CA2008165C

CA2008165C - Method of connecting plastic tubes using high frequency dielectric heating

Info

Publication number: CA2008165C
Application number: CA 2008165
Authority: CA
Inventors: Toshiharu Matsumiya; Tatsuhiko Kawaoka; Kazuo Sakamoto; Hiroshi Ogawara; Shozo Shiraishi; Hiroshi Honda
Original assignee: Sekisui Chemical Co Ltd
Current assignee: Sekisui Chemical Co Ltd
Priority date: 1989-01-20
Filing date: 1990-01-19
Publication date: 1994-08-16
Anticipated expiration: 2010-01-19
Also published as: CA2008165A1; EP0379380B1; US5093546A; EP0379380A3; JPH02192929A; DE69023519D1; EP0379380A2; DE69023519T2; JP2554733B2

Abstract

ABSTRACT OF THE DISCLOSURE

A method of connecting plastic tubes by high-frequency heating comprising preparing an electrode block having at least two electrode members each having annular bores aligned with each other, the electrode block including at least one insulator interposed between the electrode members, the insulator having a bore aligned with those of the electrode members, inserting an end portion of one tube into the one electrode member and an end portion of the other tube into another electrode member so that both tube ends keep contact with each other in the bore of the insulator, and applying a high frequency voltage between the electrode members.

Description

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BACKGROUND OF THE I2~JENTION
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1. Field o~ the invention:
The presen~ lnvent;ion relates to a method of S connecting plastic tubes by high-frequency heating, and more particularly to a method of connec~ing plastic tubes by hlqh-frequency heating ~o as ~o ensure a long, i con~inuous aonduit. The conduits are partlcularly adaptad for medical applications wha~e no hygienic ;~ 10 problems are per~ittad.

2. Description o~ ~he prior art:
To ef fect the connection between f lexible ~:
plast~c tubes or pipes such as those of polyvinyl 1 15 chlorlde~ there are at least three methods; one is a :j method of using an adheslve, another is a method of ' utilizing the fusible nature of the plastic tubes, ;l commonly called the "thermal sealing method", and the ;; third one is a method of hi~h-~re~uency heat. The 20 adheslve me~hod is s~l-explanatory. The thermal I sealin~ me~hod ~onsists o fusin~ the tube ends to be ! Joined under pressure s~ as to ensure the joint therebetween. A typlca} exa~ple of the high-frequency ¦ heating method ls disciosed in Japanese Laid-Open Patent Publ~cation NoO 5~-178214. ~his high-frequency hea~ing method consi~t~ of abutting tube ends to ~e ~oined wlthin a cylind~ical suter electrode with an inner electrode being inserted in the tubes, and then `~ applying a high frequency volta~e between the inner and outer eleatrodes. The tube ends fuse and become joined. There is a~other method o~ combining the adhesive method and the ~usion ~oint method.
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~' . A disadvantage of t:he adhesi~e method is that organic solvents such as tetrahydrofuran and cyclohexa-non contained in the adhesive are likely to remain in the ~oined tube ends and harm patien~s' health when ~he tubes are used for medical treatments such as flood transfusion and oatheters,. A transfusion bag is legally prohibited from containing an adhasive. Fox I medical applications the adhesive method must be avo~ded because of hygienic ~onsiderations.
,, 10 A disadvanta~ o the heat sealing method is ~` ;
; that the surface o ~lexible tube are likely to become carbonized be~ore ~t reach a Pusible temperature. This makes the tubes difficult to use in catheters. In ' 15 addition, tha joint strength is not sui`ficient.
, The high-fre~uency heatlng method described above has the ~ollowing disadvantages:
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i 20 One i~ a hyg~enic p~oblem. As described above, the inner electrode is inserted into the tubes, , whioh is likely to introduce germs and/or dirt into the ! tubes and unhygienically contaminate the insides :j th~reof. Anoth~r disadvantage is tha~ the inner 1 25 electrode must be manually inserted, which consumes 3 labor and time. A fu~ther disadvantage is that the tube ends may contract and tightly constrict around the ~ surface o the inner electrode to such an extent that J the interfacial adhesion prevents the inner electrode 30 from being pulled out of the tubes. ThiS also con~umes ¦ time and labor before the electro~e is wlthdrawn from the tubes. A still further disadvantage is that th~s method can be only appllcable when the tubes are open .j ,- ~.

