JP2541997B2 - Curing method with active energy rays - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for curing a curable compound with active energy rays. More specifically, it relates to a method for curing a curable compound by an active energy ray that provides a cured coating film having excellent curing speed, excellent adhesion to a substrate, excellent bending strength, and excellent weather resistance.

[Prior Art] A method for curing a curable compound used for coating metals, plastics, wood, plywood, paper, etc. by irradiation with active energy rays such as electron beams and other radiation and ultraviolet rays is already known. There is. Generally, many proposals have been made as a material which is cured by irradiation with such an active energy ray to form a coating film. Typical examples thereof include a vinyl group, a (meth) acryloyl group and a vinylidene group. , And the like. Particularly, recently, curable compounds mainly containing unsaturated polyester resins and unsaturated urethane resins have been widely used.

When irradiating these curable compounds with active energy rays, it was usually carried out at room temperature without controlling the temperature of the curable compounds, but various methods were used to increase the curing rate of the curable compounds. Is proposed.

For example, JP-A-50-56425 discloses that a photocurable coating material is cured by irradiating it with light in an inert gas atmosphere having an oxygen concentration of 3% by volume or less. A method of forming a cured coating that provides a smooth cured surface and is defect free is described.

Further, in order to prevent the generation of pinholes and the prevention of deformation, when applying the ultraviolet curable coating material, the object to be coated and / or the coating material is heated and coated before coating, and then rapidly cooled after coating to fix the coating material. Then, a method of irradiating with ultraviolet rays is described in JP-A-54-8868.

[Problems to be Solved by the Invention] However, various active energy ray-curable compositions that have been proposed so far generally include metal, plastic, and
When coated on wood, plywood, paper, etc. and cured with active energy rays, the adhesion of the coating after curing is poor, and the coating is cracked by bending for processing. It had a drawback in that It is speculated that this is because the curable compound is instantaneously cured by the irradiation of the active energy ray, and thus internal stress is generated in the coating film after curing.

The method described in JP-A-50-56425 is effective in terms of speeding up the curing rate in addition to the above-mentioned drawbacks, but it is necessary to replace the irradiation atmosphere with an inert gas, which complicates the apparatus. There is a problem. In addition, the weather resistance of the coating film after curing has not been sufficiently satisfactory.

Further, although the method described in JP-A-54-8868 is effective in preventing the generation of pinholes, it has a drawback that satisfactory weather resistance of the coating film after curing cannot be obtained. .

[Means for Solving Problems] That is, according to the present invention, when the curable compound is cured by irradiation with active energy rays, the glass transition temperature of the cured product is in the range of 40 ° C to 200 ° C. The present invention provides a method for curing a curable compound, characterized in that the curable compound is retained within a range of 10 ° C lower than the same temperature of the curable compound to 10 ° C higher than the same temperature.

In the present invention, the glass transition temperature is partially amorphous when the cured product of the curable compound (hereinafter simply referred to as “cured product”) is an amorphous substance or even when the cured product is a crystalline substance. Applies in some cases.

In the present invention, the glass transition temperature is various characteristics when the temperature coefficient of various characteristics such as expansion coefficient, heat content, refractive index, diffusion coefficient, dielectric constant, elastic modulus of the amorphous substance portion of the cured product is measured. It is the temperature defined as the inflection point of the temperature coefficient of.
The glass transition temperature of the cured product can be obtained by measuring the above temperature coefficient, but simply, the loss tangent obtained by measuring the temperature dependence of the elastic modulus of the cured product has a maximum value. Or the temperature at which the specific heat obtained by measuring the temperature dependence of the specific heat of the cured product by the differential scanning calorimetry shows an inflection point.

Examples of the curable compound to which the present invention can be applied include those in which the glass transition temperature of the cured product is within the range of 40 to 200 ° C.

In the present invention, when the curable compound is cured, it is active while maintaining the curable compound in a temperature range 10 ° C. lower to 10 ° C. higher than the glass transition temperature (hereinafter, this temperature range is referred to as “specific temperature”). It is necessary to irradiate with energy rays.

Here, at a temperature higher than 10 ° C. lower than the glass transition temperature, the weather resistance of the cured product becomes insufficient, while at a temperature higher than 10 ° C. higher than the glass transition temperature, when the curable compound is used as a coating film. However, there arises a problem that the fluidity of the coating film increases and it becomes difficult to control the film thickness.

In the present invention, the cured product means that the extraction fraction is 20% by weight or less when the cured product is extracted with a good solvent for the curable compound before curing.

