AU693220B2 - Light-weight composite plastics sheeting - Google Patents

Description

P/00/011 Regulation 3.2 0* 0 0 0

AUSTRALIA

Patents Act 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT C)TV I~ILL Name of Applicant: Actual Inventor(s): Address for Service: Douglas Godfrey Lower

INTELLPRO

Patent Trade Mark Attorneys 13th Floor, 379 Queen Street BRISBANE, QLD, 4000 (GPO Box 1339, BRISBANE, 4001) "Light-Weight Composite Plastics Sheeting" Australian Patent Application No. PM8183 filed September 1994.

Invention Title: Details of Associated Provisional Application(s) No(s): The following statement is a full description of this invention, including the best method of performing it known to me:

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'Ll 2 THIS INVENTION relates to light-weight composite plastics sheeting material and in particular, but not limited to plastics sheeting suitable for use as a substrate for screen printing, display and sign making to produce signs, display panels, hanging signs, wall signs and similar products.

It is an object of the present invention to provide a light-weight composite plastics sheeting material which is a useful alternative to similar products presently on the market.

In one aspect therefore, the present invention resides in a hollow composite plastics sheet comprising a light-weight hollow first layer having opposed surfaces separated by closely spaced webs extending in a single direction along the sheet and a second thinner layer of solid plastics adhered to the first layer.

S"Preferably the present invention resides in a hollow composite plastics ooeee ***sheet comprising a light-weight hollow first layer having opposed surfaces 0* 15 separated by closely spaced parallel webs extending in a single direction along the sheet and a second thinner layer of solid plastics adhered to the first layer.

The layers may be adhered together using a chemical or welding process but *are typically chemically joined using an adhesive. Alternatively and more preferably a hot melt adhesive is employed.

In another aspect, the present invention resides in a process for producing a hollow composite plastics sheet from first and second layers adhered together, the first layer preferably having opposed surfaces separated by closely spaced parallel webs extending along the sheet and the second layer comprising a thinner solid plastics sheet adhered to the first layer, the II0 I 1 process comprising the following steps:spray applying to the first and/or second layers, an adhesive having a droplet size of up to 1.5mm in order to prevent warping of the finished composite; (ii) subsequently joining the layers under sufficient pressure to enhance bonding but without damaging or deforming the webs of the first layer; and (iii) allowing the adhesive to fully cure.

In a further aspect, there is also provided an apparatus for producing a composite plastics sheet from first and second layers adhered together, the first layer preferably having opposed surfaces separated by closely spaced parallel webs extending in a single direction along the sheet and the second layer being a thinner solid plastics sheet adhered to the first layer, the apparatus .99999 comprising a first layer delivery means and a second layer delivery means 15 adapted to deliver the layers in mutual confronting surface to surface relation, :.":adhesive application means upstream of the first and second sheet delivery means for applying adhesive to the first and/or second layers in an amount adapted to prevent warping of the final sheet, and a layer joining unit 999* downstream of the layer delivery means joining the layers under pressure, and 20 there being provided cutting means for cutting the composite sheet into 9. 9 predetermined lengths.

In a still further aspect, there is provided a sign comprising a hollow composite plastics sheet formed from first and second layers adhered together, the first layer preferably having opposed surfaces separated by closely spaced parallel webs extending in a single direction along the sheet, the second layer being a thinner solid plastics sheet typically PVC, Polycarbonate, Polypropylene, ABS, HIPS or the like adhered to the first layer, the second layer having an outer surface carrying indicia forming a visible sign.

Preferably, the second layer is PVC which preferably carries an ultra violet inhibitor to allow the resultant sheeting to be used outdoors and the indicia has been applied according to one of the following processes:spray painting preferably by spraying an automotive acrylic lacquer, a fast drying spraying enamel using medium or fast thinners or a vinyl paint system; (ii) brush, roller or spray painting preferably using water based satin or gloss acrylics; (iii) screen printing preferably using vinyl ink, corrugated plastic inks or ultraviolet curing ink systems;

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15 (iv) an enamel paint applied subsequent to a key coat of clear or coloured o. acrylic lacquer or fast dry enamel; or a prefabricated indicia or sign being typically cast vinyl text or graphics applied to the PVC or over any of the above selected paint systems

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specified in to (iv).

