This invention relates to pallets for storing and transporting goods. Pallets are generally fabricated from wooden batons and strips. Whilst they are relatively cheap to produce, wooden pallets have the disadvantage that they are not water resistant and tend to absorb moisture which increases weight and decreases strength, and can damage the structure of the pallet through warping, shrinkage, mould and mildew growth and loosening of joints, for example by rusting and consequent weakening of the nails used to secure the wood together. They are therefore unsuitable for use in some environments, and are difficult to clean. Furthermore the porous nature of wood can lead to contamination with microbes, spores and bacteria, which can pose a risk to the goods contained therein or to those handling the pallets. Wooden pallets also have variable fire-retardant qualities and can pose a fire risk. In some circumstances plastic pallets are used, which have better water resistant qualities, but tend to pose a higher fire risk. Whilst plastic pallets may have fire-retardant added, this tends to worsen their mechanical properties. Furthermore, plastic pallets typically require a large amount of non-renewable expensive material and energy to produce, tending to make them more expensive to produce and less environmentally friendly.

The invention aims to reduce these problems.

In an aspect there is provided a method of reconditioning a plastic pallet in which the surface of a pallet is treated so as to facilitate coating of the surface, for example by modifying the surface energy of the pallet. A thermosetting plastic coating may then be provided by mixing first and second components, wherein at least one of the first and second component comprise a flame retardant, to produce a thermosetting plastic comprising the flame retardant. The thermosetting plastic can then be applied to the treated surface of the plastic pallet to recondition it for further use. This enables the reuse of plastic pallets that would otherwise need to be removed from circulation due to safety considerations. The surface treatment may comprise at least one treatment selected from the list comprising corona treatment and flame treatment, other surface treatments may be used.

In an aspect there is provided a method of treating a wooden pallet, comprising sand blasting the pallet to abrade a surface of the pallet. Sand blasting is usually applied only to metals or masonry, however the inventor has surprisingly found that sandblasting provides a rapid and effective method of surface treating a pallet. A thermosetting plastic coating can then be provided by mixing first and second components, wherein at least one of the first and second component comprise a flame retardant, to produce a thermosetting plastic comprising the flame retardant. The thermosetting plastic may then be applied to the sand blasted surface of the pallet to provide a water impermeable flame retardant coating. The pallet may be dried, for example using a kiln, prior to application of the coating. In addition to improving safety, and reducing the tendency of wooden pallets to increase in weight due to absorption of moisture, this may enable the usable life of wooden pallets to be extended and/or it may provide a method of reconditioning existing wooden pallets. The components of the plastic may be mixed immediately prior to application, and the mixture may include a catalyst. The fire retardant may comprise Alumina Trihydrate, ATH. In some examples the thermosetting plastic comprises ATH in an amount of at least 30% by weight, or in some examples at least 50%, or at least 60% by weight. In some examples the components of the thermosetting plastic may be premixed, and the mixed components may be provided as a powder. Applying the thermosetting plastic to the pallet may comprise using a dry powder coating method.

Applying the thermosetting plastic to the treated surface may comprise applying a layer having a thickness of at least 0.5mm and not more than 3mm. Alternatively, to provide a light-weight single-use coating the thermosetting plastic to the treated surface comprises applying a layer having a thickness of at least 0.2mm and not more than 0.3mm, for example a thickness of 0.25mm. This can provide a coating that is surprisingly robust when compared with other coatings of similar or greater thickness. According to one aspect of the invention there is provided a wooden pallet having a monolithic, continuous coating of an elastomer wherein the moisture content of the wooden pallet is less than 10% by weight of the wooden pallet.

According to a further aspect of the invention there is provided a wooden pallet having a substantially monolithic, continuous coating of an elastomer wherein the coating comprises one or more additives selected from flame retardants, anti-slip additives and biocides.

