Abstract:
A process is provided for making stiff, lightweight laminate materials. At least one sheet of textured lamina having raised pointed structures is forced against a softer plain lamina so as to embed the structures therein. The pointed structures raised from grooves carved into the surface of the sheet material by means of a set of teeth carried on a knife element. The pointed structures may pierce through the softer lamina such that the protruding tips may be bent over or clinched to prevent their easy withdrawal. Two such texturized lamina may be used to sandwich and pierce through the softer lamina and are co-clinched by the other. In this way a light and stiff laminate is created.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a U.S. continuation application of U.S. patent application Ser. No. 14/568,462, entitled “PROCESS FOR MAKING A LAMINATED SHEET” and filed Dec. 12, 2014, which is a U.S. continuation application under 35 U.S.C. §111(a) claiming priority under 35 U.S.C. §§120 and 365(c) to International Application No. PCT/CA2013/000501, filed May 23, 2013, which claims the priority benefit of Canadian Patent Application No. 2,780,397, filed Jun. 18, 2012, the contents of which are incorporated by reference herein in their entirety for all intended purposes. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The invention relates to laminated materials, and more particularly relates to processes for laminating by layering of lamina or plies to produce an improved structural material. 
       BACKGROUND OF THE INVENTION 
       [0003]    There is a growing need for lighter, stiffer, cheaper structural materials, preferably with all three qualities, with which to make better products. 
       SUMMARY OF THE INVENTION 
       [0004]    A laminate is made by combining at least one harder lamina (layer) with at least one softer lamina. In one embodiment, two outer harder lamina are used to sandwich a softer core or centre lamina. The harder lamina(s) are preferably made of a ductile material such as sheet steel. Each such harder lamina has at least one face surface textured such that a myriad of pointed, nail-like, piercing structures rise therefrom. Preferably the textured lamina is not perforated. The core or centre lamina is preferably of a softer, pierceable material such as sheet plastic. One or more of the textured lamina(s) are forced against at least one pierceable lamina so that it is thereby pierced and preferably penetrated through such that the pointed tips of the piercing structures are co-clinched against each other and thereby locking the three lamina together. 
         [0005]    According to a first aspect of the invention, a process is provided for making a laminate sheet. At least one face of a sheet of a first relatively hard material is provided with a surface texture having a plurality of raised and generally pointed structures. The textured face of the first material is then brought into contact with a face of a second softer material. The two faces are forced together such that at least some of the pointed structures enter the second material to form a laminate sheet. 
         [0006]    Various materials may be used. In one preferred embodiment, the first material has a Brinell hardness of more than about 80, and the second material has a Brinell hardness of less than about 30. Preferably, the first material is a metal (e.g. steel). Preferably, the second material is a plastic, resin, polymer, foam, rubber, wood, or hybrid material. 
         [0007]    In one embodiment, the second material is a curable material, in which case, the “forcing” step includes applying the second material in a partially cured state, and then allowing the second material to cure. 
         [0008]    The first and second materials may be forced together by passing the laminate sheet (or portions thereof) between rolls. Preferably, the forcing step causes at least the tips of the pointed structures to pierce through the second material, such that the tips protrude at a second face of the second material. The protruding tips may be deformed to direct them over or onto or into the second face of the second material (e.g. by rolling over the tips with a roller, or by pressing downward on the tips via a second sheet of the first material). The tips may also (but need not) interact with each other (deforming each other by contact, or interengaging together in some embodiments). 
         [0009]    The process may involve heating either or both of the first material and the second material prior to forcing the materials together. The materials may be at least partially assembled together in a heated state and then cooled. The second material may be heated to a softened state, prior to partially assembling the second material to the first material in the softened state, and the second material may be then allowed to cool and at least partially harden, prior to further forcing the materials together to form the laminate sheet. 
         [0010]    The structures may have a hooked shape. The structures may be pre-bent into a hooked shape. 
         [0011]    According to a second aspect of the invention, a continuous process for making laminate sheets is provided. A supply of sheeting of a first relatively hard material with a surface texture having a plurality of raised and generally pointed structures is provided from a continuous roll. The textured face of the first material is brought into contact with a face of a second softer material. The two faces are then forced together such that at least some of the pointed structures enter the second material to form a laminate sheet. 
         [0012]    The second material is preferably continuously fed to the first material, and the two materials are forced together downstream of the respective material feeds. Preferably, the second material is continuously rolled onto the first material. The first material may also be cut before the second material is applied (or pre-cut pieces may be provided continuously for laminating—e.g. from a magazine). Alternatively, the laminate sheet may be cut into lengths after the forcing step. 
         [0013]    A laminate sheet formed by any of the foregoing processes is also provided. 
         [0014]    According to a third aspect of the invention, a laminate sheet is provided. A first relatively hard material with a surface texture having a plurality of raised and generally pointed structures is mated to a second softer material, such that at least some of the pointed structures of the first material protrude into the second material. 
         [0015]    At least some of the pointed structures may extend completely through the second material. At least some of the tips of the pointed structures may be turned over, onto or into the second material, so as to retain the first and second materials together. 
         [0016]    According to a fourth aspect of the invention, a multi-layer laminate sheet is provided. At least one dual sided sheet forms the core of the laminate. The sheet is of a first relatively hard material and has surface texturing on two faces thereof. The surface texture has a plurality of raised and generally pointed structures. Outer layers of a second softer material are disposed on both sides of the dual sided sheet, the second material being mated to the first material such that at least some of the pointed structures of the first material protrude into the second material. 
         [0017]    The multi-layer laminate sheet may also include boundary layers of single sided sheets disposed respectively outside each of the outer layers. Each boundary layer is single sided in that it has a plurality of raised and generally pointed structures on one face thereof (the opposing face is plain). The structures on the face are disposed so as to extend into at least a portion of its corresponding outer layer. (It will be appreciated that laminates of greater complexity may also be provided using this general structure—first boundary layer, core with one or more dual-sided textured sheets, each surrounded on both sides with softer material, second boundary layer.) 
         [0018]    In one variant, at least one outer layer has at least one recess for allowing access to the pointed structures. In another variant, one outer layer has at least one relatively thinner area for allowing access to the pointed structures. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]      FIG. 1  shows a continuous process of producing a locked laminate sheet from three supply coils, the outer two lamina of having piercing structures and the center lamina being of a softer pierceable material. The three lamina are forced and locked together between pressure rolls which also causes the piercing structures to clinch against the opposing outer lamina. Heaters and/or coolers are shown that may be used to alter material hardness and thus its pierceability. 
           [0020]      FIG. 2  shows an embodiment where two sets of pressure rollers are used (e.g. when the core lamina is too hard to be pierced at normal temperatures, or too thick to be pierced through). The first rollers begin the laminating, and the second roll set fully forces the lamina together. 
           [0021]      FIG. 3  shows detail of a textured lamina sheet with piercing structures that have a tapered cross-section ending in a pointed tip, populating the surface. 
           [0022]      FIG. 3 a    shows detail of a variation using hooked structures (e.g. for embedment in a fluid core material such as cement or resin). 
           [0023]      FIG. 3 b    shows how the piercing structures can be bent over to form barbed hooks. 
           [0024]      FIG. 4  shows the same embodiment where the structures have pierced through the adjacent lamina and where the pointed tips are above its surface. 
           [0025]      FIG. 5  shows two such piercing lamina having pierced through the softer core lamina and where the tips have been clinched in the process. 
           [0026]      FIG. 6  shows an embodiment of a piercing lamina with both faces textured. 
           [0027]      FIG. 7  shows another embodiment of five layer laminate where the two outer lamina have single textured faces and the central textured lamina has both faces textured and where all three textured faces have pierced the adjacent lamina and their pointed tips have been clinched. 
