TW201826891A - Coverlay film - Google Patents

Abstract

A coverlay film is provided, capable of realizing excellent workability, operability, and followability to the FPC even if it is a thin film. A first insulating layer 12, a second insulating layer 13, and a thermosetting adhesive layer 14 are sequentially laminated on one side of a support film 11 to form the coverlay film 10. The first insulating layer 12 contains a flame retardant. The tensile elongation of the laminate 15 comprising the first insulating layer 12, the second insulating layer 13, and the thermosetting adhesive layer 14, excluding the support film 11, is 100% or more.

Description

   Cover film   

The present invention relates to a cover film, and more particularly, to a processability and bonding workability in a step of manufacturing a substrate, and to follow the unevenness or step of a flexible printed circuit board (hereinafter referred to as FPC). Cover film of a film with excellent properties.

In portable electronic devices such as mobile phones, in order to reduce the outer size of the housing and to suppress thinness, it is convenient to carry the electronic components on a printed circuit board. In addition, in order to reduce the outer size of the casing, the printed circuit board is divided into a plurality of pieces, and a flexible FPC is used for the connection line between the divided printed circuit boards, thereby allowing the printed circuit board to be folded or slid. .

In addition, since a portable information terminal (smartphone, tablet, etc.) consumes more power than a conventional mobile phone in recent years, battery retention has deteriorated. Therefore, it is necessary to increase the volume and capacity of the battery as much as possible, and there is a strong demand for miniaturization and thinning of members and components other than the battery, and for example, thinning of the entire FPC to which a cover film is bonded is required. In addition, in recent years, light-shielding properties and design properties have been valued, and coloring of cover films has been required.

Conventionally, as a cover film used for the purpose of reducing the thickness of the entire FPC, a cover film in which an adhesive is applied to a thin polyimide film is used (Patent Document 1). However, the thin polyimide film has problems of poor processability in the manufacturing steps and poor workability when attached to an FPC.

In addition, in conventional cover films, since it is difficult to reduce the thickness and lack flexibility, the followability to the FPC step is insufficient, which is a cause of problems such as voids and swelling during the heating step. Therefore, it is difficult to sufficiently reduce the thickness of the entire FPC to which the cover film is bonded.

[Prior Art Literature]

[Patent Literature]

Patent Document 1: Japanese Unexamined Patent Publication No. 9-135067

In view of the background art described above, the present invention provides a cover film which, even if it is a film, has good processing suitability and operability in the production of FPC, and has excellent followability to a step of FPC.

In order to improve the operability when FPC is bonded to the cover film, in the cover film of the present invention, an insulating layer and a thermosetting adhesive layer are sequentially laminated on one surface of the support film. In addition, the FPC can be transferred from the support film to the FPC by laminating the cover film of the present invention on the FPC via an adhesive layer and thermocompression-bonding the cover film.

In addition, in order to endure a severe bending operation and to make the FPC have good followability, in the present invention, the tensile elongation of a laminate composed of an insulating layer and an adhesive layer is increased.

In addition, in order to solve the above-mentioned problems, the present invention provides a cover film, which is formed by sequentially laminating a first insulating layer, a second insulating layer, and a thermosetting adhesive layer on one surface of a support film. The first insulating layer contains a flame retardant. After removing the support film, the tensile elongation of the laminate formed by the first insulating layer, the second insulating layer, and the thermosetting adhesive layer is 100% or more.

Preferably, the second insulating layer contains a flame retardant at a lower concentration than the first insulating layer, or does not contain a flame retardant.

Preferably, the thickness of the first insulating layer is smaller than the thickness of the second insulating layer.

The thermosetting adhesive layer preferably contains a polyurethane resin and an epoxy resin.

The polyurethane resin is preferably a phosphorus-containing polyurethane resin.

Preferably, at least one of the first insulating layer, the second insulating layer, and the thermosetting adhesive layer contains a light absorber.

In addition, the present invention provides a mobile phone using the above-mentioned cover film as an FPC protective member.

In addition, the present invention provides an electronic apparatus using the above-mentioned cover film as an FPC protective member.

According to the above-mentioned cover film of the present invention, it is possible to manufacture a thin-film cover film that can be followed without voids when it is covered with a circuit board having a step difference, etc. In subsequent solder reflow steps or plating steps, Defects due to swelling or penetration of the plating solution.

