Preparation and Application of an Aqueous Polyurethane Composite Coating with High Ductility

Abstract

The present invention relates to the preparation and application of an aqueous polyurethane composite coating with high ductility. Preparation: First, a lower-layer aqueous polyurethane slurry is coated on the surface of the target object, dried and cured to form a lower-layer aqueous polyurethane coating. Then, a middle-layer aqueous polyurethane slurry is coated on the lower-layer aqueous polyurethane coating, dried and cured to form a middle-layer aqueous polyurethane coating. Next, an upper-layer aqueous polyurethane slurry is coated on the middle-layer aqueous polyurethane coating, dried and cured to form an upper-layer aqueous polyurethane coating. Finally, it is left standing to obtain an aqueous polyurethane composite coating with high ductility. When the target object for the coating is a superfine fiber base fabric, the product is used for preparing a superfine fiber PU synthetic leather. The tensile load of the superfine fiber PU synthetic leather is ≥540 N, and the elongation at break is ≥60%. The preparation method of the present invention obtains a coating material with high strength and high ductility. The product is used for preparing a superfine fiber PU synthetic leather, and both the strength and toughness are excellent.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyurethane, and relates to the preparation and application of an aqueous polyurethane composite coating with high ductility. Background Art

[0002] In the prior art, the polyurethane commonly used for the surface coating of synthetic leather is an aqueous polyurethane with a high hard segment content and good strength. Usually, the 100% modulus is used to evaluate the hard segment content level of the aqueous polyurethane. The more the hard segment content, the greater the 100% modulus. Usually, 100% modulus ≥ 34 MPa is selected to meet the strength requirements of the material. However, the aqueous polyurethane with a high hard segment content often has insufficient ductility.

[0003] In the field of PU elastomers, it is usually adopted to add small molecule lubricants to increase the plasticity of polyurethane materials, and then increase the ductility, so that the polyurethane materials can have high ductility and toughness, and are not prone to problems such as cracking and fracture during subsequent processing and use. Such as in CN201410802061.X a halogen-free flame-retardant thermoplastic polyurethane elastomer composite material and its preparation method; in CN201310017999.6 a nano-composite polyether-based thermoplastic polyurethane elastomer composition and its preparation method, the small molecule lubricant is usually used in an amount of 0.05 - 5% of the total mass of the formula.

[0004] Improving the ductility by adding small molecule lubricants is relatively effective, and this additive is also applicable to the field of polyurethane coatings. However, for polyurethane matrices with different rigidities, the effects achieved by using small molecule lubricants to improve their ductility are different. When the 100% modulus is as high as 40 MPa, the material rigidity is too high, and it is very difficult to obtain an ideal effect through small molecule lubricants; for polyurethanes with a 100% modulus of 34 - 40 MPa, although adding small molecule lubricants to improve the ductility has a certain effect, the limit addition level of small molecule lubricants in the aqueous polyurethane with a high hard segment content is relatively low, and its limit addition amount is about 10%. When the addition amount exceeds the limit value, the ductility modification of the material will no longer increase with the increase of the addition amount. This is because after exceeding the limit addition amount, the lubricant will precipitate to the surface, making the actual concentration of small molecules distributed in the matrix not increase, but instead causing appearance problems; currently, the commonly applicable means to obtain high ductility is to select a polyurethane matrix with a lower 100% modulus, and further, a lubricant within 30% can be added. However, this means that it is impossible to obtain materials with both high strength and high ductility at the same time, because the lower the 100% modulus of the selected matrix, the worse the strength, and the addition of the lubricant can only improve the ductility and cannot increase the strength.

[0005] Therefore, it is of great significance to study a preparation method and application of an aqueous polyurethane coating with excellent strength and toughness to solve the above problems. Summary of the Invention

[0006] The object of the present invention is to solve the problems existing in the prior art and provide the preparation and application of an aqueous polyurethane composite coating with high ductility.

[0007] To achieve the above object, the technical solution adopted by the present invention is as follows:

[0008] A preparation method of an aqueous polyurethane composite coating with high ductility. First, a lower layer aqueous polyurethane slurry is coated on the surface of the target object, dried and cured to form a lower layer aqueous polyurethane coating. Then, a middle layer aqueous polyurethane slurry is coated on the lower layer aqueous polyurethane coating, dried and cured to form a middle layer aqueous polyurethane coating. Then, an upper layer aqueous polyurethane slurry is coated on the middle layer aqueous polyurethane coating, dried and cured to form an upper layer aqueous polyurethane coating. Finally, it is left standing to obtain an aqueous polyurethane composite coating with high ductility;

[0009] The middle layer aqueous polyurethane slurry contains 100% modulus aqueous polyurethane resin with a high modulus, a small molecule lubricant and water;

[0010] The upper layer aqueous polyurethane slurry contains 100% modulus aqueous polyurethane resin with a low modulus, a small molecule lubricant and water;

[0011] The lower layer aqueous polyurethane slurry contains 100% modulus aqueous polyurethane resin with a low modulus, a small molecule lubricant and water;

[0012] The 100% modulus of the 100% modulus aqueous polyurethane resin with a high modulus is 34 - 40 MPa, and the 100% modulus of the 100% modulus aqueous polyurethane resin with a low modulus is 1 - 2 MPa;

