JP2017179149A - Polyimide film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a polyimide laminate film capable of suppressing generation of phenomenon, referred to as breakage, of a polyimide film serving as a substrate in an alkali environment without separately conducting a heat treatment or elongation, when a flexible metal clad laminate is manufactured by laminating a metal layer on a polyimide film and further a flexible printed wiring board is continuously manufactured by a roll-to-roll method.SOLUTION: There is provided a non-thermoplastic polyimide laminate film having an inclination of a plastic deformation area in a stress-strain curve of 2.0 or more, preferably 2.2 or more, more preferably 2.5 or more and further tensile stress at 10% strain of 190 MPa or more. There is provided a polyimide film further preferably having storage elastic modulus in a dynamic viscoelasticity of 0.2 to 1.0 GPa and an inflection point of storage elastic modulus at 270 to 340°C.SELECTED DRAWING: None

Description

  The present invention relates to a polyimide film that can suppress the occurrence of film tearing in the manufacturing process of a flexible metal-clad laminate.

  In recent years, demand for various flexible printed circuit boards (hereinafter also referred to as FPCs) has been increasing with increasing demand for electronic products such as smartphones, tablet computers, notebook computers, and the like. Among these, a two-layer flexible printed wiring board (hereinafter also referred to as a two-layer FPC) using thermoplastic polyimide as an adhesive layer is expected to further increase demand because of its excellent heat resistance and flexibility. Recently, demands for lighter, smaller and thinner electronic devices are increasing, and in order to achieve this, the FPC to be mounted is also desired to be thinner. In addition, with the change in the production process of flexible copper clad laminates due to productivity improvement (cost reduction), demands on the load on materials such as polyimide film, particularly improvement in mechanical strength, are increasing.

  In the conventional manufacturing method of FPC, a manufacturing process including a developing process, an etching process, a resist stripping process, and the like is performed in a batch manner (non-continuous process). Conventionally, a polyimide (for example, Patent Document 1) whose resistance to an alkaline solution used in development, etching, and resist stripping processes is controlled has been reported. Moreover, the method of improving the intensity | strength of a polyimide film by high orientation is also disclosed (for example, patent document 2). Also disclosed is a technique (for example, Patent Document 3) characterized by containing 4,4'-diamino-2,2'-dimethylbiphenyl as a diamine component of a polyimide resin.

JP 2012-186377 A WO01 / 081456 JP 2009-101706 A

  When processing into FPC, there is a step of contacting with an alkaline aqueous solution, and alkali resistance is also required. However, in the roll-to-roll type which is an example of a continuous type, unlike the conventional batch type, It will contact with alkaline aqueous solution in the state where tension was applied to the longitudinal direction. As a result, the present inventors have revealed that there arises a problem that a phenomenon such as tearing in the polyimide laminated film, which has not been recognized by the alkali treatment in the conventional batch method, occurs. Further, in the step of contacting with the alkaline aqueous solution, a state in which stress is repeatedly applied in the thickness direction of the base material by spraying the chemical solution. Furthermore, since a base material is conveyed along the roll which supports a base material at the time of conveyance of a base material, a bending stress will also generate | occur | produce in a state contacted with the chemical | medical solution. These stresses also apply a load to the film, which causes the film to tear.

  In order to solve these problems, a method for suppressing cracking by performing a heat treatment in the β relaxation temperature range as disclosed in Patent Document 1 has been reported. Bring about a decline.

  Furthermore, in the material disclosed in Patent Document 2, biaxial stretching of the gel film is performed in order to achieve toughness and high strength. As a result, the number of processes increases and productivity decreases. In addition, the stretched film tends to be relatively poor in toughness due to the strong in-plane orientation of molecular chains. Therefore, even if there is no problem in the conventional batch type FPC manufacturing process, the toughness is insufficient to withstand the process of continuously manufacturing the FPC by the roll-to-roll method as described above. No polyimide material has been provided so far that does not tear even after passing through.

Patent Document 3 discloses a technique characterized by containing 4,4′-diamino-2,2′-dimethylbiphenyl as a diamine component of a polyimide resin. However, the humidity change is controlled by controlling the humidity expansion coefficient. There is no disclosure or suggestion regarding the tearing of the film in the alkaline environment as described above.
The present invention has been made in view of these problems, and its purpose is to manufacture a flexible metal laminate in accordance with a process change to a roll-to-roll system for thinning the material and improving productivity in recent years. It is providing the polyimide film which can suppress the tearing of the film which generate | occur | produces in the alkaline environment in without performing heat processing and extending | stretching separately.

  As a result of intensive studies in view of the above-mentioned problems, the present inventors have found that it is important to give a non-thermoplastic polyimide an aggregated structure in order to suppress film tearing. The agglomerated structure is related to the “yield strength” and “hardness of plastic deformation” of the polyimide film. In the present invention, these two are used as indicators of the agglomerated structure. In the present invention, by controlling the agglomeration structure by adopting a resin having a specific skeleton, the toughness is improved by suppressing film tearing in an alkaline environment without major changes to the film manufacturing process. I found out that it would be possible. Also, the polymerization method was examined and the present invention was completed.

That is, this invention relates to the following polyimide films.
1) A polyimide film, wherein the slope of the plastic deformation region in the stress-strain curve is 2.0 or more.
2) The aromatic diamine constituting the non-thermoplastic polyimide contains at least 4,4′-diamino-2,2′-dimethylbiphenyl or 4,4′-diamino-3,3′-dimethylbiphenyl in an amount of 10 to 18 mol%. It relates to the polyimide film as described in 1).
3) The polyimide film according to 1) or 2), wherein a stress at 10% strain in a stress-strain curve is 190 MPa or more.
4) The storage elastic modulus at 380 ° C. in the dynamic viscoelasticity measurement is 0.2 GPa or more and 1.0 GPa or less, and the temperature indicated by the inflection point of the storage elastic modulus is 270 ° C. to 340 ° C. The polyimide film according to any one of 1) to 3).

  The polyimide film obtained by the present invention provides a flexible metal-clad laminate that suppresses the tearing of the film that occurs in the production process of an alkaline environment and a roll-to-roll method without any special changes to the film production process. it can.

It is a schematic diagram which shows the testing method of the shaking test which concerns on the Example of this invention. It is a figure which shows the inclination of the plastic deformation area | region which concerns on the Example of this invention.

  Embodiments of the present invention will be described below. First, although the case of the polyimide film which concerns on this invention is demonstrated based on the example of the embodiment, this invention is not limited to this. The present invention is not limited to each configuration described below, and various modifications can be made within the scope shown in the claims, and technical means disclosed in different embodiments and examples respectively. Embodiments and examples obtained by appropriately combining them are also included in the technical scope of the present invention. In addition, all the academic literatures and patent literatures described in this specification are incorporated by reference in this specification. Unless otherwise specified in this specification, “A to B” indicating a numerical range means “A or more (including A and greater than A) and B or less (including B and less than B)”, respectively.

