Waterproof polyurethane coating and preparation method thereof

Abstract

The invention belongs to the technical field of surface treating agent production, and discloses a waterproof polyurethane coating, which comprises a polyurethane emulsion and an inorganic filler filled in the polyurethane emulsion, and the inorganic filler is an inorganic filler modified by a silane coupling agent; the inorganic filler is selected from at least one of calcium carbonate, kaolin, barium sulfate, magnesium oxide, calcium oxide, wollastonite, talcum powder and mica powder; the silane coupling agent is selected from at least one kind of materials from KH540, KH550, KH560 and KH570; the mass ratio of the inorganic filler modified by the silane coupling agent to the polyurethane emulsion is 1: (8-10); by adding the inorganic filler, micropores and defects in polyurethane are filled, so that moisture permeation channels are reduced, and the compactness of the material is improved; part of the inorganic filler has a good shielding effect, so that water molecules can be prevented from permeating into polyurethane, and the waterproof performance is enhanced; in addition, the invention further discloses a preparation method of the waterproof polyurethane coating.

Description

Technical Field

[0001] The present application relates to the technical field of surface treatment agent production, and in particular to a waterproof polyurethane coating and a preparation method thereof. Background Art

[0002] Pure natural leather products are based on proteins and have strong hydrophilicity and air permeability. However, the leather prepared by people will add a lot of raw materials containing hydrophilic groups such as hydroxyl, carboxyl, amino, amide, etc. during the preparation process, which makes the leather waterproof performance poor, seriously affecting the use of leather. With the increase of people's demand, improving the waterproof performance of leather has always been a goal pursued by people. As early as the 20th century, people added paraffin and animal fats and other substances with waterproof effects during the leather preparation process to achieve the purpose of improving the waterproofness of leather. Later, it gradually developed into adding modification links on the leather surface, which not only can form a uniform protective film on the surface of the leather, but also give the leather a beautiful color, which can enhance the decorative sense of the leather. The added value of the leather has been effectively improved and gradually loved and used by the public. Therefore, the waterproof coating as a leather finishing agent has become an important link in the leather processing industry, and the wide application of waterproof leather has further promoted the development of waterproof coatings.

[0003] With the progress in production and life, people have further demands on the demand and performance of leather related products. Leather products can not only meet people's most basic production and life needs, but also continue to meet the needs of the masses in terms of fashion and usability. Therefore, people hope that leather can show "three-proof" properties such as waterproof, oil-proof and anti-fouling that leather itself does not have. Fluorine-containing leather waterproofing agent conforms to people's needs and the needs of production development, and came into being, gradually entering the public's field of vision. In order to keep the leather's excellent waterproof and oil-proof properties, leather waterproofing agent is usually applied to the leather surface to form a uniform waterproof coating.

[0004] Due to the presence of CF, fluorine atoms in fluorine-containing compounds can be tightly connected to the main chain of the carbon chain, and have excellent properties that other materials cannot compare with. Therefore, they are widely used in chemical industry, industrial construction, aerospace and other fields. Due to their special excellent properties, they are also introduced into the preparation process of leather waterproofing agents. Fluorine-containing waterproofing agent coatings are used in the leather field. Leather treated with this type of waterproofing agent can not only maintain its original soft texture and good air permeability, but also has "three-proof" properties, giving leather, cotton, polyester, nylon and other materials a highly durable waterproof effect, and has excellent water resistance and aging resistance.

