US20080178436A1

US20080178436A1 - Fastener webs with microstructured particles and methods of making same

Info

Publication number: US20080178436A1
Application number: US11/627,065
Authority: US
Inventors: Zhiqun Zhang; Haiyan Zhang
Original assignee: 3M Innovative Properties Co
Current assignee: 3M Innovative Properties Co
Priority date: 2007-01-25
Filing date: 2007-01-25
Publication date: 2008-07-31
Also published as: AR065008A1; TW200913923A; EP2124664A2; JP2010516396A; MX2009007928A; WO2008091749A2; KR20090113277A; CN101621941A; WO2008091749A3

Abstract

A hook fastener capable of engaging a suitable loop fabric, and a method of forming this hook fastener, are disclosed. The hook fastener comprises a base substrate with a surface having a multitude of engaging projections, the engaging projections having a top surface and an attached end which is joined to the surface of the base substrate at a bond juncture, wherein the top surfaces of at least some of the engaging projections comprise nonlinear microstructured features, such as intersecting peak and/or valley structures.

Description

TECHNICAL FIELD

The present invention relates to methods of manufacturing fasteners, particularly male components for fasteners of the touch-and-close type, also known as hook-and-loop type fasteners.

BACKGROUND OF THE INVENTION

Hook-and-loop type mechanical fasteners for limited use applications such as fixing disposable diapers commonly use molded type hooks.
One approach is of hooks that are directly molded, disclosed for example in U.S. Pat. No. 5,315,740, assigned to Velcro, which discloses molded hooks with low displacement volumes so that it needs only to displace a small volume of loop fabric in order to engage therewith. The patent discloses a re-entrant hook, i.e., whose tip-portion curves over and down toward the base sheet from the upper end of the hook to define a fiber-retaining recess on the underside of the hook.
It is also known to cap molded stems on webs. Mushroom-shaped engaging projections obtained by this process are disclosed in U.S. Pat. No. 5,679,302 and U.S. Pat. No. 5,879,604 in which an extruded polymer layer is pressed against a mold with mold cavities, the cavities producing projecting stems, integral with the base. The terminal ends of the stems are then deformed with a heated pressure roller, forming the loop engaging projections. U.S. Pat. No. 6,054,091 discloses a similar method in which, however, the heated deforming surface gives an essentially lateral deformation to the stems during the deformation thereby forming re-entrant, J-shaped hooks with flat top portions. The solution of U.S. Pat. No. 6,627,133 differs from the previous ones in that the stemmed web, to be capped with a heated pressure roller, is manufactured with the method of U.S. Pat. No. 6,287,665, i.e., with a special mold constituted by a cylindrical printing screen. All documents mentioned in this paragraph are similar in that they flatten preformed stems by a hot roll.
U.S. patent application 2004/0031130A1 discloses a method in which a product, comprising a polymer base and stems integral with and projecting from a base is extrusion-molded with a mold roll having a multiplicity of sophisticated mold cavities. The distal ends of the stems are then heated and melted while their feet are kept cold and solid. The melted ends are then flattened with a deforming surface. The same approach, i.e., pre-heating and successively flattening stems, appears in U.S. Pat. No. 6,592,800, U.S. Pat. No. 6,248,276 and U.S. Pat. No. 6,708,378, the latter ones also disclosing capping with a rough contact surface, creating roughened flat tops of engaging projections.
Particles have been proposed to produce hook fasteners as well although none are known to be commercialized. In U.S. Pat. No. 3,550,837 a male fastener member is described whose each engaging projection is constituted by an irregularly shaped granule with a special multifaceted surface, adhesively adhered to the base. The fastener is suitable for securing a flap of a disposable carton against opening. Engaging is provided by the granules comprising a number of tiny flat planes forming a multifaceted surface.
In U.S. Pat. No. 3,922,455 nibs of various shapes are grafted onto linear filaments, the linear filaments, protruding from a base, forming the engaging elements of a male fastener component.
In PCT publication WO 01/33989, particles are, with a scatter head of a scatter coater, randomly scattered, and fixed, onto a base. Each engaging projection is constituted by several agglomerated particles, though some individual particles may also be left present.
It is an object of the present invention to provide low-cost male mechanical fasteners with advantageous properties. It was another object of the present invention to provide commercially attractive alternatives to the mechanical male fastener systems available so far and methods for making them.

