JP2001250423A - Heat-resistant dielectric foam - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a light-weight heat-resistant composite dielectric foam used in a device such as antenna and laser reflector that has heat-resistance and size stability at a temperature of 80 deg.C or more together with a specific dielectric constant not significantly varying with the temperature. SOLUTION: This heat-resistant dielectric foam is obtained by substantially uniformly dispersing a dielectric ceramic material in a heat-resistant resin foam, having a specific dielectric constant of 1.0 to 2.0, dielectric loss tangent of 0.005 or less, and specific gravity of 0.3 to 0.02 g/ml. The heat-resistant resin is preferably composed of 50 to 95 pts.wt. of a styrenic resin and 50 to 5 pts.wt. of a polyphenylene ether resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a heat-resistant dielectric foam made of a foamed dielectric material. Further, the present invention provides a foam which can be used as a dielectric, particularly a foam which can be used as a dielectric material of each layer constituting a spherical dielectric lens utilizing the principle of a Luneberg lens.

[0002]

2. Description of the Related Art A spherical dielectric lens utilizing the principle of a Luneberg lens has been known for a long time, and has been used in radar radio reflectors, antennas, and the like because of its characteristics. Japanese Patent Publication No. 43-27061 discloses a dielectric structure of this type. In this publication, the ideal shape of the spherical dielectric lens is said to have a dielectric constant of 2.0 at the center of the sphere, and the dielectric constant decreases toward the outside of the sphere, and the outermost layer has a lower dielectric constant. 1.0 in the skin
It is taught that it is a sphere whose permittivity changes continuously so that However, actually producing such a sphere having a relative dielectric constant that changes continuously involves manufacturing difficulties and a great deal of cost. Therefore, usually, a plurality of spheres (5 to 15 layers) having different relative dielectric constants are usually used. The structure in which the spherical dielectric materials are stacked in layers from the concentric center portion to the outside is defined as a spherical dielectric lens. That is, the relative permittivity of the outermost layer is set to 1.0.
The core layer at the center is manufactured as a sphere having a structure having a relative dielectric constant of close to 2.0.

As a dielectric material constituting these layered spheres, Japanese Patent Publication No. 56-38003 discloses a composite dielectric comprising a plastic dielectric and aluminum metal particles having an average particle diameter of about 0.1 mm to 1.0 mm. Materials are disclosed. Also, Japanese Patent Publication No. 60-52528,
A mixture of foamed plastic particles or inorganic hollow particles such as glass balloons and shirasu balloons and metal-coated particles whose surfaces are covered with a thin metal film at an appropriate mixing ratio so as to obtain a desired dielectric constant. A mixed dielectric material is disclosed. Furthermore, in Japanese Patent Publication No. 61-21147,
A dielectric material is disclosed in which a metal foil flake having one or both surfaces of a metal foil coated with a resin having a compatibility with a foamable resin and containing a surfactant is mixed with the foamable resin.

[0004]

By the way, spherical dielectric lenses utilizing the principle of Luneberg lenses used as radar reflectors and antennas are often used for a long time in any place outdoors. You have to assume. For example, the temperature inside the dielectric lens may exceed 80 ° C. under the sun just below the equator, and the temperature will be below freezing in midwinter at high latitudes. In order to maintain stable performance over a long period of time under such severe temperature changes, it is necessary to have sufficient heat resistance and high dimensional stability. In addition, in a temperature range (−40 to 80 ° C.) in consideration of these use conditions, unless the change in the relative dielectric constant is small, stable performance cannot be maintained. Further, as an important characteristic that determines the performance as a dielectric material for a spherical dielectric lens, there is a numerical value of a dielectric loss tangent (tan δ). This is an index indicating the dielectric loss.
If the dielectric loss tangent is large, a large loss in the dielectric constant of the material occurs, so that the performance as a laser reflector or an antenna cannot be sufficiently exhibited. Therefore, this dielectric loss tangent (t
The value of anδ) needs to be 0.005 or less. In addition, when the volume of the multilayer molded body is large, transportation and further installation thereof require a great deal of labor and cost. Therefore, it is desirable that the molded body be lightweight, that is, have a small specific gravity.

