DE2718401C2 - Flat palette made of synthetic resin - Google Patents

Description

The invention relates to a flat pallet made of synthetic resin, on the upper side and/or lower side of which at least one strand-shaped, anti-slip element made of relatively soft and flexible material is provided.

Such a flat pallet is known, for example, from US-PS 34 30 585. The anti-slip elements are glued to the flat underside of the support panel of the flat pallet.

During operation, the anti-slip elements, usually made of rubber-elastic material, are subjected to relatively high stress because they are in direct contact with the loads on the pallet, which are moved relative to the pallet during transport of the flat pallet by shaking and similar impacts. All of these stresses are transmitted via the rubber elements, which therefore often become detached or damaged after only a short period of operation.

The German utility model 19 90 278 describes a flat pallet with a plastic layer applied to its smooth upper surface. This protective layer with anti-slip properties is also subject to high levels of wear for the reasons mentioned above.

US-PS 36 77 200 describes a flat pallet in the upper side of which are provided with grooves running parallel to one another, which are intended on the one hand to reduce the weight of the pallet and on the other hand to increase the roughness of the surface.

Starting from a flat pallet of the type mentioned at the outset, the object of the invention is to design it in such a way that the anti-slip elements of the flat pallet retain their intended properties even after a long period of use, even when transporting relatively hard loads.

To achieve this object, the invention is characterized in that the element is inserted into a groove whose height is less than the height of the element and which is wider than the element.

These features make it possible for the load in question to deform the rubber-like element so that the groove is completely filled by the rubber-like element when the flat pallet is loaded. This reduces the frictional force between the load and the rubber-like element and thus noticeably increases the durability of the element. Because the anti-slip element is higher than the groove, it protrudes over the top or bottom of the actual flat pallet when not under load and can therefore exert its anti-slip properties on the load in question.

Advantageous further embodiments of the invention are characterized in the subclaims. This is explained in more detail below using exemplary embodiments. It shows

Fig. 1 - a perspective view of a flat pallet with two-sided access;

Fig. 2 - a plan view of the flat pallet shown in Fig. 1;

Fig. 3 - a front view of the flat pallet shown in Fig. 1 and

Fig. 4 - a plan view of the bottom of a modified embodiment.

Synthetic resin is used to manufacture the pallet. These include polyolefin resins, e.g. high-density polyethylene (with a density of 0.95 to 0.98 g/cm³), polypropylene and ethylene-propylene copolymers, vinyl chloride resins, e.g. polyvinyl chloride and polyvinylidene chloride, styrene resins, e.g. polystyrene, acrylonitrile-styrene copolymers and acrylonitrile-butadiene-styrene terpolymers, polyamide resins and polyester resins. Of these synthetic resins, polyolefin resins, especially polyethylene, are preferred due to their physical properties and cost-effectiveness.

These raw material resins may be mixed with an antioxidant, an ultraviolet ray absorbing agent, a foaming agent, a colorant, a pigment, an inorganic filler such as cellulose fibers, and an inorganic filler such as glass fibers, calcium carbonate and talc. From the point of view of weight, physical properties and economy, it is advantageous to manufacture the flat pallet from foamed polyolefin resin.

The flat pallets can be manufactured using any molding process, such as injection molding, blow molding, centrifugal molding, vacuum molding or casting.

It is also possible to design extruded panels as flat pallets. The flat pallets can be designed for two-sided or four-sided access.

The flat pallet is provided with several longitudinal and transverse grooves on the surface of its support board to accommodate anti-slip elements, as will be explained in more detail below. The grooves can be formed during the formation of the pallet or later by cutting or milling.

The anti-slip element is in the form of a strand, e.g. a strip or a band, and can be made of any relatively soft and flexible material which deforms suitably under a load or in engagement with conveyor rollers. It is advantageous that the material is weldable. Suitable materials consist, for example, of low density polyethylene with a density of 0.91 to 0.93 g/cm³, ethylene-vinyl acetate copolymers, ethylene-ethyl acrylate copolymers and thermoplastic rubber and of mixtures of the above. When an ethylene-vinyl acetate copolymer alone or an ethylene-ethyl acrylate copolymer alone is formed into a strand for use as an anti-slip element, the former copolymer contains up to 30% by weight of vinyl acetate, while the latter copolymer contains up to 15% by weight of ethyl acrylate. If a mixture is made with low density polyethylene, there is no limit to the content of vinyl acetate or ethyl acrylate. However, it is possible to use the above-mentioned copolymers. Furthermore, there is no limit to the ratio of low density polyethylene to copolymers.

