NO792314L - PROCEDURE FOR THE MANUFACTURING OF ARMED ARTICLES AND APPLIANCES - Google Patents

Description

Process for the production of reinforced plastic sheets and apparatus for the production thereof.

The present invention relates to a method for the production of reinforced plates of plastic, in particular of polyolefins capable of crystallization, such as e.g. polypropylene or polyethylene, as well as a device for stabilizing reinforced plates of the aforementioned type.

The invention finds application in the production of packing materials for cardboard containers and heat-insulating substances.

The reinforced plate is made up of at least three layers, the outer ones being flat sheets between which the third layer is arranged in the form of a corrugated sheet. All three layers are tied together, whereby the corrugated sheet in the middle is in contact with both flat sheets along the entire length of the waves.

Another type of reinforced plate consists of two flat sheets connected to each other by means of short ribs. The reinforced plate made in this way shows a series of parallel channels and properties that come close to reinforced plates with a corrugated middle layer.

A known method for the production of reinforced

sheets of plastic are as follows: The plastic material is heated and extruded through a head equipped with an extrusion nozzle consisting of a series of separate cores whose shape determines the shape of the channels in the product.

Compressed air is introduced into the channels in the product through holes in the cores of the extrusion dies. The extrudate is then passed between two cooling surfaces.

The strip leaving the cooling device is cut to the desired shape.

Known devices for cooling the reinforced plastic sheet web consist of two parallel arranged steel blocks arranged one above the other at a distance corresponding to the thickness of the sheet web. Each block is equipped with bores parallel to each other and arranged perpendicular to the direction of movement of the flat track. A cooling medium is passed through certain of these channels, e.g. water, while the remaining channels through small holes connect with the space between the blocks and on the other side with a vacuum source. The reinforced plate web is passed between the blocks and remains in contact with the surface of these, which improves the cooling of the web and determines the thickness.

The reinforced plastic sheets must meet a number of basic requirements for use on an industrial scale. They must be sufficiently flat, free from bends and throws, and affordable enough to be able to withstand competition from corrugated cardboard sheets. Unfortunately, reinforced plates produced according to known methods and with relatively inexpensive plastics such as polyolefins, especially polypropylene and polyethylene, have a number of defects. Firstly, there is some swelling and throwing at the edges and likewise a significant unevenness in thickness measured across the web.

The object of the invention is to produce a method for the production of reinforced plastic sheets, especially of polyolefins capable of crystallization such as polypropylene or polyethylene, free of the above-mentioned defects and furthermore a

device for carrying out this procedure.

The method and device according to the invention make it possible to stabilize the plate web made of plastic, especially of poly-olefins, in a permanent and time-independent way so that the plates neither swell nor get thrown at the edges after longer storage.

The essential thing about the method according to the invention is that the extruded web is cooled in the calibrator more intensively in the middle part than along the edges and more intensively at the outlet of the calibrator than at the inlet.

The essential aspect of the invention also lies in a reheating of the plate track to temperatures of 40-120°C/ whereby the temperature in both surfaces in the reheating zone in the outer parts is higher than in the middle part and higher in the middle zone in the reheating tunnel than in the zones near the inlet and outlet of the tunnel.

The method according to the invention takes place as follows: Plastic material, especially polyolefins such as polypropylene or polyethylene, is heated and extruded through a

head equipped with an extruder nozzle consisting of a series of separate cores whose shape determines the shape of the channels in the plate web

which is extruded. To the channels in the web being extruded, compressed air is pumped through holes in the cores of the extrusion dies. The web being extruded is passed between two cooling surfaces in a calibrator, and the web is cooled more intensely in the middle part than at the canter area and more intensely at the outlet of the calibrator than at the inlet. After the calibrator has expired, the web remains at ambient temperature until the temperatures at each point in the cross-section have equalized.

The track is then subjected to a reheating at

a temperature within the range 4 0-120°C in a suitable tunnel, whereby the reheating is carried out in such a way that the web is reheated less intensely in the middle part than along the edges and more intensely in the middle zone of the tunnel than in the zones near the inlet and the outlet.

Preferably, the temperature in the surface in the middle part is 15-40°C lower than along the edge areas and resp. 15-40°C higher in the middle zone of the tunnel than at the zones near the inlet and outlet.

The reinforced sheets of plastic, especially of polyolefins, produced as indicated above, have little dispersion in terms of the base weights across and lengthwise of the web, and this dispersion amounts to + 3% of the average value, the web is furthermore completely flat and shows no traces of throw during or after long storage.

The device according to the invention consists of a calibrator 1 and a reheating tunnel 4 arranged at a distance that is at least three times the length of the calibrator, and of transport rollers 2 and 3. The working surfaces in the calibrator are cooled in the middle part more intensely than in the edge parts , more intense at the outlet than at the inlet. The space in the reheating tunnel is different in terms of heating so that the temperature in the middle part is lower than near the tunnel walls, and the temperature in the middle part of the tunnel is at the same time higher than at the zones near the inlet and outlet.

