JPS63300596A - Electromagnetic wave shielding synthetic-resin molding - Google Patents

Abstract

PURPOSE:To form an electromagnetic wave shielding synthetic resin molding in which a knitted stitch corresponds to a transparent section by burying a conductive knitted fabric in a synthetic resin matrix to exhibit substantially regular knitting stitch. CONSTITUTION:A knitted fabric having stretchability obtained by knitting conductive fiber having 10<-4>OMEGA.cm or less of volume intrinsic resistivity is buried in a synthetic resin matrix. The fabric 2 having stretchability obtained by knitting the fiber 1 is obtained by knitting the fiber by a warp knitting or a circular knitting. To regulate the fabric, it is desired to design that the inner diameter becomes 5mm or less. When the stitch is excessively small, air bubbles remain to possibly lose its external appearance. The inner diameter of the individual stitch is desirably 0.1mm or more. Then, synthetic resin 4 becoming a matrix can use thermoplastic resin or thermosetting resin.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a synthetic resin molded product used for electromagnetic shielding.

More specifically, knitted conductive fibers with low specific volume resistivity are embedded in synthetic resin matrices, such as synthetic resin molded products, such as trays and casings, which are synthetic resins used for electromagnetic shielding of electronic devices housed in them. Regarding molded products.

[Prior art]

With advances in electronics technology, the use of plastics in electronic devices has become widespread. These are insulators that are easily charged, and electronic devices are susceptible to interference from static electricity and electromagnetic waves. To prevent these, especially as electromagnetic shielding measures, it is essential to incorporate shielding materials into the design of circuits and equipment, and to housing circuits etc. with shielding materials. 40 decibels (dB) or higher is generally required. Conventionally, as shielding materials, synthetic resins made of synthetic resins with electrical conductivity, so-called electrically conductive synthetic resins, have been used with some success. Conductive synthetic resins include short fibers such as carbon fibers and metal fibers, metal flakes, carbon black, etc., as conductive fillers, and are mixed into synthetic resins to create molded products, as well as the front and back sides of regular synthetic resin molded products. There are those in which a conductive layer is provided by metal plating, metal foil, conductive paint, metal vapor deposition, metal spraying, etc.

[Problem that the invention seeks to solve]

The kneaded molded product is generally formed by molding a conductive sheet obtained by injection molding or the like into a tray, a housing, or the like. However, in the injection molding method, for example, conductive fibers are easily cut by shearing force during the process of kneading them into molten plastic, so it is difficult to control the electrical contact between the conductive fibers, and in order to obtain the desired shielding effect, it is difficult to control the electrical contact between the conductive fibers. It is necessary to use a large amount of #a. As a result, there were drawbacks such as a decrease in strength and undesirable coloring of the molded product. Furthermore, since the container inevitably has an opaque appearance, it has been impossible to identify the electronic devices and the like housed therein from the outside. Furthermore, when a planar conductive filler kneaded sheet is heated and pressed to form it into a three-dimensional shape, there are areas where the stretch is uneven, and the contact of the conductive filler is likely to break.

Therefore, there is a drawback in that a single casing or the like inevitably has areas where the electromagnetic wave shielding effect is poor. In addition, when conductive layers are separately fixed to the front and back sides of a molded product, there is a risk that the conductive layer may peel off, causing a short circuit or breakage of the circuit of the product housed in the housing. Note that, as is well known, a wire mesh-like metal screen is used for electromagnetic shielding. Since this material is rigid and has no elasticity, it is difficult to combine it with a synthetic resin and uniformly bend and mold it into a desired shape, such as a housing.

[Purpose of the invention]

The present invention has been made to solve the above-mentioned problems, and is an electromagnetic wave shield in which a conductive knitted material that functions as an electromagnetic wave shield is embedded in a synthetic resin matrix with a regular weave. The purpose is to provide synthetic resin molded products for use. By using a transparent synthetic resin as the synthetic resin in this molded product, it is also possible to provide a synthetic resin molded product for electromagnetic shielding in which the mesh corresponds to the transparent portion.

[Means for solving problems]

The present inventor has discovered that when a stretchable knitted fabric made of metal fibers becomes larger due to stretching, the electromagnetic wave shielding effect tends to decrease, but if the size is kept below a certain level, the electromagnetic shielding effect is sufficient. It was discovered through experiments that the electromagnetic shielding effect was maintained.

Therefore, for example, the knitted material is stretched and fixed in a mold to adapt it to the shape of a desired casing, and then,
By casting and molding a desired synthetic resin material by a known method, a housing in which the knitted material is embedded in a synthetic resin matrix was obtained, and the present invention was achieved.

