ELECTROMAGNETIC SHIELDING MATERIAL

BACKGROUND OF THE INVENTION

The present invention relates to an electromagnetic shielding material for absorbing electromagnetic energy.

The electromagnetic shielding material is used, for example, as a casing material of an electronic device to 1Q prevent the leakage of undesired electromagnetic waves generated in the noise source.

Conventionally, a composite material has been used as the electromagnetic shielding material, which has been prepared by dispersing metal or conductive mate- 55 rial is dispersed in a resin. In another case, the shielding material was manufactured by providing conductive coating to the surface of a plastic material by using zinc flame spraying or painting of conductive material.

The conventional shielding material prevents the 20 transmission of the electromagnetic waves by reflecting part of them and absorbing part of them using ohmic loss.

Accordingly, the conventional shielding material has the disadvantage that undesired electromagnetic waves 25 are confined in the electronic device and their intensities increase in the same. This phenomenon leads to an interference between each of the circuits of the electronic device, or to leakage of noise from the electronic device through a connector or air hole where shielding 30 is insufficient.

It is an object of the present invention to overcome the disadvantages of the prior art by providing a new and improved electromagnetic shielding material.

It is another object of the present invention to provide an electromagnetic shielding material with high electromagnetic energy absorbing capability.

According to an aspect of the present invention, there is provided an electromagnetic shielding material having electromagnetic absorbing property comprising a composition consisting of Mn-Zn ferrite powders, conductive carbon powders and organic high molecular weight compounds; the content of the Mn-Zn ferrite powders being in the range between 30 and 70 vol%; 45 and the composition having volume resistivity in the range between 102 and 10~] ohm-cm.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows curves between the concentration of Jq carbon black and the volume resistivity of the compositions,

FIG. 2 to FIG. 4 show the relationship between the reflection amount and transmission amount of electromagnetic waves and the frequency in the present shield- 55 ing material and the comparative examples.

DESCRIPTION OF THE PREFERRED 
EMBODIMENTS 

The electromagnetic shielding material with which go the present invention is concerned has electromagnetic absorbing property and satisfies the following conditions.

(1) The electromagnetic shielding material comprises the composition which consists of Mn-Zn ferrite pow- 65 ders, conductive carbon powders and organic high molecular weight compounds. The Mn-Zn ferrite powders and the conductive carbon powders are dispersed

35

in the organic high molecular weight compounds (matrix constituent).

(2) The content of the Mn-Zn ferrite powders to the composition is in the range between 30 and 70 vol%.

(3) The volume resistivity of the composition is in the range between 102 and 10-1 ohm-cm.

The organic high molecular weight compounds used for the composition of this invention may be synthetic resin or synthetic rubber. Among the synthetic resins, thermoplastic resin, thermosetting resin or modified thermoplastic resin is preferably used.

The thermoplastic resin used as the above organic high molecular weight compounds includes, for example, poly-a-olefin such as (low density, high density, or straight chain low density) polyethylene, polypropylene, propylene-ethylene block copolymer or random copolymer; styrene resin such as polystyrene, acryloni- trile-butadiene-styrene terpolymer, styrene-butadiene block copolymer or its hydride; acrylic resin such as polymethyl metacrylate; polyvinyl halide such as poly- vinyl chloride; polyamide such as nylon 6, nylon 66; saturated polyester such as polyethylene telephthalate, polybuthylene telephthalate; polyether such as poly- phenylene oxide; polysulfone; polyphenylene sulfide; polyvinylidene fluoride, polytetrafluoroethylene; a-ole- fin-vinyl monomer copolymer such as ethylene-vinyl acetate copolymer, ethylene-acrylate copolymer.

The thermosetting resin used as the above organic high molecular weight compounds includes, for example, epoxy resin, phenol resin, unsaturated polyester resin, melamin resin, polyurethane resin etc., and the mixtures thereof.

