Thermal transfer printing process and thermal transfer printing device for curved surface decoration spraying

Abstract

The invention discloses a heat transfer printing process and a heat transfer printing device for curved surface decoration spraying, and relates to the technical field of heat transfer printing, and the heat transfer printing process comprises the following steps: step 1, firstly cleaning dirt on the surface of a workpiece; secondly, the workpiece is preheated; thirdly, ink capable of being subjected to heat sublimation is printed on the heat transfer printing carrier through an ink-jet printer according to the designed pattern; fourthly, after the to-be-preheated workpiece is cooled, the corresponding heat transfer printing carrier is attached to the workpiece in a covering mode through a worker, and a heat transfer printing device is selectively used for vacuumizing according to the shape or the heat-resisting temperature of the workpiece; 5, according to different workpiece application scenes and different heat-resistant temperatures, a worker can specifically adjust the temperature and time when the hot-air blower heats the heat transfer printing carrier; and 6, after the workpiece subjected to transfer printing is cooled to the room temperature, a worker can tear off the heat transfer printing carrier, and then the outer surface of a transfer printing layer of the workpiece is coated with a protective film.

Description

Technical Field

[0001] The invention relates to the technical field of thermal transfer, and in particular to a thermal transfer process and a thermal transfer device for curved surface decorative spraying. Background Art

[0002] In the field of workpiece spraying, two-color spraying often uses two processes. One is an offline process, in which the areas to be retained are manually masked in a special factory similar to a "workshop", and then sprayed, baked, and finally the mask is removed. This process is closer to handicraft rather than an industrial process. The other is a process derived from the mainstream production process. This process also involves manual masking operations, but allows the use of automated equipment for spraying. The efficiency of this method is relatively higher than the offline process.

[0003] However, the production efficiency of the two mainstream spraying processes is relatively low. In particular, high-temperature baking is required during the spraying process, so the energy consumption during spraying is high and the VOC emissions are also large, which is not conducive to achieving the current goal of energy conservation and emission reduction. Summary of the invention

[0004] In order to overcome the above technical problems, the object of the present invention is to provide a thermal transfer process and a thermal transfer device for curved surface decorative spraying.

[0005] The purpose of the present invention can be achieved by the following technical solution: A thermal transfer process for curved surface decorative spraying, comprising the following steps:

[0006] Step 1: First, clean the dirt on the surface of the workpiece;

[0007] Step 2: preheat the workpiece;

[0008] Step 3: Print the sublimation ink onto the thermal transfer carrier according to the designed pattern using an inkjet printer;

[0009] Step 4: After the preheated workpiece cools down, the staff will fit the corresponding thermal transfer carrier onto the workpiece and selectively use the thermal transfer device to evacuate the workpiece according to the shape or heat-resistant temperature of the workpiece;

[0010] Step 5. According to different application scenarios of the workpiece and different heat-resistant temperatures, the staff can adjust the temperature and time when the hot air blower heats the thermal transfer carrier;

[0011] Step 6: After the workpiece has cooled to room temperature, the staff can tear off the thermal transfer carrier and then apply a protective film on the surface of the workpiece transfer layer.

[0012] As a further solution of the present invention: the specific processing steps of step one are: using alcohol and ketone organic solvents to remove organic dirt such as oil, wax, resin, etc. on the surface of the workpiece coated with varnish or uncoated workpiece, and using deionized water to remove water-soluble stains and excess organic solvents.

[0013] As a further solution of the present invention: the alcohol and ketone organic solvents are ethanol and acetone.

[0014] As a further solution of the present invention: the specific processing steps of step 2 are: when preheating the workpiece to be transferred, the preheating temperature is controlled at 100-110 degrees Celsius, and the preheating time is controlled at 5-8 minutes.

[0015] As a further solution of the present invention: the specific processing process of step three is: adjust the corresponding inkjet volume according to different application scenarios of the workpiece, the inkjet volume of the thermal transfer carrier corresponding to the workpiece for external application is 150-170ml / ㎡, and the inkjet volume of the thermal transfer carrier corresponding to the workpiece for internal application is 100-130ml / ㎡.

