NO781534L - PROCEDURE FOR MAKING A CELLULOSE PRODUCT - Google Patents

Description

Procedure for the production of a cellulose product.

The present method relates to a method for the production of several layers of cellulose fiber products, for example paper, cardboard, folded cardboard, as well as a product thus obtained, and is

a further development of the invention described in UK patent no. 1,473,838. In what follows, the invention will be described with reference to the production of paper and cardboard.

In the aforementioned British patent, a method is described for wetting a dry-laid web of cellulosic fibrous material by combining a sheet of aqueous cellulose pulp or wet-laid web of cellulose fibers with a dry-laid web of cellulose fibers and consolidating the resulting combination by subjecting this to heat and Print. In the aforementioned patent it is also indicated to combine two such consolidated combinations into one. "back-to-back" relationship, whereby the wet-laid webs form the outermost layers of the product and the dry-laid webs form the inner layers of the final product. It will be understood that such a final product, produced from two pre-consolidated layer combinations, will have a relatively uniform strength throughout its thickness.

British patent no. 1.4 35,703 shows the consolidation of a dry-formed cellulose web by means of heat and pressure and the arrangement of this web between two wet-formed webs. It will also be understood that a product thus obtained will have a relatively uniform strength throughout its thickness.

The method of dry-laying cellulose fibers to give a dry-laid web, as well as the method of consolidating a dry-laid web using heat and pressure to give strength to the web, is described in UK patent no. 1,424,682. In the present description, the term "consolidation" of a dry-laid cellulosic fiber web is used in the sense that appears in the British patent. 1.4 24.68 2.

The mechanism by which consolidation by heat and pressure produces strength in a dry-laid web is not yet fully understood, but it is believed that such consolidation involves the formation of a high degree of hydrogen bonds between the fibers.

It is an aim of the present invention to provide a multi-layer cellulose fiber product with strength and stiffness concentrated in its outer layer, where in such a product the most favorable properties for wet and dry laid cellulose webs are utilized.

According to one feature of the invention it is provided

a method for producing multi-layered cellulose fibers, comprising wet-laying cellulose fibers to give first and second wet-laid layers, dry-laying cellulose fibers to give at least one dry-laid layer and arranging this or these layers between the wet-laid layers to give a product where the or the dry-laid layers are consolidated by heat and pressure, after the dry-laid layer or the dry-laid layers have been combined with at least one of the wet-laid layers. When a dry-laid sheet is combined with a wet-laid sheet in a "sandwiching" process, the two sheets are brought into contact with each other either by placing one on top of the other or by pressing them into contact with each other and the layers in the resulting combination are then firmly bound to each other, even if they can be visually separated from each other.

Preferably, it or each of the dry-laid layers will be consolidated after it has been laid between the wet-laid layers.

At least one of the wetted layers can form an outer layer of the product and preferably both outermost layers of the product are made up of wetted webs.

The consolidation is preferably carried out by compressing the combination of the one or each of the dry-laid layers with one or both of the wet-laid layers in contact with a heated consolidation cylinder by means of a number of pressure rollers arranged | ' in distance around the cylinder. The temperature for consolidation rolling is preferably at least 65°C and each pressure roller is applied with a pressure of at least 25 kp/cm. Consolidation cylinder's. temperature is preferably in the range 90 - 180°C and the line pressure provided by each pressure roller is preferably in the range 35-45 kp/cm..

The moisture content of the cellulose fibers which make up the dry-laid layer or layers is preferably in the range of 6-12% by weight immediately before the fibers are laid.

After it or each of the dry-laid layers has been dry-laid, but before it or they are combined with a wet-laid layer, it or each of the dry-laid layers can be sprayed with water to bring the moisture content up to 20-25% by weight. Alternatively, the necessary moisture content for the consolidation of the dry-laid layer or layers can be added entirely from the moisture content of the wet-laid layers or webs.

The method can also include arranging a wet-laid layer between two dry-laid layers and then applying each of the dry-laid layers between outer, wet-laid layers, before consolidation.

The method may alternatively comprise the combination of a single dry-laid layer with a wet-laid layer, which is consolidated and then combined with an outer wet-laid layer against the dry-laid layer to give a dry-laid layer arranged between two wet-laid layers. The preferred embodiment of the method includes arranging at least one dry-laid layer between a pair of wet-laid layers and then consolidating the combination.

