Cardanol modified polymerized MDI, polyurethane floor paint based on cardanol modified polymerized MDI and preparation method of polyurethane floor paint

Abstract

The invention discloses anacardol modified polymerized MDI, which is prepared by the following method: carrying out hydrolysis reaction on anacardol glycidyl ether under an acidic condition to generate anacardol derived diol; and then reacting the cardanol-derived diol with the polymerized MDI at the temperature of 75-80 DEG C. The invention further discloses polyurethane floor paint based on cardanol modified polymerized MDI. The polyurethane floor paint is prepared from a component A and a component B, the component A is hydroxyl-containing resin or polyol, and the component B comprises cardanol modified polymerized MDI. The floor paint is prepared by reacting cardanol modified polymerized MDI with a hydroxyl-containing substance, a cardanol side chain introduced by the cardanol modified polymerized MDI plays roles of'molecular diluent 'and'space shielding', and the reaction speed and system viscosity of the floor paint are reduced, so that the floor paint has excellent construction performance and low bubble characteristic. The invention further discloses a preparation method of the polyurethane floor paint based on the cardanol modified polymerized MDI.

Description

Cashew phenol-modified polymeric MDI, polyurethane floor coatings based on cashew phenol-modified polymeric MDI and their preparation methods Technical Field

[0001] This invention belongs to the technical field of polymer materials, specifically relating to polyurethane floor coatings based on cashew phenol-modified polymeric MDI, cashew phenol-modified polymeric MDI, and their preparation methods. Background Technology

[0002] Polyurethane floor coatings are widely used in industrial plants, parking lots, and commercial spaces due to their excellent abrasion resistance, chemical corrosion resistance, high elasticity, and decorative properties. Their curing system typically consists of a hydroxyl-containing resin (component A) and a polyisocyanate curing agent (component B). Using polymeric MDI (typical brands such as Huntsman's Suprasec® 2464, Wanhua Chemical's PM-200, and BASF's M20S) as component B imparts high hardness, high modulus, and excellent chemical resistance to the coating film.

[0003] However, polymeric MDI typically has an average functionality greater than 2.0, and its direct application in floor coatings faces three major technical bottlenecks: First, poor workability. Due to its high functionality and reactivity, the viscosity of the system increases rapidly after mixing with hydroxyl-containing components, resulting in a short pot life and poor leveling, making large-area application difficult. Second, high internal stress and brittleness. The high crosslinking density leads to a decrease in the flexibility of the coating film, making it prone to microcracks or loss of adhesion when subjected to temperature changes or slight deformation of the substrate. Third, significant air bubble problems. The high viscosity and rapid reaction make it difficult for air bubbles trapped during application to escape, resulting in pinholes and air bubbles in the cured coating film, affecting its appearance and protective performance.

[0004] To improve workability, inert solvents or physical diluents are often added, but this reduces VOC environmental friendliness and may impair the final performance. Cashew nut shell oil, a natural phenolic compound extracted from cashew nut shell oil, possesses a molecular structure that combines the rigidity of a benzene ring with the flexibility of a C15 long-chain alkane, making it an ideal polymer modifier. How to cleverly incorporate cashew nut shell oil into polyurethane curing systems in an appropriate manner through molecular design, while significantly improving the rheological properties during application, and perfectly balancing the overall properties of the coating film, such as hardness, flexibility, and adhesion, is a pressing technical problem to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to provide a cashew phenol-modified polymeric MDI, a polyurethane floor coating based on cashew phenol-modified polymeric MDI, and a method for preparing the same, in order to solve the technical problems of poor construction performance, poor adhesion, and bubbles appearing after curing in existing floor coatings.

[0006] According to a first aspect of the present invention, cashew phenol-modified polymeric MDI is provided, the structural formula of which is shown in formula (I):

[0007] Formula (I) where R1 is methylene or phenyl, and R2 is... , n=2~10.

[0008] This invention utilizes cashew phenol to convert into cashew phenol-derived diol, and then uses this diol to carry out a controlled prepolymerization reaction with polymeric MDI to synthesize a modified polymeric MDI with flexible long side chains. The raw material, cashew phenol glycidyl ether, is a green bio-based raw material, reducing the consumption of petroleum-based raw materials.

