|Publication number||US2750315 A|
|Publication date||Jun 12, 1956|
|Filing date||Apr 29, 1949|
|Priority date||Apr 29, 1949|
|Publication number||US 2750315 A, US 2750315A, US-A-2750315, US2750315 A, US2750315A|
|Inventors||Hubert J Tierney|
|Original Assignee||Permacel Tape Corp|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (15), Referenced by (50), Classifications (23)|
|External Links: USPTO, USPTO Assignment, Espacenet|
June 12, 1956 H. J. TIERNEY 2,750,315
PRESSURE-SENSITIVE ADHESIVE STRAPPING TAPE Filed April 29, 1949 PRESSURE-SENSITIVE ADHESIVE STRAPPING TAPE Hubert J. Tierney, St. Paul, Minn., assigner, by mesne assignments, to Permacel Tape Corporation, New Brunswick, N. J., a corporation of NewJersey Application April 29, 1949, Serial N0. 90,318
2 Claims. (Cl. 154-535) This invention is a high-strength, flexible, pressuresensitive, adhesive strapping tape adapted to be supplied. in roll form. This new type or adhesive tape is capable oi' industrial use for many purposes heretofore served by steel straps in holding together bulky and heavy articles.
It has a lengthwise tensile strength of at least 75 lbs. per inch width and can be made to have a tensile strength ranging up to several hundred pounds per inch width, and yet it is relatively quite thin considering its strength, having a thickness in the range of 5 to 20 mils. It has a very high crosswise tear resistance and cannet be torn crosswise between the fingers. It does not'havea cloth construction. it has a film or paper backing and the tacky adhesive layer contains a submerged layer of noti'- woven, hair-like, continuous, organo-synthetic textile filaments which are lineally aligned and extend from oneV end of the tape to the other.
This adhesive tape is stably and aggressively tacky and upon unwinding from the roll and application to the work it adheres instantly and rrnly upon mere contact, without use of water, solvents or heat. The pressure-.Sensitive adhesive is of the rubber-resin type and is eucohesive,
eing more cohesive than adhesive, and hence the tape can be unwound, handled with the fingers, and stripped from smooth surfaces, without leaving an adhesive residue or gurnn'iiug the iiugers.
This adhesive tape can be be employed for bundling together a plurality or" metal pipes, rods, bars, shovels, newsprint roll cores, etc. by tightly pulling the tape around them at one or more places to forni adhesivebonded straps which securely hold them together inconvenient bundles for shipment and storage. Similarly it can be used for strapping together the turns of a coil of metal strip7 heavy wire, cable, tubingY or chain, and for strapping together a plurality of such coilsfor shipment and storage; It canl be used for strapping together a plurality of packages, cartons, boxes or. cans to facilitate unitized handling, as in palleting operations. There are many other uses as, for example, in shipping stoves, lmetal cabinets and other household equipment, as well as bundles of window frames, doors, trim, ra-w lumber, wall board, panels, plywood sheets, metal roofing, plate glass, etc.
The tape cannot be severed by finger ,tearing but it can be readily cut with a knife or scissors. It, is thin, exible, supple, pliant, stretchable, and resilient, and easily fits over irregular contours to provide a tight, snug fit. It is shock-absorbing and lhas a high stock strength as well as high steady-pull strength. It can be conveniently removed from most objects such as metal, glass, plywood, wood boxes, etc., either by pulling off in a single strip, or by cutting and pulling .off in sections. When used for strapping those types of paperboard boxes where stripping off would delaminate the surface ,of the paper board, it can be cut so as to release the boxes and the portions in contact with the surfaces can be left in place.
The backing of this tape is a thin, flexible, non-woven,
States Patent O Mice non-cloth, continuous sheet material which contributes little or nothing to the extremely high effective lengthwise tensilev strength and crosswise tear strength of the tape; but it does provide substantially all of the crosswisc tensile strength and lengthwise tear resistance, and in addition provides a support and covering for the adhesive layer. As dependence is not placed upon the backing for the lengthwise tensile strength and crosswise tear strengthk of the tape, the backing can be quite thin and flexible, thereby making possible a tape which is amazingly thin and flexible considering its very high strength. The backings fall into two groups: non-fibrous film sheeting, including metal foils as well as organic polymer films.; and paper (flat or creped) which has been uniied and rendered water-resistant by treating, coating or impregnation.