The modified thermoplastic resin or the mixture thereof may be also used as the above organic high molecular weight compounds. They are especially suitable for the composition of this invention on account of exhibiting excellent mechanical performance and imparting excellent electromagnetic shielding property to the composition. Such modified thermoplastic resin can be obtained by modifying the thermoplastic resin with unsaturated carboxylic acids or their derivatives. The typical examples of the modified thermoplastic resin are modified polyethylene with maleic anhydride, modified polypropylene with maleic anhydride, etc. And, the examples of the unsaturated carboxylic acids or their derivatives are monobasic carboxylic acids having at most ten carbon atoms and at least one double bond (e.g. acrylic acid, methacrylic acid), dibasic carboxylic acid having at most fifteen carbon atoms and at least one double bond (e.g. maleic acid), and anhydride of the dibasic carboxylic acid (e.g. maleic anhydride). Maleic acid and maleic anhydride are especially preferable among them. The content of the unsaturated carboxylic acids or their derivatives to the thermoplastic resin is in the range between 0.1 and 5 wt%, and more preferably in the range between 0.3 and 3 wt%.

The synthetic rubber used as the above organic high molecular weight compounds includes, for example, ethylene-propylene rubber, styrene-butadiene rubber, isoprene rubber, and the mixtures thereof.

The carbon powders used for the composition of this invention may be carbon black such as furnace black, thermal black, channel black, acetylene black, etc. Ketjen Black (manufactured by AKZO Co., Ltd.) is a typical example of such carbon powders.

ABSTRACT

It is disclosed that the properties of epoxy resins may be improved by incorporating therein at least one metal

selected from the group consisting of boron, molybdenum, rhenium, tungsten and zirconium. The selection of a particular metal atom for incorporation into the epoxy resin or a combination of these metals will depend on the specific resin properties desired. The metal containing thermosetting resin is obtained by reacting an epoxy resin and one or more metal compounds selected from the following group:

(a) the reaction product of a polyol containing more than two hydroxy groups with boric acid;

(b) the reaction product of a polyol containing more than two hydroxy groups and a metal complex which is the reaction product of tungsten carbonyl with pyrrolidine;

(c) the reaction product of a polyol containing more than two hydroxy groups and a metal complex which is the reaction product of rhenium carbonyl with pyrrolidine;

(d) the reaction product of a polyol containing more than two hydroxy groups and a metal complex which is the reaction product of molybdenum carbonyl with pyrrolidine; and

(e) zirconium acetate.

METAL ATOM CONTAINING EPOXY RESINS

BACKGROUND OF THE INVENTION

This invention relates to thermosetting epoxy polymers containing one or more types of metal atoms chemically bonded in the polymer chain.

U.S. Pat. No. 4,185,043 to Robert C. Shaffer discloses thermoplastic and thermosetting polymers which incorporate tungsten carbonyl and/or molybdenum carbonyl 10 metal atoms. The metal atoms are incorporated into the polymers by reacting a monomer or polymer containing at least one free carboxyl group with a reaction product of tungsten or molybdenum and pyrrolidine.

U.S. Pat. No. 4,256,868 to William L. Tarasen dis- 15 closes epoxy resins containing chemically bonded metal atoms obtained by reacting an epoxy resin with a metal complex which is a reaction product of tungsten carbonyl and/or molybdenum carbonyl with pyrrolidine.

20 SUMMARY OF THE INVENTION

It has been discovered that the properties of epoxy resins may be improved by incorporating therein at least one metal selected from the group consisting of boron, molybdenum, rhenium, tungsten and zirconium. 25 The selection of a particular metal atom for incorporation into the epoxy resin or a combination of these met- ... als will depend on the specific resin properties desired. Thus, in accordance with the present invention, a metal containing thermosetting resin is obtained by reacting 30 an epoxy resin and one or more metal compounds selected from the following group:

(a) the reaction product of a polyol containing more than two hydroxy groups with boric acid;

(b) the reaction product of a polyol containing more 35 than two hydroxy groups and a metal complex which is the reaction product of tungsten carbonyl with pyrrolidine;

(c) the reaction product of a polyol containing more than two hydroxy groups and a metal complex 40 which is the reaction product of rhenium carbonyl with pyrrolidine;

(d) the reaction product of a polyol containing more than two hydroxy groups and a metal complex which is the reaction product of molybdenum car- 45 bonyl with pyrrolidine; and

(e) zirconium acetate.

