DE19748598A1 - Microporous foils - Google Patents

Abstract

The invention relates to microporous films obtained by mixing A) 55 to 99.9 wt. % thermoplastic polyamides with B) 0.1 to 10 wt. % of a salt having a solubility in water of > 5 g/100 ml at 80 DEG C and optionally C) 0 to 30 wt. % further additives, whereby the sum of the weight percentages of constituents A) to C) equals 100 %. The invention also concerns the production of a film using standard flat sheet extrusion or blown film methods and subsequent aqueous extraction of constituents B).

Description

The invention relates to microporous films, obtainable by mixing

• A) 55 to 99.9% by weight of a thermoplastic polyamide With
• B) 0.1 to 10% by weight of a salt with water solubility of <5 g / 100 ml at 80 ° C and if necessary
• C) 0 to 30% by weight of further additives,

the sum of the percentages by weight of components A) to C) being 100%,
and production of a film by means of conventional flat-sheet or blown film processes and subsequent aqueous extraction of component B).

The invention further relates to processes for producing the films according to the invention and biaxially or monoaxially oriented Films obtainable according to the processes according to the invention. About that In addition, the invention relates to the use of the Invention appropriate films for food packaging

In addition to the z. B. described in DE-A 34 26 723 sausage casings with high water and oxygen barrier properties for cooking and Cooked sausages have a significant market need for high diffusion films for air-dried, possibly additionally smoked Sausages. Here, raw meat is poured into the casing and the contents then completed by air drying and possibly smoking (for example: salami). This process is mainly in southern and Western Europe, partly also in Central Europe. In contrast to the cooked and scalded sausages, Permeation required to dry out the excess Water of the raw meat and the introduced air bubbles to reach. Provides protection against oxidative attack here the content of curing salt. For this application is currently no artificial intestine used, but natural intestine or collagen or Cellulose casings because the usual, thermoplastic ver  worked polymers have too high a water barrier. Of the Use of synthetic casings made of thermoplastically processable poly meren would be desirable because this u. a. considerably cheaper are. Furthermore, the processing of collagen or cellulose a considerable environmental impact associated with tubular films, because these as natural products always sticking with larger quantities Accompanying products (slaughterhouse waste from collagen, lignin from Cellulose) which are removed and treated by sewage action must be disposed of at great expense. Especially with the ver Broad collagen casings are always made with sulfur hydrogen emission linked.

The processes known from the prior art describe the addition of salts to thermoplastics by means of organic solvents:

• 1) JP-A 01/245 035 describes the mixing of water-soluble particles (e.g. CaCl ₂ ) with a solution of polyamides in halogen-containing solvents. The polyamide compositions are then precipitated with methanol.
• 2) EP-A 105 636, EP-A 176 992 and EP-A 176 107 disclose the addition of water-soluble salts (e.g. MgCl ₂ ) in organic solutions of the polyamide e.g. B. in DMF. The solvent is then evaporated and the salt extracted with water.
• 3) JP-A 04/898 40 discloses polyamide compositions which Salts (e.g. NaCl) as complex compounds with polyethylene Glycol contain and their use for the production of Fibers.
• 4) CA-A 766 685 discloses the dissolution of polymers in organic Solvents with the addition of salt, subsequent precipitation and Extraction of the salt. Such molding compositions are Her position of fibers and articles of clothing.

For food packaging, the addition of the above-mentioned organi solvents are toxicologically unsafe, also for the manufacturers position (environmental impact and MAK values) of such products.

The object of the present invention was therefore to be microporous Polyamide films with high water and oxygen to provide permeability, the additives of which are toxic are ecologically harmless and as simple as possible are producible.  

This task was achieved through the polyamide films defined at the beginning solved.

Preferred embodiments and methods of manufacture the films and their use are to the subclaims remove:

As component A) is used in the preparation of the invention Films 55 to 99.9, preferably 67 to 99.5, in particular 80 to 97.5% by weight of at least one thermoplastic polyamide set. Of course, mixtures of the following standing polyamides used in the films of the invention become.

The polyamides of the films according to the invention generally have a viscosity number of 150 to 300 ml / g, preferably of 170 to 250 and in particular from 185 to 225 ml / g on a 0.5 wt .-% solution in 96 wt .-% sulfuric acid at 25 ° C according to ISO 307.

Semicrystalline or amorphous resins such as z. Tie American patents 2,071,250, 2,071,251, 2,130,523, 2 130 948, 2 241 322, 2 312 966, 2 512 606 and 3 393 210 be are preferred.

