A temperature-sensitive color-changing coating for cookware surfaces and its preparation method and use

Abstract

The application discloses a temperature-sensing color-changing coating for a cooker surface and a preparation method and application thereof; the coating is composed of coatings A and B with different colors; the coating composition comprises methyltrimethoxysilane, octamethoxytrisilane, pigments A / B, a filler, a thickening agent aqueous solution, a dispersing agent, a leveling agent, isopropyl alcohol, acetic acid and deionized water; the application utilizes the color mixing between iron oxide red with different color phases and titanium dioxide and black pigments respectively, prepares two coatings with different red colors, and applies the coatings to the bottom center position of a ceramic coating non-stick pot; at normal temperature, due to the color difference between the two coatings, a certain pattern is presented; when the bottom temperature of the pot reaches 170-200 DEG C during cooking, due to the color change of inorganic pigments at high temperature, the two red colors gradually change into the same color; after the cooking is finished, with the gradual decrease of the pot temperature, the two colors are restored into different colors, and the pattern is presented again, so that the function of indicating the bottom temperature of the pot is achieved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of coatings, and particularly relates to a temperature-sensing color-changing coating for the surface of a cooking utensil, and a preparation method and use thereof. BACKGROUND

[0002] Ceramic-coated non-stick pots are favored by many consumers due to their health and safety features, as well as good non-stick properties and easy cleanability. Ceramic-coated non-stick pots need to be used at an appropriate temperature, and the oil temperature should not be too high during cooking. On the one hand, high oil temperature has an adverse effect on the durability of the ceramic coating, and on the other hand, high-temperature oxidation of cooking oil produces harmful substances such as trans fats, which affect health. Generally, the oil temperature should not exceed 170-200℃ during daily cooking, but ordinary consumers can hardly accurately perceive the oil temperature by visually observing the state of the cooking oil. In order to determine the temperature of the cooking oil in the pot, a temperature-sensing color-changing coating can be applied to the inside of the pot, and the temperature indication function can be achieved through the color change of the coating.

[0003] Temperature-sensing color-changing coatings are functional special coatings that repeatedly change color with rising or falling temperature. They are usually prepared by adding temperature-sensing color-changing pigments. Through a search, it was found that Chinese patents with application numbers 202211555569.5 and 201710908659.0 disclose a temperature-sensing color-changing paint and a preparation method thereof, which realizes the temperature-sensing color-changing function of the coating by adding a certain amount of reversibly temperature-sensing color-changing powder in microcapsules; and patent number 201710855655.0 discloses a preparation method of a temperature-changing indicating coating for the surface of a cooking utensil, which obtains the temperature-changing indicating coating by adding a heat-sensitive color-changing pigment to the ceramic coating.

[0004] The above-mentioned temperature-sensing color-changing coatings can achieve the function of indicating temperature, but the temperature-sensing color-changing pigments are prepared from an electron transfer type organic compound system, and the molecular structure of the organic compound changes due to electron transfer at a specific temperature, thereby realizing color change. Therefore, the temperature-sensing color-changing pigment is an unstable system (stable is difficult to change), and its light resistance, heat resistance, and aging resistance are far inferior to those of ordinary pigments. The excitation temperature of the temperature-sensing color-changing pigment is usually between -5℃ and 80℃, and it can withstand a high temperature of 230℃ for a short time (about 10 minutes). Therefore, when applied to the surface of a cooking utensil that works at a high temperature for a long time, the temperature-sensing color-changing coating will quickly fail to achieve the function of indicating temperature. There is an urgent need in the market to develop a temperature-sensing color-changing coating that can be applied to the surface of a cooking utensil and can achieve the function of indicating temperature at a high temperature for a long time. SUMMARY

[0005] The present application aims to provide a temperature-sensing color-changing coating for cookware surface, and its preparation method and use. The temperature-sensing color-changing coating of the present application can be applied to the surface of cookware working under long-term high temperature, and can indicate the temperature of the pot through color change, and has good durability of temperature-sensing color change.

