Patent Application
20180140915
The technical field relates generally to the use of a thermoplastic material with superior impact fatigue properties and a benign failure mechanism for use in the manufacture of baseball and softball bats as well as other devices where impact fatigue resistance would be a benefit.
Historically, baseball and softball bats were first made from wood, a material readily available and easily formed using technology available in the 19th century. (For purposes of clarity and simplification, the terms “baseball bat” or “bat,” whether singular or plural, as used herein shall apply to both baseball and softball bats, regardless of the size or type.) Subsequently, once the advantages of hollow bats were recognized, both for weight and performance reasons (the trampoline effect), the material of choice transitioned first to metals such as high performance aluminum alloys and titanium and later to composites such as graphite fiber/epoxy compounds or mixtures of graphite, glass and aramid fibers in some suitable matrix material. The use of thermoplastics, other than for toy bats (e.g., for whiffle ball), and for portions of the bat such as end caps and the handle (knob), was unknown until the invention of a replaceable barrel bat was disclosed in U.S. Pat. No. 6,875,137. This patent specifically claimed the use of polycarbonate and urethane thermoplastics for these other components such as the barrel section of the bat.
There are several compelling reasons for using a thermoplastic compound in the fabrication of a softball or baseball bat barrel section or other components susceptible to regular impact during play
Since the publication of U.S. Pat. No. 6,875,137, it is known that neither unalloyed polycarbonates nor unalloyed urethane performs well under conditions of repeated impact against hollow tubular structures. (In this context, the term “unalloyed” means that the base polymer family has not been combined with another major polymer type. For example, an alloy in this context could be achieved by combining a urethane and a nylon, or a PET molecule with an ABS molecule. The term, as used herein, is not meant to include addition of specific agents for enhancing certain properties of the base polymer, e.g., UV protection, flow characteristics, etc.) Both alloys have excellent Izod and Charpy impact resistance as measured by ASTM D256 and ISO 179/1eu respectively. What these tests results do not reveal, however, is what might be termed “impact fatigue” performance. The window of an armored car, for example, typically needs to protect its occupants from one or even dozens of bullet impacts distributed over a broad area. For this application, polycarbonate has proven to be very effective. A baseball bat, however, needs to withstand hundreds of impacts at essentially the same place. Experience has shown that for these baseball bat applications, polycarbonate usually will fail somewhere between 10 to 100 impacts, depending on the swing speed, barrel wall thickness, etc. There are no published figures in the literature for “impact fatigue” for different materials.
Another problem that has been observed with these unalloyed polymers is that when failure does occur following repeated impacts, the failure can be catastrophic, with shards of material flying away from the test article at high speed. While failure itself can probably be tolerated (it's more an issue of economics than performance), the safety aspects of this type of failure in a sporting venue is totally unacceptable. Nothing in the published literature for these or other thermoplastics addresses the long-term failure mechanism.
What is needed is a material with sufficient impact fatigue resistance to withstand several hundred ball/bat impacts and one, that when failure does occur, presents less danger from flying debris.
The design criteria and material discovery described herein improve the overall durability and safety for baseball and softball bats utilizing thermoplastic polymers for sections of the bat routinely exposed to impact.
The disclosed subject matter includes specific polymer chemistry and a rationale for choosing the best grades or alloys of that chemistry. It also addresses the portions of the bat assembly best suited for conversion to thermoplastics.
The disclosed subject matter further describes a range of attributes for the selected polymer chemistry that promote bat designs that take full advantage of the color, transparency, and opportunities for novel graphics presentation afforded by different material choices.
While the technical field of this application primarily applies to baseball and softball bats, it can more generally be applied to any device which comprises a hollow body whose walls are stressed during impact and repeated impacts in the same general location are to be expected.
In some embodiments, the device comprises a first barrel section comprising a generally cylindrical hollow body 8-14″ in length and 2-3″ diameter with walls of 0.08-0.25″ thickness developed about a central axis of revolution, a proximal first cylinder end and a distal second cylinder end, wherein the two ends are separated by a mid-section.
In some embodiments, the device further comprises a handle section comprising a straight cylindrical body 0.625-1″ diameter, a proximal first end and a distal second end, and a central axis that is collinear with the central axis of the first barrel section.
