JPH0268999A - Conductive thermoplastic resin sheet and molding thereof - Google Patents

Abstract

PURPOSE:To obtain a see-through conductive thermoplastic resin sheet having low specific gravity, high mechanical strength, excellent electromagnetic wave shielding performance and excellent moldability through a simple production system with low cost by laminating a specific conductive unwoven fabric onto a basic layer, i.e., a thermoplastic resin film, then further laminating a protective layer, i.e., a thermoplastic resin film, thereon. CONSTITUTION:Conductive unwoven fabric mainly composed of conductive fibers and thermally fusible fibers is applied onto one or both faces of a basic layer, i.e., a thermoplastic resin film, then a protective layer, i.e., a thermoplastic resin film, is further applied thereon thereafter it is heated and pressure contacted under a temperature higher than the melting point of the thermally fusible fiber, thus producing a conductive thermoplastic resin sheet. After being heated to softening state, the conductive thermoplastic resin sheet is secured between a pair of molds A and B made of rubber D where the surface of at least one mold A has heat resistance, then the molds A, B are fitted each other to produce a conductive thermoplastic resin molding. The conductive fiber includes such as stainless copper fiber, copper or copper alloy fiber or metal or metal compound coated synthetic fiber.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a thermoplastic resin sheet and a thermoplastic resin molded article having electromagnetic wave shielding properties.

[Prior Art] In recent years, with the proliferation of various electronic devices such as O/11 units, medical equipment, consumer communication equipment, and computer equipment, interference caused by electromagnetic waves emitted from these devices has become a major social problem, and electromagnetic wave shielding has become a major social problem. There is a growing demand for

A method of imparting electromagnetic wave shielding properties to electronic equipment housings, etc. is to mold and process resin filled with a high concentration of conductive filler, and apply conductive paint to the inner wall of the resin molded product. There is a way to apply it.

[The invention tries to solve:! ! ! [Problem] However, the former requires a large amount of conductive filler, which results in problems such as increased specific gravity, decreased mechanical properties, increased cost, deterioration of appearance, and decreased moldability. A point occurs. In addition, the latter is caused by a decrease in electromagnetic wave shielding properties due to peeling of the paint film,
The problem is that the production process is complicated and productivity is low. In addition, since both of them are filled with conductive filler at a high concentration, there is a problem that they are not transparent and cannot be used in applications where confirmation of the contents is required.

The purpose of the present invention is to solve the above-mentioned problems, and to provide a conductive material that has excellent electromagnetic shielding properties with a simple production method, has a light specific gravity, is low in cost, has good mechanical strength and formability, and has transparency. An object of the present invention is to provide thermoplastic resin sheets 1 to 1 and molded products.

[Means to solve the problem]

As a result of intensive Q research in order to solve the above problems, the present inventors have found that conductive lJiM and thermofusible fibers are mainly formed on one or both sides of the thermoplastic resin film (△) which is the base layer.
Conductive fibers obtained by overlapping conductive nonwoven fabrics as fibers, and then overlaying a thermoplastic resin film (B) that serves as a protective layer in contact with the nonwoven fabrics and heating and pressing at a temperature equal to or higher than the melting point of the thermofusible fibers. The thermoplastic resin sheet and the molded product obtained by molding the sheet using a special method do not impair the original properties of the plastic at all, and can be provided with electromagnetic wave shielding properties using a simple production method, and furthermore, Because of its transparency, it was discovered that it can be used in applications where it is necessary to confirm the contents, and the present invention was achieved.

That is, the present invention has the following features: 1. 1t of thermoplastic resin as the base material layer! A conductive non-woven fabric whose main constituent fibers are conductive fibers and thermofusible fibers are overlaid on one or both sides of I(A), and a thermoplastic resin film (B ) conductive thermoplastic resin sheet obtained by heating and pressing at a temperature above the melting point of the thermofusible fibers.

