FI111867B - Process and system for making a dry-formed paper material - Google Patents

Abstract

For the manufacturing of dry-formed webs of cellulose fibres there are two different ways of binding the fibres, viz. an application of glue to the web surfaces and, respectively, an admixing into the fibre charge of heat actuated binding fibres that are actuated by passing the web through a heating zone. The latter method is the better in practice, of course, in particular for liquid absorbing products, but the problem exists that the finished material is dusting with short, unbonded fibres. According to the invention it has been realized that it is possible to widely avoid this problem by auxiliary use of the first method, modified to the effect that both surfaces of the web are concurrently subjected to a supply of a very small amount of glue in foamed condition, e.g. with only 1 gram per square meter, whereby the surfaces remain permeable, but also sealing against extrusion of short fibres from inside the web.

Description

111867

The present invention relates to a process for producing dry-formed paper material by sequentially adding a web of cellulosic fibers to a forming wire and treating the web to form a bond therethrough of the fibers therein.

The invention also relates to a system for performing the method of the invention, comprising a device for applying fibers dry to a forming wire to form a fiber web and a device for activating a means for binding fibers.

The dry formed fibrous web material may be formed on the basis of dry formed cellulose fibers by suitable bonding. Arrangement of the fibers to form the current web is usually accomplished with pulp material which is defibrated and blended into an air stream that leads to loose fibers above the movable, perforated forming wire, below which is located a suction chamber for suctioning down the fibers is the desired web thickness. The products are typically used as liquid suction sheets.

It is important that the dry web is stabilized or fixed,. and in practice this is achieved in two different ways, namely by using 'glue' or by using bonding fibers: 1. Gluing: The pulp web is transported by means of a carrier wire through a gluing station, where: ' through the tunnel furnace

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'·': To open. The web is then transferred to an air wire against which it is secured by an overhead suction so that the underside of the web is visible, and then the web is passed through or over another gluing station, where the glue is sprayed towards this underside of the web, respectively. The web is then passed through another tunnel oven for drying the adhesive and final curing, after which the web is self-supporting and can be wound for storage or delivery.

By this method, sheet webs can be produced which are of relatively good quality, but the machine is demanding and sensitive to the irregularities of the gluing stations 10. A further limitation is that the method is unsuitable for thick sheet webs because it is difficult to achieve a high penetration depth of the adhesive, whereby the relatively thick layer tends to separate at a medium level where the bond is weak or completely absent. The products typically contain about 85% cellulose fibers and about 15% binder. Typical product weights can range from 50 to 120 g / m 2 because heavier products are easily delaminated. In addition, the products are poorly suited to contain superabsorbent.

2. Use of binding fibers: By this method, cellulose fibers are formed; A homogeneous mixture of heat-activated bonding fibers, also called:.:.: Also heat-bonding fibers, whereby the dry formed web material can be • 'attached simply by passing through the heating zone. In terms of system and control, this is a simpler method that can also be used to produce thick webs, since the binding fibers are uniformly present on both the outer and inner planes of the material. The weight of the product can typically be 40 -. . 800 g / m 2, and may be used with substantial mixing of superabsorbents or other additives. Achievable quality is in many

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; however, for certain applications, certain drawbacks may exist> »· • ;;; the fact that the percentage of heat-binding fibers that are already blended is, for economic * 30 reasons, typically limited to about 15%. Normally, cellulosic fibers have lengths between 0.5 and about 5 mm, while thermal bonding fibers are often 6 mm or more. In practice, this provides very good bonding of the longest cellulosic fibers, while very short cellulosic fibers are insufficiently bound. This means that the material can be dusted with short fibers, which is usually a major disadvantage, and therefore the products are mainly used as cover sheet materials in outer wraps, thus eliminating dust defects on the outside, but appearing on a large scale inside factories. effective drainage systems which cause problems themselves must be used, and it should be added that the associated suction of 'dust' implies the removal of a substantial part of the original material, thus rendering it completely redundant and thus representing a real waste. .

The invention seeks to counter said fiber dusting, which naturally leads to speculation of a higher percentage of bonded fibers of different sizes. However, this is hardly a realistic possibility, and kek-15 will find that a better solution is the combined use of the two methods, but with the gluing method in modified form.

