JPH04366103A - Photopolymerizable composition and viscoelastic product - Google Patents

Abstract

PURPOSE:To provide a photopolymerizable composition for viscoelastic product production which contains a photopolymerization initiator and is substantially solvent-free, and from which acrylic viscoelastic products having excellent viscoelastic properties can be produced at high efficiency. CONSTITUTION:The title composition comprises: (a) 60-98wt.% at least one acrylate monomer selected from the group consisting of alkyl acrylates and methacrylates in each of which the alkyl is 1-12C; (b) 2-40wt.% vinyl compound monomer having an unsaturated double bond which can copolymerize with the monomer (a); (c) a macromonomer in an amount of 1-15 pts.wt. per 100 pts.wt. of the sum of the monomers (a) and (b); and (d) a photopolymerization initiator in an amount of 0.001-5 pts.wt. per 100 pts.wt. of that sum.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to acrylate-based photopolymerizable compositions, and more specifically, the formulation of photopolymerizable compositions that can maintain both viscoelastic properties and productivity at high levels even under high-speed reaction conditions. and viscoelastic products obtained therefrom.

0002

[Prior Art] As viscoelastic products made of acrylic polymers, for example, acrylic adhesives, acrylic adhesive tapes, acrylic adhesive sheets, double-sided adhesive tapes, and adhesive processed foam products are well known. .

[0003] Acrylic adhesives have acrylic polymers as their main component, so they have excellent light resistance, weather resistance, oil resistance, etc. Acrylic adhesive tapes have surface base materials such as plastic films and paper. is widely used because it has excellent adhesive properties such as adhesive strength and cohesive strength, and aging resistance properties such as heat resistance and weather resistance.

[0004] Taking acrylic adhesive tape as a typical example of these viscoelastic products, the adhesive tape is generally made of vinyl whose main component is an acrylate monomer such as an acrylic acid alkyl ester and/or a methacrylic acid ester. It is manufactured by applying or impregnating a base material with an adhesive solution obtained by solution polymerizing a system monomer in an organic solvent, or an emulsion obtained by emulsion polymerizing in an aqueous system, and then heating and drying this.

[0005] Among the above manufacturing methods, when an adhesive solution is used, a large amount of energy is consumed to dry the adhesive solution coated or impregnated on the base material at high temperature, and it is also difficult to prevent air pollution caused by the solvent. Therefore, large-scale recovery equipment is required. Moreover, since the solvent is easily flammable, sufficient safety equipment 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, water resistance is reduced due to the emulsifier mixed in during polymerization. Moreover, since water-soluble monomers cannot be used, the types of monomers are limited, and there is a drawback that it is difficult to meet the wide variety of needs required for adhesive tapes.

By the way, US Patent No. 4,181,752
The specification uses a solvent-free photopolymerizable liquid composition in which a photopolymerization initiator such as benzoin methyl ether is contained in a vinyl monomer mainly composed of an acrylate monomer. A method for manufacturing an acrylic pressure-sensitive adhesive tape is disclosed in which the vinyl monomer is polymerized by irradiation with ultraviolet rays of 300 to 400 nm at a light intensity of 0.1 to 7 mW/cm<2>.

[0008]

This method increases the molecular weight of the vinyl monomer-based polymer by lowering the intensity of ultraviolet rays, thereby increasing adhesive strength and cohesive strength. According to this method, adhesive tapes can be manufactured without using solvents, so the problems associated with the use of organic solvents and water described above are solved.

However, since the polymerization reaction rate is slow in this method, there is a problem in that the productivity is low to put it into practical use. In other words, when the reaction speed is increased to increase productivity, the molecular weight decreases and a product with the required performance cannot be obtained.

[0010] Furthermore, as a method for solving the above problem, Japanese Patent Application Laid-Open No. 2-60981 discloses that the production and productivity of high molecular weight products are improved by changing the lamp intensity in two stages or in multiple stages. However, the productivity is still insufficient.

