AU1014783A - A method of forming a yieldable thermal bond in an autoclavable medical product implement and the like - Google Patents

Description

A METHOD OF FORMING A YIELDABLE THERMAL BOND IN AN AUTOCLAVABLE MEDICAL PRODUCT IMPLEMENT AND THE LIKE

TECHNICAL FIELD OF THE INVENTION

The invention generally relates to the assembly of fabricated parts utilizing polyvinyl chloride series resin compositions, and more particularly, to the formation of frangible, or yieldable, connections between such fabricated parts

The invention also generally relates to the assembly of autoclavable medical product implements which include frangible components. DESCRIPTION OF THE PRIOR ART

Attention is directed to the copending U.S. Patent Applications of Edward Garver entitled SUPPORT ASSEMBLY FOR A CANNULA AND THE LIKE, Serial Number 326,736, filed December 2, 1981; and AN AUTOCLAVABLE THERMOPLASTIC MATERIAL WHICH IS HEAT BONDABLE TO A CANNULA AND THE LIKE, Serial Number 326,738, filed December 2, 1981.

Attention is also directed to the copending U.S. Patent Application of Edward Garver and Kenneth Zabielski entitled TAMPER-PROOF CANNULA SUPPORT

ASSEMBLY, Serial Number 326,737, filed December 2, 1981.

Polyvinyl chloride series resin compositions constitute some of the world's largest-volume thermoplastics. This is true because such resin compositions are chemically inert and sufficiently stable, and their properties are thereby maintained over long periods of time, despite exposure to the elements; because they are versatile and can be made into products that range from soft to rigid and clear to opaque in all colors; and because they are capable of providing these above-listed benefits at an economical cost.

Plasticized polyvinyl chloride series resin compositions find widespread use in medical product implements. This is true because, in addition to the above-listed attributes, these resin compositions are approved for blood contact and are not heat-deformable in the range of sterilization temperatures (approximately 230° to 250°F) encountered during commercial autoclaving. It is often desirable to form frangible, or yieldable, connections between components in medical product implements. For example, in a cannula support assembly, it may be desirable to have a cover member which is securely joined to the hub to enclose the cannula and protect the sterile integrity of the cannula prior to use, but which can be conveniently removed when desired to expose the cannula at the instant of use. In this context, it is desirable to utilize thermal bonding techniques to securely join the cover to the hub. By utilizing heat bonding techniques, the use of adhesives or other foreign material is avoided. Furthermore, heat bonding techniques lend themselves to large scale, automated production schemes.

Unfortunately, plasticized polyvinyl chloride compositions typically utilized in medical product implements tend to form a thermal bond which increases progressively in strength as the heat history of the bond increases. As a result, the formation of the desired frangible, or yieldable, thermal bond in medical product implements which utilize plasticized polyvinyl chloride series resin compositions requires the exercise of careful control over the heat history of the bond. Without such control, the bond can easily become so strong that it is physically impossible to break it without permanently deforming the materials so joined. Such careful control of the heat history is significantly complicated, and may prove impossible, if the implements must undergo the relatively intense and prolonged heat exposure of autoclaving and pasteurization. It is thus one of the principal objects of this invention to provide a method which alters the thermal bonding characteristic of a member made of a polyvinyl chloride series resin composition to enable the formation of a yieldable thermal bond which, once established, does not substantially increase in strength as a result of subsequent heat exposure and which is selectively breakable, despite prolonged heat exposure, in response to the manual application of a force without any permanent deformation of the joined parts.

SUMMARY OF THE INVENTION

To achieve this and other objects, the present inventors have discovered that the thermal bonding characteristic of a polyvinyl chloride series resin composition can be significantly altered by the incorporation of measured amounts of silicone oil. This silicone-altered composition can be thermally bonded to a compatible material, such as polyester, in response to exposure to heat. However, once established, the thermal bond so formed does not progressively increase in strength as the heat history is prolonged or intensified. Rather, as long as the heat history does not lead to the chemical decomposition of the resin composition itself, the bond can be always selectively broken in response to the manual application of force without causing permanent deformation of the plastic materials. The present inventors have also discovered that the thermal bonding characteristic of the polyvinyl chloride series resin composition can be additionally benefically altered by the further incorporation of calcium carbonate into the polyvinyl chloride-silicone oil mixture. This further inclusion of calcium carbonate into the mixture leads to a more stable thermal bond which can always be consistently broken by a force which falls within a relatively narrowly defined range of forces.

