KR20030078999A - Polyoxymethylene resin composition - Google Patents

Abstract

PURPOSE: Provided is a polyoxymethylene resin composition, which has excellent wear resistance with maintaining the basic mechanical properties of the polyoxymethylene resin. CONSTITUTION: The polyoxymethylene resin composition comprises 100 parts by weight of a polyoxymethylene resin and 0.5 to 20 parts by weight of an ultra-high molecular weight polyethylene resin. In particular, the ultra-high molecular weight polyethylene resin has the number average molecular weight of 500,000 to 5,000,000 and the average particle diameter of 15 to 40 micrometers. Further, the composition has the tensile strength of 550 kg·cm/cm or more, impact strength of 7 kg·cm/cm or more, dynamic frictional coefficient of 0.5 or less, and specific wearing amount of 0.02 mm¬2/N·km or less.

Description

Polyoxymethylene resin composition

The present invention relates to a polyoxymethylene resin composition, and more particularly, to a polyoxymethylene resin composition which can be applied to various shapes of gears by improving wear resistance while maintaining mechanical properties of a polyoxymethylene material.

Polyoxymethylene resin is an engineering resin that has excellent mechanical properties, chemical properties such as chemical resistance and heat resistance, and balances properties, and is widely used in automobiles, machinery, electricity, and household goods. In addition, polyoxymethylene has the advantage of excellent wear resistance because it has a self-lubricating properties. However, in order to apply to the application which requires high self-lubrication property, the friction resistance and abrasion ability are insufficient, and the improvement of abrasion resistance is calculated | required.

In other words, the polyoxymethylene resin lacks abrasion resistance, and thus the coefficient of dynamic friction is high, so that the efficiency of power transmission of the gear may not be good. It is not possible to apply it where necessary.

Conventionally, a method of adding silicone oil has been introduced as a technique for improving the lubrication characteristics of polyoxymethylene resins (Japanese Patent Laid-Open No. 60-42449, Japanese Patent Application Laid-Open No. 1-204959), but there is a problem that mold contamination occurs due to silicone oil. . In addition, techniques for improving polyoxymethylene friction wear resistance include a method of adding a solid lubricant such as molybdenum disulfide and graphite, a method of adding a powdered and fibrous polytetrafluoroethylene resin, or a petroleum lubricant, an aliphatic alcohol or an ester thereof. Methods of adding lubricants are known. These known methods can satisfactorily improve the frictional wear characteristics, so that they can satisfy these requirements when sliding at low speed and low load, but the friction resistance is remarkably degraded when sliding at high speed and high load. there is a problem. In particular, when the polytetrafluoroethylene resin is added, there is a problem in that the friction resistance is excellent but the mechanical properties are poor. In addition, when lubricating agents such as petroleum lubricants, aliphatic alcohols or esters thereof are used, compatibility with polyoxymethylene resins is insufficient. Therefore, when the molding is carried out, the mold surface is moved to generate mold contaminants. There are problems such as instability, and there is a mismatch between mechanical properties, friction and wear resistance.

Accordingly, the present invention has excellent wear resistance even when sliding at high speed and high load while maintaining the mechanical properties of the polyoxymethylene resin in view of the above-mentioned problems of the prior art, which can be applied to various shapes of gears and the like. It is a technical subject to provide an oxymethylene resin composition.

In the study of the present inventors to solve the above problems, when the polyoxymethylene resin composition is molded for application to power transmission members such as gears, cams, clutches, guide rollers, etc., the tensile strength is 550Kg · cm / cm, impact strength 7 Kg · cm / cm, dynamic friction coefficient 0.5 level, specific wear amount should be 0.02㎣ / N · Km level, and polyoxymethylene is added to polyoxymethylene resin when very high molecular weight polyethylene component is added It has been found that the adhesion properties with the resin are very good, the original mechanical properties are maintained almost intact, the wear resistance is greatly improved, and all of the above properties can be satisfied.

1 is a view schematically showing a method of measuring a wear tester.

Therefore, according to this invention, the polyoxymethylene resin composition is provided with the polyoxymethylene resin composition containing 0.5-20 weight part of ultra high molecular weight polyethylene resins per 100 weight part of polyoxymethylene resins.

According to the present invention, the polyoxymethylene resin composition has a tensile strength of 550 Kg · cm / cm or more, an impact strength of 7 Kg · cm / cm or more, a dynamic friction coefficient of 0.5 or less, and a wear resistance of 0.02 ㎣ / N · Km or less. A polyoxymethylene resin composition is provided.

Hereinafter, the present invention will be described in more detail.

