A solvent-free polyurethane resin for yellowing-resistant synthetic leather, a preparation method and application thereof

Abstract

This invention provides a solvent-free polyurethane resin for yellowing-resistant synthetic leather, its preparation method, and its application. The polyurethane resin comprises three solvent-free components: A, B, and C. Component A is a hydroxyl component, component B is an isocyanate component, and component C is a catalyst component. This invention utilizes an aliphatic isocyanate (i.e., HDI trimer) with MDI and H... 12 MDI is used to synthesize the B component of polyurethane resin for solvent-free synthetic leather. Polyaspartic acid ester is combined with polyol resin as the A component. With the addition of a catalyst, the reaction between the hydroxyl component and the NCO component can be accelerated, while the reaction between polyaspartic acid ester and NCO is slower due to steric hindrance. The resin has a long working time of 600-900 seconds and high strength after curing. This resin system can meet the reaction speed requirements of solvent-free synthetic leather production and effectively improve the yellowing properties of synthetic leather products.

Description

Technical Field

[0001] This invention belongs to the field of polyurethane resin technology, specifically relating to a solvent-free polyurethane resin for yellowing-resistant synthetic leather, its preparation method, and its application. Background Technology

[0002] Solvent-free polyurethane synthetic leather is a synthetic leather product made by using solvent-free polyurethane resin as the main raw material and without adding solvents in the production process. Because there is no solvent involved in the entire process, the environmental problems caused by solvents are naturally solved.

[0003] Most solvent-free synthetic leather resins currently on the market contain three components: A, B, and C. Typically, component A is the hydroxyl group, component B is the isocyanate prepolymer, and component C is the catalyst. During application, the three components (A, B, and C) are mixed in precise measurements, coated, and then pre-cured, laminated, and cured to form the final product. The application of solvent-free synthetic leather polyurethane resins in the production of sofa leather, automotive leather, bag leather, and shoe leather is growing rapidly, and it has become one of the main green production processes in the synthetic leather industry. However, solvent-free synthetic leather suffers from poor yellowing resistance when producing light-colored products. This is because component B, the isocyanate prepolymer, is produced by reacting polyols with excess isocyanate. To maintain suitable viscosity and isocyanate content, the prepolymer contains a large amount of free isocyanate monomers. Currently, most commercially available solvent-free synthetic leather polyurethane resins use MDI-type isocyanate prepolymers, containing a large amount of free MDI monomers. During use, these free MDI monomers penetrate into the surface resin. Since MDI is an aromatic isocyanate, it is not resistant to yellowing, resulting in poor yellowing resistance in synthetic leather products. Adding anti-yellowing additives can improve yellowing resistance. These additives are usually composed of UV absorbers, antioxidants, and other auxiliaries, and they do have a certain effect on improving yellowing resistance. Similar products exist on the market, but anti-yellowing additives cannot provide long-term yellowing resistance; the yellowing resistance gradually weakens. Furthermore, the amount of additives added is relatively large, and in practical applications, it has been found to inhibit the reaction of the solvent-free resin, resulting in poor curing.

[0004] The above analysis shows that the poor yellowing resistance of solvent-free polyurethane synthetic leather is mainly due to the penetration of free MDI monomers in component B into the surface layer. Therefore, theoretically, reducing the free MDI monomers in component B would help improve the yellowing problem. However, from the synthesis principle of component B, i.e., isocyanate prepolymer, reducing free MDI monomers, from the perspective of formulation design, means reducing the NCO content of component B, which is to reduce the molar ratio of MDI to polyol. This will inevitably lead to a higher degree of polymerization and higher viscosity of the prepolymer, making it difficult to mix evenly during use, which is detrimental to the production of solvent-free synthetic leather.

[0005] Therefore, there is a need to provide an improved technical solution that addresses the shortcomings of the existing technology. Summary of the Invention

[0006] The purpose of this invention is to provide a solvent-free polyurethane resin for yellowing-resistant synthetic leather, its preparation method and application, so as to solve the problem of poor yellowing resistance in the current production of solvent-free synthetic leather.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A solvent-free polyurethane resin for yellowing-resistant synthetic leather, wherein the polyurethane resin comprises three solvent-free components, A, B and C.

[0009] Component A is a hydroxyl component, and the raw materials for its preparation include the following components in parts by mass:

[0010] Polymer polyol 30-50 parts, polyether diol 350-450 parts, polyether triol 100-150 parts, polyaspartic acid ester 80-250 parts, small molecule diol 10-30 parts, leveling agent 1-5 parts.

[0011] Component B is an isocyanate component, and the raw materials for its preparation include the following components in parts by mass:

[0012] 200-350 parts of polyether diol, 8-20 parts of small molecule diol, 200-300 parts of diphenylmethane diisocyanate, 500-600 parts of hydrogenated diphenylmethane diisocyanate, and 150-250 parts of HDI trimer;

[0013] Component C is the catalyst component, and the raw materials for preparation include the following components in parts by mass;

[0014] Bismuth carboxylate, zinc carboxylate, and carboxylates of 1,8-diazabicyclo-bicyclo[5.4.0]undecene-7.