Up to 5% by weight of starch or other binder can be applied to the or each of the dry-laid layers before combining with a wet-laid layer.

Each of the wetted layers can be deposited from an inlet box from

a form cylinder, or by means of a Fourdrinier machine.

in

According to another feature of the invention, a multi-layer cellulose-containing fiber product comprising at least

one dry-laid layer arranged between two overlying wet-laid layers and consolidated according to the method according to the first move.

In what follows, the invention shall be described under reference

ning tilde attached drawings, where

Fig. 1-5 schematically show five alternative embodiments of an apparatus according to the invention. Fig. 6 - 9 are block diagrams showing alternative methods according to the invention, and Fig. 10, 11 and 12 show schematic cross-sections through three multi-layer products according to the invention.

With reference to fig. 1 - 4 are shown in each of these

at least one device, generally indicated by 10, for dry laying of cellulose fibers and which comprises an endless, perforated forming wire 11, one or more discharge devices 12, arranged above the wire, as well as a vacuum box 13 below the wire 11 immediately below each discharge device. Dry fibers, for example wood cellulose fibers mixed with 5% starch binder and • containing 6 - 12% by weight moisture are transported by means of an air distribution system (not shown) in an air stream through the discharge device(s) 12 and down onto the upper surface of the wire 11

to provide a dry-laid fiber mat on this, as the carrier air is drawn through the wire 11 by means of the vacuum box 13. A pressure

nip is provided by the rollers 14 which give a line pressure of 8

16 kp/cm to the dry-laid mat and compacts it. Water is then sprayed onto the compacted mat from a water spray device 15 to bring the moisture content of the dry laid mat up to 20-25% by weight.

Referring in particular to Figure 1, a first is shown

and second wet forming cylinder machine indicated by 16 and 17 respectively. The first forming cylinder machine 16 comprises a

forming cylinder 18, an inlet box provided with an explosion chamber and a slot 19 of the type described in the British patent applications Nos. 19053/75 and 7070/77, in the subsequent |

referred to as a "former", for depositing a wet cellulose fiber mass on the forming roll 18, a first transfer roll 20 in contact with the forming roll 18, a second! transfer roller 21 in contact with a consolidation cylinder 22, which is heated to at least 65°C/.as well as an endless wire 23 which lies around the first and second transfer rollers 20, 21.

The second cylinder forming machine 17 likewise comprises a forming cylinder 24, a former 25 for depositing a wet fibrous cellulose mass on the forming cylinder 24, a transfer roller 26 in contact with the forming cylinder 24, a gusset cylinder 27 in

contact with the wire 23, as well as an endless wire 28 which lies around the rollers 26 and 27.

At least two pressure rollers 29 are arranged in contact with the heated consolidation cylinder to provide a pressure nip of at least 25 kp/cm around its periphery, as well as a final take-off roller 30 for transferring the web coming from the consolidation cylinder 22 to a known drying and surface treatment section (not shown).

On each of the wires 23 and 28, wet-laid cellulose webs are formed with the aid of the cylinder forms and the forms. The dry-laid web on the wire 11 is transferred onto the wet-laid web on the wire 28 by means of the transfer roller 31 in contact with the wet-laid web on the wire 28, and at a pressure of 1.7-35 kp/cm. The combined webs on the wire 28 are then transferred to the wet-laid web on the wire 23 by means of the gusset roller 27 at a pressure of 1.7 - 3.5 kp/cm, so that the dry-laid web lies between the two wet-laid webs. The three-layer web, which typically has a total moisture content of 30% by weight, is then fed to the consolidation nips arranged around the periphery of the consolidation roll at a temperature of 115°C and with a nip pressure of 45 kp/cm. The consolidated three-layer web is then fed to drying and finishing sections.

The consolidated three-layer web has a structure as shown schematically in cross-section in fig. 10 and comprises a relatively voluminous (bulky) middle dry-laid layer 32 lying between two strong skins 33 provided by the wet-laid layers. The web has been found to exhibit smooth surfaces, good folding properties, a stiffness ratio (machine direction/cross direction) in the region of 1.5:1, as well as a total stiffness of approx. twice that of a normal, dry-formed track.