As mentioned, the bonding method achieves a bonding result that is best at 20 on the web surface and worse at the middle layer of the web, but if the combined use of heat-binding fibers is merely to seal the web against dust, this can be achieved by coating the web well »· '·' · With thin surface layers. Since the cohesiveness of the web material is ensured by activating the heat-binding bonding fibers, the surface adhesive can be applied simultaneously to both sides of the self-supporting web, and both of the added layers of adhesive, both of which may be extremely thin, can be cured by relatively small capacity. When the surfaces of the web material thus exhibit a thin • ;;; This is to say that the invention is not speculation> I · • ': of any increased local bonding of said fibers to the adhesive bonding of the short fibers; 111867 4, although the effect may partly depend on the specific occurrence of increased fibrous webs on the surface, while to a lesser extent the actual surface coating.

Thus, the process according to the invention is characterized in that the binding of the fibers is accomplished by activating a combination of heat-binding fibers previously supplied by blending into cellulosic fibers and adding a binder to the web surfaces, wherein the addition is substantially below 15%, preferably 0.5-5% to bind short cellulose fibers.

The system of the invention is characterized in what is set forth in independent claim 9.

Preferred embodiments of the invention are characterized in what is set forth below in the dependent claims 2 to 8 and 10.

Thus, the web surfaces are sealed to a greater or lesser extent by adding reasonable amounts of adhesive without the requirement of adhesive penetration * 20 deep into the material. Thus, it is not critical how the adhesive is added, but one important sub-aspect of the invention is to express how the adhesive can be added in a new and very economical way to achieve the desired result.

Thus, according to the invention, it is advantageous for the adhesive to be added in a foamed state whereby it can cover the surfaces with a minimal amount of dry matter. An effect has been found that the liquid in the precipitating foam »} · is preferably deposited between the fibers by cross-cutting •; instead of general deposition on the fiber surfaces, this effect is optimal for the desired result, namely, by using small amounts of both liquid and dry matter, the binding of short fibers on the surface is achieved by remain in place 111867 5 and partially assist in sealing short and unbound fibers from intrusion of web material. This stays light and porous so that it is suitable for, for example, impregnated wipes.

A good effect can be achieved by mixing only 1-2 g binder / m 2 / side using about 2 g dry mass / l of foam dispersible in water. The foam may be formed in a conventional foaming unit, and the adhesive may then represent only about 0.2% by volume in the foamed volume. Correspondingly, the product needs to be dried with very low water, whereby the drying and curing of the adhesive can be carried out with a relatively low energy consumption in the subsequent curing zone.

The foam can be applied in any suitable manner, for example by vertical, inclined or horizontal feed of the web through opposing rolls, by controlled delivery of foam to the roll opening on both sides of the web. The web treatment of the web gives an interesting result in that the surface fibers adhere at resting positions, giving the surface a smoother and firmer character.

: 20 • \. · 'The penetration depth of the pre-foamed binder can be controlled by: · mixed wetting agents. If the penetration depth is too small, the thin binder layer on the surface will soon rub off, and if the depth is too large, this will in part result in unnecessarily high binder consumption, and 25 will give the product a plastic character with slow water absorption.

'As mentioned above, the adhesive can be dried and cured with a low energy *; but may still occur at such a high temperature '; In that the binding fibers can be reactivated, and as explained below, this can give the most excellent result that the tensile strength of the web can be almost doubled.

6, 111867

The invention provides significant results in designing manufacture for products having the desired properties without gradually changing said properties from short fiber products through extraction. Because this amount of fiber can be of significant size, the associated result is that it can be placed much better to achieve the desired properties of the final product.

A preferred embodiment of the invention is schematically illustrated in FIG.

The drawing shows a forming wire 2 having a transport space 4 below a pair of dosing ends 6, which is a pair of dosing ends 6 for supplying a mixture of loose cellulosic and thermoforming fibers 4 thereby forming a loose web 8. The latter is squeezed between 12 through the 14 air transfer stations. The wire 12 passes the web through the heating zone 16, where the heat-binding fibers are activated to bind the cellulosic fibers, normally at a temperature of 130-140 ° C. Thereafter, the now stabilized and self-supporting web is passed through rolls 18 of the c: 20 stack. Conventionally, the web, which is now a strip of product, is then wound on rolls of finished products 34.

