JPS6319329B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for extruding laminated polymer sheets. Cross-laminates of uniaxially oriented films of crystalline polymers are known to provide a generally highly advantageous combination of various strength properties. The most surprising of these is the tear transfer strength, especially when the adhesion between the layers is weak enough that the layers can peel around the notch during tearing from the notch (see U.S. Pat. No. 3,322,613). ). As a result, the laminate tears or flows in various directions and the notches lose their effectiveness. This is called the "folk effect."
Sheets of this type are particularly useful for a variety of heavy-duty objects, such as tarpaulin replacements, cover sheets, heavy-duty bags, and heavy-duty packaging films. The most suitable method for manufacturing such sheets is described in British Patent No. 816607,
This involves strongly orienting the molecules of a cylindrical film in its longitudinal direction, cutting it into a spiral shape, and spreading it in a helical direction (e.g. 45°).
This is accomplished by forming an oriented flat film, and then successively laminating this film with similarly produced flat films such that the directions of their respective orientations cross each other. By using three layers with orientation in three different directions, such as those obtained by laminating one layer oriented in the longitudinal direction with the two layers oriented in the helical direction described above, It is known that tear propagation resistance increases significantly with thickness. One of the drawbacks of the above method (and the resulting product) is that it is practically impossible to make really thin films. As a result, the economic advantages of making high strength but low weight films are not fully realized. In practice, the minimum weight of each layer that can be spiral cut and laminated is about 30 g/m ² . That is, for two-layer laminates the lower limit is about 60 g/m ² and for three-layer laminates (which is what was mentioned above and is necessary for successful use of the tear arrest effect) it is about 90 g/m 2
g/ ^m2 . A second drawback is the practical limitations on width due to the heavy mechanical parts involved in helical cutting and the rotation of the bobbin. Generally the width is limited to about 1.5-2 m. A third drawback is related to certain energy absorption values of cross-laminates. High speed tear (Elmendorf tear test) and low and high speed tensile test (TEA
A relatively low energy absorption was observed in terms of strength and Elmendorf impact strength). The highly anisotropic nature of the layer appears to be a disadvantage. For example, when a two-ply cross-laminate of this type is pulled parallel to the direction of orientation of one layer, the yield point and elongation at break are essentially determined by that layer. Initial efforts to overcome the aforementioned drawbacks and to provide a cheaper method of manufacturing products with the same or similar properties are described in the inventor's British Patent No. 1,261,397. This document discloses a method of manufacturing a cross structure in a die with rotating parts and simultaneously forming a flexible and weak intermediate zone in the same die by coextrusion. This method involves coextruding several concentric or nearly concentric layers of crystalline polymer, with every other layer of relatively flexible polymer, and infiltration from concave wall surfaces arranged in rows. and dividing the layer within the die by teeth fixed to the cylindrical die wall in the direction and outwardly from the convex wall surface. The die parts are rotated in opposite directions, thereby dividing the layers in a left-handed spiral near the face of the sheet and in a right-handed spiral near the other face of the sheet. Combing can be carried out halfway through the film or can be limited to areas near the surface. Coextrusion of the polymer before the combing step is adapted to provide a flexible and weak intermediate zone. Films extruded by this method consist of material with little molecular orientation. However, every other hard layer of "first polymer" and a soft layer of "second polymer" divided into filaments in a linear pattern by teeth give each half of the sheet a tendency to tear or flow in one direction. . The linear patterns on both sides intersect with each other and have a tendency to delaminate, resulting in a tear arrest effect similar to the "fork" effect in true cross-laminates. The above specification further provides that, instead of providing biaxially oriented layers, the laminate is biaxially oriented under conditions such that the molecular orientation is approximately uniaxial in each layer and the directions of orientation of the different layers cross each other. It is proposed that it be extended to In order to obtain such a uniaxial orientation, the second material must be very susceptible to yield. For example, when the first substance is solid, the second material is still in a molten or semi-molten state.
