JPH06102697B2 - Photopolymerizable composition - Google Patents

Description

TECHNICAL FIELD The present invention relates to an acrylate-based photopolymerizable composition, and more specifically, a specific photopolymerization having two or more photocleavage points in one molecule. It relates to a photopolymerizable composition containing an initiator, a viscoelastic product obtained from the composition, and a method for producing the same.

[Conventional technology]

As a viscoelastic product made of an acrylic polymer, for example, an acrylic pressure-sensitive adhesive, an acrylic pressure-sensitive adhesive tape, an acrylic pressure-sensitive adhesive sheet, a double-sided pressure-sensitive adhesive tape, a pressure-sensitive adhesive processed product of foams and the like are well known.

Acrylic pressure sensitive adhesives have excellent light resistance, weather resistance, oil resistance, etc. because they are mainly composed of acrylic polymers.Acrylic pressure sensitive adhesive tapes with plastic film or paper as the surface base It is widely used because of its excellent adhesive properties such as strength and cohesive strength, and aging resistance such as heat resistance and weather resistance.

Taking acrylic adhesive tapes that are typical of these viscoelastic products as an example, the adhesive tape generally contains vinyl-based monomers containing acrylate-based monomers such as alkyl acrylates and / or methacrylic acid esters as a main component. It is manufactured by coating or impregnating a substrate with a pressure-sensitive adhesive solution obtained by solution polymerization in an organic solvent system or an emulsion obtained by emulsion polymerization in an aqueous system, and heating and drying the solution.

In the above production method, when using the adhesive solution,
A large amount of energy is required to dry the pressure-sensitive adhesive solution applied or impregnated on the substrate at a high temperature, and a large-scale solvent recovery device is required to prevent air pollution due to the solvent. Moreover, since the solvent easily catches fire, a sufficient safety device is required to maintain safety.

On the other hand, when an emulsion is used, more energy is required to evaporate water than when a solvent is used, and in terms of performance, the emulsifier mixed during polymerization lowers the water resistance. Further, since a water-soluble monomer cannot be used, the types of monomers are limited, and there is a drawback that the ability to meet a wide variety of needs for adhesive tapes is weak.

By the way, in U.S. Pat.No. 4,181,752, a solvent-free photopolymerizable liquid composition containing a photopolymerization initiator such as benzoin ethyl ether in a vinyl monomer whose main component is an acrylate monomer is used. There is disclosed a method of producing an acrylic pressure-sensitive adhesive tape by irradiating this composition with ultraviolet rays having a wavelength of 300 to 400 nm at a light intensity of 0.1 to 7 mW / cm ² to polymerize the vinyl monomer.

In this method, the light intensity of ultraviolet rays is made relatively low, whereby the polymer is made to have a high molecular weight by the vinyl-based monomer, thereby enhancing the adhesive performance such as adhesive strength and cohesive strength. According to this method, the pressure-sensitive adhesive tape can be produced without using a solvent, so that the problems associated with the use of the organic solvent and water described above are eliminated. However, this method has a drawback that productivity is poor for practical use because of slow polymerization reaction rate. In this method, if it is attempted to stop the ultraviolet irradiation on the way to shorten the polymerization reaction time, the concentration of the residual monomer in the product becomes high, the odor becomes a problem, and the adhesive performance, particularly the cohesive force is lowered.

By the way, generally, in the photopolymerization of vinyl monomers such as acrylate monomers, the polymerization reaction rate is proportional to the square root of the product of the amount of photopolymerization initiator and the light intensity. Therefore,
In order to increase productivity, if the amount of photopolymerization initiator added is increased or the light intensity is increased to increase the polymerization reaction rate, the molecular weight of the resulting polymer decreases and the adhesive strength of the adhesive tape increases. The balance with cohesive force cannot be maintained at a high level. As described above, the conventional photopolymerization technology has not been able to simultaneously maintain various properties and productivity of a viscoelastic product such as an acrylic adhesive tape at a high level.

