JP2000265087A - Method for forming metal pattern - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prepare a light-transmitting electromagnetic-wave shielding material at a low cost at a high productivity by a simple and convenient method by forming a pattern on a substantially transparent substrate from a conductive ink having a specified surface resistance at a specified film thickness. SOLUTION: After a pattern is formed on a transparent substrate from a conductive ink having a surface resistance of 1.0×103 Ω/(square) or lower at a film thickness of 15 μm, a negative photoresist layer with a thickness larger than that of the pattern is formed. Then, the pattern comprising the conductive ink is masked from the back side of the substrate having the photoresist layer and all the front side is exposed to light. After all the parts of the photoresist layer other than parts having the pattern formed thereon are cured, only the photoresist on the pattern comprising the conductive ink is developed and removed. Then, a metal pattern is formed by electrolytic plating on only the pattern comprising the conductive ink by using the cured resist as a plating- resistant resist.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a metal pattern which is effective in producing a light-transmitting electromagnetic wave shielding member particularly in the field of electronic materials and building materials.

[0002]

2. Description of the Related Art Recently, as an application of a fine metal pattern processing technique, an application to a transparent electromagnetic wave shielding film for a front filter of a plasma display panel has been proposed. Hereinafter, the prior art will be described using the electromagnetic wave shield film as an example.

Various flat display panels have been developed to realize a thin, large-screen television. Among them, a plasma display panel (hereinafter, referred to as a PD) has been developed.
P) is attracting attention. The reason is that the current mainstream CRT
PD that is difficult to thin and difficult to use with TFT liquid crystal
This is because P can easily achieve this. On the other hand, PDP
Since plasma discharge is used, the amount of electromagnetic waves radiated from the screen is larger than that of CRT or TFT, and VCCI
It is difficult to satisfy regulations. Forming a conductive layer on the front filter can be used to shield electromagnetic waves radiated from the screen. On the other hand, the filter for shielding electromagnetic waves must be excellent in transparency because it is mounted on the front surface of the PDP screen. As a result, a method using a transparent conductive film has been proposed, but in this method,
Although the transparency and the image quality are excellent, the shielding properties are inferior because the surface resistance is higher than that of a metal, resulting in poorer shielding properties. On the other hand, in the conductive fiber mesh method in which electroless plating is performed on polyester fiber, the resistance is low and the shielding property is excellent, but the fiber diameter Φ is limited to about 40 μm, and furthermore, it is necessary to make the line pitch coarser in the manufacturing process. Because it is difficult
There is a drawback that the aperture ratio of the mesh is low and the transparency is inferior.

[0004] As a method of solving these problems of achieving both the aperture ratio and the electromagnetic wave shielding property, a copper foil is bonded on a polyester film with an adhesive by using an adhesive.
By applying a resist film, exposing, developing, copper chemical etching, resist stripping photolithography process, a copper mesh with a narrow line width and a wide line pitch is formed on the base material, and then a hot adhesive is applied. An electromagnetic wave shielding material thermocompression-bonded to a transparent substrate has been proposed.

This method is superior to the conventional method from the viewpoint of achieving both the aperture ratio and the electromagnetic wave shielding property, since it utilizes the fine processing by the photolithography method. However, even this method has a problem that the cost of total raw materials is high and the cost is high due to poor production efficiency.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to produce a finely processed copper mesh electromagnetic wave shielding material having both the above-described aperture ratio and electromagnetic wave shielding properties at a low cost by a simple method with excellent productivity. It was made.

