JPH05169526A - Thermal treatment of thermoplastic polyimide stretched film - Google Patents

Abstract

PURPOSE:To ensure that a thermoplastic polyimide biaxially stretched film having a specific structure has outstanding size stability and thermal resistance against solder by treating the film at a specified temperature with the concurrent process of shrinking it restrictively at a specific percentage in an opposite single or dual direction to a stretching direction. CONSTITUTION:An unstretched film obtained by melting and molding thermoplastic polyimide having a repetitive structural unit as shown by a separately provided formula is stretched in a single direction or a dual direction which forms a right angle, and this stretched film is thermally treated under a tense condition. In this case, the stretched film is thermally treated at a temperature of 250 deg.C or higher and not higher than a melting point of stretched film with the concurrent process of shrinking the film to the 5 to 20% limits in an opposite single or dual direction to the stretching direction of the film. The stretched film is thermally treated to the 10 to 15% shrinkage limits in either of the opposite directions to the stretching direction as a biaxially stretched film. In addition, the film can be thermally treated with the simultaneous process of shrinking it to the 6 to 14% limits in the opposite two directions to the stretching direction respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat treatment method for a stretched film obtained by melt-molding a thermoplastic polyimide having a specific structure and stretching it. More specifically, 280
The present invention relates to a method for producing a stretched thermoplastic polyimide film having a low heat shrinkage rate at a high temperature of ℃ or higher and having excellent dimensional stability, solder heat resistance and the like.

[0002]

2. Description of the Related Art In recent years, various industrial machines and household appliances have been reduced in size and weight, and the components constituting them have been improved in heat resistance, mechanical characteristics and dimensional stability for a long time. There is a demand for reliability. In particular, the wiring board in the electronic industry field, with the high density of terminals,
The conditions required for dimensional stability at high temperatures, such as solder heat resistance, are becoming more severe. As a material that meets such requirements, for example, there is thermoplastic polyimide (trade name: Ultem, etc.) manufactured by General Electric Company. However, the film made of the polyimide has sufficient heat resistance to satisfy the above requirements such that the mechanical strength of the film decreases at a temperature exceeding the glass transition temperature and becomes opaque and brittle at higher temperatures. Absent.

In order to solve such a problem, the present inventors proposed a stretched film made of a thermoplastic polyimide having a specific structure and a method for producing the same in a patent application relating to JP-A-3-205432. ing.
A feature of the present invention is that an unstretched film made of a thermoplastic polyimide having a repeating structural unit represented by the above formula (1) is uniaxially or biaxially stretched under specific conditions, and then 250
It is to heat-set under tension at a temperature of ℃ or higher and lower than the melting point. However, when the polyimide film obtained by this method is, for example, a biaxially stretched film, the heat shrinkage may be non-uniform in the two stretched directions, and the solder heat resistance temperature is about 260 ° C. Therefore, it cannot be said that the dimensional stability at high temperatures is sufficient.

[0004]

An object of the present invention is to obtain a stretched film obtained by melt-molding and stretching a thermoplastic polyimide having a repeating structural unit represented by the above formula (1) and having a temperature of 280 ° C. or higher. It is an object of the present invention to provide a heat treatment method which has a low heat shrinkage ratio at a high temperature and can impart excellent properties such as dimensional stability and solder heat resistance.

[0005]

Means for Solving the Problems As a result of intensive studies to solve these problems, the present inventors have found that a stretched film obtained from a thermoplastic polyimide having a repeating structural unit represented by the above formula (1). When heat treating under tension,
The present invention has been found out that the above problems can be solved by performing heat treatment while performing limited shrinkage within a specific range.

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

[0007]

[Chemical 2] An unstretched film obtained by melt-molding a thermoplastic polyimide having a repeating structural unit represented by: a stretched film by stretching in one direction or in two directions forming a right angle, and then the stretched film under tension. In the heat treatment method, the stretched film is heat-treated at a temperature of 250 ° C. or higher and lower than the melting point of the stretched film while being subjected to 5 to 20% limited shrinkage in one direction or two directions opposite to the stretching direction. This is a heat treatment method for a stretched polyimide film.

