Patent Description:
With a plastic as a matrix, a large number of bubbles are filled in the matrix by a physical or chemical method to obtain a polymer foam material. Due to a series of advantages such as low density, heat and sound insulation, high specific strength, and buffering, foam materials are widely used in fields of packaging, industry, agriculture, transportation, military, aerospace, commodities, and the like. Commonly used foam plastics include polyurethane (PU) flexible and rigid foam plastics, polystyrene (PS) foam plastics, polyethylene (PE) foam plastics, polypropylene (PP) foam plastics, etc. However, PU foam plastics are prone to having residual isocyanate during a foaming process, which is harmful to the human body and makes the foam materials unable to be recycled. PS foam plastic products are difficult to degrade and easily cause white pollution. The United Nations Environment Programme (UNEP) has decided to stop the use of PS foam plastic products. PE foam plastics have poor high-temperature resistance and are not suitable for applications in high temperature fields.

TPU has the merits of having wide hardness range, excellent wear resistance, mechanical strength, water resistance, oil resistance, chemical resistance, and mold resistance, and being environmentally friendly and recyclable. Foaming TPU particles are filled into a mold, and then subjected to hot forming with water vapor to obtain a molded foam product. Such a product not only retains the excellent performance of the original matrix, but also has excellent resilience, shape diversity, low density, which can be used in a wide temperature range. Based on the above advantages, TPU foam materials show very promising application prospects in many industrial fields (automobiles and packaging materials) and daily life fields (shoe materials, pillows, and mattresses).

Expanded thermoplastic polyurethane (E-TPU) foam material has been disclosed in patent documents <CIT>, <CIT>, <CIT>, <CIT>, and <CIT>, and a TPU resin raw material used is generally synthesized from an aromatic isocyanate such as methylene diphenyl diisocyanate (MDI). TPU foam material products will undergo long-term sunlight exposure when used outdoors. When a TPU resin foam material synthesized from an aromatic isocyanate such as MDI is under the action of ultraviolet (UV) rays, a dicarbamate bridge structure of an aromatic ring will be automatically oxidized into a quinone-imine bond or an azo compound, which is accompanied by the yellowing of a product and the decrease of mechanical properties. In patented technologies currently disclosed, a large amount of a UV-resistant additive is added to a TPU resin raw material to improve the yellowing resistance of a material, but these technologies still have the following defects: (<NUM>) The addition of the anti-UV additive cannot essentially change the yellowing nature of TPU, and with the extension of a service time of a product, the effect of the anti-UV additive will gradually decrease, which ultimately leads to greatly reduced product performance and shortened service life. (<NUM>) The anti-UV additive is usually added in a process of preparing a TPU material or subsequently modifying the TPU material. In particular, for fields that require high yellowing resistance, such as the field of shoe materials, a large amount of the anti-UV additive needs to be added to extend a service life of a product. However, the addition of a large amount of the anti-UV additive will greatly affect the stability of a TPU synthesis process and the final performance of subsequent TPU foam particles. Therefore, the development of a TPU foam material with excellent yellowing resistance is an urgent problem to be solved at present.

<CIT> provides thermoplastic polyurethane foaming particles containing thermoplastic polyurethane as a substrate resin and a pigment, and a hindered phenol compound, a benzotriazole compound and a hindered amine compound which are blended in the substrate resin, and a thermoplastic polyurethane foaming particle molded body obtained by molding the thermoplastic polyurethane foaming particles.

In order to solve the above technical problems, the present disclosure provides a yellowing-resistant TPU foam material and a preparation method thereof as set out in the appended set of claims. The prepared yellowing-resistant TPU foam material has excellent yellowing resistance, controllable foaming density, and uniform foam cell size.

The present disclosure adopts the following technical solutions to solve the above technical problems: A yellowing-resistant TPU foam material is provided, including a TPU prepared by subjecting an aliphatic diisocyanate, a chain extender, a polyol, an antioxidant, a UV absorber, and a UV light stabilizer to a reaction as defined in claim <NUM>. The TPU has a softening point of <NUM> to <NUM> which is determined by a rheometer, preferably <NUM> to <NUM>, and particularly preferably <NUM> to <NUM>; a Shore hardness of <NUM> A to <NUM> A A which determined by the Shore A durometer, preferably <NUM> A to <NUM> A, and particularly preferably <NUM> A to <NUM> A; and a melt index of <NUM> to <NUM>/<NUM> which obtained by a <NUM> load test at <NUM> according to ASTM D1238.

