WO1995013425A1

WO1995013425A1 - Sheet material manufactured piecewise and based on cellulose pulp fibres, and a method and an apparatus for manufacturing sheet material

Info

Publication number: WO1995013425A1
Application number: PCT/SE1994/001059
Authority: WO
Inventors: Bernt Olof Brattstig
Original assignee: Mo och Domsjo AB
Current assignee: Mo och Domsjo AB
Priority date: 1993-11-12
Filing date: 1994-11-11
Publication date: 1995-05-18
Anticipated expiration: 1996-05-12
Also published as: SE9303733D0; SE502000C2; SE9303733L

Abstract

The present invention relates to a sheet material manufactured piecewise and having a dry solids contents exceeding 90 % and comprised at least partially of cellulose pulp fibres, characterized in that the material contains a) a mixture of filler and pulp fibres deriving from the manufacture of paper and recovered in the form of sediment, in an amount corresponding to at least 30 and at most 95 % of the weight of the sheet material; and b) pulp fibres in the form of virgin fibres and/or secondary fibres, essentially as reinforcing fibres. The present invention also relates to a method and to an apparatus for manufacturing sheet material based on cellulose pulp fibres.

Description

Sheet material manufactured piecewise and based on cellulose pulp fibres, and a method and an apparatus for manufacturing sheet material

Technical field

The invention relates to sheet material manufactured piecewise with a dry solids content above 90% and based at least partially on cellulose pulp fibres. The sheet material is used conveniently as a protective covering material (packaging material) and/or as an advertisement carrying medium. With regard to the first mentioned reason, the material will be capable of absorbing impact forces. The cellulose pulp fibres included in the sheet material command a comparatively low price, alternatively a very low price. I addition to cellulose pulp fibres, the sheet material includes to some extent chemicals or substances of the kind used as filling material in the manufacture of paper. The starting material consists at least partially of sediment that derives from the waste treatment plant of a paper mill, this sediment containing a mixture of filler and cellulose pulp fibres. Other main starting materials are pulp fibres i the form of virgin fibres and/or secondary fibres, which serve mainly as reinforcing fibres. The invention also relates to a method of producing the aforesaid sheet material.

The invention also relates to an apparatus for producing sheet material in a non dried form, i.e. with a dr solids content in the range of 15-25%. The background art

Present day packaging of for instance paper rolls, in a paper mill, involves the use of end wall guards in the form of circular blanks made of corrugated paper board or solid fibreboard and in certain demanding cases in the form of woodfibre sheets, such as Masonite.

Corrugated fibreboard and solid fibreboard are manufactured mainly from earlier unused cellulose pulp fibres. Corrugated fibreboard respectively solid fibreboard are mostly manufactured in the form of endless webs. The finished material is cut into four sided sheets, from which the circular blanks are later cut or punched. This manu¬ facturing method results in about 25% wastage. The total investment costs for the manufacture of this starting material, i.e. corrugated fibreboard and solid fibreboard, is very high, which means that the starting materials per se command a relatively high price. Circular blanks made of this material command a still higher price, since about 25% of the material is wasted when converting the four sided starting material to circular end wall blanks (rounds).

Woodfibre sheets are made from earlier unused lignocellulosic material, for instance different types of wood, even though the material is often of low quality. The woodfibre sheets are produced in a rectangular shape and then converted to circular end wall blanks (rounds), which also results in a large amount of waste therewith making the product more expensive.

Disclosure of the invention Technical problems Relatively large quantities of sediment are obtained in the waste treatment plant of many paper mills, this sedi¬ ment being comprised substantially of filler and cellulose pulp fibres originating from the paper manufacturing process. This sediment has hitherto mostly presented a problem. The material has either been dumped, which requires access to a suitable dumping site, or has been burned, despite its low calorific value. The reuse of this material in the manu- facture of conventional paper is prohibited because, among other things, the wet stength of the secondary cellulose pul fibres is much too low for the fibres to be included in an endless paper web, such webs being advanced at high speeds. There has long been a need for a useful outlet for such sediment.

