13 Ways to Solve the Problem of Scratches on Printed Recyclable Film

Scratches on printed products refer to quality defects caused by scratches on the ink film or thin film after printing. Scratches on the surface of the film or ink film can cause damage to the film or printing ink film, which can affect the appearance of the printed product or even result in the scrapping of the printed product. Therefore, scratches on printed products have a considerable harm to the quality of flexible packaging.

Scratches on printed products have longitudinal linear scratches on the film or ink film, and the scratches on the ink film surface are basically visible to the naked eye. Scratches on the film are mostly dark, and when viewed through a light source, dark lines can be clearly seen. These dark lines not only affect the appearance of the film, but also have a certain impact on the color of the printed composite. Scratches on printed materials are often caused by mechanical external forces on the printing film or ink film.

Various types of mechanical injuries include: oven scratches, guide roller scratches, electrostatic brush scratches, foreign object scratches, etc.

1 Oven scratch:

To ensure the efficiency of thermal drying and prevent hot air overflow, most of the film inlet and outlet paths in the drying oven of the printing machine are designed with small gaps after compression to maintain the sealing performance of the oven. The narrowness of the inlet and outlet limits the swinging amplitude of the film in the feeding and drying oven, and the swinging of the film is easily scratched by the oven mouth, resulting in scratches. The causes of scratches on printed products caused by the oven are:

The film inside the oven is subjected to the pressure of drying hot air, resulting in material deformation. If there is a lack of good support from the guide rollers, the back of the film will rub against the opening of the drying oven, and longitudinal strip-shaped scratch lines will appear due to the scraping between the film and the opening of the oven;

Scratching caused by the suction of exhaust air on the film is common in the printing of soft films such as PE film. This type of film has relatively low printing tension and is dried by low heating and high wind volume. Often, the drying speed is adjusted by adjusting the inlet and outlet air volume. When the air volume is not adjusted properly, there is an imbalance between the intake and exhaust air, resulting in a large exhaust air volume. The larger exhaust air attracts the film, pulls the film, and causes it to swing. The swing of the printing film causes the printing ink to scratch the oven mouth, causing scratches on the ink film surface. In severe cases, the ink that has not dried is directly scraped off. This type of scraping basically occurs when the air volume is not adjusted properly, and the film swings due to the suction of exhaust air. The regularity of scraping is not strong, but it causes significant damage to the ink film surface. As the ink is still in a wet state, once scraped, it is usually scraped off by large pieces.

The foreign objects inside the oven scratch the film, and the printing machine’s oven is almost a hygiene blind spot. Mechanical factories rarely care about it, and flexible packaging factories rarely inspect the hygiene inside the oven. Many printing machines leave iron filings, film debris, and ink dry lumps in the oven during machining and assembly, which sometimes become foreign objects stuck at the oven mouth. If these foreign objects are not cleaned in time, they can cause damage to the film during feeding.

In order to save effort, printing workers clean the rubber rollers during the machine’s pressing operation. The ink on the rubber rollers is easily carried into the oven by the film, and the guide rollers in the oven are contaminated by ink due to the feeding support, resulting in ink accumulation and transfer on the surface of the guide rollers, forming ink blocks. Ink adheres to the surface of the guide rollers, forming hard ink blocks. When the film passes through, these hard ink blocks scrape the film, causing it to scratch.

2 Scratch on the guide roller

The guide roller of the printing machine plays an auxiliary role in feeding and supporting the film. In high-speed printing, the guide roller relies on the rotation of the bearing to drive the high-speed rotation of the guide roller to work. The rotational friction between the guide roller and the film surface is one of the characteristics of gravure printing. The high-speed rotating guide roller generates rapid friction with the high-speed running film. If the speed of the guide roller cannot synchronize with the feeding speed of the film, the guide roller will cause drag on the surface of the film.

The main cause of scratches on printed products is the scratching of the film by the guide roller.

Inert rotation of guide roller: The long-term high-speed rotation of the guide roller can cause abnormal phenomena such as lack of lubrication or internal ball wear, heat generation, and jamming of the bearing that carries high-speed rotation. This can lead to delayed material dragging friction on the printing film, which may cause damage to the film surface and result in scratches. Special attention should be paid to the guide rollers inside the drying oven and the water-cooled rollers outside the oven, which are highly susceptible to high-temperature conduction caused by oven heating. Long term use in a high-temperature environment not only affects the lubrication of bearings, but also shortens their lifespan. Moreover, the guide rollers are hidden inside the oven and are not easily noticed or valued, which can easily lead to problems such as the guide rollers not rotating and scratching the film.

