GB2063155A

GB2063155A - A fibre mat for producing mouldings

Info

Publication number: GB2063155A
Application number: GB8033890A
Authority: GB
Original assignee: Lignotock Verfahrenstechnik GmbH
Current assignee: Lignotock Verfahrenstechnik GmbH
Priority date: 1979-11-12
Filing date: 1980-10-21
Publication date: 1981-06-03
Also published as: NL8005799A; ES488731A1; IT8047944A0; IT1126949B; GB2063155B; FR2469498A1; BR8007345A; CA1164779A; AT379106B; SE8007189L; ATA509080A; SE451691B

Abstract

A fibre mat for the production of three-dimensionally moulded mouldings, for example for use as the internal lining of a motor vehicle by means of a dry process, comprises a prestrengthened layer and deformable supporting layers with which the prestrengthened layer is joined. The prestrengthened layer contains cellulose or lignocellulose fibres and is arranged as the central layer between two supporting layers. The supporting layers comprise creped, low-extension or extension- proof foil materials such as paper, plastic, metal, fabric and the like joined to the central layer surfaces whilst maintaining the pulling out properties of the creping.

Description

SPECIFICATION Afibre mat for producing mouldings The invention relates to a fibre mat for producing a three-dimensionally, moulded moulding by the dry process.

It is known to produce three-dimensionally moulded mouldings from lignocellulose fibrous materials by loosely sprinkling onto an endless conveyor belt the fibres wetted with small binder quantities, levelling the height of the fibre layer applied by a pairing roller and subsequently prestrengthening the fibre layer between pairs of rollers. This leads to a sheet-like endless extrudate which can be cut into individual sheets from which flat blanks are produced following intermediate transport. Following vapour coating of the blanks, they are placed in a compression mould and are moulded into the final moulded articles, accompanied by the curing of the binder (DAS 1,224,949). The individual sheets cut in this way initially have a low deformability and limited breaking strength.Following the vapour coating necessary for increasing the deformability for producing the three-dimensionally moulded moulding articles, the sheets no longer have a significant internal cohesion and must therefore be very carefully treated and transported. Due to their limited fibre cohesion in the steam-treated state, they can only be further shaped to a limited extent without there being thinning of the material areas tensile stressed during moulding, with the loss of fibre cohesion and the tearing of the mat.

To obviate this problem, it is known (DOS 1,453,416) to apply to the fibre mat a reinforcing fabric which can be deformed by stretching and which is pressed into the fibre layer by the rollers used for prestrengthening the mat. Here again, the bond between the reinforcing fabric and the fibre mat is largely lost through the vapourtreatment necessary prior to the final shaping. Thus, during the moulding process necessarily considerable relative movements occur between the individual fibres, which can bring about the tearing of the fibre mat.

German Patent 2,364,025 also discloses a fibre mat comprising two lignocellulose fibrous layers between which is placed in firmly adhering manner a supporting layer. The pre-moulded fibre mat has a plurality of regularly distributed zones of limited cross-section. This improves the adhesion of the supporting layer during vapour treatment, so that the tensile stresses occurring during moulding can be better distributed in the mat. In addition, such a mat extrudate can be wound onto a reel following prestrengthening, which facilitates handling and transportation.

In order to permit the manufacture of particularly thin-walled, three-dimensionally moulded mouldings, such as are for example required for the internal lining of motor vehicle interiors, a process is used (German Patent 2,338,650) in which the fibre mat is gradually moulded in a mould equipped with a plurality of force plugs which can be operated in time sequence. This gradual moulding is necessary to prevent tearing of the fibre mat. In this process, the fibre mat is gradually fed to the deformation points without there being any tearing of the fibres.

This known process used in the three-dimensional shaping ofthin-walled mouldings requires especially careful application due to the sensitivity of the fibre mats and also requires a large amount of time due to the gradual, successive moulding.

A further disadvantage of the known process is that the fibre mats must be made from top-quality wood fibre materials if they are to have satisfactory deformation characteristics, particularly in connection with the necessary small wall thickness of the mouldings. It is impossible to pass below a lower fibre length limit if the tearing of the fibre mat is to be avoided during deformation. It is therefore impossible to use shorter fibres, such as are for example obtained in the preparation of waste materials, for example waste paper, although said waste materials have completely satisfactory material characteristics, particularly in the case of the admixture of longer length fibres.