2. A conductive nonwoven fabric mainly composed of conductive fibers and thermofusible fibers is superimposed on one or both sides of the thermoplastic resin film (A) that is the base layer, and a protective layer is further applied in contact with the nonwoven fabric. After heating the conductive thermoplastic resin sheet (19) to a softened state by overlapping the thermoplastic resin films (B) and heating and pressing them at a temperature higher than the melting point of the thermofusible fibers, the surface of at least one mold is heated. A conductive thermoplastic resin molded article that is fixed between a pair of male and female molds made of heat-resistant rubber, and then shaped by fitting the two molds together.

3. The conductive thermoplastic resin sheet according to item 1 above, wherein the conductive II fiber is a stainless steel fiber, a copper or copper alloy fiber, a metal or metal compound coated synthetic fiber, a metal or metal compound composite synthetic fiber, or a mixed fiber thereof. .

4. The amount of conductive fiber used per unit area is 15 to 50 g.
/y4, The conductive thermoplastic resin sheet according to item 1 above.

5. The conductive thermoplastic resin molded product according to item 2 above, wherein the heat-resistant rubber is silicone rubber, acrylic rubber, or fluororubber.

It is related to.

Examples of the thermoplastic resin used in the thermoplastic resin films (A) and (B) in the present invention include polyethylene, polypropylene, ethylene/vinyl acetate copolymer, and ethylene/vinyl acetate copolymer.
Polyolefin resins such as ethyl acrylate copolymer; Styrenic resins such as polystyrene, acrylonitrile-butadiene-styrene copolymer, acrylonitrile-styrene copolymer; Acrylic resins such as polymethyl methacrylate; 6-nylon, 6-row Nylon, 12-
Polyamide resin such as nylon, 6,12-nylon;
Polyester resins such as polyethylene terephthalate and polybutylene terephthalate; polyvinyl chloride resins,
Mention may be made of polycarbonate, polyphenylene oxide and mixtures thereof.

These resins include heat stabilizers, weather stabilizers, plasticizers, lubricants, slip agents, antistatic agents, charge transfer polymers, nucleating agents, flame retardants, tackifiers (petroleum resins, etc.), pigments, dyes, Inorganic fillers (glass fiber, mica, talc, etc.) and organic fillers (wood flour, pulp, synthetic fibers, natural fibers, etc.) can be blended depending on the purpose.

The thickness of the thermoplastic resin film (△) is not particularly limited and is 0.05
~5. It can be freely selected within the range of Os++.

Also, thermoplastic resin 11! There is no particular limit to the thickness of J(B), but if the conductive mi protrudes from the resin layer, there is a risk of electricity passing, so the thickness must be such that the conductive fibers do not protrude from the resin layer, and at least 0. It is desirable that it is .02m+ or more.

In addition, heat-melting fibers used in the conductive nonwoven fabric include acrylic $l fibers, polyamide fibers, polynisdel resins,
There are no particular limitations on the material as long as it is polyolefin fiber, polyvinyl chloride fiber, etc., or a mixture thereof, and can be heat-sealed to the thermoplastic resin of the base material. These fibers may be blended with flame retardants, colorants, antistatic agents, charge transfer polymers, etc., if necessary.

The heat-fusible fiber has a fiber length of 5 to 100 m and a fiber diameter of 0.5
About 10 deniers are preferably used.

Next, the conductive fibers used in the present invention include metal or metal compound composite synthetic fibers, metal or metal compound coated synthetic fibers, metal or metal compound coated carbon fibers, metal or metal compound coated glass fibers, metal fibers, etc. Mixed fibers are included. Among these, stainless steel fibers, copper or copper alloy fibers, metal or metal compound coated synthetic threads, metal or metal compound composite synthetic III fibers, and mixed fibers thereof are preferably used.

The fiber diameter of the conductive fibers is preferably in the range of 5 to 50 μm. If the fiber diameter of the conductive material is less than 5 μm, fiber clumps (nep) will occur, which is undesirable;
If it exceeds m, moldability deteriorates, which is not preferable.

