Manufacturing process of high-weather-resistance TPU (Thermoplastic Polyurethane) film

Abstract

The invention discloses a manufacturing process of a high-weather-resistance TPU film, and belongs to the technical field of films. The preparation process of the TPU film comprises the following steps: under the action of a catalyst, preparing a hindered amine grafted alicyclic amino alcohol chain extender by taking isophorone diisocyanate, 4-hydroxy-2, 2, 6, 6-tetramethylpiperidine and 2-aminocyclohexanol as raw materials; the preparation method comprises the following steps: under the action of an organic bismuth catalyst, carrying out prepolymerization on polysiloxane dihydric alcohol and isocyanate, and then adding a hindered amine grafted alicyclic amino alcohol chain extender and a cross-linking regulator for polymerization to obtain a TPU polymer; and carrying out melt extrusion and tape casting on the TPU polymer. According to the method disclosed by the invention, the mechanical property and the weather resistance of the TPU film are synergistically improved, and the service life of the TPU film is effectively prolonged.

Description

Technical Field

[0001] This invention relates to the field of film technology, and more specifically, to a manufacturing process for a high weather-resistant TPU film. Background Technology

[0002] Thermoplastic polyurethane (TPU) films are widely used in outdoor advertising applications such as LED light boxes, storefront signs, and building curtain walls due to their excellent flexibility, mechanical strength, and abrasion resistance. However, existing TPU films for outdoor advertising are prone to degradation of mechanical properties and severe yellowing after long-term exposure to light and heat, failing to meet the requirements of long-term weather resistance and aesthetics in outdoor advertising. Although some films improve weather resistance by adding additives such as UV absorbers and antioxidants, these additives are prone to migration and precipitation during film preparation and use, making it difficult to simultaneously achieve both mechanical and weather resistance properties, thus limiting the further application of TPU films. Therefore, developing a TPU film for outdoor advertising that combines both mechanical and weather resistance properties has become an urgent need in the industry. Summary of the Invention

[0003] The purpose of this invention is to overcome the shortcomings of the prior art and provide a manufacturing process for a high weather-resistant TPU film.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] A manufacturing process for a high weather-resistant TPU film includes the following steps:

[0006] (a) Under the action of a catalyst, hindered amine-grafted alicyclic amino alcohol chain extender was prepared using isophorone diisocyanate, 4-hydroxy-2,2,6,6-tetramethylpiperidine and 2-aminocyclohexanol as raw materials;

[0007] (b) Under the action of an organobismuth catalyst, polysiloxane diol and isocyanate are prepolymerized, and then hindered amine grafted alicyclic amino alcohol chain extender and crosslinking regulator are added for polymerization to obtain TPU polymer;

[0008] (c) The TPU polymer is melt-extruded and cast to obtain a high weather-resistant TPU film.

[0009] Furthermore, in step (a), the ratio of isophorone diisocyanate, 4-hydroxy-2,2,6,6-tetramethylpiperidine, catalyst, ethyl acetate, and 2-aminocyclohexanol is (200-220)g:(140-155)g:(0.05-0.15)g:(500-650)mL:(113-125)g.

[0010] Furthermore, in step (a), the catalyst is an organobismuth-zinc composite catalyst or a combination of an organobismuth-zinc composite catalyst and lanthanum trifluoromethanesulfonate.

[0011] Furthermore, the specific preparation steps for hindered amine-grafted alicyclic amino alcohol chain extenders are as follows:

[0012] (1) Dissolve isophorone diisocyanate in ethyl acetate, and add dropwise a mixture of 4-hydroxy-2,2,6,6-tetramethylpiperidine, catalyst, and ethyl acetate under nitrogen protection at 50-55°C. After the addition is complete, continue the reaction under nitrogen protection at 50-55°C. After the reaction is completed, perform vacuum distillation to obtain a concentrated intermediate containing -NCO.