The solution

The present invention provides a solution to this problem, and relates to sheet material which is produced piecewise and has a dry solids content above 90% and which i based at least partially on cellulose pulp fibres, characterized in that the material contains

a) a mixture of filler and pulp fibres deriving from th manufacture of paper and recovered in the form of sediment, in an amount corresponding to at least 30 and at most 95% of the weight of the sheet material; and b) pulp fibres in the form of virgin fibres and/or secondary fibres, essentially as reinforcing fibres. The sediment may include any filler whatsoever used in the manufacture of paper, and any cellulose pulp fibres whatsoever from which different types of papers are constructed. The sediment is thus governed by the type of paper or the types of paper that are manufactured in a given paper mill.

Examples of suitable reinforcing fibres (pulps) are knotter pulp, coarse reject and fibres obtained from waste paper.

Knotter pulp is a secondary product obtained when manufacturing sulphate and sulphite pulp for instance. A closely related material is coarse reject, which is also obtained when manufacturing sulphate and sulphite pulp, for instance. Both are obtained when coarse screening and/or screening the cellulose pulp obtained after the digestion of the starting material, normally wood in the form of chips.

With regard to recovered knots and knot fragments, these are often subjected to mechanical treatment, for instance in the form of defibration or refining, before the lignocellulosic material concerned is caused to form knotter pulp in a separate material flow.

Coarse reject, or reject, is also obtained when manufacturing different types of mechanical pulps, including TMP and CTMP. Fibres of this type can be admixed advantageously in the sheet material.

Paper of different types, already used, are collected in large quantities and are commercially available. The material is referred to as waste paper and in the present case it is preferred to use low grade waste paper, i.e. a waste paper that commands a low price.

It is also possible to admix in the sheet material minor quantities of chemical pulp, such as sulphite and sulphate pulp, for instance. Unbleached (inexpensive) pulps of this kind are preferred. The admixture of bleached chemical pulp is not excluded, even though the use of this type of pulp is not preferred.

Naturally, a mixture comprising any of the aforesaid cellulose pulp fibres whatsoever may also be used as reinforcing fibres.

A common requirement of the cellulose pulp fibres on which the inventive sheet material is generally based is that they command a low price, alternatively no price at all (the sediment).

The most important constituent of the sheet material is the aforesaid sediment, which will preferably constitute at least 50% and at most 90% of the weight of the sheet material. (All percentages given in this document are percentages by weight). The remainder of the material comprises mainly cellulose pulp fibres which function mainly as reinforcing material.

In addition to filler and cellulose pulp fibres, the inventive sheet material will also include preferably at lest one chemical which has a given function. It may be necessary to include a chemical in order to impart,a desired property to the sheet material, and examples of such chemicals are chemicals which will make the material hydrophobic, colour pigments and chemicals which form a barrier layer.

Examples of chemicals that engender hydrophobicity are different types of glues and different surface tension enhancing chemicals. Concentrated waste liquor (excluding or including bleaching waste liquor) obtained from the manufacture of sulphate and/or sulphite pulp has been found to be an effective additive in obtaining sheet material whic has good flatness. The amount of chemical(s) charged and, in the case of concentrated waste liquor, retained is suitably 0.1-7% of the weight of the sheet material (excluding the chemical(s)).

The question of whether or not a colour pigment shal be added to the sheet material and, if so, which pigment is decided by the intended use of the sheet material. Examples of usable pigments are methyl violet and chrysoidine. The pigment is suitably added in an amount corresponding to 0.001-1% of the weight of the sheet materia (excluding the chemical(s)).

Polyethylene and polyvinyl alcohol have been found suitable barrier forming chemicals. The chemical is suitably added in an amount corresponding to 0.5-5% of the weight of the sheet material (excluding the chemical(s) ).

The sheet material will advantageously be flat, although a particular advantage is afforded when the materia has a corrugated or undulating cross section. This contributes towards increasing the ability of the material t absorb or withstand impact forces.

As will later be described in detail, the sheet material is produced piecewise, i.e. one piece of material o one material ply is produced at a time. Normally, eεich ply i dried so as o obtain a finished sheet material. However, after producing individual pieces having a dry solids conten within the range of 15-25%, for instance, it is quite possible to place two or more such pieces on top of one another and to press said pieces together to form a coherent sheet material having a surface weight which is a multiple o the surface weights of the individual pieces. The sheet material is then dried to a desired dry solids content, i.e. a dry solids content above 90%.

The surface weight of the finished ply will conveniently exceed 300 g/m², and preferably exceed 500 g/m². The surface weight will normally lie within the range of 900- 1500 g/m².

