A rapid method for detecting the storage stability of adhesives based on DSC thermal behavior characteristics

Abstract

This invention discloses a rapid detection method for the storage stability of UV adhesives based on DSC thermal behavior characteristics, belonging to the field of adhesive quality testing technology. Addressing the shortcomings of existing detection methods, such as long processing times, qualitative judgment only, and inability to accurately quantitatively assess the degree of deterioration, this invention constructs a three-dimensional correlation principle of "polymerization reaction initiation temperature - enthalpy change rate - prepolymerization degree," and uses differential scanning calorimetry to obtain the baseline initial reaction temperature T of fresh samples. Onset,0 Reference peak reaction temperature T Peak,0 The reference exothermic enthalpy ΔH0 and the corresponding parameter T of the sample to be tested. Onset,x T Peak,x ΔH x The invention calculates the relative temperature deviation and the relative enthalpy deviation, and takes the maximum value of the two temperature deviations as ΔT; it achieves rapid determination of sample state based on a set threshold. This invention allows for a single test to take ≤1 hour, improving efficiency by approximately 12 times. It can accurately distinguish between chemical prepolymerization and physical deterioration, and is suitable for customer return analysis, production process control, and batch quality traceability. It has the advantages of being fast, accurate, and easy to implement.

Description

Technical Field

[0001] This invention relates to the field of UV adhesive quality testing technology, specifically to a method for rapidly determining the stability of adhesives after storage / exposure using differential scanning calorimetry (DSC) parameters such as initial reaction temperature, peak reaction temperature, and exothermic enthalpy. This method is applicable to batch quality traceability of adhesives, analysis of customer return adhesive failures, and production process control. Background Technology

[0002] UV adhesives (ultraviolet-cured adhesives) are prone to deterioration during storage, transportation, or exposure, including prepolymerization, component volatilization, and moisture absorption. These changes directly affect their cured adhesive performance and service life. Therefore, accurate and rapid assessment of the storage stability of UV adhesives is crucial for quality control, failure analysis, and production process management.

[0003] However, existing detection methods have significant drawbacks:

[0004] (1) Poor method adaptability: Traditional DSC methods for detecting curing degree are mainly for epoxy adhesives and do not fully consider the characteristics of UV adhesives. Although UV-DSC isothermal curing detection technology exists, it is mainly used to study curing behavior and has not established a correlation analysis with storage stability, so it cannot be directly used to assess the degree of deterioration of adhesives during storage.

[0005] (2) Long testing cycle, only qualitative judgment: At present, the industry generally uses accelerated aging combined with viscosity testing to evaluate storage stability. This method requires placing the sample in a high temperature and high humidity environment for several days to several weeks, and then measuring the viscosity change with a viscometer. The whole process takes more than 12 hours. Moreover, the viscosity change can only provide qualitative information on "whether it has changed", and cannot accurately quantify the degree of deterioration, let alone provide accurate shelf life data.

[0006] (3) Insufficient application depth of DSC: Conventional DSC testing only records a single thermal decomposition temperature or total exothermic enthalpy to determine the thermal stability of materials. Existing technologies have not established a correlation rule between DSC characteristic parameters and the degree of storage prepolymerization, and cannot accurately capture the law of advance / shift in polymerization reaction start temperature caused by prepolymerization, thus making it difficult to quantitatively determine the degree of deterioration.

[0007] (4) Lack of traceability: Existing methods do not systematically distinguish the characteristics of "deteriorated glue", "retained sample" and "fresh sample". When quality complaints occur, it is difficult to accurately trace the root cause of the quality problem - whether it is a fluctuation in raw material batches, improper control of the production process, or a problem in the storage and transportation process.

[0008] To address the aforementioned issues, there is an urgent need for a rapid detection method for the storage stability of adhesives based on multiple DSC parameters. This method should enable the determination of the degree of deterioration within one hour through characteristic deviation analysis, providing an efficient and accurate technical means for the quality control of UV adhesives. Summary of the Invention

[0009] The technical problem this invention aims to solve is to overcome the shortcomings of existing adhesive stability testing methods, such as long testing cycles, qualitative judgment only, and inability to accurately and quantitatively assess the degree of deterioration. This invention provides a method based on DSC thermal behavior characteristics (initial reaction temperature T). Onset Peak reaction temperature T Peak A rapid detection method for exothermic enthalpy (ΔH) is developed to achieve accurate and efficient determination of the stability of UV adhesives after storage / exposure.

