TPU with easy recovery of deformation, and preparation method and application thereof

Abstract

The application discloses a TPU with easy recovery after deformation, a preparation method of the TPU and application of the TPU in manufacturing toys. The raw material composition of the TPU comprises a chain extender, a polyisocyanate and one or more polyester polyols; the polyester polyols are formed by connecting acid structural units and alcohol structural units through ester bonds, wherein the acid structural units comprise at least one of terephthalic acid, oxalic acid and adipic acid and must contain terephthalic acid, and the alcohol structural units comprise at least one of butanediol, propylene glycol and ethylene glycol; the hard segment content in the TPU is between 10wt% and 50wt%; the TPU softens at 30-60 DEG C and hardens and is shaped below 10 DEG C. The preparation method comprises the following steps: adding raw materials into a double-screw reaction extruder to perform reaction extrusion, underwater pelletizing and obtaining the TPU.

Description

Technical Field

[0001] This invention relates to the field of thermoplastic polyurethane elastomers (TPU), specifically to a TPU with easily recoverable deformation, its preparation method, and its applications. Background Technology

[0002] Most building block toys used by children today are made of hard plastics such as ABS (acrylonitrile butadiene styrene), PVC (polyvinyl chloride), PC (polycarbonate), and PP (polypropylene). Although they are lightweight and easy to mold, they are difficult to repair once damaged due to the material. Moreover, after being subjected to large external forces such as squeezing or collision, they are prone to cracking or breaking, forming sharp edges that may scratch young children and pose a safety hazard. Furthermore, once a toy is damaged, it is difficult to restore it.

[0003] Patent specification CN116462818A discloses a colorfast and antibacterial thermoplastic polyurethane elastomer, its preparation method, and its applications. This thermoplastic polyurethane elastomer is made from the following raw material components: (a) polyol, (b) isocyanate, (c) chain extender, (d) a capping agent containing hydrazide groups, and (e) a silver ion antibacterial agent. The preparation method includes: 1) blending isocyanate, polyol, and chain extender and adding the mixture to a reactive extruder through a first feeding port to obtain a thermoplastic polyurethane elastomer melt; 2) adding the capping agent containing hydrazide groups to the reactive extruder through a second feeding port to continue the reaction and obtain a hydrazide-capped thermoplastic polyurethane elastomer; 3) melt-blending the product from step 2) with the silver ion antibacterial agent to obtain the colorfast and antibacterial thermoplastic polyurethane elastomer. This colorfast and antibacterial thermoplastic polyurethane elastomer can be used in the automotive, medical, transportation, 3C electronics, daily necessities, children's toys, footwear, and apparel industries. This patented technology focuses on the antibacterial properties of TPU products, but does not pay attention to their specific use after being made into children's toys, such as their properties of deformation under stress, breakage, and recovery.

[0004] In addition, some existing technologies disclose foamed TPU or its products that can be used to make toys, such as the patent specifications with publication numbers CN110183843A and CN112622392A. These existing technologies mainly rely on foaming to obtain better elasticity. Summary of the Invention

[0005] This invention provides a deformation-recoverable TPU, its preparation method, and its application.

[0006] The TPU product of this invention has good softness at room temperature and stable shape. It is difficult for the product to break under strong external force, and it can easily recover if it is deformed by compression.

[0007] The main feature of the TPU of this invention is that it has stronger temperature sensitivity, can maintain good stiffness at 10-30°C, can soften rapidly at around 30-60°C, and can be quickly shaped below 10°C.

[0008] The TPU material of this invention combines the advantages of hard plastics, such as fast molding, light weight, environmental friendliness, and food grade. It is also easy to recover from deformation and is more likely to recover after deformation under medium pressure. It has better durability and will only deform under strong external pressure at normal indoor temperature, without breaking or forming sharp edges, making it safer to use.

[0009] To achieve the same hardness as the TPU of this invention, other existing TPU products would require higher costs, and their temperature sensitivity would be far inferior, failing to meet the requirement of easy deformation.

[0010] The specific technical solution is as follows:

[0011] In a first aspect, the present invention provides a TPU that is easily recoverable from deformation, the raw material composition of which includes chain extender, polyisocyanate and one or more polyester polyols.

