JP4261421B2 - Energy ray curable resin composition - Google Patents

Description

  The present invention relates to an energy ray curable resin composition comprising urethane acrylate. In particular, the present invention relates to a material used as a coating agent for forming a hard coat layer. Here, usable energy rays include rays such as ultraviolet rays and blue light, and electron rays and other radiation. The resin composition here is mainly in the state of oligomer or prepolymer.

In the past, it was common to use a thermosetting or solvent volatilization type resin composition for forming a coating film. However, the thermosetting type is not suitable for a substrate having no heat resistance, and the solvent volatilization type has a problem that the load on the environment is large. Therefore, in recent years, a coating method using a resin composition that can be cured by irradiation with energy rays has been developed in various fields (Japanese Patent Laid-Open No. 5-179156). However, there is a problem that the curing due to the irradiation of energy rays is accompanied by shrinkage, and the cured product is warped (warped) or cracked (cracked).
JP-A-5-179156

  In forming a coating film using a resin composition that can be cured by irradiation with energy rays, it is conceivable to increase the crosslinking density, particularly when the cured product requires high hardness. However, shrinkage at the time of curing becomes large and warping and cracking are likely to occur. Although a method of introducing an aromatic ring into the composition or structure of the resin can be considered, the viscosity becomes high and a large amount of diluent is required. If a solvent is used as the diluent at this time, the burden on the environment increases. Moreover, when an acrylate monomer is used as a diluent, problems such as insufficient physical properties of the main component occur. In particular, assuming optical use, yellowing becomes a problem if an aromatic ring is introduced into a compound at a high concentration.

  Urethane acrylate, which is often used as a resin composition that can be cured by irradiation with energy rays, has the advantage of easily controlling various physical properties, but generally has a high viscosity. Therefore, it is the actual situation that urethane acrylate having a high surface hardness of the cured coating film, a small shrinkage at the time of curing, and a low viscosity is desired. Furthermore, it is even better if the light yellowing resistance is good.

  The present invention has been made in view of the above, and in an energy ray curable resin composition made of urethane acrylate, the surface hardness of the cured product exhibits a high hardness of 5H or more in pencil hardness, and shrinkage upon curing is caused. The object is to provide a material having a small viscosity and a viscosity of 20 Pa · s or less at 40 ° C.

  The energy ray-curable resin composition of the present invention comprises an aliphatic diisocyanate (first reaction component), an isocyanurate-type trimer of aliphatic diisocyanate (second reaction component), monohydroxy mono (meth) acrylate ( It comprises a urethane acrylate obtained by reacting a third reaction component) with monohydroxytri (meth) acrylate (fourth reaction component). Here, the molar ratio of hydroxyl groups to isocyanate groups (—OH / —NCO) is 1.0 to 1.5. The molar ratio of the aliphatic diisocyanate (first reaction component) to the isocyanurate-type trimer (second reaction component) in the reaction charge ratio is 2.0 to 4.0, and monohydroxytri (meth) The molar ratio of monohydroxymono (meth) acrylate (third reaction component) to acrylate (fourth reaction component) is 0.25 to 1.0.

  In the present application, “(meth) acrylate” refers to acrylate (acrylic acid ester) or methacrylate (methacrylic acid ester), or a mixture thereof.

  “Monohydroxymono (meth) acrylate” refers to a compound having one hydroxyl group and one (meth) acrylate group in the molecule. Generally, it is an ester of one acrylic acid and one diol, one ester of methacrylic acid and one diol, or a mixture thereof. Similarly, “monohydroxytri (meth) acrylate” has one hydroxyl group and three (meth) acrylate groups in the molecule, and generally one tetraol and three acrylic acids. Or an ester with methacrylic acid.

  According to the energy ray curable resin composition of the present invention, while exhibiting a high surface hardness, it has a small cure shrinkage and a low viscosity, so that it can be used to hard coat plastic molded articles and films such as PET and polycarbonate. Useful. Moreover, since it has good light yellowing resistance and transparency, it can be applied to the optical field.

The aliphatic diisocyanate as the first reaction component used to produce the urethane acrylate is a compound having a molecular weight of less than 1000, consisting of an aliphatic linear or branched chain or an aliphatic ring. Preferable examples include those having an isocyanate group at both ends of an aliphatic straight chain having 4 to 10 carbon atoms. For example, hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), hydrogenated MDI (H ₁₂ MDI; hydrogenated diphenylmethane diisocyanate), trimethylhexamethylene diisocyanate (TMDI), or the like can be used.

