JPS5830345B2 - Thermosetting powder coating composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a low pollution thermosetting powder composition.

Recently, powder coatings have become widely used because they do not use any solvents, so there is no risk of air pollution, the coating efficiency is extremely high, and there is no fear of ignition caused by solvents.

However, powder coatings that use polyvinyl chloride, polyethylene, thermoplastic polyester, etc. as binders do not undergo three-dimensional crosslinking when heated, so they have shortcomings in solvent resistance and resistance to acids and alkalis. There were limits to its use.

On the other hand, powder coatings using thermosetting polyester as a binder are also known, but there are still many points to be improved in terms of appearance, physical properties, and chemical resistance when formed into a coating film.

On the other hand, when an epoxy resin is used, the weather resistance of the coating film is significantly inferior, and its physical properties are also unsatisfactory.

Even in acrylic resins, which have been extensively researched and developed in recent years, the blocking properties of powder coatings, the physical properties of paint films,
No material has been found that satisfies all of the conflicting requirements such as leveling properties.

In addition, there are powder coatings such as polyester and acrylic based on blocked isocyanate as a crosslinking group, but even these have drawbacks such as blocking properties of powder coatings, physical properties of the coating film, and adhesion. is the current situation.

Therefore, there is currently a strong demand for a powder coating that has good stability such as anti-blocking properties and good coating film performance.

The present invention has been made to improve the drawbacks of the prior art as described above.

That is, the present invention is directed to a compound having a boiling point of 110° C. or higher and having isocyanate groups blocked with alcohols, etherified alcohols, lactams, or oximes at both ends, and a number average molecular weight of 1.2 with a number average molecular weight of 1000 to 3000.
- An acrylic compound mainly composed of polybutadiene (I) and a (meth)acrylic acid ester of 5 to 30% by weight of a hydroxyalkyl ester monomer of (meth)acrylic acid and 95 to 70% by weight of other vinyl monomers. (I) and (n) have a ratio of blocked incyanate groups of (I) to hydroxyl groups of (III) from 4/10 to
It relates to a thermosetting powder coating composition characterized in that the ratio is 15/10 and the resulting mixture has a softening point of 80 to 160°C.

In other words, the present invention combines a hydroxyl group-containing acrylic copolymer with excellent chemical resistance and weather resistance, and an inorganic compound blocked with alcohols, etherified alcohols, lactams, and oximes having a boiling point of 110°C or higher. By using flexible 1,2-polybutadiene with cyanate groups at both ends as an essential component, it has excellent blocking resistance and improves the physical and chemical properties of the coating, especially hardness, bendability, and resistance. The objective is to provide a powder coating composition with excellent impact resistance, adhesion, water resistance, and chemical resistance.

Furthermore, it is characterized by using both a reaction between a blocked isocyanate group and a hydroxyl group and an oxidative polymerization reaction due to a double bond as a crosslinking reaction group component.

The acrylic copolymer (6) used in the present invention contains 5 to 30% by weight of a hydroxyalkyl ester of acrylic acid or methacrylic acid [hereinafter referred to as hydroxyalkyl ester of (meth)acrylic acid] monomer, and an acrylic It is obtained by copolymerizing 95 to 70% by weight of other vinyl monomers such as acid esters, methacrylic esters, acrylic acid, methacrylic acid, styrene, acrylamide, acrylonitrile, and vinyl acetate.

Examples of the hydroxyalkyl ester monomer of (meth)acrylic acid include 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 2-hydroxypropyl acrylate, and 2-hydroxypropyl methacrylate.

Further, examples of the acrylic esters include methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, etc., and examples of the methacrylic esters include methyl methacrylate, ethyl methacrylate, methacrylate, etc. Examples include butyl methacrylate, stearyl methacrylate, and benzyl methacrylate.

In the acrylic copolymer of the present invention, the amount of hydroxyalkyl ester monomer of (meth)acrylic acid is 5% by weight.
If it is less than 30% by weight, the crosslinking of the acrylic copolymer will not be sufficient, resulting in poor solvent resistance and chemical resistance.On the other hand, if it is used in excess of 30% by weight, the acrylic copolymer will not only become expensive but also brittle. This is inappropriate as it tends to result in

The acrylic copolymer of the present invention is synthesized by ordinary solution polymerization using an aromatic hydrocarbon, acetate, or ketone as a solvent, but it may also be synthesized by emulsion polymerization, suspension polymerization, bulk polymerization, etc.

