JP4453328B2 - Mold press molding glass and method for producing the same - Google Patents

Description

  The present invention relates to a glass for mold press molding and its evaluation, design and manufacturing method.

  The glass mold press molding method does not require cutting and polishing operations, and is a method for obtaining a product with high surface accuracy, and is often used for producing an aspherical lens or a substrate for a magnetic recording medium. Production of a glass product by a mold press molding method involves heating the glass to a temperature at which it is softened and deformed in a mold whose shape has been precisely processed, and then press-molding to transfer the mold shape to the glass.

  Conditions for selecting a mold used for mold press molding include high surface accuracy processing and no change in molding temperature. WC, which is a cemented carbide, is mainly used as a material. For WC, Co, Ni, Cr or the like is often used as a binder. Some of them are sintered with a small amount of TiC or TaC in consideration of corrosion resistance. Ceramics such as SiC may be used for use under high temperature conditions. There are cases where SiC is used by simply polishing the surface after sintering, and those in which surface vacancies are filled by CVD and the surface accuracy is further improved. Various SUSs may be selected depending on the pressing conditions and the molded product.

In order to improve product quality and mass productivity in mold press molding, it is necessary that the mold and glass do not melt, and it is important that the mold surface accuracy is maintained even after repeated use. .
JP-A-8-26765 JP-A-8-26766 Japanese Patent Laid-Open No. 5-1931979 JP 2001-89183 A JP 2000-1329 A JP-A-3-37130 JP-A-62-212040 Japanese Patent Laid-Open No. 10-226532

  However, depending on the type of glass, there arises a problem that the mold and the glass are fused even in a repetitive or extreme case even in a single molding. When fused, glass adheres to the surface of the mold, making it impossible to produce, impairing the surface accuracy of the mold and making it impossible to obtain a product as designed. The use of glass that does not fuse with the mold is important for improving product quality and mass productivity.

  As a method of not fusing glass, a release film on the mold surface is made of a pure metal such as Cr, Ni, W, Pt, Ir, Au, or an alloy or carbide thereof, or carbon, TiCN, TiAlN, TiN, BN, etc. Although a method for coating the film has been put to practical use, it is desired that the mold can be formed without forming a release film on the mold.

  In the present invention, a product with high surface accuracy is provided because the portion where the mold and glass are in contact with each other at the time of mold press molding is not fused to any mold and without forming a release film. It aims at providing the glass for mold press molding which can be performed, and its manufacturing method.

The method for producing a glass for mold press molding according to the present invention is a method for producing a glass for mold press molding containing 44.7 to 60% of SiO _{2 and} 0 to 4% of Al ₂ O _{3 in} terms of mass percentage. A step of preparing a composition, a step of determining the basicity of a candidate composition expressed as (total number of moles of oxygen atoms / sum of field strength of cations) × 100, and fusion property with a mold, A step of evaluating based on the obtained basicity, a step of determining that the obtained basicity is 9.5 or less and not fusing to the mold, and no fusing with the mold. The method includes a step of adopting a composition, and a step of preparing, melting, and molding raw materials so as to obtain the adopted candidate composition.

  The mold press-molding glass of the present invention is manufactured by the above method.

The glass for molding press molding of the present invention contains, by mass percentage, SiO ₂ 44.7-60%, Al ₂ O ₃ 0-4%, (total number of moles of oxygen atoms / cation field strength of cation The basicity expressed as (total) × 100 is 9.5 or less.

  ADVANTAGE OF THE INVENTION According to this invention, the glass which does not fuse | fuse with a metal mold | die can be provided. For this reason, it is not necessary to form a release film on the mold, and the manufacturing cost can be reduced. Further, the mass productivity of mold press molding can be improved, and a press product can be provided at a low cost. In addition, since it is difficult for the mold to deteriorate, it is possible to stably produce a pressed product that maintains high surface accuracy.