  As described above, when processing FPC by roll-to-roll method, in addition to tension in the longitudinal direction in the presence of an aqueous alkali solution, the batch type such as repetitive stress and bending stress in the thickness direction is used. Also, the substrate is in a state of being loaded. When a solvent is present, the strength of the polymer is generally lower than when no solvent is present. Therefore, it is preferable that the yield strength is high in order to suppress plastic deformation. Also, under repeated stress, the polymer fatigues and gradually begins plastic deformation. For this reason, even after plastic deformation has started, it was considered that the resistance value against the stress being greater (harder to plastic deformation) would be more effective in suppressing cracking.

  The present inventors diligently studied the molecular design of polyimide in order to improve the toughness of the polyimide laminated film in an alkaline environment. As a result, the aggregate structure of the non-thermoplastic polyimide layer contained in the polyimide laminate film contributes to the toughening of the polyimide film in an alkaline environment, and the aggregate structure is controlled by the primary structure of the polyimide and the polyimide production method. Thus, it was found that tearing of the film in an alkaline environment can be suppressed without greatly changing the film manufacturing process. In other words, the present inventors have found for the first time the knowledge that the polymer can easily form an agglomerated structure to perform molecular design that can express these characteristics and the toughness in an alkaline environment is improved. Is.

  The aggregated structure in the present invention means packing of molecular chains having local order. Polyimide is composed of rigid structural units such as an aromatic ring or an aromatic heterocycle, and therefore has little entanglement and hardly forms a folded chain like a general polymer. On the other hand, molecular chain packing unique to the molecular chain having an imide ring occurs, and packing of the molecular chain having the local ordering occurs. It has been found in the present invention that the aggregation structure of the polyimide is related to the toughness in an alkaline environment. The aggregation structure can be controlled by the film forming conditions and the primary structure of the polyimide film. The thermoplastic polyimide in the present invention refers to a polyimide that is softened when it is fixed to a metal fixed frame in the state of a film and heated at 450 ° C. for 2 minutes so that the original shape is not retained.

  The non-thermoplastic polyimide in the present invention retains its shape without being wrinkled or stretched when it is fixed to a metal fixed frame in the state of a film and heated at 450 ° C. for 2 minutes. Refers to polyimide.

(Slope of plastic deformation region in stress-strain curve)
The polyimide film of the present invention is characterized in that the slope of the plastic deformation region in the stress-strain curve is 2.0 or more.

  As a result of earnestly examining the durability against the tear of the polyimide film in an alkaline environment, the present inventors have satisfied the two conditions that the polyimide film is difficult to plastically deform and has a high yield strength. The present inventors have found a new finding that it exhibits high durability against tearing in an alkaline environment. In the present invention, in a polyimide laminated film containing thermoplastic polyimide and non-thermoplastic polyimide, particularly for non-thermoplastic polyimide, increasing the slope of the plastic deformation region in the stress-strain curve and increasing the yield strength. It is easier to obtain the effect by giving these two characteristics.

  The plastic deformation region and its inclination in the present invention will be described. The plastic deformation region refers to a strain region after the yield point in a stress-strain curve in a tensile test using a polyimide film. The property of “not easily plastically deformed” is intended to increase the stress greatly in the plastic deformation region, or to increase the stress required at the time of plastic deformation. The characteristic of “not easily plastically deformed” can be rephrased as the inclination in the plastic deformation region. For example, the result of measuring the tensile properties according to ASTM D882 is expressed as “slope (ie, s) −s curve slope) ”. In the present invention, the slope is between “10% strain stress” and “breaking stress” in the s-s curve. The calculation formula is shown below.

Inclination of plastic deformation region = (stress2-stress1) / (strain2-strain1)
here,
stress1: Stress at 10% strain stress2: Breaking stress strain1: 10% strain strain2: Breaking strain.

  The “material which is difficult to plastically deform” in the present invention is characterized in that “the inclination of the plastic deformation region is 2.0 or more”. It is more preferably 2.2 or more, and further preferably 2.5 or more. When it is 2.0 or more, an aggregated structure having a high degree of packing of molecular chains is formed, which is suitable and suitable as a flexible metal-clad laminate that does not tear even in a continuous FPC processing step. The slope of the plastic deformation region in the stress-strain curve should be high, but if it is too high, springback may occur. 4.5 or less is preferable and 4.0 or less is more preferable. When it is 4.5 or less, the stiffness is appropriate and the film can be easily handled.

  “Yield strength” can be evaluated by “stress at 10% strain” when tensile properties are measured according to ASTM D882. For example, “a material having a high yield strength” is intended herein as “a stress at 10% strain is 190 MPa or more”.

(Temperature indicated by inflection point of storage modulus)
The temperature indicated by the inflection point of the storage elastic modulus by dynamic viscoelasticity measurement of the polyimide film of the present invention (also referred to as E ′ inflection point temperature) is a viewpoint of relaxation of thermal stress when the metal foil is bonded by the laminating method. To 270 ° C. to 340 ° C., more preferably 280 ° C. to 330 ° C. If the temperature indicated by the inflection point of the storage elastic modulus is within this range, the temperature at which the dimensional change after heating of the flexible metal-clad laminate is evaluated (in the field of two-layer FPC, it is often evaluated at 250 ° C. ) Is small and good. Furthermore, since the temperature at which the softening of the core layer begins is lower than the temperature at the time of thermal lamination, the dimensional change is small to sufficiently relax at that temperature, and when the flexible metal-clad laminate is etched or pressed Since the positioning from the desired design can be suppressed, the handling is good.

(Storage elastic modulus at 380 ° C.)
The storage elastic modulus at 380 ° C. by dynamic viscoelasticity measurement of the polyimide film of the present invention is preferably in the range of 0.1 GPa to 0.7 GPa from the viewpoint of relaxation of thermal stress when the metal foil is laminated by the laminating method. In the range of 0.2 GPa to 0.6 GPa, more preferably in the range of 0.3 GPa to 0.5 GPa. The lower the storage elastic modulus at 380 ° C., the more effective the stress relaxation effect at the time of thermal lamination, and the smaller the dimensional change rate. On the other hand, when the storage elastic modulus at 380 ° C. is 0.2 GPa or more, the film can maintain a self-supporting property at the time of imidization or thermal lamination of the film, without reducing the productivity of the film, This is suitable because it does not adversely affect the appearance of the flexible metal-clad laminate.

