Patent Application
20050158567
The present invention relates to cling films, and more particularly to a laminate composed of a cling film layer bonded to a non-stretchable base layer, a process for making the cling film laminate, and various methods of using the cling film laminate.
The “cling” property of a polymer film is generally defined as its cohesive bonding strength, i.e. its ability to bond to itself. This cling property is also sometimes referred to as a self-adhesive property, an auto-adhesive property or a cold seal property. In any event, cling is a highly desirable property which enables polymer films having the desired cling strength to be useful in various applications, especially in the packaging and fastening industries.
Cling films have been used in multi-layer laminate structures in the past, and, in fact, cling films may themselves be multi-layer constructions. Cling film is especially well suited for use in various bundling, packaging and palletizing operations and one significant commercially important application is what is commonly referred to as “stretch wrap” film. For example, the load on a pallet may be bundled for shipping by stretch-wrapping a cling film several times around the articles stacked on the pallet. The cling film may be composed of two, three or more layers with each individual layer providing a desirable property so that the film, as a whole, possesses a desirable combination of stretch, tensile, tear resistance, puncture resistance, thermal stability and slip properties. In any event, however, when used as stretch wrap, a cling film is usually stretched as it is applied to place it under considerable tension in a face to back relationship, i.e. the front surface having cling properties engages the back surface having non-cling properties. Examples of multi-layer cling film constructions intended to be used as stretch wrap can be found in U.S. Pat. Nos. 5,049,423, 5,085,927 and 5,093,188.
Bullard et al U.S. Pat. No. 5,902,684 and Eichbauer U.S. Pat. No. 5,814,399 both disclose a multi-layered stretch wrap film intended to be stretched at least 400% from it original unstretched state. The stretch wrap film has at least four layers and is comprised of a pair of opposite outer cling layers comprising the front as well as the back surfaces of the stretch wrap film, at least one inner polymeric layer and at least one core layer. The cling layers are polyethylene copolymers comprised of ethylene copolymerized with 1 to 20 weight percent of an alpha-olefin monomer containing 3 to 12 carbon atoms. These polyethylene copolymers have a relatively high density ranging from 0.88 g/cm3 to 0.94 g/cm3, and are not metallocene catalyzed. Although the inner polymeric layer is comprised of metallocene catalyzed polyethylene copolymers, this layer is disposed between the two outer cling layers and thus does not have an exposed outer surface which can provide cling properties or function as a cling layer, but instead is intended as a puncture resistant layer for the stretch wrap film.
Another application of cling films in the packaging industry is demonstrated in Walor U.S. Pat. No. 4,905,298 and Branson U.S. Pat. No. 4,758,099 which both describe the use of cling film as a resealable closure for sealing a flexible container such as a plastic bag. Walor utilizes a modified polyvinyl chloride film to provide the cling properties while Branson utilizes a low density polyethylene treated with an additive such as ethylene vinyl acetate to provide the cling characteristic. Once again, neither Walor nor Branson utilize metallocene catalyzed copolymers.
It is also common in the packaging industry to utilize compositions referred to as “cold seals” or “cohesives” as a bonding or fastening system. A cold seal or cohesive is generally a water-based latex adhesive which is nontacky to the touch, yet adheres to itself with pressure. Cold seals are employed for a variety of uses, particularly to bond or fasten various packaging applications such as wrappers for snack foods like candy, granola bars and potato chips, sterilizable medical packaging, self-seal and tamper-evident envelopes, banding for paper money, napkins and articles of clothing, as well as for protective packaging such as fold over “blister” packages for hardware and other small items. Additionally, cold seals have been proposed for use as release-paper-free tapes such as fastening tapes for disposable diapers.
Baetzold et al U.S. Pat. No. 6,221,448 discloses a cold seal or cohesive adhesive composition which is formulated as a hot melt adhesive. The cold seal described in Baetzold et al utilizes one or more metallocene-catalyzed copolymers of ethylene and an alpha-olefin either alone as the cold seal adhesive itself or the copolymers may be formulated together with conventional waxes and tackifiers into a hot melt adhesive. The copolymers have a melt index ranging from 200 g/10 min. to 2000 g/10 min. which is appropriate for formulating a hot melt adhesive, or for applying the copolymers neat as a hot melt, but not for making a film such as a cling film, which instead should preferably be in the range of 50 g/10 min. or less and more preferably 5 g/10 min. or less.
As noted previously, cling films have also been used in the fastening industry. Kobe et al U.S. Pat. No. 5,908,695 discloses a fastener system comprised of a laminate having a contact responsive fastening layer which has a surface that possesses essentially no surface tack. The fastening layer includes a polymeric material that permits multiple fastening and releasing of the fastening layer with a target surface. The target surface may comprise either another essentially tack free surface of a like laminate, or it may simply be a non-tacky smooth surface such as glass or paper. The polyethylene copolymers described therein, however, contain only relatively low amounts of comonomer (up to 15% by weight) and are not metallocene catalyzed.
The prior art is also replete with numerous examples of constructions employed as a fastening system for disposable soft goods. The phrase “disposable soft goods” refers to articles such as disposable diapers, sanitary napkins, surgical drapes, hospital gowns, hospital pads and many other utilitarian objects wherein one or more layer is composed of a nonwoven material. Examples of fastening systems for disposable soft goods can be found in numerous U.S. patents such as U.S. Pat. Nos. 4,973,326; 4,894,060; 4,726,971; 4,585,450; 4,540,414; 4,296,750; and 4,210,144.
Disposable diapers of the type widely used today have included pressure sensitive adhesive tapes as fasteners for securing the diaper about the waist of an infant. Various other fastening systems have also been employed, such as combining the adhesive coated tape with a landing zone on the front panel of the diaper, as well as the use of hook and loop fasteners.
