JP2953792B2 - Photopolymerizable composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acrylate-based photopolymerizable composition, and more particularly to a high-activity specific photopolymerization initiator having two photocleavable points in one molecule. The present invention relates to a photopolymerizable composition, a viscoelastic product obtained from the composition, and a method for producing the same.

[0002]

2. Description of the Related Art As a viscoelastic product made of an acrylic polymer, for example, an acrylic adhesive, an acrylic adhesive tape, an acrylic adhesive sheet, a double-sided adhesive tape, a foam-processed adhesive product, and the like are well known. . Acrylic pressure-sensitive adhesives are mainly composed of acrylic polymers, so they are excellent in light resistance, weather resistance, oil resistance, etc.,
Acrylic pressure-sensitive adhesive tapes made of plastic film, paper, etc.
It is widely used because of its excellent aging performance such as heat resistance and weather resistance.

[0003] Taking a typical acrylic pressure-sensitive adhesive tape as an example of such a viscoelastic product, the pressure-sensitive adhesive tape is generally made of vinyl based on an acrylate monomer such as alkyl acrylate and / or methacrylate. A pressure-sensitive adhesive solution obtained by solution polymerization of a system monomer with an organic solution or an emulsion obtained by emulsion polymerization with an aqueous system is applied or impregnated on a substrate, and the resultant is heated and dried.

In the above-mentioned production method, when an adhesive solution is used, a large amount of energy is required to dry the adhesive solution applied or impregnated on a substrate at a high temperature, and air pollution by an organic solvent is reduced. To prevent this, a large-scale recovery device is required. In addition, since the organic solvent is easily flammable, a sufficient safety device is required for maintaining safety.

[0005] On the other hand, when an emulsion is used, more energy is required to evaporate water than when an organic solvent is used, and in terms of performance, water resistance is reduced due to an emulsifier mixed during polymerization. Furthermore, since a water-soluble monomer cannot be used, the type of the monomer is limited, and there is a drawback that the ability to respond to various needs required for the pressure-sensitive adhesive tape is weak.

Meanwhile, US Pat. No. 4,181,752
In the specification, a solvent-free photopolymerizable liquid composition containing a photopolymerization initiator such as benzoin methyl ether in a vinyl monomer containing an acrylate monomer as a main component is used. There is disclosed a method for producing an acrylic pressure-sensitive adhesive tape by irradiating ultraviolet rays of 300 to 400 nm at a light intensity of 0.1 to 7 mW / cm ² and polymerizing the vinyl monomer.

In this method, the polymer is made to have a high molecular weight by the vinyl monomer by lowering the intensity of ultraviolet light, thereby increasing the adhesive strength and cohesive strength. According to this method, since the pressure-sensitive adhesive tape can be manufactured without using a solvent, the above-mentioned problem associated with the use of the organic solvent and water is solved. However, this method has a disadvantage that the productivity is poor for practical use because the polymerization reaction rate is low. In this method, if UV irradiation is stopped halfway to shorten the polymerization reaction time,
The residual monomer concentration in the product increases, causing odor problems and deteriorating the adhesive performance, particularly the cohesive strength.

In general, in photopolymerization of a vinyl monomer such as an acrylate monomer, the polymerization reaction rate is proportional to the square root of the product of the amount of photopolymerization initiator and light intensity. Therefore, to increase the amount of the photopolymerization initiator to increase the productivity, or to increase the light intensity, to increase the polymerization reaction rate, the molecular weight of the resulting polymer decreases,
The balance between the adhesive strength and the cohesive strength of the adhesive tape cannot be maintained at a high level. As described above, the conventional photopolymerization technique cannot maintain both the physical properties and productivity of a viscoelastic product such as an acrylic adhesive tape at a high level.

In order to solve such a problem, a monomer component containing an acrylate monomer as a main component is mixed with a specific photopolymerization initiator having two or more cleavage points by light in one molecule to carry out photopolymerization. A method of obtaining a hydrophilic composition and irradiating the composition with light is disclosed in JP-A-2-160802, Japanese Patent Application No. 1-236700, and Japanese Patent Application No. 1-222081. The photopolymerization initiator used is disclosed in Japanese Patent Application
JP-A-315998 is an initiator that can be obtained by dimerizing a hydroxyacetophenone-based photoinitiator, and is disclosed in Japanese Patent Application Nos. 1-236700 and 1-222208.
No. 1 is a benzyl dialkyl ketal-based initiator and a benzoin alkyl ether-based initiator each having two or more cleavage points due to light in one molecule. According to these methods, the monomer component is rapidly polymerized, and a high-molecular-weight viscoelastic polymer having an extremely small amount of residual monomer can be obtained.