In addition, by including a light absorbing material in the insulating layer or the adhesive layer, it is possible to specifically color on one surface side of the cover film.

Based on the above, according to the present invention, it is possible to provide a cover film which can reduce the occurrence of defects caused by swelling or penetration of a plating solution in a heating step such as a solder reflow step after covering a wiring board or the like, and is rich in softness. It is thin, and even if repeated severe bending operations are repeated, the FPC protection performance does not decrease, and the bending characteristics are excellent.

10‧‧‧ cover film

11‧‧‧ support body membrane

12‧‧‧The first insulation layer

13‧‧‧Second insulation layer

14‧‧‧ thermosetting adhesive layer

15‧‧‧ stacked body

19‧‧‧ peeling film

FIG. 1 is a schematic cross-sectional view showing an embodiment of a cover film of the present invention.

Hereinafter, preferred embodiments of the present invention will be described. The present invention is not limited to the embodiment, and various changes can be made without departing from the gist of the present invention.

As shown in FIG. 1, a first insulating layer 12, a second insulating layer 13, and a thermosetting adhesive layer 14 are sequentially laminated on one surface of a support film 11. The laminated body 15 formed of the first insulating layer 12, the second insulating layer 13, and the thermosetting adhesive layer 14 can be integrally peeled off from the support film 11 and bonded to an FPC or the like.

When the cover film 10 according to the present embodiment is bonded to an FPC or the like as an adherend, the outer surface is made of a dielectric material, and the FPC lines and circuit components can be electrically insulated and protected. In addition, in order to improve the deflection characteristics of the deflection operation, the cover film of the present embodiment can reduce the overall thickness.

(Support body membrane)

Examples of the base material of the support film 11 used in the cover film 10 of the present embodiment include polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate. Polyester films such as alcohol esters; Polyolefin films such as polypropylene or polyethylene.

When the base material of the support body film 11 is, for example, a base material such as polyethylene terephthalate itself has a certain degree of peelability, the laminate body 15 can be directly laminated on the support body film 11 without performing a peeling treatment. ; The surface of the support film 11 may be subjected to a peeling treatment for easily peeling the laminate 15 from the support film 11.

In addition, in the case where the base film used as the support film 11 does not have peelability, a release agent such as an amino alkyd resin or a silicone resin may be applied and then dried by heating. Perform peeling treatment. When the cover film 10 of this embodiment is used for FPC, it is preferable that this release agent does not use a silicone resin. When a silicone resin is used as a release agent, a part of the silicone resin may move to the surfaces of the insulating layers 12 and 13 that are in contact with the surface of the support film 11, and may further move to the thermosetting property through the inside of the laminate 15. The surface of the adhesive layer 14. The silicone resin moved to the surface of the thermosetting adhesive layer 14 may reduce the adhesive force of the thermosetting adhesive layer 14.

The thickness of the support film 11 is not particularly limited because it is excluded from the overall thickness of the laminated body 15 when it is used while covering the FPC, and is usually about 12 to 150 μm. By using the support film 11, it is possible to improve processability when forming the insulating layers 12 and 13 and the thermosetting adhesive layer 14, and workability when bonding to an FPC.

The color of the support film 11 may be colorless (colorless) or colored. When the support body film 11 is colored, a color having a large contrast with respect to the color of the laminated body 15 from which the support body film 11 is removed is preferred. For example, when the laminated body 15 is a dark color such as black, the support film 11 is preferably a bright color such as white or yellow. Thereby, operability such as peeling the laminate 15 from the support film 11 or confirmation of whether the support film 11 is peeled can be improved. The coloring of the support film 11 can be performed using a known pigment, dye, or the like. Examples of the support film 11 include a white PET film having a thickness of 30 μm or more and 60 μm or less.

(Insulation)

The insulating layers 12 and 13 of the cover film 10 are insulating layers formed of a dielectric thin film resin layer or the like. A thin film resin film of a polyimide film formed using a solvent-soluble polyimide, having high mechanical strength, heat resistance, insulation, and solvent resistance characteristic of a polyimide resin. Chemically until about 260 ° C Since it is stable, it is suitable as the insulating layers 12 and 13.