[0010] This invention utilizes the principle of high-temperature-initiated thermal polymerization of adhesives to construct a three-dimensional correlation principle of "polymerization reaction initiation temperature - enthalpy change rate - prepolymerization degree". Its core mechanism lies in the following: if prepolymerization occurs during the storage of UV adhesives, the molecular chains are partially cross-linked, reducing the initiation energy required for subsequent thermal polymerization. This is manifested in a shift of the initial reaction temperature and peak reaction temperature towards lower temperatures in DSC testing, with the shift magnitude positively correlated with the prepolymerization degree. If physical changes such as solvent evaporation or moisture absorption occur, the concentration of effective reactive groups per unit mass changes, resulting in an abnormal deviation in the exothermic enthalpy.

[0011] Based on the above principles, the present invention is implemented using the following technical solution:

[0012] A rapid method for detecting the storage stability of adhesives based on DSC thermal behavior characteristics includes the following steps:

[0013] S1: Feature Benchmark Library Construction

[0014] Fresh, unstored adhesives from the same batch were selected as standard samples and tested under specified DSC conditions to obtain baseline characteristic parameters: baseline initial reaction temperature T. Onset,0、 Reference peak reaction temperature T Peak,0 The reference exothermic enthalpy ΔH0.

[0015] S2: DSC test of the sample to be tested

[0016] Perform DSC testing on the sample to be tested, with test parameters exactly the same as in step S1, to obtain the characteristic parameters of the sample to be tested: the initial reaction temperature T. Onset,x Peak reaction temperature T to be detected Peak,x Enthalpy of exothermic reaction ΔH to be tested x .

[0017] The DSC test parameters are as follows: sample amount 5~10mg, heating rate 10℃ / min, temperature scan range from room temperature 25℃ to 250℃, carrier gas is high-purity nitrogen, and the flow rate is stably controlled at 60mL / min to avoid interference of oxidation reaction on the thermal behavior curve.

[0018] S3: Characteristic Deviation Calculation

[0019] Calculate the relative deviation of the characteristics between the sample to be tested and the standard sample:

[0020] ① Relative deviation of initial temperature: ΔT Onset = (T Onset,x - T Onset,0 ) / T Onset,0 × 100%;

[0021] ② Relative deviation of peak temperature: ΔT Peak = (T) Peak,x - T Peak,0 ) / T Peak,0 × 100%;

[0022] ③ Relative deviation of exothermic enthalpy: ΔH = (ΔH x - ΔH0) / ΔH0 × 100%.

[0023] S4: Determine the overall temperature deviation ΔT:

[0024] Take the relative deviation of the initial temperature |ΔT Onset |Relative deviation from peak temperature|ΔT Peak The maximum value in | is taken as the comprehensive temperature deviation ΔT, that is:

[0025] ΔT = max(|ΔT Onset |, |ΔT Peak |).

[0026] S5: Stability Determination

[0027] Based on ΔT and |ΔH|, the sample state is determined according to the thresholds in Table 1:

[0028] Table 1

[0029]

[0030] When ΔT and |ΔH| are at different levels, the more severe level shall be used for judgment.

[0031] The following are preferred embodiments, but are not intended to limit the technical solutions provided by the present invention. The objectives and beneficial effects of the present invention can be better achieved and realized through the following preferred technical solutions.

[0032] Preferably, the heating rate of the DSC test in steps S1 and S2 is strictly controlled within the range of 5~10℃ / min, preferably 10℃ / min. At this rate, a stable baseline can be ensured, sufficient resolution of the thermal peak can be obtained, and the test cycle is moderate. The temperature scan termination temperature can be extended to 300℃ to ensure complete polymerization.