The thermoplastic rubber is not used alone, but is usually used with a low density polyethylene or the above-mentioned copolymers in a ratio of less than 30% by weight of the thermoplastic rubber based on the weight of the mixture. The term "thermoplastic rubber" includes a block copolymer of an amorphous polymer (thermoplastic) having a glass transition temperature above room temperature and an amorphous polymer (rubber) having a glass transition temperature below room temperature. In general, polystyrene-polybutadiene-polystyrene and polystyrene-polyisoprene-polystyrene are suitable for use as the thermoplastic rubber.

The anti-slip element is in the form of a strand of relatively soft and flexible material. Such a strand can be made by extruding the soft and flexible material or by cutting an extruded sheet of material into strips or tapes. In general, the anti-slip elements have a length substantially equal to the length of the support panel of the flat pallet. It is also possible to provide shorter strands with a space between them. The cross-sectional shape of the anti-slip elements can be round, rectangular or any other shape, and the dimensions are determined depending on the softness and flexibility of the anti-slip element, the weight of the load and other factors. In case a slip-preventing member is made of an ethylene-vinyl acetate copolymer containing 14% by weight of vinyl acetate and having a melt index (MI) of 1.4 and a rectangular cross-section, a width of 10 to 15 mm and a thickness of 0.5 to 3 mm, preferably 1 to 2 mm, effectively provides the desired slip-preventing properties.

The flat pallet can, for example, be provided with the strand-shaped anti-slip elements on the upper surface and the lower surface of the support board.

The number of anti-slip elements on the upper surface of the support board varies depending on the shape and weight of the load, while the number on the lower surface depends on the shape and type of conveyor, as well as the weight of the load and the pallet itself. The number of anti-slip elements is therefore determined by the type of use of the pallet.

For the surface, a plurality of the elements are provided near both ends of the support board, or 1 to 8 elements are evenly spaced over the entire surface of the support board. It is also possible to form the anti-slip elements in the form of a grid (i.e., running transversely and longitudinally). On the lower surface of the support board, 2 to 8 evenly spaced anti-slip elements are arranged near the opposite ends of the support board, although their arrangement may be the same as that on the upper surface. When a plurality of evenly spaced anti-slip elements are arranged near four sides of the support board, it is not necessary to consider the direction of attachment or the orientation of the pallet on a roller conveyor or the like.

Even if a single anti-slip element is provided along the center line of the flat pallet, sliding can be effectively prevented.

The height of the anti-slip element above the surface of the support board should be 0.5 to 3 mm, e.g. 1 to 2 mm, although deviations are possible depending on the weight of the load and the physical properties of the anti-slip elements.

If the number of anti-slip elements is small, or if their height is too high, they will be excessively deformed due to the load or the rollers of the conveyor, making it difficult to slide the load along the pallet. This not only increases the handling but also increases the resistance to the rollers. If the deformation is too large, the pallet cannot travel along an inclined conveyor. For this reason, where the anti-slip elements are mounted on the lower surface of the pallet, it is desirable that they be continuously deformed by the conveyor rollers, so that the best results can be achieved if the anti-slip elements are arranged along the entire length of the flat pallet in a direction perpendicular to the axes of the rollers. Even if the anti-slip elements are arranged discontinuously or unevenly, sufficient anti-slip can be achieved. be effected.

If the elements are too hard and too high, the flat pallet and the load vibrate.

The anti-slip elements can be attached to the support panel by welding or by means of an adhesive.

It is possible to form parallel grooves in the surface of the support panel with a depth of about 1 to 2 mm and to weld the anti-slip elements onto the bottom surfaces of the grooves. The width of the grooves is greater than the width of the anti-slip elements so that the latter have the opportunity to deform.