However, in these methods (especially in the case of a hydroxyacetophenone-based initiator), the initiator efficiency is low or the activity of the initiator radical is low. There was a disadvantage that the amount of addition had to be increased or the lamp strength had to be increased.

[0011]

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for producing a viscoelastic product from a substantially solvent-free photopolymerizable composition using a photopolymerization initiator. It is an object of the present invention to provide a novel photopolymerizable composition capable of producing an acrylic viscoelastic product having a high level of viscoelasticity. 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 inventor of the present invention has conducted intensive studies in order to solve the problems of the prior art, and as a result, the monomer component mainly composed of an acrylate monomer has two cleavage points by light in one molecule. A radical having a high initiation reactivity can be formed inside either of the two cleavage points, and a photopolymerizable composition containing a photopolymerization initiator having a high initiator efficiency is used for photopolymerization. It has been found that when an elastic product is manufactured, it is possible to obtain an acrylic viscoelastic product with a lower lamp strength, a lower initiator amount, a higher molecular weight, and excellent physical properties at a high productivity. Thus, the present invention has been completed.

[0013]

Thus, according to the present invention, (a) at least one kind selected from the group consisting of alkyl acrylates and alkyl methacrylates having an alkyl group having 1 to 12 carbon atoms. 60 to 100% by weight of an acrylate monomer and 0 to 4 of a vinyl monomer copolymerizable with the acrylate monomer
100 parts by weight of a monomer component containing 0% by weight, and (b) a photopolymerization initiator 0.001 to 5 represented by the following structural formula 2.
Parts by weight of the photopolymerizable composition.

[0014]

Embedded image [Wherein R ¹ and R ² are a linear or branched, substituted or unsubstituted alkyl group or a substituted or unsubstituted aromatic group. R ³ and R ⁴ are a linear or branched, substituted or unsubstituted alkyl or alkoxy group, or a substituted or unsubstituted aromatic group. Z
Is a substituted or unsubstituted aromatic group or a group represented by the following general formula (1).

-Ar ¹ -Y-Ar ^2- (1) wherein Ar ¹ and Ar ² are a substituted or unsubstituted aromatic group, and Y is a linear or branched, substituted Or an unsubstituted alkylene group, carbonyl group, oxygen atom, sulfur atom or single bond.) According to the present invention, the photopolymerizable composition is irradiated with light to polymerize the monomer component. Provided are a method for producing a viscoelastic product, and a viscoelastic product obtained by the method.
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 monomer 60 selected from the group consisting of alkyl acurates and alkyl methacrylates having an alkyl group having 1 to 12 carbon atoms. To 100% by weight and a vinyl monomer copolymerizable with the acrylate monomer.
% By weight.

Acrylate monomer As the acrylate monomer, an alkyl acrylate or alkyl methacrylate having an alkyl group of 1 to 14, preferably 4 to 12, carbon atoms is used. N-butyl acid,
Examples thereof include 2-ethylhexyl (meth) acrylate, isooctyl (meth) acrylate, and isononyl (meth) acrylate. These may be used alone or in combination of two or more. From the balance of tackiness and cohesiveness, etc., the homopolymer generally has an alkyl acrylate having a glass transition temperature of −50 ° C. or lower as a main component, and as a comonomer, a lower alkyl group (meth).
It is preferable to use acrylic esters or the following vinyl monomers.

