JP2010238720A - Flexible printed wiring board - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a flexible printed wiring board with excellent transparency and translucency even when a base film layer mainly contains polyethylene-2,6-naphthalene dicarboxylate. <P>SOLUTION: The flexible printed wiring board includes the base film layer mainly containing polyethylene-2,6-naphthalene dicarboxylate, a conductor layer, an adhesive layer, and a cover film layer. An aperture ratio of the conductor layer is set in a specific range by using a highly-transparent base film and highly-transparent adhesive. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a flexible printed wiring board (hereinafter also referred to as “FPC”). More specifically, the present invention relates to a flexible printed wiring board excellent in transparency and translucency using a base film layer containing polyethylene-2,6-naphthalenedicarboxylate as a main component.

Conventionally, a flexible printed circuit board (FPC) obtained by processing a flexible metal-clad laminate in which a metal foil is laminated on a polymer film is known (Patent Document 1).
A conventional flexible printed circuit board uses a polyimide film (hereinafter sometimes abbreviated as “PI film”) as a polymer film, and a PI film and a metal foil are bonded by thermosetting epoxy resin or acrylic resin. It was formed from a metal-clad laminate bonded with an agent (see Patent Document 1).

  In recent years, portable electric and electronic devices such as notebook personal computers and mobile phones have been rapidly spread, and downsizing of these portable devices has been actively performed. However, even when the size is reduced, there is a demand to have a function equivalent to or higher than that of the conventional model. Therefore, further miniaturization and higher density of the wiring circuit are required. Yes.

  In addition, while such advanced technology is required, competition for price reduction due to recent popularization of portable devices is intensifying. And since the polyimide film (PI film) conventionally used as a film for flexible circuit boards is expensive, there has been a limit to reducing the price of portable devices.

  In addition to being expensive, the PI film also has a problem of high moisture absorption and large dimensional change during moisture absorption. If the film is not conditioned during processing, the adhesion to the metal is reduced. It was. For this reason, when using a PI film, humidity control of the film has become indispensable, which has been an obstacle to improving production efficiency.

  Under such circumstances, a study of a polyethylene terephthalate (hereinafter sometimes abbreviated as “PET”) film has been started as a substitute for a polyimide film (PI film). The PET film has already been used as a film for some flexible circuit boards because it is inexpensive and has good chemical resistance, insulation and the like.

  However, the PET film has a problem in heat resistance, and its use has been limited. For example, in the heat treatment included in the membrane switch processing process, the dimensional change of the film becomes a problem, especially when the surface flatness of the film deteriorates because soldering when mounting circuit components is performed at high temperatures As a recent high-density circuit board film, it cannot be used.

  Accordingly, a search for a plastic film that is relatively inexpensive, has a low hygroscopic property, and further satisfies heat resistance has been conducted, and is abbreviated as polyethylene-2,6-naphthalenedicarboxylate (hereinafter, “PEN”). Film) has been attracting attention (see Patent Documents 2 to 4).

  However, when a polyethylene-2,6-naphthalenedicarboxylate film is used as a base film for a circuit board, the transparency is insufficient, and there is a problem that the film is colored. It could not be used as a necessary application.

JP-A-2-131933 JP-A-62-93991 JP-A-11-168267 JP 2001-191405 A

  The present invention has been made in view of such a conventional technique, that is, even when a base film layer containing polyethylene-2,6-naphthalenedicarboxylate as a main component is used, it is transparent. An object of the present invention is to provide a flexible printed wiring board excellent in translucency.

  The present inventors have intensively studied to solve the above problems. As a result, in a flexible printed wiring board including a base film layer, a conductor layer, an adhesive layer, and a cover film layer mainly composed of polyethylene-2,6-naphthalenedicarboxylate, a highly transparent base film and It has been found that the above-mentioned problems can be solved by using a highly transparent adhesive and setting the opening ratio of the conductor layer to a specific range, and the present invention has been completed.

  That is, the present invention is a flexible printed wiring board including a base film layer, a conductor layer, an adhesive layer, and a cover film layer, and the base film layer is mainly composed of polyethylene-2,6-naphthalenedicarboxylate. The conductor layer has a pattern formed by etching, the opening ratio of the conductor layer is 60 to 95%, the haze is 0.5 to 20%, and the total light transmittance is 70% or more. This is a flexible printed wiring board.

  The flexible printed wiring board of the present invention is a flexible printed wiring board excellent in transparency and translucency. For this reason, it can use suitably also in uses, such as a touchscreen which needs transparency and translucency.

It is a figure which shows the mask film used in Example 6.

Hereinafter, embodiments of the flexible printed wiring board (FPC) of the present invention will be described.
<Configuration of flexible printed circuit board>
The FPC of the present invention can have any laminated configuration that can be employed as an FPC as long as it includes a base film layer, a metal foil layer, an adhesive layer, and a cover film layer. For example, it may be an FPC composed of only four layers of a base film layer, a metal foil layer, an adhesive layer, and a cover film layer. For example, FPC comprised from five layers, a base film layer, an adhesive bond layer, a metal foil layer, an adhesive bond layer, and a cover film layer, may be sufficient.

  Furthermore, if necessary, a configuration in which two or three or more of the above FPCs are stacked may be used. In such a case, for example, a plurality of the four-layer type FPC or the five-layer type FPC may be stacked, and the FPC and the FPC may be bonded with an adhesive as necessary.

  More specifically, for example, a first FPC base film layer, a first FPC metal foil layer, a first FPC adhesive layer, a first FPC cover film layer, and a first FPC An adhesive layer for adhering to the second FPC, a base film layer for the second FPC, a metal foil layer for the second FPC, an adhesive layer for the second FPC, and a cover film layer for the second FPC A total of nine layers may be sequentially stacked.

