JP2004202262A - Liquid heating vessel - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid heating vessel in which bumping is prevented, early switching OFF is not caused by malfunction of a temperature sensor, and the antifouling property is enhanced. <P>SOLUTION: This liquid heating vessel has a fluororesin coating layer formed on the inside of the metallic vessel main body. The fluororesin coating layer in a heating part of the liquid heating vessel is formed of tetrafluoroethylene resin not containing a filler. Thickness of the tetrafluoroethylene resin coating layer is >40 to 60 μm. Surface roughness (Ra)y is 0.1-2.3 μm, and xy is ≤30. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a liquid heating container having a fluororesin coating layer and a method for producing the same, and more particularly, a liquid heating container suitable as a container for electric liquid heaters such as electric pots (jar pots), sake brewers, and humidifiers. And its manufacturing method. INDUSTRIAL APPLICABILITY The liquid heating container of the present invention prevents bumping, has no premature break due to malfunction of the temperature sensor, and has excellent antifouling properties.

  Electric liquid heaters are widely used as electric pots, sake brewers, humidifiers, and the like because they can easily and safely heat or maintain liquid. The electric liquid heater has a container for storing the liquid to be heated (liquid heating container) and a heat source. Usually, in order to heat and keep the liquid at a desired temperature, a temperature sensor (temperature sensor) is provided. Provided. These heat sources and temperature sensors are generally located on the outer surface of the bottom of the liquid heating vessel.

  One of the problems with 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 a portion where bubbles are generated due to bumping is overheated to increase the surface temperature, so that the temperature sensing unit malfunctions and a so-called premature break phenomenon occurs. That is, the power is turned off before the liquid to be heated reaches the predetermined temperature.

  Conventionally, various proposals have been made to address the bumping problem of the liquid heating container. For example, (1) a method in which a coating layer of a fluororesin is provided on the inner surface of a container (Patent Document 1), (2) a method in which a metal oxide is sprayed on the inner surface of the container to provide a bumping prevention layer (Patent Document 2), (3) ) A method of providing a boiling agent layer made of an inorganic powder or an organic polymer on the fluororesin coating layer to prevent bumping (Patent Document 3), (4) High-frequency discharge treatment on the surface of the fluororesin coating layer inside the container Alternatively, a method of imparting hydrophilicity by performing high-frequency corona discharge treatment (Patent Document 4), (5) A method of providing a coating layer containing polyethersulfone (PES) as a main component on the inner surface of a container (Patent Document 5, Patent Documents 6) and (6) Methods of forming a bumping prevention layer on the inner surface of a container by surface enlargement treatment have 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. In order to prevent bumping, for example, even if a fluorine resin coating layer is provided on the inner surface of the container by the method (1), bubbles become large and an overheating state occurs. If this overheating condition 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, for example, on the side of the container, the liquid temperature cannot be sensed when the amount of liquid is small.

  When the bumping prevention layer formed by spraying the metal oxide is provided by the method (2), 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 also reduced to 50 to 150 μm. It is necessary to increase the thickness to 400 μm. However, when the surface roughness is large, dirt such as water deposits tends to adhere to the recesses on the surface of the bumping prevention layer, so that the antifouling property is reduced. Also, when the thickness of the bumping prevention layer increases, the thermal conductivity of the container decreases. When the boiling agent layer is provided on the fluororesin coating layer by the method (3), the thickness of the boiling agent layer itself can be made relatively thin, but it is insufficient in the 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 is inevitable. When a crack occurs in the coating layer, a corrosion component or the like invades, causing blisters or progressing corrosion, so that the durability of the container is reduced. In the method (5) of providing a PES coating layer, PES is inferior in non-adhesion as compared with fluororesin, and is insufficient in antifouling properties. Further, the surface enlargement treatment method (6) is a case where a fluororesin coating is not applied, and even if bumping can be prevented, the antifouling property is inferior. If the fluororesin coating layer is subjected to a surface enlargement treatment, bumping will occur more intensely.

