SPECIFICATIONGuards for Games PlayersThis invention relates to guards for games players, in particular to leg guards for protecting the ankles, shins, knees or other parts of the legs of the players. The invention is concerned particularly with cricket pads, and it is with reference to cricket pads that the following description particularly relates.
In one aspect the invention provides a guard to be worn on the body of a games player, which comprises first outer and second inner superimposed walls secured to each other at their respective edge portions so as to define an air space between them; and resilient wad or other padding sandwiched between said first and second walls, the padding comprising a plastics material having a structure such that when compressed it permits reversible escape of air therefrom to said air space.
The said first wall is that disposed to take impact with the ball (or puck in the case of ice hockey) and said second wall is that disposed to be in contact with the leg or other part of the body of the player.
The padding is conveniently polyvinyl chloride, polyurethane or other plastics expanded or foam material of low resiliency such that deformation of the material under pressure exhibits a substantial degree of hysteresis. Hysteresis can be defined as retardation or lagging of an effect behind the cause of the effect.
Where the guards of the invention are cricket pads or other leg guards they can incorporate the periphery or other features disclosed in our U.K. Patent No.2073 009.
There is now described, by way of example and with reference to the accompanying drawings, a cricket pad according to one embodiment of the present invention. In the drawings:Figure lisa front elevation of the pad;Figure 2 is a rear elevation of the pad; andFigure 3 is a cross-section of the pad on the line Ill-Ill in Figure 2.
The pad comprises in general a first (outer) wall 10, a second (inner) wall 11 and, sandwiched between the outer and inner walls, padding 12. The outer and inner walls are of substantially the same size and shape and are secured to each other along their respective edge portions by means described below.
Outer wall 10 comprises a layer 13 of expanded, closed cell polyethylene having over the whole of its outer face a closely adherent layer of textile material 14, the two layers having been secured to each other over substantially the whole of their area of mutual contact, for example by flame bonding. The expanded polyethylene is conveniently one having a density in the range 150 to 250, especially 180 to 220 (for example 200) kg/m3.
Inner wall 11, in this preferred embodiment, comprises a layer of expanded closed cell polyethylene 15 and a superimposed layer of textile material 16, the two having been secured to each other over substantially the whole of their area of mutual contact, for example by flame bonding. The expanded polyethylene of the inner wall is conveniently one having a density in the range 40 to 60, especially 45 to 55 (for example 50) kg/m3.
The padding 12 sandwiched between the inner and outer walls and in contact with the inwardly directed face of the outer wall 10 and the outwardly directed face of the inner wall 11 comprises two components: first, a sheet of high hysteresis, open-cell plastics foam (for example polyurethane or polyvinyl chloride (PVC) foam) having a thickness, for example, in the range 5 to 10 mm, for instance about 8 mm and five like rods or other elongate pieces of high hysteresis, open-cell plastics foam disposed substantially parallel to one another and to the longitudinal axis of the pad and sandwiched between the inwardly directed face of the sheet 12 and the outwardly directed face of inner wall 11, each of the rods being located in a trough-like depression 17 formed in inner wall 11 during the process of manufacture.The cross-section of these elongate pieces can, for example, be square or other suitable rectangle though other cross-sections can be used if desired. Where the cross-section is rectangular suitable dimensions of the sides of the rectangle are, for example, in the range 1 5--30 mm. For example, with reference to Figure 3 the dimension of the sides lying substantially parallel to sheet 12 can be 20-30 mm., for instance 25 mm. or other value in the range 22-28 mm., and the dimension of the other sides can be 10-25 mm, for instance 17 mm or other value in the range 1 5--20 mm. For ease of manufacture the rods can be of the same material as sheet 12. A very suitable material is the cellular product sold by Declon Limited under the Trade MarkOrthaton.Properties of several grades of Orthaton are given below in Table 1. Excellent results have been obtained using Grade T-38. Orthaton is a high hysteresis/low resilience, open-cell polyurethane foam material that combines flexibility and durability with light weight. Under body pressure and warmth it "flows" to give a "fluid-like" fit and support thus eliminating high pressure points; it becomes firmer when subjected to sudden impact and absorbs up to 90% of impact shocks and vibrations without bounding; and it has a slow recovery rate. Because of this property the material does not "fight-back" against the compressed object as do conventional polyurethanes.
