JPH0715083B2 - Anti-chipping paint - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a chipping resistant coating, and more specifically,
For example, when it is used in the coating system of the outer surface of an automobile body, the formed coating film has excellent smoothness, and the coating film does not peel off due to the collision of pebbles even when driving in cold regions, which prevents corrosion of the steel plate of the vehicle body. Preventing chipping-resistant paint.

2. Description of the Related Art When a vehicle travels at high speed, it is inevitable that small stones collide with the painted surface of the outer skin of the vehicle. Many pebbles collide with the suspension, the hood, and the tip of the roof. The high-speed collision of pebbles causes the coating film to peel, so-called "chipping", which deteriorates the aesthetic appearance and exposes the steel plate surface at the impact portion to quickly generate rust and corrosion.
Especially in cold regions such as North America, Canada, and Northern Europe, a large amount of rock salt, gravel, etc. are sprayed on the road due to snow melting, and the coating temperature during running becomes -20 to -30 ° C or below This is a serious problem because chipping due to collision of pebbles is extremely likely to occur compared to traveling in a warm region because the coating film is frozen, and is extremely brittle and hard.

Generally, the coating system for the outer surface of automobile body is composed of iron phosphate / zinc-based chemical conversion treated steel plate, electrodeposition paint (undercoat paint),
The intermediate coating and the top coating are applied sequentially and baked, but various chemical conversion coatings, electrodeposition coatings, intermediate coatings and top coatings have been used in the past to prevent the above chipping and corrosion of steel sheets based on them. Was added. For example, in the chemical conversion treatment, different crystal forms,
Various studies have been made on the composition and physical properties of resins, the shape of pigments, and the like for electrodeposition paints, intermediate paints, and topcoat paints. Among these, as a study of the pigment shape,
For example, by blending an inorganic foil flaky pigment such as talc,
The internal stress of the coating film is reduced, and due to the gap in the coating film,
Examples of such measures include relaxation / dispersion of impact force and improvement of chipping property.

Further, between the electrodeposition coating film and the intermediate coating film, a chipping-resistant paint for forming a relatively soft coating film containing a polyester resin and a melamine resin or a blocked isocyanate compound as a main component is also applied. is there.

Problems to be Solved by the Invention In the above method which was carried out to improve the chipping resistance, the chemical conversion treatment film, electrodeposition coating, intermediate coating / top coating coating, etc. are substantially improved in the chipping resistance. It was extremely difficult.

Looking at the above-mentioned chipping-resistant paint, the polyester resin / melamine resin system has good chipping resistance in cases where the impact of pebbles is mild in warm regions, but when used at high speeds in winter in cold regions. , -20
In the case where the impact is strong at a low temperature of -30 ° C or lower, the coating film is frozen and becomes extremely hard and brittle, so that it is difficult to prevent the peeling phenomenon of the coating film. Further, when the melamine resin is replaced with a blocked isocyanate compound, the chipping resistance in the low temperature region is improved as compared with the one using the melamine resin, but it is not yet practically sufficient,
Further, when the intermediate coating material and the top coating material are applied repeatedly, wrinkles (so-called "chijimi") and irregularities are formed on the coating surface, which has a defect that the finish appearance after the top coating is remarkably deteriorated.

Furthermore, it is known to apply a chipping-resistant paint containing a maleic acid-grafted polyolefin resin as a main component on the electrodeposition coated surface, but it is sharp because the thickness of the formed coating film cannot be made thick (at most 5 to 8 μ). It involves the problem that when a small pebbles collides at high speed, the electrodeposition coating film is damaged.

Means for Solving the Problems The object of the present invention is, in particular, a coating film of a multilayer coating film composed of an electrodeposition coating film, an intermediate coating film (which may be omitted) and a top coating film formed on a surface of an automobile outer plate. We are developing a chipping-resistant paint that can prevent the paint film from peeling off even if pebbles collide while driving in cold regions without deteriorating the appearance and can form a paint film thickness of 15μ or more. As a result, a paint having the following composition was developed.

