FLEXIBLE MULTI-WALL SHEET

Abstract

The present invention is a multi-wall sheet made of a plastic with a high shear modulus intended to provide physical protection, structural support, and thermal insulation in applications where a small bending radius for the multi-wall plastic sheet is desired. The multi-wall configuration includes a generally flat outer single sheet and a contoured inner single sheet separated by a series of ribs of similar plastic material to form a connected row of longitudinal cavities or channels. The inner wall is contoured in a concave manner to form a relief between each rib. When the multi-wall sheet is flexed, each relief distorts to minimize stress in the transverse direction while maintaining high rigidity in the longitudinal direction. In another embodiment of the present invention, multiple single sheets separated by ribs and contoured similarly to that of the inner wall are added between the contoured inner wall and non-contoured outer wall.

Claims

1. A multi-wall sheet made of a thermoplastic with a relatively high shear modulus, having a structure comprising: a first wall comprising a single generally flat sheet; a second wall comprising a single sheet generally parallel to, extending a length of, and separated from the first wall, having a transverse contour of a form incorporating a series of alternating flat and arced sections each with an apex toward the first wall and extending a length of the second wall; and a plurality of ribs located between, perpendicular to, and connected to the first wall and second wall and each rib equidistant between two adjacent arcs in the transverse contour of the second wall and extending the length of the first and second walls in the longitudinal direction of the arcs.

2. A multi-wall sheet made of a thermoplastic with a relatively high shear modulus, having a structure comprising: a first wall comprising a single generally flat sheet; a second wall comprising a single sheet generally parallel to, extending a length of, and separated from the first wall, having a transverse contour of a form incorporating a series of alternating flat and arced sections each with an apex toward the first wall and extending a length of the second wall; an intermediate single sheet between, generally parallel to, extending the length of the second wall, and separated from the first wall, having a transverse contour of a form similar to the second wall and having an apex of each arc generally aligned to an apex of each arc of the second wall and extending a length of the intermediate sheet; a plurality of ribs located between, perpendicular to, and connected to the first wall and the intermediate sheet and each rib equidistant between two adjacent arcs in the transverse contour of the intermediate sheet and extending the lengths of the first wall and intermediate sheet; and a plurality of ribs located between, perpendicular to, and connected to the second wall and the intermediate sheet and each rib equidistant between two adjacent arcs in the transverse contour of the second wall and extending the lengths of the intermediate sheet and second wall.

3. A multi-wall sheet made of a thermoplastic with a relatively high shear modulus, having a structure comprising: a first wall comprising a single generally flat sheet; a second wall comprising a single sheet generally parallel to, extending a length of, and separated from the first wall, having a transverse contour of a form incorporating a series of alternating flat and arced sections each with an apex toward the first wall and extending a length of the second wall; a plurality of intermediate single sheets between, generally parallel to, extending the lengths of, and separated from the first wall and second wall, each having a transverse contour of a form similar to the second wall and having an apex of each arc of each intermediate sheet generally aligned to an apex of each arc of the second wall and extending a length of the plurality of intermediate sheets; a plurality of ribs located between, perpendicular to, and connected to the first wall and an intermediate sheet adjacent the first wall and each rib equidistant between two adjacent arcs in the transverse contour of the intermediate sheet adjacent the first wall and extending the length of the first wall and intermediate sheets; a plurality of ribs located between, perpendicular to, and connected to adjacent intermediate sheets and each rib equidistant between two adjacent arcs in the transverse contour of each intermediate sheet and extending the length of the plurality of intermediate sheets; a plurality of ribs located between, perpendicular to, and connected to the second wall and an intermediate sheet adjacent the second wall and each rib equidistant between two adjacent arcs of the transverse contour of the second wall and extending the lengths of the second wall and plurality of intermediate sheets.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The invention can be better understood with reference to the following drawings. The components in the drawings are not necessarily to scale, emphasis instead being placed upon clearly illustrating the principles of the present invention. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the views.

[0027] FIG. 1 is an isometric view of the present invention.

[0028] FIG. 2 is a sectional view in the longitudinal direction of extrusion of the present invention in a flexed, as well as unflexed, position.

[0029] FIG. 3 is a sectional view in the longitudinal direction of extrusion of an embodiment of the present invention in which a plurality of additional single sheets is incorporated between an outer wall and an inner wall.

DETAILED DESCRIPTION

[0030] While this invention is susceptible of embodiments in many different forms, there is shown in the drawings and will herein be described in detail preferred embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspects of the invention to the embodiments illustrated.

[0031] The present invention is a twin-wall sheet that incorporates a generally flat outer wall and a contoured inner wall.

