EP1192218A1

EP1192218A1 - Rigid dead-fold foils

Info

Publication number: EP1192218A1
Application number: EP00945430A
Authority: EP
Inventors: Heinz Haschke
Original assignee: Constantia-Verpackungen AG
Current assignee: Constantia-Verpackungen AG
Priority date: 1999-06-29
Filing date: 2000-06-29
Publication date: 2002-04-03
Also published as: WO2001002485A1; PL352488A1; HUP0201811A2; ATA112599A; CZ20014725A3; AT408757B

Abstract

The invention relates to plastic foils for food packagings exhibiting high "form memory capability" (dead-fold behavior) and satisfactory rigidity and consisting of special minerally filled polyolefin systems.

Description

CONSTANTIA-VERPACKUNGEN Aktiengesellschaft

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The invention relates to plastic films for food packaging, which have good dead-fold properties with improved stiffness, and to a process for their production.

Stand__d_e_Te_chnlk

According to the definition of US Pat. No. 4,965,135, "dead-fold property" means the ability of a film to permanently retain its shape after it has been folded around a packaged item to be folded, that is, not more commonly because of the "shape memory" Plastic films to return to their original condition.

It is known that aluminum foils, as almost universal packaging materials, have excellent dead-fold properties when used as wrapping foils. However, they tear easily, can be easily pierced with pointed objects and are not resistant to acids from the packaged goods. Another problem is their printability and the fact that they cannot be used as packaging material in microwave ovens.

In comparison, plastic films have significant advantages as packaging material. In order to make full use of these, however, it is necessary for many applications to switch off their shape memory and at least to some extent to achieve the aforementioned dead-fold properties. For this purpose, according to the above-mentioned US Pat. No. 4,965,135, it has been proposed to combine ductile plastics such as nylon 6 with brittle plastics such as polystyrene. This is done by coextrusion. As a result, the ductile plastics should have the strength of the film and, in conjunction, break the brittle

Polystyrene layer a certain edge dimensional stability can be achieved at the folded edges.

The disadvantage of such "combination films" is, however, their complicated manufacture in the coextrusion systems as well as the unsightly breaking behavior of the brittle film layer.

In contrast, improved films, which can even be used as so-called "twist films", i.e. US-A-5, 026, 610 describes which can be used for packaging small packaged goods such as candies by twisting the protruding film ends. While aluminum foils are practically not usable for this type of packaging because of their easy tearability, the twist foils according to US Pat. No. 5,026,610 are made by three-layer coextrusion of HDPE - HDPE / LDPE mixture - HDPE systems with subsequent uniaxial Stretching made.

However, the production of such co-extruded or multi-layer co-extruded and stretched film systems is problematic and not very economical, if only because of the very complex processes involved. In addition, pure polyolefin films show practically no dead-fold properties and moreover have relatively low stiffness in most cases. They are therefore relatively lobular and can therefore - since the stiffness of a film with a given material property (expressed by the stiffness constant as defined below) only increases with its thickness - for many applications in which the (bending) stiffness is important are used in such large thicknesses that their use is absolutely uneconomical due to the high material expenditure required.

It was therefore attempted very early to add plastics, in particular mineral fillers, in order to achieve the desired dead-fold properties and, as a rule, also a certain increase in bending stiffness. The production and use of filled plastics is - almost since the filling of rubber with soot - an almost as old technology as the commercial use of polymers (see ENCYCLOPEDIA OF POLYMER SCIENCE and TECHNOLOGY; Interscience Publishers - John Wiley & Sons, New York ; Volume 6, S 741 ff). Filled polymers are also known, for example, as materials of the type "calcium carbonate with polymers as binders" for wall paints or as highly mineral-filled packaging materials such as egg shells (approx. 95% mineral content). Although less highly filled, they are known for the production of packaging films unsuitable polymers that as Pigment concentrates, so-called master batches with fill levels of around 50% by weight, can only be used for film extrusion after adding pure polymer thinners. A typical example of such master batches is the product PAPERMATCH T 4228/50 from SCHULMAN GmbH in D-50170 Kerpen. It is a correspondingly highly filled polyethylene.

Products with low filling levels, i.e. up to about 20% by weight are known from the production of color pigmented or simply opaque plastics; however, these show practically no dead-fold properties.

An increase in the degree of filling up to approximately 30% by weight generally leads to the first appearance of dead-fold properties; however, these are not yet satisfactory for packaging applications. For example, a polyethylene filled with about 30% mineral, such as the HDE product PEL ES 288 from HOECHST, can still be extruded into a hole-free, in this respect perfect film. However, their dead-fold properties are not yet very pronounced. However, a further increase in the degree of filling beyond this limit usually leads to a massive disruption of the plastic matrix and thus - in particular with higher degrees of filling from approximately 33% by weight - to a massive impairment of the mechanical strength of such plastics and thus to a dramatic drop in the tensile strength values, their hole-free extrudability, to total porosity. This effect is even used for the deliberate production of - especially after stretching - porous and therefore breathable films. These are so-called "breathables", the degree of porosity of which depends on the amount of filler used, as described in EP-A-232 060.

