ACTIVE ENERGY RAY-CURABLE COMPOSITION

Abstract: An active energy ray-curable composition substantially comprising at least one of (meth)acrylates and oligomers thereof represented by the following general formula (I) wherein R represents a hydrogen atom or a methyl group, X represents an alkylene group in which at least one hydrogen atom may be replaced by a hydroxyl group, m is 0 or an integer of 1 to 4, Y represents a hydrocarbon group having a cyclic hydrocarbon moiety therein, and n is 1 or 2. The composition is useful as an adhesive, particularly as one in the production of optical discs.

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a composition curable by active energy rays such as ultraviolet light, electron beams or radioactive rays, and particularly to a composition which is suitably used as an adhesive in the production of optical discs. 2. Description of the Prior Art Photocurable compositions are known. For example, Japanese Laid-Open Patent Publication No. 51035/1973 discloses an ultraviolet light-curable composition comprising (a) at least one oligo ester which is selected from the group consisting of polyester acrylate, polyester methacrylate, epoxy acrylate and epoxy methacrylate having a boiling point at atmospheric pressure of at least 200°C and has an acryloyl group content of 5 to 100 mole% based on the total amount of the acryloyl and methacryloyl groups, (b) a sensitizer and (c) a thermal polymerization inhibitor. The patent document describes as the component (a). However, when an ultraviolet light-curable composition obtained by using this component is used as an adhesive, it has low tensile shear peel strength and tensile adhesion strength. U. S. Patent No. 4,150,170 describes a method of producing an ultraviolet light-curable pressure-sensitive adhesive using an ultraviolet light-curable pressure-sensitive composition comprising an alpha,beta-ethylenLically unsaturated vinyl polymerizable monomer and a benzoin C₁-C₁₂ hydrocarbon alkyl ether. For example, Example 1 of this patent describes a method in which compositions containing butyl acrylate, vinyl acetate and acrylic acid as the above monomer is used. Japanese Laid-Open Patent Publication No. 142070/1950 discloses a photosensitive adhesive consisting predominantly of a mixture of (A) 100 parts by weight of a polymeric substance containing acryloxy or methacryloxy groups represented by the following formulae (I) to (III) in the molecule wherein R represents a hydrogen atom or a methyl group, n represents an integer of 2 or 3, m is an integer of 1 to 4, and ℓ is an integer of 1 to 30, said polymeric substance being obtained by the addition-reaction of a polymeric substance having an unsaturated double bond in the molecule with an acrylic compound containing a carboxyl or hydroxyl group in the presence of an alkyl hypohalite or an N-haloamide compound, and (B) at least 50 parts by weight of cyclohexyl methacrylate. This patent document describes an example in which methacrylic-modified polybutadiene is used as the polymeric substance containing an acryloxy or methacryloxy group. EP-A-0115709 discloses compositions comprising a bis(methacryloxypolyethoxy)benzene, a vinyl compound and a curing catalyst. Such compositions may be cured either by being left to stand at ambient temperature, in the absence of oxygen, or by exposure to visible light radiation. EP-A-0182585 discloses an ultraviolet-curable resin composition comprising at least one of a series of (meth)acrylate compounds, each having an ether linkage substituted by an alkyl side chain, and a photopolymerisation initiator. The composition is used in the production of optical disc base plates. In the prior art, optical discs are produced by bonding a recording layer provided on a substrate and a lightpervious protecting material by means of a photocuring agent. A photocurable composition which can be used in this application is desirably required to have excellent tensile shear peel strength and tensile adhesion strength, effect bonding within a short period of time, and be free from components that adversely affect the recording layer, and further not to impair the optical properties such as transparency of the substrate. Photocurable compositions known heretofore do not sufficiently satisfy all of these properties. SUMMARY OF THE INVENTION It is an object of this invention to provide an adhesive having the aforesaid desirable properties in combination. Another object of this invention is to provide a novel composition curable by irradiation of active energy rays such as ultraviolet light, electron beams or radioactive rays. The above objects are achieved in accordance with this invention by an active energy ray-curable composition substantially comprising at least one (meth)acrylate, or oligomer thereof of general formula (I) wherein R represents a hydrogen atom or a methyl group and Y represents a hydrocarbon group having