Some proposals and attempts have been made in the prior art to solve these problems. 1) In Japanese Patent Publication No. 56-38003, a foamed polystyrene having a specific gravity of 0.117 g / ml is used as a plastic dielectric material, and an appropriate amount of high-purity aluminum particles having a diameter of about 0.5 to 1.0 mm is mixed therein. These are formed into a molded body using vinyl acetate polymer as a binder.
However, in this case, it is extremely difficult to uniformly mix foamed polystyrene having a low specific gravity and aluminum particles having a high specific gravity, and when a molded body is formed, a variation in specific gravity and a variation in aluminum concentration occur inside the molded body. . In addition, a vinyl acetate polymer is used as a binder, but if the amount is small, the adhesion becomes insufficient and the molded body becomes extremely brittle, and if it is large, the effect of increasing the dielectric constant when the molded body is reduced. Therefore, it is difficult to adjust the amount of the binder. Also, from this example,
The specific gravity for obtaining a relative dielectric constant of 2 needs to be 0.3 g / ml or more.

[0006] 2) Japanese Patent Publication No. 60-52528 discloses that plastic particles expanded 20 to 30 times and the surface of the expanded plastic particles is coated with a thin film of a metal such as copper or aluminum by vapor deposition or the like. This is a method in which the covered metal-coated particles are appropriately mixed, and the mixture is foamed by heat and molded. This document solves the problem of the non-uniform mixing caused by mixing derivatives having different specific gravities and the increase of the specific permittivity, which are found in the above-mentioned 1) Japanese Patent Publication No. 56-38003, in which the specific gravity is increased. A new problem has arisen. In other words, thermoforming is the process of heat-sealing resin particles in a mold to each other by the heat of steam or the like. And cannot be molded. Therefore, when the mixing ratio of the metal coating particles is increased in order to increase the dielectric constant, the fusion property of the molded article is rapidly reduced, and the molded article is weak in physical properties and cannot be used for practical use. further,
When the surface of the foamed plastic particles is deposited with a metal, it requires a great deal of labor and cost, and is not practical.

3) In Japanese Patent Publication No. 61-21147, a metal foil flake surface-treated under certain conditions is kneaded with foamed polystyrene in an extruder, formed into a strand, and then cut into pellets. According to this method, the disadvantages of the dielectric materials described in the above two publications, that the composite material cannot be mixed homogeneously, that the specific gravity increases when the relative dielectric constant is increased, and that metal separation occurs during molding, are eliminated. However, because metal foil flakes are used,
The dielectric loss tangent increases. Further, as the performance of the foamable dielectric material obtained in this document, the relationship between the relative dielectric constant and the specific gravity of the foam is disclosed in Examples, but the specific gravity of any foam is 0.3 or more. Yes, it can be seen that all are high density.

As described above, the prior art has not been able to obtain a practical and satisfactory dielectric material.
The present invention has been made based on such a background. That is, in order to obtain an appropriate dielectric material intended for outdoor use, such as a spherical dielectric lens utilizing the principle of a Luneberg lens: 1) 80 ° C. or higher, which can be used even under outdoor sunshine Especially 80
It has high satisfactory dimensional stability in the range while maintaining heat resistance of 100 ° C. to 100 ° C .; 2) a small change in relative permittivity with respect to temperature change (−40 to 80 ° C.); When the ratio is in the range of 1.0 to 2.0, the dielectric tangent must be 0.005 or less; and 4) lightweight. An object of the present invention is to provide a foamed dielectric material satisfying this problem.

The present inventor paid attention to polystyrene as a dielectric material having an excellent relative dielectric constant and an extremely low dielectric loss tangent, and its foaming performance, and made intensive studies to solve the above problems. As a result, a special combination of styrene-based blends or copolymers, as well as a special combination of resin systems selected from styrene alone as the heat-resistant resin, and a high-dielectric ceramic material selected at a specific ratio By producing a composite material by mixing with the above-mentioned resin, a novel heat-resistant foam suitable for use in a spherical dielectric lens has been invented.