The combination of the aforementioned multilayer technology with filling of only one layer to support its strength by unfilled cover layers - see EP-A-562 166 - has already been attempted. However, for reasons of feasibility of this technology, very narrow limits are set, which is why only relatively thick, for example 400 to 4000 μm thick composites, i.e. only cards and plates, can be produced in this way. It has also been shown that the possibility of producing higher-filled plastics with the producibility of soot-filled rubber for car tire production is an exception. Because of the chemical relationship of the filler, soot, which can be understood by its chemical structure as a highly condensed aromatic, organic compound, to the organic polymer, exceptionally, a very positive influence on the polymer properties is exerted, whereas fillers, which do not belong to the organic polymer Show affinity, usually lead to a drastic disturbance and thus to a deterioration in the properties of the plastic matrix (see ENCYCLOPEDIA OF POLYMER SCIENCE loc.cit. P. 751). The mineral and therefore generally relatively polar filler therefore only acts as a diluent and weakening agent in a non-polar polymer.

In order to solve this problem, it has therefore already been proposed to use oleophilized fillers. These are mineral fillers whose polarity is reduced and their affinity for non-polar environments is increased, so that their particles are coated with non-polar coating agents. According to US Pat. No. 4,153,587, this measure also does not make it possible to produce polyolefin / filler mixtures which both have good flexural strength values and, combined with them, have a useful tensile strength or, more importantly, puncture resistance or impact resistance.

Furthermore, attempts have been made to provide somewhat useful compromise formulations by coordinating the plastic parameters with the filler quantities and filler types or properties.

For example, JP-A-7 3014 423 describes a melt extrusion process in which 0.01-0.5% by weight of a fine-grain mineral such as Mg silicate or dolomite is added to polypropylene and then subjected to biaxial stretching.

According to JP-A-9 111 060, a polyolefin is mixed with 5-45% by weight of thermoplastic resin such as ethylene-vinyl alcohol copolymer as a filler. However, these products either show no usable dead-fold properties because of their too small amount of filler, or - at higher fill levels - such poor tensile strengths or puncture strengths that it is not possible to produce thin films from them, but only moldings.

Further developments are therefore preferably no longer concerned with the search for better filler-plastic formulations, but instead are based on product-specific improved applications of known, conventional formulations. In this connection, reference is made to EP-A-503 314, according to which containers made of polyolefin, preferably polypropylene, filled with 50-80% by weight of chalk, talc or mica are described. According to EP-A-494 594, packaging materials for the production of liquid containers from a skeleton layer made of a plastic / filler mixture with a multi-layer barrier layer are described, the layers being connected to one another by surface fusion in the coextrusion process and the filler being different polymer, preferably immiscible with the skeletal layer matrix plastic. According to EP-A-290 871, container lids are made from polyolefin, preferably LDPE, with 10-15% by weight of inert fillers such as mica, talc, lime or gypsum by injection molding.

Better progress with regard to higher filling levels with still relatively good mechanical properties of the plastic compositions has been achieved with the so-called high-strength-fiber-filled thermoplastic, but the resulting products such as glass fiber, asbestos fiber, metal oxide whiskers - or carbon fiber-reinforced polyesters cannot be produced as films, but can only be used for the production of sheets and moldings.

In accordance with the state of the art described above and as can be observed when converting an extruder from PE to PP processing and vice versa, the extrusion of filled PP, to which PE is added, leads to pulpy extrudates and correspondingly perforated films (= so-called “ PE incompatibility of PP ") and, on the other hand, the same phenomenon also occurs in the extrusion of appropriately filled PE to which PP is mixed (= so-called" PP incompatibility with PE "). Furthermore, the prior art teaches that the measures necessary to achieve usable puncture resistance and extrudability of non-perforated or pore-free films made of mineral-filled polyolefins, on the one hand, and the increase in the degree of filling to achieve good dead-fold properties, on the other hand, are opposed to one another. To make matters worse, in the case of films with improved stiffness, there are narrow limits to achieving this goal by increasing the degree of filling by the fact that to achieve good dead-fold properties, such a high degree of filling must be set that because of the then, given the proximity to the CPVC, the breakup of the filler phase from the polyolefin phase can only be avoided by further addition of adhesion-promoting binders, so-called “phase adhesives”. However, it is precisely through these and their inevitable plasticizer effect that the film stiffness collapses again.

In principle, however, the physical law of the limit of the so-called "critical pigment-volume concentration" (CPVC limit) remains limiting in all known formulations.

The CPVC limit is to be understood as the limit for the degree of filling of a plastic with pigments, from which the total volume of all filler particles becomes so large that not all the spaces between the filler particles can be filled with polymer binder, and therefore, when the amount of filler is increased further, the polymer matrix breaks, causing the strength of the overall system to drop drastically, right down to just organically bound ceramic materials (see ENCYCLOPEDIA OF POLYMER SCIENCE and TECHNOLOGY; Interscience Publishers - John Wiley & Sons, New York; Volume 6, p. 751).

The CPVC limit heralds itself far below this critical filling level by the fact that the filled plastic begins to become spotty or, if the filling level is increased further, films made therefrom become porous to perforated. In the context of the present invention, a “CPVC” should therefore be defined in practical application based on the aforementioned scientific definition, which is therefore not identical to the aforementioned, scientifically defined CPVC limit, but experimentally in analogy to the practical applicability in preliminary tests is determinable, and which is to be understood as the highest degree of filling - expressed in percent by weight of filler based on the sum of the weights (= 100%) of the total amount of filler plus the plastic matrix (ie the polymer matrix including any additives) - total amount in which the filler is as homogeneous as possible, ie for example by kneading in, in which a mineral-filled plastic granulate in a BAUMEISTER 45 single-screw chilli roll extruder can just be used to produce a non-porous, non-perforated and non-sticky film.

Presentation of the invention

In connection with the representation of the present invention, a distinction is made between fillers on the one hand and additives on the other: fillers are all inorganic, finely distributed as solids in the polymer matrix, plus all organic substances which are not soluble in the polymer matrix; these are so-called fillers plus inorganic pigments including inorganic and / or organic color pigments that are insoluble in the plastic matrix.