[0016] As a further solution of the present invention: the specific processing process of step 4 is as follows: for the heat-resistant workpiece and the non-heat-resistant workpiece with a curved surface, the staff can attach the corresponding thermal transfer device to the workpiece and ensure that the thermal transfer device completely covers the thermal transfer carrier. At this time, the thermal transfer device is evacuated by a vacuum pump, and a pressure of 0.1-1 atmosphere is uniformly applied to the surface of the thermal transfer carrier through the deformation of the thermal transfer device, so that the thermal transfer carrier can be completely attached to the curved workpiece;

[0017] For flat heat-resistant workpieces and non-heat-resistant workpieces, workers do not need to attach the thermal transfer device to the workpiece.

[0018] As a further solution of the present invention: the specific processing process of step 5 is as follows: the heat-resistant workpiece used externally is first heated by a hot air gun to a temperature of 180-190 degrees Celsius for a heating time of 3 minutes for pre-transfer, and then the final transfer is performed at a heating temperature of 150-160 degrees Celsius for a heating time of 5 minutes;

[0019] For heat-resistant workpieces used internally, heat them with a hot air gun at a temperature of 180-200 degrees Celsius for 3-5 minutes for heating transfer;

[0020] For heat-sensitive workpieces, use a hot air gun to heat them to 150-160 degrees Celsius for 3 to 4 minutes for heating transfer.

[0021] As a further solution of the present invention: the protective film coated on the surface of the transfer layer is a low-temperature curing acrylic polyurethane varnish or a nano-ceramic material.

[0022] A thermal transfer device for curved surface decorative spraying comprises a flexible film, wherein an exhaust hole is provided at the bottom of the flexible film, a side sealing ring is provided at the outer edge of the bottom of the flexible film, and a transfer terminal connected to the exhaust hole is provided at the top of the flexible film.

[0023] As a further solution of the present invention: the flexible film and the side sealing ring are made of elastic heat-resistant materials, and the thickness of the flexible film is between 0.5 and 4 mm.

[0024] As a further solution of the present invention: the elastic heat-resistant material is polymethylvinylsiloxane.

[0025] Beneficial effects of the present invention:

[0026] 1. In the present invention, the spraying of automobiles is achieved through thermal transfer technology, which has high flexibility. Both inkjet printing and thermal transfer technology support personalized customization, can realize designs of different styles, have low cost, and are suitable for large or small batches of personalized customization. The film materials and inks used are mostly environmentally friendly materials with low heating temperature, low energy consumption, low VOC emissions, and are more environmentally friendly.

[0027] 2. In the present invention, the thermal transfer device can uniformly apply a pressure of 0.1-1 atmospheres to the surface of the thermal transfer carrier when vacuuming, so that the thermal transfer carrier is completely attached to the curved workpiece, ensuring the completeness of the thermal transfer carrier when attached, being able to adapt to various complex car body curved surfaces, ensuring seamless transfer of patterns, avoiding pattern deformation or deviation, and when the interior of the thermal transfer device is in a vacuum state, the thermal transfer carrier on the workpiece is in a vacuum environment at this time, and the sublimation point temperature of the ink in the thermal transfer carrier will be reduced, thereby being able to well meet the heat-intolerant nature of some workpieces during transfer. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will be further described below in conjunction with the accompanying drawings.

[0029] Figure 1 It is a schematic diagram of the thermal transfer process of the present invention;

[0030] Figure 2 It is a three-dimensional schematic diagram of the thermal transfer device in the present invention;

[0031] Figure 3 It is a three-dimensional schematic diagram of the side sealing ring in the present invention;

[0032] Figure 4 Schematic diagram of the cross section of the original workpiece paint coating (left) and the cross section of the workpiece paint coating after thermal sublimation transfer (right);

[0033] Figure 5It is a cross-sectional schematic diagram of the diffusion degree of the ink in the thermal transfer carrier in the varnish at the same temperature and different time in the present invention;

[0034] Figure 6 It is a schematic diagram of the relationship between the color concentration of the substrate after transfer, temperature and time in the present invention.

[0035] In the figure: 1. flexible film; 2. exhaust hole; 3. side sealing ring; 4. adapter terminal. DETAILED DESCRIPTION

[0036] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0037] like Figure 1-6 As shown, a thermal transfer process for curved surface decorative spraying includes the following steps:

[0038] Step 1: First, clean the dirt on the surface of the workpiece;

[0039] Step 2: preheat the workpiece;

[0040] Step 3: Use an inkjet printer to print the sublimation ink on the thermal transfer carrier according to the designed pattern;

[0041] Step 4: After the preheated workpiece cools down, the staff will fit the corresponding thermal transfer carrier onto the workpiece and selectively use the thermal transfer device to evacuate the workpiece according to the shape or heat-resistant temperature of the workpiece;

[0042] Step 5. According to different application scenarios of the workpiece and different heat-resistant temperatures, the staff can adjust the temperature and time when the hot air blower heats the thermal transfer carrier;

[0043] Step 6: After the workpiece has cooled to room temperature, the staff can tear off the thermal transfer carrier and then apply a protective film on the surface of the workpiece transfer layer.

[0044] In this embodiment, specifically, the workpiece is a complex curved workpiece used in transportation vehicles (such as automobiles, airplanes, ships, high-speed railways, etc.) to achieve functions such as aesthetics, corrosion resistance, wear resistance, and weather resistance, and the thermal transfer carrier is thermal transfer paper and thermal transfer film.

[0045] In this embodiment, specifically, the specific processing steps of step one are: using alcohol and ketone organic solvents to remove organic dirt such as oil, wax, resin, etc. on the surface of the workpiece coated with varnish or the workpiece without coating, and using deionized water to remove water-soluble stains and excess organic solvents. For workpieces used externally, special acrylic polyurethane varnish is generally used because of the special requirements of mechanical properties, weather resistance and UV resistance for external applications. For workpieces used internally, ordinary polyurethane varnish or polyester / TG IC, epoxy / polyester system is generally used. For workpieces without coating, the materials are ABS, PC, PP, PVC, etc.

[0046] In this embodiment, specifically, the alcohol and ketone organic solvents are ethanol and acetone. Ethanol and acetone are relatively low in price and have good cleaning effects, and are suitable for use in mass production lines.

[0047] In this embodiment, specifically, the specific processing steps of step 2 are: when preheating the workpiece to be transferred, the preheating temperature is controlled at 100-110 degrees Celsius, and the preheating time is controlled at 5-8 minutes. By preheating the workpiece, excess water or other solvents in the varnish / substrate can be effectively removed. Otherwise, after thermal transfer, due to the introduction of water-ink in the thermal transfer carrier, the original water or solvent cannot be released through the original gaps in the varnish, and bubbles are formed on the surface of the varnish under high pressure and high humidity.

[0048] In this embodiment, specifically, the specific processing process of step three is: adjust the corresponding inkjet amount according to different application scenarios of the workpiece, the inkjet amount of the thermal transfer carrier corresponding to the workpiece for external application is 150-170ml / ㎡, and the inkjet amount of the thermal transfer carrier corresponding to the workpiece for internal application is 100-130ml / ㎡, the ink is an aqueous ink, which contains water-based ink, dispersant, water, and surfactant in the sublimation thermal transfer carrier, according to the environment in which the workpiece is in different scenarios, by changing the inkjet amount, the thickness of the thermal transfer layer on the surface of the workpiece after subsequent thermal transfer is controlled. The environmental conditions of the workpiece for external application are relatively harsh when used, so the thickness of the thermal transfer layer is relatively large, which can effectively deal with aging. The thickness of the thermal transfer layer of the workpiece for internal application is also small, which can effectively save production costs.

[0049] In this embodiment, specifically, the specific processing process of step 4 is as follows: for the heat-resistant workpiece and the heat-resistant workpiece with a curved surface, the staff can attach the corresponding thermal transfer device to the workpiece, and ensure that the thermal transfer device completely covers the thermal transfer carrier. At this time, the thermal transfer device is evacuated by a vacuum pump, and a pressure of 0.1-1 atmospheres is uniformly applied to the surface of the thermal transfer carrier through the deformation of the thermal transfer device, so that the thermal transfer carrier can be completely attached to the curved workpiece. The pressure generated by the deformation of the thermal transfer device can form an extrusion on the area of ​​the thermal transfer carrier, so that the thermal transfer carrier can be completely attached to the surface of the curved workpiece, ensuring the completeness of the thermal transfer carrier when attached, and when the interior of the thermal transfer device is in a vacuum state, the thermal transfer carrier on the workpiece is in a vacuum environment at this time. When the pressure is reduced, the sublimation point temperature of the ink in the thermal transfer carrier will be reduced, thereby being able to well meet the heat-resistant nature of some workpieces during transfer;

[0050] For flat heat-resistant workpieces and non-heat-resistant workpieces, workers do not need to attach the thermal transfer device to the workpiece.

[0051] In this embodiment, specifically, the specific processing process of step 5 is: the heat-resistant workpiece used externally is first heated by a hot air gun to a temperature of 180-190 degrees Celsius for a heating time of 3 minutes for pre-transfer, and then the final transfer is performed at a heating temperature of 150-160 degrees Celsius for a heating time of 5 minutes;

[0052] For heat-resistant workpieces used internally, heat them with a hot air gun at a temperature of 180-200 degrees Celsius for 3-5 minutes for heating transfer;

[0053] For heat-sensitive workpieces, use a hot air gun to heat them to 150-160 degrees Celsius for 3 to 4 minutes for heating transfer.

[0054] When the ink in the thermal transfer carrier is heated to a temperature exceeding the sublimation temperature, the ink vapor in the thermal transfer carrier will saturate the local area between the transfer medium and the surface of the polymer substrate. When deposited on the surface, if the residence time and temperature are maintained, the ink molecules in the thermal transfer carrier will continue to migrate / diffuse along the concentration gradient, which allows these molecules to penetrate into the interior of the polymer, thereby having lasting color stability. When the hydrophobic synthetic polymer material used for sublimation transfer is transparent or translucent (such as varnish), the ink molecules in the sublimation thermal transfer carrier can be evenly distributed in the polymer matrix at the molecular level instead of staying on the surface of the material, which visually creates a unique and attractive color effect, or produces bright colors without the need for additional surface polishing. Light is not only reflected by the boundary between the polymer surface and the air, but also refracted by the inside of the polymer matrix, eventually forming. This dyed surface layer may be only a few microns deep, but it may also be deeper, even more than 100 microns (such as Figure 4 As shown), after the transfer is completed, the ink in the thermal transfer carrier will diffuse to the bottom in the varnish layer, and the ink in the thermal transfer carrier will not diffuse to the color paint layer. Therefore, the entire thermal transfer process will not affect the performance of the varnish or the color of the color paint, avoiding the subsequent repair problems. Experiments have shown that the diffusion degree of the ink in the thermal transfer carrier in the varnish changes with the change of temperature and time ( Figure 5 and Figure 6 ), which satisfies Fick's second law of molecular diffusion. At the same temperature, as the transfer time increases, the ink in the thermal transfer carrier diffuses deeper in the varnish, and eventually tends to be uniform in the varnish layer. As the temperature increases and the time increases, the surface of the thermal transfer carrier after the ink in the varnish diffuses can show a higher concentration of color after heating at about 160-180°C for 3 to 10 minutes. However, it should be noted that no matter what heating method is used, the heating temperature must be higher than the sublimation temperature of the ink in the thermal transfer carrier and the glass transition temperature of the substrate polymer material (varnish), and in order not to affect the physical and chemical properties of the final varnish (adhesion, appearance, weather resistance, etc.), the heating temperature cannot be higher than its decomposition temperature.

