Testing coated fabrics
BS 3424-13:1999 pdf free.Testing coated fabrics 一 Part 13: Guide to the selection of methods for colour fastness to light testing.
Irradiance is defined as the amount of radiation energy incident upon a square metre of material. It is dependent Upon the spectrum of the emitted radiation, the intensity of the radiation, the distance of the test spednien front the energy source and the orientation of the test specinwn surface with respect to the incident energy.
The international colour committee, CIE, has compiled data which states that over the wavelength range 290 nni to 800 nni (UV, visible and IR radiation), an irradiance value of 550 W/m2 is recommended Whell simulating solar radiation. When considering in-adianee values caution is advised since it. is easy to be misled. The energy of a radiation source is inversely proportional to the wavelength of the radiation (UV radiation is more ‘energetic than IR radiation) so the swne intensity of ra(hation can give different irra(llanee values depending on the wavelength range over which the nwasuretnents are made.
The importance of repnxlucing sunlight has already been emphasized but it is worth reiterating.
A radiometer is a device for nwa.suring irradianre. In the context of the testing apparatus It Shotil(l be mounted in the same relative position as the test sPecimen and in the same orientation with respect to the light source. The radiation energy is not evenly distributed over the entire wavelength range. The xenon-arc lamp (when new) should conform to the spectral distriluition of LIV radiation specified in 13S 2782-5:Method 4OE:l995, 4.1.
NOTE I Although 11w Limps may 1w rnamafaetiired to confonu to BS2782-5:Me(hocl r,40E:lllWi, 4.1. there will be sign:fleant vañaton belwecn the pcctra1 distribiItionI4 of the lamps.
As.suniing that real life test experience has shown the need to mimic sunlight as closely as possible, the radiometer should measure over the wavelength range 290 nni to 800 nrn and its output should be used to automatically adjust the intensity of the lamp so that an irradianee of 554) W/m2 is applied constantly. The lamp burner should be discarded and replaced when iltis irradianue cannot be achieved.
NOTE 2 The olilpul of an adjw*ed binp will decri-a.’w in intensity over 1mw.
AST1l 1)3424 (lj intlicates that the average daily dose of radiation energy received in Miami and Arizona is 1 MJ/ni2 over the range 295 nm to 400 tim. An irnidlanee of 550 W/m2 over the waler range specified earlier is equivalent to 60 W/ni over this narrower range. Correspondingly in 1 h a radiation dose of 220 kJ/m2 will be emitted. Therefore the total daily Miami radiation dose will 1w received by the test specimen in less than 5 h. If it is also assumed that Miami sunshine is four to five times more severe than in Europe. then I h exposure at 550 W/m2 is equivalent to the average daily dose of radiation energy in typical European sunshine.
This is not a very accurate statistic and it should only be considered as a nile of thumb. More data needs to he collected either by individuals or by the textiles/plastics/rubber industries to relate exposure time in a laboratory test to real life exposure.
N( )TE 3 I W teating aiswg lamp apuons span the range 2911 nm to 400 nrn.
5 Humidity/temperature control It has already been stated that temperature is an important factor in any photochemical reaction that will occur within the test specimen. Humidity is also important, especially for the textile component of the test specimen. In each case, the critical area is at. the test specinwn itself. The temperature and humidity of the test specimen chamber influence (he test 1)111 any niea.surements should be focused at the surface of the test specimen.
Although the mercury vapour lamp light can be made to resemble that of daylight, the test. method which utilizes this light source, uS 1006:1990, Method UK-TN specilies quite simple apparatus.
nie account is made for humidity and temperature control bu not to a sufficient level for the nwthod to be regarded as a quantitative test. Indeed the method states that it is intended for use a.s a quality control test
It is recommended that a red azoic dyed cotton cloth is used to measure the “effective humidity, as defined in ISO 105-1102:1994, 4.1.3, and the apparatus adjusted accordingly.
There is also a limit a.s to how accurately the apparatus can control the humidity within the chamber. Utilizing electronic control systems awl sensitive water dispersal systems the relative humidity can be maintained at a given level within a +2 % range. Using less sophisticated control systems will broaden the range and increase the inaccuracy of the humidity level within the test chamber.
The instniment used to measure (he temperature of the test specimen is significant. Ideally, the temperature at the surface of the specimen would be measured (hrectly t)ut in reality the best that cait be achieved is to position a measurement device so that it is exposed to the light source in the sanw manner as the test specimen. Two types of thermometer are commonly used in light fastness equipment: a black-standard and a black-panel thermometer. Differences in design means that typically the black-panel temperature indicated is significantly less than the black-standard temperature. Black-standard devices approximate the temperature of (lark test specimens which have a low thermal conductmty. Since coated fabrics are poor conductors of heat, it is recommended that a black-standard thermometer is used. In order to make the temperature measurement more applicable to a range of coloured test specimens, a white-standard thermometer should also be used. Both the black-standard and white-standard thermometers are described in BS 2782-5:Method 540D.
The commonly used ASTM G26 [21 recommends a black-panel temperature of 63±3 °C. The in-use CXI)OSUC conditions, both in terms of humidity and temperature, will vary depending on the country of end-use. It is recommended that the exposure conditions specified in ISO 105-B02: 1994, clause 6 (see Table 1) are followed. This will enable normal and extreme European conditions to be recreated as well as facilitating meaningful comparisons with American test results.
6 Post exposure testing
In Wl(litiOII to Lssessing 11W (()lOLIr cliaiige of a test specimen material, it may be desirable to study the effects of light exposure on other properties such as surface texture or flexing resistance.
When conducting physical tests, test specimens may have to be reduced in size because of the geometne lintitat ions unpc)sc(l by the testing apparat LLS. This may mean that non-standard tests have to be carried out hut in such a situation it is not, definitive answers wiuch are important, rather the change In the relevant property. Therefore the physical test should be performed using smaller test specimens which have not been exposed to artificial light as well as specimens which have been exposed to the light source. iThe procedures in BS 2782-5:
Method 552k 1981, clause 4 and
BS 2782-5: Method 552A: 1981, 5.2 are recommended. It is reconunended (hat the operation of the light. fastness equipment is not changed in order to acconunodate test specimens, as this may introduce extra or unknown variables into the test.
It does not seem that post exposure testing is frequently carried out but if post exposure testing is of particular concern and larger test specimens must
be accommodated, fluorescent UV apparatus can be more versatile than typical xenon-arc machines. Alternatively, large scale xenon-arc mactunes are available but these are considerably more expensive.
7 Blue wool standards
Blue wool stan(lards are samples of wool which have been specifically dyed to give the fabric’s known light fa.stness In-operties. A nuige of eight grades are produced and are commonly used in the testing of textiles.
The principle of operation is that the blue wool standards are exposed to the artificial light source simultaneously with the test specimen. The change in colour of the test specimen is assessed visually using grey scales. When a certain level of colour change has been detected, the test specimen is visually compared to the blue wool stiul(lar(ls and the colour fastness of the test specimen is reported as being equal to one of the eight standards, There are some vanations in this technique which can be used but they are susceptible to the same inherent problems which are compounding the errors from two subjective and non-reproducible measurenwnt techniques. The method of using grey scales for visually assessing colour is well known and frequently used but does not give very repe’atable or reproducible results, particularly when the assessments are not performed by experienced personnel.BS 3424-13 pdf free download.Testing coated fabrics