The sheet material may advantageously be combined with other material plies to form a laminate. When high liquid impermeability is desired, one or both sides of the sheet material may be conveniently coated with a plastic film of any known kind. When the material is also intended to have an advertisement carrying capacity and shall exhibit good printability, one or both sides of the sheet material will conveniently be provided with a paper sheet of any known kind. The various material plies may be joined or bonded together in any known manner.

The laminate may thus also consist of all three of the aforesaid material plies.

The shape and size of the sheet material is determined by the use for which it is intended. A preferred shape is the aforesaid circular shape and the size, for instance the diameter, is decided by the size of the paper rolls in the case when the sheet material is used to protect the end wall of paper rolls on sale.

Naturally, the sheet material may also be used as a protective wrapping and generally as packaging material, and the sheet material may therefore have any shape and size whatsoever within a relatively wide range.

The invention also relates to a method of producing sheet material intermittently from an aqueous suspension which includes at least partially cellulose pulp fibres in low concentration as solid substance, characterized by delivering the suspension containing a mixture of filler and pulp fibres recovered from the manufacture of paper in the form of sediment and essentially reinforcing fibres to a firmly anchored bottom forming part of a forming apparatus, said bottom part having a given shape and volume, and thereafter moving a corresponding movable upper part of the forming apparatus down into the bottom part so that the solid substances will collect to form a coherent sheet in a space delimited by a wire or wires between said lower part and sai upper part while removing water from the forming apparatus, and by lifting the formed sheet from the lower part of the forming apparatus by means of said movable upper part and with the aid of a vacuum, and by thereafter drying the sheet to a high dry solids content.

The concentration of solid substances in the suspension when the suspension is delivered to the forming apparatus will suitably lie within the range of 0.1-2.0%.

The aforesaid suspension can also be referred to as stock. The stock will always include sediment in the earlier mentioned quantities. The initial handling of the sediment i determined by the form and nature of the sediment in each separate case. It is normally necessary to add water to the sediment and to store the sediment in a vessel. The material may also be refined. When knotter pulp and/or coarse reject is acquired in the form of bales having a high dry solids content, it is necessary to slush the material in water so a to obtain free pulp fibres. Acquired bales of other types of pulp are treated in a similar manner. The material may also be refined before it is stored in a vessel. When waste paper forms part of the starting material, the material is transformed to water carried free pulp fibres in a known manner and the resultant suspension is stored in a vessel. Materials from at least two of the aforesaid vessels are combined and mixed to form a relevant stock. Any chemicals that may be necessary are added preferably to the stock before it is introduced into the forming apparatus. When forming the sheet material, water may be draine from the material by gravitational forces, therewith converting the stock or the suspension to a coherent sheet. It will be understood in this regard that the water leaves the forming apparatus through its firmly anchored lower part. Forming of the sheet material is terminated by bringing the movable upper part of the forming apparatus down into the lower part thereof and into contact with said lower part wit the sheet material as an intermediate ply. Although the sheet material can be formed essentiall solely by self draining of the water, it is, however, advantageous to apply to the lower and/or the upper part of the forming apparatus a subpressure (vacuum) or an overpressure, at least during a part of the water draining phase (and then suitably during the latter part of this phase). From a sheet forming aspect, it is advantageous to maintain the suspension in motion prior to and during a part of the forming process, with the aid of a pump which is connected to a circulation line whose inlet and outlet ends are connected to the lower part of the forming apparatus. Due to the fineness of the filler, not all of the filler that is supplied will be retained within the sheet material, and some of this filler will accompany the water t the waste liquor cleansing plant.

After the sheet material has been formed and has bee removed from the forming apparatus, the material is dried to a dry solids content of at least 90%. The material may be dried in any known manner whatsoever. One suitable method in this regard is to use a dryin tunnel having a construction which is typical in the manufacture of paperboard. It may be necessary to supplement the equipment with infra heaters to increase drying capacity. The sheet material, for instance in the form of circular blanks, is then stacked, suitably on pallets, for delivery t the consumer.

If, for instance, the circular blanks are also to carry advertisements or of some other reason are intended to be provided with print, such as flexoprint, it is appropriat to provide one side of the sheet material with paper, optionally printed paper. Another way to obtain a smooth sid is to choose a smooth forming surface of the upper and/or lower parts and not a undulated.

