JPS6134973B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method and apparatus for forming a laminate comprising at least two films of polymeric material. Various methods are known for bonding multiple films together to form a laminate. When the film is made by extrusion, it is common to apply a pressure sensitive adhesive on one or both of the opposing surfaces of the film so that the film can be bonded by simply applying pressure between the films. The use of pressure sensitive adhesives has the following disadvantages: This means that edge-to-edge welding of the laminate is not possible, and the pressure-sensitive adhesive must be added in solution form, which complicates the method of its application. If you want to use a pressure sensitive adhesive that can be coextruded and welded into laminates,
It is necessary to use such high temperatures that handling of the film becomes difficult. Furthermore, coextruded pressure sensitive films are sticky and it is difficult to wind such films into rolls. because,
This is because pressure is applied to the film during the winding operation. The method of the present invention involves directly applying a plurality of separate films formed of at least one thermoplastic, orientable polymer, face-to-face, in a generally unrolled state, to the adjacent surfaces of each adjacent pair of films. Form a separate film sandwich sandwich by advancing it securely under tension while in contact, and while maintaining said taut sandwich sandwich condition of the separate films, oppose the film sandwich sandwich at room temperature or a temperature well below the melting point. Mechanical pressure is applied between pairs of moving rollers to ensure deflection along a number of generally closely spaced locations extending parallel to the direction of advancement, with the surface of each roller forming grooves. having alternating protruding crests, said protruding crests and grooves being circular or helical, the crests of one roller engaging the grooves of the other roller being sufficient to cause a deflection of said magnitude; the sander trenches are interpenetrated to a depth such that said positive deflections occur at alternating locations and in alternating directions perpendicular to their opposing surfaces, causing said sander trenches to be temporarily approximately evenly transversely zigzag or pleated. providing a hoop and the magnitude of such deflection is determined by mechanically processing the mutual contact surfaces of adjacent pairs of sandwich-like films along said location, thereby providing permanent lateral stretch; It is also characterized in that it is sufficient to cold-weld the film surfaces which are in contact with each other together substantially along said deflection position. The combination of pressing and stretching operations provides a surprisingly improved bonding effect compared to that obtained with pressing alone. It is surprising that an improved bonding effect can be obtained, especially at room temperature, where pressing alone does not provide an appreciable bonding effect. Thus, the combination of pressing and stretching operations provides an improved bonding effect at temperatures below the melting temperature of the surface layer. Thus, by using the method of the invention, it is possible to eliminate the need to separately supply and/or heat the adhesive polymer to raise its temperature. The invention also includes an apparatus for carrying out this method. The apparatus subjects at least two separate films of thermoplastic orientable polymer to a generally flat spread under tension with the adjacent surfaces of each adjacent pair of films in direct face-to-face contact. means for positively advancing the film sandwich to form at least a pair of separate film sandwich strips, and means for moving the film sandwich strips so advanced from said flat state in alternating directions perpendicular to the plane thereof in the direction of advance; mechanically contacting and positively deflecting the film along alternating generally closely spaced locations extending parallel to each other to temporarily create a generally uniform zigzag or pleat in the film sandwich. means for imparting a deflection, the amount of deflection being determined by mechanically processing the mutually contacting surfaces of each adjacent pair of films along said location, thereby creating a permanent lateral deflection. Along with giving stretching,
It consists of a device characterized in that it is sufficient to cold weld together film surfaces that are simultaneously in contact with each other approximately along said deflection locations. It is desirable that the stretching be carried out continuously. Stretching may be accomplished by passing the two or more films through the nip of two or preferably more pairs of intermeshed grooved rollers, the grooves of the rollers substantially extending the sheet. to extend in the longitudinal direction. In this way, pleats are formed during transverse stretching and bonding occurs. Preferably, the pleats formed by passing through one pair are at least partially leveled before passing through the next pair. At least one of the grooved rollers may be heated to improve adhesion. However, as mentioned above, all stretching under pressure is often performed at or near room temperature. It is desirable to combine the method of the invention with one or more longitudinal stretching steps, so that the laminate is stretched biaxially. It is desirable to perform longitudinal stretching after substantially completing transverse stretching. The purpose of performing longitudinal stretching following transverse stretching is to avoid severely expanded film streaks that form when grooved rollers or similar devices act on longitudinally oriented films. . Particularly when high tear propagation and puncture resistance is desired or when a relatively low yield point is acceptable, it is desirable to carry out the stretching in machinery that allows significant lateral shrinkage. This allows for a higher elongation until breakage. In order to carry out longitudinal stretching in a narrow range - as is usually desired - while at the same time allowing shrinkage, U.S. Pat.
