Abrasion-resistant inflatable film with EVOH outer layer and method for manufacturing inflatable film

Abstract

In order to produce a wear-resistant plastic laminate (1) with an outer EVOH layer (2) in the inflated film method, it is specified that the co-extruded plastic tube (14) be cooled to a temperature lower than the glass transition temperature of EVOH in the EVOH layer (2), preferably at least 5°C lower than the glass transition temperature, before entering the roller gap (20) between the draw rollers (17) and before compression between the draw rollers (17), in order to produce the wear resistance of the EVOH layer (2).

Description

Technical Field

[0001] The present invention relates to a method for manufacturing a plastic laminate comprising an outer wear-resistant EVOH layer and a plastic laminate in contact with this EVOH layer. The EVOH layer and the plastic laminate are co-extruded together in an inflatable film method, and the EVOH layer and the plastic laminate are co-extruded concentrically in one co-extrusion die to form a plastic tube. Thereby, the EVOH layer is positioned so as to be located inside the plastic tube. The co-extruded plastic tube is pulled out in the extrusion direction after exiting from the co-extrusion die, inflated by a pressurized gas to form a plastic bubble, and the plastic bubble is cooled and folded. Thereby, within the folded plastic bubble, the EVOH layers are positioned in contact with each other. The folded plastic bubble is passed through the roller gap between the drawing rollers, compressed while applying pressure at that time, and the compressed plastic bubble is cut open on the downstream side of the drawing rollers in the extrusion direction to form a plastic laminate, and separated in the EVOH layers that are positioned in contact with each other. Thereby, the EVOH layer forms an outer layer in the plastic laminate. The present invention also relates to a plastic laminate manufactured by this method.

Background Art

[0002] A plastic laminate has multiple plastic layers that are in contact with each other. Plastic laminates are often used as packaging laminates for manufacturing packaging. The plastic layers in a plastic laminate may have different functions from each other. A bonding layer, for example, primarily functions to create sufficient bonding between two plastic layers, and is positioned between the two plastic layers so that it is in contact with these two plastic layers. A sealing layer is an outer layer in the plastic laminate and functions to manufacture packaging using the plastic laminate by sealing the plastic laminates together with each other or with another packaging part at the sealing layer. A base layer is usually an inner layer in the plastic laminate and imparts important mechanical properties to the plastic laminate, such as strength, toughness, and elongation at break. A barrier layer is often used in packaging laminates and functions to create a sufficient barrier against water vapor, oxygen, or odors. In addition to these, there may, of course, be other plastic layers in the plastic laminate. The structure of plastic laminates naturally depends on their specific application and function, such as packaging lamination.

[0003] Based on Patent Document 1, a packaging laminate having multiple such layers is known as a plastic laminate, and this packaging laminate also includes an outer layer made of ethylene-vinyl alcohol copolymer (EVOH) as a thermally stable layer to improve sealing properties. This thermally stable layer can particularly increase the sealing temperature. Another layer of the packaging laminate consists mainly of polyethylene or polyethylene copolymer material for recyclability reasons. The outer EVOH layer, which is not made of polyethylene or polyethylene copolymer material, is also made extremely thin for recyclability reasons, being a maximum of 10% of the total thickness of the packaging laminate, but absolutely a maximum of 10 μm. This ensures that the thin EVOH layer does not impair PE recycling.

[0004] Co-extruded packaging laminates having an outer EVOH layer and several other plastic layers are also known from Patent Document 2. Patent Documents 3 and 4 also describe co-extruded packaging laminates having an outer EVOH layer, manufactured using the inflated film method, respectively.

[0005] Plastic laminates are often manufactured using co-extrusion methods, such as blown film extrusion or cast film extrusion. Co-extruded plastic laminates are typically wound onto rolls in large lengths and then further processed in a processing machine to form, for example, packaging. In the processing machine, the plastic laminate passes through the machine (very often at high speeds, for example, up to 600 m / min, if the plastic laminate is printed by intaglio or flexographic printing). In the processing machine, the plastic laminate usually undergoes a variety of processing steps. The plastic laminate is also deflected within the processing machine and guided, for example, by contacting rollers or other parts of the processing machine.

[0006] While plastic laminates manufactured by co-extrusion in the inflated film process, featuring an outer EVOH layer, are known from prior art, such plastic laminates have not yet penetrated the market. This may be due to problems associated with manufacturing in the inflated film process.

[0007] In plastic laminates co-extruded in the inflated film process, which have an external EVOH layer, it has been found that EVOH abrasion occurs during subsequent processing in the processing machine, even though the plastic laminate exits the inflated film equipment without noticeable defects. This abrasion appears in the form of fine fibers (typically with a thickness ranging from 10 to 30 μm and a length of several millimeters to centimeters) or as powder that adheres to the external EVOH layer or accumulates on parts of the processing machine. Such EVOH abrasion powder is unacceptable, for example, as it visually impairs the packaging produced from the plastic laminate. When such plastic laminates are used as packaging laminates for manufacturing packaging, EVOH abrasion powder can also lead to contamination of the filling, for example, during the packaging process or when the packaging is opened. Such contamination is undesirable in any case, especially in the field of food packaging. The accumulation of EVOH abrasion powder in the processing machine leads to impaired machine function and results in laborious maintenance work on machine components, such as cleaning or replacement. All of these things are highly undesirable and should be avoided during the processing of plastic laminates.

