GB2032833A

GB2032833A - Producing extruded board

Info

Publication number: GB2032833A
Application number: GB7923002A
Authority: GB
Original assignee: ZAKLADY TWORZYW SZTUCZNYCH NIT
Current assignee: ZAKLADY TWORZYW SZTUCZNYCH NIT
Priority date: 1978-10-30
Filing date: 1979-07-02
Publication date: 1980-05-14
Also published as: NL7907948A; GB2032833B; IT7925252A0; FR2440267B1; NO792314L; DE2927717A1; DE2927717C2; FI792224A; ES482762A1; IT1122864B; SE434817B; SE7906139L; FR2440267A1; ATA555279A; PT69987A; AT374738B; DK329479A

Abstract

In the production of extruded plastics armoured board, stabilization of the board is effected by successively cooling and reheating the hot strip of armoured board issuing from the extruder die. The cooling is effected in a heat-exchanging thicknesser with the flow of cooling fluid passing counter to the direction of feed of the strip and branching laterally from central longitudinal ducting to outer longitudinal ducting so that the cooling is more intense along the centre of the strip than at the side margins of the strip. The cooled strip is then subjected to ambient air after which it passes into a heater where infrared lamps heat the strip more intensively at the side margins thereof than at the central longitudinal zone thereof.

Description

SPECIFICATION A method of and apparatus for producing plastics armoured board This invention relates to a method of producing armoured board of plastics, especially polyolefines capable of crystallization, as for instance polypropylene or polythene, and to apparatus for stabilization of armoured board strip made of plastics, especially polyolefines capable of crystallization.

The invention is chiefly concerned with the manufacture of package materials for cardboard containers, and of heat insulating materials.

The armoured board is built of at least three layers, the outer whereof are flat sheets wherebetween the third layer is disposed and has the form of a corrugated sheet. All the three layers are connected inseparably with each other, the corrugated sheet being connected with both flat sheets along the entire length of its wave crest.

Another type of armoured board is composed of two flat sheets connected with each other by means of short ribs. The armoured board formed in this way presents a series of parallel channels and has properties approximating to those of the armoured board with the corrugated layer inside.

A known method of production of armoured board of plastics is as follows:~ The plastic material is heated and extruded through a head provided with an extruder die consisting of a series of separate cores whereof the form determines the form of the channels of the board strip being produced. Into the channels of the strip being extruded compressed air is introduced through holes made in the cores of the extruder die. The extruded strip is then introduced between two cooling surfaces of a thicknesser.

The strip leaving the thicknesser is cut crosswise, and contingently lengthwise, into sheets of desired format.

Known apparatus for cooling the plastic-made armoured board strip consists of two parallely disposed steel blocks spaced one above the other at a distance equal to the thickness of the board strip. Each block is provided with bores parallel to each other and disposed perpendicular to the direction of travel of the board strip. Through certain of said channels a cooling medium, for instance water, is passed, the remaining channels being connected through small holes with the space between the blocks and being connected also to a vacuum source. The armoured board strip passes between the blocks of the apparatus and remains in contact with the surfaces of the blocks, so as to improve the cooling of the strip and fix its thickness.

The armoured board sheets made of plastics must fulfil a number of basic requirements if they are to be used on an industrial scale. Thus, they must be substantially flat, free of bends and warps, and sufficiently inexpensive for them to withstand the competition with armoured cardboard, that is, board made of paper pulp.

Unfortunately, the armoured board made by the known method of such relatively inexpensive plastics as polyolefines, especially polypropylene and polythene, shows a number of disadvantages.

Among these is first of all swelling of the sheets, the warping of their edges, and finally a considerable scatter of thickness as measured across the strip.

An object of the invention is to provide a method of production of armoured board made of plastics, especially of polyolefines capable of crystallization, such as polypropylene or polythene, said board being free of the disadvantages mentioned above, and to provide apparatus suitable for carrying out said method.