In the present composition, an oxymethylene homopolymer is used as the polyoxymethylene resin as the base resin, or an oxy containing at least one oxyalkylene unit having 2 to 8 carbon atoms in a polymer main chain composed of oxymethylene units. Methylene copolymers may be used, or mixtures thereof.

The oxymethylene homopolymer is preferably an oxymethylene homopolymer which is stabilized by replacing an unstable hydroxy group with an ester group or an ether group. Such oxymethylene homopolymers are polymerized by, for example, adding anhydrous formaldehyde in an organic solvent containing organic amines, organic or inorganic compounds, metal hydroxides and basic polymerization catalysts, washing the polymer and heating in the presence of sodium acetate. It can be prepared by acetylating the ends.

An example of a method for producing an oxymethylene copolymer will be described. First, at least one of trioxane, which is a cyclic oligomer of formaldehyde, and cyclic ether, which is a copolymerization component, is dissolved in cyclohexane or benzene. And a polymerization catalyst, for example, in the presence of at least one polymerization catalyst selected from the group consisting of boron trifluoride, boron trifluoride hydrate, and a coordination compound of boron trifluoride and an organic compound having an oxygen atom or a boron atom. Block polymerization and disassemble and remove unstable ends. The cyclic ether component, which is the aforementioned copolymer, is premixed with the polymerization catalyst and then introduced into a self-cleaning stirrer. And a deactivator is added to remove the catalytic activity in the polymer, and unstable end groups can be decomposed to prepare an oxymethylene copolymer.

The ultrahigh molecular weight polyethylene resin blended into the composition preferably has a number average molecular weight of 500,000 to 5,000,000, and an average particle size of 15 to 40 µm. Moreover, it is preferable that specific gravity is 0.91-0.98. The addition amount of the ultrahigh molecular weight polyethylene resin in this composition is 0.5-20 weight part per 100 weight part of polyoxymethylene resin, More preferably, it is 1-10 weight part. When the amount of the ultra high molecular weight polyethylene resin is less than 1 part by weight, the effect of the obtained composition is insignificant, and when it is more than 10 parts by weight, the mechanical properties of the polyoxymethylene resin may be adversely affected.

In addition, a well-known additive can also be mixed in this composition in the range which does not prevent the achievement of the objective of this invention. Examples of such additives are sterically hindered phenolic, phosphpy, thioether or amine antioxidants, benzophenone or sterically hindered amine weathering agents, formaldehyde scavengers (e.g. dimer oxypolyamides, melamines, guanamines) , Benzoguanamine, N-methylolated melamine, N-methylolated benzoguanamine, thermoplastic polyurethane resins, dicyandiamide, poly (N-vinylpyrrolidone), poly (2-vinylbilidine)), release agent ( Examples: fluorine-containing polymers, silicone oils, metal salts of stearyl acids, metal salts of montanic acid or montanic acid ester waxes, colorants (dyes or pigments), sunscreens (e.g. titanium oxide or carbon black), reinforcing agents (e.g. glass Fibers, carbon fibers or potassium titanate fibers), fillers (e.g. silica, clay, calcium carbonate, calcium sulfate or glass beads), nucleating agents (e.g. talc, clay), plasticizers, adhesion aids and pressure sensitive adhesives.

The polyoxymethylene resin composition obtained in the present invention requires excellent wear resistance with a tensile strength of 550 Kg · cm / cm or more, an impact strength of 7 Kg · cm / cm or more, a dynamic friction coefficient of 0.5 or less, and a specific wear amount of 0.02 ㎣ / N · Km or less. It can be used in molded products in the field In particular, it is suitable for use in power transmission members such as gears, cams, clutches, and guide rollers.

The properties of the polyoxymethylene resin was dried for 4 hours in a vacuum at 80 ℃ vacuum mixed ultra high molecular weight polyethylene resin and then introduced into a single screw or twin screw extruder, this was sufficiently melt kneaded at 190 ℃ temperature using an extruder Next, after discharging to the spaghetti through the die and cooled to cut by using a pelletizer (Pelletizer) to make a chip state, it was prepared and evaluated by the following method.

Mechanical properties: Using an injection molding machine with an injection capacity of 75 tons, ASTM dumbbell test specimens and Izod impact specimens are molded at a cylinder temperature of 190 ° C, a mold temperature of 80 ° C, and a molding cycle of 40 seconds. The tensile strength is measured according to the method of ASTM D638 using the above-mentioned tensile test specimen, the ASTM dumbbell test specimen, and the impact strength is measured according to the method of ASTM D256 using the Izod impact test specimen.

