JPH0448697A - Electromagnetic shielding material and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain such electromagnetic shielding material that has an excellent adhesion, a high corrosion-resistant property, a high conductivity and a high electromagnetic shielding property by depositing a conductive film on the surface of an iron base material through a conductive metal thin film layer. CONSTITUTION:On the surface of an iron base material, a conductive film is deposited through a conductive metal thin film layer. For the conductive metal thin film layer, an electroless copper-plated layer or an electroless nickel- plated layer is desirable. The electroless nickel-plated layer is best suitable because it probides the electromagnetic shielding material with a high corrosion- resistant property and it enjoys an excellent adhesion with the conductive film.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an electromagnetic shielding material suitable for use in housings of electronic devices, and a method for manufacturing the same.

[Prior Art and Problems to be Solved by the Invention] In recent years, in order to prevent malfunctions caused by external noise, housings of electronic devices are usually made of conductive metal that provides corrosion resistance and conductivity on the surface of the metal base material. It is made of electromagnetic shielding material coated with adhesive paint.

This electromagnetic shielding material is manufactured by degreasing the surface of the metal base material, then chemically treating it with zinc phosphate, etc. to improve adhesion, and then applying conductive materials containing conductive materials such as conductive carbon black and conductive metal powder. It is manufactured by applying a synthetic paint and drying and curing it.

On the other hand, the conductivity and electromagnetic shielding properties of a conductive coating film are in a proportional relationship. Therefore, in order to exhibit high electromagnetic shielding properties, conductive paints containing a large amount of the conductive material are used. However, when such a conductive coating material is used, the adhesion between the base material and the conductive coating film is low and the corrosion resistance is poor, making it impossible to maintain high electromagnetic shielding properties over a long period of time. In particular, when the thickness of the conductive coating film is reduced in order to reduce the amount of expensive conductive paint used, the corrosion resistance is significantly reduced.

Therefore, an object of the present invention is to provide an electromagnetic shielding material that has excellent adhesion between a base material and a conductive coating, and also exhibits high corrosion resistance, conductivity, and electromagnetic shielding properties even when the film is thin. .

Another object of the present invention is to provide a method for producing an electromagnetic shielding material that can efficiently and inexpensively produce an electromagnetic shielding material having the above-mentioned excellent properties.

[Structure of the Invention] In order to achieve the above object, the present inventors have made extensive studies and found that (1) as in the past, iron-based When chemically treating the base material,
(2) Combining a conductive metal thin film and a conductive coating on the surface of an iron-based base material. The present inventors have discovered that even when the conductive metal thin film and conductive coating film are thin, not only the adhesion to the iron-based substrate and corrosion resistance but also the conductivity are significantly improved. completed. That is, the present invention provides an electromagnetic shielding material in which a conductive coating film is formed on the surface of an iron-based base material via a conductive metal thin film layer.

The present invention also provides a metal thin film forming step of forming a conductive metal thin film on the surface of an iron-based base material, and a metal thin film forming step on the surface of the conductive metal thin film.
Provided is a method for manufacturing an electromagnetic shielding material, which includes a coating step of applying a conductive paint.

The iron-based base material constituting the electromagnetic shielding material of the present invention includes:
Any steel material can be used as long as it has high mechanical strength and can be used to form housings, cases, etc. of electronic devices. As the iron-based base material, a steel plate-like material can usually be used.

A conductive metal thin film layer is formed on the surface of this iron-based base material. The conductive metal thin film layer can be formed of at least one of conductive metals such as aluminum, copper, silver, gold, magnesium, tungsten, molybdenum, zinc, cobalt, nickel, palladium, and cadmium. These conductive metal thin film layers may be formed by, for example, PVD or CVD methods such as vapor deposition and sputtering, but are preferably formed by electroplating, and more preferably by electroless plating. A preferred conductive metal thin film layer is an electroless copper plating layer, particularly an electroless nickel plating layer which provides high corrosion resistance and has excellent adhesion to the conductive coating film.

The thickness of the conductive metal thin film layer should normally be 0.1 μm or more, and the upper limit thereof is determined from the viewpoint of economy and productivity. When the thickness of the conductive metal thin film layer is less than 0.1 μm, it is difficult to impart high corrosion resistance. The preferred thickness of the conductive metal thin film layer is 0.5 to 10 μm1
In particular, it is about 1 to 5 μm.