The calibrator according to the invention comprises two identical units consisting of metallic blocks placed parallel above each other. In the center of each block parallel to the longitudinal axis, there is at least one channel separated from the end of the calibrator unit. To this channel and along both sides of it, a number of other parallel channels are arranged which along the block sides are connected to two common collectors parallel to the block's longitudinal axis.

In the blocks, the space between the surfaces is the working space in the calibrator. Flat iron and plates are welded to opposite surfaces of the blocks so that two are formed. chambers. Between the chambers, numerous holes are arranged in the blocks which connect the working space in the calibrator with the chambers, which in turn are connected to a vacuum pump.

The reheating tunnel according to the invention has the form of a flat rectangular prism consisting of. plates and equipped with narrow, elongated slit-like openings in both front walls. The plane determined by the slit openings divides the interior of the tunnel into two parts. At the bottom of each part, flat infrared lamps are arranged in a row perpendicular to the longitudinal axis of the tunnel, whereby the lamps that have the same place in the row form a series that runs parallel to the longitudinal axis of the tunnel. The infrared lamps in the outer series are the strongest, and those in the middle are the weakest. The infrared lamps which are arranged in the same row are equipped with a common supply line.

The method according to the invention shall be exemplified below.

Example 1

Polypropylene of the "DAPLEN EE" type with a pour coefficient of 0.4 g/10 min was heated and extruded through a head equipped with an extrusion die consisting of a series of separate cores and having a rectangular cross-section, whereby the shape determined the rectangular form of channels in the plate web that was extruded. Compressed air was supplied into the channels of the web thus extruded through holes in the core of the extrusion die. The extruded web was fed between two surfaces in a calibrator arranged 5 mm apart, and cooled more intensely in the central part than along the edges and more intensely at the outlet of the web from the calibrator than at the inlet.

The desired distribution of the cooling intensity on the surfaces in the calibrator was ensured by constructing the calibrator from two identical metal blocks arranged parallel above each other. The width of the calibrator was somewhat greater than the width of the track

which was extruded, and the length was equal to 0.75 of the band width.

In the center of each block, symmetrical about the longitudinal axis, two cylindrical channels were arranged, plugged from the extrusion head side.

Each of the channels was connected by means of a series of these vertical channels and along both sides of the block connected by means of a common collecting channel parallel to the longitudinal axis of the block.

On non-working surfaces of the block, flat chambers consisting of plates were welded on. In the block between the channels was

it made many small holes that connected with the working space in the calibrator and the chamber in the blocks.

Into the cylindrical channels in each of the blocks in the calibrator, plugged from the extrusion head side, de-mineralized water with a temperature of 12°C was led upstream of the web being extruded. The water then flowed through the channels perpendicular to the direction of movement of the track and through the collection channels on both sides of the blocks and was then released into a closed circulation system. The water that came out of the collection channels held 25°C.

At the same time, the chambers in both blocks were connected to a vacuum pump which held 20 mm of mercury in the chambers.

After the web came out of the calibrator, it was kept at room temperature until the temperature throughout the cross-section had equalized.

The track was then subjected to a reheating step to a temperature of 50-100°C in a flat tunnel. whereby the heating was carried out in such a way that the web was reheated less intensely in the middle part than along the edges and less intensely in the zones near the inlet and the outlet than in the middle zone.

The surface temperature of the web in the middle zone was 70°C in the middle of the web and increased to 100°C near the edges. in the outlet zone of the tunnel the temperature was equal to 50-70°C, and the total re-heating time for the track was equal to 70 sec.

The track in the tunnel was heated from above and below using infrared lamps of 250, 400, 650 and 1000 W arranged in nine rows parallel to the track's direction of movement in groups of

7 in each row.

The infrared lamps in the same position in the rows formed series that ran parallel to the track's direction of movement. The 1000 W lamps were arranged in the outermost series, the 650 W lamps in the following series, the 400 W lamps in the next two series and the 250 W lamps in the middle series.

Each of the nine rows was equipped with a common current source with infinite variability of the current intensity.

The central row was fed with a current of the highest intensity and this gradually decreased in successively following rows. The current to the outermost rows was not significantly above half the value of the current intensity for the middle row.

The temperature in the lane at the outlet was measured using a non-contact thermometer. The temperature in the middle row was determined by the color change of a strip painted on the plate surface, which changes color depending on the temperature. After exiting the reheating tunnel, the web was cooled to ambient temperature and cut into the desired shape.

The obtained reinforced plate consisting of polypropylene showed a basis weight of 85G g/m 2 +3%, the compressive strength of the plate was. .3.6 kgf/cm and the breaking strength at 50 C 15 kgf/cm . The plates were completely flat and showed no signs of warping either during or after storage for several days.

Example 2

A reinforced plate was produced from a copolymer of propylene and ethylene and with an leakage coefficient of 0.7 g/10 min and which was commercially available under the designation "MOPLEN EPQ-30M", in the same way as in ex. 1, except that the heating was carried out at a temperature that was 5-10°C lower, while the heating time was 60 sec.

