A FLUID TRANSFER MEMBER AND ASSEMBLY WHICH INCLUDE A RADIANT ENERGY ABSORBING WALL HAVING OPTIMAL MELT CHARACTERISTICS

Abstract: A fluid transfer member (10) has a radiant energy absorbing wall (14) which melts in response to the application of radiant energy. In accordance with the invention, the melt characteristics of the wall (14) are optimized to the greatest possible extend by providing the wall (14) with a density, or opacity, to the applied radiant energy which lies in a range of between about 3 and about 12. The density is determined by multiplying the wall's radiant energy absorbance by the thickness of the wall (14).

Description: A FLUID TRANSFER MEMBER AND ASSEMBLY WHICH INCLUDE A .RADIANT ENERGY ABSORBING WALL HAVING OPTIMAL MELT CHARACTERISTICS FIELD OF THE INVENTION This invention generally relates to fluid transfer devices. In particular, this invention relates to fluid transfer devices which include meltable portions. BACKGROUND OF THE INVENTION Granzow et al U.S. Patent 4,157,723 concerns a fluid transfer device which uses a meltable, radiant energy absorbing wall to normally seal a conduit from communication with the atmosphere. The wall is melted in response to exposure to radiant "gυli $* OMPI energy to open a fluid path through the device. By coupling two of these devices together and then applying radiant energy to melt the walls, a sterile, hermetically sealed fluid pathway can be formed between the assembled devices. Other fluid transfer devices and assemblies which use meltable, radiant energy absorbing walls are disclosed in the following U.S. Patents: Ammann et al 4,265,280 Boggs et al 4,325,417 Ammann et al 4,340,097 This general type of fluid transfer device lends itself to use in systems in which fluids are transferred in a sterile, or aseptic, manner; for example, in blood component collection and processing systems; in chemical compounding and parenteral solution formation systems; and in fluid systems associated with peritoneal dialysis. Because these systems involve the transfer of human blood and sterile parenteral solutions, it is desirable that the performance characteristics of transfer devices and assemblies be optimized to the greatest extent possible. Conventionally, it is believed that the performance characteristics of a meltable, radiant energy absorbing wall can be best optimized by maximizing the density, or opacity, of the meltable wall to the applied radiant energy. For example, when the radiant energy applied is infrared energy and/or visible light, the meltable wall conventionally includes a relatively large percentage by weight of a carbon filler to maximize its opacity to these types of radiant energy. Surprisingly, however, in accordance with this invention, it has been discovered that the performance characteristics of a meltable, radiant energy absorbing wall are not optimized at these maximum opacity levels. SUMMARY OF THE INVENTION A fluid transfer member is provided comprising means which defines a meltable wall made of a radiant energy absorbing material. The wall normally seals the member from communication with the atmosphere. In response to the application of radiant energy, the wall melts, and an opening is formed in the wall. In accordance with the invention, the meltable wall has density, or opacity, to the applied radiant energy which lies within a specially defined range of density values. Density values falling within this defined range do not maximize the opacity of the meltable wall to the applied radiant energy. Nevertheless, within this range, the desirable melt characteristics of the wall are significantly better than in a wall having an opacity which falls above or below the range. More particularly, the invention provides a meltable wall which has a density, or opacity, to the applied radiant energy (hereafter referred to simply as the "D-value") which lies within the range of about 3 <. D-value <_ about 12. The D-value is dimensionless and is directly indicative of the degree of opacity of the wall. The D-value is determined by the formula: D-value = L. In this formula, <{) represents the radiant energy absorbance of the wall, φ is itself determined by the formula and is expressed in units per centimeter: ♦ = -lnCl/lo ] L In the above-identified formulas: (1) "In" represents the natural logarithm of the bracketed ratio; (2) "I " represents the intensity of the applied radiant energy as it enters the meltable wall, expressed in watts per square centimeter, or any derivative thereof; (3) "I" represents the intensity of the applied radiant energy as it exits the meltable wall, expressed in the same terms as I ; and (4) "L" represents the thickness of the meltable wall in centimeters along the path of the applied radiant energy. Preferably, in accordance with the invention, the D-value of the meltable wall, as above defined, lies within the range of about 4 < . . D-value <_. about 6. Most preferably, in accordance with the invention, the D-value of the meltable wall, as above