WO1987005580A1

WO1987005580A1 - Pallet of polystyrene foam, method for the production thereof, and means for carrying out the method

Info

Publication number: WO1987005580A1
Application number: PCT/DK1987/000029
Authority: WO
Inventors: Flemming Hansen
Original assignee: Individual
Current assignee: Individual
Priority date: 1986-03-20
Filing date: 1987-03-20
Publication date: 1987-09-24
Anticipated expiration: 1988-09-20
Also published as: DK153377C; EP0264406A1; DK153377B; DK129786A; AU7231987A; DK129786D0

Abstract

A device for transportation or storing, such as a pallet (1) of polystyrene foam (5) for carrying goods placed on the load cover of the pallet is constructed with a core (5) of polystyrene foam which at all sides is provided with a strong, highly resilient coating (4) adhering to the core (5). The coating is primarily a polyurethane substance. The coating is applied by spraying a polyurethane substance onto a polystyrene core. Hereby is achieved a light and strong pallet with no need for inside reinforcement and with a completely even and tight surface. The pallet can thus be used partly as an ordinary pallet and partly for carrying food or the like, where heavy demands on hygiene must be met.

Description

PALLET OF POLYSTYRENE FOAM, METHOD FOR THE PRODUCTION THEREOF, AND MEANS FOR CARRYING OUT THE METHOD.

The present invention relates to a pallet of polysty¬ rene foam for carrying goods, which is placed on the upwardly turned cover plate of the pallet in its po¬ sition for use, said pallet consisting of a core of polystyrene foam which on its entire surface is pro- vided with a layer of a strong, highly resilient coating adhering to the core, whereby the cover con¬ sists of a polyurethane substance.

It is known for purposes of transportation to place goods on pallets in order to facilitate loading, un¬ loading and transportation of the goods which can thus be handled by machine, e.g. by means of fork stackers, fork lift trucks or cranes in large con¬ signments.

From DE printed specification no. 1,556,565 and US patent no. 3,330,228 pallets are known which are con¬ structed with a core of polystyrene foam which at all surfaces is provided with a strong, highly resilient coating adhering to the core.

By constructing the known pallets in this manner it becomes possible to manufacture the pallet economi¬ cally by expansion of polystyrene foam in a corre- sponding form while the pallet due to the coating at the same time becomes sufficiently rigid to serve its purpose with no need for providing the pallet with any inside reinforcement, which makes the manufaction simpler and cheaper. However, the surface of these known pallets have not been fully satisfactory in a manner as would allow them to be used e.g. in connection with the transpor- tation and storing of food, and therefore a polyure¬ thane substance has been chosen for the coating which produced a strong and highly resilient coating which was tight and gave the pallet a hitherto unknown strength while at the same a smooth surface was ob- tained which was easy to clean because the polyure¬ thane coating could stand cleaning with ordinary cleaning materials. It thereby became more ea- sthetically and hygienically acceptable to use the pallet for goods which are placed in the retail shop direct on the pallet, just as it became possible to use the pallet in such a manner that e.g. sliced or cut up meat products could be placed immediately on the pallet for further transportation, e.g. from a catering kitchen to the place where it is to be used, such as a canteen kitchen or on a plane. This could eliminate problems of high weight and handling caused by the confined space offered by a plane.

By the pallet known from the above DE printed speci- fication no. 1,556,656 it is not mentioned in any de¬ tail how the polyurethane layer is applied to the core, whereas it is explained in the mentioned US pa¬ tent no. 3,330,228 that one half, e.g. the lower half, of a mould is coated with several layers of a plastic material which can harden quickly in that the individual layers are applied when the previous layer has reached sufficient hardness. When all the layers, which may make up a total thickness of several milli¬ meters, have hardened, the coherent layers are re- moved from the mould and then assembled with cor¬ responding layers which have been cast in the upper half of the mould in order to form a hollow shell, which is subsequently filled with polystyrene foam which after expansion and hardening ties the said lower and upper layers intimately together to form the finished pallet.

