FI72286C - SAETT OCH ANORDNING FOER ATT FRAMSTAELLA ETT LAMINAT AV MINST TVAO FLEXIBLA FOLIEBANOR AV ORIENTERBART POLYMERMATERIAL. - Google Patents

Description

1 72286

The present invention relates to a method of forming a laminate from at least two flexible film webs of orientable polymeric materials and to an apparatus for carrying out the process.

Many ways of bonding films together to form a laminate are previously known. If the films are made by extrusion, the polymer adhering to one or both facing surfaces of the films is usually also extruded, so that the mere pressure between the films, often in connection with the use of heat, results in bonding.

The method according to the invention is characterized in that the film webs are joined together without binding, after which the interlocking webs are subjected to simultaneous compression and transverse orientation in areas which together form a substantially longitudinal pattern of narrow parallel lines, whereby simultaneous compression and ori-25 is performed at a temperature lower than the melting range of the opposing surfaces and is obtained by pressing alternately from one and the other laminate surface, giving a permanently or temporarily zigzag-wave cross-section to the assembled films. This procedure can be performed at room temperature.

The invention also relates to a device for carrying out this method. This device is characterized in that it comprises means for feeding two or more film webs towards the transverse stretching system, means for superimposing the films in the system, the transverse stretching system comprising means for applying pressure 2 72286 along lines extending mainly in the longitudinal direction of the films, and stretching the films in the putty direction to provide a laminate of the shape having temporarily substantially evenly distributed, substantially longitudinal folds.

Thus, the stretching is preferably performed continuously at right angles in the endless films to form the laminate in such a way that it temporarily has substantially evenly distributed, mainly longitudinal folds, applying pressure along lines extending mainly in the longitudinal direction of the films to stretch the films transversely.

This is preferably achieved by passing two or more films through a nip between two or more pairs of interconnected grooved rolls 15, in which rollers the grooves extend mainly in the longitudinal direction of the sheet. This forms folds during transverse stretching and bonding takes place. The folds 20 formed in transit through one of said pairs are preferably flattened prior to transit through the next pair.

At least one of the used grooved rollers can be heated to improve bonding. However, as described above, the entire stretching is often performed under pressure at room temperature.

The method according to the invention is preferably combined with one or more longitudinal stretching steps, whereby the resulting laminate is thus stretched biaxially. Longitudinal full stretching is preferably performed after the transverse stretching is substantially completed. Performing longitudinal stretching after transverse stretching avoids excessive striping of the film, which can occur when grooved rollers or similar devices operate on the longitudinally oriented film.

35 When a particularly high tensile strength and

II

3 72286 puncture resistance, and when a relatively low tensile limit can be allowed, the stretching is preferably performed in a machine that allows a substantially transverse contraction. This achieves a greater elongation at break. In order to allow shrinkage while performing longitudinal stretching - which is usually desirable - in a narrow zone, the laminate is preferably given fine longitudinal folds, as described in U.S. Patent No. 3,233,029. In this connection, a suitable result is usually obtained when the final step of transverse stretching is formed. fine folds remain in the sheet when this is fed into the long-stretch zone.

It is normally preferred that at least one of the facing surfaces of the films to be welded has a polymer layer with a lower melting point than the rest of the film. Both facing surfaces may include such a layer. The layer may consist of strips or spots of a polymer having a lower melting point. One of the facing pins may contain a lower melting polymer, while the other may contain a layer of release polymer spots or strips, i. a polymer that reduces the bond strength.

The films are preferably prepared by extruding a molten polymeric material and most preferably by extruding a mixture of incompatible polymers so that the mixture, when cured, forms a dispersion of the polymer in the matrix. Preferably, each melt-extruded polymer blend layer is melt stretched while in the molten state 30 prior to, during, or after extrusion to twist the polymer in each layer so as to obtain a fibril structure primarily after cleavage.

Swedish patent application SE-7507646-3, 35 from which this application is separated, describes the preferred 4,72886 methods for carrying out this extrusion, as well as the finished products made in this way and further details the substances that can be used as a polymer blend and a lower temperature melting polymer.

The invention is illustrated in the accompanying drawings, in which Figure 1 shows a process outline of the manner; Fig. 2 shows a detail of those grooved rollers 10 which perform transverse stretching in uneven zones called "stripes"; Fig. 3 shows a schematic sketch on a larger scale showing the "stripe" pattern and its orientation in a film stretched biaxially in accordance with the process draft of Fig. 1; and Figure 4 shows a cross-sectional view on a larger scale of the film of Figure 3 as it actually appears under a microscope, but for clarity the thickness is shown to be twice the width.

In Fig. 1, the part "Q" is the part of the process line if the cross-stretching and lamination of the sheet 79 is performed, and the part "R" is the longitudinal stretching part. The sheet 79 comprises two films, supplied separately and brought together but not finally bonded together into a laminate, before the first 25 rolls 72.

