Method for Producing a Supporting Web, and Supporting Web

Abstract

The invention relates to a method for producing a supporting web made of a predeterminable amount of plastic material, comprising a multitude of molded elements, which are molded inside mold cavities (12) of a forming tool (5). While applying a negative pressure at least in one portion of the mold cavities (12), enough plastic material is always applied to the mold wall (13) of the respective mold cavity in order to form a cavity (22) inside the molded element. The invention also relates to a supporting web having a multitude of molded elements that is produced by using the aforementioned method.

Description

The invention relates to a method for producing a supporting web from a definable amount of plastic material with a plurality of molded elements which are molded in mold cavities of a molding tool. Furthermore the invention relates to a supporting web with a plurality of molded elements.

WO 02/13647 A2 discloses a process for producing an adhesive closing element with a plurality of molded elements built up symmetrically and connected integrally to the support, in the form of hooking means in the form of a stalk provided with a head part, in which a moldable material is supplied to a forming zone between a pressure tool and a molding tool. In the known process viewed at least in one longitudinal section of the respective mold cavity the opposing boundary walls run continuously in a convex path, a continuously running transition between the cross sectional shapes of the stalk and head part being achieved for the hooking means of the support so that an unimpeded mold removal process takes place.

DE 198 28 856 C1 discloses a process for producing a hook and loop connector piece with a plurality of hooking means made integrally with a supporting web as molded elements, in which a thermoplastic is supplied to the gap between the pressure tool and the molding tool, in which a screen which has continuous cavities is used as forming element on the molding tool, and in which the hooking means are formed by the thermoplastic in the cavities of the screen at least partially hardening, a molding tool being used which on the side of the screen facing away from the pressure tool has a second forming element which interacts with the screen cavities, and by which the thermoplastic is molded.

EP 1 028 639 B1 discloses a process for producing a supporting web from material with several stalks which extend from at least one side of the web, the process encompassing the following steps:

• • selecting at least one first material for a first material layer,
  • selecting at least one second material for a second material layer,
  • melt molding of the first layer with a first surface and a second surface of the first material,
  • melt molding of the second layer with a first surface and a second surface of the second material,
  • connecting the first surfaces of the first and second material layer, while the layers are in the molten state, for forming a multilayer film, and
  • forming several stalks on at least the second surface of the second material layer,
  • this mold step comprising molding of several stalks of at least the first material an/or the second material and the process furthermore comprising the step of controlling the processing conditions and the thickness, viscosity, and relative quantities of the first and second material such that the first material which forms the first layer projects in or through the stalks formed on the second surface of the second later and forms part of the stalks.

Furthermore, the European document discloses a web which is produced using this process. With the known solution at least one of the two material layers is produced by coextrusion of the plastic material, in another process step the stalk ends being calandered with another forming roll in order in this way to obtained a mushroom-shaped hook fastener material.

With the known process a plurality of different embodiments of a hook and loop fastener part with preferably mushroom-shaped hook and loop fastener parts are obtained which are characterized in that the respective fastener element (stalk and head) is made solid, i.e., consists throughout of a plastic material.

On the basis of this prior art the object of the invention is to further improve the known processes and fastener systems such that their possible applications are widened. This object is achieved by a process with the features of claim 1 in its entirety and a product with the features of claim 9.

According to the characterizing part of claim 1, the process as claimed in the invention is characterized in that with application of a negative pressure, at least for a part of the mold cavities of the mold tool, so much plastic material is moved onto the mold wall of the respective mold cavity that a cavity is formed within the molded element. A supporting web made correspondingly as claimed in the invention is characterized in that the individual molded elements at least partially have a cavity.

With the solution as claimed in the invention it is possible to make a cavity in molded elements with a geometry which can be defined at will, with which a host of advantages can be achieved. In addition to saving weight and material, which benefits production costs, better heat-insulating properties can be achieved by an air cavity, and on the other hand by determining the cavity volume the stiffness for the molded element can be set so that it has adjustable resilience within definable limits. The latter plays a part especially when the molded element is designed as a mushroom-shaped hook fastener material with the result that in interaction with a fleece material or a correspondingly different hook and loop fastener material the elements which interact with one another to form the closed hook and loop fastener can be more easily moved against one another under the closing pressure; this greatly improves engagement behavior. But then more fastener elements can interact with one another by the engagement behavior which has been improved in this way; this in turn benefits the peeling strength values of the fastener and can thus lead to an increase in fastening forces.

