Patent Application
20050132544
The present invention concerns hook fasteners.
There are a variety of methods known to form hook materials for hook and loop fasteners. One of the first manufacturing methods for forming hooks involved weaving loops of monofilaments into a fibrous or film backing or the like followed by cutting the filament loops to form hooks. These monofilament loops were also heated to form headed structures such as disclosed in U.S. Pat. Nos. 4,290,174; 3,138,841 or 4,454,183. These woven hooks are generally durable and work well for repeated uses. However, they are generally expensive and coarse to the touch.
For use in disposable garments, diapers and the like, it was generally desirable to provide hooks that were inexpensive and less abrasive. For these uses and the like, the solution was generally the use of continuous extrusion methods that simultaneously formed the backing and the hook elements, or precursors to the hook elements. With direct extrusion molding formation of the hook elements, see for example U.S. Pat. No. 5,315,740, the hook elements must continuously taper from the backing to the hook tip to allow the hook elements to be pulled from the molding surface. This generally inherently limits the individual hooks to those capable of engaging only in a single direction while also limiting the strength of the engaging head portion of the hook element.
An alternative direct molding process is proposed, for example, in U.S. Pat. No. 4,894,060, which permits the formation of hook elements without these limitations. Instead of the hook elements being formed as a negative of a cavity on a molding surface, the basic hook cross-section is formed by a profiled extrusion die. The die simultaneously extrudes the film backing and rib structures. The individual hook elements are then formed from the ribs by cutting the ribs transversely followed by stretching the extruded strip in the direction of the ribs. The backing elongates but the cut rib sections remain substantially unchanged. This causes the individual cut sections of the ribs to separate each from the other in the direction of elongation forming discrete hook elements. Alternatively, using this same type extrusion process, sections of the rib structures can be milled out to form discrete hook elements. With the profile extrusion process, the basic hook cross section or profile is only limited by the die shape and hooks can be formed that extend in two directions and have hook head portions that need not taper to allow extraction from a molding surface. This is extremely advantageous in providing higher performing and more versatile hook structures. However, there is a desire to further expand the functionality of hook forming processes and to create novel hook elements with greater degrees of functionality and versatility to a variety of fibrous materials.
The present invention provides a method for forming preferably a unitary polymeric hook fastener comprising a flexible backing, and a multiplicity of spaced hook elements projecting from the upper surface of the unitary backing. The hook elements each comprise a stem portion attached at one end to the backing, and a head portion at the end of the stem portion opposite the backing. The head portion projects in different directions for some adjacent hook members which adjacent hook members each have a flat face which flat faces are mutually opposing in face to face relation.
The fastener is preferably made by a novel adaptation of known methods of making hook fasteners. The preferred method generally includes extruding a thermoplastic resin through a die, forming hook elements integrally with a base or base layer. The hook elements have a top hook head portion and a generally upstanding stem portion joined to the unitary backing. The hook elements are then cut by the methods taught, for example, in U.S. Pat. Nos. 3,266,113; 3,557,413; 4,001,366; 4,056,593; 4,189,809 and 4,894,060 or alternatively 6,209,177. The cut locations extend through at least the hook head portion and preferably at least a portion of the stem portion, generally from 1 to 100 percent of the stem portion, preferably 5 to 100 percent. Subsequently, stretching of the backing layer in a direction at an angle to the cuts (generally 90 to 45 degrees) separates the cut portions of the hook elements which cut portions then form spaced apart hooks. This creates two or more separated hook head members from a single hook element wherein the stem portion of the separated hook members have substantially flat mutually opposing faces.
