JPH0778156B2 - Acetal resin composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention provides a mold release during injection molding without substantially impairing the mechanical properties, thermal stability and appearance of a molded article originally possessed by an acetal resin. The present invention relates to an acetal resin composition having extremely improved properties.

[Conventional technology]

Acetal resin has well-balanced mechanical properties, excellent friction and wear resistance, excellent heat resistance, etc., and also has excellent fluidity. It is often a mechanical component or precision mechanical component, and such a complicated structure has, for example, a thick-walled portion, a thin-walled portion, and further, an ultra-thin-walled portion intertwined with each other, and a hollow cylindrical protrusion or the like. In many cases, it is a small part having a shape such as having a shape, and having a weight of several grams to at most several tens of grams.

In the case of a molded product with such a complicated shape, the ejection of the molded product must be as smooth as possible, and if the product is ejected and released with an excessively strong force, the product will be damaged or the molding distortion will occur. Therefore, it is very desirable to improve the releasability, since the result is that the product is stored inside the product and the effect is bad and the product is exposed during long-term use.

[Conventional technology]

Several proposals for improvement of releasability have been made so far,
For example, in JP-B-44-7544, it is possible to add an acetal resin to a low molecular weight hydrocarbon, and JP-B-45-31020.
It is proposed that the higher fatty acid amide be added to the acetal resin.

[Problems to be solved by the invention]

However, the releasing effect in these known techniques is
It does not always meet the market demand, and further improvement in releasability has been desired.

[Means for solving problems]

In view of these shortcomings of the prior art, the present inventors have found as a result of earnest research that when a low-molecular-weight hydrocarbon and a higher fatty acid amide, which are poor in effect alone, are used in combination, a remarkable synergistic effect is exhibited. Reached

That is, the present invention is an acetal resin composition obtained by adding a low molecular weight hydrocarbon having a molecular weight of 200 to 1800 and a higher fatty acid amide having a carbon number of 7 to 24 to an acetal resin.

The low molecular weight hydrocarbon having a molecular weight of 200 to 1800 used in the composition of the present invention is generally called petroleum paraffin, while the higher fatty acid amide having a carbon number of 7 to 24 has a carbon number of 7 to 24. Among the compounds of higher fatty acids and aliphatic amines, ethylene bis stearoamide, stearic acid amide, behenic acid amide and oleic acid amide are particularly preferable.

The addition amount of the low molecular weight hydrocarbon and the higher fatty acid amide to the acetal resin is 0.02 to 1.00 parts by weight with respect to 100 parts by weight of the acetal resin, and the total amount is 0.04.
A range of up to 1.02 parts by weight is suitable. If the amount is less than these lower limits, the effect is practically insufficient, whereas if the amount exceeds the upper limit, the thermal stability and the molding appearance (color tone) are deteriorated among the original properties of the acetal resin.

The acetal resin used in the composition of the present invention refers to a formaldehyde monomer or a trimer (trioxane) or tetramer (tetraoxane) thereof, which is produced from a cyclic oligomer as a raw material. Oxymethylene homopolymer consisting of, and the above raw materials and ethylene oxide, propylene oxide, epichlorohydrin, 1,3-dioxolane, 1,3-dioxepane,
An oxymethylene copolymer containing 0.1 to 20% by weight of an oxyalkylene unit having 2 to 8 carbon atoms, which is produced from a cyclic ether such as glycol formal or diglycol formal.

The composition of the present invention may further contain heat stabilizers, antioxidants, ultraviolet absorbers, pigments, fillers, glass fibers, carbon fibers and other known additives.

Although various methods for producing the acetal resin composition of the present invention can be adopted, it is essential to mix or melt-knead each component.

As an apparatus used for melt-kneading, a general kneading machine such as various extruders, kneaders, Banbury mixers, mixing rolls, etc. is used, and the kneading method at that time is a gentle kneading method such as a V-shaped blender. Mixing device or dry blending with a high-speed fluidized mixing device such as a Henschel mixer, or mixing with stirring in a state of solution, emulsion, suspension, etc., and then drying the resulting mixture is charged into the above kneader. Method, a method of adding a low molecular weight hydrocarbon and higher fatty acid amide to a homogeneous melted acetal resin composition by the above kneader, dry pelletized acetal resin composition and low molecular weight hydrocarbon and higher fatty acid amide There is a method of directly supplying the blended mixture to a molding machine.

The temperature of the melt-kneading is appropriately selected according to various conditions such as the type of acetal resin to be used, the function of the mixing and kneading device, and the purpose, but the temperature range of the melting point of the acetal resin or higher and the decomposition temperature or lower and the decomposition temperature of various additives or lower And in general
175-230 ° C is suitable.

[Operation and effect of the invention]

In the composition of the present invention, it is not clear why low molecular weight hydrocarbons and higher fatty acid amides, which show only a dilute effect by themselves, bring about excellent effects. It is speculated that, as a result of the more appropriate compatibility, it is necessary to form a kind of layer that can be easily released at the interface between the mold cavity surface and the resin.

〔Example〕

Next, the present invention will be described in more detail with reference to Examples and Comparative Examples.

In addition, in the following description, the intrinsic viscosity [η] is in p-chlorophenol to which 2% by weight of α-pinene is added.
The value measured at 60 ° C. is shown, and the addition amount [phr] is parts by weight per 100 parts by weight of the acetal resin.