defined, lies within the range of about 5.5 _ D-value_<. about 6.0. In one embodiment, the meltable wall is interposed between two fluid conduits to normally block communication therebetween. In this arrangement, an opening is formed the meltable wall in response to the application of radiant energy, thereby opening flow communication between the conduits. Other features and advantages of the invention will be pointed out in, or will be apparent from, the specification and claims, as will obvious modification of the embodiments shown in the drawings. DESCRIPTION OF THE DRAWINGS Fig. 1 is a perspective view of a fluid transfer system which employs a pair of fluid transfer members, each of which embodies the features of the invention; Fig. 2 is an enlarged side view, with a portion broken away and in section, of the fluid transfer members shown in Fig. 1 in an uncoupled relationship; OMPI Fig. 3 is an enlarged side view, with portions broken away and in section, of the fluid transfer members shown in Fig. 1 in a coupled relationship as radiant energy is being applied; Fig. 4 is an enlarged side view, similar to Fig. 3, but after the application of radiant energy and the formation of a fluid path between the members; Fig. 5 is a graph which plots the absorbance ( ) of a meltable radiant energy absorbing wall against the charcoal content of the wall; Fig. 6 is a graph which plots the diameter of the hole formed in the wall against the associated D-value; Fig. 7 is a graph which plots the temperature distribution across the wall against the associated absorbance (φ); Fig. 8 is a graph which plots the melt efficiency of the wall against the associated D-value; and Fig. 9 is a graph which plots the temperature uniformity across the wall against the associated D-value. 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. OMPI 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 EMBODIMENT A member 10 which is attachable to a conduit 12 is shown in Figs. 1 through 4. As can best be seen in Fig. 2, the member 10 comprises means which defines a meltable wall 14. When the member 10 is attached to the conduit 12, the meltable wall 14 normally seals the conduit 12 from communication with the atmosphere. In accordance with the invention, the meltable wall 14 is made of a radiant energy absorbing material. By applying radiant energy, the wall 14 is melted, and an opening is formed in the wall 14. Fluid communication is thereby opened with the associated conduit 12. As used herein, the term "radiant energy" broadly refers to energy which is in the form of electromagnetic waves, such as radio waves, infrared waves, visible light, ultraviolet waves, x-rays, and the like. Because the transfer of radiant energy requires no intervening medium, the transfer can be faster and more efficient than in conductive or convective heat transfer, both of which require an intervening medium. The member 10 may be variously constructed. In the illustrated embodiment, the member 10 includes body means 18 which is attachable to the end portion 20 of the conduit 12. In this arrangement, the meltable wall 14 is sealingly disposed on the body means 18 (see, in particular, Fig. 2). In response to the application of radiant energy, the wall 14 melts, and an opening is formed in the body means 18. In the illustrated embodiment, the body means 18 includes a housing 22 which defines a hollow interior 24 which communicates with the interior of the attached conduit 12. As is best shown in Fig. 2, the meltable wall 14 normally seals or closes the housing interior 24 from communication with the atmosphere. The housing 22 further includes a tubular conduit portion 26 which communicates with the interior 24 and which serves to interconnect the housing 22 with the conduit end portion 20. While the housing 22 may be variously attached to the end 20 of the conduit 12, in the illustrated embodiment, a hermetic, friction-fit between the end 20 and conduit portion 26 is envisioned. An elastic band 28, such as made from a latex material, preferably encircles the outer periphery of the junction to assure a fluid tight, hermetic fit. As shown in Fig. 1, the conduit 12 to which the member 20 is attached can itself be integrally connected with a container 30, such as a plastic bag. The container 30 can contain a fluid and be used to dispense fluids, or it can be empty and be used to receive fluids. In this arrangement, a manually operated inline valve member 32 (shown in phantom lines in Fig. 1) is preferably provided to normally prevent fluid communication between the container 30 and the housing interior 24. While the valve member 32 may be variously constructed, in the illustrated embodiment, it takes the form of a manually frangible valve member, such as that disclosed in Carter et al, U.S. Patent 4,294,247. Alternately, the valve member 32 may form an integral part of the member housing 22, such as disclosed in Ammann et al U.S. Patent 4,340,097. The material from which the meltable wall 14 is constructed is preferably selected to melt only at temperatures which result in the destruction of bacterial contaminants on the surface of the material (i.e., over 200 β C). In this preferred arrangement, the wall 14 can be opened only in conjunction with an active sterilization step which serves to sterilize the regions adjacent to the fluid path as the fluid path is formed. Also preferably, the housing 22 is made of a material which absorbs the applied radiant energy in lesser amounts than the wall 14. Most preferably, the housing 22 is relatively nonabsorbant of the particular type of radiant energy applied. 