic acids (phthalic anhydride, phthalic acid, isophthalic acid, terephthalic acid, etc.) ,
Examples include fumaric acid, maleic anhydride, tetrahydrofumaric anhydride, hexadromaleic anhydride, dimer acid, and polybutadiene dicarboxylic acid, and one or more of these may be used.

The method for synthesizing the hydroxyl group-containing polyester resin is as follows:
The polyhydric alcohol, dibasic acid and ε-
After charging a predetermined amount of caprolactone, the contents are heated and dissolved until stirring is possible.

Heat to 140-160°C with stirring, then heat to 2°0-23°C.
The temperature is gradually raised to 0° C. over 4 to 6 hours, and while the temperature is kept constant, the generated water is collected in a dehydration tube to allow the reaction to proceed.

After the reaction is completed, the reactants are stirred for 20 to 60 minutes at a reduced pressure of 10 to 100 mmHg and a temperature of 100 to 140°C to distill off and remove unreacted substances.

In addition, in this reaction, a ring-opening reaction of ε-caprolactone can be performed separately. After the esterification reaction of the polyhydric alcohol and dibasic acid is completed, a predetermined amount of ε-caprolactone is added to the obtained base resin, and the mixture is stirred. Lower 140~
It is also possible to react at 180°C for 2 to 8 hours.

In order to speed up the reaction, a catalyst such as tetrabutyl titanate, dibutyltin oxide, dibutyltin dilaurate, etc. is used in advance.

In addition, in order to quickly remove the generated water from the reaction system,
It is also possible to use azeotropic dehydration solvents such as toluene and xylene.

The progress of the reaction is confirmed by successively measuring the acid value, and the end point is determined when the acid value becomes 5 to 3 mg KOH/g or less based on the resin content.

After the reaction is completed, the product is cooled to 100 to 120°C, and then diluted with a solvent such as an aromatic hydrocarbon or a #acid ester compound.

The blocked isocyanate compound and hydroxyl group-containing polyester resin obtained as described above contain inorganic or organic pigments, dispersants, leveling agents, organotin compounds as dissociation catalysts, aromatic hydrocarbons, acetate ester compounds, etc. When mixed with a solvent and poured into a paint mixer such as a paint shaker or sand mill, a very smooth metal-coated urethane baking paint composition with a particle size of 10 μm or less can be obtained.

The blocked isocyanate compound and the hydroxyl group-containing polyester resin in the above coating composition are blended in a ratio of Neo group 10H group=0.8 to 1.2 (molar ratio).

If the blending ratio of NCO groups and 10H groups is less than 0.8,
The coating film may not be sufficiently cured, and the expected hardness and strength of the coating film may not be obtained.

If the blending ratio of NCO groups and 10H groups is greater than 1.2,
Excess isocyanate groups may cause side reactions with each other or with urethane bonds, reducing the processability of the coating film.
The weather resistance of the coating film may also be reduced.

The organic tin compounds used as dissociation catalysts include dibutyltin oxide, dioctyltin oxide, dibutyltin dilaurate, dioctyltin dilaurate,
There are dibutyltin diacetate, dibutyltin chloride, etc., and it is 0 for block or isocyanate compounds.
．． Add 01 to 1.0 parts by weight.

The dissociation catalyst is 0 for blocked isocyanate compounds.
．． If the amount is less than 0.01 parts by weight, no catalytic action will occur, and the crosslinking reaction of the coating will not proceed sufficiently, making it impossible to obtain the pre-designed physical properties.

If the dissociation catalyst is used in an amount greater than 1.0 parts based on the blocked isocyanenite compound, the catalytic action will be too strong and the storage stability of the resulting urethane baking paint composition will be reduced.

Further, if the dissociation catalyst is in excess, the water resistance and weather resistance of the obtained coating film will be significantly reduced, and the physical properties of the coating film will deteriorate over time.