The problem of the invention is to obviate the disadvantages inherent in the known fibre mats and their processing processes in such a way that a fibre mat is obtained which, in the manner of a deep drawing process, can be immediately moulded to a thin-walled moulding the hitherto necessary gradual moulding procedure. Furthermore, through the addition of short-fibre waste material a higher strength, smaller wall thickness moulded article can be obtained.

In the case of a fibre mat according to the preamble of the main claim,this problem can be solved by the characterizing features thereof.

Advantageous further developments of the invention according to the main claim can be gathered from the subclaims.

The term "creping" is understood to mean all shaping processes to the supporting layer which increase the surface area thereof without stretching or extending the actual material when it is pulled out in at least one direction. Such shapes can be in the form of parallel folds such as pleats and this is advantageous if a substantially groove-like, threedimensional shaping is desired. In the case of cup-shaped shaping crossing folds are recommended. The term "creping" also covers, for example, circular folds or impressions and in the case of fabrics those yarns which are crimped or overtwisted.

The advantage of the mats according to the invention is initially that the fibre layer no longer comes into contact with the mould members. Thus, the sliding characteristics of the mats according to the invention during moulding are improved in the same way as the separation characteristics after moulding. This improves the surface properties of the finished parts. In addition, during the mould closing process, the fibrous layer can be thermally insulated from the mould surfaces, so that there is no premature curing of the fibrous layer surfaces.

This improves the strength characteristics of the fibrous layer.

The two-sided covering of the fibrous layer with supporting layers increases the effective interface between the fibrous layer and the supporting layer.

This in itself considerably improves the reaction of the favourable deformation behaviour of the supporting layers on the fibrous layer. An additional important advantage is provided in this connection by the creping of the supporting layers according to the invention. The prior art, elastically deformable supporting layers, can be extended up to failure, i.e.

they cover the surface requirement necessary for three-dimensional deformation and become thin during deformation. Within the scope of their elasticity, they are initially randomly extensible, the extension being distributed in an uncontrolled manner over the entire surface area. Since it is necessary to avoid in the fibrous material local extensions which are greater than the covering or overlapping length of the fibres, the cooperation between the prior art elastic supporting layers and the fibrous layer means that locally the extensibility of the fibrous layer can be exhausted. This considerably reduces the possibility of shaping fibre mats with supporting layers according to the prior art. As opposed to this, creped supporting layers have the surface reserve necessary for shaping within the actual creping and need not cover it by a thickness loss.If the surface reserve of the creping is locally used up, tensile stresses are subsequently transferred into the adjacent areas and their surface reserve is also utilized. The shape and intensity of the creping can be selected in the way that the local extensibility necessary for shaping is ensured and the local extensibility of the supporting layer can be adapted to the covering length of the fibres.

This prevents a local failure of the fibrous layer.

The large surface area of the supporting layers in the creped state also aids the force transfer to the interface between the fibrous layer and the supporting layer. Thus, a mat is formed which is able during deformation to transfer significant tensile stresses, even in the outer area, without the local failure of the fibrous layer.

The reduction of the stretching proportion in the overall mat deformation means a more uniform thickness distribution in the finished article. This gives the particularly advantageous possibility of producing members, whose wall thickness is much less than that of the hitherto produced members. In the prior art, a finished article thickness of approximately 2mm is considered to be the lowerlimit of what is technically possible. By means of the mats according to the invention, it is possible to produce finished products with a satisfactory quality and wall thicknesses of only approximately 1 mm.

As the increase in the surface of creped supporting layers only requires limited forces during moulding, it is possible to use higher strength supporting layers for the mats according to the invention. The moulded article then has a sandwich structure comprising a medium-strength core and highstrength covering layers. The resulting improvement to the strength and rigidity of the finished products makes it possible to produce the latter with thinner walls and therefore more advantageously from the material and cost standpoint than in the prior art, whilst providing the same use characteristics.

The two-sided covering of the fibre mat with closed supporting layers also reduces the risk of damage to the mats during transportation and handling.

This is particularly important if thin-walled finished articles are sought, so that the fibre mats have only a limited thickness and consequently limited inherent stability. The two-sided supporting layer in particular considerably reduces the fracture risk of thin fibre mats during transportation.

The advantageous possibility of reducing by about a half the wall thickness of the finished articles through the use of the mats according to the invention will now be described again in general terms.