[0006] The purpose of the present application is achieved by the following technical solutions:

[0007] In a first aspect, the present application relates to a temperature-sensing color-changing coating, which is composed of coating A and coating B with different colors; wherein,

[0008] The coating A has a composition of methyltrimethoxysilane 40-45%, octamethoxytrisilane 0.5-1%, pigment A 11-13%, filler 8-10%, thickener aqueous solution 1-2%, dispersant 1-1.5%, leveling agent 1.5-2%, isopropyl alcohol 3-5%, acetic acid 3-5%, and deionized water in a remainder, based on 100% of the total weight of the coating A.

[0009] The coating B has a composition of methyltrimethoxysilane 40-45%, octamethoxytrisilane 0.5-1%, pigment B 11-13%, filler 8-10%, thickener aqueous solution 1-2%, dispersant 1-1.5%, leveling agent 1.5-2%, isopropyl alcohol 3-5%, acetic acid 3-5%, and deionized water in a remainder, based on 100% of the total weight of the coating B.

[0010] As an embodiment of the present application, the pigment A includes red iron oxide pigment and titanium white powder in a mass ratio of (8-10):1. The red iron oxide pigment is red-phase red iron oxide pigment, such as red iron oxide S130 from Shanghai Yipin Pigment Co., Ltd. The titanium white powder is white pigment, rutile type, and commercially available product, which can be selected from DuPont R-902, R930, R-706, etc.

[0011] As an embodiment of the present application, the pigment B includes red iron oxide pigment and black pigment in a mass ratio of (17-21):1. The red iron oxide pigment is yellow-phase red iron oxide pigment, such as red iron oxide S110 from Shanghai Yipin Pigment Co., Ltd.

[0012] Further, the black pigment can be selected from carbon black, iron black, manganese iron black, copper chromium black, etc.

[0013] As an embodiment of the present application, the filler is selected from mica powder, silicon powder, silicon carbide, alumina powder, talc powder, etc. In the coating system of the present application, the filler mainly plays a role in reducing the cost of the coating and increasing the solid content of the coating.

[0014] As an embodiment of the present application, the concentration of the thickening agent aqueous solution is 5-8 wt.%, and the thickening agent is one of carboxymethyl cellulose, hydroxyethyl cellulose, hydroxymethyl cellulose, and hydroxypropyl methyl cellulose. The thickening agent is prepared into an aqueous solution with a mass percentage of 5-8% with deionized water, and is used to increase the viscosity of the paint.

[0015] As an embodiment of the present application, the dispersant is selected from BYK180, BYK190, BYK2010, BYK2001, etc., which can reduce the dispersion time of pigments and fillers, stabilize the pigment dispersion, and improve the color strength and hiding power of pigments.

[0016] As an embodiment of the present application, the leveling agent is used to facilitate the formation of a flat, smooth, and uniform paint film during the drying and film-forming process. The leveling agent can be selected from, for example, BYK-333 and Dow Corning DC-57.

[0017] As an embodiment of the present application, the pH of the paint A and B systems is controlled at 3.5-4.0, respectively.

[0018] As an embodiment of the present application, the viscosity of the paint is tested with a No. 4 cup, and the viscosity of the paint A and B is controlled at 18-22 s.

[0019] In the temperature-sensitive color-changing paint of the present application, methyltrimethoxysilane is the film-forming material of the paint. On the one hand, the hydrolysis and polymerization speed of methyltrimethoxysilane is fast, which can shorten the reaction time of the paint and improve the efficiency of the paint curing production. On the other hand, Si is connected with three -OCH3, and three silicon hydroxyl groups (Si-OH) are formed after hydrolysis, and a coating with a three-dimensional cross-linked structure can be formed after polymerization, and the structure of the coating is compact and not easy to crack.

[0020] As a surface tension regulator, octamethyltrisiloxane is used to adjust the surface tension of the temperature-sensitive color-changing paint to be lower than that of the ceramic paint primer, so that good spreading and wetting can be formed, and good adhesion with the ceramic paint primer can be achieved. If the addition amount is too small, good spreading and wetting cannot be formed, resulting in poor adhesion and easy peeling of the coating. If the addition amount is too large, it will affect the adhesion of the subsequent intermediate coating and topcoat, also resulting in poor adhesion and peeling of the coating. The surface tension regulator cannot use conventional polydimethylsiloxane-based non-stick agents, such as methyl silicone oil or hydroxyl silicone oil, etc. Because the non-stick agent contains a large amount of -CH3, the surface tension of the temperature-sensitive color-changing paint is too low after addition, which makes the adhesion between the subsequent intermediate coating and topcoat and the temperature-sensitive color-changing paint poor, and easy to cause peeling of the coating.

