Colorful holographic heat transfer film and preparation process thereof

Abstract

The invention discloses a color holographic heat transfer film and a preparation process thereof, and relates to the technical field of transfer film preparation, the color holographic heat transfer film comprises a transfer film main body, the transfer film main body comprises a holographic layer, a transparent layer and a transparent layer from top to bottom in sequence, and the holographic layer is formed by compounding holographic resin and a holographic micro-nano structure material; the color layer is formed by mixing an organic pigment and an inorganic pigment; the heat transfer printing adhesive layer is composed of a hot melt adhesive and a cross-linking agent; the transfer printing film continuously penetrates through the treatment groove along a main shaft-guide shaft path, the clamping shaft is driven by the adjusting bolt to form an adjustable gap with the main shaft, it is ensured that the film surface tension is constant, the film surface is in full contact with treatment liquid, and uniform coarsening is achieved; according to the process, the uniformity of the treatment liquid is continuously kept during operation, stable microcosmic roughness is given to the film surface, adhesion of the pigment and the adhesive layer is remarkably enhanced, and the problems of pattern falling, edge warping and optical performance reduction are thoroughly solved.

Description

Technical Field

[0001] This invention relates to the field of transfer film preparation technology, specifically to color holographic thermal transfer film and its preparation process. Background Technology

[0002] Heat transfer printing can create brightly colored and richly textured holographic patterns on the surfaces of various substrates such as plastics, fabrics, and wood. As a result, it is widely used in the production of gift packaging, clothing printing, exhibition displays, and various decorative panels.

[0003] In actual production, color holographic heat transfer film usually uses polyester or polypropylene film as base film. Because these base films have relatively smooth surfaces and low surface energy, the adhesion between the coating and the base film is weak after the pigment layer and adhesive layer are directly coated. This makes the pattern easy to fall off when scratched by external force. During long-term use, especially under environmental conditions such as exposure to sunlight, high temperature and humidity or soaking in sweat, the edges of the pattern are prone to warping and blistering, and the color gradually fades, affecting the appearance and service life of the product.

[0004] To address the issue of insufficient adhesion, some manufacturers have increased the amount of coupling agent in their adhesives to improve the adhesion of the patterns by enhancing the interfacial bonding strength. While this method can indeed achieve some results in the short term, over time, excessive coupling agent tends to migrate to the surface, causing the graphic surface to become hazy and lose gloss. Furthermore, the film rolls are prone to sticking together when stored at high temperatures, making unwinding difficult and impacting subsequent processing efficiency. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a color holographic thermal transfer film and its preparation process, thus solving the problems mentioned in the background art.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a color holographic thermal transfer film and its preparation process, comprising a transfer film body, which, from top to bottom, includes: A holographic layer, wherein the holographic layer is composed of holographic resin and holographic micro / nano structure materials; A colored layer, wherein the colored layer is composed of a mixture of organic and inorganic pigments; A heat transfer adhesive layer, wherein the heat transfer adhesive layer is composed of hot melt adhesive and crosslinking agent; The base film layer is made of one of polyester film, polypropylene film or polyimide film.

[0007] Preferably, the holographic layer and the color layer are connected by an interlayer composite material, which is a transparent polymer film.

[0008] Preferably, the surface of the holographic layer has a micro-nano structure texture, and the periodic arrangement of the micro-nano structure texture forms a holographic pattern.

[0009] Preferably, the organic and inorganic pigments in the color layer are distributed in alternating layers, the thickness of the alternating layers is from micrometers to micrometers, and the number of alternating layers is from one to three. This structural design allows the color layer to maintain color vibrancy while having better weather resistance and stability, thus improving the durability of the color layer compared with the prior art.

[0010] Preferably, the heat transfer adhesive layer includes multiple adhesive layer units, each composed of hot melt adhesive and crosslinking agent in different proportions. The adhesive layer units are distributed in a gradient within the heat transfer adhesive layer, with the hot melt adhesive content gradually increasing from the base film layer towards the holographic layer. This structural design can improve the adhesion during the transfer process and the stability after transfer, providing more reliable transfer performance compared to existing technologies.

