GB2201371A

GB2201371A - Apparatus for producing tubular thermoplastic biaxially oriented film

Info

Publication number: GB2201371A
Application number: GB08729709A
Authority: GB
Inventors: Fritz Blom
Original assignee: Windmoeller and Hoelscher KG
Current assignee: Windmoeller and Hoelscher KG
Priority date: 1987-01-02
Filing date: 1987-12-21
Publication date: 1988-09-01
Also published as: DK695087A; CN87108289A; DK695087D0; GB8729709D0; JPS63188027A

Abstract

The apparatus comprises braking and retaining means (4, 5), expanding means for expanding the film in its peripheral direction, take-off means (17) for taking off at a speed which exceeds the feeding speed, and means (4, 5, 14, 16) for heating and cooling the film. The braking and retaining means consists of pairs of pinch rollers (4, 5, 6) (4) on which the flattened film forms a loop. These rollers are driven at a predetermined surface speed or are provided with brakes having adjustable braking torques. These rollers are succeeded by spaced, diverging pairs of expanding plates (6) and flattening plates, (7). Each pair of expanding plates and flattening plates is preceded or succeeded in each case by a pair of pinch rollers, between which the continuous tubular film is adapted to form a parison. The succeeding rollers, for stretching and/ or deflecting (16), guide the flattened film in the form of loops whereby the film is taken off from the parison at a speed which exceeds its feeding speed. <IMAGE>

Description

APPARATUS FOR PRODUCING TUBULAR FILMS OF SYNTEHTIC THERMOPLASTICS MATERIAL WHICH IS QUASI-BIAXIALLY ORIENTED This invention relates to apoaratus for oro- ducina tubular films of synthe .c thermoplastics material which is ouasi-biexiallv oriented, including braking and retaining means for releasing the continuously withdrawn continuous tubular film against a predeterminable resistance, exoanding means for exoanding the continuous tubular film in its peripheral direction, take-off means for taking off the continuous tubular film from the expandinq means at a steed which exceeds the feeding soeed, and means for first heating and then cooling the continuous tubular film which is oriented in its peripheral and longitudinal directions.

Prior German Patent #pplication P 36 15 445.6-15, which isnot a prior publication, discloses such an apparatus in which the expanding means and the heating and cooling means are constituted by a mandrel, which is provided with cooling sections and with heating sections. In order to ensure that the continuous tubular film which has been pulled onto the mandrel and has been exoanded can be oriented in that it is taken off at a speed which exceeds its feeding speed, the mandrel is pro- vided with braking means, which consist of a suction rinq that corresoonds to the tubular film in diameter and is provided with suction openings.

Whereas the known expanding mandrel, which is provided with cooling and hEE;ino sections, c=n be arrane e5iEtElv behind the annular extrusion die which produces the Plastic tu#ino, t',,e knawn aooaratus is relatively cornolicated and expensive in its structure and difficulties are also involved in the handling and control of the known apparatus.

There is thus a need for a generally improved apparatus for producing tubular films of synthetic thermoplastics material which is simpler in structure and can be controlled and handled more easily.

According to the present invention there is provided apparatus for producing tubular films of synthetic thermoplastics material which is quasi-bi-axially oriented, including, braking and retaining means for releasing a continuously withdrawn continuous tubular film against a predeterminable resistance, expanding means for expanding the continuous tubular film in its peripheral direction, take-off means for taking off the continuous tubular film from the expanding means at a speed which exceeds the feeding speed, and means for first heating and then cooling the continuous tubular film which is oriented in its peripheral and longitudinal directions, wherein the braking and retaining means consist of pairs of pinch rollers, which constitute retaining rollers, and/or of deflecting rollers which are so offset from each other that the flattened continuous tubular film forms a loop as it is trained around each of the deflecting rollers disposed between adjacent deflecting rollers, the pairs of pinch rollers and/or the deflecting rollers are driven at a predetermined surface speed or are provided with brakes having adjustable braking torques, the retaining rollers are succeeded in the direction of travel by spaced apart pairs of expanding plates and flattening plates, which in each pair diverge toward the respective other plates, each pair of expanding plates and flat- teninp plates is preceded and succeeded by a pair of pinch rollers, between which the cqntinuous tubular fil is inflatable with E predetermined trans- versE stretch ratio to for 2 parison and the pairs of flattening dates Cr:: suc ceded in the direction of travel by pairs of pinch rollers, which constitute stretchino rollers end/cr deflect- ing rollers for guiding the flattened continuous tubular film in thE form of loops which are oven in mutually apposite directicr#, whereby the continuous tubular film is taken off from the parison at 2 speed ##hich exceeds its feeding speed.

Thus tte apparatus of the invention has E simple structure because the continuous tubular film is flattened before it is Expanded and is expanded merely in that it is inflated to form a parison. Besides, in the apparatus of the invention the continuous tubular film is stretched between retaining and stretching rol lers in a simple manner and with the desired stretch ratio.

The apparatus of the in vention can even be used to impart a quasi-biaxial ori entation to tubular films which have previously been wound up to form rolls. The apparatus of the in vention may alternatively be arranged immediately after a blow-molding slant for making tubular films if the con tinuous tubular film is flattened before.

Preferably means for applying hot air for heating the parison are suitably provided between the expanding plates and the flattening plates. The means for applying hot air may consist of spaced aoart, annular air-distri- buting and air-collecting chambers, which are intercon nected by a cylindrical shell, which together with the parison defines an annulus, and said eir-distributinq and air-collecting chambers may be interconnected by E heating fan for circulating and reseating the hot air.The air distributinp and Bir-Collecting chambers preferably are located so that the hot air flows in contact with the outside surface of the continuous tubular film oooosite to the- #irection of travel of the latter.

