Nuclear magnetic resonance method for continuously measuring curing degree of epoxy resin adhesive

Abstract

The invention discloses a nuclear magnetic resonance method for continuously measuring the curing degree of epoxy resin glue. The nuclear magnetic resonance method comprises the following steps: 1) placing an evenly mixed epoxy resin adhesive sample in a sample cavity of a nuclear magnetic resonance spectrometer; 2) adopting a spin echo pulse sequence to continuously collect echo signals; and 3) monitoring an echo signal attenuation curve to obtain the curing rate. According to the method, the curing dynamic data are provided through the curing rate curve (the initial stage, the middle stage and the later stage are divided), so that the curing inflection point (for example, the curing stage in the middle stage is 20-60 min in the embodiment) can be accurately identified, and technological parameter adjustment (such as temperature and time) is guided. Through the nuclear magnetic resonance technology, the problems of insufficient precision, destructive operation and complex data analysis of a traditional method are solved, and an efficient, reliable and low-cost solution is provided for research, development, production and quality control of epoxy resin glue.

Description

Technical Field

[0001] The present invention relates to a nuclear magnetic resonance method for continuously measuring the curing degree of epoxy resin glue, belonging to the field of material physical property characterization. Background Art

[0002] Epoxy resin is a kind of polymer with the molecular formula (C 11 H 12 O3)n, which refers to the general name of a class of polymers containing more than two epoxy groups in the molecule. It is a condensation product of epichlorohydrin and bisphenol A (C15H16O2) or polyol. Due to the chemical activity of the epoxy group, various compounds containing active hydrogen can react with it to open the ring, thereby curing and crosslinking to form a network structure. Therefore, it is a thermosetting polymer synthetic material. Epoxy resin adhesive generally refers to the adhesive prepared with epoxy resin as the main body. Epoxy resin adhesive generally also needs to add an epoxy resin curing agent to make it cure.

[0003] As a multi-functional adhesive, epoxy resin adhesive is widely used in many fields due to its excellent physical and mechanical properties, electrical insulation properties, chemical corrosion resistance and strong bonding ability. The curing degree of epoxy resin adhesive has an important impact on the properties of the material. By precisely controlling the curing degree, the reliability and safety of the product in different applications can be ensured. Currently, the methods for measuring the curing degree of epoxy resin adhesive mainly include: 1. Differential scanning calorimetry (DSC), which determines the curing degree by recording the heat change of the sample during heating. 2. Fourier transform infrared spectroscopy (FTIR), which determines the curing degree by recording the infrared spectrum change of the sample. 3. Nuclear magnetic resonance method (NMR), which determines the curing degree by measuring the crosslinking density of epoxy resin. Among them, DSC belongs to an indirect measurement method, which is not a non-destructive test, the amount of test sample is small, and the representativeness is not good enough; although FTIR can perform non-destructive testing on the sample and can provide information at the chemical bond level, for a complex system, the absorption peaks may overlap, so data analysis and processing will become very difficult and complex. And the method of measuring the crosslinking density of resin by NMR has the problem of poor accuracy, because the molecular mobility of epoxy resin decreases significantly after curing, which will cause a large amount of signals of crosslinked chains to be lost, resulting in distortion of the crosslinking density value measured by NMR.

[0004] Nuclear magnetic resonance (NMR) method is a commonly used tool for measuring the dynamic properties of molecules. By measuring the nuclear magnetic relaxation time of a sample, it can reflect the molecular mobility. The nuclear magnetic relaxation time is a measure of how quickly the atomic nucleus returns from the excited state to the equilibrium state, and it is divided into T1 time and T2 time. The smaller the molecular weight of the sample, the stronger the mobility, and the longer the relaxation time; conversely, the larger the molecular weight, the weaker the mobility, and the shorter the relaxation time. The length of the relaxation time has a significant impact on the signal acquisition of the instrument. For samples with a long relaxation time, the instrument can collect all the nuclear magnetic signals; for samples with a short relaxation time, the instrument can only collect partial signals because all nuclear magnetic instruments have a dead time during which no nuclear magnetic signals can be collected. When the relaxation time of the sample is less than the dead time of the instrument, the instrument cannot collect the nuclear magnetic signals of the sample. For epoxy resin glue, when it is uncured, the molecules have good mobility and the nuclear magnetic signals are easily collected. However, as a large number of molecules crosslink to form a solid, the nuclear magnetic relaxation time of the solid material becomes shorter and shorter, and most of the signals disappear before they can be collected. This is also the reason why it is not accurate enough to directly measure the crosslink density by NMR method.

