Preparation method of toughened discoloration-resistant phenolic resin, binder and application of toughened discoloration-resistant phenolic resin

Abstract

The invention belongs to the technical field of phenolic resin, and particularly relates to a preparation method of toughened discoloration-resistant phenolic resin, a binder and application. The preparation method of the toughened discoloration-resistant phenolic resin comprises the following steps: reacting 2, 4-diamino-6-vinyl-S-triazine with a benzoyl chloride derivative to prepare a monoalkenyl phenyl triazine derivative; reacting unsaturated dianhydride with the nanocellulose crystal to obtain a double-bond modified nanocellulose crystal; taking a monoalkenyl phenyl triazine derivative and a monoalkenyl epoxy compound as surface modification raw materials, and carrying out in-situ graft polymerization on the double-bond modified nano cellulose crystal to obtain a modified nano cellulose crystal; in an inert atmosphere, phenol, a catalyst and a formaldehyde solution are added into a reaction kettle to be heated and mixed uniformly, a temperature rise reaction is performed, the modified nanocellulose crystals are added to be mixed uniformly, and the temperature rise reaction continues to be performed, so that the toughened discoloration-resistant phenolic resin is obtained and has excellent discoloration resistance and toughness.

Description

Technical Field

[0001] The invention belongs to the technical field of phenolic resins, and particularly relates to a preparation method, a binder and applications of a toughened, discoloration-resistant phenolic resin. Background Art

[0002] Resins formed by the polycondensation of phenolic and aldehyde compounds in the presence of acidic or alkaline catalysts are called phenol-formaldehyde resins (PF). Phenolic resins are among the earliest synthetic resins and are commonly used as resin binders in abrasive tools due to their excellent wear resistance, chemical resistance, mechanical properties, and heat resistance.

[0003] The phenolic hydroxyl groups in the phenolic resin structure are easily oxidized by oxygen in the air to form quinone compounds that have a strong absorption effect on visible light. When the oxidation of the phenolic hydroxyl groups reaches a certain level, the color change of the resin is captured by the human eye and reaches a visually visible level. As the preparation, storage, and use temperature increases and the time increases, the color of the resin changes from light to dark. During the preparation and use of abrasive tools, there are specific requirements for the color when using phenolic resin, which is related to the application scenario of the abrasive tool: for precision grinding, wood / plastic processing, and scenes with high surface treatment requirements (such as white corundum, aluminum oxide sandpaper), dark substances produced by the oxidation of dark resin may migrate to the surface of the workpiece being polished, especially when polishing light-colored or precision parts (such as aluminum alloy, wood), which will cause difficult-to-remove color spots; using light-colored resin can avoid contaminating light-colored substrates (such as light-colored wood, white plastic parts) and facilitate the observation of the color changes of the substrate during the grinding process. Therefore, to ensure that abrasive tools do not contaminate workpieces during use, ensure grinding accuracy and surface quality, and improve the storage stability and product applicability of phenolic resins, researchers in this field have conducted extensive research on preventing and controlling oxidative discoloration of phenolic resins. For example, patent CN102272258B discloses an acrylate-stabilized, phenolic resin-bonded abrasive product and a method for manufacturing the same. The product comprises a phenolic resin binder, a color stabilizer, a colorant, and abrasive particles. The color stabilizer comprises at least one acrylate. This technology improves color stability by trapping phenoloxyl radicals in the acrylate, but its low crosslinking contribution can reduce the wear resistance of the abrasive tool and shorten its service life. Patent CN111269371B discloses a method for preparing a light-colored alkylphenol phenolic resin. The method incorporates an appropriate amount of antioxidant during the preparation process, addressing the problem of darkening the color of the alkylphenol phenolic resin due to oxidation of free phenols during synthesis, as well as the problem of decreased viscosity caused by surface oxidation of the mixed unvulcanized rubber during storage. However, if this phenolic resin is used to prepare abrasive tools, the antioxidant will gradually precipitate onto the surface of the abrasive tool under high temperature or high friction conditions, and the discoloration resistance will decrease.

