JPH061945A - Coating composition for coated steel plate - Google Patents

Abstract

PURPOSE:To provide the subject composition excellent in hardness, processability, weatherability, light resistance, gloss adhesiveness, solvent resistance and contamination resistance, useful for home appliances, etc., comprising a copolyester resin, amino resin and each specific hindered amine compound and ultraviolet light abosorber at specified proportion. CONSTITUTION:The objective composition comprising (A) 50-95 pts.wt. of a copolyester resin and (B) 5-50 pts. wt. of an amino resin such as melamine resin, making a total of 100 pts.wt. (C) 0.05-5 pts.wt. of a hindered amine compound of formula I (R1 is H or 1-30C monovalent organic residue; R2-R5 are each 1-5C alkyl; R6 is n-valent organic residue; n is >=1), e.g. 4-benzoyloxy2,2,6,6- tetramethylpiperidine, and (D) 0.05-5 pts.wt. of an ultraviolet absorber of formula II (R7 is 1-18C alkyl; R8 is H or R7; X is halogen; l is 0 or 1) and/or (E) 0.05-5 pts.wt. of another ultraviolet absorber of formula III.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention has excellent adhesion to metals, high gloss, good balance of hardness and bending workability,
The present invention relates to a coating composition for coated steel sheets, which has solvent resistance and stain resistance, and is particularly excellent in weather resistance and light resistance.

[0002]

2. Description of the Related Art A precoated steel sheet (hereinafter abbreviated as PCM) obtained by coating a galvanized steel sheet, a cold rolled steel sheet, an aluminum plated steel sheet, etc. before processing has a simple coating process,
Since it has advantages such as a uniform and beautiful coating film and cost reduction, it can be used for roof materials, outer wall materials,
In recent years, its use is increasing in household electric appliances and office supplies. Particularly in recent years, the demand for home appliances such as refrigerators, ovens, and microwave ovens, which have more demanding performance, is growing rapidly.

Since PCM is required to have a high degree of workability, a copolymerized polyester resin having good workability has come to be used as a resin for PCM paints. The following are known as examples of paints using such a copolyester resin. A coating composition in which an alkyl etherified formaldehyde resin is blended with a copolyester resin comprising an aromatic dicarboxylic acid or an aliphatic dicarboxylic acid and an alkylene glycol (Japanese Patent Publication No. 61-323).
51), a coating composition in which an alkyl etherified formaldehyde resin is blended with an aromatic copolyester resin copolymerized with a polyfunctional component (JP-B-57-23714), an amino resin with a copolyester resin, and a hindered amine. A coating composition (JP-A-3-217472) in which a compound is compounded to improve weather resistance and light resistance is known, but weather resistance and light resistance under more severe conditions are insufficient.

[0004]

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention
The coating compositions disclosed in Japanese Patent No. 351 and Japanese Patent Publication No. 57-23714 have a balance of adhesion, gloss, hardness and workability,
It has excellent solvent resistance and stain resistance, but weather resistance and
It lacks light resistance and loses its gloss when used outdoors or when it is used indoors in the sunlight, and also reduces adhesion. Further, a coating composition (Japanese Patent Publication No. 3-217472) in which an amine resin and a hindered amine compound are further mixed with a copolyester resin for the purpose of improving weather resistance and light resistance is disclosed, but sufficient effects have been obtained. Absent.

Therefore, the present invention provides a coating material for coated steel sheet, which is excellent in adhesion, gloss, balance between hardness and workability, solvent resistance and stain resistance, and also forms a coating film having good weather resistance and light resistance. Made for the purpose of serving.

[0006]

As a result, as a result, the above-mentioned objects are the copolyester resin (A) and the amino resin (B).
And a hindered amine compound (C) having a specific chemical structure, and a benzotriazole compound (D) also having a specific chemical structure or a benzophenone compound (E) having a specific chemical structure. It has been found that the above is achieved by the coating composition for coated steel sheet.

