Abstract:
Touch fasteners with different portions having different material properties, and methods and apparatus for making such a product. In one embodiment, the fastener includes a cross-linkable polymer, and a first portion of the fastener is cross-linked and a second portion of the fastener is not cross-linked or is cross-linked to a degree less than said first portion. In another embodiment, the fastener is made in a continuous process on a rotating mold roll having a plurality of fastener element mold cavities extending into the mold roll from its outer circumferential surface. The method includes applying a first polymer to the mold roll and forcing some of the first polymer into the mold cavities, with some of the first polymer remaining on the surface of the mold roll in the form of a film having thickness; with a doctoring blade, removing at least some of the first polymer remaining on the surface of the mold roll to at least reduce the thickness of the film of the first polymer on the mold roll surface (in some cases, substantially all of the polymer on the mold roll surface is removed); and applying a second polymer to the mold roll, the second polymer being compatible with, and adhering to, the first polymer.

Description:
This application is a continuation (and claims the benefit of priority under 35 USC 120) of U.S. application Ser. No. 09/735,863, filed Dec. 13, 2000, now abandoned which is a divisional of U.S. application Ser. No. 09/283,474, filed Apr. 1, 1999 now is U.S. Pat. No. 6,180,205. The disclosures of the prior applications are considered part of (and are incorporated by reference in) the disclosure of this application. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to making sheet-form products, such as fasteners, with arrays of miniature projections extending from a broad surface thereof. 
     Arrays of molded male fastener elements, e.g., hooks, are often formed integrally with a sheet-form base, to provide a sheet-form fastener component. This component can then be engaged with a similar component of female fastener elements to form a “hook and loop” fastener. It is desirable that the fastener elements have good strength and toughness, so as to provide strong engagement during repeated use of the fastener. It is, on the other hand, desirable that the sheet-form base be relatively soft and flexible, e.g., to allow the base to flex with a fabric article to which it is attached and to prevent the edges of the sheet-form component from causing discomfort to a wearer. 
     SUMMARY OF THE INVENTION 
     The invention features an improved, continuously formed touch fastener product with different portions having different material properties, and methods and apparatus for making such a product. 
     The invention can provide a fastener having both relatively hard, durable regions and relatively softer, more flexible regions. In one aspect of the invention, such a fastener product is produced by forming, from a cross-linkable polymer, a plurality of molded fastener elements integral with a sheet-form base, and selectively cross-linking regions of the polymer to form the hard, durable regions. The regions that are not cross-linked remain relatively soft and flexible. In another aspect of the invention, such a fastener is produced by forming the hard, durable regions from a first polymer, and joining to the first polymer a second polymer having properties different from the first polymer to form the relatively softer, more flexible regions. 
     In one aspect of the invention, the invention features a fastener including a sheet-form base member, and, extending outwardly from, and integral with, the base member, a plurality of molded fastener elements. At least a portion of the fastener includes a cross-linkable polymer, and a first portion of the fastener is cross-linked and a second portion of the fastener is not cross-linked or is cross-linked to a degree less than the first portion. 
     Preferred embodiments include one or more of the following features. At least some of the fastener elements are cross-linked. The base member is not cross-linked. The fastener elements include a cross-linkable polymer and the base member includes a non-cross-linkable polymer, or, alternatively, both the fastener elements and the base include a cross-linkable polymer. The base member has a flexural modulus of less than about 80,000 pounds per square inch (psi), more preferably 10,000 to 60,000 psi, and the fastener elements have a flexural modulus of greater than 80,000 psi, more preferably 80,000 to 120,000 psi. The fastener elements have a flexural modulus that is at least 25% higher than that of the base member, more preferably at least 50% higher. The base has a thickness of less than 0.015 inch, more preferably about 0.001 to 0.005 inch. The cross-linkable polymer is selected from the group consisting of polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), polytethylene terephthalate) (PET), polyacrylates, polyamides, thermoplastic elastomers, and mixtures thereof. At least some of the fastener elements are male fastener elements, e.g., hooks. The hooks are cross-linked. 
     According to another aspect, the invention features a method of making a fastener including (a) forming a fastener comprising a sheet-form base member and a plurality of molded fastener elements extending outwardly from and integral with said sheet-form base member, at least a portion of the fastener being formed from a cross-linkable polymer; and (b) cross-linking the cross-linkable polymer in a manner so that a first portion of the fastener is cross-linked while a second portion of the fastener remains non-cross-linked or is cross-linked to a lesser degree than the first portion. 
