JPH05179196A - Coating material excellent in storage stability and coated metallic sheet - Google Patents

Abstract

PURPOSE:To obtain a coating material for a coated metallic sheet which can give a coating film of high processability, high hardness and high sharpness CONSTITUTION:The title material is prepared by heat melting a cross-linking agent and a modified polyester resin prepared by introducing a metal sulfonate group into a polyester resin difficultly soluble in a general organic solvent to form a homogeneous mixture and dissolving this mixture in an organic solvent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated metal plate used for applications requiring high workability, high hardness and high image clarity.
And paints therefor. The coated metal plate of the present invention is suitable for home appliances and building materials, for example, and may be used for automobiles in the future.

[0002]

2. Description of the Related Art A prepainted metal plate is punched, bent, drawn, etc. by the user and then used as the outer surface of the product as it is. Hardness) is required.

However, in the case of solvent-based paints which have been conventionally used for producing coated metal sheets, workability and hardness are generally incompatible, and coated metal sheets having excellent workability have a soft coating film and are easily scratched, Those with high hardness tend to have poor processability. For example, a coating film of acrylic paint has high hardness but poor workability, and a coating film of high molecular weight polyester paint has good workability but low hardness.

On the other hand, in recent years, coated metal plates using powder coating materials (powder precoated metal plates) are also on the market. The powder pre-coated metal sheet has excellent coating film physical properties in which hardness and workability are well balanced in comparison with a conventional coated metal sheet using a solvent-based paint. However, since powder coating cannot avoid unevenness on the surface of the coating film (so-called orange peel), the powder precoated metal plate cannot be used for applications requiring high image clarity close to a mirror surface.

The production rate of the powder precoated metal sheet is usually 20 m / m at the industrialized line speed.
less than in, production speed of solvent type paint is 60 ~ 80m
The productivity is far inferior to that of / min. The line speed of powder coating depends on the number of powder discharge guns and the capacity of the dryer, but powder coating requires a lot of time for color changing work, so normally two coating units must be prepared. However, a large initial capital investment is required to increase the line speed. Therefore, it is difficult to raise the line speed to 20 m / min or more in the industrialized coating line.

In the case of the conventional solvent type polyester paint,
Since the basic resin, polyester, must be dissolved in a solvent, a highly soluble polyester resin is used.

From the viewpoint of physical properties such as balance between workability and hardness, it is desirable to use a polyester resin having a highly symmetrical molecular structure. However, since the polyester resin having high symmetry has a remarkably low solubility in a solvent, it is unavoidable to use it as a powder coating material. A conventional polyester powder coating material is produced by heating and melting a highly symmetrical polyester resin with a crosslinking agent and pulverizing the obtained mixture.

The present inventors have previously found that the polyester resin for powder coatings, which is hardly soluble in a general organic solvent at the time of heating and melting, is well soluble in a cross-linking agent such as blocked isocyanate, and is homogeneously compatible. As a result of further investigation focusing on the fact that a molten solution can be obtained, the polyester resin for powder coatings that is compatible with the crosslinking agent in this way is soluble in general organic solvents at temperatures near room temperature. It was found that a solvent type paint can be produced and proposed (Japanese Patent Laid-Open No. 2-196876).
issue). The solvent-based paint obtained in this manner has processability,
It is suitable as a paint for coated metal plates because it has a good hardness and gives a film with high image clarity without the distorted skin of powder paint.

[0009]

However, although the coating material obtained by the above-mentioned method is excellent in coating film performance, it tends to lack the stability of the coating material, that is, tens of minutes to several hours after being dissolved in a solvent. It was found that there is a problem in coating workability and productivity because the fluidity is reduced by.

An object of the present invention is to provide a coating material for a coated metal plate which gives a coating film having high processability, high hardness and high image clarity and which is excellent in storage stability. Another object of the present invention is to provide a coated metal plate having a coating film with high processability, high hardness and high image clarity.

