JPS6035195B2 - Curing method for photocurable resin composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for curing a photocurable resin composition, and is characterized in that after reducing the content of organic solvent in the coating film, the coating film is covered with a liquid and irradiated with light. The present invention relates to a method for curing a photocurable resin composition.

As a method for crosslinking and curing a resin composition mainly composed of a compound having an unsaturated double bond as a crosslinkable reactive group,
There are two methods: a method in which a catalyst that generates radicals upon heating is added to the resin composition, and a method that uses radiation such as an electron beam or Y-ray, or a light beam as a crosslinking curing energy source. The irradiation device itself is simple, and its future development is highly anticipated.

However, if oxygen is present in the irradiation atmosphere of the light beam, the photocurable resin composition used in the method using light beams as a crosslinking curing energy source cannot be sufficiently crosslinked and hardened due to the polymerization inhibiting effect of oxygen. There were some inconveniences such as the sticky surface remaining. Therefore, methods have been proposed, such as a method in which the atmosphere for light irradiation is an inert gas atmosphere such as nitrogen or carbon dioxide, or a method in which the uncured coating film is immersed in a liquid such as water to remove oxygen and then irradiated with light. has been done.

However, with the method of creating an inert gas atmosphere as the light irradiation atmosphere, it is difficult to maintain the atmosphere completely oxygen-free, and the oxygen adsorbed on the surface of the hardened coating film is absorbed into the inert gas atmosphere. It is extremely difficult to maintain the characteristics of the atmosphere constant due to bringing in materials, etc., and creating a cured coating film with consistent quality over time requires a great deal of labor and equipment, and it also costs a lot of money to generate inert gas. .

In addition, the method of immersing an uncured coating film in a liquid and irradiating light from above the liquid is an extremely effective method for blocking oxygen from the irradiation atmosphere, but photocurable resin compositions with low molecular weight Many of them contain organic substances, so when a substrate coated with an uncured coating film is immersed in a liquid, the low molecular weight organic substances contained in the coating film are affected by the liquid and become coated. It has the drawbacks of leaching and roughening of the painted surface.

In addition, photocurable resin compositions generally tend to be highly viscous side fat compositions, and have the disadvantage that it is difficult to obtain a coated surface that is smooth and aesthetically pleasing using normal coating methods. Therefore, the present inventors investigated a method of obtaining a cross-linked cured coating film without the above-mentioned disadvantages, and found that by pre-mixing an organic solvent with the photocurable resin composition to be used, the viscosity at the time of coating was reduced. After applying it smoothly, the organic solvent remaining in the uncured coating is reduced to a level that is unaffected by the liquid.
The present invention was completed based on the discovery that by introducing the material into a liquid and irradiating it with light, a cured coating film with good smoothness could be obtained without elution of the coating film or roughening of the coating surface. The gist of the present invention is to coat a base material surface with a light-curing type resin composition containing an organic solvent, and to condition the coating film so that the content of the organic solvent is 15% or less. This is a method of curing a photocurable resin composition, which is then covered with a liquid and irradiated with light.

When designing a photocurable resin composition based on the constraints of 100% non-volatility and 100% reactivity, in order to impart toughness and flexibility to the cured coating film, it is necessary to It tends to become a resin composition.

When the resin composition has such a high viscosity, it is difficult to obtain a coated surface with good smoothness and good appearance using a normal coating method. Therefore, in the present invention, a desirable resin composition is designed in advance from the viewpoint of coating film properties and curability, and then an appropriate amount of an organic solvent is mixed in to improve coating properties, and after applying it smoothly, it is immersed in a liquid. At this time, the content of organic solvent remaining in the coating film is reduced to 15% or less, preferably 10% or less so as not to be affected by the liquid, and a guiding light beam is irradiated into the liquid. In this way, curing is completed without the uncured coating film melting or becoming rough due to the influence of the liquid. In the case of the present invention, the light beam generation source for curing may be placed in a space above the liquid or above the coating film in the liquid. Then, the light beam can be irradiated with oxygen removed from the coating surface, and the surface performance of the cured coating film will be extremely good.

In other words, in the case of light irradiation in an inert gas atmosphere, the oxygen concentration can be maintained at 1000 ppm after 1 month using the air brought into the substrate or the air brought in by the conveyor, which is barely within the range that can be achieved on an industrial line. be.

