IES990067A2

IES990067A2 - Production of plastics sheet material

Info

Publication number: IES990067A2
Application number: IE19990067A
Authority: IE
Inventors: Roy Lowe; Denis Collins; James Mcgee
Original assignee: Athlone Extrusions Dev Ltd
Priority date: 1998-02-06
Filing date: 1999-02-01
Publication date: 2000-06-28
Also published as: GB2333995B; GB2333995A; GB9902369D0; IE990066A1

Abstract

A protective film (31) is applied over the faces of formed plastics sheet material to protect the sheets in transportation and storage. The film (31) is led from one of a number of reels (33,34,35) over a guide and tensioning roller(32) and applied to a sheet (36) between a pair of nip rollers (37,38). The reels (33,34,35) which are of different width to accumulate sheets (36) of different size are mounted on a common carriage (40) having rollers (41) which run along corresponding transverse tracks (42) to position the film (31) relative to the sheet (36). The side edges of the sheet (36) are trimmed by cutting knives (50,51) and the waste sheet trim (52) is reground. The side edges of the sheet (36) are de-burred by de-burring rollers (55).

Description

“Production of Plastics Sheet Material” Introduction The invention relates to the production of plastics material and in particular to a method for producing plastics sheet material, especially plastics panels. Such panels may be thermoformed into desired shapes.

In our UK-A-2282985A, we have described a process for producing such plastics io sheet panels of high quality in a cost efficient manner.

In an increasingly competitive commercial situation, there is a need to produce such panels in an even more cost efficient manner while also maintaining the quality of the product.

Statements of Invention According to the invention there is provided a method for producing plastics panels comprising the steps oftfeeding plastics material into an extruder screw; extruding the plastics material to a molten condition; passing the extrudate through a die to form a deposit of molten plastics material; cooling the plastics material to form a sheet; adjusting the position of a reel of protective plastics film so that the film corresponds with the sheet; IE 990067 leading the protective film from the reel; applying a substantially constant tension to the protective film; and applying the protective film to at least one face of the plastics sheet.

In a preferred embodiment of the invention a substantially constant tension is applied to the protective film by applying a braking force to the reel from which the film is led.

Preferably the protective plastics film is led from one of a number of separate inline reels of film corresponding to the width of the cooled plastic sheet.

In one embodiment the method includes the steps of trimming the side edges of 15 the panel. Preferably the method includes the step of de-burring the cut side edges of the panel. Typically the cut side edges of the panel are de-burred by applying de-burring rollers to the cut side edges of the panel.

In a preferred arrangement excess film at the side edges of the panel is removed 20 and collected for recycling as the side edges are being trimmed. Preferably the excess film is collected by winding onto a waste film collection reel.

In one embodiment the trimmings removed from the panel side edges are granulated and recycled. Preferably at least portion of the trimmings are chopped to a smaller size in-line prior to granulation.

The invention also provides lamination apparatus for applying a protective plastics film to a plastics panel sheet comprising reel means for protective film, a carriage on which the reel means is mounted for adjusting the position of the reel relative to the plastics sheet, tensioning means for applying a substantially IE 990067 constant tension to the protective film drawn from the reel, and applicator means for applying the protective film to at least one face of the plastics sheet.

Preferably the tensioning means comprises a brake for applying a braking force to 5 the reel from which the film is led. Ideally, a number of separate in-line reels of film are mounted to the carriage, the reels having film widths corresponding to different widths of plastics sheet. Preferably the film applicator means comprises nip roller means which press the film to the plastics sheet. In a preferred arrangement the nip roller means includes an upper nip roller which is pressed I o down by a ram to apply the film to a plastics sheet.

In one embodiment of the invention the apparatus includes guide roller means over which the protective film is led prior to application of the film to the plastics sheet.

Preferably the carriage is mounted on a track means for adjusting the position of a protective film reel to correspond with a plastics panel. Ideally, the position of the carriage is adjustable by an adjustment means such as adjustment ratchet screws to move the carriage on the tracks. 2.0 Brief Description of the Drawings The invention will be more clearly understood from the following description thereof given by way of example only, with reference to the accompanying drawings, in which:Fig. A is a side elevational view of apparatus used in a prior art process for producing plastics panels; Fig. 1 is a side, partially cross sectional view of a gravimetric feeding apparatus used in the process of the invention; IE 990067 Fig. 2 is a plan view of a part of the apparatus of Fig 1; Fig. 3 is an end, partially cross sectional view of the apparatus of Fig. 1 in 5 one position of use; Fig. 4 is a cross sectional view of part of the apparatus of Fig. 3 in another position of use; io Fig. 5 is a side view of a multi-stage lamination apparatus used in the process of the invention; Fig. 6 is a plan view of the lamination apparatus of Fig. 5; Fig. 7 is a perspective, partially cut-away view of part of the apparatus of 15 Figs. 5 and 6; Fig. 8 is a perspective view of one lamination station of the apparatus of Figs. 5 to 7; Fig. 9 is a plan view of a trimming station used in the process of the invention; Fig. 10 is a perspective view of the trimming station; Fig. 11 is a side view of the trimming station; Fig. 12 is a perspective view of a testing apparatus used in the process of the invention; and Fig. 13 is a side, partially cross sectional view of the testing apparatus, in use.

