JPH0611798B2 - Manufacturing method of polyimide molding - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a polyimide molded article having improved moldability and mechanical properties after molding.

(Prior Art) Polyimide resin occupies an important position in the electric / electronic device industry, the automobile industry, etc. due to its excellent heat resistance and mechanical properties. Is becoming an indispensable material as is progressing. Among them, aromatic polyimide resins typified by polypyromellitimide resin disclosed in Japanese Patent Publication No. 39-22196 have extremely excellent thermal stability and are at the top of so-called heat resistant resins. On the other hand, since the fluidity is poor, molding is difficult, and improvement in moldability is desired.

(Problems to be Solved by the Invention) Therefore, as a result of intensive studies to improve the moldability of the polyimide resin, the present inventor did not complete the imide ring closure as in the conventional case, and the amic acid before ring closure was in the molecular chain. The present invention has been completed by discovering that if left untreated, the molding becomes easier and the mechanical properties after molding are improved.

(Means for Solving Problems) That is, according to the present invention, the repeating unit represented by the following general formula (I) is a main structural unit, and the imide ring closure ratio is 4 or less.
The present invention provides a method for producing a polyimide molded article, which comprises 0% or more and 95% or less of an amic acid-containing polyimide resin and pressure-molds a powdery resin.

Here, m, n, and l in the general formula are each zero or a positive integer, and Ar is a tetravalent aromatic residue containing at least one carbon 6-membered ring. As a specific example of Ar, And so on. Ar 'is a divalent aromatic or aliphatic residue, such as Etc. can be specifically listed. Further, (I) may be a single polymer or a copolymer.

A method for synthesizing such a polyimide resin is known, and the details thereof are disclosed in, for example, Japanese Patent Publication No. 39-22196, but a tetracarboxylic acid derivative (for example, dianhydride) is disclosed.
It is manufactured by reacting a polyamic acid obtained by reacting a diamine with a diamine in a suitable solvent to cause ring closure by heating. This heat ring closure can be performed in a solution, but the physical properties of the final molded product tend to be higher if the polyamic acid is once reprecipitated and then closed in the solid state. In the conventional method represented by the above-mentioned official gazette, this heating ring closure is sufficiently performed, and almost 100% is achieved.
Although the imide ring-closing rate was set to the above, the point of the present invention is not to completely perform the imide ring-closing but to leave the unclosed amic acid as it is to some extent. That is, in the general formula (I), when the imide ring closure rate is adjusted to 40% or more and 95% or less, preferably 70% or more and 90% or less, the molding becomes easy and the mechanical properties after the molding are significantly improved. Was found. Here, if the imide ring closure rate is less than 40%, gas generation during molding is intense and voids are generated in the molded product, which is not preferable, and if it exceeds 95%, the effect of improving the moldability is small, which is not preferable. Further, the amic acid has no effect unless it is present in the molecular chain of the polyimide resin, and therefore the blendability of the polyimide resin and the polyamic acid resin cannot improve the moldability.

The imide ring closure rate as referred to in the present invention can be quantified by several methods, but the infrared absorption spectrum is the most convenient. That is, the general formula (I)
The imide group having the structure as shown in Figure 6 has a characteristic absorption at 600 cm ^-1 , so it is based on the vibration of the benzene ring.
The absorption at 0 cm ^-1 is used as a standard, and the absorbance ratio a of both is used as an index of the imide ring closure rate. Next, a is measured for a sample which is considered to be 100% complete with imide ring closure, and the imide ring closure rate is determined by the following formula. In the examples described later, a sample heat-treated at 400 ° C. was used as a sample having an imide ring closure rate of 100%.

The present invention is characterized in that a polyimide resin having an imide ring closure rate of 40% or more and 95% or less, preferably 70% or more and 90% or less is pressure-molded. It is performed by raising or lowering the heating temperature at the time of ring closure. Then, in order to adjust the resin having a preferable imide ring closure rate, the ring closure temperature is preferably in the range of 150 ° C to 200 ° C. Further, when the heating temperature is 300 ° C. or higher, the imide ring closure rate becomes close to 100%, and the fluidity during molding obviously decreases.

The polyimide resin targeted by the present invention generally has poor melt fluidity. Therefore, the method according to the present invention is effective, but at the same time, two points of the form of the resin and the molding pressure are important factors that influence the characteristics of the molded product. That is, the resin must be ground into a fine powder. The molding pressure is preferably at least 500 kgf / cm ² , and more preferably 1.5 × 10 ³ kgf / cm ² or more.

The term “pressure molding” as used in the present invention means that a resin is compressed in a mold to obtain a molded product having a desired shape, but the mold is usually heated at the same time. However, after molding at room temperature, it is also possible to make the final product only by heating without applying pressure, which is generally called sinter molding. Further, the sintered molded product may be further heated and compressed to improve the physical properties.

