JP2005255784A - Method for producing liquid polymerizable (meth)acrylic resin composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a liquid (meth)acrylic resin composition excellent in heat decomposition resistance without using any special catalyst or without mixing any substance (e.g., a solvent) unnecessary for the final (meth)acrylic resin product (cured product), which method is applicable to both a methacrylic monomer and an acrylic monomer. <P>SOLUTION: The liquid polymerizable resin composition containing a (meth)acrylic polymer, a (meth)acrylic monomer, and a liquid plasticizer is produced by radically polymerizing a (meth)acrylic monomer in the liquid plasticizer containing a (meth)acrylic monomer and a radical polymerization initiator. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing a (meth) acrylic polymerizable liquid resin composition having excellent thermal decomposition characteristics, an acrylic polymerizable liquid resin composition, and a thermally conductive material.

  (Meth) acrylic resins are excellent in transparency, light resistance, and the like, and are used in various applications utilizing these characteristics. In recent years, it has also been used as a base resin for heat conductive sheets (heat conductive sheets for heat dissipation materials) used to remove heat from heat-generating electronic components built into various electrical products such as personal computers and plasma displays. It is being used (for example, Patent Documents 1 to 4), and its application range is expanding to various fields.

The (meth) acrylic resin is often provided in the form of a liquid resin composition (referred to as acrylic syrup) in which a poly (meth) acrylic polymer and a monomer are mixed (for example, Patent Document 5). The user further forms a (meth) acrylic resin final product (molded product, sheet, etc.) by cross-linking (curing) the liquid resin composition with thermal polymerization (radical polymerization) or a crosslinking agent to form a network structure. . An example of producing a (meth) acrylic resin using a special catalyst is also known (Patent Document 6 and the like).
JP 2002-30212 A JP 2003-49144 A JP 2002-155110 A JP-A-11-269438 Japanese Patent Laid-Open No. 9-67495 JP 2000-128911 A

  By the way, the present inventors have better thermal decomposition resistance than those obtained by curing a poly (meth) acrylic liquid resin composition with a crosslinking agent (for example, an isocyanate crosslinking agent) by radical polymerization. I have found that. What hardened | cured with the crosslinking agent has formed | formed bonds (CN bond derived from a crosslinking agent) other than CC bond in the network-structure part of (meth) acrylic-type resin, and the heat resistance of this crosslinked part. This is thought to be due to improved degradability. However, when a network structure is formed using a polyfunctional acrylic monomer such as alkylene glycol di (meth) acrylate, a bond other than the C—C bond is formed in the network structure portion. It has also been found that (meth) acrylic resins have sufficient thermal decomposition resistance, and considering these together, the detailed reason is not clear, but there is no unsaturated bond (that is, no radical polymerizability) It can be concluded that there is room for improvement in thermal decomposition resistance for those cured with a crosslinking agent. The (meth) acrylic resins disclosed in Patent Documents 1 and 4 are crosslinked by a crosslinking agent having no unsaturated bond (hereinafter referred to as a non-radical type crosslinking agent, for example, isocyanates, epoxy compounds, etc.). From the above viewpoint, there is room for improvement in thermal decomposition resistance. (Meth) acrylic resins may be required to be heat-resistant and decomposed. For example, in the case of thermally conductive materials (such as thermally conductive sheets), the amount of heat generated has increased due to the high performance of electronic components. There is an increasing demand for thermal decomposition resistance.

  In order to improve the thermal decomposition resistance, it is important to use a (meth) acrylic resin having a network structure formed by curing by radical polymerization. As such a (meth) acrylic resin, for example, a methacrylic monomer is polymerized in toluene, and after removing toluene, a methacrylic monomer is added to form a liquid resin (syrup), and the syrup is polymerized. Those obtained by polymerization with an initiator are known (see Examples 7 to 9 of Patent Document 5). In Patent Document 2, an acrylic monomer is radical polymerized in ethyl acetate, applied onto a PET film, and then dried. However, the (meth) acrylic resin obtained by these methods contains a solvent (toluene, ethyl acetate, etc.). That is, in these methods, although the solvent is removed on the way, it is impossible to completely remove the solvent. When the (meth) acrylic resin obtained in this way is used, there is a concern that the residual solvent will volatilize even a little, especially in applications where heat is applied (such as a heat conductive material).

  As a (meth) acrylic resin that has a network structure formed by polymerization and contains substantially no solvent, the methacrylic monomer is bulk polymerized and only a part of the methacrylic monomer is controlled by controlling the bulk polymerization. A method is known in which syrup is produced by polymerization and a methacrylic resin is produced by further polymerizing the syrup (see Examples 1 to 6 of Patent Document 5). However, it is difficult to control the reaction by the bulk polymerization method. In particular, acrylic monomers and the like are about 10 times more reactive than methacrylic monomers described in the above-mentioned patent document, so the reaction runs out of control, and acrylic syrup is produced by bulk polymerization. Can not.

  As a method capable of producing not only a methacrylic resin but also an acrylic resin, a method of photopolymerizing a coating containing an acrylic monomer and an alkanediol diacrylate and not containing a solvent is known (for example, Patent Document 3). However, even if the photopolymerization method disclosed in Patent Document 3 can be applied to a coated product, the reaction efficiency is too low when it is polymerized in a large amount in a reaction can such as acrylic syrup. Also known is a method of bulk polymerizing acrylic monomers using thioglycerol as a catalyst (Patent Document 6, etc.). However, in this method, the catalyst used is special and the cost is high. Moreover, in practice, it may not be possible to polymerize an acrylic monomer having a high polymerization rate with simple equipment, and when this catalyst is used, there is an adverse effect that hydroxyl groups are always introduced into the polymer.

