Abstract:
A method produces adhesive closure parts, where a partial segment of the surface of a support element ( 10 ) is provided with adhesive closure elements ( 3 ) which stand out from its plane by applying a plastic material that forms adhesive closure elements on the support element ( 1 ). The adhesive closure elements ( 3 ) are formed without any forming tools, at least in a given area, by depositing the plastic material in successively delivered droplets using an applicator ( 9 ).

Description:
REFERENCE TO RELATED APPLICATION 
   This application is related to U.S. patent application Ser. No. 10/312,782, filed on Dec. 30, 2002 in the name of Axel Schulte and entitled “Method of Producing Adhesive Closing Parts.” 
   FIELD OF THE INVENTION 
   The present invention relates to a method for production of adhesive closure parts, in which a backing element is provided in at least one component area of its surface with adhesive closure parts. A plastic material forming the adhesive closure part is applied to the backing element. 
   BACKGROUND OF THE INVENTION 
   DE 198 28 856 C1 discloses a conventional process for producing adhesive closure parts which is relatively expensive, especially if adhesive fastener elements produced are applied in very high packing density and are small in size. For example, in production of so-called microfasteners, the adhesive fastener elements are provided in the form of stems thickened at the ends or with side projections in very high packing densities (for example, 200 or more adhesive fastener elements per square centimeter). Form tools, such as dandy rollers, are required for shaping the stems as desired on the end side. Very high production costs are occasioned by the very large number of sieve openings, which openings may be produced by etching, electroplating, or laser treatment. 
   SUMMARY OF THE INVENTION 
   Objects of the present invention are to provide a process permitting especially economical production of adhesive fastener elements which are tightly packed in the widest possible variety of shapes desired. 
   In the process of the present invention, the adhesive fastener elements are formed without use of a form tool at least in one component area. Plastic material is deposited by at least one application device in the form of the finest possible droplets applied in succession. The places selected for deposit of the droplets are three-dimensional with respect to the shape of the particular adhesive fastener elements to be formed. 
   The process of the present invention, characterized by extremely fine droplets deposited in succession in selected places, permits formation of adhesive fastener elements of any configuration and of virtually any degree of fineness, and achieves the high packing densities desired without the need for correspondingly costly development of form tools. Control of the places of droplet deposit are accomplished by appropriate relative movements of deposit device and backing element, preferably under computer control. This process permits not only formation without difficulty of the shapes disclosed in DE 198 856 C1 referenced above, as stems with mushroom heads, with stellate heads, and the like, but also permits which shapes cannot be produced at all, or can be produced only with great difficulty, with conventional form tools, such as loops, hooks, or anchors. Such additional elements can be shaped only poorly or not at all by a form tool because of the undercuts present. 
   Preferably the application device has at least one nozzle from which the plastic material is sprayed in droplets of a size of a few picoliters. Such spray devices for centrifuging liquid plastic material may be operated by piezoelectric or electrothermal means. The plastic material can preferably be an acrylate, which sets after depositing of each droplet or group of droplets, for example, by the action of electromagnetic radiation. The deposit site can be subjected to ultraviolet radiation, or the setting can be by a chemical reaction. The plastic material may, however, also be a thermoplastic set by cooling. 
   The adhesive fastener elements may be produced at a high speed of operation, since spray application of successive drops can be carried out at a high rate. Cycle speeds of several kilohertz may be reached immediately in computer-controlled operation. An application device having a plurality of nozzles actuated simultaneously may also be provided to develop a plurality of several rows of adhesive fastener elements simultaneously. 
   Other objects, advantages and salient features of the present invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the present invention. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Referring to the drawings which form a part of this disclosure: 
       FIG. 1  is a highly simplified, diagrammatic perspective view of a device for application of a process according to a first embodiment of the present invention; 
       FIG. 2  is a diagrammatic side elevational view of the device shown in  FIG. 1 ; 
       FIG. 3  is an enlarged side elevational view of the area identified as A in  FIG. 2 ; 
       FIG. 4  is a side elevational view of a device similar to that shown in  FIG. 2 , for the production of looped adhesive fastener elements according to a second embodiment of the present invention; 
       FIG. 5  is an enlarged side elevational view of the area identified as A in  FIG. 4 ; 
       FIG. 6  is a highly simplified, diagrammatic side elevational view of a device for production of adhesive fastener elements with trough-shaped heads passed through calendars according to a third embodiment of the present invention; and 
       FIG. 7  is an enlarged side elevational view of the area identified as A in  FIG. 6 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
     FIGS. 1 to 3  illustrate the process of the present invention in which adhesive fastener elements  3  are formed on a surface of a backing element  1  in the form of a sheet of PET. Adhesive fastener elements  3  have thickened areas on their ends. In the example presented in  FIGS. 1 to 3 , the thickened areas on the ends resemble mushrooms, as seen from  FIG. 3  in particular. For the sake of clarity, the adhesive fastener elements in all the figures are illustrated greatly exaggerated in size and spaced at greatly exaggerated intervals from each other. 