  Further, for example, the four-layer type FPC or the five-layer type FPC may be bonded back to back by bonding the bottoms of two base film layers with an adhesive layer.

  In this case, for example, if the above four-layer type FPC is used, the first FPC cover film layer, the first FPC adhesive layer, the first FPC metal foil layer, the first FPC base Material film layer, adhesive layer for bonding the base films of the first FPC and the second FPC, the base film layer of the second FPC, the metal foil layer of the second FPC, the second FPC A total of nine layers of the adhesive layer and the cover film layer of the second FPC can be laminated in order.

  Also, for example, if the five-layer type FPC is used, the first FPC cover film layer, the first FPC cover film side adhesive layer, the first FPC metal foil layer, the first FPC Adhesive layer on base film side, base film layer of first FPC, adhesive layer for bonding base films of first FPC and second FPC, base film layer of second FPC , A total of 11 of the adhesive layer on the base film side of the second FPC, the metal foil layer of the second FPC, the adhesive layer on the cover film side of the second FPC, and the cover film layer of the second FPC It can be set as the structure by which a layer is laminated | stacked in order.

  Further, a laminated structure of a total of 10 layers in which the adhesive layer on the base film side of the first FPC or the adhesive layer on the base film side of the second FPC is omitted, that is, the above-described four-layer type FPC and 5 A layer type FPC may be bonded back to back.

<Base film>
(Base film material)
The base film used for the FPC of the present invention is a film containing polyethylene-2,6-naphthalenedicarboxylate as a main component. Here, the “main component” means 10 mol% or less based on the total number of moles of repeating structural units in the entire material constituting the base film.

  Such polyethylene-2,6-naphthalene dicarboxylate is one in which 2,6-naphthalenedicarboxylic acid is used as the main dicarboxylic acid component and ethylene glycol is used as the main glycol component. Here, “main” means at least 90 mol%, preferably at least 95 mol% of all repeating units in the polyethylene-2,6-naphthalenedicarboxylate used as the material of the base film of the present invention.

  The material constituting the base film layer of the present invention may be a polyethylene-2,6-naphthalene dicarboxylate alone or a copolymer of polyethylene-2,6-naphthalene dicarboxylate and other polyesters. Or a mixture of polyethylene-2,6-naphthalenedicarboxylate and other polyesters. The other component in the copolymer or mixture is 10 mol% or less, preferably 5 mol% or less, based on the total number of moles of repeating structural units.

  Polyethylene-2,6-naphthalenedicarboxylate, which is the main component of the base film of the present invention, can be produced by a conventionally known method. For example, a method of directly obtaining a low-polymerization polyester by reaction of a dicarboxylic acid and a glycol, and reacting a lower alkyl ester of a dicarboxylic acid with a glycol using one or more conventionally known transesterification catalysts, followed by polymerization Examples include a method of performing a polymerization reaction in the presence of a catalyst.

  The intrinsic viscosity of polyethylene-2,6-naphthalenedicarboxylate, which is the main component of the base film layer of the present invention, is preferably 0.40 dl / g or more at 35 ° C. in o-chlorophenol. More preferably, it is 40 to 0.90 dl / g. When the intrinsic viscosity is less than 0.40 dl / g, process cutting may occur frequently. On the other hand, when the intrinsic viscosity is higher than 0.9 dl / g, melt extrusion is difficult because of high melt viscosity, and the polymerization time becomes long, which is uneconomical.

  The polyethylene-2,6-naphthalenedicarboxylate, which is the main component of the base film layer of the present invention, includes a colorant, an antistatic agent, an antioxidant, and a catalyst within a range that does not impair the object of the present invention. Etc. may be included.

(Manufacturing method of base film)
The manufacturing method of the base film used by this invention is not specifically limited, It can manufacture using conventionally well-known film forming methods, such as a tenter method and an inflation method.

(Physical properties of base film)
The base film layer used in the present invention preferably has a thermal shrinkage at 200 ° C. of −3 to 3%. More preferably, it is −2 to 2% or less, and further preferably −1 to 1% or less. If it is less than -3% or more than 3%, it becomes difficult to form a good circuit in the step of forming a circuit board because the film has a large thermal shrinkage.

  In order to satisfy these characteristics, for example, the heat setting treatment after the film is stretched can be achieved at a temperature of (Tm-100 ° C.) or higher. Further, as a method for further suppressing thermal shrinkage, for example, a method of subjecting the obtained film to an annealing process in which heat treatment is performed at 150 to 220 ° C. for 1 to 60 seconds in an off-line process, and thereafter, cooling is performed at 50 to 80 ° C. Is mentioned.

  In addition, the substrate film used in the present invention preferably has a water absorption rate of 1.0% or less. More preferably, it is 0.8% or less, More preferably, it is 0.6% or less. When the water absorption rate exceeds 1.0%, the film absorbs moisture in the FPC manufacturing process, so that the electrical characteristics of the film are deteriorated and the circuit itself is adversely affected. For this reason, it is not preferable because an extra process is required so as not to absorb water, and handling as a film itself or a circuit becomes complicated.

  Further, the base film used in the present invention preferably has a haze of 15% or less. More preferably, it is 10% or less, and particularly preferably 5% or less. When the haze exceeds the upper limit, the transparency is deteriorated. For example, it may be difficult to use the light source such as a light emitting diode or the like to illuminate from the lower part of the FPC substrate and visually recognize the illumination on the upper part of the substrate. The smaller the lower limit of haze, the better, but most preferably 0%. The haze of the base film can be controlled by adjusting the size and addition amount of the lubricant (inert particles) to be added, and most preferably no lubricant is contained.

