A high-performance and easy-to-process TPU granule and its preparation and storage methods

Abstract

The present invention discloses a high-performance and easily processable TPU particle and its preparation and storage methods. The preparation method includes the steps of: (1) adding polyol, isocyanate, and chain extender into a reactive extruder, controlling the temperature of the reaction zone of the reactive extruder at 140-180 °C, and side-feeding a catalyst in the penultimate temperature zone of the reactive extruder; (2) the product extruded by reaction in step (1) is cooled, pelletized and enters a silo, the temperature of the silo is controlled at 0-20 °C, and a nucleating agent is side-fed inside the silo, and after mixing, the high-performance and easily processable TPU particle is obtained. The storage method: storing the high-performance and easily processable TPU particle at a constant temperature of 0-22 °C. The TPU particle of the present invention is obtained by low-temperature processing, and can significantly expand the controllable temperature range and reduce energy consumption in subsequent extrusion processing. More importantly, the products processed and manufactured have higher strength.

Description

Technical Field

[0001] The present invention relates to the technical field of thermoplastic polyurethane elastomer (TPU) production, and particularly relates to a high-performance and easy-to-process TPU particle and its preparation and storage methods. Background Art

[0002] In recent years, TPU has been more and more widely used in domestic application fields and the consumption has also been increasing. However, most of the applications are concentrated in mid- to low-end products. Due to the thermosensitive characteristics of TPU itself, the higher the processing temperature, the more serious the degradation. To obtain TPU products with high molecular weight and high strength, the TPU particles themselves need to have a relatively high molecular weight. However, the higher the molecular weight, the higher the viscosity, the more difficult the extrusion processing, and the higher the required processing temperature. After high-viscosity TPU is extruded at high temperature, the degradation is serious, and it is difficult to achieve high strength of the products.

[0003] Currently, there are similar problems in the extrusion processing of TPU for industrial belts, shoe materials, automotive dust covers, etc.

[0004] For the commonly used polyester-based TPU, the strength of the one with a high melt index (low molecular weight) is relatively low, and it can only produce some products with low requirements for product strength; the processing of TPU products with a low melt index (high molecular weight) is difficult, requires a relatively high processing temperature, has high requirements for equipment selection, and the relative strength of the produced finished products is slightly higher and cannot be further improved; moreover, the melt index cannot be infinitely reduced because too high a molecular weight will cause processing difficulties or even impossible processing, and the processing stability will also be affected. In addition, when the molecular weight of TPU products is increased to a certain extent and then continued to increase, there is little significance, because TPU itself has poor heat resistance. Too high a molecular weight can only make the equipment processing difficult and requires a higher processing temperature to meet the processing requirements, while the strength of the actual obtained finished products changes little or even may decrease.

[0005] The existing methods to improve the strength of TPU products include preparing high-strength TPU particles from the perspective of optimizing TPU raw materials. For example, the patent specification with the publication number CN 110627983 A discloses a low-density, high-strength, and high-yellowing-resistant TPU for shoe soles. Styrene-grafted polyol is used to react with aliphatic diisocyanate and small molecule chain extenders, and nano-silica is added to further enhance its physical and mechanical properties. A fast molding process of pre-mixing grafted polyester polyol and chain extender is used to prepare a low-density, high-strength, and high-yellowing-resistant TPU for shoe soles; there are also methods to prepare high-strength TPU composites from the perspective of optimizing the raw materials blended with TPU particles. For example, the patent specification with the publication number CN 112048168 A discloses a high-performance TPU composite material for automotive floor mats.

[0006] There is no existing technology that optimizes the preparation process and storage conditions of the TPU particle raw material itself to improve the strength and other properties of TPU-based products. Summary of the invention

[0007] The present invention provides a method for preparing high-performance and easy-to-process TPU particles. The TPU particles are obtained by low-temperature processing and can be further reacted in a subsequent processing and manufacturing process to obtain a high-molecular-weight, high-strength TPU-based product. The subsequent processing and manufacturing process can also be carried out at a relatively low temperature to avoid TPU degradation as much as possible.

[0008] The specific technical solutions are as follows:

[0009] A method for preparing high-performance and easy-to-process TPU particles comprises the following steps:

[0010] (1) adding polyol, isocyanate and chain extender into a reaction extruder, controlling the temperature of the reaction zone of the reaction extruder at 140-180° C., and feeding a catalyst into the second-to-last temperature zone of the reaction extruder;

[0011] (2) The product of the reaction extrusion in step (1) is cooled, pelletized and put into a silo. The temperature of the silo is controlled at 0-22° C. A nucleating agent is fed into the silo and mixed to obtain the high-performance and easy-to-process TPU particles.

