JP2002206070A - Ultraviolet curing powder coating composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an ultraviolet curing powder composition having excellent ultraviolet curability and capable of forming a film having excellent adhesion, water and chemical resistances, etc. SOLUTION: This ultraviolet curing powder coating composition is characterized by containing a urethane resin obtained by reacting a carboxy group in a urethane resin with an epoxy group in a glycidyl group-containing (meth) acrylate and further reacting the resultant hydroxy group formed by the reaction with an isocyanate group in an isocyanate group-containing (meth)acrylate as a binder component.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an ultraviolet-curable powder coating composition.

[0002]

2. Description of the Related Art Powder coatings have been spotlighted as environment-friendly coatings that contain little organic solvent and thus have a small amount of volatile components, and as recycled coatings that allow excess powder coatings to be recovered and reused.

[0003] A powder coating is formed by applying a powder to an object to be coated by a coating method such as an electrostatic coating method, and then heating and fusing to form a continuous coating film. Thermosetting powder coatings are used in applications where physical properties such as chemical resistance are required. In the case of a thermosetting powder coating, when the powder is heated and melted, the powder is formed into a coating film, and a thermosetting reaction proceeds to harden the coating film.

[0004] At present, powder coatings generally used are thermosetting powder coatings as described above, but depending on the use of the powder coating, an ultraviolet-curing powder coating which is cured by irradiation with ultraviolet light. May be required. Conventional UV-curable powder coatings are photopolymerizable by reacting isocyanate groups or glycidyl groups with hydroxyl or carboxyl groups present in resins such as acrylic resins, urethane resins, vinyl resins, and epoxy resins. It is known that a (meth) acryl group which is a functional group is introduced (Japanese Unexamined Patent Publication No. 11-511201, Japanese Unexamined Patent Publication No. Hei 8-30).
1957).

[0005]

However, such a conventional UV-curable powder coating has a problem that the adhesion of the coating film to an object to be coated, water resistance, chemical resistance and the like are insufficient. was there.

An object of the present invention is to provide a UV-curable powder coating composition which is excellent in UV-curability and can form a coating film having excellent chemical resistance such as adhesion, water resistance, acid resistance and alkali resistance. To provide things.

[0007]

The ultraviolet-curable powder coating composition of the present invention is characterized in that a carboxyl group (carboxylic acid group) in a urethane resin is substituted with an epoxy group in a glycidyl group of a glycidyl group-containing (meth) acrylate. The reaction is characterized by containing, as a binder component, a urethane resin obtained by further reacting a hydroxyl group generated by this reaction with an isocyanate group of an isocyanate group-containing (meth) acrylate.

In the present invention, a glycidyl group-containing (meth) acrylate is reacted with a carboxyl group in a urethane resin to introduce a first (meth) acrylate group.
Further, isocyanate group-containing (meth) acrylate is reacted to introduce a second (meth) acrylate group. Therefore, two photopolymerizable functional groups are introduced using one carboxyl group in the urethane resin. For this reason, since it has many photopolymerizable functional groups as compared with the binder component of the conventional ultraviolet curable powder coating material, it has excellent ultraviolet curability. Therefore, a coating film excellent in water resistance, chemical resistance, and the like can be formed.

Further, in the present invention, since a urethane resin is contained as a binder component, good adhesion to an object to be coated can be obtained by urethane bonds contained in the resin skeleton. The urethane resin in the present invention includes not only a resin having a urethane bond in the main chain of the resin, but also a modified urethane resin in which a urethane bond is introduced into another resin such as a polyester resin.

In the present invention, the glycidyl group-containing (meth) acrylate to be reacted with the carboxyl group in the urethane resin is not particularly limited as long as it has a glycidyl group and a (meth) acrylate group. Glycidyl methacrylate and glycidyl acrylate are exemplified.