[0005] Chinese patent application 201910940003.6 discloses a fluorine-containing polyurethane material with waterproof, oil-proof and anti-fouling properties, the preparation method of which is to first synthesize a dihydroxy fluorocarbon chain monomer through a mercapto-vinyl Michael addition reaction, then introduce it into polyurethane through addition polymerization reaction with a diisocyanate-terminated polyurethane prepolymer, and then obtain a fluorine-containing water-based polyurethane material with waterproof, oil-proof and anti-fouling properties through chain extension reaction and neutralization reaction respectively;

[0006] The fluorinated small molecule organic compounds in this scheme have the properties of being waterproof, oil-proof, anti-fouling, and heat-resistant, but they are easy to bond with proteins in the blood, accumulate in the human body, and affect human health; while fluorinated polymers still basically retain the properties of fluorinated small molecule organic compounds and have good biocompatibility; at the same time, due to their low chemical and biological activity, they will not affect human health. Introducing fluorinated small molecule organic compounds into polyurethane materials can not only greatly improve the water resistance and biocompatibility of polyurethane, but also significantly reduce the toxicity of fluorinated small molecule organic compounds.

[0007] It can be seen that the above scheme is to improve the waterproof performance of polyurethane by doping fluorine element into the leather finishing agent to obtain a polyurethane chain containing fluorine-containing small molecule organic compounds.

[0008] Chinese patent application 201610249143.5 discloses a high-strength polyurethane waterproof coating, the raw materials of which include, by weight: 50-55 parts of high-strength hydrophobic polyurethane, 26-29 parts of short-oil alkyd resin, 7-10 parts of potassium tripolyphosphate, 3-5 parts of zinc stearate, 0.5-0.8 parts of calcium lignin sulfonate, 5-8 parts of bentonite, 3-6 parts of light calcium carbonate, 2-5 parts of talc, 4-6 parts of butyl acetate, 1-3 parts of cyclohexanone, 0.1-0.4 parts of defoamer, 0.2-0.5 parts of leveling agent, and 0.3-0.6 parts of dispersant;

[0009] Further observation of the scheme shows that in the high-strength hydrophobic polyurethane, adding castor oil during the preparation process of phenolic resin can introduce the unsaturated bonds in castor oil into the molecular structure of phenolic resin and cross-link to form a three-dimensional network structure, thereby greatly improving the strength and brushing performance of the scheme, while improving the density of polyurethane, thereby enhancing the hydrophobic property and achieving a waterproof effect; and castor oil-modified phenolic resin and diphenylmethane diisocyanate trimer can be quickly cross-linked under the action of small molecule chain extender dipropylene glycol, cross-linking agent trimethylolethane, and catalyst dibutyltin dilaurate to form a high-strength hydrophobic polyurethane with high strength, good toughness and excellent waterproof performance; in the preparation process, high-strength hydrophobic is used. Polyurethane and short-oil alkyd resin as film-forming substances can fully cross-link and complement each other to form a coating film with excellent hydrophobic performance, thereby greatly improving the waterproof performance of polyurethane; the added potassium tripolyphosphate and zinc stearate can be dispersed in the network structure of the present invention to enhance the fireproof performance and strength of polyurethane; and calcium lignin sulfonate has good wetting and dispersibility, which can improve the construction performance of waterproof coatings and improve the flexibility of the coating film; the addition of bentonite, light calcium carbonate and talcum powder greatly improves the consistency and anti-thixotropy of the present invention, and they are evenly distributed in the polyurethane, extending the service life and storage time of the polyurethane, so that the polyurethane has high strength, high toughness and excellent waterproof performance after curing.

[0010] It can be seen that the above scheme further improves the waterproof performance of polyurethane by adding multiple additives including fillers and utilizing the interaction between multiple additives. However, it can be seen from the scheme that the scheme does not modify the inorganic filler to improve the dispersibility of the inorganic filler in polyurethane.

[0011] The problem to be solved by this scheme is: how to develop a waterproof polyurethane coating which is different from the prior art and has good waterproof ability. Summary of the invention

[0012] The purpose of the present application is to provide a polyurethane coating with good waterproof performance. The coating improves the waterproof ability of the polyurethane emulsion after curing by adjusting the mass ratio between the inorganic filler, the coupling agent and the polyurethane emulsion, thereby reducing the problems of easy water absorption or instability in a humid environment caused by the strong hydrophilicity of the polyurethane during use.

