In the production process of high-temperature cooking bag, many faults often occur. Due to the relatively high cost, it brings great economic losses to printing enterprises. The common faults include delamination of high-temperature sterilization white oil ink, delamination between printing substrate and composite substrate, surface wrinkling after high-temperature sterilization, etc. In this paper, combined with the practice, the surface wrinkling failure phenomenon after high temperature steam boiling is analyzed.
1、 Wrinkle form of high temperature cooking bag after sterilization
No matter any composite bag is required to have good flatness, true color and excellent opening, and high temperature cooking bag is no exception. There are three kinds of wrinkling phenomenon: a. the printing substrate has longitudinal, horizontal or irregular wrinkles; B. the surface of the base material and the composite substrate is wrinkled and cracked, and the flatness is very poor; C. the printing substrate shrinks, and the shrinkage part is separated from the composite substrate, and there is air in the middle, which is in the form of strip state, and the peeling strength is very poor.
2、 Classification of common substrates and structures of high temperature cooking bags
At present, most enterprises in the market use pet and NY as printing materials when printing high-temperature cooking bags. Most of the intermediate layer is made of aluminum foil, while the inner layer is made of cast CPP or boiling resistant PE film. Among them, pet has good freeze resistance and heat resistance, while NY has poor moisture resistance and is easy to absorb moisture. Aluminum foil is an important base material in flexible plastic packaging industry. It is rolled under high temperature and has silvery white luster. The aluminum foil used in soft plastic packaging is 9-15 μ m. It is not suitable to use too much tension for unwinding and winding up, which is easy to tear. Aluminum foil is not suitable to pass through too many guide rollers, which is easy to crack due to folding, which affects good barrier property. Aluminum foil has good thermal conductivity and conductivity, which makes it widely used in soft packaging. In high temperature cooking bag, aluminum foil is used as intermediate layer material It can improve the heat transfer speed and make the temperature of the food in the cooking bag even. Aluminum foil has excellent barrier property and there should be no oil stain on the surface. It is better to pretreat before printing or laminating to make the surface tension meet the required requirements, which can significantly improve the printing fastness and composite fastness of aluminum foil. However, the casting CPP reinforced film is often used as the inner layer. The casting CPP has good barrier property, high temperature resistance and boiling resistance, and has good alkali and acid resistance. The heat recovery is reduced and the heat sealing strength is excellent. It can be sterilized at 121 ℃ for 30min. When it is 30min at 100 ℃, heat sealing materials such as LDPE, LLDPE, EVA and MPE can be used.
3、 Factors of surface wrinkling of high temperature cooking bag after sterilization

If the surface wrinkling phenomenon is found, it should be carefully observed and accurately analyzed. If the printing substrate has longitudinal, transverse or irregular wrinkles. There are three points to consider and analyze: a. the drying channel temperature is too high during printing, the constant tension between winding and unwinding is not consistent, and the unwinding tension is too large, resulting in the deformation of PET film. b. The paper core of the rewinding roll is not smooth. As the volume of the winding product increases, the bottom of the winding will wrinkle vertically or horizontally, which will make the original flat printing substrate uneven. This kind of wrinkling phenomenon is not easy to eliminate in the composite process. c. There are foreign matters or too dirty in the printing traction roller. When the printing substrate passes through the foreign matter, it will slide horizontally. When the sliding substrate passes through the embossing rubber roller, it will produce wrinkles. This kind of wrinkle is regular, and there is no one in one section. The solution is: A. adjust the drying temperature according to the workshop temperature and humidity, machine speed, actual printing effect and pattern depth. It is 15 μ m for nylon and 12 μ m for pet in most high temperature cooking bags. Therefore, it is recommended that the drying temperature should be 40-60 ℃. If the drying temperature is too high, the film will not withstand high temperature and deformation, elongation and softening will occur. To adjust the constant tension of winding and unwinding, high-speed gravure printing machines have produced automatic tension controller. When the limit or set value is exceeded, the automatic alarm will be given and the automatic adjustment is very convenient. b. Exchange the paper tube with a smooth center, and pay attention to the flatness when winding. The winding tension should be small at the beginning, and then slowly increase the tension value when reaching a certain thickness, so that the winding material will not wrinkle. c. Wipe the traction roller with foreign matters clean.