In the present invention, an isocyanate group-containing (meth) acrylate is further reacted with a hydroxyl group produced by the reaction between the carboxyl group and the epoxy group in the glycidyl group. Isocyanate group-containing (meth)
The acrylate is not particularly limited as long as it has an isocyanate group and a (meth) acrylate group. For example, (meth) acryloyloxyalkyl isocyanate such as (meth) acryloyloxyethyl isocyanate and (meth) acryloyl And isocyanate. Another example is an adduct compound obtained by reacting one isocyanate group of a diisocyanate compound with a hydroxyl group of a hydroxyl group-containing (meth) acrylate group. As the diisocyanate compound, diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, tolylene diisocyanate, naphthalene diisocyanate, p-phenylene diisocyanate,
Xylylene diisocyanate, hydrogenated xylylene diisocyanate, and the like. Examples of the hydroxyl group-containing (meth) acrylate include hydroxyethyl (meth) acrylate, hydroxymethyl (meth) acrylate, and hydroxybutyl (meth) acrylate.

An ultraviolet-curable powder coating composition according to another aspect of the present invention is characterized by containing, as a binder component, a urethane resin having a photopolymerizable functional group having a structure represented by the following formula (1) at the terminal. And

[0013]

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Wherein R ₁ is hydrogen or an alkyl group having 1 to 3 carbon atoms, and R ₂ is a group represented by the following formula (2) or (3)
Wherein n is an integer of 1 to 4. )

[0015]

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(Where R ₃ is hydrogen or a group having 1 to 3 carbon atoms)
And R ₄ is an alkyl group having 1 to ₄ carbon atoms. )

[0017]

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(Where R ₅ is an aliphatic or aromatic hydrocarbon group, R ₆ is hydrogen or an alkyl group having 1 to 3 carbon atoms, and m is an integer of 1 to 4) The urethane resin having a photopolymerizable functional group having the structure of the formula (1) can be produced, for example, in the same manner as the urethane resin in the present invention. That is, a glycidyl group-containing (meth) is added to the carboxyl group in the urethane resin.
After reacting the epoxy group of the acrylate, it can be obtained by reacting the hydroxyl group generated by this reaction with the isocyanate group of the (meth) acrylate containing an isocyanate group.

Specifically, as shown in the following reaction formula,
First, an epoxy group of a glycidyl group-containing (meth) acrylate is reacted with a carboxyl group in the urethane resin.

[0020]

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By the above reaction, the following structure is introduced into the carboxyl group of the urethane resin.

[0022]

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The isocyanate group of the isocyanate group-containing (meth) acrylate is reacted with the secondary hydroxyl group formed by the reaction between the carboxyl group and the epoxy group as described above.

As the isocyanate group-containing (meth) acrylate, (meth) acryloyloxyalkyl isocyanate and (meth) acryloyl isocyanate as shown below,

[0025]

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[0026]

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Adduct compounds obtained by reacting one isocyanate group of a diisocyanate compound with a hydroxyl group of a hydroxyl group-containing (meth) acrylate as described below are exemplified.

[0028]

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R ₅ in the above formulas (3) and (Formula 11) is specifically a residue obtained by removing an isocyanate group from a diisocyanate compound. By reacting the (meth) acrylate containing an isocyanate group as described above, a urethane resin having a photopolymerizable functional group having a structure represented by the above formula (1) can be obtained.

In the present invention, the urethane resin as a raw material before the reaction of the glycidyl group-containing (meth) acrylate and the isocyanate group-containing (meth) acrylate can be synthesized by a general synthesis method. For example,
After reacting a diisocyanate compound with a polyhydric alcohol to synthesize a urethane resin, a urethane resin having a carboxyl group introduced into a terminal by reacting a dicarboxylic acid compound with the urethane resin can be used. Alternatively, a urethane resin obtained by reacting a diisocyanate with a hydroxyl group of a polyester resin having a carboxyl group at a terminal to introduce a urethane bond may be used.

