EP0267489B1 - Process and apparatus for coating and impregnating a non-woven fabric with viscous liquids - Google Patents

Description

The invention relates to a method and a device for applying and impregnating nonwovens with viscous liquids.

Nonwoven fabric is to be understood in particular to mean a structure of an irregular structure in which there is a cavity structure distributed unevenly over the surface. Such nonwovens can have natural as well as artificially produced fibers as base material, which are additionally stabilized by cross-linking. Such structures are difficult to soak, especially if the embedding process is to take place very quickly and without the inclusion of air or gas.

Such a production stage exists, for example, in the production of fiber-reinforced cellulose casings, which are preferably made from a nonwoven web and viscose.

Cellulose casings are e.g. used in the packaging of food, in particular they are used as sausage casings. A distinction is made between one-sided and two-sided viscous casings depending on the type of viscose applied during manufacture.

The form, which is viscose-coated on both sides, generally has better and more uniform embedding of the nonwoven fabric, provided that air pockets can be avoided on both sides of the nonwoven in the short time of applying the viscose. It is understandable that the targeted air displacement is easier to carry out with a one-sided coating, especially since after leaving the nozzle in which the coating is applied, there is still a free distance until the beginning of the precipitation, the one-sided displacement of the air from the fleece.

On the other hand, there are areas in which only fleece-reinforced cellulose casings that are viscose coated on both sides are used in practice. These are generally the fiber casings coated on the inside with a barrier layer. The inside of the cover has a cellulose layer for reasons of paintability, the outside has a cellulose cover for optical reasons. The usually mass-colored cellulose regenerate present on the outside optimally covers the fiber structure. This type of casing has a wide range of applications in the manufacture of scalded and cooked sausages.

It has furthermore been shown that, even in the case of unpainted goods, there are clear advantages in many areas of application when using goods which are viscose-coated on both sides. For example, with high internal friction in the filling process, the sliding behavior in casings with a cellulose inner layer is considerably more favorable because of the good surface smoothness. Such cases exist with raw sausage meat fillings or with ham guts. There is no need for additional lubricating impregnations, which are required for one-sided external viscosification. The double-sided viscosification also ensures a more uniform overall structure, which is particularly valued for sliced goods that are packaged second-hand because of the good peeling behavior and the more uniform stretching of the casing.

These examples show the importance that double-sided viscosification already has and that is reinforced if it is possible in particular to achieve the manufacturing advantages of single-sided viscose coating. The cellulose casings in tubular form which are viscose on both sides and are customary today are generally produced by first forming a nonwoven web into a tubular. Viscose is applied to this tube from both sides in the coating device (GB-A-1336850). The viscose is applied almost simultaneously for reasons of the decreasing strength in the viscose wetting of the natural fiber fleece that is usually preferred. For this, nozzle systems are used, which consist of an outer and an inner ring nozzle. Via these ring nozzles the viscose is given under pressure Quantities applied. The impregnation of the fleece without the inclusion of air is difficult because it is a highly viscous aqueous liquid.

The viscosity of the viscose is essentially determined by the solids content of cellulose and the degree of polymerization. The higher the two values, the higher the viscosity. For the processing of the viscose, one would like a low viscosity in order to quickly and optimally soak the nonwoven fabric. However, the quality of the end product increases with a high solids content and degree of polymerization. The degree of polymerization determines the shrinkage behavior and the elasticity of the regenerated cellulose, the solids content the porosity and in connection with the degree of polymerization the final strength of the shell. This results in a compromise for the production, which is usually a solids content that is actually too low.

In order to avoid the difficulties with bilateral viscosification, viscose is used with 6.5 to 7% by weight, i.e. a solid content that is not optimal.

The object of the present invention was to provide an improved device and an improved method, in particular for coating on both sides of nonwovens.

The invention relates to a device for applying and impregnating nonwovens with a viscous liquid with application nozzles, characterized in that on at least one On the web side A of the nonwoven fabric, at least 2 nozzles D1 and D3 are arranged offset in the conveying direction, the nozzle gaps 10 and 12 of which are separated from one another by a nozzle lip 19 and that, opposite this lip 19, a nozzle D2 for the counter-coating is arranged on a web side I of the nonwoven fabric,

In a preferred embodiment, web side A is the outer web side of the nonwoven. The nozzles are preferably annular slot nozzles, the outlet opening of which is 0.3 to 6 mm wide. The nozzles D1 and D3 are preferably offset from one another by approximately 2 mm to 8 mm,

The invention further relates to a method for the two-sided application and impregnation of nonwovens with a viscous liquid, at least two nozzles D1 and D3 applying the viscous liquid to at least one web side A. Nozzle D3 is arranged offset in the conveying direction to nozzle D1; The fleece is thus coated first by the nozzle D1 and then only by the nozzle D3. The counter-coating of the web side I is carried out with a nozzle D2, which is located opposite the nozzle lip common to the nozzles D1 and D3. In a preferred embodiment, the application is carried out any area through the nozzle D2 approx. 0 to 2 x 10⁻² seconds later than the order through the nozzle D1. In a further preferred embodiment, the viscous liquid emerges from the nozzle D3 at a higher pressure than from the nozzle D1. In a very particularly preferred embodiment, the outlet pressure from the nozzle is regulated in such a way that the nonwoven web to be coated moves in the direction of the outlet of the coating device due to the staggered pressure build-up.

