UV-curable resin composition

Abstract

This invention provides an ultraviolet-curable resin composition that has appropriate viscosity and shape retention suitable for molding applications such as creating brooches and other accessories, while also exhibiting excellent transparency. [Solution] An ultraviolet-curable resin composition comprising a polyfunctional urethane acrylate, a thiol, a rheology control agent, and a photopolymerization initiator, wherein the rheology control agent comprises a castor oil derivative, and the viscosity of the composition as measured by an E-type viscometer is 5,000 to 50,000 mPa·s.

Description

Technical Field

[0001] The present invention relates to an ultraviolet-curable resin composition.

Background Art

[0002] Acrylic photocurable resins are used in many fields to impart special properties to the surfaces of plastic films and plastic molded articles. For example, a hard coat film coated on a PET (polyethylene terephthalate) film to impart high hardness is widely used in touch panel products, and an adhesive film imparting viscosity to the film is used as a protective film in flat panel display products including the final product and in the manufacturing process.

[0003] Even in fields other than those where a thin film is coated on such a plastic surface to impart special properties, acrylic resins are used as casting resins for making accessories such as brooches and small items by taking advantage of their hardness and transparency (Patent Document 1). And in the past, the applicant has invented a composition comprising a bifunctional urethane (meth) acrylate resin having a number average molecular weight of 1,000 to 7,000 in a polyether backbone, a monofunctional methacrylate monomer or an aromatic acrylate monomer or an aliphatic acrylate monomer having no polar group, and a photoinitiator (Patent Document 2).

[0004] This invention was excellent in that it cured sufficiently without leaving stickiness even when cured with a black light source. However, when processing the resin into a desired shape when making accessories or the like, it deformed before ultraviolet curing, and thus was not sufficient in terms of shape retention. Also, in order to improve shape retention, there is a method of blending a filler or the like to increase thixotropy, but in that case, due to the influence of the blended filler, coloring or a decrease in the transparency of the resin may occur, and problems on the design side may arise. Therefore, there was room for improvement in order to ensure sufficient transparency while having shape retention before ultraviolet curing. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 10-264184 [Patent Document 2] Patent No. 6335853 [Overview of the project] [Problems that the invention aims to solve]

[0006] The object of the present invention is to provide an ultraviolet-curable resin composition that has excellent transparency while possessing shape retention properties suitable for molding applications such as accessories. [Means for solving the problem]

[0007] To achieve the above objectives, the invention of claim 1 provides an ultraviolet-curable resin composition comprising a polyfunctional urethane (meth)acrylate (A), a thiol (B), a rheology control agent (C), and a photopolymerization initiator (D), wherein (C) comprises a castor oil derivative, and the viscosity of the composition as measured by an E-type viscometer is 5,000 to 50,000 mPa·s.

[0008] The invention of claim 2 provides the ultraviolet-curable resin composition according to claim 1, characterized in that (A) is a polyfunctional urethane (meth)acrylate having a polytetramethylene glycol skeleton.

[0009] The invention of claim 3 provides the ultraviolet-curable resin composition according to claim 1, further comprising a phosphate ester (E).

[0010] The invention of claim 4 provides an ultraviolet-curable resin composition according to any one of claims 1 to 3, characterized in that it is a molding resin. [Effects of the Invention]

[0011] The composition of the present invention exhibits good shape retention before UV curing and also has excellent transparency, making it useful as a UV-curing molding resin suitable for handicrafts such as making accessories like brooches and small items. [Modes for carrying out the invention]

[0012] The UV-curable resin composition of the present invention comprises a polyfunctional urethane (meth)acrylate (A), a thiol (B), a rheology control agent (C), and a photopolymerization initiator (D). In this specification, (meth)acrylate includes both acrylate and methacrylate. Furthermore, (poly)ethylene glycol includes both ethylene glycol and polyethylene glycol.

[0013] The polyfunctional urethane (meth)acrylate (hereinafter referred to as polyfunctional urea) (A) used in the present invention is one of the main components that constitute the cured film. For example, it can be produced by reacting a urethane prepolymer obtained by reacting a polyol with a polyisocyanate, and further reacting hydroxy(meth)acrylate with both ends, resulting in a structure having two or more (meth)acryloyl groups and urethane bonds in one molecule.