[0007]

SUMMARY OF THE INVENTION An object of the present invention is to provide a substrate having a thickness of 15 μm and a thickness of 1.0 × 10 ³ Ω / cm on a substantially transparent substrate.
□ After forming a pattern using a conductive ink having the following surface resistance, a negative type photoresist layer is provided on the transparent substrate in a state where the thickness is larger than the thickness of the pattern. After the entire surface is exposed from the back side of the provided transparent substrate using the pattern made of the conductive ink as a mask, and the photoresist portion where the pattern made of the conductive ink is not provided is hardened, the photoresist portion is made of the conductive ink. Only the photoresist on the pattern portion is developed and removed. Then, by using an electroplating method, a metal pattern is formed by using the cured resist as a plating resist and forming a metal pattern only on the pattern made of the conductive ink.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
In the present invention, the term “substantially transparent” in the term “substantially transparent substrate” means that light having a spectral sensitivity wavelength of the resist can be transmitted during backside exposure. Examples of the substantially transparent substrate include a glass substrate,
Various films and substrates can be used as long as they satisfy the above definition, such as PET, PEN, polycarbonate, acrylic resin, polyimide, PP, PE, PVC resin, cellulose ester, butyral resin film (or plate), Also, it can be colored.
On these substrates, an undercoat layer or a surface treatment such as a corona treatment or a glow treatment may be performed as necessary for the purpose of improving the adhesion to the conductive ink or the photoresist. Further, a hard coat layer or the like may be provided on the back surface of the base, if necessary, for the purpose of scratch resistance.

As an application example of the present invention in which a metal plating pattern is provided on a substantially transparent substrate, a transparent electromagnetic wave shielding film for a PDP will be described as an example. As described above, a high aperture ratio and high conductivity are required. . for that purpose,
A highly conductive mesh pattern having a narrow mesh line width and a wide line pitch width is required. For example, Hitachi Chemical Technical Report No. 32 (1999-1) P2
Nos. 1 to 24 describe the relationship between the copper mesh line width (μm) and line pitch width (μm), the aperture ratio (%), and the shielding performance (dB) in the above-mentioned method for producing an electromagnetic wave shielding film by the copper foil etching method. Have been. As a result, the line width was 20 μm, the line pitch was 250 μm,
Conductor copper film thickness 12μm copper mesh specification, 1 ~ 1000
Shielding property 50dB, visible light transmittance 72 in MHz range
% Of high-performance. The result is VCCI
It is a value from which class B can be obtained. The reason for this is that the volume resistivity of copper is very high at about 6.2 × 10 ⁻⁶ Ωcm, which is very high.

According to the present invention, after a pattern is formed on a substantially transparent substrate by using a conductive ink, a negative type photoresist layer is formed on the transparent substrate so as to have a thickness larger than the thickness of the pattern. Provided in a state, after that, from the back side of the transparent substrate on which the layer is provided, the entire surface is exposed using the pattern made of the conductive ink as a mask, and the photoresist portion where the pattern made of the conductive ink is not provided is cured. After that, only the photoresist on the pattern portion made of the conductive ink is developed and removed. Thereafter, a metal pattern is formed only on the pattern made of the conductive ink by an electrolytic plating method. Therefore, according to the method of the present invention, the technical point for producing the metal mesh method transparent electromagnetic wave shielding member is to form a conductive ink having a surface resistance capable of electrolytic plating and forming a mesh pattern with a narrow line width. It is to be. because,
According to the method of the present invention, the conductive ink pattern having a mask function, which is one of the functions of the conductive ink pattern, and the photoresist are in contact with each other, so that the entire surface is exposed from the back surface and cured during subsequent development. Having high resolution and good resist profile of the resist can be expected, and having good resolution and profile on the conductive ink pattern to perform electrolytic plating based on the plating resist This is because the formation of a metal plating pattern is expected.

The present inventor first examined the surface resistance at which electrolytic plating was possible using various known conductive inks. As a result, if the surface resistance of the conductive ink layer was 1.0 × 10 ³ Ω / □ or less, it was confirmed that various metal platings were possible by the electrolytic plating method. On the other hand, the value of the surface resistance depends on the thickness of the conductive ink.

