Adhesives for cooking compound bags of the hottest

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Adhesives for food packaging cooking composite bags

composite film packaging materials are films with different characteristics combined with special adhesives to overcome the inherent defects of a single film. Since its appearance in the 1950s, this material has been widely used in food, medical treatment, pesticide and chemical industry due to its good comprehensive properties. According to the size deviation and appearance quality, strength and frost resistance, it can be divided into: cosmetics and other industries. Cooking bag refers to a bag made of composite film that can be used to package food, medical appliances, etc. and can withstand high-temperature steam (above 100 ℃) heating and sterilization, also known as soft packaging or soft cans that can be cooked. Compared with canned food, steamed bag food uses flexible packaging materials and vacuum packaging with reserved capacity without air, forming a compact and thin packaging form. Its heat transfer is fast, and the sterilization effect can be achieved in a short time. With the improvement of domestic consumption level, the acceleration of the pace of life of urban and rural residents, the continuous increase of travel and tourism, and the concept and mode of food consumption are quietly changing. Many families are trying to liberate from the kitchen, reduce soot pollution, and reduce housework. Soft canned food is adapting to people's daily needs in its light weight, convenience, long preservation period, sanitation, easy storage, easy disassembly and other characteristics, and is increasingly welcomed by people. According to the prediction of experts from China Food Industry Association, convenient, engineered, functional, specialized and internationally standardized food will be the general trend of food industry development in the 21st century. Convenience mainly refers to the production of instant noodles, rice, porridge, bread, and cooked food products such as convenient livestock meat, meat storage, aquatic products, eggs, vegetables, etc. Many of them put semi cooked food into composite film packaging bags, vacuumize, cook and disinfect at 125 ℃ for 45 ~ 70min after sealing, without additives, so that the food can maintain its color, aroma, taste and nutritional value to the greatest extent, which is favored by consumers

it is reported that at present, the output of cooked meat and poultry products in China is only more than 3 million tons, accounting for 6% of the total output of meat, which is far from the level that cooked meat products in developed countries account for more than 50% of the total output. If we can catch up, not only the value of meat products can be greatly increased, but also the flexible packaging used will be greatly developed. Experts predict that bagged meat food in China will grow at a rate of 20% per year in the next few years, which shows that the market of cooking composite bags has a broad prospect

at present, more than 300 composite film production lines have been built throughout the country, many of which are foreign-funded enterprises, and some have even entered the international market. Common composite film packaging materials include PE, PP, pet, PA, PVDC, PVC, PVA, Pt (also known as pyrophenol), aluminum foil or aluminized film, silicon oxide film, etc. The properties of composite film packaging materials are not only related to the selected film, but also to the properties of the composite adhesive

cooking bags can be divided into: (1) 100 ℃ boiling water resistance; (2) Resistant to 121 ℃ cooking and sterilization (sterilization at 121 ℃ for 40min.); (4. The molding temperature of polyphenylene oxide is 280 ℃ (3) 30 ℃. 3) it is resistant to high temperature cooking and sterilization at 135 ℃ (sterilization at 135 ℃ for 20-30min.). The latter is aseptic packaging. Because the packaged food is completely free of bacteria, and there is no output, which continues to grow at an average annual rate of more than 25%, the air exists, which can achieve the purpose of long-term preservation of food under non refrigerated conditions. It can be eaten both cold and hot, which is convenient to use and saves energy during preservation. Many unique properties of polyurethane adhesive make it dominant in composite film adhesives. However, the fatal weakness of universal polyurethane adhesive is its poor temperature resistance and low adhesion to metal. It cannot be used as cooking bag composite adhesive without modification. Performance requirements for the latter:

(1) it has high adhesion to a variety of materials. In order to keep fresh and store for a long time, the cooking bag needs to be composed of multiple layers. The outer layer is made of polyester film with high mechanical strength, gas resistance, moisture resistance, fragrance retention, heat resistance, transparency, cold resistance, water resistance and oil resistance, the middle layer is made of aluminum foil or PVDC with excellent barrier property and high and low temperature resistance, and the inner layer is made of polypropylene film with excellent sanitation, oil resistance, chemical resistance and heat sealing property. Composite adhesives should have good adhesion to them

(2) fast curing speed can shorten the curing time of two-component polyurethane adhesive and improve its initial adhesion at a certain temperature, which will help to improve the productivity of composite film and create good economic benefits. High initial viscosity compound glue still needs to adapt to today's rapid development of high-speed compound machine

(3) high temperature resistance requires resistance to high-temperature cooking and sterilization under heating and pressure during food processing (mentioned earlier) and the instantaneous high temperature (220 ℃) during bag making and sealing

(4) media resistant food contains salt, acid, spicy, spices, alcohol, water, sugar, sulfur, fatty acids, Oils and proteins, which have different characteristics, but they are common, that is, they may penetrate into the adhesive layer through the inner layer of the composite membrane, which plays a role of corrosion damage, leading to delamination, cracking and even failure of the packaging bag. Therefore, the adhesive must have the ability to resist the erosion of the above substances and always maintain sufficient adhesive peel strength

(5) transparency high transparency aims to improve shelf effect

(6) although the harmless composite adhesive is not in direct contact with food, the small molecules in the adhesive may migrate and penetrate into food during high-temperature cooking. Therefore, small molecules must be reduced to a minimum in the production or compounding process

it is difficult to meet the above six requirements at the same time. Because the properties of domestic adhesives can not meet the increasingly demanding requirements of the composite process, the adhesives for cooking bag production basically rely on imports, which not only costs a lot of foreign exchange, but also hinders the rapid development of the food industry. In view of this, liming Research Institute of chemical industry has researched and developed this kind of products and achieved certain results. This is summarized below

the Institute analyzed the reasons for the poor temperature resistance and adhesion to aluminum of the general polyurethane composite adhesive, designed the molecular structure, introduced the corresponding groups, and studied the synthesis process. Satisfactory results have been obtained through small-scale and expanded tests. The main technical performance indicators achieved by the product are listed in Table 1. The finished product obtained from the expanded trial production is tested on the imported compounding machine (Fuji 150 interference compounding machine in Japan) at a speed of 80m/min in the exchange hydraulic system. The composite packaging bag (pet/a1/cpp, pet/bopa/cpp) obtained is filled with 40 ℃ saturated salt water, and the cooking test (127 ℃, 45min) is carried out according to gb10004-88. The packaging bag is complete, without needle holes and delamination. The peel strength of T-type adhesive before cooking is greater than 5n/15mm, and after cooking is greater than 8.6n/15mm. Some cannot be peeled, and the substrate is damaged (see Table 2). The cooking tests were carried out on the packaging bags containing ketchup, chili sauce, 3% acetic acid (1:1:1, mass), salad oil, ketchup, 3% acetic acid (1:1:1, mass) or 4.2% acetic acid, and no delamination was found in the packaging bags. The test results show that the developed adhesive can compound high-temperature cooking food bags, and is resistant to the contents, reaching the performance of imported similar products. Toxicity is the most taboo and the least allowed in food packaging. The machine compounded packaging bag of the sample was tested by our hospital, and no small molecules were separated out. It was sent to Henan health and epidemic prevention station to be tested according to the national standard method, which met the health standard (gb9683-88) (Henan health supervision document Shi Zi 2001-069)

the Institute is wholeheartedly willing to cooperate with the composite packaging industry to carry out application tests, improve product performance, improve production technology, convert scientific research achievements into productivity as soon as possible, and produce domestic national brands

source: packaging magazine Author: ye Qingxuan, Cui Tao

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