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Plastics Testing-UL

Yangzhou Chengsen Plastics Co.,Ltd | Updated: May 02, 2018
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The evaluation of plastic materials may include the determination of material flammability (burning characteristics), ignition characteristics from various thermal and electrical sources, electrical tracking and additional electrical characteristics, and analytical tests. Property retention following exposure to long-term elevated temperature (air-oven aging), water, ultraviolet light, cold, and other outside influences may also be evaluated.

Properties evaluated by UL include:

Materials for use in special environments are investigated for specific end-use product applications where requirements exist for the retention of properties after exposure to certain critical operating and/or environmental conditions. This includes exposure to various types of ultraviolet (UV) radiation.

Color Concentrates (QMQS2)

When an end-product manufacturer orders a Recognized plastic in a custom color, the Recognized plastics supplier must stop production, clean the machinery, and proceed with a special run for the production of this custom-color. This is a time-consuming and costly procedure that is typically reflected in the cost of the order. In addition, the Recognized plastics supplier may require a large minimum order unless the order is for a neat natural resin.

The color concentrate category (QMQS2) offers end-product manufacturers faced with these challenges the option of ordering the necessary amount of the Recognized neat natural resin while also obtaining a color concentrate Recognized for use with the Recognized plastic. By dry blending the two materials without exceeding the published maximum let-down ratio, end-product manufacturers can produce the contracted part, which is typically more cost-effective than ordering a custom Recognized plastic.

Recognition of a color concentrate for use with a vertically rated Recognized base resin is specific and requires the submittal of standardized test samples. The samples consisting of the color concentrate let-down into the Recognized base resin are tested to certify that the use of the color concentrate does not compromise the flame rating of the Recognized base resin. The Recognition of color concentrates requires submittal and testing for each Recognized vertically rated base resin.

Similarly, Recognition for use with HB-rated Recognized base resins involves the submittal of standardized test samples of the color concentrate let-down into a Recognized HB-rated base resin for testing. If this testing does not compromise the HB-flame rating of the Recognized base resin, the newly Recognized color concentrate has a generic Recognition which permits its use in any Recognized HB-rated base resin of that particular generic type.

Component Concentrates (QMLJ2)

A custom-compounding plastics company typically purchases a neat natural resin from a plastics supplier and enhances that formulation by introducing an additive concentrate package to generate a new product. This newly Recognized material is tested and published under the component-plastics category (QMFZ2). The component-concentrates category (QMLJ2) permits the Recognition of the additive concentrate package that was blended with the Recognized neat base resin to produce the newly formulated Recognized plastic.

Category QMLJ2 also permits the Recognized base resin to be shipped directly to the Recognized end-product manufacturing location. The Recognized concentrate package can be shipped directly to the manufacturer as well. Before molding, resin and package are dry-blended at the specific let-down ratio by the Recognized manufacturer. For this process, the manufacturer must be Recognized under the fabricated parts, Recognized molders category (QMMY2).

This method of supplying the base resin gives the end-product company an opportunity for large scale purchasing and shipment of the base resin. The Recognized concentrate can be ordered and shipped based on production schedules. This method also provides the plastics supplier with the capability of large-scale production runs of the base resin rather than custom compounding orders.

In publishing the Recognition for the concentrate, the Recognized concentrate package, Recognized base resin supplier’s name, file number and grade designation are noted on the Recognition card. The newly formulated Recognized material designation, file number and company name are also noted.

To ensure reproducibility of the Recognized concentrate package, identification testing consisting of infrared spectroscopy (IR), thermogravinetry (TGA), and differential scanning calorimetry (DSC) testing is conducted on the Recognized concentrate package let-down into its generic carrier. Periodic testing under UL’s Follow-Up Services program is conducted.

IEC Ball Pressure Temperature (BP)

IEC ball pressure temperature, in accordance with IEC 695-10-2, is expressed as the temperature (in degrees C) at which a 5-millimeter diameter ball causes a 2-millimeter diameter or less impression on the material surface.

Outdoor Suitability

A material considered suitable for outdoor use has gone through testing in accordance with UL 746C, Polymeric Materials, Use in Electrical Equipment Evaluations as follows:

  1. 1,000 hours of xenon-arc weatherometer conditioning

  2. Water immersion for seven days at 70 degrees C.

The material is tested for flammability, mechanical impact and mechanical strength before and after exposure to these conditions. Test results may lead to one of the following outcomes:

(f1) — This footnote indicates that the material has met both UV and water exposure or immersion requirements as called out in UL 746C. The material is suitable for outdoor use with respect to exposure to ultraviolet light, exposure to water, and immersion in accordance with UL 746C.

(f2) — This footnote indicates that the material has only met or has been tested partially for UV or water exposure or immersion. The material was subjected to one or more of the following tests: UV, water exposure or immersion in accordance with UL 746C, where the acceptability for outdoor use is to be determined by UL.

Thermal-aging program

Most materials covered by this program have been investigated with respect to retention of certain critical properties including dielectric, tensile and impact as part of a longtime thermal-aging program conducted in accordance with UL 746B, Polymeric Materials, Long Term Property Evaluations.

The end-of-life of a material at each test temperature in this program is assumed to be the time when the value of the critical property had decreased to 50 percent of its original (as received) value. If a material has been investigated under the thermal-aging program, the relative temperature index (RTI), in degrees C, shown is based on a comparison with a material which has acceptable service experience and correlates numerically with the temperatures above in which the material is likely to degrade prematurely.

If a material has not been investigated under the thermal-aging program, the RTI shown is based on the generic class of the material. A tabulation of the temperature indices according to the generic material class is included in UL 746B and is based on the past field-test performance and chemical structure.

More than one RTI may be appropriate for a given material depending on the property requirements for a specific application. In certain cases, higher temperatures are permitted if so specified by the end-use product Standard.

Relative temperature index (RTI) is the maximum service temperature for a material where a class of critical property will not be unacceptably compromised through chemical thermal degradation. This spans over the reasonable life of an electrical product relative to a reference material having a confirmed, acceptable corresponding performance-defined RTI.

Electrical RTI is associated with critical electrical insulating properties.

Mechanical impact RTI is associated with critical impact resistance, resilience and flexibility properties.

Mechanical strength RTI ormechanical without impact is associated with critical mechanical strength where impact resistance, resilience and flexibility are not essential.

UL 746A Testing

UL 746A TESTING FOR ELECTRICAL PROPERTIES

The following tests determine the electrical properties of polymeric materials:

  • Dielectric breakdown voltage strength (DS)

  • Comparative tracking index (CTI)

  • High voltage tracking rate (HVTR)

  • High voltage, low current, dry arc resistance — D495

UL 746A resistance to ignition of polymeric materials

The following tests determine the resistance to ignition of polymeric materials:

  • Hot wire ignition (HWI)

  • High-current arc ignition (HAI)

  • High voltage arc resistance to ignition (HVTR)

  • Glow-wire ignitability test (GWIT, GWFI)


UL 746C

UL 746C, Polymeric Materials, Use in Electrical Equipment Evaluations revision modifications took effect on June 1, 2004. The following information summarizes the changes and provides additional guidance to help assist with product development.


To be continued.

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