The invention also provides a wooden pallet having an RFID tag attached thereto, and a monolithic continuous coating of elastomer encapsulating the pallet and the tag. The monolithic coating is such that it substantially encapsulates the pallet. The pallets of the invention may thus be completely enclosed in a coating of elastomer. By suitable selection of the coating elastomer the pallets may be provided with particular beneficial properties. Furthermore, encapsulation of the pallet in the elastomer provides a waterproof coating and may ensure that water cannot be absorbed by the wood. This helps prevent rusting of the nails and thus improves the structural integrity of the pallet, and also means that the pallet has a fixed weight. This prevents weight gain that often occurs when wooden pallets are exposed to humidity or otherwise get wet and allows users to maximise loads and/or use less fuel to transport the pallets. The coated pallet according to the invention may weigh less than a conventional wooden pallet with an ambient moisture content. For example, a pallet dried according to the invention may have a minimum moisture content of between 2 and 5%, and have a weight of less than around 20kg, typically around 18kg, as compared to for example typically around 30kg for a pallet having ambient moisture levels (eg 40% moisture). The weight of the elastomer coating including additives such as fire retardant is typically around 7kg, such that the coated pallet may have a fixed weight below 30kg; typically about 25kg.

The coating of elastomer may provide a non-slip surface which ensures safe handling, particularly on the tines of a forklift. This provides an advantage over many plastic pallets which may have a tendency to slip on the tines of a forklift, which can lead to loss of load and possible injury to bystanders. The non-slip surface may be enhanced by the incorporation of anti-slip additives into the elastomer.

The coating of the elastomer may provide high impact resistance and high tear strength improving the ability of the wooden pallet to withstand the potential damage of loading and handling operations. The coating of elastomer also prevents splinters from the wooden pallet and prevents nail protrusion providing a smooth supporting surface and improved handling.

Flame retardant properties which may meet the UL-94-VO standard may be provided by incorporation of suitable flame retardant additives into the elastomer.

Potential contamination of the wooden pallets may also be prevented by the coating of elastomer. Any microbes, spores and bacteria originally present may be killed or rendered inert in the drying process, and the coating provides a barrier to subsequent contaminants reaching the wood. The coating may readily be cleaned with water, detergent, disinfectant, pressure washing, steam cleaning etc. The elastomer may contain a biocide, e.g. a fungicide, to prevent contamination. The pallets are thus suitable for use in the food and drug industries. An identification tag, e.g. an RFID tag or other remotely readable tag having a memory and unique identification, may be secured to the wooden pallet and covered by the coating of elastomer thereby increasing the integrity of the labeled pallet. This enables the pallets and any goods on them to be tracked and traced.

The coating of the elastomer may be coloured by the incorporation of dyes or pigments in the elastomer thereby providing for visual recognition of the pallets. The lifetime of the coloured coating may be improved by the presence of a ultraviolet light stabiliser in the elastomer, which typically otherwise tends to 'yellow' significantly over a relatively short time.

The coating of elastomer improves the lifetime of wooden pallets thereby providing economic advantages. Furthermore pallets according to the invention may use less plastics materials than conventional plastic pallets; for example approximately 3.5kg of elastomer compared with 25kg or 11kg for a lightweight plastic pallet. Due to the drying and machining process, the encapsulated wooden pallet may also have a total weight less than that of conventional wooden pallets.

The coating of elastomer generally has a thickness of from 1 to 5 mm, preferably 1 to 3mm, more preferably about 2mm. In principle, any elastomer which can readily be applied to a wooden pallet to provide a monolithic, continuous coating may be used. Suitable elastomers may be selected from polyurethane, polyurea, polyaspartics, epoxy, polyurethane-polyurea hybrids or any combination thereof. Elastomers formed rapidly from the reaction of two components are particularly preferred. The preferred elastomer is polyurethane.

Polyurethane is typically supplied as two components, an isocyanate and a poly ether polyol or polyester polyol. The two components are mixed immediately prior to application, e.g. in the nozzle of a spray gun. The reaction between the components may be rapid and enhanced by the presence of a catalyst, e.g. an organotin compound, such as, dibutyl dilaurate. Preferably the components are selected so that the reaction time is less than 20 seconds, more preferably less than 5 seconds. A fast reaction time allows a first part of the wooden pallet to be spray and the immediately held or supported by the coated part to allow another part to be sprayed without damage to the coating of the first part. This allows a pallet to be completely coated in a short time.

A colouring additive may be added in the spray nozzle. Thus the coating colour may be changed by feeding different colouring into the spray head, according to requirement. Polyurethane systems are well known and commercially available from many sources. A preferred isocyanate is diphenylmethane-4-4'-diisocyanate which is commercially available from Bayer under the trade name Desmodur 1327. A preferred polyol is commercially available from Bayer under the trade name Bayflex 89-624.

The selection of polyurethane and appropriate additives can have no volatile compounds and does not cause any EPA problems or Atex requirements allowing ease of processing. The elastomer may contain additives to enhance the properties of the coating. Suitable additives include flame retardants, anti-slip additives, biocides, colourant and ultraviolet stabilizers. The additives may conveniently be added to the polyol component of a polyurethane system. Flame retardant additives are known and include hydrated fillers, halogen-containing materials, phosphorus-containing materials, antimony-containing materials and intumescent materials. A preferred flame retardant is aluminium trihydrate, e.g. commercially available from Ankerpoort NV under the trade name Portaflame. The flame retardant additives may be present in an amount of from 40 to 70%, preferably 50 to 60% by weight of the coating of elastomer.

The elastomer may comprise an anti-slip additive to improve the frictional characteristics of the surface of the coating. Suitable anti-slip additives are selected from polymer particles, e.g. polymer beads having a particle size of about 250 micron and mineral particles, e.g. fine sand, silca-quartz particles.

The elastomer may comprise a biocide, such as, a fungicide or anti-microbial agent, to prevent contamination. The elastomer may comprise a colouring agent, such as one or more dyes or pigments, to improve the appearance of the pallet and provide for visual recognition.

The elastomer may comprise an ultraviolet light stabilizer to prolong the life of the coloured coating. Suitable ultraviolet light stabilizers are known and include triazines and hindered amine light stabilizers (HALS). According to a further aspect, the invention provides a method of producing a pallet as defined above comprising: drying a wooden pallet to a surface moisture content below about 10%, and applying an elastomer coating over the outside surface of the pallet. Thus existing wooden pallets may be processed by this method to produce coated pallets according to the invention. This has the advantage that a customer may supply their own pallets to be coated, and may collect the pallets after the coating process has been applied. Thus a customer may purchase conventional pallets from existing suppliers for processing to obtain the advantages of the invention. Alternatively used or repaired pallets may also be treated according to the invention.

Preferably, the method comprises machining the outer surface of the pallet to predetermined tolerances before applying the elastomer coating. For example the surfaces of the pallet are machined to a substantially even finish. This facilitates the provision of a continuous and substantially even coating. Whilst it is known to paint or otherwise treat wooden pallets, it has been found that drying, machining and spray coating the wooden pallets with elastomer to substantially encapsulate the pallet according to the invention gives enhanced properties.

Before machining, the pallet may first be inspected, for example by a product recognition camera, to determine the size and type of pallet. The inspection may also determine whether the pallet is suitable for machining; for example, whether it has any discontinuities such as upstanding nails or fasteners or splintered timbers. Pallets which are determined not to be within dimensional tolerances set for the process may be rejected.

The method may also comprise applying an RFID tag to the surface of the pallet before applying the elastomer coating. Preferably, the RFID tag is heat resistant and formed substantially of plastics material. The tag may be applied using a heat resistant attachment member, such as a staple, formed substantially of plastics material. The tag is conveniently applied to a surface of a central member of the pallet, for example on a side surface of a pallet member which faces inwardly, to prevent damage in use of the pallet.

