Poor ink adhesion:

Poor ink adhesion:

Poor ink adhesion (poor adhesion, poor fastness) means that the ink has insufficient adhesion on the surface of the printing film. If the ink film surface is rubbed, rubbed or pulled by transparent tape, the ink film will fall off or partially form the film. Shedding phenomenon. Poor ink adhesion will seriously affect the adhesion of the ink on the film. For example, the ink film will peel off when the film is rolled up, causing smearing on the back or color bite during the overprinting process. It will also affect the interlayer bonding of subsequent film composites. will have a greater impact. These problems will cause printing quality and even composite quality problems. In serious cases, the entire batch of finished products will be scrapped, which is very harmful to flexible packaging.

The adhesion of ink to film can be divided into three dimensions depending on the lamination produced. The first is the surface properties of the film substrate, whether the film surface can allow the ink to be compatible and adherent; the second is the adhesion between the ink film and the surface of the substrate, which simply means whether the ink can firmly adhere to the film surface; the third is the ink film The cohesion and film-forming properties of the ink itself, and the film-forming properties of the ink itself. Only when these three dimensions can be solved can the problem of poor ink adhesion be completely solved.

There are many reasons that affect ink adhesion, and a comprehensive analysis needs to be carried out from the ink itself, printing film, printing process, production environment and other factors. The following explains the reasons for poor ink adhesion from these aspects:

A. Ink: There are many types of gravure printing inks, including surface printing, inner printing ink, high-temperature cooking, and some special film inks. In short, different types of films correspond to different inks, and various special inks must be used accordingly, otherwise problems such as poor adhesion may easily occur.

1. Improper ink selection: There are many types of inks for gravure printing. Different types of inks are suitable for different film materials, and the inks selected for products with different uses are also different. If the adaptability between the ink and the printing film is poor, and the affinity between the ink and the film is poor, it will lead to poor ink adhesion. Therefore, before printing, it is necessary to select the appropriate ink according to the requirements of the printing film and the products used.

2. Unreasonable ink formula: The formula of the ink directly affects its adhesion performance, especially the selection of the ink resin directly affects the performance of the ink. If the viscosity, resin, pigment, solvent and other ingredients in the ink are not properly matched and the resin binder is reduced, the film-forming performance of the ink may be reduced, the cohesion of the ink film may be reduced, and the adhesion may be reduced.

3. Improper compatibility of ink solvents: Different ink resins and different solvents have different interactions with each other, and the solvents also have different surface wetting and swelling properties of different films. Use a solvent formula corresponding to the ink resin and film. It is a reliable guarantee for printing quality. Improper solvent compatibility may lead to problems such as whitening, precipitation, flocculation, and precipitation of the ink, thereby affecting the performance of the ink and thus the adhesion.

4. Improper storage of ink: Improper storage of ink will lead to a decline in ink performance. The resin content of old ink is relatively low, precipitation and stratification due to long-term storage, use of expired ink, etc. will lead to a decline in ink performance, which in turn affects the ink on the printing film. of adhesion.

B. Printing process factors: During the printing process, adhesion may occur due to mixing of inks, overprinting of different inks, incorrect solvent compatibility, moisture absorption and emulsification of ink, excessive thickness of the ink layer, cohesion between ink resins, and incomplete drying. bad.

1. Ink mixing: When different types of inks are mixed during printing, chemical reactions occur, leading to resin precipitation, flocculation, etc. This causes a series of printing quality problems and affects the adhesion of the product.

2. Overprinting of dissimilar inks: During the printing process, dissimilar inks are used for a certain color in the middle, resulting in repulsion between the ink layers, resulting in poor ink adhesion.

3. Wrong solvent compatibility: The solvent ratio has insufficient dissolving power for the resin, or causes the ink to dry too quickly, which makes the grafting of the resin and the film difficult, resulting in poor adhesion.

4. Incomplete drying: The printing speed and the drying capacity of the equipment have a great impact on the thorough drying performance of the ink. Too fast a printing speed will lead to incomplete drying of the ink, and the ink will easily fall off, leaving no time to form good adhesion on the surface of the printing film, thus Affect adhesion.

5. The ink layer is too thick: During the printing process, if the ink layer is too thick, it will cause the ink to form an uneven coating on the surface of the printing film, and it will be difficult to dry, thus affecting the adhesion.

