Technical field of the invention

This invention relates to a method for manufacturing fiber boards, comprising the steps of desintegrating a fiber raw mate¬ rial while exposing individual fibers out of the same, diluting the fibers in water while forming a beating material which is distributed on an endless wire and dewatered in order to form a substantially uniformly thick fiber web in which the fibers are held together at least provisionally in a comparatively fluffy network, dividing said fiber web into sequential individual sheets intended for forming boards, and transferring said fiber sheets to a drying station in which they are subjected to a heat treatment in order to evaporate further water and provide an in- timate binding of the fibers in said network so as to get the sheet to form a board having a stiff nature.

Prior art

In the conventional manufacture of fiber boards, wood is used as the raw material source; usually in the form of chips or shavings which is delivered as surplus materials or by-products from saw mills after gaining sawn elements out of round timber. This chip or- shaving material is treated in the board factory by pre-conditioning with hot-water, steaming (e.g. at 120°C) and possibly a chemical impregnation treatment. Thereafter, the material is passed through a defibrator having a grinding sta¬ tion resulting in the individual fibers of the softened chip or shaving bodies being exposed. These exposed fibers are diluted in water while forming a beating material, which is then treated in the manner generally described above.

In practice, the boards are produced in two different de¬ signs, namely on one hand a porous variant, and on the other hand a hard or semi-hard variant. When porous boards are produ¬ ced the fiber sheets obtained from the wire of the take-up machine are dried in a pressure-free or relaxed condition in a relatively short period of time (1-2 hours) and under temperatu¬ res in the range of 170-180°C. When hard or semi-hard boards are produced, the fiber sheets are additionally subjected to a

treatment in a high pressure press, preferably a multiple ope¬ ning press. In particular, the sheets are pressed between plates provided with pressing wires under a pressure in the order of 35-40 kg/cm ² at the same time as they are subjected to a tempe- rature of, for example 200°C. Thereafter the sheets are heat- hardened at temperatures within the range of 160-215°C for a time of, for example 5 to 7 hours, so that a compact, strong and water-resistant board is achieved, the thickness of which (most commonly 2-9 mm) is normally quite thin compared to the thick- ness of the porous boards (most commonly 9-25 mm) . Irrespective of the design, the natural content of lignin and resin products of the wooden material which is exposed during defibration of the chips or shavings is used as the sole binding agent between the fibers of the board.

Brief description of the invention

The present invention is based on the surprising realiza¬ tion that not only is it possible, but that it is extra-ordina- rily advantageous to use, as a fiber raw material, packaging capsules made from thermoplastic-coated paperboard instead of, or as a complement to, the conventional wood raw material in the form of chips or shavings. Thermoplastic-coated paper board is mainly produced from one or several layers of a fiber pulp. At least one of these layers of fiber pulp is made from a semi-che- mical pulp and at least one of the surface layers of the finished paper board is coated with a thermoplastic in the form of polyethylene. The thermoplastic coating gives the paper board a good resistance against fluids. Polyethylene-coated paper board may therefore advantageously be utilized in packaging cap- sules for retaining fluids such as drinks, e.g. milk, juice, fruit-syrups, etc. Often the interior surface of the paper board included in such capsules is provided with an interior coating in the form of an aluminium foil (usually present in connection with capsules for retaining juice) . Such capsules, which are distributed daily in extremely large quantities in today's so¬ ciety, have previously been regarded chiefly as an environmental problem rather than as a resource of raw material. A common way of making the material included in paper board capsules useful

has previously been to simply burn the capsules so as to profit on the energy content of the material. Recently, tests have also been made in order to make use of the fiber content of the paper board with the object being to utilize the fibers as recovery fibers in the production of simpler qualities of paper. These tests have, however, had poor success, partly due to the exis¬ tence of relatively large amounts of polyethylene plastic, which is integrated in the paper board material, and partly due to the fact that during paper production the fibers are never subjected to temperatures high enough to sterilize the same. In practice, the content of polyethylene amounts to about 15 weight-% of the total weight of the paper board material; if the paper board is also coated with a metal foil the content of cellulose fibers in the paper board is reduced to less than 80 weight-%. The fibers of the paper board cannot be used as recovery fibers for the production of paper unless the same are first carefully separa¬ ted from the plastic and metal foil materials. This separation calls for a rather complicated cleaning process which is diffi¬ cult to control and very expensive to carry out. Consequently for economical reasons, recovery of paper board fibers for the purpose of paper production is impossible in practice.

