JPS6339546B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to magnesia porcelain with improved hydration resistance and a method for producing the same. Magnesia porcelain generally has higher thermal conductivity than other porcelains, and also has high high-frequency electrical insulation resistance, making it one of the most suitable materials for microwave and other integrated circuit boards. Magnesia porcelain is
However, it has the major drawback of being inferior in hydration resistance, which is a requirement for substrate materials, and for this reason it is currently not in practical use. Various attempts have been reported to improve the hydration resistance of magnesia porcelain. For example, there is a method of sintering using various additives (calcium magnesium phosphate, magnesium phosphate, etc.) as a sintering aid. Sufficient hydration resistance is not achieved. In view of the current state of the conventional methods as described above, the present invention aims to provide magnesia porcelain with improved hydration resistance and a method for producing the same. That is, according to the present invention, hydration-resistant magnesia porcelain can be obtained by forming a ceramic coating layer mainly composed of forsterite. This hydration-resistant magnesia porcelain is manufactured by the following steps (a) to (c). (a) Preliminary firing of a preformed magnesia molded body to form a porous body; (b) Impregnation of the porous body with an organosilicon compound liquid or its diluted liquid and burning it on the surface of the porous body to form a porous body. (c) sintering the silicon dioxide-coated porous body to form a ceramic coating layer mainly composed of forsterite on the surface. The present invention will be explained in detail below. The present invention improves the hydration resistance of a magnesia sintered body by forming a ceramic coating layer rich in forsterite on its surface. Forsterite (2MgO.SiO ₂ ) is generated by the reaction between silicon dioxide and magnesium oxide in the fine-particle silicon dioxide coating layer formed on the surface of the magnesia molded body during sintering. The magnesia molded body is preformed by a known method and first made into a porous body by preliminary sintering (or calcination).
A silicon dioxide coating layer is formed on the surface of this porous magnesia body as follows. That is, after a porous body is impregnated with an organic silicon compound liquid (ethyl silicate, trimethyl ethyl silane, phenyl triethoxysilane, or a diluted solution thereof), the impregnating liquid is burned on the surface of the impregnated porous body. This combustion causes the organic components to disappear (or carbonize), and silicon dioxide fine particles are deposited on the surface. The impregnating liquid inside the porous body moves to the surface by capillary action and combustion continues, producing silicon dioxide which is deposited on the surface.
Finally, the internal impregnating liquid evaporates together with the rise in temperature of the porous body (usually understood to reach about 100 to 250°C), reaches the surface, and burns. In this way, the impregnating liquid disappears, and a thin coating layer made of fine particles of silicon dioxide is formed on the surface of the porous body. An organosilicon compound is an organic compound having a silicon-carbon bond in its molecule, and as the organosilicon compound liquid, preferably ethyl silicate, trimethyl ethyl silane, or phenyl triethoxysilane is used, and if necessary, Dilute with a diluent such as ethyl alcohol or methyl ethyl ketone to obtain a viscosity suitable for impregnation. These organosilicon compounds are volatile and contribute to the continuation of combustion on the surface of the porous material, thereby contributing to the deposition of a fine particle coating layer of silicon dioxide. The porous body should be made porous to the extent that it can be impregnated with the impregnating liquid and can be sufficiently densified in the subsequent sintering, and it is sufficient if the porous body has a porosity of about 10% by volume or more. Usually this condition is 0.1~0.5μ
It is obtained by molding the magnesia raw material by a conventional method such as a doctor blade method and pre-sintering it at a temperature in the range of 900 to 1100°C. When using an organic binder such as ethyl cellulose as a molding aid,
It disappears during the heating process. Combustion of the impregnating liquid after impregnation is usually possible in the atmosphere, but it is also possible in an inert gas atmosphere with an oxygen concentration of 5 vol% or more. The magnesia porous body having the silicon dioxide coating layer thus formed is then fired and sintered. That is, by firing in an air atmosphere at a temperature of 1350 to 1450°C, dense forsterite is also generated on the surface. For the production of forsterite, the firing temperature, holding time, and reactivity of the magnesia used must be considered. This is because forsterite begins to generate a liquid phase at about 1370°C, so the reaction between this liquid phase and magnesia, the diffusion of the liquid phase, etc. are controlled. In the present invention, magnesia porcelain is mainly composed of magnesium oxide, for example, MgO of 90% by weight or more, or BeO, CaO, SiO ₂ , Al ₂ O ₃ , Fe ₂ O as unavoidable impurities during manufacturing. ₃ , _{Cr2O3 ,}
