WO1995007808A1

WO1995007808A1 - A method for manufacturing of shaped objects from paper fibres

Info

Publication number: WO1995007808A1
Application number: PCT/DK1994/000337
Authority: WO
Inventors: Flemming Nielsen
Original assignee: Flemming Nielsen
Priority date: 1993-09-17
Filing date: 1994-09-12
Publication date: 1995-03-23
Also published as: AU7609494A; EP0729402A1; DK103993D0; DK169316B1

Abstract

A method for the manufacture of shaped objects, preferably in form of plates with profiling, from paper fibres prepared by dry grinding of preferably waste paper to a particle size of approx. 3 mm and which after compression in a mould is hardened by thermal treatment. With the object of providing a durable material with sufficient strength for packing purposes without any addition of additional binding or adhesion agents other than those present in finished paper, such as paper for newspapers, printed matter for advertizing and weekly magazines, the method is characteristic in that the comminuted fibre material is compressed in the mould to a volume which is less than 50 % of the starting volume, following which and under further compression, vapour added under pressure is blown through, which a subsequent cooling by being blown through by air.

Description

A METHOD FOR MANUFACTURE OF SHAPED OBJECTS FROM PAPER FIBRES

The present invention relates to a method for the manufacture of shaped objects, preferably in form af plates with profiling, from paper fibres prepared by dry grinding of preferably waste paper to a particle size of approx. 3 mm and which after compression in a mould is cured by thermal treatment. From US Patents Nos. 3,736,221 and 3,940,466 methods of the above type are known. The object of these methods is primarily to produce fibre plates or bars which in respect of durability and strength are comparable with wood or with fibre products, which as starting materials use new cellulose mass. The known methods reguire the addition of binders, which contributes to the final strength, but which in particular influences the time of curing, which in the examples described was at least 3 minutes and up to 8 hours. In particular in the examples, where a water- insoluble binder was added, particularly long curing or baking periods were prescribed.

It is often a requirement that it should be stated on consumer goods or packaging materials how they can be disposed of after use either by re-use or depositing. This requirement is in particular of current interest in connection with packaging materials, in respect of which it is often even a requirement that the supplier takes the materials back. Packaging materials, which constitute a re¬ use of materials acceptable without depositing in protected refuse dumps or which can straightaway be combusted, will often have a most favourable position in respect of acknowledgment as packaging materials not to be returned, whereas other materials which contain even small amounts of new or environmentally risky material will have to be returned to the supplier.

The materials anufacted by the known methods contain a supplementary binder, which makes them less suited for approvement as material not liable to be returned, which in particular entails the long curing^' periods which in turn makes the manufacture of the materials costly and space- demanding. The object of the present invention is to provide a method of the type mentioned by way of introduction, by means of which dimensionally stable objects can be manufactured, said objects being suitable as shock- absorbing and supporting packaging elements. Besides, the method is to be quick and to involve a low energy consumption.

This object is met by the method according to the invention, which method is characteristic by the subject matter of the characterizing clause of claim 1. By the method according to the ivention the comminuted paper fibre material is compressed in the mould to such an extent that good contact is attained between the individual particles, whereafter during continued compression hot vapour is blown through the shaped object. The blowing through by vapour seems partly to activate the binding agent present in the paper, partly to influence the shape of the fibres in such a way that mechanical connections are created between the individual particles. The resulting material is solid and dimensionally stable with a consistency like thick paperboard. The method can also be used for the manufacture of objects with thicknesses of several centimeters, which in itself will give the shaped objects good protection abilities. The possibility of manufacturing shaped objects with large thicknesses gives a similar possibility of giving the objects a considerable strength and rigidity, which makes them suited as strength-giving elements in the packaging. Not only is the strength sufficient for making the packaging self-carrying and in itself stackable, but it is also sufficient for carrying or supporting in themselves stackable, but fragile and shock-sensitive articles. The use of substantially dry fibres and the short treatment period with vapour ensures a low energy consumption.

It has turned out that the strength of the finished shaped objects does not increase substantially by treatment with vapour for more than 20 sec. per approx. 20 mm thickness of the shaped object. According to the invention it is therefore preferable that the addition of vapour takes place in one or more periods within 20 sec. The short curing time is advantageous in mass production, as by a single production line a production can be attained, which has the same capacity as the production of goods, for which the shaped objects are to be used for instance as packaging.

According to the invention the addition of vapour takes place in form of vapour at 140°C. The hot vapour ensures the necessary activation of the paper fibres and ensures sufficient heat supply for evaporation of surplus humidity, which entails that the product by the subsequent blowing through by hot air will dry up completely at the cooling. The shaped objects can therefore be used straightaway for packaging of articles even sensitive to humidity.

