FR2548085A1 - Cooling device and manufacturing process for plastic film obtained by blowing tubing - Google Patents

Abstract

The cooling device for plastic film obtained by blowing tubing comprises, at its intermediate part, an intensive-blowing ring 10, the flux 9 of which is directed perpendicular to the tubing 1, in its upper part a top chamber 14 and 15 in which the tubing is in contact with an air flux directed tangentially to the said tubing and is characterised in that it furthermore comprises, in its lower part, a non-closed bottom chamber 3 and 4 equipped with at least one opening which can be adjusted by means of a system 5 of adjustable openings. The process for manufacturing plastic film by blowing tubing comprising on the one hand a step of extrusion-blowing of molten plastic coming from an extruder die and, on the other hand, a step of cooling the blown tube thus obtained, is characterised in that the cooling step is achieved by passing the tubing through the abovementioned device. Advantageously, the ratio of the air flowrate sucked into the bottom chamber to the air flowrate introduced into the blowing ring is between 0.1 and 0.5.

Description

 The present invention relates to a cooling device and a method for manufacturing plastic sheets obtained by blowing the sheath.

 There is already known a device for obtaining the blown sheath sheet of good clarity, consisting of a set of three juxtaposed elements; it is composed, following the path of the sheath, at its lower part, a closed chamber called annealing, then at its intermediate portion, an intensive blow ring whose air flow is directed perpendicularly at the sheath, this ring having the function of accelerating the solidification of the material, and finally at its upper part of an upper chamber in which the sheath is in contact with a flow of air directed tangentially to said sheath.

 Such a device has already been described in the European patent application published under the number 0 041 803. This device allows to extrude sheets of polyethyl # ne at an inflation rate of 2. However it has the disadvantage of not not allow a satisfactory extrusion of polyethylene sheets with an inflation rate higher than 2, cowtse is demonstrated zanis the comparative examples 5i after. On the other hand such a device has the disadvantage of being able to improve the optical properties of the sheath only for resins, such as polyethylene low density radical, ethylene / vinyl acetate copolymer and linear low density polyethylene, whose properties optics were already relatively satisfactory. By satisfactory optical properties for the application to the manufacture of sheaths is meant a haze (determined according to ASTM D 103-77) of not more than 7%. Finally, a final disadvantage of this device lies in the impossibility of improving the optical properties of the rod (compared to a conventional cooling system) while ensuring a high flow rate of material.

 The present invention aims to allow more efficient cooling when. the need arises and therefore to obtain blown sheaths of good optical properties, including clarity, haze, at a high flow rate and for a large number of resins.

 The device according to the invention comprises, at its intermediate part, an intensive blowing ring whose flow is directed perpendicularly to the sheath, this anneanzyant for accelerating the solidification of the material, at its upper part a high chamber in which the sheath is in contact with a flow of air directed tangentially to said sheath, and it is characterized in that it further comprises at its lower part an unclosed lower chamber provided with at least one opening, each opening of said non-closed chamber that can be adjusted by means of a system consisting for example of perforated discs.

In addition, said non-closed bottom chamber may have an adjustable height, advantageously obtained by a series of interlocking elements of different heights. In the same manner, the upper chamber may have an adjustable height advantageously obtained by a series of interlocking elements of different height.

 In order to better understand the invention will now be described by way of illustration and without further limiting an embodiment as an example and shown in the single figure in the appendix showing a sectional view of the device.

 The sheath of material 1 is obtained from molten material from the annular die 2, following the path of the material from the die, the sheath is first cooled moderately in the lower chamber consisting of at least two 3 and 4 interlocking elements, this chamber comprises at its lower part a system of adjustable openings 5 for adjusting the intake of sucked air 6 under the effect of the depression generated by the air flow 7 projected in the upper chamber constituted by elements 14 and 15; in this first part the sheath is cooled moderately by the air stream 8 and does not undergo significant dimensional changes. The sheath is then cooled violently by means of an air jet 9 coming out of the blowing ring 10, the direction of this jet being perpendicular to said sheath 1.After being released from the blowing ring 10, the sheath arrives in the upper chamber consisting of at least 2 interlocking elements 14 and 15, in which there is a flow of air from the blowing ring 10 through orifices 11 allowing the air to exit according to the flows 7 in the upper chamber formed by the elements 14 and 15 in the direction tangential to the sheath 1, the flow rate of the air flow 7 being modifiable by means of the adjustment system 12. It is in this upper chamber that the sheath takes its final dimension under the action of the air pressure inside it, the air pressure is introduced by the pressurizing tube 16. Finally the sheath is permanently solidified and drawn to average of the drive system 17.

