Common mistakes and countermeasures in screen printing

Have you ever printed directly with ink taken from the ink can? Have you ever repeatedly wiped away ink accumulated on the screen mesh? Have you ever experienced applying inappropriate pressure to the squeegee? If your answer to all three questions is yes, then you have committed the three major taboos in screen printing. If you can spend a little time on ink preparation, use a reusable tensioned screen, and control the angle and speed of the squeegee, you can easily avoid most of the problems encountered in the screen printing process.

Each of the problems mentioned above will directly affect the quality of the printed matter, production efficiency, and the reputation of the printing company. This article will discuss ink preparation in detail.

Almost all plasticized sol ink comes out of the factory as a concentrate. The concentration varies depending on the manufacturer, color, and type, with some even being super-concentrated. Here we will focus on discussing plasticized sol inks, as most textile printing uses this type of ink. Simply put, the ink is composed of three main components: PVC (polyvinyl chloride plastic), pigment (color), and plasticizer (or other additives).

1.PVC

PVC is an adhesive that, when melted, causes the solid pigment to adhere to the surface of the textile material. It is a finely dispersed resin, somewhat like granulated sugar. When mixed with a plasticizer or other types of additives (excluding pigments), it becomes a liquid, colorless, transparent substance that forms a very thin film when applied. Stirring it, you will find that it is easier to stir than ink with pigment, and it is easier to separate from the squeegee, with a significantly different viscosity. It is more suitable for printing than ink with pigment, and easier to print.

2. Waste

　　Pigments produce color. After being ground into fine particles, they are mixed with PVC and other additives. The ratio of its mixture with transparent PVC and other additives determines the transparency and opacity of the color. The pigment concentration of screen printing ink is higher than that of four-color printing ink. Even for the same type of ink, the pigment percentage varies from manufacturer to manufacturer, as does the viscosity, so their printability and color concentration also vary accordingly.

　　Let's do a simple experiment for comparison: one print uses ink directly from the container to print high-saturation colors, such as blue or red. The other uses the same ink with an equal amount of transparent additive, mixed well, and then printed. You will find that for most types of ink, the colors of the two prints are the same, with no significant difference. A mixture of 50% pigment ink and 50% transparent additive can fully meet the job requirements, making the printing process simpler and easier, and reducing costs. Now let's do another experiment. This time, add two parts of transparent additive to one part of the original ink. The pigment ink now accounts for only 33% of the total. It can be seen that the printability of this mixture has been further improved, and the color is still acceptable for most manufacturers' products. When preparing ink, you must test inks from different manufacturers, their types and hues, because some inks will fade when 50% additive is added, while others will not change at all.

3. Plasticizer

The additives and plasticizers used by manufacturers to prepare inks are the main factors that cause differences in ink quality, with plasticizers being the most important component, often also called reducers.

　　Adding a small amount of reducer to the ink will reduce the viscosity of the ink, thereby improving the ink's printability. Usually, no reducer is added during four-color printing, while in screen printing, the formation of ink dots is determined by the size of the mesh holes on the screen. If the mesh holes are away from the surface of the substrate, the ink dots will be deformed, and the printed image will become blurred.

　　The reducer in the container is as clear and transparent as water. If you scoop up a spoonful, it feels a bit like clear oil. When using it, strictly follow the manufacturer's instructions. If too much reducer is added, no matter how much desiccant you add, how slow the printing speed is, or how long it is in the dryer, the ink will be difficult to combine with the textile. Therefore, be cautious when adding reducer.

　　Some companies produce curable reducers. It is a mixture of reducer, PVC, and other additives in a certain proportion, which can play a drying and curing role. The appropriate use of reducer can bring benefits to the printing process, but in actual production, people often do not follow the manufacturer's instructions, abuse the amount of reducer, and evaluate whether it is appropriate through vision and feeling. Of course, this approach is very harmful.

　　If the dosage is improper, the printed image will either have an oily feel or a faded feel. In this case, users often complain about the quality of the product, while ignoring the fact that they used the wrong amount of additive when preparing the ink. Sometimes people think that reducer and thinner are the same, which leads to another misconception.

　　Reducers and thinners are very different. Only reducers reduce the viscosity of the ink, while thinners do not affect the viscosity of the ink.

　　If no reducer is added during printing, you will find that the printed product has obvious ink accumulation, and even orange peel phenomenon may occur. The surface of the printed product is uneven, with some small pits. Moreover, when the screen is lifted, some ink will be brought down from the substrate. However, with the same printing, only the appropriate amount of reducer is added to the ink, and it is found that the ink accumulation phenomenon is significantly reduced, and no ink will be adhered when the screen is lifted.

　　Less pigment means less dryness and less ink accumulation, and the reducer can further improve the occurrence of ink accumulation.