1 π By virtue of this construction, as radiant energy is applied to melt the wall 14, the housing 22 itself is not heated to any great extent. Rather, the housing 22 serves to pass the radiant energy directly to the wall 14. The transfer of radiant energy is fast and efficient. The particular material selected for the member 10 depends largely upon the type of radiant energy which is to be applied. Conventionally, radiant energy which includes infrared and/or visible light is used. In this arrangement, the member 10 is conventionally made of a material fabricated from poly(4-methy1-1-pentene), which is sold under the trademark TPX by Mitsui Chemical Company. This material has a crystalline melting point of approximately 235°C and is further discussed in Boggs et al, U.S. Patent 4,325,417. The meltable wall 14 conventionally contains large amounts by weight of a carbon filler so as to absorb radiant energy in the infrared and visible light band. The housing 22 is conventionally free of the filler and is thus relatively transparent to (i.e., generally nonabsorbant of)" this band of radiant energy. The member 10 as heretofore described can serve by itself to seal the end portion 20 of the conduit 12 from communication with the atmosphere until time of use. The application of radiant energy opens the wall 14 at the time fluid flow through the conduit 12 is desired. ■ -TEAZ OMPI Alternately, a pair of the members 10 may also be used to form a fluid transfer assembly 40 to form a connection between two fluid containers 30 and 31. More particularly, in the transfer assembly 40, the member 10 includes coupling means 34 for bringing the meltable wall 14 of one member 10 into facing contact with a corresponding meltable wall 14 of a second member. The second member is preferably constructed identically to the member 10 heretofore described. Because of this, the second member is also designated by the numeral 10 in Figs. 1 through 4. Other structural elements common to the first and second members 10 are likewise identified with the same reference numerals heretofore assigned. The coupling means 34 may be variously constructed. In the illustrated embodiment, the coupling means 34 takes the form of mating bayonet-type coupling mechanisms 36 which interlock the members 10 together with their radiant energy absorbing walls 14 in facing contact (see, in particular, Fig. 3). When exposed to a source 38 of radiant energy spaced from the assembly 40, the radiant energy absorbing walls 14 jointly melt and fuse together, as can be seen in Fig. 4. A fusion bond between the walls 14 is thereby formed. In the process of melting, the walls form an opening 16 which establishes through the members 10 a fluid path which is at once sterile and hermetically sealed about its periphery to communication with the atmosphere. Certain characteristics are desirable for each of the members 10 to optimize the performance of the assembly 40. These desirable characteristics include: (1) The opening 16 which is formed should be large enough to allow unimpeded fluid flow through and between the members 10. In this respect, it is believed that the diameter of the formed hole should approximate the interior diameter of the associated conduit 12. For example, in the case of conventional blood flow tubing, the desired minimum hole diameter is about .10 inch; (2) The fusion bond which is formed between the walls 14 during the melting process should be strong enough to protect against an accidental separation of the members 10. The fusion bond will thus protect the system 40 against an inadvertant breach in sterility. (3) As radiant energy is being absorbed by the walls 14, the resulting increase in temperatures should be distributed uniformly through each of the meltable walls 14. This uniform temperature distribution minimizes the likelihood that the localized areas of high temperatures, or "hot spots", develop during the melting process. A uniform temperature distribution reduces the potential of volatile production and a "splattering" or "bubbling" of either meltable wall 14 during the melting process; and (4) A favorable melt efficiency should be provided, so that relatively low power sources of radiant energy can be used. A favorable melt efficiency also minimizes the time involved in melting each of the walls 14. Conventionally, it has been believed that the performance characteristics of the members 