A METHOD FOR PREVENTING WATER ACCUMULATION AND ICE FORMATION ON THE EVAPORATORS AND CONDENSERS OF REFRIGERATORS

Abstract: A humidity resistant method has been developed to prevent water accumulation and ice formation on the refrigerator evaporators and condensers made of aluminium folios, while operating. In order to provide the surface properties that prevent water accumulation and ice formation an appropriate solution with a composition of a chemical formulation the wetting angle of which is between 10 DEG and 20 DEG C has been defined. The said solution was prepared using sol-gel technique and the mixture is applied on the evaporator and condenser surfaces consisting of aluminium folios, at room temperature, by immersing or spraying methods. The coated material was kept in a drying oven at a temperature between 40 DEG and 150 DEG C for 5 minutes, to 5 hours provide the required hardness and adhesion. The wetting angle measured at the coated surfaces was 10 DEG to 20 DEG C and upon testing in conditioning rooms, at a temperature of 0 DEG to -50 DEG C 8 hours to 20 days, no icing was observed on the surface.

Description: A METHOD FOR PREVENTING WATER ACCUMULATION AND ICE FORMATION ON THE EVAPORATORS AND CONDENSERS OF REFRIGERATORS The present invention is related to a method for preparing a coating material which prevents water accumulation and ice formation on the refrigerator evaporators and condensers consisting of aluminium folios, while operating; and which provides the creation of a humidity resistant surface. The coating technologies consist of important techniques that have a wide spread implementation area in the field of the material science, in recent years. The major objective is the production of a material of a superior quality with higher positive values, by coating all kinds of surfaces with varying thicknesses of the material. The sol-gel technology is employed significantly due to its various advantages, and the superior physical, mechanical and chemical properties it provides to the coated material and such qualities as extending the service life of the material. The sol-gel technology consists of applying a combination of organic polymeric components and oxide or non-oxide inorganic ceramic material and/or a composite mixture formed by organic modified non-metallic compounds. These techniques are designed, considering the function of the coating, by utilising different properties of organic and inorganic material, and are applied with suitable combinations to suitable processes. In this method, reaction is realized in water or in an organic solvent medium. A colloidal solution (SOL) containing particules of nanometric (run) dimensions, as the result of reaction and process, is translated into the position of a di-phase gel (GEL). An inorganic polymeric net is formed by the hydrolysis and condensation reactions of the hydrolyzable compounds such as metal alkoxides. A part of the hydrolyzable groups may be replaced by non-hydrolyzable and non-modified groups during the sol-gel process. At this stage, organo-substituted alkoxysilans consisting of silicon-carbon bond formed by non-functional organic groups or by functional groups giving polycondensation, polyaddition and addition reactions, are used. Here organic groups have two important functions: a) Organic groups modify the inorganic net by transferring their own characteristics to the inorganic net, b) By polymerization they constitute an organic polymeric net in addition to the inorganic net. As the result of the said method, the complementary properties of organic and inorganic phases form a composite layer on the surface, for instance, a combination of such properties as flexibility, resistance to corrosion, to scratching, to abrasion etc. In brief, the sol-gel technique is the technique of forming an organic net (mesh) by hydrolysis and condensation reactions of organic modified alkoxy compounds or by various methods. By means of the provided composition formulation of the sol gel technique, metallic surfaces are provided with hydrophilic or hydrophobic characteristics and at the same time their corrosion resistance is increased and additionally it is being used in various industrial applications for the last 5 years. For instance, polymeric materials used in the automotive sector, organic eye glasses (anti-scratch), plexyglass material (anti-scratch) may be given as examples. The object of the present invention is to realize a method for developing a moisture- and corrosion-resistant, composite coating with hydrophilic or hydrophobic characteristics that prevents water accumulation and ice-formation on the evaporators and condensers made of aluminium folios in the refrigerators, during operation by using the sol-gel technique. In order to achieve the above said object of the invention, the wetting angle between the water droplet and the aluminium folio is designed to be between 10° to 20° on hydrophobic surfaces and 90°- 110° on hydrophobic surfaces and accordingly, solutions of appropriate chemical formulations and composition have been prepared. Chemical substances