Anti-yellowing additive, preparation method of anti-yellowing additive, coating and preparation method of coating

Abstract

The invention discloses an anti-yellowing additive, a preparation method of the anti-yellowing additive, a coating and a preparation method of the coating, and relates to the technical field of anti-yellowing additives. 1 to 5 parts of 3-chloro-2 hydroxy propionitrile; 0.8 to 1.2 parts of formaldehyde; 0.1 to 0.3 part of a catalyst; 0.5 to 2 parts of 4, 4 '-diaminodiphenylmethane; and 0.3 to 0.6 part of silver oxide. According to the preparation method disclosed by the invention, a multi-functional-group framework with amino groups, hydroxyl groups, ether bonds and methylene bridges is constructed by gradually reacting and combining a regulating solution with 3-chloro-2-hydroxypropionitrile and formaldehyde; an aromatic ring structure of 4, 4 '-diaminodiphenylmethane and a conjugated system catalyzed by silver oxide are further introduced, and a triple protection mechanism of free radical capture, ultraviolet shielding and energy dissipation is formed.

Description

Technical Field

[0001] The present invention relates to the technical field of anti-yellowing additives, in particular to an anti-yellowing additive, a preparation method thereof, a coating, and a preparation method of the coating. Background Art

[0002] Coatings are prone to yellowing when exposed to light, high temperature, or an oxidative environment for a long time, resulting in a decrease in the aesthetics and functionality of the coating. Traditional anti-yellowing technologies are mainly achieved through the following two categories: Chemical anti-yellowing agents: such as ultraviolet absorbers (such as benzotriazoles) or free radical scavengers (such as hindered amines). However, their action mechanisms are single, making it difficult to cope with multiple environmental factors (such as the synergistic effect of photooxidation and thermal oxidation), and some small molecule anti-yellowing agents are prone to migration and volatilization, resulting in insufficient long-term effectiveness.

[0003] Physical shielding type: Reflect ultraviolet light through inorganic nanoparticles (such as titanium dioxide, zinc oxide). However, a high addition amount is likely to cause a decrease in the light transmittance of the coating and deterioration of mechanical properties. Summary of the Invention

[0004] In view of the problems existing in the existing anti-yellowing additives, their preparation methods, coatings, and the preparation methods of coatings, the present invention is proposed.

[0005] Therefore, the problems to be solved by the present invention are: the insufficient long-term effectiveness of traditional additives and the decrease in the light transmittance of the coating.

[0006] To solve the above technical problems, the present invention provides the following technical solutions: In the first aspect, an embodiment of the present invention provides an anti-yellowing additive, and its composition by weight is as follows, Adjusting liquid: 30 - 50 parts; 3-chloro-2-hydroxypropionitrile: 1 - 5 parts; formaldehyde: 0.8 - 1.2 parts; catalyst: 0.1 - 0.3 parts; 4,4'-diaminodiphenylmethane: 0.5 - 2 parts; silver oxide: 0.3 - 0.6 parts.

[0007] As a preferred scheme of the anti-yellowing additive of the present invention, wherein: the composition by weight of the adjusting liquid is as follows, 2-amino-3-hydroxyacetonitrile: 0.5 - 10 parts; water: 10 - 20 parts; sodium hydroxide: 0.1 - 1 part; ethanol: 25 - 40 parts.

[0008] As a preferred scheme of the anti-yellowing additive of the present invention, wherein: the purity of the 2-amino-3-hydroxyacetonitrile > 98.0%; the purity of the sodium hydroxide > 99.0%; the purity of the ethanol > 98.0%.

[0009] As a preferred embodiment of the anti-yellowing additive of the present invention, wherein: the molar ratio of 3-chloro-2-hydroxypropionitrile to 2-amino-3-hydroxyacetonitrile is (0.8 - 1.2):1; The formaldehyde is a 10% aqueous formaldehyde solution, and the molar ratio of formaldehyde to 2-amino-3-hydroxyacetonitrile is (0.8 - 1):1.

[0010] As a preferred embodiment of the anti-yellowing additive of the present invention, wherein: the catalyst is one or both of anhydrous magnesium sulfate and anhydrous sodium sulfate; The molar ratio of the catalyst to 2-amino-3-hydroxyacetonitrile is (0.08 - 0.10):1; The molar ratio of 4,4'-diaminodiphenylmethane to 2-amino-3-hydroxyacetonitrile is (0.8 - 1.25):1.

[0011] As a preferred embodiment of the anti-yellowing additive of the present invention, wherein: the purity of silver oxide is not less than 99.9%; The molar ratio of silver oxide to 2-amino-3-hydroxyacetonitrile is (0.3 - 0.6):1.

[0012] In a second aspect, an embodiment of the present invention provides a method for preparing an anti-yellowing additive, comprising the following steps: Mix 0.5 - 10 parts by weight of 2-amino-3-hydroxyacetonitrile, 10 - 20 parts by weight of water, 0.1 - 1 part by weight of sodium hydroxide, and 25 - 40 parts by weight of ethanol evenly to obtain a regulating solution; Add 1 - 5 parts by weight of 3-chloro-2-hydroxypropionitrile to the regulating solution, and react at 100 - 150 °C for 6 - 12 h to obtain a first organic phase; Add 0.8 - 1.2 parts by weight of formaldehyde to the first organic phase, and react at 70 - 90 °C for 5 - 8 h to obtain a first mixed solution; Add 0.1 - 0.3 parts by weight of the catalyst to the first mixed solution, and react at 105 - 120 °C for 2 - 4 h to carry out a condensation reaction, remove the organic phase, and obtain a first intermediate fraction; Add 0.5 - 2 parts by weight of 4,4'-diaminodiphenylmethane to the first intermediate fraction, and react at 120 - 150 °C for 6 - 12 h to obtain a second mixed solution; Add 0.3 - 0.6 parts by weight of silver oxide to the second mixed solution, and react at 80 - 100 °C for 3 - 4 h to obtain a third mixed solution; Distill the third mixed solution to obtain a second intermediate fraction, and cool and stand the second intermediate fraction to obtain the anti-yellowing additive.

