A method for detecting adulterated substances in raw lacquer using infrared spectroscopy

Abstract

The present invention relates to the field of infrared spectroscopy technology, and provides a method for detecting adulterants in raw lacquer using infrared spectroscopy technology, which solves the problem that traditional raw lacquer identification methods mainly rely on empirical judgment, are highly subjective, have low accuracy, and are difficult to meet the needs of modern quality control and market supervision. The method comprises the following steps: (1) collecting the infrared spectrum of the raw lacquer; (2) determining the threshold; (3) preparing the adulterant; (4) generating a simulated doping spectrum; (5) determining the critical coefficient K; and (6) distinguishing the adulterated sample.

Description

Technical Field

[0001] The invention relates to the field of infrared spectroscopy technology, in particular to a method for detecting doping substances in raw lacquer using infrared spectroscopy technology. Background Art

[0002] Raw lacquer is a natural water-based latex paint. Its microstructure features a latex-like dispersion of varying-sized water droplets suspended in urushiol, a substance similar to vegetable oil. This is why it is often referred to as a "water-in-oil" latex paint. As a precious natural coating, raw lacquer holds a crucial position in traditional Chinese culture and craftsmanship. Its unique properties and artistic value make it indispensable in the production of traditional handicrafts. However, with growing market demand and rising prices, adulteration of raw lacquer in the market has become increasingly serious. This not only seriously impacts the quality and performance of raw lacquer but also threatens the preservation and development of traditional craftsmanship. Traditional methods for identifying raw lacquer rely primarily on empirical judgment, such as observing color, luster, morphology, and odor; measuring solids content, blending capacity, and drying speed; and observing paint film color, gloss, transparency, fullness, and adhesion. However, these methods have significant limitations: they are highly subjective, require extensive experience, and have low accuracy, making them difficult to meet the demands of modern quality control and market regulation.

[0003] Chinese patent publication number CN85109541B discloses a method and device for inspecting the quality of raw lacquer, which adopts an extraction separation method, uses glacial acetic acid (CH3COOH) as an extraction solvent to inspect the oil-soluble impurities in the raw lacquer, and uses xylene (C8H 10 ) solvent and distilled water are used as extraction solvents to detect insoluble and water-soluble impurities in raw lacquer. The testing device is a portable accessory suitable for field work. It includes a sampler, a specially graduated test tube, a raw lacquer drying tester, an ion water purifier, an extraction solvent, and other instruments. It allows for qualitative testing based on various raw lacquer indicators, and the process is simple. However, the testing method still requires visual observation, resulting in low accuracy. Summary of the Invention

[0004] Therefore, in response to the above problems, the present invention provides a method for detecting adulterated substances in raw lacquer using infrared spectroscopy technology, which solves the problem that traditional raw lacquer identification methods mainly rely on experience judgment, have strong subjectivity and low accuracy, and are difficult to meet modern quality control and market supervision needs.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for detecting doping substances in raw lacquer using infrared spectroscopy technology comprises the following steps:

[0007] S1. Collection of infrared spectra of raw lacquer: Raw lacquer samples from different production areas were collected. Each raw lacquer sample was collected three times in parallel using infrared spectroscopy under the same conditions to obtain three raw lacquer sample spectra. A raw lacquer quality control reference library was established, and the infrared spectral characteristic absorption peaks of the raw lacquer samples were analyzed.

[0008] S2. Determination of threshold value: Using the built-in statistical function of infrared spectrum analysis software, automatically calculate and generate the matching judgment threshold value of the self-built raw lacquer quality control reference library for raw lacquer quality control;

[0009] S3. Preparation of dopant: uniformly mixing the dopant with the raw lacquer in a ratio of 3% to 31% by mass of the raw lacquer to obtain a doped raw lacquer sample, collecting an infrared spectrum of the doped raw lacquer sample to obtain a spectrum of the doped raw lacquer sample, and analyzing characteristic absorption peaks of the infrared spectrum of the doped raw lacquer sample;

[0010] S4. Generation of simulated doping spectrum: define the raw lacquer sample spectrum as A, the raw lacquer doped sample spectrum as B, and the simulated doping spectrum as C. The calculation formula of C is shown in formula (1):

[0011] (1)

[0012] In the formula, the value range of K is 0.02-0.3. During the calculation, the value of K starts from 0.02 and increases by 0.01 each time;

