Molecular weight controllable mq silicone resin for coating, and preparation method and application thereof

Abstract

The application relates to the technical field of silicone resin, and discloses a molecular weight controllable MQ silicone resin for paint, a preparation method and application thereof. The method comprises the following steps: under the condition of not adding an end-capping agent, adding silicate into an acidic aqueous phase to pre-hydrolyze, so as to obtain a Q precursor hydrolyzate; when the light transmittance of the hydrolyzate is 70-95% at 600 nm after dilution with deionized water at a mass ratio of 1:9, adding a borosiloxane regulator containing a B-O-Si bond to adjust the structure; subsequently, adding an end-capping agent to carry out end-capping reaction, and carrying out dealcoholization and dehydration treatment in the presence of an organic solvent; and then, the MQ silicone resin is obtained through phase separation, water washing, dehydration and reduced pressure distillation. The obtained MQ silicone resin has the advantages of narrow molecular weight distribution, good storage stability, good compatibility with a film-forming resin, and suitability for weather-resistant protective paint and functional decorative paint.

Description

Technical Field

[0001] This invention relates to the field of silicone resin technology, and in particular to a molecular weight controllable MQ silicone resin for coatings, its preparation method, and its application. Background Technology

[0002] MQ silicone resin is a type of organosilicon resin composed of M units represented by R3SiO1 / 2 and Q units represented by SiO4 / 2. It combines the hydrophobicity and weather resistance of organosilicon materials with the structural stability of inorganic silicon-oxygen networks, and is commonly used in high-performance coatings, weather-resistant protective coatings, and functional decorative coatings. In coating systems, the molecular weight, M / Q molar ratio, molecular weight distribution, and residual silanol content of MQ silicone resin directly affect the compatibility of the resin with the film-forming resin, the appearance of the coating film, storage stability, and weather resistance.

[0003] Existing MQ silicone resins typically use silicate esters as the source of Q units and hexamethyldisiloxane, vinyl bis-terminated resins, etc., as the source of M units, prepared under acidic conditions through hydrolysis, condensation, and end-capping reactions. While this process is relatively mature, in actual preparation, the silanol groups formed by silicate ester hydrolysis are highly reactive, and the nucleation and condensation processes of the Q precursor are easily affected by pH, temperature, dropping rate, water-to-alcohol ratio, and local concentration variations. If the end-capping agent participates in the reaction too early, it can easily lead to insufficient Q structure growth; if end-capping is too late, it may cause excessive condensation of the Q precursor, resulting in a higher molecular weight and wider distribution of the resin, and even affecting solubility and transparency.

[0004] Furthermore, traditional processes often rely on fixed hydrolysis times or fixed feed ratios to control the reaction process, lacking process criteria that reflect the actual condensation state of the Q precursor. Consequently, molecular weight fluctuations and inconsistent end-capping degrees can easily occur between different batches. Therefore, it is necessary to provide a method for preparing MQ silicone resin for coatings that can identify the suitable condensation state of the Q precursor and perform structural regulation before end-capping, thereby improving the controllability of resin molecular weight, batch stability, and coating applicability. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing MQ silicone resin with controllable molecular weight for coatings, so as to solve the problems of difficulty in judging the condensation state of Q precursor, difficulty in controlling the timing of end-capping, wide molecular weight distribution and insufficient batch stability in the existing process.

[0006] To achieve the above objectives, the present invention provides a method for preparing molecular weight controllable MQ silicone resin for coatings, comprising the following steps.

[0007] S1. Without adding a capping agent, silicate ester is added dropwise to an acidic aqueous phase with a pH of 1.2-3.0 for pre-hydrolysis. The system temperature is controlled at 35-60℃ during the addition process, and the addition time is 10-40 min. After the addition is complete, pre-hydrolysis continues for 5-45 min to obtain the Q precursor hydrolysate. In this step, the capping agent does not participate in the pre-hydrolysis process, allowing the silicate ester to preferentially hydrolyze and undergo controlled condensation, thereby forming a Q precursor with a certain size and degree of condensation. This avoids premature consumption of silanol groups by the capping agent, which could lead to insufficient Q structure growth.

