Analysis of the Causes of Bubbles in Dry-type Composite Films in Flexible Packaging

The failure of air bubbles in dry packaging composite film is very common, and there are many reasons for its occurrence. We will discuss the main factors one by one below.

1. Factors in film

1 . Film surface tension

The surface tension of the composite film must reach a certain value. If the surface tension of the film is too small, bubbles will be generated where there is little or no glue. In addition, the surface tension of the film should be uniform. If the surface tension is not uniform, the glue will be uneven, and voids and bubbles are likely to occur. Therefore, plastic films are generally subjected to surface treatment before compounding to increase the surface tension value and ensure the smooth progress of the compounding process. Before production, the surface tension of the film must be carefully and carefully checked. Once it is found that the surface tension does not meet the requirements, the surface treatment must be performed again.

2 . Thin film average thickness error and error distribution

The thickness of the composite film should be as uniform as possible, and the average thickness error should be controlled within the error range, the smaller the better. And the distribution of the average error should also be uniform. If the distribution is uneven, ribs will appear where the thickness is too large, resulting in an imbalance in the compound pressure, and gaps will appear where the pressure is low, thus forming bubbles.

3 . Film surface cleanliness

In the dry compounding process, the surface of the film to be compounded must be dry and clean. If the surface of the plastic film is not very clean and the millet has attached dirt, grease and other contaminants, it will prevent the two layers of the base material of the composite film from closely adhering. These foreign objects in the middle will also lead to the formation of gaps and bubbles. The surface of the film is not clean. In addition to cleaning with a clean cotton cloth, the film can also be corona treated again. Corona treatment can remove the dust, moisture and other oil dirt adsorbed on the surface of the film, increase the surface tension of the film, and also make the surface of the film have a good roughness, which can reduce the incidence of bubbles and other failures, and further improve the composite fastness .

4 . Moisture content of the film

For some films with strong hygroscopicity: such as PT , NY, etc., if improper storage causes it to absorb a large amount of water without treatment, it is used directly. During the compounding or aging process, the water will gradually evaporate outward, and may Make the composite membrane produce bubbles. Therefore, we must pay attention to moisture for the film with strong hygroscopicity. If it is found that the film has absorbed moisture, you can preheat and dry it before compounding.

2. Factors in ink and printing process

1 . Type and quality of ink

Correct selection of ink can also control and reduce the generation of bubbles in the composite film to a certain extent. If the affinity of the adhesive used for printing is relatively poor, it will result in a small amount of glue on the surface of the ink, and even there are areas where the coating is omitted, which is easy to form bubbles. If it is to produce retort packaging film (bag), it is necessary to use retort-resistant compound printing ink. Otherwise, bubbles may be generated after the package is cooked, and even the two layers of film at the ink are peeled off and detached. Therefore, in actual production, the appropriate type of composite ink should be selected according to the type of printing material, the nature of the content, the conditions of post-processing, and other specific conditions and requirements. This is also an aspect of ensuring the bonding strength of the composite film.

2 . Ink drying performance.

The drying performance of the ink is one of the main printing suitability of the ink. If the ink is poorly dried, especially when a large amount of solvents with high boiling points such as methylbenzine and butanol are used in the ink, there will be many solvents remaining in the ink layer After the compounding process, these residual solvents may generate many small bubbles, affecting the peel strength of the compound film. Therefore, in the printing process, the drying performance of the ink must be strictly controlled to ensure that the ink is fully dried.

3 . printing art

During the printing process, printing speed, drying temperature and other process conditions will also have a certain effect on the volatile drying of the solvent in the ink. In general, when setting the temperature of the drying oven, factors such as printing speed, ink and drying speed, the type of printing material, and the size of the printed pattern must be taken into consideration. If the printing speed is faster and the temperature of the printer's drying oven is lower, the solvent in the ink may not be completely evaporated, and these residual solvents will form some small bubbles, which will cause inclusion of bubbles in the composite film. Reduce the printing speed and increase the drying temperature appropriately.