[0013] S5, performing QC comparison on the simulated doping spectrum obtained in step S4 and the self-built raw lacquer quality control reference spectrum library to obtain the best match, and comparing the best match with a threshold;

[0014] S6. Observe the change of characteristic absorption peaks of the spectrum of the raw lacquer doped sample, and show a trend in the simulated doping spectrum as K increases;

[0015] S7. Determination of critical coefficient K: When the best matching degree is observed to be less than the threshold value and the characteristic absorption peak of the raw lacquer doped sample spectrum appears in the simulated doping spectrum as K increases, the critical coefficient K is recorded;

[0016] S8. Identification of adulterated samples: samples with the best match less than the threshold and the presence of characteristic absorption peaks of raw lacquer-doped samples are identified as adulterated; samples with the best match less than the threshold but no characteristic absorption peaks of raw lacquer-doped samples are identified as suspected adulteration; samples with the best match greater than the threshold and no characteristic absorption peaks of raw lacquer-doped samples are identified as unadulterated.

[0017] Furthermore, in step S3, the dopant is any one of raw tung oil, blending oil, urea, curing agent and diluent.

[0018] Furthermore, the infrared spectrum acquisition process is: directly dropping the raw lacquer sample onto the diamond crystal of the ATR accessory, turning on the test instrument, setting the test parameters, starting the test instrument, and obtaining the infrared spectrum of the sample.

[0019] Furthermore, the final formats of the raw lacquer sample spectrum, the raw lacquer doped sample spectrum and the simulated doped spectrum are all absorbance.

[0020] Furthermore, the curing agent is isocyanate.

[0021] Furthermore, the diluent is ethylene glycol dimethyl ether.

[0022] Furthermore, the testing instrument for collecting the infrared spectrum is a Fourier transform infrared spectrometer.

[0023] Furthermore, the test parameters are: setting the number of sample scans to 32 times and the resolution to 2.000 cm -1 , scanning range is 600-4000cm -1 .

[0024] By adopting the above technical solution, the beneficial effects of the present invention are:

[0025] Using infrared spectroscopy, a comprehensive system for identifying raw lacquer adulteration has been established. This systematic analysis of the infrared spectral characteristics of raw lacquer and its adulterants has led to the development of an objective and accurate method for evaluating raw lacquer quality. This technical solution not only helps regulate the raw lacquer market and protect consumer rights, but also provides strong technical support for the preservation and inheritance of traditional craftsmanship. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 This is the spectrum collected when the raw lacquer sample in Example 1 of the present invention is directly dropped onto the diamond crystal of the ATR accessory;

[0027] Figure 2 This is a spectrum collected by smearing the raw lacquer sample in Comparative Example 1 of the present invention on a potassium bromide salt tablet;

[0028] Figure 3 This is a spectrum collected by smearing the raw lacquer sample on a potassium bromide salt tablet after drying it at 105°C for 1 hour in Comparative Example 2 of the present invention;

[0029] Figure 4 The main spectrum and related absorption bands of the infrared spectrum of the raw lacquer sample in Example 1 of the present invention;

[0030] Figure 5 This is the infrared spectrum of the dopant in Example 1 of the present invention. DETAILED DESCRIPTION

[0031] Example 1

[0032] A method for detecting doping substances in raw lacquer using infrared spectroscopy technology comprises the following steps:

[0033] (1) Collection of infrared spectrum of raw lacquer

[0034] (1-1) Source of samples

[0035] 100g of raw lacquer samples were collected from 20 different origins, numbered 1#-20#, and sealed. The origins included Shaanxi, Chongqing, Guizhou, Sichuan, Yunnan, Shanxi, Henan, and Vietnam.

[0036] (1-2) Collection of infrared spectra

[0037] refer to Figure 1 The raw lacquer sample was directly dripped onto the diamond crystal of the ATR accessory. The Fourier transform infrared spectrometer (Nicolet iS50, Thermo Fisher Scientific, USA) was turned on. The test parameters were set and the test instrument was started. Each raw lacquer sample was measured three times to obtain a total of 60 raw lacquer sample spectra. A raw lacquer quality control reference library was established. The collected raw lacquer sample spectra were added to the self-built search library (sq-atr-s). The search library (sq-atr-s) was then used to search and compare the raw lacquer sample spectra one by one. The matching results were filled in Table 1.

