Stock material or miscellaneous articles – Structurally defined web or sheet – Continuous and nonuniform or irregular surface on layer or...
Reexamination Certificate
2001-03-19
2002-07-23
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Structurally defined web or sheet
Continuous and nonuniform or irregular surface on layer or...
C428S212000, C428S213000, C428S323000, C428S480000, C528S308000, C528S308100, C528S308600
Reexamination Certificate
active
06423396
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a laminated polyester film high in surface elastic modulus and excellent in scratch resistance, preferably excellent in transparency, optical characteristics and handling characteristics.
BACKGROUND OF THE INVENTION
Polyester films represented by polyethylene terephthalate films have hitherto been widely used as transparent films because of their good transparency and low cost. However, they are poor in scratch resistance, so that the improvement thereof has been desired.
As methods for improving the scratch resistance of polymer films, methods of forming hard coat layers on surfaces of the films as described below have generally well known:
(1) Methods of applying radiation-curing resins onto the surfaces (for example, JP-A-11-254867 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”));
(2) Methods of forming metal oxide films on the surfaces by vapor deposition (JP-A-11-77909); and
(3) Methods of forming silicon oxide films by sol-gel processes (for example, JP-A-11-279305).
However, in order to improve the scratch resistance all the methods are required to thicken the hard coat layers, which causes the disadvantages of being liable to crack in bending and of being liable to deteriorate the scratch resistance. Further, the hard coat layers are formed after the formation of the polyester films, so that the number of production steps increases to raise cost. It has therefore been desired that these disadvantages are overcome. Further, high transparency, high optical characteristics and high handling characteristics such as high bending resistance have also been desired.
For such purposes, the laminated polyester films of the invention are laminated with layers to which fine particles are added, and such constitution is also seen in polyester films for magnetic recording materials (for example, JP-A-5-169604 and JP-A-3-86542). However, in these polyester films, thin layers containing large-sized fine particles are laminated for improving running properties, and surfaces of the polyester films are uneven. These polyester films are therefore different from those of the invention requiring smooth surfaces. Further, these polyester films are thinner in thickness and smaller in the amount of fine particles added than those of the invention. Accordingly, improvement in scratch resistance due to improvement in surface elastic modulus is not achieved.
SUMMARY OF THE INVENTION
An object of the invention is to provide a laminated polyester film excellent in scratch resistance, preferably excellent in transparency, optical characteristics and handling characteristics.
The object of the invention has been attained by the following invention:
(1) A laminated polyester film having a surface elastic modulus of 5 GPa to 15 GPa on at least one side thereof;
(2) The laminated polyester film described in (1), wherein the film has a total light transmittance of 70% to 98% and a haze of 0% to 2%;
(3) The laminated polyester film described in (1), wherein the film has a number of voids developed of 100 or less per 10 &mgr;m square;
(4) The laminated polyester film described in (1), wherein the film has a center-line roughness Ra of 0 &mgr;m to 0.01 &mgr;m and a maximum height Rt of 0 &mgr;m to 0.5 &mgr;m, on the surface on at least one side thereof;
(5) The laminated polyester film described in (1), wherein a polyester layer (hereinafter referred to as “layer B”) containing fine particles having a size of 1 nm to 400 nm in an amount of 10% to 60% by weight based on the weight of layer B is laminated on at least one side of a polyester support (hereinafter referred to as “layer A”);
(6) The laminated polyester film described in (5), wherein the film has a total layer thickness of 10 &mgr;m to 300 &mgr;m and a thickness of layer B of 5 &mgr;m to 100 &mgr;m;
(7) The laminated polyester film described in (5), wherein the ratio of the particle size D of the fine particles to the thickness Tb of layer B, D/Tb, is from 10
−3
to 10
−5
;
(8) The laminated polyester film described in (5), wherein the ratio of the particle size D of the fine particles to the thickness Tb of layer B, D/Tb, is from less than 1×10
−2
to 1×10
−5
;
(9) The laminated polyester film described in (1), wherein the difference in surface elastic modulus between the front and back sides is from 0.5 GPa to 10 GPa;
(10) The laminated polyester film described in (1), wherein the polyester is a polyethylene terephthalate resin or a polyethylene naphthalate resin;
(11) The laminated polyester film described in (1), wherein the film has an unevenness in thickness of 0% to 3% in a machine direction MD and in a transverse direction TD;
(12) The laminated polyester film described in (1), wherein the film has a breaking elongation of 10% to 200% both in a machine direction MD and in a transverse direction TD; and
(13) The laminated polyester film described in (1), wherein the rate of thermal dimensional change at 100° C. for 30 minutes is from 0% to 0.3% both in a machine direction MD and in a transverse direction TD, and the unevenness in thickness in, a machine direction MD and in a transverse direction TD is from 0% to 3%.
DETAILED DESCRIPTION OF INVENTION
According to the invention, the surface elastic modulus of the polyester film is increased on at least one side thereof, thereby achieving improvement in scratch resistance. The surface elastic modulus of the polyester is preferably from 5 GPa to 15 GPa, more preferably from 5.5 GPa to 12 GPa, and still more preferably from 6 GPa to 10 GPa.
The total light transmittance of the polyester film is preferably from 70% to 98%, more preferably from 80% to 98%, and still more preferably from 85% to 98%. The haze is preferably from 0% to 2%, more preferably from 0% to 1.2%, and still more preferably from 0% to 0.7%. For achieving the high optical characteristics of the invention, the above-mentioned total light transmittance and haze are preferred.
Further, in the invention, the unevenness in thickness in a machine direction (MD) and in a transverse direction (TD) is preferably from 0% to 3%, more preferably from 0% to 2.5%, and still more preferably from 0% to 2.0%.
For improving bending properties to achieve high handling characteristics, the number of voids developed is preferably 100 or less, more preferably 50 or less, and still more preferably 20 or less, per 10 &mgr;m square (10 &mgr;m×10 &mgr;m). Further, the breaking elongation is preferably from 10% to 200%, more preferably from 20% to 180%, and still more preferably from 40% to 160%.
Further, in the invention, it has been found that the destruction of the film starts from the unevenness and projections on the surface thereof. That is to say, smoothening of the surface is preferred for improving the scratch resistance. The center-line roughness Ra of the surface of the polyester film is preferably from 0 &mgr;m to 0.01 &mgr;m, more preferably from 0 &mgr;m to 0.005 &mgr;m, and still more preferably from 0 &mgr;m to 0.001 &mgr;m, and the maximum height Rt of the surface of the polyester film is preferably from 0 &mgr;m to 0.5 &mgr;m, more preferably from 0 &mgr;m to 0.3 &mgr;m, and still more preferably from 0 &mgr;m to 0.1 &mgr;m, on at least one side thereof.
Further, the rate of thermal shrinkage at 100° C. for 30 minutes of the polyester film of the invention is preferably from 0% to 0.3%, more preferably from 0% to 0.25%, and still more preferably from 0% to 0.2%, thereby being able to prevent the long-term age shrinkage of the film when it is adhered to an exothermic body such as a surface of a television screen. Furthermore, in the invention, the unevenness in thickness of the film in a machine direction (MD) and in a transverse direction (TD) is preferably from 0% to 3%, more preferably from 0% to 2.5%, and still more preferably from 0% to 2.0%.
Such polyester films are obtained by kneading of fillers and improvement in film formation methods. The polyesters are formed from dicarboxylic acids an
Burns Doane , Swecker, Mathis LLP
Chen Vivian
Fuji Photo Film Co. , Ltd.
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