JP2011059592A - Glass polarizing element and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a glass polarizing element which allows prevention or reduction in cracks due to tensile stress mainly caused by a drawing step with a large tension, and a manufacturing method thereof. <P>SOLUTION: The manufacturing method of the glass polarizing element includes: a melting step of dissolving glass containing silver ions and chlorine ions; a silver chloride deposition step of uniformly depositing a silver chloride in molten glass to form a preform; a surface treatment step of treating both surfaces of the preform into a surface roughness of Ra 20 to 100 nm; a drawing step of heating the preform subjected to the surface treatment and drawing silver chloride particles in a uniaxial direction to form a glass sheet; and a reduction step of reducing the drawn silver chloride particles in the glass sheet. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a glass polarizing element and a method for producing the same. In particular, the present invention relates to a glass polarizing element having polarization characteristics that can be industrially used for light in the visible to near infrared region.

  Glass polarizing elements have a function of selectively allowing light having a predetermined polarization plane to pass, and are therefore widely used in various optical systems. For example, it is used for a liquid crystal display including an optical communication device and a projection type liquid crystal display.

By the way, in recent years, a projection type liquid crystal display device has been widely used as a video display device for displaying a large screen. The rear projection type liquid crystal display device is mainly used for large-sized televisions, and the front type liquid crystal display device is mainly used for presentation of personal computer data. The projection type liquid crystal display device has a configuration in which an image on a small liquid crystal element is enlarged and projected on a large screen by using a projection optical system. A technically detailed description is given in Non-Patent Document 1, for example.
Nobuo Nishida, Large Screen Display (Series Advanced Display Technology 7), Kyoritsu Publishing, Tokyo, 2002

  FIG. 1 shows a configuration of a typical projection type liquid crystal display device. The light from the light source 4 is separated into blue (B), green (G) and red (R) components by the optical components 5 to 16 and guided to the corresponding liquid crystal elements 2R, 2G and 2B. Each of the liquid crystal display elements 2R, 2G, and 2B includes incident-side polarizing elements 1R, 1G, and 1B on the incident side, and outgoing-side polarizing elements 3R, 3G, and 3B on the outgoing side. A pair of polarizing elements composed of an incident-side polarizing element and an outgoing-side polarizing element corresponding to red, green, and blue has a function of selectively allowing light having a predetermined polarization direction that has passed through the liquid crystal element. With this function, the light of the three primary colors that has passed through the liquid crystal elements 2R, 2G, and 2B becomes an image signal whose light intensity is modulated. These three primary color lights are further synthesized by the synthesis prism 17 and further projected onto the screen 19 through the enlargement projection lens system 18.

  The polarization characteristic required for the polarizing element is to transmit an optical signal having a desired polarization plane and to block an unnecessary optical signal having a polarization plane orthogonal thereto. That is, it is desirable to have a large transmittance for light having a desired polarization plane and a small transmittance for light having a polarization plane orthogonal thereto.

These transmittance ratios are called extinction ratios, and are widely used by those skilled in the art as performance indexes that express the performance of polarizing elements. When this index is used, the performance required for the polarizing element applied to the projection type liquid crystal display device is expressed as having a large transmittance and a large extinction ratio with respect to the optical signal. In the case of a projection-type liquid crystal display device, it is said that the performance required for a polarizing element is desirable to have a transmittance of 75% or more and an extinction ratio of 400: 1 or more for light of a wavelength to be used ( Patent Document 1). Of course, the transmittance and extinction ratio required for the polarizing element are determined depending on the apparatus to which the polarizing element is applied.
Japanese Patent Application Laid-Open No. 2004-77850

  When it is attempted to improve the transmittance in the visible light region in the polarizing glass, it is necessary to stretch silver chloride particles having a small particle diameter with a high load. This is due to the fact that the smaller the particle size is, the less the stress is applied to the particles when the glass is stretched. In order to produce silver fine particles having the desired aspect ratio, the smaller the particle size, the higher the load. I need.

