Silk-screen printing in-mold decoration method

Abstract

The invention discloses a silk-screen printing in-mold decoration method. The method comprises the following steps that firstly, a thin film is pretreated; 2, carrying out corona treatment on the pretreated film; 3, designing a plurality of layers of patterns, and manufacturing a corresponding screen printing plate; pouring printing ink into a screen printing plate according to the color requirement of the first layer, uniformly imprinting the printing ink to the surface of a film by using a scraper, and drying; according to the number of layers needing to be printed, the printing step of the first layer is repeated; wherein in the silk-screen printing process of a certain layer or several layers, corona treatment is carried out at the same time; and 4, cutting, forming, punching, inspecting, in-mold injection molding, film covering and inspecting are conducted on the printed film, and the decorative product is obtained. According to the in-mold decoration method disclosed by the invention, the ink can be more easily spread on the surface of a thin film, so that the adhesiveness of the ink is remarkably improved; meanwhile, the interaction force and the chemical bonding force between the ink and plastic film molecules are enhanced, and the firmness and the durability of printed patterns are ensured.

Description

Technical Field

[0001] The invention relates to the technical field of in-mold decoration, and in particular to a screen printing in-mold decoration method. Background Art

[0002] Screen printing in-mold decoration technology is a process that prints patterns and texts directly on the inner surface of the mold through screen printing, and then injects them into the plastic. This technology is widely used in the manufacture of decorative parts in the fields of automobiles, home appliances, electronic products, etc.

[0003] However, the existing screen printing in-mold decoration technology has the following problems: 1) The ink adhesion is poor, and the ink cannot adhere firmly to the surface of the film material, causing the printed pattern to fall off or become blurred during subsequent processing or use; 2) The bonding force between the ink and the plastic substrate is insufficient, resulting in unstable printing quality; 3) Inks with poor adhesion are more likely to fall off or age after long-term use or exposure to harsh environments (such as high temperature and humidity), reducing the overall durability and usability of the product. Summary of the invention

[0004] The purpose of the present invention is to provide a screen printing in-mold decoration method in view of the deficiencies in the prior art.

[0005] To achieve the above object, the technical solution adopted by the present invention is:

[0006] A screen printing in-mold decoration method is provided, comprising the following steps:

[0007] Step 1, pre-treating the film;

[0008] Step 2, performing corona treatment on the pretreated film;

[0009] Step 3: design a multi-layer pattern according to the requirements, and make a corresponding screen plate according to each layer of the separated pattern; pour the prepared ink into the screen plate according to the color requirements of the first layer, and use a scraper to evenly press the ink onto the surface of the film after the corona treatment. After the first layer is printed, let the ink dry thoroughly; repeat the printing steps of the first layer according to the number of layers to be printed;

[0010] Among them, during the screen printing process of one or several layers, corona treatment is carried out simultaneously;

[0011] Step 4: cutting, forming, punching, inspecting, in-mold injection molding, laminating and inspecting the printed film to obtain a decorative product.

[0012] Furthermore, the step 1 is specifically as follows: cutting the film, using a detergent or solvent to remove stains, grease, and dust on the surface of the film to ensure that the surface is clean and smooth; drying the cleaned film to remove surface moisture for standby use.

[0013] Furthermore, the material of the film is one or more of polycarbonate PC, polyethylene PE, polypropylene PP, and polyethylene terephthalate PET.

[0014] Furthermore, the voltage of the corona treatment machine used in the corona treatment is set to 8000-20000 V. The increase in voltage will enhance the treatment effect, but it is not a linear relationship. When the voltage is increased to a certain value, the improvement in the treatment effect will no longer be obvious; the treatment voltage is positively correlated with the thickness of the film, that is, the thicker the film, the higher the required treatment voltage.

[0015] Furthermore, the output power of the corona treatment machine used in the corona treatment is set to 2-7 kW. The power selection depends on factors such as the treatment speed, film type, and width; for example, if the treatment speed is doubled, the treatment power should also be doubled; if the film width is doubled, the treatment power should also be doubled.

[0016] Furthermore, the frequency of the corona treatment machine used in the corona treatment is set to 10 to 25 kHz.

[0017] Furthermore, the electrode gap of the corona treatment machine used in the corona treatment is set to 0.05-2 mm. The electrode gap refers to the spatial distance between the two electrodes, that is, the spatial distance from the discharge head to the edge of the ground electrode, which has two effects on the degree of treatment: on the one hand, the increase in the gap can widen the range of corona treatment, and the relative residence time of the film in the corona treatment becomes longer, which is conducive to improving the treatment effect; but on the other hand, the increase in the gap will also disperse the energy into a larger space, resulting in a decrease in the treatment intensity.

[0018] The present invention adopts the above technical solution, and has the following technical effects compared with the prior art:

[0019] The screen printing in-mold decoration method of the present invention performs corona treatment on the film, and also performs corona treatment during the screen printing process, so as to change the physical and chemical properties of the surface of non-polar polymers such as plastic films, enhance the surface polarity, and make it easier for ink to spread on the film surface, thereby significantly improving the adhesion of the ink; at the same time, the interaction force and chemical bond force between the ink and the plastic film molecules are enhanced, ensuring the firmness and durability of the printed pattern, which can not only improve the visual effect of the product, but also extend the service life of the product. In addition, the corona treatment can also increase the roughness of the plastic film surface and increase the contact area between the ink and the film, thereby further improving the printing effect. DETAILED DESCRIPTION

[0020] The present invention is further described below in conjunction with specific embodiments, but is not intended to be limiting of the present invention. It should be noted that the embodiments and features in the embodiments of the present invention may be combined with each other without conflict.

[0021] Example 1 (Screen Printing Corona Process for Membrane Switch)

[0022] This embodiment provides a screen printing in-mold decoration method, and the specific steps are as follows:

[0023] Step 1: Use precision cutting equipment to roll the polyethylene terephthalate (PET) roll into rolls of 500 mm in size. During the rolling process, remove the stains, grease and dust on the surface of the film (using a dust-sticking roller, a weak alkaline surface cleaner, etc.) to ensure that the film surface is clean, flat and dust-free; place the cleaned entire roll of film in a separate roll dryer to pre-treat the film (depending on the material and thickness and the purpose of the printed matter, the pre-treatment temperature is generally 120±10℃ and the time is 60±5 minutes) to ensure that the internal stress and pre-shrinkage rate of the film surface meet the requirements before use.

[0024] Ink: Taking TEIKUKO EG series ink as an example, the required ink is quantitatively mixed with the required solvent, hardener and other additives in the prescribed proportion within 15 minutes before printing. After mixing, use a mixer to fully stir and test the ink viscosity (generally controlled at 2500±100pa);

[0025] Step 2: Select a corona treatment machine, set the voltage to 8000±500V, the output power to 7kW, the frequency to 20±5kHz, and the electrode gap to 0.075~0.25mm. Ensure that the equipment parameters meet the requirements and the distance between the corona treatment head and the film surface is consistent. Feed the pretreated film into the corona channel of the corona treatment machine, and generate corona discharge on the film surface through high-frequency voltage, thereby changing its surface properties, increasing surface energy, and improving adhesion (dyne value>45±5).

[0026] Step 3: Design a decorative piece with multiple layers of patterns according to the requirements (the pattern includes a color layer, a protective layer, and a glue layer: the colors are red, blue, and white, etc., and use color separation software and drawing making software (such as Adobe Photoshop, Adobe Illustrator, CorelDRAW, etc.) to separate the pattern into multiple independent monochrome layers. According to the set printing process requirements, make a corresponding screen printing screen for each separated layer to ensure that the parameters such as the mesh number, opening rate, tension and thickness of each screen are adapted to the characteristics of the ink used and the set printing process requirements.

[0027] For example: for the first layer of printing, according to the color requirements of the red pattern, pour the prepared red ink into the screen plate, and use a scraper to evenly press the ink onto the surface of the corona-treated film. After the first layer of printing is completed, the film is first passed through a tunnel furnace for finger-touch drying, and then the dried film is placed on a layer rack for drying and cooling to ensure that the ink is completely dry; repeat the printing steps of the first layer, but use blue ink for the second layer of printing to ensure that the second layer of pattern is accurately aligned with the first layer of pattern, and perform the same drying treatment after printing; repeat the above steps again, use white ink for the third layer of printing, ensure that each layer of pattern is accurately aligned with the previous two layers of pattern, and dry the product in a box oven after printing.

[0028] When the second layer of ink is printed, corona treatment is performed simultaneously. The voltage of the corona treatment machine is set to 8000±500V, the output power is set to 7kW, the frequency is set to 20±5kHz, and the electrode gap is set to 0.5-2.0mm (raw material thickness: 0.5-2.0mm).

[0029] Step 4: The semi-finished product printed on the surface of the PET substrate is produced through precision target drilling equipment to produce reference positioning holes, and then the semi-finished product is embossed, formed, bent, and other processes using molding machines, bending machines, and other equipment using the positioning holes. Finally, the tooling mold is made according to the required shape, and the product required by the customer is produced using a punch press. Finally, the inspection is carried out according to the inspection standards agreed with the customer, and the product that meets the customer's requirements is finally shipped.

[0030] Example 2 (In-film decoration technology screen printing corona process)

[0031] In-mold decoration technology is a technology that embeds printed films directly into the surface of injection-molded plastic products during the injection molding process. In order to ensure good adhesion between the printed film and the plastic-based particles, corona treatment is a commonly used surface treatment method. The following is an explanation of the use of corona process in the production of in-mold decoration technology:

[0032] Step 1: There are many materials used in the film decoration technology, such as PET, PC, ABS, PMMA and various types of composite materials. The above-mentioned substrates are rolled and cut into required specifications using cutting equipment. During the processing, the stains, grease and dust on the surface of the film are removed to ensure that the surface of the film is clean, flat and dust-free, and then the material is pre-treated (pre-shrinked);

[0033] Ink: Taking NORILIT HTR series ink as an example, the required ink is quantitatively mixed with the required solvent, hardener and other additives in the prescribed proportion within 15 minutes before printing. After mixing, use a mixer to fully stir and test the ink viscosity (generally controlled at 2000±500pa)

[0034] Step 2: Select a corona treatment machine, set the voltage to 8000±500V, the output power to 7kW, the frequency to 20±5kHz, and the electrode gap to 0.25~0.5mm. (Different corona parameters are set according to the required materials) Ensure that the equipment parameters meet the requirements and the distance between the corona treatment head and the film surface is consistent. The pre-treated film is sent into the corona channel of the corona treatment machine, and corona discharge is generated on the surface of the film through high-frequency voltage, thereby changing its surface characteristics, increasing surface energy, and improving adhesion (dyne value>45±5).

[0035] Step three, design the required number of printing layers and process of the decorative parts according to the customer's appearance and color requirements (the printing layer includes the color layer, the impact-resistant layer, and the glue layer: the color layer is set differently according to the customer's appearance requirements, the impact-resistant layer is divided into the ink protection layer and the injection molded particle impact-resistant layer, and the glue layer is the layer directly welded with the injection molding). First, use 3D software (UG, CATIA, Solidworks, etc.) to convert the customer's drawings into graphic design software, and then use color separation software and drawing making software (such as Adobe Photoshop, Adobe Illustrator, CorelDRAW, etc.) to separate the pattern into multiple independent monochrome layers. According to the set printing process requirements, make the corresponding screen printing screen for each separated layer to ensure that the parameters such as the number of meshes, opening rate, tension and thickness of each screen are adapted to the characteristics of the ink used and the set printing process requirements.

[0036] After the first layer is printed (usually the base layer), the film is dried by finger touch in a tunnel furnace. Then the dried film is placed on a layer rack and returned to a drying oven for secondary curing. Dry for 60±10 minutes at 80℃±5℃ to ensure that each layer of ink is completely dry. Before repeating the printing of the next layer, the printed product needs to be subjected to secondary corona treatment. During the treatment, the process of the printed area and the non-printed area needs to be adjusted to ensure the adhesion between multiple printing inks. Each color and pattern needs to be accurately aligned with the previous layer before printing, and the same drying treatment is performed after printing. Repeat the above steps again, and the same drying treatment is performed after printing.

[0037] When the second layer of ink is printed, corona treatment is performed simultaneously. The voltage of the corona treatment machine is set to 8000±500V, the output power is set to 7kW, the frequency is set to 5±5kHz, the electrode gap is set to 0.25-0.5mm, and the speed is 50m / min.

[0038] Step 4: First, the printed film is coated with a protective film to prevent it from being damaged during the whole process. Secondly, the reference positioning holes are processed and formed on the molding mold. The formed material is then punched out into the required shape using a punching machine. The printed film is inspected for appearance to ensure that there are no problems such as missing prints, ghosting, and misalignment. The qualified film is placed in the injection mold for in-mold injection molding. During injection molding, the molten plastic is injected into the mold, and the film and plastic are solidified together to form an integrated decorative part. The injection molded decorative part is coated to enhance its surface wear resistance and aesthetics.