The amount of conductive fiber used per unit area is 15 to 50 p.
/ It is desirable that it be within the range of the buttocks. If the amount of conductive VI&H used per unit area is less than 15 g/TIt, a sufficient electromagnetic wave shielding effect will not be obtained. Moreover, if it exceeds 50 g/Td, although the electromagnetic wave shielding effect is good, the transparency is significantly deteriorated, which is not preferable.

Next, a conductive nonwoven fabric is prepared from the conductive fibers and thermofusible fibers by a known method such as a binder method, a needle punching method, a hydraulic path joining method using spun bonding, a heat fusion method, a wet paper forming method, etc. !1 and the date ff115 (1/m or less, especially 20-1009/
Those within the range of TIt are preferably used.

In addition to the above-mentioned thermofusible fibers and conductive fibers, the conductive nonwoven fabric of the present invention may contain fibers with a high melting point or 1ilff, which does not exhibit meltability, as long as it does not impair the function of the conductive nonwoven fabric. do not have.

The conductive thermoplastic resin sheet of the present invention is formed by forming a thermoplastic resin film (A) as a base material, a conductive nonwoven fabric, and a protective layer using a known method such as an extrusion lamination method, a hot roll crimping method, or a hot plate pressing method. The three thermoplastic resin films (B) are superimposed and integrated into one.

At this time, it is necessary to select temperature conditions such that the thermofusible fibers constituting the conductive nonwoven fabric are completely melted and integrated with the base layer and the protective layer.

In the case of the extrusion lamination method, first, the thermoplastic resin film (A) of the base material layer is melt-kneaded in an extruder to a resin temperature of about 180 to 300°C, and extruded into a film through a T-die. Next, a conductive non-woven fabric is superimposed on the thermoplastic resin 1 (A) which is in a molten or softened state, and the thermoplastic resin 11 is further brought into contact with the non-woven fabric to form a retaining layer! Overlap J(B). At this time, the thermoplastic resin film (B) serving as the vIi layer may be formed into a film shape in advance, or may be a resin film in a molten state. After this, the thermoplastic resin film (A) or (B) is used to completely melt the thermofusible LLN, and at the same time it is pressed with a pair of rolls heated to about 30 to 120°C, and the base material is Integrate the protective layer with the conductive nonwoven fabric.

On the other hand, in the case of the hot roll crimping method, a solidified thermoplastic resin film (A>) and a conductive nonwoven fabric are superimposed, and a thermoplastic resin film (B) is superimposed in contact with the nonwoven fabric, and at the same time,
Alternatively, after overlapping, they are melted and fixed together using a hot roll heated to about 100 to 280°C.

Next, the conductive thermoplastic resin molded article of the present invention can be obtained by the following method.

After the conductive thermoplastic resin sheet is heated to a softened state using various known heating methods, it is inserted and fixed between a pair of male and female molds as shown in FIG. 1, and press pressure is 0.
Both molds are fitted and shaped at a pressure of 1 to 20 Kg/ci and a mold temperature of approximately 10 to 100°C. At this time, the material of the surface layer of at least one mold is a heat-resistant rubber that does not cause deformation, deterioration, deterioration, etc. due to the heat of the heated conductive thermoplastic resin sheet, such as silicone rubber, acrylic rubber, etc.
It is preferable to use fluororubber or the like, and the base material of the mold is made of wood, plaster, resin (thermosetting resin) casting, metal, etc., which has sufficient strength to withstand press pressure. In addition, the gap CL between the male mold and the female mold (when the male mold and female mold are fitted without inserting a conductive thermoplastic resin sheet) is determined by the drawing ratio of the mold (the depth of the molded product). Although it differs depending on the diameter of the product (or the value multiplied by the short side), it is desirable that the target thickness of the molded product be in the range of T≧CL≧ON.

