EP1831464A1

EP1831464A1 - Method for applying a multiple layer directly to a paper, cardboard or other fibrous material continuously moving web

Info

Publication number: EP1831464A1
Application number: EP05808126A
Authority: EP
Inventors: Benjamin Mendez-Gallon
Original assignee: Voith Patent GmbH
Current assignee: Voith Patent GmbH
Priority date: 2004-12-23
Filing date: 2005-11-18
Publication date: 2007-09-12
Also published as: WO2006069851A1; JP2008525649A; US20070248763A1; DE102004062119A1

Abstract

The invention relates to a method for applying a multiple layer directly to a paper, cardboard or other fibrous material continuously moving web during production and/or finishing thereof, wherein the individual layers of the multiple layer (2) are formed by several liquid or pasty application media or liquid flows (Q1-Qn), in particular aqueous pigment suspensions. According to said invention, said individual application media or liquid flows (Q1-Qn) are contactlessly applied to the fibrous material web (1) without predrying, excess amounts and mutual mixing, wherein the application medium whose specific weight (p1 to pn) and/or viscosity (θ1 to θn) and/or surface tension (δ1 to δn) are less than said properties of the following application medium is applied to the application medium or a layer whose specific weight (p1 to pn) and/or viscosity (θ1 to θn) and/or surface tension (δ1 to δn) are greater in such a way the application medium having the greater values forms the first or lower layer (U) and the application medium having the lesser values forms the cover layer (D) on the fibrous material web (1).

Description

Process for the direct application of a multilayer on a running paper, cardboard or other fibrous web

The invention relates to a method for the direct application of a multi-layer to a running paper, cardboard or other fibrous web during its manufacture or / and finishing, the individual layers of the multi-layer being formed from several liquid to pasty application media, in particular aqueous pigment suspensions.

For reasons of economy, paper, cardboard or other fibrous webs are mainly manufactured and refined in large widths of up to 10 m and more as well as at high machine speeds.

In order to achieve good printability, these webs are to be treated by offline or online coating processes. A modern coating process in the form of contactless application is often used for this purpose, the applied medium being deposited as a contour layer on the fibrous web. The application medium consists of mixtures of mineral pigments, natural or synthetic binders and chemical auxiliaries. The smoothness or roughness of the coated substrate depends on the basic roughness or smoothness of the substrate, ie the fibrous web. In order to be able to save quantities of application medium, the aim is to carry out this application in the so-called 1: 1 process. This means that only as much medium should be applied as is to remain on the fibrous web to be coated. In contrast, the excess application method is known, in which approximately 8 to 10 times the amount of application medium is to be applied, which then has to be scraped back to the desired coat weight, for example 6-12 g / m ² , using various doctor elements. It follows that the amount to be applied is very small for a 1: 1 order. In any case, an even application layer should be achieved, which extends across the entire web width or working width.

This requirement of uniformity is all the more difficult to implement the faster the fibrous web runs in the machines and is also dependent on the quality of the fibrous web and the application medium.

Known 1: 1 applicators or units are curtain and spray applicators.

Such an application unit, which produces a closed curtain and essentially follows the force of gravity, can be found in DE-A1 197 55 625. A spray applicator, which works with pressure, is known from DE A1- 4402627.

As I said, the curtain generated with the curtain applicator and placed on the basis of certain forces, for example electrostatic forces, which are given to the application medium or fall under the influence of gravity on the running surface or the fibrous web, and also the spray jets of the spray applicator each form a contour line on the fibrous web and immobilize there after a certain time as a film.

In order to be able to achieve a high degree of coverage of the fibrous web and thus better printing properties, the fibrous web must often be painted several times.

According to the state of the art, several application units are required, which are arranged one behind the other on the web side and for the most part work with an excess order.

Reference is made to WO 98/48113-A1.

In the post-published DE-A1 10057729 application units and methods are already disclosed with which double lines, ie layers lying one above the other, can be applied with a single application unit and without contact and without excess medium. However, this often leads to mixing of the two "lines" in their border areas, which means that the second line can only be applied after intermediate drying, which means additional procedural and apparatus expenditure. This device or method is unsuitable for cases in which more than two layers are to be applied.

