JPH03103329A - Pressing mold for glass and production thereof - Google Patents

Abstract

PURPOSE:To stably mold a glass article having high precision by using a forming mold made of a dense silicon carbide ceramics containing Al2O3 fine particles uniformly dispersed in the bonded part of SiC and containing alpha-crystal as a major part of the SiC crystal. CONSTITUTION:The press-forming mold of glass is made of a dense silicon carbide ceramics containing Al2O3 fine particles uniformly dispersed in the bonded part of SiC and containing alpha-SiC crystal accounting for >=80% of the SiC crystal. The mold can be produced by the following method. Powder of alpha-SiC or beta-SiC is mixed with 0.5-10wt.% of Al2O3 powder and the mixture is crushed to obtain the raw material. The material is sintered to a density of >=94% using a hot-press or without applying a load and then sintered to a density of >=99% with a hot isostatic press(HIP).

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a glass molding press or mold that does not require a polishing step after press molding a glass object such as an optical glass lens or a magneto-optical disk substrate.

[Prior Art] In the conventional process of press-forming glass objects, there is a time-consuming process of grinding and polishing after press-forming to achieve the desired surface accuracy and surface quality, which poses difficulties in mass production. Efforts are being made to realize a one-shot press forming method for glass objects that can omit the grinding and polishing steps. This press molding method consists of the steps of simultaneously heating a mirror-finished press mold and the glass substrate, press-forming near the softening point of the glass, and taking out the glass object after slow cooling. Since it is directly transferred to the glass object, the finishing process of the glass object can be omitted.

The performance required of the mold material for this glass one-shot press molding method is that the mold surface be precise enough to be mirror-finished, and that the surface properties of the press mold will not change even under the glass press molding temperature atmosphere. glass substrates do not fuse together, and can withstand mechanical shock during pressing. Currently, glassy carbon and SiC [β-Si
Press molds coated with C by CVD are beginning to be used.

[Problems to be Solved by the Invention] As a press mold for one-shot press molding of glass, JP-A-47-11277 discloses the use of glassy carbon as a material. However, since glassy carbon is easily oxidized and has low hardness, it has drawbacks such as being easily scratched during processing or use, and its durability is insufficient. Furthermore, JP-A-60-176928 discloses a press mold for glass in which a cemented carbide base material is coated with a β-SiC film, but this may cause discoloration of the glass to be molded and fusion with the mold. The problem is that it is easy.

On the other hand, in JP-A No. 63-45135, the SiC base material (
111) A mold coated with a β-SiC film having plane orientation has been disclosed, but there remains the problem that scratches are likely to occur during grinding and polishing of the mold. On the SiC base material (
111) A press mold coated with a β-SiC film having plane orientation was not necessarily satisfactory, as the surface properties changed after press-molding the glass substrate 200 times, and a tendency to compromise appeared.

The present invention aims to solve these conventional techniques and provide a press mold for glass, which is a press mold for one-shot molding and can be used especially for glass substrates that have a high softening point and are easily reduced. be. That is, glass molds made by conventional techniques are susceptible to oxidation and scratches, discoloration of the glass substrate, tendency to fuse with the mold, transferability of the mold surface to the glass surface,
Furthermore, there is a problem in durability, and as a result, there is a problem in that high-precision glass products cannot be stably molded.It is an object of the present invention to provide a press mold for glass that improves this problem.

[Structure of the Invention] The present invention has been made to solve the above-mentioned problems, and in the press mold for glass of the present invention, in a ceramic mold, the material of the mold is bonded to the SiC bonding part. A1. O. The fine particles are evenly dispersed, and the SiC crystal 8
It is characterized by being made of dense silicon carbide ceramic in which 0% or more is α-SiC crystal.

In a preferred embodiment of the glass press mold of the present invention, the component of the dense silicon carbide ceramic is SiC in weight%.
90-99, 5% A1zos O. It is 5-10%.

In another preferred embodiment of the glass press mold of the present invention, the dense silicon carbide ceramic is composed of SiC crystals with an average aspect ratio of 3 or more.

In another preferred embodiment of the glass press mold of the present invention, the density of the dense silicon carbide sintered body (the density of the sintered body relative to the theoretical density) is 99% or more.

The method for manufacturing a press mold for glass according to the present invention includes α-Si
C or β-sic powder with Al. On powder from 05~
The raw material is mixed and pulverized with 10% by weight, sintered to a density of 94% or more by hot press sintering or pressureless sintering, and then 99% by hot isostatic press.
% or more.

Here, AIJs functions as a filler to densely sinter the silicon carbide ceramics, but at the same time it affects the properties of the sintered body surface. It is thought that this has some influence on the BC
The mold releasability from the glass substrate is better than when using a type of filler additive. However, in order to ensure mold releasability, Al2O3 must be present in a uniformly dispersed manner in the bonded portions of SiC. Also, α-SiC seems to have better oxidation resistance than β-SiC, and 80% of SiC crystals
The above α-SiC is necessary to ensure stable mold releasability. However, this α-SiC has β-
Even if SiC is used, it is generated during sintering, so it is not necessarily necessary to mix it into the raw material from the beginning. The material of the mold must be sufficiently dense and the number of closed pores must be minimized to prevent bottle holes caused by the pores from appearing on the surface of the mold. Open pores usually have a density of 94%
If so, it will almost disappear.

