JPH0798348B2 - Polyimide extrusion molding method and polyimide pellets used in this method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for extrusion-molding a thermoplastic polyimide and a polyimide pellet used in this method. More specifically, in the extrusion molding of polyimide, a stable extrusion amount, a method capable of stably producing a product without bubbles or die meal, polyimide having a specific structure, pre-crystallized to a crystallinity of a specific range. TECHNICAL FIELD The present invention relates to a method of supplying a compounded polyimide to an extruder for molding, and a polyimide pellet applied to this method.

[Conventional technology]

Aromatic polyimides have the highest heat resistance among organic polymers, as well as excellent mechanical properties, chemical resistance, and electrical insulation properties, and are used in the electrical, electronic industry, mechanical industry, nuclear power, automobile industry, etc. Widely used in the field.

In recent years, thermoplastic polyimide and its molding method have been reported.

Among the polyimides of this type, a polyimide of the general formula [I] having good extrusion moldability is used. A polyimide having a repeating structural unit represented by the formula (wherein X represents a single bond or a hexafluoroisopropylidene group) has been developed (for example, JP-A-62-205124).
Japanese Patent Laid-Open No. 62-241923).

These polyimides are thermoplastic and can be manufactured into products such as fibers, films, sheets, electric wires, rods, plates or pipes by a well-known extrusion molding method. However, among these polyimides and their molding methods, a sufficiently satisfactory molding method suitable for these polyimides has not yet been proposed for application to the extrusion molding method.

[Problems to be Solved by the Invention]

The polyimide having a repeating structural unit represented by the general formula [I] has better applicability to extrusion molding than other polyimides that are difficult to mold, and is usually processed into pellets and then used in an extruder. Supplied and molded.

However, even with such a polyimide, if the manufactured polyimide powder is processed into pellets and supplied to the extruder as it is, extrusion molding cannot be performed smoothly and a molded product is obtained. Bubbles and die meal are generated in the product, and it is difficult to obtain a product of stable quality.

Such a phenomenon is because the resin supplied to the extruder undergoes rapid plasticization due to the temperature and pressure received at the screw supply part and / or the compression part. There is a case where it is wrapped around and cannot be extruded at all. It was also found that even when the blockage does not occur, the gas that is transported together with the rapidly plasticized resin, for example, air, is not removed at the compression portion of the screw that should be originally removed and is transported to the die to generate bubbles. .

When such a phenomenon occurs, for example, in fiber processing, there is a problem that denier fluctuation due to fluctuation of extrusion amount and yarn breakage due to generation of bubbles are likely to occur.
In sheet processing, there is a problem that thickness variation due to extrusion rate variation, appearance defects due to the occurrence of air bubbles or die meal, and deterioration of mechanical strength are likely to occur, and in rod and pipe processing, extrusion rate variation There is a problem that the diameter fluctuation accompanying it, the strength decrease due to the generation of internal bubbles, the appearance defect due to the die cake is likely to occur, and further, the electric insulation is likely to be deteriorated due to the air bubbles or the die cake in the electric wire processing. Occurs.

As a solution to these problems, a temperature at which the plasticization of the resin does not rapidly proceed, that is, a method of changing the temperature condition of the extruder such as lowering the cylinder temperature of the extruder to 250 ° C. or less can be considered. However, the viscosity of the molten resin becomes abnormally high and extrusion becomes impossible, or a large amount of heat generated by shearing causes deterioration of the resin, which is not preferable. Although it is possible to change the screw shape of the extruder, it is difficult to solve the problem because the extrusion amount varies (so-called surging phenomenon), and in some cases, extrusion molding cannot be performed.

As described above, even with the above-mentioned polyimide, there is a point to be solved in the extrusion molding method, and unless this is solved, it was difficult to obtain a molded product having the required performance.

Therefore, it is an object of the present invention to provide a further improved method for extrusion molding of polyimide having excellent mechanical properties, chemical resistance and electrical insulation.

Another object is to provide an improved extrusion method which, in order to extend the applicability of a polyimide of a specific structure, gives a molded article which is applicable to that polyimide and which has a stable quality.