The extent to which the CPVC is achieved is therefore measured according to the invention by how high the degree of filling - expressed in percent by weight of all fillers relative to the total weight of the film - compared to the CPVC is, how this can be determined using the methodology specified above.

Additives are to be understood as meaning all organic substances that are miscible with the polymer matrix or in the concentration that is still soluble in it.

According to the invention, additives are to be added to the weight fraction of the plastic matrix (and not the filler fraction) when determining the CPVC and the degree of filling measured thereon. The sum of the weights of the polymer matrix plus additives is briefly referred to below as “plastic matrix”.

In the context of the invention, the degree of filling is therefore defined as: Total weight of the fillers

Degree of filling [%] = 100 x

Sum of the weights of the fillers + polymer matrix + additives

Polymer matrix in connection with the present invention is to be understood as the sum of the weights of all the polymers contained in the mixture. The polymer matrix is accordingly identical to the overall system, which consists of the so-called lin-polyolefin matrix plus all thermoplastic elastomers (TPE) in connection with the present invention. The abbreviation "lin" stands for linear. The latter are chemically or physically branched PPPE copolymers, such as so-called random-heterogeneous 2-phase rubber PPPE copolymers or thermoplastic olefin copolymer elastomers (TPO), such as ethylene-octene copolymers.

Lin-polyolefin matrix is to be understood as the sum of homopolymers, homopolypropylene and block and / or random propylene-ethylene copolymers contained in the mixture, with the exception of the aforementioned thermoplastic elastomers (TPE).

It is clear from the aforementioned definition relating to the CPVC that high degrees of filling, for example of approximately 95% calcium carbonate and 5% organic, polymeric binder, cannot be processed into flexible packaging films. These films have filler parts close to below the CPVC and are characterized in that their polymer matrix according to the above definition always has the predominant weight fraction, i.e. accounts for more than 50% by weight and thus completely envelops the filler particles, whereas the proportion of fillers in the films according to the invention always has the lower proportion by weight, i.e. represents less than 50% by weight.

In systems which predominantly consist of mineral fillers, in addition to polymers as binders, that is to say in systems which are not the subject of the present invention, the binder therefore only has the role of producing an adhesive connection between the filler particles. The object of the present invention is now to avoid the disadvantages known from the prior art and to provide films which, in addition to good dead-fold properties, also have improved rigidity with usable puncture resistance.

According to the invention, dead-fold films with improved rigidity are proposed from mineral-filled polyolefin formulations, which are characterized in that these mineral-filled polyolefin systems consist of a plastic matrix, which is composed of a polymer matrix and additives, and this polymer matrix consists of a linear (Lin) polyolefin matrix is built up, and 5 to 20% of the weight of this lin polyolefin matrix consist of thermoplastic elastomers (TPE) or of thermoplastic olefin copolymer elastomers (TPO), and wherein the lin polyolefin matrix consists of :

AI) mixtures of linear propylene homo- and / or propylene / ethylene copolymers, or from:

A2) Mixtures of 20 to 65 wt .-% polyethylene and a proportion of polypropylene in the PE-PP matrix of 80 wt .-% to 35 wt .-% PP, the polyethylene content in systems with 20 to 50 wt .-% polyethylene ("low PE systems") to 14 to 50 wt .-% LLDPE and in systems with more than 50 wt .-% polyethylene ("high PE systems") to 35.7 to 56 % By weight LLDPE is and that

C) in the plastic matrix according to AI or A2 or in main components thereof, finely ground mineral pigments are added in such an amount that the total degree of filling of the film is in a range from 2 to 10% by weight, preferably 3 is up to 7% by weight below the CPVC.

The dead-fold films according to the invention preferably contain additives such as antistatic agents, antioxidants or light stabilizers in their polymer matrix. To form the lin polyolefin matrix from thermoplastic elastomers, chemical or physically branched polypropylene / polyethylene copolymers used. This lin polyolefin matrix can also consist of thermoplastic olefin copolymer elastomers (TPO), ethylene or octene copolymers being particularly suitable in a satisfactory manner. Particularly good dead-fold properties could be produced with physically branched polypropylene / polyethylene copolymers of the random-heterogeneous 2-phase rubber-polypropylene-polyethylene copolymers type.

Higher-crystalline and lower-crystalline homo-polypropylenes are particularly suitable for the formation of the lin-polyolefin matrix according to AI.

Surprisingly, it has now been found that, despite the known, poor mixing behavior of PE and PP, non-porous films with good dead-fold properties and at the same time significantly better than conventional, filled films with similar dead-fold properties, with improved tear strength and rigidity to be provided.

Surprisingly, it was also found that rigid polyolefin films with good dead-fold properties can be produced with at the same time satisfactory puncture resistance if relatively narrow “formulation windows”, which result from the combination of two measures, are used in the formulation of the plastic matrix :

A) the selection of certain polymer combinations with regard to a combination of the compatibility properties of certain polymers with one another and their wetting / adhesion properties, and the interaction of these polymer combinations with the mineral pigments used, with regard to their overall rigidity, toughness, softening effect and their chemical or degree of physical branching and

B) appropriate matching of the filler content (the degree of filling) to the aforementioned polymer mixtures while maintaining a very specific distance, ie close below the CPVC.

Here, the proximity of the filling levels to the CPVC is exploited in order to deliberately achieve microscopic phase breaks during folding or twisting in this area of the beginning phase incompatibility, and thus at these microscopic points of the lined up and rearranging in their mutual spatial position when folding or twisting to cause mineral particles a kind of bistable state, which macroscopically manifests itself in good dead-fold properties.