  In the present invention, the basicity is defined as (total number of moles of oxygen atoms / total number of positive field strength) × 100. The field strength (hereinafter referred to as FS) in the equation is obtained by the following equation.

F. S. = Z / r ²
Z represents an ionic valence, and r represents an ionic radius. The numerical values of Z and r in the present invention refer to “Chemical Handbook Basic Edition, Revised 2nd Edition (published by Maruzen Co., Ltd., 1975)”.

Here, taking SiO ₂ as an example, how to determine the basicity of the glass will be described.

First, the number of moles of oxygen atoms is obtained. In 1 mol of SiO ₂ , 2 mol of oxygen atoms are contained. Therefore, the number of moles of oxygen atoms possessed by SiO ₂ in the glass can be obtained by multiplying the number of moles of oxygen by ₂ mol by the mole percentage of SiO ₂ in the glass composition. Similarly, the number of moles of oxygen atoms of each component is obtained, and the sum is defined as “total number of moles of oxygen atoms”.

Next, F. S. Ask for. Since the cation Si ⁴⁺ is Z = 4 and r = 0.4, F.I. S. = 25. Since 1 mol of Si ⁴⁺ is contained in SiO ₂ , F. S. Is calculated as 25 × 1 (mol) × (mol% of SiO _{2 in} the composition).

  This is calculated | required about each component and let the sum total be "the sum total of FS of a cation."

  Then, the value obtained by multiplying the value obtained by dividing the “total number of moles of oxygen atoms” by the “total number of FS of cation” by 100 is defined as “basicity of glass”.

  The mechanism by which the basicity of the glass controls the fusion will be described.

  The basicity of the glass is an index indicating how much oxygen electrons in the glass are attracted to the cations in the glass. In a glass having a high basicity, the attraction of oxygen electrons by cations in the glass is weak. Therefore, when a glass having a high basicity is in contact with a cation (mold component) that has a strong tendency to demand electrons, a cation from the mold is more likely to enter the glass than a glass having a low basicity. . When the cation which is a mold component penetrates (diffuses) into the glass, the mold component concentration in the glass phase near the interface increases. Thereby, since the difference in composition between the glass phase and the mold phase is reduced, the affinity between the two is increased, and the glass is easily wetted by the mold. It is considered that the glass and the mold are fused by such a mechanism. Therefore, as the basicity is lowered, the mold components are less likely to enter the glass, and the glass and the mold are not fused.

  When WC is used for the mold, it is considered that fusion does not occur if the basicity of the glass is 11 or less, preferably 9.5 or less. If the basicity of the glass exceeds 9.5, a tendency to fuse with the mold appears, and if it exceeds 11, the glass and the mold are fused to impair the surface accuracy of the product, and the mass productivity is remarkably deteriorated. .

  Based on the above knowledge, a method for evaluating, designing, and manufacturing a glass for mold press molding will be described.

First, a glass candidate composition that satisfies desired characteristics such as refractive index, dispersion, and glass transition point is prepared. In particular, it is desirable that the glass transition point be 800 ° C. or lower in order to perform mold press molding well. That is, if the mold is exposed to a high temperature during mold press molding, problems such as cracks in grain boundaries due to growth of surface crystal grains and fusion due to promotion of diffusion of mold components into glass are likely to occur. In order to avoid such a problem, it is effective to set the press temperature (mold temperature) to 800 ° C. or less, and the glass temperature in the vicinity of 10 ¹³ poise, which is the limit viscosity capable of press molding, that is, glass It is desirable to design the glass so that the transition point is 800 ° C. or lower. In the case of a glass having a temperature corresponding to 10 ¹³ poise higher than 800 ° C., it is necessary to heat the glass to a high temperature of 800 ° C. or higher, and between the mold maintained at a temperature of about 800 ° C. in order to prevent deterioration. Temperature difference occurs. As a result, in the process of cooling and solidifying the glass, a temperature difference occurs between the surface and the inside of the glass, resulting in a state in which the glass is greatly shrunk with respect to a predetermined shape called sink, which causes a reduction in surface accuracy.

