A method for testing the pollution resistance and aging resistance of melamine tableware

Abstract

The present invention discloses a method for testing the stain resistance and aging resistance of melamine tableware, comprising the following steps: S1. Cleaning and drying a sample, placing it in a room temperature dye solution, and soaking it for more than 10 minutes until the pH value after soaking stabilizes within a range of 6.6 to 7.0; S2. Removing the sample and drying it, placing it in a boiling dye solution, boiling it for 10 minutes, removing it, rinsing it, and then drying it; S3. Selecting the sample and placing it in a scanning electron microscope coupled with an energy dispersive spectrometer, with an accelerating voltage of 200 to 30,000 V and beam spot positions of spot 1 to spot 10, conduct elemental testing, and calculate the mass percentage M of methylene blue within the area and the mass percentage Ms of methylene blue per unit area within the area. The present invention quantifies the stain resistance results of melamine tableware, ensuring consistency in detection and judgment. It also tests the aging resistance of the melamine tableware and characterizes its durability.

Description

Technical Field

[0001] The invention relates to a method for detecting the pollution resistance and aging resistance of melamine tableware. Background Art

[0002] Melamine tableware, also known as imitation porcelain tableware, is a high-molecular polymer made from melamine-formaldehyde resin as a base material, melamine molding powder with σ-cellulose as a filler, pigments, and other additives. Melamine plastic tableware is produced through compression molding. Products include bowls, plates, cups, pots, spoons, chopsticks, trays, compartmentalized plates (dinner plates), fast food boxes, soup bowls, condiment dishes, and double-handled pots. Melamine plastic tableware is popular with consumers for its lightweight, aesthetically pleasing appearance, wide temperature tolerance, and resistance to breakage. It is particularly widely used in the fast food and children's catering industries.

[0003] Stain resistance is an important physical test item for melamine tableware. The test method is described in GB / T 41001-2021 "Melamine Plastic Tableware" as follows: "Add 0.01% rhodamine B to a container filled with pure or distilled water, place it on a heating device, and immerse the sample in boiling water for 10 minutes. After removing it, rinse it with running water and wipe it dry with filter paper. Compare and observe the containing surface (except the polished surface) with the untested sample. When the color of the tableware itself obscures the color of the dye, use a 0.01% methyl blue aqueous solution for the test." This is used to simulate and determine whether the sample is easily stained by colored foods in actual use, thereby affecting the quality.

[0004] However, in actual testing, this method has some shortcomings: (1) It cannot quantitatively determine the degree of pollution resistance, and can only qualitatively determine it by observing the severity of staining of the sample. Different people will give different quality judgments due to different standards, which will cause controversy; (2) Methyl blue is an acidic dye and also an acid-base indicator. If 0.01% methyl blue is added to the pure water or distilled water in the test system, the solution should theoretically be weakly acidic, but in actual experiments, the pure water or distilled water used may have a certain weak alkalinity, such as a pH value of 7.1. This weak alkalinity has little effect on other tests, but it will have a significant impact on the critical point of this test itself. When the temperature rises, the ion product of water increases, causing the pH value of the system to rise, which will neutralize the weak acidity of methyl blue and cause the system to be weakly alkaline. When the solution exceeds the pH value of methyl blue's color change range, the chromogenic group of methyl blue will not work, and the methyl blue aqueous solution will become lighter or even colorless, resulting in the inability to stain the sample.

[0005] Furthermore, the production of melamine tableware involves heating and pressurizing melamine powder and formaldehyde under high temperature to cure, followed by polishing to remove burrs. This process inevitably involves the adhesion of melamine raw material powder, polishing dust from melamine finished products, and other impurities (some unreacted melamine raw material powder or formaldehyde may also remain in the finished melamine product). These impurities may contain alkaline groups, making the solution alkaline, affecting the methyl blue and making the entire solution alkaline, making it impossible to dye the sample. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for detecting the stain resistance of melamine tableware, so as to solve the problems of the above-mentioned prior art such as the inability to quantify and easy misjudgment.