The filament of the first material must then be held straight by biaxial tension. Although the above-mentioned method solves in principle the problem of obtaining relatively small thicknesses and relatively wide widths in cross-laminated products, some fundamental difficulties were found in later technical developments. The extrusion method was determined to be commercially viable for producing non-oriented films with high tear transfer strength, but low impact strength due to the lack of orientation. However, the essential drawback is that
It was found in connection with subsequent biaxial stretching. As also pointed out in the above specification, a relatively large number of rows of teeth must be used in the extrusion die in order to obtain the necessary fiber thinness for drawing. However, this makes maintenance of the die difficult and frequently causes polymer chunks to "hang" between the teeth. Furthermore, due to the interaction between the teeth on one half of the die and the teeth on the other half, it is necessary to use an excessive amount of flexible interlayer material or to comb a relatively shallow surface area on both sides of the sheet. It was necessary to limit the Furthermore, it has been very difficult to establish and maintain the biaxial stretching conditions necessary to obtain the nearly uniaxial molecular orientation described above. In laminates made by the cruciate cross-combing method described above, partial melt stretching results from a combination of longitudinal stretching caused by the tapered die wall and transverse stretching caused by counter-rotation of said walls. However, the layers are divided into fibrous structures,
Combing of the layers is carried out in a direction different from the main direction of melt drawing. This difference is particularly noticeable in the center of the laminate. Just in the middle of the laminate, the main direction of melt drawing is parallel to the extrusion direction, whereas the combing takes place in a direction forming an angle to the extrusion direction. The difference between the main direction of melt drawing and the Komig direction creates a certain notch effect in the fibrous structure, which reduces the strength of the final product. A method of manufacturing a laminate of at least two layers according to the present invention comprises at least two substantially concentric tubular streams rotating two molten polymeric materials relative to each other in an annular extrusion die having one exit slot. extrusion, melt-stretching each of the tubular streams during said extrusion in substantially one direction such that the melt-stretching directions crisscross each other; and a third layer of polymeric material selected to facilitate delamination; is coextruded between the two tubular streams achieving criss-crossing melt orientation, and the separate elongated tubular streams are combined in a die with a third layer of polymeric material in between. two common streams and then, while the polymer remains in the molten state, pass the common streams from the die through an exit slot defined by two generally concentric spaced apart cylindrical walls. discharging while rotating in opposite relative directions, thereby exposing opposing surfaces of a common extruded flow adjacent to said cylindrical wall to the rubbing action of said rotating wall during passage through said outlet slot; The stretched polymer dispersion is sheared circumferentially through the thickness of a common stream, and the common extruded stream is solidified after emerging from said exit slot, with the bonding of the solidified laminates forming a laminate. It is sufficiently weakened to allow localized delamination of the film when torn, and finally consists of collecting the thus solidified tubular sheet. Preferably, opposite sides of the exit slot through which the laminate is extruded are rotated relative to each other. This is because it will subject the laminate to shear during extrusion. The cylindrical layer is preferably
82361 (see Japanese Patent Publication No. 59-32307), in order to create polymer grains along the melt-stretching direction by melt-stretching, a portion of the polymer matrix structure is formed from a dispersion of two polymers. Thus, as explained therein, after solidification of the laminate into a film, a fibrous grain structure with the main direction of tearing can be obtained. The two layers can be rotated in different directions but with substantially the same angular velocity by the method of the invention. If high tear strength is desired, the adhesion between the two layers of the laminate must be weak enough to allow localized delamination of the laminate when the laminate is subjected to tearing. One method of creating the desired weak adhesion involves forming layers of polymers that weakly adhere to each other. Another method involves coextruding polymers between layers to adjust adhesive strength. The adhesion-modifying polymer can be an elastomer that has low adhesion to the polymeric material, ie, the material forming the tubular layer. The tack-modifying polymer can be extruded in stripes or otherwise interrupted. Whether