By altering the characteristic of the polyvinyl chloride series resin composition in accordance with the invention, a yieldable thermal bond can be established which is well-suited for autoclavable medical product implements as well as for mass production techniques. Once established, the bond does not progressively increase in strength as a result of additional heat exposure, and can always be broken, when desired, in response to a force which does not cause any permanent deformation of the bonded materials. By virtue of the invention, the limited thermal bonding characteristic of the altered composition is self-contained and inherent and not dependent upon the careful control of the particular heat history of the bond.

Other features and advantages of the embodiments of the invention will become apparent upon reviewing the following more detailed description, the drawings, and the appended claims. DESCRIPTION OF THE DRAWINGS

Fig. 1 is a plan view, with parts broken away and in section, of a blood collection, storage, and sampling unit which includes a phlebotomy needle carried by a "tamper-proof" cannula support assembly which utilizes a thermal bond embodying various of the features of the invention;

Fig. 2 is a perspective view of the "tamper-proof" cannula support assembly shown in Fig. 1; Fig. 3 is a section view of the "tamper proof" cannula support assembly taken generally along line 3-3 in Fig. 2; and

Figs. 4 and 5 are perspective views showing the sequence of breaking the "tamper-proof" connection between the cover member and hub of the cannula support assembly shown in Fig. 2.

Before explaining the embodiments of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components as set forth in the following description or as illustrated in the accompanying drawings. The invention is capable of other embodiments and of being practiced or carried out in various ways. Furthermore, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting. DESCRIPTION OF THE PREFERRED EMBODIMENTS

A medical product implement in the form of a cannula support assembly 10 is shown in the drawings. As will be described in greater detail later herein, the support assembly 10 has a "tamper-proof" feature which embodies various of the features of the invention. It should be appreciated, however, that the invention which will be described herein is applicable for use in a diverse number of environments, other than in the context of the specific medical product implement illustrated and described.

With this in mind, reference is first made to Fig. 1, in which a representative blood collection, storage, and sampling unit 12 is shown. While various constructions are possible, in the illustrated embodiment, the unit 12 includes a blood collection container 14, which typically is a flexible bag made of medical grade polyvinyl chloride plastic material. A donor tube 16, which typically is also made of a flexibl medical grade polyvinyl chloride plastic material, is integrally attached to and carried by the container 14. A cannula body in the form of a phlebotomy needle 18 is attached in flow communication with the outer end 17 of the donor tube 16. The needle .18 serves after venipuncture to channel blood from a patient or donor through the donor tube 16 and into the container 14.

In this specific operative environment, the "tamper-proof" cannula support assembly 10 is utilized to support the phlebotomy needle 18. Reference is now made to Figs. 2 through 5 and to the embodiment of the assembly 10 utilized to support the phlebotomy needle 18. In this embodiment, the assembly 10 includes hub means 38 which is compact and easily handled and manipulated between the fingertips of the attendant (see, in particular. Figs. 4 and 5) . The hub means 38 supports the phlebotomy needle 18 with its operative, or beveled, end 36 extending axially beyond one end 43 of the hub means 38. The hub means 38 includes a post portion 39

(as best shown in Figs. 3 and 5) which projects outwardly from the one end 43 of the hub means 38 and concentrically encircles an adjacent section of the operative end 36 of the needle 18. While the hub means 38 may be variously constructed, in the illustrated embodiment, the hub means 38 is constructed along the lines disclosed in the copending U.S. Patent Application of Emil Soika, entitled CANNULA SUPPORT ASSEMBLY AND ITS METHOD OF MANUFACTURE, Serial Number, 326,729, filed December 2, 1981.

More particularly, the hub means 38 comprises a first, member 22 and a second member 24. The first and second members 22 and 24 each take an elongated, tubular form having an essentially uniform cross- sectional shape. As pointed out in the above-cited Soika patent application, this construction enables the manufacture of the first and second members 22 and 24 utilizing known ram or screw extrusion techniques. It should be appreciated, however, that the hub means 38 and its associated post portion 39 could also be formed as a single piece injection or compression molded unit. As is best shown in Fig. 3, the second member 24 has a main body portion 26, which is carried within a bore 42 formed in the first member 22, and opposite end portions, respectively 28 and 30, each of which is disposed outwardly of the first member 22. The second member 24 also has a bore 32 in which the shank 34 of the phlebotomy needle 18 (see Fig. 3) is secured. The shank 34 can be secured within the second member bore 32 by various means, such as by use of adhesive or epoxy bonding (as disclosed in the just referenced copending patent application of Emil Soika), or by thermal bonding, as disclosed in the heretofore cited copending U.S. Patent Applications of Edward Garver, entitled SUPPORT ASSEMBLY FOR A CANNULA AND THE LIKE AND ITS METHOD OF MANUFACTURE and AN AUTOCLAVABLE THERMOPLASTIC MATERIAL WHICH IS HEAT BONDABLE TO A CANNULA AND THE LIKE.

