JPH0456786B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a far-infrared radiator comprising a far-infrared ray emitting coating closely adhered to the surface of glass. Far infrared rays have longer wavelengths than visible light, approximately
Electromagnetic waves with a wavelength of 2.5 to 25μ generally have the property of heating a cold object when it reaches that object. This can be used in various fields, such as
It is used for drying, treatment, heating, and other general heating purposes. (Prior art) Materials that emit far-infrared rays are also called far-infrared radiating materials, and silica, titania, alumina, and other ceramic materials have been known for a long time, but since they are generally hard materials, they have not been put into practical use. It is difficult to process it into a convenient form. As a simple method, molding the powder of these far-infrared emitting materials by methods such as sintering and injection has been practiced for quite some time, but not only does it require special equipment, but it also requires a large amount of thermal energy. It is not efficient because it requires a long processing time. Therefore, methods are being used in which far-infrared radiating material powder is dispersed in a binder and formed into a slurry or paste, which is then molded or coated onto a base material. Among them, there are various methods for coating the base material, but when there is a significant difference in the coefficient of thermal expansion between the coating and the base material, the coating is likely to peel off. In Japanese Patent Publication No. 60-54888, zirconia powder
A far-infrared radiator obtained by coating a metal or ceramic substrate with a composition containing 100 parts by weight and 2 to 5 parts by weight of a silica binder such as sodium silicate, silica sol, or silica gel emulsion as SiO ₂ and heating it. is disclosed. Furthermore, JP-A No. 60-251322 discloses that a cured film consisting of an organic silicone resin and silicon carbide or titania powder is provided on the surface of a metal or ceramic, and furthermore, an organic silicone resin and Fe ₂ O ₃ −MnO−
An infrared radiator provided with a hardened coating made of CuO composite oxide powder and silica or alumina powder is shown. Furthermore, JP-A-61-117151 discloses ceramic powders such as zirconia, alumina, titania, etc.
90 parts by weight, 5 to 20 parts by weight of aluminum diphosphate, and 5 to 20 parts by weight of water glass, alumina sol, etc. as a solid content.
A far-infrared radiator is shown in which a paste or slurry containing 25 parts by weight and aggregate, or a paste or slurry to which a colloidal silica diluent is also added, is applied to metal, ceramic, etc. and cured. ing. As mentioned above, water glass such as sodium silicate, silica sol, alumina sol, water glass or alumina sol combined with aluminum diphosphate,
It has already been shown that organic silicone resins and the like can be used as binders for far-infrared radiating materials. (Problems to be Solved by the Invention) In the case of a product using an organic silicone resin as a binder, a far-infrared emitter cannot be exposed to a temperature of 400°C or higher for a long period of time.
Or, if used repeatedly, the paint film will deteriorate significantly.
This results in peeling and cannot withstand such long-term use. For products that use water glass as a binder, the slurry or paste exhibits strong alkalinity, which causes erosion of the glass when it is applied to the glass and cured, and the resulting coating film also tends to peel off during long-term use at high temperatures. Easy to wake up. Furthermore, those using silica sol, alumina sol, etc. as a binder do not have sufficient bonding strength between the coating film and the glass surface, resulting in poor adhesion and further resulting in insufficient hardness of the coating film. When using a polyphosphate as a binder, foaming tends to occur when it is applied onto glass and cured, and the coating film tends to peel off when it is cooled from a high temperature. The paint using a combination binder of aluminum biphosphate and water glass or alumina sol as shown in JP-A-61-117151 is relatively preferable when the substrate is metal or ceramics, but when the substrate is glass, As long as ordinary ceramic powder such as zirconia, titania, alumina, etc. is used as a far-infrared radiator, the difference in thermal expansion coefficient is still excessive, and it is difficult to use repeatedly when cooling from a high temperature of about 800℃ to room temperature. During this time, the coating tends to peel off from the glass surface. It is desired to provide a far-infrared radiator that does not have these drawbacks and has high thermal efficiency, or an improved coating material such as a slurry or paste for producing the far-infrared radiator. (Means for Solving the Problems) The far-infrared radiator of the present invention comprises a sol of an inorganic oxide that does not contain an alkali metal as a solid content of 100%
parts by weight, 20 to 200 parts by weight of acidic phosphate that does not contain alkali metals, and fused silica powder with a particle size of 44μ or less based on the total amount of the above-mentioned sol and the above-mentioned acidic phosphate.
