Leather surface coatings, leather containing surface coatings and their preparation methods, and bags.

Abstract

This disclosure provides a leather surface coating, leather containing the surface coating, a method for preparing the same, and bags. The aforementioned leather surface coating comprises a surface-enriched silicone-modified polyether-polyurethane prepolymer, a liquid crosslinking agent, and a film-forming aid. The surface-enriched silicone-modified polyether-polyurethane prepolymer contains hydroxyl or amino groups, and none of the surface-enriched silicone-modified polyether-polyurethane prepolymer, the liquid crosslinking agent, or the film-forming aid contains organic solvents. This leather surface coating, by compounding the surface-enriched silicone-modified polyether-polyurethane prepolymer, the liquid crosslinking agent, and the film-forming aid, can produce leather that is VOC-free, more environmentally friendly, has suitable hardness, high density, excellent three-proof performance (waterproof, dustproof, and shockproof), good adhesion to leather, and is simple to produce, thus better suited for high-end and eco-friendly leather applications.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of leather technology, in particular to a leather surface coating, a leather containing the surface coating and a preparation method thereof, and a luggage. BACKGROUND

[0002] Luggage is an item that people use frequently in their daily lives. They can help us conveniently carry clothes, books, computers and other items, making our lives more convenient. Luggage can be classified by material into leather luggage, nylon luggage, cloth luggage and plastic luggage. Leather luggage is the most common, which is usually made of animal leather such as cowhide, sheepskin and alligator skin. Because leather luggage has good texture, high quality, durability and strong plasticity, it is also loved by many consumers. However, it is prone to water absorption and dampness in a humid environment, which affects its service life.

[0003] In order to solve the problem of leather luggage being damp, some manufacturers of leather luggage have carried out surface treatment on the raw material of leather luggage, i.e. leather, so that a protective film can be formed on the surface of the leather, effectively solving the problem of leather being prone to water absorption and dampness in a humid environment.

[0004] Early leather surface coatings mostly contain a large amount of organic solvents, not only single performance, but also excessive content of organic solvents. However, with the improvement of people's living quality and the enhancement of environmental protection consciousness, the market has put forward higher requirements for luggage: such as requiring the volatile organic compounds (VOCs) of leather to be no more than 5 mg / Kg, and high-performance green and environmentally friendly leather with three-proofing (waterproof, oil-proof and stain-proof) to better adapt to the development of the market.

[0005] Therefore, a new type of solvent-free three-proofing synthetic leather has appeared on the market. For example, Chinese Patent No. CN110670376 B discloses a solvent-free three-proofing synthetic leather and a manufacturing method thereof. The present application discloses a solvent-free three-proofing synthetic leather and a manufacturing method thereof, characterized in that a mixed slurry composed of a hydroxyl or amine group terminated solvent-free fluorine-containing polyurethane prepolymer, a solvent-free crosslinking agent and an auxiliary agent is coated on a release paper, heat cured to form a film, and then a hot melt adhesive is coated and scraped to adhere to the synthetic leather base cloth by hot pressing. Further heat curing, or vacuum suction texturing, roller texturing, surface treatment, a solvent-free three-proofing synthetic leather product is prepared. The present application forms a synthetic leather coating by heat curing the fluorine-containing polyurethane slurry without any solvent, which gives the synthetic leather three-proofing effect, and can meet the requirements of customers for synthetic leather protection, oil-proofing and stain-proofing, such as automotive leather, luggage leather and wallpaper leather. The product does not contain VOCs, greatly improving the ecological grade and international market competitiveness of synthetic leather.

[0006] Although the above-mentioned solvent-free coating slurry can achieve VOC-free and improve the three-proofing effect of the leather, the fluorine-containing polyurethane prepolymer used still contains a large amount of fluorine elements, which is not environmentally friendly and cannot better adapt to the production requirements of high-grade leather.

[0007] In addition, since the above-mentioned solvent-free coating slurry introduces fluorine-containing polyurethane prepolymer and filler filling, the final prepared leather surface has high hardness, which causes poor skin-friendliness of the leather and cannot better adapt to the application of some high-end luggage; and most fillers are currently in the form of powder particles, which are difficult to uniformly disperse in the solvent-free coating slurry, resulting in poor dispersion of the fluorine-containing polyurethane prepolymer and the filler in the slurry, which is not conducive to forming a uniform and dense surface coating. SUMMARY

[0008] The purpose of the present application is to overcome the shortcomings in the prior art, provide a solvent-free and filler-free leather surface coating which is more environmentally friendly, uniform, has appropriate hardness, strong density, excellent three-proofing performance, good adhesion with leather, and is simple to produce, a leather containing the surface coating and a method for preparing the same, and luggage.

[0009] The purpose of the present application is achieved by the following technical solutions:

[0010] The leather surface coating comprises a surface-enriched organosilicon-modified polyether-polyurethane prepolymer, a liquid crosslinking agent and a film-forming aid, the surface-enriched organosilicon-modified polyether-polyurethane prepolymer contains a hydroxyl or amine group end, and the surface-enriched organosilicon-modified polyether-polyurethane prepolymer, the liquid crosslinking agent and the film-forming aid all do not contain organic solvents.

[0011] In one embodiment, the amount of the surface-enriched organosilicon-modified polyether-polyurethane prepolymer used is 80-90 parts.

[0012] In one embodiment, the liquid crosslinking agent comprises at least one of 1,6-hexamethylene diisocyanate, trimethyl-1,6-hexamethylene diisocyanate and carbodiimide.

[0013] In one embodiment, the film-forming aid comprises at least one of dibutyltin dilaurate and dodecanol ester.

[0014] In one embodiment, the amount of the film-forming aid used is 0.01-0.2 parts.

[0015] In one embodiment, the surface-enriched organosilicon-modified polyether-polyurethane prepolymer is prepared by the following steps:

[0016] Obtaining a modified epoxy polyether, wherein the branched chain of the modified epoxy polyether contains silicone;

[0017] Adding an OH-containing end-capping agent to the modified epoxy polyether to obtain an OH side-capped modified epoxy polyether;

[0018] Adding isocyanate and dehydrated polyester diol or polyether diol to the OH side-capped modified epoxy polyether to obtain a surface-enriched silicone modified polyether-polyurethane prepolymer.

[0019] A method for preparing a leather containing a surface coating, the method comprising the following steps:

[0020] Obtaining the leather surface coating according to any one of the above embodiments;

[0021] Mixing the surface-enriched silicone modified polyether-polyurethane prepolymer, liquid crosslinking agent and film-forming aid to obtain a uniformly mixed leather surface coating;

[0022] Applying the leather surface coating to the surface of the leather to obtain a semi-finished leather A;

[0023] Performing heat curing on the semi-finished leather A to obtain the leather containing a surface coating.

[0024] In one embodiment, the leather comprises at least one of cow leather, sheep leather, mink leather and pig leather.

[0025] A leather containing a surface coating is prepared by the method for preparing a leather containing a surface coating according to any one of the above embodiments.

[0026] A bag is sewn by the leather containing a surface coating according to any one of the above embodiments.

[0027] Compared with the prior art, the present application has at least the following advantages:

[0028] The surface-enriched organosilicon-modified polyether-polyurethane prepolymer added in the present disclosure is more prone to migrate and aggregate on the surface of the leather surface coating during film formation, and forms a low-surface-energy organosilicon layer, thereby reducing the wetting and spreading of pollutants such as water and ink on the surface of the leather, and improving the three-proofing performance of the leather; and since the surface-enriched organosilicon-modified polyether-polyurethane prepolymer contains hydroxyl or amine end groups, it can form a dense polyurethane protective film with the added liquid crosslinking agent, effectively preventing the penetration of water or ink molecules, and further improving the three-proofing performance of the leather; at the same time, it can also block the hydrophilic groups in the polyurethane protective film, avoiding the surface reconstruction of the hydrophilic groups, thereby reducing the intermolecular forces between the polyurethane protective film and pollutants such as ink or water, and further improving the three-proofing performance of the leather; and the present disclosure does not use organic solvents, so that the prepared leather does not contain VOCs, is more environmentally friendly than traditional fluorine-containing polyurethane prepolymers, and is particularly suitable for use in high-ecological-grade leather applications.

[0029] Since the surface-enriched organosilicon-modified polyether-polyurethane prepolymer is more prone to migrate and aggregate on the surface of the leather surface coating during film formation, it is beneficial to the spreading of the leather surface coating on the surface of the leather, effectively reducing the amount of film-forming additives used, so as to ensure that a small amount of film-forming additives can quickly form a uniform and dense protective film on the surface of the leather.

[0030] Since the leather surface coating of the present disclosure can prepare a polyurethane protective film with appropriate hardness without adding additional filler ingredients, the softness of the polyurethane protective film is better ensured, so as to better adapt to the application of some high-end luggage; and it is beneficial to the rapid and uniform dispersion of the surface-enriched organosilicon-modified polyether-polyurethane prepolymer in the leather surface coating, solving the problem of poor dispersion of traditional fillers in solvent-free slurries.

