JPH0965977A - Liquid heating vessel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the bumping from being generated and thereby, a temperature sensor from being erroneously operated, and further, improve the stain-proof property by controlling the thickness and the surface roughness of a tetrafluoroethylene resin layer applied to the inner surface of a metal vessel. SOLUTION: A tetrafluoroethylene resin coating layer containing no filler is formed on the heated part of the inner surface of a vessel main body. When this thickness is xμm and the surface roughness is yμm, it is essential that x and y satisfy formulae I, II and III. If the thickness is insufficient, it is difficult to form a film with uniform thickness and high strength. On the contrary, if the thickness is excessive, the thermal conductivity is lowered. Further, if the surface roughness is significant, the bumping preventive effect is low and the stain-proof property is degraded. If the xy value is over 46, the anti-dumping effect is deteriorated. In order to positively prevent a temperature sensor from being deactivated at an advanced timing on account of its faulty operation, it is necessary to limit the xy value to not more than 46. If the resin layer contains a significant amount of filler, no anti dumping effect can be expected, although the formulae I, II and III are satisfied, and besides, the deactivation of the temperature sensor at an advanced timing due to its faulty operation takes place.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid heating container having a fluororesin coating layer and a method for producing the same, and more specifically, an electric liquid heater such as an electric pot (jar pot), a sake bottle or a humidifier. The present invention relates to a liquid heating container suitable as a container and a manufacturing method thereof. The liquid heating container of the present invention is prevented from bumping, has no premature disconnection due to malfunction of the temperature sensor, and has excellent antifouling property.

[0002]

2. Description of the Related Art Electric liquid heaters are widely used as electric pots, sake bottles, humidifiers, etc. because they can easily and safely heat or keep the liquid warm.
The electric liquid heater has a container (liquid heating container) for containing the liquid to be heated and a heat source, and normally, in order to heat and keep the liquid at a desired temperature, a temperature sensing unit (temperature sensor) is provided. It is equipped. These heat sources and temperature sensing parts are generally located on the outer surface of the bottom of the liquid heating container. One of the problems in the electric liquid heater is the bumping phenomenon that occurs on the inner surface of the container near the heat source. When bumping occurs, a loud noise is generated, and the portion where bubbles are generated due to bumping is overheated to increase the surface temperature, causing the temperature sensing unit to malfunction and causing a so-called premature disconnection phenomenon. That is, the power is turned off before the liquid to be heated reaches a predetermined temperature.

Conventionally, various proposals have been made to deal with the bumping problem of the liquid heating container. For example,
(1) A method of forming a fluororesin coating layer on the inner surface of the container (Japanese Patent Publication No. 52-14665), and (2) A method of forming a bumping prevention layer by melting a metal oxide on the inner surface of the container (Japanese Patent Publication No. 63-51003). (3) A method for preventing bumping by providing a boiling agent layer made of an inorganic powder or an organic polymer on the fluororesin coating layer (JP-A-5-12).
3246), (4) a method of imparting hydrophilicity to the surface of the fluororesin coating layer on the inner surface of the container by high-frequency discharge treatment or high-frequency corona discharge treatment (JP-A-4-371116), (5) A method of providing a coating layer containing polyether sulfone (PES) as a main component on the inner surface of the container (JP-A-5-49539 and JP-A-5-31029), and (6) bumping on the inner surface of the container by surface enlargement treatment. A method of forming the prevention layer has been proposed.

By the way, in order to quickly heat the liquid in the container by the electric liquid heater without temperature unevenness, it is preferable to provide a heat source on the outer surface of the bottom of the container. However, in order to heat the liquid with the heat source at the bottom of the container, the electric capacity of the heat source must be increased, which makes it more difficult to prevent bumping on the inner surface of the container near the heat source. To prevent bumping, for example, even if the fluororesin coating layer is provided on the inner surface of the container by the method (1), the bubbles become large and an overheated state occurs. When this overheating state occurs on the temperature sensor, the temperature sensor operates regardless of the hot water temperature, causing premature disconnection. If the temperature sensor is provided away from the heat source and is provided, for example, on the side of the container, the liquid temperature cannot be sensed when the liquid amount is small.

When the bumping prevention layer formed by melting the metal oxide is provided by the method (2), the bumping itself is considerably reduced, but the surface roughness of the bumping prevention layer is increased to 50 to 150 μm and the layer thickness is increased. It is also necessary to increase the thickness to 50 to 400 μm. However, if the surface roughness is high, stains such as water stains are likely to adhere to the recesses on the surface of the bumping prevention layer, so that the stain resistance is deteriorated. Moreover, when the thickness of the bumping prevention layer increases, the thermal conductivity of the container decreases. By providing the boiling agent layer on the fluororesin coating layer by the method (3), the thickness of the boiling agent layer itself can be made relatively thin,
It is insufficient in terms of antifouling property.