[0015] In the solvent-free polyurethane resin for yellowing-resistant synthetic leather as described above, preferably, the polyaspartic ester is prepared by a Michael addition reaction of one of diethylenetriamine, isoflurone diamine, 4,4-diaminodicyclohexylmethane, or 3,3'-dimethyl-4,4-diaminodicyclohexylmethane with diethyl maleate.

[0016] In the solvent-free polyurethane resin for yellowing-resistant synthetic leather as described above, preferably, the polymer polyol in component A is a polyether polyol grafted with styrene-acrylonitrile copolymer.

[0017] Preferably, the polymer polyol has a functionality of 3 and a number-average molecular weight of 4000-6000.

[0018] More preferably, the styrene-acrylonitrile copolymer in the polymer polyol has a mass percentage content of 30-40%.

[0019] In the solvent-free polyurethane resin for yellowing-resistant synthetic leather described above, preferably, the polyether diol in component A is a copolymer of propylene oxide and ethylene diol; the number average molecular weight of the polyether diol is 750-2000.

[0020] Preferably, the polyether triol is a copolymer of propylene oxide and ethylene triol; the number average molecular weight of the polyether triol is 3000-5000.

[0021] More preferably, the small molecule diol in component A and / or component B is one of ethylene glycol, butanediol, and methylpropanediol;

[0022] More preferably, the leveling agent is an organosilicon leveling agent.

[0023] In the solvent-free polyurethane resin for yellowing-resistant synthetic leather as described above, preferably, the polyether diol in component B is a polyoxypropylene diol with a number average molecular weight of 1000-2000.

[0024] Preferably, the HDI trimer is a trimer of hexamethylene diisocyanate, wherein the mass percentage of NCO is 20-25%.

[0025] In the solvent-free polyurethane resin for yellowing-resistant synthetic leather as described above, preferably, the bismuth carboxylate is bismuth isooctanoate or bismuth neodecanoate.

[0026] The zinc carboxylate is zinc isooctanoate or zinc neodecanoate;

[0027] The carboxylate of 1,8-diazabicyclo-bicyclo[5.4.0]undecene-7 is one of DBU isooctanoate, DBU formate, and DBU p-toluenesulfonate;

[0028] Preferably, the mass ratio of zinc carboxylate to bismuth carboxylate is 1:8 to 1:2;

[0029] The mass ratio of zinc carboxylate to the carboxylate of 1,8-diazabicyclo-bicyclo[5.4.0]undecene-7 is 1:8 to 1:4.

[0030] A method for preparing a solvent-free polyurethane resin for yellowing-resistant synthetic leather, the method comprising the following steps:

[0031] Step 1, Preparation of Component A;

[0032] According to the mass ratio, polymer polyol, polyether diol, polyether triol, polyaspartic acid ester, small molecule diol and leveling agent are added to a closed nitrogen-sealed reactor and mixed evenly to obtain component A.

[0033] Step 2, preparation of component B;

[0034] According to the mass ratio, polyether diol, small molecule diol, diphenylmethane diisocyanate, and hydrogenated diphenylmethane diisocyanate are placed in a sealed nitrogen-sealed reactor, and then HDI trimer is added. After mixing evenly, component B is obtained.

[0035] Step 3, Preparation of component C;

[0036] Bismuth carboxylate, zinc carboxylate, and carboxylate of 1,8-diazabicyclo-bicyclo[5.4.0]undecene-7 were mixed in a sealed nitrogen-sealed reactor according to the mass ratio, and the mixture was mixed evenly to obtain component C.

[0037] Step four: Components A, B, and C are all kept at a constant temperature, and then metered and added into a mixer for stirring. After mixing, polyurethane resin is obtained.

[0038] In the preparation method of solvent-free polyurethane resin for yellowing-resistant synthetic leather as described above, preferably, in step one, the reactor is stirred at a temperature of 40-50°C for 1.5-2 hours.

[0039] Preferably, in step two, the reactor is stirred at a temperature of 85-95°C for 4.5-6 hours, then HDI trimer is added, and the reaction continues for 1.5-3 hours.

[0040] More preferably, in step three, the reactor is stirred at a temperature of 25-35℃ for 1-2 hours;

[0041] More preferably, in step four, components A, B, and C are all subjected to constant temperature treatment at 10-30℃.

[0042] A yellowing-resistant synthetic leather, wherein the yellowing-resistant synthetic leather is prepared by a solvent-free polyurethane resin preparation method for yellowing-resistant synthetic leather.

[0043] A method for preparing yellowing-resistant synthetic leather, the method comprising the following steps:

[0044] The polyurethane resin is coated onto release paper that has been pre-coated with aliphatic polyurethane resin, pre-baked, then bonded to a substrate, cured, cooled, and peeled off to obtain yellowing-resistant synthetic leather.

[0045] Preferably, the pre-baking temperature is 110-130℃ and the pre-baking time is 120-200s; the bonding pressure is 0.2-0.5MPa; after bonding, the product is placed in an oven at 120-140℃ for 8-15 minutes to mature, and then cooled and peeled off.

