Common inkjet coding and marking failures in packaging bags, extremely useful

Taking packaging bags as an example, whether it is an ordinary packaging bag or a retort pouch, no abnormalities occurred during the printing, lamination, and bag-making processes. However, during the customer's use, some bags always have incomplete inkjet printing, ink fading after high-temperature sterilization, and the phenomenon of the print color becoming lighter and lighter after coding. However, the cause could not be found during the production process, causing many troubles for customers. Shunxingyuan Packaging, a professional flexible packaging manufacturer, believes that there are many reasons for abnormal coding and inkjet printing, and uses several practical cases for analysis to help customers solve their troubles.

 

 

 

 

I. Inkjet omission

Some companies have reported: PA//CPP (1560um) combination, solvent-free lamination, retort pouch products. No abnormalities occurred during printing and lamination production, but during customer use, some bags had incomplete inkjet printing, with approximately 10% of bags missing the code.

Generally, bags are irregular during inkjet transmission, leading to inkjet omission. If 7-8 out of 100 bags do not have inkjet printing, is the incomplete inkjet printing due to omission? If it accounts for 10% of the total, it is considered inkjet omission.

 

 

 

 

Shunxingyuan Packaging believes the reasons are:

1. Too much CPP lubricant, sticking to the NY surface, resulting in low friction coefficient, and the bags are easy to slip, making inkjet printing impossible. The friction coefficient of the bag surface is less than 0.3, which is related to the base material of the PA surface layer and has nothing to do with static electricity! This is a problem with the base material.

Check the surface material, the change in the friction coefficient of the surface layer before and after use. If it becomes smaller and dispersed after lamination, it indicates that the additive floats up, causing some inkjet printing to fail. Using low-lubricant CPP and solvent-free glue that does not affect the friction coefficient can partially solve the inkjet omission.

2. Part of the BOPA film surface absorbs moisture, or ultra-low-lubricant PA film, the bag runs irregularly, overlaps or slips, causing partial inkjet omission.

3. Is the inkjet ink used the inkjet ink for NY raw materials? If there is no problem using this inkjet ink, and if the raw material structure you use frequently exhibits this phenomenon, it is recommended to use double corona PA composite CPP and check the BOPA non-surface tension value.

II. Inkjet fading

Some companies have reported: Inkjet fading after high-temperature sterilization.

High-temperature retort pouch structure: PET//AL//BOPA//RCPP (12071570), inkjet fading occurs after high-temperature sterilization, and the bag surface is not slippery. What is the reason?

The pollution of oligomers produced during the film production process affects the surface of the film, causing inkjet fading or omission during the bag-making and inkjet printing process.

 

 

 

 

Shunxingyuan Packaging believes the reasons are:

1. The low molecular weight substances in the raw materials are not heat-resistant, and the additives float up after high-temperature, hindering the inkjet ink from printing, causing inkjet fading.

2. In the cooling section of the TDO during film making, the temperature gradient is large, causing a large amount of oligomers to quickly condense on the nozzle wall of the cooling section. If the accumulated amount is large, it will fall from the nozzle wall. Falling on the film surface, it will slightly increase the haze of the film, and severely affect the adhesion of ink and adhesive, affecting the adhesion strength.

3. Air conditioning water, equipment oil stains, dust in the air, or excessive humidity in the production workshop, small water droplets attached to the film surface affect the adhesion strength of the ink.

4. Generally, the surface tension of BOPP film that has just undergone corona treatment should reach more than 40 dynes. After the film is placed for one week, it must also reach more than 38 dynes. Films with less than 36 dynes do not have sufficient adsorption strength for ink. PET reaches 50 dynes, and BOPA reaches 52 dynes.

Generally, it is best to use the film within one week, and the longest should not exceed 3 months.

5. The coding ink used does not meet the requirements of high temperature and humidity resistance. Only by using suitable materials and matching printing inks can good results be obtained.

III. Inkjet moisture absorption

Some companies have reported: PA//PE (1560um), water-boiled bag, the bag inkjet absorbs moisture and sticks together, and this situation is more serious in summer.