BRIEF DESCRIPTION OF THE INVENTION

The present invention provides a hook fastener, and a method of forming this hook fastener, capable of engaging a suitable loop fabric, comprising a base substrate with a surface having a multitude of engaging projections, the engaging projections having a top surface and an attached end which is joined to the surface of the base substrate at a bond juncture, wherein the top surfaces of at least some of the engaging projections are formed with intersecting peak and/or valley structures. In one embodiment at least some of the peak structures are discrete structures surrounded by valley structures where at least some of the discrete peak structures are bounded on three or more sides by material of the top surface at a different height. Alternatively at least some of the valley structures could be discrete valley structures surrounded by peak structures. Generally at least some of the peak structures and/or valley structures intersect at one or more locations. In various embodiments, the height of the top surface structures may be at least about 20 microns; alternatively, at least about 50 microns. In various embodiments, at least some of the engaging projections top surfaces have at least one edge with a mantle surface that defines an angle of at least about 20 degrees; alternatively, at least about 30 degrees.
The present invention also provides a hook fastener and a method of forming this hook fastener, capable of engaging a suitable loop fabric, comprising a base with a front surface and a back surface, where at least one surface has a multiplicity of engaging projections having a top surface and an attached end which is fixed to the surface of the base at a bond juncture, and wherein the top surface of at least some of the engaging projections comprises nonlinear microstructured features, and wherein the engaging projections having nonlinear microstructured features have an average height-to-diameter aspect ratio of about 0.7 or greater. In various embodiments, the height of the top surface structures may be at least about 20 microns; alternatively, at least about 50 microns.
The present invention also provides a first method for forming a fastener as described above comprising:
providing a multiplicity of suitable polymer particles;
providing a base with a front surface;
dispersing onto a microstructured contact release surface a multiplicity of polymers particles in at least one discrete area of the contact release surface where the microstructured contact release surface has nonlinear surface microstructures such as a multitude of intersecting peak and/or valley structures;
providing the polymer particles, dispersed on the contact release surface, in a semiliquid state of a suitable viscosity, at least some of the particles in the discrete regions or areas being in contact with the contact release surface for a time sufficient to transform into preform projections having an edge angle of at least 30 degrees;
conducting and fixing the front surface of the base with the terminal ends of at least some of the preform projections;
removing the base from the contact release surface thereby separating the preform projections fixed thereto,
thereby forming engaging projections projecting from the front surface of the base.
The polymer particles are generally dispersed into the microstructured contact release surface. The polymer particles can be impacted onto the structured contact release surface by gravity, electrostatic attraction, impaction or other suitable forces or any combination thereof. In a preferred method polymer particles are dispersed onto a contact release surface using electrostatic attraction to impact the particles onto the contact release surface.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic side view of an apparatus for manufacturing a fastener of the invention.

FIG. 2 is a cross sectional illustration of a base substrate with an engaging projection.

FIG. 3 is a 200× SEM top view of a contact release surface bearing pyramidal micro structures.

FIG. 4 a is a 40× SEM side view of a base film bearing engaging projections with microstructured top surfaces.

FIG. 4 b is a 100× SEM side view of a base film bearing engaging projections with microstructured top surfaces.

FIG. 5 is a cross sectional view illustrating the aspect ratio of an engaging projection.

FIGS. 6 a-6 c are drawings showing various microstructures which may be used on contact release surfaces in the present invention.