[0009] In some embodiments, the mass fraction of NCO in the cashew phenol-modified polymeric MDI is 10%-12%.

[0010] According to a second aspect of the present invention, a method for preparing the above-mentioned cashew phenol-modified polymeric MDI is provided, comprising the following steps: S1, reacting cashew phenol glycidyl ether under acidic conditions to generate cashew phenol-derived diol; S2, dissolving the polymeric MDI in an organic solvent at 70-85°C to obtain a first mixture, dissolving the cashew phenol-derived diol in an organic solvent to obtain a second mixture, heating the first mixture to 70-85°C in an inert gas atmosphere, then adding the second mixture dropwise to the first mixture while maintaining the temperature of the first mixture at (80±2)°C, and reacting at 70-85°C until the hydroxyl groups in the reaction system disappear, thereby obtaining the product.

[0011] In some embodiments, the specific steps of the reaction of cashew phenol glycidyl ether under acidic conditions in step S1 include: mixing cashew phenol glycidyl ether with an aqueous hydrochloric acid solution and heating to 100-105°C for reaction; wherein the aqueous hydrochloric acid solution is an aqueous hydrochloric acid solution with a mass concentration of 5%-15%, and the mass ratio of cashew phenol glycidyl ether to aqueous hydrochloric acid solution is 1:(1.5-2.5). The reaction formula for the hydrolysis reaction of cashew phenol glycidyl ether under acidic conditions is shown below: .

[0012] In some embodiments, the reaction time in step S1 is 10-16 hours. Preferably, the reaction time is 14 hours.

[0013] In some embodiments, step S1 includes purification after the reaction. The purification step is as follows: the mixture obtained from the reaction is cooled to room temperature and extracted three times with ethyl acetate, and the organic phases are combined; the organic phase is washed with deionized water until the aqueous phase is neutral as detected by pH test paper, and then the organic phase is dried with anhydrous sodium sulfate, filtered, and the filtrate is evaporated by rotary evaporator under conditions of 60°C water bath and -0.095 MPa to remove ethyl acetate.

[0014] In some implementations, the reaction formula for step S2 is as follows: R2 is .

[0015] In some embodiments, the molar ratio of isocyanate groups (NCO) to hydroxyl groups (OH) of cashew phenol-derived diol in step S2 is 1.8:1 to 2.2:1; preferably, the molar ratio is 2.0:1. The polymeric MDI has an average functionality of 2.2 to 3.0 and a viscosity of 100-3000 mPa·s at 25°C. The polymeric MDI can be Huntsman's Suprasec® 2464, Wanhua Chemical's PM-200, or BASF's M20S.

[0016] In some embodiments, the organic solvent in step S2 is selected from at least one of acetone, butanone, ethyl acetate, and toluene. Preferably, the organic solvent is anhydrous butanone.

[0017] In some embodiments, in step S2, the organic solvent is removed by vacuum distillation. Specifically, the reaction solution obtained after the reaction is cooled to (50±2)°C and transferred to a rotary evaporator, where the organic solvent is removed by distillation under conditions of a 65°C water bath and -0.098 MPa.

[0018] In some embodiments, the inert gas in step S2 is nitrogen.

[0019] According to a third aspect of the present invention, a polyurethane floor coating based on cashew phenol-modified polymeric MDI is provided, wherein the raw materials are composed of component A and component B; component A is a hydroxyl-containing resin or polyol, and component B includes cashew phenol-modified polymeric MDI.

[0020] This invention utilizes cashew phenol to convert into cashew phenol-derived diol, and then uses this diol to undergo a controlled prepolymerization reaction with polymeric MDI to synthesize a modified polymeric MDI with flexible long side chains. These side chains act as "molecular diluents" and "spatial shields" in the floor coating, reducing the reaction rate after mixing with component A, resulting in a viscosity more suitable for trowel application and excellent leveling properties. Furthermore, this modified polymeric MDI, as the curing agent component (component B) of the floor coating, has lower functionality than the original polymeric MDI. After reacting with component A, it forms a polyurethane floor coating with a more complete microstructure, lower internal stress, and fewer bubble defects.