By virtue of this construction, the operative end 36 of the needle 18 supported in an outwardly projecting, exposed position beyond the second member end portion which is adjacent to the end 43 of the hub means 38. In the illustrated embodiment, this is second member end portion 28. This end portion 28 thus corresponds with the heretofore described post portion 39 of the hub means 38.

The other outwardly disposed end 30 of the second member 24 readily accommodates attachment of the hub assembly 38 to the end 17 of the donor tube 16. The first member 22 preferably includes an outwardly projecting ridge or shoulder 40 which extends along one exterior surface axially of the first member bore 42. This ridge 40 serves as a reference point for the proper alignment of the beveled end 36 of the needle 18 relative to the hub means 38 during the assembly process. Proper bevel orientation is desirable, because it assures that the sharpest part of the needle 18 breaks the skin during venipuncture. In addition to facilitating the initial alignment of the beveled end 36 of the needle 18 during the assembly process, the ridge 40 functions as a visual and tactile guide in the hands of the attendant (see Fig. 5) to assist him or her in positioning the beveled end 36 during venipuncture.

The assembly 10 further includes cover means 46 which protects the sterile integrity of the phlebotomy needle 18 prior to venipuncture and which seals the needle 18 against fluid loss prior to and after use.

As can best be seen in Figs. 3 and 5, the cover means 46 has an open end portion 50 which fits concentrically about the post portion 39 (i.e., second member end 28) of the hub means 38. The cover means 46 further includes and an open interior 48 which extends from the end portion 50 and serves to enclose the operative portion 36 of the needle 18.

The cover means 46, like the hub means 38, may be variously constructed. However, in the illustrated embodiment, the cover means 46, like the hub means 38, is constructed along the lines disclosed in the above-cited Soika patent application. More particularly, the cover means 46 takes an elongated, tubular form (see Figs. 2 and 5) having an essentially uniform cross-sectional shape with oppositely spaced ends 50 and 51, between which the open interior 48 of the cover means 46 extends. As with the construction of the first and second members 22 and 24, this elongated, tubular, and generally uniform configuration enables the manufacture of the cover means 46 utilizing known ram or screw extrusion processes. However, as with the hub means 38, it should be appreciated that the cover means 46 could also be formed as an injection or compression molded piece.

Axially extending and uniformly radially spaced ridges 52 are formed on the exterior of the cover means 46 of the illustrated embodiment to facilitate the gripping and manipulation of the cover means 46 by the attendant (see Figs. 4 and 5).

As can be seen in Fig. 3, the interior diameter of the open interior 48 of the cover means 46 preferably exceeds the exterior diameter of the exposed portion 36 of the phlebotomy needle 18. Thus, when the cover means 46 is disposed on the hub means 38, the open interior 48 is spaced radially outwardly of, and thus disposed in a non-contiguous relationship with, the needle 18 along its entire outwardly disposed length. In order to affect a fluid-tight seal with the needle 18 within the confines of the open interior 48 of the cover means 46, the cover means 46 of the illustrated embodiment includes a member 54, which is preferably formed of a resiliently compressible material, such as compression molded rubber. The member 54 is insertable in a press-fit relationship through the outermost disposed open end 51 of the cover means 44 to occupy only the outermost portion of the open interior 48 (see Fig. 3).

