JPS5933353A - Polyacetal resin composition having improved thermal stability and freed from problem of mold deposit - Google Patents

Abstract

PURPOSE:To provide the titled compsn. which does not suffer discoloration nor deterioration during molding and is freed from deposition of fine powdered materials on the inner surface of a mold, by incorporating melem in a polyacetal resin. CONSTITUTION:Melem (which is obtd. by firing area, has the structure of the formula, does not have any definite melting point, is hardly decomposed by heat, and is a weakly basic compd.) is used as a heat stabilizer. 0.001-2pts.wt. melem is blended with 100pts.wt. polyacetal resin. Pref. 0.01-10pts.wt. polyamide resin is used together.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel polyacetal resin composition with improved mold deposit and thermal stability, and more particularly:
A resin composition containing melem in polyacetal resin,
The present invention also relates to a resin composition in which a polyacetal resin contains the melem and a polyamide resin.

Polyacetal resin is mainly used in the field of metal replacement, which requires toughness, oil resistance, solvent resistance, creep resistance, etc., and is used, for example, as mechanical parts and exterior parts of automobiles, electrical products, machines, etc. Therefore, polyacetal resins are required to have extremely high quality.

However, it is not possible to sufficiently prevent polyacetal resin from thermal decomposition (generation of polyaldehyde gas) by simply stabilizing the ends and adding an antioxidant.
Therefore, silver streaks (also called silver streaks, traces of gas running) that appear on molded products due to this thermal decomposition,
In order to prevent problems with molding stability, dimensional stability, strength, etc., it is necessary to incorporate a heat stabilizer.

Hitherto, polyamide resins, amide compounds, urea derivatives, hydrazine derivatives, sulfur compounds, polysaccharides, etc. have been proposed as heat stabilizers, but polyacetal resin compositions containing these are difficult to prepare in the cylinder of a molding machine. The color may change to yellowish brown due to the action of heat or oxygen, or there may be blackish brown marks on the screw, or the surface of the molded product may become glossy due to fine powder adhering to the inside of the mold (mold deposit). However, there has been a strong desire for improvement.

The present inventors have conducted extensive research to overcome these drawbacks and provide a polyacetal resin composition with excellent thermal stability. As a result, a resin composition containing a predetermined amount of melem in a polyacetal resin has been developed. The scales to achieve that purpose,
The present inventors have discovered that a resin composition in which a polyacetal resin contains a predetermined amount of the melem and polyamide resin is more likely to achieve the object due to a synergistic effect, and based on this knowledge, the present invention has been completed.

That is, the present invention provides a polyacetal resin composition with improved thermal stability and a mold deposit characterized by containing 100 parts by weight of polyacecool resin and 2 parts by weight of melem o, ooi represented by the formula: and
The mold deposit and thermal stability are further characterized by containing, per 100 parts by weight of the polyacecool resin, 2 parts by weight of the melem o, oot represented by 11 and 0 to 10 parts by weight of the polyamide resin. The present invention provides a polyacetal resin composition with improved properties.

The polyacetal resin used in the composition of the present invention is a polymer obtained by homopolymerization of formaldehyde or its cyclic oligomers such as trioxane or tetraoxane, or copolymerization with a comonomer copolymerizable with these, and is In order to prevent depolymerization, the ends of homopolymers are stabilized by esterification or urethanization, and in the case of copolymers, unstable ends are thermally decomposed.

On the other hand, melem used as a thermal stabilizer in the composition of the present invention is a weakly basic compound having a structure of formula (+1) obtained by calcination of urea, and has no melting point and cannot be thermally decomposed (< ( It has the characteristics of having a weight loss (r, s%) when heated at 300°C for 100 hours, and being almost insoluble in water and organic solvents.

The content of melem in the composition of the present invention is 100 parts by weight of polyacetal resin, 0,001 to 2 parts by weight,
Preferably it is in the range of 0.01 to 0.5 parts by weight. If the content is less than 0-001 parts by weight, the effect as a heat stabilizer will not be exhibited, and if it exceeds 2 parts by weight, the action of the base may become strong and promote thermal decomposition, which is not preferable.

In the composition of the present invention, other heat stabilizers, such as polyamide resins, amide compounds, urea derivatives, polysaccharides, cellulose, etc., or antioxidants, light stabilizers, lubricants, etc. that have a low decomposition effect on polyacetal resins, etc. can also be added.

%K When the above-mentioned melem and polyamide resin are used in combination, their synergistic effect provides excellent effects in preventing thermal decomposition, preventing screw scorching, and improving mold deposits.

In the case of Kono, the content of melem and polyamide resin is 0.001 to 100 parts by weight, respectively, per 100 parts by weight of polyacetal resin.
It is necessary that the amount is in the range of 0.01 to 10 parts by weight.