[0021] In some embodiments, when component A and component B are mixed, the ratio is from 1.05:1 to 1.20:1, based on the equivalent ratio of isocyanate groups (NCO) of component B to hydroxyl groups (OH) of component A.

[0022] In some embodiments, component B further includes polymeric MDI, the structural formula of which is... , where R1 is methylene or phenyl, and n=2~10.

[0023] In some embodiments, the polymeric MDI is polymeric diphenylmethane diisocyanate.

[0024] In some embodiments, when component B is a mixture of polymeric MDI and cashew phenol-modified polymeric MDI, the molar ratio of cashew phenol-modified polymeric MDI to polymeric MDI is 10:1 to 1:10. Preferably, the molar ratio of cashew phenol-modified polymeric MDI to polymeric MDI is 1:9 to 6:4. This mixing method can maintain the excellent workability and low-bubble characteristics of modified polymeric MDI, and further improve the crosslinking density and hardness of the coating film by introducing some high-functionality polymeric MDI, meeting more stringent wear and pressure resistance requirements, while the bubble control of the system is still better than that of the polymeric MDI system.

[0025] In some embodiments, the polyol may be selected from at least one of castor oil, polyether polyol, and polyester polyol. The polyether polyol is a polyoxypropylene ether polyol (molecular weight of 400-3000).

[0026] In some embodiments, the structural formula of the polyol is as follows: .

[0027] According to a fourth aspect of the present invention, a method for preparing a polyurethane floor coating based on cashew phenol-modified polymeric MDI is provided, comprising the following steps: mixing component A and component B to obtain a construction slurry, applying the construction slurry to the surface of a substrate, and curing the coating to obtain the final product.

[0028] In some implementations, curing is performed at 10-30°C for 8-48 hours.

[0029] Compared with the prior art, the present invention has the following significant beneficial effects: (1) By introducing a bifunctional cashew phenol-derived diol, the present invention grafts long flexible side chains onto the polymeric MDI skeleton. After mixing with component A, the side chains act as "molecular diluents" and "spatial shields," reducing the reaction rate and system viscosity, thereby extending the pot life of the mixed slurry by more than 50%, which is reflected in the low bubble properties of the floor coating film and the extension of surface drying and hard drying time. The viscosity is more suitable for scraping construction, the leveling properties are excellent, and the construction performance is greatly improved.

[0030] (2) In the cashew phenol modified polymeric MDI of the present invention, the flexible long chain of cashew phenol derived diol as "soft segment" and the inherent rigid "hard segment" of polymeric MDI form a more perfect microphase separation structure in the cured film. This structure enables the paint film to maintain a high pencil hardness (up to HB-H) while ensuring flexibility (shaft bending ≤2mm) and adhesion performance, resulting in excellent overall performance of the paint film.

[0031] (3) The raw materials are widely compatible and the performance is highly designable. The preparation method of this invention is applicable to various polymeric MDIs with a functionality greater than 2.0 (such as 2464, PM-200, M20S, etc.), and the process has strong universality. By selecting different types of polymeric MDIs, adjusting the proportion of cashew phenol-derived diols, or adjusting the type and functionality of polyols in component A, the hardness, modulus, elasticity and other properties of the coating film can be finely controlled within a wide range to meet the needs of different application scenarios.

[0032] (4) This invention successfully introduces a high proportion of bio-based raw materials such as cashew phenol-derived diol and castor oil, which reduces the consumption of petroleum-based raw materials, conforms to the direction of green chemistry and sustainable development, and is environmentally friendly.

[0033] (5) The entire synthesis process of the cashew phenol-modified polymerized MDI of the present invention is mild, requires no special equipment, the reaction is controllable, the yield is high, the process is feasible, and it is suitable for large-scale production. Attached Figure Description

[0034] Figure 1 shows the infrared spectra of polymeric MDI, cashew phenol-modified polymeric MDI, cashew phenol-derived diol, and cashew phenol glycidyl ether (CGE) of the present invention; Figure 2 shows the polyurethane floor coatings prepared in Examples 3-7 and Comparative Example 1 of the present invention. Detailed Implementation

[0035] The present invention will now be described in further detail with reference to the accompanying drawings, but the embodiments of the present invention are not limited thereto. The raw materials and reagents involved in the following embodiments are all commercially available.