[0046] Beneficial effects:

[0047] This invention utilizes aliphatic isocyanates (i.e., HDI trimers) with MDI and H 12 The B component of the polyurethane resin for solvent-free synthetic leather is synthesized by compounding MDI, and the A component is polyaspartic acid ester combined with polyol resin. With the help of a suitable catalyst, the reaction between the hydroxyl component and the NCO component can be accelerated, while the reaction between polyaspartic acid ester and NCO is slower due to steric hindrance. The resin has a longer working time. The working time of this invention reaches 600-900s. The cured strength is high. This resin system can not only meet the reaction speed requirements of solvent-free synthetic leather production, but also effectively improve the yellowing performance of synthetic leather products.

[0048] The solvent-free polyurethane resin for yellowing-resistant synthetic leather of this invention is prepared by compounding aliphatic and aromatic isocyanates to form component B. This reduces the decrease in yellowing resistance caused by the penetration of free aromatic isocyanates into the surface layer. Simultaneously, the addition of polyaspartic ester reacts with the aliphatic isocyanate to introduce urea bonds, ensuring the final strength of the synthetic leather product. Synthetic leather produced using this solvent-free polyurethane resin achieves a UV yellowing resistance level of 4 or higher and a peel strength of not less than 4 kg / 3 cm, demonstrating broad application prospects. Detailed Implementation

[0049] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention are within the scope of protection of the present invention.

[0050] The present invention will now be described in detail with reference to embodiments. It should be noted that, unless otherwise specified, the embodiments and features described in the embodiments of the present invention can be combined with each other.

[0051] This invention provides a solvent-free polyurethane resin for yellowing-resistant synthetic leather, the polyurethane resin comprising three solvent-free components: A, B, and C;

[0052] Component A is a hydroxyl component, and the raw materials for its preparation include the following components in parts by mass:

[0053] Polymer polyols 30-50 parts (e.g., 35 parts, 40 parts, 45 parts), polyether diols 350-450 parts (e.g., 380 parts, 400 parts, 420 parts, 440 parts), polyether triols 100-150 parts (e.g., 110 parts, 120 parts, 130 parts, 140 parts), polyaspartic acid esters 80-250 parts (e.g., 100 parts, 150 parts, 200 parts, 250 parts), small molecule diols 10-30 parts (e.g., 15 parts, 20 parts, 25 parts), leveling agents 1-5 parts (e.g., 2 parts, 3 parts, 4 parts).

[0054] In a specific embodiment of the present invention, polyaspartic acid ester is a sterically hindered amine, prepared by a Michael addition reaction of diethylenetriamine, isoflurone diamine, 4,4-diaminodicyclohexylmethane, or 3,3'-dimethyl-4,4-diaminodicyclohexylmethane with diethyl maleate.

[0055] In a specific embodiment of the present invention, the polymer polyol in component A is a polyether polyol grafted with styrene-acrylonitrile copolymer.

[0056] The functionality of the polymer polyol is 3, and the number average molecular weight is 4000-6000.

[0057] The mass percentage of styrene-acrylonitrile copolymer in the polymer polyol is 30-40% (e.g., 32%, 34%, 36%, 38%).

[0058] In a specific embodiment of the present invention, the polyether diol in component A is a copolypropylene oxide-ethylene diol; the number average molecular weight of the polyether diol in component A is 750-2000; and the content of ethylene oxide is 15-35% (e.g., 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%).

[0059] The polyether triol is a copolypropylene oxide-ethylene triol; the number average molecular weight of the polyether triol is 3000-5000; the content of ethylene oxide is 15-35% (e.g., 18%, 20%, 22%, 24%, 26%, 28%, 30%, 32%, 34%).

[0060] The small molecule diols in component A and / or component B are one of ethylene glycol, butanediol, and methylpropanediol.

[0061] In a specific embodiment of the present invention, the leveling agent is an organosilicon leveling agent.

[0062] Component B is an isocyanate component, and the raw materials for its preparation include the following components in parts by mass:

[0063] Polyether diols 200-350 parts (e.g., 250 parts, 300 parts, 350 parts), small molecule diols 8-20 parts (e.g., 10 parts, 12 parts, 14 parts, 16 parts, 18 parts), diphenylmethane diisocyanate (MDI) 200-300 parts (e.g., 220 parts, 240 parts, 260 parts, 280 parts), hydrogenated diphenylmethane diisocyanate (H 12 MDI 500-600 parts (e.g., 520 parts, 540 parts, 560 parts, 580 parts), HDI trimer 150-250 parts (e.g., 180 parts, 200 parts, 220 parts, 240 parts).

[0064] In a specific embodiment of the present invention, the polyether diol in component B is a polyoxypropylene diol with a number average molecular weight of 1000-2000.

[0065] HDI trimer is a trimer of hexamethylene diisocyanate, in which the mass percentage of NCO is 20-25% (e.g., 21%, 22%, 23%, 24%).

[0066] Component C is the catalyst component, and the raw materials for preparation include the following components in parts by mass;

[0067] Carboxylates of bismuth carboxylate, zinc carboxylate, and 1,8-diazabicyclo-bicyclo[5.4.0]undecene-7 (DBU).

