JP2000025051A - Production of polyamide resin molded object - Google Patents

Abstract

PROBLEM TO BE SOLVED: To supply a polyamide molded object containing no residual air bubbles therein regardless of a size and a shape, generating no unevenness on the outer surface thereof and containing an additive such as a filler or a reinforcing material in a uniformly dispersed state when the additive is added. SOLUTION: A method for producing a polyamide resin molded object by polymerizing molten lactam in a mold is characterized by polymerizing and molding lactam in the mold while successively advancing the solidification of the polymer in the mold from the lower part of the mold to the upper part thereof by adjusting the injection speed of lactam into the mold or while successively developing the temp. rise by the polymn. heating of the polymer in the mold from the lower part of the mold to the upper part thereof.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a rod-shaped or plate-shaped polyamide resin molded article by anionic polymerization of a lactam, and more particularly to a method for producing a molded article having no internal residual bubbles and adding a filler and a reinforcing material. The present invention relates to a method for producing a molded article in which materials are uniformly dispersed when added.

[0002]

2. Description of the Related Art In a method of molding a polyamide by injecting a molten lactam heated to a predetermined temperature into a preheated mold and anion-polymerizing the same, a cavity called a bubble is formed inside a molded article depending on the size and shape of the molded article. Generating defects is a problem.

[0003] This is due to a large volume shrinkage at the time of molding.
One of the factors is that the polymerization progresses at each part because a certain amount of time is required, and convection occurs after the lactam solution is injected, and the temperature of the upper solution rises in the height direction of the mold and polymerizes from the upper part. It is considered one.

[0004] In order to prevent such internal residual bubbles from being generated, a method of polymerizing a lactam solution under pressure has conventionally been proposed. In addition, when additives such as fillers and reinforcing materials having different specific gravities from the lactam solution are added, sedimentation during polymerization and the problem that it is difficult to obtain a uniformly dispersed molded product can be achieved by reducing the particle size. And increasing the viscosity of lactam liquids.

[0005]

However, it is difficult to apply the conventional method of eliminating internal residual air bubbles to the case where the molding size is increased or a molded article having a different shape in the height direction is obtained. Furthermore, there is a problem in terms of economical efficiency due to an increase in equipment costs of a molding apparatus including a mold.

In addition, when various additives are added to the lactam solution, the variation in the polymerization progress rate at each site becomes remarkable, and in addition to poor dispersion, the rate of generation of internal residual bubbles increases.
It is difficult to control both by the conventional method.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problems and relates to a method for producing a polyamide resin molded article having no internal residual bubbles irrespective of the size and shape of the molded body. Is a method for producing a molded body by polymerizing a molten lactam in a mold in the presence of an anionic polymerization catalyst and a co-catalyst, wherein the solidification of the polymer in the mold is sequentially performed from the bottom to the top of the mold. A method for producing a polyamide resin molded article, comprising carrying out polymerization molding while proceeding. Alternatively, the mold is provided with a heat detecting means, and the polymerization is performed while injecting the molten lactam so that the temperature rise due to the polymerization heat of the molten lactam injected into the mold is gradually increased from the lower part to the upper part of the mold. This is a method for producing a characterized polyamide resin molded article. In order to further increase the temperature rise due to the heat generated by the polymerization of the molten lactam from the bottom to the top of the mold,
This is a method for producing a polyamide resin molded article, which is performed by changing the injection speed of a molten lactam into a mold.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 1 is a perspective view of a molding die used in the present invention. The height is 600 mm, the width is 1200 mm, and the thickness is 20 m.
m, thermocouples 2 were set in the lower, middle and upper portions of the molding die 1 and the entire die was kept at 160 ° C.

In the present invention, concrete means for sequentially solidifying the polymer in the mold from the lower part to the upper part of the mold, or the temperature rise due to the polymerization heat of the polymer in the mold is measured at the lower part of the mold. The specific means for expressing sequentially from top to bottom is shown in FIG.
Adjust the rate at which the lactam solution is injected into the mold. That is, while the lactam solution is being injected into the mold, a polymerization reaction of the solution starts in the lower part of the mold and polymerization solidification proceeds, and the polymerization reaction generates polymerization heat, and the thermoelectric element set in the lower part of the mold 1 is heated. Pair 2 indicates the high temperature value. The polymerization molding is performed while adjusting the injection rate of the lactam solution into the mold so that the temperature of the heat generated by the polymerization is sequentially increased in the lower part, the middle part, and the upper part while checking the value of the thermocouple.