The amount of the carboxyl group in the urethane resin is preferably such that the acid value is 10 to 120 mgKOH / g. If the acid value is smaller than this, the amount of the carboxyl group is reduced, and the amount of the photopolymerizable functional group introduced is reduced, so that the ultraviolet curability may be too low. If the acid value is too high, a carboxyl group may remain even after the reaction of the glycidyl group-containing (meth) acrylate, and the corrosion resistance of the resin may be deteriorated.

The number average molecular weight of the urethane resin after the reaction of the glycidyl group-containing (meth) acrylate and the isocyanate group-containing (meth) acrylate is from 1,000 to 1,
It is preferably about 0000, more preferably 2,000 to 10,000, and even more preferably 350 to 10,000.
0 to 6000. If the number average molecular weight is too low, the blocking resistance may be inferior, and if the number average molecular weight is too high, the flow properties when the powder coating is heated and melted may be reduced.

In the present invention, the reaction condition for reacting the carboxyl group in the urethane resin with the epoxy group of the glycidyl group-containing (meth) acrylate is a general acid-
The reaction can be performed in the same manner as the epoxy reaction. The reaction temperature is, for example, 100 to 160 ° C. Further, it is preferable to use a general catalyst used for an acid-epoxy reaction. For example, amine-containing catalysts such as phenylimidazoline, phosphines such as triphenylphosphine,
A catalyst such as a quaternary ammonium salt such as tetrabutylammonium bromide can be used. The amount added
For example, it is 0.01 to 1.0% by weight.

At the time of the reaction, it is preferable to add a polymerization inhibitor. As such a polymerization inhibitor, a radical polymerization inhibitor such as phenothiazine, hydroquinone, and t-butylhydroxytoluene can be used. The addition amount is, for example, 0.01 to 1.0% by weight.

The conditions for reacting the isocyanate group-containing (meth) acrylate with the hydroxyl group generated by the reaction between the carboxyl group and the epoxy group may be the same as the general hydroxyl-isocyanate reaction conditions. it can. For example, the reaction temperature is preferably about 80 to 150 ° C., and is preferably as low as possible. If necessary, a general catalyst such as a tin catalyst can be used.

The UV-curable powder coating composition of the present invention comprises
It can be produced by using a urethane resin having a (meth) acrylate group introduced as a binder component as described above and adding a photopolymerization initiator and other additives.

As the photopolymerization initiator, photopolymerization initiators generally used for ultraviolet-curable resins can be used alone or in combination of two or more. Specifically, aromatic carbonyl compounds, anthraquinone and its derivatives, thioxanthone and its derivatives, benzoin ether and its derivatives, alphageon and its derivatives,
Benzyl alkyl acetal and its derivatives, acetophenone derivatives, phosphine oxides, and the like can be mentioned. If necessary, a photosensitizer can also be used.

As other additives, additives required for powder coatings such as pigments, surface conditioners, and flow agents can be added. As a method for producing the powder coating, a general production method can be used.For example, a binder component, a photopolymerization initiator, and other additives are melt-kneaded and mixed, and then crushed and sieved. Can be manufactured. Further, a powder coating may be obtained by another manufacturing method.

The volume average particle diameter of the powder coating of the present invention is 5 to 5.
It is preferably 50 μm, and it is more preferable to carry out classification by sieving in order to adjust the particle size distribution by removing giant particles and fine particles. When used for thin film coating or three-dimensional structure coating, the volume average particle diameter is preferably 5 to 40 μm. In particular, when a thin and smooth coating film is to be obtained, the thickness is preferably 5 to 30 μm. The volume average particle diameter can be measured by a particle size analyzer (for example, Microtrac HRAX-100 manufactured by Nikkiso Co., Ltd.).

