Claim for Priority This patent application claims the benefit of the filing date of U. S.

Provisional Patent Application Serial No. 60/484,890, of the same title, filed July 3,2003.

Technical Field The present invention relates generally to extruded polyacetal articles and more particularly to coextruded articles having a shaped profile, a polyacetal resin layer and a thermoplastic elastomer layer melt-bonded thereto. A tube so prepared can be used as a bearing-less roller that capitalizes on the lubricity of the acetal as the bearing surface with the elastomer as a soft-touch and surface grip.

Other applications include pens, bearings, conveyor rollers, fuel lines and so forth.

Background Composite articles having a hard component and a soft component are known in the art. Such articles are made in many instances by injection molding, wherein the processing is under high pressure and geometry may be controlled to a relatively high degree, as opposed to extrusion processing where die exit conditions are at essentially ambient pressure.

United States Patent No. 6,296, 797 to Ziegler et al. teaches a process for producing a composite article from a polyacetal (component a) with directly molded-on functional elements made from one or more thermoplastic elastomers (component b), and wherein components a and b have differing hardness, and the material with the greater hardness (component a) is initially premolded in a first step in a mold, and then is either cooled and removed from the mold and then placed into another, larger cavity, or is partially removed from the mold, but

remains in a portion of the mold, and is then moved to a larger cavity, or, without removal from the mold, remains in the same mold, which is enlarged by means of a movable device, and in a second step, by overmolding with the material with the lesser hardness (component b), the molding formed from component a is firmly bonded to this material and is then removed from the mold as a composite article.

Composite articles from engineering thermoplastics and polyurethane elastomers are seen in United States Patent No. 6,497, 782 to Platz et al. These articles use an adhesion promotor. The process disclosed for producing a composite article from at least one polar thermoplastic, in particular an engineering thermoplastic, involves using at least one foamed or unfoamed polyurethane elastomer, where a molding is firstly molded from the thermoplastic, and some or all of this is provided with an adhesion promoter based on acrylic- resin lacquer or polyurethane-resin lacquer comprising solvents, and then a coating which may be in full-surface or strip form or at least one other molding made from the polyurethane elastomer is used for overmolding, and the thermoplastic material is thus bonded to the polyurethane material.

Multi-layer extrusion is also well known in the art. Such processes typically require the use of specialized equipment or materials such as adhesive "tie"layers and the like as is seen from the following references.

There is disclosed in United States Patent No. 5,891, 373 to Hunter a process of making a multi-layer tube. The tube, a multi-layer hydrocarbon vapor- impermeable tube is formed with a nylon outer layer and a vapor barrier inner layer such as ETFE, bonded together by two adhesive layers. The laminated tube is coextruded. The shear on the two adhesive layers are adjusted to bias the first adhesive layer towards the nylon outer layer and the second adhesive layer towards the ETFE barrier layer. This permits rapid coextrusion of the laminated tubing. Preferably, both adhesive layers are formed from a blend of nylon and ETFE. The ratio of nylon to ETFE can be adjusted so that the first adhesive layer

is preferentially adherent to the nylon layer, and the second adhesive layer is preferentially adherent to the ETFE layer, and both adhesive layers are adherent to each other.

United States Patent No. 5,476, 120 to Brumnhofer teaches a layered tubing for use in a motor vehicle has a thick tubular inner layer formed of one or more sublayers of a synthetic resin having a predetermined hardness and a predetermined thickness and designed for use in a temperature range down to- 40°C, and a thin tubular outer crack-absorbing layer bonded externally to and surrounding the inner layer. The outer crack-absorbing layer is formed of a synthetic resin resistant to attach by lacquer solvent over the temperature range of the inner layer and having a hardness equal to at most 0.8 of the hardness of the inner layer and a thickness equal to at most 0.5 of the thickness of the inner layer.

When lacquer is intentionally or accidentally applied to such tubing and the tubing subsequently is flexed at extremely low temperatures, the lacquer will crack but the soft outer layer will not transmit the sudden change in shape and energy to the inner layer, causing a crack therein. Instead the soft outer layer will absorb the energy of the crack, leaving the underlying tubing intact and free of cracks.

