Second, the stretch packaging method Stretch packaging methods can be divided according to the use of packaging: for sales packaging and transportation packaging for two categories. Each type of product packaging equipment is different and can be divided into several different methods. a. Pull the film out from the roll, put the product on it and roll it up (or put the product in shallow pan and put it on the film), then move it to the heat sealing board, move it to a certain position, cut the film with electric heating wire, and then Move to heat seal plate for sealing. (To be continued) Best Sanitary Napkins,Sanitary Napkins Online,Disposable Sanitary Napkins,Biodegradable Sanitary Napkins Shandong Tianzige International Trade Co., Ltd , https://www.tianzigedipers.com
First, the commonly used stretch film Properties of Stretched Films (1) Adhesion after contact between self-adhesive films, during stretch winding and after wrapping, allows the packaged goods to be fastened without loosening. Self-adhesion is affected by various factors in the external environment such as humidity, dust, and contaminants. There are two main methods for obtaining self-adhesive films: one is to process glossy glossy films, and the other is to use additives that increase adhesiveness to make the surface of the film have a wetting effect, thereby improving the adhesion.
(2) Toughness Toughness is the comprehensive property of film anti-jamming and tear resistance. Tear resistance refers to the degree of tear resistance of a film when it is punctured after being tensioned. It should be noted that the value of the resistance to tearing must be transverse (ie, perpendicular to the direction of machine operation) because tearing in this direction will loosen the package but tear longitudinally and the package will remain firm.
(3) Tensile stretching is the ability of a film to produce elastic elongation after being pulled. Longitudinal stretching increases, eventually thinning the film and shortening its width. Although longitudinal stretching is beneficial, overstretching is often undesirable. As the film becomes thin and tears easily, the tension applied to the package increases.
(4) Stress retention stress retention refers to the extent to which tension applied to the film can be maintained during the stretch wrapping process. For ethylene-vinyl acetate copolymer, low-density polyethylene and linear low-density polyethylene films, the usual degree of stress retention is to stretch the original length of the film to 130% and relax to 60% to 65% in 16 hours; The vinyl chloride film relaxes to 25%.
(5) Permissible Stretching Permissible stretching refers to the maximum tensile force that can be exerted to maintain various necessary characteristics under certain applications. Allowable stretching varies with different uses. Of course, the greater the allowable draw, the less the film is used and the lower the packaging cost.
In addition to the above performance indicators, other properties such as optical properties and heat sealing properties may be important for some special packages.
2. Commonly Used Stretch Films (1) Polyvinyl chloride films are used earliest, have very good self-adhesion, good tensile and toughness, but have poor application retention.
(2) Ethylene-vinyl acetate copolymer film commonly used vinyl acetate 10% to 12%, self-adhesion, tensile, toughness and stress retention are good. It has been successfully developed domestically and has been proved to meet the requirements of rotary wrap wrapping for paper bags, plastic woven bags, corrugated boxes, and wooden plywood packages.
(3) Linear low-density polyethylene film This film appeared in 1979 and is later than polyvinyl chloride and ethylene-vinyl acetate copolymer film, but it has the best overall characteristics. Therefore, it is currently the most used stretch film. . Blown linear low density films have slightly less self-tack than polyvinyl chloride and ethylene-vinyl acetate copolymer films, but the extruded films are the same.
The stretched film made of the above materials is the final property, depending on the quality of the raw materials used and the processing technology. The properties of several stretched films are shown in Table 12-2.
Table 12-2 Â The nature of the stretch film
1. Methods used to sell packaging (1) Manual methods generally place the contents on shallow trays, especially soft and brittle products, which are easily damaged without shallow trays. There are also a number of loose products in packages that must also be platters; if the product itself has a certain degree of rigidity and firmness such as gadgets, Chinese cabbage can also be used without platters.
The manual operation process is shown in Figure 12-8. 
b. Grasp both ends of the film roll by hand and stretch it.
c. Stretch to the required extent, the two ends of the film folded down to the bottom of the film roll, pressed on the heat sealing plate seal.
(2) Semi-automatic operation mechanizes or automates part of the packaging process, which saves labor and increases productivity. The packaging form is mainly packaged with shallow pans. The mechanized parts vary according to manufacturers and users. However, the packaging is an important part of the package and stretching, to make these processes mechanized, the machine's structure is complex, the price is higher, but the generality has been weakened. Although it is possible to save some labor and increase production, it may not be cost-effective to consider it as a whole. If you only automate the supply, output, and heat seals, the packaging speed will not increase much. Therefore, semi-automatic operation is less used.
(3) Automatic operation manual operation, labor intensity of workers, single and frequent action, easily lead to fatigue of the waist, shoulders and elbows, as well as damage; coupled with high production costs, low production efficiency, automatic operation for this purpose Rapid development, the existing packaging methods used in stretch packaging machines can be roughly divided into two types:
Push-up operation method: This is the main packaging method now used for stretch packaging. See Figure 12-9 for its operation.
Stretch Packaging Technology (I)
Stretch packs were primarily used for the sale of packaging to satisfy the supermarket's packaging for meat, poultry, seafood products, fresh fruits and vegetables. Since the ideal stretched films such as polyvinyl chloride films have been used for stretch-wrapping, stretch-wrapping has developed rapidly, and has expanded from the field of sales packaging to the field of transport packaging because stretch-wrapping can be used for transport packaging. Save equipment investment, materials and energy costs. Stretch wrappers, like shrink wrappers, are also promising packaging technologies.
Stretch Film Tensile Rate (%) Tensile Strength (MPa) Self-Adhesion (g) Puncture Strength (Pa) Linear Low Density Polyethylene 550.412180960 Ethylene-Vinyl Acetate Copolymer 150.255160824 Polyvinyl Chloride 250.240130550 Low Density Polyethylene 150.21460137