[0013] The monomer units of the 100% modulus aqueous polyurethane resin with a high modulus and the 100% modulus aqueous polyurethane resin with a low modulus are the same;

[0014] In the middle-layer aqueous polyurethane slurry, for 100 parts by mass of the 100% modulus aqueous polyurethane resin, 8 to 10 parts by mass of a small molecule lubricant are correspondingly added, and the addition amount of the small molecule lubricant is close to the precipitation limit value but still within the precipitation limit; if the small molecule lubricant in the middle-layer aqueous polyurethane exceeds the precipitation limit, precipitation oil spots will be generated on the surface after film formation. These are aggregates of the small molecule lubricant and are incompatible with the aqueous polyurethane, which will make it difficult to further coat a qualified composite coating on the surface subsequently. The mass fraction of the small molecule lubricant correspondingly added for 100 parts by mass of the low 100% modulus aqueous polyurethane resin in the upper-layer aqueous polyurethane slurry and the lower-layer aqueous polyurethane slurry is at least 1.5 times that of the small molecule lubricant correspondingly added for 100 parts by mass of the low 100% modulus aqueous polyurethane resin in the middle-layer aqueous polyurethane slurry, and the addition amount of the small molecule lubricant is within the precipitation limit. If it is less than 1.5, there is no significant increase in the concentration of the small molecule lubricant in the 100% modulus aqueous polyurethane resin through concentration difference diffusion, and the ductility of the material does not show a significant increase.

[0015] As a preferred technical solution:

[0016] For a preparation method of an aqueous polyurethane composite coating with high ductility as described above, the thickness ratio of the upper-layer aqueous polyurethane coating to the middle-layer aqueous polyurethane coating is 10:90 to 17:83; the thickness of the lower-layer aqueous polyurethane coating is the same as that of the upper-layer aqueous polyurethane coating.

[0017] For a preparation method of an aqueous polyurethane composite coating with high ductility as described above, the thickness of the middle-layer aqueous polyurethane coating is 50 to 300 μm, and the thickness of the upper-layer aqueous polyurethane coating is 10 to 50 μm.

[0018] For a preparation method of an aqueous polyurethane composite coating with high ductility as described above, by mass fraction, the middle-layer aqueous polyurethane slurry contains 100 parts of 100% modulus aqueous polyurethane resin, 8 to 10 parts of a small molecule lubricant, and 70 to 500 parts of water; by mass fraction, the upper-layer aqueous polyurethane slurry contains 100 parts of low 100% modulus aqueous polyurethane resin, 12 to 22 parts of a small molecule lubricant, and 70 to 500 parts of water; by mass fraction, the lower-layer aqueous polyurethane slurry contains 100 parts of low 100% modulus aqueous polyurethane resin, 12 to 22 parts of a small molecule lubricant, and 70 to 500 parts of water;

[0019] According to actual requirements, additives such as thickeners can also be added. For example, 0.1 to 1 part of a thickener can be added to adjust the viscosity of the aqueous polyurethane coating to 1000 mPa·s to 6000 mPa·s (tested with a rotary viscometer at a test temperature of 25°C), which is more conducive to smooth coating. The thickener can be selected from Stahl company EVO RM-4417 and EVO RM-4456. These additives and their functions are all prior art. According to actual requirements, colorants can also be added to the upper-layer aqueous polyurethane slurry for color adjustment. For example, 1 to 10 parts of colorants can be added, such as the QCS-840 series of Guangzhou Qicai New Materials Co., Ltd.

[0020] For the preparation method of an aqueous polyurethane composite coating with high ductility as described above, the small molecule lubricant is triethyl phosphate. Triethyl phosphate has a high solubility in water, so that more small molecule lubricants can be added.

[0021] For the preparation method of an aqueous polyurethane composite coating with high ductility as described above, the coating method is roll coating treatment, which is a conventional coating method. Those skilled in the art can adjust the process parameters according to the target coating thickness to obtain it.

[0022] For the preparation method of an aqueous polyurethane composite coating with high ductility as described above, the standing temperature is 50 - 70 °C and the standing time is more than 48 h. The standing temperature and standing time are set because it takes a certain time for the high-concentration small molecule lubricant to diffuse into the polyurethane. The high temperature of 50 - 70 °C can accelerate the diffusion, and there is a significant difference in the elongation at break between the unstood composite coating and the stood composite coating.

[0023] For the preparation method of an aqueous polyurethane composite coating with high ductility as described above, the target object is ultra-fine fiber base cloth, non-woven fabric, woven fabric or knitted fabric.

[0024] The present invention also provides the application of the aqueous polyurethane composite coating with high ductility prepared by the method described in any one of the above, which is used for preparing ultra-fine fiber PU synthetic leather, and the target object for the coating is ultra-fine fiber base cloth;

[0025] The tensile load of the ultra-fine fiber PU synthetic leather is ≥540 N, and the elongation at break is ≥60%.

