GB2138714A

GB2138714A - Coating of plastics materials

Info

Publication number: GB2138714A
Application number: GB08410745A
Authority: GB
Inventors: Thomas Porter; Harold Beaumont; William Alfred Laurie Lewis
Original assignee: Porter Lancastrian Ltd
Current assignee: Porter Lancastrian Ltd
Priority date: 1983-04-28
Filing date: 1984-04-26
Publication date: 1984-10-31
Also published as: EP0125071A3; GB8311620D0; GB8410745D0; NO841658L; DK212984A; EP0125071A2; DK212984D0

Abstract

An enveloping coating is formed on a web of plastics material, in particular a flattened tube of weldable plastics material having had welded thereto a plurality of spouts of weldable plastics material, wherein the web is passed through a coater (32) in the form of a bath (45) of liquid containing a coating substance and then conveyed vertically from the bath (45) to a drier (34), the rate of feed of the web and the concentration of coating substance in the liquid being selected to produce a coating of desired thickness. The method is applicable to the making of a container of a plastics material which is weldable but porous to certain gases and needs to be coated with a substance which reduces the permeability to gas, but is not itself readily susceptible to welding. After coating, the contacting internal surfaces of the two halves of a tube, which surfaces have not been coated and are still weldable, can be welded together and the web formed into a plurality of individual containers each having a spout. <IMAGE>

Description

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GB 2 138 714 A 1

SPECIFICATION Coating of plastics material

The invention concerns the coating of plastics materials, and has more particular reference to a 5 method of and an apparatus for the double-sided coating of such materials in sheet or lay flat tubular form.

Field of invention

It is conventional practice in the brewing 10 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 15 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 filing and this being effected under controlled conditions. The plastics liners are 20 conventionally of polyethylene, and a typical container liner combination is disclosed in our prior United Kingdom Patent No. 1171612.

Whilst transportation, storage and dispensing utilising conventional container/liner combinations 25 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 30 adverse affect on the shelf-life of the contained beer with consequential financial disadvantage to the brewery.

Prior art

It is known to apply a barrier coating to one 35 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 40 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 45 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 50 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 55 barrier material so as to reduce the permeability thereof.

Brief statement of the invention

According to the present invention there is provided a method of forming an enveloping 60 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 65 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.

70 Preferably the coating material will be a water based polyvinylidene chloride solution.

The invention also provides apparatus for forming an enveloping coating on a web (13) of plastics material comprising: a coater (45,48) 75 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 80 substantially vertically from the coater (45.48) to the drier (31).

Brief description of the drawings

The invention will now be described further, by way of example only, with reference to the 85 accompanyin drawing, which illustrates, in diagrammatic form an apparatus for the double-sided coating of a tubular material.

In the drawings:

Fig. 1 is an overall schematic view of apparatus 90 for performing the invention; and

Fig. 1 a to 1 d are respective figures each being an enlarged portion of Figure 1.

Description of preferred embodiments

Thus, referring now the the drawing, coating 95 apparatus constructed in accordance with the invention comprises a first roller assembly 11 at the imput end 12 of the apparatus to recive and support a length of pre-welded lay-flat tubing 13 continuously delivered from a tube making 100 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 105 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 110 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 115 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 120 take-up of tubing from the output end 15, respectively.

The individual rollers 21 of the first roller assembly 11 are in closely spaced apart disposition in the initial section thereof, as

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GB 2 138 714 A 2

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 5 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 10 of one such roller and an upper, pressure roller 23 in pip-forming relationship therewith.

The accumulator roller system 19 consists of three fixed rollers 24 arranged above the plane defined by the first roller assembly, each roller 24 15 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 20 positions well above such plane, as is clearly apparent from the drawing.

The individual rollers 26 of the second roller assembly 14 are arranged in two spaced groups of closely spaced rollers, the accumulator roller 25 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 30 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.

35 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 40 the plane of assembly 14 and an operative position well below such plane.