In some embodiments, the device further comprises a transition section comprising a generally conical body revolved about a central axis collinear with the central axes of revolution of the first barrel section and the handle section, the body having a proximal first end sized to be equal in diameter and coplanar to the distal end of the handle and a distal second end sized to be equal in diameter and coplanar to the proximal first cylinder end of the first barrel section.
In some embodiments, the device further comprises a knob comprising a short cylindrical body revolved about a central axis collinear with the central axis of the handle with a proximal first end defining the proximal end of the device and a distal second end coplanar with the proximal first end of the handle.
In some embodiments, the device further comprises an endcap comprising a short cylindrical body revolved about a central axis collinear with the central axis of the first barrel section, the body having a proximal first end coplanar with the distal end of the first barrel section and a distal second end defining a distal end of the device.
In some embodiments, at least one of these sections is manufactured using a polycarbonate-siloxane block copolymer.
In some embodiments, the device further comprises a second hollow barrel section comprising a generally cylindrical body disposed concentric to and inside of the first barrel section and having a proximal first end and a distal second end, wherein the two ends are separated by a mid-section, and wherein the outside diameter of the second barrel section is smaller than the inside diameter of the hollow first barrel section and the inside diameter of the second barrel section is larger than the outside diameter of the handle section.
In some embodiments, the second barrel section is manufactured using one of a fiberglass composite, a carbon fiber composite, a metal, or a polycarbonate-siloxane block copolymer.
In some embodiments, only at least one of the first barrel section and the second barrel section are manufactured using a polycarbonate-siloxane copolymer.
In some embodiments, the handle extends beyond the proximal first end of the transition section, through and concentric to one or more of the transition section and the first barrel section.
In some embodiments, the siloxane component of the polycarbonate-siloxane block copolymer comprises a molecule within the family of polydimethylsiloxane chemistry.
In some embodiments, the polycarbonate component of the polycarbonate-siloxane block copolymer comprises a molecule within the families of bisphenol A polycarbonate or poly-(4,4 isopropyliden diphenyl carbonate).
In some embodiments, the molecular weight of the polycarbonate-siloxane block copolymer is in the range of 10,000 to 32,000 Daltons.
In some embodiments, the molecular weight of the polycarbonate-siloxane block copolymer is in the range of 24,000 to 32,000 Daltons.
In some embodiments, the Melt Flow Index of the polycarbonate-siloxane block copolymer is in the range of 2 to 12 grams per 10 minutes as measured in accordance with ASTM D1238 at a temperature of 300° C. and a load of 2.65 pounds.
In some embodiments, the Melt Flow Index of the polycarbonate-siloxane block copolymer is in the range of 2 to 6 grams per 10 minutes as measured in accordance with ASTM D1238 at a temperature of 300° C. and a load of 2.65 pounds.
In some embodiments, the tensile modulus of the polycarbonate-siloxane block copolymer is about 320,000 psi as measured in accordance with ASTM D638 at a loading rate of 50 mm/min.
In some embodiments, the tensile yield of the polycarbonate-siloxane block copolymer is about 8700 psi as measured in accordance with ASTM D638, Type I, at a loading rate of 50 mm/min.
In some embodiments, a 0.1″ thick section of the molded polycarbonate-siloxane block copolymer has a visible light transmission rate of at least 80% in accordance with ASTM D1003.
In some embodiments, a 0.1″ thick section of the molded polycarbonate-siloxane block copolymer has a visible light transmission rate of less than 20% in accordance with ASTM D1003.
In some embodiments, a 0.1″ thick section of the molded polycarbonate-siloxane block copolymer has a haze value for visible light transmission rate of less than 5% in accordance with ASTM D1003.
In some embodiments, the product graphics are disposed on the inside surface of the first barrel section and can be viewed through a sufficiently transparent first barrel section wall.
In some embodiments, the product graphics are disposed on the outside surface of the second barrel section and can be viewed through a sufficiently transparent first barrel section.
In some embodiments, the mid-section of the first barrel section is larger in diameter than the proximal first cylinder end or the distal second cylinder end.