[0038] Table 1. Comparative matching results of raw lacquer samples

[0039]

[0040] The search results show that each sample matched its own parallel sample best, with a matching degree greater than 99%. The lowest matching degree was 69.93% between samples 3# and 20#. Therefore, although all raw lacquer samples have similar characteristic peaks, there are some differences in peak height and peak shape between samples from different origins, which may be related to the differences in chemical composition and structure of raw lacquer from different origins.

[0041] The test parameters are: setting the number of sample scans to 32 times and the resolution to 2.000 cm -1 , scanning range is 600-4000cm -1 ; The ATR is attenuated total reflection; the Fourier transform infrared spectrometer comes with spectrum acquisition software OMNIC;

[0042] refer to Figure 4 The characteristic peaks of the infrared spectrum of raw lacquer are closely related to the molecular structure of its main component urushiol. The characteristic peaks of the infrared spectrum of raw lacquer mainly include: 3700–3150 cm -1Urushiol hydroxyl group (-OH) stretching vibration (intramolecular hydrogen bonding) and water OH stretching vibration; 3011 cm -1 =CH stretching vibration of urushiol side chain olefin; 2960–2850 cm -1 Saturated C-H bond stretching vibration; 1622 cm-1 C=C stretching vibration of urushiol side chain olefin; 1600–1500 cm -1 Benzene ring skeleton vibration (C=C symmetric / antisymmetric stretching); 1475 cm -1 Urushiol side chain methylene -CH2- stretching vibration (long chain characteristic); 1300–1220 cm -1 Phenolic hydroxyl group CO single bond stretching vibration. These characteristic peaks collectively characterize the chemical structure of urushiol (a derivative of catechol) and are key identification markers in the infrared spectroscopy analysis of raw lacquer. It is worth noting that when raw lacquer undergoes oxidation and deterioration, side chain alkenes are oxidized to form carbonyl compounds such as aldehydes and ketones, and C=O double bond stretching vibrations appear at 1740–1700 cm-1, with the intensity positively correlated with the degree of oxidation. These characteristic peaks collectively constitute the fingerprint identification region of raw lacquer infrared spectroscopy analysis, providing key molecular-level evidence for quality identification and oxidation state monitoring of raw lacquer.

[0043] The 20 collected raw lacquer sample spectra were classified using TQAnalyst9 spectral analysis software, and the results are shown in Table 2. Comparing the raw lacquer sample spectra, they can be roughly classified into four morphological spectrum types. Taking one sample from each category as the sample for subsequent spectrum calculation and sample doping experiments can greatly reduce the workload; 6# samples were taken from 11 Class I samples, 20# samples were taken from 3 Class II samples, 8# samples were taken from 4 Class III samples, and 18# samples were taken from 2 Class IV samples.

[0044] Table 2 Classification of raw lacquer samples

[0045]

[0046] (2) Determination of threshold

[0047] The built-in statistical function of infrared spectroscopy analysis software was used to automatically calculate the matching threshold for raw lacquer quality control using the self-built raw lacquer quality control reference library. The calculation results showed that the threshold was slightly greater than 95. This study ultimately determined that 95 was the threshold for suspected adulteration and was used to identify suspected adulteration in raw lacquer samples.

[0048] Wherein, the infrared spectrum analysis software is OMNIC spectrum analysis software;

[0049] (3) Preparation of dopants

[0050] The dopant is uniformly mixed with the raw lacquer at a ratio of raw tung oil to 9% of the mass of No. 6 raw lacquer to obtain a raw lacquer-doped sample, infrared spectrum acquisition is performed on the raw lacquer-doped sample to obtain a spectrum of the raw lacquer-doped sample, and characteristic absorption peaks of the infrared spectrum of the raw lacquer-doped sample are analyzed;

[0051] Among them, reference Figure 5 The infrared spectra of the adulterated substances showed obvious characteristic peaks independent of raw lacquer. The main characteristic peaks of raw tung oil and blending oil adulterated substances were located at 1742 cm -1 The characteristic peak of urea dopant is located at 3423 cm -1 The characteristic peak of isocyanate dopants is located at 2265 cm -1 The characteristic peak of ethylene glycol dimethyl ether dopant is located at 1037 cm -1 and 924cm -1 ,These characteristic peaks provide an important basis for doping identification;

