Precautions for the Production Process of High-Temperature Cooking Bags

1. The thickness of the base metal is balanced, the corona treatment effect is good, and the heat shrinkage rate is high

Commonly used high-temperature retort bag substrates include PET, NY, AL, RCPP, etc. The corona treatment effect of these substrates directly affects the composite strength of high-temperature retort bags. During high-temperature cooking, the substrate will shrink to varying degrees. The corona treatment of the material did not achieve the expected effect, the composite strength was low, and there was not enough force between the composite bag layers to hinder the shrinkage of the substrate, resulting in serious delamination of the bag layer after high-temperature cooking. In general, the surface tension of PET and NY used for high-temperature retort bags should reach 50mN/m, and RCPP should reach 40~42mN/m. In addition, certain additives in the substrate, such as anti-clogs, anti-slip agents, and antistatic agents, are released to the surface at accelerated temperatures, which can lead to reduced adhesion. Since the high-temperature and high-temperature cooking bag is basically in water during the sterilization process, the matrix shrinkage should be measured at 120°C for 30 minutes when measuring the shrinkage rate of the matrix. The shrinkage rate should be small and stable, especially for BOPA membrane, RCPP membrane, SCPP membrane, longitudinal and transverse moisture-proof shrinkage is recommended to be no more than 1.5%, which can be called cooking grade membrane.

The balanced thickness of each layer of the material should be uniform, the thickness deviation should not exceed 7%, and the physical and mechanical performance indicators should meet the requirements.

With aluminum foil products, in addition to its mechanical property parameters, the surface of aluminum must be dry, A and B and clean must meet the standards, that is, when checking the distilled water, they must be wet, and the number of pores must be as small as possible. Well, it cannot be stored for more than three months before use. In order to improve the fastness of the compound, the BOPA of the intermediate composite should use double-sided corona, and the corona value should not be less than 50 dyne.

2. Compatibility of cooking ink, glue and substrate

The production of composite packaging bags is a process of superimposing various properties of various materials, so it is required that the substrate, ink, glue, etc. have good compatibility and resistance to high temperature, humidity, and heat. The degree of match between them is very important. If the match is not good, the processed product may not look good or delaminate during the cooking process. According to the bonding theory, when the adhesive has the same surface tension and the same polarity as the adhesive being adhesive, the interfacial tension is the least and the bonding strength is the highest. Therefore, the surface condition of inks and glues after curing into a film and the surface condition of the substrate may vary depending on the product from different manufacturers. whether groups on different surfaces can be attracted to form intermolecular forces or chemical reactions to form chemical bonds. It determines whether various surfaces have good adhesion. Therefore, when making steaming bags, the resin types of ink and glue should be fully considered to avoid poor overall performance of steaming bags due to incompatibility of ink, glue and substrate.

The ink or glue used for high-temperature retort bags is generally a two-component polyurethane resin type. The heat resistance of the ink or glue depends primarily on the heat and moisture resistance of the polyurethane resin. The high temperature improves the reaction characteristics of ink adhesives. If the temperature and moisture resistance of inks and glues are insufficient, hydrolysis will occur at high temperatures, and the composite strength will decrease. From the characteristics of polyurethane resin systems, the amino groups and ester groups in the resin have strong polarity and are easily eroded by moisture and hydrolysis under humid and hot conditions. The hydrogen bond between the polyurethane resin and the surface of the substrate is easily broken, reducing the bond strength and even peeling off the bond layer. At present, inks and glues used in high-temperature retort bags are modified with resins or additives to improve the adhesion and heat resistance of inks and glues. Therefore, the quality of the modified resin used in inks and adhesives determines the quality of inks and adhesives. Select RCPP and SCPP for heat sealing layers according to different cooking temperatures.

RCPP or SCPP is usually used for heat sealing materials above 121°C and must be thicker than 60um. Imported products are generally recommended. The inner layer of imported RCPP contains rubber components, which are block copolymer and impact-resistant polypropylene.

3. Control of maturation time and glue loading

Due to the special sterilization method and use conditions of high-temperature retort bags, it is determined that high-temperature retort bags need to have good composite strength to weaken the influence of damp heat conditions on the quality of high-temperature retort bags, and the composite strength is closely related to the amount of glue and maturation time. Generally, the gluing amount of high-temperature retort bags needs to reach more than 4g/m2; Maturation time is another important factor affecting the composite strength, the maturation time of high-temperature retort bags generally reaches more than 72h, sometimes although this time is not reached, the adhesive layer after peeling off the bag is also dry, it seems that the maturation has been complete, but in the actual high-temperature treatment process, due to the residual stress inside it, it will still be far from the curing time of the product in terms of heat resistance, moisture resistance, and in the subsequent bag making process, it is easy to produce the phenomenon of heat separation. Therefore, in the production process of high-temperature and high-temperature retort bags, we should not blindly seek speed, and should focus on the quality of high-temperature retort bags and produce in strict accordance with the process requirements.

4. Gold, silver, ink, etc. should not be made into high-temperature retort bags

Gold and silver inks are very easy to appear penetrating pigment colors, such as Jiu Hong, Radiant Orchid, and Purple inks when they encounter water, and the temperature is high, so it is certain that they will dissolve. The copper powder and aluminum powder used in gold and silver ink are relatively active metals, and they are easy to react with moisture, grease, oxygen, etc. at high temperatures. After reaction oxidation, the appearance appears as black, greenish or even faded. Therefore, gold, silver ink and ink that are easy to permeate cannot be made into high-temperature retort bag products.