That is, in the present invention, 50 to 95 parts by weight of the copolyester resin (A) and 5 to 50 parts of the amino resin (B) are used.
Parts by weight, and 0.05 to 5 parts by weight of the hindered amine compound (C) represented by the general formula (I), the ultraviolet absorber (D) or (E) 0 represented by the general formula (II) and / or (III). The coating composition for coated steel sheet is characterized by containing 0.05 to 5 parts by weight. (However, A + B =
100 parts by weight, and C = 0.05 to 5 parts by weight and D and E = 0.05 to 5 parts by weight. )

[0008]

[Chemical 4]

(In the formula, R1 represents a hydrogen atom or a carbon number of 1 to 3)
Represents a monovalent organic residue of 0. R2 to R5 have 1 carbon atom
Represents an alkyl group of 5 to 5, and may be the same or different. n represents an integer of 1 or more, and R6 is n
Indicates a valent organic residue. )

[0010]

[Chemical 5]

[0011]

[Chemical 6]

(Wherein R7 represents an alkyl group having 1 to 18 carbon atoms, R8 represents a hydrogen atom or the same or similar alkyl group as R7, X represents a halogen atom, and l represents 0 or 1). is there.)

The structure of the present invention will be described in detail below. The copolyester resin (A) of the present invention contains a glycol component,
It is possible to copolymerize a small amount of polycarboxylic acid having a valence of 3 or more and / or a polyol having a valence of 3 or more, which is synthesized from a dibasic acid component. As the glycol component, ethylene glycol, 1,2-propanediol,
1,3-propanediol, 2-methyl-1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, diethylene glycol, neopentyl Aliphatic glycols such as glycol, 2-methyl-2-ethyl-1,3-propanediol, 2,2-diethyl-1,3-propanediol, 2-butyl-2-ethyl-1,3-propanediol, 1 Examples thereof include alicyclic glycols such as 4,4-cyclohexanedimethanol and aromatic glycols such as ethylene oxide or propylene oxide adducts of bisphenol A. One or more of these can be selected and used. Among these, ethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol,
Preferred are ethylene oxide or propylene oxide adducts of bisphenol A, ethylene oxide or propylene oxide adducts of bisphenol S, and the like.

Examples of the dibasic acid component include aromatic dibasic acids such as terephthalic acid, isophthalic acid, orthophthalic acid, and 2,6-naphthalenedicarboxylic acid, alicyclic dibasic acids such as hydrogenated terephthalic acid, and succinic acid. Adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, brassic acid,
Mention may be made of aliphatic dibasic acids such as dimer acid,
One or more of these are selected and used.
It is also possible to use a lower alkyl ester. In order to obtain sufficient coating film strength and coating film hardness, it is preferable to use terephthalic acid as one of the dibasic acid components. Examples of the dibasic acid used in combination with terephthalic acid include isophthalic acid, sebacic acid and adipic acid.

Copolymerized polyester resin (A) of the present invention
Is a ternary or quaternary or more copolymer obtained by combining the above-described preferred glycol and a preferred dibasic acid, and more preferably an amorphous one. Examples of tribasic or higher polybasic acids include trimellitic acid and pyromellitic acid. Examples of trihydric or higher polyols include glycerin, trimethylolpropane and pentaerythritol. These polybasic acids and polyols are preferably used in the range of 0 to 10 mol% based on the dibasic acid or glycol, respectively.

Copolymerized polyester resin (A) of the present invention
Is produced by melt-polymerizing a glycol component and a polyester-forming component composed of a dibasic acid or a lower alkyl ester derivative thereof. A concrete method is as follows: Dibasic acid and 1.05 to 2.0 times mol of glycol are reacted by heating at a temperature of about 150 to 240 ° C. under normal pressure in the presence of a usual esterification catalyst. Or about 240-260 ℃ without using catalyst
The reaction is performed under pressure at the temperature of. When a lower alkyl ester compound of a dibasic acid is used as a starting material, it is about 150 to 240 ° C. in the presence of a usual transesterification catalyst.
The reaction is carried out under normal pressure at the temperature of. Then, 220 to 29 under reduced pressure of 10 mmHg or less, preferably 1 mmHg or less.
Heat polycondensate at 0 ° C. At this time, it is preferable to use a polymerization catalyst.

