JP2002302662A - Thermally conductive, electrically insulating pressure- sensitive adhesive - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermally conductive, electrically insulating pressure- sensitive adhesive improved in thermal conductivity without detriment to adhesive properties. SOLUTION: This adhesive is prepared by compounding 100 pts.wt. copolymer with 50-300 pts.wt. thermally conductive, electrically insulating particles. The copolymer is prepared by photopolymerizing a photopolymerizable composition comprising an alkyl (meth)acrylate having a 2-12C alkyl group, a cross-linking monomer represented by formula (1): CH2 =CR<1> COO(CH2 CH2 O)n COCR<2> =CH2 (wherein 5<=n<=40; and R<1> and R<2> are each H or CH3 ), and a photopolymerization initiator, and has a gel content of 40-90 wt.%.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-conductive and electrically-insulating pressure-sensitive adhesive excellent in heat conductivity, electric insulation and adhesiveness.

[0002]

2. Description of the Related Art Heat-conductive, electrically-insulating, pressure-sensitive adhesives having excellent thermal conductivity, electrical insulation and adhesiveness are known, and are suitable as a heat transfer medium for conducting heat to dissipate heat in the assembly of electronic components. Used for

For example, JP-A-6-88061 discloses that 100 parts by weight of a polymer prepared from a monomer mixture containing an alkyl (meth) acrylate having an alkyl group having 2 to 12 carbon atoms and a polar monomer are disclosed. On the other hand, a heat conductive electric insulating pressure-sensitive adhesive containing 20 to 400 parts by weight of heat conductive electric insulating particles is disclosed.

In this kind of heat conductive electric insulating pressure-sensitive adhesive, the heat conductivity is mainly obtained by the heat conductive electric insulating particles, but it is necessary to improve the heat conductivity of the acrylic polymer itself as a binder. If possible, it is considered possible to further improve the thermal conductivity of the pressure-sensitive adhesive.

[0005]

However, in the above-mentioned conventional heat-conductive electrically insulating pressure-sensitive adhesive, when the thermal conductivity is improved by changing the composition of the acrylic polymer, the pressure-sensitive adhesive is used. However, there is a problem that the elasticity changes and the adhesiveness decreases, and as a result, the thermal conductivity decreases.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to provide a heat conductive electrically insulating pressure-sensitive adhesive having improved heat conductivity without lowering adhesiveness. .

[0007]

Means for Solving the Problems In order to achieve the above object, in the present invention, an alkyl (meth) acrylate having an alkyl group having 2 to 12 carbon atoms is represented by the following general formula (1). Gel fraction obtained by photopolymerizing a photopolymerizable composition comprising a crosslinkable monomer and a photopolymerization initiator,
A heat-conductive and electrically-insulating pressure-sensitive adhesive is provided, which contains 50 to 300 parts by weight of heat-conductive and electrically-insulating particles based on 100 parts by weight of a copolymer of 90 to 90% by weight. ^{_{CH 2 = CR 1 COO (CH}} 2 CH 2 O) n COCR 2 = CH 2 ...... (1) ( however, 5 ≦ n ≦ 40, R ¹ and R ² H or C
H ₃ . )

The alkyl (meth) acrylate having an alkyl group having 2 to 12 carbon atoms used in the present invention includes, for example, ethyl (meth) acrylate, n-butyl (meth) acrylate, and (meth) acrylic acid. 2-ethylhexyl, n-octyl (meth) acrylate, isooctyl (meth) acrylate, isononyl (meth) acrylate,
And lauryl (meth) acrylate. These monomers are used alone or in combination of two or more.

The crosslinkable monomer is represented by the general formula CH _{2 2
^{CR 1 COO (CH 2 CH 2}} O) nCOCR 2 = CH 2
(However, 5 ≦ n ≦ 40, R ¹ and R ² are H or C
H ₃ . ), Polyethylene glycol @ 400 di (meth) acrylate (n = 9), polyethylene glycol @ 600 di (meth) acrylate (n = 14), polyethylene glycol @ 1000 di (meth) acrylate (n = 23) ) Are preferably used. These monomers are used alone or in combination of two or more.

