SOLVENT-FREE COMPOSITIONS AND COATING OF NON-THERMOPLASTIC HYDROCARBON ELASTOMERSField of the InventionThis invention relates to a solvent-free, hot melt process for the manufacture of a non-thermosetting, pressure sensitive adhesive (PSA) from a non-thermoplastic, adherent hydrocarbon elastomer.
Background of the InventionPressure sensitive adhesives based on non-thermoplastic hydrocarbon elastomers such as natural rubber, butyl rubber, synthetic polyisoprene, ethylene-propylene, polybutadiene, polyisobutylene, or styrene-butadiene random copolymer rubber, are well known in the art. The dominant processing means of such adhesives comprise grinding the elastomer in a two-roll mill or in an internal mixer of the Banbury type, dissolving the elastomer and the REF: 23D20Other components of the adhesive in a hydrocarbon solvent, to coat the solution on a support, and dry the coated product to remove the solvent. This technology is discussed in Handboo of Pressure Sensitive Adhesive Technology, D. Satas (ed.), P. 268. Van Nostrand, N.Y., (1989). The solvent process has the disadvantage of being labor intensive, having low production percentages, and emitting large quantities of potentially hazardous solvents into the atmosphere, which requires expensive equipment for the recovery and / or incineration of the solvent. In addition, such solvent-based processes have become increasingly undesirable for use in the manufacture of adhesive tapes due to the increase in environmental and safety regulations throughout the world. A processing method, sometimes used when a relatively thick adhesive layer is desired, comprises grinding the elastomer as described above, mixing the rubber and other components of the adhesive in an internal mixer such as a Banbury mixer, and calendering the solid adhesive on a support using a stack of calenders of 3 or 4 rollers. The calendering process does not use solvent or require very expensive equipment. Additionally, this process is slow, and is only economical when coatings are desired.adhesive greater than about 2 mils (51 μ) thick. One application of the calendering process is described in US Patent No. 2,879,547 to Morris. Environmental considerations, low initial capital investment, potentially higher production percentages, and low processing costs have led to an accelerated interest in the use of the continuous hot melt composition and extrusion coating of thermoplastic adhesive compositions. The elastomers used in this technique are "thermoplastic" elastomers of the block copolymer type, including, for example, styrene-diene block copolymers. Such materials exhibit an acute reduction in viscosity at temperatures above 100 ° C, where the styrene domains soften. After cooling, the domains are reformed and the material recovers its character with properties similar to that of rubber and cohesive strength. Illustrative teachings of adhesive formulations and processes of this type are found, for example, in U.S. Patent No. 3,932,328 to Korpman, U.S. Patent No. 4,028,292 to Korpman, and U.S. Patent No. 4,136,071 to Korpman. Technology is best discussed in Handbook ofPressure Sensitive Adhesive Technology, pp. 317-373, DSatas (ed.), Van Nostrand, N.Y., (1989). Pressure sensitive adhesives, hot melt, based on er. These thermoplastic elastomers have found wide acceptance in the markets of packaging or packaging, labeling, and closure of diapers, but limited acceptance for use in paper masking tapes.
The adhesive properties of pressure sensitive adhesives made from these thermoplastic elastomers differ from those of adhesives based on non-thermoplastic hydrocarbon elastomers, and they are undesirable for many tape applications. Due to their unique adhesive properties, adhesive systems based on non-thermoplastic hydrocarbon elastomers, especially those that use natural rubber, are likely to be preserved for many applications for which thermoplastic elastomer systems are not suitable. Accordingly, there is a need to provide a method of manufacturing adhesives from such non-thermoplastic elastomers that is environmentally appropriate, economically viable and energy conserving. Hot-melt extrusion of pressure-sensitive adhesives employing non-thermoplastic hydrocarbon elastomers has been shownsuch as natural rubber. However, low molecular weight plasticizing adjuvants such as process oils, elastomeric oligomers, waxes, or other materials defined and described as plasticizers in Dictionary of Rubber, K.F. Heinisch, pp. 359-361, John iley & Sons, New York, (1974), are used as the main components in the adhesive formulations. These plasticizer builders facilitate processing but decrease the ability of the finished adhesive to hold a load and it is known in the art that they generally degrade the performance of the adhesive. Canadian Patent No. 698,518 of P. Beiersdorf & Co., discloses a solventless extrusion coating process for coating a PSA composition based on non-thermoplastic elastomers including natural and synthetic rubber, polyisobutylene and high molecular weight polyvinyl ether. The elastomer is pre-mixed and blended in a batch operation, separately, using conventional rubber processing equipment such as a two-roll mill or a Banbury mixer. The composite mixture effected is then fed to a single screw, hot extruder, and the molten coating is extruded onto a moving fabric. Plasticizer adjuvants comprising up to 54% of the formulation are used. It is believed thatthese plasticizer coadjuvants are used to accommodate the coating difficulties normally associated with the extrusion of high viscosity elastomers. Japanese Patent Application Shou 50-37692 to Fukugawa et al discloses a similar pre-grinding process of pressure sensitive adhesive ingredient mixtures for 25 minutes, feeding the pre-compounded mixtures to a hot extruder, extruding the materials at 230 ° C over a substrate, and curing it in extruded materials exposing them to electron beam radiation to increase the cohesive strength of the adhesive to improve bonding to the support. This paper describes a narrow range of materials including non-thermoplastic elastomer natural rubber and styrene-butadiene rubber (SBR). In the two examples using natural rubber, the natural rubber was mixed with a styrene-butadiene elastomer and a plasticizer builder. The plasticizer adjuvant is equal to about 87.5% of the total rubber filler, and adherent resins were not used. The non-natural rubber example included 25.8% plasticizer adjuvant. The German Provisional Patent Publication P-19 54 214.4 of Pyton AG discloses an extrusion process for the preparation of pressure sensitive adhesives that does not require a separate pre-grinding step. It's useda double screw extruder to continuously compose and coat a formulation comprised of five different types of materials. Natural rubber and / or partially vulcanized rubber, latex, polybutene with a molecular weight between 70,000 and 200,000, and polyisobutylene with a molecular weight between 100,000 and 250,000 comprises the "cohesive component". Four kinds of ingredients were required to accommodate this process. These other ingredients include polybutylene and low molecular weight polyisobutylene (less than 15,000) or natural bitumen, reactive and / or non-reactive resins, antioxidants, and various metal oxide fillers. US Patent No. 2,199,099 to Cunningham discloses that air and gases enriched with oxygen can be used to facilitate the oxidative breaking of the natural rubber in an internal mixer to reduce the molecular weight of the rubber. A continuous, hot melt extrusion process is known which employs the oxidation breakage aided by natural rubber air, followed by the addition of phenolic resin vulcanizing tackifiers and agents to form a thermosetting adhesive. In this process the molecular weight of natural rubber is reduced to such a degree that when the phenolic resin is added, the combination of rubber and resinIt can be processed at temperatures below which vulcanization occurs. Hot melt extrusion of non-thermoplastic hydrocarbon elastomers has not proven to be a commercially practical method for manufacturing pressure sensitive adhesives having the properties necessary for PSA tapes, such as masking, packaging and medical tapes. Furthermore, such processing technology has not been devised to sustain the dominant position of the natural rubber elastomer, the only major use of the non-thermoplastic hydrocarbon elastomers for those PSA tapes. According to Handbook of Pressure Sensitive Adhesive Technology, the solvent and / or water coating of PSA adhesives are the only practical techniques for manufacturing such tapes, especially when PSAs are based on high molecular weight hydrocarbon elastomers. As discussed earlier, these techniques are not entirely satisfactory. Thus, it would be desirable to provide a practical method of composing non-thermoplastic hydrocarbon elastomers in the molecular weights and compositions of interest for the PSA industry.
