JPH08188632A - Powdery photocurable composition and curing of the same - Google Patents

Abstract

PURPOSE: To obtain a powdery photocurable composition which cures with visible light and/or near-infrared light by mixing a specified cationic colorant with a boron catalyst and a powdery thermoplastic resin having a polymerizable unsaturation. CONSTITUTION: This composition essentially consists of a cationic colorant of the formula: D<+> .A<-> (wherein D<+> is a cation having an absorption at an arbitrary wavelenght in a region ranging from visible light to near-infrared light; and A<-> is an anoion of various kinds), a boron catalyst of the formula (wherein R<1> to R<4> are each an alkyl, aryl, allyl, aralkyl, alkenyl, alkinyl, silyl, or a heterocyclic group, a halogen atom or the like; and Z<+> is a cation) and a powdery thermo-plastic resin having a polymerizable unsaturation. The thermoplastic resin is desirably the one having a glass transition temperature of 20-180 deg.C, more desirably, the one having at least one polymerizable unsaturation per 2000 of the molecular weight.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a photocurable powder composition and a curing method. More specifically, even if pigments and additives with high hiding rate, fillers, dyes, etc. are included,
The present invention also relates to a powder composition that can be cured by visible light or near-infrared light and that can be cured even if it has a large thickness or poor light transmittance, and a method for curing the powder composition by photoreaction.

[0002]

2. Description of the Related Art Conventionally, most of the materials used as paints are of a type in which a resin is predominantly dissolved in a solvent.
That is, it is a method in which a paint containing a solvent is applied to a coated surface, the solvent is evaporated, and then a resin film is formed. However, the solvent used in this method is generally volatilized in the atmosphere and is difficult to collect and reuse, and improvement is strongly required from the aspects of cost, working environment and global environment. As a method for solving the problems of the above solvent-based paint, powder paint is drawing attention.
Since the powder coating material does not use a solvent at all, the above problems caused by the solvent are solved, and it is an excellent technique in terms of storage stability, handling method, and the like. However, powder coating is generally one in which solid powder coating is applied, heated and melted to form a continuous film, and then heated to a higher temperature to cause a curing reaction, and the melting and curing reactions are completely separated. It is difficult to obtain a sufficient finish of the coating film because the curing reaction partially occurs in the melting process, and since the curing reaction occurs at the melting temperature of the resin or higher, the temperature required for curing is high. was there.

On the other hand, photopolymerization involves curing, drying and printing of coating films.
It is used for various applications such as resin convex printing, print substrate making, resist or photomask, black and white or color transfer coloring sheet or making coloring sheet,
In particular, development has been carried out from the viewpoints of dealing with the drawbacks of the above solvent-based paints, energy saving, and labor saving to cope with an increase in labor costs. For example, curing by ultraviolet light is 200 to 40
The polymerizable monomer is rapidly cured by cation polymerization or radical polymerization by irradiating 0 nm ultraviolet light, and its application in the field of paints for woodworking and the like is progressing.

A powder coating which is cured by ultraviolet rays combining these techniques has been proposed (for example, JP-A-50-3.
No. 4036), it is said that solvent-free, low-temperature curing, and good finish of the coating film were achieved by making use of the characteristics of each technology. Another feature is that powder coating technology can be applied to materials that are difficult to heat to high temperatures, such as wood materials and plastics (for example, Polymer Paint Color Journal, February 9, 1994 34.
page). However, the above technique is difficult to use in a thick film coating, a colored coating film containing a pigment having a high hiding rate, etc., since it has a low ultraviolet light transmittance, and a transparent curing system that does not include a pigment, a coloring dye, etc. In a system containing a material having an increased thickness or poor transparency, ultraviolet rays did not reach the inside sufficiently, and there was a problem that curing inside the curing system was insufficient. Further, the ultraviolet light source is not necessarily inexpensive, such as a high-pressure mercury lamp, and it cannot be said to be a sufficiently satisfactory method in terms of safety such as ozone generation and the possibility of skin cancer.

