An aqueous polyurethane resin for dry pressing and its preparation method

Abstract

The present invention discloses an aqueous polyurethane resin for dry pressing and its preparation method. The raw materials include the following components in mass fractions: polyether polyol 33% - 40%, small molecule diol 0.1% - 1.5%, carboxylic acid type hydrophilic chain extender 0.8% - 1.5%, isocyanate 8% - 15%, catalyst 0.005% - 0.015%, crosslinking agent 0.1% - 0.5%, amine type chain extender 0.5% - 1.2%, neutralizing agent 0.5% - 1.5%, water 45% - 55%. The present invention uses a crosslinking agent and an amine type chain extender with a hydroxyl group as the chain extender together, forming a short molecular chain and a crosslinked network structure, thereby forming a color difference and further achieving the effect of thermal pressing change; the network structure formed by the amine type crosslinking agent can greatly improve the softening point of the resin, thereby protecting the base fabric.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyurethane resins, and particularly relates to an aqueous polyurethane resin for dry pressing and its preparation method. Background Art

[0002] With the development of the times, people pay more and more attention to the personalization of daily necessities such as clothing, luggage, stationery, leather shoes, etc., and the requirements are also getting higher and higher. The pressing and changing synthetic leather products are more and more popular in the market.

[0003] At present, the vast majority of pressing and changing synthetic leather products are still made mainly of oil-based polyurethane resins. However, the oil-based polyurethane resins have a large amount of organic solvent residues, which are potentially harmful to the human body. There are also some aqueous pressing and changing products on the market, but these products all use pressing and changing powder or pressing and changing wax emulsion to achieve the color-changing effect. For example, the document CN101603272A discloses an aqueous PU pressing and changing resin for synthetic leather, and the raw materials include: 35-45% of aqueous polyurethane resin, 25-35% of water, 5-15% of silica color-changing powder, 5-10% of matting powder, 0.3-1% of organosilicon leveling agent, 1-3% of organosilicon defoaming agent, and 0.5-2% of aqueous polyurethane thickener; the finished product has the advantages of plump hand feeling, good pressing and changing two-color effect, and delicate texture. However, the pressing and changing powder and pressing and changing wax emulsion are extremely easy to bloom and change color during high-temperature drying on the production line, with extremely high usage requirements, the production speed cannot be increased, which affects the production efficiency, and the cost is very high.

[0004] Document CN108049200A discloses a thermo - pressure - color - changing synthetic leather and its preparation method. The thermo - pressure - color - changing synthetic leather includes a transparent protective layer, a foaming layer, a base - color layer, an adhesive layer, and a base fabric which are stacked in sequence. Before thermo - pressing, the foaming layer is a gas - solid mixed system. Due to the light - scattering effect, the foaming layer presents an opaque state, thus effectively covering the base - color layer. When thermo - pressed, the foaming layer at the thermo - pressed part is compacted and becomes a single, transparent solid phase, and the light - scattering effect disappears, thus showing the color of the base - color layer. This thermo - pressure - color - changing synthetic leather does not need to add color - changing materials and can achieve the effect of changing from light color to dark color, or from dark color to light color. However, the production process of this document is relatively complex, and a multi - layer structure is required to achieve the pressure - change effect, and more raw materials result in higher costs. Document CN114108334A discloses a high - peel - strength and MEK - resistant water - borne polyurethane resin, its preparation method and application, which include the following components: polyol component, isocyanate, hydrophilic carboxylic acid - type chain extender, alcohol - type chain extender, amine - type chain extender, cross - linker, catalyst, neutralizer, and water. Among them, the polyol component includes polytetrahydrofuran diol and polycarbonate diol; the isocyanate includes dicyclohexylmethane diisocyanate; the amine - type chain extender includes alcohol - amine - type chain extender. However, in this document, a trifunctional amine - type cross - linker and an ethanolamine or diethanolamine chain extender are simultaneously mixed and added for chain - extending. Since the trifunctional amine - type cross - linker has a fast reaction rate and preferentially reacts with the isocyanate group, the monofunctional chain extender cannot be fully cross - linked, resulting in the polyurethane resin not meeting the requirements of the dry - process base pressure - change effect. Summary of the Invention

