EP0152837B1 - Method and apparatus for making fibre sheets for use as preforms for pressed articles - Google Patents

Abstract

1. Process for producing fibrous mats as a starting material for mouldings, in that shredded waste materials are mixed with thermoplastic and/or duroplastic binders, the mixture is strewn to a fleece on an air-permeable conveyor belt and under elevated temperature and under pressure the fleece is compressed to a transportable mat from which individual mouldings are produced by moulding at temperatures between 180 and 220 degrees C, characterized in that under the constant action of vacuum to the underside of the conveyor belt on a first fleece layer is loosely placed a polyester fabric or lattice with at least partly multifilament threads, a mesh width between 4 and 7 mm and with a heat-activatable, duroplastic finish with an affinity for the binder of the fibres, then a second fleece layer is strewn on the fabric or lattice and then the layers are compressed to a mat, the polyester fabric being thermally conditioned prior to its use at temperatures roughly corresponding to the moulding temperature during the production of mouldings.

Description

The invention relates to a process for the production of fiber mats as the starting material for molded parts, by mixing shredded waste materials with thermoplastic and / or thermosetting binders, spreading the mixture onto an air-permeable conveyor belt to form a nonwoven, and compressing the nonwoven at elevated temperature under pressure to form a transportable mat from which individual molded parts are produced by pressing at temperatures between 180 and 220 ° C.

In a known method of this type (DE-PS 28 45 112), the endlessly produced mat is separated into individual blanks after compression, which are dimensioned according to the molded part to be produced therefrom. The processing of these blanks into molded parts is particularly difficult if these molded parts have deep formations, since the starting material cannot absorb tensile forces, so that thinning and thus tearing of the material can occur during pressing due to combined tensile and shear forces. This also applies to other known mats that are not made from shredded waste materials, but instead, for example, from cellulose or lignocellulosic fibers.

In order to be able to produce complicated and deeply shaped molded parts from such mat blanks, one has to use further aids during the pressing process, namely a stabilizing base on which the mat is placed during the pressing process and a stabilizing pad which is arranged above the mat blank. So far, two approaches have essentially been followed, namely either designing both stabilizing layers to be elastic to rubber-elastic (DE-AS 27 01 480 and 27 59 279) or using a largely stretch-free material (DE-AS 27 13 527). The stabilization layers have the task in both cases. to enclose the mat blank between them and to carry them into the deep contours of the lower tool during the pressing process, so to ensure that the material is properly retightened. In the first case, the elastic stabilizing layers are stretched elastically during the pressing process, with at least the immediately adjacent layers of the mat blank being carried along due to frictional forces. This means that thinning and cracking can still occur here. In the second case of the largely stretch-free stabilization layers, a kind of sandwich package is deliberately created from the two layers and the mat cut in between, the mat being clamped between the stabilization layers during the pressing process and following the movement of the stabilization layers due to its tissue-like surface structure. In both cases, especially in the case of pressing operations with large strokes, it has been proposed to suspend the upper stabilizing layer elastically in order to be able to accommodate at least the idle stroke of the upper die of the press without the stabilizing layer already being stretched (e.g. DE-PS 30 01 750). In general, the pressing must also be carried out in two stages, in that in the first stage, in which the aforementioned stabilizing layers are used, a preform is produced which has the approximate contour with a generally larger wall thickness. In a second stage, the preform is then pressed into its final shape.

These measures, which are absolutely necessary in the case of complicated molded parts, naturally result in a complex system design with a preform press and a press for final deformation. In the case of extremely difficult press-molded parts, at least one of the preforming tools - usually the upper tool - has to be broken down into a large number of individual stamps in order to shape different parts of the mat blank one after the other, thereby ensuring an always perfect, i.e. H. To enable largely tension-free retightening of the mat blank (DE-AS 23 38 650). In addition, the stabilizing layers wear out over time, i. H. are permanently deformed, so that they have to be replaced in relatively short intervals of one to two weeks, which increases the cost of equipment accordingly.

The invention is based on the object of proposing a method and a system for carrying it out, with the aid of which mats can be produced which can be formed in one work step into molded parts of any shape without the aid of stabilizing layers.