JP-B-52-14665 JP-B-63-51003 JP-A-5-123246 JP-A-4-371116 JP-A-5-49539 JP-A-5-31029

An object of the present invention is to provide a liquid heating container which does not cause premature disconnection of a temperature sensor due to bumping and has remarkably excellent antifouling property, and a method for manufacturing the same.
The present inventors have conducted intensive studies to overcome the problems of the prior art, and as a result, in a liquid heating container provided with a fluororesin coating layer on the inner surface of a metal container main body, the entire inner surface of the container or the heating section The fluororesin coating layer of the (portion corresponding to the heat source and the temperature sensing unit) is formed of a tetrafluoroethylene resin (PTFE) containing no filler, and the thickness and surface roughness (Ra) of the PTFE layer ), It has been found that a bumping phenomenon can be effectively prevented, and a liquid heating container excellent in antifouling properties can be obtained without premature disconnection due to malfunction of the temperature sensor.
Even when 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 thereon, and the thickness and surface roughness (Ra) of these layers are provided. It was also found that controlling boil-off also provided an effect of preventing bumping.

  Even if the liquid heating container of the present invention is used as a container of an electric liquid heater in which the heat source and the temperature sensing unit are arranged on the outer surface of the bottom of the liquid heating container, bumping does not occur. There is no malfunction of the temperature sensor. Moreover, since a smooth PTFE coating layer is formed on the inner surface of the container, the antifouling property is remarkably excellent. Further, in order to form a smooth PTFE coating layer, a method of pressing the PTFE coating layer using a pressing device having a flat pressing surface, for example, a metal roller or a press may be used. The present invention has been completed based on these findings.

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 main body, wherein the fluororesin coating layer in at least a heating portion of the liquid heating container has no filler. When the thickness of the tetrafluoroethylene resin coating layer is x (μm) and the surface roughness (Ra) is y (μm), x and y are represented by the following formula (a). And (b) and (c) are provided.
40 <x ≦ 60 (a)
0.1 ≦ y ≦ 2.3 (b)
xy ≦ 30 (c)

Further, according to the present invention, in a method for producing a liquid heating container by press-molding a plate-shaped metal substrate having a fluororesin coating layer formed thereon, (1) forming at least a heating portion of the liquid heating container after press molding A coating layer of a tetrafluoroethylene resin containing no filler is formed on the portion to be filled, and then (2) the tetrafluoroethylene resin coating layer is pressed by a pressing device having a smooth pressing surface. When the thickness of the tetrafluoroethylene resin coating layer is x (μm) and the surface roughness (Ra) is y (μm), x and y are represented by the following formulas (a), (b) and (c). The present invention provides a method for manufacturing a liquid heating container, which comprises performing a press molding after performing a smoothing treatment so as to satisfy the condition (1).
40 <x ≦ 60 (a)
0.1 ≦ y ≦ 2.3 (b)
xy ≦ 30 (c)

Furthermore, 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 main body, wherein the fluororesin coating layer in at least a heating portion of the liquid heating container contains a filler. A base coat layer made of a fluororesin and a top coat layer made of a tetrafluoroethylene resin containing no filler, and the thickness of the base coat layer is z (μm), and the thickness of the top coat layer is x (μm), When 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). A liquid heating container is provided.
3 ≦ x (1)
40 <x + z ≦ 60 (2)
0.1 ≦ y ≦ 2.3 (3)
(X + z) y ≦ 30 (4)

  ADVANTAGE OF THE INVENTION According to this invention, the bumping phenomenon is suppressed effectively and the liquid heating container in which the premature disconnection by the malfunction of the temperature sensor was prevented is provided. INDUSTRIAL APPLICABILITY The liquid heating container of the present invention is excellent in antifouling property than conventional products 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 an electric liquid heater such as an electric pot (jar pot), a sake kettle and a humidifier.

