MXPA98000033A - Molded plastic container for food and drinks and met - Google Patents

Abstract

A multi-layer container (10) and a process for forming the same are described. The container (10) includes a support wall (12) formed of a plastic having an undesirable substance therein and polymerized at a level lower than that necessary to prevent the undesirable substance from migrating from the plastic to the contents when the contents they are in contact with the support wall (12). A protective wall (14) is provided adjacent the support wall (12) and adapted to be placed between the support wall (12) and the contents. The protective wall (14) is formed of a material that limits the migration of the undesirable substance from the support wall (12) to the contents

Description

RECI PI ENTE OF MOLDED PLASTIC FOR ALI M ENTOS AND BEBI DAS AND MET ODO BACKGROUND OF THE I NVENTION The present invention relates to plastic containers adapted to contain foods and beverages whose taste and / or odor can be affected by the materials from which the containers are made, as well as by the contaminants generated in the course of their manufacture and use. of the containers. In particular, the invention relates to containers produced from polymers subject to degradation in the course of their conversion to containers, the products of such degradation remaining trapped within their walls and being able to diffuse into the contents, thereby It affects the taste and smell of them. Similarly, the polymers may contain oligomers ie, molecular fractions that have been insufficiently polymerized, as well as monomers that have not reacted, both may diffuse into the contents of the containers, with the same effect, as mentioned above. These conditions are found particularly in polymers obtained by condensation reactions, such as polycarbonate, nylon and also polyethylene terephthalate (PET), the polymer that is predominantly used for beverage bottles and food containers. To be suitable for use in food and beverage containers, PET must provide protection of the contents against deterioration such as, in the case of non-alcoholic beverages, loss of carbonization or chemical reactions due to exposure to environmental conditions. In addition, depending on their intended use, the containers may be subject to considerable internal pressure and forces due to handling and storage. Therefore, the degrees to which the PET will be used must be capable of imparting physical properties for those forces. As is known, PET is a polymer that can be obtained in condensation by steps of terephthalic acid and ethylene glycol. The polymerization is more complete the longer the time in which it is carried out at the appropriate temperature, and can be interrupted repeatedly. Up to a certain condensation stage, the reaction is carried out in the "molten" phase, that is to say, the low viscosity state, and therefore the product is designated as the molten bath phase PET as the molten bath phase reaction. As this phase of the reaction progresses, the viscosity of the mass that is making hot reaction increases to a degree, beyond which it is impractical to continue manufacturing. The polymer obtained in this stage, and even before, has many, notably for the production of fibers and textile films. However, the molten bath phase PET has insufficient physical properties and resistance to permeation for use in large beverage bottles and some other important packaging containers. Even more importantly, the molten bath phase PET draws acetaldehyde (AA), a noxious thermal degradation product, and also some oligomers, as well as monomer constituents that have not reacted, notably ethylene glycol. AA, which is the abbreviation for acetaldehyde, CH3CHO, is a liquid with an acrid fruity odor that easily desorbs outside the walls of a container that is made of PET, in which the AA is entrained, to the contents to spoil the smell and taste of them, even in very small concentrations. Therefore, the typical specifications for non-alcoholic beverage bottles require an AA limit of 1 ppm, and even less for drinking water. Also, monomers and oligomers that have not reacted can enter the contents of the container and can, apart from interfering with the taste, constitute a health hazard according to the prevailing laws that regulate it.