The method and the apparatus according to the invention render possible the stablization of said board strip made of plastics, especially of polyolefines, in a permanent way whereby the board sheets, during and after a prolonged period of storing, do not swell.

According to the present invention we provide a method of producing plastics armoured board, comprising extruding hot plastics material to form a hot strip of armoured board, cooling the hot strip, and reheating the cooled strip to stabilize same.

Preferably the cooling is effected in a thicknesser which cools the strip more intensively along a longitudinal mid portion thereof than along longitudinal marginal portions thereof.

Preferably also the reheating is effected in a heater which heats the strip less intensively along a longitudinal mid portion thereof than along longitudinal marginal portions thereof.

Further according to the present invention we provide apparatus for use in producing plastics armoured board, comprising an extruder die having a series of separate cores whereof the form determines the form of the channels of the extruded strip, a heat exchanging thicknesser to cool hot strip from the extruder die, and a heater to reheat the cooled strip.

Preferably the thicknesser incudes a pair of spaced opposed blocks between which the hot strip passes, each block having therethrough passage means for cooling fluid comprising central longitudinal channelling having entry means at its downstream end, transverse channelling extending from the central longitudinal channelling, and outer longitudinal collector channelling connected to the lateral channelling and having outlet means at its upstream end.

A particularly advantageous process and apparatus embodying the invention will now be described:~ Plastics material, especially such polyolefines as polypropylene or polyethylene, is heated and extruded through a head provided with an extruder die consisting of a series of separate cores whereof the form determines the form of the channels of the board strip being extruded. Into the channels of the strip being extruded compressor air is pumped through holes made in the cores of the extruder die. The strip extruded is introduced between two cooling surfaces of a thicknesser, and the strip is cooled more intensively along its middle portion than along its border areas, and more intensively at the exit of the strip from the thicknesser than at its entrance into the thicknesser.On leaving the thicknesser, the strip remains at the ambient temperature until the temperatures at different points of the crosssection become equalized.

Then the strip is submitted to a reheating at the temperature of 40-1 200C in a suitable tunnel, the reheating being conducted in such a way that the strip is reheated less intensively at its middle portion than at its border areas, and that it is reheated more intensively within the middle zone of the tunnel than in the zones adjacent to the input and the output of the tunnel.

Preferably, the temperature of the strip surface along its middle portion is lower by 1 5#4O0C than along its border areas, and is higher by 1 5-400C along the middle zone of the tunnel than in zones adjacent to the input and the output of the tunnel.

The armoured board made of plastics, especially of polyolefines, so produced is characterized by low scatter of the basic weight crosswise and lengthwise the strip, amounting to + 3% of the average value, is entirely flat, and shows no traces of warping in the course of and after long-term storage.

The apparatus is composed of a thicknesser, a reheating tunnel disposed at a distance of at least three times the length of the thicknesser, and transport rollers. The working surfaces of the thicknesser are cooled within their middle portion more intensively than in their border areas, and more intensively at the output of the thicknesser than at the input thereof. The space of the reheating tunnel is differentiated in respect to the heating in such a way that in its middle portion the temperature is lower than in the vicinity of the tunnel walls, the temperature in the middle portion of the tunnel being simultaneously higher than that in the zones adjacent to the input and the output of the tunnel.

The thicknesser comprises two identical units consisting of metallic blocks disposed parallely one above the other. In the middle of each block, parallely to its longitudinal axis, at least one channel is made, stopped short of the input end of the thicknesser. To this channel, along both sides thereof, a number of transversely extending parallel channels are connected, said channels being in turn connected along the block sides with two common collecting channels parallel to the longitudinal axis of the block.

Between the blocks, the space enclosed by opposed surfaces of the blocks is the working space of the thicknesser. To said opposite surfaces of the blocks, flat irons and plates are welded to form two chambers. In the blocks, between the chambers, numerous holes are made which connect the working space of the thicknesser with said chambers which in turn are connected with a vacuum pump.

