JP2006089564A - Adhesive for folding and fixing flexible printed circuit boards - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an adhesive for folding and fixing a flexible printed circuit board having heat resistance, excellent FPC resilience and processability, a flexible printed circuit board, an electronic device, and a double-sided pressure-sensitive adhesive sheet.
A pressure-sensitive adhesive used for folding and fixing a flexible printed circuit board, comprising: (a) a cutting elongation E at the time of tensile cutting of the pressure-sensitive adhesive is 800 to 1400%, and a cutting strength T is 300 to 700 kPa. (B) The cutting strength T _{60 ° C.} at the time of tensile cutting of the pressure-sensitive adhesive after standing at 60 ° C. for 100 hours is 210 to 700 kPa.
[Selection figure] None

Description

  The present invention relates to an adhesive used for folding and fixing a flexible printed circuit board (FPC), an FPC using the adhesive, an electronic device using the FPC, and a double-sided adhesive sheet provided with an adhesive layer. In particular, the present invention relates to a pressure-sensitive adhesive for FPC folding fixing, which has heat resistance and excellent FPC resilience and processability.

  A flexible printed circuit board (hereinafter referred to as “FPC”) is a complex copper circuit formed on a flexible insulating film such as polyimide, which can be bent, stacked, folded, wound, twisted, etc. In addition, it is widely used in small and light electronic devices such as OA devices and communication devices. At present, an adhesive is used to fix the FPC to a housing or the like of an electronic device. In recent years, in order to simplify the manufacturing process, the adhesive applied on the release paper is attached to the FPC together with the release paper, and then the electronic component is mounted on the FPC with solder and the solder is reflowed (dissolved) in the furnace. (Hereinafter, this is referred to as “first pasting method”).

  In recent years, as the lead-free solder progresses, the melting point of the solder becomes higher, and the temperature in the solder reflow process is also higher than 200 ° C. For this reason, the pre-adhered adhesive is also exposed to high temperature together with the solder, and an improvement in the heat resistance of the adhesive has been demanded.

  As such an adhesive having excellent heat resistance, an adhesive composition containing an antioxidant such as a radical chain inhibitor has been proposed (see, for example, Patent Document 1).

  On the other hand, in electronic devices that are increasingly mounted, such as mobile phones, there are increasing designs in which FPCs are folded and folded in order to effectively use space and reduce the size. An adhesive is used to fix the folded / folded portions. However, since the FPC has a strong repulsive force, even if the folded / folded portions are fixed together with an adhesive, the folded and fixed portions are peeled off over time, which hinders assembly in the next process. There is a problem that the yield is reduced.

For this reason, the adhesive for FPC folding and fixing includes a (1) heat resistance that can withstand the temperature in the solder reflow process, and (2) a folded part until the folded FPC is incorporated into the electronic device in the assembly process. Is required to have repulsion resistance against FPC that does not peel off.
Japanese Patent Laid-Open No. 5-271623

  However, the pressure-sensitive adhesive composition according to Patent Document 1 has improved heat resistance, but cannot withstand the repulsion resistance of the FPC, and cannot solve the problem that the portion once folded and fixed is peeled off. It was.

  In addition, when the present inventors have made various comparative studies on FPC resilience resistance using a commercially available FPC folding-fixing adhesive, if there is an adhesive that has no resilience at all, it has excellent resilience resistance. Some were. However, in the case of commercially available adhesives with excellent resilience resistance, the adhesive is too soft, producing glue feet and glue balls during punching, and sticking to the blades and causing glue skipping etc. I found out that there was a problem. Therefore, it was found that the adhesive for FPC folding and fixing requires (3) workability in addition to (1) heat resistance and (2) FPC resilience resistance.

  An object of the present invention is to provide a pressure-sensitive adhesive for folding and fixing a flexible printed board having heat resistance and excellent FPC resilience and processability in view of the above-mentioned problems of the prior art.

  Another object of the present invention is to provide a flexible printed circuit board that is folded and fixed using the above-mentioned pressure-sensitive adhesive, an electronic device using the flexible printed circuit board as a component, and a double-sided pressure-sensitive adhesive sheet provided with a pressure-sensitive adhesive layer on both sides of a support. There is to do.

To solve this problem,
The present invention is an adhesive used for folding and fixing a flexible printed circuit board, and (a) the elongation at break E of the adhesive is 800 to 1400% and the cutting strength T is 300 to 700 kPa. And (b) a pressure-sensitive adhesive having a cutting strength T _{60 ° C.} at the time of tensile cutting of the pressure-sensitive adhesive after standing at 60 ° C. for 100 hours is 210 to 700 kPa.

  In addition, the present invention provides a flexible printed board characterized by being folded and fixed using the pressure-sensitive adhesive.

  The present invention also provides an electronic apparatus using the flexible printed circuit board as a component.

  Moreover, this invention provides the double-sided adhesive sheet characterized by providing the adhesive layer which consists of the said adhesive, and the heat resistant release paper in this order on both surfaces of the support body.