Examples of the polyimide include a thermosetting polyimide produced by a dehydration condensation reaction by heating a polyamic acid, and a solvent-soluble polyimide that is soluble in a solvent as a non-dehydration condensation type.

A general method for producing a polyimide film is to synthesize a polyamic acid as a precursor of a fluorene imine by reacting a diamine with a carboxylic dianhydride in a polar solvent, and dehydrating the ring The conversion of polyamidonic acid into polyimide. However, the temperature of the heat treatment in the step of fluorene imidization is preferably a temperature range of 200 ° C to 300 ° C. When the heating temperature is lower than this temperature, the temperature of fluorene imidization may not proceed. Not preferred; when the heating temperature is higher than the above-mentioned temperature, there is a possibility that thermal decomposition of the compound may occur, so it is not preferred.

In the cover film 10 of this embodiment, in order to further improve the flexibility of the insulating layers 12, 13, an extremely thin polyimide film having a total thickness of the insulating layers 12, 13 of less than 10 m can be used. When the thickness of the polyimide film to be used is thinner than about 7 μm, it is preferable to form a thin polyimide film by laminating on one surface of the support film 11 as a strength reinforcing material. For example, a coating solution containing polyamic acid may be cast on one surface of the support film 11 and heated to form a polyimide film.

However, the polyimide film itself has heat resistance to heat treatment at a heating temperature of 200 ° C to 250 ° C. However, in consideration of both price and heat-resistant temperature performance, a general-purpose heat-resistant resin film is used. When a film having a low heat resistance such as a polyethylene phthalate (PET) resin film is used as the support film 11, it is not possible to form a polyimide from a conventional polyimide acid which is a precursor of the imine. Methods.

The solvent-soluble polyfluorene imine is completely soluble in the solvent because the polyfluorine imidization is completed and can be dissolved in a solvent, and can be applied at a temperature of less than 200 ° C. The solvent was evaporated at a low temperature to form a film. Therefore, for the insulating layers 12 and 13, it is preferable to apply a non-dehydration condensation type solvent-soluble polyimide coating solution on one surface of the support film 11, and then dry it at a heating temperature of less than 200 ° C. Forms a thin film of polyimide resin. Thereby, it is possible to laminate an extremely thin fluorene imine film having a thickness of 1 to 9 μm on one surface of the support film 11 formed of a general-purpose heat-resistant resin film. In the same manner as the thermosetting adhesive layer 14, the insulating layers 12 and 13 are formed by coating, whereby the support film 11 can be transported along the longitudinal direction thereof, and insulation can be continuously formed thereon. The layers 12 and 13 and the thermosetting adhesive layer 14 and the like can be produced in a roll-to-roll manner, and are excellent in processability and productivity.

The non-dehydration-condensation type solvent-soluble polyfluorene imide that can be used for the insulating layers 12 and 13 of this embodiment is not particularly limited, and a commercially available coating solution of a solvent-soluble polyfluorene imine can be used. Specific examples of commercially available solvent-soluble polyimide coating solutions include Solpit 6,6-PI (Solpit Industries, Ltd.), Q-IP-0895D (PI R & D Co., LTD.), And PIQ ( Hitachi Chemical Industries), SPI-200N (Nippon Steel Chemical Co., Ltd.), RIKACOAT SN-20, RIKACOAT PN-20 (Nippon Physico Chemical), etc. The method of applying the solvent-soluble polyimide coating liquid to the support film 11 is not particularly limited, and examples thereof include a die coater, a blade coater, and a lip coater. The coating machine performs coating.

The total thickness of the insulating layers 12 and 13 of this embodiment (for example, the thickness of the polyfluorene film) is preferably 1 to 9 μm. If the thickness of the polyfluoreneimide film is less than 0.8 μm, the mechanical strength of the produced film is weak, which is technically difficult. In addition, if the thickness of the insulating layers 12 and 13 such as a polyimide film exceeds 10 μm, it is difficult to obtain a thin layered body 15 having excellent flexibility. In addition, when the total thickness of the insulating layers 12 and 13 is less than about 7 μm, it is difficult to adjust the tension at the time of taking up the roll. Therefore, it is preferable to use the support film 11 as a strength reinforcing material.

