JP5337348B2 - Method for producing adhesive film for flexible printed wiring board and adhesive film for flexible printed wiring board obtained by the method - Google Patents

Description

The present invention, the occurrence of light scattering based on the crystal in the adhesive layer of the adhesive film is suppressed, a method of manufacturing a visible light transmittance of improved flexible printed wiring board adhesive film, and a flexible printed obtained by the production method It is related with the adhesive film for wiring boards .

  With recent downsizing and higher functionality of electronic devices, more sophisticated wiring boards are required for electronic devices. For example, a flexible printed wiring board (hereinafter also referred to as FPC) generally uses a thin insulating film having flexibility as a substrate (base film), and a metal foil is heated on the surface of the substrate via various adhesive materials. A circuit pattern is formed on a metal-clad laminate bonded by pressure bonding, and a cover layer is provided on the surface. In a flexible printed wiring board (three-layer FPC) composed of three layers of an insulating film, an adhesive layer, and a metal foil, a polyimide film or the like has been widely used as an insulating film. This is because polyimide has excellent heat resistance and electrical characteristics. Moreover, as the adhesive layer, a thermosetting adhesive such as epoxy resin or acrylic resin is generally used.

  However, since the thermosetting adhesive does not necessarily have sufficient characteristics such as heat resistance, insulation, and electrical reliability, a thermoplastic polyimide resin exhibiting superior characteristics can be used instead of a thermosetting resin. It has begun to be used as an agent (see, for example, Patent Document 1). Although it can be said that the FPC obtained by the method using a polyimide material for the adhesive layer is strictly three layers, the two polyimide layers are regarded as a single body and are referred to as a two-layer FPC.

  As with other polymer materials, it is known that there are crystalline and amorphous thermoplastic polyimides. Crystalline thermoplastic polyimides are conventionally used for molded articles such as injection molding (see, for example, Patent Document 2), but are attracting attention as applications for electronic materials and for adhesives for electronic materials. There was nothing. However, the present inventor has found that crystalline thermoplastic polyimide is also very useful when used, for example, as an adhesive for FPC.

  For example, when the thermoplastic polyimide is made crystalline, the thermoplastic polyimide does not soften very near the glass transition temperature (hereinafter also referred to as Tg), and is near the melting point (hereinafter also referred to as Tm) higher than Tg. Will soften suddenly. Therefore, crystalline thermoplastic polyimide is easy to achieve both heat resistance and workability.

  Amorphous thermoplastic polyimide softens rapidly in the vicinity of Tg. Therefore, it is necessary to increase Tg in order to improve heat resistance (increase the temperature at which the adhesive layer begins to soften). However, when the temperature at which the adhesive layer begins to soften becomes high, it is inevitably necessary to increase the temperature required to bond the adhesive film to the metal foil, but the adhesive film and the metal foil are bonded to each other with high productivity. For this purpose, it is necessary to bond at a temperature about 80 to 150 ° C. higher than the Tg of the thermoplastic polyimide used for the adhesive layer.

  On the other hand, crystalline thermoplastic polyimide does not soften so much near Tg and tends to soften rapidly near Tm. Tm tends to be higher than Tg to some extent (100 to 200 ° C.). Therefore, for example, it is appropriate to have Tm between the temperature (for example, solder reflow temperature) in the environment where FPC is used and the processing temperature (bonding temperature of adhesive film and metal foil, etc.) in the FPC manufacturing process. If molecular design is performed, it can be used as an adhesive for an adhesive film having both heat resistance and workability.

For the reasons described above, crystalline thermoplastic polyimide is considered to be very useful when used, for example, as an adhesive in electronic material applications, but there are also problems inherent to crystallinity. One of them is light transmission. When crystalline thermoplastic polyimide is used as an adhesive for the adhesive film, thermoplastic polyimide crystals are present in the adhesive layer. If the crystal size at this time is large, As a result, light is scattered by the adhesive layer, and as a result, the light transmittance of the adhesive film tends to be greatly reduced. If the light transmittance of the adhesive film is low, 1) it will be difficult to carry out defect inspection at the time of manufacturing the adhesive film. 2) When managing the thickness with an on-line film thickness meter of the optical system at the time of manufacturing the adhesive film. This makes it difficult to measure the film thickness, and 3) makes it difficult to perform alignment in a process such as chip mounting.
JP-A-6-200218 Japanese Patent Laid-Open No. 11-35822

  This invention is made | formed in view of said subject, The objective is providing the manufacturing method which improves the light transmittance regarding the adhesive film which used the crystalline thermoplastic polyimide for the contact bonding layer. It is in.