Since the CPVC has not yet been exceeded, the overall properties of the polymer matrix are still utilized.

The parameters relating to the above-mentioned “formulation window” can be found in the context of a melt extrusion method known per se for determining the CPVC, the degree of filling being set according to the invention and the polymer matrix recipe being adjusted according to the rules specified according to the invention.

According to the invention, a process for the production of dead-fold films by melt extrusion of polymer granules into flat films is also proposed, which is characterized in that the polymer granules are constructed from a plastic matrix which consists of a polymer matrix and additives, the polymer matrix is built up in a "tolerance window" and that this polymer matrix consists of:

AI) mixtures of linear propylene-homo- and / or propylene / ethylene copolymers, the so-called “lin polyolefin”

Matrix "and 5 to 20 wt .-% of this lin-polyolefin matrix of thermoplastic elastomers, such as TPE, of which preferably so-called TPO, which is understood to mean thermoplastic olefin copolymer elastomers such as ethylene-octene copolymers, or

A2) from a lin polyolefin matrix, which consists of mixtures of 20 to 65 wt .-% PE and a proportion of PP from 35 to 80 wt .-% PP, the PE proportion being a very specific percentage LLDPE as Flexibilizing agent must be and 5 to 20 wt .-% of this lin polyolefin matrix made of thermoplastic see elastomers, such as TPE, preferably so-called TPO, of which thermoplastic olefin copolymer elastomers such as ethylene-octene copolymers are to be understood, with physically branched PPPE being particularly preferred, that being so-called random-heterogeneous 2-phase rubber PPPE Copolymers are to be understood, and that B) finely ground mineral pigments are kneaded into the plastic matrix according to AI or A2 or main components thereof before the melt extrusion to form the film, so that the total filling level of the finished dead-fold film in one Range of 2 to 10% by weight points, preferably 3 to 7% by weight points, below which the CPVC lies.

So-called "random-heterogeneous-2-phase rubber-polypropylene / polyethylene copolymers" are particularly preferred for the formation of Al physically branched polypropylene / polyethylene copolymers.

According to the invention, the percentage of LLDPE in the total polyethylene portion of the lin polyolefin matrix of the formulations according to A2 depends on the PE / PP ratio and thus on the percentage of total PE.

In so-called "low PE systems", ie systems whose lin polyolefin matrix has a content of 20 to 50% by weight of PE in addition to PP, the LLDPE content can be:

7 to 10% LLDPE = 100 x

(Formula la) wt .-% PE in the lin polyilline matrix

In the case of "high PE systems", ie systems whose lin polyolefin matrix has a content of more than 50% by weight PE to 70% by weight PE, the percentage of LLDPE can be:

25 to 28% LLDPE = 100 x

(Formula Ib) wt .-% PE in the lin-polyolfine matrix

In connection with the description of the invention, polyethylene All types are abbreviated to PE, HDPE means so-called “high-density polyethylene”, LDPE means “low-density polyethylene”, LLDPE means “linear low-density polyethylene” and PP “polypropylene homopolymerisates” ,

In addition to these pure polyolefins, the copolymers should be abbreviated as follows: b-PPPE for block copolymers if it is a block-propylene-ethylene copolymer; r-PPPE for random copolymers, if it is propylene-ethylene copolymers with a statistical sequence of the propylene and ethylene building blocks or simply PPPE, if the sequence of the monomer building blocks in the polymer molecule chain for the process according to the invention or the products according to the invention is not essential.

So-called "homopropylenes" are particularly suitable as linear polypropylenes for the construction of the polymer matrix according to AI. With regard to the thermoplastic elastomers (TPE) of the so-called “branched PPPE” type to be used according to the invention, “physically branched PPPE” is understood to mean those polymers which are copolymerized with so-called propylene-ethylene-random-copolymers-2-phase-block-copolymerized with ethylene- Propylene rubber - also called shorter: random heterogeneous 2-phase rubber PPPE copolymers, or RAHECO. These are, for example, plastics, which were produced by polymerizing an r-PPPE into a matrix of a b-PPPE or vice versa, the secondary molecule chains - d.s. for example that of r-PPPE - mainly only physically the main polymer molecule balls - d.s. for example that of the b-PPPE - penetrate.

These are to be distinguished from the generally known, chemically branched copolymers, that is to say, for example, from polypropylene copolymers in which polyethylene side chains are grafted onto the propylene main chain.

Suitable fillers which can be used according to the invention are: finely ground calcium carbonate, talc, gypsum, mica, magnesium silicate, titanium dioxide or mixtures thereof, which can also be used in a mixture with mineral and / or organic color pigments such as iron oxide. Calcium carbonate and / or talc are preferably pure or in a mixture with one another as fillers, in addition to orderly proportion of color pigments such as titanium dioxide as white pigment, iron oxide as brown pigment and / or carbon black as blackening pigment to increase the light barrier effect of the films.

The color pigments to be used in a minor proportion compared to the fillers are used in weight ratios of 1 part color pigment to 6 to 25, preferably 10 to 20 parts filler.

The fillers have, for example, an average grain size below 10 μm with a grain size distribution of not more than 5% by weight above 20 μm. Fillers with an average grain size of less than 7 μm and a grain size distribution of not more than 2% by weight above 10 μm are preferred.