The insulating layers 12 and 13 of the present embodiment preferably have a large tensile elongation in order to improve followability with respect to a step of the FPC. The tensile elongation of one or both of the insulating layers 12 and 13 is preferably 100% or more, and more preferably 250% or less. Here, the tensile elongation is expressed in% as the amount of elongation when the film is cut by constant-speed stretching. The larger the tensile elongation, the softer the film relative to the tensile force. Therefore, in order to provide the laminated body 15 with sufficient flexibility and to exhibit excellent followability to unevenness or step to FPC, the tensile elongation is preferably 100% or more.

When the insulating layers 12 and 13 having high tensile elongation are formed of a polyimide film, for example, a polyimide material having an aromatic unit having 3 or more carbon atoms between aromatic units is preferably used. . Further, the aliphatic unit preferably contains a polyalkyleneoxy group having an alkylene group having about 1 to 10 carbon atoms.

In addition, the water vapor permeability of the polyimide film usable in the insulating layers 12 and 13 of the present embodiment is preferably 500 g / m ² ‧ or more. In the case where the water vapor permeability is lower than this value, in the heating step such as solder reflow after covering the FPC, there may be outgassing from the residual solvent or adhesive from each layer, and moisture in the film. Water vapor generated due to rapid heating causes peeling between layers. The upper limit of the water vapor permeability is not particularly set. As long as the same material is used, the water vapor permeability is inversely proportional to the thickness. Therefore, when the thickness is reduced to increase the water vapor permeability, it is preferable to maintain the thickness within the above-mentioned range.

(Flame retardant)

In order to ensure the flame retardance of the laminated body 15, the insulating layers 12 and 13 may contain a flame retardant. Examples of the flame retardant include inorganic flame retardants such as metal hydroxides, antimony, and red phosphorus; organics such as halogens (chlorine, bromine, etc.), phosphorus, and guanidine. Flame retardant. From the viewpoint of excellent dispersibility with insulating resins such as polyimide, organic flame retardants such as phosphorus and bromine are preferred. Examples of the phosphorus-based flame retardant include aliphatic phosphates, aromatic phosphates, aromatic condensation phosphates, bisphenol phosphates, halogen-containing phosphates, halogen-containing condensation phosphates, and phosphazene compounds. Wait.

When the flame retardant is an additive flame retardant that does not react with the resin, the tensile elongation of the insulating layers 12 and 13 may decrease depending on the amount of the flame retardant added. Therefore, when the laminated body 15 is bonded to FPC or the like, it is preferable that the first insulating layer 12 as the outermost layer contains a flame retardant, and the second insulating layer 13 contains a flame retardant having a concentration lower than that of the first insulating layer 12, or The second insulating layer 13 does not contain a flame retardant. The thickness of the first insulating layer 12 is preferably smaller than the thickness of the second insulating layer 13. Examples of the thickness of the first insulating layer 12 include 0.5 to 5 μm. Examples of the thickness of the second insulating layer 13 include 2 to 9 μm.

The ratio of the resin and the flame retardant contained in the insulating layers 12 and 13 can be appropriately set. In the first insulating layer 12, the flame retardant is preferably 20 to 200 parts by weight based on 100 parts by weight of the resin. In the second insulating layer 13, the flame retardant is preferably 0 to 100 parts by weight based on 100 parts by weight of the resin. Here, “the ratio of the flame retardant to 100 parts by weight of the resin is 0 parts by weight” means that the flame retardant is not contained. The flame retardant may have a concentration distribution in the thickness direction of the insulating layer.

An interface may appear between the first insulating layer 12 and the second insulating layer 13 due to a difference in the composition of the resin or an additive, or a clear interface may not appear due to a continuous change in the composition.

The first insulating layer 12 may be a flame retardant layer separated from the second insulating layer 13 due to application, aggregation, precipitation, or the like of the electrically insulating flame retardant. In this case, the first insulating layer 12 may have a structure containing no resin or a structure containing a binder such as a resin as a flame retardant.

(Thermosetting adhesive layer)

As an adhesive layer for bonding the laminated body 15 of the cover film 10 to an FPC, the thermosetting adhesive layer 14 is preferable. As long as the thermosetting adhesive used for the thermosetting adhesive layer 14 is an electrically insulating adhesive layer, specific examples include an acrylic adhesive, a urethane adhesive, an epoxy adhesive, and a rubber. Commonly used thermosetting adhesives such as adhesives and silicone adhesives. In addition, a flame-retardant thermosetting adhesive mixed with flame retardants such as phosphorus and bromine can be suitably used, but it is not particularly limited. A phosphorus-containing compound can be used as a polyol compound or a polyisocyanate compound as a polyurethane raw material, and a polyurethane resin containing phosphorus in the molecular structure of the resin can also be used as a thermosetting adhesive. The thermosetting adhesive layer 14 preferably contains a polyurethane resin and an epoxy resin, and more preferably the polyurethane resin is a phosphorus-containing polyurethane resin.

