TPU plastic

When choosing between the material types for a certain usage, it is significant to distinct between Thermoplastic Elastomers (TPE) and Thermoplastic Polyurethane (TPU). Both are versatile polymers and have some special characteristics. They allow them to be applied in many fields. TPEs are famous for their flexibility, their readiness for processing, and their low cost. So, this makes TPEs suitable for those applications where only moderate performance is needed. Unlike TPUs, provide improved toughness, wearing, and chemical properties to serve challenging applications as well as higher performance requirements. So, in this article, we will explore TPE vs TPU, their differences, similarities, and properties.

What is TPE?

TPEs are the short form of Thermoplastic Elastomers. It’s a type of polymer that has characteristics of rubber with recyclable thermoplastic material. It is as flexible as rubber but at the same time as manageable as thermoplastics. TPEs are mostly used in those areas in which flexibility, strength, as well as ease of formulating, are considered vital.  Go to is TPE safe to know more about TPE.

What is TPU?

Thermoplastic Polyurethane (TPU) is described as a thermoplastic elastomer with very high resilience, strength, and abrasion, chemical, and oil resistance. TPU is notable for the features of both plastic and elastomeric materials and exhibits outstanding performance in many severe applications. Got to is TPU safe to know more about TPU.

TPU plastic material

Complete Process of the Manufacturing of TPE and TPU?

Let’s discuss the complete process of manufacturing both TPE and TPU.

1. Manufacturing Process of TPE

The following is the step-by-step process of Thermoplastic Elastomers manufacturing.

1. Blending

In the case of TPEs like Styrenic Block Copolymers (SBCs), the method of manufacture is by compounding the polystyrene with elastomeric polymers, i.e. polybutadiene. The composition is heated to melt it and then the solidification process is carried out to obtain the final product.

2. Polymerization

In the formation of TPEs, the propylene must be reacted with other monomers in a controlled manner. So, it can produce a thermoplastic elastomer. This process can be done through some techniques including bulk or solution polymerization.

3. Vulcanization

Concerning the production of Thermoplastic Vulcanizates (TPVs), the method used during the formation is called dynamic vulcanization. During the melt processing of this thermoplastic polymer, a cross-linking agent, i.e. sulfur is added in this process. The end product is a blend where the elastomeric part is at least partially cross-linked. Then it helps improve the material’s elasticity and mechanical characteristics.

4. Extrusion and Molding

Following the blending or polymerization, TPEs then need to be processed through extrusion or injection molding. Extrusion on the other hand involves the use of a die to extrude continuous shapes of the molten TPE. Whereas injection molding is carried out by injecting the molten material into molds to make desired shapes and products.

2. Manufacturing Process of TPU

Here is the step-by-step process of Thermoplastic Polyurethane (TPU) manufacturing.

TPE vs TPU

1. Polymerization

We make TPU using diisocyanates (for instance methylene diphenyl diisocyanate or toluene diisocyanate) and diols (e.g. polyether or polyester diols). So, this reaction is carried out in a controlled manner to produce the polyurethane polymer.

2. Compounding

After polymerization, the TPU polymer is mixed with fillers such as plasticizers, stabilizers, and colorants, to facilitate it to develop the required characteristics. In this process, melt mixing is carried out using an extruder. Although other methods may be involved at this stage.

3. Extrusion and Injection Molding

TPU like any other thermoplastic elastomer is processed by extrusion or injection molding. Although more advanced methods are used in the processing of TPU as compared to TPEs. Extrusion is the process, in which TPU is forced through a die and shaped into long profiles. While injection molding is the process of injecting the TPU into a mold to make certain parts.

4. Calendering and Casting

For some applications, TPU can also be processed through the calendering process in which TPU is turned into very thin sheets through rolling or casting. Here TPU is poured directly into films or sheets.

