Cleaning operations and precautions during the offset printing process

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Cleaning work such as printing plates, blankets, water rollers, ink rollers, etc. is one of the main contents of the daily operations of offset printing. Proficient and timely cleaning operations can not only improve the printing plate durability and the service life of the blanket, It is of great significance to ensure the quality of printing and compress the auxiliary production time so that the production can proceed smoothly.

PS version cleaning and protection

Purpose of cleaning plate

Cleaning the printing plate refers to smearing or scrubbing the plate surface with materials such as water, glue, fountain solution and gasoline. Its main purpose is:

1. Protect the printing plate. When stopping during printing, apply water or glue to the plate surface to form a layer of water film or glue film to isolate the non-graphic part of the plate from oxygen in the air to prevent the plate from getting dirty. In addition, printing plates that have just been printed or printing plates that have not been used for a long time can be protected by applying glue.

2. Dirty the layout. When oil is dirty in the non-graphic part of the printing plate, it can be removed with glue, fountain solution, fountain solution, dirt remover, cleaning solution, gasoline and other materials.

3. Improve the clarity of graphics. When the graphic part of the layout is light or enlarged, it can be wiped with gasoline, fountain solution, glue and other materials to improve the clarity of the graphic.

Ready to work

Before cleaning, various cleaning materials must be prepared in order to improve the cleaning quality and efficiency.

1. Water. Mainly used for wetting plate or cleaning plate film or cleaning paper wool, paper powder and other debris on blanket. In order to ensure the quality of wetting and cleaning, the water stored in the bucket should be kept as clean as possible without oil stains, and the water should be changed in time.

2. Glue. Also known as hydrophilic colloid, it is mainly used to coat the plate surface, remove dirt or add to the fountain solution to protect the printing plate and enhance the hydrophilic performance of the non-graphic part of the printing plate, and improve the clarity of the graphic.

Common gums are gum arabic and carboxymethyl cellulose (CMC)

3. Fountain solution. It is also called water bucket solution. It is mainly used to wet the plate or remove oil from the non-graphic parts of the printing plate. It plays a role in stabilizing and enhancing the hydrophilicity of the non-graphic parts and maintaining the balance of water and ink. The undiluted fountain solution becomes the fountain solution, which can effectively remove the dirt on the plate surface.

4. PS version cleaner. It is widely used in many printing plants, can effectively remove dirt on the plate surface, and enhance the hydrophilic performance of the blank part of the plate. The disadvantage is that the cost is too high.

Operation methods and steps

1. Selection of cleaning cloth. Cloth is the main tool for cleaning the printing plate, it must be kept as clean as possible, and there should be no hard materials such as gravel. There are mainly three types of wipes for cleaning plates: water wipes, rubber wipes and gasoline wipes. Choose the cloth must pay attention to the following four points:

1) The water wiping cloth and the rubber wiping cloth must use soft and hygroscopic cotton gauze, and can not use packaging cloth or yarn end and other materials. The water wiping cloth and the rubber wiping cloth can be shared, or they can be used separately, but they must be rinsed in clean water before use.

2) ordinary cotton cloth (such as packaging cloth, etc.) can be used for gasoline wipes, but chemical fiber fabrics or yarn ends cannot be used.

3) Water and rubber wipes must be strictly distinguished from gasoline wipes.

4) The size of the cleaning cloth should be appropriate, too large or too small are not conducive to operation. Under normal circumstances, the sum of length and width is about 80mm is more appropriate, the thin cotton gauze can be slightly larger. Of course, the operator should also be considered handy.

2. Wipe the surface of the printing plate

1) Take out the cloth after repeated rinsing in the water, and gently hold the cloth with one hand without water drops dripping to determine the water content of the cloth. In addition, the downtime is short, and the moisture content of the cloth can be less; otherwise, it can be more.

2) The method of holding the cloth is to hold the four sides and four corners in the palm of your hand, and keep it close to your palm (to prevent the edges of the cloth from scratching the printing plate or getting caught in the machine).

3) Jog the machine or make the machine run at a low speed, walk the “8” shape on the plate, and wipe the water with the plate (this will ensure that the water is applied to the plate evenly and quickly).

3. Glue on the surface of the printing plate

1) After repeatedly rinsing the tape in water, unscrew it, hold the wipe with one hand without water drops, and determine the moisture content of the wipe.

2) The grip of tape is the same as that of water cloth.

3) Dip an appropriate amount of glue according to the area of ​​the printing plate, as the glue cannot drip naturally.

