Application of paper containers in beverage packaging
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In recent years, paper containers have been used for the packaging of fruits, vegetables, dairy products and refreshing beverages. Compared with other containers, paper containers have the advantages of low cost, economical, light weight, favorable logistics, no metal dissolution and can smell. However, paper containers have lower pressure resistance and sealing precision than glass bottles and metal cans, and cannot be heat-sterilized.
First, the type of paper container
According to the material structure and shape of the paper container, the paper container can be divided into a composite carton, a paper cup, a combination can, and the like.
Composite carton: The composite carton for fruit and vegetable juices and refreshing beverages is a polyethylene composite paper container. The TetraPak composite paper structure consists of 7 layers. From the inside to the outside are polyethylene (two layers), aluminum foil, polyethylene, cardboard, printing ink, polyethylene (or wax layer).
Polyethylene: Food containers should be made of low-density polyethylene (LDPE) with good processing properties, such as no additives, adhesion and sealing properties, with a relative density of 0.917-0.925, and attention should be paid to uniformity and film adhesion during processing. , sealing and odor problems. The thickness of the composite polyethylene is 40 to 60 μm on the inner surface and 10 to 30 μm on the outer surface.
Aluminum foil: One of the reasons why aluminum foil is used for packaging is that it has the property of reflecting heat rays, aluminum foil can prevent the adverse effects of ultraviolet rays, and long-term preservation of food does not deteriorate. Aluminum foil has good moisture resistance. However, the water repellency is related to the number of pinholes in the aluminum foil. Tests by the American AICOA company show that. 9μm thick aluminum foil for packaging, average moisture permeability [g/m (m
2 · 24h) is 49, and the 13μm polyethylene composite paper has a moisture permeability of 40 to 50 μm, and the 90 μm polyethylene film has a thickness of 0.7.
The only disadvantage of aluminum foil is that there are pinholes, and pinholes are inevitable in aluminum foils with a thickness of 25 μm. Widely used 9μm thick aluminum foil has about 400 pinholes per square meter, and 7μm thick aluminum foil pinholes are more than 1000. The thickness of aluminum foil increases, the incidence of pinholes decreases, reliability is high, but the cost is high, from economy and safety. In terms of properties, the thickness of the aluminum foil used for the polyethylene composite paper is generally 7 to 10 μm.
Combination tank: The combination tank is a new type of three-piece tank. The material of the tank body is composed of polypropylene, aluminum foil and hard cardboard, which are formed by flat winding method or roll paper method. The latter is more economical and reasonable, but only round cans can be made. The can lid is made of aluminum or tinplate. The can lid and can body are sealed like a metal can with a double crimp. Since the plastic film has poor heat resistance and the sterilization temperature is limited, the combination can is sterilized by using hot air at 127 °C. It is difficult to kill bacterial spores under this dry heat condition, so the combination tank is limited to the packaging of PH and low acid beverages such as juice.
The combined tank sealing speed is up to 500 cans per minute. Compared with metal cans, the combined cans are light, low in cost, low in odor and easy to dispose. The combination tank itself is still a paper container, and the sealing property is worse than that of the metal can. It is not suitable for autoclave sterilization, and is limited to aseptic packaging or hot canning.
Second, paper container use and storage precautions
The paper container has different physical properties depending on the mode of use and the state of storage, and the productivity is lowered, the loss of the raw material paperboard is increased, and the sealing is poor. Therefore, it is necessary to strengthen the management and pay attention to the water content of the paper. For economical operation, it is desirable to control the water content from 5% to 6%. In particular, the pre-formed carton requires strict storage conditions, and should be stored for 10 to 14 days at room temperature of 21 ° C to 27 ° C and humidity of 30% before use to achieve the specified water content.
The preformed carton will be heat-sealed due to oxidation of polyethylene during storage, or may become uneven due to crease and paper fiber hardening, which may cause difficulty in feeding the filling machine. Therefore, it is necessary to carry out economic and reasonable inventory management, so that the carton can be used as soon as possible, so that advanced goods can be used first, and it must be completed within one year at the latest.