JP2001279053A - Polyacetal resin composition with good appearance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an acetal resin composition suitable for molding extrusion materials used for machined products of which good appearance is required. SOLUTION: This acetal resin composition is obtained by compounding an acetal resin with (a) 0.01-3 wt.%, based on the whole composition, of a melamine-formaldehyde polycondensate and (b) 0.1-5 wt.% of a low-molecular weight polyethylene resin.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polyacetal resin composition capable of forming a molded article having excellent appearance, and particularly to an extruded material used for a cut product requiring an appearance. It is intended to provide a polyacetal resin composition suitable for the above.

[0002]

2. Description of the Related Art Polyacetal resins have mechanical properties, heat resistance, chemical resistance, and the like.
Due to its excellent electrical and electronic properties and ease of molding, it is widely used in the fields of electric and electronic, automobiles, various machines, building materials, and functional goods.

[0003] Among the polyacetal resin products used in these fields, those produced in large quantities are mainly produced by injection molding, but large-sized parts and small varieties are obtained by solidification extrusion molding. It is generally produced by cutting a material such as a round bar or a plate-like molded product.

When these materials are formed by solidification extrusion, an annual ring-shaped ring pattern may be formed on the cross section of the material, or a whitened portion may be formed at the center. When a material having such a defective appearance is cut, the material is not only beautiful, but when the degree of the defective appearance is severe, the physical properties of the cut product are adversely affected. Therefore, a material that does not cause the above-described defective appearance is desired.

Japanese Patent Application Laid-Open No. 7-207117 discloses a polyoxymethylene resin composition having less defective appearance such as a whitened portion inside a molded product at the time of extrusion molding, wherein a sterically hindered phenol, polyolefin or There has been proposed a composition in which a copolymer of an olefin and a vinyl compound and a compound having an N-alkylalkoxy group are blended, and an improvement effect is also recognized, but the appearance is not sufficient.

[0006]

Means for Solving the Problems In view of the above problems, the present inventors have confirmed the effects of various substances. As a result, by using a polyacetal resin composition satisfying specific conditions, a polyacetal having excellent appearance was obtained. The present inventors have found that a resin molded product can be obtained, and have reached the present invention.

That is, according to the present invention, (a) 0.01 to 3% by weight of a melamine-formaldehyde polycondensate and (b) 0.1 to 5% by weight of a low molecular weight polyethylene resin are blended in a polyacetal resin as a ratio in the total composition. The present invention relates to a polyacetal resin composition comprising:

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the present invention will be described in detail.
Polyacetal resin used in the present invention is a polymer compound having an oxymethylene group (-CH ₂ O-) as the main constituent unit, a polyoxymethylene homopolymer, a copolymer containing a small amount of other constituent units in addition to oxymethylene groups (Including a block copolymer) or a terpolymer, and the molecule may have not only a linear but also a branched or crosslinked structure. There is no particular limitation on the degree of polymerization or the like.

[0009] The melamine used in the present invention (a)
Formaldehyde polycondensate is a polycondensate produced by polycondensing formaldehyde in an amount of 1.0 to 10.0 mol, preferably 1.0 to 3.0 mol, per mol of melamine by a known method. It may be insoluble or its structure may be reticulated. In addition, the carbon number is partially 1 to
The melamine may be etherified, or 50 mol% of the melamine may be substituted with another condensable substance such as dicyandiamide or benzoguanamine. Preferably, the produced melamine / formaldehyde polycondensate is insoluble in warm water, has an average degree of polymerization of 2 or more, and the average NH of the melamine repeating unit is not particularly limited, but is preferably 3.0 or more. The melamine / formaldehyde polycondensate (a) used in the present invention can be produced by a known method.
For example, melamine is added to an aqueous formaldehyde solution adjusted to pH 8 to 9, and the temperature is maintained at 60 to 90 ° C., and the mixture is dissolved and reacted with stirring. When the reaction progresses and the solution becomes cloudy, cool in an appropriate time. Then, the condensation reaction is stopped, and this is dried by a method such as spray drying to obtain a powder of a melamine-formaldehyde polycondensate.

The amount of the melamine-formaldehyde polycondensate (a) added and blended in the present invention is suitably 0.01 to 3% by weight in the total composition. This addition amount
If the amount is too small, a sufficient effect cannot be obtained. If the amount is too large, the mechanical strength tends to decrease, which is not preferable.

The (b) low-molecular-weight polyethylene resin used in the present invention is a low-polymer of ethylene, also called polyethylene wax, which is extremely low in molecular weight as compared with ordinary polyethylene. Low-molecular-weight polyethylene can be obtained by a method such as polymerization of ethylene, decomposition of high-molecular-weight polyethylene, and separation of low-polymer produced as a by-product during production of high-molecular-weight polyethylene.

The molecular weight of the low molecular weight polyethylene resin used in the present invention is suitably from 500 to 10,000. If the molecular weight is smaller than this range, bleeding out of the molded product or the like occurs, and the quality of the product is deteriorated and the value as a product is reduced. On the other hand, when the molecular weight is larger than this, the dispersibility in the polyacetal resin becomes poor, and the effect cannot be expected.

