CH636801A5 - Process and apparatus for the transverse stretching of a continuously travelling web - Google Patents

Description

The invention relates to a method for transverse stretching and for the molecular orientation of a flexible material web that is continuously moved through a device according to the preamble of claim 1. The material web can e.g. be designed as an extruded plastic mesh structure.

The invention further relates to a device for carrying out the method according to the preamble of claim 4.

A known (US-PS 4 087 226) device of the type mentioned has retaining devices for the edges of the material bale, which are designed as parallel, spaced-apart, tension frame-like endless chains, which prevent a substantial inward movement of the edges and serve as drive means continuously advance the web lengthwise as it is stretched. A pair of oppositely arranged rows of transversely spaced pressure elements are provided, which are designed as rotatable disks or as inclined driven belts. The disks or belts of one row mesh with the disks or belts of the other row in the transverse direction, so that their outer contours overlap, so that the disks or belts cause the material web to zigzag and thus an extended course from one edge to the other to take others. Thus, oppositely directed forces are exerted on the opposing surfaces of the material web at spaced locations across the width of the material web, and the material web is stretched in the transverse direction in a zigzag shape without the edges of the material web essentially changing Move inward.

The use of discs only as pressure elements has two disadvantages. For a large degree of transverse stretching, the panes must overlap very well and the angle at which the panes engage the material web is very large. The material web thus interacts with each disk at a point at which there is a large angle between the plane of the material web and the corresponding tangent of the disk. Here, the disks can tend to the material

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pushing the web backwards, which prevents proper conveyance, particularly of the central region of the material web, causing the web of material to bend backwards into the central region; the so-called back bend occurs. In addition, the degree of initial transverse stretching or transverse deflection of the material web is very high, this dimension decreasing as the material web continues over the disks. This is undesirable for many material webs and does not provide optimal stretching.

These disadvantages can be avoided simply by using two rows of inclined belts. However, the belts are disadvantageous because they are mechanically quite complex and sag under pressure unless a support device is provided, and because it is difficult to provide an anti-friction surface, e.g. to provide a low-friction surface to allow the material web to slide as desired during stretching.

The object of the invention is therefore to provide a method and a device of the type mentioned, which enables increased transverse stretching with simplified mechanical means, and also allows the initial transverse stretching mass to be reduced and the material web to slide in a simplified manner. For this purpose, the method according to the invention is characterized by the features contained in the characterizing part of patent claim 1. The inventive device is characterized by the features specified in the characterizing part of claim 4.

Since according to the invention the rotatable pulleys or rotating belts at least one of the two rows of the known device by the stationary during operation of the device, i.e. resting pressure elements have been replaced, the previously mentioned angle of attack can be reduced to a usable value and the degree of transverse stretching can be controlled more precisely. It is particularly expedient and advantageous if an essentially constant degree of stretching is sought until the maximum stretching is reached. Due to the invention, transverse stretching ratios, i.e. Ratios of the initial width to the final width, from 2.5: 1 to 10: 1, and an essential molecular orientation of the mesh strands and even the crossover areas in the form of meshes as well as an essential molecular transverse orientation in the case of foils can be produced. In addition, the printing elements that are stationary during operation can be manufactured quite cheaply. It remains possible to carry out a continuous process from the extrusion of the material web to the finished product, the process, in the case of an extruded network structure, the process steps of extrusion, optionally stretching in the conveying direction, in order to orient a square-mesh network structure in the conveying direction, and the like Includes stretching for cross orientation.

The printing elements of a row can, for. B. be designed as follows:

a) There are further pressure elements which are stationary during operation and have sliding surfaces which extend in the conveying direction. This training is particularly suitable for lightweight material webs, e.g. for packaging nets weighing up to 10 g / m2 after cross stretching.

b) Movable belts are provided which move at approximately the same speed as the material web.

c) Rotating circular disks are provided, the peripheral speed of which is essentially equal to the speed of the material web.

The pressure elements that are stationary during operation can e.g. rigid bars or tubes or parallel plates. The sliding surfaces are e.g. B. straight, preferably in a training according to a) or b), or are curved to achieve an advantageous stretching course, preferably in a training according to c).