[0008] Further, in step S1, the pH of the acidic aqueous phase is preferably 1.5-2.5; the dropping time of the silicate ester is preferably 15-25 min; the system temperature during the dropping process is preferably 40-55℃; and the pre-hydrolysis time after the dropping is completed is preferably 10-30 min. The silicate ester can be one or more of tetraethyl orthosilicate, methyl orthosilicate, polyethyl orthosilicate, and polymethyl orthosilicate. The acidity of the acidic aqueous phase can be adjusted by one or two of hydrochloric acid and sulfuric acid.

[0009] S2. The state of the Q precursor hydrolysate obtained in step S1 is monitored. When the Q precursor hydrolysate is diluted with deionized water at a mass ratio of 1:9, and the transmittance is measured at 600 nm wavelength at 25°C using a 1 cm cuvette and deionized water as a blank reference, and the transmittance is 70-95%, a borosilicate regulator is added to the Q precursor hydrolysate, and the reaction is allowed to proceed for 10-30 min to obtain a Q precursor system containing a B-O-Si bridging structure. By introducing a transmittance criterion, the control method that relies solely on reaction time can be transformed into a process control method based on the actual state of the Q precursor, which helps to reduce the influence of different batches of raw materials, temperatures, and equipment conditions on the degree of condensation of the Q precursor.

[0010] Further, in step S2, after the Q precursor hydrolysate is diluted with deionized water at a mass ratio of 1:9, and the transmittance is measured at 600 nm wavelength at 25°C using a 1 cm cuvette and with deionized water as a blank reference, the preferred transmittance is 78-92%. Then, the borosilicate modifier is added. If the transmittance is too high, it indicates that the degree of condensation of the Q precursor in the system is too low, and the molecular weight of the resin after subsequent end-capping may be too small. If the transmittance is too low, it indicates that the degree of condensation of the Q precursor is too high, and problems such as a larger molecular weight, wider distribution, or decreased solubility are likely to occur in subsequent reactions. Controlling the transmittance within the above range is beneficial for ensuring that the Q precursor is in a suitable state for end-capping and structural locking.

[0011] The borosilicate regulator is a cyclic borosilicate compound and / or an oligomeric borosilicate compound containing B-O-Si bonds in its molecule. The molar ratio (B / Q) of the borosilicate regulator (based on element B) to the silicate ester (based on Q units) is 0.0005-0.030. By controlling the amount of borosilicate regulator added, the local condensation structure of the Q precursor can be adjusted without significantly altering the main structure of the MQ silicone resin, thereby improving the uniformity of subsequent end-capping and the molecular weight distribution of the final resin. If the amount of borosilicate regulator is too low, its effect on regulating the Q precursor structure is not significant; if the amount is too high, it may lead to excessive bridging of the resin structure, affecting the resin solubility, transparency, and coating compatibility.

[0012] Further, the borosilicate regulator is obtained by alcoholysis condensation or dehydration condensation of a linear polysiloxane containing silanol groups with borate esters and / or boric acid; the number average molecular weight of the borosilicate regulator is 300-3000. The borate ester is one or more of trimethyl borate, triethyl borate, and triphenyl borate, preferably trimethyl borate and / or triethyl borate; the linear polysiloxane containing silanol groups is one or more of hydroxyl-terminated polydimethylsiloxane, hydroxyl-terminated methylphenylsiloxane, and hydroxyl-terminated methylvinylsiloxane.

[0013] S3. A capping agent is added to the Q precursor system containing the B-O-Si bridging structure obtained in step S2 to perform a capping reaction. The capping agent provides M units represented by R3SiO1 / 2, where each R is independently selected from methyl or vinyl groups. The molar ratio of the capping agent (based on M units) to the silicate ester (based on Q units) is M / Q = 0.85-1.60. The capping reaction temperature is 25-55℃, and the capping reaction time is 20-90 min, yielding the reaction system. In this step, the capping agent is added after the Q precursor has reached a suitable state and has been regulated by borosilicates. This effectively reduces the possibility of continued growth of disordered condensation and capsifies the active silanol groups on the surface of the Q precursor through the M units, thereby achieving further control over the molecular weight and structural stability of the resin.

[0014] Further, the end-capping agent comprises hexamethyldisiloxane and / or 1,3-divinyl-1,1,3,3-tetramethyldisiloxane. When the end-capping agent comprises both hexamethyldisiloxane and 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, the M units provided by 1,3-divinyl-1,1,3,3-tetramethyldisiloxane account for 5-45 mol% of the total M units provided by the end-capping agent. By adjusting the proportion of vinyl M units, the resin can be given the ability to further participate in curing or crosslinking reactions while maintaining controllable resin molecular weight, thereby meeting the requirements of different coating systems for reactivity and film-forming properties.

