Enamel products and enamel glazes

Abstract

To provide enamel with both hardness as well as impact resistance in order to improve conventional enamel, which is hard but causes deterioration of rust and corrosion resistance of enameled products due to chipping of enamel caused by impact during use or the like.SOLUTION: There is provided an enamel glaze comprising a base material containing SiO2 and one or more kinds of inorganic oxides serving as additives, wherein the mass ratio of the inorganic oxides based on 100 pts.mass of the base material is 15 pts.mass or more and 90 pts.mass or less.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an enamel product having sufficient hardness and impact resistance, and to an enamel glaze for use in producing said enamel. [Background technology]

[0002] Enamel is made by applying an inorganic glassy glaze to the surface of metals such as iron or aluminum, and then firing it so that the molten glaze adheres to the metal surface. Enamel products have higher rust and corrosion resistance, as well as stain and abrasion resistance, than products with a bare metal surface. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-228968 Summary of the Invention [Problem to be solved by the invention]

[0004] However, although enamel is hard, chipping caused by impacts during use can reduce the rust and corrosion resistance of enamel products. Therefore, there is a demand for enamel that is not only hard but also impact resistant.

[0005] Here, the enamel frit (base material) is a glassy inorganic material that forms the enamel coating and is composed of various compositions. The enamel frit melts on the surface of the substrate during firing in the enamel coating formation process and determines the main properties of the enamel coating. Therefore, it has been difficult to add impact resistance by redesigning the composition of the frit without changing its already-defined properties (Patent Document 1). [Means for solving the problem]

[0006] The present invention includes the following aspects 1 to 6: [Embodiment 1] An enamel glaze comprising a base containing SiO2 and one or more inorganic oxides as additives, a glaze for enamel, in which the mass ratio of the inorganic oxide to 100 mass parts of the base is more than 15 mass parts and not more than 90 mass parts; [Aspect 2] The enamel glaze according to aspect 1, wherein the inorganic oxide has a higher melting point than the base; [Aspect 3] The enamel glaze according to Aspect 1 or 2, wherein the inorganic oxide is one or more selected from zirconium silicate, alumina, titanium dioxide, silica stone, spodumene, and zirconium oxide; [Aspect 4] The enamel glaze according to Aspect 3, wherein the base is a silica-based base containing silicic acid and boric acid as main components, or a phosphoric acid-based base containing phosphate as main components; [Aspect 5] An enamel product obtained by using the enamel glaze according to Aspect 3 as a glaze; [Aspect 6] A method for producing an enamel product by using the enamel glaze according to Aspect 3 as a glaze and firing the product at a firing temperature of 550°C or higher and 650°C or lower;

[0007] According to the present invention, an inorganic oxide is added as a separate additive to the frit base. Therefore, even if the components constituting the base itself and the components constituting the inorganic oxide are the same, this does not mean that they are the same as the enamel glaze according to the present invention. When the enamel glaze is fired, the base melts due to heat, but the inorganic oxide does not melt and instead bonds with the molten base to form the enamel film. Therefore, for example, SiO2 in the base and SiO2 as the inorganic oxide play different roles in forming the enamel film, and are therefore distinguished in terms of their content in the enamel glaze according to the present invention. [Effects of the Invention]

[0008] The present invention realizes an enamel film with high impact resistance by adding a large amount of inorganic oxide to the base of an enamel glaze. This remarkable effect is based on the inventor's idea that goes against common sense, which is that inorganic oxides are added to prevent the enamel glaze from overfiring or to color the enamel film, and that 10 parts by mass of inorganic oxide per 100 parts by mass of base is sufficient to achieve these purposes, and that adding a large amount of inorganic oxide is not necessary.

[0009] Furthermore, because the inorganic oxide has a higher melting point than the base, it is thought that the inorganic oxide remains dispersed in the enamel film in the form of fine particles even after the firing process, and it is speculated that this has the effect of absorbing the impact from the steel ball and protecting the molten glassy base from the impact.