[0008] In plastic laminates co-extruded using the flat film method, which had an externally located EVOH layer, no such EVOH wear particles were observed. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] International Publication No. 2019 / 243456 [Patent Document 2] International Publication No. 98 / 49005 [Patent Document 3] European Patent Application Publication No. 764519 [Patent Document 4] International Publication No. 2018 / 182712 [Overview of the Initiative] [Problems that the invention aims to solve]

[0010] Therefore, the object of the present invention is to improve a plastic laminate co-extruded in an inflated film method, which has an outer EVOH layer, and a method for producing such a plastic laminate, so as to ensure that the formation of EVOH wear particles is prevented when the plastic laminate is further processed. [Means for solving the problem]

[0011] This problem is solved, according to the present invention, by cooling the co-extruded plastic tube to a temperature lower than the glass transition temperature of EVOH in the EVOH layer, preferably at least 5°C lower than the glass transition temperature, before it enters the gap between the draw rollers and before compression between the draw rollers, in order to produce wear resistance in the EVOH layer. The glass transition temperature is a known material parameter, and it can be assumed that this material parameter is known for the EVOH material used in the outer EVOH layer, for example, based on a data sheet for the EVOH material.

[0012] Experiments by the inventors have confirmed that when EVOH layers located in contact with each other in folded plastic tubes are compressed in the gap between the draw rollers at a temperature higher than the glass transition temperature, increased adhesion occurs between the EVOH layers. This leads to mechanically weakened areas on the surface of the EVOH layers during subsequent separation for forming the plastic laminate. Although these mechanically weakened areas on the surface are not visible to the naked eye in the plastic laminate, they cause a decrease in the wear resistance of the EVOH, resulting in increased wear of the EVOH during subsequent processing in a processing machine, for example, and ultimately leading to the formation of undesirable EVOH wear particles. In the inflated film method for manufacturing plastic laminates, the present invention ensures that the folded plastic tubes are cooled to a temperature lower than the glass transition temperature of EVOH, preferably at least 5°C lower than the glass transition temperature, immediately before the draw rollers, that is, before the flattened plastic tubes enter the gap between the draw rollers. This reliably prevents the formation of such mechanically weakened areas and also reliably prevents the formation of EVOH wear particles when the plastic laminate is further processed.

[0013] When polyethylene is mainly used in the plastic laminate, that is, when the polyethylene content in the plastic laminate is at least 60 vol%, preferably at least 70 vol%, and most preferably at least 80 vol%, or when polypropylene is mainly used in the plastic laminate, that is, when the polypropylene content in the plastic laminate is at least 60 vol%, preferably at least 70 vol%, and most preferably at least 80 vol%, it is possible to produce a recyclable plastic laminate that can be recycled using conventional, particularly mechanical, recycling methods. For this purpose, when polyethylene is mainly used in the plastic laminate, it is advantageous if the polyethylene content in the sealing layer is at least 80 vol%, or when polypropylene is mainly used in the plastic laminate, it is advantageous if the polypropylene content in the sealing layer is at least 80 vol%.

[0014] Similarly, if the EVOH layer is up to 10% of the total thickness of the plastic laminate, preferably up to 5%, but up to 10 μm thick, it is advantageous for the recyclability of the plastic laminate.

[0015] The present invention will be described in more detail below with reference to Figures 1 to 6, which illustrate, in an exemplary and schematic manner, advantageous configurations of the present invention without limitation. [Brief explanation of the drawing]

[0016] [Figure 1] This is a diagram showing the known basic principles of inflatable film equipment. [Figure 2] This figure shows the structure of the plastic laminate according to the present invention. [Figure 3] This figure shows an example of the structure of the plastic laminate according to the present invention. [Figure 4] This figure shows another embodiment of the structure of the plastic laminate according to the present invention. [Figure 5]It is a figure showing a test apparatus for executing a test method for measuring the abrasion resistance of an EVOH layer. [Figure 6] It is a figure showing an EVOH layer having EVOH wear powder in the form of fibers.

Mode for Carrying Out the Invention

[0017] FIG. 1 shows the well-known basic principle of an inflation film facility 10 for co-extruding a plastic laminate 1 in the inflation film method. According to the present invention, the plastic laminate 1 has an outer EVOH layer 2 and a plastic laminate 3, as shown in FIG. 2 for example. By co-extrusion, the EVOH layer 2 is in direct contact with the plastic laminate 3, that is, the surface of the EVOH layer 2 facing the plastic laminate 3 is in contact connection with the surface of the plastic laminate 3 facing the EVOH layer 2.

[0018] The well-known inflation film facility 10 includes a co-extrusion die 11 having a plurality of melt passages 12. Each melt passage 12 is connected to an extruder 13 (only one is shown for simplicity), and in this extruder 13, the plastic material is melted, and by this extruder 13, the melted plastic material is sent into the corresponding melt passage 12. In the embodiment shown in FIG. 2, two melt passages 12 are provided, whereby a two-layer plastic laminate 1 including an EVOH layer 2 and a plastic laminate 3 can be co-extruded. However, it is known that in an inflation film facility, it is also possible to co-extrude a plastic laminate 1 having more than two laminates, for example, three laminates, four laminates, five laminates or even more laminates. In such a plastic laminate 1, of course, a correspondingly larger number of melt passages 12 and extruders 13 are provided. The individual laminates of the plastic laminate 1 may contain various different plastic materials, but the outer laminate forms the EVOH layer 2.

[0019] During co-extrusion, the plastic molten material is stacked on top of each other in a desired order within the co-extrusion die 11, thereby causing the co-extruded plastic molten material to exit the co-extrusion die 11 in the form of a plastic tube 14 with concentrically arranged plastic layers. The thickness of the individual plastic layers can be adjusted as needed and does not need to be the same.