A flat pallet 1 shown in Figs. 1, 2 and 3 is designed to be supported by the forks of a forklift truck (not shown) which are inserted into the flat pallet from one side of two opposite sides. The flat pallet shown consists of a hollow rectangular body. Grooves 5 are provided in the upper surface 2 and the lower surface 3 of the support board of the flat pallet. Strand-shaped anti-slip elements 4 are welded to the bottom surfaces of the corresponding grooves 5. The anti-slip elements 4 on the upper surface and the lower surface extend at right angles to each other. As already explained, each anti-slip element must extend beyond the upper or lower surface of the support board.

Further examples are given below.

example 1

An ethylene vinyl acetate copolymer (MI: 1.4) containing 14% by weight of vinyl acetate was extruded in the form of a sheet having a thickness of 2 mm, the sheet being slit into strips having a width of 20 mm. The strips were cut to form the slip-preventing elements.

Four anti-slip elements were welded by hot air to the bottom surfaces of the grooves each having a depth of 1 mm formed on the upper surface of the support board of a flat pallet. (See Fig. 1). For comparison, a flat pallet without anti-slip elements and a wooden pallet were also manufactured. The flat pallet according to the invention and the comparison pallets were tested as follows.

A crate filled with beer bottles (26 kg) was placed on the pallets and the sliding angle at which the crate starts to slide was measured, giving the result shown in Table 1. Table 1 &udf53;sb37,6&udf54;&udf53;el10,6&udf54;&udf53;ta10,6:24,6:28,6&udf54;&udf53;tz5,5&udf54;&udf53;tw,4&udf54;&udf53;sg8&udf54;\Tested pallet\ Sliding angle&udf53;tz5,10&udf54;&udf53;tw,4&udf54;&udf53;sg9&udf54;\Palette according to the invention\ 27^28ij&udf53;tz&udf54; \Plastic pallet without&udf50;anti-sliding elements\ 14^15ij&udf53;tz&udf54; \Wooden pallet\ 24^25ij&udf53;tz&udf54;&udf53;te&udf54;&udf53;sb37,6&udf54;&udf53;el1,6&udf54;&udf53;vu10&udf54;

As this table shows, the sliding angle of the pallet according to the invention is larger than that of the comparison pallets.

Example 2

An extruded sheet of ethyl vinyl acetate copolymer was prepared in the same manner as Example 1 and cut into strips having a width of 10 mm. Several anti-slip elements from these strips were welded to the bottom surfaces of the grooves provided on the lower surface of the pallet, which was identical to Example 1 in which the anti-slip elements were provided on the upper surface of the pallet. The grooves had a depth of 1 mm and a uniform pitch of 20 mm. Anti-slip elements having a number listed in Table 2 below were welded to areas spaced 20 mm from both ends.

A roller conveyor was set at an incline of 2.1% and 24 crates filled with beer bottles (total weight 630 kg) were placed on the pallet and the pallet was placed on the conveyor with the anti-skid elements oriented at right angles to the axes of the conveyor rollers. The time required for a pallet to move downwards over 4.15 m was measured to determine the anti-skid effect.

For comparison, the same measurements were carried out with a synthetic resin pallet without any anti-slip elements (test object A), a wooden pallet made of wood dried indoors (test object B) and a wooden pallet that was stored outdoors and absorbed moisture (test object C).

The following Table 2 shows the results of the measurements. Table 2 &udf53;vu10&udf54;&udf53;vz21&udf54;&udf53;vu10&udf54;

The duration of the downward movement of the wooden pallet varied considerably depending on the conditions under which the wood was stored. In contrast, the duration of the downward movement of the comparison object A, which does not contain any anti-slip elements, is short, so that when the pallet was stopped, the box was displaced very significantly. This table also shows that with the flat pallet according to the invention, it is possible to adjust the duration of the downward movement by the number of anti-slip elements.

Example 3

• A Polyäthylen kleiner Dichte (MI 0,5; Dichte 0,925 g/cm³.
• B Äthylen-Äthylacrylat-Copolymer (MI 6)
• C Eine Mischung aus 70 Gewichtsteilen des genannten Polyäthylens geringer Dichte, aus 30 Gewichtsteilen eines Äthylvinylazetat-Copolymers (MI = 2, Gehalt an Vinylazetat: 25%.
• D Eine Mischung aus 60 Gewichtsteilen des genannten Polyäthylens geringer Dichte und 40 Gewichtsteilen des genannten Äthylen-Äthylacrilat-Copolymers.
• E Eine Mischung aus 70 Gewichtsteilen des genannten Polyäthylens geringer Dichte und 30 Gewichtsteilen eines thermoplastischen Gummis vom Typ S-B-S.

