JP5870396B2 - Polyimide film - Google Patents

Description

  The present invention relates to a polyimide film. More specifically, the present invention relates to a polyimide film having a small difference in dimensional change between the longitudinal direction and the width direction of the film, a small absolute value of each dimensional change, and excellent smoothness.

  Polyimide film has excellent heat resistance, chemical resistance, and electrical properties, so it is an electrical insulation material for wires, chip-on-film (COF), flexible printed wiring board (FPC) base film, and IC tape automated bonding ( TAB) carrier tape film, IC lead frame fixing tape, and the like.

  Recent applications of polyimide films include the use of base films for displays such as electronic paper because of their advantages such as weight reduction and flexibility, but in this application, the surface is very smooth and high dimensional stability. Is required.

  As for the surface of the film, adding particles to the film to make it slippery is generally carried out in order to ensure film transportability and handling properties in the process. As a conventional smoothing technique for polyimide films, an inorganic compound (for example, alkaline earth metal orthophosphate, dibasic calcium phosphate anhydride, calcium pyrophosphate, silica, talc) is added to polyamic acid (for example, patents). Further, a method of performing plasma treatment after forming fine protrusions on the film surface with fine particles (see, for example, Patent Document 2) is known. However, since the inorganic particles shown in these figures have a large particle size, they are not suitable as a base film for electronic paper or the like.

Further, inorganic particles having an average particle diameter of 0.01 to 100 μm are embedded and held on the polyimide surface layer, and a large number of protrusions made of the exposed inorganic particles are formed on the surface layer of the film. There is known a method of causing 1 × 10 to 5 × 10 ⁸ pieces / mm ^{2 to} exist in the substrate (for example, see Patent Document 3). This method is characterized in that the slippery effect is effectively obtained by actively exposing the inorganic particles on the surface and reducing the friction coefficient of the film surface, but the inorganic particles are partially exposed. For this reason, there is a problem in that scratches occur on the other film surface that comes into contact with the film, resulting in poor appearance.

  Furthermore, a polyimide film (for example, see Patent Document 4) in which the number particle size distribution and the number of protrusions are defined has been proposed. Although this polyimide film is excellent in smoothness, it is an indispensable dimension for display base film applications. There was no mention of stability.

JP-A-62-68852 JP 2000-191810 A Japanese Patent Laid-Open No. 5-25295 JP2011-63775

  An object of the present invention is to provide a polyimide film having a small difference in dimensional change between the longitudinal direction and the width direction of the film, a small absolute value of each dimensional change, and excellent smoothness.

  From the above background, as a result of extensive research, the inventor has provided a fine projection using inorganic particles on a base film having a low thermal expansion coefficient and a small difference between the longitudinal direction and the width direction of the film. The inventors have found that a polyimide film having high dimensional stability and a smooth surface can be obtained, and further studies have been made to complete the present invention.

That is, in the present invention, when the thermal expansion coefficient in the longitudinal direction of the film is CTE _MD and the thermal expansion coefficient in the width direction is CTE _TD , | CTE _MD -CTE _TD | is 4 ppm or less, and CTE _MD and CTE _TD are 8 a ± 3 ppm, and projections of the film surface is formed from inorganic particles having an average particle diameter of 10 nm to 100 nm, Ri surface roughness Ra of 5nm der following film, further, the film surface using a laser microscope The present invention provides a polyimide film characterized by having no projection having a height of 0.3 μm or more on the film surface when 5.6 mm ² is observed .

In the polyimide film of the present invention ,
That no machine particles are contained in an amount of 0.05 to 0.9 wt% per film resin weight,
The polyimide film is composed of an aromatic diamine component having a molar ratio of 4,4′-diaminodiphenyl ether and paraphenylenediamine of 60/40 to 90/10, pyromellitic dianhydride and 3,3 ′, 4,4. A preferable condition is that the product is made from a polyamic acid composed of an acid anhydride component having a molar ratio with '-biphenyltetracarboxylic dianhydride of 80/20 to 60/40.

