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Common problems and treatment methods in plastic gravure printing
Time: 2017-02-08 Source: Packaging Frontier Reading: 17587 times
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Wenzhou Junchuan Machinery Equipment Co., Ltd.

Specializing in the production of composite flexible packaging , the printing effect is excellent! The production of composite flexible packaging requires printing, compounding, bag cutting and other processes.

1.Scraper line or ink line appears

The reasons are as follows: the scraper blade is worn or dirt is stuck on the scraper blade; impurities are mixed in the ink; the ink fineness is not enough; the printing plate is not well polished, too rough and the ink viscosity is too high.

Solution:

a) If the scraper line moves regularly from side to side as the blade swings left and right, it can be determined that the scraper blade is worn or the dirt is stuck on the scraper blade. You can use a bamboo stick to remove the dirt on the starting line ; If the scraper is worn, it should be sharpened immediately or replaced with a new one.

b) All inks must be considered in printing. Use new ink whenever possible.

c) Ink particles are too coarse and the fineness is not enough, and lines are easy to appear. Check the fineness of the ink with a fineness meter. If the fineness is not enough, the ink needs to be replaced.

d) The printing plate is not well polished or there are small hard blocks on the surface. You can use fine sandpaper to polish the printing plate back and forth. If it still cannot be solved, you need to return to chromium and replat.

e) The ink viscosity is measured at regular intervals to maintain the stability of the ink viscosity. Conditional manufacturers can use the ink automatic viscosity controller:

2. Printing water pattern

The main causes of water streaks are: the viscosity of the ink is too low;

The engraving of the printing plate is too deep; the fluidity of the ink is poor.

a) Properly increase the viscosity of the ink;

b) Increase printing speed.

c) Adjust the scraper angle to an acute angle.

d) If the engraving is too deep and cannot be adjusted, you need to make a new plate.

e) Improve the fluidity of the ink.

3. Ink Rebound

The main reasons for the occurrence of printing stickiness are: the solvent is too slow to dry and the ink is poor in drying; the rewinding pressure during printing is too high, and the stacking pressure after printing is too high (especially high temperature weather); the temperature of the cooling water is too high. The cooling effect is not achieved; the temperature of the drying box is too high, and the wind is over the Ambassador ink to cause false drying; the surface tension of the printed non-printing surface is high (or double-sided corona),

The affinity of the non-printing surface of the film and the ink is large, and the ink is transferred.

Solution:

a) Change to a quick-drying solvent to dry the ink sufficiently.

b) Adjust the rewinding pressure and keep it as small as possible. The reeled volume {too large, the stack weight should be small.

c) Check whether the cooling water of the printing press is turned on and the water temperature {in accordance with the requirements. b) All inks must be filtered during printing. Use Xinyi whenever possible. ink.

d) Adjust the temperature and wind of the oven. Generally, it is suitable to be 50 ~ 65 ℃.

e) Check the surface tension of the film before printing. The surface tension of the printed surface is greater than the non-printed surface. It is best not to use a double-sided corona film.

4. Printing color difference

The main causes of printing chromatic aberration are: the position, angle, and pressure of the squeegee change caused by printing chromatic aberration; ink

The degree of change causes the printing color difference; the change of the ink color density leads to the brush color difference; the printing plate becomes lighter after a certain amount is printed; the printing plate

Plates cause printing color difference; when spot colors are mixed with multiple colors, if the proportion of each pigment in the ink is greatly different,

In medium, if the ink circulation is not good, it is easy to cause ink precipitation and cause brush color difference.

Approach:

a) Adjust the position, angle, and pressure of the squeegee appropriately so that the printing hue is basically consistent.

b) The ink viscosity is measured regularly to maintain the consistency of the ink viscosity. Manufacturers with conditions can equip the ink viscosity automatic controller.

c) Adjust the color density of the ink (add the original ink diluent to the ink) to keep the color density consistent.

d) Re-chromizing or re-plating of printing plate.

e) Use a printing plate cleaner to clean the plate roller.

f) Check the ink circulation system to keep the ink flowing well

it is good.