[0010]

Means for Solving the Problems Polymer materials have their own specific dielectric constants and dielectric loss tangents. Among them, polystyrene has a specific dielectric constant of 2.times. In an unfoamed state.
It is around 5, and the dielectric loss tangent keeps a low value of around 0.0002. Therefore, by appropriately foaming this polystyrene, it is possible to prepare a foam having a relative dielectric constant of about 2.5 or less according to the specific gravity difference. However, the relative dielectric constant of 1.0 to 2.0
In particular, in order to obtain a portion having a relative dielectric constant of 1.5 or more, the specific gravity must be about 0.4 or more, and the device will not be lightweight. Therefore, a material having another dielectric property is mixed in order to reduce the weight while utilizing the dielectric property of polystyrene. Here, when simply increasing the relative permittivity of the dielectric material, it is possible to use a metal powder, a metal foil (aluminum flake), or the like for the polymer material as described in the above cited document. Is not preferable because the value of the dielectric loss tangent also increases. In addition,
When a metal is used, it is not suitable because the amount of change in the relative dielectric constant with respect to a temperature change is large. On the other hand, dielectric ceramics having specific dielectric properties have an effect of increasing the relative dielectric constant by mixing with a heat-resistant foam. In addition, it has been found that, when used in the heat-resistant resin of the present invention, the conditions of the stable and high relative dielectric constant, low dielectric loss tangent, and weight reduction described above can be satisfied by mixing dielectric ceramics.

Furthermore, the heat resistance of expanded polystyrene is 80
C is the limit, and if the temperature is higher than this temperature, rapid dimensional shrinkage is observed, and a gap is generated between the layers. Therefore, it is not suitable for use in a spherical dielectric lens utilizing the principle of the Luneberg lens as described above. Therefore, in order to impart heat resistance to the styrene-based resin and ensure its dimensional stability, and to create a heat-resistant resin, the present inventors, styrene-based monomers, copolymers, or those of other resins The blend was studied. As a result, they have found that a blend of a styrene-based resin and a resin having excellent heat resistance such as a polyphenylene ether-based resin is most excellent.

Accordingly, the present invention relates to a dielectric foam in which dielectric ceramics are substantially uniformly dispersed in a foam made of a heat-resistant resin, wherein the relative dielectric constant is in the range of 1.0 to 2.0. A heat-resistant dielectric foam characterized in that it has a dielectric tangent of less than 0.005 and a specific gravity of 0.3 to 0.02 g / ml. Preferably, the heat resistant resin comprises 50 to 95 parts by weight of a styrene resin and 50 to 5 parts by weight of a polyphenylene ether resin. Further, the dielectric ceramic dispersed in the foam is mainly composed of a powder or a whisker, and the content of the dielectric ceramic is the heat-resistant resin and the dielectric constituting the foam. 5% by weight based on the total amount of ceramics
It is characterized in that it is at least 50% by weight.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION The dielectric ceramic used in the heat-resistant dielectric foam of the present invention includes barium titanate,
There are calcium titanate, magnesium titanate, strontium titanate, lead titanate and the like, and these can be used alone or in a suitable mixture. These ceramics are added in the form of powder or whiskers. Usually, it is preferable to use ceramic powder having an average particle size of 10 μm or less in consideration of dispersibility and ease of handling during granulation. In whiskers, the fiber diameter is 0.1-10μ.
m and a length in the range of about 1 to 100 μm can be used. The dielectric ceramics is used in an amount of 5% by weight to 50% by weight, preferably 2% by weight or less, based on the total amount of the heat resistant resin and the dielectric ceramics in the heat resistant dielectric foam.
The content is desirably from 0% by weight to 40% by weight. The ceramic is 50% by weight based on the total amount of the heat-resistant resin and the dielectric ceramic in the heat-resistant dielectric foam.
If the amount exceeds the above range, foaming becomes difficult, so that the obtained foam does not have a desired density, and the properties of the foam become brittle, so that it cannot be used. Conversely, if the addition to the ceramics is less than 5% by weight, the effect of improving the relative permittivity of the foam is not so large, and therefore the specific gravity cannot be reduced.

Next, the heat-resistant resin used in the heat-resistant dielectric foam of the present invention is a styrene-based blend or copolymer which utilizes the high relative dielectric constant and dielectric loss tangent of styrene, and styrene alone. Including special combinations of resin systems from Among them, the case where a polyphenylene ether-based resin was blended in order to improve the heat resistance of the styrene-based resin was most excellent. In particular, it is desirable that the heat-resistant resin is composed of a resin composed of 50 to 95 parts by weight of a styrene resin and 50 to 5 parts by weight of a polyphenylene ether resin. Further, a heat-resistant resin comprising 70 to 85 parts by weight of a styrene resin and 30 to 15 parts by weight of a polyphenylene ether resin is more preferable. In this blend, the polyphenylene ether-based resin contains 5
If the amount is less than parts by weight, the desired heat resistance (effect of increasing the melting point) with respect to polystyrene cannot be sufficiently obtained. Also, 5
When added in excess of 0 parts by weight, the heat resistance of polystyrene is improved, but foaming becomes difficult under ordinary foaming conditions, and the desired magnification cannot be achieved. In addition, the value of the dielectric loss tangent is undesirably deteriorated.