[0007] The technical solutions of the present invention are as follows:

[0008] A method for detecting the contamination resistance of melamine tableware according to the present invention is characterized in that it comprises the following steps:

[0009] S1. After cleaning the test sample with deionized water and drying it, place it in a room temperature dye solution and soak it for more than 10 minutes. Test the pH value of the soaking solution. If it exceeds 6.6-7.0, adjust the pH to within 6.6-7.0 with hydrochloric acid solution, HCl gas spray, or sodium hydroxide aqueous solution. Continue soaking for more than 10 minutes and then test the pH value again until the pH value stabilizes within 6.6-7.0. The purpose of pre-soaking is to use methyl blue aqueous solution to clean and neutralize impurities and alkaline groups attached to the sample and remaining in the sample, thereby reducing the impact on the stain resistance test.

[0010] S2. Take out the test sample and wipe it dry, place it in a boiling dyeing solution as soon as possible, soak it for 10 minutes, then take it out, rinse it with running deionized water, and wipe it dry;

[0011] S3. Select a suitable portion of the test sample as a specimen, cut it, and place it in a scanning electron microscope coupled with an energy dispersive spectrometer, with an accelerating voltage of 200 to 30,000 V, preferably 10 kV to 20 kV, and a beam spot position of spot 1 to spot 10, preferably spot 5 to spot 7; after amplifying the specimen, select a specimen area as S0; perform elemental testing on the selected area using the energy dispersive spectrometer to obtain the mass percentage content m1 of elemental sulfur (S), and calculate the mass percentage content M of methylene blue in the area and the mass percentage content Ms of methylene blue per unit area in the area; use Ms as a quantitative measure to determine the stain resistance of the specimen; the smaller the value of Ms, the better the stain resistance of the melamine tableware;

[0012] The calculation formula of the mass content M of the methylene blue is M=m1×799.80 / (32×3), where 799.80 is the molecular weight of methylene blue, 32 is the molecular weight of element S, and 3 means there are 3 sulfur atoms in the methylene blue molecule; the formula for the methylene blue content per unit area is Ms=M / S0;

[0013] The dyeing solution is prepared by adding 0.01% methyl blue by mass to a container filled with purified water or distilled water, mixing well, and adjusting the pH value to 6.6-7.0 using a hydrochloric acid solution or spraying HCl gas to obtain a dyeing solution. Preferably, the pH value of the dyeing solution is 6.8-6.9. Extensive experiments have shown that if the pH value is lower than 6.6, the H + If the concentration increases too much, the dyeing effect will be aggravated; if the pH value is higher than 7.0, the OH introduced into the sample during the boiling process will - It will neutralize the H + , making the pH value of the system higher than 7.0, causing the system to be alkaline, the methylene blue aqueous solution will fade, and the methylene blue molecules will not be adsorbed on the sample, resulting in the sample being unable to be stained.

[0014] Since melamine tableware's resistance to contamination decreases during use due to a decrease in surface quality, high-quality melamine tableware can maintain its contamination resistance for a longer period of time due to its superior materials, polymerization process, or surface treatment process. Therefore, the aging resistance of melamine tableware should also be considered as a component of the durability assessment of melamine tableware. Therefore, the present invention also provides a method for testing the aging resistance of melamine tableware, which is characterized by comprising the following steps:

[0015] D1. Place the melamine tableware sample in a constant temperature forced air oven at a temperature of 77°C ± 3°C, perform constant temperature thermal aging for a certain period of time (e.g., 24 hours), then take it out and cool it to room temperature; D2. Soak the sample in boiling water for a certain period of time (e.g., 30 minutes), take it out, wipe it dry, and cool it to room temperature; D3. Place the sample in a xenon arc lamp aging box and irradiate it with a xenon arc at a wavelength of 340nm for a certain period of time; this process is one aging cycle; D4. After performing multiple aging cycles (e.g., 10 times) on the sample as needed, test its pollution resistance according to the method of the present invention to obtain the methyl blue unit area content Ms, judge the degree of attenuation of the sample's pollution resistance, and thereby determine the aging resistance of the sample.

[0016] Preferably, the irradiation intensity of the xenon arc is (0.51±0.02) W / (m 2 ·nm), black mark temperature 50~80℃, preferably (65±3)℃.

[0017] Preferably, water spraying is performed for a certain period of time during the irradiation process, preferably, water spraying is performed for 18 minutes during every 102 minutes of xenon arc irradiation.