[0031] Since the surface-enriched organosilicon-modified polyether-polyurethane prepolymer introduces a modified polyether block, the compatibility of the leather surface coating with the leather is improved, which helps to form a polyurethane protective film with good adhesion on the surface of the leather. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0033] Figure 1 Flow chart of the surface-enriched organosilicon-modified polyether-polyurethane prepolymer of an embodiment of the present application;

[0034] Figure 2Flow chart of the method for preparing the surface-coated leather according to an embodiment of the present application;

[0035] Figure 3 is a test comparison chart of the anti-fouling performance (ink pen) of the embodiment 2 of the present application and the leather without the anti-fouling coating. Figure 3a is a comparison chart of the drawing, Figure 3b is a chart of the rubbing process, Figure 3c is a final comparison chart of the rubbing. DETAILED DESCRIPTION

[0036] For the purpose of promoting an understanding of the principles of the application, reference will now be made to the embodiments illustrated in the drawings. There is shown in the drawings, several embodiments of the application. It is readily appreciated that the instant application can be realized in other constructions and arrangements without departing from the scope of the application. In fact, the application is well suited to achieving this object with the embodiments presented herein. Accordingly, the application should not be limited to the embodiments described herein, but should be given the broadest scope of the appended claims.

[0037] It is to be understood that the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. It is to be understood that the terms "approximately" and "substantially" are used herein to represent the insubstantial difference in the precision of a numerical value, and that such insubstantial difference is within the range of error for the particular value as determined by one of ordinary skill in the art. It is to be understood that the terms "coupled" and "connected," along with derivatives thereof, are used herein to express the relationship of one element to another element in a manner that is meant to convey that the one element is directly or indirectly to the other element.

[0038] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. As used herein, the singular forms "a", "an" and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms "comprises", "comprising", "including", and "having" are is intended to be inclusive and mean that there can be additional elements other than the listed elements.

[0039] The present disclosure provides a leather surface coating, comprising a surface-enriched organosilicon-modified polyether-polyurethane prepolymer, a liquid crosslinking agent, and a film-forming aid, wherein the surface-enriched organosilicon-modified polyether-polyurethane prepolymer has a hydroxyl or amine end group, and the surface-enriched organosilicon-modified polyether-polyurethane prepolymer, the liquid crosslinking agent, and the film-forming aid are all free of organic solvents.

[0040] The leather surface coating described above, due to the surface enrichment organosilicon modified polyether-polyurethane prepolymer added in the present disclosure, the organosilicon is more easily migrated and aggregated to the surface of the leather surface coating in the film forming process, and a low surface energy organosilicon layer is formed, thereby reducing the wetting and spreading of water, ink and other pollutants on the surface of the leather, and improving the three-proofing performance of the leather; and due to the surface enrichment organosilicon modified polyether-polyurethane prepolymer containing hydroxyl or amine end groups, a dense polyurethane protective film can be formed with the added liquid crosslinking agent, effectively preventing the penetration of water or ink molecules, further improving the three-proofing performance of the leather; at the same time, it can also seal the hydrophilic groups in the polyurethane protective film, avoiding the surface reconstruction of the hydrophilic groups, thereby reducing the intermolecular forces between the polyurethane protective film and ink or water pollutants, further improving the three-proofing performance of the leather, and the present disclosure does not use organic solvents, so that the prepared leather does not contain VOCs, is more environmentally friendly than traditional fluorine-containing polyurethane prepolymers, and is especially suitable for use in high-grade ecological leather applications. Further, due to the surface enrichment organosilicon modified polyether-polyurethane prepolymer, the organosilicon is more easily migrated and aggregated to the surface of the leather surface coating in the film forming process, which is beneficial to the spreading of the leather surface coating on the surface of the leather, effectively reducing the amount of film forming additives used to ensure that a small amount of film forming additives can quickly form a uniform and dense protective film on the surface of the leather. Further, due to the leather surface coating of the present disclosure, a polyurethane protective film with appropriate hardness can be prepared without additional filler ingredients, thereby better ensuring the softness of the polyurethane protective film to better adapt to the application of some high-end luggage; and it is beneficial to the rapid and uniform dispersion of the surface enrichment organosilicon modified polyether-polyurethane prepolymer in the leather surface coating, solving the problem of poor dispersion of traditional fillers in solvent-free slurry.

[0041] In order to better understand the technical solutions and beneficial effects of the present disclosure, the present disclosure will be further described in detail below in combination with specific embodiments:

[0042] The leather surface coating of one embodiment includes a surface enrichment organosilicon modified polyether-polyurethane prepolymer, a liquid crosslinking agent and a film forming aid, and the surface enrichment organosilicon modified polyether-polyurethane prepolymer contains hydroxyl or amine end groups.

[0043] It can be understood that the traditional surface coating using fluorine contains a C-F bond in the fluorine-containing polyurethane prepolymer, which is more stable than the C-H bond, so that the F atom is closely arranged around the carbon main chain, thereby having incomparable three-proofing performance, i.e. excellent weather resistance, water repellency, oil repellency, stain resistance, chemical resistance, solvent resistance, and extremely low friction coefficient.

[0044] However, although the added fluorine element can improve the three-proofing performance of the leather, the compatibility of the fluorine-containing material with the polyurethane is poor due to the low surface energy, thereby resulting in poor adhesion of the fluorine-containing material to the surface of the leather, and thus an additional polyurethane hot adhesive needs to be added in subsequent production, such as the manufacturing method of the solvent-free three-proofing synthetic leather disclosed in Chinese CN 110670376 B, which describes that "after curing, a polyurethane hot adhesive is coated, and is hot-pressed and attached to the substrate, and is cured in an oven at 90-130°C for 1-2 min, and is cooled, and the paper and leather are separated, and are subjected to optional processes such as grain absorption, embossing, leather kneading, and surface treatment, to obtain a solvent-free three-proofing synthetic leather with water-proof, oil-proof, and stain-proof functions." Therefore, it can be seen that the operation is complicated and the cost is high.

[0045] Therefore, some scholars have tried to use silicone materials for surface treatment of leather, but in actual application, when the fluorine-containing material is simply replaced by silicone material, there is still a problem of poor compatibility of the silicone material with the polyurethane and the leather. Therefore, some scholars have modified the silicone material, such as Chinese patent CN116751513 A discloses a leather surface treatment agent, and specifically discloses that the leather surface treatment agent comprises the following raw materials: 100 parts of hydroxyl-terminated polydimethylsiloxane, 10-40 parts of polyether, 0.2-2 parts of polyether-modified silicone oil, 3-20 parts of epoxy-modified polyether, 10-50 parts of matting powder, 10-50 parts of PU resin, 200-800 parts of mixed solvent, 1-10 parts of coupling agent, and 0.2-5 parts of catalyst. As can be seen from the above, the leather surface treatment agent can improve the stability of the blended organic silicon material and PU resin and the adhesion performance of the polyurethane layer interface by using epoxy-modified polyether, hydroxyl-terminated polydimethylsiloxane, polyether, polyether-modified silicone oil, and epoxy-modified polyether together. In this way, the adhesion of the surface treatment agent to the leather is improved while also having good stain-proof performance.

[0046] However, since the above leather surface treatment agent is a solvent type polyurethane surface treatment agent, i.e. mixed solvents (petroleum ether, white kerosene and isomeric alkanes) are needed to be used as organic solvents, which makes these organic solvents easily remain in the leather and causes the VOCs content of the leather to exceed the standard, which cannot meet the requirements of higher ecological grade leather production. In order to realize the application of solvent-free organic silicon surface coating of leather, therefore, in the present disclosure, the organic silicon material is secondarily modified to prepare a surface-enriched organic silicon modified polyether-polyurethane prepolymer, which can form a uniform, dense, excellent three-proofing performance and good adhesion polyurethane protective film on the surface of the leather with the liquid cross-linking agent under the action of the film forming aid. In this way, not only the production cost of solvents and fillers is reduced, but also the leather is zero VOCs, which better meets the requirements of higher ecological grade leather production, and at the same time, the characteristics of excellent three-proofing performance and good adhesion are realized, so that the adhesion of the leather and the polyurethane protective film can be improved without additional polyurethane hot melt adhesive in subsequent production, thereby improving the service life of the leather.