Further, as the base resin for the heat-resistant resin of the present invention, in addition to the above-mentioned blend, α-methylstyrene-styrene copolymer, α-methylstyrene-acrylonitrile copolymer, styrene-α-methyl Styrene-acrylonitrile terpolymer, styrene-maleic anhydride copolymer, copolymer with styrene-maleimide derivative, styrene-acrylate copolymer, styrene-methacrylate copolymer, styrene-acryl Alternatively, it is also possible to select a styrene copolymer such as a methacrylic acid copolymer. Even in this case, the total amount of styrene or α-methylstyrene, or the total amount of styrene and α-methylstyrene contained in all the resins is 1
It must be at least 50 parts by weight in 00 parts by weight. If the content of these resins is 50% by weight or less, the value of the dielectric loss tangent when formed into a foam becomes poor, and the desired value of 0.005 or less cannot be maintained. In the present invention, the “heat-resistant resin” is not limited to the main resin component (base resin) such as the above-mentioned blend or copolymer, but also includes various additives other than the foaming agent, modifiers, and auxiliary agents. It should be understood that it means that the composition optionally contains an agent as a component thereof.

In general, to prepare a heat-resistant resin which is a blend of the above-mentioned styrene resin and polyphenylene ether resin, a conventionally known technique, for example, 1) dissolving polyphenylene ether resin in styrene monomer and starting polymerization A method of obtaining heat-resistant resin particles by adding an agent and performing suspension polymerization in an aqueous system; 2) a method of kneading and extruding a styrene-based resin and a polyphenylene ether-based resin with an extruder to obtain heat-resistant resin pellets. Can be In producing the foam of the present invention, actually, heat-resistant foamed resin particles (pellets) obtained by impregnating a heat-resistant resin with a foaming agent can be used.
The method of impregnating a foaming agent into the above-prepared heat-resistant resin can also be performed by a conventionally known technique. For example, 3) heat-resistant resin particles obtained by suspension polymerization or heat-resistant resin pellets obtained by an extruder are used. 4) A method of impregnating a foaming agent in a suspension system; 4) After a styrene-based resin and a polyphenylene ether-based resin are kneaded in an extruder, a foaming agent is added to the extruder, the heat-resistant resin is impregnated, and foamed pellets And the like.

Further, in the present invention, the heat-resistant resin must contain dielectric ceramics uniformly.
For this reason, it is conceivable to add a large amount of dielectric ceramics to the suspension polymerization system of the heat-resistant resin. However, since this polymerization system becomes extremely unstable, the dielectric ceramics can be mixed in an extruder. desirable. Therefore, the method is as follows: (A) When kneading a styrene-based resin and a polyphenylene ether-based resin with an extruder, high dielectric ceramics are also mixed at the same time to obtain ceramic-containing heat-resistant resin pellets. To obtain heat-resistant foamed resin particles uniformly containing high dielectric ceramics by impregnating a foaming agent in a suspension system with a foaming resin pellet; (B) heat-resistant resin particles obtained by suspension polymerization, or from an extruder A method of impregnating the obtained heat-resistant resin pellets with a foaming agent in a suspension system (method of the above 3)) or in an extruder,
After the styrene-based resin and the polyphenylene ether-based resin are kneaded, a foaming agent is added to the extruder, and the heat-resistant resin is impregnated with the heat-resistant resin to obtain foamed pellets (the method of the above 4)). A method of kneading and extruding particles (pellets) and a high dielectric ceramic in an extruder to obtain a heat resistant foamed resin pellet in which the high dielectric ceramic is uniformly contained; (C) a styrene resin and a polyphenylene ether in the extruder High dielectric ceramics were also added at the time of kneading with the base resin, and after kneading them, a foaming agent was added into the extruder and impregnated with heat resistant resin to obtain foamed pellets. A method of obtaining heat-resistant foamed resin pellets; In addition, when a dielectric ceramic is mixed with a heat-resistant resin having a styrene-based copolymer as a base resin, it can be basically performed according to the above-mentioned methods A) to C).