[0055] In this embodiment, specifically, the protective film coated on the surface of the transfer layer is a low-temperature cured acrylic polyurethane varnish or a nano-ceramic material. The low-temperature cured acrylic polyurethane varnish can prevent the transferred dye from diffusing back into the new protective layer varnish again due to heating, thereby ensuring the protective effect of the protective layer varnish. The nano-ceramic material is relatively dense after film formation and has good wear resistance.

[0056] A thermal transfer device for curved surface decorative spraying comprises a flexible film 1, a vent hole 2 is provided at the bottom of the flexible film 1, a side sealing ring 3 is provided at the outer edge of the bottom of the flexible film 1, a transfer terminal 4 communicating with the vent hole 2 is provided at the top of the flexible film 1, the flexible film 1 and the side sealing ring 3 are elastic heat-resistant materials, the thickness of the flexible film 1 is between 0.5 and 4 mm, and the elastic heat-resistant material is polymethylvinylsiloxane.

[0057] In the spraying industry, the substrates to which we need to apply this technology are generally three-dimensional curved surfaces. Currently, it is difficult to obtain high-resolution color images on the surfaces of these objects because traditional thermal transfer is completed by a rigid heat press, which cannot make the printed transfer paper completely fit the curved surface. Especially when the shape of the object is complex, the difficulty of transferring on a three-dimensional object lies in how to fix the printing paper on the curved surface and how to evenly heat the ink in the thermal transfer carrier to diffuse it into the varnish. Therefore, the core components of the thermal transfer device are the flexible film 1 and the side sealing ring 3. The flexible film 1 and the side sealing ring 3 are made of elastic heat-resistant materials, so the two can extend on the main plane. The sealing ring extends in a direction perpendicular to the main plane. The flexible film 1 is provided with a transfer terminal 4 connected to a vacuum pump, which can suck out the air so that the area surrounded by the side sealing ring 3 on the flexible film 1 forms a vacuum. At this time, the air outside the flexible film 1 uniformly applies a pressure of 0.1-1 bar (atmospheric pressure) on the entire film, which ensures that the flexible film 1 is completely consistent with the shape of the substrate to be decorated, and sandwiches the printed paper in the middle. It can closely fit various curved surfaces of the workpiece, such as curved surfaces, concave and convex surfaces, etc., to achieve uniform transfer of patterns. The selection of materials enables the flexible film 1 to withstand temperatures of about 100 to 180°C and can be reused many times. In addition, the selected material is impermeable to gas so as to form a vacuum between the flexible film 1 and the substrate to be decorated. A specific example is that the flexible film 1 can be made of polymethylvinylsiloxane.

[0058] The thickness of the flexible film 1 is preferably between 0.5 and 4 mm, so that the film has sufficient flexibility to cover three-dimensional substrates of various shapes, including substrates with large curvatures, and has sufficient mechanical strength to reuse the same film for multiple transfers. For various applications, a thickness of about 2 mm is a good compromise. When the side sealing ring 3 is attached to the workpiece, it can ensure that the area on the workpiece where the thermal transfer carrier is attached can maintain a stable vacuum environment, so that the thermal transfer carrier can be attached more tightly.

[0059] During subsequent quality inspection, optical or laser scanning equipment can be installed to monitor the transfer effect in real time and identify whether there are defects in the transfer process, such as bubbles, pattern misalignment, etc. If problems are found, the system can automatically stop and issue a warning, and the operator can make corresponding adjustments.

[0060] The above is a detailed description of an embodiment of the present invention, but the content is only a preferred embodiment of the present invention and cannot be considered to limit the scope of implementation of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the patent coverage of the present invention.

Claims

1. A thermal transfer process for curved surface decorative spraying, characterized in that: The following steps are involved: Step 1: First, clean the dirt on the surface of the workpiece; Step 2: preheat the workpiece; Step 3: Print the sublimation ink onto the thermal transfer carrier according to the designed pattern using an inkjet printer; Step 4: After the preheated workpiece cools down, the staff will fit the corresponding thermal transfer carrier onto the workpiece and selectively use the thermal transfer device to evacuate the workpiece according to the shape or heat-resistant temperature of the workpiece; Step 5. According to different application scenarios of the workpiece and different heat-resistant temperatures, the staff can adjust the temperature and time when the hot air blower heats the thermal transfer carrier; Step 6: After the workpiece has cooled to room temperature, the staff can tear off the thermal transfer carrier and then apply a protective film on the surface of the workpiece transfer layer.