[0014] Examples of the aforementioned polyols include polyethers, polyesters, polycarbonates, and polydienes. Among these, polyethers with high elongation are preferred, and polytetramethylene glycol (hereinafter PTMG) is even more preferred. Examples of polyisocyanates include aromatics, aliphatics, and alicyclics, but among these, non-aromatics with excellent weather resistance are preferred, and alicyclics are even more preferred because they can provide high hardness. Among alicyclics, isophorone diisocyanate (hereinafter IPDI) is particularly preferred.

[0015] There are no particular restrictions on the synthesis method of (A), and known methods can be used. The reaction may be carried out without a solvent, but since stirring may become difficult as the molecular weight of (A) increases, ketones such as MEK, aromatic inert solvents such as xylene, etc. may be used. It is preferable to use a catalyst for the reaction between the polyol and the polyisocyanate, and for the reaction between the urethane prepolymer and the hydroxy(meth)acrylate. Examples of catalysts in this case include tin-based catalysts such as dioctyltin dilaurate and dibutyltin dilaurate, and metal alkoxide-based catalysts such as cobalt naphthenate. In the reaction between the urethane prepolymer and the hydroxy(meth)acrylate, the progress of the reaction may be confirmed by the decrease in the peak originating from the isocyanate group in the infrared absorption spectrum. The reaction temperature can be set as appropriate, but 40 to 100°C is preferred, and 60 to 90°C is more preferred.

[0016] The number of functional groups in (A) above is preferably 2 to 10, more preferably 2 to 6, and particularly preferably 2, in terms of a good balance between reaction curability, curing shrinkage, and storage stability. Sufficient reaction curability can be ensured by having 2 or more functional groups, and curing shrinkage can be sufficiently suppressed by having 10 or fewer functional groups.

[0017] The weight-average molecular weight (hereinafter referred to as Mw) of (A) above is preferably 1,000 to 30,000, more preferably 1,500 to 10,000, and particularly preferably 2,000 to 6,000. Setting it to 1,000 or higher ensures sufficient shape retention, while setting it to 30,000 or lower makes it easier to adjust the viscosity to suit workability. Mw was measured and calculated as the molecular weight on a standard polystyrene basis using gel permeation chromatography with a column packed with a styrenedivinylbenzene substrate and a tetrahydrofuran eluent.

[0018] The amount of (A) is preferably 45 to 70% by weight, more preferably 50 to 65% by weight, and particularly preferably 52 to 62% by weight, relative to the total amount of solids. A concentration of 45% by weight or more ensures sufficient shape retention, while a concentration of 70% by weight or less makes it easier to adjust the viscosity to suit workability.

[0019] The thiol (B) used in this invention is added to promote the ultraviolet curing reaction of the composition. The inclusion of (B) enables an enthiol reaction that can suppress curing inhibition by oxygen, thereby improving deep curing properties and forming a film with low curing shrinkage. Primary thiols are preferred over secondary thiols due to their higher reactivity.

[0020] The number of thiol functional groups in (B) above is preferably 2 to 6, and more preferably 3 to 5. Using 2 or more functional groups is expected to accelerate the curing reaction, while using 6 or fewer functional groups ensures sufficient storage stability. For example, tetraethylene glycol bis(3-mercaptopropionate) is a bifunctional compound; trimethylolpropane tris(3-mercaptopropionate) is a trifunctional compound; pentaerythritol tetrakis(3-mercaptopropionate) is a tetrafunctional compound; and dipentaerythritol hexa-3-mercaptopropionate is a hexafunctional compound. These can be used individually or in combination of two or more. Among these, tetrafunctional pentaerythritol tetrakis(3-mercaptopropionate) is preferred due to its balanced reaction curing properties and storage stability.

[0021] The amount of (B) is preferably 3 to 15 parts by weight, more preferably 5 to 12 parts by weight, and particularly preferably 7 to 10 parts by weight, relative to the total amount of solids. A concentration of 3 parts by weight or more is expected to improve curability, while a concentration of 15 parts by weight or less ensures sufficient storage stability. Examples of commercially available products include PEMP (product name: pentaerythritol tetrakis(3-mercaptopropionate) manufactured by SC Organic Chemicals Co., Ltd.).