[Problems to be Solved by the Invention]

An object of the present invention is to provide a method of producing a viscoelastic product from a photopolymerizable composition containing substantially no solvent using a photopolymerization initiator, which is an acrylic resin having a high level of viscoelastic properties and productivity. It is to provide a novel photopolymerizable composition capable of producing a viscoelastic product.

Another object of the present invention is to provide an acrylic viscoelastic product using the photopolymerizable composition and a method for producing the same.

The present inventor has conducted extensive studies to solve the above-mentioned problems of the prior art, and as a result, a specific monomer component having an acrylate-based monomer as a main component has two or more cleavage points due to light in one molecule. When a viscoelastic product is produced by photopolymerization using a photopolymerizable composition containing a photopolymerization initiator, an acrylic viscoelastic product having a high molecular weight and excellent physical properties can be obtained with high productivity. Based on the findings, they have completed the present invention.

[Means for Solving the Problems]

Thus, according to the present invention, (a) 60 to 100% by weight of at least one acrylate-based monomer selected from the group consisting of an alkyl acrylate and an alkyl methacrylate having an alkyl group having 1 to 12 carbon atoms and 100 parts by weight of a monomer component containing 0 to 40% by weight of a vinyl monomer copolymerizable with the acrylate monomer, and (b) a photopolymerization initiator containing a photopolymerization initiator represented by the following structural formula [I] as a main component. A photopolymerizable composition comprising 0.001 to 5 parts by weight of the agent is provided.

[In the formula, two carbon chains connecting aromatic rings to each other. One has a carbonyl group (> C = 0) and the other has an alkyl ether group Here, R is a linear or branched alkyl group having 1 to 10 carbon atoms), and those positions may be interchanged in the two carbon chains. Ar represents a substituted or unsubstituted aromatic group. n shows the integer of 1-10. ] Is provided.

Further, according to the present invention, the photopolymerizable composition is irradiated with light to polymerize the monomer component, and a method for producing a viscoelastic product, and the viscoelastic product obtained by the production method. Will be provided.

Hereinafter, the components of the present invention will be described in detail.

(Monomer component) The monomer component used in the present invention is at least one acrylate-based monomer selected from the group consisting of alkyl acrylates and methacrylic acid alkyl esters having an alkyl group having 1 to 12 carbons in an amount of 60 to 100% by weight. %
And 0 to 40% by weight of a vinyl monomer copolymerizable with the acrylate monomer.

Acrylate-based monomer As the acrylate-based monomer, an alkyl acrylate or methacrylic acid alkyl ester having an alkyl group with 1 to 14 carbon atoms, preferably 4 to 12 carbon atoms is used.
Specific examples thereof include n-butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, and isononyl (meth) acrylate.

These are used alone or in combination of two or more. Due to the balance between tackiness and cohesiveness, the homopolymer usually has an acrylic acid alkyl ester with a glass transition temperature of -50 ° C or less as a main component, and as a comonomer, a (meth) arlylic acid ester of a lower alkyl group or the vinyl compound described below. It is preferable to use a system monomer.

Vinyl-based Monomers Further, other vinyl-based monomers copolymerizable with the acrylate-based monomers include, for example, acrylic acid, methacrylic acid, acrylamide, acrylonitrile, methacrylonitrile, N-substituted acrylamide, hydroxyethyl acrylate, N-vinylpyrrolidone. , Maleic acid, itaconic acid, N-methylol acrylamide, hydroxyethyl methacrylate and the like.

Further, vinyl-based monomers that form a polymer having a low glass transition temperature, for example, vinyl-based monomers such as tetrahydrofurfuryl acrylate, polyethylene glycol acrylate, polypropylene glycol acrylate, fluorine acrylate, and silicon acrylate can also be used.

These vinyl-based monomers may be used alone or in combination of two or more, but if the proportion of use in the total monomer components exceeds 40% by weight, the adhesive properties as an acrylic adhesive will deteriorate, Not preferable.

(Photopolymerization Initiator) Photopolymerization Initiator of Structural Formula [I] The photopolymerization initiator [I] used in the present invention can be produced, for example, by the following method.

