JP7551278B2 - Curable composition and its cured product - Google Patents

Description

The present invention relates to a curable composition, for example a curable composition used in the manufacture of transparent displays and adhesives, and a cured product thereof.

Recent advances in image formation technology have led to remarkable improvements in image quality in electronic devices such as liquid crystal displays and touch panels. In order to improve the reproducibility of such high-quality images, there is a demand for improvements in the quality of the screens of image display devices as well. That is, in order to enable image display devices to reproduce high-quality moving and still images with high accuracy, it is essential that displays and their adhesives have excellent transparency, i.e., be colorless and transparent.

In order to obtain a cured resin with high transparency that meets these requirements, an active energy ray-curable resin composition using a photocurable component and specific inorganic particles has been proposed (Patent Document 1). In this document, the haze is controlled as an index of transparency, and a curable composition with excellent transparency is obtained.

JP 2009-242681 A

There is a demand for transparent cured products of curable compositions used in screens of image display devices, etc., to enable brighter and clearer visibility of images. However, while conventional resin compositions such as those shown in Patent Document 1 have a certain degree of transparency, they do not consider light transmittance, and therefore do not necessarily provide sufficient clear visibility of images.
In addition, in the manufacture of electronic devices, the curable composition is required to adhere well to the main body (substrate, etc.) of the electronic device. Under such circumstances, there is still room for improvement in conventional resin compositions in terms of maintaining the quality under specified usage conditions and adhesion to the substrate.

The present invention aims to provide a curable composition that has excellent adhesion to a substrate and is capable of forming a cured product having high total light transmittance and well-controlled haze, and to provide the cured product.

In view of the above, the present inventors have conducted intensive research and found that the above problems can be solved by a curable composition comprising (A) urethane (meth)acrylate, (B) a thiocarboxylic acid derivative, (C) triallyl isocyanurate, and (D) a photopolymerization initiator, the curable composition being characterized in that the curable composition contains 50 parts by mass or more of (B) the thiocarboxylic acid derivative per 100 parts by mass of (A) urethane (meth)acrylate, and 40 parts by mass or more of (C) triallyl isocyanurate per 100 parts by mass of (A) urethane (meth)acrylate, and thus completed the present invention.

In the curable composition of the present invention, the total mass of (A) urethane (meth)acrylate, (B) thiocarboxylic acid derivative, and (C) triallyl isocyanurate is preferably 95% or more of the total mass of the curable composition.

The object of the present invention is also achieved by a transparent cured product obtained from the curable composition of the present invention.

The curable composition of the present invention has high adhesion to a substrate. Furthermore, by curing the curable composition of the present invention, a highly transparent cured product with reduced haze and high total light transmittance can be obtained.

FIG. 2 is a schematic diagram showing a plate having recesses used for producing a molded product of the present invention. FIG. 2 is a schematic diagram showing a state in which recesses in a plate are filled with the photocurable composition of the present invention. FIG. 1 is a schematic diagram showing a process in which a substrate is placed over a plate and ultraviolet light is irradiated from a light source positioned above the substrate. FIG. 2 is a schematic diagram showing a state in which the substrate and the molded product have been released from the plate.

The curable composition of the present invention is a curable composition comprising (A) a urethane (meth)acrylate, (B) a thiocarboxylic acid derivative, (C) triallyl isocyanurate, and (D) a photopolymerization initiator, and is characterized in that the curable composition comprises 40 parts by mass or more of the thiocarboxylic acid derivative (B) per 100 parts by mass of the urethane (meth)acrylate (A), and 50 parts by mass or more of the triallyl isocyanurate (C) per 100 parts by mass of the urethane (meth)acrylate (A).
The curable composition of the present invention has excellent adhesion to substrates, and the cured product thereof has high light transmittance and reduced haze, thereby exhibiting excellent transparency and transmittance.

In the present invention, haze is used as an index of transparency.
Haze is the degree of cloudiness, which indicates the degree of transparency of transparent materials such as glass, plastics, and liquids, and is expressed as a percentage of the scattered light transmittance of a test piece divided by the total light transmittance. Therefore, the smaller the value, the less scattered light transmittance there is, and the less haze there is in the material.
In the present invention, transmittance (total light transmittance) is used as an index of transparency. Transmittance is the ratio of the amount of transmitted light to the amount of light incident on the material to be measured, and is obtained as a value taking into account reflection on the material surface and absorption inside the material.
In the present invention, the haze is measured in accordance with JIS-K-7136:2000, and "transparent" or "highly transparent" means that the haze is less than 5%, preferably less than 1%.
Furthermore, in the present invention, the total light transmittance is measured by the method of JIS K7361-1, and high transmittance (excellent transmittance) means that the transmittance is 99.0% or more.
Each component will be described in detail below.

