Patent Publication Number: US-2005140059-A1

Title: Method and device for producing nonwoven moulded bodies

Description:
The invention concerns first a method for producing molded parts from a nonwoven that can be bonded by bonding agents, which is carried out basically in the manner specified in the introductory clause of claim  1 . The structure and bonding of these nonwovens are described in DIN 61210. Nonwovens of this type consist, on the one hand, of fibrous material and, on the other hand, of bonding agents for the fibers.  
      The fibers can be organic in nature, can be natural-synthetic, or can have an inorganic base. Examples include reprocessed cotton, flax, jute, polyester fibers, acrylic fibers, rock wool, or glass fiber.  
      The bonding agents are generally synthetic in nature. Materials that can be used for this purpose are thermoplastics and thermosetting plastics, such as polypropylene, polyester and phenolic resin, and epoxy resins. These agents can be applied in powdered form from solutions or dispersions. It is especially advantageous to use the bonding agents in the form of fibers, which we shall refer to as “bonding fibers” for short.  
      The nonwovens are mechanically produced by carding with web lamination or by aerodynamic means. The final product, namely, the bonded molded part, is produced by compression molding in a press that consists of a male mold and a female mold. If thermoplastic bonding agents are used, the sequence of treatment is hot-cold, whereas a cold-hot treatment sequence is used if thermosetting materials are used as the bonding agents. To improve the handling of the nonwoven during insertion in the molds, it is advisable to prebond the nonwoven mechanically and/or thermally. This can be accomplished, for example, by heating until the bonding agents in the nonwoven soften. The bonding agents in the nonwoven then produce slight interconnection of the fibers. The production process can be made especially cost-effective by combining the formation of the nonwoven and the compression molding in one operation. In this case, the nonwovens that have been treated with bonding agents are immediately placed in molds, in which they are compressed into molded parts.  
      Depending on the composition and production of the nonwovens, closed or open molded parts are used. This depends on whether the molded parts to be produced must be cooled or heated during compression. The transfer of the heat for treating the nonwoven can occur through the material of the molds or through the fluid air or through high-pressure steam.  
      The density of the molded parts falls in the range of 100 to 1,000 kg/cubic meter. The density is not always uniform and can vary within a molded part. An important use of molded parts of this type is in automobile construction, specifically, as fittings on the inside or outside of automobile bodies. They are used for acoustic insulation or sound absorption. In some cases, they can also act as support structures. Examples include floor insulation under the carpet, dashboard insulation or engine hood insulation, side paneling in the vehicle, or the headliner.  
      Molded parts of this type have been effectively used for decades, but they have the significant disadvantage that their conformability during compression molding is inadequate. There are critical mold regions in the molds, where the inner contour of the mold cavity has a strong curvature or where its profile height sharply increases. In previously known methods, exact shape adaptation to the desired inner contour of the mold is not possible.  
      Previous attempts to eliminate the disadvantage of lack of conformability have been unsuccessful. One such attempt consisted in increasing the thickness of the nonwovens. Another attempt consisted in using additional layers of nonwovens in the critical areas. However, the desired conformability could not be achieved in this way, and other significant disadvantages appeared. One of these disadvantages is the higher cost of producing these molded parts and the unwanted weight increase of the molded parts associated with this method. This is unacceptable for the use of these molded parts in the automotive sector.  
      The Japanese document JP 4[1992]-332,591 describes a method in which an air-permeable pad is covered with a surface material. This is carried out in a device that consists of two molds, in which the lower mold has air channels to which a vacuum is applied, while the upper mold has air channels through which hot air is delivered to the molded part. However, in this method, the molded part is already preshaped, so that it already has the desired geometry.  
      The Japanese document JP 6[1994]-322,651 describes a method for molding nonwoven molded parts. In this method, the raw material is covered with an air-impermeable layer and is then given the desired shape in a mold that has vacuum channels, which are arranged in the critical areas. The disadvantage of this deep-drawing method is that only molded parts with approximately the same wall thickness can be produced.  
