Quality Control of Raw Materials in Screen Printing

Product quality is related to the survival and development of each company. The quality of products depends on the five major production factors in the production process: Man, Machine, Material, Method, and Environment. That is, we often say 4MIE rules. As the domestic plastic color printing manufacturers vary greatly in scale and grade, the emphasis on the 4MIE rule and actual implementation are not the same. Due to the limitation of financial strength, for most small and medium-sized plastic color printing plants, it is relatively easy to shut down good printing materials and reduce the quality of accidents from the source. In the plastic color printing process, the raw materials are mainly films, inks and solvents. The overall principle of quality control: according to the customer's specific requirements or the characteristics of the contents of the package, post-processing to determine the appropriate film and structure; after selecting the material structure, according to different films to determine the appropriate ink, and supporting the corresponding Solvent; avoid excessive packaging or shoddy.

There are many types of films on the market today, but the most commonly used printing films are BOPP, NY, PET, and PE. In terms of printing, the most important thing is of course the effect of the surface treatment of the film, and whether the NY film is damp. When printing, the process requirements for measuring the surface tension of the film should be established. The corona effect has timeliness. If it is left for a long time, the corona effect may be reduced too much to meet the printing requirements. It is also possible to avoid the hidden troubles caused by inadvertently reversing the film surface. PE film is the focus of our attention: when the film is blown, there may be a film roll that is missing the corona treatment; the film thickness is too large or uneven to cause the corona effect to be insufficient; the blown film is added with too much of a smoothing agent or high Excessive proportion of sliding granules causes a significant reduction in corona effects. When the corona effects on both sides of the 12~15um PET film are not much different, it will easily cause the back-adhesion failure of the printed film roll. The corona requirements of the printing film: BOPP, PE ≥ 38 dynes, PET ≥ 50 dynes, NY ≥ 52 dynes. NY film does not have a great effect on the corona effect after absorbing water. It is judged whether the NY film absorbs water to see if the film is shrinking. If a film is cut into the oven for a few hours, whether it feels hard or not, if there is a tendency Hard hair, etc., the NY film absorbs too much water. In the procurement of film must explain to the supplier the use of the film and requirements, and now thin film species refinement, light said PET, NY, BOPP name, suppliers may have several varieties, but not necessarily all suitable.

When selecting a gravure ink, first consider several factors: What substrate is printed on? What kind of machine is used to print? What kind of effect do you want to get? Post-printing processing, end product use conditions? Now ink manufacturers have fierce competition and have a large selection of products. They may also dazzle our color printing plants and confirm the above points before printing. We choose the ink with the best cost performance ratio and reduce or avoid the occurrence of printing failures. . The ink supplier should not be too much, not more than three should be appropriate, different brands of ink can not be used due to blending, resulting in a large waste of the remaining ink; perhaps some color printing manufacturers hold the mind of the ink supplier's mentality, but the business should be Integrity-based, because it is necessary to pay sooner or later, there is no such need.

The three major types of inks commonly found on the market are polyamide-type surface inks, chlorinated polypropylene-type composite inks, and polyurethane inks. Different substrates choose the corresponding ink. Printed BOPP use chlorinated polypropylene composite ink, if you do not need to compound, use polyamide type of surface printing ink, if you choose general purpose polyurethane ink to print BOPP, not only high cost, adhesion fastness can not meet the requirements. NY, PET film must be printed with polyurethane ink, if chlorinated polypropylene ink printing composite, prone to low peel strength, high temperature delamination and other failures. Polyamide inks have excellent adhesion to PE film, but they can only be used for general dry packaging. When making high temperature, oil and water resistant packaging, such as milk film and bottle label, polyurethane ink should be used.

There are several basic indicators of ink is our color printing company should detect: viscosity, fineness, hue, fastness.

The required test tools include scraper bars (contrast hue, adhesion test), 3# Chaenhuai (viscosity), fineness plate (fineness). When measuring the viscosity, it is best to dilute to a specific viscosity (for example, 18 seconds/25°C) with an appropriate mixed solvent to calculate the amount of solvent added. This eliminates the "false viscosity" phenomenon that some inks may bring. It's thick, but it doesn't add any solvent.) Fastness can be measured using the national standard (GB/T 13217.7-91), but for some surface inks may not be enough, it is best to simulate the specific requirements of the product packaging and post-processing conditions for testing.

The quality of solvent quality directly affects the quality of ink printing, but for general SMEs, solvent quality is the most difficult to grasp. The main indicators for distinguishing the quality of the solvent are purity and moisture content. Quantitative qualitative detection of the solvent is best detected by chromatography, but the required instrument price is more expensive and the technical requirements are higher. If light is for printing, dry compounding processes are not taken into consideration. Here are a few simple and practical methods. Look at the appearance of the solvent. At the very least, it should be clarified and transparent. If there is turbidity or floating material, the batch of solvent should be used with caution. After smelling the odor of the solvent, the operator usually has a general impression of the odor of a particular solvent after a relatively long period of exposure to commonly used solvents. If the odor of the batch of solvents is found to be not pure, it can be confirmed that the batch of solvents is not of high purity and impurities. many. Use the dissolving effect of different principles to roughly determine the content of water in the solvent: Take a large half cup of clear toluene solvent with a 100 ml glass graduated cylinder, take a small amount of solvent such as esters or ketones to be tested, and pour the toluene into the solvent. Into the toluene, observe the presence of turbidity (milky white) phenomenon, if any, the water content in the solvent is seriously exceeded, experience shows that when the water exceeds 0.5%, this phenomenon is very obvious. The moisture content of the benzene solvent can be determined by drawing a solvent through a long glass tube and observing whether there is delamination.

There are many factors that affect the quality of printing. How can we better grasp the quality of printed matter? Each color printing company has its own management method. The quality control of raw materials is the most basic and critical process requirement in the color printing process. It is difficult to imagine that unqualified or inappropriate raw materials can guarantee the production of quality-compliant printing products. Therefore, our color printing companies must have long-lasting and effective measures. The quality of raw materials.

Reprinted from:Gaogong Machine Grid