  As a result of intensive studies in view of the above problems, the present inventors have found that the light transmittance of an adhesive film can be improved by controlling the temperature at the time of imidization of thermoplastic polyimide or after imidization, and the present invention has been completed. I came to let you.

  That is, the present invention is a method for producing an adhesive film in which an adhesive layer containing a crystalline thermoplastic polyimide is provided on at least one side of a core layer, and the means for forming the adhesive layer contains a thermoplastic polyimide precursor. The adhesive film is characterized in that after the layer to be formed is provided on at least one side of the core layer, the film is heated at a temperature equal to or higher than the melting point of the obtained crystalline thermoplastic polyimide when imidized or imidized by heating. It relates to the manufacturing method.

  A preferred embodiment relates to the method for producing an adhesive film, wherein the thermoplastic polyimide precursor layer contains a dehydrating agent and / or an imidization catalyst.

  A preferred embodiment is characterized in that when the thermoplastic polyimide precursor is imidized by heating or after imidization, it is heated in a temperature range of 20 ° C. or higher and 100 ° C. or lower than the melting point of the obtained crystalline thermoplastic polyimide. It is related with the manufacturing method of one of the said adhesive films.

  The present invention relates to an adhesive film obtained by any one of the above-described production methods, wherein the light transmittance at a wavelength of 600 nm at a total thickness of 25 μm is 30% or more.

  According to the method for producing an adhesive film of the present invention, by appropriately controlling the temperature at the time of imidation of the crystalline thermoplastic polyimide contained in the adhesive layer or after imidization, the light transmittance of the obtained adhesive film is obtained. Can be improved.

  Embodiments of the present invention will be described below.

  The present invention relates to a method for producing an adhesive film constituted by providing an adhesive layer containing a thermoplastic polyimide on at least one surface of a core layer, and an adhesive film obtained by the production method. Here, at least a part or all of the thermoplastic polyimide contained in the adhesive layer has crystallinity. In the present invention, “having crystallinity” means a clear endothermic peak (this peak temperature is defined as a melting point) due to a transition from a solid state to a molten state in differential scanning calorimetry (DSC) measurement. ). In contrast, amorphous thermoplastic polyimide is different in that it has no melting point and therefore does not show a clear endothermic peak, and only a slight endotherm is observed near the glass transition temperature.

  The core layer that can be used in the method for producing an adhesive film according to the present invention is not particularly limited, and examples thereof include a polyimide film, a polyamide film, a liquid crystal polymer film, and the like. It can be suitably used. The heat-resistant polyimide film is not limited and is preferably formed containing 90% by weight or more of non-thermoplastic polyimide. The molecular structure, film thickness, etc. of the non-thermoplastic polyimide are not particularly limited. The non-thermoplastic polyimide used for forming the heat-resistant polyimide film is generally produced using polyamic acid as a precursor. However, the non-thermoplastic polyimide may be completely imidized or imide An unconverted precursor, that is, a polyamic acid, may be included in part. Here, the non-thermoplastic polyimide generally refers to a polyimide that does not soften or show adhesiveness even when heated. In the present invention, it refers to a polyimide that is heated at 450 ° C. for 2 minutes in the state of a film, does not wrinkle or stretch, and retains its shape, or has substantially no glass transition temperature. The glass transition temperature can be obtained from the value of the inflection point of the storage elastic modulus measured by a dynamic viscoelasticity measuring device (DMA). Further, “substantially has no glass transition temperature” means that thermal decomposition starts before the glass transition state is reached.

  About the said heat resistant polyimide film, it is possible to use the well-known polyimide film marketed, for example. Examples of commercially available polyimide films include “Apical” (manufactured by Kaneka), “Kapton” (manufactured by DuPont, Toray DuPont), “Iupilex” (manufactured by Ube Industries), and the like. Of course, you may use the heat resistant polyimide film suitably produced using the conventionally well-known raw material or a manufacturing method. For example, the aromatic tetracarboxylic dianhydride and the aromatic diamine are usually dissolved in an organic solvent in a substantially equimolar amount, and the aromatic tetracarboxylic dianhydride is controlled under controlled temperature conditions. The polyamic acid varnish as a precursor is produced by stirring until the polymerization of the diamine with the aromatic diamine is completed, and a heat-resistant polyimide film can be obtained using the polyamic acid varnish.