The yellowing-resistant TPU foam material of the present disclosure has the following beneficial effects:
In a <NUM> long-term accelerated test, the foam material prepared by the present disclosure undergoes no yellowing and exhibits a yellowing resistance grade of <NUM>, indicating very excellent yellowing resistance, which is significantly better than that of the current traditional TPU foam material. The obtained foam material has a density of <NUM>/cm<NUM> to <NUM>/cm<NUM>, a controllable foaming density, a uniform foam cell size, and prominent resilience and mechanical strength. Under long-term light exposure, an aliphatic TPU will not undergo automatic oxidation of a carbamate bridge structure into a quinone-imine bond or an azo compound, which can improve the yellowing resistance.

The following improvements can be further made by the present disclosure based on the above technical solution.

Further, the aliphatic diisocyanate include one from the group consisting of hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), xylylene diisocyanate (XDI) or hydrogenated phenylmethane diisocyanate (H<NUM>MDI), cyclohexyl dimethylene diisocyanate (H<NUM>XDI), and cyclohexyl diisocyanate, or a mixture of two or more therefrom.

The above-mentioned further solution has the following beneficial effect: The above-mentioned raw materials can make the foaming material have excellent yellowing resistance.

Further, the chain extender include one from the group consisting of <NUM>,<NUM>-ethylene glycol, <NUM>,<NUM>-propylene glycol, <NUM>,<NUM>-butylene glycol, <NUM>,<NUM>-hexylene glycol, and cyclohexanedimethanol (CHDM), or a mixture of two or more therefrom.

The above-mentioned further solution has the following beneficial effect: The use of the above-mentioned raw material as the chain extender can improve the mechanical properties of the yellowing-resistant TPU foam material.

Further, an amount of the antioxidant is <NUM>% to <NUM>% of a total amount of the TPU, and the antioxidant is a hindered phenol antioxidant or a phosphite antioxidant.

Further, an amount of the UV absorber is <NUM>% to <NUM>% of the total amount of the TPU, and the UV absorber is a benzotriazole UV absorber, a formamidine UV absorber, a triazine UV absorber, or a benzophenone UV absorber.

Further, an amount of the UV light stabilizer may be <NUM>% to <NUM>% of the total amount of the TPU, and the UV light stabilizer may be a hindered amine light stabilizer.

The above-mentioned further solution has the following beneficial effect: The yellowing resistance can be further improved.

Further, the polyol include one from the group consisting of a polycarbonate polyol, a polycaprolactone (PCL) polyol, and a polyether polyol with a functionality of <NUM> to <NUM>, or a mixture of two or more therefrom.

The above-mentioned further solution has the following beneficial effect: The resilience of the prepared TPU foam material can be improved.

The present disclosure also provides a preparation method of a yellowing-resistant TPU foam material, including: subjecting a TPU to a physical foaming process to obtain the yellowing-resistant TPU foam material, where the TPU foam material has a density of <NUM>/cm<NUM> to <NUM>/cm<NUM> and a foam cell size of <NUM> to <NUM>.

The preparation method of a yellowing-resistant TPU foam material according to the present disclosure has the following beneficial effect: The preparation method can ensure that the TPU foam material prepared by foaming the TPU has excellent mechanical properties.

Further, the physical foaming process may preferably include: adding <NUM> parts by weight of the TPU, <NUM> to <NUM> parts by weight of a physical foaming agent, and <NUM> to <NUM> parts by weight of water to a pressure-resistant vessel, and stirring a resulting mixture to form a suspension; heating the suspension to <NUM> to <NUM>, making a pressure to reach <NUM> bar to <NUM> bar, and keeping the suspension at the temperature and the pressure for <NUM> to <NUM>; and discharging the suspension in the pressure-resistant vessel into an atmospheric environment to obtain the yellowing-resistant TPU foam material.

The above-mentioned further solution has the following beneficial effect: By heating the pre-mixture and controlling the pressure to realize rapid foaming, an obtained TPU foam material has excellent tensile strength and resilience.

Further, the physical foaming process may also include the following: adding <NUM> parts by weight of the TPU into an extruder for melting, and injecting a physical foaming agent at a tail end of the extruder; controlling a pressure at <NUM> bar to <NUM> bar, an extruder die temperature at <NUM> to <NUM>, and a die pressure at <NUM> bar to <NUM> bar; and extruding through a die to obtain the yellowing-resistant TPU foam material.

The above-mentioned further solution has the following beneficial effect: With the extruder, the TPU can be directly made into foam particles or foam plates, which has a wide application range.