Vinyl monomers Other vinyl monomers copolymerizable with acrylate monomers include, for example, acrylic acid, methacrylic acid,
Examples include acrylamide, acrylonitrile, methacrylonitrile, N-substituted acrylamide, hydroxyethyl acrylate, N-vinylpyrrolidone, maleic acid, itaconic acid, N-methylol acrylamide, hydroxyethyl methacrylate, and the like. Also, a vinyl monomer forming a polymer having a low glass transition temperature, for example,
Vinyl monomers such as tetrahydrofurfuryl acrylate, polyethylene glycol acrylate, polypropylene glycol acrylate, fluorine acrylate, and silicon acrylate can also be used. These vinyl monomers can be used singly or in combination of two or more. However, if the use ratio in all the monomer components exceeds 40% by weight, the adhesive properties as an acrylic adhesive are deteriorated. Absent.

(Photopolymerization Initiator) The acylphosphine oxide-based photopolymerization initiator represented by Structural Formula 1 represented by Formula 3 has two cleavage points by light in one molecule.
A radical of a phosphorus atom having high initiation reactivity can be formed inside at any of the cleavage points, and the initiator efficiency is high, so that it is possible to produce a high molecular weight polymer even under high-speed reaction conditions. Thus, high-speed production of acrylic viscoelastic products having excellent physical properties becomes possible.

[0020]

Embedded image [Wherein R ¹ and R ² are a linear or branched, substituted or unsubstituted alkyl group or a substituted or unsubstituted aromatic group. R ³ and R ⁴ are a linear or branched, substituted or unsubstituted alkyl or alkoxy group, or a substituted or unsubstituted aromatic group. Z
Is a substituted or unsubstituted aromatic group or a group represented by the following general formula (1).

-Ar ¹ -Y-Ar ^2- (1) wherein Ar ¹ and Ar ² are a substituted or unsubstituted aromatic group, and Y is a linear or branched, substituted, Or an unsubstituted alkylene group, carbonyl group, oxygen atom, sulfur atom or single bond.)]

The acylphosphine oxide photopolymerization initiator 3 of the present invention will be described. R ¹ and R ² are linear or branched, substituted or unsubstituted alkyl groups;
Alternatively, it is a substituted or unsubstituted aromatic group. Examples of the linear or branched, substituted or unsubstituted alkyl group include a methyl group, an ethyl group, an isopropyl group, an n-octyl group, a cyclohexyl group and the like. Examples of the substituted or unsubstituted aromatic group include a phenyl group, a methylphenyl group, a trimethylphenyl group, and a methoxyphenyl group.

R ³ and R ⁴ are linear or branched,
It is a substituted or unsubstituted alkyl group or alkoxy group, or a substituted or unsubstituted aromatic group. Examples of linear or branched, substituted or unsubstituted alkyl groups include, for example, methyl, ethyl, isopropyl, n
-Octyl group, cyclohexyl group and the like. Examples of the alkoxy group include, for example, a methoxy group, an ethoxy group, an isopropoxy group and a butoxy group. Examples of the substituted or unsubstituted aromatic group include a phenyl group, a methylphenyl group, a trimethylphenyl group, and a methoxyphenyl group.

Z is a substituted or unsubstituted aromatic group or one represented by the following general formula (1). —Ar ¹ —Y—Ar ² — (1) (wherein, Ar ¹ and Ar ² are a substituted or unsubstituted aromatic group, and Y is a linear or branched, substituted or unsubstituted group. Is an alkylene group, a carbonyl group, an oxygen atom, a sulfur atom, or a single bond.) Examples of the substituted or unsubstituted aromatic group for Z include a p-phenylene group.
Examples of the substituted or unsubstituted aromatic group of Ar ¹ and Ar ² include a p-phenylene group. Examples of the linear or branched, substituted or unsubstituted alkylene group of Y include a methylene group and an ethylene group.

Specific examples of the acylphosphine oxide-based photopolymerization initiator of the present invention are as follows, but are not necessarily limited thereto.

[0026]

Embedded image 1,4-bis [(benzoyl) (phenyl) (oxo)
Phosphino] benzene

[0027]

Embedded image 4,4'-bis [(benzoyl) (phenyl) (oxo) phosphino] biphenyl

[0028]

Embedded image 1,4-bis [(benzoyl) (methoxy) (oxo)
Phosphino] benzene

[0029]

Embedded image 1,1'-bis [4-[(2,4,6-trimethylbenzoyl) (methoxy) (oxo) phosphino] phenyl] methane

[0030]

Embedded image 1,1'-bis [4-[(benzoyl) (phenyl)
(Oxo) phosphino] phenyl] methane

The acylphosphine oxide-based photopolymerization initiator of the present invention comprises acid halides R ¹ COX and R ² COX.
X (X is a halogen atom) and a phosphinite or a phosphonite represented by the structural formula 9

[0032]

Embedded image [Wherein, R ³ and R ⁴ are a linear or branched, substituted or unsubstituted alkyl or alkoxy group, or a substituted or unsubstituted aromatic group. Z is a substituted or unsubstituted aromatic group or one represented by the following general formula (1).