The present invention will be described in detail below. The thermoplastic polyimide used in the present invention has a repeating structural unit represented by the above formula (1) which is already known as a heat resistant polyimide. This polyimide can be obtained by imidizing via a polyamic acid by a polymerization reaction of pyromellitic dianhydride and 4,4′-bis (3-aminophenoxy) biphenyl.

This polyimide has an acid anhydride content of 5 mol%.
If it is less than the above, other acid anhydrides may be mixed with pyromellitic dianhydride. If the diamine content is less than 5 mol%, 4,4′-bis (3-aminophenoxy) biphenyl may be mixed with another diamine. Polyimide obtained by containing other acid anhydride or diamine in an amount of 5 mol% or more has a reduced crystallinity and an increased amorphous chain portion, so even if the molecule is oriented by stretching, fixation by heat treatment becomes insufficient, It is not preferable because the dimensional stability decreases.

The polyimide used in the present invention can be obtained by subjecting these aromatic tetracarboxylic dianhydrides and aromatic diamines to a conventional and known method, for example, by suspending or dissolving the monomers or the monomers in an organic solvent. After that, the product can be obtained by a general method of heating or chemically dehydrating, separating and purifying the product.

In the method of the present invention, an amorphous film is generally produced by the melt molding method using the above-mentioned polyimide as a raw material, and the film is cooled and cast to obtain an unstretched film.
Further stretched uniaxially or biaxially, and then heat-treating the obtained stretched film under specific conditions to have excellent dimensional stability at high temperature, solder heat resistance and low heat shrinkage ratio. It is a method for obtaining a stretched thermoplastic polyimide film. The feature of the method of the present invention resides in that the stretched film obtained as described above is heat-treated under specific conditions.

The method for producing the polyimide film used in the present invention will be described in detail below. The polyimide used as a raw material is obtained by polymerizing the above-mentioned acid anhydride and diamine and then imidizing them. Preferred are those in the range of 100 to 600,000 poise under a shear rate of 400 ° C. and 200 sec ⁻¹ . Polyimides less than 100 poise tend to gel during melt molding, tend to impair the surface state of the film, tend to reduce mechanical strength, and become brittle and difficult to stretch. A polyimide having viscosity is often used.

Using these polyimides, the melt extrusion method,
An unstretched film is prepared by a calendar method or the like.
The most preferable method is 300 to 450 ° C.
Examples of the method include melting at a temperature of 2 ° C. with an extruder or the like, extruding through a slit nozzle, and cooling on a casting roll having a surface temperature of 100 to 250 ° C. to obtain an unstretched film (amorphous film).

The unstretched film to be stretched and heat-treated preferably has a density of 1.350 g / cm 3 or less, and if it exceeds 1.350, the film becomes brittle and stretch breakage occurs during stretching in the subsequent step, which is preferable. Absent. The unstretched film is stretched in the range of 230 to 320 ° C. in one direction or two directions at right angles by 1.5 to 10 times, and is divided into the following modes depending on the specific conditions of the stretching process. A method of stretching 1.5 to 5.0 times in one direction in the range of 230 to 300 ° C. (hereinafter, referred to as uniaxial stretching method). 1.5 to 3.0 times in one direction in the range of 240 to 300 ° C., and then 250 to 320 in the direction perpendicular to the stretching direction.
A method of stretching 1.5 to 3.0 times in the range of ° C (hereinafter referred to as a sequential biaxial stretching method). A method of simultaneously stretching in an area ratio of 2 to 10 in two directions perpendicular to each other in the range of 250 to 300 ° C. (hereinafter, referred to as simultaneous biaxial stretching method). In each of the above stretching methods, the water content of the film during stretching is 0.1% or more and less than 3%,
It is a method of stretching in a temperature range of 150 ° C. or more and less than the glass transition temperature.

