|Número de publicación||WO1993006183 A1|
|Tipo de publicación||Solicitud|
|Número de solicitud||PCT/US1992/007736|
|Fecha de publicación||1 Abr 1993|
|Fecha de presentación||14 Sep 1992|
|Fecha de prioridad||17 Sep 1991|
|También publicado como||EP0604578A1|
|Número de publicación||PCT/1992/7736, PCT/US/1992/007736, PCT/US/1992/07736, PCT/US/92/007736, PCT/US/92/07736, PCT/US1992/007736, PCT/US1992/07736, PCT/US1992007736, PCT/US199207736, PCT/US92/007736, PCT/US92/07736, PCT/US92007736, PCT/US9207736, WO 1993/006183 A1, WO 1993006183 A1, WO 1993006183A1, WO 9306183 A1, WO 9306183A1, WO-A1-1993006183, WO-A1-9306183, WO1993/006183A1, WO1993006183 A1, WO1993006183A1, WO9306183 A1, WO9306183A1|
|Inventores||Paul K. Sartoris|
|Exportar cita||BiBTeX, EndNote, RefMan|
|Citas de patentes (2), Citada por (10), Clasificaciones (12), Eventos legales (9)|
|Enlaces externos: Patentscope, Espacenet|
TAPE COMPOSITION UTILIZING A MULTI-LAYER FILM Background of the Invention
It has long been known to manufacture and distribute cloth or woven duct tape for various uses. The top surface of cloth duct tape as commonly used is pigmented low or medium density polyethylene. The polyethylene is applied to the tape's reinforcing scrim either through direct coating or through adhesive lamination of a preformed film. The tape is normally found in prewound roll form in which the adhesive upper layer is in direct contact with the polyethylene surface of the- lower* layer without an intervening abhesive layer. The low surface energy of the polyethylene allows the tape to be unwound for use without the undue application of force which would cause the tape to delaminate or tear.
Cloth duct tapes often contain pigments to impart color to the tape. As the pigment level in the polyethylene layer is increased, however, the resistance to unwind also increases. At critical pigment loadings, the tape cannot be used or processed due to the difficulty in unwinding. This problem means that lower pigment levels must be used, which requires, in some instances, higher cost pigments to achieve the desired effect. A tape product which can tolerate high pigment levels without adversely affecting the unwind characteristics of the tape, and which has other desirable performance characteristics is needed.
SUBSTITUTESHEET Summarv of the Invention
The present invention relates to a tape composition which comprises a multi-layer film, a fabric and an adhesive layer. The multi-layer film comprises a first top layer comprising a polymeric film having a low energy surface. The top layer is preferably translucent. The film further contains a second or bottom layer comprising a polymeric film which is characterized by high flexural strength, resistance to penetration by water or moisture, and/or a high heat deflection temperature. The multi-layer film optionally can contain additional layers disposed between the top and bottom layers as desired or needed. The film can contain as many layers as necessary to provide the desired performance characteristics.
The second or bottom layer and/or the intermediate layers preferably contain a pigment. The use of the multi-layer film allows higher pigment loadings and/or lower grade pigments to be used. Since the top translucent layer overlays the pigmented layer, the amount and/or type of the pigments used does not affect the roll unwind characteristics of the finished tape.
A reinforcing fabric is located adjacent the bottom layer of the film. The fabric may be attached to the bottom film layer with an adhesive, or may be embedded in the adhesive layer. The fabric is generally a thin layer of woven or knitted fabric or other material. The fabric can be for example, a woven cotton and/or polyester fabric, or a cotton/polyester fabric woven from blended yarns. The fabric preferably is characterized by a weave which allows the fabric to be torn preferentially in a straight line across the width of the tape. The fabric thus provides cross-directional tearing strength and tensile strength to the tape.
SUBSTITUTESHEET The tape further contains a base adhesive layer. Adhesives which can be used for the base adhesive layer are pressure sensitive adhesives. The adhesive is selected to adhere tightly to the bottom film layer and/or to the fabric, but can be easily separated from the top layer of the film when the roll is unwound. Resin tackified rubber-based adhesives are particularly useful for making the present tape.
