JPS6033245B2 - Polarizing element and its manufacturing method - Google Patents

Description

[Detailed description of the invention] The present invention relates to a method for manufacturing a polarizing element.

Linear light polarizing elements generally
This is due to the property of selectively passing the Korean radiation rays vibrating along a certain electromagnetic radiation vector and absorbing the electromagnetic radiation rays vibrating along another electromagnetic radiation vector.

Dichroic polarizers are differentially absorbing linear polarizers, ie they owe their polarizing ability to vectorial anisotropy in absorbing the incident light wave. Light entering dichroic soot encounters two different absorption coefficients: high and low. The emitted light mainly oscillates in the direction of low absorption. The most widely used type of synthetic polarizer, which is also the polarizer to which this invention is directed, is the polyvinyl alcohol-iodine composite polarizer.

It consists of a linear polyaddition contained within polyvinyl alcohol. By orienting the polyvinyl alcohol matrix in the same direction, the transition moments of the absorber are also oriented in such a way that it becomes visually dichroic. Polyvinyl alcohol film polarizers generally include a plastic support, which can be any suitable isotropic material, but is preferably cellulose acetate platylate. The support provides dimensional stability to the film and serves as a covering or protective element.
Of course, this must be transparent. The production of iodine-colored dichroic polarizers, which involves stretching polyvinyl alcohol and then dyeing with an iodine-containing dichroic colorant, is well known, e.g., April 8, 1941. Edwin date patented by date. Rand's US Patent No. 22
No. 37567.

According to that patent, a cast sheet or film of polyvinyl alcohol is first made from an aqueous solution of this material, and the dried cast sheet is then heated to a temperature at which it can be stretched by stretching, preferably in a humid atmosphere. It is disclosed that heating is performed with It is further disclosed in that patent that the stretched sheet may be bonded to a support sheet as described above. It is also disclosed that a colorant can be applied to one or both sides of the stretched sheet after cooling. After this 1943 King May 15
U.S. Pat. No. 2,375,963, issued to Alexander Thomas in D.C., describes an improvement in the process of manufacturing iodine-colored polarizers, which essentially consists of washing after iodine coloring. . This removes unbound iodine and results in a more stable product. Significant improvements in top blue self-polarizers are described in US Repatent No. 23,297, issued Nov. 28, 195 Sanno, to Mark Heyman, Jr. et al.

It is characterized by comprising a protective surface layer over an iodine-colored polyvinyl alcohol light polarizer.
The surface layer consists of an ester of polyvinyl alcohol, which ester is an ester of a polybasic acid or its derivative. To be more specific, it is an inorganic polybasic acid, and more specifically, it is boric acid. Thereby providing a polyvinyl alcohol-polyvinyl borate hybrid form. This boric acid esterification (bratio
Step n) is disclosed for significantly improving the stability of light polarizers not only against heat but also against green and ultraviolet light. This is achieved by treating the colored polarized light fader with a boric acid solution. Apparently, the esters formed on the surface of the light polarizer are believed to be polyvinyl orthoborate. The esterification reaction is accompanied by a slight decrease in the degree of molecular orientation and a loss of colorant in the reacted layer. This also causes a reduction in the dichroism of the sheet and a deterioration in its ability to pass as much as 5 to 10% of the incident light. The predominant color of the sheet also changes towards blue, ie the sheet becomes less efficient in its overall blue absorption. The reduction in blue dichroic absorption, i.e., the graying of borated polarizers,
This can be prevented by removing iodine from much of the surface layer of the sheet that is penetrated by the boric acid solution.
One method for removing this iodine is to wash the sheet with water after iodine coloring and before boric acid solution treatment. A good technique to avoid loss of blue absorption is to incorporate high levels of potassium iodide into the borate esterification solution. Obviously, this strengthens the dichromophore, which is the primary absorbing color in the blue range. After the material is borated and dried, excellent blue dichromophore stability and high levels of blue absorption are maintained. However, significant instabilities occur upon heating that result in a decrease in the absorption of red light, resulting in significant "red leakage", which occurs when two such polarizers are located at the intersection of two such polarizers. This is particularly noticeable. "Red leakage" is quite noticeable, especially in the case of polarizers with low light leakage at the lower end of the spectrum, ie the blue end. Prior art iodine-colored polyvinyl alcohol polarizers by adding zinc ions in the form of stabilizing zinc salts such as zinc chloride, zinc iodide, zinc sulfate, etc. into the polarizer after coloring. The above “red leak”
It has been found that the problem is virtually eliminated.

