WO2005042639A1

WO2005042639A1 - Method for producing polyamide/polyvinyl alcohol-based molded articles

Info

Publication number: WO2005042639A1
Application number: PCT/EP2004/012362
Authority: WO
Inventors: Sven KÖHNEN; Martin Steuer; Matthias Gutweiler
Original assignee: Kuraray Specialities Europe Gmbh
Priority date: 2003-11-03
Filing date: 2004-11-02
Publication date: 2005-05-12
Also published as: DE10351563A1; EP1687376A1

Abstract

The invention relates to a method for producing synthetic molded articles by thermoplastic processing of (A) at least one polyamide and/or copolyamide, (B) at least one polyvinyl alcohol, and (C) at least one softener. The inventive method is characterized in that the components (A), (B) and (C) for producing the molded article are added to an extruder without mixing them beforehand. The invention also relates to a molded article which is obtainable by the inventive method and to the use of such a molded article.

Description

Process for the production of polyamide-polyvinyl alcohol moldings

The present invention relates to a method for producing plastic moldings by thermoplastic processing of a polyamide, a polyvinyl alcohol and a plasticizer. In addition, the invention relates to a shaped body which is obtainable by the process according to the invention and the use of such a shaped body.

Nowadays, polyamide is widely used as packaging material for food. In particular, it is used for the production of sausage casings. In the case of smoked sausages, it is necessary that the polyamide casing has good permeability to smoke. For this purpose, according to the document DE 101 25 207 AI, polyamide-based shells are added to inert particles which form vacuoles when the sheath is stretched, or reactive substances which form gas bubbles in the film. Microporous polyamide-based films can also be obtained according to DE 19748 598 AI by adding a salt to the polyamide and removing them by aqueous extraction after the film has been produced. Finally, it is proposed in DE 198 54 769 AI to perforate a polyamide-based film tube with laser light (specks)

When packaging sensitive or perishable foods, it is also desirable that the casing has both a high permeability to smoke and a good oxygen barrier property. Films made from polyamide-polyvinyl alcohol mixtures are particularly suitable for this purpose. An ethylene-vinyl alcohol copolymer is also often added to the polyamide.

U.S. Patent No. 4,427,825 discloses a blend consisting of 1-65% by weight ethylene vinyl alcohol copolymer and a polyamide and containing no plasticizer. However, the inventors of the invention described below came to the conclusion through trials that processing polyamide with pure polyvinyl alcohol does not enable sufficiently stable long-term extrusion, since it leads to the thermal degradation of Polyvinyl alcohol is coming. The degradation products only collect in the extruder and are also pressed out of the extruder in the case of a longer extrusion time. Then the product can no longer be used. For these reasons, the use of plasticizers is absolutely necessary.

U.S. Patent No. 4,347,332 discloses a method of making a blend of 90-20% by weight polyamide, 10-80% by weight ethylene-vinyl alcohol copolymer and a plasticizer. The mixture is then heated and extruded into a film. DE 3229158 also describes a process for producing a film, in which a mixture of 90-10% by weight of polyamide and 10-90% by weight of ethylene-vinyl alcohol copolymer is first prepared, this mixture is heated and extruded. The mixture may contain up to 25% plasticizer. Finally, WO 02/078455 also describes a process in which a mixture of a polyamide and a hydrophilic compound, e.g. Polyvinyl alcohol. This mixture can additionally contain a plasticizer. According to the prior art described above, a mixture of polyamide, polyvinyl alcohol and plasticizer is first produced. In a further step, this mixture is extruded.

Special equipment is generally used for the production of the mixture, such as compulsory mixers, which place high demands on the temperature control and the course of the mixing process over time. This has a negative impact, both technically and in terms of price, on the production of the extrusion mixtures and thus indirectly on the production of the shaped articles, such as food packaging.

In practical application, a compound of polyvinyl alcohol and plasticizer is normally first prepared, since the thermoplastic processing of polyvinyl alcohol, especially with a high OH group content, requires the addition of external plasticizers. Such a compound normally contains more than 50% by weight of polyvinyl alcohol and less than 50 % By weight of glycerin, in each case based on the overall composition, and also oxidation stabilizers, extrusion aids and possibly other additives, and is provided by the manufacturer of the polyvinyl alcohol.

In the next step, the molded body mixes the compound made of polyvinyl alcohol and plasticizer with polyamide in order to obtain the final mixture, which is then melted in the extruder and turned into films or the like. is processed further. The above-described method of production used in practice is also uneconomical

Starting from the prior art mentioned, it can be regarded as an object of the present invention to provide an economical process for the production of plastic moldings based on polyvinyl alcohol which does not have the disadvantages known from the prior art.

The tasks described above, as well as others that are not expressly mentioned, but result from the context discussed above, are achieved by a method according to the present patent claim 1.

Advantageous embodiments of the method according to the invention are described in the dependent claims 2 to 13. Claims 14 to 17 contain a shaped body which can be obtained by the process according to the invention and claim 18 relates to the use of a shaped body according to the invention.