Brief Description of the InventionA process has been discovered which overcomes the disadvantages of the prior art and allows the effective and controllable processing of non-thermoplastic hydrocarbon elastomers, especially high molecular weight non-thermoplastic hydrocarbon elastomers, such as natural rubber in pressure sensitive adhesives. , adherents, without the need to employ organic solvents or significant amounts of low molecular weight plasticizer adjuvants The present invention comprises a process for the solvent-free composition of non-thermosettable PSA based on a non-thermoplastic hydrocarbon elastomer, preferably a hydrocarbon elastomer. non-thermoplastic, adherent.The process employs a continuous composition device and hot melt processing techniques.The adhesive composition can be composed without separating the pre-batching of the elastomer and without the use of significant amounts of coadjutant. before plasticizers to reduce the viscosity of the composition to make it processable. Additionally, the adhesive composition can be applied to a moving fabric directly from theComposition devices to provide a continuous method for the manufacture of a PSA tape. The process of the invention can accommodate a high molecular weight hydrocarbon elastomers, for example with a viscosity average molecular weight (Mv) of 250,000 or greater. As discussed above, it was previously believed that such elastomers could only be compounded and applied if solvent or water processing techniques were used or if significant amounts of low molecular weight plasticizer coadjuvants were employed. The process can employ either aerobic or anaerobic processing. For the purposes of this invention, aerobic processing means that available oxygen (such as compressed air) is intentionally injected into the composition device to promote oxidative cleavage of the hydrocarbon elastomer. Anaerobic processing means that gas without oxygen is intentionally injected into the composition device. However, small amounts of air may be present in the anaerobic processing in the practice of the invention. Aerobic processing can be advantageously used when the hydrocarbon elastomer will preferentially experience chain cleavage more thancrosslinking and / or extension of the chain. The aerobic processing allows a greater reduction in the molecular weight of the elastomer in a relatively short period of time. Additionally, aerobic processing allows manufacturing at lower temperatures. As a result, the thermosensitive materials can be composed as the hydrocarbon elastomer of the process of the invention. Anaerobic processing can be advantageously used when using elastomers that crosslink under oxidative conditions. This mitigates the problem of the cross-linking of these elastomers during processing. Anaerobic processing can also be used with elastomers that do not crosslink under oxidative conditions to achieve a molecular weight greater than that which could be achieved under aerobic conditions. This increases the cohesive strength of the adhesive and minimizes the degree of delayed crosslinking necessary to provide greater cohesive strength. Anaerobic processing of any type of elastomer also results in an adhesive that has lower odor and lighter color. The practice of the invention employs a continuous composition device having a sequence of alternate transport and processing zones. The elastomer is continuously transported from one area to the other by thedevice. The processing zones are capable of crushing the elastomer. They are also capable of mixing additives in the elastomer. In the process, a non-thermoplastic elastomer is fed to the first transport zone of the composition device. This first zone transports the elastomer to a first processing zone where the elastomer is crushed. The crushed elastomer is then transported to a second transport zone, where an adherent is added and the mixture of the two is transported to a second processing zone, where the adherent and the crushed elastomer are mixed to form a combination of two materials . The mixture can then be discharged from the composition device and stored for final use. Alternatively, the mixture can be applied to a fabric, preferably a moving fabric in the form of a thin film. Another aspect of the invention comprises a novel product and the process involving the use of small amounts of chemical "blowing" or "foaming" agents that release gas after thermal decomposition and create a cellular structure within the adhesive mass. The cellular structure of the adhesive changes the topography, density, compressibility and conformability of the adhesive, to allow a tape made with this adhesivepresent instant adhesion or "fast adhesion", properties superior to those received by the thinnest, non-foamed extruded adhesive and comparable with foamed adhesives prepared by evaporation of the solvent. This aspect of the invention overcomes the problems typically encountered with extruded adhesives. These problems are caused by the higher densities and uniform, non-extensible surfaces of extruded adhesives resulting in comparatively poor "fast adhesion" properties. In this aspect of the invention, an adherent is an optional, although preferred, ingredient. To facilitate the description of the invention, the following terms used herein will have the following meanings: PSA not thermosettable will mean a PSA that does not become relatively infusible and will remain in an adhesion free state upon exposure to heat. Non-thermoplastic hydrocarbon elastomer will mean a homopolymer or hydrocarbon copolymer is distinguished from a block copolymer. Pressure-sensitive adhesive will mean an adhesive that is normally adherent at room temperature and adheres to a surface after the simplecontact with the surface without the need for more pressure than that of a finger or hand. Adherent will mean a material that is miscible with at least one hydrocarbon elastomer employed in the process, having an average molecular weight of Mn of 10,000 grams per mole (g / mol) or less and a glass transition temperature (Tg) of -30. ° C or more, as measured by differential scanning calorimetry (DSC). Plasticizer adjuvant means a material having an Mn of less than 50,000 g / mol and a (Tg) of less than -30 ° C as measured by DSC.
Brief Description of the DrawingsFigure 1 is a schematic representation of a line of composition and continuous coating in the practice of the invention. Figure 2 is a schematic representation of a line of composition and continuous coating useful in the practice of the invention. Figure 3 is a schematic representation of the extruder screw design employing 9 zones. Figure 4 is a schematic representation of the extruder screw design employing 11 zones.