Furthermore the cavities can be used appropriately, for example the possibility exists of adding a coloring medium directly in the production process or later by way of injector nozzles so that subsequent coloring processes for the supporting web with molded elements, especially in the form of a hook fastener, in which the color must be imprinted first, can be omitted. In addition to conventional dyes also luminescent pigments or the like can be added as the medium. Furthermore it is possible to open cavities produced in this way in the molded element on their side facing away from the supporting web either close to the production process in time or later by means of corresponding notches so that in this way within the molded element capillaries are formed with which self-cleaning surfaces (lotus effect) can be implemented which in terms of their shape have a capillary action if it taken into consideration that the quotient of the capillary work K and adhesion work A is greater than 1 (see in this respect also DE 102 07 193 A1).

Moreover the process as claimed in the invention can be made reliable and economical in terms of production engineering, and with one production step a hook fastener material is obtained, for which in part in the prior art multistep processes with subsequent calandering of the free stalk ends for head forming are shown.

Other advantageous embodiments of the solution as claimed in the invention are the subject matter of the other dependent claims.

The process as claimed in the invention will be detailed below using one embodiment as shown in the drawings. The figures are schematic and not to scale.

FIG. 1 shows a highly schematically simplified and partially cutaway side view of a device for executing the process as claimed in the invention;

FIG. 2 shows a perspective of two screens which have been pushed into one another with cavities which are formed by the screen openings and are shown exaggerated in areas for the sake of illustration;

FIG. 3 shows highly enlarged a longitudinal section through the configuration as shown in FIG. 2;

FIG. 4 shows a hooking means as can be produced with a device as shown in FIGS. 1 to 3;

FIG. 5 shows an elevation view of the supporting web which can be produced with the device as shown in FIGS. 1 to 3 with several hooking means as molded elements according to the individual representation in FIG. 4.

FIG. 1 schematically shows parts of a device for executing the process as claimed in the invention with an extruder head 1 as the supply means for plastic material which is in the plastic or liquid state and which as a belt with a width corresponding essentially to that of the hook and loop fastener part to be produced, is supplied to a gap between the pressure tool 3 and the mold tool 5. The pressure tool is a press roll and the mold tool is a mold roll designated as a whole as 5. Both rolls are driven in the directions of rotation given in FIG. 1 with curved arrows 7 and 9 so that between them a conveyor gap is formed through which the plastic material is conveyed in the transport direction, while at the same time in the gap as the forming zone the plastic belt is formed into the supporting web 10 of the hook and loop fastener part and the supporting web 10 on the side adjoining the mold roll 5 acquires the shape necessary to form hooking means by the forming elements of the mold roll.

For this purpose the mold roll on the periphery has a screen 11 with individual cavities 12. This mold cavity 12 is shown enlarged for example in FIG. 3. Furthermore the mold cavities 12, which are not detailed, are typically distributed on the outer peripheral side in the longitudinal direction over the mold roll with its screen 11, the distribution and number being freely selectable. FIG. 3 shows a longitudinal section again of the mold cavity 12 used at the time, the boundary walls 13 opposite in the longitudinal section running continuously with a convex shape 14. It goes without saying that the indicated two boundary walls 13 with respect to the rotationally symmetrical structure of the mold cavity 12 are fundamentally part of a terminating forming wall 15 which is bordered by the screen material 11 of the mold roll. With these mold cavities 12 it is possible to produce hooking means in the form of a stalk 17 provided with a head part 16 (compare FIG. 4).

As FIG. 2 furthermore shows, the curvature of the respective path 14 in the direction of the head part 16 to be molded is made more pronounced than in the direction of the foot part 18 via which the stalk 17 is connected to the supporting web 10. It has proven especially advantageous if viewed from the longitudinal direction of the stalk 17 in the direction of the head part 16 the path 14 with its greater curvature is located above the middle, preferably starting in the upper third. To obtain the indicated mold cavities 12 with their rotationally symmetrical structure in the form of a hyperboloid, galvanic coating processes (electroplating) have been found to be favorable to production. Furthermore the convex path 14 can optionally be produced from a screen or solid grate material also by way of a laser process.

