JPS5928345B2 - rotating member - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a rotating member with excellent dimensional accuracy.

More specifically, the present invention is mainly made of polybutylene terephthalate resin, has high dimensional accuracy, and is free from uneven rotation.
It relates to rotating members such as gears, rollers, and cams with little surface wobbling or eccentricity. Polybutylene terephthalate resin has excellent mechanical properties, thermal properties, chemical resistance, self-lubricating properties, etc., so it has been used in large quantities as mechanical parts in recent years.

However, when continuously molding small rotating parts such as watch gears by injection molding from polybutylene terephthalate resin, despite the same molding conditions,
There is a problem that a considerably large dimensional difference occurs between the molded products obtained, and the yield of practically usable molded products is low. It is noticeable when molding. For this reason, although polybutylene terephthalate resin has the above-mentioned excellent properties, it has been difficult to use it for rotating parts of precision instruments that require molded products with high precision and the same dimensions. In addition, methods to improve the dimensional stability of thermoplastic resin injection molded products include optimizing injection conditions such as temperature settings, cooling time, and injection speed for the cylinder and mold of the injection molding machine, and methods for optimizing the injection conditions such as the mold gate position. Methods for optimizing the dimensional accuracy have long been known, but when molding rotating parts from polybutylene terephthalate resin, no matter which method is adopted, it is not possible to obtain a molded product with a high degree of dimensional accuracy. . Therefore, the inventors of the present invention conducted intensive studies to obtain rotating members with small dimensional variations from polybutylene terephthalate resin in a high yield. As a result, they used a relatively low molecular weight polybutylene terephthalate resin and blended it with a specific wax. The inventors have discovered that by doing so, the dimensional stability of rotating members, which are generally circular molded products, can be dramatically improved, and the present invention has been achieved.

That is, the present invention provides a rotating member formed by molding a mixture of polybutylene terephthalate resin having a relative viscosity of 1.3 to 1.75 and 0.01 to 0.7% by weight of a montan wax metal salt derivative that is solid at room temperature. This is what we provide.

Conventionally, it is well known that fatty acid derivatives, which are the main components of wax, are blended into polyester resins. Carbon number 2
A technique of adding fatty acid esters or fatty acid salts of 6 to 32 is described, but since the dimensional accuracy of injection molded products made of polyethylene terephthalate resin is significantly lower than that of polybutylene terephthalate resin, this technique It is not possible to obtain the effect of improving the dimensional accuracy of polyethylene terephthalate resin0 Moreover, polyethylene terephthalate resin molded products generally have low mechanical strength,
It is difficult to use it as a rotating member such as a gear for transmitting a large force. Also, Japanese Patent Publication No. 47-48894 and Japanese Patent Application Laid-open No. 78647-1987 disclose methods for improving the mold release properties of polybutylene terephthalate resin. For this purpose, techniques for blending fatty acid esters and fatty acid salts have been described.
The fatty acid derivative used here has a lower number of carbon atoms than the fatty acid derivative that is the main component of ordinary wax, and therefore cannot obtain the effect of improving the dimensional accuracy of the molded product.

In this way, in the conventional example described above, the technical philosophy of Ryoni is completely different in that the single component that makes up ordinary wax is blended into polyester resin to improve the mold release properties of the polyester resin. It is.

The polybutylene terephthalate resin used in the present invention is essentially a resin formed by polycondensing terephthalic acid or a terephthalic acid derivative with butanediol, but some of the acid components are made from isophthalic acid, adipic acid, and sebacic acid. and other dicarboxylic acids such as ethylene glycol, hexamethylene glycol, decamethylene glycol, polymethylene glycol, polytetramethylene glycol, and dicarboxylic acids such as dicarboxylic acids such as ethylene glycol hexamethylene glycol, decamethylene glycol, polymethylene glycol, polytetramethylene glycol, and dicarboxylic acids. include.