[0068] In a specific embodiment of the present invention, bismuth carboxylate is bismuth isooctanoate or bismuth neodecanoate;

[0069] Zinc carboxylate is either zinc isooctanoate or zinc neodecanoate;

[0070] The carboxylates of 1,8-diazabicyclo-bicyclo[5.4.0]undecene-7 (DBU) are one of the following: DBU isooctanoate, DBU formate, and DBU p-toluenesulfonate.

[0071] In a specific embodiment of the present invention, the mass ratio of zinc carboxylate to bismuth carboxylate is 1:8 to 1:2 (e.g., 1:3, 1:4, 1:5, 1:6, 1:7);

[0072] The mass ratio of zinc carboxylate to the carboxylate of 1,8-diazabicyclo-bicyclo[5.4.0]undecene-7 is 1:8 to 1:4 (e.g., 1:5, 1:6, 1:7).

[0073] This invention also provides a method for preparing a solvent-free polyurethane resin for yellowing-resistant synthetic leather, the method comprising the following steps:

[0074] Step 1, Preparation of Component A;

[0075] According to the mass ratio, polymer polyol, polyether diol, polyether triol, polyaspartic acid ester, small molecule diol and leveling agent are added to a closed nitrogen-sealed reactor and mixed evenly to obtain component A.

[0076] Step 2, preparation of component B;

[0077] According to the mass ratio, polyether diol, small molecule diol, diphenylmethane diisocyanate, and hydrogenated diphenylmethane diisocyanate are placed in a sealed nitrogen-sealed reactor, and then HDI trimer is added. After mixing evenly, component B is obtained.

[0078] Step 3, Preparation of component C;

[0079] Bismuth carboxylate, zinc carboxylate, and carboxylate of 1,8-diazabicyclo-bicyclo[5.4.0]undecene-7 were mixed in a sealed nitrogen-sealed reactor according to the mass ratio, and the mixture was mixed evenly to obtain component C.

[0080] Step four: Components A, B, and C are all kept at a constant temperature, and then metered and added into a mixer for stirring. After mixing, polyurethane resin is obtained.

[0081] In a specific embodiment of the present invention, in step one, the reactor is stirred at a temperature of 40-50℃ (e.g., 42℃, 44℃, 46℃, 48℃) for 1.5-2 hours (e.g., 1.6 hours, 1.8 hours).

[0082] In step two, the reactor is stirred at a temperature of 85-95℃ (e.g., 88℃, 80℃, 92℃, 94℃) for 4.5-6 hours (e.g., 5 hours, 5.5 hours), and then HDI trimer is added, and the reaction continues for 1.5-3 hours (e.g., 2 hours, 2.5 hours).

[0083] In step three, the reactor is stirred at a temperature of 25-35℃ (e.g., 30℃, 32℃, 34℃) for 1-2 hours (e.g., 1.2 hours, 1.5 hours, 1.8 hours).

[0084] In step four, components A, B, and C are all subjected to constant temperature treatment at 10-30℃ (e.g., 15℃, 20℃, 25℃).

[0085] This invention provides a method for preparing yellowing-resistant synthetic leather, the method comprising the following steps:

[0086] Polyurethane resin is coated onto release paper that has been pre-coated with aliphatic polyurethane resin, pre-baked, then bonded to a substrate, cured, cooled, and peeled off to obtain yellowing-resistant synthetic leather.

[0087] In a specific embodiment of the present invention, the pre-baking temperature is 110-130℃ (e.g., 115℃, 120℃, 125℃, 130℃), and the pre-baking time is 120-200s (e.g., 130s, 140s, 150s, 160s, 180s); the bonding pressure is 0.2-0.5MPa (e.g., 0.3MPa, 0.4MPa); after bonding, the product is placed in an oven at 120-140℃ (e.g., 125℃, 130℃, 135℃) for 8-15min (e.g., 10min, 12min, 14min), and then cooled and peeled off.

[0088] The yellowing-resistant synthetic leather produced using this solvent-free polyurethane resin can achieve a UV yellowing resistance level of 4 or higher, and a peel strength of not less than 4 kg / 3 cm.

[0089] Example 1

[0090] This embodiment provides a solvent-free polyurethane resin for yellowing-resistant synthetic leather, the polyurethane resin comprising three solvent-free components: A, B and C.

[0091] Component A is a hydroxyl component, and the raw materials for its preparation include the following components in parts by mass:

[0092] 30 parts of polymer polyol, 350 parts of polyether diol, 120 parts of polyether triol, 80 parts of polyaspartic acid ester, 10 parts of small molecule diol, and 1 part of leveling agent.

[0093] In component A, the polymer polyol is a vinyl polymer-grafted polyether polyol with a functionality of 3 and a number-average molecular weight of 4000, of which the vinyl polymer content is 30%.

[0094] The polyether diol is a polyoxypropylene-ethylene diol with a number average molecular weight of 1000 and an ethylene oxide content of 18%.

[0095] The polyether triol is a polyoxypropylene-ethylene diol with a number average molecular weight of 3000 and an ethylene oxide content of 25%.