[(A) Urethane (meth)acrylate]
The curable composition of the present invention contains (A) a urethane (meth)acrylate.
In this specification, the term "(meth)acrylate" is used as a general term for acrylate and methacrylate, and includes either or both of acrylate and methacrylate. The same applies to other similar expressions.
The urethane (meth)acrylate resin can be produced, for example, by synthesizing a urethane prepolymer from a polyol and a polyisocyanate, and then adding a (meth)acrylate having a hydroxyl group thereto.
Examples of the polyol that can be used include known polyols such as hydrocarbon polyols, polyether polyols, polyester polyols, polycarbonate polyols, etc. Examples of the polyisocyanates that can be used include known polyisocyanates such as aromatic polyisocyanates, aliphatic polyisocyanates, aromatic aliphatic polyisocyanates, alicyclic polyisocyanates, etc.
The curable composition of the present invention contains (A) urethane (meth)acrylate, so that the curable composition has adhesion to the substrate, and further, the cured coating film obtained by curing the curable composition has flexibility, and the possibility of peeling from the substrate is suppressed. If the number of (meth)acryloyl functional groups is too large, the crosslinking density increases, and the cured product tends to warp more and has poor toughness, so that bifunctional or trifunctional ones are preferred.

In the present invention, a urethane resin having two (meth)acryloyl groups is particularly preferably used. Furthermore, the weight average molecular weight of the bifunctional urethane (meth)acrylate is preferably in the range of 1500 to 20,000. When the weight average molecular weight of the bifunctional urethane (meth)acrylate is 1500 or more, the curing shrinkage of the bifunctional urethane (meth)acrylate is reduced, and the cured product is less likely to warp. On the other hand, when the weight average molecular weight of the bifunctional urethane (meth)acrylate is 20,000 or less, the viscosity is improved, improving the handleability in the preparation of the composition.

Examples of commercially available bifunctional urethane (meth)acrylates include U-108A, U-200AX, UA-112P, UA-5201, U-340AX, UA-511, UA-512, UA-311, UA-412A, UA-4200, UA-4400, UA-340P, and U-2235P manufactured by Shin-Nakamura Chemical Co., Ltd. E, UA-160TM, UA-6100, U-108, UA-4000, UA-122P, UA-5201, UA-512, UA-W2, UA-7000, U-2PPA, UA-NDP; Sartomer CN962, CN963, CN964, CN965, CN980, CN9 81, CN982, CN 983, CN996, CN9001, CN9002, CN9788, CN9893, CN978, CN9782, CN9783; Toagosei Chemical Industry Co., Ltd. M-1100, M-1200, M-1210, M-1310, M-1600; Negami Kogyo Art Resin UN-9000PEP, UN -9200A, U N-7600, UN-333, UN-1255, UN-6060PTM, UN-6060P, SH-500B; Kyoeisha Chemical's AH-600, AT-600; Daicel Allnex's Ebecryl 280, Ebecryl 284, Ebecryl 402, Ebecryl 8402, Ebecryl 9270, etc.

Commercially available examples of trifunctional urethane (meth)acrylates include Ebecryl 4513, Ebecryl 4740, KRM8296, Ebecryl 8296, and Ebecryl 8311 manufactured by Daicel Allnex Corporation.

(A) The urethane (meth)acrylate may be one of the above, or a combination of multiple types.

The amount of the urethane (meth)acrylate (A) used is preferably within a range of 30 to 40% by mass, and particularly preferably 34 to 36% by mass, based on the total mass of the curable composition.
By using the urethane (meth)acrylate (A) in the above proportion, the adhesion of the curable composition to a substrate to which it is applied and the flexibility of the cured coating film are improved.

[(B) Thiocarboxylic acid derivative]
The curable composition of the present invention contains (B) a thiocarboxylic acid derivative in an amount of 50 parts by mass or more, preferably in the range of 60 to 120 parts by mass, per 100 parts by mass of (A) the urethane (meth)acrylate.
In the present invention, the inclusion of the thiocarboxylic acid derivative (B) can improve the light transmittance of the cured coating film. The thiocarboxylic acid derivative (B) may be used alone or in combination of two or more kinds.