Properties of TPU

  • Flexibility: TPU provides great flexibility and elasticity for the analyses.
  • Durability: Referred for quality features such as abrasion, wear and tear resistance.
  • Chemical Resistance: Withstands oil, grease, and chemicals moderately well.
  • Temperature Range: Since they can work at high speeds, this design of UV LED can be used in a broad temperature range of -40°C to +80°C.
  • Transparency: It is possible to make TPU transparent which can be advantageous in some uses.

 Properties of TPE

  • Elasticity: Exhibits rubber-like elasticity.
  • Processability: They are easy to process as well as mold with good flow characteristics.
  • Flexibility: Usually has moderate workability but can be specially compounded to give it low or high hardness.
  • Recyclability: It can be recycled which makes it an environmentally friendly mattress.
  • Cost-Effectiveness: Usually cheaper as compared to some of the other elastomers.

Material characteristics of TPE and TPU

  1. TPE Materials: TPEs are based on several polymers, i.e. styrene block copolymers, polyolefins, and thermoplastic vulcanizates. They are regularly compounded with additives like plasticizers, stabilizers, fillers, and colorants to obtain desired characteristics. The other two are the processing help and the specialty additives which can also be utilized to improve the performance and workability.
  2. TPU Materials: TPUs are produced either from polyester or polyether diols together with diisocyanates. They contain plasticizers, stabilizers, fillers, and colors. While the others have cross-linking agents for better performance. Functional additives which are also referred to as processing resources and specialty additives are intended for altering physical characteristics and performance.

What is the difference between TPE vs TPU?

Let’s discuss the major differences between TPE and TPU in depth

1. Chemical Composition

  • TPE: This is a generic classification that contains a range of polymers falling under this category including SBCs, TPOs, and TPVs. These are a polymer that exhibits both elasticity and thermoplastic characteristics. So, they may be either blends or copolymers.
  • TPU: More precisely they are produced by polyurethanes, which are formed by the action of diisocyanates and diols. TPUs are examples of thermoplastic elastomers, however, they are chemically different from other thermoplastic elastomers. Besides this, they are made from polyurethane.

2. Material Characteristics

  • TPE: Provides softness and flexibility of the product. TPEs can be made to have moderate elasticity or high elasticity depending on the requirement of the application it will be used. These cause them to be generally more easily processed and shaped because of lower processing temperatures and viscosities.
  • TPU: This material has a notable excellent abrasion resistance, and high mechanical strength and it is chemically and oil resistant. TPUs do not lose their performance when exposed to low or high temperatures.

3. Processing and Manufacturing

  • TPE: Faster to decompose, or having lower melt viscosity. It is easier to process and therefore, cheaper to manufacture. Products made from TPE mostly undergo injection molding, extrusion as well as blow molding.
  • TPU: Needs to be processed at higher temperatures and the melt viscosity to be higher makes the processing more challenging. Nonetheless, TPU can be processed in the same manner with popular tactics such as injection mold and extrusion.

4. Performance Properties

  • TPE: Has poor abrasion resistance and mechanical strength in comparison to TPU. It may also not withstand severe chemical or high/low temperatures better than the other types.
  • TPU: It demonstrates very high tensile strength, superior abrasive characteristics, and satisfying results in low and high-temperature ranges. It offers better chemical resistance as it can handle difficult chemical environments.

5. Cost and Recyclability

  • TPE: Usually cheaper than TPU and it is easier to recycle as well. Compared to metals, its processing and material costs are usually lower. So, it is suitable for most uses.
  • TPU: Has a lower cost than TPE because it offers better performance characteristics. TPU can be tougher to recycle. So, its environmental impact might be influenced.