As can be seen in Fig. 3, the member 54 includes a chamber or pocket 56 which is configured to sealingly envelop the outermost tip 37 of the beveled end 36 of the needle 18 when the hub and cover means 38 and 46 are coupled together. The pocket 56 thereby seals the needle tip 37 from communication with the remainder of the open interior 48 of the cover means 46 and provides a positive fluid shut-off for the needle 18 within the open interior 48. Because only the outermost tip 37 of the needle 18 is in sealing contact with the pocket 56 of the member 54, there is a minimum of friction, or drag, created between the needle 18 and the cover means 46 during removal of the cover means 46 to expose the needle 18. Such removal thus does not tend to draw or suck fluid out of the needle 18. By the same token, return of the cover means 46 onto the hub means 38 is achieved with a minimum of effort. Recognizing also that it is desirable to coat the exterior of the phlebotomy needle 18 with silicone to facilitate a more comfortable venipuncture, the very limited intimate contact between the needle 18 and the cover means 46 further serves to protect the silicone coating along most of the outwardly exposed portion 36 of the needle 18 against friction loss during removal or return of the cover means 46. This construction thus also ultimately contributes to a more comfortable venipuncture.

From the foregoing, it can be .seen that the cover means 46 serves to protect the sterile integrity of the needle 18 prior to use, but can be easily removed and returned to the post portion 39 of the hub means 38 when desired.

In order to provide positive assurance that the cover means 46 has not been tampered with in a manner which compromises the sterile integrity of the needle 18, the assembly 10 includes means 41 operatively associated with the post portion 39 of the hub means 38 and the end portion 50 of the cover means 46 for forming therebetween a generally fluid-tight connection. The connecting means 41 normally secures the cover means 46 to the hub means 38 (see Figs. 3 and 4) and prevents either rotational or lateral movement of the end portion 50 relative to the post portion 39.

The connecting means 41 provided by the invention is breakable only in response to the deliberate application of a force of a predetermined magnitude upon the cover means 46 relative to the axis of the post portion 39. Only by so breaking the connecting means 41 is the user able to initially separate the cover means 46 from the hub means 38. In the preferred and illustrated embodiments, the force which serves to break the connecting means 41 is applied rotationally about the post portion 39 by twisting the cover means 46. In accordance with the invention, the magnitude of the rotational force necessary to break the connecting means 41 is more than a nominal amount of force, such as that which would be provided by a mere interference fit between the members. Thus, the chance of accidentally breaking the connecting means 41 during handling is minimized.

However, also in accordance with the invention, the force required is not large enough to permanently rotationally deform either the cover means 46 or the post portion 39 of the hub means 38. Thus, as can be seen in Fig. 5, after the connecting means 41 has been broken, both the post portion 39 and cover means 46 remain physically intact and structurally unaltered to permit a subsequent rejoining of the open end portion 50 of the cover means 46 about the post portion 39.

Preferably, the cover means 46 is resiliently deformable about. its axis in response to a rotational force which is less than the rotational force at which the connecting means 41 breaks. As will be described in greater detail later herein, this provides further visual and tactile assurance of the integrity of the connecting means 41 prior to the time it is broken. However, and further in accordance with the invention, after the connecting means 41 has been initially broken, any subsequent return or removal of the cover means 46 from the hub means 38 can be accomplished with relative ease. Thus, there can be no question that the connecting means 41 has been broken and the sterile integrity of the needle 18 has been breached.

The connecting means 41 which enables this selectively breakable connection between the end portion 50 and the post portion 39 may vary. In the preferred embodiment, the means 41 takes the form of a limited, or yieldable, thermal bond 45 which is formed along the concentric interface of the open end portion 50 about the post portion 39. This limited thermal bond 45 purposefully arises from the careful matching of the material utilized for the cover means 46 to the material utilized for the portion 50, coupled with the careful choice of the optimal bonding area therebetween. More particularly, dominating the selection of all the materials for the hub and cover means 38 and 46 of the assembly 10 is the desirability that the assembly 10 be made of materials suitable for contact with human blood. It is also highly preferred that the entire assembly 10 be autoclavable.

With regard to the hub means 38, a polyvinyl chloride plastic material is well suited for use as the first member 22. With regard to the material of the post portion 39 (which, in the illustrated embodiment, constitutes the end 28 of the second member 24) additional selection preferences arise. For example, it is desirable that the material of the entire second member 24 be solvent bondable to the medical grade polyvinyl chloride tubing 16 to facilitate its attachment thereto, as well as be thermally bondable to the needle 18 in a manner which minimizes the chance of air gaps or voids in the bond through which blood and parenteral fluids can leak.

As discussed in the previously cited copending applications of Edward Garver, the second member 24 (and thus its end 28 constituting the post portion 39) is preferably fabricated from a polyester material comprising approximately 60% by weight of a thermoplastic polyetherester manufactured and sold by E.I- DuPont as HYTREL 4056 and approximately 40% by weight of a poly (ethylene terephthalate)-based copolymer manufactured and sold by Eastman Chemical Products, Inc. as KODAR™ PETG Copolyester 6763. This polyester material is autoclavable and exhibits superior bonding characteristics to the needle 18.