[0013] To achieve the above-mentioned purpose, the present application discloses a waterproof polyurethane coating, comprising a polyurethane emulsion and an inorganic filler filled in the polyurethane emulsion, wherein the inorganic filler is an inorganic filler modified by a silane coupling agent;

[0014] The inorganic filler is selected from at least one of calcium carbonate, kaolin, barium sulfate, magnesium oxide, calcium oxide, wollastonite, talc, and mica powder;

[0015] The silane coupling agent is selected from at least one of KH540, KH550, KH560 and KH570;

[0016] The mass ratio of the inorganic filler modified by the silane coupling agent to the polyurethane emulsion is 1:8-10.

[0017] Preferably, the silane coupling agent is a mixture of KH540 and KH550, and the mass ratio of KH540 to KH550 is 2-3:1.

[0018] Preferably, the inorganic filler is a mixture of kaolin, barium sulfate and calcium oxide, and the mass ratio of kaolin, barium sulfate and calcium oxide is 2-3:1:0.5-1.

[0019] Preferably, the preparation method of the modified inorganic filler is to mix the inorganic filler and the silane coupling agent in a mass ratio of 1:1.5-2 and place them in an ethanol solvent to react at 100-115°C for 1-3 hours, and then dry to obtain an inorganic filler modified by a silane coupling agent.

[0020] Preferably, the polyurethane emulsion comprises the following components in parts by mass:

[0021]

[0022] The isocyanate is a mixture of diisocyanate and long-chain isocyanate, and the carbon number of the long-chain alkyl in the long-chain isocyanate is not less than 12;

[0023] The mass ratio of the diisocyanate to the long-chain isocyanate is 10-12:1.

[0024] Preferably, the diisocyanate is selected from at least one of toluene diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate and xylylene diisocyanate;

[0025] The long-chain isocyanate is selected from at least one of dodecylbenzene-2,4-diisocyanate, 1,12-diisocyanatotridecane, dodecyl isocyanate, tetradecyl isocyanate and octadecyl isocyanate.

[0026] Preferably, the polyester polyol is selected from at least one of polyethylene adipate diol, polybutylene adipate diol and polycaprolactone diol.

[0027] Preferably, the diol is selected from at least one of propylene glycol, butylene glycol, pentanediol and hexanediol;

[0028] The solvent is selected from any one of toluene and acetone.

[0029] In addition, the present application also discloses a method for preparing the above-mentioned waterproof polyurethane coating, comprising the following steps:

[0030] Step 1: mixing an inorganic filler and a silane coupling agent in a mass ratio of 1:1.5-2 and placing the mixture in an ethanol solvent for reaction at 100-115° C. for 1-3 hours, followed by drying to obtain an inorganic filler modified by a silane coupling agent;

[0031] Step 2: Mix polyester polyol, isocyanate and solvent at 70-90° C. and react for 2-5 hours to obtain intermediate 1;

[0032] Step 3: dissolving 2,2-dihydroxymethylpropionic acid in a solvent, and then reacting the solvent containing 2,2-dihydroxymethylpropionic acid with intermediate 1 to generate intermediate 2;

[0033] The mass of the solvent in step 2 is 70-85% of the total mass of the solvent, and the mass of the solvent in step 3 is 15-30% of the total mass of the solvent;

[0034] Step 4: Mix the diol and the intermediate 2 and react at 70-80° C. for 1.5-3 hours, then add triethylamine for neutralization reaction for 30-50 minutes, then add deionized water for emulsification to obtain a polyurethane emulsion;

[0035] Step 5: Disperse the inorganic filler modified by the silane coupling agent into the polyurethane emulsion to obtain a waterproof polyurethane coating

[0036] The beneficial effects of this application are:

[0037] The waterproof polyurethane coating disclosed in the present application fills the micropores and defects in the polyurethane by adding inorganic fillers, thereby reducing the channels for water penetration and improving the density of the material; and because some inorganic fillers have a good shielding effect, they can block water molecules from penetrating into the interior of the polyurethane, thereby enhancing the waterproof performance; at the same time, the interfacial interaction between the inorganic filler and the polyurethane matrix can improve the mechanical properties and water resistance of the material, and the filler treated by surface modification can form a better interface bonding with the polyurethane matrix, thereby further enhancing the waterproof performance of the polyurethane. DETAILED DESCRIPTION

[0038] The present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. In the description of the present invention, it should be noted that, if no specific conditions are specified in the embodiments, the conditions are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0039] Before the examples are presented, the following necessary explanations are first made on the raw materials and preparation methods involved in the examples:

[0040] The raw material information of the embodiment is shown in Table 1:

[0041] Table 1

[0042]

[0043] The preparation method of the polyurethane finishing agent in the embodiment and comparative example is:

[0044] Step 1: mixing an inorganic filler and a silane coupling agent in a mass ratio of 1:1.5 and placing the mixture in an ethanol solvent at 108±2° C. for reaction for 2 hours, followed by drying to obtain an inorganic filler modified with a silane coupling agent;

[0045] Step 2: Mix polyester polyol, isocyanate and solvent at 80±5°C and react for 3.5±0.5h to obtain intermediate 1;

[0046] Step 3: dissolving 2,2-dihydroxymethylpropionic acid in a solvent, and then reacting the solvent containing 2,2-dihydroxymethylpropionic acid with intermediate 1 to generate intermediate 2;

[0047] The mass of the solvent in step 2 is 80% of the total mass of the solvent, and the mass of the solvent in step 3 is 20% of the total mass of the solvent;

[0048] Step 4: Mix the diol and the intermediate 2 and react at 75±5°C for 2.5±0.5h, then add triethylamine for neutralization reaction for 30-50min, then add deionized water for emulsification to obtain a polyurethane emulsion;

[0049] Step 5: dispersing the inorganic filler modified by the silane coupling agent into the polyurethane emulsion to obtain a waterproof polyurethane coating;

[0050] It should be further noted that the specific formula of the polyurethane used in each embodiment and the specific selection of the inorganic filler and the silane coupling agent can be found in the specific description of each embodiment.

[0051] Examples 1-4

[0052] The formula of polyurethane emulsion is shown in Table 2:

[0053] Table 2

[0054]

[0055] It should be noted that in Examples 1-4, the polyester polyol is specifically polyethylene adipate glycol;

[0056] In Examples 1-4, the diisocyanate is specifically a mixture of toluene diisocyanate and dodecylbenzene-2,4-diisocyanate, and in Example 1, the mass ratio of the mixture of toluene diisocyanate and dodecylbenzene-2,4-diisocyanate is 10:1;

[0057] In Example 2, the mass ratio of the mixture of toluene diisocyanate and dodecylbenzene-2,4-diisocyanate is 12:1;

[0058] In Example 3, the mass ratio of the mixture of toluene diisocyanate and dodecylbenzene-2,4-diisocyanate is 11:1;

[0059] In Example 3, the mass ratio of the mixture of toluene diisocyanate and dodecylbenzene-2,4-diisocyanate is 10:1;

[0060] The solvent in Examples 1-4 is specifically acetone;

[0061] Further, the inorganic filler in Examples 1-4 is kaolin, and the silane coupling agent is KH540;

[0062] The mass ratio of the inorganic filler modified by the silane coupling agent to the polyurethane emulsion is 1:9.

[0063] Example 5

[0064] The method is basically the same as Example 1, except that the mass ratio of the inorganic filler modified by the silane coupling agent to the polyurethane emulsion is 1:8.

[0065] Example 6

[0066] The method is basically the same as Example 1, except that the mass ratio of the inorganic filler modified by the silane coupling agent to the polyurethane emulsion is 1:10.

