MXPA98008662A - Method and apparatus for use in the manufacture of a laminar unit for empa - Google Patents

Abstract

In an extrusion laminar unit system to produce a laminar unit for packaging liquid foods, a layer of thermoplastic materials contacting the product is extrusion coated on an oxygen barrier substrate from a low temperature extruder without the thermoplastics reaching Its temperature of rupture before its entrance to the extruder or at any point between its entrance to the extruder and the arrival to a cooling roller immediately downstream of a slot die of the extruder, therefore, the transmission of unpleasant taste producing compounds of the laminar unit to this liquid food can be avoided, the adhesion between the contact layer with the product and the substrate is promoted in one or more of a number of ways, for example, by co-extrusion of the contact layer with the product with a joint layer to provide good adhesion of the contact layer with the product despite its extrusion at low temperature was you

Description

METHOD AND APPARATUS FOR USE IN THE MANUFACTURE OF A LAMINAR UNIT FOR PACKAGING DESCRIPTIVE MEMORY This invention relates to a method and apparatus for use in the manufacture of a laminar unit for packaging. The desire of the patent US-A-4,657,614 is to construct a laminar unit for packaging having a carrier of paper, cardboard or for example polystyrene foam, whereby the packages manufactured from the laminar unit can be formed by Doubling to a durable form and good mechanical protection is imparted to the contents. Moreover, the desired laminar unit should be liquid-proof so as not to absorb moisture or liquid that can be brought into contact with the outside of the package, and the package must have an interior that is liquid-proof and can be sealed to the heat by joining together layers of plastic that can be fused together with the help of heat and pressure for a mechanically strong bond. Moreover, the inner layer of plastics, which is in direct contact with the contents, must have a low level of characteristic flavor in cases where the contents are constituted by food materials. The inner layer of plastics should preferably be strong and strong enough to withstand the pressures on the material caused by the formation of bends without causing the plastics to break. Moreover, the desired laminar unit must include a gas barrier layer, preferably made of aluminum sheet (Al). Thus, a number of different layers of materials are bonded to one another and this is done with the help of different binding layers. US-A-4,657,614 adds that, conventionally, when such a packaging packaging unit is manufactured, broadly speaking, two different methods are used. The first method is a method of dry rolling, in which, after applying adhesive to the laminated material (sub-subs) such as a film made of plastics and drying it, such sub-subs period is pasted to the surface of the substrate. The second method is a laminar unit extrusion method, in which a thin layer of plastics melted at a temperature as high as 300 ° C, is extruded from an extrusion die and the plastic recovery is formed on the surface of the aluminum sheet. The packaging material made of such a laminar unit manufactured by any conventional method can have an unpleasant taste that can be transferred to the contents. This inappropriate change is most often found whenever the contents are packaged for long shelf life or at high temperatures. This is because, for packaging laminates manufactured, by the method of dry lamination, for example, there is a layer of adhesive between the aluminum sheet and the plastic layer located on the inner surface of the container and the adhesive is absorbed. On the other hand, the method of extrusion lamination makes oxidative product (carboxyl group) in plastics, and the oxidative product gives an abnormal smell and deterioration of taste. US-A-4,657,614 further discloses that a container package to be filled with a beverage not only requires that it have sufficient strength so that the container is not deformed, but that it is also necessary that the internal layers of plastics be firmly adhered to the aluminum sheet so that the leakage of the drink is avoided. The patent specifies that, in order to adhere the plastics firmly to the aluminum sheet, in the case of polyethylene, (PE), for example, the PE needs to be extruded at a high temperature above 300 ° C. Plastics that are extruded to high temperature adhere well to the surface of the aluminum sheet, but, due to its contact with air for a relatively long time before forming a thin layer on the sheet, produces a high proportion of oxidative product. Contrary, if the plastics are kept at a lower temperature to avoid the formation of oxidative product, the adhesion with the sheet ds becomes weak and the malleability of the container becomes worse. The oxidative product existing in the plastics layer is gradually absorbed within the packaged contents, particularly in the situation of high temperatures, whereby the degree of absorption increases. US-A-4,657,614 concluded that, for these reasons, a package using the sheet layer manufactured by a conventional method could not be quickly heated to preserve food sensitive to taste for a long period. The solution proposed by (the patent) US-A-4,657,614 to those conventional difficulties was to extrude a film of molten plastics between a substrate network and an aluminum sheet network while a network of blown synthetic resin film was placed in the opposite side of the aluminum sheet, and then pass those materials between a pair of cylinders, with which the molten plastics join the aluminum network to the substrate network and the blown film is sealed to a surface of the aluminum network by the heat driven of the plastics through the aluminum injector; and it is said that this method reduces the eruption of oxidic product to an extreme degree. The patent noted that plastics in the film blowing process can be pressed out of the annular die at a temperature of 140 to 180 ° C while in the corresponding slot extrusion process the temperature is about 250 to 325 ° C. . It is said that one of the very considerable advantages is that the blown film emits appreciably less flavor, which is of particular importance in the packaging of food materials. In a preferred embodiment in US-A-4,657,614 a paper or cardboard carrier layer, pre-coated with an outer layer of polyethylene is passed over a cylinder and down towards a clamp between cooperating pressure and cooling