Proceeding from this, it is an object of the invention to provide a suitable method with which a multiple layer can be applied to one side of a running fibrous web without intermediate drying.

The object of the invention is achieved with the characterizing features of claim 1.

The object of the invention is achieved in accordance with claim 1 in that the individual application media are delivered to the fibrous web without contact, in each case without prior drying, that is to say wet on wet and without excess quantities, that is to say 1: 1. According to the invention, the application medium, which has a lower specific weight and / or a lower viscosity and or a lower surface tension than the next application medium or the next layer, is applied to an application medium or a layer with a higher specific weight and / or higher viscosity and / or a higher surface tension is applied. As a result, the fibrous web comes into contact with the application medium which has the highest of the values mentioned above. In other words: the first layer on the fibrous web is the layer with the highest of the values mentioned and the top layer is the application medium or the layer with the lowest values.

That e.g. lighter application media (with lower specific weight) remains on the heavier layer due to its physical buoyancy effect.

This ensures that there is no mixing or mixing or phase separation of the individual application media. Such a way - A -

The multiple layer formed can thus be built up in a very targeted manner. Above all, however, such a multilayer guarantees excellent coverage of the raw fibrous web. The fact that this can be accomplished with a single and compact application work saves huge investments, which represents a further advantage of the invention.

In an alternative according to the invention it can be provided that the individual application media for forming the multi-layer are delivered separately from one another and, during their delivery in the direction of the fibrous web, are combined or bundled into a sandwich-like multiple jet or multiple curtain and in a bundled form on the fibrous web as an already established multi-layer be applied.

The bundling can take place immediately after delivery from the machine-wide nozzle or only after individual jets or individual curtains have formed. After bundling, depending on the type of application (free jet nozzle application or curtain application), a sandwich-like jet or a sandwich-like curtain is created. In both cases, to a certain extent stabilized "prefabricated" layers lay on the fibrous web.

As an alternative to this, it is also possible to dispense the individual application media separately from one another as individual jets or individual curtains and to apply them separately to the fibrous web, where they form the said multiple layer in layers

Whether the layers are applied individually or in a bundle depends on how compact the application must be, how the space for installing the application or the type of application media to be used or depends on the product type.

In both cases it is possible to guide the individual application media or the bundled jet or curtain during their delivery in the direction of the fibrous web over a flat guide element. This guide element is preferred slanted. As a result, the beam or the multiple curtain (s) are stabilized.

In certain cases it is advantageous if individual curtains are only bundled together on this sloping guide surface and brought together to form a multi-layer or multi-curtain, which is then passed on to the fibrous web, where it is deposited and anchored on the fibrous web as an already formed and stabilized multi-layer can. For example, a sandwich-type curtain is more stable than a single curtain.

According to the invention, it is provided that the multiple layer is formed from at least two and at most ten, preferably three layers. In this order of magnitude, particularly good coverage of the raw fibrous web is possible with small amounts of individual layers.

In an embodiment of the invention it can be provided that the individual application media are emitted as a single jet or individual curtain from a machine-wide slot die or a machine-wide slot of a common nozzle, the distance between the individual jets or screens being less than 1 m, in particular less than 50 cm, but preferably about 20 cm, and the time intervals for a successive delivery from the individual wide slots are set to between 4 and 100 milliseconds.

The term "machine-wide" is to be understood as meaning at least the width of the fibrous web to be produced or refined.

So that the applied multilayer has a high smoothness, it is expedient if this multilayer is leveled or smoothed with a leveling or smoothing element. No medium is scraped off, but the layer - as I said - only leveled or leveled. A further embodiment of the invention can consist in the bundled multiple jet or multiple curtain reaching a flow rate Q _T (for total flow rate). This is made up of the sum of the individual liquid flows of the individual curtains. The total flow rate Q _T can be between 0.5 to 301 / min / m, in particular between 3 and 201 / min / m, preferably between 1 and 121 / min / m.

Application media with solids contents between 5 and 70% are particularly suitable for this multilayer.

The total coat weight applied Δ _{m Gésa} m _t can be calculated as follows:

Δno total = ∑ (hi Kj Pi) i = 2 to max. 10 (preferably 2 to 3)

where hj is the wet film thickness or the area-related volume of the individual application med iu ms per m ² , Ki is the solids content of the respective application medium and Pi is the specific weight of the respective application medium.

