IE912353A1

IE912353A1 - Process for obtaining a fold on a sheet or a tubular article¹of plastics material, in particular in the case of a tube,¹and the tube obtained

Info

Publication number: IE912353A1
Application number: IE235391A
Authority: IE
Original assignee: Cebal
Priority date: 1990-07-06
Filing date: 1991-07-05
Publication date: 1992-01-15
Also published as: IS3729A7; JPH04232725A; NO912649L; FR2664199A1; FI913273A; CA2046062A1; NO912649D0; EP0465391A1; FI913273A0; PT98240A

Abstract

The subject of the invention is a process for obtaining a fold in a plastic sheet or tubular part (1) of 0.25 to 0.8 mm thickness, characterised in that at least one folded portion of the said sheet or a longitudinal portion of the said tubular part is rolled between rolls (2, 3) gripping the said portion so as to obtain a fold crushed by this rolling having at its apex an external depth reduction lying between 2% and 15% of the said thickness, this fold then being elastically articulated. This concerns in particular the preform of the flexible skirt of a tube, and the tube so obtained. The invention is applicable to flexible tubes packaging various products, the pressings of these tubes and their shape returning being improved.

Description

Process for obtaining a fold on a sheet or a tubular article of plastics material, in particular in the case of a tube, and the tube obtained.

The invention relates to a process for shaping a sheet or a thin tubular article, typically in the packaging field.

The document FR-A-2545449 = US 4580702 teaches the obtaining of a tube of plastics material having a head moulded on a flexible skirt which is easy to press and has good stability. For this purpose, facets separated by edges are created by extrusion of the skirt then by injection moulding of the head on the skirt, the shoulder of the head comprising facets and edges which are connected to the edges of the skirt. This connection and alignment of the edges therefore ensures the elastic stability of the skirt.

This process strictly links the geometry and manufacture of the skirt and of the injection moulded head, and this is a disadvantage for mass production.

The applicants have attempted to develop a simpler process for producing a tube of which the skirt has edges and has good elastic stability.

STATEMENT OF THE INVENTION The invention relates to a process for obtaining a fold on a packaging element consisting of a sheet or of a tubular article of plastics material having a thickness of 0.25 to 0.8 mm, characterised in that at least one fold forming a double thickness of a folded back portion of said sheet or of a folded or squeezed longitudinal portion of said tubular article is rolled between rolls which grip said fold or said portion so as to obtain a fold which is crushed by this rolling operation and has at its vertex or projecting edge an external striction in depth of between 2% and 15% of said thickness, the fold consequently being permanent and elastically articulated.

The tight folding produced by such rolling produces a superficial rupture of the exterior of the fold, and the majority of the subjacent plastics material has been elastically deformed with the result that this subjacent material which has been thinned owing to the external rupture forms a hinge having an elastic return and consequently creating elastic stability of the geometry of the structure obtained. This rolling solves the problem posed and can also be employed for other problems of articulated folds on thin sheets or tubes of plastics material.

When the spacing of the rolling rolls is reduced, increasing the compression of the fold of plastics material during rolling, the extent of the external rounded striction or rupture increases. Successive pressing of the flexible tube according to the invention has been simulated, with exaggeration, and it can be concluded therefrom that this striction zone developed only slowly, said hinge thinning slightly without the risk of perforation. It has been observed that the interior of each fold does not initially have any hollows, that is to say just after rolling, and that, in practice, a hollow having a depth of less than 5% of the thickness will only develop there after successive folding operations. However, to ensure the impermeability of the fold, it is preferable to limit the gripping of the rolling operation by monitoring the extent of the external striction obtained, or again to adjust the spacing of the rolling rolls to a value of between 1.7 times and twice the thickness of the sheet or tubular article.

In the case of the tubular blank of a skirt of a tube of which the head is then moulded on one end of this skirt, at least two opposing longitudinal folds of said skirt are thus produced before moulding the head. These articulated folds can be produced either over the entire height of the skirt or only over a portion of this height, the presence of the folds at the connection of the head not impairing moulding thereof using the same tools as those used for an unfolded skirt. A significant advantage of the invention is that the same moulding operation as normal can thus be employed.