FIG. 2 is a diagram showing the relationship between the temperature rise at each part in the mold and the time when the molten lactam is injected into the mold. The temperature first rises, then rises in the middle and upper parts, and finally the temperature of each part in the mold becomes a constant value.

As described above, polymerization and solidification proceeded from the lower part to the upper part of the mold, and a polyamide resin molded body having no internal residual air bubbles was obtained. Further, when an additive of a filler and a reinforcing material having a specific gravity different from that of the molten lactam was added, the lactam liquid thickened more than the settling of the additive, so that it was possible to uniformly disperse the lactam liquid.

Here, if the polymerization speed is extremely increased by adjusting the composition and temperature of the lactam solution to be injected, the temperature of the mold, etc., an extreme difference occurs in the polymerization solidification speed in the height direction of the mold. Irregularities occur on the surface of the finished product, resulting in poor appearance and no uniform physical properties. When the injection speed is extremely reduced, similar defects occur in the polymer molded product.

[0014]

The present invention will be described below with reference to examples and comparative examples. Example 1 As a molding die, a molding die shown in FIG. 1 maintained at 160 ° C. was used. In a stainless steel container, add anhydrous ε-caprolactam 14
The resulting mixture was heated to a temperature of 140 to 160 ° C., and 33 g of tolylene diisocyanate as a polymerization promoter and 2 kg of graphite were added thereto and mixed. On the other hand, 1 kg of anhydrous ε-caprolactam was placed in another stainless steel container, and 9 g of sodium hydride (63% oily) as a polymerization catalyst was added to the container to adjust the temperature to 140 to 160 ° C. . …… Called “Solution B” Using two pumps, 5.65 kg / mi of Solution A
n, B liquid 0.35 kg / min, total 6 kg / min
The molten lactam liquid was simultaneously injected into the mold at an injection speed of. At the same time as the injection, the temperature rise due to the heat generated by the polymerization of the mixed solution in each part of the mold was measured by the thermocouple 2, and it was found that the temperature rose from the bottom to the middle and to the top. After about 30 minutes, the molded body was taken out of the mold and subjected to an internal inspection using an ultrasonic flaw detector, but no internal residual air bubbles were found. The appearance was also good, and the dispersion of graphite was also good at each part of the molded article. A tensile strength
85MPa when measured in accordance with STM D638
The above strength was exhibited, and the difference between the respective parts was within 5 MPa, which was favorable. In addition, the tensile test piece was sampled with the height direction of the mold as the length direction of the test piece. The molten lactam liquid injected into the mold was solidified from the lower part to the upper part of the mold and polymerized and formed.

Comparative Example 1 Evaluation was performed in the same manner as in Example 1 except that the injection speed ratio of the liquid A and the liquid B was the same, and the total injection speed of the molten lactam liquid was changed to 15 kg / min. The temperature rise due to the heat generated by the polymerization of the mixed solution in each part of the mold appeared in the order from top to middle and bottom. The molded article had internal residual bubbles and good appearance, but had poor graphite dispersion and good tensile strength. Further, the molten lactam liquid injected into the mold solidified from the upper part to the middle part and the lower part of the mold.

[0016]

According to the present invention, regardless of size and shape,
There is no internal residual air bubbles in the molded body, no irregularities are generated on the outer surface, and a polyamide molded body in which additives such as a filler and a reinforcing material are uniformly dispersed when added is added.

[Brief description of the drawings]

FIG. 1 is a perspective view of a molding die used in the present invention.

FIG. 2 is a diagram showing a relationship between temperature rise and time in each part in a mold when molten lactam is injected into the mold.

[Explanation of symbols]

 1 Mold 2 Thermocouple

Claims (3)

[Claims] 1. A method for producing a molded product by polymerizing a molten lactam in a mold in the presence of an anionic polymerization catalyst and a co-catalyst, wherein solidification of the polymer in the mold is performed from the bottom of the mold. A method for producing a polyamide resin molded article, comprising carrying out polymerization molding while sequentially proceeding to an upper portion. 2. A method for producing a polyamide resin molded body by injecting a molten lactam in the presence of an anionic polymerization catalyst and a co-catalyst into a mold provided with heat detecting means, wherein the molten lactam is injected into the mold. A method for producing a polyamide resin molded article, characterized in that a rise in temperature due to polymerization heat of a molten lactam is detected by the heat detecting means, and the molten lactam is injected so that the temperature rises sequentially from the lower part to the upper part of the mold. 3. The method according to claim 2, wherein the rate of injection of the molten lactam into the mold is changed to increase the temperature of polymerization heat of the molten lactam from the bottom to the top of the mold. A method for producing a polyamide resin molded article.