* Abrasion and friction characteristics: The test piece injected under the above injection conditions is 50N pressure and 30cm / sec linear speed for 30 minutes in a trust abrasion tester (manufactured by Toyo Seki Co., Ltd.) against metal (S45C) as a counter substance. The coefficient of dynamic friction and wear is measured while sliding. Briefly describing the evaluation method of the wear friction characteristics, as shown in FIG. 1, the wear tester is configured in such a way that the load and rotational speed can be varied by contacting the cylindrical specimen, and the cylindrical specimen has an inner diameter of 20 mm. This is 25 mm and the height is 15 mm. The lower specimen is to be rotated, and the upper specimen is fixed as a counterpart. Evaluation was made in the equipment prepared by the specimen as shown in the picture above and evaluated under specific conditions, and the result of the evaluation can obtain the coefficient of dynamic friction and wear.

Features and other advantages of the present invention as described above will become more apparent from the following examples. However, the present invention is not limited to the following examples.

<Examples 1-4 and Comparative Examples 1-2>

Polyoxymethylene resin (middle index 9 g / 10 min) [Kocetal K300: KTP Co., Ltd.] 100 parts by weight of the composition containing the ultra-high molecular weight polyethylene resin at a ratio as shown in Table 1 by the method described above Was prepared to measure the tensile strength, impact strength, coefficient of kinetic friction and wear. The measurement results are shown in Table 1 below. In Table 1, PE1 represents an ultra high molecular weight polyethylene resin having a molecular weight of 2 million, a specific gravity of 0.94, an apparent specific gravity of 0.4, and an average particle size of 30 μm, and PE2 represents an ultra high molecular weight of 2 million, a specific gravity of 0.94, an apparent specific gravity of 0.4 and an average particle size of 25 μm. The polyethylene resin is shown.

<Comparative Examples 2 to 8>

The same procedure as in Example 1 was repeated except that a known wear resistance improving additive was added in the ratio shown in Table 1 in place of the ultra high molecular weight polyethylene resin. The wear resistance improving additive AD1 in Table 1 represents high density polyethylene; AD2 is charged with terephthalic acid (or dimethyl terephthalate) (a) and 1,4-butanediol (b) poly (ethylene oxide) glycol (c) in a reaction vessel equipped with a rectification column and esterification under atmospheric or elevated pressure ( Or transesterification) followed by polymerization under atmospheric pressure or reduced pressure or terephthalic acid (or dimethyl terephthalate) (a) and 1,4-butanediol (b) poly (ethylene oxide) glycol (c) Polyether / ester copolymers prepared according to the method of addition to an oligomer followed by polymerization under atmospheric or reduced pressure; AD3 represents a polyethylene / methyl methacrylate copolymer prepared by adding a radical catalyst such as a peroxide to a polymer or monomer to form free radicals and then mixing the mixture with another polymer.

division Abrasion Resistance Improvement Additives Tensile Strength (㎏ · cm / ㎝) Impact strength (kgcm / cm) Dynamic friction coefficient Non-wear amount (㎣ / N · km) Kinds Content (parts by weight) Example One PE1 3 620 8.1 0.43 0.02 2 PE1 5 580 7.5 0.41 0.02 3 PE2 3 600 8.7 0.38 0.01 4 PE2 5 570 8.2 0.36 0.01 Comparative example One PE1 One 640 8.3 1.13 0.12 2 PE2 10 480 6.7 0.30 0.01 3 AD1 5 550 6.5 0.61 0.20 4 AD1 10 400 5.8 0.42 0.13 5 AD2 10 560 9.8 0.38 0.11 6 AD2 20 460 12.3 0.32 0.08 7 AD3 3 570 5.9 0.77 0.02 8 AD3 5 530 5.1 0.54 0.01

As can be seen from the results of Table 1, in the case of Comparative Examples 1 to 8, at least one of the above characteristics is insufficient, and thus it is not suitable to be applied to molded products such as gears requiring wear resistance, but polyoxy according to the present invention. The methylene resin composition has a tensile strength of 550 Kg · cm / cm or more, an impact strength of 7 Kg · cm / cm or more, a dynamic friction coefficient of 0.5 or less, and a wear resistance of 0.02 ㎣ / N · Km or less. It can be seen that it shows useful properties.

Claims (3)

Polyoxymethylene resin composition WHEREIN: The polyoxymethylene resin composition containing 0.5-20 weight part of ultra high molecular weight polyethylene resins per 100 weight part of polyoxymethylene resins. The polyoxymethylene resin composition according to claim 1, wherein the ultra high molecular weight polyethylene resin has a number average molecular weight of 500,000 to 5,000,000, and an average particle size of 15 to 40 µm. In the polyoxymethylene resin composition, polyoxymethylene having a tensile strength of 550 Kg · cm / cm or more, impact strength of 7 Kg · cm / cm or more, a dynamic friction coefficient of 0.5 or less, and abrasion amount of 0.02 dl / N · Km or less Resin composition.