or not it is desired to permit localized exfoliation, the polymer coextruded between the layers is advantageously an elastomer or a normally soft polymer. Each layer can be an array of streams, which of course merge to form a layer. Melt drawing can be carried out, for example, by reducing the thickness of a molten tubular layer during extrusion, or by changing the flow of material or the arrangement of the flow of molten material to a high flow rate, e.g., as described below with respect to FIG. This can be done by passing through a row of partitions that create resistance. Each layer may itself be formed from two or more separate layers prior to intersecting the directions of stretch and combining the layers. That is, passing two or more tubular layers of different polymers together through a common rotating die section and coextruding them into a common chamber of the same rotating die section, thereby forming a composite rotating die section. A cylindrical layer can be formed. Such a method is illustrated in the accompanying FIG. 2, in which coextrusion within a common rotating die portion occurs over an annular edge. It has been found that coextrusion over the edges in conjunction with a rotating arrangement is particularly advantageous. Preferably, the laminate after solidification is biaxially stretched in the solid state in at least two separate stages, each stage being essentially unidirectional. This stretching can be carried out at substantially room temperature. Generally, it is applied by applying pressure along a line extending substantially in the longitudinal direction of the sheet, for example by a single pass between grooved rollers having grooves parallel to the machine direction or at a small angle. It involves stretching the sheet into the shape of temporally evenly distributed, substantially longitudinal pleats. This method of drawing extrudates is described and claimed in a concurrently filed application. This method then provides lateral stretching as described therein. After the transverse stretching is completed, longitudinal stretching can be carried out, and preferably significant transverse contraction occurs during the longitudinal stretching. The polymeric material for the tubular flow can consist primarily of polyolefins. Preferably, at least one tube stream consists primarily of crystallizable polypropylene or high-density polyethylene, if a polymer for adjusting the adhesive strength is coextruded between the tube streams, suitable for this purpose. The material is ethylene propylene rubber. Details of the method for carrying out biaxial stretching, the polymeric materials that can be used for the layer materials and the properties of the products obtained by the method of the invention are described in more detail in the co-pending applications mentioned above. The apparatus for carrying out the method of the invention comprises an annular coextrusion die having an exit slot and at least two concentric cylindrical layers, each layer consisting of a stream or array of streams of molten polymeric material. means for feeding the layers toward the slot, means for rotating the layers relative to each other in the die and simultaneously melt-drawing each layer substantially in one direction, the layers passing through the exit slot. and means for adhering the layers in the die so that the directions of melt-stretching intersect each other immediately before. Preferably, the means for relatively rotating the layers in the die includes means for relatively rotating opposite sides of the exit slot. Preferably, the apparatus also includes means for coextruding a polymer between the tubular layers to adjust the adhesion between the layers. The invention will be described in more detail with reference to the accompanying drawings. FIG. 1 is a cross-sectional view of an extrusion die according to the invention. FIG. 2 shows, in various cross-sections, the principle of another extrusion die according to the invention, comprising two counter-rotating exit slots and means for extruding two layers through each slot; It shows. FIG. 3 is a process diagram of a preferred cold stretching method. FIG. 4 is a detail of a grooved roller that provides transverse stretching in uneven zones called striations. FIG. 5 is a schematic sketch on an enlarged scale of the striation pattern and orientation therein of a cross-stretched film according to the process of FIG. FIG. 6 is an enlarged cross-sectional view of the film shown in FIG. 5, which was actually observed under a microscope. However, for ease of understanding, the thickness is shown on a scale twice the width. The extrusion die shown in Figure 1 is one example of one that can be used, in which two polymers/polymer dispersions are extruded through two rows of partitions rotating in opposite directions and into a common collection chamber. The two dispersed streams 1 and 2 are fed through inlet channels in the lower part of the die into annular channels 4 and 5 in the two walls of the annular channel 6, respectively. Within the annular channel 6, the two rings 7 and 8 are moved in opposite directions by drive means, such as gears and teeth (not shown).
