Patent Application
20060258249
Articles requiring a degree of elasticity have been formed by combining elastic materials with inelastic, or less elastic, materials through various lamination processes. Often, such composite laminate articles will be stretchable because of the presence of the elastic material and the particular manner in which the elastic and inelastic materials have been bonded together during the laminating process.
Typically, such stretchable laminates are formed by joining the inelastic material to the elastic material while the elastic material or sheet is in a stretched condition. After such joining of the materials, the laminated article is then allowed to relax, which results in the inelastic component gathering in the spaces between bonding sites on the elastic sheet. The resulting laminate article is then stretchable to the extent that the inelastic material gathered between the bond locations allows the elastic material to elongate. Examples of these types of composite laminate articles and materials are set forth in U.S. Pat. Nos. 4,720,415 and 5,385,775, each of which is incorporated herein by reference thereto.
In some stretchable laminate articles, elastic strands of continuous filaments are bonded to relatively inelastic sheet materials while the elastic strands are in a stretched condition. Such elastic continuous filaments may, in certain articles, be sandwiched between two or more relatively inelastic sheets. The relatively inelastic sheets may include nonwoven webs formed by meltblowing or spunbonding various polymers. Examples of such laminates are shown in U.S. Pat. No. 5,385,775; in U.S. Pat. No. 6,057,024; and in U.S. Published Patent Application No. U.S. 2002/0104608, which are all incorporated herein by reference.
As shown in the '775 patent, elastic continuous filaments may be extruded onto a horizontally moving sheet of material. The continuous filaments are extruded from above the horizontal plane of the sheet material and directly onto the material for bonding thereto. In the '024 patent, an alternative embodiment is disclosed in which the continuous filaments are extruded vertically in a downward direction. As the filaments are extruded in a downward direction, the filaments are stretched and then laminated to one or more sheet materials.
In many embodiments in the past, an adhesive was used in order to adhere the elastic strands of continuous filaments to the sheet materials. In one embodiment, for instance, the adhesive was sprayed on the sheet material prior to contacting the filaments. Spraying the adhesive material onto the sheet materials, however, may have some drawbacks in various applications. For instance, spray devices may be difficult to control leading to over-application of the adhesive or leading to a non-uniform coverage of the adhesive on the sheet material, especially at high machine speeds and at low application rates. In fact, over-application of a hot adhesive during a spray process may cause filament breakage and machine downtime. Further, since the adhesive has to travel a distance prior to contacting the sheet material, the adhesives may experience a loss in tack prior to contacting the sheet material.
In view of the above, a need currently exists for an improved method for applying an adhesive material in between stretched elastic filaments and a nonwoven facing. A need also exists for an elastic composite laminate that has improved properties due to the manner in which an adhesive is applied.
In general, the present disclosure is directed to composite elastic materials that include a plurality of elastic continuous filaments bonded to at least one nonwoven web. The nonwoven web is laminated to the continuous filaments when the filaments are in a stretched state. Thus, when the filaments are relaxed, the nonwoven web gathers and allows the entire composite to stretch in at least one direction.
The present disclosure is more particularly directed to a method for applying an adhesive material in between the elastic continuous filaments and the nonwoven web and is directed to composite nonwoven materials produced by the process. The adhesive material is applied to the nonwoven web using a “starved” slot coating process in which the adhesive is emitted through a slot extrusion die onto the nonwoven web to form a discontinuous coating. The discontinuous coating contains amorphous elements of the adhesive material. The adhesive material is applied to a surface of the nonwoven web in a substantially uniform manner in terms of amount per area.
The starved coat process provides various benefits and advantages. For instance, the process allows for control over the placement of the adhesive on the nonwoven web. Further, the inventors have discovered that the process provides a very efficient use of the adhesive. In particular, relatively low amounts of adhesive are used that securely bond the elastic continuous filaments to the nonwoven web, even when the elastic filaments are present in a stretched state. Unexpectedly, the present inventors also discovered that the process produces composite nonwoven materials having a reduced porosity in comparison to similar composites made in which the adhesive is sprayed on the nonwoven web. The relatively low porosity provides various benefits when the composite material is used to construct various articles, such as when incorporated into absorbent garments including diapers, training pants, swim pants, adult incontinence products, feminine hygiene products, bandages and medical drapes, and the like.