Consequently, because the AA is present in the molten bath phase PET, the use of molten bath phase PET is not accepted for many forms of packaging, including some of the most important, for example, bottles for beverages. For the same reason, PET of the molten bath phase can not be used even when its physical properties are sufficient, as is the case of small bottles that are subjected to smaller stresses than large ones, since the efforts arise in proportion to the size . In order to obtain PET without the disadvantages associated with the molten bath phase PET, polymerization / condensation must be continued. Since it is impractical to continue in the molten state, additional, costly processes are added, where the molten bath phase product is cooled, comminuted to a suitable particle size to be suspended and heated in and by a stream of hot air. The product is heated in a post-condensation reaction in the solid state, preceded by the crystallization of the molten bath phase PET. Naturally, the cost of the finished PET is substantially increased by these steps. The cost of polymerizing the feed batch to the bottle-grade PET almost doubles, compared to limiting the process to the polymerization of the molten bath phase. Particularly, when the physical properties of containers made of PET of molten bath phase would otherwise be sufficient, such as for small bottles, the increase in cost is only accepted to eliminate excessive amounts of AA and other contaminants. In view of the fact that about 40% or more of the total manufacturing cost of a PET bottle is represented by the cost of PET, it is easily observed that the use of the molten bath phase resin would represent great economic benefits. There is, therefore, a need for a container and a container manufacturing process where the molten or waste bath phase PET can be used in the container without having restricted application to food and beverages as it does not contaminate them.

BRIEF DESCRIPTION OF THE NONDION The main objective of this invention is to provide a container and a process that allows the use of PET containing excessive amounts of AA and other contaminants in beverage and food containers. Another object of this invention is to provide a plastic container from polymers containing residues of its polymerization and / or other contaminants in excess of the amount acceptable for use by the container in the packaging of food and beverages. A further objective of the present invention is to provide a simpler and more economical process for manufacturing PET and other analogous polymers for conversion into food and beverage containers to reduce manufacturing costs. In accordance with the present invention, the above objects and advantages can be obtained with ease. The container of the present invention includes a support wall formed from plastic having an undesirable substance therein capable of migrating from the support wall. Preferably, the support wall is polymerized at a level lower than that necessary to prevent the undesirable substance from migrating from the plastic to the contents when the contents come into contact with the support wall. In the preferred embodiment, the plastic is PET containing acetaldehyde in an excess of 2 ppm. A protective wall is provided adjacent to the support wall and adapted to be placed between the support wall and the contents. The protective wall is formed of a material that limits the migration of the undesirable substance from the support wall to the contents, to at least an acceptable level.

In one embodiment of the invention, the protective wall or barrier serves to prevent contamination due to acetaldehyde (AA) and substances representing health hazards that represent unintentional or unavoidable waste as a result of manufacturing processes of which PET drift. In a preferred embodiment, the PET is polymerized in the molten bath phase or the molten state only, without the subsequent polymerization in the solid state, and the conversion thereof into the containers is effected in a form that provides the necessary physical properties for its intended service, notably through sufficient biaxial guidance. A process for making the container of the present invention includes the steps of polymerizing a plastic containing an undesirable substance thereto at a level lower than that necessary to prevent the undesirable substance from migrating from the plastic to the contents when the contents are they come in contact with the plastic; combining the plastic with a protective substrate and forming a mixed compound, wherein the protective substrate is formed of a material that limits the migration of the undesirable substance from the plastic to the contents, to at least an acceptable level; forming the mixed compound to an article comprising at least one of a precursor and a preform; and blow-molding the article in the container, wherein the protective substrate is placed in contact with the contents. The precursor can be formed into a preform. In the process, the combining step may comprise the step of extruding the plastic onto the substrate to form the mixed compound. Alternatively, the combining step may comprise the step of coextruding the plastic with the substrate and forming the mixed compound into one in the form of a sheet and a tube, or co-injecting the plastic with the substrate. In a particular embodiment, the protective substrate is a laminate which may include an external adhesive layer and which includes an intermediate layer of EVOH and an internal layer of PET having a low content of acetaldehyde, wherein such an inner layer is adapted to be formed to be placed to get in touch with the contents and protect the EVOH middle layer from the contents. Instead of EVOH, other substances with the same purpose can be used, for example, polymers of acrylonitriles and nylons, depending on the types of contaminants to be excluded and the abundance thereof on the walls of the container. In practice, the composition of the barrier or laminate layer is calculated based on the diffusion laws and permeation properties and solubilities reported in the literature. The aforementioned sheet or tube laminates can be produced economically in the plant housing the molten bath phase polymerization, preferably followed by the production of preforms therefrom by conventional forming and / or press cutting operations. , the same operations carried out conventionally to produce convenient plastic to distribute, in the form of pellets. The details of the present invention are set forth in the following description and the drawings in which similar reference characters illustrate similar elements.