That is, the present invention provides (A) a diisocyanate compound and an average of 2 to 1 molecule.
An organic solvent-soluble urethane polymer having a number average molecular weight of 10,000 to 100,000 and an adduct with a polyol having three hydroxyl groups (B) a hydroxyl group-containing resin having a number average molecular weight of 400 to 5000 and (C) a blocked polyisocyanate compound Based on the total solid weight of the above components (A) and (B), 30 to 90% by weight of the component (A), (B)
The content of the component is 70 to 10% by weight, the regenerated isocyanate group of the component (C) is 0.3 to 1.5 equivalent per 1 equivalent of the total hydroxyl groups in the components (A) and (B), and the glass of the heat-curable coating film The present invention relates to a chipping resistant paint having a transition temperature of 10 ° C or lower.

The chipping-resistant coating material of the present invention (hereinafter, may be abbreviated as “present coating material”) is a multi-layer coating film consisting of the above electrodeposition coating film / intermediate coating film (may be omitted) / top coating film. It is most preferable to apply it to the surface of the electrodeposition coating film, but needless to say, it is not limited to this.

Each component constituting the paint will be described.

Component (A): an adduct of a diisocyanate compound and a polyol having an average of 2 to 3 hydroxyl groups per molecule,
The organic solvent-soluble urethane polymer diisocyanate compound having a number average molecular weight of 10,000 to 100,000 is a compound having two isocyanate groups in one molecule, and examples thereof include hexamethylene diisocyanate, isophorone diisocyanate, lysine diisocyanate, and trimethylhexamethylene diisocyanate. , Methylenebis (cyclohexyl isocyanate), diphenylmethane diisocyanate, tolylene diisocyanate, xylylene diisocyanate, 1,
Examples thereof include aliphatic, alicyclic and aromatic diisocyanate compounds such as 3- (isocyanatomethyl) cyclohexane, and among them, hexamethylene diisocyanate and isophorone diisocyanate are particularly preferable.

On the other hand, a polyol is a compound which is added to the above diisocyanate compound and has an average of 2 to 3 hydroxyl groups per molecule, and is selected from alcohols having 1 to 4 hydroxyl groups in one molecule. The average content of hydroxyl groups per molecule is 2-3.
It is made up of individual pieces. Specifically, it is necessary to use alcohols having 2 to 3 hydroxyl groups in one type, and in case of 2 or more types, alcohols having 1 to 4 hydroxyl groups are used and the composition ratio is also taken into consideration. In addition, it is necessary that the average number of hydroxyl groups per molecule be contained within the range of 2 to 3. The hydroxyl group of this polyol is 1
If the average number of molecules per molecule is less than 2, the chipping resistance, toughness, etc. of the coating film will decrease, while if it is more than 3, the gelation tends to occur during the addition reaction with the diisocyanate compound, and the chipping property will also decrease. Neither is preferable.

Regarding alcohols constituting a polyol, examples of the compound having one hydroxyl group in one molecule include saturated monohydric alcohols having 1 to 20 carbon atoms such as methanol, ethanol, propanol, butanol, hexanol, and octanol. Examples of alcohols having 2 to 3 hydroxyl groups in one molecule include polycaprolactone;
Examples thereof include polyether polyols such as polytetramethylene glycol, polyprene glycol, and polyethylene glycol; polyester polyols obtained by using the polyhydric alcohol and polybasic acid exemplified in the component (B) below; and the like in one molecule. Examples of the alcohol having four hydroxyl groups include pentaerythritol and polyester resin.

Among these polyols, polycaprolactone; polyester containing cyclohexanedimethanol; polytetramethylene glycol; and the like are particularly preferable.

The number average molecular weight of the polyol is 200 to 5,000, and particularly
It is preferably in the range of 400 to 2,500 and has a molecular weight of 20.
If it is less than 0, a large amount of diisocyanate compound is required to obtain a urethane polymer having a number average molecular weight in the above range, resulting in poor compatibility with the components (B) and (C) and poor spray coating workability. If the molecular weight is more than 5,000, the amount of diisocyanate used will be small, and the toughness of the coating film will be insufficient, and the chipping resistance may decrease. The hydroxyl value of the polyol is preferably in the range of 22-840.

Regarding the addition reaction of the diisocyanate compound and the polyol, the constituent ratio of both components can be arbitrarily selected as long as the number average molecular weight of the adduct is within the above range,
Specifically, the diisocyanate compound is preferably 2 to 40 parts by weight per 100 parts by weight of the polyol.

