JPH0388739A - Calcium phosphate-based glass and humidity conditioning melting method therefor - Google Patents

Abstract

PURPOSE:To obtain the glass which is excellent in aesthetic appreciation property, mechanical strength and chemical durability by regulating absorbance per unit thickness of OH group based on moisture in calcium phosphate-based glass whose Ca/P (atomic ratio) is regulated to a specified range to a range within the prescribed value. CONSTITUTION:In the case of producing calcium phosphate-based crystallized glass whose Ca/P (atomic ratio) is 0.1-0.7, the value AOH (hereinafter simply defined as absorbance) of absorbance shown in a formula of calcium phosphate-based glass being a starting substance thereof is regulated to 0.01-0.5mm<-1>. Thereby crystallized glass described hereunder can be obtained by the ensuing crystallizing operation for the above-mentioned glass. This crystallized glass is uniform and free from a crack and a bore, etc., in grain boundary and excellent in aesthetic appreciation property. In this case, when calcium phosphate-based glass being the starting substance is melted in order to regulate absorbance to a range within the above-mentioned value, it is necessary that melting is performed in the gaseous atmosphere of 0.01-10g-H<2>O/Nm<3> absolate humidity. The above-mentioned crystallized glass has transparency very close to natural teeth free from unevenness and therefore is preferably utilized as the restorative material of a crown.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a calcium phosphate glass useful as a dental melting material and a method for melting the glass.

[Conventional technology]

Calcium phosphate-based crystallized glass has a composition similar to that of living bones and teeth, and is a dental material or artificial bone material that is attracting attention because of its compatibility with living bodies. This calcium phosphate-based crystallized glass is made by remelting the material obtained by melting and vitrifying the raw material mixture, or by directly casting the melted raw material mixture using a lost wax method etc. to produce a glass casting, and then crystallizing it by heat treatment. °ζ is produced by oxidation. Normally, this melting is carried out in the atmosphere for calcium phosphate materials as well as for metal materials.

[Problem to be solved by the invention]

Calcium phosphate-based glass materials are particularly prone to containing water, and this water includes attached water and structured water.

Adhering water is relatively easily dehydrated by heating and drying, but structural water that exists in the form of OH groups at the ends of glass molecules is difficult to dehydrate, and furthermore, this water has a great effect on the subsequent crystallization of the glass. be.

In other words, when there is a large amount of structural water in the glass, the crystallization rate of the glass increases, crystal grains grow large, and as a result, the strength of the crystallized glass decreases. Furthermore, if the crystal grains are large, the light transmittance will be uneven, and the aesthetics will be degraded in the case of dental crowns and the like. Furthermore, a large amount of water in the glass means a large number of terminal OH groups, resulting in drawbacks such as high reactivity of crystallized glass and lack of chemical stability.

On the other hand, if the water content in the glass is too low, the crystallization rate will be slow and crystallization will take a long time, which is economically disadvantageous. Furthermore, if the crystallization operation time is shortened, the degree of crystallinity is insufficient and the mechanical strength of the product is reduced.

For this reason, it is essential to maintain the moisture content in the glass at a constant rate. However, it is difficult to quantitatively measure the water content in glass;
The groups can be quantified by infrared spectroscopy, thereby indirectly measuring the structural water in the glass. That is, in spectroscopic analysis using infrared transmission method, 0-H(P-0
-H) absorption band caused by stretching vibration has a wave number of 2900
cm-' (wavelength: 3.45 μm), the absorbance per unit thickness of the sample corresponding to the number of OH groups in the glass can be determined using the following equation.