The two rings 7 and 8 are each provided with a row of partitions 9 and 10, in which two rows of openings 11 and 12 are formed, through which the two dispersions are formed, consisting of two parts 13 and 14. It is extruded into a collection chamber 15 terminating in an outlet slot 16 . Divider 9 for simplicity
and 10 are shown radially enlarged, but in reality they are positioned at an angle to the radial direction to prevent the formation of striations by the die in the extruded sheet. By extruding through the two rotating rings 7 and 8, the two dispersions are each attenuated and thereby acquire a fibrillar morphology and thus a tear direction as mentioned above. The two lines of elongated streams then combine in the collection chamber 15 to form a laminate with an intersecting fiber-like structure. The thickness of this laminate is reduced by passing through the exit slot 16 and further by conventional blowdown and blowing steps. After this, the film is stretched longitudinally and transversely at relatively low temperatures. Because of the two different fiber orientations, each half of the film exhibits a tendency to tear in different directions upon tearing.
The materials forming each of the two halves may be selected such that they weakly adhere to each other. Thereby, the material will flake off in a small area around the notch where tearing occurs, which will cause the notch effect to be lost. The die shown in FIG. 2 has four main parts: a fixed inlet part 17 for annular distribution of the polymer, a fixed bearing part 18, and two rotating parts 19 forming one outlet orifice 21, as will be explained later. and 20
Consisting of Polymer blends A and B are inlet 17
where it is distributed into concentric annular streams.
A is forced through the annular channels 22 and 23. One or two extruders can be used for this purpose. B is forced through the annular passage 24. For uniform distribution, 22, 23 and 24 are equipped with distribution boards or other distribution means (not shown). For reasons of clarity, bearings and seals between the bearing part 18, the rotating part 19 and the rotating part 20 are not shown.
The drives for 19 and 20 are also not shown. The polymer flow passes through three annular passages 22, 23 and 2
4 to 3 annular channel rows through the bearing part 18
pass through. Each channel has an annular chamber 28, 29, respectively.
and 30. The two rotating parts 19 and 20 are preferably rotated with almost constant angular velocity but in different directions as indicated by arrows 31 and 32. Each rotating part itself is
A coextrusion die for two layers, one layer consisting of A and the other layer consisting of B. For the sake of clarity, the reference numbers for the flow description are shown only for section 20, but the flow through section 19 is similar. Polymer blend A flows from chamber 29 to channel 3.
3 into the rotating section, while polymer blend B enters the rotating section from chamber 30 through channel 34. Inside the rotating part there are two annular passages 35 and 36, which communicate with channels 33 and 34, respectively, and are separated from each other by a thin annular wall 37. Passing through the edge of wall 37, A and B merge in an annular collection chamber 38 terminating in exit orifice 21. By passing through the annular channel 35 and the collection chamber 38, the thickness of the fluid sheet is greatly reduced, thereby stretching the material. The partitions between adjacent channels 33 and 34 should each be streamlined as shown. Although these are shown enlarged radially in the figures for clarity, in reality they must be configured at an angle to the radial direction to reduce the tendency for die striations. "Polymer A" is preferably a blend of two immiscible or semi-miscible polymers. On the other hand, "Polymer B" is preferably adapted to provide the sheet with suitable release properties. Polymer B can therefore consist of an elastomer that is a weak adhesive to the two layers A and can be extruded into strips. However, if channels 22 and 23 are provided with two different polymer blends, polymer B may be an adhesive that has relatively strong adhesion to the two polymer blends, and in that case it It must be extruded continuously or extruded intermittently. A preferred cold stretching method is illustrated in the step of FIG. 3, where zone "Q" is the transverse stretch line and zone "R" is the longitudinal stretch line.
The roller system in area “Q” is the driven nip roller 7.
