FR2498981A1 - LINE FOR THE PRODUCTION OF FILMS BY EXTRUSION - Google Patents

Abstract

THE PRESENT INVENTION CONCERNS A T-EXTRUSION DIE FOR PRODUCING TRANSPARENT FILMS IN A SYNTHETIC RESIN, HAVING A UNIFORM THICKNESS AND THE EDGES OF WHICH HAVE NO THICKNESSES. THIS DIE INCLUDES A BODY 1 INCLUDING A SLIT-SHAPED PASSAGE 3 THROUGH THE FUSION RESIN, LIPS FORMING A SLOT-SHAPED OUTLET ORIFICE, INTERIOR GUIDES 6 MAINLY SERVING TO VARY THE THICKNESS OF THE EDGES OF THE FILM RESULTANT EXTRUDED, AND RODS 7 TO ADJUST THE WIDTH OF THE RESULTING EXTRUDED FILM, AND IS CHARACTERIZED IN THAT THE INTERIOR GUIDES 6 ARE HOLLOWED LONGITUDINALLY AT THEIR LOWER END, SO AS TO PRESENT A SEMI-CIRCULAR SECTION AND THIS 7 CORRESPONDENTS HAVE A CIRCULAR SECTION AND ARE PLACED SO THAT THE LOWER END OF THE CORRESPONDING GUIDE 6 EMBRACES THE UPPER PART OF THE ADJACENT ROD 7 LEAVING A CERTAIN INTERVAL, PREFERABLY OF 0.1 TO 0.3MM BETWEEN THEM.

Description

The present invention relates to an extrusion die perfection-

  made of T suitable for extrusion production of films or sheets

  a thermoplastic material, such as polyethylene, and more particularly

  an advanced T-extrusion die suitable for the high-yield production of relatively thin films of uniform thickness and

  whose edges have no bulges.

  Two processes are known for producing resin films by extrusion, in particular polyethylene or polypropylene films, the first being an inflation method and the second a method using a T-die. The second method, that is, the one using a T die, has been widely used for the manufacture of impermeable plastic bags,

  especially for fertilizer packaging, by attaching a film of synthetic resin

  heated tick and a sheet of metal, "Cellophane" or craft paper, then

  by pressing them against each other.

  The present invention, which proposes a new die for producing films by extrusion, will be described below in a nonlimiting embodiment, with reference to the appended drawings, in which:

  FIG. 1 is a front view of a conventional T-extrusion die.

  2 is a partial sectional view, on a larger scale, taken along line I-I of FIG.

  FIG. 3 is a front view of a T-extrusion die con-

  form to the present invention; - Figure 4 is a sectional view taken along the line II-II of Figure 3; and FIG. 5 is a partial sectional view, on a large scale, of the lower part of the die of FIG. 4, showing the shaped passage

  cleft and lips this one.

  Referring to Figures I and 2, there is shown a conventional T-extrusion die which comprises, at each end of the T-shaped body 1 ', an inner guide

  6 ', these two guides being adjustable so as to allow the thickness to be varied.

  edge of the resulting extruded film, in order to obtain a film

  cule of uniform thickness having no extra thickness along its edges,

  these thickeners being described hereinafter as "marginal oversize".

  Each inner guide 6 'is supported by an L-shaped support rod 5' which is connected to a plate 5 ''. In addition, a rod 7 'is provided immediately under each of the inner guides to adjust the width of the extruded film

  resultant. Each of the support rods 5 'is fixed to the inner guide cor-

  corresponding 6 'in a slot-shaped passage 3' of the body 1 'of the die, the guide 6' being able to move in the passage 3 'so as to move away from or approach the end of the body 1 . The molten resin, coming from an extruder A ', is introduced into a collector 2' from which it passes to

  through the slot-shaped passage 3 ', from which it exits through an evacuation orifice

  4 'has the form of a long narrow slot to produce a film; so,

  it is easy to understand that the inner guide 6 'and the inner rod 7' of this

  ci, are exposed at both ends of the body 1 'of the die, at very high pressures by the resin, so that the first is pushed down against

  the second and comes close against it, with the result that

  state that the movement of the rod 7 'is made very difficult and sometimes almost impossible. Under these conditions, it takes a long time to adjust the width of the resin stream using the rod 7 'of the inner guide if

  difficult to move, or we have to interrupt the extrusion operation.

