MXPA00004008A - Shock absorbing component and construction method - Google Patents

Abstract

A shock absorbing component having a pair of surfaces with a plurality of inwardly extending indentations in the top and bottom surfaces. The indentations extend between the surfaces to provide support members for the shock absorbing component. At least some of the indentations are hemispherical. The surfaces may be formed of mesh material to allow the passage of gas or fluid therethrough. One or more inserts may be placed in the indentations. The shock absorbing component can be constructed by molding upper and lower shock absorbing component halves wherein the molds are configured to provide indentations in the top and bottom surfaces. The upper and lower halves are then joined to complete the shock absorbing component.

Description

COMPONENT OF ABSORPTION OF IMPACT, AND METHOD TO BUILD THE SAME BACKGROUND OF THE INVENTION FIELD OF THE INVENTION The present invention relates to impact absorption components and methods for manufacturing same. More particularly, the invention relates to flexible impact absorption components used for a variety of surfaces, including damping for medical purposes, packaging material, athletic protective filler, footwear, exercise equipment filler, seats, industrial safety filler , exercise mats and hard surface elastic covers.

DESCRIPTION OF THE RELATED TECHNIQUE Efforts to improve impact absorption materials have focused on reducing weight and improving cushioning, flexibility and stability. In particular, impact absorption materials for footwear and athletic equipment have focused on improved impact dispersion capabilities. Additionally, the modern design of the impact absorption materials takes into account the specific requirements of filling and damping for particular activities. Although the functional characteristics of the impact absorption materials are of primary importance, other factors such as cost and appearance must be taken into account for the complete satisfaction of the user. Typically, shock absorbing materials for footwear and athletic equipment use expanded plastics in foams which are then configured in numerous ways to accommodate the application requirements. In certain applications, an outer layer of rubber or other material is added, requiring stratifying both surfaces with cement where they will be joined, then activating the treated surfaces, usually with heat. The disadvantages of cementing or adhering surfaces to each other include cost, weight and appearance. The impact absorbing components have also been constructed of a cover of a thermoplastic elastomer designed to encapsulate and protect low-need synthetic foams such as polyether, polyurethane or polyurethane-polyester. Other impact absorption components typically include an air bag or cushion which can be filled or inflated with gas or fluid to a desired pressure. The disadvantages of these types of components include cost and difficulty in sealing the component.

BRIEF DESCRIPTION OF THE INVENTION The present invention is a flexible impact absorption component constructed of a flexible resin of high polymer content. The impact absorption component is characterized by two opposing surfaces, defined in the following as upper surface and lower surface. Preferably, the component is not inflated or pressurized, but rather has internal support members between the two surfaces. The internal support members for the impact absorption component are provided by indentations in one or both of the upper and lower surfaces. At least some of the indentations are hemispherical. The hemispherical indentations extend between the upper and lower surface and may be separated, or they may come into contact or bridge by hemispherical indentations extending from the surface of the opposite component. The support members formed by the hemispherical indentations in the flexible impact absorption component provide flexible resistance to the compression forces exerted on the component. The impact absorption component may also include a wall member coextensive with the upper and lower surfaces. The impact absorption component of the present invention is useful in a variety of applications, and is particularly useful for filling athletic equipment, footwear, packaging material, cushioning for medical purposes, mats, and other related objects. The impact absorption component can be constructed by molding plastic resin sheets into molds configured to achieve configurations for incorporation into specific athletic equipment, filling or packaging. The molds have projections to provide the indentations in the material for the support members. A mechanism for forming the impact absorbing component of the present invention is by thermoforming. Generally, thermoforming is a process for configuring plastic resins by heating a sheet or film of the plastic to a temperature at which the resin is flexible enough to be shaped into a desired shape, and then forcing the material into a single-sided mold. . The impact absorption component of the present invention is preferably constructed (1) by heating a first thermoplastic sheet to its forming temperature, (2) heating a second thermoplastic sheet to its forming temperature, (3) forcing the first thermoplastic sheet into a first mold configured to provide an upper component half, and forcing the second thermoplastic sheet into a second mold configured to provide a lower component half, and (4) joining the two halves together by bonding, gluing, welding, melting, coupling, or its Similary. The halves of the molds are configured to indentate either or both top and bottom surfaces at selected points to provide the internal support elements. One method of construction that is particularly preferred is to close the mold halves together while the material is at its formation temperature such that a plurality of the indentations in the halves of the impact absorbing component are fused or welded together at your points of contact. Alternatively, the impact absorption component can be constructed by blow molding. Blow molding is a process for the production of hollow thermoplastic shapes. The process is divided into two general categories: extrusion blow molding and injection blow molding. Extrusion blow molding is preferred for the construction of the impact absorbing component of the present invention. In extrusion blow molding the impact absorption structure, a molten plastic tube called a preform, is dropped or lowered from an extruder. The mold halves close around the preform, which is then expanded in such a manner that the upper and lower surfaces placed are forced against the opposite upper and lower cavity walls by the injection of air. In blow molding, the preform is expanded with a gas, usually air, until the plastic makes contact with the mold where it is held in the shape of the mold cavity while it is cooled. As with the twin sheet thermoforming process, the mold halves have protrusions that are configured to indentate the opposing surfaces of the preform at selected points to provide internal support elements.

