JP5048974B2 - Acrylic resin composition and resin sheet having electromagnetic wave absorption and thermal conductivity - Google Patents

Description

The present invention relates to a heat conductive material that has electromagnetic wave absorption performance and quickly transfers heat of a component such as an electronic device to a heat dissipation component.

In general, since electronic device parts generate heat during operation, a metal heat sink or the like is attached in the electronic device device for the purpose of preventing damage to the parts due to heat or stable operation of the parts. If necessary, the heat sink is forcibly air-cooled with a fan or the like, and parts with large heat generation are also water-cooled by water circulation or forcibly cooled using a Peltier element which is a kind of semiconductor element. It has been.

In these electronic devices, various electromagnetic wave absorbers are used for the purpose of preventing harmful effects caused by leakage of electromagnetic waves from the electronic devices and intrusion of electromagnetic waves from the outside.

As a heat conductive material used for such an electronic device, silicone-based grease or a silicone rubber sheet / silicone gel sheet with increased thermal conductivity is used in terms of thermal decomposition stability and flame retardancy. Silicone rubber sheets are common, but the silicone resin itself is not only expensive, but it cannot be easily manufactured because it requires a vulcanization process in the sheet manufacturing, and many inorganic fillers are added to the silicone resin. When filled, it becomes brittle and sheet forming is difficult. Furthermore, since the siloxane gas is generated in the silicone resin, a problem of contact failure of electronic device parts also occurs.
JP-A-9-296114 JP 2004-137432 A

The present invention is not expensive like a silicone rubber sheet or gel, does not require complicated processing, and has an acrylic resin composition having excellent thermal conductivity and electromagnetic wave absorption performance, and flexibility comprising the composition It is an object to provide a resin sheet having the following.

As a result of intensive studies on a composition comprising an acrylic copolymer as a main ingredient, the present inventors have reacted an acrylic copolymer with a compound having a glycidyl group to increase the crosslinking density, and further added a soft magnetic powder. It is preferable that a resin sheet having flexibility and excellent thermal conductivity and electromagnetic wave absorption can be obtained from a composition that is preferably a combination of soft magnetic powder and a wetting and dispersing agent. I found it.

That is, the present invention uses an acrylic copolymer having a carboxyl group and a compound having two or more glycidyl groups in one molecule as a matrix, and soft magnetic powder as a filler is 100 to 100%.
1,500 parts by weight of an acrylic resin composition, and a resin sheet obtained by processing (molding and curing the sheet), preferably 0.05 to 3 parts by weight of a wetting dispersant added. A characteristic acrylic resin composition and a resin sheet obtained by processing the acrylic resin composition.

Therefore, the resin sheet made of the acrylic resin composition of the present invention has both thermal conductivity and electromagnetic wave absorption, and transfers heat of components such as electronic devices to the cooling device, and leaks electromagnetic waves from the electronic devices. In addition, it can prevent harmful effects caused by electromagnetic waves from the outside and is extremely useful as a heat conduction material for electronic devices.

In the acrylic resin composition of the present invention, the compatibility of the soft magnetic powder as the filler is increased by combining the wetting and dispersing agent, the composition can be easily kneaded, and the resin sheet can be easily prepared.

The acrylic copolymer used in the present invention has a carboxyl group in the molecule. As a method for introducing a carboxyl group, a vinyl monomer and a monomer having a carboxyl group which can be copolymerized mainly with an acrylic monomer having no functional group, or an acrylic monomer having a carboxyl group And other acrylic monomers are copolymerized.

Furthermore, it is also possible to polymerize a monomer copolymerizable with an acrylic monomer and perform a terminal termination reaction with a carboxyl group-containing molecule as a termination reaction.

The carboxyl group of the acrylic copolymer may be at the molecular end, may be present in the middle of the molecular chain, may be present on either the side chain or the main chain, and is further randomly shared. It may be polymerized or block copolymerized. Furthermore, the structure is not a single one, and it may be a blend of acrylic copolymers of various repeating units.

Here, the acrylic copolymer preferably has a glass transition temperature (Tg) of at least a main component polymer constituting the acrylic copolymer as measured by the DSC method and is -60 ° C to -20 ° C. The glass transition temperature of the polymer may be -60 to -20 ° C. If the glass transition temperature of the main component polymer of the acrylic copolymer is too high, the composition becomes hard and is not preferable as a heat conductive sheet, and the hardness of the cured product is ASKER-C 50 or less, preferably 40 or less. .

