A photoelectric haze meter is a widely used device appropriate for measuring light transmittance and assesses the haze value for numerous transparent packaging films, photographic film bases, motorcar glass, and colored or colorless plexiglass.

What is meant by haze?

By definition, haze is the deviation of the incident ray of light caused by forward scattering as it transmits through the sample. If the transmitted light exhibits a divergence of above 2.5°, it is considered haze or luminous flux. In layman’s words, haze is the dispersion of light on the inside or surface of a transparent or semi-transparent surface, resulting in a cloudy appearance.

What is meant by transmittance?

Transmittance is the ratio of transmitted light to incident light, frequently expressed as the transmitted light percentage. Light transmittance is a pre-requisite performance index for the identification of transparency of the resin. The correlation between light transmittance and transparency is direct; higher light transmittance equates greater transparency.

The correlation between haze and transmittance:

It is crucial to understand that haze and transmittance are entirely different. The basic concept implies that as the light strikes a semi-transparent or transparent sample, some of it is reflected or transmitted, whereas others are absorbed. However, the transmitted light which manages to sustain the original propagation direction is regarded as parallel transmission. Furthermore, the part of the light which is scattered due to the sample material is identical to the scattered light introduced in the description of haze.

How does a haze meter operate?

The haze meter employs a beam of light and determines the light scattered or transmitted when it strikes a transparent or translucent material. The scattering causes a variation from the incident direction at an amount greater than 2.5°. The optical transparency of materials is determined by scattered light flux and transparent haze, which are essential parameters.

Factors affecting Haze and Transmittance Measurement:

Various factors such as sample preparation, the processing time, etc., significantly affect the determination of haze and transmittance.

  • Surface Scratch Effects on Film Transmittance and Haze

The values of haze and transmittance are measured before sample treatment. Later, the two parameters described previously are measured again and again to evaluate the influence of surface scratches on the haze and transmittance. Extensive studies have reported that scratches have a significantly lower impact on transmittance, whereas it dramatically affects haze. It was concluded that scratches should be prevented in film production and sample testing.

  • Effect of sample surface contamination on light transmittance and haze of thin films:

Like surface scratches, surface contamination significantly affects haze but mildly impacts transmittance. Specific plastic such as Pc, Ps, and others exhibit increased transmittance value from contamination and scratches on the surface. It is because of a decrease in reflection and boosts transmission when the incident light hits the scratched and contaminated sample. However, if the extent of contamination or scratches is enhanced further, the transmittance will decrease.

  • Effect of different sample thicknesses on the transmittance and haze of the film

Reports suggest that the increase in the thickness of the sample negatively affects the light transmittance but positively impacts the haze. As the thickness increases, the amount of light also absorbed increases. Hence, the amount of light that crosses the sample decreases, reducing the light transmittance. Simultaneously, if the thickness of the piece is multiplied, which increases light scattering, the haze also intensifies. Therefore, haze and transmittance should only be compared for the model with the same thickness.

How to select a suitable transmittance haze meter?

It’s essential to understand the factors that affect the quality of a haze meter as it is used to measure the haze and transmittance value of samples. The factors include:

  • Double Beam Structure Design:

The double beam haze meter consists of the following parts:

  1. Measuring Beam
  2. Energy monitoring beam
  3. Double beam (ISO standard compensation beam)

It offers the stability of the measurement results as any change in the luminous energy coming from the light bulb source is detected, and relevant adjustments and data calculation is made as per the changes. The question is; why does the luminous energy of the source change? Because it is sensitive to current, voltage, humidity, and temperature. Furthermore, the function of the monitoring beam is to measure any change in luminous energy due to the factors affecting it.

  • Meets ASTM and ISO haze standards

The most-sought-after kind of haze meter includes those that meet the ASTM D1003 standard and ISO14782/13468 standard. ASTM standard is also referred to as the non-compensation method, whereas the ISO standard is called the compensation method haze standard. The majority of the users prefer ASTM, but people are slowly shifting toward the ISO standard. It’s not difficult to fulfill the standard testing requirements of various users if the haze meter is up to the ISO and ASTM standards.

  • High repeatability

The ability of an instrument to give reproducible results is one of the fundamental benchmarks. Any data differences at various intervals can influence the results. A haze meter with high repeatability helps determine the stability state of the device.

  • Convenient operation mode and data storage mode

Storing data is made more accessible than ever as the haze meter can transfer the measurement data to a computer for quality control analysis. Furthermore, there’s an option to keep all of the measurement data and even print it with the help of a built-in printer. Multiple activities such as light source selection, calibration measurement, and standard selection can be done on the touch screen.

How to operate a haze meter?

Sample Size: Take a measurement of the sample’s thickness. If the thickness is less than 0.1mm, atleast 0.001nm and greater than 0.1mm, atleast 0.01mm

Test: To preheat, turn on the power. Two windows show two decimal numbers, the red light, which specifies the ready indicator, and the green light, “P,” which demonstrates the soon the “ready” indicator on the left side of the reading window. H is shown on the right side following a calling sound. The test switch is pressed to clear the folding sample at this particular moment. The device displays “p100.00”. “H0.00”. However, if it is not displayed on the screen, and instead P<100.0,h>0.00 is visible, it indicates that the light source is not adequately preheated. Switch off the power and switch it on at least twice under the “P100.00” and “H0.00” until the device preheats properly and stabilizes. Press the switch that says “Test.” Once the “P’ and “H” appears on the screen again, the measurement can be done.

Once the sample is installed and the indicator light is red, the light transmitted value is demonstrated in 0.1% units, and haze values are visible in 0.001% units. Soon, the indicator light becomes green. In case of re-measurement, the sample should not be removed. Press the test button to acquire numerous measurements. Later, take the mean value to enhance the accuracy of measurement. The test should be repeated by replacing the samples to determine the results of the same samples.

It’s important to note that while changing the number of the sample batch, the test button should be pressed to obtain the blank value. As the indicator light becomes red, the device presents the “P100.0” and “H0.00” results, and soon, the indicator light becomes green. The blank should only be determined once in case of multiple sample groups. Remember to press the test button after measuring the blank and evaluate the samples once the light turns green.

Plastic samples are measured by the same method if the film is firmly placed between magnetic clamps. One portion of the sample film should always be near the integrating sphere.

Two methods can measure turbidity:

The first way is a turbidimetric analysis which is analyzed by the intensity of the light that moves through the suspension. It is neatly placed on the sample stage as the standard sample, and as the test button is pushed, a P-value is demonstrated, which is the light transmittance and turbidity of the sample.

The second method utilizes the intensity of scattered light to determine the number of particles. A turbidity SiO2 standard solution is employed rather than the “H1” reading obtained from the previously distilled water. “H2” is obtained using the tested sample, and H2/H1 indicates the ppM turbidity.

FAQ:

  1. What does the haze meter difference mean?

A contrast in measured standard sample and sample data is the difference between the haze meters. It can either be positive or negative. It doesn’t matter whether the final value obtained by information is positive or negative, as it will be a positive value regardless after the addition of the absolute value sign. The knowledge about different enables us to figure out the direction of the production process.

  1. What is the best haze test value? 

Every material exhibits a different haze requirement. If the haze index of the pearlescent film is taken as an example, the haze should be ≥ 70%. White ink is purposely not used to print pearlescent film composite products to ensure that the haze does not fulfill the requirements.