[0096] Polyaspartic acid ester is prepared by Michael addition reaction of 4,4-diaminodicyclohexylmethane and diethyl maleate.

[0097] The small molecule diol is ethylene glycol;

[0098] The leveling agent is BYK9565.

[0099] Component B is an isocyanate component, and the raw materials for its preparation include the following components in parts by mass:

[0100] 200 parts polyether diol, 8 parts small molecule diol, 200 parts diphenylmethane diisocyanate (MDI), and 200 parts hydrogenated diphenylmethane diisocyanate (H12 550 parts of MDI and 250 parts of HDI trimer.

[0101] The polyether diol is a polyoxypropylene diol with a number average molecular weight of 1000;

[0102] The small molecule diol is butanediol.

[0103] The NCO content in the HDI trimer is 20%.

[0104] Component C is the catalyst component, and the raw materials for preparation include the following components in parts by mass;

[0105] A mixture of bismuth isooctanoate, zinc isooctanoate, and DBU formate, wherein the mass ratio of zinc isooctanoate to bismuth isooctanoate is 1:3 and the mass ratio of zinc isooctanoate to (DBU) formate is 1:4.

[0106] When using, the mass ratio of component A to component B is 1:0.9, and the mass of component C is 1.5% of the sum of the masses of components A and B.

[0107] The present invention provides a method for preparing a solvent-free polyurethane resin for yellowing synthetic leather, comprising the following steps:

[0108] Preparation method of component A: Component A is prepared by stirring the raw materials of each component in a closed nitrogen-sealed reactor at 40°C for 1.5 hours.

[0109] Component B is prepared using a stepwise method: polyether diol, small molecule diol, diphenylmethane diisocyanate (MDI), and hydrogenated diphenylmethane diisocyanate (H) are added. 12 In a sealed nitrogen-sealed reactor, MDI was stirred for 6 hours at 85°C. HDI trimer was then added, and the reaction continued for another 1.5 hours to obtain component B.

[0110] Preparation of component C: The carboxylates of bismuth carboxylate, zinc carboxylate, and 1,8-diazabicyclo-bicyclo[5.4.0]undecene-7 (DBU) were prepared by stirring in a sealed nitrogen-sealed reactor at 35°C for 1 hour to obtain component C.

[0111] Components A, B, and C were all treated at a constant temperature of 15°C and then metered into a high-speed mixer for stirring. The mixed materials had a working time of 900 seconds, and the resulting polyurethane resin was obtained.

[0112] Polyurethane resin is coated onto release paper pre-coated with aliphatic polyurethane resin. After pre-baking, the coated material is bonded to the substrate at a pre-baking temperature of 130℃ for 150 seconds and a bonding pressure of 0.3MPa. After bonding, the material is placed in an oven at 140℃ for 10 minutes to cure. After cooling and peeling, the yellowing-resistant solvent-free polyurethane synthetic leather is obtained. This yellowing-resistant synthetic leather can achieve a UV yellowing resistance of level 4 or higher and a peel strength of 4.5 kg / 3cm.

[0113] Example 2

[0114] This embodiment provides a solvent-free polyurethane resin for yellowing-resistant synthetic leather, the polyurethane resin comprising three solvent-free components: A, B and C.

[0115] Component A is a hydroxyl component, and the raw materials for its preparation include the following components in parts by mass:

[0116] 50 parts of polymer polyol, 450 parts of polyether diol, 150 parts of polyether triol, 150 parts of polyaspartic acid ester, 25 parts of small molecule diol, and 3 parts of leveling agent.

[0117] In component A, the polymer polyol is a vinyl polymer-grafted polyether polyol with a functionality of 3 and a number-average molecular weight of 5000, of which the vinyl polymer content is 40%.

[0118] The polyether diol is a polyoxypropylene-ethylene diol with a number average molecular weight of 2000 and an ethylene oxide content of 30%.

[0119] The polyether triol is a polyoxypropylene-ethylene diol with a number average molecular weight of 5000 and an ethylene oxide content of 35%.

[0120] Polyaspartic acid ester is prepared by Michael addition reaction of diaminodicyclohexylmethane and diethyl maleate.

[0121] The small molecule diol is butanediol;

[0122] The leveling agent used is Evonik TEGO1484.

[0123] Component B is an isocyanate component, and the raw materials for its preparation include the following components in parts by mass:

[0124] 300 parts polyether diol, 15 parts small molecule diol, 300 parts diphenylmethane diisocyanate (MDI), and 300 parts hydrogenated diphenylmethane diisocyanate (H 12 600 parts of MDI and 250 parts of HDI trimer.

[0125] The polyether diol is a polyoxypropylene diol with a number average molecular weight of 2000.

[0126] The small molecule diol is butanediol.

[0127] The NCO content in the HDI trimer is 25%.

[0128] Component C is the catalyst component, and the raw materials for preparation include the following components in parts by mass;

[0129] A mixture of bismuth neodecanoate, zinc neodecanoate, and isooctanoate of DBU, wherein the mass ratio of zinc neodecanoate to bismuth neodecanoate is 1:6, and the mass ratio of zinc neodecanoate to isooctanoate of (DBU) is 1:8.