The low-molecular-weight polyethylene resin used in the present invention may be used in an amount of 0.1 to 0.1 in the total composition.
5% by weight is suitable. If this component is too small, no effect can be expected, and even if added unnecessarily, it is not only economically disadvantageous, but also extrudes and impairs processability such as molding,
Undesirable effects also occur on mechanical properties and thermal stability.

The polyacetal resin composition of the present invention comprises (a) an opaque melamine / formaldehyde polycondensate in the polyacetal resin, and (b) a low molecular weight polyethylene resin having a refractive index different from that of the polyacetal resin. The interaction of dispersing in the article keeps the brightness of the molded article uniformly high. For this reason, when molding a solidified extruded product, it is possible to obtain a molded product having an excellent appearance with few occurrences of differences in whiteness. More preferably, the composition is capable of forming a molded article having a lightness L value of 85 or more.

The evaluation of lightness used in the present invention is as follows.
Hunter La using a colorimetric colorimeter compliant with JIS Z-8722
bEvaluate using the L value of the color system. A 3 mm-thick flat plate is formed by injection molding on a sample used for measurement. If the lightness L value is less than 85, when a solidified extruded product is formed, when a portion having a difference in whiteness is generated, a defective appearance becomes unnoticeable, which is not preferable.

The polyacetal resin composition of the present invention comprises
Various known additives may be further blended according to the purpose.
Examples of the additives include various stabilizers, lubricants, release agents, nucleating agents, weathering stabilizers, antistatic agents, heterogeneous polymers, organic modifiers, and the like. In addition, as long as the performance of the resin material intended for the present invention is not significantly reduced, inorganic, organic,
One or two or more of fibrous or plate-like fillers such as metal or powdery or granular fillers can also be used. The method for preparing the polyacetal resin composition used in the polyacetal resin molded article of the present invention is not particularly limited, and can be easily prepared by a known facility and method generally used as a conventional resin composition preparation method.

For example, after mixing the respective components, kneading and extruding with an extruder to prepare pellets, and then molding, a method of once preparing pellets having different compositions, mixing a predetermined amount of the pellets, and molding. Any method can be used, such as a method of obtaining a molded article having the desired composition after the application. Further, mixing and adding a part of the resin component as a fine powder with the further component is a preferable method for uniformly blending these components. Further, a method of preparing a masterbatch having a high concentration of these compounds and adding the masterbatch to other pellets at the time of molding can also be used.

The polyacetal resin composition of the present invention can be used for extrusion molding to obtain a molded article having good lightness. In addition, injection molding, compression molding, vacuum molding, and foam molding can be used. It may be applied to any molding method.

The use of the polyacetal resin composition of the present invention is not only extrusion molding, but also injection molding, compression molding, vacuum molding, foam molding, etc., and secondary processing such as cutting.
Although it can be applied to all applications where a polyacetal resin is usually used, it can be particularly suitably used for applications where appearance is required.

[0020]

EXAMPLES The present invention will be described in more detail with reference to the following Examples, but it should not be construed that the present invention is limited thereto. Examples 1 to 4 Polyacetal resin ("Duracon" manufactured by Polyplastics Co., Ltd.) was added to (a) melamine / formaldehyde polycondensate in the amounts shown in Table 1, and (b) low molecular weight polyethylene resin (Sanyo Chemical Industries, Ltd.) ) Made “sun wax”)
After mixing using a blender, the mixture was melt-kneaded with a 30 mm twin screw extruder to obtain a pellet-shaped composition. Next, a test piece (50 mm × 70 mm × 3 mm) was formed from the pellet using an injection molding machine.
Thickness) was prepared, and the lightness was measured as described above. Using a 30 mm uniaxial solidification extruder, a round bar of φ140 was solidified and extruded from the pellet at an extrusion speed of 5 mm / min, a cross section was cut out, and the appearance was observed. Table 1 shows the results. Comparative Examples 1 to 4 For comparison, the same evaluation was carried out for a system not containing any of (a) and (b) as shown in Table 1 and for a system containing a compound not specified in the present invention. Was. Table 1 shows the results.

[0021]

[Table 1]

(A): melamine / formaldehyde polycondensate (a '): melamine (b) -1 prepared by a known method in which the number of moles of formaldehyde charged is 1.2 per mole of melamine. Low molecular weight polyethylene resin "Sunwax 151P" manufactured by Sanyo Chemical Industry Co., Ltd. (molecular weight approx.
2,000) (b) -2: Low molecular weight polyethylene resin “Sanwax 165P” manufactured by Sanyo Chemical Industries, Ltd. (molecular weight approx.
5,000) (b) ': Polyethylene resin "HIZEX" manufactured by Mitsui Petrochemical Industries, Ltd.

[0023]

As is evident from the above results, the molded article molded using the composition of the present invention has excellent appearance, especially in applications where polyacetal resins have been used conventionally. Can be widely used for applications where

Claims (3)

[Claims] 1. A polyacetal resin having the following composition: (a) 0.01% of melamine-formaldehyde polycondensate in the total composition;
(B) a polyacetal resin composition containing 0.1 to 5% by weight of a low molecular weight polyethylene resin; 2. The polyacetal resin composition according to claim 1, wherein (b) the low molecular weight polyethylene resin has a molecular weight in the range of 500 to 10,000. 3. The polyacetal resin composition according to claim 1, wherein the lightness L value is 85 or more when formed into a flat plate having a thickness of 3 mm.