An inherent problem with the forgoing diaper fastening systems using pressure sensitive adhesive tabs is that of contamination of the tacky surfaces. Thus, talcum powder, baby oil or other foreign matter that finds its way onto either the pressure sensitive adhesive of the tab or onto the landing zone to which the pressure sensitive adhesive is adhered can reduce the reliability of the fastener, can limit the bonding strength of the adhesive, and/or can prevent fastening altogether. Although the use of hook and loop fasteners substantially overcomes the problem of reduced fastener reliability due to contaminants on pressure sensitive adhesive, hook and loop fastener systems are relatively expensive and may not be economical for use on inexpensive disposable diapers.
Disposable diapers utilizing tab fasteners which are coated with autoadhesives are also known in the art, as disclosed in Mann et al U.S. Pat. No. 5,085,655. The tab fastener disclosed in U.S. Pat. No. 5,085,655 is in the form of a laminate having an autoadhesive layer formed by an elastomer and a base carrier layer formed by a layer of thermoplastic material. The term “auto adhesive” is defined in the '655 patent as the self-adhesive or cohesive property of a polymer which enables the polymer to adhere to itself by application of pressure, but is substantially non-adhesive with respect to many other materials. The autoadhesive surface is formed of an elastomer comprising a block copolymer having rubbery segments and non-rubbery segments. The thermoplastic carrier layer is preferably a polyolefin such as polyethylene or polypropylene, or a polyester. Tab fasteners of the construction disclosed in the '655 patent, however, suffer from the disadvantage of having relatively high peel strength. The examples given in the '655 patent show peel strength of 1364-2043 g/in. This relatively high peel strength makes the block copolymer based laminate of the '655 patent difficult to function as a workable refastenable tape tab. For example, when one attempts to remove fastening tabs of this type from a diaper after they have been secured in place, the autoadhesive layer will stretch or deform due to this relatively high peel strength resulting in the possibility of permanent deformation of the tab and the inability to refasten the tab if desired. This, for example, prevents a person from checking the diaper after it has been on an infant for a period of time, and then refastening the diaper if it has not been soiled. Thus, it would be desirable to provide a laminate structure which eliminates, or at least severely limits stretching and/or deformation of an autoadhesive layer.
The present invention is directed toward a unique cling film fastener structure, a process for making the cling film fastener, and use of the cling film fastener in various applications. The cling film fastener utilizes one or more polyolefin copolymers that provide the highly desirable cling properties.
The cling film fastener has as one of its primary components a cling film layer containing one or more polyolefin copolymers that provides autoadhesive or cling surface properties. In one embodiment, the cling film layer may be a substantially non-stretchable self-supporting sheet in the form of a monolayer of the one or more polyolefin copolymers. In use, the cling film monolayer is bonded directly to a target surface so that its cling surface is exposed.
In another embodiment, the cling film fastener comprises a multi-layered laminate structure. In this embodiment, the cling film layer has one or more polyolefin copolymers that provides autoadhesive or cling surface properties bonded to or coated on a carrier layer which provides support for the cling film layer. The carrier layer itself may be a single layer or a multi-layered construction, and either, or both, of the cling film layer and the carrier layer (or any or all of the individual layers of the carrier layer) may be substantially non-stretchable so as to render the entire cling film fastener itself substantially non-stretchable. The carrier layer preferably is the component of the laminate that eliminates, or substantially limits, stretching of the cling film layer. The carrier layer thus preferably provides dimensional stability both in the longitudinal and/or the cross direction to prevent stretching or deformation of the cling film layer. In use, the carrier layer is bonded directly to a target surface so that the cling surface is exposed.
Preferably, the cling film layer, in either its monolayer or multi-layered laminate form, will stretch no more than about 50% in either direction. More preferably, stretching should be limited to no more than about 25% from its original non-stretched configuration, and most preferably stretching in either direction should be less than 10%. Stretching and/or substantial deformation of the cling film layer is undesirable as it reduces the ability of the autoadhesive surface of the polyolefin copolymers to adhere to itself. The fact that the fastener of the present invention is constructed of one or more unique polyolefin copolymers and further is substantially non-stretchable and non-deformable distinguishes the present laminate from cling films used as stretch wrap since stretch wraps typically desire at least about 200% stretchability.
The cling film fastener of the present invention is particularly useful in bonding systems and/or fastening systems for disposable soft goods, especially disposable diapers, sanitary napkins, surgical drapes, hospital gowns, hospital pads, face masks and other such objects having one or more layer composed of a nonwoven material. The fastener of the present invention is particularly useful in systems of the type including fastening tabs or tapes on the rear panel and a landing zone located on the front panel of a diaper. The fastener of the present invention may be used to provide both the fastening tabs or tapes and the reinforcing landing zone on the diapers. In such an application, the autoadhesive properties of the cling film layer may help eliminate or substantially reduce the contamination problems of the prior art systems using pressure sensitive adhesives. In addition, the autoadhesive surfaces of the cling film layer are substantially non-adhesive at ambient temperature with respect to the carrier layer thus enabling the fastener to be manufactured in the form of a web or roll for use in conventional diaper manufacturing systems. Also, a fastener composed of a cling film layer and a non-stretchable carrier layer provides the fastening system with relatively low peel, but relatively high shear strength. Preferably, when used as a disposable diaper fastening system, the peel strength is 100 g/inch or less, more preferably 600 g/inch or less, and most preferably 400 g/inch or less. On the other hand, the shear strength is preferably greater than 4 hours, and most preferably greater than 8 hours, as further described herein. Thus, the fastening tabs may be readily opened by a user without rupturing or significantly damaging the front panel and/or the landing zone of the disposable diaper while at the same time preventing stretching or deformation of the cling film layer itself so that the tabs may be refastened if desired.
The fastener of the present invention is also useful in various packaging applications. For example, the fastener could be used as a closure system for (1) snack food wrappers, such as candy, granola bars and potato chips, (2) sterilizable medical packages for items such as gauzes and bandages, (3) self-seal and tamper-evident envelopes, (4) banding for paper money, napkins and articles of clothing, (5) blister-type packages for various small articles, (6) closing corrugated boxes or other rigid packaging applications, and (7) closing plastic bags or other flexible packaging applications. In the above applications, the packaging material itself, i.e. the candy wrap material, the paper envelope material, etc., used to form the individual package would comprise the target surface to which the cling film layer (in its monolayer form) is attached or to which the carrier layer (in its multi-layered laminate form) is attached.