  Moreover, it is good also as a laminated body which further laminated | stacked the other layer on the base film used by this invention for the purpose of providing another function to the single side | surface or both surfaces. Examples of other layers mentioned here include transparent polyester films, metal thin films, and hard coat layers.

<Conductor layer>
As a conductor layer used in the present invention, any conductive material that can be used for a circuit board can be used, and for example, a metal foil can be used. As the metal foil, any conventionally known metal foil can be used. Examples of the material include copper foil, aluminum foil, steel foil, nickel foil and the like, and composite metal foil obtained by combining these and metal foil treated with other metals such as zinc and chromium compounds are also used. be able to. In the present invention, since the etching characteristics are excellent, a highly accurate circuit can be formed, and since there is no problem between the wirings, the insulation reliability is high, and further, disconnection or the like occurs in an environment such as a manufacturing process. Since there is no high connection reliability, it is preferable to use a copper foil.

  Although there is no limitation in particular about the thickness of the metal foil used as a conductor layer, Preferably it is 1 micrometer or more, More preferably, it is 3 micrometers or more, More preferably, it is 10 micrometers or more. Moreover, it is preferably 50 μm or less, more preferably 30 μm or less, and still more preferably 20 μm or less. If the thickness is too thin, it may be difficult to obtain sufficient electrical performance of the circuit. On the other hand, if the thickness is too thick, the processing efficiency at the time of circuit fabrication may be reduced.

  The metal foil is usually provided in the form of a ribbon, but the form of the metal foil used when producing the FPC of the present invention is not particularly limited. In the case of using a ribbon-like metal foil, the length is not particularly limited. Also, the width of the ribbon-like metal foil is not particularly limited, but is generally preferably about 25 to 300 cm, and particularly preferably about 50 to 150 cm.

<Adhesive layer>
In the FPC of the present invention, the adhesive layer is an essential layer. As an arrangement | positioning of an adhesive bond layer, the base film side, ie, between a base film and a conductor layer, or a cover film side, ie, a part of cover film, etc. are mentioned, for example. As the adhesive constituting the adhesive layer, a conventionally known adhesive can be used as an adhesive for FPC. In the present invention, it is desirable to use an adhesive having high transparency. Examples of such adhesives include acrylonitrile butadiene rubber (NBR) adhesives, polyamide adhesives, polyester adhesives, acrylic adhesives, and polyester polyurethane adhesives. In these, it is preferable to use the adhesive agent containing an epoxy resin and an acrylic resin. By using an epoxy resin and an acrylic resin in combination, the acrylic resin absorbs the internal strain of the epoxy resin that may be distorted by thermal cycling, and can give flexibility to the resulting adhesive cured product, and is transparent The property can be improved.
The adhesive on the base film side and the adhesive on the cover film side may be different from each other, but it is preferable to use the same adhesive.

  The thickness of the adhesive layer is not particularly limited as long as it does not hinder the performance of the FPC. The thickness after absolute drying is preferably 5 μm or more, more preferably 10 μm or more, and further preferably 15 μm or more. Moreover, it is preferably 100 μm or less, more preferably 50 μm or less, and further preferably 30 μm or less. If the thickness is too thin, it may be difficult to obtain sufficient adhesiveness. On the other hand, if the thickness is too thick, processability (drying property, coating property) and the like may be deteriorated. .

  Hereinafter, an adhesive containing an epoxy resin and an acrylic resin preferably used in the present invention will be described.

(Epoxy resin)
Examples of the epoxy resin used as the material for the adhesive layer of the present invention include novolac type epoxy resins and bisphenol A type epoxy resins. The novolac type epoxy resin and the bisphenol A type epoxy resin may be used alone or in combination.

Examples of novolak type epoxy resins include phenol novolak glycidyl ether, cresol novolac glycidyl ether, brominated phenol novolac glycidyl ether, and brominated cresol novolak glycidyl ether. A brominated novolac type epoxy resin is preferably used from the viewpoint of flame retardancy.
The epoxy equivalent of the novolac type epoxy resin is preferably 100 or more, more preferably 150 or more. Moreover, Preferably it is 1000 or less, More preferably, it is 700 or less.

Examples of bisphenol A type epoxy resins include bisphenol A diglycidyl ether, brominated bisphenol A diglycidyl ether, and methoxy group-containing silane-modified epoxy obtained by dealcoholization reaction of bisphenol A type epoxy resin and methoxysilane partial condensate. Examples thereof include resins, and it is preferable to use a methoxy group-containing silane-modified epoxy resin from the viewpoint of heat resistance and adhesion to a conductor.
The epoxy equivalent of the bisphenol A type epoxy resin is preferably 200 or more, more preferably 400 or more. Moreover, Preferably it is 1000 or less, More preferably, it is 800 or less.

(Curing agent)
A curing agent that catalyzes the curing reaction can be used for the epoxy resin, and a known curing agent for epoxy resin can be used as the curing agent. For example, a phenol resin curing agent, a polyamine curing agent, a polycarboxylic acid curing agent, and the like can be given.