Adhesive of the present invention has heat resistance, tensile and elongation at break E and breaking strength T of cut when the adhesive, 60 ° C., the tensile cleavage of 100 hours after standing the adhesive breaking strength T _{60 ° C.} Is within a specific range, the FPC resilience resistance and processability can be improved.

  Moreover, since the flexible printed circuit board and the electronic device of the present invention have the flexible printed circuit board folded and fixed using the adhesive, the FPC has excellent FPC resilience, and the FPC adhesive is peeled off during the process. There is no.

[Adhesive]
The pressure-sensitive adhesive of the present invention is for FPC folding fixing, and (a) the elongation at break E during tensile cutting of the pressure-sensitive adhesive is 800 to 1400%, the cutting strength T is 300 to 700 kPa, and (b) 60 ° C. The cutting strength T _{60 ° C.} at the time of tensile cutting of the pressure-sensitive adhesive after standing for 100 hours is 210 to 700 kPa.

  This pressure-sensitive adhesive comprises an acrylic polymer obtained by polymerizing a monomer mainly composed of an alkyl (meth) acrylate having an alkyl side chain having 4 to 14 carbon atoms, a crosslinking agent, an antioxidant, Containing. In this specification, (meth) acrylic acid means acrylic acid or methacrylic acid, and the same applies to acrylic acid or methacrylic acid derivatives.

Specific examples of the (meth) acrylic acid alkyl ester having an alkyl side chain having 4 to 14 carbon atoms include n-butyl acrylate, sec-butyl acrylate, t-butyl acrylate, n-hexyl acrylate, cyclohexyl acrylate, n-octyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, isononyl acrylate, isodecyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, sec-butyl methacrylate, t -Butyl methacrylate, n-hexyl methacrylate, cyclohexyl methacrylate, n-octyl methacrylate, isooctyl methacrylate Over DOO, 2-ethylhexyl methacrylate, isononyl methacrylate, isodecyl methacrylate, lauryl methacrylate, cyclohexyl (meth) acrylate, isobornyl (meth) acrylate.
Among these, a methacrylic acid alkyl ester having an alkyl side chain having 4 to 9 carbon atoms or an acrylic acid alkyl ester having an alkyl side chain having 4 to 9 carbon atoms is preferable, and further having 4 to 9 carbon atoms. An acrylic acid alkyl ester having an alkyl side chain is more preferred. Specifically, n-butyl acrylate, isooctyl acrylate, 2-ethylhexyl acrylate, and isononyl acrylate are preferable.

  In the acrylic polymer, a monoethylenic copolymerizable monomer copolymerizable with the (meth) acrylic acid alkyl ester having an alkyl side chain having 4 to 14 carbon atoms may be used. By using monoethylenic copolymerizable monomer and copolymerizing with the above (meth) acrylic acid alkyl ester, improvement of adhesion by introduction of functional group and polar group, maximum loss tangent (tanδ) of copolymer The value can be controlled to improve cohesion and heat resistance.

Examples of such monoethylenic copolymerizable monomers include acrylic acid, methacrylic acid, acrylic acid dimer, itaconic acid, crotonic acid, maleic acid, maleic anhydride and other carboxyl group-containing copolymerizable monomers, 2-hydroxyethyl ( Hydroxyl group-containing copolymerizable monomers such as (meth) acrylate, 4-hydroxybutyl (meth) acrylate, 6-hydroxyhexyl (meth) acrylate, N-vinyl-2-pyrrolidone, N-vinylcaprolactam, morpholine acrylate, N, Amide group-containing copolymerizable monomers such as N-dimethyl (meth) acrylamide, imide group-containing copolymerizable monomers such as cyclohexylmaleimide and isopropylmaleimide, 2- (perhydrophthalimido-N-yl) ethyl acrylate, styrene, vinyl acetate Acrylonitrile, and the like. If such a copolymerizable monomer has a pressure-sensitive adhesive layer within the range satisfying the cutting strength E and the cutting elongation T, T _{60 ° C.} defined in the present specification, the addition amount, etc. Although not particularly defined, it is preferable to add 2 to 40% by mass with respect to the monomer. When an epoxy crosslinking agent or an aziridine crosslinking agent is used as the crosslinking agent, it is preferable to copolymerize a carboxyl group-containing copolymerizable monomer, and it is more preferable to copolymerize acrylic acid.

The pressure-sensitive adhesive according to the present invention preferably has a maximum value of loss tangent (tan δ) in a temperature range of −17 to 7 ° C. If the temperature is less than -17 ° C, the cohesive force of the pressure-sensitive adhesive is extremely low, which is not preferable. On the other hand, if the temperature is higher than 7 ° C, the initial tack is too low, and it is preferable to cause problems due to temporary fixing. Because there is no. The adjustment of the maximum value of the loss tangent (tan δ) of the pressure-sensitive adhesive is within the range satisfying the cutting strength E and the cutting elongation T and T _{60 ° C.} defined in this specification, In addition to using an acrylic polymer obtained by copolymerizing a (meth) acrylic acid alkyl ester having 4 to 14 alkyl side chains and a copolymerizable monomer, a blend of two or more acrylic polymers, or an acrylic polymer A method of blending other resins may be used.

