JP2011157265A - Method for manufacturing crystallized glass - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a crystallized glass which has sufficient shielding performance against visible rays and high transmittance for infrared rays, and its transmission properties of visible rays and infrared rays are hardly degraded even in long-term use. <P>SOLUTION: The method for manufacturing the crystallized glass is characterized by containing (1) a process for preparing a raw material powder so as to have a composition which contains, by mass%, 55-73% of SiO<SB>2</SB>, 17-25% of Al<SB>2</SB>O<SB>3</SB>, 2- 5% of Li<SB>2</SB>O, 2.6-5% of TiO<SB>2</SB>, 0.01-1% of SnO<SB>2</SB>, and 0.005- 0.3% of V<SB>2</SB>O<SB>5</SB>, and substantially does not contain As<SB>2</SB>O<SB>3</SB>and Sb<SB>2</SB>O<SB>3</SB>, (2) a process for producing a precursor glass by melting the raw material powder, and (3) a process for forming crystal nuclei by heat-treating the precursor glass in a temperature range of 765-785°C for at least 10 minutes. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to crystallized glass used for a top plate of a cooker having an IH (electromagnetic induction heating device), a halogen heater or the like as a heat source.

The top plate used in cooking devices that use IH, halogen heaters, etc. as the heat source is not easily damaged (high mechanical strength and thermal shock resistance), has a beautiful appearance, and is resistant to corrosion (high chemical durability) ) And high transmittance of infrared rays, which are heat rays. As a material satisfying such characteristics, there is a low-expansion transparent crystallized glass whose main crystal is a β-quartz solid solution (Li ₂ O—Al ₂ O ₃ —nSiO ₂ (n ≧ 2)). It is used.

  Low-expansion transparent crystallized glass is prepared by mixing various glass raw materials at a predetermined ratio, melting process to melt glass raw materials at a high temperature of 1600-1900 ° C. to obtain a homogenized fluid, and various shapes by various methods. It is manufactured through a molding process for molding, an annealing process for removing strain, and a crystallization process for precipitating fine crystals. The crystallization step includes a nucleation step for precipitating microcrystals serving as crystal nuclei and a crystal growth step for growing crystals.

Since the low-expansion transparent crystallized glass produced in this way is generally transparent to visible light, when it is used as it is as a top plate, the internal structure of the cooker arranged below the top plate can be directly seen. It is inferior in appearance. Therefore, the crystallized glass itself is colored with a colorant such as V ₂ O ₅ (for example, see Patent Document 1), or a light shielding film is formed on the surface of the crystallized glass (for example, see Patent Document 2). Used in a state where the visible light is sufficiently shielded.

By the way, it is thought that coloring of glass by a coloring agent such as V ₂ O ₅ is caused (intensified) by interaction with As ₂ O ₃ or Sb ₂ O ₃ used as a fining agent. However, As ₂ O ₃ and Sb ₂ O ₃ have a large environmental load, and their use is being restricted in recent years. If As ₂ O ₃ or Sb ₂ O ₃ is simply excluded from the conventional glass composition, the coloring efficiency by the colorant tends to be lowered. Although it is possible to improve the visible light shielding effect by increasing the amount of the colorant, there is a problem that the infrared transmittance is lowered according to this method.

On the other hand, it has been proposed to add, for example, SnO ₂ or the like instead of As ₂ O ₃ or Sb ₂ O ₃ as a component that enhances the coloring efficiency of the colorant (see, for example, Patent Document 3). According to this method, it is possible to obtain a top plate that has a low environmental load and is excellent in infrared transparency and visible light shielding properties.

Japanese Patent Publication No. 3-9056 JP 2003-68435 A JP-T-2004-523446

  The crystallized glass described in Patent Document 3 has excellent infrared transmittance at the start of use, but has a problem that the infrared transmittance decreases as it is used for a long time. Being able to maintain a high infrared transmittance even after long-term use is important not only from the viewpoint of cooking performance but also from the viewpoint of energy saving.