This is a time-consuming process, and it is the ob- ject of the invention to form a pallet of the men¬ tioned type in such a manner that it can be manufac¬ tured considerably faster than the known pallets in that a smooth and pore-free surface of the pallet should be achieved simultaneously, which surface must meet very high demands on hygiene, and low manufac¬ turing costs due to a low consumption of polyure¬ thane.

This objective is achieved by a pallet according to the invention which pallet is characteristic in that the polyurethane substance is composed of a largely bifunctional aromatic isocyanate and a branched poly- ether/polyester, and in that the polyurethane sub¬ stance is applied in a thickness less than 1 mm.

It has surprisingly turned out that it is possible to make a pallet according to the invention with a strong and highly resilient coating which adheres to the core, by applying a coating substance to the fi- nished core, said coating consisting of a polyure¬ thane substance of the above composition, said sub¬ stance being applied in a thickness less than 1 mm.

By operating with a fast hardening two-component po- lyurethane, which hardens fast enough to be applied in the required thickness during one process of spraying on the polyurethane substance, it now initi¬ ally becomes possible to manufacture a core of poly- styrene foam fast and at a low price by expanding the polystyrene in traditional equipment, such as a mould, remove the expanded finished core from the mould and then to apply the necessary coating to the finished core by a simple spraying process which can be automatized, said coating partly giving the fi¬ nished product the necessary strength with no need for reinforcing the core, and partly having suffi¬ cient strength to withstand attack from any such cleaning materials as the pallet might be subjected to. By the prescribed thickness of the polyurethane substance the intended saving of polyurethane is achieved in that a sufficiently strong pallet is maintained because the polystyrene core in itself has such a strength that it meets such demands on strength as are made on such pallets. At the same time it becomes possible to colour the polyurethane substance in various colours in order that the indi¬ vidual pallet owners' pallets are distinguished from each other or in order to give data concerning the nature or destination of the commodities.

The invention also relates to a method for the manu¬ facturing of a pallet, said method being characteris¬ tic in that a polyurethane substance based on a bi- functional aromatic isoσyanate and a branched polye- ther/polyester in solvent-free form is used as polyu¬ rethane substance, said substance being applied by spraying, and in that the polyurethane substance is applied at a thickness of less than 1 mm. In order to apply polyurethane substance to a poly¬ styrene core it has proven necessary to apply the po¬ lyurethane substance in solvent-free form, whereby it becomes possible to spray a polyurethane substance onto the core of a pallet and thereby obtain a coating which is for one sufficiently strong to withstand attack from e.g. such cleaning materials as the pallet might be subjected to, and secondly, which can be applied in the sufficient thickness during one spraying process while it at the same time adheres to the polystyrene foam core without damaging this.

By operating without solvents any such detrimental effect as might be caused to the polystyrene foam core by any organic solvent is for one avoided, said polystyrene foam core having very little resistance to such attacks, in that a completely tight and cohe¬ rent film is also achieved which is decisive if the pallet is to be used in connection with food. By working with spraying an even coating of the entire surface is ensured, and the process may be au¬ tomatized order to eliminate the risk that the per¬ sonnel performing the spraying are not made subject to health injuries.

By the method according to the invention it is pre¬ ferred that a two-component polyurethane substance is used for the spraying, said substance being mixed in the nozzle immediately before being applied in the proportion 4.7 parts by volume of base to 1 part by volume of hardener, since it will then become pos¬ sible to operate with a substance with such a short "pot-life" and such a fast hardening that a layer of up to 1 mm can be applied during one spraying pro¬ cess.