TABLE 1
@ 50% RH T-36 T-38 T-41 T-47 T-50 Typical Properties Test procedure @ 22 C (72 F) Yellow Pink Blue Green White Density ASTM D1564 5.0#0.3lb/ft Cell Size Measured by micrometer 3 to 80 3 to 60 3 to 60 3 to 40 5 to 40 Mils Mils Mils Mils Mils Ball Rebound % Ball Weight=286 Grams Drop Height=20" 10% 10% 10% 5% 5% (Percent includes diameter of ball) Compression Deflection ILD ASTM D 1564 25% 30 40 69 145 500 65% 122 92 190 320 1070 (After one minute rest in lb./50 sq.in.) Compression Set (%) ASTM D1564 0% 0% 0% 0% 0% (24 hour recovery period) Tensile Strength ASTM D1564 (PSI) 19 29 44 50 51 Compression Creep (%) 2.0 psi loaded for 1000 hrs. 0% 0% 0% 0% 0% at room temperature Tensile Elongation (%) ASTM D1564 225% 175% 175% 100% 75% Tear Strength (PLI) ASTM D1564 1.5 1.8 2.0 3.5 4.5 Thermal Stability 24 hrs at 260 F 0% 0% 0% 0% 0% (% shrinkage-no load) Flammability-Standard ASTM D1692 (Horizontal) S.E. S.E. S.E. S.E. S.E.
Production ASTM D1433 (45% angle) S.E. S.E. S.E. S.E. S.E.
Flammability-special FAR 25.853b PASS PASS PASS PASS PASS Production Hysterisis 89% 80% 87% 67% 100% It will be seen from the table that the hysteresis of Orthaton T-38 is 80%; other values are suitable for use in this invention, for example 7585%. Both the sheet and the rod-like plastics foam members 12 can all have been obtained, for example by cutting or other parting operation, from a block of the plastics foam, the cutting being carried out so that both of the major faces of the sheet and all four longitudinally extending faces of each of the rod-like members are formed during said cutting or other parting operation.
As a direct consequence of this each of said faces of the sheet and rod-like members contains many open cells which, the foam being of the open-cell type, communicate with the cells in the interior of the foam.
When any of these padding members 12 is compressed its open-cell structure readily permits reversible escape of air therefrom into the air space between the first and second walls. This property and the benefits resulting therefrom are described in more detail below.
The superimposed edge portions 10.1, 11.1 of the outer and inner walls are securely bonded together, and this bond is covered along its length by a strip of tape 18 embracing the superimposed edges of the two walls and secured through them by means of stitching.
The padding 12 in the embodiment described above comprises two components: the sheet and the rod-like members. However, if desired it can comprise a further component or components; for example rod-like components can be sandwiched between sheet 12 and a second such sheet. However, instead of a two- or multi-component structure the padding can consist of a single component, for example sheet 12 alone or a similar sheet material. Such a structure is described below with reference to a second exemplary embodiment of the invention.
There is now described a cricket pad according to a second embodiment of the invention. In this embodiment the multi-component padding 12 of the first embodiment described above is repiaced by a padding comprising a single component, this being in the form of a sheet of open-cell foam of PVC, polyurethane or other suitable plastics material. This single component sheet can, for example, be of properties, dimensions and shape the same as, or similar to, sheet 12 above but it has the further feature of an array of apertures disposed over substantially the whole of its area, each aperture extending between the two major faces of the sheet.These apertures serve to facilitate ready displacement of air from the expanded foam sheet into the air space between the first and second walls when the sheet is subjected to compressive force and, similarly, permit ready re-entry of air into the cells of the foam when the compressive force is removed. The apertures can be of any suitable shape and also provided that they are consistent, on one hand, with permitting of sufficiently rapid displacement of air from and to the foam material and, on the other hand, in not impairing the strength and durability of the foam sheet. By way of example, it can be said that the apertures can be of circular, oval, square or other rectangular cross-section.
The array of apertures in the foam sheet is conveniently produced by a punching operation but whatever method is employed it is important that the apertures thus formed should be ones whose bores have a satisfactorily open-cell structure. Thus, in general the formation of the apertures by a moulding process, for example one in which an apertured sheet is formed using a mould having an array of pegs therein corresponding to the desired apertures, is not recommended as such methods tend to produce mouldings having a skin at the interfaces with the mould. It is for this reason that in the production of unapertured sheets and other resilient padding members described above with reference to Figure 3 it has been found very convenient to obtain those members by cutting or other parting from a block of the foam rather than by moulding.In a preferred form of the invention the stitching or other means used to secure together the side edge portions of the inner and outer walls does not pass through the padding sheet 12 or otherwise impede flow of air from the edge of that sheet.
The inner wall can be, for example, a foam polyolefin, for example a poly-alpha-olefin such as polyethylene or polypropylene, conveniently one having a closed cell structure. It can have, for example, a density in the range 30 to 60 kg/m3. Examples of suitable cellular polyethylenes are Frelen 30/06 (density 30 kg/m3), Frelen 50/06 (density 50 kg/m3), Lintacell 30/06 (density 30 kg/m3) and Alveolit of the 2000 range, for example 2015 (density 50 kg/m3).
A summary of the mechanical and physical properties of Aveolit 2000 is given below.
