Maya Ellison
Measuring opacity in plastics is a critical aspect of quality control in the packaging industry. Opacity refers to the property of a material that blocks light from passing through it, and it is calculated by measuring the percentage of light absorbed by the material. Several instruments are available to measure opacity in plastics, such as the EEL Opacimeter, which is based on the Packaging and Industrial Films Association (PIFA) Voluntary Standard 3/79. Other methods involve using transmission-detecting testing devices to determine the quantity of resolution in an image formed through the plastic. The quality of plastic films is essential for product protection, and opacity is a critical factor in this regard.
| Characteristics | Values |
|---|---|
| Definition of Opacity | Opacity is the property of a substrate that opposes the entry of light. |
| Calculation of Opacity | Opacity = 100% – Transmittance |
| Testing Instruments | Opacity Tester, Opacity Measuring Instruments, EEL Opacimeter, Spectrophotometers, Gloss meter, Colorimeters |
| Testing Standards | PIFA Voluntary Standard 3/79, BS ISO 2471, ISO 5631, BS ISO 11475, BS ISO 2470 |
| Testing Samples | Plastic films, pellets, plaques, coated board, carton board, etc. |
| Testing Preparation | Standardization of sample preparation method, e.g., size, thickness, scratches, etc. |
| Testing Parameters | Transmittance, haze, clarity, diffuse scattering, narrow-angle scattering, gloss, color, etc. |
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What You'll Learn
Opacity testing machines
There are several manufacturers of opacity testing machines, including Presto Stantest, Pacorr, Hexa Plast, Saumya Technocrates, Kaiser Technic, and Kant Plastology. These machines are used to test the optical characteristics of plastics, including colour, clarity, general appearance, and other directly measurable properties.
The EEL Opacimeter is another instrument used to measure the opacity of plastic. It is based on the Packaging and Industrial Films Association (PIFA) Voluntary Standard 3/79. The Technidyne Colourtouch PC spectrophotometer is also used to measure opacity, along with other surface optical properties such as CIE whiteness, brightness, and L*a*b* colour.
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Light transmission properties
Opacity is the property of a material that blocks light from passing through it. It is calculated by measuring the percentage of light absorbed by the material. Opacity testing machines are designed to measure the percentage of transmitted light that passes through a sample and deviates from the incident ray by forward scattering. This value helps determine the quality of the material. Various manufacturers offer opacity testers to measure the level of transmittance and calculate the opacity of the material.
To measure opacity in plastics, instruments such as the EEL Opacimeter are used, following the Packaging and Industrial Films Association (PIFA) Voluntary Standard 3/79. Opacity and whiteness are measured as a percentage, and an internal microprocessor compares the diffuse reflectance of the sample against black and white references to determine opacity.
Additionally, spectrophotometers are valuable tools for measuring the light transmission properties of plastics. They can measure both colour and haze, providing quantifiable results. Gloss is another factor that affects light transmission and can be measured using a gloss meter, which measures the amount of reflected light in Gloss Units.
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Testing instruments
Several testing instruments are available to measure the opacity of plastics. Opacity is the property of a substrate that opposes the entry of light. The percentage of light transmitted through a plastic sample is measured and used to calculate opacity.
The EEL Opacimeter is a widely used instrument to measure opacity in plastics. It is designed to measure the percentage of light passing through a sample that deviates from the incident ray by forward scattering. This value is then used to calculate the opacity of the material using the equation: Opacity = 100% - Transmittance. For example, if the transmittance of a material is 25.6%, then its opacity will be 74.4%.
Other instruments used to measure opacity include the Technidyne Colourtouch PC spectrophotometer, which can measure CIE whiteness, brightness, L*a*b* colour, and opacity. This instrument is used to test a range of materials, including plastic, tissue, paper, and carton board.
Additionally, a colorimeter is an instrument used to measure the concentration of coloured compounds in a solution by determining the absorbance of specific wavelengths of light. This can also be used to measure the opacity of plastics.
It is important to note that the light transmission properties of plastics are difficult to measure and characterise. Therefore, standardising the sample preparation method, such as size and thickness, is crucial for reliable and repeatable measurements. Scratches or damage to the surface of the plastic can significantly impact its transparency.
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Calculating opacity
Opacity is a property of a substrate that resists the entry of light. In the context of plastic, opacity is measured as the percentage of light transmittance that passes through a sample of plastic and deviates from the incident ray by forward scattering more than the average.
The equation to calculate the opacity of a material sample is: Opacity = 100% - Transmittance. For example, if the transmittance of a material is 25.6%, then the opacity of the material will be: Opacity = 100% - 25.6% = 74.4%.
Opacity testing machines such as the Presto Stantest and Pacorr, are used to measure the level of light transmittance through a material in order to calculate its opacity. These instruments help to determine the quality of the material.
In addition to these methods, there are also mathematical equations to calculate opacity in specific contexts, such as in Photoshop, CSS, and JavaScript. For example, in JavaScript, the following function can be used to calculate the opacity color value manually:
Function calculateTransparentColor(foregroundColor, backgroundColor, opacity) {
If (opacity < 0.0 || opacity > 1.0) {
Alert("assertion, opacity should be between 0 and 1");
}
Let foregroundRGB = colorHexToRGB(foregroundColor);
Let backgroundRGB = colorHexToRGB(backgroundColor);
Let finalRed = Math.round(backgroundRGB.r * (1-opacity) + foregroundRGB.r * opacity);
Let finalGreen = Math.round(backgroundRGB.g * (1-opacity) + foregroundRGB.g * opacity);
Let finalBlue = Math.round(backgroundRGB.b * (1-opacity) + foregroundRGB.b * opacity);
Return colorRGBToHex(finalRed, finalGreen, finalBlue);
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Gloss and reflection
Gloss is a key factor in the appearance of plastics, influencing the psychological impact of products on consumers. Gloss is a measure of how reflective a material is at a specified angle based on its refractive index. It is not a physical property of the surface, but a subjective impression.
The measurement of gloss is important to ensure the integrity of a product's appearance. Gloss meters are used to measure the specular reflection of a product's surface. This involves illuminating a sample under a defined angle and detecting the reflected light intensity. The greater the angle of illumination, the greater the amount of reflected light. A polished black glass with a refractive index of 1.567 is used as a standard and is assigned a gloss of 100 at all geometries.
To obtain a clear differentiation between high and low gloss surfaces, three geometries or different ranges are standardized. The 60° geometry is used for comparing most specimens and for determining when the 20° or 85° geometry may be more applicable. ASTM D523 covers the measurement of the specular gloss of non-metallic specimens for gloss meter geometries of 20, 60, and 85°. ASTM D2457 describes procedures for the measurement of gloss of plastic films and solid plastics, both opaque and transparent at 20, 45, 60, and 75°.
Reflection haze meters are also used to measure reflection haze, which provides further analysis of a product's appearance. Transmission haze occurs when light passes through a transparent plastic material and creates an unfocused or blurry appearance of the objects behind it.
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Frequently asked questions
Opacity is the property of a material that blocks light from passing through it.
Opacity can be calculated by measuring the percentage of light absorbed by the material. The equation is: Opacity of the Material = 100% – Transmittance.
Opacity in plastic can be measured using an opacity tester, a type of testing instrument that calculates the opacity of the material by testing the level of light transmittance.
Other methods include using a colorimeter, which measures the concentration of coloured compounds in a solution, or a spectrophotometer, which measures the amount of light absorbed or reflected by the plastic.
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