20 The first layer can be of any suitable thickness but is typically made from a plastic having a wall thickness of less than 1mm and typically less than a total layer thickness of from 2mm to 10mm and from 2 to 5 webs per centimetre in cross-section. Polypropylene is the preferred plastic for the web layer and is corona treated to printing dyne level to enable acceptance of the glued second layer when using a pressure sensitive glue system.

The second layer is preferably from .2mm to .5mm thick and is preferably a plastic that has an affinit, for or is known for its ink taking, paint taking or sign writing capacity. Preferably, the second layer is a thin PVC sheet, Most preferably, the sheet is about .4mm thick.

Where a solvent based adhesive is used to join the layers together, the adhesive is preferably applied as a spray application through a spray nozzle having apertures of about 1.2mm. The preferred adhesive is GRASP 14/23 NEOPRENE based contact adhesive reduced with 10% to 12% NTH 3035 solvent thinner, the thinner having chemical properties of 60% acetone/1 0% to toluene. Any equivalent adhesive can be used, the object being to produce a sprayable contact adhesive delivered to the surface of say the first o .lay er as a 1mm droplet size with a set-off time of 15 to 30 seconds under S.."forced air at 25 0 C coupled with assisted extraction of evaporated solvent.

o*oo 15 Adhesive is typically applied as a surface application rate of 22m 2 per litre.

The applicant has found that for a second layer of less than about in thickness that removal of at least 95 of the solvent be carried out before the sheets are joined in order to minimise the possibility of warping. The So..

applicant has also discovered that the smaller droplet sizes are preferred for 20 thin sheets of less than .5mm as larger droplets may produce a visible bumpy l o effect on the sheets when bonded particularly if second layer is less than .38mm thick.

The use of solvent based contact adhesives can induce a warp biased toward the exposed surface of the first layer under certain temperature conditions particularly cold temperature in the range of 9C-11°C building to warm temperatures of 25 0 C-30 0 C. Warping occurs in the space of 1-2 hours.

This is caused by the differing surface tensions of the layers combined with the locking effect of the contact adhesive bond. This problem is not evident with three layer sheeting. That is where the thin layer is applied to both sides of the firs* layer web material. In some cases it is therefore preferred that the second layer be applied again to the first on its opposite side to form a sandwich board balanced against warpage.

A more suitable method for the single layer board has proven to be the use of a high grade hot melt pressure sensitive adhesive which has been specially formulated to bond plastics. This provides a resilient bed of adhesive which allows movement of the layers. A suitable product is National Starch Limited 034-5541 adhesive. The consistent quality of the adhesive is most important as the equipment used to spray apply the adhesive is subject to diminished performance when affected by impurities in the adhesive compound resulting in irregular spray patterns and clogging of filters in the system. The glue is applied at the rate of 35 grams to 50 grams per square metre to the back side of the thin layer typically PVC is employed. The first layer, typically polypropylene sheet does not need to have glue applied.

20 Typically the equipment required to apply this adhesive is A typical system is ROBA MCS 30-68 operating temperatures are: Tank 135°C-1 Hoses 135°C-190°C Guns 135 0 C-190°C

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All of the components are controlled by Micro-Processor built into the system and temperature is held within 2 0 C+ from set point.

It must be noted that pump pressure, spray head speed, height of nozzle from substrate and temperature of glue all have an affect on the final spray pattern and volume of adhesive delivered to the surface. Glue that is on the upper limit of temperature (190'C) that is delivered in too great a volume to the thin PVC (second layer) substrate will have the effect of distorting the PVC (second layer) and result in a surface crinkle effect.