[0026] Invention mechanism:

[0027] When polyurethane is polymerized, active hydrogen substances of oligomer type (such as oligomer diol) and active hydrogen substances of small molecule type (such as ethylene glycol) are added simultaneously. Their active hydrogen end groups react with diisocyanate to form polyurethane molecular chains. Among them, the active hydrogen substances of oligomer type constitute the soft segment of polyurethane, and the active hydrogen substances of small molecule type constitute the hard segment of polyurethane. The soft segment provides the flexibility of the molecular chain while the hard segment provides the rigidity of the molecular chain. The higher the hard segment content, the stronger the rigidity and the lower the flexibility of the material. Usually, the rigidity of the material is evaluated at the 100% modulus level, and then the proportion of the polyurethane hard segment is evaluated. The waterborne polyurethane resin with a high 100% modulus is a polyurethane with a high hard segment content, and the waterborne polyurethane resin with a low 100% modulus is a polyurethane with a high soft segment content.

[0028] By analyzing the precipitation behavior of small molecules in polyurethane matrices with different soft segment proportions, it is considered that the proportion of the soft segment affects the solubility of small molecule additives in the polymer matrix. Polyurethane with a large proportion of soft segments can dissolve more small molecule lubricants. Polyurethane with a high soft segment proportion has good ductility by itself. Generally, no additional small molecule lubricants are needed for toughening modification. However, the strength of polyurethane with a high soft segment proportion is too low to be used for the coating of synthetic leather. What polyurethane with a high soft segment proportion needs is strength modification rather than toughening modification. Therefore, even if it has a higher solubility of small molecule additives, it cannot solve the problems faced by the existing technology. While the waterborne polyurethane with a high hard segment content, having more hard segments and fewer soft segments, has high strength, but its ductility is insufficient, and it is generally improved by adding small molecule additives.

[0029] In the initial stage of research and development, we compounded a waterborne polyurethane with a 100% modulus of 44 MPa and the same waterborne polyurethane with a 100% modulus of 1.5 MPa to adjust waterborne polyurethanes with different 100% modulus levels, that is, waterborne polyurethanes with different soft segment contents, and then adjust the strength and ductility of the coating. To ensure ideal strength, the 100% modulus of the waterborne polyurethane resin should be adjusted to at least exceed 30 MPa. Adding small molecule lubricants can improve ductility, but the improvement level is limited. This is because when the small molecule lubricant is added to more than 12 parts (that is, the addition amount of the small molecule lubricant is more than 12 wt% of the waterborne polyurethane), an oil film will precipitate, and at this time, the 100% modulus is 30 MPa.

[0030] The compatibility between the hard segment and the small molecule lubricant is poor, and the limiting precipitation concentration of the small molecule lubricant in polyurethanes with different hard segment contents is different; among them, the limiting precipitation concentration is the addition ratio of the small molecule lubricant when different ratios of the small molecule lubricant are added to the aqueous polyurethane, and then it is scraped into a film, dried at 100 °C and cooled to 25 °C, and oil spots or precipitates appear on the surface of the polyurethane film. When we set a low 100% modulus aqueous polyurethane resin with a higher concentration distribution of the small molecule lubricant above and below a high 100% modulus aqueous polyurethane resin containing a distribution of the small molecule lubricant close to the limiting precipitation concentration, it is found that the high concentration of the small molecule lubricant in the low 100% modulus aqueous polyurethane resin diffuses into the high 100% modulus aqueous polyurethane resin, significantly improving the ductility of the overall material. When the small molecule lubricant exceeds the limit concentration, a large driving force for outward diffusion is generated, and the concentration difference on both sides causes the small molecule lubricant to generate an inward diffusion driving force.

[0031] The conditions for forming a certain concentration difference to enable the small molecule lubricant to have an inward diffusion driving force are: the content of the small molecule lubricant in the upper aqueous polyurethane coating and the content of the small molecule lubricant in the lower aqueous polyurethane coating are both ≥ 1.5 times the content of the small molecule lubricant in the middle aqueous polyurethane coating.

[0032] During the preparation process, the small molecule lubricant in the upper, middle, and lower layers did not exceed the limiting precipitation concentration. The small molecule lubricant in the middle aqueous polyurethane coating was 8 - 10 parts, close to the limit concentration. After being treated at a high temperature of 50 - 70 °C for 48 hours, the small molecule lubricant in the upper and lower layers diffused into the middle layer, and the actual concentration of the small molecule lubricant in the middle aqueous polyurethane coating exceeded its limit concentration.

[0033] In the present invention, it is necessary to ensure that the polyurethanes in the upper, middle, and lower aqueous polyurethane coatings are of the same material, and the monomer units of the high 100% modulus aqueous polyurethane resin and the low 100% modulus aqueous polyurethane resin are the same, and the difference is only the content of the soft segment. When the upper layer material is replaced with a coating of another material with the same solubility, due to the poor compatibility of the two materials, the small molecule lubricant precipitates at the interface due to the existence of the concentration difference, exacerbating the material delamination.

[0034] Beneficial effects

[0035] (1) A preparation method of a high-ductility aqueous polyurethane composite coating according to the present invention, by setting a low 100% modulus aqueous polyurethane resin with a higher concentration distribution of the small molecule lubricant above and below a high 100% modulus aqueous polyurethane resin containing a distribution of the small molecule lubricant close to the limiting precipitation concentration, and using the diffusion driving force, enabling the small molecule lubricant exceeding the limit concentration to stably exist in the high 100% modulus aqueous polyurethane resin, obtaining a material with high strength and high ductility.