The heat-resistant foamed resin particles (pellets) thus produced are usually subjected to sufficient drying treatment using a drier or the like, and then separated into particles having a predetermined particle size by a sieving machine. Next, for example, a blending agent such as a lubricant and an antistatic agent is mixed with the separated heat-resistant resin particles, and then,
Sealed and packed in drums and the like. Thus, the stored heat-resistant foamed resin particles are pre-foamed to any apparent specific gravity as necessary, and then, according to a conventional method, the pre-foamed particles are filled in a mold such as a mold, and then steam is used. By heating and foaming, the pre-expanded particles are fused to each other to form a foam molded article (foam) having a desired shape (dimension).

The above-mentioned styrene-based resin in the heat-resistant resin is not limited to a homopolymer of a styrene-based monomer, but may be a copolymer with another monomer (a styrene-based monomer in a proportion of 50% or more). Made using). The styrenic monomers include substituted styrenes such as α-methylstyrene, ethylstyrene, p-chlorostyrene, etc., in addition to styrene alone. The other monomer of the copolymer includes (meth) acrylates such as methyl methacrylate, methyl acrylate, butyl methacrylate, and butyl acrylate, and vinyl monomers such as acrylonitrile, vinyl toluene, and vinyl carbazole. No.
These may be used alone or in combination of two or more. Accordingly, the styrene resin used in the present invention includes, in addition to polystyrene, poly-substituted styrene such as poly-α-methylstyrene and poly-p-chlorostyrene, as well as styrene and substituted styrene (for example, α-methylstyrene). Examples include a polymer or a copolymer of styrene and a vinyl monomer (eg, acrylonitrile). More preferred styrene resins include polystyrene, polystyrene-butadiene copolymer, polystyrene-maleic anhydride copolymer, polystyrene-acrylonitrile copolymer, and graft copolymer of styrene. The styrene resin generally has a weight average molecular weight of 150,000 to 500,000.
0, more preferably 200,0 weight average molecular weight
High molecular weight styrenic resins having a number of from 00 to 300,000 are used, but it is also possible to partially blend lower molecular weight styrenic resins.

The styrene resin is not limited to a styrene resin newly synthesized by suspension polymerization.
A styrene-based resin regenerated by recycling (recycling) a styrene-based resin foam or the like is used. It is preferable to use the regenerated styrene resin as a heat-resistant resin raw material from the viewpoint of resource recycling and environmental protection. Therefore, in recent years, the use of recycled styrenic resins is rapidly advancing. In the regenerated styrenic resin, the styrenic resin and the styrenic resin foam which were distributed and used in the market were recovered, and then the foam was reduced in volume by melting or the like, and then recovered. The styrene-based resin is finely pulverized by cutting, and the pulverized material is put into an extruder and extruded to obtain pelletized styrene-based resin particles (so-called regenerated pellets). Also, in a heat-resistant resin particle production plant, general use of off-grade heat-resistant resin particles generated in the manufacturing process, that is, styrene resin foam having a particle size of less than 0.5 mm or a particle size exceeding 2 mm. By recovering heat-resistant resin particles that are not suitable for the required quality and extruding them, the regenerated pellets obtained can also be used as the regenerated styrene resin in the styrene resin in the present invention. Can be.

A polyphenylene ether resin as a blend component with a styrene resin is represented by the following formula I:

Embedded image (Wherein R ₁ and R ₂ independently represent an alkyl group having 1 to 4 carbon atoms or a halogen atom,
Represents the degree of polymerization. ) Represents a polyphenylene ether-based resin represented by the following formula:
6-dimethylphenylene-1,4-ether), poly (2,6-diethylphenylene-1,4-ether),
Poly (2,6-dichlorophenylene-1,4-ether), poly (2-methyl-6-ethylphenylene-1,
4-ether), poly (2-chloro-6-methylphenylene-1,4-ether), poly (2-methyl-6-isopropylphenylene-1,4-ether), poly (2,6-di-n) -Propylphenylene-1,4-ether), poly (2-bromo-6-methylphenylene)
1,4-ether), poly (2-chloro-6-bromophenylene-1,4-ether), poly (2-chloro-6)
-Ethylphenylene-1,4-ether) and the like. The polymerization degree n may be 10 to 5000, and is 50
If it exceeds 00, it is difficult to obtain a uniform heat-resistant foam, and 1
If it is less than 0, it is difficult to obtain a foam having the desired heat resistance.

