The reasons for the wrinkling of the high temperature cooking bag are as follows:
1. The form of wrinkling after sterilization treatment of high temperature cooking bags
Regardless of any composite bag, the flatness is good, the color is real, and the opening is excellent. The high temperature cooking bag is no exception. There are three kinds of wrinkling phenomenon: a. printing substrate has longitudinal, lateral or irregular wrinkles; b. the substrate and the composite substrate together with surface cracking, very poor flatness; c. printing substrate shrinkage, shrinkage Separated from the composite substrate, with air in the middle, in the form of strips, often with poor peel strength.
Second, the common substrate and structure classification of high temperature cooking bags
When most companies on the market print high-temperature retort pouches, most of the printing substrates use PET and NY as printing materials, the middle layer mostly uses aluminum foil, and the inner layer heat-sealing layer uses cast CPP or boil-resistant PE film. Wait.
Among them, PET is well-formed, and it has excellent frost resistance and heat resistance; NY has poor moisture resistance and easily absorbs moisture. Aluminum foil is an important substrate in the soft plastic packaging industry. It is calendered at high temperature and has a silver-white luster. The aluminum foil used on the soft plastic packaging is 9-15Î¼m. It is not suitable to use too much tension for unwinding and winding. The tension is easy to tear. The aluminum foil should not pass too many guide rollers, and it is easy to crack due to folding, which affects good barrier. The aluminum foil has good thermal conductivity and electrical conductivity, so that it has a wide range of uses in flexible packaging. In the high temperature cooking bag, the use of aluminum foil as the intermediate layer material can improve the heat transfer speed and make the temperature of the retort pouch food uniform.
Aluminum foil has excellent barrier properties and should be free of oil on the surface. It is best to pre-treat before printing or compounding to make the surface tension meet the required requirements, which can significantly improve the printing fastness and the composite fastness of aluminum foil. Extrusion casting CPP reinforced membrane is often used as inner layer, casting CPP has good barrier property, high temperature resistance, boiling resistance, good effect on alkali acid resistance, small heat shrinkage, excellent heat sealing strength, and can reach 121 Â°C. 30min sterilization treatment, when 30 Â° at 100 Â° C, LDPE, LLDPE, EVA, mPE and other heat sealing materials can be used.
Third, the factors of surface wrinkling after sterilization of high temperature cooking bags
It has been found that the wrinkling of the surface of the retort pouch should be carefully observed to make an accurate analysis if the printed substrate is longitudinal, lateral or irregular wrinkles. Mainly from three points of analysis: a. The temperature of the drying tunnel is too high during printing, the constant tension between winding and unwinding is inconsistent, and the unwinding tension is too large to cause deformation of the PET film. b. The paper roll of the winding roll is not smooth. Due to the continuous volume increase of the finished product, the longitudinal or transverse wrinkles will occur at the bottom of the winding, which makes the originally flat printed substrate uneven. This wrinkling phenomenon is compounded. It is not easy to eliminate during the process. c. The printing traction roller has foreign matter or too dirty, and the printing substrate laterally slides when passing through the foreign matter. When the sliding substrate passes through the embossing rubber roller, wrinkles are generated, and the wrinkles have regularity. No.
Solution: a. Adjust the drying temperature according to the temperature and humidity of the workshop, the machine speed, and the actual printing effect pattern. It is 15Î¼m for most high-temperature retort pouch printing and 12Î¼m for PET, so it is recommended that the drying temperature be 40-60Â°C. The drying temperature is too high, and the film can be deformed, elongated, and softened without being subjected to high temperature. Adjusting the constant tension of winding and unwinding, now there is a high-speed gravure printing machine that has produced an automatic adjustment tension controller. When the limit or set value is exceeded, the automatic alarm is automatically adjusted, which is convenient. b. Exchange the paper tube with a smooth center, and pay attention to the flatness when winding. At the beginning, the winding tension should be small. When the thickness reaches a certain thickness, slowly increase the tension value, so that the winding material does not wrinkle. c. Wipe off the traction roller with foreign matter.
When the surface of the substrate and the composite substrate are wrinkled, the flatness is extremely poor, and the factors are: a. the printing substrate itself is wrinkled or wrinkled by printing cannot be eliminated; b. when the pressure of the hot steel roller is inconsistent or The thickness deviation of PE and CPP of composite substrate is large. When the deviation is 10Î¼m, the wrinkle phenomenon is easy to occur. c. When the composite product is wound, the bottom tension is too small, the tension on the top is too large, and one after the extrusion a phenomenon.
Solution: a. Strictly control the printing quality; b. Adjust the pressure of the steel roller to the equilibrium state, the composite substrate should not be biased as much as possible. When the composite intermediate is aluminum foil, wear the traction roller as little as possible to prevent the phenomenon of fracture; c. Adjust the winding Tension, try to be consistent.
When the substrate has wrinkles and there is a bubble strip in the middle, most of the tension is not controlled when the dry compound is combined, the tension is too large, and the tension is too tight. It is most likely to occur in NY/PE or NY/aluminum foil/CPP, especially nylon substrates. If the unwinding tension is too large, heat shrinkage will occur during the drying process and the deformation will occur. This phenomenon occurs after the finished product is cooled. The influence of the glue liquid must be 4.5g/m2 when the high temperature cooking bag is applied. The wire roller is generally Select 80Î¼m deep, if uneven coating occurs, or the quality of the glue itself is poor, it can easily cause the glue to separate from the substrate after boiling, which greatly reduces the fastness.
Solution: a. Adjust the unwinding tension, and dry it as much as possible under the condition of solvent evaporation, so as not to deform and cool and shrink; b. Increase the working concentration, choose the glue with large dry solid content, generally when the solid content is 75 %, the working concentration is 30% good; c. Select the high temperature resistant professional adhesive, it is forbidden to apply the general glue.
Fourth, the impact of the composite process
1. When printing and compounding, the ambient air must be kept dry, especially the lower the relative humidity, the higher the maximum, the maximum should not exceed 85%, otherwise it will affect the printing composite fastness.
2. Ink and adhesive: When cooking film printing, the ink thinner should be added with or without alcohol solvent as much as possible. The quality should be strictly controlled during printing. The ratio of adhesive to curing agent should be correct. It should not be replaced at will. It must be evenly coated. Excellent performance, dry basis amount of 4-5g/m2.
3, drying temperature, composite temperature and pressure: too low drying temperature will make the solvent volatilization is insufficient, easy to produce odor, and will also directly affect the composite fastness. However, if the drying temperature is too high, the surface of the adhesive coating will be conjunctiva, which will affect the evaporation of the solvent in the coating.
Generally, the drying temperature is in the range of 60 Â° C - 70 Â° C - 75 Â° C. For dry compounding, the composite roll must be heated. The purpose of heating is to soften the adhesive, increase the viscosity, and evenly distribute the adhesive on the film while maintaining The hot melt reaction state of the adhesive facilitates adhesion, and the general compounding temperature is from 60 Â° C to 70 Â° C.
There are two effects of compound pressure on the product: one is to affect the composite fastness, and the other is to affect the transparency of the composite film. The optimum composite pressure is 2.5-4kg/cm2.
4. Ripening. The purpose of curing is to make the reaction sufficient and obtain the best composite strength. Generally, the curing temperature of the cooking film bag is controlled in the range of 40 Â° C to 50 Â° C, and the ripening time is about 48 hours.
In summary, in the entire production process of the retort pouch, the choice of film, ink, adhesive, and dilution solvent plays a decisive role in the quality of the retort pouch. The retort pouch manufacturer cannot be ignored in the production process. .
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