HK1165370A - Method and device for sealing tubular plastic packaging, and resulting packaging - Google Patents

Description

Method and apparatus for sealing tubular plastic packages and packages produced thereby

Technical Field

The present invention relates to the field of hoses formed from plastic films, and more particularly to hoses formed from films in which the ends of the film are welded by adding a softened weld line.

Background

Welding by adding softened plastic wires is described in patent application WO2008/038206a 2. In this method proposed by the applicant, a weld line is extruded and welded to each end of the laminated stack and acts as an adhesive between the ends. The temperature of the weld line is high enough to ensure that it is welded to the end, so no additional energy input is required. The advantage of this method is that the attractiveness of the tube is improved because the wire is applied to the surface forming the inner surface of the container. Another advantage is the simplicity of the apparatus compared to commonly used high frequency welding apparatus.

However, the method and apparatus described in patent application WO2008/038206a2 have a number of disadvantages associated with the containers produced. These drawbacks are associated with the occurrence of three types of welding defects on the container. The first defect is an aesthetic defect, which occurs when the ends of the lamination stack are not bonded. In this case, the weld line is visible from outside the container. An illustration of this type of welding is shown in fig. 5. The ends of the laminated laminate 11 are unbonded and the space 14 between the ends is filled by the weld line 12. This type of welding has a second drawback when the lamination stack 11 comprises a barrier layer 13. A loss of barrier properties is observed in the weld zone 10 due to cracks in the layer 13. The loss of properties is proportional to the size of the gap 14 and when the ends of the laminate are not bonded or sufficiently welded, the loss of barrier properties of the container is considerable. A third drawback is mechanical defects which occur when the ends are joined but not welded together. A weld of the type shown in fig. 6 is obtained with the apparatus described in the prior art and shown in fig. 1 to 4. In this case, a very thick weld line 12 is required to compensate for the low strength of the butt weld of the laminated stack 11. The welding zone 10 has a first zone 15 formed by the interface between the wire 12 and the lamination stack 11, and a second zone 16 formed by the interface between the ends of the lamination stack. It was observed that the method and the apparatus described in the prior art were not able to weld the interface 16, the high thickness of the welding line 12 reducing the flexibility of the container in the welding zone. The unwelded interface 16 between the ends of the laminate also does not contribute to the aesthetic and barrier properties of the container. The above-mentioned drawbacks arise from the difficulty of softening the ends of the lamination stack with the energy supplied by the welding wires.

The method and apparatus described in application WO2008/038206a2 and shown in fig. 1 to 4 have further drawbacks, which are caused in particular by the fact that: the softened thread naturally flows downward under the action of gravity. Thus, the wire first comes into contact with the surface of the welding rod or, if applicable, the conveyor belt is built into the welding rod. In fig. 2, which shows a cross-section of the apparatus shown in fig. 1, the weld line 12 is placed on the metal strip 3 before it is brought into contact with the laminate stack 11. This first contact of the relatively high temperature wire with the cold metal surface is detrimental to the operation of the process, since the temperature of the wire is reduced before it comes into contact with the edge of the laminate stack to be welded. This unexpected energy loss substantially degrades the quality of the weld.

Disclosure of Invention

The problem that the invention intends to solve is to improve the quality of the weld obtained with softened extrusion wire. The invention also serves in particular to remedy the disadvantages mentioned above.

The invention relates firstly to a method for welding tubular plastic containers, comprising at least the following operations:

● a winding operation in which the laminated stack is wound;

● a locating operation in which the edges of the laminate are located;

● extrusion operation, in which softened plastic wires are extruded and deposited on the ends of the lamination stack;

● a melting operation in which the ends are melted by a weld line;

● a pressing operation in which the weld zone is co-pressed in two directions;

● cooling operation of the weld zone.

The melting operation is critical to the present invention as it serves to soften the surface of the end of the laminate. The melting of the ends of the laminate is obtained due to the thermal energy of the welding line and is carried out in the following manner:

● lines contact only the ends of the laminate,

● the duration of the operation and the energy of the weld line are sufficient to soften the ends.

The pressing operation is simultaneous with or subsequent to the melting step, the pressing operation comprising:

● press the weld lines very rapidly along the vertical axis of the laminated stack,

● and pressing the softened ends of the laminate against each other in a direction parallel to the plane of the laminate.