[0033] Preferably, high-purity nitrogen (purity ≥99.999%) is used as the carrier gas, with a stable flow rate of 60±5 mL / min, to prevent the high-temperature oxidation reaction from interfering with the measurement of the exothermic polymerization.

[0034] Preferably, the samples to be tested include, but are not limited to: customer return samples, samples after different storage conditions / times, samples after being left open, and samples produced from different batches of raw materials.

[0035] Preferably, the sample amount for DSC testing in step S2 is precisely controlled to be 5~7mg, and most preferably 6mg, in order to reduce the impact of sample amount fluctuation on the accuracy of enthalpy testing.

[0036] Preferably, the equipment accuracy requirements for using a differential scanning calorimeter (DSC) are: temperature error ≤ 0.1℃, enthalpy error ≤ ±1%, and carrier gas flow rate fluctuation ≤ 5mL / min, to ensure the accuracy and reproducibility of the test results; preferably, the enthalpy error ≤ ±0.1%.

[0037] Preferably, the sample pretreatment conditions are as follows: the sample to be tested should be placed in an environment of 25±2℃ for 30 minutes to eliminate the test deviation caused by the difference in storage temperature; an aluminum sample tray without solvent contamination should be used when sampling, and the sample tray should be tested immediately after pressing to avoid secondary deterioration caused by contact with air.

[0038] Preferably, the degradation mechanism is inferred from the variation patterns of ΔT and |ΔH|: when ΔT exceeds the threshold while |ΔH| is within the acceptable range, the degradation mechanism is determined to be dominated by chemical prepolymerization; when |ΔH| exceeds the threshold while ΔT is within the acceptable range, the degradation mechanism is determined to be dominated by physical degradation; when both ΔT and |ΔH| exceed the threshold, it is determined to be a complex degradation.

[0039] As a special case: If there is no fresh sample from the same batch as a standard sample, the baseline characteristic parameters can be determined by one of the following methods: using the statistical average of test data from multiple batches of historical fresh samples with the same formula as the baseline characteristic parameters, or using a retained sample from the same period that has been confirmed to be of qualified performance as a standard sample for DSC testing to obtain the baseline characteristic parameters.

[0040] Compared with the prior art, the present invention has the following significant advantages:

[0041] (1) Fast and efficient: Traditional UV adhesive storage stability testing uses "accelerated aging + viscosity test", which takes more than 12 hours in total; the present invention only takes 30 minutes for a single DSC test, and the total time including data calculation is ≤1 hour, which improves the testing efficiency by about 12 times and can meet the needs of batch testing and rapid release on the production line.

[0042] (2) Precise Quantification: Based on three characteristic parameters—initial temperature, peak temperature, and exothermic enthalpy—a comprehensive deviation judgment is made, explicitly taking the maximum value of the two temperature deviations as the judgment basis to avoid misjudgment based on a single parameter; three-level quantification thresholds (2%, 5%, and 10%) are set to achieve a leap from "qualitative" to "quantitative" and can accurately distinguish between qualified, slightly deteriorated, and severely deteriorated products. Examples demonstrate that this method can effectively identify two different deterioration mechanisms: chemical prepolymerization (temperature deviation-dominated) and physical deterioration (enthalpy anomaly-dominated).

[0043] (3) Easy to implement: It can directly use conventional DSC equipment and analytical balance without the need for additional special instruments; the judgment rules are simple and intuitive, and operators can master them after short-term training; the test results are digitized and can be connected to the production line MES system to realize real-time uploading and traceability of quality data, which is suitable for incoming inspection and process control of UV adhesives in the fields of 3C electronics, optical communication, and medical devices.

[0044] (4) Strong traceability: By establishing a feature benchmark library, the system compares the feature differences of returned samples, retained samples and fresh samples, and can accurately trace the root cause of quality problems - whether it is a fluctuation in raw material batches, an abnormal production process, or a problem in storage and transportation, providing a clear direction for quality improvement.