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at both ends. I~ ~he tu~es are closed at one end, the inner electrode would be confined in the conduit and could not be extracted there~rom. The applicability o~ the method is limited.

' There i~ another high-freguency heating method, which is disclosed in Japanese Laid-Open Patent Publication No. 59-232820. ~h$s pr~or method is des~gned t~ ~oin plastic plates. According to this ,~ 10 method, plastic plates are overlaid ln their end po~tions, and a pair of electrodes are placed on one of the plates, most often on the upper plate. An insulato~
; ls disposed between the two electrodes. A high-frequency vol~age is applied between the electrodes.
15 If thls method is applicable to the joining of tubes, it would be advantageous in (1) that an unhyglenic condition is unli~ely to occur, (2) that the bother of lnsertln~ an inner el~c~rode lnto the tubes is eliminated, and (3) that the method can be applied to 20 any ~ype of tube whether they may be closed at both ends or not. However,. when tubes a~e to ~e joined by th~s method, it is unavoidable that the tubes be I rotatad so as to ensure the peripheral fusion joint.
~ ~he rotation o~ tubes requires the provision of a '~ 25 rotor, which increases the production cost and prolongs the operation tim~. Neverth~less, it is likely that the . ~oint would be ~ ncompletP.
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? SuMMARY OF THE INVENTION
~ 30 j Accordingly, an object of the present ::~
invention is to provide a method of connecting plastic tubes without causing any unhygienic condition.

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; Another object of t:he present invention is to provide a method of connecting plastic tubes firmly and with less labor and time.

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According to an aspect of the invention there is provided a method of connacting plastic tubes by high-frequency heating, the method comprising the steps of . preparing an electrode block having a first electrode member and a second electrode member each having annular operation ~ 10 bores aligned so as to communicate with each other, the i electrode block including an insulator interposed between the ; first and the second electrode members, and the insulator having a bore aligned with the bores of the first and second electrode members, wherein the electrode block includes a third electrode member between the first electrode member and the second electrode member, and a further insulator so that the adjacent electrode members have one insulator therebetween, the third electrode member having a bore aligned with the bores of the first and second electrode members, inserting an end portion of one tube into the first electrode member and an end portion of the other tube into the second electrode member so that both tube ends are placed in contact with each other in the annular operati.on bores and applying a high ~requency voltage between the first and third electrode members, and between the third and second electrode members.
, Other objects and advantages of the present invention will become imore apparent for the detailed description given hereinafter; it should be understood, : :

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~S)~B1~5 ht)wev~r, that the detailed de~cript~on and specific embo~iment are given ~y way o~ illu3tration only, since varlous changes and modi~icatlon~ wlthin the spirl t and scope o~ the invention wlll become a~parent to those skilled in the ~rt ~rom this deta~led descrlption.

Thus, the joint betwaen tubes is flrm and sa~e from contamination from germs and dirt, part~cularly with an organic solvent. As a result, the conduits obtaine.d according to the present invention ar~ particularly adapted for use in ~edical treatment and medical appliances. In carrying out the method, the bother of manually inserting and withdrawing the electrode is eliminated, thereby avoiding the consumpt~on o~ time and labor.

~RIEF DESCRI~TlON OF THE D~AW~NGS

Thls inventlon may be better under~tood and :
20 i~s numerous ob~a~s and advantages will become appar- : ~
ent ~o ~hose skilled in the art by seference to the ~ .
accompanying drawing~ as follows: ~

Flg~re 1 is a sectional view showing an .
example o~ the em~odimsnt according to the present invention.