[0036] Unless otherwise specified, all raw materials used in the examples are industrial grade products. Cashew phenol glycidyl ether was purchased from Cardläne Company. Castor oil (industrial grade, hydroxyl value 160±10 mg KOH / g) was commercially available.

[0037] This invention modifies polymeric diphenylmethane diisocyanate (polymeric MDI) through molecular design. It utilizes the hydroxyl groups of cashew phenol-derived diol to polymerize with the -NCO group of polymeric MDI, synthesizing cashew phenol-modified polymeric MDI with flexible long side chains. Its functionality is lower than that of polymeric MDI, and the side chains act as "molecular diluents" and "spatial shields" in floor coatings, reducing the reaction rate after mixing with component A. Furthermore, the viscosity of cashew phenol-modified polymeric MDI is more suitable for trowel application, and it has excellent leveling properties.

[0038] Example 1 This example provides a method for preparing cashew nut glycol (CGED), comprising the following steps: In a 1000 mL three-necked flask equipped with a stirrer, thermometer, and reflux condenser, 305 g (approximately 1.0 mol) of cashew nut glycol glycidyl ether and 610 g of a 10% hydrochloric acid aqueous solution are added. Stirring is started, and the mixture is heated to reflux (temperature approximately 100-105°C), and the reaction is continued at this temperature for 14 hours. Heating is stopped, and the reaction mixture is cooled to room temperature and transferred to a separatory funnel. Extraction is performed three times with ethyl acetate (300 mL each time), and the organic phases are combined. The organic phase is washed with deionized water until the aqueous phase is neutral as determined by pH paper. Then, the organic phase is poured into an Erlenmeyer flask, and sufficient anhydrous sodium sulfate is added for drying overnight. The drying agent is removed by filtration, and the filtrate is evaporated using a rotary evaporator at a water bath at 60°C and -0.095 MPa to remove ethyl acetate, yielding 256 g of a pale yellow viscous liquid.

[0039] The product yield was calculated to be 84%. Titration analysis showed that the hydroxyl value of the product was 285 mg KOH / g, close to the theoretical value (290 mg KOH / g), indicating that the target product, cashew phenol derivative diol, was successfully synthesized.

[0040] Example 2 This example provides a method for preparing cashew phenol-modified polymeric MDI (C-MDI), comprising the following steps: (1) In a dry 1000 mL three-necked flask, nitrogen protection, a stirring device, a thermometer, and a constant pressure dropping funnel are connected. 500 g of Huntsman Suprasec® 2464 polymeric MDI (NCO mass fraction of approximately 31.5%, viscosity of approximately 200 mPa·s, functionality of approximately 2.4) and 300 mL of anhydrous butanone are added to the three-necked flask, nitrogen gas is introduced, the mixture is stirred, and the temperature is raised to 80°C to completely dissolve the polymeric MDI.

[0041] (2) In another beaker, weigh 334 g of CGED (hydroxyl value 285 mg KOH / g, hydroxyl equivalent approximately 197 g / eq) prepared in Example 1, dissolve it in 300 mL of anhydrous butanone, and pour it into a constant pressure dropping funnel. After the temperature of the three-necked flask system stabilizes at 80°C, slowly add anhydrous butanone containing CGED, controlling the dropping rate to maintain the reaction temperature at 80±2°C. The addition is completed in about 1.5 hours. After the addition is complete, continue the reaction at 80°C for 3 hours. During the reaction, take a sample every 30 minutes, coat it on a KBr salt plate, and monitor the hydroxyl characteristic peak (3450 cm⁻¹) using FT-IR. -1 The change was observed. After 3 hours, the hydroxyl peak was barely noticeable, which was considered the end point of the reaction, and the reaction solution was obtained.

[0042] (3) The reaction solution was cooled to about 50°C and transferred to a rotary evaporator. Anhydrous butanone was removed by distillation under conditions of 65°C water bath and -0.098 MPa until constant weight was obtained, yielding about 785 g of brownish-red transparent viscous liquid (C-MDI), with a yield of about 94%. The NCO mass fraction of the product was determined to be 10.1% by titration using the di-n-butylamine method.