In the heat-resistant resin of the present invention, the (volatile) blowing agent is usually used in an amount of 2 to 10 parts by weight, more preferably 2 to 5 parts by weight, based on 100 parts by weight of the styrene resin. . As the volatile foaming agent, for example, an aliphatic hydrocarbon such as propane, butane, n-pentane, isopentane, or hexane, or a halogenated hydrocarbon such as methyl chloride or Freon is used. These volatile foaming agents may be used alone or in combination of two or more. However, aliphatic hydrocarbons that do not easily cause environmental destruction are preferably used. Butane or pentane is more preferably used in view of the fact that the volatile foaming agent hardly escapes during the drying treatment of the foamable resin particles and that the amount of the foaming agent remaining when the foamed molded article is formed is small. Is most preferably used. Except for the case where off-grade heat-resistant resin particles already containing a foaming agent are used as a raw material, the styrene-based resin particles are impregnated with a volatile foaming agent.

Other various additives, modifiers and auxiliaries which can be added in appropriate amounts to the heat-resistant resin of the present invention as required include, for example, flame retardants, plasticizers, antistatic agents ,
Coloring agents, lubricants and the like. These agents are appropriately selected and used from those conventionally used in heat-resistant resin particles, and are added in the step of extruding a styrene resin or the step of impregnating a foaming agent. For example, examples of the flame retardant include hexabromocyclododecane, tetrabromobisphenol A, and pentabromomonochlorocyclohexane. Examples of the plasticizer include DO
P, DOA, DBP, coconut oil, palm oil and the like.

The dielectric foam according to the present invention, in which the dielectric ceramic is substantially uniformly dispersed in the foam made of a heat-resistant resin, has the above-mentioned problem "has a heat resistance of 80 ° C. or higher; The variation of the relative permittivity is small with respect to the change (−40 to 80 ° C.); the dielectric loss tangent is 0.005 or less in the range of the relative permittivity of 1.0 to 2.0; It is an excellent foam that satisfies all of the requirements for a dielectric foam, which is extremely lightweight, from 3 to 0.02 g / ml. Therefore, the heat-resistant dielectric foam of the present invention is a radar radio wave reflector,
For example, it can be used as a dielectric material for radar wave reflectors or antennas using a spherical dielectric lens based on the principle of the above Luneberg lens, and can be used for various other conventional applications using a dielectric material. it can.
The values of the relative permittivity and the dielectric loss tangent described in this specification can be measured by a cavity resonance method using a plate-like sample. That is, a sample having a thickness d is inserted into the cavity resonator, tuning is performed by the axial length change method, the sample to be measured is removed, and tuning is performed again by the axial length change method. Is measured. The relative permittivity and the dielectric loss tangent are calculated by applying the obtained s value and d value to a predetermined calculation formula (Keiji Suzuki, “Microwave Measurement”, High Frequency Measurement Complete Book)
No.4, Corona Publishing, 3rd edition, 1961, 180 pages-2
05).

[0025]

The present invention will be described in more detail with reference to the following examples, but these examples are not intended to limit the present invention.

