JPH0121101B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a enamel frit that can be fired at low temperatures, and contributes to resource and energy saving in enamel processing. Structure of conventional examples and their problems In general, the baking temperature of iron enamel is 800 to 870℃, which is higher than the _A1 transformation point (723℃) of iron, so the iron crystal type transforms from a iron to gamma iron during baking. The iron plate is easily deformed due to thermal distortion, and the dimensional accuracy after firing is poor, resulting in a high defective rate. Therefore, the plate thickness must be increased. Furthermore, when an iron plate is heated to a high temperature, hydrogen gas and the like adsorbed or occluded in the iron plate are significantly generated. In addition, moisture in the slip and on the iron plate reacts with carbon in the iron plate in the firing temperature range, generating carbon dioxide gas, causing bubbles and bubbles on the enamel surface.
Defects such as pinholes are more likely to occur. For example, the inner wall of the oven is made of steel plate with a thickness of 0.6 mm.
When iron enamel is baked at 800 to 870°C, the molded product is greatly deformed and many bubbles, pinholes, etc. occur, resulting in a high defect rate. On the other hand, if enamel can be fired at a low temperature below the _A1 transformation point, there will be less deformation due to thermal distortion, and there will be fewer defects such as bubbles and pinholes due to gas generation, making it possible to use thin plates with a thickness of about 0.4 mm. It is also easy to enamel objects with more complex shapes. In recent years, resource conservation and energy conservation have become important issues. By lowering the firing temperature of the enamel, fuel costs can be reduced, and by allowing the use of thin plates, material costs for the base material can be reduced. Although low-melt enamel processing technology that involves firing at low temperatures has excellent advantages,
It does not have enough properties to replace the current ordinary enamel fired at high temperatures, and is still insufficient. One of the reasons for this is that enamel is required to have a decorative function as well as a surface protection function such as heat resistance and corrosion resistance, but lead-based frits, which are conventional low melting point frits, do not have both functions. Because there was nothing to be satisfied with. Among these, in addition to the surface condition and gloss of the enamel surface, the requirements for decorative functions include:
Examples include color development of various tones, stability, etc.
Conventional low-melting hollow frits have had problems with color development, color stability, etc. Therefore, the present inventors have investigated the _A1 transformation point (723
We have developed a chemically stable enamel frit with a low softening point that can be fired at temperatures below 30°F (°C) or less, can develop colors in all tones, and is chemically stable. However, they still had the following problems. (1) Long-term storage stability of enamel glaze. (2) Dating characteristics. The problems regarding the long-term storage stability of enamel glazes using low softening point enamel frits in (1) are as follows. In order to lower the softening temperature of the enamel frit, it is necessary to add alkaline components (Na ₂ O, K ₂ O, Li ₂ O, etc.) to the glass, and compared to conventional ordinary enamel frits, the amount of alkaline components is lower. Increasing the amount is inevitable. When a enamel glaze is prepared using the low softening point enamel frit of the prior application and stored for a long period of time, the alkaline component gradually dissolves from the glass frit and has a negative effect on the glaze. When this glaze that had been stored for a long period of time was applied and fired, serious defects such as orange skin, cracks, and crack heads were observed in the enamel layer. The dipping characteristic (2) is a problem in the glazing method, that is, the dipping method in which objects are immersed in the glaze to apply the glaze, but the thixotropic properties of the glaze and the fluidity of the glass frit are important points. The low-softening enamel frit of the prior application is mainly a glass frit for the spray method, and when the dip method is used, pinholes, sink marks, etc. occur in the enamel layer, which is not desirable. Therefore, in order to solve such problems,
The inventors have devised a low softening point transparent hollow frit that has excellent long-term glaze storage and excellent dipping properties. It has the following composition. _SiO2 : 32-45% by weight _B2O3 : 7-20% by weight _F2 : 2-9% by weight _Na2O : 14-22% by weight _K2O : 0.4-5 _% by weight _Li2O : 0.3- 2% by weight CaO: 1.5-15% by weight BaO: 1.5-15% by weight ZrO ₂ : 0.5-4.5% by weight Al ₂ O ₃ : 0.5-5% by weight However, this material has poor long-term storage properties and dipping properties of enamel. Although it has the advantage of being excellent in water resistance, it was found that there were some problems with water resistance. The water resistance of enamel means that it cannot be used in places where it gets wet when used in cooking pots, pots, bathtubs, etc.
