JPH01204974A - Coating composition - Google Patents

Abstract

PURPOSE:To obtain the subject composition made useful as an automotive primer by improving its low-temperature chipping resistance, by adding a polyisocyanate to a urethane bond-containing lactone-modified polyester so as to give specified properties to the obtained composition. CONSTITUTION:The coating composition is obtained by mixing a urethane bond-containing lactone-modified polyester resin (A) (of a number-average MW of 2,000-10,000 and a hydroxyl number of 30-150) with a blocked polyisocyanate compound (B) in a ratio of 0.3-1.5, preferably, 0.5-1.2 equivalent of isocyanate groups to one equivalent of hydroxyl groups contained in component A. This composition should have a glass transition temperature of a cured film of 30-0 deg.C, an elongation at break of 100-500% at -20 deg.C and a tensile strength of 200-500kg/cm<2>. The modified polyester resin of component A is obtained by reacting 20-100pts.wt. lactone with 100pts.wt. resin solid of a polyester prepolymer and reacting the obtained product with 0.1-0.4 equivalent of a diisocyanate per equivalent of the hydroxyl groups in the resin.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a primer composition for automobiles that has excellent chipping resistance and appearance at low temperatures.

Generally, the chipping resistance of paints decreases at low temperatures. If a pebble hits the exterior of a car in areas such as North America and Europe where snow-melting salt is sprayed on roads during the winter and scratches the paint film, corrosion of the steel plate will begin.
In cold regions, there is a demand for automotive primers or intermediate coatings that are resistant to scratches even when hit by pebbles, that is, have high low-temperature chipping resistance.

[Prior Art] In response to this demand, various paint compositions, for example, paint compositions using specific pigments that do not reach the substrate even if scratched (
JP-A-53-45813) and coating compositions using isocyanate compounds (JP-A-54-73836, JP-A-57-68176) have been proposed.

However, a method using a composition containing 20 to 50 parts by weight of talc with a particle size of 10 to 20 μm (Japanese Patent Application Laid-Open No. 53-458
No. 13), since scratches caused by chipping do not easily reach the base steel plate surface, rust on the outer steel plate itself of the car body is reduced, but the problem is that the peeled area of the topcoat increases, spoiling the aesthetics and making the appearance worse.

In addition, a method using isocyanate (Japanese Unexamined Patent Publication No. 54-7
3836) has the disadvantage that chipping resistance at low temperatures is not sufficient, and in the case of the method using a compound in which polybutadiene having a hydroxyl group and isocyanate groups are reacted (Japanese Patent Laid-Open No. 57-68176), Although the chipping resistance is good, the finished appearance after the top coat is poor.

[Problems to be Solved by the Invention] The present invention has good chipping resistance at low temperatures, is resistant to scratches that reach the base steel plate, has a good appearance after being overcoated, and has good performance such as moisture resistance. The purpose is to provide a primer composition for automobiles.

[Means for Solving the Problems] The present inventors have developed a composition comprising a modified polyester resin component having a number average molecular weight of 2,000 to 10,000 modified with a lactone having a urethane bond and a block type polyisocyanate component in a specific blending ratio. By applying a coating composition having specific physical properties such as a glass transition temperature of 130 to 0 degrees Celsius, the coating film after curing of the composition has significantly improved low-temperature chipping resistance and excellent after-coat coating. The inventors have discovered that it is possible to obtain a chipping trimer for automobiles that has a good appearance and excellent properties such as moisture resistance, and has completed the present invention.

That is, the present invention provides (A) a polyester resin modified by reacting 20 to 100 parts by weight of lactone with respect to 100 parts by weight of the resin solid content of the polyester prepolymer, and 0.0. The number average molecular weight obtained by reacting 1 to 0.4 equivalents of a diisocyanate compound is 2000 to 1oooo, and the hydroxyl value is 3.
A lactone-modified polyester resin component having a urethane bond of 0 to 150, and (B) a polyisocyanate compound component in which isocyanate groups are blocked, (
A coating composition in which both components are blended in a ratio of 0.3 to 1.5 equivalents of isocyanate groups in component (B) to 1 equivalent of hydroxyl groups in component A), and a coating film after curing of the composition. The present invention provides a coating composition having a glass transition temperature of 130 to 0'C, an elongation at break of 100 to 500% at a temperature of -20C, and a tensile strength of 200 to 500 kg/cm''. .

Component (A) of the present invention is obtained by modifying the hydroxyl groups of a polyester prepolymer consisting of a polybasic acid and a polyhydric alcohol with a lactone, and then reacting it with an isocyanate.