[0004] Therefore, it is necessary to develop a light-colored phenolic resin suitable for abrasive tools that does not affect other properties and improves discoloration resistance. Summary of the Invention

[0005] To address the above-mentioned technical problem of poor color change resistance and stability, the present invention reacts 2,4-diamino-6-vinyl-S-triazine with a benzoyl chloride derivative to produce a monoalkenyl phenyl triazine derivative. The monoalkenyl phenyl triazine derivative and a monoalkenyl epoxy compound are then used as surface modification raw materials to perform in-situ graft polymerization on double-bond modified nanocellulose crystals to produce modified nanocellulose crystals whose surfaces are modified with phenyl triazine rings and epoxy groups. By regulating the feed ratio of the surface modification raw material to the double-bond modified nanocellulose crystals, the modified nanocellulose crystals can be evenly dispersed in the phenolic resin matrix. During the curing process of the phenolic resin, the epoxy groups on the modified nanocellulose crystals undergo ring opening and cross-linking reaction with the phenolic hydroxyl groups, thereby reducing the content of free phenolic hydroxyl groups in the system. At the same time, the introduced triazine ring structure can capture the free radicals generated in the heat and oxygen process, interrupting the oxidation reaction and synergistically improving the color change resistance of the phenolic resin.

[0006] In order to achieve the above objectives, the following technical solutions are adopted:

[0007] A method for preparing a toughened, discoloration-resistant phenolic resin comprises the following steps:

[0008] 1) Monoalkenylphenyltriazine derivatives are prepared by reacting 2,4-diamino-6-vinyl-S-triazine with benzoyl chloride derivatives;

[0009] 2) unsaturated dianhydride reacts with nanocellulose crystals to obtain double-bond modified nanocellulose crystals;

[0010] 3) using a monoalkenyl phenyl triazine derivative and a monoalkenyl epoxy compound as surface modification raw materials, and performing in situ graft polymerization on double-bond modified nanocellulose crystals to obtain modified nanocellulose crystals; the mass ratio of the double-bond modified nanocellulose crystals, the monoalkenyl phenyl triazine derivative, and the monoalkenyl epoxy compound is 1:0.9-1.2:0.1-0.3;

[0011] 4) Under an inert atmosphere, phenol, catalyst, and formaldehyde solution are added to a reaction kettle and heated and mixed. The temperature is raised to react. Modified nanocellulose crystals are added and mixed. The temperature is further raised to react to obtain a toughened, discoloration-resistant phenolic resin.

[0012] In step 1), the molar ratio of the amino group of the 2,4-diamino-6-vinyl-S-triazine to the acyl chloride group of the benzoyl chloride derivative is 1:1.05-1.1.

[0013] Furthermore, the benzoyl chloride derivative is selected from one or a combination of two or more of benzoyl chloride, o-methylbenzoyl chloride, p-methylbenzoyl chloride, and m-methylbenzoyl chloride.

[0014] Furthermore, the reaction of step 1) is specifically as follows: 2,4-diamino-6-vinyl-S-triazine, an acid binding agent, and a polymerization inhibitor are dissolved in an organic solvent and mixed evenly, a benzoyl chloride derivative is added dropwise at a controlled temperature, and the reaction is carried out at a controlled temperature to obtain a monoalkenyl triazine derivative.

[0015] Furthermore, the molar ratio of the benzoyl chloride derivative, acid binder, and polymerization inhibitor is 1:1.1-1.2:0.01-0.02. The organic solvent is selected from one or a combination of two or more of dichloromethane, tetrahydrofuran, and ethyl acetate. The acid binder is selected from one or a combination of two or more of triethylamine, pyridine, and N,N-diisopropylethylamine. The polymerization inhibitor is selected from one or a combination of two or more of hydroquinone, p-tert-butylcatechol, and 2,6-di-tert-butyl-p-methylphenol. The temperature is controlled at 25-40°C. The dropwise addition time is 30-60 minutes. After the dropwise addition is completed, the temperature is maintained at 25-40°C and the reaction is allowed to proceed for 3-5 hours.

[0016] Furthermore, the post-processing steps after the temperature-controlled reaction are completed further include: adding ice water, adjusting the pH to be weakly acidic, liquid separation and extraction, washing, low-temperature concentration, and column chromatography.