Furthermore, the proportion of carboxyl groups in the acrylic copolymer is potassium hydroxide (KOH)
The acid value (AV) by titration is 20 to 150, more preferably 50 to 150.

When the acid value is less than 20, the crosslinking point is not sufficient, and a heat-resistant cured product cannot be obtained, and it is not preferable in terms of flame retardancy. Furthermore, when the acid value exceeds 150, the crosslink density is excessively increased and the flexibility is insufficient.

As the acrylic monomer having no functional group as the main component of the acrylic copolymer, alkyl acrylates and alkyl methacrylates are preferable, and in particular, n-butyl acrylate (acrylic acid-n-butyl), 2- Ethylhexyl acrylate (2-ethylhexyl acrylate) is preferred.

Furthermore, examples of monomers copolymerizable with these acrylic monomers include vinyl monomers. Specifically, acrylonitrile, acrylamide, methacrylamide, N-
Dimethylacrylamide, N-dimethylmethacrylamide, N-dimethylaminoethyl acrylate, N-dimethylaminoethyl methacrylate, N-diethylaminoethyl acrylate, N-diethylaminoethyl methacrylate, vinyl acetate, styrene, α-methylstyrene, divinylbenzene, allyl ( And (meth) acrylate.

Monomers having a carboxyl group as a functional group include acrylic acid, methacrylic acid,
Itaconic acid, crotonic acid, isocrotonic acid, maleic acid, fumaric acid, citraconic acid, mesaconic acid, or functional monomers derived from these.

In the present invention, the compound having a glycidyl group that reacts with the carboxyl group of the acrylic copolymer is a compound having at least two glycidyl groups in the molecule, and the epoxy equivalent (WPE) of the compound is 80 to 80. It is preferable to be in the range of 400.

When the epoxy equivalent is 400 or more, it is necessary to add a large amount of a compound having a glycidyl group in order to react with the acrylic copolymer, so that the required performance of the obtained molded product may not be sufficiently achieved. On the other hand, if the epoxy equivalent is 80 or less , the reaction rate is too high and molding may be difficult.

As the compound having a glycidyl group used in the present invention, various compounds can be used,
Specifically, sorbitol polyglycidyl ether (SORPGE), polyglycerol polyglycidyl ether (PPGGE), pentaerythritol polyglycidyl ether (PETGE), diglycerol polyglycidyl ether (DGGGE), glycerol polyglycidyl ether (GREPGE), trimethylol Propane polyglycidyl ether (TMMPGE), resorcinol diglycidyl ether (RESDGE), neopentyl glycol diglycidyl ether (NPGDGE), 1,6-hexanediol diglycidyl ether (HDDGE), ethylene glycol diglycidyl ether (EG)
DGE), polyethylene glycol diglycidyl ether (PEGDGE), propylene glycol diglycidyl ether (PGDGE), polypropylene glycol diglycidyl ether (PPGDGE), polybutadiene diglycidyl ether (PBDGE), diglycidyl phthalate (DGEP), neohalogenated neo Pentylglycerol diglycidyl ether, bisphenol A type diglycidyl ether (DGEBA), bisphenol F type diglycidyl ether (DGEBF) and the like are used, and particularly preferably, trimethylolpropane polyglycidyl ether (TMMPGE), sorbitol polyglycidyl ether (SORPGE). ) Etc.

As an addition amount of the compound containing a glycidyl group, an acid equivalent of an acrylic copolymer is 100.
On the other hand, the epoxy equivalent is preferably in the range of 80 to 300. When the addition amount is less than the equivalent calculation of 80, the curing does not proceed sufficiently and may not be completely solidified, which is not preferable because the heat resistance and flame retardancy are deteriorated. On the other hand, when the addition amount is more than the equivalent calculation 300, it is not preferable because it remains unreacted and excessively remains in the molded product, bleed out with time and flame retardancy deteriorates.

Magnetic materials are classified as weak magnetism that is unlikely to become a ferromagnet that easily becomes a magnet by an external magnetic field. Further, ferromagnetic materials are classified into hard magnetic materials in which magnetization due to an external magnetic field is stubborn (hard) and soft magnetic materials in which softness is soft (soft). Usually, hard magnetic materials with high coercivity are used for permanent magnets, and soft magnetic materials with high permeability and low coercivity are used for electromagnets, transformers, and coil cores.