FIG. 7 is an SEM micrograph showing various microstructures which may be used on contact release surfaces in the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a fastener for engaging with a loop fabric. With reference to FIG. 2, the fastener comprises a base substrate 70 having a surface 71 with a multiplicity of engaging projections 72. The engaging projections have a top surface 73, where at least some engaging projections top surface ends form an edge 80 surrounding the projections. Opposite the top surface 73 is an attached end 74, which is attached to the front surface of the base at a bond juncture 75. There can be a mantle surface 76 extending from the top surface edge 80 to the attached end 74. The mantle surface in some embodiments has at least one contour line of a side view of the mantle surface that is strictly convex from a top surface edge to the attached end. The top surface 73 of at least some of the engaging projections has nonlinear microstructures 77. The microstructures have a vertical dimension (height or depth) 81. Such nonlinear microstructures may comprise at least some intersecting peaks 78 and/or valleys 79.
The hook fastener can have plurality of engaging projections form a discrete or continuous shape. Shape is defined as a plurality of the engaging projections that are organized into a specific area or region, where there are more or less, or different types or sizes, of engaging projections outside this region. A shape does not need to have defined edges but rather could have a gradual change in the density or distribution of the engaging projections from, e.g., a high density engaging projection area to an adjacent low density engaging projection area. This low density engaging projection area could have little or no hook engaging projections. Preferably the shape is formed by the plurality of engaging projections in a region having a relatively high density of engaging projections. The plurality of engaging projections forming a shape can extend substantially continuously in one dimension of the base substrate. The shapes could be surrounded by secondary areas having a either a different type and/or density of engaging projections. The shapes or the fastener as a whole can be formed of relatively high density regions having an average density of engaging projection of at least 1 gram per square meter (gsm) of particles, or at least 2 gsm of particles which are of a general average size of about 50 to 1000 microns or generally 50 to 500 microns. (Note that the engaging projection average size, and density of the engaging projection material, can be used to convert this measurement to the number of engaging projections per area). In another alternative, secondary regions or the fastener as a whole can have an average density of engaging projections of less than about 50 percent of the average density of engaging projections in the high density region, or less than about 25 percent of the average density of engaging projections in the high density region. For those shapes that extend continuously in one dimension of the base the shapes generally will have a minimum width dimension less than the width of the base. The shapes generally would have a minimum width dimension of greater than 1 mm or greater than 4 mm.
Engaging projections in the form of discrete shapes may be applied via a variety of methods as detailed in copending application Ser. No. 11/530,499, incorporated by reference herein.
As mentioned, the polymer particles used to form the engaging projections can be colored, tinted, pigmented, etc., for specific visual purposes. Multiple regions can be provided with different color engaging projections, or different densities or sizes of engaging projections, for specific visual effects.
The present invention also encompasses the use of adhesives, preferably pressure sensitive adhesives (PSAs). Such PSAs include a wide variety of materials known in the art, for example, natural rubber adhesives, block copolymer-based PSAs (for example, those based on elastomers available from Kraton Polymers, of Houston Tex.), acrylate-based PSAs, and silicone-based PSAs. PSAs may be chosen so as to bond well to polyolefinic thermoplastic materials (e.g. polypropylene, polyethylene, and copolymers and blends of the same), and might include, for example, the family of PSAs available from 3M Company under the designation LSE (e.g., LSE 300). Other suitable compositions may be based on silicone-polyurea based pressure sensitive adhesives. Such compositions are described in U.S. Pat. No. 5,461,134 and U.S. Pat. No. 6,007,914, for example.
In one embodiment, the PSA may be provided in an area adjacent the region bearing engaging projections. Either or both the PSA and engaging projection regions may be present as discrete or continuous regions.
The base used in the methods of the invention can be any suitable continuous or discontinuous base web such as a porous or nonporous polymer film, a laminate film, a non-woven web, a paper web, a metal films and foils or the like. The base could be modified by any known method such as by being printed, embossed, flame treated, laminated, particle coated, colored, or the like. A polymer film used as a base can be oriented or unoriented. In conjunction with the methods described later, the base film can be provided such that it possesses areas that vary in the ability to bond to the preform projection, which is yet another way of providing a substrate with engaging projection regions present in discrete shapes, patterns, and the like. The base film surface can be smooth, or can be provided with features such as projections or valleys molded into the base which could be used as ripstops, tear propagation lines or other features, which could be on the front or rear face of the base.
The surface of the base can also be roughened, for example with particles previously scattered and fixed thereon. The particles should be brought and fixed on the base in a way that at least the terminal ends of the projections can be formed from the particles. Projections can consist completely of the particles without any further modification of said particles. For bringing and fixing the particles to the (smooth or roughened) front surface, several methods are taught, e.g., random scattering and adhering, for example, in the cited PCT publication WO 01133989, the entire disclosure of which is hereby incorporated by reference.
The word “particle”, as used herein, refers to a solid, liquid or semi-liquid particle, including, for example, granules, pellets, powders and droplets. Appropriate particles can be selected based on the discussions herein. If the embodiment of this invention relying on electrostatic deposition of particles (as described later herein) is used, the particles should be chosen so as to be compatible with this process. In electrostatic deposition, particles are moved under the influence of an electric field so as to impinge on the base (whether onto selected regions or uniformly onto all regions of the base). Thus, in this instance the particles must be susceptible to having an electric charge imparted to them (otherwise they would not move under the influence of the electric field). Such methods are well known in the art and the selection of such particles is straightforward.
In terms of the properties of the engaging projections that are formed from the particles, it is preferable if at least some engaging projections are provided with a side view which strictly tapers from the top surface or top surface edge to the attached end at the front surface of the base. As used herein, a side view means a view taken perpendicular to the front surface of the base. Strictly tapering means that the nearer the engaging projection gets to the base, the narrower the projection becomes. For example, a cylinder is not a strictly tapering shape. This type of tapering will pull engaged fibers down to the front surface of the base when a shear load is applied to the fastener without the fibers being caught at a nontapered portion displaced from the front surface of the base. Thus the torque on the engaging projection is minimal so the base can be weaker, i.e., can be cheaper, more flexible, more skin friendly, thinner etc. Furthermore, the fastener may have a relatively large surface area formed by the projection tops, making the fastener smooth to the touch, while also having a relatively low total surface area of the projection attached ends connected to the base, increasing the flexibility and skin-friendliness of the fastener. The engaging projections can also be characterized by a ratio of the perimeter of area of the engaging top to the height of the engaging projection, which is generally 1.1 to 50, and is preferably 1.2 to 20. The engaging projection also generally forms a overhanging rim, which generally is the difference between the top surface area and the area of the attached end.