a cyclic hydrocarbon moiety therein, the said moiety being selected from alicyclic hydrocarbon groups, aromatic hydrocarbon groups and hydrocarbon groups containing a linkage across the cyclic moiety. BRIEF DESCRIPTION OF THE DRAWINGS Figures 1 and 2 are views showing the states of test pieces used for measuring adhesion strengths in this invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention provides an active energy ray-curable composition substantially comprising at least one (meth)acrylate and oligomers thereof, represented by the following general formula (I) wherein R represents a hydrogen atom or a methyl group and Y represents a hydrocarbon group having a cyclic hydrocarbon moiety therein, the said moiety being selected from alicyclic hydrocarbon groups, aromatic hydrocarbon groups and hydrocarbon groups containing a linkage across the cyclic moiety. In the (meth)acrylate used in the composition of this invention, the organic group constituting the portion derived from the alcohol is a hydrocarbon group which without fail has a cyclic hydrocarbon moiety. The hydrocarbon group is bonded to the (meth)acryloyloxy group directly. It is important that the hydrocarbon group constituting Y should contain a cyclic hydrocarbon group which is an alicyclic hydrocarbon group, an aromatic hydrocarbon group, or a hydrocarbon group containing a linkage across the cyclic moiety. Table 1 below shows especially preferred species of compounds of formula (I) bearing such Y groups. In the compositions of the present invention, at least one of oligomers obtained by polymerizing the (meth)acrylates with each other may also be used. The use of a photopolymerization initiator is not essential in this invention. However, when an active energy ray of a relatively low energy, for example ultraviolet light, is used, it is desirable to incorporate it in the composition of this invention. The photopolymerization initiator may be any of various known photopolymerization initiators such as those of the decomposition type which upon irradiation of UV or the like decompose and generate radicals and those of the hydrogen extraction type which generate radicals by hydrogen extraction upon irradiation. Specific examples of the photopolymerization initiator include benzoin, benzoin ethers such as benzoin methyl ether, benzoin ethyl ether, benzoin isopropyl ether and benzoin butyl ether, benzophenone compounds such as benzophenone, p-chlorobenzophenone and p-methoxybenzophenone, benzil compounds such as benzil and benzyl dimethyl ketal, and hydroxyalkylphenyl ketone compounds such as 1-(4-isopropylphenyl)-2-hydroxy-2-methyl-1-propanone, 1-phenyl-2-hydroxy-2-methyl-1-propanone and 1-(4-tert-butylphenyl)-2-hydroxy-2-methyl-1-propanone. The composition of this invention substantially contains the above (meth)acrylate and its oligomer as a main component, and preferably further contains the photopolymerization initiator. Hence, basically, it is of the solventless type. The (metha)acrylate oligomer used in the composition of this invention has an average degree of polymerization of 2 to 100, preferably 2 to 50, and more preferably 2 to 35. The amount of the (meth)acrylate oligomer used in this invention is 1 to 100% by weight, preferably 5 to 95% by weight, more preferably 10 to 90% by weight, based on the total weight of the (meth)acrylate oligomer and the (meth)acrylate monomer. The viscosity of the composition of this invention, which depends upon the average molecular weight and the content in % by weight of the (meth)acrylate oligomer, is, for example, 10 to 50,000 cps, preferably 100 to 40,000 cps, more preferably 1,000 to 30,000 cps. The composition may contain components usually incorporated in solventless adhesives, for example reactive diluents, sensitizers, thickeners, antisagging agents, storage stabilizer and plasticizers. The amount of the photopolymerization initiator which may be used in the composition of this invention is 0.01 to 10 parts by weight, preferably 0.05 to 7 parts by weight, more preferably 0.1 to 5 parts by weight, per 100 parts by weight of the (meth)acryate and its oligomer. The composition of this invention is prepared, for example, by the following procedure. At least one monomer of formula (I) and the photopolymerization initiator are fed into a four-necked flask equipped with a water-cooled jacket and a stirrer. While the contents were cooled with water with stirring, ultraviolet light was irradiated from a water-cooled high-pressure mercury lamp with an output of 100W to effect photopolymerization in an air atmosphere. The pressure of the inside of the flask was reduced with stirring, and the reaction mixture in purified form is obtained. The composition of this invention is cured as follows: The resulting reaction mixture is used to bond adhesion test pieces. Light is irradiated onto the bonded test pieces from a water-cooled high pressure mercury lamp