MXPA01001376A - A process for forming a multilayer, coinjected or coextruded article - Google Patents

Abstract

A process for coingection-molding a multilayer article comprising coinjecting at a selected coinjecting temperature (i) a first outer polymer resin layer having a viscosity at the selected coinjecting temperature, and (ii) a second inner polymer resin layer having a viscosity at the selected coinjecting temperature, wherein the ratio of the outer polymer resin viscosity to the inner polymer resin viscosity at the coinjecting temperature is less than or equal to about 2 and the coinjecting temperature is above the melting temperature of the highest melting resin and below the degradation temperature of the lowest degrading resin to form a multilayer article. A process for coextrusion is also provided.

Description

A PROCESS FOR MANUFACTURING A COEXTRIDED OR COINJECTED ARTICLE OF MULTICAPS DESCRIPTION OF THE INVENTION This application claims priority over the provisional patent application with Serial No. 60 / 097,246 filed on August 20, 1998, which is incorporated herein by reference in its entirety This invention is generally related to a process comprising co-ejecting or coextruding a structural polymer resin with one or more performance polymer resins to form a multilayer article without melt flow defects. Poly (ethylene terephthalate) (PET) is an established polymer for bottles that produces rigid bottles with excellent brilliance and clarity. These containers are manufactured in a process comprising drying the PET resin, injection molding a preform and finally molding by blow-stretching the finished bottle. The injection molding of the PET preforms requires the melting of polymer granules and the injection of the molten viscous PET material into a cavity, which also has a core rod. The molten PET forms a "skin" where it comes into contact with the wall of the cold cavity and the core rod. This skin is composed of "frozen" PET and will remain almost static through the rest of the injection molding process. At points extending radially inwardly beyond the wall of the cavity and away from the core rod, or points where the polymer does not make direct contact with the wall of the cavity or the core rod, the polymer (which still has a high temperature) remains a viscous mass that flows. This hot inner viscous material can still flow relative to the frozen skin layer although its viscosity increases as it continues to cool. In this way, a region of temperature transition in the radial direction arises as well as a corresponding function viscosity transition (due to the dependence of the viscosity of the PET relative to the temperature). Despite the changes in the melt viscosity as a function of the radial distance of the skin, the PET of the monolayer as a whole, is not affected by the cuts that develop between the frozen skin of the PET and the polymer molten that pushes to go through them. After the entire cavity has been filled using this process, the polymer is kept in the cavity until the preform has cooled sufficiently so that it can be blown immediately to form a bottle or until the preform is cool enough to be expelled . Chilled preforms that have been ejected are stored to be blow molded and - * - - * - «- •» - »reheating in the final product. By using this process, PET resin is used in a wide range of applications such as hot filled juice products, carbonated soft drinks and hot filled foods. However, PET has an insufficient barrier to meet the shelf lives of products that have the most gas barrier needs. In a particular application, in order to increase the gas barrier of a PET bottle, it is possible to inject a barrier layer into or onto a preform during the injection molding process. This barrier layer is injected into or over the melt flow stream of the PET so that the barrier polymer resin flows past the skin of the PET previously injected. This "coinjection" process allows the two resins to be injected to form a "multilayer" preform that can be blown to form the final bottle product. Unfortunately, it has been found that co-injection of a barrier polymer resin with PET can result in defects of the PET preform. A commonly observed fusion flow defect is "milestones", often called chevrons due to their V shape. Cheurons are interfacial instabilities that occur between layers. The chevrons denigrate the aesthetics of the finished article. A barrier resin that can be used in a multilayer process is an ethylene-vinyl acetate copolymer copolymer (EVOH) modified with various levels of ethylene ("grades"). It is commonly known that these "grades" of barrier resins have different melt viscosities and melting points. Usually, it would be desirable that both the melt viscosity of the barrier resin and the melting temperature of the barrier resin match the PET that is being used. Unfortunately, commercially available EVOH (regardless of grade) has a melt viscosity and a degradation temperature well below that of commercially available PET. In addition, the heat transfer of the hotter PET layer will additionally heat the EVOH above its desired processing temperature and result in a much lower melt viscosity of the barrier resin during injection molding. Most of the technology for co-injection is relatively new and is now being commercially viable for molding large-scale preforms or multilayer articles. In addition, co-injection for most practical purposes focuses almost exclusively on the use of PET (or a copolymer thereof) as the structural resin for preform molding applications. In contrast, co-extrusion is a well-established technique that is commonly applied to a wide variety of different polymers (eg, PET, copolyesters, polyolefins, PVC, styrenics, nylons, etc.) and for a much wider range of applications. In co-extrusion, a multilayer film sheet is produced compared to a molded article. As for co-injection, there are one or more "structural" layers combined with one or more "performance" layers. Structural layers usually (but not always) are cheaper than performance layers and are included to keep the total cost low (since performance layers can very often be very expensive). Examples of coextrusion include the use of a barrier layer in a packaging film, the use of a UV protective layer in an outer layer of heavy gauge sheets for weather protection against the weather, the use of crushed in the core to reduce costs , the use of adhesive / sealing layers on the exterior surface, and the use of pigmented layers and / or brilliance to change the overall aesthetics of the film / sheet. Compared to the co-injection example mentioned above, the "performance" layer in the co-extrusion does not necessarily have to be inside the multilayer structure. In the coextrusion process, the different resins are first melted in separate extruders and then joined in a feed block - a feed block is nothing more than a series of flow channels that join the layers in a uniform current. From this feed block, the multilayer material then flows through an adapter and out of a film matrix. The film matrix can be a traditional flat film / sheet matrix (eg, a hanger matrix) or it can be an annular matrix as used in blown films. Coextrusion is also used to make more complicated configurations like profiles. When reference is made to the co-extrusion in this document, it is implied that all these other co-extrusion applications are also included in addition to the traditional film / sheet applications. As with co-injection, coextrusion very often suffers from the problem of chevrons and other visual defects. These defects in coextrusion and co-injection result from the high shear stresses that develop at the layer interface during flow. These stresses are a function of the viscosities of the layers in addition to the relative position and the thicknesses of the layers, in fact, the knowledge obtained from the co-extrusion can be used to help minimize the flow defects in the co-injection. In addition, flat film coextrusion very often suffers from the problem of poor layer distribution across the width of the sheet. For example, if you take a piece of extruded film and the layers are separated, one could find that one of the layers is much thicker near the outer edges of the sheet, and very thin in the central part. The other layer would only be the opposite, that is, thin near the edges and thick in the core. Usually, it is desirable that the layers be uniform and have the same thickness across the entire width of the sheet so that the properties (eg, barrier, color, hardness, etc.) do not vary across the width. So far, the correction of these two coextrusion problems (uniformity due to poor layer distribution and flow defects) has actually been more of an art than a science. There have been some attempts to balance the viscosities of the resin (i.e. having viscosity ratios close to one) to improve the layer distribution, but this has only been met with limited success. Thus, there is a need for a process to properly select both elasticity parameter and resin viscosity and processing conditions in coextrusion so that both interfacial instabilities (ie, visual defects such as chevrons) and layer distribution can be eliminated.