10 could be optimized only by maximizing the opacity of the meltable walls 14 to the particular type of radiant energy applied. For example, a source of radiant energy which has been used is a incandescent quartz lamp which has a tungsten filament operating at about 3150 β K. This lamp emits radiant energy which lies in a continuous band encompassing mostly infrared and visible energy, although some ultraviolet radiation is included. When this source of radiant energy is utilized, the TPX material of the wall 14 conventionally contains about one percent (1%) activated charcoal by weight to maximize, to the fullest possible extent, the wall's density to the radiation band emitted by the tungsten lamp. However, in accordance with the invention, it has been discovered that, in order to optimize the melt characteristics of the radiant energy absorbing wall 14, the wall 14 must have a density, or opacity, to the applied radiant energy which lies only within a specifically defined range. More particularly, it has been discovered that the melt characteristics of the radiant energy absorbing wall 14 are optimized only when the radiant energy density of the wall (referred to as the "D-value") lies within the range of between about 3 4. D-value ≤.about 12. The D-value is a dimensionless quantity and is a function of the thickness of the wall and the ability of the wall to absorb the applied radiant energy per unit of thickness. More particularly, the D-value is determined by the formula: D-value = φ L In this formula, φ represents the radiant energy absorbance of the wall per unit of thickness and is itself determined by the following formula: φ = -In Cl/Io] L In the above the formulas, "I " represents the intensity of the applied radiant energy as it enters the wall 14 and is expressed in terms of watts per square centimeter or any other derivative thereof, such as amps, volts, lamberts, lumens, etc. "I" represents the intensity of the applied radiant energy as it exits the wall 14 and is expressed in the same term selected for Io. The numerator of the formula by which φ is determined is the natural log (In) of the ratio between I and Io and is itself negatively signed, because the ratio is a fraction. A negative sign is therefore provided before "In" in the above formula to convert φ to a positive number. In both formulas, "L" represents the thickness of the area to be melted measured along the path of radiant energy. L is expressed in centimeters. When only a single wall 14 is to be melted, L represents the thickness of only the single wall 14. However, in the case of an assembly 40 of two walls 14, as shown in Fig. 3, L represents the combined thickness of both walls 14, i.e., generally twice the thickness of the single wall 14. The range of D-values, as defined in accordance with the above formula, applies universally to any type of meltable radiant energy absorbing material, as well as to any type of radiant energy used to melt the absorbant material. When the D-value lies within the range of about 3 to about 12, acceptable hole formation and fusion bond strengths are encountered at favorable melt efficiencies and with a generally uniform distribution of temperatures across the area to be melted. ** ■- ' The range of D-values as above delineated is believed to be critical. This is because, below about 3, extremely unfavorable melt efficiencies are encountered, while above about 12, the distribution of temperatures across area to be melted becomes increasingly non-uniform and generally higher localized temperatures, or "hot spots", can occur. "Hot spots" can cause decomposition of the wall material. They can also lead to substantially higher gaseous diffusion rates and result in undesirable "bubbling" or "splattering" on the surface of the wall 14. However, when the area to be melted has a D-value which lies within the range of about 3 to about 12, temperatures are distributed relatively uniformly across the entire area to be melted, and localized hot spots do not occur. Furthermore, it has also been surprisingly discovered that, when the D-value of the facing walls in an assembly 40 falls within this prescribed range, the fusion bond between the members 10 of the assembly 40 is stronger than when conventional walls having maximum opacity are used. Preferably, the range of D-values is between about 4 and about 6. Within this narrower sub-range, it has been discovered that melt efficiencies are maximized to the greatest extent possible. Most preferably, the range of D-values is between about 5.5 and about 6.0. Within this narrowest sub-range, it has been discovered that both hole size and melt efficiency are maximized to the greatest extent possible. The invention can be further understood by reference to the following examples. OMPI EXAMPLE 1 [Absorbance (φ)] Five separate blends of the TPX material laden with activated charcoal were fabricated as follows: Charcoal Content Blend Deisignation % by Weight VI .1239 V2 .2481 V3 .3726 V4 .4975 V5 .6226 V6 (Conventional) .9901 The blends were used in the meltable walls 14 for members 10 constructed as shown in Figs. 1 through 4. A model Number 325H-PC Hughes helium neon laser was used as the source of radiant energy. The laser emits radiant energy having a wavelength of 6328 Angstroms. A 10 mm lens was used to broaden the beam. The diverging beam was aligned to impinge upon a silicon sensor photo detector which was located about 3.5 inches from the 10 mm lens. The photo detector was used in the closed loop current mode, and the current was measured on a Model 3465A Hewlett Packard Digital Multimeter. Each wall to be measured was placed in the beam at a distance of about 2.25 inches from the lens. The intensity of the radiant energy was determined both before and after each wall was inserted in the beam path. Mean and standard deviations were determined. The ratio of the detected entering and exiting intensities, i.e., I and I, respectively, was calculated . Four samples of each of the six different blends were used to determine the absorbance (φ) of each of the blends per centimeter of thickness. The following, heretofore described formula was used: φ = -ln(l/lo) L Table 1 summarizes absorbance (φ) obtained. In Table 1, φ is expressed in units per centimeter of wall thickness. Figure 5 is a graphic display of Table 1. TABLE 1 ABSORBANCE (φ ) Charcoal Photocurrent in milliamps Transmittance Thickness Absorbance ( Blend Content % Pre Post Std Dev cm per cm By Weight (I) do) (I/Io) in thickne VI .1239 3.670 .936 .149 .255 .0495 27.3 V2 .2481 3.690 .188 .070 .051 .0495 58.6 V3 .3726 3.700 .0525 .0197 .0142 .0495 85.9 V4 .4975 3.710 .00945 .00184 .0026 .0508 120.2 V5 .6226 3.715 .0115 .0051 .0031 .0502 115.1 V6 .9901 3.722 .0012 — " - " —• .00032 .0305 263.6 As can be seen in Fig. 5, the absorbance (φ) progressively increases as the percent of activated charcoal by weight in the wall increases. As will be demonstrated in Example 8, once a desired absorbance (φ) is known, one can refer to Fig. 5 to readily determine what percent by weight of activated charcoal is required. In Fig. 5, the slope of the curve is believed to be universally applicable to virtually any type of base material which is laden with activated charcoal and which has, before the addition of the activated charcoal, an inherent absorbance value of zero (i.e., it is virtually nonabsorbant of radiant energy) . The origin of the curve in Fig. 5 will change, however, if the initial or inherent absorbance of the particular base material is greater than zero. For example, if the inherent absorbance of the base material is 50 per centimeter, the applicable curve will shift and appear as shown in phantom lines in Fig. 5. Similarly, the slope of the curve itself may change if a material other than activated charcoal is used to render the base material absorbant to the applied radiant energy. In other words, just as the origin of the curve represents the inherent absorbance of the base material, the slope of the curve represents the inherent absorbance of the material which is used to render the base material radiant energy absorbant. EXAMPLE 2 (Hole Formation) A reflectively focused 8 volt, 50 watt Osram lamp, type 64607, with a focal length of approximately 1.5 inches was mounted in a lamp holder located on an optical bench. The lamp was powered by a fixed voltage power supply. Twenty each assemblies 40 with wall blends VI through V6 were separately loaded into the fixture at the focal point of the lamp and exposed to the focused radiant energy emitted with the power supply set at about 6.0 volts. In these assemblies 40, the area to be melted consisted to two walls 14 of the same blend positioned in facing contact. The assemblies 40 were exposed to the radiant energy for various amounts of time, ranging from about 5 to about 20 seconds. After the fluid path between each assembly 40 was opened, the assembly 40 was visually inspected for "bubbling" and "splattering" on the surface of the joined walls 14. These results are independently reported in Example 7. Each assembly 40 was then sectioned to gain access to the formed hole for measurements of hole size by a pin gauge technique. Table 2 summarizes the hole formation data obtained. Except where noted, the statistical evaluation is based upon a sample size of five (5). Figure 6 is a graphic display of the results summarized in Table 2. OMPI TABLE 2 CONSTANT VOLTAGE HOLE FORMATION THROUGH A PAIR OF WALLS Hole Size (Pin Gage) - inches Blend Absorbance(φ) D-value of the 7 sec 10 sec 15 sec 20 sec Of Each Area to Be Individual Melted (Fn 1 Wall per Centimeter of Thickness Nom Std Dev Nom Std Dev Nom Std Dev Nom Std Dev VI 27.3 2.7 No Hole m m .0875 .0021 .1266 .0056 .1410 .0070 V2 58.6 5.8 Pin Holes .0992 .0032 .1318 .0044 .1474 .0038 V3 85. 