[0040]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited to the following Examples, and may be modified as appropriate without departing from the scope of the invention. It can be implemented by

(Synthesis Example 1) First step: Synthesis of polyester resin having a carboxylic acid group (carboxyl group) at the terminal 163 g of 1,6-hexanediol, 408 g of neopentyl glycol, 72 g of trimethylolpropane, 1024 g of dimethyl terephthalic acid, And 0.8 g of dibutyltin oxide were charged into a 2 liter reaction vessel, heated to 180 ° C. under a nitrogen atmosphere, and then gradually heated to 210 ° C.
Heated to ° C. As the reaction vessel, a reactor equipped with a decanter equipped with a stirrer and a water-cooled condenser, a nitrogen inlet tube, and a thermometer connected to a temperature controller was used.

Incidentally, at a point of time exceeding 150 ° C., the produced methanol began to be distilled. Thereafter, the temperature was raised to 210 ° C., and this temperature was maintained for 3 hours. Thereafter, the mixture was cooled to 150 ° C., and 343 g of phthalic anhydride was added.
gKOH / g) for 2 hours. The obtained polyester resin had an acid value of 39 (mg KOH / g), a hydroxyl value of 61.5 (mg KOH / g), and a number average molecular weight of 150.
It was 0.

Second step: Synthesis of urethane resin 381 g of the polyester resin obtained in the first step was dissolved in 282 g of butyl acetate and heated to 80 ° C. At this temperature, 17.4 g of tolylene diisocyanate (TDI) was added dropwise over 2 hours, and the reaction was continued until the absorption of isocyanate disappeared by IR analysis. As a result, a urethane bond was introduced into the resin to obtain a urethane resin. The number average molecular weight of this urethane resin was 1600. The acid value remained at 39 (mgKOH / g).

Step 3: Glycidyl methacrylate (G
Addition of MA) (Introduction of First Methacrylate Group) The urethane resin obtained in the second step was converted to a solution 13
After heating to 5 ° C. and adding 1.9 g of tetrabutylammonium bromide as a reaction catalyst and 0.4 g of hydroquinone as a polymerization inhibitor, 28.5 g of glycidyl methacrylate was added dropwise over 30 minutes. Thereafter, the temperature was maintained for 2.5 hours until the acid value became 10 (mgKOH / g). By this reaction, an epoxy group of glycidyl methacrylate was added to a carboxyl group of the urethane resin, and a methacrylate group was introduced into the urethane resin. The number average molecular weight of the obtained urethane resin was 1,700.

Fourth Step: Introduction of a Second Methacrylate Group In advance, 2-hydroxyethyl methacrylate and isophorone diisocyanate (IPDI) are reacted at a molar ratio of 1: 1 to synthesize an adduct compound. 78 g of a weight% butyl acetate solution was added dropwise to the resin solution obtained in the third step at a temperature of 85 ° C. over 2 hours. The reaction was continued until the absorption of isocyanate disappeared by IR analysis. This introduced a second methacrylate group into the resin. The acid value of the obtained resin is 10
(MgKOH / g), and the number average molecular weight was 1,850.

(Synthesis Examples 2 and 3) The procedure of Synthesis Example 1 was repeated, except that the first, second, third, and fourth stages of the reaction were carried out with the formulations shown in Table 1. A urethane resin according to the invention was synthesized. Specifically, first, a polyester resin having a carboxylic acid group (carboxyl group) at a terminal is synthesized, and a urethane bond is introduced into the polyester resin to form a urethane resin, into which the first methacrylate group and the second methacrylate group are introduced. did. The acid value and number average molecular weight of the resin obtained at each stage are as shown in Table 1.

[0047]

[Table 1]

(Synthesis Example 4) First Step: Synthesis of Urethane Resin 163 g of 1,6-hexanediol, 408 g of neopentyl glycol, 72 g of trimethylolpropane and 0.8 g of dibutyltin oxide were charged into a 2 liter reaction vessel, and nitrogen was charged. Heated to 125 ° C. under atmosphere. As the reaction vessel, a reactor equipped with a decanter equipped with a stirrer and a water-cooled condenser, a nitrogen inlet tube and a thermometer connected to a temperature controller was used.