Detailed description of the inventionThe process of the invention employs a device of continuous composition. Meet a number of such devices. They may comprise a single unit or a series of interconnected units to continuously process the elastomer. The device has a sequence of alternate transport and processing sections which are interconnected. An example of a continuous composition device useful in the present invention is a twin screw extruder having a sequential series of transport and processing zones. A plurality of inlet openings are provided along the length of the extruder to facilitate the addition of the different materials, such as tackifying resins, fillers, antioxidants, plasticizing adjuvants (if desired), radiation amplifiers such as sensitizers to electron beams and photoinitiators, and other adjuvants known in the art. The addition of the materials, whether the elastomer, adherent, or other adjuvants, is done through the entrance doors to a partially filled transport zone or areas. A pump for the melt and a filter may be present either as an integral part of the extruder, or as a separate unit forfacilitate both the removal of the adhesive from the composition device and the removal of undesirable contaminants from the adhesive stream. In the practice of the process, the elastomer is added to a first transport zone of the composition device at a controlled rate, so that the elastomer does not completely fill the zone. The elastomer can be converted into pellets by grinding or extrusion before being fed to the composition device. Alternatively, by being fed directly into the composition device without milling or pelletizing using a device such as a Moriyama extruder. If the elastomer has been converted into pellets, it is preferably treated with a material such as talc to prevent agglomeration of the pellets. The elastomer is then transported by the first transport zone to the first processing zone where it is crushed. The first processing zone is typically designed to be essentially full and crush the elastomer. Additionally, the processing zone transports the elastomer to the next zone. It may be desirable to provide the first processing zone as at least two discrete processing sections separated from each other by a sectionOf transport. This allows the elastomer to be shredded in steps, with cooling of the crushed elastomer between each step. If two or more elastomers are to be processed in the invention, both can be added to the first transport zone and crushed in the first processing zone. Alternatively, the elastomers can be sequentially added to the different transport zones with sequential grinding after each addition of the elastomer. The sequential addition of the elastomer to different transport zones can also be employed when a single elastomer is used. If aerobic processing is desired, to easily inject a gas containing available oxygen, such as compressed air, into the composition device. Preferably the air is injected either in a transport section, or a transport zone located between two processing zones. Alternatively, the gas can be injected into any processing or transport zone. If the gas comprises compressed air, it is typically injected to the composition device at a pressure of 5 to 100 pounds per square inch (psig) (30-700 kilopascals (kpa)). Table I illustrates the relationship between air pressure andinherent viscosfor a smoked natural rubber sheet. TABLE ICompressed Air Pressure Flow Rate IV (psig) (kpa) SCFM (1 / hr) 60 414 35 992 1.5945 310 35 992 1.64207 35 992 1.73138 35 992 1.7869 35 992 1.810 0 35 992 1.82The natural rubber was crushed in the extruder used in Example 19. The screw speed was 180 rpm. The temperature of the melt was maintained at 163 ° C through the extruder. Air was injected and the mixture from zone 3 of the extruder. The rubber was fed to the extrudate at a rate of 57.8 kg / hr. A flow meter was used to regulate the flow of air to the composition device. Additionally, a valve can be used to control the pressure used to create or release the air pressure in the extruder. The grinding was preferably carried out in the absence of materials that could lubricate the elastomerand avoid reducing its molecular weight. This, however, requires the presence of small quantities of such materials, provided that the present amount does not effectively reduce the grinding rate. Certain other solid adjuvants, such as talc, inorganic fillers, antioxidants, and the like to the composition device can be fed to those already present during the grinding. The crushed elastomer was then passed from the first processing zone to the second transport zone. As with the first transport zone, the second transport zone is not completely filled by the elastomer. The adherent and optionally other additives are fed to the second transport zone. The resulting mixture is transported to the next processing zone where it is mixed to form a mixture or combination of materials. Numerous techniques can be used to feed those materials to the composition device. For example, a constant speed feeder such as a K-Tron weight loss feeder can be used to add solid materials. Hot drum dischargers, gear pumps and other suitable equipment can be used to feed liquids at a controlled rate to feed the liquids to the composition device. The additives present at lowConcentration can be premixed with one or more of the other components for a more accurate addition. Although substantially all of the grinding occurs in the first processing zone, some grinding may occur in the subsequent processing of the elastomer through the composition device. This additional crushing may occur in the subsequent transport or processing zones. In any case, the degree to which the elastomer must be crushed in the practice of the invention varies with each elastomer employed and the desired finished product. Generally, the elastomer must be sufficiently crushed to (i) allow the adherents and any other adjuvants subsequently added to be mixed successfully in the elastomer to form a mixture or combination (ii) to allow the mixture or combination to be extruded as a stream that is essentially free of both rubber particles and visually identifiable regions of unmixed tackifier and any other adjuvants. Once the crushed elastomer, the tackifier, and any other coadjuvants have been converted into a mixture, the composition can now be referred to as an adhesive. This adhesive typically has a viscosity at the processing temperature in therange from 500 Poise to 5000 Poise (measured at a cutting speed of 1000 sec-1). The higher viscosity adhesives can also be processed in the processes of the invention. The processing temperature of the adhesive is typically in the range of 100-200 ° C. The adhesive can be discharged from the composition device to a storage container for further use or further processing. Alternatively, it can be discharged directly onto a support in the form of a thin film. Preferably,. the support comprises a moving fabric. The thin adhesive film can be formed by pumping the adhesive through a coating matrix, optionally with the aid of a gear pump or other suitable device to develop sufficient pressure. The matrix is preferably of the variety of contacts (ie not a drip matrix) which extends the adhesive onto a moving fabric supported on a support roll. The die may have a flexible blade, a cylindrical rubber cleaner, or a rotating cylinder metal roller on the downstream side of the die opening to spread the adhesive. The matrix can be located at the outlet of the composition device to allow coating in line with the composition and extrusion operations. Alternatively, the adhesiveit can be discharged from the composition device fed to the coating matrix using a separate extruder, pump for melt, or combination of extruder and pump for the melt with sufficient pressure to force the adhesive mixture through the die. The adhesive may optionally be filtered before being fed to the coating matrix. The coated adhesive can optionally be crosslinked by exposing it to radiation, such as electron beam or ultraviolet radiation, to increase the cohesive strength of the material. The crosslinking can be carried out in line with the coating operation or it can occur as a separate process. The degree of crosslinking achieved is a matter of choice and depends on numerous factors such as the desired final product, the elastomer used, the thickness of the adhesive layer, etc. The techniques for achieving crosslinking via exposure to radiation are known to those skilled in the art. A release liner can optionally also be applied to the fabric, either before or after the application of the adhesive. That release liner may be continuous or discontinuous on the fabric and is normally on the surface of the opposite fabric to which the adhesive ultimately rests. The coatingRemovable can be applied either in line with coating or crosslinking operations, or as a separate process. Preferably a twin screw extruder is used as the device of composition in the invention. The screw extruder should be configured to crush the elastomer in the first processing zone before the addition of the adherent. Additionally, a mixture of elastomers is used in the adhesive, the first processing zone preferably allows the comminution and mixing of the elastomeric components. The extruder portion and the screw after the first processing zone should be designed to allow the addition of the adherent and other additives to the elastomer and mix the elastomer well with those materials. Preferably, the screw is designed to result in a homogeneous adhesive composition. The design of the screw to achieve the crushing, transport and mixing follows the normal practices known in the art. Namely, the screw has a sequence of transport and processing zones. Flow restriction and mixing elements are provided to achieve proper flow along the screw and obtain proper grinding and mixing. The transport zones can contain the elements of theOrdinary Arquimedes screw. The processing zones may contain cutting blocks, bolt mixers, or other elements designed for grinding, compounding and mixing. Flow restriction elements, such as trim blocks arranged with an inverted slope, reverse slope transport screws, a disk element or other device designed to restrict the flow of material, may also be present in the processing zone to ensure that the portion of the processing area that precedes those elements tends to run full of material while the next transport zone tends to run only partially full. A wide variety of non-thermoplastic hydracarbon elastomers can be employed in the present invention. These materials can be used alone or mixed in the practice of the invention. Examples of such elastomers include natural rubber, butyl rubber, synthetic polyisoprene, ethylene-propylene rubber, ethylene-propylene-diene monomer (EPDM) rubber, polybutadiene, polyisobutylene, poly (alpha-olefin) and copolymer rubber Randomization of styrene-butadiene. These elastomers "are distinguished from thermoplastic elastomers of the block copolymer type such as the styrene-diene block copolymers whichthey have vitreous end blocks attached to a block with properties similar to those of rubber, intermediate. Adherents useful in the invention preferably have a low molecular weight relative to the hydrocarbon elastomer, and a Tg greater than that of the hydrocarbon elestomer. Examples of useful tackifiers include resins and resin derivatives, hydrocarbon tackifying resins, aromatic hydrocarbon resins, aliphatic hydrocarbon resins, terpene resins ,. etc. Typically the tackifier comprises from 10 to 200 parts by weight per 100 parts by weight of the elastomer. When a foamed adhesive is desired, the blowing agent is added to the elastomer at a temperature below the decomposition temperature of the blowing agent. This is then mixed at a temperature such that it is distributed through the elastomer in a non-decomposed form. Preferably the blowing agent comprises 0.5 to 5 weight percent of the adhesive layer. However, smaller or larger amounts may be used if desired. Useful blowing agents typically decompose at a temperature of 140 ° C or higher. Examples of such materials include azo base molecules, synthetic hydrazide carbonate. The examplesSpecific to these materials are Celogen "* OT (4,4 'oxybis (benzenesulfonylhydrazide), HydrocerolMR BIF(preparations of carbonate and polycarboxylic acid compounds), Celo? in ^ AZ (azodicarboxamide) and Celogen ™ RA (p-toluenesulfonyl semicarbazide). Once dispersed, the blowing agent can be activated after extrusion, for example, by heating the extrudate to a temperature above its decomposition temperature. The decomposition of the blowing agent releases gas, such as N2, C02 and / or H20, and creates cell structures through the adhesive mass. The decomposition can be carried out before or after the adhesive is cured. Numerous coadjuvants can also be used in the adhesive. Examples of such adjuvants include antioxidants, such as hindered phenols, amines, and sulfur and phosphorus hydroperoxide decomposition entities; inorganic fillers such as talc, zinc oxide, titanium dioxide, aluminum oxide, and silica; plasticizer adjuvants such as those materials described as plasticizers in the Dictionary of Rubber, K.F. Heinish, pp.359, John iley & Sons, New York (1974), oils, elastomeric oligomers and waxes; and similar. Typically the antioxidant comprises up to 5 parts by weight per one hundred parts by weight of elastomer; the fillerinorganic comprises up to 50 part by weight per 100 parts by weight of elastomer; and the plasticizer adjuvants up to 10 percent by total adhesive weight. If a plasticizer is used, it should not exceed 10 percent by weight of the total adhesive composition. Preferably, it comprises from 0 to about 8.5 weight percent of the adhesive composition and more preferably less than 10 weight percent of the elastomer. The plasticizing adjuvants can be incorporated before, during, or after the trituration of the elastomer. However it is added, you should not avoid the effective trituration of elastomer. Preferably, the use of plasticizing adjuvants is unnecessary. Numerous organic and inorganic materials can be used as fabric in the practice of the present invention. Such materials include polymeric films, metal foils, paper, ceramic films, and the like. In addition, the fabric may comprise a plurality of fibers in a mesh-like construction. The fibers may be combined to form either a nonwoven fabric or a fabric (ie, collection of randomly arranged fibers). Virtually any PSA tape can be made by the process of the invention. Examples of suchtapes include masking tape, for packaging (such as tapes to seal and tape boxes), decorative tape, and protective film, labels, tape diaper closure, medical tape (such as tapes hospital and athletic), etc. Additionally, the process can be used to manufacture any article having a layer of a PSA based on hydrocarbon elastomer on a support. This invention is illustrated by the following examples, but the materials and amounts thereof set forth in those examples, as well as the other conditions and details should not constitute an undue limitation of this invention. A schematic representation of the configuration of a continuous composition, coating and crosslinking equipment of the type used in the invention is shown in Figures 1 and 2. The configuration represented by Figure 1 was used in Examples 1-13. The configuration represented by Figure 2 was used in Examples 14-19. Various screw configurations were used throughout the examples. Figure 3 is a schematic representation of the screw used in Examples 1-18: Figure 4 is a schematic representation of the screw used in Example 19.