1. It consists of a driven grooved roller 72, an idler roller 73, and a roller 74 with a longitudinal cross section resembling a banana. Banana rollers 74 serve to partially stretch out the corrugated hoops produced by the transverse stretching after each step. The film 79 is attached to the play roller 75
Beyond, the area “R” is a longitudinal extension line.
to go into. The film is then drawn through a water bath 76 which serves to remove the heat generated by stretching and to maintain a suitable stretching temperature, such as 20 DEG to 40 DEG. Finally, it is wound onto a bobbin 77. Arrow 78 indicates the machine direction. In FIG. 4, a pair of driven rollers 72 are shown in detail with the film 70 being pressed and stretched between the teeth 80 of the rollers 72. In FIG. 5, the relative lengths of the streaks of film 79 and the arrows therein indicate the relative amounts of orientation achieved by the biaxial stretching method shown in FIGS. 3 and 4. In FIGS. 5 and 6, the numbers indicate the above-mentioned lines A and B, respectively. It generally has varying widths and non-uniform properties. Additionally, it should be noted that the outer layers 81 and 82 of the film 79 are not necessarily symmetrical with respect to the thin middle layer 83. This asymmetry further helps in creating a tear fork. Below are examples of the invention. A series of sheets based on polyolefin blends were produced using the extrusion die shown in FIG. The diameter of the die exit slot 21 is 130 mm and the width is 1 mm.
It is. The maximum width of the collection chamber 38 was 4 mm, meaning that the amount of stretching during passage through the collection chamber to the exit slot was less than preferred. The extrusion temperature is 240°C. After cutting the cylindrical film along its length,
Stretching is first carried out in the transverse direction using 4 to 8 steps;
It is then carried out in the longitudinal direction using 2 to 4 steps. composition, width of the flat tube (a measure of blow ratio),
The stretching temperature, stretching ratio and effect are shown in the table below.
“Nov” stands for Novolene, a gas-phase polymerized polypropylene containing a relatively high amount of atactic modification;
“PE” stands for low density polyethylene, “EPR”
stands for ethylene-propylene rubber “SA872”
"7823" and "8623" are various types of polypropylene with a small content of polymerized ethylene.
EPR/PE means a 50:50 blend of ethylene-propylene rubber and low density polyethylene.

【table】

[Table] * Stretching percentage in both directions based on final product dimensions

【table】

[Table] **Final product The present invention is as described in the claims, but includes the following embodiments. (1) The method of claim 1, wherein the adhesion in the solidified laminate is sufficiently weak to permit localized delamination of the film upon tearing of the laminate. 2. The method of claim 1, wherein opposite sides of the exit slot through which the laminate is extruded are rotated relative to each other so that the laminate is subjected to shear forces during extrusion. (3) The method according to claim 1 or (2) above, wherein each cylindrical layer is made of a polymer/polymer dispersion such that the melt drawing creates grains of polymer along the direction of melt drawing. Method. (4) Claim 1 in which the two layers are rotated in different directions and with substantially the same angular velocity.
or the method described in (1), (2), or (3) above. (5) A method according to claim 1 or any one of (1) to (4) above, wherein generally weak adhesion is achieved by forming layers of polymers that weakly adhere to each other. (6) Claim 1 or (1) to (4) above, wherein generally weak adhesion is achieved by coextruding a polymer between the layers to adjust the adhesive strength.
The method described in. (7) The method according to (6) above, wherein the adhesive strength adjusting polymer is extruded or interrupted in the form of a string. (8) The method according to (6) or (7) above, wherein the adhesion-adjusting polymer is a polymer material or an elastomer that has weak adhesion to the substance forming the cylindrical layer. (9) A method according to claim 1 or any one of (1) to (8) above, wherein each layer consists of an array of flows and the melt drawing is carried out by passing the material through a row of partitions. (10) Claim 1, wherein the melt drawing is performed by reducing the thickness of the molten cylindrical layer.