[0015] S4. In the presence of an organic solvent, the reaction system obtained in step S3 is subjected to de-alcoholization and dehydration treatment at 60-95℃ for 1-6 hours to reduce residual alcohol and water in the reaction system and reduce residual silanol groups, thereby obtaining a resin system containing a B-O-Si structure. The organic solvent can be one or more of toluene, xylene, butyl acetate, and methyl isobutyl ketone. This step, through heating and organic phase extraction, allows the generated MQ silicone resin to enter the organic phase and promotes the further removal or reaction of residual alcohol, water, and some active silanol groups in the system, which is beneficial for improving the resin's storage stability and the applicability of coating formulations.

[0016] Furthermore, the de-alcoholization and dehydration treatment is preferably carried out until the moisture content in the organic phase is no higher than 0.50 wt% and the residual alcohol content is no higher than 2.0 wt%. By controlling the above indicators, the impact of residual small molecules on the coating film formation, drying rate, compatibility, and storage viscosity can be reduced.

[0017] S5. The resin system containing the B-O-Si structure obtained in step S4 is subjected to phase separation, water washing, dehydration, and vacuum distillation to remove organic solvents and low-boiling components, thereby obtaining the molecular weight controllable MQ silicone resin for coatings. The water washing can be carried out until the aqueous phase is close to neutral to reduce the impact of acid residues on the resin's storage stability and subsequent coating formulation. The vacuum distillation is used to remove organic solvents, unreacted low-boiling components, and other volatile small molecules, so that the obtained MQ silicone resin meets the requirements for volatile matter and stability of coating resins.

[0018] The present invention also provides a molecular weight controllable MQ silicone resin for coatings, wherein the MQ silicone resin is prepared by the above method and comprises M units represented by R3SiO1 / 2, Q units represented by SiO4 / 2, and borosilicate bridging units containing B-O-Si bonds; the molar ratio M / Q of M units to Q units in the MQ silicone resin is 0.70-1.40; and the ratio of the weight-average molecular weight Mw to the number-average molecular weight Mn of the MQ silicone resin, Mw / Mn, is not greater than 2.50.

[0019] Furthermore, the preferred M / Q molar ratio in the MQ silicone resin is 0.80-1.25, and the preferred Mw / Mn ratio is no greater than 2.20. This range is beneficial for balancing the resin's solubility, transparency, film-forming aid properties, and compatibility with coating film-forming resins.

[0020] This invention also provides the application of the above-mentioned molecular weight controllable MQ silicone resin for coatings in the preparation of coating compositions, wherein the coating composition comprises the molecular weight controllable MQ silicone resin for coatings and a film-forming resin. Based on 100 parts by solids of the film-forming resin, the amount of the molecular weight controllable MQ silicone resin for coatings added is 3-40 parts; the film-forming resin is one or more of acrylic resin, polyester resin, epoxy resin, fluorocarbon resin, and polyurethane resin. The MQ silicone resin can be used as a weather-modifying resin, hydrophobic modifying component, film-forming auxiliary component, or crosslinking modifying component in the coating system to improve the weather resistance, water resistance, hydrophobicity, and overall film-forming performance of the coating film.

[0021] Compared with the prior art, the present invention provides a molecular weight controllable MQ silicone resin for coatings, its preparation method and application, which has the following beneficial effects: 1. Compared with existing technologies, this invention does not add a capping agent during the pre-hydrolysis stage. Instead, the silicate ester is hydrolyzed in an acidic aqueous phase to form a Q precursor with a certain degree of condensation, avoiding premature consumption of silanol groups by the capping agent and resulting in insufficient Q structure growth. Furthermore, this invention uses the transmittance of the Q precursor hydrolysate diluted with deionized water at a wavelength of 600 nm as the process criterion, which can more directly reflect the condensation state of the Q precursor, thereby improving the accuracy of the capping timing selection.