As a method for forming a mesh pattern of the conductive ink, there are printing methods such as gravure printing and screen printing.
Alternatively, there is a photolithography method in which the conductive ink is made photosensitive, and a mesh pattern forming method by a printing method is preferable as a method capable of mass production at low cost. In particular, when the substrate is a plastic film, it is particularly preferable to form a conductive mesh pattern using a gravure printing method from the viewpoint of mass productivity. However, especially when a high-resolution pattern having a narrow line width of 20 to 30 μm is to be formed by a printing method, such as a mesh type transparent electromagnetic wave shielding member, the ink film thickness is large in order to obtain a predetermined surface resistance. In this case, it is difficult to obtain a high-resolution pattern with a narrow line width. For that purpose, the dry thickness of the ink layer is 15 μm or less,
10 μm is preferred. If it is less than this, stress may act between the conductive ink layer and the plated metal layer and the adhesion to the substrate may be impaired. However, when the metal pattern forming method of the present invention is used for a system having a wide line width such as a printed circuit wiring pattern, it is needless to say that it is not necessary to be 15 μm or less.

On the other hand, as described above, the surface resistance of the conductive ink layer depends on the thickness of the ink layer. For example, 10
^In order to obtain a surface resistance (Ω / □) of the order of ² Ω / □ with a film thickness of 10 μm or less, the volume resistivity is 10 μm.
It may be necessary to use a conductive ink of the order of ^-2 Ωcm.

On the other hand, the conductive ink is generally made of a conductive material such as fine metal powder such as silver, nickel, copper, tin and stainless steel, non-metal powder such as conductive carbon black and graphite, or aluminum powder. Fine-particle composite metal powder or the like whose surface is plated with silver or the like is used, and these conductive materials are provided in a state of being dispersed in an organic or inorganic binder. For example, many of these are provided by Acheson. Among them, the conductive ink using the metal powder has a high volume resistivity of the order of 10 ⁻³ Ωcm, and is suitable for the purpose of the present invention, but has a disadvantage that the raw material cost is high. On the other hand, if the conductive ink using a conductive carbon black and graphite, etc., raw material costs are cheap, but the dispersibility is good, the volume resistivity is generally less 10 ⁰ ~10 ^-1 Ωcm order and conductive Has disadvantages.

However, carbon-based conductive inks have recently been disclosed in JP-A-7-33883 and JP-A-7-8383.
53813, JP-A-7-41609, JP-A-1-101
373, JP-A-62-88261, JP-A-62-882
60, JP-A-64-56777, JP-A-54-3634
3, JP-A-62-199663, JP-A-63-1255
80, JP-A-1-184901, JP-A-2-28496
8. As described in JP-A-5-65366, the volume resistivity is 10 ⁻² Ωcm by using conductive ink in which a composite system of conductive carbon black and graphite is dispersed in a binder. An order of high conductivity has been obtained.

From the viewpoint of the light-shielding property of the conductive ink pattern for forming the subsequent resist pattern, whether it is a metal powder conductive ink or a carbon-based conductive ink,
Although basically sufficient, it is preferable to use a composite conductive ink material of conductive carbon black and graphite from the viewpoint of raw material costs. The high conductivity of the carbon composite conductive ink is generally achieved by combining carbon having a three-dimensional structure with graphite of tabular grains.
It is thought to be manifested by improving the connection between the tabular grains of graphite.

As specific examples of the conductive carbon used in the composite conductive ink of conductive carbon black and graphite, conventionally known conductive carbons such as acetylene black, Ketjen black and furnace black can be used. However, from the viewpoint of conductivity, Ketjen black is particularly preferred. Needless to say, it is also possible to use composite particles in which the surface of carbon black particles is coated with a metal. Regarding graphite, Nippon Graphite K.K. is available in the form of scale graphite, earth graphite, expanded graphite, specially treated graphite, calcined coke, exfoliated powder, and the like. K. S.E.K. K. Hitachi Powder Metallurgy K.K. K. , Chuetsu graphite K.K. K. Various graphites are commercially available from, for example, and any of them can be used, but use of scaly graphite, exfoliated graphite, expanded graphite and the like is particularly preferable.

As the binder to be added to the conductive ink composition having a metal or non-metallic fine particle conductive material used in the present invention, conventionally known various organic binders and inorganic binders are used.