The invention relates to a process for the production of plastic moldings by thermoplastic processing of (A) at least one polyamide and / or copolyamide, (B) at least one polyvinyl alcohol, (C) at least one plasticizer, which is characterized in that the Components (A), (B) and (C) are added to the extruder without prior mixing. Surprisingly, it was found that plastic moldings based on polyamide, polyvinyl alcohol and plasticizer can be produced in this way without a previous mixture of polyamide, vinyl alcohol (co) polymer and plasticizer having taken place.

The method according to the invention is simple and therefore less expensive than the two or multi-stage methods according to the prior art.

Furthermore, the method according to the invention requires less energy than conventional methods in order to arrive at an identical shaped body.

In addition, a more homogeneous distribution of the polyvinyl alcohol can be achieved by the process according to the invention with the same energy input.

Furthermore, the method according to the invention can be carried out on an industrial scale in known plants.

Such a method also achieves very good homogenization of the components.

The moldings according to the invention have excellent water vapor permeability and / or smoke permeability.

With the same water vapor permeability, the moldings according to the invention can have a greater film thickness. This achieves greater mechanical stability and lower oxygen permeability with the same water vapor permeability.

The moldings according to the invention have excellent mechanical properties. Polyamides which are produced from a single monomer can be used, for example by polycondensation of an ω-aminocarboxylic acid or by ring-opening polymerization of a cyclic amide (lactam). Exemplary polyamides of this type are poly (ε-caprolactam), also referred to as polyamide 6 (PA 6), poly (ω-aminoonanthic acid) (PA 7), poly (ε-capryllactam) (PA 8), poly (ω-aminopelargonic acid) (PA 9), poly (oo-aminoundecanoic acid) (PA 11), poly (ε-laurine lactam) (PA 12) and PA 13. A preferred polyamide of this type is poly (ε-caprolactam).

Polyamides which can be obtained by polycondensation of a diamine and a dicarboxylic acid can also be used. Alkanedicarboxylic acids with 4-12, in particular 6-10, carbon atoms and aromatic dicarboxylic acids can be used as dicarboxylic acids. The exemplary acids include adipic acid, azelaic acid, sebacic acid, dodecanedioic acid, and terephthalic and isophthalic acid. Particularly suitable diamines are alkane diamines with 6-12, in particular 6 to 8, carbon atoms, and also m-xylylenediamine, di- (4-aminophenyl) methane, di- (4-aminocyclohexyl) methane, 2,2-di- (4-aminophenyl) ) propane and 2,2-di- (4-aminocyclohexyl) propane. Exemplary polyamides which are obtainable by polycondensation of a diamine and a dicarboxylic acid are polyhexamethylene adipamide (PA 66), which is produced from hexamethylene diamine and adipic acid, polyhexamethylene azalamide (PA 69), polyhexamethylene sebacinamide (PA 610), polyhexamethylene dodecanamide (PA 612), PA 6T made from hexamethylene diamine and terephthalic acid), PA 61 (made from hexamethylene diamine and isophthalic acid), PA 6-3-T (made from trimethylhexamethylene diamine and terephthalic acid) and PA MXD6 (made from m-xylylenediamine and adipic acid). Preferred polyamides from a dicarboxylic acid and diamine are polyhexamethylene adipinamide (PA 66) and polyhexamethylene dodecanamide (PA 612).

The polyamides described above are referred to in the context of this invention as polyamides or homopolyamides. They are by definition out one or two uniform components are formed and are characterized by the number of carbon atoms in the one or two basic monomers. Copolyamides can also be used according to the invention. In the context of the present invention, copolyamides are polyamides which do not meet the above definition for homopolyamides. Such copolyamides can in principle be formed from any of the abovementioned amino carboxylic acids, diamines and / or dicarboxylic acids. Preferred copolyamide is copolyamide 6/66 or 66/6 and PA 6/12. Further preferred copolyamides are formed from caprolactam, hexamethylenediamine and isophthalic acid / terephthalic acid, also referred to as PA 6 / 6T or PA 6/61. Copolyamides 6/66 are particularly preferred, the proportion of caprolactam monomers preferably being 80 to 95% by weight, based on the copolyamide. All copolyamides mentioned in WO 02078455 can also be used advantageously.

Finally, according to the invention, glycol- or polyglycol-modified polyamides can also be used as polyamides, which are described in the published patent application DE 101 25 207 A1, to which express reference is made in this connection. Such glycol- or polyglycol-modified polyamides comprise at least one amide component and at least one glycol or polyglycol component,

It is expressly pointed out that all of the aforementioned polyamides, copolyamides and modified (co) polyamides can be used both individually and as a mixture of two or more (co) polyamides.

Advantageous results are obtained if the (co) polyamide or the mixture of (co) polyamides is used in the process according to the invention in an amount of 50 to 95% by weight, preferably in 70 to 90% by weight and more preferably 80-90% by weight, in each case based on the weight of the total composition. In a further advantageous embodiment of the Processes are based on the total weight of 50 to 75 wt .-% of a (co) polyamide or a mixture of copolyamides. In yet another advantageous embodiment of the process, based on the total weight, 85 to 95% by weight of a (co) polyamide or a mixture of copolyamides are used.