[0021] Acetic acid is used as pH regulator for sol-gel reaction of ceramic coating, the pH of reaction should be controlled between 3.5-4.0, methyltrimethoxysilane hydrolyzes under acidic condition and self-polymerizes to form film. The catalytic effect of acetic acid is milder than that of formic acid, which is beneficial to control the reaction speed and form more regular molecular structure.

[0022] The red iron oxide in the pigment is a common inorganic pigment, and its preparation method is divided into dry method and wet method, the calcination temperature of the dry method is 500-700 DEG C, and the wet method is dried at 300-400 DEG C, so the red iron oxide has good temperature resistance and will not decompose and deteriorate below 300 DEG C. Titanium dioxide is also calcined at high temperature, and the rutile type is usually calcined at 900-1200 DEG C, so from the manufacturing process, titanium dioxide itself is high-temperature resistant. Black pigment is usually prepared by high-temperature calcination or high-temperature baking process above 400 DEG C, so the common inorganic pigment has very good temperature resistance. However, the color of the above-mentioned inorganic pigment will change slightly with the change of heating temperature, and the color of the pigment will become deeper with the increase of temperature, and the color change will gradually recover after the temperature decreases. As long as the heating temperature does not exceed 300 DEG C, the color change is reversible. The paint A and the paint B of the present application utilize the color matching and compounding of the red iron oxide with different color phases and the white pigment or the black pigment, so that the paint shows different red colors at room temperature, and shows the same red color at the heating temperature of 170-200 DEG C due to the change of the color of the pigment, so when the two different red colors gradually change into the same color, it indicates that the temperature of the pot bottom is about 170-200 DEG C, at this time, food can be put in for cooking; after the cooking is completed, when the temperature of the pot gradually decreases, the two different colors are reappeared, so that the indicating temperature effect is achieved.

[0023] The red iron oxide pigment color phase and the ratio of the two red paints are key parameters, and the ratio is not within the range, so the same red color effect at high temperature cannot be achieved, and the indicating temperature effect cannot be achieved.

[0024] The two paints of the present application are only different in color, and the preparation methods are completely the same.

[0025] The present application also provides a preparation method of the temperature-sensitive color-changing paint, which comprises the following steps:

[0026] S1, color paste preparation: the pigment A, the pigment B, the filler, the dispersing agent and the deionized water are mixed uniformly, and are ground to a fineness of 20 microns or less to obtain the color paste A and the color paste B;

[0027] S2, the methyltrimethoxysilane, octamethyltrisiloxane, isopropyl alcohol, acetic acid, leveling agent and thickening agent aqueous solution are mixed uniformly, then the color paste A and the color paste B are added respectively to prepare the paint A and the paint B.

[0028] As an embodiment of the present application, after mixing uniformly in step S2, the paint A or the paint B is obtained after rolling for 3-4 hours at 120-150 rpm.

[0029] As an embodiment of the present application, the step S2 further comprises the following steps: the viscosity of the paint is tested by using a coating-4 cup, and is controlled to be between 18-22 s. If the coating-4 cup viscosity exceeds 22 s, isopropyl alcohol is added for adjustment. If the coating-4 cup viscosity is less than 18 s, a thickening agent aqueous solution is added for adjustment. The coating-4 cup viscosity of a conventional ceramic paint is generally 12-14 s. Since the paint is applied by using a pad printing method, the thickening agent is added to adjust the coating-4 cup viscosity to 18-22 s, so that the edge of the paint after pad printing is clear. If the coating-4 cup viscosity is < 18 s, the paint is easily integrated with the ceramic primer, resulting in unclear edge of the thermosensitive color-changing paint. If the coating-4 cup viscosity of the paint is > 22 s, the leveling property is poor, and the wear resistance of the coating is poor.

[0030] The process first hydrolyzes methyltrimethoxysilane under the catalysis of an acid to form silanol (Si-OH), and the silanols are subjected to polycondensation to generate the ceramic paint. Since the thermosensitive color-changing paint is coated on the surface of the ceramic primer, in order to achieve good adhesion with the primer, the surface tension must be less than that of the primer. Therefore, the thermosensitive color-changing ceramic paint cannot add silica sol. Since the silica sol is a hydrophilic substance, the surface is rich in -OH. After the reaction, part of the -OH remains, which increases the surface tension of the paint and causes poor wettability and poor adhesion with the primer.

