EP0441835B1

EP0441835B1 - Method for the manufacture of contour-stable objects

Info

Publication number: EP0441835B1
Application number: EP89912229A
Authority: EP
Inventors: Torben Rasmussen
Original assignee: Brodrene Hartmann AS
Current assignee: Brodrene Hartmann AS
Priority date: 1988-10-25
Filing date: 1989-10-25
Publication date: 1996-01-03
Anticipated expiration: 2009-10-25
Also published as: GR890100687A; NL8921150A; GB2251402B; AU636585B2; FI98549B; GB2251402A; WO1990004678A1; FI98549C; NZ231149A; SE9101242D0; CA2001296A1; PT92098A; NO911634D0; AU4495089A; FI912005A0; GB2243575B; DK592488A; ATA903089A; CN1025060C; ES2017055A6

Abstract

By means of a procedure for the manufacture of contour stable objects a fluidized fibre raw material is deposited on a moulding foundation through suction of a pulp of the fibre raw material on that foundation. For this purpose the foundation is applied with an easily drainable pulp created from the fluidized fibre raw material layer in such an amount and the suction is carried out controlled in such a way that on the foundation through suction a fibre raw material layer is deposited having such wall thickness that it substantially provides the desired contour stability of the object.

Description

The present invention concerns a method for the manufacture of objects of stable shape by depositing a fluidized cellulose fibre raw material on a shaping base by controlled suction of a pulp of said fibre raw material onto said base.
A fluidized fibre raw material means a starting material, which may be in wet form, of a fibrous nature and suited for the manufacture of the desired objects. Such starting material may for instance be a fibre pulp material as used for instance for trays and cartons for packaging of fragile and sensitive objects such as fruit, flowers, eggs and objects of for instance glass. The pulp material usually consists of a suspended fibrous cellulose.
It is well known for this purpose to use a production method in which the starting material in the form of a pulp is deposited against the contour forming outside of a permeable mould so as to let a gaseous working medium act upon the material through the material of the mould through a suction effect and thus shape the material on the mould.
The object of the invention is to show how this production method, suitable per se, may be used not only to manufacture relatively small and light objects but also to manufacture large, rather heavy objects with extremely high load capacity characterized by a contour stability substantially based upon a corresponding thickness of the material layer deposited on the moulding base. Compared to this, the wall thickness of the said small and light objects is rather small, and the rigidity required in practice is usually obtained by deliberately moulding the wall panels so as to e.g. reinforce the said objects in a manner to make the whole object relatively rigid by supporting each other.
According to the invention the stated objective is achieved by that as fibre raw material at least partly a long-fibred starting material is used to increase the drainability of the pulp , and that said pulp is deposited on said base in such a quantity, and that the suction is controlled in such a manner, that by said suction a fibre raw material layer is deposited with a thickness essentially providing the desired shape stability of the object.
GB Patent Specification No. 1.589.077 concerns means for moulding articles having a complex shape of variable thickness and having high precision of mouldings, this being obtained by varying the concentration of drain holes of the mould over the surface thereof, said holes eliminating the liquid phase from a fibre containing suspension.
SE Patent Specification No. 324.498 concerns a moulding screen having a differentiated pattern of perforations for obtaining variations of the wall thickness of articles moulded by suction of a fibre containing mass.
US Patent Specification No. 3.325.349 Reifers concerns means for economizing on the amount of pulp required for a given article by lessening the thickness of portions of said article. To this end, use is made of a specific perforation of a pulp moulding die.
Contrary to this known art, the gist of the invention concerns the use of a pulp which expressly is easily drainable, i.e. that a considerably increased thickness primarily is obtained by increasing the drainability of the material mass which again is obtained by making use of a long-fibred starting material and allows a well controllable and economic process of manufacture.
This will, by using the above production method also make possible to manufacture elements with high stability, such as building elements which may, contrary to the mentioned examples, exhibit relatively even and smooth outer surfaces and inherently a high degree of contour stability. The depositing of a fibre raw material layer of the defined thickness means that the negative pressure used for suction may produce a material density in the fibre raw material layer that is highest at the external surface of the material layer facing the mould surface and will have a reinforcing effect, as it is situated at a distance from the through-going centre plane of the object having been deposited.
By using the layer thickness of the object thus manufactured, the contour stability of this object may according to the invention also be increased in that one or more variations in the layer thickness are produced in and distributed over the fibre raw-material layer by correspondingly varying the suction effect locally in a common suction process for the fibre pulp quantity necessary for the manufacture of the whole object. In this way it will be possible in one and the same working step, i.e. the depositing of the fibre raw material on the moulding base, to mould both the final outside desired for the object and, by using the thickness of the material layer, a contour-stability increasing moulded structure in the actual material product constituting the object.
According to the invention such a structure may be produced with an embodiment of the method characterized in that the depositing of the fibre raw material with a thickness corresponding to the desired shape stability is carried out so as to produce a coherent structured pattern with a larger layer thickness compared to the other areas.
In this way it is possible to achieve such an interaction between the draining ability of the pulp and the suction capability of the mould surface that also elements having a large fibre-layer thickness needed for a desired load capacity may be manufactured in a rational manner.
In order to achieve local variations in the layer thickness of the fibre raw material layer of the object, a mould may be used having a mould surface, the permeability of which varies in accordance with the local variation or variations respectively of the layer thickness or the coherent structural pattern of the easily drainable fibre pulp layer deposited on the mould surface by suction.
This means that the depositing of fibre raw material on the mould surface will vary according to the permeability of this surface resulting in local variations in the suction effect which, in areas with low mould-surface permeability, causes a reduced depositing of fibre raw material in the mould surface, whereas the depositing will be high in areas with high mould-surface permeability.
As mentioned above, the method and mould as described may be used in practice for the production of objects from various fibre-containing suspensions, always in the presence of auxiliary materials that may be necessary to create coherence in the material layer produced by suction onto the mould.
For the manufacture of a pulp which is to be easily drained it is possible, according to the invention, as fibre raw material at least partly to use a starting material containing long fibres that is processed to a pulp partly by shake-out in a pulper, partly by preceding, separate, controlled dry grinding by which the starting material is divided into dosable amounts and divided into its fibres, after which the object is manufactured from the pulp produced in this manner.
