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GB/T 40969-2021 PDF in English


GB/T 40969-2021 (GB/T40969-2021, GBT 40969-2021, GBT40969-2021)
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GB/T 40969-2021: PDF in English (GBT 40969-2021)

GB/T 40969-2021
GB
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 85.060
CCS Y 30
Paper and board - Determination of colour (D50/2° diffuse
reflectance method)
[ISO 5631-3: 2015, Paper and board - Determination of colour by diffuse reflectance -
Part 3: Indoor illumination conditions (D50/2°), MOD]
ISSUED ON: NOVEMBER 26, 2021
IMPLEMENTED ON: JUNE 1, 2022
Issued by: State Administration for Market Regulation;
Standardization Administration of PRC.
Table of Contents
Foreword ... 3
1 Scope ... 5
2 Normative references ... 5
3 Terms and definitions ... 6
4 Principles ... 7
5 Instruments ... 7
6 Sampling ... 9
7 Preparation of samples ... 9
8 Test steps ... 10
9 Result calculation ... 10
10 Expression of results ... 12
11 Test report ... 12
Appendix A (Normative) Spectral characteristics of reflectance photometers for
determining CIE tristimulus values ... 13
Paper and board - Determination of colour (D50/2° diffuse
reflectance method)
1 Scope
This document describes a method for determining the color of paper and cardboard by
the diffuse reflectance method with the elimination of gloss.
This document applies to paper and cardboard for printing.
When the amount of ultraviolet radiation irradiated by the light source of the instrument
on the sample is adjusted to be consistent with the fluorescence reference standard
under CIE illuminant C provided by the authorized laboratory specified in GB/T 40277,
this method can be used for the determination of the color of paper and cardboard that
contains fluorescent whitening.
This document does not apply to paper and cardboard to which fluorescent dyes or color
dyes have been added.
2 Normative references
The following documents contain the provisions which, through normative reference in
this document, constitute the essential provisions of this document. For the dated
referenced documents, only the versions with the indicated dates are applicable to this
document; for the undated referenced documents, only the latest version (including all
the amendments) is applicable to this document.
GB/T 450 Paper and board - Sampling for testing and identification of machine and
cross direction, wire side and felt side (GB/T 450-2008, ISO 186: 2002, MOD)
GB/T 3977 Specification of colors (GB/T 3977-2008, CIE 15: 2004, NEQ)
GB/T 10739 Paper, board and pulps - Standard atmosphere for conditioning and
testing (GB/T 10739-2002, ISO 187: 1990, EQV)
GB/T 40277 Paper, board and pulps - Measurement of diffuse blue reflectance factor
(ISO brightness) - Indoor daylight conditions (GB/T 40277-2021, ISO 2470-1: 2016,
MOD)
ISO 2469 Paper, board and pulps - Measurement of diffuse radiance factor (diffuse
reflectance factor)
of the sample.
Note: The reflectance factor of a transparent specimen depends on the backing, not material properties.
3.5 X, Y, Z tristimulus values
In a given trichromatic system, the amounts of three reference color stimuli that match
the color of the stimulus under study.
Note 1: In this document, the CIE illuminant D50 and CIE 1931 (2°) standard observer are used for
defining the trichromatic system.
Note 2: According to CIE convention, when the CIE 1931 (2°) standard observer is used, the obtained
tristimulus values have no subscript [when the CIE 1964 (10°) standard observer is used, the obtained
tristimulus values have the subscript 10].
3.6 CIELAB colour space
The approximately uniform three-dimensional colour space that is drawn by rectangular
coordinates, and the magnitudes of L*, a*, and b* are specified by the formulas given in
Chapter 9.
Note: The value of L* represents the measured brightness of the sample, L*=0 corresponds to the sample
that is black, and L*=100 corresponds to the sample that is a perfect diffuse reflection surface. The values
of a* and b* represent the red-green and yellow-blue directions on the coordinates, respectively. Thus,
+a* is a measure of the redness of the sample;
-a* is a measure of the greenness of the sample;
+b* is a measure of the yellowness of the sample;
-b* is a measure of the blueness of the sample.
If both a* and b* are 0, the sample is gray.
4 Principles
Under the specified ultraviolet irradiation conditions, a tristimulus filter-type reflection
photometer or an abridged spectrophotometer is used to analyze the reflected light on
the sample, and the color coordinates under the condition of D50/2° are calculated.