On the basis of the method mentioned at the outset, this problem is solved in terms of process technology in that, under the constant action of negative pressure on the underside of the conveyor belt on a first nonwoven layer, a polyester fabric or grid with at least partially multifilament threads, a mesh size between 4 and 7 mm and a thermosetting type of equipment that is affine to the binding agent of the fibers, heat-releasable, loosely deposited, then a second non-woven layer is sprinkled on the fabric or grid, and then the layers are compressed to a mat, the polyester fabric or grid being used at temperatures such as, correspond to the pressing temperature in the production of molded parts, is annealed.

It is well known in the manufacture of mats and plates from chip or fiber material to provide tensile intermediate layers, for which threads, fabrics, foils etc. have been proposed in detail. However, these intermediate layers are used exclusively for the To improve the strength values of the mat or plate. In contrast, this measure has so far not succeeded in making the stabilizing layers for the forming process superfluous for the starting material mentioned at the beginning. For this reason, the aforementioned fiber materials, insofar as they are used for the production of molded parts, are formed exclusively with stabilizing layers. With the training according to the invention, this is no longer necessary. This goal is achieved by the method steps according to the invention through the following interaction:

The choice of polyester fabric is initially due to cost reasons, since other fabrics with comparable physical and chemical properties are more expensive. Also of particular importance are its well-known high tensile strength and, above all, its temperature resistance, even at the pressing temperatures between 180 and 220 ° C required here. The melting point of polyester fabric is above 220 ° C, where it still has the positive property that its tensile strength only decreases slightly in the higher temperature range. A disadvantage of polyester fabrics, like almost all other plastic fabrics, is the fact that it exhibits considerable thermal expansion, which, however, is reversible up to high temperatures. However, this would be disadvantageous for the method according to the invention, since the restoring forces in the manufacture of the mat after its heating and compaction would lead to material shifts within the mat, which would loosen the existing bond. The same effect would occur when the mat was formed into the press-molded part, so that tensions remain within the molded part. In both cases, this easily leads to delamination, rendering the mat or molded part unusable. This disadvantage is remedied by the further measure according to the invention in that the polyester fabric is annealed at temperatures which correspond approximately to the pressing temperature. Annealing can take place before or after finishing. As a result, the polyester fabric largely loses its original thermal expansion, with the result that it only comparatively little expands when the fleece is heated before the mat is produced, as well as when the press-molded part is produced, so that the mat or press-molded part are largely free of tension and shrinkage.

The finishing of the polyester fabric must be heat-activatable in order to at least superficially melt on the warming up of the nonwoven prior to compaction to form a mat and in this way bind the fibers of the lower and upper nonwoven layer. However, the equipment should be selected so that it can still be reactivated sufficiently after the mat has been manufactured, in order to finally fully harden during the pressing process and to fulfill its function as a supporting binder. In addition, as is known per se, the equipment serves to make the fabric resistant to sliding, so that the individual threads cannot move against one another during all processing operations and the diagonal distortion of the fabric is also minimized.

The further measure according to the invention acts in the same direction, according to which at least a portion of multifilament threads are present within the polyester fabric. On the one hand, these ensure better adhesion of the thermosetting finish, on the other hand, they impart a better bond to the neighboring fibers of the upper and lower nonwoven layer. Moreover, they facilitate - what will be discussed later - the recycling of the waste resulting from forming by trimming, which can then be more easily shredded again and can be used for the production of nonwovens.

The mesh size of 4 to 7 mm provided according to the invention ensures that fiber and binder can be exchanged between the two nonwoven layers. This is further promoted on the basis of the manufacture of the mat by applying negative pressure to the underside of the conveyor belt during the entire nonwoven manufacture. This negative pressure initially ensures that the lower nonwoven layer, after passing through a leveling device known per se, maintains a constant thickness and cannot spring open or not significantly. The fabric is then placed loosely, which essentially means that the deposit must be tension-free in order to avoid the input of forces here too. This fabric is also sucked onto the lower nonwoven layer by the negative pressure, so that it cannot deform or shift after being deposited. The same effect then occurs when the second layer of fleece is sprinkled on. Here, however, the fibers of the upper nonwoven layer are additionally drawn to the lower nonwoven layer by the relatively wide-meshed lattice structure of the fabric due to the negative pressure, so that a bond, even if still loose, is created between the two layers. When the fleece is subsequently heated, the binders are activated and the fibers are bound at least on the surface. The bond is then further improved during the final compaction to the mat. Compared to the known methods, the mat has a significantly better transport and handling strength.