  The present invention has been made paying attention to the circumstances as described above, and the object thereof is unnecessary for a (meth) acrylic resin final product (cured product) such as a solvent without using a special catalyst. Method for producing (meth) acrylic liquid resin composition excellent in thermal decomposition characteristics applicable to both methacrylic monomer and acrylic monomer without mixing in substance, acrylic liquid resin composition, and heat conductive material Is to provide.

  Another object of the present invention is to provide a method for producing a (meth) acrylic liquid resin composition, an acrylic liquid resin composition, and a heat conductive material that can suppress bleed out of the plasticizer.

  As a result of intensive studies to solve the above problems, the present inventors have paid attention to the effective use of plasticizers. There are applications where plasticity is required as a (meth) acrylic resin. For example, when a heat conductive material such as a heat conductive sheet is used, the contact area (heat transfer area) with the component is widened, and the component High plasticity (flexibility) is demanded in order to improve the followability to the above. And among the plasticizers, radical polymerization of (meth) acrylic monomers in liquid (liquid plasticizers) can be done with acrylic monomers as well as methacrylic monomers, without the use of special catalysts. Even if there is, it can be polymerized without runaway, and if necessary, the (meth) acrylic monomer or liquid plasticizer is added after the polymerization reaction is stopped or completed if necessary The liquid resin composition containing a (meth) acrylic polymer, a (meth) acrylic monomer, and a liquid plasticizer, and the acrylic syrup contains a (meth) acrylic monomer. It can be made (meth) acrylic resin by radical polymerization, and it can be found that the thermal decomposition resistance can be improved. Invention has been completed. The acrylic syrup is a radical polymerization curing type (thermal polymerization curing type) containing a (meth) acrylic monomer that is a radical polymerizable monomer, and is a non-radical crosslinking agent (isocyanate crosslinking agent, epoxy crosslinking agent). Etc.) is not a type to be cured only by. By the way, in general, acrylic syrup desirably has a low viscosity from the viewpoints of handling properties, yield during curing reaction, heat removal during syrup production, etc., and acrylic syrup is also low in the production of thermally conductive materials. Viscosity is desirable. When producing a thermally conductive material, it is necessary to add a filler (thermally conductive filler) in order to increase the thermal conductivity. The lower the viscosity of acrylic syrup, the more the filler is filled with the thermally conductive filler. This is because the amount can be increased. When acrylic syrup is cured with a non-radical type crosslinking agent, (meth) acrylic monomers are not used, and therefore only liquid plasticizers can contribute to lowering the viscosity. While it is difficult to reduce the agent, in the acrylic syrup of the present invention that is a radical polymerization curing type, a (meth) acrylic monomer can also be used as a diluent for the acrylic syrup, contributing to a reduction in viscosity. Therefore, it is easy to reduce the plasticizer ratio. Therefore, according to the present invention, bleeding out of the plasticizer from the final (meth) acrylic resin (cured product) can also be suppressed.

  That is, the method for producing a polymerizable liquid resin composition containing a (meth) acrylic polymer, a (meth) acrylic monomer, and a liquid plasticizer according to the present invention includes a (meth) acrylic monomer and a radical polymerization initiator. It has a gist in that it includes a step of radical polymerization of a (meth) acrylic monomer in a liquid plasticizer. The liquid plasticizer preferably has a mass loss of 5% by mass or less after being held at a temperature of 150 ° C. for 3 hours.

  The present invention also includes a polymerizable liquid resin composition containing an acrylic polymer having an glass transition temperature of 0 ° C. or lower, an acrylic monomer, and a liquid plasticizer. However, the polymerizable liquid resin composition does not substantially contain a solvent and a non-radical crosslinking agent (such as an isocyanate crosslinking agent or an epoxy crosslinking agent). In the polymerizable liquid resin composition, the liquid plasticizer is desirably about 10 to 70% by mass with respect to the total mass of the acrylic polymer, the acrylic monomer, and the liquid plasticizer. The amount is desirably about 10 to 500 parts by mass with respect to 100 parts by mass of the acrylic polymer.

  A heat conductive material obtained by radical polymerization of the polymerizable liquid resin composition is also included in the present invention.

  In this specification, “(meth) acrylic polymer” means a polymer in which 50% by mass or more (preferably 70% by mass or more, more preferably 80% by mass or more) of the structural unit is a (meth) acrylic acid ester. means. Further, “methacrylic polymer” means a polymer in which more than 50% by mass of the (meth) acrylic acid ester is a methacrylic acid ester, and “acrylic polymer” means that of the (meth) acrylic acid ester The polymer whose 50 mass% or more is an acrylic ester is meant.

  According to the present invention, since the production of acrylic syrup by radical polymerization of (meth) acrylic monomers is performed in a liquid plasticizer, it can be applied in common to both acrylic monomers and methacrylic monomers, and is also special. In addition, there is no need to use a new catalyst, and furthermore, the thermal decomposition resistance of the final (meth) acrylic resin (cured product) can be improved, and in addition, the volatilization of the solvent and the bleeding out of the plasticizer can be suppressed. The effect can be achieved at the same time.

