WO2000066452A1

WO2000066452A1 - Friction tier sheet and method for producing the same

Info

Publication number: WO2000066452A1
Application number: PCT/SE2000/000717
Authority: WO
Inventors: Dan Erik Lennart Molander
Original assignee: Recopac Ab
Priority date: 1999-04-16
Filing date: 2000-04-14
Publication date: 2000-11-09
Also published as: SE9901363L; SE9901363D0; SE515555C2; AU4445000A

Abstract

A friction tier sheet (10) for use as a separator when stacking articles (15) has a sheet-like substrate (11) and a friction lining (14) attached thereto. The substrate (11) and the friction lining (14) are made of materials having different coefficients of friction. The substrate (11) has recesses (12) distributed across its large faces (13), in which recesses the friction lining (14) is arranged and from which it preferably projects. The substrate (11) is made of a thermoplastic material and the friction lining (14) is made of a thermoplastic elastomeric material.

Description

FRICTION TIER SHEET AND METHOD FOR PRODUCING

THE SAME

Field of the Invention The present invention relates to a friction tier sheet, which is usable as a separator when stacking articles. The sheet has a sheet-like substrate and a friction lining, and the substrate and the friction lining are made of different materials. Moreover the invention relates to a method of producing such a friction tier sheet.

Background Art The sheets or separators have been used for a long time to facilitate and improve the stacking and handling of articles in many different industries. By arranging separators between layers of stacked articles, one has tried to obtain a more stable arrangement of articles. It is common to use sheets or trays of corrugated cardboard as separators. Also plastic sheets are available. In many cases the stacked articles and the sheets are placed on pallets for further transport and handling. In long transports, the articles and the sheets are enclosed by a shrink wrapping to ensure that the articles are kept in place. One has also tried to improve the engaging of the articles with the sheets.

EP-0 096 536 discloses a sheet of board or some other suitable sheet material . The sheet has been coated with strings of hot melt to divide the sheet into areas having higher and lower friction. Moreover the hot melt strings on the upper and lower sides of the sheet have been displaced relative to each other. As a result, the sheets can be stacked without the hot melt strings on adjoining sheets engaging with each other. The displacement of the strings results in articles, which are placed between two sheets, being in contact with areas of both high and low friction. When using sheets in the foodstuff industry, it happens that packages leak. This adds the difficulty of keeping the sheets dry and clean. The supply of liquid or moisture deteriorates the mechanical properties and func- tion of the sheets of corrugated cardboard, and besides the risk of the hot melt strings coming loose from the sheet of corrugated cardboard increases. As a rule, sheets of corrugated cardboard are not washable, which results in the sheet becoming unhygienic and not allowing reuse in a satisfactory manner. Also the friction strings are worn and come loose from the sheets when being reused. A further drawback of these prior-art sheets is that the hot melt strings must be removed from the sheets of corrugated cardboard if the corrugated cardboard is to be recovered from damaged sheets.

US-5,401,563 discloses a tier sheet of thermoplastic material. The sheet is made by extrusion and after that one or both large faces of the sheet are embossed in a pattern in order to reduce, within the embossed areas, the contact surface with articles that are placed on the sheet. By reducing the contact surfaces, also the friction which keeps the articles in place is reduced. The embossing is not carried out along the edge portions of the sheet since the purpose of the edge portion is to form a barrier having higher friction to prevent the articles from unintentionally sliding off the sheet. At the same time it is desirable for the articles be able to slide off the sheet in connection with loading and unloading. This means that the articles often engage with too low friction with the centre of the sheet and move in relation to the sheet during handling. If the friction is made too high within the edge portion of the sheet, problems arise in the unloading. Articles which with high speed slide onto the edge portion, can be braked so abruptly as to overturn. If too much rubber is added to the extruded material to increase the coefficient of friction of the material, the tier sheet will have too low rigidity and the function of the sheet is deteriorated.

US-4,899,880 discloses a separator within a different technical field m which the separator is placed between windshields disposed m upright position. The separator comprises a support of plastic material with gripping members of a resilient plastic foam fastened in recesses on one large face of the support . The support is made by extrusion and has an elongate rib shape having a length which is at least ten times the width. The gripping members have in a non-compressed condition an extent which is substantially greater than the depth of the recesses. The purpose of the separator is to uniformly distribute the force exerted by the windshields across the separator so as to achieve the desired grip by the gripping members against the windshields. When used, the windshields engage with the support and the gripping members are compressed m the recesses of the support without filling the entire recess. An object of the present invention is to provide an improved friction tier sheet which obviates the above problems of prior art .