The longitudinal folds of the blank skirt are produced either by squeezing and rolling of each fold or by passage of the entire width of the skirt between two rolls to produce two opposing folds.

Generally speaking, a sheet or a tubular article composed of various plastics materials, in particular polyethylene (PE), polypropylene (PP), polyesters, metalloplastic or plastics multi-layered materials which can comprise at least one internal barrier layer, adhesive layers, an external decorative supporting layer and an internal layer ensuring good conservation of the product contained can be folded according to the invention.

The term metalloplastic multi-layered material refers to a sheet or article having at least one internal metallic barrier layer, the surface layers being of plastics material. in the case of a tube, and for the reasons already mentioned (repeated pressing in service), it is preferable to adopt roll spacing of between 1.8 and 1.95 times the thickness of the blank skirt for the rolling of folds.

Interestingly, a circular skirt blank can be transformed into a blank having four folds arranged in cross section at the vertices of a rectangle or of a square by simultaneously rolling and gripping four longitudinal portions of said blank between four rolls having truncated cone-shaped surfaces, these surfaces surrounding the blank and gripping said portions between themselves, these rolls leaving the incurvate intermediate portions of said blank free or allowing them to slide freely. After ungripping the rolls and releasing the rolled blank, an almost rectangular or square blank is thus obtained. An octagonal blank is obtained by recommencing a similar rolling operation after having turned the blank.

Bellows-type folding comprising four external folds of vertices or edges arranged at the vertices of a rectangle and two re-entrant folds can thus be obtained by producing approaching shaping on the tubular blank creating two incurvate opposing portions on this blank and by subsequent rolling of the entire width of the blank shaped in this way, the external folds being rolled two-by-two in a superimposed manner and the re-entrant folds undergoing the same crushing as the external folds in this rolling operation. The spacing of the rolls is adjusted for the simultaneous rolling of four thicknesses of the blank, preferably to 3.6 to 3.95 times this thickness.

Bellows-type folding can also be achieved by a folding process involving four rolls such as folding in a quasi rectangle, two opposed rolls tightening and grippingt by their ends, the incurvate intermediate portions of the blank instead of leaving them free as before. These opposing rolls typically have circular edged ends which create a slight depression at the base of each re-entrant fold.

The invention therefore allows simple production of varied arrangements of sheets or skirts of plastics material bearing folds with elastic articulation, in particular folds with different spacing, the connection of the head by moulding not being disturbed in the case of a tube having a flexible skirt. The surface decoration is not affected by the folds outside the striction lines which characterise them.

The decoration of the sheet or skirt is provided prior to folding by typically introducing therein a marking element which allows the ornamentation to be read and to be positioned relative to future folds and subsequently relative to the closing weld of the tube. This technique allows folds arranged symmetrically with respect to the plane of symmetry of the tube which is perpendicular to the weld to be obtained easily, these folds preferably also being symmetrical with respect to the plane of symmetry containing the weld and joining up in this weld. Tubes having a circular, elliptical or polygonal shoulder can be obtained.

TESTS AND EXAMPLES Figure 1 shows an arrangement for rolling a tubular blank, in an axial section.

Figure 2 is a cross section through a tube having four longitudinal folds according to the invention.

Figures 3 and 3b show a sheet bearing a fold, before and after gripping with compression of this fold.

Figure 4 shows rolling with four rolls.

Figure 5 shows a means of adjusting the rolled widths.

Figure 6 shows the rolling stage of a first method of obtaining a bellows-type skirt, shown in cross section.

Figure 7 shows rolling with four rolls according to the second method of obtaining a bellows-type skirt.

Figure 8 shows a second tube according to the invention in elevation.

Figure 1 shows a tubular blank 1 of the skirt of a tube on the point of being rolled between two cylindrical rolls 2 and 3 having adjustable spacing, as indicated schematically by the double arrows 4 and 5. The blank 1 is kept at the correct height by a mandrel 6 from which it will be released by the rolling operation.

Figure 2 shows a cross section of such a blank 1 which is decorated externally in green, has a thickness of 0.5 mm and is made of PE.HD, its opposing folds 7 and 8 then 9 and 10 having been obtained by two successive rolling operations, the second rolling operation flatly gripping the blank which is angularly offset relative to the first rolling operation. The spacing between the rolls was 0.95 mm, that is 1.9 times the thickness of the blank, and a fine white hollowed line at the location of each fold was observed by pressing on the two large convex faces 11 and 12. Examination in section of a cross section of this blank demonstrates that each white line is an external striction surface such as 13 in Figure 3 having a depth of between 0.025 and 0.03 mm.

The cross section of a sheet 14 which is also made of PE.HD, has a thickness of 0.5 mm and is rolled in the same manner as the folds 7 to 10 of the blank 1 can also be seen in Figure 3. The external striction 13 has already been presented and an uneven region 15 produced by folding with compression is also noted inside the folding. This sample was subjected to 300 block folding operations between two steel plates, the length of the fold being 20 mm, the compressive stress during folding being 10 daN and the spacing observed for the plates being 0.93 mm, that is 1.86 times the thickness of 0.5 mm.

The fold spread apart between these folding operations, proving its elastic memory. In a cross section (Figure 3b) the following development was observed after the 300 folding operations: the depth of the external striction 13 was 0.048 mm and the internal relief 15 had produced a hollow 16 having a depth of 0.032 mm. Such a development, greatly exaggerating the folding operations by successive pressing of a tube filled with product, demonstrates that the proposed solution does not present any risks in practice.

Figure 4 shows the simultaneous rolling of four folds according to the invention between the truncated cone shaped surfaces such as 17 and 18 of four rolls 19 to 22. The blank 23 is squeezed longitudinally and gripped according to the rule of the invention owing to the possibilities of precise spreading apart and bringing together of the rolls 19 to 22 symbolised by the double arrows 24 and 25. The hollowed surfaces 26 of the blank 23 can slide freely on the intermediate portions 27 and 28 of the rolls 19 and 21 and a skirt having four folds of rectangular form is obtained after rolling.

Figure 5 shows a detail corresponding to the rectangle in broken lines 29 in Figure 4. A reduction 30 of the gap between the truncated cone shaped surfaces of the gap between the truncated cone shaped surfaces 17 and 18 of the rolls 19 and 20 allows the re-entry of the blank 23 between these surfaces 17 and 18 to be adjusted. Such reductions contribute to the reproducible positioning of the blanks during the rolling operation and therefore to the reproducibility of their shapes after rolling.

Figure 6 shows, on the left-hand side, the blank 31 having approaching shaping with two opposing portions 32 and 33 which are already incurvate. This blank 31 is rolled, as s soon as it leaves the approaching rolls, between the rolls 34 and 35 having roll spacing which is 3.6 to 3.95 times the thickness of the blank 31. The external folds such as 36 and 37 are rolled while superimposed, and the internal folds such as 38 are gripped in a quadruple thickness like the external folds. A bellows having elastically articulated folds with a slight striction zone at the exterior of each fold is obtained.

Figure 7 shows a second method of obtaining a bellows which differs from the rolling operation in Figure 4 only by the replacement of the intermediate portions 27 and 28 of the rolls 19 and 21 by extensions of their truncated cone shaped surfaces forming end edges 270 and 280. These truncated cone shaped surfaces and these circular edges tighten and grip, in co-operation with the rolls 20 and 22, the hollowed portions of the blank 23, a score or a slight hollow in the base of each fold is thus obtained.

Figure 8 shows a tube 100 of which the head 101 made of PE.HD is moulded on one end of its skirt 102 which is also made of PE. HD and is decorated and folded according to the invention with 8 crushed folds 8, each fold 8 and the corresponding fold 8' of the concealed face or verso being joined together in the weld 103.

INDUSTRIAL APPLICATIONS Tubes having a flexible skirt of plastic or metalloplastic material, packaging widely varied products (cosmetics, sanitary materials, pharmaceuticals, foodstuffs, maintenance materials), the pressing of these tubes and the shaping thereof being improved by the invention.

Claims

1. Process for obtaining a fold on a sheet or tubular article (1) of plastics material having a thickness of 0.25 to 0.8 mm, characterised in that at least one fold (7 to 10) forming a double thickness of a folded back portion of said sheet or of a folded or squeezed longitudinal portion of said tubular article (1; 23; 31) is rolled between the rolls (2, 3; 19 to 22; 34, 35) gripping said fold or said portion so as to obtain a fold (7 to 10) which is crushed by this rolling operation and has at its vertex an external striction zone (13) having a depth of between 2% and 15% of said thickness, this fold thus being elastically articulated.

2. Process according to claim 1, in which the spacing (24, 25) of said rolls (2, 3; 19, 2i and 20, 22; 34, 35) is between 1.7 times and twice said thickness of said sheet or tubular article (1).

3. Process according to claim 2, in the case of a said tubular article (1) which is the blank (1) of a skirt (102) of a tube (100) of which the head (101) is then moulded on one end of said skirt and in which at least two opposed longitudinal portions of said blank are rolled.

4. Process according to claim 3, in which the two said portions are rolled simultaneously by passing the entire width of said blank skirt (1; 31) between said rolls (2 and 3; 34 and 35).

5. Process according to any one of claims 3 or 4, in which said longitudinal portions are rolled between rolls (2, 3) having spacing of between 1.8 times and 1.95 times the thickness of said blank skirt (1).

6. Process according to claim 3, in which four longitudinal portions of said blank (23) are rolled simultaneously between four rolls (19 to 22) having truncated cone shaped surfaces (17, 18) gripping said portions between themselves, said rolls leaving free or sliding over said blank (23) between its said portions.

7. Process according to claim 3, in which said blank (31) is shaped according to a preliminary shape comprising two incurvate opposing portions (32, 33) and is rolled over - its entire width between two rolls (34, 35), thus simultaneously rolling four external folds (36, 37) which are superimposed two-by-two and two re-entrant folds (38), thus achieving bellows-type folding of said blank.

8. Process according to claim 7, in which the spacing of the two rolls (35, 36) is adjusted to 3.6 times to 3.95 times the thickness of said tubular blank (31).

9. Process according to claim 3, in which four longitudinal portions of said blank are rolled simultaneously between four rolls having a truncated cone shaped surface (19 to 22) gripping said portions between themselves (19, 21 and 20, 22), two opposing rolls (19, 21) thus tightening and gripping between themselves, by their circular edged ends (270, 280), two incurvate intermediate portions of said blank, so as to fold it into a bellows.

10. Process according to any one of claims 1 to 9, in the case where the sheet or the tubular article (1) or the skirt blank (102) is made of one of the plastics materials or multi-layered materials having a base of plastics materials from the following group: PE, PP, polyesters, metalloplastic multi-layered materials, or of plastics materials.

11. Process according to any one of claims 1 to 10, in which said sheet or longitudinal portion! 1) is previously decorated, the ornamentation obtained is read and said decorated sheet or portion is positioned for said rolling so as to situate its ornamentation relative to the folds (7 to 10).

12. Tube (100) having a head (101) moulded on one end of its skirt (102) of plastic or metalloplastic material, obtainable by the process according to any one of claims 1 to 11, said skirt (102) alone comprising at least two opposing, elastically articulated longitudinal folds (8, 8’), each of these folds (8, 8') comprising an external striction zone having a depth of between 2 and 15% of the depth of said skirt (102).

13. Tube (100) according to claim 12, having a welded lower end (103), the folds (8, 8') of the large faces of the filled tube ending in the weld (103).

14. Process according to any of Claims 1-11, substantially as described herein with reference to and as shown in one or more of the accompanying drawi ngs.

15. A sheet or tubular article of plastics material having a fold obtained by a process according to any of Claims 1-11 or 14.