[Means for solving problems]

The present inventors diligently studied to achieve this object. As a result, the polyimide of the repeating structural unit represented by the general formula [I] produced by polymerization is usually a powder in a semi-crystalline state, but when it is applied to extrusion molding, it is preferably a pellet as a supply form. Unexpectedly, even if it is a crystalline polyimide, the crystallinity of the pellets will be significantly reduced during the production of the pellets, resulting in an amorphous state. It has been found that the above-mentioned various problems occur when it is supplied to. Furthermore, it is possible to make a polyimide in a semi-crystalline state by heat-treating the amorphous polyimide processed into pellets under specific temperature conditions. The inventors have found that the problems can be solved and have achieved the present invention.

That is, the method of the present invention has the general formula [I] (In the formula, X represents a single bond or a hexafluoroisopropylidene group) When a polyimide having a repeating structural unit represented by the formula is supplied to a melt extruder, the polyimide obtained by polymerization is heated and melted in advance. And a polyimide pellet having a crystallinity of 5% or more, and a polyimide extrusion molding method characterized by supplying the polyimide to an extrusion molding machine for molding.

The present invention is to improve the above-mentioned problems in extrusion molding of polyimide, and to provide a polyimide having a repeating structural unit represented by the general formula [I] in a practically satisfactory state, that is, It is intended to provide a method for stably molding a product which prevents fluctuations, air bubbles, die residue, etc., has little fluctuation in wall thickness, and has excellent mechanical strength and electrical insulation.

The polyimide in the present invention has the general formula [I] (In the formula, X represents a single bond or a hexafluoroisopropylidene group) and is a polyimide having a repeating structural unit.

These polyimides include pyromellitic dianhydride and 4,
4'-bis (3-aminophenoxy) biphenyl or
2,2-bis (3-aminophenoxyphenyl) 1,1,1,3,
The following formula [II] by dehydration condensation reaction with 3,3-hexafluoropropane It can be obtained by subjecting a polyamic acid represented by the formula (wherein X has the same meaning as described above) to thermal or chemical imidization.

The polyimide to be supplied to the extruder in the present invention is processed into a pellet by heating and melting the polyimide powder produced by the above-mentioned method, or the polyimide powder that has been heat-treated in advance, and heat-treating the pellet. The resulting crystallized polyimide pellet. That is, the manufactured polyimide powder is processed into a pellet shape such as a tablet or a cylinder, and heat-treated, or the powdered product obtained by heating the manufactured polyimide powder is processed into a pellet shape such as a tablet or a cylinder shape. It is manufactured as crystallized polyimide pellets which can be further heat-treated and applied to a molding machine. A method of subjecting a polyimide powder to a heat treatment before processing into pellets, that is, the pellets obtained by the latter method, can obtain a molded product of stable quality without inclusion of bubbles in the molded product.

The polyimide pellets in the present invention are prepared by a commonly used melt extrusion method. The polyimide powder obtained by the polymerization is preferably heat-treated at 250 to 370 ° C. for 1 minute to 50 hours and then fed to the extruder. Before supplying to the extruder, it is preferable to dry at 120 to 350 ° C. for 3 to 24 hours so that the water content of the polyimide is 200 ppm or less.

Extrusion temperature is in the range of 300 ~ 450 ℃, preferably 350
~ 430 ° C. The diameter of the strand extruded in the molten state is not particularly limited, but is generally about 1 to 5 mm.
As a method of cutting into pellets, the molten strand may be water-cooled or air-cooled and then cut, or may be cut without cooling, that is, so-called hot cutting, and then water-cooled or air-cooled.

The extruder to be used may be an ordinary type which is widely used, but a vented type or a type equipped with a vacuum hopper is preferably used.

The polyimide pellets obtained in this way are in a semi-crystalline state before being processed into a non-crystalline state. In the present invention, it is necessary to heat the amorphous polyimide pellets into polyimide pellets having a crystallinity of 5% or more.

The conditions of the heat treatment are as follows.