Thus, in the co-extrusion process according to this invention, the "elasticity" of the different resin layers is so important. As the viscosity of the resin and the proper balance of both the elasticity ratio and the viscosity ratio simultaneously needed to have a uniform layer distribution and form a multilayer article, a process has been developed for the resins and the processing conditions can be optimized to eliminate these multilayer flow problems Because the multilayer flow behavior is very similar for both co-injection and co-extrusion, the method can be effectively applied for both applications. The process of the present invention forms a co-injected multi-layer article or preform of high quality as well as easily forms a co-extruded multilayer film structure. r den Kern, "by Eigl, Kukla and Langecker, in Kunststoffe vol. 88, no. 1, pp, 46-48 and 50 discloses ratios of the outer and inner polymer resin viscosities respectively greater than one and less than one medium in the context of the injection mold. DE-A-35 34 407 describes co-extrusion where the viscosity ratios of the boundary layers are not greater than 1: 1.5. No reference mentions the relationship of the elasticities ! ".? - AA.A." - J .. ".", _ --'-- - ~ e -'- of the polymers used. "Rheology in Polymer Processing," in Han, Academic Press, 1987, chapter 10, page 263-283 describes the role of the elasticity viscosity properties of the components in multilayer coextrusion processes. However, this reference does not mention the elasticity ratio between the polymer layers. The present invention relates to the elimination of melt flow defects such as chevrons of co-injected and / or co-extruded articles by minimizing inter-layer interfacial tensions, such as between a structural layer (eg, PET) and a performance layer (eg. example, barrier), in an article or multilayer molded structure. In addition, the present invention relates to the concordance of the viscoelastic flow properties of the respective layers so that the distribution of the layer is maintained in a uniform manner for the coextrusion and co-injection applications. As exemplified and broadly described herein, this invention, in one embodiment, is related to a process for co-injection molding a multilayer article comprising: co-injection molding at a selected co-injection temperature (i) a first layer of outer polymer resin comprising at least one i. to *. ? * J *, m ^. *. II lllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllllll and (ii) a second inner polymer resin layer comprising a performance polymer layer resin having a viscosity and elasticity at the selected co-injection temperature, wherein the ratio of the viscosity of the outer polymer resin to the The viscosity of the inner polymer resin at the co-injection temperature is less than or equal to about 1 and wherein the ratio of the elasticity of structural resin to the elasticity of the yield resin is approximately the reciprocal of the viscosity ratio. In another embodiment, the present invention comprises a process for coextruding a multilayer article comprising: coextruding at a selected coextrusion temperature (i) a first layer of outer polymer resin comprising at least one structural polymer resin having a viscosity and an elasticity at the selected coinjection temperature; (ii) a second inner polymer resin layer comprising a performance polymer layer resin having a viscosity and elasticity at the selected co-injection temperature, wherein the ratio of the viscosity of polymer resin exterior to the viscosity of polymer resin selected at the co-injection temperature is approximately • * < * - '• - > The ratio of the elasticity of structural resin to the elasticity of yield resin is reciprocal. Additional advantages of the invention will be set forth in part in the detailed description, including the following figures, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages of the invention will be realized and will be obtained by means of the elements and combinations particularly mentioned in the appended claims. It should be understood that both the foregoing general description and the following detailed description are exemplary and explanatory of the preferred embodiments of the invention, and not limiting of the invention, as claimed. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram of a frequency sweep to determine the dynamic viscosity data for the EVOH at 180 ° C. Figure 2 is a schematic diagram of cutting tension and velocity profiles in a polymer resin flow channel. Figure 3 is a diagram of? (A) /? (B) versus? (A) /? (B) illustrating the optimal operating region for removing the chevrons and balancing the layer thicknesses. Figure 4 is a diagram of? (A) /? (B) versus? (TO) /? (B) for the coextrusion of A / B / A from a PE cap layer (polyethylene) onto a PETG core layer (Polyethylene terephthalate-G) The points refer to the different combinations of process temperatures as mentioned in Example 1. 5 Figure 5 is a diagram of? (A) /? (B) versus? (A) / (B) for co-extrusion A / B / A of a PE cap layer (polyethylene) on a core layer of PETG (polyethylene terephthalate-G). The extrusion temperatures for the layers were kept constant at 235 ° C and the melt index PE varied from 0.9 to 3.2. Figure 6 is a diagram of? (A) /? (B) versus? (A) /? (B) for coextrusion A / B / A of a PC cap layer (polycarbonate) on a core layer of PET (polyethylene terephthalate). Extrusion temperatures for the layers were different. The present invention can be more easily understood by reference to the following detailed description of the invention, including the appended figures mentioned herein, and the examples provided therein. It should be understood that the invention is not limited to the specific processes and conditions described, since the processes and / or specific process conditions for processing molded articles as such may, of course, vary. It should also be understood that the terminology used herein is for the purpose of describing modalities rltirnátrTí »'ar ...., - .- *. . * ** :. ** ^^ ¿¡¡¡¡¡- - individuals only and does not claim to be limiting. It should also be noted, as used in the specification and appended claims, that the singular forms "a" and "an" include plural references 5 unless the context clearly dictates otherwise. For example, the reference for processing or forming an "article", "container" or "bottle" of the process of this invention is intended to comprise the process of a plurality of articles, containers or bottles. 10 A particular value and / or up to "about" or "about" another particular value can be expressed in the present range from "around" or "approximately". When the range is expressed, another modality comprises of a particular value and / or the other value particular. Similarly, when expressing values as approximations, by using the antecedent "around", it should be understood that the particular value forms another modality. The present invention is related to the Removal of melt flow defects such as chevrons from co-injected and / or co-extruded articles minimizing interfacial tensions between the layers, such as between a structural layer (e.g., PET) and a performance layer (e.g., barrier) , in an article or structure multilayer molding. Preferably, they can be minimized these melt flow defects while obtaining and retaining the preferred physical properties in the resulting article. In addition, the present invention relates to the agreement of the viscoelastic flow properties (ie, both the viscosity and elastic properties) of the respective layers so that the distribution of layers is maintained in a uniform form for the applications of coextrusion and co-injection. In one embodiment, it is possible to inject a barrier layer into a preform during the injection / molding process. The barrier layer is injected into the melt flow stream of the PET (structural layer) so that the barrier resin flows beyond the skin (from preference in the inner part) of the previously injected PET. A preferable barrier resin used in the multilayer process is EVOH modified with various levels of ethylene ("grades"). This "coinjection" process allows two resins to be injected to form a preform of "milticapas" that can be blown to form the final bottle product. However, it is commonly known that these "grades" of barrier resins have different viscosity and melting points. When there are wide differences in the melt viscosity that occur between PET and the resin of barrier, the potential for the formation of It is possible to see visible fusion defects. In addition, the ratio of the two polymers also plays an important role in the formation of visible defects. An example of a visible flow defect is a V-shaped chevron. Cheurons are interfacial instabilities that occur between the layers when the cutoff voltages at the interface exceed a critical value. Therefore, it is desirable to cause the melt viscosity of the barrier resin to match the PET resin to eliminate visible defects, particularly chevrons. To eliminate visible defects, it is necessary to develop a set of process conditions and carefully select a grade of PET or other structural polymer resin so that the melt viscosity and process temperatures can be made to match the resin as closely as possible of barrier polymer or performance. By making these parameters more closely matched, the shear stresses at the interface between the layers can be reduced thereby producing a high-quality, flexible, and more flexible multilayer container. For example, a PET modified with CHDM with an I.V. Dramatically reduced can be selected so that it can be processed in such a way that the preforms and the resulting bottles can be produced without visual defects.

One embodiment of the present invention comprises minimizing stresses by balancing the viscosity ratios of performance polymer layer / structural polymer layer in the coinjection and coextrusion process. For example, the ratio of the viscosity of the structural polymer resin divided by the viscosity of the yield polymer resin is preferably less than or equal to about 2, and more preferably less than or equal to about 1 to form an article formed of multilayers without defects of fusion flow. More preferably, the ratio of the melt viscosity of the structural resin to the melt viscosity of the yield resin is less than or equal to about 1 and greater than or equal to about 0.5. Viscosity ratios that differ widely can lead to distortion of the interface shape as well as high interfacial tensions (the latter causing chevrons). In the co-extrusion of films and sheets, interfacial instabilities most likely occur when the outer (lid) layer is very thin, typically less than 10% of the total thickness because the shear stresses during coextrusion are higher near the outer surface. To solve this, and minimize the stresses and remove the chevrons, the outer (lid) layer may have a slightly lower viscosity than the * ^^^^^^ ¿^ ^ * ^ * ^ M * '*. *. »Tn? ± A. *. ? inner layer (core). However, the viscosity ratio is even closer to one. However, for a co-injection process, the situation is reversed. The outer layer or layers preferably comprise at least one suitable structural polymer resin with a very thin inner (core) layer or layers of a performance polymer resin. While stresses are naturally much lower in the core of the flow channel where, typically, the performance resin layer flows, it is still may become high enough for chevrons to occur. For the purposes of this invention, when a multilayer article is formed by a co-extrusion or coextrusion process, the outer or outermost resin layer of the The multilayer material is defined as the layer that is closest to the surface of the metal walls, which define the flow channel. Metal walls can typically include the surfaces of the mold wall and the tip of the core, for example. Each subsequent layer towards the line The center of the flow channel is considered as an inner layer in relation to the closest layer of the walls. In other words, for each interface of two or more layers, an outer layer is defined as the closest to the surface of any wall. 25 In contrast to co-extrusion, it is preferred in the -jMfflñMli'tf ** 8 * '- "-" "« - > * «* * - - - - - - -. - * X *. * í .... * Ua» - >, ~ * co-injection if the preferable inner-yield polymer resin has a viscosity equal to or slightly greater than the viscosity of the structural polymer resin (even though the viscosity ratio is within the ranges defined above), currently, for example, the viscosity of the EVOH is much lower than that of PET at the process temperatures used, which greatly contributes to the formation of chevrons, both viscosity and elasticity will vary with temperature.Therefore, it is important to select process conditions that (a) more closely match the optimum elasticity and viscosity temperatures of the selected resins and (b) are within the known constraints, such as the melting point and the degradation temperature for each of the selected polymers. the processes of es In accordance with the invention, the co-extrusion or co-extrusion temperature should be above the melting temperature of the highest melting polymer resin used, which may or may not be the performance or structural polymer resin. In addition, the co-extrusion or co-extrusion temperature should be below the degradation temperature of the lower degradation polymer resin, which may or may not be the performance or structural polymer resin. It should be appreciated that for many combinations of structural / performance resins there will be more than one set of suitable processing temperatures within the ranges of the present invention. This is highly desirable since it allows the optimization in equipment of extrusion and variable molding. Thus, it is desirable to choose a set of optimum viscosity and elasticity temperatures which are within the fixed constraints for polymer resins and which are reasonably narrow or concordant, and provide a ratio of elasticity and viscosity within the range of the present invention. Viscoelastic Parameters In order to apply the processes described here, it is first necessary to define the properties viscoelastic of each layer as a function of temperature. Viscolásticas properties are viscosity and elasticity. Both of these parameters decrease with increasing temperature at variable speeds depending on the type of polymer (I.V., Mw, etc.). 20 Viscosity is simply the ratio of shear force exerted by a fluid divided by the applied cutting speed. The more viscous fluids than honey or oil have higher flow resistance than less viscous fluids such as water. In contrast, "elasticity" is a measurement of "memory" or "elastic capacity" of a fluid. A - * "* - ••" * "* • '• * • i - * * t-¿Highly elastic fluid, after being deformed, will try to return to its original non-deformed shape once the tension It is removed, a rubber band is an extreme example of a highly elastic material, in contrast, a material without elasticity (for example, a purely viscous fluid such as water) will have no memory of its original shape and will not try to return to its original shape afterwards. that the tension is removed Polymers fall between the two ends of purely elastic (for example, a league) and purely viscous, with the degree of elasticity depending on such things as molecular weight, degree of chain entanglement etc. polymers also has what is known as "fading memory" in other words, the memory of a polymer of a stress case will gradually decrease with the increase of time.If one applies a voltage to a polymer with a memory or fading and wait long enough before releasing it, the polymer will have little or no "return" because it no longer has memory of the case. The time it takes for the majority of memory to vanish is called "relaxation time" and is denoted as? For purposes of this invention, the relaxation time is used as a measure of "elasticity". The elasticity is important in the process of coextrusion or co-injection in particular because each time a polymer undergoes a change in the flow condition (resulting in a change in tension), the polymer retains some memory of that stress that affects its flow a little more downstream. For example, the hot channels that connect the extruder and the injection mold very often have a 90 ° elbow in the pipes to change the flow direction. This elbow imparts a different tension to the polymer as it passes through the bend. If the time it takes for the polymer to flow from the bend to the door is less than the relaxation time? then the tensions in the fold will still be remembered by the resin which can consequently affect the flow in the mold. In some cases, this can lead to the polymer filling preferentially and not symmetrically on one side of the mold of the preform. This affects the cooling behavior and possibly even the layer distributions for the multilayer preforms. For coextrusion, the imparted stresses occur when the layers first come together in the feed block and continue at different points as the polymer flows through the adapter and then into the matrix. Due to the differences in elasticity between the different layers in a multilayer flow, the elastically induced stresses in the interface will cause a gradual rearrangement of the interface as it flows through the channel.