  The polyimide film of the present invention has a small difference in dimensional change between the longitudinal direction and the width direction of the film, a small absolute value of each dimensional change, and excellent smoothness. As particularly useful.

  Hereinafter, the present invention will be specifically described.

In the polyimide film of the present invention, when CTE _MD is the thermal expansion coefficient in the longitudinal direction of the film and CTE _TD is the thermal expansion coefficient in the width direction, | CTE _MD -CTE _TD | is 4 ppm or less, and CTE _MD and CTE _TD Is 8 ± 3 ppm.

The polyimide film of the present invention is not particularly limited as long as | CTE _MD -CTE _TD | is 4 ppm or less. However, | CTE _MD -CTE _TD | is preferably 3 ppm or less, and | CTE _MD -CTE _TD | is 2 ppm or less. More preferably.

If | CTE _MD −CTE _TD | exceeds 4 ppm or CTE _MD and CTE _TD exceed the range of 8 ± 3 ppm, dimensional stability may be lost, which is not preferable.

  The polyimide film of the present invention is characterized in that protrusions on the film surface are formed from inorganic particles having an average particle diameter of 10 nm to 100 nm, and the surface roughness Ra of the film is 5 nm or less.

  In the present invention, the use of inorganic particles is superior in dispersibility and heat resistance compared to the case of using organic particles. In addition, heat resistance is difficult with organic particles, and polyimide with a high production temperature may be decomposed. The inorganic particles in the present invention may be contained in the polyimide film, and fine protrusions are formed on the surface of the polyimide film with the inorganic particles in the vicinity of the film surface as a nucleus.

  Although it will not specifically limit if the average particle diameter of the inorganic particle used for this invention exists in the range of 10 nm-100 nm, 20 nm-95 nm are preferable and 40 nm-90 nm are more preferable. This is because if the average particle diameter is 50 nm to 90 nm, the balance between the slipperiness and the unevenness of the film surface is particularly good. If the average particle size is less than 10 nm, the film's slidability effect is lowered, which is not preferable, and if it exceeds 100 nm, the particles are locally present as large particles, which is not preferable.

  The average particle diameter in the present invention is a particle selected at random from an SEM image obtained by observing a film at a magnification of 10,000 to 100,000 times using a scanning electron microscope (SEM), and the diameter (particle diameter) is selected. The average length of 30 particles is calculated to obtain an average particle diameter (length average diameter). In addition, when the number of protrusions was less than 30 in one field of view SEM image, it was set to 30 or more in multiple fields of view. Although it does not specifically limit as said scanning electron microscope used for the measurement of the average particle diameter of this invention, S5000 (brand name; Hitachi, Ltd. make) etc. are mentioned.

The material of the inorganic particles used in the present invention is not particularly limited, but silica (SiO ₂ ) or a hydrate thereof, alumina, titanium oxide, calcium phosphate, zirconium oxide, and the like are preferably used.

The inorganic particles of the present invention can be produced by a known method, and are not particularly limited. For example, JP-B-4-65006, JP-A-9-142828, JP-2007-277525, JP It can be produced by the method described in 2007-153732. Specifically, such a method comprises hydrolyzing an organosilicate in the presence of a hydrolysis catalyst such as an ammonia catalyst or an organic amine catalyst, and depositing inorganic components while proceeding with a dehydration polycondensation reaction. And so-called sol-gel method.
Moreover, a commercial item may be used for inorganic particles, for example, Snowtex UP, Snowtex OUP, Snowtex PS-S, Snowtex PS-S (above, manufactured by Nissan Chemical Industries, Ltd.), PL-1, PL -3, PL-7, PL-20, SP-03F, SP-1B (above, manufactured by Fuso Chemical Industries), colloidal silica such as Oscar (manufactured by JGC Catalysts & Chemicals).

  The polyimide film of the present invention is not particularly limited as long as the surface roughness Ra is 5 nm or less, but is preferably 4 nm or less, and more preferably 2 nm or less. If the Ra exceeds 5 nm, the performance of the transistor formed on the film may be impaired, which is not preferable.