In the present invention, a stretchable knitted fabric made of conductive fibers having a specific volume resistivity of 10-'Ω·cm or less is embedded in a synthetic resin matrix, and in the synthetic resin matrix, the knitted fabric is This invention relates to a synthetic resin molded product for electromagnetic shielding in which is stretched.

Hereinafter, the present invention will be described in detail with reference to the drawings. 1st
The figure shows an example of the molded product of the present invention, a partially broken perspective view,
Figure 2 is a schematic sectional view taken along line A-A in Figure 1;
The figure is a plan view of the conductive knitted material, and FIG. 4 is a plan view of the stretched conductive knitted material.

In the present invention, the stretchable knitted fabric (also referred to as conductive knitted fabric) 2 made by knitting conductive fibers 1 refers to a fabric knitted from conductive fibers by warp knitting, circular knitting, or the like. Typical knitting methods include garter knitting, stockinette knitting, rubber knitting, and knitting knitting, which are generally collectively referred to as knitting, but any method may be used as long as it provides a knitted fabric with elasticity. This does not limit the knitting method. For example, stockinette knitting is usually knitted on either the front stitch or the back stitch, so the knitted fabric tends to curl, whereas in rubber knitting, the front stitch and the back stitch are knitted alternately. Because it is hard to curl, it is easy to handle. In order to significantly increase the stretchability of the knitted material, it is possible to use chemically or physically crimped conductive fibers, in other words, conductive fibers having stretchability in the fiber structure. In order to achieve this, it is not necessarily necessary to use conductive fibers as described above, but rather it is desirable to use a knitted fabric that is structurally stretchable, in other words, a knitted fabric whose stretchability depends only on the stitch structure. Conductive fibers with a stretchable fiber structure are usually crimped fibers that have been subjected to conductive processing, so stretching may break the network and reduce conductivity, or create a large number of microscopic voids between the fibers. This is because air bubbles tend to remain in the molded product since the molded product is encapsulated. The stretching ratio, which is an attribute of the knitted material, may be arbitrary.

In fact, it can be used in a state where it is stretched to the maximum, but it can also be used after being stretched to an extent that does not reach the maximum. In either case, the knitted material must be stretched so that the inner diameter of the knitted stitches in the molded product is 5 mm or less. This is because if the thickness exceeds 5 mm, the desired electromagnetic shielding effect cannot be obtained.

Therefore, in preparing the knitted material used in the present invention,
It is desirable to design so that the inner diameter of the stitches measured by a predetermined method is 5n+m or less. The inner diameter of the stitches was measured as follows. Inner diameter 5 cm, meat FX3m
Prepare a circular tube with a length of 15 cm.

Cover one cut end of the circular tube with a knitted material of an appropriate size, tighten it lightly and evenly to the extent that no wrinkles occur, and fix it to the circular tube with adhesive or the like. Next, in the other cut of the circular tube, an outer diameter of 5 cm and a height of 6 cm and 5 c+a were placed.

A steel cylinder weighing 1 kg is slowly lowered. Further q
The inner diameter of the knitted fabric at the bottom of the cylinder when it is stretched to its maximum extent by applying weight is measured using a microscope equipped with a gauge.

2 in FIG. 3 shows a knitted fabric made by knitting single-filament fibers using stockinette knitting. 3 in FIG. 4 is a plan view showing a knitted fabric (back stitch) obtained by uniformly stretching this knitted fabric by the method described above. The measurement is performed by measuring the length L1 and the width W of one stitch, and the longer one is taken as the inner diameter of one stitch. Figure 5 shows a stretched knitted fabric (front stitch) made by knitting monofilament conductive fibers using stockinette knitting, and an enlarged view of one stitch. , both horizontally indicate the center of the stitch.

In this way, we randomly measured 10 stitches,
The average value is taken as the inner diameter of the stitches of the knitted product. Rubber knits and other knitted fabrics are also measured according to the above method. The same applies to the representation of the inner diameter of the stitches of the knitted material embedded in the molded product.

If the stitches are too small, deaeration will not be sufficient during molding, and a large number of air bubbles will remain in the molded product, which may impair its appearance. Therefore, it is desirable that the inner diameter of each stitch of the knitted material present in the molded product is 0.1 ms or more.

In the present invention, the specific volume resistivity is 10-4Ω・cm
The following conductive fibers are used. Such fibers are mainly made of various metal fibers, metal-coated fibers, etc., but metal fibers that have a homogeneous composition, are hard to break, and have no risk of peeling are more suitable.

