JPS61151281A - Coating composition - Google Patents

Abstract

PURPOSE:To provide a coating compsn. which prevents sagging and bittiness during coating, baking, and curing and provides good finishing film performance, by incorporating a hydroxyl group-contg. resin and a particular alkylated melamine/formaldehyde resin. CONSTITUTION:A coating compsn. comprising a hydroxyl group-contg. resin (A) and an alkylated melamine/formaldehyde resin having a number-average MW of 2,000-5,000 and an amt. of active methylol groups per triazine nucleus of 0.2-1.5mol (B) so that the wt. ratio of the resins A to B is 50/50-95/5. n-Butylated melamine/formaldehyde resin, isobutylated melamine/formaldehyde resin, and the like are desirable because of a particularly significant effect as the resin A used. If necessary, colorants, solvents, surface modifiers, substances that impart weatherability, coatability modifiers, and the like may be incorporated properly in said coating compsn.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a bake-curable liquid coating composition that has excellent sagging and scuffing resistance. More specifically, in a coating composition containing a hydroxyl group-containing resin and a specific alkylated melamine-formaldehyde resin (hereinafter referred to as melamine resin), it suppresses sagging and flaking during paint baking and curing, and provides good finished coating performance. The present invention relates to a coating composition comprising:

[Conventional technology and its problems]

The sagging resistance and scuffing resistance of paints are important factors that affect the workability of paints, and improvement thereof is strongly desired.

However, increasing the viscosity of the paint and improving its sagging resistance worsens the sagging resistance, and improving the sagging resistance by lowering the molecular weight of the resin or delaying curing reduces the sagging resistance. Therefore, it is extremely difficult to improve both at the same time. For example, a method has been proposed in which the main ingredient, ie, a hydroxyl group-containing resin, has characteristics of low reactivity and high viscosity, and this is combined with a relatively low molecular weight melamine resin of about 1000 to balance the wrinkles and sag. This method deteriorates various physical properties due to a decrease in the molecular weight of the melamine resin, is limited to a specific main ingredient, and is not necessarily satisfactory in improving wrinkles and sagging.

[Means for solving problems]

In view of these circumstances, the present inventors conducted extensive research and, contrary to conventional methods, significantly increased the molecular weight of melamine resin.
On the other hand, by significantly lowering the amount of active methylol groups, the scuffing resistance and sagging resistance have been dramatically improved. However, it was discovered that the coating film has various physical properties that are comparable to those of conventionally known coatings, and the present invention was developed based on this finding.

That is, the present invention comprises a water #R group-containing resin and a melamine resin, and the melamine resin has a number average molecule i! 2000～
5,000, the amount of active methylol groups per triazine nucleus is 0.2 to 1.5 mol, and the weight ratio of the hydroxyl group-containing resin to the melamine resin is 50,150 to 9,515. do.

The hydroxyl group-containing resin used in the coating composition of the present invention may be one that is used in ordinary baking-curing coatings, such as those with an oil length of 45% or less and a hydroxyl value of 40 to 200.
A hydroxyl group-containing alkyd resin having an acid value of 2 to 15, a hydroxyl group-containing vinyl polymer having a hydroxyl value of 20 to 200 and an acid value of 1 to 15, a hydroxyl group-containing vinyl polymer having a hydroxyl value of 20 to 200 and an acid value of O to For example, hydroxyl group-containing polyester resins such as No. 35 may be used alone or in combination or in combination, and it is also possible to add an epoxy resin as necessary.

As the melamine resin used in the coating composition of the present invention, methylolated melamine modified with an alcohol having 1 to 4 carbon atoms is used, such as methylated melamine formaldehyde resin, n-butylated melamine formaldehyde resin, isobutylated melamine Formaldehyde resin or mixed alcohol-modified melamine formaldehyde resin is used. Among these, the butylated type is particularly preferable because the effects of the present invention are remarkable.