This conductive metal thin film layer is coated with a conductive coating. The conductive coating film can be formed from a conductive paint containing a conductive material and a resin.

The above-mentioned conductive materials include conventional materials such as metal powders such as aluminum, gold, silver, copper, palladium, nickel, and alloys containing these metals; carbon materials such as conductive carbon black, graphite, and carbon fiber; Examples include powders, whiskers, and fibers coated with metals. At least one of these conductive materials is used.

Furthermore, resins include polymers capable of forming coating films, such as thermoplastic resins and thermosetting resins. Examples of thermoplastic resins include acrylic resins, styrene polymers, polyvinyl chloride, polyvinyl acetate, and ethylene.
Examples include vinyl acetate, polyester, polyvinyl acetal, polyamide, and polycarbonate. Examples of thermosetting resins include thermosetting acrylic resin, epoxy resin, epoxy ester resin, unsaturated polyester, alkyd resin, phenol resin, furan resin, urea resin, melamine resin, diallyl phthalate resin, polyurethane, polyimide, and silicone. Examples include resin.

At least one of these resins is used. Among these resins, thermosetting resins are preferred because of their excellent adhesiveness, corrosion resistance, and the like.

The ratio of the conductive material and resin in the conductive coating film cannot be defined as one type because the conductivity changes depending on the type of conductive material, etc., but the content of the conductive material is usually 5 to 80% by weight.
, preferably about 15 to 50% by weight.

The surface resistance value of the electromagnetic shielding material is, for example, 10-2 to 5×
102Ω, preferably about 10-2 to 1.5×102Ω. Particularly preferable electromagnetic shielding material is 10 to 102
It shows a surface resistance value of Ω, particularly about 10 −2 to 25 Ω.

When the conductive metal thin film layer and a conductive coating are combined, the electromagnetic shielding material exhibits high conductivity and corrosion resistance even if the conductive coating is thin. Therefore, the thickness of the conductive coating film is not particularly limited as long as it is within a range where a uniform coating film can be formed, for example, 5 μm or more, and the upper limit of the film thickness is determined from the viewpoints of economy and productivity. The thickness of the conductive coating is usually 5 to 100 μm, preferably 10 to 80 μm.
1 More preferably, it is about 15 to 50 μm.

Note that it is sufficient that at least one conductive coating film is formed on the conductive metal thin film, and the conductive coating film may be formed of two or more conductive coating films of the same type or different types. Good too. In addition, conductive coatings may contain additives such as plasticizers, dispersants, colorants, antioxidants, ultraviolet absorbers, fillers, etc., to the extent that they do not adversely affect the conductivity and properties of the coating. Good too.

The electromagnetic shielding material of the present invention only needs to have a conductive metal thin film layer and a conductive coating formed on at least one surface of an iron-based base material.

The electromagnetic shielding material of the present invention can be manufactured through a metal thin film forming step of forming a conductive metal thin film on the surface of an iron-based base material, and a coating step of applying a conductive paint to the conductive metal thin film.

Iron-based substrates are usually subjected to conventional pretreatment prior to plating. Examples of the pretreatment include degreasing treatment, pickling treatment, and surface polishing treatment.

The conductive metal thin film can be formed by conventional film forming means, for example, PVD or CVD methods such as vapor deposition and sputtering, but from the viewpoint of production efficiency, it is preferable to form it by plating. The plating process may be either an electroplating process or an electroless plating process, but the electroless plating process is preferable because it can form a uniform thin metal film with excellent adhesion easily and with high productivity.

This electroless plating treatment can be carried out by a conventional method, for example, by immersing it in an electroless plating solution containing at least the metal salt forming the metal thin film and a reducing agent. As the metal salt constituting the conductive metal thin film, conventional salts such as hydrochloride, nitrate, sulfate, hypophosphite, acetate, and alkali cyanide can be used. Among these electroless plating treatments, electroless copper plating, particularly electroless nickel plating, is preferred because it can form a highly conductive metal thin film easily and with good productivity. The nickel thin film obtained by electroless nickel plating has high conductivity and corrosion resistance, and also has excellent adhesion to the iron base material and the conductive coating film.

Examples of the reducing agent include hypophosphites, borohydride compounds, hydrazine, formaldehyde, glucose, and tartaric acid, and one or more of these reducing agents can be used. The electroless plating bath also contains conventional additives such as sodium acetate, propionic acid, lactic acid, ammonium chloride, ammonium sulfate, sodium malonate, ethylenediamine, sodium hydroxide, ED
TA etc. may be included.