  The liquid resin composition (polymerizable liquid resin composition) containing the (meth) acrylic monomer, the (meth) acrylic polymer, and the liquid plasticizer is either halfway through the (meth) acrylic monomer in the liquid plasticizer. After complete radical polymerization (radical polymerization step), it can be produced by adding a (meth) acrylic monomer and / or a liquid plasticizer as necessary (preparation step).

  Details will be described below.

[Radical polymerization process]
The radical polymerization step is the most important step according to the present invention. In the liquid plasticizer containing the (meth) acrylic monomer and the radical polymerization initiator, the (meth) acrylic monomer is radically polymerized to form a liquid resin composition ( Acrylic syrup is most important. The liquid plasticizer is an essential component in applications where plasticity (flexibility) is required (for example, a heat conductive material). There is no problem in using this liquid plasticizer, can do. Moreover, radical polymerization of (meth) acrylic monomers in this liquid plasticizer allows polymerization without runaway, not only for methacrylic monomers but also for acrylic monomers, without using a special catalyst. Can do. Since acrylic resins are superior in flexibility (plasticity) compared to methacrylic resins, the ability to polymerize acrylic monomers is also extremely important for applications that require plasticity (such as thermally conductive materials).

  Moreover, if radical polymerization is performed in a liquid plasticizer, the polymerization reaction can be stopped in the middle, and a liquid resin composition containing a (meth) acrylic monomer, a (meth) acrylic polymer, and a liquid plasticizer is obtained. It can be easily manufactured. In addition, in the preparation stage to be described later, if necessary, after the radical polymerization is interrupted or completed, a (meth) acrylic monomer or a liquid plasticizer is added to determine the component ratio of the liquid resin composition. It may be prepared.

  The polymerization rate of the (meth) acrylic monomer in the radical polymerization stage (the ratio of the raw material monomer consumed by the polymerization) is not particularly limited as long as the necessary (meth) acrylic polymer is obtained. For example, 20 mol% or more, Preferably it is 25 mol% or more, More preferably, it is 30 mol% or more. When excessively polymerized, the proportion of the (meth) acrylic monomer in the target liquid resin composition (acrylic syrup) is appropriately added after completion of the polymerization as described later. Therefore, the upper limit of the polymerization rate is not particularly limited, and may be about 100 mol%. When the addition of the (meth) acrylic monomer is not performed, the ratio of the (meth) acrylic monomer in the target liquid resin composition (acrylic syrup) at the polymerization end stage is in a predetermined range described later. What is necessary is just to set a polymerization rate, for example, it is good also as about 80 mol% or less (preferably 70 mol% or less, More preferably, it is 60 mol% or less) grade. In addition, when using several monomers as a (meth) acrylic-type monomer, you may set a polymerization rate by the total consumption rate, but usually one (meth) acrylic-type monomer which is main is another Since it is a large excess compared with the (meth) acrylic monomer, it is easy to set the polymerization rate according to the consumption ratio of the main (meth) acrylic monomer.

  The polymerization rate is calculated by the following formula by measuring the amount of residual (meth) acrylic monomer in the reaction solution after the completion of polymerization.

Polymerization rate (%) = [1-residual (meth) acrylic monomer amount / prepared (meth) acrylic monomer amount] × 100
The glass transition temperature of the obtained (meth) acrylic polymer is usually about 0 ° C. or lower, preferably about −30 ° C. or lower, more preferably about −40 ° C. or lower. The lower the glass transition temperature, the higher the flexibility of the final product obtained by curing the liquid resin composition. Therefore, the utility value when using it as a heat conductive material can be raised. In addition, since a (meth) acrylic polymer having a low glass transition temperature has a sticky feeling alone, it is necessary to mix it with a solvent in order to maintain handling properties. According to the method of the present invention, the glass transition temperature is low. Even if it is a low (meth) acrylic polymer, since it is mixed with the liquid plasticizer, it can be made substantially solvent-free without reducing handling properties. The glass transition temperature can be measured with a differential scanning calorimeter.

  The molecular weight of the (meth) acrylic polymer varies greatly depending on the polymerization rate and is not particularly limited, but the weight average molecular weight Mw is, for example, about 20,000 to 1,000,000, and the number average molecular weight Mn is, for example, 1 It is about 10,000 to 200,000. The molecular weight can be determined by gel permeation chromatography (polystyrene conversion).

  The ratio of the liquid plasticizer is the sum (100% by mass) of the liquid plasticizer and the raw material (meth) acrylic monomer before the reaction [that is, meaning that it does not include the (meth) acrylic monomer added after the polymerization]. On the other hand, it is 5 mass% or more, for example, Preferably it is 10 mass% or more, More preferably, it is 20 mass% or more. In particular, when the acrylic monomer is polymerized, it is important to set the ratio from the range that can prevent runaway during polymerization, and the total of the liquid plasticizer and the raw material (meth) acrylic monomer before the reaction ( 100 mass%), for example, 30 mass% or more, preferably 40 mass% or more, more preferably 50 mass% or more. On the other hand, suppressing the ratio of the liquid plasticizer is effective in preventing bleeding out of the plasticizer from the final product obtained by curing the liquid resin composition. The liquid plasticizer is, for example, 80% by mass or less, preferably 70% by mass or less, more preferably 60% by mass with respect to the total (100% by mass) of the liquid plasticizer and the raw material (meth) acrylic monomer before the reaction. % Or less, and particularly when the amount of the liquid plasticizer is to be reduced, it may be 50% by mass or less (for example, 40% by mass or less). In addition, when adding a (meth) acrylic monomer in the preparation step to be described later, the ratio of the liquid plasticizer in the liquid resin composition can be reduced by the addition. Therefore, in the radical polymerization step, the (meth) acrylic monomer is added. The upper limit of the liquid plasticizer may be set in consideration of the additional amount.