で表される基を１～６個有する化合物を挙げることができる。
その具体例としては、β-メルカプトプロピオン酸、２－エチルヘキシル－３-メルカプトプロピオネート、ｎ－オクチル-３－メルカプトプロピオネート、メトキシブチル－３－メルカプトプロピオネート、ステアリル-3-メルカプトプロピオネート、トリメチロールプロパン トリス（３－メルカプトプロピオネート）プロピオネート、ペンタエリスリトール テトラキス（３－メルカプトプロピオネート）、テトラエチレングリコール ビス（３－メルカプトプロピオネート）等の直鎖または分岐状の化合物、及びトリス－［（３－メルカプトプロピオニルオキシ）－ エチル]－イソシアヌレートなどの環状構造を有する化合物を含むメルカプトプロピオン酸誘導体を挙げることができ、本発明ではトリス－［（３－メルカプトプロピオニルオキシ）－ エチル]－イソシアヌレートが特に好ましく用いられる。 (B) Examples of the thiocarboxylic acid derivative include

Examples of the compound include compounds having 1 to 6 groups represented by the following formula:
Specific examples thereof include linear or branched compounds such as β-mercaptopropionic acid, 2-ethylhexyl-3-mercaptopropionate, n-octyl-3-mercaptopropionate, methoxybutyl-3-mercaptopropionate, stearyl-3-mercaptopropionate, trimethylolpropane tris(3-mercaptopropionate)propionate, pentaerythritol tetrakis(3-mercaptopropionate), and tetraethylene glycol bis(3-mercaptopropionate), and mercaptopropionic acid derivatives including compounds having a cyclic structure such as tris-[(3-mercaptopropionyloxy)-ethyl]-isocyanurate, with tris-[(3-mercaptopropionyloxy)-ethyl]-isocyanurate being particularly preferred in the present invention.

The amount of the thiocarboxylic acid derivative (B) used is preferably in the range of 25 to 40% by mass, and particularly preferably 30 to 38% by mass, based on the total mass of the curable composition.
By setting the amount of the thiocarboxylic acid derivative (B) to 25 mass % or more, the light transmittance of the cured coating film can be sufficiently obtained, and by setting the amount to 40 mass % or less, the adhesion of the curable composition to a substrate can be improved compared to the case of using the urethane (meth)acrylate alone.

[(C) Triallyl isocyanurate]
The curable composition of the present invention contains (C) triallyl isocyanurate in an amount of 40 parts by mass or more, preferably in the range of 45 to 95 parts by mass, per 100 parts by mass of (A) urethane (meth)acrylate.
Generally, triallyl isocyanurate acts as a crosslinking aid and as an adhesion imparting agent in the curable composition when added in a small amount of about 10 mass % to the curable composition. In the present invention, however, by using 40 parts by mass or more of (C) triallyl isocyanurate, the haze value of the cured coating film can be reduced, the light transmittance can be increased, and heat resistance can also be imparted.
The amount of (C) triallyl isocyanurate used is preferably in the range of 20 to 40% by mass, and particularly preferably 24 to 33% by mass, based on the total mass of the curable composition.
By using (C) triallyl isocyanurate in an amount of 20 mass % or more, it is possible to obtain a cured coating film with sufficient hardness, and by using (C) triallyl isocyanurate in an amount of 40 mass % or less, the transparency and light transmittance become particularly good and heat resistance can also be imparted.

[(D) Photopolymerization initiator]
The curable composition of the present invention contains (D) a photopolymerization initiator. Examples of the photopolymerization initiator that can be used include benzoins such as benzoin, benzil, benzoin methyl ether, benzoin ethyl ether, benzoin n-propyl ether, benzoin isopropyl ether, and benzoin n-butyl ether; benzoin alkyl ethers; benzophenone, p-methylbenzophenone, Michler's ketone, methylbenzophenone, 4,4'-dichlorobenzophenone, and 4,4'-bisdiethylaminobenzophenone; acetophenone, α- Acetophenones such as hydroxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, 2,2-diethoxy-2-phenylacetophenone, 1,1-dichloroacetophenone, 1-hydroxycyclohexyl phenyl ketone, 2-methyl-[4-(methylthio)phenyl]-2-morpholino-1-propanone, and N,N-dimethylaminoacetophenone; thioxanthones such as 2,4-dimethylthioxanthone, 2,4-diethylthioxanthone, 2-chlorothioxanthone, and 2,4-diisopropylthioxanthone; anthraquinone, chloroanthraquinone, 2-methylanthraquinone, anthraquinones such as anthraquinone, 2-ethylanthraquinone, 2-tert-butylanthraquinone, 1-chloroanthraquinone, 2-amyl anthraquinone, and 2-aminoanthraquinone; ketals such as acetophenone dimethyl ketal and benzyl dimethyl ketal; benzoic acid esters such as ethyl-4-dimethylaminobenzoate, 2-(dimethylamino)ethyl benzoate, and p-dimethylbenzoic acid ethyl ester; phenyl disulfide 2-nitrofluorene, butyroin, anisoin ethyl ether, azobisisobutyronitrile, and tetramethylthiuram disulfide.

