TEST PROCEDURE:

TESTING THE ABILITY OF PLASTIC MOULDINGS TO DISSIPATE ELECTROSTATIC CHARGE

PURPOSE:

To measure the ability of plastic moulded components treated with antistat agents to dissipate static electricity.

EQUIPMENT:

JCI 155v5 Charge Decay Test Unit

Sample Support fixture appropriate for samples to be tested

Software JCI-Graph 2.1 running on an IBM PC, Notebook or compatible

microcomputer with PCMCIA card reader

Test chamber in which humidity can be controlled to set levels

(for example JCI 191)

Temperature and humidity measuring instrumentation (included within JCI 191)

TEST SPECIMEN:

Preferably three samples or areas of each material are needed for testing. Areas need to be about 100x100mm. Ensure areas for test are free of dust and loose debris.

SUPPORT FIXTURE:

The support fixture holds test specimens on an earthed conducting surface in a defined position relative to the test aperture of the JCI 155v5. The fixture should allow new specimens to be easily mounted without scuffing or sliding of surfaces as such actions may easily tribocharge surfaces. A suitable support may be a cradle lined with aluminium foil. Different supports are likely to be needed for different shape and size specimens. The support must ensure that no part of the specimen will project into the test aperture in the instrument baseplate.

Note: 1) Measurements are not significantly affected by having the nearest surface of the specimen a few mm below the plane of the test aperture ? so a gap of a few mm will ensure safe test operation.

2) It is best for the central part of the area to be tested to lie directly under the centre of the test aperture, as this is the main area where charge will be deposited.

CONDITIONING:

Condition specimens for a minimum of 16 hours in a standard atmosphere of 20C and 50%RH and carry out tests within this atmosphere.

Note: 1) The charge decay characteristics of materials can easily be affected by surface contamination and moisture. It is therefore important to test samples and materials in the 'as received' condition without any handling, cleaning or removal of dust or dirt.

2) The areas to be tested should not be contacted by hand or by other surfaces and care should be taken not to blow or breath on the test surface.

3) For on-site measurements the temperature and humidity should be measured at the time of testing and comment made of any likely changes in the 24 hours preceding testing

4) For laboratory testing the samples or materials shall be exposed to constant standard conditions of temperature and humidity for at least 24 hours before testing with measurements carried out in these same environmental conditions. Thus 'laboratory testing' requires an environment whose temperature and humidity can be controlled for pre-conditioning and during tests. 'Standard conditions' are 23C 50%RH and 23C 12%RH - or an alternative low level humidity considered appropriate to the minimum level likely to arise in practical use.

PREPARATION:

  1. Switch-on the JCI 155v5 by pressing the power ON key.
  2. Check the instrument is set for negative corona with the corona voltage set to ?9000V and the 'charging duration' at 0.02s. Check a data memory card is present.
  3. Check there is an earth linking connection between the JCI 155v5 and the earthed support surface for the sample and of adequate length to allow easy removal of the JCI 155v5 for placement of samples
  4. Lift the JCI 155v5 off the sample support and carefully place the sample of its earthed conducting support surface. Avoid hand contact with any areas near the area to be tested. Avoid any surface rubbing actions.
  5. Ensure test set-up will remain steady and undisturbed throughout the test.
  6. Ensure that no part of the sample can rise to enter the test aperture during operation. If the sample is thin and flexible then ensure the material is lying stretched flat and without rucks.
  7. If any surface charge has built up on the sample during mounting let this decay until the 'present surface voltage' is less than +5V.

MEASUREMENTS:

  1. At least two measurements shall be made at different positions on each test sample. If the decay time is short then it will also be useful to retest at the same position to show consistency of results and lack of influence of the test on the sample surface.
  2. For all tests the initial surface voltage should be at a low level before starting - for example +5V.
  3. Measurements are to be made and recorded of the time from the initial peak voltage and both 1/e of this voltage and 10% of this voltage.

Note: The reason to measure the decay time to 10% is to take account of the fact that many materials and treatments show charge decay rates that slow up appreciably during the progress of charge decay.

4. Where there are differences in the surface form or treatment of a sample (for example, printing or different structural form) then it may be useful to test these different areas and record a relevant description.

5. Repeat steps 1 to 4 for each of the specimens.

Note: If a charge measuring sample support (for example JCI 176) is used with sheet or layer materials then measure the quantity of charge transferred to the test surface at each test. This measurement in conjunction with measurement of the initial peak voltage of the surface is used to calculate ?capacitance loading? values [2,3,4].

RESULTS:

For each test record the peak voltage, the decay time from initial peak voltage to 1/e of this and the time from initial peak voltage to 10% of this.

Calculate the mean decay times (peak voltage to 1/e and to 10%) and standard deviation where 3 or more measurements are made on a nominally identical sample.

TEST REPORT:

The following information shall be recorded:

a) date of measurements

b) description and identification of material and location of test area on sample

c) history of test sample

d) temperature and relative humidity

e) test conditions of corona charging voltage, duration, polarity and whether open or earthed backing

f) individual values of initial peak sample surface voltage and the times from initial peak voltage to 1/e and to 10% of this voltage with associated data file reference.

g) mean decay time values and assessment whether the sample passes or fails any specified acceptance criterion. (It is desirable to include graphs of variations of surface voltage and charge decay time constant during charge decay)

h) serial number of instrument used and date of most recent calibration

References:

[1] J. N. Chubb "Test method to assess the suitability of materials and surfaces to avoid problems from static electricity by measurement of the ability to dissipate corona charge" JCI Website: http://www.jci.co.uk/Measurements/ChargeDecay.pdf

[2] J. N. Chubb "Measurement of tribo and corona charging features of materials for assessment of risks from static electricity"; IEEE-IAS Meeting, Phoenix, Arizona, Oct 1999 To be published in Trans IEEE Ind Appl (This paper and copies of the overhead transparencies used are available on the JCI Website at http://www.jci.co.uk)

[3] J. N. Chubb "The assessment of materials by tribo and corona charging and charge decay" ?Electrostatics 1999? Conference, Cambridge, 29-31 March, 1999 Inst Phy Confr Series 163 p329

[4] J. N. Chubb "New approaches for testing materials" Proceedings ESA Annual meeting, Brock Univesity, Niagara Falls, June 18-21, 2000

[5] "Method for testing the eletcrostatic suitability of materials" Draft document going forward to be prepared for issue as a British Standard. March 2004.


| Home | News | Products | Specifications | Papers | Meetings | Contact JCI | Sitemap |

For best results view these pages with a Netscape Navigator browser.

John Chubb Instrumentation,
Unit 30, Lansdown Industrial Estate, Gloucester Road, Cheltenham, GL51 8PL, UK
Tel:+44 (0)1242 573347 Fax: +44 (0)1242 251388
email: jchubb@jci.co.uk

Latest site update: 09/08/2004. © John Chubb Instrumentation.