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D1746-23 – Standard Test Method Technical Guide
The ASTM D1746−23 standard specifies a test method for measuring the transparency of plastic sheeting in terms of regular transmittance (Tr). This method is primarily intended for nominally clear and colorless thin sheeting and provides a quantitative measure of see-through clarity.
📐 Test Scope and Significance
This test method covers the measurement of transparency of plastic sheeting by regular transmittance. It is applicable to any translucent or transparent material but is principally used for clear and colorless thin sheeting. The significance of this test lies in its correlation with the subjective property of “see-through,” where the ability to distinguish a distant target is quantified. The sensitivity of the test improves with decreasing incident beam and receptor angles.
⚙️ Measurement Principles and Apparatus
The angular width of the incident beam and the receptor aperture (as seen from the specimen position) should be of the order of 0.1° or less. The resolution of the measurement is largely determined by the angular width of the receptor aperture. Caution must be exercised when comparing results from different instruments due to variations in design parameters, especially for samples with low regular transmittance.
| 🟦 Parameter | 📏 Value |
|---|---|
| Incident Beam Angular Width | ≤ 0.1° |
| Receptor Aperture Angular Width | ≤ 0.1° |
| Transparency Range | 10% to 90% |
| Resolution Determined By | Receptor aperture angular width |
📊 Key Measured Properties
The primary property measured is regular transmittance (Tr), which quantifies the clarity of the sheeting. For sheeting of commercial interest, the transparency ranges from about 10% to 90% as measured by this test. Correlation with perceived clarity is good for clear materials but poor for highly diffusing materials due to interference of scattered light.
| 📐 Standard | 🔗 Description |
|---|---|
| D618 | Practice for Conditioning Plastics for Testing |
| D883 | Terminology Relating to Plastics |
| D1003 | Test Method for Haze and Luminous Transmittance |
⚠️ Caution: Results obtained from different instruments may not be directly comparable due to differences in design parameters, such as receptor aperture angular width. This is particularly relevant for samples with low regular transmittance.
💡 Tip: For consistent results, condition samples according to Practice D618 before testing. Ensure that the angular conditions of the apparatus are set to 0.1° or less as specified.
❓ Frequently Asked Questions
🔍 What is regular transmittance (Tr)?
Regular transmittance is the measure of light that passes through the plastic sheeting without being scattered. It directly correlates with the material’s clarity or see-through ability.
💡 How does angular width affect the test?
Narrower angular widths (0.1° or less) enhance the sensitivity of the measurement to differences in transparency. Wider angles can reduce resolution and affect the accuracy of results.
⚡ Why is caution needed when comparing results from different instruments?
Instrument design variations, particularly in the angular width of the receptor aperture, can lead to significant differences in measured values, especially for materials with low regular transmittance.
📌 What is the range of transparency for commercially interesting sheeting?
Under this test method, sheeting of commercial interest typically exhibits a transparency range of 10% to 90% when measured with appropriate angular conditions.