Chili 6 & .% u¿ £ - i * & > -. .... . . * *. ** * Therefore, the longer the relaxation time, the more elastic (compared to the liquid type) will be the behavior of the polymer. This elasticity ratio should fall approximately within the same range as the viscosity ratio. However, it is preferred that the elasticity ratio be reciprocal to the viscosity ratio to be out of place or in equilibrium with the trend of unmatched polymer viscosities, which may create non-uniform layers. Thus, in one embodiment of the present invention, the elasticity ratio of the structural polymer resin to the elasticity of the yield polymer resin is preferably from about 1 to equal to or less than 2. As the ratio of elasticity begins to deviate excessively from this range, non-uniformity in thickness of the layer may occur in a manner similar to the unbalanced viscosity ratio. Also, the swelling of the matrix of each polymer as it pulls from the nozzle of the injector and enters the mold is a strong function of its relaxation time. Thus, a balanced elasticity ratio between structural resins (eg, PET) and barrier performance (eg, EVOH) will lead to swellings of similar matrices that improve the flow of layer uniformity. Process temperatures, elasticity and melt viscosity have been predetermined for commercially available EVOH barrier resins, for example. Therefore, it is desirable to develop a set of process conditions and carefully select a degree of PET so that the process temperatures, elasticity and melt viscosity can be as close as possible to the yield resin to be able to eliminate the defects of flow (like chevrons) and maintain uniformity in the thickness distribution of the layers. In this way, the shear stresses at the interface between the layers can be reduced by producing a more flexible and higher quality multilayer article container of defects. The polymer melt viscosities are known to be proportional to Mw3'4, where Mw3'4 is the average weight molecular weight. Because Mw is directly related to the I.V., the melt viscosity is therefore directly proportional to I.V5'1, where I.V.5'1, is measured in phenol / tetrachloroethane 60/40 at 25 ° C. In this way, by reducing the I.V. of the PET resin, for example, the melt viscosity can also be lowered. The relaxation times of the polymer will also decrease when the I.V. decreases, so it is important to try to balance both the viscosity and elasticity ratios at the same time. Usually, this implies a barter in which both of the relationships may not be made exactly equal to l. Thus, for coextrusion, it is not necessary that the relations of both viscosity and elasticity are the same, but it is preferable that the two relations are out of place one of the other (the elasticity relationship should be reciprocal to the ratio of viscosity). In other words, if the elasticity ratio is slightly greater than one, then the viscosity ratio should be slightly less than one. This would lead to uniform interfaces between layers in coextrusion applications and it is very likely that the same behavior is true for co-injection. By making both ratios significantly lower than one or both significantly greater than one, it can lead to problems with layer uniformity. The elasticity and melting viscosity of the polyesters can be altered by modifying the polymer compositions, lowering the I.V. of the polyester, and / or by careful selection of processing conditions for both polymers. Thus, those skilled in the art could easily produce polymers having the desired elasticity and viscosity ratios using the process of the present invention. For example, a modified PET, with CHDM with an I.V. Dramatically reduced, it can be co-injected with EVOH under appropriate process conditions such that bottles and preforms can be produced without visual defects such as chevrons or other flow anomalies. Calculation of Viscosity and Elasticity (or Relaxation Time) The calculation of the viscoelastic parameters for a resin requires appropriate rheological test data. In the present invention, uency sweeps in a plate and cone rheometer are used to obtain dynamic viscosity information in the polymer portion. That test, which is well known in the art, provides a complex viscosity? *, A storage modulus G 'and a loss modulus G ", all as a function of the oscillation uency? . An example data set is shown in Figure 1 for EVOH at 180 ° C. For purposes of the detailed description, the complex viscosity? * Is approximately the same as the viscosity of? uniform cut. Similarly, the oscillation uency is approximately the same at the cutting speed for a uniform cut test. The storage module G 'is a direct measure of the "elasticity" of the polymer, while G "is related to the amount of viscous dissipation (similar to viscosity). For the optimization of the coextrusion / conjection, are the relaxation times extracted? and the zero cut viscosity? One extraction method is to fit all the data to one of many equations available in the literature. However, an easier method is to calculate the parameters graphically. Can the zero cut viscosity be calculated by extrapolating? * To very small values of? (it has a value of 93020 poise in Figure 1). For purposes of this description, we will refer to the adjusted value of? Or as simply?, Although it should be understood by the reader that the true uniform cutting viscosity? It really depends on the frequency (or speed of cut). To calculate ? should the frequency be found? where G 'and G "intersect. Time ? of relaxation can then be approximated as 1 /? * where, for this EVOH example, we obtain a value of 0.006 s. Because ? Y ? vary with temperature, it is important to repeat this measurement of dynamic viscosity at different temperatures. At least three sweeps are made for each resin. The parameters? Y ? can be adjusted to a curve for an Arrhenius equation type with an activation energy Ea having the form of:? =? exp (£ a / RT)? = Bexp (£ a / RT) where A and B are frontal factors, T is temperature and R is the gas constant. Once the A, B, and Ea / R values are adjusted, the viscosity ratio and the elasticity ratio for either of the two L ^? ^ Polymers in any given melting temperature set can be calculated. Factors for Forming Co-Injected or Coextruded Items Some factors to consider when forming multi-layered articles having minimal interfacial instabilities (ie, chevrons, wavy lines, etc.), in accordance with this invention include, but are not limited to the following: 1 Interfacial instabilities occur when the cutoff voltage at the interface between two layers exceeds a certain critical value (this value depends on the resins involved). In this way, by keeping the interface tensions at a minimum during coinjection or coextrusion, instabilities can be eliminated. 2. Cutting voltages increase as the cutting speed increases. Due to the configuration of the speed profile in the flow channel, the cutting speed tends to be at a maximum close to the walls (this can be the wall of a matrix in a coextruded structure or the wall of the mold in the co-injection) and the zero near the core of the flow channel (see Figure 2). As a result, the shear stresses are higher near the wall and lower in the core. In this way, the closer the interface is to the wall surface, the more likely the interfacial stresses will exceed the critical voltage in such a way that visual defects are formed. Interfaces near the flow channel core probably do not develop flow instabilities because the voltage is low. In this way, where the application allows (not all), it is preferable to have the interface as close to a core as possible. 3. Cutting voltages also increase when the outermost layer is at a higher viscosity than the next innermost layer. Therefore, by maintaining the viscosities where the outer layer is at a lower viscosity than an inner layer, stresses are minimized and instabilities are also minimized. The closer the interface is to the mold wall, the lower the viscosity of the outermost layer should be. 4. Cutting voltages can also be reduced by decreasing the polymer flow rate through the matrix (or the speed at which it is injected into the mold). However, lowering the flow velocity implies a reduction in the speed of the line, which is not economically attractive. 5. Coextrusion very often means that the "performance" layer is a thin cap layer on the outside of the sheet (for example, for UV blocking, brighter, heat sealing, etc.). As a general rule, when this cap layer is less than about 10% of the total sheet thickness, the interfacial tension will most likely be high enough to cause instabilities. 6. During co-extrusion, interfacial instabilities are more likely to begin to form in the planar region of the matrix just before reaching the edges of the matrix. This is because the flow channel is narrower here and the voltages are higher. 7. Unlike co-extrusion, co-injection rarely involves adding the "performance layer" as a thin-cap layer on the outer edge. In this way, it might seem that instability problems would be minor. However, co-injection involves much higher cutting speeds than co-extrusion, so that inter- tensional stresses can be significantly higher, even when they are removed away from the mold wall. In addition, the polymer cools rapidly from the surface of the wall inwardly, which effectively narrows the flow channel as the polymer solidifies and thereby elevates the stresses further. As mentioned above, the closer the barrier layer co-injected to the centerline is, the less likely instabilities are to be formed. 1. Co-injection In one embodiment to form a multi-layer article by a co-injection process according to this invention, the viscosity ratio for an outermost layer (A), which is closer to the mold wall and typically called the layer of "top", on the next lowermost layer (B), which is closest to the core and which is typically called a "core" layer, must be less than or equal to (<;) approximately 2. In other words,? (A) /? (B) < 2 where? Is it viscosity? (A) is the viscosity of the outermost layer and? (B) is the viscosity of the next innermost layer. A more preferred mode is where? (A) /? (B) is greater than or equal to about 0.5 and less than or equal to about 1 (0.5 <? (A) /? (B) < 1). For most, but not all co-injection applications, the structural resin (eg, PET) will be resin A (the outermost layer) and resin B will be the inner barrier layer since it is close to the core. In a way similar to coextrusion, if the barrier layer is in the core of the wall, then? (TO) / ? (B) it is preferred that it be closer to one. As the position of the barrier layer moves closer to the wall, then? (TO) /? (B) must be smaller, preferably approaching 0.5. However, other multilayer embodiments are contemplated in this invention. For example, a multilayer article of this invention can be prepared from the - * - * - .. ** - * • coinjection of 5 layers where (starting from one side), the layers are arranged as follows: PET / EVOH / PET crushed for EVOH / PET. In this example, the? (PET) /? (EVOH) < 2 y? (EVOH) /? (Crushed PET) < 2. Preferably, each ratio is 0.5 to l. In a preferred embodiment of that relating to the 5-ply article, the invention comprises coextruding or molding by coinjection of three or more resin at a co-extrusion or co-extrusion casting temperature selected accordingly, forming an article having more than two layers in where in each polymer resin interface, the ratio of the viscosity of polymer resin more exterior to the next viscosity of polymer resin more inner is approximately reciprocal to the ratio of polymer resin elasticity more exterior to the elasticity of the next more internal polymer resin in the same interface. In this way, to form the above 5-layer article,? (PET) < ? (EVOH) < ? (PET crushed). Unfortunately, this is not always easy since the crushed PET has an I.V. usually lower (in this way a lower viscosity) than regular PET. However, this is the optimal condition that will provide the best preform (or co-extruded film) without chevrons and / or instabilities. Also, since the viscosities depend on the temperature • t ltUl * - ^ "- 'fJ- * -. - - *. -.- - .. *. *. J ..... t ^ -" ^ 11., -.... * - * * *,.? tU because the viscosity decreases when the temperature increases, the different process temperatures help to achieve that the previous conditions can be changed (for example, the crushed PET can run colder to increase its viscosity). Note that having the viscosity ratio of? (A) /? (B) less than or equal to 2, more preferably less than or equal to about 1, helps reduce pumping pressures because there is less viscous fluid near the wall that serves as a kind of lubricant. Another embodiment involves coinjecting a multilayer article so that the viscoelastic properties of the resins (i.e., viscosity and elasticity) are properly balanced to achieve the best layer thickness uniformity. In particular, the resins are chosen in such a way that, when giving process / melt temperatures, the viscosity ratio (? (A) /? (B) as the relaxation time ratio? (A) /? (B) they are approximately less than or equal to about 2 or otherwise equilibrate according to this invention. More preferably, it is desired that the elasticity ratio be approximately reciprocal to the viscosity ratio. If this condition is not met, then the rearrangement of layers will occur in the adapter and will alter the thickness distribution. m iiitntiBíBiiirilÉtpi Bi 'i I ni i. --.- -. -. .. ***** .. - s ».. ... ..,., ....,« «.", ..