  The stress relaxation during thermal lamination in the present invention will be described. Stress relaxation during thermal lamination is performed so that the MD direction and TD direction of the film are the same as the conveyance direction (MD direction) during thermal lamination and the direction perpendicular to the MD direction (TD direction). Two types of flexible metal-clad laminates produced by laminating (normally laminating) and by rotating the film 90 ° and laminating so that the MD and TD directions are 90 ° (90 ° rotating laminating) It can be evaluated by the difference in dimensional change rate. The difference in the dimensional change rate depending on the laminating direction is related to stress relaxation and strain reduction following the plastic deformation of the metal foil during thermal lamination. That is, the smaller the dimensional change rate difference between the MD and TD directions of the normal laminate and 90 ° rotation laminate, the more the stress is relaxed, and the smaller the dimensional change rate. The difference in the dimensional change rate in the laminating direction between the normal laminate and the 90 ° rotating laminate is preferably less than 0.08%, and more preferably less than 0.04%. If the difference in dimensional change rate in the laminating direction between the normal laminate and 90 ° rotating laminate is 0.08% or less, the stress during thermal lamination can be relaxed, so the dimensional change is small and flexible metal-clad laminate. Since the positional deviation from the desired design can be suppressed when etching is performed or pressed, handling is facilitated, which is preferable.

(Shaking test)
In order to confirm whether or not the material is not torn even after the process of continuously manufacturing FPC in a roll-to-roll method, a wide and long material is obtained by providing a metal foil with a continuous method on a wide and long material. Using a flexible metal-clad laminate, a circuit is required to be formed by an FPC manufacturing process including a development process, an etching process, and a resist stripping process in a roll-to-roll manner. However, this method is not practical because it is costly and time consuming. As a long film or a long flexible metal-clad laminate as a material, the inventors cut out a test piece from both ends and a central part, and when ST was measured in a shaking test, it was 900 seconds or more. It has been found that no tearing occurs when such a material is used. The shaking test can be performed easily and at low cost, and by using a material having an ST of 900 seconds or more, a flexible metal-clad laminate that does not easily tear can be obtained.

  When ST of the polyimide film when the shaking test is performed at both ends and the center of the film is 900 seconds or more, it is used as a flexible metal-clad laminate, and a roll-to-roll continuous FPC manufacturing process Even when a flexible wiring board is manufactured, the occurrence of tearing is suppressed, but it is preferably 1500 seconds or longer, and more preferably 2000 seconds or longer.

  Since the polyimide film of the present invention is a material used for continuous FPC production as described above, it is a wide and long polyimide film. And it is a film in which ST is 900 seconds or more when a shaking test is performed at three points on both ends and the center of the film. If such a film is used, the FPC obtained through the continuous FPC process does not tear, so that the FPC can be produced efficiently.

(Polyimide)
The polyimide film of this invention is comprised from the polyimide containing a flexible block component and a rigid block component, It is characterized by the above-mentioned.

  As a result of intensive studies, the present inventors have found that “to prevent plastic deformation” and “to increase yield strength” are important for suppressing film tearing in an alkaline environment.

  The flexible block component contained in the polyimide film of the present invention is preferably thermoplastic. Furthermore, it is more preferable that the side chain of the flexible block component does not contain a bulky substituent, and is composed of a highly planar skeleton and a skeleton having a high molecular mobility of molecular chains such as ether bonds. As a result, the packing of the molecular chains becomes dense, the growth of the aggregate structure is promoted, and the final film can be provided with toughness.

  The rigid block component contained in the polyimide film of the present invention is preferably non-thermoplastic. Furthermore, it is more preferable that the monomer constituting the rigid block component contains a rigid skeleton having a high degree of free rotation of a molecular chain such as a biphenyl structure. Only rigid monomers such as pyromellitic dianhydride and 4,4'-diaminobenzene may cause insufficient molecular mobility of the polymer molecular chain. The introduction can increase the molecular mobility and promote the formation of an aggregate structure. A monomer having a skeleton having a rigid and high degree of free rotation is not limited as long as it has a biphenyl structure. For example, 4,4′-diaminobiphenyl, 4,4′-diamino-2,2′-dimethylbiphenyl, 4,4 '-Diamino-3,3'-dimethylbiphenyl, 4,4'-diamino-2,2'-dimethoxybiphenyl, 4,4'-diamino-3,3'-dimethoxybiphenyl, 3,3', 5,5 Examples include '-tetramethylbenzidine, 4,4'-bis (4-aminophenoxy) biphenyl, and the like. Among 100% of the diamine monomer component constituting the rigid block component, the monomer component having a high rigidity and a high degree of free rotation is more effective for forming an aggregated structure. However, if the content is too large, the result is obtained. Since the linear expansion coefficient of a film falls remarkably, the range which is 25 mol%-42 mol% is preferable.

  The polyimide which comprises the polyimide film of this invention is obtained by imidating the polyamic acid used as a precursor. The monomer that forms the polyamic acid will be described below.

  The diamine used in the polyimide of the present invention is not particularly limited, but an aromatic diamine is preferable from the viewpoint of heat resistance and the like. For example, 2,2′-bis [4- (4-aminophenoxy) phenyl] propane, 4,4′-diaminodiphenylpropane, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl sulfide, 3,3 '-Diaminodiphenylsulfone, 4,4'-diaminodiphenylsulfone, 4,4'-oxydianiline, 3,3'-oxydianiline, 3,4'-oxydianiline, 4,4'-diaminodiphenyldiethyl Silane, 4,4′-diaminodiphenylsilane, 4,4′-diaminodiphenylethylphosphine oxide, 4,4′-diaminodiphenyl N-methylamine, 4,4′-diaminodiphenyl N-phenylamine, 1,4- Diaminobenzene (p-phenylenediamine), bis {4- (4-aminophenoxy) pheny } Sulfone, bis {4- (3-aminophenoxy) phenyl} sulfone, 4,4′-bis (4-aminophenoxy) biphenyl, 4,4′-bis (3-aminophenoxy) biphenyl, 1,3-bis (3-aminophenoxy) benzene, 1,3-bis (3-aminophenoxy) benzene, 3,3′-diaminobenzophenone, 4,4′-diaminobenzophenone, 2,2-bis (4-aminophenoxyphenyl) propane 2,2′-dimethylbenzidine and the like, and these can be used alone or in combination. Aromatic diamines particularly preferably used for the polyimide of the present invention are 4,4′-diaminobiphenyl, 4,4′-diamino-2,2′-dimethylbiphenyl, 4,4′-diamino-3,3′-. Dimethylbiphenyl, 4,4′-diamino-2,2′-dimethoxybiphenyl, 4,4′-diamino-3,3′-dimethoxybiphenyl, 3,3 ′, 5,5′-tetramethylbenzidine, 4,4 '-Bis (4-aminophenoxy) biphenyl, 4,4'-diaminodiphenyl ether, 2,2'-bis [4- (4-aminophenoxy) phenyl] propane, p-phenylenediamine, 1,3-bis (4 -Aminophenoxy) benzene and the like are exemplified.