[0047] In order to find a better way to adapt to the development of the leather market, in the present disclosure, the surface-enriched organic silicon modified polyether-polyurethane prepolymer is more easily migrated to the surface of the leather surface coating and forms a low surface energy organic silicon layer during the film forming process, thereby reducing the wetting and spreading of water, ink and other pollutants on the surface of the leather and improving the three-proofing performance of the leather. In addition, the surface-enriched organic silicon modified polyether-polyurethane prepolymer contains hydroxyl or amine end groups, which can form a dense polyurethane protective film with the added liquid cross-linking agent, effectively preventing the penetration of water or ink molecules, and further improving the three-proofing performance of the leather. At the same time, it can also seal the hydrophilic groups in the polyurethane protective film, avoiding the surface reconstruction of the hydrophilic groups, thereby reducing the intermolecular forces between the polyurethane protective film and ink or water pollutants, and further improving the three-proofing performance of the leather. Moreover, the present disclosure does not use organic solvents, so that the prepared leather does not contain VOCs, which is more environmentally friendly than traditional fluorine-containing polyurethane prepolymers, and is especially suitable for the application of higher ecological grade leather.

[0048] It can also be understood that, since the surface-enriched organic silicon modified polyether-polyurethane prepolymer is more easily migrated to the surface of the leather surface coating and aggregated during the film forming process, it is beneficial to the spreading of the leather surface coating on the surface of the leather, effectively reducing the amount of film forming aid used, so as to ensure that a small amount of film forming aid can quickly form a uniform and dense protective film on the surface of the leather.

[0049] It can also be understood that, since the leather surface coating of the present disclosure can prepare a polyurethane protective film with suitable hardness without additional addition of filler components, the softness of the polyurethane protective film is better ensured to better adapt to the application of some high-end luggage; and it is beneficial to the rapid and uniform dispersion of the surface-enriched silicone-modified polyether-polyurethane prepolymer in the leather surface coating, solving the problem of poor dispersion of traditional fillers in solvent-free slurry.

[0050] It can also be understood that, since the surface-enriched silicone-modified polyether-polyurethane prepolymer introduces a modified polyether block, the compatibility of the leather surface coating with the leather is improved, which helps to form a polyurethane protective film with good adhesion on the leather surface, thereby improving the service life of the leather.

[0051] It can be understood that, if the amount of the surface-enriched silicone-modified polyether-polyurethane prepolymer is less than 80 parts, a dense and low-surface-energy polyurethane protective film cannot be formed, and if the amount of the surface-enriched silicone-modified polyether-polyurethane prepolymer is greater than 90 parts, the hardness of the formed polyurethane protective film is high, which leads to poor softness and skin-friendliness of the leather. Therefore, in one embodiment, the amount of the surface-enriched silicone-modified polyether-polyurethane prepolymer is controlled to be 80 parts to 90 parts to ensure that the surface energy and hardness of the finally prepared polyurethane protective film are both suitable, which not only ensures that the leather has excellent three-proofing performance, but also ensures that the polyurethane protective film has good adhesion with the leather surface, and the leather has good softness and skin-friendliness.

[0052] In one embodiment, the liquid crosslinking agent includes at least one of 1,6-hexamethylene diisocyanate, trimethyl-1,6-hexamethylene diisocyanate, and carbodiimide. It can be understood that, by using a liquid crosslinking agent, on the one hand, the leather surface coating can be spread on the leather surface to ensure that the surface-enriched silicone-modified polyether-polyurethane prepolymer can still form a film quickly in a solvent-free manner, and on the other hand, the liquid crosslinking agent can provide NCO or NH2 to ensure that it can crosslink with the hydroxyl or amine group of the surface-enriched silicone-modified polyether-polyurethane prepolymer on the leather surface to form a uniform and dense polyurethane protective film on the leather surface.

[0053] In one embodiment, the film-forming aid includes at least one of dibutyltin dilaurate, triethylenediamine, and bis(dimethylaminoethyl) ether.

[0054] In one of the embodiments, the amount of the film forming aid used is 0.01-0.2 parts. It can be understood that, due to the migration of the silicone to the surface of the leather surface coating during the film forming process, the leather surface coating is facilitated to spread on the surface of the leather, thereby reducing the amount of the film forming aid used, i.e. a small amount of the film forming aid can quickly form a uniform and dense polyurethane protective film on the surface of the leather.

[0055] It should be noted that there are also many silicone surface treatment agents currently applied in leather materials, but mainly solvent-based polyurethane, which is easy to remain in the leather, causing the VOCs content of the leather to exceed the standard, such as the leather surface treatment agent disclosed in patent No. CN 116751513 A. In order to solve this problem, some scholars have developed a non-toxic and environmentally friendly water-based polyurethane, which mainly uses water as a solvent, but the surface tension of the water-based polyurethane material is high, resulting in poor hydrophobicity of the polyurethane protective film prepared finally, and the waterproof performance cannot be achieved.

[0056] In order to find a solvent-free leather surface coating with good waterproofness, oil resistance and stain resistance, the silicone is modified again in the present disclosure to ensure that a surface-enriched silicone-modified polyether-polyurethane prepolymer is prepared. Specifically, in one of the embodiments, the surface-enriched silicone-modified polyether-polyurethane prepolymer is prepared by the following steps:

[0057] S110, obtaining a modified epoxy polyether, wherein the branched chain of the modified epoxy polyether contains silicone.

[0058] It can be understood that the catalytic heating reaction of the hydrogen-containing silicone oil and the alkenyl-terminated unsaturated linear epoxy polyether enables the hydrogen-containing silicone oil to react with the unsaturated chain in the alkenyl-terminated end of the epoxy polyether, so that the silicone can be connected to the main chain of the modified epoxy polyether as a branched chain, so as to facilitate the migration of the silicone to form a dense hydrophobic layer during film forming.

[0059] In one of the embodiments, the alkenyl-terminated unsaturated linear epoxy polyether is 10%-70% of the Si-H molar number in the hydrogen-containing silicone oil, so as to ensure that the distribution of Si-H in the main chain of the modified epoxy polyether is appropriate, which is conducive to forming a polyurethane protective film with high density and appropriate hardness on the surface of the leather.

[0060] In a preferred embodiment, the content of the alkenyl-terminated unsaturated linear epoxy polyether is 30%-70% of the Si-H moles in the hydrogen-containing silicone oil. It can be understood that when the content of the alkenyl-terminated unsaturated linear epoxy polyether is 30%-70% of the Si-H moles in the hydrogen-containing silicone oil, the content of the silicone is ensured to be high, so that on the one hand, a polyurethane protective film with a lower surface energy can be obtained, thereby improving the three-proofing performance of the leather, and on the other hand, a better hardness can be provided for the polyurethane protective film, thereby ensuring that a polyurethane protective film with a suitable hardness is obtained.

[0061] In one embodiment, the hydrogen-containing silicone oil is a linear hydrogen-containing silicone oil, which ensures that the branched linear hydrogen-containing silicone oil connected to the epoxy polyether is more easily migrated, thereby forming a silicone layer with a suitable hardness and high density on the surface of the leather.

[0062] In one embodiment, the molecular weight of the hydrogen-containing silicone oil is 100-4000, so as to ensure that the chain length of the hydrogen-containing silicone oil is appropriate, on the one hand, to ensure that it can be more easily migrated, and on the other hand, to ensure that a polyurethane protective film with a suitable hardness and high density can be finally formed.

[0063] In one embodiment, the hydrogen-containing silicone oil includes at least one of polymethyl hydrogen silicone, polyethyl silicone, and hydroxyl-containing hydrogen silicone oil.

[0064] In one embodiment, the hydrogen-containing silicone oil is a mixture of polymethyl hydrogen silicone and polyethyl silicone.

[0065] In one embodiment, the alkenyl-terminated unsaturated linear epoxy polyether is an allyl-terminated epoxy polyether. It can be understood that since the allyl-terminated epoxy polyether contains an unsaturated double bond at one end, it ensures that the hydrogen-containing silicone oil can undergo an addition reaction, and the epoxy at the other end can introduce a new -OH functional group, so as to ensure that a subsequent reaction with isocyanate can be carried out, thereby preparing a surface-enriched silicone-modified polyether-polyurethane prepolymer.

[0066] In one embodiment, the hydrogen-containing silicone oil and the alkenyl-terminated unsaturated linear epoxy polyether are heated to 90-100°C under N2 atmosphere, then a first catalyst with a mass content of 0.2%-0.5% of the reaction system is added, the reaction system is heated to 110-130°C, and is maintained for 0.5-1h, thereby obtaining a modified epoxy polyether.

[0067] S120, adding an OH capping agent to the modified epoxy polyether to react, thereby obtaining an OH side-capped modified epoxy polyether, that is, to realize a first modification of the silicone, so as to ensure that the OH side-capped modified epoxy polyether can react with isocyanate.

[0068] In one embodiment, the OH end-capping agent is used in an amount of 3.0 times to 5 times of the alkenyl end-capped unsaturated linear epoxy polyether to ensure that the OH end-capping agent can fully react with the epoxy groups.

[0069] In one embodiment, the OH end-capping agent includes at least one of methanol and ethanol.