[0013] In a third aspect, an embodiment of the present invention provides a paint containing an anti-yellowing additive, and the paint includes: Waterborne polyurethane: 100 parts by weight; deionized water: 120 - 300 parts by weight; 1,6 - hexanediol: 1 - 5 parts by weight; anti - yellowing additive: 1 - 5 parts by weight; dispersant: 0.1 - 0.5 parts by weight.

[0014] In a fourth aspect, an embodiment of the present invention provides a method for preparing a paint, and the preparation method includes: Pre - polymerize isocyanate and polyol at 30 - 60 °C for 30 min, sequentially add a chain extender and a catalyst into the reactor, react at 30 - 60 °C, and add a neutralizing agent after the reaction to obtain a waterborne polyurethane with a pH of 8.0 - 9.0; Add deionized water and a dispersant to the waterborne polyurethane, stir evenly at 25 - 30 °C to obtain a dispersion; Add 1,6 - hexanediol and an anti - yellowing additive to the dispersion, stir, and then disperse at a high speed of 1200 - 2000 r / min for 20 - 30 min, and continue to disperse at a high speed of 2000 - 3000 r / min for 20 - 80 min until emulsified without granularity to obtain the paint.

[0015] As a preferred scheme of the method for preparing the paint of the present invention, wherein: the neutralizing agent is one or more of ethylenediamine, diethanolamine, diethylamine, and dimethylamine.

[0016] Compared with the prior art, the beneficial effects of the present invention are: 1. By adjusting the step - by - step reaction combination of liquid (2 - amino - 3 - hydroxyacetonitrile / ethanol / water / sodium hydroxide) with 3 - chloro - 2 - hydroxypropionitrile and formaldehyde, a multi - functional group skeleton with amino, hydroxyl, ether bond, and methylene bridge is constructed; further introducing the aromatic ring structure of 4,4'-diaminodiphenylmethane and the conjugated system catalyzed by silver oxide to form a "radical capture (amino / hydroxyl) - ultraviolet shielding (aromatic ring) - energy dissipation (conjugated double bond)" triple protection mechanism. After the coating is aged by 1000 h QUV, the yellowing index (YI value) ≤ 3.5; the ultraviolet absorption rate is increased to 95%, and the photodegradation rate is reduced by 60%, breaking through the protection limit of a single mechanism.

[0017] 2. By regulating the molar ratio (3-chloro-2-hydroxypropanenitrile: 2-amino-3-hydroxyacetonitrile = 0.8 - 1.2:1; formaldehyde: 2-amino-3-hydroxyacetonitrile = 0.8 - 1:1) and combining it with the dehydration condensation of a catalyst (anhydrous magnesium sulfate / anhydrous sodium sulfate), the reaction is ensured to proceed directionally; through the oxidation-crosslinking synergistic effect of silver oxide (purity ≥ 99.9%), a thermally stable conjugated network can be formed. The product has a molecular weight distribution (PDI) ≤ 1.3, and the heat resistance is greatly improved; secondly, the condensation reaction time is shortened by 40%, and the by-product content < 0.5%.

[0018] 3. Through the compatibility design of the anti-yellowing additive (1 - 5 parts) with waterborne polyurethane and 1,6-hexanediol, combined with a staged high-speed dispersion process (1200 - 3000 r / min), the uniform dispersion of the additive is achieved; then, the pH is adjusted to 8.0 - 9.0 with a neutralizing agent to ensure efficient crosslinking with the isocyanate curing agent. Furthermore, the light transmittance of the coating is increased, its surface glossiness is improved, and the increase in crosslinking density extends the outdoor weather resistance life. Detailed implementation manners

[0019] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following provides a detailed description in combination with the specific implementation manners of the present invention. Obviously, the described embodiments are a part of the embodiments of the present invention, rather than all of them. The present invention can also be implemented in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0020] Example 1, an anti-yellowing additive, the composition by weight is as follows, Regulating liquid: 30 parts; 3-chloro-2-hydroxypropanenitrile: 1 part; Formaldehyde: 0.8 part; Catalyst: 0.1 part; 4,4'-diaminodiphenylmethane: 0.5 part; Silver oxide: 0.3 part.

[0021] 3-chloro-2-hydroxypropanenitrile provides a chlorine atom as a leaving group, undergoes nucleophilic substitution with 2-amino-3-hydroxyacetonitrile, and generates an intermediate connected by an ether bond, enhancing the molecular polarity; Formaldehyde condenses with amino / hydroxy groups to form a methylene bridge (-CH2-) or an oxazoline ring, constructs a crosslinked network, and improves thermal stability; 4,4'-diaminodiphenylmethane introduces a rigid aromatic ring structure, absorbs ultraviolet light through π-π conjugation, and reduces the photodegradation of the resin; The application of silver oxide enables the catalysis of the oxidation of nitrile groups (-C≡N) to amide groups (-CONH2), forming conjugated double bonds, dissipating energy through electron delocalization, and inhibiting oxidative yellowing.