Transparent film backings permit of making a tape product which is suciently transparent so that it can be applied to surfaces without markedly interfering with the visibility of underlying markings and coloration, and hence can be left in place upon shipping cartons without being conspicuous or concealing imprinted information. Transparent backings also permit of using a colored coatin g or printing upon the inner face of the backing, or a colored adhesive layer, or a combination of both, which will be visible through and protected by the backing.. This is a valuable feature in providing identifying, coding or marking information, or a decorative appearance. Film baekings are highly resistant to scutiing.
From the foregoing it will be evident that this adhesive strapping tape has numerous advantages over steel straps, wires, ropes, etc. it is easy to apply and is self-holding. It can be used for strapping cartons and fibre board boxes, and wooden articles, without cutting, crushing or breaking down the edges. The adhesive tape strappings cannot slip after application and they prevent or minimize relative shifting of articles bundled together. Further, the use of this strapping tape avoids injury to workmen since it cannot cut, prick or scrape the skin. Strapped bundles can be piled together without the straps of any bundle damaging adjacent bundles by cutting, puncturing, tearing or abrading.
The high lengthwise tensile strength and crosswise tear strength of this adhesive tape is obtained by incorporating in the pressure-sensitive adhesive layer a thin, fully embedded iayer of continuous organo-synthetic textile filaments which are lineally aligned and run lengthwise of the tape in continuous fashion. The term organosynthetic textile filaments designates the man-made, synthetic, organic polymer filaments of the textile industry, which are of such flexibility, fineness, and strength that they can be tied into hard knots; such as rayon filaments, nylon filaments, etc. These filaments possess a substantial degree of stretchability and resiliency. Each filament is a continuous, smooth-surfaced, cylindrical, mono-fiber extending without break from one end of the tape to the other (although a small number of the total filaments in any actual tape may be found to have become broken since ideal manufacturing conditions are not required).
These laments are surrounded and permanently bonded by `the adherent tacky adhesive composition to which they are united. The filaments are extremely fine and hair-like and there are a large number per inch width of the tape. They are the load-carrying elements of the tape. The tacky adhesive is water-proof, elastic, stretchy, and highly cohesive, and provides a matrix for the hair-like filaments of `such nature that the unitary adhesive and filament structure has properties peculiar to the combination and not possessed by either component alone. The continuous mono-fiber filaments can be present in the form of untwisted, free, aligned filaments. Or use can be made of aligned yarns consisting of twisted continuous filaments, these non-spun yarns being of small diameter and forming a thin layer of parallel yarns, with the adhesive not only encasing the individual yarns but penetrating into them so as to encase and bind the individual filaments thereof. These are to be distinguished from the common filaments, yarns and threads of the textile industry which are formed by spinning natural fibers or are formed by spinning staple iibers that have previously been made by chopping continuous synthetic filaments into fibers capable of being carded and spun in a manner analogous to the handling of cotton fibers.
The physical structure and resultant properties of the present tape are quite different from what they would be if yarns spun from staple fibers were employed. Such yarns would have to be of larger size to impart equivalent strength and this would make the tape much thicker and stiier. The individual fibers would not extend continuously from one end of the tape to the other, being relatively short. The intermeshed staple ibers of spun yarn cannot combine with the rubber-resin adhesive to provide an adhesive-fiber combination equivalent to that of the present tape, the fibers of a spun yarn being in close contact and mechanically restrained so that the adhesive cannot penetrate suiiiciently to directly encase each ber throughout its length. And a strong lengthwise stress will cause the intermeshed spun fibers of the yarn to pull apart.
Further details on the structural features of my novel adhesive strapping tape will be given following a description of the drawings and of the method of making the tape illustrated therein.
In the accompanying drawings:
Fig. l shows a roll of the pressure-sensitive adhesive strapping tape;
Figs. 2 and 3 are edge views of the tips of two types of tape shown in enlarged schematic fashion; and
Fig. 4 is a diagram showing an illustrative `system for the continuous manufacture of the tape.
Referring to Fig. l, there is shown a roll l of the pressure-sensitive adhesive strapping tape wound directly upon itself, the adhesive side being on the inside. As the legends indicate, this tape has a tensile strength of at least 75 lbs. per inch width and comprises a lm or paper backing carrying on its inner face a layer of pressure-sensitive adhesive containing fully embedded organo-synthetic textile filaments which are continuous mono-fibers and run lengthwise of the tape in aligned relation to each other.