The sheet obtained showed a basis weight of 860 g/m 2 +2.8%

and the flat press strength was 3.2 kgf/cm .

The stabilization device consisting of the calibrator

and the reheating tunnel according to the invention shall be described by means of an example of an embodiment with reference to the accompanying drawings in which

fig. 1 shows a stabilization device for reinforced plates made of plastic;

fig. 2 shows a perspective view of the calibrator;

fig. 3 shows a cross-section of the base unit in the calibrator

in a plane parallel to the work surface;

fig. 4 is a longitudinal section of the base unit in the calibrator along the line A-A in fig. 3, and

fig. 5 is a perspective view of the reheating tunnel, partially in section.

The stabilization device according to the invention consists of

of the calibrator 1, the transport rollers 2 and 3 and the reheating tunnel 4.

The distance between the reheating tunnel and the calibrator, measured from the downstream end of the calibrator and the upstream end of the tunnel, amounts to 5 calibrator lengths.

in-

The calibrator consists of two identical units 5 placed parallel above each other. The distance between the working surfaces is adjusted using an adjustment device depending on the thickness of the web being produced. The lower unit is firmly connected to the horizontal support frame 6. At the corners of the frame, four screws 7 are arranged, and to the upper unit four square lugs 8 equipped with an opening corresponding to the outer diameter of the screw are welded. The screws are intended for engagement with nuts 9 for use in adjusting the distance between the working surfaces in the calibrator. Each of the units is equipped with nozzles 10, 11 for supplying and removing refrigerant and 12 for connection to vacuum.

Each unit in the calibrator consists of the metal block 13 and the flat chamber 14 consisting of angles and. plates, welded to the block from a side opposite the working surface. In the middle of the block and symmetrically with the longitudinal axis, two cylindrical channels 15 are arranged, sealed from one end, and at the other end via a cylindrical chamber 16 connected to the spigot 11. Each of the channels 15 is in connection with a series perpendicular to it arranged channels 17 connected along the sides of the block by means of a common collecting channel 18 parallel to the longitudinal axis of the block. In the blocks between the channels, numerous holes 19 are arranged which connect the working space in the calibrator with the chambers in the units.. Water supplied to the connection 16 flows successively through the channels 15 and 16, and from the collection channels 17 the water is removed again through the connections 10.

The reheating tunnel has the shape of a flat rectangular prism consisting of plates and is thermally insulated and equipped with slit ports 20 in both front walls. By means of the plane determined by the slit openings, the interior of the tunnel is divided into two parts, the upper 21 and the lower 22. At the bottom of each of these parts, infrared lamps 23 are arranged with a strength of 250, 400, 650 and 1000 W, in nine rows vertically on the longitudinal axis of the tunnel with 7 lamps in each row. The lamps that have the same position in the rows make up series of nine lamps in each series. The infrared lamps in the outermost series 24 are of 1000 W each, in the adjacent series of 650 W each, in the next series of 400 W each and in the middle series of 250 W each. Each of nine rows is connected to a common feed system with infinitely variable regulation of the current intensity by means of suitable devices 25. The tunnel is permanently connected to the horizontal support frame 26.

Claims (3)

1. Process for the production of reinforced sheets of plastic, in particular of polyolefins, comprising extruding heated polymer through a head equipped with an extrusion die consisting of a series of separate cores whose shape determines the shape of channels in the web being extruded, supply of compressed air to the channels in the path that is extruded through holes in the cores of the extrusion dies and guiding the extruded path between two cooled surfaces in a calibrator, characterized in that the path is cooled more intensely in the middle part than along the edges and less intensely at the inlet to the calibrator than at the outlet from it, and that the track is then subjected to reheating to a temperature within the range of 40-120°C, whereby the track is reheated less intensely in the middle part than along the edges and more intensely in the middle zone of the tunnel than in the zones near the inlet and outlet. 2. Method according to claim 1, characterized in that the surface temperature in the reheated track is 15-40°C lower in the middle part than along the edges and 15-40°C higher in the middle zone than in the zones near the entrance and exit to the tunnel. 3.. Device for stabilizing a reinforced sheet track made of plastic, in particular of polyolefin, comprising a calibrator, characterized in that it comprises a calibrator and a reheating tunnel arranged at a distance from each other of more than three lengths of the calibrator, that h <y> is unit in the calibrator consists of a metal block (13) and a chamber (14), whereby at least one channel (15) is arranged in the block parallel to the longitudinal axis to which a number of other parallel channels (17) are connected, interconnected by the collecting channel (18), and that holes (19) are arranged between the channels that connect the working space in the calibrator with the chambers (14), and that the reheating tunnel is divided using the plane determined by the slit-like areas into two parts, each of which is equipped with infrared lamps (23) arranged in rows in such a way that the lamps that have the same position in the rows form series, whereby the infrared lamps in the outermost series (24) exhibit the highest power and those in the central series show the lowest power, and the infrared lamps in the same series are equipped with a common feed system with infinitely variable regulation (25) of the current value.