It is preferable that the hot vapour is introduced in the mould at approx. 4 atmosphere (gauge) . The high pressure ensures a complete and quick flowing through of the vapour through the shaped body, so that the temperature increases quickly and the fixation takes place. The hot vapour contributes besides to removal of residual humidity.

It has turned out that the method can be carried out by nearly all available types of waste paper. The high temperature during the fixation ensures that the shaped bodies are sterile and that there is no health risk by using also paper which has been collected from a big number of sources, where there is no guarantee of complete purity.

By the method according to the invention an effective compression is a requirement for the attainment of a suit¬ able strength and hardness, as generally better strength properties are achieved by use of a higher degree of com- pression. However, it has turned out that the strength and the stability of the shaped objects will be adequate for most packaging purposes if the pressure, under which the

2 loose fibres are compressed, only exceeds 0.7 kp/cm . It has turned out that the best strength properties are attained, if the major part of the total compression of the fibres has taken place before the admission of vapour is started. According to the invention it is preferred not to start the admission of vapour until the movable part of the mould has made 70% of its stroke.

An embodiment usable in practice of the method is characteristic in that the compression is performed by subjecting the shaped object to an increasing pressure, until the speed of compression decreases substantially, at which time the vapour is admitted, the pressure, under which the compression takes place, being substantially constant.

The invention will be described in detail in the following with reference to the drawing, in which: Figs, la and lb schematically show a plant for grinding, conditioning and mixing a base material when carrying out the method according to the invention, and

Figs. 2 - 4 show various stages of compression in the mould during the curing of the fibre mass. The plant shown schematically in Figs, la and lb prepares a base material consisting of fibres from waste paper for pressing into shape of shaped bodies which are cured by drying in a mould with movable walls. The plant comprises an inlet for raw material 1 consisting of a table 2, on which a bale of recycled paper is placed, and by means of chains 3 with rakes the material is taken to a first grinding step 4. The rakes will only to a limited extent rake the individual sheets or bound sheets to pieces, and they will therefore in a more or less even flow consisting of small bundles be conveyed to the first grinding step, the introduction therein being secured by means of an upper conveyor belt 5 running on the top side of the conveyor chains. In the first grinding step a mill

6 tears the whole sheets into smaller pieces of for instance a size of 5 x 5 cm. This maculature is by means of an air flow taken to a cyclone 7, where the pressure from the transport air is equalized through a bag filter 8.

The material removed from the bottom of the cyclone

7 through a (not shown) cellular wheel or a similar kind of lock is introduced into a second grinding step 9, which contains a mill which tears the maculature in smaller pieces with a biggest dimension of approx. 6 mm. At the outlet from the second grinding step 9 the material is to pass a screen 10 with a mesh diameter of 6 mm and is by means of an air flow taken to a second cyclone 11, where the pressure from the transporting air in a similar way as in the first step is equalized by means of a bag filter 12. Finally, the maculature is taken from the bottom of the cyclone 11 to a third grinding step 13, in which a mill further divides the maculature until it gets a woolen, towed fibre character and is able to pass a screen with a mesh size of 3 mm. The paper fibres are at this stage seen as flocks, where only to a small extent areas with the original paper structure can be seen on the individual flocks. The mesh size of this sieve is of essential importance, as a finer grinding gives a poorer fibre formation and more dust, and a coarser grinding results in reduced raking into fibres. After the third grinding step 13 the fibres are by means of an air flow taken to the last cyclone 15, from where they are later apportioned in a subsequent step. The third cyclone 15 is like the preceding ones provided with a pressure equalizer in form of a bag filter 17, which on account of the more difficult separation is more sturdily dimensioned than the filters in the preceding steps.

The cyclone 15 moreover constitutes a buffer stock, from which the paper fibres can be taken for a subsequent shaping and curing process. It is normally preferred to dose the fibres to the mould in a loose shape without any clotting. Such a dosing is carried out by means of a conveyor in form of a screw conveyor 18. The screw conveyor has an outlet 19 placed above the station in which the moulds are filled. The filling of the moulds may for instance be carried out by means of a vibration sieve 20, which partly takes care of a homogeneous or in other ways predetermined distribution of the fibres over the opening of the mould. After having been filled with fibres, the mould is taken to the next station, in which the fibres are compressed and treated with hot vapour. The fibres are delivered from the screw conveyor 18 as a loose, dry granulate, each grain of which is an approx. 3 mm paper flake with free fibres, particularly along the edges, but to some extent also on the surfaces of the flakes. The fibres are substantially straightened at the raking of the paper in the mills, and it is important to avoid introducing liquid or anything else, which may change the structure of the fibres, to the screw conveyor, as it seems to be said structure that at the subsequent vapour curing contributes substantially to the strength of the compressed product. From the vibration screen the fibre material is distributed in the mould 21, which after filling and after mounting of an upper part can be made to compress the material, for instance by means of a hydraulic cylinder 23 placed under a displaceable basis plate 22. A design of the mould is explained more detailed in connection with Figs. 2-4.