[0017] Furthermore, the volume of ice water is 1-3 times the volume of the system after the reaction. The pH is adjusted to be weakly acidic by adjusting it to 5-6 with a 5-10wt% hydrochloric acid aqueous solution. The separation extraction is to separate the organic phase, extract the aqueous phase with an organic solvent 2-3 times, and combine the organic phases. The washing is first washed with a saturated sodium bicarbonate solution 1-2 times, and then washed with water 1-2 times. The low-temperature concentration is a reduced pressure distillation at 25-40°C and 0.01-0.09MPa for 20-60min. The column chromatography mobile phase is a mixed solvent with a volume ratio of petroleum ether: ethyl acetate of 2-5:1.

[0018] In step 2), the mass ratio of the unsaturated dianhydride to the nanocellulose crystals is 0.5-0.8: 1. The cellulose nanocrystals have a crystallinity of 70-90%, a length of 100-300 nm, and a diameter of 10-20 nm.

[0019] Furthermore, the reaction of step 2) is specifically as follows: dispersing the nanocellulose crystals in an organic solvent, adding an unsaturated acid anhydride and a catalyst, and reacting under controlled temperature to obtain double-bond modified nanocellulose crystals.

[0020] Furthermore, the mass ratio of the nanocellulose crystals, catalyst, and organic solvent is 1:0.01-0.03:20-25. The catalyst is selected from one or a combination of two or more of triethylamine, 4-dimethylaminopyridine, and pyridine. The organic solvent is selected from one or a combination of two or more of benzene, toluene, xylene, dichloromethane, and chloroform. The temperature-controlled reaction is controlled at 50-80°C for 1-3 hours. After completion of the reaction, centrifugation, washing, and freeze-drying are also performed.

[0021] In step 3), the monoalkenyl epoxy compound is selected from one or a combination of glycidyl methacrylate and glycidyl acrylate.

[0022] Furthermore, the reaction of step 3) is specifically as follows: under an inert atmosphere, double-bond modified nanocellulose crystals, monoalkenyl triazine derivatives, monoalkenyl epoxy compounds, initiators, and emulsifiers are added to water for ultrasonic dispersion, and the temperature is raised to react to obtain modified nanocellulose crystals.

[0023] Furthermore, the mass ratio of the double-bond modified nanocellulose crystals, initiator, emulsifier, and water is 1:0.01-0.03:0.025-0.05:100-200. The emulsifier is selected from one or a combination of two or more of sodium lauryl sulfate, sodium hexadecyl sulfate, sodium dodecyl polyoxyethylene ether sulfate, sodium dodecylbenzenesulfonate, and sodium dodecylsulfonate. The temperature is raised to 60-80°C for 3-5 hours. The reaction is followed by centrifugation, washing, and freeze-drying. The initiator is selected from one or a combination of two of ammonium persulfate and potassium persulfate.

[0024] In step 4), the mass ratio of the phenol, catalyst, formaldehyde solution, and modified nanocellulose crystals is 100:3-5:110-130:7-10.

[0025] Furthermore, the heating and mixing step comprises heating the mixture to 45-50°C, stirring at a speed of 300-500 r / min, and maintaining the stirring speed for 10-15 minutes to ensure dissolution of the phenol. The heating reaction step comprises heating the mixture to 60-80°C and reacting for 1-3 hours. The continued heating reaction step comprises heating the mixture to 85-95°C and reacting for 0.5-1 hour. The formaldehyde solution has a concentration of 35-40 wt%. The catalyst is selected from one or a combination of two or more of sodium hydroxide, sodium carbonate, and barium hydroxide.

[0026] Furthermore, after continuing the temperature increase reaction, the temperature is lowered to 20-40° C., and dehydration is performed to adjust the solid content to 65-75 wt %.

[0027] A toughened, discoloration-resistant phenolic resin-based adhesive comprises the following raw materials in parts by weight: 40-60 parts of phenolic resin, 35-45 parts of filler, 0.1-0.3 parts of leveling agent, and water. The amount of water added is such that the viscosity of the toughened, discoloration-resistant phenolic resin-based adhesive is 1000-3000 mPa·s / 25°C.