An example of this are polymers that have different viscoelastic properties. As the two resins flow together through a channel, resin A gradually wraps around and "encapsulates" resin B. The longer the channel is, the greater the degree of encapsulation. In coextrusion, this encapsulation usually occurs in the adapter that connects the power block to the array. Therefore it is important that the adapter length be short to minimize this encapsulation. Once he The encapsulated polymer reaches the matrix, fan out to form the total width of the sheet essentially "enclosing" any distorted shape present at the end of the adapter. In order to optimize the conditions to eliminate For both visual effects and poor layer distribution, it is usually important (but not always) that both sets of conditions are met simultaneously. These "operation windows" can probably be better understood if they are displayed graphically. Figure 3 is a diagram of the relaxation ratio of? Lid /? Nucieo versus the viscosity ratio of? Lid / i "| where the ream of" lid "denotes the outermost lid layer" A "and the" core "resin "denotes the innermost core layer" B. "For any resin and process temperatures, this would produce a "point of operation" somewhere in the graph. For & e ~ **? ***? e. . that this point of operation satisfies the criterion of instability of? (TO) /? (B) < 2 and more preferably 0.5 < ? (A) /? (B) < 1 should fall on the left side of the "y axis" as denoted by the shaded area. For the flow to maintain a layer uniformity, it is preferred that the conditions fall along the 45 degree line (from the upper left corner to the lower right corner). The ellipse shown in Figure 3 represents this region. The closer the point of operation is to this diagonal line, the more uniform the layer structure will be. As the operating point moves further in any direction, the distribution of layers becomes more deficient, as shown in the diagram. If both the uniform layer distribution and the visual defect elimination can be obtained simultaneously, then the operating point should fall in the upper left quadrant along the 45 degree line (where the two operating regimes intersect). Therefore this is the true optimal process point for most coextrusion and / or co-injection applications. For co-injection applications, it is still desirable to meet these same criteria although the reciprocal equilibrium of the viscosity and elasticity ratios are for a slightly different reason. In co-injection, the problem of a poor layer distribution across the width does not exist since it is a symmetric annular flow pattern. However, as described above, by balancing the viscoelastic flow properties, it can help to minimize the opportunity for layer distortion as it flows around any of the bends or bends in the door and the connecting pipe. 2. Coextrusion There are four preferred issues for a coextruded structure or article: (1) Good distribution of layer thickness across the width of the sheet; (2) The absence of interfacial flow instabilities (e.g., wavy lines, chevrons, etc.); (3) Good layer adhesion; and (4) Minimum winding / film wrapping / ho to end. The method presented here only addresses the first two questions since good adhesion is more a matter of chemical differences between the two layers. Poor adhesion can often be corrected by a bonding layer. Likewise, the winding is mainly related to the conditions of roll cooling and very rarely is a "fatal failure".

