I. Preparation
When selecting the screen, it is necessary to pay attention to the matching of the number of screen meshes with the quality of the printed product; the stretchability of the screen should be as small as possible; the structure of the screen must be tight, otherwise it is impossible to make a screen with high quality.
If the screen is used before, the screen must first be deoiled, dust removed, and the remaining ink must be removed. Cleaning agent for cleaning mesh should be selected from the newly purchased concentrated washing agent. It is better not to use household detergent or washing powder, because it contains flavors, hand protection agents (washing spirit) and bleach (washing powder) and other additional Ingredients, but also the particles will be blocked.
When washing the screen with a washing agent, apply both sides of the screen evenly and wipe it repeatedly with a sponge. Then rinse the screen with water and dry it to ensure that there is no residual foam on the screen. After the screen has been cleaned, never touch it with your hands.
After cleaning, dry the screen in a dust-free environment. Many people still use the method of drying the fan against the wire mesh. However, the dust is relatively large. It is better to make a drying box so that the airflow can evenly flow over the surface of the screen. At the same time try to wash the net on the same day, the day coated with photosensitive adhesive, which prevents the screen from falling dust again. If the humidity of the operation site is large, it is best to install a dehumidifier to speed up screen drying.
There are still people who use rougheners to roughen the edges of the wire. This method is suitable for use in indirect platemaking methods, which improves the fastness of the photosensitive film to the screen. If we use the photosensitive emulsion method to make screen printing plates, there is no need for roughening, otherwise it will reduce the strength of the screen.
Second, the Plate making method
The most commonly used screen printing methods are the direct photosensitive platemaking method and the direct film plate making method. The following mainly introduces the new photosensitive materials and plate making processes that appear in these two methods.
Direct photosensitive adhesive plate making method
1. Photosensitive adhesive type and performance
In simple terms, the photosensitive adhesive is a colloidal liquid that can be exposed to light and can be chemically reacted. The screen can be uniformly coated with a scraper on a clean and completely dried screen to obtain a screen with sensitometric properties.
There are many kinds of photosensitive adhesives, and commonly used are diazo compound photosensitive polymers and double-sulfur photopolymer photosensitive polymers. The double-sulfurated photopolymer photopolymer has less moisture content and less shrinkage during the drying process than the diazo compound photo-sensitive adhesive. This advantage can make the graphic image on the screen plate obtain a sharp edge, and can accelerate the speed of plate making. When using water-based inks, its durability is better. As a result, bisulfide photopolymer emulsions are gradually replacing diazo compounds.
In addition to the above two kinds of photosensitive adhesives, some large-scale screen printing companies also use a pure photopolymer emulsion. Pure photopolymer emulsions can be pre-formulated, with high photosensitivity and short exposure time, but they are expensive. Screen printing using double vulcanized photopolymer adhesive.
For larger print jobs (more than 500 prints), especially with water-based inks, special water-resistant emulsions should be used. Standard double-sulfur photopolymer photopolymers and photopolymer photopolymers are very water-resistant, but they are not suitable for larger jobs.
2. Preparation of photosensitive adhesive
Whether it is a dual-sulfuration photopolymerization adhesive or a general diazo photosensitive adhesive, the finished product includes two parts, one is a gum base, and the other is a photosensitizer that reacts with light. When preparing the emulsion, first add some warm water to dissolve the sensitizer powder in the bottle (some sensitizers are dark brown liquids instead of powder). Since the sensitized gel may react with minerals in the water, it is best to use distilled water to dissolve the sensitization. Agent. The temperature of the water should not be higher than 38 °C, otherwise it will affect the performance of the sensitizer; if the water temperature is too low, the powder is not easy to dissolve. Shaking the bottle or stirring it properly helps dissolve the sensitizer.
The next step is to add the sensitizer solution to the gum base and stir it with a non-metallic rod (such as a wooden spoon, etc.), which takes about 10 minutes. When stirring, do not pull it back and forth, preferably in an “∞†shape. Then place the sensitized gel for a few hours, let the bubbles escape, and you can use it.
Photoresist is particularly sensitive to heat and should be stored below 38°C. Keep it in the refrigerator for 1 to 2 months. If the emulsion becomes a cotton-like or agglomerate, it cannot be used anymore. Pure photopolymer emulsions are already prepared at the time of sale and can be stored for up to 5 years.