used: 1-A1I epoxy-containing silans: Example 1 GPTS (3-Glycidoxypropyltrimethoxysilan) Formula : CH 2 -CH- CH 2 -O- CH 2 CH 2 CH 2 Si(OCH 3 ) 3 Example 2. GL YEO (3 - Glycidoxypropyltriethoxysilan) Formula: CH 2 -CH- CH 2 -OCH 2 CH 2 CH 2 Si(OC 2 H 5 ) 3 \o/ 2- BPA (Bisphenol-A) and its derivatives Example 1. Bisphenol - A (BPA) Example 2. Diglycidyl ether of Bisphenol A 3-Tertiaryamines, particularly MI (Methyl imidazoleve derivatives) (as hardener) Example 1. ϊmidazoles Example 2. Methyl imidazol Amines 1) 3 -Ammopropyltrimethoxysilan (AMEO) H 2 NCH 2 CH 2 CH 2 Si (OCH 3 ) 3 2) N (2Aminoethyl) - 3 Aminopropyltrimethoxysilan NH 2 (CH 2 ) 2 H(CH 2 ) 3 Si(OCH 3 ) 3 3) 3-Aminopropyltriethoxysilan H 2 NCH 2 CH 2 CH 2 Si (OC 2 H 5 ) 3 4) N,N,N trimethylethylenediamin (CH 3 ) 2 NCH 2 CH 2 NHCH 3 4 - Tensydes Example 1. Polyoxyethylene(lO) oleyl ether (Brij-96) C 18 H 35 (OCH 2 CH 2 )ιoOH Example 2. Polyoxyethylene (20) oleylether (Brij-99) C 18 H 35 (OCH 2 CH 2 ) 20 OH 5- Anhydrites Triethoxysilylpropylsuccinicanhydride (TSPSA) O \\ ^ C - CH 2 O ^ C - CH - CH 2 CH 2 CH 2 - Si(OC 2 H5) 3 Experiment 1; The GPTS BPA/Mi7AMEO mixture is prepared so that the molar ratios are respectively 100/1-60/5-20/5-20. After the hydrolysis of GPTS, BPA and Ml are added and stirred for 30 minutes. 4% Brij96 and 6% TSPSA+Brij96 (1:1 mol) are added to the mixture and stirred 30 minutes. The aluminium folio surfaces to be coated are cleaned following the below given order: Degreasing; washing with distilled water; neutralization by HNO3; washing with distilled water; washing with alcohol and drying. The cleaned aluminium folio surfaces are coated by immersing in the prepared solution or by spraying. The coated surfaces are kept in the drying oven at 120°C for 30 minutes or at 150°C for 5 minutes in order to obtain the required hardening. Experiment 2: It is prepared by adding 4% Brij96 and 7% TSPSA+Brij96 (1:1 mol) to the mixture of Experiment 1. The same procedure is used to clean the aluminium surfaces, they are coated and then hardened in the oven. Experiment 3: It is prepared by adding 5% Brij96 and 5% TSPSA+Brij96 (1 :1 mol) to the mixture of Experiment 1. The same procedure is used to clean the aluminium surfaces, they are coated and then hardened in the oven. Experiment 4: It is prepared by adding 5% Brij96 and 7% TSPSA+Brij96 (1:1 mol) to the mixture of Experiment 1. The same procedure is used to clean the aluminium surfaces, they are coated and then hardened in the oven. Experiment 5: It is prepared by adding 5% Brij96 and 4% TSPSA+Brij96 (l:lmol) to the mixture of Experiment 1. The same procedure is used to clean the aluminium surfaces, they are coated and then hardened in the oven. Experiment 6: The object of this experiment is hydrophobic coating. Inorganic polymerization is obtained by the hydrolysis and condensation of GPTS. Fluor silan used to provide hydrophobic properties is silan tridecafluoro-l,l,2,2-tetrahydro-octyl-l- triethoxysilan presented by the formula, C 6 Fi 3 CH 2 Si(OC 2 H 5 ) 3 . It is added to the mixture with a rate of 1 %. The measured wetting angle is 90°. To the mixture 1-4% fluor silan is added. Measured wetting angles are between 90° and 110°. All surfaces coated hydrophobically are subjected to humidity- resistance, adhesion and flexibility tests and found to be satisfactory. Results of the Experiments Hydrophilic : The results of the wetting angle measurements taken by using Kruss, Model K- 121 wetting angle measuring device, are given in Table 1. TABLE-1 Angle, ° % Brij 96 + % (TSPSA + Brij 96) 4 + 6 4 + 7 5 + 5 5 +7 5 +4 Initially 6 20 20 20 20 After 5 5 5 5 5 5 minutes Hydrophobic : No corrosion damage was seen on coated samples. The samples are kept in an environment with 90% humidity at 50°C for 15 days, to observe whether any corrosion damages would occur. For the testing of thermal conditions, the samples subjected to the above humidity test were kept in a 90% humid environment, at 50°C for 20 days, following their removal, they are then kept at a temperature of - 10°C for 8 hours and then they are left at the room temperature. This process has been completed in a total of 7 cycles and it has been observed that there was no degradation in the coating. Another embodiment of a coated evaporator has been mounted on an open system refrigerator and the condensation and evaporation stages have been recorded by a video camera. The same procedure is repeated with an uncoated evaporator and it has been observed that in the coated embodiment, the water drops slipped away on the surface without ice-formation, due to the hydrophobic characteristic of the surface. Whereas in the uncoated embodiment, water drops remained on the surface during the condensation stage and they accumulated as ice particles. The formulation, composition and the coating method using sol-gel technique, obtained as the result of numerous experiments have industrial applicability properties. When applied to the evaporation/condensation systems of refrigerators and similar cooling system, they will provide a considerable amount of economy in energy consumption.