The glass components and mill additives on the enamel surface gradually dissolve into water or hot water, causing the enamel surface to become uneven and become uneven, and the gloss to be significantly reduced. This is an important characteristic. Purpose of the Invention The present invention is a transparent glaze that can be fired at a temperature below the _A1 transformation point (723°C) of iron or iron-based alloys, can preserve the glaze for a long time, has excellent dipping properties, and is transparent with a low softening point and good water resistance. The purpose is to provide enamel frits. Structure of the Invention The frit of the present invention contains at least SiO ₂ , B ₂ O ₃ ,
F ₂ , Na ₂ O, K ₂ O, Li ₂ O, CaO, BaO, ZnO,
Composed of ZrO ₂ and Al ₂ O ₃ , SiO ₂ 32 to 45% by weight (hereinafter simply expressed as %), B ₂ O ₃ 7 to 20%, F ₂
2-9%, Na ₂ O 14-22%, K ₂ O 0.4-5
%, _Li2O 0.3-2%, CaO 1.5-15%, BaO
1.5-15%, ZnO 0.1-5%, ZrO ₂ 0.5-4.5%,
Contains 0.5 to 5% Al ₂ O ₃ and contains TiO ₂ , MgO,
It is characterized by containing a component selected from the group consisting of SnO ₂ and SrO in a range of 0 to 3% by weight. Description of Examples One of the important requirements for hollow frits
One is the balance of the thermal expansion coefficient with the base metal. Typical base metals include iron, stainless steel, aluminized steel, and aluminum, and it is therefore necessary to adjust the coefficient of thermal expansion of the frit to suit these base metals. Generally, the following addition formula is conveniently used as a rule of thumb for the coefficient of thermal expansion α of a frit. α= _o 〓 a _o P _o where α is the thermal expansion coefficient factor due to the oxide component of the frit, and P is the weight percentage of each component. When determining the composition of the frit, the composition must be determined with reference to this addition formula so as to provide an appropriate expansion coefficient. For example, if the base metal is a steel plate, a frit with an expansion coefficient of (85 to 105) x 10 ^-7 deg ^-1 must be selected for general enamel. If it is less than this, the enamel surface will crack, the base metal will undergo convex deformation, or the enamel layer will shrink, exposing the base metal. If the expansion coefficient of the frit is larger than the above range, phenomena such as concave deformation of the base metal or peeling of the enamel layer during cooling after firing will occur. On the other hand, in the case of a frit that is fired at a temperature below the _A1 transformation point of iron, the expansion coefficient is larger than the appropriate range (85 to 105) x 10 ^-7 deg ^-1 of currently commonly used iron frits. Value (85~
115) × 10 ^-7 deg ^-1 was the optimal range. The reason for this is that the firing temperature is approximately 100°C compared to general enamel.
Because it is 200°C lower, the thermal stress applied to the base metal is small, and the appropriate range of expansion coefficient is larger than that of general hollow frits. In this way, the expansion coefficient of the selected frit is also determined by the enamel firing temperature. Furthermore, in order to fire enamel at a low temperature, it is necessary to lower the softening point of the frit so that the frit softens and flows at the firing temperature and wets the surface of the steel plate. For example, when coating with enamel at a low temperature below the A ₁ transformation point of steel to prevent deformation of the base metal and defects such as bubbles and pinholes, the baking temperature of the enamel should be adjusted.
It is necessary to keep the temperature below 720℃. If the base metal is an aluminized steel plate or aluminized steel plate,
When the temperature exceeds 600℃, the temperature between the aluminum layer and the iron layer
The growth of the Al-Fe alloy layer becomes remarkable, and this Al-Fe
As the alloy layer grows, the adhesion between the enamel and the base metal decreases, so the firing temperature needs to be 600°C or lower. When the base metal is aluminum, the melting point of aluminum is 658℃, so the baking temperature is set at 600℃ to prevent thermal deformation of the base metal.
It is necessary to keep the temperature below ℃. In this way, the softening point of the frit is also determined by the type of raw metal used. Furthermore, in order to achieve the purpose of the present invention, the following must be taken into consideration. (b) Long life of enamel glaze As mentioned above, low softening point frit is forced to increase the alkaline content, so the chemical durability of glass frit is a key point.