[0036] (2) The waterborne polyurethane composite coating with high ductility of the present invention is used to prepare ultrafine fiber PU synthetic leather, and both the strength and toughness are excellent. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 It is a schematic diagram of the waterborne polyurethane composite coating with high ductility of the present invention;

[0038] Figure 2 The differential spectrum before and after heat treatment at 50 °C for 48 hours in Example 1;

[0039] Among them, 1 - upper waterborne polyurethane coating, 2 - middle waterborne polyurethane coating, 3 - lower waterborne polyurethane coating. DETAILED DESCRIPTION OF THE INVENTION

[0040] The present invention will be further described below in conjunction with specific embodiments. 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 taught by 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.

[0041] The test methods related to the present invention are as follows:

[0042] 100% modulus: Using a universal testing machine, measure the tensile force when the film is stretched to a breaking elongation of 100%, and then divide the tensile force by the cross-sectional area of the film before stretching, which is the 100% modulus of the material.

[0043] Tensile strength and elongation at break of the composite coating: Replace the target objects in the examples and comparative examples with flat glass, and after molding, remove the composite coating from the flat glass to prepare test samples of the composite coating; According to GB / T 1040.3 - 2006, use a universal testing machine to measure the tensile strength and elongation at break of the composite coating, where the distance between the sample markings is 100 mm and the test speed is 200 mm / min ± 10 mm / min.

[0044] Tensile load and elongation at break of the synthetic leather: The prepared synthetic leather is measured according to QBT 4909 - 2016 Waterborne Polyurethane Ultrafine Fiber Synthetic Leather.

[0045] The waterborne polyurethane resin of the present invention is an anionic waterborne polyurethane resin. The difference between the low-modulus waterborne polyurethane resin and the high-modulus waterborne polyurethane resin lies in the different proportions of the soft segment. The soft segment of the low-modulus waterborne polyurethane resin (i.e., the third part in the structural formula) is 40 times that of the soft segment of the high-modulus waterborne polyurethane resin; The two waterborne polyurethane resins are respectively:

[0046] The structural formula of the 100% modulus aqueous polyurethane resin with a 100% modulus of 44 MPa is as follows:

[0047]

[0048] The structural formula of the low 100% modulus aqueous polyurethane resin with a 100% modulus of 1.0 MPa is as follows:

[0049]

[0050] The number-average molecular weight of the high modulus aqueous polyurethane resin was determined to be 156,000; the number-average molecular weight of the low modulus aqueous polyurethane resin was 168,000. Aqueous polyurethane resins with different moduli can be obtained by blending the 100% modulus high modulus aqueous polyurethane resin and the 100% modulus low modulus aqueous polyurethane resin. In specific examples and comparative examples, the blending ratios are as follows:

[0051] The aqueous polyurethane with a 100% modulus of 1.2 MPa was obtained by uniformly mixing the aqueous polyurethane resin with a 100% modulus of 1.0 MPa and the aqueous polyurethane with a 100% modulus of 44 MPa at a mass ratio of 99.5:0.5 in water.

[0052] The aqueous polyurethane with a 100% modulus of 1.3 MPa was obtained by uniformly mixing the aqueous polyurethane resin with a 100% modulus of 1.0 MPa and the aqueous polyurethane with a 100% modulus of 44 MPa at a mass ratio of 99.30:0.70 in water.

[0053] The aqueous polyurethane with a 100% modulus of 1.5 MPa was obtained by uniformly mixing the aqueous polyurethane resin with a 100% modulus of 1.0 MPa and the aqueous polyurethane with a 100% modulus of 44 MPa at a mass ratio of 98.84:1.16 in water.

[0054] The aqueous polyurethane with a 100% modulus of 1.6 MPa was obtained by uniformly mixing the aqueous polyurethane resin with a 100% modulus of 1.0 MPa and the aqueous polyurethane with a 100% modulus of 44 MPa at a mass ratio of 98.60:1.40 in water.

[0055] The aqueous polyurethane with a 100% modulus of 1.8 MPa was obtained by uniformly mixing the aqueous polyurethane resin with a 100% modulus of 1.0 MPa and the aqueous polyurethane with a 100% modulus of 44 MPa at a mass ratio of 98.14:1.86 in water.

[0056] The aqueous polyurethane with a 100% modulus of 2.0 MPa was obtained by uniformly mixing the aqueous polyurethane resin with a 100% modulus of 1.0 MPa and the aqueous polyurethane with a 100% modulus of 44 MPa at a mass ratio of 97.67:2.33 in water.

[0057] The waterborne polyurethane with a 100% modulus of 34 MPa is obtained by uniformly mixing a waterborne polyurethane resin with a 100% modulus of 1.0 MPa and a waterborne polyurethane with a 100% modulus of 44 MPa in water at a mass ratio of 23.26:76.74.

[0058] The waterborne polyurethane with a 100% modulus of 35 MPa is obtained by uniformly mixing a waterborne polyurethane resin with a 100% modulus of 1.0 MPa and a waterborne polyurethane with a 100% modulus of 44 MPa in water at a mass ratio of 20.93:79.07.