5. Static electricity failure

Plastic films can generate static electricity due to friction during printing. Static electricity has a great impact on the quality of printed matter, and it can cause serious fire. Pay special attention during the printing process. The printing failures caused by thin film static electricity mainly include: "beard" -like ink filaments around the printed graphics; mottled shapes will appear when printing on the solid part, and the ink will not be transferred, resulting in blank parts. Although the static electricity of the film cannot be completely eliminated, it can be properly handled during the printing process to avoid static electricity failure. The main processing methods are as follows:

a) Properly increase the humidity of the air in the workshop.

b) Properly increase the printing viscosity of the ink.

c) Properly increase the proportion of alcohol and ketone solvents in the printing solvent, but do not add too much, otherwise it will affect the composite strength of the subsequent process.

d) The equipment is equipped with static elimination devices and should be maintained and inspected frequently.

6.Printing color (matte version)

The failure of the scraper to completely scrape off the ink on the non-graphic parts of the printing plate, which leads to the phenomenon that the ink is transferred to the printing substrate is called panchromatic color, also known as haze. The main causes of printing flooding are:

Insufficient precision, eccentricity, and poor chrome plating of the printing plate; insufficient blade pressure and uncomfortable angle; excessive printing viscosity of the ink; too much humidity in the workshop environment, which makes the ink flowability worse; excessive addition of alcohol solvents causes the ink Poor solubility. Approach:

a) Improving the manufacturing accuracy of plate rollers.

b) Increase the pressure of the scraper, adjust the scraper angle to 60-70 degrees, and the distance between the two cutting points is preferably 50-60cm.

c) Reduce the printing viscosity of the ink appropriately.

d) Adjust the solvent formula to reduce the proportion of alcohol solvents, and increase the proportion of ketone solvents.

Common problems and treatment methods of dry compound

1. Insufficient peel strength of the composite film

There are several situations:

The glue is not completely cured, and it is still sticky when peeled off. the reason:

1) The proportion of the binder is wrong, and the curing agent is inadequately caused to cause incomplete curing. When formulating the adhesive, it should be formulated according to the mixing parameters specified by the adhesive manufacturer;

2) The purity of the solvent is not enough. The solvent contains water or alcohol exceeding the standard. The water or alcohol reacts with the curing agent in the glue. The reduced proportion of the curing agent results in incomplete curing of the glue. The solvent used for dry compounding is ethyl ester, so every batch of ethyl ester should be sampled when entering the factory. If it is found that the purity is not enough, it should not be used.

3) The high residual solvent of the ink in the printing film causes insufficient curing of the glue. Part of the residual solvent of the ink (especially the PET ink j will react with the curing agent in the glue, thereby consuming the curing agent and causing insufficient curing of the glue.

Countermeasures: ① It is better not to compound immediately after the film is printed. If time permits, it can be left for 1 to 2 days before recombination; ② Residual solvent is detected after the film is off the machine. If the residual solvent is high, curing can be appropriately increased during compound Proportion of agent; ③ Use fast curing glue.

4) The composite film has a low curing temperature, insufficient curing time, insufficient crosslinking, and incomplete curing. Countermeasures: Increase the curing temperature or use fast curing glue.

2. Appearance of composite films

1) Small ink dots. Generally, it is less likely to appear immediately after lamination, unless it is muddy impurities. This phenomenon may occur for aluminized film for a period of time after lamination, because the ink corrodes aluminum. When the ink shows a certain acidity or alkalinity, and the amount of glue is small, it cannot form a connected layer. , This can happen:

2) Small gray dots. There are two possibilities of small gray spots, one is the uneven spots of the roller caused by uneven rollers, and the other is the uneven spots of the ink caused by uneven ink. Both possibilities are special and work-oriented. It can be solved by adjusting the process to increase the thickness of the glue.