[0022] 2. This invention introduces a borosilicate regulator containing B-O-Si bonds before the end-capping reaction, which bridges and modifies the structure of the Q precursor. This helps reduce the tendency for the Q precursor to continue its disordered condensation and improves the uniformity of the subsequent end-capping reaction. By controlling the timing and amount of the borosilicate regulator, the stability of the resin molecular weight regulation can be improved without significantly affecting the main structure and solubility of the MQ silicone resin, resulting in a resin with a narrower molecular weight distribution.

[0023] 3. After treatment with alcohol removal, dehydration, phase separation, water washing, and vacuum distillation, the MQ silicone resin obtained in this invention has low contents of residual alcohol, water, acidic substances, and low-boiling components, which helps to reduce condensation thickening and performance drift during subsequent storage. The obtained resin has good compatibility with commonly used film-forming resins and can be used in coating systems such as acrylic resins, polyester resins, epoxy resins, fluorocarbon resins, and polyurethane resins to improve the weather resistance, water resistance, hydrophobicity, and overall film-forming properties of the coating film. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0025] In this invention, the B / Q molar ratio is calculated based on the number of moles of B element contained in the borosilicate regulator and the number of moles of Q units provided by the silicate ester. The number of moles of B element in the borosilicate regulator can be theoretically calculated based on the amount of borate ester and / or boric acid used in the preparation of the regulator; if necessary, the B element content in the borosilicate regulator can also be determined by inductively coupled plasma atomic emission spectrometry and then calculated.

[0026] I. Preparation of borosilicate regulators Preparation Example 1 In a reaction flask equipped with a stirrer, thermometer, and condenser, 100g of hydroxyl-terminated polydimethylsiloxane with a number-average molecular weight of approximately 600 was added, followed by 15g of trimethyl borate. The mixture was then heated to 80-90℃ under nitrogen protection and reacted for 3 hours. Methanol generated during the reaction was removed under reduced pressure to obtain a colorless and transparent borosilicate regulator A. Analysis revealed that borosilicate regulator A contains a borosilicate structure with B-O-Si bonds and a number-average molecular weight of approximately 900.

[0027] Preparation Example 2 The preparation method of Example 1 was followed, except that 100g of hydroxyl-terminated polydimethylsiloxane with a number-average molecular weight of approximately 200 was used, and 10g of trimethyl borate was added to obtain borosilicate regulator B. Analysis showed that borosilicate regulator B contains a borosilicate structure with B-O-Si bonds and a number-average molecular weight of approximately 300.

[0028] Preparation Example 3 The preparation method of Example 1 was followed, except that 100g of hydroxyl-terminated polydimethylsiloxane with a number-average molecular weight of approximately 1500 was used, and 8g of trimethyl borate was added to obtain borosilicate regulator C. Analysis showed that borosilicate regulator C contains a borosilicate structure with B-O-Si bonds and a number-average molecular weight of approximately 3000.

[0029] II. Preparation of MQ silicone resin with controllable molecular weight for coatings Example 1

[0030] In a four-necked flask equipped with a mechanical stirrer, thermometer, dropping funnel, and condenser, 450 g of deionized water was added, and the pH of the acidic aqueous phase was adjusted to 2.0 with hydrochloric acid. The system was heated to 48 °C, and 208.3 g of tetraethyl orthosilicate was added dropwise over 20 min with stirring. After the addition was complete, pre-hydrolysis was continued for 20 min to obtain the Q precursor hydrolysate. 1 g of the Q precursor hydrolysate was diluted with 9 g of deionized water, and the transmittance was measured at 600 nm at 25 °C using a 1 cm cuvette and with deionized water as a blank reference; the transmittance was 85%.

[0031] The borosilicate regulator A obtained in Preparation Example 1 was added to the above-mentioned Q precursor hydrolysate at a B / Q ratio of 0.010, and the reaction was continued for 20 min to obtain a Q precursor system containing a B-O-Si bridging structure. Subsequently, the temperature was lowered to 40 °C, and 97.4 g of hexamethyldisiloxane was added to make the molar ratio of the end-capping agent (based on M units) to the silicate ester (based on Q units) M / Q 1.20, and the reaction was carried out for 55 min for end-capping.