[0059] The waterborne polyurethane with a 100% modulus of 36 MPa is obtained by uniformly mixing a waterborne polyurethane resin with a 100% modulus of 1.0 MPa and a waterborne polyurethane with a 100% modulus of 44 MPa in water at a mass ratio of 18.60:81.40.

[0060] The waterborne polyurethane with a 100% modulus of 40 MPa is obtained by uniformly mixing a waterborne polyurethane resin with a 100% modulus of 1.0 MPa and a waterborne polyurethane with a 100% modulus of 44 MPa in water at a mass ratio of 9.30:90.70.

[0061] The ultra-fine fiber base fabric used in the examples is the Series 500R product of Toray Industries, Inc.

[0062] The non-woven fabric used in the examples is a non-woven fabric with a thickness of 1.2 mm from Changshu Yanrui Non-woven Products Co., Ltd., item number: Leather Base Fabric - 07;

[0063] The woven fabric used in the examples is a polyester woven fabric from Dongguan Jihui Textile Co., Ltd., item number: B103 / 8P4736;

[0064] The knitted fabric used in the examples is a polyester knitted fabric with a gram weight of 220 g / m 2 from Tongxiang Jinbolai Knitting Co., Ltd., item number: XX.

[0065] Table 1 The precipitation limit addition amounts of small molecule lubricants with different 100% moduli

[0066] 100% modulus Precipitation limit of small molecule lubricant Remarks 40 MPa 9 parts (relative to 100 parts of polyurethane) Slight oil stains begin to appear at 9 parts 35 MPa 10 parts (relative to 100 parts of polyurethane) Slight oil stains begin to appear at 10 parts 30 MPa 12 parts (relative to 100 parts of polyurethane) Slight oil stains begin to appear at 12 parts 2 MPa More than 30 parts (relative to 100 parts of polyurethane) No oil stains appear when added up to 30 parts 1 MPa More than 30 parts (relative to 100 parts of polyurethane) No oil stains appear when added up to 30 parts

[0067] The term "precipitation limit" in Table 1 refers to the minimum addition ratio of the small molecule lubricant when adjusting the addition ratio of the small molecule lubricant in the waterborne polyurethane, drying at 100 °C and then cooling to 25 °C, and when oil spots or precipitates appear on the surface of the waterborne polyurethane coating.

[0068] Example 1

[0069] A preparation method of a waterborne polyurethane composite coating with high ductility is as follows Figure 1 as shown below:

[0070] (1) Roll-coat the lower-layer waterborne polyurethane slurry on the surface of the ultra-fine fiber base fabric, and dry it at 80 °C for 60 min to cure and form a lower-layer waterborne polyurethane coating 3 with a thickness of 17 μm. Among them, by mass, the lower-layer waterborne polyurethane slurry contains 100 parts of low 100%-modulus waterborne polyurethane resin, 15 parts of triethyl phosphate, and 500 parts of water; the 100%-modulus of the low 100%-modulus waterborne polyurethane resin is 2 MPa.

[0071] (2) Roll-coat the middle-layer waterborne polyurethane slurry on the lower-layer waterborne polyurethane coating 3, and dry it at 80 °C for 60 min to cure and form a middle-layer waterborne polyurethane coating 2 with a thickness of 83 μm. Among them, by mass, the middle-layer waterborne polyurethane slurry contains 100 parts of high 100%-modulus waterborne polyurethane resin, 10 parts of triethyl phosphate, and 500 parts of water; the 100%-modulus of the high 100%-modulus waterborne polyurethane resin is 34 MPa.

[0072] (3) Roll-coat the upper-layer waterborne polyurethane slurry on the middle-layer waterborne polyurethane coating 2, and dry it at 80 °C for 60 min to cure and form an upper-layer waterborne polyurethane coating 1 with the same thickness as the lower-layer waterborne polyurethane coating 3, and then let it stand at 70 °C for 60 h to obtain a waterborne polyurethane composite coating with high ductility. Among them, by mass, the upper-layer waterborne polyurethane slurry contains 100 parts of low 100%-modulus waterborne polyurethane resin, 15 parts of triethyl phosphate, and 500 parts of water; the 100%-modulus of the low 100%-modulus waterborne polyurethane resin is 2 MPa.

[0073] The tensile strength of the prepared waterborne polyurethane composite coating with high ductility is 149 N, and the elongation at break is 324%; the tensile load of the ultra-fine fiber PU synthetic leather is 540 N, and the elongation at break is 89%.

[0074] Taking the waterborne polyurethane composite coating with high ductility as the measurement sample, the concentration change of triethyl phosphate on the upper and lower surfaces and the ductility change are measured, as Figure 2 shown, it is found that the characteristic peak intensity of the phosphate ester group at 1280 cm -1 has a relatively obvious change, showing a decreasing trend after heat treatment, and there is no precipitation phenomenon on the surface of the composite material. Combining that the elongation ratio after heat treatment is 1.24 times higher than that before treatment (261%), it is speculated that triethyl phosphate in the upper and lower layers diffuses into the middle layer.