or the method described in (1) to (8) above. (11) Prior to combining the layers with mutually intersecting directions of stretch, each layer consists of passing two or more cylindrical layers of different polymeric materials together through a common rotating die section and passing them together. Claim 1 or any one of claims 1 to 11 above formed by coextrusion into a common chamber of the same rotating die section to form a hybrid, rotating cylindrical layer. Method. (12) The method according to (11) above, wherein the coextrusion in a common rotating die section occurs on an annular edge. (13) The solidified laminate is biaxially stretched in the solid state in at least two separate stages, each essentially unidirectional. The method described in (12). (14) The method according to (13) above, wherein the stretching in the solid state is performed substantially at room temperature. (15) The method according to (14) above, comprising several steps of substantially transverse stretching by sandwiching between grooved rollers having grooves parallel to the machine direction or at a small angle. (16) The method according to (15) above, which includes stretching the laminate in the longitudinal direction after the lateral stretching. (17) The method according to (16) above, wherein substantially transverse contraction occurs during longitudinal stretching. (18) The method according to claim 1 or any of (1) to (17) above, wherein the polymer material for the tubular flow mainly comprises polyolefin. (19) The method according to (18) above, wherein the polymer material for at least one of the tubular streams consists primarily of crystallizable polypropylene. (20) The method according to (18) above, wherein the polymer material for at least one of the tubular flows is made of high-density polyethylene. (21) The method according to (19) above, wherein ethylene-propylene rubber is coextruded between the cylindrical layers in order to adjust adhesive strength. 22. The apparatus of claim 2, wherein the means for relatively rotating the layers in the die includes means for relatively rotating opposite sides of the exit slot. (23) Means for forming each layer includes means for passing two or more tubular layers of different polymeric materials together through a common rotating die section and coextruding them into a common chamber of the same die section. The device according to claim 2 or (22) above, which includes means for.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of an example of a die according to the present invention, Fig. 2 is a perspective view of another die, Fig. 3 is a process diagram of cold stretching, and Fig. 4 is a partial enlargement of a grooved roller. FIG. FIG. 5 is a sketch showing the striation pattern and orientation of the stretched film, and FIG. 6 is an enlarged cross-sectional view of the film. The numbers and symbols in each figure mean the following:
Figure 1, 1 and 2... Dispersed flow, 4 and 5... Annular channel, 6... Annular path, 7 and 8... Ring, 9 and 10... Partition, 11 and 12... Opening, 13 and 14... Collection room component, 15...
...Collection chamber, 16...Exit slot, Fig. 2, 17
...Fixed inlet part, 18...Fixed support part, 19 and 20...Rotating part, 21...Exit orifice, 22
and 23... ring road, 24... ring road, 28,2
9 and 30... annular chamber, 31, 32... arrow indicating rotation direction, 33 and 34... channel, 35...
...Annular path, 37...Annular wall, Fig. 3, Q...Transverse extension line, R...Longitudinal extension line, 71
... Driven nip roller, 72 ... Grooved roller,
73...play roller, 74...banana roller, 7
5... Idle roller, 76... Water bath, 77... Bobbin, 78... Arrow indicating machine direction, 79... Film, Figure 4, 70... Film, 72... Driven roller, 80... Teeth , FIG. 5, and...streak, 79...film, FIG. 6, and...streak, 79...film, 81 and 82...outer layer, 83...intermediate layer.

Claims (1)

[Claims] 1. Extruding two molten polymeric materials in at least two substantially concentric tubular streams rotating relative to each other in an annular extrusion die having one exit slot, each of the tubular streams during extrusion having a melt-drawing direction relative to the other. said two tubular streams substantially unidirectionally melt-stretched in a criss-cross manner to achieve a criss-cross melt orientation of the third layer polymeric material selected to facilitate delamination; coextruding the separate elongated tubular streams in a die into one common stream with a third layer of polymer material in between, and then coextruding the separate elongated tubular streams in a die while the polymer remains in the molten state. A common flow from the die to
discharge through an exit slot defined by two generally concentric spaced apart cylindrical walls while rotating said cylindrical walls in generally opposite relative directions, thereby discharging a common extruded flow adjacent said cylindrical walls. The opposing surfaces are subjected to the rubbing action of said rotating wall during passage through said exit slot to shear the stretched polymer dispersion circumferentially through the thickness of a common stream and to form a common extruded stream. is solidified after emerging from said exit slot, the bond of the solidified laminate being sufficiently weak to allow localized delamination of the film when the laminate is torn, and finally the solidified laminate is A method for extruding laminated polymer sheets with improved properties comprising the steps of collecting tubular sheets.