  The mass average molecular weight of the (meth) acrylic acid alkyl ester having an alkyl side chain having 4 to 14 carbon atoms is 400,000 to 200 in terms of standard polystyrene conversion measured by gel permeation chromatography (GPC). 10,000, preferably 600,000 to 1.3 million. If the mass average molecular weight is less than 400,000, the cohesive force is lowered, which is not preferable. On the other hand, if it exceeds 2 million, it is necessary to lower the solid content concentration to adjust the viscosity of the pressure-sensitive adhesive solution. This is because it takes a long time and is not preferable.

  This acrylic polymer can be produced by a known radical polymerization method such as solution polymerization, bulk polymerization, emulsion polymerization, suspension polymerization or supercritical polymerization.

Polymerization can be initiated by peroxides such as benzoyl peroxide and lauroyl peroxide, thermal initiation using azo initiators such as azobisisobutyronitrile, acetophenone, benzoin, benzyl ketal. The starting method by ultraviolet rays, such as a system, an acyl phosphine oxide system, a benzophenone system, and a maleimide system, and the starting method by an electron beam can be arbitrarily selected.
Of these, a heat initiation method using an azo initiator such as azobisisobutyronitrile and an ultraviolet light initiation method using an acylphosphine oxide initiator are preferable.

  To the (meth) acrylic acid alkyl ester having an alkyl side chain having 4 to 14 carbon atoms, other additives are added as necessary, and these are dissolved in an organic solvent. Then, a crosslinking agent and an antioxidant are added. An adhesive solution, which is a solution that is a raw material for the previous adhesive, is prepared. The organic solvent is not particularly limited as long as it dissolves the above-described blending components and does not react with the functional group of the cross-linking agent. However, ethyl acetate, toluene, xylene, n-hexane, acetone, methyl ethyl ketone and the like are known. Conventional organic solvents can be used alone or in admixture. Of these, ethyl acetate, n-hexane, acetone, and methyl ethyl ketone are preferable.

Moreover, as a crosslinking agent added to an adhesive solution, an epoxy type crosslinking agent, an aziridine type crosslinking agent, an isocyanate type crosslinking agent, etc. are mentioned. Among these, an epoxy type crosslinking agent and an aziridine type crosslinking agent are preferable. As a method for crosslinking the pressure-sensitive adhesive, a conventionally known method can be used, but it is preferable to perform crosslinking by adding a crosslinking agent to the pressure-sensitive adhesive solution. The addition amount of the cross-linking agent is appropriately adjusted so that the cutting strength E, the cutting elongation T, and T _{60 ° C.} of the pressure-sensitive adhesive fall within the ranges in this specification. For example, in the case of an epoxy-based crosslinking agent, it is preferable to add 0.01 to 0.2 parts by mass with respect to 100 parts by mass of the adhesive.

  Examples of the antioxidant include phenol, phosphite, and thioether. Among them, those having a decomposition temperature of 200 ° C. or higher are preferable from the viewpoint of preventing thermal decomposition of the antioxidant itself due to heat in the solder reflow process. By adding an antioxidant to the adhesive solution, the heat resistance of the adhesive can be improved.

  0.02-7 mass parts is preferable with respect to 100 mass parts of adhesives, and, as for the addition amount of this antioxidant, 0.1-3 mass parts is more preferable. This is because if the addition amount is less than 0.02 parts by mass, the heat resistance of the adhesive in the solder reflow process is inferior. On the other hand, if the addition amount exceeds 7 parts by mass, aggregation due to migration of the antioxidant over time. This is because it is unfavorable because there is a concern about a decline in force.

  Various additives, ultraviolet absorbers, fillers, pigments, thickeners, tackifying resins, and the like may be further added to the pressure-sensitive adhesive as long as the performance is not impaired.

  The thickness of the pressure-sensitive adhesive is preferably 1 to 200 μm, and more preferably 10 to 150 μm. This is because if the thickness of the pressure-sensitive adhesive is less than 1 μm, the FPC rebound resistance is lowered, which is not preferable. On the other hand, if the thickness exceeds 200 μm, the workability is lowered, which is not preferable.

  The pressure-sensitive adhesive of the present invention is used for folding and fixing the FPC. FIG. 1 is a schematic diagram showing the steps from mounting an electronic component on an FPC, folding the FPC, and folding back using the pressure-sensitive adhesive of the present invention. (A) to (g) It is a schematic diagram.