[0010] When the firing temperature was 550°C to 650°C, good impact resistance was obtained by setting the mass ratio of inorganic oxide to base to 15 parts by mass or more and 90 parts by mass or less. In the ball drop test described in the following examples, a good enamel film was obtained in which no mark was observed when the steel ball was dropped, or even if a mark was observed, it was only a slight crack. This result suggests that inorganic oxides remain dispersed in the enamel film in the form of fine particles even after the firing process, and it is speculated that this is due to the effect of absorbing the impact from the steel ball and protecting the molten glass base from the impact.

[0011] The enamel glaze of the present invention can produce an enamel film that is resistant to peeling and has sufficient hardness, even at firing temperatures of 550°C to 650°C. In particular, it can produce an enamel film that is superior in impact resistance to enamel films formed at conventional high firing temperatures. Because the enamel glaze of the present invention can be formed at firing temperatures lower than conventional temperatures (750°C to 850°C), it can be used on a wider variety of metals than conventional ones, and as a result, a wider variety of enamel products can be produced.

[0012] It has been discovered that by using the enamel glaze of the present invention, enamel products having high impact resistance can be obtained while maintaining the adhesion rate of the enamel film to the surface of the metal substrate at firing temperatures of 550°C to 650°C, a temperature that aluminum can withstand. Therefore, according to the present invention, it is possible to realize an enamel product in which an enamel film is formed on a metal substrate such as aluminum, which exceeds its melting point at high temperatures of 750°C to 850°C. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a photograph showing the results of a ball drop test on an enamel film containing no additives (base only). [Figure 2] This is a photograph showing the results of a ball drop test on an enamel film when an enamel glaze made from a phosphoric acid-based base mixed with zirconium silicate (ZrSiO4) as an additive was used. [Figure 3] This is a photograph showing the results of a ball drop test on an enamel film when an enamel glaze made from a phosphoric acid-based base mixed with alumina (Al2O3) as an additive was used. [Figure 4] This photograph shows the results of a ball drop test on enamel coatings made using an enamel glaze containing titanium dioxide (TiO2) as an additive to a phosphoric acid-based base. Note that the notation "titanium oxide" in the figure refers to titanium dioxide. [Figure 5] This is a photograph showing the results of a ball drop test on an enamel film when an enamel glaze containing a phosphoric acid base and spodumene (LiAlSi2O6) as an additive was used. [Figure 6] This is a photograph showing the results of a ball drop test on an enamel film when an enamel glaze made from a phosphoric acid-based base mixed with silica (SiO2) as an additive was used. [Figure 7] This is a photograph showing the results of a ball drop test on an enamel film when an enamel glaze made from a phosphoric acid-based base mixed with zirconium oxide (ZrO2) as an additive was used. [Figure 8] This is a photograph showing the results of a ball drop test on an enamel film when an enamel glaze containing a silica-based base mixed with zirconium silicate (ZrSiO4) as an additive was used. DETAILED DESCRIPTION OF THE INVENTION

[0014] The enamel glaze of the present invention comprises a base containing SiO2 and one or more inorganic oxides as additives. The inorganic oxide is preferably one or more selected from the group consisting of zirconium silicate (ZrSiO4), alumina (Al2O3), titanium dioxide (TiO2), spodumene (LiAlSiO2), silica (SiO2), and zirconium oxide (ZrO2). The additive is preferably an inorganic oxide having a melting point higher than that of the base. The additive having a melting point higher than that of the base can also prevent overfiring of the enamel glaze. The inorganic oxides listed above can also be used as overfiring inhibitors to prevent overfiring during firing of the enamel glaze.

[0015] The base used in the enamel glaze of the present invention is not particularly limited, but preferably a silica-based base containing silicic acid and boric acid as the main components, or a phosphate-based base containing phosphate as the main component. The base used in the enamel glaze of the present invention is a vitreous inorganic material used, for example, as a ground coat or cover coat. The base used in the enamel glaze of the present invention can be, for example, a low-temperature firing base or a medium-temperature firing base, and is preferably selected from a low-temperature firing phosphate-based base, a low-temperature firing silica-based base, a medium-temperature firing phosphate-based base, a medium-temperature firing silica-based base, a titanium-based base, etc.

[0016] In the enamel glaze of the present invention, the mass ratio of the inorganic oxide to 100 parts by mass of the base is 15 to 90 parts by mass, preferably 15 to less than 90 parts by mass, more preferably 15 to 60 parts by mass, and even more preferably 15 to 30 parts by mass. When multiple types of inorganic oxides are contained, this refers to the total amount of the inorganic oxides.

[0017] The enamel glaze of the present invention is produced by mixing a base material with an inorganic oxide. The inorganic oxide may be commercially available and used as is, or may be further pulverized in a mill before use.

[0018] The enamel product of the present invention is produced using the enamel glaze of the present invention. The enamel product of the present invention is produced by applying the enamel glaze of the present invention to a molded metal substrate. The metal substrate may be a composite made of one or more of cast iron, steel plate, aluminum, or stainless steel, for example.

[0019] The enamel product of the present invention is produced by applying the enamel glaze of the present invention to a molded metal substrate, which is optionally subjected to pretreatments such as cleaning and blasting. Glazing can be carried out using one or more of the glazing methods commonly used in this technical field, such as painting, dipping, spraying, and electrostatic glazing. After glazing, the product is dried for several minutes to several tens of minutes in a drying oven, if necessary. The enamel product of the present invention can then be produced by firing in a firing oven.

[0020] Generally, after applying enamel glaze, it is conventionally fired at a high temperature of about 750°C to 850°C, and it is believed that firing at this high temperature allows the enamel glaze to adhere firmly to the metal surface. However, in the present invention, it has been discovered that by mixing 15 parts by mass or more of inorganic oxide with 100 parts by mass of base material, an enamel product with high impact resistance can be produced.

[0021] Furthermore, they found that by mixing 15 parts by mass or more of inorganic oxide with respect to 100 parts by mass of base into the enamel glaze, it is possible to produce enamel products with high impact resistance even at temperatures lower than conventional temperatures. Specific firing temperatures are, for example, 550°C or higher and 650°C or lower. A firing temperature higher than 550°C and lower than 650°C is more preferable. Furthermore, they found that when the enamel glaze of the present invention is fired at a temperature lower than conventional temperatures, it is sometimes possible to achieve higher impact resistance than enamel products fired at conventional temperatures, such as 750°C. Furthermore, according to the present invention, the adhesion rate of the enamel film to the surface of the metal substrate was sufficient, even when the firing temperature was lower than conventional temperatures, 550°C to 650°C. [Example]

[0022] (1) Manufacturing of enamel glazes Hereinafter, the inorganic oxide as an additive may be simply referred to as an additive. The enamel glazes of Production Examples 1-1 to 7-4 were each prepared by mixing the powdered base and powdered additives shown in the table below in the weight ratios shown in Table 2. In these examples, a phosphate-based or silica-based base with the composition shown in Table 1 below was used as the base. In these examples, 5 parts by mass of monopotassium phosphate, a flotation agent for uniformly dispersing the enamel glaze in water, was mixed with 100 parts by mass of the base. Furthermore, 0.2 parts by mass of NaNO2 and K2O3, stoppers for preventing dripping when applied to a metal substrate, were each mixed with the base. Furthermore, 380 g of each of the prepared mixtures was taken in Production Examples 1-1 to 7-4 and mixed with 120 ml of water to form a viscous aqueous dispersion. Hereinafter, this aqueous dispersion will sometimes be referred to as a glaze liquid. For the samples with 0 mass % additives evaluated in Table 7, five glaze liquids were prepared using the phosphoric acid-based base according to Table 1(b) among the above preparation methods, excluding the additives.

[0023] However, the bases constituting the present invention are not limited to those shown in Table 1. The SiO2 content in the phosphoric acid-based base should be substantially less than the amount of phosphoric acid. However, if the SiO2 content is too low, the viscosity of the glaze will be too low, and too many additives will be added, making it impossible to evaluate the glaze as an enamel film with high impact resistance. Therefore, the SiO2 content in the base is preferably 7% by mass or more, as shown in Table 1(b).

[0024] [Table 1]

[0025] [Table 2]

[0026] (2) Manufacturing of enamel products The enamel products of Production Examples 1-1-1 to 7-4-3 shown in Tables 3 to 6 were each produced by spraying 4 g of the glaze liquid of Production Examples 1-1 to 7-4 prepared in (1) onto a 25 mm x 25 mm x 3 mm thick steel plate (SUS304) as the metal substrate, followed by drying and firing for 10 minutes at the firing temperatures shown in Tables 3 to 6 below. The enamel film formed on the enamel product had a thickness of approximately 300 μm. The firing time is preferably approximately 2 to 15 minutes. Furthermore, five glaze liquids containing 0 mass% additive prepared in (1) were sprayed onto the metal substrate in the same manner as in the above production examples, dried, and fired for 10 minutes at 550°C, 650°C, 700°C, 750°C, and 800°C, respectively, to produce Production Examples 0-0-1 to 0-0-5.

[0027] [Table 3]

[0028] [Table 4]

[0029] [Table 5]

[0030] [Table 6]

[0031] (3) Drop ball test The enamel product manufactured in (2) was placed and fixed on a horizontal steel plate with sides of 90 mm. A cylinder with an inner diameter of 400 mm was placed and fixed vertically on the steel plate so as to surround the fixed enamel product. A spherical steel ball (224 g) with a diameter of approximately 380 mm was then allowed to drop vertically from a height of 1.5 m into the cylinder toward the enamel product fixed to the steel plate, thereby conducting a ball drop test. The surface condition of the enamel film on the enamel product impacted by the steel ball drop was recorded as shown in Figures 1 to 8, and the condition of the point where the steel ball fell near the center of the enamel product was evaluated as follows. Note that, during the evaluation, a penetrant testing liquid (Color Check (red) by Taketo Co., Ltd.) was applied to the enamel product after the steel ball drop to make the impact mark more visible. The samples that appear to be entirely colored in the figure are those that have a noticeable color due to a decrease in the gloss of the enamel surface. The fact that the sample appears to be entirely colored does not necessarily mean that it has poor impact resistance. ⊚: No impact marks or small, dot-like impact marks were found at the point where the steel ball fell. ○: A hollow crack was observed surrounding the point where the steel ball fell. △: A central point mark and a crack surrounding the central point mark were observed at the point where the steel ball fell. ×: Damage accompanied by peeling of the enamel was observed at the point where the steel ball fell.

[0032] The following tables show the results of the ball drop test evaluated by the above evaluation method, corresponding to Figures 1 to 8. Note that the notation "parts" in Figures 1 to 8 and in the following tables indicates parts by mass relative to 100 parts by mass of the base.

[0033] [Table 7]

[0034] [Table 8]

[0035] [Table 9]

[0036] [Table 10]

[0037] [Table 11]

[0038] [Table 12]

[0039] [Table 13]

[0040] [Table 14]

[0041] First, as can be seen from Table 7, the enamel film containing no additives showed damage to the enamel, including peeling, in the ball drop test regardless of the firing temperature, and was rated as x. The results in Tables 8 to 14 above show that, regardless of whether zirconium silicate, alumina, titanium dioxide, spodumene, silica, or zirconium oxide is used as an additive, adding 15 parts by mass or more of additive to 100 parts by mass of base material improves impact resistance compared to samples with an additive amount of 10 parts by mass or less. It is believed that the additive remains dispersed in the enamel film in the form of fine particles even after the firing process, and is presumed to have the effect of absorbing the impact from the steel ball and protecting the molten glassy base material from impact.

[0042] However, the addition of 15 parts by mass or more of additives tends to reduce the glossiness seen in conventional enamel coatings. This discourages those skilled in the art from adding large amounts of additives to the base. However, in the present invention, despite this conventional common technical knowledge, we have conducted research and have been able to realize enamel products with unprecedentedly high impact resistance, although the gloss of the enamel coating surface is reduced. Furthermore, the present invention can provide an enamel glaze that can realize enamel products with such excellent properties.

