Screen printing process common three kinds of matters needing attention

Have you ever printed ink from an ink can directly? Have you ever had to re-erase the ink that has accumulated on the screen? You have applied improper pressure on the squeegee. Experience? If you give the answers to all three questions in the affirmative, then you have committed three major taboos in the screen printing process. If you can take a little thought in formulating inks and use repetitively tensioned screens to control the angle and speed of the doctor blade, you can easily avoid most of the problems encountered during screen printing.

Each of the above-mentioned issues will directly affect the quality of printed matter, production efficiency, and the credibility of printing companies.

First, the deployment of ink

Almost all plastisol-type inks are concentrated when shipped from the factory, and the manufacturers, colors, and types are different. The degree of concentration is also different, and some are even super-concentrated. Here we will focus on discussing plastisol inks, as most textile printing uses this ink. Simply put, ink consists of three main components: PVC (polyvinyl chloride plastic), pigment (color) and plasticizer (or other additives).

1.PVC

PVC is an adhesive that, after hot melting, attaches a solid pigment to the surface of the textile material. It is a very finely divided dispersion resin, somewhat like white granulated sugar. When it is mixed with plasticizers or other types of additives (other than pigments), it becomes a liquid, colorless and transparent substance, and a very thin and thin film can be formed after coating. Stir it, you will find it easier to stir than the ink with Yankee, and easier to get rid of the squeegee, the viscosity is very different, it is more suitable for printing than the pigmented ink, but also easier to print .

2. Scrap

The pigment produces color, which is ground into fine particles and mixed with PVC and other additives. Its mix with transparent PVC and other additives determines the transparent and opaque properties of the color. The pigment concentration of the screen printing ink is higher than the pigment concentration of the four-color printing ink. Even for the same type of ink, the percentage of the pigment is different from that produced by different manufacturers, and the viscosity is also the same, so their printing suitability And the color density also has a certain difference.

Let's do a simple experiment to compare: A print is to print high-saturation color, such as blue or red, with the ink taken directly from the container. The other one is added with the same amount of transparent additive in the same ink and mixed evenly for printing. You will find that the color of two prints is the same for most types of ink, and there is no big difference. The mixture of 50% pigment ink and 50% transparent additive can fully meet the needs of the operation and make the printing process easier and more cost-effective. Now let's do another experiment, this time adding two clear additives to one part of the original ink. At this time, pigment inks accounted for only 33% of the total, and it can be found that the printability of this mixture has been further improved, and for most manufacturers, the color is still acceptable. When configuring the ink, you must test the inks of different manufacturers, their type and hue, because some inks will fade with 50% additives, but some will not change.

Plasticizer

The additives and plasticizers used by manufacturers to formulate inks are the most important factors causing the difference in ink quality. Among them, plasticizers are the most important ingredients, and in most cases, they are also known as reducing agents.

Adding a small amount of reducing agent in the ink will reduce the viscosity of the ink, thereby improving the printability of the ink. Usually in the four-color printing is not added reducing agent, and in the screen printing process, the formation of ink dots is determined by the size of the screen mesh hole. If the mesh leaves the surface of the substrate, the dots will be distorted and the printed image will be blurred.

The reducing agent in the container is as clear and transparent as water. If you pick up a spoon, it will feel a bit like oil, and you must strictly follow the manufacturer's instructions when using it. If too much reducing agent is added, no matter how much desiccant you add, how slow the printing, how long it takes to get through the dryer, the ink is difficult to combine with the textile. So be careful when adding reducing agents.

Some companies produce reductants that are curable. It is a mixture of a reducing agent and PVC and other additives in a proportion, which can play the role of drying and curing. The appropriate amount of reducing agent can bring benefit to the printing process, but in the actual production process, people often do not follow the manufacturer's instructions, abuse the amount of reducing agent, and use visual and sensory to evaluate whether the application is appropriate. Of course this is very harmful.

If the dose is not used properly, the printed image will either have a greasy feel or a faded feel. In this case, users often complain that the quality of the product is not good and they neglect to use the wrong dose of additive when configuring the ink.

Sometimes people think that reducing agent and diluent are the same, this concept will lead to another misunderstanding.

Reducing agents and diluents are very different. Only the reducing agent will reduce the viscosity of the ink, and the diluent will not affect the viscosity of the ink.

If you do not add reducing agent when printing, you will find that the printed product has obvious ink accumulation, even orange peel phenomenon, the surface of the printing product is very uneven, there are some pits. And when the screen is lifted, it will also carry some ink from the printing material. The same printing, just adding an appropriate amount of reducing agent in the ink, found that the phenomenon of ink deposition was significantly reduced, the screen will not stick under the ink when lifted.

Less pigment means less blight and less ink build-up, while reducing agents can further improve ink buildup. (to be continued)