Metal panel and refrigerator

Abstract

The invention provides a metal panel and a refrigerator. The metal panel sequentially comprises a pattern layer, a bonding layer and a base material layer from top to bottom, the base material layer is a cold-rolled steel sheet; the bonding layer is a hot melt adhesive layer; the pattern layer is transferred to the base material layer through a heat transfer printing process; the pattern layer is a three-dimensional ink layer which is formed by adopting a multi-stage intaglio printing technology through repeated overprinting for multiple times; the pattern layer comprises a bottom pattern layer, a middle pattern layer and a surface layer; the bottom pattern layer is a UV curing ink layer, the middle pattern layer is an epoxy resin ink layer added with glass beads, and the surface layer is an elastic ink layer containing organosilicon modified polyurethane. The pattern layer is repeatedly overprinted for multiple times through a multi-stage intaglio printing technology to form a three-dimensional ink layer, and the epoxy resin ink layer with glass beads added in the middle layer and the elastic ink layer with organosilicon modified polyurethane contained in the surface layer are matched with each other, so that the whole panel has a 3D texture touch sense, the texture of the panel is greatly improved, and the service life of the panel is prolonged. And the requirement of the user on high touch feeling is met.

Description

Technical Field

[0001] This application relates to the technical field of sheet materials, and particularly to a metal panel and a refrigerator. Background Art

[0002] In the field of modern household appliances, as an important household appliance, the appearance design and user experience of refrigerators have received increasing attention. The metal panel of a refrigerator not only serves the function of protecting the internal structure, but also directly affects the overall aesthetics and user tactile experience of the refrigerator, becoming one of the important considerations for consumers when purchasing a refrigerator.

[0003] Currently, the common types of refrigerator metal panels are mainly PCM boards and VCM boards. The PCM board, whose full name is Pre-Coated Metal, is a sheet material with an organic coating applied to a metal substrate. Its manufacturing process usually involves first surface-treating the metal substrate to enhance the adhesion of the coating, then uniformly applying the prepared organic coating to the substrate surface by means of roll coating, spraying, etc., and finally baking and curing to form a colored coating. This sheet material is widely used in refrigerator manufacturing because it has certain corrosion resistance and cost advantages. However, due to its process characteristics, in terms of color presentation, the available color systems are relatively limited, mostly basic solid colors, and it is difficult to achieve rich and diverse color changes; in terms of texture, usually only relatively simple and regular patterns can be made, appearing monotonous. Moreover, restricted by the coating material and process, the surface of the PCM board is relatively smooth and lacks texture, making it difficult to provide users with a good touch experience.

[0004] The VCM board, i.e., Vinyl Coated Metal, is a metal substrate with a plastic film with various textures and colors laminated on it. The production process generally involves first laminating the plastic film to the treated metal substrate through a special adhesive, and then going through a series of processing steps to closely bond the film and the substrate. Thanks to the characteristics of the laminated film, the VCM board can present rich and diverse texture effects, such as imitation wood grain, imitation stone grain, etc., and can meet the needs of more consumers for personalization and aesthetics in terms of appearance. However, in terms of touch, although its texture is rich, due to the material characteristics of the plastic film itself and the limitations of the lamination process, there are certain difficulties in meeting high touch requirements and it cannot provide users with a delicate, real and three-dimensional touch feeling.

[0005] In the industry, different improvement processes have been adopted for PCM boards and VCM boards respectively. For PCM boards, some manufacturers have tried to improve the coating formula by adding special pigments and additives to enrich the color variety, and at the same time adopted a new roll coating process to increase the texture diversity. However, in actual operation, due to the coating adhesion principle of PCM boards and the limitations of process equipment, the newly added pigments and additives are difficult to disperse evenly, resulting in color deviation and uneven color. Moreover, the new roll coating process has extremely high requirements for equipment accuracy, resulting in a substantial increase in costs, yet still unable to achieve complex and layered texture effects, and having little effect on improving the touch.

[0006] For VCM boards, attempts have been made to improve the touch by improving the laminating material and optimizing the laminating process. For example, using softer and more elastic film materials, as well as improving parameters such as temperature and pressure during lamination. However, in actual applications, although the softer film material improves the touch to a certain extent, it reduces the wear resistance and corrosion resistance of the film layer, resulting in problems such as scratches and wear on the refrigerator panel during daily use. Optimizing the laminating process parameters also faces difficulties. It is difficult to precisely control the temperature and pressure. Once there is a deviation, the film layer will not adhere firmly, easily causing phenomena such as blistering and peeling, seriously affecting the product quality and service life. In addition, for the improvement processes of both PCM boards and VCM boards, it is difficult to make the refrigerator metal panel meet the requirements of 3D stereoscopic touch, and it has always been unable to well meet the high-touch needs of consumers for refrigerator metal panels. Summary of the Invention

[0007] This application provides a metal panel and a refrigerator to solve the problem in the related art that the metal panel used for the refrigerator cannot achieve complex and layered texture effects.

[0008] In the first aspect, this application provides a metal panel for a refrigerator. The metal panel includes, from top to bottom in sequence: a pattern layer, a bonding layer, and a substrate layer; the substrate layer is a cold-rolled steel sheet with a thickness of 0.4 - 0.55 mm; the bonding layer is a hot melt adhesive layer with a thickness of 10 - 30 μm; the pattern layer is transferred to the substrate layer through a heat transfer printing process.

[0009] The pattern layer adopts a multi-level gravure printing technology to form a three-dimensional ink layer through multiple repeated overprints; the pattern layer includes a bottom pattern layer, a middle pattern layer, and a surface layer; the bottom pattern layer is a UV-cured ink layer, the middle pattern layer is an epoxy resin ink layer added with glass microspheres, and the surface layer is an elastic ink layer containing organosilicon-modified polyurethane; the thickness of the pattern layer is 120 - 200 μm.

[0010] In some possible implementation manners, the viscosity of the UV-curable ink of the bottom pattern layer is 2,500 to 3,000 cps, and the thickness of the bottom pattern layer is 15 ± 2 μm.

[0011] In some possible implementation manners, the particle size of the glass beads of the middle pattern layer is 5 to 8 μm, and the stacking height is 30 to 50 μm.

[0012] In some possible implementation manners, the local protrusion of the surface layer is 20 to 120 μm.

[0013] In some possible implementation manners, the adhesive used in the adhesive layer is one of ethylene-vinyl acetate copolymer, thermoplastic polyurethane elastomer or polyamide.

[0014] In some possible implementation manners, the substrate layer has a surface roughness Ra ≤ 0.1 μm, a surface tension ≥ 38 dynes, and a substrate with a silane film thickness of 200 to 500 nm, and the film adhesion is grade 0.

[0015] In some possible implementation manners, the substrate layer is obtained through three-step pretreatment of electrolytic degreasing, nano-ceramicization and silane coupling.

[0016] In some possible implementation manners, the pattern layer is transferred to the substrate layer via a transfer film through a heat transfer process. In the heat transfer process, the temperature of the silicone rubber roller is 180 to 230 °C, the pressure is 0.5 to 1.5 MPa, and the speed of the silicone rubber roller is 0.5 to 3 m / min.

[0017] In some possible implementation manners, the heat transfer film substrate is a PET film, the film thickness is 20 to 30 μm, and the PET film has a release layer, a pattern layer and an adhesive layer structure.

[0018] In a second aspect, the present application provides a refrigerator, including the metal panel described in the first aspect.

[0019] As can be seen from the above, the present application provides a metal panel and a refrigerator. The metal panel successively includes from top to bottom: a pattern layer, an adhesive layer, and a substrate layer. The substrate layer is a cold-rolled steel sheet with a thickness of 0.4 - 0.55 mm. The adhesive layer is a hot-melt adhesive layer with a thickness of 10 - 30 μm. The pattern layer is transferred to the substrate layer through a heat transfer process. The pattern layer adopts a multi-level gravure printing technology and forms a three-dimensional ink layer through multiple repeated overprinting. The pattern layer includes a bottom pattern layer, a middle pattern layer, and a surface layer. The bottom pattern layer is a UV-cured ink layer, the middle pattern layer is an epoxy resin ink layer added with glass microspheres, and the surface layer is an elastic ink layer containing organosilicon-modified polyurethane. The thickness of the pattern layer is 120 - 200 μm. The pattern layer forms a three-dimensional ink layer through multiple repeated overprinting by the multi-level gravure printing technology, and the epoxy resin ink layer added with glass microspheres in the middle layer and the elastic ink layer containing organosilicon-modified polyurethane in the surface layer cooperate with each other. The glass microspheres enhance the surface roughness and layering, and the organosilicon-modified polyurethane elastic ink endows the panel with a soft and elastic touch, making the whole panel have a 3D stereoscopic texture touch, greatly improving the texture of the panel and meeting the user's demand for high touch. Using the multi-level gravure printing and multiple repeated overprinting technologies to produce the pattern layer can achieve rich and diverse, strong three-dimensional pattern effects. The bottom UV-cured ink layer lays the foundation texture, and the middle and surface layer inks further enrich the details and layers, and can present various complex textures such as realistic wood grain and stone grain, improving the user experience. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] In order to more clearly illustrate the technical solutions of the present application, the drawings required for use in the embodiments will be briefly introduced below. Obviously, for those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0021] Figure 1 FIG. is a schematic structural diagram of the metal panel provided by the embodiment of the present application;

[0022] Figure 2 FIG. is a schematic flow diagram of the transfer process of the metal panel provided by the embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] The implementation manners described in the following embodiments do not represent all implementation manners consistent with the present application. They are only examples of systems and methods consistent with some aspects of the present application detailed in the claims.

[0024] Currently, the common types of refrigerator metal panels are mainly PCM panels and VCM panels. The full name of the PCM panel is Pre-Coated Metal, which is a type of sheet with an organic coating applied to a metal substrate. Its manufacturing process usually involves first surface-treating the metal substrate to enhance the adhesion of the coating, then evenly applying the prepared organic coating to the substrate surface by means of roll coating, spraying, etc., and finally baking and curing to form a colored coating. This type of sheet is widely used in refrigerator manufacturing because it has certain corrosion resistance and cost advantages. However, due to its process characteristics, in terms of color presentation, the available color systems are relatively limited, mostly basic solid colors, and it is difficult to achieve rich and diverse color changes; in terms of texture, usually only relatively simple and regular patterns can be made, which appears monotonous. Moreover, limited by the coating materials and processes, the surface of the PCM panel feels relatively smooth and lacks texture, making it difficult to provide users with a good touch experience.

[0025] The VCM panel, namely Vinyl Coated Metal, is a sheet with a plastic film with various textures and colors covered on a metal substrate. The production process generally involves first adhering the plastic film to the treated metal substrate through a special adhesive, and then going through a series of processing steps to make the film and the substrate tightly combined. By virtue of the characteristics of the plastic film covering, the VCM panel can present a rich variety of texture effects, such as imitation wood grain, imitation stone grain, etc., and can meet the needs of more consumers for personalization and aesthetics in terms of appearance. However, in terms of touch, although its texture is rich, due to the material characteristics of the plastic film itself and the limitations of the film covering process, there are certain difficulties in achieving high touch requirements, and it cannot provide users with a delicate, real and three-dimensional touch feeling.

[0026] The industry has adopted different improvement processes for PCM panels and VCM panels respectively. For PCM panels, some manufacturers have tried to improve the coating formula by adding special pigments and additives to enrich the color types, and at the same time adopt a new roll coating process to increase the diversity of textures. However, in actual operation, due to the coating adhesion principle and process equipment limitations of PCM panels, the newly added pigments and additives are difficult to disperse evenly, resulting in color deviation and uneven color often occurring; moreover, the new roll coating process has extremely high requirements for equipment accuracy, and the cost has increased significantly, but still cannot achieve complex and layered texture effects, and there is little effect in improving the touch.

[0027] For the VCM board, attempts have been made to improve the touch feeling by improving the film covering material and optimizing the film covering process. For example, using softer and more elastic film materials, as well as improving parameters such as temperature and pressure during film covering. However, in actual applications, although the softer film material improves the touch feeling to a certain extent, it reduces the wear resistance and corrosion resistance of the film layer, resulting in problems such as scratches and abrasions on the refrigerator panel during daily use; there are also difficulties in optimizing the film covering process parameters. It is difficult to accurately control the temperature and pressure. Once there is a deviation, the film layer will not adhere firmly, and phenomena such as blistering and peeling are likely to occur, seriously affecting the product quality and service life. In addition, for the improvement processes of both the PCM board and the VCM board, it is difficult to make the refrigerator metal panel meet the requirements of 3D stereoscopic touch feeling, and it has always been unable to well meet the consumers' high-touch requirements for the refrigerator metal panel.

[0028] Based on this, the present application provides the metal panel for a refrigerator, as Figure 1 shown, the metal panel sequentially includes from top to bottom: a pattern layer, an adhesive layer, and a substrate layer; the substrate layer is a cold-rolled steel sheet, and the thickness of the substrate layer is 0.4 - 0.55 mm; the adhesive layer is a hot melt adhesive layer, and the thickness of the adhesive layer is 10 - 30 μm; the pattern layer is transferred to the substrate layer through a heat transfer printing process;

[0029] The pattern layer adopts a multi-level gravure printing technology to form a three-dimensional ink layer through multiple repeated overprinting; the pattern layer includes a bottom pattern layer, a middle pattern layer, and a surface layer; the bottom pattern layer is a UV-cured ink layer, the middle pattern layer is an epoxy resin ink layer added with glass microspheres, and the surface layer is an elastic ink layer containing organosilicon-modified polyurethane; the thickness of the pattern layer is 120 - 200 μm.

[0030] The pattern layer in the present application adopts multi-level gravure printing, and its uniqueness lies in the multi-level design of the printing plate pits. Pits with different depths store different amounts of ink. During the printing process, different amounts of ink are transferred to the substrate. For example, deeper pits transfer more ink and form a thicker ink layer on the substrate; shallower pits transfer less ink and form a thinner ink layer. By carefully designing the depth and distribution of these pits and combining the multiple repeated overprinting process, the printed pattern can present a three-dimensional effect. In the pattern production of the metal panel, a thinner ink layer (such as a UV-cured ink layer with a thickness of 15 ± 2 μm forms the bottom pattern) is used for the bottom pattern layer to construct the basic texture, and inks with different characteristics and thicknesses are used for the middle and surface layers respectively (the epoxy resin ink added with glass microspheres has a stacking height of 30 - 50 μm, and the elastic ink containing organosilicon-modified polyurethane has local protrusions of 80 - 120 μm). Through multi-level gravure printing and multiple overprinting, the pattern gradually constructs rich levels and three-dimensionality from the bottom layer to the surface layer.

[0031] By utilizing multi-level gravure printing technology, the color and texture of the ink can also be precisely controlled. By filling inks of different colors in the pits of different levels, color mixing and superposition are achieved during the overprinting process, thereby presenting a rich variety of color effects. In terms of texture, the shape, size, and distribution of the pits can be adjusted according to design requirements.

[0032] In this application, the pattern layer is formed by multi-level gravure printing and repeated overprinting to form a three-dimensional ink layer, and the epoxy resin ink layer with glass beads added in the middle layer and the elastic ink layer containing organosilicon-modified polyurethane on the surface layer cooperate with each other. The glass beads enhance the surface roughness and layering, while the organosilicon-modified polyurethane elastic ink endows the panel with a soft and elastic touch, making the whole panel have a 3D stereoscopic texture touch, greatly improving the texture of the panel and meeting the user's demand for high touch.

[0033] Using multi-level gravure printing and repeated overprinting technology to produce the pattern layer on the metal panel can achieve rich, diverse, and highly three-dimensional pattern effects. The bottom UV-curable ink layer lays the foundation texture, and the middle and surface inks further enrich the details and layers, presenting realistic imitation wood grain, imitation stone grain, and other various complex textures, enriching the appearance design of the refrigerator panel and enhancing the overall aesthetics of the product.

[0034] The base material layer is made of cold-rolled steel sheet with a thickness controlled at 0.4 - 0.55 mm, ensuring the strength and rigidity of the panel and providing a stable support structure for the entire metal panel. The bonding layer is a hot-melt adhesive layer with a thickness of 10 - 30 μm, which can form a firm bond between the pattern layer and the base material layer, ensuring the tight combination of the pattern layer and the base material layer and preventing problems such as delamination and peeling, improving the structural stability and service life of the metal panel.

[0035] The reasonable application of different types of inks in the pattern layer, such as the bottom UV-curable ink having good curing performance and wear resistance, can ensure the clarity and durability of the basic pattern; the epoxy resin ink with glass beads added in the middle layer not only enhances the touch but also improves the hardness and wear resistance of the ink layer; the elastic ink containing organosilicon-modified polyurethane on the surface layer improves the chemical corrosion resistance and weather resistance of the panel while ensuring the touch, enabling the pattern layer to maintain good printing quality and performance during long-term use.

[0036] In some embodiments, the viscosity of the UV-curable ink of the bottom pattern layer is 2500 - 3000 cps, and the thickness of the bottom pattern layer is 15 ± 2 μm.

[0037] UV-curable inks have the characteristic of rapid curing. Under ultraviolet light irradiation, they can quickly change from a liquid state to a solid state, forming a stable ink layer. This characteristic enables the underlying pattern to be quickly fixed after printing, providing a stable foundation for the subsequent printing of the middle and top-layer inks. Since the fast curing speed not only improves production efficiency but also ensures the clarity and accuracy of the underlying pattern, achieving the precise presentation of the basic texture and ensuring the stable texture structure of the entire pattern layer. At the same time, UV-curable inks have good abrasion resistance and chemical resistance, enhancing the durability of the metal panel pattern layer, making it not easily scratched or corroded during daily use and extending the service life of the metal panel.

[0038] A viscosity of 2500 - 3000 cps enables UV-curable inks to have good fluidity and transferability during multi-level gravure printing. This viscosity range ensures that the ink can smoothly fill the pits of the printing plate without the phenomenon of ink flowing and spreading during printing due to too low viscosity, thus ensuring the printing accuracy and clarity of the underlying pattern and enabling the precise presentation of the basic texture. A thickness of 15 ± 2 μm further meets this accuracy requirement. The stable thickness provides an accurate reference for the overprinting of the subsequent middle and top-layer patterns, helping to achieve the precise superposition of the entire pattern layer and ensuring the details and overall quality of the pattern.

[0039] Appropriate viscosity helps the UV-curable ink to cure evenly under ultraviolet light irradiation. When the ink viscosity is too high, it may lead to incomplete curing, affecting the performance of the ink layer; too low viscosity may result in a loose structure of the cured ink layer. A viscosity of 2500 - 3000 cps can ensure that during the curing process, components such as photoinitiators inside the ink react fully, forming a dense and stable cured structure. A thickness of 15 ± 2 μm is also conducive to the penetration of ultraviolet light through the ink layer, achieving full curing from the surface to the inside, making the underlying pattern layer have good abrasion resistance, chemical resistance, and hardness, enhancing the overall stability and durability of the metal panel pattern layer.

[0040] In some embodiments, the glass microbeads of the middle-layer pattern layer have a particle size of 5 - 8 μm and a stacking height of 30 - 50 μm.

[0041] Epoxy resin ink itself has good adhesion and hardness, and can be closely combined with the underlying UV-cured ink layer and the surface elastic ink layer to ensure the overall structure of the pattern layer is firm. The added glass beads have a particle size of 5 - 8μm, and these tiny glass beads are evenly distributed in the ink, increasing the roughness and three-dimensional sense of the ink layer. The presence of the glass beads greatly enhances the touch feeling, making the surface of the metal panel have an obvious texture, achieving the effect of 3D stereoscopic touch feeling and improving the texture of the product. At the same time, the high adhesion and hardness of the epoxy resin ink help to improve the abrasion resistance of the pattern layer, further protect the underlying pattern, and provide reliable support for the surface ink, maintaining the overall stability of the pattern layer.

[0042] The glass beads with a particle size of 5 - 8μm are of moderate size, neither causing a rough and uncomfortable touch due to overly large particles nor being unable to effectively increase the surface roughness due to overly small particles. They are evenly distributed in the epoxy resin ink. When a person touches the metal panel, the glass beads will generate a richer change in friction with the finger, allowing the user to clearly feel the surface texture and enhancing the three-dimensional sense of the touch feeling. The stacking height of 30 - 50μm further magnifies this effect, making the texture feeling more prominent when touched, achieving the improvement of the 3D stereoscopic touch feeling of the metal panel and greatly improving the user experience.

[0043] The glass beads have good optical properties. Within this thickness range, the glass beads can refract and scatter light at multiple angles. When observing the metal panel from different angles, the light will be reflected and refracted multiple times between the glass beads, making the pattern layer present a unique luster and sense of hierarchy, making the appearance of the metal panel more vivid and textured. This optical effect not only enhances the visual attraction of the panel but also enables it to show a unique appearance effect under different lighting conditions.

[0044] The addition of glass beads increases the hardness and rigidity of the middle pattern layer. They are evenly dispersed in the epoxy resin ink and play a role similar to that of reinforcing fillers, being able to effectively resist external friction and impact. The stacking height of 30 - 50μm makes this strengthening effect more significant, improving the overall strength of the middle pattern layer, and thus enhancing the structural stability of the entire pattern layer. This helps to protect the underlying pattern layer from damage and at the same time provides stable support for the surface elastic ink layer, extending the service life of the metal panel.

[0045] The glass beads cooperate with the epoxy resin ink to improve the overall performance of the ink. The presence of the glass beads increases the viscosity and thixotropy of the ink, making it easier to control during the printing process, being able to better fill the pits of the printing plate, and ensuring the accuracy and clarity of the pattern printing. Moreover, the glass beads have relatively high chemical stability, which can improve the chemical corrosion resistance of the epoxy resin ink and enhance the protection performance of the metal panel pattern layer.

[0046] In some embodiments, the local protrusions on the surface layer are 20 to 120 μm.

[0047] The silicone-modified polyurethane elastic ink combines the advantages of the weather resistance, low surface energy of silicone and the high elasticity, wear resistance of polyurethane. This kind of ink has good elasticity and can form a soft and elastic touch layer on the surface of the metal panel. Its elastic property makes the metal panel feel more comfortable when touched, further enhancing the 3D stereoscopic touch experience. Moreover, the weather resistance of silicone and the wear resistance of polyurethane enable the surface layer to effectively resist the erosion of the external environment, such as ultraviolet rays, humid air, etc., prevent the pattern layer from fading and aging, improve the weather resistance and service life of the metal panel. At the same time, the property of low surface energy makes the surface of the metal panel not easy to be stained with stains, facilitating cleaning and maintenance.

[0048] The surface layer uses an elastic ink containing silicone-modified polyurethane, and the local protrusions are 80 to 120 μm. This parameter design greatly improves the touch of the metal panel. Silicone-modified polyurethane has good elasticity, giving the panel a soft and comfortable touch feeling. The local protrusions of 80 to 120 μm form obvious three-dimensional textures. When the finger touches the panel, the change of the texture can be clearly felt. Combined with the enhanced roughness of the middle layer of glass beads, it further strengthens the 3D stereoscopic touch effect and significantly improves the touch experience when the user interacts with the metal panel.

[0049] The elastic ink on the surface layer can form a smooth and shiny surface after curing, making the metal panel look more beautiful. Moreover, its good film-forming property can ensure that the details of the pattern are perfectly presented, without problems such as pattern deformation or blurring caused by ink drying shrinkage. The local protrusion structure of 80 to 120 μm will produce a unique light and shadow effect under light, enhancing the three-dimensional sense and layering of the panel. When observed from different angles, it presents a rich and diverse visual effect, improving the overall appearance quality of the metal panel.

[0050] Silicone-modified polyurethane itself has excellent weather resistance, wear resistance and chemical corrosion resistance. The weather resistance enables it to effectively resist the erosion of environmental factors such as ultraviolet rays and humid air, preventing the panel from fading and aging; the wear resistance ensures that the panel is not easy to have scratches even when frequently contacted and wiped during daily use, maintaining the integrity of the surface; the chemical corrosion resistance enables it to resist the corrosion of common chemical substances, such as kitchen cleaners, etc., extending the service life of the metal panel. The thickness of 80 to 120 μm further enhances this protective effect, providing a more reliable protective barrier for the underlying pattern layer and the metal substrate.

[0051] The elastic ink of the surface pattern layer has good adhesion and compatibility with the epoxy resin ink with glass beads added to the middle layer and the UV curing ink of the bottom layer. The silicone-modified polyurethane elastic ink can firmly adhere to the middle layer ink, ensuring the structural stability of the entire pattern layer and avoiding problems such as delamination and falling off. At the same time, its elastic properties can also buffer the impact of the outside world on the panel, reduce the impact on the middle and bottom ink layers, maintain the synergy between the layers of the metal panel, and ensure the stability of the overall performance of the metal panel.

[0052] In some embodiments, the adhesive used in the bonding layer is one of ethylene-vinyl acetate copolymer, thermoplastic polyurethane elastomer or polyamide.

[0053] The bonding layer uses ethylene-vinyl acetate copolymer (EVA), thermoplastic polyurethane elastomer (TPU) or polyamide (PA) as adhesives, which can improve the performance of metal panels in many aspects; EVA contains vinyl acetate groups in its molecular structure, which makes it have good adhesion to the metal substrate and the pattern layer; TPU has strong polar groups, which can form hydrogen bonds and other forces with the surfaces of different materials, and firmly bond; PA's molecular chain contains a large number of amide groups, which can be tightly combined with the oxides on the metal surface and the pattern layer materials. This makes the pattern layer firmly connected to the cold-rolled steel plate substrate, ensuring that the metal panel will not have problems such as the pattern layer falling off and warping during use, and ensuring the integrity and stability of the metal panel structure.

[0054] EVA has good flexibility and can buffer external impact to a certain extent, preventing the pattern layer from being damaged by vibration and collision; the elastic properties of TPU enable it to undergo elastic deformation when impacted, absorb energy, and protect the pattern layer and substrate; the molecular chain of PA has a certain flexibility, which can give the bonding layer impact resistance. This effectively enhances the impact resistance of the metal panel, extends the service life of the metal panel, and improves its reliability. EVA has good water resistance and can maintain stable bonding performance in a humid environment; TPU has excellent weather resistance and can resist the influence of environmental factors such as ultraviolet rays, high and low temperature changes, and is not easy to age and decompose; PA has high chemical stability and strong chemical corrosion resistance, and can resist corrosion from common chemical substances. These characteristics enable the metal panel to maintain a stable bonding effect in various complex environments, ensuring that the pattern layer and the substrate are always tightly combined, and maintaining the stable performance of the metal panel.

[0055] EVA, TPU and PA all have good thermoplasticity and are easy to melt and flow under heating conditions, making it easy to prepare the bonding layer using processes such as hot melt adhesive coating. This can achieve automated production and improve production efficiency. At the same time, the thickness of the bonding layer can be accurately controlled at 10-30μm to ensure consistency in product quality.

[0056] In some embodiments, the substrate layer has a surface roughness Ra ≤ 0.1 μm, a surface tension ≥ 38 dynes, and a substrate with a silane film thickness of 200 - 500 nm, and the film adhesion is grade 0.

[0057] The surface roughness Ra ≤ 0.1 μm of the substrate layer means that the surface of the substrate layer is extremely smooth. When the bonding layer contacts such a smooth surface, a closer fit over a larger area can be achieved, reducing the bonding voids caused by surface irregularities, enabling the adhesive to be evenly distributed on the substrate surface, and thus enhancing the bonding force between the bonding layer and the substrate layer. Surface tension

[0058] ≥ 38 dynes indicates that the substrate surface has good wettability. This makes it easier for the adhesive to spread and infiltrate on the substrate surface, enabling it to better chemically interact with the substrate surface, form stronger chemical bonding forces, and further improve the firmness of the bond.

[0059] The 200 - 500 nm silane film plays a key bridging role during the bonding process. One end of the silane molecule can chemically react with the metal atoms on the substrate surface to form stable chemical bonds; the other end can interact with the adhesive molecules, thus tightly connecting the bonding layer and the substrate layer. The film adhesion reaching grade 0 indicates that the combination between the silane film and the substrate, and between the bonding layer and the silane film is very firm, with almost no risk of peeling or separation, ensuring the stability of the overall structure of the metal panel.

[0060] In some embodiments, the substrate layer is obtained through three-step pretreatment of electrolytic degreasing, nano-ceramicization, and silane coupling.

[0061] 1. Electrolytic degreasing (electrochemical degreasing)

[0062] The purpose is to remove contaminants such as grease, mineral oil, and polishing wax on the metal surface, and at the same time roughen the surface through electrochemical action to provide a clean substrate for subsequent processing.

[0063] Process steps

[0064] Preparation of degreasing solution

[0065] Alkaline electrolyte (containing sodium hydroxide, sodium carbonate, surfactant, etc.), pH = 11 - 13, temperature 50 - 70 °C.

[0066] Electrolytic degreasing

[0067] Cathodic degreasing (metal as the cathode): Pass direct current (current density 5 - 15 A / dm 2 ), generate hydrogen to strip off the grease, and is applicable to metals such as copper and aluminum that are not resistant to anodic corrosion.

[0068] Anodic degreasing (metal as anode): Oxygen is generated to strip off grease, which can remove the risk of hydrogen embrittlement remaining after cathodic degreasing and is applicable to corrosion-resistant metals such as steel.

[0069] Time: 1 - 3 minutes, adjusted according to the thickness of the grease.

[0070] Water washing and neutralization

[0071] Hot water washing (40 - 60 °C) is used to remove the remaining lye. If it is necessary to neutralize with a 5% nitric acid solution after anodic degreasing, it can prevent film layer defects caused by the remaining lye.

[0072] 2. Nano-ceramic conversion (chromium-free conversion coating / nano-ceramic conversion)

[0073] The purpose is to form a nano-scale ceramic film (containing oxides such as zirconium, titanium, and silicon) on the metal surface to enhance corrosion resistance and at the same time provide a rough surface to improve the adhesion of the subsequent coating.

[0074] Process steps

[0075] Preparation of the ceramic conversion solution: Main components: fluozirconic acid (salt), fluotitanic acid (salt), organic carboxylic acid (such as citric acid), pH = 3 - 5, temperature 25 - 45 °C, chromium-free, an environmentally friendly process.

[0076] Ceramic conversion treatment: Dipping or spraying: The metal panel is immersed in the ceramic conversion solution, and an amorphous ceramic film (thickness 50 - 200 nm) is formed through hydrolysis reaction.

[0077] Time: 1 - 5 minutes. It is necessary to control the stirring rate to ensure the uniformity of the film layer.

[0078] Water washing and drying: Cleaning with deionized water to remove the remaining chemical solution, drying at room temperature or low temperature (≤60 °C) to avoid the film layer absorbing water and losing effectiveness.