The reaction products set forth in the foregoing sub- paragraphs (b), (c) and (d) are themselves novel compounds. 50

DETAILED DESCRIPTION OF THE 
INVENTION 

Metals for incorporation into the epoxy resin system are prepared as prepolymers prior to their reaction with 55 the epoxy polymer, except for zirconium which is introduced into the reaction as zirconium acetate. The prepolymers are prepared by reacting a polyol containing more than two hydroxy groups, such as glycerol, eryth- ritol or sdrbitol with boric acid, a molybdenium car- 60 bonyl/pyrrolidine complex, a rhenium carbonyl/pyrrolidine complex or a tungsten carbonyl/pyrrolidine complex.

The metal carbonyl/pyrrolidine complex may be prepared by one of several methods found in the litera- 65 ture, e.g., an article by Fowles et al entitled "The Reactions of Group VI Metal Carbonyls with Pyrrolidine, Piperazine and Morpholine", Inorganic Chemistry,

Vol. 3, No. 2, February 1964, pages 257-259. The reaction product consisting of pyrrolidine-metal carbonyl complex is ground to a fine powder for subsequent reaction.

The amount of metal in the organometallic precursors may be varied by increasing or decreasing the amount of polyol used in the initial reaction with boric acid or the metal carbonyl/pyrrolidine complex. The maximum amount of boron is obtained when a 3:1 molar ratio of boric acid to glycerol is used. This ratio may be decreased from 3:1 in any increment to 1:3 boric acid:- polyol depending on the. percent boron desired in the prepolymer. In most cases, 160° C. is the desired reaction temperature.

The maximum amount of tungsten is obtained when a 1:2 molar ratio of tungsten carbonyl/pyrrolidine complex to polyol is used. The amount of tungsten may be decreased in any increment to a 1:4 molar ratio of tungsten carbonyl/pyrrolidine to polyol. In most cases, 190° C. is the desired reaction temperature.

The percentage of zirconium in the final epbxide is controlled by varying the amount of zirconium acetate reacted into the epoxy copolymerization. In the final copolymerization, the amount of zirconium acetate may range from 75% by weight down to 2% by weight depending- on the desired metal content.

The epoxy resins which are suitable for use in this invention are well known in the art. An example is the diglycidyl ether of Bisphenol A, normally formed as a condensation product of epichlorohydrin and Bisphenol A (i.e., bis(4-hydroxyphenyl)dimethylmethane). Condensation products of epichlorohydrin with other polyhydric alcohols may also be used such as the diglycidyl ether of Bisphenol F (i.e., 4,4'-dihydroxybiphe- nyl). Other suitable epoxy resins include those derived from epoxidized glycerin dialiphatic esters, l,4'-bis(2,3- epoxy-propoxy)benzene; l,3-bis(2,3-epoxy-propoxy)- benzene; 4,4'-bis(2,3-epoxy-propoxy)diphenyl ether; l,8-bis(2,3-epoxy-propoxy)octane; l,4'-bis(2,3-epoxy- propoxy)cyclohexane; 4,4-bis(2-hydroxy-3,4'-epoxy- butoxy)-2-chlorocyclohexane; l,3-bis(2-hydroxy-3,4- epoxy-butoxybenzene) and l,4-bis(2-hydroxy-4,5- epoxy-pentoxy)benzene.

A commercially available epoxy resin which has been successfully used in the practice of this invention is Epon 828, a viscous diglycidyl ether of bisphenol A having an epoxy equivalent weight in the range of 230-280 and a viscosity in the range of 15,000-22,500 centipoises at 25° C. Another commercially available epoxy resin which has been used is DOW DEN-438, a polyglycidyl ether of phenol-formaldehyde novolac having an epoxy equivalent weight in the range of 176-181 and a viscosity in the range of 35,000-70,000 centipoises at 52° C.

The epoxy resin is reacted with one or more of the metal compounds by combining the materials and heating the reaction mixture, preferably within the range of from about 75° to 150° C. The amount of metal compound which is reacted with the epoxy resin may vary widely, dependent on the desired properties of the cured resin. These include the percent metal desired in the final resin, specific atomic ratios of metals desired, char forming characteristics, oxidation resistance, energy absorption, desired cure temperature and other physical properties. Preferably, the final resin comprises from about 50% to in excess of 97% by weight epoxy resin. The metallic component of the resin is an integral