[0011] The object of the present invention is to provide a photopolymerizable composition for producing viscoelastic products containing a photopolymerization initiator and substantially free of solvent, which achieves high levels of both viscoelastic properties and productivity. An object of the present invention is to provide a novel photopolymerizable composition capable of producing an acrylic viscoelastic product with high retention properties.

Another object of the present invention is to provide an acrylic viscoelastic product using the photopolymerizable composition.

[0013]

[Means for Solving the Problems] The present invention has been devised to achieve the above object, and includes an acrylate monomer (a) and a vinyl compound monomer (a) as monomer components.
b) was completed based on the knowledge that by further incorporating a macromonomer as a third essential component, it is possible to obtain an acrylic viscoelastic product that maintains both viscoelastic properties and productivity at a high level. It is something.

That is, the photopolymerizable composition according to the present invention contains at least one acrylate monomer selected from the group consisting of acrylic acid alkyl esters and methacrylic acid alkyl esters in which the alkyl group has 1 to 12 carbon atoms. ~98% by weight, (b) 2 to 40% by weight of a vinyl compound monomer having an unsaturated double bond copolymerizable with the acrylate monomer (a), and (c
) 2 to 1 per 100 parts by weight of the acrylate monomer (a) and vinyl compound monomer (b)
This is a photopolymerizable composition containing 0 parts by weight of a macromonomer and (d) 0.001 to 5 parts by weight of a photopolymerization initiator.

Each component constituting the photopolymerizable composition according to the present invention and a method for photopolymerizing the composition will be explained below.

Macromonomer In the present invention, the above monomer composition system further contains a macromonomer as a third essential component.

In general, in radical polymerization, the reaction rate (monomer disappearance rate) is 0.5 of the starting radical production rate.
Proportional to the power. The average molecular weight of the resulting polymer is inversely proportional to the 0.5th power of the initial radical production rate. Therefore, when we plotted the time required to complete the reaction and the molecular weight of the obtained polymer for many commercially available initiators, we found that there was almost no difference due to the structure of the initiator with different activity, and the obtained points were converged on a single straight line. . In other words, it was found that the above reaction theory holds not only for the initial reaction rate but also for the completion of many bulk polymerization systems.

On the other hand, in order to sufficiently exhibit adhesive performance, a polymer having a weight average molecular weight of 300,000 or more is required. However, when producing such high-performance viscoelastic products by photopolymerization, if high-speed reaction conditions are set by increasing the lamp intensity or increasing the amount of initiator to increase productivity, the molecular weight of the product will increase according to the above theory. As a result, the desired high performance cannot be obtained.

On the other hand, the reactive composition containing a macromonomer as in the present invention has a higher molecular weight than a composition that does not contain the macromonomer, even if the resulting adhesive has a molecular weight of 300,000 or less. Both adhesive strength and cohesive strength can be increased. Therefore, even a low molecular weight polymer produced under the same high-speed reaction conditions as above does not reduce the adhesive performance of the viscoelastic product. As a result, high-performance photopolymerized viscoelastic products can be produced at high speed.

[0020] The excellent performance of the reactive composition containing such a macromonomer is obtained because the polymer produced from this composition has microphase separation performance, and has both adhesive strength and cohesive strength at the same time. It is thought that it can be made higher.

It has thus been discovered that the microphase separation performance of macromonomers can be achieved even in photobulk polymerization, and the present invention has been completed.

The macromonomer used as an essential component in the present invention has a molecular weight of about several hundred to tens of thousands, and has a reactive functional group such as methacrylate, acrylate, or vinyl group added to one end of the molecule. It is something that

[0023] Preferred macromonomers used in the present invention are those having styrene, methyl methacrylate, acrylonitrile, and hydroxyethyl methacrylate as a constituent unit, and particularly preferred are those having styrene as a bone constituent unit. . Further, as the reactive functional group at the terminal of the macromonomer molecule, a (meth)acrylate group is preferable since it does not inhibit the radical growth reaction.