Advantageously each of the air-distributing and air-collectinq chambers may be sealed on the outside against the incoming and out going continuous tubular film by annular baffles, which are adjustable in diameter like an iris diaphragm.

Conveniently at least one the retaining rollers which precede the expanding and flattening plates is heatable. Said heatable roller or rollers may be used to preheat the still flattened continuous tubular film.

The means for cooling the continuous tubular film which has been heated and which is #uasi-bi- axially oriented may consist of cooling rollers. For that purpose at least one of the stretching rollers which succeed the expanding plates and flattening plates may constitute a cooling roller.

For a better understanding of the present invention, and to show how the same may be carried into effect, reference will now be made to the accompanying single figure drawing which is a dia grammatic representation of an apoaratus for ouasi-biaxially stretching continuous tubular filmssaccording to the invention.

tubular film which is not yet oriented is withdrawn from a roll 1, which consists of a tubular film and is held in an unwinding device. The tubular film is supolied to non-heated retaining mechanism 2 and is then delivered via guide rollers 3 to the oreheatino rollers 4 and further to the pinch rollers 5. An expanding station 6 which is adjustable in heiqht is disposed below said pinch rollers 5 and consists of two rollers and of two plates, which are oblique to each other. The tubular film is inflated to form E parison between said expanding station, which is adjustable in height, and the lower flattening means 7. The parison 8 is surrounded by a cylindrical housing 9, which comprises upper and lower air-collecting chambers 11.The air-collecting chambers 10 and 11 are succeeded by upper and lower iris diaphragms 12 and 13 for effecting a seal in spite of the different diameters of the tubing. Heated air is blown from an air heater 14 into the lower air-collecting chamber 11 and flows in contact with the film opposite to the direction of travel of the film. The air then enters the upper air-collecting chamber 12 and is sucked from the latter by a fan 15, from which the air is returned to the air heater 14. The film which has thus been biaxially stretched is moved through a stretching mechanism 16, which comprises feed rollers and temperature control rollers and is subsequently rewound by a winder 17.

The means for adjusting the expandinq means 6 in height may be designed as is known from German Patent Application 20 52 127 and from the corresponding U.S. Patent 3,804,572. The expanding means 6 are adjustable in height in order to ensure that the parison will always have the same diameter even if air escapes from the standing parison during operation.

If the entire stroke of the expanding means which are adjustable in height has been utilized, additional- air must be supolied. This may be effected, e.g., by means such as are known from German Patent Specification 31 19 005, and from the corresponding U.S.

Patent 4,462,779, the disclosures of which are incorporated herein by reference.

Claims

1. Apparatus for producing tubular films of synthetic thermoplastiz material which is oussi-bi- axially oriented, -incle~ing, braking and retaining means for r2leasino a continuously withdrawn continuous tubular film against å predaterminable resistance, expanding means for expanding the continuous tubular film in its peripheral direction, take-off means for taking off the continuous tubular film from the expanding means at a sosed which exceeds the feeding soled, and means for first heating and then cooling the continuous tubular film which is oriented in its peripheral and longitudinal directions, wherein the braking and retaining means consist of pairs of pinch rollers, which constitute retaining rollers, and/or of deflecting rollers which are so offset from each other that the flattened continuous tubular film forms a loop as it is trainedaround each of the deflecting rollers disposed between adjacent deflecting rollers, the pairs of pinch rollers and/or the deflecting rollers are driven at a predetermined surface speed or are provided with brakes having adjustable braking #torques, the retaining rollers are succeeded in the direction of travel by spaced apart pairs of expanding plates and flattening plates, which in each pair diverge toward the respective other plates, each pair of exoandinq plates and flattening plates is oreceded and succeeded by a pair of pinch rollers, between which the continuous tubular film is inflatable zith e predetermined transverse stretch ratio to form, a parison end the pairs of flattening dates are suc ceded in the direction of travel by pairs of pinch rollers, which constitute stretching rollers end/or deflecting rollers for guiding the flattened continuous tubuler film in the form of loops which are open in mutually opposite directions, whereby the continuous tubular film is taken off from the parison at 2 speed which exceeds its feeding speed.

2. Apper tus according to claim 1, wherein means for applying hot air for heating the pariscn are provided between the expending plates and the flattening plates.

3. Apparatus according to claim 2, wherein the means for applying hot air consist of spaced apart, annular air-distributing and air-collecting chambers, which are interconnected by a cyl,indrical shell, which together with the parison defines an znnulus, and wherein said air-distributing and air-collecting chambers are interconnected by a heating fan for circulating and reheating the hot air and are located so that the hot air flows in contact with the outside surface of the continuous tubular film opposite to the direction of travel of the latter.

4. Apparatus according to claim 3,wherein each of the air-distributinq and air-collec tino chambers is sealed on the outside against the incoming and outgoing continuous tubular film by annular baffles, which are adjustable in diameter like an iris diaphragm.

5. Apparatus accordino to cairn 1, wherein at least one of the retaining rollers which precede the expanding plates and flattening plates is heatable.

6. Apparatus according to claim 1, wherein at least one of the stretching rollers which succeed the expanding plates and flattening plates constitutes a cooling roller.

7. Apparatus for producing tubular films of synthetic thermoplastics material which is quasi-biaxial- ly oriented, substantially as hereinbefore describes with reference to and as shown in the accompanying arawing.