3. Advantages of photosensitive adhesive making screen
1) Long-lasting performance of photo-resist, can be used for various frames. Suitable for a variety of inks, including water-based fabric dye inks. Since the photoresist can be present inside the screen by coating, such a plate can represent the details of the image.
2) The screen plate made of photo sensitive adhesive can be recycled without affecting the image quality. In most cases (except for photoresists with hardeners), the used screens can be reused after they have been cleaned with solvents.
4. Coating environment
Sensitive glue is quite sensitive to light, but this does not mean that it must work in a dark environment and work under a 50W yellow light. Remember not to go near windows or where there is ultraviolet light. Double-sulfur photopolymer photopolymers and photopolymer photopolymers Specific gravity nitrogen photosensitizers are more sensitive to light and are best handled in a light-free environment.
5. Coating photosensitive adhesive
The main tool for coating emulsions is the sizing, also known as the scraper. There are many specifications for the length of the scraper. The standard size of the scraper used in the screen for printing T-shirts is 14 inches or 16 inches. The length of the scraper should be smaller than the size of the screen inner frame so that it will not touch the blank part of the screen. Some scrapers have a blunt edge and a sharp edge; some scrapers have rounded edges. The sharp edge of the scraper is used for coating, because the thin layer of photosensitive adhesive is thin, and the screen can reproduce the details of the image, which helps to obtain a high quality screen printing plate.
If the emulsion is stored in the refrigerator, it should be brought to room temperature before being poured into the scraper. (When the temperature is low, the emulsion thickens). If the edge of the scraper has a protective layer of rubber, it must be removed before use. When the coating is applied, the screen is erected, and the scraper is placed on the bottom of the outer side of the screen. The tilting scraper is slowly scraped upwards so that the photoresist is applied to the screen. Then repeat this process inside the screen. Many people think that it should be applied 2 to 3 times on the outside of the screen, and 2 to 3 times on the inside of the screen. In fact, such a coating is so thick that it easily causes problems such as underexposure or loss of image detail. The correct method is to first apply the outside of the screen so that the coating on the outside of the screen (printing surface) is thicker, and when the inside of the screen is coated, the photoresist can be scraped back to the outside of the screen. In the coating process, some of the photoresist will run out of the edge of the blade. The remaining photoresist can be removed with a cardboard.
Depending on the purpose of the screen, it is sometimes necessary to coat it several times. However, if the screen is of good quality, it is sufficient to coat the front and back surfaces once. If a double-sulfur photopolymer photopolymer or pure photopolymer photopolymer is used, it should be applied on both sides of the screen twice; if a diazo compound is used, the first coating should be applied. After the photosensitive adhesive is completely dried, it is applied once more in order to increase the thickness and prevent pinholes from appearing. For double-sulfur photopolymer photopolymers and pure photopolymer photopolymers, pinholes generally do not occur if the coating method is correct.
After coating the photosensitive adhesive, be sure to wipe the wipe clean. Otherwise, after the sensitized adhesive dries, it will form a white film on the edge, which will affect the next time it is applied. The blade of the protection scraper is also very important for the quality of glue application. If the knife edge is chipped, it will form stripes when it is applied, which will affect the quality of the plate. If there is a gap in the blade, it is better to replace the scraper and not to repair it.
6. Screen drying
The drying process should be carried out under safe light. It is best to use a drying box (homemade), equipped with a fan, so that the surface of the screen flow of air to accelerate drying. Be careful not to blow the fan directly to the screen so that the blown dust easily adheres to the surface of the photosensitive layer. In general, the screen drying takes 30 to 60 minutes. If the humidity is high, it takes 1 day to dry completely. At this time, if there is a dehumidifier, it will play a significant role.
After the screen is dry, it can be stored in a light box and stored at room temperature for up to 2 months. To increase efficiency, you can apply a batch of screens at one time and save them for use when needed.
Direct film plate method
Another platemaking method of screen printing, known as direct film platemaking, is also traditionally referred to as a hybrid process. In simple terms, the diaphragm used is a transparent acetate film coated with a photoresist.
The direct-diaphragm plate making method is simpler and easier to use than the direct photosensitive platemaking method because it does not require the preparation of photo-sensitive adhesive and the plate-making step is much less. The main advantage of the direct-diaphragm plate making method is that the lines of the printed product are smooth and clean, because when the plate is dry, there is no shrinkage, and only the film is adsorbed on the blank screen. Direct film plate making method is suitable for print products with high printing quality such as self-adhesive labels and posters.