As previously described, the cling film layer may be a multi-layered laminate composed of a coating or layer of a polyolefin copolymer providing autoadhesive or cling surface properties bonded to a carrier layer. The carrier layer in turn may also comprise a multi-layered construction. For example, a multi-layered laminate may be constructed of a cling film layer composed of one or more polyolefin copolymers, and a carrier layer comprised of a base layer (to be attached to a target surface) and a structural layer interposed between the base layer and the cling film layer. In this multi-layered construction, each of the three layers are integrally bonded together, as by coextrusion or adhesion techniques, to form the desired fastener of the present invention. In another form, however, the cling film layer can be directly bonded onto the base layer to form the desired fastener of the present invention without the structural substrate layer. For example, in this second form, the cling film layer could be directly extruded onto the base layer, or the cling film layer could be applied using any known fiber forming technology such as being melt blown or spun bond directly onto the base layer. Alternately, the carrier layer could be directly formed onto the cling film layer. For example, if the base layer is a nonwoven material, the nonwoven can be directly melt blown or spun bonded onto the structural substrate layer and/or the cling film layer.
The material useful for forming the carrier layer is any material which is substantially non-stretchable in the machine direction (longitudinally) and/or the cross machine direction (transverse). Preferably, the carrier layer is comprised of a nonwoven material, which gives the fastener a soft, cloth-like feel, or a thermoplastic film such as a polyolefin like polyethylene or polypropylene. Thus, each of the individual layers that are used to make up the carrier layer may be comprised of a nonwoven material, or a thermoplastic film such as a polyester, a polyamide, a polysulfone, an acrylic polymer, a polystyrene, a polyurethane, a polycarbonate, a halogenated polymer, a cellulosic, a polyacrylonitrile, and an ionomer based on sodium or zinc salts of ethylene/methacrylic acid, or any suitable polyolefin or combination of polyolefins such as polyethylene, polypropylene, copolymers of ethylene, copolymers of propylene, or polymers obtained from ethylene and/or propylene copolymerized with other olefins, particularly C3 to C12 olefins. Particularly preferred are nonwovens, polypropylene and linear low density polyethylene (LLDPE). Suitable LLDPEs include those having a density of between 0.90 g/cm3 to 0.94 g/cm3 with a melt index between 0.5 g/10 min. to 30 g/10 min. Suitable polypropylene is normally highly crystalline with a density range between 0.89 g/cm3 to 0.91 g/cm3 and a melt index between 0.1 g/10 min. to 300 g/10 min.
The cling film layer that provides the autoadhesive or cling properties is preferably comprised of a suitable single site or metallocene catalyzed ethylene-based copolymer of ethylene and one or more C3 to C18 alpha-olefin comonomer, or a single site or metallocene catalyzed propylene-based copolymer of propylene and one or more C2 to C18 alpha-olefin comonomer, or a blend of the ethylene-based copolymers, the propylene-based copolymers, or one or more of the ethylene-based copolymers with one or more of the propylene-based copolymers. The alpha-olefin comonomer content in the ethylene-based copolymer is at least 20% by weight, and preferably from 20% to 50% by weight. The alpha-olefin comonomer content in the propylene-based copolymer is at least 5%, and preferably 5% to 30%, and most preferably 5% to 15% by weight. Suitable ethylene-based copolymers have a density of less than 0.89 g/cm3 and preferably less than 0.88 g/cm3. Both the ethylene-based copolymers and the propylene-based copolymers have a melt index of 100 g/10 min. or less and preferably 50 g/10 min. or less and most preferably 10 g/10 min. or less.
The drawings illustrate the best mode presently contemplated of carrying out the invention.
In the drawings:
The cling film fastener has as one of its primary components a cling film layer containing one or more polyolefin copolymers that provides autoadhesive or cling surface properties. In one embodiment, the cling film layer may be a substantially non-stretchable self-supporting sheet in the form of a monolayer of the one or more polyolefin copolymers. In use, the cling film monolayer is bonded directly to a target surface so that its cling surface is exposed.
In another embodiment, the cling film fastener comprises a multi-layered laminate structure. In this embodiment, the cling film layer has one or more polyolefin copolymers that provides autoadhesive or cling surface properties bonded to or coated on a carrier layer which provides support for the cling film layer. The carrier layer itself may be a single layer or a multi-layered construction, and either, or both, of the cling film layer and the carrier layer (or any or all of the individual layers of the carrier layer) may be substantially non-stretchable so as to render the entire cling film fastener itself substantially non-stretchable. The carrier layer preferably is the component of the laminate that eliminates, or substantially limits, stretching of the cling film layer. The carrier layer thus preferably provides dimensional stability both in the longitudinal and/or the cross direction to prevent stretching or deformation of the cling film layer. In use, the carrier layer is bonded directly to a target surface so that the cling surface is exposed.
Referring now to the drawings, there is illustrated various embodiments relating to a fastening system for numerous different applications, which in the form illustrated in
A laminate such as that illustrated in
The material useful for forming the carrier layer, or any of its individual layers in a multi-layered construction, is any material which is substantially non-stretchable in the machine direction (longitudinally) and/or cross machine direction (transverse). Preferably, the carrier layer is comprised of a non-woven substrate or a thermoplastic film material. By “non-woven material” it is meant a sheet or web structure bonded together by entangling fiber or filaments (and by perforating films) mechanically, thermally or chemically. They are flat, porous, self-supporting sheets that are made directly from separate fibers or from molten plastic or plastic film. They are not made by weaving or knitting and do not require converting the fibers to yarn. The carrier layer may be either flexible or non-flexible so long as it is substantially non-stretchable. The term “flexible” means that the carrier layer may be bent to a radius of 0.5 cm without breaking or cracking.
