Method for evaluating silanol group amount on surface of silicone resin

Abstract

To provide a method for evaluating a silanol group amount on a surface of a silicone resin, which can evaluate a silanol group amount on a surface of a silicone resin.SOLUTION: A method for evaluating a silanol group amount on a surface of a silicone resin, comprises subjecting the surface of the silicone resin to analysis for Si or SiCH3 and Si-OH by time-of-flight secondary ion mass spectrometry (TOF-SIMS); and evaluating a silanol group amount based on a ratio value [Si-OH / Si or Si-OH / Si-CH3] of peak intensity derived from Si-OH to peak intensity derived from Si or SiCH3.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for evaluating the amount of silanol groups on the surface of a silicone resin.

Background Art

[0002] In order to impart water repellency to the surfaces of various molded articles, substrates, and other articles, for example, a process such as applying a paint containing a water repellent material to the surface of the article to form a coating film is performed. In recent years, in the mobility field represented by automobiles, for example, for autonomous driving, optical devices using laser light such as LiDAR (Light Detection and Ranging, Laser Imaging Detection and Ranging) have been adopted. In such optical devices, it is feared that the detection ability of the light receiving sensor may be reduced due to the adhesion of rainwater and dirt to the transparent cover that protects the sensor. Therefore, it is important to protect it with a high-performance and highly durable coating material, and sufficient water repellency performance is also required.

[0003] As water repellent materials, silicone resins, fluororesins, etc. are known. Among them, fluororesins may be a problem as causative substances for environmental pollution, and in recent years, there are concerns that their use may be restricted. Therefore, it is preferable to use a silicone resin as the water repellent material. Patent Document 1 describes a coating resin composition using a fluorine-free silicone resin.

[0004] Incidentally, according to the studies by the present inventors, it was confirmed that the water contact angle of the silicone resin coating film decreases after the weather resistance test. That is, the water repellency of the silicone resin coating film decreases after the weather resistance test. As a cause thereof, although it is a hypothesis, it is presumed that the silicone resin on the coating film surface is hydrolyzed, increasing the silanol groups (Si-OH), and the hydrophilicity of the silanol groups reduces the water repellency. That is, it is presumed that the hydrolysis breaks the siloxane bond to generate two silanol groups, and as a result, the amount of silanol groups increases. However, heretofore, an analytical method for evaluating the amount of silanol groups on the surface of the silicone resin coating film and its change has not been established.

[0005] As an analytical method for the functional groups on the coating film surface, generally, X-ray photoelectron spectroscopy (hereinafter referred to as "XPS") can be mentioned. XPS irradiates X-rays on the surface of the sample to be measured under ultra-high vacuum, and observes the kinetic energy of the photoelectrons when the photoelectrons are emitted from the sample surface into the vacuum, thereby obtaining information on the elemental composition and chemical state of the surface.

[0006] For example, Non-Patent Document 1 describes a method for analyzing hydroxy groups on the surface of a sample using XPS. Since the hydroxy groups overlap with peaks such as ether groups, the hydroxy groups on the surface of the sample are modified using a fluorine-containing labeling reagent, and the hydroxy groups can be quantified by quantifying the peak of fluorine. Specifically, it is a method of performing gas-phase chemical modification using trifluoroacetic acid as a labeling reagent.

[0007] Further, Non-Patent Document 2 describes a method for analyzing silanol groups on the surface of a silicon wafer using XPS. Specifically, it is a method of performing liquid-phase chemical modification for modifying silanol groups by using tridecafluoro-1,1,2,2-tetrahydrooctyldimethylchlorosilane as a labeling reagent and immersing a silicon wafer in a chloroform solution in which the labeling reagent is dissolved.

Prior Art Documents

Patent Documents

[0008] Patent Document 1 Japanese Patent Application Laid-Open No. 2006-257318 Non-Patent Document

[0009] Non-Patent Document 1 Journal of the Fiber Society (Fiber and Industry), Vol. 65, No. 5, P-171~P-174 (2009) Non-Patent Document 2 Surface Chemistry, Vol. 26, No. 8, pp. 492-494, 2005 Summary of the Invention Problems to be Solved by the Invention

[0010] However, in the method described in Non-Patent Document 1, the reactivity of the fluorination reagent with respect to the hydroxy groups on the sample surface is unknown, and it is also unknown whether it can be applied to silanol groups. Further, also in the method described in Non-Patent Document 2, the reactivity of the labeling reagent with respect to the silanol groups on the silicon wafer surface is unknown, and since it is necessary to immerse it in a solvent such as chloroform, in the case of a sample such as a resin coating film, there is concern that it may be affected by swelling or alteration due to the solvent.