When the high-frequency discharge treatment or the high-frequency corona discharge treatment is performed on the surface of the fluororesin coating layer by the method (4), cracks are always formed on the surface to be treated, so that the deterioration of the coating layer cannot be avoided. . When a crack is generated in the coating layer, a corrosive component or the like intrudes to cause blistering or promotes corrosion, which deteriorates the durability of the container. In the method (5) of providing a PES coating layer, PES is inferior in non-adhesiveness as compared with a fluororesin, and is therefore insufficient in terms of antifouling property. Further, the surface enlargement treatment method of (6) above is a case where the fluororesin coating is not applied, and even if bumping can be prevented, it is inferior in terms of antifouling property. If the surface expansion treatment is performed on the fluororesin coating layer, bumping will occur more violently.

[0007]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a liquid heating container which does not cause premature boiling of a temperature sensor due to bumping and has a significantly excellent antifouling property, and a method for producing the same. The inventors of the present invention have conducted extensive studies to overcome the above-mentioned problems of the prior art, and as a result, in a liquid heating container provided with a coating layer of a fluororesin on the inner surface of a metal container body, the entire inner surface of the container or a heating part. The fluororesin coating layer (the part of the container corresponding to the heat source and the temperature sensing part) is filled with tetrafluoroethylene resin (PT
FE) and controlling the thickness and surface roughness (Ra) of the PTFE layer to effectively prevent the bumping phenomenon and prevent premature disconnection due to malfunction of the temperature sensor. It has been found that a liquid heating container having excellent fouling property can be obtained. Further, even if a base coat layer made of a fluororesin containing a filler is provided, a top coat layer made of PTFE containing no filler is provided on the base coat layer, and the thickness and surface roughness (Ra) of these layers are provided. It was also found that the effect of preventing bumping can be obtained by controlling the.

The liquid heating container of the present invention does not cause bumping even when it is used as a container of an electric liquid heater in which a heat source and a temperature sensing portion are arranged on the outer surface of the bottom of the liquid heating container. There is no malfunction of the temperature sensor due to overheating. Moreover, since a smooth PTFE coating layer is formed on the inner surface of the container, the antifouling property is remarkably excellent.
Also, to form a smooth PTFE coating layer,
A method of pressing the PTFE coating layer using a pressing device having a smooth pressing surface, for example, a metal roller or a press machine may be adopted. The present invention has been completed based on these findings.

[0009]

According to the present invention, there is provided a liquid heating container having a fluororesin coating layer formed on an inner surface of a metal container body, the fluororesin coating layer being provided at least in a heating portion of the liquid heating container. Is formed of a tetrafluoroethylene resin containing no filler, and the thickness of the tetrafluoroethylene resin coating layer is x.
(Μm) and surface roughness (Ra) y (μm), a liquid heating container characterized in that x and y satisfy the following formulas (a), (b) and (c): Provided. 10 ≦ x ≦ 60 (a) 0.1 ≦ y ≦ 2.3 (b) xy <46 (c)

Further, according to the present invention, in a method of manufacturing a liquid heating container by press-molding a plate-shaped metal base material having a fluororesin coating layer formed thereon, (1) at least heating of the liquid heating container after press-molding A coating layer of a tetrafluoroethylene resin containing no filler is formed on the portion forming the part, and then (2) the tetrafluoroethylene resin coating layer is applied by a pressure device having a smooth pressure surface. By pressing, the thickness of the tetrafluoroethylene resin coating layer is set to x (μm), and the surface roughness (Ra) is set to y.
(Μm), x and y are expressed by the following formula (a),
Provided is a method for producing a liquid heating container, which comprises press-molding after performing a smoothing treatment so as to satisfy (b) and (c). 10 ≦ x ≦ 60 (a) 0.1 ≦ y ≦ 2.3 (b) xy <46 (c)

Further, according to the present invention, there is provided a liquid heating container in which a fluororesin coating layer is formed on an inner surface of a metal container body, wherein the fluororesin coating layer in at least a heating portion of the liquid heating container is a filler. A base coat layer made of a fluororesin containing a base coat layer and a top coat layer made of a tetrafluoroethylene resin containing no filler, and the base coat layer has a thickness of z (μm),
When the thickness of the top coat layer is x (μm) and the surface roughness (Ra) of the top coat layer is y (μm), x, y
And z satisfy the following formulas (1), (2), (3) and (4). 3 ≦ x (1) 10 ≦ x + z ≦ 60 (2) 0.1 ≦ y ≦ 2.3 (3) (x + z) y <46 (4)

