DE19650383A1 - Multi-layer tubular films - Google Patents

Abstract

The invention concerns multilayered biaxially stretched and thermoset tubular films composed of an inner layer (A) comprising at least one thermoplastic copolyamide as an essential component, at least one intermediate layer (B) which is composed of a polyolefin homo- or copolymer, and an outer layer (C) which is composed of at least one thermoplastic polyamide as an essential component. The tubular films are characterized in that the layer thickness ratio of (C) : (A) is between 5 : 1 and 2 : 1.

Description

The invention relates to multilayer biaxially stretched and Heat-set tubular film made up of an inner layer A) which consists of at least one thermoplastic copolyamide as essential component consists of at least one intermediate layer B), which from a polyolefin homopolymer or copolymer is built and an outer layer C), which consists of at least one thermoplastic polyamide built as an essential component is.

Furthermore, the invention relates to the use of the Invention appropriate tubular films as a sausage casing as well as the one obtained sausage casings.

The production of stretched tubular films is from US 3,456,044 known. The production of multilayer tubular films, e.g. B. by coextrusion is known from US 5 296 170.

One or more layers of polyamide are u. a. from the DE-A 39 43 024, DE-A 28 50 182, DE-A 28 50 181 and EP-A 358 038 known.

Polyamide films (unoriented or biaxially oriented) are often used as a barrier film for packaging food. Polyamide acts as a barrier medium primarily against the entry of oxygen into the packaged food, while the barrier effect against the escape of water from the food (drying out) is less. Coextrusion with polyolefins is used to improve the H ₂ O blocking effect, and coextrusion with EVOH is used to further increase the O ₂ blocking effect.

Another means of improving the barrier effect of poly amide is the admixture of partially aromatic polyamides of Types PA 6I / 6T or PA MXD6 to standard polyamides (especially to PA6). Additional quantities are of the order of 10-40% necessary. This is not just because of the high price, but also due to the greatly changed mechanical and opti properties and poorer processability the disadvantage of polyamides (see EP-A 358 038).

Biaxially oriented tubular films are used in particular in the Sausage industry used. The raw sausage (sausage meat) is in Tubular film sections filled, closed at both ends  and cooked. Because of the typical for biaxially oriented films A shrink-filled, round sausage is obtained when cooking shrink.

The known films are in terms of their water and acid permeability and the meat adhesion in need of improvement. This also applies to transparency or colorability as well Printability of the foils.

The present invention was therefore based on the object multilayer biaxially stretched tubular films are available too which have a low oxygen and water permeabili good transparency or good colorability or have good printability.

Accordingly, the films defined at the outset were found, which are characterized in that the layer thickness ratio C): A) 5: 1 to 2: 1. Preferred embodiments can be found in the subclaims.

Surprisingly, it was found that an asymmetric structure of the layers and especially through the selection of a particular copolyamide the above properties of Films are improved.

The inner layer A) of the films according to the invention, which the raw sausage mass (sausage meat) touches, shows after stretching and heat setting a layer thickness of 3 to 20, preferably 6 to 15 microns.

Suitable copolyamides as an essential component of layer A) are mixtures of
A ₁ ) 75 to 100% by weight of a partially crystalline copolyamide,
A ₂ ) 0 to 25 wt .-% of an amorphous partially aromatic polyamide.

The partially crystalline copolyamides A ₁ ) preferably have a melting point of 145 to 210 ° C., in particular 175 to 205 and very particularly preferably 180 to 200 ° C., determined by means of DSC at a heating rate of 20 ° C./min.

The amorphous polyamides A ₂ ) have a heat of fusion of <1 J / g, determined by DSC at a heating rate of 20 ° C / min. The viscosity number (VZ) of the polyamides A ₁ ) is generally from 160 to 280, preferably 185 to 250 ml / g; the VZ of the amorphous copolyamides is usually in the range from 80 to 140 ml / g, preferably 100 to 125 ml / g, determined on a 0.5% solution in 96% by weight sulfuric acid at 25 ° C. according to ISO 307.

Semicrystalline resins such as z. B. in the American patent publications 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 prefers.

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-aminocyclo hexyl) propane.

