JPH0553745B2 - - Google Patents

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). [Prior art and problems to be solved by the invention] Gypsum hemihydrate has the property of reacting with water and hardening, and is therefore used as a variety of model materials. Particularly in dentistry, it is important as a material for making models of teeth and jawbones in the oral cavity. These model materials are required to have various properties such as strength and dimensional stability, but it is particularly important that the gypsum mixture has good fluidity and good platability during molding. Generally, to create 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 mix into the cavity of the negative mold. After the vibrator is stopped and the plaster mixture is placed above the height of the negative mold, it is molded into an appropriate shape. Therefore, gypsum mixes have good thixotropic properties,
In other words, it has good fluidity when stress is applied, such as by applying vibrations with a vibrator, and when it is in a static state without stress, it stops flowing and retains its molded shape, so-called good platability. characteristics are required. 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. Furthermore, if the stacking 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. but,
If the amount of water is increased, the fluidity will be improved, but the plating performance will be deteriorated, and if the amount of water is decreased, the plating performance will be improved, but the fluidity will be deteriorated. For this reason, it has been almost impossible to obtain a gypsum kneaded product that has both good fluidity during vibration and good plating properties by adjusting the amount of water. Therefore, when pouring the gypsum mixture into the negative mold while applying vibrations, the vibration properties are good, and when the plaster mixture is left standing without applying vibrations, the flow stops and the placement is good.
It has been desired to develop a gypsum composition that has the two properties of being freely moldable. [Means for Solving the Problems] As a result of research into solving the above problems, the present inventors found that by blending a specific amount of fibrous gypsum of a specific shape into the above-mentioned gypsum hemihydrate, We have discovered that it is possible to obtain a gypsum mix that exhibits good thixotropy without substantially impairing the properties of gypsum hemihydrate, and has both good fluidity and plating properties during vibration, and we have developed this book. The invention was completed. That is, the present invention consists of (A) 100 parts by weight of gypsum hemihydrate and (B) 0.1 to less than 5 parts by weight of fibrous gypsum having a length of 10 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 the following. 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 dihydrate gypsum under atmospheric pressure, α-hemihydrate gypsum obtained by dehydrating under high water vapor pressure, α-type hemihydrate gypsum produced in an aqueous solution containing salts, etc. powder 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,
A suitable thickness is preferably 3 to 20 μm. In the gypsum composition of the present invention, it is necessary to use fibrous gypsum having an aspect ratio, that is, a ratio of fiber length/fiber diameter of 20 or more, as another essential component. If the aspect ratio is smaller than 20, sufficient mounting properties cannot be obtained, and therefore the plaster composition of the present invention is not suitable. Preferably, the fiber length is 10 to 300 μm and the fiber diameter is 0.1 to 10 μm. If the fiber length is greater than 300 μm, the resistance due to the fibers becomes large when the gypsum composition is kneaded with water, resulting in poor operability, which is not preferable. If the lower limit is 10 μm, the gypsum composition of the present invention will exhibit sufficient effects. Similarly, the fiber diameter is 10μm
If the size is larger, it becomes difficult to knead and the operability deteriorates. A lower limit of 0.1 μm is sufficient for practical use. Particularly preferably, fibrous gypsum such as anhydrite, hemihydrate gypsum, and dihydrate gypsum is employed. When fibrous gypsum is used, when the gypsum composition of the present invention is kneaded with water and the gypsum hemihydrate is hydrated and the crystals of gypsum dihydrate grow and harden, the crystal growth of the gypsum dihydrate is hindered. This is preferable because not only is the precipitated dihydrate gypsum 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, the fibrous gypsum used is hardly soluble in water, which is highly desirable. Furthermore, fibrous gypsum is preferred because it is crystalline. This is because crystalline fibrous gypsum has higher strength than other amorphous inorganic fibers, and does not break due to grinding force during the process of