In order to understand when questions (1) and (2) come into play, it is necessary to understand the adjustment of a typical coextrusion matrix and power block for the coextrusion of a flat film. Depending on the configuration of the feedblock plate, these two resins must be joined together to form a two-layer A / B structure or a 3-layer A / B / A structure. The latter, being symmetric (or "balanced") around the central plane, which is easier to do. The non-symmetrical structures tend to roll and wrap due to differences in thermal expansion and cooling during relaxation. Fortunately, for the purposes of eliminating flow instabilities and balancing layer thickness, it usually does not matter whether a structure is symmetric or not. Layer Compensation and Encapsulation The different layers are joined inside the feed block although the way in which they are attached depend on the type of feed block (for example, elex, Dow, Cloeren, etc). After the shock, the layers flow side by side through the adapter inside the matrix. The adapter can have any number of configurations in different cross section although the most common are circular and rectangular. Which is where the problems with uniformity of layer thickness usually arise in the adapter. If the viscosity (or as will be discussed later, the "elasticity") of A is less than B then it will have a tendency to wrap around or "encapsulate" as it flows through the adapter. Likewise, if B has a viscosity less than A, then it will try to encapsulate A. To keep this encapsulation to a minimum, it is usually recommended that the viscosity ratio for A and B be less than about 2 (or greater than about 0.5). This rule in general works in many cases but fails in many others. As will be discussed in the next section, this failure resulted due to the elasticity effects, which had previously been ignored, which are as important as the viscosity effects. In this way, it is important to balance the elasticity and viscosity ratios. Interfacial Instabilities While the rearrangement of layers occurs mainly in the adapter region, interfacial instabilities occur mainly in the matrix where the cutting speeds are higher (100 to 1000 s_1 in the matrix versus 10 to 30 s_1 in the adapter). When the shear stresses at the interface between the layers reach above a certain critical value, flow instabilities occur. These instabilities result in wavy lines, chevrons and curls that are '. ^ - »- - > - - - •. ^ _., ....-...,,. ... ......,. , - -. .. .. * .. -. unacceptable for most end-use applications. There are three main factors that contribute to high interfacial tensions and thus to flow instabilities. These are (a) thin-cap layers (<10% total thickness), (b) cap layers having a viscosity that is greater than the viscosity of the next innermost layer and (c) overall production speeds that They are too tall In other words, interfacial instabilities most likely occur when thin cap layers are present, particularly if the viscosity of the cap layer is greater than the core layer. This is because the cutting voltages tend to be higher near the outer wall of the adapter or the flow channel. For interfaces near the adapter core (for example, a 50/50 A / B structure), flow instabilities are very rare because the voltages are already low. Even for thin cap layers, if the cap layer viscosity remains lower than the core layer, then they can usually eliminate interfacial instabilities. This is important since thin-cap layers are very common. Finally, as mentioned in question (c) above, another simple way to eliminate flow instabilities is to reduce the speed of total production through ^ ..,. *. . ^ utt ^ aafaam ?? tt of the matrix. This will reduce interfacial shear stresses although it may result in economically unacceptable line speeds. The reduction in production speed should only be used as a "pinch" adjustment if problems arise in the line. It is better to properly select the resins in the initial design phase so that higher production speeds can be maintained. Elasticity in Coextrusion Elasticity plays an important role in coextrusion. Interestingly, the effect of the elasticity on the layer uniformity is probably more important than the viscosity, which may explain why the use of viscosity relationships rarely works only to predict the flow behavior. The first step in understanding the effects of elasticity is to define exactly what it means by "elasticity". Elasticity is the rubber-like behavior of the fluid-the ability of the fusion to have memory. At one end are materials that are purely viscous without elasticity. Examples include water, glycerin, air, etc. At the other extreme we find materials that are purely elastic without significant viscosity. Examples of purely elastic materials include leagues like most metals and solids in general. The polymer fusions fall somewhere between them, being both viscous and elastic at the same time (ie, viscoelastic). One of the easiest methods to quantify the viscous and elastic portions of the polymer melt is to measure the dynamic viscosity (or dynamic modulus) using a plate and cone rheometer. This method is well known to those skilled in the art and does not need to be described in detail herein. It will be emphasized that all these properties are functions of the effective cutting speed. As mentioned earlier, the time of elasticity and relaxation are synonymous. The preferred elasticity ratio should be approximately the reciprocal of the viscosity ratio so that the coextrusion is typically successful. If the relaxation time of the cap layer is less than that of the core layer, it will try to encapsulate the core (as if the viscosity of the cap layer were less than the viscosity of the core layer). Likewise, if the relaxation time of the cap layer is higher than the core, then the core layer will try to encapsulate the cap layer. In factIt is just as important to balance the elasticities as to balance the viscosities. After defining the two key parameters for each resin, the results can be combined and predictions about the flow can be made. It turns out that the interfacial instabilities and the layer rearrangement / uniformity can be treated independently during the analysis. This is preferable since there are times when some interfacial instabilities are allowed (for example, in opaque sheets) although the uniform layer distribution across the width of the sheet is critical. It should also be emphasized that a "good distribution of layers" really depends on the application. For most applications, it is desirable to have a constant thickness of each layer across the entire width of the sheet (this minimizes edge trimming). However, there are some applications where it is more desirable that the cap layer completely encapsulates the core (in an A / B / A structure), especially when the core layer can somehow be a hazard (even at the outer edges). ). An example of this could be where post-consumer recycling is the core layer (or some other non-FDA resin) in a food contact application. The steps to perform the coextrusion analysis to predict the flow are mentioned below: 1. Subject each resin to a dynamic viscosity sweep (plate and cone rheometer) at 3 or more different reasonable temperatures (ie, do not use temperatures where The ream can not be processed or will be degraded ^^^ j ^ & ¿U ^^^^ £ ^^ S excessively). 2. Determine? O and? for each resin and at each temperature. 3. Adjust the curve? 0 and? versus T using an Arrhenius diagram for each resin to determine activation energies and frontal factors. Those skilled in the art will understand without description how to adjust? 0 and? versus T in an Arrhenius diagram and how a detailed description of this technique is not necessary. Although not required, this will make extrapolation of the results at different temperatures easier in the latter part of the analysis. 4. Calculate the viscosity ratio and the elasticity ratio (y? A /? B as a function of the melting temperature for each resin pair.) By convention, the numerator of each resin represents the "outermost" layer and is that Closer to the wall For a two-layer coextrusion (A / B) structure, the outermost layer is usually taken as the thinnest one 5. Determine if interfacial instabilities are a problem for a given melting temperature. cap layer is thin (less than 10%)? oA / ob greater than or equal to two, then interfacial instabilities will most likely occur.It is more preferable, therefore, to keep? oA / ob less than or equal to 1 to avoid These instabilities 6. Determine the layer uniformity: If? oA /? ob and? A /? B are greater than two, then the core layer will encapsulate the cap.The degree of encapsulation increases 5 the farther you are from the layers. relations to 1. If both have less than 1, ent The lid will encapsulate the core. For a uniform layer distribution, both relations should be approximately reciprocal to each other. 10 The discussion of some of the previous steps in detail is mentioned below. Step 1: Dynamic Viscosity Each polymer in the co-extruded article structure must undergo dynamic viscosity scanning standard using a plate or cone (or a parallel plate rheometer) (See Figure 1). This is a standard test. At least three or more temperatures for each resin should be run, although these temperatures should represent "typical" extrusion temperatures. For example, for PET, temperatures of 260, 280 and 300 ° C can be used. Below 260 ° C, the polymer will not melt and above 300 ° C, the degradation becomes significant. Step 2: Determination of? O and? for Each Resin As previously described, the values for? and? must be extracted from the dynamic viscosity data ~ - ~ - -a ^ -aMMfc * »for each temperature and for each resin. The parameter? O is the viscosity? * At low cutting speeds. The relaxation point? is equal to 1 / w where w is the angular velocity where G 'and G "intersect. For many resins, G 'and G "will be" on the sheet "and within the range of the diagram for w. For some resins, however, G 'and G' 'will have to be extrapolated off the page in order to determine an intersection point. Step: Calculation of Elasticity and Viscosity Relations Once the values of? O and? are calculated for each resin of different temperatures, it is possible to determine the viscosity and elasticity ratios as a function of the melting temperature. Very often it is presumed that two resins are extruded at the same melting temperature. Even if they are melted and processed at different temperatures they will usually be balanced at some average temperature within the power block and the adapter so that the constant temperature assumption is reasonable. This is particularly true if one layer is very thin compared to the other layers. The calculation of the ratio should be repeated for each resin pair interface in the film. Step 5: Determining the Start of the Interfacial Instabilities Interfacial instabilities will usually only occur in the thin-cap layers (in the layers of - '' - thin matrix if they are near the outer edge) when the viscosity of the cap layer is greater than the core layer (elasticity here is not a significant factor). The general empirical rule then is that interfacial instabilities will occur when? Oñ /? OB is greater than or equal to 2, or more preferably less than or equal to l. In this way, to avoid instabilities,? OA /? OB is preferably less than or equal to 2 or more preferred less than or equal to 1. How low of 2 or 1 really depends on the total production speed and of the thickness of the lid layer A. For a very thin lid layer, that is, where the lid layer (exterior) is equal to or less than about 10% of the total thickness of the multilayer article and / or when high line speeds,? oA /? is less than or equal to 2 and should probably be closer to 1 to 0.5. By having a low viscosity cap layer it functions as a certain lubricant that minimizes pumping pressures as well as eliminates interfacial instabilities. This disadvantage of having a low viscosity cap layer is that there will be a tendency to encapsulate the core resin. Step 6: Determination of Layer Uniformity An adequate determination of layer uniformity across the width of the sheet requires knowledge of both viscosity and elasticity ratios.

Also, the type of extrusion where uniformity may be a problem for flat film matrices while annular matrices (eg, blown film, pipe, or preform molding) will not exhibit the same through width variability. . If the calculations for the initial resins result in unacceptable operating conditions, it is still possible to correct the problem. A number of ways to do this will be described later. These techniques apply to coinjection and coextrusion. Molecular Weight Change (or I.V.) The first and most logical method is to change the molecular weight (or I.V.) of one of the resins. This is because? 0 is proportional to Mw3'4 (or? 0 is proportional to I.V.5'1). 5 The relaxation time? also follows the same dependency Mw (or I.V.). So, for example, by increasing the I.V./MW of one of the resins, the? OA /? OB and? A /? B are changed in a similar way. In this way, if the cover layer Mw is increased also? OA /? OB and? A /? B will increase. Similarly, decreasing the lid layer M will cause the operating point to decrease. The viscosity change in the core layer (resin B) has a similar effect although the directions are reversed. Very often the choice of whether to vary the molecular weight of the core or cap layer is restricted by the resin formulations that are •• ifnr- '* - "-' + -" - - • -. ~ - - * - ».. -. * * -. ***. ***** commercially available. Addition of Branching Agent / Reticulator The change of Mw or I.V. of one of the resins causes both? oA /? oB and? A /? B to change in the same direction. There are situations where this is not desirable and it is preferred to change the elasticity and viscosity ratios independently. The addition of a branching / crosslinking agent mainly affects the elasticity and therefore is a good method for several? A /? B without significantly altering? OA /? OB- For polyesters, the branching can be a typical multifunctional branching agent as TMA or PMDA. For polyethylene, mixing in LDPE (assuming that LLDPE or HDPE is being used) can increase branching. Fusion Temperature Changes Until now, it is generally assumed that the two resins are at the same melting temperature. This is not an unreasonable assumption since some thermal equilibrium can occur in the power supply, adapter and matrix. It is still possible to run the polymers at slightly different melting temperatures (usually 25 ° C is considered the maximum temperature differential). Running a polymer at a slightly different temperature gives the same effect as if Mw had been changed. For example, if the cap layer is at a slightly warmer temperature, its elasticity and viscosity are reduced relative to the nominal melting temperature. This changes the point of operation along the same line / associated with the change of Mw / I.V. If different temperatures are used, it is necessary to modify (5) slightly since the viscosities and the relaxation times must be extracted for each polymer at the appropriate temperature. The simplest approach is used (4), setting the appropriate temperatures for each resin and then manually calculating the ratios. While the change in melting temperatures has the same effect as the change in I.V./MW, the effects are not as significant. Therefore, the variation of the melting temperature should only be used as a "pinch" adjustment in line. Changing the Power Block Design Metal cutting is always considered as a last resort and is usually applied when layer uniformity is unacceptable and it seems that no other modification works. Typically, as with a Welex block, a flow plate is altered so that when the resins collide with each other there is some compensation for the encapsulation. For example, if the cap layer encapsulates the core, the flow plate is modified so that when the layers collide for the first time, the core layer is partially enveloped.