[0028] The filler has an average particle size of 5-8 μm and is selected from one or a combination of two or more of talc powder, asbestos powder, clay powder, calcium carbonate powder, feldspar powder, calcite powder and titanium dioxide.

[0029] The toughened, discoloration-resistant phenolic resin-based adhesive may further include 0-5 parts of an auxiliary agent and 0-5 parts of a colorant. The auxiliary agent is selected from one or a combination of two or more of a defoaming agent, an anti-settling agent, and a thixotropic agent.

[0030] The colorant is not particularly limited and may be any pigment or dye commonly used in the art, including but not limited to one or a combination of iron oxide and benzidine yellow GP.

[0031] A method for preparing a toughened, discoloration-resistant phenolic resin-based binder comprises the following steps:

[0032] The phenolic resin, filler, leveling agent and water are mixed evenly and the viscosity is adjusted to obtain a toughened discoloration-resistant phenolic resin-based adhesive.

[0033] The invention discloses an application of a toughened, discoloration-resistant phenolic resin-based adhesive in sandpaper, and is used as a base adhesive and a top adhesive.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] 1. The present invention uses 2,4-diamino-6-vinyl-S-triazine to react with a benzoyl chloride derivative to prepare a monoalkenyl phenyl triazine derivative, and then uses the monoalkenyl phenyl triazine derivative and the monoalkenyl epoxy compound as surface modification raw materials to carry out in-situ graft polymerization on double-bond modified nanocellulose crystals to obtain modified nanocellulose crystals whose surfaces are modified with phenyl triazine rings and epoxy groups. By regulating the feed ratio of the surface modification raw material and the double-bond modified nanocellulose crystals, the modified nanocellulose crystals can be evenly dispersed in the phenolic resin matrix. During the curing process of the phenolic resin, the epoxy groups on the modified nanocellulose crystals undergo ring opening and cross-linking reaction with the phenolic hydroxyl groups, thereby reducing the content of free phenolic hydroxyl groups in the system; at the same time, the introduced triazine ring structure can interrupt the oxidation reaction by capturing the free radicals generated in the heat and oxygen process, thereby synergistically improving the discoloration resistance of the phenolic resin.

[0036] 2. The modified nanocellulose crystals of the present invention are well dispersed in the phenolic resin system and have a toughening effect on the phenolic resin system due to their large aspect ratio.

[0037] 3. The toughened, discoloration-resistant phenolic resin-based binder of the present invention can be used as a base glue or a top glue in sandpaper, which can improve and enhance the toughness of the sandpaper and make the grinding performance of the sandpaper higher. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 These are photos of the toughened, color-resistant phenolic resin of Example 1 before curing, after curing, and after heat aging;

[0039] Figure 2 These are photos of the toughened, discoloration-resistant phenolic resin of Comparative Example 2 before, after, and after thermal aging. DETAILED DESCRIPTION

[0040] The present invention will be further described below in conjunction with specific embodiment, but is not limited to the content on the specification sheets. Unless otherwise specified, "parts" described in the embodiments of the present invention are all parts by weight. All reagents used are commercially available reagents in this area.

[0041] 2,4-Diamino-6-vinyl-S-triazine (CAS No. 3194-70-5), manufacturer: Tokyo Chemical Industry (Shanghai) Development Co., Ltd.

[0042] Cellulose nanocrystals, brand S-VCF-01, crystallinity 70%, length: 200nm, diameter: 10nm-15nm, manufacturer: Xibao Biotechnology (Shanghai) Co., Ltd.

[0043] 2000 mesh calcium carbonate, manufacturer: Jiangxi Shanggao County Xuefeng Powder Co., Ltd.

[0044] Leveling agent 7580, manufacturer: Nanxiong Hanke Chemical Technology Co., Ltd.