[0022] Therefore, the amino / hydroxy (antioxidant), aromatic ring (anti-UV), and conjugated system (thermal stability) form a "trinity" protection, breaking through the limitations of a single mechanism.

[0023] The weight parts composition of the regulating solution is as follows. 2-Amino-3-hydroxyacetonitrile: 0.5 parts; Water: 10 parts; Sodium hydroxide: 0.1 part; Ethanol: 25 parts.

[0024] 2-Amino-3-hydroxyacetonitrile serves as the core reactant. The amino and hydroxy groups provide nucleophilic sites, and its content directly affects the molecular chain length and crosslinking density. Water and ethanol achieve the balance of reactant dissolution and phase separation through polarity regulation. Ethanol promotes the separation of the organic phase and reduces the residual impurities in the aqueous phase. Sodium hydroxide precisely controls the pH of the system, promoting the deprotonation of the amino group (-NH _ ), and enhancing the nucleophilic reaction activity.

[0025] Furthermore, the purity of 2-amino-3-hydroxyacetonitrile is 98.5%; the purity of sodium hydroxide is 99.2%; the purity of ethanol is 98.5%.

[0026] The limitation of the purity of 2-amino-3-hydroxyacetonitrile can prevent impurities (such as aminoacetic acid) from occupying the reaction sites and ensure the efficiency of nucleophilic substitution and condensation reactions. The setting of the purity of sodium hydroxide reduces the impurities of sodium carbonate and metal ions, preventing pH fluctuations and catalytic side reactions. Finally, through the setting of the purity of ethanol, the interference of methanol and aldehyde impurities is reduced, and unexpected condensation is inhibited.

[0027] Furthermore, the molar ratio of 3-chloro-2-hydroxypropanenitrile to 2-amino-3-hydroxyacetonitrile is 0.8:1; ensuring the completion of the chlorination reaction and avoiding the residual of excessive chlorinated substances from triggering subsequent condensation side reactions.

[0028] Formaldehyde is a 10% aqueous formaldehyde solution, and the molar ratio of formaldehyde to 2-amino-3-hydroxyacetonitrile is 0.8:1; by limiting the molar ratio, the hydroxymethylation and crosslinking density are balanced, preventing molecular aggregation caused by excessive condensation.

[0029] The catalyst is anhydrous magnesium sulfate; The molar ratio of the catalyst to 2-amino-3-hydroxyacetonitrile is 0.08:1; The molar ratio of 4,4'-diaminodiphenylmethane to 2-amino-3-hydroxyacetonitrile is 0.8:1.

[0030] The purity of silver oxide is not less than 99.9%, avoiding resin gelation caused by silver ion impurities; the molar ratio of silver oxide to 2-amino-3-hydroxyacetonitrile is 0.3:1, precisely regulating the degree of nitrile group oxidation, forming a moderate conjugate system, and balancing the anti-yellowing performance and the light transmittance of the coating.

[0031] Example 2, an anti-yellowing additive, the composition in parts by weight is as follows, Adjusting solution: 40 parts; 3-chloro-2-hydroxyacetonitrile: 3 parts; Formaldehyde: 1 part; Catalyst: 0.2 part; 4,4'-diaminodiphenylmethane: 1.5 parts; Silver oxide: 0.4 part.

[0032] The composition in parts by weight of the adjusting solution is as follows, 2-amino-3-hydroxyacetonitrile: 5 parts; Water: 15 parts; Sodium hydroxide: 0.5 part; Ethanol: 35 parts.

[0033] The purity of 2-amino-3-hydroxyacetonitrile is 99%; the purity of sodium hydroxide is 99.8%; the purity of ethanol is 99%.

[0034] The molar ratio of 3-chloro-2-hydroxyacetonitrile to 2-amino-3-hydroxyacetonitrile is 1:1; Formaldehyde is a 10% aqueous formaldehyde solution, and the molar ratio of formaldehyde to 2-amino-3-hydroxyacetonitrile is 1:1.

[0035] The catalyst is anhydrous sodium sulfate; The molar ratio of the catalyst to 2-amino-3-hydroxyacetonitrile is 0.09:1; The molar ratio of 4,4'-diaminodiphenylmethane to 2-amino-3-hydroxyacetonitrile is 1:1.

[0036] The purity of silver oxide is not less than 99.9%; the molar ratio of silver oxide to 2-amino-3-hydroxyacetonitrile is (0.3 - 0.6):1.

[0037] Example 3, an anti-yellowing additive, the composition in parts by weight is as follows, Adjusting solution: 50 parts; 3-chloro-2-hydroxyacetonitrile: 5 parts; Formaldehyde: 1.2 parts; Catalyst: 0.3 part; 4,4'-diaminodiphenylmethane: 2 parts; Silver oxide: 0.6 part.

[0038] The weight parts of the regulating solution are as follows: 2-Amino-3-hydroxyacetonitrile: 10 parts; Water: 20 parts; Sodium hydroxide: 1 part; Ethanol: 40 parts.

[0039] The purity of 2-amino-3-hydroxyacetonitrile is 99%; the purity of sodium hydroxide is 99.8%; and the purity of ethanol is 99%.

[0040] The molar ratio of the 3-chloro-2-hydroxypropionitrile to the 2-amino-3-hydroxyacetonitrile is 1.2:1; The formaldehyde is a 10% formaldehyde aqueous solution, and the molar ratio of the formaldehyde to the 2-amino-3-hydroxyacetonitrile is 1:1.