  Moreover, although there is no direct influence on the cooking performance, the visible light transmittance is also lowered by long-term use, so that there is also a problem that only the heated portion is easily discolored.

  Therefore, the present invention provides a crystallized glass that has sufficient visible light shielding performance, has high infrared transmittance, and does not easily lose visible light and infrared transmission characteristics even when used for a long time. Let it be an issue.

  As a result of intensive studies by the present inventors, the transmission performance of visible light and infrared rays decreases due to long-term use because crystallization has not progressed sufficiently. It was determined that the cause was a change in the composition of the glass phase. Then, it discovers that the said subject can be solved by performing heat processing so that crystallization fully advances, and proposes as this invention.

The present invention provides: (1) _{mass%, SiO 2 55~73%, Al} 2 O 3 17~25%, Li 2 O 2~5%, TiO 2 2.6~5.5%, SnO 2 A step of preparing a raw material powder so as to have a composition containing 0.01 to 1%, V ₂ O ₅ 0.005 to 0.3% and substantially not including As ₂ O ₃ and Sb ₂ O ₃ ; (2) a step of producing a precursor glass by melting raw material powder, and (3) a step of heat-treating the precursor glass in a temperature range of 765 to 785 ° C. for at least 10 minutes to form crystal nuclei. The present invention relates to a method for producing crystallized glass.

  In crystallization of the precursor glass having the above composition, a large number of crystal nuclei can be precipitated by performing a heat treatment in the temperature range of 765 to 785 ° C. for at least 10 minutes (for example, 10 minutes to 2 hours). Thereafter, by crystal growth, crystallization can sufficiently proceed in a short time. For this reason, the crystallized glass produced according to the present invention hardly undergoes crystallization even if it is subsequently heated. As a result, the composition change of the matrix glass phase accompanying heating can be suppressed, and the change with time in the transmission characteristics in the visible region and the infrared region can be reduced.

In addition, although SnO ₂ exists in the matrix glass, the color tone is likely to fluctuate. However, when heat treatment is performed under the above conditions, crystal nuclei containing a large amount of SnO ₂ are likely to precipitate, and SnO ₂ in the matrix glass is easily precipitated. The amount is reduced. Therefore, since the change in the SnO ₂ concentration in the matrix glass phase accompanying heating becomes small, the change with time in the transmission characteristics in the visible region and the infrared region is reduced also from this viewpoint.

  In addition, the coloring mechanism of the crystallized glass obtained by the manufacturing method of this invention is as follows.

In the glass, V ions are mainly present in a 3-5 pentavalent state, but it is presumed that the crystallized glass is colored due to tetravalent V ions present in the matrix glass phase. Furthermore, it is known that when the tetravalent V ions are combined with TiO ₂ present in the matrix glass phase, the degree of coloring is further increased (visible light transmittance is reduced). Thus, the coloring of crystallized glass is greatly influenced by the amount of tetravalent V ions and TiO ₂ in the matrix glass phase.

On the other hand, it has been found that the valence of V ions changes due to the presence of Sn (particularly, the redox action of Sn ions). By appropriately limiting the ratio of V ₂ O ₅ and SnO ₂ , the amount of tetravalent V ions increases, and the coloring effect of V ₂ O ₅ can be maximized.

By the way, when the crystallized glass of the present invention is used as a top plate for a cooker for a long period of time, crystallization further proceeds by heating during use. As crystallization proceeds, the matrix glass composition changes, and in the matrix glass phase, the concentrations of tetravalent V ions and TiO ₂ that do not contribute to the crystal composition are relatively increased. As a result, the binding state between tetravalent V ions and TiO ₂ changes, and the transmittance in the visible region and the infrared region changes. Therefore, if TiO ₂ is present in excess relative to tetravalent V ions, the binding state between the tetravalent V ions and TiO ₂ is less likely to change even when the matrix glass composition changes due to long-term use. Visible light transmittance hardly changes.