           [0028]      FIG. 8  shows detail of the clinching where the tips are sequentially rolled down to the final clinched position on the face of the pierceable lamina. 
           [0029]      FIG. 9  shows detail of a single piercing structure mostly embedded in a heat-softened core lamina, which may also be too thick to pierce through. 
           [0030]      FIG. 10  shows the same embodiment where the core lamina has been cooled back to hard and lamination completed by additional force causing a slight additional entry of the structure whereby a region of compression is created about the piercing structure to retain it therein. 
           [0031]      FIG. 11  shows another embodiment where the core material is the harder piercing lamina textured on both faces and the outer lamina are pierceable and are forced onto the harder core. 
           [0032]      FIG. 12  shows how a too-thick lamina may have the pointed structures clinched by providing a recess into the lamina for a punch. 
           [0033]      FIG. 13  shows exaggerated short portions of textured material. On right, the material is straight and the piercing structures are generally parallel and at right angle to the surface. On left, is the same portion of material that has been curved to show how the piercing tips must necessarily become non-parallel or convergent, moving closer together. However, if the structures have pieced into a solid lamina (not shown), the tips are thereby locked in position and unable to move relative to each other. This imparts a high degree of stiffness to the laminate. 
           [0034]      FIG. 14  shows a fragment of a workpiece showing a single cutting planed from a trough in a surface of the workpiece. 
       
    
    
     DETAILED DESCRIPTION 
       [0035]    In the following description the word “clinch” (clinching, clinchable, clinched), is used to describe the act of bending over the exposed tip of a pin- or nail that has pierced through two or more layers and extends therefrom. Clinching is common practice in the wood construction trade. Clinching is analogous to riveting in metal work, or to any other deformation of a fastener to prevent its easy withdrawal. The purpose of clinching is to impart greater cohesion between the two laminate layers that are so joined. 
         [0036]    The term “pointed structure” or “pointed structures” is used herein as a general term to describe any type of nail- or pin-like structure (or hooked or barbed structure) raised on the surface of a material (for embedding or piercing). “Piercing structure” is one embodiment where the structure is formed to pierce through a softer material in the laminating process. 
         [0037]    The term “pointed structure” or “pointed structures” is used herein as a general term to describe any type of nail- or pin-like structure (or hooked or barbed structure) raised on the surface of a material (for embedding or piercing). “Piercing structure” is one embodiment where the structure is formed to pierce through a softer material in the laminating process. 
         [0038]    In the instant invention pointed (e.g. piercing) structures have been raised from a surface of a harder lamina material. Preferably, they can pierce into an adjacent softer lamina and if longer than the soft lamina&#39;s thickness, can protrude. The protruding tips may be bent over or clinched to create the ‘locked-laminate’ embodiment of the instant invention. This piercing through and clinching brings the unexpected benefits of extraordinary stiffness to the resulting laminate. 
         [0039]      FIG. 1  shows a process for making a continuous locked-laminate material. Coil  1  supplies the first lamina  1   a  of softer pierceable material, such as polyethylene, which will become the core lamina. Coils  2  and  2   a  supply the outer second lamina  3   b  and outer third lamina  3   c  of harder material each having one face  3   a  textured with piercing structures  20 . The three lamina layers are fed between pressure rolls  4 ,  4   a . Under pressure from rolls  4 ,  4   a , the piercing structures of the two outer laminas  3   b ,  3   c  penetrate through the core lamina  1   a  and are clinched by the opposite outer lamina, continuously locking the three lamina together which can then be severed into individual sheets  6  of locked-laminate. Alternatively, the laminate  5  may be collected as a bulk product on a take-up reel (not shown) (thus, the process may be a coil-to-coil process). The bulk product may be further cut or shaped for specific applications, including cut-to-measure applications on a job site. 