[0013] (2) Add 2-aminocyclohexanol to the intermediate concentrate, reflux the reaction under nitrogen protection at 68-72℃, and distill under reduced pressure to obtain crude product; purify and dry the crude product to obtain hindered amine grafted alicyclic amino alcohol chain extender.

[0014] Furthermore, in step (b), the mass ratio of polysiloxane diol, organobismuth catalyst, isocyanate, hindered amine grafted alicyclic amino alcohol chain extender, and crosslinking regulator is (612-630):(0.5-1):(85-95):(81-87):(17-23).

[0015] Furthermore, in step (b), the isocyanate is a combination of hexamethylene diisocyanate and isophorone diisocyanate.

[0016] Furthermore, in step (b), the organic bismuth catalyst is bismuth laurylate.

[0017] Furthermore, the specific preparation steps for TPU polymer are as follows:

[0018] (1) Add polysiloxane diol and organic bismuth catalyst to the reaction vessel, and under nitrogen protection and at 70-75°C, add isocyanate dropwise. After the addition is complete, continue the reaction at 75°C to obtain the prepolymer.

[0019] (2) Add hindered amine-grafted alicyclic amino alcohol chain extender to the prepolymer, react at 90-95℃, and then add crosslinking regulator to continue the reaction at a constant temperature to obtain TPU polymer.

[0020] In summary, the present invention has the following beneficial effects:

[0021] This invention uses hindered amine grafted alicyclic amino alcohol chain extenders to prepare TPU films. The hindered amine groups efficiently capture free radicals generated by photoaging and thermo-oxidative aging, inhibiting molecular chain degradation. The hydrogen bond crosslinking network formed by the urea group structure generated in the reaction hinders the diffusion of free radicals, thereby optimizing the weather resistance of the film and achieving a synergistic improvement in mechanical properties and weather resistance. This effectively extends the service life of the TPU film and meets higher weather resistance requirements. Detailed Implementation

[0022] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1

[0024] (a) Preparation of hindered amine-grafted alicyclic amino alcohol chain extenders:

[0025] 210.6 g of isophorone diisocyanate (IPDI) was dissolved in 400 mL of ethyl acetate. Then, under nitrogen protection and at 50-55 °C, a mixture of 4-hydroxy-2,2,6,6-tetramethylpiperidine, catalyst, and ethyl acetate (containing 148 g of 4-hydroxy-2,2,6,6-tetramethylpiperidine, 0.1 g of catalyst, and 200 mL of ethyl acetate; the catalyst was 0.07 g of organobismuth-zinc composite catalyst (purchased from Guangzhou Yourun Synthetic Materials Co., Ltd., model BX1124) and 0.03 g of lanthanum trifluoromethanesulfonate) was added dropwise over 30 min. After the addition was complete, the reaction was continued under nitrogen protection and refluxed at 50-55 °C for 3 h. After the reaction was completed, the solution was evaporated under reduced pressure. Distillation (vacuum -0.08 MPa, temperature 60℃) was performed to remove 80% of ethyl acetate, yielding a concentrated intermediate containing -NCO. The concentrated intermediate was heated to 70℃, and 119.2 g of 2-aminocyclohexanol was added. The mixture was refluxed at 68-72℃ for 4 h under nitrogen protection. After the reaction, vacuum distillation (vacuum -0.09 MPa, temperature 70℃) was performed to remove the remaining ethyl acetate, yielding a viscous crude product. The crude product was cooled to 60℃, and four times its volume of anhydrous ethanol was added. After stirring, the mixture was cooled to room temperature and allowed to crystallize for 4 h. The crystals were collected by filtration, washed with cold ethanol, and then dried under vacuum (80℃, vacuum -0.09 MPa) to obtain a hindered amine-grafted alicyclic amino alcohol chain extender.

