MXPA02011932A

MXPA02011932A - Improved polyester compositions for multilayer extrusion and barrier performance.

Info

Publication number: MXPA02011932A
Application number: MXPA02011932A
Authority: MX
Inventors: Ravi Ramanathan
Original assignee: Dow Global Technologies Inc
Priority date: 2000-05-30
Filing date: 2001-05-11
Publication date: 2003-05-27
Also published as: KR20030007740A; EP1289753A2; WO2001092007A2; BR0111663A; AU2001261524A1; CA2408229A1; WO2001092007A3; JP2003534946A; CN1431954A

Abstract

Improved multi-layer coextruded blow-molded objects (such as fuel containers) having at least a barrier layer and a support layer are disclosed together with improved methods for preparing such objects. The barrier layer includes an amount of modified polyolefin having approximately the same density as the support layer, wherein the modified polyolefin is prepared by grafting an unsaturated carboxylic acid or a derivative thereof to the polyolefin, the modified polyolefin being added in an amount such that the gas-barrier layer sufficiently adheres to the adjacent layer and such that the gas barrier properties of the fabricated article are still adequate. The present invention also relates to modification of the rheology of base resins, such as PET (a preferred material for the barrier layer), so that they more closely match the rheology of high density polyethylene (a preferred material for the support layer).

Description

IMPROVED POLYESTER COMPOSITIONS FOR THE EXTRUSION OF MULTICAPAS AND BARRIER CAPACITY The present invention relates to improving the adhesion between a barrier layer and a support layer in co-extruded blow molded applications. More particularly, this invention relates to the incorporation of a modified polyethylene having adhesive properties either in the barrier layer or the support layer, wherein the modified polyethylene is prepared by transplanting an unsaturated carboxylic acid or derivative thereof to polyethylene. high density In addition, the present invention also relates to the modification of the rheology of base resins, such as PET, in such a way that they bind more closely to the rheology of high density polyethylene (a preferred material for the support layer in the applications). blow molded co-extruded). A better union in the rheological properties facilitates layer uniformity within a parison, resulting in more consistent final products.

BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION Plastics (synthetic resins) have already been used for various container applications due to their light weight, immediate availability, relatively low cost and high strength. Polyolefin resins have proven particularly useful for such applications. While the polyolefin resin possesses several desired properties, they are not particularly effective as a barrier for gases or vapors of chemicals such as hydrocarbons, alcohols, ketones, ethers, etc. In this way, polyolefin resins by themselves are not suitable for several applications where the chemical vapor container is critical for safety and environmental reasons. These applications include manufactured articles such as storage or containers or transport containers, for example, fuel tanks, conduits or membranes. In accordance with the above, efforts have been made to improve the barrier capacity of containers made of polyolefins. One such effort is EU-A-5,441, 781 which teaches a multilayer container (fuel tank), such that one layer will provide the gas barrier properties while another layer (polyolefin) will provide the support. This reference teaches that a third layer (an "adhesive layer") should be used in such a way that the barrier layer will adhere to the support layer. The reference teaches that the adhesive layer comprises a resin such as a modified polyethylene prepared by transplanting an unsaturated carboxylic acid or derivative thereof to high density polyethylene (HDPE). It would be desirable to be able to remove this adhesive layer to simplify processing and reduce costs, still having a Polyolefin-based container with gas barrier properties. Now, it has surprisingly been discovered that when low levels of certain adhesive materials such as those taught in the '781 patent, they are incorporated into a resin (such as polyethylene terephthalate, PET) showing the barrier properties of permeation to the fuel components, and, in particular, by showing the permeation barrier to the oxygenated fuel components such as methanol and ethanol, then the adhesion properties of the resin are improved, while maintaining the barrier capacity of the gas. Thus, one aspect of the invention is an improved resin comprising polyethylene terephthalate and High Density polyethylene modified with maleic anhydride (HDPE-g-MAH), wherein the modified polyethylene terephthalate comprises 10 to 2 percent of the composition, and the maleic anhydride comprises from 0.5 to 5.0% percent by weight of the modified polyethylene. It has also been found that when certain other adhesive materials (eg, LLDPE-g-MAH) are added to the PET in the same concentrations according to the aforementioned HDPE-g-MAH, the barrier capacity of the mixture is decreased. In this way, while it is possible to achieve adhesion between PET and HDPE merely by mixing in a material that is chemically compatible with each phase, the present invention is unique in that adhesion can be achieved without decreasing the barrier capacity of the barrier. This new resin can be advantageously used in multilayer structures as it will allow the removal of adhesive or tie layers. The barrier layers comprised of the resin of the invention will adhere better to the other layers, including polyolefin backing layers, eliminating the need for an adhesive or tie layer. In this way, instead of structures of 3 or 5 layers taught by the '781 patent the resin of the current invention allows for 2 or 3 layer structures. Furthermore, even if a bonding layer is still used, the adhesion between PET and a bonding layer will improve if the PET is first modified by the incorporation of maleic anhydride transplanted by high density polyethylene. According to the above, another aspect of the invention is a multilayer plastic container comprising two layers, one of which is a gas barrier layer, the other of which is a polyolefin support layer, wherein the The barrier layer includes a quantity of modified high density polyethylene, wherein the modified high density polyethylene is prepared by transplanting an unsaturated carboxylic acid or a derivative thereof to high density polyethylene, with the modified high density polyethylene being added in a amount such that the gas barrier layer adheres sufficiently to the adjacent layer. It would also be valuable to improve the adhesion properties of PET in general, so that PET can also be used more easily in applications other than containers. Thus, another aspect of the invention comprises a method for improving the adhesion properties of the barrier layer (which can be crystalline polyester resins, crystalline polyamides, crystalline polyarylates and poly (ethylene-co-vinyl alcohol) to the materials polyolefins comprising incorporating a modified polyethylene prepared by transplanting an unsaturated carboxylic acid or a derivative thereof to polyethylene, wherein the modified polyethylene is added to the polyethylene terephthalate in an amount between 2% and 10% by weight, preferably in an amount between 3% and 8% by weight. In the case of fuel tank applications, the polyethylene material is preferably high density polyethylene and the modified polyethylene is a modified high density polyethylene. Currently, co-extrusion blow molding is the preferred method for manufacturing articles made of multilayers. This method requires a sufficient rheological bond between the constituent materials in order to promote adequate layer uniformity within the ring parison dye. Conventional PET, as well as other conventional polyesters, such as poly (butylene terephthalate), poly (ethylene naphthalate), polylactic acid, polyester copolymers containing the terephthalate portion, and liquid crystalline polyarylates, show almost Newtonian behavior in the melt while H DPE resins behave decidedly non-Newtonian. In this way, the combinations of PET and HDPE have heretofore resulted in co-extruded sheets and blow-molded articles having marginal to uniform layer uniformity. According to the above, still another aspect of the present invention points out this problem by increasing the long chain branching in the polyesters, without the formation of significant degradation or gels.