The implementation of the invention results in a method which consists in moving the thread in a direction parallel to the elements of the device which are likely to be in contact with the thread. In this way, the wire does not contact elements such as solder bars or tape before contacting the laminate stack.

The invention is characterized in that the wire is moved parallel to the welding device, in particular the welding rod, optionally a belt, so that the first contact of the wire is with the lamination stack.

One feature of the present invention is that all of the energy required to perform the weld is generated by the plastic wire.

According to a first alternative of the inventive method, the wire is deposited before the positioning step.

According to a second alternative, the wires are deposited during the positioning step.

According to a third alternative, the wire is deposited after the positioning step.

The wire may be deposited on the surface of the laminate stack forming the inner surface of the container or on the surface forming the outer surface of the container. Preferably, the wire is deposited on a surface forming said inner surface.

The invention also relates to a device for carrying out the method as described above. The apparatus comprises a welding rod adapted to be surrounded by a lamination stack, means for extruding a softened plastic wire and placing it between the outer surface of the welding rod and the lamination stack located around said welding rod, the apparatus being characterized in that the welding rod is positioned vertically.

The container comprises a welding zone comprising two distinct portions:

● formed by the interface between adjacent ends of the laminated stack,

● formed by the interface between the underside of the laminated stack and the weld line.

The total thickness of the welds is less than twice the thickness of the laminate, preferably less than 1.8 times the thickness of the laminate. The strength of the weld area is greater than the strength of the laminate stack.

When the lamination stack comprises a plurality of layers, the invention is advantageous for improving the continuity of the layers in the welding zone. Thus, the barrier properties of these containers are improved and the attractiveness of the weld zone is improved.

An alternative to the invention is to use a method in which welding is performed by overlapping the ends of the laminated laminations. In this case, the weld line is located at the interface of the ends of the laminated laminates intended to be overlapped. The melting operation serves to soften the end portion.

In the case of a laminate comprising a layer that slows down the diffusion of heat, for example an aluminium or paper layer, in its thickness, it may be advantageous to use a device that preheats the edges, for example by contact, which has the effect of raising the temperature of the two edges of the laminate, thereby assisting or improving the welding conditions.

According to an alternative of the invention, the edges of the lamination stack are cut obliquely, which has the effect of increasing the lateral contact area of the lamination stack in the welding zone, this configuration also affecting the quality and strength of the weld.

Another alternative of the invention consists in using coextruded plastic wires (with barrier material in the centre of the wires), also ensuring good barrier protection to the external environment of the tube in the area defined between the edges of the laminate stack.

Drawings

The invention is described in more detail below by means of examples shown in the accompanying drawings:

FIG. 1 shows a perspective view of a prior art apparatus;

FIG. 2 shows a side cross-section of the device of FIG. 1;

FIG. 3 shows a perspective view of a second prior art apparatus;

FIG. 4 shows a side cross-section of the device of FIG. 3;

FIG. 5 shows a first alternative of prior art welding;

FIG. 6 shows a second alternative of prior art welding;

FIGS. 7 and 8 illustrate a butt welding method according to the present invention;

FIG. 7 illustrates the melting operation of the method;

FIG. 8 shows the pressing operation of the method;

FIG. 9 shows a butt weld according to the present invention;

FIG. 10 shows a cross-section of an apparatus according to the invention;

FIG. 11 shows a cross-section of the apparatus in a melting operation;

FIGS. 12 and 13 illustrate a method for welding with overlap;

FIG. 12 illustrates a melting operation;

FIG. 13 illustrates a squeezing operation;

fig. 14 shows welding in an overlapping situation according to the invention.

List of reference numerals used in fig. 1 to 9

1 welding rod

2 sizing die (height adjustable)

3 inner belt (Metal)

4 forming die

5 support pad

6 outer band

7 extruder head

8 first edge of laminated laminate

9 second edge of the laminated stack

10 welding zone

11 laminating stack (continuous strip)

12 extruded plastic wire

13 barrier layer

14 space apart

15 line-lamination stack interface

16 laminate-to-laminate interface

17 external pressing element

18 internal pressing element

19 compression force perpendicular to the surface of the laminated stack

20 compression force parallel to the surface of the laminated stack

21 thickness of the land

22 melting zone

23 compression zone

24 cooling zone

Detailed Description

The inventive method consists in using the energy contained in the welding line to:

● weld the wires to the ends of the laminate stack,

● weld the ends of the laminated stack to each other.