[0012] The polyester polyol can be formed by connecting acid structural units and alcohol structural units through ester bonds, wherein the acid structural unit may include at least one of terephthalic acid, oxalic acid, and adipic acid and must include terephthalic acid, and the alcohol structural unit may include at least one of butanediol, propylene glycol, and ethylene glycol.

[0013] The hard segment content in the easily recoverable TPU described in the first aspect is preferably between 10 wt% and 50 wt%, and more preferably between 20 wt% and 40 wt%. If the hard segment content is too low, the proportion of polyester polyol added will be higher. The polyester polyol has high viscosity, which has a greater impact on the reaction rate after mixing with isocyanate, making the reaction requirements more stringent and difficult to achieve. If the hard segment content is too high, although the reaction rate is improved, the molded product will be too hard, and the reaction will be more exothermic. If the reaction is not well controlled, it will easily lead to local overheating, affecting the product stability. The hard segment range of 10 wt% to 50 wt% is the optimal choice for formulation processing and synthesis. The range of 20 wt% to 40 wt% has higher process feasibility and better performance stability of TPU products.

[0014] The TPU described in the first aspect, which is easily recoverable from deformation, softens at 30–60°C and hardens and sets below 10°C.

[0015] The deformation-recoverable TPU isocyanate index (R value) mentioned in the first aspect can be 0.98 to 1.0, for example, 0.99.

[0016] In the first aspect, the easily recoverable TPU is characterized by a polyester polyol with a preferred number-average molecular weight of 500–5000 g / mol, more preferably 1000–3000 g / mol, such as 2500 g / mol. If the viscosity of the polyester polyol is too low, the reaction rate is too fast, and excessive exothermic reaction can easily affect product stability. If the viscosity of the polyester polyol is too high, it is not conducive to the normal progress of the reaction. Through experimental optimization, a polyester polyol with a number-average molecular weight of 1000–3000 g / mol is found to be the optimal synthetic process.

[0017] The deformation-recoverable TPU described in the first aspect is prepared by methods that can be selected from any one or more combinations of the following:

[0018] a) The acid structural unit and the alcohol structural unit are polymerized into the polyester polyol by esterification (which may include one or more of co-esterification, fractional esterification, tandem esterification, etc.) and condensation polymerization.

[0019] b) The polyester polyol is obtained by depolymerization reaction of PBAT (poly(butylene adipate-butylene terephthalate)) and / or PEAT (poly(ethylene adipate-ethylene terephthalate));

[0020] c) At least one of PBT (polybutylene terephthalate), PTT (polypropylene terephthalate), and PET (polyethylene terephthalate) is mixed with a polyester polyol (e.g., one or more of polyethylene glycol diol, polyethylene adipate diol, polyethylene glycol diol, polyethylene adipate diol, polyethylene butylene adipate diol, and polyethylene adipate diol) and / or a small molecule alcohol, heated to depolymerize, and stirred under vacuum to obtain the polyester polyol.

[0021] In c), the small molecule alcohol can be a commonly used alcoholysis agent for polyester alcoholysis in the art, such as ethylene glycol.

[0022] PBAT is a thermoplastic biodegradable plastic, a copolymer of butylene adipate and butylene terephthalate, possessing characteristics of both PBA (polybutylene adipate) and PBT. It has high strength and a low melting point. TPU products are synthesized from polyester polyols synthesized using PBAT, PEAT, and other products as raw materials. Due to the higher complexity of the molecular chain, poor regularity, and low crystallinity, the presence of benzene ring structure and a large number of hydrogen bonds provides the conditions for high strength and hardness of the product, thus giving TPU a wider range of deformation capabilities. Combined with the temperature-sensitive characteristics of TPU itself, the synthesized TPU products have higher hardness and are more sensitive to temperature.

[0023] One of the key features of this invention is the diverse synthesis methods and material selections of the polyester polyols. For example, they can be one or more of polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate, or mixtures of one or more of polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate with one or more of polyethylene adipate and polybutylene adipate. The PBAT, PEAT, PET, PBT, PTT, etc., mentioned in this invention can be virgin materials, recycled materials, regenerated materials, or any combination thereof, increasing the diversity of material selection and thus reducing raw material costs.

[0024] The deformation-recoverable TPU described in the first aspect may include at least one of ethylene glycol, propylene glycol, butanediol, and pentanediol as the chain extender.