Practical tests have shown that a mat produced in this way or blanks obtained therefrom can be processed into molded parts of any contour without the use of preforming tools and without separate stabilizing layers. The enormous cost and labor savings are obvious. In addition, the method according to the invention enables an increase in performance of up to 30%. In addition, the final strength of the molded part is improved, which is also due to the heat stability of the polyester fabric even at higher temperatures temperatures is not reduced. Due to the higher strength, the material density of the molded part and thus its wall thickness can be reduced. This is particularly important when using such molded parts for the interior of motor vehicles, since this can save weight. A mat produced according to the invention can be formed in one step in a heated press in the case of simpler molded parts without preheating. Dry preheating will have to be provided for more complicated molded parts. Finally, as already indicated, the waste resulting from trimming by trimming can easily be returned to the nonwoven production.

According to an advantageous exemplary embodiment, the cross section of at least some of the threads of the fabric or grid parallel to the plane of the nonwoven has a greater extent than perpendicular to it. For example, these threads can be band-like or oval in cross-section. If not all threads, for example in the warp or in the weft, have this cross-section, they will be provided at least in the central areas of the mat, where generally the greatest deformations occur during pressing. The cross-sectional shape has the advantage that the threads do not cut into the material during forming. .

The fabric or mesh is preferably made of phenol, phenol-resorcinol, melamine resins or styrene-butadiene latex with reactive carboxyl groups (SBR), which can be modified by the aforementioned resins and other additives. These resins or latices have the advantage that they can be heat-activated several times under certain circumstances. Otherwise they can also be used in the same form as a binder or as part of a binder system for fibers of different origins. The equipment forms a firm bond with the thermoplastic components within the fiber material or the binder under the influence of heat. As a result, the fabric or grid is firmly integrated within the mat. The aforementioned selection of materials for the equipment is also important with regard to the recycling of the waste generated during trimming. The shredded waste that is returned to the nonwoven production must not contain any components that - if they come to rest on the surface of the nonwoven - show an adhesive effect on the metal surfaces of the pressing tools. This condition is met not only by the polyester of the fabric or grid, but also by the aforementioned materials for the equipment.

In a further advantageous embodiment it is provided that the mat is wound into rolls after compaction and is processed from the roll on the occasion of the production of the press-molded parts by the transport forces directly on the mat or on the resulting after trimming of each molded part, via the remaining fabric or grate in the related waste strips.

Although it has already been proposed (DE-AS 23 65 895) to equip a wood fiber mat in the central region with a highly elastic carrier layer and to press a large number of regularly distributed zones of reduced cross-section into the mat, so that a type of honeycomb material is produced. The edge of this mat is also to be equipped with drawstrings in order to be able to wind it and the remaining waste strips on drums. A highly elastic backing layer is not able to achieve the goal set according to the invention because it is not thermally stable enough. For the rest, any kind of tensile stress on the fabric leads to relative movements with respect to the fiber layers, so that existing bonds between the materials are torn open again or shear stresses occur within the molded part. The use of different materials for the carrier layer and the drawstrings also entails a corresponding outlay for storing and incorporating the materials into the fleece. Finally, the honeycomb structure leads to irregularities in the surface and the density of the molded parts. All these disadvantages do not occur in the method according to the invention, so that mats of this type can be processed from the roll for the first time.

As already indicated, in the method according to the invention the waste strips resulting from the production of individual blanks as well as from trimming the molded parts can be shredded and added to the shredded waste materials before the nonwoven is formed.

To carry out the method, the invention is based on a known system (DE-PS 28 45112) which has a scattering device which discharges the mixture of shredded waste materials and binders onto an air-permeable conveyor belt, a suction device arranged below the conveyor belt, and a downstream device for leveling the fleece , has a device arranged behind it and above the conveyor belt for passing hot air through the fleece and then pressure rollers acting on the fleece.