  The amount of the radical polymerization initiator used is not particularly limited as long as the (meth) acrylic monomer can be radically polymerized at a predetermined polymerization rate, and can be appropriately set according to the type of the radical polymerization initiator. For example, about 0.01 to 1 part by mass, preferably about 0.05 to 0.7 part by mass, and more preferably about 0.10 to 0.5 part by mass with respect to 100 parts by mass of the (meth) acrylate monomer. is there. If necessary, the radical polymerization initiator may be added in portions, or may be added after diluting with a liquid plasticizer. When diluting with a liquid plasticizer, the required amount is used for dilution from the amount of the predetermined liquid plasticizer used.

  In the present invention, a chain transfer agent may be used as necessary. Although the usage-amount of a chain transfer agent is set suitably, it is about 0.01-2 mass parts with respect to 100 mass parts of raw material (meth) acrylate type monomers, Preferably it is about 0.05-1.5 mass parts. More preferably, it is about 0.10-1 mass part.

  The reaction temperature can also be set as appropriate. For example, it is often set from the range of about 40 to 150 ° C, preferably about 50 to 100 ° C.

  Examples of (meth) acrylic monomers include (meth) acrylic acid esters [for example, (meth) acrylic acid alkyl esters, functional groups (for example, hydroxyl groups, etc.) on the alkyl group of these (meth) acrylic acid alkyl esters. And the like; preferably (meth) acrylic acid alkyl esters] can be suitably used. Examples of (meth) acrylic acid alkyl esters include ethyl (meth) acrylate, propyl (meth) acrylate, butyl (meth) acrylate, amyl (meth) acrylate, hexyl (meth) acrylate, octyl (meth) acrylate, and nonyl. (Meth) acrylate, decyl (meth) acrylate, lauryl (meth) acrylate, tridecyl (meth) acrylate, myristyl (meth) acrylate, stearyl (meth) acrylate and the like can be mentioned. The (meth) acrylic acid alkyl esters are not limited to those in which the alkyl group is linear (normal), and may be branched, for example, iso-type or lower alkyl groups (for example, , An alkyl group having about 1 to 3 carbon atoms) substituted [for example, ethylhexyl (meth) acrylate, etc.]. In preferred (meth) acrylic acid alkyl esters, the number of carbon atoms in the alkyl group part (when the lower alkyl group is substituted, the total number of carbon atoms) is about 2 to 18 (preferably about 3 to 15). Things are included.

  The (meth) acrylic monomers may be used alone or in combination. When a plurality of (meth) acrylic monomers are combined, a plurality of (meth) acrylic acid alkyl esters may be combined. For example, (meth) acrylic acid alkyl esters and (meth) acrylic acid alkyl esters may have an alkyl group. You may use together what substituted the functional group [henceforth a modification type]. When the (meth) acrylic acid alkyl ester and the modified type are used in combination, it is recommended to use the (meth) acrylic acid alkyl ester as the main (meth) acrylic monomer.

  A preferred (meth) acrylic monomer is an acrylic monomer. When an acrylic monomer is used, the flexibility of the resulting cured acrylic resin (final product) can be increased. Therefore, for example, when manufacturing a heat conductive material etc., a heat-transfer area and followable | trackability can be improved and utility value can be raised. Further, if the flexibility of the cured product is increased by using an acrylic monomer, the amount of plasticizer used can be suppressed without adversely affecting the flexibility, and bleeding out of the plasticizer can be suppressed.

  The liquid plasticizer is not particularly limited as long as it is a non-reactive liquid substance and can plasticize the (meth) acrylic resin cured product. For example, the viscosity at a temperature of 25 ° C. is 1000 mPa · S or less and 800 mPa · S or less. More preferably, a material having a viscosity of 500 mPa · S or less, particularly 300 mPa · S or less is used. The viscosity (and the viscosity described later) can be measured using, for example, a B-type viscometer manufactured by Tokyo Keiki Co., Ltd. Table 1 below shows the rotor No. in this B-type viscometer. The relationship between the rotation number and the upper limit of the measurable viscosity is shown, and the closer the actual measured viscosity is to the upper limit, the smaller the measurement error. When the approximate viscosity of the resin to be measured is known in advance, the rotor No. used is referred to with reference to Table 1. And the combination of rotation speed. On the other hand, when the approximate viscosity is unknown, the rotor No. Is measured from a larger range to a smaller range, and the rotational speed is changed from the low speed side to the high speed side, taking into consideration the relationship shown in Table 1 below, and measuring in an appropriate range.

  Examples of the liquid plasticizer include chlorine-containing plasticizers, epoxy plasticizers, ester plasticizers [for example, aromatic carboxylic acid esters such as phthalic acid esters, trimellitic acid esters, pyromellitic acid esters; Fatty acid esters, aliphatic monobasic acid esters, aliphatic dibasic acid esters, phosphoric acid esters, etc.], liquid rubber, polymer plasticizer that is liquid at room temperature (25 ° C.) (for example, having a weight average molecular weight) Polymer plasticizer of about 5000 or less, preferably polyester plasticizer). These liquid plasticizers can be used alone or in combination of two or more.

