JPH0211625B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention has excellent thermal stability, significantly reduces deposits on the screw of the molding machine and deposits on the mold, has good appearance, and improves the appearance of the molded product. Concerning good polyoxymethylene compositions. [Prior art] Polyoxymethylene has excellent wear resistance,
Because of its fatigue resistance, creep resistance, and mechanical strength,
It is used in a wide range of fields including mechanical parts, electronic/electrical parts, building materials, and piping parts. However, compared to other resins such as polyethylene and polystyrene, polyoxymethylene does not necessarily have sufficient thermal stability due to its skeletal structure. For this reason, various efforts have been made to increase the thermal stability of polymers. As one method, it is widely known to use synthetic polyamide as a stabilizer. Although the thermal stability of polyoxymethylene is significantly improved by adding synthetic polyamide as a stabilizer, the disadvantages associated with its use cannot be overlooked. That is,
The polyamide used as a stabilizer is usually chosen to have a melting point lower than that of polyoxymethylene. For example, the 6/
66/610 copolymer polyamide, etc. These polyamides are usually in a molten or semi-molten state,
Shows significant stickiness or adhesion to metals. Therefore, when a polyoxymethylene composition containing these synthetic polyamides as a stabilizer is molded, the stabilizer or the reaction product of the stabilizer and formaldehyde may be deposited on the screw surface of the injection molding machine, the inner wall of the cylinder, or the mold surface. Precipitates and adheres.
For this reason, it becomes necessary to periodically disassemble and clean the screw and the mold, which significantly reduces the productivity of the molding process. Several proposals have been made to improve the above-mentioned drawbacks. For example, JP-A-1987-
Publication No. 145458 describes a polyoxymethylene composition prepared by adding an amide oligomer having a molecular weight of 800 to 10,000 and having an active end group of 0.02 mol % or less of the formaldehyde segment in the polyoxymethylene. However, although amide oligomers have lower adhesion and adhesion to metals than polyamides with high molecular weights, they are still insufficient. Furthermore, JP-A-50-78225 discloses that a semi-crystalline polyamide whose melting temperature is higher than that of polyoxymethylene or an amorphous polyamide whose glass transition temperature is higher than that of polyoxymethylene is incorporated into a carrier resin. It has been proposed to use stabilizers present as particles of about 5 microns or less. However, in this method, the resin used for the carrier, such as polyethylene, a copolymer of ethylene and methyl acrylate, a copolymer of ethylene and ethyl acrylate, a copolymer of methyl methacrylate and ethyl acrylate, and a Due to the poor compatibility of oxymethylene, the carrier resin and polyoxymethylene separate, resulting in peeling on the surface of the molded product or deterioration of mechanical properties. In addition, in order to impart compatibility between the carrier resin and polyamide, a copolymer of ethylene and methacrylic acid partially neutralized with zinc is used as a compatibilizer, but the presence of this compatibilizer is , has the function of lowering the softening temperature of polyamide, and the effect of preventing precipitation on the mold is hindered. Furthermore, when using a polyamide with a high melting temperature, for example, exceeding 290°C, the stability of the proposed carrier resin, such as polyethylene oxide, is compromised due to the high processing temperature during the process of dispersing the polyamide. There is a problem called. [Problems to be Solved by the Invention] The present inventors have developed a molded product that has a good appearance with less deposits on the mold, less deposits and deposits on the screw of the molding machine, and a molded product with good appearance. The present invention has been accomplished through extensive research into polyoxymethylene compositions that exhibit good thermal stability. [Means for Solving the Problems] The present invention involves dispersing 0.01 to 10% by weight of polytetramethylene adipamide particles pulverized to a particle size of about 10 microns or less using a pulverizer in a polyoxymethylene polymer. The present invention relates to a polyoxymethylene composition comprising: The present invention will be explained in detail below. The polyoxymethylene polymer used in the present invention includes conventionally known polyoxymethylene homopolymers and copolymers. That is, cyclic oligomers of formaldehyde, such as trioxane and tetraoxane homopolymers, or comonomers copolymerizable with these, such as ethylene oxide,
Refers to a copolymer of 1,4-butanediol formal. Its polymer chains are mainly −(CH ₂ O−) _o
(n is an integer of at least 400),