-Ar ¹ -Y-Ar ^2- (1) (wherein, Ar ¹ and Ar ² are a substituted or unsubstituted aromatic group, and Y is a linear or branched, substituted Or an unsubstituted alkylene group, a carbonyl group, an oxygen atom, a sulfur atom or a single bond.) R represents an alkyl group or the like] and a method known to those skilled in the art according to a known method according to JP-B-63-40799. It can be easily manufactured. In addition, those skilled in the art can also easily produce acid halides and phosphinous esters according to a known method from the literature.

The monofunctional photopolymerization initiator represented by the structural formula 1 may be used alone, but a generally used monofunctional photopolymerization initiator may be used in an amount of about 1% of the total initiator amount. They can be used together within a range of 20% by weight or less. When the photopolymerization initiator 1 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 decrease. 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.

As the monofunctional photopolymerization initiator, for example, 4
-(2-hydroxyethoxy) phenyl (2-hydroxy-2-propyl) ketone [Darocur-2959: manufactured by Merck]; α-hydroxy-α, α'-dimethyl-acetophenone [Darocur-1173: manufactured by Merck];
Acetophenones such as methoxyacetophenone and 2,2-dimethoxy-2-phenylacetophenone; benzoin ethers such as benzoin ethyl ether and benzoin isopropyl ether; ketals such as benzyl dimethyl ketal; other halogenated ketones, acyl phosphine oxides and acyl Phosphonate and the like can be mentioned.

In the photopolymerization composition of the present invention, the photopolymerization initiator containing the photopolymerization initiator represented by the structural formula 1 as a main component is used in an amount of 0.0
It is contained in a proportion of from 01 to 5 parts by weight. When the compounding ratio is less than 0.001 part by weight, the photopolymerization initiator is consumed in the early stage of polymerization by light energy, so that the unreacted monomer tends to remain, and not only the odor of the monomer remains but also the cohesive strength. Decrease. On the other hand, when the amount exceeds 5 parts by weight, the polymerization reaction speed is increased, but the decomposition odor of the photopolymerization initiator is increased, the variation in molecular weight is increased, and the adhesive performance is reduced.

The weight average molecular weight of the polymer obtained by photopolymerization is as follows:
In view of the adhesive properties, it is preferably adjusted to about 300 to 1,000,000, and more preferably to about 500 to 1,000,000. Therefore, depending on the molecular weight of the target polymer,
The mixing ratio of the photopolymerization initiator is adjusted within the above range.

(Optional component) Photocrosslinking agent In the photopolymerizable composition of the present invention, a photocrosslinking agent is contained together with the above photopolymerization initiator in order to impart heat resistance, cohesive strength at a high temperature, and the like. Is preferred.

Examples of such photocrosslinking agents include hexanediol di (meth) acrylate, (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, and neopentyl glycol di (meth) acrylate. A) acrylate, pentaerythritol di (meth) acrylate, trimethylolpropane tri (meth) acrylate, pentaerythritol tri (meth) acrylate, dipentaerythritol hexa (meth) acrylate, other epoxy acrylate, polyester acrylate, urethane acrylate, and the like.

In general, when the photo-crosslinking agent is contained in an amount of 5 parts by weight or less based on 100 parts by weight of the monomer component, a cross-linking occurs between the polymer molecules in the course of the photopolymerization reaction, and the viscoelastic product is produced. Heat resistance is improved. When the viscoelastic product is an adhesive tape, the cohesive force at high temperature increases, and the holding power at high temperature improves.

