Abstract:
A method of manufacturing linear small tubular articles to provide tubular medical articles for minimal invasive percutaneous introduction into a mammalian body. The method involves forming layers on a wire mandrel and covering with a heat shrinkable tape.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates to a process of producing linear, small diameter, smooth surface thin wall tubular polymeric composite articles. Also, the invention relates to tubular medical articles and a process for their manufacture. 
     2. Description of the Prior Art 
     Conventional commercially available tubular medical articles of small diameter and thin wall dimensions such as hypodermic needles are manufactured from metals e.g. stainless steel. However, the metals interfere with certain diagnostic procedures such as X-rays, magnetic resonance imaging (MRI), sonograms, inter alia. To overcome this problem, plastic has been suggested as a material of construction. While the plastic material can overcome some of the deficiencies of the metal articles when used with the various diagnostic procedures, generally its mechanical properties do not approach the mechanical and chemical properties inherent in metals. 
     U.S. Pat. No. 5,603,696 issued to Williams, et al. discloses molded tubular medical articles produced from specific blends of syndiotatic and isotactic crystalline polypropylene, which are produced by a molding process. The invention is directed to articles having a wall thickness of about 2 mm or less with a high clarity requirement to achieve a see-through capacity. However, the patented medical articles do not possess the mechanical properties necessary for some medical procedure. For example, they would not have the stiffness required for use as hypodermic needles. 
     Therefore, there is a need for tubular medical articles of small diameter and thin wall dimensions which have substantially improved mechanical properties and which can be produced in a process, which is efficient, economical and reproducible. 
     SUMMARY OF THE INVENTION 
     The present invention provides linear small diameter, thin wall, and tubular articles having millimeter dimensions, particularly medical articles, which overcome the deficiencies of both metallic and plastic articles of the prior art. More particularly the present invention is directed to a process for making small diameter polymeric composite tubes having thin walls more efficiently with reproducible results. 
     The process of this invention, which involves a series of simple and economical steps yields reinforced polymeric composite tubular articles having high dimensional stability, a uniform and smooth surface, including surface slipperiness, abrasion resistance, high mechanical strength and corrosion resistance. 
     In its broadest aspect the process comprises the steps of: 
     a) Subjecting a flexible mandrel to a tensioning means for providing linearity along its longitudinal axis; 
     b) Applying a prepreg around the tensioned mandrel; 
     c) Releasing the tension on the mandrel; 
     d) Covering the prepreg coated mandrel with a compression sleeve to form an assembly; 
     e) Shrinking the compression sleeve the assembly; 
     f) Applying an effective pressure for consolidating the prepreg around the assembly; 
     g) Applying tension for maintaining the linearity of the assembly to the mandrel; 
     h) Curing the prepreg under tension to form a tubular composite around the mandrel; 
     i) Releasing the tension on the mandrel; 
     j) Withdrawing the mandrel from the cured prepreg tubular composite; and 
     k) Removing the compression sleeves to yield a linear small diameter, smooth surface, thin wall tubular composite article. 
     The invention includes tubular polymeric composite articles made by the above-described process and particularly the production of hypodermic needles. The tubular composite articles of this invention have excellent tensile strength, modulus, and impact resistance. 
     It is, therefore, a primary object of this invention is to provide a process for the production a linear, small diameter, smooth surface, thin wall composite polymeric tubular article. 
     It is another object of this invention to provide tubular medical articles for minimally invasive percutaneous introduction into a mammalian body, which does not interfere with diagnostic medical procedures. 
     It is a further object of this invention to provide tubular medical articles for introducing or removing fluids from a mammalian body. 
     Yet another object of this invention is to provide a process for preparing tubular small diameter composites useful as hypodermic needles. 
     These and other objects, features and advantages will become apparent from the following description of the preferred embodiments, accompanying drawings and claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a side elevational view partially in cross section illustrating the critical step of curing the prepreg under pressure while simultaneously maintaining the mandrel under tension in the preparation of linear, small diameter smooth surface thin wall tubular polymeric composite in accordance with the present invention. 