Fig. 2 shows the bottom part of a mould for the manufacture of a plateshaped packaging element with a circumferential reinforcement along the edge, and in which the density of the reinforcement may be bigger in the finished element than in the plane centre portion. The mould comprises an outer mould box 30 with an interior frame 31 of the same width as the reinforcement. The mould box is provided with exhaust outlets 32 at the bottom, through which drying air can leave the mould. The exhausts may moreover during the filling of the mould contribute to a more homogeneous and more compact filling of the mould. The exhaustion also contributes to reducing dust nuisances at the dosing of the loose and partly heavily dusting fibre material. With tight fitting within the frame 31 a movable lower plane 33 is placed in the mould, said plane being at the filling of the mould positioned in its upper position. Both the lower plane 33 and the frame 31 are provided with perforations, through which exhaust air, vapour or cooling air can pass. The mould is filled with fibre material by letting fibre material from the vibration screen 20 sift into the mould, which may at the same time be vibrated. During the filling an exhaustion from the mould box is established as mentioned before, while the mould box is supplied with a substantially homogeneous filling, flushing the upper edge of the mould.

The paper fibres have in the loose form, in which they are introduced in the mould box 30, a density corresponding to 20-30 kg/m 3. For packaging purposes, in which the packaging is to contribute to making the packed

₃ objects stackable, a density of 350 kg/m should be reached. As a consequence of this the mould box has to be sufficiently deep to allow a linear compression ratio of

10-15. However, part of the compression may be established by a suitable exhaust in the bottom part of the mould box, an initial volume reduction of approx. 50% being attainable by means of such an exhaust. The exhaust can be made particularly heavy in those part of the object to be moulded which after the curing is to have greater strength and density than the re aing part of the object to be moulded.

In the next step of the shaping process the mould is provided with a upper plane 34 as shown in Fig. 3. The upper plane consists of an upper mould box 35 and a perforated mould top side 36. The upper plane is dimensioned to fit within the lower mould box 30. The upper plane is provided with an inlet 37, through which hot vapour or cooling air may be introduced in the subsequent process steps. As soon as the upper plane is mounted, a compression is initiated. The compression is performed at an evenly rising pressure, the maximum value of which is adapted to the hardness required by the finished product. For packaging purposes a pressure corresponding to 0.7

₂ kp/cm will in many cases be adequate. When the pressure has approximately reached its maximum value, vapour is introduced into the mould through the inlet 37. The vapour is preferably introduced at a temperature of approx. 140°C and at a corresponding pressure. Excessive vapour escapes through the exhausts 32. The vapour is added during one or more periods within a time space of approx. 20 seconds, the compression being at the same time carried out at unchanged pressure. Hereby the fibre mass can be additionally compressed, the fibres in the frayed edges of the paper flocks changing at the same time character, which results in an effective binding together of the fibres. After approx. 20 second of thermal threatment the object to be moulded cannot be compressed any more under the given pressure, and then the last step is initiated before the removal of the object to be moulded from the mould, viz. a blowing -through by air for removal of condensation from the vapour and possible excessive humidity from the fibre processing. When grinding the paper no liquid is added, but the humidity content of the starting material may vary within rather wide limits. The starting material is waste paper collected in various ways and which before being re¬ used has been tied up in bundles and stored in unheated areas. The time space of 20 seconds for the curing is a period of time which experience has shown is suitable for most types of objects to be shaped for packaging purposes. When the objects to be shaped have thicknesses of more than approx. 25 mm there may be a need for a longer curing time. The minimum curing time may, however, be determined in a simple way by testing. The curing proceeds as a front of humidity passing the material from the side, in which the vapour is blown in, and the curing of the material is finished, as soon as the front has reached the opposite side. When the hot vapour is blown in a condensation takes place in the cold fibre mass, but gradually as the material is heated by the hot vapour, the condensed humidity evaporates again, the front created by the humidity being displaced in the material. The heated material then assumes a fixed bound shape, whereas the material in front of the humid front still is dry and loose. When all the material has been heated, and the front dried up by means of the hot vapour, the curing is finished, and additional heat treatment time does not seem to impart increased strength to the compressed material.

After the compression and the heat treatment the upper plane is removed, which leaves the mould top side free. The lower plane 33 can now be raised as shown in Fig. 4. Simultaneously air may be added under pressure to the exhausts 32, whereby it becomes possible to lift the shaped object free of the mould and remove it for instance by means of a vacuum lifting plane 38. The mould is now ready to be filled again with fibre matirial in a new cycle.