Metal fibers include steel fibers, stainless steel fibers, aluminum fibers, copper fibers, copper [t,
Bronze fibers are available, but stainless steel fibers, copper fibers, aluminum fibers, sinchu fibers, etc. are preferred because they are easy to handle. These metal fibers are generally produced in various diameters by pultrusion or the like, but any material that can be knitted may be used, and there is no restriction on the diameter. When used as a single fiber, the diameter is usually preferably 2 cm or less,
11 or less is more preferable. There is no need to use 2m111 or more. When used as a twisted yarn, the preferable range is 5 to 30 μmφ×10 to about 400 yarns, and the apparent diameter is 2
It is preferably 1 m1 or less.

In the present invention, a composite twisted yarn obtained by twisting an arbitrary number of single-filament conductive fibers and single-filament organic fibers each having a diameter of 12 μm, for example, can be used as the conductive fiber. This is a particularly preferred embodiment because it is easier to knit than when only conductive fibers are used (and the weight of the molded product of the present invention is lighter).The above effect can be achieved while maintaining the network of conductive fibers. In order to achieve a uniform pattern, it is desirable that the proportion of the conductive fibers be large. Fig. 6 shows an example of a knitted fabric (back stitch) knitted by stockinette knitting in this manner, where 1 indicates the conductive fibers and 5 indicates the organic fibers. Preferred organic fibers are recycled fibers and synthetic fibers with relatively high thermal deformation and star quality, such as acrylonitrile fibers, formalized polyvinyl alcohol fibers, aliphatic polyamide fibers such as nylon-6 and nylon-66, and polyester. Examples include fibers, aromatic polyamide fibers, aromatic polyamideimide fibers, and the like.

When metal-coated organic fibers are used, a metal such as nickel, copper, or aluminum is coated on the surface of the organic fibers by a method such as electrolytic plating, electroless plating, or vacuum deposition.
A conductive fiber coated with a thickness of about 2 to 3.0 μm can be used as the conductive fiber.

The synthetic resin 4 that becomes the matrix in the molded product of the present invention is
Any known thermoplastic resin or thermosetting resin can be used, and is selected depending on the molding method and the desired quality of the molded product. Any molding method can be employed as long as it can fix the knitted material in a manner that can immediately adapt to the shape of the mold. For example, ■ Manufacture the casing directly using the casting method.

■ Creating a primary sheet in which the knitted material is embedded, and then vacuum forming this secondarily to manufacture the casing.

etc. are possible. Further, in this case, the knitted material is usually embedded in the inner layer of the synthetic resin matrix, but it can also be molded so that it is embedded in the surface layer of the matrix. The molded product of the present invention has the above-described structure, and the electromagnetic shielding effect of the knitted product does not deteriorate due to embedding and molding. Furthermore, if a transparent synthetic resin is used, a molded product whose stitches correspond to transparent parts can be obtained.

[Experiment example]

The relationship between the size of the stitches and the electromagnetic shielding effect was tested. Stainless steel fiber twisted thread Naslon@) (Sewing thread, 12μlφ x 300 threads, apparent diameter 400μm 1 Volume specific resistivity 7.2xlO-'Ω' c
a, manufactured by Nippon Dansen Co., Ltd.) and commercially available copper wire (single thread diameter 16
0μm1 Volume specific resistivity 1.7XlO-”Ω・c+a)
Six types of rubber knitted fabrics with different inner diameters of the stitches were made using
The @ wave shielding effect was measured and the results are shown in Table 1. A plastic shield evaluator TR17302 manufactured by Atopan Test Co., Ltd. was used as the measuring device. The same measuring device was used for the examples described later.

Table 1 From Table 1, as the inner diameter of the stitch becomes thicker (the electromagnetic shielding effect decreases, but if it is 5 mm or less, it is 1001
It can be seen that an electromagnetic shielding effect of 30 dB or more can be obtained at 00O. Furthermore, it can be seen that if the specific volume resistivity of the conductive fiber is low, the electromagnetic shielding effect is not affected by its type or diameter. In addition, carbon fiber twisted yarn Besphite■
HM-40 (single yarn diameter 8μ, 9XlO-'Ω・C1+1
(manufactured by Toho Rayon) was untwisted to create a yarn with less than 500 twists, and an attempt was made to knit it, but it was difficult to knit it because it was rigid. Therefore, we made this a non-stretchable lattice network, and the inner diameter of the mesh was 51 and 2.5m+a.
We made different types and conducted similar tests. As a result, the inner diameter is 2.5
011's was 31 dB, but 5+am's was 25 dB. From these facts, it can be seen that the conductive fibers that can be used in the present invention must have a volume resistivity of 10 -4 Ω·Cat or less and can be knitted.

