HK1132333B - Glass polarizer for visible light - Google Patents

Description

Glass polarizer for visible light

Technical Field

The present invention relates to a glass polarizer having industrially usable polarization characteristics for light in the visible light region. In particular, the present invention relates to a glass polarizer for visible light, which is useful as a polarizer for projection-type liquid crystal display devices and has excellent heat resistance and light resistance.

Background

In recent years, projection-type liquid crystal display devices have been widely used as image display devices for displaying large-sized screens. The rear projection type liquid crystal display device is mainly used as a large television, and the front projection type liquid crystal display device is mainly used for displaying data of a personal computer. A projection type liquid crystal display device has a structure in which an image on a small liquid crystal element is projected on a large screen in an enlarged manner by a projection optical system. For example, non-patent document 1 (large screen display) discloses a technical detailed description.

Fig. 1 shows a configuration diagram of a typical projection type liquid crystal display device. Light from the light source 4 is separated into blue (B), green (G), and red (R) components by the optical members 5 to 16, and is introduced into the corresponding liquid crystal elements 2B, 2G, and 2R, respectively. Each of the liquid crystal display elements 2R, 2G, and 2B includes incident-side polarizers 1R, 1G, and 1B on the incident side, and includes emission-side polarizers 3R, 3G, and 3B on the emission side. The polarizers of one set, which are composed of the incident-side polarizer and the exit-side polarizer corresponding to red, green, and blue, have a function of selectively passing light having a predetermined polarization direction that has passed through the liquid crystal element. With this function, light of three primary colors passing through the liquid crystal elements 2R, 2G, and 2B becomes an image signal modulated in light intensity. These three primary color lights are further synthesized by the synthesizing prism 17 and projected onto the screen 19 by the magnifying projection lens system 18.

The polarization characteristics required for the polarizer are properties of transmitting an optical signal having a desired polarization plane and blocking an unwanted optical signal having a polarization plane orthogonal thereto. That is, the light transmittance of the present invention is a characteristic of exhibiting a large transmittance for light having a desired polarization plane and exhibiting a small transmittance for light having a polarization plane orthogonal thereto.

These ratios of transmittance, referred to as extinction ratios, are widely used by those skilled in the art as performance indicators for the performance of polarizing elements. If this index is used, the performance required of the polarizing element used in the projection type liquid crystal display device is represented by a large transmittance and a large extinction ratio for an optical signal. The industrially available polarizer preferably has a transmittance of 70% or more and an extinction ratio of 10: 1, more preferably 3000: 1, with respect to light of the wavelength used (patent document 1).

In the society, there is a demand for a projection type liquid crystal display device that realizes a larger and clearer image by a smaller device. In order to achieve this demand, the application of a light source of a larger light amount and the use of a liquid crystal element of a smaller area have become recent technological trends. As a result, light having high energy density is introduced not only into the liquid crystal cell but also into the polarizers provided before and after the liquid crystal cell. For a polarizer having a function of absorbing unnecessary light, high heat resistance and light resistance are particularly required.

As a polarizer, there are a dichroic polarizer and a non-dichroic polarizer (Brewster type polarizer, etc.) that selectively absorb light depending on the polarization plane, according to the principle (see patent document 2). The dichroic polarizer is thin and does not require a special device for absorbing unnecessary light, and is therefore suitable for a projection type liquid crystal display device which is required to be miniaturized.

Currently, dichroic polarizing elements that achieve practical optical properties in the visible region are only polarizing films containing organic materials. However, a polarizer made of an organic resin has a critical disadvantage of low heat resistance (see patent document 1).

In order to overcome this drawback, a polarizing film made of an organic resin is used by being bonded to a sapphire substrate having high thermal conductivity (patent document 3). However, a polarizer bonded to sapphire having excellent thermal conductivity cannot meet the technical requirement of increasing brightness in recent years, that is, the requirement of preventing deterioration of the polarizing function due to absorption of light and heat by a polarizing element in a green region having the highest brightness, and a cooling device including a cooling fan is provided in a projection-type liquid crystal display device in order to protect an organic resin film from heat. The cooling device not only violates the social demand for miniaturization, but also causes other problems such as noise.