This particular adhesive system has no environmental problems as it is 100% Solids and has no odour so is user friendly and needs no extraction system. No drying period is required and product is ready to be bonded immediately or within a period of lhr after spray application provided that the sprayed area is kept free from dust or contaminant during this open period. As i there is no delay involved the process is continuous and output can be 9 15 increased in speed by the addition of more hoses and guns provided that the melt tank used has the capacity to accept more hoses.

Bonding is achieved by passage of the two layers through the nip of or opposed rollers with a dead weight of 100kg assisted by pneumatic pressure of 30 80 psi, for optimum result these rollers should not be left in contact with 20 the sheeting while not in motion or a pressure band effect may result.

4* a The rollers are electronically linked to the spray traverse to open and close in unison with the spray head movement. Forward movement of the product is made while sprays are at rest after completing each spray band. The distance of this movement is electronically incremented by setting the required 8 distance of movement on the computer keypad, typically 150mm per spray head is achieved. Typical distance from second layer to nozzle is 150mm with a nozzle traverse speed of 4 6 seconds per metre.

With enough spray guns connected to sufficient melt tank capacity it is possible to have the guns in a static position and arranged across the direction of travel of the second layer and therefore continuously apply adhesive to the moving second layer. This will allow high volume production when coupled with semi-automatic feed of the second layer and automatic trimming devices.

Pump pressure is 1 6 bar and air pressure to the nozzles is 2 8 bar.

Greater air pressure will result in turbulence and also generate feathers of adhesive while lower pressures will result in larger droplets which are not acceptable.

*The final product does not reach full cure until 2 3 months after manufacture and should not be used until at least 3 days old as delamination 15 of the second layer can occur in single sided sheets if bent in an arc of more than 10 degrees. Ultimate tensile strength of the adhesive selected should 5555 reach 6 kg/cm 2 minimum while 11kg/cm 2 is preferred.

,In an alternate manner the hot-melt adhesive my be applied to the first ii olayer rather than the second layer therefore allowing the use of glue 20 temperatures in the upper range which allow finer atomisation of the adhesive as sheet distortion will not occur. However this method does not suit continuous production conditions.

As an off line process, a pressure sensitive adhesive may also be roller coated onto the second layer in roll form and a silicon release liner paper applied. The resultant coated roll can then be positioned onto the rear roll carrier of the assembly machine and production carried out in a similar manner as described above in relation to the nip rollers. The lir.cr paper is rerolled in this process and can, be re-cycled. The spraying apparatus is disabled in this production process. The result is a very flat final product achieved at a greater manufactured cost. The micron thickness of the adhesive layer should be sufficient to achieve nsile strength of 6 11 kg/cm 2 In order that the present invention can be more readily understood and be put into practical effect, reference will now be made to the accompanying drawings which illustrate preferred embodiments of the present invention and wherein:- 0. Figure 'I is a perspective view illustrating a composite sheet according to the present invention; *009 Figure 2 is a section through the sheet of Figure 1 to enlarged scale; 15 Figure 3 is a schematic diagram illustrating a typical apparatus and process for producing the sheet of Figures 1 and 2; .0 Figure 4 is a perspective view of a further embodiment of an apparatus 00 for producing the sheet of Figures 1 and 2.

Referring to the drawings and initially to Figure 1, there is illustrated a 20 composite plastics sheet 10 comprising a first layer 11 having opposed surfaces 12 and 13 separated by closely spaced webs 14 and a second thinner layer adhered to the first layer 11.

The first layer is made from treated polypropylene with the surfaces 12 and 13 and the webs 14 having a wall thickness of .2mm and therefore an

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overall thickness of 5mm while the sheet 15 is a .4mm thick PVC sheet. It can be seen in Figure 1 that the surfaces 13 and 14 are ribbed providing a surface which is not conducive to application of signage because not only does the polypropylene have to be pretreated but the ribbed effect does not provide an acceptable finish.

Application of the PVC sheet 15 on the other hand provides a surface 16 to which paint and ink can be applied according to normal procedures.

