DE102020109417A1 - Process for the production of tracing paper - Google Patents

Abstract

A method for producing tracing paper is characterized by the following steps: a homogeneous starting solution (1) consisting of 12% cellulose, 77% solvent and 11% water is fed to a film caster (2) with constant pressure, the solvent being N-methylmorpholine -N-oxide (NMMO); - the homogeneous starting solution is extruded through an outlet nozzle in the film caster (2) at a pressure of 25 to 40 bar and at a temperature of 85 ° C to 115 ° C; - passes through after the extrusion the homogeneous intermediate solution with 4 to 6 m / minute, preferably 5 m / minute an air gap (3); - after the air gap (3), the homogeneous intermediate solution meets a precipitation bath (4), with the precipitation bath (4) consisting of 15 to 25% Water and 75 to 85% of the solvent NMMO, so that a film is created from the homogeneous intermediate solution.

Description

Technical area

The invention relates to a method for producing transparent paper according to the preamble of claim 1.

State of the art

Transparent paper has been a popular packaging material since its appearance in 1908 (back then as cell glass or cellophane). In the 1950s, petroleum-based foils were added and the tracing paper has now been largely replaced by them. On the one hand, the fully synthetic films can be produced much more cost-effectively, on the other hand they have some advantageous properties.

A homogeneous solution of cellulose, solvents (carbon disulfide, sodium hydroxide) and water is brought in at constant pressure. In the film caster, the solution is extruded at 3-5 bar pressure through an evenly narrow slot into a precipitation bath. The precipitation bath initiates coagulation and largely defines the crystalline structure. The precipitation bath is made up of sulfuric acid, sodium disulfide and water. The further processing steps are used for desulphurisation, bleaching, washing and surface treatment as well as drying and subsequent winding of the film.

The technology is fundamentally out of date, and no further developments have been made since 1990. The process requires the use of highly corrosive chemicals, which requires expensive materials. If not handled correctly and recycled or disposed of, the chemicals used are harmful to health and the environment.

Object of the invention

The object of the present invention is to overcome the disadvantages of the prior art. In particular, the aim is to provide a method for producing a transparent paper under environmentally friendly conditions. Difficult to handle and dangerous chemicals and highly corrosion-resistant materials should be avoided in use.

Solution of the task

The features according to claim 1 and the independent claim 9 lead to the solution of the problem.

Advantageous refinements are described in the subclaims.

The solvent for the pulp is changed to NMMO, 99.9% of which can be recycled.

This avoids the use of carbon disulphide, sulfuric acid, sodium disulphide and sodium hydroxide and the production of their reaction products. This results in a solution that has different chemical properties and thus requires a new type of technology to implement the process mechanically.

The aim is to produce an environmentally friendly and biodegradable film for packaging goods of all kinds. The process according to the invention avoids the use of environmentally harmful and health-endangering auxiliary materials. In addition, there are savings in the construction of systems according to the invention, such as the film caster.

A homogeneous starting solution of cellulose (12%), solvent (NMMO, 77%) and water (11%) is brought in at constant pressure. In a so-called film caster, the solution is extruded at a pressure of 25-40 bar at a temperature of 85-115 ° C through an evenly narrow slot into an air gap. The speed here is approx. 5 meters per minute. The air gap prevents the solution from coagulating immediately and enables desired changes to be made to the film properties, including stretching and the associated crystalline orientation of the molecules. The film is fed to a precipitation bath below the air gap. The precipitation bath consists of water (15-25%) and NMMO (75-85%). The crystalline structure of the film is fixed here. The film is then drawn off on rollers at a speed of approx. 30 meters per minute. All further processing steps are only used for washing out, surface treatment as well as drying and final winding of the film. The final film consists of cellulose and a water content of approx. 10% as well as marginal amounts of additives / surface agents.

In the context of this invention, the concept of homogeneity as a deviation from general absolute homogeneity is defined only as relative homogeneity. Relative homogeneity also includes solutions that are not absolutely homogeneous.

In particular, cellulose comprises lyocell.

N-methylmorpholine-N-oxide (or commonly abbreviated as NNMO or NMO) is an organic compound from the series of amine N-oxides and is used as an oxidizing agent in chemical reactions. NNMO is used in bishydroxylation with osmium tetroxide, asymmetric Sharpless dihydroxylation, oxidation with TPAP and Jacobsen epoxidation. It is commercially available as a pure crystalline substance, as a monohydrate and as an aqueous solution.

