The hottest screen printing plate making method

Silk printing plate making methods

first, preparations

when selecting silk, we must pay attention to the matching between the number of silk meshes and the quality of printed products; The stretch of silk should be as small as possible; The organizational structure of silk should be tight, otherwise it is impossible to make a high-quality version

if the silk is used before, first remove the oil and dust for the silk, and then wash away the residual ink. For the cleaning agent used for cleaning silk, the newly purchased concentrated detergent should be selected, and it is better not to use household detergent or washing powder, because it contains additional ingredients such as essence, hand lotion (detergent) and bleach (washing powder), and the particles in it will block

when washing silk with lotion, smear both sides of the silk evenly and wipe it repeatedly with a sponge. Then rinse the silk with water and dry it to ensure that there is no residual foam on the silk, and do not touch the silk with your hands after cleaning

after cleaning, dry the silk in a dust-free environment. At present, many people still use the drying method of blowing the fan against the silk, but such dust is large, so it is best to make a drying oven to make the air flow evenly through the silk surface. At the same time, try to wash it on the same day and apply photosensitive glue on the same day, so as to prevent dust on the silk before gluing. If the humidity of the operation site is very high, it is best to install a dehumidifier to speed up the drying of the plate

now, some people use coarsening agent to grind the edge of silk thread rough. This method is suitable for indirect plate making, which can improve the combination fastness of photosensitive film and silk. If we use the method of coating photosensitive glue to make screen printing plates, there is no need to roughen them, otherwise the strength of the silk will be reduced

II. Plate making methods

the most commonly used plate making methods are direct photosensitive adhesive plate making method and direct diaphragm plate making method. The following mainly introduces the new photosensitive materials and plate making processes in these two methods

direct photosensitive adhesive plate making method

1 Type and performance of photosensitive adhesive

in short, photosensitive adhesive is a colloidal liquid that can react chemically in the presence of light. You can get a photosensitive version by evenly coating it on the cleaned and completely dry silk with a scraper

there are many kinds of photosensitive adhesives, commonly used are diazo compound photosensitive adhesives and double vulcanized photopolymer photosensitive adhesives. Compared with diazo photosensitive adhesives, bisulfide photosensitive polymers contain less water and shrink less during the drying process. This advantage can make the graphics and texts on the plate get sharp edges, and can speed up the speed of plate making. When using water-based ink, its durability is better. Therefore, bisulfide photopolymer photoresist is gradually replacing diazo compound photoresist

in addition to the above two photosensitive adhesives, some large-scale printing companies also use a pure photopolymer photosensitive adhesive. The pure photopolymer photosensitive adhesive can be prepared in advance, with fast photosensitive speed and short exposure time, but the price is expensive. Generally, double vulcanized photopolymer photosensitive adhesive can be used for printing

for printing activities with large printing volume (more than 500 prints), especially when using water-based ink, special water-resistant photosensitive adhesive should be used. Standard double vulcanized photopolymer photoresist and pure photopolymer photoresist have good water resistance, but they are not suitable for live parts with large printing volume

2. Preparation of photosensitive adhesive

whether it is double vulcanized photopolymerization photosensitive adhesive or general diazo photosensitive adhesive, its finished product includes two parts, one is the adhesive base, the other is the photosensitive agent that reacts with light. When preparing photosensitive glue, first add some warm water to dissolve the photosensitive powder in the bottle (some photosensitive agents are dark brown liquid, not powder). Because the photosensitive glue may react with minerals in the water, it is best to use distilled water to dissolve the photosensitive agent. The temperature of water should not be higher than 38 ℃, otherwise the performance of photosensitizer will be affected; If the water temperature is too low, the powder is not easy to dissolve. Shaking the bottle or stirring properly will help to dissolve the photosensitive agent

the next step is to add the photosensitive solution to the adhesive base and stir it with a non-metallic rod (such as a wooden spoon, etc.) for about 10 minutes. Do not pull back and forth during mixing, and it is best to do it in shape. Then put the prepared photosensitive adhesive for a few hours, and wait for the bubbles to escape, then it can be used

photosensitive adhesives are particularly sensitive to heat and should be stored below 38 ℃. Put it in the refrigerator, it can be guaranteed for 1 to 2 months. If the photosensitive glue turns into cotton wadding or some blocky deposits, it can no longer be used. Pure photopolymer photosensitive adhesive has been prepared when it is sold, and its storage life is up to 5 years

3. Advantages of photosensitive adhesive production version

1) the performance of photosensitive adhesive is long-lasting and can be used for various frames. Suitable for all kinds of inks, including water-based fabric dye inks. Because the photosensitive glue can exist inside the silk through coating, this kind of printing plate can show the details of the image

2) the plate made of photosensitive glue can be recycled without affecting the image quality. In most cases (except for the photosensitive adhesive with hardener), as long as the used version is cleaned with solvent, it can be reused

4. Coating environment

photosensitive adhesive is quite sensitive to light, but this does not mean that it must work in an all black environment, just under 50W yellow light. Remember not to go near windows or places with ultraviolet light. Double vulcanized photopolymer photoresist and pure photopolymer photoresist are more sensitive to light than nitrogen photoresist, and it is best to operate in a dark environment