Other Additives In the present invention, commonly used additives such as a thickener, a thixotropic agent, a bulking agent and a filler may be added to the photopolymerizable composition. Examples of the thickener include acrylic rubber and epichlorohydrin rubber. Examples of the thixotropic agent include colloidal silica and polyvinylpyrrolidone. Examples of fillers include calcium carbonate, titanium oxide, and clay. As fillers, inorganic hollow bodies such as glass balun, alumina balun, ceramic balun; organic spherical bodies such as nylon beads, acrylic beads, silicon beads; organic hollow bodies such as vinylidene chloride, acrylic balun; polyester, rayon, nylon, etc. Monofilament and the like.

(Viscoelastic Product and Method for Producing the Same) The photopolymerizable composition of the present invention includes, for example, pressure-sensitive adhesive tapes, heat-sensitive adhesive sheets, sealing materials for buildings and automobiles, and interlayer films for vibration-proof materials. Useful for the manufacture of various viscoelastic products. To produce a viscoelastic product using the photopolymerizable composition of the present invention, usually, in order to remove oxygen dissolved in the composition, to purge with an inert gas such as nitrogen gas, or A compound capable of removing oxygen, such as phenyldiisodecyl 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.

When a pressure-sensitive adhesive tape is produced as a viscoelastic product, for example, the photopolymerizable composition is applied or poured onto a release paper, a release mold, or the like, or a plastic film, paper, cellophane, cloth, Coating or impregnating a substrate such as a nonwoven fabric or a metal foil. In the former case, an adhesive tape without a base material is obtained. When a sealing material is produced as a viscoelastic product, the photopolymerizable composition is injected into a strippable elongated mold or the like and shaped.

Applying the photopolymerizable composition to a mold or a substrate,
When impregnating or pouring, it is preferable to increase the viscosity with a thickener or a thixotropic agent so that the operation is performed smoothly. In addition, as a thickening method, for example, there is a method in which a part of the monomer component is polymerized in advance by irradiating a small amount of ultraviolet rays. For the application, impregnation or injection work, a device designed so as not to come into contact with air (oxygen) is used.

After being applied, impregnated or injected into a mold or a substrate, the photopolymerizable composition is passed through a box replaced with an inert gas and irradiated with ultraviolet light through quartz glass, pyrex glass or borate glass. And irradiation of light such as visible light. Also, even in an inert gas atmosphere, by coating the surface of the photopolymerizable composition applied, impregnated or injected into a mold or a base material with a polyester film having a mold releasing property, the air and Light irradiation may be performed while preventing contact. In this case, it is preferable to add a compound capable of removing oxygen.

As the light, ultraviolet light is usually used.
As an ultraviolet lamp, usually, a wavelength of 300 to 400 nm
A lamp having a spectrum distribution in a region is used, and specific examples include a chemical lamp, a black light lamp (trade name of Toshiba Electric Materials Co., Ltd.), a low-pressure, high-pressure or ultra-high-pressure mercury lamp, a metal halide lamp, and a microwave-excited mercury lamp. Etc. The first two lamps are used to obtain relatively low light intensity, and the last five lamps are
Used to obtain relatively high light intensity.

The light intensity is generally about 5 to 300 mW / cm ² , and the irradiation time is about 0.3 to 5 minutes, by adjusting the distance to the irradiation object and the voltage.

By irradiation with light such as ultraviolet rays, a monomer component containing an acrylate monomer as a main component is polymerized, and a viscoelastic product is obtained. With the above irradiation time (polymerization reaction time), the amount of the residual monomer is about 0.3% by weight or less, and is reduced to such an extent that the performance of the viscoelastic product is not adversely affected, thereby substantially completing the polymerization reaction. Can be done. The irradiation of light may be performed at a constant light intensity, but it is also possible to adjust the physical properties of the viscoelastic product more precisely by irradiating with different light intensity in two or more steps. .

[0049]

[Function] In the present invention, a monomer component containing an acrylate monomer as a main component has two cleavage points by light in one molecule, and a radical having a high initiation reactivity with either of the two cleavage points. Can be inside, and the initiator efficiency is high, to obtain a photopolymerizable composition containing a photopolymerization initiator, and when irradiated with light, this photopolymerization initiator is cleaved to generate radicals, At low lamp strength and lower initiator amount, the above monomer components polymerize quickly, producing a higher molecular weight, viscoelastic polymer with very little residual monomer.