6. Applications

  • TPE: Found in consumer products, automotive applications, sealing applications, gaskets, and medical devices. It is selected for applications where flexibility and costs are key requirements rather than looking for a high degree of durability.
  • TPU: Common in applications demanding high performance, i.e. manufacturing of car parts, industrial parts, sports shoe soles, and medical apparatus among others. It is best suited for products that require or want high-level abrasion, evidently chemical, and high degrees of utterance.
CharacteristicTPE (Thermoplastic Elastomers)TPU (Thermoplastic Polyurethane)
Chemical CompositionIt is generally made of various polymers (e.g., SBCs, TPOs, TPVs)It is a composition of Polyurethanes (diisocyanates + diols)
Material CharacteristicsRelatively flexible, soft, and can be rigid or flexibleShows high abrasion resistance, strong, and chemical-resistant
ProcessingQuite Easier, needs lower temperatures, and requires simpler moldingIt might require Higher temperatures and have more complex processing
Performance PropertiesGenerally have a lower abrasion and mechanical strength. Besides this, it has limited chemical resistanceHave superior abrasion resistance, high strength, and extreme temperature performance
Cost and RecyclabilityGenerally lower cost, easier to recycleHave a Higher cost and is more challenging to recycle
ApplicationsWide applications in consumer goods, automotive parts, seals,  and medical devicesMany uses in industrial parts, footwear, automotive components, and medical devices

What are the similarities between TPE vs TPU?

Both TPE and TPU belong to the thermoplastic family. So, they have many things in common. Let’s discuss these common features in detail.

  • Thermoplastic Nature: Both can be reused and recycled several times by heating the process.
  • Elastic Properties: They also get deformed, but these two materials are flexible, and they regain their original state once they are released from the deforming force.
  • Processing Methods: All three processing methods, namely injection molding, extrusion, and blow molding are used for both.
  • Customizable: Both can be of different hardness, flexibility, and strength depending on the engineering requirements.
  • Consumer Products: Both of them can be applied in car components, clinical devices, and home appliances.
  • Overlapping Use Cases: They are good for use when there is a need for flexibility and toughness for the required product.
  • Recyclability: Both are recyclable in most cases although the process of recycling may be different.
  • Environmental Resistance: They provide some extent of barrier against moisture and Ultra Violet light, depending on the formulation.
TPE injection mold

TPE injection mold

What Are the Mutual Alternatives to TPE and TPU?

MaterialDescriptionAdvantagesDisadvantages
Silicone RubberIt is an elastomer with high flexibility and temperature resistance.Excellent temperature stability and chemical resistance.Typically more expensive, and harder to process.
EPDM RubberMainly a synthetic rubber with good weather and ozone resistance.Shows high durability, good for outdoor use.It has lower flexibility than TPE and TPU.
NeopreneIt is also a synthetic rubber known for flexibility and weather resistance.Have good chemical resistance and flexibility.It has less tensile strength and abrasion resistance.
Viton (FKM)It is a fluoroelastomer with high chemical resistance.Have superior chemical and temperature resistance.Have high cost and rigidity.
Polyolefin Elastomers (POE)Flexible and versatile material similar to TPE.Has good flexibility and low density.It has limited chemical resistance compared to TPU.

What Are the Benefits of TPE Compared to TPU?

  1. Cost-Effective: Usually there is a higher production cost when manufacturing solid foods but the cost is generally lower.
  2. Ease of Processing: Reduced temperatures at which the articles can be processed, and easier molding of the material.
  3. Flexibility and Softness: A comprehensive parameter of the softness and flexibility of surgical staplers is available.
  4. Recyclability: Recyclability or reusability in form and material is the fourth criterion and states that an object should be easy to recycle or reprocess.
  5. Versatile Formulations: Exists in different forms to meet specific properties of the specific application.

What Are the Drawbacks of TPE Compared to TPU?

  • Lower Abrasion Resistance: Leaves a lot to be preferred in high-wear applications.
  • Chemical Resistance: In general, more susceptible to chemical, oil, and solvent attacks.
  • Temperature Tolerance: Reduced performance where the temperatures are either high or low.
  • Mechanical Strength: Generally it exhibits lower tensile strength and tear strength.

What Are the Benefits of TPU Compared to TPE?

