Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Light polarizing article or holographic article
Reexamination Certificate
2002-04-06
2004-11-09
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
Light polarizing article or holographic article
C264S001360, C264S001700, C264S002700
Reexamination Certificate
active
06814899
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to synthetic dichroic plane polarizers based on molecularly oriented polyvinyl alcohol sheets and, in particular, to a high efficiency K-type polarizing sheet.
BACKGROUND OF THE INVENTION
Normally, light waves vibrate in a large number of planes about the axis of a light beam. If the waves vibrate in one plane only, the light is said to be plane polarized. Several useful optical ends and effects can be accomplished by plane polarized light. For example, in the manufacture of electrooptical devices, such as liquid crystal display screens, crossed polarizers are used in conjunction with an addressable liquid crystal interlayer to provide the basis for image formation. In the field of photography, polarizing filters have been used to reduce the glare and the brightness of specular reflection. Polarizing filters (circular or otherwise) have also been used for glare reduction in display device screens.
Linear light polarizing films, in general, owe their properties of selectively passing radiation vibrating along a given electromagnetic radiation vector (and absorbing electromagnetic radiation vibrating along a second given electromagnetic radiation vector) to the anisotropic character of the transmitting film medium. Dichroic polarizers are absorptive, linear polarizers having a vectoral anisotropy in the absorption of incident light. The term “dichroism” is used herein as meaning the property of differential absorption (and transmission) of the components of an incident beam of light depending on the direction of vibration of the components. Generally, a dichroic polarizer will transmit radiant energy along one electromagnetic vector and absorb energy along a perpendicular electromagnetic vector. A beam of incident light, on entering a dichroic polarizer, encounters two different absorption coefficients, one low and one high so that the emergent light vibrates substantially in the direction of low absorption (high transmission).
Among synthetic dichroic polarizers are K-type polarizers. A K-type polarizer derives its dichroism from the light-absorbing properties of its matrix, not from the light-absorbing properties of dye additives, stains, or suspended crystalline material. Typically K-type polarizers comprise a sheet of oriented poly(vinyl alcohol) having an oriented suspension of a dehydration product of polyvinyl alcohol (i.e., polyvinylene). K-type polarizers of this kind are formed by heating the polymeric sheet in the presence of a dehydration catalyst, such as vapors of aqueous hydrochloric acid, to produce conjugated polyvinylene blocks and unidirectionally stretching the polymeric sheet prior to, subsequent to, or during the dehydration step to align the poly(vinyl alcohol) matrix. By orienting the poly(vinyl alcohol) matrix unidirectionally, the transition moments of the conjugated polyvinylene blocks or chromophores are also oriented and the material becomes visibly dichroic. A second orientation step or extension step may be employed after the dehydration step as described in U.S. Pat. No. 5,666,223 (Bennett et al.). Summary of the Invention
In general, in one aspect, the invention features a method for making a polarizer from a polymeric sheet having a predetermined original length and including a hydroxylated linear high polymer. The polymeric sheet is stretched from greater than 5.0 times to approximately 6.0 times the original length. A suitable dehydration catalyst is introduced to the polymeric sheet. The polymeric sheet and the catalyst is heated at a temperature appropriate to effect partial dehydration of the polymeric sheet wherein light absorbing, vinylene block segments are formed.
Implementations of the invention may also include one or more of the following features. The hydroxylated linear high polymer may be polyvinyl alcohol, polyvinyl acetal, polyvinyl ketal, or polyvinyl ester. The introducing step may include exposing the polymeric sheet to fuming acidic vapors. The introducing step may include coating the polymeric sheet with an acid coating. The introducing step may include placing an acid donor layer adjacent to the polymeric sheet and exposing the acid donor layer to a radiant energy to release one or more molecules of acid. The radiant energy may be thermal energy or ultraviolet light energy. The stretching may be bidirectional relaxed, bidirectional unrelaxed, unidirectional relaxed, unidirectional unrelaxed, or parabolic.
The method may include subjecting the polymeric sheet to a boration treatment at an elevated temperature. The method may also include unidirectionally extending the stretched and heated polymeric sheet greater than 0% to about 70% of the stretched length. The subjecting step and the extending step may be performed concurrently. The subjecting step may be performed before the extending step. The boration treatment temperature may be greater than about 80° C.
The method may include adding at least one dichroic dye to the polymeric sheet. The method may include subjecting the polymeric sheet to a boration treatment at an elevated temperature, wherein the adding step and the subjecting step are performed concurrently. The method may include subjecting the polymeric sheet to a boration treatment at an elevated temperature, wherein the adding step is performed before the subjecting step. The dichroic dye may be a yellow dye, a blue dye, or a combination thereof. The boration treatment may include placing the polymeric sheet in contact with an aqueous solution comprising boric acid. The boric acid concentration may range from about 5% to about 20%. The aqueous solution may include borax. The borax concentration may range from about 1% to about 7%. The at least one dichroic dye may be a yellow dye, a blue dye, or a combination thereof. The polymeric sheet may be supported on a carrier web or a support layer.
In general, in another aspect, the invention features a method for making a polarizer from a polymeric sheet having a predetermined original length and including a hydroxylated linear high polymer. The polymeric sheet is stretched from approximately 3.5 to approximately 6.0 times the original length. A suitable dehydration catalyst is introduced to the polymeric sheet. The polymeric sheet and the catalyst is heated at a temperature appropriate to effect partial dehydration of the polymeric sheet wherein light absorbing, vinylene block segments are formed. The polymeric sheet is subjected to a boration treatment at a temperature greater than about 80° C. The polymeric sheet is unidirectionally extended greater than 0% to about 70% of the stretched length.
Implementation of the invention may also include one or more of the following features. The hydroxylated linear high polymer may be polyvinyl alcohol, polyvinyl acetal, polyvinyl ketal, or polyvinyl ester. The introducing step may include exposing the polymeric sheet to fuming acidic vapors. The introducing step may include coating the polymeric sheet with an acid coating. The introducing step may include placing an acid donor layer adjacent to the polymeric sheet and exposing the acid donor layer to a radiant energy to release one or more molecules of acid. The radiant energy may be thermal energy or ultraviolet light energy.
The stretching may be bidirectional relaxed, bidirectional unrelaxed, unidirectional relaxed, unidirectional unrelaxed, or parabolic. The subjecting step and the extending step may be performed concurrently.
The method may include adding at least one dichroic dye to the polymeric sheet. The adding step and the subjecting step may be performed concurrently. The adding step may be performed before the subjecting step. The at least one dichroic dye may be a yellow dye, a blue dye, or a combination thereof. The boration treatment may include placing the polymeric sheet in contact with an aqueous solution comprising boric acid. The boric acid concentration may range from about 5% to about 20%. The aqueous solution may include borax. The borax concentration may range from about 1% to about 7%. The polymeric sheet
Balich Jason W.
Cael John J.
Nagarkar Pradnya V.
Sahouani Hassan
Vogel Kim M.
Buckingham Stephen W.
Vargot Mathieu D.
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