[0032] After end-capping, 320g of toluene was added to the system, and the temperature was raised to 80℃. The system was then kept at this temperature for 4 hours for de-alcoholization and dehydration, allowing the generated MQ silicone resin to enter the organic phase. After the reaction was completed, the system was allowed to stand and separate into two phases. The organic phase was taken and washed with deionized water until the pH of the aqueous phase was 6.5-7.0. Subsequently, the organic phase was dehydrated under reduced pressure and distilled under reduced pressure to remove toluene and low-boiling components, yielding MQ silicone resin with controllable molecular weight for coatings. Example 2

[0033] MQ silicone resin was prepared according to the method of Example 1, with the following differences: the pH of the acidic aqueous phase was 1.2; after the addition was completed, pre-hydrolysis was continued for 10 min; the Q precursor hydrolysate was diluted with deionized water at a mass ratio of 1:9, and the transmittance was measured at 600 nm wavelength at 25°C using a 1 cm cuvette and deionized water as a blank reference, with a transmittance of 70%; borosilicate regulator B obtained in Preparation Example 2 was added at a B / Q ratio of 0.0005; the end-capping agent was hexamethyldisiloxane, and the molar ratio of the end-capping agent (based on M units) to the silicate ester (based on Q units) was 0.85; the end-capping reaction temperature was 35°C, and the end-capping reaction time was 30 min; the de-alcoholization and dehydration treatment temperature was 70°C, and the treatment time was 2 h. All other conditions were the same as in Example 1. Example 3

[0034] MQ silicone resin was prepared according to the method of Example 1, with the following differences: the pH of the acidic aqueous phase was 3.0; pre-hydrolysis was continued for 30 min after the addition was completed; the Q precursor hydrolysate was diluted with deionized water at a mass ratio of 1:9, and the transmittance was measured at 600 nm wavelength at 25°C using a 1 cm cuvette and deionized water as a blank reference, with a transmittance of 95%; borosilicate regulator C obtained in Preparation Example 3 was added at a B / Q ratio of 0.030; the end-capping agent was hexamethyldisiloxane, and the molar ratio of the end-capping agent (based on M units) to the silicate ester (based on Q units) was 1.60; the end-capping reaction temperature was 50°C, and the end-capping reaction time was 75 min; the de-alcoholization and dehydration treatment temperature was 90°C, and the treatment time was 5 h. All other conditions were the same as in Example 1. Example 4

[0035] MQ silicone resin was prepared according to the method of Example 1, except that: tetraethyl orthosilicate was replaced with methyl orthosilicate in an equal molar amount of Q units; the end-capping agent consisted of hexamethyldisiloxane and 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, wherein the M units provided by 1,3-divinyl-1,1,3,3-tetramethyldisiloxane accounted for 5 mol% of the total M units provided by the end-capping agent; and xylene was used as the organic solvent. All other conditions were the same as in Example 1. Example 5

[0036] MQ silicone resin was prepared according to the method of Example 1, except that: the pH of the acidic aqueous phase was adjusted to 2.0 with sulfuric acid; tetraethyl orthosilicate was replaced with polyethyl orthosilicate in an equal molar amount of Q units; the end-capping agent consisted of hexamethyldisiloxane and 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, wherein the M units provided by 1,3-divinyl-1,1,3,3-tetramethyldisiloxane accounted for 45 mol% of the total M units provided by the end-capping agent; and the organic solvent was a mixture of butyl acetate and methyl isobutyl ketone in a mass ratio of 1:1. All other conditions were the same as in Example 1.

[0037] Comparative Example 1 MQ silicone resin was prepared according to the method of Example 1, except that borosilicate regulator A was not added. After the Q precursor hydrolysate was diluted with deionized water at a mass ratio of 1:9, and the transmittance was measured at 600 nm wavelength at 25°C using a 1 cm cuvette and with deionized water as a blank reference, the end-capping agent was directly added for end-capping. The remaining conditions were the same as in Example 1.

[0038] Comparative Example 2 MQ silicone resin was prepared according to the method of Example 1, except that the transmittance at 600 nm was not used as the process criterion, but rather borosilicate regulator A and end-capping agent were added when pre-hydrolysis was insufficient. Testing showed that before adding borosilicate regulator A, the Q precursor hydrolysate, after being diluted with deionized water at a mass ratio of 1:9, had a transmittance of 98% at 600 nm using a 1 cm cuvette at 25°C and with deionized water as a blank reference. All other conditions were the same as in Example 1.

