JP2007332419A - Method for forming electroconductive film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing an electroconductive film superior in electromagnetic shielding properties, adhesiveness and corrosion resistance on every substrate containing a resin or a glass fiber therein without cleaning the substrate and without applying a primer coat layer or an undercoat layer thereon, with great productivity and at a low cost. <P>SOLUTION: The method for forming the electroconductive film comprises the steps of: modifying the surface of a substrate made from an engineering plastic such as an ABS resin, a polycarbonate resin, a mixed resin thereof, a polyamide resin, and a mixed resin of the polyamide resin and a glass fiber, or the surface of a substrate made from glass, with an ion bombardment technique of irradiating the surface of the substrate with pulsed high-frequency plasma; and then forming the electroconductive film on the modified surface of the substrate by an ion-plating technique. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for forming a conductive film formed on the surface of various plastic molded articles and glass products.

  In order to give electromagnetic shielding properties and conductivity to plastic molded products and glass products, a method of mixing a conductive metal into these substrates, a method of applying a conductive paint to the surface of the substrate, a wet plating method There are known a method of forming a metal thin film on the surface of a substrate by a vacuum film forming method, a method of bonding a metal foil to a substrate with an adhesive, or the like.

  Among them, there is a problem that the shielding effect is low when the conductive metal is mixed into the base material or when the conductive paint is applied to the base material.

  In addition, the method of bonding the metal foil to the base material is difficult to bond when the base material has a complicated shape.

  Of the methods for forming a metal thin film on the surface of a substrate, electroless plating has been conventionally used as a wet plating method. In the electroless plating method, chromic acid etching, palladium catalyst addition, and the like are performed, so that the adhesion between the molded product and the thin film becomes strong. However, there are a problem of waste liquid treatment, a problem of a long treatment time, and a problem that plating is performed on both surfaces of a molded product.

  For this reason, it is common to select a method of forming a metal thin film on the surface of a molded product by a vacuum film forming method. For example, an aluminum film having a thickness of 2 μm to 3 μm is formed on the surface of the substrate, a copper film is formed on the first layer, and a nickel film or the like is formed on the second layer as a protective film for the first layer. By doing so, conductivity is imparted to the substrate.

  Examples of the vacuum film forming method include a vacuum deposition method, a sputtering method, and an ion plating method. Such a vacuum film-forming method is excellent in the surroundings of the film, and the conductive film can be formed on a substrate having a complicated shape.

  However, by this vacuum film formation method, a copper film was directly formed on an engineering plastic such as acrylonitrile / butadiene / styrene (ABS) resin, polycarbonate (PC) resin, mixed resin of ABS and PC, or polyamide resin. In this case, the initial adhesion between the substrate and the copper film is good, but there is a problem that the adhesion deteriorates after the moisture resistance test. Therefore, a product in which a conductive film is directly formed on these base materials has not been put into practical use.

  In order to improve the adhesion between the substrate and the film in the vacuum film formation method, a primer coat layer rich in functional groups is generally applied to the substrate, dried, and a conductive film is formed thereon. Has been done.

  However, the application of the primer coat layer increases the production process and accordingly requires treatment of waste liquid or waste gas, which is a main cause of an increase in product cost. .

  On the other hand, the following documents disclose that a high-frequency plasma is used to modify the surface of a substrate by plasma treatment or a metal thin film is formed.

  In Patent Document 1 (Japanese Patent Application Laid-Open No. 07-133361), in order to increase the adhesion of the electromagnetic wave shielding film, the surface of the ABS / PC substrate is wiped with a solvent, and then inert such as argon in a vacuum chamber. It is disclosed that the surface of a substrate is bombarded by high-frequency excitation plasma by introducing gas to form an aluminum film or a copper film and a protective film. However, in the case of a PC resin, a polyamide resin with few surface functional groups, or a mixed resin with ABS mixed with a PC resin, the film peels off at an early stage only by performing the bombardment process. It is necessary to apply a primer coat layer. Further, although the initial adhesiveness is good for the ABS resin, it has not yet been improved that the adhesiveness deteriorates after the moisture resistance test.

  In Patent Document 2 (Japanese Patent Laid-Open No. 07-70345), a primer coat layer made of a water-soluble paint is provided on the surface of a filler-containing plastic substrate such as glass fiber or carbon fiber, and then high-frequency excitation is similarly applied. A method of forming an aluminum film or a copper film by plasma is disclosed. However, in this method, although high-frequency plasma is used, the point that the primer is applied is the same as in the conventional case, and improvement in productivity and cost reduction cannot be achieved.