  In the method for producing an adhesive film according to the present invention, after the means for forming the adhesive layer containing crystalline thermoplastic polyimide has provided a layer containing the thermoplastic polyimide precursor on at least one side of the core layer In addition, it is characterized in that it is heated at a temperature equal to or higher than the melting point of the obtained crystalline thermoplastic polyimide when imidized by heating or after imidization. The “precursor” of the thermoplastic polyimide here refers to a compound generally recognized as a precursor of polyimide, for example, polyamic acid or isoimide, and the polyimide can be obtained by imidization. If it is, it will not be limited.

  A method for synthesizing the precursor of the thermoplastic polyimide is not particularly limited, and a conventionally known method can be used. As a general example, there is a method in which a diamine component and an acid dianhydride component are mixed in an organic solvent, and a polyamic acid organic solvent solution is obtained by a polymerization reaction. By appropriately selecting the structure of the diamine component and acid dianhydride component used here, it is possible to impart crystallinity to the thermoplastic polyimide obtained by imidizing the polyamic acid obtained by polymerizing them. It becomes. However, as described above, since polyimide is generally obtained by a polymerization reaction of a diamine component and an acid dianhydride component, if either one of the specific diamine component or acid dianhydride component is used, a crystalline polyimide is always produced. Although not obtained, the expression of crystallinity depends largely on the combination of the diamine component and the acid dianhydride component.

  Taking into account that there is a viewpoint of the above combination, examples of the diamine component and the acid dianhydride component that can be used as a raw material for the crystalline thermoplastic polyimide contained in the adhesive layer in the present invention are as follows: As 1,4-bis (4-aminophenoxy) benzene, 1,3-bis (4-aminophenoxy) benzene, 4,4′-bis (3-aminophenoxy) biphenyl, 4,4′-bis ( Ether-based diamines such as 4-aminophenoxy) biphenyl and phenylene-based diamines such as 1,4-diaminobenzene are preferred because they tend to exhibit crystallinity. On the other hand, as the acid dianhydride component, pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and the like are preferable because they tend to exhibit crystallinity. Of course, the diamine component and the acid dianhydride component used as raw materials for the thermoplastic polyimide of the present invention are not limited to these, and the heat obtained as a result of a specific combination of the diamine component and the acid dianhydride component. As long as the plastic polyimide exhibits crystallinity, a raw material having another structure may be used.

  In the present invention, a particularly preferred combination of a diamine component and an acid dianhydride component as raw materials for obtaining a crystalline thermoplastic polyimide is, for example, 1,4-bis (4-aminophenoxy) benzene, 1,3- A combination of bis (4-aminophenoxy) benzene and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride can be exemplified.

  In the present invention, the thermoplastic polyimide contained in the adhesive layer needs to be at least partially or entirely crystalline thermoplastic polyimide. Among these, based on the amount of the thermoplastic polyimide, from the viewpoint of moisture absorption solder resistance and workability, it is preferable that the crystalline thermoplastic polyimide is contained in the range of 85% by weight to 100% by weight, and more preferably 90% by weight to 100%. More preferably, it is contained in the range of% by weight.

  In the present invention, the conditions relating to the organic solvent used for the polymerization of the polyamic acid which is the precursor of the thermoplastic polyimide, the polymerization temperature, the polymerization concentration, etc. are not particularly limited, and can be produced under conventionally known conditions. is there.

  In the method for producing an adhesive film of the present invention, means for providing a layer containing a thermoplastic polyimide precursor on at least one surface of the core layer is not particularly limited, and a conventionally known method can be used. For example, (i) a method of forming an adhesive layer on a heat-resistant polyimide film to be a core layer, (ii) a method of forming the adhesive layer into a sheet and bonding it to the core layer, (iii) a core A method of simultaneously forming the layer and the adhesive layer by multilayer extrusion or the like can be suitably exemplified. Among these, in the case of adopting the method (i), if the polyamic acid that is a precursor of the thermoplastic polyimide contained in the adhesive layer is completely imidized, the solubility in an organic solvent may be reduced. Therefore, it may be difficult to provide the adhesive layer on the core layer. Therefore, from the above viewpoint, it is more preferable to prepare a solution containing polyamic acid which is a precursor of thermoplastic polyimide, apply this to a film to be a core layer, and then imidize.

