Low-temperature forming polyurethane resin and leather product thereof

Abstract

The present application is a kind of low-temperature forming polyurethane resin and its leather product, the polyurethane resin, comprising the reaction product of polyisocyanate, polyol mixture and chain extender;Wherein, the polyol mixture contains polyester polyol, the polyester polyol includes mass ratio of 4:1~1:2 linear aliphatic polyester polyol and branched aliphatic polyester polyol. The low-temperature forming polyurethane resin prepared leather product can significantly improve the degree of phase separation of polyurethane internal soft and hard segment micro area, the resin as synthetic leather surface layer material, with polyurethane shoe sole can have good bonding strength at lower injection temperature, not easy to delaminate, and good heat aging resistance, low temperature resistance.

Description

Technical Field

[0001] This invention relates to the field of polyurethane technology, and more specifically to a polyurethane resin for low-temperature molding, and leather products made using the low-temperature suitable polyurethane resin. Background Technology

[0002] Polyurethane synthetic leather is widely used in the clothing, footwear, bag, and furniture industries. In footwear, the sole is typically bonded to the upper via injection molding. However, because polyurethane soles are processed at relatively low temperatures (typically between 40-60℃), ordinary polyurethane synthetic leather struggles to bond with the sole at these low temperatures, easily leading to delamination. One of the current challenges facing the footwear synthetic leather industry is how to ensure good adhesion between polyurethane synthetic leather and the sole at these low temperatures while maintaining excellent mechanical properties, resistance to heat and oxygen aging, and low-temperature resistance. Summary of the Invention

[0003] Technical Problem: The purpose of this invention is to overcome the above defects and provide a polyurethane resin for low-temperature molding. Leather products made from this polyurethane resin can significantly improve the degree of phase separation between the soft and hard micro-regions inside the polyurethane. When this resin is used as a surface layer material for synthetic leather, it can have good bonding strength with the polyurethane shoe sole at a lower injection temperature, is not easy to delaminate, and has good resistance to heat and oxygen aging and low-temperature performance.

[0004] Technical solution: The present invention provides a polyurethane resin for low-temperature molding comprising a reaction product of a polyisocyanate, a polyol mixture and a chain extender; wherein the polyol mixture contains polyester polyols, and the polyester polyols include linear aliphatic polyester polyols and branched aliphatic polyester polyols in a mass ratio of 4:1 to 1:2.

[0005] The polyisocyanate includes one or more of the isocyanate compounds, such as toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isoflurone diisocyanate, dimethylbiphenyl diisocyanate, naphthalene diisocyanate, terephthalic diisocyanate, dicyclohexylmethane diisocyanate, and / or derivatives and / or modified polymers.

[0006] The chain extender includes C2-C6 diols, including one or more of ethylene glycol, diethylene glycol, propylene glycol, butanediol, pentanediol, neopentanediol, and hexanediol.

[0007] The linear aliphatic polyester polyol comprises a polyol obtained by reacting at least one linear aliphatic diol and at least one linear aliphatic dicarboxylic acid, wherein the number-average molecular weight of the linear aliphatic polyester polyol is 800-2000 g / mol.

[0008] The branched aliphatic polyester polyol comprises a polyol obtained by reacting at least one branched aliphatic diol and at least one straight-chain aliphatic dicarboxylic acid, and the number-average molecular weight of the branched aliphatic polyester polyol is 800-2000 g / mol.

[0009] The straight-chain aliphatic diols include C2-C8 straight-chain diols, including one or more of ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, heptanediol, octanediol, and nonanediol.

[0010] The aforementioned straight-chain aliphatic dicarboxylic acids include C2-C8 straight-chain dicarboxylic acids, including one or more of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, and azelaic acid.

[0011] The branched aliphatic diols contain no more than two carbon atoms in their branched structures, including 2-methyl-1,3-propanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, and 2,2,4-trimethyl-1,3-pentanediol.

[0012] The polyol mixture further contains an isoprene polymer, which includes hydroxyl-terminated polyisoprene and / or polyisoprene-grafted polyether copolymers; the hydroxyl-terminated polyisoprene has a number-average molecular weight of 1000-2000 g / mol; the polyisoprene-grafted polyether copolymer includes copolymers obtained by grafting isoprene with polyether polyols, with a number-average molecular weight of 1000-4000 g / mol, wherein the polyether polyols include polyethylene oxide polyols and / or polypropylene oxide polyols.

[0013] The molar ratio of isocyanate content to the total content of isocyanate-reactive groups in the polyisocyanate is 1:0.95 to 1:1.05.

[0014] The polyurethane resin is used as a surface material in a leather product.