5. Coating photosensitive glue

the main tool for coating photosensitive glue is the sizing device, also known as the scraper. There are many specifications for the length of the scraper. The standard size of the scraper used for printing T-shirt version is 14 inches or 16 inches. The length of the scraper should be smaller than the size of the inner frame of the version, so that it will not touch the blank part on the silk. Some scrapers have a blunt edge and a sharp edge; Some scrapers have rounded edges. The sharp edge of the scraper should be used for coating, because the photosensitive adhesive layer scraped by the sharp edge is thin, and the plate can reproduce the image details, which is helpful to get a high-quality screen printing plate

if the photosensitive glue is stored in the refrigerator, raise it to room temperature before pouring it into the scraper (when the temperature is low, the photosensitive glue thickens). If there is a rubber protective layer on the blade of the scraper, it must be removed before use. When coating, erect the silk, place the scraper on the bottom of the outer side of the silk, and slowly scrape upward with an inclined scraper to make the photosensitive glue coated on the silk. Then repeat the process on the inside of the silk. Many people believe that the outer side of the silk should be coated for 2-3 times, and the inner side of the silk should be coated for 2-3 times. In fact, such a coating is too thick, which is easy to cause problems such as insufficient exposure or loss of image details. The correct method is to first coat the outer side of the silk to make the coating on the outer side of the silk (printing surface) thicker, and when coating the inner side of the silk, the photosensitive glue can be scraped back to the outer part of the silk. During the coating process, some photosensitive glue will run out of the edge of the scraper. These left photosensitive glue can be removed with a cardboard

depending on the purpose of the plate, it sometimes needs to be coated several times, but if the silk quality is good, one coating on the front and back is enough. If double vulcanized photopolymer photoresist or pure photopolymer photoresist is used, it should be coated twice on both sides of the silk respectively; If the diazo compound photosensitive adhesive is used, the photosensitive adhesive applied for the first time shall be applied again after it is completely dry, in order to increase the thickness and prevent pinholes. For double vulcanized photopolymer photoresist and pure photopolymer photoresist, if the coating method is correct, generally there will be no pinholes

after coating the photosensitive adhesive, be sure to wipe the scraper clean. Otherwise, after the photosensitive glue is dried, a white glue film will be formed on the edge, affecting the next gluing. Protecting the blade of the scraper is also very important for the coating quality. If there is a gap in the blade, stripes will be formed during coating, which will affect the plate making quality. If there is a gap on the blade, it is better to replace it with a new scraper instead of repairing it

6. The drying process of the version should be carried out under safe light. It is best to use a drying oven (self-made ones are also acceptable) and install a fan to make the air flow on the surface of the silk to accelerate the drying. Be careful not to blow the fan directly against the wire, which is easy to make the blown dust adhere to the surface of the photosensitive adhesive layer. Generally speaking, it takes 30 ~ 60 minutes for silk to dry. If the humidity is high, it takes 1 day to dry completely. At this time, if there is a dehumidifier, it will play a great role

version can be stored in a matte box at room temperature for up to 2 months. In order to improve efficiency, you can coat a batch of plates at a time and save them for use when necessary

direct diaphragm plate making method

another plate making method of silk printing is called direct diaphragm plate making method, which is also called hybrid method traditionally. Simply put, the diaphragm used is a transparent acetate film coated with photosensitive glue

the direct diaphragm plate making method is simpler and easier to use than the direct photosensitive adhesive plate making method, because it does not need to prepare photosensitive adhesive, and the plate making steps are much less. The main advantage of direct diaphragm plate making method is that the printing lines are smooth, because when the printing plate is dry, it does not shrink, but only adsorbs the diaphragm on the blank wire. The direct diaphragm plate making method is suitable for printed materials with high printing quality requirements such as self-adhesive labels and posters

1. Selection of diaphragms

diaphragms are sold in various thicknesses in the form of rolls or sheets, taking the operating procedures of impact testing machines as an example. For general T-shirt printing, it is best to choose a diaphragm with a thickness of 38 m; For the version with a high number of wire mesh (such as 230 ~ 350 mesh/inch), a thinner diaphragm (18 m) can be selected, while for the version with a low number of wire mesh (such as 86 mesh/inch), a 60 m thick diaphragm should be selected; If color printing is carried out on black fabric, the ink volume required is large, and a thicker diaphragm is required

the diaphragm has the same photosensitive characteristics as the photosensitive adhesive. It should be operated under soft light or yellow light, and the temperature should not be too high during storage. The plate made by direct diaphragm plate making method can be stored for about one month

2. Film coating

the film coating process is to make the moisture in the silk adsorb the film on the silk by capillary action. Whether the photosensitive film is firmly attached depends on the cleanliness of some screw rods of tension machines on the market, which are T-shaped ordinary screw rods. There is a chemical reagent called wetting agent, which helps the silk absorb water in the process of adhering to the film. When sticking the film, just spray some wetting agent on the silk, wipe it evenly with a sponge, and then rinse the wetting agent with water. When there is still a lot of water on the wire, lay the diaphragm on the wire (Rough facing the wire), and then roll the inner and outer sides of the wire with a rubber roller. If there are still some places that are not bonded, spray a little water on the inner side of the wire that is not bonded, roll it with a rubber roller, and spray it on the parts that are not attached with the diaphragm at the same time

each diaphragm has its own operation method, and we only need to operate according to the instructions. After the attachment is completed, it will take about 30 minutes to dry. Then, it is revealed that there are still problems such as excessive charging items, too heavy burden, irregular charging, unfair high prices, etc. after a qualitative improvement, the bottom film of the diaphragm can be exposed. Before removing the bottom film, ensure that the wire and the film are completely dry. If it is quite difficult to remove the bottom film, it means that the silk has not been completely dried. If it is because of the high environmental humidity, remove it