[0020] According to the inflated film method of the present invention, the plastic layer of the plastic laminate 1 is co-extruded such that the EVOH layer 2 is positioned on the inside within the plastic tube 14, that is, to form the innermost plastic layer within the plastic tube 14, as indicated in Figure 1.

[0021] The plastic tube 14 is cooled after emerging from the co-extrusion die 11, which causes the plastic to begin to harden. Figure 1 suggests a cooling unit 15 that blows, for example, cold air onto the plastic tube 14. Simultaneously, after emerging from the co-extrusion die 11, the plastic tube 14 is expanded by a pressurized gas 21, such as air, blown into the plastic tube 14 to form a plastic bubble 14a. A blower supplying the pressurized gas 16 is not shown in Figure 1 for simplification. Thus, the EVOH layer 2 is located on the inner surface of the expanded plastic bubble 14a.

[0022] The plastic bubble 14a is controlled as is known by adjusting the pressurized gas 21 supplied for expansion and the pressurized gas 21 (not shown in Figure 1) released from the plastic bubble 14a, thereby preventing the plastic bubble 14 from collapsing or bursting and resulting in a stable inflated film process. The pressurized gas 21 also causes internal cooling of the co-extruded plastic tube 14.

[0023] The plastic molten material is stretched by inflating the co-extruded plastic tube 14. In inflated film extrusion, the plastic molten material is typically stretched about 2 to 3 times in the transverse direction (so-called blow-up ratio) and stretched at a ratio of 1:10 to 1:100 in the longitudinal direction (so-called draw-out ratio), in which case the draw-out ratio is also defined by the draw-out roller 17, as will be further explained below. If the co-extruded plastic laminate 1 is not stretched after co-extrusion, the co-extruded plastic layer obtains its final thickness through co-extrusion. If stretching is planned, the thickness in the plastic laminate 1 will still change due to the stretching.

[0024] The plastic bubble 14a is cooled to a temperature lower than the melting point of the plastic material of the plastic tube 14, thereby allowing the plastic tube to harden sufficiently and then be folded. For folding, a flattening device 16 may be provided, for example, an assembly of rotatably supported rollers or a guide surface, and the plastic tube 14a is passed alongside this flattening device 16, which folds the plastic bubble 14a. The optional flattening device 16 is located downstream of the molten die 11 in the extrusion direction. This folding overlaps the EVOH layers 2 located on the inside of the plastic tube 14, so that the two EVOH layers 2 are in contact with each other in the folded plastic tube 14. However, folding of the plastic bubble 14a can be performed between the draw rollers 17 without a flattening device 16. However, typically, the flattening device 16 is located upstream of the draw rollers 17 in the inflatable film equipment 10 in the extrusion direction.

[0025] The expanded and cooled, and possibly already folded, plastic bubble 14a passes through the roller gap 20 between the two draw rollers 17. The draw rollers 17 are driven to move the plastic tube 14 in the extrusion direction. The rotational speed of the draw rollers 17 substantially determines the draw ratio. In the roller gap 20 between the draw rollers 17, the folded plastic tube 14b is pressed together under pressure. This occurs because the width of the roller gap 20 is smaller than the thickness of the folded plastic tube 14b.

[0026] Downstream of the pull-out roller 17 in the extrusion direction, the folded plastic tube 14b can be redirected as needed. The folded plastic tube 14b can then be wound onto the roll 18. To produce the plastic laminate 1, the folded plastic tube 14b must be cut open, which may occur before winding onto the roll 18. This is usually done by cutting the folded edges on both sides of the folded plastic tube 14b using a cutting unit 19 (as shown in Figure 1), thereby producing a pair of flat plastic laminates 1 of equal width. The plastic laminates 1 must then be further separated from each other by peeling, so that they can be wound separately onto the roll 18. This separation process does not have to be performed directly in the inflatable film equipment 10, but can be done at a later point, for example, before the processing machine. However, the separation process is usually performed in the inflatable film equipment 10.

[0027] The plastic laminate 1 manufactured in this manner may be further stretched in the longitudinal direction (extrusion direction), transverse direction (transverse to the longitudinal direction), or both longitudinal and transverse directions before processing. The stretching of plastic laminates is well known and does not need to be explained in further detail. Substantially, during stretching, the plastic laminate 1 is stretched in one or more stretching directions at a temperature lower than the melting temperature of the plastic in the plastic laminate 1, and in the process is exposed to orientations that can alter certain properties of the plastic in the plastic laminate 1.

[0028] To prevent the formation of mechanically weakened areas on the surface of the EVOH layers 2 by this separation process in the bonded and adhering EVOH layers 2, the present invention specifies that the co-extruded and expanded plastic tube 14 is cooled to a temperature lower than the glass transition temperature of the EVOH in the EVOH layers 2, preferably at least 5°C lower than the glass transition temperature, before reaching the draw rollers 17. If the EVOH layers 2 contain various types of EVOH, the cooling is performed to a temperature at least 5°C lower than the glass transition temperature of the EVOH having the lowest glass transition temperature. This temperature is preferably achieved, for example, by folding in the flattening apparatus 16 or by introduction between the draw rollers 17, before the EVOH layers 2 come into contact with each other upstream of the draw rollers 17 in the extrusion direction, and in any case before the EVOH layers 2 are pressed against each other in the roller gap 20 between the draw rollers 17.

