Preparation of Screen Printing Substrates (I)

In order to make the substrate printable, it is necessary to prepress the substrate before printing begins. Such as paper and other sensitive to the temperature and humidity of the substrate, hanging before printing, so that the temperature and humidity of the substrate and the printing environment temperature and humidity balance, in order to ensure the accuracy of color printing. For imprinting, high-temperature-drying substrates are required. If necessary, the substrate should be preheated on the drying equipment before printing, and then printed. For those plastic substrates with small polarities, since the ink film is hard to stick to the car, it should be mechanically, physically, or chemically roughened, oxidized, or polarized prior to printing, and then printed.
Non-absorbent substrates such as metals, glass, and plastics, which are stained with dust and grease, can affect the fastness of the prints. Therefore, cleaning must be done before printing.

For substrates that are too soft and easily deformed, such as fabrics, tissue, etc., to register and position the printer during printing. Pre-printing needs to be done with tackling and other shaping treatments; for some warped hard plastic sheet materials, such as PVC and organic glass sheets, etc., in order to make it smooth, heat-setting treatment needs to be done before printing.

1. paper. In screen printing substrates, paper is widely used. As a substrate, paper is generally treated with humidity before it is printed. That is, the paper is also called hanging paper.

The moisture conditioning of paper is the process of processing the paper before printing to balance its moisture content with the temperature and humidity of the printing press to maintain the dimensional stability of the paper.

After the press paper is pressed, coated, dried, calendered and other processes, it will generally meet the requirements of the relevant standards when it is shipped from the paper mill. The water content is relatively low. However, such paper is often not directly used for printing, because it will inevitably be stretched due to moisture absorption during printing, affecting the accuracy of registration at the time of printing.
After being shipped from the factory, printing paper is often transported over long distances and stored for a long period of time. Due to the frequent changes in its environment and climate, the moisture content of the paper may not be compatible with the temperature and humidity of the printing environment, and the moisture content of the paper on the stack of paper or in different positions in the stack is often not uniform.

Printing paper is generally a good insulator, so it is often charged with static electricity during the drying and calendering process. In a dry, cold environment, paper can also be charged with static electricity due to friction during handling. Paper with static electricity is used for printing, and many troubles often occur during the paper feeding process.
For various reasons mentioned above, in order to balance the moisture content of the paper with the temperature and humidity of the printing environment; in order to make the paper (paper and paper stack) have a uniform moisture content; and in order to eliminate static electricity, the paper generally passes through before printing. Humidity treatment. This point is especially important for multicolor overlay paper. Paper for monochrome printing, although there is no registration accuracy problem, but there are electrostatic problems like multi-color printing, so it is better to conduct humidity control before printing.

There are two methods for regulating the humidity of paper, namely the natural humidity control method and the forced humidity adjustment method.

The natural humidity control method is also called "hanging drying method" and "hanging drying method." This method is simple and easy, that is, the paper is hung in the printing shop, so that the moisture content of the paper is balanced with the relative humidity of the printing shop.

Forced-moisturizing method is to hung the paper on the paper-hanging machine, and then blowing air with a certain humidity and a certain temperature to the paper to accelerate the humidity-controlling speed. After a certain period of time, the paper is then placed in a paper drying room with a temperature and humidity similar to that of the printing room for temperature and humidity balance. The temperature of air that is blown is generally 10-15°C higher than that of the pressroom, and the relative humidity is generally 10-20% higher than that of the pressroom. This method is more complex than the natural humidity control method and requires considerable equipment, but the humidity control effect is ideal.

2. Plastics. Plastic overview. Synthetic or natural polymer compounds as the basic components, under the action of external forces or heat, molecules and molecules slide, resulting in permanent deformation, we have the plasticity of this object is called plastic. Thermoplastic resins that have no plasticity, such as phenolic resins and Julian's resins, should not be strictly referred to as plastics, but we also refer to them as plastics. The main types of plastics are listed in Table 3-16 and Table 3-17. As a plastic screen-printed product, molded products, plates, films, and coated products with a star mark in the table are sold in the market, and will become indispensable materials in printing. Most of the plastics having resistance to organic solutions in the table suffer from the problem of poor adhesion to the ink and need some surface treatment before they can be used for printing.

