Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2003-07-15
2004-10-19
Teskin, Fred (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S338000, C525S940000, C528S50200C, C528S503000, C428S064400
Reexamination Certificate
active
06806322
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a hydrogenated styrene polymer; a process for producing same; etc.
More particularly, it relates to a hydrogenated styrene polymer that has excellent transparency, can be used suitably for an optical application such as an optical disk substrate, and has excellent stability, transparency in a hot and humid environment, and heat resistance; and also relates to a process for producing same; etc.
BACKGROUND ART
Hydrogenated styrene polymers can generally be produced by hydrogenating a styrene polymer, and there have been a large number of proposals for the application of hydrogenated styrene polymers to optical disks such as compact disk (CD) and digital versatile disk (DVD) by utilizing the optical characteristics of the hydrogenated styrene polymers.
For example, JP-B-7-114030 (JP-B denotes a Japanese examined patent application publication) discloses an optical disk comprising a substrate formed from a hydrogenated polystyrene resin having a vinyl cyclohexane content of 80 wt % or higher. It is described therein that, as an optical disk material, this resin has desirable properties since it has high light transmittance, and the birefringence and the water absorption thereof are very low compared with a polycarbonate resin.
With regard to applications other than optical disks, for example, JP-A-6-199950 (JP-A denotes a Japanese unexamined patent application publication) discloses a hydrogenated styrene polymer having a low content of low molecular weight components, and the utilization thereof in medical equipment, electrically insulating materials, and electronic component processing equipment.
In order to improve drawbacks of such resins, the use of a hydrogenated styrene-conjugated diene block copolymer in an optical application such as an optical disk substrate has previously been disclosed, the copolymer being incorporated with a rubber component by block copolymerization of a conjugated diene such as isoprene or butadiene with styrene.
On the other hand, JP-A-61-90345 discloses that, in an optical application, the content of fine particulate foreign matter having a size of 0.5 &mgr;m or more should not exceed a certain specific range.
Furthermore, WO 99/05210 discloses that a composition comprising a hydrogenated styrene polymer and an organic high molecular weight compound or an alcoholic ether or ester compound, which are incompatible with the polymer, can suppress cloudiness even in a hot and humid environment. However, there is no description of the cause of the cloudiness, and the mechanism by which cloudiness is prevented in such a composition is unclear.
In recent years, as a result of the development of blue lasers, next-generation high-density optical disks employing blue lasers have been intensively developed. The pit and land/groove sizes of these substrates are smaller still than those of the conventional CD, DVD, etc. More particularly, in the case of CD-ROM, a 780 nm laser is used and the track pitch is 1.6 &mgr;m, in the case of DVD-ROM, a 650 nm laser is used and the track pitch is 0.8 &mgr;m, and in the case of a next-generation high-density ROM type optical disk, a laser on the order of 400 nm is used and the track pitch is 0.4 &mgr;m or less.
As described in JP-A-61-90345, the conventional optical disk substrates only require the control of foreign matter with a size of on the order of 0.5 &mgr;m or more, but in the case of the high-density optical disks for blue lasers, it is expected that foreign matter that is smaller than the above value will greatly affect the S/N ratio, etc. of a signal. However, there has so far been no disclosure in relation to the evaluation and control of the amount of foreign matter from such a viewpoint.
The present inventors have found that, when a molding formed from a hydrogenated styrene polymer is used in a high temperature and high humidity atmosphere, spots on the order of a few &mgr;m to a few of tens of &mgr;m (here, called ‘crazing spots’ due to the appearance of the spots) appear in the entire body of the molding, and seem to be attributable to a decomposed polymer and/or a decomposed stabilizer.
The occurrence of such spots makes it difficult for the molding to be used as an optical material in a high temperature and high humidity atmosphere. In particular, in the case where it is used as an optical disk substrate, if such a defect occurs within the substrate to even the slightest extent, the S/N ratio of the optical disk substrate is significantly degraded, thereby markedly reducing the commercial value.
DISCLOSURE OF INVENTION
An object of the present invention is to provide a hydrogenated styrene polymer that has excellent heat resistance and is stable in a hot and humid environment and, in particular, in which the occurrence of crazing spots, which cause degradation of transparency in a hot and humid environment, is suppressed; a process for producing the hydrogenated styrene polymer; etc.
Another object of the present invention is to provide a hydrogenated styrene polymer that is suitable for use in an optical application such as an optical disk substrate and, in particular, an optical disk substrate for a blue laser, a container for food or medical use, a film, and a molding such as an electric/electronic component; a process for producing the hydrogenated styrene polymer; etc.
As a result of an investigation by the present inventors into the causes of crazing spots, which result in the degradation of transparency, it has been found that the content of fine particulate foreign matter having a size of 0.2 &mgr;m or more and less than 0.5 &mgr;m and the phosphorus atom content in the polymer greatly contribute to the occurrence of crazing spots, and controlling the contents of such foreign matter and phosphorus atoms to within specific ranges can provide a hydrogenated styrene polymer in which crazing spots are suppressed.
It has also been found that an optical disk substrate for a blue laser formed using such a hydrogenated styrene polymer gives very few errors, and the present invention has thus been accomplished.
That is, the present invention is a hydrogenated styrene polymer having a hydrogenated polymerized styrene unit content of at least 70 wt %, a content of fine particulate foreign matter having a particle size of 0.2 &mgr;m or more and less than 0.5 &mgr;m of at most 1×10
6
particles per g of the hydrogenated styrene polymer, and a phosphorus atom content of at most 0.01 parts by weight in 100 parts by weight of the hydrogenated styrene polymer.
Furthermore, the present invention is a molding obtained by melt molding such a hydrogenated styrene polymer.
Moreover, the present invention is a process for producing a hydrogenated styrene polymer comprising filtering, with a filter having a pore size of 0.3 &mgr;m or less, a hydrogenated styrene polymer having a hydrogenated polymerized styrene unit content of at least 70 wt %, at a temperature at which the solution viscosity thereof is at most 10 Pa·sec (100 poise) at a shear rate of 1 (1/s), and then removing a solvent from the filtrate thus obtained.
PREFERRED MODES FOR CARRYING OUT THE INVENTION
The hydrogenated styrene polymer of the present invention has an aromatic ring-hydrogenated polymerized styrene unit content of at least 70 wt %.
The ‘styrene polymer’ referred to in the present invention means a styrene homopolymer and a styrene copolymer, and the ‘hydrogenated styrene polymer’ referred to in the present invention means a hydrogenated styrene homopolymer and a hydrogenated styrene copolymer.
The hydrogenated styrene polymer of the present invention is in a broader sense a hydrogenated vinyl aromatic hydrocarbon polymer. The vinyl aromatic hydrocarbon referred to here means a compound obtained by substituting, with a vinyl group or an ethylenically unsaturated group, one hydrogen atom bonded to an aromatic ring of an aromatic hydrocarbon (benzene, naphthalene, etc.), which may have a substituent (an alkyl group having 1 to 4 carbons, an aryl group having 6 to 10 carbons, etc.).
Specifi
Hashizume Kiyonari
Kido Nobuaki
Matsumura Shunichi
Sasaki Takeshi
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