BRIEF DESCRIPTION OF THE DIAMETERS The present invention will be more readily understood from the consideration of the following drawings, in which: Figure 1 is a cross-sectional view of a container of the present invention; Figure 2 is an enlarged partial cross-sectional view taken along lines 2-2 of Figure 1; Figure 3 is a cross-sectional view of a preform from which the container of Figure 1 is molded; Figure 4 is a schematic flow diagram of the steps for manufacturing the material from which the container of Figure 1 is to be made; Figure 5 is a schematic flow diagram of alternate steps for manufacturing the material; Figure 6 is a schematic representation of the manufacture of a preform according to Figure 3, being made from the material manufactured according to the process of Figure 4; and Figure 7 is a schematic representation of the manufacture of a preform according to Figure 3, being made from the material manufactured according to the process of Figure 5.

DETAILED DESCRIPTION OF THE MODALI DADES PREFERI DAS Referring now to the drawings in detail, there is shown in Figure 1 a plastic container 10 for beverages and food having an external support wall 12 forming a structural layer designed to withstand the mechanical stresses imposed on the container in the course of the handling and use. The outer wall 1 2 is preferably made of PET, the mass of which carries reaction products such as olomers, unreacted monomers, and / or other compounds, for example, acetaldehyde (AA), and ethylene glycol. . The reaction products are present in an amount sufficient to reduce the average molecular weight of the mass substantially below that required for the performance of the container. In polymerization, the material from which the wall 1 2 external consists, as in a production condensation reaction, the aforementioned reaction products remain absorbed in the mass after cooling from the reaction temperature. After renewed heating, which may be necessary to produce the wall 12, such as by molding into preforms for the containers, the various aforementioned reaction products thereof as well as other undesirable substances can be made to be mobile due to the reduced viscosity and the formation of gas, and therefore, are able to move through the wall or other mass in accordance with the gradients of solubility and pressure that develop due to heating. There is a similar problem when waste is used with discharge products therein that represent substances that are not capable of migrating from the support wall. Accordingly, the aforementioned substances may tend to migrate out of the wall 1 or other mass by d ifusion or desorption and to the contents enclosed by the wall 1 2 when the wall 12 is in immediate contact therewith. Due to the effects of pollution, this result is undesirable. These phenomena are reported extensively in the published literature. An important example of these phenomena in the design of the containers is observed through the production of polyethylene terephthalate, in the subsequent PET, which is used extensively for packaging and drinking and is the preferred plastic for use. in the formation of the container 1 0. The PET used for containers of carbonated drinks should have an average molecular weight corresponding to an intrinsic viscosity (IV) in the range of 0.7-1.2, depending on the services that are intended, such as, for example, for use in direct contact with food and beverages, polymerized to the degree necessary to obtain this viscosity, the PET contains less of the aforementioned undesirable substances than would interfere with its use in the formation of containers and bottles for food and beverages and consequently a wall similar to the wall 12, but subject to this process would not substantially exhibit the products of migratory reaction discussed above. This is one of the main reasons for extending the condensation reaction despite the substantially increased cost. Another reason is that the mechanical properties required for certain containers are obtained. However, a large number of containers does not require the mechanical properties of the polymerized PET additionally. For example, small diameter bottles for carbonated beverages, such as 283.5 g-567g (10-20 oz.) Bottles, do not require the same sturdy material as larger containers. Consequently, PET having an IV equal to 0.70 and lower could be used, if it were not for the effect of undesirable substances or the reaction