JPH0463110B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a radiation-curable adhesive composition. [Prior Art] Conventionally, adhesive films have been manufactured by applying an adhesive prepared by dissolving a high molecular weight polymer such as natural rubber or synthetic rubber in an organic solvent onto a web such as a plastic film and drying it. There is. However, in recent years, consideration has been given to making adhesives solvent-free from the viewpoint of resource saving, energy saving, and pollution-free production. The polymer component used in this case has a low molecular weight due to viscosity constraints, so if used alone, the rubber elasticity inherent to the polymer will be impaired and the adhesive force and other properties necessary for the adhesive cannot be achieved. Therefore, efforts have been made to compensate for these characteristics by adding chain transfer agents and monomers with polar groups. However, even if the polymer component used here has excellent weather resistance, the weather resistance of the adhesive film obtained by incorporating the above-mentioned low molecular weight substances and curing with radiation tends to be significantly impaired. It was hot. In other words, when this adhesive film is attached to an adherend and exposed to sunlight, the adhesive transfers to the adherend.
If the size is this large, the film cannot be peeled off. Further deterioration may result in the film spontaneously peeling off from the adherend. [Problems to be Solved by the Invention] Therefore, as a measure to improve weather resistance, there is a conventional method, but an attempt was made to add an ultraviolet absorber. However, if it is added in an amount of less than 0.1 part, which is the usual amount, it has little effect on improving the UV absorber, and conventional ultraviolet absorbers have poor compatibility with radiation-curable oligomers. When the adhesive film was attached to an adherend, there were problems such as bleed-out of the adhesive film onto the adherend. The present invention was made in view of the above situation, and it is an object of the present invention to provide a radiation-curable adhesive for adhesive films that does not cause the UV absorber to bleed out and has excellent adhesive properties, weather resistance, etc. . [Means for Solving the Problems] That is, the present invention provides an adhesive composition mainly composed of a liquid oligomer having unsaturated double bonds in the molecule, which is provided with unsaturated double bonds that polymerize when exposed to ultraviolet rays. It is characterized by containing an absorbent. The ultraviolet absorber with an unsaturated double bond that undergoes radiation polymerization used in the present invention includes:
A molecular structure whose molecular skeleton can absorb light energy and convert it into thermal energy, such as phenyl salicylate, 2-(or 4-)hydroxybenzophenone, and 2(2'-hydroxyphenyl)benzotriazole, etc. with one unsaturated double bond
It is necessary to have one or more per molecule. Examples of unsaturated double bonds include vinyl, vinyl ether, vinyl ester, acrylic, and methacrylic groups, but particularly good results can be obtained in the present invention with acrylic, which has high reactivity and particularly excellent weather resistance. It is an ultraviolet absorber with a methacrylic group added. These may be used alone or in combination of two or more, and the total amount added is selected within the range of 0.1 to 30 parts by weight based on 100 parts by weight of the oligomer. If the amount is less than 0.1 parts by weight, the effect of improving weather resistance will be insufficient, and if it is added more than 30 parts by weight, the adhesive properties (adhesive strength, radiation curability) will deteriorate. A more preferable range of addition amount is 1 to 15 parts by weight. The oligomers having an unsaturated double bond in the molecule used in the present invention include those with unsaturated main chains such as acrylic acid alkyl esters or methacrylic acid alkyl esters, polyol acrylates, polyester alkylates, urethane acrylates, and epoxy acrylates. These are prepolymers such as acrylic oligomers, polybutadiene, polychloroprene, and polyisoprene that have one or more double bonds per molecule at the terminal or side chain. Further, the oligomer is usually in a liquid state, and its viscosity is in the range of 10 ² to 5×10 ⁵ cps at room temperature. In the present invention, particularly good results can be obtained with a highly reactive acrylic double bond-attached oligomer. Chain transfer agents used in adhesive compositions other than oligomers include butyl mercaptan, lauryl mercaptan, octyl thioglycolate, ethylene glycol dithioglycote, and pentaerythritol tetrakis (β-thiopropionate).