Among these magnetic materials, soft magnetic metal materials and soft magnetic metal oxides can be used as the soft magnetic powder used in the present invention. Specifically, Ni-Zn ferrite, Mn-Zn ferrite, Cu-Zn
-Based ferrite, Mn-Mg-based ferrite, soft ferrite such as Li-Zn-based ferrite, iron, nickel, cobalt, Fe-Co, Fe-Cr, Fe-Si, Fe-Al, Fe-Cr-Al, Fe-Si Iron alloys such as -Cr, Fe-Si-Al, Fe-Al-Si, permalloy, and carbonyl iron can be used. These soft magnetic powders may be used singly or in combination of two or more.

  The soft magnetic powder of the present invention is dispersed in the matrix. At this time, if the soft magnetic powders are in contact with each other in the matrix, a plurality of the soft magnetic powders in contact with the matrix are in contact. This powder exhibits the behavior of one large particle, so that the eddy current loss increases, the magnetic permeability decreases, and the electromagnetic wave absorbability may decrease. Therefore, it is preferable that the soft magnetic powders are dispersed in a state where they are not in contact with each other in the matrix, that is, are electrically isolated. And since the soft magnetic powder made of Fe-Si-Cr alloy has high compatibility with the acrylic copolymer as the matrix, the powders are easily dispersed in the matrix in a non-contact state. As a result, the electromagnetic wave absorptivity is hardly lowered. In addition, soft magnetic powder made of Fe-Si-Cr alloy is dispersed in the acrylic copolymer as the matrix without using a wetting and dispersing agent, and can absorb initial electromagnetic waves. However, since the powder may agglomerate over time and cannot absorb electromagnetic waves, it is preferable to use a wetting and dispersing agent.

  Further, the shape of the soft magnetic powder may be a flat shape, a needle shape, a particle shape, or the like. In particular, the flat soft magnetic powder has a large surface area and thus easily absorbs electromagnetic waves. As the size of the flat soft magnetic powder, an average thickness of 0.5 to 3 μm, an aspect ratio (particle diameter / particle thickness) of 2 to 60, and an aspect ratio of 10 to 40 are particularly preferable. . Flattening until the average thickness is 0.5 μm or less is not preferable because the magnetic permeability is lower than the original value due to the influence of processing. On the other hand, when the average thickness exceeds 3 μm, the magnetic permeability due to the eddy current is remarkably lowered, and in both cases, the electromagnetic wave absorption characteristics are lowered. Further, when the aspect ratio is 2 or less, sedimentation tends to occur in the matrix, and when it exceeds 60, the dispersibility in the matrix is remarkably deteriorated.

The amount of the soft magnetic powder added was 10% of the total amount of the acrylic copolymer and the compound having a glycidyl group.
It is 100-1500 weight part with respect to 0 weight part. If it is less than 100 parts by weight, sufficient electromagnetic wave absorptivity and thermal conductivity cannot be obtained, and if it exceeds 1,500 parts by weight, no improvement in electromagnetic wave absorptivity is observed and kneading is difficult. In particular, 300 parts by weight or more is preferable in terms of electromagnetic wave absorption performance and heat conduction performance, and 1,000 parts by weight or less in terms of workability such as kneading and defoaming of the acrylic resin composition.

The wetting and dispersing agent is adsorbed on the surface of the powder particles and has a larger charge on the particle surface, thereby increasing the electrostatic repulsion force and preventing aggregation. In addition, it functions to prevent aggregation due to the steric repulsion between the adsorbed dispersants.

As the wetting and dispersing agent used in the present invention, compounds having ester groups, hydroxyl groups, ethylene oxide, boric acid groups and / or phosphoric acid group saturated polyester copolymers, polyhydric alcohol organic acid esters, special alcohol organic acid esters, urethane-modified acrylics Copolymer, high molecular weight polyester, polycarboxylic acid copolymer, graft product of allyl alcohol / maleic anhydride / styrene copolymer and polyoxyalkylene monoalkyl ether, ammonium polyacrylate, ammonium acrylate copolymer, silicon And polymer-based ethylene oxide and / or propylene oxide adducts. Among them, ester groups,
A compound having a hydroxyl group and ethylene oxide is preferable because it is relatively easy to synthesize and is excellent in cost.