     FIG. 2 schematically illustrates a flow diagram for preparing the linear, small diameter, thin wall tubular polymeric composite articles in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In accordance with this invention linear, small diameter, thin wall tubular articles having millimeter dimensions are produced. While the present invention is directed primarily to the production of tubular medical articles, the articles may also be used in various microprocesses since they are chemically inert and have exceptional mechanical properties for their size. The tubular medical articles include hypodermic needles, stents, blood collection tubes, inter alia. 
     Referring to FIG. 1, which illustrates the components of a typical procured assembly for producing the tubular article of the invention. FIG. 1 shows a mandrel (e.g., a wire) or predetermined thickness covered with an adherent  11 , a prepreg layer  13  and overlapped with a compression sleeve  12 . As illustrated in FIG. 1, and in the process flow diagram of FIG. 2 tension is applied by tensioning means for providing linearity (i.e., straightness) to the wire along its longitudinal axis. The tension is maintained while the prepreg strip is applied to the mandrel. A compression sleeve is placed over the prepreg in envelop the coated wire to form an assembly of coated wire-uncured prepreg-compression sleeve. The sleeve is shrunk to remove any air trapped within the sleeve and to afford a tighter fit around the prepreg coated wire. An effective pressure for consolidating the prepreg strip is applied to the compression sleeve. Curing the prepreg strip forms a tubular composite around the wire. The pressure and tension are released and the wire is withdrawn to produce a linear, small diameter, smoother surface, thin wall tubular polymeric composite article. 
     The mandrel may be a flexible metal of small diameter ranging from 0.5 to 3.0 mm internal diameter. Aluminum and copper are the metals of choice since they are economical, readily available in many thicknesses and are disposable and recyclable. Preferably, these metals are in the form of a wire covered with an adherent (release agent). Adherents such as waxes, aluminum, searate, stearomides, silicone polymers and fluorocarbon polymers may be applied to the metal surface before the application of the prepreg. The use of adherents eases the removal of the mandrel from the tubular article after the prepreg cure. In this regard it is preferred to have the metal pre-coated such as a wire coated with tetrafluoroethylene. 
     The prepreg is a composition comprising mixtures of prepolymer and curing catalyst impregnated with a reinforcing material. Broadly any of the know thermoset of thermoplastic polymer systems may be used as the polymer matrix in the finished polymeric composite article. 
     The addition of a catalyst may be added to cause the polymerization of the prepolymers. The types and amounts of catalyst to be used with specific prepolymer systems are within the knowledge and scope of polymer chemists. 
     The reinforcement materials useful in forming the prepreg are fibers such as carbon fibers, aramid fibers, nylon fibers and glass fiber. The carbon fibers in graphite form are preferred for imparting the best overall mechanical properties for the purpose of the invention. It is also preferred that the fibers are oriented in a unidirectional manner along the longitudinal axis of the final composition throughout the polymer matrix. 
     The reinforcement materials may be added to the prepolymer in amounts from between about 0 to 10 weight percent of the final composite composition. 
     As will be the case with all the components involved, the amount used will be determined somewhat by the properties desired in the cured composition, which in turn, will be determined by the particular application involved, i.e., whether the final composite composition is a hypodermic needle or a composition used as transfer tubes in biological or chemical synthesis reactions. 
     The compression sleeve can be either a heat shrinkable polymer or a non-shrinking elastomer. Case of an elastomeric sleeve, external fluid or air pressure is used to collapse the sleeve around the uncured prepreg coated mandrel. The compression sleeve acts as a pressure transfer medium and helps consolidate the uncured prepreg uniformly around the mandrel. Exemplary of the heat shrinkable polymers that can be used in the practice of the present invention includes, polyolefins, such as polyethylene and polypropylene, chlorinated and sulfonated polyethylene polymers and polyesters such as polyethylene glycol terephthalate. Suitable elastomers polymeric include neoprene, butyl rubber, styrene-butadiene rubber, nitrile rubber polyvinylidene halides and copolymers of polyvinylidene halides. 