[0067] Example 7

[0068] It is basically the same as Example 1, except that the silane coupling agent is KH550.

[0069] Example 8

[0070] The method is basically the same as Example 1, except that the silane coupling agent is a mixture of KH540 and KH550, and the mass ratio of KH540 to KH550 is 2:1.

[0071] Example 9

[0072] The method is basically the same as Example 1, except that the silane coupling agent is a mixture of KH540 and KH550, and the mass ratio of KH540 to KH550 is 3:1.

[0073] Example 10

[0074] The method is basically the same as Example 1, except that the silane coupling agent is a mixture of KH540 and KH550, and the mass ratio of KH540 to KH550 is 2.5:1.

[0075] Embodiment 11

[0076] The method is substantially the same as Example 1, except that barium sulfate is used instead of kaolin.

[0077] Example 12

[0078] The method is basically the same as Example 1, except that calcium oxide is used to replace kaolin.

[0079] Embodiment 13

[0080] It is basically the same as Example 1, except that a mixture of kaolin, barium sulfate and calcium oxide is used to replace kaolin, and the mass ratio of kaolin, barium sulfate and calcium oxide is 3:1:1.

[0081] Embodiment 14

[0082] It is basically the same as Example 1, except that a mixture of kaolin, barium sulfate and calcium carbonate is used to replace kaolin, and the mass ratio of kaolin, barium sulfate and calcium carbonate is 3:1:1.

[0083] Embodiment 15

[0084] The method is substantially the same as Example 1, except that the mass ratio of the mixture of toluene diisocyanate and dodecylbenzene-2,4-diisocyanate is 8:1.

[0085] Example 16

[0086] The process is substantially the same as Example 1, except that toluene diisocyanate is used instead of the mixture of toluene diisocyanate and dodecylbenzene-2,4-diisocyanate.

[0087] Comparative Example 1

[0088] The method is basically the same as Example 1, except that the mass ratio of the inorganic filler modified by the silane coupling agent to the polyurethane emulsion is 1:7.

[0089] Comparative Example 2

[0090] The method is basically the same as Example 1, except that the mass ratio of the inorganic filler modified by the silane coupling agent to the polyurethane emulsion is 1:11.

[0091] Comparative Example 3

[0092] The method is basically the same as Example 1, except that after the polyurethane emulsion is prepared in step 4, the inorganic filler modified by the silane coupling agent is not added to the polyurethane emulsion, and the types and addition amounts of the remaining polyester polyols, diisocyanates, 2,2-dimethylol propionic acid, diols and solvents are the same as those in Example 1;

[0093] The specific preparation method is:

[0094] Step 1: Mix polyester polyol, isocyanate and solvent at 80±5°C and react for 3.5±0.5h to obtain intermediate 1;

[0095] Step 2: dissolving 2,2-dihydroxymethylpropionic acid in a solvent, and then reacting the solvent containing 2,2-dihydroxymethylpropionic acid with intermediate 1 to generate intermediate 2;

[0096] The mass of the solvent in step 2 is 80% of the total mass of the solvent, and the mass of the solvent in step 3 is 20% of the total mass of the solvent;

[0097] Step 3: Mix the diol and the intermediate 2 and react at 75±5° C. for 2.5±0.5 h, then add triethylamine for neutralization reaction for 30 to 50 min, then add deionized water for emulsification to obtain a polyurethane emulsion.

[0098] Comparative Example 4

[0099] The method is substantially the same as Comparative Example 3, except that toluene diisocyanate is used instead of the mixture of toluene diisocyanate and dodecylbenzene-2,4-diisocyanate.

