JP3033993B2 - Mold deposit preventing polyacetal resin composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a novel anti-mold deposit polyacetal resin composition, more specifically, a precipitate formed in a mold during molding such as injection molding and blow molding. The present invention relates to a polyacetal resin composition in which the formation of a so-called mold deposit is significantly suppressed and the productivity of a molded product is improved.

[Conventional technology]

BACKGROUND ART In recent years, polyacetal resins have excellent strength properties, fatigue properties, and electrical properties, and have therefore been widely used in many fields such as electrical components, office equipment components, and building materials, and their demand has been increasing year by year.

This polyacetal resin is usually molded into a desired shape by injection molding or blow molding. At this time, a so-called mold deposit occurs on the surface of the mold, and this is transferred to the surface of the molded product. There is a disadvantage in that the material is remarkably deviated or the dimensional accuracy is reduced, and it is difficult to use as a component material requiring high dimensional accuracy such as a gear. In order to reduce such troubles as much as possible, the mold used for molding the polyacetal resin must be disassembled and cleaned every time it is used, but this consumes a great deal of time and inevitably reduces productivity. .

Various studies have been made 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 containing a polyamide resin, which has excellent thermal stability, but has a high thermal stability in a molding machine cylinder during molding. There is a problem that under the action of oxygen or oxygen, the color is changed to yellowish brown, or blackish brown sticking is attached to the screw. Further, Japanese Patent Publication No. 40-21148 discloses a polyacetal resin composition containing an amidine compound such as cyanoguanidine, benzoguanamine, or a melamine compound. The poor compatibility with the polyacetal resin causes the amidine compound to bleed out and cause mold deposits. In particular, mold deposit in a high-temperature mold is remarkable.

Japanese Patent Publication No. 55-50502 discloses a polyacetal resin composition containing a water-insoluble reticulated melamine / formaldehyde polycondensate, but when the composition is produced, an insoluble reticulated network is used. Finely pulverized condensate,
In addition, uniform mixing is required, and operability is a problem.

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

Japanese Patent Application No. 57-102943 discloses a polyacetal resin composition containing a ternary stabilizer comprising an amino resin prepolymerized product of an amino-substituted triazine and formaldehyde, a sterically hindered phenol and a metal-containing compound. Although disclosed, the composition is effective in short-time molding, but mold deposits occur in long-term continuous molding, which is a practical problem.

Further, Japanese Patent Application Laid-Open No. 2-80416 discloses a polyacetal resin composition obtained by heating and kneading a polyacetal polymer not subjected to terminal stabilization treatment and melamine as a stabilizer. A large amount of formaldehyde gas is generated during the production of the stabilizer, which is problematic in workability.

[Problems to be solved by the invention]

The present invention can significantly reduce the mold deposit generated in the mold in the molding of the polyacetal resin using the mold such as injection molding and blow molding, and can improve the quality and the productivity of the molded product. An object of the present invention is to provide a polyacetal resin composition having excellent properties.

[Means for solving the problem]

The present inventors have conducted intensive research to develop a polyacetal resin composition capable of preventing the occurrence of mold deposits in a mold, and as a result, achieved the object by blending alkoxymethylmelamine with the polyacetal resin. The inventors have found that the present invention can be performed, and have completed the present invention based on this finding.

That is, the present invention relates to an alkoxymethyl melamine of the following general formula (I) in an amount of 0.1 part by weight based on 100 parts by weight of a polyacetal resin.
An object of the present invention is to provide a polyacetal resin composition for injection molding or blow molding, which does not contain glass fiber, which is added in an amount of from 01 to 10 parts by weight.

Wherein, R ₁ to R ₆ represents a hydrogen atom or an alkoxymethyl group -CH ₂ OR '(R' is an alkyl group of C ₁ ~C _8), R ₁
At least two to R ₆ means an alkoxymethyl group. Hereinafter, the present invention will be described 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 is composed of repeating oxymethylene units CH ₂ O and can be produced by homopolymerizing formaldehyde or trioxane.

On the other hand, the polyacetal copolymer has a general formula in a chain composed of oxymethylene units. Wherein R ¹ and R ² are each a hydrogen atom, an alkyl group or an aryl group, which may be the same,
And n may be an integer of 2 to 6]. An oxyalkylene unit represented by the following formula is randomly introduced.

The content of the oxyalkylene unit in the copolymer is 0.05 to 50 per 100 mol of the oxymethylene unit.
Moles, preferably in the range of 0.1 to 20 moles. Examples of the oxyalkylene unit include an oxyethylene unit, an oxypropylene unit, an oxytrimethylene unit, an oxytetramethylene unit, an oxybutylene unit, and an oxyphenylethylene unit. Among these oxyethylene units, from the viewpoint of improving the physical properties of the polyacetal resin composition, oxyethylene units CH ₂ O) ₂ O and oxytetramethylene units CH
₂ O) ₄ O is particularly preferred.

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

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

Wherein, R ₁ to R ₆ represents a hydrogen atom or an alkoxymethyl group -CH ₂ OR '(R' is an alkyl group of C ₁ ~C _8), R ₁
At least two to R ₆ means an alkoxymethyl group. For example, dimethoxymethylmelamine, trimethoxymethylmelamine, tetramethoxymethylmelamine, heptamethoxymethylmelamine, hexamethoxymethylmelamine and ethoxy instead of methoxy, propoxy,
Isopropoxy, butoxy, isobutoxy, second butoxy, third butoxy, pentyloxy, hexyloxy,
Those to which heptyloxy, octyloxy and the like are bonded can be mentioned. A mixture of these alkoxymethylmelamines or an alkoxymethylmelamine consisting of two or more alkoxy groups may be used. Of these alkoxymethylmelamines, hexaalkoxymethylmelamine is preferred, and hexamethoxymethylmelamine is particularly preferred.