Titanium compounds, tin compounds and lead compounds are used as esterification catalysts, zinc compounds, manganese compounds and cobalt compounds are used as transesterification catalysts, and antimony compounds, titanium compounds, zinc compounds and tin compounds are used as polymerization catalysts. Can be mentioned.

When the phosphorus compound is used together with the polymerization catalyst, the polymerization reactivity and the color tone of the polymer are further improved.

In this way, the reduced specific viscosity is 0.1 to 1.2.
dl / g, preferably 0.2-1.0 dl / g of copolyester resin (A) is prepared.

The amino resin (B) used in the present invention is a thermosetting resin obtained by addition reaction of formaldehyde or paraformaldehyde with melamine, benzoguanamine, urea, etc., and a part or all of its methylol group is alkyl. It is etherified. Specifically, methylol melamine, methylol benzoguanamine, methylol urea, methoxylated methylol melamine,
Methoxylated methylol benzoguanamine, methoxylated methylol urea, butoxylated methylol melamine, butoxylated methylol benzoguanamine, butoxylated methylol urea and the like can be mentioned. Among these, alkyl etherified ones are preferable, and methoxylated methylol melamine and butoxylated methylol melamine are particularly preferable, and they can be used alone or in combination.

The hindered amine compound (C) used in the present invention is represented by the above general formula (I). Specific examples of the compound represented by the general formula (I) include the following compounds. 4-benzoyloxy-2,
2,6,6-tetramethylpiperidine, bis (2,2,2
6,6-Tetramethyl-4-piperidinyl) adipate, bis (2,2,6,6-tetramethyl-4-piperidinyl) suberate, bis (2,2,6,6-tetramethyl-4-piperidinyl) sebacate , Screw (2, 2,
6,6-Tetramethyl-4-piperidinyl) phthalate, bis (2,2,6,6-tetramethyl-4-piperidinyl) isophthalate, bis (2,2,6,6-tetramethyl-4-piperidinyl) Terephthalate, bis (1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate, N, N'-bis (2,2,6,6-tetramethyl-4-piperidinyl) adipamide, bis (1, 2,2,6,6-Pentamethyl-4-piperidinyl) -n-butyl (3,5-di-t-butyl-4-hydroxybenzyl) malonate, bis (1,2,2,6)
6-pentamethyl-4-piperidinyl) diethyl malonate, bis (2,2,6,6-tetramethyl-4-piperidinyl) dibenzyl malonate, bis (2,2,6,6)
6-Tetramethyl-4-piperidinyl) benzylethyl malonate, bis (2,2,6,6-tetramethyl-4)
-Piperidinyl) -n-butyl (3,5-di-t-butyl-4-hydroxybenzyl) malonate, butanetetracarboxylic acid tetra (2,2,6,6-tetramethyl-4-piperidinyl) ester, etc. can give.

Among them, bis (2,2,6,6-tetramethyl-
4-piperidinyl) sebacate, bis (1,2,2,6,6-pentamethyl-4-piperidinyl) sebacate, 1,2,3,4
-Butanetetracarboxylic acid tetrakis (2,2,6,6-tetramethyl-4-piperidinyl) ester, poly [[6-
(1,1,3,3-Tetramethylbutyl) amino-1,3,5-triazine-2,4-diyl] (2,2,6,6-tetramethyl-
4-piperidinyl) imino] hexamethylene [(2,2,6,
6-Tetramethyl-4-piperidinyl) imino]] is preferred.

Further, a hindered amine compound having a hydroxyl group or a carboxyl group may be used for copolymerization in the polyester resin.