The selection of a polyester material for the post portion 39 to enable superior bonding characteristics to the needle 18, in turn, complicates the selection of materials for the cover means 46 to achieve the limited thermal bond 45 desired. For example, polypropylene materials, which are approved for blood contact and are autoclavable, are nevertheless unacceptable for use as the cover means 46. This is because polypropylene materials are chemically dissimilar to the polyester material of the post portion 39. As a result, unless the surface structure of the polypropylene materials is altered, for example, by flame treatment or corona discharge, it is not possible to affect any bond, thermal or otherwise, between the two materials, much less the desired limited bond 45.

Furthermore, the use of plasticized polyvinyl chloride series resin compositions, which are known and widely used autoclavable materials suited to blood contact, is also unacceptable. Such compositions are heat bondable to the compatible polyester material of the post portion 39. However, as with thermal bonds formed with these plasticized polyvinyl chloride resin compositions in general', the strength of the bond progressively increases as the heat history, or exposure, of the bond increases, reaching magnitudes well in excess of the torque resistance strength of the polyester post portion 39 (approximately 20 inch ounces). Referring to Example I in the following Table, it can be seen that, after being exposed to autoclaving (temperatures between approximately 230 F and 250ºF), it is necessary to apply a "take-off" torque consistently in excess of 22 inch ounces about the axis of the post portion 39 in order to break the thermal bond between the open end portion 50 of a vinyl cover means 46 and the polyester post portion 39. Rotational deformation of the post portion 39 results. Referring now to Example II in the following Table, it was found that the addition of coated calcium carbonate (Kotamite^™ calcium carbonate manufactured by Thompson-Weinman Company) to the vinyl did not adequately alter the thermal bonding characteristic of the polyvinyl chloride series resin composition so as to reduce the take-off torque below the torque resistance strength of the polyester post 39. After autoclaving, the resulting take-off torques were observed to vary between 19 and 26 inch ounces.

However, as can be seen in Example III of the following Table, it was discovered that the addition of a small amount (approximately 3% by weight) of silicone (Dow Corning 200, 12,500 Cs) to the vinyl did result in a significant alteration in the thermal bonding characteristic of the polyvinyl chloride series resin composition and led to a significant reduction in the strength of the thermal bond. After autoclaving, a defined range of take-off torques was provided, the greatest of which (17 inch ounces) was below the torque resistance strength of the polyester post portion 39.

As can be seen in Example IV of the following Table, it was further discovered that the addition of the coated calcium carbonate to the vinyl-silicone mixture further altered the thermal bonding characteristic of the polyvinyl chloride series resin composition, reducing the maximum take-off torque observed. The addition of calcium carbonate also led to a relatively more narrowly defined range of take-off torques than that associated with the vinyl silicone mixture alone. A more uniform finished product can thus result.

For example, sixty (60) cover means 46 were fabricated utilizing the composition of Example V in the following Table. After batch sterilization, all but six of the cover means 46 so constructed had a take-off torque which lay in the narrowly defined range of between 9 and 14 inch ounces. The maximum take-off torque experienced (one unit) was 16 inch ounces. The minimum take-off torque experienced (two units) was 8 inch ounces.

The effect of the calcium carbonate leading to a more narrowly defined range of take-off torques is surprising in light of Example II heretofore discussed.

The percent by weight of the polyvinyl chloride series resin composition in the above Table includes a polyvinyl chloride resin, a plasticizer (such as di-2-ethylhexyl phthalate), and suitable heat stabilizers (such as epoxidized vegetable oils and metal soaps). The resin composition is blended together in a rotational mixer, with the silicone being added with the stabilizers. After the blend is adequately mixed, the blend is discharged from the mixer into a ribbon blender/cooler, and the calcium carbonate is added directly to the blend. The resulting Jalend can then be extruded to form the cover means 46 shown in the drawing.

The take-off torque is measured about the axis of the polyester post portion 39 as the cover means 46 is rotated relative thereto.