In one particular embodiment, for instance, the present disclosure is directed to a method for producing a composite nonwoven material. The method includes the steps of extruding continuous filaments. The filaments comprise an elastomeric material. The elastomeric material may include, for instance, elastic polyesters, elastic polyurethanes, elastic polyamides, elastic copolymers of ethylene and at least one vinyl monomer, elastic metallocene-catalyzed polyolefins, and elastic block copolymers.
Once formed, the elastic continuous filaments are stretched and then laminated to the first side of a nonwoven web. In order to bond the stretched laminates to the nonwoven web, an adhesive material is applied to the nonwoven web from a slot extrusion die. The adhesive material forms a discontinuous coating comprising amorphous elements of the adhesive material. The adhesive material may be applied to the first side of the nonwoven web in an amount less than about 4.4 gsm, such as from about 0.5 gsm to about 3 gsm. The adhesive material may comprise, for instance, a styrenic block copolymer, a random copolymer of a polyolefin, or an amorphous polyalphaolefin. In addition to the above, any suitable hotmelt adhesive may be applied in accordance with the teachings of the present disclosure.
During application of the adhesive material to the nonwoven web, the nonwoven web may be configured to contact and slide against the slot on the slot extrusion die. The adhesive material may contact the web at a viscosity of from 500 cp to about 50,000 cp, such as from about 2,000 cp to about 20,000 cp. The temperature of the adhesive may vary depending upon the particular adhesive material used. In one embodiment, for instance, the application temperature of the adhesive may be from about 320° F. to about 350° F.
In one embodiment, the method can further include the step of laminating the elastic continuous filaments to a second nonwoven web. For example, the continuous filaments may be positioned in between the first nonwoven web and the second nonwoven web. The second nonwoven web may be laminated to the continuous filaments using an adhesive material as described above.
The nonwoven webs that are laminated to the elastic continuous filaments may vary depending upon the particular application and desired result. The nonwoven webs may comprise, for instance, meltblown webs, spunbond webs, bonded carded webs, and the like. In one embodiment, for instance, the nonwoven web comprises a spunbond web having a basis weight of from about 7 gsm to about 100 gsm, such as from about 10 gsm to about 20 gsm.
Other features and aspects of the present invention are discussed in greater detail below.
A full and enabling disclosure of the present invention, including the best mode thereof to one skilled in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying figures, in which:
Repeat use of reference characters in the present specification and drawings is intended to represent the same or analogous features or elements of the present invention.
The term “continuous filaments”, as used herein, refers to strands of continuously formed polymeric filaments. Such filaments will typically be formed by extruding molten material through a die head having a certain type and arrangement of capillary holes therein.
The term “elastic” or “elasticized”, as used herein, refers to a material which, upon application of a biasing force, is stretchable, which is elongatable to at least about 60 percent (i.e., to a stretched, biased length which is at least about 160 percent of its relaxed unbiased length), and which will recover at least 55 percent of its elongation upon release of the stretching force. A hypothetical example of an elastic material would be a one (1) inch sample of a material which is elongatable to at least 1.60 inches and which, when released, will recover to a length of not more than 1.27 inches. Many elastic materials may be elongated by more than 60 percent (i.e., more than 160 percent of their relaxed length). For example, some elastic material may be elongated 100 percent or more, and many of these will recover to substantially their initial relaxed length such as, for example, within 105 percent of their original relaxed length upon release of the stretching force.
The term “composite nonwoven fabric”, “composite nonwoven”, “laminate”, or “nonwoven laminate”, as used herein, unless otherwise defined, refers to a material having at least one elastic material joined to at least one sheet material. In most embodiments such laminates or composite fabric will have a gatherable layer which is bonded to an elastic layer or material so that the gatherable layer may be gathered between bonding locations. As set forth herein, the composite elastic laminate may be stretched to the extent that the gatherable material gathered between the bond locations allows the elastic material to elongate. This type of composite elastic laminate is disclosed, for example, in U.S. Pat. No. 4,720,415 to Vander Wielen et al., which is incorporated herein in its entirety by reference thereto.