4) The route for wiping the glue is the same as the route for wiping the water. Generally, the wiper has to be wiped 2-3 times to meet the requirements of flat, thin, uniform and complete glue layer.

4. Clean the layout with gasoline

Wash the original ink film of the graphics and text with gasoline, and print it after replacing it with new ink to ensure product quality. The operation process is as follows: first clean the layout with water cloth (if the new printing plate should completely wash off the film), then use gasoline to wipe off the ink on the layout graphics, and then thoroughly clean the layout with water cloth 1 or 2 times. The specific operation method of cleaning the layout with gasoline is basically the same as the operation method of wiping the water. (If conditions permit, you can use plate cleaning fluid instead of gasoline to clean the plate, but you should pay attention to when cleaning the plate, you should wipe the plate with water cloth in time to avoid the plate).

Problems and precautions

1. Cleaning the printing plate with water or glue (commonly known as wiping water or glue) can play a role in protecting the printing plate. Which method to choose to protect the printing plate depends on the length of downtime. Be sure to wipe the glue when the downtime is relatively long.

2. If there is a certain amount of oil stain on the water wiping cloth, it is easy to make the non-graphic part of the printing plate dirty after wiping the water. Therefore, before wiping the water, the cloth should be rinsed in water, and the water in the bucket should be replaced frequently.

3. When wiping the water, the water content of the plate should be moderate and even, and there must be no omissions, otherwise it will easily cause the disadvantages of diluting the ink color or dirty version.

4. When rubbing the glue, the glue film should be as thin, uniform and complete as possible. After a long shutdown, wipe the glue flat with a dry cloth. If the film is too thick, it will easily cause the ink absorption of dirty plates or graphics and text to decrease.

5. When wiping the glue, avoid dripping the glue onto the blanket; at the same time, the cloth should not touch the ink roller and roller pillow.

6. When the machine is shut down for a long time, the water roller should not touch the printing plate to prevent the plate from getting dirty.

7. When cleaning the printing plate with gasoline, you should pay attention to the operation sequence; when you wipe the gasoline, you should move quickly; when the cleaning is completed, you should immediately pay attention to the ink and water.

8. After scrubbing the printing plate with the cleaning solution, pay attention to immediately clean the cleaning solution on the plate surface with a water cloth to prevent the cleaning solution from ablating the printing plate.

Blanket cleaning

Common materials for cleaning blankets are water, gasoline, kerosene, pumice powder, sulfur powder, talc powder, blanket cleaning agent, blanket reducing agent, etc.

New blanket cleaning
1. There is a protective film on the surface of the new blanket. Therefore, before using the new blanket, this protective film must be removed, otherwise it will affect the ink absorption of the blanket.

2. Pour appropriate amount of kerosene on the blanket or pour kerosene onto the cloth.

3. Spread pumice powder on the blanket or dip the pumice powder with a kerosene cloth.

4. Wipe the blanket repeatedly and forcefully.

5. Pour gasoline and clean the pumice powder with a gasoline cloth.

6. Wipe the blanket clean with a dry cloth.

7. Wrap the talc powder with 2-3 cotton gauze, and evenly pour the talc powder on the surface of the blanket.

Daily cleaning of blankets

In the daily printing process, the blanket is constantly in contact with the ink and paper, and the ink on the plate and text is transferred to the paper. Therefore, certain ink, paper wool and paper powder (paper) will inevitably adhere to the blanket Fillers) and other substances. This adhesion phenomenon is more serious when the blanket is sticky, printed with inferior paper, or when the pigment particles in the ink used are coarse, heavy, and the viscosity is too low. Therefore, in the printing process, the rubber The accumulation of cloth surface and different work requirements. Regularly cleaning the blanket can ensure and improve the clarity of the picture and text, and extend the life of the blanket.

1. Prepare the materials used for cleaning, and prepare a water wipe, a gasoline wipe, and a clean dry wipe each.

2. The grip for wiping the cloth is the same as the grip for wiping the water.

3. Jog the machine or run the machine at a low speed, and wipe the water from the gripping part of the blanket to the dragging part.

4. Jog the machine slightly from the blanket to the mouth or when the machine runs to the mouth, scrub the blanket with gasoline to dissolve the ink on the blanket.

5. Jog the machine or when the machine runs to the mouth again, use a clean cloth to remove the oil stains and impurities on the surface of the blanket.

Special cleaning of blankets If the blankets are used for a long time or because of improper maintenance, a smooth film or stickiness will form on the surface of the blankets, which not only affects the clarity of printed graphics, but also causes printing work Not going smoothly. Therefore, it is necessary to wash off the smooth film or tack the blanket.