It is necessary to consider the type or amount of components that improve chemical durability. At the same time, it is also essential to check for selectively soluble components in addition to alkaline components, and these considerations will ensure the longevity of the enamel glaze. (b) Dipping characteristics One of the factors that affects the dipping characteristics is the chemical durability of the glass frit. The reason is as follows. Frog's eye clay is added to the enamel glaze as a mill additive, and the purpose of adding the frog's eye clay is to act as a suspending agent to suspend the frits and to strengthen the dry film of the applied enamel glaze. Whether the clay particles or glass frit remain suspended in the slip for a long time, or whether they aggregate into coarse particles and precipitate depends on the adsorption of ions present in the slip. That is, since the state of the glass frit changes depending on the components eluted from the glass frit, it is preferable to select a glass frit that has excellent chemical durability and has extremely low component elution from the glass frit. If a glass frit with poor chemical durability is used, the viscosity in the slip increases, resulting in poor workability and unfavorable enamel properties. Another factor that affects dipping characteristics is the fluidity of the glass frit. The reason is as follows. When performing dipping glazing, the glaze thickness is 60 to 120 μm from the viewpoint of workability, and the thickness of spray glazing is
Since the thickness is smaller than that of 120 to 200 μm, pinholes and the like tend to occur in areas where the film thickness is small. In addition, the particle size distribution of the frit during dipping is 8 to 15 g of particles of 200 mesh or more in a 50 c.c. slip, whereas when spraying
Pinholes are more likely to occur because the frit particle size is larger in the dipping glaze, which is ~10g. Therefore, it is important to select a composition such that the glass frit itself flows sufficiently at a predetermined firing temperature and coats the substrate. (c) Water resistance Factors that affect the water resistance of enamel are not only the solubility of glass frit in hot water, but also the sufficient melting reaction between glass, clay, silica powder, and other mill additives at a given firing temperature. The important thing is whether you do it. The composition of the hollow frit according to the present invention constructed based on the above considerations will be explained below. The figure shows the relationship between the weight percent of ZnO in the enamel frit, the amount of hot water dissolved in the enamel coating, and the fluidity of the frit, which the inventors found to be particularly effective in improving water resistance. In the figure, 1 is the relationship between the amount dissolved in hot water and the content of ZnO, 2
show the relationship between fluidity and ZnO content, respectively. Table 1 shows the compositions of the main frits studied by the present inventors, and Table 2 shows the properties and evaluation results of the surface condition of the enamel layer, enamel properties, durability, etc.

【table】

[Table] After mixing the glass raw materials, put the frit into the crucible.
It was prepared by melting at 1200°C for 45 minutes. The amount of dissolved alkali in hot water in the table is calculated by immersing 5 g of frits of 200 to 350 meshes in 100 c.c. of distilled water, boiling for 1 hour, removing the supernatant liquid, and using a methyl orange indicator to measure the eluted alkaline components. 0.1N―
It was titrated with H ₂ SO ₄ and the amount consumed was taken as a measure of the amount of alkali eluted. ○ indicates that the consumption of 0.1N-H ₂ SO ₄ is 1 ml or less, △ indicates 1 to 3 ml, and × indicates more than that. In addition, the fluidity of glass frit was measured by taking 2 g of frit that had passed through 200 meshes, putting the sample into a mold and press-molding it at 1 ton/cm ² to a diameter of 12.7 mm.
The sample was placed on a pretreated enameled steel plate (pickling loss: 300 mg/dm ² , nickel adhesion: 7 mg/dm ² ), and heat treated at 690°C for 5 minutes. The diameter was measured with a caliper. Those with a diameter of 18 mm or more are marked with ○, those with a diameter of 14 to 18 mm are marked with △, and those with a diameter of 14 mm or less are marked with ×. Enamel glaze consists of 1000 parts by weight of Fritz and 60 parts by weight of clay.