[Example 1] Stainless steel fiber twisted yarn Naslon ■ (apparent diameter of twisted yarn 400 ttm, single yarn diameter 12 μm x 300
A knitted fabric was made by rubber knitting using Nippon Sei Co., Ltd., which has a specific volume resistivity of 7.2 Spread it into a mold to make a forest-like molded product, stretch it, and inject epoxy resin (Dainippon Shikizai Co., Ltd., base resin Shi-2626 (L'lR/hardening agent L-2626 (LV) H = 100 + 30). After being left at room temperature (approximately 25°C) for 8 hours, it was cured at 100°C for 1 hour.

This knitted fabric exists in the molded product stretched almost uniformly, the fibers are not cut, and the inner diameter of the stitches is up to 5 +
u+, average 4 average 4ma+n were also good, and transparency was also good. Electromagnetic shielding effect is 3 at 1000MHz
1 dB, which was almost the same as the electromagnetic shielding effect of the knitted fabric itself described in the experimental example. This molded product was suitable as a casing for housing electronic components that could be viewed from the outside.

Example 2 A stockinette knit was made using the stainless steel strands described in Example 1. This was lightly stretched and placed flat in an aluminum vat, and then a transparent plastic material, ASTOL-AC, was placed on top of it.
E (g), made by The Strait Company, styrene monomer) is injected with a catalyst, cured, and has a thickness of 2
A polystyrene plate of mm was made. The inner diameter of the knitted stitches in this flat plate is 2 mm at maximum, and 1000 Ml-
1z had an electromagnetic shielding effect of 38dB. This flat plate was vacuum formed (air cushion method) to make a square tray. When knitted fabrics are molded, the inner diameter of the stitches is up to 3 mm.
It was spread out and embedded in a polystyrene matrix. This tray had an electromagnetic shielding effect of 35 dB, a smooth surface, and excellent transparency.

[Example 3] Commercially available copper wire (diameter 160 μm, volume resistivity 1.7X
A stockinette knitted fabric was made using IO-@Ω・cm). Spread this on a polyethylene sheet, add 1% by weight of heat-curing catalyst Niper BO (component benzoyl peroxide, manufactured by NOF) to unsaturated polyester liquid polymer ■ 9607 (manufactured by Ota Pharmaceutical Co., Ltd.) for molding.
Furthermore, pour in the resin liquid containing an isocyanate-based thickener.
This was covered with a polyethylene sheet and left at room temperature for several days to form a gel. Next, the front and back polyethylene sheets were peeled off, the resulting flat plate was placed in a mold, and heated and pressure molded at 130°C to produce a bowl forest-shaped polyester molded product. The average inner diameter of the stitches in this molded product is 2 mm. ! !
The magnetic shielding effect was 38 dB at 100,100 O.

[Function and effect of the invention]

(1) Even when the knitted material used in the present invention is embedded in a synthetic resin matrix, the contact between the conductive fibers does not change, so the electromagnetic shielding effect is not reduced by molding.

(2) In the molded product of the present invention, the synthetic resin matrix is continuous through the stitches, so there is no risk of peeling, and the electromagnetic shielding effect is stable over time.

(3) Since the knitted material expands and contracts structurally, it can be deep drawn, and when embedded in a synthetic resin matrix, a physically uniform molded product without wrinkles or undulations can be produced.

(4) Since the stitches can be made into transparent parts, stored items such as the casing can be seen through and identified.

(5) The knitted material has the effect of reinforcing the molded product.

[Brief explanation of drawings]

Figure 1 shows an example of the synthetic resin molded product of the present invention, a partially cutaway perspective view, Figure 2 is a sectional view taken along line A-A in Figure 1, and Figure 3 shows a conductive knitted product made of stockinette knit. FIG. 4 is a plan view of a stretched stockinette conductive knitted fabric, and FIGS. 5 and 6 are one stitch of the conductive knitted fabric. 1... Conductive fiber, 2... Conductive knitted material, 3...
Stretched conductive knitted material, 4...Synthetic resin matrix, 5...Organic fiber,
Shi...Vertical, W...Horizontal. Patent issued, applicant: Mishima Paper Co., Ltd. Figure 1, Figure 2rIl, No. 311! J Figure 4

Claims (4)

[Claims] (1) A stretchable knitted fabric made of conductive fibers with a specific volume resistivity of 10^-^4Ω・cm or less is embedded in a synthetic resin matrix, and in the synthetic resin matrix, the knitted fabric is A synthetic resin molded product for electromagnetic shielding characterized by a stretched object. (2) The synthetic resin molded product for electromagnetic shielding according to claim 1, wherein the conductive fibers are metal fibers. (3) The synthetic resin molded product for electromagnetic shielding according to claim 1, wherein the stitches of the knitted material in the synthetic resin matrix are transparent parts. (4) The synthetic resin molded product for electromagnetic shielding according to claim 1, wherein the inner diameter of the stitches of the knitted material in the synthetic resin matrix is 5 mm or less.