Turning from the materials used to the methods of the invention, a preferred general set of methods for manufacturing a male fastener component of engaging projections in accordance with the invention generally comprises the basic steps of:
providing a base with a front surface;
providing particles of polymer material;
providing a forming contact release surface of having nonlinear surface structures to provide a high surface tension suitable for interruption the flow of the at least semi-liquid or softened polymer particles;
dispersing, on the contact release surface, a multiplicity of the polymer particles;
bringing or providing the polymer particles into an at least semi-liquid or softened state of a suitable viscosity, providing preform projections (preform projection signifies a projection that to at least some extent has been preformed into the shape of the final engaging projection at the engaging end) sitting on and projecting from the release surface to corresponding terminal ends. The preform projections along their edges contacting the contact release surface will form contact angles, which contact angle is influenced by the surface energies of the polymer particles and the microstructure provided on the contact release surface. The polymer particles are maintained in a semiliquid state for a suitable period of time so that they form an acute contact angle of at least about 20 degrees on at least a portion of their edges contacting the contact release surface;
the preform projections can then be at least partially solidified for contacting and fixing to the front surface of the base with the terminal ends of at least some of preform projections, while essentially maintaining the shape of the edge formed by the contact release surface;
the preform projections are then further solidified sufficient to separate and remove the preform projections from the contact release surface thereby forming engaging projections attached to the base. These formed engaging projections project from the front surface of the base to microstructured tops, which structured tops were formed on the microstructured contact release surface. The structured tops at least partially overhang the base forming a rim, and are bordered, at least partly, by an edge having an angle, which is influenced by the acute contact angle.
The microstructured contact release surface is designed to allow a wide range of semi-liquid or softened polymer particles to be used without the need to closely matching the surface energy of the contact release surface to that of the polymer as will be discussed below.
Gravity could be used where particles are simply allowed to fall onto the contact release surface. Another way to bring particles onto the contact release surface is electrostatic deposition. In this method the polymer particles are directed toward the contact release surface by an electrostatic driving force. This is performed by providing two electrodes so as to establish an electric field therebetween. A first electrode is positioned in front of the contact release surface. A second electrode is positioned behind the contact release surface. A voltage is applied to the electrodes so as to establish an electric field therebetween. Upon the introduction of suitable particles into the gap between the first electrode and the second electrode, the particles are changed then driven under the influence of the electric field in the direction of the second electrode.
Electrostatic deposition is most advantageously performed in a vertical configuration with the second electrode positioned above the first electrode. In this arrangement the particles are driven upwards, against gravity, thus the particles that hit the contact release surface and do not attach fall back down and may be collected and/or recycled. This method has the advantage of providing for more uniform distribution of particles onto the contact release surface. All the particles will be like charged and repel one another. This will tend to keep the particles evenly distributed and keep individual particles from forming large number of unified preform projections. This method is advantageous for providing uniform distribution of particles on the contact release surface.
The polymer particles must be chosen for their suitability for electrostatic coating. The primary requirement is that under the influence of the imposed electric field, the particle develop sufficient induced charge such that sufficient force is placed on the particle by the electric field that the particle moves between the two electrodes. Preferably, the electric force should overcome gravity such that the above-described vertical configuration can be used. Fortunately, most of the materials that are appropriate for forming preform projections (namely, thermoplastic powders such as polypropylene and the like) are dielectric materials (that is, capable of having a charge induced upon being placed in an electric field). Suitable particles for forming the preform projections are also generally small and of low density (thus light in weight) making them easier to be driven via electrostatic forces upward against the force of gravity.
The particles should be placed in the gap in whatever manner will allow them to come under the influence of the electric field and be driven toward the contact release surface. Ideally, this is performed in a uniform manner. The particles may be sprayed, dropped, blown, or otherwise injected into the gap by methods well known in the art. In the above-described vertical configuration, the particles may be injected laterally into the gap by spraying. Alternatively, the particles can be brought into the gap by means of a carrier belt which, bearing the particles on its top surface, comes into the gap such that the particles are free to move toward the contact release surface by the applied electric field.
Other methods besides the afore-mentioned electrostatic deposition and gravity-assisted deposition are possible. Alternative methods to selectively bringing particles to a contact release surface include impacting the particles by a forced airstream, mechanical projection or conveying, and the like.
In the case of fusing (i.e. melt bonding), the preform projections to the base dissimilar polymeric materials may not bond well to each other. Thus, for example, the placement of preform projections of polystyrene onto a base film of polypropylene, (or vice versa) may result in little or no bond formation. However, if a compatibilizing layer is placed upon the polypropylene base film, an enhanced bond may be achieved. Such compatibilizing layers can be applied to the base continuously or in a patterned or discrete or discontinuous manner by a wide variety of methods of the art, including pattern coating, screen printing, vapor coating, plasma coating, photolithography, chemical vapor deposition, and the like.
Compatibilizing layers may comprise any of the widely known tie layers and bonding layers that are available in the art. All that is necessary is that the compatibilizing tie layer has sufficient adhesion to the base and sufficient adhesion to the polymer particle used to form the preform projection. In this approach, the polymer particles and base film may no longer need to be formed of the exact same material, or materials that are extremely close or similar in composition. This allows the base and the polymer particles to be chosen based on the physical properties most desired for each. For example, it may be desirable to chose a base film that is extremely soft and flexible, and a polymer particle that is extremely hard and rigid (or vice versa). The use of compatibilizing layers on the base film allows this to be done.
If using a contact release surface that allows the deposited particle to flow in one or more directions there is a need to properly select a suitable polymer for the particles and a contact release surface of a suitable surface energy. Other considerations with the selected particles is that they have a suitable viscosity at the temperature of the contact release surface that will wet the contact release surface within a suitable time. The surface energy of the contact release surface may be formed by known materials and methods, such as siliconized surfaces, fluorochemicals, corona discharge, flame or the like. The contact release surface must be able to release the particular polymer particles used, semi-liquefied and solidified. It is known that certain release surfaces can release certain polymers but are unable to release other polymers. For example, a polyethylene release surface can release suitable polypropylene particles but cannot release certain polyethylene particles as they tend to weld or fuse to each other. The word “release” as used herein refers to the phenomenon where the particles are detached from the contact release surface without (unacceptable) damage or loss of material of the particles or preform projections. With the invention method however the contact release surface is selected to have surface microstructures that do not allow the deposited particle for flow uninterrupted in a predetermined direction; rather, microstructures are provided to interrupt the polymer flow allowing a wider range of release energies to be used for the surface of the contact release surface with less concern about the particle overwetting the contact release surface due to flowing to much in a predetermined direction due to relative surface energies and/or contact time at a given temperature.