It is to be noted that a monomer having a polar group may be used as the alkyl (meth) acrylate and the crosslinkable monomer. Examples of such a monomer having a polar group include, for example, a carboxyl group-containing monomer such as (meth) acrylic acid, maleic acid, fumaric acid, and itaconic acid; (meth) acrylonitrile, N-vinylpyrrolidone, N-vinylcaprolactam, and acryloyl. Morpholine, (meth) acrylamide, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dimethylaminopropyl (meth) acrylate, dimethylaminopropylacrylamide,
Nitrogen-containing monomers such as N-vinylacetamide; and hydroxyl-containing monomers such as 2-hydroxyethyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, and 4-hydroxybutyl (meth) acrylate. These monomers may be used alone or
Used in combination of more than one species.

Examples of the photopolymerization initiator include 2-hydroxy-2-methyl-phenylpropan-1-one, methoxyacetophenone, 2,2-dimethoxy-2-phenylacetophenone, and phenylbis (2,4,6- Acetophenone initiators such as trimethylbenzoyl) -phosphine oxide and 1-hydroxycyclohexylphenyl ketone; benzoin ether initiators such as benzoin ethyl ether and benzoin isopropyl ether; ketal initiators such as benzyl dimethyl ketal; and other halogenated ketones , Acylphosphinoxide, acylphosphonate and the like. These crosslinking agents are used alone or in combination of two or more.

The alkyl (meth) acrylate and the crosslinkable monomer are used so that the resulting copolymer has a gel fraction of 40 to 90% by weight, preferably 50 to 80% by weight. If the gel fraction is less than 40% by weight, the degree of cross-linking is insufficient, and a network structure cannot be formed by the cross-linkable monomer, and heat cannot be conducted effectively. Conversely, when the gel fraction exceeds 90% by weight, the crosslink density becomes too high, and the flexibility is reduced, and the adhesiveness at the interface is reduced to lower the thermal conductivity.

The photopolymerization initiator is used in an amount of 0.01 to 5 parts by weight, preferably 0.05 to 5 parts by weight, based on 100 parts by weight of all monomers.
Used in the range of ~ 3 parts by weight. If the amount is less than 0.01 part by weight, the polymerization conversion rate decreases, and the monomer odor of the obtained copolymer becomes sharp. Conversely, if it exceeds 5 parts by weight, the amount of generated radicals will increase, the molecular weight will decrease significantly, and the required shear modulus may not be obtained.

Further, in order to improve the heat conductivity and the electric insulation, heat conductive electric insulating particles are used. Examples of the heat-conductive particles include aluminum oxide, aluminum nitride, titanium dioxide, boron nitride, silicon nitride, and silicon carbide. These thermally conductive electrically insulating particles are used alone or in combination of two or more.

[0015] The particle diameter of these thermally conductive electrically insulating particles is 0.5 to 150 µm, preferably 1 to 100 µm. Such thermally conductive electrically insulating particles are contained in an amount of 50 to 300 parts by weight based on 100 parts by weight of the obtained copolymer. When the amount is less than 50 parts by weight, the heat conductivity is not improved because the amount of the heat conductive electrically insulating particles is too small. Conversely, 300
If the amount is more than 10 parts by weight, the ultraviolet ray transmittance of the composition is remarkably reduced, the polymerization conversion is reduced, and the monomer odor of the obtained copolymer is sharp.

The photopolymerizable composition thus obtained is preliminarily irradiated with light, or a thickening agent such as acrylic rubber or a thixotropic agent such as colloidal silica is blended. May be adjusted.