The thickness of the thermosetting adhesive layer 14 is, for example, preferably 1 to 8 μm. The thermosetting adhesive layer 14 can be formed, for example, by coating.

The adhesive force of the thermosetting adhesive layer 14 is not particularly limited, and the measurement method is method A of 8.1.1 (90 ° direction pulling) of JIS-C-6471 "Test method for copper-clad laminated board for flexible printed wiring boards" (Stretch and peel), a range of 5 to 30 N / inch is more suitable. When the adhesive force is less than 5 N / inch, for example, the laminated body 15 adhered to the FPC may peel off or float due to heat or deflection.

If the heat-curable adhesive layer 14 is not a pressure-sensitive adhesive layer that exhibits pressure-sensitive adhesiveness at ordinary temperature, but an adhesive layer that exhibits adhesiveness by heating and pressing, it is not easy to adhere to repeated flexures. It is preferable because it is reduced. The conditions for FPC heating and pressure bonding are not particularly limited, and for example, the conditions of a temperature of 160 ° C., a pressure of 4.5 MPa, and hot pressing for 60 minutes can be exemplified.

When the laminated body 15 is heated and pressurized by the FPC, the support film 11 may be peeled and removed from the laminated body 15 in advance. Alternatively, the FPC may be directly heated and pressurized in a state where the support film 11 is laminated on the laminate 15. In this case, the support film 11 may be peeled and removed from the laminated body 15 after the FPC is subjected to a heat and pressure bonding process.

(Anchor layer)

In order to improve the adhesion between the insulating layers 12 and 13 as the base material of the laminated body 15 and the thermosetting adhesive layer 14, an anchor layer may be provided between the second insulating layer 13 and the thermosetting adhesive layer 14. (Not shown). In order to be able to withstand a bonding temperature of 150 to 250 ° C. caused by heating and pressing of the thermosetting adhesive layer 14, it is preferable to use an adhesive having excellent heat resistance for the anchor layer. In addition, an anchor layer having excellent adhesion to the insulating layers 12 and 13 and the thermosetting adhesive layer 14 is preferred. In addition, when the adhesion is sufficient, the anchor layer may be omitted, and the second insulating layer 13 and the thermosetting adhesive layer 14 may be directly contacted.

As the adhesive resin composition used for the anchor layer, a thermoplastic resin such as a polyester resin, a urethane resin, a (meth) acrylic resin, a polyethylene resin, a polystyrene resin, or a polyamide resin is preferably used. Further, it may be a thermosetting type such as an epoxy resin, an amine resin, a polyimide resin, or a (meth) acrylic resin.

The adhesive resin composition as the anchor layer is particularly preferably an adhesive resin composition in which a polyester resin composition having an epoxy group is crosslinked, or an epoxy resin as a curing agent mixed with a polyurethane resin. Adhesive resin composition. Therefore, the anchor layer has harder physical properties than the insulating layers 12 and 13 formed of a thin film such as a polyimide film. The polyester-based resin composition having an epoxy group is not particularly limited. For example, an epoxy resin (its uncured resin) having two or more epoxy groups in one molecule and two resins in one molecule can be used. It is obtained by the reaction of the above-mentioned carboxyl polycarboxylic acid and the like. For the crosslinking of the epoxy-based polyester resin composition, a crosslinking agent for an epoxy resin that reacts with an epoxy group can be used.

The thickness of the anchor layer is preferably about 0.05 to 1 m. If the thickness is such a thickness, sufficient adhesion with the thermosetting adhesive layer 14 can be obtained. When the thickness of the anchor layer is 0.05 μm or less, the adhesion between the insulating layers 12 and 13 and the thermosetting adhesive layer 14 may decrease. In addition, if the thickness of the anchor layer exceeds 1 μm, it is not effective to increase the adhesion between the insulating layers 12 and 13 and the thermosetting adhesive layer 14, but the thickness, cost, and the like of the laminated body 15 are increased, which is not preferable. The anchor layer can be formed by, for example, coating.