In an advantageous embodiment, the polyamides used have a viscosity number of 150 to 300 ml / g, preferably 170 to 250 and in particular 185 to 225 ml / g, determined on a 0.5% by weight solution in 96% by weight. -% sulfuric acid at 25 ° C according to ISO 307.

When added to the extruder, the polyamide and / or the copolyamide preferably has a bulk density in the range from 500 to 900 g / 1, particularly preferably 600-800 g / 1.

The term bulk density refers here to the quotient of the mass and the volume taken up by the substance. The bulk density is determined by pouring the substance in question into a measuring box, measuring cup or measuring cylinder and determining the weight. For the purposes of the invention, this is done in accordance with the DIN 543 standard.

The polyamide and / or the copolyamide is particularly preferably used in the form of granules when added to the extruder, the granules preferably being cylindrical in shape, the diameter preferably in the range from 0.2 to 4 mm, particularly preferably 0, 5 to 2 mm and the height in the range from 0.2 to 4 mm, particularly preferably 0.5 to 3 mm.

The second component (B) used in the process according to the invention is a polyvinyl alcohol. Such a polyvinyl alcohol (B) preferably contains at least structural units of the formula (1)

Structural units of the formulas (2) and (3) below can also be present.

The respective structural units are different from each other in every case. In particular, the structural unit of the general formula (3) does not include the structural units of the general formula (1) and / or (2).

The radical R ¹ each independently represents hydrogen or methyl, preferably hydrogen.

The radical R ² denotes an alkyl radical with 1 to 6 carbon atoms, expediently a methyl, ethyl, n-propyl, iso-propyl, n-butyl, sec-butyl, tert-butyl, n-pentyl or an n-hexyl group, advantageously a methyl or an ethyl group, in particular a methyl group. The radicals R ³ , R ⁴ , R ⁵ and R ⁶ are each independently radicals with a molecular weight in the range from 1 to 500 g / mol, advantageously hydrogen, an optionally branched, aliphatic or cycloaliphatic radical with 1 to 16 carbon atoms, which, if appropriate may contain one or more carboxylic acid, carboxylic acid anhydride, carboxylic acid ester, carboxylic acid amide and / or sulfonic acid groups.

Particularly preferred structural units of the formula (3) are derived from straight-chain or branched olefins having 2 to 18 carbon atoms, (meth) acrylic acid, maleic acid, maleic anhydride, fumaric acid, itaconic acid, (meth) acrylamides and / or ethylene sulfonic acid. Here, olefins, especially those with a terminal C-C double bond, which preferably have 2 to 6 carbon atoms, in particular ethylene, have proven to be very particularly favorable. Furthermore, structural units (3) which are derived from acrylamidopropenylsulfonic acid (AMPS) also lead to very particularly advantageous results according to the invention.

The weight fraction of structural units of the formula (1) is preferably 15.0 to 99.9% by weight, more preferably 25.0 to 99.9% by weight, even more preferably 40.0 to 99.9% by weight. % and in particular 50.0 to 99.9% by weight, based on the total weight of the polyvinyl alcohol (B).

The weight fraction of structural units of the formula (2) is preferably 0.0 to 50.0% by weight and more preferably 0.1 to 50.0% by weight, based on the total weight of the polyvinyl alcohol (B).

Taken together, the weight fraction of the structural units of the formulas (1) and (2), based on the total weight of the polyvinyl alcohol (B), is preferably at least 50% by weight, more preferably> 60% by weight, advantageously> 70% by weight %, in particular> 80% by weight. Advantageous results can also be achieved if the proportion by weight of the structural units of the formulas (1) and (2) taken together> 85% by weight, advantageously> 90% by weight, advantageously> 95% by weight, in particular > 99 wt .-%, based in each case on the total weight of the polyvinyl alcohol.

The amount by weight of structural units of the formula (3), based on the total weight of the polyvinyl alcohol (B), is preferably up to 50% by weight, more preferably less than 40% by weight, advantageously less than 30% by weight. %, in particular less than 20% by weight. Advantageous results can also be achieved if the proportion by weight of the structural units of the formula (3) is less than 15% by weight, advantageously less than 10% by weight, advantageously less than 5% by weight, in particular less than 1% by weight. %, in each case based on the total weight of the polyvinyl alcohol.

In the production of the polyvinyl alcohol (B), structural units of the formula (2) are converted into structural units of the formula (1) by hydrolysis (alcoholysis). The degree of hydrolysis of the polyvinyl alcohol (B) is hereby defined as the percentage number of structural units of the formula (1) based on the total number of structural units of the formula (1) and (2) in the polyvinyl alcohol (B).