The device of composition used in bothFigures 1 and 2 was a Werner-Pfleiderer 20 co-rotating twin screw extruder. An extruder model ZSK-30 was used in Examples 1-16. A ZSK-90 model was used in Examples 17-19. The extruders 20 and 21 were equipped with an elastomer feed hopper 22 and solid feed hoppers 24 and 26. The feed hoppers 22, 24 and 26 controlled the velocity of the material released in the extruders 20 and 21 by continuously checking the weight of the material in the feed hopper. A window 27 was provided near the discharge end of each of the extruders 20 and 21. With reference to Figure 1, a Zenith gear pump 28 was provided to measure melt of adhesive through the filter 30 and the matrix 32 An excess of adhesive was accumulated through an accumulation valve (not shown) by the pressure generated in the extruder 20. The coating matrix 32 deposited a desired thickness of adhesive on the cloth 34, which passes through the a coating roller 36. The matrix 32 had a 6 inch (15.2 cm) wide die with a rubber cleaner on the downstream side of the hole. The coating roller 36 was a chromed steel roller, whose temperature was controlled makingcirculate hot water through its interior. An electron beam crosslinking station 38 was also provided. An alternative eclipse configuration useful in the practice of the invention is shown schematically in Figure 2. In this configuration, a single screw extruder 23 was interposed between the extruder of double screw 21 and filter 30. The single screw extruder 23 was used to generate sufficient pressure to push the adhesive through the filter 30. Additionally, the Zenith gear pump 28 was used downstream of the filter to introduce the adhesive to the filter. the matrix 33. The matrix 33 was a 24-inch (61 cm) wide contact extrusion die with a rotating steel rod on the downstream side of the die to spread the adhesive over the fabric. The coating roll 37 was a temperature controlled steel roll having a rubber coating thereon. The line speed of this configuration was automatically adjusted to achieve the desired coating thickness. The screw designs employed in the Examples are shown schematically in Figures 3-4. The screw design of Figure 3 contains 9 zones. The screw design of Figure 4 contains 11 zones. Zones 1, 3, 5, 7, 9 and 11 (if present) comprise the zones oftransport. Zones 2, 4, 6, 8 and 10 (if present) comprise the processing zones. The dimensions of the different zones of each screw design are shown in Table II, as they are in the Examples in which each design was used.
TABLE II Screw Design Fig. 3 Fig. 3 Fig. 3 Fig.
Used in Examples 1-13 14-16 17-18 19Diameter (mm) 30 30 90 90Length (mm) 1160 1172 3380 3382Zone 1 (mm) 186 168 1000 482Zone 2 (mm) 70 84 260 240Zone 3 (mm) 154 125 440 230Zone 4 (mm) 56 84 200 240Zone- 5 (mm) 112 122 420 260Zone 6 (mm) 84 42 320 40Zone 7 (mm) 94 126 100 180Zone 8 (mm) 84 70 160 240Zone 9 (mm) 320 351 400 360Zone 10 (mm) - - - 240Zone 11 (mm) _ _ _ 870Example 1The synthetic polyisoprene Natsyn "* 2210 (available from Goodyear Tire and Rubber Co.) was pelletized using a Moriyama granulator and powder coated with talcum.This material was then fed to zone 1 of the twin screw extruder 20 at a speed of 68.0 g / min using a K-Tron weight loss feeder, which continuously verified the weight of the material in the hopper, the elastomer and talc were transported from Zone 1 to Zone 2 by the screw and were crushed in Zone 2. The elastomer was transported through Zones 3 and 4, where additional crushing occurred, to zone 5"where an elastomer sample was removed and found to have an inherent viscosity (IV) of 2.68 dl / g in toluene measured at a concentration of 0.5 grams per deciliter (g / dl). Arkon "* P-115 hydrogenated tackifier resin (available from Arakawa Chemical Industries, Ltd.) was dry blended with Irganox antioxidant" 1010 (available from Ciba-Geigy Corp.) at a ratio of 49 parts by weight resin to 1 part of antioxidant. This mixture was fed to the extruder 20 in zone 5 through the feed hopper 24 at a speed of 36.7 g / min. A K-Tron weight loss feeder was used to verify theweight in the hopper 24. A total of 53 parts by weight of adherent per 100 parts by weight of elastomer was fed to the extruder 20. The adhesive was transported through the remaining areas of the extruder and released to the doser 28. The metering pump 28 (see Figure 1) was adjusted to release 46.2 g / min of adhesive to extrusion die 32, which was 4.75 inches (12 cm) wide of adhesive from a masking tape support of corrugated paper at 30 ft / min (9.1 m / min) for an average coating thickness of 1.65 mils (41 μm). The temperature of the melt through the extruder was maintained at approximately 150 ° C. The coating roller 36 was maintained at a temperature of 90 ° C. The screw speed was maintained at 400 rpm. The resulting coated fabric comprised a PSA masking tape.
Example 2Example 1 was repeated except that after being coated on the corrugated paper support, the support continued to move at 30 ft / min (9.1 m / min) and the adhesive layer was exposed in line to the radiation of a beamof electrons at a dose of 6 MRads. The masked PSA masking tape had improved cohesive strength.
Example 3The equipment under conditions used in Example 1 was repeated in Example 3 with the following exceptions. A sheet of smoked natural rubber (available from Ore and Chemical Company, Inc.) was milled to particles about a quarter of an inch (0.63 cm) in diameter and powder coated with talcum powder. The rubber particles were fed to zone 1 of the twin screw extruder 20 at a speed of 68.0 g / min. The elastomer and talc were transported from Zone 1 to Zone 2. The elastomer was crushed there and was then transported through zones 3 and 4 where additional crushing occurred, to Zone 5 where a sample was removed of elastomer and it was found to have an inherent viscosity of 4.7 dm / g in toluene measured at a concentration of 0.015 g / dl. The alpha-pinene adherent resin Piccolyte ™ A-135 (available from Hercules Chemical Company, Inc.) was mixed dry with the antioxidant Irganox "* 1010 at a 55: 1 mass ratio of adherent to antioxidant.fed a total of 55 parts by weight of adherent per 100 parts by weight of elastomer to extruder 20. The mixture of adherent and antioxidant was fed to Zone 5 of the extruder at a rate of 38.1 g / min. The composite adhesive was passed through the remaining areas of the extruder and introduced into the extrusion die at a rate of 46.2 g / min to coat a width of 4.75 inches (12 cm) on a moving corrugated paper support. at 30 feet / min (9.1 m / min). The temperature of the melt of the adhesive was maintained at about 165 ° C through the extruder. The resulting adhesive tape was useful as a masking tape.
Example 4Example 3 was repeated except that the adhesive was extruded at a rate of 46.2 g / min to coat a width of 4.75 inches (12 cm) on a 1.5 mil polyethylene terephthalate support.(37 μm) thick that moved at 30 ft / min (9.1 m / min).
The resulting coated fabric continued to move at a rate of 30 feet / min (9.1 m / min) and the adhesive layer was then exposed to the radiation of an electron beam at a dose of 5MRads. Both irradiated and non-irradiated PSA tapesirradiated were useful as protective tapes. The irradiated tape had improved cohesive strength.
Example 5Example 3 was repeated except that, after being coated, the PSA tape continued to move at a speed of 30 ft / min (9.1 m / mm) and the adhesive layer was exposed in line to the radiation of an electron beam at a dose of 3RMads. The resulting irradiated tape had an improved cohesive strength.
Example 6Example 1 was repeated with the following changes. The Natsyn "* 2210 granulate and the milled smoked natural rubber sheet were fed to zone 1 of the double screw composition device 20 using separate feed hoppers.The Natsyn" * 2210 was fed at a rate of 34.2 g / min. The natural rubber was added at a speed of 34.0 g / min. The elastomers and talc were transported from Zone 1 to Zone 2, where the elastomers were crushed.
The adherent Piccolyte "* A-135 was pre-mixed with the antioxidant Irganox" * 1010 at a 55: 1 mass ratio of adherent to antioxidant and the mixture was fed to Zone 5 of the extruder at a rate of 38.1 g / min. . A total of 55 parts by weight of tackifier per 100 parts by weight of elastomer was fed to the extruder 20. The adhesive was transported through the remaining zones of the extruder and released to the extrusion die at a rate of 46.2 g / min. . This was coated on a 1.5 mil (38 μm) polyester film to a width of 4.75 inches (12 cm) using a line speed of 30 ft / min (9.1 m / min) to form an adhesive coating of 1.6 thousandths of an inch (40 μm) thick. The temperature of the melt was maintained at about 165 ° C through the extruder. The resulting PSA tape was useful as a protective tape.
Example 7Example 6 was repeated except that, after being coated, the PSA tape continued to move at a rate of 30 feet / min (9.1 m / min) and the adhesive layer was exposed in line to the radiation of an electron beam ata dose of 6 MRads. The resulting PSA tape had improved cohesive strength.
Example 8Example 1 was repeated with the following changes. A natural rubber with controlled Mooney viscosity (SMR CV60) (available from The Ore and Chemical Company, Inc.) was granulated using the Moriyama granulator and the pellets were powder coated with talc. Similarly, the cis-polybutadiene Budene ™ R1207 (available from Goodyear Tire &Rubber Company) was granulated and talc-coated. The two elastomers were fed to Zone 1 of the double screw composition device 20, using separate hoppers. The CV60 natural rubber was released at a speed of 31.9 g / min. The BudeneMR1207 was fed at 36.5 g / min. The elastomers and talcs were transported from Zone 1 to Zone 2, where the elastomers were crushed. The resin ester adhesive PentalinMRH(available from Hercules Chemical Company, Inc.) was dry blended with an Irganox® 10OlO antioxidant at a mass ratio of 65.7: 1 adherent to antioxidant. The mixture was fed to Zone 5 of the devicecomposition of double screw at a speed of 45.6 g / min. A total of 66 parts by weight of tackifier per 100 parts by weight of elastomer was fed to the extruder 10. The adhesive was transported through the remaining zones of the extruder and introduced to the extrusion die at the rate of 46.1 g / min. The adhesive was coated on a corrugated paper masking tape support at a coating thickness of 1.6 mils (40 μm). The fabric has been displaced at 30 feet / minute (9.1 m / min) and was coated with a width of 4.75 inches (12 cm). The temperature of the melt was maintained at about 150 ° C through the extruder. The resulting adhesive tape was useful as a PSA masking tape.
Example 9Example 8 was repeated except that, after being coated, the PSA tape continued to move at a rate of 30 feet / minute (9.1 m / min) and the adhesive layer was exposed in line to the radiation of an electron beam at a dose of 4 Mrads. The irradiated PSA tape had an improved cohesion strength.
Example 10Example 1 was repeated with the following changes. He used the ground smoked natural rubber sheet as described in Example 3 as well as the styrene-butadiene random copolymer rubber (SBR) Ameripol / Sympol 1011A (available from Ameripol / Sympol Company). The SBR was crushed and coated with talc using the Moriyama system. The two rubbers were fed to Zone 1 of the double screw composition device using separate feed hoppers. The natural rubber was fed at a speed of 34.0 g / min. The SBR was fed at 34.2 g / min. The elastomers and talcs were transported from Zone 1 to Zone 2, where the elastomers were crushed. The petroleum-derived adherent resin EscorezMR1304 (available from Exxon Research &Engineering Co.) was dry blended with the antioxidant Irganox ™ 10OlO at a 50: 1 mass ratio of adherent to antioxidant. The mixture was fed to Zone 5 of the double screw composition device at a speed of 34.9 g / min. A total of 50 parts by weight of adherent per 100 parts by weight of elastomer was fed to the extruder 20. The adhesive was transported through the remainder of the extruder and was introduced to the extrusion die to aspeed of 46.1 g / min. The adhesive was coated on a corrugated paper masking tape backing to a width of 4.75 inches (12 cm) at 30 feet / min (9.1 m / min) resulting in an average adhesive thickness of 1.6 mils (40 μm) ). The temperature of the melt was maintained at approximately 140 ° C through the extruder. The resulting adhesive tape was useful as a PSA masking tape.
Example 11Example 10 was repeated except that, after being coated, the PSA tape continued to move at a rate of 30 feet / min (9.1 m / min) and the adhesive layer was exposed in line to the radiation of an electron beam at a dose of 6 Mrads. The irradiated PSA tape had an improved cohesive strength.
Example 12Example 1 was repeated with the following exceptions. Mooney controlled natural viscosity rubber (CV60) is granulated using the granulator ofMoriyama and powder yourself with talcum powder. The elastomer was added to Zone 1 of the extruder at a rate of 68.4 g / min. The elastomer and talc were transported from Zone 1 to Zone 2 and crushed in Zone 2. The elastomer and talc were transported through zones 3 and 4, where additional crushing occurred, to zone 5 where an elastomer sample was removed and found to have an IV of 3.5 dl / g in toluene when measured at a concentration of 0.15 g / dl. The adherent resin Escorez1"1 * 1304 was mixed dry with the antioxidant Irganox 1010 and zinc oxide in the following quantities:Component% in Peso Escorez ™ 1304 78. 2 Zinc Oxide 20. 8 Irganox "* 1010 1 .0This mixture was added to Zone 5 where the double screw control device at a speed of 70.6 g / min. A total of 81 parts by weight of tackifier per 100 parts by weight of elastomer was fed to the extruder 20. White mineral oil was added to the extruder in Zone 7 through the injection port (not shown). A Zenith gear pump fed the oil to the extruder from aopen stainless steel container. The oil was fed by means of the gear pump at a speed of 8.34 g / min. A total of 12 parts by weight of oil per 100 parts by weight of elastomer was fed to the extruder. The resulting adhesive had 5.6% oil by weight. The adhesive was passed through the remaining areas of the extruder and introduced into the extrusion die at a rate of 104 g / min. It was coated to a width of 4.75 inches (12 cm) on a cotton cloth support that moved at 30 ft / min (9.1 m / min) to form an adhesive coating with an average thickness of 3.6 mils (9.1 μm) ). The temperature of the melt was maintained at about 165 ° C through the extruder. The resulting adhesive tape was useful as a medical tape. The tape, including the adhesive layer, was porous. Such porosity allowed perspiration and skin fat to pass through the tape.