[0005] In view of the above problems and the drawbacks of the prior art, the present invention aims to provide an accurate and simple nuclear magnetic resonance method that can be used to accurately and effectively measure and evaluate the curing degree of epoxy resin. Summary of the Invention

[0006] The object of the present invention is to provide a nuclear magnetic resonance method for continuously measuring the curing degree of epoxy resin glue, which has a large amount of test samples and good representativeness; it is a non-destructive testing method and does not affect the resin curing process; it avoids the distortion of crosslink density testing.

[0007] The principle of the method of the present invention is as follows: According to the nuclear magnetic decay characteristics of epoxy resin glue, a spin echo pulse sequence is selected to collect the signals of the sample, and the echo interval time TE is optimized so that the signals of liquid epoxy resin molecules can be completely collected, while the signals of the completely cured sample are completely attenuated. As the curing rate of the epoxy resin glue gradually increases, the nuclear magnetic signals detected by the instrument will gradually decrease. According to the size of the signals, the curing degree of the resin can be calculated, and the curing formula can be improved and studied based on the curing curve.

[0008] The nuclear magnetic resonance method for continuously measuring the curing degree of epoxy resin glue provided by the present invention includes the following steps: 1) Place the uniformly mixed epoxy resin glue sample in the sample chamber of the nuclear magnetic resonance instrument; 2) Continuously collect echo signals using a spin echo pulse sequence; 3) Monitor the echo signal attenuation curve to obtain the curing rate.

[0009] Preferably, the spin echo pulse sequence includes 90° pulses and 180° pulses, and the echo spacing time TE is set to 100 - 300 μs, preferably 200 μs.

[0010] Preferably, the nuclear magnetic resonance instrument is a low-field nuclear magnetic resonance instrument, and the magnetic field strength ranges from 0.1 to 0.5 T.

[0011] Preferably, the curing rate is obtained according to Equation (1): Curing rate = 1 - echo signal(n) / echo signal(1) (1) In the formula, echo signal(1) represents the echo signal when it is initially uncured, echo signal(n) represents the echo signal measured at the nth time, and n is an integer greater than or equal to 1 until the last stage (the curing rate is basically unchanged) of the glue curing for 1 hour.

[0012] Preferably, the time interval for continuous signal acquisition is 1 - 10 minutes.

[0013] Preferably, the curing stage of the epoxy resin glue is divided according to the curing rate curve; The curing stage includes the stages shown in the following a) - d): a) When the change amount of the curing rate is less than 3% and gradually increases, it is the initial stage. At this time, the glue viscosity is low, the curing speed is slow, and the curing curve shows a slow upward trend; b) When the change amount of the curing rate is greater than 3% and first increases and then decreases, it is the middle stage. At this time, the viscosity of the glue gradually increases, the curing speed gradually accelerates, and the curing curve shows a sharp upward trend; c) When the change amount of the curing rate is less than 3% and greater than 1% and gradually decreases, it is the later stage. At this time, the curing speed begins to slow down, and the curing curve shows a slow upward trend; d) When the change amount of the curing rate is less than 1% and there is no obvious change trend, it is the complete curing stage. At this time, after the glue is completely cured, the curing curve tends to be stable and there is no obvious change; The change amount of the curing rate refers to the difference in the curing rate between two adjacent test points.

[0014] Preferably, the initial stage is measured at an interval of 10 - 15 min, the middle stage is encrypted to an interval of 2 - 5 min for measurement, and the later stage is restored to an interval of 10 - 20 min for measurement.

[0015] By optimizing the spin echo pulse sequence, the present invention ensures that the signals of the uncured liquid resin are completely collected, and the signals are completely attenuated after complete curing, avoiding the problem of crosslinking density distortion caused by signal loss in the traditional NMR method, and significantly improving the accuracy of curing rate calculation.

[0016] The present invention uses a low-field nuclear magnetic resonance instrument to directly measure samples in situ without destroying the samples or interrupting the curing process, which is applicable to laboratory research and development and industrial on-line quality control, and avoids the problem of insufficient representativeness caused by small sampling amounts or destructive operations in the traditional DSC method.

[0017] The present invention allows the use of a completely mixed epoxy resin glue sample (such as a sample in a glass bottle) instead of micro-sampling, improving the representativeness and consistency of the test results, and is particularly suitable for quality control in batch production or complex formulations.

[0018] The present invention provides curing kinetics data through a curing rate curve (division of initial, intermediate, and late stages), enabling accurate identification of curing inflection points (such as the intermediate curing stage being 20 - 60 minutes in the examples), and guiding the adjustment of process parameters (such as temperature and time).

[0019] The present invention solves the problems of insufficient accuracy, destructive operation, and complex data analysis in traditional methods through nuclear magnetic resonance technology, providing an efficient, reliable, and low-cost solution for the research and development, production, and quality control of epoxy resin glue. Description of the Drawings

[0020] Figure 1 is the echo signal curve measured by the present invention.