Fig. 2 shows in more detail the structure of a particular type of such strapping tape. This tape has a ilm or paper backing 11 coated on the inner face with a pressuresensitive adhesive layer 12. The backing can be pre-coated with a primer when it is desired to obtain a higher bond strength between the adhesive layer and the backing. Embedded within the adhesive layer is a layer of contiguous continuous organo-synthetic filament yarns i3, of the type previously described, the tips of which are exposed to view in the drawing. These yarns nm lengthwise of the tape and are parallel to each other and to the backing and to the smooth (iiat) surface of the adhesive layer, and are referred to as being aligned. They are ordinarily laid down in a mono-layer (a layer having a thickness of one yarn) with adjacent yarns nearly touching each other (i. e. approaching to a shoulder to shoulder relation), although an occasional crossing over of yarns and an occasional bunching may result from the difficulty of obtaining an absolutely uniform alignment. Each yarn consists of a number of continuous mono-fiber 'filaments twisted together. A loose or medium twist yarn is used, as dstinguished from a tight twist yarn or thread, so as to facilitate adhesive penetration. Thus a twist value on the order of one twist per inch is suitable. Each yarn is completely encased by the pressure-sensitive adhesive, which penetrates between the yarns. The adhesive penetrates into the yarns and impregnates them s0 that the individual laments are bonded together and thereby unified by the pressure-sensitive adhesive.
Fig. 3 illustrates an alternative tape structure having a ilm or paper backing 14 coated on the inner face with a pressure-Sensitive adhesive layer 15. The backing can be primed if desired. In this case the adhesive layer has embedded within it a layer of untwisted continuous organosynthetic mono-fiber filaments i6, of the type previously described, as distinguished from yarns formed of twisted. filaments. These laments are aligned and run lengthwise of the tape and each filament is completely encased by the pressure-sensitive adhesive. The filaments overliey each other to form a layer having a thickness of the same order of magnitude as would be provided by a mono-layerl of contiguous yarns formed of the filaments.
Referring to Fig. 4, there is shown an illustrative continuous system for making the adhesive tape. Briefly, this system comprises apparatus for applying a first coating of pressure-sensitive adhesive solution to a backing sheeting which is continuously drawn from a supply roll, partially drying this adhesive coat, applying a mono-layer of lineally aligned continuous filament yarns upon the adhesive coat and embedding the yarns so they are retained in position, applying a second coating of pressuresensitive adhesive solution thereover, drying the sheeting in an oven to fully remove the solvent, and winding the adhesive sheeting in a jumbo roll. This adhesive sheeting can then be slit into desired widths and wound into adhesive tape rolls of desired length, ready for use and sale.
The following is a more detailed description.
.T he film or paper backing sheeting is continuously withdrawn from supply roll 20 (provided with a tensioning brake, not shown) and passes over guide roll 21 and under guide roll 22 so as to be in a smooth, unwrinkled condition, as it is drawn through the nip of the horizontal squeeze rolls 23 and 24, the upper of which is rubber-covered for resiliency and the lower of which has a rigid steel surface. The lower squeeze roll, 24, dips into a pressure-sensitive adhesive solution bath 25 and serves' to apply a coating of the solution upon the bottom face of the sheeting. The rolls are set so as to result in a coating weight (dry solids basis) equal to about onethird of the ultimate total adhesive coating weight. This is also controlled by the viscosity of the adhesive solution, the proportion of volatile solvent being adjusted to produce the desired viscosity. The coated sheeting then passes upwardly to and over the can drier cylinder 26, adhesive side out, where it is dried suciently to remove the bulk of the solvent. This cylinder is steam heated. The coated sheeting, adhesive side up, is then drawn horizontally to and through the nip of horizontal laminating rolls 29 and 30. The lower roll, 29, is rubbercovered and the upper roll, 30, has a rigid steel surface. These rolls have a diameter of about six inches. It is here that the yarns are laminated to the adhesive-coatedsheeting.
` The yarns are drawn from warp beams (not shown) located above each other in a tier. The sheets of yarns 31 are shown coming in from the left to the condensing comb device 32, which is shown schematically as these combing devices are well known in the textile industry. Here the yarns from the warp beams are intertted to form a single layer of contiguous yarns of the necessary density (number per inch width). For example, suppose it is desired to form a yarn layer consisting of yarns per inch, this layer to be 42 inches wide for laminating to the adhesive-coated sheet. Using warp beams which each have 600 yarns over a 54 inch width, a total of seven beams are used, thus providing 4200 yarns. The seven sheets of yarns are combined at the condensing comb (as illustrated in the drawing) and the width reduced from 54 to 42 inches, thereby securing the desired density of 100 yarns per inch width. The layer of yarns is drawn down over a one inch diameter steel doctor rod 33 and then under and around a similar doctor rod 34, and then up to and around the upper laminating roll 30, which rotates in a counterclockwise direction, meeting the adhesive-coated backing at the nip.