By the present invention quite a new field of application is provided for paper board present in great quantities in packaging capsules. In this new field of application it is not only possible, but also technically very advantageous to utilize paper board which includes palpable quantities of polyethylene. Accordingly, tests have shown that this plastic material is sof¬ tened and melts under the heat treatment which conventionally takes place when fiber raw material is dried and/or pressed in connection with the usual manufacture of fiber boards. When the plastic melts it will provide, or at least greatly contribute to, an extremely intimate binding of the fibers in the fiber network which ultimately forms the desired board. In contrast to the natural binding agent, in the form of lignin and various resin products, which is included in rather limited quantities in wooden chips and shavings respectively, a content of approxi¬ mately 15 % of polyethylene plastic in conventional recovery pa¬ per board capsules forms a quantity of binding agent which, when

properly used, gives a stronger binding or so called cross-lin¬ king of the fiber structure than lignin. For this reason the polyethylene plastic included in the recovery paper board capsu¬ les should not be regarded as a source giving rise to difficul¬ ties, but rather as a truly advantageous resource which gives the finished boards properties which at least in certain respects, namely in respect of modulus of elasticity, hydrophobi and liquid resistance, are improved in comparison with corres¬ ponding properties of conventional wooden fiber boards. It has been shown that any aluminium foil accompanying the capsules can be automatically desintegrated in connection with the paper board defibration, and may accompany the fibers in the beating material as well as in the sheets without giving rise to nega¬ tive consequences.

Brief description of the attached drawings In the attached drawings:

Fig 1 is a digrammatic, extremely simplified perspective view illustrating a board manufacturing plant of type conven¬ tionally used for the production of wooden fiber boards,

Fig 2 is an enlarged perspective view of a desintegrator inclu¬ ded in the plant according to Fig 1, and

Fig 3 is a schematic illustratation of a station included in the plant for treatment of incoming raw material in the form of recovery paper board capsules.

Detailed description of an embodiment of the invention

In Fig 1 reference numeral 1 generally designates a desin¬ tegrator or desintegrator station in which fibrous raw material is taken from a supply 2 via a conveyor 3, e.g. of the type including one or more feed screws. Reference numeral 4 generally designates a take-up machine which in a conventional manner includes an endless wire 5, at least one beating or stock regu¬ lating box 6 and one or more presses 7 as well as a cutting de¬ vice 8. The cutting device 8 cuts a fiber web fed forwardly on

the wire into individual sheets. Behind the cutting device 8 is a roller table 9. Downstreams of said cutting device is a mul¬ tiple opening press 10, which also serves as a drying station. In this station each incoming fiber sheet may, depending on requirements, on one hand be pressed with the desired pressure, and on the other hand be subjected to the heat treatment at the desired temperature. From the pressing and drying station 10 the treated fiber boards to be hardened are transferred by a car¬ riage 11 to a hardening chamber 12. The hardening chamber 17 is followed by a moistening or conditioning chamber 13 and by an unloading station 14.

Reference is now made to Figure 2 which illustrates the design of the desintegrator station 1 in an enlarged scale. In the desintegrator station 1 is included a hopper 15, in which fiber raw material can be received from the conveyor 3. A screw feeder 16, connected to the bottom outlet of the hopper 15, feeds the raw material to a column-shaped preheater 17. A pipe¬ line 18 is connected to the preheater 17 for the supply of steam. At the bottom of the preheater is an agitator 19. Fiber raw material fed into the preheater is wetted and subjected to heat treatment by way of the steam supplied through the pipeline 18, whereby the raw material is softened in order to initiate defibration. From the preheater the raw material is further con¬ veyed by a second screw feeder 20 to a defibrator generally de- signated by reference numeral 21. A beater or grinder is inclu¬ ded in the defibrator 21. In the heater the raw material is sub¬ stantially completely defibrated or desintegrated while forming a pulp of mainly individual fibers. From the defibrator 21 the fiber pulp is forwarded through a third screw feeder 22 in which a steam separator is included. Finally the pulp is fed through an outlet 23 which in turn is connected to a stock chest 24 (see Figure 1) . Water may be added to the pulp through a water supply pipe 25, in order to dilute the fiber pulp in the water while providing a beating material having a suitable dryness (e.g. within the range of 0,5-2,0, preferably about 1 %) .

The plant illustrated in Fig 1 and 2 as above described is the same in all essential elements as previously known plants designed to make possible the usual production of fiber boards

from wooden raw material, preferably in the form of chips and/or shavings.

In accordance with the present invention such used and recovered packaging capsules which were initially made from plastic-coated paper board, particularly such paper board which has been coated with polyethylene or other similar thermoplas¬ tic, are used instead of the wooden raw material or as a comple¬ ment thereto. In order to make the utilization of such capsules possible in practice for the above mentioned board manufacture, the capsules have to be coarsely decomposed and washed in a first step. Figure 3 illustrates how a decomposer device 26 (schematically shown) for the coarse decomposition is included in a station upstream of the receiving hopper 15 of desintegra¬ tor 1 together with a washing device or tank 27 and suitably also a pressing machine 28 by means of which decomposed and washed paper board pieces can be pelletized or shaped and comp¬ ressed into pellet or briquette like bodies which can be trans¬ ported through the screw feeder to the desintegrator 1 easier than differently shaped paper board pieces. Between the pressing machine 28 and the washing tank 27 is a strainer 29 arranged to dewater the washed paper board pieces. Upstream of the decompo¬ ser device 26 is a screw feeder 30 in which various forms of recovery capsules 31 can be received from a suitable store or supply 32 beside the hopper. In practice, the capsules 31 may constitute "source-sorted" (sorted at the source) , milk, juice or fruit drink packages of the type distributed in great quanti¬ ties through everyday commerce, and which, after consumption of the contents, are thrown by the consumer. In the assortment such packages which are interiorly coated with a metal foil, usually an aluminium foil, may be included. It is also conceivable to utilize, as a raw material, such capsules which are defective after manufacture and which accordingly cannot be used for ac¬ tual storing of drinks.