As used herein, the term “nonwoven web” refers to a web having a structure of individual fibers or threads that are interlaid, but not in an identifiable, repeating manner. Nonwoven webs have been, in the past, formed by a variety of processes such as, for example, meltblowing processes, spunbonding processes and bonded carded web processes.
As used herein, the term “meltblown fibers” means fibers formed by extruding a molten thermoplastic material through a plurality of fine, usually circular, die capillaries as molten thermoplastic material or filaments into a high velocity gas (e.g. air) stream which attenuates the filaments of molten thermoplastic material to reduce their diameter, which may be to microfiber diameter. Thereafter, the meltblown fibers are carried by the high velocity gas stream and are deposited on a collecting surface to form a web of randomly disbursed meltblown fibers. Such a process is disclosed, for example, U.S. Pat. No. 3,849,241 to Butin, which is incorporated herein in its entirety by reference thereto.
As used herein, the term “spunbonded fibers” refers to small diameter fibers formed by extruding a molten thermoplastic material as filaments from a plurality of fine, usually circular, capillaries of a spinerette with the diameter of the extruded filaments then being rapidly reduced as by, for example, eductive stretching or other well-known spun-bonding mechanisms. The production of spun-bonded nonwoven webs is illustrated in patents such as, for example, U.S. Pat. No. 4,340,563 to Appel et al., and U.S. Pat. No. 3,692,618 to Dorschner et al. The disclosures of these patents are incorporated herein in their entireties by reference thereto.
It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention.
The present disclosure is generally directed to a method for producing a composite elastic nonwoven material and to the material itself. More particularly, the present disclosure is directed to a starved slot coat process for applying an adhesive to a facing material in order to laminate the facing material to a plurality of stretched filaments. Through the above process, the adhesive has been found to firmly bond the elastic filaments in a stretched state to the facing material. Once relaxed, the facing material gathers forming a stretchbonded laminate that has elastic properties in at least one direction.
In one embodiment, during the starved slot coat process, the facing material contacts the slot of the slot extrusion die (or “slot die”) as the adhesive is applied to the facing. The adhesive is applied to the facing at relatively low amounts forming a discontinuous coating on the nonwoven material. Even at relatively low adhesive application rates, the process has been found to securely bond the elastic filaments to the facing without problems of delamination.
In the past, elastic filaments have been laminated to facing materials by spraying an adhesive onto the facing material, such as disclosed in U.S. Patent Application Publication No. U.S. 2002/0104608. The process of the present disclosure, however, provides many benefits and advantages in comparison to an adhesive spray process. For example, the slot coat process may allow lamination at higher line speeds and may produce laminates having a higher peel strength. Unexpectedly, the slot coat process also produces laminates having a lower porosity, which makes the material easier to handle during later converting processes. It is believed that the lower laminate porosity is due to the fact that the adhesive is applied as a discontinuous coating which creates amorphous elements of adhesive as opposed to spray fiberization which creates fine fibers that may not have as much resistance to air flow.
The starved slot coat adhesive process has been found to efficiently place adhesive on the surface of the facing material. For example, the adhesive generally only covers the fibers of the facing material and does not bridge the void areas in the material. In a spray process, on the other hand, adhesive is applied everywhere on the substrate and typically collects in the void areas on the facing. When collected in the void areas, the adhesive does not substantially contribute to bonding the facing material to the elastic substrates.
In some applications, the starved coat adhesive process has been found to only be applied to the surface of the facing material only on the fibers of the material and at substantially the high points of the material which are generally only the places on the material where the facing can be bonded to the elastic filaments.
Another advantage to the process of the present disclosure in comparison to spray processes is that since the adhesive is applied immediately to the substrate as it is emitted from the slot extrusion die, no cooling or quenching of the adhesive occurs prior to being deposited on the material. As such, adhesives with higher or faster cure rates may be used.
In the past, slot coat processes have been disclosed in which a slot die is used to dispense adhesive in order to form laminates. For instance, U.S. Pat. No. 5,750,444 to Jarrell, which is incorporated herein by reference, discloses a process for producing breathable laminates using a slot die. In the '444 patent, the adhesive is described as forming a porous random fibrous web. The adhesive is used to attach together two or more porous webs comprising woven or nonwoven materials to form laminates that remain breathable even after application of the adhesive in between the materials.