  Patent Documents 3 to 8 (Japanese Patent Laid-Open Nos. 06-145396, 06-157797, 06-240027, 06-240034, 06-240035, and 07 No. 7283) discloses that an aluminum film or a copper film is not washed on the surface of a plastic substrate in advance, and further, without providing a primer coat layer, while washing the surface of the substrate with high-frequency excitation plasma. It is disclosed to form a film. However, similarly, it can be applied to an ABS resin containing a large amount of surface functional groups and a polymer alloy thereof, but a base material made of PC resin or polyamide resin or a mixed resin of PC and ABS, which contains almost no surface functional groups, There is a problem that the film does not adhere, or a problem that the adhesion between the base material and the film is low.

  The techniques described in these documents are characterized in that high-frequency plasma excitation is performed at the time of film formation, but the adhesiveness is low, and there is no description of conditions for such high-frequency plasma excitation.

Note that the glass substrate is heated to 150 ° C. or higher to clean the surface, and the conductive film is formed by a vacuum film formation method with the surface energy of the substrate increased. Yes. However, similarly, a molded article having sufficient adhesion between the substrate and the film has not been obtained.
JP 07-133361 A Japanese Patent Laid-Open No. 07-070345 Japanese Patent Laid-Open No. 06-145396 Japanese Patent Laid-Open No. 06-157797 Japanese Patent Laid-Open No. 06-240027 Japanese Patent Laid-Open No. 06-240034 Japanese Patent Laid-Open No. 06-240035 Japanese Unexamined Patent Publication No. 07-007283

  In the present invention, these resins mixed with a base material made of ABS resin, PC resin or polyamide resin, glass fiber, etc. without washing the base material and without applying a primer coat layer or an undercoat layer. It is possible to form a conductive film excellent in electromagnetic wave shielding properties, adhesion and corrosion resistance on a substrate made of engineering plastic such as glass substrate or glass substrate with high productivity. The purpose is to enable cost reduction of products formed in the above.

  The method for forming a conductive film according to the present invention includes a base made of an engineering plastic such as an ABS resin, a PC resin, a mixed resin of ABS and PC, a polyamide resin, or a mixed resin of polyamide resin and glass fiber in a vacuum apparatus. The surface of the material or the surface of the substrate made of glass is irradiated with pulsed high-frequency plasma, and the surface of the substrate is modified by ion bombardment. A conductive film is formed by a plating method.

  In the pulsing of the high-frequency plasma, it is preferable that the pulse frequency is 0.5 kHz to 2 kHz and the duty ratio is 10% to 30%.

  As the ion source used for the ion bombardment, it is preferable to use at least one gas selected from the group consisting of argon, nitrogen and oxygen.

  In this case, it is preferable to exhaust the gas in the vacuum apparatus after the surface modification by the ion bombardment and before forming the conductive film.

  In forming the conductive film, it is preferable to use pulsed high-frequency plasma.

  Furthermore, it is preferable to form a copper film having a thickness of 0.5 μm to 1.2 μm as the conductive film.

  The method for forming a conductive film of the present invention includes a resin substrate, a resin substrate in which glass is mixed, or glass without washing the substrate and without applying a primer coat layer or an undercoat layer. A conductive film excellent in electromagnetic wave shielding characteristics, adhesion, and corrosion resistance can be formed on a substrate with high productivity. Thereby, the practical use by the low cost of the product by which the electrically conductive film was formed in the surface of a base material is achieved.

  In the present invention, the surface of a base material made of engineering plastics such as ABS resin, PC resin, mixed resin of ABS and PC, polyamide resin, or mixed resin of polyamide resin and glass fiber, or the surface of a base material made of glass In addition, when the conductive film is provided by the ion plating method, the substrate surface is subjected to ion bombardment that irradiates the surface of the substrate with pulsed high-frequency plasma without washing with a solvent or applying a primer coat layer. Then, a conductive film is formed.

  Typical resin substrates to which the present invention is applied are ABS resin, PC resin, mixed resin of ABS and PC, polyamide resin, or mixed resin of polyamide resin and glass fiber, but other engineering. The present invention can also be applied to a substrate made of plastic.