A method of coextruding diverse materials as well as a device therefor is provided in United States Patent No. 4,405, 547 to Koch et al. The coextrusion device can be used with conventional extruders and extrusion dies for forming layered products from at least two materials. It includes a manifold for receiving a plurality of extruded feed materials, and a feedblock receiving the feed materials from the manifold. The feedblock includes first and second faces, entrance ports in the first face corresponding to the number of feed materials, channel means passing through the feedblock between the first and second faces directing each feed material into at least one separate profile, and exit ports in the second face corresponding to the number of channel means, defining a first profile for each feed material. An adaptor is provided for receiving the first profiles from the

feedblock and includes first and second faces, an entrance port in the first face receiving said first profiles, an exit port in the second face corresponding to the entrance of the extrusion die and, a transition zone between the entrance and exit ports wherein the first profiles become contiguous and the overall configuration of the contiguous first profiles is adapted for receipt by the extrusion die. The device can further include a reverser plate and alternate feedblocks having different exit ports.

Despite advances in the coextrusion field, it is nevertheless difficult to find compatible diverse polymer components to make useful articles with a shaped profile due to disparities in processing temperatures and the natural tendency of diverse materials to separate. Relative to injection molding processes, extrusion operations are difficult to control, particularly where a shaped profile is sought as opposed to film or sheet.

Summary of Invention It has been found in accordance with the present invention that coextruded articles having a shaped profile and a polyacetal resin layer as well as a thermoplastic elastomer layer can be readily prepared by extruding the polyacetal at a relatively low temperature and coextruding the thermoplastic elastomer at a relatively high temperature. With proper selection of materials, no tie layers are necessary which is surprising in view of the natural lubricity of the polyacetal resin.

There is thus provided in accordance with the present invention a method of making an extruded polyacetal article with a shaped profile as well as a thermoplastic elastomer layer coextruded thereon including the steps of : extruding a melted polyacetal resin through a die having a shaped die profile; coextruding through the die with the polyacetal resin, a melted thermoplastic elastomer to form a coextruded article with a shaped profile including a thermoplastic elastomer layer and a polyacetal layer; wherein the thermoplastic

elastomer layer is melt-bonded to the polyacetal resin layer and forms a continuous layer thereon of substantially uniform thickness over at least a portion of the coextruded article. In some cases, the polyacetal resin is a polyacetal copolymer resin, while in others the polyacetal resin is a polyacetal homopolymer resin. In preferred cases, the thermoplastic elastomer is a styrene-containing block copolymer, most preferably SEBS. The SEBS resin may be functionalized with carboxyl groups, for example. In particularly preferred embodiments, no "tie"layer is used and the SEBS is directly bonded to the polyacetal layer such that the products consist of the two layers. In yet other embodiments, the thermoplastic elastomer is a urethane block copolymer.

In typical embodiments, the coextruded article is predominantly polyacetal, such as wherein the coextruded article is at least about 75% polyacetal.

The thickness of the thermoplastic elastomer layer is generally frm about 1% to about 25% of the thickness of the polyacetal layer and typically the thickness of the thermoplastic elastomer layer is from about 1 % to about 10% of the thickness of the polyacetal layer. The coextruded article may have an arcuate profile, for example, in the form of a tube defining a circular profile having an outer continuous layer over the tube of thermoplastic elastomer having a substantially uniform thickness.

The polyacetal is generally supplied to a die at a melt temperature of from about 350°F to about 375°F., typically the polyacetal is supplied to the die at a melt temperature of from about 355°F to about 365°F. On the other hand, the thermoplastic elastomer is supplied to the die at a melt temperature of from about 490°F to about 505°F ; usually between about 495°F and 505°F.

In another aspect of the invention there is provided coextruded articles having a shaped profile produced in continuous extruded lengths including an extruded polyacetal resin layer and melt-bonded thereto a continuous coextruded

thermoplastic elastomer layer, the thermoplastic elastomer layer being of substantially uniform thickness over at least a portion of the polyacetal resin layer.

