JP2000334769A - Electromagnetic wave shielding molded product and production thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic wave shielding molded product to which a conductive sheet is laminated so as to avoid a projection being a boss. SOLUTION: An electromagnetic wave shielding molded product P has such a structure that a conductive sheet 2 is forcibly torn at a boss part 3 by the pressure of the resin injected in a mold at a time of the molding of the electromagnetic wave shielding molded product to be not laminated to a resin molded article 1 to expose the resin molded article and is produced by a method wherein the conductive sheet is left in such a state that vacuum molding is not completed when the conductive sheet is subjected to vacuum molding by using an injection mold as a vacuum mold by utilizing an injection molding co- patterning method and the mold is clamped to inject a resin in a cavity in a flowable state to fill the cavity and, at this time, the conductive sheet is pressed into a recessed part becoming a boss by the pressure of the injected resin to be forcibly torn to expose the resin molded article without laminating the conductive sheet at the boss part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic wave shielding molded product and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, in a resin molded product such as a housing for storing an electronic circuit therein, electromagnetic waves leak to the outside or electromagnetic waves from the outside enter the housing as noise. To prevent this, measures are taken to shield electromagnetic waves, such as plating the surface of the molded product or attaching a conductive sheet to the surface of the molded product.

[0003]

However, in the electromagnetic wave shielding molded product obtained by the above electromagnetic wave shielding method,
In the case of a molded product having a boss, there are the following problems. In other words, in the case of plating, if the boss portion is also plated and has conductivity, conduction occurs between the screw for fixing the circuit board etc. to the molded product and the boss portion, and a problem occurs. It had to be masked and plated (or if the screw also touches the opposite front side). Further, from the viewpoint of pollution problems, it was desired to eliminate the plating step as much as possible. In the case where a conductive sheet is attached, for example, in the case of a molded product used for a housing of a personal computer, if the attached surface is a design surface on the front side, the conductive layer will be exposed to the outside. For this reason, a sheet having an appearance capable of giving a printed pattern is required for the conductive sheet, and its selection has been difficult. On the other hand, when sticking to the back side of the molded product, in order to stick the conductive sheet avoiding projections such as bosses, it is necessary to punch holes in the parts corresponding to the projections in advance by punching press etc. Met.

[0004] Therefore, an object of the present invention is to provide an electromagnetic wave shielding molded product in which a conductive sheet is laminated while avoiding projections even when a boss is provided on the back side. It is another object of the present invention to provide a method of manufacturing an electromagnetic wave shielding molded product that can easily laminate such an electromagnetic wave shielding molded product on a resin molded product without special measures such as making a hole in a conductive sheet in advance. .

[0005]

Therefore, in order to solve the above problems, in the electromagnetic wave shielding molded product of the present invention, an electromagnetic wave shielding molded product in which a conductive sheet is laminated on the surface of a resin molded product is provided. In the boss portion, the conductive sheet was not laid by the pressure of the resin injected into the mold at the time of molding the molded article and was laminated on the resin molded article, so that the resin molded article was exposed.

By doing so, it is possible to prevent a problem that the electromagnetic wave shielding molded product is electrically connected to the circuit board or the like at the boss portion. In addition, the conductive sheet does not require any work such as punching a boss portion with a punching press or the like in advance, and can be used even if the entire surface is a conductive sheet. In addition, since plating is not performed, it is not necessary to mask (plate) the boss portion, and there is no problem of pollution of the plating solution.

The method for producing an electromagnetic wave shielding molded article of the present invention is a method suitable for producing the above-mentioned electromagnetic wave shielding molded article, and comprises a conductive sheet laminated on a surface of a resin molded article. In the method of manufacturing a product, the conductive sheet is inserted between a pair of molds, and the molds are vacuum-molded as a vacuum mold, and then both molds are clamped by a simultaneous painting method of injection molding. The resin in the fluid state is injected and filled into the cavity to be solidified, and at the same time as the molding, the conductive sheet is closely adhered to the surface of the resin molded product and laminated. Vacuum forming is left incomplete, and the pressure of the injected resin forms the boss.The conductive sheet in the boss is pressed into the concave part of the boss and crushed. Without exposing the resin molding That was like.