Particularly preferred partially crystalline polyamides A ₁ ) are made of
95 to 75 wt .-% ε-caprolactam and
5 to 25% by weight of laurolactam and / or lauryllactam
or off
95 to 75% by weight ε-caprolactam,
5 to 25 wt .-% units from approximately equimolar mixtures of dicarboxylic acids such as adipic acid, suberic acid, sebacic acid, isophthalic acid and / or terephthalic acid with diamines such as hexamethylene diamine, octamethylenediamine, methylpentanediamine, m-xylylenediamine, trimethylhexamethylene diamine and / or isophorone
built up.

Particularly preferred amorphous polyamides A ₂ ) are made up of

50 to 100% by weight units of isophthalic acid and hexamethylene diamine,
0 to 50 wt .-% units of isophthalic acid or terephthalic acid and a diamine selected from the group diaminodiphenylmethane, (diaminodimethyl) diphenylmethane, isophoronediamine, methyl pentanediamine or mixtures thereof and / or
0 to 50 wt .-% units of terephthalic acid and hexamethylene diamine.

The intermediate layer B) consists of at least one layer of one a polyolefin homopolymer or copolymer.

The intermediate layer B preferably consists of a so-called functional polyolefin homopolymer or copolymer or of 3 layers B ₁ -B ₂ -B ₃ arranged one above the other, preferably B ₁ and B ₃ consisting of a functional polyolefin homopolymer or copolymer and the middle layer B. ₂ consist of a non-functional poly olefin homo- or copolymer.

Suitable polyolefin homopolymers are e.g. B. polyethylene, poly propylene and polybutene.

Suitable polyethylenes are very low polyethylenes (LLD-PE), low (LD-PE), medium (MD-PE) and high density (HD-PE) These are short or long chain branches or linear polyethylenes that are in a high pressure process in the present of radical starters (LD / PE) or in a low pressure process in The presence of so-called complex initiators z. B. Phillips or Ziegler-Natta catalysts (LLD-PE, MD-PE, HD-PE) manufactured will. The short chain branches in the LLD-PE or MD-PE are by copolymerization with α-olefins (e.g. butene, hexene or Octen) introduced.

LLD / PE generally has a density of 0.9 to 0.93 g / cm ³ and a melting temperature (determined by means of differential thermal analysis) of 120 to 130 ° C, LD-PE a density of 0.915 to 0.935 c / cm ³ and a melting temperature of 105 to 115 ° C, MD-PE a density of 0.93 to 0.94 g / cm ³ and a melting temperature of 120 to 130 ° C and HD-PE a density of 0.94 to 0.97 g / cm ³ and a melting temperature of 128 to 136 ° C.

Preferred LDPE and LLDPE as intermediate layer B), in particular B ₂ , have a density <0.92 g / cm ³ .

As the film layer B), in particular as the intermediate layer B ₂ , homopolymers or copolymers of ethylene with C3 to C10 alk-1-enes, preferably copolymers containing 2 to 8% by weight of at least one alk-1-ene with 4, 6 or 8 carbon atoms are used, which can be obtained by polymerizing the corresponding monomers with metallocene catalysts.

The flowability measured as the melt index MVI is all common 0.05 to 35 g / 10 '. The melt flow index corresponds to this the amount of polymer, which within 10 min DIN 53 735 standardized test device at a temperature of 190 ° C and 2.16 kg load is squeezed.

Suitable polypropylenes are known to the person skilled in the art and are for example in the Plastics Handbook Volume IV, Polyolefins, Carl Hauser Verlag Munich.

The melt volume index MVI according to DIN 53 735 is generally 0.3 to 80 g / 10 min, preferably 0.5 to 35 g / 10 min at 230 ° C and 2.16 kg load.

Such polypropylenes are usually produced by low pressure polymerization with metal-containing catalysts, for example with the help of titanium and aluminum containing Ziegler catalysts, or in the case of polyethylene by Phillips catalysts based on chromium Links. The polymerization reaction can with the in conventional reactors, both in the gas phase, in solution or be carried out in a slurry.

Mixtures of polyethylene with polypropylene can also be used be set, the mixing ratio is arbitrary.