  Specifically, examples of the phenol resin-based curing agent include phenol novolak resin, cresol novolac resin, bisphenol novolac resin, poly p-vinylphenol, and the like. Examples of the polyamine-based curing agent include diethylenetriamine, triethylenetetramine, and tetraethylene. Pentamine, dicyandiamide, polyamidoamine (polyamide resin), ketimine compound, isophoronediamine, m-xylenediamine, m-phenylenediamine, 1,3-bis (aminomethyl) cyclohexane, N-aminoethylpiperazine, 4,4'- Examples include diaminodiphenylmethane, 4,4′-diamino-3,3′-diethyldiphenylmethane, diaminodiphenylsulfone and the like, and polycarboxylic acid-based curing agents include phthalic anhydride, tetrahydroanhydride Phthalic acid, methyltetrahydrophthalic anhydride, 3,6-endomethylenetetrahydrophthalic anhydride, hexachloroendomethylenetetrahydrophthalic anhydride, methyl-3,6-endomethylenetetrahydrophthalic anhydride, methylhexahydrophthalic anhydride, etc. Can be mentioned. In these, it is preferable to use at least 1 type chosen from the group which consists of an aromatic amine and a phenol-type novolak resin from a viewpoint of coexistence of the pot life of adhesive composition, and low temperature hardening.

(acrylic resin)
A publicly known thing can be used for an acrylic resin used as a material of an adhesive layer of the present invention without a restriction. In the present invention, the glass transition temperature is preferably 20 ° C. or lower, imparts flexibility to the cured adhesive, and does not impair heat resistance. When glass transition temperature exceeds 20 degreeC, since the softness | flexibility of adhesive hardened | cured material deteriorates, it is unpreferable. Furthermore, when an acrylic resin having a glass transition temperature in the range of −50 to 20 ° C. is used, mixing with other components such as an epoxy resin is facilitated, the solvent is reduced, and viscosity adjustment is facilitated. In particular, if an acrylic resin having a glass transition temperature of −50 to 0 ° C. is used, it is possible to exert an effect that is hardly affected by temperature such as seasonal factors.

  As a preferable acrylic resin, for example, it has at least one functional group selected from the group consisting of a carboxyl group and a hydroxyl group, and the main component is an acrylate ester or an α-substituted acrylate ester. A point is a polymer in which at least one of the above functional groups is contained, or a polymer graft-polymerized to a polymer in which at least one of the above functional group-containing monomers is a monomer having the above main component.

  Specifically, at least one selected from the group consisting of an epoxy group-containing monomer, a carboxyl group-containing monomer, and a hydroxyl group-containing monomer as a constituent component mainly composed of one of acrylic acid ester or α-substituted acrylic acid ester A monomer having one functional group is copolymerized.

  For example, examples of the acrylic acid ester component include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, octyl acrylate, and the like. Examples of the epoxy group-containing monomer include glycidyl ethers such as vinyl glycidyl ether and allyl glycidyl ether, glycidyl acrylate, and glycidyl methacrylate. Examples of the carboxyl group-containing monomer component include acrylic acid, methacrylic acid, itaconic acid, maleic acid, and maleic anhydride. Examples of the hydroxyl group-containing monomer component include 2-hydroxyethyl methacrylate, 2-hydroxypropyl methacrylate, ethylene glycol dimethacrylate, propylene glycol dimethacrylate, and polyhydric alcohol dimethacrylates such as methoxymethyl. Examples thereof include alkoxy acrylates such as acrylate.

  These may be used alone or in combination of two or more. A particularly preferred acrylic ester component is a combination of ethyl acrylate and butyl acrylate in terms of good compatibility with the epoxy resin and excellent transparency. Furthermore, if necessary, other vinyl monomers such as vinyl chloride, vinylidene chloride, styrene, acrylonitrile, vinyl acetate and the like may be copolymerized.

  In addition, the acrylic resin component may have any functional group of an epoxy group, a carboxyl group, and a hydroxyl group, but among these, since it can contribute to the adhesion to the conductor layer and the substrate film, the carboxyl group Those having a group or a hydroxyl group are preferred.

  The blending ratio of the acrylic resin component in the preferred adhesive constituting the adhesive layer of the present invention (adhesive containing epoxy resin and acrylic resin) is not particularly limited, but the cured adhesive (adhesive layer) ) And the substrate film, it is preferably 20 to 200% by mass with respect to the epoxy resin component. When the said mixture ratio is less than 20 mass%, the adhesiveness of the hardened layer (adhesive layer) with respect to a base film becomes inadequate, On the other hand, when it exceeds 200 mass%, heat resistance tends to fall. There is.

<Physical properties of flexible printed wiring board>
[Aperture ratio]
The opening ratio of the conductor layer after pattern formation by etching is preferably 60% or more and 95% or less, more preferably 65% or more and 90% or less, and still more preferably 70% or more and 85% or less. When the aperture ratio is within the above range, the transparency and translucency of the obtained flexible printed wiring board can be reached to desired levels. The “aperture ratio” in the present invention means a ratio represented by the following formula (1).
Opening ratio = (opening width ² ÷ (opening width + conductor layer width) ² ) × 100 (1)
The shape of the opening is not particularly limited, but it is preferable that the shape of the opening is a regular triangle, a regular square, a regular hexagon, a circle, a rectangle, a rhombus, and the like, and the openings are uniformly arranged in the plane. .

The typical size of the opening serving as the light transmission portion is preferably in the range of one side or diameter of 18 to 200 μm. More preferably, it is 20-150 micrometers. If this value is too large, the electrical performance of the wiring of the conductor layer is lowered, and if it is too small, the transparency is unfavorably affected.
Moreover, it is preferable that the width | variety of the conductor layer of the part which does not form an opening part is the range of 5-50 micrometers, More preferably, it is 10-30 micrometers.

[Haze]
The FPC of the present invention has a haze of 0.5 to 20%, preferably 0.5 to 15%, more preferably 0.5 to 5%. In the present invention, the haze of the FPC can be adjusted within the above range by setting the opening ratio of the conductor layer to a specific range using a highly transparent base film and a highly transparent adhesive. . When the haze value is large, the transparency is deteriorated, and for example, it is difficult to use such as illuminating from the lower part of the FPC substrate with a light emitting diode or the like, and making the illumination visible on the upper part of the substrate. On the other hand, if it is small, the wiring of the conductor layer becomes substantially thin, and the electrical performance is insufficient.

