CA2181056A1 - Pressure sensitive adhesive tape - Google Patents

Abstract

A narrow tape of high strength and low elongation to break for use for example as a tear tape or packaging tape is formed by extruding continuously from preferably polypropylene a strip of tape and applying to the strip an adhesive layer on one surface. After extrusion and after application of the adhesive strip, the tape is drawn longitudinally by an amount sufficient to substantially fully orient the tape in the longitudinal direction to provide the required low elongation to break and high strength. The tape is extruded in a width so that when drawn the width of the drawn tape is equal to the required width of the finished tape. Instead of slitting the tape from a wide web, therefore, the tape is extruded directly in tape width without slitting or trimming thus obviating any waste. In addition the longitudinal drawing of the tape reduces the thickness of the adhesive to a thickness just sufficient to provide the required level of pressure sensitive adhesion without use of excess materials.

Description

~ WO95120018 2 1 8 1 056 PCTICA95100033 PRESSURE SENSITIVE ADHESIVE TAPE
This invention rel~tes to a pressure sensitive adhesive (PSA) tape of high tensile strength and low ~lonDc.lion in a tape width less than 2.0 inches .
Pressure sensitive adhesive tapes with which the present invention is conc~",ed are widely used as tear tapes, but in addition it may be possible to use tapes of the present invention as pressure sensitive strapping, as r~;.,ru,.,t:",e"~ for corruyate~ products and for similar purposes.
Tear tapes are widely used in packaging to tear a pa.,hdD ~9 material along a tear line defined by the tear tape. This is used in filmic pachdv ,9 materials but also ~:an be used with paper or board materials such as for soap boxes or courier elnvelopes. The tear tape thus forms a very small part of the p~.hay;lly material but provides a function which is very important for customer saLi:,rdl,liul~. It is of course desirable therefore to reduce the amount of material and cost involved in the tear tape construction.
Tear tapes con\,~"Lional'y comprise a strip of a suitable plastics material and generally poly",up;l~,)e is chosen as this is relatively i"a,.u~",h/e and yet provides the required ~trenyDth ~.lltlld~.t~ .. The tear tape can have a width generally in the ran~e 1/16th to 1/4 inch. The width is generally selected on the basis of minimum cost.
It is generally necessary to bond the tear tape to the pachdy;"g material in order to hold th~! tear tape in place during the manufacturing process and to locate the tear tape in place while it is tearing the F-- ~ l9 film to provide a clean straight tear line.
Some F ' ,9 ~,u..esses include the ~FF" _Liol1 of adhesive to the tear tape on the F~r~ line so ~hat an adhesive ~ ' is provided as part of the machine and applies the adhesive to the tear tape il~ Jial~ly prior to its ,, " n to the p,~ckay;"y film.

More recently tear tapes have been supplied in package form carrying a pressure sensitive adhesive on one surface. Such tapes are formed by slitting from a web of the tape material on which is already applied the pressure sensitive adhesive. This type of tape provides some problems in that the adhesive material extends to the side edges of the tape and therefore engages guides to cause transfer of adhesive material to the guides and can spread from the side edge of the tape onto other parts of the pacl~a~;"g mâterial which interfere with the proper operation of the structure. A tape of this type is shown in U.S. Patent 4,844,962 IMay et al assigned to Payne rcl~,ka~;.lg Limited).
In prior U.S. Patent 4,887,714 (O'Connor assigned to KT
Industries Inc.) is shown a modified form of tear tape in which the pressure sensitive adhesive is applied as a narrow bead to the tear tape core layer afterthe tear tape has been slit from a web of the film. This process has been c~llllllt:l"i..l'y successful and operates :~ali~ra-,~uli~y on the packau;"9 machine.
Other types of pressure sensitive adhesive tape are also widely used. A tape as defined herein is a core layer of an extruded polymer material having a pressure sensitive adhesive on one side thereof, low elongation to break and a width less than 2.0 inches. Low elull~aliull to break is defined herein as being generally of the order of 10 to 20 % and certainly less than 40,6. Tapes of this type can be used for various purposes including tear tapes as l~ iùl1ed above which conv.:"Li~l~a'!y have a width in the range 1/4 inch down to 1/16 inch. Tabbing tapes often have a width in the range 1.0 to 2.0 inch. n~,:.,ru~,,t,,,,t ,,l tapes often have a width in the range 0.5 to 1.0 inches. In all cases the above low el~ aLiu,1 is required for the end use stated both in the finished product and also during pruce~i"g of the tape to form the finished product during pa~ ,, ,9 of the tape, during unwinding of the package and also during ~," ) of the tape to the required substrate.