[0018] Because water, high temperature, and light significantly affect melamine aging during the simulated melamine sample washing process, xenon lamp aging and water spraying are used to simulate the hand washing or dishwasher cleaning process of melamine. The water spray volume is generally not required; it is sufficient to wet the sample, and the water volume has little effect on the test. For example, the Ci4000 xenon lamp aging chamber produced by Sweden's Atlas company has a spray flow rate of 36L / h. The constant temperature aging temperature of 77°C ± 3°C and the spraying conditions used in this invention are similar to the typical washing and drying times and environmental conditions of dishwashers, and are also the common conditions specified in GB / T 16422.2.

[0019] Compared with the prior art, the present invention has the following significant effects:

[0020] The present invention (1) ensures that the sample does not affect the acidity or alkalinity of the immersion liquid by pre-acidification and pre-immersion treatment, and ensures that the immersion liquid is not alkaline and does not discolor when boiled in water, thereby maintaining the dyeing ability. (2) The stain resistance results of melamine tableware are quantified, thereby maintaining the same evaluation results and ensuring the consistency of detection and judgment. (3) By combining the stain resistance detection method of the present invention with aging resistance, the aging resistance performance of melamine tableware can also be tested to characterize the durability of melamine tableware. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is the energy spectrum diagram of Example 1. DETAILED DESCRIPTION

[0022] The present invention will be described below in conjunction with specific embodiments, however, the scope of protection of the present invention is not limited to the following embodiments. After reading the contents of the present invention, those skilled in the art may make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the claims attached hereto.

[0023] Example 1

[0024] A method for detecting the stain resistance of melamine tableware comprises the following steps:

[0025] (1) Add 0.01% by mass of methyl blue to a container containing purified water or distilled water, mix well, add hydrochloric acid solution or spray HCl gas to prepare a dyeing solution; adjust the pH value of the dyeing solution to 6.8; then place the dyeing solution on a heating device and boil;

[0026] (2) After the test sample is cleaned with deionized water and wiped dry, it is placed in a dye solution at room temperature and soaked for 10 minutes. The pH value of the soaking solution is tested to be 7.2; if it exceeds 6.6-7.0, HCl gas is sprayed again to adjust the pH to 6.8, and the soaking is continued for 10 minutes. The pH value is then measured to be 6.9, and the system is stirred to accelerate the stabilization of the system;

[0027] (3) Take out the test sample, wipe it dry with filter paper, and place it in the dyeing solution boiled in step (1) as soon as possible. After boiling for 10 minutes, take it out, rinse it with running water, and wipe it dry with filter paper;

[0028] (4) Select a suitable part of the test sample as the specimen, cut it into suitable small pieces, and place it in a scanning electron microscope coupled with an energy dispersive spectrometer. The acceleration voltage is 10 kV, the beam spot is spot 6, the magnification is x500, and the working distance is 10 mm. After the specimen is magnified, the specimen area is selected to be S0 = 1.0 mm. 2 ; Use energy spectrometer to test the elements in the selected range, and the energy spectrum of element content is shown in Figure 1 The results are shown in Table 1, and the content of elemental sulfur (S) is m1 = 4.68wt%. The mass content M of methyl blue in the area is calculated by the formula M = m1 × 799.80 / (32 × 3), and the unit area content Ms of methyl blue in the area is calculated by the formula Ms = M / S0:

[0029]

[0030] That is, the mass content of methylene blue per square millimeter of the sample at this position is 39.0%. Ms is used to quantitatively determine the stain resistance of the sample. The smaller the value of Ms, the better the stain resistance of the melamine tableware. In order to reduce the test error, the methylene blue content per unit area Ms was tested at 5 different positions of the same sample, and the average methylene blue content per unit area of the sample was 39.4wt% / mm 2 , as shown in Table 2, this data is used to quantitatively characterize the contamination of the sample.

[0031] Table 1 Element contents measured by energy spectrometer at a certain sampling position of the sample in Example 1

[0032] element C N O Na S Total Content wt% 47.35 30.09 17.57 0.32 4.68 100.00

[0033] Table 2 The content and average content of methylene blue per unit area at different sampling locations of the sample

[0034]

[0035] Example 2

[0036] Steps (1) to (4) of Example 2 are the same as those of Example 1.

