JPH0255255A - plaster composition - Google Patents

Abstract

PURPOSE:To enable to form a gypsum composition having an extremely good thixotropic property when utilized as a raw material for various models by compounding hemihydrate gypsum with a fibrous inorganic compound having a specific shape in a specified ratio. CONSTITUTION:The gypsum comprises the following components A and B. (A) 100 pts.wt. of hemihydrate gypsum and (B) 0.1-5 pts.wt. of a fibrous inorganic compound having a length of 10-300mum, a diameter of 0.1-10mum and an aspect ratio of >=20. As the hemihydrate gypsum any known one can be adapted without being restricted. For example, beta hemihydrate gypsum obtained by dehydrating gypsum dihydrate under the atmospheric pressure, alpha hemihydrate gypsum obtained by dehydrating under a high steam pressure, alphaII type hemihydrate gypsum prepared in an aqueous solution containing a salt or the like can be employed. A fibrous gypsum such as anhydrous gypsum, hemihydrate gypsum or gypsum dihydrate is especially preferable as the fibrous inorganic compound.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a gypsum composition containing gypsum hemihydrate as a main component.

More specifically, the present invention relates to a gypsum composition having extremely good thixotropic properties when kneaded with water (hereinafter referred to as a gypsum paste).

[Problems to be solved by conventional technology and invention]

Gypsum hemihydrate reacts with water and hardens, so it is used as a modeling material.

Particularly in dentistry, it is important as a stone material for making models of teeth and jawbones in the oral cavity.

These model materials are required to have sufficient performance such as strength and dimensional stability, but it is especially important that the gypsum mixture has good fluidity and good mounting properties during molding.

Generally, to make a tooth or jawbone model, take a negative impression of the teeth or jawbone using an impression material, apply vibration to the negative mold using a vibrator, and pour a plaster paste into the cavity of the negative mold. Then, the vibrator is stopped, and the gypsum mixture is piled up to a level above the height of the negative mold, and then molded into an appropriate shape. Therefore, the gypsum mixture has good thixotropy, that is, it has good fluidity while stress is applied by a vibrator, etc., and when it is in a static state without stress, it stops flowing and is molded. It is required to have the property of retaining its shape, so-called good plating properties. If the plaster mix has poor fluidity during vibration, it will not flow into the details of the complexly shaped negative mold, resulting in only a defective plaster model. In addition, if the plating properties are poor when stationary, it will flow out due to its own weight and cannot be formed into the desired shape. Generally, the fluidity and platability during vibration are adjusted by increasing or decreasing the amount of water used to mix the gypsum composition.

That is, if the amount of water is increased, the fluidity during vibration will be improved, and if the amount is decreased, the plating performance will be improved. However, increasing the amount of water improves the fluidity described above, but worsens the plating performance (while decreasing it improves the plating performance, but worsens the fluidity. Therefore, by adjusting the amount of water, the vibration It has been almost impossible to obtain a gypsum mix that has both good fluidity and platability.

Therefore, when pouring the gypsum mixture into the negative mold while applying vibrations, it has good fluidity, but when it is left standing without applying main vibrations, the flow stops, making it easy to place and mold freely. It has been desired to develop a gypsum composition with the following properties.

[Means for solving problems]

As a result of research into solving the above-mentioned problems, the present inventors have found that by blending a specific amount of a fibrous inorganic compound with a specific shape into the above-mentioned gypsum hemihydrate, most of the properties of gypsum hemihydrate can be improved. The present inventors have discovered that it is possible to obtain a gypsum kneaded material that exhibits good tychnodrobicity without any hindrance, and has both good fluidity during vibration and good plating properties, and has completed the present invention.

That is, the present invention consists of (1) 100 parts by weight of gypsum hemihydrate and (2) 0.1 to 5 parts by weight of a fibrous inorganic compound having a length of 1 to 300 μm, a diameter of 0.1 to 10 μm, and an aspect ratio of 20 or more. This is a gypsum composition characterized by comprising:

As the gypsum hemihydrate used in the present invention, any known gypsum can be employed without any restriction. For example, β-hemihydrate gypsum obtained by dehydrating dihydrateite blue under atmospheric pressure, α-hemihydrate gypsum obtained by dehydrating with high steam oxidation, and α-hemihydrate gypsum produced in an aqueous solution containing salts.
Powder such as type hemihydrate can be used. The particle size of such gypsum hemihydrate is not particularly limited, but generally has an average particle size of 1 to 100.
μm, preferably 3 to 20 μm.

The gypsum composition of the present invention has aspect ratio, I!, as other essential components. It is necessary to use a fibrous inorganic compound having a ratio of fiber length/fiber diameter of 20 or more. Aspect ratio is 20
If it is smaller, sufficient mounting properties cannot be obtained, so it is not suitable for the gypsum composition of the present invention.

Preferably, the fiber length is 10 to 300 μm and the fiber diameter is 1 to 10 μm. The fiber length is thicker than 300μm b
When kneading the gypsum composition with water, the resistance due to the fibers becomes large and operability becomes poor, which is not preferable. The lower limit is 10μ
If m is present, the gypsum composition of the present invention will exhibit sufficient effects. Similarly, if the fiber diameter is larger than 10 μm, it becomes difficult to knead and the operability deteriorates. A lower limit of 0.1 μm is practically sufficient.

The above specific shaped fibrous inorganic compound includes:

Potassium titanate, wollastonite, talc.