cylinders. A network of aluminum sheet is also guided in the middle of the cylinders. Also inserted between the aluminum network and the carrier layer is a plastic layer extruded by groove. The layer of hot plastics, not yet solidified, is then compressed, by the cylinders, between the carrier layer and a surface of the sheet, arising a mechanical bond between the plastics and the carrier layer and between the plastics and the sheet, at the same time that the plastics are cooled and become stabilized. A coextruded film manufactured in advance and consisting of two layers of plastics, namely a layer of plastics of ethylene acrylic acid (EAA) type and a layer of plastics consisting of blown polyethylene is also introduced between the cylinders. Because these two layers of plastic have been co-extruded, they have good adhesion to one another. The loading of the heat content in the extruded plastic layer is passed to the sheet because the aluminum sheet is a much better heat conductor than the paper material of the carrier layer. At the same time that the layer of extruded plastics cools and is stabilized the sheet metal layer is thus heated and the heat is transferred to the EAA layer having a sealing temperature of about 93 ° C. Because the plate of extruded plastics has to be heated to at least 300 ° C, it has a relatively large heat content that must be dissipated. If the temperature and thickness of the extruded plastic layer is chosen correctly, sufficient heat for the achievement of a seal will be transferred to the EAA layer, which is therefore raised to a temperature exceeding 93 ° C and is made to melt from there together with its surface facing the sheet metal layer and after cooling it is bonded to the sheet metal layer. It appears that, in another preferred embodiment of US-A-4,657,614, the EAA layer is omitted and the blown film is melted directly by direct heat conduction from the Al sheet but, due to the extremely short period of time between the blown film being subjected to heat and being cooled by the cooler cylinder, the heating of the film does not give rise to any large amount of oxidative product. The above solution has the disadvantage that it is limited to the production of laminated plates incorporating a layer of material, in practice sheet metal, which is a good thermal conductor. US-A-4,657,614 discloses that, in the extrusion lamination method, the adhesive bonding mechanisms are classified into two types, that is, mechanical bonding by adhesive and chemical bonding by adhesive. Mechanical bonding by adhesive is relevant in cases where porous substrate materials such as fabrics and paper are used, in which molten polymer, particularly PE, extruded at high temperature infiltrates within fine pores between the fibers and is then solidified by cooling, providing adhesive bond between the PE and the substrate. Bonding by chemical adhesive uses intermolecular chemical strength and is used for substrate materials that have flat surfaces such as regenerated cellulose film, aluminum sheet and plastic films or those that have non-functional groups. In order to obtain satisfactory bond strength in the bond by chemical adhesive, it is necessary that the substrate material be subjected to a first treatment, and is often treated by corona discharge. It also mentions the preference that the PE used for extrusion coating be activated and that, as the method for this activation, it is a general practice that the PE is extruded at high temperatures to increase the oxygen content of the polar groups in molecules before it is brought into contact with the substrate material to provide sufficient adhesive strength. The patent adds that, with mechanical bonding of adhesive, when the temperature of the molten PE is high, its viscosity is lower thus improving the infiltration within the substrate material and thus the adhesive strength. Therefore, the lamination is made at temperatures as high as possible, provided that the PE is not decomposed. Accordingly, low density polyethylene (LDPE) is heated to, at least, 280 to 310 ° C in the conventional rolling process. In this procedure, it is necessary that the polyethylene is not decomposed and not of an offensive odor. In industrial practice, however, partial decomposition is caused to occur, giving an irritating odor of decomposed product, and much smoke is emitted during the process. It is considered that this may be due to the temperature readings given by the temperature detector equipment of conventional extruders that do not necessarily represent the maximum temperatures currently obtained in the extruders. Instead of their inaccuracy such readings are often used without a doubt as exact readings or as suitable temperature establishments in the current technical field. In the solution proposed by the patent US-A-4,657,614, the substrate is a sheet of material and a layer of polyolefin (PO) laminated thereto. In a first method, a PO film to be laminated is used by being heated to a molten network and then applied to the substrate PO. In a second method, the extruded PO, as a molten network, is applied directly to the PO of the substrate material. In these methods, the temperature of the molten network is set as low as possible in order to avoid thermal deterioration of the polyolefin. That is, the temperature of the molten network is in the range between the melting point or softening point of the polymer to be rolled and a temperature greater than that temperature per 100 ° C. The laminar unit can be used for items such as odor books, bookmarks, pamphlets, tickets, business cards, postcards, telegram paper, fans, rolled paper centers, labels, posters, building decoration materials such as wall materials and roofing material, wrapping material, such as wrapping materials for toilet paper, greeting cards and letter paper, sealing paper for paper cardboard boxes for bathroom and food and flower packaging, bags reusable bags, trash bags, anti-fungal bags, antiseptic food packaging materials, mosquito repellent labels, insecticide sheets, wrapping sheets for cultivation fruits and oxidation inhibiting packaging materials for steel pipes and machineries. In one example, a substrate was prepared by conventional extrusion lamination at 300 ° C, in which a layer of 20 microns thick LDPE was applied to the surface of quality paper of 49 g / m2. After that, a network of 50 microns of LDPE thickness was extruded at 170 ° C and was laminated under pressure to the surface of the LDPE of the substrate to obtain the laminar unit.