The support elements are inwardly directed indentations that can be configured in a variety of shapes and sizes to provide specific areas of varying degrees of flexibility for stability and damping. Preferably, the inwardly directed indentations have the shape of hemispheres extending inwardly into the cavity from opposite surfaces of the impact absorbing structure. Since the terms hemisphere and hemisphere are used in this application, as will be apparent to those skilled in the art, this invention includes within its scope indentations that have a generally hemispherical shape. For example, indentations having a hemylipsoidal shape are considered within the scope of this invention, as well as other slight variations to a real hemispherical shape. The hemispheres can be grouped closer together where greater strength is required for areas where greater pressure is exerted when the impact absorption component is used. Otherwise, the hemispheres can increase in size in areas of weight bearing to increase damping. The indentations in the upper surface can be separated or in contact with corresponding indentations in the lower surface. The corresponding indentations can be fused or welded during the thermoforming process to provide a combination of internal support element that bridges the upper and lower surfaces of the impact absorption component. One advantage of forming the impact absorption component from two sheets of thermoplastic resin is that it allows the component to be constructed of two different materials having different properties to create a variety of functional responses difficult to achieve by using only one material. For example, the bottom surface can be constructed of a thermoplastic material that is thicker, and consequently more rigid, while the top surface is constructed of a thermoplastic material that is thinner and more flexible. In addition, the indentations extending from the upper and lower surfaces made of different materials can provide support elements having double properties. For example, the lower portion of the support member provided from the more rigid thermoplastic material will provide a more rigid support member portion and thus provide greater resistance to the forces exerted on the lower portion of the impact absorption component. . The upper portion of the support element constructed from the indentation of the thinner and more flexible material will exhibit greater flexibility, and will consequently provide more damping in response to pressures exerted on the upper surface of the impact absorbing component. By varying the shapes and sizes of the support elements and the properties of the thermoplastic materials used, the designer can control the damping characteristics along the impact absorption component. The impact absorption component of the present invention can also be constructed of sheets of thermoplastic material having a mesh pattern, or having holes or grooves in the material. This structure offers the advantages of a reduced weight, and allows the transmission of media through the surfaces. The indentations in the impact absorption component may also have perforations therein, or may be formed from a mesh material, which may decrease the average rigidity of the indentation. Other means for varying the stiffness of the impact absorption structure include molding grooves in the outer walls of inserts which are then engaged within the indentations. Alternatively, the indentations and / or inserts may have a non-uniform wall thickness, so that the structure has a rigidity that varies with respect to displacement.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a perspective view of the upper surface and the lower surface of an impact absorbing component according to a preferred embodiment of the invention. Figure 2 is a perspective view of the upper and lower surfaces shown in Figure 1, with the hemispherical indentations on the upper surface supporting the hemispherical indentations on the lower surface. Figure 3 is a cross-sectional view of the upper and lower surfaces according to a preferred embodiment with the hemispherical indentations on the upper surface supporting those on the lower surface. Figure 4 is a perspective view of the upper and lower surfaces with a wall member along the periphery of the surfaces. Figure 5 is a perspective view of the upper and lower surfaces according to a preferred embodiment wherein the surfaces are made of mesh material. Figure 6 is a cross-sectional view of the upper and lower surfaces shown in Figure 5. Figure 7 is a schematic illustrating a dual sheet thermoforming process. Figure 8 is a perspective view of an impact absorbing component according to a preferred embodiment having inserts to be placed in one or more indentations on one of the surfaces of the impact absorbing component. Figure 9 is a cross-sectional view of an insert in hemispherical form in an indentation according to a preferred embodiment. Figure 10 is a perspective view of a plurality of inserts joined together by a network structure. Figure U is a perspective view of a pair of opposite hemispheres having holes or perforations therein. Figure 12 is a perspective view of a pair of opposite hemispheres having slots therein. Figure 13 is a perspective view of a pair of opposite hemispheres having longitudinal grooves in the surfaces thereof. Fig. 4 is a perspective view of a pair of opposite hemispheres having circumferential grooves in the surfaces thereof. Figure 15 is a perspective view of a pair of opposite hemispheres having varying thicknesses. Figure 16 is a partial cross-sectional view of a pair of opposing indentations and inserts according to another embodiment of the invention. Figure 17 is a graph of representative force displacement curves for the structure for absorbing impacts of the present invention. Figure 18 is a top view of a mold used to form indentations on the bottom surface and an end view in cross section of a pair of molds used to form indentations on the upper and lower surfaces according to a preferred embodiment of the invention . Figure 19 is an end view in cross section of a pair of surfaces joined together by a vertical side wall according to a preferred embodiment of the present invention.