Further details of each aspect are as follows. Uniaxial Stretching Method This is a method of stretching the unstretched film in one direction within a specific temperature range. Specific conditions for uniaxial stretching are 230 to 30.
It is stretched 1.5 to 5.0 times in one direction in a temperature range of 0 ° C., preferably 250 to 290 ° C. Under such conditions, the unstretched film is uniaxially oriented. Stretching temperature is 2
If it is less than 30 ° C, stretching is difficult, and if it exceeds 300 ° C, the film loses transparency, becomes brittle, and cannot be stretched, which is not preferable. Further, if the stretching ratio is less than 1.5 times, wrinkles may be generated in the subsequent heat treatment step, and a brittle film may be obtained, which is not preferable. It is not preferable because it causes inconvenient problems such as rustling.

As a means for stretching, a method of stretching using a pair of rolls, a method of stretching using a tenter, a method of stretching by rolling using rolls, a method of stretching by a chuck type batch type stretching machine, etc. Conventional techniques can be used. The stretching speed during stretching is 1 to 100,000.
The range of% / min is preferable. Further, it is preferable to preheat the film to such an extent that crystallization does not proceed before stretching, because smooth stretching can be performed.

Sequential Biaxial Stretching Method The above unstretched film is stretched in one direction within a specific temperature range, then stretched in a specific temperature range in a direction perpendicular to the direction, and then heat-set to produce a biaxially stretched film. Is the way to do it. The specific condition for biaxial stretching is that the first stage stretching is 24
In the temperature range of 0 to 300 ° C., preferably 250 to 290 ° C., the film is stretched in one direction by 1.5 to 3.0 times, and the second stage is stretched in a direction perpendicular to the first stage stretching direction at 250 to 320 ° C. , Preferably in the temperature range of 260 to 310 ° C., 1.5 to 3.
Stretch 0 times. The unstretched film is biaxially oriented under such conditions.

As the stretching means, conventional techniques such as a stretching method using a tenter and a batch stretching machine can be used. At that time, if the stretching temperature of the first step is less than 240 ° C, stretching is difficult,
If it exceeds, the film loses transparency, becomes brittle, and cannot be stretched. Further, if the draw ratio is less than 1.5 times, it is not preferable because wrinkles are formed in the subsequent heat treatment step or a brittle film is obtained, and if it exceeds 3.0 times, it is highly oriented during the drawing, and two-stage stretching is performed. Inconvenient problems such as breakage during stretching of the eyes occur, which is not preferable. Further, if the stretching temperature at the second stage is less than 250 ° C., stretching is difficult and tearing frequently occurs. If it exceeds 320 ° C., problems such as embrittlement of the film and tearing of the film occur, which is not preferable. The stretching ratio is preferably 1.5 to 3.0 times in view of the effect of orientation, film breakage, and the like. Stretching speed during stretching is 1
The range of -100,000% / min is preferable. Further, it is preferable to preheat the film to such an extent that crystallization does not proceed before stretching, because smooth stretching can be performed.

Simultaneous Biaxial Stretching Method The above unstretched film is simultaneously stretched in two directions perpendicular to each other in a specific temperature range in an area ratio of 2 to 10 times, and then heat set at a temperature of 250 ° C. or higher and lower than the melting point. Is a method for producing a biaxially stretched polyimide film. The specific conditions of the simultaneous biaxial stretching are as follows:
A biaxially stretched film can be obtained by stretching at a temperature range of 00 ° C., preferably 260 to 290 ° C., and an area ratio of 2 to 10 times. The unstretched film is biaxially oriented under such conditions. If the stretching temperature is less than 250 ° C., the stretching stress is high and stretching is impossible, and if it exceeds 300 ° C., the same as in the first stage stretching in the above-mentioned sequential biaxial stretching is not preferable. Further, if the stretching ratio is less than 2 times in area ratio, wrinkles or a brittle film is obtained in the subsequent heat treatment step, which is not preferable, and stretching cannot be carried out at a ratio exceeding 10 times. In these stretching methods, the stretching speed is 1 to 10
The range of 0000% / min is preferable. Further, it is preferable to preheat the film to such an extent that crystallization does not proceed before stretching, because smooth stretching can be performed.