As the glass composition is not particularly limited, glass which does not contain harmful components PbO, etc., SiO ₂ 44.7 to 60% in particular in _{mass%, Al 2 O 3 0~4%} , B ₂ O ₃ 0 to 40%, P ₂ O ₅ 0 to 40%, R ¹ O 0 to 30% (R ¹ represents an alkaline earth metal), ZnO 0 to 50%, R ² ₂ O 0 to 20% (R ² represents an alkali metal), TiO ₂ 0 to 20%, ZrO ₂ 0 to 10%, La ₂ O ₃ It is preferable to select a glass having a composition range of 0 to 40%.

  Next, the basicity of the candidate composition is determined by the method described above. The basicity may be obtained by using an information processing apparatus programmed so that the above calculation is possible. For example, when the candidate composition is input to the information processing apparatus, the F.F. S. To cation F.V. S. The basicity can be calculated and output using this sum. Note that this type of program can also be stored in an information storage medium such as a CD-ROM.

Subsequently, the fusion property with a metal mold | die is evaluated based on the calculated | required basicity. In the evaluation, it is confirmed whether the basicity is below a predetermined value, and if it exceeds the predetermined value, it is judged to be fused with the mold, and if it is below the certain value, it is not fused with the mold. Judge. In the present invention, when the mold is made of WC, this value is set to 9 . Set to 5. This value can be appropriately changed depending on the press conditions, the mold material, and the like. Similarly to the calculation of the basicity, the evaluation can be processed using the information processing apparatus. For example, a certain value may be set in advance in the computer program so that it can be discriminated whether or not the calculated basicity is equal to or less than a certain value, and the result is output. Note that this type of program can also be stored in an information storage medium such as a CD-ROM.

  Subsequently, the composition is determined based on the evaluation result.

When it is determined that the obtained basicity is not a certain value (for example, 9.5 ) or less and is fused to the mold, the composition is changed so that the basicity is a certain value or less.

  When it is determined that the obtained basicity is not more than a certain value and is not fused with the mold, the candidate composition can be adopted as it is. In the latter case, it goes without saying that the composition may be finely adjusted and the basicity may be further reduced.

In the case where there are a plurality of candidate compositions, it is only necessary to select and adopt one that has a basicity of not more than a certain value and is determined not to be fused with the mold. In this case as well, the selected candidate composition may be finely adjusted to further reduce the basicity. Also for the candidate composition basicity is not 9.5 or less, may of course be employed in terms of changing the composition such that 9.5 or less.

Here, a method for reducing the basicity by changing the composition of the glass will be described. The change in basicity is mainly due to S. The influence of is great. F. S. When the component having a large value is increased, the basicity tends to decrease. S. When a component having a small value is increased, the basicity tends to increase. For this reason, when the basicity of the glass is to be lowered, for example, relatively low S. Increase the composition ratio of SiO ₂ , B ₂ O ₃ , P ₂ O ₅ , Al ₂ O ₃ or the like having a large F. S. Small Li ₂ O with, Na ₂ O, SrO, it is sufficient to reduce BaO or the like.

  Subsequently, the raw materials are prepared so that the composition is determined by the above method.

Then, the glass for mold press molding adjusted so that basicity may be set to 9.5 or less can be obtained by fuse | melting a raw material and shape | molding in a suitable shape.

In the glass thus evaluated, designed and manufactured, when the mold press molding is performed, the mold components are difficult to diffuse into the glass. As described above, diffusion of mold components into glass is involved as a factor causing fusion. For example, when mold press molding is performed in a mold mainly composed of WC, the diffusion of W is a depth of 10 μm or more. As the process proceeds, the glass and the mold are easily fused. However, the glass of the present invention adjusted to have a basicity of 9.5 or less has a feature that W hardly diffuses into the glass and is hardly fused to the mold.

Hereinafter, the present invention will be described based on examples.

