In recent years, paper containers have been used for the packaging of fruits and vegetables, dairy products, and refreshing beverages. Compared with other containers, paper containers have the following advantages: low cost, economical, light weight, favorable for logistics, and non-metal dissolution. The pressure resistance and sealing accuracy of paper containers are inferior to glass bottles and metal cans, and they cannot be heat-sterilized.

Types of paper containers

According to the material and shape of the paper container, the paper container can be divided into a composite paper box, a paper cup, a combination can, and the like.

The composite carton used in the composite carton for fruit and vegetable juices and refreshing drinks is a polyethylene composite paper container. The Te-trapak composite paper structure consists of seven layers. From the inside to the outside are polyethylene (two layers), aluminum foil, polyethylene, cardboard, printing ink, polyethylene (or wax layer).

Paper containers for liquid packaging paper use high-strength paperboard, bleached or not bleached. The thickness of the base paper and the pulp material vary according to the type and size of the container. For example, a large-size paper box with a capacity of 500 to 1000 ml has a grammage of 300 g/m 2 , and the main pulp of the long-fiber conifer is mainly used to prevent the box from being stored during storage. Body swelling, detrimental to the appearance. For a 150-200ml small carton, the container is soft, and a thin paper board of 10 to 130g/m2 may be used. The pulp of a broadleaf tree may be mixed and the carton paper may not use fluorescent dye materials.

Polyethylene food containers should be made of low-density polyethylene (LDPE) with no additive, adhesive, and sealing properties and relative density of 0.917 to 0.925. The uniformity and film should be taken into account during processing. Adhesion, sealing and odor problems. The thickness of the composite polyethylene is 40 to 60 um on the inside and 10 to 30 um on the outside.

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 the food stored for a long period of time is not deteriorated. Aluminum foil has better moisture resistance, but water resistance is related to the number of pinholes in aluminum foil. Alcoa's test showed that the average water vapor permeability is [g/m(m2*24h)] 49 for a 9-um thick aluminum foil for packaging, and the moisture permeability is 40-50um for a 13um polyethylene composite paper and 0. 7.

The only disadvantage of aluminum foil is the presence of pinholes, which are inevitably present at 25um. The widely used 9um thick aluminum foil is about 400 per square meter, and the 7um aluminum foil has more than 1000 pinholes. When the thickness of the aluminum foil is increased, the incidence of pinholes is reduced, and the reliability is high, but the cost is also high. From the viewpoint of economy and safety, the thickness of the aluminum foil used for the polyethylene composite paper is generally 7 to 10 μm.

There are generally two types of forming methods for a composite carton: one is a folding type flat carton that is preliminarily formed by a carton forming machine, which is then formed after use, and then enters the filling machine after sterilization; the other way is to start from raw materials. Sterilization, forming, filling, and sealing are all completed in the packaging machine.

Combination tank combination tank is a new type of three-piece can, the can body material is composed of polypropylene, aluminum foil and hard cardboard, and is formed by flat winding or spiral winding. The latter is more economical and reasonable, but it can only make round cans. Can lids are made of aluminum or tinplate. Can lids, can bodies and metal cans, using double crimping seals. Since the heat resistance of the plastic film is poor and the sterilization temperature is limited, the combination canister is sterilized 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 juices and other low pH acidic beverages.
The speed of the combined tank sealing tank is as high as 500 cans per minute. Compared with metal tanks, the combined tanks are light, low in cost, low in tank odor, and easy to dispose. The combination tank itself is still a paper container and has a tighter seal than a metal tank. It is not suitable for autoclave sterilization and focuses on aseptic packaging or hot filling.

Paper container use and storage precautions

Paper containers have different physical properties depending on their use methods and storage conditions, and they cause reduction in productivity, increase in loss of raw paperboard, and poor sealing. Therefore, it is necessary to strengthen management and pay attention to the water content of paper. For economical operation, it is desirable that the water content is controlled to 5 to 6%. In particular, the pre-formed carton requires strict storage conditions. Before use, it should be stored at room temperature of 21°C to 27°C and humidity of 30% for 10 to 14 days and used after reaching the specified water content.

In the pre-formed carton, during the preservation process, the heat-sealing performance is reduced due to the oxidation of polyethylene, or the elasticity of the creases and paper fibers lose their elasticity, resulting in uneven feeding of the filling and forming machine. Therefore, it is necessary to carry out economical and reasonable inventory management so that the cartons can be used as quickly as possible so that advanced goods can be used first and completed within one year at the latest.