The thermoplastic film materials useful for forming the substantially non-stretchable carrier layer of the cling film fastener include meltable film-forming thermoplastics which preferably do not adhere to the cling film autoadhesive or cling surface at ambient temperature or service temperatures. More preferably, the thermoplastic film should have a melt temperature sufficiently close to that of the polyolefin copolymer cling film layer to enable co-extrusion of the carrier layer and the polyolefin copolymer cling film layer and formation of a permanent bond therebetween, with or without the use of an adhesive therebetween, which bond is retained after cooling. In practice, any thermoplastic film material may be used which is capable of being formed into a self-supporting continuous sheet or film having adequate mechanical properties to withstand normal handling and to fulfill the requirements of the end use application including satisfactory bonding with the polyolefin copolymer cling film layer at an elevated temperature, and to form a substantially non-stretchable carrier layer. Thus, the carrier layer is formed of a material which eliminates, or substantially limits, stretching of the polyolefin copolymer cling film layer. The carrier layer thus provides dimensional stability both in the longitudinal as well as the cross-wise or transverse direction to prevent stretching or deformation of the polyolefin copolymer cling film layer. The term “substantially non-stretchable” means that preferably, during anticipated use and/or storage, the cling film fastener will stretch no more than about 50% in either direction, and more preferably stretching should be limited to no more than 25% from its original non-stretched configuration, and most preferably less than 10% from its original non-stretched configuration. To accomplish this, one or more layers of the cling film fastener (e.g. the cling film layer, the carrier layer, and/or the individual substrates or layers of the carrier layer) must be substantially non-stretchable which will thus result in the cling film fastener itself stretching during normal use no more than about 50% in either direction, and more preferably stretching no more than about 25%, and most preferably less than 10% from its original non-stretched configuration. Additionally, the carrier layer can be made breathable by any method known in the art.
The thermoplastic film material forming the carrier layer, including any of the individual layers themselves that may comprise a multi-layered carrier layer, may comprise a wide range of polymers, copolymers, terpolymers, interpolymers and blends thereof selected to meet the end use application. Illustrative thermoplastics which may be used alone or in blends include polyolefins such as polyethylene, polypropylene and polybutylene, copolymers of ethylene and C3-C8 olefins, thermoplastic polyesters, polyamides such as nylon, polysulfones, acrylic polymers such as polyethylene acrylic acid, polyethylene ethyl acrylate, polyethylene n-butyl acrylate and polyethylene methyl acrylate, polystyrene, polyurethanes, polycarbonates, halogenated polymers such as polyvinylchloride and polyvinylidene chloride, cellulosics, polyacrylonitriles, ethylene vinyl acetate, and ionomers based on sodium or zinc salts of ethylene/methacrylic acid. The preferred thermoplastic film materials comprise polyolefins including low, medium and high density polyethylene such as low density polyethylenes (LDPE), linear low density polyethylenes (LLDPE), high pressure low density polyethylenes (HPLDPE) and very low density polyethylenes (VLDPE), and/or polypropylene.
The cling film fastener may be a self-supporting sheet which is in the form of a monolayer or in the form of a multi-layered laminate structure. As a monolayer, the fastener comprises only the cling film layer and is substantially non-stretchable, and is in the form of a self-supporting sheet of one or more polyolefin copolymers having both its inner and outer surfaces exhibiting cling properties. It may, or may not, need to be bonded to a carrier layer to form a multi-layered laminate depending upon its end use.
The cling film fastener, however, is typically in the form of a multi-layered laminate composed of the cling film layer providing autoadhesive or cling surface properties bonded to a carrier layer which in turn may also comprise a multi-layered construction. For example, the cling film layer may be composed of one or more polyolefin copolymers, and the carrier layer may be comprised of a base layer (to be attached to a target surface) and a structural layer interposed between the base layer and the polyolefin copolymer layer. In this multi-layered construction, each of the three layers are integrally bonded together, as by coextrusion or an adhesive, to form the desired fastener of the present invention. In addition, the carrier layer may include one or more other substrates either between the structural layer and the cling film layer, or between the structural layer and the base layer. For example, depending upon the tackiness of the autoadhesive surface, the carrier layer may need a release or slip layer thereon to prevent blocking when the fastener is stored in roll form. Also, depending on its end use, the fastener may need a tear resistant substrate or layer, or a puncture resistant substrate or layer. It should also be noted that in an alternate form the cling film layer that provides the autoadhesive or cling surface properties for the cling film fastener may be directly bonded (as for example by coextrusion, melt blowing or spun bonding) onto the carrier layer to form the desired laminate with or without any other layer such as the structural substrate layer. Additionally, the cling film layer and/or the carrier layer can be made breathable by any method known in the art.
The terms “autoadhesive” and “autoadhesion” and “cling” are used herein to indicate the self-adhesive or cohesive-adhesive properties of a polymeric material which enable films, layers or coatings thereof to be repeatedly adhered together by application of pressure at service temperatures or room temperatures and separated. Such materials adhesively bond to each other but are substantially non-adhesive with respect to other materials. The bonds formed by the outer cling surface may be permanent, releasable, sealable, re-sealable and/or non-resealable depending upon the desired end use. The term “service temperature” is used herein in accordance with its ordinary meaning to indicate the intended temperature or temperature range of use for the cling film fastener by the end user and/or under storage conditions of the end product. Thus, the service temperature typically ranges from a temperature of about 0° F. to a shipping and storage temperature of about 140° F. The term “self-supporting” refers to the ability of a coating, layer or film of material to independently support itself or its own weight.
The terms “fasten,” “fastening,” or “fastener” as used herein is intended to broadly refer to the attaching of one item to another whether the resultant attachment is permanent, releasable, sealable, re-sealable, non-re-sealable, reclosable, or the like. As such, these terms are intended to cover applications where cold seals, pressure sensitive adhesives, hot melt adhesives and/or curable adhesives have been used to bond two items together in the past, but is clearly not limited to such conventional adhesive bonding techniques or applications.
The individual layers of the carrier layer may be composed of a thermoplastic material and may be comprised of any suitable polyolefin or combination of polyolefins such as polyethylene, polypropylene, copolymers of ethylene, copolymers of propylene, or polymers obtained from ethylene and/or propylene copolymerized with other olefins, particularly C3 to C12 olefins. Especially preferred olefins are 1-butene, 1-hexene, 1-octene and 4-methyl pentene-1. Particularly preferred materials for use as one or more of the individual layers of the carrier layer are low, medium and/or high density polyethylene, polypropylene, and ethylenic copolymers such as linear low density polyethylenes (LLDPE) or very low density polyethylenes (VLDPE).