  The acid dianhydride used in the polyimide of the present invention is not particularly limited, but an aromatic acid dianhydride is preferable from the viewpoint of heat resistance and the like. For example, pyromellitic dianhydride, 2,3,6,7-naphthalenetetracarboxylic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, 1,2,5,6 -Naphthalenetetracarboxylic dianhydride, 2,2 ', 3,3'-biphenyltetracarboxylic dianhydride, 3,3', 4,4'-benzophenonetetracarboxylic dianhydride, 2,2 ', 3,3′-benzophenonetetracarboxylic dianhydride, 4,4′-oxyphthalic dianhydride, 3,4′-oxyphthalic dianhydride, 2,2-bis (3,4-dicarboxyphenyl) propane Acid dianhydride, 3,4,9,10-perylenetetracarboxylic dianhydride, bis (3,4-dicarboxyphenyl) propanoic dianhydride, 1,1-bis (2,3-dicarboxyphenyl) ) Ethanoic acid dianhydride 1,1-bis (3,4-dicarboxyphenyl) ethanoic dianhydride, bis (2,3-dicarboxyphenyl) methanoic dianhydride, bis (3,4-dicarboxyphenyl) ethanoic acid Anhydride, oxydiphthalic dianhydride, bis (3,4-dicarboxyphenyl) sulfonic dianhydride, p-phenylenebis (trimellitic acid monoester anhydride), ethylene bis (trimellitic acid monoester anhydride) Product), bisphenol A bis (trimellitic acid monoester anhydride), and the like. Acid dianhydrides particularly preferably used for the polyimide of the present invention are pyromellitic dianhydride, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride, benzophenone tetracarboxylic dianhydride, 4 , 4′-oxyphthalic dianhydride and the like.

  As the flexible block component diamine, 4,4′-diaminodiphenyl ether, 4,4′-bis (4-aminophenoxy) biphenyl, p-phenylenediamine, and 1,3-bis (4-aminophenoxy) benzene are suitable. Used for. As the acid dianhydride, 4,4′-biphenyltetracarboxylic dianhydride, benzophenone tetracarboxylic dianhydride, and pyromellitic dianhydride are preferably used. Furthermore, a combination including 4,4'-diaminodiphenyl ether, 4,4'-biphenyltetracarboxylic dianhydride, and pyromellitic dianhydride is particularly preferable.

  As the diamine of the rigid block component, 4,4′-diaminobiphenyl, 4,4′-diamino-2,2′-dimethylbiphenyl, 4,4′-diamino-3,3′-dimethylbiphenyl, 4,4 '-Diamino-2,2'-dimethoxybiphenyl, 4,4'-diamino-3,3'-dimethoxybiphenyl, 3,3', 5,5'-tetramethylbenzidine, 4,4'-bis (4- Aminophenoxy) biphenyl 4,4′-diaminodiphenyl ether, p-phenylenediamine, and 1,3-bis (4-aminophenoxy) benzene are preferably used. As the acid dianhydride, 4,4′-biphenyltetracarboxylic dianhydride, benzophenone tetracarboxylic dianhydride, and pyromellitic dianhydride are preferably used. Furthermore, a combination containing 4,4'-diamino-2,2'-dimethylbiphenyl or 4,4'-diamino-3,3'-dimethylbiphenyl, p-phenylenediamine, and pyromellitic dianhydride is particularly preferable.

(Linear expansion coefficient of polyimide film)
The linear expansion coefficient of the non-thermoplastic polyimide film of the present invention is preferably 5 ppm to 15 ppm. The linear expansion coefficient can usually be changed by changing the composition, but can also be controlled by changing the method of selecting the flexible block component of the present invention.

(Solvent for polyamic acid production)
As the preferred solvent for producing the polyamic acid, any solvent that dissolves the polyamic acid can be used. For example, amide solvents such as N, N-dimethylformamide, N, N-dimethylacetamide, N-methyl-2-pyrrolidone and the like can be exemplified. Among these, N, N-dimethylformamide and N, N-dimethylacetamide are particularly preferable.

(Production of polyamic acid)
As the method for producing the polyamic acid in the present invention, any known method and a combination thereof can be used. The characteristic of the polymerization method in the polymerization of the polyamic acid is the order of addition of the monomers, and various physical properties of the polyimide obtained can be controlled by controlling the order of addition of the monomers. Therefore, in the present invention, any method of adding monomers may be used for the polymerization of polyamic acid. Examples of typical polymerization methods include the following methods.

For example, the following steps (Aa) to (Ac):
(Aa) a step of reacting an aromatic diamine and an aromatic dianhydride in an organic polar solvent in an excess of aromatic diamine to obtain a prepolymer having amino groups at both ends;
(Ab) A step of additionally adding an aromatic diamine having a structure different from that used in the step (Aa). Further, an aromatic dianhydride having a different structure from that used in the step (Aa) was added so that the aromatic diamine and the aromatic dianhydride in all steps were substantially equimolar. Polymerization step,
Can be manufactured by.

Alternatively, the following steps (Ba) to (Bc):
(Ba) An aromatic diamine and an aromatic acid dianhydride are reacted in an organic polar solvent in an excess of aromatic acid dianhydride, and a prepolymer having acid anhydride groups at both ends is obtained. Obtaining step,
(Bb) A step of additionally adding an aromatic dianhydride having a different structure from that used in the step (Ba). Furthermore, an aromatic diamine having a structure different from that used in the step (Ba) is added and polymerized so that the aromatic diamine and the aromatic dianhydride in all steps are substantially equimolar. Process,
It is also possible to obtain polyamic acid by going through.

  A synthetic method (for example, steps (Aa) to (Ab), and (Ab), and (Ab), and (Ab), and Ba) to (Bb)) are referred to as sequence polymerization in the present invention. On the other hand, a synthesis method in which the diamine and acid dianhydride to be bonded are not selected in the charging order is called random polymerization in the present invention.

  In the present invention, as a preferable polymerization method for obtaining a polyimide resin effective in suppressing film tearing, sequence polymerization is preferable to random polymerization, and a flexible block component is formed for the purpose of ideally forming a block component. It is particularly preferred to use a method in which the rest of the diamine and / or acid dianhydride is used to form a rigid block component to form a non-thermoplastic polyimide precursor.