  By the way, as the particle diameter of the silver chloride particles increases, the scattering effect increases and the transmittance in the short wavelength region is reduced. For this reason, it is difficult for a polarizing glass produced by stretching a glass having a large particle diameter to realize a transmittance of 75% or more in the visible light region. In addition, when trying to improve the transmittance by stretching a glass with a large particle diameter with a large tension, the wavelength region where the orthogonal transmittance is the lowest moves to the long wavelength side, so that it is satisfactory in the visible light region. It becomes difficult to realize polarization characteristics.

  As described above, when an attempt is made to improve the transmittance in the visible light region in the polarizing glass, it is necessary to use silver chloride particles having a small particle diameter. Here, in order to produce silver fine particles having a desired aspect ratio, the smaller the particle diameter, the larger the tension required. This is because the stress is less likely to act on the particles when the glass is stretched as the particle size becomes smaller.

The inventors have clarified that the grain size of silver chloride must be 50 nm or less in order to realize a transmittance of 75% or more in the visible light region, particularly in the green light region (Patent Document 2). ).
International Publication WO2008 / 072368

  In addition, polarizing elements used in sensors and isolators require an extinction ratio of 40 dB, and the transmittance is required to be 90% or higher without AR coating. Furthermore, in order to eliminate the influence of birefringence as much as possible, it is necessary to make the size of silver halide grains present in the non-reduced region as small as possible.

However, if the particle size is reduced to this extent, the required stretching tension exceeds 500 kgf / cm ² and the probability of breaking during stretching increases. Breaking during stretching causes an increase in cost.

  Further, when the film was stretched with a stress exceeding 500 kgf / cm 2, a large tensile stress remained in the width direction of the glass sheet after stretching, causing cracks.

Patent Document 3 discloses a method of preventing cracking by performing an annealing treatment after stretching. However, the annealing treatment needs to relax the strain and gradually cool it to a temperature below the strain point. In order to alleviate strain, heating to an annealing point is generally performed, and a long time is required when annealing is performed below the glass transition temperature. When heated to the annealing point, re-sphericalization of the elongated silver halide grains proceeds even in a short time, making it difficult to obtain silver fine particles having a predetermined aspect ratio.
JP-A-2005-157402

In addition, when the film is stretched at a high roller tensile speed in order to increase the aspect ratio, a tensile stress is formed in the width direction of the glass sheet in the stretching process because the width of the preform is reduced by twice or more by stretching. . The glass sheet is pulled left and right by this tensile stress, and a crack is generated so as to tear from the center. In order to solve this, it is necessary to relieve the tensile stress or to form a compressive stress equivalent to the tensile stress. However, annealing treatment is necessary to relieve stress, and the same problem as described above occurs.

This invention is made | formed in view of the above situations, and it aims at providing the glass polarizing element which can prevent or reduce the crack resulting from an extending process, and its manufacturing method.

  In order to solve the above-mentioned problems, a method for producing a glass polarizing element according to the present invention includes a melting step of melting glass containing silver ions and chlorine ions; and a preform by depositing silver chloride inside the molten glass. A silver chloride precipitation step to be formed; a surface treatment step for processing both surfaces of the preform to a surface roughness of Ra (arithmetic mean roughness) of 20 to 100 nm; and heating the surface-treated preform to produce the silver chloride particles Extending in a uniaxial direction to form a glass sheet; and a reducing process for reducing the stretched silver chloride in the glass sheet.

  The surface treatment step can be achieved by grinding both surfaces of the preform with a # 200 to # 2000 abrasive.

As a result of sincere research and experiment, the inventors have found that silver chloride grains can be stretched with a low load by roughening both sides of the stretched preform.

  As described above, in the present invention, by using a preform having a rough surface, friction with the roller is increased, and stretching can be performed with a lower load, and the breaking during stretching is significantly reduced. . In addition, by enabling stretching under a low load, tensile stress generated in the width direction of the glass sheet can be reduced, and cracking after stretching can be prevented. Furthermore, the occurrence of slipping during stretching, which was observed when stretching a mirror-polished preform, was eliminated, and uniform tape width stretching could be realized.