The layer of yarns is pressed into the surface of the soft, partially dried, adhesive coating in going through the nip of the laminating rolls, to form a lneally aligned mono-layer of yarns which are held in place by the tackiness of the adhesive.
The laminated sheeting proceeds horizontally, yarn side up, to the coating device 35 having a support roller 36 over which the sheeting passes below a spaced doctor blade 37 behind which the adhesive solution 38 is fed, thereby spreading on the second coating of pressure-sensitive adhesive solution in an amount equal to about twothirds of the total adhesive coating weight (dry solids basis). The total adhesive coating is such that the layer of yarns in fully embedded within it and aY smooth (flat) adhesive surface is obtained.
The fully coated sheeting is then drawn into the upper part of drying oven 39, where it passes back to guide roll 40, then down to the guide roll 41 near the bottom, then forwardly to guide roll 42, up to guide roll 43, back to guide roll 44, up to guide roll 45 and then forwardly to and over guide roll 46 and out of the oven.
The dried adhesive sheeting then passes over roll 47, down under guide roll 45, and over the top of driven pull drum 49. This pull drum contacts the tacky, adhesive surface of the sheeting and exerts a pull which is responsible for drawing the backing sheeting through the entire system from its supply roll, and for drawing ther yarns to the laminating rolls from the section beams. The adhesive sheeting passes from the pull drum to and under guide roll 50 to a wind-up machine Where it iS- wound into jumbo roll 51, thus completing the manufacturing process except for the conventional subsequent slitting and tape roll winding operations.
This system can be easily modified for making adhesive sheeting of the Fig. 3 structure wherein untwisted mono-fiber filaments are employed. In this case the filaments can be supplied from spools or cones of untwisted filament tows which are mounted so as to furnish the necessary number. For example, a rayon tow may consist of 2,900 filaments of l.5 denier size, the total tow denier thus being 4,400. The tows are drawn forwardly through a guide board having a porcelain or glass-lined spacing and aligning tube for each tow. The horizontal series of tows emerging from these tubes then passes over and under a series of doctor rods where the filaments spread out to form a fairly uniform layer, and this layer of filaments can be drawn over a vibrator bar to further settle the filaments in aligned relation and produce a uniform thickness across the layer. The layer of filaments is then drawn into the laminating rolls and is combined with the adhesive-coated backing sheeting in lieu of the yarns illustrated in Fig. 3. Due to the softness of the partially dried adhesive, the filaments are all pressed in and become adhesively anchored.
Further mention will now be made of the various materials which can be employed in making the present adhesive strapping tape.
The backings fall into two groups: non-fibrous film sheeting, including metal foils as well as organic polymer films; and paper (fiat or creped) which has`been unified and rendered water-resistant by treating, coating or impregnation.
Cellulose acetate films are well suited for use as nontbrous film backings for the present tape, and have an advantage over cellophane in being resistant to prolonged contact with water. Other cellulosic films are well known but are more expensive. The backingv film can be given a micro-thin coating of a low-adhesion polymerio compound on the back face so as to reduce the force required for unwinding the adhesive tape from a roll. Cellulose tristearate, tripalmitate, and trilaurate are examples of such compounds, and will provide the back surface with an adherency to the pressure-sensitive adhesive which is less than that of a base film of cellulose acetate or cellophane. Examples of non-cellulosic films are the various vinyl polymer films, polyethylene films, rubber hydrochloride films, etc. These films are all obtainable as clear transparent film sheeting adapted for making transparent strapping tapes.
The fibrous paper types of backings may be of the kinds heretofore employed in the making of paper-backed pressure-sensitive adhesive tapes. These are generally bibulous kraft or rope papers which have been unified by impregnation with a flexible water-insoluble rubbery composition adapted to render the paper water-resistant and to bind the fibers together so as to prevent splitting or delamination of the paper under the strong force exerted upon the paper when aggressively tacky tape is unwound from rolls thereof. Creped paper, such as kraft towelling paper, is commonly used for making backings for masking tape, as this provides increased stretchability. Such unified backings are commonly backsized with a thin coating of material (such as shellac, a cellulosic lacquer, or an alkyd resin) which reduces the force required for unwinding the tape. For detailed information on the making of illustrative unified paper tape backings reference may be made to U. S. Patents Nos. 2,236,527 2,410,078 2,410,089 and 2,438,195. An impregnated paper backing is not essential. Thus chemical treatment may have been employed to unify the fibers, as with parchmentized paper. Or a dense, highly calendered paper may be used, having a coating or coatings on the exposed back surface to cover the fibers and reduce the force required for unwinding the tape, the natural interbonding of the fibers then being suicient to provide a unified paper backing that will not delaminate4 The term paper as herein used embraces not only true paper but equivalent non-woven fibrous sheetings formed of intermeshed or felted fibers.