The reheating tunnel has the form of a flat rectangular prism made of plates providing a narrow, elongated through-slot extending between opposed walls. Said slot divides the tunnel into two parts. On the bottom of each part, flat infra-red lamps are mounted in rows extending perpendicularly to the longitudinal axis of the tunnel, lamps of the same positions in the different rows forming series of lamps running parallely to the longitudinal axis of the tunnel. The infra-red lamps of the outer longitudinal series are of the highest power, while those of centre longitudinal series are of the lowest power. The infra-red lamps of each row are provided with a common supply which is infinitely variable to control the current value.

EXAMPLE 1 Polypropylene under the proprietory name DAPLEN EE which has the coefficient of discharge of 0.4 9/10 min., was heated and extruded through a head provided with an extruder die consisting of a series of separate cores of rectangular cross-section: the form of the cores determined the rectangular form of the channels of the board strip being extruded. Into the channels of the strip being extruded; through holes made in the cores of the extruder die, compressed air was introduced. The extruded strip was passed into a thicknesser between two cooling surfaces thereof spaced from one another by 5 mm, and were cooled more intensively within the middle portion of the thicknesser than in its border areas, and more intensively at the exit of the strip from the thicknesser than at its entrance into the thicknesser.

The desired distribution of the cooling intensity on the surfaces of the thicknesser was secured through designing a thicknesser consisting of two identical metal blocks disposed parallely one above the other. The width of the thicknesser was somewhat larger than the width of the strip being extruded, its length being equal to 0.75 of the strip width.

In the centre of each block, symmetrically with its longitudinal axis, were two cylindrical channels closed at the end adjacent to the head extruding the strip.

Said channels were connected by means of longitudinal series of transverse channels perpendicular thereto and disposed along both sides of the block, to outer collector channels running parallel to the longitudinal axis of the block.

At non-working surfaces of the blocks flat suction chambers were welded of flats and plates.

In the blocks, between the channels, were made several small holes to connect the working - space of the thicknesser with the chambers of the blocks.

Into the cylindrical channels of both blocks of the thicknesser, which channels are closed at the ends adjacent to the extruding head, demineralized water having a temperature of 1 20C was supplied in counter-current to the strip being extruded. Said water flowed laterally through the channels perpendicular to the direction of travel of the strip of the blocks, and it was discharged into a closed circulation system.

The temperature of water leaving the collectors was equal to 250C.

Simultaneously, the chambers of both blocks were connected to a vacuum pump which maintained within the chambers a vacuum of 20 mm of mercury.

After leaving the thicknesser, the strip of armoured board remained at the ambient temperature until the temperatures at all points of the cross-section of the strip became equalized.

Then the strip was submitted to a reheating at a temperature of 50-1 000C in a flat tunnel, the heating being conducted in such a way that the strip was reheated less intensively in its middle portion than in its border areas, and less intensively in the zones adjacent to the input and the output of the tunnel than in the middle zone thereof.

The temperature of surface of the strip in the middle zone amounted to 700C in the middle of the strip, and increased up to 1 000C in the vicinity of its edges. In the input and output zones of the tunnel the temperatures was equal to 500C and 700C respectively. The total time of reheating of the strip was equal to 70 seconds.

The strip in the tunnel was heated at the bottom and at the top by means of nine transverse rows of infra-red lamps each row having seven lamps and the lamps having the power of 250, 400, 650 and 1000 W. The lamps were thus disposed in series of nine extending parallel to the direction of movement of the strip. That is, the infra-red lamps occuping the same positions in the different rows formed series running parallely to the direction of the travel of the strip. In both outermost series infra-red lamps of the power of 1000 W were disposed; in the adjacent series lamps of 650 W; in the next two series lamps of 400 W: and in the central series infra-red lamps of the power of 250W.

Each of said nine rows was provided with a common electric current supply with infinitely variable regulation of the current intensity.

The central row was supplied with a current having the highest intensity, decreasing stepwise in successive rows. The curent supplying the outermost rows was equal to not significantly over a half of the value of intensity of the current supplying the central row.