The drive means can be designed in any suitable manner, e.g. is only pulled from the rear of the device, e.g. in training a) is an advantage. However, in the case of mesh structures, the rotating circular disks or belts are advantageously driven and provided with radial pins on their periphery interacting with the material web, so that these rotating circular disks or belts can also serve as a holding device for the longitudinal edges of the material web. It is also possible to drive all circular disks or belts and to provide them with radial pins or knurling on the periphery interacting with the material web. This has two advantages. On the one hand, the device is suitable for material web widths within a wide range; on the other hand, this measure essentially eliminates a back bending of the material web. A smaller, insignificant back-bend can occur in the form of a series of small bends running across the width of the material web, which, if necessary, can be eliminated by slight transverse stretching and heat treatment. In the case of foils as a material web, the pegs mentioned violate the edges of the foil, although as a drive means e.g. Brackets on side straps can be used, which then also serve as a holding device for the longitudinal edges.

It is particularly expedient and advantageous if the surface sections of the stationary pressure elements that come into contact with the material web are formed from an anti-friction material. All pressure elements that are stationary during operation are then provided with the anti-friction material, except possibly the outermost pressure elements, if these serve as drive means or as a holding device for the edges. The anti-friction material is also provided if the pressure elements carry pins to allow the material web to slide as far as possible on all pressure element surfaces. In other words, it is particularly expedient and advantageous if the material web can move in the transverse direction with respect to the adjacent surface sections of the pressure elements at the points at which the compressive forces act. If this transverse movement of the material web is prevented by friction, strips running in the conveying direction will be created with a different stretch dimension than the remaining stretched material web. The anti-friction material has the lowest possible coefficient of friction and is e.g. polished metal, poly-tetrafluoroethylene or anodized aluminum.

Regardless of this, the anti-friction material is not the only decisive factor, especially when the pressure elements are moved at the same speed as the material web. In this way, a satisfactory product can also be produced if there is no significant cross-slip between the material web and the pressure elements during stretching.

The retaining device for the edges can be designed in any suitable manner. So serve z. B., as previously mentioned, arranged on the outer sides rotating circular links or belts, which are provided with pins or with clamps, both as a drive means and as a holding device. Since the pins of the circular links or belts engage in the mesh of a mesh structure, the mesh structure can extend up to a mesh width

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move inward, this inward movement is not essential in practice and is normally acceptable. In general, the edge retainer engages the web before or simultaneously with the application of the compressive forces that stretch the web.

The overlap (combing) of the pressure elements can be adjustable. In this way, the entire transverse stretching exerted on the material web and the course of the stretching can be set. It is particularly expedient and advantageous if the pressure elements of at least one of the two rows can be individually adjusted by means of an adjustment direction with regard to the overlap dimension (offset width of the zigzag shape), the outermost pressure elements possibly being excluded. This can be achieved particularly expediently and advantageously by the pressure elements which are stationary during operation being pivotably mounted near one end of their sliding surfaces, the pivot bearing preferably being provided at the lower end.

Any suitable material web, e.g. stretch a film. The method can be used particularly expediently and advantageously if a mesh structure is present as the material web.

The mesh structure has e.g. Square stitches, with the strands running in the conveying and transverse directions and the stitches either actually being squares or just rectangles. The invention can also be used for so-called diamond mesh structures, the mesh strands being inclined to the conveying direction and to the transverse direction and being connected to one another at intersection areas. The diamond mesh network can e.g. stretch so that only the parts of the strands located between the crossing areas are stretched and molecularly oriented. However, it is particularly expedient and advantageous if the intersection areas are also stretched and molecularly oriented, in whole or in part, during the transverse stretching of the mesh structure web. This type of stretching is known (GB-PS 1 521 034; South African PS 76/3257).

A tubular network structure can be laid flat, i.e. in two layers, stretch and will,

if desired, cut open later. Since the edges of the flat network structure are often not stretched sufficiently well, the edges can be trimmed.