[0022] The rheology control agent (hereinafter referred to as RC agent) (C) used in the present invention is blended to impart thixotropy to the composition. For example, in the organic system, there are castor oil derivative systems, cellulose ether derivative systems, polyamide wax systems, surfactant systems, and in the inorganic system, there are silica, bentonite, surface-treated calcium carbonate, etc. The present composition contains an organic castor oil derivative.

[0023] The castor oil derivative has the property of forming a swollen gel structure, and hydrogen bonds are formed between the swollen particles and dispersed in a colloidal state to form a three-dimensional network structure, thereby imparting thixotropy. In addition, the composition containing it has a high light transmittance, so good transparency can be ensured, and by selecting an appropriate photoinitiator, the deep curing property can be easily improved.

[0024] The blending amount of the above (C) is preferably 1 to 15% by weight, more preferably 2 to 10% by weight, and particularly preferably 3 to 6% by weight based on the whole composition. By setting it at 1% by weight or more, thixotropy can be imparted to the composition, and by setting it at 15% by weight or less, over-blending does not occur and good curability can be ensured. Further, the blending amount of the castor oil derivative in (C) is preferably 50% by weight or more, more preferably 80% by weight or more, and particularly preferably 100% by weight. Examples of commercially available products of (C) include RHEOCIN and RHEOBYK-7590 (trade names: both manufactured by BYK).

[0025] The photoinitiator (D) used in the present invention generates radicals upon irradiation with ultraviolet rays, electron beams, etc., and these radicals serve as the trigger for the polymerization reaction. General-purpose photoinitiators such as benzyl ketal-based, acetophenone-based, phosphine oxide-based, etc. can be used. By arbitrarily selecting the light absorption wavelength of the photoinitiator, curability can be imparted over a wide wavelength range from the ultraviolet region to the visible light region. Specifically, 2,2-dimethoxy-1,2-diphenylethane-1-one as a benzyl ketal-based, 1-hydroxy-cyclohexyl-phenyl-ketone and 1-[4-(2-hydroxyethoxy)-phenyl]-2-hydroxy-2-methyl-1-propan-1-one as an α-hydroxyacetophenone-based, 2-methyl-1-(4-methylthiophenyl)-2-morpholinopropan-1-one as an α-aminoacetophenone-based, 2,4,6-trimethylbenzoyl-diphenyl-phosphine oxide and bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide as an acylphosphine oxide-based, etc. are available, and they can be used alone or in combination of two or more.

[0026] Among these, it is preferable to include an acylphosphine oxide-based which has high sensitivity to long wavelength light sources such as LEDs, and has a photobleaching effect where decomposition progresses with light irradiation and post-absorption disappears, thus being excellent in deep part curability. Examples of commercially available products include Omnirad TPO H (trade name: manufactured by iGM Resins).

[0027] The blending amount of the above (D) is preferably 0.1 to 8 parts by weight, more preferably 0.5 to 5 parts by weight, and particularly preferably 1 to 3 parts by weight with respect to 100 parts by weight of the radically polymerizable component. By blending within this range, the composition can be cured efficiently.

[0028] The present invention preferably further incorporates a phosphate ester (E). The inclusion of (E) improves shelf life. In particular, it is possible to suppress viscosity increase even when stored in high-temperature environments, such as around 60°C. A (meth)acrylate monomer having a phosphate ester group is preferred due to its compatibility with (A), curability, and reduced likelihood of bleeding from the cured film.

[0029] Examples of (E) include 2-(meth)acryloyloxyethyl dihydrophosphate and dipentaerythritol penta(meth)acryloyloxydihydrogen phosphate. Commercially available products include KAYAMER PM-2 and PM-21 (trade names: both manufactured by Nippon Kayaku Co., Ltd.).

[0030] The amount of (E) is preferably 0.1 to 5% by weight, more preferably 0.3 to 3% by weight, and particularly preferably 0.5 to 2% by weight, based on the total amount of solids. By keeping it within this range, it is possible to suppress the increase in viscosity even when stored in a relatively high-temperature environment, and a sufficient improvement in storage stability can be expected.

[0031] The present invention may include reactive diluents for purposes such as viscosity adjustment and improvement of reaction curing properties. These preferably have acrylic groups for compatibility with (A), and examples include (meth)acrylate monomers and (meth)acrylamide, which can be used alone or in combination of two or more. The number of functional groups is preferably three or less, more preferably two or less, and particularly preferably monofunctional. By using three or fewer functional groups, curing shrinkage can be sufficiently suppressed.