products such as AA on flavor, which are desorbed from the wall of the PET container. to beverages or food or other monomers that have not reacted and unbound monomers or oligomers that can diffuse into food from the container in amounts not allowed by sanitary regulations. In many cases, unlike the process described herein for the production of the container 10, an expensive polymerization process is used for the purpose of avoiding the abovementioned undesirable substances. According to Figures 1 and 2, the use of PET polymerized to a lesser degree, such as that having an IV ranging between 0.55 and 0.65, is possible by lining the container 10 or the wall 1 2 with a wall 14. internal protection that is capable of minimizing, or minimizing, the entry of substances that affect taste and odor, such as AA, to the contents of the recipients. The inner wall 14 preferably contains or is a material that is impermeable to the undesirable substances, such as AA and / or other monomers that have not reacted and / or the oligomers as described above by way of example. A particularly effective and preferable barrier material is EVO H which is substantially impermeable to AA, although it loses its effectiveness when contacted with water. Similarly, other suitable inner wall materials fail to retain their desired properties when exposed to the characteristics of the container contents. In addition, some of these materials can not contact the contents, since they can also suffer changes when they are in contact with them. In addition, some of the materials available and functional for the intended purposes of being waterproof to AA do not adhere easily to the external wall 12, which results in ugly and non-functional containers. Therefore, an additional layer is preferably used. Accordingly, as shown in Figure 2, the inner wall 14 is preferably made of a laminate 15 composed of several layers, each having a function. For example, in the case of an outer wall made of PET, there may be a bonding layer of an adhesive 16 adjacent to the outer wall 12, preferably followed by a barrier layer of EVOH 18, and then by one of a layer of polyolefin such as polypropylene (PP) and a preferably thin layer of PET 20 in the solid state having an acetaldehyde content, as the means to protect the EVOH layer from the water contained in the beverage or food, all shown with exaggerated thicknesses for simplicity. Additional examples of barrier layer material are Selar Nylon (Dupont), MDX6 Nylon (Mitsubishi Chemicals), acrylonitrile polymers, polyethylene naphthalate (PEN) and polyolefin-containing materials. The manufacture of such laminated structures, such as by co-extrusion, it is well known and widely practiced. Accordingly, a process for manufacturing the container 10 includes blow molding a preform 22, shown in Figure 3, whereby the preform 22 exhibits an inner layer or wall 24 and an outer layer 26, corresponding to the walls 12 and 1 4 externally, respectively, of the container 10 of Figure 1. The internal wall 24 is preferably a laminate 27 having the layers 28, 30 and 32 corresponding to the laminate 1 5 and to the layers 16, 18 and 20 previously discussed. It follows that the preform 22 is the primary article that will be made from PET containing the contaminants to which reference was made. Various processes are known for the production of lined preforms, including one according to U.S. Patent No. 4, 149, 645, and are suitable for the purposes of this invention. However, they are not suitable for taking advantage of all the savings in available costs, based on the process of the present invention, using a PET grade that is preferably polymerized to a lesser degree and with an AA content. greater than those grades that are normally used that are subject to additional polymerization and have low AA. Figure 4 schematically illustrates the process for producing at least one precursor 33 of the preform 22. Accordingly, and also referring to Figures 1-3, the PET is preferably polymerized within the IV range of .55 a. 65 at station S1 and transferred to an extruder at station S2. The transfer from station S1 to station S2 can be effected without allowing the PET to cool below the extrusion temperature, or to enter the cooled and shredded state. Preferably, the PET is extruded without being crystallized such as the sheet 34, adapted to form the wall 12, on a substrate 36, as shown in Figure 6, adapted to form the laminates 15 and 27. Referring to the Figures 4 and 6, substrate 36 is preferably produced by co-extrusion at station S3 and is attached to the PET sheet or wall 12 from station S2, whereby a mixed compound is then made and entered into a forming unit by pressing in station S3, equipped to produce the preforms 22 or the precursors thereof. The aforementioned operation at station S3 is known and practiced, usually under the designation "coupled thermoforming". The result of that operation is shown in Figure 6, in which various precursors 33 have been molded from the substrate or laminate 36 and the sheet 34 of PET, which are shown before being separated from the sheet by grinding. After roughing, a skeletal residue remains that can be recycled with or without separating its layers. The reference to the precursor 33 of the preform 22 is made because the aforementioned thermoforming process does not always allow to conveniently produce all the necessary aspects of the final preform. For example, the cords of many preforms must be threaded, which would make thermoforming impractical. In such a case, the preferential precursor is made by thermoforming, which means that an article of equal weight and dimensions is made next to the preform 22, designed to subsequently adjust to a mold to provide the final aspects such as, for example, example, dimensions and threads. These aspects can be achieved by correct operation such as, for example, compression molding, in accordance with well-known practices. The precursors can be separated from the sheet 36 in such a way that substantially no scrap is produced, as by the roughing cuts along the lines 35 in order to provide a square top part in a precursor instead of a round top . An alternative method for forming the preform 22 and the container 10 is shown schematically in Figure 5. The PET polymerization product, that is to say, the sheet 34 obtained in the station S1 and the sheet or substrate 36, similar to that shown in Figure 6, is transferred to an extruder in the station S5 equipped to produce the co-extruded tubes 40, as shown in FIG. shows in Figure 7. The practice of co-extrusion is well known, and in the present case, the tube consists of an outer layer comprising the sheet 34 of the PET of molten bath phase or other polymer, corresponding to the wall 12 external of the container 10 or the outer layer 26 of the preform 22, and an inner layer comprising a laminate or substrate 36, as described above and corresponds to the laminate 15 of the internal wall 14 of the container 10 or the laminate 27 of preform 22, emerging as tube 40 from station S5 and directed to station S6. At station S6, tube 40 is preferably subdivided into tube segments, as indicated by the dotted lines of Figure 7, forming the precursors made of the tube segments. As an additional alternative method (not polished) for introducing a barrier resin into the body or adjacent to the PET layer or the wall 12, wherein the barrier resin is preferably similar to those used with reference to the discussion of the embodiments of Figures 4 and 5, a co-injected preform may be formed in accordance with known practice or in accordance with the process discussed in U.S. Patent No. 4,149,645 cited above. The barrier resin can be co-injected in a mold along with the structural PET layer, having the undesirable substances, such that the barrier resin forms the innermost layer of the preform and inhibits the release of the substances undesirable aforementioned to the contents of the container. For all the modalities described above, it may be that the most suitable material to serve as a barrier, such as for carbonization loss, is also a suitable barrier to exclude AA, or vice versa, such as in the preferred embodiment with EVOH, and also with PEN and the nylons. In such cases, and as with the container 10, the substrate in the form of the laminate 15 comprising the internal wall 14 performs the dual task of retaining a substance within the container while excluding another undesirable substance. It will be understood that the invention is not limited to the illustrations described and shown herein, which are considered to be only illustrative of the best modes of carrying out the invention, and which are susceptible to modification of shape, size, arrangement of parts or details of the invention. operation. The invention is directed rather to understand all these modifications that are within their spirit and scope as defined by the claims.