with an output of 3 KW to cure the reaction mixture. The composition of the present invention is useful, for example, in coating and bonding various substrates, particularly transparent substrate materials, above all bonding of optical materials; for example the bonding of lenses or optical discs. When the substrate used is one which contains a component which is likely to react with a chemical substance and undergo degeneration, for example a recording layer of an optical disc, it is preferred to use a composition in accordance with this invention which substantially comprises the above (meth)acrylate oligomer from which monomer components have been removed, and as required the photopholymerization initiator. An optical disc may be provided in accordance with the invention by photocuring an assembly comprising a recording layer on a substrate, a light-pervious protecting material and an intermediate layer of the composition of the present invention. The compositions of this invention exhibit particularly firm adhesiveness to such substrates as those made of polycarbonate polymers, (meth)acrylate polymers, ethylene/cyclic olefin copolymer or olefin copolymers containing 4-methyl-1-pentene as a main component. One example of the ethylene/cyclic olefin copolymers is a copolymer of ethylene with a monomer component of the following formula (1) which monomer assumes the structure of the following formula (2) in the copolymer. In the formulae, R¹ to R¹² are identical or different and each represents hydrogen, alkyl or halogen, R⁹ or R¹⁰ and R¹¹ or R¹² may form a ring together, n is 0 or a positive number of at least 1, when R⁵ to R⁸ recur a plurality of times, they may be identical or different. According to this invention, there can be provided a novel active energy ray-curable composition which cures within a short period of time by irradiation of ultraviolet light, electron beams, radioactive rays, etc., has high adhesion strength, does not impair the optical properties of substrates, and is non-polluting because it is of the solventless type. The following examples illustrate the present invention more specifically. The adhesion strengths of the compositions in these examples were evaluated by the following methods. (i) Trensile shear peel strength The surface of a test plate, 20 x 120 x 2 mm, cut out from an injection-molded plate of a resin was lightly wiped with gauze impregnated with isopropanol, and then the composition of the invention was coated on it so that the area of adhesion became 4 cm². Another test plate was superimposed on it, and the assembly was held by quartz glass and fixed. Then active energy ray was irradiated to cure the adhesive composition. The cross-sectional surface of the test piece is shown in Fig. 1. In Fig. 1, a=120 mm, b=2 mm, and c=20 mm. The resulting test piece assembly was pulled at a rate of 50 mm/min. using a tensile tester (Model 1123 made by Instron Co.), and the tensile force was measured. The tensile shear peel strength was calculated by dividing the tensile force by the area of adhesion. (ii) Tensile adhesion strength A test piece A (30 x 12.7 x 3 mm) and a test piece B (25 x 12 x 6.3 mm) were prepared from a resin by injection molding. The surfaces of the test pieces were lightly wiped with gauze impregnated with isopropanol. The composition of the invention was then coated on the test piece A, and spread uniformly on the adhesion surface by using the test piecee B (area of adhesion=0.8 cm²). The test pieces were fixed by holding them by quartz glass so that the test piece A was situated atop. By irradiating active energy ray onto the assembly, the test pieces were cured. The appearance of the test piece assembly after bonding is shown in Fig. 2. In Fig. 2, d=30 mm, e=12.7 mm, f=3 mm, g=25 mm, h=12 mm, and i=6.3 mm. The test piece assembly was pulled at a speed of 50 mm/min. by using a tensile tester (Model 1123 made by Instron Co.), and the tensile force was measured. The tensile adhesion strength was calculated by dividing this tensile force by the area of adhesion. EXAMPLE 1 A 1-liter four-necked flask equipped with a water-cooled jacket and a stirrer was charged with 500 g of tetracyclo[4,4,0,1 2,5 ,1 7, ¹⁰]-dodecyl-3-acrylate and 1.5 g of 1-(4-isopropylphenyl)-2-hydroxy-2-methyl-1-propanone as a photopolymerization initiator. While the contents were cooled with water with stirring, ultraviolet light was irradiated for 10 minutes onto the flask by a 100W high-pressure mercury lamp placed at a distance of 10 cm from the flask to perform photopolymerization in an air atmosphere. Then, the flask was evacuated to 0.133 kPa (1 torr) by using a vacuum pump with stirring, and the reaction mixture was purified for 3 hours. The resulting reaction mixture was a transparent viscous liquid having a viscosity of 1.25 Pas (1250 cps). Gel permeation chromatography showed that the reaction mixture consisted of about 70% by weight of