Examples of polybasic acids that are constituents of the polyester prepolymer used as component (A) of the present invention include phthalic anhydride, isophthalic acid, tetrahydrophthalic anhydride, hexahydroheptalic anhydride, trimellitic anhydride, adipic acid, and sebacin. Polybasic acids commonly used for polyester production, such as acids, can be used.

Polyhydric alcohols that are other constituents of the polyester prepolymer include dihydric alcohols such as ethylene glycol, propylene glycol, diethylene glycol, polypropylene glycol, neopentyl glycol, and hexylene glycol, glycerin, trimethylolethane, and trimethylolpropane. , pentaerythritol, etc. are used. In addition, fatty acids having 8 to 18 carbon atoms, dimer acids, and the like can be used.

Polyester prepolymers can be produced by conventional methods using these raw materials.

The number average molecular weight of the polyester prepolymer used in the present invention is 1000 to 4000, and the glass transition temperature is 12
0 to 20'O is desirable.

In the present invention, lactones having 5 or more ring carbon atoms, such as δ-valerolactone, ε-caprolactone, and alkyl substituted products thereof, are added to the above-mentioned polyester prepolymer.
For example, a lactone-modified polyester resin can be produced by ring-opening polymerization of β-methyl-δ-valerolactone.

The amount of lactone to be reacted is 20 to 100 parts by weight based on 100 parts by weight of the resin solid content of the polyester prepolymer.

If it is less than 20 parts by weight, the chipping resistance of the coating film will be poor;
If the amount exceeds 0.00 parts by weight, the glass transition temperature of the final coating film will become too low, and the hardness of the coating film after applying the top coat will become low.

In the present invention, the lactone-modified polyester resin produced in this way has O
It is necessary to react a diisocyanate compound containing 01 to 0.4 equivalents of isocyanate groups.

As the diisocyanate compound used in the production of component (A) of the present invention, for example, hexamethylene diisocyanate, tolylene diisocyanate, inphorone diisocyanate, etc. can be used.

The reaction using the isocyanate can be carried out by mixing both in the above-mentioned mixing ratio and stirring at a temperature of 80° C. for about 3 hours.

If the amount of isocyanate groups in the diisocyanate compound to be blended is less than 0.1 equivalent to the hydroxyl group, sagging will easily occur during spray painting and the chipping resistance will also be poor, whereas if it exceeds 0.4 equivalent, the reaction will be delayed. The molecular weight increases, making it easier to gel, and the high molecular weight often causes defects such as stringiness during coating.

Among the lactone-modified polyester resins having urethane bonds produced in this way, those that can be used as component (A) of the present invention have a number average molecular weight of 2000 to 10.
000, and the hydroxyl value must be from 30 to 150.

If the number average molecular weight is less than 2000, it may cause sagging during painting.
The chipping resistance is poor, and when the molecular weight exceeds 10,000, a small amount of high molecular weight components are generated, causing stringiness during painting.
Pigment dispersibility and paint stability deteriorate.

In addition, if the hydroxyl value is less than 30, the crosslinking density will be insufficient, resulting in poor solvent resistance, weather resistance, strength, etc. of the coating film.
If it exceeds 150, the water resistance of the coating film will deteriorate.

The polyisocyanate compound with blocked isocyanate groups used as component (B) in the present invention is, for example, a dimer, a dimer, or a larger amount of isocyanate compounds such as hexamethylene diisocyanate, tolylene diisocyanate, and isophorone diisocyanate. Methyl ethyl ketoxime, ε-caprolactam, malonic acid diester, ethyl acetoacetate, etc., which have an active hydrogen isocyanate group contained in the isocyanate group or the reaction product of these isocyanate compounds and polyhydric alcohols such as water, ethylene glycol, and propylene glycol. It is obtained by making blocks with .

In such a blocked isocyanate compound, the isocyanate group is dissociated by heating, but (A)
The ratio of dissociable isocyanate groups to 1 equivalent of hydroxyl groups contained in the components must be 0.3 to 1.5 equivalents, preferably 0.5 to 1.2 equivalents.

If the blending ratio is less than 0.3 equivalent, the crosslinking density of the coating film will be low, resulting in defects such as decreased solvent resistance and cracking during outdoor exposure.

Moreover, even if more than 1.5 equivalents are used, the effect commensurate with the amount cannot be obtained, which is uneconomical.

In addition to the components (A) and (B), the composition of the present invention may optionally contain pigments such as titanium, talc, and carbon black, reaction catalysts such as dibutyltin dilaurate, leveling agents, and dispersants. A coating composition can be prepared by adding additives and solvents such as.