By doing so, there is no need for a prior operation such as punching out a boss portion in advance with a punching press or the like as a conductive sheet to be used, and even if the entire surface is a conductive sheet, it can. Therefore, when a sheet in which a conductive layer is formed on a base sheet is used as the conductive sheet, it is not necessary to partially form the conductive layer by a printing method so as to avoid a boss portion, and the entire surface is formed by coating or printing. You can use just what you did. For this reason, it is not necessary to prepare a conductive sheet corresponding to each molded product, such as punching or partial printing corresponding to each boss portion, for each electromagnetic wave shielding molded product having a different shape. Of course, since plating is not performed, there is no need to mask (plate) the boss portion, and there is no pollution problem of the plating solution.

[0009]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a molded article for electromagnetic wave shielding and a method of manufacturing the same according to the present invention.

[Electromagnetic Shielding Molded Product] First, FIG. 1 conceptually shows a situation in which an electroconductive sheet is laminated on a portion other than the boss and a resin molded product is exposed at the boss portion in the electromagnetic wave shielding molded product of the present invention. FIG. FIG. 3 is a partially enlarged cross-sectional view showing one embodiment of a laminated portion of a conductive sheet in the molded product of the present invention.

As shown in FIG. 1, the electromagnetic wave shielding molded product P of the present invention
Is a molded product in which the conductive sheet 2 is laminated on the surface of the resin molded product 1. In the portion of the boss 3, the pressure of the resin injected into the mold when the conductive sheet 2 is molded into the electromagnetic wave shielding molded product. It is a molded article that is not laminated on the resin molded article 1 by being crushed by the resin but exposes the resin molded article 1.

(Conductive Sheet) And the conductive sheet 2
For example, as shown in FIG. 3 which is a partially enlarged cross-sectional view of the electromagnetic wave shielding molded product P of the present invention, a sheet in which a conductive layer 22 and, if necessary, an adhesive layer 23 and the like are laminated on a base sheet 21 is used. is there. The conductive layer 2 laminated on the base sheet 21
2 is one side of the base sheet 21 (as shown in FIG.
Side or the opposite side) or on both sides of the base sheet 21 in some cases. Further, the conductive sheet may be a sheet in which a conductive filler is added to a base sheet made of a thermoplastic resin to make the base sheet itself conductive.

Preferably, such a conductive sheet 2 has vacuum formability. Due to vacuum moldability, when laminating a conductive sheet to a resin molded product by the simultaneous painting method of injection molding, the conductive sheet may be broken at the boss part and the conductive sheet may be laminated on non-planar uneven surfaces at other parts It becomes possible.

In order to impart vacuum formability to the conductive sheet, for example, a thermoplastic resin sheet may be used as the base sheet. Examples of the thermoplastic resin sheet include polyolefin resins such as polypropylene, polyethylene, and olefin thermoplastic elastomers, or acrylic resins, vinyl chloride resins, ABS resins (acrylonitrile-butadiene-styrene copolymer), polystyrene, and polyester resins. Made of, polycarbonate etc.
A resin sheet of about 300 μm can be used.

(Conductive Sheet: Conductive Layer) The conductive layer 22 is
For example, it is formed as a layer in which a conductive filler is contained in a resin binder. The conductive layer is formed by printing (or coating) a conductive ink (or coating liquid) obtained by adding a conductive filler to a vehicle made of a resin binder or the like.
It may be formed on either one side or both sides. For example, an ink is used in which a conductive filler having a particle size of about 1 to 10 μm is added to a vehicle using a vinyl resin as a resin binder. The volume resistivity of the conductive layer is preferably 1 Ω · cm or less.

Known conductive fillers include, for example, carbon powder such as Ketjen black and graphite powder, or conductive metal powder such as gold, silver, aluminum, copper, tin and nickel. good. The shape of the conductive filler is scaly, foil, powder, or short fiber. The conductive filler is usually added in an amount of about 50 to 300 parts by weight based on 100 parts by weight of the resin component.