Each test in Table 2 was conducted by the following method.

Releasing force Molded product shape: Height 27 mm, outer diameter 34 mm, thickness 2 mm Low cylinder type Releasing force: Sensitive from the sensor connected to the protruding pin located at the center of the cylindrical bottom Releasing force measuring sensor: (stock ) Techno plus manufactured by molding conditions: injection molding machine; Toshiba Ltd. IS-90B injection pressure: 800 kg / cm ² mold temperature; 60 ° C. ratio: ratio initial color tone of the release force to release force of example 1 Color difference meter: Hunter color difference meter (manufactured by Suga Test Instruments Co., Ltd.) Color of molded product before release agent added = L ₁ , a ₁ , b ₁ Color of molded product after release agent added = L ₁ , a ₁ , b ₁ Calculation formula: Judgment Criteria: ◎; △ E = 0 to 1 ○; △ E = 1 over to 2 △; △ E = over 2 to 3 ×; △ E = over 3 to 4 Residence color tone color difference meter: Hunter color difference meter (Co., Ltd.) manufactured by Suga test Instruments Co.) injection molding machine: Meiki Ltd. SJ-35A residence conditions: material temperature; 235 ° C. the residence time; before dwell 60 minutes moldings color _{= L 3, a 3, b} 3 residence after the molded product color = L ₄ , a ₄ , b ₄ calculation formula: Judgment criteria: ◎; △ E = 0 to 4 ○; △ E = over 4 to 6 △; △ E = over 6 to 8 ×; △ E = over 8 to 10 Thermal stability Equipment used: Shimadzu Corporation DT-30 test: Pyrolysis rate in air at 222 ℃, Tensile impact strength Test piece molding conditions: Molding machine; SJ-35A made by Meiki Seisakusho Material temperature; 200 ℃ Injection pressure; 500kg / cm ² Mold temperature; 80 ° C. Examples 1 to 9 and Comparative Examples 1 to 2 [η] = 1.4 dl / g, acetal resin which is an oxymethylene copolymer containing 2.5% by weight of a copolymer derived from ethylene oxide, and a thermal oxidation stabilizer. Melamine 0.2 phr, sterically hindered phenol (Irganox 1010 manufactured by Ciba-Gayky) 0.4 phr and magnesium hydroxide
An acetal resin composition containing 0.1 phr and the types and amounts of low molecular weight hydrocarbons and higher fatty acid amides listed in Table 1 was prepared using a vented twin screw extruder with L / D = 30 and a diameter of 50 mm. .

For the obtained sample, the releasing force, the appearance (color tone) of the molded product,
The thermal stability and tensile impact strength were measured and the results are shown in Table 2 as Examples 1-9.

For comparison, Tables 1 and 2 show Comparative Examples 1 and 2 in which one of the low molecular weight hydrocarbon and the higher fatty acid amide was not added and the results thereof.

Example 10 [η] = 1.4 dl / g in an oxymethylene copolymer containing 2.5% by weight of copolymerized units derived from ethylene oxide, 0.2 melamine as a thermal oxidation stabilizer, and a sterically hindered phenol (Ciba-Gayky) Company Irganox 10
10) A stabilized acetal resin composition in the form of pellets obtained by adding 0.4 phr and 0.1 phr of magnesium hydroxide, together with low molecular weight hydrocarbons and higher fatty acid amides of the types and amounts shown in Table 1, in a Hensiel mixer ( Mitsui Miike Co., Ltd.
(Made by Mfg. Co., Ltd.) and mixed at high speed, and then melt-kneaded using a twin-screw extruder with a vent having an L / D = 30 and a diameter of 50 mm to obtain an acetal resin composition.

The same test as in Example 1 was performed on the obtained sample, and the result is shown in Table 2 as Example 10.

Example 11 and Comparative Examples 3 to 4, except that the acetal resin is an oxymethylene copolymer containing 3.5 wt% of [η] = 1.4 dl / g of copolymerized units derived from 1,3-dioxepane. The same procedure as in Example 1 was carried out, and the result is shown in Table 2 as Example 11.

For comparison, Tables 1 and 2 show Comparative Examples 3 to 4 in which no low molecular weight hydrocarbon or higher fatty acid amide was added and the results thereof.

Example 12 and Comparative Examples 5-6 The same procedure as in Example 1 was carried out except that the acetal resin was an oxymethylene homopolymer in which the terminal hydroxyl group was acetylated with acetic anhydride, with [η] = 1.3 dl / g. The results are shown in Table 2 as Example 12.

For comparison, Tables 1 and 2 show Comparative Examples 5 and 6 as examples and the results when neither low molecular weight hydrocarbons nor higher fatty acid amides were added.

Claims (2)

[Claims] 1. An acetal resin composition obtained by adding a low molecular weight hydrocarbon having a molecular weight of 200 to 1800 and a higher fatty acid amide having a carbon number of 7 to 24 to an acetal resin. 2. The low molecular weight hydrocarbon and the higher fatty acid amide are added individually in an amount of 0.02 to 1.00 parts by weight with respect to 100 parts by weight of the acetal resin, and the total amount added is 0.04 to 1.02.
The acetal resin composition according to claim (1), which is parts by weight.