The temperature of the strip at the output was measured by means of a contactless thermometer.

The temperature in the middle row was determined through the change of colour of a strip painted on the board surface, and changing its colour in dependence on the temperature. After leaving the reheating tunnel the strip was cooled down to the ambient temperature and cut into sheets of required dimensions.

The obtained armoured board made of polypropylene showed the basis weight of 850 G.S.M. with tolerance of f 3%, the crushing strength of 3.6 kgf/cm2 and burst at the temperature 500 of 15 kgf/cm2. The sheets were entirely flat, and in course of and after storing for several days they showed no warping.

EXAMPLE II The armoured board was produced from a copolymer of propylene and ethylene, having the coefficient of discharge of 0.7 g/10 min, under the proprietory name MOPLEN EPQ-30M, produced by Montedison, in the same way as specified in Example I, except that the heating was conducted at temperatures accordingly lower by 5--100C, whereby the reheating time was 60 seconds.

The obtained board showed the basis weight of 860 G.S.M. with a tolerance of + 2.8% and the flat crushing strength of 3.2 kgf/cm2.

A stabilizing apparatus including a thicknesser and a reheating tunnel will now be described as an exemplary embodiment with reference to the accompanying drawings wherein:~ Fig. 1 shows the stabilizing apparatus for armoured board made of plastics; Fig. 2 is a perspective view of the thicknesser; Fig. 3 is a cross-sectional view of the bottom unit of the thicknesser, taken in a plane parallel to its working surface; Fig. 4 is a longitudinal sectional view of the bottom unit of thicknesser, taken along the line A-A of Fig. 3; and Fig. 5 is a perspective view of the reheating tunnel with an upper part thereof partially sectioned.

Referring to the drawings:~ The stabilizing apparatus consists of a thicknesser 1, transport rollers 2 and 3, and a reheating tunnel 4.

The distance between the thicknesser and the reheating tunnel, as measured from the rear end of the thicknesser to the front end of the tunnel, equals 5 times the length of the thicknesser.

The thicknesser comprises two identical units 5 disposed parallely one above the other. This distance between their working surfaces is set by means of an adjusting device to accord with the thickness of the processed armoured cardboard strip. The lower unit is inseparably connected with a horizontal supporting frame 6. At the corners of said frame four sleeves 7 are mounted. To the upper unit four square protrusions 8 are welded, each provided with an opening corresponding to the outer diameter of the sleeve. The sleeves are provided with male threads each having thereon two nuts 9 which are used for adjusting the distance between the working surfaces of the thicknesser. Each of the units is provided with stub pipes 10, 1 1 for supplying and draining the cooling medium, and with a stub pipe 12 for connecting to a source of vacuum.

Each unit of the thicknesser consists of a metallic block 13, and a flat chamber 14 made of angles and plates welded to the block at the side of its non-working surface. In the middle of the block, symmetrically of its longitudinal axis, two cylindrical channels 15 are formed, being closed at one end, and at the other end being connected through a cylindrical chamber 16 with a stub pipe 11. Each of said channels 1 5 is connected with a series of transverse channels 17 perpendicular thereto and interconnected along the sides of the block by means of common collectors 18 parallel to the longitudinal axis of the block. In the blocks, between the channels, numerous holes 19 are provided which connect the working space of the thicknesser with the vacuum chambers of the units.Water supplied to the stub pipe 11 flows successively through channels 15 and 17, and from the collectors channels 18 is drained through stub pipes 10.