IE 990067 Detailed Descriptio n Referring initially to Fig. A, there is illustrated a process for producing plastics panels as described in our UK-A-2282985A comprising the steps of mixing virgin plastics material, feeding the plastics material through a hopper 2 into an extruder screw 3 in which the material is extruded to a molten plastics condition. The extrudate is filtered in step 4 and pumped by a gear pump in step 5 to pass the extrudate under pressure to a flexible lip die 6 in which the molten plastics material is formed into a sheet of molten material of desired width and thickness. The plastics material is then passed between first and second calendar rolls 7, 8 and then between second and third calendar rolls 8, 9, the material being cooled as it passes over the rollers as will be described in more detail below. The partially cooled plastics sheet material is then passed along a conveyor 10 to a protective plastics film applying station 11 at which a film of plastics, typically polyethylene material, is applied to either one or both faces of the sheet material as will be described in more detail below. In the process of the invention, the side trimming station 12 and the continuous sheet is cut into panels of a desired length at a cutting station 13. The cut sheets are tested, collected, stacked and packaged.

Referring to Figs. 1 to 4, in the preferred process preset quantities of virgin plastics material, regrind plastics material and masterbatch material are fed into an upper feed hopper 18 having an outlet door 19 operated by a ram 20. The material is delivered from the upper hopper 18 into an intermediate hopper 21 having rapid opening outlet doors 22, 23 which are closed as the material is delivered from the upper hopper 18, The outlet doors 22, 23 are clamshell doors which are rapidly opened and closed by fast acting rams 24. A blender/mixer 25 is provided in the intermediate hopper 21 for ensuring thorough mixing of the material and rapid delivery into a main feed hopper 26.

IE 990067 In use, predetermined quantities of virgin plastics material, regrind material, and masterbatch material are delivered into the upper feed hopper 18 from separate sources in a predetermined sequence. On demand, with the clamshell or bomb doors 22, 23 closed, the outlet door 19 from the upper hopper 18 is opened to deliver the material into the intermediate hopper 21. After a preset quantity of material has been delivered, the outlet of the upper hopper 18 is closed and the material in the intermediate hopper 21 is blended by the mixer blender 25. On demand, as determined by the quantity of material remaining in the lower main feed hopper 26, the rapid acting outlet bomb doors 22, 23 are opened by automatically actuating the rams 24 to rapidly deliver the blended material from the intermediate hopper 21 into the main feed hopper 26. The cycle is repeated to maintain a constant supply of predictable quality mixed raw material for extrusion. In this way, the process is optimised as there is always high quality feed material available for further processing by extrusion. Because of this feature very efficient high speed processing is achieved. In addition, particularly because of the mixing/blending in the intermediate hopper, thorough mixing of the material is ensured which is essential for high quality colour matching.

Referring particularly to Figs. 5 to 8, there is illustrated a multi-stage lamination apparatus 30 of the invention. This is used to provide a film 31, typically of polyethylene material which is applied over at least one face of the formed plastics sheet material to protect the sheets in transportation and storage. The film 31 is led from one of a number of reels 33, 34, 35 over a guide and tensioning roller 32 and applied to a sheet 36 between a pair of spaced-apart nip rollers 37, 38. The upper nip roller 37 is pressed down by means of rams 39 to apply the film 31 to the sheet 36.

Each of the reels 33, 34, 35 of film are typically of different widths to optimally accommodate sheets of different size. The film delivery can be rapidly changed over from one reel to another so that production efficiency is optimised. The film IE 990067 is drawn from a reel at a substantially constant tension by applying a braking force through a brake controller 39 on each of the reels 33, 34, 35.

It will be noted that the reels 33, 34, 35 are mounted on a common carriage 40 having rollers 41 which run along corresponding transverse tracks 42 to accurately adjust the position of the carriage 40 and hence the film 31 to the sheet 36 travelling along a conveyor 45. Adjusting ratchet screws 46 are used to move the carriage 40 on the tracks 42. In this way, film application and usage is optimised.

