With the localization of computers in recent years, more and more workpieces need to print characters on ABS plastic keys. Although there are introductions to plastic printing in CHINA, most of them are used for decoration, and the printing area is relatively large, so the accuracy and firmness of the writing are not very high. The surface key area is small [the minimum area is [6.8×3.5)mm²]. High precision is required, and the keys are often in contact with fingers, so the adhesion of characters on the plastic keys is required to be better. The wear resistance is strong, and it should have solvent resistance, hand sweat resistance and other properties.
Because the key area is small, and the number is the largest, it is obviously inappropriate to print with the reverse paste method, so the silk screen printing method should be adopted. In order to solve the unevenness between the keys, a special fixture should be made according to the arrangement of the keys during printing.
In terms of printing materials, due to the poor brightness and color of plastic inks, and it is easy to seal the net, the adhesion of ordinary inks is not satisfactory. Therefore, it is better to choose printing materials with good brightness, not easy to seal the net, and strong adhesion to ABS plastic The key to typography.
The viscosity of the ink during silk screen printing should not be too high, otherwise the printed characters will rise up and can be picked off with fingers. If the viscosity is appropriate, it cannot be picked off with fingers (referring to normal force). In addition, after the ink is dry, spray a thin layer of varnish ( nitro varnish), which can obviously improve the brightness of the surface of the part and protect the ink layer.
Screen printing process of keyboard characters
The screen printing process of keyboard characters is generally: screen preparation → plate making → prepress processing of plastic workpieces → silk screen → initial inspection → drying → inspection.
① Screen preparation. Select 240 mesh wire mesh, stretch the mesh with a mesh stretcher, clean and dry.
② Plate making.
③Cleaning of plastic workpieces: CK-821 low-temperature degreasing agent, at a temperature of about 50°C, soak for 5 minutes to remove oil, neutralize olefinic acid, rinse with running water, and dry in the air.
④Screen printing: The plastic key is placed with a special fixture, and the screen printing ink is used for screen printing. If the printing material is too dry, it can be diluted with diluent.
⑤Initial inspection: Unqualified ones are cleaned with alcohol and reprinted.
⑥ Drying: Dry in an oven at 60°C for half an hour, or dry at room temperature for 2 hours.
⑦ Submission
a. Bonding force: After the printed matter is dry, scratch it with a nail with a force of about 500g, and the writing will not fall off.
b. Abrasion resistance: Using a cathode moving device, rubbing medium sponge, pressurizing 50g, rubbing 100,000 times, the writing does not fall off.
c. High-low temperature experiment: high temperature 70°C (30min) → normal temperature (10min) → low temperature -20°C (30min) is a cycle, a total of three cycles, no discoloration or falling off of the writing.
d. Hand sweat resistance: Use filter paper to absorb artificial sweat (recipe: sodium chloride 7g/L, urea 1g/L, lactic acid 4 g/L ) to cover the key, wipe it hard after 2 hours, and the handwriting does not fall off.
e. Water resistance: After soaking the keys in water for 24 hours, wipe them vigorously without falling off.
f. Solvent resistance: Soak the keys in alcohol or gasoline, and wipe them hard after 4 hours, and there should be basically no falling off.