DETAILED DESCRIPTION AND PREFERRED MODALITIES The present invention is an impact absorption component manufactured from a highly flexible polymer plastic resin. Depending on how the component is used, the general form of the component is configured for incorporation into another equipment. For example, the impact absorption component can form a portion of a cushion or pad in conjunction with other materials such as traditional ethylene-vinyl acetate copolymer (EVA) foam or other materials. The impact absorption component generally consists of one or more higher polymers, generally synthetic, which can be formed or molded by heat and pressure. Preferably, the higher polymers are thermoplastic polymers or thermoplastic polymers which can be made of thermofixed polymers after molding. The polymer is formed in a body member configured to be used as an impact absorbing component. Without considering the specific role of the impact absorption component, the body member generally comprises opposite surfaces, referred to as an upper surface and an opposing surface. The bottom surface is in at least a partially coextensive relationship to the top surface. The coextensive relationship between the upper and lower surfaces defines corresponding portions between the upper and lower surfaces. Preferably, the lower and upper surfaces are placed in at least one relationship partially spaced from one another. The upper and lower surfaces may be in a generally parallel planar relationship or the surfaces may be inclined to each other and finally meet. If the opposing surfaces are at least partially spaced apart from each other, the separate relationship defines a gap or cavity between the surfaces. A plurality of support elements are placed between the upper and lower surfaces. The support elements are comprised of indentations directed inward on one or both of the upper and lower surfaces. The indentations on a surface extend to a point adjacent to a corresponding indentation on the opposite surface. Adjacent, as used to describe the present invention, means that the indentation extends to a point that is at least close to the corresponding portion of the opposite surface and can be coupled with the opposite indentation. The coupling can be fixed or not fixed. In one embodiment of the present invention, one or more of the support elements are fixedly coupled or are attached to the corresponding portion of the opposing support element to retain the upper and lower surfaces in their coextensive and separate relationship. In another embodiment of the present invention, the indentations in the upper surface can be separated from the indentations in the lower surface but can be supported by applying force to the impact absorbing component. In another embodiment of the present invention, the body member further comprises a wall element which is coextensive with at least a portion of the periphery of the upper and lower surfaces. In this embodiment, the wall element can be attached to the upper and lower surfaces to retain the surfaces in their separate and coextensive relationship. Further, where the wall element is continuous along the periphery of the upper and lower surfaces, it defines a cover having internal support elements formed from the inwardly directed indentations extending into the interior of the cover. As indicated, the support elements are integral portions of the impact absorption component comprising inwardly directed indentations in the polymer materials forming the upper and lower surfaces of the impact absorption component. The supporting elements provide a controlled crushing of the material to create areas of damping and stability in the component. The support elements are configured to extend in the interval between the upper and lower surfaces and adjacent to the corresponding counter portion. The indentations can be formed on one or both upper and lower surfaces. The corresponding indentations in the upper and lower surfaces are at least close together and can be coupled to each other in a fixed or non-fixed relationship. The indented portion of the upper and lower elements may be any extension that retains sufficient non-indented surface area on the upper and lower surfaces to provide adequate support for use as an impact absorbing component. For example, components that have an indented portion of about 50% are contemplated. Referring to Figure 1, in a preferred embodiment the impact absorption component 1 comprises an upper surface 2 and a lower surface 3. The upper and lower surfaces are in plane relation generally parallel to one another, or they can be tilted to a place where the top and bottom surfaces meet. The upper and lower surfaces are in a coextensive relationship and are partially spaced apart to define a gap or cavity between the upper and lower surfaces. A plurality of inwardly directed hemispherical indentations 4, 5 on the upper and lower surfaces extend toward the opposite surface to provide internal support to the structure of the impact absorbing component. Figure 2 and Figure 3 show inwardly extending indentations resting on the upper and lower sheets. As illustrated, the indentations can have a variety of ways to form the internal support elements. In a preferred embodiment each of the indentations has a hemispherical shape, which extends in the interval between the upper and lower surfaces. As illustrated, the support elements can cooperate by contact between the corresponding patterns in the upper and lower halves of the impact absorption component. Figure 2 and Figure 3 illustrate a point of contact between the opposing indentations to form cooperating support elements in accordance with one embodiment of the present invention when the halves of the upper and lower impact absorption component are joined. The upper hemispherical indentation 4 which formed in the upper half of the impact absorption component 2 is brought into contact with a corresponding hemispherical indentation 5 in the lower half of the impact absorption component 3. The contact point can be fixed or not fixed. If it is fixed, the indentations can be joined at their point of contact either by gluing, fusing, welding or similar. In some cases the inwardly directed indentations touch or rest against the opposite impact absorbing component element or the corresponding indentations on the opposite surface, but do not stick or bond to the corresponding indentations on the opposite surface. In some cases, the design may indicate that the indentations do not engage the opposite surface until sufficient pressure is applied to the surface of the upper and lower impact absorption component to cause a contact between the indentation and the corresponding opposing indentation. Taking into account the general physical properties of the thermoplastic materials used, the size, type and grouping of support elements are determined by the functional requirements of the intentional impact absorption structure. In this way, the materials, support elements, and location of the support elements are chosen to provide greater cushioning and stability in certain areas of the impact absorption structure. Similarly, for areas of the impact absorption structure that require greater rigidity, materials, support elements and support element locations are used that provide increased stiffness or hardness. For example, indentations on the upper and lower surfaces can be grouped closer where the pressure is expected to be greater and consequently greater strength is required. The lateral stability can be improved by adding walls that extend along the periphery of the upper and lower surfaces. As mentioned, the polymers chosen to build the present invention must have sufficient flexibility to function as an impact absorption component for various uses. In general, the flexible means that give shape to the polymer component will be bent or will respond to an applied force without breaking or cracking in its hardened state. The polymers that are particularly preferred for use in the present invention are elastomers having a large elongation. In general, the greater the elongation, the greater the longevity of the flexure of the impact absorption component. Good elongation properties are also desirable to create an adequate cushioning margin in the impact absorption structure. For example, polymers with an elongation at break of about 250% to about 300% or more, when measured in accordance with ASTM D 638, are representative of desirable polymers for use in the present invention. Preferably, the impact absorption component will have a flexural longevity of at least 50,000 flexes. An indicator of such desirable bending longevity can be determined, for example, by the use of bending machines, such as Ross Flex equipment and the Satra / Bata tape flexing machine manufactured by Satra Footwear Technology Center, Kettering Northhamptonshire, England. In addition, the hardness of the material is important to obtain desirable characteristics of the impact absorption component such as integrity, lateral stability, etc. The harder materials allow the use of thinner materials for the construction of the impact absorption component and in this way decrease the weight of the component. In general, the polymers that are preferred will have a hardness ranging from about 70 on the Shore A scale to about 55 on the Shore D scale (ASTM D 2240). Other characteristics that are preferred in the material of the impact absorption component are: 1) formability, that is, the ability of the material to be molded into the desired shape of the component, 2) abrasion resistance, 3) clarity, 4) good tear resistance, 5) low density, 6) good tensile strength, 7) the ability to integrate the material into the existing processing methodology, 8) the ability to color the material and 9) cost. A high tensile strength is desired to respond to the shear forces encountered during the use of high activity. In addition, the high high tensile strength allows a thinner molding. Clarity is important to achieve an intense color contrast, which is vital for an acceptable decoration in certain applications. Transparency is another point where the cosmetic design of the impact absorption structure includes a transparent portion. The integration in the existing processing procedures includes factors such as ease of bonding the component with other materials. Wet traction and traction are also key material properties for the impact absorption component of the present invention. As noted, preferably the impact absorbing component is constructed of a thermoplastic resin. Preferred materials are those that can be easily thermoformed into desired flexible component configurations. Materials that can be thermoset after molding and maintain flexible characteristics for the impact absorption component within the present invention are included within the scope of preferred thermoformable materials. The thermosetting resins solidify or harden irreversibly when heated, due to the crosslinking between the polymer chains. Crosslinking can be achieved by using core forming agents, molding temperatures greater than the temperature of formation of the materials, radiation, etc. Once a thermosetting resin solidifies or hardens, it can not be softened again by heating. Generally, thermosetting resins are characterized by high thermal stability, high dimensional stability and high rigidity and hardness and include resins such as polyesters and urethanes. The thermoplastic resins can be crystalline or amorphous and can be repeatedly softened by heating. Amorphous thermoplastic resins include acrylonitrile-butadiene-styrene copolymer (ABS), styrene, cellulosics and polycarbonates. The crystalline thermoplastic resins include nylon, polyethylene, polypropylene and polyurethane. Examples of materials that are particularly preferred for use in the present invention include thermoplastic polyurethanes, nylon, polyesters, polyethylenes, polyamides, and the like. The following descriptions further illustrate the types of materials desirable for use in the present invention. The thermoplastic polyurethanes exhibit good flexural life, especially at high hardness, good abrasion resistance, ease of bonding, good elongation and clarity. Examples of thermoplastic polyurethanes that are preferred are Elastollan® 1100 series of polymers made by BASF Corp., Parsippany, NJ. The properties of the Elastollan® representative polymers are given in the table below.

