JPH09176566A - Polyester resin composition for paint and coated steel sheet using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyester resin for paint, having excellent hardness and workability and particularly excellent in weathering resistance and pollution- proof, and a coated steel sheet using the same. SOLUTION: This polyester resin composition for paint comprises the acid component containing more than 90mol% of an aromatic dicarboxylic acid and less than 10mol% of an aliphatic dicarboxylic acid and/or an alicyclic dicarboxylic acid and the diol component including 10-60mol% of 1,4- cyclohexanedimethanol, 10-55mol% of neopentyl-glycol and 10-55mol% of ethylene glycol, and is prepared by blending an amino resin at the ratio of 10-40wt.% to 90-60wt.% of the polyester resin having the number-average molecular weight of 10,000-25,000 and more than 30 deg.C of the glass transition point. The coated steel sheet is obtained by coating a steel sheet with the polyester resin composition for paint by means of baking finish.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a polyester resin composition for paints which has excellent hardness and workability, and in particular a coating film having excellent weather resistance and stain resistance, and a coated steel sheet using the same. It is about.

[0002]

2. Description of the Related Art In recent years, steel sheets have been preliminarily painted, mainly for home appliances such as refrigerators and microwave ovens.
Applications of pre-coated steel sheets for processing and forming are expanding.
The coating material used for the precoated steel sheet is required to have contradictory characteristics such as workability and hardness in addition to characteristics such as gloss, adhesion, and weather resistance. Currently, acrylic resin, alkyd resin, epoxy resin, etc. are used as the steel sheet resin for precoating, but none of them satisfy the required performance.
Conventionally, in order to solve such contradictory properties, a system in which a copolymerized polyester resin and an amino resin or an isocyanate compound are combined is often used, and the balance between hardness and workability is improved to some extent and put into practical use. There are also examples.

However, with conventional polyester resin systems, it is difficult to simultaneously satisfy the weather resistance required for outdoor applications such as air conditioners, even though the performances such as hardness, processability and stain resistance are satisfied. In addition, if the resin has satisfactory weather resistance, it is difficult to balance the other performances. In addition, when the polyester resin is dissolved as a pre-coating step, turbidity and coloration of the dissolved sample are often problems. Even if it is possible to solve the problem of suppressing turbidity and coloration, long-term stability (aggregate appearance , Gelling) was relatively difficult to maintain. If the long-term stability is insufficient, not only the workability of coating becomes difficult, but also the gloss of the coating film is significantly adversely affected.

[0004]

SUMMARY OF THE INVENTION In view of such a situation, an object of the present invention is to provide a polyester resin for a coating which is excellent in hardness and processability, and particularly a coating film having excellent weather resistance and stain resistance. It is to provide a coated steel sheet using the same.

[0005]

Means for Solving the Problems As a result of intensive studies to achieve the above-mentioned objects, the present inventors have found that a resin composition obtained by blending a specific amount of an amino resin with a polyester resin having a specific component composition is The inventors have found that the above problems can be solved and have completed the present invention.

That is, the gist of the present invention is, firstly, of the acid component, aromatic dicarboxylic acid is 90 mol% or more, aliphatic dicarboxylic acid and / or alicyclic dicarboxylic acid is 10 mol% or less, and diol component is Of these, 1,4-cyclohexanedimethanol is 10 to 60 mol%, neopentyl glycol is 10 to 55 mol%, and ethylene glycol is 10 to 10.
55 mol% and a number average molecular weight of 10,000 to 2
A polyester resin composition for coating composition, which is 5,000 and has a glass transition temperature of 30 ° C. or higher and 90 to 60% by weight of a polyester resin, and 10 to 40% by weight of an amino resin. Secondly, it is a coated steel sheet obtained by baking coating this polyester resin composition for paint on a steel sheet.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the present invention, examples of the aromatic dicarboxylic acid in the acid component of the polyester resin include terephthalic acid, isophthalic acid, phthalic anhydride, naphthalenedicarboxylic acid and the like, and terephthalic acid for obtaining sufficient coating strength and coating hardness. It is preferable to use isophthalate. The content of these aromatic dicarboxylic acids is required to be 90 mol% or more of the acid component in terms of hardness, weather resistance and stain resistance.

