Patent Application
20080018998
Hereinbelow, preferred embodiments of the present invention are illustrated with reference to the figures.
An ultrahigh molecular weight polyethylene porous sheet 1 is prepared (
In this state, the original polarizing plate 2 is cut with a single blade 4 for a guillotine cut to obtain a polarizing plate 3. An edge of the single blade 4 penetrates the original polarizing plate 2 from its upper surface (a principal surface unsupported by the porous sheet 1) towards its lower surface (a principal surface supported by the porous sheet 1), and it passes through the lower surface to reach all the way to the inside of the porous sheet 1 finally. In this way, the original polarizing plate 2 is cut by the single blade 4 moving across the thickness of the original polarizing plate 2.
The part pressed by the single blade 4 generally defines a straight line on a principal surface of the original polarizing plate. The original polarizing plate 2 may have a plurality of cutting plane lines, and each line is defined to extend in a form of a straight line on the principal surface of the original plate. The cutting plane lines may be aligned, for example, parallel to each other or in a grid. The original polarizing plate 2 is cut along each cutting plane line for formation of polarizing plates. Embodiments of the present invention are, needless to say, not limited to this. The present invention can be applied to various cutting embodiments using a variety of blades as long as the cutting mat employs an ultrahigh molecular weight polyethylene porous sheet and the original polarizing plate is cut by a blade moving across the thickness of the original plate.
The viscosity average molecular weight of the ultrahigh molecular weight polyethylene resin composing of the ultrahigh molecular weight polyethylene porous sheet 1 is preferably equal to or more than one million, for example in a range from one million to seven million. The compressive modulus of the porous sheet 1 (in accordance with JIS K6911; based on a slope of graph within elastic limit in a stress-time graph obtained by compressing three stacked sheets each having a thickness of 2 mm) is preferably in a range from 100 kgf/cm2 to 1000 kgf/cm2, particularly in a range from 200 kgf/cm2 to 400 kgf/cm2. The average pore diameter of the porous sheet 1 is preferably in a range from 10 μm to 100 μm, specifically in a range from 15 μm to 40 μm. The air permeability of the porous sheet 1 is preferably in a range from 0.5 cm3/cm2·second to 20 cm3/cm2·second, particularly from 1 cm3/cm2·second to 5 cm3/cm2·second, indicated by measured values based on the Frazier Permeability Test (JIS L1096). The Shore hardness (nail indentation hardness; Shore D) is preferably in a range from 30 to 52. The thickness of the porous sheet 1 is preferably in a range from 0.05 mm to 0.5 mm, specifically from 0.1 mm to 0.3 mm. The coefficient of dynamic friction of the porous sheet 1 (in accordance with JIS K7125; measured with a Bowden-Leben type testing meter with an iron ball of a 10 mm diameter adhered a PET film thereon that has a width of 2 mm and a thickness of 50 μm) is preferably equal to or less than 0.3, specifically equal to or less than 0.18.
The ultrahigh molecular weight polyethylene porous sheet 1 itself has a high elastic modulus, and the modulus may be improved further by impregnating a curable liquid in vacant pores followed by curing it. In this case, the impregnation amount of the curable liquid is adjusted to maintain the air permeability of the porous sheet 1. The enhancement of the elastic modulus by the cured liquid enables preventing the raising at the edge with more certainty when the blade 4 makes contact with the original polarizing plate 2 to start cutting in.
The curable liquid is not particularly limited, but for example, ultraviolet curable ink is preferable. The curable liquid is not limited to this, and it can employ epoxy ink, for example.
Hereinbelow, the present invention is described further in detail with Examples. It should be noted that the present invention is not limited to the Examples described below.
An ultrahigh molecular weight polyethylene porous sheet (“SUNMAP” manufactured by Nitto Denko Corporation; viscosity average molecular weight of six million, compressive modulus of 250 kgf/cm2, average pore diameter of 17 μm, thickness of 0.3 mm, Shore hardness of 48, coefficient of dynamic friction of 0.08) is prepared as a cutting mat to fix a four-layered original polarizing plate on the porous sheet. The original polarizing plate was fixed by drawing the original polarizing plate through the porous sheet from under the porous sheet.
Subsequently, a guillotine blade (a single blade) having an angle on the edge at 25 degrees was moved from above the original polarizing plate through it at a speed of 50 mm/second for cutting the original polarizing plate. At this point, the guillotine blade was moved to have the edge reach the depth of 0.1 mm below a surface of the porous sheet. This operation was repeated to make cutting plane lines on the original polarizing plate parallel and evenly spaced relative to each other, and thus ten polarizing sheets for a three-inch liquid crystal displaying device were obtained.
The maximum crack depth developed in the section of the polarizing plates, a cutting dimension error and appearance were evaluated using an optical microscope. Results of the evaluation are shown in Table 1. Here, the cutting dimension error means a ratio (%) of difference between designed dimension and actual size to the designed dimension in the direction orthogonal to the cutting plane line.
Ultraviolet curable ink (“Daicure Ink” manufactured by Dainippon Inc and Chemicals, Inc.) was impregnated in vacant pores in the same ultrahigh molecular weight polyethylene porous sheet used in the Example 1. The ultraviolet curable ink was cured by irradiation of an ultraviolet lamp to obtain an ink impregnated porous sheet. By the same process as the Example 1 other than employing this ink impregnated porous sheet as a cutting mat, ten polarizing sheets were obtained. In addition, the maximum crack depth developed in the section of the polarizing plates, a cutting dimension error and appearance were evaluated in the same way as the Example 1. Results of the evaluation are shown in Table 1.
By the same process as the Example 1 other than employing a polystyrene porous sheet as a cutting mat, ten polarizing sheets were obtained. This porous sheet was prepared by providing many minute pores with a polystyrene sheet (“Nippla Sheet” manufactured by Nippon Plastic Kogyo K.K.; 0.3 mm in thickness). In addition, the maximum crack depth developed in the section of the polarizing plates, a cutting dimension error and appearance were evaluated in the same way as the Example 1. Results of the evaluation are shown in Table 1.
By the same process as the Example 1 other than employing a recycled woodfree paper (0.3 mm in thickness) as a cutting mat, ten polarizing sheets were obtained. In addition, the maximum crack depth developed in the section of the polarizing plates, a cutting dimension error and appearance were evaluated in the same way as the Example 1. Results of the evaluation are shown in Table 1.
As shown in Table 1, the Comparative Example 1 had the large dimension error, and in the Comparative Example 2 the maximum crack depth and the dimension error became large and a problem arose in appearance. The Examples 1 and 2 could inhibit the maximum crack depth of the polarizing plate and the dimension error to a level not becoming a problem in practical use. The Example 2 had a particularly small maximum crack depth in the section.
As described above, the present invention provides a method of manufacturing a polarizing plate in which an original polarizing plate is cut accurately, cracks are not extended easily in a section and foreign substances are not attached easily on a polarizing plate to be obtained, and thus the present invention is industrially useful.
The invention may be embodied in other forms without departing from the spirit or essential characteristics thereof. The embodiments disclosed in this application are to be considered in all respects as illustrative and not limiting. The scope of the invention is indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2006-184274 | Jul 2006 | JP | national |