[0041] The catalyst is a mixture of anhydrous magnesium sulfate and anhydrous sodium sulfate; The molar ratio of the catalyst to the 2-amino-3-hydroxyacetonitrile is 0.1:1; The molar ratio of the 4,4'-diaminodiphenylmethane to the 2-amino-3-hydroxyacetonitrile is 1.25:1.

[0042] The purity of the silver oxide is not less than 99.9%; the molar ratio of the silver oxide to the 2-amino-3-hydroxyacetonitrile is 0.6:1.

[0043] Comparative Example 1: The purity of 2-amino-3-hydroxyacetonitrile, sodium hydroxide, and ethanol in Example 2 were adjusted, the purity of 2-amino-3-hydroxyacetonitrile was reduced to 95%, the purity of sodium hydroxide was 95%, and the purity of ethanol was 90%. The remaining components and proportions were the same as in Example 2.

[0044] By comparing the test indicators, an indicator parameter table is obtained.

[0045] Table 1: Parameters of Comparative Example 1 and Example 2 Index Example 2 Comparative Example 1 Product yield 92% 68% Yellowing index (YI value, 1000h QUV) 3.5 8.2 Molecular weight distribution (PDI) 1.2 1.9 Experimental method for product yield: After the reaction is completed, the product is obtained by vacuum distillation or centrifugal separation, the actual mass of the dried product is weighed, and the yield is calculated based on the theoretical mass of the reaction formula. The standard basis adopted is GB / T6284-2006.

[0046] The experimental method of yellowing index is as follows: the coating is applied to a standard white substrate (such as tinplate), and a sample is made after drying; the initial YI value is measured using a colorimeter; the sample is subjected to a QUV accelerated aging test; the YI value is measured every 240 hours, and the YI value after 1000 hours is recorded.

[0047] As can be seen from Table 1, impurities (such as glycine and sodium carbonate) occupy the reaction sites, resulting in incomplete condensation reactions; water and aldehyde impurities in ethanol trigger side reactions (such as the formation of Schiff bases).

[0048] Comparative Example 2: Adjust part of the molar ratios in Example 2, that is, the molar ratio of 3-chloro-2-hydroxypropanenitrile to 2-amino-3-hydroxyacetonitrile is 0.5:1 (the molar ratio in Example 2 is 1:1); the molar ratio of formaldehyde to 2-amino-3-hydroxyacetonitrile is 0.5:1 (the molar ratio in Example 2 is 1:1); the other components and their ratios are the same as in Example 2.

[0049] By comparing the test indicators, an indicator parameter table is obtained.

[0050] Table 2: Parameter table of Comparative Example 2 and Example 2 Index Example 2 Comparative Example 2 Ether bond content (FTIR quantification) 95% 62% <![CDATA[Crosslinking density (mol / m 3 ).]]> 1200 450 Heat resistance (YI value after baking at 150°C) 4.0 12.5 Experimental method for the ether bond content: Use a Fourier transform infrared spectrometer (FTIR, such as Nicoleti S50), equipped with a KBr tablet pressing device. The selected reagents are potassium bromide and a standard sample (polyethylene glycol). That is, mix PEG-2000 and KBr at a mass ratio of 1:100, and grind to a uniform powder; take 100 mg of the mixture, press a tablet (pressure 10 tons, keep for 2 minutes) to prepare a transparent thin film. The sample to be tested is a yellowing prevention additive sample mixed with KBr at a ratio of 1:100, and a tablet is pressed in the same way. Characteristic peak of ether bond (C-O-C): The main peak range is 1050 - 1150 cm -1 (antisymmetric stretching vibration of aliphatic ether bond); compare with the spectrum of the PEG-2000 standard sample to confirm the peak position of the ether bond. Compare with the spectrum of the PEG-2000 standard sample to confirm the peak position of the ether bond; set baseline anchor points at 1050 cm -1 and 1150 cm -1 , and use linear baseline correction; prepare a series of concentration PEG-2000 solutions (0.1% - 5%), press tablets and test under the same conditions, and calculate the ether bond content (wt%).

[0051] Experimental method for the crosslinking density: Weigh the mass of the dried coating, immerse the specimen in toluene, swell at 25 °C for 48 h until equilibrium, take out the specimen, quickly dry the surface solvent, weigh the mass after swelling, and calculate the crosslinking density.

[0052] As can be seen from Table 2, the chlorination reaction is incomplete, the ether bond connection rate decreases; the condensation crosslinking degree is insufficient, and the molecular network is loose.

[0053] Comparative Example 3: Replace the catalyst type in Example 2, that is, the catalyst is calcium chloride, and the molar ratio remains 0.09:1; the other components and their ratios are the same as in Example 2.

[0054] By comparing the test indicators, an indicator parameter table is obtained.

[0055] Table 3: Parameter table of Comparative Example 3 and Example 2 Index Example 2 Comparative Example 3 Condensation reaction time (h) 3 8 By-product content (GC-MS) 0.3% 5.8% Coating transmittance (%) 92 78 Experimental method for the condensation reaction time and by-product content: Use a gas chromatography-mass spectrometry (GC-MS) instrument to match the by-products through retention time and the mass spectrometry library (NIST), and calculate the content by the peak area normalization method.

[0056] Experimental method for the light transmittance of the coating: Coat the coating on a quartz glass sheet, and obtain a transparent coating after drying. Scan the wavelength range from 300 to 800 nm, and record the light transmittance at 550 nm.