Further, the physical foaming process may also include: adding <NUM> parts by weight of the TPU into a pressure-resistant vessel, and injecting <NUM> to <NUM> parts by weight of a physical foaming agent into the pressure-resistant vessel; making a pressure to reach <NUM> bar to <NUM> bar and keeping the pressure for <NUM> to <NUM> to make the physical foaming agent reach a dissolution equilibrium in the TPU; and heating the material with dissolution equilibrium at <NUM> to <NUM> for foaming to obtain the yellowing-resistant TPU foam material.

The above-mentioned further solution has the following beneficial effect: Pressurization is conducted first and then foaming is conducted, such that the foaming agent can completely enter the TPU, which leads to prominent foaming effect and resilience.

Further, the physical foaming agent may include one from the group consisting of nitrogen, carbon dioxide, air, methane, propane, butane, or pentane, or a mixture of two or more therefrom.

The above-mentioned further solution has the following beneficial effect: A prominent foaming effect can be achieved.

The present disclosure also provides use of the TPU foam material described above in the field of flexible foams, where the TPU foam material is particularly suitable for shoe materials, floor coverings, transportation parts, toys, and the like.

The principles and features of the present disclosure will be described below, and the examples given are used merely to explain the present disclosure, rather than limit the scope of the present disclosure.

A yellowing-resistant TPU foam material is provided, including a TPU prepared by subjecting an aliphatic diisocyanate, a chain extender, a polyol, an antioxidant, a UV absorber, and a UV light stabilizer to a reaction as set out in the appended set of claims.

Specifically, the TPU is prepared as follows: an aliphatic diisocyanate, a polyol with a molar mass of <NUM>/mol to <NUM>,<NUM>/mol, and a chain extender with a molar mass of <NUM>/mol to <NUM>/mol are mixed, and a resulting mixture is subjected to a reaction at <NUM> to <NUM> through a one-pot method or a prepolymer method in an extrusion reaction extruder to produce the TPU.

A modulation index of each component in the above reaction for preparing the TPU is <NUM> to <NUM>, which is specifically a ratio of a mole number of isocyanate in the aliphatic diisocyanate to a mole number of groups in the chain extender and polyol that are reactive to isocyanate.

The TPU has a softening point of <NUM> to <NUM>, which is determined by the Shimadzu CFT-<NUM> series rheometer; a Shore hardness of <NUM> A to <NUM> A, which is determined by the Shore A durometer; and a melt index of <NUM> to <NUM>/<NUM>, which is obtained by a <NUM> load test at <NUM> according to ASTM D1238. The foam material has a yellowing resistance grade of <NUM> to <NUM>, which is obtained at a lamp irradiation intensity of <NUM> W/m<NUM>/nm of a <NUM> UVA lamp according to ASDM-D1148 or a <NUM> irradiation test according to HG/T3689-2001A. According to ISO <NUM>-A02: <NUM>, the yellowing resistance grade is assessed under the standard light source D65, where grade <NUM> means that a material undergoes no yellowing, grade <NUM> means that a material only undergoes slight yellowing, and grade <NUM> means that a material undergoes very severe yellowing.

Specifically, the aliphatic diisocyanate is HDI, IPDI, XDI or hydrogenated phenylmethane diisocyanate (H<NUM>MDI), cyclohexyl dimethylene diisocyanate (H<NUM>XDI), and cyclohexyl diisocyanate.

The chain extender is an aliphatic, aromatic, or alicyclic glycol compound with a molar mass of <NUM>/mol to <NUM>/mol; specifically, the chain extender is <NUM>,<NUM>-ethylene glycol, <NUM>,<NUM>-propylene glycol, <NUM>,<NUM>-butylene glycol, <NUM>,<NUM>-hexylene glycol, or CHDM with <NUM> to <NUM> C atoms, or the chain extender may be <NUM>-hydroxyethyl ether, m-phenylene glycol bis(hydroxyethyl)ether, or <NUM>,<NUM>-dihydroxymethylcyclohexane; and
preferably, the chain extender may be <NUM>,<NUM>-butylene glycol.