The stabilizing salt preferably consists of lead chloride and is applied in the borate esterification solution. Therefore, the present invention involves coloring a uniaxially oriented polyvinyl alcohol film with an iodine solution and treating the colored film with an aqueous boric acid esterification solution, wherein the boric acid esterification solution has a blue absorption property. Provided is a method for manufacturing a polarizing element, the polarizing element containing potassium iodide in an amount sufficient to substantially prevent loss, and adding zinc ions to the polarizing element after the coloring.

Further, the present invention comprises a film of polyvinyl alcohol colored with iodine and stretched in the single direction, and has a colored surface layer containing polyvinyl borate, and wherein said colored surface layer substantially eliminates the loss of blue absorption. There is also provided a polarizing element, characterized in that it also contains potassium iodide in an amount sufficient to prevent the coloring from occurring, and the zinc ions are absorbed in the surface layer after coloring.

In addition to providing heat and moisture stability, the boric acid solution has also been found to prevent iodine staining from being removed during processing of the sheet.

If the iodine-colored material is treated with a solution containing only potassium iodide and zinc chloride, without boric acid,
It was found that much of the active iodine was removed. Dichroic complexes formed by polyvinyl alcohol and iodine occur in congeners of various chain lengths, such as triodides, pentiodes, etc.

Since the spectral position of the absorption peak depends on the chain length of the dichromophore, it can be seen that there is an optimum relative concentration of long and short chain units that yields the highest efficiency for different parts of the visible region. It is theorized that the presence of zinc ions in the polarizer reduces the degradation upon heating of the dichromophore responsible for red absorption.

This dichroic red degradation is clearly increased by potassium iodide, which acts in conjunction with the dichromophore responsible for blue absorption. Therefore, the zinc ions clearly stabilize the red absorption of the iodine-colored polarizers of the present invention and also prevent the dichromophores responsible for such absorption from deteriorating upon heating. The inventors note that zinc chloride has been used in redox systems in the manufacture of iodine-colored polarizing elements, and that such use was published in King Edwin, August 31, 1943. No. 2,328,219, issued to Rand.

The Rand method describes soaking cellophane sheets in a solution consisting of potassium iodide and zinc chloride before contacting them with the iodine colorant. In other words, the use of zinc chloride in the manufacture of prior art polarizing elements occurs before coloring, rather than after coloring as required by the present invention. In order to distinguish between the results achieved by the present invention and those achieved by the above-mentioned U.S. Pat.
The present invention conducted an experiment in which zinc chloride was included in the iodine coloring agent.
The results obtained and the differences between these results and those achieved with the present invention are discussed below. Generally, in manufacturing the polarizer of the present invention, a sheet of polyvinyl alcohol having a thickness of 0.000 to 0.051 mm is sized to 3.5 to 4 times its normal size by methods well known in the art. Stretch in the direction.

Stretched polyvinyl alcohol sheet with a thickness of 0.1
Laminate on one side with a layer of cellulose acetate butyrate on the 27 to 0.343 side. The cellulose acetate butyrate sheet may be provided with a scratch-resistant coating on the side opposite the side to which it was laminated to the stretched polyvinyl alcohol, such as that disclosed in U.S. Pat. No. 3,097,106. Celerose acetate butyrate can be laminated to a sheet of polyvinyl alcohol by any suitable method known in the art, but in particular with any suitable adhesive, preferably an adhesive comprising a solution of polyvinyl alcohol. I can do it. In addition, the cellulose acetate butyrate material may include isomal dyes, which provide cosmetic functions such as coloring polarizers and the like. The exposed surface of the stretched polyvinyl alcohol is then passed through the surface of the iodine tint, essentially floating along the surface.

This compound is preferably a mixture of iodine, potassium iodide and water, and is described in more detail below. Excess iodine colorant is wiped off and the sheet is then floated onto a borate composition containing potassium chloride, boric acid, zinc chloride, and water. It is then wiped, dried, abraded, and laminated to another sheet of cellulose acetate butyrate to protect both sides of the polarizer. FIG. 1 is an explanatory diagram of the method of the present invention.

FIG. 2 was passed through a "red-leak" stabilizing salt, i.e., potassium iodide-free boric acid esterification solution.

FIG. 2 is a graph showing the relationship between optical density and wavelength of an iodine colored light polarizer. FIG. 3 is similar to FIG. 2 and depicts the optical density of an iodine colored polarizer as a function of wavelength when only zinc chloride is added to the borate esterification solution.

FIG. 4 is a graph showing the optical density of an iodine-colored polarizer as a function of wavelength when only potassium iodide is added to the boric acid esterification solution as in FIG.

FIG. 5 is a graph depicting the optical density of a polarizer of the present invention as a function of wavelength when both potassium iodide and zinc chloride are added to the boric acid esterification solution.

Figure 6 graphs the optical density of an iodine-colored light polarizer as a function of wavelength when zinc chloride is added to the iodine bath, while only potassium iodide is present in the borate esterification solution. FIG.

A film of polyvinyl alcoat approximately 1.5 mil thick was uniaxially stretched to 3.6 times its original size. The stretched sheet is then laminated to a sheet of cellulose acetate butyrate coated thereon with a film of polyethylene glycol dimethyl acrylate according to the method described in US Pat. No. 3,097,106. The cellulose acetate butyrate is laminated to the polarizer with a suitable adhesive, such as polyvinyl alcohol, methanol, a cross-linking agent, and water, preferably to a thickness of 0.38 mm. Referring now to FIG. 1, a roll 1 of laminated and stretched polyvininyl alcohol-cellulose acetate butyrate material is guided over a suitable roll 2 and drawn across the surface of the iodine color plate 3.

The layer of polyvinyl alcohol contacts the surface of the casing, while the top layer of cellulose acetate butyrate is generally kept away from contact with the surface. The roll 4 is just a guide roll and does not function to float the layer on the surface of the case. The composition of the iodine colorant is iodine, potassium iodide and water, preferably in a weight ratio of 1/15.82/32.
It is 8.

The temperature of the grate is maintained at 35° C. and the residence time of any point of the web across the surface of the grate is approximately 19 seconds. Once the web is out of the bath, it passes through wiper 5, which is merely a wet towel, to case 6, where potassium iodide, boric acid, zinc chloride and water are preferably used, similar to the treatment in case 3. is 1.95/1.25/1/25.67 in weight ratio
The surface of the boric acid esterified composition consisting of
The temperature of the boric acid esterification bath is about 1650F and the residence time at any point on the web is between 25 and 30 seconds. If you get out of this position, Webb will move to the second wiping area 7.
It is preferably a perforated roll with a towel wrapped around the outside and a vacuum applied from the inside of the roll. To keep the roll moist, gently spray its outer surface with water. After being wiped dry, the web is directed to a furnace 8 where it is exposed to an air stream at approximately 94° C. to dry and then is unrolled again at 9. Samples of polarizer made essentially according to the above except for one modification of the formulation were dried for 75 minutes in the dry state to determine the thermal stability of the polarizer.
℃ for 1 hour.

In the following examples, we will compare various polarizers, especially the optical density in the visible spectrum, from 2nd to 6th in the chart.
As shown above. This shows that the polarizer of the present invention is undoubtedly superior to both prior art polarizers and polarizers made according to variations of the prior art approach. Example 1 A polarizing element was manufactured according to the method described for Figure 1 with the following modifications: Film 1 This film excluded both the first grade containing iodine and potassium iodide and potassium iodide and zinc chloride. was exposed to the second case.

Therefore, the first case consists of iodine, potassium iodide and water in a weight ratio of 1/15.82/328, and the second case consists of boric acid and water in a weight ratio of 1/20.54. Film 2 has the same weight ratio of iodine, potassium iodide, and water as in film 1, with a weight ratio of 1/15.82/328;
The weight ratio of boric acid, zinc chloride and water is 1.25/1/
Produced using a bath consisting of 25.67.

The first grade of film 3 contains iodine, potassium iodide and water in a weight ratio of 1/15.82/328, similar to the previous two.
The second bath contains boric acid, potassium iodide, and water in a weight ratio of 1/1.
It was made from a material that fits 1.56/20.54.

Film 4 is the same as the previous three, using a first bath containing iodine, potassium iodide, and water in a weight ratio of 1/15.82/328, and boric acid, potassium iodide, zinc chloride, and water in a weight ratio of 1/15.82/328. 1
．． 25 No. 1.95/1/25.67 was exposed. Film 5 consists of iodine, potassium iodide, zinc chloride, and water in a weight ratio of 1/15.82/12/328, and boric acid, potassium iodide, and water in a weight ratio of 1/1. 56/20.Exposed to the second class including 54.

After each film was dried, the samples were exposed in the dry state to 75 qo for one period, and the exposed samples were run on a Caley Model 14 spectrophotometer to measure the optical density of the polarizing element as a function of wavelength. The respective optical densities are shown in the charts from FIG. 2 to FIG. 6. In each figure, the solid line represents the optical density of the sample before exposing it to 75qo for 1 hour, and the wavy line represents that of the sample after exposing it to 75°C for 1 hour. The curve labeled dz relates to the optical density obtained when the transmission axis of the sample polarizer and the polarization axis of the spectrophotometer polarizer are perpendicular to each other, and the curve labeled dy relates to the optical density obtained when the transmission axis of the sample polarizer is perpendicular to the polarization axis of the polarizer of the spectrophotometer. It relates to the optical density of the sample polarizer when parallel to the polarization axis of the spectrophotometer polarizer.
Referring first to FIG. 2, it is clear that both the pre-heat and post-heat curves exhibit significant blue leakage at their intersection.

This is also true for the curves in Figure 3, except that it is clear that the zinc chloride significantly increases the optical density of the polarizer in the red region, an effect that the present invention intended to achieve. be. Now looking at FIG. 4, the presence of potassium iodide virtually eliminated the blue leakage of the polarizer both before and after heating.

However, the red absorption is lower than that listed in FIG. Figure 5, which depicts optical density versus wavelength for a preferred polarizer of the present invention, shows that by including zinc chloride along with potassium iodide in the boration solution, "blue leakage" is actually reduced qualitatively, and the red reaction It also shows that the reduction in "red leakage" is the highest.

In particular, note that the optical density of the polarizer in FIG. 4 is less than 1 at 75 m, while the optical density of the polarizer in FIG. 5 is greater than 1.5. 3rd 6th
The curves in the figure clearly show the difference that occurs when zinc ions are added. It is not sufficient for zinc ions to be applied anywhere during the manufacture of iodine-colored polarizers;
It must be applied next to the iodine coloring step. For example, if you compare FIG. 63 and FIG. 4, you cannot help but notice the similarity of this one curve. After heat stabilization they are practically similar. The conclusion from this is that zinc ions, when present in the colorant, do not have a significant effect on the optical response of the polarizer. If anything, it will reduce blue absorption. By means of the present invention a highly efficient polarizing element has been produced which finds utility in general as well as special cases.

A situation as close as possible to absolute extinction at the intersection point is required, for example in light-shielding glasses used by welders and others who are suddenly exposed to extremely bright visible light that is potentially harmful to the eyes. It is. Since certain modifications may be made to the above-described products and manufacturing methods without departing from the scope of the claimed invention, no modifications may be made to the above-described products and manufacturing methods contained in the above description or shown in the accompanying drawings. All matters set forth herein are provided by way of example only and should not be construed in a limiting sense. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an illustration of the method of the invention.

Figure 2 is a graphical representation of the optical density versus wavelength of an iodine-colored light polarizer passed through a boric acid esterification solution containing no ``red-leak'' stabilizing salts, i.e., potassium iodide. be. Figure 3 is similar to Figure 2;
FIG. 3 depicts the optical density of an iodine colored polarizer as a function of wavelength when only zinc chloride is added to the borate esterification solution. FIG. 4 is a graph showing the optical density of an iodine-colored polarizer as a function of wavelength when only potassium iodide is added to the boric acid esterification solution as in FIG. 3. FIG. 5 is a graph depicting the optical density of a polarizer of the present invention as a function of wavelength when both potassium chloride and zinc chloride are added to the boric acid esterification solution. Figure 6 graphs the optical density of an iodine-colored polarizer as a function of wavelength when zinc chloride is added to the iodine bath, while only potassium iodide is present in the borate esterification solution. FIG. In Figures 2-6, the solid line represents the optical density of the sample before exposing the sample to 75QO for 1 hour, and the wavy line represents the optical density of the sample after exposing the sample to 75QO for 1 hour. Figure 1 Figure 3 Figure 2 Figure 4 Figure 5 Figure 6

Claims (1)

[Claims] 1. When a uniaxially stretched polyvinyl alcohol film is colored with an iodine solution and the colored film is treated with an aqueous boric acid ester solution, the boric acid ester solution absorbs blue color. 1. A method for producing a polarizing element, comprising potassium iodide in an amount substantially sufficient to prevent loss of the polarizing element, and further comprising adding zinc ions into the polarizing element after the coloring. 2. The method according to claim 1, wherein zinc ions are added to the polarizing element after coloring by containing zinc ions in the boric acid esterification solution. 3. The method of claim 2, wherein zinc ions are provided by dissolving zinc chloride in the boric acid esterification solution. 4. The method according to any one of claims 1 to 3, wherein the boric acid esterification solution contains boric acid. 5 consisting of a uniaxially oriented polyvinyl alcohol film colored with iodine and having a colored surface layer comprising polyvinyl borate, wherein said colored surface layer is sufficient to substantially prevent loss of blue absorption. A polarizing element characterized in that it also contains potassium iodide in an amount and that zinc ions are absorbed in the surface layer after coloring.