The solution of (the patent) US-A-4,657,614 has the disadvantages that it requires the provision of an additional layer of plastics to cover the layer of plastics already covered on the sheet of material of the substrate and that the additional layer 5, a Unless it is undesirably thick, do not currently prevent the permeation of oxidation products. According to one aspect of the present invention, there is provided a method for manufacturing a packaging laminar layer, consisting of supplying a substrate providing a good one. The barrier to the transmission of oxygen, and applying said substrate to thermoplastics, product contact layers by extrusion through a slot die in an extrusion lamination station, adhesion between said contact product layer and the mentioned substrate that has been promoted, characterized in that the temperature of said product contact layer is maintained below the breaking temperature of the thermoplastic material of said product contact layer through said method. According to a second aspect of the present invention, there is provided an apparatus for use in the manufacture of a packaging laminar layer, consisting of an extruder including a slot die to produce a layer of thermoplastic material by extrusion, cooling means Immediately downstream of said slot die to cool said layer, means for supplying a substrate providing a good barrier to oxygen transmission, winding means for guiding said substrate to said layer, and adhesion promotion means for promoting the adhesion between said substrate and said layer, characterized in that said extruder is a low temperature extruder. Due to these aspects of the present invention, and particularly in which the temperature of the thermoplastic material is maintained below its breaking temperature through the method, the degree of oxidation of the material that can perniciously affect the packaged product, especially to produce flavor unpleasant in packaged food, it can be avoided. Moreover, the fact that the substrate is a good oxygen barrier minimizes the transmission of unpleasant taste producing compounds from any other layer of the laminar unit to the outside of the barrier provided by the substrate. Moreover, the promotion of adhesion between the contact layer with the product and the substrate provides good adhesion between the contact layer with the product and the substrate instead of the extrusion of the contact layer with the product below its temperature. of breaking. The breaking temperature of a thermoplastic material is the temperature at which the significant oxidation of the thermoplastic material in atmospheric air begins.