The foregoing and other features of the invention will become apparent from the discussion which follows.

Brief Description of Drawings The invention is described in detail below with reference to the Figures, wherein like numerals designate similar parts and wherein: Figure 1 is a view in perspective of a section of tube continuously extruded in accordance with the present invention; and Figure 2 is a view in elevation and cross-section of the tube of Figure 1.

Detailed Description The invention is described in detail below with reference to the Figures and various embodiments. Such description is for purposes of exemplification only and is not intended to be limitative of the invention which is defined in the appended claims.

Terminology is given its ordinary meaning as supplemented in this description. Temperatures are in degrees Fahrenheight or degrees Celsius as indicated and percent means weight percent. The materials used are described briefly below. "Shaped profile"or like terminology refers to articles which have a shape other than simply planar geometry. Example of extruded articles with a shaped profile include extruded tubing or other shapes with a closed geometric profile such as elliptical and so forth, angular profiles, arcuate profiles and the like.

Typically, crystalline polyacetal (or oxymethylene) homopolymers, also called polyformaldehydes or poly (oxymethylenes), are prepared by polymerizing anhydrous formaldehyde or trioxane, a cyclic trimer of formaldehyde. For example, high molecular weight polyoxymethylenes have been prepared by polymerizing trioxane in the presence of certain fluoride catalysts, such as antimony fluoride. Polyoxymethylenes may also be prepared in high yields and at rapid reaction rates by the use of catalysts comprising boron fluoride coordination complexes with organic compounds, as described in United States Patent No.

2, 898, 506 to Hudgin et al.

Oxymethylene homopolymers may be stabilized against thermal degradation by end-capping with, for example, ester or ether groups such as those derived from alkanoic anhydrides, e. g. , acetic anhydride, or dialkyl ethers, e. g., dimethyl ether, or by incorporating stabilizer compounds into the homopolymer, as described in United States Patet No. 3,133, 896 to Dolce et al.

Crystalline polyacetal (oxymethylene) copolymers which are especially suitable for utilization with the elastomeric copolymers of this invention will usually possess a relatively high level of polymer crystallinity, i. e. , about 60 to 80 percent or higher. These preferred oxymethylene copolymers have repeating units which consist essentially of oxymethylene groups interspersed with oxy (higher) alkylene groups. Oxymethylene groups generally will constitute from about 85 to about 99.9 percent of the recurring units in such crystalline copolymers. The oxy (higher) alkylene groups incorporated into the copolymer during copolymerization produce the copolymer by the opening of the ring of a cyclic ether or cyclic formal having at least two adjacent carbon atoms, i. e. , by the breaking of an oxygen-to-carbon linlcage. Crystalline copolymers of the desired structure may be prepared by polymerizing trioxane together with from about 0.1 to about 15 mol percent of a cyclic ether or cyclic formal having at least two adjacent carbon atoms, preferably in the presence of a catalyst such as a Lewis acid, ion pair catalysts, etc. The cyclic ether and cyclic formal preferred for use in

preparing these preferred crystalline oxymethylene copolymers are ethylene oxide and 1, 3-dioxolane, respectively. Among the other cyclic ethers and cyclic formals that may be employed are 1,3-dioxane, trimethylene oxide, 1,2-propylene oxide, 1,2-butylene oxide, 1,3-butylene oxide, 1, 4-butanediol formal, and the like.

Crystalline oxymethylene copolymers produced from the preferred cyclic ethers have a structure composed substantially of oxymethylene and oxy (lower) alkylene, preferably oxyethylene, groups, and are thermoplastic materials having a melting point of at least 150°C. They normally are millable or processable at temperatures ranging from 180°C to about 200°C, and have a number average molecular weight of at least 10,000 and an inherent viscosity of at least 1.0 (measured at about 25°C in a 0.2 wt. % solution in HFIP).