Preferred embodiments of the invention are shown and shown in the drawing

1 schematically shows a side view of a plant with a device for transverse stretching of a continuous material web,

FIG. 2 shows a side view of the device for transverse stretching according to FIG. 1 on an enlarged scale compared to FIG. 1,

3 shows a section along line III-III in FIG. 2,

4 and 5 each show a section along line IV-IV in Fig. 2 with two different positions of the device,

Fig. 6 is a perspective view of part of a pressure element of the device according to FIGS. 2 to 5, on a greatly enlarged scale and

7 shows a view of an improved pressure element, which is stationary during operation, for the device according to FIGS. 2 to 6.

In the system according to FIG. 1, a squeezing device 1 is provided in a known manner for squeezing out a one-piece plastic mesh structure or network. The mesh structure is formed using known technologies as a diamond mesh or as a square mesh. The mesh structure can be cut open so that it has only a single thickness, or can be further processed as a flat tube with a double thickness. The mesh structure as a square mesh can be stretched in the machine direction for longitudinal orientation in a stretching device 2. The mesh structure then passes into a stretching bath 3, in which a device 4 for transverse stretching is provided, and from there the mesh structure representing the material web arrives at a take-up roller 5, which receives the stretched mesh structure in the folded state. From there, the stitch structure runs around a spreader roll 6 where it is kept wide to its full unstressed width, and then to conventional textile web edge spreaders 7, known as precision edge guides, in which a pair of slightly inclined small rollers on each edge of the stitch structure is provided. The stitch structure then runs to edge cutters 8 which, if desired, cut off the edges or edges of the stitch structure which are not stretched transversely. Finally, the stitch structure arrives on a winding roll 9.

2 and 3 show further details of the device 4 for transverse stretching, which is arranged in the hot water-absorbing stretching bath 3. The device comprises two printing units, one of which is a series of rotatable circular printing elements in the form of equally spaced disks 10, e.g. have a diameter of 50 cm. The other printing unit is a series of stationary, i.e. non-moving pressure elements in the form of pressure plates 11. The pressure plates 11 can be pivoted about an axis 12 and have low friction-causing sliding surfaces 24 which extend in the conveying direction 28 of the material web and which touch the mesh structure. 2, all of the pressure plates 11 are fastened to a single crossbeam 13, which can be moved back and forth in an arcuate slot between two end positions 29 and 30 and can be fixed in the respective position by means of a lever 14, that is to say fixed in position. In particular in the event that the mesh structure has extrusion defects, the positions of the individual pressure plates 11 are preferably individually adjustable, in which case each pressure plate has its own lever 14.

In theory, the disks 10 can be made by machining a single roller; in practice, however, it is expedient to provide a number of individual disks which are supported by and fixed on a single shaft 15. The shaft 15 has a longitudinal axis 26. The disks 10 are driven in the usual way by means of the drive 16. The outermost disks 10 have holding devices for the edges of the mesh structure, prevent inward movement of the band edges and carry pins 17 which engage in the material web before it touches the periphery 10 'of the disks 10 and before the material web reaches the printing plates 11. If desired, all disks 10 carry tenons 17. But in FIG. 6 a preferred embodiment is shown, in which each disk 10 has a knurled periphery 10 'which supports the forward movement of the material web and a sliding of the material web with respect to the disks 10 in the transverse direction.

Fig. 2 also shows a pair of driven rollers 18, which are connected to one another via a roller-belt drive 19, in order to ensure that the output-side speed of the mesh structure is as great as the input-side speed and thus when passing through the device 4 for Transverse stretching of the material web in the conveying direction is prevented. Furthermore, a guide roller 20 is provided to the Ma5

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to lead to the row of disks 10.