  Examples of the imidization method for the adhesive layer include a thermal cure method in which imidization is performed by heating, a chemical cure method in which imidization is performed by adding a dehydrating agent and / or an imidization catalyst, or a method in which both are used in combination. Among these, the chemical curing method is preferable from the viewpoint of shortening the time required for imidization and improving productivity. Moreover, if chemical curing and thermal curing are used in combination, imidization can be achieved in a shorter time, and productivity can be further improved. However, as described above, the conversion from polyamic acid to polyimide generally tends to greatly reduce the solubility in organic solvents. Therefore, when performing chemical curing, the temperature control of the process is strictly performed, and the core layer It is preferable to take care so that imidization does not end before the adhesive layer is provided thereon.

  As the dehydrating agent, various dehydrating ring closure agents for polyamic acid can be used, but aliphatic acid anhydrides, aromatic acid anhydrides, N, N′-dialkylcarbodiimides, lower aliphatic halides, halogenated lower aliphatics. An acid anhydride, an aryl sulfonic acid dihalide, a thionyl halide or a mixture of two or more thereof can be preferably used. Of these, aliphatic acid anhydrides and aromatic acid anhydrides work particularly well. In addition, the imidization catalyst widely refers to a component having an effect of promoting the dehydrating and ring-closing action of the dehydrating agent on the polyamic acid. For example, an aliphatic tertiary amine, an aromatic tertiary amine, or a heterocyclic tertiary amine is used. Can be used. Of these, nitrogen-containing heterocyclic compounds such as imidazole, benzimidazole, isoquinoline, quinoline, and β-picoline are particularly preferable. Furthermore, introduction of an organic polar solvent into a solution composed of a dehydrating agent and an imidization catalyst may be appropriately selected.

  The preferable amount of the dehydrating agent is 0.5 to 5 mol, preferably 0.7 to 4 mol, based on 1 mol of the amic acid unit in the polyamic acid contained in the solution containing the dehydrating agent and the imidization catalyst. . Moreover, the preferable quantity of an imidation catalyst is 0.05-3 mol with respect to 1 mol of amic acid units in the polyamic acid contained in the solution which contains a dehydrating agent and an imidation catalyst, Preferably it is 0.2-2. Is a mole. If the dehydrating agent and the imidization catalyst are below the above ranges, chemical imidization may be insufficient, and may break during firing or mechanical strength may decrease. Moreover, when these amounts exceed the above range, the progress of imidization becomes too fast, and it may be difficult to cast into a film, which is not preferable.

  In the production method of the present invention, the adhesive layer of the adhesive film may contain organic / inorganic particles such as a filler for the purpose of controlling the linear expansion coefficient and slipperiness, for example, in addition to the thermoplastic polyimide. Good. The amount of filler added in this case may be included in the range of 0.001 to 10% by weight with respect to the adhesive layer.

  In the method for producing an adhesive film according to the present invention, it is important to control the heating temperature when producing the adhesive film in order to improve the light transmittance of the obtained adhesive film. Specifically, it is important to heat the thermoplastic polyimide precursor contained in the adhesive layer at a temperature equal to or higher than the melting point of the resulting crystalline thermoplastic polyimide when imidized by heating or after imidization. Become. Even if it is heated at a temperature lower than the melting point at the time of imidization, the thermoplastic polyimide precursor contained in the adhesive layer is imidized without any problem, so the adhesiveness of the finally obtained adhesive film and There is no problem with solder heat resistance. However, the adhesive film manufactured by heating at a temperature lower than the melting point of the crystalline thermoplastic polyimide during imidation increases the crystal grain size of the crystalline thermoplastic polyimide contained in the adhesive layer, and the resulting adhesion The light transmittance of the film is greatly reduced as compared with the case where amorphous thermoplastic polyimide is used for the adhesive layer. On the other hand, once heated at a temperature higher than the melting point of the crystalline thermoplastic polyimide, the light transmittance of the resulting adhesive film tends to be improved. The reason for this is that once the crystalline layer is heated at a temperature equal to or higher than the melting point of the crystalline thermoplastic polyimide, the adhesive layer is brought into a molten state, and this is cooled and recrystallized, whereby the crystal grain size can be reduced. thinking.