The individual hooking means shown in FIG. 4 as a molded element can be obtained with the above described process. The symmetrical structure arises directly by production in a mold cavity 12 as shown in FIG. 3. This hooking means can be made geometrically very small, for example can have a height of only 0.4 mm with a width of the fastener head of approximately 0.6 mm. The cross section of the stalk 17 in this embodiment is approximately 0.25 mm. Furthermore, as shown in FIG. 5 there can be a plurality of these hooking means on the supporting web 10. The head shape of the head part 16 need not be further reworked so that with the process as claimed in the invention the fastener material can be obtained with essentially only one production step. Furthermore, it can be provided that cuts be made in the outside contour of the inherently closed annular head part 16 in order to obtain a plurality of hooks along the head part 16. The hooking means shown in FIGS. 4 and 5 can also appear differently, especially in terms of their head part 16, for example can be provided with head geometries as is already shown in PCT/WO 00/00053.

In a concentric configuration to the screen 11 and positioned inside or underneath, there is another screen 20 which with its outer side is in direct contact with the inside of the screen 11. This additional screen 20 has a plurality of screen passages opposite the mold cavities 12 of the first screen, for example more or less 10,000 to 20,000 passage per cm², and the passages 21 which have been formed in this way are selected to be geometrically so small in diameter that they do allow air to pass, but essentially do not allow the plastic to be molded in via the extruder nozzle 1 to pass. Furthermore the forming process for the hooking elements can be controlled such that in any case before the plastic material reaches the passages 21 the forming process for the head part 16 is already completed. This can be achieved for example via suitable temperature control by way of the mold tool 5. The other screen 20 is also galvanically built up, as already described for the first screen 11. But the passages 21 can also be obtained as laser beam shots in cylindrical shape. It is possible to distribute the screen passages 21 uniformly over the entire periphery of the other screen 20 or to provide screen passages 21 only at the locations (not shown) where they are essentially covered by the mold cavity 12.

The plastic material originating from the extruder can be intaken into the mold cavities 12 by way of a vacuum or negative pressure means which is not shown and which has its supply via the interior (not shown) of the mold tool 5 in the form of a mold roller, such that on the one hand the screen passages 21 are not clogged by the inflowing plastic material and on the other the plastic material adjoins in a thin-walled manner the boundary walls 13, so that for each molded element a cavity 22 is formed, as is shown by way of example in FIG. 4 for a hooking element. This cavity 22 extends rotationally symmetrically within the hooking means from its foot part 18 via the stalk 17 and ends in the head part 16. Furthermore, this cavity 22 penetrates the supporting web 10 and in this way communicates with the exterior.

Depending on the applied negative pressure the cavities 22 can be controlled in terms of their geometrical configuration and accordingly also the wall thickness for the foot part 18, the stalk 17 and the head part 16 of the respective hooking means. By omitting the screen passages 21 or by closing these passages 21 or by applying negative pressure only to certain screen passages 21, certain individual hooking elements can also be produced free of cavities. Furthermore, with the pertinent process together with the device it is also possible to produce conventional fastener systems without a cavity 22 and selectively as necessary with a cavity 22, depending on whether the process is carried out with or without negative pressure. For a correspondingly high negative pressure it is also possible for the cavity 22 to penetrate the top of the head part 16 (not shown) so that in this way capillary tubes can be produced within the fastener material; this benefits self-cleaning of these surfaces (see in this respect the disclosure contents of DE 102 07 193 A1).

With a suitable choice of the plastic material, optionally the supporting web 10 with its molded element with cavities 22 can be produced independently. To increase the stability and especially to facilitate removal of the supporting web from the molding tool 5 with its mold cavities 12, attachment of a fastener web 23 on the back of a supporting web 10 can be recommended. To produce this fastener web 23 from a suitable plastic material, another extruder head 2 is used, as shown in FIG. 1. Provided, as is shown in FIG. 1, two extruder heads 1, 2 are used, fundamentally a multilayer structure forms for the hooking means in the form of a coextruded hook and loop fastener. But basically it is also possible to replace the other extruder head 2 by an unwinding means, from which a film-like plastic web, but also metal strip could be unwound which then forms the back of the supporting web 10. Thus, for example it would also be possible to apply an adhesive on one side to this metal strip or plastic film web, on which then the supporting web 10 to be formed remains adhering. With a suitable adhesive this material connection of the layers could also be detachable again. In the embodiment shown in the figures it is however provided that the supporting web 10 with the molded elements consists of a so-called low-density polyethylene (LDPE) material and the back or the fastener web 23 of a high-density polyethylene (HDPE) material.