[0005]

DISCLOSURE OF THE INVENTION The present invention is capable of low temperature curing as compared with conventional thermosetting powder materials, and has a light transmissive property such as a pigment addition system or a thick film system which has been difficult in ultraviolet light curing. An object of the present invention is to provide a photocurable powder composition using a light source having high safety even in a low curing system.

[0006]

Means for Solving the Problems As a result of repeated studies to solve the above problems, the present inventors have found that powder coating technology and visible light or near-infrared light have never been tried. The inventors have found that the above problems can be solved by combining polymerization techniques using light, and have completed the present invention. That is, according to the present invention, a cationic dye represented by the general formula (1): the general formula (1); D ⁺ · A ⁻ (wherein D ⁺ is in an arbitrary wavelength region from visible light to near infrared light). Is a cation having absorption, and A ⁻ represents various anions) and a boron-based catalyst represented by the general formula (2). General formula (2);

[0007]

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(In the formula, R ₁ , R ₂ , R ₃ and R ₄ are each independently an alkyl group, an aryl group, an allyl group, an aralkyl group, an alkenyl group, an alkynyl group, a silyl group, a heterocyclic group and a halogen atom. , A substituted alkyl group, a substituted aryl group, a substituted allyl group, a substituted aralkyl group, a substituted alkenyl group, a substituted alkynyl group or a substituted silyl group, Z ⁺
Represents a cation) and a powdery thermoplastic resin having a polymerizable unsaturated bond to form a photopolymerizable composition, and a photocurable powder composition that can be cured by irradiation with light after melting is obtained.

As described above, almost no attempt has been known so far to cure the powder material by photoreaction, and slight ultraviolet rays and electron beams (for example, Japanese Patent Laid-Open No. 50-72) are used.
No. 929) has been known only for photocuring of powder coatings. The present inventors have studied a polymerization initiator using near-infrared light having a long wavelength (for example, JP-A-6-7).
5374), and as a result of earnestly studying the application of a polymerization technique using near infrared light or visible light, which has never been used for the curing reaction of powder materials, the present invention has been completed. The powder composition in the present invention is suitable for general coating applications such as exterior and interior of automobile bodies and bumpers, various parts, woodworking, furniture, electronic materials, building materials, metals, plastics, inorganic materials, etc. However, not only for paint applications but also for various photocurable materials such as printing inks, adhesives,
It can be used for various applications such as solid photosensitive materials, soldering masks, and plating resists.

The combined use of the cation dye of the general formula (1) and the boron-based catalyst of the general formula (2) constituting the present invention causes decomposition of the cation dye by visible light or near-infrared light. When the color of the dye is decolored and radicals are generated, polymerization is initiated when a polymerizable unsaturated compound coexists. The decolorization reaction of the cationic dye is an irreversible reaction, and the color of the cationic dye does not impair the hue of the polymer. During the reaction, it is desirable that each component of the powder composition, the cationic dye and the boron-based catalyst be in a molten state, and in general, the composition of the present invention melts the resin having a polymerizable unsaturated bond as the main component. After heating and melting above the temperature, the curing reaction can be performed by irradiation with light having a spectral distribution at a desired wavelength. If the components in the composition remain in the solid state, the efficiency of electron transfer or chemical reaction may decrease, and the reaction time may be delayed or the reaction may be incomplete. Therefore, it is desirable that the resin for powder composition, which is the main component of the cationic dye and the boron-based catalyst of the present invention, is melted or melted at the time of melting.

The cation dye of the general formula (1) of the present invention may be a dye having absorption in an arbitrary wavelength region from visible light to near infrared light, and specifically, 400 nm to 2000 n.
It suffices if absorption is present in any wavelength region within the range of m. Among them, a cation dye having absorption in the near infrared light region is particularly preferable in consideration of light transmittance, facility safety, light stability of the initiator, operability and the like. The cation having absorption in the near infrared light region herein is a cation having absorption in the wavelength region of 740 nm or more, and preferably a compound having absorption in the wavelength region of 780 nm or more. Since near-infrared light has a longer wavelength and is superior in light transmittance to ultraviolet light that is generally used in the past, it has been difficult to use conventional ultraviolet light to add various pigments and other materials with high light concealment properties, and thickness. Good photopolymerization can be carried out even on a material having a problem.