- * - * '' '* • * - • * - * - * - - ^ .J-.l-a. . around the layer an equal amount. As the resins flow into the matrix, the cap layer will still try to flow around the core. However, another approach to minimize the amount of encapsulation is to shorten the length of the adapter. A long adapter provides more time for the resins to rearrange before reaching the matrix. The Cloeren multi-collector matrix takes this approach to one extreme as the layers literally merge into the matrix without a real adapter as they say. The Cloeren matrix is expensive but useful when the viscosity ratios (or elasticity ratios) are extreme. We would still like the layer rearrangement to happen, but there really is not enough time for it to happen. 3 . STRUCTURAL LAYER In accordance with the present invention, and in a preferred embodiment, the structural layer comprises one or more polymers that provide the required physical and mechanical properties of an article or packaging material. Suitable polymers include, but are not limited to, any polyester copolymer or homopolymer that is suitable for use in packaging, and particularly food packaging. The most preferred polyester is PET. Suitable polyesters useful in the present invention are generally known in the art and can be formed from aromatic dicarboxylic acids, dicarboxylic acid esters, dicarboxylic ester anhydrides, glycols, and mixtures thereof. Suitable partially aromatic polyesters are formed of repeating units comprising terephthalic acid, dimethyl terephthalate, isophthalic acid, dimethyl isophthalate, dimethyl-2,6-naphthalene dicarboxylate, 2,6-naphthalene dicarboxylic acid, 1,2-, 1,3-acid. and 1, 4-phenylenedioxide acetic acid, ethylene glycol, diethylene glycol, 1,4-cyclohexanedimethanol, 1,4-butanediol, and mixtures thereof. Preferably, the structural polyesters comprise repeating units comprising terephthalic acid, dimethyl terephthalate, isophthalic acid, dimethyl isophthalate, and / or dimethyl-2,6-naphthalene dicarboxylate. The dicarboxylic acid component of the polyester can optionally be modified with one or more different dicarboxylic acids (preferably up to about 20 mole%). Such additional dicarboxylic acids comprise aromatic dicarboxylic acids preferably having from 8 to 14 carbon atoms, aliphatic dicarboxylic acids preferably having from 4 to 12 carbon atoms, or cycloaliphatic dicarboxylic acids preferably having from 8 to 12 carbon atoms. Examples of dicarboxylic acids which may be composed of terephthalic acid are: phthalic acid, isophthalic acid, naphthalene-2,6-dicarboxylic acid, cyclohexanedicarboxylic acid, cyclohexanediacetic acid, diphenyl-4,4'-dicarboxylic acid, succinic acid, glutaric acid , adipic acid, azelaic acid, sebacic acid, mixtures of the same and the like. In addition, the glycol component can optionally be modified with one or more other diols other than ethylene glycol (preferably up to about 20 mole%). Such additional diols comprise diols Cycloaliphatics preferably have from 6 to 20 carbon atoms or aliphatic diols preferably having from 25 to 20 carbon atoms. Examples of such diols include: diethylene glycol, triethylene glycol, 1,4-cyclohexanedimethanol, propane-1,3-diol, butane-1,4-diol, pentane-1,5-diol, hexane-1,6-diol. , 3-methylpentanediol- (2, 4), 2-methylpentanediol- (1,), 2, 2, 4-trimethylpentan-diol- (1, 3), 2-ethylhexandiol- (1, 3), 2,2- diethylpropan-diol- (1, 3), hexanediol- (1, 3), 1,4-di- (hydroxyethoxy) -benzene, 2,2-bis- (4-hydroxycyclohexyl) -propane, 2,4-dihydroxy- 1,3,3-tetramethylcyclobutane, 2,2-20 bis- (3-hydroxyethoxyphenyl) -propane, 2-bis- (4-hydroxypropoxyphenyl) -propane, hydroxyethyl resorcinol, mixtures thereof and the like. The polyesters can be prepared from two or more of the above diols. The resin may also contain small amounts of trifunctional or tetrafunctional comonomers such as trimellitic anhydride, trimethylol propane, pyromellitic dianhydride, pentaerythriol, and other polyesters that form polyacids or polyols generally known in the art. Four . Performance Layer 5 At least one layer in a multilayer article of the present invention is a performance layer and provides the resulting article with improved physical properties. Such properties include, but are not limited to, barriers to migration (gas, vapor and / or other molecules). small), barriers to harmful light (ultraviolet light) and mechanical properties such as resistance to heat. In one embodiment, a multilayer article of the present invention where a performance layer is a barrier layer deploys barriers against improved C02 and / or 02 in comparison with the non-modified PET homopolymer article. In other embodiments, all layers are modified to display improved properties. Suitable materials for the barrier layers of the present invention comprise polyamides, ethylene-vinyl acetate copolymers (EVOH), polyalcohol ethers, fully aromatic polyesters, copolyesters based on resorcinol diacetic acid, polyalcohol amines, polyesters containing isophthalate, PEN and their copolymers and mixtures thereof. Barrier materials can be used pure or they can be modified to further improve the barrier, as with the addition -, - Ma * a ** a * te ^ • • - < - • ------ - • • -.- *** - - * .- - .... - * . ** * - *. -. of platelet particles, clay material preferably in layers, such as those obtainable from Nanocor, Southern Clay Products, Rheox and others. Suitable polyamides comprise partially aromatic polyamides, aliphatic polyamides, fully aromatic polyamides and mixtures thereof. By "partially aromatic polyamide", it is meant that the amide bond of the partially aromatic polyamide contains at least one aromatic ring and one non-aromatic species. Suitable polyamides preferably have a film-forming molecular weight, the fully aromatic polyamides preferably comprise, in the molecular chain, at least 70 mole% of the structural units derived from m-xylylenediamine or a mixture of xylylenediamine comprising m-xylylenediamine and up to 30% p-xylylenediamine and an aliphatic dicarboxylic acid having from 6 to 10 carbon atoms. These fully aromatic polyamides are further described in Japanese Patent Publications Nos. 1156/75, 5751/75, 5735/75 and No. 10196/75, and the Publicly Open Specification of Japanese Patent Application No. 29697/75. The polyamides formed from isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, meta- or para-xylylenediamine, 1,3- or 1,4-cyclohexane (bis) ethylamine, aliphatic diacids with 6 to 12 carbon atoms, amino acids • M * < M, *, A * i '"**' * - *" - aliphatic or lactams with 6 to 12 carbon atoms, aliphatic diamines with 4 to 12 carbon atoms, and other diamines and diacids that form polyamide generally known be used. The lower molecular weight polyamides may also contain small amounts of trifunctional or tetrafunctional comonomers such as trimellitic anhydride, pyromellitic dianhydride or other polyamides and polyacids forming polyamides known in the art. Preferred partially aromatic polyamides comprise: poly (m-xylylene adipamide), poly (hexamethylene isophthalamide), poly (hexamethylene adipamide-co-isophthalamide), poly (hexamethylene adipamide-co-terephthalamide), and polyhexamethylene isophthalamide-co-terephthalamide). The most preferred partially aromatic polyamide is poly (m-xylylene) adipamide). Preferred aliphatic polyamides comprise poly (hexamethylene adipamide) and poly (caprolactam). The most preferred aliphatic polyamide is poly (hexamethylene adipamide). The partially aromatic polyamides are prefer over aliphatic polyamides where thermal properties are crucial. Preferred aliphatic polyamides comprise polycapramide (nylon 6), polyammoheptanoic acid (nylon 7), poly-aminonanoic acid (nylon 9), polyundecane-amide (nylon) 11), polyarylactam (nylon 12), polyethylene-adipamide (nylon) 2,6), polytetramethylene-adipamide (nylon 4,6), polyhexamethylene-adipamide (nylon 6, 6), polyhexamethylene sebacamide (nylon 6,10), polyhexamethylene-dodecamide (nylon 6, 12), polyoctamethylene-adipamide (nylon) 8.6), polydecamethylene-adipamide (nylon 10.6), polidodecamethylene-adipamide (nylon 12.6) and polidodecamethylene-sebacamide (nylon 12.8). Suitable polyalcohol ethers comprise the phenoxy resin derived from the reaction of hydroquinone and epichlorohydrin as described in US 4,267,301 and US 4,383,101. These materials may also contain resorcinol units and may in fact all be resorcinol units as compared to the hydroquinone units for the aromatic residue. Suitable fully aromatic polyesters (very often called LCPs) are formed of repeating units comprising terephthalic acid, isophthalic acid, dimethyl-2,6-naphthalene dicarboxylate, 2,6-naphthalene dicarboxylic acid, hydroquinone, resorcinol, biphenol, bisphenol A, hydroxybenzoic acid , hydroxynaphthoic acid, and the like. The diacetic resorcinol copolymers are described in US 4,440,922 and US 4,552,948 and consist of copolyesters of terephthalic acid, ethylene glycol and a modifying diacid of 5 to 100 mol% in the composition by replacing the terephthalate units. The diacid * ....,. . ... < -., "* -.-, modifier is either m-phenyleneoxydiacetic acid or p-phenyleneoxydiacetic acid. Any of these diacids can be used either alone or as mixtures in the preparation of the copolyesters for this invention. Suitable polyalcohol amines comprise those derived from the reaction of either bis-glycidyl ether resorcinol with an alkanol amine, such as ethanolamine or hydroquinone bisglycidyl ether with an alkanol amine. Mixtures of these bisglycidyl ethers can obviously also be used in the preparation of a copolymer. Suitable polyesters comprising isophthalate comprise polyesters comprising repeating units derived from at least one carboxylic acid comprising isophthalic acid (preferably at least 10 mol%) and at least one glycol comprising an ethylene glycol. Poly (ethylene naphthalate) (PEN) copolymers comprise polyesters comprising repeat units derived from at least one carboxylic acid comprising a naphthalenedicarboxylic acid (preferably at least 20 10% by mole) and at least one glycol comprising ethylene glycol . The most preferred performance layer for barrier is a saponified ethylene-vinyl acetate copolymer (EVOH). The saponified ethylene-vinyl acetate copolymer is a polymer prepared by saponifying a * ju4tUBm * aíiB t í. *. * ~. r ..?, ..,. - ...... . - -...-. *. *. ¡*. ** * z.? T *. ». > ..-. . " ..... _. . . j. ... ....., .., .., ",., ... . i *. - - «. A -rf- .. ethylene-vinyl acetate copolymer having an ethylene content of 15 to 60% by mole to a degree of saponification of 90 to 100%. The EVOH copolymer should have a molecular weight sufficient for film formation, and a viscosity of generally at least 0.01 dL / g, especially at least 0.05 dL / g, when measured at 300 ° C in a phenol solvent / water (85% by weight: 15% by weight). Conventional processes, all of which are well known in the art, do not need to be described herein they can make the polymers of the present invention. Although not required, additives normally used in polymers can be used, if desired. Such additives include dyes, pigments, carbon black, glass fibersImpact modifiers, antioxidants, surface lubricants, release agents, UV light absorbing agents, metal deactivators, fillers, core forming agents, stabilizers, flame retardants, reheating aids, crystallization aids, acetaldehyde reducing compounds, auxiliaries of recycle release, oxygen scavenger materials, or mixtures thereof and the like. All these additives and many others and their use are known in the art and do not require further discussion. By ..... - **. Hence, only a limited number will be mentioned, it being understood that any of these compounds can be used in any combination of the layers insofar as they do not prevent the present invention from achieving its objects. The multilayer articles formed in accordance with this invention comprise films, sheets, tubes, pipes, profiles, preforms and containers such as bottles, trays, cups and the like. EXAMPLES 10 The following examples and experimental results are included to provide those of ordinary skill in the art with a full description of the particular ways in which the present invention can be carried out and evaluated, and purport to be purely 15 examples of the invention. and are not intended to limit the scope of what is considered the invention. Efforts have been made to ensure accuracy with respect to numbers (eg, amounts, temperature, etc.); however, some errors and deviations may have occurred. Unless indicated otherwise, the parts are parts by weight, the temperature is in ° C or at room temperature, and the pressure is atmospheric or near-atmospheric. Example I Coinjection of Several Degrees of PET with EVOH as 25 Barrier Layer - * -e ** ~ * tUi? Ítjatá¡ßLLÍ »*? J A .lM *. . -***-**,- .... .***.. .. .1-*.***. *. *** ..- ***. .. ** .. . .... " . , * _ "" '< i ^ 'Three different grades of PET were evaluated for use in a coinjection test with EVALCA EVOH grade F-101. The PET resins are tabulated in the following. Each one has an I.V. different and the modification level of CHDM copolymer varied slightly between them as shown. The higher the I.V. of the resin, the greater the viscosity and elasticity (the modification of the copolymer has only a minor effect).