The pigments serving as fillers are preferably kneaded into the plastic matrix before the film extrusion. The final degree of filling of the film can already be produced in the kneader and the resulting kneading compound can be granulated. In a preferred embodiment, pigment concentrates are produced, that is, in

Kneaders are masses made from a part or only individual components of the plastics used for film production, into which the total amount of pigment is kneaded, so that the pigment concentrate granules produced therefrom have filling levels of up to 60% by weight, preferably up to 50% by weight. -% exhibit.

These pigment concentrate granules are fed, for example, together with the equalizing amounts of pure polymers to achieve the desired film composition with a film filling level in the formulation window mentioned below the CPVC to the film extruder.

In a particularly preferred embodiment of the invention, a mixture of three or more granules is fed to the film extruder, namely a pigment concentrate prepared by pre-kneading, a color pigment concentrate for setting the desired film color and an unfilled polymer granulate or an unfilled polymer. Granulate / additive mixture to adjust the total mixture recipes according to AI or A2. In the case of AI), the lin-polyolefin matrix of the polymer mixtures preferably consists of systems made of linear polypropylenes - specifically, these are mixtures of highly and low-crystalline, linear propylene-homo- and / or propylene / ethylene copolymers with a maximum of 15 Mol% of PE in the PPPE copolymer. However, homopolypropylenes with MFI values _{23021ι6 of} between 8 and 20 g / 10 min are preferred, such as, for example, the PT 551 product from BOREALIS - and in particular those with high crystallinity, such as, for example, the K2XMod product from BOREALIS or mixtures thereof, with thermoplastic elastomers (TPE), such as preferably physically branched PPPE with a PE content in the PPPE copolymer of at most 35 mol% and with MFI values _230/216 greater than 5 g / 10 min, such as, for example, the product RAHECO K2033 from BOREALIS.

In the case of the lin-polyolefin matrix of the mixtures A2, A2.1 “low PE systems” with 20 to 30% by weight PE are preferably used, in which this PE fraction consists partly of LLDPE, the LLDPE fraction according to formula la depends on the total PE content and is thus 23 to 50% of the PE amount and the PE residue is HDPE and, the LLDPE types in question according to the invention having an MFI value _{19021 # 6} greater than 20 and HDPE types should have an MFI value _{190 / 21-6} between 25 and 35g / 10min In addition to this PE content, the lin polyolefin matrix is made up of a PP content of 80-70% by weight PP, which are polypropylenes may be homopolymers or copolymers. particularly preferred are PP homopolymers with an MFI value _230/21, _6/10 minutes have greater than 5 g, preferably between 8 and 20 g / 10 min.

For the A2.2 "high PE systems", 60 to 70% by weight PE is preferably used, in which the LLDPE content depends on the total PE content, according to formula Ib and then the LLDPE content

L = 35.7 to 46.7% LLDPE in addition to 100 - L wt.% HDPE, and the LLDPE types that come into question according to the invention have an MFI value of _{190/21: 6} greater than 20 g / l0 min and the HDPE types should have an MFI value of _190/21 , ₆ between 25 and 35g / l0min. The polypropylene content in these systems is 40 to 30% by weight of the PEPP matrix, and PP homopolymers or copolymers are suitable for this. PP _homopolymers having an MFI value _23021/6 greater than 5, preferably between 8 and 20 g / 10 min, are again particularly preferred _.

The low-PE systems according to A2.1 are particularly preferred. The thermoplastic elastomers (TPE), which represent an essential part of the polymer matrix according to the invention, are used for all types according to AI or according to A2 in a proportion of 5 to 20% of the weight of the lin polyolefin matrix.

The physically branched PPPE are preferably used. This is particularly preferred in a proportion of 7 to 15% by weight of the lin polyolefin matrix.

Furthermore, it has been shown that the CPVC for the systems according to AI is lower than that according to A2, namely around 35-38% by weight, so that the dead-fold properties according to the invention are good while maintaining useful puncture resistance at film fill levels from about 25 to 36% by weight, preferably from 28 to 35% by weight, of mineral fillers, including any color pigments, based on the total weight of the film.

It has also been shown that the CPVC for the HDPE-PP-LLDPE systems according to A2 is higher than that of the mixtures according to AI, namely approximately

40 - 45 wt .-%, so that the good dead-fold properties with adequate puncture resistance at film fill levels at about 30 to 43 wt .-%, preferably in the range of 33 to 42 wt .-% of mineral fillers including any Color pigments, based on the total weight of the film.

Higher degrees of filling usually also result in better dead-fold properties.

Higher stiffnesses are achieved with lower LLDPE proportions and preferably with the systems made of linear PP with 2-phase PE-PP rubber copolymers.

The promotion of recrystallization after extrusion increases the stiffness, for example by increasing the

Chili roll temperature can be achieved.

To further increase the puncture resistance, either the proportion of 2-phase rubber PPPE copolymers can be increased and / or further TPE, in particular those of the TPO type, can also be used directly in amounts of 1 to 10% by weight, preferably in amounts of 3 to 5% by weight, based on the total weight of the 1-polymer matrix, are additionally added.

The films according to the invention can be packaged in a customary manner, namely by adding additives such as antioxidants, light stabilizers and / or antistatic agents, which are added to the granulate mixture in conventional concentrations when the film extruder is drawn in.

The customary finishing processes, such as painting, printing, extrusion coating or metallization, can be applied to the films according to the invention.

The invention exemplifies the following examples:

The abbreviation "stiffness" is understood to mean the physical phenomenon of the so-called bending stiffness, to the extent that, according to Hooke's law, the relative change in length (Δl / 1) of a body due to a stretching force is proportional to the product of 1 / E (di the reciprocal of the body's modulus of elasticity) and the stretching force (k) acting on the body divided by the stretched cross-section (F).