[0043] The cashew phenol-derived diol prepared in Example 1, the cashew phenol-modified polymeric MDI prepared in Example 2, the Suprasec® 2464 polymeric MDI, and CGE were subjected to infrared spectroscopy. The results are shown in Figure 1. As can be seen from Figure 1, CGE is concentrated in the range of 3200-3600 cm⁻¹. -1 The broad peaks are attributed to the -OH stretching vibration of the alcohol hydroxyl group. Meanwhile, the saturated CH bonds of the long aliphatic side chains show peaks at 2850-2960 cm⁻¹. -1 The strong absorption peak at 1450-1600 cm⁻¹ is due to the C=C vibration of the benzene ring skeleton. -1 920-950cm -1 Epoxy characteristic peaks appear, with a peak at 2270 cm⁻¹ in the MDI 2464 spectrum. -1 The peak is the absorption peak of -NCO, at 3350 cm⁻¹. -1 The peak is the stretching vibration peak of the -NH group in the carbamate. After acid-catalyzed hydrolysis, the absorption intensity of the stretching vibration peak of the -OH group in CGE increases significantly, and it is located in the range of 920-950 cm⁻¹. -1 The intensity of the characteristic peaks of epoxy decreased, proving that CGED hydrolysis was successful. After CGED reacts with MDI 2464, the absorption peak of -NCO at 3350 cm⁻¹ weakens. -1 The peak is a further enhancement of the stretching vibration peak of -NH in the carbamate. Furthermore, the disappearance of the hydroxyl peak in CGED confirms the successful synthesis of C-MDI.

[0044] Example 3 This example provides a polyurethane floor coating based on cashew phenol-modified polymeric MDI, comprising, by weight, 30.7 parts castor oil, 13.4 parts Suprasec® 2464 polymeric MDI, and 10.8 parts C-MDI prepared in Example 2. The molar ratio of polymeric MDI to C-MDI is 2:8.

[0045] Polymerized MDI and C-MDI were placed in a 500 mL plastic beaker and stirred at 800 rpm for 3 minutes using a high-speed mechanical stirrer to obtain a uniform, free-flowing, light brown slurry. At this point, the equivalent ratio of NCO to OH was approximately 1.2:1.

[0046] Example 4 This example provides a polyurethane floor coating based on cashew phenol-modified polymeric MDI. The difference from Example 3 is that, by weight, it includes 30.7 parts castor oil, 10 parts Suprasec® 2464 polymeric MDI, and 20.17 parts C-MDI. The molar ratio of polymeric MDI to C-MDI is 4:6.

[0047] Example 5 This example provides a polyurethane floor coating based on cashew phenol-modified polymeric MDI. The difference from Example 3 is that, by weight, it includes 30.7 parts castor oil, 6.4 parts Suprasec® 2464 polymeric MDI, and 30.9 parts C-MDI. The molar ratio of polymeric MDI to C-MDI is 6:4.

[0048] Example 6 This example provides a polyurethane floor coating based on cashew phenol-modified polymeric MDI. The difference from Example 3 is that, by weight, it includes 30.7 parts castor oil, 3.3 parts Suprasec® 2464 polymeric MDI, and 40.4 parts C-MDI. The molar ratio of polymeric MDI to C-MDI is 8:2.

[0049] Example 7 This example provides a polyurethane floor coating based on cashew phenol-modified polymeric MDI. The difference from Example 3 is that, by weight, it includes 30.7 parts castor oil and 51.5 parts C-MDI.

[0050] Comparative Example 1: This comparative example provides a polyurethane floor coating based on polymeric MDI, prepared by the following method: 16 parts of Huntsman Suprasec® 2464 polymeric MDI (NCO mass fraction 31.5%, NCO equivalent approximately 133) were directly mixed with 30.7 parts of castor oil. The NCO index at this point was also 1.2.

[0051] The polyurethane floor coatings based on cashew phenol-modified polymeric MDI prepared in Examples 3-7 and the polyurethane floor coatings based on polymeric MDI prepared in Comparative Example 1 were mixed and poured or scraped onto standard test substrates: tinplate (used to test adhesion, flexibility, hardness, and film appearance): after leveling, they were cured for 7 days at room temperature (23±2℃) and relative humidity (50±5)%.