[0015] Beneficial effects: The polyurethane resin for low-temperature molding of the present invention, by utilizing the combination of polyols with different structures, can significantly improve the degree of phase separation of soft and hard segments in the micro-regions of polyurethane. When this resin is used as a surface layer material for synthetic leather, it can have good bonding strength with polyurethane shoe soles at lower injection temperatures, is not easy to delaminate, and has good resistance to heat and oxygen aging and low-temperature performance. Detailed Implementation

[0016] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0017] The present invention discloses a polyurethane resin for low-temperature molding, comprising a reaction product of a polyisocyanate, a polyol mixture, and a chain extender; wherein the polyol mixture contains a polyester polyol, and the polyester polyol mixture contains linear aliphatic polyester polyol and branched aliphatic polyester polyol in a mass ratio of 4:1 to 1:2.

[0018] The linear aliphatic polyester polyol comprises a polyol obtained by reacting at least one linear aliphatic diol and at least one linear aliphatic dicarboxylic acid, wherein the number-average molecular weight of the linear aliphatic polyester polyol is 800-2000 g / mol.

[0019] The branched aliphatic polyester polyol comprises a polyol obtained by reacting at least one branched aliphatic diol and at least one straight-chain aliphatic dicarboxylic acid, wherein the number-average molecular weight of the branched aliphatic polyester polyol is 800-2000 g / mol.

[0020] The straight-chain aliphatic diols include C2-C8 straight-chain diols, including one or more of ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, heptanediol, octanediol, and nonanediol.

[0021] Preferably, the linear aliphatic diol includes one or more of 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol.

[0022] The aforementioned straight-chain aliphatic dicarboxylic acids include C2-C8 straight-chain dicarboxylic acids, including one or more of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, octanoic acid, and azelaic acid.

[0023] Preferably, the linear aliphatic dicarboxylic acid has an even number of carbon atoms, including succinic acid, adipic acid, pimelic acid, and azelaic acid;

[0024] In some embodiments of the present invention, the straight-chain aliphatic dicarboxylic acid is adipic acid;

[0025] The branched aliphatic diols mentioned herein contain branched structures with no more than two carbon atoms, including 2-methyl-1,3-propanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, and 2,2,4-trimethyl-1,3-pentanediol.

[0026] Preferably, the branched aliphatic diol includes one or a combination of neopentyl glycol and 2-methyl-1,3-propanediol;

[0027] The polyisocyanate includes one or more of the isocyanate compounds, such as toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isoflurone diisocyanate, dimethylbiphenyl diisocyanate, naphthalene diisocyanate, terephthalic diisocyanate, dicyclohexylmethane diisocyanate, and derivatives and / or modified polymers.

[0028] In some embodiments of the present invention, the polyisocyanate includes diphenylmethane diisocyanate (MDI) and / or carbodiimide-urea ketimide modified diphenylmethane diisocyanate (carbodiimide modified MDI).

[0029] The chain extender includes C2-C6 diols, including one or more of ethylene glycol EG, diethylene glycol DEG, propylene glycol PG, butanediol BDO, pentylene glycol, neopentylene glycol NPG, and hexanediol PDO;

[0030] Furthermore, in some embodiments of the present invention, the low-temperature applicable polyurethane resin is obtained by reacting components in the following mass percentages:

[0031] Polyisocyanates 20-55%;

[0032] Polyol mixture 30-70%;

[0033] Chain extender 3-15%;

[0034] Preferably, the polyol mixture further contains an isoprene polymer;

[0035] The low-temperature suitable polyurethane resin comprises a reaction product of polyisocyanate, polyester polyol and isoprene polymer and chain extender;

[0036] The isoprene polymers include hydroxyl-terminated polyisoprene and / or polyisoprene-grafted polyether copolymers;

[0037] Furthermore, the number-average molecular weight of the terminal hydroxyl polyisoprene is 1000–2000 g / mol;

[0038] Furthermore, the polyisoprene-grafted polyether copolymer includes a copolymer obtained by grafting isoprene with a polyether polyol, with a number average molecular weight of 1000-4000 g / mol, wherein the polyether polyol includes polyethylene oxide polyol and / or polypropylene oxide polyol.

[0039] In some embodiments of the present invention, the isoprene-grafted polyether copolymer can be obtained by reacting isoprene monomer with polyether polyol;

[0040] Furthermore, in some embodiments of the present invention, the low-temperature suitable polyurethane resin is obtained by reacting components in the following mass percentages:

[0041]

[0042] The method for preparing polyurethane resin for low-temperature molding includes: reacting a mixture of polyisocyanate, polyol and chain extender in the presence of a solvent to obtain a polyurethane resin solution suitable for low-temperature molding.