Claims (20)

REIVI NDICATIONS

1. A container for storing contents, comprising: a support wall formed of a polymerized plastic containing at least one undesirable substance therein intrinsic to the polymerized plastic, wherein the plastic contains residual amounts of the undesirable substance thereof and an amount able to migrate from the plastic to the contents when the contents are put in contact with the plastic; a protective wall adjacent to the support wall and placed between the support wall and the contents, wherein the protective wall is formed of a material that limits the migration of the undesirable substance from the support wall to the contents; and wherein the container is in the form of a blow molded container with the protective wall placed to contact the contents.

2. The container according to claim 1, characterized in that the supporting wall is formed of PET having an intrinsic viscosity of less than .70 and preferably from .55 to .65, and wherein the PET contains acetaldehyde in an excess of 2 ppm.

3. The container, according to claim 1, characterized in that the protective wall includes a barrier material selected from the group consisting of EVOH, PEN and nylon.

4. The container, according to claim 1, characterized in that the protective wall is a laminate.

5. The container according to claim 4, characterized in that the laminate includes a layer of EVOH and an inner layer composed of a PET having a low content of acetaldehyde and a polyolefin, wherein the inner layer is placed to contact the contained and protect the EVOH intermediate layer from the contents.

6. The container, according to claim 1, characterized in that the protective wall includes a polyolefin.

7. The container according to claim 1, characterized in that the support wall is a molten bath phase resin polymerized in the molten state.

8. The container, according to claim 1, characterized in that the support wall is formed of PET not subjected to polymerization in the solid state.

9. The container according to claim 1, characterized in that the undesirable substance is at least one of ethylene glycol, a monomer from which the plastic of the support wall is polymerized and an oligomer produced during the polymerization of the wall plastic. of support.

10. The container according to claim 1, characterized in that at least one undesirable substance is intrinsic to the polymerization reaction, wherein the polymerization reaction is carried out at a level of polymerization leaving residual amounts.

11. A process for forming a container for storing contents, characterized in that it comprises the steps of: providing a plastic containing at least one undesirable substance therein intrinsic to the plastic, wherein the plastic contains residual amounts of the undesirable substance therein at an amount capable of migrating from the plastic to the contents when the contents are in contact with the plastic; combining the plastic containing the residual undesirable substance with a protective substrate and forming a mixed compound, wherein the protective substrate is formed from a material that limits the migration of the undesirable substance from the plastic to the contents; forming the mixed compound to an article comprising a preform; and blow-molding the preform to the container, wherein the protective substrate is placed to contact the contents.

12. The process, according to claim 11, characterized in that the mixed compound is formed to a precursor that is formed into a preform.

13. The process, according to claim 11, characterized in that the combining step comprises one of extruding the plastic on the substrate to form the mixed compound, and co-extruding the plastic with the substrate to form the mixed compound in one of the form of a sheet and a tube, and co-inject the plastic with the substrate.

14. The process according to claim 13, characterized in that it includes polymerizing a plastic so that the plastic contains the undesirable substance, the substance is intrinsic to the polymerization reaction, the polymerization being carried out at a level of polymerization that leaves residual amounts.

15. The process, according to claim 14, characterized in that between the polymerization and extrusion steps, the process further includes the step of maintaining the plastic at a temperature sufficient for the extrusion step.

16. The process, according to claim 11, characterized in that the protective substrate is a laminate, the process further comprises the step of co-extruding the laminate.

17. The process, according to claim 16, characterized in that the laminate includes an EVOH layer, and an internal layer comprising a PET layer having a low content of acetaldehyde and a polyolefin, wherein the inner layer is adapted to be formed to place itself in contact with the contents and protect the intermediate layer of EVOH from the contents.

18. The process, according to claim 16, characterized in that the laminate is a barrier to acetaldehyde, and wherein the plastic is PET containing acetaldehyde in an excess of 2 ppm.

19. The process, according to claim 13, characterized in that during the steps of extruding and forming, multiple preforms are formed, wherein each of the multiple preforms arises from a remaining portion of the mixed compound, further comprising the step of roughing each one of the multiple preforms from the remaining portion of the mixed compound.

20. The process according to claim 11, characterized in that it includes polymerizing a plastic so that the plastic contains the undesirable substance, wherein the polymerization is carried out to partially polymerize the plastic whereby the polymerization is carried out at a level of polymerization that leaves residual amounts of the undesirable substance therein in an amount capable of migrating from the plastic into the contents where the contents are in contact with the plastic.