The adhesive may be one of the various rubber-resin type pressure-sensitive tape adhesives, well known in the art, which are water-insoluble and aggressively tacky. These adhesives have a rubbery base of natural or synthetic rubber which provides cohesion (internal strength) and elasticity (a retractive force when stretched and retraction when released after stretching); and this rubber base is modified by blending with a compatible tackifier resin (such as rosin or ester gum) which serves to increase adhesion (tackiness) and decrease cohesion, with an attendant increase of stretchiness (elongation under low stresses) and decrease of elasticity. These rubber-resin tape adhesives have a proper four-fold balance of adhesion, cohesion, stretchiness and elasticity, which permits adhesive tape coated therewith to be aggressively and stably tacky and yet be capable of being stripped back from smooth surfaces to which temporarily applied without delamination or offsetting of adhesive, even though the adhesive has been coated directly upon a smooth nonfiorous film backing (such as cellophane) and has no mechanical anchorage thereto. These tape adhesives are termed eucohesive by which it is meant that they are more cohesive than adhesive such that offsetting or transfer of adhesive material does not result when the tape coated therewith is unwound from rolls or removed from surfaces to which temporarily applied, and the tape can be handled without transfer of adhesive material to the fingers. Certain synthetic polymers are inherently tacky and eucohesive and possess the above-mentioned fourfold balance of properties, and can be used as pressuresensitive tape adhesives, thus being equivalents of the rubber-resin adhesives and hence they may be regarded as being of the rubber-resin type. An example is a 75:25 copolymer of Z-ethyl-butyl-acrylate and ethylracrylate.
The rubbery bases used include crude natural rubber, Buna-S type synthetic rubber, and polyisobutylene (Vistanex). The tackifier resins include rosin, ester gum, pure hydrocarbon terpene resin of 85 C. melting point (Piccolyte), and hydrogenated indene-coumarone resin of 150 C. melting point (Nevillite resin). Zinc oxide can be included as an opacifying and reinforcing pigment when transparency is not needed. Carbon black can be included to give a black color, and titanium dioxide pigment to give a brilliant white color. Various chromatic pigments can be included to produce desired colors. For present purposes a highly aggressive tack is desired and can be obtained by using about 75 to 125 parts of tackiiier resin per 100 parts of rubber. A suitable proportion of zinc oxide, when used, is about 50 to 75 parts per 100 parts rubber, and it is combined with the rubber by milling together, as is the case when other pigments are to be incorporated. The adhesive is prepared for coating by churning together the rubber (cut into pieces) and the resin in a volatile hydrocarbon solvent (such as heptane) present in proportion to impart a suitable coating viscosity.
As previously stated, the continuous, hair-like, monofber filaments can be present either in the form of yarns formed of a plurality of twisted filaments, or in the form of untwisted, free filaments. In either case the filaments are continuous organo-synthetic textile fibers. The filaments of the yarns have a size in the range of approximately 1 to 5 deniers and should have a tenacity of at least 1.5 grams per denier. When free, untwisted, filaments are employed they may have a considerably higher denier value. The denier value is the weight in grams of a 9,000 meter length. The tenacity value is the tensile strength in grams per denier. These filaments and yarns possess a substantial degree of stretchability and resiliency. Examples of commercially available filaments are those formed of viscose rayon, cuprammonium rayon and saponified acetate rayon (Fortisan), which are all regenerated cellulose filaments; those formed of acetate rayon (cellulose acetate); those formed of nylon (a linear polyamide); those formed of Vinyon (a copolymer of vinyl acetate and vinyl chloride); those formed of Orion (a poly-acrylonitrile type); and those formed of Terylene (a poly-terephthalic acid type).
The filaments and yarns can be used in the normal form supplied by the producer, without having been subiected to any special treatment. However, if desired, they can be given a special treatment prior to incorporation in the adhesive so as to modify their properties. Thus a physical or chemical treatment, or a washing, or the application of an impregnant, or of a surface coating or sizing, may be employed to increase strength, elasticity, heat resistance, water resistance, adhesion, etc.
