JPH05154909A - Biaxially stretched polyimide film and manufacture thereof - Google Patents

Abstract

PURPOSE:To obtain a product, which has no uneven thickness, nonuniform stretching or the like and has favorable balance between longitudinal and lateral physical properties, by a method wherein unstretched film made of thermoplastic polyimide having specified structure is uniaxially stretched and, after being quenched to the specified temperature, biaxially stretched and heat-treated. CONSTITUTION:Unstretched film made of thermoplastic polyimide having the repeating constitutional unit represented by the separately shown chemical formula is successively biaxially stretched. In this case, firstly, the unstretched film is uniaxially stretched by the draw ratio of 150-400% at 240-300 deg.C. At the same time, the obtained uniaxially stretched film is quenched to the temperature ranging from 0 deg.C to the temperature, which is lower than the glass transition temperature of the uniaxially stretched film by 10 deg.C. Next, the quenched film is stretched normal to the stretching direction by the draw ratio of 150-500% at the temperature ranging from the temperature, which is higher than the glass transition temperature of the uniaxially stretched film by 5 deg.C, to the temperature, which is higher than the crystallization starting temperature of the uniaxially stretched film by 5 deg.C. In succession, the obtained biaxially stretched film is heat-treated at the temperature ranging from 250 deg.C to the melting point of the biaxially stretched film. Thus, the film is uniformly stretched as a whole in both the longitudinal and lateral directions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a biaxially stretched film made of a thermoplastic polyimide film having a specific structure and a method for producing the film. More specifically, an unstretched film made of a thermoplastic polyimide having a specific structure is rapidly cooled to a specific temperature immediately after being uniaxially stretched, and then biaxially stretched under specific conditions to obtain an excellent balance of physical properties in length and width. TECHNICAL FIELD The present invention relates to a biaxially stretched film and a method for producing the same.

[0002]

2. Description of the Related Art Heat-resistant polyimide films are widely used industrially. In particular, in applications such as electric and electronic fields, it is desired that the physical properties in both the vertical and horizontal directions are uniform, and that the physical properties in all parts of the stretched film are uniform.

For example, Japanese Unexamined Patent Publication (Kokai) No. 3-205423 discloses a method of sequentially biaxially stretching an unstretched film made of polyimide having a specific structure as a stretchable thermoplastic heat resistant film.

However, in this method, an unstretched film made of a thermoplastic polyimide having a specific structure is sequentially biaxially stretched to obtain a biaxially stretched film having excellent heat resistance, mechanical properties and dimensional stability. However, it is not always a satisfactory method for obtaining a biaxially stretched film having a uniform physical property balance in the length and width.

[0005]

An object of the present invention is to be uniformly stretched in both longitudinal and lateral directions, which is composed of a polyimide having a repeating structural unit represented by the above formula [1] and has no unevenness in thickness or stretching. The object is to provide a biaxially stretched polyimide film having good longitudinal and lateral physical properties and a method for producing the same.

[0006]

Means for Solving the Problems The inventors of the present invention have conducted diligent studies to achieve the above-mentioned objects, and as a result, uniaxially stretched an unstretched film made of a thermoplastic polyimide having a specific structure, and then obtained the uniaxially obtained film. The stretched film is rapidly cooled to a specific temperature, then biaxially stretched at a specific temperature, and further, a biaxially stretched polyimide film obtained by heat treatment has a property capable of solving the above problems. Heading, the present invention was reached.

That is, the present invention is based on the formula (1)

[0008]

When biaxially stretching an unstretched film made of a thermoplastic polyimide having a repeating structural unit represented by the following formula, the unstretched film is stretched in one direction at a temperature of 240 to 300 ° C. by 1.5 to 4 times. , 0 to (the glass transition temperature of the uniaxially stretched film-1
00) ° C., and then (glass transition temperature of the uniaxially stretched film +5) to (crystallization start temperature of the uniaxially stretched film +5) at a temperature of 1.5 ° C. in the direction perpendicular to the stretching direction. It is a method for producing a biaxially stretched polyimide film, which comprises stretching 4 times and further heat treating the obtained biaxially stretched film at a temperature of 250 to (melting point of the biaxially stretched film) ° C.

A second aspect of the present invention is a biaxially stretched polyimide film produced by the above method, which has the following characteristics (a) and (b). (B) By the method specified in ASTM D-882,
A biaxially stretched polyimide film having longitudinal and lateral differences of breaking strength, breaking elongation and elastic modulus measured at 23 ° C of 5% or less. (B) By the method specified in JIS C-2318,
A biaxially stretched polyimide film having a longitudinal and lateral difference in shrinkage of 5% or less when heated at 260 ° C. for 2 hours.