Examples of acid components other than aromatic dicarboxylic acids include aliphatic dicarboxylic acids and alicyclic dicarboxylic acids, which can be used alone or in combination of two or more. Examples of the aliphatic and alicyclic dicarboxylic acids include succinic acid, adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, 1,4-cyclohexanedicarboxylic acid and 1,3-
Examples thereof include cyclohexanedicarboxylic acid, but the content of these carboxylic acids needs to be 10 mol% or less based on the total acid components. Needless to say, when this amount exceeds 10 mol%, the hardness is lowered, but the weather resistance and the stain resistance are significantly lowered.

The diol component of the polyester resin contains 1,4-cyclohexanedimethanol, neopentyl glycol and ethylene glycol as essential components. 1,4-cyclohexanedimethanol is 10-60
It is mol%, preferably 20 to 50 mol%. 1,4-
When the content of cyclohexanedimethanol is less than 10 mol%, the hardness and workability targeted by the present invention cannot be balanced, and when it exceeds 60 mol%, the solution stability becomes poor and the resulting coating film becomes brittle. Neopentyl glycol is 10
˜55 mol%, preferably 20 to 50 mol%. If the content of neopentyl glycol is less than 10 mol%, good solution stability cannot be obtained, and if it exceeds 55 mol%, the coating film becomes hard and the workability is greatly reduced. 1 for ethylene glycol
It is 0 to 55 mol%, preferably 20 to 50 mol%.
If the ethylene glycol content is less than 10 mol%, the coating film becomes brittle and the workability deteriorates, and if it exceeds 55 mol%, the solubility in a solvent decreases.

The polyester resin of the present invention not only satisfies the above-mentioned acid component and diol component, but also has a number average molecular weight of 10,000 to 25,000.
0, preferably 12,000 to 20,000, and a glass transition temperature of 30 ° C. or higher, preferably 35 to 80.
It is necessary to satisfy the characteristic of being ° C. If the number average molecular weight is less than 10,000, the coating film becomes brittle and the workability is lowered, and if it exceeds 25,000, the stain resistance and weather resistance are lowered. Further, if the glass transition temperature is lower than 30 ° C., all other physical properties except workability are deteriorated.

The polyester resin can be produced by known polymerization methods such as those conventionally used for producing polyethylene terephthalate or polybutylene terephthalate. For example, it can be produced by transesterification or direct esterification followed by melt polycondensation reaction, and the catalyst used at that time is also the same.

An amino resin is blended with the above polyester resin. The amino resin acts as a curing agent. Examples of the amino resin include a condensate of an amine component such as melamine, urea and benzoguanamine with formaldehyde, and an etherified product obtained by etherifying the condensate with a lower alcohol such as methanol, ethanol and butanol. Among them, a melamine resin whose end is etherified with a methyl group is most preferably used. This resin is suitable for balancing the performance, and has a self-condensation reaction extremely small and a coating film having a high crosslinking density can be obtained. The degree of etherification at the terminal is preferably 3-6.

In the present invention, the mixing ratio of polyester resin and amino resin is 90/10 in terms of solid weight ratio (% by weight).
-60/40, preferably 80 / 20-70 / 30. If the proportion of polyester exceeds 90% by weight, the desired stain resistance is insufficient. Further, if it is less than 60% by weight, the workability becomes poor and the performance cannot be balanced.

Any curing catalyst can be added to the composition of the present invention. Examples of the curing catalyst include p-toluene sulfonic acid and dodecylbenzene sulfonic acid, and the amount used is preferably 1 to 5% by weight based on the amino resin. Furthermore, additives such as pigments, dispersants, antioxidants, leveling agents, and ultraviolet absorbers can be used in the composition of the present invention depending on the purpose and application.