5 Instruments
5.1 Reflection photometer
5.1.1 General rules
The geometric, spectral, and photometric characteristics of the reflection photometer
shall comply with the provisions of ISO 2469, and it shall be calibrated according to
ISO 2469.
As described in GB/T 40277, when samples containing fluorescent brighteners are
tested, the reflectance photometer shall be equipped with a radiation source with
adjustable UV content. The UV conditions shall be adjusted to be consistent with the
CIE illuminant C with the use of a reference standard.
5.1.2 Filter-type reflectance photometer
For a filter-type reflectance photometer, the overall response given by the combination
of filters and the instrument’s optical characteristics is equivalent to the CIE tristimulus
values X, Y, and Z of the sample under the conditions of CIE illuminant D50 and CIE
1931 standard colorimetric system.
When a filter-type reflectance photometer is used, the UV content irradiated on the
sample shall be consistent with that of the CIE illuminant C.
5.1.3 Abridged spectrophotometer
When the samples are tested under CIE illuminant D50 with an abridged
spectrophotometer, one of the functions allows the CIE tristimulus values X, Y, and Z
of the tested sample under the conditions of CIE illuminant D50 and CIE 1931 standard
colorimetric system is calculated with the weighted coefficient. Appendix A gives the
weighting functions required for the calculations. Among them, Table A.1 and Table
A.2 are used for instruments without a bandpass correction function, and Table A.3 and
Table A.4 are used for instruments with a bandpass correction function.
When an abridged spectrophotometer is used, the instrument shall have a UV tunable
filter with a cut-off wavelength of 395 nm or other equivalent systems. The filter shall
be adjusted, or the system shall be calibrated with the fluorescence reference standard
(5.2.3), so that the UV content irradiated to the sample is consistent with that of the CIE
illuminant C.
5.2 Reference standard
5.2.1 General rules
A reference standard, which is applied for the instrument calibration and the working
standards, shall be used frequently to ensure that the requirements of the instrument and
UV calibration can be met.
5.2.2 Non-fluorescent reference standard
It is used for photometric calibration and shall be provided by an authorized laboratory
top and bottom of the stack to protect the samples. Avoid contamination and
unnecessary exposure to light or heat.
Make a mark on one corner of the sample to identify the sample and distinguish between
the top and wire sides.
If the top side can be distinguished from the wire side, the top side shall be facing up.
If the top and wire sides of the sample cannot be distinguished, such as paper produced
by a twin-wire paper machine or coated on both sides, it shall be ensured that the same
sides of paper samples are facing up, to ensure that each side of the paper and cardboard
can be measured separately.
8 Test steps
8.1 Ensure that the instrument is calibrated in accordance with the requirements of
GB/T 40277 and the instrument manufacturer’s instructions.
8.2 Remove the protective sheets on the top and bottom of the sample stack, do not
touch the test area with hands, and measure the CIE tristimulus value (or CIELAB value,
if the instrument is designed to report the colour space directly) of the first sample
according to the operating method of the instrument. Read and record the tristimulus
values, and the values shall be accurate to 0.01.
8.3 Remove the uppermost sample and place it under the sample stack to test the value
of the next sample. Test the remaining samples in the same way until at least 10 samples
have been tested. If necessary, repeat the above procedure to test the other sides of the
samples.
9 Result calculation
9.1 CIE tristimulus values
If the bandpass of the instrument is equal to or less than 5 nm, the CIE tristimulus value
is calculated according to GB/T 3977. In addition, the CIE tristimulus values are
calculated according to the corresponding weighting function given by ASTM E308. If
the CIE tristimulus value is not directly provided by the instrument, it can be calculated
according to the tables given in Appendix A.
9.2 CIELAB coordinates
Use the CIE tristimulus values X, Y, and Z to calculate the CIELAB coordinates
according to formula (1), formula (2), and formula (3) respectively:
where:
Xn, Yn, Zn are the tristimulus values of a perfect diffuse reflector at D50/2°. These
data are given in Appendix A as “White point” values.
If any of X/Xn, Y/Yn, Z/Zn is ≤ (24/116)3, it can be replaced by the following equation:
a) If (X/Xn) ≤ (24/116)3, then (X/Xn)1/3 in formula (2) is replaced by (814/108)
(X/Xn) + 16/116;
b) If (Y/Yn) ≤ (24/116)3, then (Y/Yn)1/3 in formula (1), formula (2), and formula (3)
is replaced by (814/108) (Y/Yn) + 16/116;
c) If (Z/Zn) ≤ (24/116)3, then (Z/Zn)1/3 in formula (3) is replaced by (814/108) (Z/Zn)
+ 16/116.