This system is modified in accordance with the invention in such a way that a feed device for loosely depositing the polyester fabric or grid is arranged behind the leveling device, a second spreading device for applying the second fleece layer behind it and a further leveling device behind it. wherein the suction device or a plurality of suction devices extend from the first scattering device to the hot air device.

With this system, the requirement already indicated above is met, during the entire production of the nonwoven, to ensure a mechanical bond between the individual layers by the negative pressure acting on the nonwoven. The loose storage of the fabric or grid leaves can be achieved by synchronizing control of the conveyor belt and fabric spool.

If one does not work with individual blanks, according to a further embodiment, a winding device for rolling up the mat can be arranged behind the pressure rollers.

The invention is explained below using exemplary embodiments of the system and using the drawing.

• Figur 1, 2 eine schematische Seitenansicht der Anlage zur Mattenherstellung ;
• Figur 3 eine schematische Seitenansicht der Anlage zur Herstellung von Preßformteilen von einer Mattenrolle und
• Figur 4 eine Alternative zur Herstellung von Matten-Zuschnitten.

The drawing shows:

• Figure 1, 2 is a schematic side view of the plant for mat production;
• Figure 3 is a schematic side view of the plant for the production of molded parts from a mat roll and
• Figure 4 shows an alternative to the production of mat blanks.

The system initially has a conveyor belt 1, which is permeable to air, for. B. is formed from a fabric or grid. Above the inlet of the conveyor belt 1 into the system, a first scattering device 2 is arranged, which picks up a fiber material and delivers a head 3 via a scattering device onto the conveyor belt to form a first fleece layer 4. Behind the spreading device is a milling-like leveling device 5, which brings the fleece layer 4 to a uniform thickness.

In the conveying direction behind the leveling device 5 there is a feed device, designated overall by 6, for placing an endless polyester fabric or grid 7 on the first nonwoven layer 4. The fabric or grid 7 is located on a supply spool, from which it is drawn off by means of pull rollers 9 becomes. The fabric or grid runs over guide rollers 10 and a tensioning roller 11. The drive of the drawing rollers 9 is adjusted in relation to the speed of the conveyor belt 1 so that the fabric or mesh falls loosely in the area 12 below the drawing rollers 9, so that it is placed on the first nonwoven layer 4 without force. In the area 12 there is also a scanning device 13 which shuts down parts of the system if there is no tissue or grid in the area of the scanning device, for example the coil 8 is empty. A further scattering device 14 is arranged behind the fabric deposit, which in turn picks up fibers and releases them via a scattering head 15 to form a uniform second fleece layer 16. A milling-type leveling device 17 is again arranged behind the spreading device 14.

As can also be seen in FIG. 1, a suction device 18 is arranged below the entire conveyor belt 1, at least up to the second leveling device 17, which in the exemplary embodiment shown consists of two suction boxes 19 and 20. This suction device ensures a firm support of the first nonwoven layer on the conveyor belt 1, for maintaining the nonwoven thickness, for sucking the fabric or grid 7 onto the first nonwoven layer and finally for the second nonwoven layer 16 to adhere to the grid or fabric 7 and the first nonwoven layer 4.

Finally, the mat (see FIG. 2) reaches a belt scale 21 which measures the specific surface load and controls the second leveling device 17, possibly also the first leveling device 5, according to the desired value.

The final nonwoven 22 finally reaches a hot air device 23, by means of which hot air is pushed or sucked through the nonwoven to activate the binders. A pre-press roll 24 and a press calender 25 are arranged behind the hot air device 23, which reduce the fleece to the desired final thickness. The fleece 22 leaves the press calender 25 as a mat 26, which is moved by means of transport rollers 27 through a cooling station 28. Behind the transport rollers 27 there is a trimming device 29 which equalizes the longitudinal edges of the mat 26. The resulting edge strips can be comminuted by means of a cutting mill 30 and then bunkered at 31. The material can be withdrawn from the waste bunker 31 as required by the central comminution mill 32, which is used to produce the fibrous material fed to the spreading devices 2 and 14.