[0070] In one embodiment, a second catalyst is added when the OH end-capping agent is added to the modified epoxy polyether for reaction to quickly obtain the OH side end-capped modified epoxy polyether. Further, the second catalyst is tetrabutyl bromide, and the tetrabutyl bromide is used in an amount of 2% to 4 wt% of the mass of the reaction system.

[0071] In one embodiment, after the modified epoxy polyether, the OH end-capping agent, and the tetrabutyl bromide are refluxed at 75°C to 85°C for 10 h to 12 h, the OH end-capping agent is removed by rotary evaporation, and the transparent liquid obtained after centrifugation at 2000 rpm to 4000 rpm for 5 min to 15 min and filtration is the OH side end-capped modified epoxy polyether.

[0072] S130, adding isocyanate and dehydrated polyester diol or polyether diol to the OH side end-capped modified epoxy polyether for condensation reaction to realize secondary modification of the organosilicon, to obtain the surface-enriched organosilicon modified polyether-polyurethane prepolymer, so that the surface-enriched organosilicon modified polyether-polyurethane prepolymer is end-capped with hydroxyl or amine groups to ensure that the surface-enriched organosilicon modified polyether-polyurethane prepolymer can subsequently undergo crosslinking reaction with the liquid crosslinking agent, and the compactness of the final polyurethane protective film is improved, so as to effectively prevent the penetration of water molecules or ink molecules, thereby improving the three-proofing performance of the leather.

[0073] It can be understood that the surface-enriched organosilicon modified polyether-polyurethane prepolymer with a small molecular weight and good hydrophobic linear network structure is prepared by first adding the hydrogen-containing silicone oil, the alkenyl end-capped unsaturated linear epoxy polyether, the isocyanate, and the polyester diol or the polyether diol, which is helpful for the subsequent surface-enriched organosilicon modified polyether-polyurethane prepolymer and the liquid crosslinking agent to form a polyurethane protective film with appropriate hardness, good compactness, and good adhesion, and ensures that the organosilicon in the small-molecular surface-enriched organosilicon modified polyether-polyurethane prepolymer is easily migrated and aggregated to the surface in the film-forming process, thereby ensuring that the organosilicon can form a dense organosilicon layer on the surface of the leather, and further ensuring that the polyurethane protective film has excellent three-proofing performance. It is worth mentioning that the hydrophilic groups connected to the hydrogen-containing silicone oil can be effectively blocked by secondary modification of the hydrogen-containing silicone oil, and the waterproof performance of the present disclosure is more excellent than that of the traditional one-time modification of organosilicon.

[0074] It should be noted that if the content of the silicone layer on the surface of the polyurethane protective film is high or the embedded segment is too hard, the hardness of the polyurethane protective film will be high, which will affect the skin-friendliness of the leather. Therefore, in one embodiment, the present disclosure does not use a small molecule chain extender, mainly because the small molecule chain extender will further increase the hardness thereof, and it is not possible to ensure that a polyurethane protective film with appropriate hardness and high density is obtained.

[0075] In one embodiment, a third catalyst is also added to the OH side end-capped modified epoxy polyether to quickly prepare a surface-enriched silicone-modified polyether-polyurethane prepolymer. Further, the third catalyst is an organic bismuth.

[0076] In one embodiment, the prepared OH side end-capped modified epoxy polyether is added to a reaction kettle, and then isocyanate, a third catalyst, and part of the dehydrated polyester diol or polyether diol are sequentially added. The temperature is raised to 75-85°C, and the reaction is carried out for 1-2h, and then the remaining dehydrated polyester diol or polyether diol is added, and the reaction is continued at 55-85°C for 1-2h, until the NCO and the group are completely reacted, to obtain a surface-enriched silicone-modified polyether-polyurethane prepolymer, which is sealed for use.

[0077] It can be understood that if it is added at one time, a surface-enriched silicone-modified polyether-polyurethane prepolymer with appropriate hardness and high density cannot be formed. Therefore, by adding the polyester diol or polyether diol step by step to the OH side end-capped modified epoxy polyether, since the molecular chain of the polyester diol is longer than that of the small molecule chain extender, the hardness thereof is lower than that of the small molecule chain extender, so that a surface-enriched silicone-modified polyether-polyurethane prepolymer with appropriate hardness and high density can be ensured.

[0078] It can be understood that if the molecular weight of the polyester diol or polyether diol is too low or too high, a surface-enriched silicone-modified polyether-polyurethane prepolymer with appropriate hardness and high density cannot be ensured. Therefore, in one embodiment, the polyester diol or polyether diol is in a liquid state, and the molecular weight thereof is 600-2000, so that the molecular weight of the polyester diol or polyether diol is appropriate.

[0079] In one embodiment, the polyester diol or polyether diol includes at least one of polyhexanedioic acid-1,3-butanediol ester diol, polypropylene glycol, polyethylene glycol, polyethylene carbonate diol, and polypropylene carbonate diol.

[0080] In one embodiment, the polyester diol or polyether diol is a mixture of polypropylene glycol, polyethylene glycol and polyethylene carbonate diol, and the molecular weight of the polypropylene glycol is 2000, the molecular weight of the polyethylene carbonate diol is 1000 and the molecular weight of the polyethylene glycol is 600, so as to ensure that the mixture of various different medium and long chain polyester diols or polyether diols can provide more suitable hardness and compactness for the surface-enriched silicone-modified polyether-polyurethane prepolymer.

[0081] It can be understood that, in the entire process of preparing the surface-enriched silicone-modified polyether-polyurethane prepolymer, no organic solvent is used, so as to ensure that the surface-enriched silicone-modified polyether-polyurethane prepolymer provided does not contain VOCs, and further ensure that the polyurethane protective film finally prepared does not contain VOCs, so as to better adapt to the application of leather with higher ecological grade, and provide a surface-enriched silicone-modified polyether-polyurethane prepolymer with suitable hardness and high compactness, so as to ensure that a polyurethane protective film with high compactness and suitable hardness can be subsequently formed on the surface of the leather.

[0082] In one embodiment, the first catalyst is Karstedt's catalyst.

[0083] In one embodiment, the isocyanate includes at least one of liquid isophorone diisocyanate, 2,4-toluene diisocyanate, hexamethylene diisocyanate, and 4,4'-dicyclohexylmethane diisocyanate.

[0084] The present disclosure also provides a method for preparing a leather containing a surface coating. The method for preparing the leather containing a surface coating first uniformly mixes a surface-enriched silicone-modified polyether-polyurethane prepolymer, a liquid cross-linking agent, and a film-forming aid to obtain a uniformly mixed leather surface coating, then applies the uniformly mixed leather surface coating to the surface of the leather to obtain a semi-finished leather A, so that the leather surface coating can form a uniform coating on the surface of the leather, and then performs a heat curing operation on the semi-finished leather A, so that the surface-enriched silicone-modified polyether-polyurethane prepolymer and the liquid cross-linking agent can be cross-linked on the surface of the leather to form a polyurethane protective film with suitable hardness, high compactness, and good adhesion. The method not only has simple operation, but also does not need to additionally add a polyurethane adhesive, an organic solvent, and a filler, reduces production cost, and ensures that the leather prepared has good adhesion and three-proofing performance.

[0085] It should be noted that there are also some solvent-free three-proofing synthetic leather preparation methods at present. The polyurethane hot melt adhesive is first coated on the cured polyurethane protective film to realize the connection of the leather and the polyurethane protective film. However, due to the low surface energy of the polyurethane protective film, the adhesion between the polyurethane protective film and the polyurethane hot melt adhesive is still relatively low, which leads to the phenomenon that it is more prone to fall off during use. And, the applicant has carried out experiments according to the traditional method, but due to the fact that the surface-enriched organosilicon-modified polyether-polyurethane prepolymer is more prone to migrate to the surface during film formation, when the polyurethane hot melt adhesive is coated according to the traditional method, on the one hand, the side of the polyurethane protective film rich in organosilicon will be tightly attached to the surface of the leather, thereby causing the modified polyether block to be exposed to the air, which not only reduces the three-proofing performance, wear resistance and fastness of the leather, on the other hand, due to the very low surface energy of the polyurethane protective film after curing, if the polyurethane hot melt adhesive is coated on the cured polyurethane protective film at this time, the adhesion between the polyurethane protective film and the polyurethane hot melt adhesive is still poor. Of course, in the face of this situation, many scholars provide the method of peeling off the polyurethane protective film and the release film first, then coating the polyurethane hot melt adhesive on the modified polyether block, and finally attaching the polyurethane protective film to the surface of the leather, but there are problems such as complex operation and inaccurate attachment.