In the process of the present disclosure, on the other hand, laminates are formed in which elastic filaments are stretched and then bonded to a facing material. It was discovered that the starved slot coat process of the present invention was capable of adequately bonding the stretched filaments to the facing even at relatively low adhesive application rates. Also, it was unexpectedly discovered that the slot coat process as disclosed herein increased the porosity of the laminate in comparison to spray processes. As will be described in more detail below, the increase in porosity facilitates handling of the laminate in later converting processes.
Referring to
As shown in
The continuous filaments 14 formed in the process may have any desirable shape. In one embodiment, for instance, the filaments may have a ribbon-like shape. For instance, the filaments may have a width of from about 0.5 mm to about 1.5 mm in an unstretched state. The filaments all generally extend in the same direction and are generally parallel to each other. The actual number of continuous filaments utilized in any particular process may vary depending upon the particular characteristics desired in the final product. For example, the array of filaments may total more than about 100 strands, such as more than about 200 separate strands. For example, in one embodiment, the array of filaments may number from about 200 separate strands to as much as 2600 separate strands. A greater or lesser number of strands, however, is also possible.
As shown in
The continuous filaments may be combined at the nip with various types of facings. The facings, for example, may comprise nonwoven fabrics, woven fabrics including knitted fabrics, films, laminates, and the like. In the embodiment depicted in
Bonding of the facings to the continuous filaments is done with an adhesive material. In accordance with the present disclosure, the adhesive is applied to the facings using a slot extrusion die. For instance, as shown in
In one embodiment, the adhesive application rates applied to the nonwoven materials can be relatively low. In fact, the adhesive rate is so low that the process can be referred to as a “starved” slot coat process. For example, in one embodiment, the adhesive is applied to each of the nonwoven materials in an amount less than about 4.4 gsm, such as from about 0.5 gsm to about 3 gsm, such as from about 0.8 gsm to about 2.5 gsm.
At such low add-on rates, the adhesive does not completely coat the nonwoven materials. Instead, the adhesive forms a discontinuous coating. For example, in one embodiment, the adhesive may form amorphous elements placed over the surface of the nonwoven material. Of particular advantage, the adhesive primarily becomes applied to the nonwoven web at elevations on the web, which is the place where the web is capable of bonding with the elastic filaments 14. More particularly, the adhesive tends to coat the top surface of the fibers on the web and fails to collect or bridge the void areas in the web. Thus, little to no adhesive is wasted creating maximum adhesive efficiency.
Although the adhesive forms a discontinuous coating, however, it should be understood that the adhesive is applied in a substantially uniform manner over the surface of the nonwoven material in terms of amount per area.
In general, any suitable slot extrusion die may be used in the process of the present invention. For example, in one embodiment, a slot extrusion die commercially available from the Nordson Corporation of Westlake, Ohio may be used. One example of a Nordson slot extrusion die is disclosed in U.S. Pat. No. 5,750,444, which is incorporated herein by reference.
For exemplary purposes only, one embodiment of a slot extrusion die system is illustrated in
In one embodiment, the multiple metering station 68 may include a pumping device placed in association with each of the lines 70A-70K. In this manner, each of the lines may be operated independently of the others. Thus, the amount of adhesive flowing through each line can vary from line to line. In other embodiments, however, each line may be supplied with equal amounts of adhesive.
In one embodiment, instead of containing a pumping device, each of the lines are fed directly from a screw extruder.
Referring to
In general, any suitable adhesive material may be dispensed onto nonwoven materials in accordance with the present invention. In general, the adhesive may be, for instance, a hotmelt adhesive that is heated prior to being applied to the nonwoven materials. The adhesive may have a viscosity exiting the slot extrusion die of from about 500 cp to about 50,000 cp, such as from about 2,000 cp to about 20,000 cp. The temperature of the adhesive may vary depending upon the adhesive being used. In one embodiment, however, the adhesive may be heated to a temperature of from about 250° F. to about 400° F., such as from about 320° F. to about 350° F.