What this means is of course, the sheet of Figure 1 can be configured as a light-weight sign having indicia applied to the surface 16.

It will be appreciated also that in another embodiment, the sheet 15 can also be applied to surface 13 to provide a three layer composite sheet with signs applied on both the front and back PVC surfaces.

•Referring now to Figure 3, there is illustrated an apparatus embodying the process according to the present invention for forming a sheet of the type illustrated in Figures 1 and 2.

The apparatus includes an adhesive application means in the form of a spray unit 21 upstream of a solvent extraction unit 22 upstream of a sheet a.o.

delivery means 23 whereby the sheets 11 and 15 are delivered in continuous fashion to a sheet joining unit 24. Rollers 25 of the sheet joining unit 24 S 20 apply a predetermined pressure to the composite sheet to enhance bonding.

Upstream of the unit 24 is a cutter 26 adapted to cut the composite into predetermined sheet sizes which are then collected by the pallet loader unit 27 where sheets 10 are stacked for later use.

It will be appreciated from the foregoing, the process from spray unit 21 11 through to delivery of the sheets together at 23 involves a 15 second to second delay as the solvent is extracted from the adhesive. It will therefore be appreciated that the apparatus described above provides a continuous process for preparation of the sheets illustrated i Figures 1 and 2.

Referring now to Figure 4 there is illustrated an apparatus 30 suitable for producing the sheet of Figure 1 using a hot melt adhesive system of the type previously described. A roller 31 hold PVC sheeting, typically .38mm thick and this is fed through a pair of rollers 32 into a spray module 33 which in this case employs a pair of treated spray guns 34 and 35 mounted on i0 carriages to traverse across the PVC sheeting (shown in phantom). Two guns are illustrated but more guns may be used to increase capacity. The hot melt adhesive is applied and the PVC is incremented through onto a felt top bench •36 where a sheet of the second layer (not shown) is manually applied to the glue coated PVC. The sheet is cut and then moves through the roller assembly 37 in a non stop action to produce the finished sheet at 38. The sheet is then stored.

It will be appreciated also from the foregoing that the present invention provides in its broadest form a composite sheet made from a lightweight thin walled hollow layer and a thin solid layer adhered together and S 20 that any suitable plastics can be employed for this purpose.

Whilst the above has been given by way of illustrative example of the present invention, many variations and modifications thereto will be apparent to those skilled in the art without departing from the broad ambit and scope of the invention as set forth in the appended claims.

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Claims (13)

1. A hollow composite plastics sheet comprising a light-weight hollow first layer having opposed surfaces separated by closely spaced parallel webs extending in a single direction along the sheet and a second thinner layer of solid plastics adhered to the first layer.

2. A process for producing a hollow composite plastics sheet from first and second layers adhered together, the first layer having opposed surfaces separated by closely spaced parallel webs extending along the sheet and the second layer comprising a thinner solid plastics sheet adhered to the first layer, the process comprising the following steps:- spray applying to the first and/or second layers, an adhesive having a ~droplet size of up to 1.5mm in order to prevent warping of the finished •composite; (ii) subsequently joining the layers under sufficient pressure to enhance bonding but without damaging or deforming the webs of the first layer; S"and (iii) allowing the adhesive to fully cure.

3. An apparatus for producing a composite plastics sheet from first and second layers adhered together, the first layer having opposed surfaces separated by closely spaced parallel webs extending in a single direction along the sheet and the second layer being a thinner solid plastics sheet adhered to the first layer, the apparatus comprising a first layer delivery means and a second layer delivery means adapted to deliver the layers in mutual confronting surface to surface relation, adhesive application means upstream of S 0 a.* S *a 4 a.. S Ca.. o *e 13 the first and second sheet delivery means for applying adhesive to the first and/or second layers in -n amount adapted to prevent warping of the final sheet, and a layer joining unit downstream of the layer delivery means joining the layers under pressure, and there being provided cutting means for cutting the composite sheet into predetermined lengths.