The weld zone thus comprises two distinct portions, the first being formed by the line-lamination interface and the second by the lamination-lamination interface.

The inventive method comprises at least the following operations:

● wrapping the laminated stack to form a tubular body,

● locate the ends of the laminate stack,

● extruding a weld bead and depositing it on the end,

● use the energy of the strip to melt the end,

● the area of the weld is compressed,

● the cooling of the weld zone is carried out,

● cut the tubular body into cylindrical elements of the same length.

The key steps of the inventive method are shown in fig. 7 and 8. Fig. 7 shows a melting operation in which part of the energy of the welding line is transferred to the laminated stack to soften the end to be welded. The softened extrusion weld line 12 is in contact with the end of the laminated stack 11, the interface 15 between the line and the laminated stack having a reduced area to heat only the end to be welded. During said melting operation, the welding line 12 is in contact only with the ends of the laminated stack 11. According to a preferred embodiment of the invention, the ends of the laminated stack 11 are only in contact with the weld line 12 during the melting operation. The absence of external contact with the weld line 12 and the ends of the laminated laminate during the melting operation is a key feature of the present invention. The duration of the melting operation depends on the thickness of the laminated stack and the temperature and quality of the weld line, the duration of the melting operation is generally longer than 0.1 seconds and the temperature of the weld line is at least 50 ℃ above the melting point. Attempts are generally made to reduce the quality of the welding line in order to reduce the thickness of the weld and the cost of the container, the best quality being the result of a compromise between the minimum energy that the welding line must contain during the melting operation, the thickness of the weld to be reduced and, finally, the nature of the weld zone. These parameters can be adjusted by those skilled in the art. When the laminate 11 is a multi-layer laminate, it is not always possible and useful to soften all of the layers. In this case, the energy supplied by the weld line 12 is used to soften the layer suitable for butt welding. Generally, the resin constituting the weld line is of the same type as the weld layer of the laminate. It is advantageous to select the weld line 12 from a resin having a melting point equal to or higher than the melting point of the resin constituting the weld layer of the laminate. For example, the use of a high density polyethylene weld line facilitates the manufacture of a pipe having a laminate stack comprising multiple layers of low density polyethylene. The melting operation may be performed prior to or simultaneously with the pressing operation.

The following may occur: the laminate stack comprises a layer in its thickness that slows down the heat transfer between the weld line and the laminate stack weld layer. For example, aluminum or paper layers have been observed to slow heat transfer considerably. It sometimes becomes difficult to soften the layer located near the upper surface of the laminated laminate because the weld line is located on the lower surface. To overcome this difficulty, it is contemplated to add a heat source to the outer surface of the laminate during the fusing operation. In this case, it is advantageous to heat the upper surface by contact or by hot air.

The weld zone is compressed, either in succession to or simultaneously with the melting operation. The pressing operation shown in fig. 8 consists in:

● reduce the thickness of the weld line and compress the softened interface 15 between the laminated stack 11 and the weld line 12,

● reduce the spacing 14 between the ends and compress the interface 16 between the softened ends of the laminate stack 11.

During the pressing operation, the welded zone 10 is co-pressed in a direction called vertical and a direction called transverse. The vertical direction is perpendicular to the plane formed by the weld zone, the direction referred to as the transverse direction is parallel to the plane formed by the weld zone and perpendicular to the welding axis. The vertical pressure reduces the thickness of the weld line 10 and increases the adhesion of the weld interface between the weld line 12 and the laminated stack 11. The vertical pressure is provided by an external pressure element 17 in contact with the outer surface of the laminated stack and an internal pressure element 18 in contact with the weld line, the compression force 19 applied by the compression elements 17 and 18 reducing the thickness of the weld line and spreading it out. The pressing operation must be very rapid to avoid cooling the weld zone 10, which would prevent crushing of the wire 12 and would lead to poor quality of the welding interface 15 between the wire and the laminate. The weld area is laterally compressed prior to, together with or after the vertical compression, under the action of a lateral compression force 20 applied to the laminate stack. The transverse compression force 20 brings the edges of the laminate together and compresses the softened edges of the laminate 11 at the weld interface 16, which improves the adhesion of the weld at the interface 16. The transverse compressive force 20 has a low strength and is transmitted through the laminated stack to the interface 16. The compression of the interface 16 has the effect of substantially increasing the strength of the weld zone and improving the continuity of the barrier properties of the laminate stack in the weld zone.