3. Factors related to adhesives

1 . Adhesive viscosity

The viscosity of the adhesive has a very important influence on the fluidity, wettability and uniformity of the adhesive. In dry compounding, the viscosity value of the adhesive should be controlled within an appropriate range. If the viscosity of the adhesive is too high, the dispersibility and leveling may be poor, affecting its wettability on the surface of the composite substrate. During the glue application process, failures such as leaks and bubbles may occur.

2 . Type and quality of adhesive

The choice of adhesive must take into account the actual situation of the type, performance, post-processing conditions of the substrate and the final use of the composite material, otherwise it may affect the quality of the composite product. For example, when the contents of the package are relatively alkaline, acidic or irritating, the adhesive used must have a strong resistance to media, otherwise it may affect the adhesion fastness, locally generate small bubbles, and eventually cause compounding Film delamination and degumming.

3 . Preparation of glue

When preparing the two-component adhesive, it must be fully stirred to make it evenly dispersed, which is conducive to wetting and bonding on the composite film, reducing the occurrence of bubbles. In addition, the prepared glue should be fully degassed and then poured into the rubber tray for use. When pouring the glue, it should be slowly poured down along the edge of the rubber tray, and the glue in the rubber tray cannot be stirred vigorously. In order to avoid the formation of bubbles in the composite membrane due to the mixing of air.

4 . Thinner

At present, the diluent used in dry composite polyurethane adhesives is generally ethyl acetate, and the moisture content in ethyl acetate must not exceed 0.2% . If the purity of the diluent is not high and contains active substances such as water and alcohol, the -NCO group contained in the polyurethane will react with the active hydrogen atoms in water or alcohol, and CO2 gas will be released during the reaction , thereby generating bubbles. Therefore, we must do a good job in diluent testing to ensure its purity and control the generation of CO2 gas.

Responses:

In response to the above-mentioned major factors that affect the generation of bubbles in the composite film, active prevention and countermeasures can be taken in actual production to reduce the incidence of bubbles in the composite film and further improve the quality of the composite film.

1 . Strengthen the detection of various raw and auxiliary materials (including films, inks, adhesives, various solvents, etc.), strictly control the quality, reduce the probability of bubbles and other failures of the composite film from the source, and improve the quality of the composite film .

2 . In actual production, appropriate printing inks and compound adhesives should be selected according to different printing processes, film types and characteristics, performance and requirements of packaging contents, and subsequent processing conditions, and according to specific production conditions. Adjust and control printing and compound process parameters to ensure the quality of the compound film.

3 . In the daily operation process, the tooling must be taken care of, and the maintenance and maintenance of the tooling should be paid attention to. Before each driving and after parking, the tooling should be cleaned in time, and cleaned and adhered to the coating roller with a clean and soft cotton cloth soaked in a small amount of solvent Adhesive or other dirt on the surface of the rubber roller to avoid the adhesion of these adhesives after drying to affect the uniformity of the glue, thereby reducing the incidence of bubbles. In addition, the coating roller must be brushed repeatedly with a brush or copper brush to remove the remaining adhesive in the cavity as thoroughly as possible to avoid clogging of the cavity and affect the amount of glue and the uniformity of the glue. .

When storing the coating roller, the coating rubber roller and the composite rubber roller, they should be placed on a special support, and must not be placed directly on the ground to prevent scratches and affect the quality of the composite product. In addition, it is necessary to regularly check whether each roller is damaged, and if it is found, it should be replaced or repaired in time.

4 . The temperature and humidity of the environment in the printing workshop should be kept relatively constant. If possible, air conditioning or dehumidification (humidification) and other devices can be installed. At the same time, we must pay attention to maintaining the sanitation of the warehouse and workshop, and have good ventilation conditions to avoid foreign objects such as dust and sand particles from adversely affecting the composite process and the quality of the composite membrane.

 

 

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