The above-mentioned polyester resin, amino resin and other additives are added to a solvent to prepare a paint. As the solvent, any solvent that can dilute the polyester resin and the amino resin can be used without any limitation. For example, toluene, xylene, Solvesso 100, Solvesso 15
Aromatic hydrocarbons such as 0, aliphatic hydrocarbons such as hexane, heptane, octane and decane, and solvents such as ethyl acetate, butyl acetate, methyl cellosolve, butyl cellosolve, methyl ethyl ketone, cyclohexanone, butanol and octanol. , Its solubility and evaporation rate can be arbitrarily selected.

As the solvent, a high-boiling solvent is generally used
It is desirable to use a mixture of three or more types. Particularly, as a solvent which does not cause coating defects such as armpits and pinholes, aromatic hydrocarbon or aliphatic hydrocarbon is 70 to
30% by weight, 30% by weight of polar solvents such as esters and ketones
It is desirable to mix and use in a ratio of 70 wt%.
The coating can be performed by a known method. For example, it is possible to apply curtain flow coating, roll coating, spray coating, electrostatic spray coating method to a cold rolled steel sheet, a galvanized steel sheet, a stainless steel sheet, etc., and bake coating by drying and heating. The dry film thickness after baking is usually 10 to 30.
Paint to a thickness of μm.

The baking conditions for the polyester resin composition for paints of the present invention can be appropriately selected from the temperature at which the paint is hardened and the baking time. In the field of precoat metal, which is the aim of the present invention, it is usually 150 to 250 ° C. In the range of 30 to 120 seconds, especially at 180 to 230 ° C., 50
A range of up to 90 seconds is desirable. The coated steel sheet baked and coated in this way has the desired performances by itself, but it is preferable to preliminarily bake the primer in a thickness of 3 to 10 μm for applications in which corrosion resistance is required.

[0018]

EXAMPLES The present invention will now be described specifically with reference to examples, but the present invention is not limited to these examples. In the examples, all parts are by weight unless otherwise noted. Moreover, each test method is shown below.

(A) Gloss 60 ° C. reflection gloss retention was measured. (B) Pencil Hardness The coated surface of the coated steel sheet was subjected to a pencil scratch test according to JIS K-5400 to measure the hardness without scratches. (C) Workability Under a 5 ° C. environment, the test plate was bent 180 ° with the coated surface facing outward, and the T number at which cracks did not occur at the bent portion was displayed. The T number is 0T when 180 ° bending is performed without sandwiching anything inside the bent portion, and 1T and 2T when one plate having the same thickness as the test plate is bent. The case is 2T. (D) Weather resistance Using a sunshine weather meter, the gloss (60 ° specular reflectance) after irradiation for 1000 hours is 1 with respect to the initial gloss.
It is shown as a percentage.

(E) Contamination resistance A line was drawn on the coated surface with a magic ink (red), allowed to stand at room temperature for 24 hours, and then wiped off with ethanol-impregnated gauze. . 5: No magic mark remains 4: Magic mark remains slightly 3: Magic mark remains considerably 2: Magic mark remains thick 1: Magic cannot be wiped off at all (f) Solution stability The prepared polyester resin is cyclohexanone / It was dissolved in a mixed solvent of Solvesso 150 = 1/1 so as to have a nonvolatile content of 30%, and the state of the solution was observed after standing in a refrigerator (5 ° C.) for 30 days. The evaluation has the following three levels. ○: Transparent and no aggregates △: Turbid and aggregates ×: Gelled

(1) Production Example 1 83.0 parts of terephthalic acid and 8 parts of isophthalic acid were placed in a flask equipped with a thermometer, a nitrogen introducing tube, a vacuum device and a stirring device.
3.0 parts, 1,4-cyclohexanedimethanol 50.
5 parts, ethylene glycol 74.7 parts, neopentyl glycol 87.6 parts and zinc acetate 0.4 as a reaction catalyst
A portion was charged and the temperature was gradually raised from 170 ° C. to 220 ° C. over 4 hours to carry out a transesterification reaction. Next, the pressure was reduced to 5 mmHg over 60 minutes, and further a polycondensation reaction was performed at 230 ° C. to 250 ° C. for 2 hours under a reduced pressure of 1 to 3 mmHg.
As a result, a saturated polyester resin (A) having a number average molecular weight of 16,000 and a glass transition temperature (Tg) of 65 ° C. was obtained. The solution stability of this resin was ◯ in the above evaluation.