First, by benzoin condensation, for example, a compound A having two aldehyde groups in one molecule such as terephthalaldehyde and a compound B having one aldehyde group such as benzaldehyde are condensed in the presence of alkali cyanide. Let

When the benzene nucleus is represented by φ, 1 mole of terephthalaldehyde (OHC-φ-CHO) and 2 moles of benzaldehyde (φ
The benzoin condensation reaction with -CHO) is represented by the following formula.

OHC-φ-CHO + 2φ-CHO → φ-COCHOH-φ-COCHOH-φ The target compound can be obtained by alkylating the hydroxyl group (-OH) of this product by a conventional method.

Here, R is a linear or branched alkyl group having 1 to 10 carbon atoms, and the positions of the carbonyl group and the alkyl ether group in the two carbon chains may be interchanged.

Furthermore, when benzaldehyde having various substituents such as an alkyl group, an alkoxy group, a halogen, and an amino group is used as the compound B, the terminal aromatic group (Ar) can be a substituted aromatic group.

In the above formula [I], n is 1 to 10, but the number of n can be basically adjusted by changing the ratio of the compound A and the compound B.

For example, when the reaction molar ratio of the compound A and the compound B is 1: 2, n = 1 is produced, and when 1: 1, n = 2 is produced. When the number of n is increased, when the obtained compound is used as a photopolymerization initiator, it is possible to accelerate the polymerization reaction rate and achieve high molecular weight (high-speed high molecular weight performance).
The reaction efficiency tends to decrease. Therefore, in order to maintain the reaction activity and the high-speed high molecular weight at a high level, n is 1
It should be in the range of ~ 10.

The photopolymerization initiator represented by the formula [I] has two or more photocleavage points in one molecule, which makes it possible to produce a high molecular weight polymer even under a high-speed reaction condition. As a result, it enables high-speed production of acrylic viscoelastic products with excellent physical properties.

Monofunctional Photopolymerization Initiator The photopolymerization initiator [I] represented by the structural formula [I] may be used alone. It is preferably used in combination within the range of 20% by weight.

When the photopolymer initiator [I] is used alone, if the light intensity is relatively low, gelation may occur depending on the conditions such as the monomer composition and the adhesive strength may be reduced. However, when a monofunctional photopolymerization initiator is used in combination, gelation can be suppressed, and high-speed polymerization can be achieved even with a low initiator concentration.

Examples of the monofunctional photopolymerization initiator include 4- (2-hydroxyethoxy) phenyl (2-hydroxy-2-propylketone [Darocur 2959: manufactured by Merck &Co.]; 2-hydroxymethyl-1-phenylpropane-1-). On [Darocurure 1173: Merck &Co.]; acetophenone type such as methoxyacetophenone and 2,2-dimethoxy-2-phenylacetophenone; benzoin ether type such as benzoin ethyl ether and benzoin isopropyl ether; ketal type such as benzyl dimethyl ketal; other , Halogenated ketones, acylphosphine oxides,
Acyl phosphonate etc. can be mentioned.

In the photopolymerizable composition of the present invention, the photopolymerization initiator containing the photopolymerization initiator represented by the structural formula [I] as a main component is
The monomer component is contained in an amount of 0.001 to 5 parts by weight based on 100 parts by weight.

If this blending ratio is less than 0.001 parts by weight, the photopolymerization initiator is consumed at the initial stage of polymerization due to light energy,
Unreacted monomer tends to remain, not only the odor of the monomer remains but also the cohesive force decreases. On the other hand, when the amount exceeds 5 parts by weight, the polymerization reaction rate increases, but the decomposition odor of the photopolymerization initiator becomes severe, and the variation in molecular weight becomes large, and the adhesive performance also deteriorates.

The weight average molecular weight of the polymer by photopolymerization is preferably adjusted to about 30 to 100,000 in view of the adhesive property, and about 50 to 100.
It is even more preferable to adjust it to the maximum. Therefore, the blending ratio of the photopolymerization initiator is adjusted within the above range according to the target molecular weight of the polymer.