[0031] The present application also relates to the application of the thermosensitive color-changing ceramic paint to the ceramic coating non-stick pot.

[0032] As an embodiment of the present application, the application comprises the following steps:

[0033] A1, sand blasting: forming a rough surface on the inner surface of the pot body by sand blasting or shot blasting process;

[0034] A2, spraying ceramic primer: spraying the ceramic paint primer on the inner surface of the pot body, and curing until the coating reaches the tack-free state;

[0035] A3, pad printing: using pad printing to coat the thermosensitive color-changing paint A and the paint B respectively at the center of the pot bottom to form a preset pattern;

[0036] A4, spraying ceramic intermediate coating and ceramic topcoat: spraying the colorless transparent ceramic intermediate coating and the ceramic topcoat on the inner surface of the pot body, and curing, and then naturally cooling to obtain the finished product. Since the intermediate coating and the topcoat are both colorless and transparent, the thermosensitive color-changing pattern coated on the bottom of the pot body is clear and visible.

[0037] As an embodiment of the present application, in step A1, the rough surface has Ra=2.5-4.5 μm; the rough surface increases the contact area of the coating with the substrate, and can improve the adhesion between the pot body and the coating.

[0038] As an embodiment of the present application, in step A2, the curing temperature and the curing time are strictly controlled, and after curing, the coating only reaches the surface dry state, that is, the coating surface does not stick to the fingers when slightly touched by the fingers, but the inside of the coating is in the uncured state. If the curing temperature is high or the curing time is long, the adhesion between the primer and the subsequent midcoat and topcoat is poor, and the coating is prone to peeling, which cannot meet the requirements of actual use; if the curing temperature is low or the curing time is short, the coating surface is in a wet film state, and the state of the primer is easily damaged during subsequent pad printing. In some embodiments, the curing is carried out at 80-100 ℃ for 3-6 min.

[0039] As an embodiment of the present application, in step A2, the ceramic primer is a commercially available product, and is a two-layer or three-layer structure of a recoatable ceramic coating. The corresponding construction process is as follows: after spraying the primer, low-temperature surface drying at 60-80 ℃ for 5-8 min, pad printing or screen printing, then spraying the midcoat and / or the topcoat, and then high-temperature curing at 200-230 ℃ for 10-20 min. For example, the C M Div series black of Zhejiang Liqi New Material Co., Ltd. can be selected. The series product has a structure of primer+midcoat+topcoat, the primer is a colored paint, and the midcoat and the topcoat are both colorless and transparent. The product is specially developed for the primer requiring a preliminary curing process, and the midcoat can improve the adhesion between the primer and the topcoat. The ordinary ceramic coating generally has a single-layer or double-layer structure, and the construction method is wet-on-wet and then curing. If it is applied to the primer which is preliminarily cured and then the topcoat is sprayed, the adhesion between the primer and the topcoat is poor, and the coating is prone to peeling during use.

[0040] As an embodiment of the present application, in step A4, the curing is carried out at 230-260 ℃ for 15-20 min.

[0041] Compared with the prior art, the present application has the following beneficial effects:

[0042] (1) The present application prepares two kinds of red coatings by matching two different color phases of iron oxide red with titanium dioxide and black pigment respectively, and applies them to the center position of the bottom of the ceramic coating non-stick pot. At room temperature, a certain pattern is presented due to the difference in the color of the two coatings, and when the pot bottom temperature reaches 170-200 ℃ during cooking, the two red colors gradually change to the same color due to the color change of the inorganic pigment at high temperature; after cooking, the pot body temperature gradually decreases, and the two different colors are restored to present the pattern again, which achieves the function of indicating the pot bottom temperature.

[0043] (2) Because the daily use temperature of the pot is below 200℃, which is far less than the preparation temperature of the ordinary inorganic pigment, the inorganic pigment will not decompose and deteriorate, and can still achieve the reversible color change indicating temperature function after long-term use. The problem of short-term high temperature resistance of the temperature sensitive color change pigment and quick failure of the pot surface is overcome.

