JPH0481449A - Polyacetal resin composition free from mold-deposition property - Google Patents

Abstract

PURPOSE:To obtain the subject composition having suppressed tendency of forming a mold deposit in a mold in injection molding, etc., and having improved productivity of molded article by adding a specific alkoxymethylmelamine to a base resin. CONSTITUTION:The objective composition is produced by compounding 100 pts.wt. of a polyacetal resin with 0.01-10 pts.wt. of an alkoxymethylmelamine of formula [R1 to R6 are H or alkoxymethyl of formula -CH2OR' (R' is 1-8C alkyl); at least two of them are alkoxymethyl]. All of the groups R1 to R6 may be alkoxymethyl. Hexamethoxymethylmelamine is a preferable example of the additive.

Description

Detailed Description of the Invention [Industrial Field of Application] The present invention provides a novel polyacetal resin composition that prevents mold deposits, and more specifically, the present invention relates to a novel polyacetal resin composition that prevents mold deposits, and more particularly, to prevent deposits generated in a mold during molding such as index molding and blow molding. This invention relates to a polyacetal resin composition that significantly suppresses the formation of so-called mold deposits and improves the productivity of molded products.

[Conventional technology]

In recent years, polyacetal resin has been widely used in many fields such as electrical parts, office equipment parts, and building materials due to its excellent strong abrasive properties, fatigue properties, and electrical properties, and its demand is increasing year by year. .

This polyacetal resin is usually molded into a desired shape by injection molding or blow molding, but at this time, a so-called mold deposit is generated on the surface of the mold, and this is transferred to the surface of the molded product, resulting in the appearance of the molded product being affected. It has the disadvantage that it is difficult to use as a material for parts that require high dimensional accuracy, such as gears, because it deteriorates significantly or reduces dimensional accuracy. In order to minimize such troubles, the molds used for molding polyacetal resin must be disassembled and cleaned every time they are used, but this takes a lot of time, so it is difficult to avoid reducing productivity. do not have.

Various studies have been conducted to improve the thermal stability of this polyacetal resin and to minimize the formation of mold deposits.

For example, Japanese Patent Publication No. 34-5440 discloses a polyacetal resin composition blended with a polyamide resin, and although this composition has excellent thermal stability, it is difficult to absorb heat and oxygen in the cylinder of a molding machine during molding. The problem is that the screws may change color to yellowish brown or have blackish brown marks or adhesion on the screws. Furthermore, Japanese Patent Publication No. 40-21148 discloses a polyacetal resin composition containing amidine compounds such as cyanoguanidine, benzoguanamine, and melamine compounds. Although this composition has excellent thermal stability, the amidine compound Due to poor compatibility with polyacetal resin, the amidine compound bleeds out and causes mold deposits. Mold deposits are especially noticeable in high-temperature molds.

Japanese Patent Publication No. 55-50502 '+- discloses a polyacetal resin composition containing a water-insoluble reticulated melamine-formaldehyde polycondensate; It is necessary to pulverize the resulting condensate and mix it uniformly, which raises the question of operability.

JP-A-55-157645 discloses the use of alkoxymethylmelamine in glass fiber reinforced polyacetal resin for the purpose of improving tensile strength and impact strength.

JP-A-57-102943 discloses a polyacetal resin composition containing a ternary stabilizer consisting of an amino resin initial polymerization product of an amino-substituted triazine and formaldehyde, a sterically hindered phenol, and a metal-containing compound. Although this composition is effective in short-time molding, mold deposits occur in long-term continuous molding, which is a practical problem.

Furthermore, JP-A No. 2-80416 discloses a polyacetal resin composition containing as a stabilizer a compound obtained by heating and kneading a polyacetal polymer that has not undergone terminal stabilization treatment and melamine. During the production of the stabilizer, a large amount of formaldehyde gas is generated, which poses a problem in workability.

[Problem to be solved by the invention]

The present invention provides thermal stability that can significantly suppress mold deposits generated in the mold and improve the quality and productivity of molded products when molding polyacetal resin using a mold such as injection molding or blow molding. An object of the present invention is to provide a polyacetal resin composition with excellent properties.

[Means to solve the problem]

The inventors of the present invention have conducted intensive research to develop a polyacetal resin composition that can prevent the occurrence of mold deposits within the mold, and have achieved the objective by blending alkoxymethylmelamine into the polyacetal resin. Based on this knowledge, we have completed the present invention.