  First, (a) Adhesives 10, 10... Applied on release papers 2, 2... Are attached to predetermined portions of the back surface 1a made of FPC polyimide together with the release papers. Next, (b) the FPC is provided with the missing portions 100, 100... And punched into a predetermined shape. (C) The stainless steel reinforcing plates 3, 3... As the back plate are temporarily bonded to the back surface of the portion where the electronic component is mounted using another adhesive or the like, and the adhesive is thermally cured. (D) FPC is turned upside down. (E) Electronic components 4, 4... Such as connectors are mounted on portions corresponding to the stainless steel reinforcing plates 3, 3. This FPC is put into a reflow furnace, the solder is reflowed, and the electronic parts 4, 4. Since the solder used is a lead-free material and has a melting point in the vicinity of 200 to 230 ° C., the solder can be dissolved in the reflow furnace, for example, in an oven at 250 ° C. for 3 minutes, depending on the performance of the reflow furnace. It takes a degree.

  Then, (f) FPC is cut into a required size. Next, (g) the release paper 2 is peeled off, folded back at the fold line portion, and the adhesive 10 of the present invention is fixed to the stainless steel reinforcing plate 3 so that the FPC 1 is folded. Therefore, the adherend of the pressure-sensitive adhesive of the present invention is made of polyimide such as FPC and metal such as stainless steel. This FPC that is folded back and secured is incorporated in this shape in an electronic device such as a mobile phone in the next step.

  Since FPC has a structure in which a polyimide film is bonded to both sides of a copper circuit, the folded back has a strong repulsive force to return to the original planar structure, and is not fixed with an adhesive having a weak adhesive force. Usually, it peels off over time. Although an adhesive having a strong adhesive force may be used, as described above, since the adhesive is fixed after the solder reflow, even if the adhesive is a good adhesive at room temperature, the performance cannot always be maintained after the solder reflow. In fact, as described above, when the present inventors examined a commercially available adhesive for FPC folding and fixing, even if it is a good adhesive at room temperature, it does not have FPC resilience and peels off. There were many.

  For example, if the pressure sensitive adhesive is hard, the force to peel off due to the repulsive force of the FPC does not disperse inside the pressure sensitive adhesive, and this force is concentrated on the interface between the pressure sensitive adhesive and the adherend. It is conceivable to peel off. If the adhesive is soft, it is necessary to examine commercially available FPC folding adhesives that have FPC rebound resistance. As described above, the adhesive adheres to the blade during punching ( There have been problems such as generation of glue balls, and glue balls taken off from the blade adhere to the surface of the FPC (glue skipping). This is probably because the adhesive was too soft.

Therefore, in order to achieve both FPC resilience resistance and processability, it is considered necessary that the softness of the pressure-sensitive adhesive is within a specific range in addition to the material having heat resistance. As a result of intensive studies, the present inventors paid attention to the behavior of the pressure-sensitive adhesive at the time of tensile cutting as a guideline indicating the relationship between the softness of the pressure-sensitive adhesive and the FPC resilience and processability. That is, (a) the elongation at break E during tensile cutting of the adhesive is 800 to 1400%, the cutting strength T is 300 to 700 kPa, and (b) at the time of tensile cutting of the adhesive after being left at 60 ° C. for 100 hours. It has been found that the FPC resilience and workability are satisfied when the cutting strength T _{60 ° C.} is 210 to 700 kPa. Actually, the adhesive is processed after being left in an atmosphere of 250 ° C. for about 3 minutes in the solder reflow process, but the cutting strength E has already been obtained under the condition of heating at a somewhat low temperature of 60 ° C. for 100 hours. Since it is obvious that a pressure-sensitive adhesive that cannot be changed after processing at 250 ° C. for 3 minutes, the cutting strength T _{60 ° C.} of the pressure-sensitive adhesive after heating is examined under the conditions after being left at 60 ° C. for 100 hours. It was decided to. The cutting elongation E, the cutting strength T, and the cutting strength T _{60 ° C.} of this adhesive are measured by the following method.

Adhesives are stacked to a thickness of about 0.4 mm to produce a strip-shaped test piece having a length of 5 cm and a width of 1 cm. This test piece is attached to a tensile tester (manufactured by A & D Co., Ltd., Tensilon RTA-100, tensile mode) at a marked line interval of 2 cm and pulled until it is cut at a tensile speed of 300 mm / min. From the measurement chart, the cutting elongation E and the cutting strength T at the time of cutting are obtained.
Further, the cutting strength T after leaving for 60 hours at _{60 ° C.} is measured by the same method using the same tensile tester after the test piece prepared in the same manner is left in a 60 ° C. atmosphere for 100 hours. Can be obtained.

When the tensile elongation E of the pressure-sensitive adhesive layer before heat treatment is 800 to 1400% and the cutting strength T is 300 to 700 kPa, the force to peel off due to the repulsive force of the FPC is dispersed inside the pressure-sensitive adhesive. The rebound resistance can be improved. If the cutting strength T is too low, the pressure-sensitive adhesive becomes too soft and adversely affects processing suitability. If the cutting strength T is within the above range, processing suitability can be improved. Further, 60 ° C., 100 hours breaking strength _{T 60 ° C.} after standing is, if it is 210～700KPa, since the difference between the breaking strength T before heating is small, small changes in physical properties of the heat treatment after pressure-sensitive adhesive The stability of the agent can be made good.