[0045] Example 1

[0046] 1) 1 mol of 2,4-diamino-6-vinyl-S-triazine, 2.31 mol of triethylamine, and 0.021 mol of p-tert-butylcatechol were dissolved in 800 mL of dichloromethane and mixed. 2.1 mol of benzoyl chloride was added dropwise at 25° C. for 60 minutes, and the reaction was continued at 25° C. for 5 hours. After the reaction, ice water twice the volume of the reaction system was added, and the pH was adjusted to 5 with 10 wt % aqueous hydrochloric acid solution. The organic phase was separated, and the aqueous phase was extracted twice with dichloromethane. The organic phases were combined, washed once with saturated sodium bicarbonate solution and then washed once with water. The organic phase was concentrated by reduced pressure distillation at 35° C. and 0.08 MPa for 200 minutes. The organic phase was purified by silica gel column chromatography (using a mixed solvent of petroleum ether:ethyl acetate in a volume ratio of 2:1 as the mobile phase) to obtain a monoalkenyl triazine derivative;

[0047] 2) 100 g of nanocellulose crystals S-VCF-01 were dispersed in 2000 mL of toluene using 300 W ultrasonic power for 30 min, 80 g of maleic anhydride and 1.5 g of 4-dimethylaminopyridine were added, and the mixture was reacted at 60°C for 3 h. The mixture was centrifuged and washed three times with water and ethanol alternately. The mixture was pre-frozen in liquid nitrogen for 10 min and then freeze-dried at -50°C for 48 h at a pressure of 10 Pa to obtain double-bond-modified nanocellulose crystals.

[0048] 3) Under a nitrogen atmosphere, 100 g of double-bond-modified nanocellulose crystals, 120 g of the monoalkenyl triazine derivative obtained in step 1), 30 g of glycidyl acrylate, 3 g of ammonium persulfate, and 2.5 g of sodium lauryl sulfate were added to 20 kg of water and ultrasonically dispersed at a power of 300 W for 30 min. The mixture was heated to 75° C. and reacted for 5 h. The mixture was centrifuged, washed with water three times, pre-frozen in liquid nitrogen for 10 min, and then freeze-dried at a pressure of 10 Pa and a temperature of −50° C. for 48 h to obtain modified nanocellulose crystals.

[0049] 4) Under a nitrogen atmosphere, 100 g of phenol, 5 g of sodium hydroxide, and 130 g of a 35 wt % formaldehyde solution were added to a reactor and heated to 45° C., stirred at 300 r / min, maintained for 15 min, and then heated to 70° C. for 3 h. 10 g of modified nanocellulose crystals were added and stirred at 500 r / min for 45 min. The temperature was further raised to 95° C. for 1 h, cooled to 40° C., and dehydrated to adjust the solid content to 70 wt %. The toughened, discoloration-resistant phenolic resin was obtained.

[0050] 5) 60 parts by mass of phenolic resin, 45 parts by mass of 2000 mesh calcium carbonate, and 0.3 parts by mass of leveling agent 7580 were mixed, and water was added to adjust the viscosity to 1500 mPa·s / 25° C. to obtain a toughened, discoloration-resistant phenolic resin-based adhesive.

[0051] Example 2

[0052] The rest is the same as Example 1, except that, in step 1), benzoyl chloride is replaced by an equimolar amount of p-methylbenzoyl chloride.

[0053] Example 3

[0054] The rest is the same as Example 1, except that in step 2), the amount of maleic anhydride used is 50 g.

[0055] Example 4

[0056] The rest is the same as Example 1, except that in step 3), the amount of the monoalkenylphenyl triazine derivative used is 90 g.

[0057] Example 5

[0058] The rest is the same as Example 1, except that in step 3), the amount of glycidyl acrylate used is 10 g.

[0059] Example 6

[0060] The rest is the same as Example 1, except that in step 4), the amount of modified nanocellulose crystals used is 7 g.

[0061] Example 7

[0062] The rest is the same as Example 1, except that in step 5), the amount of phenolic resin used is 40 parts by mass.

