At the end of this module, you will be able to:
- Identify the organization whose standardized paper and board test methods are most commonly used in the U.S.
- Describe the four mechanisms of interaction between light and the surface of a sheet of paper or board
- Describe brightness testing, including principles and units
- Describe opacity testing, including principles and units
- Describe formation testing, including principles and units
- Describe color testing, including principles and units
- Describe gloss testing, including principles and units
The following key questions are answered in this module:
How does light interact with a paper surface?
The incident light can be reflected, transmitted, scattered, or absorbed.
What are common optical tests for paper?
Common optical tests include, brightness, opacity, gloss, and color and formation.
What is brightness and how is it tested?
Brightness is the visual impression of scattered light from the sheet surface. It is tested using blue light with a wavelength of 457 nanometers.
What is gloss?
Gloss measures the amount of light reflected from the sheet surface at an angle equal to the incident light.
What is formation?
Formation is an optical test that measures the uniformity of the sheet structure and orientation of fibers. Poor basis weight uniformity, thick and thin spots, equals poor formation.
Below is a transcript of the video sample provided for this module:
The light that strikes the surface of a sheet is called the incident light. And there are four mechanisms of interaction between incident light and the sheet surface. They are: Reflection: the incident light is reflected back by the surface at a reflection angle equal to the incident angle. Transmission: the incident light penetrates through the sheet surface. Scattering: the incident light is diffusely reflected in different directions; and Absorption: the incident light is absorbed into the sheet and dissipated as heat or light. These four mechanisms result in the different optical properties of paper and board. Common optical tests for paper and board include: brightness, opacity, formation, and color. For these tests only visible light and wavelengths between 380 and 720 Nanometers is considered.
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