The metal-coated urethane baking paint composition obtained by blending as described above is degreased and subjected to a chemical conversion coating treatment using phosphate or chromate, and then applied to an aluminum plate coated with a 2-7 micron thick brimer. It is applied to metal materials such as steel plates and galvanized steel plates to a film thickness of 20 to 25 microns. The board to be painted has a base material temperature of 200~2
It is hardened and dried under baking conditions of 50° C. and baking time of 30 to 120 seconds.

〔Effect of the invention〕

The metal-coated urethane baking paint composition of the present invention contains a blocked isocyanate compound consisting of an alicyclic isocyanate compound with a rigid structure and a hydroxyl group-containing polyester resin modified with ε-caprolactone, so that the hardness of the coating film is improved. It exhibits high performance and excellent bending workability.

In addition, since the curing agent uses a blocked isocyanate compound consisting of an alicyclic isocyanate compound with good heat resistance and weather resistance, compared to conventional melamine curing type paints,
There is very little yellowing or deterioration of the paint film due to ultraviolet rays or heat.

Furthermore, after the paint film is formed, urethane bonds are formed, which leads to hydrogen bonding, resulting in intermolecular attraction between paint resins and glabella adhesion of the paint film compared to conventional melamine-curing paints, which improves processability of the paint film. Adhesion can be improved.

Note that specific embodiments of the baking paint composition of the present invention include the following.

(a) A baking paint composition according to the claims, in which an alicyclic isocyanate is used as the blocked isocyanate compound.

(b) Claims in which isocyanate groups are blocked using one or more of acetoxime, methyl ethyl ketoxime, methyl isobutyl ketoxime, acetylacetone, methyl acetoacetate, and ethyl acetoacetate as a blocking agent. baking paint composition.

(C) Hydroxyl value 20 to 140 mgK based on resin solid content
OH/g, in particular 40 to 120 mg KOH/g of a hydroxyl group-containing polyester resin, (d) modified with 10 to 60 parts by weight of ε-caprolactone and droxyl groups; A baking paint composition according to the claims, which uses a polyester resin containing the polyester resin.

(e) 0.0 for blocked isocyanate compound
A baking paint composition as claimed in the claims, which contains 1 to 1.0 parts by weight of an organotin compound as a catalyst.

EXAMPLES Next, the content of the present invention will be specifically explained with reference to Examples, but the present invention is not limited by these.

The hydroxyl values shown in the examples are values measured by the phthalic anhydride-pyridine method based on JISK-1557, and the acid values are values obtained by neutralization titration using an acetone solvent.

Note that all parts in the steel represent parts by weight.

"Synthesis Example-1" 161.2 parts of neopentyl glycol and 12 parts of trimethylolpropane were placed in a four-way flask equipped with a stirrer, thermometer, gas inlet tube, condenser, and azeotropic dehydrator.
1.9 parts, isophthalic acid 173.5 parts, terephthalic acid 1
73.5 parts of ε-caprolactone, 369.9 parts of ε-caprolactone, 2.0 parts of dibutyltin oxide, and 46.2 parts of xylene were charged, and the mixture was heated to 160° C. and stirred under a nitrogen stream.

The reaction was allowed to proceed while gradually increasing the temperature from 160° C. to 220° C. over 5 hours while removing distilled water.

The reaction was further continued for 2 hours at a reaction temperature of 220°C to complete the reaction.

The acid value of the reactant was analyzed sequentially, and the end point of the reaction was defined as the point when the acid value became 5.0 mgKOH/g or less based on the resin solid content. (manufactured by Exxon) was added to adjust the solid content to 70.6% by weight.

The acid value of the obtained hydroxyl group-containing polyester resin was 3.0 mgKOH/g, and the hydroxyl value was 104.0 mgKO.
H/g, solid content 70.6f! amount%, Gardner viscosity (2
5°C) was Y.

"Synthesis Example-2 ~ IOJ The raw materials were charged in the same equipment as in Synthesis Example-1 according to the formulation shown in Table-1, and the hydroxyl group-containing polyester resins A-2 to A-10 were prepared in the same manner as in Synthesis Example-1. Synthesized.

