Flexographic production process (continued)
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development. The exposed plate is unwashed and the layout is still flat, but there is a latent image of the image and text on the plate. After developing with an organic solvent and brushing with a special brush, the photosensitive resin layer which has not been photohardened is washed and dissolved in the machine tank. The light-receiving photosensitive resin layer is polymerized and hardened, and is not dissolved by an organic solvent, so that the plate surface has an uneven shape and becomes a printing plate.
The rinsing time is proportional to the embossing depth of the layout. The time is long, the relief is deep, and conversely, the time is short and the relief is shallow. At the same time, the length of the flexographic rinse is also directly related to the temperature of the developer, the length of use, and the pressure of the brush.
It can be seen that the rinsing time is flexibly controlled according to various relevant factors. During the flexo rinsing process, the cover can be opened for inspection. When the rinsing time is insufficient, the cover can be covered and the rinsing can be continued until the requirements are met.
Preparation of developer. Common organic solvents used in the rinse are: a) trichloroethylene or tetrachloroethylene; b) trichloroethane; c) n-butanol. In the preparation of the developer, the organic solvents a) and b) are the main agents, and the ratio to c) is 4:1. However, it should be noted that the ratio is not the ratio of the quantity, but the ratio of the specific gravity of the solvent. After the solution is prepared, its standard specific gravity should be 1.42Bé, which can be measured by a specific gravity meter. If the solution exceeds 1.42B, the main agent is excessive, otherwise the main agent is insufficient.
The correct ratio of the solution is related to the length of time the developer is used, and more importantly, it affects the quality of the printing plate.
Dry (dry). The photosensitive resin layer is immersed in an organic solvent to cause the resin to absorb the solvent, i.e., to swell, and to cause stickiness. The drying is carried out in a constant temperature hot air drying oven at a temperature of 60 ° C and a drying time of 10-15 min. The drying time of the cardboard box with the thick plate is correspondingly increased. The drying mainly volatilizes the solvent absorbed by the photosensitive resin layer to restore the photosensitive resin layer to the original thickness to facilitate printing.
Post processing. In order to make the surface of the printing plate non-tacky, the following method is used to de-stick the layout.
Illumination method. Use short-wave UV to illuminate the plate for a short period of time to achieve the purpose of dirtying the plate.
Chemical law. Using a solution of dilute hydrochloric acid, water, or detergent, the plate of the dried plate is facing up, and the solution is immersed in the solution to remove the viscosity. Then rinse the remaining surface of the plate with water and dry.
Powder method. Apply a thin layer of magnesium carbonate or talcum powder to the dried plate to remove it. This method is simple, time-saving and practical, but the plate must be powdered after the post-exposure.
Post exposure. The de-bonded printing plate is placed in the exposure device with the layout facing up, and the light source is directly turned on without vacuuming, and the exposure is performed for a short time, so that the upper, middle and lower resin layers of the plate are completely hardened. Its role is to increase the hardness of the layout, increase the printing durability of the printing plate; the second is to improve the corrosion resistance of the ink solvent. Excessive exposure time will also cause the surface of the printing plate to be too hard and brittle to reduce the elasticity of the printing plate.
3 common problems and solutions in plate making
The flexographic plate making process is not too complicated, but it involves the quality of the plate, the quality of the negative film, the strength of the light source, the exposure time, the old and new development of the developing solution, and other factors. Quality issues or scrap.
The common ills and causes of the plate making process are listed in Table 1 for reference.
4 method for saving flexographic plates
When the newly purchased new material is stored in the warehouse, it must be placed on the shelf. It cannot be placed vertically, otherwise it will be deformed and cannot be stressed.
When working in the opening operation, it is necessary to avoid the sunlight or unsafe light when working in the room with yellow light. When cutting, use a ruler and a sharp knife to cut, to prevent genuine creases or shells. After cutting, the small version of the version is placed in the box, and it should be placed in a single piece. Do not put it on the side to prevent the use of the scrap.
After printing, the plate must be cleaned, talcum powder, wrapped in black paper or protected from light, stored in a dry and dark place to prevent the plate from being hard, brittle or cracked.
5 quality standards for flexible plates
Regardless of the printing process, prepress production has a great influence on the quality of printed matter. What's more, flexographic plate making is a "shape". Either it is good or it is a waste version. It is impossible to make up and correct it in the middle of the problem. This is the biggest shortcoming of flexo. At the same time, it is necessary to avoid the trouble of adding the next printing process, and must master the following quality standards:
1. The plate must have a certain hardness. Depending on the printing process, the hardness of the plate on the plate is required to be different. The flexographic surface of the Invar carton has a Shore hardness of about 30-35 degrees, and the printing plate of plastic film and paper has a Shore hardness of about 50-55 degrees.
2. The four corners of the plate are uniform and the thickness is the same. The depth of the relief of the plate should be about 1/2 of the thickness of the plate. The small text and the small space have a certain depth.
3. The edge of the text and lines should have a certain slope, and the layout is not sticky.
4. Text, lines, field version, no missing strokes, broken lines, sand holes, dirty spots, etc.
5. The size of the printing plate is accurate, the color separation plate is correct, and the bottom of the concave part is flat.
6. Netted layer version, high and low-key outlets can not be lost, the outlets are smooth, low-key parts of the outlets have a little depth.
Table 1 common disadvantages and causes of the plate making process
Malady
1, the text image is not clear
cause
1 Yin picture density does not meet the plate making standard; 2 insufficient pumping; 3 main exposure time too much
Malady
2, thin line bending, text break pen damage
Cause
1 main exposure time is insufficient, pre-exposure time is insufficient; 2 negative film has dirty spots or transparency is not high or fog; 3 flushing time is too long or brush pressure is too heavy
Malady
3, the layout relief is too shallow
Cause
1 pre-exposure time is too long; 2 flushing time is insufficient; 3 developer is stale
Malady
4, the printing plate base is not flat
Cause
1 part of the lamp is too old or not luminous; 2 brush uneven or insufficient washing time; 3 development solution is too old or the amount of solution is insufficient
Malady
5, the layout of the word map is not smooth
Cause
1 flushing liquid is too old; 2 the last page cleaning is insufficient
Malady
6, in the text, anti-white characters, lines (commonly known as hollow lines) and not
Cause
1 main exposure time too much; 2 negative image density is insufficient; 3 flushing time is insufficient
Malady
7, the plate is orange peel
Cause
1 wash plate preparation is wrong; 2 washing time is too long; 3 washing solution is too dirty
Malady
8, the layout is too sticky
Cause
1 de-sticking time is insufficient; 2 drying time is insufficient; 3 after exposure time is insufficient
Malady
9, the layout of the crack
Cause
1 baking temperature is too high; 2 after the exposure time is too much; 3 indoor ozone concentration is too high