[0057] It can be seen from Table 3 that calcium chloride has weak water absorption and cannot effectively dehydrate to promote the condensation reaction. Calcium ions may trigger the side reaction of metal ion-catalyzed oxidation.

[0058] Comparative Example 4: Replace silver oxide in Example 2 with copper oxide, and the other components and ratios are the same as in Example 2.

[0059] Through the comparison of test indicators, an index parameter table is obtained.

[0060] Table 4: Parameter table of Comparative Example 4 and Example 2 Index Example 2 Comparative Example 4 Conjugated double bond content (UV-Vis) 85% 12% Ultraviolet absorption rate (300nm) 95% 40% Initial YI value 2.0 4.5 Experimental method for the conjugated double bond content: Use a UV-visible spectrophotometer. The sample is dissolved in THF (concentration 0.1 mg / mL), with THF as the reference. Scan the wavelength range from 200 to 600 nm, and record the characteristic absorption peak of the conjugated double bond; calculate the molar extinction coefficient through the Beer-Lambert law, and quantify it in combination with the standard curve.

[0061] It can be seen from Table 4 that copper oxide cannot catalyze the oxidation of nitrile groups, so the conjugated system is not formed; impurity metal ions (Cu 2+ ) accelerate the oxidation and yellowing of the resin.

[0062] In summary, by combining the stepwise reaction of the adjusting solution (2-amino-3-hydroxyacetonitrile / ethanol / water / sodium hydroxide) with 3-chloro-2-hydroxypropanenitrile and formaldehyde, a multi-functional group skeleton with amino, hydroxyl, ether bond and methylene bridge is constructed; further introducing the aromatic ring structure of 4,4'-diaminodiphenylmethane and the conjugated system catalyzed by silver oxide, a triple protection mechanism of "radical capture (amino / hydroxyl)-UV shielding (aromatic ring)-energy dissipation (conjugated double bond)" is formed. After the coating is aged by 1000 h QUV, the yellowing index (YI value) ≤ 3.5; the UV absorption rate is increased to 95%, and the photodegradation rate is reduced by 60%, breaking through the protection limit of a single mechanism.

[0063] By controlling the molar ratio (3-chloro-2-hydroxypropanenitrile: 2-amino-3-hydroxyacetonitrile = 0.8 - 1.2:1; formaldehyde: 2-amino-3-hydroxyacetonitrile = 0.8 - 1:1) and combining it with dehydration condensation of a catalyst (anhydrous magnesium sulfate / anhydrous sodium sulfate), the reaction is ensured to proceed in a specific direction; through the oxidation-crosslinking synergistic effect of silver oxide (purity ≥ 99.9%), a thermally stable conjugated network can be formed. The product has a molecular weight distribution (PDI) ≤ 1.3, and its heat resistance is greatly improved; secondly, the condensation reaction time is shortened by 40%, and the by-product content is < 0.5%.

[0064] Through the compatibility design of an anti-yellowing additive (1 - 5 parts) with waterborne polyurethane and 1,6-hexanediol, combined with a staged high-speed dispersion process (1200 - 3000 r / min), the uniform dispersion of the additive is achieved; then, the pH is adjusted to 8.0 - 9.0 with a neutralizing agent to ensure efficient crosslinking with the isocyanate curing agent. Furthermore, the light transmittance of the coating is increased, its surface glossiness is improved, and the increase in crosslinking density extends the outdoor weather resistance life.

[0065] Example 4, a preparation method of an anti-yellowing additive, includes the following steps Mix 5 parts by weight of 2-amino-3-hydroxyacetonitrile, 15 parts by weight of water, 0.5 parts by weight of sodium hydroxide, and 35 parts by weight of ethanol evenly to obtain a regulating solution; Add 3 parts by weight of 3-chloro-2-hydroxypropanenitrile to the regulating solution and react at 130 °C for 10 h to obtain a first organic phase; Add 1 part by weight of formaldehyde to the first organic phase and react at 80 °C for 6 h to obtain a first mixed solution; Add 0.2 parts by weight of a catalyst to the first mixed solution and react at 110 °C for 3 h to carry out a condensation reaction, remove the organic phase, and obtain a first intermediate fraction; Add 1 part by weight of 4,4'-diaminodiphenylmethane to the first intermediate fraction and react at 130 °C for 10 h to obtain a second mixed solution; Add 0.4 parts by weight of silver oxide to the second mixed solution and react at 90 °C for 3 h to obtain a third mixed solution; Distill the third mixed solution to obtain a second intermediate fraction, and cool and let stand the second intermediate fraction to obtain the anti-yellowing additive.

[0066] In this example, the distillation is carried out by vacuum distillation with a vacuum degree of -0.08 MPa. Specifically, when operating, pour the third mixed solution into a round-bottom flask and install a vacuum distillation device; Turn on the vacuum pump, adjust the vacuum degree to -0.08 MPa, slowly heat up to 80 °C, and distill off the low-boiling substances (such as ethanol, water, etc.); when the temperature rises to 100 °C, replace the receiving flask and collect the fraction at 110 °C (main fraction); Stop distillation when the distillation rate significantly decreases (<1 mL / min) or the purity of the main component detected by GC ≥ 95%; cool the main fraction to 60 - 80 °C, let it stand for 12 h to precipitate crystals, and filter to obtain the anti-yellowing additive.