1. The processing of the smooth film layer of the blanket: remove the blanket and the splint from the machine, and lay it flat on a smooth surface platform. The cleaning method is the same as that of the new blanket; or clean it with water on the machine Wipe with gasoline and pumice powder.

2. Remedy for tacky blankets: Tacky blankets are mainly caused by swelling or aging of blankets due to poor durability. Severe stickiness will cause the blanket to be unusable; mild stickiness will also cause the printing paper to stick to the blanket, so the stickiness should be detected as soon as possible and the blanket should be cleaned in time.

3. The cleaning method is: first wash off the ink layer on the surface of the blanket with gasoline, and wipe it off with a dry cloth; then use the volatile solvent gasoline or add a small amount of industrial alcohol to the gasoline (you can also use rubber reducing agent ) Wipe the blanket, then wipe the surface of the blanket with talc powder and sulfur powder to reduce the viscosity of the blanket.

Problems and matters needing attention:

1. When using pumice powder, be sure to avoid pumice powder contacting the printing plate or falling into the pad, otherwise it will accelerate the wear of the corresponding parts of the printing plate.

2. The interval between daily cleaning of the blankets should be based on the accumulation of blankets and different work requirements. The general rule is: you must clean it once when you change the plate and color; you should clean it every 3000-5000 sheets in formal printing; It should be cleaned once a day before work (after shutdown); at least once during the trial printing process.

3. When jogging the machine, the fingers should be light, and the hand holding the blanket should be away from the surface of the drum; after the jogging is completed, the fingers should be away from the button during the scrubbing process.

4. When cleaning, avoid contact with solvents such as gasoline on both sides of the blanket.

5. The liner wrapped in the blanket should be narrower than the blanket to prevent the penetration of solvents such as gasoline.

6. Blankets that are not in use or long-term use should be cleaned, covered with talcum powder, covered with protective paper, and stored in an airtight container or in a well-ventilated, cool, and dry place. And other chemicals contact and avoid being squeezed. When printing on the machine, it must be cleaned like a new blanket.

7. Kerosene must not be used for daily cleaning of the blanket.

8. When using the automatic cleaning blanket device, the amount of cleaning agent should be strictly controlled.

Cleaning of the water transfer roller and the water roller (water roller velvet type) During the printing process, due to the repeated contact of the water roller and the printing plate, after using for a period of time, on the one hand, ink and other debris will be attached to the printing plate. On the one hand, the velvet structure on the surface of the water roller will be damaged. During the water transfer process, the velvet structure on the surface of the water roller will be damaged in the same way; at the same time, the ink on the water roller will be transmitted to the water transfer roller through the water channeling roller on. Therefore, the water roller fleece must be cleaned or replaced in time to restore and maintain water absorption and water transfer performance.

Prepare cleaning materials and tools

1. Cleaning materials: gasoline, water (preferably a pool with a tap);

2. Tool nylon scrubber and steel sheet.

Cleaning Put the two ends of the removed water roller on the support (or wooden pillow) of the water roller, pour gasoline on the surface of the roller, and wipe it evenly in one direction (the direction of the water roller fleece) with the board brush; wait for the roller After the ink stain on the surface is dissolved, wash it with water until there is no dissolved ink stain on the roller surface; finally scrape off the excess water with a steel sheet.

Cleaning of water bucket and water channeling roller

The more common bucket rollers are chrome-plated. In the printing process, the ink stain on the water roller will also be transmitted to the water channeling roller and the water bucket roller, which reduces its water transmission. In addition, when the downtime is long, even if there is no ink contamination on the hopper roller and the ink-blowing roller, an oxide film is formed on the surface, and at the same time, the surface of the roller absorbs debris such as oil mist dust in the air, making them original Some hydrophilic properties have changed. Therefore, the water bucket roller and the water channeling roller must be cleaned in time and regularly to achieve the purpose of restoring its hydrophilicity and evenly and comprehensively transferring water.

Cleaning materials: pumice powder, fountain solution, glue, and cloth.

1. Dip the dampening solution, then dip the pumice powder, and then wipe it back and forth on the surface of the water channeling roller and the bucket roller. After the ink and oxide film are removed, quickly wipe the surface with a damp cloth.

2. Jog the machine, turn to the remaining unwiped part, and wipe according to the appeal method until the two water rollers are all cleaned.