The ultraviolet absorber (D) and / or (E) used in the present invention is represented by the above general formula (II) or (III). An example of the compound represented by the general formula (II) is 2 (2'-hydroxy-3 ', 5'-di-t.
-Butylphenyl) benzotriazole, 2 (2'-hydroxy-3'-t-methylphenyl) -5-chlorobenzotriazole, 2 (2'-hydroxy-3 ', 5'
-Di-t-butylphenyl) -5-chlorobenzotriazole, 2 (2'-hydroxy-3 ', 5'-di-t-
Amylphenyl) benzotriazole, 2 (2′-hydroxy-5′-methylphenyl) benzotriazole,
2 (2'-hydroxy-5'-tetramethylbutyl) benzotriazole etc. are mentioned. 2 of these
(2'-Hydroxy-3'-t-butyl-5'-methylphenyl) benzotriazole is preferred.

Examples of the compound represented by the general formula (III) include 2-hydroxy-4-methoxybenzophenone and 2
-Hydroxy-4-benzyloxybenzophenone, 2
-Hydroxy-4-methoxy-4'-chlorobenzophenone, 2-hydroxy-4-dodecyloxy-benzophenone, 2-hydroxy-4-n-octoxybenzophenone, 2-hydroxy-4-stearyloxy-benzophenone and the like can be mentioned. Among these, 2-hydroxy-4-n-octoxybenzophenone is preferable. Among these UV absorbers, the use of 2 (2'-hydroxy-3'-t-butyl-5'-methylphenyl) benzotriazole is particularly effective.

Each of these stabilizers is used in an amount of 50 to 95 parts by weight, particularly preferably 60 to 9 parts by weight of the copolymerized polyester resin (A).
0 parts by weight, 5 to 50 parts by weight of the amino resin (B), particularly preferably 10 to 40 parts by weight, 0.05 to 5 parts by weight of the hindered amine compound (C) represented by the general formula (I),
Particularly preferably 0.1 to 2 parts by weight, the ultraviolet absorber (D) and / or (E) represented by the general formula (II) or (III) is 0.05 to 5 parts by weight, particularly preferably 0.1.
It contains 1 to 2 parts by weight. However, A + B =
100 parts by weight, and C = 0.05 to 5 parts by weight and D and E = 0.05 to 5 parts by weight.

The proportion of the copolyester resin is 5
If it is less than 0 part by weight, the processability of the coating film becomes insufficient.
Further, when the proportion of the copolymerized polyester resin exceeds 95 parts by weight, curing of the copolymerized polyester resin with the amino resin becomes insufficient and various physical properties such as solvent resistance of the coating film deteriorate.

If the amount of each stabilizer added is less than the above range, the effect is not sufficiently exhibited, and if the amount added is more than this range, the physical properties of the composition are adversely affected, and undesired phenomena such as blooming also occur. Will be presented.

The copolymerized polyester (A) of the present invention
In order to make the composition stable against photooxidation deterioration, the amide resin (B), the hindered amine compound (C) represented by the general formula (I), and the general formula (II) are used with respect to the copolyester (A). Alternatively, it is necessary to add both the ultraviolet absorber (D) and / or (E) represented by (III). If either of them is missing, the light resistance is higher than that of the composition of the present invention. Or weather resistance
Alternatively, both can only give a composition that is significantly inferior.

The method of blending the hindered amine compound and the ultraviolet absorber is not particularly limited and may be blended at any time during or after the polymerization of the copolyester, or may be added to the solution of the copolyester. You can
Alternatively, it may be blended when it is made into a paint.

If necessary, a curing catalyst, a pigment, a coloring agent, a leveling agent, etc. may be added to the coating composition of the present invention.

The coating composition of the present invention is generally used by dissolving it in an organic solvent. As the organic solvent, toluene, xylene, "Solvesso"# 100 (manufactured by Excel Chemical Co., Ltd.), "Solvesso"# 150 (manufactured by Excel Chemical Co., Ltd.), methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ethyl acetate, normal butyl acetate , Methyl cellosolve acetate, ethyl cellosolve acetate, isophorone, butanol, octanol, butyl carbitol and the like, its solubility and evaporation rate,
It can be arbitrarily selected depending on the economical efficiency.