As a method for solving this technical problem, an idea of applying a polarizing glass suitable for an element for optical communication has been proposed (patent document 1). However, since the wavelength of light used for optical communication is significantly different from that of visible light because the wavelength of light is in the far infrared region, it is not possible to directly apply the technique of glass polarizers for optical communication to projection type liquid crystal display devices that control light of visible light. In the invention disclosed in patent document 1, a technique for imparting effective characteristics to a glass polarizing element with respect to light in the visible light region is not disclosed, and therefore, it is difficult to realize a projection type liquid crystal display device using a glass polarizer only with the invention.

Here, the technical background of the polarizing glass will be briefly described. The polarizing glass is characterized in that metal fine particles having shape anisotropy are dispersed in orientation in an optically transparent glass matrix, and polarization characteristics are realized by utilizing an anisotropic resonance absorption phenomenon of surface plasmon (surface plasmon) present on the surface of the metal fine particles (see patent document 4 and non-patent document 2).

Fig. 2 shows the surface plasmon resonance absorption characteristics of the metal fine particles cited in patent document 4. Graph a of fig. 2 corresponds to surface plasmon resonance absorption by spherical metal fine particles. On the other hand, the resonance absorption of the metal fine particles having shape anisotropy extending in a rod shape exhibits different characteristics depending on the correlation between the polarization plane of incident light and the metal fine particles having shape anisotropy.

When the polarization plane is parallel to the longitudinal direction of the metal fine particle, the characteristic shown by B is exhibited. It is found that the wavelength of resonance absorption shifts to a longer wavelength than in the characteristic a. The resonance absorption wavelength depends on the ratio of the major axis and the minor axis of the metal fine particle, and it is known that the larger the ratio is, the larger the resonance absorption wavelength is (see non-patent document 2). On the other hand, the property represented by the characteristic C is exhibited for light having a polarization plane orthogonal to the longitudinal direction.

As can be seen from FIG. 2, this glass exhibits polarization characteristics for light in the vicinity of 600 nm. That is, light having a polarization plane parallel to the longitudinal direction of the metal particles has a small transmittance due to strong absorption. In addition, the following transmittance for light having a polarization plane parallel to the longitudinal direction of the metal particles is represented by T |%. On the other hand, light having a polarization plane orthogonal to the longitudinal direction of the metal particles is weakly absorbed because of its low absorptionThis exhibits a relatively large transmittance. Further, the transmittance of light having a polarization plane orthogonal to the longitudinal direction of the metal particles is represented by T^⊥% of the total weight of the composition. According to such a mechanism, polarization characteristics are realized. The characteristics disclosed in fig. 2 do not achieve the characteristics required for the projection-type liquid crystal display device, that is, do not achieve a sufficiently large ratio between the parallel absorption curve B and the vertical absorption curve C at 500nm to 600nm, that is, an extinction ratio, and do not achieve a sufficiently large value of parallel absorptance.

Many techniques have been proposed with respect to polarizing glass and glass polarizers using polarizing glass. Many of these techniques relate to a glass polarizer applicable to light in the infrared region (patent documents 5 and 6), and do not disclose a technique applicable to light in the visible region used in a projection-type liquid crystal display device, which is an object of the present invention.

Few inventions have been directed to glass polarizers that can be adapted for use with light in the visible region. Patent document 7 provides a polarizing element effective for light in the visible light region by utilizing the characteristics of copper fine particles having shape anisotropy (the disclosed characteristics are shown in fig. 3). However, as is clear from fig. 3, it is not possible to realize a large extinction ratio for a wavelength of 600nm or less, that is, a ratio (extinction ratio) of each of the parallel transmittance curves D, F to a value of the transmittance curve C, E perpendicular to the extension axis is small, and the value of the transmittance C is only 10 to 60%, and thus, it is not practical.

Patent document 8 discloses a technique for realizing dichroic absorption with respect to a wavelength in the visible light range, but since there is no specific and quantitative description that is applicable to the characteristics of a projection-type liquid crystal display device, that is, high transmittance and high extinction ratio, which are the objects of the present invention, it is difficult to say that a polarizer can be realized. Patent document 9 also proposes a technique for obtaining an effective extinction ratio in the visible light region, as in patent document 8, but does not disclose a technique for achieving a high transmittance.