[0032] Examples of the (meth)acrylate monomers include n-propyl(meth)acrylate, isopropyl(meth)acrylate, and butyl(meth)acrylate as linear (branched) alkyl monomers; cyclohexyl(meth)acrylate and isobornyl(meth)acrylate as alicyclic monomers; 2-hydroxyethyl(meth)acrylate and 3-hydroxypropyl(meth)acrylate as monomers having a hydroxyl group; benzyl(meth)acrylate, phenoxyethyl acrylate, and phenoxydiethylene glycol(meth)acrylate as monomers having an aromatic ring; and ethoxyethoxyethyl(meth)acrylate and (poly)ethylene glycol di(meth)acrylate as ether skeleton monomers. Examples of (meth)acrylamides include N,N-dimethyl(meth)acrylamide and acryloylmorpholine.

[0033] Among the reactive diluents mentioned above, monomers containing hydroxyl groups, monomers having aromatic rings, monomers having an ether skeleton, and acrylamides are preferred due to their good curability and dilutability. In particular, among these, 2-hydroxypropyl methacrylate, polyethylene glycol diacrylate, phenoxydiethylene glycol acrylate, N,N-dimethylacrylamide, and acryloyl morpholine are preferred.

[0034] The amount of the reactive diluent can be adjusted to the desired viscosity. For example, 15 to 45% by weight relative to the total solid content is exemplified, with 20 to 40% by weight being preferred. A concentration of 15% by weight or more makes it easier to adjust the viscosity to suit workability, while a concentration of 45% by weight or less ensures sufficient shape preservation.

[0035] The composition of the present invention may contain various additives as needed, such as stabilizers, surface modifiers, polymerization inhibitors, plasticizers, tackifiers, pigments, dyes, defoamers, thickeners, and wettability modifiers, to the extent that it does not impair performance.

[0036] The aforementioned stabilizers are added to suppress the deterioration of physical properties over time due to absorption of ultraviolet light, heat, etc. Examples of stabilizers include light stabilizers and antioxidants. Specifically, examples include ultraviolet absorbers such as benzotriazole and triazine types, and antioxidants such as hindered amine, hindered phenol, phosphite, and thioether types, which can be used individually or in combination of two or more.

[0037] The amount of the stabilizer is preferably 0.01 to 3.0% by weight, and more preferably 0.05 to 2 parts by weight, relative to the total amount of solids. By keeping the amount within this range, deterioration of physical properties over time can be suppressed. Examples of commercially available hindered amine-based stabilizers include Tinuvin 249 (trade name: manufactured by BASF Japan).

[0038] The aforementioned surface modifiers are formulated to ensure uniformity of appearance during injection molding and to improve de-foaming properties. Examples include silicone-based, fluorine-based, fluorosilicone-based, acrylic-based, and vinyl-based compounds, which can be used individually or in combination of two or more. Among these, silicone-based compounds are preferred because they have a high ability to reduce surface tension and do not fall under the category of PFAS. Furthermore, silicone-based compounds having an acrylic polymer backbone in their molecule are particularly preferred due to their excellent compatibility with (A) and acrylic-based reactive diluents.

[0039] The amount of the surface modifier is preferably 0.005 to 1.0% by weight, and more preferably 0.01 to 0.3% by weight, relative to the total amount of solids. Within this range, good uniformity of appearance and de-foaming properties can be ensured. Examples of commercially available products include Polyflow KL-700 (product name: manufactured by Kyoeisha Chemical Co., Ltd., silicone-containing acrylic polymer type).

[0040] The polymerization inhibitor is added to suppress viscosity increase during high-temperature storage. By adding a small amount of polymerization inhibitor, it is possible to effectively bring out the performance of the phosphate ester and reduce the amount of the inhibitor added. Specifically, dibutylhydroxytoluene (hereinafter referred to as BHT) is an example, and the amount added is preferably 0.03 to 0.3 parts by weight per 100 parts by weight of the photoreactive component.