[0045] (5) Wide range of applications: This invention is not only applicable to UV adhesives, but can also be extended to the storage stability assessment of other thermosetting resins, electronic packaging materials, etc., and has good universality and promotion value. Detailed Implementation

[0046] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in further detail below with reference to specific embodiments. However, those skilled in the art will understand that these embodiments are for illustrative purposes only and should not be construed as limiting the scope of protection of this invention.

[0047] To determine the optimal test parameters for the method of this invention, a systematic condition optimization experiment was conducted in the early stages, as detailed below:

[0048] 1. Selection of heating rate

[0049] The effects of four heating rates (5℃ / min, 10℃ / min, 15℃ / min, and 20℃ / min) on the test results of the same sample (newly produced batch of UV adhesive) were compared. The details are shown in Table 2.

[0050] Table 2

[0051]

[0052] Taking into account both testing efficiency and data accuracy, 10℃ / min was selected as the standard heating rate.

[0053] 2. Selection of nitrogen flow rate

[0054] The effects of three nitrogen flow rates (40 mL / min, 60 mL / min, and 80 mL / min) on the test results were compared, and the details are shown in Table 3.

[0055] Table 3

[0056]

[0057] Choosing 60 mL / min as the standard nitrogen flow rate can both fully protect the sample from oxidation and take into account economic efficiency.

[0058] 3. Selection of sample size

[0059] The effects of four sample amounts (4 mg, 6 mg, 8 mg, and 10 mg) on ​​the test results were compared, as detailed in Table 4.

[0060] Table 4

[0061]

[0062] Choosing 5-7 mg as the standard sample amount ensures optimal repeatability while maintaining the signal-to-noise ratio.

[0063] Example 1

[0064] Reference sample testing

[0065] A sample of adhesive from the same batch produced as the customer's returned adhesive was selected as the standard sample (this sample was sealed after production, stored at 4°C, and confirmed to have not deteriorated). DSC testing was performed under optimized test conditions.

[0066] Instrument: Differential scanning calorimeter (accuracy: temperature error ≤0.1℃, enthalpy error ≤±0.1%);

[0067] Sample volume: 6.0 mg (accurate to ±0.01 mg);

[0068] Heating rate: 10℃ / min;

[0069] Temperature range: 25℃~250℃;

[0070] Carrier gas: High-purity nitrogen (purity ≥99.999%), flow rate 60 mL / min;

[0071] Sample tray: Aluminum sealed tray, for testing immediately after tablet pressing;

[0072] Sample pretreatment: keep at 25℃ for 30 minutes.

[0073] Test to obtain baseline feature parameters:

[0074] ① T Onset,0 = 214.21℃;

[0075] ② T Peak,0 = 219.46℃;

[0076] ③ ΔH0 = 182.43 J / g.

[0077] Customer Recycled Adhesive 1 Test and Judgment

[0078] The sample to be tested was adhesive No. 1 returned by the customer. Characteristic parameters were obtained under the same test conditions:

[0079] ① T Onset,1 = 206.91℃;

[0080] ② T Peak,1 = 215.50℃;

[0081] ③ ΔH1 = 182.98 J / g.

[0082] Deviation calculation:

[0083] ① ΔT Onset = (206.91 - 214.21) / 214.21 × 100% = -3.41%;

[0084] ② ΔT Peak = (215.50 - 219.46) / 219.46 × 100% = -1.80%;

[0085] ③ ΔH = (182.98 - 182.43) / 182.43 × 100% = +0.30%.

[0086] Taking the maximum value of the two temperature deviations: ΔT = max(|-3.41%|, |-1.80%|) = 3.41%;

[0087] |ΔH| = 0.30%.

[0088] Judgment results: ΔT = 3.41% ∈ (2%, 5%) (slight deterioration), |ΔH| = 0.30% < 5% (acceptable). Since the judgment levels of ΔT and |ΔH| are inconsistent, the more severe level is used, and the final result is slight deterioration.

[0089] Analysis and Explanation:

[0090] (1) The necessity of the maximum value rule: If only |ΔT is used Peak If |ΔT=1.80% falls within the acceptable range (ΔT≤2%), it will be mistakenly judged as acceptable; while |ΔT Onset The value of 3.41% indicates slight deterioration. Therefore, the maximum value of the two temperature deviations must be taken as ΔT to accurately capture the prepolymerization deterioration characteristics of the sample and avoid missed judgments due to improper parameter selection.