DETAILED DESCRIPTION OF THE INVENTION The improved barrier resin of the present invention comprises a base resin which may be polyester resins. crystalline, crystalline polyamides, crystalline polyarylates or poly (ethylene-co-vinii alcohol) together with a minor amount of a modified high density polyethylene (HDPE). Preferably, the HDPE is modified with unsaturated carboxylic acid or derivative thereof, such as maleic anhydride, acrylic acid, etc. The improved barrier resin comprises 90 to 98 percent of the base resin, and 10 to 2 percent of the modified polyethylene. The modified polyethylene comprises from 0.5 to 5.0 percent by weight (preferably 0.5 to 1.4 percent) of the unsaturated or derived carboxylic acid. The resin of the present invention shows improved adhesion as compared to unmodified PET, while maintaining its barrier properties. In this way, the resin of the present invention can be advantageously used in multilayer plastic container having at least two layers, one of which is a gas barrier layer, the other of which is a polyolefin support layer. Such containers are described in EU-A-5,441, 781. Suitable polyolefin materials are described in EU-A-5,380,810, the application of Pat. of E. U. 08 / 857,817, or the Patent Application of E. U. 08 / 857,816. The preferred material to be used in the support layer is HDPE. It should be necessary to improve melting strength (eg, when preparing heavy items such as automobile fuel tanks) after methods such as those described in WO 99/10393; WO 99/10415; WO 99/10421; WO 99/10422; WO 99/10423; WO 99/10424; WO 99/10425; WO 99/10426 or WO 99/10427 can be used to modify these polyolefin materials in order to Give them higher melting strength. The containers of the present invention can consist of only two layers, but additional layers can advantageously be used. For example, it may be desired that two support layers surround the barrier layer such that the support layers contact both the contents of the container and the external environment to which the container is exposed. In addition, while the improved adhesion of the resins of the present invention allows the tie layers to be removed in most cases, in certain applications, superior adhesion between the layers may be desired, in which case the use of a coat of union can still be preferred. It should be appreciated that just as the resins of the present invention improve the adhesion of the barrier layer to a support layer, it will also improve the adhesion of the barrier layer to a tie layer. Preferred binding layers to be used in the present invention include those described in the '781 patent. Multilayer containers, which are an example of the present invention, can be produced by any means known in the art. This includes blow molding as well as coextrusion sheets followed by thermoforming with or without welding of the two or more parts to form the containers. Blow molding methods are generally preferred. For example, the resins for each layer can be plastified separately in two or more extruders, introduced in the same nozzle, laminated in the nozzle while allowing each thickness to prepare a parison that has the appearance of being of a layer. The parison can thus be inflated in a molding by application of internal air pressure in such a way that the parison comes into contact with the mold and cools down. In extrusion molding, it is advantageous that the various layers have similar rheological properties. In this regard, it has been found that by increasing the long chain branching within the polyester material used as the base barrier material, typical polyesters will have rheology that is more similar to HDPE. This is advantageous, in any case the barrier material includes the modified polyolefin to improve the adhesiveness. Base polyesters that can be altered in this regard include PET, poly (butylene terephthalate), poly (ethylene naphthalate), polylactic acid, polyester copolymers containing the terephthalate portion, and liquid crystalline polyarylates. The long chain branching may be promoted by incorporating multifunctional monomers within the initial polymerization, or by post reactor modification such as extrusion of reagent with a multifunctional branched agent. These processes are generally known in the art (see for example, EU-A-5, 536,793, EU-A-5,556,926, EU-A-5,422,381, EU-A-5, 362,763, and EU-A-5, 422,381). . Potential branched agents known in the art include trimellitic anhydride, trimesic anhydride, phthalic anhydride, pyromellitic dianhydride (PMDA) and any of the monomers containing 3 or more hydroxyl groups. Extrusion of reagent using PMDA is a preferred method for promoting long chain branches. The branched agent should be added at a level to avoid degradation significant and / or gel formation. Less than 1% by weight of the branched agent is preferred. Optionally, additives that are good nucleating agents can be used to promote crystallization of the branched polyester, to help compensate for the fact that the crystallization of branched materials is generally less thermodynamically favored compared to linear materials. Suitable nucleating agents are well known in the art (see, for example, EU-A-4,572,852; EU-A-5,431,972; EU-A-5,843,545; or EU-A-5,747,127). Thus, a particularly favored embodiment of the present invention comprises a multilayer article comprising at least one barrier layer and one support layer. The support layer is preferably H DPE, and the barrier layer comprises polyethylene terephthalate with long chain branching with a relatively small amount of HDPE to which a small amount of maleic anhydride has been transplanted. The article in this particularly favored embodiment is prepared by coextrusion blow molding. Such an article should be especially well suited to be used as a compatible fuel tank for use with oxygenated fuels. Furthermore, it has been found that the barrier properties of the barrier layer are largely dependent on the percent crystallinity (Xc) of the polymer making the barrier layer. When PET is used as the barrier layer, it is preferred that the polymer in the finished container show greater than 8 percent, more preferably 21 percent and more preferably 34 percent crystallinity, and preferably not more than 50 percent, more preferably not more than 40% as measured by Differential Scanning Calorimetry. It is expected that other barrier resins will show similar relationship between barrier properties and amount of crystallinity. The crystallinity of these barrier resins can be altered by means known in the art, such as controlling the rate of cooling and softening. It should be understood that the crystallinity can be affected by certain fuel components, such as methanol. Methanol is known to break the hydrogen bond of EVOH and thereby reduce the barrier capacity of EVOH. However, in the case of PET, we have discovered that methanol can cause solvent-induced crystallization which raises the level of crystallinity and therefore also improves the barrier capacity. The binding of hydrogen in EVOH is also known to be broken by moisture, while the barrier capacity of PET is not effected by moisture. This has particular consequences in the overall construction and design of multilayer fuel container structures. The EVOH should be prevented from being in direct contact with a fuel layer containing moisture or methanol. PET, on the other hand, does not show the same disadvantages, and may be in direct contact with the fuel. It is also generally known that in addition to the amount of crystallinity, the morphology of the crystals is another factor in improving the barrier resistance properties of the resin, but this effect is less in comparison to be made in relation to the level of crystallinity.