The present invention will be further described with reference to the accompanying drawings wherein like reference numerals refer to like parts in the several views, and wherein:
The present invention is directed to a method of forming unique hook members from a hook strip having upstanding integral hook elements. The unique hook members have a flat face and an opposing nonflat face, which flat face, is in opposing face-to-face relationship to a flat face of an adjacent hook member. The nonflat faces can be the same or different on adjacent hook members and generally at least one of the two (or more) opposing hook members has a loop engaging overhanging portion. The hook strips generally have an integral film backing formed of the same or different thermoplastic resin as the hook elements. Suitable polymeric materials from which the hook fastener portion can be made include thermoplastic resins comprising polyolefins, e.g. polypropylene and polyethylene, polyvinyl chloride, polystyrene, nylons, polyester such as polyethylene terephthalate and the like and copolymers and blends thereof. Preferably the resin is a polypropylene, polyethylene, polypropylene-polyethylene copolymer or blends thereof. The film backing is generally oriented in at least one direction and has a thickness of from 25 to 250 μm, or more preferably 50 to 150 μm. The backing of the fastener should be thick enough to allow it to be attached to a substrate by means such as sonic welding, heat bonding, sewing or adhesives, including pressure-sensitive or hot melt adhesives, and to firmly anchor the stems and provide resistance to tearing when the fastener is peeled open. However, when a fastener is used on a disposable garment, the backing should not be so thick that it is stiffer than necessary. Generally, the backing has a Gurley stiffness of 10 to 2000 as measured by TAPPI test method T543, preferably 10 to 200 so as to allow it to be perceived as soft when used either by itself or laminated to a further carrier backing structure such as a nonwoven, woven or film-type backing, which carrier backing should also be similarly soft for use in disposable absorbent articles. The optimum backing thickness will vary depending upon the resin from which the hook fastener portion is made, but will generally be between 20 μm and 1000 μm.
A first method such as shown in
The cavities 12 could be in the shape of the final hook elements as disclosed, for example, in U.S. Pat. No. 6,174,476 or 6,540,497. In this case, a generally continuously tapered hook is pulled from continuously tapered hook cavities in its final hook form or at least a partially formed hook element. Also, the extruded strip 6 could be a web provided with only partially formed hook elements or unformed hook elements forming projections. The tip portion of these projections (or the tips of partially formed hook elements) then could be subsequently formed into the desired finished hook elements 9. This would, in a preferred method, be done by deforming the tip portions using heat and/or pressure. The heat and pressure, if both are used, could be applied sequentially or simultaneously. In a preferred method, heat and pressure is selectively applied to the tip portion in a nip 14. In this case, there is provided a nip 14 having at least one first heated surface member 15 and at least one second opposing surface member 16. The nip has a gap which gap has a compression zone defined by a first entry gap width and a second end gap width. The first gap width is substantially equal to or less than the web first average thickness. The second end gap width is less than the first web thickness and is the smallest gap width of the nip 14. The final hook strip has formed hook heads 21 on the stems or projections 24 as shown in
In the specific method shown in
The extruded strip having upstanding stems can optionally be sent through a capping station as shown in
Subsequent to the optional capping step, the extruded strip is sent through a cutting station wherein the cutter 18 cuts through at least a portion of the hook elements. The cutter 18 can cut using any conventional means such as reciprocating or rotating blades, lasers, or water jets. If cutter blades are used, they are generally spaced to make a cut every 150 to 500 μm or preferably every 150 to 300 μm. Generally, at least about 50 percent of the hook elements are cut, preferably at least 75 percent and most preferably at least 90 percent.
After cutting of the hook element, the base of the strip 6 is longitudinally stretched, at a stretching station 19, at a stretch ratio of at least 2 to 1, and preferably at a stretch ratio of about 4 to 1, e.g., between a first pair of nip rollers 25 and 26 and a second pair of nip rollers 27 and 28 driven at different surface speeds. Optionally, the strip 6 can also be transversely stretched to provide biaxial orientation to the base or backing. Roller 25 is preferably heated to heat the base prior to stretching, and the roller 27 is preferably chilled to stabilize the stretched base. Stretching causes spaces between the cut portions of the hook elements, which then become the hook fastener members. Optionally, the hook strip can be stretched prior to cutting of the hook elements to provide further molecular orientation to the polymer backing.
