Patent Publication Number: US-2011047819-A1

Title: Soft, shock-damping thermoplastic elastomers

Description:
CLAIM OF PRIORITY 
     This application claims priority from U.S. Provisional Patent Application Ser. No. 60/970,402 bearing Attorney Docket Number 12007015 and filed on Sep. 6, 2007, which is incorporated by reference. 
    
    
     FIELD OF THE INVENTION 
     This invention relates to soft thermoplastic elastomers that have good shock-damping or impact energy dissipation properties. 
     BACKGROUND OF THE INVENTION 
     The world of polymers has progressed rapidly to transform material science from wood and metals of the 19 th  Century to the use of thermoset polymers of the mid-20 th  Century to the use of thermoplastic polymers of later 20 th  Century. 
     Thermoplastic elastomers (TPEs) combine the benefits of elastomeric properties of thermoset polymers, such as vulcanized rubber, with the processing properties of thermoplastic polymers. Therefore, TPEs are preferred because they can be made into articles using injection molding, extrusion and blow-molding equipment. 
     SUMMARY OF THE INVENTION 
     What the art needs is a new formulation of soft thermoplastic elastomer (TPE) that has good impact energy dissipation characteristics, which is beneficial for providing plastic articles with the property of good shock-damping. 
     “Damping” refers to the dissipation of vibrational energy. 
     “Shock-damping” refers to the absorption or dissipation of impact energy through a system, with minimum impact resilience or rebound. 
     The present invention solves that industry need by using a TPE formulation that utilizes a combination of two different styrene-based thermoplastic elastomer compounds (known also by the acronym TPE-S) to provide a plastic article with good shock-damping. 
     One aspect of the invention is a thermoplastic elastomer shock-damping system, comprising two different styrene-based thermoplastic elastomer compounds and plasticizer oil, wherein one compound is a vinyl-isoprene styrene-based thermoplastic elastomer, and the other compound is not. 
     The system can have a Shore A hardness of less than about 50 Shore A and preferably less than about 30 Shore A. 
     Optionally, the system can be cured into a thermoplastic vulcanizate. 
     Optionally, the system can be foamed. 
     Features of the invention will become apparent with reference to the following embodiments. 
    
    
     EMBODIMENTS OF THE INVENTION 
     Vinyl-Isoprene TPE-S 
     U.S. Pat. No. 4,987,914 (Maeda et al.) discloses what is meant by vinyl-isoprene styrene-based thermoplastic elastomer compound and therefore is incorporated by reference herein. 
     As reported by Maeda et al., this specific type of TPE-S is characterized by a composition comprising a block copolymer which has a numerical average molecular weight of 30,000 to 300,000 and is composed of two or more blocks consisting of aromatic vinyl units having a numerical average molecular weight of 2500 to 40,000, and one or more blocks containing a vinyl bonding content of not less than 40%, having a peak temperature of primary dispersion of tan δ of at least 0° C., and consisting of isoprene or isoprene-butadiene units in which at least a part of carbon-carbon double bonds may be hydrogenated. 
     More specifically, vinyl-isoprene TPE-S useful in this invention (“viTPE-S” for these purposes) is a block copolymer having a number average molecular weight of 30,000 to 300,000 composed of at least two blocks consisting of aromatic vinyl units each having a number average molecular weight of 2,500 to 40,000 and at least one block containing a vinyl bond content of not less than 40%, having a peak temperature of primary dispersion of tan δ of at least 0° C., and consisting of isoprene or isoprene-butadiene units in which at least a portion of the carbon-carbon double bonds may be hydrogenated. 
     viTPE-S is well known as a damping material and has the physical strength equivalent to that of vulcanized rubber. As explained in Maeda et al., viTPE-S has excellent vibration absorption and vibration damping properties. 
     viTPE-S is commercially available from Septon America in a variety of hydrogenated and non-hydrogenated grades marketed under the brand “Hybrar”. Non-hydrogenated grades are preferred because they have higher glass transition temperatures than hydrogenated grades and because they have a higher peak temperature of tan δ than do hydrogenated grades. Indeed, grade 5127 has a Tg of 8° C. and a Peak Temp. of tan δ of 20° C. For further information, one can consult http://www.septon.info/en/hybrar/what_hybrar.html. 
     Unfortunately, certain non-hydrogenated grades of viTPE-S are hard materials, approximately 60-90 on the Shore A scale. More unfortunately, viTPE-S is not friendly to oil and other emollients often used to fill and soften thermoplastic and thermoset polymers. Therefore, while non-hydrogenated viTPE-S is capable of excellent vibration absorption and shock-damping, it is not soft and can not be made soft. 
     Second TPE-S 
     The second TPE-S contributes oleophilic properties to the thermoplastic elastomer system. Any TPE-S that is softer in Durometer Shore A hardness and more oil absorbing than viTPE-S is a candidate to be the second TPE-S of the system. For distinguishing purposes, this oil absorbing TPE-S will bear the acronym “oaTPE-S”. 
     Non-limiting examples of oaTPE-S compounds include styrenic block copolymers of styrene hard blocks on either side of a middle, softer block. The softer block can butadiene (styrene-butadiene-styrene or SBS), ethylene/butylene (styrene-ethylene/butylene-styrene or SEBS), ethylene/propylene (styrene-ethylene/propylene-styrene or SEPS), isoprene (styrene-isoprene-styrene or SIS), Isobutylene (styrene-isobutylene-styrene or SIBS), etc., and combinations thereof. Any of these TPE-S compounds are oil absorbing and often mixed with paraffinic oil or other emollients to reduce Shore A scale hardness. 
     Commercially available oaTPE-S compounds are well known to those skilled in the art. Global suppliers such as Kraton Company of Houston Tex. and Kaneka of Japan make and sell a variety of grades of oaTPE-S compounds. 
     Plasticizer Oil 
     As mentioned above, paraffinic oil, also known as mineral oil, is often used to soften and fill thermoplastics, thermosets, and TPE-S which has both thermoplastic and elastomeric components. Other oils and emollients can also be used so long as they are not incompatible with the viTPE-S or the oaTPE-S. 
     Optional Additives 
     The system of two different TPE-S compounds can include conventional plastics additives in an amount that is sufficient to obtain a desired processing or performance property for the compound. The amount should not be wasteful of the additive nor detrimental to the processing or performance of the compound. Those skilled in the art of thermoplastics compounding, without undue experimentation but with reference to such treatises as  Plastics Additives Database  (2004) from Plastics Design Library (www.williamandrew.com), can select from many different types of additives for inclusion into the compounds of the present invention. 
     Non-limiting examples of optional additives include adhesion promoters; biocides (antibacterials, fungicides, and mildewcides), anti-fogging agents; anti-static agents; bonding, blowing and foaming agents; curing agents; dispersants; fillers and extenders; fire and flame retardants and smoke suppressants; impact modifiers; initiators; lubricants; micas; pigments, colorants and dyes; oils and plasticizers; processing aids; release agents; silanes, titanates and zirconates; slip and anti-blocking agents; stabilizers; stearates; ultraviolet light absorbers; viscosity regulators; waxes; and combinations of them. 
     Table 1 shows the acceptable and desirable ranges of ingredients for the thermoplastic elastomer system of the present invention. All but the two types of TPE-S and oil are optional for the present invention. 
     