3. Dip the cloth with water and take the glue to wipe the surface of the water roller.

Cleaning of the water bucket The water bucket is generally made of copper alloy material. Long-term use of the water bucket will inevitably fall into the dust and other debris. At the same time, the water bucket roller will also bring paper powder, paper wool, ink stains, etc. into the water bucket, which will not only reduce the wetting performance of the fountain solution , And will directly affect the printing quality of printed products.

Cleaning steps

1. Prepare clean water and a cloth, a brush, and a plastic catheter.

2. Remove the bucket roller

3. Pour water into the water bucket, and stir up the dirt at the bottom of the bucket with a brush, and then use the catheter (the principle of the connector) to suck out the turbid liquid in the water. While watering, scrubbing and guiding, until the water bucket is basically clean, finally clean the water bucket thoroughly with a cloth.

4. Install the water bucket roller

Problems and precautions
1. Pay attention to safety when removing the water roller. If the removed water roller does not need to be used or installed immediately, it should be placed on the water roller bracket.

2. When cleaning the water transfer roller and the water loading roller, the direction of brushing and scraping should be as same as the direction of the water roller fleece.

3. When cleaning the bucket roller and channeling roller, the amount of pumice powder dipped should be as small as possible, and at the same time, the pumice powder should be prevented from falling into the surface of the bucket or water roller.

4. The water roller should be cleaned in time, otherwise it will reduce the water delivery performance of the water delivery parts, resulting in the occurrence of ills such as dirty plates. The time for cleaning the water roller and water bucket should depend on the degree of scale and specific conditions. The general rule is:

1) When shutting down for a long time or replacing fine products, the water roller and water bucket should be thoroughly cleaned before starting.

2) In the normal printing process, if the layout is thicker, the water roller should be cleaned every day; if the layout is thin or the general product is printed, the number of cleanings can be appropriately reduced.

3) The ink stains on the water channeling roller and the water bucket roller should be cleaned in time, otherwise it will cause insufficient water supply to the printing plate, causing dirty plates and other failures, and the water roller is also very easy to get ink.

4) When changing dark ink to light ink, be sure to clean or replace the water roller fleece.

5) Before the new water roller is printed on the machine, use a clean wet cloth to gently wipe in the direction of the water roller fleece to remove the floating fluff on the surface of the water roller. Then, wipe the surface of the water roller with a suitable amount of water or fountain solution with a water-dampened cloth, so that the new water roller has a certain amount of moisture before it is used to facilitate printing. When the new water roller is on the machine, the machine can be idling for 10-20 minutes to supplement the water content of the water roller, and then shut down to wipe off the fluff attached to the water channeling roller and the water bucket roller.

Cleaning of ink fountain and ink road

Ink fountain cleaning:

1. Prepare an ink knife, a container for remaining ink, gasoline, and two quick wipes

2. Ink shoveling: Use an ink knife to shovel out the remaining ink in the ink fountain.

3. Remove the ink fountain

4. Cleaning the ink fountain roller: dip the cloth with gasoline, scrub the ink on the ink fountain roller and completely dissolve it, then wipe the ink fountain with a clean cloth to make it appear luster.

5. Cleaning the ink fountain

6. Return the ink fountain to its original working position. If it is not turned on for a long time, keep the ink fountain and ink fountain roller separated.

Ink roller cleaning

Daily cleaning In the printing process, when the color needs to be changed, and the printing is completed every day or in special circumstances, the ink roller needs to be cleaned. (The cleaning process is omitted) Therefore, cleaning the ink roller is one of the basic contents of daily operation.

Special cleaning method

In order to improve the service life and product quality of the rubber roller, the rubber roller must be removed and cleaned one by one on a regular basis. This work is especially important when the rubber roller has ink transfer failures such as oxide film formation or deinking.

Oxidative film formation of rollers refers to the materials in the ink and drying agent that penetrate into the rubber roller for a long time, so that the capillary holes on the surface of the rubber roller are closed, thereby forming a smooth oxide film. There are four methods to remove the oxide film on the rubber roller:

â‘  Put the ink roller on the bracket, use a clean cloth to dip the appropriate amount of kerosene first, then dip the pumice powder, and wipe the surface of the ink roller firmly until the smooth layer on the surface of the roller is wiped off. This method of scrubbing the ink roller is the most commonly used method of scrubbing the ink roller on a regular basis.

â‘¡ Scrub the ink roller with about 20% aqueous sodium hydroxide solution, then neutralize with weak acid, and finally rinse with clean water and wipe dry.