[0011] Preferably, it includes the following steps: S01: Provide a base film layer, said base film layer being made of one or more of polyester film, polypropylene film or polyimide film; S02: The base film layer is passed through a treatment device containing a treatment liquid, so that the surface of the base film layer comes into contact with the treatment liquid for surface roughening treatment. The treatment liquid mainly contains acidic or alkaline components, which are used to change the microstructure of the base film layer surface and enhance the adhesion of pigments to the base film layer surface. The treatment time in the tank is seconds, and then drying treatment is performed. S03: A thermal transfer adhesive layer, a color layer and a holographic layer are sequentially coated on a base film layer that has undergone surface roughening treatment. The thermal transfer adhesive layer is composed of hot melt adhesive and crosslinking agent, the color layer is composed of organic pigments and inorganic pigments, and the holographic layer is composed of holographic resin and holographic micro-nano structure materials. S04: Post-process the holographic layer to form a micro-nano structure texture on its surface. The periodic arrangement of the micro-nano structure texture forms a holographic pattern. The holographic pattern can present different color changes and visual effects at different angles.

[0012] Preferably, the processing device includes a processing tank, inside which a guiding mechanism is provided for guiding the transfer film body. The processing tank is filled with a processing liquid, and two guide shafts are provided at the top of the processing tank. The two guide shafts are connected to a drying mechanism, which is installed outside the processing tank. Tension adjustment mechanisms are installed at both ends of the processing tank. The processing tank, through the cooperation of the built-in guiding mechanism and the tension adjustment mechanisms at both ends, allows the transfer film to pass smoothly through the processing liquid under constant tension, ensuring uniform roughening. The double guide shafts at the top of the tank directly introduce the film into the integrated drying mechanism, achieving immediate drying after immersion, avoiding processing liquid residue or secondary contamination, while shortening the process and reducing thermal deformation, thereby steadily improving the adhesion between the subsequent pigment and the base film.

[0013] Preferably, the tension adjustment mechanism includes a mounting frame, which is connected to the processing groove by bolts and to a limiting frame by bolts. The limiting frame has a sliding groove inside, and this groove is slidably connected to a sliding rod. One end of the sliding rod is fixedly connected to a lifting frame, and the lifting frame is slidably connected to the limiting rod inside. A spring is fitted onto the outside of the limiting rod, and one bottom end of the limiting rod is fixedly connected to the mounting frame. The tension adjustment mechanism utilizes a floating frame composed of a spring and a sliding rod to automatically move the lifting frame up and down according to changes in membrane tension. This absorbs stress caused by speed fluctuations or membrane thickness differences in real time, maintaining constant tension in the processing section, preventing relaxation and wrinkling or excessive stretching, and ensuring consistent contact time between the roughening liquid and the membrane surface. This results in a uniform and reproducible micro-rough structure, providing a stable and reliable anchoring foundation for subsequent coatings.

[0014] Preferably, the guiding mechanism includes a main shaft located inside the treatment tank, a stirring shaft positioned below the main shaft, and blades on the surface of the stirring shaft. Both the main shaft and the stirring shaft are rotatably connected to a lifting frame. Drive wheels are mounted at the ends of both the main shaft and the stirring shaft, and these drive wheels are connected to each other via a drive belt. A clamping shaft is located on one side of the main shaft, and both ends of the clamping shaft are rotatably connected to a sliding frame. An adjusting bolt is rotatably connected inside the clamping shaft, and the sliding frame is slidably connected to the lifting frame. The guiding mechanism integrates the main shaft, the stirring shaft, and the clamping shaft into the same lifting frame. When the membrane material moves forward, it drives the main shaft to rotate, which in turn drives the blades of the stirring shaft to continuously agitate the treatment liquid via the drive wheels, preventing sedimentation and concentration stratification.

[0015] Preferably, the drying mechanism includes a guide hood installed outside the processing tank, a U-shaped channel between the guide hood and the processing tank, a top plate on top of the guide hood, an electric heating wire installed inside the guide hood and electrically connected to an external power source, an air outlet at the top of the other end of the guide hood, two strip-shaped slots on top of the top plate with scraper strips inside, and a fan embedded inside the top plate for blowing external air into the guide hood; the drying mechanism forms a U-shaped channel between the guide hood and the processing tank, and the electric heating wire drives the fan... The supplied air, after being heated, flows around the outer wall of the treatment tank along the channel, first gently preheating the treatment liquid in the tank, so that the temperature of the membrane surface gradually increases before leaving the liquid, avoiding sudden cooling and heating; then, the hot air is blown directly from the air outlet onto the just lifted membrane surface, quickly carrying away the residual liquid film on the surface, and the scraper simultaneously removes water mechanically, realizing gradient drying from low temperature to high temperature, preventing thermal deformation of the membrane material, shortening the drying time, and improving the interfacial bonding stability between the roughening layer and the subsequent coating; all electrical components mentioned in this article are connected to an external main controller and 220V mains power, and the main controller can be a conventional known device such as a computer for control.

[0016] This invention provides a color holographic thermal transfer film and its preparation process. It has the following beneficial effects: The transfer film continuously passes through the processing tank along the main shaft-guide shaft path. The clamping shaft, driven by adjusting bolts, forms an adjustable gap with the main shaft, ensuring constant film surface tension and full contact with the processing liquid, achieving uniform roughening. The roughened layer significantly increases the effective contact area between the pigment and the adhesive layer, improving adhesion and durability, while reducing surface reflection and scattering, and improving optical performance. The forward movement of the film material drives the main shaft to rotate, which, via a synchronous transmission wheel and transmission belt, drives the stirring shaft to continuously agitate the processing liquid, preventing solute sedimentation and concentration gradients, maintaining consistent roughening, thereby stabilizing the bonding strength of subsequent coatings and extending the service life of the transfer film. During operation, this process continuously maintains uniform processing liquid and imparts stable micro-roughness to the film surface, significantly enhancing pigment and adhesive layer adhesion and completely eliminating problems such as pattern detachment, edge warping, and decreased optical performance. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the processing device structure of the present invention; Figure 2 This is a side view of the structure of the present invention; Figure 3 This is a top view of the structure of the present invention; Figure 4 This is a schematic diagram of the rear view structure of the present invention; Figure 5 This is a schematic diagram of the fan structure of the present invention; Figure 6 This is a schematic diagram of the guiding mechanism structure of the present invention; Figure 7 This is a schematic diagram of the guide shaft structure of the present invention; Figure 8 For the present invention Figure 7 Enlarged structural diagram at point A in the middle; Figure 9 This is a schematic diagram of the main structure of the transfer film of the present invention.

[0018] In the diagram, 1. Transfer film body; 101. Holographic layer; 102. Color layer; 103. Thermal transfer adhesive layer; 104. Base film layer; 105. Interlayer composite material; 106. Micro-nano structure texture; 2. Guiding mechanism; 201. Main shaft; 202. Stirring shaft; 203. Transmission wheel; 204. Transmission belt; 205. Sliding frame; 206. Adjusting bolt; 207. Clamping shaft; 3. Drying mechanism; 301. Flow guide; 302. Electric heating wire; 303. Top plate; 304. Fan; 305. Scraper; 4. Tension adjustment mechanism; 401. Mounting frame; 402. Limiting frame; 403. Slide rod; 404. Lifting frame; 405. Limiting rod; 406. Spring; 5. Guide shaft; 6. Processing tank. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1: Please refer to Figure 1-9 This invention provides a technical solution: a color holographic thermal transfer film, comprising a transfer film body 1, which, from top to bottom, includes: a holographic layer 101, which is composed of holographic resin and holographic micro / nano structure materials; a color layer 102, which is composed of organic pigments and inorganic pigments; and a thermal transfer adhesive layer 103, which is composed of hot melt adhesive and crosslinking agent. The base film layer 104 is made of one of polyester film, polypropylene film, or polyimide film. The holographic layer 101 and the color layer 102 are connected by an interlayer composite material 105, which is a transparent polymer film. The surface of the holographic layer 101 has micro-nano structure textures 106, and the periodic arrangement of the micro-nano structure textures 106 forms a holographic pattern. The organic and inorganic pigments in the color layer 102 are distributed in alternating layers, the thickness of which is 1 micrometer to 10 micrometers, and the number of alternating layers is 5 to 20. The heat transfer adhesive layer 103 includes multiple adhesive layer units, which are composed of hot melt adhesive and crosslinking agent in different proportions. The adhesive layer units are distributed in a gradient in the heat transfer adhesive layer 103, and the content of the hot melt adhesive gradually increases from the base film layer 104 to the holographic layer 101. Before the base film layer 104 enters the coating process, its surface is rapidly roughened with a treatment solution to form a uniformly distributed micro-uneven texture. This roughened skeleton forms a continuous anchor with the subsequent gradient hot melt adhesive layer: the adhesive layer penetrates into the pits to complete the anchoring and gradually softens towards the color layer 102 to provide a buffer. At the same time, the alternating pigment structures in the color layer 102 are fully interlocked by the rough surface, and the interlayer composite material 105 tightly adheres the holographic micro-nano texture to the color layer 102. The whole structure forms a triple effect of mechanical locking, chemical bonding and interlayer coupling, which significantly improves the bonding strength between the pigment and the base film and completely avoids the problems of pattern peeling, edge warping and subsequent weathering failure caused by insufficient interfacial bonding of traditional smooth base films.

[0021] Example 2: Please refer to Figure 1-9 This invention provides a technical solution: a process for preparing a color holographic thermal transfer film, comprising the following steps: S01: Provide a base film layer 104, which is made of one or more of polyester film, polypropylene film or polyimide film; S02: The base film layer 104 is passed through a treatment device containing a treatment liquid, so that the surface of the base film layer 104 comes into contact with the treatment liquid for surface roughening treatment. The treatment liquid mainly contains acidic or alkaline components, which are used to change the microstructure of the surface of the base film layer 104 and enhance the adhesion of pigments to the surface of the base film layer 104. The treatment time in the tank is 10 seconds, and then drying treatment is performed. S03: A thermal transfer adhesive layer 103, a color layer 102, and a holographic layer 101 are sequentially coated on a base film layer 104 that has undergone surface roughening treatment. The thermal transfer adhesive layer 103 is composed of hot melt adhesive and crosslinking agent, the color layer 102 is composed of organic pigments and inorganic pigments, and the holographic layer 101 is composed of holographic resin and holographic micro-nano structure materials. S04: Post-process the holographic layer 101 to form a micro-nano structure texture 106 on its surface. The periodic arrangement of the micro-nano structure texture 106 forms a holographic pattern. The holographic pattern can present different color changes and visual effects at different angles.

[0022] The processing device includes a processing tank 6, inside which is a guiding mechanism 2 for guiding the transfer film body 1. The processing tank 6 is filled with a processing liquid. Two guide shafts 5 are located at the top of the processing tank 6 and are connected to a drying mechanism 3. The drying mechanism 3 is installed outside the processing tank 6. Tension adjustment mechanisms 4 are installed at both ends of the processing tank 6. The tension adjustment mechanism 4 includes a mounting frame 401, which is connected to the processing tank 6 by bolts and to a limiting frame 402 by bolts. The limiting frame 402 has a sliding groove inside, and this groove is slidably connected to a sliding rod 403. One end of the sliding rod 403 is fixedly connected to a lifting frame 404. The lifting frame 404 is connected to the limiting rod 403 inside. 05 Sliding connection, the limiting rod 405 is externally fitted with a spring 406, and one end of the limiting rod 405 is fixedly connected to the mounting frame 401; the guide mechanism 2 includes a main shaft 201, the main shaft 201 is located inside the processing tank 6, a stirring shaft 202 is provided below the main shaft 201, the surface of the stirring shaft 202 is provided with blades, the main shaft 201 and the stirring shaft 202 are both rotatably connected to the lifting frame 404, the ends of the main shaft 201 and the stirring shaft 202 are both equipped with transmission wheels 203, the transmission wheels 203 are connected to each other by transmission belt 204, a clamping shaft 207 is provided on one side of the main shaft 201, the two ends of the clamping shaft 207 are rotatably connected to the sliding frame 205, the inside of the clamping shaft 207 is rotatably connected to the adjusting bolt 206, and the sliding frame 205 is slidably connected to the lifting frame 404; In this embodiment, the transfer film is prepared by passing it around the main shaft 201 and guide shaft 5, allowing it to pass through the processing tank 6. Tightening the adjusting bolt 206 causes the sliding frame 205 to move the clamping shaft 207 towards the main shaft 201, thus clamping the transfer film between the clamping shaft 207 and the main shaft 201. As the transfer film passes through the processing tank 6, it comes into contact with the processing solution inside, resulting in a roughened surface. This surface roughening significantly improves the adhesion of pigments and adhesive layers, enhancing transfer quality and durability, while also optimizing optical properties, thereby improving the overall performance and usability of the transfer film. Lifespan; Under the pull of external equipment, the transfer film can drive the main shaft 201 to rotate, and the main shaft 201 can drive the stirring shaft 202 to rotate through the transmission wheel 203 and the transmission belt 204. While the stirring shaft 202 rotates, it can stir the treatment liquid inside the treatment tank 6, which helps to avoid the precipitation phenomenon in the treatment liquid inside the treatment tank 6, thus helping to ensure the stability of the treatment liquid in the transfer film treatment; Under the action of the spring 406, it can elastically press the lifting frame 404 downward, and the lifting frame can press the transfer film through the main shaft 201, so that the surface of the transfer film can maintain good tension, which helps to maintain good tension on the surface of the transfer film and enable it to contact the treatment liquid well.

[0023] Example 3: Please refer to Figure 1-9 This invention provides a technical solution: a process for preparing a color holographic heat transfer film. The drying mechanism 3 includes a flow guide 301, which is installed outside the processing tank 6. A U-shaped channel is provided between the flow guide 301 and the processing tank 6. A top plate 303 is installed on the top of the flow guide 301. An electric heating wire 302 is installed inside the flow guide 301 and is electrically connected to an external power source. An air outlet is provided at the top of the other end of the flow guide 301. Two strip-shaped slots are provided on the top of the top plate 303, and scraper strips 305 are provided inside the two strip-shaped slots on the top of the top plate 303. A fan 304 is embedded inside the top plate 303 to blow external air into the flow guide 301. In this embodiment, the fan 304 allows external air to be blown into the U-shaped channel inside the flow guide shroud 301. Then, under the action of the electric heating wire 302, the air blown into the flow guide shroud 301 is heated. When the heated air flows through the U-shaped channel inside the flow guide shroud 301, it can heat the processing tank 6, thereby heating the processing liquid inside the processing tank 6. The processing liquid can preheat the transfer film body 1. The heated air inside the flow guide shroud 301 will be discharged from the other end and blown towards the transfer film output from the processing tank 6, so that the transfer film can be dried under the action of hot air. At the same time, the preheating of the processing liquid can prevent the transfer film from deforming due to a sudden increase in temperature difference during drying.

[0024] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the scope of the invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

[0025] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A color holographic thermal transfer film, characterized in that: Including the transfer film body (1), from top to bottom, it includes: A holographic layer (101) is composed of holographic resin and holographic micro / nano structure materials; A colored layer (102) is composed of a mixture of organic and inorganic pigments; A heat transfer adhesive layer (103) is composed of hot melt adhesive and a crosslinking agent; The base film layer (104) is made of one of polyester film, polypropylene film or polyimide film.

2. The color holographic thermal transfer film according to claim 1, characterized in that: The holographic layer (101) and the color layer (102) are connected by an interlayer composite material (105), which is a transparent polymer film.

3. The color holographic thermal transfer film according to claim 2, characterized in that: The surface of the holographic layer (101) has micro-nano structure textures (106), and the periodic arrangement of the micro-nano structure textures (106) forms a holographic pattern.

4. The color holographic thermal transfer film according to claim 3, characterized in that: The organic and inorganic pigments in the color layer (102) are distributed in alternating layers with a thickness of 1 micrometer to 10 micrometers.

5. The color holographic thermal transfer film according to claim 4, characterized in that: The heat transfer adhesive layer (103) includes multiple adhesive layer units, each of which is composed of hot melt adhesive and crosslinking agent in different proportions. The adhesive layer units are distributed in a gradient in the heat transfer adhesive layer (103), and the content of the hot melt adhesive in the gradient distribution gradually increases from the base film layer (104) to the holographic layer (101).

6. The preparation process of the color holographic thermal transfer film according to claim 5, characterized in that: Includes the following steps: S01: Provide a base film layer (104), said base film layer (104) being made of one or more of polyester film, polypropylene film or polyimide film; S02: The base film layer (104) is passed through a treatment device containing a treatment liquid, so that the surface of the base film layer (104) comes into contact with the treatment liquid for surface roughening treatment. The treatment liquid mainly contains acidic or alkaline components, which are used to change the microstructure of the surface of the base film layer (104) and enhance the adhesion of pigments to the surface of the base film layer (104). The treatment time in the tank is 10 seconds, and then the drying treatment is performed. S03: A thermal transfer adhesive layer (103), a color layer (102), and a holographic layer (101) are sequentially coated on a base film layer (104) after surface roughening treatment. The thermal transfer adhesive layer (103) is composed of hot melt adhesive and crosslinking agent, the color layer (102) is composed of organic pigments and inorganic pigments, and the holographic layer (101) is composed of holographic resin and holographic micro-nano structure materials. S04: Post-process the holographic layer (101) to form a micro-nano structure texture (106) on its surface, and the periodic arrangement of the micro-nano structure texture (106) forms a holographic pattern.

7. The preparation process of the color holographic thermal transfer film according to claim 6, characterized in that: The processing device includes a processing tank (6), inside which a guide mechanism (2) is provided. The guide mechanism (2) is used to guide the transfer film body (1). The processing tank (6) is filled with a processing liquid. A guide shaft (5) is provided at the top of the processing tank (6). There are two guide shafts (5). The two guide shafts (5) are connected to a drying mechanism (3). The drying mechanism (3) is installed outside the processing tank (6). Tension adjustment mechanisms (4) are installed at both ends of the processing tank (6).

8. The preparation process of the color holographic thermal transfer film according to claim 7, characterized in that: The tension adjustment mechanism (4) includes a mounting frame (401), which is connected to the processing groove (6) by bolts. The mounting frame (401) is also connected to the limiting frame (402) by bolts. The limiting frame (402) has a sliding groove inside, and the sliding groove inside the limiting frame (402) is slidably connected to the sliding rod (403). One end of the sliding rod (403) is fixedly connected to the lifting frame (404), and the lifting frame (404) is slidably connected to the limiting rod (405). The limiting rod (405) is fitted with a spring (406) on the outside, and one bottom end of the limiting rod (405) is fixedly connected to the mounting frame (401).

9. The preparation process of the color holographic thermal transfer film according to claim 8, characterized in that: The guiding mechanism (2) includes a main shaft (201), which is located inside the processing tank (6). A stirring shaft (202) is provided below the main shaft (201). The surface of the stirring shaft (202) is provided with blades. The main shaft (201) and the stirring shaft (202) are rotatably connected to the lifting frame (404). The ends of the main shaft (201) and the stirring shaft (202) are equipped with transmission wheels (203). The transmission wheels (203) are connected to each other by a transmission belt (204). A clamping shaft (207) is provided on one side of the main shaft (201). The two ends of the clamping shaft (207) are rotatably connected to the sliding frame (205). The inside of the clamping shaft (207) is rotatably connected to the adjusting bolt (206). The sliding frame (205) is slidably connected to the lifting frame (404).

10. The preparation process of the color holographic thermal transfer film according to claim 9, characterized in that: The drying mechanism (3) includes a flow guide hood (301), which is installed outside the processing tank (6). A U-shaped channel is provided between the flow guide hood (301) and the processing tank (6). A top plate (303) is installed on the top of the flow guide hood (301). An electric heating wire (302) is installed inside the flow guide hood (301). The electric heating wire (302) is electrically connected to an external power source. An air outlet is provided at the top of the other end of the flow guide hood (301). Two strip-shaped slots are provided on the top of the top plate (303). Scrapers (305) are provided inside the two strip-shaped slots on the top of the top plate (303). A fan (304) is embedded inside the top plate (303) to blow external air into the flow guide hood (301).

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