[0026] (b) 624.8g of polysiloxane diol (prepared according to the method in Example 1 of the patent "A polysiloxane diol, thermoplastic organosilicon polyurethane elastomer, crosslinked polyurethane elastomer and its uses" (CN114805813A)) and 0.5g of organobismubium catalyst bismuth laurate were added to a reaction vessel. Under nitrogen protection and at 70-75°C, 89.5g of a mixed isocyanate of HDI (hexamethylene diisocyanate) and IPDI (isophorone diisocyanate) (HDI:IPDI mass ratio of 3:1) was added dropwise, with the addition time controlled at 2h. After the addition was completed, the reaction was continued at 75°C for 1.5h to obtain a prepolymer. 84.9g of hindered amine grafted alicyclic amino alcohol chain extender was added to the prepolymer, and the reaction was carried out at 90-95°C for 1h. Then, 20g of crosslinking regulator trimethylolpropane (TMP) was added, and the reaction was continued at a constant temperature for 2h. After the reaction was completed, the system was cooled to room temperature to obtain TPU polymer.

[0027] (c) The TPU polymer is transferred to a twin-screw extruder for melt extrusion (the temperatures of each section are set as follows: feeding section 142°C, melting section 163°C, homogenization section 168°C, and die head 158°C). The melt is cast by a casting machine and cooled to obtain a high weather-resistant TPU film with a thickness of 0.3 mm.

[0028] Example 2

[0029] TPU films were prepared according to the method of Example 1, but the catalyst in step (a) was changed to 0.05g of organic bismuth zinc composite catalyst (purchased from Guangzhou Yourun Synthetic Materials Co., Ltd., model BX1124).

[0030] Comparative Example 1

[0031] TPU films were prepared according to the method of Example 1, but 2-aminocyclohexanol was not added in step (a).

[0032] Comparative Example 2

[0033] TPU films were prepared according to the method of Example 1, but 4-hydroxy-2,2,6,6-tetramethylpiperidine was not added in step (a).

[0034] Comparative Example 3

[0035] TPU films were prepared according to the method of Example 1, but in step (b), an equal mass of chain extender 1,4-cyclohexanediethanol (CHDM) was used instead of the hindered amine-grafted alicyclic amino alcohol chain extender.

[0036] According to HG / T 5070-2016 "Thermoplastic Polyurethane (TPU) Films", the tensile strength and elongation at break of the TPU films prepared in Example 1, Example 2 and Comparative Examples 1-3 were tested before aging. Aging experiments were conducted on the films of Example 1 and Comparative Examples 1-4 according to GB / T16422.2-2022 "Laboratory Light Source Exposure Test Methods for Plastics - Part 2: Xenon Arc Lamp" and GB / T 7141-2008 "Test Method for Thermal Aging of Plastics". The xenon arc lamp aging method involved placing the TPU film in a xenon arc lamp exposure aging test chamber and irradiating it for 1000 hours at an intensity of 340 nm and 0.51 W / (m²·nm); the thermal aging method involved placing the TPU film at 90°C for 500 hours. The tensile strength retention rate after aging was determined according to HG / T 5070-2016 "Thermoplastic Polyurethane (TPU) Films", and the yellowing index was determined according to HG / T 3862-2006 "Test Method for Yellow Index of Plastics". The test results are shown in Table 1. Therefore, it can be seen that the method of this invention can successfully prepare TPU films with both weather resistance and mechanical properties, effectively improving the service life of the film.

[0037] Table 1

[0038]

[0039] The preparation conditions and raw material ratios of the high weather-resistant TPU film of the present invention are not limited to those shown in Example 1. In step (a), the ratio of isophorone diisocyanate, 4-hydroxy-2,2,6,6-tetramethylpiperidine, catalyst, ethyl acetate, and 2-aminocyclohexanol can be adjusted to (200-220)g:(140-155)g:(0.05-0.15)g:(500-650)mL:(113-125)g; in step (b), the mass ratio of polysiloxane diol, organobismuth catalyst, HDI and IPDI mixed isocyanate, hindered amine grafted alicyclic amino alcohol chain extender, and crosslinking regulator can be (612-630):(0.5-1):(85-95):(81-87):(17-23).

