Steel drum screen printing and plate making (3)
Steel drum screen printing and plate making (3)
Yang Wenliang
(3) Method of making screen printing plate
Usually made by photo-adhesive coating. The photosensitive adhesive coating plate making method directly applies the photosensitive adhesive on the screen, and is dried, plated, developed, and the like to form a plate film, and the specific manufacturing process is shown in FIG. 4 .
1, making a positive film negative
Positive screen negatives are required for silk screen printing. There are two ways to make a positive film, one is a manual drawing method and the other is a photo filming method.
(1) Hand-drawing method Use a brush, a pen, etc. to draw a graphic on a transparent film or tracing paper. This is a positive image of the printing plate. In order to prevent the ink on the film from being cracked after drying, a small amount of sugar can be added to the ink, and a small amount of beer can be added for the defoaming. The manual depiction method is mainly used to produce negative-looking negative films with low requirements and simple graphics. If you need to make a layer of positive film, you should use the filming method.
(2) Photographic method Using a photographic apparatus, the original is taken into a negative image, and then the negative image is turned into a negative image. If it is an original with a change in shades, you need to make a negative image of the screen, and then turn it into a picture of the net. If it is a color original, you need to make a color separation picture, and then turn the color negative film.
2, pretreatment of the wire mesh
The pretreatment of the wire mesh mainly includes two aspects of degreasing treatment and dyeing treatment.
(1) Degreasing treatment of the screen has grease and dirt, which will reduce the bonding strength between the film and the screen, and affect the quality of the plate making. Degreasing treatment is required for this purpose. There are three types of commonly used degreasing treatments:
1 Decontamination powder degrease first soak the wire mesh, then place it on a flat surface, use a brush to rub the decontamination powder, brush it on the wire mesh, rinse it with water, dry it naturally or dry it at low temperature.
2 Solvent degreasing with cotton cloth with acetone, alcohol, banana water and other solvents, scrub on the wire mesh, and dry for use.
3 Dilute the alkaline liquid degreasing with 10% sodium hydroxide solution, then rinse with water, naturally dry or low temperature drying. Metal frame is not suitable for this method.
(2) Dyeing The purpose of the dyeing process is to absorb the light shining on the screen to eliminate the diffuse reflection of the light during the printing, thereby improving the sharpness of the plate. The dyeing process is to uniformly apply the dyeing solution to the screen with a brush, and after drying, the photoresist can be applied. The staining solution is prepared by adding cresol or a red alcohol-soluble dye to an ethanol solution. If it is a colored screen, there is no need for dyeing.
3. Preparation and coating of photosensitive adhesive
(1) Preparation of Photosensitive Glue Photosensitive adhesives are generally classified into solvent-resistant and water-resistant types. Solvent-resistant photoresist for printing on water-based inks. The former screen can be removed by film removal; the latter can not be removed by film removal. Special water resistant photosensitive adhesives include nylon photosensitive adhesive and diazo photosensitive adhesive. The user must select the appropriate photoresist according to the specific conditions of the steel drum and refer to the relevant instructions.
Now introduce the formulation of several photosensitive adhesives:
1 polyvinyl alcohol photosensitive adhesive
Formulation 1: S mesh glue 100g, 8% ammonium dichromate solution 25g. S wire mesh glue is produced by Japan Kanto Chemical Co., Ltd.
The preparation method is as follows: 10 g of ammonium dichromate is dissolved in 100 g of water, and then mixed with S mesh glue in proportion, and stirred uniformly. The newly adjusted photoresist can not be used immediately, generally need to be placed in the cold and dark place for 8h. This is because many bubbles in the just-adjusted photoresist are coated on the screen to produce pinholes, and the photosensitive adhesive that has just been prepared is still poor in photographic performance.