(Solid content concentration of polyamic acid)
The solid content concentration of the non-thermoplastic polyamic acid of the present invention is not particularly limited, and it is usually 5% to 35% by weight, preferably 10% to 30% by weight. When the concentration is in this range, an appropriate molecular weight and solution viscosity are obtained.

(Polyamide acid composition)
A filler may be added to the non-thermoplastic polyamic acid of the present invention for the purpose of improving various film properties such as slidability, thermal conductivity, conductivity, corona resistance, and loop stiffness. Any filler may be used, but preferred examples include silica, titanium oxide, alumina, silicon nitride, boron nitride, calcium hydrogen phosphate, calcium phosphate, mica and the like.

  Other thermosetting resins and thermoplastic resins may be mixed with the polyimide of the present invention as long as the properties of the obtained polyimide film are not impaired. Various known techniques can be applied to the method of adding these thermosetting resins and thermoplastic resins. For example, if it is soluble in a solvent, a method of adding it to the state of polyamic acid which is a precursor of polyimide can be mentioned.

(Production method of polyimide film)
The method for obtaining the polyimide film in the present invention is not particularly limited, and various known methods can be applied. For example, the following step i) a step of reacting an aromatic diamine and an aromatic tetracarboxylic dianhydride in an organic solvent to obtain a non-thermoplastic polyamic acid solution;
ii) casting a film-forming dope containing the non-thermoplastic polyamic acid solution from a die onto a support to form a resin layer (sometimes referred to as a liquid film);
iii) a step of peeling the gel film from the support after the resin layer is heated on the support to obtain a self-supporting gel film,
iv) further heating, imidizing the remaining amic acid and drying to obtain a non-thermoplastic polyimide film;
It is preferable to contain.

  ii) Subsequent steps are roughly divided into a thermal imidization method and a chemical imidization method. The thermal imidization method is a method in which a polyamic acid solution is cast as a film-forming dope without using a dehydrating ring-closing agent or the like, and imidation is advanced only by heating. One chemical imidization method is a method of promoting imidization by using, as a film-forming dope, a polyamic acid solution to which at least one of a dehydrating cyclization agent and a catalyst is added as an imidization accelerator. Either method may be used, but the chemical imidation method is superior in productivity.

  As the dehydrating ring-closing agent, acid anhydrides typified by acetic anhydride can be suitably used. As the catalyst, tertiary amines such as aliphatic tertiary amines, aromatic tertiary amines, and heterocyclic tertiary amines can be suitably used.

  As the support for casting the film-forming dope, a glass plate, aluminum foil, endless stainless steel belt, stainless steel drum or the like can be suitably used. The heating conditions are set according to the thickness of the finally obtained film and the production rate, and after at least one of imidization or drying is partially performed, the film is peeled off from the support and is called a polyamic acid film (hereinafter referred to as a gel film). )

  Fix the end of the gel film and heat treatment to avoid shrinkage during curing, remove water, residual solvent, imidization accelerator, dehydrating ring closure agent, etc. from the gel film, and remove the remaining amic acid. Fully imidized to obtain a film containing polyimide. About a heating condition, what is necessary is just to set suitably according to the thickness and production rate of the film finally obtained.

(Manufacture of polyimide laminated film)
Using the polyimide film of the present invention, it is also possible to produce a polyimide laminated film in which another polyimide layer or an adhesive layer is laminated on at least one surface thereof. The method for producing the polyimide laminated film is not particularly limited, and various known methods can be applied. For example, a co-extrusion die may be used to simultaneously form a multilayer resin layer containing a non-thermoplastic polyamic acid that is a precursor of the polyimide of the present invention and a thermoplastic polyamic acid that can be an adhesive layer. In addition, a polyamide acid which is a precursor of the polyimide of the present invention is synthesized, and a polyimide film obtained by using the polyamide acid is collected once, and then a resin containing a thermoplastic polyamide acid newly by coating or the like thereon A layer may be formed. Since a very high temperature is required for imidization, when the resin layer other than polyimide is provided, it is preferable to adopt the latter means in order to suppress thermal decomposition. When a thermoplastic polyimide layer is provided by coating, a thermoplastic polyamic acid may be applied and then imidized, or a thermoplastic polyimide solution capable of forming a thermoplastic polyimide layer may be applied and dried. May be. Moreover, it is also possible to manufacture a polyimide laminated film by applying an acrylic adhesive or an epoxy adhesive to a polyimide film. Various surface treatments such as corona treatment and plasma treatment can be performed on the outermost surface of the polyimide laminated film.

  The total thickness of the polyimide laminated film of the present invention is preferably 6 μm to 60 μm. Even within this range, a thinner thickness is preferable because it contributes to weight reduction as an FPC and improves bendability. For example, the thickness is preferably 7 μm to 20 μm, and more preferably 7 μm to 15 μm.

(Flexible metal-clad laminate)
A flexible metal-clad laminate can be produced by attaching a metal foil to at least one surface of a polyimide laminate film. The method for producing the flexible metal-clad laminate is not particularly limited, and various known methods can be applied. For example, a continuous process by a hot roll laminating apparatus having a pair of metal rolls or a double belt press (DBP) can be used.

  The specific configuration of the means for carrying out the thermal lamination is not particularly limited, but a protective material is disposed between the pressing surface and the metal foil in order to improve the appearance of the resulting laminate. It is also preferable.

  A means of casting a multilayer organic solvent solution containing at least one of a thermoplastic polyamic acid solution and a non-thermoplastic polyamic acid solution on the metal foil can also be used. The means for casting the organic solvent solution containing the polyamic acid on the metal foil is not particularly limited, and conventionally known means such as a die coater, comma coater (registered trademark), reverse coater, knife coater and the like can be used. When the polyimide resin layer and the non-thermoplastic polyimide film in the present invention are included, or when the polyimide resin layer is provided in multiple layers, or when a resin layer other than the polyimide is provided, the above casting and heating processes are repeated a plurality of times or co-extruded. Alternatively, a means of forming a cast layer by continuous casting and heating it at a time can be suitably used. By this means, a flexible metal-clad laminate is obtained at the same time as imidization is completed. When providing metal foil on both surfaces of the resin layer, the metal foil may be bonded to the opposite resin layer surface by heat and pressure.

  The metal foil is not particularly limited, and any metal foil can be used. For example, copper, stainless steel, nickel, aluminum, and alloys of these metals can be suitably used. In general metal-clad laminates, copper such as rolled copper and electrolytic copper is frequently used, but can be preferably used in the present invention.

  Further, the metal foil having various characteristics such as surface treatment and surface roughness can be selected according to the purpose. Furthermore, a rust preventive layer, a heat resistant layer or an adhesive layer may be applied to the surface of the metal foil. The thickness of the metal foil is not particularly limited, and may be any thickness that can exhibit a sufficient function depending on the application.

  EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited only to these Examples.

  In addition, the dynamic viscoelasticity, linear expansion coefficient, tensile characteristics, stress at 10% strain, how to obtain ST as an index of toughness, and evaluation method of dimensional characteristics of non-thermoplastic polyimide in synthesis examples, examples and comparative examples Is as follows.

(Dynamic viscoelasticity)
The storage elastic modulus was obtained by measuring dynamic viscoelasticity in an air atmosphere using DM6100 manufactured by SII Nanotechnology, and plotting the correlation with the measurement temperature to read the inflection point temperature and the storage elastic modulus at 380 ° C.
Sample measurement range: width 9 mm, distance between grippers: 20 mm
Measurement temperature range: 0 ° C to 440 ° C
Temperature increase rate: 3 ° C / min
Strain amplitude: 10 μm
Measurement frequency: 1Hz, 5Hz, 10Hz
Minimum tension / compression force: 100mN
Tension / compression gain; 1.5
Initial value of force amplitude: 100mN

(Linear expansion coefficient)
The linear expansion coefficient was measured by using TMA / SS6100 manufactured by SII Nanotechnology, Inc., once heated from −10 ° C. to 400 ° C. in a nitrogen atmosphere, cooled to −10 ° C., and then again raised to 400 ° C. It was made to calculate as an average value from the linear thermal expansion coefficient in 100 to 200 degreeC at the time of the 2nd temperature increase.
Sample shape: Width 3mm
Length 10mm
Load; 3g (29.4mN)
Temperature increase rate: 10 ° C / min

(Tensile properties, 10% strain stress, slope of plastic deformation region)
The stress at 10% strain can be obtained from the measurement data of the tensile modulus. The tensile elastic modulus was measured according to ASTM D882. For the measurement, AUTOGRAPH AGS-J manufactured by Shimadzu Corporation was used, and measurement was performed in an environment of 23 ° C. and 55% RH.
Sample measurement range: 15 mm
Distance between grips: 100mm
Tensile speed: 200 mm / min

(Shaking test)
After diluting the polyimide precursor obtained in Synthesis Example 9 with DMF until the solid content concentration becomes 8% by weight, the final single-sided thickness of the thermoplastic polyimide layer (adhesive layer) is 3 μm on both sides of the polyimide film. A polyimide precursor was applied. Thereafter, heating was performed at 120 ° C. for 2 minutes. Subsequently, heating and imidization were performed at 350 ° C. for 15 seconds to obtain a polyimide laminated film. 12 μm electrolytic copper foil (3EC-M3S-HTE, made by Mitsui Metals) is arranged on both sides of the obtained polyimide laminated film, and further, protective films (Apical 125 NPI; Kaneka, thickness 125 μm) are used on both sides of the copper foil, Thermal lamination was performed under the conditions of a laminating temperature of 360 ° C., a laminating pressure of 265 N / cm (27 kgf / cm), and a laminating speed of 1.0 m / min to obtain a flexible metal-clad laminate. A flexible metal-clad laminate is cut to a size of 6.0 cm × 5.5 cm square, and a part of the metal foil is etched into a lattice shape (lattice size: 1.3 mm × 1.5 mm) as shown in FIG. A test piece was obtained. The test piece is placed in a container containing 800 mL of a 4% aqueous sodium hydroxide solution (23 ± 2 ° C.) and shaken at 23 ± 2 ° C. at a shaking speed of 230 rpm (ST) (Sec)). After etching, it was confirmed with an optical microscope that the radius of curvature inside each corner of the lattice was 50 μm or less, and a specimen having a radius of 50 μm or less was used. This test piece was put into a sodium hydroxide aqueous solution. Whether the film was torn or not was judged by stopping shaking every 100 seconds, applying light with a light box to each container in which the test piece was put, and judging that the film was torn when light passed through the test piece.

(Mock test in FPC manufacturing process)
A tension was applied to a long flexible metal-clad laminate on which a conductor pattern had been formed in advance, and the presence or absence of tearing when spraying a 5% aqueous sodium hydroxide solution at 45 ° C. with a spray was visually observed. When the time until tearing occurs is less than 900 seconds (×), when 900 seconds or more and less than 1500 seconds (△), when 1500 seconds or more and less than 2000 seconds (◯), when it is 2000 seconds or more (◎). In the case of 900 seconds or more, the possibility of tearing is low in use in the actual process.

(Dimensional change rate)
Based on JISC6481, four holes were formed in the flexible metal-clad laminate, and the distance of each hole was measured. Next, after carrying out an etching process to remove the metal foil from the flexible laminate, it was left in a temperature-controlled room at 20 ° C. and 60% RH for 24 hours. Then, each distance was measured about the said four holes similarly to the etching process front. The measured value of the distance of each hole before metal foil removal was set to D1, and the measured value of the distance of each hole after metal foil removal was set to D2, and the dimensional change rate was calculated | required by following Formula.

Dimensional change rate (%) = {(D2-D1) / D1} × 100
In addition, the said dimensional change rate was measured about both MD direction and TD direction.

  Stress relaxation at the time of thermal laminating is the case of laminating by aligning the MD direction and TD direction of the film with respect to the conveyance direction (MD direction) and the MD direction (TD direction) at the time of thermal lamination (normal lamination) It can be evaluated by the difference in the dimensional change rate between the MD direction and the TD direction of the film of the flexible laminate produced by laminating the film by 90 ° rotation (90 ° rotation lamination). In the present invention, the difference in the dimensional change rate depending on the laminating direction is “◯” when 0.04% or less, “Δ” when 0.04 to 0.08%, and “8” when 0.08% or more. × ”.

(Appearance of flexible metal-clad laminate (FCCL))
12 μm electrolytic copper foil (HTE-M3S-HTE, manufactured by Mitsui Metals) is arranged on both sides of the obtained polyimide laminated film, and further, protective films (Apical 125 NPI; manufactured by Kaneka, thickness 125 μm) are used on both sides of the copper foil. The presence or absence of wrinkles was visually observed when thermal lamination was performed under the conditions of a laminating temperature of 360 ° C., a laminating pressure of 265 N / cm (27 kgf / cm), and a laminating speed of 1.0 m / min. The case where wrinkles did not occur was indicated as “◯”, and the case where even one wrinkle occurred was indicated as “x”.