[0025] The deformation-recoverable TPU described in the first aspect may include at least one of MDI (diphenylmethane diisocyanate), TDI (toluene diisocyanate), HDI (hexamethylene diisocyanate), HMDI (dicyclohexylmethane-4,4'-diisocyanate), IPDI (isoflurone diisocyanate), and PPDI (terephthalic acid diisocyanate). Further, MDI may include at least one of 4,4'-diphenylmethane diisocyanate, 2,4'-diphenylmethane diisocyanate, and 2,2'-diphenylmethane diisocyanate.

[0026] Preferably, the TPU with easily recoverable deformation described in the first aspect has a hardness between 45D and 70D in an environment of 23±2℃ / 50%RH (relative humidity). If the hardness is below the lower limit, the shape of the TPU product is easily deformed, which is not conducive to the stability of the toy. If the hardness is too high, it is easy to be scratched if there are sharp parts when used as a toy.

[0027] The deformation-recoverable TPU described in the first aspect may further include at least one of a lubricant, an antioxidant, and a catalyst. The present invention does not impose particular limitations on the lubricant, antioxidant, and catalyst; commonly used substances in the art may be used.

[0028] This invention can prepare TPU products by one-step mixing and reaction of polyester polyol with chain extender and polyisocyanate.

[0029] Secondly, the present invention provides a method for preparing the deformation-recoverable TPU described in the first aspect, comprising:

[0030] The raw material is added to a twin-screw reactive extruder for reactive extrusion and underwater pelletizing to obtain the TPU.

[0031] In the preparation method described in the second aspect, the temperature of the reaction section of the twin-screw reactive extruder can be 170–250°C (e.g., 180–210°C), and the temperature of the cooling section can be 90–150°C (e.g., 130°C). One purpose of controlling the temperature of the reaction section between 170 and 250°C is to balance the reaction and dispersion.

[0032] In the preparation method described in the second aspect, the water temperature for underwater pelletizing is less than 30°C (e.g., 10°C). If the water temperature is above 30°C, the TPU particles will soften and deform during underwater pelletizing, making normal pelletizing impossible. Normal production is only possible when the water temperature is below 30°C.

[0033] Thirdly, the present invention provides the use of the deformable TPU described in the first aspect for making toys.

[0034] Compared with the prior art, the beneficial effects of this invention are as follows:

[0035] The TPU product of this invention achieves higher hardness with a low MDI content (existing conventional TPU requires a higher MDI content to achieve the same hardness as the TPU of this invention). The TPU product of this invention is significantly affected by temperature. This product maintains the flexibility and stiffness of TPU products, has sufficient stiffness at room temperature and excellent impact strength, and is easy to shape control. Once deformation occurs, it can be softened and reshaped in warm water and then placed in a low-temperature environment such as a refrigerator to fix and restore its shape. The operation is simple and safe.

[0036] The higher the hardness of conventional TPU products, the more difficult it is to fully recover after deformation. This is because the internal stress of TPU products is difficult to eliminate after deformation, requiring high temperatures or even complete plasticization to eliminate the internal stress. The TPU product of this invention is extremely sensitive to temperature, and can reduce internal stress between 30 and 60°C. It can also quickly set and recover its shape at low temperatures (e.g., 10°C), resulting in stronger deformation capabilities and safer use.

[0037] The TPU products of this invention have a good hand feel at 0-30℃, and their hardness and flexibility meet the requirements for use. They can be softened quickly at 30-60℃ and can be quickly shaped below 10℃. Detailed Implementation

[0038] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention.

[0039] Unless otherwise specified, the operating methods in the following examples are generally performed under conventional conditions or as recommended by the manufacturer.

[0040] Example 1

[0041] The experiment was conducted according to the following formulation: Polybutylene adipate diol was mixed with recycled PET material. The polyester raw material was melted and depolymerized by heating and stirring. The degree of reaction was monitored by stirring and vacuuming to obtain a polyester polyol with a number average molecular weight of 2500 g / mol for later use. BDO (1,4-butanediol) was used as the chain extender, and 4,4'-diphenylmethane diisocyanate was used as the isocyanate. The formulation was designed with a hard segment content of 40 wt% and an R-value of 0.99. The flow rates of each component were calculated for online verification experiments.

