Discussion on high temperature resistant cooking b

2022-08-01
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Talking about high temperature resistant cooking bags and their applications (III)

III. materials for manufacturing high temperature resistant cooking bags

the structure of high temperature resistant cooking bags has two, three, four or more layers, of which the second layer is transparent plastic/plastic, such as pet/cpp or opa/cpp. The three layers have transparent plastic/plastic models, such as pet/opa/cpp and opaque models containing aluminum foil, such as pet/al/cpp and opa/al/cpp. The four layers are opaque pet/al/opa/cpp containing aluminum foil. This structure is a puncture resistant, reinforced and high-capacity packaging bag. It is reasonable to place the OPA between Al and CPP. For more layers, the inner layer does not use pure CPP film, but uses multi-layer coextrusion film, such as pa/evoh/pp, pa/pva/PP coextrusion film plus pet or aluminum foil to form a composite with more layers, but the number is small. From the perspective of function, The four layer pet/al/opa/cpp bag with aluminum foil can fully meet the requirements of all cooked foods

for these materials used in cooking bags, it is necessary to introduce their performance and consider the serious redundant role of the real estate industry. In order to ensure the quality of cooking bags, specific requirements should also be put forward

1. Polyester film PET, also known as biaxial (or biaxial) tensile polyester film

pet (or BOPET) film is used as the outer material of cooking bags, with a thickness of 12 μ m。 It has the characteristics of high melting point, high heat resistance, high mechanical strength, high rigidity, high transparency, high fragrance resistance and high gas resistance. Due to the polarity relationship in its molecular structure, the surface tension is high. After a little corona treatment, the surface tension can reach 52mn/m (i.e. 52dyn/cm), which is very beneficial to printing and bonding. When pet is used as the outer layer material to compound with other heat sealable materials (CPP, PE, etc.) to heat seal the bag, even if the temperature is as high as 220 ℃, it will not melt and deform, and will not stick to the knife, which is conducive to the bag making of the composite film. At present, there are many PET film production suppliers in China. Most PET films can meet the high-temperature cooking of 120 ~ 128 ℃, or even 135 ℃. However, some PET films have the problem of excessive thermal shrinkage and deformation after high-temperature cooking. Therefore, when purchasing pet for high-temperature cooking, we must select products with small heat shrinkage. The Dutch legislation affirms that waste treatment should first avoid the generation of waste, so that it can be used safely

sometimes, opa/pet/cpp (PE) structure composite bags are also produced. At this time, both sides of pet need to be composite. Therefore, the double-sided corona treated bags should be selected. The surface tension of both sides should be more than 50mn/m, otherwise one side will be firm and the other side will not be firm enough

2. Nylon film OPA, also known as biaxial (or biaxial) tensile nylon film

like PET film, is used as the outer material of cooking bags in most cases, with a thickness of 15 μ, When it is necessary to manufacture heavy-duty packaging bags with good puncture resistance and large capacity, they are also used in the interlayer similar to the inner CPP, such as pet/al/opa/cpp. Up to now, the widely used OPA is made of nylon 6 obtained from the ring opening polymerization of caprolactam, while nylon 66 obtained from the condensation polymerization of adipic acid and hexanediamine is very few, and nylon 12 is even less

nylon film also has high melting point, high heat resistance, high mechanical strength, high transparency and excellent puncture resistance. Its rigidity and fragrance resistance are worse than pet, and it is relatively soft. The texture of the hand is excellent. Due to the amide group in the molecular structure, it maintains extremely high polarity and surface tension. With a little corona treatment, it can reach 52mn/m (52 dyn/cm), which is very conducive to printing and compounding. However, it is precisely because there are a large number of amide based polar groups in the molecular structure that the surface is very easy to absorb water molecules with the same polarity. In serious cases, a layer of water retention film is formed. When printing, especially when compounding with two-component polyurethane adhesive, it often causes quality problems such as poor printing, weak compounding, small bubbles or white spots. Therefore, when purchasing nylon film, Pay attention to whether the moisture-proof packaging of the product (sealed with high barrier composite film, and then put in desiccant to absorb moisture) is intact. After you buy it, you should also store it in a ventilated and dry place, not in a wet place

if both sides of OPA need to be combined, the film with surface tension not less than 50mn/m after corona treatment on both sides should be selected to ensure high composite fastness on both sides