The cation (D ⁺ ) of the present invention is not particularly limited as long as it has absorption in the wavelength region of 400 nm or more, but preferred examples are methine, polymethine, indoline, cyanine, xanthene, oxazine,
Examples thereof include thiazine, diarylmethane, triarylmethane, and cations of pyrylium-based cation dyes.
Typical examples of such cation dyes having absorption in the near infrared region include cations as shown in Table 1. Representative examples of cation dyes having absorption in the visible light region include cations shown in Table 2. More specifically, the cationic dyes described in JP-A-5-59110 can be mentioned.

[0013]

[Table 1]

[0014]

[Table 1]

[0015]

[Table 2]

The counter anion A ⁻ is an arbitrary anion, but a tetracoordinated boron anion represented by the following general formula (3) is particularly preferable. General formula (3);

[0017]

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(Wherein R ₅ , R ₆ , R ₇ and R ₈ are each independently an alkyl group, an aryl group, an allyl group, an aralkyl group, an alkenyl group, an alkynyl group, a silyl group, a heterocyclic group or a halogen atom. , A substituted alkyl group, a substituted aryl group, a substituted allyl group, a substituted aralkyl group, a substituted alkenyl group, a substituted alkynyl group or a substituted silyl group.) Specific examples include n-butyltriphenylboron ion and n-octyltriphenylboron Ion, triphenylsilyltriphenylboron ion, n-butyltrianisylboron ion, di-n-dodecyldiphenylboron ion, tetraphenylboron ion, triphenylnaphthylboron ion, tetrabutylboron ion, tri-n-butyl (dimethylphenylsilyl ) Boron ions, etc. Anions like described in the present inventors have previously filed (Japanese Patent Application Laid-Open No. 6-75374) Patent specification to.

The boron-based catalyst according to the present invention is represented by the general formula (2), and specific examples of the anionic four-coordinated boron ion include n-butyltriphenylboron ion and n-octyl. Triphenylboron ion, triphenylsilyltriphenylboron ion, n
-Butyltrianisylboron ion, di-n-dodecyldiphenylboron ion, tetraphenylboron ion,
Triphenylnaphthylboron ion, tetrabutylboron ion, tri-n-butyl (dimethylphenylsilyl)
Examples include boron ions. Further, the cation (Z ⁺ ) described in the formula is represented by the general formula (4), the general formula (4);

[0020]

[Chemical 4]

(In the formula, R ₉ , R ₁₀ , R ₁₁ and R ₁₂ are each independently a hydrogen atom, an alkyl group, an aryl group, an allyl group, an aralkyl group, an alkenyl group, an alkynyl group, a heterocyclic group or a substituted alkyl group. Group, a substituted aryl group, a substituted allyl group, a substituted aralkyl group, a substituted alkenyl group or a substituted alkynyl group), a quaternary ammonium cation or a quaternary pyridinium cation, a quaternary quinolinium cation, a diazonium cation, tetrazolium Cations, phosphonium cations, (oxo) sulfonium cations, metal cations such as sodium, potassium, lithium, magnesium and calcium, flavylium,
Organic oxygen cations such as pyranium salts, tropylium,
Examples thereof include carbon cations such as cyclopropylium, halogenium cations such as iodonium, cations of metal compounds such as arsenic, cobalt, palladium, chromium, titanium, tin and antimony, and JP-A-6-75374. There is a detailed description inside. These cationic dyes and boron-based catalysts may be used alone or in admixture of two or more.

The powder composition of the present invention is a composition which is in a solid state at room temperature, and is generally a solid composition having a solid particle size of 1 mm or less, preferably 300 microns or less. The thermoplastic resin having a polymerizable unsaturated bond is a resin having a radical polymerizable ethylenic double bond,
Any polymerizable oligomer or polymerizable polymer that is in a solid state at the time of coating and can be heated and melted when performing a curing reaction after coating may be used, such as a urethane (meth) acrylate compound, a polyester (meth) acrylate compound, an unsaturated polyester resin, Epoxy (meth) acrylate compounds, silicon (meth) acrylate compounds, melamine (meth) acrylate compounds, (meth) acryl-functional polyorganosilsesquioxanes, and the like can be mentioned.