[0079] 3. Silane coupling treatment

[0080] The purpose is to form a molecular bridge on the metal surface through silane molecules (containing -Si-O- groups and organic functional groups) to connect the inorganic substrate and the organic coating (such as paint, powder coating), improving adhesion and weather resistance.

[0081] Process steps

[0082] Preparation of the silane solution: Dilute the silane coupling agent (such as γ-aminopropyltriethoxysilane) in deionized water (containing a small amount of ethanol for solubilization), pH = 4 - 6 (adjusted with acetic acid), concentration 0.5% - 2%.

[0083] Surface treatment: Impregnation, spraying or roll coating: The silane molecules hydrolyze to form -Si-OH groups, which condense with the hydroxyl groups (-OH) on the metal surface to form covalent bonds (Si-O-Me). At the same time, the organic groups at the other end (such as amino groups and epoxy groups) react with the subsequent coating. The time is 30 seconds to 2 minutes to ensure complete wetting of the surface.

[0084] Drying and curing: Air drying at room temperature for 10 - 30 minutes, or low-temperature baking (80 - 120 °C, 5 - 10 minutes) to promote the polycondensation between silane molecules to form a network structure.

[0085] In some embodiments, the pattern layer is transferred to the substrate layer via a thermal transfer process through a transfer film. In the transfer process, the temperature of the silicone roller is 180 - 230 °C, the pressure is 0.5 - 1.5 MPa, and the speed of the silicone roller is 0.5 - 3 m / min.

[0086] In some embodiments, the substrate of the thermal transfer film is a PET film, and the film thickness is 20 - 30 μm. The PET film has a release layer, a pattern layer, and an adhesive layer structure.

[0087] As Figure 2 shown, the thermal transfer process can accurately transfer the pattern on the PET film to the substrate completely. The PET film with a thickness of 20 - 30 μm is thin and uniform, ensuring that the pattern does not deform or shift during transfer. The release layer design enables the pattern layer to be separated from the film material smoothly and transferred, ensuring that the pattern details are clearly presented. Three-dimensional patterns formed by multi-level intaglio printing, including textures composed of different ink layers in the bottom layer, middle layer, and surface layer, can be accurately replicated onto the substrate, improving the pattern production accuracy and efficiency.

[0088] The adhesive layer of the PET film plays a key role during transfer. It binds tightly to the metal substrate, enabling the pattern to adhere firmly. The adhesive layer material and process are optimized to ensure a high bonding strength between the pattern layer and the substrate. During the subsequent processing, transportation, and use of the metal panel, the pattern is not easily peeled off, cracked, or delaminated, ensuring the long-term stability of the pattern and extending the service life of the product.

[0089] The thermal transfer process in combination with the PET film structure provides a broad space for pattern design. The good flexibility and chemical stability of the PET film enable various inks to be printed on its surface, achieving diverse pattern effects. Multi-level intaglio printing combined with different inks can produce rich patterns such as imitation wood grain, imitation stone grain, and 3D stereoscopic textures, meeting consumers' diverse demands for the appearance of metal panels and enhancing the product's decorative property and market competitiveness.

[0090] The thermal transfer process eliminates the need for complex printing operations directly on the metal substrate, reducing the requirements for expensive printing equipment and special printing environments, as well as the costs of production equipment and the demands for production sites. Meanwhile, the PET film can be recycled, the release layer material is environmentally friendly, and there is less waste and pollutants generated during the entire transfer process.

[0091] The release layer of the thermal transfer film usually uses silicone materials such as silicone resin and silicone rubber. These materials endow the release layer with a series of properties, enabling it to play a crucial role in the thermal transfer process:

[0092] The molecular structure of silicone materials gives them an extremely low surface energy, generally between 20 and 24 dynes / cm. This property makes the adhesion force between the pattern layer and the release layer much smaller than the adhesion force between the pattern layer and the substrate to be transferred. During the thermal transfer process, when a certain temperature and pressure are applied, the pattern layer can smoothly detach from the release layer and transfer to the surface of substrates such as metal panels, avoiding the occurrence of pattern residue or incomplete transfer.

[0093] The thermal transfer process often needs to be carried out under certain temperature conditions. Silicone materials have excellent thermal stability and can withstand the temperatures required for thermal transfer (usually the temperature of the thermal transfer silicone roller is 180 - 230 °C) without decomposition, carbonization, or other chemical changes. This ensures the stable performance of the release layer during the thermal transfer process and guarantees the quality and efficiency of the transfer.

[0094] Silicone materials have stable chemical properties and are not easily chemically reactive with the ink in the pattern layer, the adhesive in the bonding layer, or the metal panel substrate. This enables the release layer not to have an adverse impact on the performance of other layers during the storage and use of the thermal transfer film, ensuring the overall stability and reliability of the thermal transfer film.

[0095] In some embodiments, the present application provides a refrigerator comprising the metal panel described in the above embodiments.