A further object is to provide a friction tier sheet with improved stacking properties for articles. Yet another object is to provide a friction tier sheet which can easily be recovered.

An additional object is to provide a simpler and improved method of producing a friction tier sheet.

These and other objects are achieved by a friction tier sheet and a method as defined in the independent claims. The dependent claims define particularly preferred embodiments of the invention.

The invention is based on a sheet which has a substrate with a friction lining. The friction lining is arranged in recesses m the sheet. This means that articles that are stacked on the sheet engage firmly with the friction lining, and that the friction lining remains reliably secured to the substrate even if this should be subjected to moisture or liquid. By the lining material having a higher friction than the substrate, the articles are prevented from sliding on the sheet. By the friction lining being formed of an elastomeric material, the hardness of the material can be selected according to the type of articles for which the friction tier sheets are intended. For example, it is possible to use a particularly soft elastomeric material if one wants the edges of the articles to be pressed down in the friction lining to improve the friction with a mechanical retaining effect. The possibility of choosing, as desired, also soft elastomeric material types is due to the fact that the friction lining extends into the recesses of the substrate.

The friction lining is arranged on opposite sides of the substrate to provide engagement with high friction both from above and from below between stacked sheets and articles. Moreover, the linings are interconnected on the opposite sides through holes extending through the substrate. As a result, the linings on opposite sides of the substrate are also mechanically interconnected. This increases the retaining of the linings. The holes also allow the lining material to be injection moulded from one side of the substrate when producing the friction tier sheets.

A great advantage of the invention resides in the choice of materials. Even if the substrate and the friction lining are made of materials with different coeffi- cients of friction and different degrees of hardness, the material of the substrate and the material of the friction lining can be selected among closely related polymer materials so that the recovery of used sheets is facilitated - they can easily be ground, thus making it pos- sible to immediately reuse the ground material.

According to a preferred embodiment, the substrate and the lining are made of polyolefin materials. By both the substrate and the lining coming from the same family of materials, the sheet can be recovered without necessitating separation of the different materials. Furthermore, strong material bonds are created between the sub- strate and the lining if materials from the same family of materials are used, when the lining is secured in the production by injection moulding.

In one more preferred embodiment, the lining projects form the recesses. This means that the friction lining causes good retaining of articles on the friction tier sheet in that the friction between the sheet and the stacked articles is increased.

The lining is advantageously distributed in groups in a pattern across the large faces of the sheet . As a result, the groups can be adapted to the design of the stacked articles. For example, the lining can be formed with a central field surrounded by annular lining surfaces. The central field and the rings are interconnected by means of connecting strings. When producing the sheet, it is advantageous if the different parts of the lining, such as the rings and the central fields, are interconnected. Moreover, the connecting strings result in larger friction surfaces being obtained on the large faces.

According to a preferred method, the friction tier sheet, which is usable as a separator when stacking and retaining articles thereon, is produced by the substrate being injection moulded and formed with recesses across its large faces and the friction lining being arranged in the recesses. Moreover, the substrate is formed with holes which interconnect the recesses on opposite sides of the substrate. Since the sheet is made by injection moulding, the two materials of the substrate and the lining are joined in a satisfactory manner. To permit coating of the entire substrate with linings, use is made of several nozzles, which makes the production time short. In terms of cost, producing the sheets by injection moulding yields considerable profits. In terms of quali- ty, a uniform sheet of two materials is obtained, which preferably have different coefficients of friction.

In a preferred embodiment, the friction lining is injection moulded so as to project from the large faces of the substrate, which gives an increased friction between the stacked articles and the sheet.

Brief Description of the Drawings The invention will now be described in more detail by way of an embodiment with reference to the accompany- ing drawings.

Fig. 1 is a perspective view of a preferred embodiment of the inventive sheet . Fig. 2 is a top plan view and shows one large face of the sheet . Fig. 3 is a schematic sectional view along line III-III in Fig. 2. Fig. 4 is a side view of a stack of articles with friction tier sheets placed as separators between the different layers of articles. Description of Preferred Embodiments