Particular adhesives that may be used in the present invention include various block copolymers, such as styrenic block copolymers. Such block copolymers include, for example, styrene-isoprene-styrene block copolymers, styrene-ethylene-butylene-styrene block copolymers, styrene-butadiene-styrene block copolymers, and the like.
In other embodiments, the adhesive material may comprise a random copolymer of a polyolefin. The polyolefin may be, for example, a polyethylene or a polypropylene.
In still other embodiments, an amorphous polyalphaolefin may be used. In still other embodiments, a metallocene-catalyzed elastomeric resin, such as a polyethylene or polypropylene resin can be utilized.
Commercially available adhesive materials may be obtained from Bostik, Inc., from the Dow Chemical Company, and from various other commercial sources. In some embodiments, the adhesive material may need to be heated prior to being applied to the nonwoven materials. The adhesives, for instance, may be heated to temperatures greater than 100° F., such as from about 200° F. to about 400° F. In some embodiments, the adhesive may be blended with a tackifier or may be blended with other elastomers as desired.
After the adhesive material is applied to the nonwoven webs 22 and 24, the webs are laminated to the elastic filaments 14 while the filaments are in a stretched state. As shown in
Construction of the continuous filaments 14 will now be described in greater detail including the manner in which the filaments are stretched prior to being bonded to the nonwoven facings in accordance with the present disclosure. As shown in
The rollers that carry the continuous filaments are positioned and operated so as to cause the continuous filaments to be stretched as they vertically flow through the lamination system. When a number of rollers are employed, each successive roller turns in a direction opposite to the immediately preceding roller so that the strands of continuous filaments are handed off from roller to roller. In addition, the speed of each successive roller may be varied from the preceding roller so as to obtain the desired stretching and elongation characteristics. For example, any particular roller may operate at between 1 to 10 times, and more, the speed of any preceding roller. Typically, a separate controller, such as a servomotor or a Turner drive, may be utilized to allow individual speed control for each roll and will drive each individual roll. When the speed is varied, successive rollers may turn at a faster rate to stretch or elongate the strands as they move downwardly in the vertical process. In addition, the continuous filaments are ultimately reduced to a fiber size of approximately 0.008 to 0.040 inches in diameter, and in some cases to approximately 0.015 to 0.020 inches in diameter.
The number of separate rollers used to convey the continuous filaments to the bonding location may vary depending on the particular attributes desired in the final product. In one particular embodiment, at least four rollers—a first chilled (or positioning) roller, a second chilled roller, a third unchilled roller, and a fourth unchilled roller—may be utilized. In another embodiment, only two chilled rollers may be needed before the continuous filaments are supplied to the laminator portion of the system which bonds the spunbond facing(s) to the continuous filaments in a roller nip.
In certain embodiments, the rollers may be plasma coated to provide good release properties. In other embodiments, the rollers may additionally be grooved or channeled to ensure that the extruded continuous filaments maintain a proper separation between individual filaments as the filaments pass over the surface of the rolls and flow through the system. In some embodiments, smooth rolls maybe used for one or all of the rolls. In the case where plasma-coated rolls are employed, the continuous filaments will not slip as much as they do on smooth, uncoated rolls. The plasma-coatings grips the strands and promote increased uniformity of distances between the continuous filament strands.
As suggested, any or all of the rollers may be chilled so as to more quickly quench, or harden, the continuous filaments as they are proceeding through the process. The chilled rolls may be chilled to a controlled temperature of between about 45° F. and about 60° F. (typically about 45° F. or about 50°). Simultaneous quenching and stretching may be optimized depending on the particular stretchability characteristics desired in the final product.
In one particular embodiment, the series of rollers (or roller) may be enclosed within a sealed tower structure and conditioned air, with the moisture removed, may be utilized in order to control the chilling effects of the rollers. For example, the chilled rolls may be chilled to 50° F. or less relative to the controlled dewpoint. In such cases, the temperature to which the rolls are chilled may be significantly less than 50° F., but with the conditioned air environment, the rolls may remain at 50° F.
Other various mechanisms may be utilized to quench the continuous filaments. For example, external air could be forced onto the fibers in order to control the hardening of the fibers. In other embodiments, one large roll could be used with sufficient surface area in order to quench the fibers.