A mixer such as a ball mill, an impeller disperser, a sand grind mill, a roll mill or a paint conditioner is used for producing the coating composition of the present invention. The coating is performed by a method such as roll coating, roll coater, spray coating, and electrostatic coating. The baking temperature and time are appropriately selected depending on the size and thickness of the steel plate, the curability of the paint, and the like.

[0034]

The present invention will be described below with reference to examples. All parts in the examples are based on weight. In addition, each measurement item shown in Examples and Comparative Examples complies with the following methods.

Glass transition temperature Measured by DSC.

-Reduced specific viscosity: 0.25 g of resin was dissolved in 25 ml of o-dichlorobenzene / phenol (volume ratio: 4/6) and measured at 25 ° C.

20 ° reflectance was measured using a gloss gloss meter.

Adhesiveness After the scratches that reach a goggle-shaped substrate consisting of 100 squares with a side of 1 mm on the coating film were attached using a cutter knife and a cellophane tape was pressure-bonded, it was peeled off vigorously and left without peeling. The number of eyes was measured.

Pencil hardness Measured according to JIS K5410 using Mitsubishi Uni.

Workability A coated steel sheet was bent 180 ° using a bending tester, and cracks generated in the bent portion were observed with a magnifying glass of 10 times. At this time, several bent sheets having the same plate thickness were sandwiched and tested, and the number of sandwiched sheets (R) was represented as RT. The observation results are shown below. ⊚: Very good (no crack) ○: Good Δ: Slightly bad ×: Poor (full-face crack)

Solvent resistance: The coating film was rubbed with a gauze soaked with methyl ethyl ketone, and the number of times until the substrate became glossy was shown.

Contamination resistance The coated surface was colored with red, black, and blue magic ink, and after 24 hours, the degree of coloring was wiped off with gauze impregnated with n-butanol. The results are expressed as follows. ◎: Very good (no ink marks) ○: Good △: Slightly bad ×: Bad (ink marks clearly remain)

Reference Example 320 parts of terephthalic acid, 320 parts of isophthalic acid, 143 parts of ethylene glycol, neopentyl glycol 168
Parts, bisphenol A ethylene oxide adduct 24
Three parts were charged into a reaction vessel equipped with a stirrer and a rectification tube, and an esterification reaction was carried out at 240 ° C. for 4 hours under pressure. Next, the mixture was transferred to a reaction vessel equipped with a helical ribbon type stirring blade, 0.2 part of zinc acetate, 0.1 part of antimony trioxide and 0.1 part of phosphoric acid were added, and then about 1 part was added according to a heating and depressurizing program. It was brought to a reaction condition of 275 ° C. and 1 mmHg or less over time. In that state, polycondensation reaction was performed for 2 hours and 20 minutes to obtain a pale yellow transparent polyester resin (A-1). The polyester resin (A-1) had a glass transition temperature of 67 ° C. and a reduced specific viscosity of 0.70 dl / g. 1
The composition ratio of the polyester unit obtained from the 1 H-NMR spectrum was such that the acid component was terephthalic acid / isophthalic acid = 50/5.
0 (molar ratio), glycol component is ethylene glycol /
The ethylene oxide adduct of neopentyl glycol / bisphenol A was 40/40/20 (molar ratio).

Thereafter, copolymerized polyester resins (A-2) to (A-5) whose compositions are shown in Table 1 were produced in the same manner.

[0045]

[Table 1]

Stabilizers The structures of the stabilizers used in the examples and their abbreviations are shown in Table 2.
As shown in.

[0047]

[Table 2]

