1、 Film factors
1. The surface tension of the film
The surface tension of the composite film must reach a certain value (for example, the surface tension of polyethylene film must be greater than 3.8 × 10-2n / M). If the surface tension of the film is too small, bubbles will appear in the area with little or no glue. In addition, the surface tension of the film should be uniform. If the surface tension is not uniform, the coating will be uneven, which is easy to produce holes and bubbles. Therefore, the surface of plastic film should be treated before compounding, in order to improve its surface tension and ensure the smooth progress of the composite process. Before production, the surface tension of the film must be carefully checked. Once it is found that the surface tension can not meet the requirements, the surface treatment must be carried out again.
2. Average film thickness error and error distribution
The thickness of composite film should be as uniform as possible, and the average thickness error should be controlled within the error range, the smaller the better. Moreover, the average error distribution should also be uniform. If the distribution is not uniform, ribs will appear at the place with too large thickness, resulting in the imbalance of composite pressure, and the gap will appear in the place with small pressure, thus forming bubbles.
3. Surface cleanliness of film
In the dry lamination process, the film surface must be dry and clean. If the surface of plastic film is not very clean, millet with dust, grease and other dirt, it will make the composite film between the two layers of substrate can not be tight. These foreign bodies in the middle can also lead to the formation of gaps and bubbles. The surface of the film is not clean. In addition to cleaning with clean cotton cloth, the film can be corona treated again. Corona treatment can not only remove the dust, water and other oil dirt adsorbed on the surface of the film, improve the surface tension of the film, but also make the film surface have good roughness, which can reduce the occurrence rate of bubbles and other faults, and further improve the composite fastness.
4. Water content of film
For some films with strong hygroscopicity, such as Pt, NY, etc., if they are not kept properly, they will absorb a lot of water and use them directly without treatment. In the process of compounding or aging, the water will gradually evaporate outward, and the composite film may produce bubbles. Therefore, the film with strong hygroscopicity must pay attention to moisture-proof, if the film is found to have moisture absorption, you can first preheat and dry, and then composite.
2、 Ink and printing process factors
1. Type and quality of ink
The correct selection of ink can also control and reduce the production of composite film bubbles to a certain extent. If the affinity of the adhesive used in printing is poor, the amount of glue on the surface of the ink will be less, and even there is leakage, which is easy to form bubbles. If it is the production of cooking packaging film (bag), you must use cooking resistant composite printing ink. Otherwise, the packaging may produce bubbles after cooking, and even the two-layer film peeling off at the ink position may occur. Therefore, in the actual production should be based on the type of printing material, the nature of the content, post-processing conditions and other specific conditions and requirements to choose the appropriate type of composite ink, which is also to ensure the bonding strength of the composite film.
2. Ink drying performance.

The drying performance of ink is one of the main printability of ink. If the ink is not dry well, especially when a large number of solvents with high boiling point such as methylbenzene and butanol are used in the ink, many solvents will remain in the ink layer. After the composite process, these residual solvents may produce many small bubbles, which will affect the peel strength of the composite 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 technology
In the printing process, printing speed and drying temperature and other process conditions will also have a certain impact on the volatile drying of the solvent in the ink. Generally speaking, when setting the temperature of drying oven, the printing speed, printing ink and drying speed, the type of printing material and the size of printing pattern must be considered comprehensively. If the printing speed is fast and the temperature of the drying box of the printing machine is relatively low, the solvent in the ink may not be completely volatilized, and these residual solvents will form some small bubbles, which will cause bubbles in the composite film. At this time, the printing speed should be reduced and the drying temperature should be appropriately increased.
3、 Adhesive factors
1. Viscosity of adhesive
The viscosity of the adhesive has a very important influence on the fluidity, wettability and coating uniformity of the adhesive. In dry lamination, the viscosity of the adhesive should be controlled in an appropriate range. If the viscosity of the adhesive is too high, the dispersibility and leveling property may be poor, which will affect its wettability on the surface of composite substrate, and the coating leakage and bubbles may occur during the coating process.
2. Type and quality of adhesive
The selection of adhesive must take into account the types, properties, post-processing conditions and the final use of composite materials, otherwise the quality of composite products may be affected. For example, when the contents of the package are strongly alkaline, acidic or irritant, the adhesive used must have strong resistance to medium, otherwise it may affect the bonding fastness, produce small bubbles locally, and eventually cause delamination and degumming of the composite film.
3. Preparation of glue solution
In the preparation of two-component adhesive, it must be fully stirred to make it evenly dispersed, which is conducive to wetting and bonding on the composite film and reducing the occurrence of bubbles. In addition, the prepared glue solution should be fully static degassing, and then poured into the rubber tray for use. When pouring the glue, it should slowly fall down along the edge of the rubber plate, and the glue liquid in the rubber plate should not be stirred violently, so as to avoid the formation of bubbles in the composite film due to the air mixing.
