How is stretch film measured?

Table of Contents

As a packaging tool widely used in daily life, the quality standards of stretch film have strict rules and regulations. Before the products leave the factory, they will go through a rigorous quality inspection, and they can only be sold if they are equipped with relevant certificates.

So today, we will introduce the quality testing related to stretch film to you.

stretch film measured

From a professional point of view, machine testing.

1. Lifting test

Testing instrument: Tensile film fatigue testing machine

Test method: Load the simulant equivalent to the nominal load (such as sand, rice grains, etc.) into the stretch film, then hang it on the testing machine and test 3600 times to observe whether the bag body and the belt are damaged.

2. Drop test

Testing equipment: drop tester

Test method: Put the simulant equivalent to the nominal load (such as sand, rice grains, etc.) into the stretch film, seal the bag mouth with adhesive tape, and let the bottom of the bag drop freely from a height of 0.5m from the ground. The test ground should flatten the hard ground and observe whether the bag body is damaged.

3. Water leakage test

Test method: Put the stretched film into one-fifth of the volume of clean water, the water temperature is 23℃±2℃, keep it for 1min, observe whether there are drops of water at the bottom of the stretched film, and record the observed phenomenon.

4. Sealing strength test

Testing instrument: Tensile testing machine

Test method: The sealing strength is measured according to QB/T2358-1998. The test speed is 300mm/min±50mm/min.

5. Drop impact test

Testing instrument: Dart drop impact testing machine

Test method: According to GB/T9639-1988A method, the nickel drop mass impact test shall be carried out, and a single sample shall be used.

Of course, in addition to the data and certification instructions presented by these professional quality inspections, for ordinary users, the general performance of the stretch film is what everyone pays attention to, such as high tensile strength, tear strength, and thickness. It is thin, has good transparency, and has good self-adhesion, which can wrap the object into a whole and prevent it from being scattered and collapsing during transportation.

stretch film measured

A simple instrument or a simple small experiment.

An important indicator when purchasing packaging film is the thickness of the film. But, of course, it’s difficult for users to measure it themselves because the thickness of the film is measured in microns, thinner than human hair. Therefore, factories are often differentiated using machine measurements, usually using the following measurement method.

1. β-ray thickness measurement technology

Beta ray technology is the earliest ray technology used in online thickness measurement technology. In the 1990s, it was widely used in online thickness measurement of ultra-thin stretched films. It has no requirements on the measured object, but the beta sensor is sensitive to changes in temperature and atmospheric pressure, as well as fluctuations in the stretched film. Therefore, the equipment has high requirements for radiation protection devices, and the cost of replacing the signal source is high. For example, the Pm147 source can be used for 5-6 years, the Kr85 source can be used for 10 years, and the replacement cost is about $10,000.

2. X-ray thickness measurement technology

This technology is rarely used in plastic stretch film production lines. This is because x-ray tubes have a short life and high replacement costs. Generally, it can be used for 2-3 years, and the replacement cost is about 5,000 US dollars. In addition, it is not suitable for measuring polymers composed of various elements, and the signal source is highly radioactive. Therefore, x-ray techniques are often used to measure single elements, such as steel plates.

3. Near-infrared thickness measurement technology

The fringe interference phenomenon has affected the application of near-infrared technology in online thickness measurement. Now near-infrared technology has broken through the limitation of the fringe interference phenomenon on thickness measurement of ultra-thin stretched films and can comprehensively measure the total thickness of multilayer stretched films. Due to the characteristics of infrared technology itself, the thickness of each layer of material can also be given when measuring the total thickness of the composite stretch film. Near-infrared technology can be used for biaxially oriented stretch films, cast films, and multilayer co-extruded stretch films. However, the signal source is non-radioactive, and equipment maintenance is difficult.  


Tested on appearance, stretch, self-adhesion, toughness (puncture performance), and coverage.

For the user, these special instruments and tools are not carried out when purchasing the stretch film. The professional data of the certificate certification is not easy to understand, so it needs to be judged according to experience. Therefore, only a simple test is required. The quality of the membrane can be confirmed to be consistent with our daily tests.

1. Appearance:

Good quality stretch film wholesale has a soft, natural appearance and transparency. For example, put a newspaper 20 cm below the stretch film, and you can see the words without affecting reading.

Due to the addition of plasticizers, titanium dioxide, etc., the stretch film of slightly poor quality will make the surface look bright and feel thick. Still, the transparency is poor, which is easy to distinguish.

2. Stretch:

Stretching is the ability of a stretched film to elastically elongate after being stretched, which is a property of its own. If the quality is good, the length will be extended after stretching and will not break within a certain limit (300%-700%).

An easy way to test stretch is to draw a line segment in the middle of the film with a marker, measure its length, then stretch the film with the ends of the line segment, and then measure the length of the stretched thick line segment. Dividing the two sets of data can roughly calculate the film’s stretch.

Low stretch film tension has two characteristics:

  • Uneven tension. When stretching, it is obvious that some places are stretched and thinned, and some places are almost unchanged.
  • The elongation rate is low, and the breakage phenomenon will occur when stretching.
hand stretch film8

3. Self-adhesive:

Self-adhesive refers to the adhesion between stretch films after contact, which enables the packaged items to be fastened without loosening during and after the stretch wrapping process. Generally, the stretched film’s self-adhesion can automatically adsorb together when it is in contact with the film, but it is not difficult to separate.

Self-adhesion is affected by various external factors, such as humidity, dust, and pollutants. A good stretch film has a self-adhesion of about 1N/c㎡. Wrap an ordinary egg with a stretch film, and then press the thumb-sized place. Can lift eggs. A stretched film of poor quality cannot achieve this effect.

4. Toughness (puncture resistance):

Toughness refers to the comprehensive properties of stretch film resistance to puncture and tear. The value of the hazard degree of tear resistance must be taken in the transverse direction, that is, perpendicular to the direction of machine operation, because tearing in this direction will loosen the package, and even if the longitudinal tear occurs, the package will remain firm. Therefore, stretch film The better the toughness, the better the quality.

For a small test of puncture resistance, unfold the plastic wrap normally, do not stretch it too much, fix the ends, and puncture the plastic wrap with a ballpoint pen or other pointed object. The tough film is not easily punctured. The film wraps around the nib and is stretched as the nib moves.

manual stretch film

5. Containment force

Stretch film containment force is also the most important factor in deciding if a load is safe to ship. When it comes to stretch film and pallets, containment force is key. The goal of correctly using stretch film is to move products on a pallet safely from point A to point B. You want to be able to do this safely and at the lowest cost to you. What’s the best way to use stretch film correctly? Use the right amount of containment force.

Containment force is the total force applied to your load at a given point. It’s produced by a wrap force, or tightness, multiplied by the number of stretch film revolutions. Using the right amount of stretch film containment force can be the difference between your products getting to point B in one piece or being damaged.

Through the above introduction, I believe that everyone has a certain concept of how to detect plastic wrap. Whether it is through professional institutions, professional machines, or simple manual inspection, I hope that this article will be helpful for everyone to purchase stretch films.

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Stretch film the biggest unspoken rule - Reduce 30% purchase amount