EP0925397B1 - Cellulose bonded nonwoven fiber fabric and method for the production thereof - Google Patents

Description

The invention relates to a nonwoven bonded with cellulose and a Process for its production. It also concerns the use of this Nonwoven fabric for the production of food packaging, in particular of tea bags or sausage casings.

Fiber-reinforced, seamless cellulose casings are usually made after Viscose process manufactured. This creates a tube Nonwoven, for example made of hemp fiber paper, inside and / or outside with coated with an alkaline viscose solution. The inside, external or double-viscous material is then mixed with an acidic coagulation liquid treated, the cellulose xanthate precipitates and cellulose hydrate regenerates. So much viscose solution is generally applied that the nonwoven fabric on one or both sides completely with a layer regenerated cellulose is covered. Fiber-reinforced cellulose casings are made in widely used as sausage casings.

It is also known to viscose flat webs from a nonwoven fabric. The viscous material is coagulated in the manner described regenerates. The fiber-reinforced cellulose flat films can also be used Process tubular casings if you bend them accordingly and sew the edges together, glue or seal. Such covers are also suitable itself as sausage casings.

The nonwoven fabric is made in the usual way from cellulose fibers. For As a rule, increasing its strength will bind it. So in the US-A 3 135 613 discloses the manufacture of wet strength hemp fiber paper. The increased strength is achieved by treating with a dilute alkaline viscose solution, drying and regenerating the cellulose with the help of dilute sulfuric acid. The paper is then washed until it is free is of acid and finally dried. The cover used as a binding Regenerated cellulose is so thin that the porous structure of the paper preserved.

However, a pure cellulose bond is not sufficiently resistant to alkali and hydrolysis resistant. Subsequent coating of the paper with alkaline Viscose solution partially dissolves the existing cellulose and the fibers loosen. Tubular films with such a Fiber reinforcement therefore tends to burst even when the internal pressure is low.

In order to avoid this disadvantage, nonwovens were also used are fixed solely with synthetic resins. According to GB-A 1 091 105 these are Cellulose fibers with an alkali-curable resin, for example one Polyethyleneimine resin or a polyamide crosslinked with epichlorohydrin, bound. In US-A 3 484 256 a mixture of a cationic, thermosetting resin and a polyacrylamide used. With cellulose casings reinforced with this material do not guarantee the burst resistance, which is required for certain types of sausage.

Resin bonds are generally not sufficiently thermostable. The viscose solution cannot penetrate resin-bonded nonwovens sufficiently. In addition, the resin causes the regenerated cellulose to be insufficient adheres to the fibers.

The object of the invention is to provide a nonwoven fabric in an environmentally friendly manner Provide that is wet-strength, alkali and hydrolysis-proof from the viscose is optimally penetrated and firmly with regenerated cellulose hydrate connects. In particular, the viscosities produced therefrom tubular food casings optimal strength, ductility and swellability and good shrinkage behavior.

a) Behandeln mit einer Lösung von Cellulose in einem Gemisch aus N-Methyl-morpholin-N-oxid (NMMO) und Wasser,

b) Fällen der Cellulose mit Hilfe einer wäßrigen NMMO-Lösung,

c) Waschen, um das NMMO zu entfernen, und gegebenenfalls

d) Trocknen.

This object is achieved by a nonwoven whose fibers have been bound by

a) treatment with a solution of cellulose in a mixture of N-methyl-morpholine-N-oxide (NMMO) and water,

b) precipitation of the cellulose with the aid of an aqueous NMMO solution,

c) washing to remove the NMMO, and if necessary

d) drying.

The nonwoven fabric can - as usual - be made by using a Sieve passes through a fiber pulp and the resultant The fiber fleece then dries partially or completely. The pulp preferably contains about 0.1 to 2% by weight of cellulose fibers, with hemp fibers are preferred. Other ingredients can be added to the pulp be, e.g. Resins or glues. The nonwoven can also be impregnated or are coated, preferably also with resins or glues.

In a particularly preferred embodiment, the pulp is one Polyamine-polyamide-epichlorohydrin resin (also referred to as polyamidoamine-epichlorohydrin resin), a urea-formaldehyde resin, a melamine-formaldehyde resin or a urea-melamine-formaldehyde resin is added. The amount this resin is preferably 0.5 to 2 wt .-%, based on the Total weight of the pulp. The resin migrates to the crossing points when it dries of the fibers and reacts with the fibers when curing also with itself. This further increases stability.

The nonwoven fabric according to the invention contains about 0.5 to 9% by weight, preferably 1 to 3% by weight, particularly preferably 1.5 to 2% by weight, of cellulose, based on its total weight. It can already be used as such, for example to make tea bags from it. It then preferably has a weight of about 8 to 20 g / m ² . It is particularly advantageous, however, to viscose and process it into fiber-reinforced food casings. It then preferably has a weight of 12 to 30 g / m ² , particularly preferably 15 to 28 g / m ² .

The invention thus also relates to a fiber-reinforced food casing or packaging film produced by the viscose process
is characterized in that the fiber reinforcement consists of the nonwoven fabric according to the invention. It is mainly used as a sausage casing.

