JPH02142870A - Coating composition for coated steel sheet - Google Patents

Abstract

PURPOSE:To obtain the title composition which can give a coating film excellent in solvent resistance and stain resistance and excels in adhesiveness and processability, etc., by mixing a modified polyester resin obtained by reacting a copolyester resin with an aliphatic glycidyl ether with an amino resin. CONSTITUTION:Desirably 50-95 pts.wt. modified polyester resin obtained by reacting a copolyester (e.g., a copolymer of terephthalic acid and isophthalic acid with ethylene glycol and neopentyl glycol) with an aliphatic glycidyl ether (e.g., a compound of the formula) is mixed with desirably 5-90 pts.wt. modified polyester resin desirably having a reduced specific viscosity of 0.25-2.0dl/g and an acid value of 0.2-10mgKOH/g and desirably 5-50 pts.wt. amino resin (e.g., methoxylated methyllmelamine).

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention provides a paint for coated steel sheets that has excellent adhesion to metals, and has excellent gloss, hardness, bending workability, solvent resistance, and stain resistance. Regarding the composition.

[Conventional technology]

Pre-painted steel sheets (hereinafter referred to as P C
1vi) has the advantages of a simple painting process, a uniform and beautiful coating film, and a 1° cost reduction, so it is widely used in roofing materials, exterior wall materials, household electrical appliances, etc. Its use in office supplies and the like has been increasing in recent years. Particularly recently, there has been a large increase in demand for home appliances that have stricter performance requirements.

PCM requires a high degree of workability, but conventionally PCM
Since the alkyd resins, epoxy resins, acrylic resins, etc. that have been used as paint resins lack processability, copolymerized polyester resins with good processability have come to be used.

The following are known as examples of paints using such copolymerized polyester resins. A coating composition containing an alkyl etherified formaldehyde resin and a copolymerized polyester resin consisting of an aromatic dicarboxylic acid, an aliphatic dicarboxylic acid, and an alkylene glycol was published in Japanese Patent Publication No. 61-3.
It is disclosed in Japanese Patent No. 2351. Further, a coating composition in which an alkyl etherified formaldehyde resin is blended with an aromatic copolymerized polyester resin copolymerized with a polyfunctional component is disclosed in Japanese Patent Publication No. 57-23714. Furthermore, a coating composition in which an alkyl ether formaldehyde resin is blended with a modified polyester resin obtained by reacting a copolymerized polyester resin with a special composition with an epoxy resin having a relatively large epoxy equivalent was disclosed in Japanese Patent Application Laid-Open No. 1986-
It is disclosed in Japanese Patent No. 141768.

[Problem to be solved by the invention]

The paint disclosed in Japanese Patent Publication No. 61-32351 has excellent adhesion and workability, but lacks hardness, solvent resistance, and stain resistance. In addition, the aforementioned special public
The paint disclosed in Publication No. 23714 has a certain degree of hardness and good gloss, but it has poor workability and
Solvent resistance and stain resistance are insufficient. Furthermore, the paint disclosed in JP-A-60141768 has a certain degree of hardness and is excellent in gloss, scratch resistance, and corrosion resistance, but it has poor processability, solvent resistance, and stain resistance. However, the current situation is that a coating composition with performance that can be used for high-end products such as home appliances has not been obtained.

Therefore, the present invention has excellent processability, solvent resistance, and stain resistance,
This was made for the purpose of providing a coating composition for coated steel plates that forms a coating film with high hardness and good gloss.

[Means to solve the problem]

As a result, the above object is characterized by containing a copolymerized polyester resin (a modified polyester resin obtained by reacting φ with an aliphatic epoxy compound (b) having a glycidyl ether group, and an amino resin fB). It has been found that this can be achieved by a coating composition for painted steel plates.

The configuration of the present invention will be explained in detail below.

The copolymerized polyester resin (φ) used in the present invention is synthesized from a dibasic acid and a dihydric alcohol, and may be copolymerized with a small amount of trivalent or higher polycarboxylic acid and/or trivalent or higher polyol. is also possible.

As dibasic acids, terephthalic acid, isophthalic acid, orthophthalic acid, 2,6-su7taledicarpo71.414
Aromatic dicarboxylic acids such as '-diphenyldicarboxylic acid, sodium sulfoisophthalate, Garlic Group 1 dicarboxylic acids such as l,4-cyclohexanedicarboxylic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, speric acid, azelaic acid , sebacic acid, undecanedioic acid, and dodecanedioic acid, and one or more of these may be selected and used. It is also possible to use lower alkyl esters.

In order to obtain sufficient coating film hardness and coating film strength, it is preferable to use terephthalic acid as one of the dibasic acid components.

Examples of dibasic acids preferably used in combination with terephthalic acid include isophthalic acid, succinic acid, adipic acid, sebacic acid, dodecanoic acid, and the like.