[0086] Therefore, in order to find a solvent-free leather preparation method that is simple to operate, has good adhesion, is more environmentally friendly, and has excellent three-proofing performance. The structure of the polyurethane protective film is studied in this disclosure. It is found that when the surface-enriched organosilicon-modified polyether-polyurethane prepolymer migrates to the surface during film formation, the modified polyether block will sink below the organosilicon layer, allowing the modified polyether block to be cross-linked and cured on the surface of the leather with a liquid cross-linking agent. This can improve the adhesion between the polyurethane protective film and the leather, so that the polyurethane protective film can achieve good adhesion with the leather without the need for additional polyurethane hot melt adhesive. This not only simplifies the production process, i.e. eliminates the process of coating polyurethane hot melt adhesive and separating paper leather, but also improves production efficiency and reduces costs. At the same time, it can also prepare leather that is more environmentally friendly, has no VOCs, has excellent three-proofing performance, and has good adhesion.

[0087] In an embodiment, the method for preparing the leather containing the surface coating comprises the following parts or steps:

[0088] S210, obtaining the leather surface coating according to any one of the above embodiments, and preparing the leather surface coating material according to the disclosure.

[0089] In one of the embodiments, the weight parts of the surface-enriched organosilicon-modified polyether-polyurethane prepolymer is 80-90 parts, the liquid crosslinking agent is 20-30 parts, and the film-forming aid is 0.01-0.2 parts, so that the 80-90 parts of the surface-enriched organosilicon-modified polyether-polyurethane prepolymer and the 20-30 parts of the liquid crosslinking agent can fully crosslink, and the 0.01-0.2 parts of the film-forming aid is used to form a polyurethane protective film on the surface of the leather, which has appropriate hardness, uniformity, good density and good adhesion.

[0090] It can be understood that, since the surface-enriched organosilicon-modified polyether-polyurethane prepolymer is more prone to migrate to the surface of the leather surface coating during film formation, it is beneficial to the spreading of the leather surface coating on the leather surface, effectively reducing the amount of film-forming aid used, so as to ensure that a small amount of film-forming aid can quickly form a uniform and dense protective film on the surface of the leather.

[0091] It should be noted that, since the leather surface coating of the present disclosure can prepare a polyurethane protective film with appropriate hardness without adding additional filler ingredients, the softness of the polyurethane protective film is better ensured, which better adapts to the application of some high-end luggage; and it is beneficial to the rapid and uniform dispersion of the surface-enriched organosilicon-modified polyether-polyurethane prepolymer in the leather surface coating, solving the problem of poor dispersion of traditional fillers in solvent-free slurry. Further, since the surface-enriched organosilicon-modified polyether-polyurethane prepolymer introduces a modified polyether block, it improves the compatibility of the leather surface coating with the leather, so that the modified polyether block can be crosslinked and cured with the liquid crosslinking agent on the surface of the leather, thereby improving the adhesion of the polyurethane protective film to the leather, and helping to form a polyurethane protective film with good adhesion on the surface of the leather.

[0092] S220, mixing the surface-enriched organosilicon-modified polyether-polyurethane prepolymer, the liquid crosslinking agent and the film-forming aid to ensure that the leather surface coating is uniformly mixed.

[0093] S230, applying the leather surface coating to the surface of the leather to obtain a semi-finished leather A to be heat-cured.

[0094] It can be understood that, when the leather surface coating is applied to the surface of the leather, on the one hand, the mixed leather surface coating can form a uniform coating on the surface of the leather, and on the other hand, it is beneficial to the migration of organosilicon in the surface-enriched organosilicon-modified polyether-polyurethane prepolymer to the surface, so as to ensure the formation of a uniform and dense organosilicon layer on the surface of the leather, so that the leather surface coating forms a polyurethane protective film with good adhesion after heat-curing operation.

[0095] S240, the semi-finished leather A is subjected to a heat curing operation, so that the modified polyether block can be cross-linked and cured with the liquid cross-linking agent on the surface of the leather, so that the leather surface can form an environmentally friendly, uniform, suitable hardness, dense and good adhesion polyurethane protective film, so as to ensure that the leather containing the surface coating is more environmentally friendly, has good adhesion, suitable hardness and excellent three-proofing performance.

[0096] The above-mentioned method for preparing the leather containing the surface coating first prepares the materials according to the formula, then uniformly mixes the surface-enriched organosilicon-modified polyether-polyurethane prepolymer, the liquid cross-linking agent and the film-forming aid to obtain a uniformly mixed leather surface coating, then applies the uniformly mixed leather surface coating to the surface of the leather to obtain a semi-finished leather A, so that the leather surface coating can form a uniform coating on the surface of the leather, and then the semi-finished leather A is subjected to a heat curing operation, so that the surface-enriched organosilicon-modified polyether-polyurethane prepolymer can be cross-linked with the liquid cross-linking agent on the surface of the leather to form a polyurethane protective film with suitable hardness and high density and good adhesion. Not only is the operation simple, but also there is no need to additionally add polyurethane adhesive, organic solvent and filler, which reduces the production cost and ensures that the leather with good adhesion and three-proofing performance is prepared.

[0097] In one embodiment, the leather includes at least one of cowhide, sheepskin, mink skin and pigskin. It can be understood that, since the softness and durability of cowhide, sheepskin, mink skin and pigskin are better than those of fiber woven cloth or textile cloth, they can provide better support for the polyurethane protective film, and also provide better flexibility, especially when used with the surface-enriched organosilicon-modified polyether-polyurethane prepolymer, the liquid cross-linking agent and the film-forming aid, so that the surface-enriched organosilicon-modified polyether-polyurethane prepolymer, the liquid cross-linking agent and the film-forming aid can be well spread on the surface of the leather and cross-linked and cured on the leather, thereby ensuring that the leather with good softness, good adhesion, no VOCs and excellent three-proofing performance is obtained, which is better suitable for some high-end and high-ecological-grade leather applications.

[0098] In one embodiment, the leather is all selected from head leather. Since the surface of the head leather is full-grain leather, it has better roughness, i.e. more concave-convex structures, thereby facilitating the embedding of the leather surface coating on the surface of the leather, and further improving the connection strength of the polyurethane protective film and the leather.

[0099] In one embodiment, the thickness of the leather surface coating applied to the surface of the leather is 1.0mm-5.0mm, so as to ensure that the thickness of the leather surface coating is suitable, which is conducive to subsequent heat curing and forming at high temperature.

[0100] In one of the embodiments, after the step of heat curing operation on the semi-finished leather A, further comprising the step of conveying the semi-finished leather A to the cooling chamber for natural cooling, to ensure that the polyurethane protective film can be fully cooled and shaped.

[0101] In one of the embodiments, during the heat curing operation on the semi-finished leather A, comprising the specific steps as follows: placing the coated semi-finished leather A on the conveying belt, with the surface coating of the semi-finished leather A facing upwards, so that the first heating assembly can perform high-temperature instantaneous heating operation on the surface coating; then conveying the semi-finished leather A to the lower side of the first heating assembly of the high-temperature heating chamber for high-temperature instantaneous heating, so that the surface coating can be cross-linked and cured; immediately after that, the semi-finished leather A is conveyed to the second heating assembly of the low-temperature curing buffer chamber for heating compensation, to ensure that the surface-enriched organosilicon-modified polyether-polyurethane prepolymer and liquid cross-linking agent can be fully cross-linked and cured, so as to obtain a polyurethane protective film on the surface of the leather, which has good adhesion and excellent three-proofing performance.

[0102] It can be understood that, if only high-temperature instantaneous heating is used, it cannot ensure that the surface coating is fully cross-linked and cured; if only low-temperature curing effect is used, it will result in a longer cross-linking and curing time of the surface coating, thereby affecting the production efficiency; if high-temperature curing is used for a long time, it will cause the animal leather to shrink and deform under high temperature for a long time, thereby affecting the performance of the product. Therefore, in one of the embodiments, by controlling the conditions of high-temperature instantaneous heating: 150℃-180℃, heating time 10S-30S, the surface coating layer can obtain more heat in a short time under high temperature, to ensure that the surface coating can quickly cross-link and cure, not only ensuring that the surface coating will not be damaged under high temperature, but also ensuring that the heat under high temperature does not enter the leather, effectively avoiding the phenomenon of shrinkage and deformation of the leather under high-temperature instantaneous heating; then, since the semi-finished leather A is conveyed to the second heating assembly of the low-temperature curing buffer chamber for heating compensation, the heating compensation temperature is 40℃-60℃, and the time is 60S-120S, the semi-finished leather A entering the low-temperature curing buffer chamber can continue to cross-link and cure, thereby ensuring that the surface-enriched organosilicon-modified polyether-polyurethane prepolymer and liquid cross-linking agent can fully and sufficiently react, to ensure that the polyurethane protective film can be directly shaped and fixed on the surface of the leather, not only without causing the leather to shrink and deform, but also ensuring the adhesion of the polyurethane protective film to the leather.