[0044] (3) By adjusting the viscosity and surface tension of the temperature sensitive color change paint, good wettability and adhesion between the ceramic coating and the temperature sensitive color change paint are ensured, and the edge of the pad printing pattern is clear. When applied to the ceramic coated non-stick pot, the health problems caused by high heating temperature of edible oil can be avoided, and the service life of the ceramic coated non-stick pot can be prolonged. BRIEF DESCRIPTION OF DRAWINGS

[0045] Other features, objects and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments, made with reference to the following drawings:

[0046] Figure 1 Fig. 1 is a pattern state diagram of the bottom of the pot at room temperature;

[0047] Figure 2 Fig. 2 is a pattern state diagram of the bottom of the pot at high temperature. DETAILED DESCRIPTION

[0048] The present application will be described in detail below with reference to the examples. The following examples will help those skilled in the art to further understand the present application, but do not limit the present application in any form. It should be pointed out that those skilled in the art can make several adjustments and improvements without departing from the concept of the present application. These all belong to the protection scope of the present application.

[0049] Examples 1-5

[0050] Examples 1-5 of the present application provide a ceramic coating, the composition of which is shown in Table 1. The preparation of the ceramic coating of the present application includes the following steps:

[0051] (1) Color paste preparation: mix red iron oxide pigment, titanium white or black pigment, filler, dispersant and deionized water uniformly, and grind on a basket mill to a fineness of 20μm or less to obtain color paste A;

[0052] Mix red iron oxide pigment, black pigment, filler, dispersant and deionized water uniformly, and grind on a basket mill to a fineness of 20μm or less to obtain color paste B;

[0053] (2) Prepare a thickener aqueous solution with a mass percentage of 7% carboxymethyl cellulose, and wait for use;

[0054] (3) Mix methyltrimethoxysilane, octamethyltrisiloxane, isopropyl alcohol, acetic acid, leveling agent, thickener aqueous solution uniformly, then add the color paste of step (1) respectively, and get the thermochromic ceramic coating after rolling at 130 rpm for 3.5 hours; use coating-4 cup to test the viscosity of the coating, and control at 20 s.

[0055] The application of the thermochromic ceramic coatings of Examples 1-5 on ceramic coating non-stick pots is as follows:

[0056] (1) Sand blasting: form a rough surface on the inner surface of the pot body by sand blasting process, Ra = 3.5 μm;

[0057] (2) Spray ceramic primer: spray the ceramic primer (primer in the CMD iv series black of Zhejiang Lixing New Material Co., Ltd.) on the inner surface of the pot body, and cure at 90°C for 5 min, so that the coating reaches the tack-free state;

[0058] (3) Pad printing: pad print the thermochromic coatings A and B on the center of the pot bottom respectively to form a preset pattern, such as Figure 1 ;

[0059] (4) Spray ceramic intermediate coating and ceramic topcoat: spray the ceramic intermediate coating and ceramic topcoat in the CMD iv series black of Zhejiang Lixing New Material Co., Ltd. on the inner surface of the pot body, and then cure at 245°C for 18 min, and the finished product is obtained after natural cooling.

[0060] Comparative Examples 1-4

[0061] Comparative Examples 1-4 provide a ceramic coating, the composition of which is shown in Table 1; and the preparation and application are the same as those of Example 1. The main difference between them and Example 3 is that the ratio of the pigment composition in pigments A and B is different. The comparative examples 1-4 are used to show that the ratio of red iron oxide pigment hue and titanium dioxide or black pigment in the coating system of the present application is a key parameter, and the ratio out of the range defined in the present application cannot achieve the effect of showing the same red color at high temperature, and thus cannot achieve the function of indicating temperature.

[0062] Comparative Examples 5-7

[0063] Comparative Examples 5-7 provide a ceramic coating, the composition of which is shown in Table 1; and the preparation and application are the same as those of Example 1.

[0064] Table 1 Coating composition and amount (wt.%) of examples and comparative examples

[0065]

[0066] Main performance test

[0067] The coating of the non-stick pan bottom prepared according to the above examples and comparative examples was subjected to main performance tests, the test items and methods are shown in Table 2, and the test results are shown in Table 3:

[0068] Table 2, main performance test methods of the coating

[0069]

[0070]

[0071] Table 3, main performance test results of examples and comparative examples

[0072]

[0073] The specific embodiments of the present application are described above. It should be understood that the present application is not limited to the specific embodiments described above, and various modifications or changes can be made by those skilled in the art within the scope of the claims, which do not affect the essential content of the present application.