The isocyanurate type trimer as the second reaction component is a trimer of the same aliphatic diisocyanate as described above. That is, it is a triisocyanate compound centered on an isocyanurate ring. Similar to the above, there may be mentioned a trimerized diisocyanate having an isocyanate group at both ends of an aliphatic straight chain having 4 to 10 carbon atoms. Particularly preferred is, for example, a trimer of hexamethylene diisocyanate (HDI). However, depending on the case, a trimer such as isophorone diisocyanate (IPDI) or hydrogenated MDI (H ₁₂ MDI) may be used.

  The monohydroxy mono (meth) acrylate as the third reaction component is preferably a diol composed of an aliphatic or alicyclic carbon chain having 2 to 8 carbon atoms, or a molecular chain having 4 to 12 carbon atoms including an ether bond. And an ester of acrylic acid or methacrylic acid. More preferably, it is an ester with a diol comprising an aliphatic or alicyclic carbon chain having 2 to 4 carbon atoms. Moreover, it is preferably composed of a diol in which one hydroxyl group is a secondary hydroxyl group. That is, it is a (meth) acrylate compound having one secondary hydroxyl group. Particularly preferred are 2-hydroxypropyl (meth) acrylate, 2-hydroxy-n-butyl (meth) acrylate, 3-hydroxy-n-butyl (meth) acrylate and the like.

  The monohydroxytri (meth) acrylate as the fourth reaction component is preferably a tetraol composed of an aliphatic or alicyclic carbon chain having 5 to 8 carbon atoms, or a molecular chain having 8 to 12 carbon atoms including an ether bond. It is an ester of 1 diol consisting of 3 and 3 acrylic acid or methacrylic acid. Preferably, all hydroxyl groups are composed of tetraols that are primary hydroxyl groups. In this case, the remaining hydroxyl group is also a primary hydroxyl group, and the reactivity with the isocyanate group is higher than that of the secondary hydroxyl group. Particularly preferred are pentaerythritol tri (meth) acrylate and the like.

  If the molar ratio (-OH / -NCO) of the hydroxyl group to the isocyanate group in the structure of the urethane acrylate is less than 1.0, unreacted isocyanate remains in the product, which is not preferable from the viewpoint of storage stability and the like. On the other hand, when the ratio exceeds 1.5, many unreacted hydroxyl groups remain, so that monohydroxy mono (meth) acrylate (third reaction component) and monohydroxy tri (meth) acrylate (fourth reaction component) remain unreacted. The reaction remains not a little. Therefore, problems such as a large shrinkage during the curing reaction occur.

  When the molar ratio of the aliphatic diisocyanate (first reaction component) to the isocyanurate-type trimer (second reaction component) is less than 2.0 and more than 4.0, curing occurs. The shrinkage at the time cannot be sufficiently suppressed, and the cured product is warped (warped) and cracked (cracked).

  If the molar ratio of monohydroxy (meth) acrylic acid ester (third reaction component) to monohydroxytri (meth) acrylic acid ester (fourth reaction component) exceeds 1.0, the crosslinking density becomes low and sufficient hardness is obtained. Further, when the molar ratio is less than 0.25, the toughness is lowered, which is not preferable.

The urethane acrylate of the present invention can be synthesized by a known method. For example, first, the first to fourth reaction components are charged all at a predetermined molar ratio, and a polymerization inhibitor such as hydroquinone monomethyl ether is charged. And a urethane acrylate is obtained by heating and stirring at 70-80 degreeC until there is no free isocyanate. Specific examples of the reaction component include hexamethylene diisocyanate (I), hexamethylene diisocyanate isocyanurate type trimer (II), 2-hydroxypropyl acrylate (III), pentaerythritol triacrylate (IV ) And all at once. The structural formula of each reaction component in this specific example is shown below.

  When the curable resin composition of the present invention is used as a paint, it can be diluted with an organic solvent such as ethyl acetate or methyl ethyl ketone and monomers. When diluted with a monomer, urethane (meth) acrylate and monomer It is desirable that the content of urethane (meth) acrylate in the sum of is 50% by weight or more.