Furthermore, in order to improve the blocking resistance near room temperature (40°C) and the fluidity (flowability) at high temperatures, the copolymer has a suitable number average molecular weight of 100 to 5000, and a softening temperature of 90 to 160. It is desirable that the temperature is ℃.

For the production of 1,2-polybutadiene (I) containing blocked isocyanate groups, the number average molecular weight is 1000 to 30.
1,2-polybutadiene containing hydroxyl groups at both 0'00 ends is used.

In order to obtain 1,2-polybutadiene having incyanate groups at both ends, the diisocyanate to be reacted with the hydroxyl group of the 1,2-polybutadiene is 2,4-12,
Examples include 6-, toluene diisocyanate, xylylene diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, 4,41-diphenyl diisocyanate, and 5-naphthalene diisocyanate, but preferably two incyanates in one molecule. Those having different reactivity of the groups are suitable for use, and a polybutadiene resin having incyanate groups at both terminals can be easily obtained by a conventional reaction method using an acetic acid ester or the like as a solvent.

Note that a resin obtained by reacting 1,2-polybutadiene having a number average molecular weight of 1000 and having hydroxyl groups at both ends with toluene diisocyanate is also commercially available, and such a resin may be used.

The 1,2-polybutadiene of these incyanates at both ends is blocked with alcohols, etherified alcohols, lactams, oximes, etc. having a boiling point of 110° C. or higher.

In the present invention, acids or amines that dissociate at 180° C. or higher and remain in the coating film even after dissociation and adversely affect the coating film are not suitable for use.

Further, in the present invention, pigments, fillers, various additives, etc. may be melt-kneaded at around 110°C, and therefore phenols, imidazoles, etc., which dissociate at around 100°C, are also not preferred.

Therefore, alcohols, etherified alcohols, lactams, and oximes are used, but in order to prevent undesirable phenomena such as foaming when the blocking agent evaporates from the coating after dissociation, is over 110℃,
Desirably, it is blocked with a compound having a boiling point of 125° C. or higher to enable coating to a film thickness of about 100 microns.

These blocking agents are selected to have such properties that they gradually evaporate during baking or do not pose any problem even if they remain in the coating film.

The alcohols include benzyl alcohol; the etherified alcohols include ethyl, cellosolve, butyl, and cellosolve; the lactams include ε-caprolactam; and the oximes include cyclohexanone oxime, cyclopentanone oxime, and methyl isobutyl ketone oxime. Can be mentioned.

Moreover, these blocking agents may be used in combination.

Blocked polybutadiene obtained by blocking 1,2-polybutadiene containing incyanate at both terminals with the above-mentioned blocking agent is usually prepared by blocking tertiary amines such as triethylamine and tributylamine, dibutyl chloride, etc. in a solution of ethyl acetate, butyl acetate, etc. - Easily obtained at 60-90°C using an organometallic compound such as dilaurate as a catalyst.

The thus obtained blocked polybutadiene solution is mixed with the acrylic copolymer solution and then isolated as powder particles by precipitation using a precipitant such as hexane or by spray drying or the like.

The mixing ratio of the acrylic copolymer and blocked polybutadiene is a blocked incyanate group/hydroxyl group ratio of 4.
/10 to 15/10, preferably 5/10 to 10/
Up to 10 is appropriate.

When the isocyanate content is less than this ratio of 4/10, crosslinking becomes insufficient and chemical resistance, solvent resistance, and water resistance deteriorate.

On the other hand, when there are more isocyanate groups than 15/IQ,
This is undesirable because the rubber-like properties increase, the resulting powder tends to stick, and the condition of the coated surface deteriorates.

The most important thing is that these mixed and isolated powder coating compositions have a softening temperature of 80 to 160°C in order to improve blocking resistance and maintain good leveling properties of the coating film.
In order to obtain a powder that is large and has good storage stability at 40°C,
The composition of the acrylic copolymer and the mixing ratio with polybutadiene must be determined.