(Optional component) Photocrosslinking agent In the photopolymerizable composition of the present invention, in order to impart heat resistance and cohesive force at high temperature, it is preferable to include a photocrosslinking agent together with the above photopolymerization initiator. .

Examples of such a photocrosslinking agent include hexanediol di (meth) acrylate, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, neopentyl glycol di (meth) acrylate, Pentaerythritol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate
Acrylate, dipentaerythritol hexa (meth)
There are acrylate, other epoxy acrylate, polyethylene acrylate, urethane acrylate and the like.

Such a photo-crosslinking agent is generally contained in an amount of 5 parts by weight or less with respect to 100 parts by weight of the monomer component, whereby cross-linking occurs between polymer molecules during the photopolymerization reaction, and the heat resistance of the viscoelastic product is improved. improves. When the viscoelastic product is an adhesive tape, the cohesive force at high temperature is increased, and the holding power at high temperature is improved.

Other Additives Further, in the present invention, the photopolymerizable composition may be mixed with a commonly used additive such as a thickener, a thixotropic agent, a filler and a filler.

Examples of the thickener include acrylic rubber and epichlorohydrin rubber.

Examples of thixotropic agents include colloidal silica and polyvinylpyrrolidone.

Examples of the extender include calcium carbonate and titanium oxide clay.

Fillers include inorganic hollow bodies such as glass balun, alumina balun, ceramic baln; organic spherical bodies such as nylon beads, acrylic beads, and silicon beads; organic hollow bodies such as vinylidene chloride, acrylic balun; polyester, rayon, nylon, etc. Short fibers;

(Viscoelastic product and method for producing the same) The photopolymerizable composition of the present invention can be used for various adhesives such as adhesive tapes, heat-sensitive adhesive sheets, sealing materials for construction, automobiles, etc. Useful for manufacturing elastic products.

To produce a viscoelastic product using the photopolymerizable composition of the present invention, it is usually purged with an inert gas such as nitrogen gas or phenyl to remove oxygen dissolved in the composition. A compound capable of removing oxygen such as diisodecyl phosphite, triisodecyl phosphite, and stannous octoate is added. By adding a compound having an oxygen removing ability, sufficient polymerization (curing) can be realized even if the oxygen concentration in the atmosphere is high to some extent.

As a viscoelastic product, for example, in the case of producing an adhesive tape, a photopolymerizable composition is applied or injected onto a release paper, a release form, or a plastic film,
It is applied or impregnated on a substrate such as paper, cellophane, cloth, non-woven fabric, and metal foil. In the former case, an adhesive tape without a base material is obtained. When a sealing material is manufactured as a viscoelastic product, the photopolymerizable composition is poured into a peelable elongated mold or the like.

When applying, impregnating or injecting the photopolymerizable composition onto a mold or substrate, it is preferable to thicken with a thickener or a thixotropic agent so that the work can be carried out smoothly. In addition to this method, for example, a method of irradiating a small amount of ultraviolet rays to preliminarily polymerize a part of the monomer component may be used as the thickening method.

An apparatus devised so as not to come into contact with air (oxygen) is used for these coating, impregnating or injecting operations.

After coating, impregnating or injecting into a mold or substrate, the photopolymerizable composition is passed through a box replaced with an inert gas,
Irradiation of light such as ultraviolet rays and visible light is carried out through quartz glass, Pyrex glass, and borate glass. Also,
Even in an inert gas atmosphere, by covering the surface of the photopolymerizable composition applied, impregnated or injected into a mold or a base material with a polyester film having releasability, air (oxygen) and The contact may be prevented and the light irradiation may be performed. In this case, it is preferable to add a compound capable of removing oxygen.

Ultraviolet rays are usually used as the light. As the UV lamp, one having a spectral distribution in the wavelength range of 300 to 400 nm is usually used. Specific examples include a chemical lamp, a black light lamp (trade name of Toshiba Denshi Co., Ltd.), low pressure, high pressure, and ultra There are high-pressure mercury lamps, metal halide lamps, microwave-excited mercury lamps, and the like. The front two lamps are used to obtain a relatively low light intensity, and the rear four lamps are used to obtain a relatively high light intensity.