The individual application media or liquid flows flow out of the application nozzle for the purpose of forming the multiple jet or multiple curtain, each with a specific outflow speed, which can be calculated as follows:

Vi = Qi / Si,

where Qi in m ³ / min / m is the flow rate of each individual application medium and Si in m is the gap width of the gap slot emitting the application medium.

Mixing of the individual application media in the bundled multiple jet or multiple curtain and / or in the multiple layer can be avoided according to the invention, the higher the difference in viscosity and / or the surface tension and / or the specific weight between the individual application media or layers. The inventor has recognized that the lower the differences in the expansion behavior of the individual media or liquid flows, the more stable the multiple curtain then produced.

According to the invention, a viscosity difference in the range of <50%, in particular <30%, preferably = <10%, should be set.

The viscosity (according to Brookfield 100 rpm) of the first layer below should be between 500 and 100mPas.

In a further embodiment of the invention it can be provided that the acting expansion forces on the individual adjacent application media have a maximum difference of 30%, in particular <20%, preferably 0 <5%, the adjustment of the expansion force difference by adding chemical additives such as thickeners is set on the basis of acrylic ester or acrylic acid or methaacrylic acid or acrylamide or acrylonitrile etc. and the percentage of these chemical additives being 0.01 to 3 T, in particular 0.01 to 0.5 T, preferably 0.01 to 0.2 T is and T is the proportion per 100 parts of the dry amount of pigment in the selected coating color.

It is also very advantageous if the multilayer is formed in such a way that the fineness of the mineral pigments, such as calcium carbonate or kaolin or TiO2 or talc, increases upwards. This means that the layer with the finer mineral pigments it contains, i.e. the smallest diameter of the pigment particles should be present in the respective overlying layer, the top layer of the multilayer then ultimately containing the finest pigment and the greatest degree of whiteness of the pigments.

The following mixing ratios are suggested: - 100 T (T = TeNe) CaCO3 (*) - 100 T kaolins

- CaCO3 and kaolin mixtures with 5 to 50 T kaolin (*) - CaC03 + kaolin and TiO2 or talc in different proportions, the proportion of CaCO3 and kaolin predominating

((*): based on the dry weight of the pigment or pigments contained, i.e. only carbonate or only kaolin)

Amounts of binder, based on the dry weight of the pigments contained, can be in the order of 4 to 20 parts.

Suitable binders are natural binders such as starch (corn, potatoes, tapioca, wheat, barley etc.), cacein, etc. and synthetic binders such as latices (based on styrene-butadiene or acrylate-based, etc.).

Can help

- Thickeners to adjust the viscosity and elasticity (0.01 to 10 T) - Emulsifiers or surfactants to adjust the curtain stability (0.01 to 3 T)

- Defoamer to avoid foaming (0.01 to 1 T)

- Optical brighteners with associated "carriers" 0.01 to 23 T

- Wet strength agent (crosslinker) 0.01 to 3 T

- Special media (lubricants, etc.) 0.01 to 1 T - shading substances for coloring the coating colors 0.1 to 5 T

- Surface-active substances to reinforce the separation between the interfaces of the individual films in the multilayer curtain 0.01 to 1 T may be provided, where T means the percentage of the agent per 100 parts of the dry amount of pigment in the application medium.

The application of the multi-layer can be carried out most advantageously with a curtain applicator, with which several different liquid to pasty application media in the form of several or in the form of a bundle and closed curtain essentially following gravity and / or directed under the influence of electrostatic forces running fibrous web are delivered. Alternating, it is also possible to apply the multilayer with a spray or free jet applicator, with which several different liquid to pasty application media in the form of several jets or in the form of a single bundled jet directed under pressure on the fibrous web to the running fibrous web be delivered.

The invention will be explained in more detail below on the basis of exemplary embodiments.

Show it:

Figure 1: a schematic representation of the principle of the invention using the example of a fibrous web coated with a multilayer by means of a curtain applicator

Figures 2 to 5: a schematic representation of curtain applicators according to the invention with which a multilayer according to the invention is applied

Figure 6: a schematic representation of the principle of the invention with representation of speed profiles in a multiple curtain

The same components or elements are provided with the same reference symbols in the figures.