Acid value, hydroxyl value, solid content of the obtained polyester resin,
Properties such as viscosity are also summarized in Table-1.

“Example-1 Polyester resin A-132,8 obtained in Synthesis Example-1
Part, Blocked Isocyanate IPDI-81358 (
22.5 parts (Hüls GmbH, West Germany), 30°9 parts titanium oxide (Tiebeke CR-90, manufactured by Ishihara Sangyo), KP-3
31 (Shin-Etsu Silicone: 10% xylene solution) 1.5
parts, 10% dibutyltin dilaurate/xylene solution 0
．． 4 parts were placed in a polyethylene container along with 100 parts of glass beads (5 mm φ), and the mixture was tightly sealed and stirred for 30 minutes using a Red Devil Paint Shaker.
A white paint P-1 was obtained.

The glass beads and the paint were separated using a 50-100 mesh R cloth, and further defoamed under reduced pressure.

The obtained paint was applied to a zinc phosphate treated rolled steel plate specified by JI'S G3303 <70mmX150mmXo, 3
mmt), apply the primer paint shown in Table 4 to a dry film thickness of 5
A dry film thickness of 20 μm was applied to a test panel coated with a coating thickness of 20 μm.
It was coated with a bar coater so that it became m.

Baking conditions are base material temperature (PMT) 210-220℃,
The baking time was 30 seconds, and immediately after hardening, the sample was immersed in cold water to be rapidly cooled to obtain a test piece.

"Examples 2 to 12. Comparative Examples 1 to 4" Table 2 shows the polyester resins obtained in Synthesis Examples 2 to 10 in the same manner as Example 1.
Then, paints P-2 to P-16 were prepared using a paint shaker by blending blocked isocyanate, titanium oxide, additives, thinner, etc. according to the layer composition shown in Table 3.

These paints were applied and baked in the same manner as in Example-1 to obtain test pieces.

The abbreviations in Table 1 are as follows.

(Leaving space below) I PD I-81358 Manufactured by HulsAG IPDIaffi form Methyl ethyl ketoxime block form, NGO content 13.6%, solid content 65±lvt% IPDI-B1370 Huts AGTAI PD I 3ffi form Acetoxime block form, NGO content 13 .7%.

Solid content 60±1wt% Cymel 303 Mitsui Cyanamid Co., Ltd. Methylolated melamine resin 10% KP-331/Xylene Shin-Etsu Silicone 10% xylene solution of defoaming agent KP-331 10% FC430/Xylene 3M Dispersing aid FC430 10 % xylene solution 10% DBTDL / 10% xylene dibutyltin dilaurate 20% xylene solution 20% PTS / benzyl alcohol para-toluene sulfonic acid 20% benzyl alcohol solution Thinner Tulpetz 15-0 / Ethyl glycol acetate - 50:50 (vt /vt) Pencil hardness: Scratch hardness based on JIS 54006.14 Impact resistance: DuPo based on JIS K5400 B, 13.3
ntl kg
: <80/100 Workability 01 Bending test O: Good Δ: Cracks ×: Cracking Solvent resistance Methyl ethyl ketoxime rubbing 200 times O: Good
△: Scratches X: Cracking Salt water resistance Salt spray test 35 based on JIS K54007.8 $
±1°C, 16H spray + 8H rest for 20 cycles O without niblister △With niblister

Color difference (ΔE) after 200 hours of 10 hours of irradiation + 2 hours of fogging
) and gloss retention rate (60°C) Brimer paint formulation Belacolite 46-1893 120 Cymel 303 6.2 Tybake
CR-9022,2 Zinc Chromate 22,220%PS
T/Benzyl Alcohol 1.3 Thinner 42.5 Veraflite 46-1893

Claims (1)

[Claims] A metal-coated urethane baking paint composition with excellent processability and weather resistance, consisting of a hydroxyl group-containing polyester resin, a blocked isocyanate compound, an organic tin compound, an organic solvent, and a paint additive.