〔Effect of the invention〕

The composition of the present invention thus obtained has significantly less precipitation/adherence to the screw of the molding machine and deposits to the mold, has a good appearance, and is thermally stable with good appearance of the molded product. Excellent in sex. Next, deposits of the composition on the molding machine screw,
This article describes the method for evaluating precipitates on molds and thermal stability. (a) Evaluation method for deposits on molding machine screws Using an injection molding machine N-70A manufactured by Nippon Steel Corporation (cylinder temperature 200°C), a flat plate of 100 x 50 x 2 mm was continuously molded for two weeks (injection time 8 seconds, cooling time 2 seconds,
After the entire cycle (15 seconds, mold temperature 105℃), observe the screw for dirt. (b) Method for evaluating deposits on the mold Perform molding in the same manner as in (a) above, and observe the number of molding shots where stains occur on the cavity surface of the mold. (c) Thermal stability evaluation method Arburg injection molding machine, Arburg All−
rounder150 (cylinder temperature 230℃) and 100×
Using a mold for a 12.6 x 3 mm test piece (mold temperature: 80°C), the composition was allowed to stay in the molding machine and then molded, and the surface of the test piece was found to have silver streaks due to the gas generated by the decomposition of the resin. Measure the critical residence time that occurs. [Example] Examples are shown below, and % and parts in the examples are by weight unless otherwise specified. Production Example 1 Production of 4,6-nylon A 4,6-nylon oligomer (number average molecular weight approximately 1000) was pulverized using a jet mill I-20 manufactured by Nippon Neumatic Co., Ltd. The particles were classified using Akiyukatsu (manufactured by Akiyukatsu) to satisfy the desired particle size. The obtained oligomer is 210
℃ in a stream of nitrogen for the desired time. Example 1 The oligomer with a particle size of 5μ or less in Production Example 1 was
After heating for hours, micronized 4,6-nylon having a number average molecular weight of about 30,000 and an active end group concentration of 6.7×10 ^-5 mol/g was obtained. 100 parts of a polyoxymethylene homopolymer (number average molecular weight approximately 40,000) obtained by terminally acetylating this 4,6-nylon, pentaerythrityl-tetrakis [3-(3,5-di-t-butyl-4-
hydroxyphenyl) propionate]
Irganox1010 (Ciba Geigy Corporation) 0.5 to 0.3 parts
The mixture was mixed using a twin-screw extruder PCM-30 manufactured by Ikegai Tekko Co., Ltd. (cylinder temperature 200°C, screw rotation speed 80 rpm).
It was kneaded using. Table 1 (1) shows the evaluation results regarding the adhesion of the obtained composition to the molding machine screw, precipitation on the mold, and thermal stability. In addition, a molding test was conducted to evaluate the peelability. The peelability evaluation conditions were as follows: using the same injection molding machine and mold as in the evaluation method for deposits on screws, injection time 8 seconds, cooling time 2 seconds, total cycle time 15
The mold temperature was set at 60° C., and the injection pressure was set at 1100 Kg/cm ² . Ten shots of each sample were molded, and peeling, especially near the gate, was visually judged.
The appearance of this molded sample was good. The peeling results are shown in Table 1 (2). Comparative Example 1 In place of 4,6-nylon in Example 1, 6/6-nylon was used.
The same procedure as in Example 1 was carried out except that 0.5 part of ternary copolymer polyamide of 66/610 (weight ratio 50/35/15) was added. However, the particle size of ternary copolymer polyamide is 0.1
~0.2μ was used. The evaluation results of the various properties obtained are shown in Table 1 (1). Further, a molding test was conducted in the same manner as in Example 1. The surface of this molded sample was observed to have irregularities due to polyamide particles, and its appearance was poor. The peeling results are shown in Table 1 (2). Example 2 The oligomer with a particle size of 5μ or less in Production Example 1 was