[0032] Referring to FIG. 1, an orthogonal view of the present invention 1 in a flat, or un-flexed, position is shown. The twin-wall sheet is comprised of a first wall 2; a second wall 3 that is generally parallel to and of the same length and width as the first wall 2, and a plurality of ribs 4 located at periodic intervals between, perpendicular to, and attached to the first wall 2 and second wall 3 to establish the overall thickness of the twin-wall sheet shown as D. The first wall 2 is generally flat in this position, has a longitudinal length shown as L, transverse width shown as W, thickness shown as t.sub.o, and typically serves as the outer wall of the twin-wall sheet 1 in applications in which the twin-wall sheet serves as a covering or enclosure, or any other application where the purpose of utilizing the twin-wall sheet is to provide an insulated separation between a generally interior environment and an exterior condition. The form of the second wall 3 has a thickness shown as t.sub.i and incorporates periodic concave relief arcs 5 between each pair of adjacent ribs 4 which have thickness t.sub.r and typically serves as the inner wall of the twin-wall sheet 1 in applications in which the twin-wall sheet serves as a covering or enclosure, or any other application where the purpose of utilizing the twin-wall sheet is to provide an insulated separation between a generally interior environment and an exterior condition. The preferred form of the curvature of the concave reliefs is a filleted half-circle; however, other circular section, elliptical or higher-order curve variations with different degrees of fillet may also be used for specific optimization of bending stress characteristics of the present invention. The specific dimensions and overall shape of the twin-wall sheet 1 in all its forms are generally unlimited, however, those practiced in the art will appreciate that specific dimensions are dictated by its functionality and a particular application.

[0033] Referring to FIG. 2, a sectional view in the longitudinal direction of extrusion of the present invention in a flexed position, as well as an unflexed position, is shown. FIG. 2 shows the extrusion profile of the flexed position of the present invention 1a superimposed on the unflexed position of the present invention 1 in order to demonstrate the intent of the functionality of the present invention. Applying an equal pair of forces to the extents of the outer wall 2 along the longitudinal direction while supporting the inner wall 3 in a manner that maintains static equilibrium with the forces on the outer wall 2, causes tension, T, transversely along the outer wall 2 and compression, C, transversely along the inner wall, between the applied forces, further causing the relief portions 5 of the inner wall to distort, resulting in an overall transverse curvature if radius R. Since a minimum R is largely dependent on the depth, average radius, and periodicity of each relief 5, the Shear Modulus is used only to describe the initial bending resistance and it approaches the Modulus of Elasticity of the thermoplastic material as the thickness of the inner wall approaches zero. The Shear Modulus is proportional to the total thickness of the twin-wall sheet, D; an average of the wall thicknesses t.sub.o, t.sub.i, and t.sub.r; the periodicity of the ribs 4; and the Modulus of Elasticity of the material. The present invention is anisotropic such that its rigidity in the longitudinal direction is similar to that of the prior art.

[0034] Referring to FIG. 3, a sectional view in the longitudinal direction of extrusion of an embodiment of the present invention 6 in which a plurality of intermediate single sheets 9 is incorporated between an outer wall 7 and an inner wall 8 is shown. When the form of this embodiment is flexed around a longitudinal axis, the reliefs incorporated into the form of each intermediate single sheet distort simultaneously with each other as well as the reliefs incorporated into the form of the inner wall 8. The radii and depths of the intermediate sheet reliefs may differ between intermediate sheets and from those of the inner wall, depending on the intermediate sheet spacing and rib periodicity, in order to minimize overall distortion and bending resistance of the twin-wall sheet. The specific dimensions and overall shape of the multi-wall sheet 6 in all its forms are generally unlimited, however, those practiced in the art will appreciate that specific dimensions are dictated by its functionality and a particular application.

[0035] The present invention can be constructed of a wide range of translucent or opaque thermoplastic materials including but not limited to polycarbonate, acrylic, unplasticized PVC, PET, or high-density polypropylene. Those practiced in the art will appreciate that the present invention is typically formed through extrusion and can alternatively be formed through other techniques including, but not limited to, 3-D printing or ultrasonic welding as dictated by the specific application.

[0036] Specific examples of applications of the present invention include small greenhouses with curved roofs, cylindrical plant protectors, hoop houses, crop tunnels, roll-up semi-rigid signs, and structures such as room dividers or display frames where a small bending radius may be desired.

[0037] It should be emphasized that the above-described embodiments of the present invention, particularly any preferred embodiments, are merely possible examples of implementations set forth for a clear understanding of the principles of the invention. Many variations and modifications may be made to the above-described embodiments of the invention without substantially departing from the spirit and principles of the invention. All such modifications are intended to be included herein within the scope of this disclosure and the present invention.