[0041] The viscosity of this composition at 25°C, measured using an E-type viscometer, is 5,000 to 50,000 mPa·s, preferably 6,000 to 40,000 mPa·s, and more preferably 8,000 to 30,000 mPa·s. A viscosity of 5,000 mPa·s or higher improves workability and facilitates casting, while a viscosity of 50,000 mPa·s or lower ensures good reproducibility of the casting mold and good bubble release.

[0042] Viscosity was measured using a rotor with a cone angle of 3°R17.65, and the value was read one minute after the start of rotation. The measurement rotation speed was set to 5 rpm for viscosity values ​​between 1,000 and 30,000 mPa·s, and to 3 rpm for viscosity values ​​above 30,000 mPa·s.

[0043] The TI value (thixotropic index value) of this composition is preferably 2.0 to 8.0, more preferably 2.5 to 6.0, and particularly preferably 2.7 to 5.5. A value of 2.0 or higher ensures sufficient shape retention, while a value of 8.0 or lower ensures sufficient casting mold reproducibility and bubble release. The TI value was measured using the same rotor as used for viscosity measurement, but at one-tenth the rotation speed of the viscosity measurement, and the viscosity (referred to as viscosity 2) was measured again. The value obtained by dividing viscosity 2 by the initially measured viscosity was then used.

[0044] This composition is preferably solvent-free. When this composition is poured into a casting mold and cured, being solvent-free eliminates the need to allow for solvent drying time. Note that "solvent-free" means excluding the intentional inclusion of solvents for dilution purposes in the composition, and does not mean removing even trace amounts of volatile components contained in each component of the composition. The solvent content refers to 5% by weight or less, typically 1% by weight or less.

[0045] The present invention will be described in more detail below with reference to examples and comparative examples, but these are merely examples and are not limiting. Unless otherwise stated, measurements were taken under conditions of 25°C and 65% relative humidity. The amounts of ingredients are expressed in parts by weight on a solid content basis. [Examples]

[0046] Example 1 In a light-shielding bottle, (A) Ureac A (reaction product of PTMG and IPDI reacted with hydroxy(meth)acrylate, Mw. 3000), (B) PEMP (trade name: manufactured by SC Organic Chemicals, pentaerythritol tetrakis(3-mercaptopropionate)), (C) RHEOBYK-7590 (trade name: manufactured by BYK, castor oil derivative), (D) OmniradTPO (manufactured by iGM, acylphosphine oxide type), (E) KAYAMER PM-2 (trade name: manufactured by Nippon Kayaku Co., Ltd.), and Light Ester HOP(N) (trade name: manufactured by Kyoeisha Chemical Co., Ltd., 2-hydroxypropyl methacrylate) as a reactive diluent were mixed in the amounts listed in Tables 1 and 2, and stirred for at least 15 minutes using a stirring and degassing machine until homogeneous to prepare the UV-curable resin composition of Example 1.

[0047] Examples 2-10 In addition to the materials used in Example 1, 9EG-A (product name: manufactured by Kyoeisha Chemical Co., Ltd., PEG400# diacrylate), MIRAMER M140 (product name: manufactured by Miwon, phenol EO modified acrylate), ACMO (product name: manufactured by KJ Chemicals, acryloyl morpholine), and DMAA (product name: manufactured by KJ Chemicals, dimethylacrylamide) were used as reactive diluents, KL-700 (product name: manufactured by Kyoeisha Chemical Co., Ltd., organic group-containing polydimethylsiloxane) as a surface modifier, Tinuvin 249 (product name: manufactured by BASF Japan, hindered amine type) as a stabilizer, and dibutylhydroxytoluene as a polymerization inhibitor. The mixture was stirred for at least 15 minutes using a stirring and degassing machine until homogeneous, according to the formulations shown in Tables 1 and 2, to prepare the UV-curable resin compositions of Examples 2 to 10.

[0048] Comparative Examples 1-6 In addition to the materials used in the examples, Aerosil RX200 (product name: manufactured by Nippon Aerosil Co., Ltd., fumed silica), Disparon 6650 (product name: manufactured by Kusumoto Chemical Co., Ltd., fatty acid amide wax), and Disparon 6700 (product name: manufactured by Kusumoto Chemical Co., Ltd., fatty acid amide wax) were used as RC agents, and the mixtures were stirred for at least 15 minutes using a stirring and defoaming machine until homogeneous to prepare the UV-curable resin compositions of Comparative Examples 1 to 6, according to the formulations shown in Table 3.