An inorganic composition containing 100 to 500 parts by weight,
A cured film of the inorganic composition having a thickness of 30 to 150 μm is provided on the surface of the glass by applying it to the surface of the glass, drying it, and curing it by heating. . The inorganic oxide sol used in the inorganic composition of the present invention is a liquid in which colloidal particles such as silica, titania, zirconia, alumina, and tin dioxide are stably dispersed in water, a water-soluble organic solvent, or a mixture thereof. be. The size of this colloidal particle is 2~
250 mμ, and these sols can be easily obtained by known methods. The concentration of the inorganic oxide in the sol is preferably about 20 to 50% by weight. In addition, this sol preferably contains as little sodium, potassium, lithium, and other alkali metals as possible, and such an inorganic oxide sol that does not contain an alkali metal component is a stabilized inorganic oxide sol. can be easily obtained by a known method, for example, by treatment with a cation exchange resin. Preferred examples include acidic aqueous silica sol and aqueous alumina sol. The acidic phosphate that does not contain alkali metals used in the present invention may be any known acid phosphate, but aluminum salts, calcium salts, etc. with high binding strength are preferable. Examples include aluminum acid. The fused quartz powder used in the present invention includes:
It is preferably 44μ or less, and usually about 0.5 to 20μ is suitably used. Fused quartz is made by melting naturally produced silica powder using an electrofusion method, etc.
It is obtained by cooling in a glassy state, and is usually produced as a powder product by pulverization, but amorphous silica obtained by other methods can also be used. Fe ₂ O ₃ , as a coloring pigment in fused silica powder
It is preferable to use MnO ₂ , CoO, Cr ₂ O ₃ , CuO, etc. in a mixture of 40% by weight or less based on fused silica. In addition, as extender pigments, crystalline silica, alumina,
It is also possible to mix zirconia, mullite, cordillite, petalite, etc. in an amount of about 40% by weight or less based on the fused silica powder. The inorganic composition used in the present invention can be obtained by thoroughly mixing the inorganic oxide sol that does not contain an alkali metal, the acid phosphate that does not contain an alkali metal, and the fused silica powder. It will be done. The preferable inorganic composition includes the above-mentioned alkali metal-free inorganic oxide sol, the solid content of which is 100 parts by weight, the above-mentioned alkali metal-free acidic phosphate, 20 to 200 parts by weight, the above-mentioned sol and acidic phosphate. 100-500 per 100 parts by weight of mixture with phosphate
and the above-mentioned fused quartz powder in an amount equal to parts by weight. In addition to the above, the inorganic composition used in the present invention may include any other components such as dispersants, surfactants, etc. as long as the purpose of the present invention is achieved.
Antifoaming agents, viscosity modifiers, water, water-soluble organic solvents, etc. may be mixed. The solid content concentration of these inorganic compositions is preferably about 50 to 80% by weight. The far-infrared radiator of the present invention can be obtained by applying the above-mentioned inorganic composition onto the surface of a glass substrate, drying it, and then heating and curing the resulting coating film. The glass used here may be any ordinary glass with a heat resistance of 400 to 1000°C, but low expansion glasses such as quartz glass, crystallized glass, and Vycor glass are preferred. The above-mentioned inorganic composition can be easily applied by a conventional method such as spraying, brushing, dipping, or the like. Further, drying may be carried out at room temperature, but may also be forced drying, for example, at elevated temperature, as long as the uniformity of the coating film is maintained. By this drying, a coating film is formed on the surface of the glass, and the thickness of the coating film is preferably about 30 to 150 μm. Next, this dry coating film can be converted into a cured film by heating. Although this heating is carried out at a high temperature, it is possible to form a hardened film emitting far infrared rays on the surface of the glass by holding the glass at a temperature of usually 450° C. or lower, preferably about 300 to 400° C., for 0.25 to 1 hour. (Function) The alkali metal-free inorganic oxide sol and the alkali metal-free acid phosphate used in the present invention form a preferable binder due to their synergistic action. In particular, this alkali metal-free binder does not corrode the glass when it comes into contact with the base glass. However, for 100 parts by weight of the solid content of the above sol,
If the proportion of the acidic phosphate is less than 20 parts by weight, the hardness of the coating tends to be insufficient or the adhesion of the coating to glass tends to be poor. On the other hand, if the proportion of acidic phosphate is as high as 200 parts by weight or more, foaming may occur when the coating film dries, or the coating may easily peel off from the glass surface when it is rapidly cooled from 800°C by water cooling or the like. The fused silica powder that is added has a very small coefficient of thermal expansion, and is particularly effective for coatings formed on quartz glass.