As the lamp used for irradiating the photopolymerizable composition with light, a lamp having an emission distribution at a light wavelength of 400 nm or less is used. Examples thereof include a low-pressure mercury lamp, a medium-pressure mercury lamp, a high-pressure mercury lamp, and an ultra-high-pressure mercury lamp. , A chemical lamp, a black light lamp, a microwave excitation mercury lamp, a metal halide lamp, and the like. The intensity of irradiation of the photopolymerizable composition by the lamp is a factor that affects the degree of polymerization of the obtained copolymer, and is appropriately controlled.

Photopolymerization in the present invention is inhibited by oxygen in the air or oxygen dissolved in the photopolymerizable composition. Therefore, light irradiation must be performed using a method capable of eliminating the inhibition of oxygen reaction. As one of the techniques, there is a method in which the photopolymerizable composition is covered with a film made of polyethylene terephthalate or Teflon (registered trademark) to cut off contact with oxygen, and light is irradiated through the film.

The composition may be irradiated with light through a light-transmitting window in an atmosphere in which oxygen has been replaced by an inert gas such as nitrogen gas or carbon dioxide gas. In this method, in order to sufficiently complete the polymerization of the reactive composition until the conversion becomes 99.7% or more, the oxygen concentration in the irradiation atmosphere is 5000 ppm or less, preferably 30 ppm or less.
Desirably, it is 0 ppm or less.

(Function) The heat conductive electric insulating pressure-sensitive adhesive thus obtained is obtained by crosslinking a polymer of an alkyl (meth) acrylate with a crosslinking monomer of a diacrylate having a polyethylene glycol chain. In cooperation with the action of the electrically insulating particles, the thermal conductivity of the obtained copolymer is improved.

The reason is considered as follows. That is, the crosslinkable monomer improves the flow of free electrons by having an ether bond in which an oxygen atom having a lawn pair is present, and is effective even with a small amount of addition by forming a network structure of the crosslinkable monomer. Is exhibited. Then, the free electrons can be moved by applying a stress such as thermal energy or the like, and the thermal energy can be moved. This is considered to allow efficient heat conduction.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, in order to specifically explain the present invention, some examples showing an example of the present invention and some comparative examples showing a comparison with the example will be given.

Example 1 In a separable flask equipped with a stirrer, a cooler, a thermometer and a nitrogen gas inlet, 98 parts by weight of n-butyl acrylate, 2 parts by weight of acrylic acid, polyethylene glycol @ 600 diacrylate ( n = 1
4) 0.05 parts by weight of phenylbis (2,4,6-trimethylbenzoyl) -phosphine oxide (trade name “Irgacure 81” of Ciba Specialty Chemicals)
9 ") 0.2 parts by weight, 124 parts by weight of boron nitride and 88 parts by weight of silicon carbide were added, and the mixture was stirred until uniformly dispersed, and then purged with nitrogen to remove dissolved oxygen. I got

The above photopolymerizable composition may be added to black light
5mW / cm irradiation intensity using a pump ^TwoPreliminary light
When exposed, the viscosity rises as the temperature rises
Was. Therefore, when the temperature rises by 5 ° C., the light irradiation is stopped.
I did. Weight of the resulting partially polymerized thickened photopolymerizable composition
The conversion is 3.7% by weight and the viscosity is 2200 cps.
Was.

Next, the partially polymerized and thickened photopolymerizable composition is coated on a release-treated polyester film (PET film) having a thickness of 38 μm, and this is coated with the same polyester film (PET film) as described above. Film)
Using a chemical lamp, the lamp height is set so that the irradiation intensity becomes ² mW / cm ² , and light is irradiated for 8 minutes to perform photopolymerization, and a 0.5 mm thick thermally conductive electrically insulating pressure-sensitive adhesive is used. Was manufactured. The residual monomer of this heat conductive pressure-sensitive adhesive was less than 0.1% by weight, indicating excellent adhesive performance.

(Example 2) Polyethylene glycol # 6
Instead of 0.05 parts by weight of 00 diacrylate (n = 14), 0.05 parts by weight of polyethylene glycol @ 400 diacrylate (n = 9) was used. Otherwise in the same manner as in Example 1, a heat conductive electrically insulating pressure-sensitive adhesive was produced.