(Light absorbent)

In order to impart light-shielding properties to the laminated body 15 in a state of being adhered to the FPC, or to improve designability, any layer constituting the laminated body 15 may contain a light absorbing material. For this purpose, the layer capable of containing a light absorbing material is one or both of the insulating layers 12 and 13, the thermosetting adhesive layer 14, or may be provided on the insulating layers 12 and 13 and the thermosetting adhesive. Examples of the arbitrary layers between the agent layers 14 include, for example, at least any one layer or two or more of the insulating layers 12 and 13, for example, the thermosetting adhesive layer 14 and the anchor layer. The heat-curable adhesive layer 14 may include a light absorber, or the insulating layers 12 and 13 formed of a solvent-soluble polyfluorene imide may include a light absorber. When the light-absorbing agent-containing layer (light-absorbing layer) also serves as at least any one of the insulating layers 12 and 13 or the thermosetting adhesive layer 14, it can be suppressed compared to a case where another light-absorbing layer is laminated. The laminated body 15 is preferably increased in thickness.

Examples of the light absorber include one or more black pigments selected from the group consisting of non-conductive carbon black, graphite, aniline black, cyanine black, titanium black, black iron oxide, chromium oxide, and manganese oxide. Or color pigments. The type, blending amount, and the like of the light absorber are preferably selected so that the light absorption layer maintains electrical insulation.

The light-absorbing material formed of a black pigment or a colored pigment is preferably contained at 0.1 to 30% by weight in any one of the layers. It is preferred that the average particle diameter of the primary particles of the black pigment or colored pigment observed by SEM is about 0.02 to 0.1 μm. The thickness of the light absorbing layer is preferably larger than the particle diameter of the light absorbing agent so that the particles of the light absorbing material are not exposed.

The light transmittance of the laminated body 15 from which the support film 11 is removed is preferably 5% or less. Examples of the light transmittance include visible light transmittance and total light transmittance.

In order to effectively reduce the light transmittance and improve the light-shielding property, a black pigment such as carbon black is preferable in the light-absorbing material. As the black pigment, a black color material such as silica particles may be immersed so as to be black only on the surface layer portion, or may be formed of a black coloring resin or the like and the whole may be made of black. In addition, the black pigment may contain particles exhibiting a nearly black color, such as gray, blackened brown, or blackened green, in addition to pure black, and may be used as long as it is a dark color that is difficult to reflect light.

(Release film)

In order to protect the thermosetting adhesive layer 14, the cover film 10 may have a release film 19 bonded to the thermosetting adhesive layer 14. Examples of the base material of the release film 19 include polyester films such as polyethylene terephthalate, polybutylene terephthalate, and polyethylene naphthalate; polypropylene or Polyolefin film. These substrate films are coated with a release agent such as an amino alkyd resin or a silicone resin, and then dried by heating to perform a release treatment. Since the cover film 10 according to this embodiment is bonded to the FPC in a state where the release film 19 is removed, it is preferable not to use a silicone resin for the release agent. This is because when a silicone resin is used as the release agent, a part of the silicone resin moves to the surface of the thermosetting adhesive layer 14 in contact with the surface of the release film 19, and the thermosetting adhesive layer 14 is adhered. The possibility of weakening the force.

The thickness of the release film 19 is not particularly limited because it is excluded from the entire thickness of the laminated body 15 when it is used while covering the FPC, and is usually about 12 to 150 μm.

(Cover film)

The cover film 10 according to the present embodiment can be applied to a cover film having excellent flexural properties that can be bonded to an FPC subjected to repeated flexing operations. In addition, the FPC to which the cover film of this embodiment is bonded can be used in various electronic devices such as a mobile phone, a notebook computer, and a portable terminal.

As a method for manufacturing the cover film 10 according to the present embodiment, the support film 11 includes the insulating layers 12 and 13 and the thermosetting adhesive layer 14 in order from the side closer to the support film 11. A method of laminating materials by applying them. In addition, as described above, the release film 19 may be bonded to the thermosetting adhesive layer 14.