1. Selection of diaphragm
Membranes are sold in rolls or leaflets and come in a variety of thicknesses. For general T-shirt printing, a film with a thickness of 38 μm is preferred; for a screen with a high mesh number (for example, 230-350 mesh/inch), a thinner diaphragm (18 μm) may be used. If the number is low (eg 86 mesh/inch), a 60 μm thick film is used; if the color printing on black fabric requires a larger amount of ink, a thicker film is required.
The diaphragm has the same sensitization characteristics as the photopolymer, and should be operated in soft lighting or yellow light, and the temperature should not be too high during storage. The screen made by the direct film plate method can be stored for about 1 month.
2. Foil
The filming process is to make the moisture in the screen rely on "capillarity" to adsorb the film on the screen. Whether the photosensitive film is attached firmly or not depends on the degree of cleanliness of the screen. There is a kind of chemical agent called "wetting agent", which helps the screen to absorb moisture during the process of adhering the film. Just apply some "wetting agent" to the screen and wipe it with a sponge and apply it with water. The "wetting agent" can be rinsed. When there is a lot of water on the screen, it is necessary to spread the film on the screen (roughly facing the screen) and then use a rubber roller to roll the inside and outside of the screen. If there are still some areas that are not sticky, spray a little water on the inside of the screen where there is no adhesion, roll with a rubber roller, and spray to the area where the diaphragm is not attached.
Each diaphragm has its own method of operation. We only need to follow the instructions. After the attachment is completed, it will take about 30 minutes to dry. Then, the bottom film of the film is peeled off and the exposure can be performed. Before removing the bottom film, make sure that the screen and the film are completely dry. If the bottom film is peeled off, it is difficult to completely dry the screen. If it is because of the high humidity, the film can be dried for a period of time after the bottom film is removed.
Many manufacturers prefer to use the direct-diaphragm plate-making method because the plate-making speed is high and the plate-making process is simple. However, if you use the direct-diaphragm plate-making method and you always do not get a satisfactory plate, check whether the mesh size is higher than 200 mesh/inch.
In the case of high-mesh screens for the production of colored halftone printing plates, the use of direct photographic platemaking methods still holds an advantage.
When selecting the screen, it is necessary to pay attention to the matching of the number of screen meshes with the quality of the printed product; the stretchability of the screen should be as small as possible; the structure of the screen must be tight, otherwise it is impossible to make a screen with high quality.
If the screen is used before, the screen must first be deoiled, dust removed, and the remaining ink must be removed. Cleaning agent for cleaning mesh should be selected from the newly purchased concentrated washing agent. It is better not to use household detergent or washing powder, because it contains flavors, hand protection agents (washing spirit) and bleach (washing powder) and other additional Ingredients, but also the particles will be blocked.
When washing the screen with a washing agent, apply both sides of the screen evenly and wipe it repeatedly with a sponge. Then rinse the screen with water and dry it to ensure that there is no residual foam on the screen. After the screen has been cleaned, never touch it with your hands.
After cleaning, dry the screen in a dust-free environment. Many people still use the method of drying the fan against the wire mesh. However, the dust is relatively large. It is better to make a drying box so that the airflow can evenly flow over the surface of the screen. At the same time try to wash the net on the same day, the day coated with photosensitive adhesive, which prevents the screen from falling dust again. If the humidity of the operation site is large, it is best to install a dehumidifier to speed up screen drying.
There are still people who use rougheners to roughen the edges of the wire. This method is suitable for use in indirect platemaking methods, which improves the fastness of the photosensitive film to the screen. If we use the photosensitive emulsion method to make screen printing plates, there is no need for roughening, otherwise it will reduce the strength of the screen.
Second, the Plate making method
The most commonly used screen printing methods are the direct photosensitive platemaking method and the direct film plate making method. The following mainly introduces the new photosensitive materials and plate making processes that appear in these two methods.
Direct photosensitive adhesive plate making method
1. Photosensitive adhesive type and performance
In simple terms, the photosensitive adhesive is a colloidal liquid that can be exposed to light and can be chemically reacted. The screen can be uniformly coated with a scraper on a clean and completely dried screen to obtain a screen with sensitometric properties.