  The surface roughness Ra of the polyimide film of the present invention was calculated by measuring a range of 20 μm square with a probe microscope. The probe microscope used for the measurement of the present invention is not particularly limited, and examples thereof include SPA400 / SPI3800N (manufactured by SII Nano Technology).

The polyimide film of the present invention is characterized in that when a film surface of 5.6 mm ² is observed using a laser microscope, there is no protrusion having a height of 0.3 μm or more on the film surface. Exceeds 0.3μm projection is because there are cases impair the performance of the transistor to be formed on the film.

The projections having a height of 0.3 μm or more in the present invention were observed at 10 points at random with a magnification of 1000 times using a laser microscope, and a total observation area of 5.6 mm ² was ensured. When there was no protrusion of 0.3 μm or more in the entire observation range, it was judged that there was no protrusion of 0.3 μm or more. Although the laser microscope used for the measurement of this invention is not specifically limited, VK-9700 (brand name: product made by Keyence) etc. are mentioned.

  The blending ratio of the inorganic particles used in the present invention is not particularly limited, but may be uniformly dispersed in the film at a ratio of 0.05% by weight or more and 0.9% by weight or less with respect to the weight of the film resin. A ratio of 0.1% by weight or more and 0.8% by weight or less is more preferable from the viewpoint of easy slipping effect. If it exceeds 0.9% by weight, the mechanical strength may decrease or surface roughening may occur due to aggregation between particles, and if it is 0.05% by weight or less, sufficient slipperiness effect is not seen. Neither is preferred.

  Next, the manufacturing method of the polyimide film of this invention is demonstrated in detail below. The production process includes, for example, (1) a process of polymerizing an aromatic diamine component and an acid anhydride component in an organic solvent to obtain a polyamic acid solution, and (2) inorganic particles having an average particle diameter of 10 to 100 nm. Preparing a slurry dispersed in the same organic solvent as the organic solvent, and adding the slurry in any of the steps (1); (3) the polyamic acid solution obtained in the step (2); A step of obtaining a gel film by cyclization can be included.

  Step (1) is a step of obtaining a polyamic acid solution by polymerizing an aromatic diamine component and an acid anhydride component in an organic solvent.

  Specific examples of the aromatic diamine are not particularly limited as long as the effects of the present invention are not hindered, but paraphenylenediamine, metaphenylenediamine, benzidine, paraxylylenediamine, 4,4′-diaminodiphenyl ether, 3,4 ′. -Diaminodiphenyl ether, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylsulfone, 3,3'-dimethyl-4,4'-diaminodiphenylmethane, 1,5-diaminonaphthalene, 3,3'-dimethoxy bench Zin, 1,4-bis (3methyl-5aminophenyl) benzene or amide-forming derivatives thereof. Among these, the amount of diamines such as paraphenylenediamine and 4,4′-diaminodiphenyl ether, which have the effect of increasing the tensile modulus of the film, is adjusted, and the tensile modulus of the finally obtained polyimide film is 4.0 GPa. It is preferable to make it above. These aromatic diamines can be used alone or in admixture of two or more. Of these aromatic diamines, paraphenylenediamine and 4,4'-diaminodiphenyl ether are preferred. When paraphenylenediamine and 4,4′-diaminodiphenyl ether are used in combination, 69/31 to 90/10 (molar ratio) of (i) 4,4′-diaminodiphenyl ether and (ii) paraphenylenediamine It is more preferable to use at 70/30 to 85/15 (molar ratio).

  Specific examples of the acid anhydride component are not particularly limited as long as the effects of the present invention are not hindered, but pyromellitic acid, 3,3 ′, 4,4′-biphenyltetracarboxylic acid, 2,3 ′, 3, 4'-biphenyltetracarboxylic acid, 3,3 ', 4,4'-benzophenonetetracarboxylic acid, 2,3,6,7-naphthalenedicarboxylic acid, 2,2-bis (3,4-dicarboxyphenyl) ether , Pyridine-2,3,5,6-tetracarboxylic acid, or acid anhydrides such as amide-forming derivatives thereof, preferred are acid tetraanhydrides of aromatic tetracarboxylic acids, pyromellitic acid dianhydride And / or 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride is particularly preferred. These acid anhydride components can be used alone or in admixture of two or more. Of these, it is more preferable to use pyromellitic dianhydride and 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride at 80/20 to 60/40 (molar ratio), It is particularly preferable to use at 75/25 to 65/35 (molar ratio).