     Preferred embodiments include one or more of the following features. Step (b) is performed using electron beam radiation. The cross-linkable polymer is a thermoplastic elastomer that is capable of increasing at least 25% in flexural modulus upon substantially complete cross-linking. The fastener is formed entirely of a thermoplastic elastomer. The fastener elements are hooks. The hooks are cross-linked during step (b). At least a portion of the base is not cross-linked during step (b). 
     In yet another aspect, the invention features a method of making a fastener including (a) forming a fastener comprising a sheet-form base member and a plurality of molded fastener elements extending outwardly from and integral with said sheet-form base member, by forming a first portion of the fastener from a cross-linkable polymer, and joining the first portion to a second portion of the fastener that is formed from a second polymer; and (b) at least partially cross-linking the first cross-linkable polymer. The invention further features fasteners made by this method. 
     According to another aspect of the invention, the invention features a method of making a continuous fastener product having an array of fastener elements extending from a sheet-form base. The method includes: (a) providing a mold roll defining a plurality of fastener element mold cavities extending into the mold roll from the outer circumferential surface of the mold roll; (b) applying a first polymer to a surface of the mold roll and forcing some of the first polymer into the mold cavities, with some of the first polymer remaining on the surface of the mold roll in the form of a film having thickness; (c) with a doctoring blade, removing at least some of the first polymer remaining on the surface of the mold roll after step (b) from the surface of the mold roll to at least reduce the thickness of the film of the first polymer on the mold roll surface; (d) applying a second polymer to the mold roll, the second polymer being compatible with the first polymer and adhering thereto; (e) solidifying the first polymer in the mold cavities to form fastener elements; and (f) removing the fastener elements from the mold cavities. 
     Preferred implementations of the method include one or more of the following features. In step (c), substantially all of the first polymer that remains on the mold roll after step (b) is removed by the doctoring blade. The first polymer is applied by an extruder. The second polymer is applied by an extruder. The first polymer is cross-linkable and the method includes cross-linking the first polymer after removal from the mold roll. The first polymer is relatively harder than the second polymer. The second polymer is more elastic, when solidified, than the first polymer. The method includes, after step (d), bonding a third polymer to the second polymer. 
     According to another aspect of the invention, the invention features a method of making a continuous fastener product having an array of fastener elements extending from a sheet-form base. The method includes: (a) providing a mold roll defining a plurality of fastener element mold cavities extending into the mold roll from the outer circumferential surface of the mold roll; (b) applying a first polymer to the surface of the mold roll and forcing some of the first polymer into the mold cavities, with some of the first polymer remaining on the surface of the mold roll in the form of a film having thickness; (c) with a doctoring blade, removing at least some of the first polymer remaining on the surface of the mold roll after step (b) from the surface of the mold roll to at least reduce the thickness of the film of the first polymer on the mold roll surface; (d) applying a tie layer to the mold roll, the tie layer being compatible with and adhering to the first polymer; and (e) applying a second polymer to the tie layer. 
     Preferred implementations of the method include one or more of the following features. The first and second polymers are different materials. The tie layer comprises an adhesive. The tie layer comprises a polymer. 
     The present invention can provide a fastener having both relatively hard, durable regions and relatively softer, more flexible regions. The inventor has found that such a fastener can be provided by forming, from a cross-linkable polymer, a plurality of molded fastener elements integral with a sheet-form base, and selectively cross-linking regions of the polymer to form the hard, durable regions. The regions that are not cross-linked remain relatively soft and flexible. Alternatively, such a fastener can be provided by forming the hard, durable regions from a first polymer, and joining to the first polymer a second polymer having properties different from the first polymer to form the relatively softer, more flexible regions. 
     Advantageously, the hard and soft regions can be positioned as desired to suit a particular application. Thus, in certain cases where it is desired that the fastener elements be relatively stiff and durable, while the base be soft and flexible, the fastener elements are cross-linked to a desired degree while the base is not cross-linked or is cross-linked to a lesser degree than the cross-linking of the fastener elements. Alternatively, the fastener elements can be formed of a first, relatively hard polymer, and the base from a second, relatively soft polymer. 
     Certain aspects of the invention also enable the formation of fastener products having relatively stretchable (i.e., rubbery or elastic) bases and relatively stiff or rigid fastener elements. Such products are useful, for instance, in diaper closures, where the elasticity of the base can help to maintain an engagement shear force on the fastener elements. 