EXAMPLES In the Examples, the following terms should have the indicated meanings: "PET 1" is conventional PET (Lighter ™ L90A from The Dow Chemical Company), which has an inherent viscosity of 0.77, determined at 0.5% concentration (w / v ) and 23 ° C in phenol / 1,2-diclolobenzene solution (60/40 by weight). "PET 2" is a modified PET prepared by reactively extruding PET1 with 0.45% by weight of pyromellitic dianhydride (PMDA), followed by solid state advance for 14 hours at a temperature of 196 ° C. GPC-DV was used to analyze the resulting polymer and it was determined that PET2 showed an increase in the weight average molecular weight (from 46 to 135 kg / mol), a broader polydispersity index (from 1.9 to 5.3) as it is compared to PET1. PET2 had an inherent viscosity of 2.28, determined in 0.5% concentration (w / v) and 23 ° C in phenol / 1,2-diclolobenzene solution (60/40 by weight). "PET3" is a nucleated PET (Versatray ™ 12822 from Eastman Chemical Company), which has an inherent viscosity of 0.89, determined at 0.5% concentration (w / v) and 23 ° C in phenol / tetrachloroethane solution 60/40 in weight). EXAMPLES 1-4 The following examples were prepared to demonstrate improved cohesiveness of multilayer articles wherein the barrier layer includes a modified polyolefin according to the present invention. invention. The multilayer bottles were prepared on a Bekum Blow Molding Machine BM-502, running at a production speed of approximately 42 pounds per hour. The bottle weight was approximately 60 g (total draft weight 85-90 g). The PET barrier layer was the inner layer, and in all cases showed a melting temperature of about 254 ° C. The support layer in each case was HDPE (Lupolen ™ 4261A HDPE obtained from BASF). The binding layer if presented was ADMER ™ SF-700, an EVA adhesive obtained from Mitsui Petrochemicals. The results of these evaluations are shown in the table Table I EXAMPLE BARRIER LAYER UNION LAYER RESULT 1 PET1 yes Good adhesion 2 PET2 yes Better adhesion than in Example 1 3 PET1 none Delamination within one hour 4 PET2 none No delamination even after 2 weeks EJ EMPLOS 5-8 The following examples were prepared to demonstrate the improved processing characteristics when using a material from polyester having long chain branching wherein the amount of long chain branching in the polyester material is selected in such a way that the rheology of the polyester material binds more closely to the rheology of a support layer, according to the present invention. The fused viscosity of HDPE (Lupolen ™ 4261A HDPE obtained from BASF), PET1, PET2 and PET3 were thus characterized using a Rheomtrics RMS800 equipped with a parallel sheet accessory and configured to operate in the linear viscoelastic regime. The information is reproduced in Figure 1 and indicates that PET2 shows rheology similar to HDPE, and substantially different from PET1 or PET3. saw 0. 1 1 10 100 deflection force [1 / s] Figure 1 EXAMPLES 9-13 Permeation Test The permeability of CM 15 Fuel through the films of free duration of the barrier materials is measured at 41 ° C (+/- 1 ° C) using the following procedure. A test film, 4 inch diameter disk with a thickness between 1 and 100 thousand, is installed between the two chambers of the test cell. The CM15 fuel (mixture comprising 42.5 / 42.5 / 15% volume of toluene / isooctane / methanol, 95 mL) is added to the upper chamber, placed on top of the test specimen film, and the flow of helium at 10 mL / min is passed through the lower chamber. As the fuel is permeabilized through the