Optical: systems and elements – Polarization without modulation – Polarization by optical activity
Reexamination Certificate
2002-09-19
2004-07-06
Chang, Audrey (Department: 2872)
Optical: systems and elements
Polarization without modulation
Polarization by optical activity
C359S483010, C359S485050, C359S494010, C359S506000
Reexamination Certificate
active
06760156
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a process of producing a polarizer and a polarizer obtained by the process concerned. And the present invention relates to a polarizing plate using the polarizer concerned. Furthermore, a visual display, such as a liquid crystal display, an organic EL display, a PDP (plasma display panel), using the polarizing plate concerned.
2. Description of the Prior Art
Heretofore, as a polarizer used in a liquid crystal display or the like, a polyvinyl alcohol film dyed with iodine has been used since the polarizer has both of a high transmittance and a high polarization degree. The polarizer is usually used as a polarizing plate laminating, on its single side or both sides, a protective film such as the films made of triacetylcellulose. In recent years, higher performance has been required for liquid crystal display. Thus, a higher transmittance and a higher polarization degree have been required for polarizers. Various polarizer-producing processes, which comply with such requests, are suggested.
There is suggested, for example, a process of subjecting a polyvinyl alcohol film to uniaxial dry stretching, dyeing the film and then dipping the film in an aqueous solution containing boric acid of 70 to 85° C. temperature (JP-A-8-240715). However, according to this production process, a polarizer having a sufficiently high polarization degree has not yet been produced. Furthermore, the following processes are suggested; processes of performing stretching treatment at two stages and further performing the stretching treatment at the second stage in a treating bath containing a boron compound, for example, a process of stretching a polyvinyl alcohol film 4 times or less uniaxially in dry, dyeing the film and further stretching the film 1.5 times or more under the condition containing a boron compound (JP-A-10-288709), and a process of stretching a polyvinyl alcohol film 4 to 8 times uniaxially in dry, dyeing the film, and then stretching the film 1.1 to 1.8 times in an aqueous boric acid solution (JP-A-11-49878). According to such processes, a polarizer having a considerably high polarization degree can be obtained. However,a higher polarization degree is required for polarizers. When the stretch ratio at the second stage in the treating bath containing the boron compound is made large to keep the polarization degree high in such processes, the stretched film is broken easily. Therefore, a polarizer having a high polarization degree cannot be stably obtained.
An object of the present invention is to provide a process of producing stably a polarizer that has a high polarization degree and a high transmittance, which is made of a polyvinyl alcohol film.
And other object of the present invention is to provide a polarizer obtained by the producing process, a polarizing plate utilizing the polarizer and further a visual display utilizing the polarizing plate.
SUMMARY OF THE INVENTION
As a result of repeated examinations carried out wholeheartedly by the present inventors to solve the above-mentioned problems, a process of producing a polarizer shown below was found out and the present invention was completed.
The present invention relates to a process of producing a polarizer, comprising the steps of:
subjecting a non-stretched polyvinyl alcohol film to uniaxial dry stretching treatment to give a stretch ratio of 4 times or less,
dyeing the film,
and then subjecting the film to uniaxial stretching treatment to give a stretch ratio of less than 1.5 times under the condition containing a boron compound.
In the present invention, the stretch ratio in the dry stretching (the first stretch ratio) is controlled to 4 times or less and the stretch ratio in the stretching under the condition containing the boron compound (the second stretch ratio) is controlled to less than 1.5 times, so that the total stretch ratio (the product of the first stretch ratio in the dry stretching and the second stretch ratio in the stretching under the condition containing the boron compound) is adjusted to less than 6. In this way, a polarizer having a high polarization degree and a high transmittance is stably produced. The first stretch ratio in the dry stretching is preferably from 3 to 4 times, and the second stretch ratio in the stretching under the condition containing the boron compound is preferably 1.45 times or less. The total stretch ratio is preferably from 4.5 to less than 6 times. The first stretch ratio and the second stretch ratio are controlled outside the above-mentioned ranges, whereby the total stretch ratio can be adjusted to less than 6 times. However, when the first stretch ratio in the dry stretching is set to more than 4 times, a polarizer having a sufficiently high polarization degree cannot be obtained. When the second stretch ratio in the stretching under the condition containing the boron compound is set to 1.5 or more, the stretched film is liable to break.
In the above-mentioned process of producing a polarizer, when the uniaxial stretching treatment is performed under the condition containing the boron compound, the shape ratio (the film MD direction size /the film TD direction size) of the film to be subjected to the uniaxial stretching treatment is preferably set to 1.2 or more. By setting the shape ratio to 1.2 or more, a polarizer having a high polarization degree can stably be obtained. The shape ratio is preferably set to 1.5 or more. The shape ratio is set to about 10 or less from the viewpoint of the size of the treating bath.
In the above-mentioned process of producing a polarizer, the transmittance of the polarizer is preferably 43% or more and the polarization degree thereof is preferably 96% or more. The polarizer having the transmittance of 43% or more perform good optical properties. In order to make the optical properties better, the polarization degree is more preferably 96% or more; further preferably 97% or more.
And the present invention relates to a polarizer obtained by the above described process.
And the present invention relates to a polarizing plate with which an optical transparent protective layer is prepared at least in one side of the above described polarizer.
In the above-mentioned polarizing plate, comprising at least one of a retardation plate, a viewing angle compensation film, a reflective plate, a transflective plate and a brightness enhancement film, is used.
Furthermore, the present invention relates to a visual display using the above-described polarizing plate.
DETAILD DESCRIPTION OF THE INVENTION
Polyvinyl alcohols or derivatives thereof are used for a material of a non-stretched film in a process of producing a polarizer of the present invention. As derivatives of polyvinyl alcohol, in addition to polyvinyl formals, polyvinyl acetals, etc. may be mentioned, and derivatives modified with olefins, such as ethylene and propylene; unsaturated carboxylic acids, such as acrylic acid, methacrylic acid, and crotonic acid; alkyl esters of the above described unsaturated carboxylic acids and acrylamide etc. may be mentioned. Generally, polyvinyl alcohol with approximately 1000 to 10000 of degree of polymerization and approximately 80 to 100 mol % of degree of saponification is used.
In addition, additives, such as plasticizers, may also be contained in the above described polyvinyl alcohol film. As plasticizers, polyols and condensates thereof, etc., for example, glycerin, diglycerin, triglycerin, ethylene glycol, propylene glycol, polyethylene glycols, etc. may be mentioned. Although an amount of the plasticizers used is not especially limited, it is preferable to be set no more than 20% by weight in the non-stretched film.
The polyvinyl alcohol film (non-stretched film) is subjected to dry stretching to give a stretch ratio of 4 times or less, so as to produce a stretched film. The method of the uniaxial dry stretching treatment is not particularly limited. For example, any one selected from the following methods may be adopted; a method described in Japanese Patent No. 152
Kondo Seiji
Nishida Akihiro
Tsuchimoto Kazuki
Chang Audrey
Curtis Craig
Nitto Denko Corporation
Westerman Hattori Daniels & Adrian LLP
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