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Thermoplastic Rubber

Thermoplastic Rubber

Thermoplastic Rubber

TPR is a kind of rubber with high elasticity, high strength, high resilience, but also has the characteristics of injection molding, environmental protection, non-toxic and safe, wide range of hardness, excellent coloring, soft touch, weather resistance, fatigue resistance It has excellent temperature resistance, excellent processing performance, no need for vulcanization, and can be recycled to reduce costs. It can be molded by two-shot injection molding, covered and bonded with PP, PE, PC, PS, ABS and other matrix materials, or molded separately. TPR has both the processing properties of thermoplastics and the physical properties of vulcanized rubber. It can be described as a combination of advantages of plastics and rubber.Thermoplastic rubber is occupying territory that was originally only vulcanized rubber. In the past ten years or so, the rapid development of the electronics, communications and automobile industries has driven the rapid development of the thermoplastic rubber market.
 
TPR is usually an elastic material with a low elastic modulus, which can be repeatedly stretched to more than twice its original length at room temperature, and has the ability to almost completely recover to its original length after the stress is relieved. The early material with this characteristic was thermoset rubber, but many injection moldable thermoplastic rubber TPR series are replacing traditional rubber. In addition to being used in their basic form, TPR is also widely used for the modification of rigid thermoplastics, usually to improve impact strength. This is quite common for sheets and general molding grade composite materials.
 
TPR has the physical and mechanical properties of vulcanized rubber and the processing properties of thermoplastics. Since there is no need to undergo thermal vulcanization, the product can be produced using general plastic processing equipment. This feature shortens the production process of the rubber industry by 1 /4, saves energy consumption by 25% to 40%, and increases efficiency by 10 to 20 times. It can be called another revolution in materials and technology in the rubber industry.
 
Features of TPR
1. It can be processed by general thermoplastic molding machine without special processing equipment.
2. Easy to recycle and reduce costs. The waste produced during the production process (escape burrs, extrusion of waste rubber) and the final waste products can be directly returned for reuse; used TPR products can be recycled after simple regeneration, reducing environmental pollution and expanding sources of renewable resources.
3. A wider range of applications. Because TPR combines the advantages of rubber and plastic, it has opened up new application areas for the rubber industry.
 
Tensile properties of TPR
Tensile properties
Tensile properties are test values ​​​​used to describe how an elastomer will behave when stretched. There are several commonly used tests that show how elastomers will perform in the end-use environment.
 
Tensile strength at break
This test value is also called ultimate tensile strength. In this test, the elastomer test piece was stretched until it broke. The force required to break the material was also measured at the same time. The unit is usually pounds per square inch (psi) or megapascals (MPa). Elastomers with high ultimate tensile strength are less likely to break when compared with elastomers with lower test values.
 
Tear strength
This test value shows how well the elastomer resists tearing. The tear strength test is basically the same as the fracture tensile strength test, but there is a V-shaped notch on one side of the test piece as an expansion point. The tested material was stretched to tear completely, and the force to tear the test piece was also recorded at the same time. The unit is usually pounds per inch (psi) or kilonewtons per meter (kN/m).
 
Stretch modulus
In the tensile modulus test, the elastomer is stretched to various lengths, and its resistance to stretching is also measured separately. This test value is usually expressed as the tensile strength of the elastomer corresponding to various percentages of its length to the original length, such as the tensile strength at 50%, 100%, or 300%. The resistance of an elastomer to stretching may be strong at first, but it will become weaker as it stretches (called "neckedness").
 
Elongation at break
Elongation is not a measure of how difficult or easy it is to stretch the material, but just how long it can be stretched before it breaks. The elongation at break is expressed as a percentage of its original length. Some soft elastomers can be stretched to more than 1000% of their original length before breaking. The elongation of soft TPR elastomers is generally much higher than that of hard rigid materials.
 
Factors affecting the test value
The molding method of the test piece and the direction of melt flow will affect the test value of its tensile properties. Therefore, for many elastomers, the tensile properties in both the flow direction and the transverse direction have to be measured.
 