     Other features and advantages of the invention will be apparent from the drawings, the following description, and the claims. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a side cross-sectional view of a fastener according to one embodiment of the invention. 
         FIG. 2  is a diagrammatic view of a process for making the fastener of FIG.  1 .  FIG. 2A  is an enlarged diagrammatic view of the portion of the process of  FIG. 2  shown in box A. 
         FIG. 3  is a diagrammatic view of an alternative process for making the fastener of FIG.  1 . 
         FIG. 4  is a diagrammatic view of a process for making fasteners according to an alternative embodiment of the invention. 
         FIGS. 5-5D  are cross-sectional side views of fasteners according to alternative embodiments of the invention. 
         FIGS. 6 and 7  are diagrammatic views of alternative processes for making fasteners of the invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Referring to  FIG. 1 , fastener  10  includes a plurality of hooks  12  that are integral with, and extend from, a sheet-form base  14 . The hooks and base may be formed from the same cross-linkable polymer or, alternatively, may be formed of different polymers. If they are formed from different polymers the hook-forming polymer is cross-linkable; the other polymer can be either cross-linkable or non-cross-linkable. Hooks  12  are cross-linked, while the base  14  is not cross-linked or is cross-linked to a lesser degree than the hooks. As a result, the hooks are tough and durable, while the base is soft and flexible. 
     The base should be sufficiently strong to withstand its intended use without tearing or other damage, while also being relatively thin and flexible, to give good “drape”. Preferably, the base is less than 0.005 inch thick, more preferably from about 0.001 to 0.003 inch thick. 
     The hooks have a significantly higher flexural modulus than the base, preferably at least 25% higher and more preferably at least 50% higher. 
       FIG. 2  illustrates a suitable process for forming the fastener shown in FIG.  1 . As shown in  FIG. 2 , a cross-linkable polymer  16  is extruded by extruder  18  onto a roll  19  having hook forming cavities  20  (e.g., as described in U.S. Pat. No. 4,872,243, the disclosure of which is incorporated herein), forming hooks  21  extending from a base  22 . It is noted that this step is shown merely as an example, and can be replaced by any desired method of molding hooks on a base, e.g., the processes described in U.S. Pat. Nos. 4,894,060, 4,794,028 and 5,441,687, the disclosures of which are incorporated by reference herein. 
     The resulting hook-carrying base  22  then passes to a cross-linking station A, shown in further detail in FIG.  2 A. At cross-linking station A, the base  22  passes through a bath of an inert shielding fluid  24 , e.g., a solution of salts of heavy metals such as barium, or a cooled bath of liquid mercury, while the hooks  21  remain above the surface  26  of the fluid. While the base  22  is in the bath, the hooks are exposed to radiation (arrows E), e.g., electron beam radiation, causing the hooks to cross-link or partially cross-link. If it is desired that the base of the hooks remain flexible, the hooks can be partially submerged in the bath along with the base. 
     An alternative process is shown in FIG.  3 . In this process, the bath of shielding fluid is omitted, and instead the hook-carrying base  22  passes through a series of rolls  28 ,  30 ,  32 . The arrangement of the rolls causes the base  22  to bend around rolls  28  and  32 , forming bent areas. Electron beams E 1 , E 2 , that point in the machine direction (in the plane of the page, in FIG.  3 ), are then directed at the bent areas. Thus, the electron beams will cross-link the hooks without significantly affecting the base. If desired, more rolls can be provided downstream of roll  32 , in a similar arrangement, to provide more bent areas at which radiation can be directed. 
     Polymers that are suitable for use in this embodiment of the invention are those that can be molded to form fastener elements and can subsequently be selectively cross-linked, as described above. Suitable polymers include polyvinyl chloride (PVC), polyvinylidene fluoride (PVDF), poly(ethylene terephthalate) (PET), polyacrylates, polyamides, thermoplastic elastomers, e.g., HYTREL elastomers and PEBAX elastomers, and mixtures thereof. Polyester-based thermoplastic elastomers, e.g., HYTREL elastomers, and polyether/polyamide-based thermoplastic elastomers, e.g., PEBAX elastomers, are preferred. Many of these polymers will require suitable cross-linking agents in order to cross-link when exposed to radiation. Suitable cross-linking agents are well known to those skilled in the art. Suitable polymers that contain electron beam cross-linking agents include thermoplastic elastomers available from Zylon Corp., Monsey, N.Y. 10952, under the trade name “ZYLON EBXL TPE”. The cross-linkable polymer can also include additives such as fillers, stabilizers, accelerators, and the like, as is well known. 