The minimum total denier value of the filaments per inch width of tape is about 9,000 for viscose rayon filaments of medium tenacity of obtain a tensile strength of at least 75 lbs. per inch width'. Filaments of higher tenacity permit of a lower total denier.
The following tape structure examples give an idea of the amazing strength that can be obtained in strapping tapes which are thin and highly flexible.
Example 1 This transparent strapping tape had the structure shown in Fig. 2. It had a transparent cellulose acetate film backing of 1.5 mils thickness. The thickness of the pressuresensitive adhesive layer was 6.0 mils, the total caliper thickness of the tape thus being 7.5 mils. The yarn layer consisted of a mono-layer of contiguous yarns numbering 100 per inch width. The yarns were of 100 denier size and each yarn was formed of 40 continuous viscose rayon filaments (semi-high tenacity) of 2.5 denier size, having a medium twist. Thus for each inch of width there were 4,000 filaments having a total denier value of 10,000.
A transparent rubber-resin pressure-sensitive adhesive was used and the tape as a whole was transparent in the sense that it could be applied to surfaces without obscuring the colorings and markings. The adhesive transparentizes the filaments, as it surrounds them and has approximately the same refractive index.
This strapping tape had a lengthwise tensile strength of lbs. per inch width and an elongation at break of 15%. The crosswise tensile strength was 15 lbs. per inch widt of the tested piece of tape, and the crosswise elongation at break was 5%.
Example 2 This strapping tape likewise had the structure shown in Fig. 2, and had a transparent cellulose acetate film backing of 1.5 mils thickness. The pressure-sensitive adhesive layer was 9 mils thick, the total caliper thickness of the tape being 10.5 mils. The adhesive contained carbon black pigment, giving the tape a black appearance. The backing film, although actually untinted, had the appearance of being a glossy black film, due to an optical illusion effect. The yarn layer consisted of a mono-layer of contiguous yarns numbering per inch width. The yarns were of 300 denier size and each yarn was formed of 60 continuous viscose rayon filaments (semi-high tenacity) of 5 denier size, having a medium twist. Thus for each inch of width there were 6,000 filaments having a total denier value of 30,000. The caliper diameter of this yarn, measured under tension, is about 7 mils. The diameter of the yarn as determined by a measuring microscope, without tension, is l0 to 13 mils, which indicates the fact that the yarns have a loose twist and become compressed when incorporated in the tape adhesive. The diameter of an individual viscose filament of 5 denier size is 0.84 mil. The diameter is proportional to the square root of the denier value; thus a 2.5 denier viscose filament (as used in the preceding example) has a diameter of 0.59 mil.
This strapping tape had a lengthwise tensile strength of 180 lbs. per inch width and an elongation at break of 14%. The crosswise tensile strength was 15 lbs. per inch and the crosswise elongation at break was 5%. The lengthwise tensile strength of the yarn-reinforced adhesive layer per se (i. e. without the backing film) was also 180 lbs; per inch width, but its crosswise tensile strength was so low that it could readily be pulled apart between the fingers.
By using-nylon yarns of 210 denier size, per inch width, in the foregoing construction, the lengthwise tensile strength can be increased to about 350 lbs. per inch width.
Example 3 This tape was like that of the preceding example except that the pressure-sensitive adhesive was pigmented with zinc oxide, and the backing was a creped towelling paper unified by a vulcanized rubber-resin-zinc oxide impregnant (see Kellgrens U. S. Patent No. 2,410,078), of the same type employed in the manufacture of masking tapes. The caliper thickness of the backing was 7 mils and the thickness of the adhesive tape was l5 mils.
This strapping tape had a tensile strength of lbs. per inch width and an elongation at break of 18%. The crosswise tensile strength was l1 lbs. per inch and the crosswise elongation at break was 20%.
Example 4 viscose rayon filaments of 1.5 denier size and there were 11,600 filaments per inch width; these being supplied from tows containing 2900 filaments each.
This strapping tape had a lengthwise tensile strength of 160 lbs. per inch width and an elongation at break of 6%. The Crosswise tensile strength was 15 lbs. per inch and the Crosswise elongation at break was The foregoing tensile test measurements were all made on a Thwing Albert Electro-Hydraulic Tensile Tester, Model 37-4, the lower jaw moving at 12 inches per minute.