WO 95/20018 2 t 8 1 0 5 6 PCT/CA95/00033 An extruded matlerial is disclosed iri Canadian Patent 977,629 IPlicoflex Houston Inc.) in wh~ch a strip of material is extruded onto a drum and cooled following which it is then l,~,,,,r~,lt.;l to a second drum and an adhesive material is applied to one surface. DUNII~LIt:~lll of the drum the tapeis drawn by 25% to 50% which creates a material which is heat ~ aLI~, and of high ~lonuc.Liùl~. The tape of Plicoflex is often referred to in the s~,euiriudLiùn as a film and it is certainly not clear whether the material as extruded is intended to be extruded in the width of the finished tape or whether slittin~ is intended. In any event the finished tape is intended to havea width greater than 2.0 inche3 in view of the stated end use of the tape. The material as extruded must be rlelatively wide ~much greater than 2.0 inches) in view of the Lt~ . IP disclosl~d for applying the adhesive. The patent also refers on a number of occasions to "trimming" the film. Such a tape material as disclosed in Plicoflex is entirely unsuitable for the tape structure with which the present invention is conc~"~ad, that is the hi~h strength, low ~:onyc,liù,, tapes as defined above.
A further coextrlJded pressure sensitive adhesive material is disclosed in U.S. Patent 4,379,806 (Johnson & Johnson) in which a base polymer film is extruded with an adhesive material with the coextrusion causing a bonding effect between the layers. The patent i"l~,.,l,a"u~s use of the words "tape" and "film" but it is almost certainly clear that this material is indeed extruded in web width since the patent refers to trimmin~ of the edges of the material and slittin~ the material into tape width using conventional 1~,1)l 1 , :es Generally, tear tal~es are manufactured by slitting an extruded web of pol~u, u~ e or other suitable material which is oriented either r 'Iy or biaxially by con~ventional ~uc~ i"g. This web is then slit into a plurality of lon~ifl~ ", "y continuous side-by side tapes which can be coated WO 95120018 2 1 8 1 0 5 6 PCT/CAg5100033 with adhesive in a process sl~hsequPnt to the slitting as in the O'Connor patentset out above or can be coated in web width with the adhesive prior to slitting as in the May patent above.
There is an ongoing requirement to yet further reduce the costs of manufacture of PSA tape and to manufacture a PSA tape with minimum materials and minimum waste of materials in an efficient and cost effective manner and it is one object of the present invention to provide a method of manufacturing a tape and a tape so manufactured which provides such improvements .
According to one aspect of the invention there is provided a method of forming a single pressure sensitive adhesive tape of high strength and low el~"~ n co"~ ;"~q extruding a core layer of plastics material so as to define on the core layer as extruded a first surface, a second surface opposed to the first surface and two opposed side edges, the core layer being suL~Lall~ !y longitudinally continuous and having a ~ d~L~ d first width;
applying onto the first surface a layer of a ~ d first thickness of a hot-melt pressure sensitive adhesive material; 5l~hs~ erlt to the ~F" ~ of the adhesive layer, ~LI~l-;ll;,lg the core layer and the adhesive layer carried thereby so as to cause longitudinal o~ llLali~l) of the core layer to an extent to provide for the tape a low ~lun~alion to break, so as to cause a reduct~on in thickness of the adhesive layer and such that a width of the core layer between the side edges is reduced by the ~ from the first width to a second width equal to that of the single tape and less than 2.0 inches; the single tape being formed without slitting or trimming so that side edges of the single tape are defined by said two opposed side edges; and winding the single tape into a package.
This method in which the core layer is drawn such that a thickness of the adhesive layer is reduced can be used to cause the thickness ~ wo 95~20018 5 2 1 8 1 0 5 6 PcT~cAgsl00033 of the adhesive to be less than can com,~"Lioll~lly be obtained with hot-melt adhesive at speeds greater than can normally be obtained. Thus a thickness of less than 0.001 inch at a tape production or winding rste greater than 500 ft/min can be achieved.
The core layer is ~irectly extruded in tape width that is the edges of the core layer as extrudedl form the edges of the finished tape without slitting.
A release agent can be applied if required to the side of the tape opposite to the adhesive although the increased adhesion between the adhesive and the core layer may avoid the necessity for the release layer. If applied the release agent can be is i~ ylldlt:d in a separate release layer coextruded with the core layel~. The release layer is a COIIl,uai ' !~ polymer in which is illll.lt,~lldltd a releast! agent of a conventional type. The amount ofthe release agent may be of the order of 2 to 109~ and this amount can be reduced relative to conventional amounts by the fact that the coextrusion of the core layer and the hot melt adhesive provides a greater bond between the layers thus reducing the tender~cy of the adhesive layer to be stripped away by adhesion to the opposite side of the core layer. The use of the separate layer reduces the amount of the release agent used so as to reduce overall cost.
Coloring of the finished tape can be effected simply by 3dding a coloring agent into the polymer extruding the core layer.
The finished tape di",ansiorls can lie in the range of 0.03 to 2.0 inch in width and 0.0005 to 0.010 inch in thickness. The method of the invention can allow manufacture of a tear tape of reduced width relative to conventional tapes for example down to 1/32 inch which reduces material content and increases the lengl:h of tape which can be supplied on a package to improve the efficiency of p, oceO~i"g . The pressure sensitive hot melt adhesive is applied to the extruded core layer before the tape is oriented to its wo 95/20018 2 1 8 1 0 5 6 PCT/CA95/00033 final thickness snd width. When using a stretch of the order of 800%, the tape is 2pplu, illlal~.1y three times wider at the point of adhesive _ ~" )n than the finished width and it is therefore easier in this invention to apply the adhesive in a strip which is equal to or less than the width of the tape.
Alternatively the hot melt adhesive can be coextruded with the core layer at the initial die either in full tape width or if required in ~educed width. in this 2rrangement it may be necessary to provide coolin~ of that part of the die throu~h which the adhesive passes since the adhesive ~enerally can not tolerate temperatures required for the polymer for the extrusion process.
When usin~q poly~,,uu,ll~ne it is necessary to obtain the required u,opt5,li_s defined above to stretch the core Isyer by an amount ~enerally in the ranoe 600 to 900 % which is ~,~r~,dLly at least 700% and more p,~rt ,dbl~ 800%. The tape is of course thicker prior to the stretching and the thickness is reduced by the orienting process. As the hot-melt adhesive is applied to the cast polymer core layer or coextruded with the core layer prior to the orientin~ process the thickness of the adhesive is reduced ~(ù~OlLi~llaL~ly during the Oli~lllalii:~ll. This is extremely important because it is the goal of the present invention to have a minimal amount of adhesive in r ~ where h~h bonds are not required. The adhesive layer in the finished tape is thus r ,t:rt:,aL,ly less than 0.001 inch and more ~ rt Idbly less than 0.0005 inch.
This feature is especially important because it is very difficult to apply hot melts in II,;ck"esse~ less than 0.0005 inch. For best advantage PSA
tapes for low tack: ~" .ls have a finished thickness of adhesive in the 0.0001 to 0.0003 inch ran~e and this can be readily obtained in the present invention.