The crystallized glass obtained by the production method of the present invention is a crystallized glass containing a β-quartz solid solution as a main crystal. However, the β-spodumene solid solution (Li ₂ O) is transformed from the β-quartz solid solution by heating over a long period of use. _{-Al 2 O 3 -nSiO 2 (n} ≧ 4)) to occur crystal transition, has a property of causing cloudiness. When white turbidity occurs in the crystallized glass, the appearance changes and the infrared transmittance decreases due to scattering. As ₂ O ₃ and Sb ₂ O ₃ are known to be components having a large effect of promoting crystal transition. Since the crystallized glass obtained by the production method of the present invention does not substantially contain As ₂ O ₃ and Sb ₂ O ₃ , it does not easily undergo crystal transition, and the transmittance change in the visible region and the infrared region due to long-term use is small. It has the characteristics.

Further, As ₂ O ₃ and Sb ₂ O ₃ are considered to have a large environmental load, and their use is being restricted in recent years. Since the crystallized glass obtained by the production method of the present invention does not substantially contain these components, it can reduce the environmental load at the time of disposal. In the present invention, “substantially does not contain” refers to a level in which these components are not intentionally added as raw materials but mixed as impurities contained in various glass raw materials. Specifically, the content is It means 0.1% or less.

  Secondly, the method for producing crystallized glass of the present invention further includes (4) a step of growing crystals by heat-treating the precursor glass on which crystal nuclei are formed at a temperature range of 800 to 930 ° C. for at least 10 minutes. It is characterized by including.

  According to this configuration, crystallization is further facilitated, and the temporal change in transmission characteristics in the visible region and the infrared region can be further reduced.

  Thirdly, the present invention relates to a crystallized glass produced by any one of the above production methods.

  Fourth, the crystallized glass of the present invention is characterized in that the absorbance change rate at a wavelength of 700 nm after heat treatment at 900 ° C. for 50 hours is 20% or less.

  Fifth, the present invention relates to a top plate for a cooker using any one of the above crystallized glasses.

In the production method of the present invention, first, by mass%, SiO ₂ 55 to 73%, Al ₂ O ₃ 17 to 25%, Li ₂ O 2 to 5%, TiO ₂ 2.6 to 5.5%, SnO ₂ 0 The raw material powder is prepared so as to have a composition containing 0.01 to 1%, V ₂ O ₅ 0.005 to 0.3% and substantially not including As ₂ O ₃ and Sb ₂ O ₃ . The reason for limiting the composition in this way will be described below.

SiO ₂ is a component that forms a glass skeleton and constitutes a β-quartz solid solution. The content of SiO ₂ is 55 to 73%, preferably 60 to 71%, more preferably 63 to 70%. When the content of SiO ₂ decreases, the thermal expansion coefficient tends to increase, and it becomes difficult to obtain crystallized glass having excellent thermal shock resistance. In addition, chemical durability tends to decrease. On the other hand, when the content of SiO ₂ is increased, the meltability of the glass is lowered, or the viscosity of the glass melt is increased, so that it is difficult to form the glass.

Al ₂ O ₃ forms a glass skeleton and is a component constituting a β-quartz solid solution. The content of Al ₂ O ₃ is 17 to 25%, preferably 17.5 to 24%, more preferably 18 to 22%. When the content of Al ₂ O ₃ decreases, the thermal expansion coefficient tends to increase, and it becomes difficult to obtain crystallized glass excellent in thermal shock resistance. In addition, chemical durability tends to decrease. On the other hand, when the content of Al ₂ O ₃ increases, the meltability of the glass decreases and the viscosity of the glass melt increases, which tends to make it difficult to form the glass. Further, the glass tends to be devitrified due to the precipitation of mullite crystals, and cracks are likely to be generated in the glass from the devitrified portion, so that molding becomes difficult.

