JPS6141221B2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to an investment material for tooth casting.

Metal molded products for teeth such as metal crowns and inlays are
A wax material is injected into the impression-taken plaster model to form a wax mold, and this wax mold is made of a binder such as gypsum, phosphate, or ethyl silicate, and a refractory material such as silicic acid anhydride powder or cristobalite. The tooth is buried in the investment material, and then the investment material is heated to dissolve the wax mold to form a cavity in the investment material, and hot water containing a molten tooth casting alloy is poured into the cavity. Then, it is cooled and solidified and then cast. In the process of casting and molding described above, when the investment material is heated to melt the embedded wax mold, as the investment material expands, the cavity formed by the wax mold also expands, and this expanded When the molten alloy injected into the cavity is cooled and solidified, it contracts and a metal molded product of a desired shape is obtained. However, conventionally used investment materials use fireproof materials such as silicic acid anhydride and cristobalite, which have a relatively low density and low thermal expansion. Then, the shrinkage of the casting alloy was corrected by further expanding it by means of water absorption expansion, hardening expansion, etc. However, when the investment material is subjected to large water absorption expansion and hardening expansion during hardening, the investment material expands toward the opening of the cylindrical casting ring in which it is filled, so the amount of expansion in the vertical and horizontal directions is different. Therefore, there was a problem in that the void space was deformed and it was difficult to obtain a metal molded product with a desired shape.

In view of the above problems, there has been a need for investment materials that expand a large amount when heated and have a small amount of expansion when hardened.

As a result of intensive research in response to the above-mentioned needs, the inventors of the present invention have found that ceramics such as quartz glass, which have been made highly dense by heat treatment under high pressure, expand significantly when heated to return to the original quartz glass. Moreover, they found that the amount of shrinkage during the cooling process after heating was small, and that this performance was suitable as an investment material for tooth casting.

In other words, the present invention provides high-density quartz glass that is made highly dense through heat treatment under high pressure and expands greatly upon heating, but has a small amount of shrinkage in the cooling process after heating, or a combination of the high-density quartz glass and silicic anhydride. This is an investment material for tooth casting characterized in that a bonding material is mixed into the mixture.

The high-density quartz glass used in this invention is
It is manufactured by a high-pressure method that is known as one of the means for growing ceramic single crystals. For example, when quartz glass is used at a pressure of 10GPa or less and a temperature of 700℃ or less,
It can be obtained by performing pressure heat treatment for a heating time of 10 minutes or less, then cooling to room temperature, and then lowering the pressure to normal pressure. The density of high-density quartz glass depends on the above pressure, and the relationship between pressure and density is shown in the graph of FIG. 1. As shown in Figure 1, normal quartz glass with a density of 2.2 g/cm ³ begins to become denser at a pressure of 3 GPa, and as the pressure increases, the density increases, and at a pressure of 8 GPa, it becomes denser.
A product of 2.6 gcm ³ was obtained, and the higher the temperature during pressurization, the higher the density at a relatively lower pressure. Therefore, the density of high-density quartz glass is determined by the pressure at the time of pressurization,
A desired result can be obtained by appropriately selecting and combining temperatures.

High-density quartz glass has a large amount of thermal expansion upon heating, and a small amount of contraction during the cooling process after heating.A specific example of the thermal expansion during heating will be described below.

Octahedral pyrofluorite is used as a pressure medium, and in this pressure medium, a cylindrical quartz glass with a diameter of 10 mm and a length of 12 mm, a graphite heater, and a thermocouple made of an alloy of platinum/rhodium = 87/13 are installed. This was installed in an MA-8 high pressure generator, pressurized with a 10,000 ton press at the appropriate pressure and temperature, held for 10 minutes, allowed to cool naturally, depressurized, and produced high-density quartz glass with different densities. was manufactured.

Next, the high-density quartz glass was cut into a cylindrical sample with a length of 10 mm, and the coefficient of linear expansion (%) of this sample was measured and calculated using a thermal dilatometer (manufactured by Rigaku Denki Co., Ltd.).

FIG. 2 is a graph showing changes in linear expansion coefficients of silica glass having different densities. As seen in the graph of FIG. 2, the higher the density, the greater the rate of increase in the coefficient of linear expansion, and the higher the coefficient of linear expansion. The coefficient of linear expansion of quartz glass with a density of 2.557 g/ ^cm3 reaches approximately 4% two hours after the start of heating.
It can be seen that even after being held at 1000°C, expansion continues as the heating time increases.

Figure 3 is a graph showing the relationship between temperature and coefficient of linear expansion when the heating rate of quartz glass with a density of 2.557 g/cm ³ is different. has been shown to increase.

Figure 4 is a graph showing the relationship between heating time and coefficient of linear expansion when heating temperature is raised in stages. It can be seen that there is no significant difference in the expansion rate.

As can be understood from the graphs in Figures 2 to 4 above, the amount of expansion when high-density quartz glass is heated can be controlled arbitrarily by changing the degree of densification, heating temperature, heating time, etc. be able to.

When using the above-mentioned high-density quartz glass as an investment material for casting, the high-density quartz glass returns to the original quartz glass when heated, so the amount of shrinkage in the cooling process after heating is extremely small. but,
The amount of shrinkage during the cooling process can be adjusted by mixing a binder such as gypsum or phosphate with high-density quartz glass, or by further mixing silicic anhydride.

Figure 5 shows only high-density quartz glass with a density of 2.557 g/cm ³ (graph A), and the above-mentioned high-density quartz glass.
A mixture of 75 parts by weight and 25 parts by weight of gypsum (a-CaSO ₄ 1/2 H ₂ O) (graph B), and a mixture of 37.5 parts by weight of high-density quartz glass, 37.5 parts by weight of silicic anhydride, and 25 parts by weight of gypsum.
This is a graph showing the coefficient of linear expansion when a three-way mixture (graph C) with parts by weight was heated and maintained at 680°C and then cooling was started 2.5 hours after the start of heating. As can be seen in the graph in Figure 5, the coefficient of linear expansion of A, which is made only of high-density quartz glass, does not decrease during the cooling process after 2.5 hours of heating, and there is almost no cooling contraction. B and C, in which silica glass and the same amount of silicic acid are mixed, show a slight decrease in linear expansion coefficient during the cooling process and undergo slight cooling shrinkage. Furthermore, even in the case of gypsum or a mixture of gypsum and silicic acid, the coefficient of linear expansion reaches 1.7% 2.5 hours after the start of heating, and it tends to expand if the heating time is further extended.

The coefficient of linear expansion in Figure 5 above is calculated by crushing high-density quartz glass in an agate mortar and adding 30% by weight to this powder.
After adding and kneading water, gypsum, and silicic acid, a dry sample for a cylinder with a length of 10 mm was prepared, and the values were measured and calculated in the same manner as above.

As explained above, since this invention uses advanced fossil quartz glass as an investment material for casting, the amount of thermal expansion during heating is larger than that of conventional glass, so it is necessary to use measures such as water absorption expansion and hardening expansion. does not require. In addition, the amount of expansion of high-density quartz glass can be determined by appropriately combining conditions such as the degree of densification of quartz glass, heating temperature, heating time, heating rate, binding material, and whether or not silicic anhydride is mixed. Since it is adjustable, it can be changed arbitrarily depending on the amount of casting shrinkage of the alloy material. In addition, high-density quartz glass has low shrinkage during the cooling process after heating, so metal molded products of desired shapes can be obtained, and the shrinkage can be increased by mixing binders, silicic anhydride, etc. be able to. Therefore, since the dental casting investment material of the present invention does not need to be expanded by water absorption or hardened and expanded, a metal molded product of a desired shape can be obtained.

[Brief explanation of the drawing]

Figure 1 is a graph showing the relationship between pressure and density during the production of high-density quartz glass, Figure 2 is a graph showing the relationship between heating time and coefficient of linear expansion of high-density quartz glass with different densities, and Figure 3 is a graph showing the relationship between heating time and coefficient of linear expansion for high-density quartz glass with different densities. The second one with different heating rates
Figure 4 is a graph showing the same relationship as Figure 2 due to stepwise temperature increase. Figure 5 is a graph showing the same relationship as Figure 2 due to gradual temperature increase. It is a graph showing the relationship between the coefficient of linear expansion and time during the heating and cooling process of a mixture C of density quartz glass, gypsum, and silicic acid.

Claims (1)

[Claims] 1 High-density quartz glass that has been made high-density by heat treatment under high pressure and expands greatly when heated, but has a small amount of shrinkage in the cooling process after heating, or a mixture of the high-density quartz glass and silicic anhydride, An investment material for tooth casting characterized by containing a bonding agent.