As FIG. 4 shows in particular, the cavity 22 can lead to a hooking element which is made with very thin walls and therefore when engaged with other hooking means including the so-called fleece or hook material can be accordingly flexible in hooking behavior; this increases the number of hooking possibilities and consequently leads to an improved fastening force situation for the individual hooking means. Especially in the clothing and diaper industry where hook and loop fasteners should have “gentle behavior” to prevent skin injuries, the fastener elements built up in this way with cavities 22 are more than advantageous. Furthermore, it is possible during or after the production process to fill the cavity 22, for example with a coloring medium, so that later dyeing of the fastener can be omitted. Luminescent media can also be placed in the cavities 22 in this way; this increases design possibilities for the fastener.

The process as claimed in the invention need not be limited to application to fastener elements; rather there is a plurality of embodiments for the most varied types of molded elements. Thus for a modified screen structure with the illustrated forming process only cylindrical stalks 17 with correspondingly cylindrical cavities 22 can also be attained. Depending on the structure of the mold cavity for the mold tool 5, in this way a plurality of embodiments is conceivable. The two screens 11, 20 when worn can be easily removed from the actual mold roll and replaced by new screens. The possibility at least also exists of producing the other screen 20 as a one-piece component of the mold roll or altogether a mold roll with the mold cavity gradient 12 in addition to screen passages 21.

The plastics to be processed can be diverse, for example in the form of polyamides or polyolefins, such as polypropylene or polyethylene (HDPL and LDPL). Furthermore other thermoplastics are used, such as polyester, polyethylene terephthalate, polystyrenes, polycarbonates, polymethyl methacrylates, ethylene vinyl acetate copolymers including acrylate modified ethylene, vinyl acetate polymers and ethylene acrylic acid copolymers as well as polyethylene styrenes. Furthermore the use of duroplastics is conceivable, as is use of elastomers such as naturally or synthetically producible rubber including styrene block copolymers with portions of isoprene, butadiene, or ethylene (butylene) blocks. Furthermore, the use of metallocene-catalyzed polyolefin, polyurethane or polydiorganosiloxanes is possible. If these webs with the molded elements are not obtained completely in the coextrusion process, but for example from the combination of a metallic strip with a plastic supporting web, pressure sensitive adhesives or hot-melt adhesives are used to join the strip and web. To stiffen the respective web and for strengthening, ductile thermoplastics can be used, such as nylon or polyvinyl chloride. The molded element article produced in this way can also be provided with coatings which can also be deposited by evaporation or doctoring. Furthermore, to produce structuring in the sense of self-cleaning surfaces, aftertreatments are possible, whether with a laser, ultrasound, or the like. Furthermore manufactured materials which are biodegradable can be used.

Claims

1. A method for producing a supporting web (10) from a definable amount of plastic material with a plurality of molded elements which are molded in mold cavities (12) of a molding tool (5), characterized in that with application of a negative pressure, at least for a part of the mold cavities (12) always so much plastic material is moved onto the mold wall (13) of the respective mold cavity (12) that a cavity is formed within the molded element (22).

2. The process as claimed in claim 1, wherein the respective cavity (22) in an assignable molded element can be closed at least to one side by a fastener web (23).

3. The process as claimed in claim 2, wherein at least one of the webs (10, 23) is formed from a coextrudate.

4. The process as claimed in claim 2, wherein at least one of the webs (10, 23) is formed from a blocking layer—also in metallic form.

5. The process as claimed in claim 2, wherein the cavities (22) of the molded elements on their side opposite the fastener web (23) are formed such that they communicate with the exterior.

6. The process as claimed in claim 1, wherein the molded elements are made as stalks (17) or as ones which are provided at least in part on the respectively free end of the stalk (17) with a head part (16).

7. The process as claimed in claim 1, wherein the cavities (22) are filled with at least one medium.

8. The process as claimed in claim 1, wherein the mold tool (5) is formed from a mold roll or a mold belt and wherein in addition to at least one forming layer (screen 11) there is a layer (another screen 20) for applying the negative pressure.

9. Supporting web (10) with a plurality of molded elements, especially produced by a process as claimed in one of the preceding claims which have at least in part one cavity (22).

10. The supporting web as claimed in claim 9, wherein the respective cavity (22) of a molded element is closed on at least one side by a fastener web (23).