The coating/drying station 18 provides for plural coating operations on the tubing and, in the case of the embodiment illustrated, comprises first 45 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 50 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 55 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 60 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 65 and are coupled together by a belt 43 tensioned by a jockey pulley 44, the roils being driven.

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 in put roll 41 repositioned to operate in a coating mode, as will hereinafter be explained.

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.

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.

To ready the machine for operation, after having threaded up the machine by means of the leader tube 51 and cooperating structure, roller 41/48 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.

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 dispertion 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.

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.

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.

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

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achieving satisfactory coating.

Although we prefer to utilise a two stage coating/drying station, the invention is not limited to the use of two stages, since it may be found 5 sufficient in some instances to use a single stage or more than two stages.

It may be found convenient to include a conventional discharge treater at the input end of the machine to increase the critical tension of the 10 surface of the material of the tubing so as to improve the wettability of such surface.

Claims

1. A method of forming an enveloping coating on a web of plastics material including applying

15 the web a liquid containing a coating substance and moving the so-coated web vertically or substantially vertically to and through a drying zone, the proportion of the coating substance in the liquid, and the rate of advance of the web 20 having been 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 is a flattened tube of plastics material.

3. A method as claimed in claim 1, wherein the 25 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 and the

30 web is passed through the bath.

6. A method as claimed in claim 5, wherein the web leaves the bath upwards to the drying zone.

7. A method as claimed in any preceding claim wherein coating is effected in two stages.

35 8. A method as claimed in claim 5 or claim 7 when appendant to claim 5, wherein the web passes around a roller immersed in the bath in the or each coating stage.

9. A method of forming an enveloping coating 40 on a web of plastics material substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.

10. Apparatus for forming an enveloping coating on a web of plastics material comprising;

45 a coater whereat the web can be contacted with a liquid containing a coating substance; a drier; means for passing the web to the coater; and means for passing the web vertically or substantially vertically from the coater to the drier. 50 11. Apparatus as claimed in claim 10, and further including web take-up and release means for accumulating and releasing web prior to the coater.

12. Apparatus as claimed in claim 10 or 11 and 55 further including a second coater and a second drier, the web being guided to pass vertically or substantially vertically from the second drier.

13. Apparatus as claimed in claim 10, 11 or 12 wherein the or each coater includes a bath for the

60 liquid and a roller disposed to immerse the web in the bath.

14. Apparatus as claimed in any preceding claim and including a plurality of rollers arranged to define a web travel path.

65 15. Apparatus as claimed in claim 14, 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. .

70 16. Apparatus as claimed in any of claims 10 to 15 and further including at a downstream end thereof means for cutting lengths from the coated web and/or performing a welding operation thereon.

75 17. Apparatus as claimed in claim 16 and including a web accumulating and release means immediately upstream of the cutting and/or welding means.

18. Apparatus as claimed in any of claims 10 80 to 17 wherein the or each drier includes infra-red and/or hot air drying components.

19. Apparatus for forming an enveloping coating on a web of plastics material substantially as hereinbefore described with reference to and a

85 illustrated in the accompanying drawings.

20. A web of plastics material formed with an enveloping coating by the method of any of claims 1 to 9 or by the apparatus df any of claims 10 to 19.

90 21. 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 95 method as claimed in any of claims 1 to 9 or by the apparatus of any of claims 10 to 19 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. 100 22. A method as claimed in claim 21, 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 105 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.

110 23. A method as claimed claim 1 or 2 wherein the plastics material is polyethylene and the coating substance is polyvinylidene chloride.

24. A method as claimed in claim 21,22 or 23 including the step of refraining from puncturing 115 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. 120 25. A container made by a method as claimed

GB 2 138 714 A

being a liner for a metallic container for a beverage.

in any of claims 21 to 24.

26. A container as claimed in claim 25 and

Printed in the United Kingdom for Her Majesty's Stationery Office, Demand No. 8818935, 10/1984. Contractor's Code No. 6378. Published by the Patent Office, 25 Southampton Buildings, London, WC2A 1AY, from which copies may be obtained.