Dispersing of the particles onto the contact release surface by gravity can be performed in any suitable way, for example, by scattering the particles with a scatter unit. Other methods have been mentioned herein. The particles should be dispersed at a rate per unit surface area so that they form preform projections where one particle can form one preform projection, which may merge. The particles can be brought into the at least semi-liquid state before, during and/or after dispersing of the particles onto the contact release surface. “At least semi-liquid” means liquid or semi-liquid. A suitable way of liquefying will depend on the properties of the selected polymer, and can include, for example, heating, thinning, solving, emulsifying, dispersing etc.
A solidity (degree or extent of solidification) suitable for contacting and fixing the preform projections on the contact release surface with the front surface of the base can be decided by the skilled person, depending on the particular circumstances. It will usually, but not necessarily, mean a more solid state than the one in which the preform projections have been formed on the contact release surface. Preferably the preform projections should be solid enough to keep, at least partly, their shape while being contacted with the front surface of the base. It usually primarily means keeping at least a minimum free height and also a suitable edge angle of the preform projections. Setting the necessary solidity in the preform projections will be material-dependent, and can include cooling, drying, heating, crosslinking, curing, chemical treatment etc. The preform projections of suitable solidity, sitting on the contact release surface, can be covered by the base front surface such that the front surface of the base can contact and fix with the preform projection terminal ends. The fixing of the terminal ends of the preform projections to the front surface of the base can be obtained for example by, adhering with an added adhesive (for example, a pressure sensitive adhesive, hot melt adhesive, or UV-cure adhesive), crosslinking with ultraviolet irradiation, or it can utilize the inherent adhesion of the contacting materials (the base front surface or the preform projections) or fusing. The preform projections when they are removed from the contact release surface should be solid enough to keep, at least partly, their shape during the separation from the contact release surface. It usually primarily means keeping a suitable overall shape, with particular respect to the edge angle formed, but preserving a suitably strong bond with the front surface of the base. The base generally should be solid enough to keep its form and separate the preform projections from the contact release surface. The top surface structure will be largely determined by the contact release surface. Post treatments could however be used that would make the top surface essentially flat or droop, such as a noncontact heat treatment. If small numerous projections are advantageous it is preferable if, in the methods, that at least some of the separate preform projections comprise exactly one polymer particle per preform projection.
It is preferable if, in the methods, at least some of the preform projections are provided with contact angles of between about 20° and about 85°, preferably about 30° and about 80°. This would be the range of contact angles for most of the individual preform projections. For a preferred embodiment this range would be the mean contact angle for the preform projections.
It is preferable if, in the methods, at least some engaging projections are provided with a profile in which, in each side view thereof, the engaging projection strictly tapers (preferably is strictly convex) from the flattened top or top edge to the front surface of the base. This is usually very easy to achieve by this method, which typically creates semi-lenticular preform projections, like water drops.
If drops of liquids are deposited onto a solid release surface with higher surface energy (or surface tension) than the liquid, the liquid if given enough time will typically perfectly wet the solid, with a contact angle of zero. With liquids, each “solid-liquid” pair has a contact angle, between zero and 180°, with which the liquid drop will, approximately, wet the solid. With semi-liquid, e.g., softened thermoplastic, particles, the process of forming a contact angle is a time-temperature phenomenon. With the contact release surface a high surface energy will cause the particle to wet faster but it will be more difficult to finally separate the contact release surface from the preform projections. Also if the surface energy of the contact release surface is too high in relation to that of the polymer particles there is greater opportunity for unintentional operator error forming a preform projection that is excessively wet to the contact release surface. The danger of overwetting the contact release surface is lower if the surface energy of the contact release surface is not higher than the first surface energy (that of the particle) plus 60 mJ/m². The present invention uses nonlinear microstructures (e.g. intersecting peaks and/or valleys) to alter this process by intercepting the polymer flow across the contact release surface. The polymer flow can be interrupted and/or partially redirected allowing the use of higher surface energy contact release surfaces with less likelihood of overwetting.
As discussed herein, the use of the surface energy (i.e. wettability properties) of a relatively smooth contact release surface in order to control the spreading of the edges of the preform projection (thus to control the size and shape of the preform projection) and to control the ease with which the preform projection is removed from the contact surface, is not the only possible approach. In the present invention, the use of a nonlinear microstructured contact release surface has been found to be advantageous. Such methods take advantage of the fact that microstructured features may exhibit a “speed bump” effect in which a feature (e.g. a peak, ridge, groove, valley, depression, rut, furrow, post, well, hole, knob, nodule, and the like) tends to impede flow or spreading of a liquid.
Thus, it is useful to use a provide a contact release surface with nonlinear microstructured features that do not allow any lateral direction (that is, along the face of the contact release surface) in which there is no physical barrier to flow. Such nonlinear microstructures include any that are not limited to purely linear uninterrupted features (such as continuous linear parallel grooves), and include any in which it is not possible for a flowable liquid to travel more than, e.g., 0.5 mm laterally along the contact release surface in any direction without encountering a microstructured feature. It should be noted that for the purpose of interrupting, impeding, or minimizing fluid flow, such features do not have to present a complete barrier. That is, discrete features (such as posts or holes), even if interrupted by gaps, may still present a barrier to flow if the gaps are sufficiently small (for example, in the range of about 200 microns or less).
The feature may project upward from the contact release surface (thus resulting in the formation of an inward projecting microstructured feature in the top surface of the engaging projection formed therefrom), or may project downward into the contact release surface (thus resulting in the formation of an outward projecting feature in the top surface of the engaging projection formed therefrom). Such features may have a vertical dimension (e.g. height or depth) of from around 5 microns to around 300 microns or more. Such features may thus comprise a multitude of nonlinear projections or indentations, and include patterns with linear cross hatched peaks, ridges and/or valleys; intersecting peaks and/or valley structures such as pyramidal or microprism or so called cube corner structures; and the like. Such nonlinear microstructures also include those in which locally linear and/or parallel structures may be present, but in which nevertheless it is not possible to traverse more than e.g. 0.5 mm in any lateral direction along the surface of the contact release surface without encountering a barrier to flow. Such structures include for example discontinuous ridges or valleys; circular concentric ridges or valleys; ridges or valleys which are present in S-shaped curves; and the aforementioned cross hatched structures in which parallel features are interrupted by intersecting features.