mixing it with hemihydrate gypsum to produce the gypsum composition of the present invention. The fibrous form can be maintained, and as a result, sufficient thixotropy can be exhibited during kneading of the gypsum composition. In addition, since the surface area of crystalline fibrous gypsum is smaller than that of amorphous inorganic fibers, the amount of water required to knead the gypsum composition is small, and as a result, the hardened product obtained by curing is reduced. strength increases. In the present invention, the amount of fibrous gypsum added is suitably in the range of 0.1 or more and less than 5 parts by weight per 100 parts by weight of gypsum hemihydrate. That is, if the amount of the fibrous inorganic compound added is less than 0.1 part by weight, the thixotropic properties of the gypsum kneaded material obtained from the gypsum composition will not be expressed, and if an amount of water that provides sufficient fluidity is added, Adhesiveness is not improved sufficiently. Furthermore, 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 plaster 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 such as citric acid, tartaric acid, malic acid, succinic acid, oxalic acid, acetic acid and their salts,
Amino acids and their salts such as glycine, alanine, valine, leucine, cysteine, aspartic acid, glutamic acid, boric acid, sulfuric acid, hydrochloric acid, phosphoric acid,
Inorganic salts such as sodium salts such as nitric acid, lithium salts, potassium salts, magnesium salts, calcium salts, and aluminum salts, protein hydrolysates and formaldehyde condensates of their salts, and sucrose;
Sugars such as starch and pectin can be used. It is generally preferable to add these curing time regulators in an amount of 0.01 to 5.0 parts by weight per 100 parts by weight of gypsum hemihydrate. 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, lignosulfonate, formalin condensate of naphthalene sulfonate, etc. can be used. Generally, these water reducing agents may be added in an amount of 0.01 to 5.0 parts by weight per 100 parts by weight of gypsum hemihydrate. 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 understood from the above explanation, the plaster composition of the present invention has good thixotropic properties, so when pouring the plaster mix into a negative mold while applying vibration, , it is possible to completely pour into the details of the negative mold, and when the vibration is stopped and the mold is allowed to stand still, the flow stops, allowing the mold to be plated and molded into the desired shape. 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, 2 and Comparative Examples 1 to 10 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, the fluidity has an angle of 20° with respect to the horizontal.
5 ml of gypsum mix was placed on top of a semicircular vinyl chloride gutter with a diameter of 20 mm, vibration was applied for 10 seconds, the distance that the gypsum mix fell was measured, and this falling distance was defined as fluidity. As a result of separately examining 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 mm or more, the flow into the negative mold is complete. Further, the consistency was measured by the method of JIS T6605, and if the consistency was 42 mm or less, the plating performance was good. Therefore, a consistency of 42 mm or less was considered good, and a consistency of more than 42 mm was considered poor. Furthermore, a negative mold of the tooth was actually taken using an alginate impression material (trade name: Toxo A-1), and a mixture of each plaster composition was poured into this negative mold while being vibrated with a vibrator. After the pouring was completed, The vibrator was stopped, and the kneaded material was heaped up and molded. 2
After a period of time, the cured model was taken out and comprehensively evaluated by checking whether the details had completely filled in, whether the mold had been retained, and whether the model surface was rough.

【table】

[Table] Parts indicate parts by weight.
〓〓Water mixing ratio〓 represents the weight ratio of the mixing water to the gypsum composition.

【table】

【table】

[Claims]

1. For 100 parts by weight of solid content in the aqueous slurry containing calcium silicate crystal secondary particles and wood fibers,
After adding 0.05 to 1.0 parts by weight of a cationic flocculant and 0.01 to 1.0 parts by weight of an anionic flocculant or nonionic flocculant in such a range that the total amount of both does not exceed 1.5 parts by weight, the slurry is made into a paper, A method for producing a calcium silicate plate, which comprises laminating the obtained sheets, drying after pressure forming, or drying simultaneously with pressure forming. 2. The manufacturing method according to claim 1, wherein the content of wood fibers is 2 to 10% by weight in the solid content of the aqueous slurry containing calcium silicate crystal secondary particles and wood fibers.