• Bereitstellen einer Suspension, die Cellulosefasern und vorzugsweise zusätzlich auch mindestens ein Polyamin-Polyamid-Epichlorhydrinharz enthält,
• Formen eines Faservlieses aus der Suspension (z.B. durch Abfiltrieren über ein Schrägsieb),
• teilweises oder vollständiges Trocknen des Vlieses,
• Aufbringen einer Lösung aus Cellulose in NMMO/Wasser auf das Vlies,
• Ausfällen der Cellulose mit Hilfe einer wäßrigen NMMO-Lösung,
• Waschen des Vlieses (in der Regel mit Wasser) bis das Vlies praktisch frei von NMMO ist und
• Trocknen bis der gewünschte Grad an Restfeuchte erreicht ist.

Part of the present invention is also a process for producing the nonwoven fabric according to the invention, which comprises the following steps in the order given:

• Providing a suspension which contains cellulose fibers and preferably additionally at least one polyamine-polyamide-epichlorohydrin resin,
• Forming a nonwoven fabric from the suspension (for example by filtering through an inclined sieve),
• partial or complete drying of the fleece,
• Applying a solution of cellulose in NMMO / water to the fleece,
• Precipitation of the cellulose with the aid of an aqueous NMMO solution,
• Washing the fleece (usually with water) until the fleece is practically free of NMMO and
• Dry until the desired level of residual moisture is reached.

Treatment with the cellulose / NMMO / water solution is preferably done by immersing in an appropriate bath.

The cellulose / NMMO / water solution preferably contains about 0.5 to 2.0 % By weight of cellulose, based on their total weight. That as a solvent NMMO / water mixture used preferably consists of 85 to 90% by weight made of NMMO and 15 to 10% by weight water. The production of Cellulose / NMMO / water solutions is also in DE-A 196 07 953 described.

The NMMO aqueous solution used for precipitation preferably contains about 5 up to 15% by weight of NMMO, particularly preferably about 10% by weight of NMMO, based on their total weight.

The nonwoven fabric according to the invention optimally fulfills the tasks set Wise. In particular, it shows a higher wet and dry strength. It also has the desired porous surface structure. The after The method according to the invention is applied cellulose from NMMO solution more compact, dense and crystalline (55 to 65% crystalline fraction) than that after applied to the viscose process (34 to 42% crystalline fraction). she will therefore in a subsequent coating of viscose solution or others alkaline solutions attacked significantly less. That represents another Advantage of the nonwoven fabric according to the invention.

At least as important as the higher crystallinity is the fact that have the nonwovens according to the invention produced in a simple manner. Different As with the viscose process, there are no exhaust air or wastewater problems with the Manufacturing on. The NMMO is approximately 99.5% recovered.

To make a packaging film or food wrap Sheets of the nonwoven fabric according to the invention are viscose-coated on one or both sides. Seamless, tubular films or envelopes can be obtained if the sheets from the nonwoven fabric are bent into a tube and on the Outside and / or inside with a common alkaline viscose solution soaked and coated. Then the viscous surface with an acidic spin liquid customary for the precipitation of the viscose usually contains sulfuric acid. The spin fluid can become be in a bath, which is the viscous, possibly tubular curved, fibrous web passes through, or it is applied to the with the help of a nozzle viscous fiber web applied. After going through the manufacturing process of films made of cellulose hydrate usual regeneration and washing baths the fiber-reinforced cellulose film is dried. That is in the end product Nonwoven covered on one or both sides with a cellulose layer, so that whose surface structure is no longer visible.

Should the tubular food casing according to the invention as a sausage casing can be used, it can still be on the inside and / or outside provided with the usual coatings or impregnations become. For example, a barrier layer can be inside and / or outside against atmospheric oxygen or water vapor. Depending on the type the sausage meat can also have an inner coating to improve the Peeling behavior or to improve the adhesion between meat and casing Bring advantages. Finally, in certain cases, a fungicide is indicated Coating on the outside. To get colored sausage casings, color pigments can also be found in the cellulose layer, e.g. Soot or TiO2. The tubular sausage casing can be advantageous in shape of "caterpillars" (gathered sections, one end of which has already been tied off can be) or laid flat and rolled up as "roll goods" in the trade to be brought.

The invention is illustrated by the following examples. All
Percentages are percentages by weight, unless stated otherwise.

example 1

Hemp fibers were deposited on a sloping sieve to a coarse-structured fiber paper of 21 g / m ² using a customary process from a paper pulp in which the proportion of cellulose fibers is 0.1 to 0.2%. The paper was transported over large diameter heated rollers and dried. The dry paper web was then passed through a runner containing a 0.8% cellulose solution in an 87.7% aqueous NMMO solution at a temperature of 95 ° C. The paper was gently squeezed off and passed through a second runner containing a 15% NMMO solution at a temperature of 20 ° C. In a third runner with pure water, the remaining NMMO was extracted. Then it was dried again and wound up. The cellulose content of the nonwoven fabric was approximately 1.2%. When wet, it had a tensile strength (average of the longitudinal and transverse tensile strength) of 6.5 to 7 N / mm ² and an elongation at break (average of the longitudinal and transverse tensile elongation) of 7 to 8%, based on the initial length. When treated in 6% sodium hydroxide solution for 10 minutes, the nonwoven lost only 15 to 20% of its strength, the elongation at break remained unchanged. When the fiber fleece was impregnated with an alkaline viscose solution, the viscose penetrated perfectly, and the precipitated cellulose hydrate adheres very well to the fibers.