[0039] Comparative Example 3 MQ silicone resin was prepared according to the method of Example 1, except that the pre-hydrolysis time was significantly extended, and borosilicate regulator A and end-capping agent were added after excessive condensation of the Q precursor. Before adding borosilicate regulator A, the Q precursor hydrolysate, diluted with deionized water at a mass ratio of 1:9, showed a transmittance of 65% at 25°C, using a 1 cm cuvette and deionized water as a blank reference, at a wavelength of 600 nm. All other conditions were the same as in Example 1.

[0040] Comparative Example 4 MQ silicone resin was prepared according to the method of Example 1, except that tetraethyl orthosilicate, borosilicate regulator A, and hexamethyldisiloxane were added simultaneously at the initial stage of the reaction, the "pre-hydrolysis without end-capping agent" step was omitted, and the transmittance of the Q precursor was not determined. All other post-treatment conditions were the same as in Example 1.

[0041] Comparative Example 5 MQ silicone resin was prepared according to the method of Example 1, except that the borosilicate regulator A obtained in Example 1 was replaced with boric acid in an equal molar amount of element B. Specifically, after the Q precursor hydrolysate was diluted with deionized water at a mass ratio of 1:9, and the transmittance was measured at 600 nm wavelength at 25°C using a 1 cm cuvette and deionized water as a blank reference, 0.62 g of boric acid was added to make the molar ratio of element B to silicate ester (based on Q units) B / Q 0.010. The reaction was continued for 20 min, and then a capping agent was added for capping. The remaining conditions were the same as in Example 1. Test methods

[0042] 1. Molecular weight and molecular weight distribution testing: The number-average molecular weight (Mn) and weight-average molecular weight (Mw) of MQ silicone resin were determined by gel permeation chromatography, and the Mw / Mn ratio was calculated. Tetrahydrofuran was used as the mobile phase, and narrow-distribution polystyrene was used as the calibration standard. The test was conducted according to the size exclusion chromatography principle of ASTM D5296.

[0043] 2. M / Q molar ratio test; quantitative method used. 29 Si-NMR was used to determine the integrated areas of M and Q units in MQ silicone resin, and the M / Q molar ratio was calculated based on the integrated areas.

[0044] 3. Residual silanol content test: Fourier transform infrared spectroscopy was used to determine the characteristic absorption peak of Si-OH in MQ silicone resin, and semi-quantitative analysis was performed in combination with the standard sample curve to obtain the residual silanol content.

[0045] 4. Accelerate storage stability testing MQ silicone resin was prepared into a toluene solution with a solid content of 50 wt%, and stored in a sealed container at 50°C for 30 days. The viscosity was measured before and after storage, and the viscosity increase rate was calculated using the following formula: Viscosity growth rate = (viscosity after storage - viscosity before storage) / viscosity before storage × 100%.

[0046] 5. Evaluation of resin compatibility and transparency: Mix MQ silicone resin and hydroxyl acrylic resin at a solid mass ratio of 20:100, add butyl acetate to adjust the solid content to 50wt%, stir evenly, and let stand at 25℃ for 24h. Observe whether layering, precipitation or fogging occurs. At 25℃, use a 1 cm cuvette and butyl acetate as a blank reference to measure the transmittance at a wavelength of 600nm.

[0047] 6. Coating performance testing; the coating was prepared according to GB / T 1727. Pull-off adhesion was determined according to GB / T 5210; water resistance was determined according to GB / T 1733, with an immersion time of 240 h; 60° gloss was determined according to GB / T 9754; water contact angle was measured using a contact angle meter, with deionized water as the test solution, a single drop volume of 5 μL, and 5 different locations were tested for each sample, with the average value taken; artificial weathering was conducted according to GB / T 1865, with an aging time of 1000 h, and the appearance after aging was rated according to GB / T 1766, and the 60° gloss retention rate was calculated.

[0048] Application Example 1 A polyurethane acrylic varnish composition was obtained by mixing 100 parts of hydroxyl acrylic resin, 20 parts of MQ silicone resin obtained in Example 1, and an appropriate amount of hexamethylene diisocyanate trimer curing agent to achieve an NCO / OH molar ratio of 1.05. Butyl acetate was added to adjust the application viscosity, and the mixture was stirred thoroughly. This composition was sprayed onto the surface of a treated aluminum plate, leveled at room temperature for 10 minutes, dried at 80°C for 30 minutes, and then cured at 23°C and 50% relative humidity for 7 days to obtain a coating film.