6. Ink absorbs moisture and emulsifies: The ink resin absorbs moisture and emulsifies, resulting in a decrease in the adhesive force and cohesion of the resin, resulting in a decrease in adhesion.

7. Long-term use of ink: Long-term recycling of ink results in inconsistent transfer rates of resins, pigments, and solvents in the ink, which breaks the internal balance of the ink; ink fatigue caused by long-term cyclic flushing, etc., causes the adhesion of the ink to decrease. .

8. The proportion of resin is too low: Excessive dilution of ink leads to a reduction in resin content. The reduction in ink resin leads to a decrease in adhesion, resulting in poor adhesion.

C. Printing film: The performance of the printing film needs to maintain its adhesive properties. Factors that affect the film adhesion include surface tension, compatibility with the ink resin, film surface cleanliness, additive precipitation and other factors.

1. Surface tension of the film: Commonly used plastic films such as polyethylene, polypropylene, nylon, polyester, etc. have a very smooth surface and have no affinity for ink. Ink is not easy to adhere to it, so it needs to be treated to change its surface condition and chemistry. Structure, increasing surface roughness and intermolecular polarity can make the ink adhere firmly. The adhesion of ink on the surface of the printing film is closely related to the surface tension of the printing film. If the surface tension of the printing film is lower than the surface tension of the ink, it will be difficult for the ink to form good adhesion on the surface of the printing film. Therefore, the printing film should be properly treated (such as corona impact) before printing to increase its surface tension.

2. Matching between the film and the ink resin: The affinity between the film and the ink resin determines the adhesion of the ink to the film.

3. Film surface cleanliness: Pollutants on the surface of the printing film will affect the adhesion of the ink. For example, impurities such as oil and dust can cause the adhesion between the ink and the printing film to decrease.

4. The printing film absorbs moisture: Some printing films, such as nylon, polyester, etc., easily absorb moisture. The surface tension of the printing film after absorbing moisture is reduced, resulting in poor ink adhesion.

5. Precipitation of additives: Most printing films contain various additives, such as antistatic agents, slip agents, opening agents, plasticizers, anti-aging agents, etc. These additives precipitate to the surface of the film to form a barrier layer, which damages the adhesion of the ink to the base film and greatly reduces the printing fastness.

6. Storage: The film is stored for an extended period, or the storage conditions are not suitable, resulting in a decrease in the surface properties of the film and a decrease in the adhesion of the ink to the substrate.

D. Environmental factors: The temperature and humidity of the environment will also have an impact on the adhesion of the film.

1. Ambient temperature: Temperature determines the activity of molecular motion. Under higher temperature conditions, the viscosity of the ink decreases, the surface activity of the film increases, the transfer and adhesion properties of the material are improved, and the leveling and wetting of the ink solvent is improved. The resistance is increased, therefore, the ink can get better adhesion.

2. Humidity: Humidity also has a certain impact on the adhesion performance of the ink. Excessive humidity will form a water droplet barrier layer on the film, and water vapor will enter the ink to emulsify the ink resin. The high humidity environment will reduce the drying performance of the ink, etc. Unsuitable high Wet environmental conditions may cause ink adhesion to decrease.

To sum up, the reasons for poor ink adhesion involve many aspects such as ink, film, printing process, and environment. In the actual printing process, the reasons can be analyzed and corresponding solutions can be taken according to the following specific conditions to improve the adhesion of the ink on the surface of the printing film.

1. Choose ink that matches the film, try to choose better quality ink, and avoid poor adhesion from the source of the ink;

2. Select a solvent that matches the ink and printing conditions to maintain good solubility, dryness, and wetting properties of the solvent.

3. Perform good surface treatment on the film to maintain its surface adhesion properties. Be sure to check the surface tension of the film before putting it on the machine.

4. Strict storage management of ink and film, and do a good job of avoiding heat, moisture and dust.

5. Materials should be used on a first-in, first-out basis to avoid overuse.

6. Avoid over-thinning the ink. Add an appropriate amount of ink-adjusting oil before using the old ink to maintain the usage of the connecting material.

7. Avoid mixing or mixed printing of different types of inks, which will cause ink repulsion and affect adhesion.

8. Ensure that the ink film is dry and thorough;

9. Control the temperature and humidity of the environment, especially to prevent moisture from mixing into the ink.