  As the monomers used for dilution, known and commonly used monomers can be used. Among them, typical examples include 2-ethylhexyl (meth) acrylate, styrene, methyl (meth) acrylate, tetrahydrofurfuryl (meth) acrylate, Phenoxyethyl (meth) acrylate, isobornyl (meth) acrylate, ethylene glycol di (meth) acrylate, propylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate, polypropylene glycol di (meth) acrylate, 1,4-butane Diol di (meth) acrylate, 1,6-hexanediol di (meth) acrylate, EO modified bisphenol di (meth) acrylate, PO modified bisphenol di (meth) acrylate, EO modified trimethylolpropane tri (meth) acrylate , PO-modified trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, tris ((meth) acryloxyethyl) isocyanurate, dipentaerythritol hexa (meth) acrylate, dipentaerythritol penta (meth) acrylate Etc. These may be used independently and may use multiple types together.

  If necessary, a photopolymerization initiator is added to the energy beam curable resin composition of the present invention.

  The type of the photopolymerization initiator is not particularly limited, and known ones can be used. Typical examples include 1-hydroxycyclohexyl phenyl ketone and 2-hydroxy-2-methyl-1-phenylpropane-1. -One, benzyl dimethyl ketal, benzoin isopropyl ether, benzophenone and the like. These may be used alone or in combination.

  Moreover, the addition amount in the case of using a photoinitiator is about 1 to 10 weight% with respect to the sum total of the urethane acrylate and the said monomer used as needed, and about 3 to 5 weight% is preferable.

  Furthermore, the energy ray curable resin composition of the present invention includes a light stabilizer, an ultraviolet absorber, a catalyst, a colorant, an antistatic agent, a lubricant, a leveling agent, an antifoaming agent, a polymerization accelerator, if necessary. Antioxidants, flame retardants, infrared absorbers, surfactants, surface modifiers, and the like can be added.

  The energy ray source for curing the energy ray curable resin composition of the present invention is not particularly limited, and examples include high pressure mercury lamp, electron beam, γ ray, carbon arc lamp, xenon lamp, metal halide lamp and the like. .

The energy ray curable resin composition of the present invention can be used as a coating agent for forming a hard coat layer of an automobile bumper, a home appliance, an information recording medium or the like.
The energy ray curable resin composition of the present invention has a low viscosity in the state where no solvent is added, and the viscosity at 40 ° C. by an E-type rotational viscometer is preferably 20 Pa · s or less, more preferably 10 Pa · s or less. It is. Therefore, a good coating can be easily performed.

  Hereinafter, the present invention will be described with reference to examples and comparative examples. In the following, the blending ratio and “%” are all based on weight unless otherwise specified.

[Synthesis of Urethane Acrylate (A) in Examples]
In a flask, 117.6 g (0.7 mol) of hexamethylene diisocyanate, 151.2 g (0.3 mol) of an isocyanurate type trimer of hexamethylene diisocyanate, 0.55 g of hydroquinone monomethyl ether, 2-hydroxy 128.7 g (0.99 mol) of propyl acrylate and 693 g (1.54 mol) of pentaerythritol triacrylate are charged and reacted under the conditions of 70 to 80 ° C. until the residual isocyanate concentration becomes 0.1% or less. The urethane acrylate A was obtained.

[Synthesis of Urethane Acrylate (B) of Comparative Example 1]
A flask was charged with 168 g (1 mol) of hexamethylene diisocyanate, 0.58 g of hydroquinone monomethyl ether, and 990 g (2.2 mol) of pentaerythritol triacrylate, and reacted in the same manner as in Synthesis Example 1 to obtain urethane acrylate B.

[Synthesis of Urethane Acrylate (C) of Comparative Example 2]
504 g (1 mol) of isocyanurate type trimer of hexamethylene diisocyanate, 0.47 g of hydroquinone monomethyl ether, and 429 g (3.3 mol) of 2-hydroxypropyl acrylate were reacted in the same manner as in Synthesis Example 1, and urethane acrylate C was obtained.

The reaction molar ratios for the urethane acrylates of the above Examples and Comparative Examples are shown in Table 1.

[Evaluation of urethane acrylates of Examples and Comparative Examples 1 and 2]
About the urethane acrylate obtained by the said synthesis example and the comparative synthesis example, the physical property was measured in the following ways. The results are shown in Table 2.

Viscosity: Viscosity was measured (Pa · s) at 40 ° C. using an E-type viscometer.

-Refractive index: Measured with an Abbe refractometer at a measurement temperature of 25 ° C.

Curing shrinkage: The specific gravity at 20 ° C. before and after curing of the resin cured under the following conditions was measured with a pycnometer, and the volume shrinkage was obtained by the following formula.

Volume shrinkage (%) = [(specific gravity after curing−specific gravity before curing) / specific gravity after curing] × 100
Pencil hardness: Measured according to JIS K 5400. The hardness without scratches was determined.

