JPH0571370B2 - - Google Patents

Description

[Detailed description of the invention]

<Industrial Field of Application> The present invention relates to a method for manufacturing aromatic polyimide molded products with less occurrence of cracks and cracks. <Conventional technology> Aromatic polyimide resin has excellent heat resistance,
In recent years, it has been used in various fields due to its mechanical properties, sliding properties, etc. Among them, the special public official 1977-22196
The polyimide resin of the formula () disclosed in the publication has extremely high heat resistance and is useful.

[C] There are two known methods for molding polyimide resins: hot press method and sintering method.
The details are disclosed in Publication No. 49-5737. <Problems to be Solved by the Invention> However, since polyimide resin has high heat resistance, it has a problem that it has poor fluidity and is difficult to mold. A particularly big problem is during molding.
If cracks or cracks occur, refusion is virtually impossible, and the cracks or cracks that occur remain in the final product, causing a decrease in strength. The main cause of cracks and cracks during molding is gas generation, and the sources of this gas are (i) residual solvent and hygroscopic moisture, and (ii) ring-closing water when residual amic acid undergoes imide ring-closing. For gases derived from (i) and (ii) above,
The hot press method described in Japanese Patent No. 22196 requires delicate timing for degassing and high operator skill, making it extremely difficult to mold thick materials (thickness of 10 mm or more). Further, as an improved method of this hot pressing method, there is a sintering method disclosed in Japanese Patent Publication No. 49-5737, and this method certainly suppresses the occurrence of cracks and the like. However, this method has the problem that the density of the final molded product is low because the pressure is not increased during the fusion process, and the mechanical strength is particularly inferior to that of the hot press molding method. The object of the present invention is therefore to establish a manufacturing method that eliminates the problems associated with these conventional molding methods and that can easily produce molded products with less occurrence of cracks and cracks and with good physical properties. <Means for solving the problem> That is, the present invention solves the following problems: (a) General formula ()

[Chemical formula] (In the formula, Ar is a tetravalent aromatic residue, and Ar ^- is a divalent aromatic residue.) An aromatic polyimide resin whose main structural unit is a repeating unit represented by The first step is to form a green compact by applying a pressure of 100 to 10,000 Kgf/cm ² under a temperature condition of 250°C. ,0..1~300
a second step of heat-treating for a period of time ^;
This is a method for producing an aromatic polyimide molded article, which comprises a third step of applying pressure. In the above general formula, Ar is a tetravalent aromatic residue having at least one 6-membered carbon ring, of which each divalent is bonded to an adjacent carbon atom in the benzene ring of the Ar group. It is characterized by, specifically,

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Examples include [Formula]. Furthermore, Ar' is a divalent aromatic residue having 1 to 4 carbon 6-membered rings, such as

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Examples include [Formula]. Also, () may be a single polymer,
It may be a copolymer. A particularly useful polyimide is poly(4,4 ^- oxydiphenylenepyromellitimide) represented by the formula ().