The heat treatment temperature is preferably 250 to 370 ° C. Heat treatment temperature is 250
If the temperature is lower than ℃, crystallization is very slow and the practicality is poor, which is not preferable. Also, even if it exceeds 370 ℃, crystallization is slow,
Further, since the melting of the resin is started, the resin is liable to be welded or decomposed, which is not preferable. Particularly preferably, it is 290 to 330 ° C.

The heat treatment time is not particularly limited because it varies depending on the heat treatment temperature and the crystallinity, but it is usually 1 minute to 50 minutes.
Heat treatment for an hour. If it is less than 1 minute, sufficient crystallization does not occur, and subsequent fluctuation of the extrusion amount, inability to extrude, and generation of bubbles occur, which is not preferable. Further, if it exceeds 50 hours, decomposition due to heat occurs, which causes discoloration and foaming during extrusion, which is not preferable. Especially, the practically preferable heat treatment time is
It is about 30 minutes to 10 hours.

The polyimide having a repeating structural unit represented by the general formula [I] applied to the present invention is heat-treated under the above-mentioned conditions to give a polyimide pellet having a crystallinity of usually 5% or more. In order to obtain a polyimide pellet of 5% or more, the heat treatment temperature may be further increased, the heat treatment time may be further extended, or the heat treatment may be repeated twice or more. In this case, preferable results are obtained. It may be obtained. If the degree of crystallinity is less than 5%, the amount of extrusion during extrusion may change, or extrusion may become impossible, resulting in foaming, die cake, etc., which is not preferable. Although the upper limit of the crystallinity is not particularly specified, the pellet obtained by heat treatment has a maximum crystallinity of 50%, and a preferable crystallinity range is 5 to 50%, more preferably 10 to 50%.

The heat treatment is preferably performed by heating in air or an inert gas such as nitrogen, carbon dioxide gas, helium, neon or argon, and particularly preferably in an inert gas for preventing oxidative deterioration of the polyimide. Furthermore, it is preferable to stir during the heat treatment in order to prevent partial fusion of the resin.

The crystallinity of the molding polyimide in the present invention is determined by the density gradient tube method. That is, the density of an amorphous material obtained by rapidly cooling a melt of polyimide and the crystal density of the crystallized material from X-ray diffraction and structural analysis are obtained in advance, and the density of the polyimide (sample) is measured. And the formula [II
I] Can be obtained by

It should be noted that the polyimide of the general formula [I] may contain an inorganic filler such as carbon or glass and an additive such as a pigment in a range in which crystallization is not significantly suppressed.

In the method of the present invention, crystalline polyimide pellets having a crystallinity of 5% or more prepared as described above are supplied to a known melt extruder, heated and melted, and molded and imparted by a die, and cooled. It is solidified and formed into fibers, films, sheets, covered electric wires, plates, rods, pipes and the like.

Also in this case, it is preferable that the produced polyimide pellets have a water content of 200 ppm or less before being supplied to the melt extruder. Moisture content of polyimide is 200p
The method is not particularly limited to be pm or less,
Generally, it is kept at a temperature of 100 ° C or higher at which the polyimide does not melt, usually at a temperature of 350 ° C or lower for 3 to 24 hours.
Further, it is effective to replace the atmosphere with air, nitrogen, etc., and the treatment may be further performed under reduced pressure.

The molding temperature in the melt extruder is in the range of 300-450 ℃,
It is preferably 350 to 430 ° C. If the molding temperature is less than 300 ° C, the resin does not melt and extrusion is difficult. On the other hand, if the temperature exceeds 450 ° C., the decomposition of the resin progresses, and decomposition foaming, die line, decomposition residue, etc. occur, and the appearance and performance of the product are impaired, which is not preferable.

The melt extruder to be used may be an ordinary type which is widely used, but a vent type or one having a vacuum hopper is preferably used.

〔Example〕

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

In addition, the measuring method of the characteristic value of the polyimide described in the Example is shown below.