AO)l = (A29[1O-A4(100)/l
(mm″″Xi (1) A, 2900: wave number 29
Absorbance of infrared absorption peak near 00 cm-' A4000: Absorbance of infrared absorption at wave number 40 Ocm-' (background) t Thickness of Niglass plate sample [m''!] [Means for solving the problem] Book The inventors have repeatedly studied the manufacturing conditions of calcium phosphate glass, which is the starting material for producing calcium phosphate crystallized glass, and have found that there is an equilibrium relationship of moisture between the molten material of this glass and the atmosphere. We found that the amount of moisture in the glass depends on the absolute humidity in the atmosphere at the time of melting, and also on the ratio of calcium to phosphorus in the glass composition.
When producing a calcium phosphate-based crystallized glass in which /P is 0.1 to 1.7, the absorbance value AO of the calcium phosphate-based glass that is the starting material according to the above formula (1)
H (hereinafter simply referred to as absorbance) is 0.01 to 0.5 mm-
', it is possible to produce uniform crystallized glass with excellent aesthetics without cracks or bores at grain boundaries through the subsequent crystallization operation, and in order to keep the absorbance within the above value range. When melting, the absolute humidity is 0.01~1
The present invention was completed by discovering that this is possible by conducting the process in a gas atmosphere of 0 g-820/Nm3.

[Structure and operation of the invention]

When preparing phosphate glass by melting it in the atmosphere, the atmospheric humidity changes from moment to moment depending on the season, weather, time of day, ventilation conditions in the melting area, presence of air conditioning, etc., so the moisture in the glass is high. When melted in an atmosphere, the amount increases, and the absorbance varies in the range of 70.5 to 4 mm.When crystallizing phosphate glass with an absorbance exceeding 1 mm, the crystal grains become coarser and Cracks and bores occur in the crystallized glass, resulting in an opaque appearance and inferior mechanical strength and chemical durability. In addition, the absorbance is 0.5 to 1
When a glass in the range mn+-' is crystallized, the absorbance becomes l
Although the transparency is better than when it exceeds mm-', the structure becomes directional according to the crystal growth direction and disorder is likely to occur, resulting in unstable mechanical strength and chemical durability and a white appearance. Because of the appearance of spots, it is less aesthetically pleasing as a dental crown restoration material. On the other hand, in the case of a phosphate glass having an absorbance of 0.01 mm<-1> or less, the crystallization rate becomes extremely slow, resulting in the disadvantage that crystallization takes a long time.

Crystallized glass obtained by crystallizing phosphate glass with an absorbance in the range of 0.01 to 0.5-1 has a structure in which fine crystals are densely aggregated without any specific directionality.
In addition to exhibiting stable high mechanical strength and chemical durability,
Since it has a transparency that is very close to that of natural teeth without unevenness, it is suitable as a dental crown restoration material.

The method for producing glass having an absorbance range according to the present invention will be described in detail below.

The calcium phosphate glass of the present invention is basically composed of two components: phosphoric acid and calcium oxide, or three components: phosphoric acid, calcium oxide, and alumina, and also contains alkali metal oxides to lower the melting point and viscosity, and improve strength. It contains rare earth oxides, various coloring agents, coloring aids, etc. It can also be applied to mixed glasses of this calcium phosphate glass and various glasses including other silicate glasses.

The humidity-controlled melting method for calcium phosphate glass of the present invention can be applied both when melting and reacting a raw material mixture and when remelting a raw material melt that has been rapidly cooled and vitrified and then ground.
It can also be used for melting when casting into shapes such as dental crowns in science and technology. In normal manufacturing methods for dental crowns, etc., the raw material is melted by the glass supplier, and the melting during casting is often performed by a dental technician.Therefore, there is a difference between raw glass melting and melting during casting. It is customary to carry out under different atmospheric humidity conditions. Furthermore, if the melting times differ between melting the raw material and remelting, a difference will occur in the humidity conditions of the melting atmosphere. As described above, each melting causes a change in the water content in the glass, making it difficult to always obtain the optimum crystallized glass. However, according to the method of the present invention, each of the above melting processes can be performed under the same atmospheric humidity conditions, making it possible to obtain a calcium phosphate glass containing a certain amount of moisture, and thus making it possible to achieve optimal crystallization. It is.

