A rapid detection method for gel time of powder coatings based on near infrared spectroscopy

Abstract

The present invention discloses a rapid detection method for the gel time of powder coatings based on near infrared spectroscopy, comprising the following steps: S1, collecting the powder coating to be tested as the powder coating to be tested sample; S2, collecting the near infrared spectrum of the powder coating to be tested sample; S3, inputting the collected near infrared spectrum into the correlation model between the near infrared spectrum and the gel time, and outputting the gel time of the powder coating to be tested. Compared with the gel time instrument test method, the near infrared spectroscopy method provided by the present invention is faster and simpler to operate, green and environmentally friendly, and the gel time test process does not cause damage to the powder coating, providing rapid guidance for the product quality control of the film-forming material polyester resin and the powder coating production process.

Description

Technical Field

[0001] The invention belongs to the technical field of powder coating detection, and more specifically, the invention relates to a rapid detection method for the gel time of powder coating based on near infrared spectroscopy. Background Art

[0002] Powder coating is a solid powdered synthetic resin coating composed of solid resin as film-forming material, pigment, filler and additives. During the baking process, the resin is first melted and then solidified into a coating film after chemical cross-linking. The coating film has the functions of protecting the substrate and being beautiful. The use of powder coating conforms to the "Four E Principles" - Ecology, Excellent of finish, Economy and Energy. Over the past half century, with the rapid development of industries such as steel, petrochemicals, non-ferrous metals, equipment manufacturing and electronic information, especially the rapid development of the three largest consumer areas of the powder coating industry, automobiles, ships and equipment manufacturing, the supporting powder coating industry has also developed by leaps and bounds. At the same time, due to the increasingly stringent requirements for environmental protection, especially the restrictions on the use of volatile organic compounds (VOCs) by laws and regulations, the powder coating industry faces huge development opportunities.

[0003] The gel time test is the time required for a certain volume of powder coating to become an indeformable object after melting under specified conditions. Powder gel time is an important indicator of resin and powder coating. It is a simple method to express the characteristics and quality control of powder coating, and reflects the reactivity of the system. At present, the gel time test of powder coating mainly adopts the gel time instrument, and its operation steps are as follows: take 0.25mL sample on the automatic temperature control plate preheated to the specified temperature, in a concave cup shape, when all the cup-shaped materials melt, start timing, and use a very low hot melt pointed stirring needle to stir the melted material in a certain direction on the entire surface of the sample. When it starts to thicken, continue stirring, and use the stirring needle to raise the melted material by about 10mm every 2-3 seconds. When the formed filament becomes brittle, breaks or can no longer be pulled out of the melt, stop the stopwatch, and the recorded time is the gel time.

[0004] From the perspective of the gel time test process, the test is affected by many factors, such as temperature control, stirring speed and reaction speed of different testers, accuracy of stopwatch, etc. Especially for the gel time test of powder coatings with long or short gel time, the error will be greater. When testing the gel time of large batches of samples, it is impossible to feedback the test results in time. Summary of the invention

[0005] The invention provides a rapid detection method for the gel time of powder coatings based on near infrared spectroscopy, aiming to improve the above problems.

[0006] The present invention is implemented as follows: a rapid detection method for the gel time of powder coatings based on near infrared spectroscopy, the method specifically comprising the following steps:

[0007] S1. Collect the powder coating to be tested as the powder coating sample to be tested;

[0008] S2, collecting near infrared spectrum of the powder coating sample to be tested;

[0009] S3. Input the collected near infrared spectrum into the correlation model between the near infrared spectrum and the gelation time, and output the gelation time of the powder coating to be tested.

[0010] Furthermore, the method for constructing a correlation model between the near infrared spectrum and the gelation time is as follows:

[0011] S21. Collect different batches of powder coatings as powder coating standard samples, where the polyester resin model in the different batches of powder coatings is the same;

[0012] S22, testing the gelation time of each powder coating standard sample as the standard gelation time;

[0013] S23. Collect near infrared spectra of each powder coating standard sample:

[0014] S24, inputting the standard gelation time and near-infrared spectrum of each powder coating standard sample into the spectrum analysis software OPUS, and constructing a correlation model between the near-infrared spectrum and the gelation time.