[0063] Example 8

[0064] 1) 1 mol of 2,4-diamino-6-vinyl-S-triazine, 2.31 mol of triethylamine, and 0.021 mol of p-tert-butylcatechol were dissolved in 800 mL of dichloromethane and mixed. 2.1 mol of benzoyl chloride was added dropwise at 25° C. for 60 minutes, and the reaction was continued at 25° C. for 5 hours. After the reaction, ice water twice the volume of the reaction system was added, and the pH was adjusted to 5 with 10 wt % aqueous hydrochloric acid solution. The organic phase was separated, and the aqueous phase was extracted twice with dichloromethane. The organic phases were combined and washed once with saturated sodium bicarbonate solution and then with water. The organic phase was concentrated by low-temperature distillation at 35° C. and 0.08 MPa for 200 minutes, and then column chromatography was performed (using a mixed solvent of petroleum ether:ethyl acetate in a volume ratio of 2:1 as the mobile phase) to obtain a monoalkenyl triazine derivative.

[0065] 2) 100 g of nanocellulose crystals S-VCF-01 were dispersed in 2000 mL of toluene using 300 W ultrasonic power for 30 min, 50 g of maleic anhydride and 1.5 g of 4-dimethylaminopyridine were added, the reaction was controlled at 60°C for 3 h, centrifuged, washed three times alternately with water and ethanol, pre-frozen in liquid nitrogen for 10 min, and then freeze-dried at a pressure of 10 Pa and a temperature of -50°C for 48 h to obtain double-bond-modified nanocellulose crystals;

[0066] 3) Under a nitrogen atmosphere, 100 g of double-bond-modified nanocellulose crystals, 120 g of the monoalkenyl triazine derivative obtained in step 1), 30 g of glycidyl acrylate, 3 g of ammonium persulfate, and 2.5 g of sodium lauryl sulfate were added to 20 kg of water and ultrasonically dispersed at a power of 300 W for 30 min. The mixture was heated to 75° C. and reacted for 5 h. The mixture was centrifuged, washed with water three times, pre-frozen in liquid nitrogen for 10 min, and then freeze-dried at a pressure of 10 Pa and a temperature of −50° C. for 48 h to obtain modified nanocellulose crystals.

[0067] 4) Under a nitrogen atmosphere, 100 g of phenol, 5 g of sodium hydroxide, and 110 g of a 35 wt % formaldehyde solution were added to a reactor, heated to 45° C., stirred at 300 r / min, maintained for 15 min, and then heated to 70° C. for 3 h. 10 g of modified nanocellulose crystals were added and stirred at 500 r / min for 45 min. The temperature was further raised to 95° C. for 1 h, cooled to 40° C., and dehydrated to adjust the solid content to 70 wt %. The toughened, discoloration-resistant phenolic resin was obtained.

[0068] 5) 60 parts by mass of phenolic resin, 35 parts by mass of 2000 mesh calcium carbonate, and 0.3 parts by mass of leveling agent 7580 were mixed, and water was added to adjust the viscosity to 1500 mPa·s to obtain a toughened, discoloration-resistant phenolic resin-based adhesive.

[0069] Comparative Example 1

[0070] The rest is the same as Example 1, except that step 1) is omitted and in the original step 3), an equal mass of 4-benzhydrylstyrene is used to replace the monoalkenyl triazine derivative.

[0071] Comparative Example 2

[0072] The rest is the same as Example 1, except that in step 3), an equal mass of monoalkenyl triazine derivative is used instead of glycidyl acrylate.

[0073] Application Examples

[0074] Weight: 120g / m 2 The Zhejiang Jinchang Special Paper Co., Ltd. model P-1 base paper is used as the base material, with a longitudinal tensile strength of ≥11kgf and a transverse tensile strength of ≥5kgf.

[0075] AF180 brown corundum (Yuzhou Runtian New Materials Co., Ltd.) was used as the abrasive.

[0076] The adhesives prepared in the above examples and comparative examples were used as base glue and double glue to prepare the following sandpaper:

[0077] 1. Apply primer on the surface of the base paper with a glue amount of 40g / m 2 Then, the brown corundum of abrasive AF180 is planted in the base glue. After pre-drying, the surface of the paper base forms a base glue layer, and the bottom of the abrasive is embedded in the base glue layer to obtain a composite layer. The planting amount of sand is 180g / m 2 The pre-drying temperature program is: from room temperature, heating to 80℃ for 40min, 80℃ / 50min; from 80℃, heating to 100℃ for 10min, 100℃ / 1h; take out of the furnace when the temperature drops to 60℃.