However, the invention has a post-coupled station 20, in which the web 22 is provided · with a binder foam bilaterally, preferably leading the web downward 25 around a deflection roll 24 to a so-called foulard unit consisting of a pair of rolls 26 and a non-described upper means for applying the impregnating compound 28 to the upper roll spacing * · * on both sides of the downwardly guided web 22.

»· 30 Thus, it is possible to control the delivery of the impregnating compound partly by adjusting the gap between the connected rolls and partly by adjusting the flow of the compound ': to a higher or lower level above the roll opening, e.g. Furthermore, the delivery in this case can be adjusted by the dry solids content of the binder (for example, between 5 and 15%) and by adjusting the foam density, for example between 20 and 100 g / l.

The hardness / softness of the product can be controlled by selecting a binder which is a hard or soft film, respectively, while the hydrophilicity / hydrophobicity properties of the product can be controlled by means of suitable pre-foaming agents or additives.

After passing the unit 22, the web 22 is taken to the belt 30 through a heating tunnel 32 where the web, preferably by the addition of hot air, is heated to rapidly evaporate the aqueous portion of the foam 28, after which the web is wound on a conventional delivery roll 34.

Surprisingly, it has been found that using a suitably high temperature in the tunnel furnace 32, preferably 130-140 ° C, not only achieves efficient water evaporation but also improves the tensile strength of the web product by up to 25-100%. This cannot be explained by the very reasonable application of adhesive to the outer surfaces of the web 22, but by other factors, however: ** 20

As the web 8 passes through the rolls 10, it is pressed against the carrier wire 2, which is a "normally woven mesh fabric made of intersecting yarns / • goats which, through interconnected intersections, form local, * upwardly protruding and lowered portions, At the protruding portions * ♦ 25, the fibers in the web are pressed excessively as they pass past the rolls 10 so that the fibers thus locally pressed down are particularly sensitive to the welding effect in the heating zone 16.

* [However, this condition is exacerbated by the fact that as the passage unit 14 passes, the web ';;: somewhat loosens due to weak traction and web movement, f · * · 30 necessary to remove the web from the forming wire and transfer it to the transport wire, just as loosening occurs when transferring from the conveyor wire to the oven wire. Besides, the compressed web has 111867 8 specified expansion powers, and thus the initially well-compressed fibers are not all well-compressed when passing through the curing tunnel 16.

However, as the web 22 subsequently passes through station 20, a new compression of the web 5 and a certain increase in cohesiveness in the surface layers of the web occurs such that not only said water evaporation from the foamed adhesive during passage through the next oven unit 32 occurs operating at about the same temperature as in the tunnel 10 16, for example at about 140 ° C.

Thus, the adhesive treatment of the web is some kind of catalyst for the next achievement of significantly increased tensile strength of the web material.

The immediate result of the invention, namely bonding or compacting the "dust fibers" while retaining the non-compacted surface, is also advantageous in another way because the retained amount of said fibers just below the solid surface layers has a significant liquid-spreading effect which is very important for absorbent products. For many of these products, it is almost known in advance that * 20 fluid deliveries during use occur only within the product range, and a superabsorbent must be dosed for the desired absorption capacity. If the product may exhibit good distribution, the administration of superab- * · sorbent can be minimized.

4 i # I> · v '25 There is a reason to emphasize that water-based foam can be added super ... on both sides of a product having a central layer of absorbent material without the need for said material to be activated with water.

For example, the product may have a fiber base layer of 70 g / m 2, a superabsorbent middle layer of 30 g / m 2, and a fiber coating layer of 30 g / m 2.

»· * · 9 111867

The invention is also advantageous in the case of filter materials in which both a significantly reduced dusting and a sustained concentration of short fibers have a positive effect.

According to the invention, it is possible to use a binding foam as a carrier for color pigments, whereby these are added prior to foaming, whereby a certain coloring of the products can be produced in the simplest way. However, since the binder is normally used in very modest amounts, only pastel dyeing can be achieved unless the process is specifically adapted to 10 more effective dyes.