Example 1 85 parts by weight of a polystyrene resin as a main raw material and 15 parts by weight of a polyphenylene ether resin, and an average particle diameter of 1 as a high dielectric substance
Into an extruder, 25 parts by weight (20% by weight) of barium titanate having a particle size of 0 μm or less is extruded in the form of a strand, followed by melting by heating and kneading with a screw, and then extruding the strand in a rotary pelletizer. Cut and pelletized. 5 g of 1500 gr of heat-resistant resin pellets containing the obtained dielectric material
Into an autoclave, and further add ion-exchanged water 25
00gr, 15 g of tricalcium phosphate and 0.15 g of sodium dodecylbenzenesulfonate as a dispersing agent were charged into the autoclave, and then, while stirring this mixture, 150 g of n-pentane as a volatile blowing agent (based on resin pellets). 10% by weight). Next, the temperature of the aqueous suspension in the autoclave was raised to 130 ° C., and this state was maintained for 6 hours to impregnate the resin pellets with n-pentane. After this treatment, the aqueous suspension was cooled to room temperature, and the resulting heat-resistant composite dielectric foamed resin particles were washed with water, dehydrated with a centrifuge, dried with a dryer, and then aged at 20 ° C. for 5 days at room temperature. The heat-resistant composite dielectric foamed resin particles thus obtained were pre-foamed with steam to have a bulk specific gravity shown in Table 1. After the pre-expanded particles are aged, they are put into a molding die of an automatic molding machine and molded, and are then molded into a 30 ×
A molded product of 30 × 5 cm was obtained. 50 parts of this molded product
A sample was cut out to a size of × 50 × 1.0 mm, and a relative dielectric constant and a dielectric loss tangent (tan δ) at 12 GHz were measured by a cavity resonance method using the plate-like sample. The results are shown in Table 1.
In addition, a sample having a size of 10 × 10 × 2.5 cm was cut out from the above-mentioned molded product, and was cut out on the 5th day after foam molding.
It was placed in a 5 ° C. oven and kept there for one week. After that, remove the sample from the oven, its vertical and horizontal length,
The thickness and the thickness were measured, and the change (shrinkage) from the size before being placed in the oven was determined as a dimensional change rate. It is recognized that the smaller the rate of dimensional change, the smaller the dimensional shrinkage of the foam molded article and the higher the heat resistance.

Example 2 In Example 1, the polystyrene resin as the main raw material was
Example 1 was repeated except that the parts by weight and the polyphenylene ether resin were changed to 30 parts by weight.

Comparative Example 1 In Example 1, 10 parts of polystyrene resin as a main raw material was used.
Example 1 was repeated except that the polyphenylene ether resin was not used as 0 part by weight, and barium titanate was not added as a high dielectric substance. Comparative Example 2 In Example 1, the polystyrene resin as the main raw material was changed to 10
The same procedure as in Example 1 was carried out except that the polyphenylene ether resin was not used as 0 parts by weight. Comparative Example-3 In Example 1, the main raw material polystyrene resin was changed to 40.
Example 1 was repeated except that the parts by weight and the polyphenylene ether resin were changed to 60 parts by weight.

The results are summarized in Table 1.

The following can be understood from the results shown in Table 1. 1) In the system containing 15 parts by weight of the polyphenylene ether resin of Example 1 and 20% by weight of barium titanate as a high dielectric substance, it is possible to secure a desired relative dielectric constant of 2.0 or more within a specific gravity of 0.3 or less. Yes, and the dielectric loss tangent is low. Further, the dimensional change rate in an 85 ° C. oven is also 0.2 to 0.3.
%, Which is a low value. 2) In the system of Example-2 containing 30 parts by weight of the polyphenylene ether resin and 20% by weight of barium titanate as a high dielectric substance, the specific gravity of 0.3 or less and the desired relative dielectric constant of 2.0 or more can be secured. Yes, and the dielectric loss tangent is low. Furthermore, the dimensional change rate in an 85 ° C. oven is also 0.1 to 0.2.
%, Which is a low value. On the other hand, 3) Comparative Example-1 is a system in which polyphenylene ether resin and barium titanate as a high dielectric substance are not added. Was a low value within 1.5. Although the value of the dielectric loss tangent is low, the dimensional change in an 85 ° C. oven is as large as 1.7 to 2.3%,
It has been found that use at this temperature causes large dimensional shrinkage. 4) Comparative Example-2 is a system in which the polyphenylene ether resin is not added, but the relative dielectric constant and the dielectric loss tangent are good, but the dimensional change in an 85 ° C. oven is 1. It was as large as 6 to 1.8%, and it was found that use at this temperature caused large dimensional shrinkage. 5) In Comparative Example-3, the polyphenylene ether resin was 60
Although it is a system with many parts by weight, the foaming power is low and the specific gravity is heavy. Further, since the amount of the polyphenylene ether resin is large, the value of the dielectric loss tangent is also high.

Example 3 102 parts by weight of heat-resistant foamed particles (including 85 parts by weight of a polystyrene resin and 15 parts by weight of a polyphenylene ether resin and 2 parts by weight as a blowing agent) already containing a blowing agent;
As a high dielectric substance, 67 parts by weight (40% by weight) of barium titanate having an average particle size of 10 μm or less is put into an extruder, which is melted by heating and kneaded with a screw, extruded in a strand form, and then extruded. The strand was cut by a rotary pelletizer to obtain a heat-resistant composite dielectric foamed resin pellet containing a foaming agent.
The pellets were evaluated from prefoaming to molding in the same manner as in Example-1. Table 2 summarizes the results.

