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Excerpt from above true-PDF:
GB 31604.7-2023
GB
NATIONAL STANDARD OF THE
PEOPLE'S REPUBLIC OF CHINA
National food safety standard - Food contact materials and
products - Decolorization test
ISSUED ON. SEPTEMBER 6, 2023
IMPLEMENTED ON. MARCH 6, 2024
Issued by. National Health Commission of the People's Republic of China;
State Administration for Market Regulation.
Table of Contents
Foreword... 3
1 Scope... 4
2 Principle... 4
3 Reagents and materials... 4
4 Instruments and equipment... 5
5 Analysis steps... 5
6 Result presentation... 8
Appendix A Examples of typical grey scale and 9-step chromatic transference
scale for assessing staining... 10
National food safety standard - Food contact materials and
products - Decolorization test
1 Scope
This standard specifies the test methods for discoloration of plastic materials and
products used in food contact.
This standard is applicable to the determination of soak solution coloring and wipe
decolorization of food-contact plastic materials and products with colorants.
2 Principle
The decolorization test is divided into two parts. soak solution coloring and wipe
decolorization. The soak solution coloring uses food simulants or chemical alternative
solvents obtained from the migration test. The grey scale or 9-step chromatic
transference scale for assessing staining is used to evaluate the grade of soak solution
coloring. For wipe decolorization, absorbent cotton moistened and saturated with food
simulants is used to wipe the food contact surface of the sample, and the coloring grade
of the absorbent cotton after wipe is evaluated by using the grey scale or 9-step
chromatic transference scale for assessing staining.
3 Reagents and materials
Unless otherwise stated, the reagents used in this method are of analytical grade and the
water is second-grade water specified in GB/T 6682.
3.1 Reagents
3.1.1 Glacial acetic acid (C2H4O2).
3.1.2 Absolute ethanol (C2H6O).
3.1.3 Isooctane (C8H18).
3.1.4 95% ethanol.
3.1.5 Vegetable oil (olive oil, corn oil). It shall comply with the requirements of GB
5009.156.
5.1.2 Blank test
Process food simulants or chemical alternative solvents that are not in contact with the
sample to be tested according to 5.1.1, and the soak solution obtained is the blank soak
solution.
5.1.3 Coloring grade assessment
Experimenters shall have no color vision impairment. If laboratory personnel wear
corrective glasses, their lenses must have uniform spectral transmittance throughout the
visible spectrum. If an experimenter performs continuous colorimetry, the person shall
rest for a few minutes at certain intervals to ensure the quality of visual colorimetry.
Take colorimetric tubes with stoppers, add 50 mL of the soak solution that has been
cooled to room temperature and the blank soak solution respectively, and place them
on the colorimetric tube rack in the color assessment booth. Place the colorimetric tube
rack and grey scale or 9-step chromatic transference scale for assessing staining on the
same plane in the color assessment booth, and the experimenter shall observe it in the
horizontal direction. Visually evaluate the grey scale or 9-step chromatic transference
scale grade to which the color difference between the soaking solution and the blank
soaking solution belongs. The corresponding number is the coloring grade of the soak
solution.
When there is a difference in the coloring grade of the soak solutions between two
parallel samples and it affects the presentation of the results of the decolorization test,
additional assessors need to participate in the evaluation. If it is determined that the
difference in the results of parallel samples is caused by the visual difference of the
assessors, there shall be at least three people who give a consistent grade before the
results can be reported. If it is determined that the difference in the results of parallel
samples is not caused by the visual difference of the assessors, the samples need to be
prepared again to evaluate the coloring grade of the migration test soak solution.
When comparing multiple batches of sample soak solutions at the same time, the soak
solutions that are prepared with the same food simulant and assessed as the same
coloring grade need to be compared together to ensure the accuracy of the assessment
of each batch of sample soak solutions. When the color difference between a certain
batch of sample soak solution and the blank soak solution is inconsistent with other
batches evaluated at the same time, the coloring grade of the soak solution shall be re-
evaluated.
5.2 Wipe decolorization
5.2.1 Sample preparation
The samples shall be pretreated in accordance with GB 5009.156, and 2 wipe
decolorization samples shall be prepared for each food simulant. Experimenters are
required to wear disposable nitrile gloves for the wipe test, and ensure that the nitrile
gloves worn do not discolor during the entire test process.