An amount of the antioxidant is preferably <NUM>% to <NUM>% and more preferably <NUM>% to <NUM>% of a total amount of the TPU, and the antioxidant is preferably a hindered phenol antioxidant or a phosphite antioxidant, specifically Irganox1010, Irganox1076, Irganox1098, Irganox3114, Irganox126, Irgafos168, or Irgafos <NUM> of BASF. An amount of the UV absorber is preferably <NUM>% to <NUM>% and more preferably <NUM>% to <NUM>% of the total amount of the TPU, and the UV absorber is preferably be a benzotriazole UV absorber, a formamidine UV absorber, a triazine UV absorber, or a benzophenone UV absorber, specifically TinuvinP, Tinuvin327, Tinuvin328, Tinuvin329, Tinuvin234, Tinuvin312, TinuvinUV-<NUM>, or TinuvinUV-<NUM> of BASF. An amount of the UV light stabilizer is preferably <NUM>% to <NUM>% and more preferably <NUM>% to <NUM>% of the total amount of the TPU, and the UV light stabilizer is preferably a hindered amine light stabilizer, specifically Tinuvin571, Tinuvin770, Tinuvin622, Tinuvin944, or Tinuvin144.

The polyol is one from the group consisting of a polycarbonate polyol, a polyester polyol, and a polyether polyol with a functionality of <NUM> to <NUM>, or a mixture of two or more therefrom, where the polyether polyol preferably has a molar mass of <NUM>/mol to <NUM>,<NUM>/mol and the polyether polyol preferably has a molar mass of <NUM>/mol to <NUM>,<NUM>/mol.

Preferably, the polyol is a polyether polyol with a functionality of <NUM>. Specifically, the polyether polyol more preferably is poly(ethylene glycol adipate) (PEA), poly(diethylene glycol adipate) (PDA), poly(butylene glycol adipate) (PBA), poly(propylene glycol adipate) (PPA), polypropylene glycol (PPG), or poly(tetramethylene ether)glycol (PTMEG); and even more preferably a mixture of PBA and PTMEG.

A preparation method of a yellowing-resistant TPU foam material included: <NUM> of HDI, <NUM> of <NUM>,<NUM>-butylene glycol, <NUM> of a mixture of PBA and PTMEG in a mass ratio of <NUM>:<NUM>, a hindered phenol antioxidant, a benzotriazole UV absorber, and a hindered amine light stabilizer were added into a twin-screw reaction extruder and subjected to a reaction at <NUM> to <NUM> to obtain a TPU, where the benzotriazole UV absorber was TinuvinP and added at a specific amount <NUM>% of a total amount of the TPU; the hindered amine light stabilizer was Tinuvin571 and added at a specific amount <NUM>% of the total amount of the TPU; and the TPU particles had a softening point of <NUM>, a Shore hardness of <NUM> A, and a melt index of <NUM>/<NUM>;.

A preparation method of a yellowing-resistant TPU foam material included: <NUM> of IPDI, <NUM> of <NUM>,<NUM>-butylene glycol, <NUM> of PTMEG, a hindered phenol antioxidant, a benzotriazole UV absorber, and a hindered amine light stabilizer were added into a twin-screw extruder and subjected to a reaction at <NUM> to <NUM> to obtain a TPU, where the hindered phenol antioxidant was Irganox1010 and added at a specific amount <NUM>% of a total amount of the TPU; the benzotriazole UV absorber was Tinuvin <NUM> and added at a specific amount <NUM>% of the total amount of the TPU; the hindered amine light stabilizer was Tinuvin <NUM> and added at a specific amount <NUM>% of the total amount of the TPU; and the TPU particles had a softening point of <NUM>, a Shore hardness of <NUM> A, and a melt index of <NUM>/<NUM>;.

A preparation method of a yellowing-resistant TPU foam material included: <NUM> of hydrogenated XDI, <NUM> of <NUM>,<NUM>-butylene glycol, <NUM> of PBA, a hindered phenol antioxidant, a benzotriazole UV absorber, and a hindered amine light stabilizer were added into a twin-screw extruder and subjected to a reaction at <NUM> to <NUM> to obtain a TPU, where the hindered phenol antioxidant was Irganox1076 and added at a specific amount <NUM>% of a total amount of the TPU; the benzotriazole UV absorber was Tinuvin312 and added at a specific amount <NUM>% of the total amount of the TPU; the hindered amine light stabilizer was Tinuvin622 and added at a specific amount <NUM>% of the total amount of the TPU; and the TPU particles had a softening point of <NUM>, a Shore hardness of <NUM> A, and a melt index of <NUM>/<NUM>;.