[0049] Application Example 2 Using 100 parts of hydroxyl polyester resin, 3 parts of MQ silicone resin obtained in Example 1, and an appropriate amount of hexamethylene diisocyanate trimer curing agent, the NCO / OH molar ratio was adjusted to 1.05. A mixed solvent of butyl acetate and xylene was added to adjust the application viscosity, and the mixture was stirred until homogeneous to obtain a polyester varnish composition. A coating film was prepared according to the method of Application Example 1.

[0050] Application Example 3 Using 100 parts of hydroxyl fluorocarbon resin, 40 parts of MQ silicone resin obtained in Example 1, and an appropriate amount of hexamethylene diisocyanate trimer curing agent, the NCO / OH molar ratio was adjusted to 1.05. Butyl acetate was added to adjust the application viscosity, and the mixture was stirred evenly to obtain a fluorocarbon varnish composition. A coating film was prepared according to the method of Application Example 1.

[0051] Application Comparative Example 1 The coating composition was prepared according to the method of Application Example 1, except that MQ silicone resin was not added.

[0052] Table 1. Test results of MQ silicone resin structure and stability

[0053] Table 2. Test results of coating composition and coating film performance

[0054] Results Analysis As shown in Table 1, Example 1, using median or near-median process conditions, yielded an MQ silicone resin with a Mw / Mn ratio of 1.62, a residual silanol content of 0.28 wt%, a viscosity increase of 3.5% after 30 days of storage at 50°C, and a 600nm transmittance of 93% after blending with hydroxyl acrylic resin. This indicates that the resin obtained under these conditions has a narrow molecular weight distribution, few residual active groups, good storage stability, and good coating compatibility. Examples 2 and 3 cover low-end and high-end key parameters, respectively. Although their overall performance is slightly lower than that of Example 1, it is still superior to the comparative examples, demonstrating that within the scope defined by this invention, MQ silicone resins with controllable molecular weight and suitable for coating systems can be obtained.

[0055] Comparative Example 1 shows that without the addition of a borosilicate regulator, the resin molecular weight distribution becomes wider and the residual silanol content increases. Comparative Examples 2 and 3 show that insufficient or excessive condensation of the Q precursor is detrimental to subsequent end-capping and molecular weight control. Comparative Example 4 shows that if a co-feeding one-pot method is used, it is difficult to form a Q precursor with controllable state, and the stability and compatibility of the resulting resin decrease significantly. Comparative Example 5 shows that ordinary boric acid cannot replace borosilicate regulators containing B-O-Si bonds. Therefore, it is evident that the "pre-hydrolysis without end-capping agent, 600nm transmittance determination, borosilicate regulator bridging adjustment, and subsequent end-capping locking" in this invention have a synergistic effect.

[0056] As shown in Table 2, when the MQ silicone resin obtained in Example 1 is used in acrylic, polyester, and fluorocarbon coating systems, the resulting coatings exhibit good adhesion, water resistance, hydrophobicity, and gloss retention after artificial weathering. Compared with the comparative example without the addition of MQ silicone resin, the MQ silicone resin of this invention can significantly improve the water contact angle and gloss retention after aging, and improve the water resistance and weather resistance of the coating, indicating that it is suitable as a functional silicone resin component for coatings.

[0057] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a molecular weight controllable MQ silicone resin for coatings, characterized in that, Includes the following steps: S1. Without adding a capping agent, silicate ester is added dropwise to an acidic aqueous phase with a pH of 1.2-3.0 for pre-hydrolysis. The system temperature during the dropwise addition is 35-60℃, and the dropwise addition time is 10-40 min. After the dropwise addition is completed, the pre-hydrolysis is continued for 5-45 min to obtain the Q precursor hydrolysate. S2. After diluting the Q precursor hydrolysate obtained in step S1 with deionized water at a mass ratio of 1:9, at 25°C, using a 1 cm cuvette and with deionized water as a blank reference, when the transmittance is measured at a wavelength of 600 nm and is 70-95%, a borosilicate regulator is added to the Q precursor hydrolysate and the reaction is carried out for 10-30 min to obtain a Q precursor system containing a B-O-Si bridging structure. The borosilicate regulator is a cyclic borosilicate compound and / or an oligomeric borosilicate compound containing B-O-Si bonds in its molecule. The molar ratio of the borosilicate regulator (based on element B) to the silicate ester (based on Q units) is 0.0005-0.