[0052] Cement mortar board (used for testing abrasion resistance and impact resistance): cured for 7 days under the same conditions.

[0053] Glass plate (used to observe appearance and bubble condition): Cured under the same conditions.

[0054] The polyurethane floor coating obtained by the above method was subjected to multiple performance tests according to the following standard methods. All tests were conducted after the coating was fully cured for 7 days under standard conditions (temperature 23±2℃, relative humidity 50±5%), unless otherwise specified.

[0055] 1. Surface drying time and actual drying time (1) The test standard refers to GB / T 1728-1979 "Determination of drying time of paint film and putty film".

[0056] (2) Test method for surface drying time: The finger touch method is used. After the paint film is prepared on the glass plate, it is placed in an environment of 25°C. The surface of the paint film is touched with a finger at regular intervals. When it does not feel sticky, it is considered to be surface dry. The required time is recorded.

[0057] Drying time: The filter paper pressing method was used. A piece of qualitative filter paper (smooth side in contact with the paint film) was placed on the paint film, and a drying time tester (200g, base area 1cm²) was lightly pressed on the filter paper. 2 After 30 seconds, remove the testing apparatus, flip the sample over, and if the filter paper falls freely and there is no filter paper fiber residue or loss of gloss on the paint film, it is considered fully dry. Record the time required.

[0058] 2. Impact resistance (1) The test standard refers to GB / T 1732-1993 "Test method for impact resistance of paint film".

[0059] (2) Test method: Use a paint film impact tester. Place a tinplate coated with paint film on the groove of the impactor, with the paint film facing upwards. Drop a weight (1 kg) freely from a specified height (usually 50 cm) to impact the paint film at the center of the sample. Check whether the paint film at the impact deformation point shows cracking, peeling, or other phenomena. Express the maximum impact height (cm) without cracking or peeling, or directly record "pass" / "fail" (at the specified height).

[0060] 3. Bubble assessment (mechanical bubble / reaction bubble) (1) The test method is to assess the situation of bubbles introduced during construction and bubbles generated by reaction, using a combination of visual observation and rating.

[0061] (2) Sample preparation: Pour the well-stirred construction slurry onto a clean glass plate placed horizontally, and let it flow naturally to form a paint film with a thickness of about 1 mm.

[0062] (3) Evaluation criteria: observation after 7 days of maintenance.

[0063] Rated "Excellent": The paint film surface is as smooth as a mirror, and no visible bubbles or pinholes are visible when viewed from the side under a light source.

[0064] The rating is "Good": The paint film surface is generally smooth, with only a very small number (≤3) of tiny pinholes at the edges or in localized areas.

[0065] The rating is "poor": A small number of scattered bubbles or pinholes are visible on the paint film surface.

[0066] The rating is "poor": There are a large number of dense bubbles or pinholes on the paint film surface, which affects the appearance.

[0067] It should be noted that "mechanical bubbles" mainly evaluate the removal of bubbles introduced by stirring and scraping; "reaction bubbles" are indirectly evaluated through the final paint film appearance, and are bubbles formed because the CO2 gas produced by the reaction fails to escape in time.

[0068] 4. Surface effect (1) Test method Under standard light source, visually observe and record the overall state of the cured paint film surface, including leveling, gloss uniformity, orange peel, pinholes and other defects.

[0069] No bubbles: The surface is flat and smooth, without defects.

[0070] Minor bubbles: There are a few visible defects in a local area, but they do not affect the overall appearance.

[0071] Foaming: Obvious defects exist on the surface, affecting flatness and appearance.

[0072] 5. Pencil hardness (1) The test standard refers to GB / T 6739-2006 "Determination of paint film hardness by pencil method for paints and varnishes".

[0073] (2) Test Method: A set of Zhonghua brand drawing pencils, ranging from the softest (6B) to the hardest (9H), were used. The sample was fixed on a horizontal surface with the paint film facing upwards. Holding the pencil at a 45° angle to the sample, the pencil was advanced forward at a speed of approximately 1 cm / s, with the applied force ensuring the pencil tip did not break. The tests were conducted sequentially from softest to hardest until a hardness grade that could not scratch the paint film was found. This grade was reported as the paint film pencil hardness.