[0011]

As a result of intensive studies on the problem of paint stabilization, the present inventors have found that by introducing a metal sulfonate group into a highly symmetrical polyester molecular chain, Further, they have found that the polyester resin, which was hardly soluble in a general-purpose solvent, is solubilized in isophorone or cyclohexanone, and the stability of the coating material is significantly improved, and the present invention has been completed.

That is, the gist of the present invention is to: A mixture, and a coating obtained by dissolving the obtained mixture in an organic solvent, and 2) a base chemical conversion film formed on the surface of a metal plate by at least one of a phosphate treatment and a chromate treatment,
It is a coated metal plate having a cured coating film formed from the above paint.

In the present specification, a general organic solvent means one having a solubility parameter in the range of 7.5 to 11.5. Examples of such solvents include toluene, xylene, cellosolve acetate, butyl acetate, cyclohexane, methyl ethyl ketone, isophorone and the like. In addition, “poorly soluble” means that the solubility in the solvent is less than 10% by weight at a temperature around room temperature (10 to 35 ° C.), and “dispersible or soluble” means stable at 10% by weight or more. Means that.

The modified polyester resin used in the present invention is
It is a resin that is first solubilized by introducing a metal sulfonate base into a polyester resin that is poorly soluble in general organic solvents. More specifically, terephthalic acid is used as the acid component in an amount of 60 mol% based on the total acid component.
Or more, preferably 65 mol% or more, ethylene glycol as a glycol component is 60 mol% or more, preferably 65 mol% or more with respect to the total glycol components, and the acid component having a sulfonate metal base or the glycol component is the total acid. 0.1 to the total amount of the component or total glycol component
It is a polyester resin copolymerized with 5 mol%, preferably 1 to 2 mol%. The modified polyester resin can be powdered at room temperature and can be dispersed or dissolved in a general organic solvent such as cyclohexanone or isophorone.

Examples of acid components that can be used in combination with terephthalic acid include isophthalic acid, orthophthalic acid and 2,6-
Aromatic dicarboxylic acids such as naphthalenedicarboxylic acid, alicyclic dicarboxylic acids such as tetrahydrophthalic acid and hexahydrophthalic acid, aliphatic dicarboxylic acids such as succinic acid, adipic acid and sebacic acid, and, if necessary, trimellitic acid Polyvalent carboxylic acids such as pyromellitic acid are used.

As the glycol component which can be used in combination with ethylene glycol, propylene glycol, 1,4
-Butanediol, diethylene glycol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, 3,3-dimethylolheptane, 3-
Methylpentanediol, aliphatic diols such as 1,9-nonanediol, cyclohexanedimethanol, tricyclodecanedimethanol, alicyclic glycols such as hydrogenated bisphenol A, ethylene oxide or / and propylene oxide adducts of bisphenol A, etc. In addition, polyhydric alcohols such as glycerin, trimethylolethane, trimethylolpropane and pentaerythritol are used.

As the acid component or glycol component having a metal sulfonate group, 5-sodium sulfoisophthalic acid, 5-potassium sulfoisophthalic acid, sodium sulfoterephthalic acid, 2-sodiumsulfo-
1,4-butanediol, 2,5-dimethyl-3-sodium sulfo-2,5-hexanediol and the like can be mentioned.

In the present invention, the terephthalic acid component and the ethylene glycol component are preferably 60 mol% or more with respect to the total acid component and the total glycol component. If the content of terephthalic acid and ethylene glycol is less than 60 mol%, the high workability, which is the object of the present invention, may not be obtained. When the content of the acid component or glycol component having a metal sulfonate group is less than 0.1 mol%, the dispersibility or solubility in an organic solvent is deteriorated,
If it exceeds mol%, the water resistance tends to deteriorate, which is not preferable.

The glass transition temperature of the modified polyester resin used in the present invention is preferably 40 ° C. or higher, more preferably 55 ° C. or higher. When it is less than 40 ° C,
The hardness of the obtained coating film tends to decrease.

