Common problems and solutions in printing
- Categories:Gravure plate technology
- Time of issue:2013-10-17 12:30
Common problems and solutions in printing
- Categories:Gravure plate technology
- Time of issue:2013-10-17 12:30
1. Poor overprinting
Phenomenon: In multi-color printing, the ink is printed on the first printed ink film, resulting in repulsion. In addition, the second color sticks the first color down, causing reverse overprinting.
Reason: The ink in the front is not fully dried, and the ink in the back dries too fast, resulting in excessive viscosity at the moment of printing. The high adhesion during printing causes the general gloss ink to be prone to poor overprinting, and sometimes the compatibility of adjacent color inks is poor. This situation also occurs at a time.
Countermeasures: 1. Printing plate
1. The engraved version is easier to cause failure than the corroded version.
2. Increase the color depth of the layout
2. Printing plate stage
1. Use quick-drying thinner to speed up the drying of the ink or strengthen the heating and drying of the previous color.
2. Use slow-drying thinner to slow down the drying of the following ink, and at the same time reduce the viscosity of the oil without running water lines
3. The position of the squeegee of the back color is closer to the printing direction to reduce the printing pressure and increase the printing speed.
4. Blow to the second color layout.
Phenomenon: Bubbles are generated in the ink tank during printing, and the bubbles overflow, hindering ink circulation. Phenomenon such as mottle or polishing will affect the quality of the printed matter. The previous phenomenon is relatively easy to eliminate, but there are large and many bubbles, and the amount of bubbles is small but it is difficult to eliminate
Reason: The surface tension of the ink is too large, and the ink circulation device is defective.
Countermeasures: 1. Adjust the ink viscosity in an appropriate range.
2. Add defoamer. However, excessive addition will damage the adhesion and compounding. Note that sometimes there will be adverse effects, but foaming will be more pronounced.
3. Prevent the air in the circulation device from being flushed into the ink.
4. Eliminate the drop of ink and the place where the ink does not flow in the circulation device.
Phenomenon: The printing on the full-page part of the printed matter is not smooth, and the spot-like pattern appears, which reduces the printing effect.
Reasons: 1. The printing speed is slow and the ink drying is slow.
2. The ink is too thin.
3. Ink with high thixotropy is easy to cause mottle phenomenon.
4. Water-based gravure ink has poor wettability to plate rollers and paper, and it is prone to mottle.
5. Influence of static electricity.
Countermeasures: 1. Improve the fluidity of the ink.
2. Use quick-drying solvents.
3. Increase the printing speed within the possible limit.
4. Use pigments with less oil absorption.
5. Reduce the problems caused by static electricity.
6. Select the type of printing plate and screen angle.
Plate making method Corroded plate Engraved plate
Screen angle 45 degrees 15-30 degrees
Version depth 〉32µ 28µ
Roller hardness 70---80 degrees
Fourth, block version
Phenomenon: The ink in the printing plate's dots dries during printing, to the point that the dots appear incomplete in the printed matter.
Reasons: 1. The ink dries too fast.
2. The binder in the ink has poor solubility. After printing, the ink in the plate roller's dots cannot be completely dissolved, causing a vicious circle. The dust from the paper and film mixed in the ink during printing is also the cause of plate blocking.
Countermeasures: 1. Use chronic solvents. However, the effect of slow drying on the post-printing process is worth noting.
2. Use a solvent with good dissolving power.
Five, water absorption and deterioration
Phenomenon: When printing for a long time, the resin will precipitate and gel in the ink, causing gloss changes, poor transfer, and blockage.
Reason: The moisture in the air is slowly mixed into the ink during printing, and the solubility of the ink becomes poor during printing for a long time, which is the cause of this phenomenon. Alcohol-containing nitrated surface inks appear more frequently. Especially in high humidity, small printing area, and low ink consumption, it is easy to cause this phenomenon.
Countermeasures: 1. The ink tank should be sealed well to reduce the contact area with air.
2. Add a solvent compatible with water (such as ethyl acetate, cellosolve).
3. Add new ink to avoid reuse of old ink.
Phenomenon: The ink film whitens during drying, the gloss of the printed surface, and the subsequent changes in properties such as strength. Once there is a change, there is no remedy.
Reason: When the ink transferred to the surface of the film dries, the evaporation balance of the solvent is destroyed, causing the resin to be insoluble, turbid, and locally gelled, which is called [resin whitening]. At the same time, the solvent volatilizes and absorbs heat during the drying process, the surface of the film is very cold, and the moisture in the air mixes into the ink coating to cause gelation, which is called [water whitening]. Usually bleaching refers to [water bleaching]. Nitrated surface inks with a lot of alcohols, which frequently cause malfunctions, are prone to occur in high humidity environments.
Countermeasures; 1. Improve the drying capacity of the printing press.