Quite apart from the weight and material saving of 50% the necessary overall moulding time is reduced to approximately half. The moulding time when moulding wood fibre materials is mainly due to the inadequate thermal conductivity of this material group. Athickness reduction means a correspondingly faster thorough heating (in practice this means fixed moulding times/millimetre of material). This makes it possible to increase the utilization rate of the investment-intensive large compression presses and can be increased in the same proportion as the number of necessary cost-intensive moulds can be reduced. Thus, considerable rationalization can be obtained with the mats according to the invention.

The punctiform or linear, fixed joining of the supporting layers to one another at preferably regular intervals in accordance with the invention additionally improves the overall characteristics of the mat. This brings about a reciprocal limitation of the fibrous layer areas, which can only be internally displaced but are reciprocally fixed on a larger area basis. This obviates the risk of larger areas displacements of the fibrous mats during the moulding process, so that during the deformation of the mat a more uniform material distribution is achieved. This effect is roughly comparable with the behaviour of modern punctiform or linear quilted eiderdowns where a uniform distribution of the filling is still ensured if the eiderdown is shook or rolled up.

According to an advantageous further development of the invention, the supporting layer creping is a cross-creping. This leads to an improved deformability of these layers.

It may also be advantageous if the supporting layers are perforated (e.g. by needling). The perfora-tion makes the supporting layers gas-permeable, so that the mats according to the invention can easily be thermally treated, e.g. with steam. The gas permeability resulting from the perforation also aids the extraction of moisture from the mat during moulding.

As the deformation characteristics of the supporting layers need no longer be provided by the actual material and instead result from the creping, all crepable materials can be used for the supporting layers for the mats according to the invention.

Creped fabric made from natural or synthetic fibres can be used in the same way as creped plastic foils. Supporting layers of creped metal foils are also possible, particularly if the finished article must have a maximum resistance to moisture action. Supporting layers made from creped paper can be used with particular advantage, because this material can be inexpensively obtained and is easily processed.

Fibre mats according to the invention can also have creped supporting layers made from different materials on the top and bottom of the mat. This makes it possible, e.g. to provide the visible side of the finished article with a supporting layer selected on the basis of decorative standpoints, whilst the supporting layer used on the side which is not visible is selected only on the basis of cost standpoints.

If impregnatable supporting layers are used it can be particularly advantageous for them to contain a thermoseffing, duroplastic resin. Also they can, for example, be preimpregnated with phenolic or melamine resins. Thus, during hot moulding, a high finish, high-strength surface layer is obtained giving the finished article sandwich characteristics. This is particularly advantageous when moulding thinwalled articles.

Unlike in the prior art used as a basis for the invention and where the supporting layers used firmly adhere by their entire surface area to the fibrous layer, it is not always necessary with the mats according to the invention for there to be a whole-area, firm adherence with the supporting layers.

As a result of the punctiform or linear interconnection of the supporting layers, areas are formed in which the fibrous layer is adequately fixed between the supporting layers. For special shaping problems, such a mat construction can be advantageous.

However, it is generally preferable to fix the entire surface area of the supporting layers to the fibrous layers by means of an adhesive. This improves the force initiation conditions for the necessary reshaping forces.

The adhesive used for this purpose can be adhesives acting in a thermoplastic manner. However, it is also possible to use contact or solvent adhesives.

It is particularly economic and advantageous from the manufacturing standpoint if the supporting layers are precoated with the adhesive used.

The joining together of the supporting layers in punctiform or linear manner according to the invention can take place by known textile aids, e.g. by sewing or stitching. It is more advantageous from the production standpoint if the punctiform or linear interconnection of the supporting layers is brought about by adhesion. In this case, the corresponding adhesive joints of the supporting layers are produced by the adhesive used for bringing about the whole-area adhesion of the supporting layer to the fibrous layer. This is the best solution from the production and cost standpoints.

Like the fibre mats according to the prior art, the fibre mats according to the invention are preferably provided with thermosetting binders and are mainly hot-moulded to moulded articles. In this case, it is particularly advantageous if the punctiform or linear connections between the individual supporting layers are made in such a way that the connection points or lines are dissolved in the mould heat.

During the closing of the compression mould the connecting points still exercise the hitherto described functions. However, after intense contact with the mould surfaces during the building up of the moulding pressure, the connecting points dissolve and permit a material exchange in these local areas, so that the connection points or lines can no longer be seen on the finished article. If the supporting layers are joined together by textile processes, the solubility in heat can be brought about through using thermoplastic stitching threads. In the case of adhesive joints, the joining strength can be eliminated in the heat by using adhesives whose binding force decreases in the presence of heat.