As the organic binder, thermoplastic,
Either thermosetting or electromagnetic radiation curable may be used. For example, vinyl resins (vinyl chloride resins, (meth) acrylate resins, vinylidene resins, vinyl acetate resins, etc.), polyester resins, urethane resins, acrylonitrile resins, phenol resins, epoxy resins, polycarbonates Melamine-based resin, olefin-based resin, halogenated polyolefin, acetal-based resin, polyimide, polysulfone, polyphenylene oxide, cellulose-based resin, silicone-based resin, fluorine-based resin and the like, but are not limited thereto. These resins may be used in the form of an emulsion dispersed in water. Further, a thermosetting agent, a photocuring agent, or the like may be added to these compositions.

Examples of the inorganic binder include silica, tin oxide, aluminum oxide, zirconium oxide,
Glass frit (lead borosilicate glass, bismuth glass, or the like) or a conventionally known glass frit can be used, but is not limited thereto. These inorganic binders are generally used for the purpose of forming a vitreous film having high hardness and excellent abrasion resistance by baking the ink after forming a pattern of a conductive ink or a glass substrate. It is used when the purpose is to provide a conductive ink layer having good adhesion on the top.

In the present invention, the conductive ink composition comprises:
Usually, water or an organic solvent is used, but as is conventionally known, in the case of an electromagnetic radiation-curable conductive ink composition, a solvent is eliminated by using a liquid reactive oligomer or the like as a binder. Is also possible.

As the organic solvent, conventionally known solvents can be used according to the purpose. For example, hydrocarbons (toluene, xylene, etc.), chlorinated hydrocarbons (methyl, ethyl, chlorobenzene, etc.), ether alcohols (ethoxyethanol, methyl cellosolve, etc.), esters (acetate, etc.), alcohols (ethanol, etc.) ,
Isopropyl alcohol, etc.), ketones (cyclohexanone, methyl ethyl ketone, etc.), acid amides (dimethylformamide, etc.), but are not limited thereto.

When the carbon-based conductive ink is used, the mixing ratio of graphite and conductive carbon is in the range of 1: 9 to 9: 1 by weight, and more preferably in the range of 4: 6 to 8: 2. preferable. If the ratio of the carbon is more than the above range, the resistance tends to increase, and if the ratio decreases, the connection between the graphite particles deteriorates, and the resistance also tends to increase.

When the carbon-based conductive ink is used, the mixing ratio of the total amount of graphite and carbon and the binder is 80/20 to 20/80 in terms of the weight ratio of the total amount of the conductive agent / binder. 30 / 70-7
A range of 0/30 is preferred. If the amount of the conductive agent is less than this range, it is difficult to obtain the desired conductivity, and if the amount is too large, the film strength becomes weak. In addition, the mixing ratio when the metal-based conductive ink is used is the same.

The mixing ratio of the solvent depends on the method of coating, and is not particularly limited. For example, when printing is performed by a gravure method for mass production and a pattern is formed, the viscosity of the ink is 10%. It is preferable to mix so as to be ~ 100 cp. In the case of the screen printing method, the thickness is preferably 10 to 1000 p.

The conductive ink composition used in the present invention may further contain, if necessary, a leveling agent, a plasticizer, a dispersant, an anti-settling agent, a lubricant, a matting agent, and the like. Further, the conductive ink composition of the present invention is produced by uniformly dispersing the above-mentioned components using a usual dispersing machine such as a ball mill, a sand mill, a bead mill, a two-roll mill, and a paint shaker.

In the present invention, after a pattern is formed by the above-described method using a conductive ink, if necessary, it is heat-cured by a far-infrared ray or the like as conventionally known.
The conductivity of the conductive ink pattern may be further improved.

In the case of producing an electromagnetic wave shielding member by the above-described method using the conductive ink, a mesh pattern is formed, and then a photo-curing type photosensitive resist is formed on the patterned transparent substrate with a film having a pattern. It is provided in a state larger than the thickness.