      The document U.S. Pat. No. 2,459,804 describes a device for producing felt hats and similar objects. In a first arrangement, the raw material is uniformly laid down on a male mold that contains vacuum channels. A vacuum is applied to the vacuum channels for this purpose. In a second step, this male mold with the raw material is brought together with a corresponding female mold. The material located between the two molds is pressed into the desired shape under the action of heat. However, in this method, a vacuum is not applied to the vacuum channels of the male mold. Another embodiment also has a mold that consists of a male mold and a female mold, in which the felt material is arranged between these two parts of the mold. Both molds have air channels. The male mold is filled with high-pressure steam, which penetrates the female mold through the air channels of the male mold, through the molded part and then through the air channels of the female mold. This high-pressure steam serves to shape the molded part. This device likewise cannot provide exact shape adaptation in the critical mold areas.  
      These disadvantages are eliminated by the method specified in claim  1 . In this method, in the step specified in the characterizing clause of claim  1 , in which the mold is closed, pointwise regional suction is applied to the preliminary product present in the mold, at least in the aforesaid critical profile regions. This sucks out the air trapped inside the nonwoven. During this suction process, a stream of air can move the nonwoven that has been treated with bonding agents from the interior of the mold towards the contour of the mold. The pressed fibers remain in their conformal position until the integrated bonding agents have cooled and hardened. When the finished molded part is removed from the mold, it has the desired, exactly adapted profile even in the critical regions.  
      One possibility for producing the molded parts in a so-called “thermoplastic technique” is specified in method claim  3 . A second possibility, which characterizes the so-called “thermosetting technique”, is specified in method claim  9 .  
      The invention is also aimed at a device for carrying out a method of this type. The special measures of the device of the invention are described in claim  11 . The special feature consists in the assignment of a suction device to the mold. One or more suction lines lead from the suction device and are connected at well-defined points of the mold. Suction channels lead from the connection points of these suction lines, penetrate the wall of the mold, and open on the inner contour of the cavity. 
    
    
      Other measures and advantages of the invention are specified in the dependent claims and the following description and are shown in the drawings. The drawings illustrate a specific embodiment of the invention.  
       FIG. 1  shows a schematic cross section of a preliminary product produced from the nonwoven, which consists of a prebonded nonwoven that has been treated with bonding agents.  
       FIG. 2  illustrates a first step of the method, in which the preliminary product is subjected to heating until the bonding agents soften.  
       FIG. 3  shows the next step of the method, in which the preliminary product heated as illustrated in  FIG. 2  is placed in a two-part mold, in which it is treated in a special way that will be described in detail below.  
       FIG. 4  shows this special treatment, which occurs in a step of the method with the mold closed.  
       FIG. 5  shows the molded part produced by the method of the invention. 
    
    
       FIG. 1  shows a schematic cross section of a preliminary product  10 , which will be used to explain the method of the invention in greater detail with reference to the drawings. This preliminary product  10  is a nonwoven produced by aerodynamic means. The nonwoven is a homogeneous mixture of, for example, four components. A first component, which is identified by reference number  11  in  FIG. 1 , is a so-called bicomponent fiber, which has a covering consisting of thermoplastic material around a central fiber core. This component is the “bonding agent” in the nonwoven, namely, in the form of the “bonding fiber” mentioned earlier. Other components, which are shown in  FIG. 1  in fiber form and are identified by reference number  12 , can be of various types. Instead of fibers, a portion of the mixture components can also consist of foam flocks. A mixture of reprocessed cotton, polypropylene fibers, and possibly polyurethane foam flocks has been found to be effective. The mixing ratio of these bonding agents  11  and the three other components mentioned above can be 15:45:15:25 wt. % in the order specified above.  
      To allow better handling of the nonwovens, the fiber elements  11 ,  12  should already adhere to one another somewhat. This is best accomplished by slight heating of the nonwoven, which results in the formation of adhesion points  13  between the fibers  11 ,  12 . The preliminary product  10  is formed in this way. This type of prebonding of the nonwoven can also be produced mechanically instead of thermally.  
