Haze and Transmittance Test for Wrap Films: Comprehensive Guide

Wrap films, including stretch films and packaging films, are used in a variety of applications, from packaging to protection and transportation. These films often need to maintain a certain level of transparency to allow for visibility of contents while also providing effective protection against external elements.

 
Haze Meter and Luminous Transmittance meter

The Role of Haze and Light Transmittance in Packaging

Haze and light transmittance directly impact the clarity and appearance of the wrap film, which is essential for consumer perception, especially in food packaging and retail environments. Inadequate haze levels can result in poor visual appeal, while improper transmittance can compromise the effectiveness of the wrap in protecting products. Testing ensures that films meet the required specifications for optical clarity and transparency.

Transmittance and haze are two very important optical properties of transparent materials.

Haze is strongly related to scattered and transmitted luminous flux; Transmittance is the percentage of luminous flux through the medium to the total incident luminous flux.

Haze characterizes the state of turbidity and irregularity within transparent or translucent materials, and transmittance indicates the ability of a material to transmit light.

Haze is the ratio of the scattered light flux to the transmitted light flux that deviates from the incident light direction when parallel light passes through a material sample, and is expressed as a percentage. Usually only the scattered light flux that deviates from the direction of incident light by more than 2.5 degrees is used to calculate the haze.

Transmittance is the ability of light to pass through the medium of a material object, and is the percentage of the luminous flux that passes through the material medium to its incident luminous flux.

How Haze and Transmittance and are Calculated?

During the test, when there is no incident light, the received light flux is 0. When there is no sample, all the incident light passes through, and the received light flux is 100, which is denoted as T1. At this point, parallel light is absorbed by the light trap, and the received light flux is the instrument’s scattered light flux, T3. Then, the sample is placed, and the instrument receives the transmitted light flux, which is T2. If the parallel light is absorbed by the light trap, the received light flux is the sum of the sample and the instrument’s scattered light flux, T4. Based on the measured values of T1, T2, T3, and T4, the transmittance and haze values can be calculated.

The transmittance Tt is calculated according to the following formula:

Tt(%)=T2/T1*100

The haze value H is calculated according to the following formula:

H(%)=(T4/T2-T3/T1)*100

Generally speaking, transmittance and haze have an inverse relationship. Materials with high transmittance tend to have low haze, and vice versa. However, the relationship between the two is not always this way, and sometimes the results can be opposite.

Guiding Standards for Haze and Transmittance Testing

Several international standards guide the measurement of haze and transmittance, ensuring accuracy and consistency across testing procedures.

ASTM D1003 – Standard Test Method for Haze and Luminous Transmittance of Transparent Plastics

ASTM D1003 is the most commonly used method for measuring haze and light transmittance in transparent plastics, including wrap films. This test uses a haze meter to measure the degree of light scattering and the percentage of light transmitted through a sample.
Know More About ASTM D1003

ISO 13468 – Plastics — Determination of the total luminous transmittance of transparent materials

ISO 13468 provides a detailed procedure for testing the haze of plastic films, focusing on precise measurement conditions and equipment to evaluate how much light is scattered through the film.
Know More About ISO 13468

ISO 14782 – Plastics — Determination of haze for transparent materials

ISO 14782 outlines a method for measuring the haze and light transmittance of plastic films. It specifies the equipment, procedure, and conditions necessary to ensure accurate and repeatable results.

Know More About ISO 14782

ASTM D1044 –Standard Test Method for Resistance of Transparent Plastics to Surface Abrasion by the Taber Abraser

While not directly related to haze, ASTM D1044 is a key standard for testing the abrasion resistance of films, which can impact the film’s transmittance and overall clarity during use.
Know More About ASTM D1044

Test Overview

The Haze and Transmittance Test is typically performed using standardized test methods like ASTM D1003, ISO 14782, ISO 13468, and ASTM D1044. These standards outline the procedures for measuring the optical properties of transparent films, including haze and light transmittance, which are critical to determine how the film will perform in practical applications such as packaging, displays, and other industrial uses.

Step-by-Step Test Procedure

1.Sample Preparation

Sample Selection: Select a representative film sample for testing. Ensure the film is clean and free from dirt, scratches, or other imperfections that could influence the measurement.

Sample Size: The film sample is typically required to be large enough to fully cover the test aperture of the haze meter, typically a circular area of around 50 mm or more in diameter.

2. Instruments Setup

Haze Meter Calibration: The haze meter must be calibrated according to the manufacturer’s instructions. Calibration ensures that the instrument provides accurate readings. Calibration is usually done with a certified standard material that has known haze and transmittance values.

Place the sample film between the instrument’s light source and the detector. The film should be positioned in such a way that light passes through it.

3. Parameter Setting

Choose the test standard, test item of Haze, transmittance or both, and the light source, such as Light A, Light C, or Light D65.

4. Start Test

Measure a standard sample as baseline and then measure the tested samples. Test result will display on the screen and user can compare the results. 

FAQs about Haze and light transmittance test

What is the difference between haze and luminous transmittance in plastic films?

Haze refers to the scattering of light as it passes through a material, which causes a loss of clarity and results in a cloudy appearance. Luminous transmittance, on the other hand, measures the percentage of visible light that passes through the material without scattering. While haze quantifies the clarity or transparency loss, luminous transmittance assesses how much light can actually pass through the material, which is important for applications like packaging and visual displays.

How does the haze and luminous transmittance test impact packaging materials?

For packaging materials, particularly in industries like food and pharmaceuticals, the clarity and light transmittance of the packaging material are critical. High haze values can reduce the product’s shelf appeal by making it appear cloudy or opaque, while optimal luminous transmittance ensures that labels, product details, or the contents of the packaging remain visible. The test helps manufacturers ensure that their films meet aesthetic and functional requirements for clarity and transparency.

What is the role of the haze meter in conducting these tests?

A haze meter is used to measure the amount of scattered light passing through a film. It typically works by directing a beam of light through the sample material and using detectors to measure both transmitted and scattered light. The difference between these readings helps calculate haze and transmittance values. This instrument is essential for providing precise, objective, and reproducible results required by international testing standards. 

How is the luminous transmittance percentage calculated during testing?

Luminous transmittance is calculated as the ratio of the transmitted luminous flux through the material to the incident luminous flux. This is usually expressed as a percentage:Luminous Transmittance FormulaThis value indicates how much light (in terms of visible spectrum) passes through the material, which is crucial for evaluating the transparency and optical clarity of films used in various applications.

Can haze and luminous transmittance testing be applied to materials other than plastic films?

Yes, haze and luminous transmittance testing can be applied to a variety of materials beyond plastic films, including glass, coatings, and laminates. However, the specific testing methods and equipment may vary depending on the material’s properties. For example, while ASTM D1003 is commonly used for plastic films, additional standards or modifications may be required for other materials to account for differences in light scattering behavior or surface characteristics.

Which standards are used to perform haze and transmittance testing?

The primary standards for haze and luminous transmittance testing include:

  • ASTM D1003: The standard test method for haze and luminous transmittance of transparent plastics.
  • ISO 14782: This standard specifies the method for determining the light transmittance of plastic films and sheets.
  • ASTM D1044: Provides guidelines for determining the haze and clarity of plastics subjected to abrasive wear. These standards ensure consistent, repeatable testing and accurate data for material performance evaluation.

    • More Tests For Wrap Film