[C] This method of synthesizing polyimide is known,
The details are disclosed in Japanese Patent Publication No. 39-22196, but after a tetracarboxylic acid derivative (e.g. dianhydride) and a diamine are reacted in an organic polar solvent (e.g. amide solvent) to form a polyamic acid, This can be obtained by imide ring closure. It is preferable to leave an appropriate amount of amic acid units without complete imide ring closure, since this increases the cohesiveness during molding and improves the physical properties of the molded product, particularly the mechanical strength. Furthermore, even if the amic acid units are left as described above, molded products without cracks or cracks can be easily obtained by the method of the present invention. Further, the polyimide resin used in the present invention is desirably a fine powder with an average particle size of 50 mm or less, preferably 20 mm or less, but a fibrous (or pulp) type can also be used. The first step of the present invention is the step of compressing the polyimide resin to form a green compact, and the heating temperature is room temperature to 250°C, preferably 220°C or lower, more preferably 100°C or lower, and gas generation It is necessary to suppress it as much as possible. If the temperature exceeds 250°C, gas generation increases and cracks are likely to occur, which is undesirable. Further, the pressure is preferably 100 to 10,000 Kgf/cm ² , preferably 500 to 10,000 Kgf/cm ² . If it is less than 100Kgf/ ^cm2 , compression will be insufficient and only a molded product with low strength will be obtained in the end, which is undesirable.
Pressure exceeding f/cm ² is not practical. The pressurization time varies depending on the thickness, and if the thickness is 1 mm, it may take about a few seconds, but there is no problem in applying pressure for a longer time. When the thickness is 10 mm, it is preferable to apply pressure for 3 minutes or more. The green compact obtained in the first step is then subjected to a second step. The purpose of the second step is to remove gas components contained in the green compact, and when heated and compressed in the third step. Another point is to prevent cracks and cracks from occurring. This second step is carried out at a temperature of 350 to 500° C. for 0.1 to 300 hours in a vacuum or an inert gas atmosphere such as nitrogen or argon. It is not preferable to use it in the air because the resin will deteriorate. Further, if the temperature is less than 350°C, the removal of gas components will be insufficient, which is not preferable, and if it exceeds 500°C, the resin will thermally decompose, which is not preferable. A more preferred temperature range is 370-450°C. Also, compacted powder,
When the temperature is rapidly raised to the above temperature range, a large amount of gas is generated at once, which tends to cause swelling. Therefore,
It is necessary to take time to raise the temperature to the extent that it does not swell. In case of thickness 10mm, usually 3 to 30
A heating rate of °C/hour is preferred. The heat treatment time referred to in the present invention, that is, 0.1 to 300 hours, is
The time after reaching the above temperature range, preferably 0.2 to 100 hours. If the heat treatment time is shorter than the above range, the removal of gas components will be insufficient, which is undesirable; if it is longer, the resin will deteriorate, which is undesirable. Also, the thicker the molded product, the longer it is necessary to heat treat it. The heat-treated body obtained in the second step is subsequently subjected to a third step. The purpose of the third step is to increase the density of the molded product by pressurizing it at high temperature, and as a result, to improve the mechanical strength. The temperature and pressure conditions for the third step are 350~
500℃, 50-5000Kgf/ ^cm2 , preferably,
370~480℃, 100~5000Kgf/ ^cm2 . If the temperature is lower than the above range, there will be no effect of improving the density, which is undesirable, and if it is higher, the resin will deteriorate, which is undesirable. Moreover, if the pressure is less than 50 Kgf/cm ² , the density will not be improved, which is not preferable. In addition, the pressurization time is
Usually about 5 to 60 minutes is good. The conventional hot press method is the second method of the present invention.
Because this process is not carried out, gas is generated violently during molding, and it is extremely difficult to obtain molded products without cracks or cracks, especially when it comes to thick products (approximately 10 mm thick or more). However, in the present invention, since the gas is sufficiently removed in the second step, the amount of gas generated in the third step is negligible, and molded products without cracks or cracks can be produced without complicated degassing operations. can be easily obtained. Various fillers can be added to the polyimide resin used in the present invention as needed, and examples of such fillers include fluororesin, graphite, molybdenum disulfide, boron nitride, mica, Examples include talc, glass fiber, carbon fiber, aramid fiber, potassium titanate fiber, copper, lead, aluminum, and various metal oxides. <Examples> Hereinafter, the present invention will be further explained in detail by giving examples. In addition, the bending test in the examples was conducted on molded products.
This was done by cutting out a test piece measuring mm x 13 mm x 3 mm. Production example 1 Production of polyimide-A 4,4'-diaminodiphenyl ether (DDE)
60.07 g (0.3 mol) was dissolved in 1.2 N,N-dimethylacetamide (DMAc), and 65.44 g (0.3 mol) of pyromellitic dianhydride (PMDA) was gradually added thereto. After the addition was completed, stirring was continued for another hour, and 〓inh (in DMAc, concentration 0.5 g/dl,
A polyamic acid solution with a temperature of 2.00 (measured at 30°C) was obtained. Next, the temperature was adjusted to 30℃, and 3.5 parts of acetone was added to make a homogeneous solution. When 180ml of acetic anhydride and 200ml of pyridine were added while stirring vigorously, a yellow powder of polyimide precipitated. After washing with acetone, in the air,
It was dried at 160°C for 5 hours to obtain polyimide-A powder. Production Example 2 Production of Polyimide-B In Production Example 1, except that a mixture of 2.81 g (0.1 mol) of PMDA and 64.45 g (0.2 mol) of benzophenone tetracarboxylic dianhydride was used as the tetracarboxylic acid component. Polymerization was carried out in a similar manner to obtain polyimide-B powder. Production Example 3 Production of Polyimide C In Production Example 1, a mixture of 16.22 g (0.15 mol) of paraphenylenediamine and 64.87 g (0.15 mol) of bis[4-(4-aminophenoxy)phenyl]sulfone was used as the diamine component. , and 88-27 g of ^3,3- ,4,4 ^- biphenyltracarboxylic dianhydride as a tetracarboxylic acid component.
Polyimide-C powder was obtained by polymerization in substantially the same manner except that (0.3 mol) was used. Example 1 Molding was carried out as follows using polyimide-A powder. (First step) 300 g of polyimide A powder was put into a 100 mm x 100 mm square mold, and after pressurizing for 10 minutes at a mold temperature of 80° C. and a pressure of 2000 Kgf/cm ² , the mold was taken out to obtain a green compact. The thickness of the green compact was 22.4 mm, and the density was 1.34 g/cm ³ . (Second Step) The green compact obtained in the first step was placed in a nitrogen purge chamber, heated from 100° C. to 450° C. at a rate of 5° C./hour, and further heat-treated at 450° C. for 1 hour. After cooling, the heat-treated body taken out had a density of 1.35 g/cm ³ . (Third step) The heat-treated body obtained in the second step was placed in a 100 mm x 100 mm square mold, and the mold temperature was 450°C and the pressure was 1000 Kgf/cm ²
After pressurizing for 20 minutes under these conditions, it was taken out to obtain a molded product (thickness 20.4 mm, density 1.43 g/cm ³ ). During this period, even though no degassing operation was performed, the molded product had no cracks or cracks, and its mechanical properties were good as shown in Table 1. Comparative Example 1 In Example 1, the green compact obtained in the first step was directly subjected to the third step and hot press molded. However, a large amount of gas was generated during heating and pressurization, and even if degassing operations were performed frequently, cracks occurred, and in the end no molded product could be obtained. Comparative Example 2 In Example 1, the heat-treated body that had undergone the second step was cut and subjected to a bending test. The results are shown in Table 1, and it can be seen that this heat-treated product (that is, a sintered product according to the conventional molding method) has lower strength and elastic modulus than the molded product obtained by the present invention.