Examples include thiol compounds such as, disulfides such as diphenyl disulfide, and halides such as carbon tetrachloride, carbon tetrabromide, chloroform, and dichlorobenzene. These may be used alone or in combination of two or more. These chain transfer agents are added to suppress excessive crosslinking during radiation curing. For that purpose, the amount added should be 0.2 to 20% by weight, preferably
It is necessary to select it in the range of 2 to 15% by weight. If this amount is less than 0.2% by weight, the effect of suppressing crosslinking will be insufficient, and if it exceeds 20% by weight, curing will be insufficient and cohesive force will be insufficient, which will adversely affect adhesive properties. On the other hand, monomers having polar groups used in the present invention include acrylic acid, methacrylic acid, itaconic acid, maleic acid, crotonic acid, acryloyloxyethyl hydrogen phthalate, 2-acrylamido-2-methylpropane-sulfonic acid, 3 -Chloro-2-acryloyloxypropyl methacrylate, 2-acrydophosphooxyethyl acrylate, 2-acrydophosphooxypropyl methacrylate, di(2-methacryloyloxyethyl) phosphate, di(2-acryloyloxyethyl phosphate) ), etc. Particularly advantageous are monomers endowed with phosphate radicals with high dissociation constants. The amount of these monomers with acidic groups added is 0.5
~30 parts by weight. If this amount is less than 0.5% by weight, the effect of interfacial force will be insufficient, and 30
If the amount exceeds % by weight, the radiation effectiveness and the physical properties of the effect coating will deteriorate, which is not preferable. In carrying out the present invention, in addition to the compositions described above,
Additives such as diluting monomers and tackifiers may be added, and a small amount of solvent may also be added. The radiation used in the present invention refers to active energy rays,
Ionizing radiation such as alpha rays, beta rays, gamma rays, neutron beams, accelerated electron beams, and ultraviolet rays. The dose of ionizing radiation can range from 0.5 to 50 Mrad, but is preferably about 1 to 10 Mrad. In the case of ultraviolet rays, the wavelength range is approximately 180 nm and 460 nm, and a high-pressure mercury lamp or the like is suitable as the source. Also, when irradiating, care must be taken in the irradiation atmosphere. That is, since the generated radicals are inhibited by oxygen in the air, it may be necessary to use an inert gas such as nitrogen to maintain an appropriate oxygen concentration. [Function] The adhesive tape obtained by the present invention has good rubber elasticity, excellent adhesive properties, and excellent weather resistance. The reason for the improved weather resistance is that as a result of adding unsaturated double bonds to ordinary ultraviolet absorbers, their compatibility with adhesive compositions such as oligomers has improved, making it possible to add them in large quantities. Also, most of the added material is radiation-cured and incorporated into the system through covalent bonds, so it has excellent cohesive strength and does not easily bleed out. Furthermore, by introducing an unsaturated double bond into the ultraviolet absorber, the light←→heat exchange function of the ultraviolet absorber is not adversely affected. The present invention will be further explained below with reference to Examples. (1) Synthesis of radiation-curable oligomer (1-a) 10 parts of ethyl acrylate, butyl acrylate
70 parts, 30% metaglycidyl acrylate 20 parts