The third cathegory which the invention relates to is apparatus for producing intermittently sheet material having a dry solids content within the range of 15-25% and comprised at least partially of cellulose pulp fibres, this apparatus being characterized in that it includes a firmly anchored lower part having a given shape and volume and including a perforated or otherwise liquid permeable materia layer which extends generally horizontally and above said layer a wire, and water removing means, and means for applying a subpressure (vacuum) or overpressure, and a movable upper part which has a given volume and which fits well into said lower part and which includes a perforated or otherwise liquid permeable material layer, a wire located beneath said layer, and means for applying a subpressure (vacuum).

According to one embodiment of the invention, the upper part of the forming apparatus is also provided with means for applying an overpressure. It is fully conceivable to use one and the same means to create either a vacuum or a overpressure.

According to one preferred embodiment of the invention, the perforated or otherwise liquid permeable material layer in the lower part and/or the upper part of th forming apparatus is placed against a supportive device. Although this material layer may be flat, an advantage is gained when the material is undulated, which will also result in an undulated sheet material. The materia layer may be made permeable to liquid with the aid of a plurality of elongated slots whose total length corresponds, for instance, to the diameter of the upper part minus 200 mm and a width which lies within the range of 0.1-3 mm, for instance. The distance between respective slots is suitably 1-10 mm. Also, rows of holes having a diameter within the range of 0.5-10 mm for instance may be used. The upper part of the forming apparatus is always equipped with vacuum generating means. This means is preferably also constructed to enable water to be removed from the forming apparatus with the aid thereof.

The forming apparatus, including the lower part and the upper part of said apparatus, may have any desired cross sectional shape, and the horizontal material layers are surrounded by a sealing mantle or by a peripheral part in th form of an upstanding or slightly inclined coaming. The cross sectional shape is decided by the type of sheet material to be manufactured. The round or circular shape is preferred, since the sheet material produced is well suited as an end wall guard for paper rolls. If rectangular sheet material is required, for example, a rectangular cross section is choosen.

Advantages

The sheet material according to the invention can be produced relatively cheaply, since the starting material is very cheap. Piecewise manufacture enables the sheet material to be tailor-made in accordance with requirements with regard to shape and size, i.e. the amount of waste making the product more expensive is small. The invention also enables low quality cellulose pulp fibres, for instance fibres of poor wet strength, to be recovered and used for something useful. The invention also enables small scale production plants to be constructed and to work with local raw materials. Individual paper mills are able to convert their sediment to a retailable end product, this sediment normally constituting a load on the paper manufacturing process as a whole.

Brief description of the drawing

In Figure 1 a preferred embodiment of the apparatus according to the invention is shown.

Best mode of carrying out the invention

In the following primarily different embodiments of the apparatus according to the invention with reference to Figure 1 are described and also enumerates a number of tests in which the sheet material according to the invention is compared with commercially available sheet material.

As will be seen from Figure 1, the forming apparatus according to the invention is comprised of a firmly anchored lower part 1 and a movable upper part 2.

Both parts have a circular cross section and the diameter is determined by the use to which the material produced in the apparatus is intended. If end wall guards fo newly manufactured paper rolls are to be manufactured, the diameter is determined by the diameter of the paper rolls. Paper rolls normally have a diameter in the range of 1-3 metres and the diameter may, for instance, be 1.3 metre.

The main parts of the lower part 1 are a vertically extending or upstanding mantle part 3 and a within that horizintally situated part against which the sheet material is formed. This latter part may be constructed in different ways. In the illustrated case, said part includes, as seen from the bottom, a supportive device 4 which comprises, for instance, a network of flat irons anchored (for instance welded) to the surrounding mantle part. The supportive devic 4 supports a perforated or otherwise liquid permeable material layer 5. This layer may be comprised of sheet metal in which round holes or elongated slots have been formed. Th sheet will preferably be undulated, as shown in Figure 1.

The material layer 5, for instance the plate, seals tightly against the surrounding mantle 3. The mantle 3 may extend vertically or may be inclined slihtly either inwardly or outwardly. However, the upper part 2 and the lower part 1 must always be constructed so as to fit one in the other.

The mentioned plate 5 is covered by a forming wire 6 made of plastic and/or metal.

Although not shown in the Figure, there is located beneath the forming part a funnel shaped liquid collecting device which merges with or enters a drainage pipe 7 provide with a valve 8. A further pipe 9 which includes a valve 10 i connected to the pipe 7. This latter pipe may be used in generating a subpressure (vacuum) or an overpressure in the funnel shaped space beneath the forming part.