That is, in the present invention, 0 parts by weight of alkoxymethyl melamine of the following general formula (I) is added to 100 parts by weight of the polyacetal resin.
．． The present invention provides a mold deposit-preventing polyacetal resin composition characterized in that 01 to 10 parts by weight are added.

(I) / \ R [In the formula, R1-R6 represent a hydrogen atom or an alkoxymethyl group -CH20R'(R' is a C1-C8 alkyl group), and at least two of R-R6 mean an alkoxymethyl group . ] Hereinafter, the present invention will be explained in detail.

The polyacetal resin used in the composition of the present invention may be a polyacetal homopolymer or a polyacetal copolymer.

The polyacetal homopolymer has oxymethylene units +
It consists of repeating CH2o+ and can be produced by homopolymerizing formaldehyde or trioxane.

On the other hand, a polyacetal copolymer has a general formula [wherein R and R2 are each a hydrogen atom, an alkyl group, or an aryl group, and they may be the same or the same] in a chain consisting of oxymethylene units. (n is an integer from 2 to 6) The oxyalkylene units may be different from each other (n is an integer from 2 to 6).

The content of the oxyalkylene units in this copolymer is 0.05 per 100 moles of oxymethylene units.
-50 mol, preferably 0.1-20 mol. Examples of the oxyalkylene units include oxyethylene units, oxyethylene units, oxytrimethylene units, oxytrimethylene units, oxybutylene units, and oxyphenylethylene units. Among these oxyethylene units, oxyethylene units -++CH2)20+ and oxytrimethylene units 10-CH2)40-)- are particularly preferred from the viewpoint of improving the physical properties of the polyacetal resin composition.

The polyacetal copolymer can be produced, for example, by copolymerizing at least one selected from formaldehyde, trioxane, and polyoxymethylene with a cyclic ether.

The alkoxymethyl melamine used in the composition of the present invention is represented by general formula (I).

R [In the formula, R1 to R6 represent a hydrogen atom or an alkoxymethyl group -CH20R'(R' is an alkyl group of 01 to c8), and at least two of R1 to R6 represent an alkoxymethyl group. ] For example, dimethoxymethylmelamine, l-rimethoxymethylmelamine, tetramethoxymethylmelamine, heptamethoxymethylmelamine, hexamethinemethylmelamine, and in place of the above methoxy, ethoxy, propoxy, isopropoquine, butoxy, isobutoxy, sec-butoxy, Examples include those in which tertiary butoxy, pentyloxy, hexyloxy, heptyloxy, octyloxy, etc. are bonded. A mixture of these alkoxymethylmelamines or an alkoxymethylmelamine composed of two or more types of alkoxy groups may be used. Among these alkoxymethylmelamines, hexaalkoxymethylmelamine is preferred, and hexamethoxymethylmelamine is particularly preferred.

Alkoxymethyl melamine is polyacetal resin 100
0.01 to 10 parts by weight, preferably 0.1 parts by weight
It is used in a range of 5 parts by weight. If it is less than 0.01 part by weight, it will not be effective in preventing the occurrence of mold deposits;
If it exceeds 0 parts by weight, the thermal stability will be significantly lowered and mold deposits will occur, which is not preferable.

Alkoxymethylmelamine is produced by a conventionally known method. For example, by reacting melamine with formaldehyde,
Examples include a method of producing hexamethylolmelamine and then reacting it with excess methyl alcohol to obtain hexamethoxymethylmelamine.

In addition to visual judgment during actual injection molding, the criterion for mold deposit prevention ability is the amount of pyrolytic volatile matter, and the composition of the present invention usually has a pyrolytic volatile matter amount of 1200.
ppm or less.

If desired, the composition of the present invention may contain other heat stabilizers such as amide compounds, urea derivatives, polysaccharides, cellulose, etc., or those having a decomposing effect on the polyacetal resin, to the extent that the object of the present invention is not impaired. Low antioxidants, light stabilizers, lubricants, etc. may be added, and other additives other than glass fibers commonly used in polyacetal resins, such as inorganic light stabilizers, carbon fibers, pigments, and polymers. , lubricating oil, etc. may also be added.

〔Effect of the invention〕

According to the present invention, by blending alkoxymethyl melamine with polyacetal resin, the formation of mold deposits that adhere to the inside of the mold during molding such as injection molding can be significantly suppressed, and the productivity of molded products can be improved. At the same time, a polyacetal resin composition with excellent thermal stability can be easily obtained.