When the FPC performs a flexing operation, the cover film 10 of the present embodiment is preferably used by being bonded to the FPC in a state of the laminate 15. Here, the laminated body 15 is a laminated body in which the support film 10 and the release film 19 are removed from the cover film 10 when the cover film 10 has a release film 19; and the case where the cover film 10 does not include a release film 19 Below, it means the laminated body from which the support film 11 was removed. The laminated body 15 may contain the said anchor layer, a light absorption layer, etc.

The total thickness of the laminated body 15 is preferably 15 μm or less, and examples thereof include 5 to 15 μm and 12 μm or less. The tensile elongation of the laminate 15 is preferably 100% or more, and may be 150% or more or 150% or less.

[Example]

Hereinafter, the present invention will be specifically described by way of examples.

(Example 1)

As the supporter film 11, a polyethylene terephthalate (PET) film having a thickness of 50 μm subjected to a peeling treatment on one side was used.

A solvent-soluble polyimide resin containing 50 parts by weight of a phosphorus-based flame retardant relative to 100 parts by weight of the resin was cast-coated on one surface of the support film 11 so that the thickness after drying was 1 μm. The coating liquid is dried to form the first insulating layer 12.

Coating the first insulating layer 12 with a solvent-soluble polyimide resin with a dry elongation of 170% without a flame retardant so that the thickness after drying is 3 μm The second insulating layer 13 is formed by drying the liquid.

A thermosetting adhesive was applied to the second insulating layer 13 so that the thickness after drying was 8 μm, and dried to form a thermosetting adhesive layer 14 to obtain a cover film of Example 1. In this thermosetting adhesive, 2.4 parts by weight of a polyfunctional epoxy resin (manufactured by Toyobo: HY-30) and 4.7 parts by weight are sequentially added to 100 parts by weight of a phosphorus-containing polyurethane resin solution (manufactured by Toyobo: UR3575). Fumed silica (manufactured by Japan Aerosil: R972) and stirred.

(Examples 2 and 3)

The ratio of the phosphorus-based flame retardant contained in the first insulating layer 12 was set to 100 parts by weight in Example 2 and 150 parts by weight in Example 3, except that the ratio was the same as that of Example 1. In this manner, the covering films of Examples 2 and 3 were obtained.

(Examples 4 to 6)

The coating liquid for forming the second insulating layer 13 is a coating liquid of a solvent-soluble polyfluorene imide resin containing 20 parts by weight of a phosphorus-based flame retardant with respect to 100 parts by weight of the resin. In the same manner as in Examples 1 to 3, the cover films of Examples 4 to 6 were obtained.

(Example 7)

A cover film of Example 7 was obtained in the same manner as in Example 2 except that the thickness of the first insulating layer 12 was 2 μm and the thickness of the second insulating layer 13 was 7 μm.

(Comparative example 1)

A coating liquid for forming the first insulating layer 12 is a coating liquid for a solvent-soluble polyfluorene imide resin that does not contain a flame retardant, and a coating liquid for forming the second insulating layer 13 is a coating liquid A coating film of Comparative Example 1 was obtained in the same manner as in Example 1 except that a solvent-soluble polyimide resin coating solution containing 100 parts by weight of a phosphorus-based flame retardant with respect to 100 parts by weight of the resin was used. .

(Comparative example 2)

A solvent-soluble polyimide resin having a lower tensile elongation after coating and drying was used as the solvent-soluble polyimide resin used to form the insulating layers 12 and 13 except that the same was used as in Example 2. Method to obtain a cover film of Comparative Example 2.

(Measurement method of tensile elongation)

According to IPC-TM-650 2.4.19, the measurement was performed with a sample size of 15 mm wide, a chuck distance of 100 mm, and a measurement speed of 50 mm / minute (measurement was performed with the number of samples N = 5, and the average value was taken).

The laminated body from which the support film was removed was used as a sample, and the tensile elongation of the laminated body was measured.

On one side of the same release film as the support film, a coating liquid for forming a second insulating layer is applied, and the release film is removed after drying to obtain a monomer of the second insulating layer, which is used as a sample. , Measure the tensile elongation of the second insulating layer.