When the curable compound is irradiated with an active energy ray to be cured, the curable compound can be maintained at a specific temperature by (1) applying the curable compound or the like or an article to be coated with the curable compound in advance. A method of placing in a constant temperature bath controlled to a specific temperature to reach temperature equilibrium, then taking out, and rapidly irradiating with active energy rays to cure
(2) The curable compound or the curable compound is obtained by bringing the curable compound or the object to be coated with the curable compound into contact with a flat and / or roll-shaped heat bath equipped with a heating and cooling device. A method of irradiating an active energy ray to cure after the temperature of an object to be coated to which the compound is applied reaches a specific temperature, and (3) a constant temperature gas in which the irradiation atmosphere of the active energy ray is controlled to a specific temperature, for example, nitrogen. The temperature of the curable compound or the like or the object to be coated on which the curable compound has been applied is replaced with a specific temperature range by irradiating with an inert gas such as carbon dioxide, carbon dioxide, helium or argon and / or air. Examples thereof include, but are not necessarily limited to, these methods.

Examples of the curable compound to which the method of the present invention can be applied include a prepolymer and a low molecular weight compound having an active energy ray-sensitive group such as a vinyl group, a (meth) acryloyl group, an allyl group and a vinylidene group. .

Examples of the low molecular weight compound having an active energy ray-sensitive group include a monofunctional or polyfunctional (meth) acrylate compound and a vinyl compound having a boiling point of 150 ° C. or higher under normal pressure. It can be illustrated.

Polyfunctional compound: 2-hydroxyethyl acrylate, 2
-Hydroxypropyl acrylate, tetrahydrofurfuryl acrylate, butoxyethyl acrylate, ethyldiethylene glycol acrylate, 2-ethylhexyl acrylate, cyclohexyl acrylate, dicyclopentadiene acrylate, polyethylene glycol acrylate, polypropylene glycol acrylate, methyltriethylene glycol acrylate, diethylaminoethyl acrylate, 7 -Amino-3,7-
Acrylic compounds such as dimethyloctyl acrylate,
Methacrylic compounds such as 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, polypropylene glycol methacrylate, diethylaminoethyl methacrylate, vinylpyrrolidone, vinylphenol, acrylamide, vinyl acetate, vinyl ether, styrene and general formulas: [Wherein R ¹ is a hydrogen atom or a methyl group, R ² is a hydrogen atom or a methyl group, and R ³ is an alkyl group having a C _{1 to} C ₈ alkyl group or a C _{1 to} C ₁₂ alkyl group. Is an enyl group, and n is an integer of 1 to 12].

Polyfunctional compounds: trimethylolpropane triacrylate, ethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate , Polyester diacrylate, diallyl adipate, diallyl phthalate, triallyl isocyanurate.

Examples of the prepolymer having an active energy ray sensitive group include urethane-modified (meth) acrylate, polyester-modified (meth) acrylate, epoxy-modified (meth) acrylate, and alkyd-modified (meth) acrylate.

In the present invention, these curable compounds may be used alone or in combination of two or more kinds, and when two or more kinds are used in combination, the glass transition temperature of the cured product of the mixture is applied.

Further, in the case of containing the additives described below, the glass transition temperature of the mixture of the curable compound and the additives is applied.

The method of the present invention is at least one compound selected from a prepolymer having an active energy ray-sensitive group and a compound having an active energy ray-sensitive group, and the glass transition temperature of the cured product thereof is about 40 to 200 ° C. Can be suitably applied to the curable composition of, the curability, active energy ray polymerization initiator, active energy ray sensitizer, active energy ray absorber, antioxidant, polymerization inhibitor as required. , Organic and inorganic pigments, plasticizers, surfactants and other additives may be included.

Examples of the active energy ray used in the present invention include ultraviolet rays, electron beams, γ rays, neutron rays, and β.
Rays, X-rays and the like can be used, but it is particularly preferable to use ultraviolet rays or electron beams from the viewpoints of control of active energy rays and ease of introduction into the manufacturing process of the active energy ray irradiation apparatus.

When the active energy rays are ultraviolet rays, it is preferable to use a photopolymerization initiator in combination with the curable compound, and as the photopolymerization initiator, 2,2′-dimethoxy-2-phenylacetophenone,
Acetophenone, benzophenone, xanthone, fluorenone, benzaldehyde, fluorene, anthraquinone, triphenylamine, carbazole, 3-methylacetophenone, 4-chlorobenzophenone, 4,4'-dimethoxybenzophenone, 4,4'-diamino Benzophenone, Michler's ketone, benzoin propyl ether,
Benzoin ethyl ether, benzyl dimethyl ketal, 1- (4-isopropylphenyl) -2-hydroxy-2-methylpropan-1-one, 2-hydroxy-
Examples thereof include 2-methyl-1-phenylpropan-1-one and thioxanthone compounds.

These photopolymerization initiators are used alone or in combination of two or more.

Synthesis Example 1 4,4'-Dicyclohexylmethane diisocyanate 2 was placed in a flask equipped with a thermometer, a stirrer and a reflux condenser.
37.3g, dibutyltin dilaurate 0.5g and mixed solvent of methyl ethyl ketone and cyclohexanone (volume ratio 50: 5
0) 550g was charged. After heating these mixtures to 60 ° C., 222.4 g of polybutylene adipate (Nipporan 4009 manufactured by Nippon Polyurethane Co., Ltd.), polyoxyethylene bisphenol A ether (with the dropping funnel being careful not to raise the temperature of the system). DA-350F manufactured by NOF CORPORATION 173.8
g, acrylic acid adduct of propylene oxide adduct of bisphenol A (Kyoeisha Yushi Co., Ltd. epoxy ester 30
02A, 49.4g 2-hydroxyethyl acrylate 9.6g, 4
Polyhydric alcohol compound (Adeka quadrol manufactured by Asahi Denka Co., Ltd.)
A uniform mixture of 6.1 g and 500 g of a mixed solvent of methyl ethyl ketone and cyclohexanone (volume ratio 50:50) was added dropwise, and after completion of the addition, the mixture was reacted at 60 ° C. for 8 hours to give a curable prepolymer (1) and methyl ethyl ketone. A mixture with cyclohexanone (weight ratio 40:60) was obtained. It was confirmed from this infrared absorption spectrum that no isocyanate group remained in the system.

Synthesis Example 2 A flask equipped with a thermometer, a stirrer and a reflux condenser was charged with 345 g of toluene diisocyanate and 0.5 g of dibutyltin dilaurate. After heating these mixtures to 60 ° C, pay attention not to raise the temperature of the system from the dropping funnel, taking care that polytetramethylene glycol (PTMG 1000 manufactured by Mitsubishi Kasei), 661.0 g ethylene glycol 4
A homogeneous mixture of 1.0 g and 153.4 g of hydroxyethyl acrylate was added dropwise. Further, 133.3 g of vinylpyrrolidone was added to the system in order to reduce the viscosity of the synthetic system. After the completion of the dropping, the mixture was reacted at 60 ° C for 8 hours to obtain a vinylpyrrolidone mixture of the curable prepolymer (2) (weight ratio 90:10). About this product, an isocyanate group remained in the system by infrared absorption spectrum. I confirmed that I did not.

Synthesis Example 3 To a flask equipped with a thermometer, a stirrer and a reflux condenser, 120.6 g of toluene diisocyanate, 0.5 g of dibutyltin dilaurate and 158.4 g of isobornyl acrylate as a diluting monomer were added.

After heating these mixtures to 60 ° C, pay attention to the temperature of the system from the dropping funnel, taking care not to raise the temperature of the system. Polytetramethylene glycol (PTMG 3000 manufactured by Mitsubishi Kasei) 103
A mixture of 9.3 g and 40.2 g of 2-hydroxyethyl acrylate dissolved in 200 g of isoboronyl acrylate as a diluting monomer and uniformly mixed was added dropwise. After completion of the dropping, the mixture was reacted at 60 ° C. for 8 hours to obtain a mixture (weight ratio 77:23) of curable prepolymer (3) and isobornyl acrylate. The infrared absorption spectrum of this product confirmed that there were no isocyanate groups in the system.

[Examples 1 to 6, Comparative Examples 1 to 3] Curable prepolymer (1) having an active energy ray-sensitive group synthesized by the method shown in Synthesis Examples 1, 2 and 3.
If necessary, a compound having an active energy ray-sensitive group, a photopolymerization initiator, and a photosensitizer are added to (2) and (3) at a ratio shown in Table 1 to prepare a curable composition (A),
(B) and (C) were obtained.

Each of these curable compositions (A), (B) and (C) is cast onto a Teflon sheet, and those containing a solvent are sufficiently desolvated under reduced pressure in advance,
While holding each curable resin composition at room temperature, each composition was cured by irradiation with ultraviolet rays or electron beams. The cured coating films of the respective compositions (A), (B) and (C) thus obtained were peeled off from the Teflon sheet and each composition was measured using an automatic viscoelasticity measuring device (manufactured by Toyo Baldwin Co., Ltd.). The temperature dependence of the loss tangent of the cured coating film of No. 1 was measured.
The measurement conditions are a strain frequency of 35 Hz and a heating rate of 2 ° C./min.
The temperature at which the loss tangent of the cured coating film of each of the compositions (A), (B) and (C) exhibits a maximum value is defined as the glass transition temperature and is shown in Table 1.

Then, in the same manner as described above, the curable compositions (A), (B) and (C) were applied on a Teflon sheet and on a polyester film (Lumirror 75 micron thickness manufactured by Toray Industries, Inc.).
Was cast, and those containing a solvent were sufficiently removed in advance under reduced pressure to prepare an uncured coating film having a film thickness of 50 μm. Then, as shown in Table 2, the temperature of each cast film at the time of irradiation was changed and each composition was cured by irradiation with ultraviolet rays or electron beams. Next, each cast film in Examples 1 to 6 and Comparative Examples 1 to 3 was previously placed in an atmosphere having the same temperature as the active energy ray irradiation atmosphere such as ultraviolet rays and electron beams, and the temperature of each cast film and the active energy ray irradiation. After confirming that the temperature of the atmosphere reached the thermal equilibrium sufficiently with the platinum resistor, the active energy ray was irradiated. Further, the temperature of the cast film at the time of irradiation with active energy rays was changed for each of the curable compositions (A), (B) and (C).

In this way, as shown in Table 2, cured coating films corresponding to Examples 1 to 6 and Comparative Examples 1 to 3 were obtained.

[Test Example] Regarding these cured coating films prepared on the Teflon sheet in Examples 1 to 6 and Comparative Examples 1 to 3, after peeling the cured coating film from the Teflon sheet, weathering was performed according to ASTM D750-55T. A weather resistance test was performed with an odometer. That is, water spraying was repeated every 6 hours for 1 hour, and after 100 hours, the polymerization-cured coating film was taken out, and the degree of color deterioration of the polymerization-cured coating film was compared. Table 2 shows the results of evaluation, in which those marked with yellowing were evaluated as unsuitable (x), and those with a slight degree of yellowing were evaluated as suitable (∘).

In addition, the tensile modulus of the cured coating film before and after the weather resistance test
It was measured according to K-7113, and when the change in tensile modulus before and after the weather resistance test was less than 20%, the weather resistance was good, and when it was 20% or more, the weather resistance was poor.

Furthermore, for cured coatings made on polyester film, JIS is used to judge the quality of the adhesion to the substrate.
A cross-cut test was conducted according to K-5400. The results of the cross-cut test are shown in Table 2 in which even one of 100 crosshatches is peeled, the substrate adhesion is poor, and when no crosshatch is peeled, the substrate adhesion is good. The cured coating films obtained in Examples 1 to 6 and Comparative Examples 1 to 3 were tested for the presence of surface tack, and Table 2 shows the evaluation results.

[Effects of the Invention] The present invention has the following effects.

1. According to the curing method of the present invention, a cured coating film having excellent weather resistance can be obtained.

2. According to the curing method of the present invention, it is possible to obtain a cured coating film having excellent adhesion performance to a substrate.

3. According to the curing method of the present invention, an excellent curing rate can be realized.

4. According to the curing method of the present invention, surplus thermal energy generated at the time of irradiation with active energy rays can be used and energy cost can be reduced.

5. The curing method of the present invention can be suitably used for curing a coating material for an optical fiber, curing a magnetic recording layer of a magnetic recording medium, and the like.

Front page continuation (72) Inventor Yoshio Matsumura 2-11-24 Tsukiji, Chuo-ku, Tokyo Japan Synthetic Rubber Co., Ltd. (72) Inventor Robert E. Ansel United States Illinois, Hoffman, Ill., Caldwell Lane, 1440 (56) References JP-A-51-66323 (JP, A)

Claims (1)

(57) [Claims] 1. When curing a curable compound by irradiating it with an active energy ray, the glass transition temperature of the cured product is
10 from the same temperature of the curable compound in the range of 40 ~ 200 ℃
A method for curing a curable compound, which comprises holding the curable compound within a range of a temperature lower by 10 ° C to a temperature higher by 10 ° C than the same temperature.