1. Field of the Invention
The present invention generally relates to a durable polyoxymethylene composition and a ramp including a durable polyoxymethylene composition. In particular, the present invention is directed to a durable polyoxymethylene composition as well as a ramp including a durable polyoxymethylene composition with excellent micro-wear-resistant property and extremely small amount of wear debris under a high humidity and high temperature condition, or under a low humidity and low temperature condition.
2. Description of the Prior Art
A polyoxymethylene resin is a widely used engineering resin due to its well-balanced mechanical properties, remarkable chemical resistance and sliding properties as well as the good friction wear performance. Recently, attempts have been made to use such polyoxymethylene resin as material for a ramp in a hard disk drive. When other resins are added to increase the wear-resistant property of the polyoxymethylene resin, lamination or mold deposits often occurs and wear-resistant property accordingly is lowered due to low compatibility. To overcome these problems, it is necessary to clean the molds more frequently so the yield is lower. Addition of inorganic fillers may increase the surface hardness, but excess addition of inorganic fillers or micro-meter size inorganic fillers result in more wear debris that damages the metal parts or contaminates the parts in the hard drive, which in turn jeopardizes the durability. In view of the above, the lubricants and the additives in the polyoxymethylene resin currently have many problems such as compatibility and dispersibility.
For example, US 2008/0037175 discloses a ramp including a polyoxymethylene resin and a colorant for a hard disk drive. The ramp has an outgas level of 20 μg/g or less. U.S. Pat. No. 7,088,555 discloses a ramp having a surface hardness of 2.6 GPa or more.
However, in the aforementioned conventional technologies, no description is yet made to a polyoxymethylene resin with excellent micro-wear-resistant properties, and further, no proposal for attempting to reduce wear debris from a polyoxymethylene resin ramp is found.
USPTO Backgrounds
USPTO Backgrounds