It is desirable to have very narrow longitudinal pleats in the laminate, similar to that disclosed in No. 3,233,029.
In this regard, suitable results are obtained when the thin pleats formed by the last step of transverse stretching are maintained in the sheet as it is fed into the longitudinal stretching region. is normal. It is usually desirable for at least one opposing surface of the film to be welded to have a lower melting point than the remaining film. Both opposing surfaces may include such a layer. The layer may be in the form of a strip or spot of low melting polymer. One opposing surface may contain a low melting point polymer and the other may contain a layer of spots or strips of release polymer, ie, reducing the strength of the bond. The film is preferably made by extrusion of a molten polymeric material, but most preferably by extrusion of a blend of polymers that, once solidified, are immiscible such that the blend contains a dispersion of one polymer in the matrix. Each layer of the extruded polymer blend is thinned while melting before, during, or after extrusion to distort the polymer in each layer into a fibrous grain structure with a predominant orientation that is fissile after solidification. desirable. Suitable methods for carrying out this extrusion, along with a description of the final product made by the method, and a full description of the materials that can be used as polymer blends and as low melting point polymers.
It is described in the original specification of Japanese Patent Application No. 1982-82361. Hereinafter, the present invention will be explained with reference to embodiments with reference to the accompanying drawings. In FIG. 1, section Q is the portion of the line where transverse stretching and lamination is performed on sheet 79, and section R is the longitudinal stretching line. Sheet 79 includes a pair of films that are fed separately and brought together, but are not ultimately bonded together as a laminate before first roll 72. The system of rollers of category Q is
It consists of a roller 71, an idle roller 73, and a roller 74 having a cross section similar to a banana. Banana rollers 74 after each step serve to stretch out the pleats created by the transverse stretching. Idle roller 75
Beyond this point, the sheet 79 enters the longitudinal stretching line in section R, where the sheet is heated to a suitable stretching temperature, e.g.
It is pulled through a water bath 76 which serves to maintain the temperature at 40°C. Finally, the sheet is wound onto the bobbin 77. Arrow 78 indicates the machine direction. FIG. 2 shows in detail a pair of driven grooved rollers 72 with a sheet 79 being pressed between teeth 80 of rollers 72 and stretched. In FIG. 3, the relative lengths of the arrows with respect to the striations in sheet 79 indicate the relative amount of orientation achieved by the biaxial stretching method shown in FIGS. 1 and 2. In FIG. 4 as well as in FIG. 3, the numbers indicate streaks A and B having varying widths and unequal properties throughout. Furthermore, the outer layer 8 of the sheet 79
It should be noted that 1 and 82 are not necessarily symmetrical with respect to the thin intermediate layer 83. This asymmetry further helps create a tearing fork. Following are some examples of the invention, in which all percentages are by weight. Example 1 A three-layer cylindrical film having the following composition is extruded. Intermediate layer (70% of total): Blend of gas-phase isotactic polypropylene (“Novolene”) with high atactic content and 15% ethylene-vinyl acetate copolymer (16% vinyl acetate). surface layer on both sides (one is the whole
10% and the other 20% of the total): Ethylene-vinyl acetate copolymer (16% vinyl acetate) - serves as a low melting point layer. The polypropylene has a melt index of 0.3 to 0.6 according to ASTM D1238 condition L, and the ethylene-vinyl acetate copolymer has the same
It is ASTM and has a melt index of 2.5 according to Condition E. A cylindrical film is extruded from a 1mm wide slot at 180℃ to 230℃, and the melted state is 0.130.
Pull to mm. The blow ratio is kept very low, usually 1.2:1. It is then helically cut into a flat film with a 45° grain angle. Two such helically cut films are fed through seven sets of grooved rollers at 20° C. with the grains perpendicular to each other and their thin surface layers facing each other. (See Figures 1 and 2). The width of each groove is 1 mm and the width of each ridge is 0.5 mm.