The roll system in part "Q" consists of drawn press rolls 71, drawn groove rollers 72, running rolls 73 and banana rolls 74. After each step, the banana rolls smooth out the corrugations formed in the transverse stretching. Over the running rolls 75, the film 79 passes to a part "R", i.e. a longitudinal stretching part, where it is stretched through a water bath 76, which cancels the stretching heat and maintains a suitable stretching temperature, e.g. 20-40 ° C. Finally, it is wound on a reel 77. Arrow 78 indicates the machine direction.

Figure 2 shows in more detail two drawn, grooved rollers 72 and a film 79 which are compressed and stretched between the teeth 80 of the rollers 72.

In Figure 3, the relative lengths of the arrows in the "strip groups" I and II of the film 79 give an idea of the relative orientation dimensions achieved by the biaxial stretching process shown in Figures 1 and 2.

Figure 3, as well as Figure 4, I and II show "strip zones" A and B, which generally have a variable width and uneven nature. It should also be noted that the outer layers 81 and 82 of the film 79 are not always symmetrically located around the thin intermediate layer 83. This asymmetry contributes to the groove "branching out".

The following are examples which illustrate the invention and in which all percentages are by weight.

Example 1

The three-layer tubular film is extruded with the following composition: Interlayer (70% kaikes-20 ta): a mixture of 85% isotactic polypropylene of the gas phase type ("Novolen") with a large amount of atactic polypropylene and 15% ethylene vinyl acetate-copolymer (16% vinyl acetate). Both surface layers (one 10% of everything, the other 20% of everything): 25 ethylene-vinyl acetate copolymer (16% vinyl acetate) - which acts as lower temperature melting, adhesive layers.

The polypropylene has a melt index of 0.3-0.6 according to ASTM D 1238, condition L, and the ethylene-vinyl acetate 30 copolymer has a melt index of 2.5 according to the same ASTM standard but condition E. The tubular film is melt-pressed from a 1 mm wide gap at a temperature of 180-230 ° C and stretched to 0.13 in the molten state. The blowing rate is kept very low, namely 1.2: 1.

35 It is then cut along a helical line into a planar film, 6 72286, the fibrous structure of which extends at an angle of 45 ° to the longitudinal direction of the film. The two films thus cut, in which the fibrous structure extends at right angles to each other and the thinnest surface layers face each other, are fed at a temperature of 20 ° C through seven pairs of grooved rolls, cf. Figures 1 and 2. The width of each groove is 1 mm and the width of each back is 0.5 mm. The interconnection of the backs (height difference between the peaks) is 2 mm. In each case, after the passage between the two groove rollers, the wrinkles formed in the laminate are smoothed.

Due to the machining between the grooved rolls and the presence of lower temperature melt copolymer layers, the two films are cold welded together with a relatively low bond strength, the peel strength measured is 10 g / cm, and at the same time their transverse stretching takes place. After seven transits at 20 ° C, a film is fed once between two corresponding grooved rolls having the same dimensions and the same coupling, but heated to 120 ° C, forming strips with a strong bond.

Finally, the laminate is stretched longitudinally in three steps using a stretch zone of about 1 cm (to reduce transverse distortion). The last stretching step is adjusted so that the total transverse-cold-thinning ratio and the total length-cold-thinning ratio are equal, whereby the result of these, i. surface stretch ratio is 2.4: 1.

The test results were compared to an LD polyethylene film of kraft grade quality with a basis weight of 85% and a melt index of 0.3 according to the same ASTM standard, condition E; the laminate had a basis weight of 100 g / m 2 and the polyethylene film had a basis weight of 185 g / m 2.

The impact resistance measured according to the ball drop test (ball diameter 61 mm and weight 320 g) is: 100 2 2 35 g / m for laminated film 5.5 m; 180 g / m for polyethylene 7 72286 film 2.0 m. Heavy tear strength: tear at 100 mm / min, total sample width 5 cm, shear length 10 cm: 100 g / m for laminated film 5.9 2 kg in machine direction and 6.8 kg in the transverse direction; 180 g / m 5 for a polyethylene film 1.3 kg. Elmendorff tear strength (impact tear): the test is a modification of the standard test and is intended to be more symmetrical tear, results: 100 g / m for laminated film in the longitudinal direction 441 kpcm / 2 2 2 cm, in the transverse direction 334 kpcm / cm; 180 g / m for a polypropylene film, 167 kpcm / cm in the longitudinal direction and 172 kpcm / cm in the transverse direction.

The body is delaminated from the film by peeling it off and its structure is examined under a microscope. The main layers have a clearly fibrous shape with tortuous fiber structure directions.

Example 2 The procedure of Example 1 is repeated here with the following modification: the composition of the three-layer, co-extruded film is as follows: Intermediate layer (70% of all): 85% isotactic polypropylene (same type as in Example 1) and 15% ethylene-propylene rubber (approximately the same melt index as polypropylene). Both surface layers (15% each): ethylene-vinyl acetate copolymer (same species as in Example 1).