  In the present invention, the organic solvent used for forming the polyamic acid solution is not particularly limited. For example, sulfoxide solvents such as dimethyl sulfoxide and diethyl sulfoxide; N, N-dimethylformamide, N, N-diethylformamide and the like Formamide solvents; N, N-dimethylacetamide (DMAc), acetamide solvents such as N, N-diethylacetamide; pyrrolidone solvents such as N-methyl-2-pyrrolidone and N-vinyl-2-pyrrolidone; Examples include phenolic solvents such as o-, m-, or p-cresol, xylenol, halogenated phenol, and catechol; or aprotic polar solvents such as hexamethylphosphoramide and γ-butyrolactone. Or as a mixture Better bur, further xylene, the use of aromatic hydrocarbons such as toluene are also possible.

  The polymerization method may be carried out by any known method, and is not particularly limited. For example, (i) the aromatic diamine component is first put in an organic solvent, and then the acid anhydride component is converted into the aromatic diamine component. (Ii) a method in which the total amount of the acid anhydride component is first put in a solvent, and then the aromatic diamine component is added in an amount equivalent to the acid anhydride component for polymerization. (Iii) After one aromatic diamine component is put in a solvent, after mixing for a time required for the reaction at a ratio of 95 to 105 mol% of the acid anhydride component with respect to the reaction component, the other aromatic diamine component is mixed. A method in which a diamine component is added, and then an acid anhydride component is added so that the wholly aromatic diamine component and the acid anhydride component are approximately equal in amount, and polymerization is performed, and (iv) the acid anhydride component is placed in a solvent. After that, one side of the reaction components After mixing for a time required for the reaction at a ratio of 95 to 105 mol% of the aromatic diamine component, an acid anhydride component is added, and then the other aromatic diamine component is replaced with a wholly aromatic diamine component and an acid anhydride component. (V) A method in which a polymer is added so as to be approximately equal to each other and polymerized, and (v) a polyamic acid solution (A ) To prepare a polyamic acid solution (B) by reacting the other aromatic diamine component and the acid anhydride component in an excess amount in another solvent, and then each polyamic acid obtained A method of mixing the solutions (A) and (B) to complete the polymerization. In (vi) and (v), when the polyamic acid solution (A) is prepared in excess, the polyamic acid solution (B ) In the acid anhydride component When the acid anhydride component is excessive in the polyamic acid solution (A), the aromatic diamine component is excessive in the polyamic acid solution (B), and the polyamic acid solutions (A) and (B) are mixed to perform these reactions. And a method for preparing the wholly aromatic diamine component and the acid anhydride component to be used in an equivalent amount.

  The polyamic acid solution thus obtained preferably contains 5 to 40% by weight of solid content, more preferably 10 to 30% by weight. The viscosity of the polyamic acid solution is a value measured by a rotational viscometer method using a Brookfield viscometer in accordance with JIS K6726_1994, and is not particularly limited, but is preferably 10 to 2000 Pa · s (100 to 20000 poise), The thing of 100-1000 Pa.s (1000-10000 poise) is more preferable from the point of supply of the stable liquid feeding. Moreover, the polyamic acid in the organic solvent solution may be partially imidized.

  In the step (2), a slurry is prepared by dispersing inorganic particles having an average particle diameter of 10 to 100 nm in the same organic solvent as the organic solvent, and the slurry is added at any stage of the step (1). It is a process to do. The preparation of the slurry is not particularly limited, and examples thereof include a method of dispersing the inorganic particles in the organic solvent described above (for example, a polar solvent such as N, N-dimethylacetamide (DMAc)) to form a slurry. In order to obtain the slipperiness of the film, the prepared slurry is dispersed in the organic solvent or solution at any stage of the step (1) at the blending ratio of the inorganic particles. The timing of adding the inorganic particles is not particularly limited as long as it is before the cyclization reaction, and step (2) is not necessarily performed after step (1). For example, (i) an organic solvent before polyamic acid polymerization In addition, an inorganic particle slurry dispersed in the same organic solvent (for example, polar solvent) as the organic solvent used for the production of polyimide may be added, and (ii) the polyimide is added to the polyamic acid solution obtained by the polymerization reaction. An inorganic particle slurry dispersed in the same organic solvent (for example, a polar solvent) as the organic solvent used in the production of may be added, but is preferably added to the polyamic acid solution.

  Step (3) is a step of obtaining a gel film by cyclizing the polyamic acid solution obtained in the step (2). The method of cyclizing the polyamic acid solution is not particularly limited. Specifically, (i) a method of obtaining a gel film by casting the polyamic acid solution into a film and thermally dehydrating and cyclizing ( Thermal cyclization method), or (ii) a method in which a gel film is prepared by mixing the polyamic acid solution with a cyclization catalyst and a conversion agent to chemically decyclize, and obtaining a gel film by heating (chemical cyclization method). The latter method is preferable in that the linear thermal expansion coefficient of the resulting polyimide film can be kept low.

  The cyclization catalyst is not particularly limited, and examples thereof include aliphatic tertiary amines such as trimethylamine and triethylenediamine; aromatic tertiary amines such as dimethylaniline; and heterocycles such as isoquinoline, pyridine and β-picoline. A tertiary amine etc. are mentioned, The 1 or more heterocyclic tertiary amine chosen from the group which consists of isoquinoline, a pyridine, and (beta) -picoline is preferable. Examples of the conversion agent include, but are not limited to, aliphatic carboxylic anhydrides such as acetic anhydride, propionic anhydride, and butyric anhydride; aromatic carboxylic anhydrides such as benzoic anhydride, and the like. Preference is given to benzoic anhydride. The content of these conversion agents is not particularly limited, but is preferably about 10 to 40% by weight and more preferably about 15 to 30% by weight with respect to 100% by weight of the polyamic acid solution.

  Although it does not specifically limit about the film forming method of a film, For example, it can form into a film with a continuous film forming apparatus using the said polyamic acid solution. Specifically, the polyamic acid solution is formed into a film shape through a slit-shaped base, cast on a heated support, undergoes a thermal ring-closing reaction on the support, and has a self-supporting gel. It becomes a film and is peeled from the support.

  The support is not particularly limited, and examples thereof include a metal (for example, stainless steel) rotating drum, an endless belt, and the like. The temperature of the support is (i) a liquid or gas heat medium, and (ii) an electric heater. And is not particularly limited.

  The gel film is preferably heated to 30 to 200 ° C., more preferably 40 to 150 ° C. by heat received from a support, heat received from a heat source such as hot air or an electric heater, and a ring-closing reaction is performed. It becomes self-supporting by drying volatile matter, and is obtained by peeling from the support.

  A polyimide film can be obtained from the peeled gel film, and the method is not particularly limited, but suitable examples will be described below. The peeled gel film is usually stretched in the running direction while regulating the running speed with a rotating roll. Stretching in the running direction is performed at a magnification of 1.05 to 1.9 times, preferably 1.1 to 1.6 times, and more preferably 1.1 to 1.5 times. The gel film stretched in the running direction is introduced into a tenter device, and both ends in the width direction are held by the tenter clip, and stretched in the width direction while running with the tenter clip. Stretching in the width direction is performed at a magnification of 1.05 to 2.3 times, preferably 1.1 to 2.0 times, and more preferably 1.1 to 1.7 times. The film is heated with hot air, an infrared heater or the like for 15 seconds to 10 minutes. Next, heat treatment is performed with hot air and / or an electric heater at a temperature of 250 to 500 for 15 seconds to 20 minutes to obtain a polyimide film.

  The thickness of the polyimide film of the present invention is not particularly limited, but is preferably in the range of 3 μm to 250 μm, and more preferably in the range of 10 μm to 80 μm. If it is thinner or thicker than this, the film-forming property of the film is remarkably deteriorated. The width of the polyimide film of the present invention is not particularly limited.

  The polyimide film thus obtained may be annealed as necessary. Annealing treatment causes thermal relaxation of the film and can reduce the heat shrinkage rate. The annealing temperature is not particularly limited, but is preferably 200 to 500 ° C. Since heat shrinkage at 200 ° C. can be suppressed to 0.05% or less for both the MD and TD of the film by thermal relaxation from the annealing treatment, a preferable effect of further increasing the dimensional accuracy can be obtained. Specifically, it is preferable to perform annealing treatment by running the film in a furnace at 200 to 500 ° C. under low tension. The time during which the film stays in the furnace is the processing time, but it is controlled by changing the running speed, and the processing time is preferably 30 seconds to 5 minutes. If the treatment time is shorter than this, heat is not sufficiently transferred to the film, and if the treatment time is longer, the film becomes superheated and the flatness is impaired. Moreover, 10-50 N / m is preferable and the film tension at the time of driving | running | working has more preferable 20-30 N / m. When the tension is lower than this range, the running property of the film is deteriorated, and when the tension is high, the heat shrinkage rate in the running direction of the obtained film is increased, which is not preferable.

  In order to give adhesion to the obtained polyimide film, the film surface may be subjected to electrical treatment such as corona treatment or plasma treatment or physical treatment such as blast treatment. The pressure of the atmosphere in which the plasma treatment is performed is not particularly limited, but is usually in the range of 13.3 to 1330 kPa, preferably in the range of 13.3 to 133 kPa (100 to 1000 Torr), and in the range of 80.0 to 120 kPa (600 to 900 Torr). Is more preferable.

  The effects of the present invention will be described below with reference to examples, but the present invention is not limited thereto.

  In addition, each characteristic value in an Example was measured by the method described below.

[CTE]
TMA-50 manufactured by Shimadzu Corporation was used, and measurement was performed under the conditions of a measurement temperature range: 50 to 200 ° C. and a heating rate: 10 ° C./min.

[Average particle size]
SEM image observed at a magnification of 10,000 to 100,000 using a scanning electron microscope (SEM) S5000 (trade name; manufactured by Hitachi, Ltd.) after depositing Ag on the film at an angle of 5 °, sputter-coating Pt. Particles were randomly selected from the above, the diameter (particle diameter) was determined, and the average length of 30 particles was calculated as the average particle diameter (length average diameter). In addition, when the number of protrusions was less than 30 in one field of view SEM image, the number was set to 30 or more in multiple fields of view.

[Surface roughness Ra]
Measurement was performed at 20 μm square using SPA-400 / SPI3800N manufactured by SII Nano Technology.

[Protrusions with a height of 0.3 μm or more]
Ten points were randomly observed with a KEYENCE laser microscope VK-9700 at a magnification of 1000 times, and a total observation area of 5.6 mm ² was secured. The number of all the observation ranges was defined as the number of protrusions.

[Example 1]
Pyromellitic dianhydride (molecular weight 218.12) / biphenyltetracarboxylic dianhydride (molecular weight 294.22) / 4,4'-diaminodiphenyl ether (molecular weight 200.24) / paraphenylenediamine (molecular weight 108.14) Was prepared at a molar ratio of 70/30/70/30, and a silica slurry having an average particle diameter of 80 nm was added to 18.5 wt% in DMAc added to 0.5 wt% with respect to the film resin weight. The resulting solution was polymerized to give a 3000 poise polyamic acid solution.

  Then, after this polyamic acid solution was cooled at minus 5 ° C., 15% by weight of acetic anhydride and 15% by weight of betapicoline were mixed with 100% by weight of the polyamic acid solution. After this mixed solution was cast on a rotating drum at 90 ° C. for 30 seconds, the obtained gel film was stretched 1.2 times in the longitudinal direction while being heated at 100 ° C. for 5 minutes. Next, both ends in the width direction were held and stretched 1.3 times in the width direction while heating at 270 ° C. for 2 minutes, and then heated at 380 ° C. for 5 minutes to obtain a film having a thickness of 38 μm. The obtained characteristics are shown in Table 1.