Since little stress is generated due to differences in thermal expansion, cracking or peeling from the glass surface does not occur.
Furthermore, this fused silica powder has a large far-infrared radiation effect, so it improves the thermal efficiency of the far-infrared radiator. However, if the amount of fused quartz powder mixed in is as high as 500 parts by weight or more based on 100 parts by weight of the binder mixture of the sol and acidic phosphate, the viscosity of the inorganic composition increases, and the conventional coating method This makes coating operations, for example by spraying, brushing, dipping, etc., difficult and, due to the reduction in the relative concentration of the binder, does not result in a desirable coating. In addition, if the amount of fused quartz powder mixed in is too small, the film tends to become dull, so the binder 100 described above
It is preferable that 100 parts by weight or more of fused quartz powder be mixed with respect to parts by weight. 40 parts by weight or less of Fe ₂ O ₃ to the fused silica powder,
When a coloring pigment such as CoO, Cr ₂ O ₃ , CuO, MnO ₂ is used in combination, the efficiency of far-infrared radiation can be further improved without interfering with the action of the fused silica powder. Further, when only fused quartz powder is used, a white film is formed, but a colored film can be obtained by mixing the above-mentioned pigment. However, if this pigment content is as high as 40% by weight or more based on the fused silica powder, the thermal expansion coefficient of the coating will significantly exceed the base material glass's thermal expansion coefficient when it is made of highly heat-resistant glass such as quartz glass. becomes large to an unfavorable range, and peeling of the coating is likely to occur. In order to increase the far-infrared radiation efficiency, the thickness of the coating made of the inorganic composition of the present invention must be 30 μm or more, and if this thickness is less than 30 μm, the hiding property is insufficient. However, if the thickness is 150μ or more, cracks and peeling due to heat shock are likely to occur during rapid cooling such as water cooling from a high temperature such as 800°C. quartz glass, crystallized glass,
A low-expansion base material such as Vycor glass provides good heat shock resistance during rapid cooling from high-temperature heating. (Example) The commercially available A ₁ below is used as an inorganic oxide sol that does not contain alkali metals, the commercially available A ₂ below is used as water glass used in comparative examples, and the commercially available acid phosphate salt that does not contain alkali metals. The following commercial products B ₁ and B ₂ were used as fused silica powder, the following commercial products C ₁ and C ₂ were used as extender pigments, and the following commercial products D ₁ were used as extender pigments.