After the film had left the spray head, it was stretched more strongly as a melt, namely from a thickness of 1 mm to 0.065 mm (60 g / m 2). Studies in polarized light showed that the resulting melt stretching at this time corresponded to about 35% uniaxial cold stretching. After cutting along the helical line, a three-layer laminate was made. The third layer placed in the middle had a longitudinally stretched fibrous structure obtained by cutting the same film lengthwise.

The lamination and stretching were performed on the same machine 8 72286 as in Example 1, but all steps were performed at 20 ° C, adjusting the equipment to a total surface stretch ratio of 2.5: 1 to give a surface laminate of the finished laminate 2 of 72 g / m 2. The peel strength of the interlayer bond was measured to be 10 g / cm. Microscopic examinations showed the structure to be similar to Example 1.

The test results were as follows:

For example, a 2-layer film, non-directional, 3-layer, tu LDPE-cal -__ 72 g / m2_vo, 184 g / m ^

Impact resistance 1000 g x m 530 g x m

Extension tear strength KSx 848 g x m 307 g x m (Slow tearing) PSxx 1120 g x m 620 g x m 15 Breaking load KS 11.1 kg 10.6 kg (2.5 cm wide samples) PS 8.3 kg 10.7 kg

Elongation at break KS 286% 467%

Elongation at break PS 347% 620%

Shrinkage KS 28% 20 1 min at 130 ° C PS 14% 1 min at 155 ° C KS 58% PS 41% x Machine direction xx Transverse direction il

Claims (18)

A method of forming a laminate (79) from at least two flexible film webs (81,82,83) of orientable polymeric material, characterized in that the film webs (81,82,83) are joined together without binding, and then into the joined webs (81, 82). , 83) applying simultaneous compression and transverse orientation in regions (1,11) which together form a pattern of narrow parallel lines extending mainly in the longitudinal direction of the webs, the simultaneous compression and orientation being performed at a temperature lower than the melting range of the opposing surfaces and providing a printing club alternately on the second and second laminate surfaces, permanently or temporarily imparting zigzag to corrugated cross-sectional films (81,82,82). A method according to claim 1, characterized in that the stretching is performed mainly at room temperature. A method according to claim 1, characterized in that it is performed by passing two or more films (81, 82, 83) through a nip between interconnected grooved rollers (72), in which rolls the grooves (80) run mainly in the longitudinal direction of the film. A method according to claim 3, characterized in that the distance from the center of the groove (80) to the center of the groove (80) adjacent to the same roll (72) is about 1.5 mm and the coupling depth is about 2 mm. Method according to Claim 3 or 4, characterized in that a plurality of pairs of engaging, grooved rollers (72) are used and the films are guided successively through the pressing point of each pair. 10 72286 A method according to claim 5, characterized in that the corrugations which form as a result of the passage through one pair of rollers are smoothed before passing through the next pair of rollers. Method according to one of Claims 3 to 6, characterized in that at least one roll (72) is heated in order to improve the bonding. Method according to one of Claims 3 to 6, characterized in that the stretching under pressure 10 is carried out mainly at room temperature. Method according to one of Claims 1 to 8, characterized in that the laminate (79) is stretched in the longitudinal direction in one or more separate steps (R). 9 72286 A method according to claim 9, characterized in that a substantially transverse contraction is allowed during longitudinal stretching. Method according to one of the preceding claims, characterized in that at least one of the facing surfaces of the films (81, 82, 83) to be bonded consists of a polymer layer with a melting point lower than that of the rest of this film. Method according to Claim 10, characterized in that the layer of low-melting polymer consists of strips or spots. Method according to one of the preceding claims, characterized in that each film (81, 82, 83) is formed by extrusion from a mixture of incompatible polymers, so that the mixture, when cured, forms a dispersion of the polymer in the polymer matrix. Device for carrying out the method according to claim 1, characterized in that it comprises means for feeding two or more film webs (81,82,83) towards the transverse stretching system (Q), means for superimposing the films (81,82,83). in the system, wherein the transverse stretching system (Q) comprises means (72) for applying pressure along lines extending mainly in the longitudinal direction of the films (81,82,83) and at the same time stretching the films (81,82,83) in the transverse direction to provide a laminate (79) having temporarily substantially evenly distributed, substantially longitudinal folds. Device according to claim 14, characterized in that the means for applying pressure 10 and stretching the films comprise a pair of interlocking grooved rollers (72) and means for guiding the films (81, 82, 83) through a nip between these rollers, the grooves (80 ) run mainly in the longitudinal direction of the membranes. Device according to claim 15, characterized in that it comprises a plurality of pairs of interlocking, grooved rollers (72) and means for guiding the films (81,82,83) through the pressing points of each pair in turn. Device according to claim 15 or 16, characterized in that it comprises means for heating the at least one grooved roll (72). Device according to one of Claims 14 to 17, characterized in that it also comprises means 25 (R) for longitudinally stretching the laminate (79). 12 72286