Suitable ethylene-based copolymers for use as the individual layers of the carrier layer comprise a major proportion by weight of ethylene copolymerized with a minor proportion by weight of an alpha-olefin monomer containing about 3 to about 12, preferably about 4 to about 10, and more preferably about 4 to about 8, carbon atoms. These resins have a polydispersity which is preferably in the range of from about 2 to about 7.
Ethylene-based copolymers for use as the individual layers of the carrier layer are those commonly referred to as linear low density polyethylenes (LLDPE) and very low density polyethylenes (VLDPE). Preferably the ethylene-based copolymers employed are those having from about 1 to about 20, preferably from about 1 to about 10 weight percent of said higher alpha-olefin monomer copolymerized therein. In addition, the alpha-olefin monomer employed in the ethylene-based copolymer is selected from the group consisting of 1-butene, 3-methyl-1-butene, 3-methyl-1-pentene, 1-hexene, 4-methyl-1-pentene, 3-methyl-1-hexene, 1-octene and 1-decene. Particularly preferred are the 1-butene, 1-octene and 1-hexene alpha-olefins. The LLDPE resins may be prepared at relatively low pressures employing coordination-type catalysts. Reference may be made to U.S. Pat. Nos. 3,645,992, 4,076,698, 4,011,382, 4,163,831, 4,205,021, 4,302,565, 4,302,566, 4,359,561 and 4,522,987 for more details of the manufacture and properties of LLDPE resins including those which are particularly useful herein.
The LLDPE resins that can be used in the carrier layer herein have a density ranging from about 0.90 to about 0.940 g/cm3, more commonly from about 0.90 to about 0.93 g/cm3, and a melt index (I2) of from about 0.5 g/10 min. to about 30 g/10 min., preferably from about 1 to about 10 g/10 min., as determined by ASTM D1238. Particularly preferred are those LLDPE resins possessing densities within the range from about 0.917 to about 0.920 μm/cm3 and a melt index of from about 2.0 to about 5.0 g/10 min., as determined by ASTM D1238. Examples of such LLDPE resins include those set forth in U.S. Pat. No. 5,273,809, which is incorporated herein by reference in its entirety. Such LLDPEs and methods for making them are well known in the art and are readily available commercially.
The VLDPE resins that may be used in the carrier layer herein have a density ranging from about 0.880 to about 0.912 g/cm3, more commonly from about 0.89 to about 0.91 g/cm3, and a melt index of from about 0.5 to about 5 g/10 min., preferably from about 1 to about 3 g/10 min. Such VLDPEs and methods for making them are well known in the art and are readily available commercially.
Suitable polypropylene is normally solid and isotactic having a wide ranging melt index between 0.1 g/10 min. to 300 g/10 min. Such polypropylene is normally crystalline with a density range of from about 0.89 g/cm3 to about 0.91 g/cm3 for isotactic polypropylene. Such polypropylenes and methods for making them are well known in the art and are readily available commercially.
The thermoplastic materials useful in the carrier layer, and particularly, the LLDPE and VLDPE resins, can be blended with minor amounts, e.g., up to about 40 weight percent total, of one or more other suitable resins to achieve a desired range of physical/mechanical properties in the film product. Thus, for example, such resins as ethyl vinyl acetate (EVA) copolymer, high pressure low density polyethylene (HPLDPE), and other LLDPE resins may be used for blending to obtain useful mixtures for forming one or more layer of the carrier layer of the present invention.
The thermoplastic polymer material providing the autoadhesive or cling surface properties for the cling film layer may be composed of a thermoplastic material or blends of thermoplastic materials which are selected from the group consisting of polyolefins, acrylic modified polyolefins, vinyl acetate modified polyolefins, and acrylic polymers. The polyolefin may be polypropylene or polyethylene. The acrylic modified polyolefin may be a copolymer of polypropylene or polyethylene and an acrylic. Likewise, the vinyl acetate modified polyolefin may be a copolymer of polypropylene or polyethylene and vinyl acetate.
The thermoplastic polymer material that provides the autoadhesive or cling properties for the cling film layer is preferably comprised of a suitable single site or metallocene catalyzed ethylene-based copolymer comprising a major portion by weight of ethylene and a minor portion by weight of a C3 to C18 alpha-olefin comonomer, or a single site or metallocene catalyzed propylene-based copolymer comprising a major portion by weight of propylene and a minor portion by weight of a C2 to C18 alpha-olefin comonomer, or a blend of the ethylene-based copolymers, the propylene-based copolymers, or one or more of the ethylene-based copolymers with one or more of the propylene-based copolymers. The alpha-olefin comonomer preferably contains 3 to 12 carbon atoms, more preferably contains 4 to 10 carbon atoms, and most preferably contains 4 to 8 carbon atoms. More particularly, the alpha-olefin comonomer may be selected from 1-butene, 1-pentene, 3-methyl-1-butene, 3-methyl-1-pentene, 1-hexene, 4-methyl-1-pentene, 1-dodecene, 3-methyl-1-hexene, 1-octene, and 1-decene. Particularly preferred is 1-octene copolymerized with ethylene.
The alpha-olefin comonomer content in the ethylene-based copolymer is at least 20% by weight and in the range of from 20% to 50% by weight, preferably from 25% to 50% by weight, more preferably from 30% to 50% by weight. Suitable ethylene-based copolymers have a density as determined by ASTM D-792 of 0.89 g/cm3 or less and in the range of from 0.89 g/cm3 to 0.85 g/cm3, preferably between 0.88 g/cm3 and 0.85 g/cm3, and most preferably between 0.875 g/cm3 and 0.85 g/cm3. Suitable ethylene-based copolymers also have a melt index at 190° C. under 2.16 kg as determined by ASTM D1238 of 100 g/10 min. or less, preferably 50 g/10 min. or less, more preferably 10 g/10 min. or less, and most preferably 5 g/10 min. or less.