FIG. 1 shows a fibrous web 1 onto which a multiple layer 2 consisting of several different liquid flows Q1, Q2, Q3, Q4; Qn (five different media are shown in the example) is applied directly. The

The thickness of the multilayer 2 is relatively constant and depends on the topography

Fiber web surface relatively independent. You can see that the individual

Liquid flows in the selected example are given in the form of as many individual curtains V1 to Vn falling perpendicularly on the fibrous web 1. The contactless curtain application used for this is not shown here. The individual liquid streams Q1 to Qn consist of several coating colors, which can differ in their composition or rheology and each consist of a mixture of mineral pigments, natural or synthetic binders and chemical auxiliaries.

The individual liquid streams Q1 to Qn are passed on to the fibrous web without contact and without prior drying - i.e. wet in wet and without excess amounts - that is to say without contact. It is according to the invention that the application medium, which has a lower specific weight p and / or a lower viscosity η and or a lower surface tension δι than the next application medium or the next liquid flow or the next layer, on an application medium or Layer with a higher specific weight and / or higher viscosity and / or a higher surface tension is applied. It is thereby achieved that the fibrous web 1 comes into contact with that application medium which has the highest values (this is then Q1 with specific weight p1, viscosity η1 and surface tension 51. In other words: as the first layer, or lower layer U is the layer with the highest values on the fibrous web and, as the top layer D, that application medium Qn or that layer with the lowest values of p, η, or δ.

You can put it like this:

p1> p2> p3> p4> pn .... pi

η1> η2> η3> η4> ηn .... ηi

δ ₀ »δ1>δ2>δ3>δ4> δn .... δi (where δo is the surface tension of base paper, δ1-n, that of the individual layers of color) FIG. 2 shows the application of the invention using the example of a double-curtain applicator unit 3, shown in cross section and schematically, for applying the multiple layer 2, as described in principle in FIG.

Two feed chambers 4 and 5 for two different application media or liquid flows Q1 and Q2 can be seen, which are applied in the form of two spatially separated curtains V1 and V2 to an inclined guide surface 6. The guide surface 6 is inclined in the direction of the first curtain V1. On this guide surface 6, the two curtains V1 and V2 are combined or bundled to form a double layer 7 and in this bundled form, i.e. placed as a multiple curtain 8 (here double curtain) and thus delivered to the fibrous web 1 running underneath in the running direction L. The layer resulting from the second curtain V2 or a liquid flow Qn comes to lie on the fibrous web as the cover layer D. The cover layer D has the finer particles and the lower values than the lower layer U of the layer or of the liquid flow Q1 or the further layers also underneath in the case of several curtains. The length of the bundled vertically falling curtain is approximately 50 to 300 mm.

Finally, a blade-like leveling element 9 is also shown in FIG. 2, which is to equalize and smooth the applied multilayer 2 - here double layer.

FIG. 3 shows another principle of applying a multilayer 2. In contrast to the solution shown in FIG. 2, there is no guide surface 6 here. The curtains V1 and V2 are bundled into a multiple or double curtain 8 under the action of electrostatic forces. A corresponding electrode 10 pulls the curtains V1 and V2 shown here towards the center, so that here too the curtain V2 again forms the upper layer, that is to say the top layer D of the multiple coating 2 according to FIG. 1.

In the variant shown in FIG. 4, the application medium Q1 and Q2 resulting from distribution chambers 4 and 5 becomes immediately after emerging from the slot nozzle 11 of the order work 3 bundled without a guide surface or other forces are involved. Only to separate the two different application media Q1 and Q2 is a partition 12, for example made of polytetrafluoroethylene, inside the application unit 3. It can be seen that the existing curtain V2 is again as top layer D according to the explanation occurs in Figure 1.

FIG. 5 is intended to show that the multilayer can also be delivered onto the fibrous web 1 from two individually delivered curtains V1 and V2 without prior bundling. In the case of the multiple layer 2, V2 is deposited again as the cover layer D. Leveling elements 9 are also shown again in FIGS. 4 and 5.

It should also be added that the applicator units 3 shown in FIGS. 2 and 3 contain several parallel slot nozzles 11, which are fed by separate feed systems 13 and 14, respectively.