A preparation method of a yellowing-resistant TPU foam material included: <NUM> of hydrogenated diphenylmethane diisocyanate, <NUM> of <NUM>,<NUM>-butylene glycol, <NUM> of PTMEG, a hindered phenol antioxidant, a benzotriazole UV absorber, and a hindered amine light stabilizer were added into a twin-screw extruder and subjected to a reaction at <NUM> to <NUM> to obtain a TPU, where the hindered phenol antioxidant was Irganox1098 and added at a specific amount <NUM>% of a total amount of the TPU; the benzotriazole UV absorber was TinuvinUV-<NUM> and added at a specific amount <NUM>% of the total amount of the TPU; the hindered amine light stabilizer was Tinuvin944 and added at a specific amount <NUM>% of the total amount of the TPU; and the TPU particles had a softening point of <NUM>, a Shore hardness of <NUM> A, and a melt index of <NUM>/<NUM>;.

A preparation method of a yellowing-resistant TPU foam material included: <NUM> of hydrogenated diphenylmethane diisocyanate, <NUM> of <NUM>,<NUM>-butylene glycol, <NUM> of PTMEG, a hindered phenol antioxidant, a benzotriazole UV absorber, and a hindered amine light stabilizer were added into a twin-screw extruder and subjected to a reaction at <NUM> to <NUM> to obtain a TPU, where the hindered phenol antioxidant was Irgafos168 and added at a specific amount <NUM>% of a total amount of the TPU; the benzotriazole UV absorber was TinuvinUV-<NUM> and added at a specific amount <NUM>% of the total amount of the TPU; the hindered amine light stabilizer was Tinuvin144 and added at a specific amount <NUM>% of the total amount of the TPU; and the TPU particles had a softening point of <NUM>, a Shore hardness of <NUM> A, and a melt index of <NUM>/<NUM>;.

A preparation method of a yellowing-resistant TPU foam material included: <NUM> of IPDI, <NUM> of <NUM>,<NUM>-butylene glycol, <NUM> of PTMEG, a hindered phenol antioxidant, a benzotriazole UV absorber, and a hindered amine light stabilizer were added into a twin-screw extruder and subjected to a reaction at <NUM> to <NUM> to obtain a TPU, where the hindered phenol antioxidant was Irgafos618 and added at a specific amount <NUM>% of a total amount of the TPU; the benzotriazole UV absorber was Tinuvin234 and added at a specific amount <NUM>% of the total amount of the TPU; the hindered amine light stabilizer was Tinuvin571 and added at a specific amount <NUM>% of the total amount of the TPU; and the TPU particles had a softening point of <NUM>, a Shore hardness of <NUM> A, and a melt index of <NUM>/<NUM>;.

The molded foam products prepared in Examples <NUM> to <NUM> were tested. A tensile strength, an elongation at break, a tearing strength, and a resilience were tested by a tensile machine. According to ASDM-D1148, a <NUM> UVA lamp was used to test at a lamp irradiation intensity of <NUM> W/m<NUM>/nm to obtain a yellowing resistance grade I; and according to HG/T3689-2001A, a <NUM> irradiation test was conducted to obtain a yellowing resistance grade II. Specific test data were shown in the table below:.

Claim 1:
A yellowing-resistant thermoplastic polyurethane (TPU) foam material comprising a TPU prepared by subjecting an aliphatic diisocyanate, a chain extender, a polyol, an antioxidant, an ultraviolet (UV) absorber, and a UV light stabilizer to a reaction,
wherein:
the aliphatic diisocyanate comprises one or more from the group consisting of hexamethylene diisocyanate (HDI), isophorone diisocyanate (IPDI), xylylene diisocyanate (XDI) or hydrogenated diphenylmethane diisocyanate (H<NUM>MDI), cyclohexyl dimethylene diisocyanate (H<NUM>XDI), and cyclohexyl diisocyanate,
the chain extender comprises one or more from the group consisting of <NUM>,<NUM>-ethylene glycol, <NUM>,<NUM>-propylene glycol, <NUM>,<NUM>-butylene glycol, <NUM>,<NUM>-hexylene glycol, and cyclohexanedimethanol (CHDM),
the polyol comprises one or more from the group consisting of a polycarbonate polyol, a polyester polyol, and a polyether polyol with a functionality of <NUM> to <NUM>, and
wherein the TPU has
a yellowing resistance grade of <NUM> to <NUM>, which is obtained at a lamp irradiation intensity of <NUM> W/m<NUM>/nm of a <NUM> UVA lamp according to ASDM-D1148, or a <NUM> irradiation test according to HG/T3689-2001A, or according to ISO <NUM>-A02: <NUM> using the standard light source D65, and
a softening point of <NUM> to <NUM> which is determined by a rheometer, a Shore hardness of <NUM> A to <NUM> A which determined by the Shore A durometer, and a melt index of <NUM> to <NUM>/<NUM> which obtained by a <NUM> load test at <NUM> according to ASTM D1238.