The degree of hydrolysis in the polyvinyl alcohol (B) is preferably in the range from 50 to 99.9%, advantageously in the range from 70 to 99.9%, advantageously in the range from 80 to 99.9%, even more advantageously in the range from 80 to 92% and especially in the range of 84 to 99.9%. Particularly advantageous results can be observed in the context of the present invention with a degree of hydrolysis in the range from 87 to 99.7%, more preferably in the range from 90 to 99.5% and in particular in the range from 90 to 95%.

The total number of structural units of the formula (3) is preferably in the range from 0.1 to 20 mol%, advantageously in the range from 2 to 19 mol%, in particular in the range from 2.5 to 17 mol%, in each case based on the Total number of structural units of the formula (1), (2) and (3). advantageous Results are within the scope of the present invention for a total number of structural units of the formula (3) in the range from 3.0 to 15 mol%, in particular in the range from 3.5 to 13 mol%, in each case based on the total number of structural units of the Formula (1), (2) and (3) to achieve.

In a particularly preferred embodiment of the present invention, the polyvinyl alcohol (B) is an ethylene-vinyl alcohol copolymer with 1 to 19 mol%, preferably 2 to 10 mol%, units (3) which are derived from ethylene and 75 up to 99 mol%, preferably 90 to 98 mol%, of units (1), where R ^{1 is} hydrogen, in each case based on the content of units (1), (2) and (3). Such copolymers are commercially available, for example, under the trade name Exceval®.

In the context of the present invention, the polyvinyl alcohol (B) can have a syndiotactic, isotactic and / or atactic chain structure. Furthermore, it can optionally be present both as a random and as a block copolymer.

With the method according to the invention, all known polyvinyl alcohols can be processed thermoplastically. This means that both low-viscosity, partially hydrolyzed and highly viscous, fully hydrolyzed polyvinyl alcohols can be processed thermoplastic. Mixtures of different polyvinyl alcohols can also be processed thermoplastically.

However, the present invention is not limited to the use of "conventional" polyvinyl alcohols. Rather, the use of graft copolymers has also proven to be particularly favorable. These are expediently obtained by grafting the vinyl ester or esters onto at least one polyalkylene glycol, preferably polyethylene glycol or polypropylene glycol, in particular polyethylene glycol, in a known manner, and then partially or completely hydrolyzing the ester groups, preferably in methanol. Particularly advantageous graft copolymers have 1 to 50 % By weight, preferably 10 to 50% by weight, of alkylene oxide and 50 to 99% by weight, preferably 50 to 90% by weight, of units (2) and / or (3).

Valuable information on the production of graft copolymers which are particularly suitable according to the invention can be found in the publications WO 03/020823 A1, DE 1 081 229 A and DE 1 094457 A, the disclosure of which is hereby expressly incorporated by reference.

The viscosity of the polyvinyl alcohol (B) is of minor importance according to the invention; in principle, both low-molecular and high-molecular polyvinyl alcohols (B) can be used. Nevertheless, in the context of the present invention it has proven to be particularly favorable that the polyvinyl alcohol (B) has a viscosity in the range from 2 to 70 mPas, preferably in the range from 2 to 40 mPas, advantageously in the range from 3 to 30 mPas, in particular in the range from 3 to 15 mPas (measured as a 4% by weight aqueous solution according to Höppler at 20 ° C, DIN 53015).

According to a particularly preferred embodiment of the present invention, the thermoplastically processable polyvinyl alcohol (B) is internally plasticized, ie it has suitable comonomer units (3) which compare the melting temperature of the polyvinyl alcohol (B) with the melting temperature of the polyvinyl alcohol (measured by means of DSC) without it Reduce units. Particularly suitable comonomer units in this context have one or more ethylene glycol (-O-CH ₂ -CH ₂ -O-) and / or propylene glycol units (-0-CH (CH ₃ ) -CH ₂ -0-).

When added to the extruder, the polyvinyl alcohol particularly preferably has a bulk density in the range from 200 to 800 g / 1, particularly preferably 350-600 g / 1.

According to a particular aspect of the present invention, the polyvinyl alcohol can have a particle size when added to the extruder have at most 1 mm, particularly preferably at most 200 μm, this size being able to be determined by a sieve analysis.

According to a further aspect, the particle size distribution can preferably have a maximum in the range from 500 μm to 3 mm, particularly preferably in the range from 800 μm to 1.2 mm.

Advantageous results are obtained if, in the process according to the invention, the polyvinyl alcohol (B) and the plasticizer (C) are used together in an amount of 5 to 50% by weight, based on the weight of the total composition. The sum of both components (B) and (C) is preferably 10 to 30% by weight, more preferably 20 to 30% by weight, in each case based on the weight of the overall composition. In a further advantageous embodiment of the method, the sum of both components (B) and (C) is 25 to 50% by weight, based on the total weight. In yet another advantageous embodiment of the method, the sum of both components (B) and (C) is 5 to 15% by weight, based on the total weight.