[0091] (2) Necessity of dual-parameter coupling judgment: The temperature parameter (ΔT) indicates slight deterioration, while the enthalpy parameter (|ΔH|) indicates compliance, and the two levels are inconsistent. According to the rules of this invention, the more severe level (slight deterioration) is taken as the final judgment, which reflects the principle of risk priority. If only a single type of parameter is relied upon, chemical prepolymerization will be missed (only |ΔH| is considered), and the significance of prepolymerization cannot be verified (only ΔT is considered, but the parameter selection is inappropriate).

[0092] Analysis of the degradation mechanism: The enthalpy remained almost unchanged (0.30%), indicating no significant physical degradation (such as solvent evaporation or moisture absorption); however, the initial temperature shifted significantly to a lower temperature (3.41%), indicating that chemical prepolymerization occurred. The peak temperature shift was relatively small (1.80%), suggesting that prepolymerization mainly affects the reaction initiation stage, with a relatively delayed impact on the peak reaction stage. The multi-parameter detection system of this invention can precisely capture the change characteristics at different stages.

[0093] Example 2

[0094] Reference sample testing

[0095] Same as in Example 1, the baseline parameters are:

[0096] ① T Onset,0 = 214.21℃;

[0097] ② T Peak,0 = 219.46℃;

[0098] ③ ΔH0 = 182.43 J / g.

[0099] Customer Resistance Test and Judgment

[0100] The sample to be tested was adhesive No. 2 returned by the customer. Characteristic parameters were obtained through testing:

[0101] ① T Onset,2 = 202.98℃;

[0102] ② T Peak,2 = 212.40℃;

[0103] ③ ΔH2 = 177.56 J / g.

[0104] Deviation calculation:

[0105] ① ΔT Onset = (202.98 - 214.21) / 214.21 × 100% = -5.24%;

[0106] ② ΔT Peak = (212.40 - 219.46) / 219.46 × 100% = -3.22%;

[0107] ③ ΔH = (177.56 - 182.43) / 182.43 × 100% = -2.67%.

[0108] Taking the maximum value of the two temperature deviations: ΔT = max(|-5.24%|, |-3.22%|) = 5.24%;

[0109] |ΔH| = 2.67%.

[0110] Judgment results: ΔT = 5.24% > 5%, |ΔH| = 2.67% ≤ 5%, indicating severe deterioration.

[0111] Analysis and Explanation:

[0112] (1) If only |ΔT is used Peak Using |ΔT| as a criterion, ΔT = 3.22% falls within the range of mild deterioration (2% < ΔT ≤ 5%), which would underestimate the degree of sample deterioration; while |ΔT| Onset The value of 5.24% exceeds the threshold for severe deterioration. The maximum value of the two temperature deviations is used to accurately identify severe deterioration and avoid misuse due to underestimating the risk.

[0113] (2) Comparison with Example 1: In Example 1, |ΔT Onset |and|ΔT Peak The cases are categorized into two levels: qualified and mild. In Example 2, the cases are categorized into two levels: mild and severe. Both examples demonstrate that, regardless of the threshold boundaries, the rule of taking the maximum value is a necessary means to ensure accurate judgment.

[0114] (3) Enthalpy parameter analysis: |ΔH| decreased slightly (-2.67%), still within the acceptable range, indicating that the sample was mainly modified by chemical prepolymerization and there was no significant physical change.

[0115] Example 3

[0116] Reference sample testing

[0117] Newly produced adhesive from the same batch was selected as a standard sample, and baseline characteristic parameters were obtained through testing:

[0118] ① T Onset,0 = 216.85℃;

[0119] ② T Peak,0 = 221.98℃;

[0120] ③ ΔH0 = 137.61 J / g.

[0121] Sample testing after being left open for one day

[0122] Samples of the newly produced adhesive were placed openly in a fume hood at room temperature (25±2℃) for 24 hours before testing.