Maintaining a certain roller speed allows the appropriate degree of elastic stretch to allow the puckers to form in the final laminate. The positioning chilled roller 12 normally turns at a surface speed in the range of about 3-10 feet per minute (“fpm”), while the first vertically-placed chilled roller turns at about 5 to about 15 fpm. The next roller turns at about 7 to about 18 fpm, while the last roller, when applied and used, turns at a speed of about 12 to about 100 fpm. These ranges are approximate, and can vary depending upon the conditions and final product configuration desired.
In one particular embodiment, the first roll may turn at approximately 5 fpm;
the second roll at approximately 6 fpm; the third roll at approximately 11 fpm; and the fourth roll at approximately 26 fpm. Another embodiment utilizes a first roll speed of 10 fpm; a second roll speed of 20 fpm; a third roll speed of 40 fpm; and a fourth roll speed of 80 fpm. In this embodiment, the speed of the nip rollers is approximately 75 fpm. In a further embodiment, the speed of the first chilled roll may be approximately 400 fpm; the speed of subsequent rolls may be approximately 750 fpm to stretch the continuous filaments; the speed of the composite material being formed at the nip rollers may be approximately 1500 fpm; and the winding roller speed (to allow relaxation and, thus, gathering of the spunbond facings) may be approximately 700 fpm.
After passing through the series of rollers and becoming stretched, the continuous filaments are then bonded to the nonwoven materials 22 and 24 using the slot extrusion die as described above. The nonwoven materials 22 and 24 may be any suitable webs or laminates, including meltblown nonwoven webs, spunbond nonwoven webs, carded webs or even woven webs. In one particular embodiment, a polypropylene spunbond facing having a basis weight of approximately 0.4 oz/yd2 may be employed.
The system employs nip rolls 19 and 20 to apply pressure to the adhesive-coated facing and the continuous filaments to result in the necessary lamination. The outer facing is bonded together with the continuous filaments at a fairly high surface pressure, which may be between about 20 and 300 pounds per linear inch (“pli”). A typical bonding pressure may be about 50 pli or about 100 pli.
The bonder, or nip roll, (sometimes referred to as “laminator”) section of the laminating apparatus performs the primary stretching on the continuous filaments. The speed ratio of the bonder or nip rolls relative to the chilled rolls can be varied, and in most cases is between about 2:1 and 8:1 and in some is approximately 4:1 to 6:1.
After bonding of the facing(s) to the continuous filaments to form a spunbond/elastomeric continuous filament/spunbond laminate, the laminate is then allowed to relax and contract to an unstretched or less stretched, condition. The laminate is then wound onto the take-up roll 21 via a surface driven winder. The speed ratio of the winder relative to the bonder rollers results in relaxation of the stretched continuous filaments and a retraction of the laminate into a gathered state as the laminate is wound onto the roll. For example, the winder speed to bonder roll speed may be approximately 0.3 to about 1.0, and may be from about 0.5 to 1.0. The contraction of the continuous filaments results in a gathered, stretchable laminate article where the outer facing(s) is gathered between the bonding points.
The overall basis weight of the laminate can vary, but in some applications is between about 2 and about 4 ounces per square yard (“oz/yd2”). In one particular embodiment, the basis weight is between about 2.85 and about 3.2 ozlyd2.
Various types of compositions and various processing conditions may be utilized to form the elastic continuous filaments. For example, a Kraton® brand elastic polymer may be fed into an extruder where the polymer is melted at a controlled temperature of between about 2600 and 460° F., and in certain instances at about 385°. In other embodiments, depending on the particular polymer employed, the melt temperature may be approximately 470° F. to 480° F. The polymer is then extruded through a predetermined number of apertures in a die head in a generally downward direction into separate continuous filaments at a pressure of approximately 300 to 4000 psi (typically from about 1500 to about 2000 psi). As explained below, various die hole configurations may be utilized in the present invention.
One particular class of polymers that may be utilized in the present process is the Kraton® G series of polymers distributed by Shell Chemical Company (now available from Kraton Products U.S.-LLC). Various Kraton® polymers may be utilized.