All plasticizers known to the person skilled in the art and compatible with polyvinyl alcohol and mixtures thereof can be used as plasticizers (C). Preferred plasticizers are alcohols, preferably polyhydric alcohols and their derivatives, such as glycols (e.g. glycol, diglycol, triglycol and polyethylene glycols), glycerol, diols and triols, and mixtures thereof. A particularly preferred plasticizer is glycerin.

In a particular aspect, the plasticizer can be added in liquid form. The dynamic viscosity of the plasticizer when added to the extruder is preferably in the range from 0.1 to 10000 mPa * s, in particular 0.2 to 2000 mPa * s, these values being able to be measured, for example, in accordance with DIN 53015. This value is measured at the plasticizer addition temperature. The plasticizer is preferably added at a temperature in the range from 0 ° C. to 140 ° C., particularly preferably in the range from 25 ° C. to 100 ° C.

A particular advantage of the present invention is that overall less of the above-mentioned plasticizer can be used than is necessary in comparison to the pre-compounding of polyvinyl alcohol with plasticizer and the subsequent mixing of this pre-compound with polyamide.

When polyvinyl alcohol (B) is pre-compounded with the plasticizer (C), the amount of plasticizer is at least 10% by weight, based on the weight of the polyvinyl alcohol. This minimum amount is necessary because otherwise the melt viscosity of the polyvinyl alcohol is too high at the usual processing temperatures. As a result, the torque extruder required for mixing rises sharply. On the other hand, an increase in the processing temperature leads to thermal damage to the polyvinyl alcohol.

The plasticizers used according to the invention also function as plasticizers for polyamide. It was found that the melt is relatively low-viscosity when the above-described compound of polyvinyl alcohol (B) and plasticizer (C) is added to polyamide, in which the proportion of plasticizer based on the polyvinyl alcohol is 10% by weight or more. The low viscosity of the melt in turn leads to problems in its processing and to a lack of melt stability.

It has been shown in the context of the present invention that the plasticizer (C) can be used in an amount of less than 10% by weight, based on the polyvinyl alcohol (B), if the polyamide (A), the polyvinyl alcohol (B) and the plasticizer is added to the extruder without prior mixing and mixed therein. In an advantageous embodiment of the method, between 2 and 10% by weight of plasticizers can be used and are particularly advantageous between 3 and 8% by weight, based in each case on the weight of the polyvinyl alcohol (B). The proportions of polyamide (A) can be selected as previously stated. The polyvinyl alcohol (B) and the plasticizer (C) can also be used together in the proportions by weight stated above, provided that the proportion of the plasticizer (C) is based on (B) as indicated above.

These measures achieve a sufficiently high viscosity of the melt, so that the mixture can be processed without problems. On the other hand, the viscosity is still low enough to allow processing on the extruder without having to use high torques and high temperatures.

The small amount of plasticizer described above has an economic advantage due to the raw material savings achieved. Furthermore, the disadvantageous effects of premature exudation of the plasticizer can be reduced by the relatively small amount of plasticizer. This applies in particular if the polyamide / polyvinyl alcohol glycerol bodies according to the invention are used as food packaging. On the outside of the packaging, perspiration of the plasticizer leads to an uncomfortable feeling when touched and poor adhesion of printing inks or labels. On the inside, however, leaking plasticizer penetrates the food, which is absolutely undesirable from a health and taste point of view.

The small amount of plasticizer described above and the advantages described with it can be achieved particularly well with glycerin as plasticizer.

In the preceding sense, the present invention also relates to a mixture of at least one polyamide and / or copolyamide (A), at least one polyvinyl alcohol (B) and at least one plasticizer (C), the proportion of the plasticizer (C) being less than 10% by weight. -%, Based on the Polyvinyl alcohol (B) is preferably between 2 and 10% by weight and particularly advantageously between 3 and 8% by weight,

Lubricants, antiblocking agents, oxidation stabilizers, pigments, dyes, solid plasticizers, fillers and / or other polymeric compounds can be used as further, preferably solid additives.

Furthermore, it is also possible according to the invention to use bubble formers which are described in the document DE 101 207 AI, to which express reference is made in this connection.

According to the invention, all methods known to the person skilled in the art can be used for thermoplastic processing. Accordingly, all devices known to the person skilled in the art and suitable for this purpose can also be used. However, melt extrusion and therefore the use of melt extruders is preferred. Self-cleaning twin-screw extruders are particularly preferably used. It was found that particularly good homogenization of the mixture is possible with twin screw extruders.

The selection of suitable extruder screws, the geometries of which correspond to the corresponding process engineering tasks, e.g. Feeding, conveying, homogenizing, melting and compressing have to be adapted to the general knowledge of the person skilled in the art.

Conveying elements preferably have an incline in the range from 15 ° to 40 °, the length of the individual elements being 30 to 90 mm. These conveyor elements can be obtained from the Leistritz company under the designation GFA 2-15-30 up to GFA 2-40-90.

The gradient of mixing elements is preferably 10 ° to 20 °, particularly preferably approximately 15 °. The length is preferably in the range from 30 to 60 mm, which can be obtained from Leistritz under the designation GFM 2-15-30.