When the surface of the base material and the composite substrate are wrinkled together, the flatness is very poor. The factors are: a. the wrinkling of the printing substrate itself or the wrinkling during printing cannot be eliminated; B. when the pressure at both ends of the hot steel roller is inconsistent or the thickness deviation of the composite substrate PE and CPP is large, the wrinkle phenomenon is very easy to appear when the deviation is 10 μ m; C. the bottom tension is too small and the upper tension is too large when the composite product is rolled up A phenomenon that occurs after pressing. Solutions: A. strictly control the printing quality; B. adjust the steel roller pressure to a balanced state, and the composite substrate should not deviate as far as possible. When the aluminum foil is in the middle of the composite, the traction roller should be less worn to prevent fracture; C. the winding tension should be adjusted to be consistent as far as possible.
When there are wrinkles and bubbles in the middle of the substrate, the tension is not well controlled during dry lamination, and the tension is too large and too tight. In NY / PE or NY / aluminum foil / CPP, it is most likely to occur, especially in nylon substrate. If the unwinding tension is too high, it will shrink and deform in the drying channel, which will occur after the finished product is cooled. Under the influence of the glue, the dry solid content of the high-temperature cooking bag must reach 4.5g/m2, and the wire roller should generally be 80 μ m deep. If uneven coating occurs, or the quality of the glue itself is poor, it is easy to produce the glue liquid which is separated from the base material after boiling Reduce its fastness. The solutions are as follows: A. adjust the unwinding tension, dry at low temperature as far as possible under the condition of solvent volatilization, so as to avoid deformation and cooling shrinkage; B. increase the operation concentration and select the glue with large dry solid content, which is generally good when the solid content is 75% and the operation concentration is 30%; C. select the professional adhesive with high temperature resistance, and prohibit the general glue liquid coating.
4、 Influence of composite process
1. When printing compound, it is necessary to keep the ambient air dry, especially the lower the relative humidity, the better, and the maximum should not exceed 85%. Otherwise, the composite fastness of printing will be affected.
2. Ink and adhesive: when cooking film printing, the ink thinner shall be added with or without alcohol solvent as far as possible. The printing quality shall be strictly controlled. The ratio of adhesive and curing agent shall be correct and can not be changed at will. The coating must be uniform with excellent performance, and the dry base weight shall be 4-5g / m2.
3. Drying temperature, compound temperature and pressure: too low drying temperature will make the solvent volatilization insufficient, easy to produce odor, and will directly affect the composite fastness. But if the drying temperature is too high, it will make the adhesive coating epidermal conjunctiva, affect the solvent volatilization in the coating, and also have a certain impact on the film. Generally, the drying temperature is within the gradient of 60 ℃ - 70 ℃ - 75 ℃. For dry lamination, the composite roller must be heated. The purpose of heating is to soften the adhesive, increase the viscosity, make the adhesive evenly distributed on the film, and keep the hot-solution reaction state of the adhesive for easy bonding. The general composite temperature is 60 ℃ - 70 ℃. Composite pressure has two effects on the product: one is the composite fastness, the other is the transparency of the composite film. The best composite pressure is 2.5-4 kg / cm2.
4. Ripening. The aim of curing is to make the reaction full and obtain the best composite strength. Generally, the curing temperature of cooking film bag is controlled in the range of 40 ℃ - 50 ℃, and the curing time is about 48 hours.
To sum up, in the whole production process of cooking bag, the selection of film, ink, adhesive and diluting solvent plays a decisive role in the quality of cooking bag, which can not be ignored in production.
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.