(Follow-up evaluation method)

On a polyimide film having a thickness of 12.5 μm, on a test pattern formed with a copper circuit pattern having a thickness of 75 μm and L / S = 75 μm / 75 μm, the heat-curing adhesive surface of the film was overlaid. Lamination was performed by thermal lamination at a speed of 1 m / minute. After the support film 11 was peeled off, hot pressing was performed under the conditions of 160 ° C., 4.5 MPa, and 65 minutes to obtain a follow-up evaluation sample.

Observing the cross-section of the obtained sample, it was evaluated as "◎" when it followed the line pattern very well and its appearance was good, and it was evaluated as "○" when it followed the line pattern well but the edge of the line became thin. A case where it floated from the line pattern without following it, or a case where the coating film at the edge portion of the line was broken was evaluated as "×".

(Evaluation method of flame retardancy)

The obtained cover film was hot-pressed on a polyimide film having a thickness of 12.5 μm using the above-mentioned method (refer to the evaluation method of followability) to obtain a sample for evaluating flame retardancy. The flame retardancy was evaluated in accordance with the method of the UL-94 Thin Material Vertical Burning Test (ASTM D4804). The flame retardancy was evaluated as "◎" when the flame was not fired, and the flame retardancy was evaluated as "" if the flame was not burned to the mark. (Circle), and the case where it burned to the left and right of the mark was evaluated as "(△)", and the case where it burned above the line and did not have flame retardancy was evaluated as "x".

(test results)

For Examples 1 to 7 and Comparative Examples 1 to 2, the cover film was evaluated by the above-described evaluation method, and the obtained evaluation results are shown in Table 1.

In the columns of the first insulating layer and the second insulating layer, "parts by weight" means parts by weight of the flame retardant with respect to 100 parts by weight of the resin. "PI1" refers to the solvent-soluble polyfluorene imine resin used in Example 1, and "PI2" refers to the solvent-soluble polyfluorene imine resin used in Comparative Example 2.

In the column of the material of the heat-adhesive adhesive layer, “PU1” refers to a heat-adhesive adhesive containing a flame-retardant polyurethane used in Example 1.

The "thickness of the laminate" refers to the thickness of the entire cover film from which the support film is removed, and the "total thickness" refers to the thickness of the entire cover film including the support film.

In addition, as a phosphorus-based flame retardant, [(CH ₃ ) ₂ C ₆ H ₃ O] ₂ P (O) OC ₆ H ₄ OP (O) [OC ₆ H ₃ (CH ₃ ) ₂ ] ₂ .

From the results shown in Table 1, it was found that when the tensile elongation of the laminate was 100% or more, the followability was good. That is, when the tensile elongation of the laminate is low, the followability to the step is poor. When the tensile elongation of the second insulating layer is low, it is found that the tensile elongation of the laminate also tends to decrease.

In addition, in Comparative Example 1 in which a flame retardant was not added to the first insulating layer and a flame retardant was added to the second insulating layer, the total amount of the flame retardant contained in the first insulating layer and the second insulating layer. Although larger than those of Examples 1 to 7, in the samples in which the support film was peeled, the first insulating layer as the outermost layer had low flame retardancy, and therefore the flame retardancy of the entire laminate was also deteriorated.

Claims (8)

    A cover film, characterized in that a first insulating layer, a second insulating layer, and a thermosetting adhesive layer are sequentially laminated on one surface of a support film, and the first insulating layer contains a flame retardant and is removed. After the support film, the tensile elongation of the laminate formed by the first insulating layer, the second insulating layer, and the thermosetting adhesive layer is 100% or more.         The cover film according to item 1 of the scope of the patent application, wherein the second insulating layer contains a flame retardant at a lower concentration than the first insulating layer, or does not contain a flame retardant.         The cover film according to item 1 or 2 of the scope of the patent application, wherein a thickness of the first insulating layer is thinner than a thickness of the second insulating layer.         The cover film according to any one of claims 1 to 3, wherein the thermosetting adhesive layer contains a polyurethane resin and an epoxy resin.         The cover film according to item 4 of the scope of patent application, wherein the polyurethane resin is a phosphorus-containing polyurethane resin.         The cover film according to any one of claims 1 to 5, wherein at least one of the first insulating layer, the second insulating layer, and the thermosetting adhesive layer contains light Absorbent.         A mobile phone is formed by using the cover film described in any one of claims 1 to 6 as an FPC protection member.         An electronic instrument is formed by using the cover film described in any one of the scope of patent applications 1 to 6 as an FPC protection member.