SE451691B - APPLICATION OF A FIBER MAT FOR MANUFACTURING BENEFITS THROUGH DRY PRESSURE AND FIBER LAYERS - Google Patents

Description

In order to remedy this problem, it is known (DE-OS 14 53 416) to lay on the fibrous mat a reinforcing fabric which can be formed by expansion, which is pressed into the fibrous layer by means of the rollers used for the pre-stabilization of the mat. Here too, the connection between the reinforcing path and the fibrous mat is loosened at the base required before the final forming, so that considerable relative movements of the individual fibers inevitably take place during the pressing process, which can lead to wear of the fibrous mat.

DE-PS 23 64 025 also discloses a fiber mat which consists of two lignocellulosic layers, between which a moldable support layer is arranged adhesive, the pre-pressed fiber mat having a plurality of regularly distributed zones with small cross-sections. In this way, the adhesion of the carrier layer is also improved during the basing so that it can better distribute tensile forces which occur during the pressing into the carpet. In addition, such a mat strand can be wound up on a roll after the pre-stabilization, thereby facilitating handling and transport.

In order to be able to produce thin-walled three-dimensionally pressed molded parts, which are required, for example, for the inner lining of passenger compartments in vehicles, a method is used (DE-PS 23 38 650), in which the fiber mat is stepwise pressed into a mold provided with several pistons which can be actuated . This stepwise pressing is necessary to prevent abrasion of the fibrous mat. In this method, the fibrous mat gradually moves elastically to the molding sites without any tearing of the fibers. This known method, used in three-dimensional forming of thin-walled molded parts, requires a special careful handling due to the sensitivity of the fibrous mat and is also time-consuming due to the pressing performed step by step in succession.

A further disadvantage of the prior art is that the fiber mats must be made of high-quality wood fiber materials if they are to still have satisfactory forming properties, especially at a necessary small wall thickness of the mold parts. A certain lower limit for the fiber length cannot be exceeded if tearing of the fiber mat is to be avoided during molding. For this reason, the use of shorter length fibers has hitherto been excluded, such fibers which, for example, occur in the reprocessing of waste materials, for example paper waste, despite the fact that these waste materials, especially when blending in longer length fibers, have satisfactory material properties per se.

The object of the invention is to eliminate the disadvantages occurring in known fiber mats and their processing methods and to provide a fiber mat which, according to the principle of tensile pressing, without stepwise pressing as hitherto in one process, can be pressed into a thin-walled molded part and with the addition of short-fiber waste materials lead to a molded part with a higher strength at reduced wall thickness.

This object is solved by the use of a fiber mat according to the preamble of the main patent claim by the features stated in its characterizing part.

Suitable embodiments of the invention according to the main claim appear from the subclaims.

The term "creping" refers to all designs of the carrier layer which, when pulled out in at least one direction, allow an increase in the surface of the carrier layer without stretching or expanding the material itself. Such designs may consist of parallel folds in the same manner as a pleat, which is suitable when a substantially groove-shaped three-dimensional shape is desired. For a shell-like formation, intersecting folds are recommended.

The term "creping" also includes, for example, annular folds or imprints and in the case of yarns also those yarns which are crimped or twisted. The advantage of the mats according to the invention consists only in the fact that the fibrous layer itself no longer comes into contact with the pressing tools. mats according to the invention during the pressing, as well as the separation properties after the pressing This clearly improves the surface properties of the finished parts. In addition, during the closing process of the tool, a thermal insulation of the fibrous layer from the tool surfaces can be achieved thereby preventing the fibrous layer from surfaces cure too early, thereby improving the strength properties of the fibrous layer.

The coverage of the fibrous layer on both sides with carrier layers increases the effective interface between fibrous layers and carrier layers. Only in this way can the repercussion of the favorable forming ratio of the carrier layers on the fibrous layer already be considerably improved. The creping according to the invention of the carrier layers thereby means an additional significant advantage. The elastically moldable carrier layers belonging to the state of the art are stretchable all the way to fracture, i.e. they cover the surface requirement necessary for the three-dimensional molding from their volume and thin out during the molding. As a result, within the framework of their elasticity, they are first optionally stretchable and the stretching or expansion is distributed uncontrolled over the entire surface.

Since local expansions in the fibrous material which are greater than the covering length of the fibers must be avoided, the interaction between the elastic support layers belonging to the state of the art and the fibrous layer means that local outgrowths of the expandable capacity of the fibrous layer can occur. This considerably limits the design possibility of fiber mats with carrier layers according to the state of the art. In contrast, creped berry layers contain the surface reserve necessary for the design in the creping itself and do not have to cover this by a loss of thickness. If the creping's surface reserve is utilized locally, the traction forces are then transferred to the adjacent area and its surface reserve is utilized. The shape and intensity of the creping can be chosen so that the local expansion capacity necessary for the design is ensured and the local expansion capacity of the carrier layer can be adapted to the covering length of the fibers.