[0042] Using a twin-screw reactive extruder, the reaction section temperature is set to 180-210℃, the cooling section temperature is set to 130℃, and the pelletizing water temperature is set to 10℃ for underwater pelletizing, packaging, and warehousing.

[0043] 5 kg of TPU was sampled and dried at 100°C for 3 hours using a dehumidifying hopper. Then, test pieces were injection molded using an injection molding machine. The test pieces were placed in a 100°C oven for 24 hours of curing, and then placed in a constant temperature (23±2°C) and constant humidity (50%RH) laboratory for 48 hours for later use.

[0044] Test hardness and Vicat softening point.

[0045] Example 2

[0046] Referring to the formulation of Example 1, the spare polyester polyol was replaced with polybutylene adipate diol with a number average molecular weight of 2500 g / mol. The rest of the formulation and production process remained unchanged. The produced products were packaged and stored. The drying test method was the same as in Example 1, and the hardness and Vicat softening point were tested.

[0047] Example 3

[0048] Following the formulation of Example 2, the hard segment content was increased to produce a product with an actual hardness of 60D. The remaining formulations, processes, and testing methods were the same as in Example 1.

[0049] Table 1 shows the product performance test results for each embodiment.

[0050] Table 1

[0051]

[0052] As shown in Table 1, comparing Example 1 and Example 2, Example 2 has a significantly lower hardness for the same hard segment content, but its Vicat softening point is significantly higher than that of Example 1. Comparing Example 1 and Example 3, it can be seen that Example 3 uses more MDI and has the highest Vicat softening point for the same hardness. In other words, the Vicat softening points, ranked from highest to lowest, are Example 3, Example 2, and Example 1. Example 1 exhibits the best temperature sensitivity, as evidenced by the changes in creases at 40°C.

[0053] Moreover, the test pieces hardened significantly when placed at 10°C, with Example 1 showing the most significant change in hardness, demonstrating excellent high-temperature deformation and low-temperature recovery effects.

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

Claims

1. A type of easily deformable TPU used in toy manufacturing, characterized in that, The TPU raw material composition includes chain extenders, polyisocyanates, and one or more polyester polyols; the chain extenders include at least one of ethylene glycol, propylene glycol, butanediol, and pentanediol; The polyester polyol is formed by connecting acid structural units and alcohol structural units through ester bonds, wherein the acid structural units include at least one of oxalic acid, adipic acid and terephthalic acid, and the alcohol structural units include at least one of butanediol, propylene glycol and ethylene glycol; the number average molecular weight of the polyester polyol is 1000~3000 g / mol. The hard segment content in the TPU is between 20wt% and 40wt%; The TPU softens at 30~60℃ and hardens and sets below 10℃. The TPU has a hardness between 45D and 70D at 23±2℃ / 50%RH.

2. The use according to claim 1, characterized in that, The polyester polyol is prepared by any one or more combinations of the following methods: a) Acid structural units and alcohol structural units are esterified and polymerized into the polyester polyol; b) Poly(butylene adipate-butylene terephthalate) PBAT and / or poly(ethylene adipate-ethylene terephthalate) PEAT are depolymerized to obtain the polyester polyol; c) At least one of polybutylene terephthalate (PBT), polypropylene terephthalate (PTT), and polyethylene terephthalate (PET) is mixed with a polyester polyol and optionally a small molecule alcohol, heated to depolymerize, and stirred under vacuum to obtain the polyester polyol.

3. The use according to claim 1, characterized in that, The polyisocyanate includes at least one of MDI, TDI, HDI, HMDI, IPDI, and PPDI.

4. The use according to claim 1, characterized in that, The raw material composition also includes at least one of lubricant, antioxidant, and catalyst.

5. The use according to any one of claims 1 to 4, characterized in that, The preparation methods of TPU include: The raw material is added to a twin-screw reactive extruder for reactive extrusion and underwater pelletizing to obtain the TPU.

6. The use according to claim 5, characterized in that, The temperature of the reaction section of the twin-screw reactive extruder is 170~250℃, and the temperature of the cooling section is 90~150℃.

7. The use according to claim 6, characterized in that, The temperature of the reaction section of the twin-screw reactive extruder is 180~210℃, and the temperature of the cooling section is 130℃.

8. The use according to claim 5, characterized in that, The water temperature for underwater pelleting is less than 30°C.

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