The sheet 10 according to the invention illustrated in the drawings and usable as a separator has a substrate 11 of a thermoplastic material, such a polypropylene or high density ethylene. The substrate 11 is essentially rectangular and has recesses 12 distributed across the large faces 13 of the substrate 11. A lining material 14 has been arranged in the recesses 12 so as coincide with or preferably project from the large faces 13. A material having a higher coefficient of friction than the material of the substrate 11 is used as lining material 14. Preferably, however, a material is used, which belongs to the same group of plastic materials as the material of the substrate 11 but which has the form of a thermoplastic elastomeric material so as to have rubber-like pro- perties. For example, the lining material 14 can be a thermoplastic elastomer (TPE) , such as Santoprene^® (can be supplied by Advanced Elastomer Systems N.V. , Belgium) or the like. Since the material of the substrate 11 and the material of the lining 14 are closely related, a very strong adhesion between the two materials is obtained. The securing of the lining 14 is further increased by its extending down in the recesses 12 of the substrate 11. By arranging the lining 14 in recesses 12, also the engaging surface between the substrate 11 and the lining 14 is increased, thereby making the securing stronger.

Furthermore, the friction tier sheet 10 will be washable and thus also reusable since it is made of plastic materials which withstand high temperatures and also certain chemicals.

The function of the substrate 11 is to provide rigidity of the sheet 10 to allow it to give adequate support to articles 15 which are placed on the substrate 11. At the same time the substrate 11 should be impact resistant, have a low weight and withstand great variations in temperature without the material properties deteriorating . The function of the lining 14 is to provide satisfactory retaining of articles 15 on the sheet 10. The lining 14 therefore has a higher coefficient of friction compared with the substrate 11. By the lining 14 having rubber-like properties, it will, when suitable hardness properties are chosen, be deformed by the articles 15 placed on the sheet 10. In such a case, the articles 15 will also be retained by some sort of mechanical securing. The design of the lining 14 is preferably adjusted to the articles 15 that are to be stacked on the sheet 10. By articles 15 is meant all products suited for stacking, such as packages, machine elements or other commercial goods.

If the substrate 11 has a hardness of 80-120 Shore A, the lining 14 should have a lower hardness of about 50-75 Shore A so as not to be worn or damaged when using the sheet 10. According to the invention, it is particularly advantageous to distribute the lining 14 across the large faces 13 in a pattern, which comprises groups of lined areas. Preferably the lining 14 comprises groups of areas with a central field 16 and rings 17 which are placed round the same and which by means of connecting strings 18 are connected with the central field 16. This can have the form of a continuous lining surface 14. In the preferred embodiment, the lining rings 14 and the central circular field 16 are arranged in groups of nine. The rings 17 of the groups are in turn via connecting strings 18 connected with adjoining rings 17 belonging to other groups. In this context, rings 17 relate to all essentially closed forms of lining 17, such as circles, ellip- ses, triangles, squares, rectangles, polygons etc.

According to a second embodiment of the friction lining 14, it consists of friction studs distributed in groups in a pattern. The friction studs are preferably circular and continuous like the central field 16, which has been described above. The studs are arranged in recesses 12. The dimensions and the function of studs conform with the rings 17 and the central field 16. The form of the studs can also be varied like the rings 17 and the central fields 16 in the above embodiment. Grooves in the studs can result in a good fit for adequate retaining of articles 15 by friction and mechanical engagement .

Fig. 3 is a sectional view of the sheet 10, from which it is evident how the lining 14 is arranged in recesses 12 in the substrate 11. It is also evident that the lining 14 extends down to the large faces 13 of the substrate 11 to ensure a well secured lining 14. It is also shown how holes 19 extend through the substrate 11 and connect the recesses 12 on the opposite large faces 13 of the substrate 11. As mentioned above, this results in a mechanical connection between the linings 14 on the opposing large faces 13 of the substrate 11. Each ring 17 and central field 16 have a hole 19 connecting them with the corresponding ring 17 and field 16 on the opposite large face 13 of the substrate. The linings 14 on the opposite surfaces 13 of the substrate 11 preferably have a corresponding pattern. This gives the articles 15 stacked in layers the same good retaining from above as well as from below. This so-called double frictional effect between two sheets gives an excellent retaining of the articles. In longer transports, this double fric- tional effect can be reinforced by using, for example, a shrink wrapping to compress the stacked sheets 10 against the articles 15, such as tins. It goes without saying that the pattern of the linings 14 can be varied on the opposite sides 13 of the substrate 11 as long as good retaining of the articles 15 is ensured.

The preferred sheet 10 has a length and width in a range extending from about 400 x 200 mm to about 1200 x 800 mm. The thickness of the sheet is about 2-10 mm, preferably about 3 mm. The lining 14 extends past the large faces 13 by about 0.1-0.5, preferably about 0.2 mm. The recesses 12 extend down in the substrate 11 by about 0.5-1 mm. The rings 17 of the lining 14 preferably have an inner diameter of about 40 mm and an outer diameter of about 50 mm. The central fields 16 preferably have a diameter of about 50 mm.

