Nine performance requirements for plastic films in packaging bags, none of which can be missing

Whether it's a single-layer packaging bag or a composite packaging bag, packaging bags have basic requirements for the appearance, specifications and deviations, transparency, and gloss of the plastic film. Today, Shunxingyuan Packaging, a professional flexible packaging manufacturer, will take you to understand the nine performance requirements for plastic film in packaging bags one by one.

1. Appearance

The surface of the plastic film should be smooth and flat, without wrinkles or only a small number of creases, without obvious unevenness, black spots, impurities, crystal points, and lumps, no stripes, scars, or burst muscles, no bubbles, pinholes, or cracks. The aluminum plating layer of the aluminum-plated film should be uniform, and obvious bright stripes or uneven surfaces are not allowed. In addition, the film surface should be clean and free of dust and oil stains.

2. Specifications and Deviations

The width and thickness of the plastic film and its deviations should meet the requirements, and it should be uniform in thickness, with small deviations in thickness in the horizontal and vertical directions, and the deviation distribution should be relatively uniform. In addition, the thickness of the aluminum plating layer of the aluminum-plated film should also meet the requirements.

3. Transparency and Gloss

For transparent plastic films, the light transmittance is high, generally reaching more than 92%. For opaque plastic films, such as white films, high whiteness and good opacity are required. In addition, the plastic film should also have good gloss.

4. Physical and Mechanical Properties

The physical and mechanical properties of plastic films mainly include tensile strength, elongation at break, tear strength, impact strength, etc. In addition, the firmness of the aluminum plating layer on the aluminum-plated film should also meet the requirements.

5. Water Vapor Transmission Rate

It represents the amount of water vapor that permeates the plastic film material under certain conditions, such as the mass of water vapor permeated per square meter of a 25um thick plastic film within 24 hours at a relative humidity of 90% and a temperature of 30℃. To a certain extent, it represents the moisture resistance of the film material. Different film materials have different water vapor transmission rates, which also determines their application range.

6. Oxygen Transmission Rate

It represents the amount of oxygen that permeates the plastic film material under certain conditions, such as the volume of oxygen permeated per square meter of a 25um thick plastic film within 24 hours at a relative humidity of 90% and a temperature of 23℃. Different film materials also have different oxygen transmission rates.

7. Geometric Dimensional Stability

Plastic films must have a certain degree of geometric dimensional stability. Otherwise, if the shrinkage rate is too large, they are easily deformed during printing and lamination due to mechanical force or heat, which will not only affect the register accuracy but also cause wrinkles and curling, seriously affecting product quality and production efficiency.

8. Chemical Stability

Plastic films come into contact with inks, adhesives, and certain organic solvents during printing and lamination. These are chemical substances, so plastic films must have a certain resistance to these chemical substances so as not to be affected.

9. Surface Tension

For example, the surface tension of biaxially oriented polypropylene film and low-density polyethylene film is required to reach more than 3.8 × 10-2 N/m, and nylon film, polyester film, and polyester aluminum-plated film also have corresponding indicators. Generally speaking, plastic films must be surface-treated before printing or lamination to improve their surface tension and allow for smooth printing and lamination.

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