Note 1: (24/116)3 ≈ 0.008856.
Note 2: (814/108) ≈ 7.787.
Note 3: When (Y/Yn) ≤ (24/116)3, formula (1) is replaced by L* = 903.3(Y/Yn).
9.3 Dispersion of results
Since the three-dimensional statistical calculation is very complicated, the following
simple method is recommended to evaluate the color difference.
Calculate the mean < L*>, < a*>, and < b*> of the L*, a*, and b* values.
The deviation of each sample from the mean is calculated according to formula (4):
where:
ΔL*, Δa*, and Δb* --- The difference between the L*, a*, b* of the sample and the
corresponding mean < L*>, < a*>, < b*>.
Calculate the mean < ΔEab*> of the ΔEab* values to obtain the Mean of “Colors’
Differences from the Mean” (MCDM), which represents the dispersion of the color in
the CIELAB colour space, and is expressed by the spatial radius around the mean point.
Appendix A
(Normative)
Spectral characteristics of reflectance photometers for determining CIE
tristimulus values
A.1 Filter-type reflectance photometer
The spectral characteristics of a reflectance photometer consist of a light source, an
integrating sphere, glass optics, filters, and a photodetector. When evaluating the
sample with the CIE illuminant D50, it shall be ensured that filters are used in
conjunction with other optical characteristics of the instrument to give the overall
responses that are equivalent to the CIE tristimulus values X, Y, and Z of the CIE 1931
(2°) standard chromaticity system.
A.2 Abridged spectrophotometer
A.2.1 General rules
The measured tristimulus values are obtained by summing the products of the spectral
reflectance factors and the weighting functions specified in ASTM E308 for the
illuminant C and CIE 1931 (2°) observer.
The data for “checksum” and “white point” is given at the bottom of each column in
Table A.1, Table A.2, Table A.3, and Table A.4. The “checksum” is the algebraic sum
of the items. For convenience, it provides a check value to ensure that the table is copied
correctly if it needs to be copied. Due to rounding off, these checksums may not be
identical to the “white point” values below them. The values in each column of the table
have been rounded to three decimal places. When converting tristimulus values that are
calculated by using these tables to CIELAB or CIELUV coordinates, or for any other
purpose that requires the ratio of the sample tristimulus value to the “white point”, these
“white points”, rather than other data, shall be used as Xn, Yn, Zn.
When values at the top or bottom of the range are not available, the following
instructions given in ASTM E308 shall be followed.
The wavelength range is between 360 nm~780 nm. When β(λ) data are not available
over the entire wavelength range, all wavelengths for which data are not available are
weighted at the shortest or longest wavelength to make spectral data available, i.e.:
a) All wavelengths (360 nm, ...) for which test data are not available are weighted to
the next higher weight for which such data are available;
b) All wavelengths (…, 780 nm) for which test data are not available are weighted
to the next lower weight for which such data are available.
In the absence of fluorescence, the spectral radiance factor can be replaced by the
spectral reflectance factor, or referred to as the spectral reflectance factor R(λ).
A.2.2 Procedure for using data without bandpass correction
When the spectral data have not been corrected for bandpass correlation and not been
corrected for the case where the bandpass is approximately equal to the test interval,
Table A.1 and Table A.2 shall be used; when the test interval of the data is 10 nm, Table
A.1 shall be used; when the test interval of the data is 20 nm, Table A.2 shall be used.
Table A.1 and Table A.2 apply a correction for the spectral bandpass correlations that
are built into the calculation of tristimulus values.
A.2.3 Procedure for using data with bandpass correction
Tables A.3 and A.4 shall be used when the spectral data have been corrected for
bandpass correlation and corrected for the case where the bandpass is approximately
equal to the test interval (for example by the instrument manufacturer); when the test
interval of the data is of 10 nm, Table A.3 shall be used; when the test interval of the
data is 20 nm, Table A.4 shall be used.
Note 1: Table A.3 and Table A.4 have been attached to this document to allow for calculations by using
instruments that do not require bandpass correction, that is, have been built into the instrument and
applied to the reported raw data.
Note 2: Raw reflectance data will vary from instruments, which depends on whether they have built-in
bandpass correction. However, after proper use of the weighting table, the resulting chromaticity values
are nearly identical.
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Source: Above contents are excerpted from the PDF -- translated/reviewed by: www.chinesestandard.net / Wayne Zheng et al.