Example 4 Heat-resistant foamed particles already containing a foaming agent (polystyrene resin 50 parts by weight, α-methylstyrene resin 30 parts by weight,
In an extruder, 20 parts by weight of an acrylonitrile resin, 102 parts by weight (including 2 parts by weight as a foaming agent) and 40 parts by weight (29% by weight) of barium titanate having an average particle diameter of 10 μm or less as a high dielectric substance were charged. The procedure was performed in the same manner as in Example 3 except that the sample was charged.

Comparative Example 4 Example 3 was carried out in the same manner as in Example 3, except that barium titanate as a high dielectric substance was not added.

The results are summarized in Table 2.

From the results shown in Table 2, the following can be understood. 1) Example-3 is an example in which 40% by weight of a high dielectric material is kneaded into heat-resistant foamed particles having a composition of 85 parts by weight of a polystyrene resin and 15 parts by weight of a polyphenylene ether resin as a base resin. A relative dielectric constant of 2.11 was shown at 0.18. Also, the value of the dielectric loss tangent satisfied 0.005 or less, and the dimensional change at 85 ° C. was small. 2) In Example-4, 50 parts by weight of polystyrene resin, α-
In this example, 29% by weight of a high dielectric material is kneaded into a heat-resistant foam made of a terpolymer of 30 parts by weight of a methylstyrene resin and 20 parts by weight of an acrylonitrile resin as a base resin.
The specific dielectric constant was 2.00 at a bulk specific gravity of 0.20. Also, the value of the dielectric loss tangent satisfied 0.005 or less, and the dimensional change at 85 ° C. was small. 3) On the other hand, Comparative Example-4 is a system in which a high dielectric material was not added to heat-resistant foamed particles having a composition of 85 parts by weight of polystyrene resin and 15 parts by weight of polyphenylene ether resin as a base resin. Although the value of the dielectric loss tangent was low and the dimensional change was small, even when the bulk specific gravity was 0.44, the relative dielectric constant was 1.
The value was as low as 56.

[0036]

As described above, according to the present invention, 80
The dimensional stability is maintained while maintaining the heat resistance of at least 100 ° C .; the change in the relative dielectric constant is small with respect to the temperature change (−40 to 80 ° C.); Having a dielectric loss tangent of 0.005 or less; specific gravity of 0.3 to 0.0
A lightweight and excellent dielectric foam of 2 g / ml can be provided. These dielectric foams are dielectric materials, especially dielectric materials intended for outdoor use, such as spherical dielectric lenses utilizing the principle of Luneberg lenses,
Can be used for various applications.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) C08K 7/00 C08K 7/00 C08L 25/04 C08L 25/04 101/00 101/00 H01Q 15/08 H01Q 15/08 // (C08L 25/04 (C08L 25/04 71:12) 71:12) F term (reference) 4F074 AA32 AA77 AC35 AE04 BA36 BA37 BA38 BA40 BA44 BA53 CA23 CA34 CA38 CC22X CC24Y CC47 DA02 DA22 DA47 4J002 BC031 BC041 BC061 BC071 CH072 DE186 EA017 EB027 FA066 FA086 FD116 FD327 GQ02 5G303 AA10 AB06 AB07 AB20 BA01 BA12 CA01 CA09 CB03 CB06 CB17 CB32 CB35 5J020 AA02 BB02 BD03

Claims (3)

[Claims] 1. A dielectric foam in which dielectric ceramics are substantially uniformly dispersed in a foam made of a heat-resistant resin, having a relative dielectric constant in a range of 1.0 to 2.0. And a dielectric tangent having a value of 0.005 or less and a specific gravity of 0.3 to 0.02 g / ml. 2. The heat-resistant resin is a styrene-based resin 50.
To 95 parts by weight and polyphenylene ether resin 5
2. The heat-resistant dielectric foam according to claim 1, comprising 0 to 5 parts by weight. 3. The dielectric ceramic dispersed in a foam is mainly composed of a powder or a whisker, and the content of the dielectric ceramic is the same as that of the heat-resistant resin constituting the foam. 2. The heat-resistant dielectric foam according to claim 1, wherein the amount is from 5% by weight to 50% by weight based on the total amount of the dielectric ceramics.