After confirming that the contents were melted and became uniform, tolylene diisocyanate (TDI) 17.4 was obtained.
g was dropped over 3 hours and aged for 1 hour to introduce a urethane bond into the polyhydric alcohol to synthesize a urethane resin.

Second Step: Modification of Polyester Next, the temperature was cooled to 100 ° C. or less, and the urethane resin was modified with polyester by adding 1024 g of dimethyl terephthalate. The obtained polyester-modified urethane resin had an acid value of 35 (mgKOH / g) and a number average molecular weight of 1,800.

Third step: Glycidyl methacrylate (G
Addition of MA) (Introduction of First Methacrylate Group) In the same manner as in the third step of Synthesis Example 1, an epoxy group of glycidyl methacrylate was added to a carboxyl group (carboxylic acid group) of a urethane resin to introduce a methacrylate group. . The number average molecular weight of the obtained resin was 1,850, and the acid value was 5.0 (mgKOH / g).

Fourth Step: Introduction of a Second Methacrylate Group In the same manner as in the fourth step of Synthesis Example 1, the hydroxyl group formed in the third step was added to isophorone diisocyanate and hydroxyethyl methacrylate in a molar ratio of 1: 1. The adduct compound was added. The number average molecular weight of the obtained resin is 20.
The acid value was 5.0 (mgKOH / g).

(Synthesis Examples 5 and 6) The first stage, the second stage, the third stage,
Then, the reaction of the fourth step was performed to synthesize a urethane resin into which a methacrylate group was introduced.

[0054]

[Table 2]

(Synthesis Example 7) A polyester resin having a terminal carboxylic acid group was synthesized in the same manner as in the first step of Synthesis Example 1. A methacrylate group was introduced into this polyester resin in the same manner as in the third and fourth steps of Synthesis Example 1. Therefore, a resin having a methacrylate group introduced into the polyester resin was obtained. The acid value of the obtained resin is 11 (mgKOH / g), and the number average molecular weight is 1
700.

(Examples 1 to 7 and Comparative Examples 1 to 3) The resins obtained in Synthesis Examples 1 to 7 were spray-dried using a spray drier and then preliminarily mixed in the proportions shown in Tables 3 and 4. This mixture was further kneaded at 120 ° C. using a mixer (“Buscon kneader” manufactured by Buss Corp.). After kneading, the mixture was finely pulverized with an atomizer, and then sieved with a 200 mesh sieve to obtain a powder coating. The particle diameters of the obtained powder coatings are as shown in Tables 3 and 4. The particle diameters of the powder coatings shown in Tables 3 and 4 are volume average particle diameters determined by a laser light scattering method.

The resin used in Comparative Example 3 was the same as in Resin Example 1.
This is the resin finished in the third stage. Irgacure, an initiator, is an initiator manufactured by Ciba Specialty Chemical.

Using the powder coating obtained as described above, an SPC steel plate was applied by electrostatic coating to form a coating film.
The SPC steel sheet is preheated to 120 ° C. in advance, the powder coating is electrostatically coated thereon, and the powder coating is heated and melted by holding at 120 ° C. for 20 minutes, and then irradiated with 4500 mj of ultraviolet light. Cured. The film thickness of the coating film is as shown in Tables 3 and 4.

The resulting coating film was subjected to a curability evaluation test,
An adhesion evaluation test, an acid resistance test, and an alkali resistance test were performed by the following methods.・ Curability: The surface of the coating film is 20 with a cloth soaked with acetone.
The film was rubbed twice and evaluated as ○ when no change occurred in the coating film, and as X when scratched or dissolved.

Adhesion: A 1 mm square cut was made in the coating film, an adhesive tape was stuck thereon, and then peeled off to evaluate the adhesion. A sample having 100% adhesion was evaluated as ○, a sample having 80 to 50% adhesion as Δ, and a sample having less than 80% as X.

