Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2001-08-13
2003-01-07
Niland, Patrick D. (Department: 1714)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C524S496000, C524S508000, C524S537000
Reexamination Certificate
active
06503974
ABSTRACT:
DETAILED DESCRIPTION OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to a vibration-damping thermoplastic resin composition and an article molded therefrom. More specifically, it relates to a thermoplastic resin composition in which the thermoplastic resin comprises a specific amorphous thermoplastic resin and a methyl methacrylate resin and which is excellent in vibration dampability as well as dimensional accuracy, rigidity and heat resistance and is low in weight; and an article molded therefrom.
2. Prior Art
In recent years, along with an increase in the speeds of writing and reading information in office automation equipment, the demand for imparting the vibration dampability against the vibration source produced by a driving system to the components constituting the equipment has been growing together with the demand for improving the rigidity and heat resistance of each of the components, and it has also been demanded that the vibration dampability be imparted to a thermoplastic resin composition and an article molded therefrom. For example, for an optical disk such as CD-ROM, a so-called high-speed revolution of at least 30 times is on its way to becoming mainstream. In this case, a turntable which directly acts on the revolution of the disk, chassis for supporting these, and the like are demanded to have good vibration dampability. Similarly, for an optical printer, high-speed revolving polygon mirrors, optical boxes or supporting the mirrors, and the like are demanded to have good vibration dampability and, along with an increase in the printing speed, the demand for the good vibration dampability has also been increasing.
However, since a thermoplastic resin alone generally has extremely poor vibration dampability, there is the problem that it lacks vibration dampability against an increase in the speeds of the office automation equipment mentioned above. Rubber is an example of a material having high vibration dampability. However, since such a material lacks rigidity, an inorganic filler or the like must be filled densely in the material. As a result, the material has a high specific gravity, whereby it cannot satisfy the demand. The material must be light in weight for high-speed revolution, and the lighter the weight is, the higher the natural frequency becomes. Further, to adapt to a high-temperature environment caused by the environment under which the equipment is used and/or by the heat generated by the internal components of the equipment, heat resistance is also an important factor. Such highly demanded properties can never be achieved when rubber is used as the thermoplastic resin.
Meanwhile, in addition to rubber, a liquid crystal polymer such as a wholly aromatic polyester is known as a resin having high vibration dampability. However, since the resin is a crystalline resin which exhibits extremely strong anisotropy, an article molded therefrom is liable to warp, so that it cannot be sufficiently applied to the fields in which high dimensional accuracy is desired. Further, as to the dimensional accuracy, factors associated with time are also important, and low water absorption is also desired.
Japanese Patent Laid-Open Publication No. 9-40840 proposes a resin composition with high rigidity and excellent vibration dampability which is obtained by adding a vibration-damping elastomer and a specific whisker into a thermoplastic resin. The resin composition, however, cannot satisfy all the above currently demanded properties such as vibration dampability, low specific gravity and small warpage of a molded article at high levels.
Problems to be Solved by the Invention
It is the object of the present invention to provide a thermoplastic resin composition which has not only good vibration dampability but also excellent dimensional accuracy, rigidity and heat resistance and is light in weight; and an article molded therefrom.
The present inventors have made intense studies to attain the object. As a result, it has been found that the above object can be attained by a thermoplastic resin composition obtained by mixing an amorphous thermoplastic resin having a specific loss tangent (tan &dgr;) value and a deflection temperature under load of not lower than a given temperature and a methyl methacrylate resin in a specific ratio. The present invention has been completed by this finding.
Means for Solving the Problems
That is, according to the present invention, there is provided a vibration-damping thermoplastic resin composition comprising (a) 50 to 90 wt % of an amorphous thermoplastic resin (component A) having a loss tangent (tan &dgr;) value measured at 40° C. and 18 Hz in accordance with JIS K7198 of 0.01 to 0.04 and a deflection temperature under load measured under a load of 1.82 MPa in accordance with ASTM D648 of not lower than 120° C. and (b) 50 to 10 wt % of a methyl methacrylate resin (component B), wherein an article molded from this resin composition has the following physical properties (1) to (4), i.e., (1) a loss factor of 0.04 to 0.08, (2) a water absorption measured when immersed in water at 23° C. for 24 hours in accordance with ASTM D570 of not higher than 0.30 wt %, (3) a specific gravity measured in accordance with JIS K7112 of 1.05 to 1.3, and (4) a deflection temperature under load measured under a load of 1.82 MPa in accordance with ASTM D648 of 110 to 170° C.
The thermoplastic resin composition of the present invention and an article molded therefrom will be described in more detail hereinafter.
The thermoplastic resin used as the component A of the present invention is an amorphous resin having a loss tangent (tan &dgr;) value measured at 40° C. and 18 Hz in accordance with JIS K7198 of 0.01 to 0.04. The tan &dgr; is preferably 0.012 to 0.035. When it is smaller than 0.01, the vibration dampability of the vibration-damping thermoplastic resin composition of the present invention is not satisfactory, while when it is larger than 0.04, it is not preferable from the viewpoint of dimensional accuracy. Further, the thermoplastic resin used as the component A has a deflection temperature under load measured under a load of 1.82 MPa in accordance with ASTM D648 of not lower than 120° C., preferably not lower than 122° C. A representative resin which satisfies these conditions is selected from an aromatic polycarbonate resin, a polysulfone resin, an amorphous polyarylate resin and a cyclic polyolefin resin (such as a polynorbornene resin) which satisfy the conditions. Of these, the aromatic polycarbonate resin or the cyclic polyolefin resin is preferable, and the aromatic polycarbonate resin is particularly preferable. These may be used alone or in admixture of two or more, and even when resins are of the same type, they may be used alone or in admixture of two or more.
According to the studies of the present inventors, it has been found that an aromatic polycarbonate resin obtained as the component A by using a bisphenol having the following specific structure is a particularly suitable resin which as a loss tangent (tan &dgr;) value and a deflection temperature under load that satisfy the above suitable ranges and which can constitute a resin composition having excellent dimensional accuracy, heat resistance and rigidity.
That is, the aromatic polycarbonate resin which is suitable as the component A is exemplified by a polycarbonate resin containing 1,1-bis(4-hydroxyphenyl)-3,3,5-trimethylcyclohexane represented by the following structural formula (1) (to be sometimes abbreviated as “bisphenol TMC” hereinafter) in a proportion of at least 20 mol % based on 100 mol % of the total of all aromatic dihydroxy components.
That is, the aromatic polycarbonate resin which is preferable as the component A contains the above bisphenol TMC in a proportion of at least 20 mol %, preferably 30 to 80 mol %, based on 100 mol % of the total of all aromatic dihydroxy components. When the proportion of the bisphenol TMC is higher than or equal to 20 mol %, the thermoplastic resin composition has a high loss tangent (tan &dgr;
Arakawa Nobuyuki
Ogasawara Satoshi
Niland Patrick D.
Sherman & Shalloway
Teijin Chemicals Ltd.
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