The light intensity can be adjusted by adjusting the distance to the irradiation target and the voltage.
Generally, the irradiation time is about 5 to 300 mW / cm ² , and the irradiation time is about 0.3 to 5 minutes.

By irradiation with light such as ultraviolet rays, a monomer component containing an acrylate-based monomer as a main component is polymerized to obtain a viscoelastic product. Irradiation time within the above range (polymerization reaction time)
Thus, the polymerization reaction can be substantially completed to the extent that the residual monomer content is about 0.5% by weight or less and does not adversely affect the performance of the viscoelastic product.

The light irradiation may be performed with a constant light intensity,
The physical properties of the viscoelastic product can be adjusted more precisely by irradiating the light in two or more stages with different light intensities.

[Action]

In the present invention, a monomer component containing an acrylate-based monomer as a main component contains a specific photopolymerization initiator having two or more photocleavage points in one molecule to obtain a photopolymerizable composition. Upon irradiation with light, the photopolymerization initiator is cleaved to generate radicals, the above-mentioned monomer components are rapidly polymerized, and a polymer having a high-molecular-weight viscoelasticity with a very small residual monomer amount is produced.

The mechanism by which the polymer thus obtained can be made to have a higher molecular weight is not necessarily clear, but when a compound having two or more photocleavage points in one molecule is used as a photopolymerization initiator, a polyfunctional radical is generated by the cleavage. Occurs. Then, polymer molecules are generated starting from this polyfunctional radical, and when the radicals are recombined to some extent, the length of the generated polymer from the starting point to the reaction stop point is the same as that of conventional monofunctional photopolymerization initiation. Even if it is short as in the case of the agent, each polymer molecule extends in multiple directions starting from the initiator by the polyfunctional radical, and therefore it can be presumed that the polymer has a high molecular weight as a whole.

〔Example〕

Hereinafter, the present invention will be specifically described with reference to synthetic experimental examples, examples and comparative examples, but the present invention is not limited to these examples.

[Synthesis Experimental Example 1] Synthesis of Photopolymerization Initiator (Part 1) A photopolymerization initiator [I] was synthesized according to the following chemical reaction formula.

[In the above formula, the two carbonyl groups may be on the side closer to the central benzene nucleus or on the side farther from the central benzene nucleus. ] 1) Benzoin condensation reaction In a 300 ml flask, 65 ml of 95% ethanol, 50 m of distilled water
l, terephthalaldehyde 30g, benzaldehyde 50g,
5 g of sodium cyanide was added, and the mixture was heated under reflux for 1 hour. After cooling, the solids were filtered, then washed with water and dried to give the product.

2) Ethyl etherification 10 g of the above-mentioned benzoin condensate was dissolved in 100 ml of dry ethanol, and hydrochloric acid gas was blown into it to react for 24 hours. Then, dry nitrogen gas was blown in to expel the hydrochloric acid gas, and then the solvent was distilled off to obtain the target compound as a viscous syrup. The target compound is a mixture of carbonyl groups and ethyl ether groups at different positions. This was used as a photopolymerization initiator (P ₁ ).

[Synthesis Experimental Example 2] Synthesis of Photopolymerization Initiator (Part 2) Benzoin condensation and ethyl etherification were performed in the same manner as in Synthetic Experimental Example 1 except that terephthalaldehyde was 67 g and benzaldehyde was 53 g, and the target compound was obtained. Got This was used as a photopolymerization initiator (P ₂ ).

<Evaluation of Physical Properties> Measurement of Physical Properties of Adhesive Tape For the double-sided adhesive tapes obtained in Examples and Comparative Examples, the weight average molecular weight of the adhesive (measured only when the photo-crosslinking agent was not added) was measured by the following measurement method. The amount of monomers, the adhesive strength, and the holding power were measured.

(1) Weight average molecular weight By gel permeation chromatography (GPC), standard polystyrene was used as a reference, tetrahydrofuran was used as an eluent, and detection was performed using a refractometer.