[0043] The solvent includes one or more of dimethylformamide, dimethylacetamide, ethyl acetate, methyl ethyl ketone, and toluene; preferably, dimethylformamide.

[0044] The viscosity of the solution is controlled at 100–200 Pa·s / 25℃.

[0045] In some embodiments of the present invention, the molar ratio of the isocyanate content to the total content of groups reactive with isocyanate in the polyisocyanate is 1:0.95 to 1:1.05.

[0046] Preferably, the low-temperature suitable polyurethane resin may also contain one or more of the following common additives in the art: antioxidants, ultraviolet absorbers, and leveling agents.

[0047] The method for preparing the low-temperature applicable polyurethane resin can be carried out by integral polymerization or stepwise prepolymerization. For example, in integral polymerization, a mixture of polyisocyanate, polyol and chain extender is directly added to a solvent and reacted fully to obtain a solution containing the low-temperature applicable polyurethane resin; in stepwise prepolymerization, a portion of the polyisocyanate and polyol mixture is first added to a solvent to react and obtain a prepolymer, and then a chain extender and the remaining polyisocyanate are added to the solution to continue the reaction to obtain a solution containing the low-temperature applicable polyurethane resin.

[0048] In some embodiments of the present invention, the method for preparing low-temperature applicable polyurethane resin employs a stepwise prepolymerization method:

[0049] First, a mixture of polyisocyanate and polyol is added to a solvent and stirred at 50-60°C to obtain a prepolymer. Then, a chain extender and the remaining polyisocyanate are added, and the temperature is raised to 70-80°C to continue the reaction. When the solution viscosity reaches 160-200 Pa·s / 75°C, polyurethane is obtained. A certain amount of solvent and a terminator can be selectively added to terminate the reaction and stirred thoroughly. The solution containing the low-temperature suitable polyurethane resin is then obtained with a viscosity of 100-160 Pa·s / 25°C.

[0050] Preferably, the isoprene polymer and the polyester polyol are mixed together to obtain a polyol mixture, which is then reacted with the polyisocyanate.

[0051] In the above preparation process, catalysts can be selectively added to increase the reaction rate, such as organobismuth catalysts and / or organotin catalysts; in the later stage of the reaction, terminators can be selectively added to adjust the degree of reaction, avoid excessive NCO residue, and control the solution viscosity, such as small molecule monohydric alcohols.

[0052] The leather products prepared using the present invention contain the low-temperature applicable polyurethane resin as the surface material.

[0053] As an example, the method for preparing the leather product is as follows:

[0054] A low-temperature suitable polyurethane resin solution is coated onto release paper as a top layer resin. After drying at 90–140°C for 2–5 minutes, a polyurethane resin top layer material is obtained. An intermediate layer resin is coated onto the top layer resin and kept at 100–120°C for 60–90 seconds to obtain a semi-cured intermediate layer. A base fabric is then attached to the semi-cured intermediate layer and cured at 120–150°C for 3–7 minutes. After separating the release paper, a leather product is obtained.

[0055] The principles and features of the present invention are described below with reference to implementation examples. The examples are provided to help those skilled in the art better understand the present invention.

[0056] Examples 1 to 7 are shown in the table below:

[0057]

[0058]

[0059] Examples 8-15 are shown in the table below:

[0060]

[0061]

[0062] Comparative Examples 1-5 are shown in the table below:

[0063]

[0064]

[0065] The polyurethane resin solutions in the above examples and comparative examples were prepared using the same stepwise prepolymerization method. The solid content of the solutions was controlled at 30%, and the molar ratio of isocyanate content to the total content of isocyanate-reactive groups in the polyisocyanate was maintained in the range of 1:0.95 to 1:1.05.

[0066] Preparation of test samples:

[0067] (1)Synthetic leather

[0068] A low-temperature suitable polyurethane resin solution was coated onto release paper as the top layer resin. After drying at 120°C for 5 minutes, a polyurethane resin top layer material was obtained. An intermediate layer resin was coated onto the top layer resin and kept at 105°C for 60 seconds to obtain a semi-cured intermediate layer. The base fabric was then attached to the semi-cured intermediate layer and cured at 140°C for 5 minutes. After separating the release paper, a synthetic leather sample was obtained.

[0069] (2) Injection Molded Shoes

[0070] A shoe last fitted with synthetic leather is placed into a shoe mold cavity, and polyurethane raw material at a temperature of 50-60℃ is injected into the mold through an automatic injection machine to form the shoe sole. After pressing, drying and curing, the injection-molded shoe is obtained.