Acrylate Monomer The acrylate monomer is the main monomer component of the composition of the present invention and is used in the production of known photopolymerized acrylic viscoelastic products.

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

These monomers may be used alone or in combination of two or more. Considering the balance between adhesiveness and cohesiveness, the main component is usually an acrylic acid alkyl ester with a homopolymer glass transition temperature of -50°C or lower, and (meth) of a lower alkyl group is used as a comonomer.
It is preferable to use acrylic acid ester or the following vinyl monomer.

Vinyl monomers Other vinyl monomers that can be copolymerized with the acrylate monomer include, for example, acrylic acid, methacrylic acid,
Examples include acrylamide, acrylonitrile, methacrylonitrile, N-substituted acrylamide, hydroxyethyl acrylate, carboxyethyl acrylate, N-vinylpyrrolidone, maleic acid, itaconic acid, N-methylol acrylamide, and hydroxyethyl methacrylate.

Particularly preferred among these vinyl monomers are acrylic acid, carboxyethyl acrylate and N-vinylpyrrolidone. These monomers have the characteristics that they themselves have the effect of promoting the polymerization reaction and have a small effect of lowering the molecular weight during the accelerated reaction.

Also usable are vinyl monomers that form polymers with a low glass transition temperature, such as tetrahydrofurfuryl acrylate, polyethylene glycol acrylate, polypropylene glycol acrylate, fluorine acrylate, and silicone acrylate.

Photopolymerization initiator Examples of the monofunctional photopolymerization initiator include 4-(2-hydroxyethoxy)phenyl(2-hydroxy-2-propyl)ketone [Darocur 2959: manufactured by Merck & Co., Ltd.];
α-Hydroxy-α,α'-dimethylacetophenone [Darocur 1173: manufactured by Merck & Co., Ltd.]; Acetophenone initiators such as methoxyacetophenone and 2,2-dimethoxy-2-phenylacetophenone; Benzoin such as benzoin ethyl ether and benzoin isopropyl ether Ether initiators; ketal initiators such as benzyl dimethyl ketal; others include halogenated ketones, acylphosphinoxides, acyl phosphonates, and the like.

Crosslinking Agent In the photopolymerizable composition of the present invention, a polyfunctional vinyl compound is added as a crosslinking agent together with the above photopolymerization initiator in order to impart heat resistance and cohesive strength at high temperatures to the viscoelastic product. It is preferable to contain it as

Examples of such crosslinking agents include hexanediol di(meth)acrylate, (poly)ethylene glycol di(meth)acrylate, (poly)propylene glycol di(meth)acrylate, and neopentyl glycol di(meth)acrylate. Acrylate, pentaerythritol di(meth)acrylate, trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate, dipentaerythritol hexa(meth)acrylate, other epoxy acrylates,
Polyester acrylate, urethane acrylate, etc. are used.

Such a crosslinking agent is generally contained in an amount of 5 parts by weight or less per 100 parts by weight of the monomer components. The use of a crosslinking agent causes crosslinking between polymer molecules during the photopolymerization reaction, improving the heat resistance of the viscoelastic product. When the viscoelastic product is an adhesive tape, the cohesive force at high temperatures increases and the holding power at high temperatures improves.

Tackifier The photopolymerizable composition according to the present invention may contain a tackifier called a tackifying resin.

[0035] The tackifier used here includes rosin resin, modified rosin resin, terpene resin,
Terpene phenol resin, aromatic modified terpene resin, C
5 and C9 petroleum resins, coumaron resins, etc.

Other Additives The photopolymerizable composition according to the present invention may contain commonly used additives such as thickeners, thixotropic agents, extenders and fillers.

[0037] As the thickener, acrylic rubber, epichlorohydrin rubber, etc. are used.

As the thixotropic agent, colloidal silica, polyvinylpyrrolidone, etc. are used.