The mechanism for increasing the molecular weight of the obtained polymer is not necessarily clear, but is presumed as follows. The acylphosphine oxide-based photopolymerization initiator represented by the chemical formula 1 has two cleavage points by light in one molecule, and radicals can be efficiently generated by irradiation with light at either of the two cleavage points. Occurs. As a result, a benzoyl radical having ordinary initiation reactivity is formed together with a bifunctional radical having a phosphorus atom radical having a high initiation reactivity at both terminals.

The polymer molecule formed from the starting point of the bifunctional radical has a high molecular weight. I mean,
When the growing radical starting from the bifunctional radical is recombined to some extent, the length of the polymer produced from the starting point to the reaction stopping point is the same as that of the conventional monofunctional photopolymerization initiator. Even if it is so short, each polymer molecule extends in two directions starting from an initiator that becomes a bifunctional radical, so that the overall length is doubled.

Since the bifunctional radical is more active than the benzoyl radical generated at the same time, it grows faster. As a result, the ratio of the polymer having a double molecular weight starting from the bifunctional radical becomes relatively larger than the polymer starting from the benzoyl radical, and the molecular weight becomes higher as a whole of the blending system. Therefore, it is considered that the polymer becomes higher than the system containing the conventional monofunctional initiator as well as the conventional polyfunctional initiator.

Therefore, at the same polymerization rate, the polymer becomes higher than the conventional system containing a polyfunctional initiator as well as the conventional monofunctional initiator. Moreover, since the initiator efficiency is high, the generated radical concentration is the same even with a lower initiator and lower lamp intensity, so that the polymerization rate does not change even with a lower initiator and lower lamp intensity. This makes it possible to produce a high-molecular-weight polymer even under high-speed reaction conditions. As a result, high-speed production of an acrylic viscoelastic product having excellent physical properties becomes possible.

[0054]

EXAMPLES Hereinafter, the present invention will be described specifically with reference to Examples and Comparative Examples, but the present invention is not limited to only these Examples.

<Measurement of physical properties> Measurement of physical properties of pressure-sensitive adhesive tape The weight-average molecular weight of the pressure-sensitive adhesive (measured only when no photocrosslinking agent was added) was measured for the double-sided pressure-sensitive adhesive tapes obtained in Examples and Comparative Examples by the following measurement method. ), Residual monomer amount, gel fraction / swelling degree, adhesive strength and holding power were measured.

(1) Weight-average molecular weight A sample solution obtained by dissolving in tetrahydrofuran and leaving it for 24 hours to remove insolubles was subjected to gel permeation chromatography (GPC) to measure the refractive index using standard polystyrene as a reference. It measured using.

(2) Amount of residual monomer A gas chromatograph (GC-6A, Shimadzu) having a separation column obtained by treating chromosorbW carrying polyethylene glycol (trade name: 20M, manufactured by Gas Chromo Corporation) with acid and a flame ionization detector. (Manufactured by Seisakusho). Note that the measurement sample was an adhesive sample 100
mg was dissolved in 5 cc of methyl acetate to obtain 2 cc, and 2 cc of this solution was mixed with 2 cc of an internal standard solution in which 2-ethylhexyl methacrylate was dissolved in methyl acetate.

(3) Reaction Completion Time A part of the sample is sampled at regular intervals (for example, every minute) from a test sample in which a photopolymerization reaction is occurring.
The amount of residual monomer is measured by the method of (2). The remaining monomer amount is plotted on the logarithmic axis of the semilogarithmic graph, the remaining monomer amount is plotted against the irradiation time, and those points are connected. The time when the amount of the residual monomer became 0.3% by weight of the sample (that is, the time when the polymerization rate became 99.7% by weight) was read from the graph, and the time was defined as the reaction completion time.

(4) Gel Fraction / Swelling Ratio 100 mg of an adhesive sample was dissolved in tetrahydrofuran,
After leaving for 4 hours, the mixture was filtered through a 200-mesh stainless steel filter. It was determined by measuring the weight of the swelled gel collected by filtration and the weight of a dried gel obtained by drying the swelled gel at 100 ° C. for 2 hours.