Electroless plating baths include, for example, acidic baths with a pH of about 3 to 6;
A neutral bath with a pH of about 7, an alkaline bath with a pH of about 3 to 6, etc. may be used, and either a low temperature bath or a high temperature bath may be used.

The thickness of the metal thin film produced by electroless plating can be controlled simply by adjusting the immersion time in the bath.

The surface of the conductive metal thin film may be treated with chromic acid or its salt. When a conductive metal thin film is treated with chromic acid or its salt, corrosion resistance and long-term adhesion to the conductive coating film can be ensured.

In the coating process, a conductive paint is applied to the surface of the conductive metal thin film.

The type of conductive paint is not particularly limited, and may be either a water-based paint or a solvent-based paint, for example.

As described above, the conductive paint contains a conductive material and a resin. The appropriate content of conductive material in resin is
Although it varies depending on the type, usually resin/conductive material -20 to 95/80 to 5 parts by weight, preferably 50 to 85 parts by weight.
It is about 150 to 15 parts by weight. When the content of the conductive material is less than the above range, it is difficult to improve electromagnetic shielding properties, and when it exceeds the above range, the adhesion of the conductive coating film is likely to deteriorate. A preferred conductive paint is a baking type paint that has excellent adhesion and durability.

Note that water-based or solvent-based conductive paints contain solvents such as water, alcohols, aliphatic hydrocarbons, aromatic hydrocarbons, esters, ketones, and ethers, depending on the type. Furthermore, it may contain an antifoaming agent, a viscosity modifier, a surfactant, a leveling agent, the various additives mentioned above, and the like.

In the coating process, conventional coating methods such as dipping, roll coating, spray coating, etc. can be employed.

In the method of the present invention, since a conductive metal thin film is interposed between the iron-based base material and the conductive coating film, even if the conductive coating film is thin, it exhibits high corrosion resistance and conductivity. Furthermore, the intervening conductive metal thin film effectively exhibits the conductivity of the conductive paint. Therefore, an electromagnetic shielding material exhibiting high electromagnetic shielding properties can be obtained by applying the conductive paint once without increasing the film thickness by applying the conductive paint multiple times, resulting in high productivity. Moreover, since only a small amount of expensive conductive paint is used, it is economically advantageous. Therefore, in the coating process, 1
It is preferable to apply the conductive paint so that the coating film thickness that can be formed by multiple coatings, for example, the coating film thickness after drying, is about 10 to 50 μm, particularly about 15 to 45 μm.

Note that the same or different types of conductive paints may be applied multiple times on the conductive metal thin film. When coating a conductive paint with high corrosion resistance on a conductive metal thin film and then applying a conductive paint with high conductivity, for example, even if the coating thickness is as thin as 20 to 50 μm, high corrosion resistance can be achieved. It is possible to obtain an electromagnetic shielding material that exhibits excellent properties and has a significantly small surface resistance value. Moreover, when a thick conductive coating film of, for example, about 50 to 100 μm is formed by this method, the surface resistance value becomes even smaller. Examples of conductive paints with high corrosion resistance include paints containing thermosetting resins such as epoxy resins and epoxy ester resins. Examples include paints containing conductive carbon black and 20 to 30% by weight of nickel powder.

The conductive paint applied to the conductive metal thin film can be subjected to a drying or curing process to form a conductive coating film, depending on the type of the conductive paint. Drying and curing can be performed at a temperature of about room temperature to 250°C. In addition, when the resin contained in the conductive paint is a thermosetting resin, low temperature, e.g.
If the paint is cured at a temperature of about 100 to 170°C, high corrosion resistance can be imparted. Also, high temperature, for example, 170~
When the paint is cured at about 250°C, the surface resistance value of the electromagnetic shielding material tends to decrease.

Note that preferred embodiments of the present invention are as follows.

(A) A conductive coating film is formed on the surface of the iron base material via a conductive metal thin film layer with a thickness of 0.5 to 10 μm, preferably 1 to 5 μm, and has a surface resistance value of 10 to 5 × 10 Ω.
Electromagnetic shielding material.

(B) An electromagnetic shielding material in which the conductive metal thin film layer is an electroless plating layer.

(C) Electromagnetic shielding material which is a conductive metal thin film layer or an electroless copper plating layer, especially an electroless nickel plating layer.