[0075] Comparative Example 1

[0076] A preparation method of a waterborne polyurethane composite coating is basically the same as that of Example 1, except that by mass parts, the addition amounts of triethyl phosphate in the upper, middle, and lower layers are 12, 10, and 12 parts respectively (that is, the mass parts of triethyl phosphate in the upper and lower waterborne polyurethane coatings are less than 1.5 times that of the middle waterborne polyurethane coating).

[0077] The tensile strength of the obtained waterborne polyurethane composite coating is 153 N, and the elongation at break is 268%; the waterborne polyurethane composite coating is used to prepare an ultrafine fiber PU synthetic leather, and the tensile load of the ultrafine fiber PU synthetic leather is 549 N, and the elongation at break is 58%.

[0078] Comparing Comparative Example 1 with Example 1, it can be found that the elongation at break of the waterborne polyurethane composite coating and the prepared ultrafine fiber PU synthetic leather in Comparative Example 1 is significantly lower than that in Example 1, because the concentration difference of the small molecule lubricant in Comparative Example 1 does not promote inward diffusion.

[0079] Example 2

[0080] A preparation method of a waterborne polyurethane composite coating with high ductility is as follows:

[0081] (1) Roll-coat the lower waterborne polyurethane slurry on the surface of the ultrafine fiber base fabric, and dry it at 80 °C for 60 min to cure and form a lower waterborne polyurethane coating with a thickness of 10 μm; among them, by mass parts, the lower waterborne polyurethane slurry contains 100 parts of low 100% modulus waterborne polyurethane resin (that is, waterborne polyurethane with a high soft segment content), 14 parts of triethyl phosphate, and 70 parts of water; the 100% modulus of the low 100% modulus waterborne polyurethane resin is 1.5 MPa;

[0082] (2) Roll-coat the middle waterborne polyurethane slurry on the lower waterborne polyurethane coating, and dry it at 80 °C for 60 min to cure and form a middle waterborne polyurethane coating with a thickness of 90 μm; among them, by mass parts, the middle waterborne polyurethane slurry contains 100 parts of high 100% modulus waterborne polyurethane resin (that is, waterborne polyurethane with a high hard segment content), 8 parts of triethyl phosphate, and 70 parts of water; the 100% modulus of the high 100% modulus waterborne polyurethane resin is 40 MPa;

[0083] (3) Roll-coat the upper waterborne polyurethane slurry on the middle waterborne polyurethane coating, and dry it at 80 °C for 60 min to cure and form an upper waterborne polyurethane coating with the same thickness as the lower waterborne polyurethane coating, and then let it stand at 50 °C for 48 h to obtain a waterborne polyurethane composite coating with high ductility; among them, by mass parts, the upper waterborne polyurethane slurry contains 100 parts of low 100% modulus waterborne polyurethane resin, 14 parts of triethyl phosphate, and 70 parts of water; the 100% modulus of the low 100% modulus waterborne polyurethane resin is 1 MPa.

[0084] The prepared waterborne polyurethane composite coating with high ductility has a tensile strength of 207 N and an elongation at break of 255%; the tensile load of the microfiber PU synthetic leather is 621 N and the elongation at break is 60%.

[0085] Example 3

[0086] A preparation method of a waterborne polyurethane composite coating with high ductility, the specific steps are as follows:

[0087] (1) Roll-coat and treat the lower-layer waterborne polyurethane slurry on the surface of the superfine fiber base fabric, and dry it at 80 °C for 60 min to cure and form a lower-layer waterborne polyurethane coating with a thickness of 12 μm; among them, by mass, the lower-layer waterborne polyurethane slurry contains 100 parts of 100% modulus waterborne polyurethane resin (i.e., waterborne polyurethane with a high soft segment content), 15 parts of triethyl phosphate, and 250 parts of water; the 100% modulus of the 100% modulus waterborne polyurethane resin is 1 MPa;

[0088] (2) Roll-coat and treat the middle-layer waterborne polyurethane slurry on the lower-layer waterborne polyurethane coating, and dry it at 80 °C for 60 min to cure and form a middle-layer waterborne polyurethane coating with a thickness of 100 μm; among them, by mass, the middle-layer waterborne polyurethane slurry contains 100 parts of 100% modulus waterborne polyurethane resin (i.e., waterborne polyurethane with a high hard segment content), 9 parts of triethyl phosphate, and 250 parts of water; the 100% modulus of the 100% modulus waterborne polyurethane resin is 35 MPa;

[0089] (3) Roll-coat and treat the upper-layer waterborne polyurethane slurry on the middle-layer waterborne polyurethane coating, and dry it at 80 °C for 60 min to cure and form an upper-layer waterborne polyurethane coating with the same thickness as the lower-layer waterborne polyurethane coating, and then let it stand at 60 °C for 50 h to obtain a waterborne polyurethane composite coating with high ductility; among them, by mass, the upper-layer waterborne polyurethane slurry contains 100 parts of 100% modulus waterborne polyurethane resin, 15 parts of triethyl phosphate, and 250 parts of water; the 100% modulus of the 100% modulus waterborne polyurethane resin is 1.5 MPa.

[0090] The prepared waterborne polyurethane composite coating with high ductility has a tensile strength of 191 N and an elongation at break of 298%; the tensile load of the microfiber PU synthetic leather is 601 N and the elongation at break is 76%.

[0091] Example 4

[0092] A preparation method of a waterborne polyurethane composite coating with high ductility, the specific steps are as follows:

[0093] (1) Roll-coat the lower-layer aqueous polyurethane slurry on the surface of the non-woven fabric, and dry it at 80 °C for 60 min to cure and form a lower-layer aqueous polyurethane coating with a thickness of 20 μm. Among them, by mass, the lower-layer aqueous polyurethane slurry contains 100 parts of low 100% modulus aqueous polyurethane resin (i.e., aqueous polyurethane with a high soft segment content), 16 parts of triethyl phosphate, and 100 parts of water. The 100% modulus of the low 100% modulus aqueous polyurethane resin is 1.6 MPa;

[0094] (2) Roll-coat the middle-layer aqueous polyurethane slurry on the lower-layer aqueous polyurethane coating, and dry it at 80 °C for 60 min to cure and form a middle-layer aqueous polyurethane coating with a thickness of 200 μm. Among them, by mass, the middle-layer aqueous polyurethane slurry contains 100 parts of high 100% modulus aqueous polyurethane resin (i.e., aqueous polyurethane with a high hard segment content), 8.5 parts of triethyl phosphate, and 80 parts of water. The 100% modulus of the high 100% modulus aqueous polyurethane resin is 36 MPa;

[0095] (3) Roll-coat the upper-layer aqueous polyurethane slurry on the middle-layer aqueous polyurethane coating, and dry it at 80 °C for 60 min to cure and form an upper-layer aqueous polyurethane coating with the same thickness as the lower-layer aqueous polyurethane coating, and then let it stand at 55 °C for 52 h to obtain a waterborne polyurethane composite coating with high ductility. Among them, by mass, the upper-layer aqueous polyurethane slurry contains 100 parts of low 100% modulus aqueous polyurethane resin, 14 parts of triethyl phosphate, and 100 parts of water. The 100% modulus of the low 100% modulus aqueous polyurethane resin is 1.2 MPa.

[0096] The prepared waterborne polyurethane composite coating with high ductility has a tensile strength of 184 N and an elongation at break of 377%.

[0097] Example 5

[0098] A preparation method of a waterborne polyurethane composite coating with high ductility is as follows:

[0099] (1) Roll-coat the lower-layer aqueous polyurethane slurry on the surface of the woven fabric, and dry it at 80 °C for 60 min to cure and form a lower-layer aqueous polyurethane coating with a thickness of 25 μm. Among them, by mass, the lower-layer aqueous polyurethane slurry contains 100 parts of low 100% modulus aqueous polyurethane resin (i.e., aqueous polyurethane with a high soft segment content), 18 parts of triethyl phosphate, and 200 parts of water. The 100% modulus of the low 100% modulus aqueous polyurethane resin is 1.3 MPa;

[0100] (2) Roll coat the middle - layer aqueous polyurethane slurry on the lower - layer aqueous polyurethane coating, and dry it at 80 °C for 60 min to cure and form a middle - layer aqueous polyurethane coating with a thickness of 250 μm. Among them, by mass fraction, the middle - layer aqueous polyurethane slurry contains 100 parts of 100% modulus aqueous polyurethane resin (i.e., aqueous polyurethane with a high hard - segment content), 8.5 parts of triethyl phosphate, and 180 parts of water; the 100% modulus of the 100% modulus aqueous polyurethane resin is 36 MPa.

[0101] (3) Roll coat the upper - layer aqueous polyurethane slurry on the middle - layer aqueous polyurethane coating, and dry it at 80 °C for 60 min to cure and form an upper - layer aqueous polyurethane coating with the same thickness as the lower - layer aqueous polyurethane coating, and then let it stand at 65 °C for 54 h to obtain an aqueous polyurethane composite coating with high ductility. Among them, by mass fraction, the upper - layer aqueous polyurethane slurry contains 100 parts of low 100% modulus aqueous polyurethane resin, 16 parts of triethyl phosphate, and 200 parts of water; the 100% modulus of the low 100% modulus aqueous polyurethane resin is 1.6 MPa.

[0102] The tensile strength of the obtained aqueous polyurethane composite coating with high ductility is 201 N, and the elongation at break is 398%.

[0103] Example 6

[0104] A preparation method of an aqueous polyurethane composite coating with high ductility, the specific steps are as follows:

[0105] (1) Roll coat the lower - layer aqueous polyurethane slurry on the surface of the knitted fabric, and dry it at 80 °C for 60 min to cure and form a lower - layer aqueous polyurethane coating with a thickness of 50 μm. Among them, by mass fraction, the lower - layer aqueous polyurethane slurry contains 100 parts of low 100% modulus aqueous polyurethane resin (i.e., aqueous polyurethane with a high soft - segment content), 20 parts of triethyl phosphate, and 300 parts of water; the 100% modulus of the low 100% modulus aqueous polyurethane resin is 1.8 MPa.