By the way, when the above-mentioned conductive thermoplastic resin sheet is molded by vacuum forming or pressure forming, if the protective layer is inserted so that it is in contact with the mold, the conductive fibers will break into the base material at some corners of the molded product. There is a phenomenon in which it digs into the layer and causes cracks. On the other hand, if the base material layer is inserted so as to be in contact with the mold, the conductive fibers will break through the protective layer at some of the corners of the molded product, which is undesirable.

Further, the press molding method is also not preferred because the same phenomenon as the vacuum molding method and the pressure molding method occurs when the clearance between the male mold and the I is larger than the thickness of the conductive thermoplastic resin sheet.

〔Example〕

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

(Examples 1 and 2, Comparative Examples 1 to 4) On one side of a hard vinyl chloride sheet (width: 500 mm) with a thickness of 0.8 m, a vinyl chloride type am < Teviron made by Teijin@) with a fiber diameter of 2 denier and a fiber length of 51 m + was applied. Fiber diameter 8 μm, 1! Various conductive nonwoven fabrics (width: 450 mm) prepared by blending fiber length 35rR1R austenitic stainless steel fibers (Hiki Seisen Naslon) in the proportions shown in Table 1 and using acrylic resin as a binder were layered.

Next, a hard vinyl chloride film (width 500 m) with a thickness of 0.2 m was further layered on top of each nonwoven fabric, and then
It was passed between two hot rolls heated to 0° C., and 3R was fused and fixed to obtain a conductive vinyl chloride sheet. The electromagnetic wave shielding effect of the obtained sheet was actually measured, and the results are shown in Table 1.As is clear from the table 1, the conductive vinyl chloride sheet made of conductive non-woven fabric mixed with a specific amount of stainless steel fiber is excellent. It can be seen that it has a good electromagnetic wave shielding effect and also has excellent transparency.

In addition, the electromagnetic wave shielding effect is based on a sample size of 150 m x 150
Spectrum Analyzer TR
4172, a plotter 7470A, and a plastic shielding material evaluator TR17301. In addition, regarding transparency, Nippon Denshoku Kogyo @ turbidity meter (N
It was expressed as the total light transmittance measured using DH-200, based on ASTM D-1003).

[Table 1] (Example 3) Crystalline propylene homopolymer (VFR=22g/10m
1n) as the core component, propylene, ethylene, butene.
1 random copolymer (ethylene content 5.0% by weight, butene-1 content 4.5% by weight, VFR = 12'j/1 ol
In ) is considered a sheath component? ! Synthetic fiber H (fiber diameter 3 denier, all length 51M) 15g/Trt and austenitic stainless fiber (Hiki Seisen ■ Naslon, fiber diameter 8μm)
A conductive nonwoven fabric was obtained by a heat fusion method from 25g/g/fiber length (35 rm).

Next, crystalline propylene homopolymer (MFR-2,5
g/10m1n >99.45% by weight 1・3.2・4
-Bis(p-methylbenzylidene)sorbitol 0.2
5% by weight and tris(2,4-di-t-butylphenyl)
A polypropylene pellet containing 1% by weight of phosphite Oo, 0.1% by weight of tetrakis [methylene (3,5-di-butyl-4-hydroxy-hydrocinamate)] memene, and 0.1fffffi% of calcium stearate was made into a caliber. Melt and knead with a 65#I extruder, width 6
It was extruded into a film at a resin temperature of 250° C. through a T-die of 00 rM to obtain a conductive polypropylene sheet with a thickness of 1.2 m. Next, the conductive nonwoven fabric was layered on one side of the sheet, and a 50 μm thick polypropylene film was then placed in contact with the nonwoven fabric and fused together using two thermo rolls heated to 170°C. , a conductive polypropylene sheet was obtained.

The sheet is heated and softened and inserted between the molds shown in FIG.
The upper and lower molds were fitted together with a press pressure of 7 Ky/ci G to form a cylindrical tray with a diameter of 350 m and a depth of 80 m as shown in Fig. 2. At this time, silicone rubber (hardness 60) is used for the surface layer of the male mold, and the gap (CL) between the male mold and the female mold is 0.
．． 9 to 1.1#I.