The decomposer device 26 may be any known or arbitrary de- vice, e.g. a screw desintegrator, which is suitable to effecti¬ vely tear or destroy great quantities of paper board. Washing device 27 preferably operates with water as a washing agent. Chemical cleaning agents may be added to the wash water in order

to achieve an optimum cleaning effect . It is important that the washing device 27 be located downstream of the decomposer 26 in order to make possible a washing of the decomposed, relatively small paper board pieces which have their outer surface as well as their inner surface exposed to the washing liquid. It should also be point out that the paper board material will automati¬ cally be dewatered when the same is agglomerated and compressed in the pressing machine 28, whereby said material will be given the desired dryness when it reaches the preheater 17 of desin- tegrator 1.

A cleaning basin 33 is also included in the station shown in Figure 3. From the cleaning basin 33 the wash water can be returned to the washing tank 27 via a recirculation piping sys¬ tem 34. From the supply 35 of pellets fed out from the pressing machine 28 the material can be forwarded to the desintegrator station 1 by the conveyor 3 shown in Figure 1.

In practice the use of recovery paper board capsules as a fiber raw material according to the invention can be realized in a number of alternative ways. According to a first alternative said material can be used as the single fiber raw material in each individual board. It is also possible to use a mixture of recovery fibers gained from used paper board on one hand, and fibers, which have been gained from wooden raw material, such as chips or shavings, in the conventional manner, on the other hand. According to a third alternative, it is possible to construct the individual fiber board from two or more fiber layers having different characteristics, at least one of the layers being completely or partly produced by means of recovery fibers from paper board. In a preferred embodiment the quantities of paper board recovery fibers in the finished board are within the range of 80-100 %.

Except for the treatment of the material between the supply and the receiving hopper 15 of the desintegrator, the proper production of fiber boards from paper board recovery fibers as the single or partial fiber raw material, is carried out substantially in the same manner as in the conventional pro¬ duction by means of fibers from wooden raw material. Thus the

fiber mass is fed from desintegrator 1, in the form of a beating material, out on the wire 5 of the take-up machine. The fiber mass is dewatered to form a substantially evenly thick, conti¬ nuous fiber web in which the fibers are held together at least provisionally in a comparatively fluffy network. The fiber web is divided, by the cutting device 8, in sequential individual sheets which are transferred to the drying station 10. In the drying station 10, the individual sheets are subjected to a heat treatment and also may be subjected to pressing in order to eva- porate further water and provide an intimate binding of the fibers in the network to make the individual sheet forming a board of a stiff nature. Thereafter, in the production of hard fiber boards, a treatment in hardening chamber 12 and moistening chamber 13 takes place. During the heat treatment in drying sta- tion 10 a heating of the fibers to at least 150°C occurs, whereby the thermoplastic deposited on the fibers is melted. The melted plastics flows out and forms diminutive points of connection between individual fibers in the network while securing an extremely strong cross-linking. By the fact that the thermoplas- tic is included in the starting material in such great quanti¬ ties, such as about 15 %, a very large number of bindings will be created, whereby not only is strong cross-linking achieved, but also a far-reaching hydrophobation of the finished board is achieved, i.e. the board will have very good resistance to water. In this connection, another advantage of the large con¬ tent of thermoplastic in the fiber raw material is as follows . The plastic will be softened already in connection with the treatment in station 1, whereby the plastic tends to bind to the lumen of the fiber such fibrils which would otherwise during the subsequent dewatering on wire 5 render the penetration of the water through the fiber web more difficult. Thus, due to the relatively great quantity of thermoplastic, a beating material is obtained which can easily be dewatered on the wire. Tests performed have shown that a semi-chemical pulp in a pure condi- tion (i.e. without thermoplastic) gives a dewatering degree of about 40° chopperriegler, while a corresponding pulp having about 15 % thermoplastic included in the mixture will give a dewate¬ ring degree in the order of 10° chopperriegler.

The advantages of the invention are obvious. Recovery paper board capsules for various forms of drinks are present in large quantities and may after sorting at the source be collec¬ ted at a low cost for the board manufacturer. Thereafter, it is not only possible to use this material as a fiber raw material, but there are technical advantages sin the form of an improved dewatering degree, increased modulus of elasticity in the finished board as well as improved water resistance and increa¬ sed strength in comparison with corresponding boards made from wooden raw material only. Moreover, the invention makes it pos¬ sible for the packaging manufacturer to fulfill existing requi¬ rements on re-utilization of the packaging material in a simple and economically effective manner.