The melamine resin in the present invention has a number average molecular weight of 2000 to 5.
000, preferably 2500 to 4500. When the number average molecular weight exceeds 5,000, the critical underarm film thickness decreases rapidly. On the other hand, the number average molecular weight is 200
When it is less than 0, the sag limit film thickness decreases rapidly, so that the effects of the present invention cannot be obtained.

The amount of methylol groups contained in the melamine resin is 0.2 to 1.5 mol, preferably 0.2 mol per triazine nucleus.
-1.0 mol, more preferably 0.3-0.7 mol is used.

If the amount of methylol groups exceeds 1.5 mol per triazine nucleus, the scuffing resistance will be significantly reduced. Furthermore, if the amount of the methylol group is less than 0.2 mol, the reactivity with the hydroxyl group-containing resin decreases, resulting in a decrease in the practical performance of the coating film.

The number of moles of alkoxy groups in the melamine resin is preferably 1.8 to 3.0 moles per triazine nucleus in the butylated melamine formaldehyde resin. When the number of moles is less than 1.8 moles, the compatibility with the hydroxyl group-containing resin is poor;
The practical performance of the coating film will deteriorate, and if it exceeds 3.0 mol, the curability will be poor due to the plasticizing effect of the alkoxy group.
The physical properties of the coating film deteriorate. In the case of a methylated melamine formaldehyde resin or a mixed etherified melamine formaldehyde resin, the number of moles of alkoxy groups per triazine nucleus is preferably 3.0 to 5.0 moles. If the number of moles is less than 3.0 moles, the compatibility of the hydroxyl group-containing resin will be poor, while if it exceeds 5.0 moles, the curability will be poor.

The appropriate blending ratio of the hydroxyl group-containing resin and melamine resin in the coating composition of the present invention is 50,150 to 9,515 in solid weight ratio. If this blending ratio is less than 50,150, the melamine resin will be excessive, and the melamine resin that does not react with the hydroxyl groups in the hydroxyl group-containing resin will remain in the baked coating, resulting in low hardness.
Only a poorly cured coating is obtained. Also, this blending ratio is 9
If it exceeds 515, although the melamine resin reacts sufficiently, most of the hydroxyl groups in the hydroxyl group-containing resin remain unreacted, resulting in a coating film with a low degree of curing and insufficient strength.

The coating composition of the present invention contains components contained in ordinary coatings, namely colorants (pigments, dyes), solvents (organic solvents, water),
In addition, additives such as surface conditioning agents (silicone oil, leveling agents), curing accelerators, weatherability imparting agents (ultraviolet absorbers, etc.), coating workability regulators, improving agents, etc. may be added as appropriate. I can do it.

〔Effect of the invention〕

By adding a specific melamine resin to the coating composition of the present invention, effects such as sagging resistance and scuffing resistance are significantly improved, and other physical properties are also good.

〔Example〕

Synthesis examples of hydroxyl group-containing resins used in Examples and Comparative Examples of the present invention are shown below. Note that parts and percentages in the examples are based on weight.

Synthesis Example 1 (Synthesis of hydroxyl group-containing alkyd resin) Stirrer,
Add 300 ml of coconut oil to a four-necked flask equipped with a thermometer, reflux condenser with dehydration trap, and nitrogen gas introduction device.
0.15 parts of lithium hydroxide and 132 parts of trimethylolpropane were charged and alcohol exchanged at 250°C for 1 hour, followed by 10 parts of trimethylolpropane.
0 parts of pentaerythritol, 357 parts of hexahydrophthalic anhydride, 40 parts of phthalic anhydride, p-
50 parts of tert-butylbenzoic acid and 4 parts of xylene
0 part was added and held at 160°C to 180°C for 3 hours, then gradually raised from 180°C to 220°C over 2 hours, and further dehydrated at 220°C for 3 hours until the acid value reached 10. , the hydroxyl value is 100, and the number average molecular weight (M
An alkyd resin having n) of 2500 was obtained.

Next, this resin was diluted with xylene to a resin solid content of 60% to obtain the desired alkyd resin (1).
I got it.