(Synthesis of non-thermoplastic polyimide precursor)
(Synthesis Example 1)
In a glass flask having a capacity of 2000 ml, 333.87 g of N, N-dimethylformamide (hereinafter also referred to as DMF) and 5 of 4,4′-diamino-2,2′-dimethylbiphenyl (hereinafter also referred to as m-TB) were added. .56 g, 3.93 g of p-phenylenediamine (hereinafter also referred to as PDA) was added, and 12.27 g of pyromellitic dianhydride (hereinafter also referred to as PMDA) was gradually added while stirring in a nitrogen atmosphere. . Stirring was performed for 30 minutes after visually confirming that PMDA was dissolved. Thereafter, 16.59 g of 4,4′-diaminodiphenyl ether (hereinafter also referred to as ODA) was added, followed by 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride (hereinafter also referred to as BPDA). 18.09 g was gradually added. After visually confirming that BPDA was dissolved, 5.55 g of PMDA was added and stirred for 30 minutes. Finally, a solution prepared by dissolving 0.48 g of PMDA in DMF to a solid content concentration of 7.2% was prepared, and this solution was gradually added to the reaction solution while paying attention to an increase in viscosity. When the viscosity at 23 ° C. reached 2500 poise, addition and stirring were stopped to obtain a polyimide precursor.

(Synthesis Example 2)
To a glass flask having a capacity of 2000 ml, 334.13 g of DMF, 4.43 g of m-TB, and 3.76 g of PDA were added, and 10.92 g of PMDA was gradually added while stirring under a nitrogen atmosphere. Stirring was performed for 30 minutes after visually confirming that PMDA was dissolved. Thereafter, 16.71 g of ODA was added, and then 18.41 g of BPDA was gradually added. After visually confirming that BPDA was dissolved, 5.31 g of PMDA was added and stirred for 30 minutes. Finally, a solution prepared by dissolving 0.46 g of PMDA in DMF so as to have a solid content concentration of 7.2% is prepared, and this solution is gradually added to the reaction solution while paying attention to an increase in viscosity. When the viscosity at 23 ° C. reached 2500 poise, addition and stirring were stopped to obtain a polyimide precursor.

(Synthesis Example 3)
To a glass flask having a volume of 2000 ml, 334.06 g of DMF, 2.99 g of m-TB, and 4.57 g of PDA were added, and 11.05 g of PMDA was gradually added while stirring under a nitrogen atmosphere. Stirring was performed for 30 minutes after visually confirming that PMDA was dissolved. Thereafter, 16.91 g of ODA was added, and then 18.64 g of BPDA was gradually added. After visually confirming that BPDA was dissolved, 5.37 g of PMDA was added and stirred for 30 minutes. Finally, a solution prepared by dissolving 0.46 g of PMDA in DMF so as to have a solid content concentration of 7.2% is prepared, and this solution is gradually added to the reaction solution while paying attention to an increase in viscosity. When the viscosity at 23 ° C. reached 2500 poise, addition and stirring were stopped to obtain a polyimide precursor.

(Synthesis Example 4)
334.13 g of DMF and 16.71 g of ODA were added to a glass flask having a capacity of 2000 ml, and 18.41 g of BPDA was gradually added while stirring under a nitrogen atmosphere. After visually confirming that BPDA was dissolved, 2.73 g of PMDA was gradually added and stirred for 30 minutes. Thereafter, 4.43 g of m-TB and 3.76 g of PDA were added, and then 13.50 g of PMDA was added and stirred for 30 minutes. Finally, a solution prepared by dissolving 0.46 g of PMDA in DMF so as to have a solid content concentration of 7.2% is prepared, and this solution is gradually added to the reaction solution while paying attention to an increase in viscosity. When the viscosity at 23 ° C. reached 2500 poise, addition and stirring were stopped to obtain a polyimide precursor.

(Synthesis Example 5)
To a glass flask having a capacity of 2000 ml, add 334.26 g of DMF, 4.34 g of 4,4′-diamino-3,3′-dimethylbiphenyl (hereinafter also referred to as o-TB), and 2.21 g of PDA, and under nitrogen atmosphere. While stirring, 8.02 g of PMDA was gradually added. Stirring was performed for 30 minutes after visually confirming that PMDA was dissolved. Thereafter, 19.09 g of ODA was added, followed by gradual addition of 18.03 g of BPDA. After visually confirming that BPDA was dissolved, 7.87 g of PMDA was added and stirred for 30 minutes. Finally, a solution prepared by dissolving 0.45 g of PMDA in DMF so as to have a solid content concentration of 7.2% is prepared, and this solution is gradually added to the reaction solution while paying attention to an increase in viscosity. When the viscosity at 23 ° C. reached 2500 poise, addition and stirring were stopped to obtain a polyimide precursor.

(Synthesis Example 6)
33.99g of DMF, 1.51g of m-TB, and 5.39g of PDA were added to a glass flask having a capacity of 2000ml, and PMDA 11.19g was gradually added while stirring in a nitrogen atmosphere. Stirring was performed for 30 minutes after visually confirming that PMDA was dissolved. Thereafter, 17.12 g of ODA was added, and then 18.87 g of BPDA was gradually added. After visually confirming that BPDA was dissolved, 5.44 g of PMDA was added and stirred for 30 minutes. Finally, a solution prepared by dissolving 0.47 g of PMDA in DMF so as to have a solid content concentration of 7.2% was prepared, and this solution was gradually added to the reaction solution while paying attention to an increase in viscosity. When the viscosity at 23 ° C. reached 2500 poise, addition and stirring were stopped to obtain a polyimide precursor.

(Synthesis Example 7)
33.91 g of DMF and 6.24 g of PDA were added to a glass flask having a capacity of 2000 ml, and PMDA 11.33 g was gradually added while stirring under a nitrogen atmosphere. Stirring was performed for 30 minutes after visually confirming that PMDA was dissolved. Thereafter, 17.34 g of ODA was added, and then 19.11 g of BPDA was gradually added. After visually confirming that BPDA was dissolved, 5.51 g of PMDA was added and stirred for 30 minutes. Finally, a solution prepared by dissolving 0.47 g of PMDA in DMF so as to have a solid content concentration of 7.2% was prepared, and this solution was gradually added to the reaction solution while paying attention to an increase in viscosity. When the viscosity at 23 ° C. reached 2500 poise, addition and stirring were stopped to obtain a polyimide precursor.

(Synthesis Example 8)
To a glass flask having a capacity of 2000 ml, 334.47 g of DMF and 11.14 g of m-TB were added, and 10.30 g of PMDA was gradually added while stirring under a nitrogen atmosphere. Stirring was performed for 30 minutes after visually confirming that PMDA was dissolved. Thereafter, 15.76 g of ODA was added, followed by gradual addition of 17.37 g of BPDA. After visually confirming that BPDA was dissolved, 5.01 g of PMDA was added and stirred for 30 minutes. Finally, a solution prepared by dissolving 0.43 g of PMDA in DMF so as to have a solid content concentration of 7.2% is prepared, and this solution is gradually added to the reaction solution while paying attention to an increase in viscosity. When the viscosity at 23 ° C. reached 2500 poise, addition and stirring were stopped to obtain a polyimide precursor.