Examples of dihydric alcohols include aliphatic diols such as ethylene glycol, propylene glycol, l,4-butanediol, i,s-bentanediol, 1.6hexanediol, diethylene glycol, and neopentyl glycol, and 1,4-cyclohexane. Examples include cyclic diols such as dimetator, aromatic diols such as ethylene oxide or propylene oxide adducts of bisphenol A, and one or two of them are selected and used.

It is preferable to use ethylene glycol as one of the dihydric alcohol components in order to easily form a paint and to obtain a strong coating film. Examples of dihydric alcohols preferably used in combination with ethylene glycol include neopentyl glycol, 1,4-cyclohexane dimetatool, and ethylene oxide or propylene oxide adducts of bisphenol A.

Examples of trivalent or higher polybasic acids include trimellitic acid and pyromellitic acid. Examples of trivalent or higher polyols include glycerin, trimethylolpropane, and pentaerythritol. These polybasic acids and polyols are preferably used in an amount of 0 to 10 mol% relative to the dibasic acid or dihydric alcohol, respectively.

The present invention provides a non-grade copolymerized polyester resin which is made into a ternary, more preferably quaternary or higher copolymer by combining the above-mentioned preferred dibasic acid and preferred dihydric alcohol.

In addition, the copolymerized polyester resin used in the present invention 11vlI (as φ, the reduced specific viscosity is 0.15 to 0.9 dl/y
, acid value 0.8-80-KOH, #, preferably 1
~40 da KOH/y is suitable.

The copolymerized polyester resin (, z) of the present invention is produced by a conventional method for producing high molecular weight polyesters, which involves polycondensation under high vacuum by transesterification or direct esterification.

Examples of the aliphatic epoxy compound (b) having a glycidyl ether group used in the present invention include monoglycidyl ether compounds such as glycerol diglycidyl ether, trimethylopropane diglycidyl ether, 2-ethylhexylglycidyl ether, and ethylene glycidyl diglycidyl ether. Ether, diethylene glycol diglycidyl ether, number average molecule M 150-1.000 polyethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, number average molecule! 190～1,
Diglycidyl ether compounds such as 000 polypropylene glycol diglycidyl ether, butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, 1,6-hexanesiol diglycidyl ether, glycerol diglycidyl ether, trimethylolpropane diglycidyl ether, Examples include triglycidyl ether compounds such as glycerol triglycidyl ether and trimethylolpropane triglycidyl ether, and one or two types of these can be used. Among these epoxy compounds, those having an epoxy equivalent of 600 or more are preferable,
In particular, diglycidyl ether compounds having an epoxy equivalent of 400 or less are preferred. Such epoxy compounds include ethylene glycol diglycidyl ether, diethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, diglopylene glycol diglycidyl ether, butanediol diglycidyl ether, neopentyl glycol diglycidyl ether, 1.
6-hexanethiol diglycidyl ether and the like. By using such an aliphatic epiquine compound having a glycidyl ether group, it is possible to obtain the excellent coating film performance that is the objective of the present invention, and it is possible to obtain the excellent coating film performance that is the object of the present invention. With epoxy compounds, only those with poor coating performance can be obtained.

The modified polyester-fat (A) of the present invention is obtained by reacting a copolymerized polyester resin (φ) with an aliphatic epoxy compound (b) having a glycidyl ether group. The copolymerized polyester m is 0.2 to 5, preferably 0.5 to 3.
A preferred embodiment is to blend the lubricant and the epoxy compound and carry out the process in a molten state in a mixer such as an extruder, or in a solution state by dissolving it in an organic solvent. During the reaction, a commonly used epoxy ring-opening catalyst may be used if necessary.

The modified polyester resin (A) thus obtained has a reduced specific viscosity of 0.25 to 2.0 dl/y, preferably 0.
．． 4-1.5 dl/y, acid value 0.2-10 Da K O
H/y is suitable for the present invention.

The amine resin 1.13) used in the present invention refers to a thermosetting detergent resin obtained by adding formaldehyde or paraformaldehyde to melamine, benzoguanamine, urea, etc., and alkyl etherification of some or all of its methylol groups. This is what I did. Specific examples include methylolmelamine, methylolbenzoguanamine, methylolurea, methoxylated methylolmelamine, methoxylated methylolbenzoguanamine, methoxylated methylolurea, butoxylated methylolmelamine, butquinated methylolbenzoguanamine, and butoxylated methylolurea.

Among these, alkyl etherified ones are preferred, and particularly preferred are methoxylated methylolmelamine and butoxylated methylolmelamine, each of which can be used alone or
Or they can be used together.

The coating composition of the present invention is a modified polyester resin (A) 5
Preferably, the resin contains 0 to 95 parts by weight: i part and 5 to 50 parts by weight of the amine resin (B).

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

The coating composition of the present invention is generally used after being dissolved in a suitable solvent. Teha, toluene, as an organic solvent,
Ki/Ren, “Nolpets” #1OO1 “Nolpets I
l#1501 It can be arbitrarily selected from methyl ethyl ketone, methyl isobutyl ketone, cyclohexanone, ethyl acetate, n-butyl acetate, methyl cellosolve acetate, ethyl cellosolve acetate, etc. depending on its solubility, evaporation rate, and economic efficiency.

Mixing machines such as a ball mill, an impeller disperser, a sand grind mill, a roll mill, and a paint conditioner/crucian carp are used for producing the coating composition of the present invention. Painting can be done by roll coating, roll coater, spray painting, etc.
i'1fl i! This is done by methods such as painting. The baking temperature and time are appropriately selected depending on the size and thickness of the steel plate, the hardenability of the paint, etc.

〔Example〕

The present invention will be explained below with reference to Examples. In the examples, the term "part" simply indicates a part.

Each measurement item followed the method below.

(1) Reduced specific viscosity (ηsp/C) mBaO, 25fwo-dissolved in a mixed solvent of dichlorobenzene/phenol (capacity 4/6) 25jIl and measured at 25°C.

(2) Acid value resin 0.50f was dissolved in dichloromethane 25111/, using phenolphthalein as an indicator, and heated to 1150 N.
, titrated with KOH ethanol solution.

(3) Gloss The 60° reflectance was measured using a crossmeter.

(A) Use a cutter to make scratches in the shape of 100 squares on each side on the pickling paint film, press sellotape on them, and then vigorously (grip, peel off). The number of goban eyes that remained without being removed was measured.

(5) Judgment was made based on JIS K5401 using a pencil hardness tester.

(6) Bending the coated steel plate 180 degrees using the formability bending test,
A crack in the mud was observed at the bend using a 10x magnifying glass. 3T refers to the case where three steel plates of the same thickness are sandwiched at the bent part, and 2T refers to the case where two steel plates are sandwiched. The observation results were as follows.

◎: Extremely good (no cracks) ○: Good △: Slightly poor ×: Poor (full cracks) (7) The coating film was rubbed with gauze impregnated with solvent-resistant methyl ethyl ketone, and the number of times the coating was rubbed until the base was exposed was indicated. .

(8) Stain resistance The painted surface was colored with black and blue marker ink, and after 24 hours, it was wiped off with gauze impregnated with n-butanol and the degree of coloring was observed. The results were as follows.

◎: Extremely good (no ink marks) O: Good △: Slightly poor ×: Poor (ink marks clearly remain) Reference 4 Example 1 404 parts of dimethyl terephthalate, 373 m of dimethyl isophthalate, 268 parts of ethylene glycol, neopentyl glycol 300 parts of the solution was charged into a reaction vessel equipped with a stirrer and a rectification tube together with 034 parts of zinc vinegar, and transesterification was carried out from 100°C to 240°C over 3 hours.

Next, transfer to a reaction vessel equipped with a helical ribbon stirring blade.
After adding 0.16 parts of antimony trioxide, the mixture was heated to 275°C for about 1 hour according to the temperature increase and pressure reduction program.
The reaction conditions were brought to below IlmllHg, and the Afj (f3'ff reaction was carried out for 2 hours and 1O minutes) in this state.

The obtained co-donated polyester resin (1) was pale yellow and transparent, and as a result of composition analysis by NMR, the acid component was terephthalic acid/isophthalic acid -52/48 (molar ratio), and the glycol ash content was ethylene glycol/neo. Pentyl glycol - 55/45 (molar ratio), glass transition temperature measured by DSC 69°C, reduced specific viscosity 0.60, fa
The value was 1.9. Thereafter, polyester resins (1) to (8) whose compositions are shown in Table 1 were cast in the same manner. Polymers containing trimellitic acid or cono-phosphoric acid as a copolymerization component are returned to normal pressure after the polycondensation reaction of the other copolymerization components is completed; The samples were obtained by adding a predetermined amount of acid and then adding a predetermined amount of succinic anhydride at 240° C. for 30 minutes, and for those containing cono-phosphoric acid, performing an addition reaction at 220° C. for 30 minutes under a nitrogen stream.

Reference Example 2 100 parts of copolymerized polyester resin (1) was heated to 18% at 50°C.
After vacuum drying for an hour, the epoxy compound (E
1 part was added and reacted at 250°C using a twin screw extruder. The obtained modified polyester resin (1) was pale yellow in color, had a reduced specific viscosity of 0.60, and a waterfall value of 0.8. Similarly, modified polyester resins (1
) to (1'l) were produced.