Methods for making the present tape composition are also the subject of the present invention. In general, the multi-layer film is formed by coextruding at least two polymer resins which form a multi-layered film having the desired properties. The multi-layer film is then combined with the fabric and the base adhesive layer to form the finished product. In one embodiment of the present .method, fabric having an open weave is used, which permits the base adhesive to penetrate through the fabric. In this embodiment, the fabric is positioned adjacent the bottom layer of the multi-layer film, and the adhesive is coated onto the fabric layer. The adhesive penetrates the voids between the threads of the fabric and attaches to the bottom layer of the film, thereby forming an adhesive bond with the film and embedding the fabric layer in the adhesive. In another embodiment, a closely woven fabric is used which contains very small voids and therefore does not permit the base adhesive to penetrate. In this case, the fabric is attached to the bottom layer of the film by coating the film or the fabric with an adhesive and contacting the film with the fabric under conditions sufficient to form a adhesive bond between the film and the fabric. Corona treatment of the bottom side of the film that is attached to the fabric is commonly used to improve the film to adhesive bond. The base adhesive is then coated onto the exposed side of the fabric forming the finished tape.
SUBSTITUTE SHEET The tape composition of the invention has superior unwind properties, particularly at high unwind speeds. The present invention includes a method for reducing the unwind resistance of a tape, particularly at high speeds. It has been found that the present tapes utilizing a multi-layer film of the above composition exhibit significantly reduced unwind resistance at processing speeds, which are generally from about 300 to about 650 feet per minute. The lower unwind resistance at these speeds allows faster and more efficient manufacturing processes to be used. The tape retains sufficient unwind resistance at low speeds however, to maintain the integrity of the tape roll.
SUBSTITUTESHEET Brief Description of the Drawings
Figure 1 is a schematic illustration showing a cross-sectional view of the tape of the present invention having a multi-layered film.
Figure 2 is a schematic illustrating showing a cross-sectional view of the tape of the present invention having a bi-layered film and an adhesive layer between the fabric and the film. .
SUBSTITUTESHEET Detailed Description of the Invention
The tape of the present invention comprises a multi-layer film, a fabric and a base adhesive layer. There may be an additional adhesive layer between the bottom film layer and the fabric for bonding the fabric to the film, if desired or needed. The structures of two different embodiments of the tape are shown schematically in the Figures.
Referring to the Figures, Figure 1 shows a cross-sectional view of one aspect of the present tape. In this embodiment, tape 10 comprises a multi-layered film, represented by layers 12, 20 and 14, a fabric 16 and an adhesive 18. The multi-layer film is a coextruded film comprising a first top layer 12 comprising a polymeric material which forms a film having a low energy surface. The top layer 12 is preferably transparent or translucent. Polymeric materials appropriate for use in the top layer 12 include thermoplastic polymers, copolymers or polymer blends which form a film having a low surface energy. A film having a surface energy of less than 30 dynes/cm is preferred. The surface energy must be sufficiently low to allow the tape roll to be unwound for use without undue stress which can cause delamination of the adhesive or film layers. Polymers or copolymers which satisfy this criteria include, for example, low density polyethylene, medium density polyethylene, fluorocarbon polymers or copolymers, and silicone polymers or copolymers. Low or medium density polyethylene is preferred for this purpose.
Low density polyethylene (LDPE) is particularly preferred due to its [Availability and cost. LDPE is a branched form of polyethylene having a density of from about 0.910 to about 0.940 grams per cubic centimeter (g/cc). Medium density polyethylene (MDPE) refers to
SUBSTITUTESHEET polyethylene polymers having a density of about 0.940 g/cc.
The film has a second or bottom layer 14 comprising a polymeric material which exhibits high flexural strength or stiffness, a high heat deflection temperature and has a low rate of water vapor transmission. A polymer having heat deflection temperature of at least 120°F, and preferably at least 140°, and a water vapor transmission rate of less than about 1.25, and preferably less than 1.0, gm/mil/100in/24 hours is preferred. A polymer having a flexural modulus of at least 140 x 103 psi is preferred. The bottom layer 14 can comprise thermoplastic polymers, copolymers or polymer blends which form films which exhibit at least one and preferably all .of the above characteristics. The second layer also can provide improved tape appearance by bridging the gaps in the woven fabric, if it exhibits high stiffness. Polymers or copolymers which satisfy these criteria include high density polyethylene (HDPE) and polystyrene blends.