Various objects, features, and advantages of the disclosed subject matter can be more fully appreciated with respect to the following detailed description of the disclosed subject matter when considered in conjunction with the following drawings, in which like reference numerals identify like elements.
In the following description, numerous specific details are set forth regarding the systems and methods of the disclosed subject matter and the environment in which such systems and methods may operate to provide a thorough understanding of the disclosed subject matter. It will be apparent to one skilled in the art, however, that the disclosed subject matter may be practiced without such specific details, and that certain features, which are well known in the art, are not described in detail to avoid complication of the disclosed subject matter. In addition, it will be understood that the embodiments described below are exemplary, and that it is contemplated that there are other systems and methods that are within the scope of the disclosed subject matter.
For purposes of clarity, the use of the term “siloxane” as used herein (e.g., polycarbonate-siloxane block copolymer) is understood to also include “polysiloxane” chemistries. In some embodiments, the block formed by this polysiloxane molecule can be hundreds or thousands of units long. Also, whenever used herein, the term “about” is meant to define a value of plus or minus 10% of the nominal value listed.
As noted above, multiple thermoplastic polymers are advertised in the marketplace with excellent impact performance as defined by Izod and Charpy test methods. These test methods do not, however, adequately characterize the impact fatigue properties of these materials when tested as hollow tubular structures typical of a baseball bat's barrel section or other hollow components of a bat subject to impact with a baseball or softball. These methods also do not adequately characterize the failure mechanism. Failures which occur catastrophically, with shards violently ejected from the bat test section clearly are inappropriate for use in any sporting venue, especially those used by children. Failures which result in permanent deformation of the product are less serious. For market acceptance, a bat should be able to withstand hundreds of impacts, preferably greater than 500 impacts by the intended player segment. For safety, the bat should fail benignly, with slow growth of any failure mechanism and the complete absence of shattering or the ejection of shards.
A wide variety of materials were selected for testing, all with strong recommendations from manufacturers sales representatives and technical specialists for the materials. These included:
Testing occurred over a period of approximately five years and involved over 150 bats of various types, both sample bats using various thermoplastic polymers and wall thicknesses in the barrel section and “controls”—purchased, commercially available bats made from traditional composite or aluminum alloys to help rank relative performance for each batter. Testing included a combination of field testing, lab testing using air cannons, lab testing using robotic batting machines, and high speed photography. Field testing occurred both outdoors in a typical softball diamond setting and indoors using batting cages. In both situations batters chosen to participate were primarily adult males playing in softball leagues at “A” or “B” levels of competition (most competitive) and capable of hitting a regulation softball (as defined by the Amateur Softball Association or the United States Specialty Sports Association) between 350 and 450 feet. (The objective was to subject the bats to as high a level of impact as could be expected in the most competitive settings and to rate durability as the number of hits to failure under this worst-case scenario.) Lab testing with air cannons involved the use of balls accelerated to speeds as high as 110 miles per hour and directed at specific locations on a stationary bat. Lab testing with robotic batting machines involved using a machine to rotate a bat up to speeds that would yield a ball/bat impact equivalent to that from the combined speed of a pitched ball and a swung bat. High speed photography was done at shutter speeds up to 10,000 frames per second to capture the 0.001-0.003 second duration of the ball/bat impact so the degree of distortion of both ball and bat could be observed. The bat distortions of interest consisted of both hoop (circumferential) compression and axial bending.
Sample bats used in testing generally were fabricated as a group of injection molded and/or extruded components inertially welded (also known as friction welding) together to create a barrel subassembly. This construction is illustrated in
The bat design illustrated in
Testing yielded the following observations:
Analysis of the initial test results (up through testing with the EXL1433T) identified bats made using the polycarbonate/siloxane block copolymer chemistry as clearly superior to bats made from all the other tested polymers in both impact fatigue and the ability to avoid flattening under impact. That said, bat barrels incorporating the EXL1433T performance were still not sufficiently durable to meet the goal of 300-500 impacts before failure. Further research suggested that impact fatigue performance might be related to the molecular weight of the specific polycarbonate-siloxane copolymer selected. While the specific molecular weight of the polymers being tested was not available to the research team (not published), data was published on the relative Melt Flow Index (MFI) of all the EXL products and the value of the MFI has been observed to have an inverse correlation with molecular weight, i.e., as molecular weight goes up, the molecules get longer and become more intertwined, leading to higher viscosity at melt and lower MFI. (Melt Flow Index is defined by ASTM D1238 and ISO 1133. It is also sometimes referred to as Melt Volume Flow. The units of measure are grams/10 minutes and cubic centimeters/10 minutes, respectively. For this family of polymers, the test is conducted at 300° C. using a weight of 2.65 pounds.) It is believed that this molecular intertwining was the reason behind enhanced impact fatigue. As a secondary benefit of this low MFI, it was found that the ease of manufacturing using an extrusion press was also improved. Manufacturing trials and field performance of EXL1033C supported the durability hypothesis that lower MFI correlated with better impact fatigue life, as the number of impacts to benign failure climbed into the range of 500-1000 impacts.
