Preparation before starting flexo

Years of flexographic printing practice tell us that the meticulous pre-press preparation is very important. If the pre-press work is not done properly, careless and hasty, then there will be small problems and embarrassment of big problems, not only will waste raw and auxiliary materials, reduce the product qualification rate, affecting the product Quality has caused serious economic losses, and may also delay delivery time, reducing the reputation of the enterprise. Therefore, the author believes that optimizing human resources and carefully doing every preparation work before flexo printing start-up is crucial to our work.

The specific preparation work before the flexible start-up mainly includes the following points:

1. Inspection and maintenance of equipment

Equipment is the basis for producing high-quality products, and careful maintenance and maintenance of machinery and equipment is very necessary. First of all, the surface of the machine, paper feed, static electricity and dust removal parts should be carefully cleaned, and all the paper rollers of the machine should be scrubbed to reduce the dirt and sticky phenomenon in the printing production. Then, add lubricating oil to the gears of the machine and each oil injection port to reduce wear. Also check whether there is any looseness in each transmission chain and connection parts, and master the working status of the equipment.

Second, master the pre-press process requirements

1. Familiar with the standard proofs, including the color status of the proofs, the main features of the pictures and the main technical requirements.

2. Review the printing color sequence, if there is something wrong, you can put forward a modification opinion. Under normal circumstances, small ink volume, line text, and four-color small graphics and text are printed on the front. It is easy to dry, the oven temperature is low, the paper deformation is small, and the overprint is relatively stable; large solid, gold ink, silver ink and ink Large amounts of graphics and text are printed at the back.

3. Understand the main performance characteristics of the printing materials, especially the main performance of the inks and solvents used.

Third, the inspection of the preparation and post

For the plate rollers used, the plate rollers produced by the same manufacturer and the same batch should be selected. Check whether the roller bearing rotates smoothly and replace it if there is any abnormality. Check whether the gear is clean, and clean it with kerosene in time, and apply grease after finishing. Remove the reel shaft and check for damage. Clean the ink in the ink tray and ink fountain, and clean the ink pump, hose and ink roller. Clean the plate cylinder and anilox roller.

Take out the new printing plate before affixing the plate, wipe the front and back with alcohol, clean the residue, and then cut the plate. According to the number of teeth of the plate roller, cut out the appropriate size printing plate.

If the cutting size is slightly larger, after the plate is pasted, there will be excess at the plate interface. Some colleagues will use the blade to cut off the plate roller directly, so it will inevitably scratch the plate roller. As time goes by, many scratches will appear on the plate roller.

If the size of the cut is slightly smaller, the gap at the interface of the attached plate is large, and the sealing tape cannot be stuck on it flatly, it will foam, and the plate will often be wiped during printing, and the solvent will penetrate, resulting in the interface of the plate The sealing tape is lifted everywhere, and unnecessary dirty spots appear on the surface of the printed product.

Therefore, it is best to cut it with a sharp blade at the time of cutting, so that it is clean and tidy, and does not drag mud and water. Blunt knife cutting, after the printing plate is cut, there will be many burrs on the edge, which will affect the product's overprint. The plate mounting tape should be flat against the surface of the plate roller without air bubbles. When attaching the plate, carefully align the lens to ensure that the overprint line of the plate is horizontal and vertical. Each plate must be repeatedly checked and verified to be correct before it can be sealed. The edge of the sealing tape should be flattened tightly with the back of the blade or a smooth tool with a fluted edge.

4. Optional anilox roller and pressure adjustment

Corresponding anilox roller is selected according to the process sheet. When selecting, there may be several anilox rollers with the same number of lines, the length of use is different, the surface wear is different, and some even have scratches. You must know the use status of each anilox roller, which specific One can be carried out according to the graphic features of the product, to avoid blindness, and it will be handy to operate.

Flexographic printing is light pressure printing, and the adjustment of pressure is one of the keys to the success or failure of printing. Since the pressure adjustment range is very small, it should be carefully operated during adjustment. The requirements of flexo for pressure are very strict, which directly determines the reproduction of graphics and text and affects the quality of printing. With years of experience in operating the machine, the author believes that it is best to use the same plate roller and a feeler gauge to adjust the pressure in each color group, so that the adjusted pressure is almost the same.