[0052] (4) Generation of simulated doping spectra

[0053] The spectrum of the raw lacquer sample is defined as A, the spectrum of the raw lacquer doped sample is defined as B, and the simulated doped spectrum is defined as C. The calculation formula of C is shown in formula (1):

[0054] (1)

[0055] In the formula, the value of K starts from 0.02 and increases by 0.01 each time, and the maximum value does not exceed 0.3;

[0056] The final formats of the raw lacquer sample spectrum, the raw lacquer doped sample spectrum and the simulated doped spectrum are all absorbance;

[0057] (5) performing a QC comparison between the simulated doping spectrum obtained in step (4) and the self-built raw lacquer quality control reference spectrum library to obtain the best match, and comparing the obtained best match with the threshold value, that is, observing whether the best match is <95;

[0058] (6) Observe the changes in the characteristic absorption peaks of the raw lacquer doped sample spectrum, and as K increases, a trend is shown in the simulated doping spectrum;

[0059] (7) Determination of critical coefficient K

[0060] If the best match is less than the threshold value and the characteristic absorption peak of the raw lacquer adulterated sample spectrum appears in the simulated doping spectrum as K increases, record the K value corresponding to when both of the above conditions are met, that is, the best match falls below 95 for the first time and the characteristic peak of the adulterant is clearly visible. This K value is considered the minimum detectable ratio required to identify the specific adulterant, and the critical coefficient K is recorded;

[0061] Assuming that there is no reaction between the raw lacquer sample and the adulterant, and that their respective infrared absorption peaks do not shift or change, mathematical calculations can be performed using the raw lacquer sample spectrum and the adulterant spectrum to simulate infrared spectra of different adulterants and doping ratios. This can be used to evaluate the effect of the doping ratio on the matching degree and the minimum estimated doping concentration at which the adulterant will have its own independent characteristic absorption peak in the mixture spectrum.

[0062] Doping calculations were performed on samples 6#, 8#, 18#, and 20#, with K values ​​(K value represents the conversion coefficient of the infrared spectrum peak absorbance of the adulterant, indirectly reflecting the ratio of the adulterant to the raw lacquer) ranging from 0.02 to 0.3. The calculation results were fed into the sample QC library for comparison to observe the effect of K value on the matching degree and estimate the lower limit of the concentration of suspected adulterants. Given that the QC comparison matching degrees of the 20 raw lacquer samples with the sample QC library were all greater than 95, a matching degree of 95 was used as the boundary to investigate the possibility of lacquer sample adulteration;

[0063] Table 3 lists the approximate critical coefficient K values ​​when the matching degree is less than 95%. Alternatively, a K value between 0.02 and 0.3 is used for calculation, and the characteristic absorption peaks of visible impurities are observed and the peak positions are recorded. Table 4 lists the approximate critical coefficient K values ​​when the visible dopant absorption peaks are generated.

[0064] Table 3 (Raw Lacquer A + K × Adulterant B) Comparison of QC Comparison of Computed Spectra with a Matching Degree < 95% Critical K Value and Matching Degree

[0065]

[0066] Table 4 (Raw Lacquer Sample A + K × Adulterant B) Critical K value and peak position when characteristic absorption peaks of adulterants are visible in the calculated spectrum

[0067]

[0068] From the spectrum calculation results (Table 3, Table 4), we can see that:

[0069] Raw tung oil, blending oil, curing agent (isocyanate), and diluent (ethylene glycol dimethyl ether) have main absorption peaks that do not overlap with the raw lacquer absorption peak. When the K value is 0.02, the absorption peaks of the dopants can be seen. When the K value is 0.07, the matching degree drops below 95.

[0070] When the urea K value is 0.05, the absorption peak of the dopant is visible, and when the K value is 0.10, the matching degree drops below 95;

[0071] In summary, for the above five dopants, combined with the appearance of the characteristic peaks of the dopants and the condition that the matching degree is less than 95, the K value is between 0.07 and 0.10. Theoretically, based on this speculation, doping judgment can be made for doped raw lacquer with a doping amount greater than 10%.

