Dry lamination is a lamination method currently used in our flexible packaging industry. There are many factors that affect the final lamination quality, including process parameters, adhesive selection and formulation.
First, the standard process parameters of dry compound
1. Compound key parameters
Oven temperature: 50 ~ 60 ℃; 60 ~ 70 ℃; 70 ~ 80 ℃
Compound roll temperature: 70 ~ 90 ℃
Compound pressure: The compound roller pressure should be increased as much as possible without damaging the film .
Specific situation description:
(1) When the transparent film is compounded, the temperature of the oven and the compound roll and the ventilation conditions (air volume, wind speed) in the oven have a great effect on transparency. The upper limit is adopted when the printed film is PET; the lower limit is adopted when the printed film is BOPP;
(2) For composite aluminum foil, if the printing film is PET, the temperature of the composite roller must be higher than 80 ° C, usually adjusted between 80 ~ 90 ° C. When the printing film is BOPP, the temperature of the composite roller should not exceed 80 ° C.
2. Curing process parameters
(1) Curing temperature: 45 ~ 55 ℃
(2) Curing time: 24 ~ 72h
The two-component adhesive does not have the ideal bonding strength immediately after the compound is machined down. The product needs to be sent to a curing room and cured at 45 ~ 55 ℃ for 24 ~ 72h. (Ordinary transparent bag 24h, aluminum foil bag 48h, The cooking bag is 72 h). In addition, the ventilation of the curing chamber is also important. Adequate ventilation can reduce the curing time and further reduce the solvent residue.
Precautions for the preparation and use of glue
1.Standard preparation method
First pour the main agent into the compounding barrel, dilute with 1/3 of the solvent, stir well, add the curing agent, and stir while adding. After homogenization, add the remaining solvent.
2.Use of remaining glue
After diluting the remaining glue solution by 2 times, seal it. When working the next day, use it as a diluent and mix it into the newly prepared glue solution. When making highly demanding products, do not exceed 20% of the total. If the solvent moisture content is qualified, the prepared glue solution will not change much after storage for 12 days, but because the composite film cannot be immediately judged as qualified, the remaining glue solution may cause great losses if used directly.
Third, common composite quality problems and solutions
1. Poor transparency
(1) Improper use of adhesive: The adhesive itself is dark in color. Or the adhesive has insufficient fluidity and poor flatness, and cannot be fully spread on the base film. As a result, transparency is poor.
Generally speaking, the higher the solid content of the main agent, the better the fluidity, and the more favorable it is for spreading on the film. Therefore, the glue with a solid content of 75% is better than 50% in the market, and 50% is better than 40%. For composite films with high transparency requirements, it is difficult to meet the requirements if the glue with a solid content of 50% or 40% is selected.
(2) Process issues
A. The inlet temperature of the drying tunnel is too high or no temperature gradient, the inlet temperature is too high, and the drying is too fast, so that the solvent on the surface of the glue layer evaporates quickly, and the surface is crusted. Then, when the heat penetrates into the inside of the glue layer, the The solvent vaporizes and breaks the glue film to form a ring like a volcanic vent, which makes the glue layer opaque.
B. The compound rubber roller or scraper is defective and cannot be pressed at a certain point, forming a gap and opaque.
C. There is too much dust in the ambient air, there is dust in the hot air blowing into the drying tunnel after gluing, and it sticks to the surface of the rubber layer. There are many small points sandwiched between the two base films when compounding, causing opacity. Solution: The air inlet uses a high-mesh filter to eliminate dust in the hot air.
D. The amount of glue is insufficient. When there is a blank space, small air bubbles are trapped, causing variegated or opaque. The sizing amount should be checked to make it sufficient and uniform.
E. No rubber spreader or rubber spreader is clean.
(3) Reason for substrate
The surface tension is not high, and the glue solution is not sufficiently wettable. After drying, the glue film is uneven, and it appears to be distributed little by little. It is commonly known as "hemp face mask".
2.Small bubbles in the composite membrane
(1) Reasons for raw materials
The surface tension of the base film is too low, and the wettability is poor; the water content in the diluent is too high, and NCO in water and the curing agent generates CO2 to form bubbles.
(2) Process reasons
A. The pressure of the compound rubber roller is insufficient or the surface temperature of the steel roller is too low, the activation of the adhesive is insufficient, the fluidity is insufficient, the adhesive with the same dots has uneven flow, and tiny voids cause extremely small bubbles.
B. The angle between the composite roll and the film is not appropriate, and the wrapping angle is too large, causing air bubbles. The roll film should enter the compound roll as tangentially as possible.
C. The air humidity is too high, the workshop environment is dirty, and dust adheres to the surface of the film. The dust particles lift up the two layers of film, forming a circle of gaps around.
3. Wrinkle of composite film
Compounded products show wrinkles, especially at both ends of the roll. The wrinkles are flattened on one substrate, and the other substrate protrudes to form a "tunnel".
(1) Material reasons
The initial tack of the adhesive is insufficient; the surface tension of the substrate is insufficient.
(2) Process reasons
A. Two kinds of base film unwinding tension are not suitable, one is too large and the other is too small.
For example: BOPP / AL composite, if BOPP tension is too high, it will be heated in the drying tunnel, it will be stretched, and the aluminum foil tension is unlikely to be large. In addition, the elongation rate is small. .
B. The amount of glue is not enough and uneven, causing bad adhesion and wrinkles in some places.
C. The winding tension is too small, the winding is not tight, and there is a relaxation phenomenon after lamination, which provides the shrinking space for the substrate to be shrunk. If the take-up tension is large, the roll is compacted and compacted, and it will be solidified in the curing room immediately after the machine exits, even if the process is not suitable, there will be no wrinkles.
D. The temperature of the oven is too low and not ventilated. Too much residual solvent causes the adhesive to dry insufficiently. The insufficient initial tack provides the possibility of displacement of the two base films.
Fourth, the conclusion
There are many factors that cause dry composite quality problems, and they affect each other. Once a quality problem is found, it is difficult to pinpoint the cause immediately, and the company needs to investigate one by one. Therefore, in daily production, companies should develop a good habit of recording process parameters and standardize the operating habits of employees. This not only helps the company to obtain stable product quality, but also facilitates data comparison when quality problems occur. Find the cause of the problem, so as to solve the problem quickly and improve production efficiency.