(D) The thickness of the conductive coating is 5 to 1.00 g m, preferably 10 to 50 μm, and more preferably 15 to 45 g m.
Electromagnetic shielding material with μm.

(E) A metal thin film forming step of forming a conductive metal thin film with a thickness of 0.5 to 10 μm, preferably 1 to 5 μm, on the surface of the iron-based base material by electroless plating, and forming a conductive metal thin film on the surface of the conductive metal thin film. 1. A method for producing an electromagnetic shielding material, comprising a coating step of applying a magnetic paint once.

(F) The amount of conductive paint applied once in the coating process is 10 to 50 μm, especially 15 to 45 μm in film thickness after drying or curing.
A method for manufacturing an electromagnetic shielding material.

(G) The ratio of resin to conductive material is resin/conductive material -20 to 95/80 to 5 parts by weight, preferably 50 to 85 parts by weight.
A method for manufacturing an electromagnetic shielding material using a conductive paint in an amount of 150 to 15 parts by weight.

(H) A method for producing an electromagnetic shielding material using a conductive paint whose resin is a thermosetting resin.

(1) A method for producing an electromagnetic shielding material, in which a conductive paint with high corrosion resistance is applied on a conductive metal thin film, and then a conductive paint with high conductivity is applied.

(J) After applying a conductive paint containing a thermosetting resin on the conductive metal thin film, preferably sequentially applying the conductive paint by the method described in (1) above, and curing at a low temperature to obtain a film thickness of 20 ~
A method for manufacturing an electromagnetic shielding material that forms a conductive coating film of about 100 μm.

[Effects of the invention] Since the electromagnetic shielding material of the present invention has a conductive metal thin film layer, it has excellent adhesion between the iron-based base material and the conductive coating film, and has high adhesion even if the film thickness is thin. Exhibits corrosion resistance, electrical conductivity, and electromagnetic shielding properties.

Further, in the method for producing an electromagnetic shielding material of the present invention, the thickness of the conductive coating film can be reduced, so that an electromagnetic shielding material having the above-mentioned excellent properties can be produced efficiently and at low cost.

[Examples] The present invention will be described in more detail below based on Examples.

Example 1 5p of width 80mm, length 120mm and thickness 1.2 fields
After a CC steel plate was subjected to alkaline degreasing treatment, water washing, pickling, and water washing, electroless nickel plating treatment was performed under the following conditions to form an electroless nickel plating thin film with a thickness of about 3 μm.

(a) Composition of electroless nickel plating solution Nickel sulfate 30 g/J Sodium acetate 10 g/J Sodium hypophosphite 10
g/J (b) Bath temperature: 90°C (e) Plating time: 9 minutes Next, the electroless nickel plated thin film surface was sprayed with an epoxy ester resin-based conductive paint containing 5fr% of conductive carbon black in the solid content. An electromagnetic shielding material was produced by painting and baking in a drying oven at a temperature of 160° C. for 20 minutes to form a conductive coating film with a thickness of 40 μm.

The thickness of the conductive coating is determined by cutting the electromagnetic shielding material.
Measurement was made using a microscopic photograph of the cut surface.

Further, an electromagnetic shielding material was produced in the same manner as above except that the baking conditions were changed to a temperature of 180'' Cl2O for minutes.

Comparative Example 1 Width: 80 mm, length: 120 mm, and thickness: 1.2 mm
A 5 pcc steel plate was subjected to alkali degreasing treatment, washed with water, pickled, and washed with water, and then surface conditioned with a titanium colloid aqueous solution, and then treated with a commercially available zinc phosphate chemical conversion treatment solution under the following conditions,
A phosphate film was formed on the surface.

(a) Treatment temperature: 55°C <b> Treatment time: 7 minutes (c) Drying conditions: 80°C for 20 minutes Then, the surface of the phosphate-treated steel plate was spray-painted with the conductive paint used in Example 1, An electromagnetic shielding material was produced in the same manner as in Example 1.

Example 2 A 5 pcc steel plate was subjected to electroless nickel plating in the same manner as in Example 1, and the electroless nickel plated thin film surface was coated with epoxy containing 5% by weight of conductive carbon black and 15% by weight of nickel powder in the solid content. An electromagnetic shielding material was prepared by spray painting an ester resin-based conductive paint and baking it in a drying oven at a temperature of 160° C. for 20 minutes to form a conductive coating film with a thickness of 25 μm.