Fig. 9 shows butt welding of the method. The weld zone 10 has two distinct weld zones:

● the interface 15 between the line 12 and the underside of the laminate 11,

● the interface 16 between the ends of the laminate.

In contrast to the welding obtained with the methods and apparatuses described in the prior art, the interface 16 between the ends of the lamination stack 11 is welded. The distance between the ends of the barrier layer is shorter than 60 micrometer, preferably shorter than 30 micrometer. Thus, the properties of the container are improved, that is to say:

● better continuity of barrier and mechanical properties in the weld zone,

● lower weld thickness.

The thickness 21 of the weld can be reduced compared to prior art welds. The thickness 21 of the weld according to the invention is advantageously less than twice the thickness of the lamination stack. Preferably, the thickness is less than 1.8 times the thickness of the laminate stack.

Fig. 10 shows an apparatus according to the invention. The tube is formed continuously by the gradual enveloping of the welding rod 1 over the entire circumference, with the strip of lamination stack 11 being pulled down from above across the forming die 4. The laminated laminate 11 of PE or PP (or other material) (single or multiple layers) is then welded longitudinally by depositing a softened extruded plastic wire 12 inside the tube. As shown in fig. 10, the welding rod 1 is vertically positioned. In this way, the wire 12, which is also vertically displaced, is not in contact with the bar 1 but directly in contact with the lamination stack 11.

The apparatus includes a zone 22, referred to as a melt zone, for performing the melting operation of the method. The length of the zone 22 is determined by the thickness of the laminate and the speed of travel of the laminate. In the melt zone 22, the ends of the laminated stack and the softened weld line 12 remain in contact. The wire 12 and the ends of the laminated stack are not otherwise in contact with the elements of the apparatus in the melt zone 22.

The apparatus comprises a region 23 called a squeeze region for performing a squeeze operation, the region 23 being short because the duration of the squeeze operation must be short. In the region 23, the weld zone is co-extruded in a direction referred to as vertical and a direction referred to as transverse. The vertical compression that compresses and spreads weld line 12 is shown in fig. 10. The weld zone is squeezed between the support pad 5 and the sizing die 2, the support pad 5 applying pressure to the outer surface of the laminated stack and the sizing die 2 applying pressure to the weld line. The pressing zone 23 is short, so the duration of the pressing operation is short. Many other compression devices may be used than the device shown in fig. 10. The compression roller may be advantageous when the resin constituting the weld line 12 or the outer surface of the laminated stack causes deposition on the compression tool. The pressing tool is preferably cooled. Another alternative is to use a belt that travels at the same speed as the lamination stack and contacts the weld area when compressed. This alternative is used to avoid friction between the weld zone and the tool during the pressing and cooling operations. Some devices use a single conveyor belt on the outer or inner surface of the weld. Other devices have two strips located on both sides of the welding area and in contact with said welding area only during the pressing operation. The apparatus shown in fig. 10 also applies a transverse compressive force that compresses the softened edges of the laminated laminate. The transverse pressure is applied by a forming die 4, the geometry of the forming die 4 in the pressing zone having the effect of lightly pressing the ends of the laminated laminate. Advantageously, in the pressing zone, the forming die 4 has a diameter slightly smaller than the diameter of the tubular body formed by the outer surfaces of the laminated stack 11.

The apparatus includes a zone 24 called a cooling zone for performing a cooling operation. In this zone, the weld is cooled between the support pad 5 and the sizing die 2. In the cooling zone, elements may also be added to improve the roundness of the produced tube. The length of the cooling zone 24 is generally reduced because the heated area is localized. The length of the zone 24 is adjusted according to the thickness of the laminated stack, the thickness of the weld line and the speed of travel of the laminated stack.

Fig. 11 shows a cross-section of the apparatus at the melt zone 22, and fig. 11 shows that the softened weld line 12 is only in contact with the end of the laminated stack 11. The weld line 12 is not in contact with the rod 1 and the forming die 4. The vertical positioning of the apparatus is particularly advantageous to avoid any contact of the welding line 12 with the tool, not only during the production of the tubular body, but also during the start and stop phases.