[0037] (5) Select a suitable part of the test sample as the specimen, cut it into suitable small pieces, and place it in a scanning electron microscope coupled with an energy dispersive spectrometer. The acceleration voltage is 15 kV, the beam spot is spot 7, the magnification is x1000, and the working distance is 10 mm. After the specimen is magnified, the specimen area is selected to be S0 = 1.0 mm. 2 ; Actual tests show that the smaller the beam spot size, the weaker the signal; the larger the size, the longer the dead time (dead time: the time required for the counting measurement system in the quantitative analysis of energy spectrum method to recover after processing a pulse signal to be able to process the next pulse signal, see GB / T for details) 17359-2012 "Quantitative Analysis by Microbeam Spectrometry"). Long peaks can be slow or even absent, leading to test failure. Low magnification can increase the test area and sampling coverage, improving data representativeness. However, due to the influence of the actual sample surface (such as curved surfaces and incomplete surfaces), too low a magnification can lead to poor accuracy. Larger magnifications reduce the test area, improving data stability but also reducing data representativeness. The working distance is the distance between the front edge of the objective lens and the focal point on the sample surface when the sample surface is in focus. Each instrument has its optimal working distance (the optimal distance for this instrument is 10 mm). Excessively large or small working distances will result in weak signals, affecting the energy spectrum test results. Changing the voltage also has a significant impact on the results. Methyl blue stains melamine samples only to a certain depth of the surface. High voltage allows for deeper surface testing, but too deep a depth will eliminate the methylene blue staining. Too high a voltage will result in more internal substrate samples that are not stained with methylene blue, affecting the data. However, too low a voltage reduces the depth, making it insufficient for comprehensive detection of sample staining. The element test was performed in the selected range using an energy spectrometer. The energy spectrum results of the element content are shown in Table 3, and the content of elemental sulfur (S) was m1 = 5.15 wt%. The mass content M of methyl blue in the area was calculated by the formula M = m1 × 799.80 / (32 × 3), and the unit area content of methyl blue Ms in the area was calculated by the formula Ms = M / S0:

[0038]

[0039] That is, the mass content of methylene blue per square millimeter of the sample at this position is 42.9%. Ms is used to quantitatively determine the pollution resistance of the sample. The smaller the value of Ms, the better the pollution resistance of the melamine tableware. In order to reduce the test error, 5 different positions of the same sample were selected to test the methylene blue content per unit area Ms, and the average content of methylene blue per unit area of the sample was 42.0wt% / mm 2 . As shown in Table 4.

[0040] Table 3 Element contents measured by energy spectrometer at a certain sampling position of the sample in Example 2

[0041] element C N O Na S Total Content wt% 47.89 30.06 16.84 0.07 5.15 100.00

[0042] Table 4 The content of methyl blue per unit area and the average content at different sampling locations of the sample

[0043]

[0044] Example 3

[0045] The method for testing the aging resistance of melamine tableware comprises the following steps:

[0046] D1. Place the melamine tableware sample in a constant temperature forced air oven at 77℃±3℃, heat age it at constant temperature for 24 hours, then remove it and cool it to room temperature; D2. Place the sample in boiling water and immerse it for 30 minutes, remove it and wipe it dry, and cool it to room temperature; D3. Place the sample in a xenon arc lamp aging box and irradiate it with a xenon arc at a wavelength of 340nm for 120 minutes. The irradiation intensity of the xenon arc is (0.51±0.02)W / (m 2 ·nm), the black mark temperature is 65°C; this process is one aging cycle; D4, after the sample is subjected to 10 aging cycles as needed, its pollution resistance is tested according to the method of Example 1, and the average value of the methyl blue unit area content Ms is 47.3wt% / mm 2 , it is judged that the anti-pollution ability of the test sample has decreased.

[0047] After a certain period of aging under simulated usage conditions, melamine tableware will have scratches and small cracks on the surface. Increase the amount of methyl blue dyeing and set it to 50.0wt% / mm 2 As the qualified value of aging pollution resistance, after 10 aging cycles, the methyl blue content per unit area of the sample is still less than 50.0wt% / mm 2 , it indicates that the sample has good resistance to aging pollution.

