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(11) | EP 0 125 071 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Coating of plastics materials |
| (57) Coating of plastics materials |
[0001] The invention concerns the coating of plastics materials, and has more particular reference to a method of and an apparatus for the double-sided coating of such materials in sheet or lay flat tubular form.
FIELD OF THE INVENTION
[0002] It is conventional practice in the brewing industry and in the brewery trade to utilise bulk containers for the transportation, storage and dispensing of beer and like liquids, there being a disposable plastics liner in the form of a closed bag having a spout applied to the surface thereof disposed within the container to receive the liquid. By virtue of its manner of manufacture, the liner is initially sterile, access being had to the interior thereof only on filling and this being effected under controlled conditions. The plastics liners are conventionally of polyethylene, and a typical container. liner combination is disclosed in our prior United Kingdom Patent No. 1171612.
[0003] Whilst transportation, storage and dispensing utilising conventional container/liner combinations as aforesaid has been widely adopted and has been found to be eminently satisfactory, the inherent permeability of the polyethylene material used in the manufacture of the liners to such as oxygen, carbon dioxide and nitrogen may have an adverse affect on the shelf-life of the contained beer with consequential financial disadvantage to the brewery.
PRIOR ART
[0004] It is known to apply a barrier coating to one side of a plastics material in sheet form so as to reduce the permeability thereof, but the nature of the barrier material is such as to make difficult,if not impossible, the subsequent welding of such plastics materials, whether by high frequency or other methods conventionally practised in the art. In particular, it is impractical to utilise a coated plastics material in sheet form in the commercial manufacture of a liner of the kind intended for application to a bulk storage container, since such manufacture would involve the high frequency welding of a coated surface in forming the sheet into a bag or in applying a spout to the surface thereof. Hithertofore it has been considered impracticable satisfactorily to coat the outer surface of an extruded tube of plastics material, and it is, therefore, the object of the present invention to provide a method of and an apparatus for coating the outer surface of polythene or other plastics material in lay-flat tubular form with a barrier material so as to reduce the permeability thereof.
BRIEF STATEMENT OF THE INVENTION
[0005] According to the present invention there is provided a method of forming an enveloping coating on a web (13) of plastics material including applying to the web (13) a liquid containing a coating substance characterised in that the so-coated web (13) is moved vertically or substantially vertically to and through a drying zone (31), and in that the proportion of the coating substance in the liquid, and the rate of advance of the web (13), are chosen in accordance with a desired thickness of the coating substance on the web.
[0007] The invention also provides apparatus for forming an enveloping coating on a web (13) of plastics material comprising: a coater (45,48) whereat the web (13) can be contacted with a liquid containing a coating substance; a drier (31) characterised in that there is provided means for passing the web (13) to the coater (45, 48) and means for passing the web (13) vertically or substantially vertically from the coater (45,48) to the drier (31).
BRIEF DESCRIPTION OF THE DRAWINGS
[0008] The invention will now be described further, by way of example only, with reference to the accompany drawing, which illustrates, in diagrammatic form an apparatus for the double-sided coating of a tubular material.
[0009] In the drawings:
Fig. 1 is an overall schematic view of apparatus for performing the invention; and
Fig. la to are respective figures each being an enlarged ld portion of Figure 1.
DESCRIPTION OF PREFERRED EMBODIMENTS
[0010] Thus, referring now to the drawing, coating apparatus constructed in accordance with the invention comprises a first roller assembly 11 at the imput end 12 of the apparatus to receive and support a length of pre- welded lay-flat tubing 13 continuously delivered from a tube making machine (not shown) and having had a plurality of spouts (not shown) welded to one of the two halves of the tubing 13 at spaced-apart positions commensurate with the eventual size of the containers to be formed. A second roller assembly 14 at the output end 15 of the apparatus functions to receive and support coated tubing during passage thereof from the apparatus. The first and second roller assemblies 11, 14 are arranged in horizontal, substantially aligned dispositions, and a plurality of drive roller units 16, 17 are provided at the input and output ends 12, 15 respectively, of the apparatus. A coating/drying station 18 is provided intermediate the said roller assemblies. Accumulator roller systems 19, 20 are provided at the input and output ends, respectively, to accommodate any temporary differential between the throughput of the coating/drying station 18 and the rate of delivery of tubing 13 to the input end 12 or the rate of take-up of tubing from the output end 15, respectively.