Fig. 4 shows how a plurality of sheets 10 are used to stack articles 15, such as six-packs of aluminium cans. The articles 15 are arranged in layers between the sheets 10. By the substrate 11 being made of polypropy- lene, it will have a low weight which facilitates handling when moving and stacking . The Figure shows three layers of articles 15, but the number of layers can be varied as desired. Since the articles 15 are reliably retained on the sheets 10, the need for additional wrap- ping is eliminated.

When producing the sheet 10, first the substrate 11 is injection moulded in a first mould which forms recesses 12 and holes 19. Then the substrate 11 is moved to a second mould and the lining 14 is applied in the recesses 12 by injection moulding. The recesses 12 serve as ducts in the injection moulding of the lining 14. The holes 19 cause the friction lining to be injection moulded in one shot from the side of one large face of the sheet. The two separate moulds could also be replaced by a mould with movable cores or rotating splits. Producing the sheet by injection moulding gives increased possibi- lities of designing the recesses and friction lining according to the products that are to be stacked on/ between the horizontally arranged sheets. The friction lining obtains good bonding with the recesses and fills the entire recesses. It will be appreciated that a number of modifications of the above embodiment of the invention are feasible within the scope of the appended claims. As mentioned above, the pattern of the friction lining 14 could be varied according to different articles 15 and, for exam- pie, comprise circular groups of lining material 14. In certain cases, it is possible that the lining 14 need not project from the recesses 12 across the large faces 13 to obtain adequate retaining of the articles 15.

Claims

1. A friction tier sheet which is usable as a sepa- rator when stacking and retaining articles (15) thereon and which has a sheet -like substrate (11) and a friction lining (14) attached thereto, the substrate (11) and the friction lining (14) being made of materials having different coefficients of friction, c h a r a c t e r i s e d in that the substrate (11) has recesses (12) distributed across its two large faces (13) , that said recesses on opposite sides of the substrate are interconnected via at least one through hole (19) , that the friction lining (14) is fastened in the recesses, that the friction lining on one side of the substrate is interconnected with the friction lining on the other side of the substrate via said at least one through hole (19) , and that both the substrate (11) and the friction lining (14) are made of polymer, the material of the substrate (11) being a thermoplastic material and the material of the friction lining (14) being a thermoplastic elastomeric material.

2. A sheet as claimed in claim 1, c h a r a c t e r i s e d in that the substrate (11) and the lining (14) are essentially made of olefin plastics.

3. A sheet as claimed in claim 1 or 2 , c h a r - a c t e r i s e d in that the substrate (11) is made of polypropylene material and the lining (14) is made of a thermoplastic elastomeric material on the basis of olefin polymer material .

4. A sheet as claimed in claim 1, 2 or 3 c h a r - a c t e r i s e d in that the friction lining (14) projects from the recesses (12) .

5. A sheet as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that the recesses (12) and the lining (14) are distributed in groups across the large faces (13) in the form of a pattern which com- prises a central field (16) and rings (14) arranged round the same, and comprises connecting strings (18) between the central field (16) and the rings (17) .

6. A sheet as claimed in claim 5, c h a r a c t e r i s e d in that also adjoining rings (17) in the pattern are interconnected by means of connecting strings (18) .

7. A sheet as claimed in claims 5 and 6, c h a r a c t e r i s e d in that connecting strings (18) are also arranged between the rings (17) in adjoining groups of the pattern.

8. A method of producing a friction tier sheet, which is usable as a separator when stacking and retaining articles thereon, and which has a substrate (11) with a friction lining (14) , in which method the substrate (11) is produced and provided with the friction lining (14) on its large faces (13) , c h a r a c t e r i s e d in that the substrate (11) is injection moulded and formed with recesses (12) across its two large faces (13), that the substrate (11) is provided with at least one hole (19) which connects the recesses (12) of the opposite large faces (13) with each other, and that the friction lining (14) is arranged in the recesses (12) by injection moulding in such manner that the friction lining (14) on one side of the substrate is interconnected with the friction lining (14) on the other side of the substrate via said at least one through hole (19) .

9. A method as claimed in claim 8, c h a r a c - t e r i s e d in that the friction lining (14) is arranged in the recesses (12) so as to project from the large faces (13 ) .