[0011]

[0012] From the above, if a measurement method capable of directly quantifying without modifying the silanol groups on the sample surface can be established, the surface state of the silicone resin coating film can be accurately grasped, and further, by evaluating the change over time in the amount of silanol groups, it is considered that the change in state due to the decomposition of the siloxane bond can be confirmed, which is useful.

Means for Solving the Problem

[0013] The inventors of the present invention earnestly studied and found that the amount of Si-OH on the surface of a silicone resin can be evaluated by evaluating the value of the ratio of the peak intensity derived from Si-OH to the peak intensity derived from Si or SiCH by time-of-flight secondary ion mass spectrometry (hereinafter referred to as "TOF-SIMS"), and thus completed the present invention. 3 That is, one aspect of the present invention for solving the above problems is as follows. That is, one aspect of the present invention for solving the above problems is as follows.

[0014] (1) Analyze Si or SiCH and Si-OH on the surface of the silicone resin by time-of-flight secondary ion mass spectrometry (TOF-SIMS), and evaluate the amount of silanol groups on the surface of the silicone resin based on the value of the ratio of the peak intensity derived from Si-OH to the peak intensity derived from Si or SiCH [Si-OH / Si or Si-OH / Si-CH]. 3 And Si-OH, and evaluate the amount of silanol groups on the surface of the silicone resin based on the value of the ratio of the peak intensity derived from Si-OH to the peak intensity derived from Si or SiCH 3 [Si-OH / Si or Si-OH / Si-CH 3 .

[0015] (2) Analyze the surface of the silicone resin by the time-of-flight secondary ion mass spectrometry two or more times at intervals of a predetermined period, and evaluate the change in the amount of silanol groups. The method for evaluating the amount of silanol groups on the surface of the silicone resin according to (1) above.

[0016] (3) Based on the change in the amount of silanol groups, evaluate the change over time in the water repellency on the surface of the silicone resin. The method for evaluating the amount of silanol groups on the surface of the silicone resin according to (2) above.

Advantages of the Invention

[0017] According to the present invention, it is possible to directly quantify the silanol groups on the surface of the silicone resin without modifying them, and to provide a method for evaluating the amount of silanol groups on the surface of the silicone resin, which is useful for purposes such as confirming the change over time of the coating film surface.

Brief Description of the Drawings

[0018]

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Mode for Carrying Out the Invention

[0019] The method for evaluating the amount of silanol groups on the surface of the silicone resin of the present embodiment (hereinafter, also simply referred to as "the evaluation method of the present embodiment") is to perform analysis of Si or SiCH 3 and Si - OH on the surface of the silicone resin by time - of - flight secondary ion mass spectrometry (TOF - SIMS), and evaluate the amount of silanol groups by the value of the ratio of the peak intensity derived from Si - OH to the peak intensity derived from Si or SiCH 3 [Si - OH / Si or Si - OH / Si - CH 3 .

[0020] In the evaluation method of this embodiment, the time-dependent change in the amount of silanol groups on the silicone resin surface is directly evaluated by TOF-SIMS. That is, for the silicone resin surface, Si or SiCH 3 and Si-OH are analyzed by TOF-SIMS, and the value of the ratio of the peak intensity of Si-OH to the peak intensity of Si or SiCH 3 , [Si-OH / Si or Si-OH / Si-CH 3 , can be used to evaluate the amount of silanol groups on the silicone resin surface. In TOF-SIMS measurement, the ionization efficiency changes for each measurement. Therefore, in order to evaluate quantitatively, it is necessary to express it as a ratio to a reference peak. Thus, in the evaluation method of this embodiment, two peaks of Si or Si-CH 3 are used as appropriate reference peaks.

[0021] TOF-SIMS is a technique that irradiates the surface of a sample to be measured with an ion beam (primary ion) and mass-analyzes the secondary ions emitted from the sample surface. That is, by irradiating the sample with an ion beam (primary ion), ions (secondary ions) are emitted from the sample surface, and the difference in the flight time (proportional to the square root of the mass) until the secondary ions reach the detector is used to separate each secondary ion by mass. Thereby, since the mass spectrum of the secondary ions is obtained, component analysis of the sample surface becomes possible. In the evaluation method of this embodiment, TOF-SIMS is used to identify the peak of Si or SiCH 3 and the peak of Si-OH, and the amount of Si-OH is evaluated by comparing the peak intensity of Si-OH with the peak intensity of the peak of Si or SiCH 3 as a reference.