The above (D) photopolymerization initiators can be used alone or in combination of two or more, but it is preferable to use an α-hydroxyacetophenone-based photopolymerization initiator in order to improve the surface properties without impairing the flexibility of the cured product.

The photopolymerization initiator (D) is added in an amount of preferably 0.1 to 10 parts by mass, and more preferably 0.3 to 5 parts by mass, per 100 parts by mass of the urethane (meth)acrylate (A).

The total mass of the above-mentioned (A) urethane (meth)acrylate, (B) thiocarboxylic acid derivative, and (C) triallyl isocyanurate is preferably 95% or more of the total mass of the curable composition, which allows the properties of high total light transmittance and well-controlled haze to be obtained.

To adjust the viscosity, a known diluent, particularly a reactive diluent, can be used. In particular, a monofunctional (meth)acrylate compound, which is a compound having one ethylenically unsaturated group in the molecule, is preferred because of its high dilution effect.

[Other ingredients]
The curable composition of the present invention may contain other components in addition to the above-mentioned components, provided that the effects of the present invention are not impaired. Examples of additives that may be blended include photocurable monomers, silicone-based and fluorine-based defoamers, leveling agents, known and commonly used thermal polymerization inhibitors, ultraviolet absorbers, silane coupling agents, plasticizers, foaming agents, flame retardants, antistatic agents, antioxidants, antibacterial and antifungal agents, etc.

The curable composition of the present invention may contain a thermosetting component as long as the desired properties are not impaired, but generally no thermosetting component is used. As a result, a cured product with better transparency and light transmittance and less change over time can be obtained.

The curable composition of the present invention has high adhesion to substrates, making it easy and reliable to bond to the substrate and improving the durability of the equipment or parts to which it is bonded.

[Method of curing the curable composition]
The curable composition of the present invention, which is composed of the above-mentioned components, can be photocured to form a cured product. For curing, the curable composition is applied to a substrate such as quartz glass, and then irradiated with active energy rays to cure. The curable composition of the present invention preferably has a viscosity of 1 to 50 dPa·s.

As a coating method, any of the following methods can be used: dip coating, flow coating, bar coating, and screen printing. As a light source for irradiating active energy rays, low pressure mercury lamps, medium pressure mercury lamps, high pressure mercury lamps, ultra-high pressure mercury lamps, xenon lamps, metal halide lamps, etc. are suitable. In addition, UV-LEDs, laser beams, electron beams, etc. can also be used as active energy rays.

[Method of curing and molding the curable composition]
Here, a method is illustrated with the aid of drawings, in which a plate having recesses on its surface is used, the recesses are filled with the curable composition of the present invention, the filled curable composition is cured by ultraviolet light, and the cured product is removed from the recesses to obtain a molded product.

Figure 1 shows a plate (1) with a recess (2) on its surface. Generally, a plate made of metal such as stainless steel is used.

Figure 2 shows the state (3) in which the plate has been filled with the curable composition of the present invention. In general, the curable composition is filled into the recesses of the plate using a doctor knife or the like.

Figure 3 shows the process of covering the curable composition of the present invention with a substrate (4) and then irradiating it with ultraviolet light from a light source (5) above to cure the curable composition of the present invention. Generally, a transparent film made of polyethylene terephthalate or polycarbonate that transmits ultraviolet light is used as the substrate (4).

Figure 4 shows the state in which the cured product is released from the plate (1) to obtain a cured molded product (6). The series of steps from Figure 1 to Figure 4 can be carried out continuously by using dedicated publicly known equipment for each step.