  This pressure-sensitive adhesive can be produced by adding a crosslinking agent and an antioxidant to a pressure-sensitive adhesive solution, applying the mixture on a release paper after stirring, and drying. The release paper preferably has heat resistance even at a temperature of 250 ° C., for example, glassine paper, fine paper, craft paper, nonwoven fabric, metal foil, polyimide film, polyethylene naphthalate film (PEN), polyether ether ketone film (PEEK), polyparaphenylene sulfide film (PPS), polytetrafluoroethylene film (PTFE), and laminates thereof. The surface of the release paper is preferably subjected to a release treatment such as silicone treatment or fluorine treatment in order to improve the peelability from the adhesive. Glassine paper, high-quality paper, and kraft paper are preferably subjected to sealing treatment with polyvinyl alcohol (PVA) in order to uniformly perform the mold release process.

[FPC, electronic equipment]
FIG. 2 is a schematic plan view showing an embodiment of the FPC 1 provided with the adhesive 10 having the stainless steel reinforcing plate 3 and the release paper 2, and (a) is a schematic plan view of the back surface 1a of the FPC 1 before being folded and fixed. (B) is a schematic plan view of the surface 1a of the FPC 1 after the release paper 2 is peeled off and folded back and fixed with a fold line. These are enlarged views of the FPC in the steps (f) and (g) of FIG.

  The FPC according to the present embodiment is one that is folded and fixed using the above-mentioned pressure-sensitive adhesive. The FPC in FIG. 2 includes an FPC 1 having a structure in which a polyimide film is bonded to both sides of a copper circuit, an adhesive 10 provided on the back surface 1a, and a stainless steel reinforcing plate 3 as another adherend. It is configured. In addition, the structure of FPC and the material of a reinforcement board are not limited to this. In FIG. 2, the adhesive 10 applied on the release paper 2 is pasted on a predetermined portion of the back surface 1a of the FPC together with the release paper, and after the electronic component mounting process and the solder reflow process, it is shown in FIG. 2 (a). The release paper 2 is peeled off and folded back as shown in (b), and the back surface 1 a made of polyimide of the FPC 1 and the stainless steel reinforcing plate 3 are fixed with an adhesive 10. Since the FPC according to the present embodiment has the FPC folded back and fixed using the above-mentioned pressure-sensitive adhesive, it has excellent FPC resilience resistance, and the FPC pressure-sensitive adhesive does not peel off during the process.

  In addition, the electronic device of the present invention incorporates the FPC that is folded and fixed as it is as a component. Since this electronic device has the FPC folded and fixed using the above-mentioned pressure-sensitive adhesive, it has excellent FPC resilience resistance, and the FPC pressure-sensitive adhesive is peeled off before the step of incorporating the FPC into the electronic device. Absent.

[Double-sided adhesive sheet]
In the double-sided pressure-sensitive adhesive sheet of the present invention, a pressure-sensitive adhesive layer composed of the above-mentioned pressure-sensitive adhesive and a heat-resistant release paper are provided in this order on both sides of a support. This double-sided pressure-sensitive adhesive sheet is composed of a support, a pressure-sensitive adhesive layer made of the above-mentioned pressure-sensitive adhesive provided on both sides of the support, and a heat-resistant release paper provided thereon.

  As this support, films such as polyimide, polyethylene naphthalate (PEN), polyether ether ketone (PEEK), polyparaphenylene sulfide (PPS), which are materials that can withstand high temperatures close to 250 ° C. in the solder reflow process, metal Examples thereof include foils and laminates thereof. As heat-resistant release paper, the same glassine paper, fine paper, kraft paper, non-woven fabric, metal foil, polyimide film, polyethylene naphthalate (PEN), polyether ether ketone (PEEK), poly Examples include paraphenylene sulfide (PPS), polytetrafluoroethylene film (PTFE), and laminates thereof. In addition, the surface of the heat-resistant release paper is preferably subjected to a release treatment such as silicone treatment or fluorine treatment in order to enhance the peelability from the pressure-sensitive adhesive layer. In addition, release paper made from paper is preferably not subjected to polyethylene film laminating or clay coating in order to improve heat resistance.

  The coating amount of the pressure-sensitive adhesive layer is appropriately set according to the required performance, but the coating amount on each surface of the support is preferably 1 to 200 μm after drying, and preferably 10 to 150 μm. More preferred. This is because if the coating amount of the pressure-sensitive adhesive layer is less than 1 μm, the FPC resilience resistance is lowered, which is not preferable. On the other hand, if it exceeds 200 μm, the processability of the double-sided pressure-sensitive adhesive sheet is lowered, which is not preferable.

  This double-sided PSA sheet can be produced by forming a PSA layer and heat-resistant release paper on both sides of the support. This pressure-sensitive adhesive layer can be formed by applying a pressure-sensitive adhesive on a heat-resistant release paper with a roll coater or a die coater, etc. Conventionally known methods such as a method of applying on the body can be appropriately used.

  Since this double-sided PSA sheet uses a heat-resistant material as the support and heat-resistant release paper in addition to the PSA layer, the FPC solder reflow process must be performed with the heat-resistant release paper still attached. Can do.

  Hereinafter, the present invention will be described in more detail by way of examples. The present invention is not limited to the following examples.

(Preparation of adhesive solution A)
Using a reaction vessel equipped with a stirrer, a cold flow cooler, a thermometer, a dropping funnel and a nitrogen gas inlet, 89.9 parts by mass of butyl acrylate, 10.0 parts by mass of acrylic acid, 0.1 mass of 4-hydroxybutyl acrylate Part and 0.03 part by mass of 2,2′-azobisisobutylnitrile as a polymerization initiator were dissolved in a mixed solvent consisting of 63 parts by mass of ethyl acetate and 100 parts by mass of acetone. Subsequently, it superposes | polymerizes at 65 degreeC for 6 hours, 0.2 mass part of additional 2,2'- azobisisobutyl nitrile and 45 mass parts of ethyl acetate are added to this, and also it superposes | polymerizes for 6 hours, The mass mean molecular weight 900,000 A polystyrene copolymer solution was obtained. Ethyl acetate was added to this acrylic copolymer solution to obtain a pressure-sensitive adhesive solution A having a nonvolatile content of 30% by mass.

(Preparation of adhesive solution B)
Except having changed into 85 mass parts of butyl acrylate and 15 mass parts of acrylic acid, it superposed | polymerized similarly to the adhesive solution A, and obtained the acryl-type copolymer solution of the mass mean molecular weight 840,000. Ethyl acetate was added to the acrylic copolymer solution and mixed uniformly to obtain an adhesive solution B having a nonvolatile content of 30% by mass.

(Preparation of adhesive solution C)
Except for changing to 85 parts by mass of 2-ethylhexyl acrylate, 5 parts by mass of acrylic acid, and 10 parts by mass of N-vinyl-2-pyrrolidone, polymerization was carried out in the same manner as the adhesive solution A, and an acrylic copolymer having a mass average molecular weight of 880,000 was obtained. A polymer solution was obtained. Ethyl acetate was added to this acrylic copolymer solution and mixed uniformly to obtain an adhesive solution C having a nonvolatile content of 30% by mass.

(Preparation of adhesive solution D)
Except that the polymerization initiator was changed to 1,1-azobis (1-acetoxy-1-phenylethane), polymerization was performed in the same manner as the pressure-sensitive adhesive solution A, and an acrylic copolymer solution having a mass average molecular weight of 810,000 was obtained. Obtained. Ethyl acetate was added to this acrylic copolymer solution and mixed uniformly to obtain an adhesive solution D having a nonvolatile content of 30% by mass.

(Preparation of adhesive solution E)
Except having changed into 95 mass parts of butyl acrylate and 5 mass parts of acrylic acid, it superposed | polymerized similarly to the adhesive solution A, and obtained the acrylic type copolymer solution with a mass mean molecular weight 900,000. Ethyl acetate was added to the acrylic copolymer solution and mixed uniformly to obtain an adhesive solution E having a nonvolatile content of 30% by mass.

(Preparation of adhesive solution F)
Polymerized in the same manner as the adhesive solution A, except that 90 parts by mass of 2-ethylhexyl acrylate, 10 parts by mass of acrylic acid, and the polymerization initiator 2,2′-azobisisobutylnitrile were changed to 0.02 parts by mass, An acrylic copolymer solution having a mass average molecular weight of 1,000,000 was obtained. Ethyl acetate was added to the acrylic copolymer solution and mixed uniformly to obtain an adhesive solution F having a nonvolatile content of 30% by mass.

(Preparation of adhesive solution G)
Except having changed into 80 mass parts of butyl acrylate, 10 mass parts of methyl acrylate, and 10 mass parts of acrylic acid, it superposed | polymerized similarly to the adhesive solution A, and obtained the acrylic type copolymer solution with a mass mean molecular weight 900,000. Ethyl acetate was added to the acrylic copolymer solution and mixed uniformly to obtain an adhesive solution G having a nonvolatile content of 30% by mass.

(Preparation of adhesive solution H)
Except having changed into 93 mass parts of butyl acrylate and 7 mass parts of acrylic acid, it superposed | polymerized similarly to the adhesive solution A, and obtained the acrylic type copolymer solution with a mass mean molecular weight 900,000. Ethyl acetate was added to the acrylic copolymer solution and mixed uniformly to obtain an adhesive solution H having a nonvolatile content of 30% by mass.

(Preparation of adhesive solution I)
Except having changed into 92 mass parts of butyl acrylate and 8 mass parts of methacrylic acid, it superposed | polymerized similarly to the adhesive solution A, and obtained the acryl-type copolymer solution of the mass mean molecular weight 760,000. Ethyl acetate was added to the acrylic copolymer solution and mixed uniformly to obtain an adhesive solution I having a nonvolatile content of 30% by mass.

(Preparation of adhesive solution J)
Polymerization was performed in the same manner as the pressure-sensitive adhesive solution A except that the polymerization initiator was changed to benzoyl peroxide to obtain an acrylic copolymer solution having a mass average molecular weight of 800,000. Ethyl acetate was added to the acrylic copolymer solution and mixed uniformly to obtain an adhesive solution I having a nonvolatile content of 30% by mass.

[Example 1]
(Preparation of adhesive)
0.2 parts by mass of a cross-linking agent (“E-AX” manufactured by Soken Chemical Co., Ltd., epoxy-based cross-linking agent, solid content: 5% by mass), antioxidant (Irganox 1010, Ciba Specialty Chemical Co., Ltd.) 0.3 parts by weight, stirred for 15 minutes, and coated with adhesive on heat-resistant glassine paper with a thickness of 90 μm after release to a thickness of 50 μm after drying And dried at 70 ° C. for 3 minutes. Next, after the glassine paper having a thickness of 120 μm subjected to the release treatment was bonded, the sheet was aged at 40 ° C. for 2 days to obtain a sheet-like pressure-sensitive adhesive having a thickness of 50 μm.

[Example 2]
A pressure-sensitive adhesive was prepared in the same manner as in Example 1 except that the pressure-sensitive adhesive solution was changed to B.

[Example 3]
A pressure-sensitive adhesive was prepared in the same manner as in Example 1 except that the addition amount of the crosslinking agent “E-AX” was changed to 0.16 parts by mass.

[Example 4]
A pressure-sensitive adhesive was prepared in the same manner as in Example 1 except that the pressure-sensitive adhesive solution was changed to C.

[Example 5]
A pressure-sensitive adhesive was prepared in the same manner as in Example 1 except that the pressure-sensitive adhesive solution was changed to D.

[Comparative Example 1]
A pressure-sensitive adhesive was prepared in the same manner as in Example 1 except that the pressure-sensitive adhesive solution was changed to E and the addition amount of the crosslinking agent “E-AX” was changed to 0.3 parts by mass.

[Comparative Example 2]
A pressure-sensitive adhesive was prepared in the same manner as in Example 1 except that the pressure-sensitive adhesive solution was changed to F and the addition amount of the crosslinking agent “E-AX” was changed to 0.5 parts by mass.

[Comparative Example 3]
A pressure-sensitive adhesive was prepared in the same manner as in Example 1 except that the pressure-sensitive adhesive solution was changed to G and the addition amount of the crosslinking agent “E-AX” was changed to 0.3 parts by mass.

[Comparative Example 4]
A pressure-sensitive adhesive was prepared in the same manner as in Example 1 except that the pressure-sensitive adhesive solution was changed to H.

[Comparative Example 5]
A pressure-sensitive adhesive was prepared in the same manner as in Example 1 except that the pressure-sensitive adhesive solution was changed to I.

[Comparative Example 6]
A pressure-sensitive adhesive was prepared in the same manner as in Example 1 except that the crosslinking agent was changed to 2.0 parts by mass of “Coronate L” (manufactured by Nippon Polyurethane Co., Ltd., isocyanate-based crosslinking agent, solid content: 45% by mass).

[Comparative Example 7]
A pressure-sensitive adhesive was prepared in the same manner as in Example 1 except that the pressure-sensitive adhesive solution was changed to J.

  About the adhesive created in Examples 1-5 and Comparative Examples 1-7, it tested by the method shown below and the evaluation result was shown in Table 1.

(1) Cutting strength and cutting elongation of the adhesive Peel off the aged adhesive release paper and superimpose it until the thickness is about 0.4 mm to form a strip-shaped test piece with a length of 5 cm and a width of 1 cm. Created. This test piece is attached to a tensile tester (A & D Co., Tensilon RTA-100, tensile mode) with a marked line spacing of 2 cm, pulled until it is cut at a pulling speed of 300 mm / min, and the strength T when cut from the chart. (Cut strength) and elongation E (cut elongation) were determined.
Further, the cutting strength T _{60 ° C.} after standing at 60 ° C. for 100 hours was measured in the same manner using a strip-shaped test piece that was left in a 60 ° C. atmosphere for 100 hours.

(2) FPC resilience test (i) In the center of a flexible printed circuit board (FPC) having a width of 15 mm made of polyimide 12.5 μm / rolled copper foil 18 μm / polyimide 25 μm, thickness 0.1 mm, width 15 mm, length 6 mm The stainless steel plate was bonded with an adhesive sheet. The adhesive sandwiched between the release papers is processed into a length of 4 mm and a width of 15 mm, and the release paper with a thickness of 120 μm is peeled off, parallel to a position 2 mm away from the stainless steel plate as shown in FIG. Affixed by hand.

  (Ii) The FPC to which the adhesive was applied was left in an oven at 250 ° C. for 3 minutes and allowed to stand at 23 ° C. and 50% Rh for 1 hour.

  (Iii) After peeling off the remaining release paper attached to the adhesive, as shown in FIG. 2 (b), the FPC is folded back into two, and the adhesive is fixed to the stainless steel plate by hand bonding, and the test piece is attached. Created.