The modified polyester resin used in the present invention is polymerized by a known method. The modified polyester resin is
Reduced viscosity (dl / g) 0.1-0.4, especially 0.14
It is desirable that it is 0.30. If the reduced viscosity is less than 0.1, the processability is poor, and if it exceeds 0.4, the melt viscosity may be too high. Therefore, a high temperature is required during heating and melting with a crosslinking agent described later, and the polyester resin is a crosslinking agent. There is a fear of gelation because it reacts with.

As the cross-linking agent, a cross-linking agent which has hitherto been used for producing a thermosetting polyester powder coating material can be used. Examples of suitable crosslinking agents are ε-caprolactam, blocked isocyanates blocked with phenol and the like, and melamine modified with methyl alcohol, butyl alcohol and the like.

The mixing ratio of the modified polyester resin and the crosslinking agent is not particularly limited, but the polyester resin can be dissolved after heating and melting, and when dissolved in a solvent, the polyester resin dissolves at a concentration of 10% by weight or more at around room temperature. It is necessary to use the crosslinking agent in such an amount. When an excessive amount of the cross-linking agent is used, the polyester resin can be easily solubilized, but the processability of the coating film of the obtained paint may be deteriorated. The amount of a suitable crosslinking agent is modified polyester resin,
It depends on the type of the cross-linking agent and the solvent, and is appropriately determined by an experiment, but usually 10 to 40 parts by weight, preferably 20 to 40 parts by weight of the modified polyester resin.
30 parts by weight.

The heating and melting of the modified polyester resin and the cross-linking agent are carried out at a temperature above the flow initiation temperature of the modified polyester resin and below the cross-linking initiation temperature of the cross-linking agent used, for example below the dissociation temperature of the blocked isocyanate, or of the melamine resin. The temperature is lower than the self-condensation initiation temperature. The heating is continued until the polyester resin and the cross-linking agent are dissolved and a homogeneous molten solution-like mixture is obtained.

The molten solution thus obtained is cooled, and the solidified mixture is crushed to preferably a size that is easily dissolved in a solvent, and then dissolved in one or more general organic solvents as described above, whereby the mixture is extremely preserved. The solvent-based paint of the present invention having good stability can be obtained. If necessary, conventional paint additives such as pigments, defoaming agents, leveling agents and dispersants are added. These additives may not be added to the solvent, but may be mixed with one of the components before heating and melting the modified polyester resin and the crosslinking agent, for example.

As a general organic solvent for dissolution, cyclohexanone, isophorone and the like are preferable, and it is preferable to use an amount such that the concentration of the modified polyester resin is 10% by weight or more.

By applying the coating material of the present invention to a metal plate and heating and curing the coating film, a metal plate having high processability, high hardness and high image clarity can be obtained. As the metal plate that can be used, cold-rolled steel plate, zinc-based, zinc alloy-based, aluminum-based,
Examples thereof include plated steel plates such as aluminum alloy plates, aluminum plates, and stainless plates, but are not limited to these.

Before applying the coating material of the present invention, it is desirable to subject the base metal plate to a base treatment by at least one of the conventional phosphate treatment and chromate treatment. Without this base treatment, good coating adhesion may not be obtained.

If particularly high corrosion resistance is required, a primer containing a rust preventive pigment may be applied after the above-mentioned base treatment. As such a primer, an epoxy type, a polyester type, or a urethane type is suitable.

The paint of the present invention can be applied by a usual method such as roll coating or spraying. After coating, the coating film is baked by heating means such as an oven to crosslink the resin to obtain a cured coating film. This heating is usually performed at 150 to 250 ° C. for about 1 to 5 minutes.

The coated metal plate of the present invention has a cured coating film having a film thickness of 10 μm or more, usually 10 to 25 μm, formed in this manner.