This avoids a cold break on the fiber layer itself. In addition, the large surface of the carrier layers in the creped state has a favorable effect on the power transmission at the interface 10 between 20 25 25 25 35 451 691 5 between fiber and carrier layers. In total, a mat is thus obtained which is able to transmit tensile forces of considerable size even in the outer area during molding without local breakage on the fiber layer.

The return of the tensile pressing part during the entire carpet formation means a more uniform thickness distribution in the finished part. This gives rise to the particularly advantageous possibility of manufacturing parts whose wall thickness is clearly less than the parts manufactured so far. In the current state of the art, a thickness of a finished part of about 2 mm is considered as the lower limit of the technological possibility. With carpets according to the invention, finished parts with wall thicknesses of about 1 mm can be manufactured with satisfactory quality.

Since the surface enlargement of creped support layers during molding requires only small forces, support layers with high strength can be used for the carpets according to the invention. The press part then has a sandwich structure which consists of a medium-solid core and high-strength cover layers. The resulting improvement in the strength and rigidity of the finished parts makes it possible to manufacture finished parts with the same use properties thinner and thus more favorable from a material and cost point of view than at the hitherto known state of the art.

The coverage of the fiber mat on both sides with closed carrier layers finally reduces the risk of damage to the mats during transport and handling.

This point of view is especially important when thin-walled finished parts are sought and the fiber mats as a result have only a small thickness and thus self-stability.

Especially the risk of breakage of thin fiber mats during transport is considerably reduced by the carrier layers applied on both sides.

The advantageous possibility, if necessary, of reducing the wall thickness of finished parts through the use of the carpets according to the invention to about half, is finally described once again in its total significance. 10 15 20 25 30 35 451 691 6 In addition to the weight and material savings of 50%, the necessary total pressing time is reduced to approximately «half. The pressing time when pressing wood fiber material is essentially due to the poor thermal conductivity of this material group. A reduction in thickness means a correspondingly faster heating (in practice, fixed pressing times per mm of material are calculated). Thus, the load ratio of the investment-intensive large presses can be increased proportionally to the same degree as the number of necessary cost-intensive press tools can be reduced.

The rationalization gain that can be achieved with the carpets according to the invention is thereby considerable.

The point or line-shaped fixed connection according to the invention of the support layers with each other at preferably regular distances also improves all the properties of the carpet. In this way, areas of the fiber layer are delimited relative to each other which are only displaceable in themselves but over larger surfaces are mutually fixed.

This eliminates the risk of gradual displacements of the fiber mats during the pressing process, so that in total during the formation of the mat a more uniform material distribution is obtained. This effect is approximately comparable to the ratio of modern dotted or lined upholstery quilts, in which a uniform distribution of the filling is ensured, even when the upholstery is shaken or rolled.

A suitable further education according to the invention consists in that the creping of the carrier layer is a cross-creping. As a result, these layers obtain an improved forming ability.

It can also be beneficial if the carrier layers are perforated (for example by means of needles). The perforation makes the carrier layers gas-permeable so that the mats according to the invention can be thermally supported without difficulty, for example base. In addition, the gas permeability achieved by the perforation favorably affects the dehumidification of the carpet during the actual pressing. 10 15 20 25 30 35 451 691 7 Since the forming properties of the carrier layers no longer have to be given by the material itself but are determined by the creping, for the carpets according to the invention all crepable materials can be used as the carrier layer.

Creped fabric of artificial or natural fibers can be used as well as creped plastic foils. Support layers of creped metal foils are also possible, especially since the finished part must have great resistance to moisture.

Particularly suitable are carrier layers of creped paper, as this material can be obtained cheaply and can be easily processed.

In addition, fiber mats according to the invention can also have creped support layers at the top and bottom of the mat of different materials. This makes it possible, for example, to provide the visible side of the finished part with a carrier layer which is selected according to decorative points of view, while the carrier layer on the non-visible opposite side is chosen according to cost point of view. If a submersible carrier layer is used, it may be particularly suitable if these carrier layers contain a thermosetting, duroplastic resin. They may, for example, be pre-soaked with phenolic or melamine resins. In this way, during hot pressing, a highly refined, high-strength surface layer is formed which gives the finished part sandwich properties. This is especially advantageous when pressing thin-walled parts.

In contrast to the state of the art on which the invention is based, and in which the carrier layers used there over the entire surface are adhesively connected to the fibrous layer, it is not in any case necessary with the carpets according to the invention that the carrier layers are made adhesive over the entire surface.

Due to the point- or line-shaped fixed connection of the support layers to each other, areas arise in which the fibrous layer is sufficiently fixed between the support layers. For special design problems, such a design of the carpet may be suitable. As a rule, however, it is better to fix the carrier layers adhesively over the entire surface of the fibrous layer by means of an adhesive. 10 15 20 25 30 35 451 691 8 When adhering over the entire surface of the support layers, the force initiation conditions for the necessary forming forces are improved.

The adhesives used for this can be thermoplastic adhesives, but it is also possible to use contact adhesives or solvent adhesives. It is especially economically and technically favorable if the carrier layers are coated in advance with the adhesive used in each case.

The point or line-shaped connection according to the invention of the carrier layers with each other can in a manner known per se take place by textile aids, for example by means of a seam or a stitch. However, it is more technically favorable if the point or line connection of the carrier layers to each other takes place by gluing. In this case, the corresponding gluing of the carrier layers can be achieved with the aid of the glue, with which the adhesion of the carrier foils over the entire surface of the fibrous layer is also achieved. In terms of manufacturing technology and cost, this is the most favorable solution.

Fiber mats according to the invention are - like fiber mats belonging to the prior art - preferably provided with thermosetting adhesives and are pressed predominantly hot into molded parts.

In hot pressing, it is particularly suitable if the point or line connections of the carrier layers to each other are designed in such a way that the connection points or lines are soluble in the heat of the press. During the closure of the mold, the connection points still have the functions described so far, after intensive contact with the press surfaces during the construction of the press press, however, the connection points are loosened and allow in these local areas a material exchange so that the connection points or lines no longer mark the finished part. If the carrier layers are connected to each other by textile methods, the solubility in heat can be achieved by using thermoplastic sewing threads. In the case of adhesive joints, the bond strength in heat can be eliminated by using adhesives whose bonding force releases heat.

A particular advantage of the mats according to the invention is that their forming properties are no longer predominantly determined by the quality of the fibrous material used. For example, in the case of carpets belonging to the state of the art, it is not or only to a very limited extent possible to reuse production waste, as in the processing of the production waste the fiber length is shortened and an addition of processed production waste strongly affects the carpet's forming properties. In the carpets according to the invention, the shaping property of the carrier layers dominates. This makes it possible to completely add the production waste to the processed berry layers during food production and thus achieve a cost-effective and raw material-saving waste-free production.

The middle layers of the carpets are pre-stabilized but have in the initial state a clearly smaller density than in the pressed state. The deformability of these middle layers is improved before pressing by thermal digestion, for example basing, their moisture content must, if they are to be sufficiently malleable, amount to more than 10%. This is a press technique insofar as a disadvantage is that the dehumidification during the hot pre-pressing requires additional pressing time.

The moisture content during pressing can lead to the formation of steam bubbles, especially when steam-permeable support layers are used. Even the perforation of the support layers, which is proposed in the above application to obviate this disadvantage, does not completely eliminate the danger of vapor blistering as the proportion of perforation at the total surface of the support layers is naturally small. The formation of steam blisters either leads to a high waste ratio or requires a correspondingly complicated pressing technique to be eliminated (intermediate unloading gave the press during the pressing of the finished part). Both burden the entire procedure's finances.

A suitable further training according to the invention therefore lies in the fact that the density of the pre-stabilized middle layer before pressing is substantially corresponding to its density in the finished part and that the moisture content in this middle layer is less than 10%.

The lower moisture content first has the advantage that the pressing time can be further shortened and that steam bubbles no longer appear in the pressing part. Because the density of the pre-stabilized middle layer already substantially corresponds to the density of the finished part, the tendency of this layer to absorb moisture uncontrolled during intermediate storage is also small, so that its preconditioning can be maintained over a longer period. Further advantages arise from the fact that carpets with such strongly densified middle layers are less voluminous and thereby require less storage space and from the fact that their handling and transport stability is considerably improved relative to hitherto known carpets.