The following synthetic resins were produced:

• A Low density polyethylene (MI 0.5; density 0.925 g/cm³.
• B Ethylene-ethyl acrylate copolymer (MI 6)
• C A mixture of 70 parts by weight of the low density polyethylene mentioned, 30 parts by weight of an ethyl vinyl acetate copolymer (MI = 2, vinyl acetate content: 25%.
• D A blend of 60 parts by weight of said low density polyethylene and 40 parts by weight of said ethylene-ethyl acrilate copolymer.
• E A mixture of 70 parts by weight of the low density polyethylene mentioned and 30 parts by weight of a thermoplastic rubber of the SBS type.

Each of the resins was extruded into a strand having an elliptical cross section (3 mm thick, 10 mm wide), and four anti-slip members each having a depth of 1 mm and a width of 10 mm were welded from the strand into the grooves and provided on the lower surface of the resin pallet (identical to the pallet used in Example 1 in which the anti-slip members were provided on the upper surface of the pallet). The anti-slip members were provided on the surface at a pitch of 20 mm (except for 20 mm at each end portion of the support board). The duration of the downward movement of the pallets provided with the anti-slip members made of the respective resins was measured in the same manner as in Example 2, and the result is shown in Table 3. Table 3 &udf53;sb37,6&udf54;&udf53;el10,6&udf54;&udf53;ta10,6:18,6:28,6&udf54;&udf53;tz5,5&udf54;&udf53;tw,4&udf54;&udf53;sg8&udf54;\MeÅobject\ Duration of downward movement&udf50;(sec.)&udf53;tz5,10&udf54;&udf53;tw,4&udf54;&udf53;sg9&udf54;\A\Æ9.0&udf53;tz&udf54; \B\ 10.8&udf53;tz&udf54; \C\ Æ9.7&udf53;tz&udf54; \D\ 10.2&udf53;tz&udf54; \E\ Æ9.5&udf53;tz&udf54;&udf53;te&udf54;&udf53;sb37,6&udf54;&udf53;el1,6&udf54;&udf53;vu10&udf54;

Each measuring object has a longer downward movement compared to flat pallets without sliding-preventing elements.

Claims (11)

1. Flat pallet made of synthetic resin, on the top and/or bottom of which at least one strand-shaped, anti-slip element made of relatively soft and flexible material is provided, characterized in that the element ( 4 ) is inserted into a groove ( 5 ) whose height is less than the height of the element ( 4 ) and which is wider than the element ( 4 ). 2. Flat pallet according to claim 1, characterized in that it consists of polyolefin resin. 3. Flat pallet according to claim 2, characterized in that the polyolefin resin contains a high density polyethylene. 4. Flat pallet according to one of claims 1 to 3, characterized in that the anti-slip element ( 4 ) consists essentially of a polymer or copolymer of ethylene. 5. Flat pallet according to claim 4, characterized in that the main component of the anti-slip element ( 4 ) contains a low density polyethylene. 6. Flat pallet according to claim 4, characterized in that the main component of the anti-slip element ( 4 ) contains an ethylene vinyl acetate copolymer. 7. Flat pallet according to claim 6, characterized in that the vinyl acetate content of the ethylene-vinyl acetate copolymer is less than 20 percent by weight. 8. Flat pallet according to claim 4, characterized in that the anti-slip element ( 4 ) consists essentially of an ethylene-ethyl acrylate copolymer. 9. Flat pallet according to claim 8, characterized in that the ethyl acrylate content of the ethylene-ethyl acrylate copolymer is less than 15 percent by weight. 10. Flat pallet according to one of claims 1 to 9, characterized in that the anti-slip element ( 4 ) projects between approximately 0.5 and 3 mm above the top or bottom of the flat pallet. 11. Flat pallet according to one of claims 1 to 10, characterized in that the anti-slip element ( 4 ) is welded to the bottom surface of the groove ( 5 ).