JP2006328417A - Powder coating composition curable with actinic energy ray - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a powder coating composition having excellent storage stability and capable of forming a cured coating film having excellent curability with actinic energy rays when applied to a coating object. <P>SOLUTION: The powder coating composition curable with actinic energy rays comprises, as essential components, (A) a resin containing ≥2 oxetane functional groups in one molecule on an average and having a glass transition temperature of 40-100°C and a number-average molecular weight of 1,000-15,000, (B) a polyepoxide having a glass transition temperature of 40-100°C and (C) a photo-cationic polymerization initiator. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a novel active energy ray-curable powder coating composition.

  Conventionally, a powder coating composition has attracted attention as a coating excellent in pollution prevention and protection of the global environment because it hardly contains volatile components such as organic solvents.

  The photo cationic polymerization powder coating composition using the epoxy group-containing powder resin is superior in thermal stability to the photo radical polymerization powder coating composition using the vinyl group-containing powder resin. Good coating film formation by heating and melting after production and powder coating. However, active energy ray curable resins using photocationic polymerization of epoxy groups have the advantage that they are not affected by oxygen during curing and have recently begun to be used in many applications. There was a problem that the photosensitivity was poor compared to the linear radical polymerization.

  The present invention has been made for the purpose of developing a powder coating composition having excellent curability by active energy rays.

  The inventors of the present invention have made extensive studies to eliminate the drawbacks of the prior art. As a result, it has been found that when an oxetane functional group and an epoxy group are used in combination as a cross-linking functional group, the photosensitivity is improved, and as a result, the photocationic polymerization rate is increased, and the present invention has been completed.

  Thus, according to the present invention, (A) the following general formula (I)

(In the formula, R ₁ represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a fluorine atom, a fluoroalkyl group having 1 to 6 carbon atoms, an allyl group, an aryl group, an aralkyl group, a furyl group, or a chenyl group). A resin having an average of two or more oxetane functional groups represented by the formula: a glass transition temperature in the range of 40 to 100 ° C., and a number average molecular weight in the range of 1,000 to 15,000, An active energy ray-curable powder coating composition (hereinafter referred to as “B”) containing a polyepoxide having a glass transition temperature in the range of 40 to 100 ° C. and (C) a cationic photopolymerization initiator as essential components This is referred to as a “powder coating composition”).

  The active energy ray-curable powder coating composition of the present invention is excellent in storage stability and can form a cured coating film excellent in curability by active energy rays when applied to an object.

  The powder coating composition of the present invention will be described below.

  The powder coating composition is characterized by comprising, as main resin components, a resin (A) having a oxetane functional group represented by the above formula (I) as a crosslinking functional group and a polyepoxide (B).

Oxetane functional group-containing resin (A): In the definition of R ₁ in the formula (I), the “alkyl group having 1 to 6 carbon atoms” may be linear or branched, for example, methyl , Ethyl, n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, n-hexyl and the like. The “C 1-6 fluoroalkyl group” is a group in which at least one hydrogen atom of the alkyl group is substituted with a fluorine atom, and examples thereof include fluoropropyl, fluorobutyl, trifluoropropyl and the like. The “aryl group” may be monocyclic or polycyclic, and the aromatic ring may be substituted with one or more alkyl groups having 1 to 6 carbon atoms, such as phenyl, toluyl , Xylyl, naphthyl and the like. The “aralkyl group” is an aryl-alkyl group in which the aryl part and the alkyl part have the above-mentioned meanings, and examples thereof include a benzyl group and a phenethyl group.

R ₁ is particularly preferably an alkyl group having 1 to 6 carbon atoms, particularly 1 to 4 carbon atoms, such as methyl or ethyl.

  The oxetane functional group is bonded to the side chain or main chain of the resin (A) through a bond containing oxygen such as an ether bond, an ester bond, a urethane bond, or a hydrocarbon containing one or more of these bonds. It is preferable.

  The oxetane functional group can be present in the resin (A) at an average of at least about 2 or more, preferably an average of about 3 to about 30 per molecule. When the average number of oxetane functional groups is less than about 2 per molecule, the active energy ray curability is lowered, which is not preferable.