[0040] The above description is merely a preferred embodiment of the present invention. The scope of protection of the present invention is not limited to the above embodiments. All technical solutions falling within the scope of the present invention's concept are within the scope of protection of the present invention. It should be noted that for those skilled in the art, any improvements and modifications made without departing from the principles of the present invention should also be considered within the scope of protection of the present invention.

Claims

1. A process for making a high weatherable TPU film, characterized in that, The method comprises the following steps: (a) preparing a hindered amine grafted alicyclic amino alcohol chain extender by using isophorone diisocyanate, 4-hydroxy-2,2,6,6-tetramethylpiperidine and 2-aminocyclohexanol as raw materials under the action of a catalyst; (b) pre-polymerizing polysiloxane dihydric alcohol and isocyanate under the action of an organic bismuth catalyst, and then adding the hindered amine grafted alicyclic amino alcohol chain extender and a crosslinking regulator to perform polymerization to obtain a TPU polymer; (c) melt extruding and flow forming the TPU polymer to obtain a high-weather-resistant TPU film.

2. The process for making a high weatherable TPU film according to claim 1, wherein, In step (a), the isophorone diisocyanate, 4-hydroxy-2,2,6,6-tetramethylpiperidine, catalyst, ethyl acetate and 2-aminocyclohexanol are used in a ratio of (200-220) g:(140-155) g:(0.05-0.15) g:(500-650) mL:(113-125) g.

3. The process for making a high weatherable TPU film according to claim 1, wherein, In step (a), the catalyst is an organic bismuth-zinc composite catalyst or a combination of the organic bismuth-zinc composite catalyst and lanthanum triflate.

4. The process of claim 1, wherein the process further comprises the steps of: a. applying a primer layer on the surface of the TPU film; b. applying a top coat layer on the primer layer; and c. applying a protective layer on the top coat layer. The hindered amine grafted alicyclic amino alcohol chain extender is prepared by the following steps: (1) dissolving the isophorone diisocyanate in ethyl acetate, and then dropping the mixture into a mixture of 4-hydroxy-2,2,6,6-tetramethylpiperidine, catalyst and ethyl acetate under nitrogen protection at 50-55 DEG C, and continuing the reaction under nitrogen protection at 50-55 DEG C after the dropping is completed; after the reaction is completed, performing a reduced-pressure distillation treatment to obtain an intermediate concentrated solution containing -NCO; (2) adding 2-aminocyclohexanol to the intermediate concentrated solution, and refluxing the mixture under nitrogen protection at 68-72 DEG C, and then performing a reduced-pressure distillation after the reaction to obtain a crude product; purifying and drying the crude product to obtain the hindered amine grafted alicyclic amino alcohol chain extender.

5. The process of claim 1, wherein the process further comprises the steps of: a. applying a primer layer on the surface of the TPU film; b. applying a top coat layer on the primer layer; and c. applying a protective layer on the top coat layer. In step (b), the polysiloxane dihydric alcohol, organic bismuth catalyst, isocyanate, hindered amine grafted alicyclic amino alcohol chain extender and crosslinking regulator are used in a mass ratio of (612-630):(0.5-1):(85-95):(81-87):(17-23).

6. The process of claim 1, wherein the process is characterized by, In step (b), the isocyanate is a combination of hexamethylene diisocyanate and isophorone diisocyanate.

7. The process of claim 1, wherein the process is characterized by, In step (b), the organic bismuth catalyst is bismuth laurate.

8. The process of claim 1, wherein the process is characterized by, The TPU polymer is prepared by the following steps: (1) adding the polysiloxane dihydric alcohol and organic bismuth catalyst into a reaction kettle, and then dropping the isocyanate into the reaction kettle under nitrogen protection at 70-75 DEG C, and continuing the reaction at 75 DEG C after the dropping is completed to obtain a pre-polymer; (2) adding the hindered amine grafted alicyclic amino alcohol chain extender into the pre-polymer, and then reacting the mixture at 90-95 DEG C, and then adding the crosslinking regulator to continue the constant-temperature reaction to obtain the TPU polymer.

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