[0100] Performance Test:

[0101] Waterproof performance test:

[0102] The polyurethane coatings prepared in the above examples and comparative examples were made into films, and their waterproof properties were tested according to JC / T 864-2023;

[0103] Emulsification difficulty test:

[0104] Since the polyurethane coating is prepared by neutralizing the intermediate di and triethylamine in step 4 and then adding deionized water for emulsification, and the presence of long-chain isocyanate in isocyanate may affect the emulsification time of deionized water, the emulsification time of deionized water in the preparation process of different embodiments and comparative examples is statistically analyzed to determine the difficulty of emulsification of each embodiment;

[0105] The specific test method is that in the preparation process of the polyurethane coating, the speed of each embodiment and the comparative example during the emulsification process is controlled to be the same (the speed is 1500 rpm), and the emulsions after emulsification all show an appearance of no stratification and no agglomeration, and the emulsification time is counted, and then the difficulty of emulsification is judged from the length of the emulsification time. The longer the emulsification time, the more difficult the emulsification;

[0106] The specific results are shown in Table 3:

[0107] Table 3

[0108]

[0109]

[0110] Result analysis:

[0111] 1. It can be seen from Examples 1-4 that when the addition amount of each raw material in the polyurethane emulsion in the finishing agent is slightly adjusted, the water absorption rate and emulsification time of Examples 1-4 fluctuate, but the overall fluctuation range is relatively small;

[0112] 2. It can be seen from Examples 1 and 5-6 that when the mass ratio between the inorganic filler modified by the silane coupling agent and the polyurethane emulsion is slightly adjusted, the water absorption rate of the finishing agent increases with the increase in the proportion of the inorganic filler modified by the silane coupling agent, but overall, the change in the water absorption rate is relatively small;

[0113] 3. It can be seen from Examples 1 and 7-10 that, on the one hand, when silane coupling agent KH550 is used to replace silane coupling agent KH540, the water absorption rate of Example 7 relative to Example 1 does not show an obvious fluctuation trend. Further observation of Examples 8-10 shows that when silane coupling agent KH540 and silane coupling agent KH550 are used to replace silane coupling agent KH540 in Examples 8-10, the water absorption rates of Examples 8-10 relative to Example 1 are inhibited to varying degrees. It is speculated that the reason for this phenomenon may be that, on the one hand, the mixed use of KH550 and KH540 forms a more uniform and stable interface layer between the inorganic filler and the polyurethane matrix during the mixing process of the inorganic filler and the polyurethane emulsion; this interface layer can effectively prevent the penetration of water, thereby improving the waterproof performance of the material;

[0114] On the other hand, the mixed use of the two and the modification of the inorganic filler further enhance the bonding ability between the inorganic filler and the polyurethane emulsion, thereby improving the waterproof ability of the coating agent;

[0115] Further observation of Example 10 shows that when the mass ratio of KH540 and KH550 is adjusted to 2.5:1 in Example 10, the water absorption rate of Example 10 has a further improvement trend. It can be seen that when the mass ratio of KH540 and KH550 is 2.5:1, the above-mentioned silane coupling agent has a more significant improvement on the stability of the interface layer and the bonding ability between the inorganic filler and the polyurethane emulsion;

[0116] 4. It can be seen from Examples 1 and 11-12 that when Examples 11 and 12 use barium sulfate or calcium oxide to replace kaolin, the water absorption of Examples 11-12 is improved to a certain extent relative to Example 1, and when Example 13 uses a mixture of kaolin, barium sulfate and calcium oxide to replace kaolin, the water absorption of Example 13 is more obviously inhibited relative to Example 1. It is speculated that the reason for this phenomenon may be that the use of kaolin, barium sulfate and calcium oxide together may cause the filler to form a more complex physical barrier in the finishing agent, thereby increasing the path length of water penetration, thereby improving the waterproof performance of the finishing agent;

[0117] However, further observation of Example 14 shows that Example 14 also uses three inorganic fillers in combination and the only difference from Example 13 is that Example 14 uses calcium carbonate to replace calcium oxide, but Example 14 does not achieve a water absorption rate similar to that of Example 13. The reason may be that calcium carbonate cannot form a complex physical barrier with kaolin and barium sulfate in the finishing agent, or the density of the generated physical barrier is relatively low, resulting in a decline in the waterproof performance of the finishing agent compared with Example 13.