[0106] (2) Roll coat the middle - layer aqueous polyurethane slurry on the lower - layer aqueous polyurethane coating, and dry it at 80 °C for 60 min to cure and form a middle - layer aqueous polyurethane coating with a thickness of 300 μm. Among them, by mass fraction, the middle - layer aqueous polyurethane slurry contains 100 parts of 100% modulus aqueous polyurethane resin (i.e., aqueous polyurethane with a high hard - segment content), 10 parts of triethyl phosphate, and 280 parts of water; the 100% modulus of the 100% modulus aqueous polyurethane resin is 34 MPa.

[0107] (3) Roll coat the upper aqueous polyurethane slurry on the middle aqueous polyurethane coating, dry it at 80 °C for 60 min to cure and form an upper aqueous polyurethane coating with the same thickness as the lower aqueous polyurethane coating, and then let it stand at 70 °C for 55 h to obtain an aqueous polyurethane composite coating with high ductility; among them, by mass, the upper aqueous polyurethane slurry contains 100 parts of low 100% modulus aqueous polyurethane resin, 18 parts of triethyl phosphate and 300 parts of water; the 100% modulus of the low 100% modulus aqueous polyurethane resin is 1.8 MPa.

[0108] The prepared aqueous polyurethane composite coating with high ductility has a tensile strength of 209 N and an elongation at break of 412%.

Claims

1. A preparation method of an aqueous polyurethane composite coating with high ductility, characterized in that: First, a lower layer of waterborne polyurethane slurry is coated on the surface of the target object, and the lower layer of waterborne polyurethane coating is formed by drying and curing. Then, a middle layer of waterborne polyurethane slurry is coated on the lower layer of waterborne polyurethane coating, and the lower layer of waterborne polyurethane coating is formed by drying and curing. Then, an upper layer of waterborne polyurethane slurry is coated on the middle layer of waterborne polyurethane coating, and the upper layer of waterborne polyurethane coating is formed by drying and curing. Finally, the coating is allowed to stand to obtain a waterborne polyurethane composite coating with high ductility. The static temperature is 50-70℃ and the static time is more than 48h; The middle layer waterborne polyurethane slurry comprises a high 100% modulus waterborne polyurethane resin, a small molecule lubricant and water; The upper waterborne polyurethane slurry comprises a low 100% modulus waterborne polyurethane resin, a small molecule lubricant and water; The lower layer of waterborne polyurethane slurry comprises a low 100% modulus waterborne polyurethane resin, a small molecule lubricant and water; The 100% modulus of the high 100% modulus waterborne polyurethane resin is 34 to 40 MPa, and the 100% modulus of the low 100% modulus waterborne polyurethane resin is 1 to 2 MPa; The high 100% modulus waterborne polyurethane resin has the same monomer units as the low 100% modulus waterborne polyurethane resin; In the middle layer of aqueous polyurethane slurry, 8 to 10 parts by mass of small molecule lubricant are added for every 100 parts by mass of aqueous polyurethane resin with a high modulus of 100%; the mass fractions of small molecule lubricant added for every 100 parts by mass of aqueous polyurethane resin with a low modulus of 100% in the upper layer of aqueous polyurethane slurry and the lower layer of aqueous polyurethane slurry are at least 1.5 times the mass fractions of small molecule lubricant added for every 100 parts by mass of aqueous polyurethane resin with a low modulus of 100% in the middle layer of aqueous polyurethane slurry.

2. The preparation method of a waterborne polyurethane composite coating with high ductility according to claim 1, characterized in that, The thickness ratio of the upper water-based polyurethane coating layer to the middle water-based polyurethane coating layer is 10:90 to 17:83; the thickness of the lower water-based polyurethane coating layer is the same as the thickness of the upper water-based polyurethane coating layer.

3. The preparation method of a waterborne polyurethane composite coating with high ductility according to claim 2, characterized in that, The thickness of the middle layer waterborne polyurethane coating is 50 to 300 μm, and the thickness of the upper layer waterborne polyurethane coating is 10 to 50 μm.

4. The preparation method of a waterborne polyurethane composite coating with high ductility according to claim 1, characterized in that, The middle layer of aqueous polyurethane slurry comprises, by weight, 100 parts of aqueous polyurethane resin with high 100% modulus, 8 to 10 parts of small molecule lubricant and 70 to 500 parts of water; the upper layer of aqueous polyurethane slurry comprises, by weight, 100 parts of aqueous polyurethane resin with low 100% modulus, 12 to 22 parts of small molecule lubricant and 70 to 500 parts of water; the lower layer of aqueous polyurethane slurry comprises, by weight, 100 parts of aqueous polyurethane resin with low 100% modulus, 12 to 22 parts of small molecule lubricant and 70 to 500 parts of water.

5. The preparation method of a waterborne polyurethane composite coating with high ductility according to claim 1, characterized in that, The small molecule lubricant is triethyl phosphate.

6. The preparation method of a waterborne polyurethane composite coating with high ductility according to claim 1, characterized in that, The coating method is roller coating.

7. The preparation method of a waterborne polyurethane composite coating with high ductility according to claim 1, characterized in that, The target object is microfiber-based fabric, non-woven fabric, woven fabric or knitted fabric.

8. Use of the waterborne polyurethane composite coating with high ductility prepared by the method according to any one of claims 1 to 6, characterized in that: Used to prepare microfiber PU synthetic leather, the target material for coating is microfiber base cloth.

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