Such microstructured surfaces may preferably be engineered or designed surfaces rather than those generated by random methods (e.g. by the random deposition of particles, or by abrasion or roughening). In one embodiment, the microstructured features are provided as a regular or repeating array of features.
Such microstructured features on the contact release surface may result in the formation of complementary features on the top surface of the preform projection, and consequently on the thus-formed engaging projection. (These features may not be the exact mirror image of those on the contact release surface, since the liquid may not completely wet and/or fill the contact release surface features completely; or the formed features may be distorted in the act of removing the engaging projection from the contact release surface). The existence on the contact release surface of microstructured physical barriers to flow in all lateral directions (in contrast to essentially flat contact release surfaces), has been found to result in a preform projections (hence engaging projections formed therefrom) with significantly higher height to diameter aspect ratio, as detailed later in Example 1. That is, this approach tends to provide engaging projections, which are taller and thinner in contrast to approaches using relatively flat and smooth contact release surfaces. Such engaging projections can have significant advantages in terms of the ability of the projections to engage to fibrous substrates. Such engaging projections also may provide for easier release of the projections from the contact release surface. In one embodiment, engaging projections of the current invention exhibit height to diameter aspect ratios of about 0.7 or greater. In another embodiment, engaging projections of the current invention exhibit height to diameter aspect ratios of about 1.0 or greater.
The choice of microstructured features may be combined with the choice of material from which the contact release surface is formed, in order to provide further control over the flow and spreading properties of liquids thereupon. Surface coatings may also be applied to the features for the same purpose. Such surface coatings may also enhance the ability to remove the solidified preform projection from the contact release surface.
An exemplary nonlinear pyramidal microstructured contact release surface is shown in the scanning electron micrograph of FIG. 3. Other exemplary nonlinear microstructured contact release surfaces that may be useful in methods of the present invention are illustrated in the drawings of FIGS. 6 a-6 c, and the SEM micrograph of FIG. 7.
It is preferable if, in the methods described above for thermoplastic preform projections (which can also be termed protrusions throughout), the fixing of the front surface of the base with the terminal ends of at least some of the preform projections comprises fixing by heat or fusing.
Fixing by heat can include melting one or the other of the preform projections or the base front surface, depending on the materials and pressure etc. Preferably both the preform projections and the front surface of the base are allowed to potentially melt, and are thereby fused. The particles must be liquefied enough during the fusing to suitably form the contact angle, but must remain solid enough, to permit keeping their edge angles on the contact release surface. It is preferred that the thermoplastic polymer particles have a melt flow rate of between 1 and 90 grams per 10 minutes at the conditions appropriate for the selected polymer.
In the subsequent step of the above method, the fixing by heat comprises maintaining the contact release surface at a temperature lower than the softening temperature of the polymer particles or preform projections while contacting the front surface of the base with the attachment ends of at least some of the preform projections. The back surface of the base is preferably heated by subjecting it to a heated gas. However, other heating methods such as radiant or IR heat may be used. If heated gas is used, the gas pressure at the back surface of the heated base is typically higher than the pressure (e.g. a gas pressure) at the front surface of the heated base, thereby pressing the heated base against the terminal ends of at least some of the preform projections to enhance the fixing thereof to the base. The pressure difference may be enhanced, for example, by applying vacuum from beneath the contact release surface or the front surface of the base.
It is further the object of the present invention to provide a new fastener product, readily achievable through the methods above, having corresponding advantages.
The product of the invention is a fastener for engaging with a loop fabric, a sheet-form base having a front surface with a multiplicity of solid and preferably essentially solid or rigid engaging projections. The engaging projections have a top end and an attached end (which can also be termed throughout as a foot). The attached end is joined to the base front surface at a fixing portion. In that there is a fixing of the engaging projections to the front surface of the base, the base and the engaging projection can be formed of different materials or the same materials. The at least one engaging projection projecting from the base front surface can be formed to have a structured surface established by the structured contact release surface. The top will also generally overhang the base at least partly, where the overhanging portion is also referred to as rim.
The top of the engaging projection as formed will also generally have a definite edge bordering the top. The engaging projection will also have a mantle surface, meeting the top along the edge, extending from the edge of the top to the attached end of the engaging projection at the front surface of the base. The mantle surface and the top surface close to form acute edge angles generally along the entire edge.
During use, the engaging projections should essentially behave as solid bodies fixed to a base, which preferably is flexible. As used herein, a strictly convex contour line of an engaging projection, in a side view is convex when looking from the outside and not straight. A strictly convex shape for the lower surface of the overhanging rim or mantle surface has been found to be beneficial because it gives a relatively large thickness to the at least one engaging projection. In at least one side view of the at least one engaging projection, the mantle surface is preferably strictly convex at least at a part thereof adjacent to the edge. This convex shape provides strength to the edge of the rim overhanging the base. A convex shape also effectively leads engaging fibers down towards the base, thereby reducing torque load on the engaging projections and the base where they are attached, as was discussed above. In a different preferred embodiment the engaging projection is strictly tapered from the top to the front surface of the base in at least one side view of the at least one engaging projection.
The engaging projection, in at least one side view of the mantle surface can be strictly convex. or strictly taper from the projection top to the front surface of the base. The mantle surface and the top surface of the engaging projections define edge angles. These edge angles are advantageously along the entirety of the edge and can have an angle of between about 20° to about 85° or between about 30° and about 80°.
The material of the front surface of the base can differs from the material of at least one engaging projections mantle surface where they are attached. Such an arrangement can be achieved by the use of base film and preform projections comprised of different materials, with the use of compatibilizing layers if necessary. It is even more advantageous if the material of the front surface of the base is softer than the material of the mantle surface of the at least one engaging projection as determined, for example, by differing Shore hardness values.
It is also advantageous for some uses if the fastener base is elastically extensible within a plane of the base, and the material of the mantle surface of the at least one engaging projection is non elastomeric. The base can comprise elastomer materials including elastic laminates or the like. This can make an elastic fastener product, which can be especially beneficial, for example, with diapers and wrapping tapes.
The invention fastener can also be formed on the surface of a variety of base materials. This could be a film as described above but could be any suitable surface such as a fabric, nonwoven, metal sheet or foil, molded plastic, paper, breathable film, laminate etc, as described above for the first method