  In the manufacturing process as well, the cost reduction was achieved by reducing the mirror polishing process of the preform. By roughening the surface of the preform, it is possible to transmit stress to the silver chloride grains even under a smaller load, and an excellent transmittance and extinction ratio can be realized. Furthermore, it became possible to weaken the tightening pressure of the stretching roller by increasing the frictional force. The roller clamping pressure is an important factor for achieving stretching and preventing slipping. However, if the clamping pressure is too large, the stress strain formed on the glass will affect the possibility of breakage. Was raised. Further, since the frictional force during stretching increases, slippage of the glass sheet during stretching is reduced, and a stretched glass sheet having a stable width can be obtained as compared with a mirror polished preform.

  If the surface of the preform is not ground and only silver chloride particles are deposited, a uniform thickness cannot be obtained, and a large stress is generated in the thin part, resulting in the probability of fracture. Will increase. In the present invention, the problem has been overcome by grinding the stretched preform and not performing mirror polishing thereafter.

As a result, it is possible to stably manufacture a polarizing glass having excellent transmittance and extinction ratio in the visible to near infrared region.

FIG. 1 is an explanatory diagram showing a configuration of a general projection type liquid crystal display device to which the present invention is applicable.

  Hereinafter, the best mode for carrying out the present invention will be described in detail using embodiments.

  The manufacturing technique for carrying out the present invention is carried out by devising a preform manufacturing process based on a known technique for manufacturing a polarizing glass for infrared rays.

  First, a glass batch having a predetermined composition is prepared. At this time, pay attention to the following matters and select the composition and raw materials. As a glass applied to a polarizing element used in the visible light region, it is necessary to select a glass that does not have so-called photochromic characteristics, whose transmittance is deteriorated by light irradiation. For this purpose, the glass raw material must be devised such as strictly avoiding copper oxide impurities. Further, the addition amount of silver and halogen is finally selected so that the transmittance and extinction ratio can be compatible.

  Next, the glass batch is melted and poured into a mold to produce a plate-like glass. Next, in the production technique of the present invention, silver halide is precipitated by heat treatment. At this time, the heat treatment temperature is at least 20 ° C. lower than the softening point, preferably 30 ° C., and preferably 40 ° C. or lower in the visible light polarizing element.

  Next, both surfaces of the preform on which the silver chloride particles are deposited are ground so that the surface roughness is Ra 20 to 100 nm. In order to obtain a surface roughness of Ra 100 nm, it is usually possible to use an abrasive with a roughness of about # 600. However, when the heat treatment after grinding is performed at a high temperature, a grinding material having a roughness of about # 200 can be used.

  Preferably, the both sides of the preform are ground with an abrasive of roughness # 200 to # 2000. The roughness of grinding is changed depending on the roller material to be stretched. When rubber is used as the roller material, rough grinding is preferably performed in order to achieve a large frictional force. Preferably, a large frictional force can be realized by selecting # 200 to # 1000 as the abrasive. When a hard material such as ceramics is used as the roller material, if rough grinding is performed, a large stress is generated on the unevenness of the grinding. Therefore, in such a case, it is preferable to select # 800 to # 2000 as the abrasive.

  Next, the preform having the ground surface (rough surface) as described above is stretched. In the stretching step, the glass viscosity is adjusted so that the silver halide grains have an appropriate aspect ratio and the target stretching load is adjusted, and the preform is stretched to form a glass sheet.

  Thereafter, the glass sheet stretched as described above is subjected to a reduction treatment. The time for performing the reduction treatment varies depending on the intended extinction ratio, but in the polarizing element for visible light, since the grain diameter is as small as 50 nm or less, it is necessary to reduce the silver halide grains deeper in the thickness direction. On the other hand, in the polarizing element for sensors and isolators, since the particle diameter is larger than that of the polarizing element for visible light, it can be reduced in a shorter time.

  The reduced glass sheet is formed with an antireflection film as necessary to complete the polarizing element of the present invention.

(Example 1)
The raw materials prepared so as to achieve the target composition ratio were put into a 10 liter platinum crucible and melted while stirring at a temperature of 1450 ° C. After melting for a certain time, the melt was poured into a mold to produce a glass block. Thereafter, it was molded and heat treated at a temperature 50 ° C. lower than the softening point for 4 hours to precipitate uniform silver chloride particles. Both the front and back sides of the glass preform on which silver chloride was deposited were ground with # 600 alumina abrasive.

  The ground preform was stretched with a load of 100 kgf. The probability of occurrence of breakage during stretching was 0%. The stretched glass sheet was subjected to reduction treatment at 440 ° C. for 20 hours. The width of the glass sheet was 24 to 26 mm, which was smaller than that of the mirror-polished preform.

  The glass sheet was processed to a desired size, and an AR coating was applied to reduce the reflectance in the green region to obtain a glass polarizer.

  As shown in FIG. 2, when the transmittance of the completed glass polarizing element was measured, the average transmittance from 500 to 600 nm was 83%, and the extinction ratio was 30 dB.

(Comparative Example 1)
The raw materials prepared so as to achieve the target composition ratio were put into a 10 liter platinum crucible and melted while stirring at a temperature of 1450 ° C. After melting for a certain time, the melt was poured into a mold to produce a glass block. Thereafter, it was molded and heat treated at a temperature 50 ° C. lower than the softening point for 4 hours to precipitate uniform silver chloride particles. The glass preform on which silver chloride was deposited was mirror-polished on both sides with cerium oxide having a particle size of 2 μm.

  Next, the mirror-polished glass preform was heated and stretched with a load of 120 kgf. The probability of breakage during stretching was 16%. The stretched glass sheet was subjected to reduction treatment at 440 ° C. for 20 hours. The width of the glass sheet varied widely from 24 to 30 mm.

  The glass sheet was processed to the desired size, and an AR coating was applied to reduce the reflectance in the green area.

  As a result of measuring the transmittance of the completed glass polarizing element, as shown in FIG. 2, the average transmittance from 500 to 600 nm was 82%, and the extinction ratio was 30 dB.

  The preform (Example 1) whose surface was ground and the mirror-polished preform (Comparative Example 1) exhibited the same transmittance characteristics as described above. However, the preform subjected to the grinding treatment could be stretched with a lower load.

(Comparative Example 2)
The raw materials prepared so as to achieve the target composition ratio were put into a 10 liter platinum crucible and melted while stirring at a temperature of 1450 ° C. After melting for a certain time, the melt was poured into a mold to produce a glass block. Thereafter, it was molded and heat treated at a temperature 50 ° C. lower than the softening point for 4 hours to precipitate uniform silver chloride particles. The glass preform on which silver chloride was deposited was not subjected to grinding or mirror polishing.

  Next, the glass preform was heated and stretched with a load of 120 kgf. The probability of breakage during stretching was 100%. (10 breaks / 10 stretches) Since everything was broken, a polarizing element could not be obtained.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various design changes and the like can be made without departing from the technical idea described in the claims. is there.

Claims (6)

In the method for producing a glass polarizing element,
A melting step for melting glass containing silver ions and chlorine ions;
A silver chloride precipitation step of depositing silver chloride inside the molten glass to form a preform;
A surface treatment step of processing both sides of the preform to a surface roughness of Ra 20 to 100 nm;
A stretching step of heating the surface-treated preform and stretching the silver chloride particles in a uniaxial direction to form a glass sheet;
And a reduction step of reducing the stretched silver chloride in the glass sheet.   2. The method for producing a glass polarizing element according to claim 1, wherein, in the surface treatment step, both surfaces of the preform are ground with a # 200 to # 2000 abrasive. 3.   In the silver chloride precipitation step, the molten glass is molded and heated at a temperature lower by at least 20 ° C. than the softening point to uniformly precipitate silver chloride to form a preform. The manufacturing method of the glass polarizing element of description.   A projection type liquid crystal display device using the glass polarizing element according to claim 1.   A photoelectric sensor using the glass polarizing element according to claim 1.   An isolator using the glass polarizing element according to claim 1.

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