It also includes those containing up to 10% by weight of viscosity, talc, etc., singly or in combination. Forsterite used as a coating layer has the following characteristics: its dense sintered body has high hydration resistance, its coefficient of thermal expansion is smaller than that of the base magnesia porcelain, and the difference is slight, and like magnesia porcelain it can be used at high frequencies. It is optimal because it has excellent electrical insulation properties and the same sintering temperature range as magnesia, and the presence of the forsterite coating layer makes magnesia porcelain more hydration resistant than conventional porcelain. greatly improved. The thickness of the forsterite coating layer required to achieve good hydration resistance is typically on the order of 2 to 100 microns, but may vary depending on the nature of the base magnesia porcelain. Apparent density after sintering 3.3
For magnesia porcelain of ~3.5 mm, a thickness of the above order is sufficient. When taking the hydration weight increase by the test shown in the Examples as an index of hydration resistance, the preferable lower limit is about 0.04 mg/cm ² hr, which can be achieved with a forsterite layer thickness of about 2 μm or more. Further, the most preferable value of 0.01 mg/cm ² hr or less is achieved with a forsterite layer thickness of about 10 μm. Examples of the present invention will be shown below. The following raw material mixture was mixed for 15 hours in an alumina ball meal with an internal volume of 3 to form a slurry. Magnesium hydroxide (purity 98% by weight, Tomita Pharmaceutical, Type MS) 500g Water-soluble acrylic resin (Chuo Rika Kogyo, Rikabond ESZ-1311) 50g Polyethylene oxide resin (Steel Chemical Industries, Ltd.,
PEO-1) 5g Water 800g Calcium carbonate 9g Next, this slurry was degassed under vacuum for 10 minutes, then casted onto an acetate film using a doctor blade method, air-dried for 15 hours, and a thickness of 1
A green sheet with a width of 320 mm was obtained. Cut this into a size of 150 x 187.5 mm, and heat it in an electric furnace to a size of 1150 mm.
A magnesia calcined substrate with an open porosity of about 20% was obtained by calcining at ℃ for 1 hour. Next, ethyl silicate [Si
(OC ₂ H ₅ ) ₄ ] (Yoneyama Pharmaceutical Reagent Grade 1) was prepared, and the calcined body was immersed in it for 10 seconds to impregnate it. This impregnated body was ignited and ethyl silicate was burned over the entire surface, producing silicon dioxide particles of approximately 0.1μ. Some of these particles were released into space, but most of them adhered and deposited on the surface of the substrate, leaving a thickness of approximately
A silicon dioxide fine particle layer of 20μ was formed. The substrate obtained by firing this in an electric furnace at 1450° C. for 1 hour had a layer with a thickness of about 3 to 5 μm rich in forsterite formed by the reaction between MgO and SiO ₂ on the surface. The size of the sintered product is 100 x 125
×0.67tmm. The thermal conductivity, hydration resistance, transverse rupture strength, dielectric constant, and dielectric loss tangent of this sintered product were measured in comparison with those of a sintered product made by a conventional method, and the results shown in Table 1 were obtained.

[Table] As described above, the magnesia porcelain according to the present invention has been recognized to have significantly improved hydration resistance, and other properties are also satisfactory. The present invention can be used for products with complex shapes, and is also effective not only for sheet molded products but also for products made by pouring press molding, extrusion molding, etc., and has great advantages. Furthermore, the magnesia porcelain of the present invention can be used not only as a material for integrated circuit boards, but also for other purposes requiring hydration resistance and water resistance.

Claims (1)

[Claims] 1. Hydration-resistant magnesia porcelain having a ceramic coating layer mainly composed of forsterite on its surface. 2. A method for producing magnesia porcelain having a ceramic coating layer mainly composed of forsterite on its surface, which comprises the following steps (a) to (c). (a) Preliminary firing of a preformed magnesia molded body to form a porous body; (b) Impregnation of the porous body with an organosilicon compound liquid or its diluted liquid and burning it on the surface of the porous body to form a porous body. (c) sintering the silicon dioxide-coated porous body to form a ceramic coating layer mainly composed of forsterite on the surface.