[0022] In the evaluation method of this embodiment, the surface of the silicone resin is analyzed by TOF-SIMS two or more times at intervals of a predetermined period, and the change in the amount of silanol groups is evaluated to evaluate the change over time in the amount of Si-OH. The predetermined period is preferably a period in which a significant change in the amount of silanol groups is confirmed. For example, in a weather resistance test, it can be set to 0.1 to 3000 hours. The number of times of analysis by TOF-SIMS is two or more, and it can be appropriately set according to the period of analysis by TOF-SIMS. For example, it can be set to 2 to 5 times.

[0023] In this embodiment, based on the change over time in the amount of silanol groups obtained by analysis by TOF-SIMS, the change in the water repellency on the surface of the silicone resin can be evaluated. Details will be described later.

[0024] Here, an example of the structure of the silicone resin to which the evaluation method of this embodiment can be applied is shown below.

[0025] [Chemical formula] [x represents an integer from 5 to 160.]

[0026] The silicone resin represented by the structural formula (1) can be cured in one liquid by the dehydration condensation of Si-OH groups with each other. The coating film is transparent and has high hardness, and a water-repellent coating film with a water contact angle exceeding 90° can be obtained. However, as described above, the water contact angle of the coating film of the silicone resin decreases after the weather resistance test, that is, the water repellency decreases. As described above, it is presumed that the siloxane bond (Si-O-Si) in the silicone resin hydrolyzes over time to change into two silanol groups (Si-OH HO-Si), and the water repellency decreases due to the increase in the hydrophilic silanol groups. Hereinafter, the authenticity of this presumption was evaluated by TOF-SIMS for the silicone resin represented by the above structural formula (1) as follows.

[0027] First, a sample to be measured was prepared as follows. A 200-μm glass cloth tape was attached to a blue plate glass as a spacer, and a silicone varnish diluted to NV (non-volatile content) 20% was uniformly applied. Then, after drying at 80 °C for 10 minutes using a dryer, it was thermally cured at 110 °C for 2 hours to obtain a cured coating film.

[0028] Using the cured coating film obtained as described above as a sample, a QLab-made QUV weather resistance tester was used, and in an 80 °C environment, ultraviolet rays (UVB-313) were irradiated at an illuminance of 0.62 W / m 2 (wavelength 310 nm) for 20 hours, and then exposed to an environment where the cycle of holding at 50 °C for 4 hours in a dew condensation environment was repeated, and the water contact angle was measured after a predetermined time had elapsed in each case. The measurement of the water contact angle was carried out in accordance with JIS R3257 using a DropMaster DM-501 manufactured by Kyowa Interface Science Co., Ltd. The volume of the water droplet was 2.0 μL, and the average (n = 5) contact angle was determined, and the wettability was evaluated based on its magnitude.

[0029] On the other hand, TOF-SIMS measurements were performed on the above sample before and during the weather resistance test. The measurement conditions are shown below. Measuring device: TRIFT III manufactured by ULVAC-PHI, Inc. Primary ion: Au + , and a neutralizer gun was also used in combination to suppress the charging of the sample surface during measurement. Measurement time: 3 minutes Acceleration voltage: 5.0 kV Dose amount: 1×10 13 ions / cm 2 Below Capture voltage: 4.5 kV Capture current: 2 μA (as DC) Measurement area: 200 μm Detected ions: Positive ions

[0030] Figure 1 shows the TOF-SIMS spectrum as a result of the TOF-SIMS measurement as described above. As shown in Figure 1, a peak of Si appears at m / z value = 28, and Si-CH appears at m / z value = 43 3It can be seen that the peak of appears at m / z value = 45 as the peak of Si-OH. That is, the peak (m / z value = 45) derived from the Si-OH groups of the coating film was detected, and it was confirmed that the Si-OH groups of the coating film can be directly measured. Based on the above measurement data, the Si-OH relative ratio was calculated from the following formula. (Number of counts of Si-OH groups / Number of counts of reference peak) × 1000 The reference peak is the peak of Si or Si-CH 3 .

[0031] As described above, the water contact angle of the silicone resin surface decreases with time, and the water repellency decreases. Figure 2 is a graph showing the relationship between the Si-OH relative ratio and the water contact angle. That is, it can be seen that the smaller the water contact angle, the larger the Si-OH relative ratio. On the other hand, Figure 3 is a graph showing the relationship between the water contact angle (□ plot) and the Si-OH relative ratio (● plot) with respect to the elapsed time of the weather resistance test. From Figure 3, it can be seen that the Si-OH relative ratio increases with time, and the water contact angle decreases with time. From Figures 2 and 3, it is considered that there is a correlation between the Si-OH groups and the water contact angle. That is, from these results, it is considered that the Si-O-Si bonds on the coating film surface are hydrolyzed and the Si-OH groups are increasing.