The feature of the present invention is that by rapidly cooling the uniaxially stretched film, the crystallization is suppressed as much as possible in the stretching atmosphere, and the uniaxially stretched film is biaxially stretched within a temperature range in which the crystallization can be suppressed as much as possible. To do. By adopting such a method, it is possible to produce a biaxially stretched film having a good balance of physical properties in length and width.

By stretching an unstretched film at a specific temperature, the properties of the uniaxially stretched film obtained change,
This is because the crystallization start temperature of the stretched film shifts to a lower temperature side than the crystallization start temperature of the unstretched film, which facilitates crystallization. When a uniaxially stretched film with advanced crystallization is biaxially stretched, uniform stretching becomes difficult. for that reason,
It is presumed that the obtained two-stretched film has unevenness in thickness and unevenness in stretching due to uneven distribution of crystals and amorphous regions.

In the present invention, the glass transition temperature, the crystallization start temperature and the melting point of the uniaxially stretched film or the biaxially stretched film are determined by a differential thermal analyzer (DuPont, DuP).
ont-1090, thermal analyzer)
Temperature rising rate 4 ° C / min. It was measured at. The crystallization start temperature is the temperature at which the onset of heat generation due to crystallization is detected in the differential thermal analysis. That is, this is the temperature at which the endothermic and exothermic curve in the differential thermal analysis starts rising as an exothermic peak due to the start of crystallization.

The polyimide used in the present invention is a thermoplastic polyimide having a repeating structural unit represented by the above formula [1]. This thermoplastic polyimide has the formula (2) [Chemical Formula 3] obtained by the polymerization reaction of pyromellitic dianhydride and 4,4′-bis (3-aminophenoxy) biphenyl.

[0014]

[Chemical 3] It can be obtained by imidizing the polyamic acid represented by

As the polyimide used in the present invention, pyromellitic dianhydride is used as the acid dianhydride, but other acid dianhydrides may be mixed and used as long as it is less than 5 mol%. Similarly, 4,4′-bis (3-aminophenoxy) biphenyl is used as the diamine, but other diamines may be mixed and used as long as it is less than 5 mol%.

Acid anhydrides other than pyromellitic dianhydride,
Alternatively, a polyimide obtained by using a diamine other than 4,4′-bis (3-aminophenoxy) biphenyl in an amount of 5 mol% or more has a decreased crystallinity and an increased amorphous chain portion, and therefore, is oriented by molecular orientation by stretching. However, fixing by heat treatment becomes insufficient, and dimensional stability decreases, which is not preferable.

The biaxially stretched polyimide film of the present invention is
Using the thermoplastic polyimide obtained by the above reaction as a raw material, first, an amorphous film is produced by a usual melt molding method, and this is cooled and cast to obtain an unstretched film.

The method for stretching the biaxially stretched polyimide film of the present invention is a sequential biaxial stretching method. The unstretched film is stretched in one direction at a specific ratio with a free width or a fixed width, and the obtained uniaxially stretched film is brought into close contact with a cooling roll or the like and rapidly cooled to a specific temperature.

Then, at a specific temperature, the film is stretched at a specific ratio in a direction perpendicular to the stretching direction to obtain a biaxially stretched film. Further, the obtained biaxially stretched film is heat-treated at a specific temperature to be crystallized to successively obtain a biaxially stretched film.

After the uniaxial stretching, the temperature at which the obtained uniaxially stretched film is rapidly cooled is in the temperature range of 0 ° C to (glass transition temperature (Tg) -100 of the uniaxially stretched film), preferably room temperature to The temperature range is 50 ° C., and the time until the uniaxially stretched film is brought into close contact with the cooling roll is 10
It is desirable to be less than a second. When the cooling temperature exceeds (the glass transition temperature (Tg) -100 of the uniaxially stretched film) ° C., crystallization of the uniaxially stretched film is promoted, and it becomes difficult to uniformly stretch the biaxially stretched film. It is not preferable because it becomes difficult to adjust the stretching ratio and a biaxially stretched film having a good balance of physical properties in length and width cannot be obtained. Further, if the temperature is lower than 0 ° C., the temperature of the stretching roll or the like close to the cooling roll may be lowered, and the uniaxially stretched film may be whitened, which is not preferable.