With reference to fig. 2 shows the first and second wet laying machines 34 and 35, which respectively comprise the cylinder forming machines 36 and 37, the formers 38 and 39, as well as the endless wires 40 and 41, and which are arranged so that each former supplies the mass directly to each its wire. There are arranged two dry-laying sections 10/, each of which with respect to structure and operation is as shown in fig. 1, and arranged so that successive dry-laid webs are transferred onto the wet-laid web on the wire 40 by means of the transfer rollers 42 and 43 at a line pressure of 1.7 - 3.5 kp/cm. The wet-laid web on the wire 41 is then transferred onto the dry-laid webs on the wire 40 by means of the transfer rollers 44 at a line pressure of 1.7 - 3.5 kp/cm, so that the dry-laid webs lie between the outer wet-laid webs . Water spraying devices 49 are arranged at a distance along the wire 40's direction of movement, so that sufficient moisture is provided to the dry-laid webs, so that the multi-layer web has a total moisture content of 30% and is thus ready for consolidation.

The four-ply web is then transferred to the consolidation cylinder 45 and nips are arranged along the periphery by means of pressure rollers 46, where the web is consolidated at the temperature and pressure described with reference to fig. 1. The consolidated web is then transferred to finishing sections (not shown).

The consolidated, four-layer web has a structure which is schematically shown in cross-section in fig. 11, and comprises two relatively voluminous, dry-laid middle webs 47 "sandwiched" between strong skins 48 provided by the wet-laid webs.

With reference to fig. 3 shows an arrangement for wet and dry laying devices, corresponding in terms of design and operation to that shown in fig. 2 (corresponding parts are given the same reference number as in Fig. 2) except that a further wet laying machine 50, corresponding to machine 34, is arranged between the dry laying machines, so that a wet laid layer can be "sandwiched" between the two dry laid paths . It will be noted that water spray devices 49 are directed at the dry laid webs before they leave the dry laying machines.

The five-layer web which is consolidated by means of the apparatus of fig. 3 has a structure which is schematically shown in cross-section in fig. 12

and comprises in sequence an outer wet-laid layer 51, a voluminous dry-laid layer 52, a middle wet-laid layer 53, a voluminous dry-laid layer 54 and an outer wet-laid layer 55. It has been found that the wet-laid layer 53 provides additional moisture to. ensure consolidation of the innermost parts of the dry-laid tracks.

With reference to fig. 4 shows a dry laying machine 10, first and second wet forming machines 56 and 57, as well as a consolidation cylinder 58. The wet forming machines 56, 57 each comprise a round wire 59, 60 each immersed in a trough, formers 61

and 62, endless wires 63 and 64, transfer rollers 65, 66 which press the wires against the round wire cylinders, and transfer rollers 67 and 68 which press the wires towards the consolidation cylinder.

The endless wire 11 of the dry forming machine is passed around the transfer rollers 69 and 70, which are spaced around the periphery of the consolidating cylinder 58 which provides sufficient pressure to provide consolidating nips. A further consolidation roll 71 abuts the consolidation cylinder in its peripheral area between the rolls 69 and 70. It will be seen that the endless wire 11 of the dry forming machine is held against the surface of the consolidation cylinder over part of its periphery. A water shower 15 is applied to the dry-laid web before it reaches the consolidation cylinder to bring the web's water content up to that required for consolidation.

The wet and dry laying machines are arranged so that the wet laying machine 56 applies a wet laid web to the consolidation cylinder, the dry laying machine 10 applies a dry laid web on top of the wet laid web on the consolidation cylinder, and the combined webs are consolidated at temperature and pressure as described with reference to fig. 1, the wet laying machine 57 applies a second wet laid web to the consolidated, combined webs on the consolidation cylinder at a line pressure of 25 kp/cm to provide a three-ply web of the type described with reference to FIG. 10. The three-ply web is then removed from the consolidation cylinder and taken to per se known drying and finishing sections (not shown).

Fig. 5 schematically shows a side section of dry-laying and wet-laying machines that can be used in the production of a four-layer track as schematically shown in fig. 11.