PROPERTY ASTM UNITS GRADES 1190A 1154D 1154D Gravity D-792 gr / cc 1.13 1.16 1.19 specific Hardness D-2240 Shore D 42 ± 2 53 ± 2 73 ± 2 Resistance to D-412 Mpa 32 40 40 traction Lengthening D-412% 575 460 350 @ to rupture Resistance to D-1044 mg 45 75 75 abrasion Nylon exhibits good tensile strength and thus can be molded thinner. In addition, they have low density, and therefore are lighter and exhibit a good longevity to bending. An example of a preferred nylon polymer for use in the present invention is Zytel 714 made by E.l. DuPont de Nemours & Co., Wilmington, Delaware. The representative properties of Zytel 714 are provided in the following table: PROPERTY ASTM UNITS ZYTEL 714 Specific gravity D-792 grlcc 1.02 Hardness D-2240 Shore D 55 Tensile strength D-638 MPa 27.2 Stretch @ break D-638% 260 Polyesters have good low density, ease of cementing, tensile strength and stretch. An example of Preferred polyester polymers are the various polymers of the Whittler series of thermoplastic elastomers manufactured by E. I. Dupont de Nemours and Company. Hytrel polymers are block copolymers of polybutylene terephthalate and long chain polyether glycols. The properties of representative examples of the Hytrel polymers are provided in the following table: PROPERTY ASTM UNITS GRADES 4056 5555HS G-4774 Specific gravity D-792 gm / cc 1.16 1.16 1.20 Hardness D-2240 Shore D 40 55 47 Resistance to D-638 MPa 28 40 20.7 traction D-638% 550 500 275 Stretching @ rupture The polyamides present good resistance to breakage, high elasticity, low density, good bending life and clarity. An example of a preferred polyamide material is Pebax manufactured by Atochem, Paris, France, which is a polyether block amide thermoplastic elastomer. The properties of the representative Pebax polymers are provided in the following table: PROPERTY ASTM UNITS GRADES 533 4033 3533 Specific gravity D-792 gm / cc 1.01 1.01 1.01 Hardness D-2240 Shore D 55 40 35 Resistance to D-638 MPa 44 36 34 traction D-638% 455 485 710 Stretching @ rupture Another example of a preferred polymer is Suriyn, manufactured by E. I. Dupont de Nemours and Company. Suriyn is a cross-linked thermoplastic polymer (ionomer) of ethylene and methacrylic acid copolymers which have good breaking strength, low density and good flex life. The properties of the Suriyn ionomers are provided in the next box: PROPERTY ASTM UNITS GRADES 9020 9450 Specific gravity D-792 gm / cc 0.96 0.94 Hardness D-2240 Shore D 55 54 Resistance to D-638 MPa 26.2 21.4 pull D-638% 510 500 Stretch @ break As indicated, the description of the properties of the specific polymers is made for the purpose of illustrating the types of polymers having desirable properties for use in the impact absorption components of the present invention. Many other polymers with similar properties are suitable for use in the present invention. In addition, the data provided is based on available information and can not be used for direct comparisons between polymers or to guide precise design specifications. For example, ASTM tests allow alternative methods to develop property data. In addition, other ingredients added to the polymers, such as fillers, reinforcing agents, dyes, etc. they can cause variations in the properties. A preferred method for building the impact absorbing component of the present invention is to mold sheets of a highly flexible polymer plastic resin to form the upper and lower surfaces of the component and then bond the surfaces to complete the impact absorbing component. The preferred materials, as indicated, are sheets of flexible thermoplastic resins that can be heated and molded into the desired shapes of the impact absorption component. An example of a particularly preferred thermoplastic sheet material is the 94 Shore A thermoplastic polyurethane sheet such as that available from Argotec, Inc., Greenfield, MA. The leaves are generally approximately 0.025 cm thick. The thickness of the sheet is selected in accordance with the design criteria, but will generally vary from about 0.10 cm to about 0.254 cm depending on the particular properties of the material. For example, the particularly preferred thickness for the 94 Shore A thermoplastic polyurethane ranges from about 0.15 cm to about 0.20 cm. In one embodiment of the present invention, a sheet of a first flexible thermoformable material is heated to its formation temperature and then molded into a corresponding first mold configured to form a superior surface of the impact absorbing component from the material. A sheet of a second flexible thermoformable material is heated to its forming temperature and molded into a corresponding second mold configured to form a lower surface of the component from the material. The molds are then configured to provide indentations in one or both of the upper and lower surfaces formed from the corresponding protrusions in one or both of the molds. Once molded, the upper and lower surfaces of the impact absorbing component are cooled sufficiently to be removed from the mold and then brought together. One advantage of the thermoforming of the double-leaf impact absorption structure is the ability to use two different materials having different properties to create a variety of functional values that are not possible with only one material. For example, the impact absorption component can be constructed from materials having different thicknesses. In addition, the indentations used to create the impact absorption function can all be connected during the molding process. This is highly advantageous when constructing an impact absorption component that has adequate damping and stability, without adding additional costly operations. For example, a particularly preferred method of constructing the impact absorption component of the present invention is through the use of specially designed double-sheet thermoforming molds and techniques. Thermoforming in general is a process for forming thermoplastic resin by heating a plastic resin sheet or film to a temperature sufficient to make the resin flexible enough to give it the desired shape. Usually. The material is heated uniformly throughout its normal formation temperature. The normal formation temperature is determined by heating the material to the highest temperature at which it still has sufficient heat stress to be manageable, lower than the material degrading temperature. Preferably, the material will have adequate hot tensile strength to allow the material to expand uniformly in and around the mold. The material at its formation temperature is then attached to its edges and forced into a mold on one side, traditionally a temperature-controlled aluminum mold, by applying a vacuum to the side of the material mold to force the material into the mold. Positive air pressure is also generally applied to the surface of the material opposite the mold side of the material to help force the material firmly into the mold. When the sheet material is at its formation temperature, the material is essentially tempered (released from tension). To avoid the formation of tension, the hot sheet must be forced against the mold as quickly as possible by applying vacuum and air pressure. Once molded, the part cools down to its fixing temperature which is the temperature at which the part hardens sufficiently to allow the removal of the part of the mold without deforming the molded part. The molded part is then cleaned of the surplus material, which is generally present at the edges of the molded article where it has been fastened. If desired, the surplus material can be recycled. The double sheet thermoforming uses, in particular, two sheets of heated material at its formation temperatures, the upper sheet forced towards an upper half of the mold and a lower sheet forced towards a corresponding lower half of the mold. The two halves of the mold are pressed together and the pressure of the two molds pressing the sheets together at their formation temperature effectively welds the two materials together at their points of contact. The contact points may be along the periphery of the upper and lower halves of the impact absorption component and between the indentations and corresponding portions of the opposite element. In addition, the contact points can be between the corresponding indentations. As indicated, the air pressure can be applied between the sheets to help force the material firmly into the molds. Particularly preferred materials for double sheet thermoforming must have good specific heat, that is, the hot sheet retains its temperature for a sufficient time in the process to easily join the surfaces at their contact points. The thermoplastic polyurethane, for example, has good specific heat. The thermoforming process of the impact absorption component of the present invention is illustrated by reference in a general manner in FIG. 7. With respect to FIG. 7, two rolls of thermoplastic sheets 30 and 31 are fed with rolls 32 and 33 on rollers. 34 towards the sheet heaters 35 to raise the temperature of the sheet to its substantially normal forming temperature. The sheet is then advanced to the forming station 36 having an upper component mold 37 and a lower component mold 38. Alternatively, separate thermoplastic sheets can be used in place of continuous rolls of thermoplastic sheets. In said process, the sheets move from station to station (ie, from heat to mold). The mold halves are closed together and the vacuum is applied to the mold halves to force the upper sheet material in the upper mold 37, and the lower sheet material towards the corresponding lower mold 38. Air pressure can also be applied between the sheets to help firmly force the materials into the molds. The mold halves remain closed for a sufficient time to weld together the upper and lower materials at their points of contact. For 94 Shore A thermoplastic polyurethane from 0.1524 to 0.2032 cm. of thickness, for example, the sheets are molded at approximately 204.4 ° C and a cycle time of approximately 20 sec. The mold halves are then removed and the formed impact absorption component 39 is removed from the mold after sufficient cooling and sent down the line for cleaning. In constructing the impact absorbing structure of the present invention, it has been found that pressurizing the cavity between the two mold halves is useful to prevent the opposing surfaces from collapsing and unnecessary extra welds to be formed. It is preferable to pressurize the space between the two molds during the demolding operation to avoid such collapse and unwanted welding. In addition, pressurizing this space between the mold halves helps rush the opposing surfaces against the mold halves so that each sheet conforms to the mold surface accurately and completely, and helps to join the indentations in the surface (s) against any insertion that may be placed in the molds. As described, the upper and lower surfaces of the impact absorbing component may be constructed of different thermoplastic materials. Therefore, a number of advantages can be planned in the component. For example, the upper surface may be composed of a thicker and heavier thermoplastic material, while the lower surface is composed of a thinner and lighter thermoplastic material. Similarly, having corresponding support elements from two different materials increases the ability of the designer to build different degrees of flexibility or strength in specific areas of the impact absorption component. By varying the materials used in terms of specific properties such as tensile strength, material thickness and elongation and varying the indentation configurations to form support elements, a number of consistently reproducible regions of desired strength and flexibility can be designed in the component of impact absorption to meet specific requirements. For example, a thicker and more rigid material can be used as the top surface and a thinner and more flexible material can be employed as the bottom surface. The indentation extending from the upper surface of a stiffer material would form a stiffer upper portion. The indentation extending from the lower surface would provide a more flexible and "softer" lower support member. Consequently, cooperative support elements are provided that have double features that allow the functional response of the support elements to be more accurately designed. Further, where the component includes a wall element, the wall element can be formed of two materials, i.e., the wall can be divided between the surfaces of upper and lower impact absorption components. Alternatively, the impact absorption component can be constructed by blow molding and preferably extrusion blow molding. In extrusion blow molding, a preform (a round hollow tube) of molten thermoplastic resin is first extruded, then trapped between the two halves of the mold. The preform expands against the mold cavity with air pressure to form the opposite surfaces of the impact absorbing structure. After the preform is molded to provide indentations on the opposing surfaces, the structure is cooled and removed from the mold. In the preferred embodiment, one or more of the indentations directed inward on the opposing surfaces have a hemispherical shape. As shown in Figure 4, the upper element 2 is attached to the lower food 3 and preferably the elements are joined to a wall element 8 of its outer periphery. Extending in the interval between the upper and lower elements, there is a plurality of inwardly directed indentations 4, 5 to provide internal support to the structure of the impact absorption component. As indicated above, one or more of the indentations are hemispherical in shape. In the preferred embodiment, the diameter of each indentation of hemispherical shape can be anywhere from about .317 cm to 1.27 cm. The indentations of hemispherical shape in the upper and lower elements can be supported and / or can be joined using adhesive or other means. The hemispherical indentations in the upper and lower elements are preferably formed of flexible, highly polymeric plastic resin sheets that can be heated and molded into these components. Alternatively, indentations of hemispherical shape are they can form by molding under blown a thermoplastic resin. The hemispherical indentations are integral portions of each impact absorption component to provide a controlled collapse of the material and thus create cushioning and stability areas as desired. An important advantage of the hemispherical shape for the impact absorption indentations is the improved fatigue resistance during the life of the structure. The hemisphere has better resistance to cracking when subjected to compression than other shaped indentations. Other advantages of the hemispherical indentations include better performance throughout the deformation cycle by force, reduction in stress and deformation in the material used for the upper and lower portions, and ease of molding. As used in this application, the term "hemisphere" generally includes hemispherical shapes and is not limited to those having the precise dimensions of a hemisphere, but also includes hemylipsoidal forms. The hemispherical shape has the advantage of a smooth load definition curve, increasing the perceived performance of the impact absorption system. In addition, the hemispherical shape minimizes the stresses and deformations induced in the material from which the indentation is made. Consequently, indentations that use the hemisphere design are more durable than the damping members of other designs made of the same material. The stress distribution of the hemispherical indentations improves the life of the impact absorption structure and controls cushioning and comfort, without the need to insert foam or another filler between the upper and lower surface, or to inject air or some another gas or fluid in the interval between the upper and lower surface. Hemispherical shaped indentations can be combined with other indentations on the lower and lower surfaces to provide damping characteristics as needed for different activities. In a preferred embodiment, at least one passage extends through one or both surfaces of the impact absorption structure, which provides a path for air or other means to communicate between the interior and exterior of the structure. Therefore, the internal cavity between the upper and lower impact absorption components preferably does not trap air, nor any other gas or fluid, but allows it to escape from the interval during compression, so as not to interfere with the damping. The additional air passages can be used on both the upper and lower surface as desired to provide additional air flow. As shown in Figures 8 and 9, one or more indentations 109 on the upper surface 106 or on the lower surface 107 can be adapted to receive inserts 117, 118 at this location. For example, each of the inserts may be a hemispherical shaped rubber plug 117 that fits into each of the hemispherical patterns. Preferably, the hemispherical rubber plug is shallow. The inserts can be used to adjust the damping characteristics of the impact absorption component. Alternatively, the hemispherical-shaped inserts 116 may be joined together using the mesh-like structure 110 shown in FIG. 10. The mesh-like structure provides an effect similar to a trampoline. The mesh-like structure can be formed from the same plastic of the upper or lower elements, or a material softer than the elements, if desired.