     Thermoset polymers are extensively cross-linked polymers upon curing, which do not significantly soften upon heating. Typically thermoset polymers are cured causing cross-linking forming a final composite product. The curing may be any type of curing which causes cross linking, e.g. free radical catalysts, humidity, heat, radiation or air curing. Thermoset polymer systems may include a polymer and/or prepolymer. The systems also may include additional agent, which enhance the cross linking process such as catalysts. Examples of thermoset polymers include the following: 
     Phenol-formaldehyde 
     Melamine-formaldehyde 
     Urea-formaldehyde 
     Polyurethane 
     Unsaturated polyester 
     Epoxy 
     Phenolic aniline 
     Furan 
     Polyester 
     Polyurethane 
     Polyphenylene sulfide 
     Polyamide 
     Silicone 
     Polyacrylate 
     Polymethylacrylate 
     Novolac 
     Phenolic 
     Alkyd 
     Aramid 
     The thermoset polymer systems may incorporate a suitable catalyst selected from free radical, Natta-Ziegler, Lewis acid, Friedel-Crafts or a photo initiator and sensitizers for radiation initiated curing. 
     More particularly among the thermoset polymer systems epoxy resins, phenolic resins, aramid Polyamide and Novolac resins are preferred. Most preferred are epoxy resins, which are particularly suited for the production of hypodermic needles because of their inertness to chemical attack especially from biological fluids. Particularly suitable epoxy resins are those derived from diglycidyl ether of bisphenol with the appropriate modifiers and curing agents. However, other epoxy resins are those derived from diglycidyl ether of bisphenol with the appropriate modifiers and curing agents. However, other epoxy resins can also be used such as diglycidyl ethers of resorcinol, dihydroxy dephenyl, hydroquinone, novolacs, etc. These can be modified by the addition of modifying resins. These preferably amine resins and appropriate curing agents and solvents. Certain materials can be used to serve both as a solvent for the resin and also to participate in the curing reaction such as liquid amines. The epoxy resins are cured by many types of materials, including polyamines, polyamides, polysulfides, urea- and phenol-formaldehyde, and acids or acid anhydride, through coupling or condensation reactions. 
     Thermoplastic polymers are materials, which soften upon heating and harden upon cooling. The softening/hardening cycles may be repeated many times. 
     Examples of thermoplastic polymers are the following: 
     Polyethylene 
     Polypropylene 
     Polystyrene 
     Polyvinyl chloride 
     Polyvinyl alcohol 
     Polytetrafluoroethylene 
     Copolymer of poly (tetrafluoroethylen-ethylene) 
     Polymethyl methacrylate 
     Polymethyl methacrylate copolymers 
     Copolymer of poly (methylacrylate-acrylonitrile) 
     Polybutadidne 
     Polyoxymethylene 
     Polymethylene terephalate 
     Polycarbonate 
     Poly e-caprolactam 
     Polyhexamethylene adipamide 
     Polysulfane 
     Cellulose acetate 
     Cellulose acetobutyrate 
     Cellulose 
     Polyisoprene 
     Polychloroprene 
     Copolymer of poly (isobutene-isoprene) 
     Bromo butyl rubber 
     Chlorosulfonated polysthylene 
     Polyethyl acrylate 
     Copolymer of poly (ethylene-vinyl acetate) 
     Nitrile rubber 
     Copolymer of poly(ethylene-propylene) 
     Polyurethane rubber 
     Polysulfide 
     Silicone rubber 
     Polyvinyl butyrate 
     Polyvinyl fluoride 
     Polyvinylidene fluoride 
     Polyester 
     Polyacetal 
     Polyamide 
     Polysulfone 
     Polyethylene oxide 
     Copolymer of poly (styrene-butadiene) 
     Copolymer of poly 
     (styrene-butadiene-acrylonitrile) 
     It will be readily appreciated b those skilled in the art that such catalysts will not be incorporated in any polymer system whether thermoplastic or thermoset where such may be cured by heat alone. 