Li ₂ O is a component that constitutes a β-quartz solid solution, has a great influence on crystallinity, and lowers the viscosity of the glass to improve the meltability and moldability. The content of Li ₂ O is 2 to 5%, preferably 2.3 to 4.7%, more preferably 2.5 to 4.5%. When the content of Li ₂ O is reduced, the glass tends to be devitrified by mullite crystals, and cracks are likely to be generated in the glass from the devitrified portion, so that molding becomes difficult. Moreover, when crystallizing glass, it becomes difficult to precipitate β-quartz solid solution crystals, and it becomes difficult to obtain crystallized glass excellent in thermal shock resistance. Furthermore, the meltability of the glass tends to decrease or the viscosity of the glass melt tends to increase, making it difficult to mold the glass. On the other hand, when the content of Li ₂ O increases, the crystallinity becomes too strong and coarse crystals are likely to precipitate in the crystallization process. As a result, it becomes cloudy and a transparent crystallized glass cannot be obtained or is easily damaged. It becomes difficult to form.

TiO ₂ is a component constituting a crystal nucleus for precipitating a crystal in the crystallization step, and has an action of enhancing the coloration of tetravalent V ions. The content of TiO ₂ is 2.6 to 5.5%, preferably 2.6 to 5%, more preferably 2.8 to 4.8%, and still more preferably 3 to 4.5%. When the content of TiO ₂ decreases, the amount remaining in the matrix glass phase without being used as crystal nuclei decreases, so that it is difficult to combine with tetravalent V ions, and the color development efficiency tends to be low. In addition, when crystallization proceeds with long-term use, as described above, the concentration of tetravalent V ions and TiO ₂ in the glass matrix increases, and the bonding state of the two changes. (Especially, the color becomes darker). Furthermore, since a sufficient number of crystal nuclei are not formed, the grain size of crystals grown from the individual crystal nuclei becomes large (coarse crystals), and it becomes difficult to obtain a crystallized glass that is cloudy and transparent. On the other hand, when the content of TiO ₂ increases, the glass tends to be devitrified from the melting step to the molding step, and it becomes easy to break, so that molding becomes difficult.

SnO ₂ is a component that enhances color development by increasing tetravalent V ions, which are coloring components. SnO ₂ content is 0.01-1%, 0.03-0.7%, 0.03-0.6%, 0.03-0.3%, 0.03-0.25%, especially It is preferable that it is 0.05 to 0.23%. When the content of SnO ₂ is reduced, tetravalent V ions are not efficiently generated, so that the coloring effect is hardly increased. When the content of SnO ₂ is increased, the glass tends to be devitrified when it is melted and molded, so that the molding becomes difficult. Further, even with the same composition, the color tone tends to change easily due to slight differences in melting conditions and crystallization conditions.

V ₂ O ₅ is a coloring component. The content of V ₂ O ₅ is preferably 0.005 to 0.3%, 0.01 to 0.3%, 0.02 to 0.2%, particularly preferably 0.03 to 0.15%. When the content of V ₂ O ₅ is reduced, the coloring becomes thin and the visible light cannot be sufficiently shielded. On the other hand, when the content of V ₂ O ₅ increases, the infrared transmittance tends to decrease. Further, the crystal transition from the β-quartz solid solution to the β-spodumene solid solution is likely to cause white turbidity.

Note that As ₂ O ₃ and Sb ₂ O ₃ are not substantially contained for the reasons described above.

  In addition to the above, various components can be added as long as the required properties are not impaired.

MgO is a component that dissolves in β-quartz solid solution crystals instead of Li ₂ O. The content of MgO is 0 to 1.5%, preferably 0 to 1.4%, more preferably 0.1 to 1.2%. When the content of MgO is increased, the crystallinity becomes too strong and tends to devitrify, and as a result, the glass is easily broken and molding becomes difficult.