The engagement of the ridges with each other (difference in level between the tops) is 2 mm. During each pass through a set of grooved rollers, the folds formed in the laminate are straightened.
Due to the mechanical action between the grooved rollers and due to the presence of the low melting point copolymer layer, the two films are cold-welded with a relatively low cleavage value and -
Peel strength measured 10 gr/cm - and simultaneously pulled in the cross direction. After seven passes at 20°C, the laminate is passed once through a similar set of grooved rollers having the same dimensions and interlocking but heated to 120°C. This creates a strong bond line. Finally, the laminate is longitudinally oriented (to minimize cross-shrinkage) by stretching in three stages with approximately 1 cm stretch hooks. This last stretch is adjusted so that the total transverse cold-stretch ratio and the total longitudinal cold-stretch ratio are equal. The area-stretch ratio is 2.4:1. Comparing the test results of this product to a strong bag low density polyethylene film having an 85% higher square meter weight and a melt index of 0.3 according to the same ASTM conditions E.Gauge, this laminate has a
gr/m ² and 185gr/m for polyethylene film.
It was ^m2 . The impact strength (measured by dropping a ball with a diameter of 61 mm and a weight of ³²⁰ gr) is
5.5m, 180gr/ ^m2 polyethylene film
2m, tongue tearing resistance: (tearing at a speed of 100mm per minute,
For a 100gr/ ^m2 laminated film with a total sample width of 5cm and a cut length of 10cm, the weight is 5.9Kg in the machine direction and 6.8Kg in the transverse direction.
For Kg, 180gr/ ^m2 polyethylene film
1.3kgr, Elmendorf Tear Resistance (Impact-Tear): (This test is a modification of the standard that targets a more symmetrical tear). Result: 100gr/ ^m2
A laminated film of 441Kgcm/m ² in the longitudinal direction and 344Kgcm/cm ² in the lateral direction, and a polypropylene film of 180gr/m ² has a density of 167Kg/cm ² in the longitudinal direction and 172Kgcm/cm 2 in the lateral direction.
cm ² , when a piece of the sheet is peeled off and its structure examined microscopically, it is seen that the main layer has a distinct fibrous texture with a zigzag grain direction. Example 2 Repeat the procedure in Example 1 with the following changes. A three-layer coextruded film has the following composition. Intermediate layer (70% of total): a blend of 85% isotactic polypropylene (same type as in Example 1) and 15% ethylene-propylene-rubber (approximately the same melt index as polypropylene). Surface layers on both sides (each 15% of the total): ethylene-vinyl acetate copolymer (same type as in Example 1), film;
After coming out of the die, it melted strongly - became thinner. i.e. 1mm thickness to 0.065mm (60gr/m ² )
I pulled it up to The resulting melt-orientation corresponded to approximately 35% uniaxial cold-stretching as examined in polarized light. After spiral cutting, two of the films were glued together with a third film to create a 3-Bly laminate. A third layer placed in between had a longitudinal grain direction obtained by longitudinally cutting the same film. Lamination and stretching were carried out on the machinery of Example 1, but all steps were carried out at 20°C and the equipment was adjusted to produce a total area-to-stretch ratio of 2.5:1. This resulted in a final film laminate thickness of 72 gr/m ² . Peel strength of interlayer adhesion was measured up to 10gr/m ² . When examined under a microscope, the structure was similar to that of Example 1. The following test results were obtained.