030. S3. Add a capping agent to the Q precursor system containing the B-O-Si bridging structure obtained in step S2 to carry out a capping reaction. The capping agent provides M units represented by R3SiO1 / 2, wherein each R is independently selected from methyl and vinyl. The molar ratio M / Q of the capping agent (based on M units) to the silicate ester (based on Q units) is 0.85-1.

60. The capping reaction temperature is 25-55℃ and the capping reaction time is 20-90 min to obtain the reaction system. S4. In the presence of an organic solvent, the reaction system obtained in step S3 is subjected to de-alcoholization and dehydration treatment at 60-95℃ for 1-6 hours to reduce the residual alcohol and water in the reaction system and reduce the residual silanols, thereby obtaining a resin system containing a B-O-Si structure. S5. After phase separation, water washing, dehydration and vacuum distillation to remove organic solvents and low-boiling components, the molecular weight controllable MQ silicone resin for coatings is obtained.

2. The preparation method according to claim 1, characterized in that, In step S1, the pH of the acidic aqueous phase is 1.5-2.5, the addition time of the silicate ester is 15-25 min, the system temperature during the addition process is 40-55℃, and the pre-hydrolysis continues for 10-30 min after the addition is completed.

3. The preparation method according to claim 1, characterized in that, In step S2, the Q precursor hydrolysate is diluted with deionized water at a mass ratio of 1:

9. When the transmittance is measured at 600 nm wavelength at 25°C using a 1 cm cuvette and with deionized water as a blank reference, and the transmittance is 78-92%, the borosilicate modifier is added.

4. The preparation method according to claim 1, characterized in that, The silicate ester is one or more of tetraethyl orthosilicate, methyl orthosilicate, polyethyl orthosilicate, and polymethyl orthosilicate; the acidity of the acidic aqueous phase is adjusted by hydrochloric acid and / or sulfuric acid.

5. The preparation method according to claim 1, characterized in that, The borosilicate regulator is obtained by alcoholysis condensation or dehydration condensation of borate esters and / or boric acid with a linear polysiloxane containing silanol groups; the number average molecular weight of the borosilicate regulator is 300-3000.

6. The preparation method according to claim 5, characterized in that, The borate ester is one or more of trimethyl borate, triethyl borate, and triphenyl borate; the linear polysiloxane containing silanol groups is one or more of hydroxyl-terminated polydimethylsiloxane, hydroxyl-terminated methylphenylsiloxane, and hydroxyl-terminated methylvinylsiloxane.

7. The preparation method according to claim 1, characterized in that, In step S3, the end-capping agent includes hexamethyldisiloxane and / or 1,3-divinyl-1,1,3,3-tetramethyldisiloxane; when the end-capping agent includes both hexamethyldisiloxane and 1,3-divinyl-1,1,3,3-tetramethyldisiloxane, the M units provided by 1,3-divinyl-1,1,3,3-tetramethyldisiloxane account for 5-45 mol of the total M units provided by the end-capping agent.

8. The preparation method according to claim 1, characterized in that, In step S4, the organic solvent is one or more of toluene, xylene, butyl acetate, and methyl isobutyl ketone.

9. A molecular weight controllable MQ silicone resin for coatings, characterized in that, The MQ silicone resin is prepared by the method described in any one of claims 1-8, and comprises M units represented by R3SiO1 / 2, Q units represented by SiO4 / 2, and borosilicate bridging units containing B-O-Si bonds. The molar ratio of M units to Q units in the MQ silicone resin, M / Q, is 0.70-1.

40. The weight-average molecular weight Mw to the number-average molecular weight Mn of the MQ silicone resin is not greater than 2.

50.

10. The application of the molecular weight controllable MQ silicone resin for coatings according to claim 9 in the preparation of coating compositions, characterized in that, The coating composition comprises a film-forming resin and a molecular weight controllable MQ silicone resin for coating; the amount of the molecular weight controllable MQ silicone resin for coating is 3-40 parts per 100 parts of solid mass of the film-forming resin; the film-forming resin is one or more of acrylic resin, polyester resin, epoxy resin, fluorocarbon resin, and polyurethane resin.

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