The coating composition of the present invention thus produced can be applied to mild steel, aluminum, plastic, etc. by air spraying, electrostatic coating, or the like, and then baked at a temperature and time sufficient to dissociate the blocked isocyanate. Can be done.

If the object to be coated is mild steel, after chemical conversion treatment, the dry coating thickness is 20
A cationic electrodeposition coating with a thickness of ~40 μm is applied and baked, and the coating composition of the present invention is applied thereon to a dry film thickness of ~30 μm, and after being left for 30 seconds to several minutes, a polyester resin intermediate coating is applied. After applying Nipico No. 1500 intermediate coat (manufactured by Nippon Oil & Fats Co., Ltd.) to a dry film thickness of 30 to 60 μm, it was baked at a temperature of 140°C for 30 minutes, and then a melamine/alkyd resin top coat melamine was applied. No
, 1500 White (manufactured by Nippon Oil & Fats Co., Ltd.) with a coating thickness of 20 to 5.
A coating film with good chipping resistance can be obtained by coating to a thickness of 0 μm and baking at a temperature of 140° C. for 30 minutes.

The primer coating film coated with the coating composition of the present invention and cured at a temperature and time sufficient to dissociate the blocked isocyanate groups has a glass transition temperature of -30 to 0°C,
It is necessary that the elongation at break at a temperature of -20°C is 100 to 500%, and the tensile strength is 200 to 500 kg/cm''.

The coating composition of the present invention is required to form a coating film having physical properties expressed by the above numerical values, and a coating film having such physical properties has chipping resistance at a low temperature of about -20°C. It has a very good quality and an excellent appearance, and is useful as an optimal coating composition for automobiles.

[Effects of the Invention] The coating composition of the present invention has excellent chipping resistance at low temperatures and has a good appearance after topcoating, and particularly when used as a chipping primer for automobiles, it has extremely excellent resistance compared to conventional coatings. In addition to exhibiting chipping resistance, it has the advantage of being resistant to scratches, having a good appearance after topcoating, and having excellent properties that automobile coatings should have, such as moisture resistance and gasoline resistance.

Therefore, the coating composition of the present invention can be widely used and useful for coating automobiles and other objects.

[Example] The content of the present invention will be explained in more detail with reference to Examples and Comparative Examples below. In addition, in the following, parts represent parts by weight.

Production Example A1-88 Production of ε-caprolactone modified polyester resin solution having urethane bonds Modified polyester resin solution A1 As the first stage reaction, a flask equipped with a stirrer, a rectification column, a water separator, a cooling tube and a thermometer To this, 235 parts of isophthalic acid, 139 parts of adipic acid, 55 parts of trimethylolpropane, 124 parts of neopentyl glycol, and 144 parts of 1,6 hexanediol were added, heated and stirred, and the condensation water produced from 160°C to 230°C. 4 while distilling it out of the system.
The temperature was raised at a constant rate over time. When the temperature was raised to 230°C, 15 parts of xylene was gradually added, and the temperature was raised to 230°C.
The condensation reaction was continued while maintaining the temperature at 30°C.

The reaction was terminated when the acid value became 5 or less, and a polyester prepolymer solution was obtained.

Next, as a second stage reaction, after cooling the above solution to 100'0, xylene was recovered under reduced pressure, and 613 parts of ε-caprolactone and 0.2 parts of dibutyltin dilaurate were added.
The reaction continues at a temperature of 150°C.

After cooling to 100°C when the solid content reaches 98% or more,
Add 250 parts of xylene and 250 parts of methyl ethyl ketone.

Furthermore, as a third stage reaction, 34 parts of hexamethylene diisocyanate is added dropwise at 80° C. in a nitrogen gas stream to continue the reaction. Unreacted isocyanate groups were tracked by IR through time-lapse sampling, and when they disappeared, 340 parts of toluene was added to obtain ε-caprolactone-modified polyester resin solution A1 having urethane bonds. Non-volatile content is 59
．． 2% by weight, festival viscosity (Gardner, 25°C) is U1
The resin acid value was 2.3.

Based on the formulation shown in Table 1, ε-caprolactone modified polyester resin A having urethane bonds in the same manner as above.
2-A8 were manufactured in a similar manner to A1. Table 1 shows the special values of the resin solution obtained.

(Left below) Examples 1 to 5 and Comparative Examples 1 to 3 Paint Preparation Examples 1 to 5 and Comparative Examples 1 to 3 were prepared by using the resin solution (A) produced in the production example as shown in Table 2, respectively. Eight types of brimers were prepared using the paint formulations shown in Table 3.