Take-off torques which lie within the ranges associated with Examples III, IV, and V require a deliberate application of force, and are thus not susceptible of being inadvertently or accidently developed. Nevertheless, the deliberate application of force needed to generate take-off torques within this defined range is well within the physical capabilities of the average user without undue effort or fatigue. The more narrowly defined ranges of take-off torques associated with Examples IV and V are preferred, because they enable a more uniform finished product. In order to uniformly achieve the relatively narrowly defined range of take-off torques associated with Examples IV and V, it was determined that the surface area of the interface between the open end portion 50 and post portion 39, along which the thermal bond 45 is formed, is preferably between approximately .04 square inches and approximately .06 square inches.

Furthermore, in order to uniformly achieve the relatively narrowly defined range of take-off torques associated with Examples IV and V, it was determined that a heat exposure cycle of approximately 250°F for approximately 30 minutes is preferred to set the bond.

After this initial heat exposure cycle, the hub means 38 and attached cover means 46 can be handled and batch sterilized and pasteurized as a finished assembly 10, as shown in Fig. 2. The desired limited strength of the thermal bond between the cover means 46 and the post portion 39 (as measured in terms of the take-off torques expressed in the Table) does not significantly increase during the additional heat exposure occasioned by autoclaving and pasteurization.

For example, eighteen (18) cover means 46 were fabricated utilizing the composition of Example V and, together with the polyester post portion 39, were exposed to approximately 250°F for seventy-five (75)continuous hours. After this prolonged heat exposure, all but three of the cover means 46 so constructed had a take-off torque which lay in the narrowly defined range of between 9 and 14 inch ounces. More significantly, none of the cover means 46 had a take-off torque which exceeded 14 inch ounces. While the particular ranges of take-off torques associated with Examples IV and V can vary in absolute terms from those found in the Table according to the surface area of the bond 45 and the specific heat history utilized, they nevertheless have been observed to consistently remain below levels at which rotational deformation of the post portion 39 occurs. The bond 45 thus lends itself well to mass production, automated manufacturing techniques. By virtue of the limited thermal bond 45 as heretofore described, the assembly 10 is indeed "tamper-proof". As shown in Figs. 4 and 5, in order to initially remove the cover means 46, it is necessary to deliberately twist the cover assembly 46 relative to the hub means 38 until the requisite take-off torque is reached. It should be appreciated that the bond 45 could also be broken by laterally pulling on the cover means 46, but the effort involved in this technique would far exceed that associated with twisting.

Furthermore, the materials of Examples III, IV and V in the above Table are each semi-rigid and resiliently deformable in response to torques less than the requisite take-off torque. Thus, the presence of the bond 45, which normally serves to resist the twisting of the cover means 46 about the post portion 39, causes the cover means 46 to resiliently twist or deform about itself (see Fig. 4) before enough torque is developed to break the bond 45. This resilient twisting of the cover means 46 does not permanently deform the cover means 46. The user is thus able to quickly test the presence of the bond 45, and thus the sterile integrity of the needle 18, by observing whether or not it is possible to initially resiliently twist or deform the cover means 46 about itself, without effecting the subsequent ability to rejoin the cover means 46 about the post portion 39.

It has been further observed that the breakage of the bond 45 between the polyester material of the post portion 39 and the vinyl-silicone-calcium carbonate material of the cover means 46 (Examples IV and V) is accompanied by an audible "snapping" sound.

By virtue of the invention, if the cover means 46 can be removed from the hub means 38 without resilient deformation and/or without an audible "snapping" sound, this serves as a clear indication that the thermal bond 45 has in all likelihood been previously broken. The cover means 46 has thus probably been previously removed and returned. The sterile integrity of the needle 18 is subject to question. It has been further observed that the material of Examples IV and V relaxes in the presence of heat. By virtue of this desirable characteristic, the end portion 50 of the cover means 46 can be normally dimensioned for a tight interference fit upon the post portion 39. This fit temporarily secures the cover means 46 to the post portion 39 during the manufacturing process. This fit also provides 'intimate contact along the bonding area to facilitate the formation of a hermetic thermal bond. However, during heat exposure and the formation of the thermal bond 45, the end portion 50 of the cover means 46 relaxes and conforms to the exterior dimension of the post portion 39.

Thus, after the thermal bond 45 is broken, the end portion 50 of the cover means 46 is virtually free spinning about the post portion 39.

This free spinning fit greatly facilitates the removal of the cover means 46 at time of venipuncture and the subsequent return of the cover means 46 upon the post portion 39, if desired. It also serves as a further outward indication, that the bond 45 has been broken.