Flgures 2 to 4 are sectional views showing various modified examples of the embodiment.

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' E;SCRIPTION OF THE PP~EFER~ED EMBODIMENTS

Referring to Fig. 1 ther~3 i5 provided a elactrod~ block 10 which in~ludes a first eleatrode memb~r 11 and a secon~ ~lactrode member 12. The electrode members ll and 12 have the same diameter, and are mad0 o the sam~ electrode materlal. The el~ctrode members ll and 1~ have annu:Lar operation bores llc and 12c, respectively. The two bores ~lc and 12c are ~ligned ~o as to communicate with each other. The ~or~s llc and 12c accommodate tube ends ln their - bu~iny posture. ~he refsrence numeral 13 denotes an ; insulator interposed between the first and second ` electrods members ll and 12. In order to position the :j 15 insulator 13 and th~ electrode members 1~ and 12 in ~heir proper ~elative posl~ions the first and the , sacond electrode member~ 11 and 12 are respectively :~ p~ovided with rece~ses lla and 12a, and the insulator 13 is provided with proiections 13a and 13b so that the pro~ections 13a, 13b flt ~nto the corresponding recesses lla and 12a to ensure a firm `I ~oint between the insulator 13 and the elec~rode .`~ members ll, 12. :

The insulator 13 has a bore 13c which is :
.~ aligned with the annular operation bores llc and l~c of ~.`~ th~ flrst and second ele~trode members 11 and 12.
'.~ Tubes 30a and 30b are inserte~ into the bores l~c, 12c and 13c in which the ends of the tubes 30a and 30b are placed i~ abutment with each other as shown in Fig, 1 or overlaid ln their ioining end portions as s~own in Fig. 2.
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`t~5 ~ -- 7 ., , . . , ~ he insulator 13 is made o~ a materlal having a larger specific dlelectri~ constant than that of the tubes to be joined. In addition, it is pre~erred that the insulator material hai~ such a high me?ting point as to be safe from deformatlon at an elevated te~perature, and is not likely to contaminate the tubes with ~erms andJor dir~. ~or example, when ~he tubes are made o~ flexible polyvinyl chloride, polytetra-~luorethylene such as Te~ron (trade mark) can be used.
The su~face area of the bore 13c affects the intensity of. ~he electric field between the flrst electrode . member ll and the second electrode member 1~. If the :~ surface area of the bore 13c is excessively large as ~, compared with the high-frequency output, the electric -........... 15 fleld bacomes less intense. If the surface area of the bore 13c is exaessively small, the heat cannot reach a w~de ranga of tubes 30a and 30b. The ratio o~
the ~urface area o~ ths bore 13a to the high-frequency ~, output i~ normally s~t to about ~0 to 9.1 c~2/kW ;
1 20 pr~ferably 10 to 0.1 cm2/kW, and more preferably 3.0 to , 0.1 cm2/kW.

;ll Th~ electrode members 11, 12 (Figs. 1 and 2) and 14, 15 and 16 (Figs. 3 and 4) and the insulators 13 (~igs. l-and 2) and 17 and 18 (Figs. 3 and 4) can be an annular one-piece body or alternatively, can be composed of two or more spilt body members.

Therè 15 provided an all-purpose high-~requency power source 20 connected be~ween the electrode members 1~ and 1~, the power source 20 having a high-~requency oscillator tube. The output and the osc1lleting frequency are det~rm1ned ln accordance with .~
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the material and dimension of the plastic tubes to be ~oined sto that the tubes are adequately he~ted.
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The method described above is carried out in . 5 the following manner:

Refe~ring to Fi~. l, the tubes 30a and 30 are lnserted into the bores llc and 12c of the electrode members 11 and 12 until the tube ends come :. lO into abutment with each other withln the bore 13c of the insulator 13. It is prefer~ed ~hat ths abutting tuba ends keep contact with the inside ~urface of the bore 13c. Then the powe~ source 20 is turned on to apply a high-frequency voltage between ~he electrode . 15 members lla and l~a. A high-frequency alternating j~ electric field is established along the annular body and the bore 13c o~ the ~nsulator 13. The high-frequency alternatlng alectric ield establ$shed in the bore 13c is s~rongsr toward the outer periphery o~ the 20 annular body of the insulator 13 to such an extent as to be equal to the intensity o~ electric ield passing ~l th~ough the insulator 13. The tubes 30a and 30b are ¦ exposed to the intensiied high-fre~uency electrio field, which is subject to an appropriate ad~ustment of 25 the ~requency and output of high-f~equency voltage in `t ~ccordance with ~he given conditions such as the nature of the tube material and size of the tubes. The ends of the tubes 30a and 30b are sub~ected to induction heating and becomes ~usibly joined to each other. When 30 a sotening temperature is reached, the power source ~0 is turned off. The joined tube ends are allowed to t cool untll their joint becomes firm. The connected tube~ are then pulled ou~ of the electrode block lO.

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As is evident from th~ foregoing des~ription, the tubes are sufficiently heated by induction heat without causing a carbonlzinS~ problem, thereby ensuring a stron~ and firm ~oint between the tubes. It is no~
~ ~ nec~s~ary to employ an outer el~ctrode and an inner :~ electrode and to insert the inner electrode lnto the tubes at the risk o~ unhygienic contamination of the :` tubes. It is also adva~ta~eous in that there ls no ~'1 : problem of the tubes contracting and constricting over :~. 10 the electrode thereby preventing the electrode from :- beln~ pulled out of the tubes owing ~o interfacial ~ adhe~ion between khe tubes and the electrode.
, '~, Fig. 2 shows a modifled version in which the , 15 tubes 30a and 30b are placed ln a telescopic manner at ~ their ends. A high-~requency voltage is applied ,~ .be~ween ~he electrod~ members 11 and 1~ so that ~he peripheral portlons o~ both tube ends are fused and ~1 ~oined, ` 3 20 . Fig. 3 shows a further modified version . chara~terized by the provision of three electrode . member~ 14, 15 and 16 with the interposit~on of two , insulators 17 and 18. A~ described above, the three :~ 25 electrode members 14, 15 and 16 are coaxially arranged ¦ so as to enable their bores 14c, 15c and 16c to communicate with one another. This embodiment is ~ adapted for ~olning three tubes 30a, 30~ and 31. The ;.~ third tube 31 strengthens the ~oin~ bet~een the `~ 30 tubes 30a and 30b, and further ensures a watertight joint. The reference numerals ~Oa and 20b denote power sources. As a procedure the third tube 31 is placed to mantle the abutting two tubes 30a and 30b, and the "'. ;.
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:, ' t, 8~i5 mantled tubes are inser~ed into the electrode block 10 until the abutting tube ends posltion within the middle electrode member 15. At thls sta~e a high-frequency voltage is applied by the power ~ou~ce 20a for a given period of time, and then by the other ~ower source 20b.
The power sources 20a and 20b can be combined into a ~ingle unit which i~ turned o~ and of by a switch, or altsrnatively, the two ~ower sources can be slmultaneously operated.
!; 1 0 Th~ operation of the power source 20a enables the ~ube 30a and the ~hird tube 31 to ~usibly join in their contacting parts, and the operation o the power I source 20b enables the tube 30b and the third tube 31 :l 15 to ~usibly ~oin in their contacting parts.
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1 Fig. 4 shows an embodiment in which the third : ~ube 31 is inserted lnto the tubes 30a and 30b. The Y ~uslon Joint amon~ the tubes 30a, 30b and 31 is 20 ef~ected in the same manner.