[0078] 2. Apply glue to the surface of the composite layer obtained in step A, with a glue amount of 60g / m2 After curing, the curing temperature program is: from room temperature, heating to 80℃ for 40min, 80℃ / 50min; from 80℃, heating to 100℃ for 10min, 100℃ / 1h; from 100℃, heating to 110℃ for 10min, from 110℃, heating to 120℃ for 10min, 120℃ / 60min, take out of the furnace when the temperature drops to 60℃, regain moisture, knead and roll up to obtain sandpaper.

[0079] The sandpaper prepared in the above examples and comparative examples was subjected to the following performance tests:

[0080] Flexibility: The test is carried out in accordance with the flexibility test method of coated abrasive sandpaper in accordance with the Chinese machinery industry standard JB / T 7498-2018. The smaller the value, the better the flexibility.

[0081] Color: The L, a, and b values ​​measured by a colorimeter are three coordinate parameters based on the CIE Lab color space, used to quantify and describe color characteristics. The L value reflects the lightness or darkness of a color, ranging from 0 (pure black) to 100 (pure white). A higher value indicates a brighter color, while a lower value indicates a darker color.

[0082] L value before curing: The toughened, discoloration-resistant phenolic resin prepared in step 4) was coated on a 25.4 mm × 76.2 mm × 1 mm glass sheet at a coating amount of 2 g / 3 cm × 1 cm (length × width). A piece of white A4 paper was placed under the glass sheet to ensure consistent background light. The resin L0 value was measured using a portable colorimeter CR-400 (Konica Minolta) in Lab mode.

[0083] L value after curing: Color comparison of sandpaper after curing: The glass piece coated with liquid in A is cured in a blast drying oven: bake at 80℃ for 30 minutes, 90℃ for 30 minutes, 100℃ for 30 minutes, 110℃ for 30 minutes, 120℃ for 30 minutes and 130℃ for 30 minutes, measure the L1 value after the resin is cured, and calculate ΔL1=L0-L1.

[0084] L value after heat aging: Chromaticity after heat aging: Place the resin in a constant temperature aging box at 90℃ for 24 hours, measure the L2 value after heat aging, and calculate ΔL2=L1-L2.

[0085] Table 1 Performance test results

[0086] project Flexibility mm <![CDATA[L0]]> <![CDATA[ΔL1]]> <![CDATA[ΔL2]]> Example 1 2 90.4 3.9 6.3 Example 2 2 90.2 3.8 6.7 Example 3 3 88.3 4.8 7.8 Example 4 4 90.8 4.3 8.0 Example 5 4 89.4 5.4 4.2 Example 6 4 90.9 5.5 7.6 Example 7 5 91.2 4.0 6.5 Example 8 4 84.5 7.1 9.1 Comparative Example 1 3 90.4 4.8 16.6 Comparative Example 2 6 90.2 10.7 12.4

[0087] As can be seen from Table 1, the toughened color-resistant phenolic resin prepared by the present invention has good toughness and color-resistant performance. As can be seen from the Examples and Comparative Examples, glycidyl acrylate and triazine structure have a significant impact on the color-resistant performance of the resin, and the two work together to make the phenolic resin show excellent and stable color-resistant performance during preparation, curing, use or long-term storage. As can be seen from the flexibility test, by adjusting the relative amount of the grafted monomer on the surface of the modified nanocellulose crystals, modified nanocellulose crystals that are well dispersed in the phenolic resin system and have a toughening effect on the phenolic resin system can be obtained.

[0088] The above detailed description is a specific description of one feasible embodiment of the present invention. This embodiment is not intended to limit the patent scope of the present invention. Any equivalent implementation or modification that does not depart from the present invention should be included in the scope of the technical solution of the present invention.