     Cross-linking can be effected using various techniques, e.g., electron beam or ultraviolet radiation, heat, or any other desired technique suitable for the selected polymer. The cross-linking conditions are selected based on the polymer used and the properties desired. 
     In alternative embodiments, a first polymer is used to form the hooks and a second polymer is used to form the base. Thus, the hook-forming polymer can be cross-linkable and the base-forming polymer can be non-cross-linkable (or not cross-linkable under the conditions used to cross-link the hook-forming polymer), so that it is not necessary to “mask” the base during cross-linking of the hooks. Alternatively, the hook-forming polymer can be harder than the base-forming polymer, and both polymers can have the desired properties without cross-linking. 
     A suitable process for forming such a two-polymer fastener is shown in  FIG. 4. A  first extruder  35  extrudes a first, hook-forming polymer  38  onto mold roll  40 , forcing some of the polymer into hook-forming cavities  42  and leaving a layer of polymer on the surface of the mold roll. As mold roll  40  rotates in the direction of arrow A, doctoring blade  44  removes some or all of the polymer on the surface of the mold roll without disturbing the polymer in cavities  42 . The removed polymer, which has been exposed to air while on the mold roll and may have begun to solidify, may be either discarded or returned to the hopper for remelting. The thickness of polymer left on the surface of the roll by the doctoring blade will depend, in part, on how close the blade is positioned to the surface of the mold roll (the position is adjustable in the direction indicated by arrow B). In some cases, the sharp, distal end of blade  44  rides against the mold roll, thereby literally scraping off essentially all of the polymer on the surface of the roll. In such cases it is recommended that the end of the blade be coated with a lubricious material to avoid damaging the surface of the mold roll. In other cases, the position of the blade is adjusted to leave a predetermined thickness of polymer on the roll, to become a part of the base of the product. In such cases, the doctoring blade effectively trims the polymer thickness rather than actually “scraping” against the surface of the roll. Next, a second extruder  47  extrudes a second, base-forming polymer  50  onto the surface of the mold roll (or onto any of polymer  38  left on the surface of the roll by blade  44 ). A gear pump  36 ,  48 , is positioned at the outlet of each extruder, to accurately control the rate of polymer delivered to the mold roll. The final thickness of the base of the product is then adjusted by roll  52 , rotating in the direction of arrow C, and the finished fastener product  60  is stripped from the mold roll  40  by passing it around exit roll  54 . 
     For forming a fastener product having a relatively stretchable base and relatively stiff fastener elements, a urethane may be employed for the hook-forming polymer  38  and a rubber-filled polyethylene or polyester based thermoplastic may be employed for the base-forming polymer  50 . An example of such a base-forming material is ARNITEL EM400, available from DSM. 
     Examples of various fasteners that can be formed using the process shown in  FIG. 4  (or modifications of this process) are shown in  FIGS. 5-5D . 
       FIG. 5  shows a fastener  62 , in which the hooks  64  are formed of a first polymer and the base  66  is formed of a second polymer. Using the process shown in  FIG. 4 , such a fastener can be formed by scraping substantially all of the first polymer off of the surface of the mold roll prior to applying the second polymer. 
       FIG. 5A  shows a fastener  68 , in which the hooks  70  and the upper portion  72  of the base  74  are formed of a first polymer, and the lower portion  76  of base  74  is formed of a second polymer. Using the process shown in  FIG. 4 , such a fastener can be formed by adjusting doctoring blade  46  away from the mold roll surface so that a thin layer of the first polymer remains on the mold roll surface when the second polymer is applied. When using a stiff first polymer and a flexible or stretchable second polymer, the layer of first polymer is preferably sufficiently thin, as determined by the positioning of the doctoring blade, to enable the rupture of the thin layer of first polymer upon the initial stretch of the second polymer layer, such as during the initial engagement of a diaper tab. Subsequently, the rigidity of the thin layer of the first polymer does not detract from the stretchability of the base of the fastener product. 