However, when the material is immersed in a liquid such as water and irradiated with light, it is extremely easy to reduce the oxygen concentration from several ppm to several tens of ppm. Therefore, when comparing the performance of the cured coating obtained by the curing method of the present invention with that obtained by curing by irradiation in the air when using the same resin composition, it is found that the cured film obtained by the curing method of the present invention is better. It has several levels of superior performance.

What is even more advantageous is that when irradiating liquids such as water, the effect of heat emitted at the same time as the light emitted from the irradiation source is blocked, making it possible to easily avoid an increase in the temperature of the object to be treated. This makes it extremely easy to apply the treatment to substrates with low heat resistance, especially plastic films and sheets.

In carrying out the present invention, water is particularly suitable for the liquid layer provided on the coated surface, but other materials such as liquid paraffin can also be used.

The photocurable resin composition used in the present invention is not particularly limited as long as it can be polymerized and cured by radicals generated by light irradiation. It is a compound having one or more (meth)acryloyl groups in its side chain, and specific examples thereof include the following compounds. The first is polyol (meth)acrylates,
It is a reaction product of polyols such as ethylene glycol, diethylene glycol, butanediol, hexanediol, glycerin, trimethylolpropane, neobentyl glycol, bentaerythritol, diventaerythritol, etc., and (meth)acrylic acid.

The second type is polyester di(meth)acrylates, which are the reaction products of a polyester whose repeating unit has 2 to 20 terminal hydroxyl groups obtained by condensing a diol and dicarboxylic acid, and (meth)acrylic acid. .

The third is a (meth)acrylic acid addition reaction product of a polyepoxy compound, and the polyepoxy compound is a polyglycidyl derivative derived from a hydroxyl group-containing compound such as a polyhydric alcohol or peacephenol A and epichlorohydrin. - Polyepoxy compounds such as polyglycidyl ethers derived from esters or polyhydric carboxylic acids and epichlorohydrin, epoxidized soybean oil, epoxidized linseed oil, and epoxidized polybutadiene; The addition reaction between the polyepoxy compound and acrylic acid or methacrylic acid is preferably carried out at a molar ratio of epoxy groups to carpoxyl groups in the range of about 2/1 to 1/1.

The fourth type is polyfunctional urethane acrylates, which are obtained by reacting a polyisocyanate compound with a (meth)acrylic monomer containing a hydroxyl group or an oligomer containing a (meth)acryloyl group and a hydroxyl group. It can be obtained by using various polyhydroxy compounds as chain extenders in some cases.

The fifth type is (meth)acrylic monomers that are mainly used to adjust the viscosity of the composition.It is desirable that these monomers have low volatilization from the uncured coating film, such as (
meth)acrylic acid 2/hydroxyethyl, (meth)acrylic acid 2/hydroxypropyl, (meth)acrylic acid 2
・Ethylhexyl, (meth)acrylic acid carbitol,
Examples include pendyl (meth)acrylate, cyclohexyl (meth)acrylate, and tetrahydrofurfuryl (meth)acrylate. In addition, styrene, vinyltoluene, and the like may also be used. The sixth type is a so-called unsaturated polyester obtained by condensing an unsaturated polycarboxylic acid such as maleic anhydride with another polycarboxylic acid and a polyhydric alcohol.

Furthermore, a thermoplastic resin is also mixed in order to adjust the viscosity of the composition and balance the physical properties of the coating film. In the present invention, a composition in which one or more of these compounds are arbitrarily mixed is used, and the composition includes materials such as urethane acrylate, which can impart toughness, flexibility, and properties to the cured coating, but has a high When blending 30% by weight or more of a viscosity compound,
The method of the present invention is particularly effective.

Next, specific examples of organic solvents used for diluting the photocurable resin composition include methanol, ethanol, and n-fluoride.

Ro/gunol, isopro/gunol, n-butanol,
Toluene, xylene, 1.1.1 trichloroethane, propylene glycol monomethyl ether, methyl ethyl ketone, methyl isobutyl ketone, ethyl formate, ethyl acetate, butyl acetate, amyl acetate, ethylene glycol chetyl ether, acetic acid ethylene glycol monomethyl ether , diacetone alcohol, cyclohexanone, light solvent naphtha, and other organic solvents commonly used in paints and inks, and monovinyl compounds with a boiling point of 165° C. (760 mmH) or lower and a molecular weight of 145 or lower. There is no particular limit to the amount of these organic solvents added to the photocurable resin composition before coating, but it is preferable to dilute them so that a sufficiently smooth coating surface can be obtained using a normal coating method. It is preferable not to use too much of the solvent so that the removal of the solvent before introducing the uncured coating into the liquid is not excessive.