Synthesis Example 2 (Synthesis of hydroxyl group-containing vinyl polymer) 800 parts of xylene, 200 parts of n-butanol, and azobisisobutylene were added to a 3β separable colben equipped with a reflux condenser, a dropping funnel, a thermometer, and a stirring blade. 15 parts of nitrile, t
5 parts of ert-butyl peroxide and 300 parts of styrene, 220 parts of n-butyl methacrylate, 300 parts of 2-ethylhexyl acrylate, 150 parts of 2-hydroxyethyl methacrylate, 30 parts of acrylic acid.
A mixed solution consisting of 50% of the acid value was added dropwise at a uniform rate over 6 hours at 120°C, and the reaction was completed by maintaining the same temperature for 5 hours after the completion of the dropwise addition, resulting in a vinyl polymer (II
) was obtained.

Synthesis Example 3 (Synthesis of hydroxyl group-containing polyester resin) 200 parts of isophthalic acid, 200 parts of phthalic acid, and 2 parts of adipic acid were placed in a four-necked flask equipped with a stirrer, thermometer, and water separator.
Add 37 parts of neopentyl glycol, 365.3 parts of neopentyl glycol, and 124 parts of trimethylolpropane, and heat and stir while stirring.
The temperature was raised to 80°C. The temperature was raised from 180°C to 230°C at a substantially constant rate over 5 hours, and then maintained at 230°C. Furthermore, 720 parts of xylene was gradually added, and the method was switched to an azeotropic condensation method. The acid value of the resin was monitored over time while maintaining the reaction temperature at 230°C, and the reaction was terminated when the acid value reached 4.0. The obtained polyester resin (I[[) was oil-free with a hydroxyl value of 54, a nonvolatile content of 60%, and a number average molecular weight of 3,000.

The melamine resin used in the present invention is synthesized by a known conventional method. Examples of synthesis of the melamine resin used in the present invention are shown below.

Synthesis Example 4 Koei Formit NB (Hemiformer solution manufactured by Koei Chemical Industry Co., Ltd.) (Reaction of formaldehyde and butanol in a mixture consisting of 40% formaldehyde, 50% n-butanol, and 10% water) 387 parts, n-butanol 626 parts of melamine, 198 parts of melamine, and 318 parts of water were placed in a four-necked flask, and the pH of the reaction system was adjusted to 7.5 with a 20% aqueous sodium hydroxide solution and heated. After methylolation was performed by keeping the mixture under reflux for 10 minutes, the pH was lowered to 6.1 using 20% phosphoric acid, dehydration was performed using decanethisilane, and etherification reaction was performed for 12 hours. After the etherification reaction was completed, the solvent was removed under reduced pressure at 60 to 80°C, and then the nonvolatile content was adjusted to 60% with xylene and n-butanol. The molecular weight of the obtained n-butylated melamine formaldehyde resin' (melamine resin ■) was determined by Gelvermitsusilane chromatography using a polystyrene calibration curve. Its number average molecular weight was 3,600. The number of moles of methylol groups per triazine load was 0.6.

Also, the number of moles of n-butoxy groups per triazine truck is 2.
．． It was 3.

Synthesis Example 5 Koei Formit IB (hemiformal solution manufactured by Koei Chemical Industry ■) (reaction of formaldehyde and isobutanol in a mixture consisting of 40% formaldehyde, 50% isobutanol, and 10% water) 760 parts, 303 parts of isobutanol , 204 parts of melamine were placed in a four-round flask, the pH of the reaction system was adjusted to 7.0 with a 20% aqueous sodium hydroxide solution, and the mixture was heated. After methylolation by keeping under reflux for 10 minutes, the pH was adjusted to 6 using 20% phosphoric acid.
．． 0 and dehydrated with decanethisilane, followed by an etherification reaction for 16 hours. 60~ after completion of etherification reaction
After removing the solvent under reduced pressure at 80°C, the nonvolatile content was adjusted to 60% with xylene and 1so-butanol.

The number average molecular weight of the obtained 1so-butylated melamine formaldehyde resin (melamine resin ■) was 2600, and the number of moles of methylol groups per triazine load was 0.6.1s.
The number of moles of o-butoxy groups was 2.5.

Synthesis Example 6 743 parts of Koei Formit IB, 452 parts of isobutanol, 200 parts of melamine, and 174 parts of water were placed in four Lof flasks, and the pH of the reaction system was adjusted to 8.6 with a 20% aqueous sodium hydroxide solution and heated. . After being kept under reflux for 10 minutes to carry out methylation, p
Lower the H to 7.2 and dehydrate by decantation to 1
The etherification reaction was carried out for 5 hours. After the etherification reaction, the solvent was removed under reduced pressure at 60 to 80°C, and then xylene, n-
The nonvolatile content was adjusted to 60% with butanol. Obtained n
The number average molecular weight of the -butylated melamine formaldehyde resin (melamine resin (■)) was 1350, the number of moles of methylol groups per carload of triazine was 1.4, and the number of moles of n-butoxy groups was 2.3.

Synthesis Example 7 673 parts of Koei Formit NB, 404 parts of isobutanol, 200 parts of melamine, and 144 parts of water were placed in a four-necked flask, and the pn of the reaction system was adjusted to 9.0 with a 20% aqueous sodium hydroxide solution. Heated. After methylolation was performed by keeping the mixture under reflux for 10 minutes, the pn was lowered to 7.0 using 20% phosphoric acid, dehydration was performed using decanethisilane, and etherification reaction was performed for 11 hours. After the etherification reaction was completed, the solvent was removed under reduced pressure at 60 to 80°C, and the nonvolatile content was adjusted to 60% with xylene and isobutanol. The obtained isobutylated melamine formaldehyde resin (melamine resin ■) had a number average molecular weight of 1450, a mole number of methylol groups per liazine nucleus of 1.1, and a mole number of isobutoxy groups per liazine nucleus of 2.4.

Example 1 Alkyd resin I obtained in Synthesis Example 1 (solid content 60%)
70 parts, 30 parts of melamine resin I obtained in Synthesis Example 4 (solid content 60%) and titanium white (manufactured by Ishiya Sangyo ■, R-CR9).
3) Tsurupetz 100 (
Add a diluting solvent consisting of 60 parts of Esso Standard Petroleum (mixed solvent), 20 parts of xylene, 10 parts of cellosolve acetate, and 10 parts of n-butanol, and dilute with Ford Cup Na4 at 20°C for 30 seconds to obtain the diluted paint. Obtained.

This paint was spray coated at 25°C with a spray pressure of 4 kg/-, and after setting for 30 minutes, it was baked at 140°C for 20 minutes to evaluate the film performance.

To evaluate the side of the paint film, the above diluted paint was 0.3 x 20
Mark a 0x300 tin plate into four equal parts, increase the number of coats from the top, spray paint with different film thicknesses, set for 1 minute after finishing the coat, Immediately, baking was carried out at 160° C. for 20 minutes, and the thickest point of the coating film where no armpits appeared was measured to determine the limit film thickness at armpits.

Also, to evaluate the sagging of the paint film, the above paint adjusted to have a non-volatile content of 65% was coated on a 1100 x 300 square glass plate at a rate of 0.152.
After painting with a mill applicator, it was set horizontally for 3 minutes, then stood upright for 15 minutes, and immediately baked at 160°C for 20 minutes while standing upright, and the state of the sauce was observed.

These results are shown in Table-1.

Comparative Example 1 Melamine resin (Synthesis Example 6 instead of H) in Example 1
A white paint (2) was prepared at the same mixing ratio using the melamine resin (I[+) synthesized in Example 1, diluted in the same manner as in Example 1, and painted under the same conditions to determine the side effects, sagging, and coating film performance. was evaluated. The results are shown in Table-1.

Example 2 In Example 1, a white paint was prepared using the melamine resin (II) synthesized in Synthesis Example 5 instead of the melamine resin (1) at the same blending ratio, and diluted in the same manner as in Example 1. The paint was painted under the same conditions, and the wrinkles, sagging, and paint film performance were evaluated. The results are shown in Table-1.