Formulation 2: Mino 100# wire mesh glue or 200# wire mesh glue 100g, 4% ammonium dichromate 20g. Mino 100#, 200# wire mesh glue is produced by Japan Fuji Pharmaceutical Co., Ltd., 100# is a thick film type, and 200# is a solvent resistant type.
The preparation method is the same as that of Formula 1.
Formulation 3: 32# EZ wire mesh glue 100g, 10% ammonium dichromate solution 20g. 32#EZ Wire Mesh is produced by Nazdal Corporation of the United States. The preparation method is the same as that of Formula 1.
2 gelatin photosensitive adhesive
Formulation: gelatin 180g, citric acid 10g, alcohol 20mL, water 1000mL, red strontium potassium 30g, ammonium dichromate 10g, barium sulfate 10g, ammonia water 55mL.
The preparation method is as follows: the above substances are dissolved and filtered by heating, and the glue liquid is easy to freeze, so it is kept at a relatively high temperature (for example, 70 ° C), and is applied to the back of the screen in a dark room.
3 nylon photosensitive adhesive
Formulation 1: ternary nylon 200g, methylene bis acrylamide 50g, benzoin ether 2g, diethanolamine 0.4mL, benzophenone 5g, ethanol 1000mL, active K blue dye 2g, phthalic anhydride 0.8mL.
The preparation method is as follows: dissolve ternary nylon with 750mL of ethanol; dissolve other additives with 250mL of ethanol, heat and stir while stirring; after the two kinds of liquid preparations are fully dissolved, mix, dissolve the active K blue dye with a small amount of hot water, and add The mixture was thoroughly stirred and filtered for use.
Formulation 2: ternary nylon 100g, methylene diacrylamide 30~40g, benzophenone 6~7g, active K blue dye 1g, ethanol 400~500mL.
Formulation 3: ternary nylon 100g, ammonium dichromate 20~40g, ethanol 400~500mL. Dissolve the ternary nylon in ethanol; dissolve the ammonium dichromate with a small amount of hot water, mix the above two solutions, stir well, and filter for use.
The easiest way is to buy photo-sensitive adhesives from the market. For example, the high-strength nylon photographic adhesive made by Shanghai Zhonghua Printing Factory is made of multi-component nylon as a film-forming agent, with cross-linking agent, sensitizer and other auxiliary materials. The following features:
a. Water, acid and alkali resistant, organic solvent resistant, anti-toluene, xylene, cyclohexanone, acetophenone, ethyl acetate, banana water, gasoline, fire oil and other solvents.
b. The photographic tolerance is large, the resolution is high, the minimum line width can reach 0.025mm, and the network cable version can be made.
c. Thick film screen can be made, the coating film can reach 0.20mm or more.
d. Easy to operate, nylon photosensitive glue is single-liquid type, can be operated in bright room (can be operated under fluorescent light, but not in daylight); the light source is UV (can be printed under sunlight), developing With industrial ethanol, it can be cleaned with a brush.
e. High printing durability, the number of prints can reach more than 100,000 times.
f. It can be prefabricated. After the glue is finished, the screen will be stored and used for printing.
g. The glue has a long storage period and is stored in the dark at room temperature. The validity period can be more than 2 years.
h. Suitable for all kinds of screen printing plates.
Its shortcoming is that it can't be off the net, and it can't make the screen use repeatedly. If you can use the screen repeatedly, you can buy Italian A38 (oily) photoresist or Dutch Autosal Plus II adhesive. Use it to make plates, if the pattern is not ideal, use the release powder to remove, and then re-plate, until satisfied. Its coating thickness is easy to grasp, and the sensitivity is large; the resolution, printing durability and graphic clarity are better than those made in China.
(2) Coating of photosensitive adhesive There are various coating methods for photosensitive adhesive, such as stainless steel tank coating method, brush coating method, casting coating method, plastic film coating method and machine coating method. Among them, the stainless steel tank coating method is more commonly used. When coating, the film surface must be free of spots, uniform in thickness, and shiny after drying. The coating thickness is generally 10 to 30 μm. If the coating layer is too thin, the edges of the printed image tend to be rough and jagged; if the coating layer is too thick, the amount of ink permeation will be affected.