         [0040]    Rolls  4 ,  4   a  can press against the entire width of the material “sandwich” or just in localized areas (e.g. edges). 
         [0041]    If lamina  1   a  is too hard to be readily pierced and/or too thick for the piercing structures  20  to extend completely through it, heaters  10  may be used to soften the material. Coolers  11  may then be used to cool the laminate strip  5  prior to cutting into laminate sheets  6 . 
         [0042]    In another embodiment, stiff, sheet core lamina  1   b , such as polycarbonate, shown in  FIG. 2 , may be similarly laminated between the outer textured lamina as described above, but with a variation comprising using heaters  10  to enable partial piercing leaving a small contact gap of, say, 5% of structure height, between each lamina after passing through first rollers  4   c ,  4   d . Coolers  11  then return the lamina  1   a  to a harder state after which second rollers  4 ,  4   a  complete the piercing and bring full contact. In this way the piercing structures are forced a short distance into the too-stiff or too-thick core lamina whereupon a region of considerable compressive tension is created about each piercing structure and resulting in an unexpected retention force. Since these structures naturally have a tapered cross-section, a secondary taper-fit retention (well known in the mechanical field) is achieved adding further retentive strength. This all results in an exceptionally rigid, low-cost laminate suitable for a wide range of uses. The sheets may be cut into shorter laminate pieces  6   a.    
         [0043]    In  FIG. 3  is shown the textured face  3   a  and plain face  3  of harder outer lamina  3   b ,  3   c  which may be the same or of different materials such as steel-steel or steel-aluminum. Piercing structures  20  have piercing, pointed tips  20   a . In  FIG. 4  the tips  20   a  are shown to pierce through lamina  1   a  and extend thereabove.  FIG. 3 a    shows that the structures can have a hook shape. For example, the hooks may be inherently formed in the initial process to prepare the textured outer lamina (for example, using the process described in co-pending application “Bulk Textured Material Sheeting”, Canadian Patent Application No. TBA, of the same applicants, filed in Canada on May 29, 2012; or the process described for example in any of Canadian Patent Nos. 1,330, 521; 1,337,622; or 2,127,339, the disclosures of all of which are incorporated herein by reference). According to one embodiment, the initial process used to prepare the textured outer lamina that inherently forms the hooks is a technique disclosed in Canadian Patent No. 2,127,339 that is applicable to readily machinable material, which is defined in the context of the embodiments of the invention as a material from which a cutting blade may plane or gouge a continuous cutting or shaving which can be smoothly curled out of the cutting plane without fracture. For example, by reference to the enlarged fragmentary view in  FIG. 14 , a tongue  16  (also referred to herein as a “pointed structure” according to one embodiment) is planed or gouged out of a surface  12  from a trough  14  which initially increases in depth as a forming tool (e.g. forming tool  24  as shown in FIGS. 9 and 10 of Canadian Patent No. 2,127,339) penetrates the surface  12  to a depth during translational movement and then continues at a substantially constant depth as the translational movement of a cutting edge of the forming tool continues, the resulting cutting being deflected in a curved path up a surface of the forming tool so as to form the tongue  16 . Alternatively, more straight upright (e.g. nail-like) structures may be pre-bent into more hook-shape structures. Such pre-bending can be done using rollers or a press arrangement between flat platens so as to bend the thinner tips over into hooks. The hook shape provides a means to engage or attach the textured surface  3   a  to a flowable-type core material after which it solidifies encasing the hooks. For example such an arrangement can be used to secure the textured face  3   a  to an applied, non-cured or non-solid materials such as cements, resins, melted polymers, adhesives and the like. In so doing a thicker core material  1   a  can be used since the clinching does not require that the core be pierced through. 
         [0044]      FIG. 3 b    shows how the structure tips  20   a  can be further formed or bent over to form retroverted hooks or barbs  20   b . Such barbs can be used to advantage to engage fabrics, soft lamina, and to be forced into heated lamina. The barb shape is well known to resist removal which adds another locking action to the instant lamination invention. 