  As such engineering plastics, syndiotactic polystyrene, polyamide, polyacetal for crystalline resins, polycarbonate, modified polyphenylene ether for non-crystalline resins, polyphenylene sulfide, fluororesin, polyether ketone for crystalline heat-resistant super resins Examples of the liquid crystal polymer, polyether nitrile, and amorphous heat-resistant super resin include polysulfone, polyethersulfone, polyarylate, polyamideimide, polyetherimide, and thermoplastic polyimide.

  The primer coat layer was indispensable for improving the adhesion between the surface of the plastic molded product and the conductive film, but in the present invention, the surface of the base material is modified by ion bombardment to thereby form the conductive film and the base material. And the step of forming a primer coat layer becomes unnecessary.

  The present invention is characterized in that it is pulsed when the gas introduced into the vacuum apparatus is used as high-frequency plasma. By pulsing the high frequency plasma, the peak of the high frequency voltage rises, and the peak value becomes 1.5 to 2 times the input power. Furthermore, the peak of the inrush current for each pulse becomes even higher. Thereby, the modification effect with respect to the surface of the base material by the ion bombardment of high frequency plasma is remarkably improved.

  A frequency of 13.56 MHz is adopted as the high-frequency plasma.

  Further, in the pulsing of the high-frequency plasma, a preferable modified surface can be obtained by setting the pulse frequency to 0.5 kHz to 2 kHz and the duty ratio to 10% to 30%.

  If the frequency of the pulse exceeds 2 kHz and becomes too high, the peak value of the high-frequency voltage decreases, which is not preferable. If it is less than 0.5 kHz, the overall energy decreases, which is not preferable.

  Further, the pulse formation of the high-frequency plasma is not preferable if the duty ratio exceeds 30%, and the peak value of the high-frequency voltage decreases. If the duty ratio is less than 10%, the overall energy is reduced, which is not preferable.

  Ion bombardment ion species are generated using argon, nitrogen, oxygen, or a mixed gas thereof. The determination of which gas to use is specifically selected according to the type of substrate, the required adhesion, and the cost. When a copper film is formed on a substrate made of polyamide resin, it is particularly required to obtain a strong adhesion between the substrate and the copper film. In such a case, high purity oxygen gas, high purity are required. Nitrogen gas or a mixed gas of high purity oxygen and argon is used. However, from the viewpoint of cost, it is preferable to use argon gas in normal applications.

  In order to excite these gases at a high frequency in the vacuum apparatus, the gases are introduced into the vacuum apparatus and ionized at a high frequency generated from a high frequency generation power source. When the pulse is on, ion bombardment of positive ions with high energy promotes modification of the substrate surface. When the pulse is off, electrons and argon positive ions gathered near the surface of the substrate Attempts to leave, but argon ions are heavy, so they stay near the surface and gradually increase in density. As a result, a bombard roughening effect is obtained, and the surface of the substrate is activated by the excited ion species. This further increases the adhesion strength between the activated surface and the conductive film provided thereon.

  The time for performing ion bombardment is preferably about 3 minutes. If the time for ion bombardment is too short, the surface modification of the substrate will not be sufficient, and if it is too long, the temperature of the substrate will rise, and part of the surface may melt, and sufficient adhesion will be achieved. It may not be obtained.

  Moisture and released gases are released from the substrate by ion bombardment. Therefore, if the film is formed as it is after the ion bombardment, a fragile layer may be formed at the interface between the film and the base material. It is desirable to do. The exhaust time is preferably 1 minute to 2 minutes. If the exhaust time is too short, such as less than 1 minute, the harmful gas may not be exhausted sufficiently. If it exceeds 2 minutes, the productivity is lowered, which is not preferable.

  Thereafter, film formation of a conductive film such as copper is started. As a material for the conductive film, it is desirable to use copper having high conductivity and low cost. Also in this case, it is desirable to form the conductive film in a state where pulsed high frequency plasma is generated. By pulsing the high frequency output, the peak value of the waveform increases and the plasma density also increases. As a result, the cleaning effect of the base material surface by gas positive ions is enhanced, and the copper structure formed by the ionization of copper, which is a conductive film material, becomes a chain structure, and the film is cut into the base material. The adhesion between the substrate and the substrate is increased.

  For forming the conductive film, an ion plating method is used in which a high melting point target is dissolved by an electron gun, a metal is evaporated, and a film is formed on a substrate. By using the ion plating method, a conductive film can be formed at a high film formation rate over a wide area. Film formation can be performed by either a batch method or a continuous method.