An outer viscose tube (caliber 75 mm) with this fleece as reinforcing The insert reached a burst pressure (wet) of 79 kPa, i.e. 15.5% over the usual setpoint; the static elongation at 21 kPa was 82.5 mm (permitted range: 80.3 to 83.3 mm). Mechanically gathered hoses could be processed on automatic filling machines. The covers were more stable than the standard sleeves provided with the usual fiber insert.

Example 2

An amount (0.8%) of still water-soluble polyamine-polyamide-epichlorohydrin resin was added to the hemp fiber pulp so that the resin content of the dried paper reached approximately 2%. The nonwoven fabric was then produced from this and dried, as described in Example 1. It had a weight of 23.7 g / m ² . It was first run through a 95 ° C. solution of cellulose in 87.7% NMMO, then through a 10% NMMO solution at 20 ° C. and then through a water skid, dried again and wound up. In the wet state the tensile strength was 8 to 9 N / mm ² (mean lengthways + crossways) and the elongation at break 6 to 6.5%. When treated with alkali, this fleece only lost 12 to 15% of its wet strength, the elongation at break remained unchanged. The nonwoven fabric was formed into a tube and impregnated on the outside with an alkaline viscose solution. The 90 mm caliber hose obtained after acid precipitation and normal regeneration reached a burst pressure of 72 kPa, ie 17% above the usually required setpoint. The static elongation at 21 kPa was 100.5 mm (target range: 99 to 102 mm). The casings were extremely stable, could be gathered without problems and filled with sausage mass on automatic filling machines. The filling, shrinking, maturing and peeling behavior was normal.

Example 3

Analogously to Example 1, a hemp fiber paper with a basis weight of 25.4 g / m ^{2 was} produced. It was then passed through a 1.2% cellulose solution in 87.7% aqueous NMMO at 90 ° C., then precipitated in a 12% NMMO solution, washed in a further water bucket, then dried and wound up. The paper showed a tensile strength of 9 N / mm ² and an elongation at break of 7% when wet.

A hose of 120 mm caliber viscose on the outside showed the usual precipitation and regeneration a burst pressure of 64 kPa or 18.5% above the nominal value, the static elongation was 135 mm at 21 kPa (Target range: 133 to 137 mm). It was easy to process.

Claims (10)

1. A nonwoven fiber fabric whose fibers were bonded by

   a) treatment with a solution of cellulose in a mixture of N-methylmorpholine N-oxide (NMMO) and water,

   b) precipitation of the cellulose using an aqueous NMMO solution,

   c) washing to remove the NMMO and, if appropriate,

   d) drying.
2. A nonwoven fiber fabric as claimed in claim 1, wherein the cellulose content is from 0.5 to 5, preferably from 1 to 3, in particular from 1.5 to 2, % by weight, in each case based on its total weight.
3. A nonwoven fiber fabric as claimed in claim 1 or 2, wherein the fibers are hemp fibers.
4. A process for producing a bonded nonwoven fiber fabric having the following stages in the sequence specified:

   providing a suspension which comprises cellulose fibers,

   forming a nonwoven fiber fabric from the suspension,

   partial or complete drying of the nonwoven fabric and

   bonding of the nonwoven fabric,

   which comprises, for the purpose of bonding, applying to the nonwoven fabric a solution of cellulose in an NMMO/water mixture, precipitating the cellulose using an aqueous NMMO solution, washing the nonwoven fabric virtually free from NMMO and drying it.
5. The process as claimed in claim 4, wherein the suspension additionally comprises at least one polyamine-polyamide-epichlorohydrin resin, a urea-formaldehyde resin or a melamine-formaldehyde resin.
6. The process as claimed in claim 4, wherein the solution is applied by immersing the nonwoven fabric into a bath containing a cellulose/NMMO/water solution.
7. The use of the nonwoven fiber fabric as claimed in claims 1 to 3 for producing teabags or as reinforcement in packaging films, in particular in tubular food casings which are produced by the viscose process.
8. A fiber-reinforced food casing or packaging film produced by the viscose process, wherein the fiber reinforcement consists of a nonwoven fiber fabric as claimed in one or more of claims 1 to 3.
9. The process for producing the food casing or packaging film as claimed in claim 8, in which a nonwoven fiber fabric is viscose-coated on one or both sides, wherein the nonwoven fiber fabric corresponds to claims 1 to 3.
10. The process as claimed in claim 9, wherein the nonwoven fiber fabric was bent to form a tube prior to the viscose-coating.