[0043] When the firing temperature was 550°C to 650°C, a mass ratio of additive to base of 15 to 90 parts by mass resulted in a rating of ⊚ or ∘, and a good enamel film was obtained in which no steel ball impact marks were observed, or even if impact marks were observed, they were limited to minor cracks. Adding more than 90 parts by mass of additive tended to result in damage accompanied by peeling, resulting in a lower rating. It is believed that the amount of particulate additive was too high relative to the base that melts during firing, which tends to make the enamel film brittle. Furthermore, as an overall trend, enamel coatings fired at high temperatures of 750°C showed that as the mass proportion of additives decreased to 10 parts by mass or less, they were more prone to cracking and peeling than enamel coatings fired at low temperatures, and were found to be more vulnerable to impacts, a result consistent with the conventional properties of enamel coatings.

[0044] The mass ratio of the additive to 100 parts by mass of the base is 15 to 90 parts by mass, preferably 15 to less than 90 parts by mass, more preferably 15 to 60 parts by mass, and even more preferably 15 to 30 parts by mass. The low-temperature firing temperature is 550°C to 650°C, more preferably 550°C to less than 650°C.

[0045] The type of additive is not particularly limited, but it is preferably one or more additives selected from zirconium silicate, alumina, titanium dioxide, silica stone, spodumene, and zirconium oxide.

[0046] (4) Nanoindentation test Nanoindentation testing is a testing method that quantitatively measures the hardness and rigidity of a sample by pressing a diamond indenter into the sample surface under load and directly measuring the indentation depth with a displacement meter. Nanoindentation testing was performed on enamel using IWX15426 (a low-temperature phosphate-based enamel glaze) as the base material, with the additives and firing temperatures shown in the table below, to determine the nanoindenter hardness and Young's modulus.

[0047] The measurement conditions for the nanoindentation test described in Table 15 are as follows: Equipment: G200 (Agilent Technologies) Maximum pressing force: 100mN Indenter: Berkovich indenter (diamond, apex angle 115 degrees) Load time: 30 seconds The nanoindenter hardness and Young's modulus shown in each table were calculated in accordance with JIS Z2255.

[0048] [Table 15]

[0049] According to the results shown in Table 15, enamel films using zirconium silicate as an additive and fired at 550°C and 650°C, when the mass ratio of zirconium silicate to 100 parts by mass of the base was 5 to 30 parts by mass, had a nanoindenter hardness of 4.5 GPa or more and a Young's modulus of 58 GPa or more. There was no significant difference in the hardness and resistance to deformation of the film compared to when fired at 750°C. In fact, when no additive was added (0 parts additive, base only), the nanoindenter hardness and Young's modulus obtained at firing temperatures of 550°C and 650°C changed significantly, with the 650°C firing showing higher values than the 550°C firing. However, Table 7 clearly shows that the impact resistance was low at all firing temperatures.

[0050] Therefore, according to the present invention, by adding 15 mass parts or more of additives to 100 mass parts of base, a unique effect of high impact resistance of the enamel film can be obtained, which cannot be determined by film properties such as nanoindenter hardness and Young's modulus.This can be said to be a remarkable effect that even a person skilled in the art in this technical field could not easily have achieved based on the prior art.

Claims

1. SiO ２ and one or more inorganic oxides selected from zirconium silicate, alumina, silica stone, spodumene, and zirconium oxide, A method for producing an enamel product, comprising using as a glaze an enamel glaze in which the mass ratio of the inorganic oxide to 100 parts by mass of a base is 30 parts by mass or more and 90 parts by mass or less, and firing the glaze at a firing temperature of 550°C or more and lower than 650°C.

2. SiO ２ and an inorganic oxide selected from spodumene and zirconium oxide, The mass ratio of the inorganic oxide to 100 parts by mass of the base is 30 parts by mass or more and 90 parts by mass or less.

3. The base is a silica-based base containing silicic acid and boric acid as main components, or a phosphoric acid-based base containing phosphate as main components. The enamel glaze according to claim 2.

4. An enamel product obtained using the enamel glaze according to claim 2 as a glaze.

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