[Table] The embodiments of the present invention are listed below. (1) The method according to claim 1, wherein the stretching is carried out substantially at room temperature. (2) A method according to claim 1, which is carried out by passing two or more films through the nip of interlocking grooved rollers, wherein the grooves extend substantially in the longitudinal direction of the films. Method described. (3) The method according to item 2 above, wherein the distance from the center of one groove to the center of an adjacent groove of the same roller is approximately 1.5 mm, and the engagement depth is approximately 2 mm. (4) The method according to item 2 or 3 above, wherein there are a plurality of pairs of interlocking grooved rollers, and the film is passed through each pair of nips in series. (5) The method according to item 4, wherein the pleats formed by passing one pair are flattened before passing the next pair. (6) The method according to any one of items 2 to 5 above, wherein at least one roller is heated to improve adhesion. (7) The method according to any one of the above items 2 to 5, wherein the stretching under pressure is performed at approximately room temperature. (8) The method according to any one of the above items 2 to 7, wherein the laminate is stretched in one or more stages in the longitudinal direction. (9) The method according to item 8 above, wherein the lateral stretching is essentially completed before the longitudinal stretching begins. (10) The method described in the preceding item 8 or 9, in which considerable lateral shrinkage is allowed during longitudinal stretching. (11) At least one of the opposing surfaces of the film to be bonded includes a layer of a polymer having a lower melting point than the rest of the film. The method described in one of the above. (12) The method according to item 10 above, wherein the layer of the low melting point polymer is in the form of streaks or dots. (13) Each film is formed by extruding a blend of polymers that, when solidified, are immiscible so that the blend contains a dispersion of one polymer in a polymer matrix. The method according to item 1 or any one of items 1 to 12 above. (14) means for applying pressure and stretching the film including a pair of interlocking grooved rollers and means for passing the film through the nip of the rollers, the grooves extending generally in the longitudinal direction of the film; The device according to claim 2. 15. The apparatus of claim 14, comprising a plurality of pairs of interlocking grooved rollers and means for passing the film through the nip of each of the rollers in series. (16) The apparatus according to item 14 or 15, comprising means for heating at least one grooved roller. (17) The apparatus according to claim 2 or any one of claims 14 to 16, further comprising means for longitudinally stretching the laminate. (18) The apparatus according to item 17, wherein all means for longitudinally stretching the laminate are positioned so as to stretch the laminate after it has been stretched laterally.

[Brief explanation of the drawing]

Figure 1 is a process line showing one method.
The figure is a detailed view of the "grooved roller" that stretches the uneven areas called "streaks" in the lateral direction.
Fig. 4 is an enlarged cross-sectional view of the film shown in Fig. 3, which was actually observed with a speculum. The thickness is shown on a scale of twice the width scale to ensure accuracy. 71... Driven nip roller, 72... Grooved roller, 73... Idle roller, 74... Banana roller, 7
5...Idle roller, 76...Water bath, 77...Bobbin, 7
9...sheet, 80...teeth.

Claims (1)

Claims: 1. A method of simultaneously laterally stretching and laminating together a plurality of separate films formed of at least one thermoplastic, orientable polymer, wherein said separate films are generally spread out. in a state in which the adjacent surfaces of each adjacent pair of films are positively advanced under tension in direct face-to-face contact to form a separate film sanderch, and the said taut sanderch state of the separate films At room temperature or well below the melting point, the film sandwich is passed by mechanical pressure between an opposing pair of moving rollers into a large number of approximately closely spaced, extending parallel to the direction of advancement. the surface of each roller has protruding peaks alternating with grooves, said protruding peaks and grooves being circular or helical; The crest of the ridge is inserted into the groove of the other roller to a depth sufficient to produce a deflection of said magnitude, and said definite deflection occurs at alternating positions and alternately in a direction perpendicular to its opposing surface. to temporarily impart a substantially even transverse zigzag or pleated hoop to said sandwich film, the magnitude of such deflection being such that the mutual contact surfaces of adjacent pairs of sandwich films are brought into said position. along the flexure to provide a permanent lateral stretch, while at the same time being sufficient to cold weld the mutually contacting film surfaces together approximately along said deflection location. How to characterize it. 2. In an apparatus for simultaneously laterally stretching and laminating together films of thermoplastic orientable polymers, at least two separate films of said polymers are laid out in a generally flat spread, with each adjacent pair means for positively advancing the film under tension in direct face-to-face contact of adjacent surfaces of the film to form at least a pair of separate film sandwich trenches, and a film sandwich trench so advanced as described above; said mechanical contact and positive deflection from a flat state in alternating directions perpendicular to said plane, along alternating generally closely spaced locations extending parallel to the direction of advancement. means for temporarily imparting a substantially uniform zigzag or pleated loop to the film sandwich, the amount of deflection being such that the mutually contacting surfaces of each adjacent pair of films are mechanically processed along the location to thereby provide permanent lateral stretch, and at the same time sufficient to cold-weld bond the mutually contacting film surfaces together approximately along said deflection location. A device characterized by: