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Injection molding process of silk screen printing of injection molded parts

by:Vowin Rapid Prototyping     2023-02-14
In the injection molding process of silk screen printing of injection molded parts, the secondary processing of plastic injection molding products is relative to the primary processing: that is, the products formed by the primary injection molding process are processed again. The secondary injection molding process of plastic products mainly includes surface decoration, machining, assembly, etc. The surface decoration methods of injection molding process products include silk screen printing, pad printing, hot stamping, thermal transfer printing, water transfer printing, decals, spraying, electroplating, planting, etc. Cashmere, wrapped cloth, etc.; machining methods such as drilling, turning, milling, bending, rolling, etc.; assembly mainly includes hot-melt welding, ultrasonic welding, etc. The secondary injection molding process of plastic products can increase the added value of the product, and can form products that cannot be formed in one process. The following Shanghai Mulan Injection Molding Factory introduces the main secondary processing methods of plastic products.

Silk screen printing is the abbreviation of 'screen printing'. Screen printing is the injection molding process of stretching silk fabrics, synthetic fiber fabrics or wire mesh on the screen frame, and silk screen printing of injection molded parts. Shanghai Mulan Injection Molding Processing Factory adopts manual engraving of paint film or photochemical plate-making to make screens printing plate. Modern screen printing technology is to use photosensitive materials to make screen printing plates by means of photographic plate making. During printing, through the extrusion of the scraper, the oil is transferred to the substrate through the mesh of the graphic part, forming the same graphic as the original. Screen printing equipment is simple, easy to operate, easy to print and plate-making, with low cost and strong adaptability. The common printed products with a wide range of screen printing applications include: color oil paintings, posters, business cards, bound covers, commodity signs, and printed and dyed textiles.

1. Necessary equipment for silk screen printing of injection molded parts

(1) Picture: graphic film.

(2) Wire mesh: according to the material, it is divided into nylon mesh, polyester mesh and metal mesh; according to the number of mesh: 200~300 mesh is more commonly used.

(3) Screen frame: aluminum alloy or wooden frame.

(4) Screen printing machine: used for automatic screen printing.

(5) Fixtures: Install and fix the screen printing table, fixing clips, etc. of the screen board.

(6) Squeegee (squeegee): made of polyurethane material.

(7) Infrared heater: drying silk screen pattern.

(8) Screen printing pattern materials: including ink, solvent, additives, etc.

2. Injection molding process of silk screen printing of injection molded parts

The injection molding process of silk screen printing of injection molded parts is as follows.

Pattern design→Film output→Manufacturing screen frame→Putting net→Scraping photosensitive glue and blowing dry→Confirm the position to place the film and place the film→Exposure→Water rinse→Select the ink to adjust the color→Adjust the viscosity→Place the blank (before putting it Check whether it is qualified)→Fix fixture, screen, workpiece alignment→Printing→Drying→Drying→Inspection→Packaging

3. Screen printing injection molded parts design requirements and screen printing equipment selection

(1) Try to avoid steps and bosses around the printed pattern, and if unavoidable, the steps or bosses should be at least 7mm away from the graphic.

(2) The choice of ink should be determined according to the printing substrate. Different substrates have a greater influence on the ink adhesion. Special inks are used for special pattern effects, such as color-changing inks and mirror-effect inks.

(3) Selection of screen: the finer the pattern, the larger the mesh of the screen should be, and the thickness of the ink is proportional to the thickness of the photosensitive adhesive, but the printing cost is high. Metal mesh and carbon fiber mesh are used for high-definition patterns. For the printing of circuit boards, the effect of colored mesh is better than that of white. Colored mesh can reduce the refraction during photosensitive and reduce the impact on pattern accuracy.

(4) Selection of squeegee (squeegee): the harder the hardness, the finer the pattern. The color of the squeegee material is yellow, red, green, blue, and brown, and the hardness increases in sequence. The Shore hardness ranges from 55° to 90°.

(5) The screen frame is required to be firm and not deformed.

(6) Silk-screen plastic substrate

① The substrates of silk screen plastic parts are generally divided into polar substrates and non-polar substrates. Polar substrates and non-polar substrates will also have differences in ink selection due to different materials, such as PC, ABS, etc., should choose their corresponding inks for silk screen printing. Generally, non-polar substrates have poor adhesion to ink, and surface treatment is required before silk screen printing to ensure adhesion. ②Screen printing substrates require clean appearance, no oil stains, no oily release agent during injection molding, and no internal stress in the parts.

4. Effect of screen printing pattern

(1) Mirror effect: It is used for reverse printing of transparent parts. This kind of ink has poor adhesion and needs to be printed with a protective layer.

(2) Multi-color patterns: manual silk screen printing has an impact on the color registration accuracy, multi-color generally adopts automatic printing, which is suitable for mass production of small parts, and the investment cost of injection molding process equipment is high.

(3) Gradient effect: It can produce simple patterns with light and dark changes.

(4) Color change effect: the color changes according to the temperature and orientation.

(5) Gloss: semi-bright, matte surface effect.

5. Quality inspection of silk screen pattern

(1) Adhesion: cross-cut method (GB9286-88).

(2) Color: meet the color requirements of the sample or color card.

(3) Lines: The pattern lines are uniform in thickness.

(4) Color registration: the color registration position of the pattern is accurate.

(5) Pattern continuity: whether the silk screen pattern is broken.

(6) Position: Whether the position of the silk screen pattern meets the requirements of the drawing.

(7) Completeness: Whether there are missing strokes or incomplete strokes.

(8) Other special requirements: friction resistance, aging resistance, solvent resistance, etc. meet the requirements.
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