1、BRITISH STANDARD BS 4618-4.3: 1974 Recommendations for The presentation of plastics design data Part 4: Environmental and chemical effects Section 4.3: Resistance to colour change produced by exposure to light IMPORTANT NOTE. Before reading this Recommendation it is essential to read the General Int
2、roduction to this series of Recommendations, issued separately. UDC 001.8:678.5/.8:535.683.13BS4618-4.3:1974 BSI 11-1999 The following BSI references relate to work on these recommendations: Committee reference PLC/36/5 Draft for comment72/54279 ISBN 0 580 08353 5 A British Standard does not purport
3、 to include all the necessary provisions of a contract. Users of British Standards are responsible for their correct application. Compliance with a British Standard does not of itself confer immunity from legal obligations. Summary of pages This document comprises a front cover, an inside front cove
4、r, pagesi andii, pages1 to5 and a back cover. This standard has been updated (see copyright date) and may have had amendments incorporated. This will be indicated in the amendment table on the inside front cover. Amendments issued since publication Amd. No. Date CommentsBS4618-4.3:1974 BSI 11-1999 i
5、 Contents Page Introduction 1 1 Procedures 2 2 Form of presentation 2 Appendix A Methods of exposure 3 Appendix B Determination of degree of colour change 4 Figure 1 Example of rating system applied to different materials 4 Table 1 Exposure stages 4ii blankBS4618-4.3:1974 BSI 11-1999 1 Introduction
6、This Section deals with colour change on exposure to light; the effects of weathering influences such as wind and rain, are excluded, as are the effects of light exposure on properties other than colour. The data are intended to be applicable to plastics used in situations inside buildings where mat
7、erial can receive radiation from sun and from artificial illumination. Colour change in plastics materials is often a complex phenomenon, representing the net effect of different reactions proceeding simultaneously, or of changes in the various components of the material. Such changes may be either
8、in the lighter or darker direction and where two or more constituents are involved with changes proceeding at different rates both the rate and the direction of the overall colour change is likely to vary during the course of exposure. A full description of the colour change performance of a materia
9、l accordingly requires several observations taken after different exposure durations. From the designers point of view, the problem is to limit the colour change to an acceptable amount during the service life of the article concerned. The degree of change which can be accepted requires to be consid
10、ered in relation to each application. In some cases a fair amount of change may be permissible especially if the change is uniform all over and is only lightening or darkening but with the original hue preserved. At the other extreme, where components made from different materials have to maintain a
11、 colour match, it may be necessary to ensure no more than small colour changes in each of them. The procedure given in this Section uses simple visual comparisons with physical standards which are recognized both nationally and also internationally by the International Organization for Standardizati
12、on (ISO). These methods give results of sufficient accuracy for most industrial design applications. The use of instrumental methods for determining the amount of light exposure offers the prospect of greater accuracy, but at present there is no agreed procedure for overcoming the many problems invo
13、lved in their use. The physical standard for resistance to colour change is the blue wool scale 1)which comprises a set of seven dyed blue wool cloth patterns of different degrees of light fastness. No.1 fades the most rapidly and No.7 the least rapidly. In producing the scale the intention was that
14、 each higher number should take twice as long to fade as the one below, and this has been approximately achieved. The geometric grey scale 2)is used in conjunction with the blue wool standards to give a measure of the total light dosage received. The grey scale comprises pairs of grey patterns havin
15、g differing defined degrees of contrast from zero contrast at No.5 to maximum contrast between pale grey and dark grey for No.1. A given degree of light exposure can be obtained by exposing until a specified blue wool standard shows a change equivalent to a specified contrast as found by comparison
16、with the grey scale. For example, a change in blue wool standard7 equivalent to a contrast of4 on the grey scale represents about one years exposure to daylight in the UnitedKingdom. A desired amount of exposure can thus be specified as “blue wool standardX to grey scale contrast N” and can be obtai
17、ned by inspecting the blue wool standards frequently during the test so as to determine the time at which the contrast N on standard X is reached. By following this procedure, ratings for resistance to colour change can be obtained at several different known amounts of exposure. Specimens which are