3. Aluminum foil al

aluminum foil is a metal material. The thickness of 9 μ M soft aluminum foil has complete moisture resistance, gas resistance and light resistance. Without mechanical damage and pinholes, it is completely impermeable to moisture, air (O2, N2, CO2, etc.) and light, and has extremely high heat resistance and oil resistance. Therefore, the composite bag made of aluminum foil has excellent properties such as full sealing (like tinplate cans), high fragrance preservation, high oil resistance and high temperature resistance. It is the highest grade composite soft packaging material

however, as aluminum foil used in cooking bags, three points should be paid attention to. First, the surface should be clean, free of oil and dust, and have a high surface tension. When using a simple method, that is, using distilled water for inspection, it should be completely soaked, and the surface tension should be more than 72mn/m. If the oil stain is serious, the composite fastness will be low, especially after high-temperature cooking, delamination and stripping will occur. Second, the number of pinholes should be small. Originally, aluminum foil should be the best barrier material, but if there are pinholes, it will be greatly discounted. Gas, wet steam and light will quickly and directly penetrate, and the contents will soon deteriorate. In general, the thicker the aluminum foil, the less the number of pinholes, for example, 7 μ M thick is 200 holes per square meter, 9 μ M thick is 100 holes per square meter, 11 μ M thick is less than 30 holes per square meter, and the hole diameter is not more than 20 μ m。 Third, the texture should be soft, not easy to break when folded, and have good toughness. The purchased aluminum foil should be stored in a dry state, and should not be stored for too long. It should be used as fresh as possible to prevent the aluminum foil from moisture absorption, oxidation and deterioration

4. Cast polypropylene cpp

used in cooking bags as the inner layer material for contacting food contents and heat sealing bags, most of which are cast polypropylene films without stretching, with a thickness of 70 μ m~80 μ m. Only a few use high density polyethylene (HDPE) to make 121 ℃ cooking bags

cpp has high chemical stability, can resist the corrosion of many media (such as acid, alkali, spicy, salty, oil, wine, aromatic spices, etc.), is non-toxic and tasteless, and has high safety and hygiene. It can also be made into bags by heat sealing. It has better heat resistance than HDPE, and the maximum service temperature can reach 145 ℃

as a CPP with high temperature cooking resistance, it should not be made of homopolypropylene, but should be made of CO polypropylene or polypropylene pellets modified by blending. This is required by the process conditions of high-temperature cooking of cooking bags. Because the CPP made of homopolypropylene is brittle after high-temperature cooking, it is difficult to pass the drop test, and it is easy to crack at the seal, resulting in content leakage. The so-called co polypropylene is a copolymer containing about 5% ethylene or long chain alkene monomers, such as butene, octene and about 95% propylene. The so-called polypropylene modified by blending is made by blending ethylene propylene resin, polyisobutylene or rubber with homopolypropylene in a certain proportion. The CPP film made of CO polypropylene or blend modified polypropylene has a soft feel, poor transparency than homopolypropylene, and large extensibility. When it is stretched under normal conditions or after high-temperature cooking, it shows strong toughness, metallic luster, high sealing strength, and good pressure resistance and drop resistance. In the early 1980s, Shanghai used j-230 polypropylene from Beijing Yanshan Petrochemical Company to produce CPP with 121 ℃ high resistance and warm cooking when changing the indenter or anvil. In the early 1990s, Changzhou plastic factory introduced CPP film specially for cooking bags, and its comprehensive performance was better than that of CPP made from j-230. At that time, CPP films were available in many places, but in addition to the limitation that the maximum service temperature was only 121 ℃, there were still shortcomings in the comprehensive performance. In recent years, Shanghai wisteria, Wuxi Huanya, Shanghai Meifeng, Hubei Jiangyu Zhongshan Zhongsheng, etc. all have such products. The CPP provided by fosu group has good comprehensive performance in addition to being able to withstand 130 ℃ or even 135 ℃ high temperature cooking. At present, there are many manufacturers that can provide this kind of CPP film all over the country, and the selection range is wider. When we select CPP, we should also pay attention to its surface tension. If it can be 40 ~ 42mn/m during compounding, it can be used with confidence. If it can be 39mn/m, it can also be used carefully. However, if it is only 38mn/m or even lower, it cannot be used! This is very important

in recent years, the demand for high temperature cooking at 135 ℃ has become more and more popular, but there are not many CPPs that can really withstand this high temperature. The imported ones include トレ -3701 from Japan's tosilu or xrc-18 from Japan's Mitsui products. Domestic CPPs are still rare. After cooking at 135 ℃, many domestic CPPs will be seriously brittle, have poor oil resistance, and even become mushy. Therefore, it is very important to select suitable CPP if you want to make a cooking bag that can withstand 135 ℃. (to be continued)

Shanghai Shenhua Technology Co., Ltd. Zhang lieyin

information source: Guangdong packaging (the sixth issue in 2005)

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