In the present invention, the content of organic solvent in the uncured coating film is reduced by 15% by passing a photocurable resin composition containing these organic solvents onto a substrate and passing it through a heating zone or leaving it to stand. % or less, preferably 10% or less, and the content is 15% or less.
If the amount exceeds 5%, it is not preferable because when introduced into a liquid, the coating film may sag due to the influence of liquids such as water, or the coating surface may become rough.

In the present invention, it is preferable to mix a photopolymerization initiator into the photocurable resin composition. , in n-butyl normal, benzisoisobutyl ether, benzyl, benzophenone, anthraquinone, chloranthraquinone, 2
．． Examples include 2-diethoxyacetophenone, which is used alone or in combination of two or more, and in some cases, an amine compound is used as a sensitizing agent.

The blending ratio of these photopolymerization initiators to the resin composition is 0.
．． It is 1 to 10% by weight. Further, fillers, matting agents, anti-aging agents, antistatic agents, fluidity regulators, and colorants can be mixed into these photocurable resin compositions by conventional methods.

Plastic films, plastic sheets, plastic molded products, etc. are most effective as materials that can be applied to the present invention, but other materials include metal plates, metal films,
There are no particular limitations as long as the base material is not extremely damaged by liquids such as water, such as special paper, synthetic leather, glass materials, inorganic materials, wood materials, woven or knitted fabrics, or non-woven fabrics.

When carrying out the present invention, the light rays to be irradiated onto the photocurable resin composition described above are preferably ultraviolet rays with a wavelength of 1,800 to 4,500 μm, and examples of light sources include low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, arc lamps, There are xenon lamps, gallium lamps, etc.

Furthermore, although the curing method of the present invention is often used for transparent protective coats and colored protective coats, it can also be applied to printing, film formation, casting product formation, and the like. Examples are given below to explain the method of the present invention in more detail.

In addition, in the examples, parts mean parts by weight.

Examples of compounds used as components of the photocurable resin composition are shown below.

Compound A: Maleic anhydride/mol, phthalic anhydride/mol, and 2.08 mol of jettylene IJ col were condensed by a conventional method, and vinyltoluene was added so that the solid content was 80%.

Compound B: Pentaerythritol tetraacrylate Compound C: 480 parts of Epiquat #1001 (bisphenol A type epoxy resin manufactured by Shell Chemical Co., Ltd.) and 15 parts of acrylic acid.
Epoxy acrylate compound D obtained by reacting Ikarito: A polyester obtained by reacting methacrylic acid with the terminal end of a polyester with a molecular weight of about 1200 obtained from 1 mol of adipic acid and 2.05 mol of neobentyl glycol. Acrylate compound E: Polyurethane acrylate compound obtained by reacting 415 parts of volicaprolactone diol, 140 parts of xylylene diisocyanate, and 120 parts of 2-hydroxyethyl acrylate F: Carbitol acrylate Compound G: Tetrahydro acrylate EXAMPLES Photocurable resin compositions of experiment numbers 1 to 5 as shown in Table 1 were prepared by mainly combining the above-mentioned compounds.

Table 2 shows the surface characteristics of the coating film obtained by curing this photocurable resin composition under the substrate curing conditions shown in Table 2.

Note that Tables 1 and 2 also show comparative examples.

Table-1 Table-2 <Test method> Surface hardness: Pencil hardness using Mitsubishi Juni Acid resistance: 10% day 2S04, 25oo, thin r, Alkali resistance: 10% NaOH, 2500, mottled r, immersion resistance Solvent property: toluene, 25oo, fine r, immersion test results are displayed using a 5-step method.

5 best.

Claims (1)

[Claims] 1. A photocurable resin composition containing an organic solvent is coated on the surface of a base material, and after the organic solvent content in the coating film is 15% or less, a liquid A method for curing a photocurable resin composition, which comprises covering the composition with light and irradiating it with light. 2. The curing method according to item 1, wherein a plastic film or a plastic sheet is used as the base material. 3. The curing method according to item 1, which uses a photocurable resin composition containing 30% by weight or more of urethane acrylate.