  The timing for heating the adhesive film at a temperature equal to or higher than the melting point of the crystalline thermoplastic polyimide contained in the adhesive layer is not particularly limited. During the manufacturing process of the adhesive film (when imidizing), or subsequent process (imidized) Either). For example, in the case of heating to the melting point or higher during the production process of the adhesive film, the following will be exemplified corresponding to each means (i) to (iii).

  In the case of producing an adhesive film by the means (i), for example, after applying an adhesive solution to be an adhesive layer to a heat-resistant polyimide film to be a core layer, first, most of the organic solvent in the adhesive solution is removed. Therefore, heating is performed at a relatively low temperature. The temperature at this stage is preferably in the range of 50 to 200 ° C. Next, heating is performed at a high temperature in order to remove the solvent remaining slightly in the adhesive layer and imidize the thermoplastic polyimide in the adhesive layer. The temperature at this stage is preferably 250 ° C. or higher. If almost no solvent remains in the adhesive layer, heat is applied over the melting point of the crystalline thermoplastic polyimide at this stage to remove the solvent, imidize the thermoplastic polyimide in the adhesive layer, and melt the adhesive layer. May be performed in one step. Since the temperature above the melting point of crystalline thermoplastic polyimide is quite high, if the film is rapidly cooled after heating, the adhesive film may shrink rapidly and the appearance may deteriorate. Is preferred.

  When producing an adhesive film by the means (ii), first, a single layer sheet of an adhesive layer is prepared. Also in this case, it is preferable to heat the adhesive solution at a relatively low temperature and gradually increase the heating temperature in order to remove the organic solvent, as in the method (i). Here, if the thermoplastic polyimide in the adhesive layer is completely imidized, the temperature required for bonding the single layer sheet of the adhesive layer to the core layer tends to increase. Therefore, it is preferable to bond the adhesive layer sheet to a core layer such as a heat-resistant polyimide film in a state where imidization is incomplete, and then perform imidization and melting of the adhesive layer by heating at a temperature equal to or higher than the melting point. .

  When the adhesive film is produced by the means (iii), the core layer and the adhesive layer are simultaneously formed by multilayer extrusion or the like, and then heated to remove the solvent, imidize the adhesive layer, and melt the adhesive layer. The temperature step may be performed in the same manner as (i).

  Note that, as described above, an adhesive film may be once manufactured and heated in a subsequent step by applying a temperature equal to or higher than the melting point of the crystalline thermoplastic polyimide. In this case, since it can be considered that the solvent does not remain in the adhesive layer, it is possible to heat from the beginning by applying a temperature higher than the melting point of the crystalline thermoplastic polyimide. However, when the adhesive film is heated rapidly, the adhesive film may rapidly expand and the appearance may be deteriorated. Therefore, it is preferable to gradually increase the ambient temperature. Even after heating, as described in the means (i), it is preferable to gradually cool by lowering the ambient temperature.

  In the present invention, the temperature above the melting point of the crystalline thermoplastic polyimide contained in the adhesive layer is not particularly limited as long as it is equal to or higher than the melting point, but the specific temperature is 20 times higher than the melting point of the thermoplastic polyimide. A temperature higher by at least 50 ° C. is preferable, and a temperature higher by at least 50 ° C. is particularly preferable. Since the one where the said heating temperature is higher can melt | dissolve a thermoplastic polyimide reliably also for a short time, it becomes easy to make light transmittance of the adhesive film obtained and the productivity of an adhesive film compatible. However, if the heating temperature is too high, thermal decomposition of the thermoplastic polyimide occurs, and the properties as an adhesive film may be deteriorated. Therefore, it is preferable to keep the heating temperature at most at the melting point of the crystalline thermoplastic polyimide + 100 ° C. or less.

  The heating means is not particularly limited, and for example, either a hot air method or a far infrared method may be used, and both may be used in combination. As for the heating method, either batch processing or continuous processing may be used, but continuous processing is preferable from the viewpoint of productivity of the adhesive film.