The addition amount of the wetting and dispersing agent is 10% of the total amount of the acrylic copolymer and the compound having a glycidyl group.
It is 0.05-3.0 weight part with respect to 0 weight part. If the wetting and dispersing agent is less than 0.05 parts by weight, the compatibility of the soft magnetic powder with the resin tends to be low, and kneading tends to be impossible. If the addition amount is small, the powder particles collide with each other and agglomerate, the apparent particle diameter becomes large and sedimentation separation occurs at an early stage. Moreover, when it adds more than 3.0 weight part, viscosity increase and gelatinization will be caused, the sclerosis | hardenability of a sheet | seat will worsen, and resin sheet preparation will become difficult.

  When forming the acrylic resin composition of the present invention into a sheet, the molding method is not particularly limited, and for example, a coating method, extrusion molding, injection molding, or the like can be adopted, and among them, the coating method Is preferred. The reason is that, by adopting the coating method, for example, a thin film sheet having a thickness of 0.5 mm or less can be formed in a single step.

  The viscosity when the soft magnetic powder is mixed in the matrix of the present invention is preferably 5000 to 80,000 cps. For example, when a thin film sheet of 0.5 mm or less is produced, the viscosity is 2 Particularly preferred is ˜60,000 cps. Since the soft magnetic powder has a large specific gravity, precipitation is likely to occur when the viscosity is less than 5000 cps, and the resulting sheet is likely to cause streaks and unevenness. On the other hand, if it exceeds 80,000 cps, the fluidity is insufficient, and sheet processing may be difficult.

  Further, the acrylic resin composition of the present invention may use a heat conductive filler in order to improve the heat conductivity. As the thermally conductive filler, nitrides such as boron nitride and aluminum nitride, metal oxides such as alumina and magnesia, and metal powders such as silicon carbide, carbon, copper, silver, and aluminum can be added. Since the metal powder has high electric conductivity, an increase in eddy current may be caused and the electromagnetic wave absorbability may be lowered. Therefore, a metal hydroxide having high compatibility with the acrylic resin composition of the present invention, insulating properties and excellent flame retardancy is preferable, and particularly a metal hydroxide having a decomposition temperature of 250 ° C. or higher. Specifically, aluminum hydroxide, magnesium hydroxide, barium hydroxide and the like are preferable.

In addition, the measuring method of the said decomposition temperature is TGA (Thermo Gravim) only for a filler.
With an electrical analyzer), the temperature is measured at a temperature rising rate of 10 ° C./min from room temperature to 600 ° C. in an air atmosphere, and the temperature causing the weight loss is measured to obtain the decomposition temperature.

The addition amount of the heat conductive filler is preferably 25 with respect to 100 parts by weight of the acrylic copolymer.
The range is from 0 to 500 parts by weight. When the addition amount is small, improvement in thermal conductivity cannot be expected. When the addition amount is large, the thermal conductivity is improved, but processing becomes difficult, which may not be suitable for production.

Further, it is possible to add a filler such as metal carbonate such as calcium carbonate, clay, kaolin and the like, which is not necessarily excellent for transferring heat.

The size and shape of these fillers are not particularly limited, but the particle size is approximately 0. 0.
It is particularly preferably 5 to 30 μm and a spherical shape. When the particle diameter is smaller than 0.5 μm, the viscosity of the liquid becomes too high when added to the matrix resin, and conversely, when the particle diameter is larger than 30 μm, it is difficult to be mixed into the matrix resin. When cured to obtain a resin sheet, the filler is difficult to disperse uniformly.

It is also possible to combine fillers having the same composition and different particle sizes. When it is necessary to increase the filler, the viscosity of the composition can be lowered by combining several types having different particle diameters.

Furthermore, a catalyst, a flame retardant, an antioxidant, a weather stabilizer, a heat stabilizer, etc. can be appropriately added to the composition of the present invention as needed, depending on the required performance, to the main agent and curing agent. It is.

As a method of blending an acrylic copolymer with a wetting and dispersing agent, a soft magnetic powder, and other fillers added as necessary at an appropriate ratio, each is weighed and mixed and stirred. The mixing and stirring method at this time is not particularly limited, and is selected according to the composition of the polymer, the viscosity, the type of soft magnetic powder, and the blending amount. Specifically, a dissolver mixer, a homomixer, etc. It is possible to use a stirrer. Further, the blended and stirred composition may be filtered for the purpose of removing a lump of undispersed soft magnetic powder and other fillers, if necessary. It is preferable to defoam bubbles generated by mixing and stirring under reduced pressure.