Fibrous materials such as gypsum hemihydrate, anhydrite, gypsum dihydrate, carbon, tantalum, silicon carbide, silicon nitride, silica, alumina, silica-alumina, dolomite, kaolin, bauxite, kyanite, magnesia, and glass can be used. Particularly preferably, fibrous gypsum such as anhydrite, hemihydrate, and dihydrate is used. When fibrous gypsum is used, when the gypsum composition of the present invention is kneaded with water and the gypsum hemihydrate is hydrated and dihydrate blue crystals grow and harden, the crystal growth of the dihydrate gypsum is hindered. This is preferable because not only is the precipitated dihydrate blue and fibrous gypsum combined and hardened, it is possible to obtain a model with higher strength and hardness.

Since the gypsum composition of the present invention is used after being kneaded with water, it is desirable that the fibrous inorganic compound used is sparingly soluble in water.

Furthermore, the fibrous inorganic compound is preferably crystalline. This is because crystalline fibrous inorganic compounds have higher strength than amorphous ones.

In the process of mixing the gypsum composition of the present invention by mixing it with gypsum hemihydrate, no breakage occurs due to the grinding force, and the shape of the fibers can be maintained, resulting in sufficient thixotropy when the gypsum composition is kneaded. It can be demonstrated. In addition, since the surface area of crystalline fibrous inorganic compounds is smaller than that of amorphous compounds, less water is required to knead the gypsum composition, and as a result, the hardened product obtained by curing strength increases.

In the present invention, the amount of the fibrous inorganic compound added is
A range of 1 to 5 parts by weight of C1 is suitable for 100 parts by weight of 1F. That is, the amount of added fibrous inorganic compound is 0.1
If the amount is less than 1 part by weight, the thixotropic properties of the gypsum kneaded product obtained from the gypsum composition will not be expressed, and if water is added in an amount that provides sufficient fluidity, the plating properties will not be sufficiently improved. Moreover, if the amount added exceeds 5 parts by weight, the strength and surface smoothness of the plaster model will decrease, making it impossible to obtain a precise 5-growth mold.

In addition to the components described above, a curing time regulator can be added to the gypsum composition of the present invention in order to adjust the curing time. All conventionally known curing time regulators can be used. For example, organic acids and their salts such as citric acid, tartaric acid, malic acid, succinic acid, oxalic acid, acetic acid, glycine, alanine, valine, leucine,
Amino acids and their salts such as cysteine, aspartic acid, and glutamic acid; inorganic salts such as sodium salts, lithium salts, potassium salts, magnesium salts, calcium salts, and aluminum salts; protein hydration; Formaldehyde condensates of decomposition products and their salts, and substances such as sucrose, starch, and pectin can be used. These curing time regulators are generally gypsum hemihydrate 100%
It is preferably added in an amount of 0.01 to 5.0 parts by weight.

Further, a water reducing agent may be added for the purpose of increasing the fluidity of the gypsum kneaded product. As the water reducing agent, melamine formaldehyde resin, lignin sulfonate, formalin condensate of naphthalene sulfonate, etc. can be used. These water reducing agents are generally 0.01 to 5.0 parts by weight per 100 parts by weight of hemihydrate IF.
It may be added within the range of parts by weight.

Furthermore, other additives such as pigments may be added to the extent that the effects of the present invention are not significantly reduced.

〔effect〕

As can be understood from the above explanation, the plaster composition of the present invention has good thixotropic properties, so when pouring the plaster mix into the negative mold while applying vibration, You can pour it completely with the fine residue, and if you stop the vibration and let it stand, the flow will stop, and you can arrange it in the desired shape.
Can be molded. The gypsum compositions of the present invention are particularly useful as modeling materials, but can also be used as other molding materials.

〔Example〕

The present invention will be described in more detail with reference to Examples below, but the present invention is not limited thereto.

Examples 1 to 9 and Comparative Examples 1 to 8 The fluidity and platability of the plaster compositions shown in Table 1, each containing a predetermined amount of each component, were measured. Table 1 shows the finished state and kneading properties of the obtained model. Table 2 shows the properties of the fibrous inorganic compounds used in the Examples and Comparative Examples.

In addition, fluidity was determined by placing the gypsum mixture of No. The distance that the object flowed down was measured, and this falling distance was defined as fluidity. As a result of a separate investigation of the relationship between the fluidity obtained by this method and the actual flow into the details of the negative mold, it was found that if the fluidity is 140 or more, the flow into the negative mold is complete.

In addition, 1. The consistency was measured by the method of TIS T6605, and if the consistency was 42 m or less, the plating performance was good. Therefore, consistency of 42ffl or less is good.

Those exceeding 42 m were considered defective.

Furthermore, the product name of alginate impression material is Tokun-A-1.
A negative mold of the tooth is taken using a mold, and a mix of each plaster composition is poured into this negative mold while being moved by a vibrator.After pouring is finished, the vibrator is stopped and the mix is raised and molded. did. After 2 hours, remove the cured model and hold the mold to make sure that every detail is completely filled in.
Check whether the surface is rough and whether the surface of the model is rough.
A comprehensive evaluation was made.

Claims (2)

[Claims] (1) (A) 100 parts by weight of gypsum hemihydrate (2) Length: 10 to 300 μm, diameter: 0.1 to 10 μm
and a fibrous inorganic compound with an aspect ratio of 20 or more.
A gypsum composition comprising 1 to 5 parts by weight