TPU (Thermoplastic Polyurethane) with deformation easy to recover as well as preparation method and application thereof

Abstract

The invention discloses TPU (thermoplastic polyurethane) with deformation easy to recover, a preparation method of the TPU and application of the TPU in manufacturing toys. The TPU raw materials comprise a chain extender, polyisocyanate and one or more polyester polyols; the polyester polyol is formed by connecting an acid structural unit and an alcohol structural unit through an ester bond, the acid structural unit comprises at least one of terephthalic acid, oxalic acid and adipic acid and must comprise terephthalic acid, and the alcohol structural unit comprises at least one of butanediol, propylene glycol and ethylene glycol; the content of hard segments in the TPU ranges from 10 wt% to 50 wt%; tPU is softened at 30-60 DEG C, and is hardened and shaped at 10 DEG C or below. The preparation method comprises the following steps: adding the raw materials into a double-screw reactive extruder for reactive extrusion, and carrying out underwater pelletizing to obtain the TPU.

Description

Technical Field

[0001] The invention relates to the field of thermoplastic polyurethane elastomer (TPU), and in particular to a TPU with easy-to-recover deformation, and a preparation method and application thereof. Background Art

[0002] Most of the building block toys used by children nowadays are hard plastic products such as ABS (acrylonitrile-butadiene-styrene), PVC (polyvinyl chloride), PC (polycarbonate), and PP (polypropylene). Although they are light and easy to shape, they are difficult to restore once damaged due to the limitations of the material. Moreover, they are prone to form sharp edges after cracking or breaking due to large external forces such as squeezing or collision, which may scratch young children and pose a safety hazard. Moreover, once the toy is damaged, it is difficult to restore it.

[0003] The patent specification with publication number CN116462818A discloses a discoloration-resistant antibacterial thermoplastic polyurethane elastomer, a preparation method and its application. The thermoplastic polyurethane elastomer is made of the following raw material components: (a) polyol, (b) isocyanate, (c) chain extender, (d) end-capping agent containing hydrazide group and (e) silver ion antibacterial agent. The preparation method comprises: 1) adding isocyanate, polyol and chain extender to a reaction extruder through a first feeding port after blending, and reacting to obtain a thermoplastic polyurethane elastomer melt; 2) adding the end-capping agent containing hydrazide group to the reaction extruder from a second feeding port, and continuing to react to obtain a hydrazide-terminated thermoplastic polyurethane elastomer; 3) melt blending the product of step 2) with the silver ion antibacterial agent to obtain the discoloration-resistant antibacterial thermoplastic polyurethane elastomer. The discoloration-resistant antibacterial thermoplastic polyurethane elastomer can be used in the fields of automobiles, medical treatment, transportation, 3C electronics, daily necessities, children's toys, shoes and clothing. This patented technology focuses on the antibacterial properties of TPU products, but does not focus on the specific usage of TPU products after they are made into children's toys, such as deformation under force, breakage, and recovery.

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

[0005] The invention provides a TPU with easy-to-recover deformation and a preparation method and application thereof.

[0006] The TPU product of the present invention has good softness at room temperature and stable shape. It is difficult for the product to be broken by strong external force, and it can be easily restored if it is squeezed and deformed.

[0007] The TPU of the present invention has the main characteristics of being more sensitive to temperature, being able to maintain good stiffness at 10-30°C, being able to soften rapidly at about 30-60°C, and being able to be quickly shaped at a temperature below 10°C.

[0008] The TPU material of the present invention has the advantages of fast molding of hard plastic, light material, environmental protection, food grade, etc., and is easy to recover from deformation. It is easier to recover after being deformed by medium pressure during use, and has better durability. Moreover, it will only deform but not break when squeezed by strong external force at normal indoor temperature, and it cannot form sharp edges, so it is safer to use.

[0009] If other existing TPU products want to achieve the same hardness as the TPU of the present invention, the required cost is higher, and the temperature sensitivity is far worse than the TPU product of the present invention, and the requirement of easy deformation is not met.

[0010] The specific technical solutions are as follows:

[0011] In a first aspect, the present invention provides a deformation-recoverable TPU, the raw materials of which include a chain extender, a polyisocyanate and one or more polyester polyols.

[0012] The polyester polyol can be formed by connecting an acid structural unit and an alcohol structural unit through an ester bond, 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 deformation-recoverable TPU described in the first aspect is preferably between 10wt% and 50wt%, and further preferably between 20wt% and 40wt%. If the hard segment content is too low, the polyester polyol addition ratio is high, the polyester polyol has high viscosity, and has a greater impact on the reaction rate after mixing with isocyanate, and has more stringent reaction requirements, which is not easy to achieve. If the hard segment content is too high, although the reaction rate is improved, the hardness of the molded product is too high, and the reaction is more exothermic. If the reaction is not well controlled, it is easy to cause local overheating, affecting the stability of the product. The hard segment range of 10wt% to 50wt% is the optimal choice for formula processing and process synthesis. The process feasibility is higher in the range of 20wt% to 40wt%, and the performance stability of the TPU product is better.

[0014] The deformation-recoverable TPU described in the first aspect softens at 30-60° C. and hardens and sets at below 10° C.

[0015] The isocyanate index (R value) of the easily deformable TPU described in the first aspect may be 0.98 to 1.0, such as 0.99.

[0016] In the first aspect of the TPU with easy deformation recovery, the number average molecular weight of the polyester polyol is preferably 500-5000 g / mol, more preferably 1000-3000 g / mol, for example 2500 g / mol, etc. If the viscosity of the polyester polyol is too low, the reaction rate is fast, and excessive heat release is easy to affect the stability of the product. If the viscosity of the polyester polyol is too high, it is not conducive to the normal reaction. After experimental optimization, the synthesis process of the polyester polyol reaction with a number average molecular weight of 1000-3000 g / mol is the best.

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

[0018] a) the acid structural unit and the alcohol structural unit are esterified (which may include one or more of co-esterification, fractional esterification, tandem esterification, etc.) and polycondensed to form the polyester polyol;

[0019] b) obtaining the polyester polyol by depolymerization 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 polyester polyol (for example, one or more of polyethylene oxalate diol, polyethylene adipate diol, polyethylene oxalate diol, polypropylene adipate diol, polybutylene oxalate diol, and polybutylene adipate diol, etc.) and / or a small molecule alcohol, heated for depolymerization, and vacuum-stirred to obtain the polyester polyol.

[0021] In c), the small molecule alcohol may be an alcoholysis agent commonly used in the art for alcoholysis of polyesters, such as ethylene glycol.

[0022] PBAT is a thermoplastic biodegradable plastic, a copolymer of butylene adipate and butylene terephthalate, with the characteristics of PBA (polybutylene adipate) and PBT, high strength and low melting point. The TPU product is further synthesized by synthesizing polyester polyols using PBAT, PEAT and other products as raw materials. The molecular chain is more complex, the regularity is poor, the crystallinity is low, the benzene ring structure and the presence of a large number of hydrogen bonds provide the conditions for high strength and hardness of the product, thereby giving TPU a wider deformation ability. Combined with the temperature sensitivity of TPU itself, the synthesized TPU product has higher hardness and is more sensitive to temperature.

[0023] The synthesis method and material selection of the polyester polyol of the present invention are diverse, which is one of the important features of the present invention. For example, it can be one or more of polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate, or it can be a mixture of one or more of polyethylene terephthalate, polypropylene terephthalate, and polybutylene terephthalate with one or more of polyethylene adipate, polybutylene adipate, etc. The PBAT, PEAT, PET, PBT, PTT, etc. mentioned in the present invention can be virgin materials, recycled materials, regenerated materials, or any combination thereof, which increases the diversity of material selection and thus reduces the cost of raw materials.

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

[0025] In the first aspect of the TPU with easily recoverable deformation, the polyisocyanate may include at least one of MDI (diphenylmethane diisocyanate), TDI (toluene diisocyanate), HDI (hexamethylene diisocyanate), HMDI (dicyclohexylmethane-4,4'-diisocyanate), IPDI (isophorone diisocyanate), and PPDI (p-phenylene 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 hardness of the easily deformable TPU described in the first aspect is between 45D and 70D in an environment of 23±2°C / 50%RH (relative humidity). If the hardness is lower than 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 when used as a toy if there are sharp parts.

[0027] The deformation-recoverable TPU described in the first aspect may further include at least one of a lubricant, an antioxidant, a catalyst, etc. The present invention does not particularly limit the lubricant, the antioxidant, and the catalyst, and any commonly used substance in the art may be used.

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

[0029] In a second aspect, the present invention provides a method for preparing the deformation-recoverable TPU according to the first aspect, comprising:

[0030] The raw materials are added into a twin-screw reaction extruder for reaction extrusion and underwater pelletizing to obtain the TPU.

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

[0032] In the preparation method of the second aspect, the water temperature of the underwater pelletizing is less than 30°C (e.g., 10°C). If the water temperature is above 30°C, the TPU particles will become soft and deformed during underwater pelletizing, and the pelletizing operation cannot be performed normally. Normal production can only be performed when the water temperature is below 30°C.

[0033] In a third aspect, the present invention provides use of the deformation-recoverable TPU described in the first aspect for making toys.

[0034] Compared with the prior art, the present invention has the following beneficial effects:

[0035] The TPU product of the present invention obtains higher hardness at a low MDI dosage ratio (the existing conventional TPU needs to use a larger MDI dosage ratio to achieve the same hardness as the TPU of the present invention). The TPU product of the present invention is extremely significantly affected by temperature. The product maintains the flexibility and stiffness of the TPU product, has sufficient stiffness at room temperature and excellent impact strength, is easy to control the shape, and once deformation occurs, it can be softened with warm water and then placed in a low-temperature environment such as a refrigerator to restore the shape. The operation is simple and the safety is high.

[0036] The higher the hardness of conventional TPU products, the more difficult it is to completely recover after deformation, because the internal stress of TPU products is difficult to eliminate after deformation, and high temperature or even complete plasticization is required to eliminate the internal stress. The TPU products of the present invention are extremely sensitive to temperature, and the internal stress can be reduced between 30 and 60°C. They can quickly restore to shape at low temperatures (such as 10°C), have stronger deformation ability, and are safer to use.

[0037] The TPU product of the invention has a good hand feel at 0-30°C, and its hardness and flexibility meet the use requirements. It can be quickly softened at 30-60°C and can be quickly shaped at below 10°C. DETAILED DESCRIPTION

[0038] 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.

[0039] 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.

[0040] Example 1

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

[0042] Use a twin-screw reaction extruder, set the reaction section temperature at 180-210°C, the cooling section temperature at 130°C, the pelletizing water temperature at 10°C, perform underwater pelletizing, and pack and store.

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

[0044] Test hardness and Vicat softening point.

[0045] Example 2

[0046] Refer to the formula of Example 1, wherein the standby polyester polyol is replaced with polybutylene adipate diol, with a number average molecular weight of 2500 g / mol, and the rest of the formula and production process remain unchanged, the produced products are packaged and put into storage, and the baking material testing method is the same as in Example 1, and the hardness and Vicat softening point are tested.

[0047] Example 3

[0048] According to 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 those of Example 1.

[0049] Table 1 shows the performance test results of the products in various embodiments.

[0050] Table 1

[0051]

[0052] As shown in Table 1, when Example 1 is compared with Example 2, the hardness of Example 2 is significantly lower at the same hard segment content, but the Vicat softening point is significantly higher than that of Example 1. When Example 1 is compared with Example 3, it can be seen that at the same hardness, more MDI is used in Example 3, and the Vicat softening point is the highest. In other words, the Vicat softening points are ranked from high to low as Example 3, Example 2, and Example 1, and Example 1 has the best sensitivity to temperature. It can also be seen from the change of the crease at 40°C that Example 1 has the best temperature sensitivity.

[0053] Moreover, the test piece hardened obviously when placed at 10°C, and the hardness change of Example 1 was the most obvious, with excellent high-temperature deformation and low-temperature recovery effects.

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

Claims

1. A TPU with easy deformation recovery, characterized in that: The raw material composition includes a chain extender, a polyisocyanate and one or more polyester polyols; The polyester polyol is formed by connecting an acid structural unit and an alcohol structural unit through an ester bond, wherein the acid structural unit includes at least one of terephthalic acid, oxalic acid, and adipic acid and must include terephthalic acid, and the alcohol structural unit includes at least one of butanediol, propylene glycol, and ethylene glycol; The hard segment content in the TPU is between 10wt% and 50wt%, preferably between 20wt% and 40wt%; The TPU softens at 30-60°C and hardens and sets at below 10°C.

2. The TPU according to claim 1, characterized in that The number average molecular weight of the polyester polyol is 500 to 5000 g / mol, preferably 1000 to 3000 g / mol.

3. The TPU according to claim 1 or 2, characterized in that The polyester polyol is prepared by a method selected from any one or more combinations of the following: a) synthesizing the polyester polyol through esterification and polycondensation of acid structural units and alcohol structural units; b) obtaining the polyester polyol by depolymerization of PBAT and / or PEAT; c) mixing at least one of PBT, PTT and PET with polyester polyol and / or small molecule alcohol, heating and depolymerizing, and vacuuming and stirring to obtain the polyester polyol.

4. The TPU according to claim 1, characterized in that The chain extender includes at least one of ethylene glycol, propylene glycol, butanediol, and pentanediol; The polyisocyanate includes at least one of MDI, TDI, HDI, HMDI, IPDI, and PPDI.

5. The TPU according to claim 1, characterized in that The hardness of the TPU under an environment of 23±2° C. / 50% RH is between 45D and 70D.

6. The TPU according to claim 1, characterized in that The raw material composition also includes at least one of a lubricant, an antioxidant, and a catalyst.

7. The method for preparing TPU according to any one of claims 1 to 6, characterized in that: include: The raw materials are added into a twin-screw reaction extruder for reaction extrusion and underwater pelletizing to obtain the TPU.

8. The preparation method according to claim 7, characterized in that: The reaction section temperature of the twin-screw reaction extruder is 170-250° C. (eg, 180-210° C., etc.), and the temperature of the cooling section is 90-150° C. (eg, 130° C., etc.).

9. The preparation method according to claim 7 or 8, characterized in that: The water temperature of the underwater pelletizing is less than 30° C. (eg, 10° C., etc.).

10. Use of the TPU according to any one of claims 1 to 6 for making toys.

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