[0103] It is worth mentioning that by heating the semi-finished leather A, the leather is also softened and slightly expanded, thereby increasing the contact area between the leather and the surface coating, so as to ensure that the polyurethane protective film can be directly formed and fixed on the surface of the leather, and the connectivity between the polyurethane protective film and the leather is better, and the phenomenon that the polyurethane protective film is easily separated after long-term use is effectively avoided.

[0104] In order to ensure that the surface coating can be fully and quickly cured by instant heating at high temperature, in one embodiment, the heating area of the first heating assembly is equal to the area of the surface coating, and the first heating assembly is arranged towards the surface coating of the semi-finished leather A, and the other surfaces of the semi-finished leather A are not provided with the first heating assembly, so that the surface coating can fully absorb heat under the condition of single high-temperature heating, the surface coating is quickly cross-linked and cured, and the heat is effectively prevented from entering the inside and bottom of the leather, thereby effectively solving the phenomenon that the leather is easily shrunk and deformed by instant heating at high temperature.

[0105] In order to avoid the phenomenon that the leather is shrunk and deformed in the low-temperature curing buffer chamber, in one embodiment, the second heating assembly of the low-temperature curing buffer chamber includes a first heating subassembly and a second heating subassembly, the first heating subassembly is arranged towards the surface coating of the semi-finished leather A, and the second heating subassembly is arranged around the side wall of the surface coating, so that the second heating assembly can fully heat and compensate the surface coating, thereby ensuring that the surface-enriched organosilicon-modified polyether-polyurethane prepolymer and the liquid cross-linking agent can fully and sufficiently react, and the adhesion between the polyurethane protective film and the leather is ensured; especially when the heating compensation temperature is 40-60°C and the time is 60-120S, the surface-enriched organosilicon-modified polyether-polyurethane prepolymer and the liquid cross-linking agent can fully react, and the phenomenon that the leather is easily shrunk and deformed at high temperature is effectively avoided.

[0106] In one embodiment, in the horizontal direction, the lowest point of the heat transfer of the second heating subassembly is flush with the lowest point of the surface coating, so as to avoid that too much heat of the second heating subassembly is transferred to the leather and causes the leather to be easily shrunk and deformed, the phenomenon that the leather is easily shrunk and deformed in the low-temperature curing buffer chamber is effectively avoided, and the heat generated by the second heating subassembly can soften and slightly expand the leather to the greatest extent, thereby increasing the contact area between the leather and the surface coating, better improving the connectivity between the polyurethane protective film and the leather, and effectively avoiding the phenomenon that the polyurethane protective film is easily separated after long-term use.

[0107] The present disclosure also provides a leather containing surface coating prepared by the method for preparing leather containing surface coating according to any one of the above embodiments. It can be understood that the leather prepared by the method for preparing leather containing surface coating according to the present disclosure can use animal skin as the base, and use surface-enriched organosilicon-modified polyether-polyurethane prepolymer, liquid crosslinking agent and film-forming aid as the surface coating, so as to obtain leather with better softness, better adhesion, no VOCs and excellent three-proofing performance, which is better suitable for the application of some high-end and high-ecological-grade leather, and the operation is simple, and there is no need to additionally add polyurethane adhesive, organic solvent and filler, which effectively reduces the production cost and has high production efficiency.

[0108] The present disclosure also provides a luggage prepared by sewing the leather containing surface coating according to any one of the above embodiments. It can be understood that the leather is cut according to the actual production needs, and then sewn to obtain the required luggage.

[0109] The above-mentioned luggage uses leather as the base, and especially cooperates with the use of the surface coating of the present disclosure, so that the surface-enriched organosilicon-modified polyether-polyurethane prepolymer and the liquid crosslinking agent can be well crosslinked and fixed on the surface of the leather, and a polyurethane protective film with no VOCs, environmental protection, good density, appropriate hardness and good adhesion can be obtained, so as to improve the three-proofing performance and softness of the luggage, which is better suitable for the application of high-end and high-ecological-grade luggage, and the hardness of the formed polyurethane protective film is appropriate, which better maintains the structure of the luggage, effectively avoids the luggage being too soft to affect the three-dimensional structure of the luggage, and is especially suitable for the application of high-end women's bags.

[0110] Compared with the prior art, the present disclosure has at least the following advantages:

[0111] 1. The surface-enriched organosilicon-modified polyether-polyurethane prepolymer added in the present disclosure is more prone to migrate and aggregate on the surface of the leather surface coating during film formation, and forms a low-surface-energy organosilicon layer, thereby reducing the wetting and spreading of water, ink and other pollutants on the surface of the leather, and improving the three-proofing performance of the leather; since the surface-enriched organosilicon-modified polyether-polyurethane prepolymer contains hydroxyl or amine groups, it can form a dense polyurethane protective film with the added liquid crosslinking agent, effectively preventing the penetration of water or ink molecules, and further improving the three-proofing performance of the leather; at the same time, it can also seal the hydrophilic groups in the polyurethane protective film, avoiding the surface reconstruction of the hydrophilic groups, thereby reducing the intermolecular forces between the polyurethane protective film and ink or water pollutants, and further improving the three-proofing performance of the leather; and the present disclosure does not use organic solvents, so that the prepared leather does not contain VOCs, is more environmentally friendly than traditional fluorine-containing polyurethane prepolymers, and is especially suitable for the application of high-ecological-grade leather.

[0112] 2. The surface-enriched organosilicon-modified polyether-polyurethane prepolymer is more prone to migrate and accumulate on the surface of the leather surface coating during film formation, which is conducive to the spreading of the leather surface coating on the leather surface and effectively reduces the amount of film-forming aids, so as to ensure that a small amount of film-forming aids can quickly form a uniform and dense protective film on the leather surface.

[0113] 3. The leather surface coating of the present disclosure can prepare a polyurethane protective film with appropriate hardness without adding filler ingredients, which better ensures the softness of the polyurethane protective film to better adapt to the application of some high-end luggage; and is conducive to the rapid and uniform dispersion of the surface-enriched organosilicon-modified polyether-polyurethane prepolymer in the leather surface coating, solving the problem of poor dispersion of traditional fillers in solvent-free slurry.

[0114] 4. The surface-enriched organosilicon-modified polyether-polyurethane prepolymer introduces a modified polyether block, thereby improving the compatibility of the leather surface coating with the leather, and helping to form a polyurethane protective film with good adhesion on the leather surface.

[0115] The following examples are given to illustrate some specific embodiments. If % is mentioned, it means percentage by weight. It should be noted that the following examples do not exhaust all possible cases, and the materials used in the following examples can be obtained from commercial sources unless otherwise specified.

[0116] It should be noted that in the formula of the examples and comparative examples, the hydrogen-containing silicone oil is polymethyl hydrogen siloxane (PHMS-4000, PHMS-2000, PHMS-3000) from Zhejiang Runhe; the alkenyl-terminated unsaturated linear epoxy polyether is allyl-terminated epoxy polyether (APEE500) from Yangzhou Chenhua New Material Co., Ltd.; the first catalyst is Karstedt's catalyst, the OH end-capping agent is methanol, and the second catalyst is tetrabutylammonium bromide (TBAB) from Shanghai Titan Science and Technology Co., Ltd.; the third catalyst is an organic bismuth catalyst from Zhejiang Demei Doctorda Polymer Material Co., Ltd.; the isophorone diisocyanate, 1,6-hexamethylene diisocyanate, and hexamethylene diisocyanate are from Zhejiang Demei Doctorda Polymer Material Co., Ltd.; the polyethylene glycol (PEG-600), polypropylene glycol (PPG-2000), and polypropylene carbonate diol-1000 are from China Reagent Co., Ltd.; the dibutyltin dilaurate and dodecanol ester are from Shandong Yuanjin; the top layer cowhide is from Dongguan Hansi Leather Industry Co., Ltd.; the 4,4'-dicyclohexyl methane diisocyanate and trimethyl-1,6-hexamethylene diisocyanate are from Shandong Dennon New Material Technology Co., Ltd.; and the glass fiber (FR52G30BLNC010) is from DuPont, USA.

[0117] Example 1

[0118] S1, 20 Kg of PHMS-2000 and 4.5 Kg of APEE500 (40% of Si-H molar) were added into a reaction kettle equipped with nitrogen condensation reflux tube, thermometer, mechanical stirrer, and heated to 90℃ under N2 atmosphere. Then 0.2% of Karstedt's catalyst was added, and the reaction system was heated to 118℃ and stirred vigorously for 0.5h to obtain the modified epoxy polyether.

[0119] S2, the modified epoxy polyether prepared in S1, 28 kg of methanol and 3% of tetrabutylammonium bromide based on the mass of the reaction system were added into a reaction bottle equipped with magnetic stirring, thermometer and condenser, and refluxed at 80℃ for 10h. Then the methanol was removed by rotary evaporation, and the resulting transparent liquid was centrifuged in a centrifuge at 4000 rpm for 10 min, and then filtered to obtain the OH-terminated modified epoxy polyether, which was ready for use.