_D2 and _D3 were prepared. A ₁ : Aqueous silica sol with a particle size of 60 mμ and _a SiO2 concentration of 30% by weight, A ₂ : JIS No. 3 sodium water glass with a solid content of 40% by weight, B ₁ : Monobasic aluminum phosphate with a concentration of 40% by weight. B ₂ : No. Calcium monophosphate powder, C ₁ : Fused quartz powder with an average particle size of 10 μm, C ₂ : Fused quartz powder with an average particle size of 90 μm, D ₁ : Extender pigment (Dipyroxide Color #9510 manufactured by Dainichiseika Chemical Co., Ltd.), D ₂ : Extender pigment (303T manufactured by Bayer), _D3 : Alumina powder with an average particle size of 5μ. By mixing these raw materials with the compositions listed in Table 1, the inorganic compositions Q ₁ to Q ₅ used in the examples of the present invention listed in Table 1 and the inorganic compositions R 1 to R ₁ used in the comparative examples are prepared. R ₁₁ was prepared. Next, these inorganic compositions were spray-coated onto a transparent quartz glass plate, and then heated at 500° C. for 30 minutes to dry the coating film, followed by heat curing. The thicknesses of the coatings obtained are shown in Table 2. Next, the obtained coating was measured for (a) surface hardness, (b) hot water resistance, (c) heat resistance, and (d) heat shock resistance using the following test methods. (a) Surface hardness Measure pencil hardness according to JIS K-5400. (b) Hot water resistance After soaking in warm water at 60℃ for one week, take it out.
Pencil hardness is measured according to JIS K-5400. (c) Heat resistance After leaving the film in an oven at 800℃ for 8 hours, take it out and visually observe the state of the film. Mark ○ if there is no peeling or cracking, and mark × if peeling or cracks have occurred. Represent by a mark. (d) Heat shock resistance The state of the coating was visually observed after taking it out of the 800℃ furnace and immediately putting it into water at room temperature 10 times.
Those with peeling or cracking are indicated with an x mark. The results of these tests are shown in Table 2.

【table】

【table】

[Table] Furthermore, the film obtained from the composition of _Q1 above was measured using a radiation characteristic measuring device EM manufactured by JASCO Corporation.
-101 was used to measure the spectrum of far infrared emissivity at wavelengths of 2 to 30μ, and it was found that at wavelengths of 2.7μ or more, 95 to
A spectrum showing 100% emissivity was obtained, and it was confirmed that the far-infrared emissivity was extremely high. In addition, compositions R ₁ and R ₁₀ in the table are examples that do not contain silica sol, R ₃ is an example in which the proportion of acid phosphate is too high, and R ₇ is an example in which the particle size of the fused silica powder is too large.
R 8 is an example in which the thickness is 44μ or more, R ₈ is an example in which the film thickness is 150μ or more, and R ₉ is an example in which the film thickness is 30μ or less. The films obtained using R ₁ , R ₃ , R ₇ , R ₈ , R ₉ and R ₁₀ had sufficient heat resistance, but all had insufficient heat shock resistance. In addition, compositions R ₂ and R ₄ in the table are examples in which acid phosphate is absent or insufficient, R ₅ and R ₆ are examples in which the proportion of fused silica powder is too large or too small, and R ₁₁ is an example in which the proportion of fused silica powder is too large or too small. This is an example in which water glass is used instead of , and it does not contain acid phosphate. These R ₂ , R ₄ , R ₅ ,
The films obtained using R ₆ and R ₁₁ had insufficient heat resistance and heat shock resistance.
Furthermore, in the example using _R5 , cracks also occurred when it was applied to glass and dried and cured. (Effects of the Invention) According to the present invention, a far-infrared radiator can be obtained which is made of a glass substrate and a hardened coating that is tightly adhered to the surface and has high surface hardness, water resistance, heat resistance, and heat shock resistance. . In particular, when a film is formed on glass to a thickness of about 30 to 150 microns, a far-infrared radiator with excellent heat shock resistance can be obtained, and its far-infrared emissivity is also high. The far-infrared radiator of the present invention is useful for dryers, treatment instruments, heating devices, and other heaters with high thermal efficiency.

Claims (1)

[Claims] 1 100 parts by weight of an inorganic oxide sol that does not contain an alkali metal as its solid content, 20 to 200 parts by weight of an acidic phosphate that does not contain an alkali metal, and a total amount of the sol and the acidic phosphate that is 100 parts by weight. An inorganic composition containing 100 to 500 parts by weight of fused silica powder with a particle size of 44μ or less is applied to the surface of the glass, dried, and heated to harden. , the thickness that adheres to this
A far-infrared radiator provided with a cured film of the inorganic composition having a thickness of 30 to 150μ.