[0074] 6. Flexibility (shaft bending test) (1) The test standard refers to GB / T 6742-2007 "Bending test of paint and varnish (cylindrical shaft)".

[0075] (2) Test method: Use a set of cylindrical rods of different diameters (e.g., 2mm, 4mm, etc.). With the paint film of the painted tinplate facing outward, bend it 180° around the rod at a uniform speed within 2-3 seconds. Observe the paint film of the bent part with a 4x magnifying glass. The flexibility is represented by the smallest rod diameter (mm) in which the paint film does not crack or peel off. For example, "≤2mm" means passing the 2mm rod bending test.

[0076] 7. Adhesion (cross-cut test) (1) The test standard refers to GB / T 9286-1998 "Cross-cut test of paint and varnish film".

[0077] (2) Test Method: Use a cross-cutting tool to cut six parallel cuts on the tinplate coating, spaced 1 mm or 2 mm apart. Then, make the same number of cuts perpendicularly to form a grid pattern. Gently brush away any debris with a soft brush. Firmly adhere pressure-sensitive tape (e.g., 3M 610) to the grid area, then quickly peel it off at a 60° angle within 0.5-1.0 seconds. Rate the coating according to the proportion of area detached from the substrate, comparing it to a standard chart (0 being the best, 5 the worst). Record the rating result in the report, such as "1".

[0078] The experimental results are shown in Table 1. Surface drying time, complete drying time, bubbles, and surface finish reflect the performance of the construction process. Table 1 shows that the polyurethane floor coating film in Comparative Example 1 dries quickly, exhibiting shorter surface and complete drying times. However, it has many bubbles and severe surface foaming, indicating that the high-functionality unmodified MDI reacts violently and has high viscosity, making it difficult for trapped bubbles to escape during construction, resulting in a short application window and poor film appearance. In Examples 3 to 7, the polyurethane floor coating films showed significantly extended surface and complete drying times with increasing cashew phenol-modified polymeric MDI (C-MDI) ratio, and continuously improved bubble control and surface finish. The "mechanical bubble / reactive bubble / surface finish" results improved from "poor / poor / foaming" in Example 3 to "excellent / excellent / no bubbles" in Example 7. This clearly demonstrates that the introduction of flexible long-chain cashew phenol effectively reduces the system's reactivity and viscosity, extends the pot life, and greatly improves the leveling properties and bubble removal ability of the slurry.

[0079] Hardness, flexibility, and adhesion reflect the mechanical properties of the paint film. Table 1 shows that the paint film of Comparative Example 1 has high hardness (3H) but only average flexibility (2mm). In contrast, the polyurethane floor coatings of Examples 3-7 of this invention significantly improve workability while maintaining excellent hardness (HB to H) and flexibility. This is attributed to the more complete microphase separation structure formed by the introduction of long-chain cashew phenols. All examples and the polyurethane floor coatings of Comparative Example 1 achieved the highest adhesion level (Level 1), indicating that the modification method of this invention did not impair the adhesion between the paint film and the substrate, and its core mechanical properties are excellent.

[0080] Table 1 Performance of various polyurethane floor coatings

[0081] The results above show that by adjusting the mixing ratio of polymeric MDI and cashew phenol-modified polymeric MDI, the overall performance of the floor coating can be precisely controlled within a continuous range. Specifically, for the ratio of polymeric MDI to cashew phenol-modified polymeric MDI in polyurethane floor coatings, a higher proportion of polymeric MDI is suitable for complex substrates, applications requiring a bubble-free, perfect appearance, and stress relaxation; a higher proportion of cashew phenol-modified polymeric MDI is suitable for scenarios requiring excellent workability and high flexibility. The polyurethane floor coating prepared in Example 5 achieves the best balance of workability, hardness, and flexibility. By simply adjusting the mixing ratio of cashew phenol-modified polymeric MDI to unmodified polymeric MDI, the drying speed, final hardness, and flexibility of the coating film can be continuously and linearly adjusted without changing the main raw materials, meeting the diverse needs of different application scenarios, from high-wear-resistant industrial flooring to high-decorative commercial flooring.