The breaking temperature for thermoplastics varies depending on the particular composition of the thermoplastics. The breaking temperature for a selection of thermoplastics each usable as a contact layer with the product is given immediately: Material (grade) Speed Melt material melt flow temperature in ° C). VFF LDPE (high pressure autoclave) 4 250-280 LLDPE ("DOWLEX" 3010E) 5.5 260-280 lone ("SURLYN" 1652) 5.5 260-280 EVA (16% vinyl acetate) 3 220-240 The low temperature extruder can be a rotary extruder substantially without screws with a gear pump; a planetary roller extruder with a gear pump; a twin screw extruder; a screw extruder with a screw designed for low temperature extrusion; or an extruder of the type conventionally used to melt film of the thermoplastic material. The use of a low temperature extruder has the advantage that the present system is easily applicable to a conventional line of extrusion coating, simply with the replacement of a conventional, high temperature extruder, which is extruding the contact layer with the product, by a low temperature extruder that performs the same function. The adhesion between the contact layer with the product and the substrate can be promoted by one or more surface treatments (such as flame treatment, corona discharge treatment, or plasma treatment) of the receiving surface of the substrate.; applying an adhesive to that receiving surface, whose application can be carried out either by the manufacture of the substrate or in an extrusion line by coating producing the laminar unit; the preheating of the substrate; treatment with "ALDYNE" R (using electrodes to deposit a layer of glass on a substrate, particularly on a barrier layer of aluminum sheet); and co-exuding, in the low temperature extruder, a layer of low temperature equalizer, for example "SURLYN" R or "PRIMACOR" *, in addition to the contact layer with the product. The substrate consists of a barrier layer which constitutes a good barrier to oxygen and thus to the passage to the contact layer with the product, of oxidation compounds or others which could give an unpleasant taste to the contact layer with the product and / or to the product. A material that is a good barrier to oxygen in the present context is a significantly better barrier to oxygen than LDPE. To be a good oxygen barrier, a 25 micron thick sheet of material has an oxygen transmission rate (TR) of less than 1,000 milliliters / square meter / atmospheric pressure difference / day, and preferably has a TR less than 100 Examples of such materials are ethylene vinyl alcohol (EVOH) polyamide (PA), cellophane, grease-proof paper; and coatings of silicone oxide (SiOx)) (e.g., glass), metal (e.g., aluminum), and metal oxide (e.g., A10 *). Thus, the barrier layer may consist of one or more metal sheets (eg, aluminum); a polymeric barrier layer, for example EVOH or PA; a polymeric material covered by a deposition process (for example with a metal, metal oxide, or glass coating); fat-proof paper; and cellophane. The contact layer with the product may be one or more polymers, especially one or more POs, for example linear LDPE (LLDPE), LDPE, very LDPE (VLDPE), high density polyethylene (HDPE) or polypropylene (PP); "METALOCENE" POs; Bimodal POs; copolymers of polyolefinic acid (for example EAA); ionomers; vinyl ethylene acetate (EVA); mixtures of such polymers; and such filled polymers. Advantageously, the contact layer with the product is PO, preferably PE, more preferably LDPE with good organoleptic properties. In order for the invention to be clearly understood and quickly brought into effect, reference will now be made, by way of example, to the appended drawings, in which: Figure 1 shows diagrammatically an extrusion coating line making a The packing layer is shown, and Figures 2 to 4 show diagrammatic cross sections through varieties of the sheet unit that can be produced by variations of the extrusion coating line. Referring to Figure 1, the paperboard l is fed from a roll 3 to the clips between a pair of cylinders 4 and 5 of a first extrusion rolling station in which the cylinder 5 is a cooling cylinder. As an alternative, a ready roll 2 of paperboard is also shown. A molten PE film is supplied from a die groove of a high temperature extruder 7 to the clamp 7. The PE layer thus supplied is to constitute the outer surface (with respect to the board to be formed in the laminar unit) of the Laminar plate of packaging. The network 2 thus formed is advanced to a second extrusion rolling station in which it enters the clamp between a pair of cylinders 8 and 9 of which the cylinder 9 is a cooling cylinder. Also fed into the clamp is a network 10 of an oxygen barrier substrate, in this example aluminum sheet, fed from a supply roll 11, while in the paperboard layer 1 and the aluminum sheet network 10 it is introduced a molten film 13 of a polymeric leveling material from a slot die of a high temperature extruder 12. The network 14 thus formed then advances to a third and final rolling extrusion station in which it is passed between a pair of rollers 15 and 16, of which the roller 16 is a cooling roller. Here, a molten film 17 consisting of a polymeric equalizing layer 18 and a PE layer 19, which directly contacts the cooling roller 16, is coextruded between the aluminum sheet layer 10 and the cooling roller 16. is co-extruded from a low temperature extruder 20, which is thus positioned so that its slot die 21 is at a horizontal level as close as practical to the horizontal level of the clamp between the rollers 15 and 16, and to minimize the potential for oxidation of the molten film 17, particularly the contact layer with the product PE 19, before it is cooled by the cooling roller 16. The network 22 thus formed is then wound onto a roll 23 to be transported to, for example, a converter plant where the network is converted into blankets to form liquid packing cartons in which the outer layer PE 6 is sealed to the heat and pressure inside, the layer of co Contact with the PE product 19. The manufacturing line illustrated in Figure 1 has the particular advantage that it can be formed simply by replacing the high temperature final extruder, in a conventional extrusion retrieval line with a low temperature extruder. 20. The low temperature extruder 20 can be an "INSTAMELT" R rotary extruder system available from Extrusion Systems, Inc., 1549 S. Fairground, Midland, Texas, United States of America, or a rotary roll extrusion system available from Entex Rust & Mitschke GmbH of Heinrichsstrasse 67, D-44805 Bochum, Germany. An example of a packaging laminar unit produced on the line shown in FIG. 1 is as follows.

Reference No. Layer material Preferred scale of the layer "thickness" of the layer 6 LDPE 5-20 1 CART0NCILL0 140-450 13 LDPE 5-20 10 ALUMINUM SHEET 15-25 18"SURLYN" "3-10 19 LDPE 10-50 The LDPE supplied to the extruder 20 should not be brought to a temperature at or above its breaking temperature prior to its entry into the extruder 20 and should not be raised to, or beyond, its breaking temperature at any point between the entrance into the extruder 20 and the cooling roller 16. This is preferably also true for the equalizing layer 18. An example of a packaging laminar unit produced on a variation of the line of FIG. 1 is shown in FIG. 2 and includes an oxygen barrier substrate 10 in the form of a polyethylene terephthalate (PET) film 27 with a deposited deposit 28 of Al or SiO. The substrate 10 is bonded to the cardboard layer 1 and to the contact layer with the product 19 by means of respective equalizing layers 25 and 29. The layer 29 can be co-extruded with the layer 19 and in these circumstances is such that its temperature of breaking is above the coextrusion temperature of the extruder 20. The coating 28 is on the inner side of the PET film 27 to form a barrier against the transmission of flavor-removing compounds from the PET layer 27 to the product. An example of a packaging laminar unit of FIG. 2 is as follows: Reference layer No. Layer material Preferred layer thickness range (g / m2) 6 LDPE 5-20 1 CARTÓ CILLO 140-450 25 LDPE 5-20 10 PET coated with Al 8-20 or SiO. 29 EMA 5-20 19 LDPE 10-50 [EMA is ethylene methacrylic copolymer]. Again, the LDP supplied to the extruder 20 to constitute the LDP layer 19 should not be brought to the temperature of, or above, its breaking temperature prior to its entry into the extruder 20 and should not be raised to or beyond its breaking temperature at any point between the inlet inside the extruder 20 and the cooling roller 16. This is preferably also true for the equalizing layer 29. An example of the packaging laminar unit produced on another variation of the line of FIG. shown in Figure 3 and includes an oxygen barrier substrate 10 in the form of an extrusion coating layer EVOH on the inside of the paperboard layer 1. The layer 10 is bonded to the contact layer with the product. by means of an equalizing layer 32 of anhydride modified PO, preferably anhydride modified LLDPE, coextruded with layer 19 and having its breaking temperature above the temperature of coexusion. An example of the packaging laminar unit of FIG. 3 is as follows: Layer reference No. Layer material Preferred layer thickness 6 LDPE 5-20 1 CART0NCILL0 140-150 10 EVOH 3-25 32 LLDPE 3-10 19 LDPE 10-50 The LDPE supplied to the extruder 20 to constitute the layer 19 should not have been brought to a temperature at or above its breaking temperature prior to its entry into the extruder 20 and should not be raised to, or beyond, its breaking temperature at any point between its entry into the extruder 20 and the cooling cylinder 16. This is preferably also true in the equalizing layer 32. An example of a packaging laminar unit produced on a further variation of the line of the figure 1 is shown in Figure 4 and includes an oxygen barrier substrate 10 in the form of an EVOH film 35 carrying equalizing layers 36 and 37 to the exterior and interior thereof. The substrate 10 is laminated by extrusion to the cardboard layer 1 by the LDPE 13 and the contact layer with the product 19 is coated by extrusion on the layer 37. Layers 36 and 37 are of modified anhydride P0, preferably LLDPE modified anhydride . An example of a packaging laminar unit of FIG. 4 is as follows: Reference layer No. Layer material Preferred layer thickness scale 6 LDPE 5-20 1 CART0NCILL0 140-450 13 LDPE 5-20 10 LDPE / EVOH / LDPE 8-20 19 HDPE 10-50. The HDPE supplied to the extruder 20 to constitute the LDPE layer 19 should not be brought to a temperature at or above its break temperature prior to its entry into the extruder 20 and should not be raised to, or beyond, its breaking temperature at any point between its entry into the extruder 20 and the cooling roller 16.

Claims (7)

NOVELTY OF THE INVENTION CLAIMS

1. - A method for manufacturing a laminar unit for packaging consisting of supplying a substrate (10) that provides a good barrier to the transmission of oxygen, and applying the substrate to thermoplastics, contact layers with the product (19) by extrusion through of a slot die (21) in an extrusion lamination station, the adhesion between said contact layer with the product (19) and the substrate (10) being promoted, characterized in that the temperature of the contact layer with the product (19) is maintained below the breaking temperature of the thermoplastic materials of said contact layer with the product (19) through said method.

2. A method according to claim 1, further characterized in that the temperature of the thermoplastics of the contact layer with the product (19) has been maintained below its breaking temperature before being delivered to the rolling station by extrusion.

3. A method according to claim 1 or 2, further characterized in that the adhesion has been promoted by one or more surface treatments of the receiving surface of the substrate (10); applying an adhesive to the receiving surface of the substrate (10); preheating the substrate (10); using electrodes to deposit a layer of glass on the substrate (10); and coextruding, in a low temperature extruder, a low temperature equalizing layer (18) and the contact layer with the product (19).

4. A method according to claim 1, 2 or 3, further characterized in that the barrier layer (10) consists of one or more metal sheets, an oxygen barrier polymeric layer, a polymeric material coated by a deposition process, grease proof paper, and cellophane.

5. A method according to any of the preceding claims, further characterized in that said contact layer with the product consists of one or more of a poleolefino, a copolymer of poleolefinic acid, an ionomer, an ethylene vinyl acetate.

6. Apparatus for use in the manufacture of a laminar unit for packaging, consisting of an extruder (29), which includes a slot die (21) to produce a layer (19) of thermoplastic materials by extrusion, cooling means ( 16) immediately downstream of said groove die (21) to cool said layer (18) means (11) to supply a substrate (10) providing a good barrier to oxygen transmission, half rollers (15) to guide the mentioned substrate (10) to said layer (19), and adhesion promotion means (20 and 21) to promote adhesion between the substrate (10) and said layer (19), characterized in that said extruder (20) It is a low temperature extruder (20).

7. An apparatus according to claim 6, further characterized in that said low temperature extruder is one or more of a rotary extruder substantially without screws with a gear pump; a planetary roller extruder with a gear pump; a twin screw extruder; a screw extruder with a screw designated for low temperature extrusion; and a character extruder conventionally used to melt film of said thermoplastic material.