[0071] The above samples were subjected to the following performance tests:

[0072] (1) Low temperature folding resistance

[0073] The prepared leather samples were subjected to a low-temperature flexural endurance test at -15℃, in accordance with QB / T 2714.

[0074] (2) Thermo-oxidative aging

[0075] Place the prepared leather sample in an oven at 130℃ for 72 hours and observe whether the surface of the leather sample is sticky. The stickier the surface, the worse its heat and oxygen aging resistance.

[0076] (3) Flexibility resistance

[0077] Refer to GB / T3903.1 to test whether the leather sample and the sole of the injection-molded shoe separate after reaching the specified number of flexing cycles.

[0078] (4) Peel strength

[0079] According to GB / T 21396, tensile testing machines are used to test injection molded shoes. The higher the peel strength, the stronger the adhesion between the synthetic leather and the polyurethane sole.

[0080] (5) Jungle stripping strength

[0081] The injection-molded shoes were placed in a constant temperature and humidity chamber at (70±2)℃ and (95±5)% relative humidity for one week, and the peel strength between the synthetic leather and the polyurethane sole was tested using a tensile testing machine in accordance with GB / T21396.

[0082] The performance test results of the samples are shown in the table below:

[0083]

[0084]

Claims

1. A polyurethane resin for low-temperature molding, characterized in that, This polyurethane resin is a reaction product obtained by reacting polyisocyanate, polyol mixture, and chain extender. The polyol mixture contains polyester polyol and isoprene polymer, wherein the polyester polyol is a straight-chain aliphatic polyester polyol and a branched aliphatic polyester polyol with a mass ratio of 4:1 to 1:

2. The isoprene polymer is a hydroxyl-terminated polyisoprene or a polyisoprene-grafted polyether copolymer. In the reaction raw materials of polyurethane resin, the mass percentage of isoprene polymer is 10~23.34%; The number-average molecular weight of the hydroxyl-terminated polyisoprene is 1000~2000 g / mol; The polyisoprene-grafted polyether copolymer includes a copolymer obtained by grafting isoprene with a polyether polyol, with a number average molecular weight of 1000~4000 g / mol, wherein the polyether polyol is a polyethylene oxide polyol or a polypropylene oxide polyol.

2. The polyurethane resin for low-temperature molding according to claim 1, characterized in that, The polyisocyanate is one of toluene diisocyanate, diphenylmethane diisocyanate, hexamethylene diisocyanate, isoflurone diisocyanate, dimethylbiphenyl diisocyanate, naphthalene diisocyanate, terephthalic diisocyanate, or dicyclohexylmethane diisocyanate.

3. The polyurethane resin for low-temperature molding according to claim 1, characterized in that, The chain extender includes C2-C6 diols, including one or more of ethylene glycol, diethylene glycol, propylene glycol, butanediol, pentylene glycol, neopentylene glycol, and hexanediol.

4. The polyurethane resin for low-temperature molding according to claim 1, characterized in that, The linear aliphatic polyester polyol comprises a polyol obtained by reacting at least one linear aliphatic diol and at least one linear aliphatic dicarboxylic acid, wherein the number-average molecular weight of the linear aliphatic polyester polyol is 800~2000 g / mol.

5. The polyurethane resin for low-temperature molding according to claim 1, characterized in that, The branched aliphatic polyester polyol comprises a polyol obtained by reacting at least one branched aliphatic diol and at least one straight-chain aliphatic dicarboxylic acid, and the number-average molecular weight of the branched aliphatic polyester polyol is 800~2000 g / mol.

6. The polyurethane resin for low-temperature molding according to claim 4, characterized in that, The straight-chain aliphatic diols include C2-C8 straight-chain diols, including one or more of ethylene glycol, propylene glycol, butanediol, pentanediol, hexanediol, heptahydrin, and octanediol. The aforementioned straight-chain aliphatic dicarboxylic acids include C2-C8 straight-chain dicarboxylic acids, including one or more of oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, and octanoic acid.

7. The polyurethane resin for low-temperature molding according to claim 5, characterized in that, The branched aliphatic diols contain no more than two carbon atoms in their branched structures, including 2-methyl-1,3-propanediol, neopentyl glycol, 3-methyl-1,5-pentanediol, and 2,2,4-trimethyl-1,3-pentanediol.

8. The method for preparing polyurethane resin for low-temperature molding according to claim 1, characterized in that, The molar ratio of isocyanate content to the total content of groups reactive with isocyanate in the polyisocyanate is 1:0.95 to 1:1.

05.

9. An application of the polyurethane resin for low-temperature molding as described in claim 1, characterized in that, The polyurethane resin is used as a surface material in a leather product.

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