      As  FIG. 2  shows, this preliminary product  10  is placed between two heating plates  14 ,  15 , where the bonding fibers  11  soften to the desired extent. The penetration of the heat for heating and softening the bonding fibers  11  is illustrated in  FIG. 2  by the wavy arrows  16 . With the aforementioned composition of the preliminary product  10 , the heating plates  14 ,  15  produce a temperature of, e.g., 200° C. for one minute. During this treatment in  FIG. 2 , the bonding agents develop their effect to the desired extent and lead to an intermediate state  20  of the preliminary product, which is shown in  FIG. 3 . In this intermediate state, the bonding agents  11  have become fully active and have produced a strong bond  23  between the fibers  11 ,  12 . When the nonwoven has been converted to this intermediate state  20 , it is immediately sent to the compression molding step. This compression molding is carried out in a two-part mold, which is shown in  FIG. 4  and has the special design shown in  FIG. 3 .  
      The mold consists of a male member  21  and a female member  22 , which, in the closed state shown in  FIG. 4 , enclose a cavity  24  between them, which is the negative of the desired profile of the finished molded part  30 . The appearance of this molded part is shown, for example, in  FIG. 5 . As was described earlier, a finished product  30  of this type can have critical profile regions, which are labeled  32  and  33  in  FIG. 5 . The profile regions  32  consist of regions where the contour profile  31  of the molded part  30  shows strong curvature, which is symbolically illustrated in  FIG. 5  by a radius of curvature  34 . Other critical profile regions  33  occur in places where there is a sharp increase in the profile height, which is labeled  35 . The problems are best illustrated by the negative profile of the two mold members  21 ,  22  indicated in  FIG. 3 .  
      In the present case, one of the mold members  21  has a relatively simple, e.g., flat, inner contour  25 , but the other mold member  22  has a complicated relief with a jagged inner contour  26 . If, as illustrated in  FIG. 3 , the preliminary product  10  in intermediate state  20  is placed in the cavity  24  and then cooled with the mold  21 ,  22  closed, it would not be expected in the state of the art that the nonwoven would enter the contour regions  27 ,  28  of the mold. Instead of the nonwoven conforming to the inner contour  26 , the critical contour regions  27 ,  28  would not be filled by the intermediate product  20 . If the intermediate product  20  is then cooled between the cool molds  21 ,  22 , the finished molded part would have profile deviations in the aforementioned critical profile regions  32 ,  33 . The molded part  30  would not have the desired quality.  
      However, the method in accordance with the invention achieves this by means of the special press shown in  FIG. 3 . As is illustrated schematically in  FIG. 3 , a suction device  17  is assigned to the mold members  21 ,  22 , and a multiplicity of suction lines  18  leads out from the suction device. The suction lines  18  are connected at well-defined points  19  of the two mold members  21 ,  22 , at which at least one suction channel  29  originates. These suction channels  29  open in all of the critical contour regions  27 ,  28  of the inner contour  26 , but it is also advantageous to run them as far as the inner contour  25  of the opposing mold member  21 . The suction channels  29  pass through the wall of the mold members  21 ,  22 . It is sufficient to provide the suction channels  29  only at certain points in these contour regions  27 ,  28 . A diameter of the suction channels  29  of about 1 millimeter is sufficient.  
      As  FIG. 3  also shows, the suction device  17  can have a control unit  36 , which predetermines the time of initiation and the duration of the suction action of the device  17  and determines them as a function of the progress of the formation of the molded part in the cavity  24 . The resulting effects are shown in  FIG. 4 . The suction device  17  has an air outlet  38 .  