(2) Amount of residual monomer A gas chromatograph (GC-6A, manufactured by Shimadzu Corporation) having a separation column obtained by acid-treating chromosorb W carrying polyethylene glycol (trade name: 20M manufactured by Gascro Industrial Co., Ltd.) and a hydrogen flame ionization detector. ) Was used for the measurement. The measurement sample was 2 cc of a solution prepared by dissolving 100 mg of the adhesive sample in 5 cc of methyl acetate, and 2 cc of this solution
It was prepared by mixing with 2 cc of internal standard solution in which ethylhexyl methacrylate was dissolved in methyl acetate.

(3) Adhesive strength A 25 μm thick polyester film is attached to one side of a double-sided adhesive tape to form an adhesive tape with a width of 25 mm and a length of 300 mm, and this is attached to a steel plate that is ground with a # 280 paper file. A part of 100 to 120 mm in length from one end is reciprocated with a 2 kg roller and pasted under the conditions of 23 ° C and 65% RH.
The other end of this tape was peeled by an Instron tensile tester at a speed of 300 mm / min in the opposite direction of the 180 degree angle, and the peeling resistance at that time was measured to obtain the adhesive force (g / 25 mm width).

(4) Holding power An aluminum foil with a thickness of 100 μm is attached to one side of a double-sided adhesive tape to form an adhesive tape with a width of 25 mm, and one end of the tape is adhered to a steel plate polished with # 280 paper file. Stick it back and forth with a 2 kg roller so that the area is 25 mm wide and 25 mm long, fix a 1 kg weight to the other end of this tape, hang it at an ambient temperature of 100 ° C, and weigh it together with the tape. Was measured as the holding force (time).

This holding power is usually measured at 40 ° C,
The measurement was performed under severe conditions of ℃, the measurement time was shortened, and the measurement was terminated at a maximum of 150 hours.

Example 1 To 100 parts by weight of a monomer component consisting of 97% by weight of 2-ethylhexyl acrylate and 3% by weight of acrylic acid, 0.5 parts by weight of the photopolymerization initiator (P ₁ ) obtained in Synthesis Experimental Example 1 was added, The mixture was stirred with a stirrer and uniformly mixed to produce a photopolymerizable composition.

The resulting photopolymerizable composition was purged with nitrogen gas to remove dissolved oxygen, and then impregnated into a nylon nonwoven fabric on a transparent polyester film treated with a release agent, and its surface was covered with the same film as above, This was passed through a squeeze roll of an applicator to make the thickness uniform. Then, using an ultra-high pressure mercury lamp, a light intensity of 10 mW / cm ² (wavelength 365 n
(m center). As a result, 99.7% of the monomers were polymerized and the time required to reach a substantially completed state was
It was 1.5 minutes. The weight average molecular weight of the obtained polymer is 3
It was 50,000. In this way, a double-sided adhesive tape having a film thickness of 220 μm was manufactured.

[Comparative Example 1] A double-sided pressure-sensitive adhesive tape was prepared in the same manner as in Example 1 except that monofunctional Irgacure 651 (benzoin methyl ether; manufactured by Ciba-Geigy) was used as a photopolymerization initiator and the compounding amount was 0.5 part by weight. Although the time required for completion of the polymerization was 1.5 minutes and was the same as in Example 1, the weight average molecular weight of the obtained polymer was only 220,000, and the cohesive force was small.

[Comparative Example 2] A double-sided pressure-sensitive adhesive tape was prepared in the same manner as in Comparative Example 1 except that the blending amount of Irgacure 651 was 1.0 part by weight. Although the time required for completion of the polymerization was 0.7 minutes, which was faster than that in Example 1, the weight average molecular weight of the obtained polymer was as small as 140,000 and the polymer had no cohesive force.