~ WO 95/20018 7 2 1 8 1 0 5 6 PCTICA9~ODD33 The coextruded release layer is also of course reduced in thickness during the vri~,,Lalion step thus producing a thickness of the releaselayer in the finished tape whicl1 is ~,~r~,ably less than 0.0001 inch.
When usin~ polyester as the polymer for extruding the core layer, the amount of extension necessary for obtaining the required p,upe,Li~s is at least 300% and ~ rt:~duly 501û%. This dirrt ~,.ce in the amount of stretch of the other layers is taken into zccount in del~r"~;" ,9 the original ~ s~s of the layers as extruded.
One other benefit of this process is there is no trim waste as the polymer is extruded in a profilr- that will be totally consumed by the process.
Also this process produces finished rolls of PSA tape that are totally splice free as the extruder can run continuously.
This approach to the manufacture of tapes is entirely opposed to current thinking in which the ~xtrusion step is effected in extruders which are of i"~ ,9 magnitude and capital cost in view of the expected improvement in efficiency obtained by scale. However this ~ lliri~alllly increases the difficulty and cost of the slitting and winding stages for the manufacture of individual narrow adhesive tapes. Slitting is particularly difficult in narrow PSA
tape in view of the difficulty oi~ slitting through the adhesive layer.
Splicing PSA is a major problem as it is. difficult to get PSA
splicing tape to stick to th~ release coated side of the film. For this reason most manufacturers use a twr3 side sticky tape with a film in the center which does not have the physical ~,up.:,Li~... of the PSA tape. It is too thick, and production equipment is down while a splice is being made which is very costly. There is also a grea~ danger of rolls not winding up properly after stopping and starting for splices. This process ~ lal~ these problems. In addition the process uses cheaper base raw materials rather than more ,uel~:~h/G partly converted materials. Yet further, the use of hot-melt adhesive 2 1 8 1 0 5 6 PCTIC~9S/00033 avoids the use of volatile organic chemicals (VOC'S) which are becoming less acc~ aL,I~ in these env;ru,,,,,e,,L~lly conscious times.
The above details relate to âny high strength, low elongation PSA
tape which can be used in various end uses. In the tear tape end use, the amount of adhesive necessary can be relatively small so the adhesive has the Lll;~klldss~s defined above and a width generaliy of the order of 90% to 70 %
of the width of the tape itself.
When used for strapping or similar l~; lru,1~",~"L type tapes, the amount of 2dhesive carried on the tape is O;~llirical,Lly increased so the thiGkness of the adhesive in the finished tape may be of the order of 0.0005 to 0.002 inch. Again however the width of the adhesive may be less than the width of the tape to prevent clr ~lar~uLion of the adhesive at the edqes of the tape and to prevent ~ a~..llellL of the adhesive with guides and the like. In such an a"a,)~",~,lL, however, the width of the adhesive may be as much as 90 % of the width of the tape.
In order to achieve the nec~sa(y stren~qth and elon~qation ,G~upe~Li_O required for the above tape, it is necessary to effect drawing of the extruded tape to an amount in the range 300 to 800% to achieve suL,OLa"Li311y complete ori~"LuLioll, d.:ue,, ,9 on the type of polymer used. This ~qenerally results in a decrease in the thickness of the tape layer by an amount which can be as much as 66% when oLI~Lull;l)9 by 800%, thus similarly reducing the thickness of the adhesive by the same p~lut:llLa~e. In order to achieve the finished thickness required, therefore, it is necessary to apply adhesive to a thicker amount as defined above.
One e",L ~ "L of the invention will now be described in conjunction with the accu"",a"ying drawings in which:
Figure 1 is a cross sectional view through an extruded film su~La"L:. :ly illllll~d;aL~ily after extrusion.
:

~ wo 95/20018 9 2 1 8 1 0 5 6 PCTICA9~00033 Fi~ure 2 is a cr~ss sectional view of the film and layer of Figure 1 after ~ cll:.,g to effect orientation of the film.
Fi~ure 3 is a side elevational view showing sGl~e", y a process for forming the structures of Figures 1 and 2.
Figure 4 is a top plan view of the 5CI)ellla~i~. illustration of Fi~ure 3.
The process illLlstrated in Fi~ures 3 and 4 includes an extruder head 10 with a barrel 11 and a screw 12 operated by a motor 13. The extrusion head further includes a die 15 acting to extrude a generally flat corelayer 16 of the polymer aftel shaping into a required shape within the die slot.The shape of the die thus provides on the core layer a top surface 17 a bottom surface 18 and two ~pposed side surfaces 19 and 20.
In the e."b~u; "I-"L shown in Figure 1 the extruded core layer is coextruded with a lower layer 22 c~n,le~ l~d to the core layer by a tie layer 23.
For the purpose of providing the coextrusion the head 10 shown only 5~.11t:111ai- 'y will of course include more than one polymer supply screw for injecting the different ty~es of polymer forming the layers 21 22 and 23 and supplying them to the dil~ 15.
Upon emerging from the extrusion head the extruded core layer simply enters a water batl- 5CIl~ i' 'Iy indicated at 24 for illllll~diaL~:
quenchin~ to a cooled condition.
Also coextruded with the core layer is an adhesive layer 27 of a hot-melt type. However as an alternative the adhesive can be applied by a casting system du.r~ l: Ll~alll of the quenching 24.
The adhesive is of the hot-melt pressure sensitive type so that when set the adhesive is responsive simply to contact to actuate the adhesive effect.