Kneading elements include composite discs with a gradient of 30 ° to 90 °. Preferred kneading elements contain at least two, particularly preferably at least 5, disks. These kneading elements can be obtained from the company Leistritz under the designation KB 5-2-30-30 up to KB 5-2-30-90.

The information with regard to the conveying elements, mixing elements and kneading elements relate to extruders, in particular twin-screw extruders with a screw diameter of 27 mm. If extruders with a different diameter are used, the length of the individual elements in particular can change accordingly.

In order to further increase the mixing and kneading effect, returning elements, so-called "links", can be installed after the respective mixing and kneading zones. In this way, a particularly homogeneous distribution of the polyvinyl alcohol can surprisingly be achieved.

According to a particular aspect of the present invention, the temperature of the extruder up to the addition of the plasticizer can be less than or equal to 120 ° C., the temperature can particularly preferably be in the range from 40 to 80.

After the addition of the plasticizer, the extruder can preferably have at least one kneading element. The extruder particularly preferably has at least two, particularly preferably at least five kneading elements.

Kneading elements are known to the person skilled in the art and are described, for example, in common sales brochures of the extruder manufacturers, for example from Leistritz. According to the invention, components (A), (B) and (C) are not mixed before they are added to the extruder. Accordingly, at least two of these components are fed separately into the extruder, it being possible for these components to be added to the extruder at one feed point or at different feed points.

The individual components (polyamide (A), polyvinyl alcohol (B), plasticizer (C) and possibly other additives) can be added in any spatial order. However, the solid polyamide (A) and the polyvinyl alcohol (B) are preferably fed in the feed zone of the extruder. For example, polyamide (A) and polyvinyl alcohol (B) can be added together with the plasticizer in the feed zone of the extruder. However, the plasticizer is preferably added in one of the zones of the extruder following the feed zone. The plasticizer is particularly preferably added spatially separated from the polyamide (A) and polyvinyl alcohol (B).

According to a particular aspect of the present invention, the addition of the polyamide and / or the copolyamide and the polyvinyl alcohol can take place at a lower L / D ratio than the addition of the plasticizer.

The polyamide and / or the copolyamide are preferably added at an L / D ratio in the range from 0 to 5, particularly preferably 0.1 to 3.

The polyvinyl alcohol can preferably be added at an L / D ratio in the range from 0 to 10, preferably 0.1 to 5. The addition of the polyvinyl alcohol can preferably be carried out after the addition of the polyamide and / or the copolyamide. The addition of the polyvinyl alcohol is preferably carried out at an L / D ratio in the range from 0.1 to 5 later than the addition of the polyamide and / or the copolyamide. The plasticizer is preferably added at an L / D ratio in the range from 0 to 15, particularly preferably 3 to 8. The plasticizer is particularly preferably added at an L / D ratio in the range from 0.1 to 5 later than the addition of the polyvinyl alcohol.

The L / D ratio is known in the professional world. Here L stands for the length of the screw and D for the diameter of a screw. Extruders with similar L / D ratios generally have similar extrusion properties. It is therefore common to specify the L / D ratio, with the diameter D of the screw generally also being specified. The length specification "for an L / D ratio of 0 to 5" thus results from the multiplication of the specified L / D ratio of 5 by the screw diameter D, which is also known. For a screw diameter of 30 mm, the specification means "for an L / D ratio of 0 to 5 "that the polyamide and / or the copolyamide is added in a range from 0 mm to a length of 150 mm, based on the starting point of the screw. If the diameter of the screw is 10 mm, the polyamide and / or the copolyamide is added within a range from 0 to 50 mm. Since the addition points have an extension over length, it should be noted that this information refers to the point of indentation that is closest to the starting point.

Particularly preferably, at least one mixing element is provided in the extruder before the plasticizer is added. Mixing elements are known in the art.

Further liquid additives can be added together with the plasticizer or via one or more further separate liquid doses. Solid additives can either be dissolved or suspended in the plasticizer or added via a further solids metering device, which is preferably located either in the feed zone or in one of the zones following the feed zone. A side-mounted screw feeder is particularly preferred for the addition of solid additives. In the feed range of the screw extruder, cylinder temperatures in the range from 20 to 60 ° C. are preferably set. The feed area is followed by zones in which the material is melted and homogenized, followed by the discharge area (nozzle or tool). The melt is preferably homogenized by using kneading blocks. In the melting and homogenization range, temperature profiles in the range from 130 to 250 ° C., particularly preferably 150 to 230 ° C., are preferably set. Temperatures in the range from 170 to 230 ° C. are preferably set in the discharge area. When carrying out the method according to the invention, an increasing temperature profile from the feed zone to the tool is particularly preferably used with regard to the setting of the heating zones of the extruder. The temperature profile used varies depending on the polyamide (A) and polyvinyl alcohol (B) used. For example, low-viscosity, partially hydrolyzed polyvinyl alcohols (B) can be operated at significantly lower temperatures than high-viscosity, fully hydrolyzed polyvinyl alcohols (B). The maximum barrel temperatures in the homogenization range of the extruder are between 190 and 230 ° C for partially saponified polyvinyl alcohols and between 200 and 250 ° C for fully saponified polyvinyl alcohols.