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. The liquid heating container of the present invention is usually used as a container of an electric liquid heater. An electric liquid heater such as a jar pot has a basic configuration as shown in FIG. That is, in the electric liquid heater 1, the heat source 3 and the temperature sensing unit 4 are arranged in close contact with each other on the outer surface of the bottom of the metal container body 2. The heat source 3 and the temperature sensing unit 4 may be integrated with the container body 2 or may be separately separated. A coating layer 5 of fluororesin is usually formed on the entire inner surface of the container body 2. In the present invention, the PTFE coating layer 6 containing no filler is provided on the inner surface of the heating portion of the container corresponding to the heat source 3 and the temperature sensing portion 4. A PTFE layer containing no filler may be provided as a fluororesin coating layer only on the inner surface of the heating part (usually the bottom part) of the heating container, but from the viewpoint of antifouling property, the entire surface of the inner surface of the container is filled with the filler. PTFE not containing
It is preferable to form a coating layer. A PTFE layer containing a filler or another fluororesin coating layer may be provided on the inner surface of the container body other than the heating section.

The liquid heating container body is made of a metal base material such as aluminum, aluminum alloy, iron or stainless steel. In the present invention, the PTFE coating layer containing no filler is formed on at least the heating portion on the inner surface of the container body. As the PTFE, a PTFE coating such as a commonly used PTFE dispersion can be used. The PTFE coating layer in the heating portion of the container body contains substantially no filler. P
The TFE layer may contain a very small amount of filler within the range that does not impair the object of the present invention, but it is preferable that the TFE layer contains no filler at all.

A coating layer of another fluororesin may be formed on a portion other than the heating portion on the inner surface of the container body, such as a side surface. Other fluororesins include, for example, P
Examples thereof include FA (tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer) and FEP (tetrafluoroethylene / hexafluoropropylene copolymer). From the viewpoint of productivity, it is preferable to form a PTFE coating layer containing no filler on the entire inner surface of the container body. If desired, the PTFE coating layer containing no filler may be formed only on the heating portion on the inner surface of the container body, and the fluororesin coating layer may not be provided on the side surface or the like. Even when the PTFE coating layer containing no filler is formed on the entire inner surface of the container body, the layer thickness and surface roughness represented by the formulas (a), (b) and (c) are The relationship only needs to be possessed by the PTFE layer of the heating section, and other portions such as the side surface do not necessarily have to satisfy these equations.

In the present invention, a PTFE coating layer containing no filler is provided on at least the heated portion of the inner surface of the container body. The thickness of this coating layer is x (μm) and the surface roughness (Ra) is y (μm). ), It is necessary that x and y satisfy the following formulas (a), (b) and (c). 10 ≦ x ≦ 60 (a) 0.1 ≦ y ≦ 2.3 (b) xy <46 (c) The thickness of the PTFE coating layer is 10 to 60 μm, preferably 20 to 50 μm. If this thickness is too thin, it is difficult to form a uniform and high-strength coating film. On the contrary, if it is too thick, the thermal conductivity decreases. The surface roughness (Ra) of the PTFE coating layer is 0.1 to 2.3 μm, preferably 0.2 to 2.0 μm, more preferably 0.2 to
It is 1.6 μm. If the surface roughness is too large, the effect of preventing bumping will be small and the antifouling property will also deteriorate.

In the present invention, the product xy of the thickness x (μm) of the PTFE coating layer and the surface roughness (Ra) y (μm).
Must be less than 46 (xy <46). x
The y value is preferably 40 or less, more preferably 30 or less. Even if the values of the thickness and surface roughness of the PTFE coating layer satisfy the expressions (a) and (b), the xy value is 4
If it exceeds 6, the bumping prevention performance deteriorates, and premature disconnection occurs due to a malfunction of the temperature sensor. If the xy value is 46,
Although there is a limit that does not cause premature disconnection due to a malfunction of the temperature sensor, it is necessary to set the xy value to less than 46 in order to surely prevent premature disconnection. If the PTFE coating layer contains a significant amount of filler, the formula (a),
Even if the conditions (b) and (c) are satisfied and the xy value is less than 46, there is no bumping prevention effect and premature disconnection occurs due to a malfunction of the temperature sensor. When a coating layer of another fluororesin such as PFA or FEP or a polyimide resin (PI) is provided, bumping will occur even if the xy value is less than 46 and no filler is included. No preventive effect can be obtained.

The coating layer of a fluororesin such as PTFE can be formed by coating a fluororesin coating on a metal substrate by a conventional method, drying and sintering. In order to create a liquid heating container, a mechanical method (eg, blasting), an electrochemical method (eg, electrolytic etching) is usually performed on the surface of a metal base material on a plate such as aluminum, aluminum alloy, or stainless steel. Fine irregularities are formed by chemical methods (eg, chemical etching) (roughening treatment)
Then, after applying a primer coating if desired, then
Fluorine resin paint is coated, dried and baked,
A metal substrate having a fluororesin coating layer is prepared. In this case, PTF containing no filler in at least the portion forming the heating portion of the liquid heating container after press molding.
A coating layer of E is formed. As the plate-shaped metal base material, one which is cut into a disk shape in advance is usually used, and after forming the fluororesin coating layer, press molding is carried out to mold it into a container. In some cases, a disk-shaped metal base material is press-molded in advance to form a container, and then, after roughening treatment, at least a heating part is coated with a PTFE coating containing no filler, dried, and then baked. You may.

The fluororesin paint such as PTFE may be coated by any of a roller coating method, a spin coating method and a spray coating method. When the fluororesin paint is a powder paint, an electrostatic powder coating method can be applied. In this case, the drying step is unnecessary.
The thickness of the PTFE resin layer can be arbitrarily adjusted within the range of 10 to 60 μm by changing the coating conditions.
At this time, the product xy of the thickness x (μm) of the PTFE resin layer and the surface roughness (Ra) y (μm) is less than 46 (xy <4.
6) so that the surface roughness (Ra) of the coating layer
Must be controlled. In particular, it is necessary to reduce the surface roughness (Ra) as the thickness of the PTFE resin layer becomes thicker or the bumping prevention property is enhanced.

After forming the PTFE resin coating layer, if it is necessary to reduce the surface roughness (Ra) so that xy <46, the metal base material on which the fluororesin coating layer is formed is placed between the metal rollers. Smoothing is performed by passing it through a mirror or by mirror polishing. Among the smoothing treatments, a method of pressurizing and smoothing a plate-shaped metal base material on which a fluororesin coating layer such as PTFE is formed with a pressurizing device having a smooth pressurizing surface such as a roller or a press, It is preferable because a surface having a uniform and small surface roughness can be formed, and the surface is simple. For the roller surface and the press surface, mirror-finished metal, its plated product, ceramics, ceramic coating product, high heat resistant engineering plastic, etc. can be used. Depending on the case, a mirror-finished stainless steel plate or the like may be used as the pressing surface, and pressing may be performed through this.
The surface roughness (Ra) of the pressing surface is usually 2.0 μm or less, preferably 1.0 μm or less, and can be 0.5 μm or less. When the PTFE coating layer is pressed by a pressing device having a smooth pressing surface, the PTFE coating layer is usually pressed after being baked, but in some cases, a hot roller or a heat press machine is used to perform unbaking or semi-baking. The PTFE coating layer may be heated and pressed at a temperature equal to or higher than the sintering temperature of PTFE to perform the smoothing treatment and the firing at the same time.

By forming such a PTFE coating layer on at least the heating part of the liquid heating container,
As described in Examples below, it is possible to obtain a liquid heating container that does not have premature disconnection due to a malfunction of the temperature sensor and has extremely excellent antifouling properties. On the other hand, as shown in the comparative example below, fluorine such as PFA or FEP other than PTFE can be obtained even when the same PTFE is used as the resin, whether it contains a filler, or does not contain a filler. It has been found that when a resin is used, it is prematurely cut even if the requirements such as xy <46 are satisfied. This is probably because PTFE containing no filler has a very excellent non-adhesiveness on the surface of the coating layer. Moreover, even if the PTFE containing no filler is on the surface,
It has been found that if the requirements such as xy <46 are not met, premature disconnection occurs. This is the PTFE layer thickness x (μ
It is presumed that the smaller the m) is, the lower the thermal conductivity can be prevented, and the smaller the surface roughness (Ra) y (μm), the easier the bubbles are to separate from the coating surface of the bottom surface. It

In the liquid heating container of the present invention, a PTFE coating layer containing no filler is formed on the entire inner surface or the heating portion, and the coating layer has the above-mentioned (a),
Since the adjustment is performed so as to satisfy the requirements of (b) and (c), the bumping phenomenon is effectively suppressed, and premature disconnection due to a malfunction of the temperature sensor can be prevented. Moreover, since the PTFE coating layer containing no filler is excellent in non-adhesiveness, it is excellent in antifouling property. The liquid heating container of the present invention does not require a boiling agent and is inexpensive. Further, unlike the method of performing high-frequency discharge treatment or high-frequency corona discharge treatment, the product of the present invention does not cause cracks on the surface of the fluororesin coating layer that cause strength deterioration or corrosion. Moreover, since the product of the present invention is not subjected to the hydrophilic treatment, it is more excellent in antifouling property than the conventional product.

According to another aspect of the present invention, even if a coating layer made of a fluororesin containing a filler is formed on the inner surface of the metal container body, the fluororesin coating layer (base coat) is formed at least in the heating section. Layer), a top coat layer made of PTFE containing no filler is formed, and the thickness of each layer and the surface roughness (Ra) of the top coat layer are controlled within a specific range to prevent the bumping phenomenon. Can be prevented. In this case, the thickness of the base coat layer is z (μm), and the thickness of the top coat layer is x.
(Μm), and the surface roughness (Ra) of the top coat layer is y.
(Μm), x, y and z are expressed by the following formula (1),
It is necessary to satisfy (2), (3) and (4). 3 ≦ x (1) 10 ≦ x + z ≦ 60 (2) 0.1 ≦ y ≦ 2.3 (3) (x + z) y <46 (4)

PTF containing no filler for the topcoat layer
If the thickness (x) of the E layer is 3 μm or more, even if the underlying base coat layer is a fluororesin layer containing a filler,
The total thickness (x + z) of both layers is 10 to 60 μm, preferably 20 to 50 μm, and the surface roughness (Ra) of the top coat layer is 0.1 to 2.3 μm, preferably 0.2 to
2.0 μm, more preferably 0.2 to 1.6 μm, and the product of the total thickness (x + z) and the surface roughness (y) is 46.
Less than 40 μm, more preferably less than 30 μm
If it is m or less, bumping can be prevented.

Examples of the fluororesin for forming the base coat layer include PTFE, PFA and FEP. The blending ratio of the filler is not particularly limited, but is usually 0.01 to 20% by weight, preferably 0.5 to
It is about 10% by weight. Examples of the filler include commonly used fillers, for example, inorganic fillers such as carbon, mica and silica. As the top coat layer, PTFE containing substantially no filler, preferably no filler, is used. As a method for adjusting the surface roughness (Ra) of the top coat layer to a desired range, a metal base material having a coating layer (base coat layer / top coat layer) formed thereon as described above is passed between metal rollers,
A smoothing treatment method such as pressurizing with a pressurizing device having a smooth pressurizing surface such as a roller or a press, or mirror-polishing can be mentioned.

[0025]

EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples and comparative examples, but the present invention is not limited to these examples. The evaluation method of physical properties is as follows. (1) Surface Roughness (Ra) It was measured using a surface roughness meter according to the method of measuring the center line average roughness (Ra) defined in JIS B-0601.

(2) Prevention of bumping (prevention of premature cutting) The liquid heating container was set in a jar pot, and the degree of premature cutting of the temperature sensor was observed. The actual jar pot is a separate type in which the heat source (heater) and the temperature sensor are separated from the container. When water is put into the set liquid heating container and heated, the water boils at 100 ° C, and the heat of the container heats up. When the temperature sensor on the bottom detects 100 degrees Celsius as it is gradually transmitted to the bottom, the boiling lamp blinks and the heater is turned off after 30 seconds. Also, when the temperature of the water in the container approaches approximately 100 ° C., steam is vigorously coming out from the steam escape port on the upper part of the actual machine. Therefore, by measuring the time difference between the time when the steam comes out and the time when the boiling lamp blinks, the presence or absence of premature disconnection can be known. That is, if the water boils before the flashing of the boiling lamp and the steam comes out first, it can be evaluated as good without premature disconnection. On the other hand, when steam does not come out even when the boiling lamp blinks, and steam finally comes out after a delay, the temperature sensor sensed 100 ° C, but the water temperature did not reach 100 ° C. This indicates that premature disconnection has occurred. Therefore, the time difference (seconds) from the time when steam came out was measured based on the flashing time of the steam lamp. If this time difference (timing at which steam comes out) is negative, it can be determined that there is an effect of preventing early disconnection (bumping). The longer the time difference between the time when steam comes out and the time when the boiling lamp blinks, the greater the effect of preventing early disconnection and the better the performance. On the contrary, if steam comes out after the boiling lamp blinks, this time difference becomes positive,
Performance will be poor. The bumping prevention property was evaluated in the following three stages. ◯: When the steam release timing is negative, Δ: When the steam release timing is zero, ×: When the steam release timing is positive.

(3) Antifouling property A 5 cm × 10 cm sample was prepared in the same manner as in each of the examples and comparative examples, and this sample was placed in an aqueous solution prepared by dissolving 5 g of calcium carbonate and 5 g of magnesium carbonate in 90 g of pure water. It was dipped, left at 85 to 95 ° C. for 20 days, taken out, washed with water and dried, and then the amount of the deposit on the coating layer was measured.

[Example 1] An aluminum alloy disc [ASB-O material manufactured by Kobe Steel, Ltd.] having a plate thickness of 1.15 mm was used as a base material, and this was used as an anode in a 3% NaCl aqueous solution for 20 Q.
Electrochemical etching was performed with an electric quantity of / cm ² to form fine irregularities on the surface of the aluminum alloy disc. further,
This surface was anodized in a 15% H ₂ SO ₄ solution at 15 V for 5 minutes to form a hard layer on the etched surface. On this surface, a PTFE dispersion (Polyflon D-1F manufactured by Daikin Industries, Ltd.) containing no filler was spin-coated to a thickness of 30 μm, dried at about 100 ° C., and then baked at 380 ° C. for 15 minutes. did. The obtained PTFE
The surface roughness (Ra) of the coating layer was measured by a surface roughness meter and found to be 1.6 μm. This PTFE coated disc was passed through a metal roller and pressed to smooth the surface.
By changing the pressure of the metal roller, the surface roughness (Ra) is 0.6 μm, 1.0 μm, and 1.2 μm.
Each sample was manufactured as a prototype. The PTFE-coated disc containing no surface-filled filler was press-molded into a container shape in a jar pot, which was set in an actual jar pot, and water was actually boiled to evaluate the presence or absence of premature cutting. In the present Example 1, when Ra = 0.6 μm, the timing (time difference) at which steam comes out is −100 seconds, and the premature premature cutting prevention performance (prevention of bumping) is good, and when Ra = 1.0 μm, − When Ra = 1.2 μm for 50 seconds, −
Although the time difference gradually decreased to 20 seconds, there was no premature disconnection and it was within a good range. Moreover, as a result of the antifouling property test, in all the products of the present invention, the amount of deposits was 0.02 mg / c
It was extremely small as m ² and showed extremely excellent antifouling property.

[Comparative Example 1] In the same manner as in Example 1, a PTFE of Ra = 1.6 μm not surface-smoothed was used.
PT with a coating plate and its surface roughened by sandpaper etc. to Ra = 2.0 μm
When an FE-coated plate was prepared and then press-molded, and the same actual machine test was conducted, Ra = 1.6 μm
The thing of +10 seconds, it cuts off early and is defective, and
In the case of Ra = 2.0 μm, the performance was even worse at +40 seconds and was poor. In each of these samples, the value of xy was 46 or more.

[Example 2] In Example 1, the spin coating conditions were changed, and PTFE containing no filler was used.
The dispersion was coated to a resin thickness of 20 μm, and after firing under the same conditions, the PTFE coated disc was smoothed through a metal roller, and then the surface was roughened using sandpaper to obtain a surface roughness Ra. Is 1.0 μm,
1.2 μm, 1.6 μm, and 2.0 μm samples were prepared. This was pressed into a jar pot shape, and the presence or absence of premature cutting was evaluated. As a result, all samples were within the good range. Especially, the one with a small Ra showed particularly good performance.

Comparative Example 2 A sample having a resin thickness of 20 μm and a surface roughness Ra = 2.3 μm was manufactured in the same manner as in Example 2. When this was pressed into a jar pot shape and evaluated, it was at the limit of the good limit. As for the antifouling property, the amount of deposits was 0.06 mg / cm ² , which was about 3 times the amount of deposits as compared with Example 1.

Example 3 In Example 1, the spin coating conditions were changed, and PTFE containing no filler was used.
The dispersion was coated so that the resin thickness was 40 μm, and after firing under the same conditions, this PTFE coated disc was smoothed through a metal roller to obtain a surface roughness Ra of 0.
Trial samples of 3 μm, 0.6 μm, 1.0 μm, and 2.0 μm were made. This was pressed into a jar pot shape, and the presence or absence of premature cutting was evaluated. As a result, all samples were within the good range. Above all, the one with a small Ra has a particularly good performance.

Comparative Example 3 By the same method as in Example 3, the resin thickness was 40 μm, and the surface roughness Ra was 1.2 μm, 1.5.
Each sample of μm and 2.0 μm was manufactured. As a result of pressing this in a jar pot shape and evaluating it, all samples were within the defective range. Especially, the one with a large Ra had a particularly bad performance.

Example 4 In Example 1, the spin coating conditions were changed to obtain PTFE containing no filler.
The dispersion was coated to a resin thickness of 50 μm, and after firing under the same conditions, the PTFE coated disc was smoothed through a metal roller to give a surface roughness Ra of 0.
Each sample of 4 μm and 0.6 μm was manufactured. This was pressed into a jar pot shape, and the presence or absence of premature cutting was evaluated. As a result, all samples were within the good range. Among them, the one having a small Ra showed particularly good performance.

Comparative Example 4 In the same manner as in Example 4, the resin thickness was 50 μm and the surface roughness Ra was 1.0 μm and 1.5.
Each sample of μm and 2.0 μm was manufactured. As a result of pressing this in a jar pot shape and evaluating it, all samples were within the defective range. The xy value of each of these samples was 46 or more. Especially, the one with a large Ra had a particularly bad performance.

[Comparative Example 5] In Example 1, instead of the PTFE dispersion containing no filler, a PTFE dispersion containing 5% carbon or 5% mica was coated to a resin thickness of 30 μm. After firing under the conditions, the PTFE coated disc was smoothed through a metal roller, or the surface was roughened with sandpaper so that the surface roughness Ra was 0.6 μm, 1.0 μm, and 2.
Each sample of 0 μm was manufactured as a prototype. This was pressed into a jar pot shape, and the presence or absence of premature cutting was evaluated. as a result,
Premature cutting occurred in all the samples, resulting in a failure.

[Comparative Example 6] In Example 1, instead of the PTFE dispersion containing no filler, PFA containing no filler or PF containing 5% of carbon was used.
A dispersion is coated to a resin thickness of 30 μm, and after firing under the same conditions, the PFA coated disc is smoothed through a metal roller, or the surface is roughened with sandpaper so that the surface roughness Ra is 0. 0.6 μm, 1.0
Each sample of μm and 2.0 μm was manufactured. This was pressed into a jar pot shape, and the presence or absence of premature cutting was evaluated. As a result, premature cutting occurred in all samples, resulting in a failure.

[Comparative Example 7] In Example 1, in place of the PTFE dispersion containing no filler, FEP, ETFE or PI containing no filler was used in a resin thickness of 3
After coating to 0 μm and firing under the same conditions,
The coated disc is smoothed through a metal roller, or the surface is roughened with sandpaper to give a surface roughness Ra of 0.6μ.
m, 1.0 μm, and 2.0 μm samples were manufactured as prototypes. This was pressed into a jar pot shape, and the presence or absence of premature cutting was evaluated. As a result, premature cutting occurred in all samples, resulting in a failure. The results of these Examples and Comparative Examples are collectively shown in Tables 1 and 2.

[0039]

[Table 1]

[0040]

[Table 2]

The results of these examples and comparative examples are shown in FIG. In FIG. 2, the surface roughness (Ra) of the PTFE coating layer is plotted on the horizontal axis, and the steam discharge timing (time difference from the flashing time of the boiling lamp) is plotted on the vertical axis.
A graph was made for each thickness of the resin coating layer. Numerical values in the figure represent xy values.

[Example 5] An aluminum alloy disc [ASB-O material manufactured by Kobe Steel, Ltd.] having a plate thickness of 1.15 mm was used as a base material, and this was used as an anode in a 3% NaCl aqueous solution for 20Q.
Electrochemical etching was performed with an electric quantity of / cm ² to form fine irregularities on the surface of the aluminum alloy disc. further,
This surface was anodized in a 15% H ₂ SO ₄ solution at 15 V for 5 minutes to form a hard layer on the etched surface. On this surface, PTFE dispersion in which 5% of carbon was added as a filler [Polyflon D-1 manufactured by Daikin Industries, Ltd.
F] was spin-coated to a thickness of 20 μm, dried at about 100 ° C., and a PTFE dispersion containing no filler [Polyflon D-1F manufactured by Daikin Industries, Ltd.] having a thickness of 5 μm. Was spin-coated so as to have the desired thickness, dried at about 100 ° C., and baked at 380 ° C. for 15 minutes. This PTFE coated disc was passed between metal rollers and pressed to smooth the surface. By changing the pressing force of the metal roller or the like, the surface roughness Ra becomes 0.
6 μm, 1.0 μm, and 1.6 μm samples were manufactured as prototypes. The PTFE-coated disc with the surface smoothed was press-molded into a container shape in a jar pot, which was set in an actual jar pot, and water was actually boiled to evaluate the presence or absence of premature cutting. As a result, when Ra = 0.6 μm, the timing (time difference) at which steam comes out is −110 seconds, and the premature premature cutoff prevention performance (anti-bumping property) is good, and Ra = 1.
When it is 0 μm, it is −60 seconds, and when Ra = 1.6, −
At 20 seconds, there was no premature disconnection, which was within a good range. In addition, as a result of the antifouling test, all of the products of the present invention had an extremely small amount of deposits of 0.02 mg / cm ^2, and exhibited extremely excellent antifouling properties.

[Comparative Example 8] In Example 5, a sample having a surface roughness (Ra adjusted to 2.0 µm) was trial-produced without performing the smoothing treatment. This sample was pressed into a jar pot shape and quickly cut. The presence or absence was evaluated, etc. As a result, premature cutting occurred and it became defective.

[Embodiment 6] In Embodiment 5, the thickness of the base coat layer was changed to 30 by changing the conditions of spin coating.
The top coated layer having a thickness of 10 μm is coated with the resin and baked under the same conditions, and the PTFE coated disc is smoothed through a metal roller to obtain a surface roughness Ra of 0.6 μm and 1.0 μm. Each sample was created.
This was pressed into a jar pot shape, and the presence or absence of premature cutting was evaluated. As a result, all samples were within the good range. Especially, the one with a small Ra showed particularly good performance.

[Comparative Example 9] In Example 6, samples having surface roughnesses Ra of 1.2 µm and 1.6 µm were prepared by changing the smoothing conditions. This was pressed into a jar pot shape, and the presence or absence of premature cutting was evaluated. As a result, premature cutting was observed in all the samples. Surface roughness R
Even if a is small, if the value of (x + z) y becomes 46 or more,
It can be seen that the effect of preventing bumping cannot be obtained. The results are collectively shown in Table 3.

[0046]

[Table 3]

[0047]

According to the present invention, there is provided a liquid heating container in which the bumping phenomenon is effectively suppressed and premature disconnection due to malfunction of the temperature sensor is prevented. The liquid heating container of the present invention is excellent in antifouling property as compared with the conventional product because the coating layer on the inner surface is excellent in non-adhesiveness. The liquid heating container of the present invention is suitable as a container for electric liquid heaters such as electric pots (jar pots), sake bottles, and humidifiers.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of one embodiment of an electric heater using the liquid heating container of the present invention.

FIG. 2 Thickness of PTFE coating layer and surface roughness (R
It is a figure which shows the relationship between a) and the premature disconnection by the malfunction of a temperature sensor.

[Explanation of symbols]

 1 Electric Liquid Heater 2 Liquid Heater (Main Body) 3 Heat Source 4 Temperature Sensing Part 5 Fluororesin Coating Layer 6 PTFE Coating Layer Without Filler

Claims (3)

[Claims] 1. A liquid heating container in which a fluororesin coating layer is formed on an inner surface of a metal container body, wherein the fluororesin coating layer in at least a heating portion of the liquid heating container does not contain a filler. When the thickness of the ethylene tetrafluoride resin coating layer is x (μm) and the surface roughness (Ra) is y (μm), x and y are the following formulas (a): ,
A liquid heating container satisfying (b) and (c). 10 ≦ x ≦ 60 (a) 0.1 ≦ y ≦ 2.3 (b) xy <46 (c) 2. A method for producing a liquid heating container by press-molding a plate-shaped metal base material having a fluororesin coating layer formed thereon, comprising: (1) at least a portion forming a heating part of the liquid heating container after press-molding. A coating layer of a tetrafluoroethylene resin containing no filler is formed, and then (2) the tetrafluoroethylene resin coating layer is pressed with a pressurizing device having a smooth pressurizing surface, thereby The thickness of the fluorinated ethylene resin coating layer is x (μ
m) and the surface roughness (Ra) is y (μm),
A method for producing a liquid heating container, comprising performing a smoothing treatment so that x and y satisfy the following formulas (a), (b) and (c), and then performing press molding. 10 ≦ x ≦ 60 (a) 0.1 ≦ y ≦ 2.3 (b) xy <46 (c) 3. A liquid heating container in which a fluororesin coating layer is formed on the inner surface of a metal container body, wherein the fluororesin coating layer in at least the heating portion of the liquid heating container is made of a fluororesin containing a filler. And a topcoat layer made of a tetrafluoroethylene resin containing no filler, wherein the thickness of the basecoat layer is z (μm) and the thickness of the topcoat layer is x (μm). Liquid heating, wherein x, y and z satisfy the following equations (1), (2), (3) and (4), where y (μm) is the surface roughness (Ra) of container. 3 ≦ x (1) 10 ≦ x + z ≦ 60 (2) 0.1 ≦ y ≦ 2.3 (3) (x + z) y <46 (4)