8.5 No Hole .0920 .0034 .1238 .0067 .1424 .0051 V4 120.2 12.2 No Hole .0994 .0049 .1250 .0074 .1356 .0069 V5 115.1 11.6 No Hole — .0946 .0030 .1246 .0106 .1342 .0061 V6 263.6 16.0 No Hole .0966 .0016 .1230 .0035 .1316 .0043 Footnote li D-value is determined according to the heretofore defined formula (D-value >> -) L), where L represents the combined thickness of two assembled walls, i.e., twice their individual thickness. As can be seen in Fig. 6, the diameter of holes formed in assembled walls having D-values of about 3 to about 12 is substantially equal to or better than the holes formed in the assembled walls having higher D-values. As can be also seen in Fig. 6, surprisingly, when the D-values lie in the sub-range of about 5.5 to about 6.0, hole formation characteristics are optimized at all exposure times. EXAMPLE 3 (TENSILE PULL TEST) The force required to pull apart the fused assemblies using either the V2 blend (D-value 5.8) or the conventional V6 blend (D-value 16.0) was determined using an Instrom Tensile Test Machine. The results are summarized in Table 3. TABLE 3. Failure Point Connector Pounds V6 16.5 V6 5 .5 V6 20.5 V6 22 .0 V6 19.5 V2 26.0 V2 26.0 V2 25 .0 V2 23 .5 V2 25.5 > * K Xϊ OMPI ^ , ΕO As can be seen, surprisingly, the V2 blend, which has an D-value of only 5.8, has a significantly higher tensile strength than the conventional blend V6, having a much higher D-value of 16.0. EXAMPLE 4 (TEMPERATURE DISTRIBUTION) An accurate mathematical model was developed to predict the temperature distribution across the meltable wall as the hole is formed. To develop the model, the heat transfer equation was solved in closed form and evaluated at different points in time. In developing the model, the following assumptions were made: (1) That thermal properties, such as heat conduction and capacity, remain constant with time, temperature, and charcoal content; (2) That there is no heat loss from either the front surface or back surface of the walls, i.e., insulated walls; (3) That the two walls are in intimate contact in the assembly (as shown in Fig. 3) with no thermal contact resistance existing between them; and (4) That the radiant energy absorption is non-specular. The model was reduced to a boundary value problem and was solved using an integral transform technique that removes the space variable. The integral transform and its inversion formula used, along with the general solution for heat conduction in a single dimension of finite length, is detailed in Ozisik, M.N., Boundary Value Problems of Heat Conduction, 1968, International Textbook Company. The absorbed radiant energy enters the solution by way of the heat generation function. A definition of the symbols used in the mathematical model appears in Table 4. OMPI 2 6 TABLE 4 Definition of Symbols Symbol Definition Units C P Specific Heat cal/gm "C k Thermal Conductivity Cal cm/sec cm 2 P Density gm/c α Thermal Diffusivity = k/p C p cm 2 /sec L Thickness of the Area cm To Be Melted τ o Incident Lamp Intensity cal/sec cm 2 Φ Absorptivity 1/cm X Distance Into Membrane cm t Time sec T Temperature °C g Heat generation term cal/cm 3 sec ζ Thermal time constant = l/α(ττ/L) 2 sec XX Pi 3,1415927 The following briefly summarizes the steps used in developing the model. The local intensity was expressed: = I - φ The heat generation term, or energy deposition rate, was expressed : g = dl/dx = Io φe-Φx The resulting boundary value problem of heat conduction was given by the following system of equations: 3 2 T + g (x t) ■ 1 3T in 0 < x < L ; t > 0 3 x 2 ό 3t - ~ + h£T = f x (t) for x = 0, t > 0 + k + h 2 T = f 2 (t) for x = L, t > 0 T = F(x) in 0 < x < L; t = 0 The boundary conditions that apply to the meltable membrane wall are (1) that, since it is assumed that there is no heat loss through either the front or back face of the wall, then f.(t) = f ? ^ 1 "- ~ -*' an<:i 2 ) that the initial temperature (T) is 0. When the boundary conditions and heat generation term are substituted into the above-described system, and solved by methods outlined in the foregoing Ozisik reference, the following solution results: -φL <-• m -φL MTTX) „ (ππr) 2 t λ T(x,t) = Io(l-e)αt + 2Io ∑ (l-(r) e )Cos L 1-1 Lk. Lk (1+ (-π φL) ~ ) (rn-V ) ~ m = 1 where m = 1, 2, 3, . . . OMPI « 2 8 In the above solution, the factor: - α(ro ττ) 2 t L will hereafter be referred to as the "transient function". The temperature distribution solution is solved for time periods after the above-identified transient function has decayed, using the material properties of TPX (Mitsui Grade RT18) as found in Table 5: TABLE 5 Properties of Polymethylpentene (TPX, Mitsui Grade RT18) ' Density = 0.833 gm/cm 3 Melting Point Tm = 240 β C Thermal Conductivity k = 4.x 10 cal cm/sec cm 2 Specific Heat Cp = 0.47 cal/gm β C Thermal Diffusivity (Calculated) = 1.0 x 10 cm 2 /sec Heat or Fusion hf = 45 cal/gm Figure 7 plots the temperature distribution across the meltable wall for several absorbance values (<)), based upon the foregoing solution and using only a single source of radiant energy. In Fig. 7, the "incident face" is the side of the meltable wall facing the radiant energy source. 