The use of a pulper as an essential step in the processing of the fibre raw materials for producing a pulp from which the desired objects are to be manufactured takes place inter alia in cases where the fibre raw materials are received in the form of dry substances in bales, for instance as paper waste.
Heavy turbulence is produced in the pulper, causing different parts of the material to rub against each other so as to be pulverized and the raw material divided into fibres.
Especially in the case of heterogeneous material, such as waste or recycled paper, it has to be anticipated that this separation is carried out successively so that the fibres released first are exposed to a higher degree of additional substantial processing than the fibres released later. In other words: the processing in the pulper will proceed in an uncontrolled and hence non-uniform manner. The additional processing mentioned results in an increase in both the degree of grinding (°SR-Schopper-Riegler) and thus the formation of mucus in the pulper, which negatively affects the subsequent draining of the object manufactured from the pulp and increases the shrinkage of the object during draining and drying of its material.
With the method according to the invention it is achieved that the pulper is at least partly supplied with a fibre raw material, the fibres of which are already to a substantial degree separated into single fibres, for which reason they are more immediately and simultaneously susceptible to the self-grinding effect and mixing effect obtained in the pulper. As the pulper processes a more uniform raw material, the grinding degree obtained in the pulper through self-grinding may also be adjusted to be more uniform and the above-mentioned binding of water in the pulp leaving the pulper will thus be more controllable.
The same procedure will, however, also result in other advantages, especially valuable in the case of recycling of paper waste.
Recycled paper waste exists in many different qualities and gradings. If, prior to the shake-out in the pulper, this material is exposed to a separate, controlled dry grinding, it is often possible to use an inferior and hence cheaper material quality, than if the dividing process were solely carried out as a shake-out in the pulper.
The present invention also encompasses an embodiment, according to which the preceding separate dry grinding as mentioned above is carried out as a multiple-stage process, making it possible to separate the starting material in dosable amounts in an especially efficient manner.
In this particular manner it is also possible to separate e.g. waste paper material containing plastic, water resistant paper, plastic laminated cartons and paper, into fibres and other particles to the extent desired. Separated constituents other than paper can be removed before entering the pulper, or it is possible, since they exist in comminuted form, to let these constituents enter into the subsequent production process.
According to an embodiment of the method the long-fibre starting material having been subjected to a separate, controlled dry grinding is added in measured amounts to the pulp already having been produced in the pulper and subjected to a common time-limited shake-out with said pulp.
In this manner an object can be manufactured, the fibre material of which is partly mainly bound by hydrogen fibre bindings, partly has been mixed with air-suspended fibre material in which glue is normally used for binding. Experience has shown that in this manner it is possible to abandon a traditional complete hydrogen binding of the whole pulp, which means that the drainage time and hence the production time for the object can be substantially reduced. Furthermore, the method makes it possible to obtain a strict control of the desired strength properties of the object, as it will be possible to have strict control of these by adding glue.
These advantages are of major importance for a rational and hence economical industrial manufacture, also of large objects of stable shape by applying the suction technique described.
It will e.g. be possible to carry out a multiple-stage dry grinding by the use of a shredder followed by a treatment in a hammer mill, which can thus receive the material from the shredder in dosable amounts and exposes the material to a further grinding process before it, if necessary also in special dosable amounts, is added to the pulper for the actual shake-out processing.
The separate, controlled dry grinding of the fibre raw materials prior to their shake-out in the pulper suggested according to the invention also provides the possibility for the co-application of recycling waste paper in cases where the objects to be manufactured must be shrink-proof and dimensionally stable. A starting material with a high content of wood fibre causes less shrinkage than if the fibres were cellulose fibres. Experience has shown that by using the method according to the invention it is even possible to add to a wood paper raw material a substantial amount of cheap recycling paper including carton waste, which does not necessarily contain wood, since it is possible, due to the preceding separate controlled dry grinding of the raw material, to manufacture a pulp causing no undesired shrinkage of the objects manufactured.
It is a well-known principle in the manufacture of objects from a fluidized fibre raw material to utilize auxiliary materials such as fillers, chemicals and binding agents. The auxiliary materials decide whether the objects manufactured shall be more or less strong, hard or transparent, or weak, soft and capable of absorbing. The present invention is also advantageous in connection with the use of such auxiliary materials.
The division of the manufacturing process in mulitple stages actually increases the possibility of adding the auxiliary materials at different stages of the total manufacturing process. The open structure of the final pulp achieved as a result of this particular invention, even facilitates a better access for auxiliary materials so that e.g. a binding material may be applied more or less integrating on the surface of the objects in order to increase the strength of the wall. The addition of auxiliary material under the preceding, separate controlled dry grinding will in an especially beneficial manner be able to contribute towards a particularly uniform distribution of the auxiliary materials in the fibre mass being produced. It is, of course, also still possible to add the auxiliary materials to the pulper.
Furthermore, it lies within the scope of the invention that the shake-out in the pulper is carried out as a manufacturing process dependent on the preceding separate controlled grinding. In other words: the degree of self-grinding achieved in the pulper can be matched to the degree of the grinding according to the circumstances having been carried out at the preceding dry grinding stage(s). As an example, to a paper pulp, which in the pulper is divided into a normal degree of 60° SR (° Schopper-Riegler), dry grounded fibre material may be added, after which the mixture is processed in the pulper for another 5 minutes. Objects manufactured from such a mixture pulp may be provided with an especially great thickness, porosity and permeability. That means that the products can have good drainage qualities and can therefore also be manufactured with large wall thicknesses.
An easily drainable pulp manufactured according to the invention will without problems facilitate a uniform application of the fibre suspension over the mould, even when manufacturing objects with large wall thickness.
Waste paper, also called return paper, may be very inhomogeneous, and may contain fibres with a large variety of fibre lengths. Experience has shown, however, that the average fibre length is so large that the above mentioned advantages, especially as regards drainage and structure, may be achieved when this paper material is included in the manufacturing process.
The method according to the invention may also be used for the processing of so-called virgin material.