The viscous liquid is preferably alkali cellulose (= viscose). This preferably has a viscosity of 300 to 500 falling ball seconds, in particular 350 to 400 falling ball seconds. 310 falling ball seconds correspond to 40,000 mPa.s. The solids content of the viscous liquid is preferably 7.5 to 9.0% by weight. The viscous liquid may contain additives that improve the appearance and properties, e.g. Color pigments, adhesives or release agents, as well as substances that regulate the adhesive and reactive properties.

The manufacturing process for a cellulose casing according to the invention preferably proceeds as follows:
The web cut from nonwoven depending on the viscose tube diameter to be produced is formed into a tube with an overlap. In the device according to the invention, the hose is impregnated and coated on both sides with viscose. After passing through an air gap the viscose-coated nonwoven tube into a precipitation bath, where the viscose is precipitated, while maintaining regenerated cellulose. The regenerated cellulose is then washed, passed through a plasticizer bath and dried under supporting air. The amount of water to be evaporated depends on the level of the solid content of cellulose in the viscose. Higher solids content means lower water content, which is another reason to be able to process high solids contents via the nozzle.

The coating according to the invention takes place in a cascade-like manner starting with an outer coating via an annular nozzle. The distribution of the outer viscose systematically increases the pressure on the nonwoven, and the full pressure load is only reached when the coating device passes through at the end of the annular gap that exists between the nozzle bodies inside and outside to guide the nonwoven web. At the same time, the nonwoven is floated through the viscose and transported through the nozzle combination with an outflowing viscose without significant frictional stress. Surprisingly, the viscose distribution optimizes the increase in pressure on the nonwoven fabric so that a draft-free structure of the viscose goods is achieved even with thin nonwoven fabrics.

In the known manufacturing processes, small and large draw creases usually occur in the viscose tube. These are caused by the tensile force on the viscous hose below the nozzle, essentially caused by the frictional forces of the nozzles when applying viscose. They are a sign of production uncertainty, can lead to unnecessary product failure and disrupt the uniform visual impression of the finished product. These disadvantages can be avoided according to the invention.

Fig. 1:

Einen Querschnitt durch eine Beschichtungsvorrichtung

Fig. 2:

Eine Düsenhälfte mit vereinfachter Viskoseverteilung

Fig. 3:

Eine vergrößerte Darstellung des Ringspalts, durch den das Vlies bei der Beschichtung läuft.

A preferred device according to the invention is described below:
They represent:

Fig. 1:

A cross section through a coating device

Fig. 2:

One half of the nozzle with simplified viscose distribution

Fig. 3:

An enlarged view of the ring gap through which the fleece runs during coating.

The viscosing process takes place in the device according to FIG. 1. The nonwoven fabric formed into a tube runs over a cylindrical calibration mandrel 3. The tube runs between an outer nozzle combination 1 and the assigned inner nozzle 2. The outer combination consists of two individual nozzles 5 and 6. The viscose is guided via a pump and inlet 7, not shown, into the annular chamber 9 of the nozzle 5, which is dimensioned such that a pressure loss to be neglected during Distributing the viscose occurs. The viscose which is under pressure flows through a narrow nozzle gap 10 onto the nonwoven fabric. The procedure for the second outer nozzle 6 via inlet 8, annular chamber 11 and nozzle gap 12 is similar. Viscoses with different properties can be fed in via inlet 7 and 8. In the normal case where a single viscose type is used, there will be a single inlet, for example in the annular chamber 11, and the inlet to the second annular chamber 9 takes place via an adjustable ring opening 14 (FIG. 2). The cross-section 14 is adjusted by means of a screw 13. This allows the viscose distribution to be optimized during production without any problems.

Separately to the outer nozzles, the inner nozzle 2 is fed via a viscose feed, not shown. The viscose passes through the collecting space 15 into the nozzle gap 16, from there under pressure on the nonwoven fabric 4.

3 shows the coating process and its principle of action. The nonwoven fabric 4 initially runs along the outer nozzle lip 18 and is exposed to viscose via the nozzle gap 10. The pressure is generally such that the viscose does not rise in the 17 A annular gap. The high viscosity leaves ventilation channels free. In the area of the outer nozzle lip 19, the counteracting takes place via the inner nozzle gap 16. This embeds the fleece without excessive pressure. The inner nozzle lip 21 ends under the nozzle gap 10 for optimal fleece support. Subsequently the pre-coated fleece runs into the pressure zone between nozzle lips 19 and 20. The viscose flows over the nozzle ring gap 12. Since the highest pressure drop exists along the outer nozzle lip 20, the viscose is forced to exit via the annular gap 17 E. It thus moves the sensitive, now viscose-damped nonwoven fabric towards the nozzle outlet without stressing the nonwoven fabric.