Examples of this are polyamides, which differ from lactams with 7 to Derive 13 ring members, such as polycaprolactam, polycapryllactam and polylaurin lactam and polyamides, which are produced by the reaction of Dicarboxylic acids can be obtained with diamines.

As dicarboxylic acids are alkanedicarboxylic acids with 4 to 12 ins special 6 to 10 carbon atoms and aromatic dicarbon acids can be used. Here are only adipic acid, azelaic acid, Sebacic acid, dodecanedioic acid and terephthalic and / or isophthalic acid called as acids.

Particularly suitable diamines are alkane diamines with 6 to 12, in particular 6 to 8 carbon atoms and m-xylylenediamine, Di- (4-aminophenyl) methane, di- (4-aminocyclohexyl) methane, 2,2-di- (4-aminophenyl) propane or 2,2-di (4-aminocyclohexyl) propane.

Preferred polyamides are polycaprolactam and copolyamides 6/66 and copolyamides from caprolactam and terephthalic acid / isophthal acid (e.g. PA 6 / 6T, PA 6 / 6I).  

Copolyamides 6/66 are particularly preferred, the proportion of Caprolactam monomers preferably 80 to 95 wt .-% based on the copolyamide is.

Mixtures of the above polyamides are also preferred, in particular up to 25% by weight of partially aromatic and / or Amorphous polyamides such as PA6I or PA6I / 6T can exist.

As component B) in the preparation of the invention Film compositions 0.1 to 10, preferably 0.5 to 7 and in particular from 2.5 to 5% by weight of at least one salt with a water solubility of <5 g / 100 ml, preferably <10 g / 100 ml used at 80 ° C.

Salts B) with water solubility are preferred <10 g / 100 ml, preferably <20 g / 100 ml at 80 ° C. As soluble speed in the present case is the content of B) in g per 100 ml Water defines that at the temperature given above is in equilibrium with excess solid salt B).

Preferred salts are those which contain anions, selected from the group of halides, carbonates, hydrogen carbonates, sulfates, hydrogen sulfates, phosphates, hydrogen phosphates, nitrates, acetates or formates, contain and Cations selected from the group of the 1st to 3rd main group, preferably alkaline earth and / or alkali metal ions, of the periods systems or ammonium cations.

Particularly preferred salts B) are NaCl, NaNO ₃ , Na ₂ SO ₄ , Na ₂ CO ₃ , NaHCO ₃ , sodium acetate, KCl, KNO ₃ , K ₂ SO ₄ , K ₂ Cl ₃ , MgCl ₂ , CaCl ₂ or mixtures thereof called. The salts B) can be mixed in as a 10 to 90% solution or as a fine-grained solid, the mean particle size (d ₅₀ value) of the component B) when mixed in as a solid, preferably from 1 to 100 μm, in particular 1 to 50 μm , especially 3 to 20 µm, is.

The proportion of particles with one particle is preferably size ≧ 80, preferably ≧ 50 µm, at most 1%.

In addition to the essential components A) and B), the shape masses for the production of the polyamide films further additives and processing aids C). Their share is usually up to 30% by weight, preferably up to 10% by weight, based on the total weight of components A) to C).  

Common additives are, for example, stabilizers and Oxidation retarders, heat decomposition and decomposition agents through ultraviolet light, lubricants and mold release agents, color substances, pigments and antiblocking agents.

Lubricants and mold release agents, which can usually be added up to 1% by weight of the thermoplastic composition, are, for example, long-chain fatty acids or their derivatives such as stearic acid, stearyl alcohol, alkyl stearates and amides, and esters of pentaerythritol with long-chain fatty acids. Calcium stearate, zinc stearate and ethylene-bis-stearylamide are preferred. SiO ₂ , Na AlSiO ₃ and CaCO ₃ particles may be mentioned as antiblocking agents.

Organic dyes such as nigrosine and pigments can also be used such as titanium dioxide, cadmium sulfide, cadmium selenide, phthalocyanines, Ultramarine blue and carbon black can be added as colorants.

Sodium phenylphosphinate, aluminum can be used as nucleating agents oxide, silicon dioxide, nylon 22 and preferably talc are, usually in amounts up to 1 wt .-%.

The molding compositions according to the invention can be prepared according to known methods take place. The Her preferably takes place position by adding component B) and optionally C) to melt component A).

Expediently, extruders such. B. A screw or twin screw extruders or other conventional Plasticizing devices such as Brabender mills or Banbury Mills.