[0011] The individual rollers 21 of the first roller assembly 11 are in closely spaced apart disposition in the initial section thereof, as considered in the direction of feed, whilst the remaining rollers are relatively widely spaced to receive the accumulator roller system 19 as will hereinafter be made apparent. Two drive roller units 16 are provided at the input end of the machine, such units being located one at either side of the accumulator roller system 19, and each unit comprising a lower roller 22 arranged in alignment with the individual rollers 21 and in lieu of one such roller and an upper, pressure roller 23 in nip-forming relationship therewith.
[0012] The accumulator roller system 19 consists of three fixed rollers 24 arranged above the plane defined by the first roller assembly, each roller 24 lying in register with a respective one of the rollers of such assembly, and two vertically adjustable rollers 25 arranged between the fixed rollers 24 and movable between inoperative positions below the plane of the roller assembly and operative positions well above such plane, as is clearly apparent from the drawing.
[0013] The individual rollers 26 of the second roller assembly 14 are arranged in two spaced groups of closely spaced rollers, the accumulator roller system 20 being located between such groups. Three drive roller units 17 are provided at the output end of the machine, such units 17 each comprising a lower roller 27 in horizontal alignment with the individual rollers 26 and a pressure roller 28 in nip forming relationship therewith. A drive roller unit 17 is provided at each end of assembly 14 whilst the third such unit is located immediately after accumulator roller system 20.
[0014] The accumulator roller system 20 consists of two spaced rollers 29 in alignment with the rollers of the second roller assembly 14 and a vertically adjustable roller 30 intermediate roller 29 and movable between an inoperative position above the plane of assembly 14 and an operative position well below such plane.
[0015] The coating/drying station 18 provides for plural coating operations on the tubing and, in the case of the embodiment illustrated, comprises first and second stage systems 31 of like form. Each system includes a dip coater 32, an infra-red heater 33 and a drying chamber 34, the tube passing vertically from the coater 32 to and through the chamber 34, the heater 33 being located directly adjacent the inlet aperture 36 at the underside of the drying chamber 34. Cooling means 37 are provided adjacent the outlet aperture 38 of the drying chamber and through which the tubing passes on leaving such chamber 34. Two horizontally spaced rolls 39, 40 are provided adjacent the cooling means, roll 39 being in alignment with outlet aperture 38 and cooperating with split input roll 41, shaped to accommodate the spout, at the lower end of the drying chamber to define a substantially vertical path for the tubing through the stage and roll 40 being in vertical alignment with a guide roll 42 arranged at substantially the same horizontal level as input roll 41. Rolls 39, 40 are both chilled rolls and are coupled together by a belt 43 tensioned by a jockey pulley 44, the rolls being driven.
[0016] Each dip coater 32 comprises a constant-level overflow coating trough 45, an input roll 46 in advance of such trough, a collect/recirculate trough 47 to receive overflow coating material from trough 45, and a dip roller 48, being'input roll 41 repositioned to operate in a coating mode, as will hereinafter be explained.
[0017] The apparatus thus far described provides for the continuous double-sided coating of a lay-flat tubular material (or other sheet material) passed therethrough, coated material advancing to a welder/separator unit generally indicated at 49, and the individual bags being advanced to a packaging station, not shown.
[0018] However, the arrangement illustrated also includes means for initially threading up the apparatus, such means comprising an endless chain 50 which passes through the coating/drying station 18 (but not the dip coaters 32) and carries a leader tube 51 attachable to the leading edge of an incoming length of tubing, support and drive rollers 52 being provided for such chain. It is to be understood that the chain 50 and leader tube 51 and the related rollers 52 will be utilised only for start up purposes, and once the machine is properly threaded up such structures will not be used.
[0019] To ready the machine for operation, after having threaded up the machine by means of the leader tube 51 and cooperating structure, roller4l/48 being in the raised input mode position during such threading up, the leader tube 51 is separated from the tubing and roller 41/48 is lowered to bring the tubing into the coating trough 45.
[0020] In practising the method we have applied a coating of PVDC to a lay-flat tube of LDPE having a film thickness of 0.18 mm by passing the same through a dip coater containing a dilute aqueous dispersion of the coating material, solids concentration of the disper- tion being less than 25% by weight and the rate of advance of the tube being approximately 1.5 metres per minute. The applied coating was dried at approximately 82°C. After coating as aforesaid the tube was found to have a coating weight of approximately 8 grams per square metre.
[0021] It is to be understood that satisfactory coating may well be achieved using different values for the solids content of the dispersions, for the throughput rate and for the drying temperature, and the values of these, and or any other relevant parameters, will be chosen . according to the specific circumstances.