The stainless steel tank coating operation process is as follows:
a. Pour the photoresist into the stainless steel tank to half the capacity of the tank.
b. Tilt the screen plate at 70°.
c. The stainless steel tank is in contact with the lower end of the wire mesh, and while the groove is inclined to flow out of the photosensitive glue, the groove is slowly lifted up and coated along the screen surface. It should be noted that the coating should be slow, otherwise bubbles will be generated.
d. Turn the screen frame upside down and apply it again as described above.
e. Blow the hot air at 32~36 °C to make the film surface dry.
f. Apply 2~4 times according to the above steps until the film surface is shiny.
4, dry
During the coating process, although the photosensitive film has been dried, it needs to be further dried before printing. It is generally dried by hot air. The drying temperature is preferably around 35 ° C, and it is not allowed to exceed 40 ° C. Do not allow dust to fall on the film surface during drying, otherwise pinholes and the like may occur. After drying, it should be printed as soon as possible to ensure the quality of plate making.
5, printing version
First use a soft brush to clean the screen film, the sun-dried glass and the positive film, then put the negative film and the frame with the wire mesh into the printing box, and see the negative film in the silk through the printing glass. Position the frame and set it to the final exposure.
In order to allow the positive film to be adhered to the photosensitive film of the screen, it is preferable to use a printing box with a vacuuming device. The printing plate can use light such as arc lamp, fluorescent lamp, high pressure mercury lamp, xenon lamp, incandescent lamp and daylight. The exposure time varies greatly depending on the type of photosensitive adhesive, the thickness of the photosensitive film, the type of light source, the distance between the light source and the screen, and the specific exposure time is preferably determined by a test method. The specific operation is as follows: firstly, cover the light barrier and place it under 1000W/220V high-pressure mercury lamp for 5min, then cover the photo film on the screen for 10~20min. During the exposure process, the frame is about 30cm away from the high-pressure mercury lamp and cooled by a fan (if using a cold light source, it can be cooled without a fan).
6, development
Dip the dried plate in water for 1~2min, and then rinse it off with water after the non-photosensitive part absorbs water. The film with good solvent resistance should be developed with warm water (35 ° C) for 1~2 min, then rinsed with warm water of about 42 °C. The nylon photosensitive film needs to be soaked or brushed with ethanol to develop. The development time of the plate should be as short as possible.
7, dry again
Drain the plates first, then use a sponge to blot the water at the corners of the plate, then dry with hot air or dry naturally. If hot air drying is used, the hot air temperature should not exceed 40 °C, otherwise the printed image will be out of shape, otherwise the screen will be slack.
8, revision and de-filming
(1) After the revision plate is dried, it is generally necessary to perform small trimming, such as clogging of pinholes in the plate. Block the pinhole to apply the plate of the photosensitive adhesive, and then sensitize for 5min, or use the net to fill the net.
(2) The film on the screen can be removed when the plate-making is wrong or when the old plate needs to be replaced. The screen after removing the film can continue to be used.
The method of removing the film: first remove the residual ink on the screen printing plate, then apply the two sides of the silk printing plate with the de-coated film or the release film powder or soak in the de-coated film agent, after 5 to 10 minutes, the film is issued. White, then rinse with water (or scrub with a sponge). After the film is removed, the screen is dried. The de-coating agent is hydrogen peroxide, hypochlorous acid solution, sodium hydroxide solution, ammonia water, lactic acid, and the like.
The photosensitive plate coating method has high quality, good effect and economical and practical, so this plate making method is the most important plate making method in modern screen printing. Other plate making methods include hand-engraving plate making method, non-photosensitive glue coating method and carbon. Plain paper plate making method, photosensitive film making method, infrared plate making method and electronic plate making method.
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