The advantages of the new coating system described compared to the usual nozzles are particularly great when using viscose with high viscosity, e.g. greater than 250 falling ball seconds. Particularly positive results are obtained in the range from 300 to 500 falling ball seconds, in which known methods are unsatisfactory.

In practice, the system of double loading from the outside and single coating via the inner nozzle described in the example is sufficient to build up the cascade-shaped viscose load with the wedge effect of the viscose pressure build-up. The double action is preferably on the outside because these nozzles are more easily accessible for the viscose feed; it could of course also be inside.

It is of course also possible to divide the viscose onto even more individual nozzles inside and outside if several viscose layers of different structures are required to achieve certain properties of the cellulose tube. The number of ring nozzles inside or outside can be an even or odd number.

EXAMPLES Example 1 (comparative example )

A viscose produced according to customary methods is applied to a nonwoven fabric made of natural fibers with 21 g / m² paper basis weight and 322 mm cutting width with the following data. Solids content cellulose: 7.7% by weight Use of carbon disulfide: 29% by weight on cellulose Sodium hydroxide solution: 5.7% by weight Degree of polymerization: 530

The viscosity of this viscose is 410 falling seconds at 20 ° C. This viscose can only be processed to a limited extent with the usual viscous system at a production speed of 750 m / h. Sufficient soaking is not achieved in the overlap area of the seam; there are air pockets. There is a strong unevenness in the distribution of viscose on the nonwoven fabric due to excessive tensile forces or frictional forces in the nozzle. The finished product shows strongly fluctuating pressures.

Example 2

Example 1 is repeated, but the viscose was applied according to the invention with a device according to FIG. 1. The application speed was 750 m / h.

A smooth, completely uniformly impregnated cellulose tube is obtained.

18,1

g/m Zellulose

31

Gew.-% Glyzerin bezogen auf Zellulose

7

Gew.-% Wasser

The composition of the finished hose was:

18.1

g / m cellulose

31

% By weight of glycerin based on cellulose

7

% By weight water

The cellulose tube was pressed open with water. It burst at overpressure of 0.69 bar.

The nonwoven embedding showed no air pockets.

The subsequent painting could be carried out better on the particularly flat surface than was the case with goods made with low-viscosity viscose and the usual nozzle system.

Example 3

Example 2 is repeated with a cellulose casing made of non-woven fabric with 17 g / m² paper basis weight and 200 mm cutting width. The same good results are obtained.

Example 4

There is a one-sided coating with the nozzle combination D1 and D3. The cylindrical calibration mandrel 3 forms the support of the fleece tube until the viscose coating has ended. About the A viscose is applied in accordance with Example 1 to nozzle D1. It additionally contains a coloring. The same viscose is applied via nozzle D3. A fiber fleece with a cutting width of 206 mm and a paper weight of 21 g / m² is coated at a speed of 800 m / h. Total fleece embedding is achieved with perfect seam penetration. The regenerated cellulose layer is even without color streaks.

Example 5 (comparison)

The viscosification is carried out with the substances and the same processing speed as in Example 4. However, a conventional nozzle is used which has only one annular gap pressurized with viscose, through which the viscose reaches the nonwoven fabric.

This time the cellulose intestine shows no complete integration of the fibers, but clearly recognizable non-embedded fibers. The seam is not sufficiently saturated and the sheath breaks under pressure, which is why a seam glue is additionally required in the viscous process. The viscose distribution is noticeably distributed over the color stripes.

Claims (8)

1. An apparatus for applying a viscous liquid to nonwoven materials to saturation point by means of applicator nozzles, characterized in that, on at least one side A of the web-form nonwoven material, at least two nozzles D1 and D3 are arranged offset from one another in the transport direction, their slots 10 and 12 being separated from one another by a lip 19, and in that a nozzle D2 for the backing is arranged opposite the lip 19 on one side I of the web-form nonwoven material.
2. An apparatus as claimed in claim 1, characterized in that the side A corresponds to the outside and the side I to the inside of the web.
3. An apparatus as claimed in claim 1 or 2, characterized in that the nozzles are annular slot nozzles with a 0.3 to 6 mm opening.
4. An apparatus as claimed in any of claims 1 to 3, characterized in that the nozzles D1 and D3 are arranged offset by 2 to 8 mm from one another.
5. A process for applying a viscous liquid to nonwoven materials to saturation point by means of nozzles, characterized in that at least two nozzles D1 and a nozzle D3 offset therefrom in the transport direction are arranged on at least one side A of the web-form nonwoven material, the viscous material is applied through the nozzle slots 10 and 12 separated by a lip 19 and the side I of the web opposite the side A is coated by a nozzle D2 arranged opposite the nozzle lip 19.
6. A process as claimed in claim 5, characterized in that the viscous liquid emerges from the nozzle D3 under a higher pressure than from the nozzle D1.
7. A process as claimed in claim 5 or 6, characterized in that the outflow of the viscous liquid from the nozzles is controlled so that the web of nonwoven material to be coated is moved towards the outlet of the coating unit.
8. A process as claimed in any of claims 5 to 7, characterized in that viscose is used as the viscous liquid.

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