Precautions for production process of high-temperature cooking bag
1. The thickness of the base metal is balanced, the corona treatment effect is good, and the heat shrinkage rate is high
The commonly used high-temperature cooking bag base materials include PET, NY, Al, RCPP, etc. The corona treatment effect of these substrates directly affects the composite strength of high-temperature cooking bags; In the process of high temperature cooking, the substrate will have different degrees of shrinkage. 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 prevent 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 cooking bags should reach 50 N/m, and the RCPP should reach 40~42 N/m. In addition, some additives in the base material, such as anti-blocking agent, anti-skid agent and antistatic agent, accelerate the release to the surface at high temperature, which may lead to the reduction of adhesion. Since the high-temperature and high-temperature cooking bag is basically in water during sterilization, the substrate shrinkage should be measured at 120 ℃ for 30min when measuring the substrate shrinkage. The shrinkage rate should be small and stable, especially for BOPA film, RCPP film and SCPP film. It is recommended that the longitudinal and transverse moisture-proof shrinkage rate should not exceed 1.5% before it can be called cooking grade film.
The balance thickness of each layer of material shall be uniform, the thickness deviation shall not exceed 7%, and the physical and mechanical performance index shall meet the requirements.
When using aluminum foil products, in addition to its mechanical performance parameters, the surface of aluminum must be dry, A and B and cleaning must meet the standards, that is, when checking distilled water, they must be wet, and the number of pores must be as small as possible. Well, the storage time before use cannot exceed three months. In order to improve the composite fastness, the intermediate composite BOPA should adopt double-sided corona, and the corona value should not be less than 50 dynes.
2. Compatibility of cooking ink, glue and substrate
The production of composite packaging bags is a process of superposing various properties of various materials, so the substrate, ink, glue, etc. are required to have good compatibility and high temperature, humidity and heat resistance. The matching degree between them is very important. If the matching degree is not good, the processed products may have poor appearance or delamination during the cooking process. According to the bonding theory, when the adhesive and the adhesive have the same surface tension and the same polarity, the interfacial tension is the lowest and the bonding strength is the highest. Therefore, the surface condition of the ink and glue after curing and film forming and the surface condition of the substrate may vary with the products of 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, the resin type of ink and glue should be fully considered when making steam bags to avoid the poor overall performance of steam bags due to the incompatibility of ink, glue and substrate.
The ink or glue used for high-temperature cooking bags is generally two-component polyurethane resin type. The heat resistance of ink or glue mainly depends on the heat resistance and moisture resistance of polyurethane resin. High temperature improves the reaction characteristics of ink adhesive. If the temperature and humidity resistance of ink and glue are insufficient, hydrolysis will occur at high temperature, and the composite strength will be reduced. From the characteristics of the polyurethane resin system, the amino and ester groups in the resin have extremely strong polarity and are vulnerable to moisture erosion and hydrolysis under humid and hot conditions. The hydrogen bond between the polyurethane resin and the surface of the base material is easy to be damaged, which reduces the bonding strength and even the bonding layer falls off. At present, the ink and glue used in high-temperature cooking bags are modified with resins or additives to improve the adhesion and heat resistance of the ink and glue. Therefore, the quality of the modified resin used in the ink and adhesive determines the quality of the ink and adhesive. RCPP and SCPP for heat sealing layer are selected according to different cooking temperatures.
RCPP or SCPP is usually used for heat sealing materials above 121 ℃, and the thickness must be greater than 60um. It is generally recommended to use imported products. The inner layer of imported RCPP contains rubber components, which are block copolymer and impact resistant polypropylene.
3. Control of curing time and gluing amount
Due to the special sterilization method and use conditions of the high-temperature cooking bag, it is decided that the high-temperature cooking bag needs good composite strength to reduce the impact of the humid and hot conditions on the quality of the high-temperature cooking bag, and the composite strength is closely related to the amount of glue and the curing time. Generally, the gluing amount of high-temperature cooking bags should reach more than 4g/m2; Curing time is another important factor that affects the composite strength. The curing time of high-temperature cooking bags generally reaches more than 72h. Sometimes, although this time can not be reached, the adhesive layer is also dried after the bag is peeled off, and it seems that the curing has been completed. However, in the actual high-temperature treatment process, due to the residual stress inside, it will still be far from the heat and moisture resistance of products with sufficient curing time, And in the subsequent process of bag making, it is easy to produce the phenomenon of heated delamination. Therefore, in the production process of high-temperature and high-temperature cooking bags, we should not blindly seek speed, but focus on the quality of high-temperature cooking bags, and strictly follow the process requirements.
4. Gold, silver and ink are not suitable for high-temperature cooking bags
Gold and silver inks are very easy to appear penetrating pigment colors, such as nine red, radiant blue, and purple inks. In addition to high temperature, dissolution is certain. The copper powder and aluminum powder used in gold and silver ink are highly reactive metals, which are easy to react with water, grease, oxygen, etc. under high temperature. After reactive oxidation, the appearance will be black, green or even faded. Therefore, gold, silver ink and ink prone to penetration cannot be used as high-temperature cooking bag products.