Example 13Example 12 was repeated except that, after being coated, the PSA tape continued to move at a rate of 30 ft / min and the adhesive layer was exposed in line to the electron beam radiation at a dose of2 MRads using an acceleration potential of 175 kV. The irradiated PSA tape had an improved cohesive strength. The adhesive layer retained its porosity.
Example 14The sheet of natural smoked rubber cut into ribbons was milled to particles about a quarter of an inch (0.63 cm) in diameter and powder coated with talcum.-This was fed into Zone 1 of the twin screw extruder at a speed of 68.0 g / min. The temperature in zones 2 to 4 was maintained at 168 ° C. After zone 5 the temperature of the melt was maintained at 110 ° C. Air was injected and ventilated from zone 3 of the extruder. The pressure and flow rate were adjusted to achieve a rubber IV (measured in samples removed in Zone 5) of 2.1 dl / g in toluene when measured at a concentration of 0.15 g / dl. The speed of the extruder was 320 rpm. The adherent Escorez ™ 1310 was mixed with the M-20 Petrochemical available at Mitsui Petrochemical at a ratio of 65 parts of Escorez1 * 1310 to 1 part of M-20 by weight. This mixture was then added to zone 5 at a rate of 44.9 g / min. A total of 65 parts by weight of adherent per 100 parts of elastomer was fed.
Titanium dioxide was added to zone 7 at a speed of 6.1 g / min. Liquid tricresyl phosphate was added to zone 9 at a rate of 2.0 g / min and trifenium phosphite was added, or liquid to the same zone at a rate of 0.3 g / min.This mixture resulted in a content of Total liquids of 2% adhesive The composite adhesive was coated on a corrugated paper masking tape support using a die with a flexible steel blade The speed of the fabric was 60 ft / min (18.2 m / min) and the adhesive was coated to a thickness of 1.5 mils (38 μm) .The adhesive layer of the moving fabric was irradiated and exposed to an electron beam operation at an acceleration potential of 165 kV with a dose of 2 MRads The resulting irradiated PSA tape was useful as a masking tape.
Example 15Natural rubber with controlled viscosity(SMR CV 60) was granulated with the Moriyama granulator and fed to zone 1 of the extruder at a speed of 68.0 g / min. The speed of the extruder was set at 470 rpm. The air pressure and the flow velocity in zone 3 were adjusted to achieve an IV of the rubber (measured on asample removed in zone 5) of 1.5 dl / g when a concentration of 1.5 g / dl was measured. The temperature in zones 2 to 4 was maintained at 195 ° C. After zone 5 the temperature of the melt was maintained at 100 ° C. The Goodyear ingtack Plus adherent resin was mixed with the Irganox ™ 1010 antioxidant from Ciba-Geigy at a ratio of 40.1 parts Wingtack Plus to 1.3 parts Irganox® 1 1010 by weight. This mixture was added to zone 5 at a speed of 50.5 g / min. A total of 72 parts by weight of adherent per 100 parts of elastomer was fed. The composite adhesive was coated on a 2 mil (51 μm) biaxially oriented polypropylene film at a coating thickness of 1.5 mils (38 μm). The fabric moved at a speed of 30 feet / min (9.1 m / min). The resulting product was useful as a tape for PSA packaging.
Example 16Example 15 was repeated except that, after being coated, the belt continued to move at a speed of 30 ft / min (9.1 m / min) and the adhesive layer was irradiated in line by exposure to an electron beam at adose of 9 MRads. The resulting PSA tape had a greater cohesive strength.
Example 17CV60 natural rubber was milled and powder coated with talcum powder. The rubber was added to Zone 1 of the extruder at a rate of 116 lb / hr (52.7 kg / hr). The extruder screw operated at 225 rpm. The elastomer and talc were transported from Zone 1 to Zone 2 and crushed in Zone 2. The adherent Escorez 1304 was added at a rate of 34.8 lb / hr (15.8 kg / hr) to zone 3. It was added Escorez 1034 additional at a speed of 59.2 lb / hr (26.9kg / hr) to the area .. Irganox 1010 was added with the adherent stream to zone 5 at a rate of 1.2 lb / hr (0.55 kg / hr). Zinc oxide was also added to Zone 5 at a rate of 24.9 lb / hr (11.3 kg / hr). A total of 81 parts by weight of adherent and 21 parts by weight of zinc oxide per 100 parts by weight of elastomer were fed to the extruder. White mineral oil was added to Zone 7 at 13.9 lb / hr (6.3 kg / hr). The resulting adhesive had 5.6% by weight of oil. The adhesive was introduced to a 24 inch (61 cm) wide contact extrusion die with a dipstick.rotating steel on the downstream side of the die space to spread the adhesive on the fabric. The adhesive was applied at a rate of 250 lb / hr (113.6 kg / hr) and coated on a 24 inch (61 cm) wide cotton cloth backing. The line speed was automatically adjusted to achieve an adhesive coating thickness of 3.7 mils (94 μm). The temperature of the melt was maintained at approximately 130 ° C through the extruder. The resulting PSA tape was useful as a porous medical tape.
Example 18Example 17 was repeated except that, after being coated, the PSA tape continued to move at a speed that was automatically adjusted to maintain the thickness of the adhesive coating at 3.7 mils (94 μm). The moving adhesive layer was exposed in line to the radiation an electron beam at a dose of 5 MRads. The PSA tape retained its porosity and had an improved cohesive strength.