The resin used as the resin binder is, for example, vinyl chloride-vinyl acetate copolymer, vinyl chloride
Vinyl alcohol copolymer, vinyl chloride-vinyl acetate-
Maleic acid copolymer, poly (meth) acrylate,
Acrylic resin such as poly (meth) ethyl acrylate, poly (meth) butyl acrylate, methyl (meth) acrylate-butyl (meth) acrylate copolymer [(meth) acrylic acid is acrylic acid or methacrylic acid Meaning], a chlorinated polyolefin resin, a two-component curable urethane resin, or the like may be used. The solvent for the ink (or coating liquid) is selected according to the vehicle resin and the printing (or coating) method. As far as possible, a material that easily evaporates is preferred.

Incidentally, as the conductive layer 22, in addition to the above,
Thin films such as conductive metals such as gold, silver, aluminum, copper, tin and nickel, conductive metal oxides such as ITO (indium tin oxide), tin oxide and indium oxide are formed by a method such as vacuum evaporation and sputtering. It may be a layer formed on one or both sides of the base sheet.

(Conductive Sheet: Adhesive Layer) The adhesive layer 23 may be appropriately provided on the side of the conductive sheet which is in contact with the injection resin in order to improve the adhesion to the injection resin, if necessary. good. As the adhesive layer, for example, acrylic resin, chlorinated polyolefin resin such as chlorinated polypropylene, vinyl acetate resin, vinyl chloride-vinyl acetate copolymer, polyamide resin, polyisoprene rubber, polyisobutyl rubber, styrene butadiene rubber and the like Rubber, urethane resin,
Epoxy resin or the like is used.

(Resin Molded Product) The resin to be injection-molded as the resin molded product 1 is selected according to the required physical properties of the product, cost, and the like. For example, ABS (acrylonitrile-butadiene-styrene copolymer) resin, AS (acrylonitrile-styrene copolymer) resin, styrene resin, vinyl chloride resin, acrylic resin, polycarbonate resin, or polyethylene, polypropylene, polybutene, polymethylpentene, It is a thermoplastic resin such as an ethylene-propylene copolymer, an ethylene-propylene-butene copolymer, or a polyolefin resin such as an olefin thermoplastic elastomer. In the case of a thermoplastic resin, the conductive sheet is crushed at the boss portion in a state where heat is applied together with the pressure at the time of injection.

The resin to be injection-molded may be a curable resin as long as it can break the conductive sheet by the resin pressure at the time of injection. When the curable resin is a two-component curable resin, examples thereof include a urethane resin, an unsaturated polyester resin, and an epoxy resin. The curable resin is injected in a fluidized state at room temperature or appropriately heated. In the case of a curable resin, the conductive sheet is crushed at the boss portion by the pressure at the time of injection or the pressure and heat.

(Conductive Sheet of Boss) At the portion of the boss 3, the conductive sheet 2 is crushed by the pressure of the resin injected into the mold when the electromagnetic wave shielding molded product P is molded, and the resin molded product 1 It is not laminated and the resin molding 1 is exposed. Usually, on or around the boss 3, a conductive sheet whose sheet structure or original shape has been broken by being crushed is integrated with a resin molded product to form an electromagnetic wave shielding molded product. . The electromagnetic wave shielding molded article of the present invention having such a boss portion can be obtained by the following method for producing an electromagnetic wave shielding molded article of the present invention.

[Method of Manufacturing Electromagnetic Shielding Molded Product] The method of manufacturing the electromagnetic wave shielding molded product of the present invention is a method suitable for manufacturing the electromagnetic wave shielding molded product of the present invention, and utilizes the so-called injection molding simultaneous painting method. To manufacture.

As described in JP-B-50-19132 and JP-B-43-27488, a sheet is inserted between a pair of dies, and then both are painted. The mold is clamped, the resin in the fluid state is injected into the cavity formed by both molds, filled and solidified.At the same time as molding, the sheet is adhered and laminated on the surface of the resin molded product. This is a method for producing a resin molded product in which the sheet is opened and all the sheets are laminated, as a molded product with a picture.

The injection molding simultaneous painting method basically has various forms. In the production method of the present invention, preferably, the conductive sheet is heated and softened, and then vacuum-formed (including vacuum-pressure forming). The sheet is preformed in the following manner. As a result, the conductive sheet can be laminated on the uneven surface of the portion other than the boss while following the uneven shape, and electromagnetic wave shielding measures for the uneven surface such as the back side of the housing can be performed by simultaneous injection molding painting method. Becomes possible. In addition, in the preforming of the conductive sheet, it is preferable to use the mold for injection molding also as a vacuum forming die, but the conductive sheet preformed by a vacuum forming die different from the injection molding die is used for the injection molding die. It can also be transported and inserted inside. The conductive sheet used may be either a single sheet or a continuous strip. The injection molding machine used may be either a horizontal type or a vertical type.

Next, the method for producing an electromagnetic wave shielding molded product of the present invention will be further described in one form thereof.

First, as a sheet supply step, FIG.
As shown in FIG. 2A, when a mold composed of a pair of a mold Ma (core mold) and a mold Mb (cavity mold) is in an open state as shown in FIG. The conductive sheet 2 is supplied, and the conductive sheet 2 is pressed and fixed to the mold Ma by a sheet clamp (not shown) having a frame shape in plan view. In this case, if the conductive sheet has an adhesive layer, it is needless to say that the adhesive layer is on the injection resin side. Also,
The mold materials of the molds Ma and Mb are not particularly limited, and include iron, carbon steel,
Conventionally known mold materials such as metals such as various iron alloys or nonmetal materials such as ceramics may be appropriately selected and used.

Next, as a heating softening step, a hot plate (not shown) is inserted between the two dies from a retracted position outside the dies, and the conductive sheet is heated and softened. In addition, what is necessary is just to select and use a conventionally well-known thing suitably for a hot plate. For example, an electric heater embedded in a block made of metal or ceramic, or a sheet-like so-called sheet heating element made of heat-resistant resin or metal may be used. Further, the hot plate may be provided with a vent hole for blowing out compressed air for forming the conductive sheet into vacuum air. Further, the hot plate may be of a contact heating type in which heating is performed by conductive heat in close contact with the conductive sheet, or a non-contact heating type in which heating is performed by radiant heat without contacting the conductive sheet.

Then, as a stretching step, as shown in FIG. 2B, the conductive sheet 2 is drawn through a suction hole 5 provided in the mold Ma and stretched to form a vacuum, thereby forming the conductive sheet 2 into a mold Ma. Preforming along the cavity surface of Usually, the vacuum forming step includes at least the heat softening step and the stretching step.

FIG. 2C shows the state after the completion of the stretching step. As shown in FIG. 2C, in the present invention, in the stretching step, the conductive sheet 2 is formed along the cavity surface shape corresponding to the shape of the molded product. The conductive sheet 2 is not completely formed in the portion other than the concave portion 4 forming the concave portion 3. In order for the vacuum forming of the conductive sheet 2 to remain incomplete in the concave portion 4, no air vent such as a suction hole is provided in the concave portion 4, and after the entire periphery of the concave portion 4 comes into contact, the conductive portion becomes conductive in other portions. What is necessary is just to make it into a core-shaped shape in which an elastic sheet | seat is extended. In this case, as shown in FIG.
In the process from the state of (A) to the state of FIG.
The conductive sheet 2 contacts the cavity surface around the entire periphery of the concave portion 4 and covers the concave portion 4, so that the air in the concave portion 4 is suppressed from being exhausted. In the concave portion 4, vacuum forming remains in an incomplete state. Will be.

Next, as a mold clamping step, the hot platen is retracted from between both molds to a retracted position outside the mold, and then both molds are clamped. Next, as an injection step, a resin in a flowing state such as a heated and molten state is injected and filled into a cavity formed by both molds.

FIG. 2D shows that, in the injection step, the resin R in a flowing state injected from the gate 7 provided in the mold Mb (cavity mold) is formed by the clamped mold Ma and the mold Mb. This shows a state in which the inside of the cavity to be filled is being filled.

In the present invention, during this injection step,
The conductive sheet 2 existing in a state where vacuum forming is not completed so as to cover the concave portion 4 serving as a boss is pressed into the concave portion 4 by the resin pressure of the injected resin. The temperature has already dropped due to contact with the mold, etc.
The moldability at the time of the stretching step is not exhibited. For this reason, the conductive sheet 2 is forcibly pressed into the recess 4 and is torn. Accordingly, a structure in which the conductive sheet 2 is not laminated and the resin molded article 1 is exposed is obtained at the boss 3 portion of the magnetic wave shielding molded article.

Thereafter, in a solidification step, the injected resin is solidified by cooling, a curing reaction or the like. Next, as a removal process, after the resin is solidified by cooling or the like, the mold is opened and the molded product is removed to obtain an electromagnetic wave shielding molded product. If there is an unnecessary portion of the conductive sheet that has protruded around the molded product, trimming is appropriately performed.

[0035]

Next, the present invention will be described in more detail by way of examples.

[Example]

A conductive sheet 2 as shown in FIG. 3 was prepared by forming a conductive layer 22 and an adhesive layer 23 on one surface of an acrylic resin film having a thickness of 125 μm as a base sheet 21 in this order. The conductive layer 22 includes 40 parts by weight of graphite powder as a conductive filler, and vinyl chloride-vinyl acetate-vinyl alcohol copolymer 20 as a binder resin.
Parts by weight, solvent (1: 1 of methyl ethyl ketone and toluene)
A mixture of 40 parts by weight (weight ratio mixture) was applied to form a layer having a volume resistivity of 0.01 Ω · cm and a thickness of 20 μm. In addition, as the adhesive layer 23, a layer having a thickness of 3 μm was formed by gravure printing an ink made of a mixed resin of an acrylic resin and a vinyl chloride-vinyl acetate copolymer.

An electromagnetic wave shielding molded product using the above conductive sheet was tested in a notebook personal computer housing. The size of the housing is 300mm in width, 250mm in length, and 7m in thickness
m, a boss for mounting a component is formed in a hollow cylindrical shape having an outer diameter of 6 mm, an inner diameter of 2 mm, and a length (height) of 5 mm on the back side of the molded product, and protrudes at 10 places. Fig. 2
As shown in the sectional view of (D), it is a mold composed of a pair of a core mold (male mold) Ma and a cavity mold (female mold) Mb. In this case, the gate 7 is provided on the cavity side Mb, the cavity mold Mb is used as a fixed mold, and the conductive sheet is vacuum-formed with the core mold Ma and the core mold Ma is used as a movable mold. .

Then, using the conductive sheet, an electromagnetic wave shielding molded product was manufactured by the simultaneous injection molding and painting method. As shown in FIG. 2A, first, the conductive sheet 2 is inserted between both the core mold Ma and the cavity mold Mb in the mold opened state such that the adhesive layer side faces the injection resin side.
The sheet was pressed and fixed to the parting surface of the core mold Ma with a sheet clamp, and the sheet was supplied. Core mold Ma and cavity mold M
b was made of carbon steel. Next, a hot plate of an infrared radiation heating system is inserted between the molds, and after a heating softening step of heating the conductive sheet in a non-contact manner, the core mold is used as a vacuum forming mold, and the conductive sheet is preformed by vacuum forming. Then, the softened conductive sheet is formed into a shape along the cavity surface excluding the core-shaped concave portion 4 to complete the stretching step, and FIG.
(C) was set. The conductive sheet 2 is in a state where the concave portion 4 is covered so as to cover the concave portion 4 without being vacuum formed in the concave portion 4 portion.