[0031]

The coating composition of the present invention is a solvent-type coating composition previously proposed by the present inventors by introducing a small amount of a metal sulfonate group into a poorly soluble polyester resin having good physical properties, which was conventionally formed into a powder coating composition. Compared with paint, the viscosity stability of paint is remarkably high.
The coating stability is improved. It is still unclear why a small amount of metal sulfonate has such an effect, but it is an extremely effective means for designing the balance between hardness and workability, and it can be said to be an epoch-making technology.

[0032]

The present invention will be described in detail below with reference to examples. In the examples, “parts and%” means “parts by weight” and “% by weight” unless otherwise specified.

Production Example In a reaction vessel equipped with a stirrer, a condenser and a thermometer,
Dimethyl terephthalate 601.4 parts, dimethyl isophthalate 329.8 parts, dimethyl 5-sodium sulfoisophthalate 14.8 parts, trimellitic anhydride 2
8.8 parts, 556.0 parts of ethylene glycol, 194.5 parts of neopentyl glycol and 0.51 part of tetrabutyl titanate were charged, and the transesterification reaction was performed from 160 ° C to 220 ° C over 4 hours. Next, the pressure in the system is gradually reduced, and the pressure is reduced to 5 mmHg over 40 minutes.
Furthermore, a polycondensation reaction was performed at 240 ° C. for 30 minutes under a vacuum of 3 mmHg or less. As a result of composition analysis such as NMR, the obtained copolyester (a) was found to have a molar ratio of acid components of terephthalic acid / isophthalic acid / 5-sodium sulfoisophthalic acid / trimellitic acid = 62/34/1/3. The molar ratio of the glycol component was ethylene glycol / neopentyl glycol = 75/25. The reduced viscosity was measured to be 0.25 and the glass transition temperature was 58 ° C.

In the same manner as above, metal sulfonate group-containing polyester (b) and comparative polyesters (c) to (e) having the compositions shown in Table 1 were synthesized. Among the comparative polyesters, (c) and (d) are poorly soluble polyesters, and (e) is a readily soluble polyester. Further, the metal sulfonate group-containing polyesters (a) and (b) are
It is a resin in which a metal sulfonate group is introduced into the skeletons of the poorly soluble polyesters (c) and (d), respectively.

Table 1 shows the reduced viscosity and glass transition temperature of each polyester resin. The reduced viscosity was measured at 30 ° C. by dissolving 0.10 g of the polyester resin in 25 cc of a mixed solvent of phenol / tetrachloroethane (volume ratio 6/4). Further, the glass transition temperature is measured by a differential scanning calorimeter (DS
The measurement was performed using C) at a temperature rising rate of 20 ° C./min. As a sample, 5 mg of the sample was placed in an aluminum pressing lid type container and crimped before use.

[0036]

[Table 1]

Example 1 100 parts of polyester (a) containing a metal sulfonate group was added with titanium dioxide pigment (Taipek R930 manufactured by Ishihara Sangyo) 6
0 part was added, the mixture was heated to 120 to 130 ° C. to dissolve the resin, and kneaded for about 15 to 30 minutes. Thereafter, 20 parts of blocked isocyanate (IPDI B1530 manufactured by Daicel Hüls) was added as a cross-linking agent, and further kneaded at the same temperature for about 15 to 30 minutes to obtain a molten solution in which the resin and the cross-linking agent were homogeneously compatible. ..

After the molten solution was cooled to room temperature, the obtained mixture was pulverized to about 500 μm so as to be easily dissolved in a solvent and dissolved in cyclohexanone to prepare a solvent type coating material (A) having a solid content concentration of 50%. did. The polyester resin concentration of the paint was 28%.

A hot-dip galvanized steel sheet (0.5 mm thick, 60 g / m ² per side) was coated with the above-mentioned coating material (A) by roll coating on a base material which had been subjected to a zinc phosphate-based undercoating treatment (drying). The coating film was cured by baking at a film thickness of 15 μm) at a temperature of 250 ° C. for 2 minutes to obtain a coated steel plate sample (a).