In organic synthesis, NNMO is used as an oxidizing agent. In combination with TPAP, it is used to produce aldehydes from primary alcohols, whereby the water is removed by molecular sieves. A carboxylic acid is obtained in the presence of unbound water. In the Upjohn dihydroxylation of olefins with osmium tetroxide, NMO is used as a co-oxidant. An asymmetric variant here is the Sharpless dihydroxylation. NMMO can be used to remove O- and N-allyl protecting groups under oxidative conditions.

NMMO is used technically as a solubilizer in lyocell production. Cellulose is precipitated here from a solution in NMMO with water.

A use in a process for the production of tracing paper or cellophane has not been known up to now.

Figure list

• 1 zeigt eine Seitenansicht eines Filmgiessers und die 2 zeigt eine geschnittene Ansicht der 1.

Further advantages, features and details of the invention emerge from the following description of preferred exemplary embodiments and with reference to the drawings; this shows the following in the figures:

• 1 Fig. 13 shows a side view of a film caster and Figs 2 shows a sectional view of the 1 .

A homogeneous starting solution 1 made of cellulose (12%), solvent (NMMO, 77%) and water (11%) is brought in at constant pressure. In a so-called film caster 2 will be the solution 1 with 25-40 bar pressure and a temperature of 85-115 ° C through an evenly narrow slot in an air gap 3 extruded. The speed here is approx. 5 meters per minute. The air gap 3 prevents the solution from coagulating immediately 1 and enables the desired changes to be made to the film properties, including stretching and the associated crystalline orientation of the molecules. Below the air gap 3 the film becomes a precipitation bath 4th fed. The felling bath 4th is made up of water (15-25%) and NMMO (75-85%). The crystalline structure of the film is fixed here. The film is then drawn off on rollers at a speed of approx. 30 meters per minute. All further processing steps are only used for washing out, surface treatment as well as drying and final winding of the film. The final film consists of cellulose and a water content of approx. 10% as well as marginal amounts of additives / surface agents.

List of reference symbols

1

solution

2

Film caster

3

Air gap

4th

Precipitation bath

Claims (9)

Process for the production of tracing paper characterized by the following steps: - a homogeneous starting solution (1) consisting of 12% cellulose, 77% solvent and 11% water is fed to a film caster (2) with constant pressure, the solvent N-methylmorpholine-N is oxide (NMMO); - The homogeneous starting solution is extruded in the film caster (2) at a pressure of 25 to 40 bar and at a temperature of 85 ° C to 115 ° C through an outlet nozzle; - After the extrusion, the homogeneous intermediate solution passes through an air gap (3) at 4 to 6 m / minute, preferably 5 m / minute; - After the air gap (3), the homogeneous intermediate solution meets a precipitation bath (4), whereby the precipitation bath (4) consists of 15 to 25% water and 75 to 85% of the solvent NMMO, so that a film is created from the homogeneous intermediate solution. Procedure according to Claim 1 , characterized in that the film is drawn off over rollers at a speed of 30 m / minute. Procedure according to Claim 1 or 2 , characterized in that the film is washed out. Method according to one of the preceding claims, characterized in that the film is dried. Method according to one of the preceding claims, characterized in that the film, consisting of 90% cellulose and 10% water, is wound up. Film caster for the production of tracing paper according to the method of Claims 1 until 5 , with a solvent feed and an outlet nozzle and the precipitation bath (4), characterized in that the homogeneous starting solution (1) consisting of 12% cellulose, 77% solvent and 11% water can be fed to a film caster (2) at constant pressure, the solvent being N-methylmorpholine-N-oxide (NMMO), wherein the homogeneous starting solution (1) can be extruded through the outlet nozzle into the air gap (3) at a pressure of 25 to 40 bar and at a temperature of 85 ° C to 115 ° C and then into the precipitation bath (4) from 15 to 25% Water and 75 to 85% of the solvent NMMO can be brought. Film caster after Claim 6 , characterized in that the distance between the outlet nozzle and the precipitation bath (4) can be changed. Film caster after Claim 6 or 7th , characterized in that an outlet width of the outlet nozzle can be changed. Use of pulp and solvent NMMO for the production of tracing paper.

Images