Description of Exemplary Deposition Methods

Reference is made to the method depicted in FIG. 1. Using a first subset method of the invention, polymer powder granules are provided, as polymer particles 36. A base 4 sheet is fed into the system from a suitable source. A contact release surface 40 is provided on a release conveyor 39 that is driven around two drive rollers 11. The contact release surface 40 is kept horizontal. The contact release surface may bear microstructured features as described elsewhere herein.
At the beginning of the operation cycle, the horizontal contact release surface 40 is kept at an elevated temperature by a hot plate 24. This could be done under the release conveyor 39, though further hot chambers, on the top side of a release conveyor, could also be utilized. A scatter unit 42 is used to evenly disperse the polymer particles 36 onto moving contact release surface 40. (Optionally, the particles are dispersed onto a stationary mask 31, with solid regions of the mask intersecting falling particles and open areas of the mask allowing particles to fall onto the moving release surface 40 in a predetermined pattern.) The particles are distributed on the contact release surface 40 to form preform projections 37. The release surface 40 can be cooled prior to the heating element 24. Cooling is also important for later preserving the contact angle of the preform projections 37, and can be provided by a steel cooling plate 45 at a controlled temperature under the contact release surface 40. The cooled preform projections 44 are made solid and suitable for contacting with the front surface 20 of the base 4. The base 4 is laid over the preform projections 44 on the contact release surface 40. The front surface 20 of the base 4 contacts the terminal ends of the preform projections 44. A hot air blowing unit 23 can be fixed above the back surface 3 of the base 4. Hot gas 21 is blown on the back surface 3 of the base 4, which could be done while the release conveyor 39 and the base 4 are together kept in motion in a lateral direction 25. Each point of the base 4 is exposed to the hot air for a time sufficient to soften and fix the terminal ends of the preform projections 44 to the front surface 20 of the base 4. Then the base is cooled, which could be done by air blower 12. The base 4, with the engaging projections 13 fixed thereto, is separated and removed from the contact release surface 40, and is then wound up on a reel (not shown).
Using this method the engaging projections 13 formed will have top surfaces bearing microstructured features (imparted by the microstructured features of the contact release surface), with a rim overhanging the base 4 typically in all directions, and bordered, typically all around, by an edge whose angle essentially corresponds to the contact angle. The vast majority of the engaging projections will strictly taper (strictly convex), in each side view thereof, from the microstructured top to the attached end at the front surface 20 of the base 4.
Other deposition methods are also possible as described elsewhere herein.

EXAMPLES

Example 1

Method for Deposition of Particles with Microstructured Top Surfaces

An apparatus was used similar to that depicted in FIG. 1. A contact release surface (shown in FIG. 3) was provided comprising a nickel plate bearing a pattern of pyramidal microstructured features comprising intersecting peaks and valleys. The contact release surface bearing these microstructures was prepared in similar manner to the methods described in U.S. Pat. No. 4,588,258 (incorporated herein by reference). The contact release surface was coated with a fluorochemical benzotrizaole compound similar to that described in U.S. Pat. No. 6,376,065 (incorporated herein by reference). The contact release surface was present as a horizontal sheet on the top surface of a moving shuttle that could be moved laterally, in order to simulate the continuous belt conveyor system of FIG. 1.
High density polyethylene particles of size range of about 80-200 microns diameter (available under the designation Rowalit N100-20 from Rowak AG, Zurich, Switzerland) were placed into a gravity-operated scatter unit (a hopper with a feeding wheel and an underlying screen).
At the beginning of the operation cycle, the horizontal contact release surface was brought to a temperature of about 170° C. by a heating element located underneath the conveyor shuttle. The shuttle was moved laterally at a speed of approximately 0.17 meters per second underneath the scatter unit, which was used to evenly disperse the polymer particles on the heated contact release surface at an average density of about 16 g/m². A mask was not used. The particles were heated by the heat of the contact release surface and thereby kept softened or melted into a semiliquid state. Several seconds after the particles where distributed on the release surface, they formed preform projections as described previously. Then the shuttle conveyor was used to move the release surface over a cooling plate and halted in position so as to cool the release surface down to a temperature of about 70° C. Thereby the preform projections were made solid and suitable for contacting with the front surface of a base film.
A base film was provided comprising a high density polyethylene film of basis weight 30 g/m². The base film was laid over the preform projections on the contact release surface such that the front surface of the base contacted the terminal ends of the preform projections. A hot air blowing unit which was fixed about 15 mm above the back surface of the base film, was used to blow air at a measured temperature of about 600° C. against the back surface of the base. The shuttle, which carried the release contact surface with the preform projections and base film, was moved laterally at approximately 0.17 meters per second underneath the hot air blowing unit. Each point of the base was thus exposed to the hot air, for a short period (typically one second or less), such that the base was softened enough to be fixed with the terminal ends of the preform projections. The terminal ends also melted from the heat to a suitable extent to fuse the preform projections to the base. The base film with attached projections was then cooled. The base, together with the engaging projections fixed thereto, was then removed from the contact release surface.
Engaging projections were thus formed that bore microstructured top surfaces (as shown in FIGS. 4 a and 4 b).