[0012] The key to the present invention is to control the reaction degree of TPU particles, so that the TPU particles can be formed and packaged at low temperature, and the molecular weight of the TPU particles can be controlled to be lower than normal. When the downstream customers use the materials, the products are thawed and enter the reaction state during the baking process. The products react during the extrusion process, and the performance is further improved, so as to finally obtain a high molecular weight and high strength TPU product.

[0013] During the TPU extrusion process, there are two processes: material reaction to promote molecular weight increase and high temperature molecular weight degradation. In the general processing process of making TPU-based products and products with existing technology, the TPU reaction is close to a complete state, so the molecular weight of TPU will hardly increase or increase very little during the extrusion process of downstream customers to make TPU-based products and products, while the degradation of TPU in the screw is always going on. The two reactions are mainly degradation, which makes the molecular weight of the product drop significantly during extrusion and the product strength decreases.

[0014] The principle by which the present invention can obtain high-performance products is to enhance the reaction ability of TPU particles in the extruder, enabling TPU to be in the rapid reaction stage during the processing of TPU-based products by downstream customers. Moreover, because the initial molecular weight of the TPU pellet is relatively low, it can be stably processed at a lower temperature. After the screw temperature is reduced, the degradation reaction of TPU during processing becomes weaker. That is, the present invention enables the TPU product to be stably extruded at a relatively low temperature, strengthens the synthesis reaction of TPU, and weakens the degradation reaction of TPU, thereby enabling the molecular weight of the TPU finished product to be maintained or even increased, thus improving the strength of the product.

[0015] In the preparation method of the high-performance and easy-to-process TPU particles, in step (1), the polyol can be a polyester polyol, and the number-average molecular weight is preferably 1000 - 3000 g / mol, which can ensure that the TPU has a high molecular weight when the reaction is complete.

[0016] Specifically, the polyester polyol can be a polyol synthesized from one or more of ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol and adipic acid (AA).

[0017] In the preparation method of the high-performance and easy-to-process TPU particles, in step (1), the catalyst is side-fed at the penultimate temperature zone of the reactive extruder, and its main purpose is to initially control the reaction degree of TPU.

[0018] As a preference, in the preparation method of the high-performance and easy-to-process TPU particles, in step (1), based on the mass of the polyol, the addition amount of the catalyst does not exceed 100 ppm.

[0019] In a preferred example, in the preparation method of the high-performance and easy-to-process TPU particles, in step (1), the catalyst is one or more of organotin catalysts and organobismuth catalysts.

[0020] In the preparation method of the high-performance and easy-to-process TPU particles, in step (2), the product obtained by reactive extrusion in step (1) enters the silo after cooling, and its main purpose is to further control the reaction degree of TPU.

[0021] As a preference, in the preparation method of the high-performance and easy-to-process TPU particles, in step (2), the product obtained by reactive extrusion in step (1) is cooled by a cold air blower, and the temperature of the cold air blower is controlled at -40 to 20°C.

[0022] In the preparation method of the high-performance and easy-to-process TPU particles, in step (2), the temperature of the silo is controlled at 0 - 22°C, and a nucleating agent is side-fed inside the silo. Its main purpose is to reduce the reaction rate of TPU and at the same time ensure that TPU can react rapidly when processing TPU-based products subsequently.

[0023] Preferably, in the method for preparing the high-performance and easy-to-process TPU particles, in step (2), the amount of the nucleating agent added does not exceed 200 ppm of the total mass of the TPU particles.

[0024] In a preferred example, in the method for preparing high-performance and easy-to-process TPU particles, in step (2), the nucleating agent includes at least one of montmorillonite, silica, multi-walled carbon nanotubes, calcium carbonate, glass beads, and diatomaceous earth, and the powder particle size is 100nm-50μm.

[0025] Preferably, in the method for preparing the high-performance and easy-to-process TPU particles, the raw material formula for preparing the high-performance and easy-to-process TPU particles controls the R value to be between 0.995-1.002, and the hard segment content to be between 35wt%-45wt%, the main purpose of which is to ensure that the TPU has high molecular weight and high strength when the reaction is complete. The R value is the isocyanate index, which represents the molar ratio of isocyanate groups (-NCO) to hydroxyl groups (-OH) in polyols, isocyanates, and chain extenders.

[0026] The present invention further provides high-performance and easy-to-process TPU particles prepared by the preparation method.

[0027] In the TPU particles of the present invention, the addition of a catalyst can have an initiating effect, and the addition of a nucleating agent is beneficial to improving the strength of the product.