Hereinafter, the present invention will be described in detail.
The liquid heating container of the present invention is generally used as a container for 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 disposed in close contact with 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 separated separately. Usually, a coating layer 5 of a fluororesin is formed on the entire inner surface of the container body 2. In the present invention, a PTFE coating layer 6 containing no filler is provided on the inner surface of the heating section of the container corresponding to the heat source 3 and the temperature sensing section 4. A PTFE layer containing no filler may be provided as a fluororesin coating layer only on the inner surface of the heating portion (usually the bottom portion) of the heating container. It is preferable to form a PTFE coating layer containing no. 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 vessel body is made using a metal base material such as aluminum, aluminum alloy, iron, and stainless steel.
In the present invention, a 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 paint such as a commonly used PTFE dispersion can be used. A filler is not substantially contained in the PTFE coating layer in the heating section of the container body. The PTFE layer may contain a very small amount of filler within a range that does not impair the object of the present invention, but it is preferable that the PTFE layer does not contain any filler.

  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, for example, on the side surface. Examples of other fluororesins include PFA (tetrafluoroethylene / perfluoroalkylvinyl ether copolymer), FEP (tetrafluoroethylene / hexafluoropropylene copolymer), and the like. 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, a 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. Further, even when a PTFE coating layer containing no filler is formed on the entire inner surface of the container body, the layer thickness and the surface roughness represented by the above formulas (a), (b) and (c) are not satisfied. The relationship only needs to be included in the PTFE layer of the heating unit, and it is not always necessary to satisfy these expressions in other parts such as the side surface.

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). At this time, it is necessary that x and y satisfy the following expressions (a), (b) and (c).
40 <x ≦ 60 (a)
0.1 ≦ y ≦ 2.3 (b)
xy ≦ 30 (c)

  The thickness of the PTFE coating layer is more than 40 μm and 60 μm or less. If the thickness is too large, 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, and more preferably 0.2 to 1.6 μm. If the surface roughness is too large, the effect of preventing bumping is small, and the antifouling property is also reduced.

  In the present invention, the product xy of the thickness x (μm) of the PTFE coating layer and the surface roughness (Ra) y (μm) needs to be 30 or less (xy ≦ 30). Even if the thickness and surface roughness of the PTFE coating layer satisfy the above-mentioned formulas (a) and (b), if the xy value exceeds 30, the bumping prevention performance is reduced, and the temperature sensor is prematurely disconnected due to malfunction. Is generated.

  When the PTFE coating layer contains a significant amount of a filler, the formulas (a), (b) and (c) are satisfied. Premature disconnection occurs due to malfunction. Further, when a coating layer of another fluororesin such as PFA or FEP or a polyimide resin (PI) is provided, even if the xy value is 30 or less and no filler is included, bumping occurs. No prevention effect can be obtained.

  The coating layer of a fluororesin such as PTFE can be formed by coating a metal substrate with a fluororesin paint, drying and sintering the coating in a conventional manner. In order to make a liquid heating container, a mechanical method (eg, blasting), an electrochemical method (eg, electrolytic etching), and a mechanical method (eg, blasting) are usually applied to the surface of a metal substrate on a plate of aluminum, aluminum alloy, stainless steel, or the like. After forming fine irregularities (roughening treatment) by a chemical method (eg, chemical etching) or the like, performing a primer coating treatment as desired, then coating with a fluororesin paint, drying and firing, and A metal substrate having a resin coating layer is prepared. In this case, a filler-free PTFE coating layer is formed on at least a portion of the liquid heating container where the heating section is to be formed after press molding. As the plate-shaped metal substrate, usually, one cut in advance into a disk shape is used, and after forming a fluororesin coating layer, it is press-molded and molded into a container. In some cases, a disc-shaped metal base material is pre-pressed to form a container, and after roughening treatment, at least a heating portion is coated with a PTFE paint containing no filler, dried, and fired. May be.

  Coating with a fluororesin paint such as PTFE may be performed by any method such as a roller coating method, a spin coating method, and a spray coating method. When the fluororesin coating is a powder coating, an electrostatic powder coating method can be applied. In this case, a drying step is unnecessary. By changing the coating conditions, the thickness of the PTFE resin layer can be arbitrarily adjusted. At this time, the surface roughness (Ra) of the coating layer is adjusted so that the product xy of the thickness x (μm) of the PTFE resin layer and the surface roughness (Ra) y (μm) becomes 30 or less (xy ≦ 30). You have to control. In particular, it is necessary to reduce the surface roughness (Ra) as the thickness of the PTFE resin layer increases or the bumping prevention property is increased.

