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D4969-17 – Standard Test Method Technical Guide
📐 Scope and Classification
This specification, D4969‑17 (Reapproved 2022), covers glass fabric impregnated, coated, and sintered on both sides with PTFE to a nominal thickness of 0.318 mm (0.015 in.) or less. It is intended for electrical, chemical, and mechanical uses. Structural fabrics (thickness >0.381 mm), single‑sided coatings, and laminate materials are excluded. Values are in SI units per IEEE/ASTM SI‑10. The standard was developed in accordance with internationally recognized principles of standardization.
Six types of PTFE‑coated glass fabric are defined in Table 1. The classification uses a one‑line specification system with defined cells. Terminology follows ASTM D883 for plastics and D123 for textiles. A “structural fabric” is defined as having a thickness greater than 0.381 mm, and a “lot” is one production run or a uniform blend of two or more runs.
⚠️ Important: This specification does not cover structural fabrics (thickness >0.381 mm), single‑sided PTFE coatings, or materials used for laminates.
⚙️ Test Methods and Requirements
Property requirements are determined by various ASTM test methods. Key tests include dielectric breakdown voltage per D149, DC resistance per D257, thickness per D374, air permeability per D737, and tearing strength per D1424. Additional methods such as D751 for coated fabrics and D902 for flexible resin‑coated glass fabrics are referenced. Conditioning of test specimens follows Practice D618.
Other referenced documents include D579 for greige woven glass fabrics, D3892 for packaging, D4441 for PTFE dispersions, and IEEE/ASTM SI‑10 for SI units. ISO 12086‑2 and ISO 13000‑1/2 are mentioned for dielectric testing comparisons, but no direct ISO equivalent exists.
| 🟦 Property | 📏 Test Method | 🎯 Specification |
|---|---|---|
| Thickness (nominal) | D374 | ≤0.318 mm (0.015 in.) |
| Dielectric Breakdown Voltage | D149 | Typical ≥3 kV |
| Air Permeability | D737 | As specified for type |
| Tearing Strength | D1424 | ≥10 N typical |
| DC Resistance | D257 | High (insulating) |
💡 Tip: When specifying material, use the one‑line system outlined in Section 4.2 for clear identification of the required type and its associated properties.
❓ Frequently Asked Questions
🔍 What is the maximum nominal thickness covered by this standard?
The maximum nominal thickness is 0.318 mm (0.015 in.) as defined in the scope.
💡 How are the six types of PTFE‑coated glass fabric differentiated?
The six types, described in Table 1, differ in weave construction, coating thickness, and performance characteristics to suit specific applications.
⚡ Which test method is used for dielectric strength?
ASTM D149 is the specified test method for measuring dielectric breakdown voltage at commercial power frequencies.
📌 Are ISO standards referenced in this specification?
ISO 12086‑2 and ISO 13000‑1/2 are mentioned for dielectric testing, but this specification is not equivalent to any ISO standard.