WO2000066358A2

WO2000066358A2 - Reinforced structural foam article and method for making same

Info

Publication number: WO2000066358A2
Application number: PCT/US2000/011007
Authority: WO
Inventors: Robert L. Stevens
Original assignee: Stevens Robert L
Priority date: 1999-04-30
Filing date: 2000-04-24
Publication date: 2000-11-09
Also published as: WO2000066358A9; WO2000066358A3; AU6746300A

Abstract

A reinforced structural foam article includes one or more skin layers (12, 14) bounding a structural foam layer (18) to form a composite structure. One or more reinforcing layers or members (20) are embedded within the composite structure. The reinforcing layer may include flexible, sheet-like materials, such as woven fabrics, or rigid support members, which may be provided separately or in assemblies or subassemblies. The article may be formed by rotational molding, wherein the reinforcing member or layer is supported within a mold cavity, the skin layers are formed by a first moldable plastic charge, and the intermediate foam layer is formed by a subsequent charge including an appropriate blowing agent. The reinforcing member is then embedded within the article during the molding process. Fittings may be provided for further reinforcement and for attachment of the article into further assemblies or subassemblies.

Description

REINFORCED STRUCTURAL FOAM ARTICLE AND METHOD FOR MAKING SAME

BACKGROUND OF THE INVENTION

1. Field Of The Invention

The present invention relates generally to field of reinforced foam or sheet structures, particularly to articles which may be used for structural, transportation, container, armor and similar purposes made of a reinforced shock and energy absorbing material. Still more particularly, the invention relates to a structural foam article including a reinforcing layer or members imbedded therein.

2. Description Of The Related Art Various configurations have been proposed for strong, tough, multi-ply materials for use in such applications as structural articles, supports, body armor, vehicle armor, and so forth. In commonly available structures, high tensile strength, tough materials may be employed for support and to resist loading, impact, penetration by projectiles, and the like. In certain applications calling for protective or tough, flexible supports, ballistic materials such as Kevlar have been employed. The same materials are sometimes used for containers, bags, netting or other general purpose applications. Similar structures have been proposed for protective clothing. For example, various garments are available with multi-ply arrangements of various fabrics which have good resistance to tearing and puncture. Vehicle armor is typically made of one or more layers of metallic or other impact-resistant material.

Other applications requiring tough support material include containers, mechanical supports, and transport or material handling components. For example, stretchers, cargo handling articles, and the like must typically offer good load support and durability in relatively light-weight structures. Many such structures are presently made of wood or an assembly of different materials which, when combined, provide the needed mechanical properties with reduced weight.

While the existing structures are adequate for certain purposes, they are not without drawbacks. For example, existing protective and support materials often do not absorb energy of impact or reduce the potential for injury to a degree desired. In protective clothing and similar applications, while tough fabrics and other materials may prevent or reduce the risk of penetration by projectiles, they may nevertheless allow a significant degree of blunt trauma which can cause serious injury to a wearer. Moreover, where body armor, vehicle armor and other applications are envisaged for multi-ply protective materials, these have not conventionally been capable of sufficiently absorbing and distributing kinetic energy upon impact.

In other applications, such as material handling and load supports, existing structures often do not provide a desired degree of structural stiffness and toughness to resist loading, impact, and marring during use. Moreover, the strength-to-weight properties of materials such as plywood, used in many material handling applications, may be less than desired, ultimately reducing the net load which can be handled. In addition, existing composite structures and assemblies, including plastics, metal, cloth, and molded or assembled resinous articles, often require timely manufacturing, assembly and finishing operations, and offer only limited design flexibility in terms of contours, integral handles, and similar features.

There is a need, therefore, for an improved technique for making strong, light, load-bearing or impact-resistant articles for these and other applications. In the field of protective gear, there is a need for articles capable of preventing or reducing the likelihood of penetration, such as by projectiles, while also reducing the risk of blunt trauma. There is also a need for articles of this type which can be used in other settings, such as for material handling, load-bearing structures, protective shelters, and so forth, and which offer good structural properties, as well as a high level of energy absorption and good resistance to loading, penetration and so forth. There is, at present, a particular need for a structure which can be easily manufactured and configured to meet the various needs of these diverse applications.

SUMMARY OF THE INVENTION The present invention provides a technique for forming a reinforced structural foam article designed to respond to these needs. The article may take any suitable form, and the technique is particularly well suited to the creation of tough, load-bearing and impact- resistant articles. In the field of protective structures, the invention is useful for fashioning body armor, vehicle armor, protective clothing, protective and energy absorbing clothing inserts, and so forth. In material handling and structural applications, the inventive technique provides tough, light-weight transport articles (e.g. stretchers, load spreaders), protective shelters, and so forth.

Articles fabricated in accordance with the invention may be based upon reinforcement by a variety of means, such as rigid structural members or a strong fabric layer embedded in a structural foam composite. Moreover, the structural foam may be formed by a variety of techniques, such as rotational molding. The articles may be conformed to specific desired contours to respect space and configuration constraints of specific applications. In the case of personal armor, the articles may follow body contours of users. For containers and load-bearing articles, the forms may be designed to facilitate their assembly in vehicles or containers, or their integration with other elements of a container or material handling system.

The technique allows for the formation of articles including at least one outer skin layer, and a foam layer extending from the skin layer. The reinforcing elements, members or layer is embedded in the article, at least partially in the foam layer. Where desired, the articles may include outer skin layers on both sides of the foam layer, or skin layers that completely envelope the foam layer. The reinforcement may be partially or completely embedded in the article. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a sectional perspective view of a reinforced structural foam article illustrating the various layers of the article in one exemplary configuration;

Figure 2 is a sectional illustration of a pair of molds used to form an article such as that illustrated in Figure 1 ;

Figure 3 is a detailed view of the interior of the molds shown in Figure 2 during the molding process used to form the article;

Figure 4 is a detailed view like that of Figure 3, showing the growth of a structural foam layer which will embed the reinforcing layer of the structure; Figure 5 is a flow chart illustrating exemplary steps in the creation of an article such as that shown in Figure 1 through the progressive steps illustrated in Figures 3 and

4;

Figure 6 is a sectional view of a further embodiment of a reinforced article in which a rigid framework is embedded within a molded body; Figure 7 is a partial sectional view of a reinforced structural article in which a fitting or similar connector element is received; and

Figure 8 is a partial sectional view through an alternative configuration of a reinforced article in which structures are provided for receiving fasteners used to attach the article into an assembly or subassembly.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS Turning now to the drawings, and referring first to Figure 1 , a reinforced structural foam article, designated generally by the reference numeral 10, is illustrated as including a first skin layer 12, a second skin layer 14, and first and second portions 16 and 18 of a structural foam layer therebetween. A reinforcing layer 20 is embedded in the article in contact with the first and second structural foam layer portions 16 and 18. The article thus presents an inner surface 22 along the exterior of skin layer 12 and an outer surface 24 defining layer 14. The internal surfaces of skin layers 12 and 14, namely surfaces 26 and 28, respectively, are integral with the portions 16 and 18 of the structural foam layer to provide good adherence of the structural foam layer to the skin layers. It should be noted that, while in a present embodiment described herein, the article 10 includes outer skin layers 12 and 14 which bound the foam layer on both sides thereof, the skin layers need not be identical to one another, and where desired, one of the skin layers may be eliminated entirely. The reinforcing layer 20, which may include various structures, members, fabrics, and so forth as described in greater detail below, is then embedded in the foam layer either completely or partially (e.g., the reinforcing layer or elements may extend to the outer surface of the article, such as through a skin layer).

Skin layers 12 and 14, and the structural foam layer defined by portions 16 and 18 may be made of any suitable moldable material, such as polyethylene. In a presently preferred embodiment, the skin layers and the structural foam layer are made of similar materials to facilitate their processing and homogeneous bonding and, where appropriate, recycling. For example, these layers may be made of a non-crosslinked polyethylene available commercially from various sources, such as Exxon Chemical Canada, under the designation Escorene. As described in greater detail below, the structural foam layer includes a blowing or foaming agent in admixture with the moldable plastic material to produce the structural foam body. Any suitable blowing agent may be employed for this purpose, such as an agent commercially available from Bayer Corp. of Pittsburgh, Pennsylvania or Uniroyal Chemical Co. of Middlebury, Connecticut under the designation Ficel. Moreover, any suitable material may be used for reinforcing layer 20. However, at present, flexible materials are preferred, such as fabrics made of high tensile strength, tough materials, such as materials available under the commercial designations Kevlar and Spectra.

As described more fully below, the reinforcing layer may include rigid or substantially rigid structural members, such as plates, beams, standoffs, and so forth. Such reinforcing elements may be linked to one another to form a grid work or framework for adding the desired mechanical properties to the composite article. Where desired, both rigid and flexible reinforcing elements may be provided. It should also be noted that, while in the described embodiment a single reinforcing layer is illustrated, multiple plies of such materials may be employed. Moreover, where the materials have directional properties, the plies may vary in orientation to provide additional resistance to puncture and enhanced energy absorption. Similarly, such layers may be spaced or offset from a center line of the article, as illustrated in the figures, or may lie generally along the center line. Where appropriate, the layers may be positioned adjacent to one or both of the skin layers.

Figure 2 illustrates an exemplary configuration for molds or dies used to form the article of Figure 1. In the embodiment illustrated in Figure 2, the mold assembly, designated generally by reference numeral 30, includes first and second mold halves 32 and 34, which may be brought together and joined to surround a mold cavity 36. The mold cavity is bounded by interior surfaces 38 and 40 which, in the illustrated embodiment, define the contours of inner and outer surfaces 22 and 24 (see Figure 1) of the resulting article. For example, surfaces 38 and 40 may define a partial or full chest plate such that the molded article fits a generalized or customized contour of a wearer of a resulting body armor article. Similarly, the contours defined by these surfaces may define panels for use in such applications as vehicle armor, helmets, load bearing members, stretchers, shields, shelter components, and so forth.

In the process of forming article 10, described in greater detail below, the mold halves 32 and 34 are brought together and the reinforcing layer is held within the mold by any acceptable manner. In the illustrated embodiment, for example, mold halves 32 and 34 present retention surfaces 42 which are brought to bear on a reinforcing sheet material or fabric 20 to hold the material within the mold. Moreover, the material preferably only partially divides the cavity 36 to prevent the free flow of moldable plastic material around the reinforcing material during the molding process. Alternative arrangements for enabling such material flow might include openings in the reinforcing material, openings adjacent to the edges of the mold, and so forth. When the material is fixed within the mold, force is exerted on the mold halves, as illustrated by arrows 44 in Figure 2, to hold the reinforcing layer securely within the mold during the molding process. As will be appreciated by those skilled in the art, such force may be exerted by any appropriate clamp, fastener assembly, and so forth. While the article of Figure 1 may be formed by any suitable molding process, in a presently preferred embodiment, the article is formed by rotational molding to create a skin-foam-skin cross-sectional structure in which the reinforcing layer, fabric or rigid framework is embedded. Figures 3 and 4 illustrate the progressive formation of the structural foam material with the embedded reinforcing layer. This process may be carried out through exemplary steps in Figure 5.

Referring to Figures 3, 4 and 5, the molding process, represented generally by the reference numeral 100 in Figure 5, begins at step 102 where the reinforcing layer is secured in the mold. Again, this may be accomplished in any suitable manner, such as by retaining the peripheral edge of the reinforcing layer as shown in Figure 2. Next, as noted at step 104 in Figure 5, the mold is closed and secured. At step 106 a skin layer charge of moldable plastic material is injected into the mold cavity 36. This charge will generally include a sufficient quantity of material to form the inner and outer skin layers as the mold and forming article are heated and rotated. Thus, the particular composition and volume of the charge will depend upon the configuration and size of the article being molded.

At step 108, the mold, along with the reinforcing material and the skin layer charge, is heated and rotated. As will be appreciated by those skilled in the art, this rotational molding process includes insertion of the mold into a rotational molding oven which is heated to a sufficient temperature to melt the plastic charge within the mold. The mold is rotated during such heating, generally along three orthogonal axes to promote flow of the plastic material around the mold cavity to form the skin layers. The speed of rotation, the combination of rotation about the orthogonal axes, dwell times, and so forth, will depend upon such factors as the geometry of the article, the desired thickness of the skin layers, and so forth. Moreover, as will be appreciated by those skilled in the art, where a single skin layer, or dissimilar skin layers are desired, these may be formed by controlling deposition, melting and fusion of the skin layer charge by proper orientation and motion of the mold during the rotational molding process. Figure 3 illustrates in section the growth of skin layers 12 and 14 during the heating and rotating of step 108. As illustrated in Figure 3, the plastic charge is melted along the interior surfaces 38 and 40 of the mold, and begins to accumulate, filling the mold cavity from these surfaces in an inward direction. The skin layers continue to grow as indicated by arrows 46 in Figure 3, until substantially all of the first charge is fused.

Returning to Figure 5, at step 110, the foam layer charge is then injected into the mold. As noted above, this foam layer charge may include any suitable plastic material, which may be identical to the plastic material used to form the skin layers. Moreover, the foam layer charge includes a blowing agent which promotes the creation of a structural foam during the molding process. In the presently preferred rotational molding process, the mold is then heated and rotated as indicated at step 112.

As the mold is progressively heated and rotated, the portions 16 and 18 of the structural foam layer began to form along the interior surface of the skin layers 12 and 14.

Again, the particular rotation, temperatures, dwell times, and so forth, involved in step 112 will vary depending upon the type and configuration of the article being formed. In general, however, the structural foam layers continue to form along the skin layers until the entire mold cavity 36 is filled, as indicated by arrows 48 in Figure 4. Ultimately, the structural foam layer surrounds, secures and embeds the reinforcing layer in place within the article.

Following formation of the structural foam layer, the mold is cooled and the article is removed from the mold as indicated at step 114 in Figure 5. Finally, the article may be trimmed and assembled with other materials, subassemblies, structures, and the like, as indicated at step 116.

As discussed above, the reinforced structural foam article of the present invention may include rigid or semi-rigid members provided either independently or in a grid work or framework. Figure 6 illustrates a configuration in accordance with this aspect of the present technique. In the structure of Figure 6, a reinforced article 120 includes a first skin layer 12, a second skin layer 14, and first and second portions of a foam layer 16 and 18, formed in accordance with the foregoing discussion. A reinforcing member, designated generally by reference numeral 122, is provided within the article, at least partially embedded within the foam layer defined by portions 16 and 18. In the embodiment of Figure 6, the reinforcing member includes a series of reinforcing elements

124 which are rigid members, such as metallic plates or beams. To maintain the members in the desired orientation and spacing during molding, standoffs 126 space the members from the skin layer 14, while intermediate standoffs 128 space the members from one another. As will be appreciate by those skilled in the art, such standoffs may be provided on one or both sides of the article, or may be eliminated where sufficient positioning is obtained through other means (e.g., support within the mold, fusible standoffs, etc.).

The article of Figure 6 is fabricated in accordance with the general process described above. Thus, reinforcing member 122, along with other such members, where desired, is supported within a mold, and the mold is closed to receive charges of moldable plastic material. In a rotational molding operation, the mold, with the reinforcing member supported therein, receives a charge for forming skin layers 12 and 14, followed by a rotation and heating of the mold to create the skin layers. A subsequent charge of plastic material, with the desired blowing agent provided in the charge admixture, is then inserted into the mold to form first and second portions of the structural foam layer 14 and 16. Again, as noted above, interstices between the components forming the reinforcing member 122 are substantially filled by either the skin layers or by the structural foam layer. The article is then removed from the mold after the desired cure period.

For integration of the reinforced structural foam article of the present technique into larger assemblies or structures, various reinforcing and assembly fittings may be provided as illustrated in Figures 7 and 8. In the embodiment of Figure 7, a reinforced article 130, including a fastener system, is illustrated. The fastener system of Figure 7 is specifically adapted for providing secure passage of an attachment article through the reinforced structure following molding. Article 130 of Figure 7 thus includes, by way of example, a bushing 132 which is molded within the article in accordance with the foregoing procedure. That is, the bushing is fitted into the mold and remains in place through formation of the skin layers 12 and 14, and the first and second portions of the foam layers 16 and 18. In the embodiment illustrated in Figure 7, a reinforcing layer 20 is provided, although rigid frameworks such as that illustrated in Figure 6 may also be included, or may replace the layer 20 of Figure 7.

In the specific embodiment shown in Figure 7, bushing 132 includes a flange 134 at one end thereof, and a threaded sleeve 136 extending from the flange. Internal threads

138 are provided on sleeve 136 for receiving an insert 140 which, itself, has a threaded outer surface 142. Thus, following molding and assembly, a through- fitting is provided, offering the possibility for mounting additional structures to the reinforced article, or assembly of the reinforced article into a larger assembly or subassembly.

A further alternative fastening system is illustrated in Figure 8 for a reinforced article 144. Figure 8 illustrates two exemplary external fastener types, designed specifically to receive fasteners which do not extend fully through the article. In one exemplary embodiment, a winged insert system 146 is provided, while in a further alternative, a flanged insert system 148 is used. Either system is designed to receive a threaded fastener such as a screw or bolt 150. In the case of winged system 148, a series of radially-extending wings 152 are provided for preventing rotational displacement of a sleeve 154 embedded within the reinforced article. Sleeve 154 is supported within the mold and embedded within the article as described above with respect to the system of Figure 7. Thereafter, fastener 150 may be secured within the sleeve and substantial torque applied to the fastener without displacement or pull out of the sleeve from the article.

In the case of the flanged system 148, a front flange 156 is formed on an insert sleeve 158, in addition to a rear flange 160. Front and rear flanges 156 and 160 offer substantial resistance to pull out of the insert during assembly of the article with other components. As will be appreciated by those skilled in the art, the features of the winged system 146 and flange system 148 may be combined to provide enhanced resistance to rotation and pull out.

While the invention may be susceptible to various modifications and alternative forms, specific embodiments have been shown by way of example in the drawings and have been described in detail herein. However, it should be understood that the invention is not intended to be limited to the particular forms disclosed. Rather, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the following appended claims.