Claims

Method for the manufacture of objects of stable shape by depositing a fluidized cellulose fibre raw material on a shaping base by controlled suction of a pulp of said fibre raw material onto said base, characterized in
a) that as fibre raw material at least partly a long-fibred starting material is used to increase the drainability of the pulp, and

b) that said pulp is deposited on said base in such a quantity, and that the suction is controlled in such a manner, that by said suction a fibre raw material layer is deposited with a thickness essentially providing the desired shape stability of the object.
Method in accordance with claim 1, characterized in that one or more variations in the layer thickness are produced in and distributed over the fibre raw-material layer by correspondingly varying the suction effect locally in a common suction process for the fibre pulp quantity necessary for the manufacture of the whole object.
Method in accordance with claim 2, characterized in that the depositing of the fibre raw material with a thickness corresponding to the desired shape stability is carried out so as to produce a coherent structured pattern with a larger layer thickness compared to the other areas.
Method in accordance with claim 1, characterized in that the long-fibred starting material is processed into a pulp partly by shake-out in a pulper, partly by a preceding, separate, controlled dry grinding, whereby the starting material is separated into dosable amounts and divided into its fibres, after which the object is manufactured from the pulp produced in this manner.
Method in accordance with claim 4, characterized in that the preceding separate dry grinding controlled process is carried out as a multiple-stage process.
Method in accordance with any of the claims 4 or 5, characterized in that the long-fibred starting material having been subjected to a separate, controlled dry grinding is added in measured amounts to the pulp already having been produced in the pulper and subjected to a common time-limited shake-out with said pulp.