These crystalline oxymethylene copolymers preferably are stabilized to a substantial degree prior to being utilized with the elastomeric copolymers of this invention. This can be accomplished by degradation of unstable molecular ends of the polymer chains to a point where a relatively stable carbon-to-carbon linkage exists at each end of each chain. Such degradation may be effected by hydrolysis, as disclosed, for example, in United States Patent No. 3,219, 623 to Berardinelli.

The crystalline oxymethylene copolymer may also be stabilized by end- capping, again using techniques well known to those slcilled in the art. End- capping is preferably accomplished by acetylation with acetic anhydride in the presence of sodium acetate catalyst.

A particularly preferred class of crystalline oxymethylene copolymers is commercially available from Ticona LLC under the designation CELCON acetal copolymer; which may be, for example, copolymers of trioxane with suitable comonomers and may have exemplary melt indices of 1.5, 2.5, 9.0 up to about 27.0 g/10 min. or more when tested in accordance with ASTM D1238-82.

Copolymers also include oxymethylene terpolymers having oxymethylene groups, oxy (higher) alkylene groups such as those described above, further including a

different, third group interpolymerizable with oxymethylene and oxy (higher) alkylene groups. The third monomer may be a bifunctional compound such as diglycide. Examples of suitable bifunctional compounds include the diglycidyl ethers of ethylene glycol; 1,4-butanediol ; 1,3-butanediol ; cyclobutane- 1,3-diol ; 1,2-propanediol ; cyclohexane-1, 4-diol and 2, 2,4, 4-tetramethyl- cyclobutane-1, 3-diol, with butanediol diglycidyl ethers being perhaps most preferred.

Additives such as plasticizers, formaldehyde scavengers, mold lubricants, antioxidants, fillers, colorants, reinforcing agents, light stabilizers and other stabilizers, pigments, and the like, can be used with the compositions of this invention so long as such additives do not materially affect the desired interaction between the polyacetal and the thermoplastic elastomer. Suitable formaldehyde scavengers include cyanoguanidine, melamine and melamine derivatives and the like. Suitable mold lubricants include alkylene bisstearamides, long-chain amides, waxes, oils, and polyether glycides and the like.

Further details concerning suitable polyacetals are found in the following references.

United States Patent No. 3,639, 192, issued February 1,1972 to Burg et al., discloses for use as adhesives copolymers of formaldehyde or trioxane with 1 to 60% by weight, preferably 1 to 30% by weight, of a cyclic ether, cyclic and/or linear acetal, e. g. , 1,3-dioxolane, and/or an allcyl glycidyl formal, polyglycol diglycidyl ether or bis (alkane triol) triformal. Example 5 discloses a terpolymer of 97.95 wt. % of trioxane, 2 wt. % of ethylene oxide, and 0.05 wt. % of 1,4- butanediol diglycidyl ether.

United States Patent No. 3,337, 507, issued August 22,1967 to Gutweiler et al., teaches the formation of high molecular weight copolymers obtained by polymerizing a mixture of trioxane and any of certain polyformals. Example 4 of

the patent shows the use of a polyformal which is a clear highly viscous oil at 70°C. obtained by polymerizing a mixture of 1/3 mole of trioxane and 1 mole of dioxolane in the presence of p-nitrophenyl-diazonium fluoroborate as catalyst.

Japanese Kokai Sho 42-22065 of Yarnaguclzi et al., published October 30, 1967, discloses copolymers of trioxane and an aperiodic ring compound, e. g. , 1,3- dioxolane, prepared in liquid sulfur dioxide, and in Example 1 shows a copolymer of trioxane and 64 mol % of 1,3-dioxolane.

Thermoplastic elastomers are readily available as is seen in the Kirk- Othmer, Encyclopedia of Chemical Technology, Fourth Ed. , Vol. 9 (Wiley).