[0118] 5. Further observation of Example 1 and Example 15 shows that when Example 15 increases the proportion of dodecylbenzene-2,4-diisocyanate in diisocyanate, the water absorption rate of Example 15 shows a certain downward trend relative to Example 1, but observation of its emulsification time shows that its emulsification process takes a significantly longer time;

[0119] 6. It can be seen from Example 1 and Comparative Example 1 that when the proportion of inorganic filler in the finishing agent is increased in Comparative Example 1, the final finishing agent product cannot be prepared in Comparative Example 1. Although the polyurethane emulsion presents a good appearance during the emulsification process, with the subsequent addition of excessive inorganic fillers, the inorganic fillers agglomerate in the polyurethane emulsion and cannot be dispersed;

[0120] Further observation of Comparative Example 2 shows that when the proportion of inorganic filler in the finishing agent is reduced in Comparative Example 2, the water absorption rate of the inorganic filler is improved. The reason is that the proportion of inorganic filler in the finishing agent is too small, which leads to a decrease in shielding effect, so that more water molecules penetrate into the interior of the polyurethane, affecting the waterproof performance;

[0121] It can be seen from the comparative example 3 that when no inorganic filler is added to the polyurethane finishing agent, the waterproof performance of the comparative example 3 has a significant downward trend. Although part of the long-chain isocyanate is used in the diisocyanate to provide hydrophobic groups to improve the waterproof performance of the material, and the waterproof ability of the material is improved, it is not as obvious as that of Example 1.

[0122] 7. Further, by observing Example 1 and Example 16, it can be seen that the difference between Example 1 and Example 16 is that the composition of the diisocyanate is different. The diisocyanate in Example 1 is a mixture of toluene diisocyanate and dodecylbenzene-2,4-diisocyanate, and the mass ratio of the mixture of toluene diisocyanate and dodecylbenzene-2,4-diisocyanate is 10:1;

[0123] In Example 16, the diisocyanate contains only toluene diisocyanate;

[0124] Further observation of the water absorption rate between the two shows that the water absorption rate of Example 1 is reduced by about 4.6% relative to that of Example 16;

[0125] At the same time, it can be seen from comparative example 3 and comparative example 4 that the difference between the two is also the different composition of diisocyanate. The diisocyanate in comparative example 3 is a mixture of toluene diisocyanate and dodecylbenzene-2,4-diisocyanate, and the mass ratio of the mixture of toluene diisocyanate and dodecylbenzene-2,4-diisocyanate is 10:1.

[0126] In Comparative Example 4, the diisocyanate contained only toluene diisocyanate;

[0127] Further observation of the water absorption between the two shows that the water absorption of Comparative Example 3 is about 2.9% lower than that of Comparative Example 4;

[0128] It can be seen that the difference between the two groups of cases lies in the different compositions of isocyanates, so the difference in water absorption between the two groups of cases should be close in theory. However, in fact, there is a difference in water absorption between the two groups of cases. The only difference between Example 1 and Example 16 and Comparative Example 3 and Comparative Example 4 is that inorganic fillers are added to Examples 1 and 16, while inorganic fillers are not added to Comparative Example 3 and Comparative Example 4. Therefore, it is speculated that the reason why the water absorption of Example 1 is further reduced relative to Example 16 may be due to the synergistic effect between the inorganic filler and the long-chain isocyanate. The principle may be that the part of the polyurethane chain involving the long-chain isocyanate may further react chemically with the inorganic filler, thereby improving the interfacial bonding strength between the filler and the polyurethane matrix, thereby further preventing the penetration of moisture.