In addition, after melting and homogenization, volatile components can be removed from the melt by degassing at normal pressure or by applying a vacuum. The degassing preferably takes place immediately before the extruder tool. In the event that a melt pump is used for even delivery, the degassing is located immediately in front of the melt pump.

By using appropriate tools, such as flat nozzles, ring nozzles or profile tools, it is possible to produce molded articles directly using the method according to the invention. In this way, moldings such as flat films, blown films, pellets, fibers or monofilaments can be produced. The Shaped bodies are cooled after leaving the extruder die by methods known to those skilled in the art. The production of pellets is preferred. After leaving the extruder die and cooling, these are granulated by methods known to those skilled in the art. The production of films, in particular film tubes, is also preferred.

The present invention thus also relates to moldings which can be obtained by the process according to the invention and consequently comprise components (A), (B) and (C) and, if appropriate, additives. The most preferred molded body is a pellet. Likewise preferred molded articles are foils. If it is a film, it can be post-treated by stretching (e.g. mono- and / or biaxial) and / or heat setting by methods known to those skilled in the art.

According to a particular aspect of the present invention, special shaped articles have a matrix phase which preferably comprises the polyamide and / or copolyamide and domains which comprise polyvinyl alcohol and are distributed in the matrix phase. The average size of the polyvinyl alcohol domains is preferably less than or equal to 0.08 μm, preferably less than or equal to 0.06 μm.

The size of the domains can be determined by scanning electron microscopy. The size specified refers to the smallest extent of the domains in a dimension that is measured by the center of gravity of the domains. In the case of spherical domains, this size therefore relates to the diameter.

According to a particular aspect of the present invention, the domains, which preferably comprise polyvinyl alcohol, are preferably spherical. In the context of the present invention, the term spherical denotes that the domains preferably have a spherical shape, it being obvious to the person skilled in the art that due to the production methods, domains also have may be contained in another shape, or that the shape of the domains may differ from the ideal spherical shape.

Accordingly, the term spherical means that the ratio of the largest dimension of the domains to the smallest dimension is a maximum of 4, preferably a maximum of 2, these dimensions being measured in each case by the center of gravity of the domains. At least 70, particularly preferably at least 90%, based on the number of domains, are preferably spherical.

According to a further preferred embodiment, the domains have an ellipsoidal shape. The ratio of the greatest extent of the domains to the smallest extent is preferably in the range from 100: 1 to 1.1: 1, particularly preferably in the range from 20: 1 to 5: 1, these expansions being in each case due to the center of gravity of the domains be measured.

The domains are subject to a size distribution. The specified value refers to the mean of the number average.

The shape of the domains depends, among other things, on the extrusion conditions. The greater the extrusion speed, the greater the ratio of the largest extension of the domains to the smallest extension. Furthermore, the viscosity of the melt shows an influence during extrusion. The lower the flowability of the melt, the greater the ratio of the largest expansion of the domains to the lowest expansion.

According to a particular aspect of the present invention, the shaped body has a large number of domains. As a result, a particularly high water vapor permeability is achieved. The number of domains based on the volume, referred to below as the domain density, is preferably at least 1000 per mm ³ , particularly preferably at least 100 per μm ³ and very particularly preferably at least 200 μm ³ . The domain density can be through Scanning electron microscopy can be determined, the number of domains of a volume unit being counted. Any number of two-dimensional successive cuts can be made in order to obtain corresponding volume information. Cuts that are made perpendicular to each other are also helpful here.

A two-dimensional section preferably shows at least 100 domains per mm ² , particularly preferably at least 0.01 domains per μm.

The inventive foils show excellent mechanical properties.

The present invention also relates to the use of the moldings described above. For example, they can be used to package solid and liquid products. If the molded body is a film, this can be used in particular for packaging and wrapping food, in particular sausages.

If the shaped bodies are pellets, these can in turn be further processed in downstream units to form injection molded articles, blown and flat films of different thicknesses, and fibers and monofilaments.

As described at the beginning, according to the previous procedure of the manufacturer of the shaped bodies, the polyvinyl alcohol / plasticizer compound is obtained and mixed with polyamide to produce the final shaped bodies (eg films). A disadvantage of this procedure is that the mixing ratios must always be adhered to exactly in order to achieve consistent quality, which in practice is associated with relatively great effort for the manufacturer of the shaped body. The use of pellets for further processing into the final shaped bodies may be advantageous compared to the direct production of the final shaped body from the three components polyamide (A), polyvinyl alcohol (B) and plasticizer (C). In this case, the manufacturer of the final molded body, usually a plastics processor, only has to process one component (the pellet) instead of having to deal with the handling and metering of three components. The latter task can be performed separately by the pellet manufacturer.

In this sense, the present invention also relates to the provision of pellets and the use of pellets produced according to the invention for further processing into other shaped articles. In particular, the pellets produced can be processed further into food packaging. In this context, further processing into plastic casings for packaging sausage is preferred.