18、more resistant than standard7 can be rated by an extension of the scale using successive exposures of standard7. For design purposes it is necessary to consider the grey scale rating at the exposure duration which will be important in practice. In making a test, the blue wool standards are exposed t
19、o light concurrently with the test specimens. When the required amount of exposure has been reached, the colour change in the test specimen is compared with the grey scale to determine which step of the scale corresponds most closely with the change in the test specimen. The number of this step then
20、 indicates the resistance to colour change of the specimen. 1) SeeBS1006 “Methods for the determination of colour fastness of textiles to light and weathering”, Test1 “Colour fastness to light: daylight” and ISO/R105/I “Tests for the colour fastness of textiles”. 2) SeeBS2662 “Grey scale for assessi
21、ng change in colour” andISO/R105/I “Tests for the colour fastness of textiles”.BS4618-4.3:1974 2 BSI 11-1999 It is quite practicable to equate the contrast between the grey patterns of the grey scale visually with changes of a different character in the test specimens. This is because the comparison
22、 is made solely on the basis of overall visual contrast between exposed and unexposed material without reference to the particular direction of the change. To supplement the numerical grey scale rating a description of the nature of the change is also given. The rating system given in this Section i
23、s particularly suitable for design data purposes, and differs from the widely used system (e.g.BS1006) in which the change in the specimen is compared directly with the changes in the blue wool standards, and the rating given is the number of the blue wool standard which shows a similar contrast bet
24、ween exposed and unexposed portions. A note on the latter system is included inAppendix B as it may be of importance in some design situations. The source of light used for testing is normally daylight with the specimens protected by window glass. The use of laboratory sources such as xenon or carbo
25、n arcs for accelerated testing is also included. Although it is considered that the colour change caused by exposure to daylight is of basic importance to a designer, data may be required for sources such as fluorescent lamps, commonly employed in buildings. The same methods of measuring amounts of
26、exposure and assessing resultant colour changes should be applied irrespective of the source of radiation employed during exposure. 1 Procedures Data should be obtained on the effects of exposure to light in accordance withAppendix A. NOTEIt should be noted, however, thatAppendix A does not necessar
27、ily give all the detail required for carrying out a test and reference should be made to the specific test method. The degree of colour change should be determined in accordance withAppendix B. 2 Form of presentation The results for colour change of a material should be presented in graphical form,
28、showing the grey scale rating plotted against the exposure stage. For each exposure stage, the duration of exposure to reach the stage may be given. The following information should also be given: 1) manufacturers description and identification of the material including the type common name (e.g.in
29、accordance with BS3502 3) ); 2) specimen thickness and method of preparation; 3) for daylight exposures: location of exposure site and month of year in which exposure commenced; 4) for other than daylight exposures: details of light source and exposure conditions; 5) any other relevant information i
30、ncluding nature of light used for inspection of sample; 6) date of publication. 3) BS3502 “Schedule of common names and abbreviations for plastics and rubbers”.BS4618-4.3:1974 BSI 11-1999 3 Appendix A Methods of exposure A.1 Daylight A.1.1 Apparatus. Test racks and fittings should be constructed of
31、materials which will not affect the materials under test in any way. The exposure case should consist essentially of an open-bottomed box covered with a framed lid of glass and containing a removable rack for carrying the test specimens and blue wool standards. The open bottom of the box should be c
32、overed with a wire-cloth screen with a mesh size of about0.16mm. The whole apparatus should be designed so as to provide adequate ventilation to avoid excessive build-up of heat. The rack should be designed to support the specimens at each end with at least50mm lengths of specimens being freely expo
33、sed. The lid should comprise a sheet of good quality window glass3mm thick, transmitting less than1% of normally-incident light at wavelengths less than300nm and approximately90% from370nm to380nm through the visible spectrum 4) . It should be spaced75mm from the rack to ensure adequate ventilation,