Although not shown in the Figure there are arranged in the lower edge of the moveable upper part 2 three layers or elements which correspond to the layers or elements 4, 5 and 6, although in a reverse order. It is also necessary to secure the wire 6 in the upper part 2 in some suitable way, so as to counteract the force of gravity. A subpressure (vacuum) can be generated in the space above the layers or elements 6, 5 and 4 through of the pipe connector 11.

It is fully possible to exclude the supportive device 4 in both the lower part 1 and the upper part 2. It is preferred that the lower part 1 will include an inlet line 12 and an outlet line 13.

The stock or suspension can be delivered to the firmly anchored lower part 1 in any one of a number of different ways. For instance, the stock or supension can be introduced with the aid of a pivotal pipe (not shown in the Figure) whose outlet orifice is located inwardly of the mantle 3. This pipe is swung to one side after having delivered the intended amount of suspension. The suspension can also be delivered generally tangentially through the inlet line 12.

After having delivered the suspension to the lower part 1 of the forming apparatus, the valve 8 on the outlet line or pipe 7 is opened. Removal of water from the suspen¬ sion commences as the pipe is opened. The water runs gravitationally through the wire 6 and through the slots in the plate 5, down into the collecting device and leaves the apparatus through the drainage pipe 7.

When the volume of suspension has decreased to about half of its original volume for instance, the movable upper part 2 is moved down into the lower part 1. The major part of the water present in the original suspension is removed via the drainage pipe 7 by the force of gravity and by the action of bringing the parts of the forming apparatus together, while, at the same time, forming a coherent sheet from the solid substances present in the suspension. There is formed in the space between the two wires 6 a round sheet having a dry solids content within the interval 15-25%. In the illustrated case, a vacuum is applied in the space in the upper part 2 above said forming part through a hose or a pipe whose one end is connected to the pipe connector 11 and the other end of which is attached to a vacuum pump (not shown in the Figure). The upper part 2 is then lifted from the lower part 1, wherewith the sheet material will accompany the upper part 2 as a result of the vacuum generated therein, and the upper part is moved to a suitable position and the vacuum is broken so that the sheet material will fall down (is placed) onto an underlying surface. A vacuum can be applied in the funnel shaped space beneath the lower part 1 of the forming part during the whol of the water removing process or preferably during a part of this process. This is achieved by opening the valve 10 in th pipe or line 9 (which is connected to a vacuum pump). This vacuum is broken when a finished sheet has been formed.

It is fully possible to have vacuum applied in both the lower part 1 and the upper part 2 during the water removal phase. In this case, it is necessary to arrange the pipe connector 11 and the line or pipe extending therefrom i a manner to enable water withdrawn by suction in the appara¬ tus to be taken care of. Furthermore, the upper part may include a funnel shaped water collecting device (not shown i the Figure).

It is also possible to remove all water with the aid of a vacuum via the upper part 2, in which case the lower part 1 will function essentially as a suspension collecting container.

Finally, instead of applying a vacuum, it is possibl to subject both the lower part 1 and the upper part 2 to an overpressure, meaning that the water will be pressed from th suspension and the formed sheet. In such cases, it is necessary to replace the vacuum pump with a pressure generating device, such as a compressor, for instance.

It has been found advantageous from a sheet forming aspect to allow the suspension to circulate via the lower part 1 and the outlet line 13 and a circulation line (not shown in the Figure) connected to the outlet line 13 and the inlet line 12, prior to and/or at the beginning of the sheet forming process. The suspension is circulated with the aid o a pump (not shown in the Figure) connected to the circulatio system.

The manner in which the sheet material is handled after having been formed in the aforedescribed manner is dealt with in other parts of this document.

Example 1

Tests were carried out with the use of an apparatus according to the invention similar to the apparatus shown in Figure 1. The apparatus had an internal diameter of 130 cm. Stock was prepared consisting of 80% sediment obtained from a paper mill in which coated (the coating layer in a quantity of 25 g/m² comprised kaolin clay, binder and possibly other additives in smaller amounts) wood containing printing paper (60% bleached groundwood pulp and 40% bleached sulphite pulp) having a surface weight of 80 g/m² was produced, and 20% unbleached sulphite pulp. Calculated on 1.9 kg of solid substance in the stock, there were added 2 kg of sulphite cooking waste liquor (not mixed with bleaching waste liquor) having a solid substance content of 50%. The reten¬ tion of sulphite cooking waste liquor was estimated to be about 10%. This addition is effective in lowering surface tension and also in increasing dry strength. Water was added to the stock to achieving a pulp consistency of 1% in the stock or the suspension.