the unreacted monomer and about 30% by weight of oligomers (dimer to eicosamer). Adhesion test pieces of TPX® (brand TR-18, a product of Mitsui Petrochemical Industries, Ltd.) were bonded by using the resulting reaction mixture. By irradiating light for 30 minutes from a 3KW high-pressure mercury lamp at a distance of 15 cm, the reaction mixture applied to the test pieces was cured. The adhesion strengths of the resulting bonded test sample are shown in Table 2. EXAMPLE 2 Adhesion test pieces of polycarbonate were bonded by the same method as in Example 1 using the reaction mixture obtained in Example 1. The results are shown in Table 2. EXAMPLE 3 Adhesion test pieces of poly(methyl methacrylate) were bonded by the same method as in Example 1 using the reaction mixture obtained in Example 1. The results are shown in Table 2. EXAMPLE 4 Adhesion test pieces of ethylene/tetracyclododecene copolymer (ethylene 57 mole%; =0.44 dl/g) were bonded by the same method as in Example 1 using the reaction mixture obtained in Example 1. The results are shown in Table 2. The was measured at 135°C using decalin as a solvent. EXAMPLE 5 The same reaction as in Example 1 was carried out except that 500 g of cyclohexyl acrylate was used as the monomer, 1 g of 1-phenyl-2-hydroxy-2-methyl-1-propanone was used as the photopolymerization initiator, and the time of irradiating ultraviolet light was changed to 15 minutes. The reaction mixture obtained was a transparent viscous liquid having a viscosity of 2.61 Pas (2610 cps). Gel permeation chromatography showed that the reaction mixture consisted of about 40% by weight of the unreacted monomer and about 60% by weight of oligomers (dimer to hexacosamer). Adhesion test pieces of ethylene/tetracyclododecene shown in Example 4 were bonded by using this reaction mixture by the same method as in Example 1. The results are shown in Table 2. EXAMPLE 6 Example 5 was repeated except that norbornyl acrylate was used as the monomer. The results are shown in Table 2. The resulting reaction mixture was a transparent viscous liquid having a viscosity of 1.86 Pas (1860 cps). EXAMPLES 7-9 Example 5 was repeated except that each of the monomers indicated in Table 3 was used. The results are shown in Table 2. The viscosity and appearance of the reaction mixture obtained in each of the examples shown in Table 3. EXAMPLES 10-11 Example 5 was repeated except that each of the adherends shown in Table 2 was used. The results of the test are shown in Table 2. EXAMPLE 12 Example 5 was repeated except that 250 g of tetracyclo[4,4,0,1 2,5 ,1 7,10 ]dodecyl-3-acrylate and 250 g of dicyclopentenyloxyethyl acrylate were used as the monomer. The results are shown in Table 4. The resulting reaction mixture was a transparent viscous liquid whose viscosity is shown in Table 4. EXAMPLE 13 A reaction mixture was prepared as in Example 1 except that 400 g of tetracyclo[4,4,0,1 2,5 ,1 7,10 ]dodecyl-3-acrylate and 100 g of bisoxyethyl bisphenol A diacrylate were used as the monomer and the ultraviolet light was irradiated for 30 minutes. The resulting reaction mixture had a viscosity of 26.5 Pas (26,500 cps.) Using the reaction mixture, the same adhesion test as in Example 5 was carried out. The results are shown in Table 4. COMPARATIVE EXAMPLES 1-17 Example 5 was repeated except that each of the acrylates indicated in Table 5 was used as the monomer. The results of the adhesion tests and the viscosities of the resulting reaction mixtures are shown in Table 5.

Claims: 1. A composition curable by exposure to active energy rays substantially comprising at least one (meth)acrylate or oligomer of general formula (I) wherein R represents a hydrogen atom or a methyl group, and Y represents a hydrocarbon group having a cyclic hydrocarbon moiety therein, the said moiety being selected from alicyclic hydrocarbon groups, aromatic hydrocarbon groups and hydrocarbon groups containing a linkage across the cyclic moiety. 2. A composition according to claim 1 wherein the (meth)-acrylate represented by general formula (I) is selected from tetracyclo[4,4,0,1 2,5 , 1 7,10 ]-dodecyl-3-acrylate, cyclohexyl acrylate, norbornyl acrylate, dicyclopentanyl acrylate, dicyclopentenyl acrylate, and isoboronyl acrylate. 3. A composition according to any one of the preceding claims which further comprises a photopolymerization initiator. 4. Use of a composition as claimed in any one of claims 1 to 3 as an adhesive. 5. Use according to claim 4 wherein the adhesive is used in the production of optical discs. 6. Use according to claim 5 wherein an assembly comprising a recording layer provided on a substrate, a light-pervious protecting material and an intermediate layer of the curable composition is photocured to provide an optical disc.

Inventors: INAGAKI, HAJIME, YAMANE, KENJI
Applicants: MITSUI PETROCHEMICAL INDUSTRIES, LTD.
Application year: 1987
Main classification: C08F20
IPC codes: C08F2, C08F22, G11B7