[0130] When using, the mass ratio of component A to component B is 1:1.1, and the mass of component C is 3% of the sum of the masses of components A and B.

[0131] The present invention provides a method for preparing a solvent-free polyurethane resin for yellowing synthetic leather, comprising the following steps:

[0132] Preparation method of component A: Component A is prepared by stirring the raw materials of each component in a closed nitrogen-sealed reactor at 50°C for 3 hours.

[0133] Component B is prepared using a stepwise method: polyether diol, small molecule diol, diphenylmethane diisocyanate (MDI), and hydrogenated diphenylmethane diisocyanate (H) are added. 12 In a sealed nitrogen-sealed reactor, MDI was stirred for 5 hours at 95°C. HDI trimer was then added, and the reaction was continued for another 3 hours to obtain component B.

[0134] Preparation of component C: The carboxylates of bismuth carboxylate, zinc carboxylate, and 1,8-diazabicyclo-bicyclo[5.4.0]undecene-7 (DBU) were prepared by stirring in a sealed nitrogen-sealed reactor at 25°C for 2 hours to obtain component C.

[0135] Components A, B, and C were all treated at a constant temperature of 30°C and then metered into a high-speed mixer for stirring. The mixed materials had a working time of 600 seconds, and the resulting polyurethane resin was obtained.

[0136] Polyurethane resin is coated onto release paper pre-coated with aliphatic polyurethane resin. After pre-baking, the coated material is bonded to the substrate at a pre-baking temperature of 110℃ for 120 seconds and a bonding pressure of 0.5MPa. After bonding, the material is placed in an oven at 120℃ for 8 minutes to cure. After cooling and peeling, the yellowing-resistant solvent-free polyurethane synthetic leather is obtained. This yellowing-resistant synthetic leather can achieve a UV yellowing resistance of level 4 or higher and a peel strength of 6.5 kg / 3cm.

[0137] Example 3

[0138] This embodiment provides a solvent-free polyurethane resin for yellowing-resistant synthetic leather, the polyurethane resin comprising three solvent-free components: A, B and C.

[0139] In this embodiment, component A and its preparation method are the same as in Example 1, component B and its preparation method are the same as in Example 2, and component C and its preparation method are the same as in Example 1.

[0140] When using, the mass ratio of component A to component B is 1:1.2, and the mass of component C is 2.5% of the sum of the masses of components A and B.

[0141] The method for preparing a yellowing-resistant synthetic leather provided in this embodiment follows the steps below:

[0142] Components A, B, and C were all treated at a constant temperature of 30°C and then metered into a high-speed mixer for stirring. The mixed materials had an 800-second working time, and the resulting polyurethane resin was obtained.

[0143] Polyurethane resin is coated onto release paper pre-coated with aliphatic polyurethane resin. After pre-baking, the coated material is bonded to the substrate at a pre-baking temperature of 110℃ for 180 seconds and a bonding pressure of 0.4MPa. After bonding, the material is placed in an oven at 130℃ for 15 minutes to cure. After cooling and peeling, the yellowing-resistant solvent-free polyurethane synthetic leather is obtained. This yellowing-resistant synthetic leather can achieve a UV yellowing resistance of level 4 or higher and a peel strength of 7.5 kg / 3cm.

[0144] Example 4

[0145] This embodiment provides a solvent-free polyurethane resin for yellowing-resistant synthetic leather, the polyurethane resin comprising three solvent-free components: A, B and C.

[0146] In this embodiment, component A and its preparation method are the same as in Example 2, component B and its preparation method are the same as in Example 1, and component C and its preparation method are the same as in Example 2.

[0147] When using, the mass ratio of component A to component B is 1:0.8, and the mass of component C is 3% of the sum of the masses of components A and B.

[0148] The method for preparing a yellowing-resistant synthetic leather provided in this embodiment follows the steps below:

[0149] Components A, B, and C are all treated at a constant temperature of 30°C and then metered into a high-speed mixer for stirring. The mixed materials have a working time of 750 seconds. Polyurethane resin is obtained after mixing.

[0150] Polyurethane resin is coated onto release paper pre-coated with aliphatic polyurethane resin. After pre-baking, the coated material is bonded to the substrate at a pre-baking temperature of 130℃ for 120 seconds and a bonding pressure of 0.2MPa. After bonding, the material is placed in an oven at 130℃ for 10 minutes to cure. After cooling and peeling, the yellowing-resistant solvent-free polyurethane synthetic leather is obtained. This yellowing-resistant synthetic leather can achieve a UV yellowing resistance of level 4 or higher and a peel strength of 5.5 kg / 3cm.

[0151] Compare with Example 1

[0152] The difference between this comparative example and Example 2 is that the polyaspartic acid ester in component A is replaced with 0 parts, the preparation method of component A is the same as in Example 2, and the preparation methods of components B and C are the same as in Example 2.

[0153] When using, the mass ratio of component A to component B is 1:0.9, and the mass of component C is 3% of the sum of the masses of components A and B.