The humidity-controlled melting method of the present invention is characterized by flowing a gas at a constant humidity into the atmosphere of the melt in the melting furnace, and the atmosphere gas includes air, oxygen, nitrogen, argon, helium, carbon dioxide, etc. can be used. These are generally packed in cylinders, but in the case of air, it is also possible to send atmospheric air using a compressor or pump. Among these various gases, it is more preferable to use an oxidizing gas such as oxygen, air, or carbon dioxide. This is to prevent some of the oxygen from leaving the glass during melting, resulting in a reduced state, which prevents cracks from forming during subsequent crystallization.

The atmospheric gas is adjusted to an appropriate moisture content.

Various methods are used to control humidity, but for example, if the moisture content of the atmospheric gas is lower than the target moisture content, such as gas packed in a cylinder, water can be converted into a gas by bubbling in a constant temperature water bath. After saturating the air, the humidity is controlled by cooling it with a humidifier and dehumidifying some of the moisture.

Although it is possible to control humidity only by bubbling in a constant temperature water tank, more precise humidity control can be achieved by dehumidifying with a humidifier. Furthermore, when the moisture content of the atmospheric gas is lower than the target value, for example when indoor air is used, it is possible to simply dehumidify some of the moisture by direct humidity control. The moisture-containing gas leaving the humidity controller is introduced into the melting furnace after monitoring its humidity.

Water content is 0.01-10g-H20/Nm in absolute humidity
3, and adjust according to the Ca/P ratio. If the Ca/P ratio is high, set it low. This humidity is 10g-H2
When it exceeds 0/Nm3, crystal grains become large during crystallization, and mechanical strength and aesthetics deteriorate. Also, the value is 0
．． If it is less than 01g-H20/Nw', the crystallization rate during the crystallization operation will be slow and the degree of crystallinity will be low, resulting in a decrease in strength, which is not preferable.

It is the structural water in the glass that actually affects crystallization, but experiments have shown that there is a linear correlation between the amount of structural water in the glass and the absolute humidity of the atmosphere that has reached equilibrium. found. In reality, the amount of moisture in the glass is determined by the measured absolute humidity of the atmospheric gas after a certain period of time (approximately 1 hour in the gas flow range described below), the absolute humidity of the device determined in advance, and the amount of moisture in the glass. It can be determined from the correlation of

Although the type and shape of the melting furnace does not matter, an electric furnace with good airtightness is preferable and requires an inlet/outlet for gas. A relatively open furnace with only a gas inlet can be used, but accurate humidity control cannot be expected. The gas flow rate per minute is suitably 0.1 to 5 times the void volume of the furnace.

Gas from the melting furnace is vented through a humidity monitor.

The humidity in the air in a room (melting chamber) in which a melting furnace is installed is subject to seasonal and temporal fluctuations, and as a result, the atmosphere of the melting furnace is inevitably affected by this. Even if the melting furnace is completely airtight, when opening and closing the furnace lid, the gas inside the furnace will inevitably be replaced by the air in the melting chamber, even if only temporarily, so it is recommended to control the humidity of the entire chamber if possible. is preferred. This is especially necessary when the air in the melting chamber is used as the atmospheric gas.

〔Example〕

Example 1 The air conditioner in the melting chamber was started to keep the humidity in the room constant. Oxygen gas was bubbled into the water in a thermostatic chamber at 35°C at a flow rate of 1 cubic meter per minute from an oxygen cylinder to saturate the water, and then passed through a humidifier to an absolute humidity of 3 g-1h O/min.
Nm3 and introduced into an electric furnace with an internal volume of 2 liters heated to 1360°C.

When the humidity of the gas discharged from the furnace reaches a certain level, Ca 0
21.8% by weight, Al2O39.3% by weight, P2O66
A mixed powder of calcium carbonate, alumina and phosphoric acid equivalent to 8.9% by weight was placed in a platinum crucible with an internal volume of 100 ml.
00g at a time, put into the furnace and start melting.