An example of carrying out the method by use o~ the arrangement o~ Fig. 3 will be descri~ed:

The electrode block 10 included annular electrode members 14, 15 and 16 of copper, having an I outside diamete~ o~ 30 mm, an lnside diameter o~ 6 mm i and a length of 30 mm. Annular insulators 17 and 18 ¦ were disposed ~etween'the electrode members 14 and 15, ¦ 30 and between the electrode members 15 and 16, respectively. The insulators 17 and 18 were ~ade of Teflon, havlng an outside diameter o 30 mm, an inside dlameter of 6.0 mm and a length of 5.0 mm. The ZC)08~

.,insulators 17 and 18 were arranged coaxially of the electrode members 14, 15 and 16.

;Tubes 30a and 30b o~ flexible polyvinyl chloride (Shore (A) Hardness a~ 20C: 80) having an ou~lde dlamet~r of 4.0 mm, an in~ide dlameter o~
,2.0 mm a~d a length of 3.0 ~, w~re ~nserted in a covering tube 31 o th~ same material, havin~ an ,~outside diameter of 6,0 mm, an inside dlameter o~

4.0 mm and a length of 80 mm. The electrode member~ 14, 15 and 16, and the insulators 17 and 18 had .bores 14c, 15a, 16c and 17c and 18c, respectively, and ~`were coaxially arranged so that the bores lgc to 18c communicated with one anothe~. The tu~es 30a and 30b were placed into abutment with each other at a mid~le point of the covering tube 31. ~he tubes 30a, 30b Imantled by the covering ~ube 31 were placed in the .Ibores 14c to 18c. At this stage the power our~es 20a ¦and 20b were turned on and a high-frequency voltage of 2Q 40.46 MHZ was appli~d ~or four seconds. As a result, the tubes 30a and ~Ob were Joined to the covering tube 31 over a distance o~ about 17.5 mm from the respective open ends. In this way the tubes 30a and .30b wera connected to each other into a conduit. T~e !25 high-frequency oscillator incorporated in the power sources 20a and 20b had an ou~put of 3 KW.

The ~oined tubes 30a and 30b, hereinafter refer~ed to as conduit, had a good appearance. !The condult wa~ sterilized by high pressure steam (121C x ~0 min ) and then was sub~ected ~o a tensile test (the pulling spe~d: 200 mm/min). A fracture in the conduit was found under a load of about 1.8 kg/mm~, i ., ~OiQB1~5 The conduit was ascertained to have sufficient joints between the tubes. Sixty ml of clean water was confined in the condult, ant~ wa8 allowed to stand for ;l 24 hour~ at a room temperature. Then the number o~
i~ 5 lmpurlties in dispersion thereln wa~ counted. To carry out tha test, the procedure followed the prescriptions ~, set for plastlc contalner~ ~or trans~usion by the Authorlty o~ the Japan Pharmacopoela. The instrument employed was an automatic counter of a light ., 10 shutt~rin~ type. The results are ~hown in Table 1. It w~ll be apprec~ated from Table 1 that the number o~
~ dispersed impurities 16 not dierent from that - measured be~or~ the water was put in the conduit. The ~esults show that the lnslde o~ the condult was kept ~5 hyglenic with no contamination. ~;

Another tes was oonducted by conflning 60 ml of ~istilled watar used ~or in~eo~on ~n~ ~usibly sealing bo~ open ends of the conduit. The distilled , 20 water was prepared in accordance with the Japan `l Pharmaaopoeia Prescriptions. The conduit containing the watcr was subjected ~o a sterizing treatmen~ by a high pressure steam of 121C for 20 ~in. Then the 3 water was examined by a high velocity liquid 25 chrom~tography to see the a~ount o~ tetrahydro~uran ~¦ (THF) content. The results a~e shown in Table ~. It wlll be noted from Table 2 that the amount of tetrahydro~uran did not di~fer bètween the before and after tests. Non-presence of detrlmental organic 30 solvent was also ascertained.
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Impuritl~s Fine particle~ (number/ml) , size The invention Comparative Prior to ,~ method I test 1 ~m c 0.7 86.5 0.6 2 ~m s 0.2 45.3 0.2 5 ~m < 0 22.1 0 ~0 ~m < 0 10.5 0 ~i! 25 ~m < 0 6.7 0 :! 50 ~ o 4. 2 o Table 2 Speclmen Tetrahydrofur~n content (ppm) No. The invention Comparative Prior to method II test For comparison, the known methods described I above were ~lso tested~