[0072] (8) Identification of adulterated samples

[0073] If the best match degree is less than the threshold and the characteristic absorption peak of the raw lacquer-doped sample appears, it is judged as doped; if the best match degree is less than the threshold but the characteristic absorption peak of the raw lacquer-doped sample does not appear, it is judged as suspected doped; if the best match degree is greater than the threshold and the characteristic absorption peak of the raw lacquer-doped sample does not appear, it is judged as undoped.

[0074] Example 2

[0075] The difference from Example 1 is that in step (3), the blending oil and the raw lacquer are mixed uniformly in a ratio of 10% of the mass of the blending oil to the raw lacquer No. 6. The other technical solutions are the same as those in Example 1.

[0076] Example 3

[0077] The difference from Example 1 is that in step (3), urea and raw lacquer are mixed uniformly in a ratio of 9% of the mass of raw lacquer No. 6. The other technical solutions are the same as those in Example 1.

[0078] Example 4

[0079] The difference from Example 1 is that in step (3), the isocyanate curing agent is mixed evenly with the raw lacquer at a ratio of 3% of the mass of the raw lacquer No. 6. The other technical solutions are the same as those in Example 1.

[0080] Example 5

[0081] The difference from Example 1 is that in step (3), ethylene glycol dimethyl ether and raw lacquer are uniformly mixed in a ratio of ethylene glycol dimethyl ether to 10% of the mass of No. 6 raw lacquer. Other technical solutions are the same as those in Example 1.

[0082] Comparative Example 1

[0083] refer to Figure 2 The difference from Example 1 is that in step (1-2), the raw lacquer sample is smeared on a potassium bromide salt tablet instead of directly dropping the raw lacquer sample on the diamond crystal of the ATR accessory. The other technical solutions are the same as those in Example 1.

[0084] Comparative Example 2

[0085] refer to Figure 3 The difference from Example 1 is that in step (1-2), the raw lacquer sample is dried at 105°C for 1 hour and then smeared on a potassium bromide tablet, rather than directly dropping the raw lacquer sample onto the diamond crystal of the ATR accessory. The other technical solutions are the same as in Example 1.

[0086] Comparison of data collected using the three methods of Example 1, Comparative Example 1, and Comparative Example 2 revealed that the method of Example 1 had the worst repeatability. This is likely due to the uneven distribution of the raw lacquer on the potassium bromide salt tablets and the uneven application thickness, resulting in significant variations in the absorption peak intensities, hindering comparison in subsequent doping experiments. The method of Comparative Example 1 exhibited much better repeatability due to the removal of water and low-volatility components after drying the stock solution. However, this also removed a significant amount of information from the infrared spectrum. The acquisition method of Comparative Example 2 offered the best stability. When testing liquid samples using the ATR (attenuated total reflectance) method, the depth of incidence remained relatively constant. The detection depth depends primarily on the refractive index of the ATR crystal, the sample, and the frequency of the incident light, resulting in good repeatability. Only a single drop of liquid was required to completely cover the crystal's sensing surface, eliminating the need for special sample preparation and enabling direct analysis of free-flowing liquids or highly viscous samples. Therefore, the method of directly applying the stock solution dropwise onto the ATR crystal was selected as the data collection method for all following experiments.

[0087] According to the critical coefficient K recorded in Example 1, Example 2, Example 3, Example 4, and Example 5, it can be known that:

[0088] (1) Since the main absorption peaks of raw tung oil, blending oil, curing agent (isocyanate), and diluent (ethylene glycol dimethyl ether) do not overlap with the absorption peak of raw lacquer, the absorption peaks of the dopants can be seen when the K value is 0.02, and the matching degree drops below 95 when the K value is 0.07;

[0089] (2) When the K value of urea is 0.05, the absorption peak of the dopant is visible. When the K value is 0.10, the matching degree drops below 95.

[0090] In summary, for the above five dopants, combined with the conditions of the appearance of the characteristic peak of the dopant and the matching degree lower than 95%, the K value is between 0.07 and 0.10.

[0091] The doping identification results of Example 1, Example 2, Example 3, Example 4, and Example 5 are shown in Table 5.

[0092] Table 5 QC comparison results of adulterated samples and adulteration discrimination

[0093]

[0094] The test data in Table 5 demonstrates high accuracy for identifying five common adulterants: raw tung oil, blended oil, urea, curing agent, and diluent. The accuracy reached 92% for adulteration ratios between 3% and 10%, and 96% for ratios between 26% and 33%. The sensitivity for adulteration identification for raw tung oil, blended oil, urea, curing agent (isocyanate), and diluent (ethylene glycol dimethyl ether) ranged from 3% to 10%. This identification method, capable of quickly and accurately identifying common adulterants in raw lacquer, is of great significance for regulating the raw lacquer market and protecting traditional craftsmanship.

