ANSI T 524 OM-2013 Color of paper and paperboard (45 0 C 2).pdf

1、 TAPPI/ANSI T 524 om-13 SUGGESTED METHOD 1972 OFFICIAL METHOD 1979 REVISED 1986 REVISED 1994 REVISED 2002 REVISED 2007 REVISED 2013 2013 TAPPI The information and data contained in this document were prepared by a technical committee of the Association. The committee and the Association assume no li

2、ability or responsibility in connection with the use of such information or data, including but not limited to any liability under patent, copyright, or trade secret laws. The user is responsible for determining that this document is the most recent edition published. Approved by the Standard Specif

3、ic Interest Group for this Test Method TAPPI CAUTION: This Test Method may include safety precautions which are believed to be appropriate at the time of publication of the method. The intent of these is to alert the user of the method to safety issues related to such use. The user is responsible fo

4、r determining that the safety precautions are complete and are appropriate to their use of the method, and for ensuring that suitable safety practices have not changed since publication of the method. This method may require the use, disposal, or both, of chemicals which may present serious health h

5、azards to humans. Procedures for the handling of such substances are set forth on Material Safety Data Sheets which must be developed by all manufacturers and importers of potentially hazardous chemicals and maintained by all distributors of potentially hazardous chemicals. Prior to the use of this

6、method, the user must determine whether any of the chemicals to be used or disposed of are potentially hazardous and, if so, must follow strictly the procedures specified by both the manufacturer, as well as local, state, and federal authorities for safe use and disposal of these chemicals. Color of

7、 paper and paperboard (45/0, C/2) 1. Scope1.1 This method specifies a procedure for measuring the color of paper or paperboard with tristimulus filter colorimeters or spectrophotometers incorporating directional (45/0) geometry and CIE (International Commission on Illumination) illuminant C. NOTE 1:

8、 TAPPI T 527 “Color of Paper and Paperboard (d/0, C/2)” describes a similar procedure using diffuse illumination and normal viewing. 1.2 In the method, tristimulus values X (red), Y (green), and Z (blue), appropriate to the CIE-1931 (2) standard observer, are calculated from reflectance measurements

9、 Rx, Ry, and Rz. or from R () data. Color can then be expressed in various color space systems: 1. Hunter L, a, b 2. CIE L*, a*, b* 3. L*, C*, h 4. Dominant wavelength, purity, luminosity 5. Color difference, E, E*, E*94, E (CMC) 1.3 Instruments equipped with microprocessors which give direct inform

10、ation relating to different color scale systems conform to this method only if the means of measurements and calculation conform to the descriptions herein. T 524 om-13 Color of paper and paperboard (45/0, C/2) / 2 2. Significance 2.1 The color appearance of paper and paperboard is important for its

11、 aesthetic value in marketing packaged products, as an aid to distribution of multi-ply forms, to differentiate pages or sections of published literature, in art work, and in many other applications. 2.2 A numerical definition of color is essential to good quality control and to customer-producer re

12、lationships. 3. Definitions 3.1 Dominant wavelength (of an illuminated object), the wavelength of spectrally pure energy which when mixed with the illuminant in suitable proportions will match the color of the specimen. 3.2 Purity, excitation, the ratio of the distance on a CIE chromaticity diagram

13、between the achromatic point and the specimen point to the distance along a straight line from the achromatic point through the specimen point to the illuminant spectrum locus. The term “saturation” is also applied to this quantity. 3.3 Luminosity, the scale of perception representing a colors simil

14、arity to achromatic colors between black and white. This quantity is also known as “luminance” and “luminous reflectance.” 3.4 L, a, b, L*, a*, b*, these symbols are used to designate color values as follows: L, L* represents lightness increasing from zero for black to 100 for perfect white; a, a* r

15、epresents redness when positive, greeness when negative; and b, b* represents yellowness when positive, blueness when negative. When a* and b* are simultaneously zero, they represent grey. 3.5 L*, C*, h, L* is as described in 3.4, C* represents chroma, and h represents hue angle. 3.6 E, E*, E (CMC),

16、 the overall color difference values take into account lightness/darkness differences as well as chromatic differences. The intent is for a given value of E, E*, E (CMC), to represent the same visual perception of color difference anywhere in color space. 4. Apparatus 4.1 Instrumental components1, c

17、onsisting of a means for fixing the location of the surface of the specimen, a system for proper illumination of the specimen, suitable filters, gratings, or other optical components for altering the spectral character of the rays reflected from the specimen, photosensitive receptors to receive the

18、reflected rays, and a means for transforming the receptor outputs to tristimulus functions. 4.2 Spectral characteristics 4.2.1 Incident light. The spectral power distribution of the light incident on the specimen determines the extent to which reflected light may be augmented by fluorescence. The pr

19、oduct of the spectral power distribution of the source and spectral transmittance of the glass lenses and infrared absorbing filter in the incident system should correspond to the energy distribution given as a function of wavelength in Table 1. This relative spectral power distribution may be appro

20、ximated by a select combination of a tungsten filament source, a heat absorbing filter, and UV trimming filter in the incident beam. If the paper or paperboard being measured by a spectrophotometer contains no fluorophores (fluorescent components, i.e., optical brightness), the spectral distribution

21、 of incident light will not affect the measurement of color, provided that sufficient energy is available at each wavelength of measurement. 4.2.2 Light energy. The light energy incident on the test specimen should not appreciably heat or fade the specimen during the measurement. An infrared absorbi

22、ng filter (heat filter) in the incident beam will normally prevent overheating the specimen. 1Names of suppliers of testing equipment and materials for this method may be found on the Test Equipment Suppliers list in the set of TAPPI Test Methods, or may be available from the TAPPI Quality and Stand

23、ards Department. 3 / Color of paper and paperboard (45/0, C/2) T 524 om-13 Table 1. Relative spectral energy distribution incident on the specimen Wavelength, nm Relative energy, E 320 0.1 340 2.4 360 7.9 380 14.3 400 22.0 420 30.9 440 43.6 460 58.9 480 78.3 500 100.0 520 121.8 540 144.7 560 169.7 5

24、80 188.4 600 200.8 620 204.6 640 199.8 660 187.3 680 169.2 700 144.4 Table 2. Tristimulus functions for CIE Illuminant C/2 Wavelength, nm Ecx Ecy Ecz 360 -0.001 -0.000 -0.006 380 -0.011 -0.000 -0.054 400 0.089 -0.001 0.393 420 2.919 0.085 14.033 440 7.649 0.511 38.518 460 6.641 1.382 38.120 480 2.36

25、4 3.206 19.564 500 0.069 6.910 5.752 520 1.198 12.876 1.442 540 5.591 18.258 0.357 560 11.750 19.588 0.073 580 16.794 15.991 0.026 600 17.896 10.696 0.013 620 14.018 6.261 0.003 640 7.457 2.902 0.000 660 2.746 1.008 0.000 680 0.712 0.257 0.000 700 0.153 0.055 0.000 720 0.034 0.012 0.000 740 0.007 0.

26、003 0.000 760 0.002 0.001 0.000 780 0.000 0.000 0.000 SUM 98.073 100.000 118.232 T 524 om-13 Color of paper and paperboard (45/0, C/2) / 4 4.2.3 Spectral response. The overall spectral response of the instrument, as determined by the combination of the spectral distribution of incident light on the

27、specimen, the absorption characteristics of the filters and other light altering optics, and the photosensitive response of the receptors to light reflected from the specimen, shall simulate the CIE color-matching functions weighted by the relative spectral energy distribution of CIE Illuminant C/2

28、given in Table 2. All color spectrophotometers conforming to this method, T 524, must use the integration tables contained in ASTM E308 (Table 5.6), “Standard Practice for Computing the Color of Object by Using the CIE System,” for the computation of tristimulus values X, Y, and Z. 4.3 Geometric cha

29、racteristics. The angle of viewing is required to be separated from the angle of illumination in such a manner that only rays reflected diffusely from the test specimen enter the receptor, thereby excluding specular reflectance from the reading. The illuminating beam shall be centered about an axis

30、of 45 0.5 from the normal to the specimen surface. The direction of viewing shall be perpendicular 0.5 to the specimen surface. The angle between the axis and any ray of either the illuminating or viewing beam shall not exceed 22.5. NOTE 2: Interchange of incident and viewing directions is allowed u

31、nder this method. 4.4 Photometric characteristics. The photometric system must be linear over the entire scale to within 0.2% of full scale. Photometric linearity may be determined by following the procedure described in TAPPI T 1217 “Photometric Linearity of Optical Properties Instruments.” The ins

32、trument must be sufficiently stable that the reflectance factor reading will not fluctuate by more than 0.1% of full-scale deflection while the measurement is being made. 5. Standards 5.1 Primary reflectance standard1. The primary reflectance standard (100%) is an ideal uniform diffuser with a perfe

33、ctly reflecting and diffusing surface (the perfect reflecting diffuser). 5.2 Calibration standards1. Reflectance values assigned to calibration standards shall be traceable to an instrument calibrated in terms of the primary reflectance standard and having geometric and spectral characteristics cons

34、istent with this method. 5.3 Specific calibration standards1. Specific calibration standards, colored similar to the paper to be tested, may be used to minimize the effect of spectral and geometric differences between instruments whose results are being compared. The “specific calibration” values fo

35、r these standards should be established by first exchanging paper samples of the type of paper to be compared. The paper sample and the ceramic standard must not form a metameric pair. 5.4 Black standard a black cavity with a reflectance factor which does not differ from its nominal value by more th

36、an 0.2 reflectance units at all wavelengths. 6. Calibration 6.1 Check the calibration of photometric scales at reasonable time intervals (at least monthly) in a manner to insure linearity and accuracy over all ranges. Accomplish calibration by placing a series of neutral filters of known transmittan

37、ce in the incident beam, or by measuring the reflectance factor of calibrated opaque specimens. NOTE 3: Reference (1) describes procedures for use of a set of special test panels in calibration of major photometric, spectral, and geometric characteristics of the instrument. 6.2 Photometric linearity

38、 and proper spectral response of the instrument are key factors for determining accurate color measurements. Colored standards should be carefully measured and their results intercompared to assure color measurement accuracy of the apparatus. NOTE 4: Clean ceramic or glass standards, if necessary, u

39、sing the procedures provided by the supplier of the standards. 6.3 Place the black standard against the specimen aperture and adjust the zero setting of the instrument. 6.4 Replace the black standard with a white calibration standard and set the instrument to the calibrated reflectance value of the

40、standard at each filter position or wavelength, as appropriate. 5 / Color of paper and paperboard (45/0, C/2) T 524 om-13 7. Test specimen From each test unit of the paper obtained in accordance with TAPPI T 400 “Sampling and Accepting a Single Lot of Paper, Paperboard, Containerboard, or Related Pr

41、oduct,” cut the sample to be tested into pieces large enough to extend at least 0.25 in. (6.35 mm) beyond all edges of the instrument aperture. Assemble the pieces into a pad which is thick enough so that doubling the pad thickness does not change the test readings. (With creped or other bulky paper

42、s care must be taken to avoid pillowing of the pad into the instrument by too much pressure.) Do not touch the test areas of the specimens with the fingers, and protect them from contamination, excessive heat, or intense light. 8. Procedure 8.1 Operate the instrument in accordance with the manufactu

43、rers instructions. Allow adequate warm-up time to ensure stable results. 8.2 Calibrate the instrument as described in Section 6. 8.3 Place the opaque pad of sample sheets with the side to be measured against the specimen aperture and with the machine direction parallel to the light beam, and obtain

44、the reflectance values Rx, Ry, and Rz and/or the reflectance spectra. 8.4 Move the uppermost test piece to the bottom of the pad and obtain the reflectances of the newly exposed specimen. Repeat this process until five specimens have been tested. NOTE 5: Some materials may yield a different result,

45、depending on whether the sample is illuminated from “upstream” or “downstream” with respect to the machine direction. In those cases tests should be made for both orientations and the results averaged. 8.5 Recheck the instrument calibration and retest the sample if any of the calibration reflectance

46、s show a drift greater than 0.1% full scale. 9. Calculations NOTE 6: The use of the three filter system may result in small to significant differences from the values obtained using the full function for the tristimulus value X depending upon the spectral characteristics of the sample (4). 9.1 Calcu

47、late the tristimulus values X, Y, and Z for each specimen from: X = 0.78341 Rx+ 0.19732 Rz Y = Ry Z = 1.18232 Rz or by using the integration tables in ASTM E308, “Standard Practice for Computing the Color of Object by Using the CIE System,” for a spectrophotometer. 9.2 Calculate color in one of the

48、following color space systems: (most instruments are equipped with microprocessors which do the necessary computational work). 9.2.1 Hunter L, a, b. Calculate Hunter color values from: L = 100 (Y/Y0)1/2 a = Ka(X/X0-Y/Y0)/(Y/Y0)1/2 b = Kb(Y/Y0-Z/Z0)/(Y/Y0)1/2 Constants for the above equations for ill

49、uminant C/2 are X0= 98.073, Y0= 100, Z0= 118.232, Ka= 175.0, and Kb= 70.0. If desired, calculate color difference from: E = (L2+ a2+ b2)1/2 T 524 om-13 Color of paper and paperboard (45/0, C/2) / 6 9.2.2 CIE L*, a*, b* (CIELAB). Calculate CIELAB color values from: (preferred) L* = 116 (Y/Y0)1/3 - 16 a* = 500 (X/X0)1/3- (Y/Y0)1/3 b* = 200 (Y/Y0)1/3- (Z/Z0)1/3 where: X/X0, Y/Y0, and Z/Z0 0.01. The constants X0, Y0, and Z0are given in paragraph 9.2.1. If desired, calculate color difference from: E* = (L*2+ a*2+ b*2)1/2 9.2.3 L*, C*, h. C