3 White spots. It is easy to appear when the ink on the surface is discolored. Mostly appear in the composite of aluminized film. There are two reasons for this: one is that the hiding power of the ink's natural color is not strong or the coverage is uneven, especially the white ink, which allows the aluminum color to penetrate out, and small white spots are formed where the aluminum color does not penetrate; the second is the process reason, the drying tunnel temperature (Especially the first-grade drying tunnel) is too high or the glue is too thick, which causes the surface of the rubber layer to condense in the first-grade drying tunnel. When the ethyl ester is washed out in the second or third-stage drying tunnel, the glue is squeezed out to show the original color of the ink. . The solution is to increase the hiding power of the ink or adjust the appropriate temperature for the first, second, and third drying channels, and gradually increase the temperature. Avoid excessive primary temperatures.

4) Small crystal point. There are more small crystal points on the transparent film, there are two kinds of bumps, and the causes are different: most of the small crystal points that are protruding are due to the glue, or it may be because the machine is not cleaned. The method of eliminating small crystal points is to strictly follow the correct compounding method, and the machine must be cleaned after use. The recessed small crystal points, carefully observed with a magnifying glass, will find small bubbles in them. This is mainly It is caused by too much water.

5) Small scars. Mainly due to the uneven activation of the film, the same scars appear in the printing process, of course, it can be caused by too long activation time.

6) Wavy pattern. Wavy patterns easily occur on the white film, mainly due to the irregular molecular weight of the glue. After the hot drying tunnel and the hot roller, the elastic polymer chain shrinks, and the molecular shrinkage of different molecular weights is inconsistent. This unevenness of internal shrinkage causes wavy patterns. The reason for the emergence of this Ministry of Social Affairs should consider the glue.

7) The influence of the film on the surface quality. Various reasons for the smoothness and uniformity of the film surface may cause similar phenomena to the above six phenomena. To distinguish the cause of the film or the above six cases, you can carefully observe the film without the film with a magnifying glass. Since the transparent glue is between the two films, it forms a composite film with the two films. Spots, waves, etc. on small films are magnified, and many situations require careful observation to detect problems.

3. Tunneling phenomenon of composite film

Due to the shrinkage of the film after lamination, the edge part or the central part is like an earthworm-like delamination, which is called a composite film tunnel phenomenon. The reasons for this phenomenon are as follows:

1) The poor tension control during the compounding process causes the composite substrate to shrink after the compounding and the shrinkage ratio is greatly different, which destroys the bonding of the glue layer of the composite film and produces a tunnel phenomenon. The solution is to use different composite substrates when compounding The tensile properties of the film are properly set. 2) The film is wrinkled and uneven in thickness. In order not to wrinkle the composite film during compounding, increase the tension to compound and cause the composite film to tunnel. The solution is to check the state of the film when it is unrolled during lamination. If the film is wrinkled or shaken, it will not be used.

3) The molecular weight of the adhesive is small, resulting in a low initial adhesion of the composite film, which causes a tunneling phenomenon of the composite film. The solution is to choose a high molecular weight, high cohesion, fast curing adhesive.

4) Due to the excessive coating amount of the adhesive, the composite film is not completely cooled after the heat-sealing roller, and the adhesive layer still has a certain fluidity, which causes the tunnel phenomenon of the composite film. The solution is to reduce the coating amount of the adhesive appropriately.

4. Poor smoothness of composite film

The slip of the composite film is poor, and the friction between the films is large, which reduces the opening performance and operation performance of the composite film. The main reasons for the poor slip of the composite film are:

1) The curing temperature of the composite film is too high. Treatment method: reduce the aging temperature, the aging temperature is preferably not more than 50 ℃, if time permits, it can be naturally matured better.

2) The slip of the composite substrate is poor. Treatment method: composite film spray

3) The composite film absorbs moisture. Handling method: Pay attention not to get water during storage and transportation. When the indoor humidity is too high, pay attention to the film protection.