Method for specifying the water content of the unstretched film during stretching: In this embodiment, the polyimide used in the present invention is an unstretched polyimide film, and when stretching and heat setting, the water content is specified. It is a method of producing a polyimide film having excellent performance by adjusting the content within the range and stretching at a temperature lower than the glass transition temperature which has been considered to be very difficult in the past. That is, it is a method of stretching an unstretched film containing at least 0.1% of water during stretching in the range of 150 ° C. or higher and lower than the glass transition temperature. The water content during stretching of the unstretched film used in the present stretching method is at least 0.
It is preferably 1%. Its water content is 0.1%
If it is less than the above range, the rigidity of the film is increased, the tension at the time of stretching is increased to make it difficult to stretch, or the film is devitrified due to the generation of microvoids and the mechanical strength is significantly lowered, which is not preferable. The upper limit of the water content is not particularly limited, but is usually less than 3%. A particularly preferable water content is 0.2 to 2%. The polyimide used in the present stretching method contains 0.5% or more of water in a state of being placed in a normal atmosphere, and can be absorbed in warm water to absorb about 3% of water.

In the present stretching method, the stretching temperature is in the range of 150 ° C. or higher and lower than the glass transition temperature, and the stretching ratio is 1.2.
It is preferably about 2.5 times. Stretching at a temperature exceeding the glass transition temperature causes a decrease in the water content during stretching, and also causes extreme orientation, which makes stretching difficult. In this stretching method, the film can be uniaxially stretched or biaxially stretched by a roll stretching method using one or more pairs of rolls, a tenter system, or a batch stretching machine. In this stretching method, the stretching speed is preferably such that the rate of increase in the length of the film is 10 to 10,000% / min. The stretched film thus obtained is heat-treated in order to increase the density and improve the dimensional stability and mechanical properties.

The heat treatment method for the stretched film in the present invention will be described in detail below. The stretched polyimide film obtained by the above method has a temperature of 250 ° C. or higher and a temperature lower than the melting point of the stretched film, preferably 270 to 370.
℃, more preferably 1 to 5 in the range of 310 to 370 ℃
It is heat-treated for 000 seconds under tension while being subjected to limited shrinkage. When the heat treatment temperature is lower than 250 ° C., it is not preferable because the heating is insufficient and the heat setting is not performed, or the heat setting is insufficient and the dimensional stability and the solder heat resistance are deteriorated. On the other hand, if it exceeds the melting point, the film is deformed by softening, which is not preferable.

In the heat treatment method of the present invention, when a stretched film is heat-treated, the film is contracted in a specific range in a tensioned state by applying tension to the film in one or two directions opposite to the stretching direction of the film. While heat treatment. One direction of the stretched direction and the opposite direction of the stretched film, for uniaxially stretched film, is the direction opposite to the stretched direction, for biaxially stretched film, one of the two directions stretched. It is the opposite direction. In addition, the two directions opposite to the stretching direction are directions opposite to the respective stretching directions of the biaxially stretched film. That is, when the heat treatment method of the present invention is applied to a uniaxially stretched film, the heat treatment is performed in a direction opposite to the stretching direction while subjecting to limited shrinkage under tension. When applied to a biaxially stretched film, it is heat-treated while being subjected to limited shrinkage under tension in a direction opposite to either one of the stretching directions or in two directions opposite to the stretching direction.