Films according to the invention preferably have a thickness in the range from 1 to 200 μm, particularly preferably 20 to 50 μm.

Particularly preferred molded articles are films which can be used in particular for packaging food. These films are characterized by a high water vapor permeability. The water vapor permeability is preferably at least 250 g / m ² day, particularly preferably at least 400 g / m ² day and very particularly preferably at least 520 g / m ² day, measured according to DL 53 122-74, at a temperature of 30 ° C. and 65% relative humidity.

According to a further aspect of the present invention, the water vapor permeability of a film produced according to the invention directly or by further processing of pellets is preferably less than 500 g / m ² -d, more preferably less than 200 g / m ² d and in particular 50 to 100 g / m ² -d according to DIN 53 122-74 at a relative humidity of 65% and a temperature of 30 ° C.

Films produced according to the invention preferably have an oxygen permeability of less than 50 cm ³ / m ² 'atm-d at a relative humidity of 65% and a temperature of 30 ° C (according to DIN 53 380-69). The oxygen permeability is more preferably less than 20 cm ³ / m ² -atm d.

The water absorption of the pellets or foils according to the invention is preferably more than 10% and more preferably 10-15% when stored in water until saturated (according to DIN 53495). The water absorption at 50% relative humidity and 23 ° C to saturation is preferably more than 4%, and more preferably 4-10%.

example

85% by weight of polyamide 6 (Ultramid B35 from BASF), 14% by weight of polyvinyl alcohol, with a degree of hydrolysis of 92% and a viscosity of 30 mPas (as a 4% by weight aqueous solution at 20 ° C.), and 1% by weight of glycerol was fed directly and without prior mixing into a Leistritz twin screw extruder type ZSE 27 GL 1200 with a screw diameter of 27 mm, an L / D of 40 and 9 heating zones. The temperature setting of the heating zones increased between 30 and 240 ° C in zones 1-6, 240 ° C in zones 6-9. The nozzle temperature was 240 ° C. Strands were extruded, which were cooled in a water bath and then granulated.

Claims

claims

1. A process for the production of plastic moldings by thermoplastic processing of (A) at least one polyamide and / or copolyamide, (B) at least one polyvinyl alcohol and (C) at least one plasticizer, characterized in that components (A), ( B) and (C) for the production of the shaped body without prior mixing in an extruder.

2. The method according to claim 1, characterized in that one uses as component (A) polyamide 6, polyamide 66, polyamide 612 and / or copolyamide 6/66.

3. The method according to claim 1 or 2, characterized in that the polyamide and / or copolyamide (A) is used in an amount of 50 to 95 wt .-% based on the total composition.

4. The method according to one or more of claims 1-3, characterized in that the polyvinyl alcohol (B) and the plasticizer (C) are used together in an amount of 5 to 50 wt .-% based on the total composition.

5. The method according to one or more of claims 1-4, characterized in that the plasticizer is used in an amount of less than 10 wt .-%, based on the polyvinyl alcohol (B).

6. The method according to one or more of claims 1-5, characterized in that one uses a polyvinyl alcohol with a degree of hydrolysis of more than 70%.

7. The method according to one or more of claims 1-6, characterized in that the addition of the polyamide and / or the copolyamide and the polyvinyl alcohol takes place before the addition of the plasticizer.

8. The method according to claim 7, characterized in that at least one mixing element is provided in the extruder before adding the plasticizer.

9. The method according to one or more of claims 1-8, characterized in that the temperature of the extruder is less than or equal to 120 ° C until the addition of the plasticizer.

10. The method according to one or more of claims 1-9, characterized in that the plasticizer is added in liquid form

11. The method according to one or more of claims 1-10, characterized in that the polyamide and / or copolyamide has a bulk density in the range of 500 to 900 g / 1 when added to the extruder.

12. The method according to one or more of claims 1-11, characterized in that the polyvinyl alcohol has a bulk density in the range of 200 to 800 g / 1 when added to the extruder.

13. The method according to one or more of claims 1-12, characterized in that the extruder has at least one kneading element after adding the plasticizer.

14. Molded body obtainable by a process according to at least one of claims 1-13.

15. Shaped body comprising (A) at least one polyamide and / or copolyamide, (B) at least one polyvinyl alcohol and (C) at least one plasticizer, the polyamide and / or the copolyamide being a matrix phase and Polyvinyl alcohol forms domains which are dispersed in the matrix phase, characterized in that the size of the polyvinyl alcohol domains is smaller than 0.08 μm.

16. molded article according to claim 14 or 15, characterized in that the polyamide and / or the copolyamide forms a matrix phase and the polyvinyl alcohol domains which are dispersed in the matrix phase, the domain density being at least 1000 per mm ³ .

17. molded article according to one of claims 14 to 16, characterized in that it is a pellet or a film.

18. Use of a molded body according to one of claims 14 to 17 as a food packaging or for further processing into a food packaging.