190 litres of the suspension were poured into the lower part 1 of the forming apparatus. The valve 8 and the valve 10 were both opened and a vacuum of 0.5 bar was generated via the line or pipe 9. Dewatering of the suspension downwards was then initiated and the water removed was carried away via the line 7. When so much water had been removed so as to cause the water plane to disappear, the upper part 2 of the forming apparatus was lowered down into the lower part 1 and brought against the formed sheet. The lower part 1 and the upper part 2 both included a supportive device 4, a liquid permeable drilled steel plate 5 having a hole diameter of 6 mm, and a phosphor bronze wire 6 (having 27 and 24 wires per centimeter respectively and a wire diameter of 0.22 mm). The steel plate 5 in the lower part 1 had an undulating surface, as shown in Figure 1. The upper part 2 included corresponding elements 4, 5 and 6 although in the reverse order and with the difference that the drilled steel plate 5 was flat and not undulated as in the case of the plate 5 in the lower part 1. The upper part 2 was placed under a vacuum of 0.5 bar via the connecting pipe 11. At the same time, the vacuum in the lower part 1 was broken, by closing the valve 10. The upper part 2 was then lifted together with the formed sheet material from the lower part 1, with the sheet material held in the upper part, and place on an iron plate. The vacuum in the upper part 2 was broken and the upper part moved to its starting position. A per- forated steel plate was placed on top of the sheet material and the plate loaded with a surface pressure of 50 kp/m². The sheet material was then placed together with the two plates in a drying furnace having a temperature of 135°C. The sheet material then had a dry solids content of about 20%. The sheet material was dried to a dry solids content of 95%. The sheet material was then removed from the furnace, together with the two plates, whereafter the plates were removed leaving a sheet material with a surface weight of 1000 g/m² and a thickness of about 7 mm. This material according to the invention, in the for of circular blanks, was then tested with regard to its ability to prevent damage to paper rolls when used as end wall guards for paper rolls from the paper mill. Two wrapped paper rolls were placed on a floor surface one above the other. The bottom end of the bottom paper roll was protected by the sheet material according to the invention, with its undulating surface facing downwards. The following four objects were placed between the aforesaid bottom end of the bottom roll and the floor surface and on said surface with the intention of establishing whether or not the end wall guard and the paper roll protected thereby would be damaged:

a) A nut having a thickness of 9 mm. b) A thread forming screw having a diameter of 10 mm. c) A stone having a height of 12 mm. d) A piece of concrete having a height of 19 mm.

The paper rolls were allowed to stand in the de- scribed way for one week. The wrapping or packaging was then opened and the impressions in both the end wall guard and the paper roll were studied.

The test was repeated in the same way, but with the other end of the paper roll facing downwards and with the use of an end wall guard comprising conventional circular blanks of corrugated paperboard of the type BC 220 and having a surface weight of 720 g/m².

The result was judged with regard to the following three factors:

The configuration of the impression in the end wall guard.

2. The nature of the impression in the paper roll.

3, The effect on the usability of the paper roll.

The results of these assessments were as follows;

End wall guard according to End wall guard according to

Object the invention the standpoint of techniques

Nut 1. 3 mm, unbroken surface 1. 0.5-1 mm, unbroken surface

2. Slight effect 2. Slight effect

3. None 3. None

Screw 1. 2 mm, slight rupture 1. 3 mm, broken surface

2. Slight effect 2. Pronounced damage

3. None 3. Risk of web fracture

Stone 1. 3 mm, unbroken surface 1. 4 mm, broken surface

2. Slight effect 2. Pronounced damage

3. None 3. Risk of web fracture

Concrete 1. 10 mm, unbroken surface 1. 10 mm, broken surface

2. Deep, but gentle edges 2. Deep, sharp edges

3. Probably none 3. Risk of web fracture As will be seen from the aforegoing, the sheet material according to the invention that was used as end wal guards for paper rolls withstood the disturbing effects of the objects in a better way than the typical corrugated paperboard end wall guards. This is remarkable in view of th fact that the corrugated paperboard circular blanks command much higher price than circular blanks in the form of sheet material according to the invention.