The alpha-olefin comonomer content in the propylene-based copolymer is at least 5%, preferably 5% to 30%, and most preferably 5% to 15% by weight, and the preferred copolymer is a propylene-ethylene copolymer. The propylene-based copolymers have a melt index (measured at 230° C.) of less than 100 g/10 min., preferably less than 50 g/10 min. and more preferably less than 25 g/10 min.
“Blends” may comprise two or more ethylene-based copolymers or two or more propylene-based copolymers, or one or more ethylene-based copolymers with one or more propylene-based copolymers. Where a blend of copolymers is used, the calculated density of the blend should also fall under the above limits, i.e. less than 0.89 g/cm3. For example, a blend of 70% of an ethylene-based copolymer having a density of 0.870 g/cm3 and 30% of a propylene-based copolymer having a density of 0.885 g/cm3 will result in a final blend having a calculated density of 0.875 g/cm3.
Useful single site or metallocene catalyzed ethylene-based polymers are available from, among others, Dow Chemical Company and Exxon Mobil Chemical Company who are producers of single site or constrained geometry catalyzed polyethylenes. These resins are commercially available as the AFFINITY and EXACT polyethylenes (see Plastics World, pp. 33-36, January 1995), and also as the ENHANCED polyethylene and EXCEED line of resins. These ethylene-based copolymers are also available under the ENGAGE brand from DuPont Dow Elastomers. The manufacture of such polyethylenes, generally by way of employing a metallocene catalyst system, is set forth in, among others, U.S. Pat. Nos. 5,382,631, 5,380,810, 5,358,792, 5,206,075, 5,183,867, 5,124,418, 5,084,534, 5,079,205, 5,032,652, 5,026,798, 5,017,655, 5,006,500, 5,001,205, 4,937,301, 4,925,821, 4,871,523, 4,871,705 and 4,808,561, each of which is incorporated herein by reference in its entirety. These catalyst systems and their use to prepare such copolymer materials are also set forth in EP0600425A1 and PCT applications WO 94/25271 and WO 94/26816.
The single site or metallocene catalyzed propylene-based copolymers are available under the VERSIFY brand from The Dow Chemical Company. The manufacture of such polypropylenes is also based on using a metallocene or single site catalyst system and is based on Dow's INSITE technology.
The thermoplastic polymer coatings used to provide the autoadhesive or cling properties may also contain known and conventional cling additives to augment the cling property that, at least in the case of the particularly preferred resins, is inherently exhibited. Examples of useful cling additives include poly-isobutylenes having a number average molecular weight in the range of from about 1,000 to about 3,000, preferably about 1,200 to about 1,800, as measured by vapor phase osmometry, amorphous atactic polypropylenes, e.g., those having an average molecular weight of about 2000, and polyterpenes and ethylene-vinyl acetate copolymers containing about 3 to about 90 weight percent copolymerized vinyl acetate. The optional cling additive can be present in a concentration of from about 0.5 to about 10 weight percent of the resin.
Additionally, small amounts, less than 25% by weight and more preferably less than 10% by weight of modifiers can be added to modify the autoadhesive or other characteristics of the cling layer. Examples of these include tackifying resins, plasticizers, waxes, fillers, antioxidants, colorants, antiblocking agents, antistatic agents, UV stabilizers, etc.
Additionally, the cling surface may be modified to improve and/or change the blocking or cling properties, peel strength and/or shear strength in other ways. This may be accomplished by mechanical means (e.g. embossing or stamping techniques) or via the use of energy (e.g. UV, RF, microwaves or heat).
The thermoplastic polymer coatings used to provide the autoadhesive or cling properties may also be treated to such known and conventional post-forming operations as corona discharge, chemical treatment, flame treatment, etc., to modify the printability or ink receptivity of the surface(s) or to impart other desirable characteristics thereto. Thus, the fastening structure of the present invention may be pigmented, transparent, opaque or contain printing on selected portions thereof.
The thermoplastic polymer coatings used to provide the autoadhesive or cling properties is preferably constructed entirely from either an ethylene-based copolymer or propylene-based copolymer produced by single site or metallocene catalyst technology as defined herein. However, the thermoplastic polymer coating may also comprise a blend of one or more of the metallocene catalyzed copolymers with a second resin material. The second material may be an olefin polymer resin such as a polyolefin like polypropylene or polyethylene, an acrylic modified polyolefin, a vinyl acetate modified polyolefin or an acrylic polymer. For example, this may include, but is not limited to, LLDPE, LDPE, HPLDPE, VLDPE, propylene based resins or combinations thereof. If the second resin material is to be incorporated with the metallocene or single site-catalyzed resin, it is preferred to maintain the level of the metallocene-catalyzed resin to at least about 60wt. %. The resultant blended polymer mixture maintains the desired properties of the metallocene-catalyzed material and may be more economical for certain applications.
The thermoplastic polymer coatings may be directly coextruded onto or bonded with an adhesive to the structural substrate of the cling film layer in any conventional manner. Alternately, if it was desired to eliminate the structural substrate of the cling film layer, the polymer coating could be extruded directly onto the base carrier layer or could be coextruded along with the base carrier layer or be melt blown or spun bound directly onto the base carrier layer.
In one embodiment, and for example when used in a nonwoven soft goods application (e.g.
The fastener of the present invention may be prepared by extrusion processing of the cling film layer directly onto the carrier layer using any conventional commercially available apparatus. Alternately, the cling film layer may be adhesively bonded to the carrier layer. Any other bonding method may be used to bond the cling film layer to the carrier layer, e.g. ultrasonic, thermal, pressure bonding, microwave, RF, etc. In addition, the carrier layer could be directly formed onto the cling film layer. For example, if the carrier layer is a nonwoven material, the nonwoven can be directly melt blown or spun bonded onto the cling film layer. If an adhesive is used to bond the layers of the fastener together, the adhesive may be any suitable hot melt adhesive, and may be applied using any standard application equipment either to the cling film layer or to the carrier layer or to both. Typical add-on levels for the adhesive layer would be from about 1 g/sq. meter to about 20 g/sq. meter. It should be noted that the particular apparatus selected, whether it be a co-extrusion apparatus or a coater/lamination apparatus, may depend upon the differences in processing temperatures and rheologies of the materials forming the cling film layer, the carrier layer, and the optional adhesive layer. The overall thickness of the fastener or laminate can vary widely and is application specific. Generally, however, the laminate will be 0.2 mils to 40 mils thick, and typically ranging between 0.5 and 20 mils in thickness.