2. A thermal transfer process for curved surface decorative spraying according to claim 1, characterized in that: The specific processing steps of step 1 are: using alcohol and ketone organic solvents to remove organic dirt such as oil, wax, resin, etc. on the surface of the workpiece coated with varnish or uncoated workpiece, and using deionized water to remove water-soluble stains and excess organic solvents.

3. A thermal transfer process for curved surface decorative spraying according to claim 2, characterized in that: The alcohol and ketone organic solvents are ethanol and acetone.

4. A thermal transfer process for curved surface decorative spraying according to claim 1, characterized in that: The specific processing steps of step 2 are: when preheating the workpiece to be transferred, the preheating temperature is controlled at 100-110 degrees Celsius, and the preheating time is controlled at 5-8 minutes.

5. The thermal transfer process for curved surface decorative spraying according to claim 1, characterized in that: The specific processing process of step three is: adjust the corresponding inkjet volume according to different application scenarios of the workpiece. The inkjet volume of the thermal transfer carrier corresponding to the workpiece for external application is 150-170ml / ㎡, and the inkjet volume of the thermal transfer carrier corresponding to the workpiece for internal application is 100-130ml / ㎡.

6. The thermal transfer process for curved surface decorative spraying according to claim 1, characterized in that: The specific processing process of step 4 is as follows: for the heat-resistant workpiece and the non-heat-resistant workpiece with a curved surface, the staff can attach the corresponding thermal transfer device to the workpiece and ensure that the thermal transfer device completely covers the thermal transfer carrier. At this time, the thermal transfer device is evacuated by a vacuum pump, and a pressure of 0.1-1 atmosphere is uniformly applied to the surface of the thermal transfer carrier through the deformation of the thermal transfer device, so that the thermal transfer carrier can be completely attached to the curved workpiece; For flat heat-resistant workpieces and non-heat-resistant workpieces, workers do not need to attach the thermal transfer device to the workpiece.

7. The thermal transfer process for curved surface decoration spraying according to claim 1, characterized in that: The specific processing process of step 5 is as follows: the heat-resistant workpiece used externally is first heated by a hot air gun to a temperature of 180-190 degrees Celsius for a heating time of 3 minutes for pre-transfer, and then the final transfer is performed at a heating temperature of 150-160 degrees Celsius for a heating time of 5 minutes; For heat-resistant workpieces used internally, heat them with a hot air gun at a temperature of 180-200 degrees Celsius for 3-5 minutes for heating transfer; For heat-sensitive workpieces, use a hot air gun to heat them to 150-160 degrees Celsius for 3 to 4 minutes for heating transfer.

8. The thermal transfer process for curved surface decorative spraying according to claim 1, characterized in that: The protective film coated on the surface of the transfer layer is low-temperature cured acrylic polyurethane varnish or nano ceramic material.

9. The thermal transfer device for curved surface decoration spraying according to claim 1, characterized in that: The flexible film (1) comprises a flexible film (1), wherein a vent hole (2) is provided at the bottom of the flexible film (1), a side sealing ring (3) is provided at the outer edge of the bottom of the flexible film (1), and a transfer terminal (4) communicating with the vent hole (2) is provided at the top of the flexible film (1).

10. A thermal transfer device for curved surface decoration spraying according to claim 9, characterized in that: The flexible film (1) and the side sealing ring (3) are made of elastic heat-resistant materials, and the thickness of the flexible film (1) is between 0.5 and 4 mm.

11. A thermal transfer device for curved surface decoration spraying according to claim 10, characterized in that: The elastic heat-resistant material is polymethylvinylsiloxane.

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