Flow direction
Like many other properties of elastomers, stretch properties are affected by the orientation of polymer molecules during molding. Therefore, depending on whether the stretching is performed along the flow direction of the polymer during molding or along the transverse direction, the stretching characteristics may vary greatly .
 
Test piece (Extrusion molding is relative to injection molding)
Some tests were performed with injection-molded test pieces, while other tests were performed with extruded test pieces. Since the test values ​​​​of different types of test pieces are significantly different, it is very important that only the test values ​​​​of the same type of test pieces can be compared.
 
Compression set of TPR
The compression set value is the amount of permanent deformation that occurs when a material is compressed to a certain shape at a certain temperature and maintained for a certain period of time.
The commonly used ASTM test method (ASTM D395) requires that the material be deformed (compressed) by 25% and maintained for a certain period of time. Let it recover for 30 minutes before measuring this sample.
23 °C (room temperature)
22 hours, 70 hours, 168 hours (1 week), 1000 hours (42 days).
70 °C
22 hours, 70 hours, 168 hours (1 week), 1000 hours (42 days).
121 °C
22 hours, 70 hours, 168 hours (1 week), 1000 hours (42 days).
150 °C
22 hours, 70 hours, 168 hours (1 week), 1000 hours (42 days).
The resulting test value is the percentage of the material sample that failed to return to its original height. For example, 40% compression set means that this thermoplastic rubber only recovers 60% of the compressed thickness. 100% compression set means that the thermoplastic rubber has not recovered at all, that is, it has maintained a compressed state.
Compression set is often confused with creep. However, compression set is the amount of deformation that occurs under a certain constant strain condition, and creep is the amount of deformation that occurs under a certain constant stress condition.
 
Applicable temperature of TPR
The term applicable temperature is used to roughly define the highest temperature at which a certain material is suitable for use.
The applicable temperature depends on many factors, including performance requirements, length of contact time, presence or absence of load, and design structure of the workpiece.
Some commonly used suitable temperature measurement methods are Vicat softening temperature, heat distortion temperature (HDT), American Safety Testing Laboratory (UL) method, semi-tensile strength and other proprietary methods, which vary by industry.
Examples of applications requiring higher applicable temperatures include automobiles, transportation, hydraulic hoses, and mine cables. Examples of applications that do not require a higher applicable temperature include general indoor uses, such as personal care products and handles on kitchen utensils, telephone tube cables, and toys.
 
Application of TPR
Thermoplastic rubber has gradually replaced PVC and rubber materials that have been restricted by import and export in recent years with its special properties and environmentally friendly and non-toxic characteristics, and has been used more and more widely:
(1) Garden tools: hand saws, high branch shears, shovel, shovel pruning shears, hedge trimmers, garden saws, garden scissors, grass rakes, steel forks, pruning shears, flower tools, snow shovel, small hoe, pruning The handles of saws, grass shears, etc. are covered with rubber.
(2) Sanitary ware: shower head, spray gun, sewage pipe, hose, etc.
(3) Daily necessities: handles (knives, combs, scissors, suitcases, toothbrush handles, etc.), foot pads, ice trays, table mats, bottle cap linings, backpack bases and other rubber and plastic products.
(4) Sports equipment: handles (golf, various rackets, bicycles, ski equipment, skating equipment, etc.), diving equipment (fins, goggles, snorkel, flashlight, etc.), brake blocks, sports pads, etc.
(5) Tool materials: hand tools (screwdriver, hammer, hammer and other handles).
(6) Automobile and motorcycle parts: automobile mudguards, gearshift covers, door and window seals, gaskets, steering wheels, dust jackets, pedals, projection lamp shells, motorcycle (bicycle) handles, etc.
(7) Stationery: erasers, pen covers, gaskets, etc.
(8) Medical equipment: suction balls, instrument handles, wheels, straps, containers, gaskets, gas masks, various pipe fittings, corks and related medical supplies, etc.
(9) Wire and cable: cable shell, connector, plug cover, etc.
(10) Wheel encapsulation: trolley wheels, medical casters, industrial casters, etc.
(11) Information components: game steering wheel, handle, mouse cover, cushion, shell cover, CD packaging box and other soft shockproof parts, etc.
 
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