Claims

1. A waterproof polyurethane coating, characterized in that: It comprises a polyurethane emulsion and an inorganic filler filled in the polyurethane emulsion, wherein the inorganic filler is an inorganic filler modified by a silane coupling agent; The inorganic filler is selected from at least one of calcium carbonate, kaolin, barium sulfate, magnesium oxide, calcium oxide, wollastonite, talc, and mica powder; The silane coupling agent is selected from at least one of KH540, KH550, KH560 and KH570; The mass ratio of the inorganic filler modified by the silane coupling agent to the polyurethane emulsion is 1:8-10.

2. The waterproof polyurethane coating according to claim 1, characterized in that: The silane coupling agent is a mixture of KH540 and KH550, and the mass ratio of KH540 to KH550 is 2-3:

1.

3. The waterproof polyurethane coating according to claim 1, characterized in that: The inorganic filler is a mixture of kaolin, barium sulfate and calcium oxide, and the mass ratio of kaolin, barium sulfate and calcium oxide is 2-3:1:0.5-1.

4. The waterproof polyurethane coating according to claim 1, characterized in that: The preparation method of the modified inorganic filler is to mix the inorganic filler and the silane coupling agent in a mass ratio of 1:1.5-2 and place the mixture in an ethanol solvent to react at 100-115°C for 1-3 hours, and then dry the mixture to obtain the inorganic filler modified by the silane coupling agent.

5. The waterproof polyurethane coating according to claim 1, characterized in that: The polyurethane emulsion comprises the following components in parts by mass: The isocyanate is a mixture of diisocyanate and long-chain isocyanate, and the carbon number of the long-chain alkyl in the long-chain isocyanate is not less than 12; The mass ratio of the diisocyanate to the long-chain isocyanate is 10-12:

1.

6. The waterproof polyurethane coating according to claim 5, characterized in that: The diisocyanate is selected from at least one of toluene diisocyanate, diphenylmethane diisocyanate, dicyclohexylmethane diisocyanate, isophorone diisocyanate and xylylene diisocyanate; The long-chain isocyanate is selected from at least one of dodecylbenzene-2,4-diisocyanate, 1,12-diisocyanatotridecane, dodecyl isocyanate, tetradecyl isocyanate and octadecyl isocyanate.

7. The waterproof polyurethane coating according to claim 5, characterized in that: The polyester polyol is selected from at least one of polyethylene adipate diol, polybutylene adipate diol and polycaprolactone diol.

8. The waterproof polyurethane coating according to claim 5, characterized in that: The diol is selected from at least one of propylene glycol, butylene glycol, pentanediol and hexanediol; The solvent is selected from any one of toluene and acetone.

9. A method for preparing a waterproof polyurethane coating according to any one of claims 4 to 8, characterized in that: The following steps are involved: Step 1: mixing an inorganic filler and a silane coupling agent in a mass ratio of 1:1.5-2 and placing the mixture in an ethanol solvent for reaction at 100-115° C. for 1-3 hours, followed by drying to obtain an inorganic filler modified by a silane coupling agent; Step 2: Mix polyester polyol, isocyanate and solvent at 70-90° C. and react for 2-5 hours to obtain intermediate 1; Step 3: dissolving 2,2-dihydroxymethylpropionic acid in a solvent, and then reacting the solvent containing 2,2-dihydroxymethylpropionic acid with intermediate 1 to generate intermediate 2; The mass of the solvent in step 2 is 70-85% of the total mass of the solvent, and the mass of the solvent in step 3 is 15-30% of the total mass of the solvent; Step 4: Mix the diol and the intermediate 2 and react at 70-80° C. for 1.5-3 hours, then add triethylamine for neutralization reaction for 30-50 minutes, then add deionized water for emulsification to obtain a polyurethane emulsion; Step 5: Disperse the inorganic filler modified by the silane coupling agent into the polyurethane emulsion to obtain a waterproof polyurethane coating.

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