Claims

1. Sheet material manufactured piecewise and having a dry solids content greater than 90% and comprised at least partially of cellulose pulp fibres, characterized in that the material contains

a) a mixture of filler and pulp fibres deriving from the manufacture of paper and recovered in the form of sediment, in an amount corresponding to at least 30 and at most 95% of the weight of the sheet material; and b) pulp fibres in the form of virgin fibres and/or secondary fibres, essentially as reinforcing fibres.

2. Sheet material produced piecewise according to Claim 1, characterized in that the material contains sediment according to a) in an amount corresponding to at least 50% and at most 90% of the weight of the sheet material.

3. Sheet material produced piecewise according to Claims 1-2, characterized in that the material contains a chemical which renders the material hydrophobic and/or colour pigment and/or a barrier layer.

4. Sheet material produced piecewise according to Claims 1-3, characterized in that the surface weight of the material exceeds 300, preferably 500 g/m².

5. Sheet material produced piecewise according to Claims 1-4, characterized in that the material has an undulating cross section.

6. Sheet material produced piecewise according to Claims 1-5, characterized in that the material forms part of a laminate.

7. Sheet material produced piecewise according to Claim 6, characterized in that the laminate furthermore comprises of a paper sheet or a plastic sheet fastened to the sheet material.

8. Sheet material produced piecewise according to Claims 1-7, characterized in that the material has a round shape and is used as end wall guards for paper rolls.

9. A method of producing intermittently sheet material from an aqueous suspension which includes at least partially solid substances in the form of cellulose pulp fibres in low concentration, characterized by delivering a suspension which contains a mixture of filler and pulp fibres recovered from a paper manufacturing process in the form of sediment, and essentially reinforcing fibres, to a firmly anchored lower part having a given shape and given volume of a forming apparatus whereupon moving a corresponding, movable upper part of the forming apparatus down into the lower part so as to collect the solid substances in the form of a coherent sheet in a space between the lower part and the upper part delimited by a wire or wires, while removing water from the forming apparatus; and lifting the formed sheet from the lower part of the forming apparatus with the aid of the mentioned movable upper part and with the aid of a vacuum; and thereafter drying the sheet to a high dry solids content.

10. A method according to Claim 9, characterized by placing the lower and/or the upper part of the forming apparatus under subpressure (vacuum) or an overpressure during at least part of the water removal phase.

11. A method according to Claims 9-10, characterized by maintaining the suspension in motion prior to and/or during part of the forming process with the aid of a pump connected to a circulation line whose inlet and outlet ends respectively are connected to the lower part of the forming apparatus.

12. Apparatus for producing intermittently sheet material having a dry solids content within the range of 15-25% and comprised at least partially of cellulose pulp fibres, characterized in, that the apparatus shows a firmly anchored lower part (1) having a given form and given volume containing a perforated or otherwise liquid permeable material layer (5) which is placed essentially horizontally, and above said layer a wire (6) and means for removing water (7, 8) and means for applying a subpressure (vacuum) or overpressure (9, 10), and a movable upper part with a given volume (2) which fits well into the lower part, containing a perforated or otherwise liquid permeable material layer (5) and a beneath said layer situated wire (6) and means (11) for applying a subpressure (vacuum).

13. Apparatus according to Claim 12, characterized in that the upper part (2) also includes means for applying an overpressure.

14. Apparatus according to Claims 12-13, characterized in that the perforated or otherwise liquid permeable material layer (5) rests against a supportive device (4) in the lower part and/or the upper part.

15. Apparatus according to Claims 12-14, characterized in that the perforated or otherwise liquid permeable material layer (5) is undulated.

16. Apparatus according to Claims 12-15, characterized in that the upper part (2) includes means for removing water.

17. Apparatus according to Claims 12-16, characterized in that the lower part (1) and the upper part (2) have any desired cross sectional shape and are surrounded by a sealing mantle or peripheral coaming in the form of an upstanding or slightly inclined edge part (3).

18. Apparatus according to Claims 12-17, characterized in that the mantle part (3) or peripheral coaming of the lower part has mounted thereon an inlet pipe (12) and an outlet pipe (13) for connection to a circulation line and a pump.

19. Apparatus according to Claims 12-18, characterized in that the lower part (1) and the upper part (2) have a circular cross section.