Also suitable as intermediate layer B), in particular as intermediate layer B ₂ , are copolymers of ethylene with α-olefins such as propylene, butene, hexene, pentene, heptene and octene or with non-conjugated dienes such as norbornadiene and dicyclopentadiene. Copolymers B) are understood to be both statistical and block copolymers.

Statistical copolymers are usually made by polymerization a mixture of different monomers, block copolymers sequential polymerization of different monomers receive.

Other suitable polymers are those described above Polyolefin homo- and copolymers, which 0.1 to 20, preferred as 0.2 to 10 and in particular 0.2 to 5 wt .-% (based on Contain 100 wt .-% of the polyolefin of functional monomers  (so-called functional or modified polyolefin homo- or copoly merisate).

Among functional monomers are said to be carboxylic acid, acid anhydride, acid amide, acid imide, carboxylic acid ester, amino, Hydroxyl, epoxy, oxazoline, urethane, urea or lactam group-containing monomers are understood to be a reactive Also have a double bond.

Examples include methacrylic acid, maleic acid, maleic acid anhydride, fumaric acid, itaconic acid and the alkyl esters of before standing acid or its amides, maleimide, allylamine, Allyl alcohol, glycidyl methacrylate, vinyl and isopropenyloxazoline and methacryloylcaprolactam and vinyl acetate.

The functional monomers can be obtained either by copoly merisation or by subsequent grafting into the polymer chain introduce. The graft can be either in solution or in the Melt take place, with radical initiators such as Per oxides, hydroperoxides, peresters and percarbonates are also used that can.

Such polymers are generally commercially available (Polybond®, Exxelor®, Hostamont®, Admer®, Orevac® and Epolene®, Hostaprime®).

Particularly preferred films according to the invention contain an intermediate layer B, which consists of at least 3 layers B ₁ to B ₃ .

With such a structure, it is advantageous to further improve the barrier properties that layers B ₁ and B ₃ , in particular made of a polyolefin homopolymer or copolymer modified with acid-functional monomers, and layer B ₂ ) made of an unmodified polyolefin homopolymer or copolymer consists.

The layer thickness of the intermediate layer B is in general in total from 10 to 25, preferably from 12 to 18 microns.

With a 3-layer structure B ₁ -B ₂ -B ₃ , the thicknesses of B ₁ and B _{3 are} usually 0.5-4, preferably 1-2 µm; the layer thickness of the middle layer B ₂ at 5-23, preferably 7-16 µm.

Those polyamides are suitable for the outer layer C) which have already been described above for the inner layer A) were.

 Particularly preferred polyamides are polyamide 6 and mixtures of PA6 with up to 25% by weight, preferably up to 10% by weight of one partially aromatic amorphous polyamide (see inner layer A) and Compositions of 70 to 95% by weight PA6 with 5 to 30% by weight an aliphatic copolyamide. The layer thickness of the outside layer C) is generally from 10 to 50 in total before moves from 15 to 30 µm.

In addition to the essential components, the individual polymers components for the production of the films further additives and Processing aids included. Their share is in the Usually up to 10% by weight, preferably up to 5% by weight, based on the total weight of the respective polyamide or polyolefin form mass that form the individual layers.

 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 plasticizers.

Lubricants and mold release agents which can generally be added to 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, stearic acid alkyl esters and amides and esters of pentaerythritol with long-chain fatty acids. Amide waxes of C ₁ to C ₆ monoamines or C ₂ to C ₆ diamines with a C ₁₄ to C ₂₈ monocarboxylic acid are particularly preferred. Preferred compounds are ethylene distearylamide or ethylene diol amide, which are contained in amounts of 300 to 3000, preferably 1000 to 2000 ppm, based on the respective layer-forming polymer. SiO ₂ , Na AlSiO ₃ and CaCO ₃ particles may be mentioned as antiblocking agents. Preferably only the inner layer A contains an antiblocking agent and only the outer layer C contains a wax in quantities of 1000-3000 ppm.

 Inorganic pigments such as titanium dioxide, ultramarine blue, Iron oxide and carbon black, as well as organic pigments like phthalo cyanine, quinacridone, perylene and dyes such as nigrosine and Anthraquinones can be added as colorants.  