[0015] Furthermore, the method for constructing a correlation model between the near-infrared spectrum and the gelation time based on the spectrum analysis software OPUS is as follows:

[0016] The near-infrared spectra and corresponding gelation times of all powder coating standard samples were imported into the spectral analysis software OPUS. Based on the optimization function, the correlation model between the near-infrared spectra and gelation time constructed by various methods in different bands was obtained. The multivariate scattering correction method with the smallest mean square error RMSECV was selected at 5450.1cm -1 ~4599.6cm -1 The correlation model 1 between the near-infrared spectrum constructed by the band and the gelation time was used to delete the singular points that deviated from the correlation model 1 based on the cross-check method. Based on the multivariate scattering correction method, the singular points at 5450.1cm -1 ~4599.6cm -1 The correlation model between the band-reconstructed near-infrared spectrum and the gelation time, as for the above method, the correlation model between the near-infrared spectrum and the gelation time is repeatedly corrected until the linear coefficient between the gelation time prediction value output by the correlation model between the near-infrared spectrum and the gelation time and the standard gelation time value reaches the set value.

[0017] Furthermore, the formula of the powder coating is as follows:

[0018] Polyester resin: 558g, TGIC: 42g, barium sulfate: 250g, titanium dioxide: 150g, leveling agent: 10g, benzoin: 3g, brightener: 3g.

[0019] Compared with the gel time instrument test method, the near-infrared spectroscopy method provided by the present invention is faster, simpler, greener and more environmentally friendly. The gel time test process does not damage the powder coating, and provides rapid guidance for product quality control of the film-forming material polyester resin and the powder coating production process. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 A flow chart of a method for rapid detection of gel time of powder coatings based on near infrared spectroscopy provided in an embodiment of the present invention;

[0021] Figure 2 A schematic diagram of a near infrared spectrum set of multiple powder coating standard samples provided by an embodiment of the present invention;

[0022] Figure 3 A schematic diagram of the relationship between the model prediction value and the test value of the gel time provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0023] The specific implementation modes of the present invention are further explained in detail below by describing the embodiments with reference to the accompanying drawings, so as to help those skilled in the art to have a more complete, accurate and in-depth understanding of the inventive concept and technical solution of the present invention.

[0024] Figure 1 A flow chart of a method for rapid detection of gel time of powder coatings based on near infrared spectroscopy provided in an embodiment of the present invention, the method specifically comprises the following steps:

[0025] S1. Collect different batches of powder coatings as powder coating standard samples, and the polyester resin model in the different batches of powder coatings is the same;

[0026] The powder coating was prepared according to the following formula: polyester resin: 558 g, TGIC (triglycidyl isocyanurate): 42 g, barium sulfate: 250 g, titanium dioxide: 150 g, leveling agent (GLP588): 10 g, benzoin: 3 g, brightener (701B): 3 g.

[0027] Place all raw materials in the same sample bag; shake the sample bag by hand, mix it preliminarily, and then pour it into the SLJ-40 extruder with the following parameters: zone I temperature: 100℃±5℃, zone II temperature: 110℃±5℃, frequency: 45 Hz, to obtain flake material; add the flake material into a coffee grinder, grind it into powder, and sieve it with a 180-mesh sieve to obtain a powder coating.

[0028] S2. Testing the gelling time of each standard sample of powder coating as the standard gelling time;

[0029] The gel time of all powder coating samples is tested according to the following requirements and is used as the standard gel time:

[0030] Take 0.25mL of the sample and place it on an automatic temperature control plate preheated to the specified temperature, in a concave cup shape. When all the cup-shaped materials are melted, start timing, and use a very low-melting pointed stirring needle to stir the melted material in a certain direction on the entire surface of the sample. When it starts to thicken, continue stirring, and at the same time, raise the melted material by about 10mm every 2-3 seconds through the stirring needle. When the formed wire becomes brittle, breaks, or can no longer be pulled out of the melt, stop the stopwatch, and the recorded time is the standard gelation time.