[0029] This cooling can be achieved by properly cooling the plastic tube 14 between the co-extrusion die 11 and the draw roller 17, by reducing the extrusion speed of the plastic tube 14 (which increases the cooling time), or by extending the section between the co-extrusion die 11 and the draw roller 17. Basically, a combination of these measures is also possible, but reducing the extrusion speed is usually undesirable because it reduces the output of the inflated film equipment 10. Therefore, the temperature of the plastic tube 14 upstream of the roller gap 20 between the draw rollers 17 can be reliably monitored, controlled, and adjusted in the inflated film equipment 10.

[0030] According to the present invention, it is important that the plastic tube 14 reaches a desired temperature lower than the glass transition temperature of EVOH in the EVOH layer 2, preferably at least 5°C lower than the glass transition temperature, before it enters the gap 20 between the draw rollers 17, that is, before it is pressed together between the draw rollers 17. Although the draw rollers 17 are usually temperature-controlled in the inflatable film equipment 10, it would be too late if the plastic tube 14 were only cooled to a desired temperature lower than the glass transition temperature of EVOH in the EVOH layer 2 between the draw rollers 17. This is because the EVOH layers, which are already in contact with each other, would adhere too strongly due to the pressing, which would result in mechanically weakened areas on the surface of the EVOH layer 2 during subsequent separation.

[0031] It has been found that the abrasion resistance of the EVOH layer 2 is reduced in any plastic laminate 1 having an outer EVOH layer 2 co-extruded in the inflated film method described above, without the measures according to the present invention. This results in EVOH abrasion debris if the plastic bubble 14a is not cooled to a temperature lower than the glass transition temperature of EVOH in the EVOH layer 2, preferably at least 5°C lower than the glass transition temperature, before reaching the draw roller 17, and is subsequently processed. This is due to the mechanical weakening of the outer EVOH layer 2 in the plastic laminate 1 based on mechanically weakened areas on the surface of the EVOH layer 2 caused by the separation process in the EVOH layers 2 located in contact with each other, which results in abrasion of the EVOH layer 2 when processed further. The abrasion resistance of the EVOH layer 2 is thus reduced, and undesirable EVOH abrasion debris is generated when processed further. In plastic laminates 1 manufactured by flat film or lamination methods, with an outer EVOH layer 2, this negative effect of reduced abrasion resistance of the EVOH layer 2 was not observed.

[0032] When the co-extruded plastic laminate 1 is further stretched after co-extrusion, the negative effect of reduced abrasion resistance is enhanced by the stretching and high orientation of EVOH in the stretching direction. This even increases EVOH abrasion debris without the measures according to the present invention.

[0033] In all cases, the manufacturing method according to the present invention improves the abrasion resistance of the outer EVOH layer 2 in the plastic laminate 1 compared to a plastic laminate 1 co-extruded in an inflated film method that has an outer EVOH layer and is not manufactured according to the present invention. This also applies to plastic laminate 1 that is additionally stretched. Therefore, the properties of plastic laminate 1 co-extruded in an inflated film method are significantly improved by the measures according to the present invention, which for the first time enables further processing of such plastic laminate 1 without undesirable EVOH abrasion particles.

[0034] The inventors' investigation revealed a strong correlation between the wear resistance of the EVOH layer 2 and the temperature of the plastic tube 14 before it entered the roller gap 20 between the drawer rollers 17. In contrast, changes in the EVOH type in the EVOH layer 2, the structure of the plastic laminate 3 of the plastic laminate 1, or other process parameters of the inflated film method had no verifiable effect on wear resistance.

[0035] A proprietary test method was developed to measure the abrasion resistance of EVOH layer 2. This test method is a standard test and is based on known measurements of the coefficient of friction as defined in many standards, e.g., ASTM D1894 or ISO 8295. In this test, a carriage equipped with the test object is pulled on the test surface and the resulting tensile force is measured. The test is performed under a predetermined framework, such as a specified temperature (e.g., room temperature of 23°C), with a specified size test object, a specified weight, and a specified tensile speed.

[0036] However, to measure abrasion resistance, the coefficient of friction is not determined. Instead, a tensile process is repeated over a specified number of cycles, and then the surface of the test object (EVOH layer 2) is evaluated to see whether abrasion in the form of fibers or powder occurs on its surface. If there is no abrasion in the form of fibers or powder, EVOH layer 2 has the required abrasion resistance; if there is abrasion in the form of fibers or powder, EVOH layer 2 does not have the required abrasion resistance.

[0037] Figure 5 shows the test apparatus 30 used in a test method to test the wear resistance of the EVOH layer 2.

[0038] The test apparatus 30 for measuring wear resistance includes a flat mounting table 31 and a carriage 32 having a known mass. The carriage 32 is placed on the mounting table 31. The carriage 32 and the mounting table 31 are movable relative to each other, and normally the mounting table 31 is stationary while the carriage 32 is moved on the mounting table 31 (as in the configuration shown in Figure 5). However, for the test, it is not important whether the carriage 32 moves on the mounting table 31 or whether relative motion is performed by the mounting table 31. The mounting table 31 may be made of, for example, a metal plate, a glass plate, or a plastic plate.

[0039] A single piece of plastic laminate 1 is placed on the mounting table 32 and the carriage 32, and as shown in Figure 5, the EVOH layer 2 of the plastic laminate 1 is located on the outside of the mounting table 2 and the carriage 32. Thus, plastic laminate 1 to plastic laminate 1 is tested. Thus, the EVOH layer 2 of the plastic laminate 1 provided on the carriage 32 faces the EVOH layer 2 of the plastic laminate 1 provided on the mounting table 31. When the carriage 32 with the plastic laminate 1 is placed on the mounting table 31 with the plastic laminate 1, both EVOH layers 2 facing each other are in contact. When relative motion occurs between the mounting table 31 and the carriage 32, both EVOH layers 2, which are in contact with each other, slide against each other and rub against each other. The pieces of plastic laminate are positioned so that the relative motion occurs in the direction of extrusion of the plastic laminate 1.