Five, ink preparation

1. Before starting the machine, the ink should be fully stirred, especially the ink that has been placed in the warehouse for a long time, and the viscosity is large. After the large bucket is fully stirred, pour into the small bucket. According to the viscosity of the ink, add a small amount of pH adjustment liquid, add a special diluent to the gold and silver ink, and then stir in a clockwise or counterclockwise direction to evenly distribute the pigment particles in the connecting material, so that the ink printing Adaptability is optimal.

2. For old ink or skinned ink, it is better to filter with 300 mesh mesh. The gold and silver ink can be filtered with a thicker mesh cloth to remove the solidified particles of the skin, to avoid damage to the doctor blade and the anilox roller, and to prevent the printed product from being dirty.

3. Generally, the stability of ink is poor, and the color will deepen when the new ink is left for a period of time. If there are spot color ink products, it is best to mix them in proportion one or two days before printing, stir them uniformly and fully according to one aspect, and then place the cover to make the stability of spot color ink hue and printing suitability reach the best state. .

Six, check the doctor blade and knife holder

When installing the squeegee blade, carefully check whether the blade is damaged. If it is not available to reduce waste and cost, it can be used in a color group that is not accessible by the text. When the ink tray is not filled with ink, the anilox roller cannot rotate in contact with the doctor blade to avoid damage to the anilox roller. When the squeegee works on the anilox roller, check whether its length and position are appropriate to the position of the anilox roller, and check whether there is leakage of ink on both sides of the anilox roller. The length of the doctor blade is preferably equal to the length of the anilox roller, which can reduce the waste of ink and the phenomenon of flying ink during the high-speed operation of the machine.

7. Control of printing tension

In flexographic printing, the printing tension refers to the sum of the tensile force generated by the tension device on the printing material and the tensile force the printing material is subjected to during printing. The change of printing tension is one of the main reasons that affect the accuracy of overprinting and determines the rate of rejects. For the unit-type flexo printing machine, the tension between the color units does not need to be adjusted. In order to eliminate the interference on the tension of the paper belt when the plate cylinder is pressed, the diameter of the impression cylinder body of each unit should be 0.01 larger than the previous group ~ 0.02mm, the impression cylinder of each unit cannot be changed at will.

The register of the unit-type flexo printing machine is often not ideal at low speed (15m / min). This is because the friction resistance and inertia of the machine parts have not yet entered a stable state. Once the machine enters the high-speed state, the registration effect Can be improved. Therefore, the coarse adjustment can be completed as soon as possible when the machine is at low speed (register error is within 1mm), and then with the increase of the vehicle speed, the registration fine adjustment is completed on the main console.

8. Preparation for post-processing

Under normal circumstances, products are cut into large sheets after printing, and then post-processes such as bronzing, rolling bumps, die cutting and so on. If the product printed by the flexographic printing machine is an on-line forming product, the indentation is formed by the yin-yang indentation roller pressing the paper under a certain pressure. Put on the negative roller first on the machine, carefully check whether there are foreign objects in each creasing line slot, so as to avoid damaging the male tool or bursting the wire after the machine.

When the mold is hoisted onto the machine, it cannot collide with the equipment and the tool used. After installation, carefully adjust to ensure that the body and the outer roller body are in a vertical state, laying a solid foundation for the zero alignment of the male and female rollers. Install the male roller in the same way. When the male roller and female roller are aligned, they should be aimed at the zero position. After meshing, move the machine by hand to ensure that it runs smoothly. Then install the pressure frame and pressure gauge. Look at the pressure gauge when the machine is running at low speed. Pressurize slowly on both sides at the same time, which is subject to the full indentation line. If the indentation line is not full enough, the line has burst, which means that the positioning of the male and female rollers is incorrect. You need to fine-tune the positioning gear of the male roller. After adjustment, lock the gear and apply grease.

There are many preparations for flexo printing before it is turned on. As long as one of the preparations is not in place, it will affect the quality of the printed product to a certain extent. "Details determine success or failure" is the best interpretation of pre-press work, and plays an important role in improving the quality of printed products.

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