Fig. 12 to 14 show an alternative embodiment of the invention in which the ends of the laminated stack are welded in overlap.

Fig. 12 shows the method in an operation called melting. During the melting operation, the weld line 12 is located between the overlapping ends of the laminated stack 11. Part of the energy of the wire 12 is transferred to the ends to soften them.

Fig. 13 shows an operation called pressing during which a pressing force 19 is applied perpendicular to the surface of the laminated stack. This compression force has the effect of reducing the thickness of the wire 12 and covering the ends of the laminated stack 11.

Fig. 14 illustrates an overlap weld performed in accordance with the present invention. The thickness 21 of the welding zone 10 is less than twice the thickness of the laminate, preferably less than 1.8 times the thickness of the laminate 11. The weld line 12 covers the edges of the laminated laminate at the edges of the weld.

The use of a softened co-extruded weld line (with barrier material in the center of the line) is sufficient to improve barrier protection at the weld zone.

Claims (20)

1. Method for welding tubular plastic containers, comprising at least the following operations:

a. a winding operation in which the lamination stack (11) is wound;

b. -a positioning operation, in which the ends (8, 9) of the lamination stack (11) are positioned adjacent to each other;

c. an extrusion operation in which a softened resin thread (12) is extruded and deposited on the ends (8, 9);

d. a melting operation in which the ends (8, 9) are melted by the wire (12);

e. a pressing operation in which the weld zone (10) is pressed;

f. a cooling operation in which the welded portion is cooled.

2. The method of claim 1, wherein the end portions (8, 9) are positioned adjacent to each other.

3. A method according to claim 1, wherein the end portions (8, 9) are positioned above each other.

4. The method according to any one of the preceding claims, characterized in that during the melting operation the wire (12) is in contact only with the end portions (8, 9).

5. The method of any of the preceding claims, wherein the duration of the melting operation is longer than 0.1 seconds.

6. The method of any one of the preceding claims, wherein the melting operation is performed by the wire and a second heat source together.

7. Method according to any of the preceding claims, characterized in that during the pressing operation the weld zone (10) is co-pressed in a vertical direction and in a transverse direction towards the end portions (8, 9).

8. The method according to any one of the preceding claims, characterized in that during the pressing operation, the wire (12) is spread apart and the thickness of the weld zone (10) is reduced.

9. A method according to any one of the preceding claims, characterized in that during the pressing operation, the end portions (8, 9) are pressed against each other.

10. The method according to any one of the preceding claims, characterized in that during the extrusion operation the thread (12) is moved in a direction parallel to the elements of the apparatus supporting the lamination stack (11) so that, once extruded, the first contact of the thread (12) is directly with the lamination stack (11).

11. Manufacturing method according to claim 9, wherein the wire (12) is moved vertically in the direction of gravity.

12. A method as claimed in any one of the foregoing claims, characterized in that the wire (12) is deposited during the positioning operation.

13. The method according to any one of claims 1 to 10, characterized in that the wire (12) is deposited after the positioning operation.

14. A tubular container obtained by the method defined in any one of the preceding claims.

15. A container according to claim 14, characterized in that at the weld it has a thickness of less than twice the thickness of the laminate stack (11).

16. Apparatus for carrying out the method as defined in any one of claims 1 to 12, comprising a welding rod (1) suitable to be surrounded by a lamination stack (11), means (7) for extruding a softened plastic wire (12) and placing it between the outer surface of the welding rod (1) and the lamination stack (11) located around the rod (1), characterized in that the welding rod is positioned vertically.

17. The apparatus of claim 15, further comprising a preheated conveyor belt (3) located on the welding rod (1) such that the softened wire (12) is located between the conveyor belt (3) and a lamination stack (11) surrounding the rod (1).

18. The apparatus as claimed in either of claims 16 and 17, comprising an outer drive belt (6) and an adjustable support pad (5) positioned so as to exert pressure on the lamination stack (11) and the softened plastic wire (12) between the drive belt (6) and the welding rod (1) in the direction of the welding rod (1).

19. The apparatus of any one of claims 16 to 18, wherein said means (7) for extruding and positioning a softened plastic wire (12) are located on the upper surface side of said welding rod (1).

20. The apparatus of any one of claims 16 to 19, wherein said means (7) for extruding and positioning a softened plastic wire (12) is located on a lower surface side of said welding rod (1).