       
         
           
               
             
               
                 TABLE 1 
               
             
            
               
                   
               
               
                 Ranges of Ingredients 
               
            
           
           
               
               
               
               
            
               
                   
                 Ingredient 
                   
                   
               
               
                   
                 (Wt. Percent) 
                 Acceptable 
                 Desirable 
               
               
                   
                   
               
               
                   
                 viTPE-S 
                 10-50 
                 20-40 
               
               
                   
                 oaTPE-S 
                 10-50 
                 15-35 
               
               
                   
                 Plasticizer Oil 
                 10-50 
                 20-40 
               
               
                   
                 Wax 
                   0-2% 
                   0.1-0.5% 
               
               
                   
                 Anti-oxidant 
                   0-4% 
                  0.05-0.2% 
               
               
                   
                 Dusting Agent 
                   0-1% 
                   0-0.5% 
               
               
                   
                 Other Optional 
                   0-10% 
                   0-5% 
               
               
                   
                 Additives 
               
               
                   
                   
               
            
           
         
       
     
     Processing 
     The preparation of compounds of the present invention is uncomplicated. The compound of the present can be made in batch or continuous operations. 
     Mixing in a continuous process typically occurs in an extruder that is elevated to a temperature that is sufficient to melt the polymer matrix (approximately 115° C.-200° C.) with addition either at the head of the extruder or downstream in the extruder of the solid ingredient additives. Plasticizer oil can be pre-mixed with the oaTPE-S in a ribbon blender or optionally added downstream by side feeding into the barrel. Extruder speeds can range from about 50 to about 500 revolutions per minute (rpm), and preferably from about 100 to about 300 rpm. Typically, the output from the extruder is pelletized for later extrusion or molding into polymeric articles. 
     Mixing in a batch process typically occurs in a Banbury-type mixer that is also elevated to a temperature that is sufficient to melt the polymer matrix to permit addition of the solid ingredient additives. The mixing speeds range from 60 to 1000 rpm. Also, the output from the mixer is chopped into smaller sizes for later extrusion or molding into polymeric articles. 
     Subsequent extrusion or molding techniques are well known to those skilled in the art of thermoplastics polymer engineering. Without undue experimentation but with such references as “Extrusion, The Definitive Processing Guide and Handbook”; “Handbook of Molded Part Shrinkage and Warpage”; “Specialized Molding Techniques”; “Rotational Molding Technology”; and “Handbook of Mold, Tool and Die Repair Welding”, all published by Plastics Design Library (www.williamandrew.com), one can make articles of any conceivable shape and appearance using compounds of the present invention. 
     Usefulness of the Invention 
     TPE-S of the present invention, based on the combination of viTPE-S and oaTPE-S and oil provides shock-damping. As such, and with the advantage of being capable of being injection molded or extruded, soft plastic articles needing impact energy dissipation features can be made from formulations of the present invention for such uses as seals, closures, shoe insoles, and other articles previously made from foamed plastics, soft rubber, etc. A system of the present invention, when used as a shoe insole, can provide cushioned shock absorption with minimal rebound. 
     Table 2 shows an example of the present invention. 
     