The polyolefin layer B or the outer layer C is preferably colored, in particular in the case of a multilayer structure, the intermediate layer B ₂ with customary pigments or dyes.

 The production of the respective molding compounds can in itself known methods.

Lubricants and / or antiblocking agents are preferred by external coating of the granules (so-called external lubrication) brought, the lubricant on the granules z. B. on is drummed.

When adding pigment or antiblocking agent, this is preferably done Production of a batch (concentrate) from polymer and additives, wherein 5 to 50, preferably 15 to 35% by weight of the additive, e.g. B. incorporated into a polyamide matrix using conventional extruders be tested. This concentrate is then usually called physical mixture mixed with other polymer granules and the granulate mixture processed into foil.

In the case of a colored film, the pigmentation preferably takes place in the intermediate layer B or, in the case of a 3-layer structure, in the intermediate layer B ₂ . In addition to a colored pigment, the outer layer A) can be obtained with 0.01 to 1, preferably 0.1 to 0.3% by weight of a white pigment, e.g. B. TiO ₂ are added.

According to the invention, the films described in the opening paragraph Made in such a way that the components are made using conventional Coextrusion process produces a multilayer film. The Solidification of the film is usually carried out in such a way that the film by means of rollers or other suitable devices passed through a water bath or tempered air flow becomes.

For the production of biaxially oriented films the primary foils in the usual way after solidification at least 1.5 times, preferably at least 2 times lengthways and stretched across. You can do this, for example, through leadership of the foils over rollers with different rotational speeds to reach. In the case of biaxially oriented films, they stretch immediately Devices attached laterally to the side of the film Width.  

In the case of biaxially oriented tubular films, for example, a Pressure of 1 to 3 bar placed in the hose, the pressure depends on the desired dimensions of the film.

 The longitudinal / transverse stretch ratio is preferably 1: 2 to 1: 5, preferably 1: 2.5 to 1: 3.5.

For good and reproducible caliber accuracy with biaxial To achieve oriented foils, it is advantageous, however Films after the molten discharge from the extruder in a first stage at temperatures of 0 to 25 ° C, preferably Cool 3 to 10 ° C and then in a second stage Temperatures of 50 to 95 ° C, preferably 60 to 90 ° C to heat men.

After stretching the films, they can be heated with rollers or with hot air (approx. 80 to 195 ° C) or steam (60 to 100 ° C) can be heat set. The foils are for example wise over rollers through a closed container with tempe air flow or steam flow. The lingering time is usually 0.3 to 10 sec, preferably 1 to 3 sec.

Preferred biaxially oriented films exhibit after thermo fix a shrinkback value of 5 to 25%, preferably 10 to 20%. The shrinkback value is usually determined by one-minute boiling of the film in boiling water determined.

The asymmetrical is essential for the properties of the foils Layer thickness ratio C): A) from 5: 1 to 2: 1, preferred 4: 1 to 3: 1, these values refer to the foils after stretching and heat setting.

The total wall thickness is preferably 20 to 100, preferably 25 to 55 and in particular 30 to 40 µm, the tube diameter for tubular films 10 to 200, preferably 25 to 100 mm.

The films according to the invention are notable for good water and oxygen permeation properties. You are a good one dyeable and easy to print on. Therefore they are suitable Films according to the invention as packaging material for pasty Food. For food, the preferred ver sausage casings for cooked and scalded sausages as well as for cheese sausages and to call the stomach.

Examples

The following components were used:
PA6 = polyamide 6 with VZ 250 ml / g (0.5% solution in 96% sulfuric acid, ISO 307), Ultramid® B4 from BASF AG
PA6 / 66 = copolyamide 6/66 from 85 parts of monomers of PA6 and 15 parts of monomers of PA 66 with a melting point of 193 ° C., VZ 246 ml / g, Ultramid® C4 from BASF AG
Wax = ethylene-bis-stearylamide, melting point 144 ° C
EAA = ethylene-butyl acrylate-maleic anhydride (MA) copolymer made from 90% ethylene, 8% butyl acrylate, 2% MSA, (Bynell® 2174 from DuPont)
Ionomer = Zn ionomer of an ethylene-acrylic acid copolymer with 3.5% acrylic acid content, (Surlyn®3426 from DuPont).