〔Example〕

EXAMPLES Next, the present invention will be explained in more detail with reference to examples, but the present invention is not limited to these examples in any way.

In addition, the characteristics of the resin composition were determined according to the following method.

(1) Generation of mold deposit (MD) Using an injection molding machine, the cylinder temperature is 200°C, the mold temperature is 70°C.
In the continuous injection molding operation of molded products with a length of 75mm, a width of 14mm, and a thickness of 2mm, a pin gate mold (no scrap removal) was used, and the surface of the molded product was glossy due to ~ID generation. The number of moldings was determined and evaluated until it started to disappear.

(2) Generation of Silver Streaks Using an injection molding machine, the composition was allowed to stay at a cylinder temperature of 230°C, and the critical residence time at which silver streaks caused by decomposed formaldehyde gas would occur on the molded product was determined and evaluated.

(3) Pyrolysis volatile content: Place 10 g of the sample into a cylindrical stainless steel container with an inner diameter of 50 mm and a depth of 50 mm. Place a stainless steel lid on top and seal it. Place this in a silicone oil bath at 200°C. After 180 minutes of immersion, the amount of volatile matter adhering to the stainless steel top lid was determined, and the amount of volatile matter [ppm] was determined by pyrolysis.
(w/w)).

In addition, the two lids should be kept at 25°C so that volatile matter may easily adhere to them.
Cooling water is passed through.

Examples 1 to 5, Comparative Examples 1 to 3 Polyacetal resin copolymer [MI 9.0 g/1
0 minutes, 190℃, 2.16kg)] 1100 weight and 2
．． Hexamethoxymethylmelamine was blended in various proportions into a mixture with 0.3 parts by weight of 2'-methylenebis(4-methyl-6-t-butylphenol) and granulated using an extruder to obtain a polyacetal resin composition. It was prepared, its properties were determined, and it was evaluated. The results are shown in Table 1.

As can be seen from Table 1, the mold deposit prevention ability of the composition containing a predetermined amount of hexamethoxymethylmelamine is excellent. If it is less than 0.01 part by weight, the ability to prevent mold deposits will be poor, and if it exceeds 10 parts by weight, the thermal stability will be significantly lowered and mold deposits will occur significantly.

Examples 6 to 7 Polyacetal resin compositions were prepared in the same manner as in Example 3, except that hexabutoxymethylmelamine and tetramethoxymethylmelamine were used instead of hexamethoxymethylmelamine in Example 3, and their properties were determined. The results are shown in Table 1. Each had excellent mold deposit prevention ability.

Example 8, Comparative Example 4 Homopolymer (M114g/
A polyacetal resin composition was prepared in the same manner as in Example 3 except that 190° C. for 10 minutes, 2.16 kg) was used, and its properties were determined. The results are shown in Table 1. Also,
Table 1 also shows the results without the addition of hexamethoxymethylmelamine. The mold deposit prevention ability was significantly superior to that without additives.

Comparative Examples 5-6 A polyacetal resin composition was prepared in the same manner as in Example 3, except that melamine and N-methylolated melamine were used instead of hexamethoxymethylmelamine in Example 3,
The characteristics were determined and the results are shown in Table 1. Melamine, N
- Both methylolated melamine and melamine had little effect on preventing mold deposits, and could not be put to practical use.

(Margin below)

Claims (1)

[Scope of Claims] 1. A mold deposit-preventing polyacetal resin composition, characterized in that 0.01 to 10 parts by weight of alkoxymethyl melamine represented by the following general formula (I) is added to 100 parts by weight of polyacetal resin. ▲There are mathematical formulas, chemical formulas, tables, etc.▼ (I) [In the formula, R_1 to R_6 represent a hydrogen atom or an alkoxymethyl group -CH_2OR'(R' is an alkyl group of C_1 to C_8), and at least two of R_1 to R_6 means an alkoxymethyl group. 2. The mold deposit-preventing polyacetal resin composition according to claim 1, wherein an alkoxymethyl melamine in which R_1 to R_6 of the alkoxymethyl melamine are all alkoxymethyl groups is added. 3. The mold deposit-preventing polyacetal resin composition according to claim 2, wherein hexamethoxymethylmelamine is added.