[0123] ① T Onset,3 = 216.85℃;

[0124] ② T Peak,3 = 222.65℃;

[0125] ③ ΔH3 = 172.99 J / g.

[0126] Deviation calculation:

[0127] ① ΔT Onset = (216.85 - 216.85) / 216.85 × 100% = 0%;

[0128] ② ΔT Peak = (222.65 - 221.98) / 221.98 × 100% = +0.30%;

[0129] ③ ΔH = (172.99 - 137.61) / 137.61 × 100% = +25.71%.

[0130] Taking the maximum value of the two temperature deviations: ΔT = max(|0%|, |+0.30%|) = 0.30%;

[0131] |ΔH| = 25.71%.

[0132] Judgment results: ΔT = 0.30% < 2%, |ΔH| = 25.71% > 10%, indicating severe deterioration.

[0133] Analysis and Explanation:

[0134] (1) Identification of physical deterioration: The temperature of the sample showed almost no shift (0.30%), indicating that no chemical prepolymerization had occurred; however, the enthalpy surged by 25.71%, indicating that a significant physical change had occurred—solvent evaporation led to an increase in the concentration of effective reactants per unit mass. This proves that the present invention can not only detect chemical deterioration but also effectively identify physical deterioration, providing comprehensive coverage.

[0135] (2) Dual parameter complementarity: If only temperature parameter is detected, it will be mistakenly judged as qualified; if only enthalpy parameter is detected, it is impossible to distinguish between physical deterioration and chemical deterioration; the combination of the two can both identify deterioration and infer the deterioration mechanism.

[0136] Example 4

[0137] Reference sample testing

[0138] Newly produced adhesive from the same batch was selected as a standard sample, and baseline characteristic parameters were obtained through testing:

[0139] ① T Onset,0 = 216.85℃;

[0140] ② T Peak,0 = 221.98℃;

[0141] ③ ΔH0 = 137.61 J / g.

[0142] Sample testing after one day of low-temperature sealed storage

[0143] After sealing the newly produced adhesive, store it in a 4°C refrigerator for 24 hours. After removing it, test it according to the pretreatment conditions (25°C constant temperature for 30 minutes):

[0144] ① T Onset,4 = 216.68℃;

[0145] ② T Peak,4 = 221.05℃;

[0146] ③ ΔH4 = 137.89 J / g.

[0147] Deviation calculation:

[0148] ① ΔT Onset = (216.68 - 216.85) / 216.85 × 100% = -0.08%;

[0149] ② ΔTPeak = (221.05 - 221.98) / 221.98 × 100% = -0.42%;

[0150] ③ ΔH = (137.89 - 137.61) / 137.61 × 100% = +0.20%.

[0151] Taking the maximum value of the two temperature deviations: ΔT = max(|-0.08%|, |-0.42%|) = 0.42%;

[0152] |ΔH| = 0.20%.

[0153] Judgment results: ΔT = 0.42% ≤ 2%, |ΔH| = 0.20% ≤ 5%, which is qualified (not deteriorated).

[0154] Analysis and Explanation:

[0155] This example demonstrates the processing logic when parameter levels are consistent in a two-parameter coupling determination. Combined with other embodiments, this invention has fully verified the following rules through real-world examples:

[0156] (1) When ΔT and |ΔH| are of the same level, the judgment is made directly according to that level;

[0157] (2) When the levels of ΔT and |ΔH| are inconsistent, the more severe level shall be used for judgment;

[0158] (3) By observing the variation patterns of ΔT and |ΔH|, the degradation mechanism can be further inferred: temperature shift is dominated by chemical prepolymerization, and enthalpy anomaly is dominated by physical degradation.

[0159] The above rules together constitute a complete two-parameter coupled judgment system, ensuring that samples with different deterioration mechanisms and different degrees of degradation can be accurately identified.

[0160] Example 5

[0161] Reference sample testing

[0162] Newly produced UV adhesives from the same batch were selected as standard samples, and baseline parameters were obtained through testing.

[0163] ① T Onset,0 = 218.32℃;

[0164] ② T Peak,0 = 223.67℃;

[0165] ③ T Peak,0 = 158.24 J / g.