2181056 ecrlC~ g~/ooo33 ~3 f~ e//';S~<'3.~.f~) Downstream of the water quenching is provided an orientation section 30 including capstan rollers (preferably of the type known as Godet rollers~ 31 and 32. As is well known orientation of an ext~uded fiim or strip isnecessary to generate structurai stability and the required longitudinal strength and low elongation. This is achieved by simply stretching of the film and this case the stretching is effected monoaxialiy that is longitudinally simply by driving the capstan roller 32 at an increased speed relative to the capstan roiler 31. In practice the amount of stretching required is of the order of 300 to 800% and this is well known to achieve the required orientation of the film or strip .
The cross section of the oriented core layer is shown in Figure 2 and it will be noted that both the width W1 and the thickness T1 of the tape body indicated at 25A excluding the adhesive !ayer 27 are decreased relative to the corresponding width W and thickness T of the tape body 25 as extruded.
At the same time of course the thickness H1 of the adhesive layer 27A is significantly reduced relative to the thickness H of the layer 27 as applied.
Downstream of the orientation stage 30 is provided a winding station 33 which acts to wind the tape as shown in Figure i into a package the package having a width greater than the width of the tape so that the tape is trave~sed across the package during the winding process.
The tape is thus produced continuously at a tape production rate preferably in excess of 2000 feet per minute. Tne winding station 33 is p~eferably of a type which allo~s automatic change of one filled package for an empty spool in order that the tape can be continuously wound without wastage.
The process invol~es no siitting of the tape from any ~,vider tape structure or web structure so there is no waste and all the material that is extruded forms part of the finali~ed tape wound into. the package.
h~ rlt~ SH-ET(RULE g1) ISAIEP
.

~ 2181056 Turnin~ to the tape structure shown in Fi~ures 1 and 2, the coextruded tape structure of Figure 1 includes a layer 21 which is of a plasticsmaterial formin~ the structural stren~qth for the tape. The core layer 21 therefore is formed of 8 suitable plastics material for example polypropylene which has suitable strengtll p, upe~ for formin~ a tear tape for tearin~
F-~ _ Iq film and is of su~table cost. The layer 22 is formed of a material which has release ~ I)ala~ relative to the adhesive layer 27A. The release layer 22 can therefcre be formed of a polymer which is illlul~llaLt:d with a release material such as silicorle. In some cases the polymer layet 21 and 22 may be GOIII~JdliLI~ so they can be coextruded without the necessity for a tyin~q layer 23. In oth~r cases a bonding or tie layer 23 is necessary to ensure the formation of the different layers into an inte~ral structure definingthe tape body. In yet another alla~ "l, the main body of the core layer is formed from the illlulugllaLtzl~ polymer and only a thin tie layer is coextrudedon top of the polymer to attal~h to the 3dhesive layer.
In the finished t~pe structure shown in FirJure 2, the width of the tape body 25A less than 2.0 inch and is F~ lably in the ranr~e 0.03 to 1.0 inch and the thickness T1 i~ rr-~al,ly in the range 0.0005 to 0.010 inch.
These d;."~" ,i~ns are similar to those used in conventional tear tapes. The thickness of the adhesive la)l~er after the Ol;~.llaLiOII stage is less than 0.001 inch and prt:r~,dLI~ less than 0.0005 inch and more Fllt~ rably in the ran~qe 0.0001 to 0.0003 inch. This thickness of adhesive is sufficient to provide the minimal adhesive effect necessary in the p-~ Jl,' 19 structure. However this thickness of adhesive cannot be achieved usin~ a conventional hot-melt adhesive r,~' '.)ri techniq~es and the minimum thickness which can be achieved usin~ such rr~r" 1 techniques is of the order of above 0.0005 inch and then only at relatively slow speed. In the present invention, therefore, the ~rr~ lion of tlle adhesive prior to the o,ie,,Laliun sta~qe allows wo 95/20~1\ 2 1 8 1 0 5 6 PCT/CA95/00033 ~
the adhesiYe to be applied in a thickness in the ran~e 0.001 to 0.003 inch as shown in Figure 3 following which ~ l9 of the tape by an amount in the order of 800% to 900% will reduce the thickness of th~ adhesive layer to the above stated ~."al,~ions. It will also be noted that the adhesive is applied in a band so that side edges 27B and 27C of the band of adhesive both when applied and in the finished tape are spaced inwardly of the side edges 19 and 20 of the tape body. This ensures that the adhesive in the finished tear tape isspaced from the ed~es of the tape to prevent d~9ladaLiul1 and blocking.
In the finished tape structure shown in Figure 4, therefore, the tape body 25A is formed of pol~r",up~ e having a longitudinal strength which is sufficient to effect tearing in the conventional tear tape operation. The layer 22 of the tape body acts as a release coating for en~a~ing the adhesive layer 27A of the next underlying tape.
In coextruding the three layers of the core layer, the release layer and the hot melt adhesive layer, these materials are coextruded through a slot having the required ~" "ansio~s so that the thickness and width of the tape thus formed is such that, after the required sl~ 9 to provide the necessary degree of Olit:llLaliOI-, the ~ nsivlls of thickness and width are tailored to the requirements of the finished tape.
As is known, the temperature for the extrusion of the base polymer is of the order of 450 to 500F for ,~oly",up~ e and 550F for polyester. Hot melt adhesives at this temperature can break down and therefore it is necessary to effect coolin~ of a part of the die so that the hotmelt adhesive is supplied at the required temperature for proper handling of thehot melt adhesive. This is generally of the order of 300 to 350F. The extrusion is plt:rt:laL,ly effected at the order of 500 feet per minute. A suitable allal~llle~ll for the extrusion head is shown in the above ",~r,li~ned patent toJohnson and Johnson.