[Example 2]
Except that the silica slurry having an average particle size of 80 nm was changed to a silica slurry having an average particle size of 50 nm, polymerization and film formation were performed in the same manner as in Example 1 to obtain a 38 μm-thick polyimide film. The obtained characteristics are shown in Table 1.

[Example 3]
Polymerization and film formation were carried out in the same manner as in Example 1 except that 0.8% by weight of silica slurry having an average particle size of 10 nm was added to the film resin weight to obtain a 38 μm-thick polyimide film. The obtained characteristics are shown in Table 1.

[Comparative Example 1]
Pyromellitic dianhydride (molecular weight 218.12) / biphenyltetracarboxylic dianhydride (molecular weight 294.22) / 4,4'-diaminodiphenyl ether (molecular weight 200.24) / paraphenylenediamine (molecular weight 108.14) Was prepared at a molar ratio of 70/30/85/15, and a silica slurry having an average particle size of 80 nm was added to 18.5 wt% in DMAc added to 0.8 wt% based on the film resin weight. The solution was polymerized to obtain a 3000 poise polyamic acid solution. This polyamic acid solution was converted into polyimide using a continuous film forming apparatus and simultaneously dried and solidified to obtain a polyimide film having a thickness of 38 μm. The obtained characteristics are shown in Table 1.

[Comparative Example 2]
Polymerization and production were carried out in the same manner as in Example 1 except that the silica slurry having an average particle diameter of 80 nm was changed to a silica slurry having an average particle diameter of 50 nm and the stretching in the longitudinal direction was 1.1 times and the stretching in the width direction was 1.5 times. A polyimide film having a thickness of 38 μm was obtained. The obtained characteristics are shown in Table 1.

[Comparative Example 3]
Polymerization and film formation were carried out in the same manner as in Example 1 except that 0.5% by weight of silica slurry having an average particle diameter of 200 nm was added to the film resin weight to obtain a 38 μm-thick polyimide film. The obtained characteristics are shown in Table 1.

[Comparative Example 4]
Polymerization and film formation were carried out in the same manner as in Example 1 except that 0.03% by weight of silica slurry having an average particle size of 80 nm was added to the film resin weight to obtain a 38 μm-thick polyimide film. The obtained characteristics are shown in Table 1. There was a problem with the transportability of the film, and the surface became rough due to scratches on the surface.

[Comparative Example 5]
Polymerization and film formation were carried out in the same manner as in Example 1 except that 1.1% by weight of silica slurry having an average particle diameter of 50 nm was added to the film resin weight to obtain a 38 μm-thick polyimide film. The obtained characteristics are shown in Table 1. The amount of particles added was large and aggregation occurred and the surface roughness became rough.

  The polyimide film of the present invention has a small difference in dimensional change between the longitudinal direction and the width direction of the film, a small absolute value of each dimensional change, and excellent smoothness. As particularly useful.

Claims (3)

When the thermal expansion coefficient in the longitudinal direction of the film is CTE _MD and the thermal expansion coefficient in the width direction is CTE _TD , | CTE _MD −CTE _TD | is 4 ppm or less, and CTE _MD and CTE _TD are 8 ± 3 ppm. has protrusions on the film surface is formed from inorganic particles having an average particle diameter of 10 nm to 100 nm, Ri surface roughness Ra of 5nm der following film, further, observed film surface 5.6 mm ² with a laser microscope A polyimide film characterized by having no protrusions with a height of 0.3 μm or more on the film surface . 2. The polyimide film according to claim 1, wherein the inorganic particles are contained at a ratio of 0.05 to 0.9 wt% per film resin weight. The polyimide film is composed of an aromatic diamine component having a molar ratio of 4,4′-diaminodiphenyl ether and paraphenylenediamine of 60/40 to 90/10, pyromellitic dianhydride and 3,3 ′, 4,4. '- it is intended that the molar ratio of biphenyl dianhydride is prepared from the polyamic acid consisting of an acid anhydride component is 80 / 20-60 / 40 to claim 1 or 2, characterized in The polyimide film as described.