Claims: CLAIMS 1. A method for preparing sol-gel coating material characterized in that the GPTS / BPA / MI / AMEO mixture is prepared so that their molar ratios are respectively 100 /1-60 / 5-20 / 5-20, after the hydrolysis of GPTS, BPA and Ml are added and stirred for 30 minutes; 2-10% Brij96 and 1-12% [TSPSA + Brij 96] (1 :1 mol) are added to the mixture and stirred 30 minutes; that the aluminium folio surfaces which are cleaned by degreasing; washing with distilled water; neutralization by HNO3; washing with distilled water; washing with water and drying are coated by the prepared solution using either immersion or spray techniques; and that the coated surfaces are kept in the drying oven at 120°C for 30 minutes or at 1 0°C for 5 minutes in order to obtain the required hardening. 2. A method for preparing sol-gel coating material according to Claim 1, characterized in that the ratio of Brij 96 in the said formulation is 4% and the ratio of [TSPSA+Brij 96] (1:1 mol) in the said formulation is 6%. 3. A method for preparing sol-gel coating material according to Claim 1, characterized in that the ratio of Brij 96 in the said formulation is 4%, and the ratio of [TSPSA+Brij 96] (1 : 1 mol) in the said formulation is 5%. 4. A method for preparing sol-gel coating material according to Claim 1, charcterized in that the ratio of Brij 96 in the said formulation is 5% and the ratio of [TSPSA+Brij 96] (1 :1 mol) in the said formulation is5%. 5. A method for preparing sol-gel coating material according to Claim 1, characterized in that the ratio of Brij96 in the said formulation is 5%, and the ratio of [TSPSA+Brij 96] (1 : 1 mol) in the said formulation is 7%. 6. A method for preparing sol-gel coating material according to Claim 1, characterized in that the ratio of Brij96 in the said formulation is 5%, and the ratio of [TSPSA+Brij 96] (1 :1 mol) in the said formulation is 4%. 7. A method for preparing sol-gel coating material according to Claims 1 to 6 wherein the surface wetting angle is reduced to approximately 10° to 20° at the moment the water drop contacts with the aluminium surface (hydrophilic property) and to 10° in 5 minutes after the moment of contact. 8. A method for preparing sol-gel coating material characterized in that the GPTS / BPA / MI / AMEO mixture is prepared so that their molar ratios are respectively 100 /1-60 / 5-20 / 5-20, after the hydrolysis of GPTS, BPA and Ml are added and stirred for 30 minutes; 1-4%) fluor silan is added to the mixture and stirred 30 minutes; that the aluminium folio surfaces which are cleaned by degreasing; washing with distilled water; neutralization by HNO3; washing with distilled water; washing with water and drying are coated by the prepared solution using either immersion or spray techniques; and that the coated surfaces are kept in the drying oven at 120°C for 30 minutes or at 150°C for 5 minutes in order to obtain the required hardening. 9. A method for preparing sol-gel coating material according to Claim 8, wherein the surface wetting angle is increased to 90°- 110° at the moment the water drop contacts with the aluminium surface (hyrophobic property). 10. A method for preparing sol-gel coating material according to Claims 1 and 8 characterized in that the sol-gel coating solution in the said composition is coated homogenously on the surface, by immersing or spraying techniques and hardened by being kept in the drying oven, at a temperature of 40°- 150° for 5 minutes to 5 hours.

Inventors: AKAY MUEGE, AKAY, MUEGE
Applicants: AKAY MUEGE, ARCELIK AS, AKAY, MUEGE, ARCEL&IDOT
Application year: 1999
Main classification: F25D
IPC codes: C09D183, C09K3, C23C18, F25B47