An important advantage of mats according to the invention is that their deformation characteristics is no longer preponderantly determined by the quality of the fibrous materials used. Thus, e.g. in the prior art mats it is not possible or is only possible to a limited extent to concomitantly use production waste, because during the preparation of the latter the fibre length is reduced and an addition of treated production waste considerably impairs the deformation characteristics of the mat. In the case of the mats according to the invention, the deformation properties of the supporting layers predominant. Thus, it is possible to use production waste, including processed supporting layers in the production of mats, thereby ensuring an inexpensive waste-free production, which saves raw materials.

The central layers of these mats are prestrengthened, but in the initial state have a much lower density than in the moulded state. The deformability of the central layers is improved by thermal action, e.g. steam treatment prior to moulding. If they are to be adequately deformable, they must have a moisture content above 10%. This is a disadvantage from the moulding standpoint, because moisture extraction during the hot final moulding process requires additional moulding time.

During moulding, the moisture content can lead to steam bubble formation, particularly if steamimpermeable supporting layers are used. The perforation of the supporting layers proposed for the purpose of eliminating this disadvantage also fails to completely eliminate the risk of steam bubble formation, because the perforated proportion of the overall surface area of the supporting layers is naturally small. Steam bubble formation either leads to an increased quantity of waste material or requires a correspondingly complicated moulding procedure serving for the elimination thereof (intermediate relief of the press during the moulding of the final article) if these factors reduce the economy of the overall process.

Thus, according to an advantageous further development of the invention, the density of the prestrengthened central layer prior to moulding approximately corresponds to its density in the finished article, the moisture level thereof being below 10%.

The low moisture content initially has the advantage that the moulding time can be further reduced and that steam bubbles do not occur in the moulded article. As the density of the prestrengthened central layer corresponds approximately to that of the finished article, said layer has only a limited tendencyto uncontrolied moisture absorption during intermediate storage, so that its preconditioning can be maintained over a relatively long period. Further advantages result from the fact that mats with central layers compressed to this extent are less voluminous and consequently required less storage space. In addition, their handling and transportation stability is considerably improved compared with known mats.

The central layers of mats according to the invention must also have adequate deformability in correspondingly, highly compressed state, which generally requires additional measures. Thus, for example, according to an advantageous embodiment, the central layer of such mats comprises at least one sheet of creped paper or cardboard impregnated with thermoplastic or duroplastic binders. The entire surface area of creped papers, cardboard, woven or non-woven fabrics is uniformly finely folded. Such structures consequently have an overall surface area which is a multiple of that corresponding to the external dimmensions of the corresponding webs. They are therefore able to cover the increase in the surface area required for producing the three-dimensional shape from the "stored surface area" of the pleating (creping).In the case of a suitable shape of the creping folds (cross-creping in which the corresponding web is finely folded in two directions at right angles to one another) the corresponding material has ahigh deformability in all the directions in question. The increase in the surface area is made possible by smoothing the folds, without the material being subject to higher tensile stresses resulting from the deformation. Thus, the creping of the central layer permits the necessary deformation thereof and creped papers which have already reached their final density can be fabricated and impregnated without difficulty. They can contain pulverulent fillers in addition to cellulose fibres.

Textile central layers can also be used for producing mats according to the invention. Thus, for example, it is possible for the central layer to comprise at least one sheet of creped fabric or non-woven fabric impregnated with duroplastic or thermoplastic binders. Here again, the necessary deformability of the central layer is obtained by impregnating the per se inadequately deformable woven or non-woven fabric.

Particularly favourable conditions are provided if adequate deformability is ensured on the basis of the material used for the central layer of the mats.

This is for example the case if the central layer is a thermoplastic material filled and/or reinforced pre ferably with cellulose or lignocellulose materials.

Such a mat can be hot-moulded without taking special precautions. Particular advantages are obtained in connection with moulded articles which are to be exposed to thermal stressing in subsequent use if the creped supporting layers are made from metal. This improves both the dimensional stability of the articles in heat and also reduces the heat absorption due to the favourable reflection conditions of the supporting layer.

Creped papers, cardboards, fabrics, woven or non-woven fabrics impregnated with binders, as proposed for the central layer material of the mats according to the invention can only be creped in a limited thickness. According to a further develop mentofthe inventive principle, it is therefore advantageous to use central layers comprising an interlaminar bond of one of more materials of the described type. The individual sheets of the central layer can then be joined by sewing, stitching or needling.

This can in particular be advantageous if the individual sheets are formed from paper, cardboard, woven or non-woven fabrics. If textile joining processes are used, it is advantageous for the joining threads to be made from thermoplastic materials, which are readily deformable during hot-moulding.

A further advantageous possibility of constructingthe core layer as an interlaminar bond is brought about by producing the latter by an adhesive which softens in the presence of heat.

This procedure has the advantage that the central layers can built up in random thickness from individual layers with good deformation characteristics, whose reciprocal joint becomes flexible during hot moulding, so that the deformation characteristics of the individual layers can be fully utilized.

Due to the fact that in the interlaminar bond, the materials can be combined virtually at random, further adaptation scope is obtained for the characteristics of the moulded article.

Central layers according to the invention can be wholly or partly produced from recycled materials.

The creped papers or cardboards of the central layers can for example be recycled papers or cardboards, whose qualities are inadequate for other uses. This also applies to non-woven fabrics or woven fabrics made from synthetic and/or natural fibres. In both cases, the primary products for producing the mats according to the invention can be obtained from the appropriate industry.

It is also possible to produce the central layers from filled and/or reinforced thermoplastic materials using low-grade thermoplastic material waste, such as is e.g. obtained in the form of coated paper waste and cable industry waste and which cannot be used for other purposes. Colour differences and impurities do not play an important part in connection with the use according to the invention. Inadequate mechanical strength characteristics, such as can occur when using mixed waste, can be compensated by a suitable selection of the supporting layers.

The mats according to the invention are produced on the basis of the prior art. The central layer is applied to the lower supporting layer which serves as the conveyor belt. The upper supporting layer is then supplied from a reel and the assembly formed by the supporting layers and the central layer is passed between the pairs of rollers used for prestrengthening and said layers are joined together.

The perforations can be obtained by pairs of rollers provided with corresponding needles, which in each case pass through a supporting layer and partly penetrate the central layer.

Claims

1. Afibre mat for producing three-dimensionally moulded mouldings comprising a prestrengthened layer containing cellulose or lignocellulose fibres and deformable supporting layers with which the fibrous layer is joined, characterised in that the fibrous layer is arranged as the central layer between two supporting layers and that the supporting layers comprise creped, low-extension or extension-proof foil materials, such as for example paper, plastic, metal, fabric, and the like, joined to the central layer surfaces, whilst maintaining the pulling out properties of the creping.

2. Afibre mat as claimed in claim 1, in which the creping comprises juxtaposed parallel folds.

3. Afibre mat as claimed in claim 1, in which the creping comprises cross-folds.

4. Afibre mat as claimed in any one of claims 1 to 3, in which the depth of the creping is matched to the length of the fibres of the central layer in such a way that after pulling out the creping, the fibre assembly of the central layer is not interrupted, so that the shape and intensity of creping is adapted to the covering length of the fibres.

5. A fibre mat as claimed in any one of claims 1 to 4, in which the surfaces of the crepe supporting layers facing the central layer are joined to the latter by gluing or adhesion.

6. A fibre mat as claimed in any one of claims 1 to 4, in which the supporting layers are joined together in punctiform or linear manner at intervals by adhesion or sewing through the central layer.

7. Afibre mat as claimed in claim 6, in which the punctiform or linear connections can be dissolved by heat.

8. A fibre mat as claimed in any one of claims 1 to 7, in which the creped supporting layers are provided with perforations.

9. Afibre mat as claimed in any one of claims 1 to 8, in which the central layer has a high proportion of short fibres and is creped in the same way as the supporting layers.

10. Afibre mat as claimed in claim 9, in which the central layer comprises at least one sheet of paper or cardboard recovered from paper waste and impregnated with thermoplastic or duroplastic binders.

11. Afibre mat as claimed in claim 9, in which the central layer comprises at least one sheet of creped woven or non-woven fabric impregnated with thermoplastic or duroplastic binders.

12. Afibre mat as claimed in claim 9, in which the central layer comprises a thermoplastic material filled with cellulose or lignocellulose.

13. Afibre mat as claimed in any one of claims 9 to 12, in which the central layer comprises a plurality of layers interconnected by adhesion or sewing.