[0067] In this example, through the combination of high-purity raw materials, such as the purity of 2-amino-3-hydroxyacetonitrile being 99% and the purity of silver oxide being 99.9%, and the precise control of process parameters, the efficient preparation and performance breakthrough of the anti-yellowing additive were achieved: 3-chloro-2-hydroxypropanenitrile completes nucleophilic substitution (10 h) with 2-amino-3-hydroxyacetonitrile at 130 °C to form a stable ether bond; formaldehyde condenses to form a methylene bridge cross-linked network, improving thermal stability; 4,4'-diaminodiphenylmethane introduces a rigid aromatic ring, and the ultraviolet absorption rate reaches 96%; silver oxide catalyzes the oxidation of the nitrile group to a conjugated double bond, and the energy is dissipated through electron delocalization, reducing the yellowing index compared with traditional additives.

[0068] Through staged distillation and standing, in this example, the temperature during standing is 60 - 80 °C, which can effectively remove low-boiling substances.

[0069] Example 5, a preparation method of an anti-yellowing additive, includes the following steps: Mix 0.5 parts by weight of 2-amino-3-hydroxyacetonitrile, 10 parts by weight of water, 0.1 parts by weight of sodium hydroxide, and 25 parts by weight of ethanol evenly to obtain a regulating solution; Add 1 part by weight of 3-chloro-2-hydroxypropanenitrile to the regulating solution and react at 100 °C for 12 h to obtain a first organic phase; Add 0.8 part by weight of formaldehyde to the first organic phase and react at 70 °C for 8 h to obtain a first mixed solution; Add 0.1 part by weight of a catalyst to the first mixed solution and react at 105 °C for 2 h to carry out a condensation reaction, remove the organic phase, and obtain a first intermediate fraction; Add 0.5 part by weight of 4,4'-diaminodiphenylmethane to the first intermediate fraction and react at 120 °C for 12 h to obtain a second mixed solution; Add 0.3 part by weight of silver oxide to the second mixed solution and react at 80 °C for 4 h to obtain a third mixed solution; Distill the third mixed solution to obtain a second intermediate fraction, cool and let the second intermediate fraction stand to obtain the anti-yellowing additive.

[0070] The implementation steps of this example are the same as those of Example 4.

[0071] Example 6, a preparation method of an anti-yellowing additive, includes the following steps: Mix 10 parts by weight of 2-amino-3-hydroxyacetonitrile, 20 parts by weight of water, 1 part by weight of sodium hydroxide, and 40 parts by weight of ethanol evenly to obtain a regulating solution; Add 5 parts by weight of 3-chloro-2-hydroxypropanenitrile to the regulating solution, and react at 150 °C for 6 h to obtain a first organic phase; Add 1.2 parts by weight of formaldehyde to the first organic phase, and react at 90 °C for 5 h to obtain a first mixed solution; Add 0.3 parts by weight of a catalyst to the first mixed solution, and react at 120 °C for 2 h to carry out a condensation reaction, remove the organic phase, and obtain a first intermediate fraction; Add 2 parts by weight of 4,4'-diaminodiphenylmethane to the first intermediate fraction, and react at 150 °C for 6 h to obtain a second mixed solution; Add 0.6 parts by weight of silver oxide to the second mixed solution, and react at 100 °C for 3 h to obtain a third mixed solution; Distill the third mixed solution to obtain a second intermediate fraction, and cool and let stand the second intermediate fraction to obtain the anti-yellowing additive.

[0072] The implementation steps of this example are the same as those of Example 4.

[0073] Comparative Example 5 (lacking the silver oxide catalysis step), its preparation method includes: Mix 5 parts by weight of 2-amino-3-hydroxyacetonitrile, 15 parts by weight of water, 0.5 parts by weight of sodium hydroxide, and 35 parts by weight of ethanol to obtain a regulating solution; add 3 parts by weight of 3-chloro-2-hydroxypropanenitrile to the regulating solution, and react at 130 °C for 10 h; add 1 part by weight of formaldehyde and react at 80 °C for 6 h; add 0.2 parts by weight of a catalyst and carry out a condensation reaction at 110 °C for 3 h; then add 1 part by weight of 4,4'-diaminodiphenylmethane and react at 130 °C for 10 h; directly carry out vacuum distillation to obtain the product.

[0074] Comparative Example 6 (simplifying the reaction steps), its preparation method includes: Mix the raw materials with the same ratio at one time, react at 120 °C for 8 h, and then directly distill to obtain the product.

[0075] Table 5: Parameter table of Comparative Example 5, Comparative Example 6, and Examples 4-6 Item Example 4 Example 5 Example 6 Comparative Example 5 Comparative Example 6 Ultraviolet absorption rate (%) 96.2 95.8 96.5 73.1 64.8 Yellowing index (YI) 2.2 2.3 2.1 4.8 6.2 Thermal stability retention rate (%) 95.2 94.8 96.1 78.3 61.7 Product purity (%) 97.5 96.8 98.2 85.6 79.3 Crystalline yield (%) 92.1 90.5 93.8 81.2 75.6 Reasons for the performance decline due to the absence of silver oxide catalysis in Comparative Example 5: Without silver oxide catalysis, the nitrile group (-CN) cannot be effectively oxidized to form a conjugated double bond system; the conjugated system is incomplete, and an effective electron delocalization channel cannot be formed to dissipate ultraviolet energy; lacking the support of the conjugated structure, the overall molecular rigidity decreases and the thermal stability decreases.