â‘¢ Wet the ink roller with about 10% sodium hydroxide aqueous solution, then wipe it with kerosene and pumice powder with a cloth, and finally rinse with water and wipe dry.

â‘£ Wet the ink roller with kerosene and polish it with a fine iron emery cloth. During operation, the ink roller should be turned evenly and the pressure should be light and consistent to avoid unevenness of the rubber roller. This method is more thoroughly cleaned than the above method, but because it is difficult to master, it also has a lot of damage to the ink roller itself, so you should use it carefully.

Ink roller deinking

That is, due to the ink emulsification and the poor performance of the ink roller to transfer ink, a hydrophilic foundation is formed on the surface of the ink roller, resulting in the phenomenon that the ink roller does not absorb ink. This phenomenon is common when printing yellow or black, especially on some domestic small offset printing machines.

Treatment of iron (or copper) channel ink roller deinking: first wash off the emulsified ink on the ink roller with gasoline, then use a clean cloth dipped in kerosene and pumice powder to thoroughly clean the ink roller, then use a clean piece The cotton gauze is dipped in copper plating solution (copper sulfate solution) to wipe the surface of the ink roller evenly. When a bright copper layer is formed on the surface of the ink roller, wipe the ink roller again with a gasoline cloth.

Rubber roller deinking: If improper use and maintenance, plastic (or nylon) ink roller and rubber roller will still deink. The deinking of the plastic ink roller and the aging treatment of the rubber roller are basically the same. First wash the rubber roller with gasoline, then use a cloth to dip 5% sodium hydroxide aqueous solution and pumice powder, and wipe the ink roller vigorously. The surface until the smooth film layer on the surface of the ink roller is wiped off, and finally the ink roller is washed with gasoline.

However, the best way to prevent deinking is to prevent, that is, make some adjustments from the process, for example: reduce the acidity of the fountain solution, reduce the amount of glue, and reduce the moisture on the surface.

Problems and matters needing attention:

1. Do not clean the ink fountain while the machine is running.

2. If the ink fountain or ink path is not cleaned properly, the following faults will occur:

1) When the dark ink is changed to the light ink, the light ink is seriously affected by the dark ink, so when cleaning the light ink, when the primary color ink is cleaned, some light ink should be added to the ink fountain. After cleaning it with ink, if you still feel that it has not been cleaned, you can repeat it again.

2) The ink dries on the ink fountain roller, ink fountain blade and ink roller, which affects the normal delivery of ink and even causes the production of rubber roller deinking and other failures.

3) The rubber roller should be removed periodically for cleaning. The interval for regular cleaning is one week.

4) When cleaning the rubber roller, it is strictly forbidden to use ketone and ester organic solvents.

Other cleaning operations

Cleaning the back of the machine plate

1. Observe whether there is residual ink stain on the back of the printing plate.

2. Touch the back of the printing plate to see if there are impurities such as dry pimples and ink skin.

Use a water cloth to wipe off the rubber on the back of the plate, and use a gasoline cloth to wipe off the ink on the back of the plate. And then clean it again.

Precautions:

1. When handling the printing plate, please handle it gently to prevent the printing plate from being scratched or bruised.

2. This work directly affects the smooth progress of the printing process, and the printing durability of the printing plate on the machine must be carried out carefully, and sloppy actions are absolutely not allowed.

Cleaning of printing plate and rubber roller shell; cleaning of impression roller; cleaning of roller pillow.

Precautions:

1. Pay attention to cleaning the above items in time to ensure the cleanliness of the above rollers and roller pillows.

2. It is strictly forbidden to use hard iron to scratch the surface of the roller, nor to use sandpaper to polish the surface of the roller pillow and roller.

Regular cleaning of the roller pillow can ensure the smooth operation of the machine and can never be ignored.

Introduction of several special cleaning agents:

With the continuous progress of the printing process, various cleaning fluids (agents) have also emerged, and gradually developed towards higher efficiency and more professionalism, which is convenient for us to operate and also improves the quality of production. Let us introduce several professional Cleaning agent (liquid):

1.

PS plate cleaner is used to remove the dirt of PS plate in the printing process

2. Offset printing paste (also known as PS plate treatment agent) Product features: It can remove the dirt and aging ink on the surface of the PS plate; clean the layout without damaging the pattern, can improve the quality of the print; stable and safe performance Non-toxic. How to use: After soaking this product with sponge or cotton yarn, you can wipe off the dirty surface of the plate, and it can also be used as an opening cleaner before printing.

3. Ink cleaning agent

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