In order to guarantee high stability and optimal conditions when forming the multi-layer curtain 8, the following conditions must be observed, among other things:

1. The outflow speed of the individual application media from the nozzle or at the point where they are bundled is selected so that in the cross section of the curtain 8 a speed profile is similar to the speed profiles shown in FIG. Case a) The outflow speed of all application media or liquid flows Q1 to Qn is the same, so that a speed profile without a relative speed is established between the phase boundaries of the individual liquid application media. No shear or stretch processes take place at the phase boundaries in the multiple curtain.

Case b) The flow rate decreases continuously from the center of the multi-layer curtain to the outside. The inner application media have a larger one Outflow velocity than the outer application media. The speed difference between adjacent application media must ideally not be higher than 20% (preferably <10%, and particularly preferably <5%). The speed profile becomes convex.

Case c) The flow rate increases continuously from the center of the multilayer curtain to the outside. The inner media have a lower speed than the outer media. The speed difference between neighboring media should ideally not be higher than 20%. The speed profile becomes concave.

Speed profiles with a zigzag-like course are unsuitable for the formation of multi-layer curtains because relative speeds initiate stretching and mixing processes that deform, arch or disrupt the multi-layer or multilayer curtain.

In all the figures shown, it is the case that the finer and whiter pigments, such as those of calcium carbonate or kaolin or TiO 2 or talc, form the top layer D of the multilayer 2. The method according to the invention thus enables a high-quality application layer.

The invention is therefore particularly suitable for paper and cardboard webs which are said to have high printing properties.

Reference symbol list

1 fibrous web

2 multilayer

3 double curtain application

4 feed chamber

5 feed chamber 6 guide surface

7 double layer

8 multiple curtain

9 leveling element

10 electrode 11 slot nozzle

12 partition

13 feeding system

14 Feed system D top layer L running direction p, Pi specific weight

Q1, Q2, Q3, ... Qn liquid flow

Q _T total flow rate

Si gap width of the slot nozzle U lower layer

V1, V2, V3, ... Vn single curtain

Vi Outflow speed of the individual application medium or liquid flow Δm total coat weight hj wet film thickness or area-related volume of the individual application medium or liquid flow

Kj solids content of the individual application medium or

Liquid flow pi specific weight of the individual application medium or

Liquid flow η, ηi viscosity δ, δi, δo surface tension

Claims

1. Process for the direct application of a multi-layer on a running paper, cardboard, or other fibrous web during its manufacture and / or finishing, the individual layers of the

Multiple layers (2) of several liquid to pasty application media or liquid streams (QI-Qn), in particular aqueous pigment suspensions, are formed, characterized in that the individual application media or liquid streams (QI-Qn) without prior drying, without excess quantities and without mutual Mixing is delivered contactlessly to the fibrous web (1), the application medium having a lower specific weight (p1 to pn) and / or a lower viscosity (η1 to ηn) and or a lower surface tension (51 to δn) than the next application medium or has the next layer, is applied to an application medium or a layer with a higher specific weight (p1 to pn) and / or higher viscosity (n1 to nn) and / or a higher surface tension (51 to δn), so that on the fibrous web (1) as the first layer or sub-layer

(U) that application medium with the highest values and as a covering layer (D) that application medium with the lowest values.

2. The method according to claim 1, characterized in that the individual application media or liquid flows (QI-Qn) are released separately from one another and during their delivery in the direction of the The fibrous web (1) is brought together or bundled into a sandwich-like multiple jet or multiple curtain (8) and applied in a bundled form to the fibrous web as a multi-layer (2) which has already been established.

3. The method according to claim 1, characterized in that the individual application media or liquid streams (QI-Qn) are delivered separately from one another as individual jets or individual curtains (V1, V2 ... Vn) and applied separately to one another on the fibrous web (1) , where they then form the multilayer (2).

4. The method according to one or more of the preceding claims, characterized in that the individual application media or liquid flows (QI-Qn) are delivered separately from one another as individual jets or individual curtains (V1, V2 ... Vn) and during their delivery in the direction of the fibrous web (1) are each guided over a flat guide surface (6).