  The liquid plasticizer may be liquid at room temperature, but is preferably liquid even at low temperatures (for example, about −10 ° C., particularly about −20 ° C.). For example, the freezing point is about −10 ° C. or less (preferably − Those having a temperature of about 20 ° C. or less or those having no freezing point are recommended. Such a liquid plasticizer can maintain the plasticizing effect even when used at a low temperature.

  Preferred liquid plasticizers also include liquid plasticizers excellent in heat resistance (particularly liquid plasticizers that are liquid even at low temperatures and excellent in heat resistance). When the liquid plasticizer excellent in heat resistance is used, the heat resistance of the (meth) acrylic resin cured product can be increased. Therefore, for example, even a cured product used in a thermal environment such as a heat conductive material can prevent the plasticity from being lowered by heat, and increase the utility value of such a cured product. Can do.

  As a liquid plasticizer excellent in heat resistance, for example, weight loss after holding at a temperature of 150 ° C. for 3 hours [= (mass before holding−mass after holding) / mass before holding] is 5% by mass or less. (Preferably 3% by mass or less, more preferably 1% by mass or less) can be used.

Liquid plasticizers having excellent heat resistance are often selected from liquid plasticizers having aromatic rings (particularly benzene rings). For example, phthalate esters include didecyl phthalate, diundecyl phthalate, and phthalic acid. In many cases, di-C _8-15 alkyl esters of phthalic acid such as didodecyl (preferably di-C _9-13 alkyl esters of phthalic acid) are applicable. Trimellitic acid esters include trimellitic acid tri-C _7-14 alkyl esters such as trioctyl trimellitic acid, trinonyl trimellitic acid, tridecyl trimellitic acid (preferably trimellitic acid tri-C _8-12 alkyl esters). The pyromellitic acid esters include pyromellitic acid tetra C _6-13 alkyl esters (preferably pyromellitic acid tetra C _7-10 alkyl esters). The phosphoric acid esters may be trivalent groups in which a C _1-3 alkyl group may be substituted on a benzene ring such as cresyl diphenyl phosphate, tricresyl phosphate, trixylenyl phosphate, and the like. Phenyl phosphates are often applicable. Commercially available liquid plasticizers having excellent heat resistance may be used, such as dinormaldecyl phthalate [Vinizer 105 manufactured by Kao Corporation], di-C _10-12 alkyl phthalate, etc. [Vinicizer 124 manufactured by Kao Corporation], Tri-2-ethylhexyl trimellitate of trimellitic acid [Trimmex T-08 manufactured by Kao Corporation], Trioctyl trimellitic acid [manufactured by Asahi Denka Kogyo Co., Ltd. Adeka Sizer C-8 etc.], trimellitate tri-normal octyl [Kao Co., Ltd. Trimex N-08, Trimex New-NSK; Asahi Denka Kogyo Co., Ltd. Adeka Sizer C-880 etc.], Tri Mellitic acid triisononyl [Adekasizer C-9N manufactured by Asahi Denka Kogyo Co., Ltd.], trimellitic acid triisodecyl trimellitate [Kao Corporation] Trimex T-10; Adeka Sizer C-10 manufactured by Asahi Denka Kogyo Co., Ltd.] Trimellitic acid mixed alcohol ester [Adeka Sizer C-79 manufactured by Asahi Denka Kogyo Co., Ltd., Adeka Sizer C-810, etc. ], Pyromellitic acid tetraoctyl [Adekasizer UL-80 made by Asahi Denka Kogyo Co., Ltd.], pyromellitic acid mixed alcohol ester [Adekasizer UL-100 made by Asahi Denka Kogyo Co., Ltd.], cresyl diphenyl Phosphate [Clonitex CDP manufactured by Ajinomoto Fine Techno Co., Ltd.], tricresyl phosphate [Clonex TCP manufactured by Ajinomoto Fine Techno Co., Ltd.], Trixylenyl phosphate [Kronitex manufactured by Ajinomoto Fine Techno Co., Ltd.] TXP etc.] can be exemplified.

  These liquid plasticizers excellent in heat resistance can be used alone or in combination of two or more.

  Examples of the radical polymerization initiator include azo initiators and organic peroxides. A radical polymerization initiator can be used individually or in combination of 2 or more types.

  Examples of the azo initiator include 2,2′-azobisisobutyronitrile, dimethyl 2,2′-azobis (2-methylpropionate), 2-phenylazo-2,4-dimethyl. -4-methoxyvaleronitrile and the like are included.

  Examples of the organic peroxide include ketone peroxides such as methyl ethyl ketone peroxide; hydroperoxides such as cumene hydroperoxide; diacyl peroxides such as benzoyl peroxide and lauryl peroxide; dicumyl peroxide Dialkyl peroxides; peroxyketals such as 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane; t-amylperoxy-2-ethylhexanate, t-butylperoxy -2-ethylhexanate, t-amylperoxy-3,5,5-trimethylhexanate, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanate, 1,1,3 3-tetramethylbutylperoxy-2-ethylhe Alkyl peresters such as sanate, t-butylperoxy-3,5,5-trimethylhexanate, t-butylperoxypivalate; t-butylperoxyisopropyl carbonate, t-butylperoxy-2-ethylhexyl carbonate Percarbonates such as 1,6-bis (t-butylperoxycarbonyloxy) hexane.

  As the chain transfer agent, various known chain transfer agents can be used, and examples thereof include α-methylstyrene dimer, carbon tetrachloride, thiol compounds (for example, n-dodecyl mercaptan) and the like.