Example 2 As in Example 1, after subjecting a hot dip galvanized steel sheet to a zinc phosphate-based undercoating, a commercially available solvent-type epoxy-modified polyester resin coating (Flex Paint 11 manufactured by Nippon Paint Co., Ltd.) was used.
0) was used to form a primer film having a dry film thickness of 8 μm, and then the paint (A) was applied under the same conditions as the test piece (A) to obtain a coated steel plate sample (A).

Example 3 Using the metal sulfonate group-containing polyester (b), a solvent type coating material (B) having a solid content concentration of 50% (polyester resin concentration of 28%) was obtained in the same manner as in Example 1. Then
The paint (B) was applied under the same conditions as for the test piece (A) on the hot-dip galvanized steel sheet on which the surface treatment was performed in the same manner as in Example 1.
A coated steel plate sample (C) was obtained.

Comparative Examples 1 to 2 Using the comparative polyesters (c) to (d), in the same manner as in Example 1, the solvent type coating material (C) having a solid content concentration of 50% (polyester resin concentration of 28%), respectively. (D) and coated steel sheet samples (D) to (E) were obtained.

Comparative Example 3 Using the comparative polyester (e), a solvent type coating material (E) having a solid content concentration of 50% was obtained in the same manner as in Example 1. Then
A zinc phosphate-based base treatment was carried out in the same manner as in Example 2, and then a paint (E) was applied under the same conditions as the test piece (a) on a hot dip galvanized steel sheet provided with a primer film of a commercially available solvent-type epoxy-modified polyester resin paint. Painted steel sheet sample (F)
Got

The stability of each of the obtained coating materials and the workability and hardness of each coated steel sheet were examined. The paint stability indicated the time until the paint lost its fluidity. The workability was evaluated by sandwiching a steel plate having the same thickness (0.5 mm) between two test pieces of the same coated steel plate, bending it by 180 degrees, and using the minimum number of plate scissors without cracks. The pencil hardness is the maximum hardness without scratches. The results are shown in Table 2.

[0045]

[Table 2]

From Table 2, the polyester-based paint of the present invention in which a metal sulfonate group is introduced into a poorly soluble polyester is
The paint showed good paint stability, and the coated metal plate obtained by applying this paint had excellent workability and hardness. On the other hand, the poorly soluble polyester-based paint containing no metal sulfonate group had poor paint stability, while the solvent-based paint using the easily-soluble polyester resin had low workability (hot-dip galvanized steel sheet was used as an example. The case is shown).

[0047]

EFFECT OF THE INVENTION Conventionally, when a sparingly soluble polyester resin is melted by heating with a crosslinking agent to be solubilized in a solvent and used as a solvent type paint, the stability of the paint is poor, and the time from the preparation of the paint to the application of the paint is low. Limited, the paint had to be prepared just before painting. According to the present invention, by introducing a metal sulfonate group into a poorly soluble polyester resin, the stability of the paint is significantly improved, the coating work can be afforded, a large amount of the paint is prepared, and the paint is applied at a later date. Therefore, there is an advantage that the productivity is remarkably improved.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Akihiro Yauchi 4-53-3 Kitahama, Chuo-ku, Osaka City Sumitomo Metal Industries Co., Ltd. (72) Inventor Toshiaki Shiota 4-53-3 Kitahama, Chuo-ku, Osaka No. Sumitomo Metal Industries Co., Ltd.

Claims (3)

[Claims] 1. A modified polyester resin in which a metal sulfonate base is introduced into a polyester resin which is poorly soluble in a general organic solvent is heated and melted together with a crosslinking agent to form a uniform mixture, and the obtained mixture is used as an organic solvent. Paint that is dissolved in. 2. A coated metal plate having a base chemical conversion film formed on at least one of a phosphate treatment and a chromate treatment on the surface of the metal plate, and a cured coating film formed from the paint according to claim 1. 3. Between the underlying chemical conversion coating and the cured coating,
The coated metal plate according to claim 2, which has a film formed from an epoxy-based, polyester-based, or urethane-based primer having an anticorrosive pigment.