4 and 5 show the transverse stretching of the mesh structure with two different settings of the pressure plates 11. The mesh structure is drawn in dashed lines and is deflected according to FIGS. 4 and 5 by the alternating interaction of the disks 10 and the pressure plates 11 into a zigzag shape, whereby it is stretched transversely in a stretch ratio of about 2.25: 1 or 5.5: 1. In practice, the pressure plates 11 can mesh with the disks 10 so deep that stretching ratios of e.g. 4: 1.6: 1 or 8: 1. The pressure plates 11 are particularly shaped, as seen in the axial direction of the disks 10, so that an essentially uniform stretching dimension is achieved until the maximum stretching is reached. In addition, initially the sliding surfaces 24 of the pressure plates 11 pass into the periphery 10 'of the disks 10, as a result of which the transverse stretching gradually increases from zero, so that a noteworthy bending back of the material web is avoided. 2, the lower ends of the plates 11 are circular and are mounted on the pivot axis 12, so that the starting points 25 of the sliding surfaces 24 of the pressure plates 11 extending in the conveying direction 28 of the material web essentially lie on a connecting straight line 27 between the axis 26 of the disks 10 and the pivot axis 12 are.

As already explained, the transverse stretching serves to molecularly orient the strands of the mesh structure or to stretch and orient a film transversely. If the mesh structure has square meshes, the transverse strands are stretched and molecularly oriented. If the mesh structure has diamond loops, the strands which are inclined to the conveying direction of the mesh structure are stretched and molecularly oriented between the crossing regions, the mesh structure, if desired, can be stretched to such an extent that the crossing regions of the strands are wholly or partly stretched, as a result of which hexagonal stitches result.

The design of the sliding surfaces 24 of the printing elements 11 contacting the material web is particularly problematic at higher speeds or stretching ratios, since if the thickness of each printing element 11 is too large in the region of its surface section 23 that comes into contact with the material web, strips of the material web tend to to remain undrawn where the material web has contact with the pressure elements 11; on the other hand, there are few difficulties with regard to heating and tearing. On the other hand, if the thickness mentioned is small, then the unstretched strips of the material web are insignificant or nonexistent, but there is a greater heating and the risk of tearing at higher speeds. This problem can be reduced or eliminated by a special design of the sliding surfaces 24 touching the material web, as is shown in FIG. 7 with the sectional views using a pressure element 11.

636801

The cross-sectional configurations of the pressure plate 11 according to FIG. 7 are shown at five different locations along the pressure plate 11. As the cross section shows, the surface section 23 mentioned is partially wedge-shaped, the thickness of the pressure element 11 in the section 23 increasing in the conveying direction of the material web, so that at the end of the transverse stretching this thickness is approximately twice as large as at the beginning. When this measure is used, the undrawn stripes of the mesh structure can be reduced in width or even avoided at all, the device being able to be operated at a relatively high speed without heating and tearing problems. As shown in FIG. 7, the desired design can be achieved in that the pressure plate 11 is initially tapered in the region of the section 23 and is rounded off at the end. At the initial portion of the web-contacting sliding surface 24, which extends from the initial point 25 to the point at which the first cross section is shown in FIG. 7, there is a uniform thickness; the degree of curvature of the surface section 23 then increases gradually and continuously, e.g. from a radius of 3 mm to a radius of 6 mm until the last cross section shown in FIG. 7 is reached; thereafter the thickness in the area of the surface section 23 remains constant until the end of the pressure plate 11. The web-contacting sliding surface 24, which is formed by the sections 23, is e.g. covered with polytetrafluoroethylene; however, the entire pressure plate 11 is preferably made of stainless steel or anodized aluminum.

4 or 5, the material web is deflected in a zigzag shape from the transverse direction when it is gripped by the pressure plates 11 which mesh with the pressure disks 10. The pressure elements 10, 11 thus exert pressure forces on the two surfaces of the material web, specifically at spaced locations 21 and 22 across the material web, the directions of the pressure forces on the two material web sides alternating across the material web. The spaced apart locations 21 and 22 are offset from one another across the material web in a zigzag shape. 4 and 5 show that the offset width of the zigzag shape is variable. In Fig. 4 there is an offset width B of the locations 21 and 22, and in Fig. 5 there is an offset width A of the locations 21, 22. This variable offset width results in a variable spacing of the locations 21, 22 from one another. The offset width A, B of the locations 21, 22 of the zigzag shape determines the distance between adjacent locations 21, 22 and is also the measure of the mutual overlap of the peripheries of the printing elements 10, 11. Since the material web is held in the transverse direction at its longitudinal edges by means of the pins 17 in the transverse stretching, the width of the material web is naturally increased in the transverse stretching, one can say that the pressure elements 10, 11 causing the transverse stretching also form through their mutual combing (overlapping of their peripheries) a store for the widened material web. The broadening of the material web is absorbed by the less or more deep combing of the elements 10, 11 from the offset width A, B of the zigzag shape (FIGS. 4, 5).