That is, first, a resin solution was diluted with 3-methoxybutyl acetate as a mill base, and a pigment was further mixed therein, and then dispersed in a sand mill until the pigment particle size became 20 μm or less to obtain a mill base. Subsequently, post-additives were mixed one after another to prepare a brimer.

(Leaving space below) Table 2 1) Teikoku Kako Co., Ltd. JR602 2) Mitsubishi Chemical Industries, Ltd. Carbon Black MA100 3) Sumitomo Bayer Urethane Co., Ltd. Desmodur KL5-2540 4) Esso Standard Sekiyu Co., Ltd. Mixed solvent test Preparation of Pieces Eight types of paints from Examples 1 to 5 and Comparative Examples 1 to 3 were each diluted with a diluting solvent consisting of 70 parts of toluene and 30 parts of ethyl acetate.
) The viscosity was adjusted to

The above-mentioned viscosity-adjusted paint was applied by air spray to a dry film thickness of 20 to 25 μm on a 100 x 150 x 0.8 mm zinc phosphate-treated dull steel plate electrodeposited (20 μm), and then heated for 3 minutes. After leaving it for a while, apply a polyester resin intermediate coating (Part Meiko Pico N manufactured by Nippon Oil & Fats Co., Ltd.).
o, 1500 intermediate coat) was air sprayed wet-on-wet so that the dry coating thickness was 40 to 50 μm. After being left at room temperature for 10 minutes, it was baked at a temperature of 140° C. for 30 minutes.

Next, a polyester resin top coat (manufactured by Nippon Oil & Fats Co., Ltd., part name: Melami No. 15) was applied onto the obtained intermediate coat film.
00 White) was air-sprayed to a dry coating thickness of 30-40 μm. After leaving at room temperature for 10 minutes, temperature 1
Test pieces of each example and comparative example were prepared by baking at 40° C. for 30 minutes.

The dry film thicknesses of the primer, intermediate coat, and top coat were as shown in Table 4.

In the test of Chipping Slimer alone, it was air-sprayed onto a tin plate to a dry film thickness of 50 μm, left at room temperature for 10 minutes, then baked at a temperature of 140°C for 60 minutes.
A free film was prepared using the mercury amalgam method and used for testing.

Comparative Example 4 On the same electrodeposition coating as in Examples 1 to 5, an intermediate coat and a top coat were applied and baked in the same manner as in the example, without applying a primer.

Coating film performance test results The coating film performance test results of the primers of Examples 1 to 5 and Comparative Examples 1 to 3, and the sagging and overall coating performance of the intermediate coated surface of Examples 1 to 5 and Comparative Examples 1 to 4 are as follows. It is shown in Table 5.

(The following is a blank space) As is clear from Comparative Examples 1 to 4 in Table 5 above, in Comparative Example 1, the amount of ε-caprolactone modification was less than 20% based on the solid content of the polyester prepolymer. Although an improvement in chipping resistance is observed compared to Comparative Example 4, which does not have the same property, it cannot be said to be at a sufficient level.

Further, in Comparative Example 3, even if modified with a large amount of ε-caprolactone, the glass transition temperature of the cured coating film exceeds 0° C., so the chipping resistance is insufficient as in Comparative Example 1.

On the other hand, in Comparative Example 2, the isocyanate group of hexamethylene diisocyanate is less than 0.1 equivalent per 1 equivalent of hydroxyl group of the ε-caprolactone modified polyester resin, so the molecular weight is difficult to increase and there are few urethane bonds with high polarity. Therefore, the melt viscosity is low, and sagging occurs during the temperature rising process until the blocking agent of the blocked isocyanate dissociates.

Table 5 shows that the coatings of Examples 1 to 5 based on the present invention not only have excellent chipping resistance at low temperatures;
This shows that the primer has excellent workability including sagging resistance, and has no deterioration in coating film performance.

Claims (1)

[Claims] 1 (A) Resin solid content of polyester prepolymer 10
Obtained by reacting a polyester resin modified by reacting 20 to 100 parts by weight of lactone with 0.1 to 0.4 equivalents of a diisocyanate compound per equivalent of hydroxyl group contained in the resin. Number average molecular weight is 200
0 to 10,000 and a hydroxyl value of 30 to 150, and (B) a polyisocyanate compound component in which isocyanate groups are blocked. The isocyanate group of component (B) is 0.3 relative to the equivalent weight.
A coating composition containing both components in a proportion of ~1.5 equivalents, wherein the glass transition temperature of the coating film after curing of the composition is -30 to 0°C, and the elongation at break is -20°C. ℃ 100-500%, tensile strength 200-500k
A coating composition that is g/cm^2.