  because of the complete immobility of the rod 7 ', which decreases very

  drastically the performance of the operation. In addition, when the molten resin from the extruder A 'passes through the collector 2', the transition to form

  slot 3 'and the slot-shaped discharge port 4'a between the ends

  lips 4 ', in order to be shaped into a film called super

  When applied to a substrate, for example paper, the resulting laminate has marginal extra thicknesses on both sides. These extra thicknesses (which can

  30 mm width, for example) are then cut and

  Marginal sutures thus cut are then driven out by a blower (not shown) to finally be rolled up as waste on a reel.

  driven by a variable speed motor (not shown). We understand easily

  This represents the loss of a considerable percentage of resin used

  and waste of electrical energy.

  Moreover, in the conventional T extrusion die, the molten resin entering the space designated by the reference "X" in FIG. 2 solidifies in contact with the air and adheres to the surfaces surrounding this space. X. It follows from this that the molten resin from the extruder A 'forms a current

  irregular, and consequently produces a film whose transparency and uniformity

  Thickness form is not satisfactory until the solidified resin has been removed. Until now, we tried to remove this solidified resin, more or less oxidized or scorched. However, it is difficult to perform this operation regularly and to remove the oxidized resin, in particular

  that present in the space referenced X, using a metal rod

  line, which introduces a considerable loss of time in the whole of the production operation of the film. It should also be noted that the resulting films nevertheless have the aforementioned drawbacks, since the oxidized or scorched resin can not be completely removed with the

straight metal rod.

  To eliminate, at least partially, the aforementioned drawbacks,

  Japanese Utility Model Application No. 53-48366 (now brought to the

  birth of the public under number 54-152274) was filed by the Japanese company

  "Jyohoku Seiko Co. Ltd.", headed by the present inventor Mokichi Maejima.

  In the application thus filed, the inner guide 6 'and the rod 7' thereof are designed to be supported so as to be kept spaced apart from one another even under very high pressure. of the molten resin, as seen in Figure 2. This distance must be of the order of 0.1 to 0.5 mm. When this distance is less than 0.1 mm, the resin in

  fusion entering the space B 'is oxidized or scorched because its quality and

  sion undergoes a considerable decrease through the space B ', so that the rod 7' of the inner guide sticks to the oxidized or scorched resin and can not be removed; on the other hand, when the gap is greater than 0.5 mm, the resin entering the space B 'is subjected to a very high pressure, which

  makes the movements of said rod difficult.

  Moreover, the Japanese utility model application of the company "Jyohoku Co. Ltd.". No. 54-139553 discloses an extrusion die which differs from that described in the aforementioned application No. 53-48366, only in the fact

  that the rod of the inner guides is supported by a piece easily removed.

  vable <not shown), thus allowing not only this rod of support

  and remove the inner guide, but also remove the oxidized resins and other glued in the collector of the f iliere. In addition, the same company filed a Japanese utility model application No. 53-12374, now published in the Utility Model Gazette No. 55-53388, which describes a new instrument for removing the resin that is found in the form of a rod having a particular configuration adapted for use in

  aforementioned T-dies. Thus, the aforementioned disadvantages have been partially

eliminated.

  however, even using the T-molds perfected above, to produce a resin film, it is found that the marginal extra thicknesses of the films thus produced have not been diminished as much as would have been expected depending on the nature of the resin used. This is how, for example, * 35 that. in the case of the use of the T-die claimed in Japanese Utility Model Application No. 54-139553 to produce a film from a synthetic resin (manufactured under the trademark "YUKALON LK50" by the Society

  "Mitsubishi Yuka Co. Ltd") the film thus obtained did not exhibit

  marginal thicknesses, this being equivalent to saying that the f ilière had an effect of suppression of marginal excess thicknesses of 100%; on the other hand, in the case of the use of the same die to produce a film with other synthetic resins (produced under the trademark "YUKALON LK30" and "NUC 8008" by the same company), the films thus produced had marginal marginal thicknesses and it was found that the die had marginal margins of 70% and 80%

the "YUKALON LK30" and the "NUC 8008".