[Table] Example 2 Using polyimide-B powder, molding was carried out as follows. (First step) 150 g of polyimide B powder was placed in a 100 mm x 100 mm square mold, and a pressure of 4000 Kgf/cm ² was applied at room temperature for 10 minutes to obtain a green compact (thickness: 11.1 mm, density: 1.35 g). /
^cm3 ). (Second step) Put the green compact obtained in the first step into a vacuum oven,
Raise the temperature from room temperature to 400℃ at a rate of 10℃/hour,
Further heat treatment was performed at 400°C for 1 hour. The heat-treated sample taken out after cooling had a density of 1.36 g/cm ³ . (Third step) The heat-treated body obtained in the second step was placed in a 100 mm x 100 mm square mold, and the mold temperature was 400°C and the pressure was 500 kgf/cm ² .
After heating for 30 minutes, it was taken out to obtain a molded product (thickness
10.2mm, density 1.43g/ ^cm3 ). Even though no degassing operation was performed, a good molded product was obtained, and its physical properties were also excellent as shown in Table 2. Comparative Example 3 In Example 2, the green compact obtained in the first step was directly subjected to the third step, and hot press molding was performed. However, a large amount of gas was generated during molding, and even if degassing was performed, it was not possible to prevent the occurrence of cracks and cracks, and in the end no molded product could be obtained. Comparative Example 4 In Example 2, the heat-treated body that had undergone the second step was cut and subjected to a bending test. The results are shown in Table 2, and the strength was lower than that of the molded product of Example 2.

[Table] Example 3 Using polyimide-C powder, molding was carried out as follows. (First step) 600g of polyimide-C powder was put into a 130mm mold, and the mold temperature was 150℃ and the pressure was 800Kgf/ ^cm3 .
Pressure was applied for 40 minutes to obtain a green compact (thickness: 33.5 mm, density:
1.35g/ ^cm3 ). (Second step) The green compact obtained in the first step was placed in a vacuum oven, heated from 150°C to 420°C at a rate of 2°C/hour, and then heat-treated at 420°C for 2 hours (density
1.37g/ ^cm3 ). (Third step) The heat-treated body obtained in the second step was put into a 130 mm mold, and after pressurizing at a mold temperature of 420°C and a pressure of 600 kgf/cm ² for 30 minutes, it was taken out to obtain a molded product ( Thickness 30.4mm,
Density 1.44g/ ^cm3 ). It is a good molded product with no cracks or cracks, and the bending strength/elastic modulus is 1.440/
It was excellent at 35000 (Kgf/cm ² ). Example 4 After dry-blending 180 g of polyimide-A powder with 120 g of graphite powder (manufactured by Nippon Graphite Co., Ltd.), the entire amount was put into a 100 mm x 100 mm square mold, and then the first and second molds were mixed in exactly the same manner as in Example 1. 2. Performed the third step. Obtained molded product (thickness 17.7 mm, density 1.64 g/cm ³ )
It was in good shape with no cracks or cracks, and had an excellent bending strength of 1020 kgf/cm ² . <Effects of the Invention> According to the manufacturing method of the present invention, a thick molded product can be easily obtained without performing complicated operations such as degassing that require skill. Moreover, the obtained molded product has high density, high strength, and high elastic modulus. The polyimide molded product thus obtained has excellent heat resistance, mechanical properties, sliding properties, etc.
Useful for electrical/electronic parts, automobile parts, office equipment parts, aircraft parts, etc.

Claims (1)

[Claims] 1 (a) A repeating unit represented by the general formula ( ⁾ The first step is to form a green compact by applying a pressure of 100 to 10,000 Kgf/cm ² to an aromatic polyimide resin having the main structural unit under a temperature condition of room temperature to 250°C; (b) forming the green compact; , a second step of heat treatment for 0.1 to 300 hours at 350 to 500°C in a vacuum or an inert gas atmosphere ^;
A method for producing an aromatic polyimide molded article, comprising a third step of applying pressure.