Preference is given to producing a batch (concentrate) from A) and B), 1 to 60, preferably 15 to 35% by weight of the Salt B) are incorporated into a polyamide matrix. This The concentrate is then usually used in the film extrusion as physical mixture with polyamide granules ver thins so that the proportions described above of salt B) can be achieved in the polymer matrix. The addition substances C) can be used in this production method both in the batch incorporated as well as in the subsequent dilution of the Concentrates are added to the polymer melt.

Component B) can also advantageously be used with component A) can be mixed by using component B) as an aqueous solution or Introduces dispersion into the melt of the polyamide A). In this  Case, the particle size of the salt B) is not so important because the solution is usually prepared prior to mixing.

The concentrations of such aqueous solutions or dispersers ions are usually in the range from 10 to 90, preferably as from 25 to 50 wt .-%.

The solutions or dispersions can be pumped into the Melt the thermoplastics A) with the addition of if necessary Add component C) and then degas the ver steaming water by means of suitable devices, such as. B. Twin screw extruder with degassing devices.

According to the invention, the polyamide films described at the outset made in such a way that one can mix the components ten A) to C) by means of conventional wide slot or blown film ver drive produces a film and then component B) ent at least partially from the film by aqueous extraction distant (pore formation).

When the films are solidified by means of wide-slit film Ver will usually drive the melt of components A) to C) to a temperature of 10 to 130 ° C, preferably 20 to 100 ° C, abge by extrusion on appropriately tempered metal rollers cools.

In the case of solidification by means of blown film processes, the Usually the hose is extruded and passed through an air flow optionally cooled, and / or by air cooling the Inside the hose or through a water bath, which if necessary Component B) may contain cooled.

The temperature of the water bath during consolidation is usually <25, preferably <15 and in particular 4 to 10 ° C.

For the production of mono- or biaxially oriented films become the primary foils in the usual way after solidification by at least 1.5 times, preferably at least 2 times in stretched in at least one direction. You can do this, for example by guiding the foils over rollers with different rotations reach speed. Stretch for biaxially oriented films at the same time devices attached to the side of the film in width. The stretching ratios are preferably <2.3 and in particular in the longitudinal and transverse directions 2.5 to -3.5.  

In the case of biaxially oriented tubular films, for example, a Put pressure of 1 to 3 bar in the film tube, whereby the pressure depends on the desired dimensions of the film judges.

The film tube is preferably biaxial during manufacture oriented tubular films with a water bath cooled to a temperature of 3 to 15 ° C and thus solidified and then through a second water bath with temperatures of 60 reheated to 90 ° C, the residence times 1 to 10 seconds and then as described above stretched.

After stretching the films, they can be placed in hot air (approx. 80 to 160 ° C) or water vapor (160 to 180 ° C) thermo be fixed. For this purpose, the foils are used for example tempered rollers or through a corresponding tempe water bath or closed container with tempered water Air flow passed.

Preferred mono- or biaxially oriented films have the following Heat setting a shrinkback value of 2 to 20%, preferably have 3 to 10%. The shrinkback value is usually by immersing the film in hot water at 100 ° C for one minute certainly.

The film can then be extracted further by this by a water bath at temperatures from 30 to 90 ° C for 1 to 30 s.

Depending on the type of solidification, the extraction of the Foils (removal of component B)) by the for solidification and / or water bath used for reheating (or one aqueous solution of salt B)) or by a second water bath (or aqueous solutions of component B)) are carried out. Extraction is preferably carried out through a cascade of several baths. This extraction is preferably carried out at temperatures from 50 to 99, especially at temperatures from 60 to 80 ° C.

The dwell times in the continuous extraction are usually from 3 to 50, preferably from 5 to 25 sec.

It is also possible to first ver the film consolidate and, if necessary, subsequently print and / or to gather and the extraction only before filling the film, e.g. B. with raw meat. For discontinuous extraction through z. B. Placing the film in water are longer dwell times  times required, which are usually in the range of 1 min to 2 h, preferably from 5 min to 1 h.

The microporous films should be preferred after the extraction still 0 to 50, preferably 0.1 to 20 and in particular 1 to 10% by weight, based on B) of the amount of salt B) used contain.

The films of the invention are characterized by high water and Oxygen permeation properties. Show at the same time special biaxially oriented tubular films of high caliber accuracy. The films according to the invention are therefore suitable as Packaging material for food. When it comes to food as a preferred use sausage casings for smoked and air to call dried sausages.