WO 95/20018 PCT~CA9~J00033 ~; 13 It will be noted that the extrusion head generating the single tape is i"depend~5"l of other extrllsion heads so that it is i"depel,d~"l of L]lt:dk~of any other line. The extrusion head is also ~s~oci l~d with the individual winding head for the particullar tape line. The line can therefore run effectively continuously i,,de~ d~,,Lly of other lines so that the finished package of tape is effectively splice free.
Du~L'~loLI~al1l oF the extrusion head, the extruded tape is i",~"edi~ft~ily quenched in water to obtain the required cooling and settin~q ofthe suLOLalli 'y liquid materials into an amorphous plastics material prior to the o,i~"LaLion steps described above to obtain the required ~,up~,Lits of the finished tape structure.
It will be duplt:u;aLt d that the manufacture of the tape as a coextruded core layer with the ~ lloiOI~5 of the core layer tailored to produce, by the aL~t:L~l,;"~q, a tape of the required thickness and width allowsthe tape to be formed withoult the necessity for any slittin~ or trimming of theedges of the tape of any t~pe. The side ed~qes of the tape are therefore constituted by the same s~d~ edges of the core layer with those side ed~qes simply being modified in, ~"Oion and position durin~q the oLlt Lull ,~ process.
This absence of slitting or tlimming ensures that there is zero waste in the process of the manufacture o~ the tape.
This process is entirely opposite to the current thinkin~q in the manufscture of tape. In current dev~l~p",~"LO the initial extrusion process is of i~ Oillg size so that an extrusion line is of a massive nature including a huqe capital initial cost. Sucl1 large extruded films need therefore to be slit a number of different times so as to ~qraiually reduce the very wide initial film into a number of smaller films throu~qh a number of slitting stages. In the final ptucessi"~q of tear tape, ~or example, therèfore, the master roll may only be ofthe order of 2 inches wide for the manufacture of 32 tapes of 1/16 inch width WO 95120018 2 1 8 1 0 5 6 PCTICA95100033 ~
each. It will be d~.~,r~:. iaL~d that this number of slitting stages includes hi~h c~"l,.,lwdLy and difficulty leading to the possibiiity of a large number of breakdowns. The slitting of adhesive coated film is also very difficult since the slitting knives are very much influenced by the collection of adhesive which can occur onto the knife surface. Even very thin slittin~ knives in total add upto a s~ lliriuall~ prupo,Lion of the width of the film to be slit so that there is a relatively high drag. However despite these difficulties of slitting, the econ~",i~ of the process are de,oendd"l upon the massive initial extrusion process and the present invention goes exactly against this trend providing an r~xtrusion head of a size tailored to match the individual tape. This process isrendered economic by the fact that the very small extrusion line can run effectively continuously without any ~Lul~pd~:s for break down of adjacent lines. In addition the processing speed is very high in view of the fact that the adhesive is applied at the extrusion sta~e or shortly Ill~ arl~l and prior to the e:lull ,g step so the extrusion stage can run at a speed of the order of 500 feet per minute leading to a winding speed in the range 1500 to 4000 feet per minute depen ,~ upon the type of material to be ~uue~d.