Comparative Example 2

Deposition of Particles without Microstructured Top Surfaces

An apparatus was used similar to that depicted in FIG. 1. A contact release surface was provided comprising a polytetrafluoroethylene-coated glass fiber web, with a slightly textured surface, available from Lörincz kft, Hungary, under the designation Chemglas 100-6. The surface energy of the contact release surface 40 was about 18.5 mJ/m². The contact release surface was present as a horizontal sheet on the top surface of a shuttle that could be moved laterally, in order to simulate the continuous belt conveyor system of FIG. 1.
High density polyethylene particles of size range of about 80-200 microns diameter (available under the designation Rowalit N100-20 from Rowak AG, Zurich, Switzerland) were placed into a gravity-operated scatter unit (a hopper with a feeding wheel and an underlying screen).
At the beginning of the operation cycle, the horizontal contact release surface was brought to a temperature of about 170° C. by a heating element located underneath the conveyor shuttle. The shuttle was moved laterally at approximately 0.17 meters per second underneath the scatter unit, which was used to disperse the polymer particles on the heated contact release surface at an average density of about 16 g/m²in the particle deposited regions. The particles were heated by the heat of the contact release surface and thereby softened or melted into a semiliquid state. Several seconds after the particles were distributed on the release surface, they formed preform projections. Then the release surface was moved over a cooling plate and halted in position so as to cool the contact release surface to a temperature of about 70° C. The preform projections were thus made solid and suitable for contacting with the front surface of a base film.
A base film was provided comprising a polypropylene film with a basis weight of 74 g/m²(available under product designation FL-3054 from 3M Company, St Paul, Minn.). The base film was laid over the preform projections on the contact release surface such that the front surface of the base contacted the terminal ends of the preform projections. A hot air blowing unit which was fixed about 15 mm above the back surface of the base film, was used to blow air at a measured temperature of about 600° C. against the back surface of the base. The shuttle, which carried the release contact surface with the preform projections and base film, was moved laterally at approximately 0.17 meters per second underneath the hot air blowing unit. Each point of the base was thus exposed to the hot air, for a short period (typically one second or less), such that the base was softened enough to be fixed with the terminal ends of the preform projections. The terminal ends also melted from the heat to a suitable extent to fuse the preform projections to the base. The base film with attached projections was then cooled. The base, together with the engaging projections fixed thereto, was then removed from the contact release surface.
Analysis
The average height 51 and average diameter 52 (at the top), as illustrated in FIG. 5, were measured for a large number of engaging projections of the samples of Example 1 and Comparative Example 2. The height/diameter aspect ratio was then calculated for the two types of engaging projections and is shown in Table 1.

TABLE 1

Hook Head Aspect Ratio (Hook Height to Hook Head Diameter)

	Height/Diameter Ratio

	Comparative Ex. 2	0.34
	Example 1	0.76

All patents, patent applications, and publications cited herein are each incorporated herein by reference in their entirety, as if individually incorporated by reference. All numbers are assumed to be modified by the term ‘about’. Various modifications and alterations of this invention will become apparent to those skilled in the art without departing from the scope of this invention, and it should be understood that this invention is not to be unduly limited to the illustrative embodiments set forth herein.

Claims

1. A hook fastener capable of engaging a suitable loop fabric, comprising;

a base substrate with a surface having a multitude of engaging projections, the engaging projections having a top surface and an attached end, wherein the attached end is joined to the surface of the base substrate at a bond juncture, and wherein the top surface of at least some of the engaging projections are formed with intersecting peak and/or valley structures.

2. The hook fastener of claim 1, wherein at least some of the peak structures are discrete structures surrounded by valley structures.

3. The hook fastener of claim 2, wherein at least some of the discrete peak structures are bounded on three or more sides by material of the top surface at a different height.

4. The hook fastener of claim 1, wherein at least some of the valley structures are discrete valley structures surrounded by peak structures.

5. The hook fastener of claim 1, wherein at least some of the peak structures intersect at one or more locations.

6. The hook fastener of claim 1, wherein at least some of the valley structures intersect at one or more locations.

7. The hook fastener of claim 1, wherein at least some of the engaging projections' top surfaces are ellipsoidal in shape.

8. The hook fastener of claim 1 wherein the top surface structures have a height of at least about 20 microns.

9. The hook fastener of claim 1 wherein the top surface structures have a height of at least about 50 microns.

10. The hook fastener of claim 1, wherein at least some of the engaging projections' top surfaces are non-ellipsoidal in shape.

11. The hook fastener of claim 1, wherein at least some of the engaging projections' top surfaces have at least one edge with a mantle surface that defines an angle of at least about 20 degrees.

12. The hook fastener of claim 1, wherein at least some of the engaging projections' top surfaces have at least one edge with a mantle surface that defines an angle of at least about 30 degrees.

13. A hook fastener capable of engaging a suitable loop fabric comprising,

a base substrate with a surface having a multitude of engaging projections, the engaging projections having a top surface and an attached end, wherein the attached end is joined to the base substrate at a bond juncture, and wherein the top surface of at least some of the engaging projections comprise nonlinear microstructured features, and wherein the engaging projections with nonlinear microstructured features have an average height-to-diameter aspect ratio of about 0.7 or greater.

14. The hook fastener of claim 13, wherein the engaging projections have an average height-to-diameter aspect ratio of about 1.0 or greater.

15. The hook fastener of claim 13, wherein the nonlinear microstructured features have a height of at least about 20 microns.

16. The hook fastener of claim 13, wherein the nonlinear microstructured features have a height of at least about 50 microns.