However, the present invention is not limited to this or any particular polymer or material from which to form the continuous filaments. For example, various materials, including the following, may be used: polypropylene, polyethylene, polyesters, polyethylene terephthalate, polybutane, polymethyldentene, ethylenepropylene co-polymers, polyamides, tetrablock polymers, styrenic block copolymers, polyhexamethylene adipamide, poly-(oc-caproamide), polyhexamethylenesebacamide, polyvinyls, polystyrene, polyurethanes, thermoplastic polymers, polytrifluorochloroethylene, ethylene vinyl acetate polymers, polyetheresters, polyurethane, polyurethane elastomerics, polyamide elastomerics, polyamides, viscoelastic hot melt pressure sensitive adhesives, cotton, rayon, hemp and nylon. In addition, such materials may be utilized to extrude single-constituent, bi-constituent, and bi-component filaments within the scope of the presently described invention.
Other exemplary elastomeric materials that may be used include polyurethane elastomeric materials such as those available under the trademark ESTANE from B. F. Goodrich & Co., polyamide elastomeric materials such as those available under the trademark PEBAX from the Rilsan Company, and polyester elastomeric materials such as those available under trade designation HYTREL from E. I. DuPont De Nemours & Company.
However, the invention is not limited to only such elastomeric materials. For example, various latent elastic materials such as the Arnitel-brand polymers may be utilized to provide the necessary elasticity characteristics to the continuous filaments.
Likewise, the above-referenced materials, and others, may be utilized in forming the outer facings of the presently described laminate. In particular, various webs may be utilized that are formed from elastomeric or nonelastomeric fibers. Various polyester elastic materials are, for example, disclosed in U.S. Pat. No. 4,741,949 to Morman et al., which is incorporated herein in its entirety by reference thereto. Other useful elastomeric polymers also include, for example, elastic copolymers of ethylene and at least one vinyl monomer such as, for example, vinyl acetates, unsaturated aliphatic monocarboxylic acids, and esters of such monocarboxylic acids. The elastic copolymers and formation of elastomeric fibers from these elastic copolymers are disclosed in, for example, U.S. Pat. No. 4,803,117, which is also incorporated herein in its entirety by reference thereto.
Various processing aids may also be added to the elastomeric polymers utilized in the present invention. For example, a polyolefin may be blended with the elastomeric polymer (e.g., the A-B-A elastomeric block copolymer) to improve the processability of the composition. The polyolefin should be one which, when so blended and subjected to an appropriate combination of elevated pressure and elevated temperature conditions, is extrudable in blended form with the elastomeric polymer. Useful blending polyolefin materials include, for example, polyethylene, polypropylene and polybutene, including ethylene copolymers, propylene copolymers and butene copolymers. A particularly useful polyethylene may be obtained from the U.S.I. Chemical Company under the trade designation Petrothene NA 601 (also referred to herein as PE NA 601 or polyethylene NA 601). Two or more of the polyolefins may be utilized. Extrudable blends of elastomeric polymers and polyolefins are disclosed in, for example, U.S. Pat. No. 4,663,220, which is incorporated herein in its entirety by reference thereto.
Referring to
As shown in
The continuous filaments are combined at the nip with various types of facings. In the embodiment depicted in
In accordance with the present invention, a slot extrusion die 123 is used to apply an adhesive material to the facing 122, while a slot extrusion die 153 is used to apply an adhesive material to the spunbond facing 124.
In the embodiment illustrated in
As stated above, the use of a starved slot coat extrusion process as described above provides various advantages. For example, unexpectedly it was discovered that the starved slot coat process decreases the porosity of the resulting laminate, even at relatively low adhesive application rates. For example, laminates as shown in
Having a lower porosity facilitates handling of the material in later converting processes. For example, such laminates are well suited for use in the construction of absorbent articles, such as diapers. During the production of a diaper, the elastic laminate typically needs to be cut, manipulated and bonded into place. During these process steps, vacuum is often used in order to convey and move the material. Lowering the porosity of the material greatly facilitates the ability to manipulate the material using a vacuum or suction force. Ultimately, materials made according to the present invention may be processed at higher machine speeds greatly increasing throughput.
The present invention may be better understood with respect to the following examples.
Testing Procedures
During the examples that follow, the following tests were performed on the samples that were produced.