Claims (24)

CLAIMS:

1. A method of forming a single pressure sensitive adhesive tape of high strength and low elongation to break comprising extruding a core layer of plastics material so as to define on the core layer as extruded a firstsurface, a second surface opposed to the first surface and two opposed side edges, the core layer being substantially longitudinally continuous and having apredetermined first width; applying onto the first surface a layer of a predetermined first thickness of a hot-melt pressure sensitive adhesive material; subsequent to the application of the adhesive layer, stretching the core layer and the adhesive layer carried thereby so as to cause longitudinal orientation of the core layer to an extent to provide for the tape said low elongation to break, so as to cause a reduction in thickness of the adhesive layer and such that a width of the core layer between the side edges is reduced by the stretching from the first width to a second width equal to that of the single tape and less than 2.0 inches; the single tape being formed without slitting or trimming so that side edges of the single tape are defined by said two opposed side edges; and winding the single tape into a package.

2. The method according to Claim 1 including providing on the second surface characteristics in a layer coextruded with the core layer which allow release of the second surface from contact with the adhesive material.

3. The method according to Claim 1 or 2 wherein the adhesive layer is stretched to a thickness less than 0.001 inches.

4. The method according to Claim 3 wherein the adhesive layer is stretched to a thickness less than 0.0005 inches.

5. The method according to any preceding claim wherein the adhesive layer is applied along a central portion of the second surface and has side edges of the layer spaced from the side edges of the core layer.

6. The method according to any preceding claim wherein the core layer is stretched to a thickness less than 0.003 inches.

7. The method according to Claim 6 wherein the core layer is stretched to a thickness less than 0.001 inches.

8. The method according to any preceding claim wherein the core layer is extruded through a die slot independent of die slots for other tapes and wherein the single tape is wound on a winding head directly associated with the die slot and independent of winding heads for other tapes.

9. The method according to any preceding claim wherein said single tape has a width in the range 0.0625 to 0.25 inches.

10. The method according to any preceding claim wherein the core layer is extruded from polypropylene and wherein the core layer is stretched by an amount in the range 600 to 900% and preferably of the order of 800% to provide said low elongation to break.

11. The method according to any one of Claims 1 to 9 wherein the core layer is extruded from polyester and is stretched by at least 300% to provide said low elongation to break.

12. The method according to any preceding claim wherein the core layer is stretched such that the tape has an elongation to break less than 40%.

13. The method according to any preceding claim including providing the release characteristics in a layer coextruded with the core layer wherein the layer has a thickness less than 0.0001 inch.

14. A package of tape comprising a pressure sensitive adhesive tape of high strength and low elongation to break comprising a core layer of plastics material extruded so as to define on the core layer as extruded a firstsurface, a second surface opposed to the first surface and two opposed side edges, the core layer being substantially longitudinally continuous and having a predetermined first width less than 2.0 inches and the core layer being longitudinally oriented and being formed without slitting or trimming so that side edges of the tape are defined by said two opposed side edges as extruded; and a layer of a hot-melt pressure sensitive adhesive material carriedon the first surface.

15. The package according to Claim 14 including a second layer coextruded with the core layer on the second surface of the core layer formed of a material having a component therein arranged to provide release characteristics to reduce adhesion between the adhesive layer and the second layer in the package.

16. The package according to Claim 14 or 15 wherein the adhesive layer has a thickness less than 0.001 inches.

17. The package according to Claim 16 wherein the adhesive layer has a thickness less than 0.0005 inches.

18. The package according to any one of Claims 14 to 17 wherein the adhesive layer is applied along a central portion of the second surface and has side edges of the layer spaced from the side edges of the core layer.

19. The package according to any one of Claims 14 to 18 wherein the core layer has a thickness less than 0.003 inches.

20. The package according to Claim 19 wherein the core layer has a thickness less than 0.001 inches.

21. The package according to any one of Claims 14 to 20 wherein said tape has a width less than 0.5 inches.

22. The package according to Claim 21 wherein said tape has a width in the range 0.0625 to 0.25 inches.

23. The package according to any one of Claims 14 to 22 wherein the tape is continuous without splice in the tape throughout the package.

24. The package according to any one of Claims 14 to 23 wherein the tape has an elongation to break of less than 40%.