Target surfaces are those surfaces the fastener or cling film laminate of the present invention is bonded to. Target surfaces which are useful in the invention may be selected from a wide variety of materials. Examples of useful target surfaces include the surfaces of those materials previously identified as being useful for the individual layers of the carrier layer as well as polymeric materials such as polycarbonate, polyacrylonitrile, butadiene-styrene polymers, poly(methylmethacrylate), polyamide, ethylene vinylacetate copolymer, treated and untreated poly(ethylene terephthalate), Surlyn®, polystyrene, acrylonitrile butadiene-styrene polymer, polypropylene, and polystyrene. Target surfaces also include metallic surfaces such as stainless steel; glass; paper of all types including cardboard, paperboard and coated paper stock; enamel coated substrates; and particularly nonwoven surfaces. The fastener or cling film laminate of the present invention may be bonded in any manner to the target surface. For example, the bond may comprise a pressure sensitive adhesive coated on the carrier layer or the target surface, a hook and loop reclosable fastener, a mushroom-shaped reclosable fastener, an ultrasonic weld, a mechanical bond, or a thermal bond. The exact choice of target surface to be used is dependent upon the needs of the user.
Referring now to
The cling film layer 2 is formed of a suitable thermoplastic polymer material, such as polyethylene. The exterior surface 3 of layer 2 is autoadhesive in that it mutually adheres to like autoadhesive surfaces, but is otherwise substantially non-adhesive. The carrier layer 4 is formed of a non-woven material and includes exterior surface 6a which does not adhere to surface 3 when they are pressed together at room temperature or elevated storage temperature conditions, even when wound under tension in large diameter rolls. Accordingly, the laminate 1 may be self-wound or stacked without a release liner thus enabling the laminate to be manufactured in the form of a web or roll for use in conventional diaper manufacturing systems.
As shown in
As further illustrated in
As shown best in
Referring now to
Referring now to
It should be noted that instead of adhesively attaching ears 35 and 36 to waist portions 10f and 11f of the diaper, ears 35 and 36 could also be formed integrally as part of the back sheet or outer liner 12f for the disposable diaper. In other words,
In a further alternative embodiment, the cling film laminate may serve as a fastening system for a feminine care pad or sanitary napkin 41 as shown in
As shown in
In the illustrated embodiment, the back or rear wall 80 has a height slightly greater than the height of front wall 79 to define an upper edge 81 which cooperates with an upper edge 82 of front wall 79 to determine an access opening 83 into the bag 78 when the upper edges 81, 82 are separated. In accordance with the present invention, a cling film fastener 84 is applied along the inner surface of upper edge 81 having its cling surface exposed and directed toward front wall 79. In addition, a second cling film fastener 85 is applied along upper edge 82 of front wall 79 with its cling surface exposed and extending toward rear wall 80. Thus, when pressure is applied to upper edges 81 and 82 so that the cling surface of fastener 84 engages the cling surface of fastener 85, the two opposing cling surfaces adhere to one another to close opening 83 as illustrated in
The improved peel and shear properties of laminates made in accordance with the present invention are illustrated by the data reported in Table 1 below. For each laminate tested the peel strength was 50 g or less and shear strength was acceptable (all samples held for at least 8 hours), not only at room temperature but also after aging at elevated temperatures.
Method for Preparing the Cling Laminates:
The cling films were laminated using a Nordson coater/laminator. A pressure sensitive hot melt adhesive was used at an add-on level of 10 grams per square meter and was applied using standard meltblown application equipment. The adhesive was applied to the film substrate and nipped to the non-cling side of the cling film after an open time of 250 milliseconds. After bonding the two substrates together, the resultant cling laminate was wound onto itself. The adhesive used to prepare the laminates was H2545 and is available from Bostik Findley, Inc. The nonwoven is a standard spunbond polypropylene nonwoven with a basis weight of 14 gsm available from Avgol Nonwoven Industries.
Peel Test Method:
The peel test was performed using an Instron tensile tester with a crosshead speed of 36 inches/minute. A two inch wide sample of laminate was placed with the cling side to the cling side of a second laminate of the same width. A 500 gram roller was used to compress the laminates before testing. The test method used was a standard 180 degree peel test. The average peel strength in grams is reported in the tables. Duplicates were also tested after they were stored in an incubator oven for a period of 24 hours at 100° F. and 120° F. The laminates were not bonded during the elevated temperature storage. After aging the samples were tested as before.
Shear Test Method:
A two inch wide sample of cling laminate was placed in contact with a second laminate with the cling sides touching. The overlap area was two inches by 1½ inches. A standard 500 gram roller was used to compress the structure. A 500 gram weight was used to stress the bonded area in a modified 180° shear configuration while in an incubator oven at 100° F., i.e. the shear sample was placed around a 6 inch core member with the bonded area at about the 9 o'clock position. If the bond held for a period of four hours, it was considered to have passed the test.
Pactiv APM 3-2015 stretch film is available from Pactiv Corporation, 1900 West Field Court, Lake Forest, Ill. 60045.
Presto films are available from Presto Products Company, P.O. Box 2399, Appleton, Wis. 54912.
Paragon films are available from Paragon Films, Inc., 3500 West Tacoma, Broken Arrow, Okla. 74012.
Depending upon the end use requirements of the fastening system on the finished article, the desired peel strength could be higher than that described in Example 1, i.e. up to 1000 g/inch.