[0120] S3, 7 kg of OH-terminated modified epoxy polyether, 23 kg of isophorone diisocyanate, 25 kg of polypropylene glycol-2000 (dehydrated) and 0.03 kg of organic bismuth were added into a reaction kettle, and heated to 85℃ for 2h. Then the remaining 40 kg of polypropylene glycol was added, and the reaction was continued at 85℃ for 2h, and the molar ratio of -NCO to -OH was controlled at 1:2, until the -NCO and -OH groups were completely reacted, to obtain a surface-enriched silicone-modified polyether-polyurethane prepolymer, which was sealed for use.

[0121] S4, 40 kg of the surface-enriched silicone-modified polyether-polyurethane prepolymer, 10 kg of 1,6-hexamethylene diisocyanate and 0.005 kg of dibutyl tin dilaurate were added into a mixing tank for mixing to obtain a uniformly mixed leather surface coating.

[0122] S5, the leather surface coating prepared in S4 was uniformly coated on the head layer of cowhide, and the thickness of the coating was controlled at 1.0 mm to obtain a semi-finished leather A to be heat-cured.

[0123] S6, the semi-finished leather A was placed on a conveyor belt with the surface coating of the semi-finished leather A facing upwards, and the conveyor belt sent the semi-finished leather A to the lower part of the first heating assembly of a high-temperature heating chamber for 10s of high-temperature instantaneous heating at 150℃, and then the semi-finished leather A was sent to the second heating assembly of a low-temperature curing buffer chamber by the conveyor belt for 70s of heating at 50℃, and the lowest point of the second heating subassembly of the second heating assembly was controlled to be flush with the lowest point of the leather surface coating in the horizontal direction, and then the conveyor belt sent the semi-finished leather A to a cooling chamber for natural cooling to obtain a leather containing surface coating.

[0124] Example 2

[0125] S1, 20Kg of PHMS-2000 and 2.25Kg of APEE500 (60% of Si-H molar) were added to a reaction kettle equipped with a nitrogen condensation reflux tube, a thermometer, and a mechanical stirrer, and stirred vigorously under N2 atmosphere and heated to 100°C. Then 0.2% of Karstedt's catalyst based on the mass of the reaction system was added, the reaction system was warmed to 120°C, and stirred vigorously for 0.5h to obtain a modified epoxy polyether.

[0126] S2, the modified epoxy polyether prepared in S1, 30kg of methanol and 3% of tetrabutylammonium bromide based on the mass of the reaction system were added to a reaction bottle equipped with a magnetic stirrer, a thermometer, and a condenser, and refluxed at 80°C for 10h, then rotary evaporation was used to remove methanol, and then centrifuged in a centrifuge at 4000 rpm for 15 min, and the transparent liquid obtained by filtration was the OH-terminated modified epoxy polyether, ready for use.

[0127] S3, 7kg of OH-terminated modified epoxy polyether, 35kg of 4,4'-dicyclohexyl methane diisocyanate, 25kg of polypropylene glycol-2000 (dehydrated), 10kg of polypropylene carbonate diol-1000 (dehydrated), 5kg of polyethylene glycol-600 (dehydrated), and 0.1kg of organic bismuth were added to a reaction kettle, warmed to 85°C and reacted for 2h, then the remaining 25kg of polypropylene glycol-2000 (dehydrated), 5kg of polypropylene carbonate diol-1000 (dehydrated), and 5kg of polyethylene glycol-600 (dehydrated) were added and the reaction was continued at 85°C for 2h, and the molar ratio of -NCO to -OH was controlled at 1:2, until the -NCO and -OH groups were completely reacted, to obtain a surface-enriched silicone-modified polyether-polyurethane prepolymer, which was sealed for later use.

[0128] S4, 42kg of surface-enriched silicone-modified polyether-polyurethane prepolymer, 12kg of trimethyl-1,6-hexamethylene diisocyanate, and 0.008kg of dibutyltin dilaurate were added to a mixing tank and mixed to obtain a uniformly mixed leather surface coating.

[0129] S5, the leather surface coating prepared in S4 was evenly coated on the head layer of cowhide, and the thickness of the coating was controlled at 1.5mm to obtain a semi-finished leather A to be heat-cured.

[0130] S6, the semi-finished leather A is placed on the conveying belt with the surface coating of the semi-finished leather A facing upwards, the conveying belt sends the semi-finished leather A to the lower side of the first heating assembly of the high-temperature heating chamber for 12S of high-temperature instant heating at 160℃, then the semi-finished leather A is sent to the second heating assembly of the low-temperature curing buffer chamber by the conveying belt for 80S of heating at 55℃, and the lowest point of the heat transfer of the second heating subassembly of the second heating assembly is controlled to be flush with the lowest point of the leather surface coating in the horizontal direction, then the conveying belt sends the semi-finished leather A to the cooling chamber for natural cooling, and the leather containing the surface coating is obtained.

[0131] Example 3

[0132] S1, 15Kg of PHMS-3000 and 10.1Kg of APEE500 (14.8% of Si-H molar number) are added into a reaction kettle equipped with a nitrogen condensation reflux tube, a thermometer and a mechanical stirrer, and stirred vigorously under N2 atmosphere and heated to 90℃. Then 0.2% of Karstedt's catalyst based on the mass of the reaction system is added, the reaction system is warmed to 110℃, and stirred vigorously for 0.5h to obtain a modified epoxy polyether.

[0133] S2, the modified epoxy polyether prepared in S1, 33.8kg of methanol and 2.8% of tetrabutylammonium bromide based on the mass of the reaction system are added into a reaction bottle equipped with a magnetic stirrer, a thermometer and a condenser, and refluxed at 80℃ for 12h, then the methanol is removed by rotary evaporation, and then centrifuged in a centrifuge at 4000 rpm for 15 min, and the transparent liquid obtained by filtration is the OH-terminated modified epoxy polyether, which is ready for use.

[0134] S3, 7kg of OH-terminated modified epoxy polyether, 15kg of hexamethylene diisocyanate, 25kg of polypropylene glycol-2000 (dehydrated) and 0.01kg of organic bismuth are added into a reaction kettle, and warmed to 85℃ for 2h, then the remaining 23kg of polypropylene glycol-2000 (dehydrated) is added, and the reaction is continued at 85℃ for 2h, and the molar ratio of -NCO to -OH is controlled at 1:2, until the -NCO and -OH groups are completely reacted, to obtain a surface-enriched silicone-modified polyether-polyurethane prepolymer, which is sealed for use.

[0135] S4, 45kg of surface-enriched silicone-modified polyether-polyurethane prepolymer, 15kg of isophorone diisocyanate and 0.01kg of dodecanol ester are added into a mixing tank for mixing to obtain a uniformly mixed leather surface coating.

[0136] S5, the leather surface coating prepared in S4 is uniformly coated on the head layer of cowhide, and the thickness of the coating is controlled to be 2.0mm to obtain a semi-finished leather A to be heat-cured.

[0137] S6, the semi-finished leather A is placed on the conveying belt with the surface coating of the semi-finished leather A facing upwards, the conveying belt sends the semi-finished leather A to the lower part of the first heating assembly of the high-temperature heating chamber for 30 seconds of 180°C high-temperature instant heating, then the semi-finished leather A is sent to the second heating assembly of the low-temperature curing buffer chamber by the conveying belt for 120 seconds of 60°C heating, and the lowest point of the second heating subassembly of the second heating assembly is controlled to be in the horizontal direction and the lowest point of the surface coating of the leather in the horizontal direction is flush, then the conveying belt sends the semi-finished leather A to the cooling chamber for natural cooling, and the leather containing the surface coating is obtained.

[0138] Comparative Example 1

[0139] The difference from Example 2 is that the steps of S1 / S2 / / S3 are omitted, and all the raw materials used in Example 2 are directly mixed with 0.008 kg of trimethyl-1, 6-hexamethylene diisocyanate and 0.008 kg of dibutyl tin dilaurate in S4 to obtain the leather surface coating, and the others remain unchanged.

[0140] Comparative Example 2

[0141] The difference from Example 2 is that in S3, the mixed use of polypropylene glycol-2000 (dehydrated), polypropylene carbonate glycol-1000 (dehydrated), and polyethylene glycol-600 (dehydrated) is changed to the single use of polypropylene glycol-2000 (dehydrated), and the total use amount remains unchanged, and the others remain unchanged.

[0142] Comparative Example 3

[0143] The difference from Example 2 is that in S3, the mixed use of polypropylene glycol-2000 (dehydrated), polypropylene carbonate glycol-1000 (dehydrated), and polyethylene glycol-600 (dehydrated) is changed to the single use of polypropylene carbonate glycol-1000 (dehydrated), and the total use amount remains unchanged, and the others remain unchanged.