[0040] How the relative motion between the mounting table 31 and the carriage 32 is caused is not important to this test method. In the embodiment shown in Figure 5, the carriage 32 is coupled to a cable 33. The cable 33 is pulled (indicated by force F), causing the carriage 32 to move on the mounting table 31 over a predetermined section s at a predetermined relative velocity v.

[0041] The test method is carried out at room temperature (23°C) using the following test parameters.

[0042] The carriage 32 weighs 200g, and the contact area A of the carriage 32 with the mounting table 31 is 60mm x 66mm, with larger dimensions in the direction of relative velocity v. This weight is 495.4 N / m 2This imparts a surface load to the EVOH. The relative velocity v is 100 mm / min. The section s over which the EVOH layers 2, positioned in contact with each other, are moved at relative velocity v is 300 mm. The carriage 32 is moved relative to the mounting table 31 five times, back and forth, using these test parameters. That is, the mounting table 31 and carriage 32 are placed back to their starting positions in each iteration, and the relative motion is repeated using the test parameters. Each time, the EVOH layers 2, facing each other, rub against each other. After that, the EVOH surface of the EVOH layer 2 of the tested plastic laminate 1 is examined. This examination is performed visually, and this examination allows for the confirmation of any EVOH wear particles that may be generated.

[0043] If EVOH wear particles in the form of fibers or powder are detected during the post-test investigation, then EVOH layer 2 does not possess the required wear resistance. If no EVOH wear particles are detected, then EVOH layer 2 possesses the required wear resistance.

[0044] Figure 6 shows an enlarged partial view of the EVOH layer 2 of the plastic laminate 1, showing EVOH wear particles 35 in the form of EVOH fibers. The EVOH wear particles 35 in the form of EVOH fibers can be seen with the naked eye.

[0045] All tested plastic laminates 1 manufactured using the inflated film method according to the present invention, which are equipped with an outer EVOH layer 2, did not exhibit EVOH wear particles 35 when the above test method was performed. In contrast, plastic laminates 1 manufactured using the inflated film method, which are equipped with an outer EVOH layer 2 whose glass transition temperature is not lowered before entering the roller gap 20 between the drawer rollers 17, exhibited significant EVOH wear particles 35 and therefore lacked the wear resistance required for continued processing.

[0046] The effects of the present invention are demonstrated based on a specific example. For this example, a plastic laminate 1 having an EVOH / Tie / HDPE structure was manufactured by the inflated film method and, after co-extrusion, stretched longitudinally at a ratio of 4.5:1. The symbol " / " in the laminate structure indicates a direct contact connection between two adjacent layers. The outer EVOH forms the EVOH layer 2, and the Tie / HDPE forms another plastic laminate 3. The Tie layer is a binding layer to ensure bonding adhesion in the plastic laminate 1 and consists of LLDPE-g-MAH (linear low-density polyethylene grafted with maleic anhydride (MAH)). The Tie layer has a thickness of 2 μm. The EVOH layer 2 consists of EVOH containing 100% and 32 mol% ethylene and has a thickness of 2 μm. EVOH has a glass transition temperature Tg of 60°C. The HDPE layer of another plastic laminate 3 is 16 μm thick and consists of HDPE with a density of 0.95 and an MFI of 1.0 (190°C / 2.16 kg). The HDPE may contain small amounts (up to 5% by weight) of common and known processing additives for co-extrusion.

[0047] The EVOH / Tie / HDPE structure of plastic laminate 1 was manufactured using the inflated film method. In one case (Case A), the temperature of the plastic bubble 14a before entering the roller gap 20 between the draw rollers 17 was 55°C (5°C lower than the glass transition temperature Tg). In another case (Case B), the temperature of the plastic bubble 14a before entering the roller gap 20 between the draw rollers 17 was 60°C (corresponding to the glass transition temperature Tg). Both plastic laminates 1 were tested using the test method described above.

[0048] In Case A, EVOH wear particles 35 were not detected. In contrast, EVOH wear particles 35 were detected in Case B.

[0049] This result also occurs when different types of EVOH with different ethylene content are used in the EVOH layer 2. This result is independent of other process parameters of the inflated film method, such as the melting temperature, draw ratio, or blow-up ratio in the extruder 13. Similarly, this result was found to be independent of the stretching parameters of the stretching process following co-extrusion, such as the stretching temperature during the stretching of the plastic laminate 1. Likewise, this result was found to be independent of the inflated film equipment. The test was repeated using three different inflated film equipment 10, and the same results were always obtained.

[0050] The only critical process parameter for obtaining the wear resistance of the EVOH layer 2 is the temperature of the plastic bubbles 14a co-extruded in the inflated film method before they enter the roller gap 20 between the draw rollers 17, i.e., immediately before contact with the draw rollers 17 occurs. This temperature must be lower than the (possibly lowest) glass transition temperature Tg of EVOH in the EVOH layer 2, and preferably at least 5°C lower than the glass transition temperature Tg.

[0051] As described below, various structures of the plastic laminate 1 with an outer EVOH layer 2 are possible. Basically, the structure of the plastic laminate 3 is arbitrary. This is because the wear resistance of the EVOH layer 2 is extremely important, and the structure of the plastic laminate 3 mainly depends on the specific application of the plastic laminate 1.