A crosslinking reaction promoter or a dissociation catalyst can be added to the resulting coating composition, but in the case of a reaction between a blocked isocyanate group and a hydroxyl group, triethylamine,
Tertiary amines represented by morpholine, bismuth nitrate,
Organometallic compounds such as dibutyl tin dilaurate are usually used in an amount of 1% by weight or less based on the non-volatile content of the paint.

If the amount exceeds 1% by weight, the reaction occurs rapidly, causing undesirable properties such as shrinkage of the coated surface and foaming caused by the dissociating agent, which is unsuitable.

On the other hand, as the oxidative polymerization accelerator for 1,2-polybutadiene in (I), a metal compound such as cobalt naphthenate or zirconium tintenate may be used in an amount of 1% by weight or less based on the non-volatile content of the paint.

If it is more than that, it is not preferable because it tends to adversely affect the physical properties and weather resistance of the coating film.

The reaction accelerator with the hydroxyl group and the oxidative polymerization accelerator accompanying the dissociation of the blocked incyanate group should be selected and used appropriately depending on the properties of the desired coating film, but they should be used in combination. It is also possible to add less than % by weight.

In addition, coloring pigments such as titanium oxide and phthalocyanine blue permanent red, extender pigments such as talc, silica and barium sulfate, and silicone surface conditioners can be mixed as necessary, as in the case of ordinary paint formulations.

These resins, reaction accelerators, and various pigments are mixed and coarsely pulverized, then melted and mixed using a heating roll, an extruder heating kneader, etc., and then cooled and pulverized.

In addition, when no pigment is used, a reaction accelerator or the like can be added to the product, which is roughly pulverized, then further finely pulverized, and used as it is.

The powdered coating composition prepared and prepared as described above was applied by a normal coating method per 150 mesh wire mesh passages.
For example, it is electrostatically applied to polished steel plates, zinc phosphate treated steel plates, etc., and is applied at a temperature of 160 to 200°C for a
Baked for minutes.

The coating film thus obtained has a smooth surface and excellent physical properties and chemical resistance.

The composition of the present invention has the advantages of acrylic copolymer (6) in hardness, flowability, and blocking resistance, and 1 in (I).
- It has the rubbery properties that are the advantage of 2-polybutadiene, and excellent results can be obtained by organically bonding these together through crosslinking.

This is because in the case of a composition in which an acrylic copolymer is simply mixed with 1,2-polybutadiene that does not contain isocyanate groups, the composition is soft and has extremely poor flexibility and chemical resistance. is also clear.

Therefore, the use of 1,2-polybutadiene (I) in which both terminals are blocked isocyanated according to the present invention is of great significance.

Hereinafter, the details of the present invention will be explained with reference to Examples.

In the examples, "parts" are expressed as "parts by weight."

Example 1 330 parts of xylene was placed in a flask equipped with a stirrer, a condenser, and a thermometer, and heated to 90°C.

To this, 100 parts of styrene, 93 parts of butyl methacrylate,
A mixture of 70 parts of butyl acrylate, 65 parts of 2-hydroxyethyl methacrylate, 2 parts of methacrylic acid, and 7 parts of α·d-azobisisobutyronitrile was added dropwise over 2.5 hours.

Thereafter, the reaction was further continued for 4 hours at the same temperature to obtain an acrylic copolymer (4).

On the other hand, polybutadiene inocyanated at both ends (NIS
SO-PB TP-1001: Nippon Soda ■Product name) 20
0 parts of ε-caprolactam, 22 parts of ε-caprolactam, 0.5 parts of dibutyltin dilaure, and 0.5 parts of tertiary-butylhydroxytoluene were reacted at 85°C for 8 hours under a nitrogen stream using the same reaction vessel as above. , blocked isocyanated polybutadiene (B) was synthesized.

222 parts of (B) were mixed with 195 parts of the above (A) and precipitated in a large amount of hexane to isolate the mixed resin.

The functional group ratio of the obtained resin composition was -10710 blocked isocyanate groups/hydroxyl groups in the acrylic copolymer.

After isolation, it was ground to 150 mesh or less using a grinder to obtain a powder coating.

The coating showed no blocking properties even after being left at 35°C for 7 days, and its softening point was 100°C.

Apply normal electrostatic powder coating to zinc phosphate treated steel plate, 1
The coating film baked at 80°C for 30 minutes had a smooth and beautiful finish.