[0144] Comparative Example 4

[0145] The difference from Example 2 is that in S3, the mixed use of polypropylene glycol-2000 (dehydrated), polypropylene carbonate glycol-1000 (dehydrated), and polyethylene glycol-600 (dehydrated) is changed to the single use of polyethylene glycol-600 (dehydrated), and the total use amount remains unchanged, and the others remain unchanged.

[0146] Comparative Example 5

[0147] The difference from Example 2 is that in S4, 0.25 kg of filler (glass fiber) is also added for mixing, and the others remain unchanged.

[0148] Comparative Example 6

[0149] The difference from Example 2 is that the high-temperature instant heating in S6 is omitted, and the leather is directly heated in the low-temperature curing buffer room 92S.

[0150] Comparative Example 7

[0151] The difference from Example 2 is that the low-temperature curing buffer room heating in S6 is omitted, and the leather is directly heated in the high-temperature instant heating 92S.

[0152] Comparative Example 8

[0153] The difference from Example 2 is that the steps of S5 / S6 are different, that is, in Comparative Example 8, S5 uniformly coats the leather surface coating prepared in S4 on release paper, with a coating film thickness controlled at 1.0 mm, and then enters the oven for curing to obtain a dried polyurethane protective film; S6, polyurethane hot melt adhesive is coated on the polyurethane protective film, and then hot-pressed with the head layer of cowhide, enters the 130°C oven for curing for 2 min, cools, and the paper-leather is separated.

[0154] The leather prepared in the above Examples 1-3 and Comparative Examples 1-8 is respectively subjected to appearance detection, three-proofing performance, wear resistance, hand feel, and folding resistance detection.

[0155] Appearance detection: under strong light, observe whether there are defects on the surface of the treated leather.

[0156] Three-proofing performance: including water resistance, oil resistance, and stain resistance detection, the specific detection steps are as follows:

[0157] Water resistance: water is dropped on the surface of the leather of Examples 1-3 and Comparative Examples 1-8, respectively, and then the water contact angle is directly detected by a contact angle measuring instrument to infer the water resistance of the leather, wherein the larger the water contact angle, the better the water resistance;

[0158] Oil resistance: soybean oil is dropped on the surface of the leather of Examples 1-3 and Comparative Examples 1-8, respectively, and the erasing of the soybean oil on the coating is observed.

[0159] Stain resistance: an oily marker is used to draw a line on the surface of the leather of Examples 1-3 and Comparative Examples 1-8, respectively, and it is observed whether the trace can be completely erased with a paper towel.

[0160] Wear resistance: the wear resistance of the leather of Examples 1-3 and Comparative Examples 1-8 is tested using a Martindale wear tester, with a load of 100 g and 800 mesh sandpaper as the abrasive.

[0161] Hand feel test: the treated leather surface is touched with the hand to judge the hand feel (softness ranking: softness level 1 > softness level 2 > softness level 3 > softness level 4).

[0162] Folding resistance: The folding resistance of the leather of Examples 1-3 and Comparative Examples 1-8 was tested according to the method specified in QB / T 2714, and the state of the leather was observed every 5,000 times to see if the leather surface delaminated or cracked, and the highest folding resistance without delamination or cracking was recorded. The test was performed to 100,000 times, and the folding resistance could reflect the adhesion of the polyurethane protective film and the head layer of the leather

[0163] UV folding resistance: The leather of Examples 1-3 and Comparative Examples 1-8 was treated in a UV aging test chamber for 48 h at a temperature of 50℃, and then the folding resistance was tested according to the method specified in QB / T 2714.

[0164] Low-temperature folding resistance: The leather of Examples 1-3 and Comparative Examples 1-8 was treated in a low-temperature test chamber for 48 h at a temperature of -5℃, and then the folding resistance was tested according to the method specified in QB / T 2714.

[0165] Table 1

[0166]

[0167]

[0168] As can be seen from Examples 1-3 and Comparative Example 1 in Table 1 above, when the surface-enriched silicone-modified polyurethane prepolymer, liquid crosslinking agent and film-forming aid are used in combination, the waterproof, anti-aging and anti-folding properties of Examples 1-3 are significantly better than those of Comparative Example 1, and in particular, the waterproof performance is more excellent. Among them, the comprehensive indicators of Example 2 are the best, and the leather has both high-temperature and low-temperature resistance, thereby improving the service life of the leather.

[0169] As can be seen from Example 2 and Comparative Examples 2-4 in Table 1 above, when a plurality of polyesters or polyether diols with different molecular weights are used in Example 2, the comprehensive indicators are significantly better than those of Comparative Examples 2-4, thereby ensuring that the leather of Example 2 has appropriate hardness, softness and adhesion, and thus, under the condition of meeting the softness, the three-dimensional structure, wear resistance and folding resistance of high-end luggage are also ensured.

[0170] As can be seen from Example 2 and Comparative Example 5 in Table 1 above, when the filler is added to Comparative Example 5, the softness of the leather is directly reduced, and the wear resistance and folding resistance are also affected.

[0171] As can be seen from Example 2 and Comparative Examples 6-7 in Table 1 above, when high-temperature instant heating and low-temperature curing buffer chamber heating are used in Example 2, the shrinkage and deformation or yellowing of the leather during the heat curing process can be effectively improved, and the leather has excellent waterproof, anti-aging and anti-folding properties.

[0172] From the above Table 1, Example 2 and Comparative Example 8, when the conventional polyurethane hot melt adhesive is used in Comparative Example 8, not only the problem of poor three-proofing performance exists, but also the characteristics of good high and low temperature folding endurance and abrasion resistance are reduced.

[0173] The above described examples only express several embodiments of the present application, which are described in more detail and in more detail, but cannot be understood as a restriction on the scope of the patent. It should be noted that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of the present application. Therefore, the protection scope of the present application patent should be subject to the appended claims.

Claims

1. A surface coating for leather, characterized in that, The leather surface coating includes a surface-enriched organosilicon-modified polyether-polyurethane prepolymer, a liquid cross-linking agent, and a film-forming aid, the surface-enriched organosilicon-modified polyether-polyurethane prepolymer contains a hydroxyl or amine end, and the surface-enriched organosilicon-modified polyether-polyurethane prepolymer, the liquid cross-linking agent, and the film-forming aid all do not contain an organic solvent; The surface-enriched organosilicon-modified polyether-polyurethane prepolymer is 80-90 parts by weight; The liquid cross-linking agent is 20-30 parts by weight; The film-forming aid is 0.01-0.2 parts by weight; the surface-enriched organosilicon-modified polyether-polyurethane prepolymer is prepared by the following steps: Obtain a modified epoxy polyether, wherein hydrogen-containing silicone oil and alkenyl-terminated unsaturated linear epoxy polyether are subjected to catalytic heating reaction to obtain the modified epoxy polyether, and the branched chain of the modified epoxy polyether contains silicone; The hydrogen-containing silicone oil includes at least one of polymethyl hydrogen siloxane, polyethyl siloxane, and hydroxyl-containing hydrogen silicone oil; the molecular weight of the hydrogen-containing silicone oil is 100-4000; The alkenyl-terminated unsaturated linear epoxy polyether is 30%-70% of the number of moles of Si-H in the hydrogen-containing silicone oil; An OH end-capping agent is added to the modified epoxy polyether to obtain an OH side-capped modified epoxy polyether; An isocyanate and a dehydrated polyester diol or polyether diol are added to the OH side-capped modified epoxy polyether to obtain a surface-enriched organosilicon-modified polyether-polyurethane prepolymer; The polyester diol or the polyether diol is added to the OH side-capped modified epoxy polyether in steps; the polyester diol or the polyether diol is in a liquid state, and the molecular weight is 600-2000.

2. The leather surface coating according to claim 1, characterized in that, The liquid cross-linking agent includes at least one of 1,6-hexamethylene diisocyanate, trimethyl-1,6-hexamethylene diisocyanate, and carbodiimide.

3. The leather surface coating according to claim 1, characterized in that, The film-forming aid includes at least one of dibutyltin dilaurate and dodecanol ester.

4. A method for producing a leather containing a surface coating, characterized in that, The method for preparing the leather containing the surface coating includes the following steps: Obtain the leather surface coating according to any one of claims 1-3; Mix the surface-enriched organosilicon-modified polyether-polyurethane prepolymer, the liquid cross-linking agent, and the film-forming aid to obtain a uniformly mixed leather surface coating; Apply the leather surface coating to the surface of the leather to obtain a semi-finished leather A; Perform heat curing on the semi-finished leather A to obtain the leather containing the surface coating.

5. The method for preparing surface-coated leather according to claim 4, characterized in that, The leather includes at least one of cowhide, sheepskin, mink skin, and pigskin.

6. A leather containing a surface coating, characterized in that, The method for preparing the leather containing the surface coating is prepared according to claim 4 or 5.

7. A luggage case characterized by, The leather containing the surface coating is sewn according to claim 6.

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