  1. Superior Abrasion Resistance: Extreme wear nature provides a very good performance in applications that are likely to wear out quickly.
  2. Chemical and Oil Resistance: Not easily decomposed by chemical solvents and other chemicals.
  3. High Performance at Extremes: Resistant to high and low temperatures of both ambient and dry ice.
  4. Strong Mechanical Properties: Superior tend strength and increased impact qualities.
  5. Customizable: Comesity of hardness and elasticity, options.

What Are the Drawbacks of TPU Compared to TPE?

  • Higher Cost: As a homemade product, it will be more expensive to produce than traditional consumer products.
  • Processing Complexity: It needs high temperatures and specific apparatus or instruments.
  • Recycling Challenges: When it comes to recycling it is more difficult to do so compared to the TPE.
  • Limited Formulations: There are fewer types compared to TPE as a result of development.

When to Choose TPE?

  • Cost-Efficiency: When budget is an issue, as with TPE, the use of this form can be less costly.
  • Simple Processing: For applications wherein easy molding is required and the molding temperature is comparatively low.
  • Flexibility: When the application of the rubber products involves elements that require softness and flexibility such as grips or seals.
  • Recyclability: While for production that is environmentally friendly with relation to its impact and easy to recycle.
  • General Use: These are the applications that do not require high-level performance from the brushes.

When to Choose TPU?

  • Durability: Where there is going to be high wear and friction and high abrasiveness is required.
  • Chemical Resistance: When working with chemicals, oils or solvents are to be encountered Individuals that have to wear gloves include those when working with.
  • Temperature Extremes: When it comes to high temperatures and even for low temperature application could also be attained.
  • Mechanical Strength: If high tensile and impact strength applications are required.
  • Special Performance Needs: for such specific needs to be met by various built environments, one can refer to customized properties like
TPU injection mold

TPU injection mold

Conclusion

In conclusion, TPE Vs. TPU, despite the similarities, TPE and TPU are different materials with their notable features and drawbacks in the aspects of usage. TPEs are relatively cheaper, and their processing is also easier as compared to other elastomer. This makes it versatile to use. At the same time, TPUs are designed for the highest loads and requirements in terms of wear, heat, and chemical resistance. As for the differences in properties of TPE and TPU, it is possible to state the following: The superiority or inferiority of TPE as compared to TPU depends on the special demands of the material, cost considerations, and technological capabilities of further processing of the product.

Frequently Asked Questions

Q1. What is the primary difference between TPE and TPU?

The most significant distinction is that TPU is a particular kind of TPE. However, it has higher potential regarding its strength, resistance to chemicals or solvents, and adapted temperature segments.

Q2. Are TPU and TPE recyclable?

Recycling of TPE and TPU is possible although the options that are available for recycling are limited as compared to other thermoplastic elastomers.

Yes, TPE is recyclable; the same case applies to TPU materials as well.

Q3. Which of the two is cheaper, TPE or TPU? 

TPE has a slightly lower cost as compared to TPU.

Q4. How does TPU differ from TPE concerning their applications

TPU is suitable where reinforcement is necessary, the application is exposed to chemicals or harsh environments, and the application also needs to withstand high heat.

Q5. Can TPE be used in regions with extraordinary climate conditions?

There are some disadvantages related to TPE. Due to this, it may not be as equally effective as TPU specifically in severe conditions.

TPU portable computer cover

What is TPU Injection Molding

TPU injection molding refers to the process of injecting Thermoplastic Polyurethane (TPU) into a mold to produce a finished product. TPU is a type of material that exhibits the properties of both thermoplastics and elastomers. It is often used to produce products that require flexibility, durability, and resistance to abrasion.

TPU injection molding is a versatile process that can be used to produce a wide variety of products, including footwear, industrial parts, medical devices, and more. It offers many benefits over traditional manufacturing methods, including lower costs, faster production times, and greater design flexibility. TPU materials are also recyclable, making them a more sustainable option for manufacturers.

TPU (Thermoplastic polyurethane) injection molding process has many methods, including injection molding, blow molding, compression molding, extrusion molding, etc., among which injection molding is most commonly used. use the injection molding process to mold TPU into required TPU injection molding parts, which are divided into three stages: pre plasticizing, injection, and ejecting out. The injection machine is divided into plunger type and screw type. Screw type injection machine is recommended because it provides uniform speed, plasticization, and melting.

TPU phone cover molding

TPU phone cover molding

1. Design of injection machine

The barrel of the injection machine is lined with copper-aluminum alloy, and the screw is chrome plated to prevent wear. The length diameter ratio of screw L / D = 16 ~ 20 is better, at least 15; the compression ratio is 2.5/1 ~ 3.0/1. The length of the feeding section is 0.5L, the compression section is 0.3L, and the metering section is 0.2L. The check ring shall be installed near the top of the screw to prevent backflow and maintain the maximum pressure.

The TPU should be processed with a self flow nozzle, the outlet is an inverted cone, the nozzle diameter is more than 4mm, less than 0.68mm of the main channel collar inlet, and the nozzle should be equipped with a controllable heating belt to prevent material solidification.

From an economic point of view, the injection volume should be 40% – 80% of the quantitative amount. The screw speed is 20-50 R / min.

2. Mold design for TPU injection molding

Mold design should pay attention to the following points when molding with tpu material injection molding:

(1) shrinkage of molded TPU molding parts

Shrinkage is affected by the hardness of raw materials, thickness, shape, molding temperature, mold temperature, and other molding conditions. Generally, the shrinkage range is 0.005-0.020cm/cm. For example, a 100 x 10 × 2mm rectangular test piece shrinks in the length direction of the gate and the flow direction, and the hardness of 75A is 2-3 times larger than that of 60 shore degree. The effect of hardness and thickness of TPU on shrinkage is shown in Figure 1. It can be seen that when the hardness of TPU is between 78a and 90a, the shrinkage decreases with the increase of thickness; when the hardness is between 95A and 74d, the shrinkage slightly increases with the increase of thickness.

(2) Runner and cold slot well

The main runner is a section of the runner connecting the injector nozzle to the shunt channel or cavity in the mold. The diameter should be expanded inward, with an angle of more than 2 degree, so as to facilitate the removal of flow channel vegetations. The shunt channel is the channel connecting the main channel and each cavity in the multi-groove mold, and its arrangement on the mold should be symmetrical and equidistant. The flow channel can be circular, semi-circular and rectangular, with a diameter of 6-9mm. The runner surface must be polished like the cavity to reduce flow resistance and provide a faster filling speed.

A cold well is an empty place (extra extend runner) at the end of the main runner, which is used to catch the cold material produced between the two injections at the end of the nozzle, so as to prevent the diversion runner or gate from blocking by cold material. When the cold material is mixed into the mold cavity, the internal stress of the product is easy to occur. The diameter of the cold material hole is 8-10 mm, and the size is about 6 mm long.

(3) gate and vent

The gate is the runner connecting the main flow channel or the shunt channel and the cavity. Its cross-sectional area is usually smaller than the runner passage, which is the smallest part of the runner system, and its length should be short. The gate shape is rectangular or circular, and the size increases with the thickness of the product.

The thickness of the product is less than 4mm, with a diameter of 1mm; the thickness of the gate is 4-8mm, with a diameter of 1.4mm; the thickness of the gate is more than 8mm, with a diameter of 2.0-2.7mm. The gate position is generally selected at the thickest part of the product, which does not affect the appearance and use, and is at right angles to the mold, so as to prevent shrinkage and avoid spiral pattern.

Exhaust or venting slot is a kind of slot type air outlet opened in the mold, which is used to prevent the molten material from entering the mold from getting involved in the gas and to discharge the gas from the mold cavity.

Otherwise, the products will have air holes, poor fusion, insufficient filling or air trap, and even burn the products due to high temperatures caused by air compression, resulting in internal stress of the products. The exhaust port can be set at the end of the melt flow in the mold cavity or on the parting line of the plastic mold, which is a 0.15mm deep and 6mm wide pouring slot.

It is necessary to control the TPU mold temperature as evenly as possible to avoid warping and twisting of the parts, below are some TPU injection molding products we made before. If you have any requirement for TPU or TPE injection molding  products, welcome to contact us.

TPU injection molding

TPU injection molding

3 Molding conditions

The most important molding condition of TPU (Thermoplastic polyurethane) is the temperature, pressure and time that affect the flow and cooling of plasticization. These parameters will affect the appearance and performance of TPU injection molding parts. Good processing conditions should be able to obtain even white to beige parts.

(1) Temperature

The temperature to be controlled in the TPU plastic injection molding process includes barrel temperature, nozzle temperature, and mold temperature. The first two temperatures mainly affect the plasticization and flow of TPU, and the second one affects the flow and cooling of the TPU injection molding part.

  • Barrel temperature – the selection of barrel temperature is related to the hardness of TPU material. The melting temperature of TPU with high hardness is high, and the highest temperature at the end of the barrel is also high. The temperature range of the barrel used for processing TPU is 177 ~ 232 ℃. The temperature distribution of the barrel is generally from one side (rear end) of the hopper to the nozzle (front end), gradually increasing, so as to make the TPU temperature rise steadily and achieve the purpose of uniform plasticization.
  • Nozzle temperature – the nozzle temperature is usually slightly lower than the maximum temperature of the barrel to prevent the possible salivation of molten material in the straight-through the nozzle. If the self-locking nozzle is used to prevent salivation, the nozzle temperature can also be controlled within the maximum temperature range of the barrel.
  • Mold temperature – mold temperature has a great influence on the internal performance and apparent quality of TPU products. It depends on the crystallinity of TPU and the size of products. Mold temperature is usually controlled by constant temperature cooling medium such as machine water.
    TPU has high hardness, high crystallinity, and high mold temperature. For example, Texin, hardness 480A, mold temperature 20-30 ℃; hardness 591A, mold temperature 30-50 ℃; hardness 355d, mold temperature 40-65 ℃. The mold temperature of TPU products is generally 10-60 ℃. Mold temperature is low, melting material is frozen too early and streamline is produced, which is not conducive to the growth of spherulites, so that the crystalline of products is low, and late crystallization process will occur, which will cause post shrinkage and performance change of products.
  • Pressure – the injection process is pressure including plasticizing pressure (back pressure) and injection pressure. When the screw retreats, the pressure on the top of the melt is the backpressure, which is regulated by the overflow valve. Increasing the back pressure will increase the melt temperature, reduce the plasticizing speed, make the melt temperature uniform and the color mixture uniform, and discharge the melt gas, but will extend the molding cycle. The backpressure of TPU is usually 0. 3 ~ 4MPa. Injection pressure is the pressure exerted on TPU by the top of the screw. Its function is to overcome the flow resistance of TPU from the barrel to the cavity, to fill the mold with molten material, and to compact the molten material.
    The flow resistance and filling rate of TPU are closely related to the melt viscosity, while the melt viscosity is directly related to TPU hardness and melt temperature, that is, the melt viscosity is not only determined by temperature and pressure, but also by TPU hardness and deformation rate. The higher the shear rate is, the lower the viscosity is; the higher the hardness of TPU is, the higher the viscosity is.
    Relationship between viscosity and shear rate of resin with different hardness (240℃). At the same shear rate, the viscosity decreases with the increase of temperature, but at the high shear rate, the viscosity is not affected as much by temperature as at a low shear rate. The injection pressure of TPU is generally 20 ~ 110MPa. The holding pressure is about half of the injection pressure, and the backpressure should be 1. Below 4MPa to make TPU plasticized evenly.
  • Cycle time – the cycle time required to complete an injection process is called the molding cycle time. Cycle time includes filling time, holding time, cooling time and other times (opening, demoulding, closing, etc.), which directly affects labor productivity and equipment utilization. The forming cycle of TPU is usually determined by hardness, thickness, and configuration. The high hardness cycle of TPU is short, the thick cycle of the plastic part is long, the complex cycle of plastic part configuration is long, and the forming cycle is also related to mold temperature. The TPU molding cycle is generally between 20-60s.
  • Injection speed – the injection speed mainly depends on the configuration of TPU injection molding products. Products with thick end face need lower injection speed, while products with thin end face need faster injection speed.
  • Screw speed – The processing of TPU injection molding products usually requires a low shear rate, so a lower screw speed is appropriate. The screw speed of TPU is generally 20-80r / min, so it is preferred to be 20-40r / min.

(2) Shutdown treatment

As TPU (Thermoplastic polyurethane) may degrade in extended time under high temperature, PS, PE, acrylate plastic or ABS should be used for cleaning after shutdown; if the shutdown lasts for more than 1 hour, heating should be turned off.

TPU plastic Injection molding

TPU plastic molding

(3) Post-treatment of products

Due to the uneven plasticization of TPU in the barrel or the different cooling rates in the die cavity, it often produces uneven crystallization, orientation, and contraction, which leads to the existence of internal stress in products, which is more prominent in thick-walled products or products with metal inserts. The mechanical properties of products with internal stress are often reduced, and the surface of products is craze or even deformed and cracked. The way to solve these problems in production is to anneal the products.

The annealing temperature depends on the hardness of TPU injection molding products. Products with high hardness have higher annealing temperatures and lower hardness temperatures. Too high temperatures may cause warpage or deformation of products, and too low temperatures cannot eliminate internal stress. TPU should be annealed at low temperature for a long time, and the products with lower hardness can be placed at room temperature for several weeks to achieve the best performance. The hardness can be annealed 80 ℃× 20h under shore A85, and 100 ℃× 20h above A85. Annealing can be carried out in the hot air oven, pay attention to the position not to locally overheat and deform the products.

Annealing can not only eliminate internal stress but also improve the mechanical properties. Because TPU is a two-phase form, phase mixing occurs during TPU hot working. When the TPU injection molding product is cooled rapidly, due to its high viscosity and slow phase separation, it must have enough time to separate and form a micro area, so as to obtain the best performance.

(4) Inlaid injection molding

In order to meet the needs of assembly and service strength, TPU injection molding parts need to be embedded with metal inserts. The metal insert is first placed in a predetermined position in the mold and then injected into a whole product. Because of the great difference of thermal properties and shrinkage between the metal insert and TPU, the TPU products with insert are not firmly bonded.

The solution is to preheat the metal insert because the temperature difference of the melt is reduced after preheating so that the melt around the insert can be cooled slowly and the shrinkage is relatively uniform during the injection process, and a certain amount of hot material feeding effect can occur to prevent excessive internal stress around the insert.

TPU is easy to inlay and the shape of inlay is not limited. Only after the inlay is degreased, it is heated at 200-230 ℃ for 1. The peel strength can reach 6-9kg / 25mm in 5-2min. In order to obtain a stronger bonding, the insert can be coated with adhesive, then heated at 120 ℃, and then injected. In addition, it should be noted that the TPU used should not contain lubricants.

(5) Recycling of recycled materials

In the process of TPU injection molding processing, wastes such as the main flow channel, shunt channel and unqualified products can be recycled. According to the experimental results, 100% recycled material can be fully utilized without adding new material, and the mechanical properties are not seriously reduced.

However, in order to keep the physical and mechanical properties and injection conditions at the best level, it is recommended that the proportion of recycled material be 25% ~ 30%. It should be noted that the type and specification of recycled materials and new materials should be the same.

The polluted or annealed recycled materials should not be used. The recycled materials should not be stored for too long. It is better to granulate and dry them immediately. Generally, the melt viscosity of recycled materials should be reduced and the forming conditions should be adjusted.

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