CODIXX markets polarizing glass effective in the visible light region by using a manufacturing technique in which silver ions are introduced by diffusion from the glass surface, fine silver particles are deposited by heat treatment, and then, the fine silver particles are subjected to drawing to impart shape anisotropy thereto (non-patent document 3). However, the ion diffusion step is generally unstable, and the concentration distribution of silver ions can occur in the thickness direction of the glass, so that the size of the generated silver particles tends to be non-uniform. As a result, there is a disadvantage that the characteristic of the polarizer varies. Further, since the extended particles are solid metallic silver particles, the particles must be extended with a greater extension tension than silver halide particles extended in a droplet state, and there is a problem that glass is easily broken during extension.

Infrared light glass polarizers for communications, which are widely used in industry, are manufactured by a method different from the above method. That is, as shown in patent documents 4 and 5, a manufacturing method is employed in which silver halide is temporarily precipitated and then reduced to produce fine silver particles. However, the polarizer produced by this production method does not exhibit practical performance that can be used in the visible region (patent document 5). For example, fig. 1 of patent document 5 (cited as fig. 4 in the present invention) and paragraph [0022] of the specification are explained as follows. [.. silver halide glasses do not meet this requirement when making light polarizers that are effective over the entire region of 400-700 nm. ]

As described above, there is no glass polarizer for visible light that can be applied to a projection-type liquid crystal display device based on a stable manufacturing technique that can be widely used industrially.

Patent document 1: japanese patent laid-open publication No. 2004-77850

Patent document 2: japanese Kohyo publication No. 2002-519743

Patent document 3: japanese patent laid-open publication No. 2000-206507

Patent document 4: U.S. Pat. No. 4,479,819 publication

Patent document 5: japanese patent No. 1618477

Patent document 6: japanese patent No. 2740601

Patent document 7: japanese patent No. 2885655

Patent document 8: japanese Kokai publication Hei-2004-523804

Patent document 9: japanese examined patent publication (Kokoku) No. 2-40619

Patent document 10: japanese patent No. 2628014

Patent document 11: japanese patent No. 3549198

Non-patent document 1: sitagliptin, large screen デイスプレイ (シリ - ズ tip デイスプレイ technical 7), simultaneous publishing, imperial dynasty and over 2002

Non-patent document 2: link, M.A.EI-Sayed, J.Phys.chem.B103(1999) pages 8410-8426

Non-patent document 3: Wood I and I materials Vol.52, No.12, 102-107

Disclosure of Invention

The purpose of the present invention is to provide a technique for realizing a glass polarizer having excellent transmittance and extinction ratio for light in the visible light region (500nm to 600nm) using a glass containing silver halide as a starting material, which can be applied to a projection-type liquid crystal display device or the like.

The glass polarizer of the present invention utilizes surface plasmon resonance of metal fine particles having shape anisotropy and dispersed in a glass in an oriented manner. The prior art shown in fig. 4 cannot realize the performance that a polarizer applicable to a projection type liquid crystal display device should have using the same principle. The reason for this will be described with reference to fig. 2.

Curve C of fig. 2 shows that surface plasmon resonance absorption exists around about 380nm for light having a polarization plane orthogonal to the longitudinal direction of the metal fine particle having shape anisotropy. At the same time, curve C of fig. 2 also shows that its influence relates to the range from 500nm to 600 nm. This effect means an effect of transmitting light having a polarization plane to pass through at a relatively high transmittance. Meanwhile, the absorption of light having a polarization plane parallel to the longitudinal direction is shown by a curve B, indicating that a large difference in absorptance, i.e., transmittance, occurs in the vicinity of 600nm due to the difference in the polarization plane.

In the case of a polarizer suitable for light in the infrared region, since the wavelength of transmitted light is far from the wavelength of resonance absorption, the above-mentioned influence is negligible, and there is no problem in practical use. In contrast, when a polarizing element for visible light is to be implemented, the above-described influence cannot be ignored. Therefore, in order to realize a glass polarizer suitable for visible light in the green region, a new technical means for minimizing light absorption in the wavelength region of 500nm to 600nm is required. As a simple technical means, the transmittance for the transmitted light can be improved by suppressing such absorption by reducing the concentration of the metal particles, but in the case of employing such a technical means, it is difficult to suppress light having a polarization plane to be suppressed. As a result, the desired extinction ratio cannot be achieved.

The inventors, after studying this problem, found that the transmittance near 500nm can be improved by reducing the size of the silver particles. That is, it was found that by using silver particles made of silver halide having a particle diameter of 40nm or less, the transmittance T for light having a polarization plane perpendicular to the longitudinal direction of the metal fine particles can be increased^⊥％。

In addition, when silver halide having a small particle diameter is used, a particular effect is produced in which the transmittance T | |% of light blocked by the polarizer, that is, light having a polarization plane parallel to the longitudinal direction of the metal fine particles having shape anisotropy is suppressed to a small value up to around 500 nm. As a result, not only can silver halide with a small particle size be usedTo increase the transmittance T of light to be transmitted in the vicinity of 500nm^⊥% while maintaining a large extinction ratio.

The present invention is based on the conventional technique in that a glass material in which silver halide is dispersed and precipitated is used as a starting material, but it is necessary to add several additional techniques in order to achieve a function effective for light in the visible light region.

In the conventional technique of using a silver halide polarizing glass for optical communication used in the near infrared region of 1.3 to 1.5 μm, particles of a mixed crystal of silver chloride and silver bromide and having a particle diameter of 50nm or more are elongated to produce a polarizing glass. Therefore, the technique related to the polarizing glass for visible region of the present invention is not disclosed at all.

In the present invention, the particle size of the silver particles and the components for precipitating the silver halide particles were examined in detail, and it was found that the transmittance T of light to be transmitted in the vicinity of 500nm can be improved when the particles of silver chloride containing no bromine were used alone^⊥% and increase extinction ratio.

In a projection type liquid crystal display device, a mercury lamp is used as a light source, and a visible light source often contains an ultraviolet light component. The glass on which the fine particles of silver halide are precipitated has the following characteristics: if ultraviolet light is irradiated to the glass, an absorption band from a visible region to a near infrared region is generated, and the glass is colored; this characteristic is widely known under the name of photochromic glass, and is returned to a state before irradiation when ultraviolet light is blocked.

In the transmission spectrum (T | | spectrum) of light having a polarization plane parallel to the longitudinal direction of the metal fine particles having shape anisotropy in fig. 2, the wavelength region of 500 to 700nm is easily absorbed, but a transmission peak is generated in the wavelength region of 300 to 400nm due to the inversion mode of surface plasmon resonance absorption. Since the band light corresponds exactly to the photosensitive wavelength of silver halide, the silver halide remaining inside the polarizing glass without being reduced is photosensitive, thereby reducing the transmittance in the visible region. Therefore, as the polarizing glass for the visible region of the present invention, a material that does not exhibit photochromism is preferably selected.

As prior arts related to a polarizing glass which does not exhibit photochromism, there are: the mother glass composition is limited to be substantially free of CuO (molar ratio (R)₂O-Al₂O₃)：B₂O₃< 2.5) (patent document 9); substantially free of CuO and added with an effective amount of CeO for maintaining silver in the glass in an oxidized state₂The technique of (patent document 10); and K substantially not containing CuO and limited to contain much₂And BaO is added to strengthen the alkali component of the glass, thereby preventing silver from being reduced to metallic silver (patent document 11).

In the present invention, by adding 0.5 to 5 wt% of an alkali oxide as a nitrate as a glass raw material in glass melting, silver can be dissolved into ions in glass, and photochromic-free glass can be obtained. That is, CuO and CeO, which have been used as oxidizing agents for silver in the prior art, are not added₂And a photochromic-free glass can be obtained without limiting the composition of the mother glass.

As described above, according to the present invention, it is possible to provide a glass polarizer having a transmittance of 75% or more and an extinction ratio of 25dB or more in a wavelength region of 500nm to 600 nm. A projection type liquid crystal display device using a glass polarizer having such properties and excellent heat resistance and light resistance (particularly ultraviolet resistance) can use a light source with higher energy, and as a result, a small and brighter display device can be realized. In addition, although the performance of the conventional resin polarizing film deteriorates due to heat or light, the use of polarizing glass having excellent heat resistance and light resistance makes it possible to maintain a high image quality state of the projection type liquid crystal display device.

Drawings

Fig. 1 is a conceptual diagram of an optical engine of a liquid crystal projector (patent document 1).

Fig. 2 shows absorption spectra of the extended oriented silver particles and the non-oriented silver particles (patent document 4).

Fig. 3 is a graph showing the transmittance of light polarized by visible light due to the elongation of copper particles (patent document 7).

Fig. 4 is a graph showing the light transmittance of visible light polarization by extension of silver particles (patent document 7).

FIG. 5 is a graph showing the light transmittance and extinction ratio in the wavelength range of 480nm to 620nm of example 1.

FIG. 6 is a graph showing the light transmittance in the wavelength range of 480nm to 620nm and the extinction ratio of example 2.

FIG. 7 is a graph showing the light transmittance in the wavelength range of 480nm to 620nm and the extinction ratio of example 3.

FIG. 8 is a graph showing the light transmittance in the wavelength range of 480nm to 620nm and the extinction ratio of example 4.

FIG. 9 is a graph showing the light transmittance in the wavelength range of 480nm to 620nm and the extinction ratio of example 5.

FIG. 10 is a graph showing the light transmittance in the wavelength range of 480nm to 620nm and the extinction ratio of example 6.

FIG. 11 is a graph showing the light transmittance and extinction ratio in the wavelength range of 480nm to 620nm of comparative example 1.

FIG. 12 is a graph showing the light transmittance and extinction ratio in the wavelength range of 480nm to 620nm of comparative example 2.

Detailed Description

Hereinafter, embodiments of the present invention will be described. The manufacturing technique for carrying out the present invention is based on a known technique for manufacturing polarizing glass for infrared rays, and is realized by adding a technique for refining precipitated particles of silver halide and a technique for preventing the occurrence of photochromism.

First, a glass batch having a predetermined composition is prepared. In this case, the components and raw materials are selected in consideration of the following matters. For glasses suitable for polarizers used in the visible light region, it is necessary to select glasses having no so-called photochromic property in which transmittance is deteriorated by light irradiation. Therefore, the glass raw material needs to take measures to strictly avoid the contamination of copper oxide impurities. The amount of silver halide introduced is selected so as to achieve both the transmittance and the extinction ratio.

A glass batch having a predetermined composition dissolved therein is poured into a mold to produce a plate-like glass. Next, metal halide particles are precipitated in the mother glass by heat treatment. Generally, the precipitation conditions are such that the particle size decreases as the heat treatment temperature is lower and the heat treatment time is shorter. The heat treatment conditions are optimized according to the kind and composition of the glass.

The mother glass in which the metal halide particles having an average particle diameter of 40nm or less are dispersed is processed into a plate-like preform by a predetermined process and is conveyed to an elongation step.

In the elongation step, the preform is elongated by adjusting the viscosity (directly, heating temperature) and elongation tension (force for elongating glass, i.e., load on glass) of the glass so that the reduced metal particles have an appropriate aspect ratio.

The glass after elongation is subjected to a reduction treatment so that a part or all of the silver halide particles after elongation become silver particles. The time, temperature and atmosphere of the reduction treatment determine the depth of the layer of reduced metal particles present near the surface and must therefore be carefully determined to achieve the final properties. After that, an antireflection film is formed to complete the polarizing element of the present invention.

Examples

The present invention will be described in more detail below with reference to examples and comparative examples. Table 1 shows examples and comparative examples. In addition, the technical scope of the present invention is not limited to the following examples.

TABLE 1

	Example 1	Example 2	Example 3	Example 4	Example 5	Example 6	Comparative example 1	Comparative example 2
									Temperature of Heat treatment (. degree.C.)	590	600	610	615	620	630	640	650
Heat treatment time (Hr)	4	5	5	5	5	5	5	5
									Average particle diameter of silver chloride (nm)	18	23	25	28	32	37	45	55
Viscosity of glass when extended (poise)	10	10	10	10	10	10	10	10
									Glass preform transport speed (mm/min)	5	5	5	5	5	5	5	5

	Example 1	Example 2	Example 3	Example 4	Example 5	Example 6	Comparative example 1	Comparative example 2
									Drawing speed of glass (mm/min)	160	160	120	120	120	100	80	80
Extension tension (kgf/cm))	650	600	550	530	510	500	450	400
									Hydrogen reduction temperature (. degree. C.)	445	445	440	435	430	425	420	420
Hydrogen reduction time (Hr)	6	6	6	6	6	6	6	6
									Average transmission (T)％)	82	79	78	77	76	75	63	51
Minimum extinction ratio (dB))	27	25.5	29	26	26	25	8.7	8.4

First, the SiO is added to the reaction mixture in an amount of weight percent₂：58.01％、B₂O₃：18.3％、Al₂O₃：9.5％、LiO₂：1.9％、Na₂O：2.0％、K₂O: 9.6%, Ag: 0.32%, Cl: 0.37% of SiO₂、H₃BO₃、Al(OH)₃、Li₂CO₃、NaNO₃、(Na₂CO₃)、K₂CO₃NaCl and AgCl are used as raw materials to be mixed to prepare raw material ingredients. At this time, NaNO as a nitrate raw material was used₃(sodium nitrate) 2 wt% Na was prepared₂And O. The raw material batch was melted at 1430 ℃ for 4 hours in a platinum crucible having a capacity of 300cc, and then poured into a mold and pressed with a roll to obtain a plate-like glass having a thickness of approximately 250X 60X 2.5 mm.

The plate-like glass was heat-treated to precipitate silver chloride particles. The particle size of the silver chloride particles was controlled by the heat treatment temperature and the heat treatment time shown in table 1. Table 1 also shows the results of measuring the average particle diameter of the silver chloride particles by an electron microscope.

The obtained glass preform was vertically set in an extension furnace, the transfer speed and the withdrawal speed of the preform were balanced, and the preform was transferred downward at a constant speed while being heated and extended. The viscosity and extension tension (load applied to the glass per unit area) of the glass during extension are shown in table 1. The elongation tension is controlled mainly by the glass heating temperature. (their speed settings are also shown in table 1).

After the glass ribbon after elongation was cut into a length of about 50mm and both sides were polished, it was subjected to a heat treatment under reducing conditions (temperature, time) shown in table 1 while flowing hydrogen gas at a rate of about 1.5 l/min in a reducing furnace.

Then, a film forming step is performed in which, after cleaning and drying, a plurality of samples are set in a deposition chamber, and SiO is formed on both surfaces of the samples by a sputtering method or a vacuum deposition method₂And Ta₂O₅Alternating 4 layers of film (anti-reflective film) to have an anti-reflective effect.

The polarization characteristics of the polarizing glass thus produced are also shown in table 1. Further, fig. 5 to 10, 11 and 12 show transmittance spectra (T) of light having a polarization plane orthogonal to the longitudinal direction of the metallic silver particles in the wavelength region of 500nm to 600nm (practically, 480nm to 620nm) in examples 1 to 6 and comparative examples 1 to 2^⊥%) and extinction ratio in this wavelength region.

The average transmittance T of light having a polarization plane orthogonal to the longitudinal direction of the metallic silver particles in a wavelength region of 500 to 600nm in the transmission spectrum, measured by using a spectrophotometer^⊥Percent and the average transmittance T | |%, of light having a polarization plane parallel to the longitudinal direction of the metallic silver particles, and extinction were calculated by the following formulaAnd (4) the ratio. In addition, Table 1 shows the minimum extinction ratio in the wavelength region of 500nm to 600 nm.

Extinction ratio (dB) 10 × log₁₀(T^⊥％/T||％)

As is clear from table 1, the average particle diameter of the deposited silver chloride decreases as the heat treatment temperature decreases if the glass composition is the same. Under the condition that the average particle diameter is less than or equal to 40nm (examples 1 to 6), the average transmittance (T) of light with a polarization plane perpendicular to the longitudinal direction of the metallic silver particles is obtained in the wavelength region of 500nm to 600nm^⊥％_500～600nm) 75% or more, and a polarization characteristic in which the minimum extinction ratio in the wavelength region is 25dB or more.

In the case of comparative examples 1 and 2 having an average particle diameter of more than 40nm, as shown in Table 1, even when a relatively low elongation tension is used, and T is adjusted to be^⊥The transmission spectrum and extinction ratio are shifted to the long wavelength side simultaneously to change the extension condition and the reduction condition, and the average transmittance (T) of 75% or more cannot be obtained in the wavelength region of 500nm to 600nm^⊥％_500～600nm) And a minimum extinction ratio of 25dB or greater.

Comparative example 3

Dissolution the Cl: 0.1%, 0.2% in 0.37% by weight with an equimolar amount of Br: the glass substituted by 0.23% and 0.45% was heat-treated so that the average particle diameter of the silver halide particles became 18nm in the same manner as in example 1 to prepare a glass preform, and the glass preform was prepared into a polarizing glass by the same method and under the same conditions as in example 1 to compare the polarization characteristics. As a result, both spectra of light of the polarization plane orthogonal to the major axis and minor axis directions of the metallic silver particles were shifted to the long wavelength side as a whole with an increase in Br amount, and the average transmittance and the minimum extinction ratio at 500nm to 600nm were reduced from 82 dB and 27dB of example 1, which are only Cl, to 76 dB, 25dB, 68 dB, and 8dB, respectively.