barrier film in the lower chamber, it is swept in a helium stream from the test cell and injected through an injector cycle at the front end of a Chrompack Poraplot capillary column. U of 25 m, 0.53 mm of ID operating at 140 ° C using a helium flow of 10 mL / min as the vehicle gas. The GC separates, identifies by the retention time, and quantifies the fuel components that have been permeabilized through the specimen film. The data and time of the injection, permeation identities and maximum gross area counts of the permeabilized components are stored in a computer file for further analysis. Using a multi-port valve, 16 helium sample streams are reviewed by the GC; Each stream is tested for the fuel component content in an eight-hour interval. Fifteen of the 16 sample streams are connected to the specimen film permeation cells. The sixteenth current is from a gas cylinder containing a mixture of reference of 50 ppm each of toluene, isooctane, and methanol, with a helium preparation. The reference gas information is used to calibrate the GC gross area account information to determine the ppm levels of the fuel components in the sample streams of the permeation cells. The specimen test films were prepared by compression molding using a 6 inch by 6 inch by 5 mil thick mold in a Pasadena Hydraulics, Inc. Press. The EVOH material was Eval ™ F01A, with 32 mol percent ethylene. The EVOH was compression molded using the following conditions: 1) fusing the resin in the mold for 4 minutes at 1000 pounds of pressure applied at 210 ° C; 2) Press the resin for 6 minutes at 40,000 pounds of pressure applied at 210 ° C; and 3) cool the mold slowly, for one hour, at 50 ° C under 40,000 pounds of applied pressure. The PETE resins were molded under similar conditions except that in step 1, the mold was heated to 280 ° C. The fuel barrier properties were measured on thin film specimen of various materials. These evaluations produced the following results, as shown in Table II. Table II f The permeation was not yet in a stable state when this measurement was taken, the permeation was still increasing slowly. As shown in Table II, the EVOH reached steady state permeation at 400 hours and the experiment was stopped, although all the permeations were rigorously an order of magnitude lower than the steady state permeation of EVOH. The permeation experiment for PET3 was discontinued at this time. The permeations in PET1 and PET2 reached stable state after 3500 hours. Contrary to expectations, the PET2 material has less permeability than PET1. PET2, being branched long chain, was not expected to crystallize as efficiently as PET1. However, it is believed that the branching in PET2 is performed as a homogeneous nucleation site, similar to heterogeneous nucleation in PET3, as shown in the 900-hour permeation information. EXAMPLES 14-17 The effect of the level of crystallinity on PET fuel barrier properties was evaluated according to the following procedure. The PET2 samples were prepared having varying levels of crystallinity (Xc). Examples 14-16 were prepared by fusing, cooling rapidly and then softening the material at 130 ° C for 10, 20 or 30 seconds, respectively. Example 17 was prepared by melting followed by slow cooling. The levels of crystallinity were estimated using DSC. Permeability measurements were conducted as in Examples 9-13, and permeability rates after 350 hours are reported in Table ll: Table III Sample Xc Permeability rate after 350 hours (g * mil) / m2 * day) 14 2 Immeasurably high 15 8 12 16 21 6 17 34 4

