JPH0121181B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a polyoxymethylene composition with excellent weather resistance. Polyoxymethylene is a resin widely used in automobiles, machinery, and electrical parts because of its excellent mechanical strength, fatigue resistance, and self-lubricating properties. However, polyoxymethylene has poor weather resistance, and when used outdoors for a long time, it has the disadvantage that its appearance deteriorates due to a decrease in mechanical strength, the occurrence of cracks, whitening of the surface, etc. Therefore, in the field of outdoor use such as automobile exterior parts and agricultural equipment, there is a strong demand for improved weather resistance of polyoxymethylene. Conventionally, as a method for improving the weather resistance of polyoxymethylene, one of the following three methods has been used to color polyoxymethylene with carbon black. The first is the colored pellet method, in which resin pellets and carbon black are mixed and kneaded using an extruder, the second is the masterbatch method, in which the resin mixed with a large amount of carbon black is diluted with natural pellets, and the third is the colored pellet method. This is a dry color method in which a dry blend of natural polyoxymethylene pellets and carbon black is directly molded. However, molded products obtained by any of these three methods do not satisfy the severe weather resistance required for automobile exterior parts and the like. There are also proposals for a polyoxymethylene composition containing carbon black and an acid acceptor, in which the particle size of the carbon black is 30 microns or less (Japanese Patent Publication No. 46-21451, Japanese Patent Publication No. 17865-1972).
I still can't say it's enough. As a result of extensive research, the present inventors have discovered that a carbon black-containing polyoxymethylene composition with excellent weather resistance can be obtained by using powdered polyoxymethylene, and have completed the present invention. Surprisingly, it has also been found that the impact strength of the polyoxymethylene composition is significantly better than that of polyoxymethylene kneaded with carbon black using commercially available polyoxymethylene pellets. That is, the present invention is made by mixing powdered polyoxymethylene with an average particle size of 1 mm or less with 0.1 part by weight or more of carbon black having a particle size of 10 to 50 mμ per 100 parts by weight of the polyoxymethylene, and uniformly dispersing the mixture. This is a characteristic polyoxymethylene composition. The polyoxymethylene used in the present invention is a polyoxymethylene homopolymer or a polyoxymethylene copolymer in which most of the main chain is composed of oxymethylene chains, and specifically, formaldehyde or trioxane, which is a cyclic oligomer of formaldehyde, Tetraoxane etc. alone,
Further, one or more comonomers copolymerizable with these (for example, ethylene oxide, 1,4-butanediol formal, etc.) are further combined,
It refers to a product obtained by polymerization or copolymerization that is stabilized against decomposition from the terminal group. In use, customary heat stabilizers, antioxidants and known additives can be added, and the addition of different polymers is also permissible. It is also possible to use polyoxymethylene that has been kneaded with a stabilizer and then ground. The polyoxymethylene powder must have an average particle size of 1 mm or less, preferably 0.5 mm or less; polyoxymethylene powder with an average particle size larger than 1 mm will not provide a composition with excellent weather resistance. The carbon black used in the present invention is carbon black manufactured by the furnace method, channel method, or acetylene method, and has a particle size of 10 to 50 mμ.
It is within the range of . If the particle size is less than 10 mμ or more than 50 mμ, a composition with excellent weather resistance cannot be obtained. The amount of carbon black added is 0.1 to 10 parts by weight, preferably 0.2 to 6 parts by weight, per 100 parts by weight of polyoxymethylene. If the amount is less than 0.1 part by weight, a composition with excellent weather resistance cannot be obtained, and if it exceeds 10 parts by weight, the thermal stability and mechanical strength will be poor and it is not practical. The polyoxymethylene composition of the present invention is obtained by mixing and melting the above-described powdered polyoxymethylene, carbon black, and optionally a heat stabilizer and other additives. Specifically, the above-mentioned mixture is mixed using a known mixer such as a high-speed mixer such as a Henschel mixer or a tumble mixer, and then polyoxymethylene and carbon black are melt-mixed using an extruder or the like.
For extruders and the like, it is necessary to ensure that there is no resin retention area and to take sufficient consideration to the rise in resin temperature due to frictional heat. Also, Banbury mixer,
It is also possible to use a mixer capable of melt mixing, such as a kneader. The polyoxymethylene composition of the present invention thus prepared satisfies the severe weather resistance required for automobile exterior parts. In the present invention, by having the above-described structure, the dispersibility of carbon black becomes extremely good. This dispersion effect is particularly pronounced in the case of polyoxymethylene, a highly crystalline resin such as the present invention, compared to other resins such as polyethylene and vinyl chloride. This dispersion state is determined by the amount of carbon black in a sample/ ^mm2 cut to 2 μm (thickness) with a microtome in the direction perpendicular to the flow direction of the extruded pellets.
It can be expressed as the number of aggregates of 10 μm or more. For example, the number of aggregates in Example 2 (average polyoxymethylene particle size 0.3 mm) and Comparative Example 1 (approximately 3 mm), which will be described later, are 2 and 20, respectively, indicating a 10-fold improvement, but the same Under these conditions, in the case of polyethylene (Santech DL6810 manufactured by Asahi Kasei (MI 10 g/10 min)), the results were 7 and 10, respectively, an improvement of only about 1.4 times. This specific improvement in the dispersion state is unexpected, and it is possible to achieve sufficient dispersion even under mild melt-kneading conditions, making it possible to prevent the thermal decomposition of polyoxymethylene, which has strong thermal decomposition properties As described above, it is possible to obtain a polyoxymethylene composition with extremely excellent weather resistance and impact resistance. The present invention will be described below with reference to Examples.