[0154] A method for preparing synthetic leather using solvent-free polyurethane resin for yellowing-resistant synthetic leather: Components A, B, and C are first kept at a constant temperature of 30°C and then metered into a high-speed mixer for stirring. After mixing, the mixture has a workable time of 600 seconds. The mixture is then coated onto release paper pre-coated with aliphatic polyurethane resin. After pre-baking, the coated material is bonded to a substrate at a pre-baking temperature of 110°C for 120 seconds and a bonding pressure of 0.5 MPa. The bonded material is then placed in a 120°C oven for 8 minutes of curing, followed by cooling and peeling to obtain yellowing-resistant solvent-free polyurethane synthetic leather. This yellowing-resistant synthetic leather exhibits a UV yellowing resistance of level 4 or higher and a peel strength of 2.2 kg / 3 cm.

[0155] Compare with Example 2

[0156] The difference between this comparative example and Example 2 is that the hydrogenated diphenylmethane diisocyanate (H) in component B is removed. 12 The MDI and HDI trimer were both changed to 0 parts, and the diphenylmethane diisocyanate (MDI) was changed to 1000 parts; the preparation method of component B was the same as in Example 2; the preparation methods of components A and C were the same as in Example 2.

[0157] When using, the mass ratio of component A to component B is 1:1, and the mass of component C is 3% of the sum of the masses of components A and B.

[0158] A method for preparing synthetic leather using solvent-free polyurethane resin for yellowing-resistant synthetic leather: Components A, B, and C are first kept at a constant temperature of 30°C and then metered into a high-speed mixer for stirring. After mixing, the mixture has a workable time of 450 seconds. The mixture is then coated onto release paper pre-coated with aliphatic polyurethane resin. After pre-baking, the coated material is bonded to a substrate at a pre-baking temperature of 110°C for 100 seconds and a bonding pressure of 0.5 MPa. After bonding, the material is placed in an oven at 120°C for 5 minutes to cure, then cooled and peeled off to obtain solvent-free polyurethane synthetic leather. This yellowing-resistant synthetic leather exhibits approximately level 3 resistance to UV yellowing and a peel strength of 6.3 kg / 3 cm.

[0159] The data on yellowing resistance and peel strength of the synthetic leather prepared in the examples and control examples are shown in Table 1 below.

[0160] Table 1. Yellowing resistance and peel strength of synthetic leather in the examples and control examples.

[0161]

[0162] As shown in the table above, the solvent-free polyurethane resin for yellowing-resistant synthetic leather prepared in the embodiments of the present invention has a long workability time, reaching 600-900 seconds. This extended workability time facilitates the coating process during synthetic leather preparation, reduces sticking to the coating due to resin curing, and thus lowers the defect rate of synthetic leather products. By adding polyaspartic acid ester and reacting with aliphatic isocyanate to introduce urea bonds, the peel strength of synthetic leather products can be improved, resulting in high strength after curing. The preparation of component B by compounding aliphatic and aromatic isocyanates can reduce the decrease in yellowing resistance caused by the penetration of free aromatic isocyanates into the surface layer, thereby improving the yellowing resistance of synthetic leather. This resin system not only meets the reaction rate requirements of solvent-free synthetic leather production but also effectively improves the yellowing resistance of synthetic leather products.

[0163] In summary: This invention utilizes aliphatic isocyanates (i.e., HDI trimers) with MDI and H 12 The B component of the polyurethane resin for solvent-free synthetic leather is synthesized by compounding MDI, and the A component is polyaspartic acid ester combined with polyol resin. With the help of a suitable catalyst, the reaction between the hydroxyl component and the NCO component can be accelerated, while the reaction between polyaspartic acid ester and NCO is slower due to steric hindrance. The resin has a longer working time. The working time of this invention reaches 600-900s. The cured strength is high. This resin system can not only meet the reaction speed requirements of solvent-free synthetic leather production, but also effectively improve the yellowing performance of synthetic leather products.

[0164] The solvent-free polyurethane resin for yellowing-resistant synthetic leather of this invention is prepared by compounding aliphatic isocyanates and aromatic isocyanates to form component B. This reduces the decrease in yellowing resistance caused by the penetration of free aromatic isocyanates into the surface layer. Simultaneously, the addition of polyaspartic ester reacts with the aliphatic isocyanate to introduce urea bonds, ensuring the final strength of the synthetic leather product. Synthetic leather produced using this solvent-free polyurethane resin achieves a UV yellowing resistance level of 4 or higher and a peel strength of not less than 4 kg / 3 cm, demonstrating broad application prospects.

[0165] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A solvent-free polyurethane resin for yellowing-resistant synthetic leather, characterized in that, The polyurethane resin is prepared using three solvent-free components, A, B, and C, as raw materials. Component A is a hydroxyl component, and the raw materials for preparation consist of the following components in parts by mass: Polymer polyol 30-50 parts, polyether diol 350-450 parts, polyether triol 100-150 parts, polyaspartic acid ester 80-250 parts, small molecule diol 10-30 parts, leveling agent 1-5 parts. Component B is an isocyanate component, and the raw materials for its preparation consist of the following components in parts by mass: 200-350 parts of polyether diol, 8-20 parts of small molecule diol, 200-300 parts of diphenylmethane diisocyanate, 500-600 parts of hydrogenated diphenylmethane diisocyanate, and 150-250 parts of HDI trimer; Component C is the catalyst component, and the raw materials for its preparation consist of the following components: Bismuth carboxylate, zinc carboxylate, and carboxylates of 1,8-diazabicyclo-bicyclo[5.4.0]undecene-7; The polymer polyol in component A is a polyether polyol grafted with styrene-acrylonitrile copolymer.