The trimmed mat 27 prepared for further processing can then be wound up into a roll or a wrap or, as FIG. 4 shows, broken down into individual blanks. For this purpose, the mat 27 runs on a cutting table 33 with a cross cutter 34. Simultaneously or previously, the mat 27 has been cut in the longitudinal direction, so that two cuts 35 are formed behind the cross cutter 34, which are pivoted onto lateral stacks 37 by means of swiveling suction lifters 36 be filed. FIG. 4 also shows the alternative with dash-dotted lines in which the mat 27 is wound up into a roll 38.

FIG. 3 shows a schematic view of an embodiment for the production of press-molded parts from a mat 27 wound into a roll 38. The system has, as an essential component, a molding press 39 with a heated upper tool 40 and a heated lower tool 41. In the embodiment shown, the press stroke is carried out by the upper tool 40. A heating furnace 42 is arranged in front of the molding press 39 and there is a separating device 43 behind the molding press 39 and a winding device 44 behind it.

The mat roll 38 is mounted on a spool 45 in front of the heating furnace 42. The mat 27 is withdrawn from the roll 38 in cycles by means of the winding device 44. It first passes through the heating furnace 42 for activating the binding agents and arrives in the molding press 39 in the next working cycle. The molding tools 40, 41 are closed, so that a molded part is formed in the mat, which due to its still existing integration into the surrounding mat material is next Work cycle arrives in the separating device 43. There, the molded part 46 is separated from the mat by a punching process and guided away to the side, while the remaining mat is by means of the winding device device 44 is in turn wound up into a roll. As already described for the edge strips with reference to FIG. 2, this material can be fed to a comminution device and then to the plant for the production of fibrous material.

Claims (7)

1. Process for producing fibrous mats as a starting material for mouldings, in that shredded waste materials are mixed with thermoplastic and/or duroplastic binders, the mixture is strewn to a fleece on an air-permeable conveyor belt and under elevated temperature and under pressure the fleece is compressed to a transportable mat from which individual mouldings are produced by moulding at temperatures between 180 and 220 °C, characterized in that under the constant action of vacuum to the underside of the conveyor belt on a first fleece layer is loosely placed a polyester fabric or lattice with at least partly multifilament threads, a mesh width between 4 and 7 mm and with a heat-activatable, duroplastic finish with an affinity for the binder of the fibres, then a second fleece layer is strewn on the fabric or lattice and then the layers are compressed to a mat, the polyester fabric being thermally conditioned prior to its use at temperatures roughly corresponding to the moulding temperature during the production of mouldings.

2. Process according to claim 1, characterized in that the cross-section of at least part of the threads of the lattice or fabric has a greater extension parallel to the plane of the fleece than at right angles thereto.

3. Process according to claims 1 or 2, characterized in that the finish of the fabric or lattic comprises phenolic, phenol-resorcinol-melamine resins or modified SBR latexes (styrenebutadiene latex with reactive carboxyl groups).

4. Process according to one of the claims 1 to 3, characterized in that, following compression, the mat is wound into rolls and is processed from the roll in connection with the production of the mouldings, in that the transporting forces act directly on the mat or on the waste strips obtained after trimming each moulding and linked via the remaining fabric or lattice.

5. Process according to claim 4, characterized in that the waste strips are shredded and added again to the shredded waste materials prior to fleece formation.

6. Plant for performing the process according to one of the claims 1 to 5 with a control mechanism discharging the mixture of shredded waste materials and binders onto an air-permeable conveyor belt, a suction mechanism positioned below the conveyor belt, a device for levelling the fleece connected downstream of the control mechanism, a device for passing hot air through the fleece positioned behind and above the conveyor belt and pressure rollers acting on the fleece, characterized in that behind the levelling device (5) is provided a supply device (6) for loosely applying a polyester fabric or lattice (7), behind it a second strewing device (14) for applying a second fleece layer (16) and behind it a further levelling device (17), the suction mechanism (18) or several suction mechanisms (19. 20) extending from the first strewing device (2) into the vicinity of the hot air device (23).

7. Plant according to claim 6, characterized in that a winding mechanism for rolling up the mat (27) is positioned behind the pressure rollers (24, 25).

Images