  After forming the PTFE resin coating layer, if it is necessary to reduce the surface roughness (Ra) so that xy ≦ 30, pass the metal substrate having the fluororesin coating layer formed between metal rollers. Alternatively, a smoothing process is performed by mirror polishing. In the smoothing process, a method of pressing a plate-shaped metal base material on which a fluororesin coating layer such as PTFE is formed with a pressing device having a smooth pressing surface such as a roller or a press machine, It is preferable because a surface having a uniform and small surface roughness can be formed and the method is simple. For the roller surface and the press surface, mirror-finished metal, plated material thereof, ceramics, ceramic coating material, engineering plastic having high heat resistance, and the like can be used. In some cases, a mirror-finished stainless steel plate or the like may be used as the pressing surface, and the pressing may be performed through the stainless steel plate. The surface roughness (Ra) of the pressing surface is usually 2.0 μm or less, preferably 1.0 μm or less, and may be 0.5 μm or less.

  When the PTFE coating layer is pressed by a pressing device having a smooth pressing surface, the pressing is usually performed after baking the PTFE. In some cases, the unbaked or semi-baked PTFE is heated using a hot roller or a hot press. The PTFE coating layer may be heated and pressurized at a temperature equal to or higher than the sintering temperature of PTFE, and the smoothing treatment and the sintering may be performed simultaneously.

  By forming such a PTFE coating layer on at least the heating portion of the liquid heating container, as described in a later example, a liquid having no premature break due to a malfunction of the temperature sensor and having an extremely excellent antifouling property. A heating vessel can be obtained. On the other hand, as shown in a comparative example below, even if the same PTFE is used as the resin, even if a filler is contained, or even if the filler is not contained, fluorine such as PFA and FEP other than PTFE is used. When a resin was used, it was found that the resin was quickly cut off even when requirements such as xy ≦ 30 were satisfied. One reason for this is considered to be that PTFE containing no filler has extremely excellent non-stickiness on the surface of the coating layer.

  Further, it has been found that even if the PTFE containing no filler is on the surface, if the requirements such as xy ≦ 30 are not satisfied, the PTFE is prematurely cut off. This is because the smaller the PTFE layer thickness x (μm) is, the more the thermal conductivity can be prevented from decreasing, and the smaller the surface roughness (Ra) y (μm) is, the more bubbles are separated from the bottom coating surface. This is presumed to be easier.

  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 satisfies the requirements (a), (b) and (c). As a result, bumping phenomenon is effectively suppressed, and premature disconnection due to malfunction of the temperature sensor can be prevented. In addition, the PTFE coating layer containing no filler is excellent in anti-fouling properties because of its excellent non-adhesiveness. The liquid heating container of the present invention does not require a boiling agent and is inexpensive. In addition, unlike the method of performing the high-frequency discharge treatment or the high-frequency corona discharge treatment, the product of the present invention does not cause cracks on the surface of the fluororesin coating layer, which cause strength deterioration and corrosion. In addition, since the product of the present invention has not been subjected to the hydrophilic treatment, the antifouling property is superior to 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 main body, at least in the heating section, the fluororesin coating layer (base coat layer) A bumping phenomenon is prevented by forming a top coat layer made of PTFE containing no filler thereon and controlling the thickness of each layer and the surface roughness (Ra) of the top coat layer to a specific range. Can be.

In this case, when the thickness of the base coat layer is z (μm), 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 It is necessary to satisfy the following expressions (1), (2), (3) and (4).
3 ≦ x (1)
40 <x + z ≦ 60 (2)
0.1 ≦ y ≦ 2.3 (3)
(X + z) y ≦ 30 (4)

  If the thickness (x) of the PTFE layer containing no filler in the top coat layer is 3 μm or more, the total (x + z) of the thicknesses of both layers even if the base coat layer below is a fluororesin layer containing a filler. Is more than 40 μm and 60 μm or less, 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. If the product of the total thickness (x + z) and the surface roughness (y) is 30 μm or less, bumping can be prevented.