After the bags are made, they are sent to the customer's warehouse. The inkjet printing is done by the customer to print the production date. The time the customer uses is only a few days away from the factory, and the longer the time, the worse the inkjet printing.

 

 

 

 

Shunxingyuan Packaging believes the reasons are:

1. Material structure: Whether the water resistance of the base material matches the inkjet. The outer layer is PA, and the type of inkjet printer ink is not easy to print. The inkjet ink for frozen products generally uses Japanese inkjet ink.

2. If the production workshop of the food factory has high humidity, the slip performance of the film is different, and the water absorption rate of the film is different, but it is mainly the problem of lubricant. PA film will absorb some water, and the film additive and small water droplets in the air cause film surface adhesion.

3. The use and inkjet printing time of the bags should be arranged reasonably. Use them immediately after receiving the goods, and the inkjet printing effect will be better. The storage time of printed products should be reduced as much as possible.

IV. Cannot spread, not slippery, astringent

PET//PE combination, solvent-free lamination.

Customers reported that it cannot spread, is not slippery, and is astringent on the automatic inkjet printer.

Shunxingyuan Packaging believes the reasons are:

1. Solvent-free composite PE film is easy to increase the friction coefficient and cause astringency; the friction coefficient of the PE film for bag-making products is generally required to be: 0.1--0.15.

2. A large amount of PE film additives float up.

3. High humidity in the air makes the film surface astringent.

4. The surface tension of the film surface is too large.

V. Inner layer shrinkage, delamination during coding

BOPP/VMPET/PE composite packaging bags (VMPET aluminum-plated surface is laminated with PE film). After being placed for a few days (within one week), it was found that the PE layer at the edge of the sealing edge retracted inward by about 0.5mm. In this case, delamination will occur during coding.

This product uses solvent-free lamination technology, and the ratio of A glue to B glue is 100:58 (the standard ratio is 100:60), cured at 42℃ for 30 hours.

Shunxingyuan Packaging believes the reasons are:

Based on the observed phenomena, the aluminum plating layer does not transfer, but after the aluminum-plated surface and PE film are laminated, the peel strength is low. During heat sealing, there is a significant heat shrinkage stress phenomenon in the PE film at the sealing knife position. This stress is greater than the peel strength between the aluminum-plated surface and the PE film, resulting in the PE layer at the sealing edge contracting inward by 0.5mm and delamination during coding.

VI. Dyne value is a crucial factor directly affecting printing results

Dyne value is a crucial factor directly affecting printing results; higher dyne value leads to better ink adhesion.

For example: PET film is a polar film with excellent barrier properties and strong leak resistance. Without surface tension treatment, it has a dyne value of 45-50, meaning that regardless of the type of ink used by the soft pack inkjet printer, the printing firmness on PET film materials is excellent.

VII. The color of printed bags with metal inks often fades during coding and marking

Use the appropriate adjusting gold oil for different materials to prevent gold ink oxidation and discoloration.

Minimize the storage time of printed products and laminate them as soon as possible.

Summary

1. Absolutely do not use recycled materials

Using recycled materials will reduce the smoothness of the film surface.

Some manufacturers add excessive lubricants to improve the smoothness of the film surface, which will cause a decrease in the surface tension of the film, and the bonding strength of the ink is naturally difficult to guarantee.

Excessive temperature will cause the contents of the raw materials to seep out, affecting the surface tension of the film.

2. Higher surface tension of the film is beneficial for coding

Generally, the surface tension of BOPP film should reach 40 dynes, PET 50 dynes, and BOPA 52 dynes. Below these tensions, there is no adhesion to the ink.

Metal ink affects the clarity of coding and marking. (This contradicts the rough surface)

3. Absolutely do not use one ink for multiple purposes

Some films only have adhesion with printing inks that have affinity for themselves. Conduct a printing ink matching test before mass production.

4. Printing speed and drying temperature should be proportional

The printing speed should not be too fast, and the drying temperature is generally 30-40℃. This is to allow the ink to complete curing and volatilization, strengthening the ink adhesion.

5. Solvent-free lamination is prone to high friction coefficient

6. Workshop temperature and humidity control is very important. Control the environmental humidity appropriately during production.

Especially for solvent-free lamination, the relative humidity is generally below 70%.