5. The composite film is wrinkled. Causes of composite film wrinkling.

1) The composite substrate itself is wrinkled. Treatment method: pay attention to check the state of the composite film when compounding, and do not use it if there are uneven thickness, lotus leaf edges, wrinkles, etc.

2) Wrinkle of composite film caused by imbalance of guide roller and composite roller. Treatment method: Check and adjust each guide roller and compound roller to balance.

Three. Common problems and processing methods of extrusion compound

Poor composite strength

Reasons for poor composite strength:

1) The resin surface is insufficiently oxidized. Countermeasures: increase the resin temperature; reduce the speed of the production line; increase the air gap (air gap refers to the distance from the die opening of the 1-type touch head to the tangent line of the composite roll and the cooling roll)

2) The resin temperature is too low. Countermeasures: increase the resin temperature; high back pressure (resin pressure); check the heater for failure.

3) The compound pressure is insufficient. Countermeasure: Increase compound pressure.

4) The AC agent is not completely dried. Countermeasures: Increase drying temperature; decrease line speed; increase drying wind.

5) The surface activity of the substrate is insufficient and the corona value is low. Countermeasure: Use the corona pen or the corona test solution to detect the halo treatment value of the substrate before production on the machine.

2. uneven thickness

The main reasons are:

1) The temperature of the T-die is not set properly. Countermeasure: Adjust the temperature set by the T-die.

2) The mold gap of T-shaped IZl is not uniform. Countermeasure: Adjust the die gap of the T-die.

3) T-shaped die mouth is dirty. Countermeasure: Stop and clean the die.

3. Composite wrinkling

Reasons for compound wrinkle:

1) The composite silicone roller is damaged or has poor roundness. Countermeasure: Polish or replace the compound silicone roller:

2) The guide roller is unbalanced. Countermeasure: Check and adjust each guide roller to balance the guide roller.

3) The line speed is too low. Countermeasure: Increase the line speed.

4) The tension is too small. Countermeasure: Increase tension.

5) The problem with raw materials is. Countermeasure: Replace raw materials.

4. Poor transparency of composite film

Reasons for poor transparency of the composite film:

1) The extrusion temperature of the extruder is too low, resulting in poor plasticization of the resin. Countermeasure: Set and control the corresponding extrusion temperature according to the performance characteristics of the resin and the actual production conditions to ensure that the resin plasticizes well. This is one of the prerequisites for improving the transparency of the composite film.

2) The surface temperature of the cooling steel roller is too high, and the cooling effect is too poor, which greatly reduces the transparency of the composite film. Countermeasure: appropriately reduce the temperature of cooling water and the surface temperature of the cooling steel roller. Generally speaking, the temperature of the water introduced by the cold member is controlled below 20 ° C, and the surface temperature of the cooling steel roller is controlled below 60 ~ C.

3) The transparency of the substrate itself is not good. Countermeasure: Replace the substrate with good transparency.

5. Composite membrane gel and fisheye spots

the reason:

1) The temperature of the extruder is improperly set, especially the temperature of the die and the resin is too low, resulting in poor plasticization of the resin, which causes the shark skin phenomenon or fish-like spots on the molten resin. Countermeasure: Adjust the extrusion temperature of the extruder and the temperature of the resin to appropriate values to ensure that the resin is plasticized well.

2) The resin contains water, which affects the plasticization of the resin. Countermeasures: Stir and dry the resin to remove the moisture contained in it, so that the resin can be fully plasticized.

3) Other resins with different melt indexes or densities are mixed in the resin to make the resin poorly plasticized or incompletely plasticized. Countermeasure: Replace the resin with appropriate melt index and density.

4) The barrel is not thoroughly cleaned when replacing the resin. Other resins or impurities remaining in the barrel have an adverse effect on the plasticization of the resin. Countermeasure: Thoroughly clean the barrel to remove the influence of impurities.


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