[Preparation process]
In the preparation step, a (meth) acrylic monomer, a liquid plasticizer, or the like is added to the polymerization reaction mixture obtained as described above as necessary. A liquid resin composition can be obtained by appropriately preparing the components. In the present invention, since radical polymerization can be stopped in the middle, the preparation step is not necessarily required, and the polymerization reaction mixture may be used as it is as a liquid resin composition.

  Such a liquid resin composition can be cured (network structure) by radical polymerization, and the thermal decomposition resistance of the cured resin can be improved as compared with the case of curing with a non-radical type crosslinking agent. Further, since the (meth) acrylic monomer can be used as a diluent for the liquid resin composition, the ratio of the plasticizer can be easily reduced while satisfying the low viscosity. On the other hand, in the case of curing with a non-radical polymerization type crosslinking agent, it is difficult to reduce the liquid plasticizer because only the liquid plasticizer can substantially contribute to lowering the viscosity. . That is, according to the liquid resin composition of the present invention, since the plasticizer ratio can be easily reduced, bleeding out of the plasticizer from the (meth) acrylic resin final product (cured product) can also be suppressed. In particular, when an acrylic resin is cured using an acrylic monomer, the flexibility is enhanced by using an acrylic monomer, so even if the plasticizer ratio is reduced, the cured resin (final product) The required flexibility can be ensured. Therefore, bleed out can be suppressed while maintaining flexibility, which is extremely effective.

  A particularly preferred liquid resin composition contains an acrylic polymer having an glass transition temperature of 0 ° C. or less, an acrylic monomer, and a liquid plasticizer, and substantially contains a solvent, an isocyanate crosslinking agent, and an epoxy crosslinking agent. Non-compositions are included.

  The ratio of the liquid plasticizer is, for example, 70% by mass or less, preferably 50% by mass or less, and more preferably 40% by mass with respect to the total mass of the (meth) acrylic polymer, the (meth) acrylic monomer, and the liquid plasticizer. It is about mass% or less. The smaller the proportion of the liquid plasticizer, the more the bleeding out of the plasticizer from the (meth) acrylic resin cured product can be prevented. The ratio of the liquid plasticizer can be reduced by suppressing the amount of liquid plasticizer used from the beginning or by adding a (meth) acrylic monomer after polymerization. The ratio of the liquid plasticizer is, for example, 10% by mass or more, preferably 15% by mass or more, and more preferably, with respect to the total mass of the (meth) acrylic polymer, the (meth) acrylic monomer, and the liquid plasticizer. It is about 20% by mass or more. When the plasticizer is insufficient, the flexibility of the obtained cured product is insufficient, and the value of the sheet is reduced when, for example, the cured product is used as a heat conductive material.

  A (meth) acrylic-type monomer is 10 mass parts or more with respect to 100 mass parts of (meth) acrylic-type polymers, Preferably it is 30 mass parts or more, More preferably, it is 50 mass parts or more. When there are too few (meth) acrylic monomers [that is, when there are too many (meth) acrylic polymers], the viscosity of a liquid resin composition may become too high. Therefore, when the liquid resin composition is cured in an appropriate shape (for example, a sheet shape), workability may be reduced, and the surface smoothness of the obtained cured product may be reduced. On the other hand, a (meth) acrylic-type monomer is 500 mass parts or less with respect to 100 mass parts of (meth) acrylic-type polymers, Preferably it is 400 mass parts or less, More preferably, it is 300 mass parts or less. When there are too many (meth) acrylic monomers, the resin and the liquid plasticizer are easily separated when the liquid resin composition is cured.

You may add a polyfunctional monomer to the said liquid resin composition as needed. The polyfunctional monomer is a compound having a plurality of ethylenic double bonds, and examples thereof include polyfunctional (meth) acrylic monomers, divinylbenzene, diallyl phthalate, and triallyl cyanurate. The polyfunctional (meth) acrylic monomers include (poly) ethylene glycol di (meth) acrylate, (poly) propylene glycol di (meth) acrylate, 1,4-butanediol di (meth) acrylate, neopentyl glycol Di (meth) acrylates such as di (meth) acrylate and 1,6-hexanediol di (meth) acrylate (preferably C _2-8 alkanediol di (meth) acrylate); trimethylolpropane tri (meth) acrylate Tri (meth) acrylates such as; tetra (meth) acrylates such as pentaerythritol tetra (meth) acrylate; di, tri, and / or tetra (meth) acrylates such as dipentaerythritol hexa (meth) acrylate Condensates and the like are included. The said polyfunctional monomer can be used individually or in combination of 2 or more types.

  The amount of the polyfunctional monomer is, for example, 5 parts by mass or less, preferably 3 parts by mass or less, more preferably 1 part by mass with respect to a total of 100 parts by mass of the (meth) acrylic monomer and the (meth) acrylic polymer. It is about the following.

  In addition, the liquid resin composition, if necessary, a polymerization inhibitor, reinforcing fibers, organic filler, low shrinkage agent, mold release agent, thickener, antifoaming agent, wetting and dispersing agent, thixotropic agent, UV absorbers, UV stabilizers, antioxidants, flame retardants, pigments, magnetic substances, antistatic agents, electromagnetic wave absorbers, thermosetting resins, etc. may be added without departing from the scope of the present invention. Good.

  It should be noted that the effect of the present invention becomes clearer when the liquid resin composition does not substantially contain a non-radical type crosslinking agent (isocyanate crosslinking agent, epoxy crosslinking agent, etc.), but deviates from the object of the present invention. As long as it is not, a non-radical type crosslinking agent may be added as a secondary.