[0005] The object of the present invention is to provide a water - borne polyurethane resin for dry - process pressure - change without pressure - change powder or pressure - change wax emulsion, and the production efficiency can be greatly improved by optimizing the process to solve the problems of complex processing technology and high cost of the existing water - borne polyurethane resin.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0007] A water - borne polyurethane resin for dry - process pressure - change of the present invention is characterized in that its raw materials include the following components in mass fractions: polyether polyol 33% - 40%, small - molecule diol 0.1% - 1.5%, carboxylic - acid - type hydrophilic chain extender 0.8% - 1.5%, isocyanate 8% - 15%, catalyst 0.005% - 0.015%, cross - linker 0.1% - 0.5%, amine - type chain extender 0.5% - 1.2%, neutralizer 0.5% - 1.5%, water 45% - 55%;

[0008] The cross - linker is diethylenetriamine and / or triethylenetetramine; the amine - type chain extender is ethanolamine and / or diethanolamine;

[0009] The molar ratio of the isocyanate to the total molar amount of the polyether polyol, carboxylic acid type hydrophilic chain extender and small molecule diol chain extender is 1:(0.6 - 0.85); the molar ratio of the neutralizer to the carboxylic acid type hydrophilic chain extender is (0.95 - 1.05):1; the mass of the crosslinking agent is 0.2% - 1.5% of the total mass of the isocyanate and the polyether polyol; the mass of the amine chain extender is 1% - 3% of the total mass of the isocyanate and the polyether polyol;

[0010] Among them, the polyether polyol is a difunctional polyether polyol with a number average molecular weight of 1800 - 2200; preferably, the polyether polyol is at least one of polytetrahydrofuran diol, polycaprolactone diol, polycarbonate diol, and polypropylene glycol;

[0011] The small molecule diol is at least one of propylene glycol, ethylene glycol, 2 - methyl - 1,3 - propanediol, 1,4 - butanediol, neopentyl glycol, and 1,6 - hexanediol;

[0012] The isocyanate is selected from one or a combination of more than one of toluene - 2,4 - diisocyanate, toluene - 2,6 - diisocyanate, 4,4′ - diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, and dicyclohexylmethane diisocyanate;

[0013] The carboxylic acid type hydrophilic chain extender is at least one of 2,2′ - bis(hydroxymethyl)propionic acid (DMPA) and 2,2′ - bis(hydroxymethyl)butyric acid, and its dosage accounts for 1.5% - 4.5% of the total weight of the polyether polyol and the isocyanate;

[0014] The catalyst is an organic bismuth catalyst; the neutralizer is ammonia water, diethylamine and / or triethylamine, preferably triethylamine.

[0015] For the aqueous polyurethane resin for dry pressing and shaping described in the present invention, after film formation, it is detected with reference to GB / T 19250 - 2013, and the elongation at break of the film ≥ 500%, the modulus ≥ 2 MPa, and the strength ≥ 5 MPa.

[0016] The preparation method of the aqueous polyurethane resin for dry pressing and shaping described in the present invention is characterized by including the following steps:

[0017] (1) Under the action of the catalyst, the polyether polyol, carboxylic acid type hydrophilic chain extender, small molecule diol and the isocyanate are subjected to a one - step prepolymerization reaction at 80 - 90 °C until the NCO value test is qualified to obtain an NCO - terminated prepolymer;

[0018] (2) Add acetone to the prepolymer and stir evenly; control the system temperature at 35 - 45 °C, add the neutralizing agent and stir to react to form a salt; then cool down to 20 - 25 °C, add water at 3 - 15 °C and stir to emulsify to obtain an unextended emulsion;

[0019] (3) To the unextended emulsion, first add the amine chain extender and stir to react for 20 - 60 min, then add the crosslinking agent and continue to react for 20 - 60 min; heat up to 40 - 50 °C and evacuate to remove acetone to obtain the aqueous polyurethane resin;

[0020] The NCO value of the prepolymerization reaction in step (1) is 2.1% - 2.7% of the total mass fraction, preferably 2.40%.

[0021] The use of the aqueous polyurethane resin for dry pressing and changing is to formulate it into a resin slurry, coat it as a foaming layer on a synthetic leather base fabric, and use it to prepare a directly coated base for dry pressing and changing; the formulation of the resin slurry usually includes: 100 parts of the aqueous polyurethane resin for dry pressing and changing, 10 - 60 parts of filler, 0.1 - 1 part of thickener, and 0.5 - 3 parts of color paste;

[0022] The viscosity of the resin slurry is 25000 - 30000 CPS;

[0023] The filler includes at least one of heavy calcium carbonate, light calcium carbonate, kaolin, and wood powder.