[Examples 2 to 5] 2 parts by weight of the photopolymerization initiator (P ₁ ) obtained in Synthesis Experimental Example 1 was added to 100 parts by weight of a monomer component consisting of 97% by weight of 2-ethylhexyl acrylate and 3% by weight of acrylic acid, Further, 0 (no addition), 0.05, 0.1, and 0.2 parts by weight of hexanediol diacrylate was added as a photocrosslinking agent, and the mixture was uniformly stirred to obtain a photopolymerizable composition in the form of a liquid syrup.

Using this syrup, a double-sided pressure-sensitive adhesive tape was prepared in the same manner as in Example 1. The lamp intensity at that time is 20 mw
In / cm ^2, the irradiation time was 1.5 minutes. Furthermore, the adhesive strength and holding power of the obtained double-sided adhesive tape were measured. The results are shown in Table 1.

[Examples 6 to 9] 2 parts by weight of the photopolymerization initiator (P ₂ ) obtained in Synthesis Experimental Example 2 was added, and hexanediol diacrylate as a photocrosslinking agent was added to 0 (no addition), 0.05 and 0.1, respectively. , 0.2 parts by weight, light intensity of 40 mw / cm ^2, and irradiation for 0.7 minutes to obtain double-sided pressure-sensitive adhesive tapes in the same manner as in Examples 2 to 5. The physical properties of the obtained double-sided pressure-sensitive adhesive tape were evaluated, and the results are shown in Table 1.

As is clear from Table 1, according to the present invention, a high-molecular-weight polymer can be obtained even in a high-speed reaction, and by adding an appropriate amount of a crosslinking agent, excellent adhesive physical properties can be exhibited.

[Comparative Examples 3 to 6] 0.5 parts by weight of Irgacure 651 was added as a photopolymerization initiator, and 0 (no addition), 0.1, 0.2 and 0.4 parts by weight of hexanediol diacrylate was used as a photocrosslinking agent.
Double-sided pressure-sensitive adhesive tapes were prepared in the same manner as in Examples 2 to 5, except that the light intensity was 10 mw / cm ² and the irradiation time was 1.5 minutes.

The physical properties of the double-sided pressure-sensitive adhesive tape thus prepared were evaluated, and the results are shown in Table 1.

In Comparative Examples 3 to 6, since the molecular weight of the main chain polymer is small, the adhesive force is high in the non-crosslinked state but the holding force is small, and conversely, the adhesive force is low in the crosslinked state, and the interface breakage easily occurs. The holding power is also low.

[Effect of the Invention] In the photopolymerizable composition of the present invention, a monomer component containing an acrylate-based monomer as a main component contains a photopolymerization initiator having two or more photocleavage points in one molecule. ,
When this composition is irradiated with light, a polymer having a high molecular weight is produced even under a high-speed reaction condition, so that a viscoelastic product excellent in stress dispersibility, conformability and flexibility can be obtained with good productivity.

When the present invention is applied to the production of an adhesive tape, for example, a solvent, a drying energy, and a solvent recovery device as in the conventional method are not required, so that the production can be performed at a low cost by a simple process of resource saving and energy saving.

Claims (3)

[Claims] (A) 60 to 100% by weight of at least one acrylate-based monomer selected from the group consisting of (a) alkyl acrylate and methacrylic acid alkyl ester having an alkyl group having 1 to 12 carbon atoms, and the acrylate-based monomer. Vinyl-based monomer copolymerizable with monomer 0 to
A photopolymerizable composition containing 100 parts by weight of a monomer component containing 40% by weight, and (b) 0.001 to 5 parts by weight of a photopolymerization initiator containing a photopolymerization initiator represented by the following structural formula [I] as a main component. . [In the formula, two carbon chains connecting aromatic rings to each other. One has a carbonyl group (> C = 0) and the other has an alkyl ether group Here, R is a linear or branched alkyl group having 1 to 10 carbon atoms), and those positions may be interchanged in the two carbon chains. Ar represents a substituted or unsubstituted aromatic group. n shows the integer of 1-10. ] 2. A method for producing a viscoelastic product, which comprises irradiating the photopolymerizable composition according to claim 1 with light to polymerize the monomer component. 3. A viscoelastic product obtained by the method according to claim 2.