         [0045]    In  FIG. 5  two harder outer lamina&#39;s structures are shown to have pierced right through core lamina  1   a  such that their tips have been clinched by pressure against the opposing outer lamina creating the locked-laminate of the instant invention.  FIG. 6  shows the harder lamina  3  with both faces textured with piercing structures such that it will be the core between two softer outer lamina (e.g. as shown in  FIG. 7 ). In  FIG. 7  the same double textured lamina is shown as a core lamina with softer pierceable lamina on either side and with outer harder textured lamina on the outside creating a five layer lamination which can all be clinched together. 
         [0046]      FIG. 8  shows only two lamina for clarity of the progression of the tips  20   a  being clinched while passing between rollers to the fully clinched tip  20   b  by being pressed together against a hard third surface such as an anvil. Also shown in  FIG. 8  are examples of how the tips may be reverted  20   c  so as to be pointing pack into the lamina, and crushed  20   d  where the effect is akin to riveting. 
         [0047]      FIGS. 9 and 10  show a detail of one piercing structure  20  on lamina  3   a  engaged almost fully into pre-softened lamina  1   c  leaving a small contact gap  30  therebetween. After second pressing, post-hardened lamina  1   d  (lamina  1   c  is cooled to normal hardness) is pierced an additional distance to close the contact gap and create a ‘compressive tension envelope’  40  about the entire structure. This of course applies to all structures in such a lamination process. 
         [0048]      FIG. 11  shows the rolling lamination process applied to a core of double-textured harder lamina  3   a  with softer outer lamina  1   a  which outer lamina may be of the same or different materials and thickness. 
         [0049]    In  FIG. 12  is shown two different methods of clinching when too-thick laminate prevents the tips from protruding. Flange  1   a ′ provides a thinner edge portion through which the piercing structures can emerge to be clinched. Recess or cavity  41  into thicker lamina  1   e  also provides the same access to the tips for clinching. A clinching tool (e.g. small roller or platen) may be pressed down into the recess  41  or at the thinner edge to locally clinch the exposed piercing structures. In this way, specific areas of the laminate may be clinched and other areas not. 
         [0050]    In  FIG. 13  is shown a section of harder lamina  3  with exaggerated piercing structures having a generally parallel disposition at right angles to the lamina face. When this same section is curved, the structure tips must necessarily remain at right angles to the textured lamina which they are intrinsic with, and protrude from, and so their tips are shown to move together or converge at least somewhat. If however the illustrated section is part of the locked lamination materials detailed above, the tips are locked in position preventing their convergence which, in turn, imparts a high degree of resistance to be bending where each structure adds resistance to bending. In this way an exceptionally stiff laminate is created from relatively non-stiff lamina. When the tips are clinched, a further substantial increase in strength is realized from the pull-apart or peel resistance that is thereby imparted to the lamination. 
         [0051]    Such locked-laminate material may then be formed using different known fabrication methods including bending, drawing, punching, and the like. Such fabrication methods may be augmented by heating the laminate to allow the structure&#39;s tips  50   a  to move through the softened lamina to their new angular relationship ( FIG. 13 ), and then be locked there when the lamina cools back to normal hardness returning the desired stiffness to the now-formed laminated sheet. 
         [0052]    Although the foregoing description refers to three- and more-ply laminates, it will be appreciated that simple two-ply laminates can be created using one harder (textured) material and one softer (pierceable) material, using the same roller arrangement described above (with suitable modifications) to “lock” the material together. 
         [0053]    The foregoing description illustrates only certain preferred embodiments of the invention. The invention is not limited to the foregoing examples. That is, persons skilled in the art will appreciate and understand that modifications and variations are, or will be, possible to utilize and carry out the teachings of the invention described herein. The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest purposive construction consistent with the description as a whole.