DINStandard UnitApparent density 53 420 kg/m3 50Tensile strength lengthwise 5,6crosswise 53 571 kp/cm2 4,0(Specimen thickness 3 mm)Elongation lengthwise 280crosswise 53 571 % 210(Specimen thickness 3 mm)Tear resistance lengthwise 2,8crosswise 53 575 kp/cm 1,8(Specimen thickness 3 mm)Compressive strength20% deflection 53 577 kp/cm2 0,4550% deflection 1,2Thermal conductivity at 0 C kcal/m.h.0C 0,037Working temperature range "C -80 up to+80Watervapourtransmission 53 122 g/m2.24h 1,2(Thickness 2 mm)The outer wall can be, for example, a foam polyolefin, for example a poly-a/pha-olefin such as polyethylene or polypropylene, conveniently one having a closed cell structure.Suitable expanded polyethylenes are ones having a density in the range 160-240 kg/m3, especially 180/220 kg/m3.
Suitable commercial products are, for instance, cellular products sold under the trade marks Alveolit (sold by Alveo A.G) and Frelen 200/05 density 200 kg/m(sold by the firm Carl Freudenberg). By way of example there are given in Table 2 below properties of the irradiation cross-linked polyethylene foam sold under the trade mark Alveolit 0500 Type A by Alveo A.G.
TABLE 2
DIN Properties Standard Unit A Density 53420 kg/m3 200 Tensile strength lengthwise 53571 N/mm2 2.30 crosswise 1.80 Elongation lengthwise 53571 % 210 crosswise 170 Compressive strength deflection 30% 260 50% 53577 kPa 450 70% 900 Compression set 22 h charge 23"C (296 K) 53572 % deflection 25% 1/2 h after discharge 6 24 h after discharge 2 deflection 50% 1/2 h after discharge I 18 24 h after discharge 7 Working temperature range "C -80 +100 Water absorption in 7 days 0.4 28 days 53428 Vol.-% 0.6 Water vapor transmission (5 mm) 53122 g/m2. 24 h 0.12 Water vapor diffusion factor p 52615 - 15000 In general the thickness of a plastics foam sheet comprising the inner wall is greater than a plastics foam sheet comprising the outer wall. Thus, the inner wall foam sheet has a lesser density but greater thickness than the outer wall. The thickness of the inner wall plastics sheet is dictated mainly by its comfort factor and conveniently has a thickness of 10 mm or other value in the range 815 mm.On the other hand, the outer wall serves to a large extent as a means of providing shape and stiffness to the pad and, in consequence, a relatively small thickness will suffice, for example 5 mm or other value in the range 3-8 mm. Although thicker material can be used for the outer wall-even greater than the thickness of the inner wall-it is in general not necessary.
The drawings show a single pad suited for a user's right leg. A pair of pads can, for example, comprise two identical pads as shown, for instance, in Figures 1 to 3, or a pair can consist of two like, though not identical, pads having such differences as may be necessary or desirable to suit right and left legs.
The pad of the drawings has a series of slots in the respective side margins of the pad to receive straps for securing the pad on the user's leg; and two of the straps are shown, one being a buckle strap and the other a tongue strap for engagement therewith.
The pad has formed in the surface of outer wall shallow grooves to simulate the stitching of a conventional canvas pad.
The pad can be provided with slits or other ventilation means (not shown), preferably passing through both the inner and outer walls, to enhance the comfort of the user, especially in hot climates.
The pad described above with reference to the drawings has substantial advantages over a conventional canvas pad. First, it has a weight of about half that of a conventional pad of senior grade.
Secondly, it transmits through the pad a much smaller proportion of the force of a cricket ball striking its outer surface.
Although the precise mode of operation of the cricket pads and other leg guards of this invention is not fully understood it appears that the excellent protective effect of the guards depends to a large extent upon the padding disposed between the outer and inner walls. For example, where the leg guard is a cricket pad a ball propelled at substantial velocity such as by a fast bowler, when it strikes the outer surface of the outer wall causes inwardly directed deflection of the wall, that is towards the shin of the batsman's leg and this inward deflection applies a compressive force to the padding. As described above, the force results in air being expelled quite rapidly from the interior of the padding component or components and a reduction in the thickness of the latter.This deformation is of a plastic rather than of a resilient nature and provides a damping effect; the practical result is that the pad not only protects a batsman's leg but that excessive rebound of the ball from the pad is avoided. As the laws of cricket provide that a batsman is "out" if the ball strikes in succession that bat and the pad and is then caught by a fielder it is of the upmost importance that the amount of rebound obtained when the ball strikes the pad should be as small as possible. The relative lack of success of prior art cricket pads of plastics material can be attributed to a large extent to the excessive amount of rebound of ball from pad.
The comfort provided by the pads or other guards of the invention can be enhanced by the use of an auxiliary sheet 19 of cushioning material whose outline is shown by chain lines in Figures 2 and 3. This material can be attached to the rear face of the guard, for example by means of tabs 20 of a pressure-responsive securement material two of which are shown in Figure 2 carried by the rear face of the guard. A suitable securement material is that sold under the Trade Name "Velcro".
The cushioning material can, for example, be a sheet of polyvinyl chloride (PVC) foam.