[Total light transmittance]
The FPC of the present invention has a total light transmittance of 70% or more, preferably 80% or more, more preferably 85% or more. In the present invention, the total light transmittance of the FPC is adjusted within the above range by setting the opening ratio of the conductor layer to a specific range using a highly transparent base film and a highly transparent adhesive. be able to. When the value of the total light transmittance is small, the transparency is deteriorated. For example, it is difficult to illuminate from the lower part of the FPC board with a light emitting diode or the like and to make the illumination visible on the upper part of the board.

<FPC manufacturing method>
The FPC of the present invention can be manufactured using any conventionally known process except that the material of each layer described above is used. As a preferred embodiment, first, an adhesive layer is laminated on a base film layer, and a metal foil layer is laminated thereon to form a desired product pattern (hereinafter referred to as “base film side three-layer half”). Product)). Next, a semi-finished product in which an adhesive layer is laminated on the cover film layer (hereinafter referred to as “cover film-side semi-finished product”) is manufactured. And the method of obtaining 5 layers of FPC can be mentioned by bonding together the obtained base film side semi-finished product and cover film side semi-finished product. In the following, preferred embodiments are described in detail.

(Manufacturing method of base film side semi-finished product)
The base film side semi-finished product is, for example,
(A) A base film mainly composed of polyethylene-2,6-naphthalenedicarboxylate is coated with a mixed solution of an epoxy resin and an acrylic resin to be an adhesive layer, dried, and further on the adhesive layer. A process of bonding a metal foil to be a conductor layer to
(B) It can be obtained by a production method including a step (hereinafter referred to as “heat treatment step”) of heat-treating the laminate comprising the base film layer, the adhesive layer and the conductor layer obtained in (A).
Conditions such as temperature and time during the heat treatment step can be appropriately set depending on the composition of the adhesive resin used.

(Circuit formation)
A conventionally well-known method can be used for formation of the circuit to the conductor layer (metal foil layer) of the obtained base film side semi-finished product. An active method may be used and a subtractive method may be used. In the present invention, the subtractive method is preferable.
Any pattern can be used as the circuit wiring pattern. Specifically, in the FPC of the present invention, the wiring thickness of the circuit of the fine wiring pattern portion can be 100 μm or less, further 50 μm or less, and particularly 30 μm or less. It can also be. The thickness of the wiring is preferably 5 μm or more, more preferably 10 μm or more, and further preferably 20 μm or more from the viewpoint of the electrical performance of the wiring.

The interval between the wirings in the fine wiring pattern portion can be set to 300 μm or less, can be set to 200 μm or less, and further can be set to 150 μm or less. The distance between the wirings is preferably 18 μm or more, more preferably 20 μm or more, and further preferably 25 μm or more from the viewpoint of the electrical performance of the wiring.
The base film side semi-finished product on which the obtained circuit is formed may be used as it is for pasting with the cover film side semi-finished product, and after the release film is pasted and stored, the cover film side It may be used for pasting with semi-finished products.

(Manufacturing method for semi-finished product on cover film)
The cover film side semi-finished product can be manufactured, for example, by applying an adhesive to the cover film. Moreover, the apply | coated adhesive agent can be bridge | crosslinked as needed. In a preferred embodiment, the adhesive layer is semi-cured.
The obtained cover film-side semi-finished product may be used as it is for pasting with the base-side semi-finished product. They may be used together.

(Lamination of base film side semi-finished product and cover film side semi-finished product)
The base film-side semi-finished product and the cover film-side semi-finished product are usually stored in the form of a roll, for example, and then bonded together to produce an FPC. The method of bonding is not particularly limited, and any method can be adopted. For example, they can be bonded together using a press or a roll or the like, and both can be bonded together while heating by a method using a heating press or a heating roll device.

  For example, when the adhesive layer in a semi-finished product is in an uncured or semi-cured state, it can be cured by proceeding with a crosslinking reaction of the adhesive layer by heating at the time of bonding. Yes, by heating, a final product with the adhesive layer completely cured can be easily obtained.

<Application>
The FPC of the present invention can be used for various products for which FPC has conventionally been used. Since the FPC of the present invention is particularly high in transparency, it can be suitably used for products that are illuminated with a light emitting diode or the like and the illumination is visually recognized on the upper part of the substrate. A specific final product in which the FPC of the present invention is used includes, for example, a transparent conductive film of a touch sensor.

  When the FPC of the present invention is used as a touch sensor, for example, an FPC obtained by bonding the base film side semi-finished product and the cover film side semi-finished product obtained by etching a copper foil into a mesh or the like is used as an injection mold. There is a method of integrally molding with a molded plate with an electrode by inserting into the cavity and injecting molding resin into the cavity (insert molding).

  In addition, when the surface on which the conductive portion (copper foil) of the above-mentioned bonded sample is formed by insert molding is a three-dimensional curved surface (see FIG. 1), if it is an electrode made of conventional ITO, There was a risk of causing cracks. However, in the present invention, since the selection range of the electrode material is wide, it is possible to select and use a material resistant to deformation.

  EXAMPLES Hereinafter, although an Example etc. demonstrate this invention further more concretely, this invention is not limited by these Examples. Note that “%” in Examples and the like means “% by mass” unless otherwise specified.

<Measurement and evaluation method>
In Examples and Comparative Examples, the following items were measured and evaluated by the following methods.