[0022] It is to be appreciated that various of the rollers hereinmentioned will be split or apertured, as necessary, to accommodate the spout as applied to the tubing.
[0023] We have found that satisfactory coating of the tubing is effected and it is believed that the vertical path of the tubing in its passage from the coating trough to and through the dryer, allied to a correct selection of coating material and dilution thereof and throughput speed, is a major factor in achieving satisfactory coating.
1. A method of forming an enveloping coating on a web (13) of plastics material including
applying to the web (13) a liquid containing a coating substance characterised in
that the so-coated web (13) is moved vertically or substantially vertically to and
through a drying zone (31), and in that the proportion of the coating substance in
the liquid, and the rate of advance of the web (13), are chosen in accordance with
a desired thickness of the coating substance on the web.
2. A method as claimed in claim 1, wherein the web (13) is a flattened tube of plastics
material.
3. A method as claimed in claim 1, wherein the plastics material is polyethylene.
4. A method as claimed in claim 3, wherein the coating substance is polyvinylidene
chloride.
5. A method as claimed in claim 4, wherein the coating substance is contained in a
bath (45) and the web (13) is passed through the bath (45).
6. A method as claimed in claim 5, wherein the web (13) leaves the bath (45) upwards
to the drying zone (31).
7. A method as claimed in any preceding claim wherein coating is effected in two stages.
8. A method as claimed in claim 5 or claim 7 when appendant to claim 5, wherein the
web (13) passes around a roller (48) immersed in the bath (45) in the or each coating
stage.
9. Apparatus for forming an enveloping coating on a web (13) of plastics material
comprising: a coater (45,48) whereat the web (13) can be contacted with a liquid containing
a coating substance; a drier (31); characterised in that there is provided means for
passing the web (13) to the coater (45, 48); and means for passing the web (13) vertically
or substantially vertically from the coater (45, 48) to the drier (31).
10. Apparatus as claimed in claim 9, and further including web take-up and release
means (19) for accumulating and releasing web (13) prior to the coater (45, 48).
11. Apparatus as claimed in claim 9 or 10 and further including a second coater (45,
48) and a second drier (31), the web (13) being guided to pass vertically or substantially
vertically from the second drier (45, 48).
12. Apparatus as claimed in claim 9, 10 or 11 wherein the or each coater includes
a bath (45) for the liquid and a roller (48) disposed to immerse the web (13) in the
bath (45).
13. Apparatus as claimed in any preceding claim and including a plurality of rollers
(21, 22, 24, 25, 46, 48, 41, 39, 40, 26 to 30) arranged to define a web travel path.
14. Apparatus as claimed in claim 13, wherein those rollers which engage one face
of the web are apertured, grooved, or otherwise formed to accommodate a series of
spouts outstanding from the one face of the web (13).
15. Apparatus as claimed in any of claims 9 to 14 and further including at a downstream
end thereof means (14) for cutting lengths from the coated web and/or performing a
welding operation thereon.
16. Apparatus as claimed in claim 15 and including a web accumulating and release
means (29, 30) immediately upstream of the cutting and/or welding means.
17. Apparatus as claimed in any of claims 9 to 16 wherein the or each drier includes
infra-red and/or hot air drying components.
18. A web of plastics material formed with an enveloping coating by the method of
any of claims 1 to 8 or by the apparatus of any of claims 9 to 17.
19. A method of making containers comprising forming a flattened tube of weldable
plastics material, welding to one part of the tube at spaced locations a plurality
of spouts of weldable plastics material, treating the so-formed bag stock by a method
as claimed in any of claims 1 to 8 or by the apparatus of any of claims 9 to 17 to
form an externally coated bag stock, and further processing the bag stock to form
individual containers each having at least one of said spouts.
20. A method as claimed in claim 19, wherein said further processing includes forming
a weld transversely of the stock upstream of and downstream of each spout or group
of spouts and serving the stock on the sides of said welds remote from the spout or
group of spouts to form one container, each said weld being formed between adjacent
internal forces of the two halves of the flattened stock and so not coated with said
substance.
21. A method as claimed in claim 19 or 20 wherein the plastics material is polyethylene
and the coating substance is polyvinylidene chloride.
22. A method as claimed in claim 19, 20 or 21 including the step of refraining from
puncturing the one part of the tube to which the spout is welded, within a through-passage
of the spout, until immediately before the container is due to be filled, so maintaining
the interior of the container closed and sterile until immediately before filling.
23. A container made by a method as claimed in any of claims 19 to 22.
24. A container as claimed in claim 23 and being a liner for a metallic container
for a beverage.