From the foregoing, it should be appreciated that the limited thermal bond 45 as heretofore described is broadly applicable for use in diverse situations whenever it is desired to removably secure one member (corresponding to the cover means 46) about an associated post member (corresponding to the post portion 39 of the hub means 38). The thermal bond 45 results in the tamperproof connection between the cover means 46 and hub means 38. This connection is hermetic in nature, and thus serves to preserve the sterile integrity of the needle 18 or 20 prior to use; it is purposefully limited in strength and is not effected by subsequent heat exposure, thus tolerating autoclaving and pasteurization; it provides a take-off torque below that at which deformation of the post portion 39 occurs, thus preserving the structural integrity of the post portion 39 for subsequent rejoining of the cover means 46; and it permits the user to quickly and easily determine whether the sterile integrity of the cannula has been compromised prior to venipuncture. Various of the features of the invention are set forth in the following claims.

Claims (15)

1. A method of altering the thermal bonding characteristics of a polyvinyl chloride series resin composition to enable the formation of a thermal bond with a compatible material, which bond is selectively breakable in response to the application of a force which does not cause permanent deformation of the series resin composition or compatible material, regardless of prolonged heat exposure, said method comprising the step of introducing silicone into the resin composition so that the resulting mixture includes approximately 3% by weight of the silicone.

2. A method according to claim 1 and further including the step of introducing calcium carbonate into the resin composition-silicone mixture so that the final mixture includes approximately 20 to 25% by weight of the calcium carbonate.

3. A method of forming between a member fabricated of a polyvinyl chloride series resin composition and a member fabricated of a polyester composition a thermal bond which is selectively breakable in response to the application of a force which does not cause permanent deformation of either member, regardless of prolonged heat exposure, said method comprising the steps of introducing silicone into the resin composition as it is being fabricated so that the resulting mixture includes approximately 3% by weight of the silicone, bringing the member made of the resulting resin composition-silicone mixture into contact with the member made of the polyester composition, and exposing the two members at their point of contact to heat sufficient to thermally bond the members together.

4. A method according to claim 3 and further including the step of introducing calcium carbonate into the resin composition-silicone mixture as it is being fabricated so that the final mixture includes approximately 20 to 25% by weight of calcium carbonate.

5. A member according to claim 3 or 4 and further including the step of fabricating the polyester composition of approximately 60% by weight of a thermoplastic polyetherester and approximately 40% by weight of a poly (ethylene terephthalate)-based copolymer.

6. A method according to claim 5 wherein said heat exposure step includes exposure att approximately 250°F for approximately 30 minutes.

7. A method according to claim 5 wherein said step of bringing the members into contact includes forming an area of contact of approximately .05 square inches.

8. A method according to claim 3 wherein said step of introducing silicone includes forming a mixture which includes more than 50% by weight of the resin composition and approximately 3% by weight of the silicone.

9. A method according to claim 8 and further including the step of introducing calcium carbonate into the resin composition-silicone mixture to arrive at a final mixture which includes approximately 72% to 77% by weight of the resin composition, approximately 3% by weight of the silicone, and the calcium carbonate comprising the remainder of the mixture.

10. In an autoclavable medical product implement, a method of forming between a first member and a second member a thermal bond which is selectively breakable in response to the application of a force which does not cause permanent deformation of either member, regardless of prolonged heat exposure, said method comprising the steps of fabricating the first member of a first chemical composition which includes more than 50% by weight of a polyvinyl chloride series resin composition and approximately 3% by weight of silicone, fabricating the second member of a second chemical composition which includes an autoclavable polyester material, bringing the first and second members into contact, and exposing the two members at their point of contact to heat sufficient to thermally bond the members together.

11. A method according to claim 10 wherein said first member fabrication step includes introducing calcium carbonate into the resin composition-silicone composition.

12. A method according to claim 11 wherein said first member fabrication step includes fabricating the first material so as to include approximately 72% to 77% by weight of the resin composition, approximately 3% by weight, of the silicone, and the remainder of the first material comprising calcium carbonate.

13. A method according to claim 10 or 11 or 12 wherein said second member fabrication step includes fabricating the second material to include approximately 60% by weight of the thermoplastic polyetherester and approximately 40% by weight of a poly (ethylene terephthalate)-based copolymer.

14. A method according to claim 13 wherein said heat exposure step includes exposure at approximately 250°F for approximately 30 minutes.

15. A method according to claim 14 wherein said step of bringing the two members together includes forming an area of contact of approximately .05 square inches.