The flexible packaging compounding process is the most critical part of the quality management of the entire flexible packaging production. If the control is not good, it will not only waste the cost of the previous printing process, but also have a very negative impact on the product delivery time.
I. Factors Affecting the Quality of Dry-Laminated Flexible Packaging
1.Selection of glue type
Many flexible packaging companies have serious misunderstandings when choosing glue. The specific manifestation is which one is cheaper and which one is used by me. Which one uses it well. I also use it. I blindly follow the trend. In fact, each company has its own product characteristics, and the raw materials of the film are different. Therefore, when choosing glue, you should first choose reasonably according to the customer's requirements and product structure. For example, some light packaging can choose water bonding The second is to choose the appropriate adhesive according to the company's equipment capabilities. For example, low-speed laminating machines or medium-speed laminating machines cannot meet the technical requirements of water-based adhesives. The three-layer structure has different glue amount, which type of glue to be tested can not only meet the product composite requirements, but also save costs. After all, the price of glue with different solid content is different. For example, light packaging such as muskmelon seed bag does not necessarily need to be produced with 75% solids adhesive.
2.Glue ratio method
Some enterprises' compound workshops are still using wooden sticks to stir the glue, and they are still dispensing glue. Not only are they not weighed with precision electronic scales, there is no specific system that requires the way, time, and direction of mixing.
The formulation of the adhesive should be rationally formulated in consideration of the product structure, the depth of the screen roller, the size of the glue, the compound, and the printed materials. It must be accurate, standard, and refined. Only in this way can the product quality be grasped. It should be prepared according to the concentration of the operating solution specified in the process work instruction; first add the main agent to an appropriate amount of ethyl acetate, start stirring into a vortex, then drip into the curing agent and stir, then pour the remaining solvent and stir thoroughly Mix until homogeneous and filter with a strainer.
The sizing amount is the sum of the total amount of glue attached to the surface area of the substrate when the substrate is bonded to the substrate. The sizing amount control is very important, and it is the core of the quality control of the whole compounding process. The sizing amount is too low, the peeling strength of the product after compounding is low, or even delamination. If the sizing amount is too high, the composite film will wrinkle, resulting in quality problems such as tunnels, stiffening, and sticky edges. One is not conducive to cost control, and the other is The solvent is not easy to evaporate, and odors remain. Therefore, it is very important to determine the appropriate sizing amount.
Table 1 Sizing amount of common structure
4.The correct choice of screen roller
The normal selection of the screen roller is very important, not only related to the amount of glue, but also an important key point of cost control. There are still many misunderstandings in the use of anilox rollers in many companies, such as the use of 120-line anilox rollers for common structure products and 150-line ones for boiled products. These are all examples where the screen roller is not used properly. In general, when we use polyurethane two-component adhesives, the number of wire rolls for common products is 140 ~ 170, the boiled products are 110 ~ 120, and the cooking products are 90 ~ 100.
5.Setting of drying temperature
The drying temperature is determined by the boiling point of the solvent, the temperature resistance of the material, the amount of glue, the type of adhesive, etc., and it must be matched with the compound production speed to completely evaporate the solvent of the adhesive coated on the film. If the drying temperature is too low, the volatilization rate of the solvent will be slow, there will be more solvents remaining in the adhesive and the printing film, and the compound fastness will be poor. If the drying temperature is too high, the film will be stretched, wrinkled, and tunneling will occur after compounding; at the same time, the solvent will evaporate sharply, and there will be false drying, and the residual solvent will exceed the standard.
The drying tunnel and oven drying temperature should be set from low to high. When the film just enters the drying tunnel, the solvent in the adhesive will evaporate easily. The temperature should be lower to make it slowly evaporate. As the viscosity of the adhesive increases, it is difficult for the solvent to evaporate. The temperature should be increased to completely evaporate the residual solvent and become a film with a certain viscosity. If the temperature of the first oven is set too high, when the coated film enters, the solvent does not have time to volatilize, and the surface is dried. The unvolatile solvent is directly sealed in the film layer, and it cannot be volatilized and cleaned in time after compounding. Residual excess and odor are normal. This requires us to set the gradient drying temperature, and we must pay attention to keeping the drying box clean and tidy.
Generally, we set the first, second, third, and fourth temperature in the drying tunnel. The first three segments are 45 ～ 60 ℃, 60 ～ 70 ℃, 70 ～ 80 ℃. If there is no cooling shaft in the rear section of the oven, then The temperature of the drying tunnel in the fourth stage should be slightly lower than that in the third stage.
6. Compound roll temperature and pressure
Increasing the compounding temperature and pressure helps to improve the secondary flowability of the adhesive, prompting the adhesive to quickly wet the second substrate and enter the pores on the surface of the substrate, so that the glue completely wets the substrate, thereby Improved composite strength. Generally, the compounding temperature is 55 to 80 ° C, and the compounding pressure is 46 kg / cm2.
7.Setting of compound tension
Compound tension is roughly divided into winding tension, unwinding tension, traction tension, and oven tension. The tension is too small, which is prone to tunneling and wrinkling. The tension is large, which is prone to stretch and deformation. After compounding, there are problems such as curling and pattern size misalignment. In the normal production process, the tension should be set according to the films of different structures, and the tension of the materials should be reasonably set according to the respective properties of BOPP, PET, PA, PE, CPP and other materials.
8.Purity of solvent
Most of the solvent products purchased by flexible packaging companies come from distributors. In addition, some companies do not have the relevant equipment to test the purity of solvents, so that the solvent purity is blank. The purity of the solvent is very important for compounding.
Table 2 Water content of different grades of solvents
9.Corona treatment of composite materials
Table III Corona requirements for common films
10. Product maturation time and temperature control
The curing time and temperature control of the composite product should be determined according to the type of film printed, the type of composite material, the amount of adhesive and sizing, the packaging requirements of the product, and performance.
Table 4 Control of curing process for common products of flexible packaging
Second, refined management helps improve product quality
Understand the factors that affect the quality of dry composite, how to control these factors? This requires companies to conduct standardized and refined management of the workshop, adopt SOP standard operations, and implement process data management, which helps us to control quality, Reduce batch quality issues.
Among the flexible packaging enterprises, only a few companies have the concept of "process data control", and even fewer can perform detailed refinement. Many companies still have a workshop-type thinking. Each captain, each machine, and the same product have different operating methods and different quality data. Each has its own ownership, as long as the production is not outrageous. This status quo of management is very unreliable. There is only one such result, the quality is unstable, so quality problems are emerging endlessly, and the dependence on the captain is very large.
Under the current shortage of various captains in flexible packaging enterprises, the establishment of process data not only helps the enterprise to obtain stable quality, but also helps the enterprise to quickly cultivate various talents who can independently operate the equipment. For example, when the product is first compounded, we create the product process data, which is what we call the process card. With the first-hand process data, when the same product is produced again, there are many processes that can apply the same parameters, saving the time and cost of repeated samples by the enterprise.