     Whenever used in this specification the terms set forth above have the following definitions: 
     “Assembly” means an uncured prepreg composition over lapped with a compression sleeve. 
     “Composite” means a cured prepolymer impregnated with a reinforcing material. 
     “Matrix polymer” means a thermoplastic or thermoset prepolymer in which the reinforcing material may be dispersed. 
     “Prepolymer” means a resin monomer, co-monomer, oligomer or other molecular subanite capable of being polymerized. 
     “Prepreg” means a composition comprising a prepolymer and an appropriate catalyst mixture if necessary with a reinforcing material. 
     EXAMPLE 
     A rectangular sheet of an uncured unidirectional carbon fiber/epoxy prepreg of 120 denier and 135 g areal film weight is cut to a needle length of 100 mm then cut into narrow strips having a width according to the following formula: 
     
       
           W= 2 πd   
       
     
     Wherein w=width and d=diameter of the tubular article. 
     A length of copper wire covered with a polytetrafluoroethylene film is cut 60 mm longer than the prepreg length. The cut wire is placed on a first or bottom platen. Tension is applied by tensioning means for providing linearity (straightening) to the wire along its longitudinal axis. Tensioning means can be a fixed and moveable clamp or two moveable clamps. After the wire is straightened, it is secured to the first platen surface. An edge of the prepreg strip having the dimensions, as arrived above, is placed lengthwise and in contact with the length of the wire. A second or top moveable platen is positioned above and in contact with the edge of the prepreg strip. Under a slight pressure, the second platen is moved parallel to the bottom platen to wrap the remaining portion of the prepreg strip completely around the wire. The top platen is then removed and a compression sleeve of a polyethylene film is placed around the uncured prepreg coated wire, an effective amount of heat for shrinking and compressing the sleeve around the prepreg to form an assembly. 
     The exposed wire ends of the mandrel within so-formed assembly were placed in a jig comprising one fixed and one moveable clamp. An effective degree of tension for maintaining the linearity of the mandrel is applied by the moveable clamp controlled by a horizontally disposed screw adjustment. 
     The jig was placed in an oven maintained at about 120° C. until the carbon fiber reinforced epoxy prepreg was cured. After cooling the cured composite was removed from the jig, the compression sleeve and the wire were removed. A linear small diameter, smoother surface, thin wall open-end tubular composite was formed. 
     Heat curing under tension overcomes the linear thermal expansion of the wire to maintain straightness of the tubular composite. 
     The production of non-metallic hypodermic needles is a precise and detailed practice because at small diameters (i.e., less than 3 mm) it is difficult to maintain linearity or straightness of the mandrel. Consequently, the resulting needle article has the same deficiency. In the course of the development of this invention, a tubular article was made by wrapping uncured composite material around a rigid mandrel, then over wrapping with a shrink tape, shrinking the tape and curing the composite material to form the tube without tensioning the mandrel. 
     It was found that during the tape-wrapping step, the radial tension when applying the tape distorted the mandrel causing the resulting tubes to be misaligned. Further, the tape leaves a helical witness lines on the tube surface. In addition, the adhesion forces developed during the curing process make the extraction of the mandrel difficult and the resulting article is damaged and off-specification. 
     COMPARATIVE EXAMPLE 
     A narrow tape of the same prepreg composite of Example 1 having a width of 1 mm was wrapped on a bias around a rigid steel mandrel treated with a polytetrafluoroethylene spray as a release agent. A shrink tape of polyethylene was wrapped over the prepreg tape. An effective amount of heat was applied to shrink the tape around the prepreg to form an assembly. The assembly was cured in an oven maintained at about 120° C. When the shrink tape was removed, a helical witness line remained in the cured prepreg surface. Then the steel mandrel line is extracted but the straightness of tubular article was distorted. Also the tubular article produced did not have a smooth surface such as produced in Example 1. 
     While preferred embodiments of the various aspects of the invention have been described in detail, those of ordinary skill will recognize modifications thereof still falling within the spirit and scope of the inventive concepts. 
     The embodiments of the invention in which an exclusive property or privilege is desired, is defined in the following claims.