By means of the method steps described shaped objects of paper fibres may be manufacted. These shaped objects are in particular suited for packaging purposes, in respect of which it is a particular advantage that during the manufacture no ancillary materials whatsoever are added. The shaped objects take in respect of environment exactly the same position up in the consuming chain as the waste paper, from which they have been manufactured, and waste paper is not considered problematic, being among others combustible.

Samples of the material manufactured according to the invention have been tested and assessed in respect of their suitability as packagaing material. The material is assessed on basis of plateshaped objects with a thickness of 9.3 mm and 22.0 mm, respectively. The plates have during

₂ the manufacture been compressed at a pressure of 0.7 kp/cm and cured by through-blowing by vapour at a temperature of approx. 140°C. The measurements taken comprise a measurement of density, stacking strength, compression resistance and shock-absorption resistance. The density has been measured to:

9.3 mm sample 363 kg/m3

22 mm sample 367 kg/m3

The stacking strength has been measured to: in respect of 9.3 mm material the force is 3.65 kN/m, in respect of 22 mm material the force is

7.25 kN/m

The compression resistance is measured with articles of size 70 x 70 mm, which are exposed to a force of 10 kN. A lasting deformation of 6% was measured.

The shock-absorption resistance has been measured by a standardized drop test, and the results have been compared with corresponding tests with expanded polystyrene (EPS) . A poorer ability to absorp shock-acceleration forces than in case of EPS was ascertained, but the resistance towards decomposition at repeated loading was considerably better. Where EPS after 4 drop tests was without effect, the material manufactured according to the invention showed no sign of decomposition after 10 drop tests.

The result of the test is summed up in the following conclusion;

- The strength properties of the material in its longitudinal and latitudinal direction are poorer than in the optimum direction of corrugated fibreboard.

- The material has less lasting deformation than many other materials used for packaging purposes.

- The cushioning effect of the material towards shock is poorer than in case of many other materials, but sufficiently good to be used for less frail products, like for instance kitchen hardware and the like.

By the method according to the invention a generally applicable packaging material is manufactured, said material constituting a 100% re-use of available paper materials. The manufacturing process is quick, the hardening being carried out by a thermal treatment with vapour within a time space of at the most 20 seconds. After a short through-blowing by air at ambient temperature the shaped object manufactured is ready for use. The manufacturing process is so simple and so little resource- demanding that it may be established in connection with the place, where the packaging is to be used, and consequently, there is no need for a store for finished packages in connection with the production requiring packaging. It should in particular be emphasized that the material is sterilized by the vapour treatment, and irrespective of the fact that starting materials are used, which have not been controlled in respect to bacterial purity, shaped objects are made, which are from a hygienic point of view impeccable.

The example described relates to a plate-shaped object with reinforcements in form of thickenings. The method is also applicable for the manufacture of both objects of a more complicated shape, in which frail objects to be transported, can be packed, and objects in form of plane or corrugated plates. The objects can moreover be manufactured with varying density, the mould being designed in such a way that certain parts of the shaped objects are subjected to a substantially higher pressure during the vapour flow than the remaining parts.

Claims

C L A I M S

1. A method for the manufacture of shaped objects, preferably in form af plates with profiling, from paper fibres prepared by dry grinding of preferably waste paper to a particle size of approx. 3 mm and which after com¬ pression in a mould is hardenend by thermal treatment, c h a r a c t e r i z e d in that the comminuted fibre material is compressed in the mould to a volume, which is less than 50% of the starting volume, following which and under further compression, vapour added under pressure is blown through, with a subsequent cooling by being blown through by air.

2. A method according to claim 1, c h a r a c t- e r i z e d in that the admission of vapour is made in one or more periods of time within 20 seconds per approx. 20 mm thickness of the shaped object.

3. A method according to claim 1 or 2, c h a r a c t¬ e r i z e d in that vapour is added at approx. 140°C.

4. A method according to claim 1, 2 or 3, c h a r a c t¬ e r i z e d in that the paper fibres are derived from un- sorted waste paper.

5. A method according to claim 1, c h a r a c t e r¬ i z e d in that the pressure, under which the mould is compressed, during the compression of the paper fibres in

2 the mould, corresponds to at least 0.7 kp/cm .

6. A method according to claim 1, c h a r a c t e r¬ i z e d in that the compression before admission of vapour is at least 70%.

7. A method according to any of the claims 1-6, c h a r a c t e r i z e d in that the compression is performed by subjecting the shaped object to an increasing pressure until the compression speed decreases substan¬ tially, at which time vapour is added, the pressure, under which the compression takes places being kept substantially constant.