  Examples of the fluororesin that forms the base coat layer include PTFE, PFA, FEP, and the like. The mixing ratio of the filler is not particularly limited, but is usually about 0.01 to 20% by weight, preferably about 0.5 to 10% by weight. Examples of the filler include generally used fillers, for example, inorganic fillers such as carbon, mica, and silica. As the top coat layer, PTFE containing substantially no, preferably no, filler is used.

  As a method for adjusting the surface roughness (Ra) of the top coat layer to a desired range, as described above, a metal substrate having a coating layer (base coat layer / top coat layer) formed thereon is passed between metal rollers, And a smoothing method such as pressing with a pressing device having a smooth pressing surface such as a press machine, or mirror polishing.

Hereinafter, the present invention will be described more specifically with reference to Reference Examples, Examples, and Comparative Examples, but the present invention is not limited to only 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) specified in JIS B-0601.

(2) Prevention of bumping (prevention of premature break)
The liquid heating container was set on an actual jar pot, and the degree of premature disconnection of the temperature sensor was observed. The actual jar pot is a separate type in which a heat source (heater) and a temperature sensor are separated from the container. When water is put into a set liquid heating container and heated, the water boils at 100 ° C. When the temperature gradually reaches the bottom and the temperature sensor on the bottom senses 100 ° C, the boiling lamp flashes and the heater turns off 30 seconds after that. Also, when the temperature of the water in the container approaches about 100 ° C., the steam rushes out of the steam outlet at the top of the actual machine.

  Therefore, by measuring the time difference between the time at which the steam is released and the time at which the boiling lamp blinks, it is possible to determine whether or not the steam has run out. That is, if the water boils before the flashing of the boiling lamp and the steam comes out first, it can be evaluated that the water is good without a short break. On the other hand, if steam does not come out even if the boiling lamp flashes and steam comes out late, it means that the water temperature has not reached 100 ° C even though the temperature sensor senses 100 ° C. Indicates that premature disconnection has occurred. Therefore, the time difference (second) from the time when the steam was released was measured based on the blinking time of the steam lamp. If the time difference (timing of steam release) is negative, it can be determined that there is an effect of preventing premature explosion (bumping). The longer the time difference between the time when the steam is released and the time until the boiling lamp starts blinking, the greater the effect of preventing the premature break and the better the performance. Conversely, if steam comes out after the boiling lamp flashes, this time difference becomes positive, and the performance becomes poor.

The bumping prevention property was evaluated on the following three levels.
○: When the steam release timing is negative,
Δ: When the steam release timing is zero,
×: When the steaming timing is positive.

(3) Antifouling property A sample of 5 cm × 10 cm was prepared in the same manner as in each of Reference Examples, Examples and Comparative Examples, and this sample was placed in an aqueous solution in which 5 g of calcium carbonate and 5 g of magnesium carbonate were dissolved in 90 g of pure water. It was immersed, left at 85 to 95 ° C. for 20 days, taken out, washed and dried, and the amount of deposits on the coating layer was measured.

[Reference Example 1]
Using an aluminum alloy disk [ASB-O material manufactured by Kobe Steel Co., Ltd.] having a thickness of 1.15 mm as a base material, electrochemical etching was performed using the anode as an anode in a 3% NaCl aqueous solution at an electric quantity of 20 Q / cm ^2. Then, fine irregularities were formed on the surface of the aluminum alloy disk. Further, this surface was subjected to anodizing treatment in a 15% H ₂ SO ₄ solution at 15 V for 5 minutes to provide a hard layer on the etched surface. The surface is spin-coated with a filler-free PTFE dispersion [Polyflon D-1F manufactured by Daikin Industries, Ltd.] to a thickness of 30 μm, dried at about 100 ° C., and baked at 380 ° C. for 15 minutes. did.