 A second object of the invention consists in a process for manufacturing plastic sheets by blowing a sheath, comprising on the one hand a step of extrusion blow molding of molten plastic material originating from an extruder die and on the other hand a cooling step of the blown sheath thus obtained, characterized in that the cooling step is carried out by passing the sheath through a device of the type previously described. In particular, it is advantageous that the ratio of the air flow sucked into the low chamber to the air flow introduced into the blowing ring is between 0.1 and 0.5.

 The method according to the invention has the advantages of obtaining films of good properties (clarity, haze) from resins such as radical polyethylene, high density polyethylene, polypropylene, polybutene-1, linear low density polyethylene and mixtures thereof, having a melt index (determined according to ASTM D 1238/73) of between 0.1 and 10 dg / min. In particular, the process according to the invention makes it possible to produce films having good optical properties from radical polyethylene having a melt index greater than 3 dg / min, whereas this resin has hitherto been reserved for the manufacture of objects. In addition, this method also makes it possible to obtain films with significantly higher flow rates and / or inflation rates than those authorized by the process of European Patent Application No. 0 041 803. In order to obtain to better understand the advantages of this method over the prior art, the following examples are given for illustrative and not limiting.

EXAMPLES 1 to 4
Films 40 m thick are made by extrusion blow molding of molten plastic material from the extruder die, and then cooled by the device described above and shown in the appended figure. The characteristics of the die and the cooling device are as follows: die with a diameter of 50 mm and a gap of 0.5 mm.

- cooling device: height of the lower chamber: 250 mm,
height of the upper chamber: 250 mm
The ratio k of the air flow sucked into the lower chamber to the air flow introduced into the blowing ring is shown in Table I below.

The inflation rate TG (ratio of the diameter of the sheath to that of the die, and the flow rate of material Q (expressed in kg / hour) are those also indicated in Table I below.

The material used is a radical low density polyethylene marketed under the trade name Lotrene FA 0401 (manufactured by CdF Chimie) having a melt index of 4 dg / min (measured according to SSTM standard D 1238-73) and a density of 03918.

In Table I are further indicated - the extrudability noted (+) when the blown sheath is free from optical defects such as scratches, denoted (-) when the blown sheath has such optical defects.

the result of the measurements of clarity (C3, expressed in% and determined according to the ASTM D 1746-78 standard.

TABLE I

<tb> Example <SEP> Q <SEP> TG <SEP> R <SEP> E <SEP> C
<tb><SEP> 1 <SEP> 3 <SEP> 2 <SEP> 0.47 <SEP> + <SEP> 46
<tb> 2 <SEP> 6.9 <SEP> 2 <SEP> 0.49 <SEP> + <SEP> 41
<tb> 3 <SEP> 4.1 <SEP> 3.2 <SEP> 0.13 <SEP> + <SEP><SEP> 62
<tb> 4 <SEP> 6.9 <SEP> 3.2 <SEP> 0.15 <SEP> + <SEP> 49
<Tb>
COMPARATIVE EXAMPLES 1A TO 4A
Films having a thickness of 40 ssm are manufactured by extrusion blowing the same plastic material as that used in Examples 1 to 4 above, and then cooling by means of a device of the type described in European Patent Application No. 004 041. 803. In Table II below are reported on the one hand the operating conditions such as Q, TG and R, and on the other hand the results of properties obtained on the blown sheath.

TABLE II

<tb> Example <SEP> Q <SEP> TG <SEP> R <SEP> E <SEP> C
<tb> lA <SEP> 3 <SEP> 2 <SEP> 0 <SEP> - <SEP> 38
<tb> 2A <SEP> 6.9 <SEP> 2 <SEP> 0 <SEP> - <SEP><SEP> 36
<tb> 3A <SEP> 4.1 <SEP> 3.2 <SEP> 0 <SEP> - <SEP><SEP> 61
<tb> 4A <SEP> 6.9 <SEP> 3.2 <SEP> 0 <SEP> - <SEP><SEP> 41
<Tb>
EXAMPLES 5 to 8
The material used is low-density radical polyethylene marketed under the trademark Lotrène FB 5026 (manufactured by
CdF Chemistry) having a melt index of 0.6 dg / min (measured according to the standard ASIM D 1238-73) and a density of 0.921. In Table III below, the operating conditions such as Q, TG and R are reported. that the results obtained on the blown sheath 40 m thick.

