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Adapting to technological innovations and people’s individual pursuit of electronic, digital products and silk screen processing technology to the surface of the product have been welcomed by many people. It became very popular in the industry, therefore silkscreen printing method is often used in our company, especially for companies with their own brands where the logo is required on the product surface.
The screen printing process consists of printing the logo or pattern on a screen with a film and then, using an squeegee to print the ink onto the surface of the substrate. The logo is printed on the surface of the product.
Screen printing definitions
Screen printing is a printing technique where a mesh is used to transfer ink onto a substrate, except in areas made impermeable to the ink by a blocking stencil. A blade or squeggee is moved across the screen to fill the open mesh apertures with ink, and a reverse stroke then causes the screen to touch the substrate momentarily along a line of contact. This causes the ink to wet the substrate and be pulled out of the mesh apertures as the screen springs back after the blade has passed. One color is printed at a time, so several screens can be used to produce a multi colored image or design.
Pretreatment process of metal silk screen
For screen printing on metal surfaces, the surface has to be pre-prepared. The pre-treatment process of metal surfaces is also called pre-printing processing. There are many ways to pre-process metal surfaces, such as degreasing, polishing, wire drawing, oxidation, sand surface treatment, spray pain etc. These processes can be used alone or in combination to achieve the desired effect according to the different requirements of the product and the conditions of the underlying material.
1.The purpose of the pre-processing is mainly twofold:
(1) Decorative, which means removing some defects of the aluminium plate material to increase the aesthetics of its surface
(2) Manufacturability, which means that the surface finish of the material is changed by pre-treatment processes to enhance the adhesion of the printing coating on it.
2. There are many methods for metal pre-treatments such as:
Before the degreasing treatment process, in order to make the metal surface have a certain affinity for the coating printing, it is required to remove oil stain from the surface of the metal material. Generally speaking, the oil contamination of the package can be removed with fine soft orange powder. The oil contamination during machining can be scrubbed with organic solvents or chemically degreased with alkaline solutions.
Polishing is a common method to overcome the surface defects and to improve the surface finish. Polishing can be roughly divided into three categories: mechanical, chemical and electrochemical.
Mechanical polishing- at first rough polishing the surface with a cloth wheel polishing machine and polishing paste, then fine polishing with a fine cloth wheel, therefore the material can achieve the desired smooth effect. Mostly used for decorative treatment of anodized dyes signs. For mechanically polished aluminium plates, in order to obtain good brightness and good oxidation results.
Chemical polishing is mostly performed in acidic solutions. Electrochemical polishing is a higher surface finishing method, which can obtain a brighter mirror polishing effect and reduce the surface oxidation of metal materials by the atmosphere.
3. Advantages of silk screen processing
1. Wide application area and applicable ink.
2. After printing, the ink has good adhesion and can be displayed for a long time.
3. The screen printing process is not limited by the size of the object, and can be printed at demand.
4. Good resistance to sunlight, acid and alkali.
5. The printing methods are flexible and can be printed either manually or mechanically. Screen printing process is simple and easy.
6. The cost is low to print a beautiful three-dimensional realistic pattern.
7. Decorative product.
8. The ink is safe to use and conducive to environmental protection.
4. Important factors is silk screen processing
(1) There is no ink on the surface of the substrate (uneven ink leakage) the reasons are:
1. The screen mesh number is too high and the ink permeability is poor.
2. Photosensitive film is too thick and ink permeability is weak.
3. Scratches on the blade.
4. Insufficient squeegee pressure or uneven pressure.
5. Excessive gap between screen printing plate and substrate.
6. Ink viscosity is too high and low penetration.
7. Ink returned to the glue.
8. Little in on the screen.
9. Uneven printing table.
(2) After printing the ink bleeds and it’s causing side or virtual shadows and blurred text, the reason why are as the following:
1. Squeegee blade edge wear and tear, poor ink breakage effect in squeegee.
2. Squeegee printing angle is too small, resulting in excessive ink supply.
3. The ink viscosity is too low, therefore the ink will bleed after printing.
4. The ink and the solvent are unevenly stirred, therefore the ink with lot of solvent after printing has a penetrating phenomenon.
5. Solvent remains after screen printing plate cleaned.
6. Screen printing plate and substrate overprint rules are misaligned.
7. Incorrect selection of ink and screen mesh, fine ink thickness and too low screen mesh.
8. Silk screen pause or repeats halfway.
9. Excessive squeegee force when returning ink, a small amount of print material has been squeezed out of the mesh.
(3) Causes of network blocking
1. Substrates are not booth or have a low strength, which can cause clogging due to powder and hair loss.
2. The pigment and other solid particles in the ink ale big, therefore it might block the mesh when printing.
3. High and low temperature, high volatility of solvent and volatility in the ink might cause network blockage. Moreover low temperature, poor ink fluidity are also one of the blocking network reasons.
4. The screen printing plate is left for a long time, or cleaned before printing might also causing blockage.
5. The pressure during scraping is too high and the curvature of the squeegee is large, which might result in surface contact during the scraping.
Each time the scraping ink is not cleaned by the squeegee, the residual ink reminds on the printing plate and the screen is too small after scraping. Therefore the plate cannot be separated from the substrate and the printing surface of the place adheres to the ink when it’s lifted, which is likely to cause the blockage.
Our aim is to provide the best products quality for our customers and enhance the competitiveness of customer’s projects. Your satisfaction is our priority. You are welcome to send us an inquiry and we will discuss it further. Weimi’s team will serve you with pleasure!