In Fig*5, two discharge heads 101 and 102 are shown for dry laying of cellulose fibres. to form two consecutive cellulose webs, one on top of the other, on a perforated movable forming wire or belt 103. Below the wire 103 and immediately below the discharge heads 101 and 102 are respectively arranged the vacuum boxes 104 and 105 to draw the fibers down on the wire. A pressure former 106 deposits a web of wet cellulose mass on a second movable forming wire or belt 107. The mass deposited on the wire 107 is dewatered by dewatering foils 108 and vacuum boxes 109. The dry-laid webs on the forming wire 103 are transferred onto the wet-laid web on the forming wire 107 by the gusset rollers 110 , 111 at a line pressure of 1.7 3.5 kp/cm. The gusset roller 111 is adjustable as indicated by the arrows 112. A second web of wet cellulose mass is deposited from a trough-former 113 on an endless wire 114 when this is guided around a winding cylinder 115. A further layer of cellulose mass can optionally be deposited on the other web that already lies on the wire 114 by means of a projection former 116. De-watering foils and a collection suction hood 118 are arranged for de-watering the web on the wire 114. The combined dry-laid and wet-laid webs on the wire 107 are transferred to the wet-laid web on the wire 114 by means of rubber rubber rollers 119 at a line pressure of 1.7 - 3.5 kp/cm, so that they*', dry- laid webs lie between the wet-laid webs provided respectively by the troughless former 106 and the wet-laid web provided by the trough former 113. The obtained four-layer web over-| is fed from the wire 114 onto a further second endless wire 120 by means of the transfer roller 120 around which the wire 114 is laid in contact with the vacuum transfer roller 112 around which the wire 120 is laid. Vacuum provided by the roller 122 ensures that the web is transferred to the wire 120.

The web carried by the wire, 120 is passed around part of the circumference•

of a consolidation cylinder 123 heated to a temperature of 115°C and pressed against the surface of the consolidation cylinder 123 by means of three pressure rollers 124 - which abut against the underside of the wire 120, and which in the nips provide a line pressure of at least '25 kp/cm , preferably 35 - 45 kp/cm around the periphery of the cylinder 123.

The consolidated four-layer web 125, the structure of which is schematically shown in cross-section in FIG. 11, is then taken by the consolidation cylinder 123 to known drying and surface treatment sections (not shown).

The operation of the procedure is shown in block form in the attachments

fig. 6-9, from which it can be seen that a dry-laid inner web is combined with at least one wet-laid web before it is consolidated, and preferably, as shown in fig. 6-8, are placed between two wet-laid lanes before consolidation.

The wet laid webs can be formed with a basis weight in the range 10 - 100 g/m 2 and the dry laid web(s) with a basis weight in the range 20 - 300 g/m 2 , which gives a total basis weight for the product in the range of 40 - 900 g/m 2. In a typical installation, each of the wet-laid outer layers may have a basis weight of 30 g/m 2 and the inner, dry-laid web a basis weight of 200 g/m 2, giving a total basis weight of 260 g /m<2>.

The attached table shows certain properties of cardboard produced according to the invention compared to cartons produced according to known dry-laying and wet-laying techniques.

In the table, A indicates a dry-laid board comprising two outer layers of bleached cellulose pulp and a middle layer of flash-dried mechanical pulp,

B and C are typical wet-formed cartons,

D is a double-lined wet-formed white board comprising two outer layers of bleached cellulose pulp and an inner layer of mechanical pulp, E is a two-layer board consisting of wet-laid dg dry-laid web, and F and G are two three-layer boards according to the invention and comprises a dry-laid track arranged between two wet-laid tracks and

then consolidated,

MD indicates the carton's machine direction, and

XD indicates the transverse direction of the carton.

From the table it can be seen that the dry-laid carton (A) is almost "square" in the sense that the stiffness ratio in the machine direction and the transverse direction is approximately equal to 1, while the wet-formed cartons (B, C, D) have a stiffness ratio of 3 or more, and is consequently not "quadratic". However, the overall stiffness of the wet-formed cartons (determined by ^MD.XD) is significantly higher than that of the dry-laid carton.

The multi-layer cartons (E, F, G) have stiffness ratios comparable to that of the dry-laid carton (A), but have a total stiffness of is comparable to that for the wet-sealed cartons (B, C, D). In particular, the overall stiffness of the cartons (F, G) according to the invention is significantly better than that of the ! some of the wetted cartons. Consequently, a carton manufactured according to the invention will combine the stiffness of a wet-laid carton with the "square" properties of a dry-laid carton.

A further advantage of the carton manufactured according to the present invention is that the middle part of the carton is relatively voluminous and has low strength compared to the strength and the higher density of the wet-formed outer layers, and thus concentrates the product's strength in the outer layers and thereby promoting the cardboard's folding or folding properties.