  When the surface roughness (Ra) of the obtained PTFE coating layer was measured with a surface roughness meter, it was 1.6 μm. This PTFE coated disk was passed between metal rollers and pressed to perform a smoothing treatment. By changing the pressing force of the metal roller, samples having surface roughness (Ra) of 0.6 μm, 1.0 μm, and 1.2 μm were prototyped.

This PTFE-coated disk having no surface-filled filler was press-molded into a jar pot inner container shape, and this was set in an actual jar pot actual machine. In the present reference example 1, when Ra = 0.6 μm, the steam release timing (time difference) is −100 seconds, and the very early cut-off prevention performance (bumping prevention property) is good. When Ra = 1.0 μm, − In the case of 50 seconds and Ra = 1.2 μm, although the time difference gradually decreased to −20 seconds, there was no premature break and it was within a favorable range. In addition, as a result of the antifouling test, the amount of deposits was extremely small at 0.02 mg / cm ^2, and exhibited extremely excellent antifouling properties.

[Comparative Example 1]
In the same manner as in Reference Example 1, a PTFE-coated plate having a surface smoothness of Ra = 1.6 μm and a surface roughened with sandpaper or the like to be roughened to Ra = 2.0 μm. A PTFE coated plate was prepared and then press-molded, and the same actual machine test was performed. As a result, those with Ra = 1.6 μm were prematurely cut off in +10 seconds, were defective, and Ra = 2 At 0.0 μm, the performance was worse and worse at +40 seconds. In each of these samples, the value of xy was 46 or more.

[Reference Example 2]
In Reference Example 1, a PTFE dispersion containing no filler was coated so as to have a resin thickness of 20 μm by changing the spin coating conditions, and after baking under the same conditions, the PTFE coated disk was smoothed through a metal roller. After that, the surface was roughened using a sandpaper to prepare each sample having a surface roughness Ra of 1.0 μm, 1.2 μm, 1.6 μm, and 2.0 μm.

  This was pressed into a jar pot shape, and the presence or absence of premature break was evaluated. As a result, all samples were within the good range. In particular, those with smaller Ra showed particularly good performance.

[Comparative Example 2]
In the same manner as in Reference Example 2, a sample having a resin thickness of 20 μm and a surface roughness Ra of 2.3 μm was prototyped. As a result of pressing this into a jar pot shape and evaluating it, it was almost at a good limit. As for the antifouling property, the amount of the deposit was 0.06 mg / cm ² , and the amount of the deposit was about three times as large as that in Example 1.

[Reference Example 3]
In Reference Example 1, the PTFE dispersion containing no filler was coated so as to have a resin thickness of 40 μm by changing the conditions of spin coating, and after baking under the same conditions, the PTFE coated disk was smoothed through a metal roller. Each sample having a surface roughness Ra of 0.3 μm, 0.6 μm, 1.0 μm, and 2.0 μm was prototyped. This was pressed into a jar pot shape, and the presence or absence of premature break was evaluated. As a result, all samples were within the good range. In particular, those having a small Ra had particularly good performance.

[Comparative Example 3]
In the same manner as in Reference Example 3, samples having a resin thickness of 40 μm and surface roughness Ra of 1.2 μm, 1.5 μm, and 2.0 μm were prototyped. This was pressed into a jar pot shape and evaluated. As a result, all the samples were within the defective range. In particular, those having a large Ra had particularly poor performance.

[Example 1]
In Reference Example 1, a PTFE dispersion containing no filler was coated so as to have a resin thickness of 50 μm by changing the conditions of spin coating, and after baking under the same conditions, the PTFE coated disk was smoothed through a metal roller. Each sample having a surface roughness Ra of 0.4 μm and 0.6 μm was prototyped. This was pressed into a jar pot shape, and the presence or absence of premature break was evaluated. As a result, all samples were within the good range. In particular, those having a small Ra exhibited particularly good performance.

[Comparative Example 4]
In the same manner as in Example 1, each sample having a resin thickness of 50 μm and a surface roughness Ra of 1.0 μm, 1.5 μm, and 2.0 μm was prototyped. This was pressed into a jar pot shape and evaluated. As a result, all the samples were within the defective range. Each of these samples had an xy value of 46 or more. In particular, those having a large Ra had particularly poor performance.