Claims

1. A molded plastic composite article comprising: at least a first skin layer made of a moldable plastic material; a plastic foam layer bonded to and extending from the first skin layer; and a reinforcing element molded into and embedded into at least a portion of the foam layer to provide structural reinforcement of the composite article.

2. The article of claim 1 , further comprising a second skin layer made of a moldable plastic material, wherein the plastic foam layer is bonded to and extends between the first and the second skin layers.

3. The article of claim 2, wherein the first and second skin layers are made of the same moldable plastic material.

4. The article of claim 1 , wherein the first skin layer and the foam layer are made of the same moldable plastic material.

5. The article of claim 4, wherein the plastic material comprises polyethylene.

6. The article of claim 1, wherein the reinforcing element includes a sheet material extending generally parallel to the skin layer.

7. The article of claim 6, wherein the sheet material comprises a woven fabric.

8. The article of claim 1, wherein the reinforcing element includes at least one rigid member extending through at least a portion of the foam layer.

9. The article of claim 8, wherein the reinforcing element includes a plurality of rigid members forming a reinforcing framework.

10. The article of claim 9, wherein the plurality of rigid members are spaced from one another, and wherein portions of the foam layer are disposed within interstices between the rigid members.

11. The article of claim 1 , wherein the reinforcing element extends to at least one of the skin layers.

12. The article of claim 2, wherein the reinforcing element extends to the first and second skin layers.

13. The article of claim 1, wherein the reinforcing element is configured to be accessed through the first skin layer for attachment of the article into an assembly.

14. The article of claim 13, wherein the reinforcing element is threaded.

15. A reinforced composite structure, the structure comprising: a first rotational molded plastic skin layer; a rotational molded foam layer bonded to and extending from the first skin layer; and a reinforcing framework embedded in at least the foam layer and extending generally parallel to the first skin layer.

16. The structure of claim 15, further comprising a second rotational molded plastic skin layer, wherein the foam layer is bonded to and extends between the first and second skin layers.

17. The structure of claim 16, wherein the first and second skin layers are formed simultaneously from a single charge of plastic.

18. The structure of claim 15, wherein the reinforcing framework includes a plurality of rigid members spaced from one another within the foam layer.

19. The structure of claim 18, wherein portions of the foam layer are disposed within interstices between the rigid members.

20. The structure of claim 15, wherein the reinforcing framework includes a sheet material.

21. The structure of claim 15 , wherein the reinforcing framework includes a woven fabric.

22. A method for making a reinforced composite article, the method comprising the steps of: disposing at least one reinforcing member in a mold die, the die having first and second inner peripheral walls; rotational molding at least a first plastic skin layers along the first peripheral walls, respectively; and rotational molding a foam layer extending from the first skin layer, the foam layer bonding to the first skin layer and at least partially embedding the reinforcing member therein.

23. The method of claim 22, comprising the step of rotationally molding a second plastic skin layer along the second peripheral wall, and wherein the foam layer is molded to extend between the first and second skin layers.

24. The method of claim 23, wherein the first and second skin layers are molded simultaneously.

25. The method of claim 22, wherein the reinforcing member is disposed within the die prior to forming the first skin layer.

26. The method of claim 23, wherein the first and second skin layers and the foam layers are include the same moldable plastic material.

27. The method of claim 22, wherein the reinforcing member includes a sheet member.

28. The method of claim 22, wherein the reinforcing member includes a woven fabric.

29. The method of claim 22, wherein the reinforcing member includes at least one rigid member.

30. The method of claim 22, wherein the reinforcing member includes a framework of rigid members, and wherein the foam layer extends at least partially between the rigid members.

31. A method for making a reinforced article, the method comprising the steps of: forming first and second plastic skin layers extending generally parallel to one another; forming a plastic foam layer between the first and second skin layers to bond the foam layer to inner surfaces thereof and to embed at least one reinforcing member therebetween.

32. The method of claim 31 , wherein the first and second skin layers and the foam layer are formed by rotational molding.

33. The method of claim 31 , comprising the further step of supporting the reinforcing member within a die cavity prior to forming the skin layers.

34. The method of claim 31 , wherein the reinforcing member includes a rigid member disposed at least partially within the foam layer.

35. The method of claim 31 , wherein the reinforcing member includes a framework of rigid members disposed at least partially within the foam layer, and wherein a portion of the foam layer extends within interstices between the rigid members.

36. The method of claim 31 , wherein the reinforcing member includes a sheet material.

37. The method of claim 31 , wherein the reinforcing member includes a woven fabric.