(1) Glass transition temperature and melting point The glass transition temperature (Tg) and melting point (Tm) were measured by the DSC method. The sample was about 10 mg and was measured at a temperature rising rate of 4 ° C./min, and Tm was defined as the peak temperature of the melting curve.

(2) Melt viscosity The melt viscosity was measured using a Koka type flow tester, and an apparent shear rate of 200 sec ⁻¹ and an apparent viscosity at 400 ° C. were calculated.

(3) Crystallinity The density (Xobs) at 23 ° C was measured by the toluene-carbon tetrachloride-based density gradient tube method, and the non-crystalline density (Xam) and the crystal density (Xobs) were measured.
cr) and the following formula.

Here, Synthesis Example 1 of crystal density 1.459g / cm ² non crystal density 1.327g / cm crystal density of ² Synthesis Example ² 1.438g / cm 2 non crystal density 1.292g / cm ² [Synthesis Example 1] stirrer, reflux In a reaction vessel equipped with a condenser and a nitrogen introducing tube, 368.4 g (1 mol) of 4.4'-bis (3-aminophenoxy) biphenyl and N, N-dimethylacetamide 2
After charging 344 g, 218.1 g (1 mol) of pyromellitic dianhydride was added in portions under a nitrogen atmosphere while paying attention to the rise of the solution temperature, and the mixture was stirred at room temperature for about 20 hours. To the thus obtained polyamic acid solution, 30.3 g (0.3 mol) of triethylamine and 30.6 g (0.3 mol) of acetic anhydride were added over about 30 minutes, followed by stirring for about 30 minutes. 2000g in this solution
Was charged and the polyimide powder was filtered off at 30 ° C. The obtained polyimide powder was washed with methanol and acetone, and then dried at 300 ° C. for 8 hours in a nitrogen atmosphere to obtain 517 g of polyimide powder. The obtained polyimide was a crystalline resin having Tg of 248 ° C., Tm of 386 ° C. and a crystallinity of 35%, and a melt viscosity of 4,500 poises.

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 of about 1.8 mmφ. This was cut into about 3 mm in the length direction to obtain pellets. This polyimide resin pellet showed a peak (Tcc) of cold crystallization at 296 ° C in DSC, and further, the density was
It was an amorphous resin having a crystallinity of 1% and a weight of 1.327 g / cm ³ . This pellet is designated as polyimide A.

[Synthesis Example 2] 4,4'-bis (3-aminophenoxyphenyl) -1,1,1.3,3,3-hexafluoropropane 259.2 was placed in a reaction vessel equipped with a stirrer, a reflux condenser and a nitrogen inlet tube. g
(0.5 mol) and 1713 g of m-cresol were added, and 109.1 g (0.5 mol) of pyromellitic dianhydride was added in portions under a nitrogen atmosphere while paying attention to the rise of the solution temperature, and then at room temperature for about 2 hours. Stir it.

Then, it heated and heated up in nitrogen atmosphere. The solution became an orange transparent solution at around 60 ° C, and the temperature was further raised, and when stirring was continued at 150 ° C, pale yellow polyimide powder gradually began to precipitate in about 1 hour. The mixture was stirred for 5 hours under heating and then filtered to obtain a polyimide powder. The powder was washed with methanol and acetone, dried under reduced pressure at 180 ° C. for 24 hours, and further dried at 300 ° C. for 8 hours in a nitrogen atmosphere to obtain 319 g of polyimide powder. The obtained polyimide was a crystalline resin having Tg of 271 ° C., Tm of 390 ° C. and a crystallinity of 28%, and a melt viscosity of 6500 poise.

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 of about 1.8 mm. This was cut into about 3 mm in the longitudinal direction to obtain pellets.
This polyimide resin pellet showed a peak of cold crystallization (Tcc) at 296 ° C in DSC, and a density of 1.292 g / c.
It was an amorphous resin having a crystallinity of 0% at m ² . This pellet is designated as polyimide B.