The structure of the present type of pressure-sensitive adhesive strapping tape provides the following features:
The lineally aligned, continuous, hair-like, organosynthetic textile filaments and the surrounding rubberresin type pressure-sensitive adhesive provide a reinforced adhesive layer of novel construction having novel properties. These mono-fiber filaments are individually encased and permanently bonded by the aggressively tacky adhesive to which they are individually united, even when present in twisted yarns. This adhesive has elasticity and it is quite stretchy. This can be clearly demonstrated by separating the adhesive layer from the tape backing, as by making a tape with a normal cellophane (nonrnoistureproofed) backing and then removing the cellophane by moistening it and peeling off. The filamentcontaining adhesive layer can be pulled Crosswise between the ngers to two or three times its initial width without rupturing. Because of this property of the adhesive, together with the fact that it is permanently bonded to the filaments by virtue of its aggressive tackiness, the filaments are capable of movement relative to each other and relative to the backing without rupture of the bond between adhesive and filaments, without rupture of the bond between the adhesive and the backing, and without internal rupture of the adhesive. Not only does this make for a high degree of lengthwise and Crosswise flexibility but it permits of elongation of the yarns or free iilaments when the tape is stressed, and of their retraction when the stress is decreased or removed, so as to fully capitalize upon their stretchability and resiliency. It may be noted that these organo-synthetic textile filaments and yarns possess a substantial degree of stretchability and resiliency, unlike glass filaments and yarns, and the present tape construction fully utilizes this property. A very important feature is that this structure allows a relative shifting of the mono-fiber filaments so that when the tape is subjected to non-uniform stresses the load will be more effectively distributed as between the various filaments, thereby more nearly equalizing the strains on the yarns or free filaments and increasing the effective resistance of the tape to breaking. This is of particular value in obtaining a maximum resistance to shock stresses such as are produced, for example, when a bundle of steel rods is dropped on the floor and the adhesive tape straps are suddenly subjected to strong bursting forces which are non-uniform across the width and along the length of the tape.
The mono-fiber filaments are clamped, as it were, along their continuous lengths by the permanently adherent adhesive and this adhesive is highly cohesive. The effect of this is to increase the effective tensile strength of the embedded yarns or free filaments, their combined tensile strength being greater than the aggregate strength of an equal number of uncoated yarns or free filaments. The adhesive further serves to absorb and damp shock forces, because of its yieldable and resilient nature, thereby increasing the effective strength of the yarns or free filaments in respect to shock stresses. It should be noted that the adhesive has a low tensile strength per se, a layer of non-reinforced adhesive being quite easily pulled out between the fingers to the breaking point. Hence it is evident that a combination or co-active effect is involved.
A further co-active effect is involved in respect to the backing. The backing is clamped to the layer of yarns or free filaments by the tacky, stretchable, adhesive. When the tape is elongated under a lengthwise pull it is found that a backing of limited stretchability can elongate to a greater extent before rupture than otherwise is the case. Moreover, if a backing is used which will break before the filaments break, the continuity of the tape and its lengthwise strength is retained since the filaments are the load-carrying elements.
The organo-synthetic mono-fiber textile filaments do not adhere to rubber. A continuous man-made filament which is encased by rubber can be pulled out, being a smooth-surfaced cylinder held only by friction. This is in contrast to natural fibers. A yarn formed of twisted continuous organo-synthetic filaments has only a limited degree of anchorage to rubber in which encased. In the present adhesive strapping tape the organo-synthetic yarns and filaments require no special treatment in order to be firmly bonded, owing to the fact that the rubberresin type adhesive, unlike rubber per se, wets the fiber surfaces and has a strong specific adhesion to them. And as above pointed out, this adhesive bond is not broken by movement of the filaments inasmuch as the adhesive is very stretchy. The wetting action of the adhesive also facilitates its penetration between the filaments so as to thoroughly contact their surfaces.
The organo-synthetic textile filaments are sensitive to the presence of water and are permeable thereto, in varying degrees depending upon the particular kind. Viscose and other regenerated cellulose rayon fibers are especially moisture-permeable. These fibers are weaker when moist than when in a normal dry state, but when dried to an extreme they become brittle and weak. Cellulose fibers are not dimensionally stable and they shrink or expand as the moisture content varies. 'ln the present construction, the yarns and filaments all run lengthwise of the tape and are sheathed by a waterproof, moistureproof, hydrophobic adhesive. The filaments are exposed to the air only atv the ends of the tape, where it has been cut. Thus the filaments preserve their initial state which they have when incorporated into the adhesive and this initial state can be controlled for optimum properties. Gain or loss of moisture can take place at only a very slow rate since the hair-like filaments are extremely long relative to cross-sectional area and are exposed to the atmosphere only at the ends of the tape, and in a roll of tape the filaments are many yards long and the inner end of the tape is covered.
Since the yarns or filaments are aligned and run straight they are in a condition of maximum strength, unlike the undulating threads of woven cloth which cross over each other and bear into each other when a strong pulling force is applied. This also makes for greater lengthwise and Crosswise flexibility, and there are no fiber ends exposed at the side edges of the tape. The yarns can be closer together than in woven cloth, and untwisted filaments can be used. These factors all contribute to making possible extremely strong adhesive strapping tapes having maximum flexibility and suppleness and minimum thickness.
As previously mentioned, the present adhesive strapping tape also has novel structural properties in that the lengthwise tensile strength and Crosswise tear strength are mainly due to the lineally aligned filaments embedded Within the pressure-sensitive adhesive (i. e. to the filamentreinforced pressure-sensitive adhesive layer), whereas the Crosswise tensile strength and lengthwise tear resistance are mainly due to the backing. Thus the backing and the reinforced adhesive layer perform distinct functions in respect to strength properties. Crosswise tensile strength and lengthwise tear strength are of secondary importance for strapping purposes. The present construction avoids an unnecessary degree of Crosswise tensile strength and lengthwise tear strength and thereby makes possible not only greater economy in manufacture but improved properties which are important, such as flexibility, suppleness, and thinness. Thus it is possible to employ ordinary cellulose acetate lm backings, obtaining the advantage of thinness, exibility, transparency, and a smooth, glossy, seuil-proof back surface.
Using laments designed to provide a tape having a lengthwise tensile strength of about 100 lbs. per inch width or higher, it is found that as the lengthwise load ing force is increased, the distribution of stress as between backing and reinforced adhesive layer shifts so that as the breaking point of the tape is approached the laments are carrying substantially the full load. Hence it is that the lengthwise tensile strength of the tape (pounds per inch width load at breaking) is found to be substantially the same as the lengthwise tensile strength of the adhesive coated lilaments in the absence of the backing. This is illustrated by the data of Example 2. Even in the case of tape so constructed as to have a lengthwise tensile strength of 75 lbs. per inch width, the strength is mainly due to the filaments embedded in the adhesive layer. This is in contrast to pressuresensitive adhesive tapes having a substantially lower tensile strength, where the tensile strength of the tape is more nearly comparable to that of the backing per se, in which cases the backing contributes a large factor. In the case of a tape having a non-reinforced adhesive layer, the backing is substantially entirely responsible for the tensile strength of the tape, in diametric contrast to the present adhesive tape.
Having described various embodiments of my invention for purposes of illustration rather than limitation, what I claim is as follows:
1. A normally tacky and pressure-sensitive adhesive tape comprising a non-woven backing, a layer of soft rubbery and cohesive bonding coat comprising a soft rubber thereon, a layer of parallel strands of strong, high tenacity nylon extending longitudinally of said tape on said bonding coat and spaced laterally from each 40 other, and a continuous layer of a normally tacky and pressure-sensitive adhesive covering said layer of strands 12 and said bonding coat, in which adhesive tape the spaces between the adjacent strands are substantially lled with pressure-sensitive adhesive and covered to the substantial exclusion of air, said strands being disconnected mechanically from each other and being retained in their individual positions solely by adhesive means.
2. A normally tacky and pressure-sensitive adhesive tape comprising a brous paper backing impregnated with a composition comprising a soft rubber, a layer of soft, rubbery and cohesive bonding coat thereon, a layer of parallel strands of strong, high tenacity material eX- tending longitudinally of said tape and spaced laterally from each other on said bonding coat, and a continuous layer of a normally tacky and pressure-sensitive adhesive covering said layer of strands and said bonding coat, in which adhesive tape the spaces between the adjacent strands are substantially lled with said bonding coat and covered to the substantial exclusion of air, said strands being disconnected mechanically from each other and being retained in their individual positions solely by adhesive means.
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|U.S. Classification||428/295.4, 24/DIG.110, 206/813, 428/297.1, 428/496, 156/178, 206/411, 428/354, 428/493, 24/16.00R|
|International Classification||C09J7/04, C09J7/02, B32B37/00|
|Cooperative Classification||B32B2309/10, Y10S206/813, Y10S24/11, B32B37/20, B32B37/1284, C09J7/045, B32B2309/105|
|European Classification||B32B37/20, B32B37/12D, C09J7/04B6|