[0039] As the filler, calcium carbonate, titanium oxide, clay, etc. are used.

Examples of fillers include inorganic hollow bodies such as glass balloons, alumina balloons, and ceramic balloons; organic spherical bodies such as nylon beads, acrylic beads, and silicon beads; organic hollow bodies such as vinylidene chloride balloons and acrylic balloons; polyester and rayon. , single fibers such as nylon are used.

Photopolymerization process conditions The lamp used for light irradiation has a light wavelength of 400 nm.
Those having the following emission distributions are used, examples of which include low-pressure mercury lamps, medium-pressure mercury lamps, high-pressure mercury lamps, ultra-high-pressure mercury lamps, chemical lamps, black light lamps, microwave-excited mercury lamps, metal halide lamps, and the like. Among these, ultra-high-pressure mercury lamps efficiently emit light in the active wavelength region of the initiator, and emit short-wavelength light that reduces the viscoelastic properties of the resulting polymer through crosslinking, and heat-evaporates the reaction composition. This is preferable because it does not emit much light with long wavelengths. Particularly, this effect of the lamp is exhibited in a so-called water-cooled type lamp in which a circulating water jacket is attached to the lamp.

The intensity of irradiation of the reactive composition by the lamp is a factor that influences the degree of polymerization of the resulting polymer, and is appropriately controlled depending on the performance of the desired product. When a common cleavage type initiator having an acetophenone group is blended, the illumination intensity is preferably in the range of 0.1 to 100 mw/cm2.

Photopolymerization in the present invention is inhibited by oxygen in the air or oxygen dissolved in the reactive composition. Therefore, light irradiation must be performed using a method that can eliminate the inhibition of oxygen reaction. One of the methods is
There is a method in which the reactive composition is covered with a film made of polyethylene terephthalate or Teflon to cut off contact with oxygen, and the composition is irradiated with light through this film. Alternatively, the composition may be irradiated with light through a light-transmitting window in an atmosphere in which oxygen is replaced with an inert gas such as nitrogen gas or carbon dioxide gas. In the latter method, in order to sufficiently complete the polymerization of the reactive composition to a degree of conversion of 99.7% or more, the oxygen concentration in the irradiation atmosphere must be 5000 ppm or less. The molecular weight of the polymer product obtained by photoirradiation of the composition decreases with increasing atmospheric oxygen concentration. In order to obtain a molecular weight comparable to that of a product obtained by polymerization in a completely inert atmosphere, the atmospheric oxygen concentration must be 1000 ppm or less. Furthermore, the extremely thin surface layer portion of the reactive composition is more susceptible to reaction inhibition by oxygen than the interior of the polymer, resulting in a decrease in cohesive force. In order for this surface layer to have the same degree of cohesiveness as the interior, the atmospheric oxygen concentration must be 300 ppm.
The following is desirable.

When light irradiation is carried out in the inert zone, a certain amount of inert gas is always introduced into this zone in order to keep the atmospheric oxygen concentration at a low level. This introduced gas generates an air current on the surface of the reactive composition, causing monomer evaporation. The airflow velocity required to keep this evaporation level low is preferably such that the relative velocity of the composition moving with the substrate in this zone is 1 m/sec or less, more preferably 0.1 m/sec or less. sec or less. If the airflow velocity is set to about 0.1 m/sec, evaporation due to the airflow can be substantially suppressed.

[0045]

[Function] By incorporating the macromonomer into the blended composition of the present invention, a viscoelastic product having high performance can be obtained even if the polymer molecular weight is 300,000 or less. the result,
Since the reaction rate can be increased, the photopolymerization productivity of high performance viscoelastic products can be significantly improved.

[0046]

[Example] Next, in order to specifically explain the present invention,
Examples illustrating an example of the present invention and some comparative examples illustrating comparison therewith will be listed, as well as performance test results of each viscoelastic product obtained.