Next, a box was made using the two obtained molded products, and a 400μ
A source that emits electromagnetic waves with an electric field strength of V/m was set up, and a die ball amplifier was placed 3 m away from the box to measure the electric field strength at this position, which was 82 μ/TrL. Ta. Therefore, it can be seen that the molded product of the present invention has an excellent electromagnetic wave shielding effect. In addition, the total light transmittance was 75%, and the transparency was also excellent.

(Comparative Example 5) The polypropylene sheet used in Example 3 was softened by heating and kept for 2! Vacuum forming was performed with the layer not in contact with the mold to obtain a cylindrical tray with a diameter of 350 HR and a depth of 8011 III. (GI type mold is used.) However, the conductive fibers are retained near some corners of the tray.
It broke through the a-layer and was exposed on the surface, making it unusable.

(Comparative Example 6) The polypropylene sheet used in Example 3 was heated and softened, and vacuum forming was performed in a state where the 3fJ was in contact with the mold to obtain a cylindrical tray with a diameter of 350s+ and a depth of 80m.

(A male mold was used.) However, near some corners of the tray, the conductive fibers dug into the base material layer, causing cracks.
It was not practical.

〔Effect of the invention〕

Thermoplastic resin 11 which is the base material layer! A conductive non-woven fabric whose main constituent fibers are conductive fibers and thermofusible fibers is superimposed on one or both sides of (A>, and a thermoplastic resin film (B) that serves as a protective layer is further superimposed in contact with the non-woven fabric. The conductive thermoplastic resin sheet obtained by heating and press-bonding at a temperature higher than the melting point of the heat-fusible fiber, and the molded product obtained by shaping the sheet using a special method, have excellent productivity, have a light specific gravity, It has good mechanical strength and formability, and has an excellent electromagnetic wave shielding effect as well as transparency, making it suitable for floppy disks and C.
It can be suitably used for D-IC card cases, CRT shielding materials, shield room/clean room partitions, electronic equipment housing shielding materials, etc.

[Brief explanation of the drawing]

Figure 1 shows a mold made of heat-resistant rubber placed on the surface of the base material.
A cross-sectional elevational view of a male and female mold pair consisting of a single-digit male mold and a female mold made of only FU material is shown. FIG. 2 is a perspective view of a cylindrical tray molded in Example 3.

Claims (5)

[Claims] 1. A conductive nonwoven fabric whose main constituent fibers are conductive fibers and thermofusible fibers is superimposed on one or both sides of the thermoplastic resin film (A), which is the base material layer, and a thermal layer is further applied to form a protective layer in contact with the nonwoven fabric. A conductive thermoplastic resin sheet obtained by laminating plastic resin films (B) and heating and pressing them at a temperature higher than the melting point of the thermofusible fibers. 2. A conductive nonwoven fabric whose main constituent fibers are conductive fibers and thermofusible fibers is superimposed on one or both sides of the thermoplastic resin film (A), which is the base material layer, and a thermal layer is further applied to form a protective layer in contact with the nonwoven fabric. After heating the conductive thermoplastic resin sheet obtained by overlapping the plastic resin films (B) and heating and pressing them at a temperature higher than the melting point of the thermofusible fibers to a softened state, the surface of at least one mold is heat-resistant. 1. A conductive thermoplastic resin molded article that is fixed between a pair of male and female molds made of rubber and then shaped by fitting both molds together. 3. 2. The conductive thermoplastic resin sheet according to claim 1, wherein the conductive fibers are stainless steel fibers, copper or copper alloy fibers, metal or metal compound coated synthetic fibers, metal or metal compound composite synthetic fibers, and mixed fibers thereof. 4. Claim 1, characterized in that the amount of conductive fiber used per unit area is 15 to 50 g/m^2.
The conductive thermoplastic resin sheet described in . 5. 3. The conductive thermoplastic resin molded article according to claim 2, wherein the heat-resistant rubber is silicone rubber, acrylic rubber, or fluororubber.