2 9 As can be seen in Fig. 7, the temperature distribution becomes increasingly more uniform (i.e., a "flatter" distribution curve) across the wall as absorbance (φ) values decrease. Therefore, with decreasing absorbance, the chance of localized "hot spots" and the attendant undesirable "bubbling" or "splattering" will diminish significantly. The conventional formulation (V6) has an absorbance of about 250 per centimeter, placing its temperature distribution somewhat between E and F in Figure 7. EXAMPLE 5 (Theoretical Melt Efficiency) Using the mathematical model heretofore described, the energy required bring the far side of the wall (i.e., the side opposite to the incident face) up to a given temperature can be calculated as a function of D-value. This relationship is directly indicative of the melt efficiency of the wall 14. This plot is shown on Figure 8, and has been normalized to the energy requirements at infinite absorbance. Fig. 8 clearly shows that maximum melt efficiencies occur at D-values of between about 3 and about 6. At D-values below about 3, melt efficiencies significantly deteriorate. It is significant to recall that, as shown in Fig. 6, hole formation is also optimized within the same range of D-values at which optimal melt efficiency is achieved (i.e., between about 3 and about 6). "ξV E OMPI V^ IPO EXAMPLE 6 (Theoretical Temperature Uniformity) Using the model, the temperature differential between the incident face and the far side face can be plotted as a function of D-value. The results are shown in Figure 9. Fig. 9 clearly shows that, as the D-values are successively reduced from about 12 toward 3, the distribution of heat across the wall becomes increasingly more uniform. Thus, the formation of localized "hot spots" is avoided. Actual data confirms the validity of the foregoing theoretical model in generally assessing the melt characteristics of a radiant energy absorbing wall. For example, the model indicates that the principal effect of lowering the D-value is to reduce the range of temperature existent within the wall during the melting phase (see, in particular. Figs. 7 and 9). The model also indicates that the energy requirements are optimized in D-values falling within the range of about 3 to 6 (see, in particular, Fig. 8). Actual data confirms these indications. For example, the tensile pull tests (Example 3) confirm that increased fusion strengths occur at lower D-values. This is because, at lower D-values, the heat penetrates deeper into the wall as a result of the more uniform temperature distribution indicated by the model, and the melt zone does become, in fact, more uniform. Furthermore, as Example 7 confirms. "hot spots" and attendant "splattering" and "bubbling" are in fact eliminated at lower D-values. This confirms that more uniform distributions of temperatures do in fact occur at lower D-values, as again indicated by the model. EXAMPLE 7 ("Splattering") The "splattering" characteristic of conventional walls (V6 blend) is demonstrably avoided with materials of lesser D-values. More particularly, during the test conducted in the foregoing Example 2, the splattering phenomona was noted for all of the walls of the conventional V6 blend for both the 15 and 20 second exposures. Splattering was most serious at the 20 second exposure. On the other hand, there was no detectable splattering of any of the five blends VI through V5 having lesser D-values at any of the exposure levels. From the foregoing Examples 1 through 7, it can be seen that, at D-values of between about 3 and about 12, significant improvements in the overall performance characteristics of a meltable, radiant energy absorbing wall can be achieved. These improvements are more apparent at D-values of between about 4 and about 6, and most apparent at D-values of between about 5.5 and about 6.0. The following Example 8 is provided to illustrate how the invention can be used in selecting a meltable radiant energy absorbing wall having optimal melt characteristics. - REAtT" OMPI 3 2 EXAMPLE 8 (Hypothetical) (1) Assume that one requires a meltable wall having a overall thickness (L) of about .06 cm. To obtain the most preferred D-value of about 6, the absorbance (φ) must be about 100 per centimeter; i.e., if D-value = φ L, then φ = D-value L By referring to Fig. 5, one can see that approximately .35% by weight of activated charcoal is required to achieve this absorbance level. (2) Assume that one has a thermoplastic blend containing about .5% by weight of activated charcoal. By first referred to Fig. 5, one can determine that this blend has an absorbance (φ) of about 150 per centimeter. If one wants to use this blend as a meltable radiant energy absorbing wall having optimized melt characteristics (i.e., a D-value of about 6.0), the thickness of the meltable wall should be about .04 cm; i.e., L = D-value Φ It should be appreciated that, in either of the foregoing hypothetical examples, the absorbance (φ) could be determined experimentally, without the use of Fig. 5. Various of the features of the invention are set forth in the following claims.