4. A sign comprising a hollow composite plastics sheet formed from first and second layers adhered together, the first layer having opposed surfaces separated by Liosely spaced parallel webs extending in a single direction along the sheet, the second layer being a thinner solid plastics sheet selected from typically PVC, Polycarbonate, Polypropylene, ABS, HIPS or the like adhered to the first layer, the second layer having an outer surface carrying indicia forming a visible sign.

A sign according to claim 4 wherein the second layer is PVC which carries an ultra violet inhibitor to allow the resultant sheeting to be used outdoors and the indicia has been applied according to one of the following processes:- spray painting preferably by spraying an automotive acrylic lacquer, a fast drying spraying enamel using medium or fast thinners or a vinyl paint system; (ii) brush, roller or spray painting preferably using water based satin or gloss acrylics; (iii) screen printing preferably using vinyl ink, corrugated plastic inks or ultraviolet curing ink systems; (iv) an enamel paint applied subsequent to a key coat of clear or coloured 14 acrylic lacquer or fast dry enamel; or a prefabricated indicia or sign being typically cast vinyl text or graphics applied to the PVC or over any of the above selected paint systems specified in to (iv).

6. The invention according to any one of the preceding claims wherein the first layer is typically made from a plastic having a wall thickness of less than 1mm and a total layer thickness of from 2mm to 10mm and a web density of from 2 to 5 webs per centimetre in cross-section.

7. The invention according to any one of the preceding claims wherein the second layer is from .2mm to .5mm thick and is a plastic that has an affinity for or is known for its ink taking, paint taking or sign writing capacity.

8. The invention according to any one of the preceding claim employing a solvent based adhesive to join the layers together, the adhesive is being o. applied as a spray application through a spray nozzle having apertures of about 1.2mm the spray being delivered to the surface of the first or second layer as a 1mm droplet size with a set-off time of 15 to 30 seconds under forced air at 250C coupled with assisted extraction of evaporated solvent.

9. The invention according to any one of claims 1 to 7 wherein the layers are joined using a high grade hot melt pressure sensitive adhesive which has S' been specially formulated to bond plastics thereby providing a resilient bed of adhesive which allows movement of the layers.

The invention according to claim 9 wherein the glue is applied at the rate of 35 grams to 50 grams per square metre to the back side of the thin layer.

11. The invention according to claim 3 wherein the apparatus includes a hot melt glue system consisting of a melting tank of sufficient power and size to melt the required volume per hour to cater to required output. The melted adhesive being passed through heated hoses to heated spray gun modules under hydraulic pressure created by an electronic pump. At the gun modules heated air is introduced to force the hot fluid out of a spray nozzle in an atomised fan pattern having a droplet size of .5mm or less.

12. The invention according to any one of the preceding claims wherein another thin layer is applied to the opposite side of the first layer so that the first layer is sandwiched in order to inhibit warping of the composite sheet.

13. A hollow composite plastics sheet and method of making same substantially as described with reference to Figures 4 of the accompanying drawings. DATED this 1st day of May 1998 CONCEPT SCREENPRINTS PTY LTD By its Patent Atorneys INTELLPRO «o o I 16 ABSTRACT A composite plastics sheet 10 comprising a first layer 11 having opposed surfaces 12 and 13 separated by closely spaced webs 14 and a second thinner layer 15 adhered to the first layer 11. The first layer is made from treated polypropylene with the surfaces 12 and 13 and the webs 14 having a wall thickness of .2mm and therefore an overall thickness of 5mm while the sheet 15 is a .4mm thick PVC sheet. It can be seen in Figure 1 that the surfaces 13 and 14 are ribbed providing a surface which is not conducive to application of signage because not only does the polypropylene have to be pretreated but the ribbed effect does not provide an So,. acceptable finish. Application of the PVC sheet 15 on the other hand provides a surface 6 16 to which paint and ink can be applied according to normal procedures. C -i4- a