  ZnO is a component that dissolves in the β-quartz solid solution crystal in the same manner as MgO. The content of ZnO is 0 to 1.5%, preferably 0 to 1.4%, more preferably 0.1 to 1.2%. When the content of ZnO increases, the crystallinity tends to be too strong. For this reason, if the glass is molded while being slowly cooled, the glass tends to devitrify and break, and thus, for example, it is not suitable for molding by the float process.

ZrO ₂ is a component constituting a crystal nucleus for precipitating crystals in the crystallization step, like TiO ₂ . The content of ZrO ₂ is 0 to 2.3%, preferably 0 to 2.1%, more preferably 0.1 to 1.8%. When the content of ZrO ₂ increases, the glass tends to be devitrified in the melting and forming process of the glass, making it difficult to form the glass.

The total amount of TiO ₂ and ZrO ₂ is 3.8 to 6.5%, preferably 4.2 to 6%. When the total amount of these components increases, the glass tends to be devitrified in the melting and forming process, and it becomes difficult to form the glass. On the other hand, when the total amount of these components is too small, crystal nuclei are not sufficiently formed, and the crystal is likely to be coarsened. As a result, it becomes difficult to obtain a crystallized glass that is cloudy and transparent.

P ₂ O ₅ is a component that promotes phase separation of glass. Since crystal nuclei are likely to be generated at the place where the glass is phase-separated, P ₂ O ₅ serves to assist the formation of crystal nuclei. The content of P ₂ O ₅ is 0 to 2%, preferably 0.1 to 1%. When the content of P ₂ O ₅ increases, phase separation occurs in the melting step, so that it becomes difficult to obtain a glass having a desired composition and tends to be opaque.

Na ₂ O is a component that lowers the viscosity of the glass and improves glass meltability and moldability. The content of Na ₂ O is 0.5% or less, preferably 0.3% or less, more preferably 0.2% or less. When the content of Na ₂ O is too large, crystal transition from β-quartz solid solution to β-spodumene solid solution is promoted, and thus white turbidity due to crystal coarsening is likely to occur. In addition, the thermal expansion coefficient tends to be high, and it becomes difficult to obtain crystallized glass excellent in thermal shock resistance.

In order to reduce the viscosity of the glass and improve the meltability and moldability, it is possible to add up to 5% in total of K ₂ O, CaO, SrO and BaO. CaO, SrO, and BaO are components that cause devitrification when the glass is melted. Therefore, the total amount of these components is preferably 2% or less. Moreover, since CaO has the effect | action which accelerates | stimulates the crystal transition from (beta) -quartz solid solution to (beta) -spodumene solid solution, it is better to refrain from using as much as possible.

As a clarifier, SO ₂ and Cl may be added alone or in combination as necessary. The total amount of these components is desirably 0.5% or less. As ₂ O ₃ and Sb ₂ O ₃ are also clarifying components, but are components that are considered to have a large environmental load, and it is important that they are not substantially contained.

  When a colored transition metal element (for example, Cr, Mn, Fe, Co, Ni, Cu, Mo, Cd, etc.) not described above is contained, infrared rays are absorbed or the ability to reduce Sn ions is lost (the colored transition metal). The element reacts with Sn ions, and as a result, the reaction between V ions and Sn ions may be hindered).

  The raw material powder prepared as described above is melted to obtain a crystalline precursor glass. Although a melting temperature is not specifically limited, In order to fully advance vitrification, it is preferable that it is 1600-1900 degreeC, for example. In addition, as a shaping | molding method of a molten glass, various shaping | molding methods, such as a blow method, a press method, a rollout method, and a float method, are applicable. The formed precursor glass is subjected to annealing as necessary.