Claims

1. A method for preparing a toughened, discoloration-resistant phenolic resin, characterized in that: The steps include: 1) Monoalkenylphenyltriazine derivatives are prepared by reacting 2,4-diamino-6-vinyl-S-triazine with benzoyl chloride derivatives; 2) unsaturated dianhydride reacts with nanocellulose crystals to obtain double-bond modified nanocellulose crystals; 3) using a monoalkenyl phenyl triazine derivative and a monoalkenyl epoxy compound as surface modification raw materials, and performing in situ graft polymerization on double-bond modified nanocellulose crystals to obtain modified nanocellulose crystals; the mass ratio of the double-bond modified nanocellulose crystals, the monoalkenyl phenyl triazine derivative, and the monoalkenyl epoxy compound is 1:0.9-1.2:0.1-0.3; 4) Under an inert atmosphere, phenol, catalyst, and formaldehyde solution are added to a reaction kettle and heated and mixed. The temperature is raised to react. Modified nanocellulose crystals are added and mixed. The temperature is further raised to react to obtain a toughened, discoloration-resistant phenolic resin.

2. The method for preparing the toughened color-resistant phenolic resin according to claim 1, wherein: In step 1), the molar ratio of the amino group of the 2,4-diamino-6-vinyl-S-triazine to the acyl chloride group of the benzoyl chloride derivative is 1:1.05-1.1; the benzoyl chloride derivative is selected from one or a combination of two or more of benzoyl chloride, o-methylbenzoyl chloride, p-methylbenzoyl chloride, and m-methylbenzoyl chloride.

3. The method for preparing the toughened color-resistant phenolic resin according to claim 1, wherein: The reaction conditions of step 1) are as follows: 2,4-diamino-6-vinyl-S-triazine, an acid binding agent, and a polymerization inhibitor are dissolved in an organic solvent and mixed evenly, a benzoyl chloride derivative is added dropwise at a controlled temperature, and the reaction is carried out at a controlled temperature to obtain a monoalkenyl triazine derivative.

4. The method for preparing the toughened color-resistant phenolic resin according to claim 1, wherein: In step 2), the mass ratio of the unsaturated dianhydride to the nanocellulose crystals is 0.5-0.8:1; the cellulose nanocrystals have a crystallinity of 70-90%, a length of 100-300 nm, and a diameter of 10-20 nm.

5. The method for preparing the toughened color-resistant phenolic resin according to claim 1, wherein: The reaction conditions of step 2) are as follows: dispersing the nanocellulose crystals in an organic solvent, adding an unsaturated acid anhydride and a catalyst, and reacting under controlled temperature to obtain double-bond modified nanocellulose crystals.

6. The method for preparing the toughened color-resistant phenolic resin according to claim 1, wherein: In step 3), the monoalkenyl epoxy compound is selected from one or a combination of glycidyl methacrylate and glycidyl acrylate.

7. The method for preparing the toughened color-resistant phenolic resin according to claim 1, wherein: The reaction conditions of step 3) are as follows: under an inert atmosphere, adding double-bond modified nanocellulose crystals, monoalkenyl triazine derivatives, monoalkenyl epoxy compounds, initiators, and emulsifiers to water for ultrasonic dispersion, and heating the reaction to obtain modified nanocellulose crystals; the mass ratio of the double-bond modified nanocellulose crystals, initiator, emulsifier, and water is 1:0.01-0.03:0.025-0.05:100-200.

8. The method for preparing the toughened color-resistant phenolic resin according to claim 1, wherein: In step 4), the mass ratio of the phenol, catalyst, formaldehyde solution, and modified nanocellulose crystals is 100:3-5:110-130:7-10; and after continuing the temperature increase reaction, the temperature is lowered to 20-40° C. and dehydrated to adjust the solid content to 65-75 wt %.

9. A toughened, discoloration-resistant phenolic resin-based adhesive, comprising the following raw materials in parts by weight: 40-60 parts of a phenolic resin prepared by the preparation method according to any one of claims 1 to 8, 35-45 parts of a filler, 0.1-0.3 parts of a leveling agent, and water, wherein the amount of water added is such that the viscosity of the toughened, discoloration-resistant phenolic resin-based adhesive is 1000-3000 mPa·s / 25°C.

10. The method for preparing the toughened, discoloration-resistant phenolic resin-based binder according to claim 9, characterized in that: The steps include: The phenolic resin, filler, leveling agent and water are mixed evenly and the viscosity is adjusted to obtain a toughened discoloration-resistant phenolic resin-based adhesive.

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