JPH0336612B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention provides a corrosion-resistant mold release material for molten metal (hereinafter referred to as
Corrosion-resistant mold release material), especially for cast iron crucible surfaces that come into contact with molten corrosive metals such as aluminum alloys, zinc alloys, and lead alloys, and when performing natural gravity casting or low-pressure casting of molten light metals such as Al, Mg, Zn, and Sn. This invention relates to a corrosion-resistant mold release material that can be applied to the surface of a casting mold to prevent corrosion of molten metal and improve durability. [Conventional technology] Conventionally, as these corrosion-resistant mold release materials, powders of boron nitride (BN), titanium oxide (TiO ₂ ), graphite, etc. are mixed with water,
A method is known in which a solution obtained by dispersing the material in oil, a solvent, etc., or a solution in which a binder is added thereto is used as a corrosion-resistant mold release material, and the material is coated on a base material and baked. However, the paint film of this corrosion-resistant mold release material peels and cracks at high temperatures of 700°C or higher, making it difficult to use as a corrosion-resistant mold release material for molten metal, and even when baking the paint film onto a base material. If the rate of heating and cooling is not slow, peeling, cracking, blistering, etc. will occur, resulting in the drawback that baking requires a long time. [Problems to be Solved by the Invention] An object of the present invention is to provide a corrosion-resistant mold release material that solves the above drawbacks. [Means for solving the problem] That is, the present invention provides boron nitride in an amount of 30 to 80% by weight,
1-18% by weight of a low melting point glaze with a melting point of 300-700°C, the remainder being an inorganic pigment, 20-60 parts by weight, a silicone resin, 20-60% by weight, and the remainder being an organic solvent in which the silicone resin is soluble. This is a corrosion-resistant mold release material for molten metal containing 80 to 40 parts by weight of a liquid composition. The present invention will be explained in more detail below. The present invention includes BN, a low melting point glaze with a melting point of 300 to 700°C (hereinafter simply referred to as a low melting point glaze), an inorganic pigment,
It is a corrosion-resistant mold release material containing a silicone resin and a silicone resin-soluble organic solvent, and when applied to a substrate and baked, a coating film with excellent corrosion resistance and mold release properties is formed. The powder composition used in the present invention consists of BN, a low melting point glaze, and an inorganic pigment. BN is present in the powder composition at 30-80% by weight. When BN exceeds 80% by weight, the adhesion with the base material decreases, causing peeling and cracking, and when BN exceeds 80% by weight,
If it is less than that, corrosion resistance and mold releasability will deteriorate. Since BN imparts corrosion resistance and mold releasability to the coating film, its purity is desirably 90% or higher. The particle size has a great effect on the adhesion to the base material.
It is desirable that the thickness be 10μ or less. The low melting point glaze is present in the powder composition at 1-18% by weight. If it exceeds 18% by weight, the mold releasability and heat resistance will deteriorate, and if it is less than 1% by weight, the adhesion to the substrate will decrease and the coating will peel or crack. In the present invention, a low melting point glaze refers to a glaze whose melting point is
It is 300-700℃. A specific example of this is borosilicate glass glazes and clays containing Al ₂ O ₃ , MgO, Na ₂ O, etc., which are generally commercially available as frits and clays, and which have melting points of 300 to 300.
It is 700℃. The reason for using a low melting point glaze is that when the corrosion-resistant mold release material of the present invention is applied to a base material and baked, the adhesion between the coating film and the base material decreases400
The corrosion-resistant mold release material softens at temperatures around 700 to 900 °C, and reacts with SiO ₂ produced by thermal decomposition of silicone resin to compensate for the loss of adhesion.
This is because at high temperatures, it reacts with the inorganic pigment and increases its adhesion to the base material. The inorganic pigment is present in the balance of the BN and the low melting point glaze, i.e. 2 to 69% by weight in the powder composition. If the inorganic pigment exceeds 69% by weight, the BN content will be relatively low, resulting in poor mold releasability, and if it is less than 2% by weight, peeling or cracking will occur in the coating film. Commercially available inorganic pigments include TiO ₂ , Al ₂ O ₃ ,
White pigments such as BaSO ₄ and black pigments such as iron oxide (Fe ₃ O ₄ ) can be used. The particle size is preferably 10 μm or less in consideration of reactivity with the low melting point glaze and adhesion to the substrate, and the melting point is preferably higher than that of the low melting point glaze. Inorganic pigments react with SiO ₂ produced by thermal decomposition of silicone resin and low-melting-point glazes, preventing peeling and cracking of the coating film that occurs during baking or rapid heating and cooling, and creates a coating film with strong adhesion. is necessary to obtain. The liquid composition used in the present invention consists of a silicone resin and an organic solvent (hereinafter simply referred to as a solvent) in which the silicone resin is soluble. Silicone resin is 20-60% by weight in liquid composition
Make it exist. If the silicone resin content exceeds 60% by weight, the amount of gas generated during thermal decomposition increases, causing blistering in the coating film. On the other hand, if it is less than 20% by weight, the adhesion to the base material at low temperatures will decrease, and moreover, it will form.
The amount of SiO ₂ also decreases and the adhesion to the base material decreases.