As a photo-curable photosensitive resist,
Conventionally known various photopolymers can be used,
The photocurable photopolymer used in the present invention is a photopolymer type photopolymer because it is a thick film resist, it should be highly sensitive, it has plating resistance, and it is as inexpensive as possible. It is preferred to use Particularly as meeting these requirements, for example,
"Photopolymer Technology" (published by Nikkan Kogyo Shimbunsha, 1988/12/30 first edition) P364-380, P
Photopolymerizable photosensitive resins used in printed wiring boards described in 401-423 are preferred. Such photopolymers are commercially available from various companies in the form of a photosensitive dry film, or in the form of a liquid resist, as a solvent development type or an alkaline water development type such as sodium carbonate. It is preferable to use an alkaline water developing type dry film resist or a liquid resist. Further, those used as plating resists are particularly preferable.

As a method for providing the photocurable photopolymer on the substrate having the conductive ink pattern in a state where the thickness of the conductive ink is larger than that of the conductive ink, when a dry film resist is used, When a liquid resist is used, it can be provided by various conventionally known coating methods. In the latter case, it is suitable for mass production and has particularly good conformability to the conductive ink pattern. The former case is characterized in that it can be easily manufactured, and if the followability of unevenness is a problem, a vacuum laminator may be used.

The thickness of the photosensitive resist varies depending on the object to which the metal pattern forming method of the present invention is used. For example, when copper plating is used for electromagnetic wave shielding, the thickness of the plated copper may be about 1 to 15 μm. In this case, the thickness of the resist layer is the thickness of the conductive ink plus the required metal plating. A resist thickness of the film thickness is required. Further, in the case of a wiring pattern of a printed wiring board, a copper film thickness of about 40 μm may be required, and in that case, the resist film thickness becomes large.

Various additives such as an ultraviolet absorber, a colorant for adjusting the color tone, and a heat ray cutting agent may be added to these photoresists as needed. In particular, it is effective when the present invention is used as an electromagnetic wave shielding member for PDP.

A conductive ink pattern is provided on a substantially transparent substrate, and a photo-curing type photoresist layer is provided on the front surface in a state where the thickness is larger than the thickness of the pattern. In the step of exposing the front surface from the back side of the transparent substrate using the conductive ink pattern as a mask, usually, the spectral sensitivity of the photoresist is in the near ultraviolet region. Can be done. Regarding the mask performance of the conductive ink pattern, it is generally sufficient if the optical density is 3.0 or more, but the film thickness is 1 μm or more regardless of whether it is a metallic conductive ink or a carbon-based non-metallic conductive ink. Then, the condition is fully satisfied. In particular, when a carbon-based conductive ink is used, the effect is remarkable. In the case of the present invention,
As described above, since the mask and the resist are completely adhered without any gap, it is advantageous also from the viewpoint of resolution.

As for the removal of the uncured resist on the conductive ink pattern portion, an organic solvent or alkaline water may be used as described above. However, from the viewpoint of environment and cost, the resist is developed with alkaline water such as sodium carbonate. It is preferable to remove the uncured resist.

The photo-cured resist is used as a plating resist on the conductive ink pattern portion by electrolytic plating.
As a method of performing metal plating such as copper, nickel, silver, gold, solder, or a copper / nickel multilayer or a composite system, a conventionally known method can be used, and there are various books on these methods. (For example, "Surface treatment technology overview"
Technical Data Center Co., Ltd., first edition of 1987/12/21,
P281 to 422) Which metal is provided by electrolytic plating depends on what the present invention is used for. For example, when the present invention is used as an electromagnetic wave shielding member, plating is easy and the conductivity is high. It is preferable to use copper because it is excellent in that it can be plated even on a thick film and the cost is low. To explain with an example of electrolytic plating,
Immerse the substrate in a bath containing copper sulfate, sulfuric acid, etc. as a main component,
The plating is performed by applying a current at a temperature of 10 to 40 ° C. and a current density of 1 to 20 amps / dm ² .

In the present invention, the metal profile is plated only on the conductive ink pattern based on the plating resist formed by the photolithography method, so that the pattern profile is very good even with a thick metal pattern. It is.

When the metal pattern forming method of the present invention is used as an electromagnetic wave shielding member, it may be used as it is or may be provided with a protective film. If necessary, a transparent substrate (or film) having another function such as a heat ray cut function layer may be bonded via an adhesive. In such a case, if necessary, the adhesion may be controlled by surface treatment of the transparent film of the member, and the material may be used as a transfer peeling sensitive material.