  Next, heat treatment is performed on the precursor glass at a temperature range of 765 to 785 ° C. for at least 10 minutes. Crystal nuclei can be precipitated in the heat treatment step. When the heat treatment temperature is out of the range, a sufficient number of crystal nuclei are hardly formed. The temperature range of 765 to 785 ° C. is the range where nucleation is most likely to occur, and crystal nuclei can be sufficiently formed. However, if the heat treatment time is shorter than 10 minutes, the color immediately after crystallization is light and tends to cause white turbidity. On the other hand, even if the heat treatment time is too long, the amount of crystal nuclei formed is hardly increased, which is disadvantageous in terms of productivity and energy. Therefore, the upper limit of the heat treatment time is preferably 10 hours or less, 3 hours or less, particularly 2 hours or less.

  The precursor glass in which the crystal nuclei are formed is further subjected to a heat treatment to grow crystals, thereby obtaining a desired crystallized glass. Here, the heat treatment is preferably performed at 800 to 930 ° C, preferably 850 to 920 ° C, more preferably 870 to 890 ° C for at least 10 minutes in order to sufficiently promote crystallization. When the heat treatment time is shorter than 10 minutes, the color immediately after crystallization is light and tends to cause white turbidity. On the other hand, even if the heat treatment time is too long, the amount of crystal nuclei formed is unlikely to increase, which is disadvantageous in terms of productivity and energy. Therefore, the upper limit of the heat treatment time is preferably 10 hours or less, 3 hours or less, particularly 2 hours or less.

  The crystallized glass obtained by the production method of the present invention has a thickness of 3 mm and a transmittance at a wavelength of 700 nm of 35% or less, more preferably 30% or less, thereby sufficiently shielding the internal structure of the cooker. It becomes possible. On the other hand, when displaying temperature, thermal power, etc. using LED etc., it is desirable that the transmittance at a wavelength of 700 nm is 15% or more, and further 18% or more at a thickness of 3 mm. Thereby, when it uses for the top plate of a cooking appliance, it becomes possible to fully recognize the display by LED etc. through crystallized glass.

  The crystallized glass of the present invention is preferably 3% thick and has a transmittance at a wavelength of 1150 nm of 85% or more, more preferably 86% or more, because it can efficiently transmit heat rays (infrared rays).

  In addition, even if it uses for a long time for uses, such as a top plate for cookers, it is preferable that a high infrared transmittance is not impaired, and further, the visible light transmittance is not easily changed. Specifically, the crystallized glass of the present invention is 3 mm thick, and the change in transmittance at a wavelength of 1150 nm after heat treatment at 900 ° C. for 50 hours as an accelerated test is 5% or less, 3% or less, particularly 2% or less. Preferably there is. In the acceleration test, the change in transmittance at a wavelength of 700 nm is preferably 5% or less, 3% or less, particularly 2% or less.

  The crystallized glass of the present invention preferably has an absorbance change rate at a wavelength of 700 nm of 20% or less, particularly 10% or less after heat treatment at 900 ° C. for 50 hours. The absorbance change rate is calculated by the following formula.

Absorbance = −log ₁₀ (transmittance (%) / 100)
Absorbance change rate = (absorbance after heat treatment−absorbance before heat treatment) / absorbance before heat treatment × 100 (%)

The thermal expansion coefficient in the temperature range of 30 to 750 ° C. of the crystallized glass of the present invention is preferably −10 to 30 × 10 ⁻⁷ / ° C., more preferably −10 to 20 × 10 ⁻⁷ / ° C. When the thermal expansion coefficient is in this range, the glass has excellent thermal shock resistance. In the present invention, the thermal expansion coefficient is a value measured with a dilatometer.

  The crystallized glass obtained by the production method of the present invention may be subjected to post-processing such as cutting, polishing, bending, reheating press, etc., and the surface may be painted or filmed.

  The crystallized glass thus produced can be used as a top plate for IH cookers equipped with IH heaters, halogen heater cookers equipped with halogen heaters, gas cookers equipped with gas burners, and the like.