Claims: CLAIMS 1. A member attachable to a conduit and comprising means defining a meltable wall made of radiant energy absorbing material for normally sealing the conduit from communication with the atmosphere and for forming, in response to the application of radiant energy to melt said wall, an opening in said wall, said wall having a Density to the applied radiant energy which lies within the range about 3 . Density _ about 12, wherein Density = φ L; and wherein represents said wall's absorbance of the applied radiant energy, expressed in units per centimeter, as determined by the formula: Φ = -lnCl/lo] . L and in which In represents the natural logarithm of the bracketed ratio [i/lo]; I represents the intensity of the applied radiant energy as it enters said wall, expressed in watts per square centimeter or any derivative thereof; I represents the intensity of the applied radiant energy as it exits said wall, expressed in L represents the thickness of said wall in centimeters. 2. A member according to claim 1 and further including body means attachable to the end portion of the conduit, and wherein said meltable wall is sealingly disposed on said body means and is operative for forming, in response to the application of radiant energy to melt said wall, an opening in said body means. 3. A member according to claim 2 wherein said body means is made of a material having a density to radiant energy which is less than said wall. 4. A member according to claim 2 wherein said body means is made of a material which, compared to said wall, is relatively nonabsorbant of the radiant energy absorbed said wall. 5. A member according to claim 1 wherein said meltable wall is made of material having a melting temperature of at least 200 β C. 6. A member according to claim 1 wherein said Density is between about 4 and about 6. 7. A member according to claim 1 wherein said Density is between about 5.5 and about 6.0. 8. An assembly for sealing and connecting the end portions of a pair of conduits, said assembly comprising housing means having walls enclosing a hollow interior, said housing means further including spaced first and second passage means each communicating with said hollow interior and each adapted for communicating with a respective conduit end portion. meltable wall means extending across said hollow interior in the interval between said spaced first and second passage means, said meltable wall means being made of a material having a Density to the applied radiant energy which lies in the range of about 3 _<__. Density ≤. about 12, said wall means being operative for normally blocking flow communication between said first and second passage means through said hollow interior and for forming, in response to the application of radiant energy through said housing means walls to melt said meltable wall means, an opening establishing flow communication between said first and second passage means through said hollow interior, wherein said Density = φ L; and wherein φ represents the absorbance of said wall means of the applied radiant energy, expressed in units per centimeter, as determined as follows: φ - -lnCl/lo] . L and in which In represents the natural logarithm of the bracketed ratio Cl/lo]; I represents the intensity of the applied radiant energy as it enters said wall, expressed in watts per square centimeter or any derivative thereof; I represents the intensity of the applied radiant energy as it exits said wall, expressed in - MEAl OMPI 3 L represents the thickness of said wall means in centimeters. 9. An assembly according to claim 8 wherein said Density of said meltable wall means is between about 4 and about 6. 10. An assembly according to claim 8 wherein said Density of said meltable wall means is between about 5.5 and about 6.0. 11. An assembly according to claim 8 wherein said meltable wall means has a melting temperature of at least 200 β C. 12. An assembly according to claim 8 wherein said walls of said housing means are made of a material having a Density to the applied radiant energy, as determined in the same manner for said meltable wall in claim 8, which is less than about 3. 13. An assembly according to claim 12 wherein said Density of said housing means wall is less than about 1.

Inventors: BILSTAD ARNOLD C, BROWN RICHARD I, FOLEY JOHN T, BILSTAD, ARNOLD, C., BROWN, RICHARD, I., FOLEY, JOHN, T.
Applicants: BAXTER TRAVENOL LAB, BAXTER TRAVENOL LABORATORIES, INC.
Application year: 1983
Main classification: B65B3
IPC codes: A61J1, A61M39, B29C65, F16L37