(Synthesis Example 9)
334.13 g of DMF, 4.43 g of m-TB, 16.71 g of ODA and 3.76 g of PDA were added to a glass flask having a capacity of 2000 ml, and 18.41 g of BPDA was gradually added while stirring in a nitrogen atmosphere. After visually confirming that BPDA was dissolved, 16.23 g of PMDA was added and stirred for 30 minutes. Finally, a solution prepared by dissolving 0.46 g of PMDA in DMF so as to have a solid content concentration of 7.2% is prepared, and this solution is gradually added to the reaction solution while paying attention to an increase in viscosity. When the viscosity at 23 ° C. reached 2500 poise, addition and stirring were stopped to obtain a polyimide precursor.

(Synthesis Example 10)
To a glass flask having a capacity of 2000 ml, 657.82 g of DMF, 10.53 g of ODA, and 32.39 g of 2,2-bis [4- (4-aminophenoxy) phenyl] propane (hereinafter also referred to as BAPP) were added, and a nitrogen atmosphere was added. 16.95 g of benzophenonetetracarboxylic dianhydride (hereinafter also referred to as BTDA) was gradually added while stirring at -1. After visually confirming that BTDA was dissolved, 14.34 g of PMDA was added and stirred for 30 minutes. Thereafter, 14.22 g of PDA was added and stirred for 5 minutes. Subsequently, 29.83 g of PMDA was added and stirred for 30 minutes. Finally, a solution in which 1.72 g of PMDA was dissolved in DMF to a solid content concentration of 7.2% was prepared, and this solution was gradually added to the above reaction solution while paying attention to an increase in viscosity. When the viscosity at 23 ° C. reached 2500 poise, addition and stirring were stopped to obtain a polyimide precursor.

  Table 1 shows polymerization prescriptions and polymerization methods of Synthesis Examples 1 to 10.

(Synthesis of thermoplastic polyimide precursor)
(Synthesis Example 11)
To a glass flask having a volume of 2000 ml, 645.94 g of DMF and 23.67 g of 4,4′-bis (4-aminophenoxy) biphenyl (hereinafter also referred to as BAPB) were added, and BPDA 15. 75 g was gradually added. After visually confirming that BPDA was dissolved, 61.54 g of BAPP was added, and then 33.63 g of PMDA was added, followed by stirring for 30 minutes. Finally, 1.40 g of PMDA was dissolved in DMF so that the solid content concentration was 7.2%, and this solution was gradually added to the reaction solution while paying attention to increase in viscosity. When the viscosity at 23 ° C. reached 1000 poise, addition and stirring were stopped to obtain a polyimide precursor.

  32.5 g of a curing agent composed of acetic anhydride / isoquinoline / DMF (weight ratio 8.53 / 2.52 / 21.46) was added to the polyimide precursor (65 g), and stirring and defoaming were performed at a temperature of 0 ° C. or less. And it cast-coated on the aluminum foil using the comma coater. This resin film is heated at 120 ° C. for 3 minutes, then the self-supporting gel film is peeled off from the aluminum foil and fixed on a metal fixing frame, and dried at 250 ° C. for 1 minute, 300 ° C. for 200 seconds. -A polyimide film having a thickness of 20 μm was obtained by imidization. When this film was fixed to a metal fixing frame and heated at 450 ° C. for 2 minutes, it was confirmed that the film did not retain its shape and was thermoplastic.

Example 1
32.5 g of a curing agent composed of acetic anhydride / isoquinoline / DMF (weight ratio 15.51 / 3.87 / 13.12) was added to the polyimide precursor (65 g) obtained in Synthesis Example 1, and 0 ° C. or less. The mixture was stirred and degassed at a temperature of 5 ° C and cast onto an aluminum foil using a comma coater. After heating this resin film at 115 ° C. × 100 seconds, the self-supporting gel film is peeled off from the aluminum foil and fixed to a metal fixing frame, and dried at 250 ° C. × 15 seconds, 350 ° C. × 79 seconds. A polyimide film having a thickness of 12.5 μm was obtained by imidization. When this film was fixed to a metal fixing frame and heated at 450 ° C. for 2 minutes, the shape was maintained, and it was confirmed that the film was non-thermoplastic. Table 2 shows the film properties and ST of the obtained polyimide film.

(Example 2 to Example 5)
The same procedure as in Example 1 was performed except that the polyimide precursor obtained in Synthesis Example 1 was changed to Synthesis Examples 2 to 5. When this film was fixed to a metal fixing frame and heated at 450 ° C. for 2 minutes, the form was maintained, and it was confirmed that both were non-thermoplastic. The film characteristics and ST are shown in Table 2.

(Comparative Examples 1 to 5)
The same procedure as in Example 1 was performed except that the polyimide precursor obtained in Synthesis Example 1 was changed to Synthesis Examples 6 to 10. When this film was fixed to a metal fixing frame and heated at 450 ° C. for 2 minutes, the shape was maintained, and it was confirmed that the film was non-thermoplastic. The film characteristics and ST are shown in Table 2.

(Discussion)
From the results in Table 2, the introduction of a rigid and highly free biphenyl skeleton increased the slope of the plastic deformation region compared to the system not containing the biphenyl skeleton (Comparative Examples 2 and 5). As the amount of biphenyl skeleton introduced was increased, the slope of the plastic deformation region was increased, and ST was also increased. From these results, it can be seen that the introduction of the biphenyl skeleton promotes the agglomeration structure of the resin layer and makes it difficult to plastically deform, and thus is excellent in tear resistance.

1. Metal foil Polyimide film Strain 1 (10% strain)
4). Strain 2 (breaking strain)
5). Stress1 (Stress at 10% strain)
6). Stress2 (breaking stress)
7). 7. s-s curve of Comparative Example 5 S-s curve of Example 2

Claims (4)

  A polyimide film, wherein an inclination of a plastic deformation region in a stress-strain curve is 2.0 or more.   The aromatic diamine constituting the non-thermoplastic polyimide contains at least 10 to 18 mol% of 4,4′-diamino-2,2′-dimethylbiphenyl or 4,4′-diamino-3,3′-dimethylbiphenyl. The polyimide film according to claim 1, wherein:   The polyimide film according to claim 1 or 2, wherein a stress at 10% strain in a stress-strain curve is 190 MPa or more.   The storage elastic modulus at 380 ° C. in dynamic viscoelasticity measurement is 0.2 GPa or more and 1.0 GPa or less, and the temperature indicated by the inflection point of the storage elastic modulus is 270 ° C. to 340 ° C. Item 4. The polyimide film according to any one of Items 1 to 3.