Suitable elastomers may include: polyurethane/elastomer block copolymers; polyester elastomer block copolymers; polyamide/elastomer block copolymers; polyetherimide/polysiloxane block copolymers; polypropylene/EPDM or EPR blends; polypropylene/EPDM dynamic vulcanizates ; polypropylene/butyl rubber dynamic vulcanizates; polypropylene/natural rubber dynamic vulcanizates; polypropylene nitrile rubber dynamic vulcanizates ; PVC/nitrile rubber blends; and halogenated polyolefin/ethylene interpolymer blends The thermoplastically processable elastomers used may be TPE-Us (thermoplastic polyurethane elastomers). These materials are typically multi- block copolymers which have built up from rigid urethane segments and flexible long-chain diol segments. The rigid urethane segments here are obtained from a reaction between diisocyanates and chain extenders. The diisocyanates used may be aromatic, alicyclic or aliphatic diisocyanates. Preference is given here to

diphenylmethane 4, 4'-diisocyanate (MDI), tolylene diisocyanate (TDI), m- xylylene diisocyanate, p-xylylene diisocyanate, naphthylene diisocyanate, diphenyl diisocyanate, 4,4'-methylenebis (cyclohexyl isocyanate), isophorone diisocyanate and 1,6-hexamethylene diisocyanate. The chain extenders used are short-chain aliphatic, alicyclic or aromatic diols or diamines with a molar mass of less than 500 g/mol, preferably less than 300 g/mol, preferably those such as ethylene glycol, propylene 1, 3-glycol, propylene 1,2-glycol, 1, 4-butanediol, 1,5- pentanediol, 1,6-hexanediol, 1, 4-cyclohexanediol, ethylenediamine, hexamethylene-diamine, xylylenediamine and 4,4'-diaminodiphenylmethane.

The flexible long-chain diol segments may be selected from the class consisting of polyetherdiols, polyesterdiols, polyetheresterdiols and polycarbonatediols with a number-average molar mass in the range from 500 to 5000 g/mol, preferably from 1000 to 3000 g/mol. The polyetherdiols may be prepared by ring-opening polymerization of cyclic C. sub. 2-C. sub. l2 ethers, such as ethylene oxide, propylene oxide or tetrahydrofuran. The polyesterdiols may be obtained by esterification reactions of dialcohols (examples of those preferably used here being ethylene glycol, propylene 1,3-glycol, propylene 1,2-glycol, 1,4- butanediol, 1,3-butanediol, 2-methylpropanediol, 1,5-pentanediol, 3-methyl-1, 5- pentanediol, 1,6-hexanediol, neopentyl glycol, nonanediol, and 1, 10-decanediol) and dicarboxylic acids (examples of those preferably used here being glutaric acid, adipic acid, pimelic acid, suberic acid, sebacic acid, terephthalic acid and isophthalic acid) or by corresponding transesterification reactions. It is also possible to obtain polyesterdiols of this type by ring-opening polymerization of lactones (examples of those preferably used here being caprolactone, propiolactone and valerolactone). The polycarbonates may be obtained by reacting dialcohols (examples of those preferably used here being ethylene glycol, propylene 1,3-glycol, propylene 1,2-glycol, 1,4-butanediol, 1,3-butanediol, 2- methylpropanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1, 6-hexanediol, neopentyl glycol, nonandiol and 1, 10-decanediol) with diphenyl carbonate or phosgene.

Either polyesterurethane elastomers or polyetherurethane elastomers may be used in the composite articles described here. The hardness range of the elastomers is from about Shore A 65 to about Shore D 75. The hardness here is also a measure of the proportion of rigid urethane segments to flexible long-chain diol segments. The melt index of the products is measured at various temperatures, depending on the melting behavior of the rigid urethane segments.

It is also a measure of the degree of addition (molar mass of the entire chains).

The elastomers may be foamed or unfoamed as is well known in the art.

Styrene-containing block copolymers are preferred thermoplastic elastomers for use in connection with the invention. Such polymers are based on styrene and either isoprene or butadiene. A Shore A hardness of from 65-75 is typical for butadiene-based copolymers, whereas isoprene-containing polymers tend to be much softer. Butylene-containing resins are preferred. Especially preferred are styrene-ethylenebutylene-styrene (SEBS) block copolymers. Such copolymers are described in detail in the Kirk-Othmer Encyclopedia of Chemical <BR> <BR> Technology, Fourth Ed. , Vol. 9, pp. 22-25, the disclosure of which is incorporated herein by reference.