This example was performed to determine the effect of aging on the peel strength of cling laminates constructed in accordance with the present invention, and to compare the data obtained with that of prior art laminates disclosed in U.S. Pat. No. 5,085,655. Accordingly, the peel test method described in Example 1 was once again performed on two inch wide samples of laminate except using a crosshead speed of 10 inches/minute. The average peel strength in grams is reported in Table 2A initially, after one hour, after one day and after 13 days for laminates made in accordance with the present invention. All samples were stored at room temperature (RT) for the designated time period. These data are then compared to the results reported in Mann et al U.S. Pat. No. 5,085,655 which describes a prior art laminate using a styrene-ethylene-butylene-styrene (SEBS) block copolymer or an ethylene-propylene rubber (EPR) as an autoadhesive layer. The Mann et al data is reported in Table 2B.
One can conclude from the above data that the peel strengths of the cling laminates of the present invention tested do not increase to any significant degree during aging, even after 13 days of aging. In contrast, the peel strengths of the prior art laminates increased dramatically over time.
As a further comparison, the peel and shear properties of several currently available commercial diaper fastening systems were obtained and tested in the same manner as for Example 1. The data is illustrated in Table 3 below. It is to be noted that the peel strength for the tape fastening systems tested are significantly higher than the laminates of the present invention and increase substantially during aging for 8 hours at 100° F.
Peel Values for Various Commercial Fastening Systems:
Several samples of commercially sold diapers were obtained for testing. Two of them used a conventional pressure sensitive tape tab and two used a mechanical fastener system. The same basic peel test that was described previously was used with the following modifications.
The landing zone for each diaper was cut out of the diaper. In the case of the pressure sensitive tape tab, the landing zone consisted of a piece of polypropylene film bonded to the backsheet with a release coating on an outward side. The pressure sensitive tape tab was placed on the release side of the structure and rolled down with a 500 gram roller. In the case of the mechanical fastener, the landing zone consisted of a “loop” material bonded to the backsheet of the diaper. The “hook” tab portion was placed in contact with the “loop” side of the landing zone and rolled down with a 500 gram roller. A 180 degree peel test was performed using the same conditions as noted before. The average peel strength was noted. The pressure sensitive tape tabs were also aged while bonded for eight hours at 100° F. to see if the peel strength changed. The mechanical fasteners were not aged since the bonds should be unaffected by aging.
Shear tests were also run in accordance with the method set forth in Example 1 on Samples 1 and 2 of Example 3. All samples passed the four hour test initially. No shear testing was performed on the aged samples. However, it is expected that the aged samples would pass.
Although shear testing was not performed on Samples 3 and 4 of Example 3, it is expected that they would pass this test.
This example was performed to determine the peel strength of various three layer cling film laminates constructed in accordance with the present invention using a Davis Standard extruder. The peel test method described in Example 1 was used to obtain the data reported in Table 4. In Table 4, the letter “c” refers to a calculated density, or a calculated melt index for the polymer blends.
The laminates were produced on a Davis Standard coextrusion unit having three separate layers. The die itself was 10 inch wide and 20 mils thick, fed by three extruders with the screw Length/Diameter ratios of about 15 to 30 to 1. The screw diameters were one inch or one and half inch, with rotational speeds of about 4 to 20 rpm. The melt was heated progressively along three zones with a final temperature of about 190° C. to 230° C. The film was extruded onto a chilled metal roll at about 60° F., then contacted a second roll heated at 100° F. The line speed was about 12 to 15 meters/min. The film samples were tested a few days afterwards for peel performance.
Top layer was the “cling” film copolymer (or blend of copolymers) as noted above.
Middle layer was the structural layer of the carrier layer for the laminate and comprised Tuflin 7021 which is a LLDPE having a density of 0.914 g/cm3 and a melt index (MI) of 3.2 g/10 min.
Bottom layer was the base layer of the carrier layer for the laminate and comprised a high density polyethylene with a density of 0.934 g/cm3 and a MI of 2.7 g/10 min.
Each film layer was 1 mil thick
Affinity and Tuflin grades available from Dow Chemical Co.
Engage grades available from DuPont Dow Elastomers
The high density polyethylene used for the bottom layer is available from Atofina Petrochemicals
The data illustrate that the peel strengths for the present cling film laminates increase as the density decreases, and the cling film laminates are more than adequate for use in fastening and bonding systems as described herein whereas prior art cling films did not have sufficient peel strength. The relationship between density and peel strength is also illustrated in
This example was performed to determine the peel'strength of various cling film layers constructed in accordance with the present invention using a Randcastle Monolayer extruder. The peel test method described in Example 1 was used to obtain the data reported in Table 5. In Table 5, the letter “c” refers to a calculated density, or a calculated melt index for the polymer blends.
Films were produced on a Randcastle lab-scale monolayer extrusion unit, and each film was 3 mils thick. The die itself was 6 inch wide fed by one extruder with a screw Length/Diameter ratio of about 20 to 1. The screw speed was about 4 to 25 rpm. The melt was heated along four zones with a final temperature of about 180° C to 240° C. The film first met a chilled metal roll at about 60° F. The line speed was about 0.4 to 1.5 meters/min. Film samples were then tested a few days afterwards for peel performance.
The data illustrate that the peel strengths for the present cling film laminates increase as density decreases, and the cling film laminates are more than adequate for use in the fastening and bonding systems as described herein. This relationship between density and peel strength is further illustrated in
It should be noted that in the above Example 5, Affinity VP 8770 is an example of the substantially non-stretchable, self-supporting sheet or monolayer embodiment of the cling film fastener of the present invention. In addition, it should be noted that the cling surfaces of the films made on the Randcastle extruder unit (Example 5) were not as smooth as the cling surfaces of the films made on the Davis Standard unit (Example 4) resulting in the same copolymer (e.g. Affinity VP 8770) having a higher peel strength when its cling surface is smooth and untextured. This demonstrates that vary-ing the texture of the cling surface results in different peel strengths for the same density copolymer.
This application is a Continuation-In-Part of U.S. patent application Ser. No. 10/700,761, filed Nov. 4, 2003.
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10700761 | Nov 2003 | US |
| Child | 10867438 | Jun 2004 | US |