HDPE is particularly preferred for this purpose. HDPE is linear polyethylene, or polyethylene having a very low degree of branching, with a density of from about 0.940 g/cc to about 0.970 g/cc or higher.
One or more desired characteristics can be imparted to the film by including additional intermediate layers in the film. For example, if the bottom layer 14 has high flexural strength but lacks heat deflection properties, one or more additional layers comprising a polymer film having such properties can be coextruded with the first and second layers resulting in a multi-layer film having all of the desired characteristics. This optional layer (or layers) can be positioned between the first and second layers, or
SUBSTITUTE SHEET after bottom layer 14, and is represented by numeral 20 in Figure 1. The film can contain as many intermediate layers as necessary to obtain the properties desired. The multi-layer film has a total thickness of about 1.0 to 2.0 mils. The clear top layer is preferably about 0.3 mils and the pigmented bottom layer or layers can be up to about 1.7 mils thick.
The multi-layer film preferably contains one or more pigments to impart color to the tape. Color is imparted to the tape by dispersing a pigment or pigment blend of the appropriate color in the polymer resin which forms the tape backing. However, the addition of pigment to the resin increases the surface energy of the film which forms from the resin. This higher surface energy results in an increase in the resistance of the tape to -unwinding. To counter this effect, tape manufacturers have had to use less pigment, which mean that more expensive pigments often must be used to achieve the desired color. In the present tape composition the pigments are contained in the bottom and/or intermediate layers, and the top, low surface energy layer which overlays it is translucent or transparent. Thus, higher pigment loading and less expensive pigments can be used in the tape without negatively affecting roll unwind and other properties of the tape.
The fabric 16 can be any woven or knitted fabric including, for example, woven cotton or polyester fabric or cotton/polyester fabric woven from blended yarns. Stitch bonded materials having about 22 to 24 strands per inch can also be used. The fabric 16 is selected so that it resists tearing or splitting along its longitudinal axis and tears in a straight line across its transverse axis. This allows a portion of the tape to be neatly torn off for use without the
SUBSTITUTE SHEET necessity for cutting the tape. Materials which are particularly useful as fabric in the present composition include cotton, cotton/polyester or 100% polyester fabrics having a thread count of preferably from about 10 to about 60 threads per inch, in which the weave or other structure is selected in a manner known per se to permit cross-directional tearing. The adhesive 18 can be any pressure sensitive adhesive. The adhesive 18 is selected so that it forms a tight adhesive bond with the fabric and with the bottom layer of the film. Pressure sensitive adhesives which are useful in the present invention include, for example, polyacrylates, such as poly(ethylhexyl acrylate), and resin tackified rubber based adhesives. Resin tackified rubber based pressure sensitive adhesives are particularly preferred.
The film layer used for the face portion of the tape is prepared by coextruding polymer resins to form a multi-layered film. Methods of coextrusion are well known in the art. In general, films or sheets consisting of two or more different polymers are produced by mixing molten streams of the polymer resins from a like number of extruders into a multi-manifold die. Coextrusion is used to combine materials to provide combinations of properties that cannot be obtained in a single polymer, the coextruded layers are permanently combined with each other to form a unitary coextrudate.
The fabric and the base adhesive layer are then applied to the coextruded film. If a closely woven fabric is used, the fabric can be attached to the bottom layer of the film with adhesive. The adhesive can be applied by any known technique for applying films.
SUBSTITUTE SHEET A preferred method of making the present tape is by calendering. Calendering is a process used for the continuous manufacture of coated webs. The pressure sensitive adhesive is passed between pairs of highly polished, temperature-controlled rolls under high pressure. The spacing between the calender rolls ensures that an even layer of adhesive of a desired thickness is coated. In this method, if a closely woven fabric is used, the fabric is coated on both sides with adhesive in the calendering operation and one side is laminated to the bottom of the multilayer film with this same adhesive coating. If the fabric has a sufficiently open weave, both the fabric and the film are passed through the calender together with the fabric in contact with the bottom of the multilayer film. The adhesive.-is pressed through the voids of the fabric during the calendering operation and bonds to the film, and the fabric becomes embedded in the adhesive layer. In a preferred embodiment of the present invention, a tape product was manufactured utilizing a 1.8 mil 2-layer coextruded film for the tape backing. The top layer was non-pigmented low density polyethylene and the bottom layer was pigmented high density polyethylene. A tape utilizing a single layer 2.25 mil film of pigmented low-density polyethylene was processed in the identical manner for comparison. Both films were extruded and combined with a fabric and adhesive to form the finished product. The fabric and adhesive were applied to the film using a 3-roll calender. The fabric was a woven cotton/polyester fabric and the adhesive was a resin tackified rubber-based adhesive.