Further analysis of the test results suggested that the “secret sauce” for the family of materials exhibiting the best performance was a siloxane molecule that was co-polymerized with polycarbonate. Several patents have been filed by GE describing this technology including U.S. Pat. No 4,397,973, 5,194,524 and 5,455,310, which are incorporated herein by reference.
Toward the end of the test program, samples of various polycarbonate-siloxane thermoplastics were sourced from Idemitsu and prepared to our specifications by a US-based distributor. This Idemitsu product worked marginally better than the Sabic product and was subsequently identified as being comprised of a polycarbonate molecule based either on bisphenol A or poly-(4,4 isopropyliden diphenyl carbonate) chemistry combined with a siloxane component based on polydimethylsiloxane chemistry. The molecular weight of the best products tested ranged from 10,000 to 32,000 Daltons and, preferentially, from 24,000 to 32,000 Daltons. The Melt Flow Index for the best products was also identified as 2-12 grams/10 minutes and, preferentially, 2-6 grams/10 minutes.
While
In some embodiments, all the components of the barrel subassembly 20 and the second barrel section 30 are fabricated using a polycarbonate-siloxane copolymer thermoplastic. In this case, it may be advantageous to weld various pieces together to simplify final assembly of the bat or to permanently position one component relative to another. In some embodiments, these components are ultrasonically or inertially welded together using techniques that are well known in the field. In other embodiments, the materials of construction for each component may vary. For example, the first barrel section 21 and the second barrel section 30 may be fabricated from the polycarbonate-siloxane copolymer while other less impacted components such as the end cap 24 or knob or transition 23 are manufactured from an alternative, possibly lower cost thermoplastic. In some embodiments, the first barrel section 21 might be made from the polycarbonate-siloxane copolymer while the second barrel section is made from aluminum or a composite material such as fiberglass/epoxy or carbon fiber/epoxy, both with a higher modulus of elasticity and therefore stiffer and capable of reducing the hoop deflection of the first barrel section 21 more or adding more ballast weight than if any thermoplastic material was used for the second barrel section 30. In yet another embodiment, the choice of first barrel section 21 and second barrel section 30 materials might be reversed, with the stiffer material used for the first barrel section 21 and the polycarbonate-siloxane copolymer material used for second barrel section 30. Thus, in addition to helping to manage the weight distribution and center of mass of the bat, the material chosen for the second barrel section 30 can also help to control the overall barrel subassembly 20 hoop deflection and thus the overall bat performance level.
Manufacturers who can provide this polycarbonate-siloxane copolymer generally can add certain other proprietary compounds to the basic copolymer to enhance color, clarity or cold weather performance, though sometime at the expense of lower impact fatigue life. For specific marketing/commercial purposes, this may still be desirable. For example, in some embodiments it is advantageous to put the product graphics on the inside of a clear first barrel section 21 or to dispose them onto the outer surface of the second barrel section 30. In this condition, the graphics are less likely to be damaged and it can add a sense of depth visually that is not possible with graphics mounted on the outside surface of barrel subassembly 20.
This application relates to and claims priority under 35 U.S.C. § 119(e) to U.S. Provisional Patent Application No. 62/259250, titled “Polycarbonate-Siloxane Copolymer Use in Baseball and Softball Bats,” which was filed on Nov. 24, 2015 and is hereby incorporated by reference herein in its entirety.