Claims

1. A thermochromic paint for cooktop surfaces, characterized in that, The coating is composed of coating A and coating B with different colors; wherein, The coating A is composed of methyltrimethoxysilane 40-45%, octamethyltrisiloxane 0.5-1%, pigment A 11-13%, filler 8-10%, thickener aqueous solution 1-2%, dispersant 1-1.5%, leveling agent 1.5-2%, isopropyl alcohol 3-5%, acetic acid 3-5%, and deionized water in balance, based on 100% of the total weight of the coating A; The coating B is composed of methyltrimethoxysilane 40-45%, octamethyltrisiloxane 0.5-1%, pigment B 11-13%, filler 8-10%, thickener aqueous solution 1-2%, dispersant 1-1.5%, leveling agent 1.5-2%, isopropyl alcohol 3-5%, acetic acid 3-5%, and deionized water in balance, based on 100% of the total weight of the coating B; The pigment A comprises red iron oxide pigment and titanium white powder with a mass ratio of (8-10):1; The pigment B comprises red iron oxide pigment and black pigment with a mass ratio of (17-21):1; the black pigment is selected from at least one of carbon black, iron black, manganese iron black, and copper chromium black; In application, at room temperature, a certain pattern is presented due to the difference in red color between the two coatings; when the temperature of the cookware reaches 170-200℃ during cooking, the two red colors gradually change to the same color due to the color change of the inorganic pigment at high temperature; at the end of cooking, the pattern is presented again as the temperature of the cookware gradually decreases and the two red colors return to different colors, thereby achieving the function of indicating the temperature of the bottom of the pot.

2. The thermochromatic paint for cooktop surfaces according to claim 1, characterized in that, The filler is selected from at least one of mica powder, silicon powder, silicon carbide, alumina powder, and talc powder.

3. The thermochromatic paint for cooktop surfaces according to claim 1, characterized in that, The concentration of the thickener aqueous solution is 5-8 wt%; the thickener is one of carboxymethyl cellulose, hydroxyethyl cellulose, hydroxymethyl cellulose, and hydroxypropyl methyl cellulose.

4. The thermochromatic paint for cooktop surfaces according to claim 1, characterized in that, The pH of the coating A and B systems is controlled at 3.5-4.0, respectively; the viscosity of the coating A and B is controlled at 18-22 s.

5. A method for preparing a thermochromic paint for cooktop surfaces according to claim 1, characterized in that, The method comprises the following steps: S1, color paste preparation: mixing pigment A and pigment B with filler, dispersant, and deionized water uniformly, and grinding to a fineness of 20 μm or less to obtain color paste A and color paste B; S2, mixing methyltrimethoxysilane, octamethyltrisiloxane, isopropyl alcohol, acetic acid, leveling agent, and thickener aqueous solution uniformly, and then adding color paste A and color paste B respectively to prepare coating A and coating B.

6. The method for preparing a thermochromatic paint for cooktop surfaces according to claim 5, characterized in that, Step S2 further comprises the following steps: testing the viscosity of the coating with a coating-4 cup to control it within 18-22 s; if the viscosity of the coating-4 cup exceeds 22 s, isopropyl alcohol is added for adjustment; if the viscosity of the coating-4 cup is less than 18 s, thickener aqueous solution is added for adjustment.

7. Application of the temperature-sensitive color-changing coating for the surface of cookware according to claim 1 to ceramic-coated non-stick pots.

8. Use according to claim 7, characterized in that, Comprising the following steps: A1, sand blasting: forming a rough surface on the inner surface of the pot body by sand blasting or shot blasting process; A2, spraying ceramic primer: spraying a ceramic coating primer on the inner surface of the pot body, and curing the coating to a tack-free state; A3, pad printing: thermally color-changing paint A and paint B are respectively coated in the center of the bottom of the pot by pad printing to form a preset pattern; A4, spraying ceramic basecoat and ceramic topcoat: the inner surface of the pot is sprayed with colorless transparent ceramic basecoat and ceramic topcoat, and the finished product is obtained after curing and natural cooling.

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