The amount of Al201 contained in the material of the mold is 0.
The content is preferably 5 to 10% by weight in order to suppress the tendency of the glass substrate to fuse. In order to improve durability, the content of Altos is more preferably 3 to 8% by weight. The material for the mold is preferably one in which SiC crystals in the structure are developed into columnar or plate shapes, and it is preferable to use a material with an average aspect ratio of 3 or more when measured in cross section. In order to develop such a structure, it is better to set the average crystal grain size to several microns or more to obtain better results. It has also been found that it is easier to obtain a structure with a large aspect ratio when β-SiC powder is used as a raw material. The density of the sintered body (the density of the sintered body relative to the theoretical density) is preferably 99% or more so that almost no closed pores appear on the surface of the mold.

In order to manufacture such a press mold, the pressureless sintering method is currently insufficient, and the method for manufacturing a press mold for glass of the present invention utilizes a hot isostatic press. However, since it requires binding at high temperatures and a suitable encapsulant cannot be found, the material must be sintered in advance using a pressureless sintering method or a hot press sintering method to a density of 94% or higher, which eliminates open pores. It is necessary to perform hot isostatic press sintering.

"Examples" The content of the present invention will be explained below with reference to Examples, but the Examples are merely illustrative of embodiments of the present invention and are not intended to limit the present invention in any way.

The press-molding die for glass shown in FIG. 1 has an upper die 1 which is a flat plate and a lower die 2 which has a concave surface and has a diameter of 40 mm, and is used for press-molding a spherical glass lens having a convex surface on one side. In the figure, 3 is a support, and 4 is a glass base to be molded.

The material for glass molds is made by adding AlzOa fine powder to β-SiC or α-SiC fine powder in the proportions shown in Table 1, wet mixing and pulverization using a ball mill, and then heating the mixture at 2000°C. It was hot pressed using a graphite mold at 300 kg/cm2, and then hot pressed at 2000°C and 1500 kg/cm2. A sintered body with a density of 99% or more is obtained through isostatic pressing, which is then ground into the shape shown in Figure 1.Finally, the press molding surface that will come into contact with the glass substrate is polished using ultra-fine diamond abrasive grains. It was polished to a mirror surface with a flatness accuracy of 0.02μ in maximum roughness.

A glass base of borosilicate optical glass BK7 was supplied to the press mold for glass produced in this way, and N2 or A
The mold and the glass base were heated and held at 730° C. in an inert atmosphere of 40° C., pressed for 60 seconds at a press pressure of 40 kg/c, and after slow cooling, the glass molded body was taken out. The results are shown in Table 1, and the surface roughness of the mold was well transferred to the glass lens obtained by the present invention, and no change was observed in the surface properties of the mold, and the glass lens obtained by the present invention could be used satisfactorily as is. It was of a quality that could be used as a glass lens. We tried press molding 200 times using the same mold,
The results of investigating changes in the surface properties of press molds were
It is also shown in the table. In addition, 8 to 9 in Table 1 are comparative examples, and the density of the sintered bodies used for the oval molds was 99% or higher, and the maximum roughness of the mold surface was polished to the same level. It is.

Furthermore, Table 2 shows the results of a similar press-molded glass lens experiment in which the glass base was changed to soda lime glass. Relief! - Pressing conditions do not need to be limited to the above conditions, for example, 0.5 to 5 at 1800 to 2100 °C
The pressure may be 50 to 400 kg/cm, and the hot isostatic press conditions are 1800 to 2100 kg/cm.
Appropriate conditions may be selected within the range of 500 to 2000 kg/cm2 for 0.5 to 5 hours at ℃. As a result, a glass press-molding mold with excellent surface properties, mold releasability, and durability can be obtained, and one-shot press molding of glass lenses and the like can be stably performed.

In addition, the α-SiC crystallization rate when β-SiC is used as a raw material is calculated from the peak value obtained by X-ray diffraction method.
It was obtained by calculating the composition values of C (4H, 6H, 15R structure) and β-SiC (3C structure).

Table 1 Press molding results of borosilicate optical glass BK7 Table 2 Press molding results of soda lime glass? [Effects of the Invention] In the glass press mold of the present invention, the main constituent phase of the material is α-SiC, which is difficult to fuse with glass due to its physical properties and has good oxidation resistance, and also has good results as a filling aid for this purpose. By creating a dense silicon carbide ceramic in which fine particles of Al2O, which exhibits The mirror-polished surface of the mold, which has no holes, is directly transferred without any deterioration in quality.The molded glass product does not require the time-consuming grinding or polishing process, and the mold is durable. . This glass press or mold can also be used to mold borosilicate glass, which has a high melting point, and can be used to mass-produce glass products at low cost, and has great industrial effects.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of a press molding die for a glass lens according to an embodiment of the present invention. In the figure, 1 is an upper die, 2 is a lower die, and a base material. 3 is a support, 4 is a gala-15' younger brother! mother

Claims (5)

[Claims] (1) In a ceramic mold for press-molding glass, the material of the mold is Al_2O in the joint part of SiC.
_3 A press molding die characterized by being made of a dense silicon carbide ceramic in which fine particles are evenly dispersed and 80% or more of SiC crystals are α-SiC crystals. (2) In claim 1, the components of the dense silicon carbide ceramic are SiC90 to 99.5% Al_2O by weight%.
_30.5-10% glass mold. (3) A press mold according to claim 1 or 2, wherein the dense silicon carbide ceramic is made of SiC crystals having an average aspect ratio of 3 or more. (4) A press mold according to any one of claims 1 to 3, wherein the density of the dense silicon carbide sintered body (sintered body density relative to theoretical density) is 99% or more. (5) Al_2O in α-SiC or β-SiC powder
The raw material is prepared by adding 0.5 to 10% by weight of the powder of _3 and mixing and pulverizing it, sintering it to a density of 94% or more by hot press sintering or pressureless sintering, and then 99% by hot isostatic pressing. A method for manufacturing a press mold for glass, characterized by sintering it to a density of % or more.