Next, the glass polarizers obtained in examples 1 to 6 and comparative examples 1 and 2 were irradiated with a 500W xenon lamp for 15 minutes at a distance of 40cm, and the presence or absence of photochromic properties was determined by visually observing the color change of the glass due to the irradiation and measuring the change in transmittance at 650nm before and after the irradiation. As a result, it was confirmed that no photochromic property was exhibited in any of the polarizers obtained in examples 1 to 6 and comparative examples 1 and 2, and no change was observed before and after the irradiation. This means that the glass polarizer of the present invention does not cause deterioration of polarization characteristics and deterioration of transmittance characteristics even when irradiated with ultraviolet light and visible short-wavelength light.

Comparative example 4

Using NaNO as the nitrate source₃(sodium nitrate) 0.2 wt% of Na was introduced₂O, and a raw material batch was mixed without using any other nitrate raw material, and the raw material batch was dissolved to obtain a glass having the same composition as described above, and photochromic properties were clearly observed in a glass polarizer produced from the glass under the same conditions with irradiation of a xenon lamp. This is because the unreduced silver chloride particles inside the glass polarizer are exposed to light to cause a decrease in transmittance at 650 nm.

As described above, by controlling the average particle diameter of the silver chloride precipitated and dispersed in the mother glass to 40nm or less depending on the heat treatment conditions, good polarization characteristics, that is, an average transmittance (T) of 75% or more can be realized in the green wavelength region of 500 to 600nm^⊥％_500～600nm) And an extinction ratio of 25dB or greater.

Further, a polarizer which does not exhibit photochromic properties, that is, which does not cause deterioration of polarization properties and deterioration of transmittance properties even when irradiated with ultraviolet light or visible short-wavelength light, can be obtained by introducing a compound containing substantially no copper as a glass component and a nitrate as a glass raw material into a portion corresponding to 0.5 to 5 wt% of the glass oxide composition and melting the introduced compound.

As described above, according to the present invention, it is possible to provide a light-emitting element having an average transmittance (T) of 75% or more in a green wavelength region of 500nm to 600nm^⊥％_500～600nm) And an extinction ratio of 25dB or more. It can be used for liquid crystal display devices such as liquid crystal projectors with sufficient performance. In addition, if a conventional polarizer used by attaching a polarizing film made of a resin having weak heat resistance and ultraviolet resistance to sapphire, quartz glass, or a glass substrate is considered, the optical engine itself of the projector can be simplified by replacing the mother glass with the glass polarizer of the present invention which is borosilicate glass having excellent heat resistance and thermal shock resistance, and for example, cooling measures including a cooling fan can be reduced or eliminated. Further, the glass polarizer of the present invention does not exhibit photochromic properties and hardly deteriorates other performances, so that high quality of image quality of the liquid crystal projector can be maintained as it is, and as a result, the life of the liquid crystal projector itself can be extended.

Claims (3)

1. A glass polarizer for visible light, which is produced by heating and elongating a borosilicate glass having silver halide particles dispersed and precipitated therein by heat treatment, and then reducing at least a part of the silver halide particles oriented and elongated in the glass to metallic silver particles,

in a wavelength region of 500nm to 600nm of light having a polarization plane orthogonal to the longitudinal direction of uniaxially oriented dispersed metallic silver particles having shape anisotropy, the average transmittance is 75% or more, and the extinction ratio in the wavelength region is 25dB or more,

the silver halide particles dispersed and precipitated in the glass by the heat treatment have an average particle diameter of 40nm or less.

2. The glass polarizer for visible light according to claim 1,

the silver halide particles dispersed and precipitated in the glass by the heat treatment are particles of silver chloride.

3. The glass polarizer for visible light according to claim 1 or 2,

the borosilicate glass is an alkaline earth aluminoborosilicate glass which does not exhibit photochromic properties, and is obtained by introducing a compound substantially free of copper as a glass component and melting the glass raw material in an amount corresponding to 0.5 to 5 wt% of the glass oxide composition using a nitrate.