2. Adjust the humidity and temperature of the printing workshop.
3. Reduce the content of alcohol solvents.
4. Add a small amount of slow-drying solvent (such as cellosolve, butyl acetate)
7. Volcanic crater phenomenon
Phenomenon: The printed surface or the varnished surface produces crater-like bumps, causing the image to be rough and low in gloss.
Reason: This phenomenon is likely to occur in heat-curing varnishes. The coating is overheated in the early stage of drying, and a dry film is formed on the surface. The solvent in the lower layer cannot overflow smoothly and break through the surface film, forming a crater phenomenon.
Countermeasures: Excessive hot air drying will only dry the surface and produce an inverse effect. The temperature of the oven should preferably be a "low temperature-high temperature-low temperature" arched temperature distribution. From the perspective of ink and varnish, the use of slow-drying solvents makes it difficult to form a surface film.
Phenomenon: Odor is produced during printing, or the printed matter itself emits odor, which causes the operator to feel unpleasant.
Reason: The odor of additives and solvents in the resin, the odor of acrylic resin or the odor of activity in the pigment are the reasons for this situation. The smell that is different from the normal situation in printing can cause unpleasantness, such as ester solvents in publishing and printing and ketone solvents in packaging. The odor of printed matter is caused by residual solvents, film adhesives, and composite resins.
Countermeasures: 1. Do not use binders and plasticizers with a strong smell.
2. Improve the drying capacity and use fresh air to blow away the solvent vapor.
3. Use less slow-drying solvents.
4. In case of odor, take remedial measures such as re-drying the printed matter and ventilation.
Phenomenon: Pigment precipitation leads to color changes, and pigment precipitation can cause problems such as dirty plates and blockages.
Reasons: 1. The dispersibility of the pigment in the continuous material is poor, and the pigment agglomerates.
2. Pigment dispersion (grinding) is insufficient and precipitation occurs. In this case, the precipitation is harder.
3. The viscosity is too low, the binder has no holding power to the pigment, and the stirring effect is poor, resulting in precipitation.
Countermeasures: 1. Use agglomeration inhibitors and precipitation inhibitors.
2. Pigment (grinding) is sufficient.
3. Use pigments and binders with good miscibility.
4. The ink in the tank should be mixed evenly before use.
Ten, back through
Phenomenon: Ink penetrating on the physical side of printing.
Reasons: 1. The permeability of the printing substrate is large.
2. The viscosity of the ink is low.
3. Poor drying of ink.
4. The ink has poor fluidity.
Countermeasures; 1. Use fast-drying solvents and increase printing speed.
2. Improve printing viscosity.
3. Improve the drying capacity of the machine.
4. Switch to ink with good fluidity.
Phenomenon: The printing surface is polished due to poor ink transfer.
Reasons: 1. The ink viscosity is high
2. The scraping performance of the scraper is poor.
3. The printing plate is blown by the wind to make the ink transfer poor.
Countermeasures: 1. Reduce ink printing viscosity.
2. The blade of the scraper is extended.
3. Add slow-drying solvent.
4. Confirm the hardness of the pressure roller
5. The air cannot be blown directly or indirectly on the printing plate.
6. The position of the mobile exhaust fan for solvent discharge is also the cause of the malfunction.
12. Beard (static mustache)
Phenomenon: Short hairy ink filaments appear on the edges of images and text.
Reason: The ink viscosity is too low or the printing plate net is too deep, and the pressure of the impression cylinder is too large. There are many cases caused by static electricity.
Countermeasure: Prevent static electricity.
1. Sprinkle water or release water vapor at the printing site to lower the temperature and increase the humidity at the printing site.
2. Use anti-static equipment and take grounding measures to the guide roller on the machine to prevent it from contacting with the lubricating oil of the bearing part and insulating it.
3. The effect of adding alcohols, methyl ethyl ketone, acetone, etc. as antistatic agents is remarkable. But such substances will make the ink adhesion strength worse.
Thirteen, poor follow-up
Phenomenon: The phenomenon that the ink has no adhesion on the printed substrate. Now due to the improvement of ink, this phenomenon no longer exists. The adhesion of ink is usually measured by the tape peeling method, and the judgment standard is determined by the company.
Reasons: 1. The wrong type of ink is used, or the resin used as the ink binder is insufficient, and the adhesive strength of the resin itself is poor.
2. The surface treatment of the substrate is not enough.
3. Coating with additives etc.
4. The film absorbs moisture.
5. The ink is whitened or deteriorated by moisture absorption.
6. Insufficient heating during printing.
7. The printing ink is too thin or the solvent of the old ink is out of balance.
Countermeasures: 1. Add varnish, etc. to increase resin content.