The above-mentioned thermoplastic resin refers to a resin that softens and becomes plastic when heated and hardens again when cooled, and is a resin defined in the Chemical Dictionary (Morikita Shuppan 1986). Various production methods have been proposed for these polymerizable resins (for example, JP-A-50-72929).
No. JP-A-3-59019). The above-mentioned polymerizable resin is the main component that determines the physical properties of the cured product, and is selected and blended according to the physical properties such as hardness, strength, durability and adhesion required for various applications.

From the characteristics of the powder material, the glass transition temperature is preferably 20 ° C. or higher because it is required to be in a solid state at room temperature, and more preferably 60 ° C. or higher in consideration of storage in a high temperature state. Is. Further, it is inconvenient for the glass transition temperature to be too high because it needs to be melted at the time of curing, and 180 ° C. or lower is preferable. Considering the energy saving required for heating, more preferably 120 ° C.
It is the following.

The number of polymerizable unsaturated bonds is preferably 1 or more per 2000 of the molecular weight of the polymerizable resin. More preferably, it is in the range of 1 to 10. If the amount of polymerizable unsaturated bonds is too small, the curing reaction may end insufficiently and unreacted components may remain, which may reduce the durability of the cured product, or the required physical properties such as hardness may not be expressed. The crosslinking reaction of unsaturated bonds may occur more than necessary, causing internal stress due to shrinkage during curing, and decreasing the adhesiveness, flexibility, etc. of the cured product. The number of unsaturated bonds per molecular weight is generally stated in the manufacturer's catalog of the above unsaturated compounds. Alternatively, it is possible to determine the number of unsaturated bonds per molecular weight by measuring the molecular weight by a general method such as GPC and then quantifying the polymerizable unsaturated bond by a commonly used method such as a titration method.

If desired, the composition of the present invention may contain polymerizable unsaturated monomers. Examples of the polymerizable unsaturated monomer include various (meth) acrylic monomers, monomers having a styrenic double bond, vinyl bonds such as vinyl ester and vinyl ether, and monomers having allyl bond such as allyl ester and allyl ether. To be The polymerizable unsaturated monomer is blended for the purpose of controlling operability such as viscosity of the composition and controlling physical properties of the cured product such as hardness and flexibility. The polymerizable unsaturated monomer is preferably a compound which is in a solid state at room temperature in order to maintain the powder form of the composition of the present invention. More preferably melting point 40
It is a compound above ℃.

In the curing reaction of the photocurable powder composition of the present invention, generally, the composition is heated and melted at a melting temperature or higher so that the powder particles are continuously connected without maintaining the original particle shape. After changing to the state, 4 depending on the absorption wavelength of the light absorbing dye.
This is achieved by irradiation with light having a spectrum in the wavelength region of 00 nm or more. For example, a halogen lamp, a xenon lamp, sunlight, etc. are used. As mentioned above, these light sources are generally cheaper than mercury lamps, metal halide lamps, etc. used in the conventional UV photopolymerization, and are free from ozone generation, skin cancer, etc., and easy to take safety measures. It also has the feature of being. In the photo-curing reaction, it is preferable to irradiate light under a low oxygen concentration in order to reduce polymerization inhibition by oxygen. For example, it is possible to accelerate the polymerization by reducing the oxygen concentration by blowing the above inert gas onto the surface of the cured product in an atmosphere of an inert gas such as nitrogen, argon, carbon dioxide or the like.

The cationic dye represented by the general formula (1) and the boron-based catalyst represented by the general formula (2) in the present invention can be used in an arbitrary ratio, and generally 10: 1 to 1:50.
It is used in a (molar ratio) ratio, but in order to completely carry out the curing reaction and the decoloring reaction of the dye, it is preferable to use the boron-based catalyst in a larger amount than the cationic dye. That is, the range of 1: 1 to 1:50 (molar ratio) is particularly preferable.