  When a copper film is formed as the conductive film, the film thickness is set to a range of 0.5 μm to 1.2 μm. If the film thickness is less than 0.5 μm, the resistance value becomes high, sufficient electromagnetic wave shielding characteristics and conductivity cannot be obtained, the original structure of the film becomes rough, and the corrosion resistance is remarkably lowered. If it exceeds 1.2 μm, the electromagnetic wave shielding characteristics will be equivalent to that of metallic copper, but the film stress will be strong and will not peel off after initial deposition, but the possibility of peeling after the moisture resistance test will increase. In addition, it is not preferable to make the film thicker than necessary, because it takes time to form the film and may reduce the productivity.

  In order to use the conductive film as an electromagnetic wave shielding film, a nickel alloy or a tin alloy is formed as a protective film on the conductive film so as to have a film thickness of 0.05 μm to 0.5 μm. desirable. If the film thickness is less than 0.05 μm, the protective film has more pinholes and the corrosion resistance is reduced. If the film thickness exceeds 0.5 μm, there is no change in performance despite the increase in thickness, and the film formation time Is unfavorable because it increases the productivity and decreases the productivity.

Example 1
A base material for a cellular phone casing formed of a mixed resin in which ABS and polycarbonate were mixed by 50% each was used.

  The substrate was placed in an electron beam ion plating apparatus (AAIH-W36200SBT, manufactured by Shinko Seiki Seisakusho Co., Ltd.) without cleaning the surface and without applying an undercoat to the surface. The ion plating apparatus was equipped with an electron gun (manufactured by JEOL Ltd., JEBG-203G), and a circuit capable of pulse control was connected to a high frequency power source (JEOL Ltd., JST-16F power source). In the vacuum chamber of the ion plating apparatus, a metal jig for rotating and revolving the base material was disposed on the surface of the base material so as to form a uniform film.

Next, the vacuum chamber was evacuated to a vacuum degree of 5 × 10 ⁻³ Pa, and then argon gas was introduced to 3.2 × 10 ⁻² Pa.

  The frequency of the high frequency plasma is 13.56 MHz, the high frequency output is 1.0 kW, the high frequency plasma is pulsed so that the frequency is 1 kHz, and the duty ratio is 20%, and is discharged for 3 minutes. Argon ion bombardment was applied to the surface of the material.

  Next, ion bombardment was stopped and the released gas was evacuated for 1 minute.

  Subsequently, copper was ionized under the same high-frequency excitation conditions, and a copper film was formed as a first layer on the surface of the substrate. The film thickness was 0.9 μm.

  Next, a protective film made of an Sn-5 wt% Cu-7 wt% Cr alloy was formed as a second layer in the same vacuum chamber under the condition that high frequency excitation was not performed. The film thickness was 0.2 μm.

  Evaluation of the obtained conductive film was performed by visual inspection, initial tape adhesion test, tape adhesion test after 60 ° C. × 95% × 240 h moisture resistance test, and tape adhesion after 85 ° C. × 240 h heat resistance test. Tests, surface resistance measurements and 48 h salt spray tests were performed. As a tape adhesion test, a 1 × 1 mm cut is made on the surface of the conductive film with a knife, cellophane tape (CT1835, manufactured by Nichiban Co., Ltd.) is applied to 100 squares, and the tape is peeled off. A cross-cut tape test was conducted to check whether peeling occurred between the metal layer and the metal layer. The obtained evaluation results are shown in Table 1.

(Example 2)
A film was formed and evaluated in the same manner as in Example 1 except that a mixed resin in which polyamide resin and glass fiber were mixed by 50% each was used for the base material. The performance of the obtained conductive film was the same as that of Example 1.

(Example 3)
A glass substrate with an ITO film formed on a base material, covered with a stainless steel mask with a wiring width of 0.2 mm, the ion bombardment time was 5 minutes, and the film thickness of the first layer was 1.0 μm. The film formation was performed in the same manner as in Example 1, and the obtained conductive film was evaluated. The performance of the obtained conductive film was the same as that of Example 1. Further, in the initial tape adhesion test, there was no peeling of the wiring, so the standard for use as a copper wiring board was satisfied.

(Comparative Example 1)
Film formation was performed in the same manner as in Example 1 except that the high-frequency plasma was pulsed so that the frequency was 0.4 kHz. However, abnormal discharge occurred between the metal jig and the chamber during ion bombardment, and high-frequency power could not be input. In addition, the abnormal discharge caused damage to the film, resulting in scratches and burns.