[Example 1] 95 g of 2-ethylhexyl acrylate, 3 g of acrylic acid, 1.0 g of photopolymerization initiator (manufactured by Merck & Co., trade name "Darocur 1173"), 2-polystyryl methacrylate (Sa) which is a macromonomer
manufactured by rtomer Co., Ltd., product number "13K-RC")
3.0 g were stirred and mixed until uniform. Each of the obtained reactive compositions was coated onto a tape-shaped base material using a comma coater to a thickness of 35 μm. Oxygen concentration 300ppm
An ultra-high pressure mercury lamp is used as a radiation source in the inert zone, and the lamp intensity on the irradiation surface is 30 mw/cm2 (365n
The lamp height was set so that the intensity value was measured with a light intensity measuring device UVR-1 (manufactured by Tokyo Kogaku Kikai Co., Ltd.) having maximum sensitivity at m. In this state, ultraviolet rays were irradiated for 1 minute, and the amount of residual monomer in the resulting tape sample was measured. [Comparative Examples 1 to 4] 2-ethylhexyl acrylate 95
g, 5 g of acrylic acid, 1.0 g of photopolymerization initiator (manufactured by Merck & Co., trade name "Darocur 1173") and 2.0 g of acrylic rubber (manufactured by Toyo Rubber Co., Ltd., product number "PS250")
were stirred and mixed until homogeneous. The obtained reactive composition was coated onto a substrate using a comma coater to a thickness of 35 μm. An ultra-high pressure mercury lamp was used as a radiation source in an inert zone with an oxygen concentration of 300 ppm, and the lamp height was set so that the lamp intensity on the irradiated surface was 8 mw/cm2. In this state, UV irradiation was performed for 1 minute (Comparative Example 1), 2 minutes (Comparative Example 2), 3 minutes (Comparative Example 3), and 4 minutes (Comparative Example 4), and the tape samples obtained at each stage were The amount of residual monomer was measured.

[Comparative Examples 5 to 6] In the formulation of Comparative Example 1, the photopolymerization initiator "Darocur 1173" was replaced with "Irgacure 184" at 0.5 g (Comparative Example 5) and 1.0 g (Comparative Example 6).
A reactive composition was obtained in the same manner as in Comparative Example 1, except that the following was changed, and a coated sample was prepared on a substrate using a comma coater to a thickness of 35 μm. This sample was irradiated with ultraviolet rays until the amount of residual monomer was 0.3%.

The above results are summarized in the following table.

UV irradiation time (minutes) Residual monomer amount (%)
Example 1 1
0.27 Comparative example 1
1 3.0
Comparative example 2 2
1.2
Comparative example 3 3
0.55 Comparative example 4 4
0.20
Comparative example 5 5.3
0.3 Comparative example 6
3.2 0.3
As can be seen from this measurement result, in the system containing the macromonomer of the present invention, even when the ultraviolet irradiation time, that is, the reaction time was controlled at a high speed of 1 minute,
It is clear that there is very little residual monomer.

[Examples 2 to 5] In addition to Example 1, 0.07 g of hexanediol diacrylate was added as a crosslinking agent.
(Example 2), 0.09g (Example 3), 0.13g (
A tape sample was prepared in the same manner as in Example 1, except that a reactive composition was obtained by adding 0.2 g (Example 4) and 0.2 g (Example 5) respectively, and the amount of residual monomer, holding power, and sp tack were determined. The force was measured.

[Comparative Examples 7 to 15] 95 g of 2-ethylhexyl acrylate, 5 g of acrylic acid, 0.5 g of photopolymerization initiator (manufactured by Merck & Co., trade name "Darocur 1173") and 2.0 g of acrylic rubber (manufactured by Toyo Rubber Co., Ltd.) ,Item Number"
PS250'') were stirred and mixed until uniform. In Comparative Examples 7 to 10, 0.05 g (Comparative Example 7), 0.07 g (Comparative Example 8), 0.09 g (Comparative Example 9) and 0.13 g (Comparative Example 10) of hexanediol diacrylate were used as a crosslinking agent. Each was added. Each of the obtained reactive compositions was coated onto a substrate using a comma coater to a thickness of 35 μm. An ultra-high pressure mercury lamp was used as a radiation source in an inert zone with an oxygen concentration of 300 ppm, and the lamp height was set so that the lamp intensity on the irradiated surface was 8 mw/cm2. In this state, irradiation was performed for 5 minutes, which is the time required to complete the polymerization.