(1) Total light transmittance, haze Using turbidity measuring device (trade name: NDH2000) manufactured by Nippon Denshoku Industries Co., Ltd., according to measurement method A of JIS K 7105 “Testing method for optical properties of plastics” The total light transmittance Tt (%) and the diffused light transmittance Td (%) were obtained. The haze ((Td / Tt) × 100) (%) was calculated using the total light transmittance Tt (%) and the diffuse light transmittance Td (%) obtained.

(2) Water absorption rate A sample film was cut into a 100 mm square by a method according to JIS K7209 A method, dried at 100 ° C. for 24 hours, and then weighed. Subsequently, it was immersed in water at 23 ° C. for 24 hours and weighed again. The water supply rate was calculated by the following formula.
Water absorption rate (%) = {(mass increased by immersion) / (sample mass before immersion)} * 100

(3) Heat shrinkage rate Marks were attached to the film samples at intervals of 30 cm, heat treatment was performed in an oven at 200 ° C. for 10 minutes without applying a load, and the distance between the marks after heat treatment was measured. For each of the film continuous film forming direction (MD direction) and the direction perpendicular to the film forming direction (TD direction), the thermal shrinkage ratio R (%) was calculated by the following formula.
R (%) = {(L1-L2) / L1} × 100
Here, L1 is the distance between the gauge points before the heat treatment, and L2 is the distance between the gauge points after the heat treatment.

(4) Solder heat resistance It measured by the method described in JIS C6471, and evaluated by the following references | standards.
○: There is no shrinkage in the film, and there is no peeling between the film and the copper foil, and there is no swelling. ×: There is great shrinkage in the film, and there is peeling and swelling between the film and the copper foil.

<Example 1>
[Preparation of Base Film (A-1)]
To a mixture of 100 parts by mass of dimethyl 2,6-naphthalenedicarboxylate and 60 parts by mass of ethylene glycol, 0.03 parts by mass of manganese acetate tetrahydrate salt is added, and the temperature is gradually raised from 150 ° C to 240 ° C. The transesterification reaction was carried out.
During the reaction, when the reaction temperature reached 170 ° C., 0.024 parts by mass of antimony trioxide was added, and spherical silica particles having an average particle size of 0.4 μm and a particle size ratio of 1.1 were obtained. , 6-Naphthalenedicarboxylate composition was added so as to be 0.1% by mass in 100% by mass. After completion of the transesterification reaction, trimethyl phosphate (a solution heated in ethylene glycol at 135 ° C. for 5 hours under a pressure of 0.11 to 0.16 MPa: 0.023 parts by mass in terms of trimethyl phosphate) was added.

The obtained reaction product was transferred to a polymerization reactor, heated to 290 ° C., and subjected to a polycondensation reaction under a high vacuum of 0.2 mmHg or less to obtain a polyethylene-2,6-naphthalenedicarboxylate polymer. . The intrinsic viscosity (measured with an o-chlorophenol solution at 25 ° C.) of the obtained polymer was 0.61 dl / g.
The polymer was dried at 170 ° C. for 6 hours and then fed to an extruder. An unstretched film was obtained by melting in an extruder at a melting temperature of 305 ° C. and extruding it through a slit die having an opening of 1 mm onto a rotary cooling drum having a surface temperature of 60 ° C.

  The obtained unstretched film was stretched 3.4 times in the longitudinal direction at 140 ° C., and then stretched 3.8 times in the transverse direction at 140 ° C. Further, a heat setting treatment at 235 ° C. for 5 seconds and a relaxation treatment at 3% at 200 ° C. were carried out, and the mixture was uniformly removed and cooled to room temperature, thereby obtaining a biaxially stretched PEN film having a thickness of 25 μm. Furthermore, the obtained biaxially stretched PEN film was post-heat treated at 205 ° C. by a suspended relaxation heat treatment method to finally obtain a base film (A-1). The base film (A-1) has a heat shrinkage rate of 0.2% in the film continuous film forming direction (MD direction) and a heat shrinkage rate of 0.0% in the direction perpendicular to the film forming direction (TD direction). The water absorption was 0.3% and the haze was 6%.

[Preparation of Adhesive Composition (B-1)]
A reactor equipped with a mixer and a condenser was charged with 75 parts by mass of ethyl acrylate and 25 parts by mass of butyl acrylate, and heated to 80 to 85 ° C. Subsequently, 0.05 parts by mass of t-butyl peroxybenzoate as a polymerization catalyst and 2 parts by mass of methyl ethyl ketone were added, and the temperature was kept for 4 to 8 hours to obtain a polymer reacted at a polymerization rate of 20 to 30%. After cooling, methanol was added to precipitate the polymer, and the supernatant was removed. Subsequently, the methanol remaining in the polymer was dried, and then methyl ethyl ketone was added to obtain an acrylic resin dispersion having a solid content of 15%.

  20.0 g of a methoxy group-containing silane-modified epoxy resin (trade name: Composelan E-103, manufactured by Arakawa Chemical Industries, Ltd.) obtained by dealcoholizing a bisphenol A type epoxy resin and a methoxysilane partial condensate is obtained as described above. 66.7 g (15% solid content) of the resulting acrylic resin dispersion, 0.64 g of aromatic amine (trade name: MDA-220, manufactured by Mitsui Takeda Chemical Co., Ltd.) as a curing agent for epoxy resin, and toluene as a solvent 34 g was added and dissolved uniformly to prepare an adhesive composition (B-1).

[Manufacture of copper-clad laminate]
The adhesive composition (B-1) obtained above was applied to the base film (A-1) obtained above with a lip coater so that the thickness after curing would be 15 μm, and 60 ° C. For 3 minutes. Subsequently, the surface of the adhesive composition (B-1) on an electrolytic copper foil having a thickness of 12 μm (Furukawa Circuit Foil, trade name: F2-WS (12 μm)) at 80 ° C. and a pressure of 0.5 MPa. The copper-clad laminate (C-1) was produced by overlapping and subsequently heating at 140 ° C. for 1 hour.