  The adhesive film according to the present invention obtained by the above production method can have improved light transmittance. The light transmittance is affected by the total thickness of the adhesive film, the core layer, and the thickness of the adhesive layer. Therefore, even though the crystalline thermoplastic polyimide contained in the adhesive layer has the same particle size, There is a difference in permeability. Considering this point, when the total thickness of the adhesive film is 25 μm, the light transmittance at 600 nm is preferably 30% or more. More preferably, it is 35% or more. When the light transmittance at a thickness of 25 μm is equal to or more than the above value, even when the total thickness of the adhesive film or the thickness configuration of each layer is changed, the light transmittance is sufficiently secured, and defect inspection at the time of manufacturing the adhesive film And thickness management can be performed without any problem, and alignment in a process such as chip mounting can be performed without any problem.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to these. In addition, melting | fusing point (Tm) of the thermoplastic polyimide used by the contact bonding layer in an Example and a comparative example, and the light transmittance of the adhesive film were measured or evaluated as follows.

[Melting point of thermoplastic polyimide]
The thermoplastic polyimide precursor solution obtained in the synthesis example was cast on a shine surface of 18 μm rolled copper foil (BHY-22B-T, manufactured by Nikko Metal Co., Ltd.) so that the final thickness was 20 μm. Drying was performed at 200 ° C for 2 minutes, 250 ° C for 2 minutes, 300 ° C for 2 minutes, and 350 ° C for 1 minute. After drying, the copper foil was removed by etching and dried at 50 ° C. for 30 minutes to obtain a single layer sheet of thermoplastic polyimide.

  Using the obtained thermoplastic polyimide single layer sheet, DSC220 manufactured by Seiko Instruments Inc. was used as a reference, and the temperature was increased from 0 ° C. to 450 ° C. at a temperature increase rate of 10 ° C./min and a temperature decrease rate of 40 ° C./min. The peak of the endothermic chart in the temperature raising step was taken as the melting point.

[Light transmittance of adhesive film]
The adhesive films obtained in each Example and Comparative Example were measured under the measurement wavelength region of 800 to 200 nm and the measurement speed of 480 nm / min with JASCO's Ubest-30, and the light transmittance at a wavelength of 600 nm was evaluated. .

[Metal foil peel strength of flexible metal-clad laminate]
18 μm rolled copper foil (BHY-22B-T; manufactured by Nikko Metal) is disposed on both sides of the adhesive films obtained in the examples and comparative examples, and protective materials (Apical 125 NPI; manufactured by Kaneka) are disposed on both sides thereof. Using a roll laminator, thermal lamination was performed continuously under the conditions of a laminating temperature of 380 ° C., a laminating pressure of 196 N / cm (20 kgf / cm), and a laminating speed of 1.5 m / min, to produce a flexible metal-clad laminate. Using the prepared flexible metal-clad laminate, a sample was prepared according to “6.5 Peel strength” of JIS C6471, and a 5 mm wide metal foil part was peeled off at 180 ° under a condition of 50 mm / min. It peeled and the load was measured.

(Synthesis Example 1; Synthesis of thermoplastic polyimide precursor)
637.0 g of N, N-dimethylformamide (hereinafter also referred to as DMF), 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (hereinafter also referred to as BPDA) in a glass flask having a capacity of 2000 ml. 28.2 g of 1,4-bis (4-aminophenoxy) benzene (hereinafter also referred to as TPE-Q) and 1,3-bis (4-aminophenoxy) with stirring under a nitrogen atmosphere. ) 45.4 g of benzene (hereinafter also referred to as TPE-R) was added and stirred at 25 ° C. for 1 hour. A solution in which 2.0 g of TPE-R was dissolved in 27.0 g of DMF was separately prepared, and this was gradually added to the above reaction solution while paying attention to the viscosity and stirred. When the viscosity reached 1200 poise, the addition and stirring were stopped to obtain a polyamic acid solution.

(Synthesis Example 2: Synthesis of thermoplastic polyimide precursor)
To a glass flask having a volume of 2000 ml, 637.0 g of DMF and 68.2 g of BPDA were added, and 65.8 g of TPE-R was added while stirring under a nitrogen atmosphere, followed by stirring at 25 ° C. for 1 hour. A solution in which 2.0 g of TPE-R was dissolved in 27.0 g of DMF was separately prepared, and this was gradually added to the above reaction solution while paying attention to the viscosity and stirred. When the viscosity reached 1200 poise, the addition and stirring were stopped to obtain a polyamic acid solution.