The middle layers of carpets according to the invention must still be well mouldable even in the corresponding highly densified state. This usually requires further action. For example, an advantageous embodiment of such mats consists in that the middle layer consists of at least one layer of creped paper or cardboard soaked in thermoplastic or duroplastic adhesives. In the case of creped paper, cardboard, fabric or folds, its entire surface is uniformly finely pleated. Such formations also have a total area which amounts to several times that which corresponds to the external dimension of the corresponding paths. They can therefore cover the surface enlargement of the "surface stock" of folding (creping) necessary for the production of the three-dimensional shape. In the case of a suitable shape on the creases of the crepe (cross-creep, in which the corresponding web is folded in two mutually perpendicular directions), the corresponding material has a large deformation ability in all existing spatial directions, the surface enlargement being possible by smoothing the creases without subjecting greater forming resulting tensile loads. The creping of the middle layer consequently enables its necessary deformation, f. Q; 10 15 20 25 30 35 451 691 ll creped paper, which already has its final density, can be prefabricated and soaked without problems. In addition to the cellulose fibers, they can also contain powdered fillers. Even middle layers with textile construction can be used to realize carpets according to the invention. For example, it is possible for the middle layer to consist of at least one layer of creped fabric or fold, which is soaked with dyroplastic or thermoplastic adhesives. Even in this case, the necessary deformation ability of the middle layer is obtained in that the per se only unsatisfactorily formable fabric or folds is creped. If the middle layer in carpets according to the invention is of a material which is sufficiently malleable, there are particularly favorable conditions. This is the case, for example, when the middle layer is a thermoplastic plastic, preferably filled with cellulose or lignocellulosic material, and / or reinforced. Such a mat can be thermoformed without further action. For molded parts which in later use are exposed to thermal loads, special advantages arise when the creped support layers consist of metal. This improves the dimensional stability of the part in heat as well as reduces heat absorption through the favorable back-radiation conditions of the carrier layer.

Creped, binder-soaked paper, cardboard, fabric or folds proposed as a middle layer material for carpets according to the invention are only crepable in limited thickness. When further developing the inventive idea v, it is therefore advantageous to use a middle layer which consists of a layer joint of one or more materials of the type described. The connection between the individual layers of the middle layer can then take place by sewing, stitching or needling.

This can be especially advantageous as the individual layers consist of paper, cardboard, fabric or folds.

If textile bonding methods are used, it is suitable that the bonding threads consist of thermoplastic which is well moldable in hot pressing. Another suitable possibility of forming the core layer as a layer dressing consists in that the layer dressing is produced by means of glue which softens in heat. In this method, the advantage is that middle layers of any thickness are built up of individual layers with good formability, the interconnection of which becomes flexible during hot pressing so that the deformation properties of the individual layers can be fully utilized.

As a result of the fact that the materials can be combined almost optionally in this layer joint, an additional adaptation clearance arises for the properties of the press part.

At the state of the art, the middle layer according to the invention can today be wholly or partly made of recycled material. The creped paper or paperboard in the middle layers can be, for example, recycled paper or cardboard, the quality of which is not sufficient for other uses. The same applies to fabrics or skins of man-made and / or natural fibers. In both cases, pre-products for the manufacture of carpets according to the invention can be provided by the associated industry. Even the middle layer of filled and / or reinforced thermoplastics can be produced from thermoplastic waste with little value, which occurs, for example, in the form of coated paper waste and waste from the cable industry and which cannot be utilized in any other way. Color differences and impurities do not play a significant role in the use according to the invention, insufficient mechanical strength properties which may occur, for example in the use of mixed waste, can be compensated by suitable choice of carrier layer.

The carpets according to the invention are produced in connection with the prior art.

The middle layer is applied to the lower carrier layer serving as a conveyor belt, whereupon the upper carrier layer is supplied from a supply roll and the joint formed by the carrier layers and the middle layer is passed between the pair of rollers serving for stabilization and connected to each other. To achieve a stick perforation can be used. 451 691 13 with pairs of rollers provided with corresponding needles, the needles of which at least penetrate a carrier layer and partially penetrate into the middle layer.

Claims (3)

451 691 10 15 20 14 PATENT REQUIREMENTS 1. l. Use of a fibrous mat with several layers, consisting of a fibrous layer, which at its two surfaces each has a creped cover foil and which cover foils are connected to each other in a point-by-point or linear manner by means of, for example, sewing, for production of molded parts by dry pressing, characterized in that the shape and intensity of the cover foil creping and the overlapping length of the fibers in the fibrous layer are so adapted to each other that in local stretching within the stretching possibility of the creping the fiber layer is not inadvertently thinned or weakened. Fiber layer for use according to claim 1, in which the point or line connection of the cover foils is achieved without the use of adhesives and / or fibers, characterized in that the adhesive and / or the fibers consist of one so under the pressing conditions relation material, that the connection is dissolved during the pressing process for the production of the molded part. Fiber layer for use according to claim 1, characterized in that the creping of the cover foils consists of intersecting creping folds.