  EXAMPLES Next, although this invention is demonstrated in detail using an Example, this invention is not limited to these Examples.

  Sample No. 1 to 10 are Examples, Sample Nos. 11 to 14 are comparative examples.

  Glass raw materials were prepared so as to have the compositions shown in Tables 1 to 3, and melted at 1600 ° C. for 20 hours and further at 1700 ° C. for 4 hours using a platinum crucible. Two spacers having a thickness of 5 mm were placed on the carbon plate, molten glass was poured out between the spacers, and the plate was formed into a uniform thickness with a roller.

  The obtained plate-like sample was put into an electric furnace maintained at 700 ° C., held for 30 minutes, then turned off, and cooled (annealed) to room temperature in the furnace over 10 hours.

  Next, the cooled sample was crystallized by heat treatment in an electric furnace to obtain crystallized glass. The heat treatment profile of each sample is shown in Tables 1-3. The rate of temperature increase from room temperature to the nucleation temperature is 15 ° C./min, the rate of temperature increase from the nucleation temperature to the crystal growth temperature is 10 ° C./min, and the temperature decrease from the crystal growth temperature to room temperature is 80 ° C./min. did.

  Each crystallized glass was evaluated for transmittance and devitrification in the visible and infrared regions.

  The transmittance was measured for 700 nm and 1150 nm using a spectrophotometer (V-760 manufactured by JASCO Corporation) by processing each crystallized glass into a 3 mm-thick sample whose surfaces were mirror-polished. The measurement conditions were a measurement range of 1500 to 380 nm and a scan speed of 200 nm / min. Moreover, the transmittance | permeability was similarly measured about the sample which performed the heat processing (acceleration test) for 50 hours at 900 degreeC. Furthermore, the rate of change in absorbance after the acceleration test was calculated according to the above formula.

  The devitrification was evaluated for 24 hours by holding each sample on a platinum foil in an electric furnace set at 1350 ° C., and evaluating whether devitrification occurred. If no devitrification was confirmed, “◯” was indicated. If devitrification was confirmed, “x” was indicated.

  As is clear from Tables 1 to 3, sample No. It can be seen that the 1 to 10 crystallized glasses can sufficiently shield light in the visible region and have high infrared transmittance, and the rate of change in absorbance in the visible region is small even in an accelerated test assuming long-term use.

  On the other hand, sample No. The crystallized glass of 12 to 14 had a large absorbance change rate in the visible region after the acceleration test. Sample No. The crystallized glass No. 11 was cloudy in appearance.

  The crystallized glass of the present invention is suitable as a top plate for cooking appliances such as gas, IH and halogen heaters. It can also be used for observation windows for high-temperature furnace observation, fireproof windows, etc., in which low-expansion crystallized glass having a β-quartz solid solution as a main crystal is conventionally used.

Claims (5)

(1) in _{mass%, SiO 2 55~73%, Al} 2 O 3 17~25%, Li 2 O 2~5%, TiO 2 2.6~5.5%, SnO 2 0.01~1% , containing _V 2 _O 5 0.005 to 0.3%, the step of formulating the raw material powder so as to be substantially free composition of _as 2 _{O 3} and _Sb 2 _{O 3,} (2) raw material powder A process for producing a precursor glass by melting, and (3) a process for forming crystal nuclei by heat-treating the precursor glass in a temperature range of 765 to 785 ° C. for at least 10 minutes. Method.   The crystallized glass according to claim 1, further comprising the step of (4) heat-treating the precursor glass having crystal nuclei formed in a temperature range of 800 to 930 ° C for at least 10 minutes to grow crystals. Manufacturing method.   A crystallized glass produced by the production method according to claim 1.   4. The crystallized glass according to claim 3, wherein the absorbance change rate at a wavelength of 700 nm after heat treatment at 900 ° C. for 50 hours is 20% or less.   A top plate for a cooker using the crystallized glass according to claim 3 or 4.