  (Iv) The test piece was left at 23 ° C. and 50% RH for 1 hour, then placed in an oven at 60 ° C. and left for 100 hours, and then the presence or absence of peeling of the folded portion of the FPC was visually evaluated. FIG. 3 is a schematic plan view of the FPC that is folded and fixed after the FPC repulsion resistance test, (a) is a schematic plan view of the FPC in which peeling of the folded portion did not occur, and (b) is a diagram of the folded portion. It is a schematic plan view of FPC in which peeling occurred. Moreover, in Table 1, the case where peeling of the folded-back portion did not occur was indicated as ◯, and the case where peeling occurred was indicated as ×.

(3) Punching workability The 120 μm-thick release paper of the adhesive sandwiched between the release papers is peeled off, and a 50 μm-thick polyethylene terephthalate (PET) film (Ester-A4100, manufactured by Toyobo Co., Ltd.) is a 2 kg roller. Bonded in one round trip. Next, this was cut into a size of 10 mm in width and 100 mm in length from the PET film side with a mainspring blade. The release paper 2 side of the pressure-sensitive adhesive 10 was fixed with a holder, and the PET film 20 side was pulled at a speed of 300 mm / min and peeled while maintaining the angle between the release paper 2 and the PET film 20 at 15 °. . The cutting process of the cut cut surface was observed with an optical microscope (KH-2700, Hilox, magnification 250 times), and the state of the pressure-sensitive adhesive when peeling off was determined by the generation of glue feet 40 and glue balls (cut glue) Evaluation was made based on the presence or absence of a lump of adhesive made of feet. FIG. 4 is a photograph observing the peeling process of the pressure-sensitive adhesive 10 at the time of evaluation of punching workability, (a) is a photograph of the pressure-sensitive adhesive 10 having good processability, and (b) is a paste foot 40 generated. It is a photograph of the pressure-sensitive adhesive 10 having poor processability. Moreover, in Table 1, the case where processability was favorable was set as (circle), and the case where processability was bad was set as x.

From the results of Examples 1 to 5 and Comparative Examples 1 to 7, it was found that the adhesives of Examples 1 to 5 had good FPC resilience resistance and processability. From this result, the cut elongation E, the cut strength T, and the cut strength T _{60 ° C.} affect the FPC resilience resistance and processability, and the numerical values such as the FPC resilience resistance and processability indicate the extent. It was confirmed that the physical properties that are difficult to represent can be expressed by using a cutting elongation E, a cutting strength T, and a cutting strength T _{60 ° C.}

Further, from the above results, the tensile elongation of the adhesive for FPC folding fixing is 800 to 1400% at the time of tensile cutting, the cutting strength T is 300 to 700 kPa, and the tensile strength of the adhesive after being left at 60 ° C. for 100 hours. It was confirmed that when the cutting strength T _{60 ° C.} at the time of cutting is 210 to 700 kPa, the FPC resilience resistance and workability are excellent.

  Specific examples of electronic devices suitable for use of the flexible printed circuit board using the adhesive of the present invention include a mobile phone, a portable personal computer, a portable information terminal device (PDA), a digital still camera, and the like. .

It is the schematic diagram which showed the process until it mounts an electronic component in FPC, FPC is folded back, and it adheres and fixes using the adhesive of this invention, (a)-(g) is a schematic diagram of each process. . It is a schematic plan view which shows one Embodiment of FPC which provided the adhesive which has a stainless steel reinforcement board and a release paper, (a) is a schematic plan view of the back surface of FPC before folding and fixing, (b) is peeling release paper FIG. 3 is a schematic plan view of the surface of the FPC after being folded and fixed at a fold line. It is a schematic plan view of FPC which turned back and fixed after the FPC repulsion resistance test in an Example, (a) is a schematic top view of FPC in which peeling of the folding part did not generate | occur | produce, (b) is peeling of the folding part. It is a schematic plan view of FPC which generate | occur | produced. It is the photograph which observed the peeling process of the adhesive at the time of the punching process evaluation in an Example, (a) is a photograph of an adhesive with favorable workability, (b) is bad in processability with which the glue foot generate | occur | produced. It is a photograph of an adhesive.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Flexible printed circuit board 2 Release paper 10 Adhesive

Claims (4)

An adhesive used for folding and fixing a flexible printed circuit board,
(A) Cutting elongation E at the time of tensile cutting of the adhesive is 800 to 1400%, cutting strength T is 300 to 700 kPa,
(B) A pressure-sensitive adhesive having a cutting strength T _{60 ° C.} of 210 to 700 kPa at the time of tensile cutting of the pressure-sensitive adhesive after standing at 60 ° C. for 100 hours.   A flexible printed circuit board, which is fixed by folding back using the pressure-sensitive adhesive according to claim 1.   An electronic apparatus comprising the flexible printed circuit board according to claim 2 as a component. A double-sided pressure-sensitive adhesive sheet comprising a pressure-sensitive adhesive layer made of the pressure-sensitive adhesive according to claim 1 and a heat-resistant release paper in this order on both surfaces of a support.

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