Production of the foils

With a 5-layer extruder with 45 mm extruders (3-layer drive by using 2 extruders) were multilayer films together with the layer structures and layers mentioned in Tab. 1 settlements made. The melt temperatures in the multi-layer head were 235 ° C each, the hose diameter at the nozzle was 50 mm. The film tube was cooled with a water bath at 6 ° C. folded and heated to 70 ° C with a second water bath. The hose was then passed through two pairs of rollers enclosed air bubble around each Stretched 2.5 times (lengthways and crossways). After that, the slide hose with a residence time of 1.2 seconds through a heated to 120 ° C Thermofixing tunnel directed and wound up.

The layer thicknesses are on the stretched and heat-set Slides covered.

The following were measured on the foils:
Oxygen permeation at 100% rel. Humidity on the A side and 50% rel. Humidity on the C side, at 23 ° C, in [ml / m ² d bar], based on DIN 53 380.
Water permeation 90 to 0% rel. Humidity at 23 ° C, according to ISO 2528, in [g / m ² d].
Weight loss after filling a tube section of 30 cm length with water and storage for 42 days at 23 ° C / 50% rel. Humidity, based on the original amount of water (in% by weight).

The compositions of the films and the results of the measurements are shown in the table.  

Production of colored foils Example 9

Analogous to Example 7, but a layer of 90% LDPE (density 0.917) and 10% of a 30% soot batch based on LDPE was used as layer B2. Layer C was matted with 0.3% of a 65% TiO ₂ batch in PA6. The tubular film was intense and matt black.

Example 10

Analogous to Example 7, but the outer layer C was pigmented (with the addition of 0.3% of a 65% TiO ₂ batch as a matting agent). A mixture of 68% Ultramid®B4, 10% Ultramid®C4, 22% of a 24% carbon black batch in PA6 was necessary to achieve the same color depth as in Example 9.

Example 11

Analogous to example 7, but with layer B2 7% LDPE and 3% of a 25% perylene red batch based on LDPE. The Tubular film was easily stretchable and intensely red.

Example 12

As example 7, but as layer C a mixture of 80% Ultramid®B4, 10% Ultramid®C4, 10% of a 20% perylene red bat ches used in PA6. The extruded tube was very stiff and burst when trying to inflate, making one oriented slide was not possible.

Claims (8)

1. multilayer biaxially stretched and heat-set tubular film composed of an inner layer A) which consists of at least one thermoplastic copolyamide as an essential component, at least one intermediate layer B) which is composed of a polyolefin homo- or copolymer and an outer layer C) , which is built up at least from a thermoplastic polyamide as an essential component, characterized in that the layer thickness ratio C): A) is 5: 1 to 2: 1. 2. Tubular film according to claim 1, characterized in that the inner layer thickness A) from 3 to 20 µm, the intermediate layer thickness B) from 10 to 20 µm and the outer layer thickness C is from 10 to 50 µm. 3. tubular films according to claim 1 or 2, characterized in that the inner layer A) from a mixture of
A ₁ ) 75 to 100% by weight of a partially crystalline copolyamide,
A ₂ ) 0 to 25 wt .-% of an amorphous partially aromatic polyamide
is constructed. 4. tubular films according to claim 3, characterized in that the copolyamide A ₁ ) has a melting point of 145 to 210 ° C. 5. tubular films according to claims 1 to 4, characterized in that the intermediate layer B) consists of at least 3 layers B ₁ to B ₃ . 6. Tubular films according to claim 5, characterized in that the layers B ₁ ) and B ₃ ) consist of a polyolefin homo- or copolymer modified with acid-functional monomers and the layer B ₂ ) consists of an unmodified polyolefin homo- or copolymer. 7. Use of the tubular films according to claims 1 to 6 as a sausage casing for boiled and scalded desert as well as cheese sausage and Hem stomach. 8. Sausage casings, available from the tubular films according to the Claims 1 to 6.