Comparative Example 2 A white paint (3) was prepared at the same blending ratio using the melamine resin (■) synthesized in Synthesis Example 7 instead of the melamine resin (1) in Example 1, and diluted in the same manner as in Example 1. hand,
Painting was performed under the same conditions, and the underarm, sagging, and paint film performance were evaluated. The results are shown in Table-1.

Example 3 Vinyl polymer (■) obtained in Synthesis Example 2 (solid content 50%)
) 100 parts, melamine resin (I) obtained in Synthesis Example 4 (
Add Tsurupetz 100 to a clear paint mixed with 36 parts (solid content 60%) and mix it in a Ford cup size 4 at 20°C.
A diluted clear paint was obtained.

The evaluation of the side of the paint film was as follows: 0.8 x 1 of the above clear paint
Mark the untreated steel plate of 00 x 300 Tsuru into 5 equal parts and increase the number of coats from the top.
The coating was spray coated with different film thicknesses, and immediately baked at 160°C for 10 minutes without setting. The rest was carried out in the same manner as in Example 1.

Also, to evaluate the sagging of the paint film, a diluting solvent consisting of 100 parts of Tsurupetz 100 and 100 parts of Tsurupetz 150 (mixed solvent made by Esso Standard Oil ■) was used to evaluate the non-volatile content of 50%.
Example 1 was carried out in the same manner as in Example 1, except for using the above-mentioned clear paint adjusted to . The results are shown in Table-1.

Comparative Example 3 In Example 3, a clear paint was prepared using the melamine resin (I[[) synthesized in Synthesis Example 6 instead of melamine resin (1), with the same blending ratio, and diluted in the same manner as in Example 3. The paint was painted under the same conditions, and the underarms and sagging were evaluated. The results are shown in Table-1.

Example 4 In Example 3, a clear paint was prepared using the melamine resin (II) synthesized in Synthesis Example 5 instead of the melamine resin (1), and the clear paint was diluted in the same manner as in Example 3. It was painted under the same conditions and evaluated for underarms and sagging. The results are shown in Table-1.

Comparative Example 4 In Example 3, the melamine resin (IV) synthesized in Synthesis Example 7 was used instead of the melamine resin (I), a clear paint was prepared with the same blending ratio, and the same was diluted as in Example 3. It was painted under these conditions and evaluated for underarms and sagging. The results are shown in Table-1.

Example 5 Polyester resin (■) obtained in Synthesis Example 3 (solid content 6
0%) 70 parts, melamine resin (I) obtained in Synthesis Example 4
(solid content 60%) 30 parts, white paint dispersed with 60 parts of titanium white, 60 parts of Tsurupetz 100, 20 parts of xylene
parts, cellosolve acetate 10 parts, n-butanol 10 parts
A diluted paint was obtained by adding a diluting solvent consisting of 50% to 100% and diluting the mixture at 20° C. in a Ford Cup-4 for 30 seconds. This paint was applied under the same conditions as in Example 1, and the underfill, sagging, and paint film performance were evaluated.

The results are shown in Table-1.

Comparative Example 5 In Example 5, a clear paint was prepared using the melamine resin (Iff) synthesized in Synthesis Example 6 instead of the melamine resin (, I) at the same blending ratio, and diluted in the same manner as in Example 5. Painting was performed under the same conditions, and the underarm, sagging, and paint film performance were evaluated. The results are shown in Table-1.

Claims (1)

[Claims] It contains a hydroxyl group-containing resin and an alkylated melamine formaldehyde resin, and the alkylated melamine formaldehyde resin has a number average molecular weight of 2000 to 5000 and an amount of active methylol groups per triazine nucleus of 0.2 to 5000.
1.5 mol, and the weight ratio of the hydroxyl group-containing resin and the alkylated melamine formaldehyde resin is 50/50 to 95.
A coating composition characterized in that: /5.