Water-based polyurethane topcoat resin for environmentally-friendly synthetic leather and preparation method thereof

Abstract

This invention discloses an environmentally friendly waterborne polyurethane topcoat resin for synthetic leather and its preparation method. The waterborne polyurethane topcoat resin comprises: 7-11% diisocyanate, 17-22% polymeric diol, 0.9-1.5% nonionic hydrophilic chain extender, 0.5-0.7% tertiary amine polyol chain extender, 0.7-1.0% small molecule diol chain extender, 0.1-0.4% small molecule diamine chain extender, 0.002-0.005% catalyst, 6-12% diluent, and 55-65% deionized water. The waterborne polyurethane topcoat resin and its preparation method proposed in this invention not only possess excellent hydrolysis resistance and heat resistance, but also solve the problems of weak bonding and low peel strength between existing waterborne polyurethane topcoats and solvent-free interlayers.

Description

Technical Field

[0001] This invention belongs to the technical field of resins used in synthetic leather, and particularly relates to an environmentally friendly water-based polyurethane surface layer resin for synthetic leather and its preparation method. Background Technology

[0002] Since the beginning of the 21st century, synthetic leather products have been successfully applied in various fields such as sofas, clothing, footwear, electronic packaging, and decoration due to their excellent performance and beautiful appearance. However, traditional synthetic leather products still use a large amount of toxic and harmful solvents such as DMF, methyl ethyl ketone (MEK), and ethyl acetate. Under the background of environmental protection and green manufacturing, the synthetic leather industry has also ushered in a new generation of environmentally friendly synthetic leather products: water-based solvent-free synthetic leather. This is made by using water-based polyurethane surface resin combined with a solvent-free foaming layer, and then bonding it with an environmentally friendly substrate.

[0003] However, the poor bonding between waterborne polyurethane resin and the solvent-free two-component foam layer leads to low peel strength, and even problems such as direct delamination between the solvent-free layer and the top layer, limiting the production and application of waterborne solvent-free synthetic leather. Researchers have discovered that this delamination phenomenon is related to dimethylolpropionic acid (DMPA) introduced into the waterborne polyurethane. When the waterborne polyurethane is dried and formed into a film, the top layer polyurethane exhibits weak acidity, which affects the molecular chain growth of the two-component solvent-free foam layer.

[0004] Based on this theory, Chinese patent CN10835401B discloses a waterborne polyurethane topcoat resin that bonds well with a two-component solvent-free layer. In this patent, the waterborne polyurethane is prepared using a nonionic hydrophilic chain extender and a self-made sodium sulfonate polymer polyol as raw materials. Although this avoids the influence of DMPA on the waterborne polyurethane topcoat, the stability of the sodium sulfonate polymer polyol synthesis has always been a challenge in the domestic industry due to the high melting point, strong polarity, and poor solubility of sodium sulfonate monomers. While the waterborne polyurethane synthesized using a nonionic hydrophilic chain extender and a self-made sodium sulfonate polymer polyol does not become weakly acidic after drying and film formation, and peeling is acceptable with some two-component solvent-free layers, low peeling performance still occurs when encountering two-component solvent-free layers containing delayed-action acidic catalysts. Chinese patent CN112521581A also discloses a waterborne polyurethane topcoat resin that bonds well with a solvent-free layer. In this patent, the waterborne polyurethane topcoat resin is prepared using N,N'-bis(2-hydroxyethyl)ethylenediamine, a diamine chain extender with hydroxyl groups. By introducing reactive hydroxyl groups that can react with the solvent-free layer into the molecular chain, the peel strength between the solvent-free layer and the waterborne polyurethane topcoat is improved. However, those skilled in the art of waterborne polyurethane synthesis generally agree that the post-chain extension efficiency after emulsification is very low, and most waterborne polyurethane resin molecules contain a large number of amino and hydroxyl groups. Therefore, the extent to which introducing a small amount of reactive hydroxyl groups through post-chain extension alone helps improve the peel strength between the solvent-free layer and the waterborne polyurethane topcoat requires further investigation. Summary of the Invention

[0005] Based on the above-mentioned technical problems, this invention proposes an environmentally friendly waterborne polyurethane surface layer resin for synthetic leather and its preparation method. The waterborne polyurethane surface layer resin not only has excellent hydrolysis resistance and heat resistance, but also solves the problems of poor bonding and low peel strength between existing waterborne polyurethane surface layers and solvent-free intermediate layers.