It is not limited to these. Example 1 End-stabilized polyoxymethylene homopolymer powder with an average particle size of 0.12 mm (MI approximately 12 g/10 min)
To 100 parts by weight, 0.5 parts by weight of 6/66/610 ternary copolymer polyamide and 0.25 parts by weight of Irganox 1010 manufactured by Ciba Geigy were added as heat stabilizers, and carbon black manufactured by Columbian Carbon was added.
Add 0.4 parts by weight of Raven 1500. 10 kg of the polyoxymethylene, heat stabilizer, antioxidant, and carbon black mixture were mixed in a Henschel mixer (manufactured by Mitsui Miike Seisakusho, internal volume 75) at a rotational speed of 820 rpm for 3 minutes at room temperature. The mixture was processed using a L/D=32 50 mm pent-type single screw extruder manufactured by Tanabe Plastics Co., Ltd., at a cylinder temperature of 200°C and a screw rotation speed of 120 r.pm.
Melt and mix under the following conditions. Using the polyoxymethylene molding material, a molded piece for testing is molded using an injection molding machine (N70A manufactured by Japan Steel Works). The composition formulation and carbon black particle size are shown in Table 1, and the properties and weather resistance of the composition are shown in Tables 2 and 3. The composition has excellent weather resistance and falling weight impact strength.
This is superior to Comparative Example 1 in which the polyoxymethylene powder and the heat stabilizer were made into a melt-mixed composition and then again made into a melt-mixed composition with carbon black. Furthermore, the weather resistance satisfies the requirements for automotive exterior parts. Comparative Example 1 Polyoxymethylene homopolymer powder (MI approx.
To 100 parts by weight (12 g/10 minutes), 0.5 parts by weight of 6/66/610 terpolymer polyamide as a heat stabilizer and 0.25 parts by weight of Irganox 1010 manufactured by Ciba Geigy were added to 100 parts by weight of the same compound as in Example 1. Mix with a shell mixer at 820 rpm for 3 minutes at room temperature. Using the same 50 mm extruder manufactured by Tanabe Plastics Co., Ltd. as in Example 1, this mixture was heated at a cylinder temperature of
Melt and mix at 200℃ and screw rotation speed 120rpm. After drying the thus obtained cylindrical polymer with a diameter of 2.5 m and a length of 4 mm at 80°C for 3 hours, 0.4 parts by weight of carbon black was added and mixed under the same conditions in the Henschel mixer. ,
This is melt-mixed again under the same conditions in the extruder.
The polyoxymethylene pellets thus obtained were molded into test pieces of the same shape using an injection molding machine (N70A manufactured by Japan Steel Works) under the same conditions as in Example 1. The composition formulation and carbon black particle size are shown in Table 1.
The physical properties and weather resistance of the composition are shown in Tables 2 and 3. Example 2 Polyoxymethylene homopolymer powder MI approximately 12
g/10 minutes), 0.5 parts by weight of 6/66/610 ternary copolymer polyamide as a heat stabilizer and 0.25 parts by weight of Irganox 1010 manufactured by Ciba Geigy were added to 100 parts by weight, and the mixture was melt-kneaded to form a sphere with an average diameter of 3 mm. Polyoxymethylene (the polyoxymethylene is commercially available as Tenac 5010 manufactured by Asahi Kasei Corporation) is used in an atomizer-type pulverizer to obtain a pulverized polymer having an average particle size of 0.3 mm. Add 0.4 parts by weight of Raven 1500 to this pulverized polymer,
A polyoxymethylene composition is obtained by the method described in Example 1. The formulation of the composition is shown in Table 1, and the physical properties and weather resistance are shown in Table 2. This composition has excellent weather resistance compared to Comparative Example 1. Example 3 The same Tenac 5010 as in Example 2 was ground to obtain a ground polymer with an average particle size of 0.5 mm. Example 1 0.4 parts by weight of Raven 1500 was added to this pulverized polymer.
A polyoxymethylene composition is obtained by the method described.
The formulation of the composition is shown in Table 1, and the physical properties and weather resistance are shown in Tables 2 and 3.
Shown below. Compared to Comparative Example 1, it has excellent weather resistance and falling weight impact strength. Moreover, it satisfies the weather resistance required for automobile exterior parts and the like. Examples 4 to 10 A heat stabilizer and 0.4 parts by weight of carbon black were added to an end-stabilized polyoxymethylene homopolymer powder (MI about 12 g/10 min) with an average particle size of 0.12 mm, and the method described in Example 1 was carried out. to obtain the composition. Table 4 shows the carbon black properties, formulation, thermal stability, falling weight impact strength, and weather resistance of these compositions. These compositions have better weather resistance than Comparative Examples 2 to 8, which are compositions of the same composition in which polyoxymethylene is melt-mixed with a heat stabilizer, pelletized, and then the pellets and carbon black are melt-mixed. Excellent falling weight impact strength. Comparative Examples 2 to 8 Polyoxymethylene homopolymer powder (MI approx.
To 100 parts by weight (12 g/10 minutes), 0.5 parts by weight of 6/66/610 ternary copolymer polyamide as a heat stabilizer and 0.25 parts by weight of Irganox 1010 manufactured by Ciba Geigy were added to 100 parts by weight of Henschel, the same as in Example 1. Mix with a mixer at 820 rpm for 3 minutes at room temperature. This mixture was prepared using the same 50 mm extruder manufactured by Tanabe Plastics Co., Ltd. as in Example 1, and the cylinder temperature was 200°C.
Melt and mix at a screw rotation speed of 120 rpm. The diameter obtained in this way is 2.5 mm and the length is 4.
After drying a cylindrical polymer of mm size at 80°C for 3 hours, carbon black was added in the amount shown in Table 4, mixed in the Henschel mixer under the same conditions, and then mixed in the extruder under the same conditions. Melt and mix again. The polyoxymethylene pellets thus obtained were molded into test pieces of the same shape using an injection molding machine (N70A manufactured by Japan Steel Works) under the same conditions as in Example 1. Table 4 shows the carbon black properties, formulation, thermal stability, falling weight impact strength, and weather resistance of these compositions. Table 5 shows the relationship between standard weather meter weather resistance time and tensile strength and elongation.