The reheating tunnel has the form of a flat rectangular prism made of plates and is thermally insulated, the prism being provided with through slot ports 20 in opposed front walls. By the plane containing the slot ports, the tunnel is divided into two parts, namely, an upper part 21 and a lower part 22. On the bottom of each of these parts infra-red lamps 23 having the power of 250,400, 650, and 1000 W are installed in nine rows perpendicular to the longitudinal axis of the tunnel, there being seven lamps in each row. The lamps occupying the same positions in the rows form longitudinal series, there being nine lamps in each series. The infra-red lamps in both outermost series 24 have the power of 1000 W each; those in adjacent series 650 W each those in the next adjacent series 400 W each; and those in the central series 250 W each. Each of the nine rows has its lamps connected to a common supply system having a knob 25 enabling infinitely variable regulation of the current intensity. The tunnel is inseparably connected to a horizontal supporting frame 26.

Claims

1. A method of producing plastics armoured board, comprising extruding hot plastics material to form a hot strip of armoured board, cooling the hot strip, and reheating the cooled strip to stabilize same.

2. A method according to claim 1, wherein the cooling is effected in a thicknesser which cools the strip more intensively along a longitudinal mid portion thereof than along longitudinal marginal portions thereof.

3. A method according to claim 2, wherein the thicknesser cools the strip less intensively along an upstream transverse portion thereof than along a downstream transverse portion thereof.

4. A method according to claim 2 or 3, wherein the cooled strip on leaving the thicknesser is exposed to the ambient air prior to being reheated.

5. A method according to any one of the preceding claims, wherein the reheating is effected in a heater which heats the strip less intensively along a longitudinal mid portion thereof than along longitudinal marginal portions thereof.

6. A method according to claim 5, wherein the reheating of the strip is more intensive along the longitudinal mid portion thereof than along upstream and downstream transverse portions thereof.

7. A method according to claim 5 or 6, wherein the reheating is effected at temperatures in the range of 400C to 1 200C.

8. A method according to claim 7, wherein the surface temperature of the reheated length of strip is 150--400C lower along its longitudinal mid portion than along its longitudinal marginal portions, and is 1 50#O0C higher along the upstream and downstream transverse portions.

9. A method according to any one of the preceding claims, wherein plastics material in the form of heated polymeric material is extruded through a head provided with an extruder die having a series of separate cores whereof the form determines the form of the channels of the extruded strip, and compressed air is introduced through holes in the cores of the extruder die into the channels of the strip being extruded.

10. A method according to any one of the preceding claims, wherein the plastics material is a polyolefine capable of crystallization.

11. A method of producing plastics armoured board, substantially as hereinbefore described with reference to Example I to Example II.

12. Plastics armoured board whenever produced by the method of any one of the preceding claims.

13. Apparatus for use in producing plastics armoured board, comprising an extruder die having a series of separate cores whereof the form determines the form of the channels of the extruded strip, a heat-exchanging thicknesser to cool hot strip from the extruder die, and a heater to reheat the cooled strip from the thicknesser.

14. Apparatus according to claim 13, wherein the thicknesser and heater are spaced from each other a distance of at least three times the length of the thicknesser.

1 5. Apparatus according to claim 13 or 14, wherein the thicknesser includes a pair of spaced opposed blocks between which the hot strip passes, each block having therethrough passage means for cooling fluid comprising central longitudinal channelling having entry means at its downstream end, transverse channelling extending from the central longitudinal channelling, and outer longitudinal collector channelling connected to the lateral channelling and having outlet means at its upstream end.

16. Apparatus according to claim 15, wherein the opposed blocks have therein vacuum chambers, and vacuum passages extending from the vacuum chambers to the opposed faces of the blocks.

17. Apparatus according to any one of claims 13 to 1 5, wherein the heater includes a pair of opposed box housings defining between them a slot-like tunnel for through passage of the strip, and transverse rows of infra-red lamps in the box housings, the transverse rows of lamps in each box housing forming longitudinally extending central, intermediate and outer series of lamps, and the lamps of the outer series being more powerful than the lamps of the intermediate series which in turn are more powerful than the lamps of the central series.

18. Apparatus according to claim 17, wherein each row of lamps has an individual electrical supply system which is adjustable to vary the current value.

1 9. Apparatus for use in producing plastics armoured board, substantially as hereinbefore described with reference to the accompanying drawings.