[0095] Although the present invention has been particularly shown and described in conjunction with preferred embodiments, it will be understood by those skilled in the art that various changes in form and details may be made to the present invention without departing from the spirit and scope of the invention as defined in the appended claims, and all such changes are within the scope of protection of the present invention.

Claims

1. A method for detecting doping substances in raw lacquer using infrared spectroscopy, characterized in that: The following steps are involved: S1. Collection of infrared spectra of raw lacquer: Raw lacquer samples from different production areas were collected. Each raw lacquer sample was collected three times in parallel using infrared spectroscopy under the same conditions to obtain three raw lacquer sample spectra. A raw lacquer quality control reference library was established, and the infrared spectral characteristic absorption peaks of the raw lacquer samples were analyzed. S2. Determination of threshold value: Using the built-in statistical function of infrared spectrum analysis software, automatically calculate and generate the matching degree judgment threshold value of raw lacquer quality control reference library for raw lacquer quality control; S3. Preparation of a doping substance: uniformly mixing the doping substance with the raw lacquer in a ratio of 3% to 31% by mass of the raw lacquer to obtain a doped raw lacquer sample, collecting an infrared spectrum of the doped raw lacquer sample to obtain a spectrum of the doped raw lacquer sample, and analyzing characteristic absorption peaks of the infrared spectrum of the doped raw lacquer sample; S4. Generation of simulated doping spectrum: define the raw lacquer sample spectrum as A, the raw lacquer doped sample spectrum as B, and the simulated doping spectrum as C. The calculation formula of C is shown in formula (1): (1) In the formula, the value range of K is 0.02-0.

3. During the calculation, the value of K starts from 0.02 and increases by 0.01 each time; S5, performing a QC comparison between the simulated doping spectrum obtained in step S4 and a raw lacquer quality control reference spectrum library to obtain the best match, and comparing the best match with a threshold; S6. Observe the change of characteristic absorption peaks of the spectrum of the raw lacquer doped sample, and show a trend in the simulated doping spectrum as K increases; S7. Determination of critical coefficient K: When the best matching degree is observed to be less than the threshold value and the characteristic absorption peak of the raw lacquer doped sample spectrum appears in the simulated doping spectrum as K increases, the critical coefficient K is recorded; S8. Identification of adulterated samples: samples with the best matching degree less than the threshold value and the presence of characteristic absorption peaks of raw lacquer-doped samples are identified as adulterated; samples with the best matching degree less than the threshold value but no characteristic absorption peaks of raw lacquer-doped samples are identified as suspected adulteration; samples with the best matching degree greater than the threshold value and no characteristic absorption peaks of raw lacquer-doped samples are identified as unadulterated; Wherein, in step S3, the doping substance is any one of: raw tung oil, blending oil, urea, curing agent and diluent; The infrared spectrum acquisition process is as follows: directly dropping the raw lacquer sample onto the diamond crystal of the ATR accessory, turning on the test instrument, setting the test parameters, starting the test instrument, and obtaining the infrared spectrum of the sample.

2. The method for detecting doping substances in raw lacquer using infrared spectroscopy according to claim 1, characterized in that: The final formats of the raw lacquer sample spectrum, the raw lacquer doped sample spectrum and the simulated doped spectrum are all absorbance.

3. The method for detecting doping substances in raw lacquer using infrared spectroscopy according to claim 1, characterized in that: The curing agent is isocyanate.

4. The method for detecting dopants in raw lacquer using infrared spectroscopy according to claim 1, characterized in that: The diluent is ethylene glycol dimethyl ether.

5. The method for detecting doping substances in raw lacquer using infrared spectroscopy according to claim 1, characterized in that: The testing instrument for collecting the infrared spectrum is a Fourier transform infrared spectrometer.

6. The method for detecting doping substances in raw lacquer using infrared spectroscopy according to claim 1, characterized in that: The test parameters are: set the sample scanning times to 32 times, the resolution to 2.000cm -1 , scanning range is 600-4000cm -1 .

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