The coating film performance was as shown in the comparative test results table described later.

Comparative Example 1 37.6 parts of a compound obtained by blocking both ends of toluene diisocyanate with ε-caprolactam was added to the first 195 parts, and the mixture was similarly isolated with hexane and pulverized to prepare a paint.

(Functional group ratio niblock isocyanate group/hydroxyl group -10
/10) The coating composition passed a blocking test at 35°C for 7 days and had a softening point of 120°C.

The performance of the coating film obtained by electrostatic powder coating and baking at 180° C. for 30 minutes is shown in the comparative test results table.

It is clear from this that the coating film of the present invention was far superior in hardness, bending resistance, impact resistance, and chemical resistance.

Example 2 The acrylic copolymer (4) synthesized in Example 1 was used.

200 parts of the above Nl5SO-PBTP-100, 23 parts of cyclohexanone oxime, 0.5 part of dibutyltin dilaure, and 0.5 part of tert-butylhydroxytoluene were reacted at 70°C for 9 hours in the same manner as in Example 1. isocyanate blocked polybutadiene (C
) was obtained.

5234 parts of Preg and 223 parts of (C) were mixed and isolated in hexane.

The ratio of the flocked isocyanate to the hydroxyl group in the acrylic copolymer is block isocyanate group/hydroxyl group = 8.4.
/10.

This resin was mixed with 140 parts of titanium oxide, a silicone surface conditioner, and 61 parts of dibutyl tin dilaurate, and kneaded at 100°C using an extruder.
Grind it into pieces smaller than mesh and paint it in the same way as in Example 1.
Baked at 5°C for 30 minutes.

The powder coating showed no blocking property even after being left at 35°C for 7 days, and its softening point was 95°C.

As for the coating film performance, as shown in the comparison test results table, it had a good appearance and showed excellent results in hardness, bending tests, etc.

Example 3 The acrylic copolymer synthesized in Example 1 was used.

1,2-polybutadiene containing hydroxyl groups at both ends (NISSO-PB G-2000: Nippon Soda
(trade name), 25 parts of 4·l-diphenylmethane diisocyanate, 125 parts of butyl acetate, and 0.5 part of triethylamine were added, and stirring was continued under a nitrogen atmosphere for 3 hours.

Thereafter, the mixture was heated to 50° C. and the reaction was continued for 10 hours to obtain incyanated polybutadiene.

Next, 12 parts of ε-caprolactam, 0.5 part of dibutyltin dilaurate, and 0.5 part of tert-butylhydroxytoluene were added, and the reaction was continued at 85°C for 9.5 hours to obtain blocked polybutadiene (D).

150 parts of 1J and 263 parts of 0 were mixed and the mixed resin was isolated in hexane.

Functional group ratio is blocked isocyanate group/hydroxyl group -5/1
It was 0.

The isolated resin, 30 parts of phthalocyanine blue, 1 part of silicone surface conditioner, and 0.5 part of zirconium naphthenate were mixed and kneaded using an extruder, and then
It was crushed into pieces smaller than mesh.

The obtained powder coating did not block even after being left at 35°C for 7 days, and its softening point was 95°C.

After electrostatic powder coating the paint on a zinc phosphate treated steel plate,
The performance of the coating film obtained by baking at 180° C. for 30 minutes is shown in the comparative test results table.

Example 4 165 parts of xylene and 165 parts of butyl acetate were placed in a flask equipped with a stirrer, a condenser, and a thermometer, and heated to 95°C.

A mixture consisting of 150 parts of styrene, 52.5 parts of methyl methacrylate, 78 parts of butyl acrylate, 49.5 parts of dihydroxyethyl methacrylate, and 7 parts of α·α'-azobisisobutyronitrile was added over 2.5 hours. dripped.

Thereafter, the reaction was further carried out at 90 to 95°C for 4 hours to synthesize an acrylic copolymer (5).

The NlSO-PBTP-1 was prepared in the same manner as in Example 1.
001200 parts, ethylene glycol monoethyl ether 17.5 parts, dibutyl tin dilaurate 0.5
1 part and 0.5 part of tert-butylhydroxytoluene were reacted to form an isocyanate-blocked polybutadiene (
) was obtained.