The tape made from the thinner multi-layered film had the better appearance and was easier to process due
SUBSTITUTESHEET to its easier high-speed roll unwind character. The multi-layer tape composition exhibits reduced unwind resistance at high speeds which allows manufacturing operations for making the rolls of tape to proceed faster and more efficiently. For example, cloth tapes are generally manufactured in large rolls, which can be, for example, 50 inches wide and wider. The large rolls are "slit" into smaller rolls (usually 2 inches wide) for use by the consumer. The unwind resistance of an "as calendered" full width, supply roll of tape can vary from negligible to so high that the backing tears on unwind. To form commercially useful rolls of tape, the full width supply roll is converted to smaller rolls by unwinding it, sending it through a slitter that cuts it into shorter, narrower widths for end use or sale and rewinds it. If the unwind resistance is too low, the tape unwinds easily in the manufacturing plant, but its adhesion to its backing is too low to form a coherent roll which is necessary to be of practical use. If the unwind resistance is too high, the tape will adhere well in the end use application, but is difficult to unwind in the plant for slitting. If the unwind resistance is too high, the mechanisms on the slitting machines which unwind the tape are greatly stressed and burn out. Plant slitting speeds can vary from a normal running speed of about 300 ft./min. for a manual slitter to a normal running speed of about 650 ft/min. or more for an automated slitter. Tapes of the present invention avoid these problems by providing a product having low unwind resistance at high speeds such as those used in the slitting operation, e.g., greater than 300 ft/min., but has higher unwind resistance at low speeds, such as those a user would employ. Thus, the present tape composition provides a unique combination of properties.
SUBSTITUTE SHEET In an example illustrating the high speed properties of the present tape, tapes using the same type of adhesive and fabric but two different films, were compared. Tape 81 contained the standard low density polyethylene 3 mils thick with 0.5% of aluminum pigment; and tape 82 contained coextruded 1.8 mil thick LD/HD polyethylene film with no pigment in the top LD polyethylene layer. Both tapes were made by the calendaring method described above.
The adhesion to the backing, which is indicative of the low speed unwind characteristics, and the high speed unwind resistance of the two tapes were compared. The results are shown in the Table:
Film 81 Film 82
Adhesion to backing 29.3 31.2
(oz./in. ) +
Unwind resistance 4.5 3.7
+ Pressure Sensitive Tape Council Test Method PSTC-1 ++ 600 ft./min. unwind speed
The above data in the Table show that the tape containing the standard pigmented LD polyethylene (Film 81) had a slightly lower adhesion to backing when compared to the tape utilizing the coextruded polyethylene, but that its unwind resistance at 600 ft./min. was more than 21% higher. These results indicate that the high speed unwind resistance of the tape tends to be lower as the pigment in the release surface of the film is reduced, without adversely
SUBSTITUTESHEET affecting the adhesion to backing characteristic required for product use.
The tapes of the present composition and method are strong, flexible and moisture proof, and provide an improved appearance compared to previously available tapes of the same type made with a single face layer. The present tapes achieve superior appearance and performance with a higher film pigment level, a stiffer film and/or a more heat resistant film. Since lower grade pigments and thinner film gauges can be used, the raw material costs for producing the tape are reduced. The present tapes exhibit improved roll unwind properties which results in a higher grade product and lower processing costs.
SUBSTITUTE SHEET Equivalents
One skilled in the art will be a able to ascertain many equivalents to the specific embodiments described herein. Such equivalents are intended to be encompassed by the scope of the following claims.
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|Clasificación internacional||C09J121/00, C09J7/04, C09J7/02, B32B27/12|
|Clasificación cooperativa||C09J7/0296, B32B27/12, C09J2400/263, C09J2201/162, C09J2423/006, C09J2421/00|
|Clasificación europea||B32B27/12, C09J7/02K9F|
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