It is necessary to adjust the number average molecular weight of the urethane polymer [component (A)] thus obtained within the range of 10,000 to 100,000, preferably 20,000 to 80,000. If the number average molecular weight is less than 10,000, chipping resistance is reduced. Is insufficient, and when an intermediate coating material is subsequently applied, the intermediate coating film will have tingling and unevenness, while the number average molecular weight is 10
If it exceeds 0.000, spray coating may result in poor graining, resulting in poor smoothness of the coating film and poor compatibility with the components (B) and (C).

Furthermore, the urethane polymer has a hydroxyl value of 100 or less,
Particularly, it is preferable that each of them is 1 to 50 and the isocyanate group value is 3 or less.

And, the urethane polymer is an ordinary organic solvent for coating materials, for example, hydrocarbon-based, alcohol-based, ester-based,
It can be used by dissolving it in a ketone type or ether type.

Component (B): Hydroxyl group-containing resin having a number average molecular weight of 400 to 5,000. Specific examples thereof include a polyester resin having a hydroxyl group and having the above molecular weight, a polyether, or a urethane-modified product thereof.

First, for a polyester resin containing a hydroxyl group, a polybasic acid having two or more carboxyl groups in one molecule and a polyhydric alcohol having two or more hydroxyl groups in two molecules are esterified by a usual method. Obtained by As the polybasic acid and polyhydric alcohol, usual ones can be used. As the former, aromatic compounds such as phthalic anhydride, isophthalic acid, terephthalic acid, trimellitic anhydride, tetrahydrophthalic anhydride, hexahydrophthalic anhydride and hymic acid anhydride are used. Alternatively, an alicyclic system is preferable, and further succinic anhydride, adipic acid, sebacic acid, azelaic acid, dodecanedicarboxylic acid, maleic anhydride and the like can be used in combination, and the latter ethylene glycol, propylene glycol, 1,
6-hexanediol, diethylene glycol, neopentyl glycol, triethylene glycol, ester diol 204, bisphenol dihydroxypropyl ether, cyclohexanedimethanol, glycerin, trimethylolethane, trimethylolpropane and the like can be mentioned.

Next, as the polyether having a hydroxyl group, for example,
Examples thereof include polytetramethylene glycol, polypropylene glycol, polyethylene glycol, polyoxypropylene glycol, polyoxypropylene-polyoxyethylene glycol and the like. Further, examples of the urethane-modified product include compounds obtained by reacting the above polyester and / or polyether with the diisocyanate compound exemplified in the above-mentioned component (A).

In the present invention, a polyester resin containing a hydroxyl group is particularly preferable.

The component (B) has a number average molecular weight of 400 to 5,000, preferably 800 to 3,000, and a hydroxyl value of 50 to 200, particularly 70 to 150. When the number average molecular weight of the component (B) is less than 400, the cohesive force of the coating film is reduced and the corrosion resistance and moisture resistance are poor, while when it is more than 5,000, the compatibility with the component (A) is reduced.

Component (C): Blocked Polyisocyanate Compound A compound obtained by blocking the isocyanate group in a polyisocyanate compound having two or more isocyanate groups in one molecule with a blocking agent.

The polyisocyanate compound is one or more selected from the diisocyanate compound itself exemplified as the raw material of the component (A) and an adduct obtained by reacting the diisocyanate compound and a polyol compound in excess of isocyanate groups. Can be used. Among these, as the polyol compound, a polyether polyol or a polyester resin having a number average molecular weight of 500 to 1,500 among the polyols used in the component (A) is preferable, and the addition reaction of the polyol compound and the diisocyanate compound is preferable. The ratio of isocyanate group / hydroxyl group (equivalent ratio) is preferably 1.2 to 4/1. When the diisocyanate compound is used alone, hexamethylene diisocyanate, isophorone diisocyanate, methylenebis (cyclohexyl isocyanate), 1,3- (isocyanatomethyl) cyclohexane and the like are particularly preferable.

As the blocking agent, one known per se can be used,
For example, one or more selected from oxime-based, phenol-based, caprolactone-based, and phenol-based can be used, and these block all free and active isocyanate groups in the polyisocyanate compound. Of the above, it is preferable to use an oxime-based blocking agent.

The blocked polyisocyanate compound is inactive at room temperature, but when heated to a dissociation temperature (about 120 ° C.) or higher, the blocking agent dissociates, the isocyanate group is regenerated, and the hydroxyl groups in the above components (A) and (B) Can be cross-linked.

The present coating composition contains the above-mentioned components (A), (B) and (C) as the main components, and based on the total solid weight of the above-mentioned components (A) and (B), the content of the component (A) is 30 to 30%. 90% by weight, preferably 40 to 80% by weight, the component (B) is 70 to 10% by weight, preferably 60 to 20% by weight, and the regenerated isocyanate group of the component (C) is the components (A) and (B). It is 0.3 to 1.5 equivalents, preferably 0.4 to 1.2 equivalents, per 1 equivalent of the total hydroxyl groups, and the glass transition temperature of the heat-cured coating film is 10 ° C or lower.

When a coating composition containing less than 30% by weight of component (A) is applied and then an intermediate coating composition or a top coating composition is applied, creases and dents are generated in the applied coating film, while when it exceeds 90% by weight, spray coating is applied. There is a problem that the state of atomization is poor and it is difficult to finish a smooth coating film.

Further, regarding the blending ratio of the component (C), if the above equivalent ratio of the regenerated isocyanate group is less than 0.3, the curability is insufficient and thus chipping resistance, water resistance, etc. are reduced, while 1.
If it is larger than 5, further improvement in performance cannot be expected.

Further, in the present coating composition, it is necessary that the above components (A), (B) and (C) are the main components, and the glass transition temperature of the cured coating film is + 10 ° C or lower, preferably 0 ° C or lower. When the glass transition temperature is higher than 10 ° C, the low temperature chipping resistance is deteriorated, which is not preferable. The glass transition temperature is easily adjusted by the composition of the components (A), (B) and (C) and the ratio of each component.

The glass transition temperature is measured by coating the present coating composition containing the above-mentioned components (A), (B) and (C) as the main components so as to have a thickness of 25μ based on the cured coating film. It is a dynamic glass transition temperature measured by using a coating film heated and cured at a dissociation temperature or higher and using a vibron at a frequency of 110 Hz and a temperature rising rate of 3 ° C./min.

Further, regarding the cured coating film of the present coating composition, the tensile elongation at break of the isolated coating film at -20 ° C is 50 to 600%, particularly 70 to 5%.
It is preferably in the range of 00%. The tensile elongation at break is a value measured using a universal tensile test with a constant temperature bath (Autograph S / D type manufactured by Shimadzu Corporation), and the sample length is 20.
mm, and the pulling speed was 20 mm / min. The isolated coating film of the present coating composition was applied to a tin plate so as to have a thickness of 25 μm based on the formed coating film, heated at 140 ° C. for 30 minutes to cure, and then isolated by the mercury amalgam method.

The present coating composition contains the above-mentioned components (A), (B) and (C) as the main components, but in addition thereto, various auxiliary agents such as a leveling agent, an anti-sagging agent and a curing accelerator can be added.

Further, in order to maintain the film thickness and improve the finish of the intermediate coating, an inorganic pigment such as titanium oxide, barium sulfate, talc, or silica is added in an amount of 30 to 1 with respect to 100 parts by weight of the total resin in the coating composition.
It is preferable to add it by 00 parts by weight.

The present coating composition can be coated with an organic solvent selected from the above to have a viscosity suitable for coating, and can be coated by, for example, spray coating, electrostatic coating, dip coating or the like. A suitable coating thickness is 15 to 30μ based on the cured coating. The coating film is cross-linked and cured by heating it to a dissociation temperature of the blocking agent of the block polyisocyanate compound [component (C)] or higher, for example, 120 ° C. or higher.

This paint is a layer of a multilayer coating film consisting of a conventional electrodeposition coating film, an intermediate coating film (which may be omitted) and a top coating film, especially between the electrodeposition coating film and the intermediate coating film or the top coating film. When applied to No. 1, the chipping resistance of the multi-layer coating film in the low temperature region was remarkably improved, and the finishability was also good.

That is, a cationic or anionic electrodeposition coating is applied to a steel plate that has been appropriately degreased and surface-treated, and after heating and curing, this coating is applied to the surface of this electrodeposition coating as a cured coating. It is coated to a thickness of 10 to 35μ, preferably 15 to 25μ. It does not matter if the coating film of this paint is heat-cured and then the intermediate paint or topcoat paint is applied.However, if the intermediate paint or the like is applied in an uncured state without heat-curing the coating film of this paint, conventional coating This is advantageous because there is no need to significantly change the process. Then, after coating and heating the intermediate coating material, the intermediate coating film itself or the coating film of the uncured main coating material that has already been applied is also cured at the same time,
Apply topcoat paint and let it harden. To apply this topcoat paint, 1 coat 1 bake method, 2 coat 1 bake method,
Solid color finish and metallic finish such as 2 coat 2 bake system, 3 coat 1 bake system, 3 coat 2 bake system and the like can be mentioned. In these coating methods, the intermediate coating may be omitted, the main coating may be applied, and the top coating may be applied after being cured by heating or without being cured by heating.

The electrodeposition coating material, intermediate coating material, top coating material and the like in the coating step may be appropriately selected according to the purpose from those which are generally used.

Action, effect By interposing the coating film of the present paint having the above composition and physical property value as one layer of the multilayer coating film, even if a strong impact such as pebbles is applied to the coating film at a low temperature of -20 ° C or lower. However, most of the impact energy was absorbed in the coating film of this paint, it did not spread to the lower electrodeposition coating film, and it was almost eliminated that both the intermediate coating film and the top coating film were physically damaged. is there. In other words, it seems that the coating film of this paint has a cushioning effect against the impact force from the outside.

Further, even when the coating film of the present coating material was not cured by heating and was coated with the intermediate coating material or the top coating material in an uncured state, no creases or irregularities were observed and the smoothness was remarkably improved.

Next, production examples, examples and comparative examples relating to the present invention will be described. Both parts and% are based on weight.

I. Production Example 1) Production Example of (A) Component (A-1): Polycaprolactone having a number average molecular weight of 1250 in a flask and an average number of hydroxyl groups per molecule of 2.0 (hydroxide value 90) (manufactured by Daicel Corp.) To 700 parts of Praxel 212), 760 parts of toluene was added, dissolved by heating and further refluxed to remove a trace amount of water. While maintaining this solution at 80 ° C., a mixed solution of 94 parts of hexamethylene diisocyanate and 400 parts of methyl ethyl ketone was added dropwise over 1 hour, and then 0.04 parts of dibutyltin diacetate as a urethane-forming catalyst was mixed with 32 parts of toluene. In addition, keep for 2.5 hours, Gardner viscosity (20 ℃)
V, NCO value of 1 or less, hydroxyl value of 2, number average molecular weight of 40,000 as determined by GPC (gel permeation chromatography)
A urethane polymer solution of was obtained.

(A-2): 432 parts of 1,4-cyclohexanedimethanol and 292 parts of adipic acid were placed in a flask and heated from 160 ° C. to 2
The temperature was raised to 20 ° C. over 2.5 hours, and the temperature was maintained at 220 ° C. for 1 hour. Then, 40 parts of toluene was added and reacted under reflux until the acid value became 1 or less, and toluene was added to obtain a 40% polyester varnish. Has an average of 2 hydroxyl groups per molecule, and has a hydroxyl value
172, the number average molecular weight was 654. This 40% in a flask
Polyester varnish 727 parts, polycaprolactone (manufactured by Daicel Corp., Praxel 308, average number of hydroxyl groups per molecule 3, hydroxyl value 195, number average molecular weight 860) 363 parts of 40% toluene solution containing 145 parts (dehydrated and refluxed) Then, 223 parts of methyl ethyl ketone was added and maintained at 100 ° C., and 166 parts of isophorone diisocyanate was added dropwise over 1 hour. Next, dibutyltin diacetate 0.12 was mixed with 23.2 parts of toluene, and the reaction was continued for 2.5 hours. Gardner viscosity Z, NCO value
A 40% urethane polymer solution having a hydroxyl value of 0.5 or less, a hydroxyl value of 34, and a number average molecular weight of 69,000 was obtained.

(A-3): Similar to (A-2) above, using 236 parts of 1,6-hexanediol, 118 parts of succinic acid, 22 parts of toluene for dehydration / reflux, and 296 parts of diluted toluene, a number average molecular weight of 318,
Acid value 1 or less, OH value 353, 2 hydroxyl groups per molecule 5
A 0% polyester varnish was obtained. Next, using 496 parts of this 50% polyester varnish, 137 parts of tolylene diisocyanate, 190 parts of methyl ethyl ketone, 140 parts of toluene, 0.02 part of dibutyltin diacetate, a reaction is carried out at 70 ° C., a hydroxyl value of 3, an NCO value of 0.5 or less, A urethane polymer having a number average molecular weight of 38,000 was obtained.

2) Production Example of Component (B) (B-1): In a flask, trimethylolpropane 27
Add 4 parts, 944 parts of 1,6-hexanediol, 462 parts of hexahydrophthalic anhydride and 876 parts of adipic acid, and add 160 ° C.
To 230 ° C. over 3 hours and maintained at 230 ° C. for 1.5 hours, 114 parts of xylene was added to obtain 80% polyester varnish. This polyester varnish had a Gardner viscosity X, an acid value of 10, a number average molecular weight of 1550 and a hydroxyl value of 108.

(B-2): trimethylolpropane 314 in the flask
Parts, neopentyl glycol 808.5 parts, phthalic anhydride 296
Parts, tetrahydrophthalic anhydride 760 parts and adipic acid 2
After adding 57 parts and heating from 160 ° C to 230 ° C over 3 hours and holding at 230 ° C for 1 hour, 11 parts of xylene was added and the reaction was continued while dehydrating and refluxing. % Polyester varnish was obtained. This polyester varnish has a Gardner viscosity of U, an acid value of 0.6, a hydroxyl value of 119,
The number average molecular weight was 1780. Next, 1.2 parts of hexamethylene diisocyanate was added to 100 parts of this 60% polyester varnish, and urethane modification reaction was carried out at 80 ° C. The urethane-modified polyester varnish obtained has a Gardner viscosity of Y and an OH value.
The number average molecular weight was 104 and the number average molecular weight was 2,300.

3) Production Example of Component (C) (C-1): Tolylene diisocyanate 5 mol, molecular weight
An addition reaction product of diisocyanate and polyol, consisting of 1 mol of 1,000 ± 100 polytetramethylene glycol and 1 mol of trimethylolpropane, all free NCO groups being 50% xylene / cellosolve of blocked polyisocyanate blocked with methyl ethyl ketoxime. The content of the regenerated isocyanate group in the acetate solution was 3.7%.

(C-2): Addition reaction product consisting of 3 mol of tolylene diisocyanate and 1 mol of trimethylolpropane, a free polyisocyanate group being a 60% xylene / cellosolve acetate solution of a blocked polyisocyanate blocked with methyl ethyl ketoxime to give a regenerated isocyanate. The group content was 7%.

II. Examples and Comparative Examples The paints (Examples) and comparative paints (Comparative Examples) were prepared by blending the components (A), (B) and (C) obtained in the above Production Examples in the ratios shown in Table 1. ) Was manufactured.

In Table 1, the blending amount of each component is based on the solid content weight, and the NCO group / OH group is the equivalent of the regenerated isocyanate group in the component (C) and the OH group in the components (A) and (B). Is a ratio.
A chipping-resistant coating composition is prepared by adding 48 g of titanium oxide, 12 g of barium sulfate and 0.1 g of dibutyltin laurate to 100 parts by weight of the total solid content of the mixture of the components (A), (B) and (C). Got Further, the glass transition temperature and the elongation at break elongation were measured based on the method described above for the single cured coating film of the present coating material (including the one for comparison).

III. Coating film performance test results Epoxy resin-based cationic electrodeposition coatings of the paints obtained in the examples and comparative examples were applied to a steel sheet that had been cured by heating at 16 ° C for 30 minutes, and 20 ± 5μ based on the cured coating film. Spray coating for 1 minute at room temperature, then apply polyester resin / melamine resin intermediate coating to 40μ based on the cured coating, then heat at 140 ° C for 30 minutes The coating film such as the main coating material and the intermediate coating film were simultaneously cured. Further, a polyester / melamine resin-based top coating material was applied to the surface of this layer by 40 μm and baked at 140 ° C. for 30 minutes to prepare a test plate.

Using the test plate thus obtained, various coating film performance tests were conducted, and the results are also shown in Table 1 above.

The test method is as follows.

(1) Spray coating workability Ford cup # 4/20
Diluted to 20 ± 2 seconds at ℃, and visually observed the atomized state and the coated surface when sprayed with an air spray gun.
The no was evaluated. ⊚: Good, Δ: Slightly inferior.

(2) Smoothness of the intermediate coating film The steel plate is coated with electrodeposition paint / main paint / intermediate coating paint, and the coating test plate baked as described above is used. The sharpness was rated as good (⊚) to inferior (x) on a five-point scale.

(3) Visibility of the top coating film The top coating material (solid color or metallic color enamel) is further applied to the intermediate coating material coated plate used in (2),
Use a paint test plate that has been baked and dried. The image clarity evaluation method is the same as the method described in (2) (evaluation of fluorescent lamp image).

(4) Chipping resistance A stepping stone tester (Suga Tester Co., Ltd., JA-400 type) is used.
Attach the coating test plate [same as the one created in (3)] vertically to the sample holder of the tester, and inject 50 g of No. 7 crushed stone with a pressure gauge of the same tester at an air pressure of 4 kg / cm ² to crush the crushed stone. Collide with the test plate at a right angle. The test plate is washed with water and dried, and the coating film that has floated up due to chipping is removed with adhesive tape, and the degree of peeling damage is good (⊚) to poor (x).
It was judged in stages. For low temperature chipping test, -30 ~
The coating test plate was immersed in a dry ice / methanol solution cooled to -35 ° C for 5 minutes to 10 minutes, taken out, and immediately (within a few seconds) a chipping test was performed by the above method. The temperature of the test plate during chipping is -20 ± 5 ° C.

(5) Moisture resistance A wet tester (Suga Tester Co., Ltd.) was used. Relative humidity 98
%, The coating test plate prepared in the same manner as in (3) is placed in a tank maintained at a temperature of 49 ± 1 ° C. and left for 240 hours.

Immediately after taking out, water drops and the like were wiped off, and the presence or absence of abnormalities such as blisters and stripes on the surface of the top coating film was evaluated. Compared to the coating test plate before the moisture resistance test, those that did not change were accepted (⊚), and △ had less blisters and streaks.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Receipt Takagi 4-17-1, Higashi-Hachiman, Hiratsuka-shi, Kanagawa Kansai Paint Co., Ltd. (72) Inventor Kenji Seko 4-1-1, Higashi-Hachiman, Hiratsuka, Kanagawa Kansai Paint Co., Ltd. (72) Inventor Katsuyoshi Yoshida 7-3 Satsuki-cho, Kanuma City, Tochigi Prefecture Kansai Paint Co., Ltd. (72) Inventor Tsukasa Hanada 7-3 Satsuki-cho, Kanuma City, Tochigi Prefecture Kansai-Paint Shares In-company (72) Inventor Yozo Oi 7-3 Satsuki-cho, Kanuma City, Tochigi Prefecture Kansai Paint Co., Ltd. Inspector Hiroyuki Taniguchi (56) References JP 62-4754 (JP, A) JP 62 -220563 (JP, A) JP 60-156766 (JP, A) JP 54-25067 (JP, B2) JP 58-46225 (JP, B2)

Claims (1)

[Claims] 1. An organic solvent-soluble urethane polymer (B) having a number average molecular weight of 10,000 to 100,000, which is an adduct of (A) a diisocyanate compound and a polyol having an average of 2 to 3 hydroxyl groups per molecule. Based on the total solid weight of the component (A) and the component (B), the component (A) is 30 to 90 based on the total weight of the component (A) and the component (B). % By weight, (B)
The content of the component is 70 to 10% by weight, the regenerated isocyanate group of the component (C) is 0.3 to 1.5 equivalent per 1 equivalent of the total hydroxyl groups in the components (A) and (B), and the glass of the heat-curable coating film A chipping resistant coating material having a transition temperature of 10 ° C or lower.