(5) Adhesive Strength A 25 μm-thick polyester film is adhered to one side of a double-sided adhesive tape to form an adhesive tape having a width of 25 mm and a length of 300 mm. The adhesive tape is applied to a stainless plate polished with a # 280 paper file. , 100-120 length from one end of the tape
mm part was reciprocated with a 2 kg roller and pasted, and the other end of the tape was applied at a speed of 300 mm / min with an Instron tensile tester at 23 ° C. and 65% RH.
Peeling was performed in the opposite direction of the 0-degree angle, and the peeling resistance at that time was measured and defined as the adhesive strength (g / 25 mm width).

(6) Holding force A 100 μm-thick aluminum foil was adhered to one side of the double-sided adhesive tape to form an adhesive tape having a width of 25 mm.
One end of the tape was reciprocated with a 2 kg roller so as to have an adhesive area of 25 mm in width and 25 mm in length on a stainless steel plate polished with a No. 280 file, and 1 kg of tape was attached to the other end of the tape. Fix the weight and add this to 100
The sample was suspended in an atmosphere at a temperature of ° C., and the time required for the weight to fall together with the tape was measured, and the measured value was defined as the holding force (time). This holding force is usually measured at 40 ° C., but is measured under severe conditions of 100 ° C. to reduce the measuring time,
The measurement was stopped at 0 hour.

Example 1 A compound of the formula (1) of the photopolymerization initiator represented by the structural formula (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. 0.000 parts by weight,
The mixture was uniformly mixed by stirring with a stirrer to produce a photopolymerizable composition. The resulting photopolymerizable composition was purged with nitrogen gas to remove dissolved oxygen, then impregnated in a nylon nonwoven fabric on a transparent polyester film treated with a release agent, and the plane was covered with the same film as above. Was passed through a squeezing roll of an applicator to make the thickness uniform. Next, an ultra-high pressure mercury lamp was used for this, and the light intensity was 5.0 mW / cm.
Irradiation at ² (wavelength 365 mm center). As a result, 9
The time required until 9.7% by weight of the monomer was polymerized and the polymerization was substantially completed was 1.75 minutes. The weight average molecular weight of the obtained polymer was 3590,000.
In this way, a 160 μm-thick double-sided pressure-sensitive adhesive tape was produced.

Example 2 As a photopolymerization initiator, 0.50 part by weight of a compound of formula 7 was added, and the light intensity was increased to 10 mW / c.
A double-sided pressure-sensitive adhesive tape was prepared in the same manner as in Example 1 except that m ² was used. The time required for completing the polymerization was 1.8.
After 5 minutes, the weight average molecular weight of the obtained polymer was 399.4, and the time was almost the same, but the molecular weight was as in Example 1.
It was slightly higher.

Comparative Example 1 As a photopolymerization initiator, 4-
From (2-hydroxyethoxy) phenyl (2-hydroxy-2-methyl-propyl) ketone (trade name: Darocure-2959: manufactured by Merck Ltd.) and 1/2 mole of isophorone diisocyanate, a method described in JP-A-2-160802 (Hereinafter abbreviated as GI-1), the compounding amount was 2.00 parts by weight, and the light intensity was 20 mW /
except that the cm ² is Example 1 and was created a double-sided adhesive tape in a similar way, but the weight average molecular weight of the obtained polymer was approximately equivalent to 337,000 next Example 1, polymerization completed It took 2.40 minutes, and it took time.

Comparative Example 2 A double-sided pressure-sensitive adhesive tape was prepared in the same manner as in Comparative Example 1, except that the light intensity was changed to 40 mW / cm ² . The time required for the completion of the polymerization was 1.75 minutes, which was the same as that in Example 1. However, the obtained polymer had a small weight average molecular weight of 291,000 and was inferior in cohesive strength.

[Comparative Example 3] Monofunctional Irgacure 651 (benzyldimethyl ketal; manufactured by Ciba Geigy) was used as a photopolymerization initiator, and the compounding amount was 0.7 part by weight.
A double-sided pressure-sensitive adhesive tape was prepared in the same manner as in Example 1 except that the light intensity was changed to 6.7 mW / cm ^2, and the weight average molecular weight of the obtained polymer was 323,000, which was almost the same as in Example 1. However, the time required for completing the polymerization was 3.
It took 70 minutes and took a very long time.

