JP2709828B2 - Phosphate investment material for dental casting - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a phosphate investment compound kneading solution for dental casting.

[Conventional technology]

The progress of dental precision casting technology such as crowns is remarkable,
Technology for casting new castable ceramics castings by the lost wax method instead of various metal castings is being developed. Castable ceramics are cast by injecting a high-melting-point ceramic melt into a space formed by heating and burning out a wax mold buried in an investment material, similarly to conventional metal-based casting.

At this time, since large coagulation contraction of about 2% occurs depending on the type, it is necessary to increase the space by the coagulation contraction in advance. This is usually compensated for by the expansion of the investment during curing and the expansion during heating. For this reason, a phosphate-based investment material that can provide heat resistance and large expansion is suitable for casting of castable ceramics.

The current phosphate investment is intended for casting high-melting metals, using ammonium dihydrogen phosphate and magnesium oxide as the main binder for silica-based refractory, and using colloidal silica liquid for this. After mixing, NH ₄ MgPO ₄
· 6H ₂ O crystals to generate a, is characterized in that to obtain a strong tissue strength and large setting expansion by the growth of the crystal.

[Problems to be solved by the invention]

When this phosphate-based investment material is used for casting a material having high brittleness such as castable ceramics, there is a problem that the casting is easily broken when the casting is removed from the mold. In order to reduce the structural strength of the investment material, a method using a kneading liquid or water having a low colloidal silica content for relaxation is known. However, in this method, the curing expansion is extremely small,
It cannot be obtained at all and cannot compensate for solidification shrinkage, which hinders casting accuracy. In other words, there is a demand for a method for reducing the structural strength of a phosphate-based investment material while maintaining a large hardening expansion.

[Means for solving the problem]

The present inventors have studied colloidal silica of the kneading solution of the phosphate-based investment material, and by controlling the particle size and concentration of the colloidal silica, control the size of hardening expansion and the tissue strength. It has been found that the present invention is possible. That is, the colloidal silica contained has a particle diameter of 20 μm or more and 5 μm or more.
To use a phosphate investment material kneading solution for dental casting in a range of from about 95% by weight to about 95% by weight of less than 20 µm and from 5 to 5% by weight and having an SiO ₂ concentration of 1 to 30% by weight in a colloidal silica dispersion. .

[Action]

Colloidal silica for kneading investment materials conventionally used for dental casting has a particle diameter of 20 μm or less. Conventionally, this fine single particle colloidal silica is used to fill fine voids existing in the tissue, and then NH 3
₄ has measured an increase in the setting expansion quantity by the growth of MgPO ₄ · 6H ₂ O crystals. However, if the amount of the colloidal silica dispersion used is increased in order to increase the curing expansion, the amount of water also increases, and the curing expansion does not increase. Further, even if an attempt is made to increase the concentration of the colloidal silica dispersion so as not to increase the water content, the limit is about 45% by weight from the viewpoint of flow.

The present invention is characterized in that colloidal silica having a large particle diameter of 20 μm or more is used in combination.
As a result of the particle size blending with the fine particles of less than m, the filling of the voids is carried out more efficiently in small amounts. That is, when the colloidal silica having a large particle diameter is used in combination, the same amount of the colloidal silica can provide about twice as much expansion as the conventional one.

Further, as this colloidal silica dispersion is diluted with water, the degree of swelling upon curing gradually decreases. In addition, it was found that the degree of dilution was almost linear. That is, since the desired hardening expansion can be obtained by using colloidal silica having a large particle diameter, the desired hardening expansion can be obtained by diluting the same with water. In addition, as the concentration of colloidal silica decreases, the water content increases, and the tissue strength decreases. In addition, since the colloidal silica having a large particle diameter is used, the number of tangential melting points that develop a bonding force is reduced, the binder effect is weakened, and the investment material has excellent dismantling properties.

[Configuration of the invention]

The colloidal silica of the present invention has a size of less than 20 μm and a size of less than 20 μm.
It is used in combination with one having a size of μm or more. Preferably, they are 10 to 20 μm and 20 to 100 μm, respectively. The colloidal silica having this particle size range is obtained by using commercially available colloidal silica or by dispersing silicic anhydride in water. If necessary, various known surfactants may be used to obtain a stable dispersion.

The mixing ratio of the two types of colloidal silica is 5 to 95% by weight of 20 μm or more and 95 to 5% by weight of less than 20 μm. In this mixing method, two types of colloidal silica dispersions having a predetermined concentration, for example, 20% by weight, are prepared, and respective predetermined amounts may be mixed. Alternatively, silicic anhydride having two types of particle diameters may be mixed and dispersed in water. Good. It is also possible to disperse silicic anhydride having a predetermined particle size and a continuous particle size in water.

Next, the colloidal silica concentration in the colloidal silica dispersion is set to 1 to 30% by weight. If the concentration is less than 1% by weight, no curing expansion will be exhibited, and if it exceeds 30% by weight, dispersion will be insufficient. The dispersion may be prepared by diluting a colloidal silica dispersion having a predetermined concentration or dispersing silicic anhydride directly in water so as to obtain a desired concentration.

Other silica-based refractory materials, ammonium dihydrogen phosphate, magnesium oxide, etc., which are used for general phosphate-based investment materials can be used, and a casting method and a casting method using a lost wax method are the same as conventional methods. Is fine.

Since the immersion type according to the present invention has a higher degree of hardening expansion than the conventional type, it can be effectively used not only for the ceramic type described above but also for the conventional metal type.

〔Example〕

Example 1 100 g of a phosphate-based investment material consisting of 84 parts by weight of silica, 10 parts by weight of ammonium dihydrogen phosphate, and 6 parts by weight of magnesium oxide, each having a particle diameter of 10 to 20 μm having a SiO ₂ concentration of 20% by weight.
Add 20 ml of a kneading solution obtained by mixing the m and 40-60 μm colloidal silica water-acid solution at an equal ratio, and manually knead in a rubber kneader.
After conducting vacuum kneading for 40 seconds and vacuum kneading for 20 seconds, the obtained slurry was tested by a conventional method. As a result, a curing expansion coefficient of 2.05% and a compressive strength after firing at 800 ° C. of 80 kg / cm ² were obtained.

Further, the same coefficient of expansion was tested after kneading using a diluted kneading solution obtained by adding 10 ml of water to 10 ml of the above kneading solution, and the coefficient of expansion was 0.
The compression strength after firing at 98% and 800 ° C was 35 kg / cm ² .

Comparative Example 1 The same test as in Example 1 was conducted by adding 20 ml of a colloidal silica aqueous acid solution having a particle size of 10 to 20 μm and a SiO ₂ concentration of 20% by weight to 100 g of the same phosphate-based investment material as in Example 1. Had a coefficient of expansion of 1.02% and a compressive strength after firing at 800 ° C. of 82 kg / cm ² .

[Effects of the Invention] As is clear from the examples, by using the large particle size colloidal silica of the present invention as a part of the kneading liquid, about twice the high curing expansion coefficient can be obtained with the same quality investment material. By diluting the kneading solution, the expansion coefficient of curing could be arbitrarily reduced, and at the same time, an investment material having excellent dismantling properties could be obtained.

This makes it possible to apply castable ceramics, which are easily broken, to molds, and at the same time, to metal castings, it is possible to apply investment materials with excellent dismantlement.

Claims (1)

(57) [Claims] The colloidal silica contained has a particle size of 20 μm.
m to 5 to 95% by weight, less than 20 μm to 95 to 5% by weight, and a colloidal silica dispersion having a SiO ₂ concentration of 1 to 30% by weight. liquid.