Preferably, each of the inserts 117, 118 is made of rubber, as SBR rubber and may have a hardness of about 35 to 95 on the Shore A scale. In a preferred embodiment, the inserts are rubber stoppers with little depth. Preferably, each insert has a shallow cavity therein. However, the inserts may be solid rubber plugs or, if desired, may have another internal structure for specific applications. The inserts may have a shape to conform to various different indentations in the same structure including hemispherical, conical, or other shapes. The inserts can be attached to each indentation by adhesive. Or, as discussed above, during the thermoforming of the impact absorption structure the inserts can be attached to each indentation. In a preferred embodiment, the inserts are attached to indentations on the upper and lower surface using the following method. First, the insert is conditioned by a sandblasting or other techniques to prepare the outer surface of the rubber. Subsequently, a size and an adhesive are applied to the rubber surface, which will be in contact with the indentations. Preferably, the sizing is a chlorine based sizing and the adhesive is a urethane based on a heat activated adhesive. Next, the insert is placed in a mold having cutting areas configured to the shape of the insert. The twin sheets of the thermoplastic are heated to a desired temperature (350 to 450 degrees) and enter the upper and lower molds, as shown in Figure 7. Preferably, each insert has an air passage therethrough and, as discussed above in the description, the mold also includes air passages through it which, when the insert is placed in the mold, is aligned so that air passes through the insert. Negative pressure or vacuum is applied through the air passages aligned in the mold and insert, to drive the thermoplastic heated against the mold to form the thermoplastic in the form of various indentations in the mold and against the inserts placed in the mold. A needle can also be inserted through one or more air passages in the upper or lower elements and positive air pressure is provided between the mold halves to drive the indentations in the upper and lower elements against the insert which is placed in the upper and lower elements. mold. This provides a method of securing the inserts in each of the indentations. As described above, it has been discovered that the application of negative pressure through the aligned steps in the mold and inserts helps to securely attach the inserts to the thermoplastic sheets. Additionally, the use of heat-activated adhesives applied to the outer surface of the inserts helps the inserts to attach directly to the sheets. The indentations and inserts can be adapted to make one part of the impact absorption structure more rigid in compression than the other part. There are several ways to provide this difference in compression. A smaller hemispherical radius can be used for indentations in one part of the structure. Inserts made of a material with a higher modulus of elasticity can be used in the designs on a part of the structure. Alternatively, inserts with a greater wall thickness can be used for indentations in a part of the structure. In an alternative embodiment, as shown in Figure 5 and 6, the thermoplastic material used to make the impact absorption component is made of a mixed material or is drilled with holes or grooves before or after molding the indentations in the same. By using a mesh or holes or indentations in the thermoplastic material, media can pass through the impact absorption structure at a controllable speed and / or direction while still allowing damping or other key functional attributes of the structure. The transmission speed of the medium can be controlled by the size of the hole, or the dimensions of the mesh. Also, the weight of the impact absorption structure can be minimized or decreased below a structure without mesh. The thermoplastic material may have a mesh pattern, holes or grooves, prior to the molding of the indentations, but it is also contemplated that the mesh, holes or grooves may be formed in the material after making the indentations using the mold. All thermoplastic resin or part of it used to make the shock absorbing structure may have a mesh pattern, holes or openings. For example, the mesh can be located only within a specific area so that the media can be transmitted through only part of the impact absorption structure. Preferably, the mesh pattern, holes or openings will have dimensions such that means such as air, gas, water, other fluids or particles can be transmitted through them at a speed and / or direction that can be controlled. Also, the mesh pattern, holes or openings can be configured to allow temperature, humidity, and other environmental components to be transmitted through them. The shock absorbing structure of the present invention can also be constructed of transparent material, or of a laminated product such as thermoplastic urethane. The thermoplastic resin may have strands of material to help prevent bending of the sheets or preform during the molding process. Preferably, the strands are made of nylon or other materials with higher melting points than the sheets or preform. It is also contemplated that indentations in the shock absorbing structure may have perforations. For example, hemispherical indentations in a preferred embodiment may include perforations or cuts in the surface of the hemisphere, as shown in FIGS. 11 and 12. These perforations have the effect of decreasing the average rigidity of the indentation and changing the shape of the indentation. Force displacement curve. Preferably, each structure must retain the hemispherical or hemielipsoidal shape, and have more solid material than open space.

