A method for preparing and applying a microfiber leather impregnated with an aqueous polyurethane emulsion.

Abstract

This invention discloses a method for preparing and applying a waterborne polyurethane emulsion for impregnating microfiber leather, belonging to the field of polyurethane emulsion technology. The raw material formulation of the waterborne polyurethane emulsion includes the following components: polyol component, isocyanate, chain extender, crosslinking agent, and neutralizing agent. This invention uses high-molecular-weight polycarbonate polyol as a raw material to synthesize waterborne polyurethane. The high mechanical strength of the hard segments and the increased molecular weight of the polyurethane improve the mechanical properties of the polyurethane. Simultaneously, a certain amount of TMP with three active hydroxyl groups is introduced into the linear waterborne polyurethane molecular structure to react with the prepolymer and form a crosslinked network structure. This allows the polyurethane emulsion to be distributed in a network pattern during dispersion, reducing the emulsion particle size and increasing the number of polyurethane molecules per unit volume. The resulting crosslinked structure after curing is stable. This invention overcomes the shortcomings of existing waterborne polyurethane resins for microfiber impregnation, such as poor adhesion and poor mechanical properties.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of polyurethane emulsion, and particularly relates to a preparation method and application of a water-based polyurethane emulsion for super fiber leather impregnation. BACKGROUND

[0002] Super fiber leather (full name: super fiber synthetic leather) is a base cloth with three-dimensional network structure made of super fiber as a substrate, and a polyurethane elastomer network structure, a nylon bundle structure and a microstructure simulating real leather collagen are formed in the substrate, so that the super fiber leather has similar elasticity, softness and fullness to real leather, and also has excellent mechanical properties. As the third generation of artificial leather products, the super fiber leather has developed to the present, and its many aspects of performance have reached or even surpassed the natural leather itself, and the external characteristics of the super fiber leather have gradually approached to the natural leather. In recent years, the super fiber leather has gradually expanded its market scale because of its advantages of proper use of non-natural resources, low price, high production efficiency and the like in the production process.

[0003] In the production process of the super fiber leather, the impregnation step is very important. The impregnation process is to impregnate polyurethane (PU) emulsion into the gap of the super fiber base cloth by pressure rolling, and to obtain similar texture to natural leather by using the adhesive structure of PU. The process conditions and the performance of the polyurethane used in the impregnation process determine the style, hand feeling, elasticity and mechanical properties of the super fiber leather.

[0004] At present, the polyurethane impregnated super fiber leather produced on the market is mainly solvent type polyurethane impregnated products. This is because the solvent type polyurethane has excellent performance in all aspects and has a mature wet impregnation process, so that the super fiber leather product prepared has excellent performance and unique hand feeling. However, the use of solvent type polyurethane causes serious environmental pollution and resource waste due to the residue and volatilization of organic solvents in the use process, and the recovery and utilization of organic solvents cause the increase of production cost under the promulgation of relevant policies. Therefore, the use of solvent type polyurethane is becoming more and more inconvenient, and the market urgently needs water-based polyurethane which can replace solvent type polyurethane to enter the production link. Therefore, it is necessary to improve the defects of the mechanical properties and hand feeling of the water-based polyurethane. SUMMARY

[0005] The problem to be solved by the present application is to develop a new type of water-based polyurethane emulsion which can improve the defects of the existing water-based polyurethane used for impregnating super fiber leather, so that the super fiber leather prepared by using the water-based polyurethane has excellent hand feeling and similar external characteristics to natural leather.

[0006] The technical scheme adopted by the present application to achieve the above purpose is:

[0007] The first objective of this invention is to provide an aqueous polyurethane resin emulsion, wherein the raw material formulation of the aqueous polyurethane resin emulsion comprises the following components: polyol component, isocyanate, catalyst, hydrophilic carboxylic acid chain extender, alcohol chain extender, amine chain extender, crosslinking agent, neutralizing agent and water.

[0008] According to some embodiments of the present invention, the polyol component is a polycarbonate polyol (PCDL) with a number average molecular weight of 500, 1000, 2000 or 3000.

[0009] Preferably, the polyol component is a polycarbonate polyol (PCDL) with a number average molecular weight of 2000.

[0010] According to some embodiments of the present invention, the isocyanate is isophorone diisocyanate (IPDI).

[0011] According to some embodiments of the present invention, the catalyst is dibutyltin dilaurate (DBTDL).

[0012] According to some embodiments of the present invention, the hydrophilic carboxylic acid chain extender is 2,2-dimethylolpropionic acid (DMPA).

[0013] According to some embodiments of the present invention, the alcohol chain extender is 1,4-butanediol (BDO).

[0014] According to some embodiments of the present invention, the crosslinking agent is trimethylolpropane (TMP).

[0015] According to some embodiments of the present invention, the amine chain extender is ethylenediamine (EDA).

[0016] According to some embodiments of the present invention, the neutralizing agent is triethylamine (TEA).

[0017] According to some embodiments of the present invention, the molar ratio of -NCO groups to -OH groups of the polyol component in the isocyanate is 1.2-1.4:1.

[0018] Preferably, the aqueous polyurethane resin emulsion components are PCDL1000 30g, IPDI 17.47g, DBTDL 0.30g, DMPA 2.02g, BDO 1.01g, TEA 1.21g, EDA 1.09g, and H2O 105.90g;

[0019] Or PCDL2000 30g, IPDI 11.83g, DBTDL 0.30g, DMPA1.78g, BDO 0.89g, TEA 1.07g, EDA0.93g, H2O 93.00g;

[0020] Or PCDL2000 30g, IPDI 18.69g, DBTDL 0.30g, DMPA2.14g, BDO 1.07g, TMP 1.61g, TEA1.29g, EDA1.12g, H2O 111.84g.

[0021] The second objective of this invention is to provide a method for preparing an aqueous polyurethane resin emulsion, comprising the following steps:

[0022] (1) After dehydrating the polyol component, add isocyanate and organic reagent, and then add catalyst to react and prepare prepolymer;

[0023] (2) Add hydrophilic carboxylic acid chain extender, alcohol chain extender and crosslinking agent to the prepolymer obtained in step (1) in sequence to complete the chain extension reaction of the prepolymer. Add organic reagents during the reaction to reduce the viscosity of the reaction system.

[0024] (3) After the chain extension reaction in step (2) is completed, the temperature is lowered, and then a neutralizing agent, water and amine chain extender are added and stirred to emulsify and obtain a uniform emulsion. After removing the organic reagents by vacuum distillation, the waterborne polyurethane emulsion is obtained.

[0025] According to some embodiments of the present invention, in step (1), the dehydration is carried out by heating to 100-120°C for 1-2 hours under a nitrogen atmosphere.

[0026] According to some embodiments of the present invention, in step (1), the mass ratio of the polyol component to the isocyanate is 30:(10-30).

[0027] Preferably, in step (1), the mass ratio of the polyol component to the isocyanate is 30:(10-20).

[0028] According to some embodiments of the present invention, in step (1), the mass ratio of the polyol component to the catalyst is 30:(0.1 to 0.5).

[0029] According to some embodiments of the present invention, in step (1), the organic reagent is acetone.

[0030] According to some embodiments of the present invention, in step (1), the mass-to-volume ratio of the polyol component and acetone is 30 g: (3-7) mL.

[0031] According to some embodiments of the present invention, in step (1), the temperature of the reaction system drops to 70-80°C after the polyol component is dehydrated.

[0032] According to some embodiments of the present invention, in step (2), the chain extension reaction temperature is 60-70°C.

[0033] According to some embodiments of the present invention, in step (2), the mass ratio of the polyol component to the hydrophilic carboxylic acid chain extender is 30:(1.6 to 2.6).

[0034] According to some embodiments of the present invention, in step (2), the mass ratio of the polyol component to the alcohol chain extender is 30:(0.7-1.3).

[0035] According to some embodiments of the present invention, in step (2), the mass ratio of the polyol component to the crosslinking agent is 30:(0-1.8).

[0036] According to some embodiments of the present invention, in step (2), the organic reagent is acetone.

[0037] According to some embodiments of the present invention, in step (3), the reduced temperature is 35-45°C.

[0038] According to some embodiments of the present invention, in step (3), the mass ratio of the polyol component to the neutralizing agent is 30:(0.8 to 1.6).

[0039] According to some embodiments of the present invention, in step (3), the mass ratio of the polyol component to the amine chain extender is 30:(0.8-1.4).

[0040] According to some embodiments of the present invention, in step (3), the mass ratio of the polyol component to water is 30:(80-140).

[0041] Preferably, the components in the preparation of the waterborne polyurethane resin emulsion are PCDL1000 30g, IPDI 17.47g, DBTDL 0.30g, DMPA 2.02g, BDO 1.01g, TEA 1.21g, EDA 1.09g, and H2O 105.90g;

[0042] Or PCDL2000 30g, IPDI 11.83g, DBTDL 0.30g, DMPA 1.78g, BDO 0.89g, TEA1.07g, EDA0.93g, H2O 93.00g;

[0043] Or PCDL2000 30g, IPDI 18.69g, DBTDL 0.30g, DMPA2.14g, BDO 1.07g, TMP 1.61g, TEA 1.29g, EDA1.12g, H2O 111.84g.

[0044] The third technical solution adopted in this invention is as follows: A method for reducing internal cracks in microfiber leather is achieved by impregnating microfiber leather with an aqueous polyurethane emulsion prepared using the second technical solution. The method includes the following steps:

[0045] (1) Take the waterborne polyurethane prepared by the second technical solution, add thickener, crosslinking agent and wetting agent, stir, and prepare waterborne polyurethane slurry;

[0046] (2) The island fiber base fabric is treated with plasma and then impregnated in the water-based polyurethane slurry prepared in step (1) to obtain the impregnated base fabric.

[0047] (3) The impregnated base fabric is subjected to two dips and two grouts to obtain a base fabric after two dips and two grouts;

[0048] (4) The base fabric after two dips and two nips is immersed in a demulsifying solution, then pre-dried with infrared radiation, and then dried to obtain waterborne polyurethane impregnated microfiber leather.

[0049] According to some embodiments of the present invention, the waterborne polyurethane in step (1) is DIC WLI-630AR with a solid content of 49%; the thickener in step (1) is an associative thickener DH-72165; the crosslinking agent in step (1) is aminopropidine modified isocyanate; and the wetting agent in step (1) is polyether modified silicone oil.

[0050] According to some embodiments of the present invention, the mass ratio of waterborne polyurethane to thickener in step (1) is 80 to 120:0.6, and specifically 100:0.6.

[0051] According to some embodiments of the present invention, the mass ratio of aqueous polyurethane emulsion to crosslinking agent in step (1) is 80-120:0.8, and specifically 100:0.8.

[0052] According to some embodiments of the present invention, the mass ratio of aqueous polyurethane emulsion to wetting agent in step (1) is 80-120:0.5, and specifically 100:0.5.

[0053] According to some embodiments of the present invention, the plasma treatment conditions in step (2) are a nitrogen atmosphere, a gas flow rate of 50 sccm, a vacuum degree of 50 Pa, and a treatment time of 10 min.

[0054] According to some embodiments of the present invention, the soaking time in step (2) is 0.5 to 2 hours, and can be specifically 1 hour.

[0055] According to some embodiments of the present invention, the parameters for the second dip and second rolling in step (3) are a first pressure of 20-40 kg / cm². 2 The second pressure is 5-20 kg / cm².2 Specifically, the initial pressure can be set to 30 kg / cm². 2 The second pressure was 10 kg / cm². 2 .

[0056] According to some embodiments of the present invention, the demulsifier solution in step (4) is a 6-10 wt% sodium sulfate solution or anhydrous ethanol, specifically an 8 wt% sodium sulfate solution.

[0057] According to some embodiments of the present invention, the demulsification soaking time in step (4) is 2 to 5 minutes, specifically 3 minutes.

[0058] According to some embodiments of the present invention, in step (4), infrared pre-drying is to keep both sides of the base fabric uniformly irradiated with infrared light and maintain the surface temperature at 60°C for 10 minutes.

[0059] According to some embodiments of the present invention, the drying temperature in step (4) is 110°C and the time is 20 min.

[0060] The beneficial effects achieved by this invention are as follows:

[0061] In this invention, polycarbonate polyol is selected from the polyol component of waterborne polyurethane. The waterborne polyurethane prepared using it has high mechanical properties and wear resistance. When introduced into the impregnation process of microfiber leather, it can significantly improve the tear strength and polyurethane component cracking problem after the impregnated microfiber leather is prepared. Furthermore, due to the introduction of crosslinking agents, multifunctional monomers are introduced to form a network crosslinked structure of linear waterborne polyurethane, making the molecular structure more compact. During emulsification, the volume of the emulsion particles formed by the aggregation of chain segments is reduced. Even if the synthesized polyurethane component has the characteristics of large molecular weight and small particle size, it is not easy to migrate when impregnated into the microfiber leather. Moreover, the mechanical properties are excellent after curing and crosslinking. Finally, the microfiber leather impregnated with waterborne polyurethane emulsion has a very compact internal structure, and the crosslinking and curing of polyurethane inside is significantly improved, resulting in a smooth surface and a firm and full feel of the microfiber leather. Attached Figure Description

[0062] Figure 1 This is a schematic diagram of the synthesis process of waterborne polyurethane emulsion.

[0063] Figure 2 The image shown is an infrared spectrum image of the film formed in Example 5.

[0064] Figure 3 Images showing the emulsion particle size distribution of Examples 1, 2, 3, 5 and Comparative Examples 1, 2, 3.

[0065] Figure 4 The energy storage modulus versus temperature curves are for Examples 2, 3, 5 and Comparative Examples 1, 2, 3.

[0066] Figure 5 The images shown are cross-sectional electron microscope (EM) images of microfiber leather. (a), (b), (c), and (d) are cross-sectional EEM images of microfiber leather in Example 5 and Comparative Examples 1, 2, and 3, respectively, to observe the curing of waterborne polyurethane inside the microfiber leather. Detailed Implementation

[0067] Unit area cracks: Take 5 1cm samples from the surface of microfiber leather. 2 In a given area, after applying a certain tensile force, the number of cracks that appear within it is counted, and finally the average number of cracks per unit area is calculated.

[0068] Specific compression resilience: The compression properties of the microfiber synthetic leather base fabric were measured using a YG(B)141D digital fabric thickness gauge. First, the compression resilience under light pressure (0.0196 N / cm) was measured. 2 The thickness (T0) of the base fabric under heavy pressure (0.49 N / cm) was measured. 2 Thickness (T) under ) s Finally, release the pressure and allow the base fabric to recover for 60 seconds before measuring its thickness (T). r The specific compressibility modulus (R) is calculated using the following formula.

[0069]

[0070] Example 1

[0071] 30g of polycarbonate diol (PCDL500) with a number average molecular weight of 500 was added to a four-necked flask equipped with a mechanical stirrer and a condenser. The mixture was heated to 100℃ under a nitrogen atmosphere to dehydrate for 1 hour, then cooled to 75℃. 28.75g of isophorone diisocyanate (IPDI) and 5ml of acetone were added and stirred for 30 minutes. Then, 0.3g of dibutyltin dilaurate (DBTDL) was added and the reaction was carried out for 4 hours. After that, the temperature was lowered to 65℃ and 2.50g of 2,2-dimethylolpropionic acid (DMPA) was added. Then, 1.25g of 1,4-butanediol (BDO) was added every hour. During this period, 5-10ml of acetone was added to reduce the viscosity of the reaction system. After the reaction was completed, the temperature was lowered to 40°C, 1.51 g of triethylamine (TEA) was added and stirred for 30 min, then the temperature was lowered to room temperature, 1.31 g of ethylenediamine (EDA) and 130.64 g of deionized water were added, and the mixture was emulsified and dispersed at 1200 r / min for 30 min. Finally, acetone was removed by rotary evaporation to obtain an aqueous polyurethane emulsion.

[0072] Take 100g of the synthesized waterborne polyurethane emulsion and add 0.6g of thickener (DH-72165), 0.8g of crosslinking agent (aminopropyl nitrile modified isocyanate), and 0.5g of wetting agent (polyether modified silicone oil). Stir magnetically for 30min to prepare the required waterborne polyurethane slurry. After plasma treatment of the island fiber base fabric in a nitrogen atmosphere at a gas flow rate of 50sccm for 10min, impregnate it in the waterborne polyurethane slurry. After impregnation for 1 hour, perform a two-dip, two-roll process on the base fabric. The first pressure is 30kg / cm², and the second pressure is 10kg / cm². After weighing, the liquid retention rate of the base fabric is calculated to be 70%. Immerse the rolled base fabric in a prepared 8wt% sodium sulfate solution for 3min, then perform infrared pre-drying to maintain the fabric surface temperature at approximately 60℃ for 10min. Afterward, transfer it to a 110℃ hot air oven for drying for 20min to obtain waterborne polyurethane impregnated microfiber leather.

[0073] The prepared waterborne polyurethane microfiber leather had a weight gain of 20.8%, and after repeated stretching, the surface showed obvious cracking, with a unit area (1 cm²) of [missing information]. 2 There are 4 internal cracks; the microfiber leather has excellent elasticity, with a compression recovery rate of 4.05%.

[0074] Example 2

[0075] The raw material formulation of the waterborne polyurethane emulsion prepared in this embodiment is shown in Table 1. Compared with Example 1, the polyol polymer used in this embodiment is polycarbonate diol (PCDL1000) with a molecular weight of 1000. The resulting waterborne polyurethane microfiber leather had a weight gain of 19.9%, and surface cracking occurred after repeated stretching, with a unit area (1 cm²) of [missing information]. 2 There are 2.2 internal cracks; the microfiber leather has excellent elasticity, with a compression recovery rate of 4.11%.

[0076] Example 3

[0077] The raw material formulation of the waterborne polyurethane emulsion prepared in this embodiment is shown in Table 1. Compared with Example 1, the polyol polymer used in this embodiment is polycarbonate diol (PCDL2000) with a molecular weight of 2000. The resulting waterborne polyurethane microfiber leather had a weight gain of 21.8%, and surface cracking occurred after repeated stretching, with a unit area (1 cm²) of [missing information]. 2 There are 1.8 internal cracks; the microfiber leather has excellent elasticity, with a compression recovery rate of 4.09%.

[0078] Example 4

[0079] The raw material formulation for the aqueous polyurethane emulsion prepared in this embodiment is shown in Table 1. Compared with Example 1, the polyol polymer used in this embodiment is polycarbonate diol (PCDL3000) with a molecular weight of 3000. A stable aqueous polyurethane emulsion could not be obtained.

[0080] Example 5

[0081] The raw material formulation of the waterborne polyurethane emulsion prepared in this embodiment is shown in Table 1. Compared with Example 3, this embodiment added 3% by mass of the internal crosslinking agent TMP. The resulting waterborne polyurethane microfiber leather had a weight gain of 22.1%, and after repeated stretching, there was no obvious surface cracking. The unit area (1 cm²) was [missing information]. 2 The number of internal cracks is 0.6; the microfiber leather has excellent elasticity, with a specific compression recovery rate of 4.45%.

[0082] Comparative Example 1

[0083] The raw material formulation of the waterborne polyurethane emulsion prepared in this comparative example is shown in Table 1. Compared with Example 5, the polyol polymer used in this comparative example is polyethylene glycol (PEG2000) with a molecular weight of 3000. The resulting waterborne polyurethane microfiber leather had a weight gain of 18.5%, and the surface cracked significantly after repeated stretching, with a unit area (1 cm²) of [missing information]. 2 There are 3 internal cracks; the microfiber leather has average elasticity, with a compression recovery rate of 3.10%.

[0084] Comparative Example 2

[0085] The raw material formulation of the waterborne polyurethane emulsion prepared in this comparative example is shown in Table 1. Compared with Example 5, the polyol polymer used in this comparative example is polypropylene glycol (PPG2000) with a molecular weight of 2000. The resulting waterborne polyurethane microfiber leather had a weight gain of 18.8%, and the surface cracked significantly after repeated stretching, with a unit area (1 cm²) of [missing information]. 2 There are 2.8 internal cracks; the microfiber leather has average elasticity, with a compression recovery rate of 3.16%.

[0086] Comparative Example 3

[0087] The raw material formulation of the waterborne polyurethane emulsion prepared in this comparative example is shown in Table 1. Compared with Example 5, the polyol polymer used in this comparative example is polytetrahydrofuran diol (PTMG2000) with a molecular weight of 2000. The resulting waterborne polyurethane microfiber leather had a weight gain of 18.8%, and surface cracking occurred after repeated stretching, with a unit area (1 cm²) of [missing information]. 2 There are two internal cracks; the microfiber leather has average elasticity, with a compression recovery rate of 3.60%.

[0088] Table 1: Raw material formulation of waterborne polyurethane resin emulsion

[0089] Example 1 Example 2 Example 3 Example 4 Example 5 Comparative Example 1 Comparative Example 2 Comparative Example 3 PCDL 500 / g 30 PCDL 1000 / g 30 PCDL 2000 / g 30 30 PCDL 3000 / g 30 PEG 2000 / g 30 PPG 2000 / g 30 PTMG 2000 / g 30 IPDI / g 28.75 17.47 11.83 9.01 18.69 18.69 18.69 18.69 DBTDL / g 0.30 0.30 0.30 0.30 0.30 0.30 0.30 0.30 DMPA / g 2.50 2.02 1.78 1.66 2.14 2.14 2.14 2.14 BDO / g 1.25 1.01 0.89 0.83 1.07 1.07 1.07 1.07 TMP / g 0 0 0 0 1.61 1.61 1.61 1.61 TEA / g 1.51 1.21 1.07 1.00 1.29 1.29 1.29 1.29 EDA / g 1.31 1.09 0.93 0.85 1.12 1.12 1.12 1.12 H2O / g 130.64 105.90 93.00 86.70 111.84 111.84 111.84 111.84

[0090] After centrifugation and degassing of the waterborne polyurethane emulsion at 10000 r / min for 10 min, it was uniformly dispersed in a tetrafluoroethylene mold and cured by air drying at room temperature for 48 h and then dried at 40℃ for 12 h to obtain a polyurethane film. Its physicochemical properties and film-forming stability are shown in Table 2. Mechanical properties were tested according to the national standard GB / T 1040.1-2018, and the test results are shown in Table 3.

[0091] Table 2: Physicochemical properties and film-forming stability of Examples 1-5 and Comparative Examples 1-3

[0092]

[0093]

[0094] Table 3: Mechanical properties of waterborne polyurethane films

[0095] Example 2 Example 3 Example 5 Comparative Example 1 Comparative Example 2 Comparative Example 3 Breaking strength / MPA 7.55 11.00 15.88 4.32 4.71 5.06 Breaking elongation / % 650.3 633.7 716.7 800.3 788.9 792.4

[0096] The adhesion performance of the cured waterborne polyurethane emulsion was tested according to the standard ASTM D3359-09 (adhesion test standard); the average value of three tests was used to evaluate the coating peeling rate, and the test results are shown in Table 4.

[0097] Table 4: Adhesion properties of waterborne polyurethane films

[0098] Example 2 Example 3 Example 5 Comparative Example 1 Comparative Example 2 Comparative Example 3 Glass plate 3B 3B 4B 4B 4B 4B PET film 2B 3B 4B 3B 3B 3B Teflon mold 3B 3B 4B 3B 3B 3B

[0099] Emulsion particle size: 0.5 ml of aqueous polyurethane emulsion was diluted 100 times, and the particle size and distribution were measured using a particle size analyzer. The emulsion particle size distribution image is shown below. Figure 3 As shown, the increase in PCDL molecular weight leads to a larger relative molecular mass of waterborne polyurethane, making it more difficult for the long polyurethane chains to emulsify and disperse in water, thus increasing the emulsion particle size. Furthermore, the growth of the soft PCDL segments also increases the flexibility of the waterborne polyurethane molecular chains, causing the segments to entangle during emulsification and dispersion, resulting in larger dispersed particle sizes. With a gradual increase in TMP content, the emulsion particle size of the waterborne polyurethane initially decreases, but the particle size distribution becomes wider. After adding TMP, the long waterborne polyurethane chains form a network cross-linked structure, resulting in smaller emulsion particles formed by agglomeration during emulsification and dispersion.

[0100] Energy storage modulus versus temperature profile: The elastic modulus of the waterborne polyurethane membrane was analyzed using a dynamic thermomechanical analyzer. According to the instrument's dimensional requirements, clean, uniformly thick, and bubble-free portions of the WPU membrane were cut and fixed in the instrument. The membrane was heated from -90°C to 90°C at a rate of 5°C / min in an N2 environment, with a testing frequency of 0.5Hz. The energy storage modulus versus temperature profile is shown below. Figure 4As shown, Example 5 has a higher high-temperature energy storage modulus and better resilience, making it more suitable for the production process of water-based polyurethane impregnated microfiber leather. The elasticity of Comparative Examples 1-3 is much lower than that of Example 5.

[0101] Cross-sectional electron microscopy image of microfiber leather: Waterborne polyurethane-impregnated microfiber leather was cut, and the cross-sectional morphology of the sample was observed using a scanning electron microscope (SEM) at a scanning voltage of 5 kV. The cross-sectional electron microscopy image of the microfiber leather is shown below. Figure 5 As shown, it can be seen that the microfiber leather prepared by impregnation in Example 5 has a more compact structure due to the addition of TMP, and the waterborne polyurethane is mostly solidified in a film-like form inside it. In contrast, the microfiber leather prepared by waterborne polyurethane in Comparative Examples 1-3 has a loose structure, and the waterborne polyurethane is mostly distributed in a stringy form inside it.

[0102] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method of reducing cracks in microfiber leather, characterized by, The method comprises the following steps: (1) Take the aqueous polyurethane emulsion, add thickening agent, crosslinking agent and wetting agent, stir, and prepare the aqueous polyurethane slurry; the components of the aqueous polyurethane resin emulsion are PCDL2000 30 g, IPDI 18.69 g, DBTDL 0.30 g, DMPA 2.14 g, BDO 1.07 g, TMP 1.61 g, TEA 1.29 g, EDA 1.12 g, and H2O 111.84 g; The preparation method of the aqueous polyurethane resin emulsion comprises the following steps: S1, after dehydration of PCDL2000, add isophorone diisocyanate and acetone, and then add dibutyltin dilaurate; after dehydration, the temperature of the reaction system is reduced to 70-80℃; S2, add 2,2-dimethylol propionic acid, 1,4-butanediol and trimethylolpropane to the prepolymer obtained in step S1 in sequence to complete the chain extension reaction of the prepolymer, and add acetone to reduce the viscosity of the reaction system during the reaction; the chain extension reaction temperature is 60-70℃; S3, after the chain extension reaction in step S2 is completed, reduce the temperature, then add triethylamine, water and ethylenediamine, stir to emulsify to obtain a uniform emulsion, remove the organic reagents by vacuum distillation, and obtain the aqueous polyurethane emulsion; the reduced temperature is 35-45℃; (2) The island fiber base cloth is treated by plasma, and then immersed in the aqueous polyurethane slurry prepared in step (1) to obtain an immersed base cloth; (3) The immersed base cloth is subjected to double dipping and double rolling to obtain a double-dipped and double-rolled base cloth; (4) The double-dipped and double-rolled base cloth is soaked in a demulsification solution, then pre-dried by infrared, and then dried to obtain an aqueous polyurethane impregnated microfiber leather.

2. The method according to claim 1, wherein the plasma treatment in step (2) is performed in a nitrogen atmosphere with a gas flow of 50 sccm and a vacuum degree of 50 Pa for 10 min; and the infrared pre-drying in step (4) is performed by uniformly irradiating the base cloth with infrared light from both sides, and maintaining the surface temperature at 60℃ for 10 min.

3. A microfiber leather prepared by the method according to claim 2.

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