A 5-layer structure was co-injected consisting of PET / EVOH / PET / EVOH / PET. The EVOH layer was relatively close to the outside of the structure (i.e., near the wall) so high interfacial tensions were expected. The cylinder temperatures for the PET samples were nominally 285 ° C while the cylinder temperatures for the EVOH were 185 ° C. However, the heat transfer calculations show that because the EVOH layer is so thin, and is surrounded by the hotter PET, it quickly reaches a temperature of about 170 ° C. This temperature is used to calculate? Y ?. The operation points for each of these three PET resins with PET were determined in accordance with this invention. Only Resin # 1 was predicted to have a good uniform layer distribution and no instabilities / chevrons. An injection molding test was carried out using samples # 1 and # 2. Previous attempts with sample # 3 had already shown that it would not work without causing chevrons. Ba or identical molding conditions, the molded parts using sample # 1 were free of chevrons while the parts molded with sample # 2 had visible flow defects in the form of chevrons. EXAMPLE 2 Determination of an Optimal Coextrusion Venue for a Coating Cap / Core / Coating Cap layer of Polyethylene on PETG 6163 A thin layer of polyethylene (Eastman Chemical Company CM 27057-F (2.0 MI)) was coextruded on both sides of a PETG 6763 sheet. PETG 6763 is a copolyester commonly used in the film and sheet forming industry and has an IV = 0.76 dl / g (as measured in 60 wt% / 40 wt% phenol / tetrachloroethane at 25 ° C). The total thickness was approximately 40 mils with the polyethylene cap layers having 10% thickness each. The width of the film was approximately 20 inches. The fact that the cover layers are thin makes interfacial instabilities a distinct possibility. Polyethylene (PE) had a melt index of 2.0. The dynamic viscosity measurements were made at 220, 240 and 260 ° C for the PETG and 230, 250 and 270 ° C for the polyethylene and the values of? Y ? they were extracted from each temperature. A graph of these values was made together with the Arrhenius curve adjustment. Based on the diagram, the viscosity of the PETG is higher at lower temperatures but becomes lower above about 235 ° C. Because both of these resins can be processed over a wide range of melting temperatures (from about 200 ° C to 300 ° C), it is desirable to find the best set of temperatures to optimize the process. To test the method to optimize conditions, the designed experiment was performed around the melting temperatures of PE and PETG. The running conditions were the following: This provided a temperature dispersion i11 * «*. ¿^^^^ covering a range of possible processing conditions. The viscosity ratio and the elasticity ratio (PE over PETG since PE is the outermost layer) were determined for each of the previous runs according to the method mentioned in the detailed description (See Figure 4). Runs 1 and 5 will probably provide the best layer uniformity since they are closest to the optimum layer thickness. As you move to the lower left in Figure 4 (for example, Run 4), you can predict that The thickness of the cap layer will be thicker near the edges and thinner near the center. As one moves to the upper right corner of Figure 4 (for example, Run 2), it can be predicted that the opposite will occur. 15 Because the PE has a poor adhesion in the PETG, it was possible to detach the layers and measure the thicknesses across the width. The thickness of the cap layer was from thick at the edges to thick at the center as one moved from the left corner below the upper right corner in Figure 4. Similarly, there is a crossing in the distribution of thickness in the same place where the optimal process conditions were predicted (between Corrida 1 and Corrida 5). Based on the model, it is predicted that the run conditions will be obtained optimum when both extruders are set to approximately ij »aMMlM * ¿ía¡tottlÉlM¿ A ¿¿> . Ii i, i Ii -Mi n i I. ^ MM IÍ. < l »J ^^ JIiMlMlá-IÉ¿« MMJM- ^ J «- ^ - ^ lMM» ^ *. MIÉÉMM »M ^ ^ l ^ a ^ 220 ° C. This prediction is verified by the experimental data. Example 3 Determination of the Optimal Degree of Polyethylene to be Coextruded with PETG at 235 ° C In this example, the extrusion temperature was set at 235 ° C for both PET and PETG. On the other hand, the conditions of the coextrusion equipment were the same as in Example 2. Three different PE's were evaluated including PE's from Eastman Chemical Company: CM-27053-F (0.9 MI), CM-27057-F (2.0 MI) and CM-27058 F (3.2 MI). The higher the melt index (MI), the lower the molecular weight of the resin. This decrease in molecular weight also correspondingly causes a decrease in both the viscosity as in the elasticity. The operating points for these three coextruded resins on PETG at 235 ° C are shown in Figure 5. In addition, a small graph inserted at each point shows the thickness distribution of the PET cap layer for each value of MI. As with the change in melting temperature in Example 2, changing the MI for the PE from high to low causes the layer distribution of the cap layer to be very heavy at the outer edges to very heavy in the center. The optimal value of MI for the layer distribution uniform occurs that is around 2.2 to 2.4. Without - "'- * -» > ** < "- **" However, the merger index sample of 2.0, which was closest to the optimum area, was also the best sample. MI had small chevrons as predicted by the model Example 4 Coextrusion of Eastman PET 9921 with 5% Polycarbonate Cap Layer to MAKROLON 2608 Coextruded a multilayer PET structure with a thin polycarbonate (PC) cap layer. Polycarbonate adds surface gloss and also helps harden the polymer as it softens at higher temperatures (the glass transition temperature of PET is 80 ° C and polycarbonate is 150 ° C). it is thin, the formation of interfacial instabilities is a significant problem Figure 6 shows the operating points for the different extrusion temperatures (PET and PC temperatures were set equal) Below a process temperature of 275 ° C, it was predicted the occurrence of instabilities. Extrusion tests on a 2.5"extruder with a 24" film matrix confirmed the above. The process temperature was set at 290 ° C or more to be able to eliminate the chevrons. This corresponds in the diagram to a viscosity ratio of about 0.75 as one would expect for a relatively thin cap layer. The t j. *. . *! ......... ... .. ..... ...... . **. * .. ly. nm-- - ~ »- - - .-- • - -...- *. * ** ********** *?.? ** , > faa > ? «Jg.