[0031] S3. Collect near infrared spectra of each powder coating standard sample:

[0032] All powder coating standard samples were placed in 2 cm diameter and 5 cm high vials, and spectral scanning was performed under the following near infrared conditions to obtain near infrared spectra of all powder coating standard samples. The near infrared spectra are shown in the attached figure. Figure 2 As shown:

[0033] Resolution: 4cm -1 ; Sample scanning time: 64 times; Background scanning time: 64 times; Scanning wave number range: 12800cm -1 ~4000cm -1 .

[0034] S4, inputting the standard gelation time and near infrared spectrum of each powder coating sample into the spectrum analysis software OPUS, and constructing a correlation model between the near infrared spectrum and the gelation time;

[0035] The near-infrared spectra and the corresponding gelation time of all powder coating samples were imported into the spectral analysis software OPUS. Based on the multivariate scattering correction method and the vector normalization method, the correlation model between the near-infrared spectra and the gelation time was constructed. The correlation model 1 with the smallest mean square error RMSECV was selected. It was obtained by multivariate scattering correction method at 5450.1 cm -1 ~4599.6cm -1The band was constructed by removing the singular points that deviated from the correlation model 1 based on the cross-validation method, and the multivariate scattering correction method was used at 5450.1cm -1 ~4599.6cm -1 The correlation model between the near-infrared spectrum and the gelation time reconstructed by the band, as for the above method, the correlation model between the near-infrared spectrum and the gelation time is repeatedly corrected until the linear coefficient between the predicted gelation time value output by the correlation model between the near-infrared spectrum and the gelation time and the standard gelation time value reaches the set value. Improve the prediction accuracy of the model. The parameters of the model finally selected are: cross-validation mean square error RMSECV = 0.423, dimension 9, and the relationship between the predicted value and the true value obtained by cross-validation is shown in the attached figure. Figure 3 , Figure 3 The predicted value in is the gelation time output by the correlation model between infrared spectrum and gelation time, the true value is the standard gelation time, and the linear coefficient is R 2 =0.9962, relative analytical difference RPD=16.3, offset=0.0127.

[0036] S5. Collect the powder coating to be tested as the powder coating sample to be tested, collect the near-infrared spectrum of the powder coating sample to be tested, input the near-infrared spectrum and the gelation time into the correlation model, and output the gelation time of the powder coating to be tested.

[0037] According to the spectrum test conditions of the powder coating standard sample, a near-infrared scan is performed on the powder coating sample to be tested to obtain a near-infrared spectrum of the powder coating to be tested. The formula of the powder coating standard sample is the same as the formula of the powder coating sample to be tested. The near-infrared spectrum of the powder coating sample to be tested is input into a correlation model between the near-infrared spectrum and the gelation time. The correlation model between the near-infrared spectrum and the gelation time automatically outputs the gelation time of the powder coating to be tested, and the gelation time is a predicted value.

[0038] Powder coating standard samples 1 to 10 are taken from 10 different batches of powder coatings. For these 10 powder coating samples, the gel time is obtained by using a gel time meter and the correlation model between the near infrared spectrum and the gel time provided by the present invention. The gel time is measured by the gel time meter (model GT-16) and the gel time is obtained by using the correlation model between the near infrared spectrum and the gel time. The gel time is called the model prediction value of the gel time. The model prediction value of the gel time in Table 1 is compared with the measured value of the gel time. The test error of the two is less than 5s. According to the requirements of the national standard GB / T 16995-1997, the difference between the two test results is less than 5% of the minimum value. It is roughly estimated that for a gel time of 300 seconds, a difference of 15s between the two test results is allowed, which can meet the requirement that the test error of the same sample is within 15s.

[0039]

[0040] Table 1 Comparison of the deviations between the model predicted values ​​and the measured values ​​of gelation time

[0041] At the same time, powder coating samples 11-1 to 11-6 are from the same batch of powder coatings. The gel time of these 6 powder coating samples is obtained by using the gel time meter and the correlation model between the near infrared spectrum and the gel time provided by the present invention. From the model prediction value of the gel time in Table 2 and the measured value of the gel time, the average values ​​of the gel time tests of the same powder sample are consistent, both of which are 300s. However, in terms of repeatability, the repeat deviation (0.17%) of the gel time of the powder coating predicted by the correlation model between the near infrared spectrum and the gel time is significantly lower than the repeat deviation (1.08%) of the gel time of the powder tested by the gel time meter. This shows that the repeatability of the prediction of the correlation model between the near infrared spectrum and the gel time is higher.

[0042] Powder coating sample number Measured value of gelation time / s Model predicted value of gel time / s 11-1 297 300 11-2 303 300 11-3 300 299 11-4 295 300 11-5 303 300 11-6 301 299 Average value / s 300 300 Relative standard deviation 1.08％ 0.17％

[0043] Table 2 Repeated comparison of measured values ​​of gelation time and model predicted values

[0044] The present invention is described above by way of example in conjunction with the accompanying drawings. It is obvious that the specific implementation of the present invention is not limited to the above-mentioned method. As long as various non-substantial improvements are made using the method concept and technical solution of the present invention, or the concept and technical solution of the present invention are directly applied to other occasions without improvement, they are all within the protection scope of the present invention.

Claims

1. A rapid detection method for the gel time of powder coatings based on near infrared spectroscopy, characterized in that: The method specifically comprises the following steps: S1. Collect the powder coating to be tested as the powder coating sample to be tested; S2, collecting near infrared spectrum of the powder coating sample to be tested; S3, inputting the collected near infrared spectrum into the correlation model between the near infrared spectrum and the gelation time, and outputting the gelation time of the powder coating to be tested; The formula of the powder coating is as follows: Polyester resin: 558g, TGIC: 42g, barium sulfate: 250g, titanium dioxide: 150g, leveling agent: 10g, benzoin: 3g, brightener: 3g; The method for constructing the correlation model between the near infrared spectrum and the gelation time is as follows: S21. Collect different batches of powder coatings as powder coating standard samples, where the polyester resin model in the different batches of powder coatings is the same; S22, using a gel time instrument to test the gel time of each powder coating standard sample as the standard gel time; S23. Collect near infrared spectra of each powder coating standard sample: S24, inputting the standard gelation time and near-infrared spectrum of each powder coating standard sample into the spectrum analysis software OPUS, and constructing a correlation model between the near-infrared spectrum and the gelation time.

2. The rapid detection method of gel time of powder coating based on near infrared spectroscopy as claimed in claim 1, characterized in that: The method for constructing the correlation model between the near-infrared spectrum and the gelation time based on the spectrum analysis software OPUS is as follows: The near-infrared spectra and corresponding gelation times of all powder coating standard samples were imported into the spectral analysis software OPUS. Based on the optimization function, the correlation model between the near-infrared spectra and gelation time constructed by various methods in different bands was obtained. The multivariate scattering correction method with the smallest mean square error RMSECV was selected at 5450.1cm -1 ~4599.6cm -1 The correlation model between the near-infrared spectrum and the gelation time constructed by the band was used to delete the singular points that deviated from the correlation model based on the cross-check method. The multivariate scattering correction method was used to correct the correlation between the near-infrared spectrum and the gelation time at 5450.1 cm -1 ~4599.6cm -1 The band-reconstructed correlation model between the near-infrared spectrum and the gelation time is repeatedly corrected by the above method until the linear coefficient between the predicted gelation time value output by the correlation model between the near-infrared spectrum and the gelation time and the standard gelation time value reaches the set value.

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