Acid resistance test: A coating film with a square cut in a square of 1 mm was immersed in a 10% sulfuric acid aqueous solution for 1 hour. When an abnormality such as peeling or swelling occurred, it was evaluated as x.

Alkali resistance test: A coating film with a square cut in a square of 1 mm was immersed in a 5% aqueous solution of sodium hydroxide for 1 hour. ○, × when abnormalities such as peeling or swelling occurred
Was evaluated.

[0063]

[Table 3]

[0064]

[Table 4]

As is clear from the results of the coating film performance tests shown in Tables 3 and 4, the coating films of Examples 1 to 7 using the ultraviolet-curable powder coating composition according to the present invention have excellent curability. It can be seen that they have excellent adhesion, acid resistance and alkali resistance. As is clear from Example 1 and Comparative Example 3, Comparative Example 3 using the urethane resin terminated in the third stage in Synthesis Example 1 did not obtain good coating performance, In Example 1 using the urethane resin of the present invention in which a methacrylate group was further introduced at a stage, good coating film performance was obtained. Further, as is apparent from the comparison between Examples 1 and 2 and Comparative Examples 1 and 2, in Examples 1 and 2 in which a urethane bond was introduced and a urethane resin was used, good adhesion to an object to be coated was exhibited. A coating has been obtained.

[0066]

According to the present invention, ultraviolet curability is excellent,
An ultraviolet curable powder coating composition capable of forming a coating film having excellent adhesion, water resistance, chemical resistance and the like can be obtained.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Tetsuro Kashino 19-17 Ikedanakacho, Neyagawa-shi, Osaka F-term in Nippon Paint Co., Ltd. (reference) 4J038 DG081 DG311 DG321 FA281 GA06 MA02 MA14 NA04 NA12 PA17

Claims (7)

[Claims] 1. A carboxyl group in a urethane resin is reacted with an epoxy group of a glycidyl group-containing (meth) acrylate, and a hydroxyl group generated by the reaction is further reacted with an isocyanate group of an isocyanate group-containing (meth) acrylate. An ultraviolet-curable powder coating composition comprising the obtained urethane resin as a binder component. 2. The isocyanate group-containing (meth) acrylate is an adduct compound obtained by reacting one isocyanate group of a diisocyanate compound with a hydroxyl group of a hydroxyl group-containing (meth) acrylate. 3. The ultraviolet-curable powder coating composition according to item 1. 3. The diisocyanate compound is at least one selected from diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, tolylene diisocyanate, naphthalene diisocyanate, p-phenylene diisocyanate, xylylene diisocyanate, and hydrogenated xylylene diisocyanate. The ultraviolet-curable powder coating composition according to claim 2, wherein 4. The ultraviolet-curable powder coating composition according to claim 1, wherein the isocyanate group-containing (meth) acrylate is (meth) acryloyloxyalkyl isocyanate or (meth) acryloyl isocyanate. 5. The ultraviolet curable powder coating composition according to claim 1, wherein the glycidyl group-containing (meth) acrylate is glycidyl (meth) acrylate. 6. An ultraviolet-curable powder coating composition comprising, as a binder component, a urethane resin having a photopolymerizable functional group having a structure represented by the following formula (1) at a terminal: Embedded image (Wherein, R ₁ is hydrogen or an alkyl group having 1 to 3 carbon atoms, R ₂ is a photopolymerizable functional group represented by the following formula (2) or (3), and n is 1 to 4) It is an integer.) (Here, R ₃ is hydrogen or an alkyl group having 1 to 3 carbon atoms, and R ₄ is an alkyl group having 1 to ₄ carbon atoms.) (Here, R ₅ is an aliphatic or aromatic hydrocarbon group, R ₆ is hydrogen or an alkyl group having 1 to 3 carbon atoms, and m is an integer of 1 to 4.) 7. The urethane resin has a number average molecular weight of 1
000 to 10,000
7. The ultraviolet-curable powder coating composition according to any one of 6.