      As has already been mentioned, the preliminary product  10  in the hot intermediate state  20  is placed in the cavity  24  between the two mold members  21 ,  22 , which are then closed. The cavity is then sealed media-tight. The suction device  17  described above is activated immediately after the mold members  21 ,  22  have been closed. It applies suction to the enclosed nonwoven, which is still in the hot intermediate state  20 , as is illustrated in  FIG. 4  by suction arrows  37  at each of the suction channels  29 . During this suction  37 , airflow occurs inside the hot nonwoven intermediate product  20 , which causes the large numbers of fibers  11 ,  12  to be carried along and moved toward the contours  25 ,  26 . This occurs above all in the critical contour regions  27 ,  28  illustrated in  FIG. 3 . The ultimate result of this movement of fibers in the mold cavity  24  is a conformal position of the fibers  11 ,  12  in the two mold members  21 ,  22 . When the suction  37  is applied, as shown in  FIG. 4 , the hot air inside the nonwoven is removed. This removal of the hot air leads to more rapid, intense cooling of the intermediate product, which results in rapid bonding of the nonwoven.  
      The result of this process is apparent from the cross section of the finished product  30  in  FIG. 5 . Due to the suction treatment at  37  in  FIG. 4 , a conformal course of the contour profile  31  is obtained, even in the critical profile regions  32 ,  33 . A molded part  30  of the highest quality is obtained.  
      In many applications of the device of the invention, it is sufficient to apply the suction effects  37  only in the area of one of the mold members, i.e., member  22 , namely, where the critical profile regions  32 ,  33  are located. However, as  FIG. 3  shows, suction channels  29  are provided in both mold members  21 ,  22  in the present case.  
      The nonwoven does not have to be realized as a preliminary product  10  with prebonded adhesion points  13 , but rather it could be directly subjected to the heat treatment between the heating plates  14 ,  15  or, alternatively, it could be subjected to the heat treatment in heated mold members  21 ,  22 . Instead of the aforementioned nonwoven, an alternative nonwoven could be formed in three layers and could consist, for example, of a bicomponent fiber, reprocessed cotton, and polypropylene in a ratio of 20:60:20 wt. %. In this connection, the nonwovens can have a weight of 200-600 g per square meter.  
      The nonwovens can be covered on both sides or on one side with moldable decorative layers or layers of plastic, which are also carried along during the suction treatment to conform to the inner contours of the mold. If possible, these cover layers should be permeable to the suction air.  
      The aforementioned suction treatment  37  in the invention occurs as soon as the two mold members  21 ,  22  are closed. A short surge of suction is sufficient here. Instead of one surge of suction, several surges of suction could be applied in succession, whose duration and suction maximum are adapted to the individual structure of the nonwoven.  
     List of Reference Numbers  
     
         
           10  preliminary product  
           11  bonding agent, bicomponent fibers  
           12  organic or mineral fibers of  10   
           13  adhesion points between  11 ,  12   
           14  first heating plate ( FIG. 2 )  
           15  second heating plate ( FIG. 2 ).  
           16  arrow showing flow of heating and softening heat from  14 ,  15  to  10  ( FIG. 2 )  
           17  suction device ( FIG. 3 )  
           18  suction lines of  17  ( FIG. 3 )  
           19  points of connection of  18  at  21 ,  22  ( FIG. 3 )  
           20  hot intermediate state of  10  ( FIG. 3 )  
           21  first mold member, male mold  
           22  second mold member, female mold  
           23  bonding points between  11 ,  12 , bonds ( FIG. 3 )  
           24  cavity between  21 ,  22   
           25  inner contour of  21  ( FIG. 3 )  
           26  inner contour of  22  ( FIG. 3 )  
           27  critical contour region on  26  ( FIG. 3 )  
           28  critical contour region on  26  ( FIG. 3 )  
           29  suction channel in  21 ,  22  ( FIG. 3 )  
           30  finished molded part, finished product ( FIG. 5 )  
           31  contour profile of  30  ( FIG. 5 )  
           32  critical profile regions of  30 , strong curvature of  31   
           33  critical profile region of  30 , sharp increase in height of  31   
           34  radius of curvature of  31  at  32   
           35  profile height at  33   
           36  control unit  
           37  arrow of air suction  
           38  air outlet at  17  ( FIG. 3 )