[0048] Example 4

[0049] The method for testing the aging resistance of melamine tableware comprises the following steps:

[0050] D1. Place the melamine tableware sample in a constant temperature forced air oven at 77℃±3℃, heat age it at constant temperature for 24 hours, then remove it and cool it to room temperature; D2. Place the sample in boiling water and immerse it for 30 minutes, remove it and wipe it dry, and cool it to room temperature; D3. Place the sample in a xenon arc lamp aging box and irradiate it with a xenon arc at a wavelength of 340nm. The irradiation intensity of the xenon arc is (0.51±0.02)W / (m 2·nm), the black mark temperature is 65°C, and after irradiation for 102 minutes, the xenon arc lamp is turned off and the deionized water provided by the xenon arc lamp aging box equipment is sprayed at a flow rate of 36L / h for a total of 18 minutes; this process is one aging cycle; D4, after 10 aging cycles of the sample as needed, its pollution resistance is tested according to the method of Example 1, and the average value of the methyl blue unit area content Ms is 51.7wt% / mm 2 . Set to 50.0wt% / mm 2 As the qualified value of aging pollution resistance, after 10 aging cycles, the methylene blue content per unit area of the sample is higher than 50.0wt% / mm 2 It is judged that the pollution resistance of the test sample has declined significantly, and its resistance to aging pollution is poor. After normal use, it is easy to be stained and the quality deteriorates.

[0051] Since the humid heat conditions of Example 4 are more conducive to the aging of the melamine sample, the presence of water molecules in a heated environment makes it easier for the melamine molecular chains to break down, and water molecules are more likely to enter the tiny cracks of the melamine product and remain, causing the cracks to enlarge, making the melamine more susceptible to aging, more easily stained during use, and having a reduced anti-fouling ability, and an increased content of methyl blue per unit area.

Claims

1. A method for detecting the pollution resistance of melamine tableware, characterized in that: The following steps are involved: S1. After cleaning the test sample with deionized water and drying it, place it in a dye solution at room temperature and soak it for more than 10 minutes. Test the pH value of the soaking solution. If it exceeds 6.6-7.0, adjust it to within 6.6-7.0, continue soaking for more than 10 minutes, and then test the pH value again until the pH value after soaking is stable within 6.6-7.

0. S2. Take out the test sample, wipe it dry, place it in a boiling dyeing solution, boil it for 10 minutes, take it out, rinse it with running deionized water, and wipe it dry; S3. Select a suitable area on the test sample as a specimen, cut it, and place it in a scanning electron microscope coupled with an energy dispersive spectrometer at an accelerating voltage of 200 to 30,000 V and a beam spot position of spot 1 to spot 10. After magnifying the specimen, select a specimen area as S0. Perform elemental analysis on the selected area using the energy dispersive spectrometer to obtain the mass percentage of elemental sulfur, m1, and calculate the mass percentage of methylene blue within the area, M, and the mass percentage of methylene blue per unit area, Ms. The stain resistance of the sample is quantitatively determined using Ms. The smaller the value of Ms, the better the stain resistance of the melamine tableware.

2. The method for detecting the stain resistance of melamine tableware according to claim 1, wherein: The calculation formula of the mass content M of the methyl blue is M=m1×799.80 / (32×3); the formula of the methyl blue content per unit area is Ms=M / S0.

3. The method for detecting the stain resistance of melamine tableware according to claim 1, wherein: The dyeing solution is prepared by adding 0.01% by mass of methyl blue into a container filled with purified water or distilled water, mixing the mixture evenly, and then adjusting the pH value to 6.6-7.0 using a hydrochloric acid solution or spraying HCl gas to obtain a dyeing solution.

4. A method for detecting the aging resistance of melamine tableware, characterized in that: The following steps are involved: D1. Place the melamine tableware sample in a constant temperature forced air oven at a temperature of 77℃±3℃, perform constant temperature thermal aging for 24 hours, then take it out and cool it to room temperature; D2. Place the sample in boiling water and immerse it for 30 minutes, take it out and wipe it dry, and cool it to room temperature; D3. Place the sample in a xenon arc lamp aging box and irradiate it with a xenon arc at a wavelength of 340nm for 102 minutes or 120 minutes; this process is one aging cycle; D4. After performing multiple aging cycles on the sample as needed, test its pollution resistance according to the method described in any one of claims 1 to 3, obtain the methyl blue unit area content Ms, judge the degree of attenuation of the sample's pollution resistance, and thereby determine the aging resistance of the sample.

5. The method for detecting the aging resistance of melamine tableware according to claim 4, characterized in that: The irradiation intensity of the xenon arc is (0.51±0.02) W / (m 2 nm), black mark temperature 50~80℃.

6. The method for detecting the aging resistance of melamine tableware according to claim 4, characterized in that: During the irradiation step D3, water spraying is added.

7. The method for detecting the aging resistance of melamine tableware according to claim 6, characterized in that: During the irradiation in step D3, 18 minutes of water spraying was added for every 102 minutes of xenon arc irradiation.

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