[0076] Advantages of the stepwise reaction of this method: The first step of nucleophilic substitution: 2-amino-3-hydroxyacetonitrile and 3-chloro-2-hydroxypropanenitrile form a stable ether bond under alkaline conditions; The second step of condensation crosslinking: Formaldehyde forms a methylene bridge (-CH2-) directionally to construct a three-dimensional network structure; The third step of aromatic ring introduction: 4,4'-diaminodiphenylmethane is precisely incorporated to provide a rigid backbone and ultraviolet absorption groups; The fourth step of catalytic oxidation: Silver oxide catalyzes the conversion of nitrile groups to improve the conjugated system.

[0077] In Comparative Example 6, by the one-step method, all components coexist, and multiple competitive reactions and side reactions occur; the reaction sequence cannot be controlled, resulting in an irregular molecular structure; the formation sites of methylene bridges are random and the crosslinking efficiency is low.

[0078] Example 7, a coating containing an anti-yellowing additive.

[0079] In an alternative embodiment, the coating comprises: Waterborne polyurethane: 100 parts by weight; Deionized water: 200 parts by weight; 1,6-Hexanediol: 3 parts by weight; Anti-yellowing additive: 3 parts by weight; Dispersant: 0.3 parts by weight.

[0080] When the coating is applied to the casings of mobile phones / laptop computers and the dials of smart watches, it has a high light transmittance and a low haze, maintaining a metallic texture or a transparent effect. The synergistic effect of the anti-yellowing additive and the waterborne polyurethane is excellent in terms of anti-yellowing, weather resistance, environmental friendliness, etc., and at the same time has multi-scenario adaptability and function expansion potential.

[0081] In another alternative embodiment, the coating comprises: Waterborne polyurethane: 100 parts by weight; Deionized water: 120 parts by weight; 1,6-Hexanediol: 1 part by weight; Anti-yellowing additive: 1 part by weight; Dispersant: 0.1 parts by weight.

[0082] In a third alternative embodiment, the coating comprises: Waterborne polyurethane: 100 parts by weight; Deionized water: 300 parts by weight; 1,6-Hexanediol: 5 parts by weight; Anti-yellowing additive: 5 parts by weight; Dispersant: 0.5 parts by weight.

[0083] Example 8, a method for preparing a coating, comprising: The isocyanate and polyol are pre-polymerized at 45 °C for 30 min. The chain extender and catalyst are sequentially added into the reactor, and the reaction is carried out at 45 °C. After the reaction is completed, a neutralizing agent is added to obtain an aqueous polyurethane with a pH of 8.0; The isocyanate and polyol are pre-polymerized at 45 °C to balance the reaction rate and the orderly growth of the molecular chain, and avoid side reactions caused by high temperature, such as the formation of urethane.

[0084] In this example, the chain extender is a small molecule diol; the catalyst is dibutyltin dilaurate; The application of the small molecule diol precisely regulates the ratio of the hard segment to the soft segment to form a microphase separation structure, with both coating hardness and flexibility.

[0085] The neutralizing agent is ethylenediamine; The catalytic efficiency is increased by 50% compared with traditional amine catalysts, and the reaction time is shortened to 45 °C / 30 min, avoiding high-temperature energy consumption; Selectively catalyze the reaction of isocyanate with hydroxyl group, inhibit side reactions (such as the reaction of isocyanate with water to generate CO2 bubbles), and ensure a smooth coating surface. Stabilize the resin pH at 8.0 to ensure the stability of the aqueous polyurethane emulsion, and the storage period > 12 months without precipitation.

[0086] Deionized water and a dispersant are added to the aqueous polyurethane, and the mixture is stirred evenly at 25 °C to obtain a dispersion; 1,6-Hexanediol and an anti-yellowing additive are added to the dispersion, and after stirring, it is dispersed at a high speed of 1600 r / min for 25 min, and then continuously dispersed at a high speed of 2500 r / min for 50 min until emulsified without particles to obtain a coating.

[0087] Primary dispersion, that is, high-speed dispersion at 1600 r / min for 25 min, realizes the preliminary wetting and mixing of the anti-yellowing additive and 1,6-hexanediol; Secondary dispersion, that is, high-speed dispersion at 2500 r / min for 50 min, and the shear force breaks through the agglomeration energy barrier of the additive.

[0088] Example 9, a method for preparing a coating, comprising: The isocyanate and polyol are pre-polymerized at 30 °C for 30 min. The chain extender and catalyst are sequentially added into the reactor, and the reaction is carried out at 30 °C. After the reaction is completed, a neutralizing agent is added to obtain an aqueous polyurethane with a pH of 8.5; In this example, the chain extender is a small molecule diol; the catalyst is dibutyltin dilaurate; the neutralizing agent is diethanolamine; Deionized water and a dispersant are added to the aqueous polyurethane, and the mixture is stirred evenly at 27 °C to obtain a dispersion; Add 1,6 - hexanediol and anti - yellowing additive to the dispersion liquid, stir, and then disperse at a high speed of 1200 r / min for 20 min. Continue to disperse at a high speed of 2000 r / min for 20 min until emulsified without granularity to obtain the coating material.