[0039] Comparative Example 1

[0040] The difference between using corona treatment in the third step and not using corona treatment in the third step is:

[0041] 1) Surface energy

[0042] Before corona: The surface energy is low, usually between 30-40mN / m (the specific value depends on the material).

[0043] After corona treatment: The surface energy is significantly increased, usually reaching 50-60mN / m or higher. This enhances the adhesion between the material and the substrate.

[0044] 2) Contact angle

[0045] Before corona: The contact angle is large, usually above 80°, indicating that the material surface is relatively hydrophobic.

[0046] After corona treatment: The contact angle decreases significantly, usually below 40°, indicating that the material surface becomes more hydrophilic, promoting the adhesion of inks and adhesives.

[0047] 3) Adhesion

[0048] Before corona: The adhesion between the ink and the substrate is weak, which may cause the ink to fall off or peel off.

[0049] After corona: Adhesion is significantly enhanced, usually through peel tests (such as 180° peel test) can achieve higher dyne values, ensuring the film is firmly adhered after molding.

[0050] 4) Printing quality

[0051] Before corona: The ink adheres poorly and may fall off or fade.

[0052] After corona treatment: ink adhesion is enhanced, printing effect is clearer and more durable, and defective product rate is reduced.

[0053] 5) Wear resistance

[0054] Before corona: The diaphragm surface is relatively smooth, with poor wear resistance and is easily scratched or worn.

[0055] After corona treatment: The enhanced surface energy and adhesion improve the wear resistance, and the diaphragm is less likely to be damaged during use.

[0056] 6) Treatment time and intensity

[0057] Before corona treatment: No corona treatment was performed, so the relevant parameters are invalid.

[0058] After corona: The treatment time is usually between 0.1 seconds and 10 seconds, and the voltage is between 1-5kV. The specific parameters need to be adjusted according to the material properties and equipment settings.

[0059] 7) Gas flow

[0060] Before corona: no treatment, no effect on gas flow.

[0061] After corona: The gas flow rate is usually between 0.5L / min and 5L / min to ensure the stability of corona discharge.

[0062] Through corona treatment, the surface properties of IML film are significantly improved, the adhesion to the substrate and the printing quality are enhanced, and the overall performance and market competitiveness of the product are improved. In practical applications, the parameters of corona treatment should be reasonably adjusted according to the specific material and process requirements to achieve the best effect.

[0063] The above description is only a preferred embodiment of the present invention, and does not limit the implementation mode and protection scope of the present invention. For those skilled in the art, it should be aware that all solutions obtained by equivalent substitutions and obvious changes made using the contents of the specification of the present invention should be included in the protection scope of the present invention.

Claims

1. A screen printing in-mold decoration method, characterized in that: The steps include: Step 1, pre-treating the film; Step 2, performing corona treatment on the pretreated film; Step 3: design a multi-layer pattern according to the requirements, and make a corresponding screen plate according to each layer of the separated pattern; pour the prepared ink into the screen plate according to the color requirements of the first layer, and use a scraper to evenly press the ink onto the surface of the film after the corona treatment. After the first layer is printed, let the ink dry thoroughly; repeat the printing steps of the first layer according to the number of layers to be printed; Among them, during the screen printing process of one or several layers, corona treatment is carried out simultaneously; Step 4: cutting, forming, punching, inspecting, in-mold injection molding, laminating and inspecting the printed film to obtain a decorative product.

2. The screen printing in-mold decoration method according to claim 1, characterized in that: The step 1 specifically includes: cutting the film, using a detergent or solvent to remove stains, grease, and dust on the surface of the film to ensure that the surface is clean and flat; drying the cleaned film to remove surface moisture for standby use.

3. The screen printing in-mold decoration method according to claim 1, characterized in that: The material of the film is one or more of polycarbonate resin PC, polyethylene PE, polypropylene PP, and polyethylene terephthalate PET.

4. The screen printing in-mold decoration method according to claim 1, characterized in that: The voltage of the corona treatment machine used in the corona treatment is set to 8000-20000V.

5. The screen printing in-mold decoration method according to claim 1, characterized in that: The output power of the corona treatment machine used in the corona treatment is set to 2-7 kW.

6. The screen printing in-mold decoration method according to claim 1, characterized in that: The frequency of the corona treatment machine used in the corona treatment is set to 10 to 25 kHz.

7. The screen printing in-mold decoration method according to claim 1, characterized in that: The electrode gap of the corona treatment machine used in the corona treatment is set to 0.05-2 mm.