The tag may be applied at the beginning of the process before drying the pallet. The pallet is preferably dried to a surface water content below about 10%, and preferably below about 8%, for example in a kiln. The kiln may include moisture and temperature sensors for measuring the surface water content of the pallet, and controlling the drying process. Although there may be some variation in the overall moisture content, it is found that measurement of the surface moisture gives a good measure of the overall moisture content as with a typical wooden pallet, wicking of moisture tends to equalize moisture levels throughout the material relatively quickly. A more precise correlation between surface moisture readings and overall moisture readings can be obtained for a particular pallet material and handling conditions by measuring total moisture content of test or calibration samples if desired.

The method preferably comprises using the RFID tag to store dimensions and/or other properties, such as a measure of drying time, weight or a measure of moisture content or tolerances associated with the pallet, either directly on the tag or in a database referenced by an id on the tag. Preferably the pallet is machined by a router on the exposed or visible surfaces, and is then turned over to machine the remaining surfaces. Coating the pallet preferably comprises spray coating. The elastomer material may be as defined above, and is preferably fast drying. Preferably a central member of the pallet is coated first, then the remainder of the surfaces exposed to the spray coater are coated whilst the coating on the central member cures . The pallet may then be gripped using the coated central member and manipulated in three dimensions to expose the remaining surfaces to the coater. Preferably the pallet is manipulated for example by a robot, and the spray head may also be robotically movable to produce an even spray, minimise overspray and to reduce spray time. This is important in allowing the process to have a high throughput rate.

Preferably, after spraying, the finished pallet is checked, preferably using a product recognition camera, and the RFID tag may also be read, with the pallet then being stored for collection according to information obtained from the tag.

The method may conveniently be automated, using powered conveyors and robots. The method may thus be used to process pallets quickly and in large quantities. Thus the method provides a relatively inexpensive way of improving the qualities of wooden pallets.

According to yet another aspect, the invention provides a method of processing wooden pallets comprising:

receiving a wooden pallet for coating;

inspecting the pallet for suitability;

applying an RFID tag to a surface of the pallet containing information concerning the pallet; drying the pallet in a kiln;

machining the surface of the pallet to predetermined tolerances excluding the area where the RFID tag is positioned;

coating the pallet with elastomer material using a spray coater;

inspecting the pallet for finish;

reading the RFID tag; and storing the pallet for collection according to information obtained from the tag.

In order that the invention may be more readily understood, reference will now be made, by way of example, to the accompanying drawings, in which;

Figure 1 is a top view of a pallet suitable for processing in accordance with the invention;

Figure 2 is an underneath perspective view of the pallet of Figure 1 ; Figures 3, 4 and 5 together show a flow diagram showing the components in a process for producing a pallet according to one embodiment the invention.

Referring to Figures 1 and 2, a wooden pallet 2 comprises three legs or stringers 3, 4, 5, which comprise parallel spaced wooden batons. To the upper surfaces of these are attached a plurality of thinner wooden strips 6 forming the top deck or load surface of the pallet 2. The strips 6 are placed close together and extend across the pallet perpendicular to the legs 4. For simplicity, only the edge strips 6 are shown in Figure 2.

It will be appreciated that reference to the wood material of the pallet may include wooden products such as compressed wood or chipboard, etc.

Referring also to Figures 3, 4, and 5, which show an example of a process according to the invention, wooden pallets for processing may be delivered to an unloading area 8. The pallets are conveyed by a first transfer conveyor 10, and are picked up one at a time by a robot on a load cell section for weighing each pallet. The robot then offers each pallet to a tagging station 12 where an RFID tag is stapled to the pallet, for example using a plastic staple, on a side face 11 of a centre leg 4 of the pallet. The tag may include information such as a pallet identification code, a job identification code, and other data relevant to the pallet. The pallet is transferred from the tagging station to a further conveyor 14 and to an optical checking station 16. An optical check comprises inspecting the pallet with a product recognition camera to check the pallet size/type and that it is within dimensional tolerances for the process. At this stage a failed pallet is rejected and conveyed to a reject station 18 for manual checking.

A pallet which has passed the check is conveyed to a weighing station 20 where the weight of the pallet is logged. A further transfer conveyor 22 takes the pallet to a stacking station 23 where it is stacked by a robot on a gravity conveyor 24. The stacked pallets may then be transferred by forklift to a kiln 26, via a storage area 28. The pallets are dried in the kiln according to requirement. Moisture and temperature sensors are used to dry the pallets until they have a moisture content of about 8 to 10% by weight.

The kiln dried pallets are then unloaded by forklift onto a gravity roller conveyor 32 via a holding area 30, to a second weighing station 34 which may comprise a load cell in the final section of the conveyor. The pallet is then transferred via a conveyor 36 to a machining station 38. A robot picks up each pallet and places four pallets on the bed of a router where vacuum grippers hold them in place. The router reads the tag to identify the type of pallet and then machines the pallet on all faces to a set tolerance in accordance with the information obtained. The robot then turns over the pallets and the process is repeated on the other side. The router is programmed to ensure it does not machine the area where the tag is positioned. The pallets are transferred from the machining station via another conveyor 40.

A robot removes the pallets and places them individually vertically on a powered conveyor 42 with the underside facing spray bays of painting stations 44. The pallets travel along the conveyor and into holding station in front of each spray bay. A robot with a polyurethane spraying head sprays the centre leg first and then continues spraying the underside of the pallet. A handling robot then picks up the pallet by gripping the coated centre foot and manipulates the pallet together with the moving spray head to minimize overspray and reduce spraying time.

When the pallet is completely coated it is placed face down on a powered conveyor 46. The final 1.2m section is a gravity roller conveyor and mounted on a load cell. At an optical check station 48 a robot picks up the pallet, checks it for size/type and finish using a product recognition camera and reads the RFID tag to identity the customer or pallet maker. If the pallet does not pass the check, it it sent to a reject station 50. Otherwise the pallet is transferred via a further weighing station 52 to a sorting station 54 where a robot stacks the pallet in correct place. The pallets ready for collection by the customer or pallet maker are transferred to a storage area 56, and thence to a delivery station 58 and loading area 60 as required.

As can be seen in the drawings, at each stage of the process, there may be a reader (eg 62) which reads the tag and sends data to a server (eg 64). In this way each pallet can be tracked through the process. Data such as the dimensions and tolerances and drying time for each pallet can also be collected. This data can be used by a computer control system for obtaining process information for controlling the process, for billing and also for quality control purposes.

For example data concerning rejection of pallets, or manual intervention required, for a batch of pallets associated with a customer may be used in deriving the charge to be made to that customer. Also, pallets can be graded according to the data concerning dimensional tolerances.

Previously manufactured pallets may be finished or reconditioned so as to prolong their usable life, or to improve their properties. These methods of finishing or reconditioning may be applied to either wooden or plastic pallets. It has been found that thermosetting plastic coatings, such as polyurethane, may be of particular use in this context.

For example, to recondition a pre -used plastic pallet, the surface of a pallet may be treated so as to facilitate coating of the surface. To facilitate coating the surface energy of the pallet can be increased to improve the wetting characteristics of the pallet. Examples of such surface treatments include corona treatment and flame treatment.

A thermosetting plastic coating comprising a flame retardant may then be applied to the treated surface to recondition it for further use. This enables the reuse of plastic pallets that would otherwise need to be removed from circulation due to safety considerations.

A similar treatment may also be applied to wooden pallets. Surface treatment of wooden pallets can be a particular problem. However, the inventor in the present case has found that it is possible to use a sand blasting treatment to abrade a surface of the pallet. As will be appreciated in the context of the present disclosure, sand blasting is not a treatment that is usually applied to wood however the inventor has found that this treatment is of particular advantage when surface treating wooden pallets to receive a coating. A thermosetting plastic coating may then be applied to the sand blasted surface of the pallet to provide a water impermeable flame retardant coating to enable the usable life of wooden pallets to be extended and/or to recycle used wooden pallets.