Examples 1 to 5 100 parts of the copolyester resin (A-1) was dissolved in 150 parts of a mixed solvent of cyclohexanone / "Solvesso" 150 (manufactured by Excel Chemical Co., Ltd., weight ratio 50/50). 100 parts of this solution, 50 parts of titanium oxide, 10 parts of methoxylated methylol melamine ("Cymel" 303, manufactured by Mitsui Cyanamid), 0.2 part of ρ-toluenesulfonic acid (20% solution of benzyl alcohol) as a catalyst,
Bis (2,2,6,6-tetramethyl-4-piperidinyl) sebacate (C-1) 0.2 part, 2 (2'-hydroxy-
3'-t-Butyl-5'-methylphenyl) benzotriazole (D-1) 0.2 part, the above mixed solvent 40 parts and glass beads were added, and the pigment was dispersed using a paint conditioner, and then glass beads. Was removed to obtain a coating composition. The mixing ratio in the coating composition is 80 parts of polyester resin, 20 parts of amino resin, and 0.4 parts of hindered amine compound. The weight ratio of the total amount of polyester resin and amino resin to titanium oxide as a pigment is 1: 1. The coating composition obtained is 70 × 150 × 0.5 mm
After coating with a bar coater to a film thickness of about 20 μm on a chromate-treated electrogalvanized steel sheet having the above size, baking was performed at 180 ° C. for 20 minutes. Table 3 shows the test results of the obtained coated steel sheet. The weather resistance of this coated steel sheet was examined by irradiating it with light in a sunshine weatherometer. The black panel temperature in the sunshine weather orometer was 63 ° C. and water was sprayed for 18 minutes every 2 hours. The weather resistance was evaluated by the time when the gloss of the coating film was 80% of the initial value. The results are shown in Table 3. Moreover, the light resistance of the coated steel sheet was examined by irradiating with light in a fade-o-meter.
The temperature in the fade-o-meter was set to 50 ° C., and the light resistance was evaluated at the time when the gloss retention rate was 80%, like the weather resistance. The results are shown in Table 3.

The copolyester resin (A-1) was added to (A
-2) to (A-5) instead of "Cymel" 303 or "Cymel" 3 as methoxylated methylol melamine
25 (manufactured by Mitsui Cyanamid Co., Ltd.)
When 03 was used, ρ-toluenesulfonic acid (20% solution of benzyl alcohol) was added as a catalyst, and
A coating composition was prepared in the same manner with the coating composition shown in. The total amount of the copolymerized polyester resin and the amino resin and the weight ratio of titanium oxide as the pigment are all 1: 1 and the same. After each coating composition obtained was applied in the same manner, it was baked in the same manner, and the physical properties of the coating film were evaluated and the weather resistance and light resistance were examined. The test results are shown in Table 3.

Comparative Examples 1 to 7 Copolymerized polyester resins (A-1) to (A-5) were used at the blending ratios shown in Table 3 to prepare coating compositions in the same manner as in Examples, coating film properties, weather resistance and The light resistance was evaluated. The results are shown in Table 3.

[0051]

[Table 3]

From the results shown in Table 3, Examples 1 to 5 using the hindered amine compound are superior in weather resistance and light resistance as compared with Comparative Examples, and have good balance between hardness and workability and solvent resistance. Recognize.

[0053]

EFFECTS OF THE INVENTION The coating composition for coated steel sheet of the present invention is a coating film having excellent weather resistance and light resistance, high gloss and adhesiveness, a balance between hardness and workability, and good solvent resistance and stain resistance. Form.

Claims (1)

[Claims] 1. Copolymerized polyester resin (A) 50 to 95
Parts by weight, 5 to 50 parts by weight of the amino resin (B), and the hindered amine compound (C) of the general formula (I) 0.
05 to 5 parts by weight, and 0.05 to 5 parts by weight of the ultraviolet absorber (D) represented by the general formula (II) and / or the ultraviolet absorber (E) represented by the general formula (III). A characteristic coating composition for a coated steel sheet. (However, A + B = 10
0 parts by weight, and C = 0.05 to 5 parts by weight,
D and E = 0.05 to 5 parts by weight. ) [Chemical 1] (In the formula, R1 represents a hydrogen atom or a monovalent organic residue having 1 to 30 carbon atoms. R2 to R5 each represents an alkyl group having 1 to 5 carbon atoms and may be the same or different. n represents an integer of 1 or more, and R6 represents an n-valent organic residue.) [Chemical 3] (However, R7 represents an alkyl group having 1 to 18 carbon atoms, R7
8 represents a hydrogen atom, the same as R7, or a similar alkyl group. X is a halogen atom and l is 0 or 1. )