Examples

The following components were used:
Component A1: PA6 with a viscosity number (VZ) of 250 ml / g (0.5% in 96% by weight H ₂ SO ₄ at 25 ° C according to ISO 307), Ultramid® B4 from BASF AG
Component A2: PA66 with a VZ of 195 ml / g, Ultramid® A4 from BASF AG
Component B1: NaCl, average particle size: 18 µm (d ₅₀ value)
1% of the particles are ≧ 43 µm
(Solubility at 80 ° C was 31 g / 100 ml solvent water)
Component B2: NaCl as a 25% by weight aqueous solution
Component B3: CaCl ₂ as a 35% aqueous solution
(Solubility: 67 g / 100 ml water at 80 ° C).

Production of molding compounds

The components A1 and A2 were on a twin-screw extruder, ZSK30 from Werner & Pfleiderer, at 250 ° C (for PA6) or 280 ° C (for PA66) with the respective amounts of salt or salt solution (Quantity based on salt) made up. In the case of The solution water became salt solutions by vacuum degassing (300 mbar) away.  

Film production

• A) unoriented film from the specified mixtures was at 250 ° C (PA6) or 275 ° C (PA66) with a Weber 30 mm blow Film extruder as an unoriented blown film with a thickness of 50 µm manufactured (air cooling). The film was then with 20 sec residence time through a water bath at 80 ° C and then dried.
• B) from the specified mixtures was at 250 ° C with a Extruder from Plamex GmbH a primary tube of 300 µm made by cooling the film with 10 ° C cold water has been. Then the hose was filled with water at 70 ° C bath heated at 3 sec dwell time and then with internal air pressure stretched 2.8 × lengthways and crossways. Then was first Heat set in air at 150 ° C for 4 sec. In a second Process step was the at 80 ° C in water at 25 sec Dwell time extracted. Then the film was blown off dried with hot air and wound up.

The following was measured on the foils:

• - O ₂ permeation on films after conditioning for 24 h at 100% moisture, 23 ° C [ml 100 µm / m ² d bar] according to DIN 53 380
• - H ₂ O permeation 85 to 0% [g 100 µm / m ² d] according to DIN 53 122.

The compositions of the films are the results of Measurements and can be found in the table.  

Claims (13)

1. Microporous films, obtainable by mixing

• A) 55 to 99.9% by weight of a thermoplastic polyamide
• B) 0.1 to 10 wt .-% of a salt with a water solubility of <5 g / 100 ml at 80 ° C and optionally
• C) 0 to 30% by weight of further additives,

the sum of the percentages by weight of components A) to C) being 100%,
and production of a film by means of conventional flat-sheet or blown film processes and subsequent aqueous extraction of component B). 2. Microporous film according to claim 1, in which as component B) Salts with anions selected from the group of halides, Carbonates, hydrogen carbonates, sulfates, hydrogen sulfates, Phosphates, hydrogen phosphates, nitrates, acetates or formates and cations selected from the group of metals of the 1st to 3rd main group of the periodic table or ammonium be set. 3. Microporous film according to claims 1 or 2, in which component B) consists of NaCl, NaNO ₃ , Na ₂ SO ₄ , Na ₂ CO ₃ , NaHCO ₃ , sodium acetate, KCl, KNO ₃ , K ₂ SO ₄ , K ₂ CO ₃ , MgCl ₂ , CaCl ₂ or mixtures thereof is built up. 4. Microporous film according to claims 1 to 3, in which component B) has an average particle size (d ₅₀ ) of 1 to 100 microns. 5. Microporous film according to claims 1 to 4, in which the Component B) with a proportion of particles of at most 1% has a particle size ≧ 80 µm.   6. Process for the production of microporous films according to claims 1 to 3, characterized in that the Component B) as an aqueous solution with a salt content of 10 to 90% with evaporation of the solution water in one Mixes the melt of component A) and using conventional Broad-slit or blown film process produces a film and then component B) by aqueous extraction removed from the slide. 7. Process for the production of microporous films according to Claims 1 to 5, characterized in that the com components A) and B) and optionally C) mixed and by means of usual slot or blown film process a film produces and then component B) by aqueous Extraction removed from the slide. 8. The method according to claim 7, characterized in that one the film solidified before extraction. 9. The method according to claims 7 or 8, characterized records that the film after solidification by at least is stretched 2.5 times in at least one direction and then component B) is extracted. 10. The method according to claim 9, characterized in that one the film after stretching in hot air or steam heat-set and then extracted component B). 11. Use of the microporous films according to claims 1 to 5 and available according to the process conditions of Claims 6 to 10 as packaging material for food. 12. Use of the microporous films according to claim 11 as Sausage casing for air-dried and / or smoked sausages. 13. Microporous films obtainable according to claims 1 to 10 containing 0 to 50% by weight after extraction on B), the amount B) used according to claim 1.