2. The solvent-free polyurethane resin for yellowing-resistant synthetic leather as described in claim 1, characterized in that, The polyaspartic acid ester is prepared by a Michael addition reaction of diethylenetriamine, isoflurane diamine, 4,4-diaminodicyclohexylmethane, or 3,3'-dimethyl-4,4-diaminodicyclohexylmethane with diethyl maleate.

3. The solvent-free polyurethane resin for yellowing-resistant synthetic leather as described in claim 1, characterized in that, The polymer polyol has a functionality of 3 and a number-average molecular weight of 4000-6000. The styrene-acrylonitrile copolymer in the polymer polyol has a mass percentage content of 30-40%.

4. The solvent-free polyurethane resin for yellowing-resistant synthetic leather as described in claim 1, characterized in that, The polyether diol in component A is a copolymer of propylene oxide and ethylene diol; the number average molecular weight of the polyether diol in component A is 750-2000. The polyether triol is a copolymer of propylene oxide and ethylene triol; the number average molecular weight of the polyether triol is 3000-5000. The small molecule diol in component A and / or component B is one of ethylene glycol, butanediol and methylpropanediol; The leveling agent is an organosilicon-based leveling agent.

5. The solvent-free polyurethane resin for yellowing-resistant synthetic leather as described in claim 1, characterized in that, The polyether diol in component B is a polyoxypropylene diol with a number average molecular weight of 1000-2000; The HDI trimer is a trimer of hexamethylene diisocyanate, wherein the mass percentage of NCO is 20-25%.

6. The solvent-free polyurethane resin for yellowing-resistant synthetic leather as described in claim 1, characterized in that, The bismuth carboxylate is either bismuth isooctanoate or bismuth neodecanoate; The zinc carboxylate is zinc isooctanoate or zinc neodecanoate; The carboxylate of 1,8-diazabicyclo-bicyclo[5.4.0]undecene-7 is one of DBU isooctanoate, DBU formate, and DBU p-toluenesulfonate; The mass ratio of zinc carboxylate to bismuth carboxylate is 1:8 to 1:2; The mass ratio of zinc carboxylate to the carboxylate of 1,8-diazabicyclo-bicyclo[5.4.0]undecene-7 is 1:8 to 1:

4.

7. A method for preparing a solvent-free polyurethane resin for yellowing-resistant synthetic leather as described in any one of claims 1 to 6, characterized in that, The preparation method includes the following steps: Step 1, Preparation of Component A; According to the mass ratio, polymer polyol, polyether diol, polyether triol, polyaspartic acid ester, small molecule diol and leveling agent are added to a closed nitrogen-sealed reactor and mixed evenly to obtain component A. Step 2, preparation of component B; According to the mass ratio, polyether diol, small molecule diol, diphenylmethane diisocyanate, and hydrogenated diphenylmethane diisocyanate are placed in a sealed nitrogen-sealed reactor, and then HDI trimer is added. After mixing evenly, component B is obtained. Step 3, Preparation of component C; Bismuth carboxylate, zinc carboxylate, and carboxylate of 1,8-diazabicyclo-bicyclo[5.4.0]undecene-7 were mixed in a sealed nitrogen-sealed reactor according to the mass ratio, and the mixture was mixed evenly to obtain component C. Step four: Components A, B, and C are all kept at a constant temperature and then added to a mixer according to the metering. After mixing, polyurethane resin is obtained.

8. The method for preparing the solvent-free polyurethane resin for yellowing-resistant synthetic leather as described in claim 7, characterized in that, In step one, the reactor is stirred at a temperature of 40-50℃ for 1.5-2 hours. In step two, the reactor is stirred at 85-95℃ for 4.5-6 hours, then HDI trimer is added and the reaction continues for 1.5-3 hours. In step three, the reactor is stirred at a temperature of 25-35℃ for 1-2 hours. In step four, components A, B, and C are all subjected to constant temperature treatment at 10-30℃.

9. A yellowing-resistant synthetic leather, characterized in that, The yellowing-resistant synthetic leather is prepared using the solvent-free polyurethane resin for yellowing-resistant synthetic leather as described in claim 7 or 8.

10. A method for preparing yellowing-resistant synthetic leather as described in claim 9, characterized in that, The preparation method includes the following steps: The polyurethane resin is coated onto release paper that has been pre-coated with aliphatic polyurethane resin, pre-baked, then bonded to a substrate, cured, cooled, and peeled off to obtain yellowing-resistant synthetic leather. The pre-baking temperature is 110-130℃ and the pre-baking time is 120-200s; the bonding pressure is 0.2-0.5MPa; after bonding, it is placed in an oven at 120-140℃ for 8-15 minutes to mature, and then cooled and peeled off.

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