Thereafter, as a mold clamping step, the hot plate was retracted to a retracted position outside the mold, and both molds Ma and Mb were clamped. Next, as an injection step, the ABS resin was injected into the cavity formed by both molds at a resin temperature of 220 ° C. and a mold temperature of 50 ° C. (both the core mold Ma and the cavity mold Mb). At this time, as shown in FIG. 2D, the conductive sheet 2 covering the opening of the concave portion 4 forming the boss is
The resin was pressed into the recess by the resin pressure at the time of injection of the resin and was broken.

After the resin is cooled and solidified in the solidification step,
In the take-out step, the mold is opened, and the conductive sheet 2 is laminated and integrated with the resin molded product 1 as shown in FIG. 1, and the resin molded product is exposed without being broken and laminated at the boss 3 portion. An electromagnetic wave shielding molded product P was obtained.

[0042]

According to the electromagnetic wave shielding molded product of the present invention, it is possible to prevent the electromagnetic wave shielding molded product from being electrically connected to a circuit board or the like at the boss portion. In addition, the conductive sheet does not require any work such as punching a boss portion with a punching press or the like in advance, and can be used even if the entire surface is a conductive sheet.
In addition, since plating is not performed, it is not necessary to mask (plate) the boss portion, and there is no problem of pollution of the plating solution.

According to the method for manufacturing an electromagnetic wave shielding molded product of the present invention, there is no need for a prior operation such as punching out a boss portion in advance by a punching press or the like as a conductive sheet to be used, and Can also be used as a conductive sheet. Therefore, when a sheet in which a conductive layer is formed on a base sheet is used as the conductive sheet, it is not necessary to partially form the conductive layer by a printing method so as to avoid a boss portion, and the entire surface is formed by coating or printing. You can use just what you did. For this reason, it is not necessary to prepare a conductive sheet corresponding to each molded product, such as punching or partial printing corresponding to each boss portion, for each electromagnetic wave shielding molded product having a different shape. Of course, since plating is not performed, there is no need to mask (plate) the boss portion, and there is no pollution problem of the plating solution.

[Brief description of the drawings]

FIG. 1 is a sectional view conceptually illustrating an electromagnetic wave shielding molded product of the present invention.

FIG. 2 is a conceptual diagram illustrating a method of manufacturing an electromagnetic wave shielding molded product according to the present invention.

FIG. 3 is a partially enlarged cross-sectional view showing an example of the electromagnetic wave shielding molded product of the present invention and a conductive sheet used for the molded product.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 resin molded product 2 conductive sheet 3 boss 4 concave portion (of cavity surface forming boss) 5 suction hole 6 parting surface 7 gate 21 base material sheet 22 conductive layer 23 adhesive layer Ma type (core type) Mb type ( Cavity type) P Electromagnetic wave shielding molded product R Injected resin in flowing state

Claims (2)

[Claims] 1. An electromagnetic wave shielding molded product in which a conductive sheet is laminated on a surface of a resin molded product, wherein at a boss portion of the molded product, the pressure of a resin injected into a mold at the time of molding the molded product at the boss portion. An electromagnetic wave shielding molded product that is not laid down on the resin molded product by being crushed by the resin and the resin molded product is exposed. 2. A method of manufacturing an electromagnetic wave shielding molded product in which a conductive sheet is laminated on a surface of a resin molded product, wherein the conductive sheet is inserted between a pair of molds by an injection molding simultaneous painting method, and the mold is inserted. After vacuum forming as a vacuum forming mold, both molds are clamped, the resin in the flow state is injected into the cavity formed by both molds, filled and solidified, and the surface of the resin molded product is electrically conductive at the same time as molding. When the sheets are adhered and laminated, the boss portion of the molded article is left incompletely formed by vacuum forming the conductive sheet, and the boss portion is formed in a mold concave portion that forms the boss by the pressure of the injected resin. A method for manufacturing an electromagnetic wave shielding molded product, wherein a resin molded product is exposed without laminating the conductive sheet at the boss portion by pressing and breaking the conductive sheet.