In this way, the curable composition of the present invention can be molded in advance and used. In the molding method in which the composition is filled in the recesses and then photocured, there is no inhibition of curing by oxygen, so that the thickness can be increased, and it is possible to make the composition as thick as 5 mm at its thickest point.
The curable composition of the present invention can be used for transparent screens such as touch panels, and as insulating materials such as solder resists, interlayer insulating materials, and coverlays. The curable composition of the present invention may also be used as a solder dam. Furthermore, since the composition of the present invention has good adhesion, it can also be used as an adhesive, particularly a colorless and transparent adhesive used for transparent screens, etc.

The present invention will be described in more detail below with reference to examples and comparative examples. The present invention is not limited to the following examples, and all "parts" and "%" described below are based on mass unless otherwise specified.

[Examples 1 to 8, 10, Reference Example 9, and Comparative Examples 1 to 3]
Each of the components shown in Table 1 below was kneaded in the amount of parts shown for each component in Table 1 using a planetary centrifugal mixer to prepare each of the curable compositions.
The resulting curable compositions were each evaluated as follows.

1. Printability Evaluation Each of the curable compositions of Examples 1 to 8, 10, Reference Example 9, and Comparative Examples 1 to 3 was printed on the entire surface of a quartz glass substrate using a screen printing device equipped with a 300 mesh printing plate made of polyester (Tetron (registered trademark)) so that the film thickness after curing would be 10 μm.
The surface condition of the coating film was visually observed 5 minutes after printing and evaluated according to the following criteria. The results are shown in Table 1.

○ The entire surface of the substrate is coated smoothly and uniformly with the curable composition. × Traces of burst bubbles are observed on the surface of the curable composition, and the coating surface is uneven.

2. Evaluation of dryness to the touch (tack evaluation)
The curable compositions of Examples 1 to 8, 10, Reference Example 9, and Comparative Examples 1 to 3 were printed over the entire surface of a quartz glass substrate using a screen printing device equipped with a 300-mesh printing plate made of polyester (Tetron (registered trademark)). The resulting coating film was exposed to a light intensity of 1000 mJ/ ^cm2 using a metal halide lamp to cure the coating film. The coating film thus obtained (film thickness 10 μm) was used as a cured film for evaluation and was evaluated according to the following criteria. The results are shown in Table 1.

◎ When the coating film is touched with a finger, fingerprints are not left on the surface of the coating film, and the coating film does not stick to the finger. 〇 When the coating film is touched with a finger, fingerprints are left on the surface of the coating film, but the coating film does not stick to the finger. × When the coating film is touched with a finger, fingerprints are left on the surface of the coating film, and the coating film sticks to the finger.

3. Pencil Hardness Evaluation A cured film similar to the one used in 2. Evaluation of Dryness to Touch above was prepared, and its surface hardness was measured using a pencil hardness tester (manufactured by Toyo Seiki Seisakusho Co., Ltd.). In this test, 3H and 4H pencils sharpened to a flat tip were pressed against each test piece at an angle of about 45° with a load of 1 kg, and moved at least 7 mm at a speed of 0.5 to 1 mm/s, and the state of peeling of the coating film was evaluated according to the following criteria. The results are shown in Table 1.

◎ No peeling of the coating with a 4H pencil. 〇 No peeling of the coating with a 3H pencil. × The coating peels off with a 3H pencil.

4. Adhesion Evaluation The adhesion of the cured coating film (film thickness 10 μm) similar to that used in the pencil hardness evaluation above was evaluated in accordance with JIS K 5600-5-6 by making cross-cuts in a 10 mm x 10 mm grid pattern using a cross-cut guide to form 100 x 100 grids. The number of remaining grids was visually observed according to the following criteria. The results are shown in Table 1.

○ No peeling was observed in the grid of the coating film. × Peeling was observed in one or more grids of the coating film.

5. Evaluation of total light transmittance The total light transmittance of the same cured coating film (film thickness 10 μm) as that used in the above 3. Evaluation of pencil hardness was measured in accordance with JIS K 7361-1 using a UV-visible spectrophotometer V-670EX (manufactured by JASCO Corporation).
In this evaluation, the ratio of transmitted light to incident light over the entire wavelength range of 300 to 780 nm used in the evaluation is shown. The measurement results are shown in Table 1.

6. Haze (cloudiness) evaluation For the same cured coating film (film thickness 10 μm) as that used in 3. Pencil hardness evaluation above, haze was measured using an ultraviolet-visible spectrophotometer V-670EX (manufactured by JASCO Corporation) in accordance with JIS K 7136. As described in JIS K 7136, haze is a value expressed as a percentage of the scattered light transmittance of a test piece divided by the total light transmittance, and the total light transmittance value was determined in accordance with JIS K 7361-1. The measurement results are shown in Table 1.