Further, an electromagnetic shielding material was produced in the same manner as above except that the baking conditions were changed to a temperature of 180'' Cl2O for minutes.

Comparative Example 2 An electromagnetic shielding material was produced in the same manner as in Example 2, except that the SPCC steel plate was treated with phosphate in the same manner as in Comparative Example 1.

Example 3 A 5 pcc steel plate was subjected to electroless nickel plating in the same manner as in Example 1, and the electroless nickel plated thin film surface was coated with acrylic material containing 3% by weight of conductive carbon black and 26% by weight of nickel powder in the solid content. Spray paint with resin-based conductive paint and bake in a drying oven at a temperature of 160°C for 20 minutes.
An electromagnetic shielding material was produced by forming a conductive coating film with a thickness of 30 μm.

Further, an electromagnetic shielding material was produced in the same manner as above except that the baking conditions were 180° C. for 20 minutes.

Comparative Example 3 An electromagnetic shielding material on which a conductive coating was formed was produced in the same manner as in Example 3, except that the SPCC steel plate was treated with phosphate in the same manner as in Comparative Example 1.

Example 4 A 5 pcc steel plate was subjected to electroless nickel plating in the same manner as in Example 1, and the electroless nickel plated thin film surface was spray-painted with the conductive paint used in Example 1, and after being left at room temperature for 10 minutes. The conductive paint used in Example 3 was spray coated. After that, it was baked in a drying oven at a temperature of 160°C for 20 minutes, and the lower layer had a film thickness of 20 μm and the upper layer had a film thickness of 20 μm.
An electromagnetic shielding material was produced by forming a conductive coating film with a total thickness of 40 μm.

Example 5 A 5 pcc steel plate was subjected to electroless nickel plating in the same manner as in Example 1, and the electroless nickel plated thin film surface was spray-painted with the conductive paint used in Example 1, and after being left at room temperature for 10 minutes. The conductive paint used in Example 3 was spray-painted. After that, it was baked in a drying oven at a temperature of 160°C for 20 minutes, and the lower layer had a thickness of 40 μm, the upper layer had a thickness of 40 μm, and
An electromagnetic shielding material was produced by forming a conductive coating film with a total thickness of 80 μm.

Then, the surface resistance values of the electromagnetic shielding materials obtained in each Example and Comparative Example were measured under the condition that the distance between the electrodes was 3 am.

Corrosion resistance was determined by cutting a 5aa long cut line that reached the substrate approximately at the center of the test piece, and using JIs Z 237.
A 100-hour salt water spray test was conducted in accordance with No. 1 and evaluated based on the following criteria.

Corrosion resistance evaluation criteria 10: No rust or blisters at all 9: Slight rust on the upper cut line 8: Part of the cut line has mackerel 7: Rust or blisters 1 mm wide from the cut line Occurrence 6: Rust or blisters occur within a width of 1.5 mm from the cut line 5: Rust or blisters occur within a width of 2 mm from the cut line 4: Rust or blisters occur within a width of 3 mm from the cut line 3: S from the cut line Rust or blisters occur in a width of 10 mm from the cut line 2: Rust or blisters occur in a width of 10 mm from the cut line 1: Rust or blisters occur on the entire surface The results are shown in the table.

(Hereinafter, blank space) As is clear from the table, the electromagnetic shielding material of each example was
The surface resistance value is significantly lower than that of the electromagnetic shielding material of the comparative example, and the material has excellent corrosion resistance.

In addition, regarding the electromagnetic shielding material of each example, salt water spray 2
After 4 hours, the adhesion of the coating film was measured with a spacing of 3 mm and a diagonal of 1.
When evaluated by six goban eyes tests, all of them were 1
The score was 6/16, indicating that there was no peeling and the adhesion was excellent.

Patent applicant: Kowa Kogyo Co., Ltd.

Claims (3)

[Claims] 1. An electromagnetic shielding material characterized in that a conductive coating film is formed on the surface of an iron-based base material via a conductive metal thin film layer. 2. The electromagnetic shielding material according to claim 1, wherein the conductive metal thin film layer is an electroless nickel plating layer. 3. A method for producing an electromagnetic shielding material, comprising a metal thin film forming step of forming a conductive metal thin film on the surface of an iron-based base material, and a coating step of applying a conductive paint to the surface of the conductive metal thin film. .