Porosity was measured using procedure number STM 3801. Porosity was measured using a Frazier air permeability tester. The units are cubic feet per minute per square foot (cfm per ft2).
Elongation was measured test procedure number STM 529-W. Elongation may be tested using any suitable tensile testing equipment, such as those available from the Syntech Corporation of Cary, N.C., or from the Instron Corporation of Canton, Mass.
In a Peel Test, a laminate is tested for the amount of force needed to pull the layers of the laminate apart. The peel strength was measured using testing procedure number STM 751-W. The samples were tested in the cross machine direction. Any suitable tensile testing equipment may be used in order to perform the procedure.
The following example was performed in order to determine the effect of the slot coat extrusion process on the porosity of nonwoven laminates.
In this example, two spunbond webs were laminated together. The spunbond webs used were made from polypropylene and had a basis weight of 0.42 osy.
Nine samples were produced and tested. In the first three samples, an adhesive was sprayed between the spunbond webs using a uniform fiber depositor (“UFD”) available from ITW Dynatec of Hendersonville, Tenn. under the name Dynafiber™ UFD nozzle. The uniform fiber depositor had one inch wide nozzles and contained fourteen capillaries per nozzle. The adhesive used in conjunction with the spray device was adhesive number H2808-07 obtained from Bostik, Inc. and is an SIS-based adhesive. This particular adhesive is well suited for use in spray processes.
When spraying the adhesive between the spunbond webs, two different uniform fiber depositors were used that were positioned adjacent to each web.
In the remaining six samples produced, the spunbond webs were laminated together using a slot extrusion die. In particular, the slot extrusion die was model number BC62 obtained from the Nordson Corporation. The slot on the slot extrusion die has a 0.15 inch gap and was 20 inches wide.
The adhesive used in conjunction with the slot extrusion die was HX9375-01 obtained from Bostik, Inc., which is a polyolefin copolymer blend. This particular adhesive is somewhat stiff and therefore does not always produce a uniform spray pattern. The adhesive is well suited for use with slot extrusion dies.
The adhesive was heated prior to being applied to the nonwoven webs using the slot extrusion die. In sample numbers 4 and 5 below, the extruder was heated to a temperature of from about 340° F. to about 345° F. In the remaining samples, however, the extruder was heated to a temperature of from about 355° F. to about 360° F.
The adhesive add-on rates were the same for both the spray process and the slot extrusion die process, and range from 1 gsm to 3 gsm.
The following results were obtained:
As shown above, laminates formed using the slot extrusion die had a lower porosity than the laminates produced using the spray device.
In this example, elastic laminates were produced according to the present invention and tested for various properties. In order to produce the laminates, a process similar to the one illustrated in
The facing comprised a polypropylene spunbond web having a basis weight of 0.4 osy.
The elastic continuous filaments were made from elastomeric block copolymers. Specifically, the elastic filaments were made using KRATON G2838 polymer available from Kraton products.
The same two adhesives identified in Example No. 1 were applied to the spunbond facing to produce the different samples. In particular, in the first five samples, adhesive HX9375-01 available from Bostik, Inc. was used, while in the remaining seven samples, adhesive number H2808-07 also obtained from Bostik, Inc. was used. The adhesive was applied to the spunbond web in amounts from 1.5 gsm to 2.5 gsm. The elastic filaments were laminated to the spunbond web at a basis weight of 10 gsm and were stretched 5.6 percent when attached. The temperature of the adhesive was varied depending upon the sample.
In one sample, Sample No. 12 below, the adhesive was applied using the uniform fiber depositor as described in Example 1 for purposes of comparison.
The following results were obtained:
As shown above, the samples made according to the present invention had a much lower porosity than the control sample. As shown in the above table, the peel strength of samples made with the H2808-07 adhesive was generally less than the peel strength of the laminates made with the HX9375-01 adhesive. As explained in Example No. 1 above, the HX9375-01 adhesive is better suited for use with a slot extrusion die.
These and other modifications and variations to the present invention may be practiced by those of ordinary skill in the art, without departing from the spirit and scope of the present invention, which is more particularly set forth in the appended claims. In addition, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to limit the invention so further described in such appended claims.