The invention also relates to a means for carrying out the above method for producing a pallet of poly¬ styrene foam to be used when carrying goods which can be placed on the cover plate of the pallet, said means being characteristic in that the means is made up of a solvent-free polyurethane substance based on a bifunctional, aromatic isocyanate and a branched polyether/polyester, whereby the means is designed so that it can be applied by spraying in that such a substance is easily applied to a core of polystyrene foam without damaging this and at the same time, as mentioned earlier, it produces a tight, coherent film.

The means according to the invention makes it pos¬ sible to produce a pallet of the herein described type, just as it is imperative in order that the me¬ thod according to the invention is carried out in an expedient and economically sound manner.

It is moreover according to the invention preferred that the means has a viscosity, thixotropy and a hardening time that enables it to be sprayed onto the polystyrene in a layer of up to 1 mm during one pro¬ cess, preferably a viscosity of 60-65/E4 for the base, which during the spraying is mixed with a neat hardener, and a pot-life of half an hour at 20°C.

The invention is described in further detail below with reference to the drawing, in which fig. 1 is a top view of an embodiment for a pal¬ let according to the invention,

fig. 2 is a section along the line II-II in fig. 1,

fig. 3 is a bottom view of the embodiment shown in fig. 1,

fig. 4 is a side view of the same embodiment along the line IV-IV in fig. 3,

fig. 5 is a section along V-V in fig. 3, and

fig. 6 is a section of fig. 5 on a larger scale.

A pallet according to the invention is shown from above in fig. 1, and it is seen that it is designed with a levelled coherent top side 1 which is smooth and coated with a coating 4 (as is clearly seen from fig. 6) of a polyurethane substance. From fig. 2 it is seen that the pallet is constructed with a core 5 primarily of polystyrene foam which is constructed in one piece with supporting ribs 3 at its under sur- face, said supporting ribs defining the fork channels 2 which enable handling by means of a traditional fork stacker or fork lift truck.

In order to reduce the material consumption hollow spaces 6 are arranged in the under surface which partly serve to save material thereby making the pal¬ let lighter in weight and partly contribute to making the pallet stronger. These hollow spaces may for in¬ stance be constructed like pyramids or truncated cones extending up to the load cover of the pallet in that it is decisive that the cross section of the hollow spaces decreases evenly upwards in order to make the stripping of formwork easier. For the same reason the supporting ribs are primarily made with a cross sectional profile which decreases downwards for instance in a trapeziform, in that there is an even supporting plate 7 on which the pallet can rest.

The whole pallet is coated with a coating 4 of polyu- rethan which covers all surfaces as indicated in fig. 6.

From fig. 3, which shows the pallet according to the invention seen from below, it is seen that ribs and recesses without receding edges are arranged, and the shown embodiment is a one-way pallet. The more detail¬ ed embodiment of the pallet is further seen in figs. 4 and 5 which show the pallet from the side and in a section along the supporting ribs.

One further aspect of the invention is constituted by a polyurethane substance to which for component A a mixture of a bifunctional aromatic isocyanate is used, viscosity adjusting means, fillers, dehydrants, coloured pigments and perhaps other auxiliary materi¬ als such as antifoam agents, and for component B is used a branched polyether/polyester, which substance surprisingly has proven to be capable of being ap- plied to the polystyrene foam for the formation of a strong, highly resilient coating which adheres to the polystyrene foam. Hereby it becomes possible from po¬ lystyrene foam, which is easily shaped to any re¬ quired configuration, in a simple manner to make pro- ducts that are so superior in strength and surface characteristics that e.g. pallets can be manufactured which will carry an ordinary load and stand ordinary handling merely on the basis of the polystyrene foam, just as the product has a surface which can be cleaned to such an extent that it might be used as coating for e.g. fish boxes of polystyrene, whereby their strength is improved considerably while it at the same time becomes possible to clean them suffici- ently for being used again.