4. Diluent
At present, the diluent used in dry composite polyurethane adhesive is ethyl acetate, and the moisture content in ethyl acetate should not exceed 0.2%. If the diluent is not of high purity and contains active substances such as water and alcohol, the NCO group contained in polyurethane will react with the active hydrogen atom in water or alcohol, and CO2 gas will be released at the same time of reaction to form bubbles. Therefore, it is necessary to do a good job in diluent detection to ensure its purity and control the generation of CO2 gas.
4、 Factors of dry composite process and tooling
1. Glue amount
Too little glue is also the cause of bubbles. If the amount of glue is insufficient, small bubbles will be mixed in the gap. In the actual production, the appropriate amount of glue should be determined according to the different requirements of packaging contents. The adjustment of coating amount is mainly considered from the following three aspects: first, the number of wire and the depth of mesh hole of anilox roller used for gluing affect the size of gluing amount; second, the concentration of glue liquid; third, the soft and hard degree, pressure, angle of scraper and pressure of cot.
2. Drying temperature and exhaust air volume of drying channel
Drying temperature is too low, adhesive drying is not enough, solvent evaporation is not complete, will produce small bubbles. If the drying temperature is too high, it will make the adhesive blister, or make the adhesive layer epidermal conjunctiva, which will affect the volatilization of the solvent inside the coating, and also cause the residual solvent and the formation of micro bubbles. In general, in the actual production, the temperature of the three drying channels of the dryer should be set according to the heat resistance of the base material, the compound linear speed and the solvent content in the glue solution, so as to make the solvent fully dry, strictly control the residual amount of solvent and reduce the occurrence rate of bubbles. Generally speaking, it is suitable to control the drying temperature of the three drying channels at 50-60 ℃, 60-70 ℃ and 70-80 ℃ respectively.
3. Speed of composite line
The rate of compound linear velocity directly affects the volatilization of solvent in adhesive. If the composite linear speed is too fast, the time for the substrate to pass through the drying channel is short, which is not conducive to the solvent volatilization, and the adhesive drying is not sufficient, resulting in excessive residual solvent, which may make the composite film produce bubbles. Therefore, it is necessary to master the compound line speed and solvent volatilization speed in actual production.
4. Surface temperature of composite steel roller
If the surface temperature of the composite steel roller is too low, the activation degree of the adhesive will be affected. If the activation of the adhesive is insufficient, the leveling property is poor, and the formation of small voids will lead to the generation of small bubbles. Generally, the surface temperature of composite steel roller is controlled at 50 ~ 90 ℃. The properties of the composite substrate, the thickness of the composite film and the composite linear velocity should also be considered.
5. Compound pressure
If the composite pressure is too small, the bonding between the composite substrate is not tight, which will lead to the generation of small bubbles. Generally, the compound pressure is controlled at 40 ~ 50N.
6. Compound angle
If the composite angle is too large, air will be easily trapped between the two layers of composite film, which will lead to bubbles and tunnel phenomenon, especially when the film material is thick and hard. Therefore, the smaller the compound angle, the better.
7. Ripening degree
After compounding, the two-component polyurethane adhesive should be aged at 40-50 ℃ for 24-28 hours. If the curing time is not enough, there will be small bubbles.
8. Residual solvents
In the drying process of the compound product in the drying channel, the cleaner the solvent in the adhesive is required to volatilize, the better. If the solvent is not evaporated completely, the residual solvent will gradually accumulate and form tiny bubbles on the cooled composite film. Moreover, the residual solvent ethyl acetate in the glue is a good solvent for ink binders, which will gradually penetrate into the ink layer and soften the ink, thus forming bubbles in the ink. If there are more residual solvents, the drying temperature of the drying channel should be properly increased, the compound linear speed should be reduced, and the exhaust air volume should be increased to make the solvent fully volatilized.
9. Dry recovery machine tooling
The coating roller, the coating cot and the composite cot are the three most important parts in the tooling of the dry duplicating machine. This paper only introduces the influence of these three parts on the formation of the composite film bubble.
(1) Coating roll
The function of the coating roller is to transfer the adhesive to the film surface under a certain pressure, which has a certain relationship with the generation of bubbles in the composite film. Due to the coating roller mesh depth directly affects the size of the coating amount, therefore, if the coating roller mesh hole is blocked, or some mesh holes are damaged, it will directly affect the size of the coating glue and the uniformity of the coating, giving the composite film bubble manufacturing opportunities. Especially in the hot summer, it is more likely to occur in the coating roller mesh plug phenomenon, so it is necessary to clean the coating roll in time.
(2) Coating cot
The function of the coating cot is to give the coating roller a certain pressure and transfer the adhesive on the coating roller to the film. The soft and hard degree of cots, pressure size also has a certain impact on the coating amount. If the surface damage, dents, sand holes, or the hardness of the surface rubber layer is inconsistent, it will cause uneven gluing pressure and amount, resulting in bubbles. Therefore, the surface of coated cots should be smooth, without indentation, scratch, pit and other defects.