   The backing element  1  rests on a guide roller  5  which may be driven in both directions of rotation for execution of controlled rotary steps. The backing element  1  may be moved back and forth (as shown by the curved arrow  7  in  FIG. 2 ) in the Y axis direction within a droplet application area situated inside an application area A. Droplets of liquefied plastic material are applied by an application device  9 , which may be moved in the Z direction or axis (see double arrow  11  in  FIG. 2 ) and in the direction of the X axis (see double arrow  13  in  FIG. 1 ) perpendicular to the Z axis. Consequently, the location selected for droplet application relative to the backing element  1  may be three-dimensional. The guide roller  5 , and accordingly the backing element  1 , as well the application device  9 , move correspondingly. As an alternative, the application device  9  could move along all three axes (X, Y, and Z) relative to the backing element  1 . 
   The application device  9 , in the example illustrated in  FIGS. 1 to 3 , has a nozzle  15  through which the liquefied plastic material is sprayed. In the operating situation shown in  FIG. 3 , the nozzle  15  assumes a position relative to the backing element  1  such that the stem of an adhesive fastener element  3  is built up by successive spraying of droplets, each of a few picoliters. In the situation illustrated in  FIG. 3 , the stem sprayed through the nozzle  15  has been built up to about one third of its height, preferably under computer control, at a high rate of 2 kilohertz, for example. The droplets which have been applied set during the intervals between spraying processes. This setting can be accomplished in various ways, for example, by spray application of a hardening medium or by supply of energy, by ultraviolet irradiation in particular. In the present case ultraviolet lamps  17  are provided in addition to the application device  9  for irradiation of the application area A with ultraviolet radiation. For the setting processes, the application device  9  preferably is withdrawn along the Z axis and/or the backing element  1  is displaced by movement of the guide roller  5  along the Y axis before the corresponding elements are returned to the position selected for drop application in the following spray process. 
     FIGS. 4 and 5  illustrate an application of the process for production of adhesive fastener elements in which adhesive fastener elements  19  in the form of loops are formed on the backing element  1 . In the process, two stems  23  are first built up for each loop, and are then bent over in arcs as illustrated in  FIG. 5 . 
     FIGS. 6 and 7  illustrate the production of adhesive closure parts with adhesive fastener elements  21  formed by first building up stems  23  without thickened areas on the ends. A pressure gap is formed by a calendar roller  25  operating in conjunction with a mating roll  27 . The thickened end areas of the adhesive fastener elements  21  are formed as trough-shaped (see  FIG. 7 ) by calendering on the ends of the stems  23 . 
   Liquefied acrylates, the viscosity of which may be adjusted by addition as desired of a reactive thinner, for example, are suitable as plastic material to be applied in droplet form. The hardenability by ultraviolet radiation can be promoted, preferably, by addition of a photoinitiator. 
   In one example the plastic material contains as acrylic material of 90 percent Ebecryl 4835, a prepolymer made by the UCB company, 8 percent HDDA (UCB company) as a reactive thinner for viscosity adjustment, and 2 percent Darocur 1173, made by the Ciba-Geigy company, as a photoinitiator. 
   In another example, 90-percent Ebecryl 4835 and 4-percent Ebecryl 230 from the UCB company are provided as acrylate materials. 4-percent HDDA from the UCB company is employed as a reactive thinner, and 2-percent Darocur from the Ciba-Geigy company is used as a photoinitiator. 
   Plastic materials of different compositions may, of course, also be employed for application of the process of the present invention. Backing elements of a different nature, such as textile materials, or moulded elements provided for special applications may be provided in place of a sheet of polyethylene. 
   The present invention is described in the foregoing on the basis of examples in which the adhesive fastener elements as a whole are in the form of droplets spray-applied in succession. The process may, of course, also be applied to advantage in such a way that simply formed stems of adhesive fastener elements may, when straight stems, for example, are involved, be produced conventionally with form tools, with no additional expense, as initial material onto which droplets of the geometric configurations desired are then sprayed to produce finished adhesive fastener elements. 
   While various embodiments have been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the appended claims.