In another embodiment, one or more of the hemispherical indentations has a mesh pattern. Like perforations in the hemispheres, the use of mesh helps to decrease the average stiffness of the indentation. In another embodiment, one or more of the inserts may be formed of a mesh material, or have holes or openings. The inserts are configured to fit into the indentations on one or both of the opposing surfaces of the shock absorbing structure. By forming inserts of a mesh material or a material having perforations or cuts in its walls, the rigidity of the impact absorption structure can be changed. In another embodiment of the present invention, as shown in Figures 13 and 14, each insert may have one or more grooves molded into its outer walls. The corresponding indentation may also have one or more grooves molded into its walls during thermoforming. Each slot has the effect of increasing the average stiffness of the impact absorption structure and changing the shape of the force displacement curve. Each slot can be oriented from the crest of the hemispherical indentation to its base, or around the hemisphere in circumferential form. The grooves are oriented in other directions, including grooves around each hemisphere in helical form, or combinations of grooves having different orientations can also be used. In another embodiment as shown in Figure 15, the indentations or inserts have an irregular wall thickness. For example, the base of the hemisphere may have a thickness greater than its peak, and vice versa. Irregularities provide the structure with properties of non-linear load displacement. Figure 16 shows a pair of hollow inserts 84 that are adhered to the hemispherical indentations 85 with the tip or ridge 86 of each cut insert. Or, the tip or crest of each insert may consist of a thin layer of rubber. The inserts of these designs have the advantage of being softer in smaller loads and more rigid when greater forces are applied to the structure of absorption of impacts. By changing the structural elements in the design, it is possible to manipulate the force displacement characteristics of the impact absorption structure, including controlling the non-linear condition of the impact absorption structure. Non-linear condition means that the impact absorption structure has a stiffness at lower displacements, but a stiffness different from higher displacements, or more generally, that rigidity is itself a displacement function. Figure 17 shows examples of force displacement curves. Curve A is the linear relationship described by the linear equation F = kx where k is the slope of the "stiffness" line. Curve B is a non-linear relationship in which stiffness increases at higher displacements. This is typical of foams and other cushioning materials which "completely crush" when compressed to deformations greater than 0.5 (ie, more than 50% of their original thickness). Curve B has the disadvantage of being an inefficient impact energy absorber, since most of the impact energy is absorbed at higher force levels. It has the advantage that the maximum load speed during an impact is relatively low. The curve C shows a non-linear relationship in which the stiffness decreases as the displacement of the shock absorber apparatus decreases. An impact absorption structure with a characteristic curve like this has the advantage that the energy of an impact is absorbed at relatively low forces. It has the disadvantage that the maximum loading speed, which occurs at the first moment of impact in this case, is higher. Figure 18 shows a top view of a mold used to form indentations in the lower surface according to a preferred embodiment of the invention. The lower half of the mold 50 has a plurality of projections of hemispherical shape 52 which are placed in a series of rows and columns to form indentations in the lower surface of the thermoplastic material which is applied thereto. The lower half of the mold 50 also includes a series of linear protrusions 54 along a first axis and linear protrusions 55 along a second axis perpendicular to the first axis. Each intersection 56 between the linear protrusions 54 and 55 preferably has rounded corners. Linear projections 54, 55 are used to form linear indentations on the surface of the thermoplastic material that fits said mold. Preferably, the lower half of the mold 50 is used to form hemispherical and linear indentations on the lower surface and the upper half of the mold 51 is used to form hemispherical indentations on the upper surface. Linear indentations provide grooves in the bottom surface. The linear indentations, which are directed inward so that the crest of each linear indentation faces the opposite surface, preferably have sufficient depth to contact or rest on the opposite surface. As shown in the cross sectional end view, in a preferred embodiment the linear indentations alternate with hemispherical indentations so that each hemispherical indentation is positioned adjacent to a linear indentation. Preferably, the linear indentations are configured to provide a series of intersecting rows and columns which form support elements between the two surfaces. The hemispherical indentations 52 on the lower surface preferably rest on the hemispherical indentations 53 on the upper surface. An advantage of configuring linear indentations directed inward on one or both opposing surfaces is that the indentations form flexible slots that increase the flexibility of the shock absorbing structure. In this embodiment, it is preferred that the crest of each linear indentation be in the same plane as the lower surface. Therefore, each hemispherical indentation on the lower surface is surrounded by a depression located between the rows and columns of the linear patterns. Figure 19 shows a cross sectional end view of a preferred embodiment for a vertical side wall between the upper sheet 61 and the lower sheet 62. The perimeter 64 of the lower sheet 62 is formed in the middle of the mold so as to be directed vertically upwards from the lower sheet, and the perimeter 63 of the upper sheet is molded in a similar manner so that it is directed vertically upwards, but at a small angle so as to extend outward to make contact with the perimeter 64 of the lower sheet. Preferably, the perimeter 64 of the lower sheet is made of such a dimension to be slightly larger than the perimeter 63 of the upper sheet. The two perimeters are supported to form a vertical side wall 65 that connects the edges of the upper and lower elements. The above description is intended to illustrate the invention. Many other variations will be apparent to those skilled in the art and such variations are included within the scope of the present invention.