There are many kinds of photosensitive adhesives, and commonly used are diazo compound photosensitive polymers and double-sulfur photopolymer photosensitive polymers. The double-sulfurated photopolymer photopolymer has less moisture content and less shrinkage during the drying process than the diazo compound photo-sensitive adhesive. This advantage can make the graphic image on the screen plate obtain a sharp edge, and can accelerate the speed of plate making. When using water-based inks, its durability is better. As a result, bisulfide photopolymer emulsions are gradually replacing diazo compounds.
In addition to the above two kinds of photosensitive adhesives, some large-scale screen printing companies also use a pure photopolymer emulsion. Pure photopolymer emulsions can be pre-formulated, with high photosensitivity and short exposure time, but they are expensive. Screen printing using double vulcanized photopolymer adhesive.
For larger print jobs (more than 500 prints), especially with water-based inks, special water-resistant emulsions should be used. Standard double-sulfur photopolymer photopolymers and photopolymer photopolymers are very water-resistant, but they are not suitable for larger jobs.
2. Preparation of photosensitive adhesive
Whether it is a dual-sulfuration photopolymerization adhesive or a general diazo photosensitive adhesive, the finished product includes two parts, one is a gum base, and the other is a photosensitizer that reacts with light. When preparing the emulsion, first add some warm water to dissolve the sensitizer powder in the bottle (some sensitizers are dark brown liquids instead of powder). Since the sensitized gel may react with minerals in the water, it is best to use distilled water to dissolve the sensitization. Agent. The temperature of the water should not be higher than 38 °C, otherwise it will affect the performance of the sensitizer; if the water temperature is too low, the powder is not easy to dissolve. Shaking the bottle or stirring it properly helps dissolve the sensitizer.
The next step is to add the sensitizer solution to the gum base and stir it with a non-metallic rod (such as a wooden spoon, etc.), which takes about 10 minutes. When stirring, do not pull it back and forth, preferably in an “∞†shape. Then place the sensitized gel for a few hours, let the bubbles escape, and you can use it.
Photoresist is particularly sensitive to heat and should be stored below 38°C. Keep it in the refrigerator for 1 to 2 months. If the emulsion becomes a cotton-like or agglomerate, it cannot be used anymore. Pure photopolymer emulsions are already prepared at the time of sale and can be stored for up to 5 years.
3. Advantages of photosensitive adhesive making screen
1) Long-lasting performance of photo-resist, can be used for various frames. Suitable for a variety of inks, including water-based fabric dye inks. Since the photoresist can be present inside the screen by coating, such a plate can represent the details of the image.
2) The screen plate made of photo sensitive adhesive can be recycled without affecting the image quality. In most cases (except for photoresists with hardeners), the used screens can be reused after they have been cleaned with solvents.
4. Coating environment
Sensitive glue is quite sensitive to light, but this does not mean that it must work in a dark environment and work under a 50W yellow light. Remember not to go near windows or where there is ultraviolet light. Double-sulfur photopolymer photopolymers and photopolymer photopolymers Specific gravity nitrogen photosensitizers are more sensitive to light and are best handled in a light-free environment.
5. Coating photosensitive adhesive
The main tool for coating emulsions is the sizing, also known as the scraper. There are many specifications for the length of the scraper. The standard size of the scraper used in the screen for printing T-shirts is 14 inches or 16 inches. The length of the scraper should be smaller than the size of the screen inner frame so that it will not touch the blank part of the screen. Some scrapers have a blunt edge and a sharp edge; some scrapers have rounded edges. The sharp edge of the scraper is used for coating, because the thin layer of photosensitive adhesive is thin, and the screen can reproduce the details of the image, which helps to obtain a high quality screen printing plate.
If the emulsion is stored in the refrigerator, it should be brought to room temperature before being poured into the scraper. (When the temperature is low, the emulsion thickens). If the edge of the scraper has a protective layer of rubber, it must be removed before use. When the coating is applied, the screen is erected, and the scraper is placed on the bottom of the outer side of the screen. The tilting scraper is slowly scraped upwards so that the photoresist is applied to the screen. Then repeat this process inside the screen. Many people think that it should be applied 2 to 3 times on the outside of the screen, and 2 to 3 times on the inside of the screen. In fact, such a coating is so thick that it easily causes problems such as underexposure or loss of image detail. The correct method is to first apply the outside of the screen so that the coating on the outside of the screen (printing surface) is thicker, and when the inside of the screen is coated, the photoresist can be scraped back to the outside of the screen. In the coating process, some of the photoresist will run out of the edge of the blade. The remaining photoresist can be removed with a cardboard.