(Comparative Example 2)
Except that the high-frequency plasma was pulsed so that the frequency was 5 kHz, film formation was performed in the same manner as in Example 1, and the obtained conductive film was evaluated. The result of the initial tape adhesion test was 100/100 and there was no peeling, but the result of the tape adhesion test after the moisture resistance test was 90 to 95/100, and peeling occurred partly.

(Comparative Example 3)
Film formation was performed in the same manner as in Example 1 except that the high-frequency plasma was pulsed so that the duty ratio was 10%. However, abnormal discharge occurred between the metal jig and the chamber during ion bombardment, and high-frequency power could not be input. In addition, the abnormal discharge caused damage to the film, resulting in scratches and burns.

(Comparative Example 4)
Except that the high-frequency plasma was pulsed so that the duty ratio was 30%, film formation was performed in the same manner as in Example 1, and the obtained conductive film was evaluated. The result of the initial tape adhesion test was 100/100 and there was no peeling, but the result of the tape adhesion test after the moisture resistance test was 90 to 95/100, and peeling occurred partly.

(Comparative Example 5)
Except for setting the ion bombardment time to 2 minutes, film formation was performed in the same manner as in Example 1, and the obtained conductive film was evaluated. The result of the initial tape adhesion test was 100/100 and there was no peeling, but the result of the tape adhesion test after the moisture resistance test was 90 to 95/100, and peeling occurred partly.

(Comparative Example 6)
Except for setting the ion bombardment time to 5 minutes, film formation was performed in the same manner as in Example 1, and the obtained conductive film was evaluated. The result of the initial tape adhesion test was 100/100 and there was no peeling, but the result of the tape adhesion test after the moisture resistance test was 90 to 95/100, and peeling occurred partly.

(Comparative Example 7)
Except that the evacuation time after ion bombardment was 0.5 minutes, film formation was performed in the same manner as in Example 1, and the obtained conductive film was evaluated. The result of the initial tape adhesion test was 100/100 and there was no peeling, but the result of the tape adhesion test after the moisture resistance test was 90 to 95/100, and peeling occurred partly.

(Comparative Example 8)
When the copper film was formed, film formation was performed in the same manner as in Example 1 except that the high frequency excitation was stopped, and the obtained conductive film was evaluated. The result of the initial tape adhesion test was 100/100 and there was no peeling, but the result of the tape adhesion test after the moisture resistance test was 90 to 95/100, and peeling occurred partly.

(Comparative Example 9)
The film that can be pulse-controlled was removed, and a high-frequency power source (manufactured by JEOL Ltd., JST-16F power source) was used as it was, and the high-frequency plasma was not pulsed. The obtained conductive film was evaluated. The result of the initial tape adhesion test was 95 to 98/100, and initial peeling occurred in part.

(Comparative Example 10)
Film formation was performed in the same manner as in Example 1 except that the rubber-based undercoat was applied in an amount of 0.4 to 0.5 μ without washing the ABS / PC base material and the high frequency plasma was not pulsed during the plasma and film formation process. And the obtained conductive film was evaluated. No peeling occurred in the initial tape adhesion test or the tape adhesion test after the moisture resistance test.

Claims (7)

  In the vacuum apparatus, the surface of the base material made of engineering plastic or the surface of the base material made of glass is irradiated with pulsed high-frequency plasma to modify the surface of the base material by ion bombardment. A method for forming a conductive film, comprising forming a conductive film on a surface of a modified substrate by an ion plating method.   The method for forming a conductive film according to claim 1, wherein the engineering plastic is an ABS resin, a polycarbonate resin, a mixed resin of ABS and polycarbonate, a polyamide resin, or a mixed resin of a polyamide resin and glass fiber.   3. The method of forming a conductive film according to claim 1, wherein in the pulsing of the high-frequency plasma, a pulse frequency is set to 0.5 kHz to 2 kHz, and a duty ratio is set to 10% to 30%.   The method for forming a conductive film according to claim 1, wherein at least one gas selected from the group consisting of argon, nitrogen, and oxygen is used as the ion source used for the ion bombardment.   5. The method for forming a conductive film according to claim 4, wherein the gas in the vacuum apparatus is exhausted after the surface modification by the ion bombardment and before the film formation. .   6. The method for forming a conductive film according to claim 1, wherein pulsed high-frequency plasma is used for forming the conductive film.   The method for forming a conductive film according to claim 1, wherein a copper film having a thickness of 0.5 μm to 1.2 μm is formed as the conductive film.