[0089] Example 10, a method for preparing a coating material, comprising: Pre - polymerize isocyanate and polyol at 60 °C for 30 min, sequentially add a chain extender and a catalyst into the reactor, react at 60 °C, and add a neutralizing agent after the reaction ends to obtain an aqueous polyurethane with a pH of 9.0. In this example, the chain extender is a small - molecule diol; the catalyst is dibutyltin dilaurate; the neutralizing agent is a mixture of diethylamine and dimethylamine. Add deionized water and a dispersant to the aqueous polyurethane, stir evenly at 30 °C to obtain a dispersion liquid. Add 1,6 - hexanediol and anti - yellowing additive to the dispersion liquid, stir, and then disperse at a high speed of 2000 r / min for 30 min. Continue to disperse at a high speed of 3000 r / min for 80 min until emulsified without granularity to obtain the coating material.

[0090] It should be noted that the above examples are only used to illustrate the technical solutions of the present invention and are not restrictive. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the present invention.

Claims

1. An anti-yellowing additive, characterized in that: Its weight composition is as follows: Adjusting liquid: 30 - 50 parts by weight; 3-chloro-2-hydroxypropanenitrile: 1 - 5 parts by weight; Formaldehyde: 0.8 - 1.2 parts by weight; Catalyst: 0.1 - 0.3 parts by weight; 4,4'-diaminodiphenylmethane: 0.5 - 2 parts by weight; Silver oxide: 0.3 - 0.6 parts by weight.

2. The anti-yellowing additive according to claim 1, characterized in that: The weight composition of the adjusting liquid is as follows: 2-amino-3-hydroxyacetonitrile: 0.5 - 10 parts by weight; Water: 10 - 20 parts by weight; Sodium hydroxide: 0.1 - 1 part by weight; Ethanol: 25 - 40 parts by weight.

3. The anti-yellowing additive according to claim 2, characterized in that: The purity of the 2-amino-3-hydroxyacetonitrile > 98.0%; the purity of the sodium hydroxide > 99.0%; the purity of the ethanol > 98.0%.

4. The anti-yellowing additive according to claim 3, wherein: The molar ratio of the 3-chloro-2-hydroxypropanenitrile to the 2-amino-3-hydroxyacetonitrile is (0.8 - 1.2):1; The formaldehyde is a 10% aqueous formaldehyde solution, and the molar ratio of the formaldehyde to the 2-amino-3-hydroxyacetonitrile is (0.8 - 1):

1.

5. The anti-yellowing additive according to claim 4, wherein: The catalyst is one or both of anhydrous magnesium sulfate and anhydrous sodium sulfate; The molar ratio of the catalyst to the 2-amino-3-hydroxyacetonitrile is (0.08 - 0.10):1; The molar ratio of the 4,4'-diaminodiphenylmethane to the 2-amino-3-hydroxyacetonitrile is (0.8 - 1.25):

1.

6. The anti-yellowing additive according to claim 5, characterized in that: The purity of the silver oxide is not less than 99.9%; The molar ratio of the silver oxide to the 2-amino-3-hydroxyacetonitrile is (0.3 - 0.6):

1.

7. A method for preparing the anti-yellowing additive according to any one of claims 1-6, characterized in that: It includes the following steps: Mix 0.5 - 10 parts by weight of 2-amino-3-hydroxyacetonitrile, 10 - 20 parts by weight of water, 0.1 - 1 part by weight of sodium hydroxide, and 25 - 40 parts by weight of ethanol evenly to obtain the adjusting liquid; Add 1 - 5 parts by weight of 3-chloro-2-hydroxypropanenitrile to the adjusting liquid, and react at 100 - 150 °C for 6 - 12 h to obtain the first organic phase; Add 0.8 - 1.2 parts by weight of formaldehyde to the first organic phase, and react at 70 - 90 °C for 5 - 8 h to obtain the first mixed liquid; Add 0.1 - 0.3 parts by weight of the catalyst to the first mixed liquid, and react at 105 - 120 °C for 2 - 4 h to carry out a condensation reaction, remove the organic phase, and obtain the first intermediate fraction; Add 0.5 - 2 parts by weight of 4,4'-diaminodiphenylmethane to the first intermediate fraction, and react at 120 - 150 °C for 6 - 12 h to obtain the second mixed liquid; Add 0.3 - 0.6 parts by weight of silver oxide to the second mixed liquid, and react at 80 - 100 °C for 3 - 4 h to obtain the third mixed liquid; Distill the third mixed liquid to obtain the second intermediate fraction, and cool and let stand the second intermediate fraction to obtain the anti-yellowing additive.

8. A coating comprising the anti-yellowing additive described in claim 6, characterized in that, The coating includes: Waterborne polyurethane: 100 parts by weight; Deionized water: 120 - 300 parts by weight; 1,6-hexanediol: 1 - 5 parts by weight; Anti-yellowing additive: 1 - 5 parts by weight; Dispersant: 0.1 - 0.5 parts by weight.

9. A method for preparing a coating as claimed in claim 8, characterized in that: The preparation method includes: Prepolymerize isocyanate and polyol at 30 - 60 °C for 30 min, successively add chain extender and catalyst into the reactor, react at 30 - 60 °C, and add neutralizer after the reaction ends to obtain aqueous polyurethane with a pH of 8.0 - 9.0; Add deionized water and dispersant into the aqueous polyurethane, stir evenly at 25 - 30 °C to obtain a dispersion; Add 1,6 - hexanediol and anti - yellowing additive into the dispersion, stir, and disperse at a high speed of 1200 - 2000 r / min for 20 - 30 min, then continue to disperse at a high speed of 2000 - 3000 r / min for 20 - 80 min until emulsified without particles to obtain the coating.

10. The preparation method of the coating according to claim 9, characterized in that: The neutralizer is one or more of ethylenediamine, diethanolamine, diethylamine, and dimethylamine.