Layer uniformity was generally good as predicted by the model. Through this application, reference is made to several publications. The descriptions of these publications are incorporated herein by reference in their entirety in order to fully describe the current state of technology to which this invention pertains. It will be apparent to those skilled in the art that various modifications and variations may be made to the present invention without departing from the spirit and scope of the invention. Other embodiments of the invention will be apparent to those skilled in the art considering the specification and practice of the invention described herein. It is intended that the specification and examples be considered as exemplary only, the true spirit and scope of the invention being indicated by the following claims.

Claims (3)

CLAIMS 1. A process for co-injection molding a multi-layer article characterized in that it comprises: co-injection molding at a selected co-injection temperature (i) a first layer of outer polymer resin comprising at least one structural polymer resin having a viscosity and an elasticity at the selected coinjection temperature; Y (ii) a second inner polymer resin layer comprising a performance polymer layer resin having a viscosity and elasticity at the selected co-injection temperature, wherein the ratio of the viscosity of the outer polymer resin to the The viscosity of the inner polymer resin at the co-injection temperature is less than or equal to about 1 and wherein the ratio of the elasticity of structural resin to the yield elasticity of resin is approximately reciprocal to the viscosity ratio. 2. The process according to claim 1, characterized in that the component (i) comprises a polyester. 3. The process according to claim 2, characterized in that the polyester is a homopolymer or a copolymer. The process according to claim 1, characterized in that the component (i) comprises an aromatic polyester comprising repeated units of terephthalic acid, dimethyl terephthalate, isophthalic acid, dimethyl isophthalate, dimethyl-2,6-naphthalene dicarboxylate, acid 2, 6-naphthalenedicarboxylic acid, 1,2-, 1,3- or 1,4-phenylenedioxydoacetic acid, ethylene glycol, diethylene glycol, 1,4-cyclohexanedimethanol (1,4-CHDM), 1, -butanediol, or mixtures thereof . 5. The process according to claim 1, characterized in that component (i) comprises poly (ethylene terephthalate) or a copolymer thereof. 6. The process according to claim 1, characterized in that the component (ii) is a barrier resin. 7. The process in accordance with the claim 1, characterized in that the component (ii) comprises a polyamide or a copolymer thereof, a copolymer of ethylene vinyl acetate (EVOH), a polyalcohol ether, a fully aromatic polyester, a copolyester based on resorcinol diacetic acid, a polyalcohol amine, a polyester containing isophthalate, poly (ethylene naphthalate) or a copolymer thereof, or a mixture thereof. 8. The process according to claim 7, characterized in that the polyamide comprises a partially aromatic polyamide, an aliphatic polyamide, a
1. ? *. * Fully aromatic polyamide, or a mixture thereof. 9. The process according to claim 1, characterized in that the component (ii) comprises a saponified ethylene-vinyl acetate copolymer (EVOH). The process according to claim 1, wherein the component (i) comprises poly (ethylene terephthalate) or a copolymer thereof, the component (ii) comprises an ethylene-vinyl acetate copolymer (EVOH), and the ratio of the The viscosity of component (i) at the viscosity of component (ii) at the selected co-injection temperature is less than or equal to about 1. 10. The process according to claim 1, characterized in that component (i) comprises poly ( ethylene terephthalate) or a copolymer thereof, component (ii) comprises an ethylene-vinyl acetate copolymer (EVOH), and the ratio of the viscosity of component (i) to the viscosity of component (ii) at the co-injection temperature selected is less than or equal to about 1 and greater than or equal to about 0.5. 11. The process in accordance with the claim 1, characterized in that it comprises co-injection molding at least three polymers at a co-injection temperature selected thereby forming a 5-layer article wherein at each polymer resin interface, the viscosity ratio of the outermost polymer resin the viscosity of the next innermost polymer resin at the co-injection temperature is less than or equal to about 1 and the elasticity ratio for each interface is approximately reciprocal to the viscosity ratio at that same interface. 12. A multi-layer article produced by the process according to claim 1. 13. The article according to claim 12, characterized in that it is in the form of 10 a preform or container. 14. The article according to claim 12, characterized in that it is in the shape of a bottle. The process according to claim 15 1, characterized in that the viscosity ratio and the elasticity ratio are defined by a shaded area of the ellipse shown in Figure 3. 16. A process for extruding a multi-layer article characterized in that it comprises: coextruding at a selected coextrusion temperature (i) a first outer polymer ream layer comprising at least one structural polymer resin having a viscosity and an elasticity at the selected co-injection temperature; and (ii) a second 25 inner polymer ream layer comprising a resin ÜMBÜMM ^ Abri ..... * ..... .. * ... of performance polymer layer having a viscosity and elasticity at the selected co-injection temperature, wherein the ratio of the viscosity of the outer polymer resin to the viscosity of the inner polymer resin at the co-injection temperature is approximately reciprocal to the ratio of the elasticity of the structural resin to the elasticity of the performance resin. 17. The process according to claim 16, characterized in that component (i) or (ii) is a barrier resin. 18. The process according to claim 16, characterized in that the component (i) or (ii) comprises a polyamide or a copolymer thereof, a copolymer of ethylene vinyl acetate (EVOH), a polyol ether, a fully aromatic polyester, a copolyester based on resorcinol diacetic acid, a polyalcohol amine, a polyester containing isophthalate, poly (ethylene-naphthalate) or a copolymer thereof, or a mixture thereof. 19. The process according to claim 18, characterized in that the polyamide comprises a partially aromatic polyamide, an aliphatic polyamide, a fully aromatic polyamide or a mixture thereof. The process according to claim 16, characterized in that the component (i) or (ii) comprises a saponified ethylene-vinyl acetate copolymer • -'-- • -í (EVOH). 21. The process according to claim 16, characterized in that the component (i) or (ii) comprises a polyester. 22. The process in accordance with the claim 16, characterized in that the component (ii) comprises a polyester. 23. The process according to claim 22, characterized in that the polyester is a homopolymer or a copolymer 24. The process according to claim 16, characterized in that the component (i) or (ii) comprises an aromatic polyester comprising a repeated unit of terephthalic acid, dimethyl terephthalate, isophthalic acid, dimethyl isophthalate, dimethyl-2,6-naphthalene dicarboxylate, 2,6-naphthalenedicarboxylic acid, 1,2-, 1,3- or 1,4-phenylenedioxydoacetic acid, ethylene glycol , diethylene glycol, 1,4-cyclohexanedimethanol (1,4-CHDM), 1, -butanediol, or a mixture thereof. 25. The process in accordance with the claim 16, characterized in that component (i) or (ii) comprises poly (ethylene terephthalate) or a copolymer thereof. 26. The process according to claim 16, characterized in that the component (i) comprises an ethylene-vinyl acetate copolymer (EVOH), and the component (ii) comprises poly (ethylene terephthalate) or a copolymer thereof, and the ratio of the viscosity of the outer polymer resin to the viscosity of the inner polymer resin and the ratio of the elasticity of the outer polymer resin to the elasticity of the inner polymer resin at the coextrusion temperature is greater than or equal to approximately 1. 27. The multi-layer article produced in accordance with the process in accordance with the 10 claim 16. The article according to claim 27, characterized in that it is in the form of a film, sheet, tube, pipe or profile. 29. The process according to claim 15, characterized in that it comprises coextruding three or more resins at a selected coextrusion temperature thereby forming an article having more than two layers wherein at each interface of the polymer resin, the ratio viscosity of the polymer resin more exterior to the
2. The viscosity of the following innermost polymer resin is approximately reciprocal to the ratio of the elasticity of the polymer resin more exterior to the elasticity of the next innermost polymer resin in that same interface. 25 30. The process in accordance with the claim jj! ^^ as £ ¡& * ^^^^^^^ 16 or 29, characterized in that the first outer polymer layer has a thickness that is equal to or less than about 10% of the total thickness of the multilayer article and in wherein the viscosity ratio of the outermost resin interface is equal to or less than about 1. 31. The article according to claim 29, characterized in that it is in the form of a film. 10 32. The process in accordance with the claim 16, characterized in that the viscosity ratio and the elasticity ratio are defined by the shaded area of the ellipse shown in Figure
3. 3. tSmg¡? ÉS g¡¡ ^ ¿, '** "-" -