In the case of heat treatment by any of the above methods, the limiting shrinkage rate is preferably in the range of 5 to 20%. A more preferable range is 10 to 15% in the case of limited shrinkage in one direction, and 6 to 14% in the case of limited shrinkage in two directions. If the limiting shrinkage ratio is less than 5%, the relaxation of the tensile stress caused by the heat shrinkage of the film itself during heat treatment is insufficient, and the film may be wrinkled or broken, which is not preferable. In addition, the residual stress of the obtained film increases the heat shrinkage rate, resulting in poor solder heat resistance. Further, the heat shrinkage of the obtained film becomes non-uniform in two directions. If the limiting shrinkage ratio exceeds 20%, the film becomes inferior in flatness due to sagging during heat treatment, which is not preferable.

The following method is exemplified as a method of restricting shrinkage to the above range under tension. Method of limiting shrinkage in one direction under tension: A tenter stretching machine or a batch type stretching machine is preferably used. When a tenter stretching machine is used, it is suitable for heat treatment under limited shrinkage in one direction in the width direction of the film. When a batch type stretching machine is used, it is suitable for heat treatment under restricted shrinkage in one direction of a uniaxially stretched film or in one direction of a biaxially stretched film. In either case, the shrinkage rate of the film is 10 to
10000% / min. The heat treatment is performed to a predetermined shrinkage ratio while narrowing the chuck spacing and so on. The shrinkage rate of the film is 10,000% / min. If it exceeds, the film may be wrinkled or torn, which is not preferable.

Method of limiting shrinkage in two directions under tension: A batch-type stretching machine is preferably used. The shrinkage rate of the film is 10 to 10000% / min. So that the chuck spacing is narrowed in two directions at the same time to a predetermined spacing, heat treatment is performed. The shrinkage rate of the film is 10,000% / min.
If it exceeds, the film may be wrinkled or torn, which is not preferable. The stretched film heat-treated by such a method has improved properties at high temperatures such as dimensional stability and solder heat resistance, and also has good transparency, so that it is mainly used as an electrical insulating material and recording medium at high temperatures. Materials,
It is useful as a dielectric material.

[0027]

The present invention will be described in more detail with reference to the following examples. In addition, the measuring method of the characteristic value of the polyimide film described in the Example is shown below.

(1) Heat shrinkage rate 260 according to the method specified in JIS C-2318.
The shrinkage ratio after heating at 0 ° C. or 280 ° C. for 1 hour was measured in two directions, that is, a film flow direction perpendicular to each other (hereinafter, referred to as X) and a direction perpendicular to the direction (hereinafter, referred to as Y).

(2) Solder heat resistance The sample was floated on the surface of a solder bath at 260 ° C. or 280 ° C. for 30 seconds, and the deformation state of the sample was evaluated. When there is no deformation, it is indicated by ○, and when it is deformed, it is indicated by ×. Production Example of Biaxially Stretched Film Thermoplastic polyimide having a repeating structural unit represented by the general formula (1) (manufactured by Mitsui Toatsu Chemicals, Inc .: trade name; N
ew-TPI) powder was dried at 180 ° C. for 24 hours, and 2
It was extruded from a nozzle having a diameter of 2 mm at 400 ° C. by a 5 mm vent type extruder, cooled, and then cut to obtain pellets.
The pellets are dried at 180 ° C. for 24 hours, melted at 410 ° C. by a 25 mm extruder, extruded from a slit die having a width of 150 mm (spacing 0.4 mm), and taken up by a roll at 220 ° C. to obtain an unstretched film having a thickness of about 100 μm. Obtained.
The unstretched film is processed by a batch stretching machine (Iwamoto Seisakusho Co., Ltd.)
Manufacturing: Type: BIX-703), preheated at 280 ° C. for 5 minutes, stretched 2.7 times in the X direction, immediately after that, stretched 3 times in the Y direction, and biaxially stretched to a thickness of about 15 μm. I got a film.

Examples 1 to 3 The biaxially stretched film obtained by the above method is shown in [Table 1].
After raising the temperature to the prescribed heat treatment temperature shown in Table 1, under tension [Table 1]
Under the conditions shown in (1), the heat treatment was performed while the shrinkage was restricted. The heat-shrinkage rate and solder heat resistance of the obtained heat-treated biaxially stretched film were evaluated, and the results are shown in [Table 1]. In the films obtained in Examples, heat shrinkage was not observed at 260 ° C., the heat shrinkage rate was low even at 280 ° C., and X,
The difference in the two Y directions was also small. The solder heat resistance was good at both 260 ° C and 280 ° C.

Examples 4 to 5 Regarding the biaxially stretched film obtained by the above method,
After the temperature was raised to the predetermined heat treatment temperature shown in [Table 1], the heat treatment was performed under tension under the conditions shown in [Table 1] while performing the limited shrinkage in only one direction. The heat-shrinkage rate and solder heat resistance of the obtained heat-treated biaxially stretched film were evaluated, and the results are shown in [Table 1]. The film had a small heat shrinkage and good solder heat resistance at 280 ° C.

Comparative Example 1 The biaxially stretched film obtained by the above method was heat-treated in the same manner as in Example 1 except that the restricted shrinkage rate was 3% in each of the X and Y directions. The heat-shrinkage rate and solder heat resistance of the obtained heat-treated biaxially stretched film were evaluated, and the results are shown in [Table 1]. Heat shrinkage was observed at 260 ° C, and the tendency was further increased at 280 ° C. Further, the solder heat resistance at 280 ° C. was poor.

Comparative Example 2 With respect to the biaxially stretched film obtained by the above-mentioned method, except that the limiting shrinkage rate was 25% in each of the X and Y directions,
Heat treatment was tried in the same manner as in Example 2. However, wrinkles were generated in the film during the heat treatment, resulting in a film having poor flatness. The heat-shrinkage rate and solder heat resistance of the obtained heat-treated biaxially stretched film were evaluated, but the properties were inferior to those of the examples.

[0034]

[Table 1]

[0035]

The thermoplastic polyimide stretched film obtained by the method of the present invention is a stretched film exhibiting excellent dimensional stability at a high temperature of 280 ° C. or higher. In particular,
No heat shrinkage is shown at 260 ° C, and the heat shrinkage rate at 280 ° C is small. It also has excellent solder heat resistance at 280 ° C. Therefore, it is suitable for use in electric wire coatings used under high temperatures, materials for electrical insulation of liners such as motors and transformers, materials for precision components such as base films for recording media, electrical and electronic components such as flexible printed circuit boards and capacitors. You can

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification number Reference number within the agency FI Technical display location // B29K 79:00 B29L 7:00 4F C08L 79:08 (72) Inventor Issei Okada Aichi Prefecture 2-1, Tango-dori, Minami-ku, Nagoya-shi Mitsui Toatsu Chemical Co., Ltd. (72) Inventor Yasuko, 2-1-1, Tango-dori, Minami-ku, Nagoya-shi, Aichi Mitsui Toatsu Chemical Co., Ltd.

Claims (3)

[Claims] 1. Formula (1) [Chemical Formula 1] An unstretched film obtained by melt-molding a thermoplastic polyimide having a repeating structural unit represented by: a stretched film by stretching in one direction or in two directions forming a right angle, and then the stretched film under tension. In the heat treatment method, the stretched film is heat-treated at a temperature of 250 ° C. or higher and lower than the melting point of the stretched film while being subjected to 5 to 20% limited shrinkage in one direction or two directions opposite to the stretching direction. Heat treatment method for stretched polyimide film. 2. The stretched film is a biaxially stretched film, and 10% to 15% in either direction opposite to the stretching direction.
The heat treatment method according to claim 1, wherein the heat treatment is performed while the shrinkage is limited. 3. The heat treatment method according to claim 1, wherein the stretched film is a biaxially stretched film, and the heat treatment is performed while the shrinkage is restricted by 6 to 14% in each of two directions opposite to the stretching direction.