Comparative Example 4 A double-sided pressure-sensitive adhesive tape was prepared in the same manner as in Comparative Example 3, except that the amount of Irgacure 651 was changed to 1.0 part by weight. The time required for completing the polymerization was 2.17 minutes, which was longer than in Example 1. The weight average molecular weight of the obtained polymer was as small as 225,000, and the cohesion was small. Examples 1-2 and Comparative Examples 1-4
Table 1 shows the results.

[0068]

[Table 1]

[Examples 3 to 6] A compound of formula 7 among photopolymerization initiators represented by structural formula 1 was added to 100 parts by weight of a monomer component consisting of 95 parts by weight of 2-ethylhexyl acrylate and 5 parts by weight of acrylic acid. Was added, and hexanediol diacrylate was further added as a photocrosslinking agent at 0 (not added), 0.05, 0.10,
0.20 part by weight was added and stirred uniformly to obtain a photopolymerizable composition of a liquid syrup. Example 1 using this syrup
A double-sided pressure-sensitive adhesive tape was prepared in the same manner as described above. At that time, the lamp intensity was 10 mW / cm ² and the irradiation time was 1.
7 minutes. Table 2 shows the results. As is clear from Table 2, according to the present invention, a high-molecular-weight polymer can be obtained even in a high-speed reaction, and further excellent adhesive properties can be exhibited by adding a photocrosslinking agent.

[Comparative Examples 5 to 8] 1.00 parts by weight of Irgacure 651 was added as a photopolymerization initiator, and hexanediol diacrylate was added as a photocrosslinking agent at 0 (no addition), 0.10, and 0.10, respectively. A double-sided pressure-sensitive adhesive tape was prepared in the same manner as in Examples 3 to 6, except that the light intensity was 12 mW / cm ² and the irradiation time was 1.7 minutes, using 0.20 and 0.40 parts by weight. The physical properties of the double-sided pressure-sensitive adhesive tape thus produced were evaluated, and the results are shown in Table 2. Comparative Example 5
In the case of 8, since the molecular weight of the main chain polymer is small, the adhesive force is high in the non-crosslinked state, but the holding power is small. became.

[0071]

[Table 2]

[0072]

According to the photopolymerizable composition of the present invention, a monomer component containing an acrylate monomer as a main component has two cleavage points due to light in one molecule. Even though radicals with high initiation reactivity can be generated inside, and the initiator efficiency is high, it contains a photopolymerization initiator, and when this composition is irradiated with light, a polymer with a high molecular weight is produced even under high-speed reaction conditions Therefore, a viscoelastic product excellent in stress dispersibility, followability, flexibility and the like can be obtained with high productivity.

Further, the photopolymerization of this photopolymerization composition gives
When a viscoelastic product is manufactured, an acrylic viscoelastic product having a lower lamp strength, a lower initiator amount, a higher molecular weight, and excellent physical properties as described above can be obtained with high productivity.

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

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Claims (3)

(57) [Claims] (1) 60 to 100% by weight of at least one acrylate monomer selected from the group consisting of alkyl acrylate and alkyl methacrylate having an alkyl group having 1 to 12 carbon atoms, and the acrylate monomer 100 parts by weight of a monomer component containing 0 to 40% by weight of a vinyl monomer copolymerizable with the monomer;
(B) Photopolymerization initiator 0.0 represented by the following structural formula 1
A photopolymerizable composition comprising from 0.01 to 5 parts by weight. Embedded image [Wherein R ¹ and R ² are a linear or branched, substituted or unsubstituted alkyl group or a substituted or unsubstituted aromatic group. R ³ and R ⁴ are a linear or branched, substituted or unsubstituted alkyl or alkoxy group, or a substituted or unsubstituted aromatic group. Z
Is a substituted or unsubstituted aromatic group or a group represented by the following general formula (1). —Ar ¹ —Y—Ar ² — (1) (wherein, Ar ¹ and Ar ² are a substituted or unsubstituted aromatic group, and Y is a linear or branched, substituted or unsubstituted group. Alkylene group, carbonyl group, oxygen atom, sulfur atom or single bond.)] 2. A method for producing a viscoelastic product, comprising 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.