Injury to guide rollers: The guide rollers of printing machines are often made of aluminum rollers, which are easily deformed by external forces such as hard objects hitting them, resulting in sharp protrusions. If not dealt with in a timely manner, the film can be easily scratched by the rotation of the guide rollers during film feeding. 3. There are hard objects such as lumps and ink particles on the surface of the guide roller: During the printing process, ink is transferred to the guide roller, forming hard blocks, particles, etc. on the guide roller. During the rotation and transportation of the guide roller with the film, the hard objects scratch the ink film.

Incorrect threading of film: Due to incorrect threading of film, the force on the film surface changes, and sometimes the threading changes cause direct scratching of the film against other fixed beams and other objects of the equipment, resulting in scratches on the printed product.

Non parallel guide rollers: The imbalance between the guide rollers causes uneven force on the film, resulting in a certain degree of scratching on the film surface.

The flipping roller of the anti printing frame scratches, and due to the fixed roller of the anti printing turning roller, there is a huge angular contact between the turning of the film, which can easily cause scratches on the film surface due to inadequate cooling or unclean surface

3 The electrostatic brush scratches

To eliminate static electricity caused by high-speed printing, printing units are equipped with electrostatic brushes. Anti static brushes are usually installed on aluminum alloy racks, with the brush head about 2-3mm away from the film position. Such a small distance can easily cause changes during ink transfer or production, resulting in direct contact between the brush and the film. Generally, the surface softness of a new electrostatic brush is not a problem, but long-term use of the electrostatic brush may cause it to age and become hard, or the electrostatic brush may be contaminated with ink. Dry ink can make the brush harder, and careless operation can cause the electrostatic brush to touch the thin film. Friction between the high-speed running thin film and the hard brush can easily scratch the surface of the thin film. There is also the use of copper wire placed on the film surface to eliminate static electricity. As the diameter and rotation of the film roll change, the hard copper wire causes friction and scratches on the film, resulting in scratches.

4 Mechanical scratch

The traction roller, winding pressure roller, and rubber roller used for unwinding and unwinding are not clean, or during operation, due to the uncleanliness of the film or the presence of small gravel in the environment, some foreign objects adhere to the rotating roller, forming hard particles on the surface, especially the rubber roller, which is prone to adhere to foreign objects and form slight protrusions. The presence of hard protrusions on these rollers causes mechanical scratches on the surface of the film under the combined pressure of film operation and roller rotation. Especially when the rotation speed of the roller is different from that of the film, the strain caused is even more severe.

The problem of printing scratch is basically inseparable from the above points. After understanding the causes, it is not difficult to solve the problem of printing scratch. As long as the following 13 points are achieved, it is highly likely to solve the scratch problem of printing in the printing process:

Regularly inspect and clean the printing machine, keep the equipment clean, ensure that the guide rollers are free of foreign objects, dirt and protrusions, and the surfaces of the traction rollers, rubber rollers, pressure rollers, etc. are clean;

Accurately threading the film to avoid unnecessary scratches caused by errors in the threading circuit;

Correctly install the electrostatic brush, keep a distance of 2-3mm between the brush and the film, and replace the brush that is stained with ink or aged in a timely manner to avoid the hardened brush head scratching the film;

When printing soft thin films, it is necessary to control the tension of the printing film to avoid film oscillation caused by insufficient tension;

Adjust the inlet and outlet air pressure inside the oven to avoid deformation and swinging of the film due to air pressure. Pay attention to keeping the edge of the oven mouth smooth and not touching the film;

When cleaning the guide rollers, check the rollers and also check the flexibility of their rotation to ensure that each roller rotates smoothly and freely;

Pay attention to the cleanliness of the workshop environment and ensure that no dust or foreign objects enter the workshop;

Avoid scrubbing the rubber rollers while the machine is running, and prevent the guide rollers in the oven from being contaminated by ink;

Correctly use the method of eliminating static electricity, do not use hard copper wire to contact the film surface, and avoid scratching;

Avoid using hard tools such as hammers to strike the guide rollers. If there are deformations or sharp protrusions on the surface of the guide rollers, they must be ground flat.

When printing on the reverse side, ensure accurate feeding of the reverse printing frame and normal operation of the air cooling of the flipping roller to avoid scratching the film surface.

Establish operational standards and regulations, provide sufficient pre job and on-the-job training, practical education and assessment for employees, and strengthen their skills;

Regular management supervision and inspection to ensure that employees comply with standards and regulations.

Longdapac, as the leading recyclable pouches manufacturer in China, is doing a good job in recyclable film printing. With the effort of engineers and printers in the workshop, we are now able to print the best quality in the industry for recyclable packaging.

13 Ways to Solve the Problem of Scratches on Printed Recyclable Film

1 Oven scratch:

2 Scratch on the guide roller

3 The electrostatic brush scratches

4 Mechanical scratch

PCR PE Pouches

Mono-material Pouches

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Flexible packaging factory

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