[Synthesis Example 3] 4,4'-bis (3-aminophenoxyphenyl) instead of 4,4'-bis (3-aminophenoxy) biphenyl
-Synthesis 1 except that 400.5 g (1 mol) of sulfide was used
A polyimide pellet was obtained in the same manner as in. The glass transition temperature of the pellets by the DSC method was 230 ° C, and no crystal melting point was observed. This pellet is referred to as polyimide C.

[Examples 1 to 5] 2 kg of polyimide A was placed in a stainless steel container,
It was placed in a closed hot air dryer. The inside of the dryer was sufficiently replaced with nitrogen, and heat treatment was performed at 310 ° C. for 5 hours while flowing nitrogen at 1 / min, and the temperature was returned to room temperature. The pellet crystallinity after heat treatment was 31% as calculated by the density method.

The pellets were dried at 180 ℃ for 24 hours, fed to a 25 mm extruder equipped with a vacuum hopper, heated and melted at 410 ℃, width 150
A sheet having a thickness of about 0.5 mm was obtained by extruding from a mm slit die (gap: 0.5 mm) and allowing to cool naturally in the air. At this time, the screw rotation speed was changed within the range of 5 to 150 rpm as shown in Table 1, but no problems such as variation in extrusion amount and generation of bubbles were observed. The details of the results are shown in Table 1.

[Examples 6 to 10] Polyimide A was treated in air by changing the temperature and time of heat treatment (in these examples, immediately after the heat treatment, the polyimide A was taken out from the dryer and cooled by blowing air at room temperature with stirring. 5 pellets having different crystallinity were obtained. A sheet was obtained using these pellets in the same manner as in Example 2. As a result, no problems such as fluctuations in extrusion rate and bubble generation were observed. The details of the results are shown in Table 1.

[Comparative Examples 1 to 5] Polyimide A was subjected to sheet molding in the same manner as in Example 1 without heat treatment at the screw rotation speed shown in Table 1. As a result, it was confirmed that the amount of extrusion varied, that extrusion was impossible, and that bubbles were generated. The details of the results are shown in Table 1.

[Comparative Example 6] Polyimide A was heat treated under the conditions shown in Table 1 to obtain a crystallinity.
3.5% pellets were obtained. Sheet molding was performed in the same manner as in Example 2. As a result, it was confirmed that the extrusion amount varied and bubbles were generated. The details of the results are shown in Table 1.

[Example 11] The same method as in Example 2 was repeated except that the pellets heat-treated in the same manner as in Example 2 were used, a nozzle having a diameter of 0.3 mm was attached to the extruder at the time of melt extrusion, and the take-up speed was 2 m / min. I got the raw yarn. As a result, average extrusion rate 7.5g / min, fluctuation range 3%
And the fluctuation of the extrusion rate was small. Also, there was no problem of thread breakage.

[Comparative Example 7] An attempt was made to obtain a raw yarn in the same manner as in Example 11 except that polyimide A was used, but yarn breakage frequently occurred and the yarn could not be obtained.

[Example 12] The same pellets as in Example 2 were used to measure the diameter during melt extrusion.
A 20 mm diameter round bar was manufactured with a sizing die that was equipped with a 20 mm nozzle and kept at approximately 50 ° C. As a result, the variation in diameter was about 5%, and there were no bubbles inside, and a good molded product was obtained.

Comparative Example 8 An attempt was made to obtain a round bar in the same manner as in Example 12 except that Polyimide A was used. However, it could not be said to be a round bar because the extrusion amount fluctuated remarkably and remarkable bubbles were generated inside.

[Example 13] When polyimide B was heat-treated at 260 ° C for 28 hours and at 310 ° C for 5 hours in a nitrogen atmosphere, crystalline pellets having a crystallinity of 23% were obtained.

These pellets are dried at 180 ℃ for 24 hours, supplied to a 25mm extruder, heated and melted at 400 ℃, extruded from a slit die with a width of 150mm (gap 0.5mm), naturally cooled in the air, and a sheet of about 0.5mm. Got At this time, the screw rotation speed was 10 rpm, but the extrusion rate fluctuation was 3%, and no problem such as bubbles was observed.