(3) Composite cot
The function of composite cot is to fit two layers of film together under certain temperature and pressure. If there are defects on the surface of the composite cot, such as scratches, dents, sand holes, etc., these parts will form a gap when compounding, and the pressure will not be compacted, thus making the composite film produce small bubbles. In addition, if the surface aging degree of the composite cot is different and the hardness is not consistent, it is easy to cause bubbles.
5、 Environmental factors of workshop
1. Ambient temperature and relative humidity
The environmental temperature and humidity are too high, too low are not conducive to the production of composite membrane. If the temperature and relative humidity in the workshop are too high, water will be mixed into the prepared glue solution and bubbles will be produced. In addition, if the relative humidity is too high, the plastic film is easy to absorb the moisture in the air, especially the plastic film with high hygroscopicity, such as nylon and cellophane, resulting in the formation of bubbles after compounding. On the contrary, if the temperature and relative humidity in the workshop are relatively low (e.g. in cold and dry winter), and there is no air conditioner installed in the workshop, the dispersion of adhesive is not good, the wetting and adhesion to the film are not good, and bubbles will also be generated.
Generally speaking, the temperature of workshop should be controlled at 18 ~ 25 ℃, and the relative humidity should be kept at 60% ~ 70%.
2. Environmental sanitation in the workshop
The environmental sanitation in the workshop also has a great influence on the quality of composite products. If there are a lot of dust, impurities and other particles in the air, then these particles are adsorbed on the plastic film, or fall into the coating roller, composite roller and glue liquid, which will affect the tightness of the two-layer composite substrate. When the two membranes are jacked up, small bubbles are formed. Therefore, it is necessary to keep the workshop clean and sanitary, reduce the floating dust in the air, and should often clean the drying channel, and try to keep the workshop in a good sealing state.
6、 Conclusion
In view of the above factors that affect the formation of bubbles in the composite membrane, active preventive and response measures can be taken in the actual production to reduce the occurrence rate of bubbles in the composite membrane and further improve the quality of the composite membrane.
1. Strengthen the detection of various raw and auxiliary materials (including films, inks, adhesives, solvents, etc.), strictly control the quality, reduce the occurrence rate of bubbles and other faults of the composite membrane from the source, and improve the quality of the composite membrane.
2. In the actual production, the appropriate printing ink and composite adhesive should be selected according to different printing process, type and characteristics of film, performance and requirements of package contents and subsequent processing conditions, and the printing and laminating process parameters should be adjusted and controlled according to the specific production conditions to ensure the quality of the composite film.
3. In the daily operation process, pay more attention to the tooling, and pay attention to the maintenance and maintenance of the tooling. Clean the tooling in time before and after each start-up and after parking. Clean and soft cotton cloth soaked with a small amount of solvent is used to wipe the adhesive or other dirt adhered to the surface of coating roller and rubber roller, so as to avoid the influence of adhesive on the uniformity of coating after drying, so as to reduce the occurrence rate of bubbles 。 In addition, for the coating roller, brush its mesh hole repeatedly with a brush or copper brush to remove the remaining adhesive in the mesh hole as thoroughly as possible, so as to avoid blocking the mesh hole and affecting the coating amount and coating uniformity.
When storing the coating roller, coating cot and composite cot, it should be placed on the special support, and it is not allowed to be directly placed on the ground, so as to prevent damage and affect the quality of composite products. In addition, it is necessary to regularly check whether there is any damage to the rollers. Once the damage is found, it should be replaced or repaired in time.
4. The environment temperature and humidity in the printing workshop should be kept relatively constant. If possible, air conditioning or dehumidification (humidification) devices can be installed. At the same time, attention should be paid to keep the environment in the warehouse and workshop clean, and have good ventilation conditions, so as to avoid the adverse effects of dust, sand and other impurities on the composite process and the quality of composite membrane.
Dongguan Beite packaging materials Co., Ltd. - located in Dongguan City, the world's manufacturing city, is a subsidiary of Beite packaging (China) Co., Ltd., with a plant area of 6000 square meters. It is a flexible packaging enterprise integrating R & D, production and sales. It has a complete set of domestic advanced production equipment, a scientific and humanized management system and a group of experienced technical personnel For backing, to provide customers with quality products and first-class service. The company produces composite bags, roll film, fruit bags, aluminum foil bags, suction mouth bags, self-supporting bags, zipper bags, anti-static bags, special-shaped bags, etc., which are suitable for the internal and external packaging of food, daily chemicals, electronics, toys, medicine, cosmetics, industrial products and other industries. We uphold the integrity of cooperation, good quality, good service business philosophy, won the industry's approval, products sold to all over the world; welcome friends from all walks of life to inquire, visit our factory to investigate guidance and business negotiations.