After melting for 1 hour, the crucible was taken out and the melt was poured onto a carbon plate to cool and vitrify.

Example 2 Calcium phosphate glass having the same composition as in Example 1 was prepared by melting, cooling and vitrifying without flowing an atmospheric gas, and the resulting glass was ground into pieces of 1 mm or less.

An electric furnace is prepared in the same manner as in Example 1, and the oxygen gas has the same absolute humidity and flow rate. 50g of the pulverized material was placed in a platinum crucible with an internal volume of 50m1, and the mixture was inserted into the furnace, and when the humidity of the gas discharged from the furnace reached a certain level, the temperature was started to increase.
After melting at 60° C. for 75 minutes, the crucible was taken out and the melt was poured onto a carbon plate to cool and vitrify.

Example 3 A melting furnace with an incomplete seal and an internal volume of 160 cT[I3 was heated to 1360°C, and the indoor air was heated to an absolute humidity of 3 g-H20/ using the humidity controller used in Example 1. N.T.I.T.
The humidity was adjusted to 3 and introduced into the furnace directly above the platinum crucible at a flow rate of 500 rnl/min.

A log of the glass prepared in Example 2 was placed in a platinum crucible of approximately 10 ml and set in a furnace. Melting was carried out for 15 minutes,
It was poured into a mold preheated to 500°C and cast into the shape of a tooth crown. This cast body was then treated at 700° C. for 10 hours to crystallize it.

Comparative Example 1 The glass obtained in Example 2 was melted in a melting furnace in the same manner as in Example 3 in the summer (absolute humidity 15 g - 120/Nm") without flowing gas, and after casting, it was packed and crystallized.

Example 4 Ca/P (atomic ratio 0
．． Using phosphoric acid and calcium carbonate mixed powder equivalent to No. 55, the gas was nitrogen gas, and the absolute humidity was 7 g-820.
/ Nwr' melted, cast and crystallized.

〔Effect of the invention〕

In Examples 1 and 2, plate-shaped samples with a thickness of 3 mm were prepared and their absorbances were measured and found to be 0.1±0.
It was 05mm'. However, the glass melted in Comparative Example 1 has a considerably high water content of 0.9 mm' before crystallization. As a result, the bending strength after crystallization was 1500 kg/cd in Example 3 and 350 kg/cd in Comparative Example 1.
There was a considerable difference in appearance from C-, and the appearance was also translucent milky white with no unevenness in Example 3, whereas Comparative Example 1 was quite opaque with uneven color and white spots, and the aesthetics were also quite different. was. In addition, the measured value of infrared absorbance of the sample of Example 4 was 0.3±0.
05n+m-' had the same amount of ice and water.

In addition, in Example 3.4 and Comparative Example 1, 3x4x32
When rod-shaped samples of rnm were crystallized and immersed in a 1% lactic acid aqueous solution at 37°C for 7 days and the elution amounts were measured, they were 1.9, 2.2 and 4.5 mg, respectively.
It was found that the product of the present invention is also chemically durable.

This shows that the humidity-controlled melting method of the present invention is particularly useful for samples with high moisture content, such as calcium phosphate glasses, and by adjusting the moisture content to an appropriate level.
It can be seen that dental materials with excellent aesthetics, mechanical strength, and chemical durability can be produced.

Claims (2)

[Claims] (1) The atomic ratio of phosphorus to calcium, Ca/P, is 0.
The absorbance value per unit thickness of OH group based on the moisture in the calcium phosphate glass is 0.01 to 1.7.
Calcium phosphate glass characterized by having a thickness in the range of 0.5 mm^-^1. (2) The atomic ratio of phosphorus to calcium, Ca/P, is 0.
1 to 1.7, the calcium phosphate glass is melted in a gas atmosphere with an absolute humidity of 0.01 to 10 g-H_2O/Nm^3. Moisture-controlled melting method for glass.