  The present invention has been developed to eliminate the disadvantages

  precedents and to make it possible to obtain transparent films, thick

  uniform and with no marginal extra thickness, and what

  whatever the nature of the resin used.

  Above all, the functions of the main components of a T-extrusion die according to the present invention will be explained with particular reference to FIGS.

(1) lips 4.

  The lips 4 delimit between them a slot-shaped discharge orifice 4a through which a molten resin is extruded at high pressure (for example, between 200 × 10 5 and 300 × 10 5 Pa in order to be put into the form of a film (FIG. 4) The width of the slot-shaped orifice 4a between the ends of these lips 4 can be modified or adjusted, at will, by means of adjusting screws (not shown) provided on the outer sides of the body

  1 of the die, which allows to adjust the thickness of the resulting film.

(2) Collector 2.

  A manifold 2, located in the center of the body 1 of the die, extends longitudinally inside thereof (Figures 3 and 4), the collector having a circular cross section, elliptical or otherwise. The molten resin arriving

  an extruder, spreads along the collector before heading towards the ori-

  slot-shaped evacuation chamber 4a.

(3) Passage in the form of a slot 3.

  A slot-shaped passage 3, through which the molten resin passes, is

  provided between the collector 2 and the slot-shaped orifice 4a (Figure 4).

(4) Interior guides 6.

  An inner guide 6 is provided at each end of the die body so as to extend from the collector 2 to the vicinity of the orifice 4a (Figure 4). The inner guides 6 serve to vary the thickness of the edges of the resulting extruded film, although they have some

  influence on the width of the film, by co-operation with the stems cor-

respondantes.

(5) Rod 7 of the inner guides.

  At each end of the die body, a guide rod 7 is placed just above the slot-shaped orifice 4a, between the latter and the lower end of the inner guide, but at a distance from this end. lower. This rod can be moved together with the inner guide to adjust the width of the molten resin stream,

  thereby adjusting the width of the resulting extruded film (Figures 3 to 5).

  (6) Support rod 5 connected to the inner guide.

  At each end of the die body is provided a support rod.

  port 5 whose diameter and strength are greater than those of conventional rods, to prevent them from flexing under the pressure of the molten resin, this rod extending through the collector to become fixed

  securely to the inner guide to hold it in place (Figures 3 and 4).

  In the body I of the T-extrusion die according to the present invention, comprising the collector 2, the slot-shaped passage 3 and the

  4, the support rod 5 connected to the inner guide 6 extends outwards.

  beyond the end of the body 1 and is provided at its outer end with a drive C of the support rod by means of which the inner guide can be moved away from or closer to the end of the body of the spinneret

  in order to vary the thickness of the edges of the resulting extruded film.

  The support rod 5, intended to support the inner guide 6, is placed

  so that it can be moved by sliding contact with the wall of the

  2, as shown in FIG. 4.

  In addition, the rod 7 of the inner guide is spaced a certain distance from the guide 6 to ensure its free movement together with the inner guide, even during the extrusion process during which the resin exerts pressure very high on the inner guide, its support rod 5 and the rod 7 of the inner guide, as shown more particularly in Figures 4 and 5. More precisely, it is seen in these figures that the inner guide 6 has at its lower end a recess having a semicircular shape in cross-section, while the guide rod 7 has a circular section, the guide 6 and the rod 7 to be placed - such that the rounded recess of the lower end of the first kiss the upper part of the second, leaving between them a

  certain interval, preferably between 0.1 and 0.3 mm.

  The operation of the present invention is described below in

  reference to Figures 3 to 5 of the accompanying drawings.

  As seen in Figures 3 to 5, the molten resin from the extruder A is introduced into the manifold 2 where it passes through the passage 3 to be extruded through the slot-shaped orifice 4a. forming a film. An inner guide 6 is provided at each end of the body 1 of the die which encloses the collector 2, the passage 3 and the hole in the form of

  slot 4a, thus changing the thickness of the edges of the resulting extruded film.

  aunt. The support rod 5 connected to the upper part of the inner guide 6 extends beyond one of the ends of the body 1 of the die and is coupled to the drive device C, while the opposite support rod s extending beyond the other end of the body 1 is connected to the actuating device

  C '. The support rod 5 must have a diameter sufficient to be able to

  placed slidingly on the entire wall of the collector or on part of it (Figure 4). It is preferable that the support rod can come into contact with the entire wall of the collector, in order to retix the oxidized resin or other materials attached thereto. The rod 7 is placed just below and at a predetermined distance (preferably 0.1 to 0.3 mm) from the hollow end of the inner guide 6, to prevent the latter from coming into contact with the rod. 7, even when the molten resin develops

very high pressure.

  The width of the sheet of molten resin flowing through the slit-shaped passage 3 is first determined, roughly, by the inner guides 6 respectively disposed at the two opposite ends of the body 1 of the die and then precisely by the rods 7 placed directly under the corresponding inner guides 6. As seen in FIG.

  conventional T, an unnecessary amount of molten resin is likely to

  in the space B 'delimited by the inner guide 6' and the rod 7 'of that

  ci, since this space has very large dimensions, which results in stagnation, oxidation and / or scorching of the molten resin in this space, with the result that it is impossible to accurately determine the width of the the resin melt in the passage 3 ', and the effect of eliminating marginal increments is not as clear as one might have wished, these edges having a certain extra thickness which depends in particular on the nature

of the resin used.

  In contrast, in the T-die of the present invention, as shown in FIG.

  4 and 5, the inner guide 6 and its rod 7 are placed relative to each other so that the hollow end of the hollow guide

  hugs or covers the upper part of the stem

  valle (preferably from 0.1 to 0.3 mm) between them, thus ensuring the presence between them of a much smaller space than that of conventional dies, with the result that the width of the resin sheet in The fusion that passes through the passage 3 is first roughly determined by the inner guide 6, then finally accurately by the inner rod 7, without resulting in stagnation of the molten resin in the space B (which is defined by the inner guide 6 and the side plate 8) and without leakage thereof along the support rod 5 and the extension of the guide rod outwards

of the die body.

  In addition, since the molten resin entering the space B by the gap between the walls delimiting the passage 3 and the inner guide 6, comes out of the gap (preferably from 0.1 to 0, 3 mm) between the inner guide and the rod 7, the resin can not scorch or burn

  in the space B, neither to fix oneself to the walls which delimit this space. It is pre-

  that the gap has a width of about 0.2 mm. When this gap exceeds 0.3 mm, the resulting film has marginal excess thicknesses

  which depend on the resin used as in the case of traditionally

  since an excessive amount of the molten resin passes from the space B in the passage 3 to exit through the slot-shaped orifice 4a. On the other hand, when the width of this gap is less than 0.1 mm, there is a stagnation of the resin entering the space B, so that it becomes oxidized and

  attaches to its walls, which is undesirable.

  In the case where the T-dies of the present invention have been used,

  to produce films with resins supplied under the trademark "YUKALON LK 30" by the company "Mitsubishi Yuka Co"., under the trademark "YUKALON LK 50" by the same company and under the trademark "NUC 8008" by the company "Nippon Unica Co.",

  all the films were obtained with a uniform thickness and did not

  felt no marginal extra thickness, which corresponds to an effect of

  marginal margins of 100%.

Claims (2)

  A T-extrusion die for producing films of a high-pressure thermoplastic synthetic resin which comprises a body (1) having a collector (2) for containing a certain resist of molten synthetic resin and a slit-shaped passage (3) for directing the molten resin to a slot-shaped discharge orifice (4a), adjustable lips for adjusting the width of the orifice (4a) at will between their lower ends, inner guides (6) to vary the thickness of the edges of the resulting extruded film, which can be moved perpendicular to the direction of the   resin stream and in the slot-like passage (3) at each end   of the die body, and rods (7) to adjust the width of the barrel.   resulting lug, movable between the inner guides (6), together therewith, parallel to the direction of movement of the inner guides and within the slot-shaped passage (3), at each end of the body (1). ) of the die, characterized in that the end of each of the inner guides (6) is recessed so as to present in cross section a shape   semi-circular, and in that the corresponding rod (7) has a section presenting   a corresponding circular form, and is placed in such a way that   the recessed lower end of the guide (6) embraces the upper part of the-   said rod (7) by providing a certain interval between them.   2. extrusion die according to claim 1, characterized in that the gap between the recessed lower end of the inner guide (6) and the upper part of the corresponding rod (7) is between 0.1 and 0.3 mm.