IES80413B2 - Production of plastics sheet material - Google Patents

Abstract

To produce plastics panels preset quantities of virgin plastics material, regrind and masterbatch are fed into an upper feed hopper (18) hung on outlet door (19) operated by a ram (20). The material is delivered, on demand, from the upper hopper (18) into an intermediate hopper (21) with outlet clamshell doors (22,23) which are rapidly opened and closed by fast acting rams (24) to deliver supply material into the main feed hopper (26), A constant supply of predictable quality mixed raw material is provided for extrusion to form panels.

Description

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 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 products comprising the steps of: feeding preset quantities of virgin plastics material, regrind plastics material and masterbatch material into an upper feed hopper; delivering the material from the upper hopper into an intermediate hopper having rapid acting outlet doors which are closed as the material is being delivered from the upper feed hopper; on demand, opening the rapid acting outlet doors of the intermediate c hopper to rapidly deliver a preset mixture into a main feed hopper; on demand, closing the outlet doors of the intermediate hopper and ‘ί delivering a new batch of material from the upper feed hopper into the intermediate hopper for delivery into the main feed hopper; . 5 extruding the plastics material from the main feed hopper into a molten condition; and 10 forming the extrudate into a desired product. In a preferred embodiment of the invention the method includes the step of blending the mixture in the intermediate hopper. 15 Preferably the virgin plastics material, regrind material, and masterbatch material are delivered into the upper hopper from separate sources in a predetermined sequence. 20 In one embodiment of the invention the outlet doors of the intermediate hopper are operated by fast acting ram means which are actuated to rapidly open and close the outlet doors of the intermediate hopper, on demand. Preferably the outlet doors of the intermediate hopper are clamshell doors. 25 In one embodiment of the invention the plastics products are plastics panels and the method includes the steps of:- passing the extrudate through a flexible lip die to form a sheet of molten plastics material of desired width; passing the molten plastics material over a calendar roll for cooling the 30 material; passing the cooled plastics material along a conveyor; and cutting the material to a desired size to form sheets of plastics material.

In one embodiment of the invention the method includes the steps of: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; 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.

Preferably a substantially constant tension is applied to the protective film by applying a braking force to the reel from which the film is led.

In this case 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.

In a preferred embodiment the method includes the steps of trimming the side edges of the panel.

Preferably the method includes the step of de-burring the cut side edges of the panel. In this case preferably the cut side edges of the panel are de-burred by applying de-burring rollers to the cut side edges of the panel.

In one embodiment of the invention excess film at the side edges of the panel 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. Most preferably, the trimmings removed from the panel side edges are granulated and recycled.

In one embodiment of the invention at least portion of the trimmings are chopped to a smaller size in-line prior to granulation.

In one embodiment of the invention the method includes the testing an extruded plastics panel for dimensional stability on thermoforming, the testing method comprising the steps of:cutting a defined sample of the plastics panel across the width of the panel; laying the sample on a table; moving the table with the sample in position into a heating positioning; heating the sample for a preset period corresponding to the thickness of the panel; removing the table with the heated sample in position from the heating position; and comparing the dimensions of the sample, after heating, with those of the sample prior to heating.

Preferably one face of the sample is heated in the heating position by heating the sample-receiving table. Preferably the table is heated by circulating a heating fluid through the table.

In one embodiment of the invention one face of the sample is heated in the heating position by applying radiant heat to the face of the panel. Preferably radiant heat is applied by infra red heating means located above the sample table in the heating position.

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; 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 one position of use; Fig. 4 is a cross sectional view of part of the apparatus of Fig. 3 in another position of use; 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; 5 Fig. 7 is a perspective, partially cut-away view of part of the apparatus of Figs. 5 and 6; 10 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; 15 Fig. 10 is a perspective view of the trimming station; Fig. 11 is a side view of the trimming station; 20 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. 25 Detailed Description • 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 , 30 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 Ί 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 process of the invention 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.

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 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 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 34 are de-burred by passing the cut sheet 34 between de-burring rollers 55 on opposite sides of the sheet 34.

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.

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.

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

Claims (5)

1. A process for producing plastics products comprising the steps of:feeding preset quantities of virgin plastics material, regrind plastics material and masterbatch material into an upper feed hopper; delivering the material from the upper hopper into an intermediate hopper having rapid acting outlet doors which are closed as the . material is being delivered from the upper feed hopper; on demand, opening the rapid acting outlet doors of the intermediate hopper to rapidly deliver a preset mixture into a main feed hopper; on demand, closing the outlet doors of the intermediate hopper and delivering a new batch of material from the upper feed hopper into the intermediate hopper for delivery into the main feed hopper; extruding the plastics material from the main feed hopper into a molten condition; and forming the extrudate into a desired product.

2. A method as claimed in claim 1, including the step of blending the mixture in the intermediate hopper, preferably wherein the virgin plastics material, regrind material, and masterbatch material are delivered into the upper hopper from separate sources in a predetermined sequence.

3. A method as claimed in claim 1 or 2 wherein the outlet doors of the intermediate hopper are operated by fast acting ram means which are actuated to rapidly open and close the outlet doors of the intermediate hopper, on demand, preferably the outlet doors of the intermediate hopper are clamshell doors. 5

4. A method as claimed in any preceding claim, wherein the plastics products are plastics panels and the method includes the steps of:passing the extrudate through a flexible lip die to form a sheet of molten plastics material of desired width; io passing the molten plastics material over a calendar roll for cooling the material; passing the cooled plastics material along a conveyor; and 15 cutting the material to a desired size to form sheets of plastics material.

5. A method for producing plastics products substantially as hereinbefore described with reference to the accompanying drawings and plastics products whenever produced by the method as claimed in any preceding claim.