Solution polymerization was carried out in a solution of , and the solvent was removed to synthesize a solvent-free copolymer with a viscosity of 50° C.-1×10 ⁴ cps. Next, this copolymerized pre-oligomer was subjected to an addition reaction with 5 parts of acrylic acid to impart double bonds to the side chains. (1-b) 75 parts of α-ethylhexyl acrylate, 15 parts of methyl methacrylate, and 10 parts of metaglycidyl acrylate were copolymerized in the same manner as in (1-a) above to add a double bond to the side chain. (2) Synthesis of unsaturated double bond-added ultraviolet absorber (2-a) For 1 mol of 2,2',4,4'-tetrahydroxybenzophenone, add 2 sodium hydroxide.
mol in 300 ml of methanol at 50°C,
10 in 10wt% MEK after complete removal of moisture
The reaction was carried out with 2 mol of acrylic acid chloride at ℃, and the reaction product was purified by distillation. (2-b) 2',4'-dihydroxyphenyl salicylate was synthesized in the same manner as in (2-a). Example 1 To 100 parts by weight of the oligomer synthesized in (1-a), 10 parts by weight of pentaerythritol tetrakis-(βthiopropionate), 10 parts by weight of di(2-acryloyloxyethyl) phosphate, and (2) −
0.1 part by weight of the ultraviolet absorber synthesized in a) was added to prepare an adhesive composition. Example 2 An adhesive composition was prepared in the same manner as in Example 1, except that the amount of the ultraviolet absorber was changed to 10 parts by weight. Comparative Examples 1, 2, 3 Comparative Example 1 was obtained by removing the UV absorber from the formulation of Example 1, and 2, 2', 4,
Comparative Example 2 was prepared by adding 0.05 part by weight of 4'-tetrahydroxybenzophenone, and Comparative Example 3 was prepared by adding 0.1 part by weight of 4'-tetrahydroxybenzophenone. Example 3 100 parts by weight of the oligomer synthesized in (1-b), 5 parts by weight of butylmethylcaptan, 15 parts by weight of acroyloxyethyl hydrogen phthalate, and (2-b)
5 parts by weight of the ultraviolet absorber synthesized in step 1 was added to prepare an adhesive composition. Example 4 An adhesive composition was prepared in the same manner as in Example 3, except that the amount of the ultraviolet absorber was changed to 15 parts by weight. Comparative Examples 4, 5, 6 Comparative Example 4 was obtained by removing the ultraviolet absorber from the formulation of Example 3, and comparison was made by adding 0.05 parts by weight of 2',4'-dihydroxyphenyl salicylate as an ultraviolet absorber. Comparative Example 6 was prepared by adding 0.1 part by weight of Example 5. These compositions are applied to a polyethylene film (thickness
60μm) so that the coating thickness is 10μm,
Electron beam irradiation device (linear filament type, Energy Science
Inc. (trade name: Electrocurtain) under a nitrogen gas atmosphere (O ₂ concentration 500 ppm) and irradiated with 6 Mrad to create an adhesive film. This adhesive film was subjected to an adhesive strength test using a Tensilon type tensile tester. The tensile speed was 20 mm/min (20°C). It was also attached to a SUS-430BA board and peeled off after 2 hours.
A curing test was conducted by visually observing whether the adhesive adhered to the board surface. For adhesive films that showed no abnormalities in the curing test, accelerated weather resistance tests were conducted using a sunshine weather meter.
(ATLAS CDMC type, closed carbon arc type) The results are shown in Table 1.

【table】

〔Effect of the invention〕

As is clear from the results of the above examples, according to the present invention, since the ultraviolet absorber with unsaturated double bonds is blended, it has excellent adhesive strength and cohesive force, and can be added in a large amount. It has become possible to provide a radiation-curable adhesive with weather resistance.

Claims (1)

[Scope of Claims] 1. In an adhesive composition comprising a liquid oligomer having an unsaturated double bond in the molecule, a chain transfer agent and a reactive monomer having a polar group, an unsaturated oligomer is added to 100 parts by weight of the liquid oligomer. 1. A radiation-curable pressure-sensitive adhesive composition comprising 0.1 to 30 parts by weight of an ultraviolet absorber imparted with saturated double bonds. 2. The radiation-curable adhesive according to claim 1, wherein the ultraviolet absorber having an unsaturated double bond has phenyl salicylate, hydroxybenzophenone, or hydroxyphenylbenzotriazole in its molecular skeleton. Composition.