Example 1
After diluting the polyamic acid solution obtained in Synthesis Example 1 with DMF to a solid content concentration of 8.5% by weight, a thermoplastic polyimide layer is formed on both sides of a 17 μm-thick heat-resistant polyimide film (Apical 17FP, Kaneka). After applying polyamic acid so that the final one-side thickness of (adhesive layer) was 4 μm, heating was performed at 140 ° C. for 1 minute. Subsequently, heating was performed at 250 ° C. for 10 seconds, 350 ° C. for 10 seconds, 450 ° C. for 10 seconds, and 200 ° C. for 2 seconds to obtain an adhesive film.

(Example 2)
The polyamic acid solution obtained in Synthesis Example 1 was diluted with DMF until the solid concentration was 14% by weight. To this diluted polyamic acid solution, an imidization accelerator consisting of acetic anhydride / isoquinoline / DMF (weight ratio 1.5 / 0.4 / 8.2) was added at a weight ratio of 50% with respect to the polyamic acid solution, Stirring was performed. Using the obtained mixed solution, an adhesive layer was formed in the same manner as in Example 1 to obtain an adhesive film.

(Example 3)
An adhesive film was obtained in the same manner as in Example 1 except that the polyamic acid solution obtained in Synthesis Example 2 was used instead of the polyamic acid solution obtained in Synthesis Example 1.

Example 4
An adhesive film was obtained in the same manner as in Example 2, except that the polyamic acid solution obtained in Synthesis Example 2 was used instead of the polyamic acid solution obtained in Synthesis Example 1.

(Comparative Example 1)
After diluting the polyamic acid solution obtained in Synthesis Example 1 with DMF to a solid content concentration of 8.5% by weight, a thermoplastic polyimide layer is formed on both sides of a 17 μm-thick heat-resistant polyimide film (Apical 17FP, Kaneka). After applying polyamic acid so that the final one-side thickness of (adhesive layer) was 4 μm, heating was performed at 140 ° C. for 1 minute. Subsequently, heating was performed at 250 ° C. for 10 seconds, 370 ° C. for 10 seconds, and 200 ° C. for 2 seconds to obtain an adhesive film.

(Comparative Example 2)
An adhesive film was obtained in the same manner as in Comparative Example 1, except that the polyamic acid solution obtained in Synthesis Example 2 was used instead of the polyamic acid solution obtained in Synthesis Example 1.

  Table 1 shows the results of evaluating the properties of the adhesive films obtained in each of the examples and comparative examples.

  As shown in the comparative example, when not heated at a temperature equal to or higher than the melting point of the thermoplastic polyimide contained in the adhesive layer, although the adhesion strength with the metal foil can be secured, the resulting adhesive film is light transmissive. It became inferior result. On the other hand, in the Example heated at the temperature more than melting | fusing point of a thermoplastic polyimide, it has resulted in improving a light transmittance.

Claims (4)

A method for producing an adhesive film for a flexible printed wiring board in which an adhesive layer containing crystalline thermoplastic polyimide is provided on at least one surface of a core layer, wherein the adhesive layer forming means contains a thermoplastic polyimide precursor A flexible printed wiring comprising: providing a layer on at least one surface of a core layer, and then imidating or imidizing the core layer by heating, and then heating at a temperature equal to or higher than a melting point of the obtained crystalline thermoplastic polyimide. Manufacturing method of adhesive film for board . The method for producing an adhesive film for a flexible printed wiring board according to claim 1, wherein the thermoplastic polyimide precursor layer contains a dehydrating agent and / or an imidization catalyst. After or imidation during imidization by heating a thermoplastic polyimide precursor obtained crystalline thermoplastic polyimide 20 ° C. higher temperatures or higher than the melting point, and wherein the heating at a temperature range 100 ° C. higher temperatures The manufacturing method of the adhesive film for flexible printed wiring boards of Claim 1 or 2. It is an adhesive film for flexible printed wiring boards obtained by the manufacturing method of any one of Claims 1 thru | or 3 , Comprising: Total thickness is 25 micrometers and the light transmittance of wavelength 600nm is 30% or more, It is characterized by the above-mentioned. An adhesive film for flexible printed wiring boards .