Referring to Figs. 9 to 11, using cutting knives 50, 51, the side edges of the sheet 36 are trimmed and waste sheet trim 52 is delivered under the conveyor for regrinding in a grinder 53. If desired, particularly for larger sized waste, the waste may be pre-chopped in a chopper 54 prior to grinding.

To improve quality, the side edges of the cut sheet 36 are de-burred by passing the cut sheet 34 between de-burring rollers 55 on opposite sides of the sheet 36.

Referring particularly to Figs. 11 and 12, to check the dimensional stability of sheets or panels manufactured using the process of the invention, sample strips which are typically 500 mm wide and 100 mm long are first cut from the sheets. The sample 80 is laid on a table 81 of a reversion testing apparatus 79. The testing apparatus 79 comprises a bed 83 having tracks 82 on which the table is mounted for movement inwards and outwards illustrated particularly in Fig. 13. The apparatus 79 also includes a head part 88 housing two banks 84, 85 of infrared heaters in a carriage 86 which is height adjustable by a handle-operated, screw 87, as illustrated. The heaters 84, 85 are positioned over the sample table 81 when the table is in the testing position illustrated in dotted outline in Fig. 13.

The table 81 has a heat exchange surface below the bed which is provided by a pipe network 90 in the bed. The pipes are supplied with heating/cooling fluid lines 91, 92.

IE 990067 In use, with the cut sample 80 in position, the table 81 is moved into the heated position underneath the heaters 84, 85. The sample is then heated from below and on top for a preset period corresponding to the thickness of the panel from which the sample was cut. After heating, the table with the heated sample in position is withdrawn to the position illustrated in Fig. 12, the sample is removed and the dimensions of the sample, after heating, are compared to those of the sample prior to heating. In this way, the sample is rapidly reversion tested to a high level of accuracy. io The invention may be applied to any suitable plastics material, either a unitary material or one having a number of layers. One such material is a base of acrylonitride - butadiene - styrene with a coating of polymethyl methacrylate.

The invention is not limited to the embodiments hereinbefore described which may be varied in construction and detail.

Claims

1. A method for producing plastics panels comprising the steps of:5 feeding plastics material into an extruder screw; extruding the plastics material to a molten condition; passing the extrudate through a die to form a deposit of molten I o plastics material; cooling the plastics material to form a sheet; adjusting the position of a reel of protective plastics film so that the 15 film corresponds with the sheet; leading the protective film from the reel; applying a substantially constant tension to the protective film; and applying the protective film to at least one face of the plastics sheet.

2. A method as claimed in claim 1, wherein a substantially constant tension is applied to the protective film by applying a braking force to the reel from 25 which the film is led, preferably the protective plastics film is led from one of a number of separate in-line reels of film corresponding to the width of the cooled plastic sheet, preferably the method includes the step of trimming the side edges of the panel, preferably the method includes the step of de-burring the cut side edges of the panel, preferably the cut side edges of the panel are de-burred by applying de-burring rollers to the cut side edges of the panel, preferably excess film at the side edges of the panel IE 990067 ίο is removed and collected for recycling as the side edges are being trimmed, preferably the excess film is collected by winding onto a waste film collection reel, preferably the trimmings removed from the panel side edges are granulated and recycled, preferably at least portion of the trimmings are 5 chopped to a smaller size in-line prior to granulation.

3. Lamination apparatus for applying a protective plastics film to a plastics panel sheet comprising reel means for protective film, a carriage on which the reel means is mounted for adjusting the position of the reel relative to 10 the plastics sheet, tensioning means for applying a substantially constant tension to the protective film drawn from the reel, and applicator means for applying the protective film to at least one face of the plastics sheet.

4. Lamination apparatus as claimed in claim 3 wherein the tensioning means 15 comprises a brake for applying a braking force to the reel from which the film is led, preferably a number of separate in-line reels of film are mounted to the carriage, the reels having film widths corresponding to different widths of plastics sheet, preferably the film applicator means comprises nip roller means which press the film to the plastics sheet, preferably the nip 20 roller means includes an upper nip roller which is pressed down by a ram to apply the film to a plastics sheet, preferably the apparatus includes guide roller means over which the protective film is led prior to application of the film to the plastics sheet, preferably the carriage is mounted on a track means for adjusting the position of a protective film reel to correspond with 25 a plastics panel, preferably the position of the carriage is adjustable by an adjustment means, preferably the adjustment means comprises adjustment ratchet screws to move the carriage on the tracks.

5. Plastics panels whenever manufactured by a method of claims 1 or 2 30 and/or using an apparatus of Figs 3 or 4.