Claims (20)

NOVELTY OF THE INVENTION CLAIMS

1. - An impact absorption component comprising: a) an upper surface (2) made of a flexible resin of high polymer content; b) a lower surface (3) made of flexible resin of high polymer content, at least partially coextensive to said upper surface, said coextensive relationship defines corresponding opposite portions of said upper and lower surfaces; c) a plurality of support elements comprising inwardly directed hollow indentations (4, 5) with concave depressions facing outwardly on said upper and lower surfaces (2, 3), a plurality of indentations on each of the surfaces upper and lower that have a hemispherical shape, said indentations (4) in said upper surface adjoin said indentations (5) in the lower surface.

2. The impact absorption component according to claim 1, further characterized in that it comprises a passage through at least one of the upper and lower surfaces (2, 3).

3. The impact absorption component according to claim 1 or 2, further characterized in that it comprises a wall element (8) coextensive with at least a portion of the periphery of said upper and lower surfaces (2, 3) .

4. - The impact absorption component according to claim 1, 2 or 3, further characterized in that a hemispherical insert (117, 118) adheres to one of the plurality of indentations (4, 5) in at least one of the upper and lower surfaces (2, 3).

5. The impact absorption component according to claim 4, further characterized in that at least one of the hemispherical inserts (117, 118) has non-uniform wall thickness.

6. The impact absorption component according to claim 1, further characterized in that it comprises at least one groove in the external surface of at least one of the indentations (4, 5).

7. The impact absorption component according to any of claims 1 to 6, further characterized in that said upper and lower surfaces (2, 3) are composed of different polymers.

8. The impact absorption component according to any of claims 1 to 6, further characterized in that said upper surface (2) has a different thickness than the lower surface (3).

9. The impact absorption component according to any of claims 1 to 6, further characterized in that the high polymer content flexible resin forming at least one of the upper and lower surfaces (2, 3) comprises a material having a plurality of openings therein sufficient for the transmission of fluids therethrough.

10. - The impact absorption component according to any of claims 1 to 6, further characterized in that the indentations (4, 5) in at least one of the upper and lower surfaces (2, 3) have perforations therein.

11. The impact absorption component according to any of claims 1 to 6, further characterized in that at least one of the indentations (4, 5) has a different wall thickness on the crest of the indentation at the of the foundation of the ndentation.

12. The impact absorption component according to claim 1, further characterized in that it comprises a plurality of linear indentations (55) in at least one of the upper and lower surfaces (2, 3).

13. The impact absorption component according to claim 12, further characterized in that the linear indentations (55) are arranged in a series of rows and columns.

14. The impact absorption component according to claim 1, further characterized in that the indentations (4), 5) are the only support for separating the upper and lower surfaces (2, 3).

15. The impact absorption component according to claim 12, further characterized in that the inserts of hemispherical shape each have at least one passage extending therein.

16. The impact absorption component according to claim 13, further characterized in that at least one of the inserts of hemispherical shape has at least one groove in the external surface thereof.

17. An impact absorption structure comprising: (a) first and second generally planar thermoplastic surfaces, each thermoplastic surface having a plurality of indentations formed generally hemispherical therein, the crest of each hemispherical indentation on the first thermoplastic surface being makes contact with the crest of each hemispherical indentation on the second thermoplastic surface; and (b) a plurality of linear indentations in the first thermoplastic surface, the linear indentations are brought into contact with the second thermoplastic surface.

18. The impact absorption structure according to claim 17, further characterized in that the linear indentations are arranged in a series of rows and columns.

19. The structure of impact absorption according to claim 18, further characterized in that each linear indentation in a row intersects a linear indentation in a column, the intersection has rounded corners.

20. The impact absorption structure according to claim 17, further characterized in that each hemispherical indentation is positioned next to a linear indentation.