Composite flexible packaging material seal

[Chinese Packaging Network News] As a heat-sealing layer of composite packaging materials, because it is directly in contact with the packaged goods, and most of the packaged goods are foods, so first of all to take into account its hygienic, but also take into account its transparency Sex, resistance to penetration, good heat sealability, and openability. The following is a brief explanation of the materials used for the heat seal layer of composite packaging materials.

First, polyethylene film

The polyethylene used for the composite heat seal layer is mainly low density polyethylene and linear low density polyethylene (also some products use medium density and high density polyethylene film as the heat seal layer), and two types of polyethylene are generally used. Use after a certain proportion of blending.

According to different processing methods, it can be divided into blown film, cast film and extrusion coating film. The thickness of the polyethylene film used for compounding depends on the requirements of the packaged product. Different thicknesses may be selected. The thickness may be about 20μ and the thickness may be greater than 100μ. Since there are many additives, especially slip agents, in the resin used to produce the film, attention should be paid to the migration of additives during production.

Metallocene polyethylene can be said to be a revolution in polyethylene resin, making films made of metallocene polyethylene have good hot-tack strength, heat-sealing strength, and certain resistance to sealing contamination.

At present, the films produced by blending metallocene polyethylene and low-density polyethylene have been widely used in oil bags, shampoo bags, detergent bags, and the like. At present, most of the heat-sealing layer of the composite package is made of polyethylene, such as instant noodles, biscuits, mustard, and pickles. The blown plastic film and cast film are subjected to EDM in the middle of the process so that the surface tension of the film is greater than 38 dyne/cm.

Second, polypropylene film

Polypropylene films can also be divided into blown film (under-blowing water-cooling method), cast film and extrusion coating film. Among polypropylene films, cast polypropylene film (ie, CPP film) is the most widely used one. It is mainly used in high-temperature cooking packaging, high transparency requirements of the packaging, with CPP film aluminum plated aluminum plated CPP After (VmCPP), it is used in the packaging of puffed foods and instant noodles.

The raw materials for CPP for high temperature cooking and CPP for aluminum plating are different from the raw materials for ordinary CPP, and there are special requirements. In addition to the common binary copolymers, the high temperature resistance can be The best; and the raw material of the aluminum plating CPP is preferably a terpolymer.

In order to save costs, some companies may use polypropylene blown film as the inner layer for less demanding products. When the film is produced, the surface is also subjected to EDM. It is preferable that the surface tension of the film is greater than 40 dyne/cm.

Third, cover film

Most of the foods available on the market, such as jelly, cold drinks, yogurt, and fruit milk, are packed in plastic cups and plastic bottles, and the cups and bottles are sealed with a film. Some requirements can be opened, while others do not need to be opened. The unsealed heat-seal layer is generally used for packaging of milk, fruit milk, etc. The cup or bottle body is basically made of high-density polyethylene (HDPE) resin.

The inner layer material can be made of the same material as the cup body (bottle body). On the one hand, good sealing strength is required, and on the other, openability is required. For this particular requirement, the choice of heat seal layer is very important.

At the same time, the material with two functions is modified EVA. EVA-ethylene-vinyl acetate copolymer, it has good adhesion with polypropylene, polystyrene, etc., but it is different from the molecular structure of polypropylene, polystyrene, when heat-sealed, the two resins can not be completely Spread, infiltrate, melt together. Can only form a clear interface adhesion. Therefore, the modified EVA is used as the heat seal layer of the cover film, which not only has sufficient heat seal strength but also has easy peelability.

Fourth, special heat sealing material

In some special occasions packaging, such as coffee packaging, meat packaging, body packaging, etc., will use some special heat sealing materials, such as ionomer, EAA (ethylene-acrylic acid copolymer), EEA ( Ethylene-ethyl acrylate, EMAA (ethylene-methacrylic acid) and the like. These special materials need to be imported from developed countries such as Europe, the United States, Japan, etc. The original materials were relatively less used in China.

However, with the rapid development of China's national economy, the demand for packaging materials is also increasing. The use of these special heat seal materials has also become more widespread.

Fifth, co-extruded film

With the development of the packaging industry and fierce competition in the market, more and more disadvantages of single-layer films have gradually appeared, which restricts the popularization and application of resins. The use of co-extrusion blown film or co-extruded casting process to produce co-extruded film has the following advantages:

1. Reducing production costs: For example, to improve the heat-sealing properties of the film, many manufacturers now use LDPE and mLLDPE blends to produce films. The increase in the cost per ton of material produced in a single-layer facility is higher than the increase in cost per ton of material produced in a multi-layer co-extrusion facility.

2, improve the performance of the heat seal layer:

(1) Barrier properties: High-barrier materials such as NY and EVOH are used in the production of co-extruded films, which can significantly improve the gas barrier properties of the film.

(2) Heat-sealing performance, the appropriate mLLDPE can be used to improve the heat seal strength, hot-tack strength, seal-off temperature, and heat seal temperature range of the film.

(3) physical properties, use of suitable resins, can improve the film's tensile strength, tear strength, impact strength and elongation at break. In addition, according to the different requirements of customers, choose different resins and different grades of resin, used to improve the film stiffness, optical properties, surface friction coefficient and so on.

In short, because of the excellent performance and reasonable price of the co-extruded film, it has achieved rapid development. At present, coextruded films have grown from two-layer, three-layer to five-layer, seven-layer, nine-layer, or even more.