  The viscosity of the liquid resin composition can be appropriately set according to the use of the composition. For example, when a sheet-like material or a tape-like material is produced, a low-viscosity material is preferred in consideration of workability. In particular, when producing a heat conductive sheet for heat dissipation material, it is recommended to add a heat conductive filler to the liquid resin composition to increase the heat conductivity, as will be described later. When the heat conductive filler is added, the viscosity of the liquid resin composition is remarkably increased. Therefore, in consideration of workability, the viscosity of the liquid resin composition before adding the heat conductive filler may be sufficiently low. Desired. The viscosity (temperature 25 ° C.) of the liquid resin composition before adding the heat conductive filler is, for example, 5000 mPa · S or less, preferably 3000 mPa · S or less, more preferably about 2200 mPa · S or less. In particular, in the case of an acrylic liquid resin composition, it is easy to reduce the viscosity. For example, it can be about 1000 mPa · S or less, preferably about 500 mPa · S or less, and more preferably about 300 mPa · S or less.

  The liquid resin composition obtained as described above can be cured by further adding a radical polymerization initiator, and can be made into a final product. The final product is intended for a wide range and is not particularly limited. However, the final product is preferably a final product (heat conductive material) for heat conduction (for heat dissipation). The heat conductive material is usually a sheet, but may be a fluid (putty, water tank, etc.).

  When using a liquid resin composition for a heat conductive material, it is recommended to harden after adding a heat conductive filler to a liquid resin composition. The thermally conductive filler is effective for increasing the thermal conductivity of the thermally conductive material. Examples of the heat conductive filler include inorganic fillers (oxides such as aluminum oxide, magnesium oxide, zinc oxide and silicon oxide; hydroxides such as aluminum hydroxide and magnesium hydroxide; carbides such as silicon carbide; Aluminum nitride, boron nitride, nitride such as silicon nitride), metal filler [silver, copper, aluminum, iron, zinc, nickel, tin, and alloys thereof (such as copper-tin alloy)], carbonaceous Examples thereof include fillers (carbon, graphite, etc.), and inorganic fillers are often used. The said heat conductive filler can be used individually or in combination of 2 or more types.

  The shape of the heat conductive filler is not particularly limited, and various shapes such as a spherical shape, a scale shape, a fiber shape, and a crushed shape can be used.

  As the heat conductive filler, it is recommended to use a material having excellent heat conductivity. For example, it is recommended to use one having a thermal conductivity of about 20 W / m · k or more. The thermal conductivity can be measured using a thermal conductivity measuring device (such as “TPA-501” manufactured by Kyoto Electronics Industry Co., Ltd.) using a hot disk method after sintering the filler.

  When adding a heat conductive filler, it is 50-1500 with respect to a total of 100 mass parts of the main components [(meth) acrylic-type monomer, (meth) acrylic-type polymer, liquid plasticizer] of a liquid resin composition, for example. It is recommended to add about part by mass, preferably about 100 to 1300 parts by mass.

  As the radical polymerization initiator, the same ones as described above can be used. Moreover, you may use together a hardening accelerator, a hardening acceleration assistant, etc. with a radical polymerization initiator.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention.

Production Examples 1-7
In a glass container equipped with a thermometer, stirrer, gas inlet tube, reflux condenser and dropping funnel, the first (meth) acrylic monomer [and optionally the second (meth) acrylic monomer], 1 liquid plasticizer and chain transfer agent were charged and replaced with nitrogen gas so that the oxygen concentration in the gas phase portion in the reaction vessel was 0.1% by mass or less (preparation stage). The temperature was raised to a predetermined temperature (A), and a polymerization initiator diluted with a liquid plasticizer for dilution as needed was dropped from a dropping funnel over a predetermined time (reaction start stage). Next, stirring was continued at a predetermined temperature (B) for a predetermined time (reaction continuation stage). A polymerization initiator was further added as necessary, and stirring was continued for a predetermined time at a predetermined temperature (C) (reaction aging stage). The polymerization was terminated by blowing air and cooling to obtain mixtures A to G containing polymers A to G and the like. In any case, there was no runaway polymerization reaction. Details are as shown in Table 2 below.

  In Table 2, the polymerization rate was determined by calculating the amount of the first (meth) acrylic monomer remaining by gas chromatography (GC).

Preparation Examples 1-7
The above mixtures A to F were mixed with various other substances at the ratios shown in Table 3 below to prepare (meth) acrylic liquid resin compositions A to G having the compositions shown in Table 3 below. Of these (meth) acrylic liquid resin compositions, those that do not substantially contain (meth) acrylic monomers (about 0.02% by mass) are cured with a non-radical type crosslinking agent. Categorized as “for crosslinking”. On the other hand, those containing substantially a (meth) acrylic monomer are cured by radical polymerization (thermal polymerization) and are therefore referred to as “polymerizable”.

Example 1
100 parts by mass of methacrylic polymerizable liquid resin composition A, 1 part by mass of t-amylperoxy-2-ethylhexanate (made by Kayaku Akzo Co., Ltd., trade name “Trigonox 121-50E”) as a radical polymerization initiator, 0.1 part by mass of antifoaming agent (BIC Chemie, trade name “A-515”), 400 parts by mass of aluminum oxide (manufactured by Showa Denko KK, product number “AS-10”; thermal conductivity 30 W / m · k) Was uniformly kneaded and then defoamed. The defoamed material is poured into a glass cell having a PET film that has been subjected to a release treatment on the bottom so that the thickness is 1 mm, and heated in an oven at a temperature of 100 ° C. for 1 hour, and then at a temperature of 120 ° C. for 1 hour. And polymerized (cured).