2. Try to print with high density conditions.
3. Replace the ink.
4. Avoid the above other situations.
Phenomenon: Poor ink transfer with pinholes appears on the printing surface.
Reasons: 1. The occasion where the ink wets the film poorly.
2. When the ink uses silicone additives, this phenomenon is likely to occur when the additives are excessive or insufficiently dispersed in the ink. But now due to the improvement of the base material, there are fewer pinhole failures.
Countermeasures: 1. Select a solvent suitable for the substrate
2. Confirm the added amount of additives and maintain proper viscosity
15. Flow lines, overflow
Phenomenon: Ink is a phenomenon where water-like markings appear on the solid part, and the ink overflows from the pattern part.
Reasons: 1. The viscosity of the ink is too low.
2. The fluidity of the ink is not good.
Countermeasures: 1. Add original ink or filler to increase viscosity.
2. Improve printing speed.
3. Turn the angle of the blade of the scraper into an acute angle.
4. If the version is too deep, change the version to lighter.
5. Improve the fluidity of the ink.
Phenomenon: Poor transfer of gravure dots, spot-like dot defects appear in the printed matter. Small dots and more highlights appear.
Reasons: 1. The surface of the substrate is uneven, and the mesh point of the plate roller is in poor contact.
2. Low printing pressure.
3 The ink has high viscosity.
4. The ink dries quickly.
5. Blocking or printing plate wear is large.
Countermeasures: 1. Choose a smooth substrate, and use electrostatic ink-absorbing printing on a rough substrate, which has a better effect.
2. Increase the printing pressure.
3. Corresponding to the printing speed to reduce the printing viscosity.
4. Use slow-drying solvents to reduce the drying speed.
5. Clean the printing plate and redo the worn-out plate
17. Screening phenomenon
Phenomenon: The mesh-like phenomenon appears in the same continuous field part.
Reason: 1. Ink reason
① The ink has high viscosity and it is difficult to enter the printing plate dots.
② It dries too fast and loses fluidity.
③ Insufficient ink.
2. Version Kun reason
① The quality of the edition is poor.
② The plate roller is eccentric.
③ Poor chrome plating
3. Scraper pressure is too high
4. Insufficient printing pressure.
Countermeasures; 1. Use slow-drying solvent to adjust viscosity and drying speed. Insufficient ink, adjust the amount of ink in the ink tank.
2. It is difficult to solve the problems caused by the mixing of the plates, and the printing plates can only be improved.
3. Adjust the pressure of the scraper and the pressure roller.
Phenomenon; the phenomenon of curling of the printed surface of the substrate
Reasons: 1. The ink film on the substrate is thick.
2. The solid part is prone to curling. The flexibility of the ink connection, the thickness of the substrate and the water content will affect the curling phenomenon.
Countermeasures: 1. Add plasticizer to increase the flexibility of the connection
2. Use water vapor to increase the moisture content of the printed matter.
3. Coat the back of the substrate with water, water---glycerin solution and other curling inhibitors.
Nineteen, static point failure
Phenomenon: Static electricity is generated when the plastic film passes through the printing machine, causing printing failure. The silky whiskers around the pattern part are called "beards". The solid part bears mottled shape, or the ink does not transfer, resulting in a blank part. Sparks caused by accumulated static electricity are the cause of fires.
Reason: The high-resistance substance is rubbed, or comes into contact with other objects, and generates static electricity when peeling off. Paper and plastic film are poor conductors, and they are charged with static electricity when they pass through the printing machine.
Countermeasures: 1. Increase indoor air humidity.
2. After printing, contact the inside of the film with the static eliminator
3. The guide roller should also remove static electricity.
4. Improve the printing viscosity of the ink.
Twenty, plowing appearance
Phenomenon: In the overprinting part of the ink, when the second color ink is transferred to the dry ink layer of the first color, the first color ink is re-dissolved, and part of it is mixed into the second color ink. The ink using polyamide resin is due to the re-dissolution of polyamide. Good sex can easily cause this phenomenon.
Reason: It is affected by the viscosity of the ink, the drying speed, and the depth of the plate.
Countermeasures: 1. Changing the depth of the version to the shallower will improve.
2. Processing methods at the printing stage
①Improve the printing viscosity of the second color ink.
② Shorten the drying time.
A. Use a quick-drying agent.
B. Increase printing speed.
C. Blow hot air immediately after printing.
21. Poor set
Phenomenon: In the case of multi-color printing, the printing position is not correct, resulting in misalignment and blanking.
Reason: There is a problem with the operation process or the automatic registering device itself has a problem.
Countermeasures: review the following items:
1. The reason for the operation process.
① Whether each roller is running normally.
② Whether the brake adjustment is good.
③ Whether the set of plates is loose.
④ Whether the left and right stamping pressures are consistent, and whether the stamping roller hardness is good.
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