Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2002-02-14
2003-12-16
Buttner, David J. (Department: 1712)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S522000, C525S084000, C525S085000, C525S309000, C525S310000, C359S742000, C359S819000
Reexamination Certificate
active
06663953
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a Fresnel lens base sheet which can be used as screens of projection televisions, microfilm readers or the like, can be used as transmission screens, possesses excellent impact resistance and environmental resistance, and is suitable for the formation of a lens layer of an ultraviolet-cured resin.
BACKGROUND ART
Projection screens such as transmission screens are extensively used for projecting television images, microfilm images or the like to realize contemplated displays. This type of projection screen generally comprises a combination of lens sheets such as lenticular lens sheets and Fresnel lens sheets. By virtue of this construction, when a viewer observes the screen, the screen is bright and the angle of visibility is increased.
Light transparent materials used in these lens sheets include methacrylic resins or styrene resins possessing excellent transparency, lightfastness, scratch resistance and the like and, at the same time, excellent moldability. Lens sheets have been molded, for example, by press molding, extrusion, cast molding, or injection molding. In recent years, however, from the viewpoint of high productivity, a method has become adopted wherein a lens layer of an ultraviolet-cured layer is formed on a light transparent sheet.
Methacrylic resins used as a substrate for this lens sheet have a relatively high water absorption. For example, in the case of a methacrylic resin having an initial length of 1000 mm, when the relative humidity is changed from 50% to 90%, or from 90% to 50%, the expansion or contraction level is 1.6 mm. In general, when the water absorption has caused a change in dimension of the lens sheet, the warpage or lift of the screen occurs, disadvantageously resulting in deteriorated optical characteristics or the separation of the lens sheet from a frames
On the other hand, in the case of a styrene resin having low water absorption, disadvantageously, the lightfastness is poor, and the lens sheet undergoes a change in color which lowers light transmittance.
Further, both the methacrylic resin and the styrene resin have poor impact resistance, and, consequently, the Fresnel lens sometimes causes breaking, cracking, or the like, for example, during the production thereof or in transit and thus is rejected.
In order to solve these problems, Japanese Patent Laid-Open No. 341101/1993 proposes a method wherein a styrene-diene copolymer is dissolved in a mixture composed of an aromatic vinyl monomer, a (meth)arrylic ester monomer, and a polyfunctional unsaturated monomer, the mixture is polymerized, and a Fresnel lens is prepared from the polymer. Japanese Patent Laid-Open No. 3502/1994 proposes a method wherein a Fresnel lens is prepared using a styrene resin containing a noncrosslinking resin. Japanese Patent Laid-Open No. 147664/2000 proposes a Fresnel lens prepared by casting a monomer mixture containing an (meth)acrylate monomer, a styrene monomer and transparent resin beads. These techniques, however, are unsatisfactory for the formation of a Fresnel lens base sheet which is suitable for the formation of a lens layer of an ultraviolet-cured resin and has excellent impact resistance and environmental resistance.
DISCLOSURE OF THE INVENTION
Accordingly, it is an object of the present invention to provide a Fresnel lens base sheet which is suitable for the formation of a lens layer of an ultraviolet-cured resin and has excellent impact resistance and environmental resistance and can realize excellent image quality.
In order to attain the above object, the present inventors have made extensive and intensive studies and as a result have found that a specific rubber-modified styrene resin comprising a rubber-like elastic material as dispersed particles and a copolymer of a styrene monomer with an acrylic (methacrylic) ester monomer as a continuous phase is suitable for the formation of a lens layer of an ultraviolet-cured resin and can provide a Fresnel lens base sheet having excellent impact resistance and environmental resistance. This has led to the completion of the present invention.
Thus, according to one aspect of the present invention, there is a Fresnel lens base sheet suitable for the formation of a lens layer of an ultraviolet-cured resin, said base sheet being formed of a rubber-modified styrene resin comprising a rubber-like elastic material as dispersed particles and a styrene resin as a continuous phase,
(i) the styrene resin constituting the continuous phase being a copolymer of a styrene monomer (A) represented by formula (1)
wherein R
1
represents hydrogen or a methyl group; and R
2
represents hydrogen or an alkyl group having 1 to 5 carbon atoms, with an acrylic (methacrylic) ester monomer (B) represented by formula (2)
wherein R
3
represents hydrogen or a methyl group; and R
4
represents an alkyl group having 1 to 8 carbon atoms, the proportions of the monomer (A) and the monomer (B) being 75 to 25% by weight and 25 to 75% by weight, respectively, wherein the total amount of the monomers (A) and (B) is 100% by weight,
(ii) the content of the rubber-like elastic material in the dispersed phase being 3 to 20 parts by weight based on 100 parts by weight of the styrene resin,
(iii) the diameter of dispersed particles of the rubber-like elastic material constituting the dispersed phase being 0.3 to 1.0 &mgr;m,
(iv) the transmittance of light at 360 nm being not less than 50%.
The Fresnel lens base sheet is preferably an base sheet for a light-diffusive Fresnel lens suitable for the formation of a lens layer of an ultraviolet-cured resin, wherein the rubber-modified styrene resin is preferably a rubber-modified styrene resin composition comprising: 100 parts by weight of the rubber-modified styrene resin; and 0.1 to 5 parts by weight of transparent fine particles which are different in a refractive index difference by ±(0.005 to 0.040) from the rubber-modified styrene resin and have an average particle diameter of 5 to 30 &mgr;m.
Further, a lenticular lens and/or a prism and/or a linear Fresnel lens may be provided on at least one side of the Fresnel lens base sheet.
BEST MODE FOR CARRYING OUT THE INVENTION
The present invention will be explained in more detail.
The copolymer constituting the continuous phase comprises 75 to 25% by weight of a styrene monomer (A) and 25 to 75% by weight of an acrylic (methacrylic) ester monomer (B) (the total amount of the styrene monomer and the acrylic (methacrylic) ester monomer being 100% by weight). The amount of the styrene monomer is preferably not less than 40% by weight and less than 60% by weight. When the amount of the styrene monomer is less than 25% by weight, the dimensional stability is poor due to moisture absorption. On the other hands when the amount of the styrene monomer exceeds 75% by weight, the weathering resistance is disadvantageously poor.
The degree of polymerization of the styrene resin constituting the continuous layer is not particularly limited. From the viewpoint of extrudability and the like, however, the degree of polymerization is preferably set so that the rubber-modified styrene resin has an MFR in the range of 0.3 to 5.0 as measured under condition 8 (temperature 200° C./load 5 kgf) according to JIS K 7210. The total amount of the styrene monomer, the acrylic (methacrylic) ester monomer, and the polymerization solvent contained in the rubber-modified styrene resin according to the present invention is preferably not more than 0.10% by weight from the viewpoint of environment at the time of forming of an base sheet. The total amount of origomers, such as dimers and trimers, formed from a styrene monomer and an acrylic (methacrylic) ester monomer is preferably regulated to not more than 0.8% by weight, more preferably not more than 0.6% by weight. A total amount of origomers of more than 0.8% by weight is causative of the contamination of roll at the time of forming of the base sheet. This unfavorably leads to a poor appearance of the base sheet.
In the present invention, styrene, &agr;-methylstyrene, p
Hanamoto Keiji
Honda Makoto
Kamiya Shunji
Asahi Kasei Kabushiki Kaisha
Buttner David J.
Parkhurst & Wendel L.L.P.
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