The time required until the uniaxially stretched film is brought into close contact with the cooling roll is preferably less than 10 seconds, and if it exceeds 10 seconds, crystallization is promoted, which is not preferable.
With a cooling roll, a uniaxially stretched film is run, and
It is a known roll for cooling, and a roll whose surface temperature and surface shape with which the uniaxially stretched film comes into contact is as uniform as possible is preferable. The peripheral speed of the cooling roll is 1 to 40 m / mi.
n. It is preferably in the range of. Note that instead of using the cooling roll, cooling may be performed using cold air. Alternatively, they may be used together for cooling. Further, when using a batch type stretching machine, it is also possible to quench using dry ice or the like.

Specific conditions for carrying out the successive biaxial stretching are that the stretching temperature of the first axis is 240 to 300 ° C., preferably 250.
C. to 290.degree. C., in one direction 1.5 to 4.
Stretch to 0 times.

The biaxial stretching is carried out at a temperature of (glass transition temperature of uniaxially stretched film + 5) ° C. to (crystallization start temperature of uniaxially stretched film + 5) ° C., preferably 260 to 2
In the temperature range of 80 ° C., stretching is performed 1.5 to 5 times in the direction perpendicular to the stretching direction of the first axis. Stretching at less than (glass transition temperature of uniaxially-stretched film +5) ° C causes extremely large stress, which causes whitening and breakage. When it exceeds (crystallization initiation temperature of uniaxially-stretched film +5) ° C, fine crystals are formed in the film. However, it is not preferable because it can cause stretching unevenness. At this time, the preheating time on the first and second axes is 3
0 seconds to 10 minutes. If the time is less than 30 seconds, the entire film will not reach the stretching temperature and the film will be whitened, and if it exceeds 10 minutes, fine crystals will be generated, which will cause uneven stretching, which is not preferable. Stretching speed is 1-10
The range of 0000% / min is preferable.

As a means for stretching, conventionally known methods such as a method of stretching using a pair of rolls, a method of stretching with a tenter, and a method of stretching by rolling with rolls can be used.

Further, after the biaxial stretching, the obtained biaxially stretched film has a temperature of 250 ° C. to the melting point of the biaxially stretched film, preferably 270 to 370 ° C. in the temperature range of 1 to 50.
By heat-treating for 00 seconds for crystallization, the mechanical properties and dimensional stability of the obtained biaxially stretched film can be improved.

The thickness of the film in the present invention varies depending on the application and is not particularly limited, but is usually 0.1 μm or more, 5
It is less than mm.

Hereinafter, the present invention will be described in more detail with reference to examples.

[0028]

EXAMPLES The method for measuring the characteristic values of the polyimide described in the examples is shown below.

(1) Glass transition temperature Differential thermal analyzer (DuPont-10 manufactured by DuPont)
90, thermal analyzer), 4 ° C / mi
n. It was measured at a temperature rising rate of.

(2) Tensile test According to ASTM D-882, at 23 ° C., the X direction of the sample (the flow direction of the film in the melt molding method), the Y direction
Tensile tests were carried out (in the direction perpendicular to the X direction in the film plane), and the breaking strength, breaking elongation and initial elastic modulus were measured.

(3) Heat Shrinkage According to JIS C-2318, the shrinkage after heating at 260 ° C. for 2 hours was measured.

(4) Solder heat resistance The sample was floated on the surface of a solder bath at 260 ° C. for 30 seconds,
If there is no deformation, it is indicated as O, slightly deformed as Δ, and deformed as X.

Production Example of Unstretched Film In a reaction vessel equipped with a stirrer, a reflux condenser and a nitrogen introducing tube, 368.4 g (1 mol) of 4,4′-bis (3-aminophenoxy) biphenyl and N, N were added. -Introducing 2,500 g of dimethylacetamide, adding 213.7 g (0.98 mol) of pyromellitic dianhydride in portions under nitrogen atmosphere while paying attention to the rise of the solution temperature, and further adding phthalic anhydride. Add 5.92 g (0.04 mol) and stir at room temperature for about 20 hours, then add 30.3 g (0.3 mol) triethylamine and 304.6 g (0.3 mol) acetic anhydride over about 30 minutes. And then add 30
Stirred.

2500 g of methanol was inserted into this solution, and the polyimide powder was filtered off at 30 ° C. After washing the obtained polyimide powder with methanol and acetone, it was dried at 300 ° C. for 8 hours in a nitrogen atmosphere,
8 g (96% yield) of polyimide powder was obtained.

The obtained polyimide powder was dried at 180 ° C. for 24 hours, melted at 410 ° C. by a 25 mm vent type extruder, extruded from a nozzle having a diameter of 2 mm, and naturally cooled to obtain a strand having a diameter of about 1.8 mm. .. This was cut into about 3 mm in the longitudinal direction to obtain pellets.

The pellets were dried at 180 ° C. for 24 hours, fed to a 25 mm extruder, heated and melted at 410 ° C.,
It was extruded from a slit die having a width of 150 mm (gap of 1.0 mm) and taken out by a roll at 220 ° C. to obtain a film having a thickness of about 100 μm.

Examples 1 and 2 Both ends of an unstretched film (20 cm square size) were fixed and mounted on a stretcher (high temperature batch stretching machine manufactured by Iwamoto Seisakusho) under the conditions shown in [Table 1]. The film was stretched to a predetermined ratio in the X direction (which is the flow direction of the film in the melt extrusion method), and then the film was immediately cooled to 30 ° C. using dry ice with the film attached. The film was once removed, cut into 10 cm square pieces, fixed in both directions, and stretched at a predetermined ratio in the Y direction (the direction perpendicular to the X direction in the film plane) under the conditions shown in [Table 1]. Further, heat treatment was performed at 310 ° C. for 10 minutes with the film attached.

Prior to the stretching, straight lines were formed on the unstretched film in the longitudinal and transverse directions at intervals of 1 cm, and when the biaxial stretching was completed, the distance between the straight lines was measured to confirm the substantial stretching ratio. As a result, the obtained biaxially stretched film was stretched uniformly as a whole, and the stretching ratio in the vertical and horizontal directions was good.

The physical properties of the obtained sequential biaxially stretched film were evaluated by the methods described above. As a result, the breaking strength, the breaking elongation, the elastic modulus, and the heat shrinkage ratio were all superior to those of Comparative Examples described later. Further, there was almost no difference in the vertical and horizontal characteristics, and it was confirmed that the film was a biaxially stretched film having a good balance of physical properties in the vertical and horizontal directions. The obtained results are shown in [Table 1].

[0040]

[Table 1]

Comparative Examples 1 to 3 Biaxially produced in the same manner as in Example 1 according to the conditions shown in Table 1 except that the uniaxially stretched film obtained by stretching in the X direction was not quenched. A stretched film was obtained.

In Comparative Example 1, the film was broken during the biaxial stretching. The biaxially stretched films obtained in Comparative Examples 2 and 3 were found to have a large difference in physical properties in length and width. The obtained results are shown in [Table 1].

[0043]

The biaxially stretched polyimide film obtained by the method of the present invention is a film stretched uniformly in the machine and transverse directions, and the longitudinal and transverse differences in the characteristic values such as breaking strength, breaking elongation, elastic modulus and heat shrinkage ratio. There is almost no difference, and the balance of physical properties in the vertical and horizontal directions is extremely good. Furthermore, since it has excellent heat resistance, chemical resistance, mechanical properties and dimensional stability, it is used for electrical and electronic industries such as wire coating materials, insulation materials for liners such as motors and transformers, flexible printed circuit boards, capacitor materials, etc. Alternatively, it is useful as a material for precision parts such as a recording medium base film.

Front Page Continuation (72) Inventor Issei Okada 2-1-1, Tango-dori, Minami-ku, Nagoya-shi, Aichi Mitsui Toatsu Chemicals, Inc. (72) Inventor Yoshiyuki Katsuyama 2-1-1, Tango-dori, Minami-ku, Aichi Mitsui Toatsu Chemical Co., Ltd.

Claims (2)

[Claims] 1. Formula (1) [Chemical Formula 1] When sequentially biaxially stretching an unstretched film made of a thermoplastic polyimide having a repeating structural unit represented by,
The unstretched film was stretched at a temperature of 240 to 300 ° C. in one direction by 1.5 to 4 times, and the obtained uniaxially stretched film was 0 to
(Glass transition temperature of the uniaxially stretched film −100) ° C.
And then drawn at a temperature of (glass transition temperature of the uniaxially stretched film +5) to (crystallization start temperature of the uniaxially stretched film +5) ° C. in the direction perpendicular to the stretching direction by 1.5 to 5 times. Then, the obtained biaxially stretched film is further heat-treated at a temperature of 250 to (melting point of the biaxially stretched film) ° C., a method for producing a biaxially stretched polyimide film. 2. A biaxially stretched polyimide film produced by the production method according to claim 1, which has the following characteristics (a) and (b). (B) By the method specified in ASTM D-882,
A biaxially stretched polyimide film having a breaking strength, a breaking elongation, and an elastic modulus measured at 23 ° C, which are within 5% in length and width. (B) By the method specified in JIS C-2318,
A biaxially stretched polyimide film having a longitudinal and lateral difference in shrinkage of 5% or less when heated at 260 ° C. for 2 hours.