Furthermore, gluing and surface-improving agents can be added to the mass for the wet-formed webs before these are laid, and thus the need to apply glue and surface-improving agents to the finished product is avoided.

It is not necessary to add water to the wet-laid web because the water content in the wet-laid webs can be sufficient to provide consolidation of the dry-laid miter web.

Alternative choices of wet forming machines are available for the method of the invention. For example, conventional troughless formers or round wire machines or Fourdrinier machines equipped with vacuum boxes can be used.

Although four embodiments have been described, it will be understood that there are many possibilities for the production of a multi-layer product comprising a dry-laid web arranged or gusseted between two outer wet-laid webs. E.g. for dry laying, a number of dry laying heads can be used for one dry laying wire. Vacuum cylinders can be used in connection with the wet laying wires. One small degree of consolidation can be added to the dry-laid web before it is combined with wet-laid webs, after which the combination is given a full consolidation action. Dry fibers can also be laid directly on a wet-laid track. Dry-laid webs can be combined with wet-laid webs and then joined back-to-back (ie dry-to-dry) before final consolidation.

The temperature for the consolidation cylinder is typically in the range 65 - 18<0>°C and the consolidation pressure applied by each consolidation roller is in the range 25 - 45 kp/cm, but temperature and pressure outside these ranges are possible for special applications.

Up to 15% by weight of starch can be added to the dry fibres.

The foldability of the multi-layer product produced according to the invention can advantageously be compared with the foldability of the best wet-sealed cartons.

Claims (17)

1. Method for the production of a multi-layered cellulose fiber product, characterized by wet-laying cellulose fibers to give a first and second wet-laid web, dry-laying cellulose fibers to give at least one dry-laid web and placing it or each of the dry-laid webs between wet-laid webs to provide a product wherein the or each of the dry-laid webs is consolidated by means of heat and pressure after it is combined with at least one of the wet-laid webs. 2. Method according to claim 1, characterized in that each dry-laid track is consolidated after it is placed between the wetted lanes. 3. Method according to claim 1, characterized by . that the consolidation is carried out by pressing the combination of the one or each of the dry-laid webs with one or both of the wet-laid webs in contact with a heat consolidation cylinder provided with a number of pressure rollers arranged around the cylinder. 4. Method according to claim 3, characterized in that the consolidation cylinder is used at a temperature of at least 65°C. 5. Method according to claim 4, characterized in that the consolidation cylinder is used at a temperature in the range 90 - 180°C. 6. Method according to claims 1-5, characterized in that each pressure roller is applied with a line pressure of at least 25 kp/cm. 7. Method according to claim 6, characterized in that each of the pressure rollers is applied with a line pressure in the range 3 5 - 4 5 kp/cm. 8. Method according to claims 1-7, characterized in that the moisture content of the cellulose fibers which provide the or each of the dry-laid webs is used with a moisture content in the range of 6-12% by weight immediately before the fibers are laid. 9. Method according to claims 1-8, characterized in that after the or each of the dry-laid tracks is dry-laid, but before it or they are combined with a wet-laid track, the wet-laid tracks or tracks are sprayed with water to bring the moisture content up to 20 - 25% by weight. 10. Method according to claims 1-8, characterized in that the moisture required to consolidate the or each of the dry-laid webs is entirely provided by the moisture content of each of the wet-laid webs. 11. Method according to claims 1-10, characterized in that up to 5% by weight of starch or other binder is added to the or each of the dry-laid webs before the dry-laid webs are combined with a wet-laid web. 12. Method according to claims 1-11, characterized in that the wetted web provides an outermost layer of the product. 13. Method according to claim 12, characterized in that both outer layers of the product are provided by wet-laid webs. 14. Method according to claims 1 - 13, characterized by adding a wet-laid web between two dry-laid webs and then arranging on each side of the dry-laid webs outer wet-laid webs before consolidation. 15. Method according to claims 1-13, characterized by combining a single dry-laid track with a wet-laid track, consolidating the combination and then arranging a second wet-laid track with the dry-laid track to provide a dry-laid track between two wet-laid tracks. 16. Method according to claims 1-13, characterized by arranging at least one dry-laid track between a pair of wet-laid tracks and then consolidating the combination. 17. Method according to claims 1-16, characterized in that each wet-laid web is deposited from an inlet box provided with an outlet slot, cylinder forms or trough turning machine or with the help of a Fourdrinier machine.