Examples 2-5
The same procedure as in Example 1 was performed except that acrylic polymerizable liquid resin compositions B to E were used instead of the methacrylic polymerizable liquid resin composition A.

Comparative Example 1
Liquid resin composition for acrylic crosslinking F 100 parts by mass, 0.35 parts by mass of hexamethylene diisocyanate as a crosslinking agent, 0.05 parts by mass of dibutyltin dilaurate as a urethane reaction accelerator, defoaming agent (trade name, manufactured by BYK Chemie, Inc. "A-515") 0.1 parts by mass, aluminum oxide (manufactured by Showa Denko Co., Ltd., product number "AS-10"; thermal conductivity 30 W / m · k) 400 parts by mass were uniformly kneaded and then defoamed did. The defoamed material is poured into a glass cell having a PET film subjected to a release treatment on the bottom so that the thickness becomes 1 mm, and heated in an oven at a temperature of 80 ° C. for 1 hour and then at a temperature of 100 ° C. for 1 hour. And crosslinked (cured).

Comparative Example 2
The same procedure as in Comparative Example 1 was performed except that the acrylic resin liquid G for crosslinking was used in place of the acrylic resin liquid F for crosslinking.

  The sheet-like cured products obtained in Examples 1 to 5 and Comparative Examples 1 to 2 were evaluated as follows.

[Heat-resistant]
The sheet-like cured product was heated in an oven at a temperature of 130 ° C. for 168 hours, and the mass, thermal conductivity, and hardness before and after heating were examined. Details are as follows.

1) Mass The mass before and after heating was measured, and mass loss was calculated based on the following formula.

Weight loss (%) = (mass before heating−mass after heating) / mass before heating × 100
2) Thermal conductivity A sheet-like cured product is laminated to a thickness of 10 mm, and heat at a temperature of 25 ° C. of the laminate is measured using a rapid thermal conductivity meter (product number “QTM-500”) manufactured by Kyoto Electronics Industry Co., Ltd. Conductivity was measured.

3) Hardness The sheet-like cured product was laminated to a thickness of 10 mm, and the hardness of the laminate was measured using an Asker rubber hardness meter C type manufactured by Kobunshi Keiki Co., Ltd. according to JIS K 7312.

[Heat-resistant decomposition]
The heating (130 ° C.) of the sheet-like cured product was further continued until the heating time reached 504 hours, and the hardness after heating was examined in the same manner as described above.

  The results are shown in Table 4.

  Although the liquid resin compositions F and G for crosslinking contain a large amount of liquid plasticizer as 76 to 77% by mass, the viscosity is already 1550 to 1950 mPa · S, so it is difficult to further reduce the liquid plasticizer. (See Table 3). Moreover, since Comparative Examples 1 and 2 using these crosslinkable liquid resin compositions F and G are of a crosslink curing type, when heated at a high temperature (130 ° C.) for an extremely long time (504 hours), the sheet is thermally decomposed and bleed occurs. Occurred (see Table 4). Therefore, there is room for improvement in heat decomposition resistance.

  On the other hand, the polymerizable liquid resin compositions A to E can suppress the amount of the liquid plasticizer used while maintaining a viscosity equal to or lower than that of the liquid resin compositions F and G for crosslinking (see Table 3). ). In particular, the acrylic liquid resin compositions B to E can achieve further lower viscosity than the methacrylic liquid resin composition A (see Table 3). In addition, the liquid resin compositions A to E can be produced without substantially using a special catalyst or solvent. In particular, it is worth noting that the acrylic liquid resin compositions B to E can be produced without substantially using a special catalyst or solvent.

  Moreover, the polymerizable liquid resin compositions A to E do not generate bleed even when heated at a high temperature for an extremely long time, and are excellent in heat decomposition resistance (see Table 4). In particular, the polymerizable liquid resin compositions A to D containing trimellitic acid ester having excellent heat resistance as a liquid plasticizer have less heat change after heating (particularly weight loss) and are more excellent in heat resistance (Tables). 4).

Claims (5)

  (Meth) acrylic polymer, (meth) acrylic, characterized by including a step of radical polymerization of (meth) acrylic monomer in a liquid plasticizer containing (meth) acrylic monomer and radical polymerization initiator A method for producing a polymerizable liquid resin composition comprising a monomer and a liquid plasticizer.   2. The method for producing a polymerizable liquid resin composition according to claim 1, wherein the liquid plasticizer has a mass loss of 5% by mass or less after being held at a temperature of 150 ° C. for 3 hours.   A polymerizable liquid resin composition containing an acrylic polymer having an glass transition temperature of 0 ° C. or less, an acrylic monomer, and a liquid plasticizer, and substantially free of a solvent, an isocyanate crosslinking agent, and an epoxy crosslinking agent . The liquid plasticizer is 10 to 70% by mass with respect to the total mass of the acrylic polymer, the acrylic monomer, and the liquid plasticizer,
The polymerizable liquid resin composition according to claim 3, wherein the acrylic monomer is 10 to 500 parts by mass with respect to 100 parts by mass of the acrylic polymer. A heat conductive material obtained by radical polymerization of the polymerizable liquid resin composition according to claim 3.