[0032] On the one hand, in order to confirm that the cause of the decrease in the water contact angle in the weather resistance test is water, the changes in the water contact angle in tests other than the weather resistance test, namely the heat resistance test, the light resistance test, and the damp heat resistance test, were also measured. The graphs shown in Fig. 4 show the relationship between the water contact angle and the elapsed time in each test. Also, the graphs shown in Fig. 5 show the relationship between the relative ratio of Si-OH and the elapsed time in each test. In both Fig. 4 and Fig. 5, the ○ plot represents the result of the weather resistance test, the △ plot represents the result of the heat resistance test, the □ plot represents the result of the damp heat resistance test, and the ◆ plot represents the result of the light resistance test. From Fig. 4 and Fig. 5, it can be seen that the relative ratio of Si-OH and the water contact angle change over time only in the weather resistance test. From the results of Fig. 4 and Fig. 5, it can be seen that in the heat resistance, light resistance, and damp heat resistance tests, the decrease in the water contact angle does not occur, and the change in the relative ratio of Si-OH hardly occurs. Therefore, the factor causing the decrease in the water contact angle in the weather resistance test is water, and it is considered that the Si-OH groups increase due to the adhesion of water to the coating surface. Note that the damp heat resistance test is a test conducted in an environment containing moisture, but in this test, since the moisture is in a gaseous state, it does not affect the water contact angle.

[0033] As described above, it has been shown that the decrease in the water contact angle, that is, the decrease in water repellency, is caused by an increase in the amount of silanol groups due to the hydrolysis of siloxane bonds.

[0034] In the above evaluation of Si-OH, the change in the amount of silanol groups was evaluated by the change in the value of the ratio [Si-OH / Si] of the peak intensity of Si-OH to the peak intensity of the peak of Si, that is, the peak serving as a reference, which is the peak of Si. In the evaluation method of the present embodiment, such a reference peak may be the peak of Si-CH 3 . Fig. 6 shows the case where the peak of Si is used as a reference, and Fig. 7 shows the case where the peak of Si-CH 3 is used as a reference, and both show the relationship between the relative ratio of Si-OH and the water contact angle. The coefficient of determination R 2 value, which is the square of the correlation coefficient R, is 0.5124 when the peak of Si is used as a reference, and Si-CH 3is 0.9621 when based on the peak of Si-CH 3 It can be seen that the correlation between the Si-OH relative ratio and the water contact angle is higher when based on the peak of Si-CH 3 is considered to be because Si-CH 3 has a side chain structure of the same siloxane main chain as Si-OH and their ionization efficiencies are similar. From this result, it is preferable to calculate the Si-OH relative ratio using Si-CH

[0035] The evaluation method of this embodiment is useful for developing a silicone resin with improved weather resistance, that is, a silicone resin capable of maintaining water repellency for a long period. That is, when trying to develop such a silicone resin, by using the evaluation method of this embodiment, the change over time of the amount of silanol groups can be easily evaluated. Therefore, if a silicone resin with no increase or a small increase in the amount of silanol groups is synthesized in a weather resistance test, it can be evaluated as a silicone resin with a small change over time in water repellency. For example, when developing a silicone resin capable of maintaining water repellency by imparting a water-repellent functional group to a silanol resin, the evaluation method of this embodiment enables determination of whether water repellency is maintained.

[0036] As a method for improving weather resistance, it is considered effective to reduce the Si-OH groups on the hydrophilic surface to make it difficult to mix with water, or to introduce a water-repellent component to suppress the intrusion of water into the main chain.

Claims

1. Analyze Si or SiCH on the surface of the silicone resin by time-of-flight secondary ion mass spectrometry (TOF-SIMS), ３ and analyze Si-OH, and the ratio value [Si-OH / Si or Si-OH / Si-CH ３ of the peak intensity derived from Si-OH to the peak intensity derived from Si or SiCH ３ is used to evaluate the amount of silanol groups. A method for evaluating the amount of silanol groups on the surface of a silicone resin.

2. The method for evaluating the amount of silanol groups on the surface of a silicone resin according to claim 1, wherein the analysis of the surface of the silicone resin by the time-of-flight secondary ion mass spectrometry is performed two or more times at predetermined intervals, and the change in the amount of silanol groups is evaluated.

3. The method for evaluating the amount of silanol groups on the surface of a silicone resin according to claim 2, wherein the change in the water repellency over time on the surface of the silicone resin is evaluated based on the change in the amount of silanol groups.

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