186 parts of □□□ and 18.5 parts of (F12) were mixed and the mixed resin was isolated in hexane.

The functional group ratio of the obtained resin is blocked isocyanate group/
The ratio of hydroxyl groups was 14/10.

The resin was mixed with 120 parts of titanium oxide, 1 part of a silicone surface conditioner, and 0.5 part of dibutyltin dilaure, and passed through an extruder to form a powder of 150 mesh or less.

This powder composition passed the anti-blocking test at 3°C for 7 days and had a softening point of 90°C.

The performance of the coating film obtained by baking at 180° C. for 20 minutes after application as in each of the above Examples is shown in the comparative test results table.

Comparative Example 2 1,2-polybutadiene (NIS) was added to 186 parts of (8) above.
A similar paint was prepared by mixing 100 parts of SO-PB B-1000 Nippon Soda (trade name).

The paint had a tendency to block slightly after being heated at 35°C for 7 hours, and its softening point was 82°C.

The performance of the coating film obtained by baking it at 180° C. for 30 minutes after coating it on the object to be coated, as in each of the above Examples, is shown in the comparative test results table.

As a result, the chemical resistance, solvent resistance, and water resistance were clearly poor, and the flexibility and hardness were also inferior to those of the present invention.

Example 5 The same acrylic copolymer as in Example 4 was used.

Cyclohexanone oxime 12 was added to 250 parts of incyanated polybutadiene solution synthesized according to Example 3.
7 parts, 0.5 parts of dibutyl tin dilaurate, and 0.5 parts of tert-butyl hydroxytoluene.
The reaction was carried out at 0°C for 8 hours to obtain incyanate-blocked polybutadiene (G).

134 parts of iJ and 263 parts of (G) were mixed, and the mixed resin was precipitated in hexane, separated and dried.

The functional group ratio is blocked isocyanate group/hydroxyl group = 10/
It was 10.

Add 1 part of silicone surface conditioner and dibutyl to the mixed resin.
Chin dilaurate 05 parts, zirconium naphthenate 0
．． 5 parts were mixed and ground to obtain a powder composition of 150 mesh or less.

Even when the composition was left at 35°C for 7 hours, no blocking occurred and the softening point was 92°C.

Then, after electrostatic powder coating on the zinc phosphate treated board, it was heated to 200°C.
The coating film obtained after baking for 0 minutes was smooth and exhibited excellent performance as shown in the comparative test results table.

Hardness: According to JIS-5400 6.14 Adhesion: Cut 100 goblets of 17n11L each in the vertical and horizontal directions, and the remaining number after peeling off the cellophane tape is shown.

Impact resistance: According to JIS-5400 6.13 (50
0fXX"×crrL) Boiling water resistance: Judging the coating film with the naked eye after being immersed in water for 8 hours.

Flexibility: According to JIS-5400 6.15 (10
關φ) Film thickness: Measured using an electromagnetic film thickness meter.

The solvent-resistant Niratsuka Thinner was constantly soaked in absorbent cotton and brought into contact with the paint film for 15 minutes.

Alkali resistance: Judging the coating film with the naked eye after immersing it in a 5% NaOH aqueous solution for 24 hours.

Acid resistance: Visual judgment of coating film after immersion in 5% H2SO4 aqueous solution for 24 hours.

In the table, ○ indicates no abnormality, △ indicates slightly bad, and × indicates very bad.

From the comparative test results table, it is clear that the coating film obtained from the composition of the present invention has both hardness and flexibility, and also has excellent chemical resistance and water resistance.

Claims (1)

[Claims] 1,2-polybutadiene (I) having a boiling point of 1110°C or higher and having isocyanate groups blocked with alcohols, etherified alcohols, lactams, or oximes at both ends and a number average molecular weight of 1000 to 3000; , an acrylic copolymer (9) mainly composed of a (meth)acrylic acid ester of 5 to 30% by weight of a hydroxyalkyl ester monomer of (meth)acrylic acid and 95 to 70% by weight of another vinyl monomer; The ratio of the blocked isocyanate group of (I) to the hydroxyl group of (6) is from 4/10 to 15/10, and the softening point of the resulting mixture is 80-16
A thermosetting powder coating composition characterized by a temperature of 0°C.