[0028] The present invention also provides a storage method for the high-performance and easy-to-process TPU particles, wherein the high-performance and easy-to-process TPU particles are stored at a constant temperature of 0-22°C.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] The present invention obtains high-performance and easy-to-process TPU particles through low-temperature processing. The TPU particles can be further reacted in the subsequent processing and manufacturing process to obtain high-molecular-weight, high-strength TPU-based products. The subsequent processing and manufacturing process can also be carried out at a relatively low temperature to avoid TPU degradation as much as possible. The controllable temperature range in the subsequent extrusion process is significantly expanded, the energy consumption is reduced, and more importantly, the processed products have higher strength. DETAILED DESCRIPTION

[0031] The present invention will be further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0032] The operating methods in the following examples without specifying specific conditions are usually carried out under conventional conditions or under conditions recommended by the manufacturers.

[0033] Example 1

[0034] Polyethylene adipate glycol (Mn = 2000 g / mol), 4,4'-diphenylmethane diisocyanate (MDI) were selected, and 1,4-butanediol was chosen as the chain extender. The hard segment content was 38 wt%, and the R value was controlled at 0.998. The measured components were injected into the reactive extrusion machine through a flow meter. The temperature of each zone of the reactive extrusion machine was controlled at 135 °C (pouring port temperature zone), 150 °C (first reaction zone), 160 °C (second reaction zone), 170 °C (third reaction zone), 175 °C (fourth reaction zone), 170 °C (fifth reaction zone), 150 °C (sixth reaction zone), 130 °C, 100 °C, 100 °C, 100 °C. After the sixth reaction zone was a cooling section. Stannous octoate catalyst was side-fed in the penultimate temperature zone. Calculated based on the mass of polyethylene adipate glycol, the addition amount was 20 ppm. After underwater pelletizing, it entered the silo through a cooling fan. The temperature of the cooling fan was controlled at -10 °C, and the temperature of the silo was controlled at 10 °C. At the same time, nucleating agent diatomaceous earth was side-fed into the large silo. Calculated based on the total mass of TPU particles, the addition amount was 100 ppm, and lubricant polyethylene wax was 200 ppm. After sampling and testing the moisture in the large silo to be qualified, it was bagged and shipped out.

[0035] The whole bagged material was put into a dehumidifying drying hopper, dried at 95 °C for 3 h and then extruded using an extruder. The temperature of the extruder was controlled at 170 °C - 180 °C - 190 °C - 185 °C from the feeding port to the die head. After extrusion, the current change was recorded, and the molecular weight was tested by sampling the extruded strip; the remaining material was injection molded into sheets for physical property testing.

[0036] Example 2

[0037] After packaging on the basis of Example 1, it was placed in a constant temperature storage for 3 months. The temperature of the storage was controlled at 20 ± 2 °C, and the rest of the tests remained unchanged.

[0038] Comparative Example 1

[0039] Polyethylene adipate glycol (Mn = 2000 g / mol), 4,4'-diphenylmethane diisocyanate (MDI) were selected, and 1,4-butanediol was chosen as the chain extender. The hard segment content was 38 wt%, and the R value was controlled at 0.998. The measured components were injected into the reactive extrusion machine through a flow meter. The temperature of the reactive extrusion machine was controlled at 150 °C, 180 °C, 190 °C, 190 °C, 200 °C, 190 °C, 170 °C, 150 °C, 130 °C, 130 °C, 130 °C. After underwater pelletizing, it entered the silo. The temperature of the silo was controlled at 55 °C. At the same time, lubricant polyethylene wax was side-fed into the large silo, and the addition amount was 200 ppm. After sampling and testing the moisture in the large silo to be qualified, it was bagged and shipped out.

[0040] Put the whole packaged material into the dehumidifying and drying hopper, dry it at 95°C for 3 hours, and then extrude it using an extruder. The temperature of the extruder is controlled from the feeding port to the die head at 170°C - 180°C - 190°C - 185°C. Record the current change after extrusion, and take samples of the extruded strips to test the molecular weight; use the remaining material for injection molding to make tablets for physical property testing.

[0041] Comparative Example 2

[0042] On the basis of Comparative Example 1, after packaging is completed, put it into the warehouse. The warehouse temperature is about 30°C, without specific temperature control, store it for 3 months, and the rest of the tests remain unchanged.

[0043] Comparative Example 3

[0044] The difference from Example 1 is that no catalyst and nucleating agent are added, and the rest of the conditions remain unchanged.

[0045] Comparative Example 4

[0046] The difference from Comparative Example 3 is that a cold air blower is not used for cooling, and the temperature of the material bin is controlled at 55°C, and the rest of the conditions remain unchanged.