The invention has proved possible to foam-coat a heat-bonded, air-spreaded product containing only a few percent binder fibers, for example 5%, by adding an increased amount of gum binder, for example 15 to 10%, which makes it possible to produce essentially "latex . Thus, the same abrasion-resistant surface as conventional spraying of the binder is achieved, but without the associated limitation on the maximum thickness of the web, which is usually 100-120 g / m2. At such thicknesses 20, it has been necessary to impregnate the web to avoid delamination of the product, but this may not be the case at present, which means, among other things, that relatively low density products can be manufactured. When supplied with a significantly reduced amount of adhesive according to the invention, the thick products contain a significantly increased amount of cellulosic non-adhesive film, and thus have optimum absorption capabilities.

* * • · »* ':' It is advantageous for the process that the binder addition is performed at only one site of the system and not at two sites as in the prior art. In addition, it is most advantageous to avoid conventional spraying stations, which cause many problems both in operation and maintenance, although, for example, fou-Lard provides a good and even handling result and is easy to maintain. However, other foaming techniques, such as wire coating, could be used.

In principle, nothing prevents the addition of the binder foam to the web prior to its thermal bonding, in which case it may be sufficient to use a single heating zone to react both the binder fibers and the sizing agent.

Finally, a few examples of the preparation of special products 10 according to the invention are given: A. Foam control. producing a hydrophilic product.

An air-coated product of 60 g / m 2 consisting of 85% wood pulp 15 fiber with maximum long fiber content and 15% heat-binding fiber is foam-coated with a foulard with a roll opening set at 0.6 mm . The pre-foamed binder is produced as follows:

Binder Mixture Specification: "20 11.1% Sarpifan WRG (Stockhausen, Germany): .. v 0.2% Rohagal 10 n (Rbhm GmbH, Germany): '·· 88.7% water * * • · • t · * · • «·

The binder is foamed to a density of 20 g / l.

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If the foam level in the foulard is about 4 cm, add more on each side of the product.

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1.5 g of binder (100% solids) per m2.

• · · ;;; After foaming, the product is dried in the usual manner, for example, • · *: * 30 at 140 ° C.

B. Foam Coating. preparation of a hydrophobic product.

u. 111867

The product is prepared in the same manner as above, but with different binder-mixing specificity: 5 Binder mixing specification: 11.1% Sarpifan WRG (Stockhausen, Germany) 2.0% Stokal STA (Stockhausen, Germany) 86.9% water * »* I ·

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Claims (10)

A process for producing dry-formed paper material by sequentially applying a web of cellulosic fibers to a forming wire and treating the web 5 to provide a bond to the fibers therein, characterized in that the fiber binding is provided by significantly less than 15%, preferably 0.5 to 5%, for binding short cellulosic fibers on surfaces. Method according to Claim 1, characterized in that the binder is added in an amount of 0.5 to 10 g dry matter / m2 of the surface of the web. 3. A method according to claim 1, characterized in that the binder is added to the web surfaces after the web has been stabilized by heat-activation of the heat-binding fibers, and that the binder is cured by transient heating of the web at such a high temperature that reactive fibers are reactivated. Process according to Claim 1, characterized in that the binder. is added in a foamed state, i.e. water / air as a carrier. > · · 5. A method according to claim 4, characterized in that the web material, despite the addition of an aqueous binder, is produced by one or more middle layers containing or consisting of a superabsorbent material. Process according to Claim 1, characterized in that the binder is used in admixture with pigments. , Λ 30! · 13 111867 A process according to claim 1, characterized in that a web comprising 10 to 25% of heat-binding fibers and a binder dosage of 0.5 to 10 g / m 2 is used to produce the mainly heat-bonded material. 8. A method according to claim 1, characterized in that a web of 3 to 7% of thermally bonded fibers and a binder application of 5 to 20 g / m 2 of surface area is used for the preparation of the binder-bound material. A system for performing the method of claim 1, comprising a device for applying fibers dry to a forming wire to form a fiber web, and a device for activating a means for bonding fibers, characterized by a combination applicator of the type operating on fiber-based blended thermoforming fibers; is a heating zone, and the presence of a station to add relatively small amounts of binder 15 to the web surfaces, namely to render the finished material sufficiently free of dust. System according to claim 9, characterized in that the binder station comprises means, such as a foulard, for adding the binder in the foam carrier. »1 ·> · ♦ I« · * 1 · * • · * · * · • * I t 1 »# ·« I · • III · I · • · t · »I · · I · ·. »>» · • »m 111867