Alkoxymethylmelamine is a polyacetal resin 100
It is used in an amount of 0.01 to 10 parts by weight, preferably 0.1 to 5 parts by weight based on parts by weight. If the amount is less than 0.01 part by weight, there is no effect of preventing the generation of mold deposit, and if it exceeds 10 parts by weight, the thermal stability is remarkably reduced, and the mold deposit is undesirably generated.

Alkoxy methyl melamine is produced by a conventionally known method. For example, there is a method of reacting melamine with formaldehyde to produce hexamethylolmelamine, and then reacting with excess methyl alcohol to obtain hexamethoxymethylmelamine.

As a criterion for the ability to prevent mold deposit, in addition to visual judgment by actual injection molding, there is a pyrolysis volatile content, and the composition of the present invention usually has a thermal decomposition volatile content of 1200 pp.
m or less.

The composition of the present invention does not contain glass fibers, but, if desired, other heat stabilizers, such as amide compounds, urea derivatives, polysaccharides, cellulose, etc., or polyacetal as long as the object of the present invention is not impaired. Antioxidants with a low decomposing effect on the resin, light stabilizers, lubricants and the like may be added, and other additives other than glass fibers that are usually used in polyacetal resins, for example, inorganic fillers,
Carbon fibers, pigments, polymers, lubricating oils and the like can also be added.

〔The invention's effect〕

According to the present invention, by mixing alkoxymethylmelamine with a polyacetal resin, during molding such as injection molding, formation of a mold deposit adhering to a mold can be significantly suppressed, and productivity of a molded article can be improved. At the same time, a polyacetal resin composition having excellent thermal stability can be easily obtained.

〔Example〕

Next, the present invention will be described in more detail with reference to Examples.
The present invention is not limited in any way by these examples.

The properties of the resin composition were determined according to the following method.

(1) Generation of mold deposit (MD) An operation to continuously injection-mold a molded product with a length of 75 mm, a width of 14 mm and a thickness of 2 mm at a cylinder temperature of 200 ° C and a mold temperature of 70 ° C using an injection molding machine. In the above, the number of molded articles was obtained and evaluated until the surface of the molded article began to lose luster due to MD generation, using a pin gate mold (without degassing).

(2) Generation of Silver Streak The composition was retained at a cylinder temperature of 230 ° C. using an injection molding machine, and a limit residence time at which a silver streak due to decomposition formaldehyde gas was generated in a molded product was obtained and evaluated.

(3) Pyrolysis volatile content A 10 g sample is placed in a cylindrical stainless steel container with an inner diameter of 50 mm and a depth of 50 mm. A stainless steel lid is placed on the upper part, and the container is sealed. After immersion, the amount of volatiles adhering to the stainless steel upper lid 180 minutes later was determined and defined as the amount of pyrolysis volatiles [ppm (w / w)].

In addition, cooling water of 25 ° C. is passed through the upper lid so that volatile components easily adhere.

Examples 1-5, Comparative Examples 1-3 Polyacetal resin copolymer [MI 9.0 g / 10 min (190
° C, 2.16 kg)] 100 parts by weight and 2,2'-methylenebis (4-
(Methyl-6-t-butylphenol) in a mixture with 0.3 parts by weight of hexamethoxymethylmelamine in various ratios, and granulated by an extruder to prepare a polyacetal resin composition. . The results are shown in Table 1.

As can be seen from Table 1, the composition to which a predetermined amount of hexamethoxymethyl melamine is added has an excellent ability to prevent mold deposit. If the amount is less than 0.01 part by weight, the ability to prevent mold deposit is inferior, and if it exceeds 10 parts by weight, the thermal stability is remarkably reduced and mold deposits are remarkably generated.

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

Example 8, Comparative Example 4 As a polyacetal resin, a homopolymer (MI14g / 10
Min (190 ° C., 2.16 kg)], a polyacetal resin composition was prepared in the same manner as in Example 3, and its properties were determined. The results are shown in Table 1. Table 1 also shows the results without hexamethoxymethylmelamine. The mold-deposit preventing ability was remarkably excellent as compared with the case where no additive was added.

Comparative Examples 5-6 Except for using melamine and N-methylolated melamine instead of hexamethoxymethyl melamine of Example 3,
A polyacetal resin composition was prepared in the same manner as in Example 3, and its properties were determined. The results are shown in Table 1. Both melamine and N-methylolated melamine had little effect of preventing mold deposit, and were not practical.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁷ , DB name) C08L 59/00 C08K 5/3492

Claims (4)

(57) [Claims] 1. Prevention of mold deposit for injection molding or blow molding without glass fiber, characterized in that 0.01 to 10 parts by weight of alkoxymethyl melamine of the following general formula (I) is added to 100 parts by weight of polyacetal resin. Water-soluble polyacetal resin composition. Wherein, R ₁ to R ₆ represents a hydrogen atom or an alkoxymethyl group -CH ₂ OR '(R' is an alkyl group of C ₁ ~C _8), R ₁
At least two to R ₆ means an alkoxymethyl group. ] 2. A composition according to claim 1, wherein R _{1 to} R ₆ of the alkoxymethyl melamine are all alkoxymethyl groups. Or a blow molding mold deposit preventing polyacetal resin composition. 3. The polyacetal resin composition for injection molding or blow molding according to claim 2, wherein hexamethoxymethyl melamine is added to the composition. 4. A mold for injection molding or blow molding which does not contain glass fibers according to claim 1, wherein 0.1 to 5 parts by weight of alkoxymethylmelamine is added to 100 parts by weight of polyacetal resin. An anti-deposit polyacetal resin composition.