[0021] Figure 2 is the curing rate curve measured by the present invention. Detailed Embodiments

[0022] The experimental methods used in the following examples are all conventional methods unless otherwise specified.

[0023] The materials, reagents, etc. used in the following examples can be obtained from commercial sources unless otherwise specified.

[0024] Epoxy resin glue formulation: The mass ratio of resin to curing agent is 3:1. After mixing the two components evenly, pour them quickly into a glass test bottle, and then transfer the test bottle to the sample chamber of a low-field nuclear magnetic resonance analyzer.

[0025] Use the low-field nuclear magnetic resonance analyzer LMR-Area (magnetic field strength range of 0.165T) of Beijing Lamore Technology Development Co., Ltd. to detect the sample, using a spin echo pulse sequence, which includes a 90-degree pulse and a 180-degree pulse, and the echo spacing TE is set to 200 μs. This TE can ensure the detection of all signals of uncured resin, and when the resin is completely cured, this TE can ensure the complete attenuation of the sample signal.

[0026] Test once every 5 minutes for 75 consecutive times. The interval time and the number of measurements are adjusted according to the curing speed of the specific epoxy resin adhesive. The test results of the test time and the echo signal magnitude are shown in Table 1 below: Table 1 Test Results of Echo Signal

[0027] Draw the attenuation curve of the echo signal magnitude and the curing rate curve, and calculate the change amount of the curing rate, as Figure 1 and Figure 2 shown.

[0028] Calculate the curing rate using the following formula: Curing rate (n) = 1 - Echo signal (n) / Echo signal (1) where Echo signal (1) represents the magnitude of the echo signal measured at the first moment, and Echo signal (n) represents the magnitude of the echo signal measured at the nth measurement.

[0029] Calculate the change amount of the curing rate using the following formula: Change amount of curing rate (n + 1) = Curing rate (n + 1) - Curing rate (n) where Curing rate (n + 1) represents the curing rate calculated at the (n + 1)th moment, and Curing rate (n) represents the curing rate calculated at the nth moment.

[0030] According to the curing rate and the change amount of the curing rate curve, it can be known that the initial curing stage of this epoxy resin adhesive is 0 - 20 minutes (the change amount of the curing rate is less than 3%), the middle curing stage is 20 minutes - 60 minutes (the change amount of the curing rate is greater than 3%), the late curing stage is 60 minutes - 90 minutes (the change amount of the curing rate is less than 3% and greater than 1%), and after 150 minutes is the complete curing stage (the change amount of the curing rate is less than 1%).

Claims

1. A nuclear magnetic resonance method for continuously measuring the curing degree of epoxy resin glue, comprising the following steps: 1) Place the uniformly mixed epoxy resin glue sample in the sample cavity of a nuclear magnetic resonance instrument; 2) Continuously collect echo signals using a spin echo pulse sequence; 3) Obtain the curing rate by monitoring the echo signal attenuation curve.

2. The nuclear magnetic resonance method according to claim 1, characterized in that: The spin echo pulse sequence includes 90° pulses and 180° pulses, and the echo spacing time TE is set to 100 - 300 μs.

3. The nuclear magnetic resonance method according to claim 1 or 2, characterized in that: The nuclear magnetic resonance instrument is a low-field nuclear magnetic resonance instrument, and the magnetic field strength range is 0.1 - 0.5 T.

4. The nuclear magnetic resonance method according to any one of claims 1 to 3, characterized in that: The curing rate is obtained according to Equation (1): Curing rate = 1 - echo signal(n) / echo signal(1) (1) In the formula, echo signal(1) represents the echo signal when initially uncured, and echo signal(n) represents the echo signal of the nth measurement.

5. The nuclear magnetic resonance method according to any one of claims 1-4, characterized in that: The time interval for continuous signal acquisition is 1 - 10 minutes.

6. The nuclear magnetic resonance method according to any one of claims 1-5, characterized in that: Divide the curing stage of the epoxy resin glue according to the curing rate curve.

7. The nuclear magnetic resonance method according to claim 6, wherein: The curing stage includes the stages shown in a) - d) below: a) When the change amount of the curing rate is less than 3% and gradually increases, it is the initial stage; b) When the change amount of the curing rate is greater than 3% and first increases and then decreases, it is the middle stage; c) When the change amount of the curing rate is less than 3% and greater than 1% and gradually decreases, it is the later stage; d) When the change amount of the curing rate is less than 1% and there is no obvious change trend, it is the fully cured stage; The change amount of the curing rate refers to the difference in the curing rate between two adjacent test points.

Images