[Table] * Terminal-stabilized polyoxymethylene powder and stabilizer were melt-mixed and crushed into pellets using an extruder, and then carbon black was added and melt-mixed again (excluding Example 1).

【table】

【table】

【table】

【table】

[Table] Example 11 Using the method described in Example 2, the
(Manufactured by Polyplastics Co., Ltd. MI9g/10
) to obtain a pulverized product with an average particle size of 0.3 mm.
1.0 parts by weight of Denka Black powder (manufactured by Denki Kagaku Kogyo Co., Ltd.) is added to this pulverized polymer, and a composition is obtained by the method described in Example 1. Table 5 shows the carbon black properties of this composition and the weather resistance of the composition. This composition has excellent weather resistance compared to Comparative Example 9, which uses Diuracon M90-02 pellets and has the same composition.

【table】

Claims (1)

[Scope of Claims] 1. Carbon black having a particle size of 10 to 50 mμ is mixed with powdered polyoxymethylene having an average particle size of 1 mm or less and 0.1 part by weight or more per 100 parts by weight of the polyoxymethylene, and the mixture is uniformly dispersed. A polyoxymethylene composition characterized by: 2. The polyoxymethylene composition according to claim 1, wherein the weight ratio of carbon black to powdered polyoxymethylene is 0.1 to 10 parts by weight per 100 parts by weight of powdered polyoxymethylene. 3. The polyoxymethylene composition according to claim 1 or 2, wherein the powder polyoxymethylene particle size is 0.5 mm or less.