The hook elements and members are generally of height of from 0.1 mm to 2 mm, preferably from about 0.10 to 1.3 mm in height, and more preferably from about 0.2 to 0.5 mm in height. The hooks have a density on the backing preferably of from 25 to 500 hooks per square centimeter, and more preferably from about 200 to 500 hooks per square centimeter. With capped hooks, the stem portions have a diameter adjacent the heads of preferably from 0.05 to 0.7 mm, and more preferably from about 0.1 to 0.3 mm. The capped heads project radially past the stem portions away from the flat cut face of the hook structure preferably by, on average, about 0.01 to 0.3 mm, and more preferably by, on average, about 0.02 to 0.25 mm and have average thicknesses between their outer and inner surfaces (i.e., measured in a direction parallel to the axis of the stems) preferably from about 0.01 to 0.3 mm and more preferably from about 0.02 to 0.1 mm. The capped heads have an average diameter (i.e., measured radially of the axis of the capped heads and the stems) to average capped head thickness ratio preferably from 1.5:1 to 12:1, and more preferably from 2.5:1 to 6:1.
For most hook-and-loop uses, the hooks may be distributed substantially uniformly over the entire surface area of the hook strip, usually in a square, staggered or hexagonal array.
Referring now to, for example,
The hook fastener hook elements following cutting are shown in
The individual hook members will have at least one flat face extending along one face of the stem portion and continuing along the head portion. The head portion of at least some of the hook members will have an overhanging portion extending beyond the stem for engaging a loop or fiber or another hook head portion. As shown in
In
In
In FIGS. 9(a and c), the cut line bisects the hook element at a bias which when separated, as shown in
FIGS. 10(a) and 10(b) are enlarged views of multiple hook members 74, 74′, 74″ and 74′″ cut from a single mushroom-type hook element with flat faces and overhanging loop engaging portions 79. The overhang portion 79 extends radially away from the flat faces.
In certain applications, it has been discovered that very low hook densities are desirable. For example, hook densities of less than 100, preferably less than 70 and even less than 50 hooks per square centimeter are desirable when used to attach to low loft nonwovens using a relatively large area flexible hook fastener tab or patch. This low spacing has been found to increase the hooking efficiency of the individual hook elements, particularly relative to low cost and otherwise ineffective nonwoven materials not traditionally used as loop products. The hook tab or patch is also made flexible by suitable selection of the polymer forming the base layer and/or by the stretching of the base layer reducing its thickness, to a preferred range of 100 μm to 25 μm. Biaxial orientation can be used to further reduce the hook density to the desired range for a large area hook fastener.
A large area fastener when used on a garment type application such as diapers, see
When a large area (oversized) fastener as shown in
Use of large area fasteners reduces the manufacturing complexity of a garment such as an absorbent article by eliminating the need for additional bond points or multiple fasteners to stabilize the fastening system of e.g., the front and rear waist regions. The addition of bond points or additional fasteners increases the complexity of the manufacturing process.
Specifically, a large area hook fastener, is capable of directly engaging an outer surface of a diaper provided with a relatively low loft nonwoven without the need for an expensive loop patch. The large area flexible hook fastener can also prevent inadvertent opening of the closure due to the large contact and attachment area creating a more stable garment closure. The oversized hook fastener could also be used in a prefastened pull-on type garment, due to its large area of contact, making the garment suitably stable for packaging and subsequent use.
A mechanical fastener hook web (KN-2536, 3M Co., St. Paul, Minn.), similar to that depicted in
A mechanical fastener hook web (KN-3457, 3M Co., St. Paul, Minn.), similar to that depicted in
A mechanical fastener hook web was extruded and cut as in Example 2. The cut web was cut a second time by passing the web through the cutting station. The cutting station and blades were arranged such that the cuts were made in the machine direction of the web. This resulted in the individual hook elements being cut twice producing 4 smaller hook elements.