Additional information on styrene/olefin elastomer compositions is found in European Patent Nos. 1,216, 821 and 1, 128, 955 to Ziegler et al., and DE 19845235 C2, the disclosures of which are also incorporated herein by reference.

Suitable modified styrene-olefin elastomers are compositions based on thermoplastic styrene-olefin elastomers (TPE-S). These compositions generally comprise from 20 to 85% by weight, preferably from 35 to 70% by weight, of maleic anhydride-functionalized and/or non-functionalized high-molecular-weight tri-block copolymers which have been built up from rigid end-blocks of styrene and from flexible middle blocks of olefin, and from 15 to 70% by weight, preferably from 20 to 50% by weight, of non-olefinic thermoplastic material.

Based on the styrene-olefin block copolymer content, the composition comprises,

in addition, at least 5 parts by weight respectively and not more than 200 parts by weight respectively of lubricating plasticizer and/or inorganic filler per 100 parts by weight of styrene-olefin block copolymer.

The styrene-olefin block copolymers include those described, for example, in EP-A-710703 and EP-A-699519, which are incorporated herein by way of reference. The styrene-olefin block copolymers preferably comprise about 30 mol% of styrene and 70 mol% of olefin, the middle block of olefin having preferably been built up from ethylene units and butylen units.

By varying the proportions of functionalized and non-functionalized styrene-olefin triblock copolymers, non-olefinic thermoplastic material, plasticizer and inorganic filler it is possible to prepare modified styrene-olefin elastomers with a variety of properties. The elastomer composition may also comprise conventional stabilizers and processing aids.

The TPE-S compositions according to the invention have a Shore A hardness in the range from 30 to 90, preferably from 40 to 80. This hardness may be adjusted via the proportions of the plasticizers and of the thermoplastic component. Plasticizers which may be used are paraffinic mineral oils, synthetic oils, semisynthetic oils, ester plasticizers, etc.

The thermoplastic content in the styrene-olefin elastomers may generally be olefinic thermoplastics, such as polyethylene, polypropylene or polyolefin elastomers, if desired reinforced with talc or filled with glass fiber. Preferebly, the styrene-olefin elastomer is modified by compounding with non-olefinic thermoplastic material, and the non-olefinic thermoplastic material includes thermoplastic polymers, such as polyacetal or thermoplastic polyesterurethane elastomers, thermoplastic polyetherurethane elastomers, thermoplastic polyesters, such as polyethylene terephthalate and polybutylene terephthalate, thermoplastic polyesterester elastomers, thermoplastic polyetherester elastomers, thermoplastic

polyetheramide elastomers, thermoplastic polyamides, thermoplastic polycarbonates, thermoplastic polyacrylates, acrylate rubbers or styrene- acrylonitrile-acrylate rubbers (ASA), if desired filled with glass fibers or with glass beads. The resultant modified styrene-olefin elastomers have a Shore A hardness in the range from about 30 to about 90, preferably from about 40 to about 80.

Both the polyacetal and the modified styrene-olefin elastomer composition may generally comprise conventional additives, such as stabilizers, nucleating agents, mold-release agents, lubricants, fillers, reinforcing materials, pigments, carbon black, light stabilizers, flame retardants, antistats, plasticizers and optical brighteners and so forth as noted above.