[Comparative Example 5]
In Reference Example 1, instead of the PTFE dispersion containing no filler, a PTFE dispersion containing 5% of carbon or 5% of mica was coated so as to have a resin thickness of 30 μm, fired under the same conditions, and then coated with PTFE. Each sample having a surface roughness Ra of 0.6 μm, 1.0 μm, and 2.0 μm was prototyped by smoothing the disk through a metal roller or roughening the surface with sandpaper. This was pressed into a jar pot shape, and the presence or absence of premature break was evaluated. As a result, premature breaks occurred in all samples, resulting in failure.

[Comparative Example 6]
In Reference Example 1, in place of the PTFE dispersion containing no filler, a PFA containing no filler or a PFA dispersion containing 5% carbon was coated so that the resin thickness became 30 μm, and baked under the same conditions. Thereafter, the PFA-coated disk was smoothed through a metal roller, or the surface was roughened with sandpaper, and samples having surface roughness Ra of 0.6 μm, 1.0 μm, and 2.0 μm were prototyped. This was pressed into a jar pot shape, and the presence or absence of premature break was evaluated. As a result, premature breaks occurred in all samples, resulting in failure.

[Comparative Example 7]
In Reference Example 1, in place of the PTFE dispersion containing no filler, FEP, ETFE or PI containing no filler was coated so that the resin thickness became 30 μm, and after being baked under the same conditions, the coated disc was coated. Each sample having a surface roughness Ra of 0.6 μm, 1.0 μm, and 2.0 μm was prototyped by smoothing through a metal roller or roughening the surface with sandpaper. This was pressed into a jar pot shape, and the presence or absence of premature break was evaluated. As a result, premature breaks occurred in all samples, resulting in failure.
The results of these Examples, Reference Examples and Comparative Examples are collectively shown in Tables 1 and 2.

  FIG. 2 shows the results of these Reference Examples, Examples and Comparative Examples. In FIG. 2, the horizontal axis indicates the surface roughness (Ra) of the PTFE coating layer, and the vertical axis indicates the timing at which steam is released (the time difference from the blinking time of the boiling lamp), and is graphed for each thickness of the PTFE resin coating layer. did. Numerical values in the figure represent xy values.

[Reference Example 4]
Using an aluminum alloy disk [ASB-O material manufactured by Kobe Steel Co., Ltd.] having a thickness of 1.15 mm as a base material, electrochemical etching was performed using the anode as an anode in a 3% NaCl aqueous solution at an electric quantity of 20 Q / cm ^2. Then, fine irregularities were formed on the surface of the aluminum alloy disk. Further, this surface was subjected to anodizing treatment in a 15% H ₂ SO ₄ solution at 15 V for 5 minutes to provide a hard layer on the etched surface. This surface is spin-coated with a PTFE dispersion [Polyflon D-1F manufactured by Daikin Industries, Ltd.] containing 5% of carbon as a filler to a thickness of 20 μm, dried at about 100 ° C., and Then, a PTFE dispersion containing no filler (Polyflon D-1F, manufactured by Daikin Industries, Ltd.) was spin-coated to a thickness of 5 μm, dried at about 100 ° C., and baked at 380 ° C. for 15 minutes.

  This PTFE coated disk was passed between metal rollers and pressed to perform a smoothing treatment. Each sample having a surface roughness Ra of 0.6 μm, 1.0 μm, and 1.6 μm was prototyped by changing the pressing force of a metal roller or the like.

The surface-smoothed PTFE-coated disk was press-molded into a jar pot inner container shape, and this was set in an actual jar pot machine. As a result, when Ra = 0.6 μm, the steam release timing (time difference) is −110 seconds, so that the premature break prevention performance (bumping prevention property) is very good, and when Ra = 1.0 μm, −60 seconds and Ra = In the case of 1.6, the time was -20 seconds, and there was no premature break at all, which was within a good range. In addition, as a result of the antifouling test, all of the products of the present invention exhibited an extremely low antifouling property with an attached amount of 0.02 mg / cm ² .