The result (if F is the body width b times the body thickness d) is the elongation stiffness, which is defined as St _D = E xd to: St _D = k / bx 1 / Δl.

In analogy to this, the bending stiffness St _B for a rectangular body of length 1, width b and thickness d is given as the moment M in Newton meters [Nm] which is required to measure this body (this film strip) of a certain dimension (1, b, d) in a defined geometric arrangement (as prescribed in H. Markström: "The Elastic Properties of Paper - Test Methods and Measurement Instruments" - Lorentzen & Wettre, Stockholm 1993, ISBN 91-971765-0-8) around the radius R to bend - in analogy to the above-mentioned definition of elongation stiffness - according to the definition: St _E ≡ M / bx R = M / (bxl / R). As described there, this definition results from integration of the Hooke's law: St _B [Nm] = ₁₂ x E xd ³ (E in [N / m ² ]; d in [m])

This results in the force k _B required to build up the bending moment M (= k _B x 1) at the end of the force arm with length 1 for the bending - in the context of the present invention, briefly called “stiffness measurement value”, approximately to:

k _B [mN] = _B K _st x Vi _{oo ooo} ^x d ³ with the film thickness d in [μm]

when k _B is expressed in millinewtons, and the term ^_1/12 x E / 1 = _B K _st in connection with the present invention is referred to (also briefly mentioned in the examples stiffness constant) as the "bending stiffness constant" and this is represented in units kp / mm ³ .

Since the achievement of the stiffness values of a film is trivial simply by choosing a correspondingly higher film thickness - because the stiffness simply increases very strongly, namely with the third power of the thickness -, the term “stiff” or “stiffness” should be used in the present description of the invention "To describe a film property, only the bending stiffness constant _B K _st defined above is used as a" material constant "for a comparative description of the product properties. Only the attribute stiff should be used if this size exceeds a certain value. However, since the stiffness mentioned above also depend on other parameters, there is no absolute constancy of the stiffness "constant" over large thickness ranges. Therefore, only stiffness constants should be used for comparison purposes, insofar as these were measured on foils of the same thickness.

Order of magnitude, i.e. on foils in the thickness range of less than 50 μm with one another, or on foils in the thickness range of 50-100 μm with one another, or on foils in the thickness range of 100-200 μm with one another, - but not measured by comparing stiffness "constant", for example extremely thin (like 35 μm) foils with those measured on 150 μm thick cards.

Within the scope of the present invention, only "rigid" should be referred to as foils with rigidity constants according to the aforementioned definition above 250 kp.mπr ³ . For the comparability of the measured values given in the examples with regard to puncture resistance, the physical phenomenon of the limit of the elasticity of a film in the event of a sudden impact should be understood in connection with this, expressed in the energy [in mJ] which is necessary for a body of a certain geometry to adhere clamped test film can penetrate (so-called fall bolt test).

For the puncture resistance values given in the examples given below, the mean value from 10 measurement results of puncture tests to determine the impact energy, in which just half of the test foils are penetrated, should be understood in accordance with DIN standard 53 443 in concreto. Dart drop value "). The measurements are carried out on film test pieces measuring 10 x 70 cm, which are cut out of the film to be tested transversely to the direction of extrusion. For each penetration test, an undamaged piece of the film strip is fixed all around on a free, round impact surface of 5 cm in diameter The test specimen is a cylindrical solid aluminum bolt of 20 grams in weight with a diameter of 24 mm, is rounded at the end face in a hemispherical shape and is dropped from different heights in a downpipe onto the clamped test surface According to E = mgh is the impact energy in [mJ] if m (the bolt mass) is measured in grams g (the gravitational acceleration) in [m / s ² ] and the head h in [m].

For the comparability of the data on the dead-fold properties given in the examples, the ratings given are given as classifications in a wrinkle test. A 10 x

10 cm square piece of film loosely crumpled into a ball of about 2 cm in diameter and after it was placed on a flat plate, its automatic unfolding was observed.

An aluminum foil has excellent dead-fold properties because it practically no longer unfolds at all (wrinkle test: grade 0-1). Grade 5 means that the ball opens spontaneously to a slightly crumpled flat film, as is the case, for example, with a conventional, unfilled polyethylene or polypropylene film, which even despite folding and even if it bends around sharp edges, "spring back" again and again into its original, unfolded flat shape.

Ways ".zur_Ausführ_ung_der__Erfindung

B_e_ispLeL_l (system made of linear PP with 2-phase PE-PP rubber copolymer; highly rigid)

The following pigment concentrates were first prepared in a heatable 2-screw kneader and granulated immediately after they were discharged and then dried to a water content below 0.1%:

Mixture PP-T50: equal _{parts by} weight of a linear PP _homopolymer with MFI _230/216 = 9 and talcum powder (98% <7 μm).

Mixture MBW _PP 60: 40% by weight of the same linear PP homopolymer as for mixture PP-T50 and 60% by weight Ti0 ₂ (rutile type, 97% <10 μm)

The following granulate mixture was fed to a flat film extruder with a "chill roll":

87 kg / h of a mixture of PP-T50 plus 45.3 kg / h of pure, minerally unfilled PP homopolymer as used for the production of mixture PP-T-50 plus 7.5 kg / h of mixture MBW60 plus 10.2 kg / h of a physically branched PEPP of approximately the same MFI, and 3.75 kg / h of a conventional antistatic agent based on an ethoxylated amine in PP.

The film formulation corresponds to a fill level of 31%, with a share of the physically branched PEPP based on the net weight of the plastic matrix of around 10%.