[0082] In summary, this invention successfully resolves the core contradiction between the "poor workability" (fast drying, high foaming, poor leveling) and the "imbalance in mechanical properties of the coating film" (high hardness but brittleness) of traditional polymeric MDI floor coatings by chemically modifying polymeric MDI with cashew phenol-derived diol. Excellent overall performance: The provided polyurethane floor coating extends the application period, significantly improves leveling and defoaming capabilities, and endows the cured coating film with excellent overall mechanical properties.

[0083] The above descriptions are merely some embodiments of the present invention. Those skilled in the art can make various modifications and improvements without departing from the inventive concept of the present invention, and these all fall within the scope of protection of the present invention.

Claims

1. Cashew nut phenol-modified polymeric MDI, characterized in that, Its structural formula is shown in equation (I): Equation (I) in which, R1 is methylene or phenyl, R2 is... ，n=2~10。 2. The cashew phenol-modified polymeric MDI according to claim 1, characterized in that, The mass fraction of NCO in the cashew phenol-modified polymeric MDI is 10%-12%.

3. The method for preparing cashew phenol-modified polymeric MDI according to claim 1 or 2, characterized in that, The process includes the following steps: S1, reacting cashew phenol glycidyl ether under acidic conditions to generate cashew phenol-derived diol; S2, dissolving polymeric MDI in an organic solvent at 70-85°C to obtain a first mixture, dissolving the cashew phenol-derived diol in an organic solvent to obtain a second mixture, heating the first mixture to 70-85°C in an inert gas atmosphere, then adding the second mixture dropwise to the first mixture while maintaining the temperature of the first mixture at (80±2)°C, and reacting at 70-85°C until the hydroxyl groups in the reaction system disappear, thus obtaining the final product.

4. The method for preparing cashew phenol-modified polymeric MDI according to claim 3, characterized in that, The specific steps for the reaction of cashew phenol glycidyl ether under acidic conditions in step S1 include: mixing cashew phenol glycidyl ether with hydrochloric acid aqueous solution and heating to 100-105℃ for reaction; the hydrochloric acid aqueous solution is a hydrochloric acid aqueous solution with a mass concentration of 5%-15%, and the mass ratio of cashew phenol glycidyl ether to hydrochloric acid aqueous solution is 1:(1.5-2.5).

5. The method for preparing cashew phenol-modified polymeric MDI according to claim 3, characterized in that, The average functionality of the polymeric MDI is 2.2 to 3.0, and the molar ratio of the isocyanate group to the hydroxyl group of the cashew phenol-derived diol in the polymeric MDI is 1.8:1 to 2.2:

1.

6. The method for preparing cashew phenol-modified polymeric MDI according to claim 4, characterized in that, Step S1 includes purification after the reaction. The purification steps are as follows: after cooling the mixture obtained from the reaction to room temperature, it is first extracted three times with ethyl acetate and the organic phases are combined; then the organic phase is washed with deionized water until the aqueous phase is neutral; then the organic phase is dried with anhydrous sodium sulfate, filtered, and the filtrate is distilled off with ethyl acetate by rotary evaporation under conditions of 60°C water bath and -0.095 MPa.

7. A polyurethane floor coating based on cashew phenol-modified polymeric MDI, characterized in that, Its raw materials consist of component A and component B; component A is a hydroxyl-containing resin or polyol, and component B includes cashew phenol-modified polymeric MDI as described in claim 1 or 2, wherein the equivalent ratio of the hydroxyl groups of component A to the isocyanate groups of component B is 1:1.05 to 1:1.

20.

8. The polyurethane floor coating based on cashew phenol-modified polymerized MDI according to claim 7, characterized in that, The polyol is selected from at least one of castor oil, polyether polyol, and polyester polyol.

9. The polyurethane floor coating based on cashew phenol-modified polymerized MDI according to claim 7, characterized in that, Component B also includes polymeric MDI; the molar ratio of cashew phenol-modified polymeric MDI to polymeric MDI is 10:1 to 1:

10.

10. The method for preparing the polyurethane floor coating based on cashew phenol-modified polymeric MDI according to any one of claims 7 to 9, characterized in that... Includes the following steps: The construction slurry is obtained by mixing component A and component B, and then applied to the surface of the substrate. After curing, the slurry is ready.

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