An example of the composition of the components A and B, could be a composition where component A contains 10.2 percent by weight of a branched polyalcohol con- sisting of polyether and polyester groups with an 0H- content of approx. 50% and a viscosity at 23°C of approx. 3,500 +/- 300 mPa x s, mixed with 15.2 per¬ cent by weight of a branched polyalcohol containing polyether and polyester groups with an OH-centent of approx. 5.3% and a viscosity at 23°C of approx. 420 mPa x s.

Furthermore, component A contains 7.4 percent by weight of a paste consisting of equal parts of zeo- lite in molecular form (nominal pore diameter 3 A) and castor oil, and 50.8 percent by weight of barium sulphate, 4.2% chromium dioxide green, and 0.3% per¬ cent by weight of a degassing agent.

Component B can consist of 11.9 percent by weight of a solvent-free polyisoσyanate based on diphenylme- thane diisocyanate with a NCO-content of approx. 31% and a viscosity at 23°C of 120 +/- 25 mPa x s. The preferred proportion between the components A and B is 1000 percent by weight : 135 percent by weight and 1000 cm³ : 180 cm³.

The polyurethane substance is made primarily from Desmodur (5) VL and Desmophen (R) 1150, which are re¬ gistered trademarks of the firm of Bayer, Leverkusen, Germany, for a largely bifunctional aromatic isocya- nate and a branched polyether/polyester, re¬ spectively, both in pure form.

The substance comprises fillers such as barytes, cal¬ cium carbonate or talcum, viscosity adjusting means, agents for the adjustment of the thixotropic proper¬ ties, dehydrants, coloured pigments such as white, blue, black, green, yellow, brown, or red pigments, perhaps in a mixture such as Bayertitan R-KB-2 from Bayer, Miloriblau from the firm of Gustav Siegle, Stuttgart-Feuerbach or Bayferrox 306, Chromdioxidgriin GN, Bayferrox 415, Bayferrox 640 and Bayferrox 140, respectively, all from Bayer.

Claims

11P A T E N T C L A I M S

1. Pallet of polystyrene foam for carrying goods, which is placed on the upwardly turned cover plate of the pallet in its position for use, said pallet con¬ sisting of a core (5) of polystyrene foam which on its entire surface is provided with a layer of a strong, highly resilient coating (4) adhering to the core (5), whereby the coating (4) consists of a poly- urethane substance, c h a r a c t e r i z e d in that the polyurethane substance (4) is composed of a largely bifunctional aromatic isocyanate and a branched polyether/polyester, and in that the polyu¬ rethane coating (4) har a thickness of up to 1 mm.

2. Method for the production of the pallet according to claim 1, wherein a core (5) of polystyrene foam is coated on its entire coherent surface (1) with a layer of a strong, highly resilient coating (4) adhe- ring to the core (5), said coating (4) being of a po¬ lyurethane substance, c h a r a c t e r i z e d in that there as polyurethane substance is used a polyu- rethan substance (4) based on a bifunctional aromatic isocyanate and a branched polyether/polyester in solvent-free form, which is applied by spraying, and in that the polyurethane substance (4) is applied in a thickness of less than 1 mm.

3. Method according to claim 2, c h a r a c t e - r i z e d in that by the spraying there is used a two-component polyurethane substance (4) which is mixed in the nozzle immediately before spraying in the proportion 4.7 parts by volume of base to 1 part by volume of hardener.

4. Means for carrying out the method according to claim 2 for producing the pallet according to claim 1, where a core (5) of polystyrene foam is coated on its entire surface with a coating (4) consisting of a polyurethane substance (4), c h a r a c t e r i ¬ z e d in that the means is a solvent-free polyure¬ thane substance (4) based on a bifunctional aromatic isocyanate and a branched polyether/polyester, where- by the means is designed so that it can be applied by spraying.

5. Means according to claim 3, c h a r a c t e r i ¬ z e d in that the means has such a viscosity, thix- otropy and hardening time that it can be applied in a layer of up to 1 mm, primarily a viscosity of 60- 65/E4 for the base and a pot-life of half an hour at 20°C.