The silicone resin does not need to be a special one, and commercially available products are sufficient. Commercially available products include liquid types made by dissolving silicone resins in organic solvents, and modified silicone resins made by mixing these with alkyl resins, acrylic resins, phenolic resins, epoxy resins, etc., but any of these can be used. The viscosity is preferably about 1000 to 5000 cP. Silicone resin acts as a binder for the powder composition and improves adhesion to the substrate at temperatures from room temperature to about 300°C, and also thermally decomposes at high temperatures to generate SiO ₂ . It reacts with the low melting point glaze and inorganic pigment to form a coating film that is stable and has good adhesion to the substrate. The solvent may be present in the liquid composition in an amount of 40 to 80% by weight; if the amount is less than 40% by weight, the miscibility with the powder composition and the workability during application will deteriorate. On the other hand, if it exceeds 80% by weight, the dispersed powder composition tends to settle and separate. Any solvent may be used as long as it is compatible with the silicone resin, such as toluene and xylene. The solvent improves the miscibility of the powder composition and the liquid composition and the workability when coating the composition on a substrate. The corrosion-resistant mold release material of the present invention comprises the above powder composition 20 to 60%
This is a mixture of 80 to 40 parts by weight of the above liquid composition. If the proportion of the powder composition is less than 20 parts by weight, the content of BN, which exhibits mold releasability, and the low melting point glaze and inorganic pigment, which control adhesion to the base material, will be low, resulting in decreased mold releasability or peeling. Cracks may occur. Further, if the proportion of the liquid composition exceeds 80 parts by weight, the dispersed powder composition tends to settle and the coating film becomes blistered due to the thermal decomposition gas of the silicone resin. On the other hand, if the proportion of the powder composition exceeds 60 parts by weight, the mixability becomes poor and uniform dispersion becomes impossible, and workability during application also decreases. In addition, since the proportion of the liquid composition is less than 40 parts by weight and the content of silicone resin is reduced, the adhesion to the substrate is improved.
In particular, the adhesion strength at low temperatures decreases. In order to manufacture the corrosion-resistant mold release material of the present invention, the powder composition and the liquid composition may be placed in a mixer at the above-mentioned ratio and mixed for several hours. To use the corrosion-resistant mold release material of the present invention, apply the undiluted solution as it is or dilute it with a solvent to a base material such as cast iron, stainless steel, or steel by an appropriate coating method such as brushing or spraying at room temperature. It only needs to be dried, and no special measures are required. [Example] Hereinafter, the present invention will be explained in more detail with reference to Examples. In addition, all percentages and parts in Examples are shown on a weight basis. Example 1 50% BN powder (particle size 5μ or less), fritted glass as a low melting point glaze (particle size 5μ or less, melting point 500℃)
5% and BaSO ₄ as inorganic pigment (particle size less than 5μ)
40 parts of a powder composition consisting of 45% composition and 60 parts of a liquid composition consisting of 40% silicone resin and 60% toluene as a solvent were blended and mixed uniformly in a ball mill. This was spray-coated to a thickness of 1 mm in a cast iron crucible with an internal volume of 2 for an aluminum die-casting machine, and dried at 200°C for 1 hour. This crucible was attached to a die-casting machine, and aluminum alloy (ADC12) molten at a temperature of 700°C was repeatedly cast. As a result, the corrosion resistance shown below was 70,000 times or more, and the mold releasability was also good. (1) Corrosion resistance: The number of times the cast iron crucible is cast until its coating is corroded by molten aluminum. (2) Mold releasability: Visual observation of the ease with which aluminum attached to a cast iron crucible peels off. Comparative Example 1 Example except that a corrosion-resistant mold release material having a composition of 40% TiO ₂ (particle size 5μ or less), 20% kaolinite as a binder, and 40% boiled oil (linseed oil) as a dispersion medium was used. When the test was carried out in the same manner as in 1, the corrosion resistance was 7,000 times. Moreover, the mold releasability was poor. Example 2 The same corrosion-resistant mold release material as in Example 1 was spray applied to the surface of a cast iron mold (SKD-6) with a capacity of 3 to a thickness of 1 mm, and dried at a temperature of 200°C for 1 hour. Next, an aluminum alloy (AC4C) molten at a temperature of 700 to 780°C was placed in this mold and natural gravity casting was performed. As a result, it was possible to perform casting 50 times, and the mold releasability was also good. The number of castings was determined by checking the surface condition of the product taken out from the mold and determining the number of times seizure occurred. Comparative Example 2 The same procedure as in Example 2 was conducted except that a commercially available mold covering material made of graphite powder dispersed in water was used, and the number of castings was 12. Examples 3 to 6 Comparative Examples 3 to 5 BN powder (particle size 5μ or less), fritted glass (particle size 5μ or less, melting point 500°C), iron oxide as an inorganic pigment (particle size 5μ or less), silicone resin, and toluene The proportions shown in Table 1 were uniformly mixed using a ball mill. This was spray-coated to a thickness of 200 μm on an iron plate, dried at room temperature, and then placed in a furnace at a temperature of 700°C and baked for 30 minutes. The adhesion of the obtained substrate was evaluated by applying tape to the coating film and peeling it off.The substrate was then immersed in an aluminum alloy bath (700℃) and cooled after 10 minutes, 100 times. The state of adhesion of aluminum to the surface of the base material was repeatedly examined. The results are shown in Table 1.

[Table] ○…No abnormalities observed in the coating film.
×...Peeling and cracking occurred in the paint film [Effect of the invention] The corrosion-resistant mold release material of the present invention has superior corrosion resistance and mold release properties compared to conventional products, so it can significantly extend the life of the paint film. If used as a mold covering material, the number of casting cycles can be significantly extended.

Claims (1)

[Claims] 1. 20-60 parts by weight of a powder composition containing 30-80% by weight of boron nitride, 1-18% by weight of a low-melting glaze with a melting point of 300-700°C, the balance being an inorganic pigment, and 20-60 parts by weight of a silicone resin.
A corrosion-resistant mold release material for molten metal comprising 60% by weight and 80 to 40 parts by weight of a liquid composition in which the remainder is an organic solvent soluble in silicone resin.