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Claims (11)

636801 PATENT CLAIMS 1. A method for transverse stretching and molecular orientation of a flexible material web continuously moving through a device, on the two surfaces of which pressure forces (10, 11) are exerted, at spaced apart locations (21, 22) across the material web, the Longitudinal edges of the material web are prevented from transverse movement inwards, the directions of the compressive forces (10, 11) on the two surfaces alternating across the material web, the spaced apart locations (21, 22) being offset from one another across the material web in a zigzag manner , the offset width (A, B) of the zigzag shape being changed in the conveying direction, so that this results in a changed spacing of the points (21, 22) from one another, characterized in that at least those compressive forces which are exerted on one of the surfaces of the material web , carried out by means of pressure members (11) held stationary during operation which are provided with sliding surfaces (24) which extend along the material web movement course. 2. Application of the method according to claim 1 in a material web as a plastic mesh structure. 3. Application according to claim 2, characterized in that the plastic mesh structure has a network forming strands which are connected to one another at their crossing areas, the network strands being inclined both to the material web movement course and to the material web transverse direction, so that a Diamond network is present, so that the crossover areas are stretched and molecularly oriented when the material web is stretched. 4. Apparatus for carrying out the method according to claim 1, in which a pair of rows of pressure elements (10, 11) arranged opposite one another, between which the material web is movable, and holding devices (17) are provided for the edges of the material web, wherein the rows extend in the transverse direction of the device, and wherein the pressure elements (10) of one row mesh with the pressure elements (11) of the other row, so that the outer contours of the pressure elements (10) of the one row, seen in the transverse direction, with overlap the outer contours of the pressure elements (11) of the other row (A, B), characterized in that the pressure elements (11) at least of the other row are stationary during operation of the device and have sliding surfaces (24) which extend in the direction of a movement path intended for the material web passing through. 5. The device according to claim 4, characterized in that the certain surface area (23) to come into contact with the material web of the stationary printing elements (11) during operation of the device is formed from an anti-friction material. 6. The device according to claim 4, characterized in that the pressure elements (10, 11) of at least one of the rows can be individually adjusted with respect to the overlap dimension (A, B) by means of an adjusting device (13, 14). 7. The device according to claim 4, characterized in that the pressure elements (11), which are stationary during operation, can be pivoted near one end of their sliding surfaces (24) (12) are stored and are adjustable with regard to the overlap dimension (A, B). 8. The device according to claim 4, characterized in that the thickness of each pressure element (10, 11) of at least one row increases in the region of its surface section (23) determined to come into contact with the material web in the conveying direction (28) of the material web (FIG. 7 ). 9. The device according to claim 7, characterized in that the starting point (25) of the sliding surfaces (24) extending in the conveying direction (28) of the material web of the printing elements (11) which are stationary during operation essentially on a connecting straight line (27) between a center ( 26) of the peripheries (10 ') of the pressure elements (10) of one row and the pivot point (12) of the pressure elements (11) which are stationary during operation. 10. The device according to claim 4, characterized in that along the conveying direction (28) of the material web, the degree of overlap (A, B) of the sliding surfaces (24) of the pressure elements (11) which are stationary during operation with the peripheries (10 ') of the pressure elements (10) which is a row from a starting point (25) increasing evenly. 11. The device according to claim 4 or 10, characterized in that the pressure elements (10) are a series of circular disks which are rotatably mounted (28) by means of a common shaft (15), characterized in that the extending in the conveying direction of the web Sliding surfaces (24) of the pressure elements (11) which are stationary during operation are concavely curved with respect to the axis (26) of the circular disks (10).