  Tables 1 to 3 show candidate compositions (Nos. 1 to 12) of glass for mold press molding.

Next, the basicity of each candidate composition was determined and shown in Tables 4-6. As a result, no. 2, 3, 5, and 7 had a basicity of 9.5 or less, and it was judged that fusion did not occur when mold press molding was performed with WC.

Subsequently, no. A glass raw material was prepared so as to be a glass having a composition of 1 to 12 , and melted at 1300 to 1500 ° C. for 3 to 5 hours using a platinum crucible. Further, the glass melt was molded, and the glass transition point, the fusion property with the mold, and the diffusion depth of W after the mold contact were evaluated . The results are shown in Table 4-6.

As a result, salt base resistance degree is 9.31 or less No. It was confirmed that the samples 2, 3, 5 and 7 had a fusion rank of A, and there was no diffusion of the mold components toward the inside of the glass.

On the other hand, No. whose basicity is in the range of 9.5-11. 1, 4, 6 and 8 had a W diffusion of 1.02 to 6.25 μm in the glass internal direction. No. with basicity exceeding 11. In Nos. 9 to 12, fusion with the mold was observed, and the diffusion of W in the glass internal direction reached a depth of 10 μm or more.

In addition, in the present Example, although demonstrated using the method of employ | adopting what becomes basicity 9.5 or less, it is not limited to this, About the basicity exceeded 9.5 , It goes without saying that a method employed after changing the composition to 9.5 or less can also be implemented.

  The glass transition point is measured by preparing a glass raw material and melting it at 1300 to 1500 ° C. for 3 to 5 hours using a platinum crucible, and then pouring the glass melt on a carbon table and annealing it to obtain a size of φ5 × 20 mm. After processing, the differential thermal dilatometer was used. The linear portion of the low temperature region and the abnormal expansion region of the thermal expansion curve obtained by the differential thermal dilatometer was extended, and the temperature corresponding to the point where they intersected was determined as the glass transition point.

The fusion property with the mold was evaluated as follows. First, glass raw materials are prepared and melted at 1300-1500 ° C. for 3-5 hours using a platinum crucible, and then the glass melt is poured onto a carbon table and annealed to obtain a cylindrical sample having a diameter of 5 mm and a height of 5 mm. It was processed into. Next, the sample was allowed to stand on the WC mold, heated to 800 ° C. in an N ₂ atmosphere, and held for 15 minutes. After heating, the sample was removed, the inside of the 5 mm diameter circle on the surface of the mold that was in contact with the sample was observed, and the degree of fusion was divided into 4 ranks A to D as shown in Table 7. In this evaluation, it can be determined that ranks A and B are not fused, and ranks C and D are fused.

  The diffusion depth of W after contact with the mold is obtained by vertically dividing the sample removed from the mold after heating, taking a cross section from the mold contact surface toward the inside of the glass, and analyzing by electron probe microanalysis (EPMA). Went. From the analysis result, the diffusion depth of W from the mold-glass interface toward the inside of the glass was determined.

Claims (3)

A method for producing a glass for mold press molding containing 44.7 to 60% SiO _{2 and} 0 to 4% Al ₂ O _{3 in} terms of mass percentage, comprising preparing a candidate composition, and (number of moles of oxygen atoms The sum of the cation field sum) and the step of determining the basicity of the candidate composition expressed as 100, and the step of evaluating the fusibility with the mold based on the determined basicity, A step of determining that the obtained basicity is 9.5 or less and not fused with the mold, a step of adopting a composition determined not to be fused with the mold, and a candidate composition adopted The method of manufacturing the glass for mold press molding characterized by including the process which mix | blends a raw material so that it may become, and fuse | melts and shape | molds.   A mold press-molding glass produced by the method of claim 1. SiO ₂ 44.7-60%, Al ₂ O ₃ 0-4% by mass percentage, ( basicity expressed as (sum of moles of oxygen atoms / sum of field strength of cations) × 100) The glass for mold press molding characterized by having a 9.5 or less.