In a preliminary test, a CPVC of 37% had been determined for this recipe by extrusion of 35 μm foils with a gradual increase in the percentage of filling, with otherwise the same ratios of the non-mineral components. According to formula 1, this results in a filling degree range according to the invention of 37 minus 2 to 10 di 27 to 35, preferably of: 37 minus 3 to 7 di 30 to 34 Weight - ' ^■

Films with a thickness of 50, 60, 70 and 90 μm were produced. All films showed excellent dead-fold properties (wrinkle test grade 3). High thicknesses even gave very good fold-in properties. Stiffness constant: 559

Puncture resistance measured as a dart drop value: 40 mJ on a 26 μm film.

Ver_gLe chsbeisμie L

The same pigment concentrates as described in Example 1 were used to make a conventional filled film:

Vexgleichsbei

A commercially available, conventionally filled (degree of filling 52% of calcium carbonate) PP film was examined.

Dead-fold properties crumple test: grade 2; Indeed: Puncture resistance: film behaves brittle and fragile like a thin egg shell. Dart drop value measured on the 50μm thick film: 14 mJ - corresponding to the empirical relationship of RF '= RF x (d' / d) ^2.2 around 3.5 for a film thickness of 26 μm - i.e. for most applications unusable.

Stiffness constant: 240 (i.e. comparatively not really stiff in spite of the high degree of filling, but rather lobed).

Eeis_p_i≤_l_ 2 (HDPE-PP-LLDPE system of the type low-PE; - set stiff)

The following pigment concentrates were first produced in a heatable 2-screw kneader, granulated immediately after they were discharged and then dried to a water content of less than 0.1%:

Mixture HDPEKT50: 50 parts by weight of an HDPE with MFI 190 / 21.6 32 g / 10 min with 25 parts by weight of chalk (99% <10 μm) and 25 parts by weight of talc (98% <7 μm)

Mixture LLDPEKT50: 50 parts by weight of an LLDPE with MFI _190/21/6 = 1.2 g / lOmin with 25 parts by weight of chalk (99% <lOμm) and 25 parts by weight of talc (98% <7μm)

Mixture PP-KT50: 50 parts by weight of a PP / PE random copolymer with 8 mol% PE / 92 mol% PP with an MFI _{230/21> 6} = 8 g / 10 min with 25 parts by weight Chalk (99% <lOμm) and 25 parts by weight talc (98% <7μm)

Mixture MBB _HD 20: 80% by weight of the same HDPE as for mixture

HDPEKT50 uses plus 20% by weight of an organic brown pigment

Preblend compounds were produced from these granulated mixtures by simple, cold mixing:

PP compound: 44 parts by weight of PP-KT50 plus 17 parts by weight of pure PP / PE copolymer (MFI _230/216 = 8 g / lOmin) plus 6.3 parts by weight

Share physically branched PEPP with MFI 230 / 21.6 PE compound: 14 parts by weight of HDPEKT50 plus 12 parts by weight of LLDPEKT50

The following granulate mixture was fed to a flat film extruder with chill roll:

67.3 kg / h PP compound + 26 kg / h PE compound + 7.2 kg / h MBB _HD 20.

The film formulation corresponds to a fill level of 36.3% with a polymer matrix composition of: 71% PP in addition to 29% PE, the latter 31% LLDPE and a proportion of the physically branched PEPP based on the net weight of the total plastic matrix of around 10%.

In a preliminary test, a CPVC of 43% had been determined for this recipe by extrusion of 35 μm foils with a gradual increase in the proportion of filling, with otherwise identical ratios of the non-mineral components. This results in a degree of filling range according to the invention of 43 minus 2 to 10 d.i. 33 to 41, - preferably from: 43 minus 3 to 7 d.i. 36 to 40% by weight).

A film with a thickness of 37 μm was produced, which was colored deep brown.

It has very good dead-fold properties (wrinkle test grade 1) and shows one

Flexural rigidity constant: 356

The puncture resistance measured as a dart drop value was 26 mJ on the 37 μm film.

VergLe.lchsb≤j.spi_e1_3_:

Conventional PP films filled with 33% of a mixture of 56% chalk and 44% talc were examined.

Foil thickness: 65 μm

Dead fold properties significantly worse (wrinkle test grade 2-3); Bending stiffness constant: 147 The puncture resistance values measured on the 65 μm thick film as a dart drop value were: 260 mJ - corresponding to the empirical relationship of RF ^λ = RF x (d '/ d) ^2.2 around 75 mJ for a 37 μm film.

The puncture resistance is therefore relatively satisfactory; the bending stiffness is not, however, so that the film appears extremely lobed.

An increase in the degree of filling to improve the dead-fold properties was found to be impossible, since the CPVC value was already found to be 35% for such a formulation, which was not synergistically adapted to the mineral filling. Therefore, this conventional recipe no longer left any scope in terms of filling. This also explains the fact that no thinner films than around 35 μm could be produced free of pores or holes, since the film formulation was already in the area of the breaking of the plastic matrix around the mineral filling.

Similarly, no acceptable stiffness was adjustable; the material behaved very poorly according to the measured stiffness constant; - An increase in rigidity by increasing the degree of filling was not possible for the reasons mentioned.