[Manufacture of cover film]
The adhesive composition (B-1) obtained above was applied to the base film (A-1) obtained above with a lip coater so that the thickness after curing would be 20 μm, and 60 ° C. For 3 minutes. Subsequently, by overlapping the surface of the adhesive composition (B-1) on the release treatment surface of a release film having a thickness of 25 μm (manufactured by Teijin DuPont Films, trade name: PUREX A31 (25 μm)), A cover film (D-1) was prepared.

[Circuit formation]
A photosensitive resist (manufactured by AZ Electric Material, trade name: AZTPM-606) is laminated on the copper foil surface of the copper clad laminate (C-1) obtained above, and a mask film (wiring width: 25 μm, opening width: 400 μm × 400 μm mesh pattern) was exposed at 800 mJ using an exposure machine (made by Ushio Tech, model: EC30), and then developed with 0.8% potassium hydroxide (KOH) aqueous solution to transfer the pattern. . Next, the copper foil is etched away using a 42% ferric chloride solution at 40 ° C., and then the resist pattern used for circuit formation is changed to an organic alkali TMAH (Tetra-methyl-ammonium-hydride) 2. By removing using 38 wt% aqueous solution, the circuit laminated board (E-1) which formed the circuit by electrolytic copper foil was produced.

[Manufacture of flexible printed wiring boards]
Next, the cover film (D-1) obtained above was punched and punched with a mold to form a portion necessary for electrical connection. Subsequently, the circuit laminate of the circuit laminate (E-1) obtained above was overlaid so that the adhesive layer surface of the cover film (D-1) was in contact, and press laminate (80 ° C. × 30 minutes, pressure : 4 MPa) and after-curing (140 ° C. × 60 minutes) to finally obtain a flexible printed wiring board.
Table 1 shows the characteristics of the obtained flexible printed wiring board. The flexible printed wiring board of this example was excellent in transparency and heat resistance.

<Examples 2-5, Comparative Examples 1-2>
A flexible printed wiring board was produced in the same manner as in Example 1 except that the base film, the adhesive composition, and the mask pattern were changed as shown in Table 1. Table 1 shows the characteristics of the obtained flexible printed wiring board.

[Base film]
(A-2)
To a mixture of 100 parts by mass of dimethyl naphthalene-2,6-dicarboxylate and 60 parts by mass of ethylene glycol, 0.03 parts by mass of manganese acetate tetrahydrate salt is added as a transesterification catalyst, and gradually from 150 ° C. to 240 ° C. The transesterification reaction was carried out while raising the temperature.
Subsequently, when the reaction temperature reached 170 ° C., 0.024 parts by mass of antimony trioxide was added. After completion of the transesterification reaction, trimethyl phosphate (a solution heated in ethylene glycol at 135 ° C. for 5 hours under a pressure of 0.11 to 0.16 MPa: 0.023 parts by mass in terms of trimethyl phosphate) was added. The reaction product was obtained.

The obtained reaction product was transferred to a polymerization reactor, heated to 290 ° C., and subjected to a polycondensation reaction under a high vacuum of 27 Pa or less to obtain polyethylene-2,6-naphthalenedicarboxylate. The obtained polymer had an intrinsic viscosity (measured with an o-chlorophenol solution at 25 ° C.) of 0.61 dl / g, and was a polymer containing substantially no particles.
The polymer was dried at 170 ° C. for 6 hours and then fed to an extruder. It is melted in an extruder at a melting temperature of 305 ° C., filtered through a stainless steel fine wire filter having an average opening of 17 μm, passed through a slit-shaped die having an opening of 2 mm, extruded onto a rotary cooling drum having a surface temperature of 60 ° C., and rapidly cooled. Thus, an unstretched film was obtained.

  The obtained unstretched film was preheated at 120 ° C., further heated with an IR heater at 900 ° C. from above 15 mm between low-speed and high-speed rolls, and stretched 3.1 times in the longitudinal direction. Subsequently, the film stretched in the longitudinal direction was supplied to a tenter, and stretched 3.2 times in the transverse direction at 145 ° C. Further, the obtained biaxially oriented film was subjected to a heat setting treatment at 240 ° C. for 40 seconds and a relaxation treatment of 3% at 200 ° C., and then uniformly cooled and cooled to room temperature to obtain a thickness of 100 μm. A biaxially stretched PEN film was obtained. Furthermore, the obtained biaxially stretched PEN film was post-heat treated at 205 ° C. by a suspended relaxation heat treatment method to finally obtain a base film (A-2). As for the characteristics of the base film (A-2), the heat shrinkage rate in the film continuous film forming direction (MD direction) is 0.1%, and the heat shrinkage rate in the direction perpendicular to the film forming direction (TD direction) is 0. 0%, water absorption was 0.3%, and haze was 0.4%.

(A-3)
A Toray DuPont product name: Kapton; type H film having a thickness of 25 μm was used as the base film (A-3).

(A-4)
Polyethylene terephthalate (intrinsic viscosity: 0.66 dl / g) was dried at 160 ° C. for 3 hours and then fed to the extruder. An unstretched film was obtained by melting in an extruder at a melting temperature of 295 ° C. and extruding it through a slit die having an opening of 1 mm onto a rotary cooling drum having a surface temperature of 20 ° C.