[0006] This invention proposes an environmentally friendly waterborne polyurethane surface resin for synthetic leather, comprising the following raw materials in weight percentages: 7-11% diisocyanate, 17-22% polymeric diol, 0.9-1.5% nonionic hydrophilic chain extender, 0.5-0.7% tertiary amine polyol chain extender, 0.7-1.0% small molecule diol chain extender, 0.1-0.4% small molecule diamine chain extender, 0.002-0.005% catalyst, 6-12% diluent, and 55-65% deionized water.

[0007] In this invention, a combination of a nonionic hydrophilic chain extender and a tertiary amine polyol chain extender is used as a chain extender to synthesize a waterborne polyurethane topcoat resin. This avoids the weak acidity effect of anions such as carboxylates or sulfonates on the emulsion, and also makes the waterborne polyurethane topcoat resin weakly alkaline. This promotes the molecular chain growth reaction of the two-component solvent-free foam layer and forms chemical bonds between the topcoat and the foam layer, thereby greatly improving the bonding force and peel strength between the waterborne polyurethane topcoat and the solvent-free intermediate layer.

[0008] Preferably, the diisocyanate is an aromatic diisocyanate and / or an aliphatic diisocyanate;

[0009] Preferably, the diisocyanate is a mixture of aromatic diisocyanate and aliphatic diisocyanate, and the molar ratio of aromatic diisocyanate to aliphatic diisocyanate is 1:1-2.

[0010] Preferably, the aromatic diisocyanate is at least one of 2,4-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, or terephthalic diisocyanate; the aliphatic diisocyanate is at least one of isophorone diisocyanate, hexamethylene diisocyanate, or 4,4-dicyclohexylmethane diisocyanate.

[0011] In this invention, the inventors discovered that when aromatic and aliphatic diisocyanates are blended as diisocyanates, the resulting waterborne polyurethane topcoat resin and solvent-free intermediate layer resin exhibit superior molecular matching, mutual attraction, and crystallization. This also improves the bonding strength and hydrogen bonding between the waterborne polyurethane topcoat and the solvent-free intermediate layer. Furthermore, due to the introduction of aromatic diisocyanates into the waterborne polyurethane molecular chain, the resulting polyurethane film possesses superior mechanical properties and abrasion resistance. Moreover, when the molar ratio of aromatic to aliphatic diisocyanates is 1:1-2, the matching effect between the resulting waterborne polyurethane topcoat resin and the solvent-free foaming layer resin is optimal, resulting in greater peel strength between the two.

[0012] Preferably, the polymeric diol is a polyether diol and / or a polyester diol;

[0013] Preferably, the polymeric diol is a mixture of polyether diol and polyester diol, and the mass ratio of polyether diol to polyester diol is 2-3:1.

[0014] Preferably, the number-average molecular weight of the polymeric diol is 1500-2500 g / mol;

[0015] Preferably, the polyether diol is at least one of polytetrahydrofuran diol, polyethylene glycol, or polypropylene glycol, and the polyester diol is at least one of polycarbonate diol, poly(1,4-butanediol adipate) or poly(ethylene adipate) diol.

[0016] Preferably, the nonionic hydrophilic chain extender is a Y-shaped dihydroxyl polyether, the specific structure of which can be found in the diagram. Figure 1 As shown;

[0017] Preferably, the nonionic hydrophilic chain extender is YmerN120.

[0018] Preferably, the tertiary amine polyol chain extender is at least one of N-methyldiethanolamine, N-ethyldiethanolamine, or N-propyldiethanolamine;

[0019] Preferably, the mass ratio of the tertiary amine polyol chain extender to the nonionic hydrophilic chain extender is 1:1.7-2.4.

[0020] In this invention, the inventors discovered that, compared to secondary amine polyol chain extenders, tertiary amine polyol chain extenders provide suitable alkalinity, thus effectively promoting the molecular chain growth reaction of the solvent-free interlayer in the two-component system, thereby improving the bonding force and peel strength between the resulting waterborne polyurethane top layer and the solvent-free interlayer. Furthermore, when nonionic hydrophilic chain extenders and tertiary amine polyol chain extenders are used in combination, in order to optimize the bonding force between the resulting waterborne polyurethane top layer resin and the two-component interlayer, the ratio of nonionic hydrophilic chain extenders to tertiary amine polyol chain extenders needs to be appropriately controlled. Specifically, the mass ratio of the tertiary amine polyol chain extender to the nonionic hydrophilic chain extender is limited to 1:1.7-2.4.

[0021] Preferably, the small molecule diol chain extender is at least one of ethylene glycol, 1,2-propanediol, 1,4-butanediol, or neopentyl glycol; and the small molecule diamine chain extender is at least one of ethylenediamine, propylenediamine, isophorone diamine, or hexamethylenediamine.

[0022] Preferably, the catalyst is at least one of stannous octoate or dibutyltin dilaurate, and the diluent is at least one of acetone, butanone, or N-methylpyrrolidone.

[0023] Preferably, the waterborne polyurethane surface resin further includes 0.01-0.1% of additives;

[0024] Preferably, the additive is at least one of an antioxidant, a light stabilizer, or an ultraviolet absorber.

[0025] This invention also proposes a method for preparing the above-mentioned water-based polyurethane surface resin for environmentally friendly synthetic leather, comprising the following steps:

[0026] S1. First, mix and react the polymer diol, nonionic hydrophilic chain extender, small molecule diol chain extender and diisocyanate, then add the catalyst and tertiary amine polyol chain extender to react until NCO reaches the theoretical value, and obtain the prepolymer.

[0027] S2. Add a diluent to the prepolymer to reduce viscosity, and then add deionized water under high-speed stirring to disperse it, thereby obtaining a dispersion product;

[0028] S3. Add a small molecule diamine chain extender to the dispersion product to carry out a chain extension reaction. After removing the diluent, the waterborne polyurethane surface resin is obtained.

[0029] Preferably, in step S1, the reaction temperature is 70-75℃, and the reaction continues until NCO reaches the theoretical value; in step S2, the high-speed stirring rate is 1000-1500 rpm.

[0030] Compared with the prior art, the present invention has the following advantages:

[0031] (1) This invention uses a combination of nonionic hydrophilic chain extender and tertiary amine polyol chain extender to prepare waterborne polyurethane emulsion, which successfully avoids the weak acidity of the emulsion caused by anions such as carboxylate and sulfonate. At the same time, an appropriate amount of small molecule diol with tertiary amine structure is introduced into the molecular chain, making the surface layer of waterborne polyurethane weakly alkaline, which promotes the molecular chain growth reaction of materials such as two-component solvent-free materials. It can also be used for solvent-free materials containing weakly acidic delayed catalyst systems, and has a wider range of applicability.

[0032] (2) Currently, most two-component solvent-free materials on the market are aromatic system combinations. This invention uses a blend of aliphatic and aromatic diisocyanates, which greatly improves the bonding force between the waterborne polyurethane surface layer and the solvent-free material, as well as the hydrogen bonding effect. At the same time, the introduction of aromatic diisocyanate into the waterborne polyurethane molecular chain gives the polyurethane film better mechanical properties and wear resistance. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the structure of the two-terminal hydroxyl polyether with a "Y"-shaped structure described in this invention. Detailed Implementation

[0034] The present invention will now be described in detail through specific embodiments. However, these embodiments are clearly provided for illustrative purposes and are not intended to limit the scope of the present invention.

[0035] Raw materials used: PTMG-2000 (polytetrahydrofuran diol, molecular weight 2000, produced by Taiwan Dalian Chemical Industry Co., Ltd.); PCD-5652 (polycarbonate diol, molecular weight 2000, produced by Asahi Kasei Corporation); MDI-50 (diphenylmethane diisocyanate, produced by Wanhua Chemical); TDI (2,4-toluene diisocyanate, produced by Cangzhou Dahua); HMDI (4,4-dicyclohexylmethane diisocyanate, produced by Wanhua Chemical); IPDI (isophorone diisocyanate, produced by Wanhua Chemical); YmerN120 (nonionic hydrophilic chain extender, produced by Pastor, Sweden); DMPA (dimethylolpropionic acid, produced by Pastor, Sweden).

[0036] N-MDEA (N-methyldiethanolamine, produced by Shandong Sannet Chemical Technology Co., Ltd.); EG (ethylene glycol, reagent bottle); EDA (ethylenediamine, reagent bottle); catalyst (organic bismuth catalyst 8108).

[0037] Example 1

[0038] An environmentally friendly waterborne polyurethane surface resin for synthetic leather comprises the following raw materials by weight: MDI-50: 54.3g, IPDI: 80g, PTMG-2000: 202.35g, PCD-5652: 82.65g, YmerN120: 16g, N-MDEA: 8g, EG: 13g, EDA: 4.2g, catalyst: 0.05g, antioxidant I-1010: 0.3g, acetone: 138g, and deionized water: 918g.

[0039] The above-mentioned waterborne polyurethane surface layer resin was prepared by the following method:

[0040] (1) PTMG-2000, PCD-5652, YmerN120, EG and antioxidant I-1010 were added to the reaction flask according to the above formula. The mixture was dehydrated under reduced pressure at 120°C for 1.5 h. After the mixture was cooled to 50°C, MDI-50 and IPDI were added. The mixture was reacted at 75°C for 2 h. During the reaction, a catalyst was added. Then N-MDEA was added. The reaction was continued at 70°C for 2 h. A sample was taken and the NCO% was determined by di-n-butylamine titration. When the NCO% was lower than the theoretical value, the reaction was stopped to obtain the prepolymer.

[0041] (2) After cooling the prepolymer to 35°C, acetone was added to reduce viscosity, and then deionized water was added under high-speed stirring at 1300 rpm for emulsification and dispersion to obtain a dispersion product.

[0042] (3) Add EDA to the dispersion product to carry out a post-chain extension reaction. After the reaction is completed, remove acetone by vacuum distillation at 50°C to obtain the waterborne polyurethane surface resin for the environmentally friendly synthetic leather.

[0043] Example 2

[0044] An environmentally friendly waterborne polyurethane surface resin for synthetic leather comprises the following raw materials by weight: TDI: 50.3g, IPDI: 84g, PTMG-2000: 195.35g, PCD-5652: 89.65g, YmerN120: 17g, N-MDEA: 9g, EG: 13g, EDA: 4.6g, catalyst: 0.05g, antioxidant I-1010: 0.3g, acetone: 140g, and deionized water: 920g.

[0045] The above-mentioned waterborne polyurethane surface layer resin is prepared by the following method:

[0046] (1) PTMG-2000, PCD-5652, YmerN120, EG and antioxidant I-1010 were added to the reaction flask according to the above formula. The mixture was dehydrated under reduced pressure at 120°C for 1.5 h. After the mixture was cooled to 50°C, TDI and IPDI were added. The mixture was reacted at 75°C for 2 h. During the reaction, a catalyst was added. Then N-MDEA was added. The reaction was continued at 70°C for 2 h. A sample was taken and the NCO% was determined by di-n-butylamine titration. When the NCO% was lower than the theoretical value, the reaction was stopped to obtain the prepolymer.

[0047] (2) After cooling the prepolymer to 35°C, acetone was added to reduce viscosity, and then deionized water was added under high-speed stirring at 1300 rpm for emulsification and dispersion to obtain a dispersion product.

[0048] (3) Add EDA to the dispersion product to carry out a post-chain extension reaction. After the reaction is completed, remove acetone by vacuum distillation at 50°C to obtain the waterborne polyurethane surface resin for the environmentally friendly synthetic leather.

[0049] Example 3

[0050] An environmentally friendly waterborne polyurethane surface resin for synthetic leather comprises the following raw materials by weight: TDI: 25.3g, MDI-502: 8.3g, HMDI: 89g, PTMG-2000: 195.35g, PCD-5652: 89.65g, Ymer N120: 17g, N-MDEA: 10g, EG: 13g, EDA: 4.6g, catalyst: 0.05g, antioxidant I-1010: 0.3g, acetone: 140g, and deionized water: 920g.

[0051] The above-mentioned waterborne polyurethane surface layer resin was prepared by the following method:

[0052] (1) PTMG-2000, PCD-5652, YmerN120, EG and antioxidant I-1010 were added to the reaction flask according to the above formula. The mixture was dehydrated under reduced pressure at 120°C for 1.5 h. After the mixture was cooled to 50°C, TDI, MDI-50 and HMDI were added. The mixture was reacted at 75°C for 2 h. During the reaction, a catalyst was added. Then N-MDEA was added. The mixture was reacted at 70°C for another 2 h. A sample was taken and the NCO% was determined by di-n-butylamine titration. When the NCO% was lower than the theoretical value, the reaction was stopped to obtain the prepolymer.

[0053] (2) After cooling the prepolymer to 35°C, acetone was added to reduce viscosity, and then deionized water was added under high-speed stirring at 1300 rpm for emulsification and dispersion to obtain a dispersion product.

[0054] (3) Add EDA to the dispersion product to carry out a post-chain extension reaction. After the reaction is completed, remove acetone by vacuum distillation at 50°C to obtain the waterborne polyurethane surface resin for the environmentally friendly synthetic leather.

[0055] Example 4

[0056] An environmentally friendly waterborne polyurethane surface resin for synthetic leather comprises the following raw materials by weight: HMDI: 150g, PTMG-2000: 195.35g, PCD-5652: 89.65g, YmerN120: 17g, N-MDEA: 10g, EG: 13g, EDA: 4.6g, catalyst: 0.05g, antioxidant I-1010: 0.3g, acetone: 140g, and deionized water: 920g.

[0057] The above-mentioned waterborne polyurethane surface layer resin was prepared by the following method:

[0058] (1) PTMG-2000, PCD-5652, YmerN120, EG and antioxidant I-1010 were added to the reaction flask according to the above formula. The mixture was dehydrated under reduced pressure at 120°C for 1.5 h. After the mixture was cooled to 50°C, HMDI was added and the mixture was reacted at 90°C for 2 h. During the reaction, a catalyst was added. Then N-MDEA was added and the reaction was continued at 85°C for 2 h. The sample was taken and the NCO% was determined by di-n-butylamine titration. When the NCO% was lower than the theoretical value, the reaction was stopped and the prepolymer was obtained.

[0059] (2) After cooling the prepolymer to 35°C, acetone was added to reduce viscosity, and then deionized water was added under high-speed stirring at 1300 rpm for emulsification and dispersion to obtain a dispersion product.

[0060] (3) Add EDA to the dispersion product to carry out a post-chain extension reaction. After the reaction is completed, remove acetone by vacuum distillation at 50°C to obtain the waterborne polyurethane surface resin for the environmentally friendly synthetic leather.

[0061] Example 5

[0062] An environmentally friendly waterborne polyurethane surface resin for synthetic leather comprises the following raw materials by weight: MDI-50: 54.3g, IPDI: 80g, PTMG-2000: 202.35g, PCD-5652: 82.65g, YmerN120: 15.5g, N-MDEA: 10.5g, EG: 13g, EDA: 4.2g, catalyst: 0.05g, antioxidant I-1010: 0.3g, acetone: 138g, and deionized water: 918g.

[0063] The above-mentioned waterborne polyurethane surface layer resin was prepared by the following method:

[0064] (1) PTMG-2000, PCD-5652, YmerN120, EG and antioxidant I-1010 were added to the reaction flask according to the above formula. The mixture was dehydrated under reduced pressure at 120°C for 1.5 h. After the mixture was cooled to 50°C, MDI-50 and IPDI were added. The mixture was reacted at 75°C for 2 h. During the reaction, a catalyst was added. Then N-MDEA was added. The reaction was continued at 70°C for 2 h. A sample was taken and the NCO% was determined by di-n-butylamine titration. When the NCO% was lower than the theoretical value, the reaction was stopped to obtain the prepolymer.

[0065] (2) After cooling the prepolymer to 35°C, acetone was added to reduce viscosity, and then deionized water was added under high-speed stirring at 1300 rpm for emulsification and dispersion to obtain a dispersion product.

[0066] (3) Add EDA to the dispersion product to carry out a post-chain extension reaction. After the reaction is completed, remove acetone by vacuum distillation at 50°C to obtain the waterborne polyurethane surface resin for the environmentally friendly synthetic leather.

[0067] Comparative Example 1

[0068] An environmentally friendly waterborne polyurethane surface resin for synthetic leather comprises the following raw materials by weight: MDI-50: 54.3g, IPDI: 80g, PTMG-2000: 202.35g, PCD-5652: 82.65g, DMPA: 10g, triethylamine: 7.53g, EG: 13g, EDA: 4.2g, catalyst: 0.05g, antioxidant I-1010: 0.3g, acetone: 138g, and deionized water: 918g.

[0069] The above-mentioned waterborne polyurethane surface layer resin was prepared by the following method:

[0070] (1) PTMG-2000, PCD-5652, EG and antioxidant I-1010 were added to the reaction flask according to the above formula. The mixture was dehydrated under reduced pressure at 120°C for 1.5 h. After the mixture was cooled to 50°C, MDI-50 and IPDI were added. The mixture was reacted at 75°C for 2 h. During the reaction, a catalyst was added. Then DMPA and a small amount of acetone were added. The mixture was reacted at 65°C for another 2 h. A sample was taken and the NCO% was determined by di-n-butylamine titration. When the NCO% was lower than the theoretical value, the reaction was stopped and the prepolymer was obtained.

[0071] (2) After cooling the prepolymer to 35°C, add the remaining amount of acetone to reduce viscosity, then add triethylamine for neutralization reaction, and then add deionized water under high-speed stirring at 1300 rpm for emulsification and dispersion to obtain the dispersion product.

[0072] (3) Add EDA to the dispersion product to carry out a post-chain extension reaction. After the reaction is completed, remove acetone by vacuum distillation at 50°C to obtain the waterborne polyurethane surface resin for the environmentally friendly synthetic leather.

[0073] Comparative Example 2

[0074] An environmentally friendly waterborne polyurethane surface resin for synthetic leather comprises the following raw materials by weight: TDI: 50.3g, IPDI: 84g, PTMG-2000: 195.35g, PCD-5652: 89.65g, YmerN120: 17g, EG: 18g, EDA: 4.6g, catalyst: 0.05g, antioxidant I-1010: 0.3g, acetone: 140g, and deionized water: 920g.

[0075] The above-mentioned waterborne polyurethane surface layer resin was prepared by the following method:

[0076] (1) PTMG-2000, PCD-5652, YmerN120, EG and antioxidant I-1010 were added to the reaction flask according to the above formula. The mixture was dehydrated under reduced pressure at 120°C for 1.5 h. After the mixture was cooled to 50°C, TDI and IPDI were added. The mixture was reacted at 75°C for 4 h. During the reaction, a catalyst was added. Samples were taken and NCO% was determined by di-n-butylamine titration. When the NCO% was lower than the theoretical value, the reaction was stopped and the prepolymer was obtained.

[0077] (2) After cooling the prepolymer to 35°C, acetone was added to reduce viscosity, and then deionized water was added under high-speed stirring at 1300 rpm for emulsification and dispersion to obtain a dispersion product.

[0078] (3) Add EDA to the dispersion product to carry out a post-chain extension reaction. After the reaction is completed, remove acetone by vacuum distillation at 50°C to obtain the waterborne polyurethane surface resin for the environmentally friendly synthetic leather.

[0079] The examples and comparative examples were prepared into working slurries with a viscosity of 4000 CPS / 25℃ according to the formulations shown in Table 1 below. The working slurries were then coated onto release paper (blade gap controlled at 0.15 mm) and dried at 120℃ for 4 min to obtain an aqueous top layer. The two-component solvent-free material was then stirred evenly and coated onto the aqueous top layer (coating gap controlled at 0.3 mm). The mixture was then pre-cured at 100℃ for 1.5 min, followed by bonding with the base fabric. Finally, the mixture was baked at 135℃ for 4 min, and then the leather sample was peeled off from the release paper.

[0080] Table 1 Formulation of working slurry used in water-based surface coatings

[0081] raw material Thickener Leveling agent Water-based black paste Waterborne polyurethane surface resin Quality (portions) 0.4 0.15 3 100

[0082] The aforementioned solvent-free intermediate layer generally consists of three components: A, B, and C. Component A is a mixture of hydroxyl-terminated polymer polyols, component B is a mixture of isocyanate-terminated modified isocyanates, and component C is a catalyst. In the comparative sampling of this invention, two different types of two-component solvent-free materials are used. Solvent-free material I is a conventional solvent-free material with a moderate reaction rate, and catalyst C does not contain a delayed catalyst. Solvent-free material II contains a portion of a delayed catalyst in catalyst C. Solvent-free material I can be products of grade XCNS-3007A / XCNS-3007B manufactured by Asahikawa Chemical, and solvent-free material II can be products of grade XCNS-2003A / XCNS-2003B manufactured by Asahikawa Chemical.

[0083] The peel strength of the leather samples obtained from the test examples and comparative examples was tested (peel strength test: a 3cm wide strip of hot melt adhesive was applied to the surface of the leather sample, and after cutting, it was tested using a universal tensile testing machine, and the peel strength was recorded). The results are shown in Table 2 below.

[0084] Table 2. Peel strength of leather samples obtained from the examples and comparative examples.

[0085] Peel strength (N / 3cm) I. Solvent-free materials II. Solvent-free materials Example 1 97 96 Comparative Example 1 21 20 Example 2 94 95 Comparative Example 2 76 41 Example 3 96 96 Example 4 53 47 Example 5 65 63 Competing resins on the market 47 24

[0086] As shown in the table above, compared to Comparative Example 1 which used DMPA as a hydrophilic chain extender, Example 1, which used a combination of a nonionic hydrophilic chain extender and a tertiary amine polyol chain extender, exhibited a higher peel strength for the waterborne polyurethane surface layer compared to the two-component solvent-free layer. Similarly, compared to Comparative Example 2 which used only a nonionic hydrophilic chain extender, Example 2, which used a combination of a nonionic hydrophilic chain extender and a tertiary amine polyol chain extender, also showed a higher peel strength for the waterborne polyurethane surface layer compared to the two-component solvent-free layer. Furthermore, compared to Example 4 which only used... Aliphatic diisocyanates are used as diisocyanate sources. In Example 3, both aliphatic and aromatic diisocyanates are used as diisocyanate sources. The waterborne polyurethane surface layer obviously has higher peel strength than the two-component solvent-free layer. Furthermore, compared with Example 5, although a nonionic hydrophilic chain extender and a tertiary amine polyol chain extender are used as chain extenders, the ratio of the two does not meet the requirement of 1.7-2.4:1. Therefore, the improvement in peel strength of the waterborne polyurethane surface layer in Example 1 is not significant.

[0087] Therefore, it can be seen that the present invention uses a combination of nonionic hydrophilic chain extender and tertiary amine polyol chain extender as raw materials, and uses a blend of aliphatic and aromatic diisocyanates as the source of diisocyanate. The resulting waterborne polyurethane topcoat resin has good bonding strength with the two-component solvent-free layer, high peel strength, and wide applicability to solvent-free materials of different systems.

[0088] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A water-based polyurethane surface layer resin for environmentally friendly synthetic leather, characterized in that, The raw materials include the following percentages by weight: diisocyanate 7-11%, polymeric diol 17-22%, nonionic hydrophilic chain extender 0.9-1.5%, tertiary amine polyol chain extender 0.5-0.7%, small molecule diol chain extender 0.7-1.0%, small molecule diamine chain extender 0.1-0.4%, catalyst 0.002-0.005%, diluent 6-12%, and deionized water 55-65%. The mass ratio of the tertiary amine polyol chain extender to the nonionic hydrophilic chain extender is 1:1.7-2.4; The tertiary amine polyol chain extender is at least one of N-methyldiethanolamine, N-ethyldiethanolamine, or N-propyldiethanolamine; the nonionic hydrophilic chain extender is Ymer N120. The diisocyanate is a mixture of aromatic diisocyanate and aliphatic diisocyanate, and the molar ratio of aromatic diisocyanate to aliphatic diisocyanate is 1:1-2.

2. The waterborne polyurethane surface layer resin for environmentally friendly synthetic leather according to claim 1, characterized in that, The aromatic diisocyanate is at least one of 2,4-diphenylmethane diisocyanate, 2,4-toluene diisocyanate, or terephthalic diisocyanate; the aliphatic diisocyanate is at least one of isophorone diisocyanate, hexamethylene diisocyanate, or 4,4-dicyclohexylmethane diisocyanate.

3. The waterborne polyurethane surface layer resin for environmentally friendly synthetic leather according to claim 1, characterized in that, The polymeric diol is a polyether diol and / or a polyester diol.

4. The waterborne polyurethane surface resin for environmentally friendly synthetic leather according to claim 3, characterized in that, The polymeric diol is a mixture of polyether diol and polyester diol, and the mass ratio of polyether diol to polyester diol is 2-3:

1.

5. The waterborne polyurethane surface layer resin for environmentally friendly synthetic leather according to claim 3, characterized in that, The number-average molecular weight of the polymeric diol is 1500-2500 g / mol.

6. The waterborne polyurethane surface layer resin for environmentally friendly synthetic leather according to claim 3, characterized in that, The polyether diol is at least one of polytetrahydrofuran diol, polyethylene glycol, or polypropylene glycol, and the polyester diol is at least one of polycarbonate diol, poly(1,4-butanediol adipate) diol, or poly(ethylene adipate) diol.

7. The waterborne polyurethane surface layer resin for environmentally friendly synthetic leather according to any one of claims 1-6, characterized in that, The small molecule diol chain extender is at least one of ethylene glycol, 1,2-propanediol, 1,4-butanediol, or neopentyl glycol; the small molecule diamine chain extender is at least one of ethylenediamine, propylenediamine, isophorone diamine, or hexamethylenediamine.

8. The waterborne polyurethane surface layer resin for environmentally friendly synthetic leather according to any one of claims 1-6, characterized in that, The catalyst is at least one of stannous octoate or dibutyltin dilaurate, and the diluent is at least one of acetone, butanone, or N-methylpyrrolidone.

9. The waterborne polyurethane surface layer resin for environmentally friendly synthetic leather according to any one of claims 1-6, characterized in that, The waterborne polyurethane surface resin also includes 0.01-0.1% additives; The additive is at least one of antioxidants, light stabilizers, or ultraviolet absorbers.

10. A method for preparing the waterborne polyurethane surface layer resin for environmentally friendly synthetic leather according to any one of claims 1-8, characterized in that, Includes the following steps: S1. First, mix and react the polymer diol, nonionic hydrophilic chain extender, small molecule diol chain extender and diisocyanate, then add the catalyst and tertiary amine polyol chain extender to react until NCO reaches the theoretical value, and obtain the prepolymer. S2. Add a diluent to the prepolymer to reduce viscosity, and then add deionized water under high-speed stirring to disperse it, thereby obtaining a dispersion product; S3. Add a small molecule diamine chain extender to the dispersion product to carry out a chain extension reaction. After removing the diluent, the waterborne polyurethane surface resin is obtained.

11. The method for preparing the waterborne polyurethane surface layer resin for environmentally friendly synthetic leather according to claim 10, characterized in that, In step S1, the reaction temperature is 70-75℃, and the reaction continues until NCO reaches the theoretical value; in step S2, the high-speed stirring rate is 1000-1500 rpm.

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