Comparative Example 1 Polyethylene glycol # 6
Instead of 0.05 parts by weight of 00 diacrylate (n = 14), 0.05 parts by weight of hexanediol diacrylate was used. Otherwise in the same manner as in Example 1, a heat conductive electrically insulating pressure-sensitive adhesive was produced.

Comparative Example 2 Polyethylene glycol # 6
Instead of 0.05 parts by weight of 00 diacrylate (n = 14), 0.05 parts by weight of polyethylene glycol # 200 diacrylate (n = 4) was used. Otherwise in the same manner as in Example 1, a heat conductive electrically insulating pressure-sensitive adhesive was produced.

Comparative Example 3 Polyethylene glycol # 6
Instead of 0.05 parts by weight of 00 diacrylate (n = 14), 0.01 parts by weight of polyethylene glycol @ 400 diacrylate (n = 9) was used. Otherwise in the same manner as in Example 1, a heat conductive electrically insulating pressure-sensitive adhesive was produced.

Comparative Example 4 15 parts by weight of boron nitride and 11 parts by weight of silicon carbide were used instead of 124 parts by weight of boron nitride and 88 parts by weight of silicon carbide. Otherwise, Example 2
In the same manner as in the above, a heat conductive electrically insulating pressure-sensitive adhesive was produced.

<Measurement of Thermal Conductivity> Using the heat conductive and electrically insulating pressure-sensitive adhesives obtained in the above Examples and Comparative Examples,
The thermal conductivity was measured with a rapid thermal conductivity meter (Kemtherm QTM-D3, manufactured by Kyoto Electronics Industry Co., Ltd.).

The measurement is performed by superposing the sample on a standard sample (silicone rubber, glass, silicone brick, Hastelloy steel) and heating with the probe of the above apparatus, and the temperature rise when only the standard sample is heated. The thermal conductivity is automatically calculated from the deviation from the rate. The unit of the thermal conductivity is W / (m · K). Table 1 shows the results.

<Measurement of Gel Fraction> In each of the above Examples and Comparative Examples, except that no thermally conductive electrically insulating particles (boron nitride and silicon carbide) were used, the same as each Example and each Comparative Example was carried out. Thus, a copolymer was produced.

About 0.1 g (initial weight A) of this copolymer was immersed in a glass bottle containing 50 g of tetrahydrofuran, sealed, and allowed to stand at 40 ° C. for 24 hours.
The mixture was filtered through a 0-mesh stainless steel mesh, and the residue (insoluble matter) on the stainless mesh was removed in an oven at 110 ° C for 24 hours.
After drying for a time, take it out, measure its dry weight B, and determine the gel fraction (% by weight) = (dry weight B / initial weight A)
× 100 was calculated. Table 1 shows the results.

[0035]

[Table 1]

[0036]

As described above, according to the present invention, a heat conductive and electrically insulating pressure-sensitive adhesive having improved heat conductivity can be obtained without lowering the adhesiveness. Therefore, the heat conductive electrically insulating pressure-sensitive adhesive of the present invention can be suitably used as a heat transfer medium for conduction for releasing heat in the assembly of electronic components.

Claims (1)

[Claims] 1. A photopolymerizable composition comprising an alkyl (meth) acrylate having an alkyl group having 2 to 12 carbon atoms, a crosslinkable monomer represented by the following general formula (1), and a photopolymerization initiator. Gel fraction obtained by photopolymerization of
A heat-conductive and electrically-insulating pressure-sensitive adhesive comprising 50 to 300 parts by weight of thermally-conductive and electrically-insulating particles with respect to 100 to 100% by weight of a copolymer of 90 to 90% by weight. ^{_{CH 2 = CR 1 COO (CH}} 2 CH 2 O) n COCR 2 = CH 2 ...... (1) ( however, 5 ≦ n ≦ 40, R ¹ and R ² H or C
H ₃ . )