5.2.2 Preparation of food simulants for moistening absorbent cotton
The food simulant used for moistening absorbent cotton is selected according to the
total migration test provisions in the corresponding product standards, GB 31604.1, and
GB 5009.156.When vegetable oil is selected as the food simulant, liquid coconut oil is
used for the wipe test. If coconut oil solidifies, it can be melted by heating at a constant
temperature of 30 °C.
5.2.3 Preparation of absorbent cotton
Take absorbent cotton, cut it into a size of 2 cm×2 cm in an area of uniform thickness,
with a mass of 0.25 g~0.30 g, and completely wet it with the food simulant selected in
5.2.2.
5.2.4 Experimenter's practice and confirmation of wiping force value
Take a plate or sheet of the same material as the sample to be tested, and place it on an
electronic balance (or other equivalent device that can display the wiping force value);
the experimenter presses the moistened absorbent cotton with the pulp of two fingers
(index finger and middle finger) to wipe back and forth 100 times in an area of about 4
cm×2 cm at a speed of about 1 time/s (wipe the absorbent cotton back and forth for one
round in the direction of the sample test, counting as 1 time). When wiping, apply force
evenly along the test surface, and observe the mass display on the electronic balance
throughout the process to ensure that the mass display during the entire wiping process
is stable within the range of 1.0 kg±0.2 kg.
After three consecutive wiping exercises, if the mass display of the electronic balance
in the whole process of wiping is stable in the range of 1.0 kg±0.2 kg, it is indicated
that the wiping force value of the experimenter met the requirements.
5.2.5 Wipe decolorization test
Within an area of approximately 4 cm×2 cm on the food contact surface of the sample,
press the moistened absorbent cotton with the pulp of two fingers (index finger and
middle finger), and apply a wiping force that meets the requirements of 5.2.4 along the
sample surface to wipe back and forth 100 times at a speed of 1 time/s, to obtain
absorbent cotton after wiping. If an experimenter performs a continuous wipe
decolorization test, the person shall rest for a few minutes at certain intervals to ensure
the stability of the wiping force value.
5.2.6 Blank test
Use the sample of the same material that was confirmed not to be decolorized by wipe
decolorization test as the blank sample, and prepare blank absorbent cotton according
to 5.2.1~5.2.5.
5.2.7 Coloring grade assessment [Translator's note. here should be Wipe
decolorization grade assessment]
Place the wiping absorbent cotton, blank absorbent cotton, and grey scale or 9-step
chromatic transference scale for assessing staining on the same plane of the color
assessment booth. The incident light is at an angle of about 45° to the surface of the
absorbent cotton, and the observation direction is roughly perpendicular to the surface
of the absorbent cotton. Visually evaluate the grey scale or 9-step chromatic
transference scale grade to which the color difference between the absorbent cotton
after wiping and the blank absorbent cotton belongs. The corresponding number is the
wipe decolorization grade.
When there is a difference in the wipe decolorization grade of two parallel samples and
it affects the presentation of the results of the wipe decolorization test, more assessors
need to participate in the evaluation. If it is determined that the difference in the results
of parallel samples is caused by the visual difference of the assessors, there shall be at
least three people who give a consistent grade before the results can be reported. If it is
determined that the difference in the results of parallel samples is not caused by the
visual difference of the assessors, the samples need to be prepared again to assess the
grade of wipe decolorization.
When conducting wipe decolorization tests on multiple batches of samples at the same
time, it is necessary to compare the wiping absorbent cotton that is used for the same
food simulant and assessed as the same grade together to ensure the accuracy of the
wipe decolorization test assessment for each batch of samples. When the color
difference between the wiping absorbent cotton and the blank absorbent cotton of a
certain batch of samples is inconsistent with other batches of samples evaluated at the
same time, the wipe decolorization grade of this batch of samples shall be re-evaluated.
6 Result presentation
When the assessed grade of the soak solution coloring test result is grade 5, 4-5, or 4.5,
the soak solution coloring test result is represented as negative; when the assessed grade
of the soak solution coloring test result is grade 1~4, the soak solution coloring test
result is represented as positive.
When the assessed grade of the wipe decolorization test result is grade 5, 4-5, or 4.5,
the wipe decolorization test result is represented as negative; when the assessed grade
of the wipe decolorization test result is grade 1~4, the wipe decolorization test result is
represented as positive.
......