[0052] The EVOH layer 2 in plastic laminate 1 consists of at least 80 vol% ethylene-vinyl alcohol copolymer (EVOH), preferably 100 vol% EVOH. EVOH is available in various configurations. For the EVOH layer 2, EVOH with an ethylene content of up to 50 mol%, preferably 24 mol% to 50 mol%, is used. Depending on the ethylene content in the EVOH, for example, the melting temperature of the EVOH is 155°C (48 mol% ethylene content) to 190°C (27 mol% ethylene content). The glass transition temperature Tg of the EVOH in the EVOH layer 2 is typically 50°C (48 mol% ethylene content) to 63°C (27 mol% ethylene content). These physical parameters, particularly the glass transition temperature (Tg), and other physical parameters such as the melt flow index (MFI), density, water vapor transmission rate (WVTR), and oxygen transmission rate (OTR) of EVOH, can be assumed to be known for each EVOH material, as they are evident from the datasheets of the EVOH material manufacturers.

[0053] Preferably, only EVOH, i.e., 100 vol% EVOH, is used in EVOH layer 2. However, a mixture of EVOH and a small proportion, i.e., up to 20 vol% ethylene(co)polymer, can also be used. The ethylene(co)polymer can be 0.94-0.97 g / cm³. 3 High-density polyethylene (HDPE) with a density of 0.915~0.935 g / cm³ 3 Polyethylene can be in the form of a homopolymer such as low-density polyethylene (LDPE) or another PE homopolymer having a density of , or in the form of a copolymer such as linear low-density polyethylene (LLDPE), metallocene linear low-density polyethylene (mLLDPE), ethylene vinyl acetate copolymer (EVA), ethyl methacrylate (EMA), ethylene / acrylic acid copolymer (EAA), or ethylene-butyl acrylate copolymer (EBA).

[0054] The plastic laminate 3 of the plastic laminate 1 has at least one plastic layer.

[0055] Based on co-extrusion in the inflated film method, the polymers in all plastic layers of plastic laminate 1 according to the present invention have a maximum MFI of 4, preferably a maximum MFI of 3, at 190°C and 2.16 kg, which differs from polymers used in the flat film extrusion method (which typically have an MFI of up to 6-8). Even when individual polymer raw materials in the MFI range of 5-4 can be fully used in both methods, a typical inflated film has an average MFI of 0.3-1.5 for all plastics used in the composition of plastic laminate 1, while films produced by the flat film extrusion method and BOPE films have an MFI greater than 1.5. This makes it possible to infer the manufacturing process based solely on the MFI of the polymers used in plastic laminate 1.

[0056] The plastic laminate 3 is preferably composed of multiple layers, that is, multiple plastic layers that are co-extruded together with the outer EVOH layer 2.

[0057] In one possible embodiment shown in Figure 3, the plastic laminate 3 comprises a binder layer 4 (tie layer), a substrate layer 5, and a sealing layer 6, resulting in an EVOH / Tie / substrate layer / sealing layer structure. Co-extrusion causes the binder layer 4 to be in direct contact with the EVOH layer 2, and the substrate layer 5 to be in direct contact with the binder layer 4. In the case of a co-extruded sealing layer 6, the sealing layer 6 is in direct contact with the substrate layer 5. If an additional binder layer is provided between the substrate layer 5 and the sealing layer 6 to enhance bonding adhesion, this additional binder layer 4a (tie layer) is in direct contact with the substrate layer 5 and the sealing layer 6, resulting in an EVOH / Tie / substrate layer / tie / sealing layer structure.

[0058] In this context, "directly" means that the surfaces of each plastic layer facing each other are in contact and connected.

[0059] However, the base layer 5 or the sealing layer 6 may be composed of multiple layers, that is, they themselves may include multiple co-extruded plastic layers located in direct contact with each other.

[0060] The binding layer in the plastic laminate 1, such as binding layer 4 or 4a, primarily works to achieve sufficient bonding adhesion in the plastic laminate 1. A suitable binding layer is preferably made of a polymer with increased polarity based on a polymer that is compatible with polyethylene with respect to recyclability, such as a maleic anhydride-modified polyolefin (e.g., PE or PP), ethylene vinyl acetate copolymer (EVA), ethylene / acrylic acid copolymer (EAA), ethylene-butyl acrylate copolymer (EBA), or similar polyolefin copolymer, particularly a PE copolymer.

[0061] However, as shown in Figure 4, the sealing layer 6 can also be bonded to the plastic laminate 3 only after co-extrusion of the EVOH layer 2 and the plastic laminate 3, for example, by extrusion lamination, extrusion coating, or adhesive lamination with a suitable bonding layer 4a. During lamination, the sealing layer 6 is bonded to the plastic laminate 3 by a suitable laminating adhesive, for example, a polyurethane adhesive based in the case of extrusion coating, and a polyolefin copolymer, particularly a PE copolymer, based in the case of extrusion lamination. The thickness of the laminating adhesive is preferably 1 to 5 g / m². 2 Alternatively, a conventional polyurethane-based adhesive of 2-5 g / m² is preferable. 2 Alternatively, when using extrusion lamination, the amount is 5-20 g / m². 2 That is the case.

[0062] In a preferred configuration, the plastic laminate 3, and optionally the sealing layer 6, also consist primarily of polyethylene (PE) material and a small proportion of a recyclable compatible material. “Primarily” means that the proportion of PE in the plastic laminate 3, and optionally the sealing layer 6, is at least 60 vol%, preferably at least 70 vol%, and very particularly preferably at least 80 vol%. A high polyethylene content allows for the production of a recyclable plastic laminate 1.