Depending on the purpose of the screen, it is sometimes necessary to coat it several times. However, if the screen is of good quality, it is sufficient to coat the front and back surfaces once. If a double-sulfur photopolymer photopolymer or pure photopolymer photopolymer is used, it should be applied on both sides of the screen twice; if a diazo compound is used, the first coating should be applied. After the photosensitive adhesive is completely dried, it is applied once more in order to increase the thickness and prevent pinholes from appearing. For double-sulfur photopolymer photopolymers and pure photopolymer photopolymers, pinholes generally do not occur if the coating method is correct.
After coating the photosensitive adhesive, be sure to wipe the wipe clean. Otherwise, after the sensitized adhesive dries, it will form a white film on the edge, which will affect the next time it is applied. The blade of the protection scraper is also very important for the quality of glue application. If the knife edge is chipped, it will form stripes when it is applied, which will affect the quality of the plate. If there is a gap in the blade, it is better to replace the scraper and not to repair it.
6. Screen drying
The drying process should be carried out under safe light. It is best to use a drying box (homemade), equipped with a fan, so that the surface of the screen flow of air to accelerate drying. Be careful not to blow the fan directly to the screen so that the blown dust easily adheres to the surface of the photosensitive layer. In general, the screen drying takes 30 to 60 minutes. If the humidity is high, it takes 1 day to dry completely. At this time, if there is a dehumidifier, it will play a significant role.
After the screen is dry, it can be stored in a light box and stored at room temperature for up to 2 months. To increase efficiency, you can apply a batch of screens at one time and save them for use when needed.
Direct film plate method
Another platemaking method of screen printing, known as direct film platemaking, is also traditionally referred to as a hybrid process. In simple terms, the diaphragm used is a transparent acetate film coated with a photoresist.
The direct-diaphragm plate making method is simpler and easier to use than the direct photosensitive platemaking method because it does not require the preparation of photo-sensitive adhesive and the plate-making step is much less. The main advantage of the direct-diaphragm plate making method is that the lines of the printed product are smooth and clean, because when the plate is dry, there is no shrinkage, and only the film is adsorbed on the blank screen. Direct film plate making method is suitable for print products with high printing quality such as self-adhesive labels and posters.
1. Selection of diaphragm
Membranes are sold in rolls or leaflets and come in a variety of thicknesses. For general T-shirt printing, a film with a thickness of 38 μm is preferred; for a screen with a high mesh number (for example, 230-350 mesh/inch), a thinner diaphragm (18 μm) may be used. If the number is low (eg 86 mesh/inch), a 60 μm thick film is used; if the color printing on black fabric requires a larger amount of ink, a thicker film is required.
The diaphragm has the same sensitization characteristics as the photopolymer, and should be operated in soft lighting or yellow light, and the temperature should not be too high during storage. The screen made by the direct film plate method can be stored for about 1 month.
2. Foil
The filming process is to make the moisture in the screen rely on "capillarity" to adsorb the film on the screen. Whether the photosensitive film is attached firmly or not depends on the degree of cleanliness of the screen. There is a kind of chemical agent called "wetting agent", which helps the screen to absorb moisture during the process of adhering the film. Just apply some "wetting agent" to the screen and wipe it with a sponge and apply it with water. The "wetting agent" can be rinsed. When there is a lot of water on the screen, it is necessary to spread the film on the screen (roughly facing the screen) and then use a rubber roller to roll the inside and outside of the screen. If there are still some areas that are not sticky, spray a little water on the inside of the screen where there is no adhesion, roll with a rubber roller, and spray to the area where the diaphragm is not attached.
Each diaphragm has its own method of operation. We only need to follow the instructions. After the attachment is completed, it will take about 30 minutes to dry. Then, the bottom film of the film is peeled off and the exposure can be performed. Before removing the bottom film, make sure that the screen and the film are completely dry. If the bottom film is peeled off, it is difficult to completely dry the screen. If it is because of the high humidity, the film can be dried for a period of time after the bottom film is removed.
Many manufacturers prefer to use the direct-diaphragm plate-making method because the plate-making speed is high and the plate-making process is simple. However, if you use the direct-diaphragm plate-making method and you always do not get a satisfactory plate, check whether the mesh size is higher than 200 mesh/inch.
In the case of high-mesh screens for the production of colored halftone printing plates, the use of direct photographic platemaking methods still holds an advantage.
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