Although various additives may be added to the polyimide molded article of the present invention as needed to impart desired properties,
Examples of such additives include fluororesins, graphite, molybdenum disulfide, mica, talc, glass fibers, carbon fibers, aluminum, silver and various metal oxides. These additives may be blended in the course of polymerization or may be blended before molding, but in any case, it is desirable to uniformly disperse them.

Hereinafter, the present invention will be described in more detail with reference to examples. In addition,
In the examples, the resin is crushed by Hosokawa Micron Co., Ltd.
Bantam mill was used. The pressure molding was performed by the following method. That is, the mold is filled with resin and a pressure of 3 × 10 ³ kgf / cm ² is applied at room temperature. Next, this is gradually heated and finally heated to 450 ° C. During this temperature raising process, gas is generated due to dehydration of residual amic acid, so pressure is released from time to time to release the gas. After keeping at 450 ° C for 5 minutes, it is cooled while being pressurized, and taken out when it becomes 300 ° C or less. Next, from this molded product, 65 mm × 13 mm × 3
mm test pieces were cut out and subjected to tensile and bending tests.

Example 1 4,4'-Diaminodiphenyl ether (DDE) 60.
07 g (0.3 mol) was dissolved in 1.2 N, N-dimethylacetamide (DMAc), and pyromellitic dianhydride (PMDA) 65.44 g (0.3 mol) was gradually added thereto. When the stirring was continued for another hour after the addition was completed,
_inh (measured in DMAc at a concentration of 0.5 g / d at 30 ° C.) is 2.
24 polyamic acid solutions were obtained. Next, this was gradually added to a mixed solvent consisting of toluene 10, 0.5 acetic anhydride and 0.5 pyridine with vigorous stirring, and the resulting precipitate was passed. This was washed twice with acetone, dried in a hot air dryer at 100 ° C for 8 hours, and further pulverized,
Heat treatment was performed at 170 ° C. for 5 hours in a vacuum dryer. The imide ring closure rate of the obtained polyimide resin powder was 77% when measured by infrared absorption spectrum. Subsequently, this powder was pressed and subjected to tensile and bending tests. The results are shown in Table 1, and had excellent properties as compared with those obtained by 100% imide ring closure as in Comparative Examples described later.
That is, it was found that leaving unclosed amic acid improves the fluidity and coalescence during molding, and improves the mechanical properties of the molded product.

Example 2 DDE 60.07 g (0.3 mol) was dissolved in 1.2 DMAc, PMDA 32.72 g (0.15 mol) and benzophenone tetracarboxylic dianhydride (BTDA) 48.33 were dissolved in this.
g (0.15 mol) was added slowly. When stirring was continued for an additional 1 hour after the addition was completed, η _inh (in DMAc, concentration 0.5 g / d
, Measured at 30 ° C.) was 1.82 to obtain a polyamic acid solution. After reprecipitation, drying, and pulverization in the same manner as in Example 1, heat treatment was performed in a vacuum dryer at 200 ° C. for 5 hours. The imide ring closure rate of the obtained copolymerized polyimide resin powder was measured by infrared absorption spectrum and found to be 85%. Subsequently, this powder was pressed and subjected to tensile and bending tests. The results are shown in Table 2 and were superior to those obtained by 100% imide ring closure.

Comparative Example 1 In Example 1, the heat treatment by the vacuum dryer was 330
When it was carried out at 0 ° C., a polyimide resin powder having an imide ring closure rate of about 100% was obtained. The results of tensile and bending tests of the pressure-molded product using this are shown in Table 1, but they were inferior to those of the example in which the amic acid was left as in the example.

Comparative Example 2 In Example 2, the heat treatment by the vacuum dryer was 330
When it was carried out at 0 ° C., the polyimide resin powder obtained had an imide ring closure rate of about 100%. Table 2 shows the results of tensile and bending tests of pressure-molded products using the same, but they were inferior to the examples.

(Effects of the Invention) As is clear from the examples and comparative examples, when the method according to the present invention is used, the moldability of a polyimide resin that is originally difficult to mold is improved, and as a result, the mechanical properties of the molded product are improved. It is considered that this is because the amic acid remained, so that the molecules moved easily during pressurization and the cohesiveness between the powders increased. The polyimide molded product thus obtained has excellent heat resistance, mechanical properties, sliding properties, etc., and is useful for electric / electronic device parts, automobile parts, office machine parts, aircraft parts, and the like.

Claims (1)

[Claims] 1. A amide acid-containing polyimide resin in which a repeating unit represented by the following general formula (I) is a main structural unit, and an imide ring closure rate is 40% or more and 95% or less, and a powdery resin. A method for producing a polyimide molded article, which comprises press molding. (Where m, n and l are each a zero or positive integer, Ar is a tetravalent aromatic residue containing at least one carbon 6-membered ring, Ar 'is a divalent aromatic or aliphatic residue. .)