After heating for hours, atomized 4,6-nylon having a number average molecular weight of about 25,000 and an active end group concentration of 8 x 10 ^-5 mol/g was obtained. 100 parts of this 4,6-nylon terminal-stabilized polyoxymethylene copolymer (ethylene oxide 2%, number average molecular weight approximately 30,000), 2,
0.2 parts to 0.4 parts of 2'-methylene-bis-(4-methyl-6-t-butylphenol) were mixed, a composition was prepared in the same manner as in Example 1, and each property was evaluated. Shown in the table. Comparative Example 2 The same procedure as in Example 2 was carried out except that 0.2 part of nylon-12 was added instead of 4,6-nylon.
The results are shown in Table 2. Examples 3 to 8 In Example 1, the characteristics and addition amount of 4,6-nylon were varied and evaluated in the third
Shown in the table. Example 9 4,6-nylon oligomer synthesized with a slight excess of 1,4-diaminobutane (number average molecular weight approximately 990, -NH ₂ concentration 135 × 10 ^-5 mol/g, -
COOH concentration 67×10 ^-5 mol/g) was acetylated with acetic anhydride to reduce the terminal -NH concentration to 25×10 ^-5 mol/g, and then pulverized in the same manner as in Production Example 1.
The 4,6-nylon oligomer with a particle size of 5 μm or less was obtained by classification. The properties of the composition obtained by replacing the 4,6-nylon oligomer thus obtained with the 4,6-nylon of Example 1 were evaluated. No dirt was observed on the screw of the molding machine, and no deposits on the mold were observed for more than 4,000 shots. Comparative Example 3 According to the method described in JP-A-53-78255,
16 parts by weight of 66-nylon (n≒20000) and 84 parts by weight of a copolymer (carrier resin) consisting of 79% by weight polyethylene and 21% by weight methyl acrylate were added to 285%
The mixture was uniformly mixed and extruded using an Ikegai PCM-30 twin-screw extruder set at ℃. When the dispersion diameter of 66-nylon particles was measured using a polarizing microscope, all of them were 1.
A very uniform distribution of ~2 micrometers was observed. Furthermore, 6.25% of the above polyamide carrier resin mixture was added to terminally acetylated polyoxymethylene with n≒40,000 and no stabilizer mixed therein.
Ikegai Tekko PCM− added by weight% and set at 200℃
The mixture was kneaded and extruded using a 30 twin screw extruder. As an antioxidant, 0.2 parts by weight of Irganox 1010 was added to polyoxymethylene as in Example 1. This resin composition was subjected to a molding test in the same manner as in Example 1. Although the appearance of the molded sample was similar to that of Example 1, the releasability was evaluated using the same criteria as in Example 1, and the value was 8/10, which was extremely poor.

[Table] means adhesion.

[Table] Represents Yotsuto in molecules.

【table】

【table】

Claims (1)

[Scope of Claims] 1. A polyoxymethylene composition comprising 0.01 to 10% by weight of polytetramethylene adipamide particles pulverized by a pulverizer to a particle size of about 10 microns or less dispersed in a polyoxymethylene polymer. . 2. The polyoxymethylene composition of claim 1, wherein the polytetramethylene adipamide has a dispersed particle size of about 5 microns or less. 3. The polyoxymethylene composition of claim 2, wherein the polytetramethylene adipamide has a dispersed particle size of about 2 microns or less. 4. The polyoxymethylene composition according to claim 1, wherein the active end group concentration of polytetramethylene adipamide is 100×10 ⁻⁵ mol/g or less. 5. The polyoxymethylene composition according to claim 4, wherein the polytetramethylene adipamide has an active end group concentration of 50×10 ⁻⁵ mol/g or less.