Self-adhesive and screen printing problems (lower)

15. If there is no problem with the quality of the ink, what are the causes of air bubbles in the silk screen printing process? How to deal with it?

A: The reason and solution: (1) The viscosity of the ink is wrong, it must be diluted. (2) The speed of squeegee is fast, the net distance is large, and air bubbles are pulled out because the screen bomb is too fast from the substrate. (3) The wrong solvent is used, and miscibility with the ink is poor, so it is necessary to use a special solvent for the ink. (4) Use of a quick-drying solvent under conditions of high temperature and low humidity causes the surface conjunctiva to become too fast and bubbles appear. (5) Air bubbles due to the surface of the substrate are not easily wetted. (6) Ink expired.

16. What are the consequences of uneven stretching tension?

A: (1) In some places, the ink layer is thick. In some areas, the ink layer is thin and the thickness is not uniform. (2) Distorted pattern text. (3) Local graphics may produce ambiguity. (4) Distortion or misalignment of halftone dots caused by dot printing, resulting in color cast.

17. What is the network distance adjustment?

Answer: (1) It is mainly based on the tension adjustment of the stretch net, the tension net distance is small, and vice versa. (2) According to the size of the frame, the large frame distance of the frame is also large.

18, the size of the net under normal tension will affect what?

Answer: (1) First, the net distance is large, the scraping pressure of the scraper is large, and the screen is susceptible to premature aging (the screen tension loss is large). (2) The net distance is small, and the screen cannot be ejected from the workpiece immediately to make the pattern dirty. Therefore, in the case where the screen has a certain tension, it must be ensured that the scraping pressure of the squeegee is minimized in the screen printing process, and the screen can be ejected from the workpiece immediately.

19, why different types, different uses, different suppliers of ink must use different solvents? What happens when solvents are used incorrectly?

A: Because there is no ink that is universal, there are many kinds of materials for the substrates. Therefore, when the ink is selected, the binder resin in the ink must be compatible with the material of the substrate (workpiece). Otherwise, the adhesion will be affected. The solvent in the medium has a dissolution effect on the substrate, so the ink can be firmly bonded to the workpiece. Because the ink is different in the resin, so the solvent is also different, if indiscriminate use or misuse will appear the following: (1) will affect the color of the ink (2) will affect the overall performance of the ink, such as: adhesion, poor solvent resistance, silk screen suitability Not so good. (3) Severe ink will cause agglomeration and lead to production scrap.

Therefore, all kinds of inks have their own special solvents, and they cannot be added or misplaced.

20. Solvents The solvents in the ink are classified into fast drying, dry drying, and slow drying. What are the different types of solvents used?

A: The solvent drying rate is determined by the evaporation (flux) speed of the solvent itself, and the steaming speed is determined by their boiling point.

Fast-drying solvent: The boiling point is generally 100°C and 150°C.

Dry solvent: the boiling point is generally 150 °C 200 °C

Slow dry solvent: The boiling point is generally above 200°C

Each type of solvent is not a single type of solvent. They are all made from a mixture of several solvents to control the drying speed of the ink. Therefore, generally, full-automatic screen printers use fast-drying solvents; manual screen printing and slow-drying solvents at high temperatures and low humidity; and use of dry solvents in air-conditioned and humidity-controlled environments. If the wrong solvent is used, it will cause blocking and reticulation; the material will be eroded and cracked, so it is very important to choose the appropriate solvent.

21, what is the thixotropy of ink, what effect?

A: The ink will become thicker after standing for a certain period of time, the viscosity will also increase, and it will become thinner after stirring and the viscosity will become smaller. This is the thixotropy of the ink. The thixotropy of ink facilitates screen printing to improve printing accuracy.

22. What is the reason for the increased resistance of silver paste?

Answer: (1) Drying is not complete, ie, the drying temperature is not enough, the time is not enough, or the drying method is not good. (2) The printing thickness does not meet the temperature required for the silver paste. The printing thickness is thin, and the silver and silver connections are not strong. (3) When the cylinder is opened, the stirring is not complete, resulting in a low silver content in the upper layer of the cylinder, an increase in the square resistance of the ink, a high silver content in the lower layer, and an impaired adhesion. Because silver has a large proportion, which is more than ten times that of water, it easily sinks to the bottom, so it should be thoroughly stirred.

23. What are the reasons for the poor adhesion of carbon paste and silver paste?

Answer: (1) The carbon paste and the silver paste are not mixed evenly before being mixed, resulting in high powder content, which affects the binding force with the sheet. (2) Silver carbon ink that has not been thoroughly mixed or not with the same resin as the binder after mixing. (3) Incomplete drying. (4) The surface tension of the substrate is small and the ink wettability is poor.

24, what is the sheet resistance? How to calculate?

Answer: The resistance value per unit area of ​​unit thickness is called sheet resistance. The unit is ohms/square/mil. The unit thickness is mil. 1 mil = 25um, expressed in Ω/□ (25um thickness). Calculation methods: (1) Measure the length L of the measured line, the width W of the line, and the thickness T (mil) of the line. (2) Use an ohmmeter to measure the resistance R (ohm) at both ends of the line. (3) L/W = number of blocks n of the circuit under test, R/n = resistance value per square block. (4) Square resistance Ω/□ = R/n/T

25. What should be noticed when using conductive silver or carbon paste?

Answer: (1) Stir before use, so that the upper and lower layers of the full cylinder ink can fully meet the requirements of the design ratio. At the same time, silver and carbon paste have high viscosity and certain thixotropy. After full mixing, screen printing adaptability is improved. (2) Each time the printing is completed, the remaining ink should be kept in a clean container. The next time the pulp is used, the last remaining ink is used, and if necessary, a new ink is added and then printed. (3) Sealed, stored under low-temperature drying, removed from the low temperature 4 hours before use, allowed to return to room temperature, and still be fully agitated before printing. (4) Avoid adding solvent as much as possible. If necessary, strict measurement is needed to avoid adding more solvent.

26, what are the three primary colors of light, what are the three primary colors?

Answer: (1) The three primary colors of light: red, green and blue.

(2) The three primary colors of pigments: magenta, yellow and cyan.

27. What are the precautions for color matching?

Answer: (1) Accurately weigh and record in detail the amount of each color ink including data, name, and code number. (2) Different types of inks cannot be mixed with each other. (3) The thinner should be added after the ink is adjusted well, and stir evenly. (4) The principle of shallow depth should be adopted in the color matching process. (5) The observation color should be under the same light source, the same angle, and viewing. (6) Thickness of the ink layer affects the color. (7) Different substrates affect the color.

28, what factors determine the amount of ink in the screen printing (the depth of the ink color)?

Answer: (1) Screen: In case of the same number of meshes, the thickness of the screen is less ink.

B. The mesh with the same mesh and the same diameter as the twill weave has more ink under the screen than the plain weave.

(2) The printing surface of the screen printing plate has a large amount of ink under the photosensitive layer, and vice versa.

(3) Squeegee process: A. Squeegee printing speed is slower.

B. The angle between the squeegee and the substrate is much lower.

C, scraper soft ink and more.

D, scraper blade tip, less ink, knife-edge pure (arc type) ink more.

Source: Shenzhen self-adhesive web