The object of the present invention can be achieved by generally using the polymerization initiator comprising the cationic dye and the boron-based catalyst of the present invention in an amount of 0.01% by weight or more based on the entire composition. If it is less than that, the polymerization may not be performed sufficiently. It is preferably in the range of 0.05 to 10% by weight. It is not preferable from the economical point of view to use too much. Two
It is also possible to use one or more cationic dyes and a boron-based catalyst in combination. In particular, it is preferable to use a visible light-absorbing cation dye and a near-infrared light-absorbing cation dye together in consideration of efficient use of light source spectrum, cost, storage stability balance, and the like. The mixing ratio of two or more kinds of dyes is arbitrary, but from the viewpoint of storage stability to light and light transmittance, it is necessary to add 20 mol% or more of the total dyes containing near-infrared light absorbing cationic dyes. Is preferred.

Various additives may be added to the composition of the present invention for the purpose of efficiently promoting the curing reaction. For example, an oxygen scavenger for reducing polymerization inhibition by oxygen,
Examples include various polymerization accelerators. Examples of the oxygen scavenger include various amine compounds, various phosphine compounds, phosphite compounds, various reducing agents, singlet oxygen scavengers, and the like. Specifically, N, N, 2,4,6-pentamethylaniline, triphenyl Examples thereof include phosphine, N-phenylglycine, various transition metal compounds, hindered amine compounds known as light stabilizers (HALS), and oxygen scavengers described in JP-A-2-103544. Examples of the polymerization accelerator include chain transfer agents and electron-accepting substances. Specific examples include thiol compounds such as mercaptobenzothiazole, thioketones, various peroxides, bisimidazole compounds, triazine compounds, iodonium salts, and sulfonium. Examples include aromatic onium salts such as salts.

Furthermore, any pigments, additives, fillers and the like can be added to the polymerizable composition containing the initiator of the present invention. Examples of the additive here include a leveling agent and a dispersant which are generally used as an additive for powder coatings, and examples of the filler include powder, spherical, fibrous, whisker-like, and scale-like. Various types of organic substances, inorganic substances, or their composites and mixtures. Further, as described above, since the polymerization initiator of the present invention uses a cationic dye having absorption in a long wavelength region, a black pigment such as carbon black having low light transmittance, aluminum,
Even if it contains a metallic pigment such as titanium, photopolymerization can be caused, and various pigments thereof can be added. As described above, the composition of the present invention is suitable as a photocurable material such as a paint, an ink, an adhesive and a resist, and is expected to contribute to the improvement of the global environment. Conventional reaction curable materials required a large amount of solvent in order to dissolve the polymer component before curing, but the photocurable powder composition of the present invention does not contain a solvent or a low boiling point compound, so it is not necessary to protect nature or resources. It is also very useful from the viewpoint of protection.

[0032]

EXAMPLES The present invention will be described below with reference to examples. (Example 1) Epoxy acrylate resin (manufactured by Showa Polymer Co., Ltd., product name VR60, glass transition temperature: about 70 ° C, theoretical molecular weight: 1950, number of polymerizable unsaturated groups: 2), 70 g, diacetone acrylamide, a polymerizable monomer (melting point: 56 ° C)
30 g, near-infrared light absorbing cationic dye (Table 1, No. 3,
(Anion is n-butyltriphenylboron anion)
0.1g Boron-based catalyst (tetrabutyl ammonium n
-Butyltriphenylboron) (0.5 g) was melt-kneaded at about 100 ° C., cooled, pulverized and classified to obtain a powder composition having a particle size of 140 mesh or less.

Example 2 A cationic dye is shown in Table 1 No. 1
Sample 2 was prepared in the same manner as in Example 1 except that the compound of Example 2 was used.

(Example 3) Unsaturated polyester (trade name HETRON92G glass transition temperature 105
C. Sample 3 was prepared in the same manner as in Example 1 except that the molecular weight and the number of unsaturated bonds were changed.