[0063] In the plastic laminate 3, a specific type of PE such as LDPE, LLDPE, MDPE, HDPE, or PE copolymer can be used, or a mixture of different types of PE, or multiple laminates of different types of PE can be used, thereby obtaining the desired PE ratio.

[0064] While the PE content can approach 100 vol%, it typically never reaches 100 vol% due to the presence of common additives in plastic laminate 1 (e.g., slip additives, antiblocking additives, dyes, fillers, etc.). Additives are sometimes added in small amounts (up to 5 vol%). However, based on their small quantity, these additives do not impair the recyclability of the packaging laminate 1.

[0065] The sealing layer 6 is mainly made of PE material, and the percentage of PE in the total polymer amount of the sealing layer 6, without the addition of mineral-based or other fillers or additives, is preferably at least 80 vol%. In this case, different types of PE, such as LDPE, LLDPE, MDPE, HDPE, or PE copolymers, can be used in pure form, as mixtures, or in multilayers.

[0066] In addition to the PE content (and possible additives), the remaining plastic material that may be present in the plastic laminate is preferably a compatible polyolefin material that does not impair recyclability. As compatible polyolefin materials, basically all types of polyethylene, especially ethylene copolymers, such as ethylene vinyl acetate copolymer (EVA), ethyl methacrylate (EMA), ethylene / acrylic acid copolymer (EAA), or ethylene-butyl acrylate copolymer (EBA), can be considered. Similarly, as compatible polyolefin materials, polypropylene (PP) or cycloolefin copolymer (COC) can also be used in amounts up to 20 vol%. In the case of PP, preferably, polypropylene random copolymers, polypropylene copolymers with ethylene as a comonomer (usually 5-15 mol%), or polypropylene homopolymers that are sufficiently compatible with linear PE types such as mLLDPE, LLDPE, or HDPE are used to obtain at least limited recyclability.

[0067] PE and compatible polyolefin materials may exist in the plastic laminate 3, and optionally in the sealing layer 6, as a mixture or in the form of multiple layers, comprising one (or more) PE layers and one (or more) layers made of compatible polyolefin materials.

[0068] In a particularly advantageous configuration, HDPE is mainly used in the base layer 5 of the plastic laminate 3, and the HDPE content is at least 60 vol%, preferably at least 70 vol%, and very preferably at least 80 vol%.

[0069] In another configuration, the base layer 5 is mainly made of polypropylene (PP). In this configuration, the sealing layer 6 is also made of PP.

[0070] The co-extruded plastic laminate 1 can also be stretched in one direction (usually longitudinally) or two directions before being bonded to the sealing layer 6. This has the special advantage that the asymmetric structure with EVOH in the outer laminate is less prone to curling (so-called "curling"). However, the sealing layer 6 is preferably not stretched in this case.

[0071] The degree of elongation is preferably at least 4:1 in the longitudinal direction. Unidirectional stretching can be carried out significantly more easily and inexpensively than bidirectional stretching, and is therefore preferred.

[0072] It should be noted that in inflated film extrusion, the extrusion gap (typically 1.5–2.5 mm for inflated films) is significantly larger than the final thickness of the extruded film (typically 10–200 μm). The extruded molten material is stretched at a temperature well above the melting point of the extruded polymer, thereby reducing its thickness. In inflated film extrusion, the molten material is typically stretched, for example, by about 2–3 times in the transverse direction (the so-called blow-up ratio) and by a ratio of 1:10–1:100 in the longitudinal direction (the so-called draw-out ratio). However, the effect of this stretching during extrusion molding cannot be compared to the stretching of plastic films. This is because stretching is usually performed at a temperature slightly below the melting point of the polymer, which allows for the permanent alignment of misaligned polymers and subcrystalline regions in the stretching direction.

[0073] EVOH is indeed produced from ethylene, such as polyethylene, but it does not form polyethylene or polyethylene copolymer, but rather a unique polymer class. Therefore, EVOH poses a problem, particularly with respect to the recycling of plastic laminate 1. To avoid negatively impacting the recyclability of plastic laminate 1, the EVOH layer 2 preferably has a thickness of up to 10%, preferably up to 5%, of the overall thickness of plastic laminate 1 (including the sealing layer 6 and optionally a bonding layer between the sealing layer and the substrate layer 5), but is absolutely no more than 10 μm (regardless of the overall thickness). If the plastic laminate 1 includes multiple EVOH layers, for example in the form of a barrier layer, these EVOH layers together preferably have a thickness of up to 10%, preferably up to 5%, of the overall thickness of plastic laminate 1 (including the sealing layer 6 and optionally a bonding layer between the sealing layer and the substrate layer 5), but is absolutely no more than 10 μm (regardless of the overall thickness). Based on the small thickness of the EVOH layer 2, the recyclability of the plastic laminate 1 is not compromised. This is particularly advantageous when combined with a plastic laminate 3 consisting mainly of PE or PP material.

[0074] In the plastic laminate 3, further plastic layers may be provided. Particularly preferably, an additional barrier layer made of EVOH may be provided, for example, between the bonding layer 4 and the substrate layer 5, or between the substrate layer 5 and the sealing layer 6. Based on bonding adhesion, it may be advantageous for such an EVOH barrier layer to be bonded to the plastic laminate on both sides by bonding layers (Tie layers). Thus, possible structures result, for example, as EVOH / Tie / EVOH / Tie / substrate layer (e.g., HDPE) / sealing layer or EVOH / Tie / substrate layer (e.g., HDPE) / Tie / EVOH / Tie / sealing layer or EVOH / Tie / EVOH / Tie / substrate layer (e.g., HDPE) / Tie / sealing layer, where the symbol " / " indicates that the two layers are in direct contact with each other.