Examples 1 to 6 100 parts of modified polyester (a) fat (1) was mixed with cyclohexanone/cellosolve acetate/toluene (mineral ratio 3
0150/20) Dissolved in 233 parts of mixed solvent. 100 parts of this solution, 35 parts of titanium oxide, 4 parts of methoxylated methylolmelamine ("Cymel" 325, manufactured by Mitsui Cyanamid), and 83 parts of the above mixed solvent were kneaded in a ball mill to obtain a coating composition.

Modified polyester tree B'# Change (1) to (n) to (g) and the same applies hereafter? A coating composition was obtained. Each of the obtained coating compositions was coated on a 70 x 150 x O, 6 m galvanized steel plate with a bar coater to a film thickness of 20 μm, and then baked at 180° C. for 20 minutes. Table 4 shows the test results of the obtained coated steel plate.

Comparative Examples 1 to 6 Unmodified copolymerized polyester resins (1) to (3)
and (6) to (8) were used to prepare a coating composition in the same manner as in Example 1, and the physical properties of the coating film were evaluated. The results are shown in Table 4.

From the results in Table 4, copolymerized polyester resins (1) to (3
It can be seen that Comparative Examples 1 to 3, in which the materials () were used without epoxy modification, had poor processability, solvent resistance, and stain resistance compared to the Examples. In addition, epoxy-unmodified copolyester resins (6) and (7) have the same reduced specific viscosity and acid value as the modified polyester resins (Il) and 11α), respectively.
The same applies to Comparative Examples 4 to 6 using , (8).

Reference Example 3 100 parts of copolymerized polyester resin (A) and 150 parts of cyclohexanone/"Tsurupets" (Takejjlt50
150) After charging 150 parts of the mixed solvent into a reaction vessel equipped with a stirrer and a reflux cooling tube and heating and dissolving it at 130°C with stirring, 4 parts of the Epoquine compound (E2) shown in Table 2 and 0% tri-n-butylamine as a catalyst were added. .03 part was added and reacted at 140-150°C for 3 hours. Further, the above-mentioned mixed solvent was added, and a solution with a solid content of 30% was taken out.

The obtained modified polyester resin (■1) has a reduced specific viscosity of 0
．． 85, and the acid value was 3.7. Similarly, modified polyester resins (Vll) to (XI') as shown in Table 5 were prepared.
was manufactured. In the production of modified polyester resins (XI Town and (XI*)), the reaction was carried out at 140 to 150°C for 6 hours.

=25 Examples 7 to 10 100 parts of the modified polyester resin (■) solution, 35 parts of titanium oxide, butoxylated methylolmelamine ("Superbenokaq", G-821-60, manufactured by Dainippon Ink)
5 parts and 80 parts of the mixed solvent used in Reference Example 3 were kneaded in a ball mill to obtain a coating composition. A coating composition was similarly obtained by replacing the modified polyester resin (Vll'') solution with the solution of αD to α).

Each of the obtained coating compositions was divided into 70 x 150 x 0.6
It was coated on a Bonderite 144-treated steel plate (mg) using a bar coater to a film thickness of 20 μm, and then baked at 260° C. for 1 minute. The test results obtained are shown in Table 6.

Comparative Examples 7 to 12 Coating compositions were obtained in the same manner as in Example 7 except that the modified polyester resin (Vil) solution was replaced with (XI'') and (■ town).

Also, copolymerized polyester resins (A), (5), (9
) and uo were each dissolved in the mixed solvent used in Reference Example 3 to give a solution with a solid content of 30% to prepare a copolymerized polyester resin solution. This solution was used to prepare a coating composition in the same manner as in Example 7, and the physical properties of the coating film were evaluated. The results are shown in Table 6.

From the results in Table 6, Comparative Example 7 using a polyester resin modified with an aromatic epoxy compound having a glycidyl ether group, and Comparative Example 8 using a polyester resin modified with an aromatic epoxy resin having a glycidyl ether group, Compared to Example 7 and Example 8, the hardness is lower and the solvent resistance is lower.
It can be seen that the stain resistance is poor. Moreover, Comparative Example 9 and Comparative Example 10 used copolymerized polyester resins (A) and (5) without epoxy modification. In addition, modified polyester resin (VM), copolymerized polyester resin (9) having the same reduced specific viscosity and acid value as ([), α
It is clear that Comparative Examples 11 and 12 using Q also have lower hardness than the Examples, and are inferior in solvent resistance and stain resistance.

〔Effect of the invention〕

The coating composition for painted steel sheets of the present invention has good workability despite having both hardness and has a coating film with excellent solvent resistance and stain resistance.

Claims (1)

[Claims] Modified polyester resin (A) and amino resin (B) obtained by reacting a copolymerized polyester resin (a) with an aliphatic epoxy compound (b) having a glycidyl ether group
A coating composition for painted steel plate, characterized by containing the following.