Such polybutylene terephthalate resin is an orthochlorophenol solution of 100T! 0.5gr concentration per 11,
Relative viscosity is 1.30 to 1.75 when measured at 25°C
If the relative viscosity of the polybutylene terephthalate resin is less than 1.30, the mechanical strength of the resulting rotating member will be too low. This is not preferable because the dimensional stability is significantly reduced.

The montan wax metal salt derivative (hereinafter referred to as wax) used in the present invention is, for example, montan wax, which is a hard wax that is solid at room temperature obtained by distilling asphaltic cutlet charcoal at high temperature or extracting it with a solvent, or its ester. Alkali metals such as sodium and potassium or calcium,
It is partially or completely modified into the form of metal salts of alkaline earth metals such as magnesium and barium.

A representative example of this montan wax metal salt derivative is Hoechst Wax 0p manufactured by Hoechst, which can be easily obtained and used. 0.
01 to 0.7% by weight, preferably 0.05 to 0.7% by weight; if the amount added is 1% by weight or more, it will result in a decrease in the heat resistance and mechanical properties of the molded product, which is undesirable. In addition to the above-mentioned polybutylene terephthalate resin and wax, the rotating member of the present invention may optionally include inorganic powders such as talc, clay, and titanium dioxide, reinforcing agents such as glass fiber and glass beads, ethylene bisstearylamide, and polysiloxane. mold release agents, metal soaps, plasticizers such as fatty acid esters, flame retardants, antistatic agents, heat stabilizers, pigments, or known resins other than polybutylene terphthalate such as polyethylene, polypropylene, EVA,
30 weight polyolefin resins such as EVA modified products, polyamide resins, polyester resins, etc.? It can be mixed within the following range.

The rotating member of the present invention can be obtained by first melting and mixing polybutylene terephthalate resin and wax in an extruder, or by obtaining a resin containing a relatively high concentration of wax in the form of pellets and mixing it with a wax-free resin. A mixture of resin and wax can be obtained by mixing in solid form and adjusting the wax content within the target range, or by attaching it to the surface of a pellet-like resin, but it is particularly desirable to melt and mix the resin and wax. This method involves melt-mixing a portion of the resin and mixing it with virgin resin.

Next, the mixture obtained by the above method can be injection molded or extrusion molded to obtain the desired rotating member, but injection molding is particularly preferred. Applications of the rotating member obtained by the present invention include gears, rollers, cams, number wheels, door wheels, case bearings, etc., but it is generally useful as a circular or circular rotating member that requires a high degree of dimensional accuracy. 6〇〇The present invention will be explained in detail below with reference to Examples.

Example 1 Polybutylene terephthalate (PB) with a relative viscosity of 1.37
T) and polyethylene terephthalate (PET) pellets with a relative viscosity of 1.27, a montan wax metal salt derivative (partial metal salt of montanic acid ester "Hoechst Wax 0P" manufactured by Hoechst) was added in the amount shown in Table 1. The mixture was mixed so that it adhered to the pellet surface.

The PBT mixture was molded using an injection molding machine with a cylinder temperature set at 240°C and a surge gate mold with 16 disks, 2 m1 thick [11, 20 wm in diameter] set at 70°C, and 100 shots were made for each sample in succession. Molded.

In addition, the PET mixture was heated at a cylinder temperature of 260°C and a mold temperature of 1°C.
1 disk of the same PBT mixture was prepared at 40°C.
00 shots were molded and the standard deviation value of dimensional variation was measured. The results are shown in Table 1. As is clear from the results in Table 1, in PBT, the dimensional accuracy of the molded product is significantly improved by adding wax, whereas in PET, the dimensional accuracy is hardly improved even if wax is added.

Claims (1)

[Claims] 1. A rotating member formed by molding a mixture of polybutylene terephthalate resin having a relative viscosity of 1.3 to 1.75 and 0.01 to 0.7% by weight of a montan wax metal salt derivative that is solid at room temperature.