2 plastic pretreatment and operation methods. The plastic printing pretreatment method is as follows: The polyethylene film and the molded product are subjected to flame treatment and plasma discharge treatment before printing. In order to adapt to its special purpose, inks with good fixing performance are now invented without the need for plastic pretreatment.

Table 3-16 Thermosetting Resins (Compression Molding)

Name Thermal deformation (18.5kfg/cm2) Resistance to organic solvents * Phenol-formaldehyde resin (PF) 115 ~ 125 °C Resistance to common solvents * Urea - Formaldehyde (UF) 125 ~ 145 °C Resistance to all solvents * Melamine formaldehyde (MF) 150 °C Non-invasive epoxy resin (EP) 50-290°C Resistant to all solvents Unsaturated polyester (hardness for injection molding) (UP) 60-200°C Slightly affected by ketone, chlorinating agent Furan resin (asbestos-filled) ( FF) - Resistant to all solvents Xylene resin (cellulose filled) (XF) - Resistant to all solvents Silicone (glass filled) (SI) >482°C Resistant to all solvents Diallyl phthalate (glass fiber reinforced) ( DAP) 165~250°C are not invaded

Table 3-17 Thermal plastic resin (injection molding, compression molding)

Name Heat Deflection Temperature (18.5kgf/cm2) Resistance to Organic Solvents* Polyvinyl Chloride (PVC)
Hard and soft 54~74°C Soluble in ketone, ester, THF Polyvinyl butyral (PVB) - Alcohol soluble polyvinyl alcohol (PVA) - Stabilized polyvinylidene chloride (PVDC) - Stable polymer Vinyl fluoride (PVF) 88-77°C Solvent resistant to common solvents Chlorinated polyether - Almost all solvents resistant* Polystyrene General Purpose (PS)
Impact resistance 104~100°C Soluble in aromatic solvent, chlorinated solvent*Polystyrene-acrylonitrile copolymer (SAN) 88~104°C Soluble in ketone, ester, chlorinated solvent *ABS 94~107°C Soluble in ketones, esters, chlorinated solvents * Polyethylene high concentration (PE)
Medium concentration, low concentration, 43-54°C
32~40°C Almost all solvents Ethylene-vinyl acetate copolymer (EVA) - Soluble in aromatic, chlorinated solvents * Polypropylene non-denatured (PP)
Impact resistance 52~60°C
99~104°C Almost resistant to all solvents* Polyamide monopolymer (PA)
Copolymers from 124°C to 110°C Almost all solvents resistant * Polymethyl methacrylate (PMMA) molding 70~104°C
70~100°C Soluble in ketone, ester, aromatic, Chloroplast solution MAA, Styrene copolymer 85~99°C Soluble in ketone, ester, aromatic, chlorinated solution * Impact resistance MMA 74~102°C Ibid MMA, a-methyl ethylene copolymer 118-122°C Ibid* Nylon 6 injection
66 pressure type 67 ~ 70 °C
66~104°C Soluble in common solvent Ethyl cellulose (EC) 46~88°C Almost all solvents resistant* Polyethylene urethane (PETP) 240~245°C Almost all solvents resistant* Polyurethane (PU) ) - Isotactic polychlorotrifluoroethylene (PCTEF) 126°C Swelling polytetrafluoroethylene (PTFE) in a halogenating agent 121°C Totally free from attack Polyvinylidene chloride (PVdF) 91°C Almost all solvents polyphenylene ether ( PPO) 185~193°C soluble in aromatic, chlorinated solvents

All of them are not infringed. Since polyethylene has poor solvent resistance, it is preferable not to use a solvent such as a fat solvent or methanol to perform pretreatment and substrate regeneration.

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