[0166] Composite Deterioration Sample Testing

[0167] The sample to be tested was a sample of this batch of adhesive after being stored in a non-sealed container at a constant temperature of 40°C for 5 days (this condition simultaneously promotes chemical prepolymerization and solvent evaporation):

[0168] ① T Onset,5 = 210.75℃;

[0169] ② T Peak,5 = 216.89℃;

[0170] ③ ΔH5 = 172.36 J / g.

[0171] Deviation calculation:

[0172] ① ΔT Onset = (210.75 - 218.32) / 218.32 × 100% = -3.47%;

[0173] ② ΔT Peak = (216.89 - 223.67) / 223.67 × 100% = -3.03%;

[0174] ΔH = (172.36 - 158.24) / 158.24 × 100% = +8.92%.

[0175] Taking the maximum value of the two temperature deviations: ΔT = max(|-3.47%|, |-3.03%|) = 3.47%; |ΔH| = 8.92%.

[0176] Judgment results: ΔT = 3.47% ∈ (2%, 5%] (slight deterioration), |ΔH| = 8.92% ∈ (5%, 10%] (slight deterioration). The two are of the same level and are judged as slightly deteriorated.

[0177] Example 6

[0178] Comparative experimental design of different detection methods

[0179] Fifteen batches of UV adhesive samples with different degrees of deterioration were selected (verified by actual use: 5 batches qualified, 5 batches slightly deteriorated, and 5 batches severely deteriorated). The method of this invention and the traditional viscosity method were used for testing, and the detection speed, quantitative ability and accuracy were compared.

[0180] Method testing of the present invention

[0181] DSC testing was performed under the test conditions of Example 1, ΔT and |ΔH| were calculated, and the level was determined according to the threshold. The test time for each sample was approximately 45 minutes (including sample pretreatment, testing, and data analysis).

[0182] Traditional viscosity testing

[0183] The same batch of samples were placed in an 85℃ oven for accelerated aging tests. Viscosity changes were measured every 24 hours until the viscosity change rate exceeded 10% or reached 7 days. The testing instrument was a rotational viscometer, and the testing time for each sample was approximately 7 days (including accelerated aging time and viscosity testing).

[0184] Comparison results

[0185] The comparison results are shown in Table 5.

[0186] Table 5

[0187]

[0188] Comparison Conclusion

[0189] The detection method of the present invention is compared with the traditional method, and the conclusions are shown in Table 6.

[0190] Table 6

[0191]

[0192] Analysis: The method of this invention improves detection speed by two orders of magnitude compared to the traditional viscosity method (45 minutes vs. 7 days). The fundamental reason is that the traditional viscosity method relies on accelerating the aging process (requiring several days to accumulate detectable viscosity changes), while this invention directly detects the thermal behavior characteristics of the adhesive in its current state, without waiting for the aging process to complete. This fundamental difference enables this invention to achieve truly "rapid detection." Furthermore, it allows for the quantitative grading of the degree of deterioration, providing a more accurate basis for quality control decisions, significantly superior to existing technologies.

[0193] Example 7

[0194] Reproducibility test

[0195] Take qualified samples from the same batch and repeat the test 10 times under the same test conditions. Calculate the coefficient of variation of the characteristic parameters. The details are shown in Table 7.

[0196] Table 7

[0197]

[0198] The results show that the method has good test reproducibility, with a temperature parameter variation coefficient of <0.3% and an enthalpy parameter variation coefficient of <1.5%, providing a statistical basis for threshold setting.

[0199] Threshold rationality verification

[0200] Thirty batches of samples that had passed actual use verification, 15 batches of slightly deteriorated samples, and 10 batches of severely deteriorated samples were selected and blindly tested using the method of this invention. The results and the actual situation's compliance rate are shown in Table 8.

[0201] Table 8

[0202]

[0203] The verification results show that the 2%, 5%, and 10% thresholds set in this invention have good discrimination and accuracy.