Since the mesh pattern of the present invention can be used in a state where it is embedded with a resist material, it can exhibit excellent performance in transparency and sharpness.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below on the basis of embodiments, but the present invention is not limited to these embodiments.

Example 1 10.0 parts by weight of a polyester resin (manufactured by Toyobo KK, trade name: Byron 300) was dissolved in a solvent consisting of 80 parts by weight of toluene, and then, Graphite (Chuetsu Graphite Co., Ltd.) was used. (Trade name: CPB-30) and 3.0 parts by weight of Ketjen Black EC (manufactured by Lion Corporation) were further mixed. The resulting mixture is 2 mm
Using Φ zirconia beads, the mixture was dispersed with a paint shaker for 10 hours to obtain a conductive ink composition. This ink composition was appropriately diluted with toluene, and glow-treated for the purpose of improving adhesion by a gravure printing method. On a 100 μm-thick polyester film, the line width was 20 μm, the line pitch was 250 μm, and the ink dry film thickness was 2.5 μm. Was printed. After that, 10
Heat cured for minutes. The solid resistivity of the obtained conductive ink had a volume resistivity of 2.0 × 10 ⁻² Ωcm and a surface resistance of 3.5 × 10 ² Ω / □. The optical density is 4.
It was 5 or more. Next, on this mesh pattern, a photosensitive dry film resist film (resist film thickness of about 15 μm) for plating resist of an alkali development (sodium carbonate water) type, which is commercially available as a photosensitive dry film for producing a printed wiring board. After the cover film was peeled off, it was laminated with a vacuum laminator with good adhesion. Next, from the back surface of the polyester film, using a conductive ink mesh pattern as a mask, the entire surface is irradiated with ultraviolet rays, and only the photosensitive layer having no mesh pattern is photo-cured, and then a predetermined sodium carbonate aqueous developer is used. The photosensitive layer on the mesh pattern was removed. Next, using a treatment solution for electrolytic copper plating (copper sulfate 75 g / l, sulfuric acid 190 g / l, chloride ion 50 ppm, and cover cream PCM 5 ml / l manufactured by Meltex Co., Ltd.), a predetermined method (25 ° C.,
In accordance with 5 A / cm ² ), a 12 μm-thick copper plating was applied only on the conductive ink mesh pattern, which is the resist opening. Next, the copper-plated surface of the film together with the photocured resist was bonded to a transparent acrylic substrate (8 μm thick) via an acrylic adhesive. The shielding property of the obtained transparent electromagnetic wave shielding member is 1 to 1, 0 or 1.
50 dB and a visible light transmittance of 71% were achieved over the frequency range of 00 MHz.

[0041]

As is clear from the above description, the method of the present invention makes it possible to easily produce a high-performance transparent electromagnetic wave shielding member as a front filter for a PDP with high productivity. Further, the electromagnetic wave shielding member according to the present invention is also effective for application to window glass and the like for preventing electromagnetic wave interference in buildings. Furthermore, although the present invention has been described mainly with reference to the production of an electromagnetic wave shielding member as an example, the metal pattern forming method of the present invention can be applied not only to the production of an electromagnetic wave shielding member but also to the formation of various metal wiring patterns.

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Claims (1)

[Claims] 1. A film having a thickness of 15 μm on a substantially transparent substrate.
After forming a pattern using a conductive ink having a surface resistance of 1.0 × 10 ³ Ω / □ or less, a negative type photoresist layer is formed on the transparent substrate so as to have a thickness larger than the thickness of the pattern. Provided in a state, after that, from the back side of the transparent substrate on which the layer is provided, the entire surface is exposed using the pattern made of the conductive ink as a mask, and the photoresist portion where the pattern made of the conductive ink is not provided is cured. After that, only the photoresist on the pattern portion made of the conductive ink is developed and removed. Thereafter, a metal pattern forming method in which the cured resist is used as a plating resist by electrolytic plating, and a metal pattern is formed only on the pattern made of the conductive ink.