Example 19The shredded and milled smoked natural rubber calender was added to zone 1 of the double screw composition device at a rate of 79.35 lb / hr (36 kg / hr). Air was injected and mixed in zone 3. The air pressure and flow velocity were adjusted to achieve an IV of the rubber (measured in a sample removed in zone 7) of 2.0 dl / g. in toluene when measured at a concentration of 0.15 g / dl. The screw speed was 150 rpm and the wall temperature of the extruder in zone 2 to 5 was maintained at 200 ° F. (93) ° C. Adhesive resin Escorez "1 * 1304 was added to zone 9 at a rate of 68.2 lb / hr (31 kg / hr) Titanium dioxide was added to zone 9 at a rate of 1.6 lb / hr (0.7 kg) The antioxidant of Irganox ™ 1010 was added to zone 9 at a rate of 0.8 lb / hr (0.36 kg / hr) .The temperatures of the extruder walls in zones 7 through 11 were maintained at 250 ° F ( 121 ° C.) The extruder transport and pumping lines were also maintained at 250 ° F (121 ° C) .The adhesive was introduced into the die at a rate of 150 lb / hr (68.1 kg / hr) and coated on a corrugated paper masking tape holder, the speed of the line was adjustedautomatically to achieve a coating thickness of 2 mils (51 μm). The adhesive layer of the moving fabric was irradiated in line by exposure to radiation from an electron beam at a dose of 4 MRads. The PSA tape was useful as a masking tape. Although the present invention has been described with respect to the specific embodiments, the invention is not intended to be limited to those embodiments. Rather, the invention is defined by the claims and equivalents thereof.
Example 20The CV60 natural rubber was granulated with a Moriyama granulator and granules or pellets polished with talc. The granulated CV60 was then fed to Zone 1 of the extruder at a rate of 68.0 g / min. The elastomer was transported from Zone 1 to Zone 2, where the elastomer was crushed. The adherent resin Escorez "1304 was mixed dry with the antioxidant Irganox ^ 1010 and Celogen ^ OT in the following quantities:Components% in Peso Escorez ™ 1304 96.7 Irganox 1010 1.1 CelogenMR 2.2This mixture was added to Zone 5 of the double screw composition device at a speed of 63.2 g / min. The adhesive was transported through the remainder of the extruder and introduced to the extrusion die at a rate of 46.1 g / min. The adhesive was coated on a corrugated paper masking tape backing to a width of 4.75 inches (12 cm) at 30 feet / min (9.1 m / min) resulting in an average adhesive thickness of 1.6 mils (40 microns) ). The melt temperature of the composite adhesive was maintained below 140 ° C through the extruder. The resulting PSA tape continued to move at a rate of 30 feet / min (9.1 m / min) and the adhesive layer was exposed in line to the radiation of an electron beam at a dose of 3 MRads. A portion of the resulting adhesive tape was rolled up on a roll and heated to 150 ° C (300 ° F) for 1 minute to decompose the Celogen® OT. Samples of foamed and unfoamed adhesive tapes were then tested to determine their characteristics offast adhesion using a Rolling Sphere Test (RBT). This test was carried out as follows: RBT: The RBT test is described in Test Methods for Pressure-sensitive Tapes, 10a. Edition, Pressure-Sensitive Tape Council, 401, North Michigan Avenue, Chicago, Illinois 60611-4267. The test was described in this publication as PSTC-6. This test measures the distance a small steel sphere travels through a sample placed horizontally from the adhesive surface of the tape after being accelerated downward on an inclined plane from a fixed height; the shorter the bonding time of the adhesive surface, the faster the steel sphere will accelerate, and the smaller the distance the sphere will travel through the surface of the tape before stopping. The tapes with better conformability and shorter bonding times will thus exhibit lower adhesion values with Rolling Sphere. This test was carried out at two temperature conditions with a sphere of 7/16"(11.1 mm) in diameter of 7 gm. These results were:It can be seen that the foamed tapes exhibit shorter RBT values than their non-foamed counterparts. This reflects the improved formability that the foaming process imparts to the adhesive surface.
Example 21CV60 natural rubber and Ameripol / Synpol ™ 1011A styrene-butadiene were granulated with a Moriyama granulator and powder coated with talc. The two rubbers were fed to Zone 1 of the double screw composition device using separate feed hoppers: a CV60 at 37.4 g / min, styrene-butadiene at 30.6 g / min. The elastomers and talc were transported from Zone 1 to Zone 2, where the elastomers were crushed. The Escorez ™ 1304 adhesive resin was dry mixed with the antioxidant Irganox ™ 1010, titanium dioxide coloring agent, and CelogenMROT in the following quantities:Component% in Peso Escorez 1304 91. 7 Irganox ™ 1010 1. , 7 Titanium dioxide "3., 3 CelogenMR 3.
This mixture was added to Zone 5 of the double screw composition device at a speed of 40.8 g / min. The adhesive was transported through the remainder of the extruder and was introduced to the extrusion die at a rate of 46.1 g / min. The adhesive was coated on a corrugated paper masking tape support to a width of 4.75 inches (12 cm) and 30 ft / min (9.1 m / min) resulting in an average adhesive thickness of 1.6 mils (40 microns) ). The melt temperature of the composite adhesive was maintained below 140 ° C through the extruder. The PSA tape continues to move at the speed of 30 feet / min(9.1 m / min) and the adhesive layer was exposed in line to the radiation of an electron beam at a dose of 4 MRads. A portion of the resulting adhesive tape was rolled onto a roll and heated to 150 ° C (300 ° F) for 1 minute to decompose the Celogen® OT. Samples of the foamed and non-foamed tapes were tested belowto determine the value of RBT. Those results are given below:Example 2The adhesive described in Example 20 was coated on a corrugated paper masking tape support and cured with an electron beam in line. A separate portion of the tape was coated as described in Example 20, but not cured with an electron beam in line. The resulting roll of uncured tape was then unwound and run between two electrically heated plates at 15 feet / min (4.6 m / min) so that the tape was heated to 230 ° F (160 ° C) to foam the adhesive. The continuous foamed tape is then exposed to the radiation of the electron beam at a dose of 4 MRads. The samples of foamed and unfoamed tape were then tested to determine the value of RBT. The results are given below:Example 23The adhesive described in Example 21 was coated on a corrugated paper masking tape carrier and cured with an electron beam at 4 MRads. A separate portion of the tape was not cured with a beam of electrons in line. The resulting roll of uncured tape was then unrolled and ran between two electrically heated plates at 15 feet / min (4.6 m / min) so that the tape was heated to 230 ° F (160 ° C) to foam the adhesive. The foamed tape then continued at 15 feet / min (4.6 m / min) and the adhesive layer was exposed to the radiation of an electron beam at a dose of 4 MRads. Samples of the foamed and unfoamed tapes were then tested to determine the value of RBT. The results are given below:It is noted that in relation to this date, the best method known to the applicant to carry out the aforementioned invention, is that which is clear from the present description of the invention. Having described the invention as above, property is claimed as contained in the following: