How to test the strength of thin films produced by three-layer co extrusion blown film machine

1、 The Importance of Thin Film Strength Testing

The film produced by the three-layer co extrusion blown film machine is widely used in packaging, agriculture, construction and other fields, and its strength performance directly affects the product's performance and safety. Film strength is an important indicator for measuring its ability to resist external damage, including tensile strength, tear strength, impact strength, and other aspects. Through scientific strength testing, the quality stability, process rationality, and applicability range of the film can be evaluated, providing data support for production process optimization and quality control.

2、 The main methods for testing the strength of thin films

1. Tensile strength test

Tensile strength testing is the fundamental method for evaluating the mechanical properties of thin films, mainly measuring the performance of the film under tensile force.

Testing standard: Usually conducted in accordance with GB/T 1040.3-2006 "Determination of Tensile Properties of Plastics" or ASTM D882 standard.

Testing equipment: Electronic universal material testing machine.

Test steps:

Preparation of standard specimens: Cut the film into specified dumbbell shaped or elongated specimens

Set test parameters: including fixture spacing, tensile speed (usually 100mm/min or 500mm/min)

Install the sample: Clamp both ends of the sample in the upper and lower fixtures of the testing machine

Conduct testing: Start the testing machine and record the changes in force values during the stretching process

Result calculation: Obtain parameters such as tensile strength and elongation at break through stress-strain curves

Notes:

The sample should be free of defects and creases

The testing environment should be controlled under standard temperature and humidity conditions (usually 23 ± 2 ℃, 50 ± 5% RH)

The number of samples in each group shall not be less than 5, and the average value shall be taken

2. Tear strength test

Tear strength reflects the ability of a film to resist crack propagation and is particularly important for packaging materials.

Testing method:

Elmendorf method (GB/T 11999-2008): suitable for thinner films

Pant tearing method (ASTM D1938): suitable for thicker films

Elmendorf method testing steps:

Cut the film into rectangular specimens measuring 63 × 76mm

Make a 20mm long incision in the center of the short side of the sample

Install the specimen on the pendulum tear testing machine

Release the pendulum and record the force required to tear the specimen

Calculate the tearing force per unit thickness (mN)

Influencing factors:

The quality of the incision directly affects the test results

The clamping force of the sample should be moderate to avoid sliding or excessive deformation

The testing direction should consider the orientation direction of the film

3. Impact strength test

The commonly used methods for evaluating the ability of a thin film to resist sudden impact loads include:

Pendulum impact method (GB/T 8809-2015):

Use a pendulum impact testing machine

Measure the energy absorbed by sample fracture

The result is expressed in kJ/m ²

Dart impact method (ASTM D1709):

Use a dart impact tester

Measure the impact energy when 50% of the sample ruptures

The result is expressed as g or J

Test points:

The sample should be flat and wrinkle free

State adjustment is required before testing

The impact point should be kept away from the clamping edge of the specimen

4. Peel strength test (for composite films)

For multi-layer co extruded films, interlayer bonding strength is a key indicator.

Test method (GB/T 8808-1988):

Peel off the sample from the starting port in advance

Peel off at a certain angle (usually 90 ° or 180 °) and speed (100-300mm/min)

Record the force curve during the peeling process

Calculate the average peel force (N/15mm)

Notes:

The peeling angle needs to be consistent

The peeling speed affects the test results

Environmental temperature and humidity should be controlled

3、 Factors affecting test results

Sample preparation: cutting method, dimensional accuracy, edge quality

Testing environment: An increase in temperature usually reduces strength, and humidity affects certain materials

Test speed: Increasing speed generally leads to an increase in strength values

Film orientation: The mechanical properties have anisotropy, and the testing direction should be indicated

Material composition: The proportion and compatibility of different layer materials affect the overall strength

4、 Analysis and Application of Test Data

Process optimization: Adjust extrusion temperature, inflation ratio, traction speed and other parameters through strength testing feedback

Quality control: Establish upper and lower limits for strength indicators and monitor production stability

Product development: Evaluate the performance of new material formulations or structural designs

Standard compliance: Verify whether the product meets industry standards or customer requirements

5、 Special testing methods

Creep testing: Evaluating the deformation characteristics of thin films under long-term loading

Fatigue testing: simulating repeated stress situations in actual use

Strength testing after environmental aging: evaluating the strength retention rate of the film after exposure to environmental factors such as UV, humidity, and heat

6、 Selection of testing standards

Appropriate testing standards should be selected based on the end use of the film:

Packaging film: focusing on tear and impact strength

Agricultural film: emphasizing tensile strength and weather resistance

Architectural film: focus on long-term load capacity and puncture strength

7、 The content of the test report

The complete strength test report should include:

Sample information (material, thickness, production date, etc.)

Testing standards and methods

Test environment conditions

Testing equipment and parameters

Raw data and calculation results

Result analysis and conclusion

Through systematic and scientific strength testing, the film performance produced by the three-layer co extrusion blown film machine can be comprehensively evaluated, providing reliable basis for product research and development, quality control, and process improvement.