When the tubes made of the same material were ~oined by the thermal s~aling method, it was found that the conduit fractured a~ the ~oint under a load of 0.8 to 1.0 kg. The high-frequency heatlng method employing the inner ~lectrode was tested in the following manner:
, ~ , ~ tsr a stainless elect~ode ha~ing an outslde diameter of 2 mm was insert~d into a first tube ha~ins~ an outside diameter of 4 mm and an inside diamete~ of 2 mm, a second tt~be having an ~utside dlameter o~ ~ mm and an inside diameter of 4 mm was Z0~8~
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conn~cted to the ~irst tubs i.n an overlaying state over .~ a length o~ 10 mm. The overlaid parts o~ the first and .; second tubas were placed within an annular electrode .~ block of copper having an outsida diameter o~ 6 mm and 5 were fus~bly ~otn~d by hiyh-frequency heating. The ; applied h-1gh-~requency was 40 MH~ and the application of voltag~ continued for four secon~s. The overlapplng : parts of 10 mm were ~olned. The tests were conducted:~1 by the same procedure as that adopted to test the 1~ present inventlon, and the tensil2 stren~th and the degre~ o~ contamlnation were lik~wlse examined. As ~ shown in T~ble 1, ~he inslde~ of the tubes are found remarkably contaminat2d as compared with the results of l the present invention. ~he ~olning operation took a :, 15 longer ti~e by a few seconds than under the present invention~ Ater the open ends of ~he t~bes were ~ sealed with tetrahydrofuran and th~ test condult was i~ allowed to s~and for ~4 hours, as Tabl~ 2 lndicat~s, a ~ considerable amount o organlc solvent was presQnt.
.1 20 The method o~ the present invention is . particularly adapted for maklng condu~ts used in . transfusion bags, blood bags, bags for continuous ;~ ambulatory periton~um dialysis (CAPD) but the ~ethod of ~S the present invention can be used for any other use, j for example, the connect~on of tube and infusion bag ~ :.
nozzle, ~ube catheter and infusion bag nozzle, Infusion bag and nozzle in whlch hi~hly hygienic considerations are r~quired.
It is understood that various other modi~ica-'~ tions will be apparent to and can be readily made by ~ those ek1lled ln the art wlthout departing from the ', ~ ~' ;~ f)~ s : -- :L5 --. ~ :
scope and s~irit of th~ 9 invention, Accordingly, it i~
~, not intended that the SCOp8 of th~ claims appended ; hereto be limited to the d~scriptlon as set forth h~rein, but rather that the clalms be construed as en-compassing all the features o~ patentable novelty that .~ reside in the present invent~on, including all featu~es that would be treated as Rquivalents thereof by those !I skilled in the art to which ~his inventlon ~ertains.
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Claims

1. A method of connecting plastic tubes by high-frequency heating, comprising the steps of:
preparing an electrode block having a first electrode member and a second electrode member each having annular operation bores aligned so as to communicate with each other, the electrode block including an insulator interposed between the first and the second electrode members, and the insulator having a bore aligned with the bores of the first and second electrode members, wherein the electrode block includes a third electrode member between the first electrode member and the second electrode member, and a further insulator so that the adjacent electrode members have one insulator therebetween, the third electrode member having a bore aligned with the bores of the first and second electrode members, inserting an end portion of one tube into the first electrode member and an end portion of the other tube into the second electrode member so that both tube ends are placed in contact with each other in the annular operation bores and applying a high frequency voltage between the first and third electrode members, and between the third and second electrode members.

2. A method according to claim 1, wherein a further tube covers the end portions of the tubes so as to ensure the joint among the three tubes.