parts by weight, 60 parts by weight of silica powder, 1 part by weight of sodium nitrite, 10 parts by weight of pigment, and 620 parts by weight of water were put into a ball mill and milled for about 3 hours. The solid content of 200 mesh or more in .c. was adjusted to 10 g. In this glaze, pre-treated size 100 x 100
mm, thickness 0.6mm SPP steel plate (pickling loss 300mg/d
m ² , nickel adhesion amount 7 mg/dm ² ) was immersed and glazed by the dip method. Then dry, 710
A test plate was prepared by baking at ℃ for 5 minutes. In addition, in order to observe the long-term storage stability of the slips, the slips were placed in a plastic container, left in a constant temperature bath at 35°C for 10 days, and then test plates were prepared using the dip method as described above. Surface condition of the enamel layer (yuzu skin, pinholes,
(Cracks, etc.) are the results of visual observation of the enamel surface of the test plate; ○ mark indicates that yuzu skin, pinholes, cracks are not observed, and × mark indicates that they are observed. Gloss is measured by shining light on the test plate at an incident angle of 45° and a reflection angle of 45°, and measuring the reflectance of light. ○ mark indicates reflectance of 80 or more, △ mark indicates reflectance of 80 to 70, and × mark indicates reflectance of 70 or less. shows. The water resistance of the enamel layer was evaluated by immersing the test plate in pure water at 98°C and determining the weight loss value after 3 hours. 〇mark is
10 mg/dm ² or less, △ mark is 10 to 30 mg/dm ² , × mark is
Indicates 30 mg/dm ² or more. Evaluation was also made based on the reduction in gloss of the test plate after boiling for 3 hours as compared to before the test.
〇 indicates that the gloss change rate is within 10%, and × indicates that it is 10% or more. The adhesion of the enamel layer is evaluated using a PEI adhesion tester, and those with a value of 90% or more are rated 〇,
70-90% is shown as △, and 70% or less is shown as ×. In addition, as a comprehensive evaluation, those that met the purpose of the present invention and were effective were marked with a circle, and those that were not effective were marked with an x. Based on the above results, the reasons for determining the content of each component in the hollow frit of the present invention will be described. (1) ZnO ZnO is an alkaline earth metal oxide and has the property of lowering the softening point, but in particular, it has the property of improving water resistance and water resistance, and is essential for the present invention. It is a component of Figure 1 shows the relationship between the weight percent of ZnO, the amount of hot water dissolved in the enamel coating, and the fluidity of the frit. Without the addition of ZnO, the amount dissolved in hot water was extremely large, but by adding 0.1% or more, the amount decreased to less than 10 mg/m ² and water resistance improved. However, if it exceeds 5%, fluidity deteriorates. Frits No. 1 to 6 in Table 1 are those with varying ZnO content, but when ZnO exceeds 0.1%, as shown in Table 2, the water resistance is determined by the amount dissolved in hot water and the gloss. It can be seen that the rate of change is small. In particular, if the gloss changes significantly before and after the water resistance test, this is particularly undesirable because when visually inspected in actual use, a clear difference will be recognized between above and below the waterline. Addition of ZnO has a great effect in reducing the rate of change in gloss. However, if it exceeds 5%, the fluidity of the frit becomes low and pinholes are formed on the enamel surface, which is not preferable. From these points, the proportion of ZnO is in the range of 0.1 to 5%. (2) SiO ₂ Generally, as the amount of SiO ₂ in the frit increases, the softening point increases and the coefficient of thermal expansion decreases.
Therefore, in order to make a frit with a low softening point,
It is necessary to reduce SiO ₂ . The amount of _SiO2 is 32
% or less, the solubility of the frit in hot water increases, a citron skin appears on the enamel surface, and the water resistance is poor. In addition, pinholes and cracks appeared on the surface of the enamel made by dipping and firing the glaze after 10 days of storage at 35°C. On the other hand, if it exceeds 45%, the softening point becomes high and it becomes impossible to sinter at a temperature below the _A1 transformation point, which is the objective of the present invention. From these points of view, the appropriate proportion of SiO ₂ is in the range of 32 to 45%. As raw materials for SiO ₂ , silica and feldspar are used, but ZrO ₂ ·SiO ₂ and Na ₂ SiF ₆ are also mixed in. (3) B ₂ O ₃ The main raw materials for B ₂ O ₃ are borax (Na ₂ B ₄ O ₇・10H ₂ O), anhydrous borax (Na ₂ B ₄ O ₇ ), and boric acid (H ₃ BO ₃ ) etc. are used. Mix these with each frit material and heat to 1200℃.