5. The method according to one or more of the preceding claims, characterized in that the individual application media or liquid streams (QI-Qn) are delivered separately from one another as individual jets or individual curtains (V1, V2 ... Vn) and during their delivery in the direction of the

The fibrous web (1) is guided over a flat guide surface (6), on which they are merged or bundled to form a multilayer (2), then carried on as a sandwich-like multiple jet or multiple curtain (8) to the fibrous web (1), where this is deposited and anchored as a multiple layer (2) already formed on the fibrous web (1).

6. The method according to one or more of the preceding claims, characterized in that the multiple layer (2) is formed from at least two and at most ten, preferably three layers.

7. The method according to one or more of the preceding claims, characterized in that the individual application media or liquid flows (QI-Qn) as a single jet or individual curtain (V1, V2 ... Vn) each of a machine-wide slot nozzle (1 1) or one machine width each

Slit of a common nozzle are given, the distance between the individual jets or curtains (V1, V2 ... Vn) smaller than

1 m, in particular less than 50 cm, but preferably about 20 cm, and the time intervals for a successive delivery from the individual slot nozzles (1 1) to = <2s, in particular 0 = <1s, preferably

= <0.5s can be set.

8. The method according to one or more of the preceding claims, characterized in that the multilayer (2) applied to the fibrous web (1) is leveled or smoothed with a leveling or smoothing element (9).

9. The method according to one or more of the preceding claims, characterized in that the bundled multiple jet or multiple curtain (8) reaches a flow rate (Qi) which is composed of the flow rates or liquid flows (QL..Qn) of the individual layers and ( Qi) is between 0.5 to 30 l / min / m, in particular between 3 and 20 l / min / m, preferably between 1 and 121 / min / m.

10. The method according to one or more of the preceding claims, characterized in that

Application media or liquid flows (QI-Qn) to form the multilayer (2) can be selected, the solids content between 5 and 70%.

11. The method according to one or more of the preceding claims, characterized in that the individual application media or liquid flows (QI-Qn) to form the multiple layer (2) are each acted upon by an outflow rate which is calculated as follows:

Vi = Qi / Si,

where Qi [in m ³ / min / m] is the flow rate of each one

Application medium or liquid flow (QI-Qn) and Si [in m] indicates the gap width of the slot nozzle (1 1) from which the individual application medium is dispensed.

12. The method according to one or more of the preceding claims, characterized in that thorough mixing of the individual application media or

Liquid flows (QI-Qn) in a bundled multiple jet or

Multiple curtain (8) and / or the multiple layer (2) is avoided, the higher the difference in viscosity (η) and / or the surface tension

(δ) and / or the viscoelastic properties or the stretchability or the stretching force and / or the specific weight (p) between the individual application media or liquid flows (QI-Qn) or

Layers.

13. The method according to claim 12, characterized in that the stretching force of the individual adjacent application media or liquid flows (QI-Qn) is at most 30%, in particular <20%, preferably 0 <5%, the stretching force being set by adding chemical additives, such as thickeners based on acrylic ester or acrylic acid or methacrylic acid or acrylamide or

Acrylonitrile, etc. is set and wherein the percentage of the chemical additive is 0.01 to 3 T, in particular 0.01 to 0.5 T, preferably 0.01 to 0.2 T and T is the proportion per 100 parts of the dry pigment amount of respective application medium or liquid flow (QI-Qn), in particular of coating color.

14. The method according to one or more of the preceding claims, characterized in that the multiple layer (2) is formed such that that layer with the finer mineral pigments contained, i.e. the least

Diameter of the pigment particles, such as calcium carbonate or kaolin or TiO2 or talc, is present in the respective overlying layer, the top layer (D) of the multilayer (2) then containing the finest pigment and the whiteness of the pigments.

15. The method according to one or more of the preceding claims, characterized in that the application of the multilayer (2) is carried out with a curtain application unit (3) with which several different liquid to pasty application media or

Liquid flows (QI-Qn) in the form of several or in the form of a bundle and closed curtain (8) following the force of gravity and / or steered under the influence of electrostatic forces are emitted to the running fibrous web (1).

16. The device according to one or more of the preceding claims, characterized in that the multilayer (2) is applied with a spray or free jet application unit, with which several different liquid to pasty application media in the form of several jets or in the form of a single bundled jet directed under pressure on the fibrous web (1) are directed to the running fibrous web ( 1) are submitted.