[0049] Preparation of evaluation samples Three g of the resin composition at room temperature was placed in a silicone mold (Elber Co., Ltd., Silicone Motif RSSD-2, 20 mm x 32 mm x t5 mm). The resin was cured by irradiating it from a height of 4 cm above the resin surface using an LED lamp XSR-120 LED & UV LAMP2 (Elber Co., Ltd.) at an output of 6 W, wavelength of 365 nm + 405 nm for 1 minute, and then from the back for another minute. The cured product was then removed from the silicone mold and left at 23 ± 2 °C for 30 minutes to be used as an evaluation sample.

[0050] Table 1 JPEG2026088795000001.jpg126154

[0051] Table 2 JPEG2026088795000002.jpg124153

[0052] Table 3 JPEG2026088795000003.jpg120158

[0053] The evaluation method was as follows:

[0054] Viscosity: A Toki Sangyo RC-550 cone-plate viscometer was used for measurement. The cone angle was 3°R17.65, the temperature was 25±1℃, and the rotation speed was 5 rpm for 1,000 to 30,000 mPa·s and 3 rpm for 30,000 mPa·s and above. The evaluation method was to mark values ​​between 5,000 and 50,000 mPa·s as ○ and values ​​outside this range as ×.

[0055] TI value: Using the same rotor as during viscosity measurement, viscosity (referred to as viscosity 2) was measured again at one-tenth the rotational speed of the viscosity measurement, and viscosity 2 was divided by the initially measured viscosity (0.5 rpm for 5 rpm, 0.3 rpm for 3 rpm). The evaluation method was to mark values ​​between 2 and 8 as ○, and values ​​outside this range as ×.

[0056] Total light transmittance (transparency): The above evaluation samples were measured using a Haze-GARD2 haze meter manufactured by Toyo Seiki Seisakusho in accordance with JIS K7361-1. The evaluation method was as follows: ◎ for over 90%, ○ for 80-90%, and × for less than 80%.

[0057] Haze (Transparency): The above evaluation samples were measured using a HAZE-GARDi haze meter manufactured by Vic Gardner, in accordance with JIS K7136. The evaluation method was as follows: less than 10% = ◎, 10-20% = ○, and over 20% = ×.

[0058] Shape retention: A cone shape with a base diameter of 5 mm and a height of 10 mm was created. The height was then measured after 30 minutes, and the retention rate (height after 30 minutes / 10 mm) was calculated. The evaluation method was as follows: ◎ for a retention rate of 100% (shape unchanged), ○ for 70% or more, and × for less than 70%.

[0059] The evaluation results of the examples are shown in Tables 4 and 5. Table 4 JPEG2026088795000004.jpg91135

[0060] Table 5 JPEG2026088795000005.jpg90135

[0061] The evaluation results for the comparative examples are shown in Table 6. Table 6 JPEG2026088795000006.jpg84135

[0062] The resin compositions in the examples showed good performance in all aspects, including viscosity, TI value, total light transmittance, haze, and shape retention.

[0063] On the other hand, Comparative Example 1, which had a viscosity below the lower limit, exhibited poor shape reproducibility, and Comparative Examples 2-4, in which the RC agent did not contain a castor oil derivative, were inferior in either TI value, transparency, or shape retention. Furthermore, Comparative Example 5, which did not contain (B), did not harden, and Comparative Example 6, which did not contain (C), had low viscosity and TI value, as well as poor shape retention; all of these were unsuitable for the present invention.

Claims

1. An ultraviolet-curable resin composition comprising a polyfunctional urethane (meth)acrylate (A), a thiol (B), a rheology control agent (C), and a photopolymerization initiator (D), wherein (C) contains a castor oil derivative, and the viscosity of the composition as measured by an E-type viscometer is 5,000 to 50,000 mPa·s.

2. The ultraviolet-curable resin composition according to claim 1, characterized in that (A) is a polyfunctional urethane (meth)acrylate having a polytetramethylene glycol skeleton.

3. The ultraviolet-curable resin composition according to claim 1, further characterized by containing a phosphate ester (E).

4. An ultraviolet-curable resin composition according to any one of claims 1 to 3, characterized in that it is a resin for molding.

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