In Comparative Examples 11 to 14, the same coated samples as Comparative Examples 7 to 10 were coated with a lamp intensity of 20 m.
Irradiation was carried out for 1.5 minutes as the minimum time required to complete the polymerization at w/cm2.

Furthermore, in Comparative Example 15, a coated sample similar to Comparative Example 11 except that 0.2 g of hexanediol diacrylate was added as a crosslinking agent was irradiated for 1.5 minutes at a lamp intensity of 20 mw/cm2. Ta.

The amount of residual monomer, holding power and sp adhesive strength of the tape sample thus obtained were measured.

The above results are summarized in the following table.

[0056]


Irradiation time Residual monomer amount
Holding power sp adhesive strength
(minutes) (%
) (hr)
(g/25mm) Example 2 1
0.30
3.6 1300
Example 3 1
0.29 5.5
1200 Example 4
1 0.25
80 10
50 Example 5 1
0.22 100
900 Comparative example 7
5 0.32
2.0 1
250 Comparative example 8 5
0.29 24
1200 Comparative example 9
5 0.28
100
1200 Comparative example 10 5
0.30 1
00 1050 Comparative example 11
1.5 0.3
0.1
1600 Comparative Example 12 1.5
0.28
0.5 1400 Comparative example 1
3 1.5 0.3
3 0.4
1200 Comparative Example 14 1.5
0.29
1.0 1000 Comparative Example 15 1.5 0.
3 0.5
700 As can be seen from the above measurement results, even if the compounding system of the present invention is not used, if the polymerization completion time (ultraviolet irradiation time) is set to about 5 minutes and the reaction is controlled slowly,
It is possible to make the product exhibit sufficient performance. but,
Productivity is extremely poor due to the long polymerization completion time. Also,
If the reaction is controlled at high speed so that the polymerization completion time is about 1.5 minutes, productivity is good, but in this case sufficient holding power cannot be obtained.

In contrast to these comparative examples, in the system containing the macromonomer of the present invention, even when the reaction time was controlled at a high speed of 1 minute, an adhesive with high performance in both adhesive strength and holding power was obtained. was able to create.

[0058]

[Effects of the Invention] According to the photopolymerizable composition of the present invention, since a macromonomer is blended, viscoelastic products can be manufactured in a solvent-free process under high-speed reaction conditions, and in addition, high-performance viscoelastic products can be manufactured. Can be done.

[0059] By making production possible under such high-speed reaction conditions, it is possible to increase the productivity of high-performance viscoelastic products. Furthermore, the macromonomer does not inhibit the wide range of adhesive properties exhibited by the properties of other monomers, and as a result, the composition according to the present invention can retain the ability to exhibit a wide range of adhesive properties.

Claims (2)

[Claims] Claim 1: (a) The number of carbon atoms in the alkyl group is 1
60 to 98% by weight of at least one acrylate monomer selected from the group consisting of acrylic acid alkyl esters and methacrylic acid alkyl esters of
and (b) 2 to 40% by weight of a vinyl compound monomer having an unsaturated double bond copolymerizable with the acrylate monomer (a), (c) the acrylate monomer (a) and the vinyl compound monomer (b). ) macromonomer blended in an amount of 1 to 15 parts by weight based on 100 parts by weight in total, and (d) 0.001 to 0.001 of a photopolymerization initiator.
5 parts by weight of a photopolymerizable composition. 2. An acrylic viscoelastic product obtained by irradiating the composition according to claim 1 with ultraviolet rays.