Examples of suitable materials in addition to those exemplified below includeThermolast K STC 7849/42 (Kraiburg, DE) Shore hardness A 75, density 1. 15 g/cm3 ; which is reported to be a composition made from high-molecular- weight, functionalized and non-functionalized SEBS block copolymer, lubricating plasticizer, non-olefmic thermoplastic (proportion 44% by weight), inorganic filler and stabilizer, using, per 100 parts by weight of SEBS block copolymer, 180 parts by weight of non-olefinic thermoplastic and at least 5 parts by weight of, respectively, lubricating plasticizer and filler. Another suitable thermoplastic elastomer isThermolast K STC 7849/43 (Kraiburg, DE); Shore hardness A 45, density 1. 06 g/cm3 ; a composition made from high-molecular-weight, functionalized and non-functionalized SEBS block copolymer, lubricating plasticizer, non-olefinic thermoplastic (proportion 25% by weight), inorganic filler and stabilizer, using, per 100 parts by weight of SEBS block copolymer, 80 parts by weight of non-oleEmic thermoplastic and at least 5 parts by weight of, respectively, lubricating plasticizer and filler.

The polymer layers are coextruded to form a bilayer tube, for example, by any suitable coextrusion method utilizing, for example, any of the devices noted

above in United States Patent Nos. 5,891, 373 to Hunter ; 5,476, 120 to Brurnfahofer 4,405, 547 to Koch et al. The layers could be combined using a combining block prior to a slot extrusion die or multimanifold die.

In connection with a combining block, parallel openings within the block are fed from two or more extruders, one for each resin. The melts flow in laminar fashion through the die. Careful control of resin viscosity must be obtained to provide smooth flow, and the resins must be compatible in order to bond together properly. A more preferred method uses a multimanifold die to bring the melt streams together within the die. This allows use of resins with a wider difference in viscosity since fewer changes in flow patterns are necessary. Multimanifold dies are preferably tubular. The most common types of coextrusion are AB, ABA, or ABC where A is one polymer system, B is another (of the same polymer type or different), and C is a third polymer type. Where two polymers may not adhere sufficiently, it is possible to extrude a tie or adhesive layer in the coextrusion.

Ionomer resins may be used as such tie layers.

Using such equipment and the foregoing materials, a coextruded tube 10 of continuous length is produced as is shown in Figures 1 and 2. Tube 10 is continuously produced by coextrusion and thus has indeterminate length. Tube 10 has a circular or cylindrical core 12 of polyacetal resin coated with an outer coextruded flexible coating 14 consisting of thermoplastic elastomer thereabout which may be foamed or unfoamed. Coating 14 is uniform wall thickness 16, less than 10% of the wall thickness 18 of core 12. Preferably, coating 14 surrounds the outer surface of the core as shown.

Most preferably, the thermoplastic elastomer resin is provided to the coextrusion die at a melt temperature of at least 100°F higher than the temperature that the polyacetal is supplied to the die. At least about 125°F higher or about 140°F higher is preferred. Typical polyacetal resins useful in connection with the invention have a melt-extrusion temperature window of from about 360°F to

about 390°F and are supplied to the coextrusion die at a temperature of about 360°F. On the other hand, a SEBS resin may have a melt-extrusion temperature window of from about 480°F to about 510°F and is suitably provided to the coextrusion die at a temperature of about 500°F.

Example Utilizing a coextrusion apparatus with a multimanifold die, the following resins were coextruded to produce a continuous tube as shown in Figures 1 and 2.

Resin Source Celcon M 15HP Ticona LLC Themolast K TC7 HAZ Kraiburg Celcon M15HP is a high molecular weight polyacetal copolymer, while Thermolast K TC7 HAZ is a SEBS composition believed to be made from high- molecular-weight, functionalized and non-functionalized SEBS block copolymer, lubricating plasticizer, non-olefmic thermoplastic, inorganic filler, stabilizer, plasticizer and filler.

The resin compositions were co-extruded under the following (approximate) conditions: (A) Polyacetal Extrusion Conditions, Extruder 1 Temperature Zone 1 340 F Temperature Zone 2 350 F Temperature Zone 3 360 F Die 370 F (B) SEBS Extrusion Conditions, Extruder 2

Temperature Zone 1 470 F Temperature Zone 2 480 F Temperature Zone 3 490 F Die 500 F While the invention has been described in detail in connection with numerous potential embodiments, modifications to those embodiments within the spirit and scope of the present invention, set forth in the appended claims, will be readily apparent to those of slcill in the art.