[0096] The pattern layer formed by using multi-level intaglio printing and multi-pass overprinting techniques has rich layering and three-dimensionality. The bottom UV-cured ink layer lays the foundation texture. The middle epoxy resin ink layer with glass beads and the top elastic ink layer containing organosilicon-modified polyurethane cooperate with each other to present realistic diverse textures such as imitation wood grain and imitation stone grain, greatly enhancing the overall aesthetics of the refrigerator, meeting consumers' demands for the personalization and high-end of the refrigerator appearance, and making it more competitive in the market. The glass beads in the middle layer enhance the surface roughness, and the organosilicon-modified polyurethane elastic ink on the surface layer gives the panel a soft and elastic touch, forming a 3D stereoscopic texture touch. When users touch the refrigerator door body, they can feel the unique texture, saying goodbye to the monotonous touch of traditional refrigerator panels, and enhancing the pleasure during use and the quality sense of the product. The cold-rolled steel plate is used as the base material with a thickness of 0.4 - 0.55 mm, ensuring the strength and rigidity of the panel, enabling the refrigerator door body to withstand collisions and frictions during daily use. The bonding layer uses hot melt adhesive with a thickness of 10 - 30 μm, ensuring the tight combination of the pattern layer and the base material and being not easy to fall off. At the same time, the characteristics of each ink layer in the pattern layer also contribute to improving durability. The bottom UV-cured ink and the middle epoxy resin ink have good abrasion resistance, and the top elastic ink has weather resistance and chemical corrosion resistance, effectively resisting the erosion of oil stains, cleaning agents, etc. in the kitchen and extending the service life of the refrigerator.

[0097] As can be seen from the above embodiments, the present application provides a metal panel and a refrigerator. The metal panel sequentially includes from top to bottom: a pattern layer, a bonding layer, and a base material layer; the base material layer is a cold-rolled steel plate with a thickness of 0.4 - 0.55 mm; the bonding layer is a hot melt adhesive layer with a thickness of 10 - 30 μm; the pattern layer is transferred to the base material layer through a heat transfer process; the pattern layer adopts a multi-level intaglio printing technique to form a three-dimensional ink layer through multiple repeated overprinting; the pattern layer includes a bottom pattern layer, a middle pattern layer, and a top layer; the bottom pattern layer is a UV-cured ink layer, the middle pattern layer is an epoxy resin ink layer with glass beads added, and the top layer is an elastic ink layer containing organosilicon-modified polyurethane; the thickness of the pattern layer is 120 - 200 μm. The pattern layer forms a three-dimensional ink layer through multiple repeated overprinting by using a multi-level intaglio printing technique, and the middle epoxy resin ink layer with glass beads added and the top elastic ink layer containing organosilicon-modified polyurethane cooperate with each other. The glass beads enhance the surface roughness and layering, and the organosilicon-modified polyurethane elastic ink gives the panel a soft and elastic touch, making the panel have a 3D stereoscopic texture touch as a whole, greatly improving the texture of the panel and meeting users' demands for high touch.

[0098] For the similar parts between the embodiments provided in this application, reference can be made to each other. The specific embodiments provided above are only several examples under the general concept of this application and do not constitute a limitation on the protection scope of this application. For those skilled in the art, any other embodiments extended based on the solution of this application without creative efforts fall within the protection scope of this application.

Claims

1. A metal panel, characterized in that: The metal panel is used for a refrigerator, and the metal panel includes, from top to bottom, a pattern layer, a bonding layer and a substrate layer; the substrate layer is a cold-rolled steel plate, and the thickness of the substrate layer is 0.4-0.55 mm; the bonding layer is a hot-melt adhesive layer, and the thickness of the bonding layer is 10-30 μm; the pattern layer is transferred to the substrate layer by a thermal transfer process; The pattern layer adopts multi-stage gravure printing technology to form a three-dimensional ink layer through repeated overprinting; the pattern layer includes a bottom pattern layer, a middle pattern layer and a surface layer; the bottom pattern layer is a UV-curable ink layer, the middle pattern layer is an epoxy resin ink layer with glass beads added, and the surface layer is an elastic ink layer containing silicone-modified polyurethane; the thickness of the pattern layer is 120 to 200 μm.

2. The metal panel according to claim 1, characterized in that: The UV curing ink viscosity of the bottom pattern layer is 2500-3000 cps, and the thickness of the bottom pattern layer is 15±2 μm.

3. The metal panel according to claim 2, characterized in that: The glass beads in the middle pattern layer have a particle size of 5 to 8 μm and a stacking height of 30 to 50 μm.

4. The metal panel according to claim 1, characterized in that: The local protrusions of the surface layer are 20 to 120 μm.

5. The metal panel according to claim 1, characterized in that: The adhesive used in the bonding layer is one of ethylene-vinyl acetate copolymer, thermoplastic polyurethane elastomer or polyamide.

6. The metal panel according to claim 1, characterized in that: The surface roughness of the substrate layer is Ra≤0.1 μm, the surface tension is ≥38 dynes, the silane film thickness is 200-500 nm, and the film layer adhesion is level 0.

7. The metal panel according to claim 6, characterized in that: The substrate layer is obtained through three-step pretreatment of electrolytic degreasing, nano-ceramicization and silane coupling.

8. The metal panel according to claim 1, characterized in that: The pattern layer is transferred to the substrate layer via a transfer film through a thermal transfer process. In the transfer process, the temperature of the silicone roller is 180-230° C., the pressure is 0.5-1.5 MPa, and the speed of the silicone roller is 0.5-3 m / min.

9. The metal panel according to claim 1, characterized in that: The thermal transfer film substrate is a PET film with a film thickness of 20 to 30 μm. The PET film has a release layer, a pattern layer and an adhesive layer structure.

10. A refrigerator, characterized in that: A metal panel comprising any one of claims 1 to 9.

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