Claims

CLAIMS 1. An article made of multilayer plastic comprising at least two layers, one of which is a gas barrier layer, the other of which is a polyolefin support layer, wherein the barrier layer includes a quantity of modified polyolefin which has approximately the same density as the support layer, wherein the modified polyolefin is prepared by transplanting an unsaturated carboxylic acid or derivative thereof to the polyolefin, the modified polyolefin being added in an amount such that the barrier layer of gas adhere sufficiently to the adjacent layer and in such a way that the gas barrier properties of the manufactured article are not decreased compared to the barrier properties of a manufactured article wherein the barrier layer does not include a quantity of modified polyolefin . 2. An article manufactured according to claim 1, characterized in that the barrier layer is resins of crystalline polyesters, crystalline polyamides, crystalline polyarylates or poly (ethylene-co-vinyl alcohol) crystalline. 3. An article manufactured according to claim 2, characterized in that the barrier layer comprises homopolymers or copolymers of polyethylene terephthalate. 4. An article manufactured according to claim 1, characterized in that the modified polyolefin is modified high density polyethylene. 5. An article manufactured according to claim 1, characterized in that the modified polyolefin contains 0.5 to 5.0 weight percent of the carboxylic acid or derivative. 6. An article manufactured according to claim 1, characterized in that the modified polyolefin contains from 0.8 to 1.2 weight percent of the carboxylic acid or derivative. 7. An article manufactured according to claim 1, characterized in that the carboxylic acid derivative is maleic anhydride. 8. An article manufactured according to claim 1, characterized in that the modified polyolefin is present in the barrier layer in an amount of from 2 to 10 weight percent of the barrier layer. 9. An article manufactured according to claim 1, characterized in that the barrier layer adheres directly to the polyolefin support layer. 10. An article manufactured according to claim 1, characterized in that the article is a container, a conduit or a membrane. eleven . An article manufactured according to claim 1, characterized in that the polyolefin support layer is high density polyethylene. 12. An article manufactured according to claim 3, characterized in that the modified polyethylene terephthalate has been rheologically altered by optimal co-extrusion with the polyolefin layer. 13. An article manufactured according to claim 12, characterized in that the polyethylene terephthalate has been altered rheologically through branching. 14. An article manufactured according to claim 1, characterized in that the barrier layer has a crystallinity level of at least 21 percent. 15. An article manufactured according to claim 14, characterized in that the barrier layer has a crystallinity level of at least 34 percent. 16. An article manufactured according to claim 1, characterized in that the manufactured article is manufactured by blow molding, thermoforming, dual sheet forming or multi-component injection molding. 17. A method for improving the adhesion properties of polyesters to polyolefin materials comprising incorporating a modified high density polyethylene prepared by transplanting an unsaturated carboxylic acid or a derivative thereof to high density polyethylene, wherein the high density polyethylene The modified one is added to the polyethylene terephthalate in an amount between 2 and 10 weight percent polyester. 18. The method according to claim 17, characterized in that the polyester ester is polyethylene terephthalate, and the unsaturated carboxylic acid or a derivative thereof is made of maleic anhydride. 19. An improved resin comprising polyethylene terephthalate and polyethylene modified with maleic anhydride, wherein the polyethylene terephthalate comprises 90 to 98 percent of the composition, the modified polyethylene comprises 10 to 2 percent of the composition, and the maleic anhydride comprises 0.5 to 5.0 weight percent of the modified polyethylene. 20. An improved co-extruded multilayer article comprising a polyester material having long chain branching and a supporting layer comprising high density polyethylene, wherein the amount of long chain branching in the polyester material is it is selected in such a way that the rheology of the polyester material binds more closely to the rheology of the support layer. 21. A process for improving the processability of a blow molded article having two or more polymeric layers comprising: adjusting the rheology of one of the layers by promoting the long chain branching so that the rheology of the adjusted layer is joined more closely to the rheology of the unadjusted layer. 22. The process according to claim 21, characterized in that the long chain branching is adjusted by incorporating the multifunctional monomers. 23. The process according to claim 21, characterized in that the long chain branching is adjusted by extrusion of reagent with a multifunctional branching agent. RESU MEN Improved multilayer coextruded blow molded objects (such as fuel containers) having at least one barrier layer and a support layer are described together with the improved methods for preparing such objects. The barrier layer includes a quantity of modified polyolefin having approximately the same density as the support layer, wherein the modified polyolefin is prepared by transplanting an unsaturated carboxylic acid or a derivative thereof to the polyolefin, with the modified polyolefin being added to the polyolefin. an amount such that the gas barrier layer adheres sufficiently to the adjacent layer and such that the gas barrier properties of the manufactured article are still adequate. The present invention also relates to the modification of the rheology of the base resins, such as PET (a preferred material for the barrier layer), such that they bind more tightly to the rheology of high density polyethylene (a material preferred for the support layer).