[Examples 14 to 16] Polyimide B was heat treated according to Example 1 under the conditions (temperature and time) shown in Table 1 to obtain three types of pellets having different crystallinity. Dry these pellets at 180 ° C for 24 hours and
It was supplied to a 5 mm extruder, heated and melted at 400 ° C., extruded from a slit die having a width of 150 mm (gap: 0.5 mm), and naturally cooled in the air to obtain a sheet of about 0.5 mm. At this time, the screw rotation speed was 10 rpm, but there were no problems such as fluctuations in extrusion amount and bubbles. The details of the results are shown in Table 1.

[Comparative Examples 9 to 10] Polyimide B was used as it is (Comparative Example 10) or polyimide B was heat-treated at 280 ° C for 5 minutes in the same manner as in Example 1 to obtain pellets having a crystallinity of 2.5% (Comparative Example). 9). Extruded sheets were obtained from these pellets in the same manner as in Example 14. However, fluctuation of the extrusion rate and generation of bubbles were observed. The details of the results are shown in Table 1.

Example 17 Using the pellets used in Example 13, the diameter during melt extrusion
Attach a 0.3mm nozzle to the extruder, and pick up speed is 2m /
A raw yarn was obtained in the same manner as in Example 2 except that the min was set.

As a result, the average extrusion rate was 6.8 g / min, the fluctuation range was 6%, and the fluctuation in the extrusion rate was small. Also, there was no problem of thread breakage.

[Comparative Example 11] An attempt was made to obtain a raw yarn in the same manner as in Example 17 except that polyimide B was used, but yarn breakage frequently occurred, and a yarn could not be obtained.

Example 18 Using the pellets used in Example 13, a 20 mm diameter nozzle was attached at the time of melt extrusion, and a sizing die maintained at about 50 ° C. was used to produce a 20 mm diameter round bar. As a result, the variation in diameter was about 8%, and there were no bubbles inside, and a good molded product was obtained.

[Comparative Example 12] An attempt was made to obtain a round bar in the same manner as in Example 18 except that Polyimide B was used. However, it could not be said to be a round bar because the extrusion amount fluctuated remarkably and remarkable bubbles were generated inside.

[Comparative Example 13] Polyimide C was heat-treated at 250 ° C for 48 hours in a nitrogen atmosphere, but no crystallinity was observed by the DSC method and the X-ray method. The heat-treated polyimide C was dried at 180 ° C. for 24 hours, and a sheet was formed in the same manner as in Example 2. As a result, it was found that the average extrusion rate was 7.5 g / min and the fluctuation range was 53%, the variation in the extrusion rate was large, and bubbles and die residue were generated in the obtained sheet.

[Effects of the Invention] Extrusion molding method of the polyimide resin in the present invention not only solves the fundamental problem in extrusion molding such as fluctuation of the extrusion amount during extrusion molding, inability to extrude, but the gas transported together with the resin is As a result of being eliminated along with the melting of the resin, secondary problems such as mixing of gas into the product or the resulting die residue can be solved, which is extremely effective for extrusion molding of polyimide resin.

Claims (6)

[Claims] 1. A general formula [I] (In the formula, X represents a single bond or a hexafluoroisopropylidene group) A polyimide having a repeating structural unit represented by the formula is processed into a pellet, and this is heat-treated to obtain a polyimide having a crystallinity of 5% or more. An extrusion molding method for polyimide, which comprises supplying to a melt extruder. 2. The method according to claim 1, wherein the heat treatment is carried out at a temperature of 250 to 370 ° C. 3. The method according to claim 1, wherein the crystallinity is 5 to 50%. 4. A general formula [I] obtained by polymerization. (In the formula, X represents a single bond or a hexafluoroisopropylidene group) A polyimide having a repeating structural unit represented by the formula is processed into pellets, which are then heat treated to have a crystallinity of 5% or more. Polyimide pellets for extrusion molding. 5. The polyimide pellet according to claim 4, wherein the heat treatment is performed at a temperature of 250 to 370 ° C. 6. The polyimide pellet according to claim 4, which has a crystallinity of 5 to 50%.