General situation of development
In 18 10, French n. apel uses glass containers. Later, in 18 10, Durand obtained a patent for using metal containers and glass containers in Britain. Early metal containers were made of thin iron plates and welded by soldering. These containers are large and bulky, difficult to seal, and have many shortcomings and low production efficiency. It was not until 1823 that the sealed can with small holes in the lid was further invented. After loading food, cover a small round cover on the small hole of the cover, heat it in boiling water bath, immediately weld and seal the round cover with solder, and then sterilize it. 1903 An empty metal can appeared. It takes the overlapping seam welding of the tank body and the double pressure welding of the tank body and the tank cover as the main sealing structure, and the rubber ring lining the tank cover is the key to success. The hygienic quality of food in canned food is improved because of the reduction of solder contact area, so it is called hygienic canned food. By the middle of the 20th century, the manufacturing technology of canned containers was further improved, and welding cans produced by resistance welding appeared. In addition to tinplate, metal containers also include aluminum or aluminum-magnesium-aluminum-manganese alloy. Because of its good ductility, it is often used to produce deep-drawing cans and easy-to-open cans. The glass container has developed from the initial heavy spiral type to the rotary type, and it is light and easy to open.
Type of container
So far, there are many kinds of canned containers, such as tinplate cans, aluminum cans, glass cans and plastic composite film bags. In addition, containers such as paper cans and all-plastic cans are still available, but they are not used much, and are limited to some specialty products and dry food.
tinplate can
It is the most widely used and the largest number of canned containers in the canned industry. It is tinned steel sheet (that is, low-carbon steel sheet with pure tin on both sides, commonly known as tinplate). Most of them are made into double-curling cans, and some are made into flat cupping devices (also called bottom-flushing cans or two-piece cans), which are not deep. According to the different shapes of tanks, they can be divided into round tanks (including vertical round tanks and flat round tanks), square tanks, trapezoidal tanks, oval tanks and horseshoe tanks. It is customary to call several empty cans other than round cans special-shaped cans. According to whether the inner wall of the tank is coated with a protective layer, it can be divided into paint cans (including acid-resistant paint cans and sulfur-resistant paint cans) and ordinary iron cans. Tinplate cans used for canned fruits are mostly flat iron vertical round cans, and some fruits with more anthocyanins or higher acid content use acid-resistant paint cans.
Glass jar
Because glass has the advantages of good chemical stability, no chemical reaction with food, cleanliness and convenience for consumers to observe the state and quality of food in canned food, canned glass still occupies a large proportion. The United States is the country that produces the most glass jars, followed by Germany, France, Japan and Britain. However, the glass jar has some disadvantages, such as hard and brittle texture, small thermal conductivity and expansion coefficient, easy to break, heavy weight and inconvenient transportation. The glass jar is made of soda-lime glass. It is made of quartz sand, soda ash and limestone in a certain proportion, melted at a high temperature of 1500℃, and then slowly cooled, molded and cast. If different molds are used in cooling molding, glass jars with different shapes and volumes can be made. In order to improve its thermal stability and meet the needs of tank storage technology, it is generally necessary to conduct another heating and annealing treatment. Good quality glass jars should be transparent, colorless or slightly cyan, with uniform thickness and a round and flat mouth; Flat bottom; The tank body shall be straight and smooth, and there shall be no serious defects such as bubbles, cracks, stone chips and streaks. According to the sealing form and the cover used, the commonly used glass jars are mainly as follows: ① Roll-sealed glass jars. Used for the storage of canned fruits, there are Soviet OKO-83- 1 models. It consists of a tank body, a tinplate tank cover and a rubber band. Push it with the roller of the glass jar sealing machine, and then press the lid edge and rubber band tightly on the edge of the glass jar mouth. This kind of glass jar is characterized by good sealing performance and can withstand pressure sterilization, but it is difficult to open. The capacity quota is 0.5 liters. ② Rotary glass jar. The lid of the jar is made of tinplate, and there is a cover claw inside the lid. The neck of the glass jar is threaded to coincide with the cover claw, and a rubber ring or plastisol is padded between the cover and the jar mouth. When sealing, the cover claw is aligned with the thread line and can be sealed by clockwise rotation. According to the number of cover claws and thread lines on the can cover in a few days, there are four-spin cans, six-spin cans and three-spin cans. This can is more convenient to open and rotate. ③ Grab the glass jar. The tank cover is made of tinplate or aluminum plate, and rubber or plastic is poured inside. There is no thread in the neck of the water tank. When sealing, press the can cover downward, and as long as the can cover is bent inward several times, the can mouth will be hooked to realize sealing. ④ Side seal or jacketed glass jar. The container can be cup-shaped or straight-mouthed, and the inner side of the hook of the tank cover is bent and embedded with a rubber gasket, so that when the tank cover is closed and buckled on the outer flange of the tank mouth, the sealing performance is guaranteed. It is more convenient to drive. The lid is made of tinplate. Suitable for holding foods with high sugar content.
aluminium pot
It is a metal container made of aluminum plate or aluminum alloy plate, with metallic luster, light weight and corrosion resistance. Because aluminum has good ductility, it is mostly made into cupping, especially small deep-bottomed cupping and easy-to-open cupping. In order to improve the corrosion resistance of aluminum cans, ethylene epoxy and other coatings are often coated on the inner wall of aluminum cans. The trademark is printed directly on the outer wall of the jar. Suitable for fruit and vegetable juice drinks, aquatic products and canned fruits and vegetables.
Composite plastic film bag
Also known as swallowing bag or soft can, it is called autoclaved composite plastic film bag. Bagged food, used to replace metal cans or glass cans, can be preserved for a long time after sterilization, which is called soft cans. This kind of film bag was first developed by the Tix Development Center of the US Army in the early 1960s, put into production in the 1970s, and spread to Japan and Europe. In the late 1980s, Japan produced the most soft cans, followed by the United States. Composite plastic film is usually made of three layers of substrates bonded together. The outer layer is about 12 micron polyester, which plays a role in strengthening and resisting high temperature. The middle layer is about 9 microns of aluminum foil, which has metallic luster and can increase the appearance after printing. Toyo Canning Company of Japan later switched to composite can film (RP-F) to produce soft cans, and the sterilization temperature can reach about 120℃. In order to facilitate short-term sterilization at high temperature, composite membrane materials Hi-RP-F and URP-F with high temperature resistance and ultra-high temperature sterilization were developed, in which Hi-RP-F can resist high temperature of about 135℃ and URP-F can resist high temperature of about 150℃. Its inner substrate is made of special polypropylene with high temperature resistance. Composite plastic film bags have the advantages of light weight, small volume, convenient opening, high temperature resistance and storage resistance, which can maintain the proper quality of food and meet the needs of tourism, navigation and mountaineering, so they have developed rapidly. China was successfully trial-produced in the late 1970s, and now it has been put into production, replacing some metal and glass cans. It is expected that the use of composite plastic film bags will have greater development at home and abroad in the future.