  The oxetane functional group-containing resin (A) has a glass transition temperature of 40 to 100 ° C, preferably 50 to 80 ° C, and a number average molecular weight of 1,000 to 15,000, preferably 3, Each having a range of 000 to 10,000. When the glass transition temperature is lower than 40 ° C., the coating has poor blocking resistance. On the other hand, when the glass transition temperature is higher than 100 ° C., the finished appearance (smoothness, etc.) of the coating film is inferior. When the number average molecular weight is less than 1,000, the blocking resistance of the paint and the weather resistance of the coating film are inferior. On the other hand, when the number average molecular weight exceeds 15,000, the finished appearance of the coating film is inferior. The glass transition temperature (Tg, ° C) described above is obtained as follows. That is, using a differential scanning calorimeter (DSC), about 10 mg of a sample weighed in a sample pan is heated to 100 ° C., held for 10 minutes, and then rapidly cooled to −20 ° C. Thereafter, the temperature is raised at a rate of 10 ° C./min to determine the glass transition temperature.

  The oxetane functional group-containing resin (A) contains an average of two or more oxetane functional groups in one molecule, has a glass transition temperature in the range of 40 to 100 ° C., and a number average molecular weight of 1,000 to 15,000. As long as it is within the range, it can be used without particular limitation. Specifically, for example, polyester resins, acrylic resins, alkyd resins, and modified resins thereof are included.

  Representative examples of the method for introducing an oxetane functional group into the above-described resin are shown below.

  (1) Polybasic acids (for example, (anhydrous) phthalic acid, isophthalic acid, terephthalic acid, (anhydrous) maleic acid, adipic acid, azelaic acid, etc.) and polyhydric alcohols (for example, ethylene glycol, neopentyl glycol, propylene glycol) 1,6-hexanediol, glycerin, pentaerythritol, trimethylolpropane, etc.), and if necessary, a mixture of monobasic acids is esterified in the presence of an esterification catalyst to produce a polycarboxylic acid polyester resin. The following formula derived from the triol component in the polyester resin by esterifying the resulting resin with a triol component such as trimethylolpropane

  A polyester resin having a cyclic polycarbonate is produced by introducing a 1,3-diol residue of the above, followed by reaction of the residue with diethyl carbonate, followed by decarboxylation.

  (2) After reacting triol such as trimethylolpropane with diethyl carbonate to produce a hydroxyl group-containing cyclic carbonate, decarboxylation is performed to give a hydroxyl group at one end and an oxetane functional group at the other end. Complementary functional groups such as isocyanate groups, lower alkoxy groups (for example, methoxy, ethoxy) that produce hydroxymethyl oxetane and then react complementary to the hydroxyl group of the oxetane but do not substantially react with the oxetane group , A resin obtained by reacting a resin having a lower alkoxycarbonyl group (for example, methoxycarbonyl, ethoxycarbonyl) or the like (for example, an acrylic resin having an isocyanate group, a polyester resin having a methyl ester group, or the like).

(3) an unsaturated monomer containing the functional group and radical polymerizable unsaturated group (for example, acryloyl group, methacryloyl group, vinyl group, etc.) that reacts complementarily with the 3-ethyl-3-hydroxymethyloxetane; To produce an unsaturated monomer having a radically polymerizable unsaturated group at one end of the molecule and an oxetane functional group at the other end, then the unsaturated monomer, if necessary, other radically polymerizable unsaturated Monomer (for example, C ₁ -C ₂₄ alkyl of (meth) acrylic acid such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, etc. Or cycloalkyl esters; 2-hydroxypropyl (meth) acrylate, potassium Rorakuton modified (meth) C ₂ -C ₈ hydroxyalkyl esters of (meth) acrylic acid such as ethyl hydroxyethyl acrylate; (meth) carboxyl group-containing unsaturated monomers such as acrylic acid; styrene, alpha-methyl styrene, vinyl Aromatic vinyl compounds such as toluene; fluorine-containing unsaturated monomers such as perfluorobutylethyl (meth) acrylate and perfluoroisononylethyl (meth) acrylate; polymerizable amides such as (meth) acrylamide; (meth) Polymerized nitriles such as acrylonitrile) and radical (co) polymerized.

  (4) A product obtained by reacting the hydroxyl group-containing cyclic carbonate with a resin having the complementary functional group to introduce the cyclic carbonate into the resin, and then decarboxylating the cyclic carbonate to convert it into an oxetane functional group.

  (5) reacting the hydroxyl group-containing cyclic carbonate with the functional group reacting in a complementary manner and an unsaturated monomer containing a radical polymerizable unsaturated group to react with the radical polymerizable unsaturated group and the other at one end of the molecule; An unsaturated monomer having a cyclic carbonate at the terminal is produced, and then the unsaturated monomer is radically (co) polymerized with the above-mentioned other radical polymerizable unsaturated monomer, if necessary, to form a cyclic carbonate in the (co) polymer. After introducing the cyclic carbonate, the cyclic carbonate is decarboxylated and converted into an oxetane functional group.

Polyepoxide (B): The polyepoxide (B) used in the present invention contains an average of about 2 or more, preferably about 2 to 10 epoxy groups per molecule, and has a glass transition temperature in the range of 40 to 100 ° C. It is resin which is. If the number of the epoxy groups is less than about 2 on average in one molecule, the active energy ray curability is lowered, which is not preferable. On the other hand, when the glass transition temperature is lower than 40 ° C., the blocking resistance of the paint is inferior.

  The glass transition temperature (Tg, ° C) described above is determined by the above-described differential scanning calorimeter (DSC).

  The polyepoxide (B) has a number average molecular weight of about 120 to 200,000, preferably about 240 to 80,000. When the number average molecular weight is less than about 120, the durability of the coating film is lowered. On the other hand, when the number average molecular weight exceeds about 200,000, there is a disadvantage that the coating workability is inferior.

  Specific examples of the polyepoxide (B) include, for example, glycidyl group-containing ethylenically unsaturated monomers such as glycidyl (meth) acrylate, methyl glycidyl (meth) acrylate, and allyl glycidyl ether, and 3,4-epoxycyclohexylmethyl (meth) acrylate. It is obtained by radical (co) polymerizing an epoxy group-containing ethylenically unsaturated monomer such as an alicyclic epoxy group-containing ethylenically unsaturated monomer such as the above and other radical polymerizable unsaturated monomers as necessary. (Co) polymers; glycidyl ether compounds such as diglycidyl ether, 2-glycidylphenyl glycidyl ether, 2,6-diglycidylphenyl glycidyl ether; Si group-containing compounds; dicyclopentadiene dioxide, bis (2,3-epoxycyclopentyl) ether, epoxycyclohexenecarboxylic acid ethylene glycol diester, bis (3,4-epoxycyclohexylmethyl) adipate, 3,4-epoxycyclohexylmethyl- Alicyclic epoxy group-containing compounds such as 3,4-epoxycyclohexanecarboxylate and 3,4-epoxy-6-methylcyclohexylmethyl-3,4-epoxy-6-methylcyclohexanecarboxylate; bisphenol A type epoxy resin; bisphenol F type epoxy resins; cresol novolac type epoxy resins; phenol novolac type epoxy resins and the like are included.

  The blending ratio of the oxetane functional group-containing resin (A) and the polyepoxide (B) is about 0.1 to 0.1 parts by weight of the polyepoxide (B) based on 100 parts by weight of the oxetane functional group-containing resin (A). The preferred range is 100 parts by weight, preferably in the range of about 1-50 parts by weight.

Photocationic polymerization initiator (C): The photocationic polymerization initiator (C) used in the present invention is a compound that generates a cation by an active energy ray and initiates cationic polymerization of an oxetane functional group and an epoxy group, Examples thereof include hexafluoroantimonate salts, pentafluorohydroxyantimonate salts, hexafluorophosphate salts, hexafluoroarsenate salts and other photocationic polymerization initiators represented by the following formulas (II) to (XVI). .

_{^{Ar 2 I + · X - (}} II)
[In the formula, Ar represents an aryl group such as a phenyl group, and X ⁻ represents PF ₆ ⁻ , SbF ₆ ⁻ , or AsF ₆ ⁻ ]
Ar ₃ S ⁺ · X ⁻ (III)
[Wherein Ar and X − have the same meaning as above]

[Wherein R ² represents an alkyl group having 1 to 12 carbon atoms or an alkoxy group having 1 to 12 carbon atoms, n represents an integer of 0 to 3, and X ⁻ has the same meaning as described above]

[Wherein Y ⁻ represents PF ₆ ⁻ , SbF ₆ ⁻ , AsF ₆ ⁻ or SbF ₅ (OH) ⁻ ]

[Wherein X ⁻ has the same meaning as above]

[Wherein X ⁻ has the same meaning as above]

[Wherein X ⁻ has the same meaning as above]

[Wherein R ³ is an aralkyl group having 7 to 15 carbon atoms or an alkenyl group having 3 to 9 carbon atoms, R ⁴ is a hydrocarbon group or hydroxyphenyl group having 1 to 7 carbon atoms, and R ⁵ is an oxygen atom. Or an alkyl group having 1 to 5 carbon atoms which may contain a sulfur atom, and X ⁻ has the same meaning as described above.

[Wherein R ⁶ and R ⁷ each independently represents an alkyl group having 1 to 12 carbon atoms or an alkoxy group having 1 to 12 carbon atoms]

[Wherein R ⁶ and R ⁷ have the same meaning as above]

Commercially available products of the photocationic polymerization initiator (C) include, for example, Cyracure UVI-6970, UVI-6990 (all of which are manufactured by Union Carbide, USA), Irgacure 264 (Ciba Geigy), CIT-1682 (Japan). Soda Co., Ltd.). Among the above compounds, salts having PF ₆ − as an anion are preferable from the viewpoint of toxicity and versatility.

  The blending ratio of the above cationic photopolymerization initiator (C) is generally 0.01 to 20 parts by weight with respect to 100 parts by weight (based on solid content) of the total amount of the resin (A) and the polyepoxide (B). The amount is preferably 0.05 to 15 parts by weight, more preferably 0.1 to 10 parts by weight. If the blending ratio is less than 0.01 parts by weight, curability, workability and the like are lowered. Conversely, if it exceeds 20 parts by weight, storage stability, finished appearance of the cured product, yellowing and the like are lowered, which is not preferable. .

Powder coating composition: The powder coating composition of the present invention includes, for example, an initiator (C) and, if necessary, other additives in an organic solvent solution of resin (A) and an organic solvent solution of polyepoxide (B). In the case of blending, a solid powder coating composition can be obtained by removing the solvent, and then finely pulverizing with a pulverizer to produce a powder coating, and the resin (A) and polyepoxide ( When B) is a solid powder resin, after blending resin (A), polyepoxide (B), initiator (C) and other additives as required, dry blend with a mixer, Next, the powder coating material can be produced by heating, melt-kneading, cooling, and finely pulverizing. The average particle size of the powder coating composition is about 1 to 100 microns, preferably about 5 to 60 microns.

  Other additives include, for example, color pigments, fillers, fluidity modifiers, antiblocking agents, UV absorbers, UV stabilizers, surface stabilizers, anti-waxing agents, antioxidants, charge control agents, and curing accelerators. Agents and other resins.

  The active energy ray-curable powder coating composition of the present invention is powder-coated by a method such as electrostatic powder coating (for example, corona charging type, friction charging type) or fluidized immersion coating on an object to be coated. A film is formed by heating and melting at a temperature of ˜160 ° C. for 1 to 10 minutes. By irradiating this coating film with ultraviolet rays, a cured coating film can be formed by cationic polymerization.

  As the ultraviolet irradiation source, a mercury lamp, a xenon lamp, a carbon arc, a metal height lamp, sunlight or the like can be used. Although the irradiation conditions of ultraviolet rays are not particularly limited, it is preferable to irradiate light containing ultraviolet rays within a range of 150 to 450 nm for several seconds or more in air or in an inert gas atmosphere. In particular, when irradiating in air, it is preferable to use a high-pressure mercury lamp.

  Hereinafter, the present invention will be described more specifically with reference to examples. “Parts” and “%” are based on weight.

Production Examples 1-3
A reactor vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and dropping device was charged with 85 parts of toluene, heated to 110 ° C. while blowing nitrogen gas, and then the monomer mixture shown in Table 1 from the dropping device. A solution in which 4 parts of 2,2′-azobis (2-methylbutyronitrile) was dissolved was added dropwise over about 3 hours. After completion of the dropwise addition, the reaction was terminated by leaving it at 110 ° C. for 2 hours. Thereafter, toluene was removed by distillation under reduced pressure and cooled to obtain acrylic resins (a) to (c). Table 1 shows the glass transition temperature of the obtained resin by DSC measurement, the number average molecular weight by GPC (gel permeation chromatography) measurement, and the number of functional groups in one molecule.
Production Example 4
A reactor vessel equipped with a thermometer, thermostat, stirrer, reflux condenser and dropping device was charged with 85 parts of toluene, heated to 110 ° C. while blowing nitrogen gas, and then the monomer mixture shown in Table 1 from the dropping device. A solution in which 4 parts of 2,2′-azobis (2-methylbutyronitrile) was dissolved was added dropwise over about 3 hours. After completion of dropping, the mixture was allowed to stand at 110 ° C. for 5 hours, and then 0.05 part of hydroquinone monomethyl ether and 0.3 part of tetraethylammonium bromide were added, and 14.7 parts of acrylic acid was added while blowing nitrogen gas to air. After dropping over a period of time, the reaction was terminated after leaving it for 5 hours to confirm that the acid value was 1 or less. This resin solution is poured into 5 liters of n-hexane, filtered through a silk cloth, spread in a large stainless steel vat, and dried in a dark room at room temperature for 7 days to give a white photoradically polymerizable unsaturated polymer powder (d). Obtained. Table 1 shows the glass transition temperature of the obtained polymer (d) by DSC measurement, the number average molecular weight by GPC (gel permeation chromatography) measurement, and the number of functional groups in one molecule.

Examples 1 and 2 and Comparative Examples 1 to 4
100 parts of the acrylic resin listed in Table 2 and 1 part of the photopolymerization initiator were dry-blended with a Henschel mixer at room temperature, and then melt-kneaded with an extruder. Next, after cooling, it was pulverized by a pin disc mill and filtered through a 150 mesh sieve to obtain a powder coating composition. The blocking resistance of the obtained powder coating composition was evaluated. The results are shown in Table 2.

In addition, the powder coating compositions obtained in Examples 1 and 2 and Comparative Examples 1 to 3 were electrostatically coated on an aluminum plate having a thickness of 0.3 mm so as to have a film thickness of about 30 μm. After heating and melting at 140 ° C. for 5 minutes to form a coating film, the coating film was cured by ultraviolet irradiation with a 120 W / cm ² high-pressure mercury lamp. In Comparative Example 4, the coating was heated and melted at 100 ° C. for 5 minutes in order to suppress curing of the coating film during heating and melting. Various tests were performed on the obtained coated plate. The results are shown in Table 2.

  The test methods in Table 2 are as follows.

Blocking resistance of the paint: The powder paint was placed in a cylindrical container having a bottom area of about 20 cm ² so that the height was 6 cm, and allowed to stand at 30 ° C. for 7 days. Thereafter, the powder paint was taken out and the state was observed according to the following criteria.

A: Good without any solidity,
○: Slightly hardened but easily loosened with fingers,
△: A lump that cannot be loosened unless pressed with your fingers.
×: A mass that is not loosened even when strongly pressed with a finger.

Appearance of coating film: The finished appearance of the coating film was evaluated from the gloss and smoothness according to the following criteria.

A: Good,
○: Slightly inferior in smoothness but good glossiness
Δ: Slightly inferior in smoothness and glossiness
*: Smoothness and glossiness are inferior.

Photocuring minimum irradiation amount: The UV-irradiated coating film was rubbed five times with gauze impregnated with methyl ethyl ketone, and the minimum ultraviolet irradiation amount (mJ / cm ² ) that did not swell or dissolve was measured.

Light surface curability: The coating film irradiated with UV light twice the minimum UV irradiation amount was rubbed with gauze impregnated with methyl ethyl ketone, and the glossiness of the surface after rubbing was evaluated according to the following criteria.

◎: Good even when rubbing 5 times or more,
○: Good up to 2-4 rubbing,
X: Gloss can be pulled by one rubbing.

Claims (2)

(A) The following general formula (I)

(In the formula, R ₁ represents a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, a fluorine atom, a fluoroalkyl group having 1 to 6 carbon atoms, an allyl group, an aryl group, an aralkyl group, a furyl group, or a chenyl group). A resin having an average of two or more oxetane functional groups represented by the formula: a glass transition temperature in the range of 40 to 100 ° C., and a number average molecular weight in the range of 1,000 to 15,000, An active energy ray-curable powder coating composition comprising (B) a polyepoxide having a glass transition temperature in the range of 40 to 100 ° C. and (C) a cationic photopolymerization initiator as essential components. The active energy ray-curable powder coating composition according to claim 1, wherein the resin (A) is at least one selected from polyester resins, acrylic resins, alkyd resins, and modified resins thereof.