       
         
           
               
             
               
                 TABLE 2 
               
             
            
               
                   
               
               
                 Formulation (Wt. %) 
               
            
           
           
               
               
               
            
               
                 Ingredient/Commercial Source 
                 Purpose 
                 1 
               
               
                   
               
            
           
           
               
               
               
            
               
                 Hybrar 5127 TPE (Septon America, 
                 viTPE-S Matrix 
                 27.3 
               
               
                 Pasadena, TX) (84 Shore A) 
               
               
                 Kraton G1641H SEBS (Kraton, Houston, 
                 oaTPE-S Matrix 
                 22.2 
               
               
                 TX) 
               
               
                 Hydrobrite 550 PO Mineral Oil 
                 Softener Oil 
                 49.5 
               
               
                 (Sonneborn, Tarrytown, NY) 
               
               
                 Kemamide E Ultra Erucamide wax 
                 Mold Release 
                 0.3 
               
               
                 (Chemtura, Middlebury, CT) 
                 Agent 
               
               
                 Irganox 1010 Phenolic Antioxidant (Ciba, 
                 Anti-oxidant/UV 
                 0.1 
               
               
                 Tarrytown, NY) 
                 Package 
               
               
                 Weston TNPP Phosphite Anti-oxidant 
                 Anti-oxidant 
                 0.3 
               
               
                 (Chemtura) 
               
               
                 Microthene 709FA High Density 
                 Dusting Agent 
                 0.3 
               
               
                 Polyethylene (Equistar, Houston, TX) 
               
               
                   
               
            
           
         
       
     
     The example was made using a Werner-Pflederer twin-screw extruder set at 115° C. in zone 1; 65-188° C. in zones 2-6; with a die temperature at 200° C. The extruder rotated at 250 rpm. All ingredients were added at Zone 1, except that 30 wt. % oil (60% of the oil amount) was pre-mixed into the oaTPE-S matrix using a high intensity mixer, and the remainder of the oil was added at the injection port on the side of the barrel. The melt-mixed compound was pelletized for further handling. 
     Pellets of all Examples were molded into tensile test bars using a Van Dorn injection molding machine, operating at 200° C. temperature. 
     Table 3 shows experimental results of physical properties. 
     
       
         
           
               
             
               
                 TABLE 3 
               
             
            
               
                   
               
               
                 Test Results 
               
            
           
           
               
               
               
               
            
               
                   
                 Test 
                 ASTM 
                 1 
               
               
                   
                   
               
            
           
           
               
               
               
               
            
               
                   
                 Melt Flow Index (g/10 min.) 190° C. and 
                 D1238 
                 97 
               
               
                   
                 2.16 kg 
               
               
                   
                 Ultimate Tensile Strength (psi) parallel to 
                 D412 
                 392 
               
               
                   
                 flow 
               
               
                   
                 Ultimate Tensile Strength (psi) 
                 D412 
                 384 
               
               
                   
                 perpendicular to flow 
               
               
                   
                 Elongation at Break (%) parallel to flow 
                 D412 
                 977% 
               
               
                   
                 Elongation at Break (%) perpendicular to 
                 D412 
                 980% 
               
               
                   
                 flow 
               
               
                   
                 50% Modulus (psi) parallel to flow 
                 D412 
                 24 
               
               
                   
                 50% Modulus (psi) perpendicular to flow 
                 D412 
                 24 
               
               
                   
                 100% Modulus (psi) parallel to flow 
                 D412 
                 29 
               
               
                   
                 100% Modulus (psi) perpendicular to flow 
                 D412 
                 27 
               
               
                   
                 200% Modulus (psi) parallel to flow 
                 D412 
                 40 
               
               
                   
                 200% Modulus (psi) perpendicular to flow 
                 D412 
                 39 
               
               
                   
                 300% Modulus (psi) parallel to flow 
                 D412 
                 58 
               
               
                   
                 300% Modulus (psi) perpendicular to flow 
                 D412 
                 55 
               
               
                   
                 Tear Resistance (pli) parallel to flow 
                 D624 
                 37 
               
               
                   
                 Tear Resistance (pli) perpendicular to flow 
                 D624 
                 42 
               
               
                   
                 Specific Gravity 
                 D792 
                 0.89 
               
               
                   
                 Shore A Hardness (10 sec. dwell) 
                 D2240 
                 6 
               
               
                   
                 Compression Set (%) at 23° C. 
                 D395 
                 14% 
               
               
                   
                   
               
            
           
         
       
     
     The example exhibited a dramatically reduced hardness (6 Shore A in penultimate row of Table 3) compared with a Shore A hardness of the viTPE-S alone (84 Shore A). 
     The invention is not limited to the above embodiments. The claims follow.