However, in the composition of the present invention, other additives commonly used in polyacetal resins such as glass fibers, inorganic fillers, carbon fibers, pigments, polymers,
Lubricating oil and the like may also be added.

In the composition of the present invention, the polyacetal resin and the heat stabilizer can be mixed by a commonly used melt-mixing method, and when used together with other compounding agents, they may be melt-mixed at the same time. Good too. The heat stabilizer is more effective when dispersed as a fine powder, so it can be used after being pulverized to the microscopic level, or it can be blended with 10 to 100 times the amount of polyacetal resin, extruded, pelletized, and then frozen and pulverized. A masterbatch may be prepared, and this may be blended with a terminal-stabilized polyacetal resin, extruded, and pelletized. In this case, the extrusion temperature is preferably in the range of 180 to 200°C.

Although the melem-containing polyacecool resin composition of the present invention is slightly inferior in thermal decomposition prevention effect compared to the heat-stable acetal resin composition conventionally used industrially, there is no problem in practical use, especially in cylinders. Retention discoloration (
Melem's heat resistance, discoloration resistance, formaldehyde absorption and It exhibits excellent effects due to its mold releasability and other properties.

In addition, the polyacetal resin composition of the present invention containing melem and polyamide resin exhibits excellent effects in terms of discoloration due to retention in the cylinder, scorching on the screw, mold deposit, etc. due to their synergistic effect. In addition, it also exhibits excellent effects in preventing thermal decomposition.

Next, the present invention will be explained in more detail with reference to Examples.

The thermal stability of the resin composition was evaluated by examining the amount of gas generated, discoloration due to retention, occurrence of scorching, and occurrence of mold deposit (hereinafter abbreviated as MD) according to the following method.

1 pellet of sample into a cocked syringe containing 20 ml of gas generating acid.
．． (Insert the aluminum boat loaded with the aluminum boat and insert the cylinder moistened with heat-resistant silicone oil. After replacing the internal air with nitrogen 15 times, immerse it in a silicone oil bath at 230℃, and after 20 minutes, the actual Gas generation amount is 8 Cml/n with volume increase (measured volume value - blank test volume value)
shall be.

Place 500 mF (Pereso) in a test tube with a retention discoloration diameter of 8, and
After heating in a silicone oil bath at 0°C for 60 minutes, it was rapidly cooled and expressed by the color rank at that time.

Color rank ◎ White ○ Mu Pale yellowish brown × × Brown burnt and MD occurred Using a 1-ounce injection molding machine, the cylinder temperature was 200°C
In continuous injection molding at a mold temperature of 80° C., it is expressed as the number of days until minute burns occur on the surface of the molding machine screw, and the number of moldings until the surface of the molded product starts to lose its luster due to MD occurrence.

Examples 1 to 7, Comparative Examples 1 to 7 Powdered terminal acetylated polyacetal homopolymer (
Ho ), or trioxane and ethylene oxide (weight ratio 1f) that have been heat treated to decompose unstable ends O: 2
) and 100 parts by weight of copolymer (Co) with melem finely ground with a ball mill and antioxidant 2.2'-methylenebis(4-methyl-6-tert-butylphenol) 0
．． 25 parts by weight was blended and extruded at 190°C to pelletize. After drying this at 80° C. for 14 hours, a thermal stability test was conducted. The results are shown in Table 1.

As is clear from Table 1, the resin composition containing melem is slightly inferior in thermal decomposition prevention property compared to the resin composition containing polyamide resin, but it is within a range that does not cause any problems in practical use. It can be seen that it is far superior in terms of discoloration, scorching, and mold deposits.

Example 8.9 Polyamide heat stabilizer (IJy6/Ny66/Ny61
0=60/20/2 (1) and a polyacetal resin composition containing melem was evaluated for thermal stability.

The results are shown in Table 2.

As is clear from Table 2, the system that combines a polyamide heat stabilizer and melem is superior to the system that uses only polyamide in terms of thermal decomposition, retention discoloration, scorching, and mold deposits. I know that there is.

Patent applicant: Asahi Kasei Industries, Ltd. Agent Akira Agata 405-

Claims (1)

[Scope of Claims] (1) A polyacetal resin composition with improved mold deposit and thermal stability, characterized by containing 0.001 to 2 parts by weight of melem represented by the formula per 100 parts by weight of polyacetal resin. 2 Ioo parts by weight of polyacetal resin, 0.001 to 2 parts by weight of melem expressed by the formula, and 0 parts by weight of polyamide resin
．． A polyacetal resin composition having improved mold deposit and thermal stability, characterized in that it contains 01 to 10 parts by weight.