Hereinafter, the present invention will be described in more detail with reference to experimental examples.
(Examples 1-10, Comparative Examples 1-8)
Tables 1 to 3 show the acrylic copolymer, soft magnetic powder, metal hydroxide, wetting and dispersing agent and curing agent.
Were blended in the proportions shown below and degassed under reduced pressure to obtain an acrylic resin composition. This composition was coated on a polyester film having a surface subjected to silicon release treatment so as to have a predetermined thickness. After coating, it was cured by heating in an oven at 190 ° C. for 13 minutes. Furthermore, it was cured by being allowed to stand at room temperature for 24 hours, and was peeled off from the polyester film to obtain an acrylic resin sheet. The obtained resin sheet was evaluated as follows. The evaluation results are shown in Tables 1-3.

<Evaluation details>
The thermal conductivity was measured using a rapid thermal conductivity meter QTM-500 (manufactured by Kyoto Electronics Industry Co., Ltd.).
The electromagnetic wave absorptivity was evaluated by the maximum attenuation rate from 100 MHz to 1 GHz by the KEC method.
Workability was evaluated as follows.
A: Can be kneaded with low viscosity, can be made into a sheet
○: Viscosity is slightly high, but kneading and sheeting are possible
△: High viscosity and slightly difficult to knead;
×: High viscosity, difficult to knead, difficult to form a sheet

※比較例２乃至４及び比較例８は、シート化が難であるため、熱伝導率、電磁波吸収性それぞれについて測定することが出来なかったため、不可とした。

* Since Comparative Examples 2 to 4 and Comparative Example 8 were difficult to form into sheets, it was impossible to measure the thermal conductivity and the electromagnetic wave absorptivity.

Acrylic copolymer 1; CB-3060 (manufactured by Soken Chemical Co., Ltd.), molecular weight 3000, acid value 62
Acrylic copolymer 2; CB-3A2 (manufactured by Soken Chemical Co., Ltd.), molecular weight 5000, acid value 63
Curing agent 1; Denacol EX-313 (manufactured by Nagase ChemteX Corporation), glycerin polycyclic ether Curing agent 2; Denacol EX-521 (manufactured by Nagase ChemteX Corporation), polyglycerin polycyclic ether soft magnetic powder Body 1; BSF-714 (made by Toda Kogyo Co., Ltd.), soft ferrite soft magnetic powder 2; S-1281 (made by Toda Kogyo Co., Ltd.), carbonyl iron soft magnetic powder 3; JEM-S (Mitsubishi) Material Co., Ltd.), Fe-Si-Cr alloy metal hydroxide 1; Hysilite H-42 (manufactured by Showa Denko KK), aluminum hydroxide metal hydroxide 2; Kisuma 5A (Kyowa Chemical Industry) ) Magnesium hydroxide wetting and dispersing agent 1; BYK-W909 (manufactured by Bick Chemie Shahan Co., Ltd.), boric acid ester wetting and dispersing agent 2; BYK-W9010 (Bick Chemie Shahan Corporation) Ltd.), a copolymer with acid groups

Claims (5)

  Add an acrylic copolymer having a carboxyl group as a functional group and a compound having two or more glycidyl groups in one molecule as a matrix, and add 100 to 1,500 parts by weight of at least a soft magnetic powder as a filler. In addition, 0.05 to 3 parts by weight of a wetting dispersant is added to 100 parts by weight of the acrylic copolymer, and the wetting and dispersing agent is adsorbed on the surface of the soft magnetic powder so that the particle surface has a larger electric valence. An acrylic resin composition characterized in that it has an electrostatic repulsive force to prevent agglomeration and prevents agglomeration by the steric repulsive force between adsorbed dispersants.   2. The acrylic resin composition according to claim 1, wherein the soft magnetic powder has a flat shape, an average thickness of 0.5 to 3 [mu] m and an aspect ratio of 2 to 60.   The acrylic according to claim 1 or 2, wherein the soft magnetic powder is one kind selected from soft ferrite, carbonyl iron, and Fe-Si-Cr alloy, or a combination of two or more kinds. -Based resin composition.   250 parts by weight or more and 500 parts by weight or less of at least one selected from aluminum hydroxide, magnesium hydroxide, and barium hydroxide are added as a heat conductive filler to 100 parts by weight of the acrylic copolymer. The acrylic resin composition according to any one of claims 1 to 3. A resin sheet obtained by molding and curing the acrylic resin composition according to any one of claims 1 to 4 into a sheet shape.