-Light yellowing resistance: The initial YI value of the cured product and the YI value after the accelerated light deterioration test were measured with a color difference meter SE2000 type manufactured by Nippon Denshoku Co., Ltd. The accelerated light deterioration test was performed by irradiating the cured product with ultraviolet rays of 3200 mJ / cm ² using a high-pressure mercury lamp 80 W / cm. The light yellowing resistance of the cured resin is evaluated based on the YI values after the initial and accelerated light deterioration tests thus obtained. The initial YI value is 2 or less and the YI value after the test is 10 The following were considered acceptable.

-Transparency: The transparency of the cured product was visually determined as follows.

            ○: Transparent. X: There is turbidity.

Curing conditions: Urethane acrylate / Irgacure 184 (polymerization initiator; Irgacure is a trademark of Geigy) = 100/3 (weight ratio) were mixed and dissolved uniformly. And it apply | coated with the 100-micrometer applicator bar on the glass plate, and irradiated the ultraviolet-ray of the integrated illumination intensity 170mJ / cm < ² > using the 80w / cm high pressure mercury lamp.

  As can be seen from Table 2, the urethane acrylates of the examples had a sufficiently low viscosity before curing and a volume shrinkage ratio upon curing, and exhibited a sufficient pencil hardness after curing. Moreover, the light yellowing resistance and transparency of the cured product were also good. On the other hand, in Comparative Example 1 synthesized by a conventional general urethane acrylate formulation, the viscosity was low and the pencil hardness and transparency were good, but the volumetric shrinkage during curing was large. Moreover, light yellowing resistance was quite large.

  On the other hand, in Comparative Example 2 synthesized only from the trimer and monoacrylate, the viscosity before curing and the volume shrinkage during curing were low, and the light yellowing resistance and transparency were good, but the pencil hardness of the cured product was It was considerably lower than that of the example.

Claims (4)

An aliphatic diisocyanate that is at least one selected from hexamethylene diisocyanate, isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, and trimethylhexamethylene diisocyanate;
Isocyanurate type triisocyanate obtained by trimerizing at least one aliphatic diisocyanate selected from hexamethylene diisocyanate, isophorone diisocyanate, and hydrogenated diphenylmethane diisocyanate ;
A first (meth) acrylate that is at least one selected from 2-hydroxypropyl (meth) acrylate, 2-hydroxy-n-butyl (meth) acrylate, and 3-hydroxy-n-butyl (meth) acrylate; ,
It consists of urethane acrylate produced from the second (meth) acrylate which is pentaerythritol tri (meth) acrylate, and the molar ratio of each reaction component at this time is within the range shown by the following formulas (1) to (3). An energy ray-curable resin composition characterized by being.
Hydroxyl group / isocyanate group (—OH / —NCO) = 1.0 to 1.5 (1)
Aliphatic diisocyanate / isocyanurate type triisocyanate = 2.0 to 4.0
(2)
First (meth) acrylate / second (meth) acrylate = 0.25 to 1.0 (3)   A coating agent for hard coat, comprising the energy ray-curable resin composition according to claim 1 and having a viscosity (E-type rotational viscometer, 40 ° C) of 20 Pa · s or less in a state where no solvent is added.   A cured product having a pencil hardness of 5H or more obtained by curing the energy beam curable resin composition according to claim 1 or 2. An aliphatic diisocyanate that is at least one selected from hexamethylene diisocyanate, isophorone diisocyanate, hydrogenated diphenylmethane diisocyanate, and trimethylhexamethylene diisocyanate;
Isocyanurate type triisocyanate obtained by trimerizing at least one aliphatic diisocyanate selected from hexamethylene diisocyanate, isophorone diisocyanate, and hydrogenated diphenylmethane diisocyanate ;
A first (meth) acrylate that is at least one selected from 2-hydroxypropyl (meth) acrylate, 2-hydroxy-n-butyl (meth) acrylate, and 3-hydroxy-n-butyl (meth) acrylate; ,
The second (meth) acrylate, which is pentaerythritol tri (meth) acrylate, is charged all at once so that the molar ratio is within the range of the following formulas (1) to (3), stirred, mixed and heated. A method for producing an energy ray-curable resin composition, characterized in that urethane acrylate is produced by the method.
Hydroxyl group / isocyanate group (—OH / —NCO) = 1.0 to 1.5 (1)
Aliphatic diisocyanate / isocyanurate type triisocyanate = 2.0 to 4.0
(2)
First (meth) acrylate / second (meth) acrylate = 0.25 to 1.0 (3)