(2) Production Examples 2 to 5 According to Production Example 1, a saturated polyester resin B having the composition, number average molecular weight and glass transition temperature shown in Table 1,
C, D and E were manufactured. The number average molecular weight of these resins,
Table 1 shows the glass transition temperature (Tg) and the solution stability. (3) Comparative Production Examples 1 to 8 Saturated polyester resins F having the composition, number average molecular weight, and glass transition temperature shown in Table 1 according to Production Example 1
M was produced. Table 1 shows the number average molecular weight, glass transition temperature (Tg), and solution stability of these resins.

Examples 1 to 5 and Comparative Examples 1 to 8 Each of the obtained copolyesters A to M is a cyclohexanone / solvesso 150 mixed solution (weight ratio 50/50).
Was dissolved in the solution and the nonvolatile content was adjusted to 30%. 100 parts of the above polyester resin solution, 38 parts of titanium oxide (trade name: Taipaque CR-50, manufactured by Ishihara Sangyo), hexamethoxymethylol melamine (trade name: Cymel 303, nonvolatile content 9)
8%, Sumitomo Chemical Co., Ltd. 8 parts, leveling agent (trade name:
Miki Leveling, Kyoeisha Yushi Kagaku Kogyo Co., Ltd.) 2 parts, curing catalyst (trade name: Catalyst 4040) 0.2 part, cyclohexanone / solvesso 150 (1: 1) mixed solution 30
A part was dispersed and kneaded for 1 hour using a paint shaker to prepare a paint. The obtained coating material was applied onto a zinc phosphate-treated mild steel sheet (trade name: Bonde Steel Sheet, manufactured by Nippon Test Panel Co., Ltd.) having a thickness of 0.7 mm so as to have a dry film thickness of 15 to 20 μm, and the final mild steel sheet was coated. Baking was performed for 60 seconds with a hot air dryer so that the ultimate temperature was 220 ° C. Table 2 shows the evaluation results of the properties of the obtained coating film.

Comparative Example 9 The mixing ratio of polyester resin and amino resin was 50:50.
A coating material was prepared and baked and coated in the same manner as in Example 1 except that (polyester resin 20 parts, amino resin 20 parts) was used. Table 2 shows the evaluation results of the properties of the obtained coating film.

Comparative Example 10 The mixing ratio of polyester resin and amino resin was 95: 5.
A coating material was prepared in the same manner as in Example 1 except that (38 parts of polyester resin and 2 parts of amino resin), and was baked and coated. The properties of the resulting coating film are shown in Table 2.

[0026]

[Table 1]

[0027]

[Table 2]

[0028]

When the polyester resin composition for paints of the present invention is used, it is possible to obtain a coating film which is excellent in hardness and processability, and is particularly excellent in weather resistance and stain resistance, which are the drawbacks of conventional polyester resins. A coated steel sheet having this coating film formed on the steel sheet is excellent in these characteristics.

Claims (2)

[Claims] 1. Among the acid components, aromatic dicarboxylic acid is 90
Mol% or more, aliphatic dicarboxylic acid and / or alicyclic dicarboxylic acid 10 mol% or less, 1,4 of diol components
Cyclohexanedimethanol is 10 to 60 mol%, neopentyl glycol is 10 to 55 mol%, ethylene glycol is 10 to 55 mol%, the number average molecular weight is 10,000 to 25,000, and the glass transition temperature is A polyester resin composition for paints, which is compounded in an amount of 10 to 40% by weight of an amino resin with respect to 90 to 60% by weight of a polyester resin having a temperature of 30 ° C or higher. 2. A coated steel sheet obtained by baking coating the polyester resin composition for paint according to claim 1 on a steel sheet.