[0047] Comparative Example 5

[0048] On the basis of Comparative Example 2, adjust the extrusion temperature of the extruder. Because at the temperature of Comparative Example 2 (170°C - 180°C - 190°C - 185°C), the equipment current is too high, the load is large, and there is an unstable extrusion situation. Reheat and verify, and finally confirm that the extrusion temperature is controlled from the feeding port to the die head at 190°C - 200°C - 210°C - 205°C. Record the current change after extrusion, take samples of the extruded strips to test the molecular weight; use the remaining material for injection molding to make tablets for physical property testing.

[0049] Table 1 Comparison Table of Performance Data of Each Example and Comparative Example

[0050]

[0051] By comparing Examples 1 and 2, it can be seen that the processing effects of directly using the TPU particles of the present invention and using them after being placed for 3 months are basically the same, and there is not much change in strength and molecular weight. Comparative Examples 1 and 2 are TPU products produced by the general existing technology. It can be seen that the TPU products just after production are in an incomplete reaction state, with a relatively low molecular weight and a not very high extrusion current, but still higher than those of Examples 1 and 2. After being placed for 3 months, the reaction degree is improved, the molecular weight is significantly increased, but the extrusion current is much higher, and there is an unstable extrusion phenomenon, with large current fluctuations. After increasing the temperature (Comparative Example 5), normal extrusion can be carried out, but the actual molecular weight and strength of the extruded products are relatively low. That is to say, although the initial TPU particles have a relatively high molecular weight, due to the combined action of high temperature and shear during the normal extrusion process, severe degradation occurs.

[0052] From the comparison between Example 1 and Comparative Examples 3 and 4, it can be seen that the addition of the catalyst and nucleating agent and the control of the material temperature are very crucial. Without control, it will have a great impact on the product performance.

[0053] In summary, the present invention controls the reaction degree of TPU through low temperature, and maintains the long-term high performance and easy processing ability of TPU particles through low temperature preservation. If the reaction temperature is too high during the preparation process of TPU particles at the beginning, it is still difficult to fully prevent the reaction from proceeding only by subsequent low temperature preservation.

[0054] In addition, it should be understood that after reading the above description of the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms also fall within the scope defined by the appended claims of this application.

Claims

1. Preparation method of a high-performance and easy-to-process TPU granule, characterized in that, it includes the steps: (1) Add polyol, isocyanate, and chain extender into a reactive extruder, control the temperature of the reaction zone of the reactive extruder at 140 - 180 °C, and side-feed a catalyst in the penultimate temperature zone of the reactive extruder; the polyol is a polyester polyol, and the polyester polyol is a polyol synthesized from one or more of ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol and adipic acid; the raw material formula for preparing the high-performance and easy-to-process TPU granule controls the R value between 0.995 - 1.002 and the hard segment content between 35wt% - 45wt%; the R value is the isocyanate index, indicating the molar ratio of the isocyanate group -NCO to the hydroxyl group -OH in the polyol, isocyanate, and chain extender. (2) The product obtained by reactive extrusion in step (1) is cooled, pelletized and enters a silo, the temperature of the silo is controlled at 0 - 22 °C, a nucleating agent is side-fed inside the silo, and after mixing, the high-performance and easy-to-process TPU granule is obtained; the nucleating agent includes at least one of montmorillonite, silica, multi-walled carbon nanotubes, calcium carbonate, glass microspheres, and diatomite.

2. The preparation method according to claim 1, characterized in that, in step (1), based on the mass of the polyol, the addition amount of the catalyst does not exceed 100 ppm.

3. The preparation method according to claim 1 or 2, characterized in that, in step (1), the catalyst is one or more of organotin catalysts and organobismuth catalysts.

4. The preparation method according to claim 1, characterized in that, in step (2), a cold air blower is used to cool the product obtained by reactive extrusion in step (1), and the temperature of the cold air blower is controlled at -40 to 20 °C.

5. The preparation method according to claim 1, characterized in that, in step (2), the addition amount of the nucleating agent does not exceed 200 ppm of the total mass of the TPU granule.

6. The preparation method according to claim 1 or 5, characterized in that, in step (2), the particle size of the nucleating agent powder is 100 nm - 50 μm.

7. High-performance and easy-to-process TPU granule prepared by the preparation method according to any one of claims 1 - 6.

8. Storage method of the high-performance and easy-to-process TPU granule according to claim 7, characterized in that, store the high-performance and easy-to-process TPU granule at a constant temperature of 0 - 22 °C.

Images