       FIG. 5B  shows a fastener  78 , in which the hooks  80  are formed of a first polymer  82  and a second polymer  84 , and the base  86  is formed of a third polymer  88 . To form this fastener, the process shown in  FIG. 4  is modified so that the first extruder  35  applies an amount of the first polymer that only partially fills the mold cavities, and then another extruder (not shown in  FIG. 4 ) applies the second hook-forming polymer to completely fill the cavities. The process then continues as shown in  FIG. 4 , with scraping and application of the base-forming polymer by extruder  47 . If the two polymers  82 ,  84  are not compatible, or do not adhere well to each other, a thin tie layer of adhesive, or a third polymer that adheres well to both polymers  82  and  84 , can be applied between polymers  82  and  84 . This can be accomplished by replacing extruder  47  with a co-extrusion die, or by other known methods of applying tie layers. 
       FIG. 5C  shows a fastener  90  in which the hooks  92  are formed of three different polymers  94 ,  96 ,  98 . This fastener would be formed in a manner similar to that described below with reference to  FIG. 5D , adding a further extruder to apply the third hook-forming polymer. This embodiment can provide combinations of properties difficult to obtain with only two polymers. Alternatively, the middle polymer  96  may be used as a “tie layer” to bond polymers  94  and  98  if, for example, these polymers are incompatible or do not adhere well to each other. 
       FIG. 5D  shows a fastener  100  in which the base  102  and a lower portion  104  of hooks  106  are formed of a first polymer, and the upper portion  108  of the hooks is formed of a second polymer. This fastener would be formed by the process of  FIG. 4 , by only partially filling the molding cavities using extruder  35 , and then completing the filling of the cavities with extruder  47 . 
       FIGS. 6 and 7  show alternative processes for forming a two-polymer fastener. In the process shown in  FIG. 6 , the first and second polymers are applied to the mold roll by a coextruder  110 . In the process shown in  FIG. 7 , the hook-forming polymer is applied to the mold roll by an extruder  112 , and most of the polymer is scraped from the surface of the mold roll by a doctoring blade  114 , leaving a thin film of polymer, as described above with reference to FIG.  4 . The base-forming polymer  116  is then laminated to the thin film of hook-forming polymer while the latter is still on the mold roll, such as in the nip between the mold roll and roll  118 , as shown. 
     The hook-carrying base that is formed using any of the processes shown in  FIGS. 4 ,  6  and  7  can be partially cross-linked, if one of the polymers (preferably the hook-forming polymer) is cross-linkable. If the other polymer is not cross-linkable, or not cross-linkable under the same conditions, it is not necessary to mask or shield that component. Thus, for example, an electron beam can be directed at the entire fastener (positioned so that it hits at least the portions to be cross-linked) at a station (not shown) that is downstream of the processes shown in  FIGS. 4 ,  6  and  7 . If both polymers have the desired properties for a given application without cross-linking, the hook-carrying base formed by the processes shown in  FIGS. 4 ,  6  and  7  can be used “as-is”, without a further cross-linking step. 
     Polymers that are suitable for use in the fasteners shown in  FIGS. 5-5D  include the above-described cross-linkable polymers, if cross-linking is used. If cross-linking is not used, suitable polymers for the relatively hard portions of the fastener include polypropylenes, e.g., PROFAX 7823 polymer, commercially available from Montell USA, Inc., and other relatively hard polymers such as PET and polyamides, e.g., polyamide 6/6 and polyamide 6. Preferably, the relatively hard polymer has a flexural modulus of at least 80,000, more preferably at least 120,000 psi. Suitable polymers for the relatively soft portions include vulcanized blends of polypropylene and EPDM, e.g., SANTOPRENE polymers, commercially available from Advanced Elastomer Systems, Inc., and other relatively soft polymers such as those commercially available under the trade names HYTREL and PEBAX. Preferably, the relatively soft polymer has a flexural modulus of greater than 80,000, more preferably about 10,000 to 60,000 psi. It is preferred that the two polymers be compatible, i.e., that they adhere to one another and that they be relatively inert with respect to each other (or, if they are reactive, that such reaction does not have a significant deleterious effect on the desired properties of the polymers). If they are incompatible, a tie layer can be used to join them, as discussed above. 
     Other embodiments are within the claims. For example, while  FIG. 1  shows loop-engageable, hook-shaped fastener elements, the fastener elements may be of any desired shape (e.g., mushrooms, loops, multi-directional hooks, or spikes). The touch fastener can also include other raised structures such as veins, ridges, or rip-stopping formations, which would preferably be selectively cross-linked with the fastener elements. 
     Moreover, while the touch fastener shown in  FIG. 1  includes a non-cross-linked base and cross-linked fastener elements, for other applications other regions of the fastener are cross-linked and non-cross-linked.