[0075] The plastic laminate 1 is typically 10-40 μm thick, so the thickness of the EVOH layer 2 is preferably 1 μm-4 μm. The thickness of the substrate layer 5 is preferably 5-35 μm. The thickness of the bonding layer 4 is typically 1-5 μm. If a sealing layer 6 is present, the plastic laminate 1 is typically 10-120 μm thick. The thickness of the sealing layer 6 is typically 20-100 μm.

Claims

1. A method for producing a plastic laminate (1) comprising an outer wear-resistant EVOH layer (2) and a plastic laminate (3) in contact with the EVOH layer (2), wherein the EVOH layer (2) and the plastic laminate (3) are co-extruded together in an inflated film method, the EVOH layer (2) and the plastic laminate (3) are co-extruded concentrically in a co-extrusion die (11) to form a plastic tube (14), thereby positioning the EVOH layer (2) to be located on the inside within the plastic tube (14), and the co-extruded plastic tube (14) is pulled out in the extrusion direction after emerging from the co-extrusion die (11) and expanded with pressurized gas (21) In a method for forming a plastic bubble (14a), cooling and folding the plastic bubble (14a) so that the EVOH layers (2) are in contact with each other within the folded plastic bubble (14a), passing the folded plastic bubble (14a) through the gap (20) between the draw rollers (17) and compressing it while applying pressure, cutting open the compressed plastic bubble (14b) downstream of the draw rollers (17) in the extrusion direction to form a plastic laminate (1), separating the EVOH layers (2) that are in contact with each other, thereby forming the outer layer of the plastic laminate (1), A method characterized by cooling a co-extruded plastic tube (14) to a temperature lower than the glass transition temperature of EVOH in the EVOH layer (2), preferably at least 5°C lower than the glass transition temperature, before it enters the roller gap (20) of the draw roller (17) and before it is compressed between the draw rollers (17), in order to provide wear resistance to the EVOH layer (2).

2. The method according to claim 1, characterized in that the co-extruded plastic laminate (3) is formed from a binder layer (4) and a base layer (5) that is in direct contact with the binder layer (4), and the binder layer (4) is in direct contact with the EVOH layer (2) in the plastic laminate (1).

3. The method according to claim 1 or 2, characterized in that the co-extruded plastic laminate (1) is stretched downstream of the draw roller (17) in the extrusion direction, preferably only in the longitudinal direction.

4. The method according to any one of claims 1 to 3, characterized in that a plastic laminate (1) is bonded to a preferably unstretched sealing layer (6) after co-extrusion and optionally after stretching, and the sealing layer (6) is bonded to a plastic laminate (3) of the plastic laminate (1), preferably to a bonding layer (4a) between the plastic laminate (3) and the sealing layer (6).

5. The method according to claim 1, characterized in that the co-extruded plastic laminate (3) is formed from a binder layer (4), a base layer (5) that is in direct contact with the binder layer (4), and a sealing layer (6) that is in direct contact with the base layer (5), wherein the binder layer (4) is also in direct contact with the EVOH layer (2) in the plastic laminate.

6. The method according to claim 1, wherein the co-extruded plastic laminate (3) is formed from a bonding layer (4), a base layer (5) in direct contact with the bonding layer (4), another bonding layer (4a) in direct contact with the base layer (5), and a sealing layer (6) in direct contact with the other bonding layer (4a), characterized in that the bonding layer (4) is also in direct contact with the EVOH layer (2) in the plastic laminate.

7. In the plastic laminate (3), polyethylene is mainly used, that is, at least 60 Vol%, preferably at least 70 Vol%, and very preferably 80 Vol%, in the polyethylene content of the plastic laminate (3), or In the plastic laminate (3), polypropylene is mainly used, that is, at least 60 vol%, preferably at least 70 vol%, and most preferably at least 80 vol%, in the proportion of polypropylene in the plastic laminate (3). The method according to any one of claims 1 to 6, characterized in that

8. When polyethylene is mainly used in the plastic laminate (3), the polyethylene content in the sealing layer (6) is at least 80 vol%, or When polypropylene is mainly used in the plastic laminate (3), the proportion of polypropylene in the sealing layer (6) is at least 80 vol%. The method according to any one of claims 4 to 7, characterized in that

9. The method according to any one of claims 1 to 8, characterized in that the EVOH layer (2) is up to 10% of the total thickness of the plastic laminate (1), preferably up to 5%, but with a maximum thickness of 10 μm.

10. A plastic laminate having an outer abrasion-resistant EVOH layer (2), manufactured by the method described in any one of claims 1 to 9.

11. The plastic laminate according to claim 10, characterized in that when a first small piece of plastic laminate (1) is attached to a carriage (32) having a weight of 200 g and a mounting area of ​​60 x 66 mm and placed on a second small piece of plastic laminate (1) attached to a mounting table (31), the EVOH layer (2) of the first small piece of plastic laminate (1) and the EVOH layer (2) of the second small piece of plastic laminate (1) are positioned in contact with each other, and when the first small piece and the second small piece of plastic laminate (1) are moved relative to each other five times in succession and under the action of the weight of the carriage (32) at a relative speed (v) of 100 mm / min along a section (s), the wear resistance of the EVOH layer (2) is achieved in such a way that there are no EVOH wear particles on the surface of the EVOH layer (2).

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