Example 4 Cationic dyes are listed in Table 1 No. 1
Sample 4 was prepared in the same manner as in Example 3 except that the compound of Example 4 was used.

Example 5 Sample 5 was prepared in the same manner as in Example 1 except that the cation dye was changed to the compound of No. 8 in Table 2 (general name: crystal violet, anion being chlorine anion) which is a visible light absorbing dye. did.

Example 6 Sample 6 was prepared in the same manner as in Example 1 except that the cation dye was changed to the compound of No. 4 in Table 2 (the anion was tetraphenylboron anion) which was a visible light absorbing dye.

Example 7 Sample 7 was prepared in the same manner as in Example 1 except that 5 g of aluminum paste (Showa Aluminum Powder, trade name SAP561PS) was added.

Comparative Example A comparative sample was prepared in the same manner as in Example 7 except that 5 g of 2,2-diethoxyacetophenone as an ultraviolet photopolymerization initiator was added instead of the cationic dye and the boron-based catalyst.

[Polymerization test and evaluation of curability of sample] Each of the prepared samples was heated and melted at 120 ° C., and then coated on an aluminum substrate with an applicator so as to have a thickness of 100 μm. A halogen lamp with an output of 1500 W having a spectral distribution in the first embodiment is used.
Irradiation was carried out for 5 minutes through a wavelength cut filter of 800 nm or less in Examples 4 and 7, and for 5 minutes through a wavelength cut filter of 800 nm or more in Examples 5 and 6. The photoreaction caused the color of the cationic dye to be completely decolored and a curing reaction to occur, whereby a cured coating film was obtained. The surface hardness and the coating film were peeled from the substrate and the hardness of the back surface of the coating film was measured. Pencil hardness was used as the index of hardness. As a result, it was confirmed that both the front surface and the back surface of the coating film were practically sufficiently cured (Table 3).

[0041]

[Table 3]

[Polymerization test of comparative sample] The prepared comparative sample was applied to an aluminum substrate in the same manner as in the above-mentioned polymerization test, and then irradiated with a high-pressure mercury lamp having a spectral distribution in the wavelength range of 200 to 400 nm for 5 minutes. Although the surface of the coating film was slightly cured, when pressed with a finger, the composition inside the coating film leached out in an uncured state, and hardness measurement was impossible.

[0043]

EFFECTS OF THE INVENTION According to the present invention, it is possible to cure at a lower temperature than before, and a curing reaction does not occur during melting, and a thick film,
Provided are a photocurable powder composition and a curing method capable of curing even a curing system having a low light transmittance, which has been difficult with conventional ultraviolet rays such as a pigment addition system.

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Claims (4)

[Claims] 1. A photocurable resin containing as an essential component a cationic dye represented by the general formula (1), a boron-based catalyst represented by the general formula (2), and a powdery thermoplastic resin having a polymerizable unsaturated bond. Powder composition General formula (1); D ⁺ · A ⁻ (In the formula, D ⁺ is a cation having an absorption in an arbitrary wavelength region from visible light to near infrared light, and A ⁻ is various anions. General formula (2); (In the formula, R ₁ , R ₂ , R ₃ and R ₄ are each independently an alkyl group, an aryl group, an allyl group, an aralkyl group, an alkenyl group, an alkynyl group, a silyl group, a heterocyclic group, a halogen atom or a substituted alkyl group. Group, a substituted aryl group, a substituted allyl group, a substituted aralkyl group, a substituted alkenyl group, a substituted alkynyl group or a substituted silyl group, and Z ⁺ represents a cation) 2. The powder composition according to claim 1, wherein the glass transition temperature of the thermoplastic resin having a polymerizable unsaturated bond is in the range of 20 ° C. to 180 ° C. 3. The polymerizable unsaturated group in the thermoplastic resin is present in an amount of 1 or more per 2,000 of molecular weight.
Powder composition. 4. The composition is heated and melted to form a continuous film, which is then polymerized and cured by irradiating visible light and / or near infrared light having a spectral distribution in the absorption wavelength region of the cation dye. The method for curing the powder composition according to claim 1, 2 or 3.