[0024] According to the embodiments of the present invention, the dry pressing and changing synthetic leather is tested with reference to the standard GB / T 38612 - 2020, and the peel strength is 80 - 100 N / 3 cm; tested with reference to the standard GB / T 38465 - 2020, it can be flexed more than 100,000 times at normal temperature (20 - 40 °C) and more than 80,000 times at low temperature (-20 - -5 °C).

[0025] The aqueous polyurethane resin for dry pressing and changing of the present invention does not need to add pressure - changing powder or hot - pressing color - changing wax emulsion during use. Only add color paste, and it can be hot - pressed to change color at 160 °C after preparing the finished base. The color - changing temperature is low and the color - changing effect is good.

[0026] Compared with the prior art, the present invention has the following advantages:

[0027] The present invention uses a crosslinking agent (diethylenetriamine and / or triethylenetetramine) and an amine chain extender with a hydroxyl group (ethanolamine and / or diethanolamine) as the chain extender together. The multi-functional crosslinking agent enables the resin to form a partial network structure, while the amine chain extender makes the resin form shorter molecular chains. At the same time, the hydroxyl component in ethanolamine or diethanolamine forms hydrogen bonds with polar groups such as urethane in the aqueous polyurethane. Therefore, the crosslinking agent and the chain extender in the present invention react together to form a network structure with short molecular chains and crosslinking. When this structure is hot-pressed, the shorter molecular chain segments are more easily deformed, and the color powder wrapped therein is deposited accordingly, resulting in an increase in color concentration, thus forming a color difference, and further achieving the effect of hot-press color change. Although the hot-press effect of the linear short molecular chains is good, its softening point is very low, and it is easy to damage the base fabric during the hot-press color change process. At this time, the network structure formed by the amine crosslinking agent can greatly increase the softening point of the resin, thereby protecting the base fabric. Therefore, the ratio of the crosslinking agent and the amine chain extender in the present invention should be within an optimized range to obtain a perfect aqueous resin for dry-press color-changing base fabric.

[0028] The aqueous polyurethane resin of the present invention is used for preparing a directly coated base fabric for dry-press color change, which has low requirements for production equipment, a simple production process, low cost, and the physical properties of the obtained dry-press color-changing base fabric all meet the standards, and it has a soft and plump hand feeling and a good color change effect. Detailed implementation mode

[0029] The following combines specific embodiments to further elaborate the present invention. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. In addition, it should be understood that after reading the content of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

[0030] Examples 1 to 4

[0031] The raw material formula of the aqueous polyurethane resin for dry-press color change is shown in Table 1. Among them, the isocyanate is toluene-2,4-diisocyanate TDI, the polyether polyol is PTMG2000, the small molecule alcohol chain extender is ethylene glycol, the amine crosslinking agent is diethylenetriamine, and the amine chain extender is diethanolamine.

[0032] The preparation method of the aqueous polyurethane resin for dry-press color change includes the following steps:

[0033] (1) Put PTMG2000, the carboxylic acid type hydrophilic chain extender DMPA and ethylene glycol into the reaction kettle and stir evenly, then add TDI, and carry out a one-step prepolymerization reaction at 80-85 °C with an organic bismuth catalyst for 4 h; take a sample from the sampling port and use the di-n-butylamine method to titrate and test the residual isocyanate content. When the theoretical NCO value test is qualified (accounting for 2.4% of the total mass fraction), a prepolymer is obtained;

[0034] (2) Dilute the prepolymer with acetone, stir for 30 min to obtain a homogeneous prepolymer solution; control the temperature at 40 °C, add the neutralizing agent triethylamine, and stir for 15 min to carry out the reaction to form a salt; then cool the reaction kettle to 25 °C, and add water at 8 °C within 2 - 3 min for stirring and emulsification to obtain an unextended emulsion;

[0035] (3) Add an aqueous solution of diethanolamine to the unextended emulsion within 5 min, stir and react for 30 min, then add an aqueous solution of diethylenetriamine, and continue to stir and react for 30 min; then raise the temperature to 45 °C, evacuate to -0.09 Mpa to remove acetone, and after no acetone flows out, cool to below 30 °C for discharging, thus obtaining the aqueous polyurethane resin for dry pressing and shaping.

[0036] Table 1 Raw materials of the aqueous polyurethane resins in Examples 1 - 6 and Comparative Examples 1 - 4, parts by weight

[0037]

[0038]

[0039] Example 5

[0040] The raw material formula of the aqueous polyurethane resin for dry pressing and shaping is shown in Table 1. Among them, the isocyanate is isophorone diisocyanate (IPDI), the polyol is PPG2000, the small molecule alcohol chain extender is 1,4 - butanediol, the amine cross - linker is diethylenetriamine, and the amine chain extender is diethanolamine.

[0041] The preparation method of the aqueous polyurethane resin for dry pressing and shaping includes the following steps:

[0042] (1) Put polyether polyol PTMG2000, carboxylic acid - type hydrophilic chain extender DMPA and 1,4 - butanediol into the reaction kettle and stir evenly, then add IPDI, and carry out a one - step prepolymerization reaction at 85 - 90 °C with an organic bismuth catalyst for 6 h; take a sample from the sampling port, use the di - n - butylamine method for titration to test the residual isocyanate content, and when it reaches the theoretical NCO value and passes the test (accounting for 2.22% of the total mass fraction), obtain the prepolymer;

[0043] (2) Dilute the prepolymer with acetone, stir for 30 min to obtain a homogeneous prepolymer solution; control the temperature at 40 °C, add the neutralizing agent triethylamine, and stir for 15 min to carry out the reaction to form a salt; then cool the reaction kettle to 25 °C, and add water at 8 °C within 2 - 3 min for stirring and emulsification to obtain an unextended emulsion;

[0044] (3) Add an aqueous solution of diethanolamine to the unchain-extended emulsion within 5 min, stir and react for 30 min, then add an aqueous solution of diethylenetriamine and continue to stir and react for 30 min; then raise the temperature to 45 °C, evacuate to -0.09 Mpa to remove acetone, and after no acetone flows out, cool to below 30 °C and discharge to obtain the aqueous polyurethane resin for dry pressing and shaping.

[0045] Example 6

[0046] The raw material formula of the aqueous polyurethane resin for dry pressing and shaping is shown in Table 1. Among them, the isocyanate is toluene-2,4-diisocyanate (TDI), the polyether polyol is PTMG2000, the small molecule alcohol chain extender is ethylene glycol, the amine chain extender is ethanolamine, and the amine crosslinking agent is triethylenetetramine.

[0047] The preparation method of the aqueous polyurethane resin for dry pressing and shaping includes the following steps:

[0048] (1) Put polyether polyol PPG2000, carboxylic acid type hydrophilic chain extender DMPA and ethylene glycol into the reaction kettle and stir evenly, then add TDI, and carry out a one-step prepolymerization reaction at 80 - 85 °C with an organic bismuth catalyst for 4 h; take a sample from the sampling port and use the dibutylamine method to titrate and test the residual isocyanate content. When the theoretical NCO value test is qualified (accounting for 2.4% of the total mass fraction), obtain the prepolymer.

[0049] (2) Add acetone to the prepolymer to dilute it, stir for 30 min to obtain a homogeneous prepolymer solution; control the temperature at 40 °C, add the neutralizing agent triethylamine, and stir and react for 15 min to form a salt; then cool the reaction kettle to 25 °C, and add water at 8 °C and stir for emulsification within 2 - 3 min to obtain the unchain-extended emulsion.

[0050] (3) Add an aqueous solution of ethanolamine to the unchain-extended emulsion within 5 min, stir and react for 30 min, then add an aqueous solution of triethylenetetramine and continue to stir and react for 30 min; then raise the temperature to 45 °C, evacuate to -0.09 Mpa to remove acetone, and after no acetone flows out, cool to below 30 °C and discharge to obtain the aqueous polyurethane resin for dry pressing and shaping.

[0051] Comparative Example 1

[0052] Comparative Example 1 is basically the same as Example 1, the difference is that: all diethanolamine is used to completely replace diethylenetriamine and diethanolamine.

[0053] Comparative Example 2

[0054] Comparative Example 2 is basically the same as Example 1, the difference is that: all diethylenetriamine is used to replace diethylenetriamine and diethanolamine in Example 1.

[0055] Comparative Example 3

[0056] Comparative Example 3 was basically the same as Example 1, except that: the amount of diethanolamine used was 15 parts, and the amount of diethylenetriamine used was 3 parts.

[0057] Comparative Example 4

[0058] Comparative Example 4 was basically the same as Example 1, except that: the amount of diethylenetriamine used was 10 parts, and the amount of diethanolamine used was 7 parts.

[0059] Comparative Example 5

[0060] Comparative Example 5 was basically the same as Example 1, except that: during chain extension, diethanolamine and diethylenetriamine were mixed and then added to the reaction kettle simultaneously for reaction for 30 min.

[0061] Comparative Example 6

[0062] Comparative Example 6 was basically the same as Example 1, except that: during chain extension, first diethylenetriamine was used for chain extension reaction for 30 min, and then diethanolamine was added for chain extension reaction for 30 min.

[0063] The aqueous polyurethane resins of Examples 1 to 6 and Comparative Examples 1 to 6 were made into resin slurries, which were coated on the synthetic leather base fabric as the foaming layer for preparing the direct coating base for dry pressing and deformation; the resin slurry included: 100 parts of aqueous polyurethane resin, 2 parts of foaming agent, 0.5 part of thickener, 0.5 part of color paste and 30 parts of heavy calcium; it was stirred until the viscosity of the mixed solution was 25000 CPS, and the foam was stabilized for 10 min.

[0064] The resin slurry was scrape-coated on the non-woven fabric, the scraping thickness was 60 filaments, and after scraping, it was placed in an oven at 70 °C for 2 min, at 90 °C for 2 min, at 120 °C for 2 min, and at 150 °C for 2 min; then it was taken out to obtain the dry pressing and deformation base.

[0065] The aqueous polyurethane resins used in Examples 1 to 6 and Comparative Examples 1 to 6 were tested with reference to GB / T 19250-2013, and the results are shown in Table 2.

[0066] Table 2 Performance test results of the aqueous polyurethane resins of Examples 1 to 6 and Comparative Examples 1 to 6

[0067]

[0068] The dry-process pressure-variable bass leather prepared in Examples 1-6 and Comparative Examples 1-6 was subjected to peel strength testing with reference to Standard GB / T 38612-2020 and flexing performance testing with reference to Standard GB / T 38465-2020. The results are shown in Table 3. Among them, the evaluation criteria for the flatness of the leather samples are as follows: excellent means the leather sample surface is smooth without concavities and convexities; good means the leather sample surface is basically smooth with fine concavities and convexities; poor means the leather sample surface has many concavities and convexities.

[0069] Table 3 Performance test results of the dry-process pressure-variable basses in Examples 1-6 and Comparative Examples 1-6

[0070]

[0071]

[0072] From the data in Table 2 and Table 3, it can be seen that in Examples 1-6, a waterborne polyurethane resin was obtained by using diethanolamine for pre-chain extension and then diethylenetriamine for re-chain extension. Compared with Comparative Examples 1-6, the waterborne resins prepared in Examples 1-6 have appropriate molecular weights and crosslinked structures, which can ensure good hot pressing effects during hot pressing and good heat resistance of the dry-process bass at high temperatures. At the same time, the prepared dry-process bass has high peel strength, more than 100,000 flexing times at room temperature, and more than 80,000 flexing times at low temperature. The physical properties all meet the standards, and it has a soft and plump handfeel and excellent pressure-variable effects.

[0073] In Comparative Example 1, only diethanolamine was used as the chain extender, and the synthesized emulsion had a low molecular weight and no crosslinked structure, resulting in extremely poor heat resistance of the bass during heating and pressure change. In Comparative Example 2, only diethylenetriamine was used as the crosslinking agent, and the synthesized emulsion had a high crosslinking density and good heat resistance, but the pressure-variable effect of the dry-process bass prepared was very poor and could not achieve hot pressing color change. In Comparative Example 3, excessive diethanolamine was used for pre-chain extension first, and then diethylenetriamine was used for crosslinking. Most of the residual isocyanate groups had been blocked by the front-end diethanolamine, and the addition of diethylenetriamine later could not play a crosslinking role. The effect of the dry-process bass prepared was close to that of Comparative Example 1, with extremely poor heat resistance. In Comparative Example 4, excessive diethylenetriamine was used for crosslinking first, and then partial diethanolamine was used for chain extension. The excessive diethylenetriamine reacted fully, and the heat resistance of the dry-process bass prepared was good, but its crosslinked structure led to extremely poor hot pressing color change effects. In Comparative Example 5, the chain extender and the crosslinking agent were added simultaneously. Since the trifunctional crosslinking agent had a fast reaction rate and preferentially reacted with the isocyanate groups, the monofunctional chain extender could not be fully chain-extended, resulting in a poor pressure-variable effect of the dry-process bass prepared. Therefore, the crosslinking agent in the present invention must be added later, and the monofunctional chain extender must be added first, and the two can only have a pressure-variable effect under specific ratios and reaction times.

[0074] In Comparative Example 6, diethylenetriamine was added first for cross-linking reaction, and then diethanolamine was added for end-capping. The reaction of diethylenetriamine in the front stage increased the molecular weight. At the same time, the isocyanate group would react with water to continue chain growth, resulting in too large molecular weight of the emulsion and poor compression set effect after preparing the dry base leather.

Claims

1. An aqueous polyurethane resin for dry pressing and shaping, characterized in that, Its raw materials include components with the following mass fractions: polyether polyol 33% - 40%, small molecule diol 0.1% - 1.5%, carboxylic acid type hydrophilic chain extender 0.8% - 1.5%, isocyanate 8% - 15%, catalyst 0.005% - 0.015%, crosslinking agent 0.1% - 0.5%, amine type chain extender 0.5% - 1.2%, neutralizer 0.5% - 1.5%, water 45% - 55%; The crosslinking agent is diethylenetriamine and / or triethylenetetramine; the amine type chain extender is ethanolamine and / or diethanolamine; the mass of the crosslinking agent is 0.2% - 1.5% of the total mass of the isocyanate and polyether polyol; the mass of the amine type chain extender is 1% - 3% of the total mass of the isocyanate and the polyether polyol; The preparation method of the aqueous polyurethane resin for dry pressing and shaping includes the following steps: (1) Under the action of the catalyst, the polyether polyol, carboxylic acid type hydrophilic chain extender, small molecule diol and the isocyanate are subjected to a one-step prepolymerization reaction at 80 - 90 °C until the NCO value test is qualified to obtain an NCO-terminated prepolymer; (2) Acetone is added to the prepolymer and stirred evenly; the system temperature is controlled at 35 - 45 °C, and the neutralizer is added and stirred to react to form a salt; then the temperature is lowered to 20 - 25 °C, and water at 3 - 15 °C is added for stirring and emulsification to obtain an unextended emulsion; (3) To the unextended emulsion, first the amine type chain extender is added and stirred for 20 - 60 min, and then the crosslinking agent is added and the reaction continues for 20 - 60 min; the temperature is raised to 40 - 50 °C and vacuum is applied to remove acetone, thus obtaining the aqueous polyurethane resin.

2. The aqueous polyurethane resin for dry pressing according to claim 1, characterized in that, The molar ratio of the isocyanate to the total molar number of the polyether polyol, carboxylic acid type hydrophilic chain extender and small molecule diol chain extender is 1:(0.6 - 0.85); the molar ratio of the neutralizer to the carboxylic acid type hydrophilic chain extender is (0.95 - 1.05):

1.

3. The aqueous polyurethane resin for dry pressing according to claim 1, wherein The polyether polyol is a difunctional polyether polyol with a number average molecular weight of 1800 - 2200; the small molecule diol is at least one of propylene glycol, ethylene glycol, 2-methyl-1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,6-hexanediol; the isocyanate is one or a combination of more of toluene-2,4-diisocyanate, toluene-2,6-diisocyanate, 4,4´-diphenylmethane diisocyanate, isophorone diisocyanate, hexamethylene diisocyanate, dicyclohexylmethane diisocyanate.

4. The aqueous polyurethane resin for dry pressing according to claim 1, wherein The carboxylic acid type hydrophilic chain extender is at least one of 2,2´-bis(hydroxymethyl)propionic acid, 2,2´-bis(hydroxymethyl)butyric acid, and its dosage accounts for 1.5% - 4.5% of the total weight of the polyether polyol and the isocyanate.

5. The aqueous polyurethane resin for dry pressing according to claim 1, characterized in that, The catalyst is an organic bismuth catalyst; the neutralizer is ammonia water, diethylamine and / or triethylamine.

6. The aqueous polyurethane resin for dry pressing according to claim 1, characterized in that, The NCO value of the prepolymerization reaction in step (1) is 2.1% - 2.7% of the total mass fraction.

7. Use of the aqueous polyurethane resin for dry pressing and shaping according to any one of claims 1 to 5, characterized in that, It is formulated into a resin slurry and coated on the synthetic leather base fabric as a foaming layer for the preparation of a directly coated base for dry pressing and shaping.

8. Use of the aqueous polyurethane resin for dry pressing and shaping according to claim 7, characterized in that, The formulation of the resin slurry includes: 100 parts of the aqueous polyurethane resin for dry pressing and deformation, 10 to 60 parts of filler, 0.1 to 1 part of thickener, and 0.5 to 3 parts of color paste.

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