When heating, melting, and vitrifying,
For example, borax has a very low melting point of 747°C, and plays an important role in reacting with other components of the frit and melting it. In addition, the B ₂ O ₃ component is a characteristic of enamel,
It is important for improving adhesion and gloss. B ₂ O ₃ is 20
% or more, the solubility in hot water increases and the water resistance of the enamel surface also becomes low, which is not preferable. Moreover, if it is less than 7%, the gloss as the enamel property will decrease, and the adhesion will also be poor, which is not preferable. From these points, the appropriate range for B ₂ O ₃ is 7 to 20
%. Moreover, the value of SiO ₂ /B ₂ O ₃ also affects the amount of hot water dissolved in the frit and the fluidity. As shown in Table 1, SiO ₂ /B ₂ O ₃ preferably has a value of 2 to 5;
If it is less than 2, the amount dissolved in hot water will be large and the slip cannot be stored for a long time, and if it is more than 5, the fluidity of the frit will be low and pinholes will occur on the enamel surface, which is not preferable. (4) Raw materials for F ₂ F ₂ include fluorite (CaF ₂ ), cryolite (3NaF・AlF ₃ ), sodium fluoride (NaF),
Aluminum fluoride (AlF ₃ ), sodium silicate (Na ₂ SiF ₆ ), potassium silicate (K ₂ SiF ₆ ), etc. are used. The _F2 component scatters in an amount of 20 to 50% of the theoretical amount during glass melting, but the optimum range shown in the present invention is the weight percent of _F2 contained in the produced glass frit. When the F ₂ content exceeds 9%, many bubbles are generated on the surface of the enamel, resulting in poor appearance, and the crucible is likely to be eroded during glass melting, which is also an industrial problem. If F ₂ is less than 2%, the fluidity of the frit will be low, pinholes will occur on the enamel surface, and gloss and adhesion will decrease, which is not preferable. From these points, the optimum range for _F2 is 2 to 9%. (5) Alkali metal oxide R ₂ O Monovalent alkali metal oxide Na ₂ O,
K ₂ O and Li ₂ O are strong melting agents and are important components that lower the softening point of the frit and increase its fluidity. However, if the amount used is too large, the resistance of the frit to aqueous solutions will decrease, and if the frit dissolves in water after milling and is used after long-term storage, the viscosity will deviate greatly from the optimal viscosity range for dipping, or the frit will become enamel. Yuzu skin and cracks may appear on the surface. It is also a component that reduces the water resistance of the enamel surface. Among these components, the effect of lowering the softening point is in the order of Li ₂ O > Na ₂ O > K ₂ O, and the selection and content ratio of R ₂ O are important. Na ₂ O is a component that improves the fluidity of the frit, and the raw material cost is low among R ₂ O, but it has a negative effect on the hot water dissolution amount of the frit, the storage stability of the frit, and the water resistance, so the amount added is limited. Caution is required. If the Na ₂ O content exceeds 22%, the amount dissolved in hot water will increase, the storage stability of the slip will be poor, and the appearance of yuzu skin and cracks on the enamel surface will be undesirable. If it is less than 14%, the fluidity of the frit will decrease, the gloss and adhesion of the enamel will decrease, and pinholes will occur on the surface, which is not preferable. From these points, the appropriate range for Na ₂ O is 14 to 22
%. K ₂ O is a component that increases the fluidity of the frit, but when used alone it is less effective than Li ₂ O and Na ₂ O, but when combined with Li ₂ O and Na ₂ O, it becomes stable and has a lower softening point. Low frit can be obtained. If the K ₂ O content exceeds 5%, the solubility of the frit in hot water will increase, and both the storage stability and water resistance of the slip will decrease, which is not preferable. From these points of view, K ₂ O is preferably 5% or less. Li ₂ O is the most effective component in lowering the softening point of the frit compared to the aforementioned Na ₂ O and K ₂ O, and is an essential component of the present invention. However, since it tends to have an adverse effect on the surface condition of the enamel, in particular causing orange skin and a decrease in gloss, care must be taken with the amount added. If the Li ₂ O content is 0.3% or less, the fluidity of the frit will be significantly reduced and many pinholes will occur on the enamel surface. Moreover, when it becomes more than 2%,
Yuzu skin appears on the enamel surface, and gloss and water resistance also decrease. From these points, the appropriate range for LiO ₂ is 0.3~
It is 2%. As mentioned above, the amount of each alkali metal oxide added is also important, but the value when the total amount of these components is expressed as [Na ₂ O] + [K ₂ O] + [Li ₂ O] is also A suitable range is 17-25%. 17%
If it is less than 25%, the fluidity will be insufficient, and if it is more than 25%, the amount of hot water dissolved will be large, making it impossible to store the slip for a long time. (6) CaO and BaO CaO and BaO are alkaline earth metal oxides, and although they have no effect when used alone, they are components that significantly improve fluidity when used together, making it possible to perform dipping, which is the purpose of the present invention. It is an essential ingredient. Furthermore, CaO tends to maintain the thixotropic properties of the slip, and can maintain appropriate specific gravity and viscosity during dipping glazing.
It is effective in making the film thickness uniform during coating, and can also improve the long-term storage stability of the slip. When CaO is less than 1.5%, fluidity is low;
In addition, the thixotropy of the slip is insufficient, and if it exceeds 15%, the amount of hot water dissolution of the frit becomes large, and if the slip is stored for a long time, orange skin and cracks will occur on the enamel surface, which is not preferable. When BaO is less than 1.5%, the fluidity is low and pinholes occur on the enamel surface. Moreover, if it exceeds 15%, the amount of hot water dissolved in the frit will increase and the erosion of the crucible will increase, which is not preferable. Also, the total amount of CaO and BaO is [CaO] + [BaO]
This total amount is also an important value for dipping properties; if it is less than 9%, the fluidity will be low, and if it is more than 21%, the long-term shelf life of the slip will be poor. From the above points, the appropriate range for CaO is 1.5 to 15
%, the appropriate range for BaO is 1.5 to 15%, and the appropriate range for the total amount of [CaO] + [BaO] is 9
~21%. In addition to calcium carbonate and calcium hydroxide, fluorite and dolomite are also used as raw materials for the CaO component. As the BaO component, barium carbonate, barium nitrate, barium fluoride, etc. are used. (7) ZrO ₂ ZrO ₂ reduces the amount of frit dissolved in hot water,
It is an essential component of the present invention, as it has the effect of improving the long-term shelf life of the slip and also preventing erosion by the glass component of the zircon bricks used for the inner walls of glass melting furnaces. If ZrO ₂ is less than 0.5%, the amount of hot water dissolved in the frit is large and the zircon bricks in the glass melting furnace are eroded to a large extent, which is not preferable. If it exceeds 4.5%, the fluidity of the frit will decrease, which is not preferable. From these points, the appropriate range of ZrO ₂ is
It is 0.5-4.5%. As the ZrO ₂ component, since purified ZrO 2 is expensive, it is preferable to use zircon (ZrO ₂ .Si ₂ O) because it is cheaper and melts easily during glass melting. (8) Al ₂ O ₃ Al ₂ O ₃ is a component that particularly improves the chemical durability of the frit, and is an essential component of the present invention. If the Al ₂ O ₃ content is less than 0.5%, the amount of hot water dissolved in the frit will be very large, and the storage stability of the slip will be poor, which is not preferable. In addition, when the content exceeds 5%, the hot water solubility of the frit decreases, but the fluidity of the frit is poor and when fired below the _A1 transformation point of steel, the glass does not fully melt with the pigments and clay, and the water resistance test When this is carried out, the amount of hot water dissolved in the enamel layer becomes large, which is not preferable. From these points, a suitable range for Al ₂ O ₃ is 0.5 to 5%. The raw materials for Al ₂ O ₃ are alumina, aluminum hydroxide, cryolite, and feldspar. (9) Other components The hollow frit of the present invention contains TiO ₂ ,
MgO, _SnO2 , SrO, etc. may be added.
These components can improve the chemical durability of the frit, and have the property of not coloring the frit when added in small amounts. TiO ₂ has the function of reducing the amount dissolved in hot water and improving water resistance, but if it exceeds 3%, the frit becomes milky, so it is not suitable for the transparent frit that is the object of the present invention. From this, TiO ₂ is preferably 3% or less. As a raw material for TiO ₂ , there are anatase type and rutile type crystal structures, but either one may be used as a raw material. If MgO exceeds 3%, the enamel surface becomes matte and the gloss decreases, which is not preferable. If the SnO ₂ content exceeds 3%, the amount dissolved in hot water will increase, and if the slip is stored for a long time, bubbles will form on the enamel surface, which is not preferable. If the SrO content exceeds 3%, the amount dissolved in hot water will increase, which is not preferable. From these points, TiO ₂ , MgO, SnO ₂ and
A component selected from the group consisting of SrO can be added in an amount of 3% or less. No. 3 in Table 1 as an example, No. 1 as a comparative example
I will explain about it. The raw material for the glass has a composition as shown in Table 3, which is sufficiently stirred in a mortar or V-blender, and then put into a waxite crucible. This crucible was placed in an electric furnace heated to 1200°C, and after the furnace reached 1200°C again, it was kept for 30 minutes, and the molten glass was placed in cold water and then dried. Using this glass frit, the mill composition shown in Table 4 was put into a ball mill, and milling was carried out so that the weight of glass, etc. remaining on 200 mesh sieves was 10 g per 50 c.c. of slip. . When the viscosity of the resulting slip was measured using a B-type viscometer, No. 1 had a viscosity of 1,600 centipoise, and No. 3 had a viscosity of 1,550 centipoise, indicating that both had a viscosity and thixotropy suitable for dipping. As a base material, a steel plate for enamel with a thickness of 0.8 mm was molded into the shape of a pot. After degreasing as a pre-treatment, it was immersed in sulfuric acid with a concentration of 7% and a temperature of 70°C for 5 minutes. It was immersed in a 15 g/aqueous solution of nickel sulfate for 5 minutes, and then neutralized and dried. This base material was dipped in slip, pulled up and applied by a dipping method to remove excess slip, and then dried. Then, it was baked at 710°C for 5 minutes. When the gloss of these pots No. 1 and No. 3 was measured using a gloss measuring device, it was 83 for No. 1 and 84 for No. 3. Then, fill the pot with pure water up to half of its internal volume, heat the pot on a gas stove for 100 hours while replenishing the pot to maintain a constant water level, and then wash and dry the enamel surface, then immerse it in water. The gloss level of the surface was measured. No. 1 has a gloss of 45, and No. 3 has a gloss of 78, indicating that No. 3, which contains ZnO, has good water resistance. It can be applied to various parts.

【table】

[Table] Effects of the invention Compared to conventional enamel fired at a high temperature of 800°C or higher, it can be used at temperatures below the _A1 transformation point of the pot, so thin plates can be used with less firing distortion, resulting in resource-saving and energy-saving products that are lighter in weight. . Furthermore, the slip can be stored for a long time, which has been a problem with conventional low-melting enamel, and it is possible to put into practical use enamel products that can be glazed by dipping and have excellent water resistance.

[Brief explanation of drawings]

The figure shows the relationship between the amount dissolved in hot water, the fluidity of the frit, and the ZnO content when the enamel coating was tested for water resistance.

Claims (1)

[Claims] 1. At least SiO ₂ , B ₂ O ₃ , F ₂ , Na ₂ O, K ₂ O,
Composed of Li ₂ O, CaO, BaO, ZnO, ZrO ₂ and Al ₂ O ₃ , with 32-45% by weight of SiO ₂ and 7-20% of B ₂ O ₃
% by weight, 2-9% by weight of _F2 , 14-22% by weight of _Na2O , 0.4-5% by weight of _K2O , 0.3-2% by weight of _Li2O , 1.5-15% by weight of CaO, Contains 1.5-15% by weight of BaO, 0.1-5% by weight of ZnO, 0.5-4.5% by weight of _ZrO2 , 0.5-5% by weight _{of Al2O3} , and _TiO2 ,
A low softening point transparent hollow frit characterized by containing a component selected from the group consisting of MgO, SnO ₂ and SrO in a range of 0 to 3% by weight. 2 As for the content ratio of each component, the value of SiO ₂ /B ₂ O ₃ is in the range of 2 to 5, and the total amount of CaO and BaO is in the range of 9 to 5.
In the range of 21% by weight, Na ₂ O, K ₂ O and Li ₂ O
The low softening point transparent hollow frit according to claim 1, wherein the total amount of is within the range of 17 to 25% by weight.