7. Heat resistance test (total light transmittance and haze evaluation after heat treatment)
7-1. Preparation of heat-treated samples
A cured coating film similar to that used in the above 3. Pencil hardness evaluation was stored in a hot air circulating drying oven at 100° C. for 2 hours to prepare a heat-treated sample.
7-2. Evaluation of total light transmittance and haze of heat-treated sample The total light transmittance and haze value of the heat-treated sample thus obtained were determined by the same measurement methods as those in 5. Evaluation of total light transmittance and 6. Evaluation of haze (cloudiness) above. The measurement results are shown in Table 1.

8. Light resistance test (total light transmittance and haze evaluation after exposure treatment)
8-1. Preparation of exposure-treated samples
The same cured coating film as that used in the above 3. Pencil hardness evaluation was exposed to light of 20 J/cm ² from a metal halide lamp on the entire surface to prepare an exposure-treated sample.
8-2. Evaluation of total light transmittance and haze of exposed sample The total light transmittance and haze value of the exposed sample thus obtained were determined by the same measurement methods as those in 5. Evaluation of total light transmittance and 6. Evaluation of haze (cloudiness). The measurement results are shown in Table 1.

Details of the materials listed in the table are given below.
Ebecryl 8402: Bifunctional urethane acrylate, photocurable urethane resin, manufactured by Daicel-Allnex Co., Ltd. TAIC: Triallyl isocyanurate , manufactured by Mitsubishi Chemical Corporation TEMPIC: Tris-[(3-mercaptopropionyloxy)-ethyl]-isocyanurate, manufactured by SC Organic Chemical Co., Ltd. Omnirad (registered trademark) 184: 1-hydroxycyclohexyl-phenyl ketone, manufactured by IGM Resins KBM-5103: 3-acryloxypropyltrimethoxysilane, manufactured by Shin-Etsu Chemical Co., Ltd. Light Ester P-1M: Mono(2-hydroxyethyl methacrylate) phosphate, manufactured by Kyoeisha Chemical Co., Ltd. Flowlen AC-2300C: Olefin polymer (defoamer), manufactured by Kyoeisha Chemical Co., Ltd. Polyflow KL-700: Silicone-containing polymer (substrate wetting agent), manufactured by Kyoeisha Chemical Co., Ltd.

From the above, it is evident that the curable composition of the present invention has excellent printability, and the cured product thereof has excellent physical properties in terms of dryness to touch, pencil hardness and adhesion.
Furthermore, the cured product of the present invention has a high light transmittance of 99.0% or more both at the initial value and after exposure to a heat resistance test and a light resistance test, and the haze value is also suppressed to 1.5% or less both at the initial value and after exposure to a heat resistance test and a light resistance test. This shows that the cured product of the present invention is particularly suitable as a transparent protective material for liquid crystal displays, touch panels, etc., and maintains its beautiful initial colorless and transparent state even during long-term harsh use.

The present invention is not limited to the configurations and examples of the above-described embodiments, and various modifications are possible within the scope of the gist of the invention.

Reference Signs List 1: Plate 2: Recess 3: Photocurable composition 4: Substrate 5: Light source 6: Molded product

Claims (3)

(A) urethane (meth)acrylate,
(B) a thiocarboxylic acid derivative,
(C) triallyl isocyanurate, and (D) a photopolymerization initiator,
A curable composition comprising:
The (B) thiocarboxylic acid derivative is tris-[(3-mercaptopropionyloxy)-ethyl]-isocyanurate ,
(B) 50 parts by mass or more of the thiocarboxylic acid derivative per 100 parts by mass of the urethane (meth)acrylate (A);
The composition contains 40 parts by mass or more of the (C) triallyl isocyanurate relative to 100 parts by mass of the (A) urethane (meth)acrylate,
The amount of the urethane (meth)acrylate (A) used is 30 to 40% by mass based on the total mass of the curable composition,
The curable composition, wherein the amount of the thiocarboxylic acid derivative (B) used is 25 to 40 mass % based on the total mass of the curable composition. The curable composition according to claim 1, wherein the total mass of the (A) urethane (meth)acrylate, the (B) thiocarboxylic acid derivative, and the (C) triallyl isocyanurate is 95% or more of the total mass of the curable composition. A transparent cured product obtained from the curable composition according to claim 1 or 2.

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