TABLE III

<tb> Example <SEP> Q <SEP> TG <SEP> R <SEP> E <SEP> C
<tb><SEP> 5 <SEP> 3 <SEP> 2 <SEP> 0.14 <SEP> + <SEP> 16
<tb><SEP> 6 <SEP> 6.8 <SEP> 2 <SEP> 0.18 <SEP> + <SEP> 16
<tb><SEP> 7 <SEP> 3 <SEP> 3,2 <SEP> 0,26 <SEP> + <SEP> 21
<tb><SEP> 8 <SEP> 6.8 <SEP> 3.2 <SEP> 0.11 <SEP> + <SEP> 20
<Tb>
COMPARATIVE EXAMPLES SA to 8A
40 m thick blown sheath was made by extrusion blow molding from the same plastic material used in Examples 5 to 8; but this time taking, to cool the sheath, a device of the type described in European Patent Application No. 0 041 803. The operating conditions as well as the results obtained are reproduced in the table TV below, in which FIG. quoted extrudability (0) indicates that blown duct can not be obtained.

TABLE IV

<tb> Example <SEP><SEP> Q <SEP> TC <SEP><SEP> R <SEP> E <SEP> C
<tb><SEP> SA <SEP> 3 <SEP> o <SEP> 2 <SEP> 0 <SEP> - <SEP> 11
<tb><SEP> 7A <SEP> 3 <SEP> 3,2 <SEP> 3,2 <SEP> 0 <SEP> o
<tb><SEP> 8A <SEP> 6.8 <SEP> 3.2 <SEP><SEP> O <SEP><SEP> - <SEP><SEP> 20
<tb><SEP> i <SEP><SEP>
<Tb>
COMPARATIVE EXAMPLES 9 and 9A
In Table V below are reported the results obtained on linear low density polyethylene marketed under the trademark Lot rex FW 1290 (manufactured by CdF Chimie), having a melt index ldg / min and a density of 0.919. equal to 3 kg / h and the inflation rate is 2. In Example 9, the cooling system is the device described above; in Example 9A it is of the type described in European Patent Application No. 0 041 803.

T represents the disorder expressed in% and determined according to ASTM standard
D 103-77.

TABLE V

<tb> Example <SEP> E <SEP> R <SEP> T
<tb><SEP> 9 <SEP> + <SEP> 0.36 <SEP> 6.7
<tb><SEP> 9A <SEP><SEP> - <SEP> 0 <SEP> 7.6
<Tb>

Claims (9)

 1. Device for cooling plastic sheets obtained by blowing the jacket comprising at its intermediate portion an intensive blowing ring whose flow is directed perpendicular to the sheath, at its upper part a high chamber in which the sheath is in contact with a flow air.directed tangentially to said sheath, characterized in that it further comprises at its lower part an unclosed lower chamber provided with at least one opening.  2. Cooling device according to claim 1, characterized in that at least one opening of the unclosed lower chamber is adjustable.  3. Cooling device according to claim 2, characterized in that said opening is adjustable by means of a disk system with holes.  4. Cooling device according to one of claims 1 to 3, characterized in that the height of said unclosed lower chamber is adjustable.  5. Cooling device according to one of claims I to 4, characterized in that the height of the upper chamber is adjustable.  6. A method of manufacturing plastic sheets by blowing sheath, comprerItant firstly a step of extrusion blow molding of molten plastic material from a die e # ruder and second step of cooling the sheath blown thus obtained, characterized in that the cooling step is carried out by passing the sheath through a device according to one of claims 1 to 5.  7. Method according to claim 6, characterized in that the ratio of the air flow sucked into the low chamber to the air flow rate introduced into the blowing ring is between 0.1 and 0.5.  8. Method according to one of claims 6 and 7, characterized in that the plastic is a resin selected from polyethylene, polypropylene, polybutene-1 and mixtures thereof.  9. Method according to claim 8, characterized in that the melt index of said resin is between 0.1 and 10 dg / min.