Preparation of screen printing substrates (below)

Vinyl chloride is widely used in transparent films, water pipes, etc. due to its high water resistance and chemical resistance, as well as its low cost of the medium. However, due to the poor solvent resistance, ethane and heptene solvents that are fat-based are required for the reproduction of prints. In addition, its heat distortion temperature is extremely low, so pay close attention to it.

Propylene is used in various aspects such as boards and molded articles, and its mechanical strength is high and its weatherability is strong. Before printing, it is necessary to understand and confirm the performance and characteristics of various plastic plates and molded articles. To effectively clean the printed surface and remove static electricity. In particular, if the surface of the hard plate is not pre-treated, it is difficult to ink. When regenerating after printing and performing pre-treatment, special attention should be paid to it because of cracks. Polyacetals are printed on the right, requiring pre-treatment and special inks. Polymeric esters (PETP), whether pre-treated, primers or special inks, are very effective.

Other plastics should be scrubbed with methanol or a fat-based solvent before printing to degrease and remove dust, and then select the appropriate ink for printing. Since the molded product is likely to remain on the surface due to the cleaning agent, it is preferable to use a hydrocarbon or methanol scrubbing, and ultrasonic cleaning is also possible.

a. In addition to electrostatic treatment. In screen printing, since the substrate is mostly a polymer material, various electrostatic failures occur. This is mainly due to poor printing due to electrification of materials, printing defects due to dust adhesion, and printing defects caused by electrification of the screen ink in the country. Basically, these faults can be solved by removing the power.

AC type static elimination equipment. The most popular AC-type static eliminating device consists of three parts: a high-voltage power supply, a high-voltage line, and an electrode.

High-voltage power supplies are generally mostly 7 kV to 10 kV, and high-voltage line cables generally use insulated voltage cables (15 kV). Install the wires at the shortest distance, and use the protective insulating tube for the wires, which should be performed within the power capacity range.

In addition to electrodes with dozens of models, electrodes are selected that are compatible with the purpose of removing electricity. Electrostatic devices are used in screen printing. They are generally used for electricity removal and dust removal, and electrodes with brushes are often used. The screen is electrostatic due to the movement of the squeegee, so it is better to install the electrode in the squeegee.
Electrostatic dust removal equipment. The dust removal operation of the substrate is the cause of static electricity. Therefore, this dust removal operation must be performed while removing electricity. Equipment with a dust removal function has been commercialized and praised.

b. Flame treatment. There are many kinds of plastics, first of all to confirm what kind of material is used in printing, in order to prevent the ink in the fixation of obstacles. For example, polyethylene that is not subjected to flame treatment has extremely low adhesion to ink; polypropylene, when used as a substrate, requires high adhesion to the ink and must be processed. Its treatment methods include corona discharge treatment, flame treatment, and drug treatment. The corona discharge treatment is the best, but it is not applicable to the substrate of the molded product. This is caused by the equipment and the structure. The molded product is almost all flame treated.

Flame treatment uses a special gas burner to mix propane gas with air to make the flame temperature above 1100 degrees to process the substrate. When the substrate (molded product) comes into contact with a high temperature flame in an instant, an oxide film forms on the surface. Because of the high temperature flame, be very careful when handling the surface of the substrate. The effect test generally uses the water test method. The treated substrate is placed in water. After cooling, it is observed whether the water is attached to the surface of the entire substrate like oil to determine whether an oxide film is formed. When the treatment effect is not sufficient, the surface of the substrate is droplet-shaped. For soft polyethylene, polypropylene, etc., the water test is more difficult to judge, and the method of applying the coating method is used, and the effect is good. Treated substrates should avoid contact with water and it is best to print immediately. When the flame treatment method is used, if the flame is to be enhanced only from the viewpoint of improving printability, there are many problems with the molded product, such as shrinkage errors and deformations, so care must be taken. In addition, shrinkage errors may also occur when the molded product after normal processing is cooled. Therefore, it is preferable to enter the printing process as soon as possible. Nowadays, more and more printers are being used to supply and print products. This type of machine allows the substrates to enter the printing process with softness, less unevenness and temperature, saving man-hours and exquisite products.

3. metal.

     Metals used as substrates include iron, stainless steel, chromium, nickel, and aluminum. The use of these materials directly for printing is rare, and the use of coating, electroplating, and anodized metal has been frequently used. When pretreating metal, it is important to confirm the type of metal. For general metal pretreatment, mechanical grinding or chlorine-based solvents, fluorine-based solvents can be used to remove the contamination of most organic substances on the metal surface, and then chemical treatment is performed with an oxidizing drilling acid to improve the surface of the metal. Performance for optimal adhesion of inks and coatings.

1 aluminum. The aluminum plate has two kinds of untreated aluminum plates and anodized aluminum plates. Most of these aluminum plates are surface-coated and reused. The coating is generally vinyl resin coating: Acrylic acid, propylene polymer coating and methacrylic resin coating; Phthalate resin coating: Phthalic acid resin coating, styrene alkyd resin coating, melamine resin coating; Phenolic resin coatings: phenolic resin coatings and epoxy resin coatings; paint-based coatings: nitrocellulose coatings; polyamino carbamate resin coatings. The above coatings are transparent and colored.

2 plastic plating plate. ABS, AS polymeric ester plating plate has been industrial production. The electroplating layers include copper, nickel, cobalt, nickel-cobalt alloys, chromium, and tin. It is made by electroless plating, vacuum evaporation and anode sputtering. Because of the plastic plating, special attention should be paid in the heat drying process.

4. Fabric. Including cotton, wool, silk, vinylon, cellulose acetate, nylon, acrylic ester and so on. These fabrics are dyed with acidic and basic dyes. To remove the glue on the fiber cloth before printing, it is washed and bleached.

5. Ceramics. Pottery generally includes pottery, hard porcelain, porcelain, porcelain and so on. These porcelains are not the same temperature at the time of firing. In addition, in order to print patterns on porcelain, decals must be attached and fired.

6. Glass. The classification of glass is as follows: 1 Flat glass. Thin plate glass, thick plate glass, toughened glass (glass that has been heat-treated and increased in mechanical strength), mirror glass, etc.

2 cylindrical glass. Household glassware, lighting glassware, glass bottles, glassware for physical and chemical experiments, medical glassware, glass for electronic tubes, and the like.
3 fiberglass.
4 optical glass. Screen-printed substrates are made of optical glass. Hydrogen fluoride and etching inks are used during etching. In the pretreatment, ultrasonic cleaning, dilute acid cleaning, and alcohol scrubbing can be used to remove oil, moisture, and dust.

7. rubber. Rubber includes natural rubber, nitrile rubber, propylene rubber, urethane rubber, and fluororubber. Some of these rubbers that need to be pre-processed before being printed can also be printed directly, so it is important to understand the properties of each rubber before printing.

8. Copper plated laminates for printed circuit boards. One of the insulating materials is a board made by laminating paper, glass cloth, polyester cloth, etc. impregnated with phenolic or epoxy resin. This board has two kinds of single-sided and double-sided copper plating. This kind of insulating material must be degreased, derusted, and pre-treated with a grinder and electromagnet during pretreatment.

9. Alumina ceramics. It is a material mainly composed of alumina (Al2O3) and is used for thick film integrated circuits. Alumina ceramics have better conductivity, mechanical strength and high temperature resistance. It should be noted that ultrasonic washing is required.






Source: Bison