[Comparative Example 8]
In Reference Example 4, a sample whose surface roughness (Ra was adjusted to 2.0 μm) was trial-produced without performing the smoothing treatment. The sample was pressed into a jar pot shape, and the presence or absence of premature break was evaluated. , Premature disconnection occurred and became defective.

[Reference Example 5]
In Reference Example 4, the conditions of spin coating were changed so that the thickness of the base coat layer was 30 μm and the thickness of the top coat layer was 10 μm. After baking under the same conditions, the PTFE coated disk was coated with a metal roller. And samples having surface roughness Ra of 0.6 μm and 1.0 μm were prepared. This was pressed into a jar pot shape, and the presence or absence of premature break was evaluated. As a result, all samples were within the good range. In particular, those with smaller Ra showed particularly good performance.

[Comparative Example 9]
In Reference Example 5, the samples having the surface roughness Ra of 1.2 μm and 1.6 μm were prepared by changing the conditions of the smoothing treatment. This was pressed into a jar pot shape, and the presence or absence of premature break was evaluated. As a result, premature break was observed in all samples. It can be seen that even if the surface roughness Ra is small, the bumping prevention effect cannot be obtained when the value of (x + z) y is 46 or more.
Table 3 shows these results collectively.

  The liquid heating container of the present invention prevents bumping, has no premature break due to malfunction of the temperature sensor, and has excellent antifouling properties, so that it can be used for electric liquid heating in electric pots (jar pots), sake cans, humidifiers, etc. It can be used as a container for vessels.

1 is a schematic sectional view showing a structure of an embodiment of an electric heater using a liquid heating container of the present invention. It is a figure which shows the relationship between the thickness of a PTFE coating layer, surface roughness (Ra), and premature breakage by malfunction of a temperature sensor.

Explanation of reference numerals

1 electric liquid heater 2 liquid heater (main body)
Reference Signs List 3 Heat source 4 Temperature sensing unit 5 Fluororesin coating layer 6 PTFE coating layer without filler

Claims (3)

A liquid heating container in which a fluororesin coating layer is formed on an inner surface of a metal container main body, wherein the fluororesin coating layer in at least a heating portion of the liquid heating container is formed of a tetrafluoroethylene resin containing no filler. When the thickness of the tetrafluoroethylene resin coating layer is x (μm) and the surface roughness (Ra) is y (μm), x and y are represented by the following formulas (a), (b) and A liquid heating container satisfying (c).
40 <x ≦ 60 (a)
0.1 ≦ y ≦ 2.3 (b)
xy ≦ 30 (c) In a method for producing a liquid heating container by press-molding a plate-shaped metal substrate having a fluororesin coating layer formed thereon, (1) a filler is contained in at least a portion of the liquid heating container which forms a heating portion after press molding. (2) pressurizing the tetrafluoroethylene resin coating layer with a pressing device having a smooth pressing surface, thereby forming the tetrafluoroethylene resin coating layer. When the thickness of the layer is x (μm) and the surface roughness (Ra) is y (μm), smoothing is performed so that x and y satisfy the following expressions (a), (b) and (c). A method for producing a liquid heating container, comprising performing press molding after performing a treatment.
40 <x ≦ 60 (a)
0.1 ≦ y ≦ 2.3 (b)
xy ≦ 30 (c) A liquid heating container in which a fluororesin coating layer is formed on an inner surface of a metal container main body, wherein the fluororesin coating layer in at least a heating portion of the liquid heating container is filled with a base coat layer made of a fluororesin containing a filler. And a thickness of the base coat layer is z (μm), a thickness of the top coat layer is x (μm), and a surface roughness of the top coat layer ( A liquid heating container wherein x, y and z satisfy the following formulas (1), (2), (3) and (4) when Ra) is y (μm).
3 ≦ x (1)
40 <x + z ≦ 60 (2)
0.1 ≦ y ≦ 2.3 (3)
(X + z) y ≦ 30 (4)

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