  The obtained unstretched film was stretched 3.6 times in the machine direction at 105 ° C., and then stretched 3.8 times in the transverse direction at 115 ° C. Further, a heat setting treatment at 230 ° C. for 5 seconds and a relaxation treatment at 3% at 200 ° C. were carried out, and the mixture was uniformly cooled and cooled to room temperature, whereby a 25 μm-thick biaxially stretched polyethylene terephthalate film (base film ( A-3)) was obtained. The film has the following characteristics: 4.1% heat shrinkage in the continuous film forming direction (MD direction), 1.5% heat shrinkage in the direction perpendicular to the film forming direction (TD direction), and water absorption. 0.4% and haze were 5%.

[Adhesive composition]
(B-2)
A reactor equipped with a mixer and a condenser was charged with 75 parts by mass of ethyl acrylate and 25 parts by mass of butyl acrylate, and heated to 80 to 85 ° C. Subsequently, 0.05 parts by mass of t-butyl peroxybenzoate as a polymerization catalyst and 2 parts by mass of methyl ethyl ketone were added, and the temperature was kept for 4 to 8 hours to obtain a polymer reacted at a polymerization rate of 20 to 30%. After cooling, methanol was added to precipitate the polymer, and the supernatant was removed. Subsequently, the methanol remaining in the polymer was dried, and then methyl ethyl ketone was added to obtain an acrylic resin dispersion having a solid content of 15%.

  As epoxy resin, 7.5 g of bisphenol A type epoxy resin (Dainippon Ink Chemical Co., Ltd., trade name: EPICLON 850), phenol novola type epoxy resin (Dainippon Ink Chemical Co., Ltd., trade name: EPICLON) N-770-70M), 66.7 g of the acrylic resin dispersion obtained above (solid content 15%), 1-cyanoethyl-2-undecylimidazole (Shikoku Chemicals) as a curing agent for epoxy resin Co., Ltd., trade name: Curezol C11Z-CN ") was added to 0.04 g, and 45 g of toluene was added as a solvent, and dissolved uniformly to prepare an adhesive composition (B-2).

<Example 6>
[Circuit formation]
Photosensitive resist (manufactured by AZ Electric Material, trade name: AZTPM-606) is laminated on the copper foil surface of the copper clad laminate (C-1) prepared in Example 1, and the mask film (slit width) shown in FIG. Using a mesh pattern containing 40 μm: metal layer width 25 μm, opening width 400 μm × 400 μm), exposure was carried out at 800 mJ with an exposure machine (made by Ushio Tech, model: EC30), then 0.8% potassium hydroxide (KOH) The pattern was transferred by developing with an aqueous solution. Next, the copper foil is etched away using a 42% ferric chloride solution at 40 ° C., and then the resist pattern used for circuit formation is changed to an organic alkali TMAH (Tetra-methyl-ammonium-hydride) 2. By removing using 38 wt% aqueous solution, the circuit laminated board (E-2) which formed the circuit by electrolytic copper foil was created.

[Manufacture of flexible printed wiring boards]
Next, the cover film (D-1) obtained in Example 1 was punched and punched with a mold to form a portion necessary for electrical connection. Subsequently, the circuit laminate of the circuit laminate (E-2) obtained above was overlaid so that the adhesive layer surface of the cover film (D-1) was in contact, and press laminate (80 ° C. × 30 minutes, pressure : 4 MPa) and after-curing (140 ° C. × 60 minutes) to obtain a flexible printed wiring board.

[Production of touch panel]
Next, the flexible printed wiring board and the electrode are placed so that the electrode terminals of the molded plate with electrodes are exposed by inserting the obtained flexible printed wiring board into an injection mold and injecting polycarbonate resin into the cavity. Integrated with a molded plate.
Then, the transparent acrylic double-sided adhesive film with a peeling sheet was affixed on the base film (A-1) surface of the cover film (D-1).
Furthermore, a carbon film was formed on the electrode terminal portion by printing and drying a carbon paste to obtain a capacitive touch panel.

[Evaluation of touch panel]
The release sheet was peeled off, and the obtained capacitive touch panel was attached to an organic EL surface light emitting panel of a DVD player.
The attached capacitive touch panel hardly recognized the presence of electrodes even when viewed from the input side, and did not hinder the visual recognition of the display screen. Moreover, the slit formed in the electrode was not visually recognized, and the design was not impaired by the slit.
Next, when this capacitive touch panel and an external touch position detection circuit (driver) were connected and touched with a finger according to the instructions displayed on the screen, it was possible to input without malfunction.

1 Mesh pattern 2 Slit 3 Electrode terminal part

Claims (7)

A flexible printed wiring board including a base film layer, a conductor layer, an adhesive layer, and a cover film layer,
The base film layer is a layer containing polyethylene-2,6-naphthalenedicarboxylate as a main component,
The conductor layer is patterned by etching, the opening ratio of the conductor layer is 60 to 95%,
A flexible printed wiring board having a haze of 0.5 to 20% and a total light transmittance of 70% or more. The base film layer is a biaxially stretched film,
2. The flexible printed wiring board according to claim 1, wherein the biaxially stretched film has a heat shrinkage rate of −3 to 3% at 200 ° C., a water absorption rate of 1% or less, and a haze of 15% or less.   The flexible printed wiring board according to claim 1, wherein the adhesive layer is a layer containing an epoxy resin and an acrylic resin.   The flexible printed wiring board according to claim 1, wherein the cover film layer is a layer containing polyethylene-2,6-naphthalenedicarboxylate as a main component.   The flexible printed wiring board according to claim 1, wherein the conductor layer is formed with a pattern having a line width of 30 μm or less.   The flexible printed wiring board according to claim 1, wherein the flexible printed wiring board is three-dimensionally processed.   The flexible printed circuit board according to claim 1, wherein the flexible printed circuit board is a touch sensor component.

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