Claims

1. A rapid detection method for the storage stability of adhesives based on DSC thermal behavior characteristics, characterized in that, Includes the following steps: S1: Constructing characteristic reference library: Selecting fresh adhesive of the same batch as standard sample, obtaining reference initial reaction temperature T Onset,0 , reference peak reaction temperature T Peak,0 , and reference heat release enthalpy ΔH0 by DSC test; S2: DSC test on the sample to be tested: Perform DSC test on the sample to be tested to obtain the initial reaction temperature T. Onset,x Peak reaction temperature T to be detected Peak,x Enthalpy of exothermic reaction ΔH to be tested x ; S3 Characteristic deviation calculation: Calculate the relative deviation ΔT between the initial temperature of the sample to be tested and the standard sample. Onset Peak temperature relative deviation ΔT Peak The relative deviation of exothermic enthalpy ΔH; S4: Determine the overall temperature deviation ΔT: Take |ΔT Onset |and|ΔT Peak The maximum value in | is taken as the comprehensive temperature deviation ΔT; S5: Stability Determination: The sample state is determined based on the following deviation thresholds: (1) Qualified: ΔT ≤ 2% and |ΔH| ≤ 5%; (2) Slight deterioration: ① 2% <ΔT ≤ 5% and 5% <|ΔH| ≤ 10%; ② Or ΔT ≤ 2% and 5% < |ΔH| ≤ 10%; ③ Or 2% < ΔT ≤ 5% and |ΔH| ≤ 5%; (3) Severe deterioration: ΔT > 5% or |ΔH| > 10%; When the judgment levels of ΔT and |ΔH| are inconsistent, the more severe level shall be used as the final judgment result.

2. The method according to claim 1, characterized in that, The parameters for the DSC test in steps S1 and S2 are as follows: heating rate 5~10℃ / min, temperature scan range from room temperature to 25~300℃, carrier gas is inert gas, and flow rate is stably controlled at 60±5mL / min.

3. The method according to claim 2, characterized in that, The preferred heating rate is 10℃ / min, and the carrier gas is high-purity nitrogen with a purity ≥99.999%.

4. The method according to claim 1, characterized in that, If there is no fresh sample from the same batch as the standard sample in step S1, the baseline characteristic parameter can be determined by one of the following methods: using the statistical average of test data of multiple batches of historical fresh samples with the same formula as the baseline characteristic parameter, or using a retained sample from the same period that has been confirmed to be qualified as the standard sample for DSC testing to obtain the baseline characteristic parameter.

5. The method according to claim 1, characterized in that, The samples to be tested in step S2 include: customer return samples, samples after different storage conditions, and samples produced from different batches of raw materials.

6. The method according to claim 1, characterized in that, The sample amount for the DSC test in step S2 is 5~10mg, preferably 5~7mg.

7. The method according to claim 1, characterized in that, The sample to be tested in step S2 needs to be pretreated before testing: place the sample to be tested in an environment of 25±2℃ for 30 minutes to eliminate the test deviation caused by the difference in storage temperature.

8. The method according to claim 1, characterized in that, The accuracy requirements for the DSC used are: temperature error ≤ 0.1℃, enthalpy error ≤ ±1%, and carrier gas flow rate fluctuation ≤ 5mL / min.

9. The method according to claim 1, characterized in that, The method is based on the three-dimensional correlation principle of "polymerization reaction start temperature - enthalpy change rate - prepolymerization degree". That is, the higher the prepolymerization degree, the greater the shift of the start temperature and peak temperature of the thermal polymerization reaction towards the lower temperature, and the shift is positively correlated with the prepolymerization degree; physical deterioration is manifested as abnormal deviation of exothermic enthalpy.

10. The method according to claim 1, characterized in that, The degradation mechanism is inferred from the variation patterns of ΔT and |ΔH|: when ΔT exceeds the threshold while |ΔH| is within the acceptable range, the degradation mechanism is determined to be dominated by chemical prepolymerization; when |ΔH| exceeds the threshold while ΔT is within the acceptable range, the degradation mechanism is determined to be dominated by physical degradation; when both ΔT and |ΔH| exceed the threshold, it is determined to be a complex degradation.

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