34、 and its unobstructed area should be greater than that of the rack to avoid shading. The exposure case should be sited so that the exposed surfaces of specimens are at an angle of45 to the horizontal, and facing due south. No obstruction in an easterly, southerly or westerly direction should subtend
35、 a vertical angle greater than20 at the centre of the case, nor should any in a northerly direction subtend a vertical angle greater than70 at the centre of the case. These conditions apply to the northern hemisphere and should be modified appropriately for locations in the southern hemisphere. NOTE
36、Further details on daylight exposure are given in ISO/R877 “Plastics. Determination of resistance of plastics to colour change upon exposure to daylight” (currently under revision). A.1.2 Test specimens and blue wool standards. The specimens should be in the form of strips about20mm wide. They shoul
37、d be mounted on the racks with a space of about6mm between adjacent specimens using for example a clamping device of an inert material. One strip of each blue wool standard from3 to7 is mounted in the same way. The portions of the specimens and blue wool standards at each end used for mounting may b
38、e screened from light by opaque closely-fitting covers. The specimens and standards are then exposed simultaneously for24hours per day. Comparison specimens and blue wool standards should be retained and stored in the dark. When the specimens are removed for inspection, they may, if necessary, be wa
39、shed free of surface dirt with soap and clean water, using a minimum of abrasion, then allowed to dry, before being rated for colour change in accordance withAppendix B. A.2 Interior lighting Data may also be obtained using artificial light sources employed in buildings, for example fluorescent tube
40、s. The exposure conditions should be chosen to correspond to the application concerned. The principal parameters of importance are: 1) intensity of illumination (or power of source and distance from specimen); 2) temperature of specimen (and relative humidity if moisture-sensitive); 3) durations of
41、illumination (if not continuous). Where applicable, the provisions ofA.1.2.should be followed. A.3 Accelerated testing with laboratory light sources The principal laboratory light sources used are: 1) xenon arcs; 2) carbon arcs; 3) special fluorescent tubes. Where applicable, the provisions ofA.1.2
42、should be followed. Mercury vapour discharge lamps do not simulate daylight and should not be used unless justified by special circumstances. In no case should the specimen be exposed to appreciable amounts of radiation of wavelengths significantly shorter than those occurring in daylight (i.e.not s
43、horter than300nm). Suitable filters should be used where appropriate. NOTEFurther details on exposure to xenon arcs and carbon arcs are given inISO/R879 “Plastics. Determination of resistance of plastics to colour change upon exposure to light of a xenon lamp” andISO/R878 “Plastics. Determination of
44、 resistance of plastics to colour change upon exposure to light of the enclosed carbon arc”. (Both documents are currently under revision.) 4) This transmission is typical of3mm window glass.BS4618-4.3:1974 4 BSI 11-1999 Appendix B Determination of degree of colour change The blue wool standards are
45、 inspected frequently during exposure until the first stage of exposure inTable 1 is reached (standard3 faded to a contrast of4 on the grey scale with the unexposed comparison standard). The specimens are then inspected and the contrasts between the50mm exposed portions of the specimens and the unex
46、posed comparison specimens are determined by means of the grey scale. It is often convenient to use the contrast between the freely exposed and covered portions of the test specimens and blue standards for checking the progress of exposure, but the data reported should always be based on the contras
47、t with the unexposed comparison specimens and blue standards. If the specimen shows a change approximately half-way between two standards, an appropriate half rating should be given. For example, a ratingGS3-4 means that, at the stated exposure stage, the contrast between exposed and unexposed porti
48、ons of the specimen is greater than grey scale4 but less than grey scale3. Exposure is then continued as before until the second stage of exposure inTable 1 is reached(4/1) and the specimens again rated in the same way. The procedure is repeated for stages5/1,6/1 and7/1. After this, all the exposed
49、blue standards are removed and disposed of. A fresh blue standard7 is mounted as before, denoted standard7/2, and exposure continued until it shows a contrast equal to grey scale4. This is stage7/2, and the contrasts between exposed and unexposed portions of the specimens are rated as before by means of the grey scale. Blue standard7/2, is then discarded and replaced by a fresh blue standard7, denoted7/3, and exposure continued until it shows a contrast equal to grey scale4. Rating of the specimens is then carried out as before. The procedure is repeated as often as r