B £ ispi_eL_3 (HDPE-PP-LLDPE system of the type: high-PE - highly tear-resistant / less stiff)

Mixture HDPEKT50: 50 parts by weight of an HDPE with MFI 190/21 _{# 6} = 32 g / 10 min with 25 parts by weight of chalk (99% <10 μm) and 25 parts by weight of talc (98% <7 μm)

Mixture LLDPEKT50: 50 parts by weight of an LLDPE with MFI _{190/21> 6} = 1.2 g / lOmin with 25 parts by weight of chalk (99% <lOμm) and 25 parts by weight of talc (98% <7μm)

Mixture PP-KT50: 50 parts by weight of a PP / PE random copolymer with 8 mol% PE / 92 mol% PP with an MFI _{230 / 21ι6} = 8 g / 10 min with 25 parts by weight of chalk (99% <10 μm) and 25 parts by weight of talc (98% <7 μm)

Mixture MBW _LL 60: 40% by weight of the same LLDPE as used for mixture LLDPEKT50 plus

60% by weight Ti0 ₂ (rutile type, 97% <10 μm)

PP compound: 4.5 parts by weight of PP-KT50 plus 15.5 parts by weight of pure r-PPPE (MFI _{230 / 21ι6} = 8g / 10min) plus 6.2 parts by weight of a physically branched PEPP with MFI ₂₃₀₂₁₆ = 8g / 10min

PE compound: 22.9 parts by weight of LLDPEKT50 plus 1 part by weight of LLDPE

(with MFI _{190 / 21.6} = 1.2 g / lOmin) plus 42.9 parts by weight of HDPEKT50.

The following granulate mixture was fed to a flat film extruder with Chili roll:

26.2 kg / h PP compound + 66.8 kg / h PE compound + 5 kg / h MBB _LL 60 + 2 kg / h of a common antistatic based on an ethoxylated amine and gycerin monostearate in HDPE.

The film formulation corresponds to a degree of filling of 38.2% with a polymer matrix composition of: 60% PE, of the latter 40% LLDPE in addition to 40% PP and a 2-phase PE-PP rubber copolymer proportion based on the net weight of the Total plastic matrix of around 10%.

In a preliminary test, a CPVC of 45% had been determined for this recipe by extrusion of 35 μm foils with a gradual increase in the percentage of filling, with otherwise identical ratios of the non-mineral components. This results in a filling degree range according to the invention of 45 minus 2 to 10 d.i. 35 to 43, - preferably from: 45 minus 3 to 7 d.i. 38 to 42% by weight.

A film with a thickness of 37 μm was produced.

The film had very good dead-fold properties (wrinkle test grade 1 ) .

With a stiffness constant: 310

The puncture resistance, measured as a dart drop value, gave: 158 mJ on the 37 μm film.

Industrial applicability

The plastic films according to the invention have the dead-fold property that is essential for packaging films in an extremely satisfactory form, since, owing to the special polymer matrix in connection with the fillers used, they have a high "shape memory", ie they return after, for example Do not rewind (twist) to the original state as usual. The wrapped goods are therefore well protected against moisture and dirt.

Claims

1. Dead-fold films with improved rigidity from mineral-filled polyolefin formulations, characterized in that these mineral-filled polyolefin systems consist of a plastic matrix, which is composed of a polymer matrix and additives, and wherein this polymer matrix consists of a linear (lin) polyolefin Matrix is built up, and 5 to 20% of the weight of this lin polyolefin matrix consist of thermoplastic elastomers (TPE) or of thermoplastic olefin copolymer elastomers (TPO), and wherein the lin polyolefin matrix consists of:

C) in the plastic matrix according to AI or A2 or in main components thereof, finely ground mineral pigments are added in such an amount that the total degree of filling of the film is in a range from 2 to 10% by weight.

Points, preferably 3 to 7% by weight points below the CPVC.

2. Dead-fold films according to claim 1, characterized in that the additives used in the polymer matrix are antistatic and / or antioxidants and / or light stabilizers.

3. Dead-fold films according to claim 1 or 2, characterized in that the lin-polyolefin matrix made of thermoplastic elastomers (TPE) chemically or physically branched Has polypropylene / polyethylene copolymers.

4. Dead-fold films according to one of claims 1 to 3, characterized in that the lin polyolefin matrix consists of thermoplastic olefin copolymer elastomers based on ethylene-octene copolymers.

5. Dead-fold films according to one of claims 1 to 4, characterized in that the lin-polyolefin matrix based on physically branched polypropylene / polyethylene copolymers sol-che of the random-heterogeneous-2-phase type -Rubber-polypropylene / polyethylene copolymers.

6. Dead-fold films according to one of claims 1 to 5, characterized in that component AI of the lin polyolefin matrix consists of higher-crystalline and lower-crystalline homopropylenes.

7. Dead-fold films according to one of claims 1 to 6, characterized in that the polymer matrix as a thermoplastic

Elastomeric (TPE) physically branched PPPE of the type of random heterogeneous 2-phase rubber PPPE copolymers contains and in an amount of 7 to 15% of the weight of the lin polyolefin matrix according to AI or A2.

8. Dead-fold films according to one of claims 1 to 7, characterized in that the fillers are finely ground mineral pigments in pure form or mixtures from the group of the following fillers: calcium carbonate, talc, gypsum, mica, magnesium silicate, titanium dioxide , mineral color pigments such as

Iron oxide, and that these fillers have an average particle size below 10 μm with a particle size distribution of not more than 5% by weight above 20 μm, preferably an average particle size below 7 μm, with a particle size distribution of no more than 2% by weight above 10 μm.

9. A process for the production of dead-fold films by melt extruding polymer granules into flat films, characterized in that the polymer granules are constructed from a plastic matrix which consists of a polymer matrix and additives. ven exists, wherein the polymer matrix is built up in a "tolerance window" and that the polymer matrix consists of:

AI) Mixtures of linear propylene-Ho o and / or propylene / ethylene copolymers, the so-called "lin-polyolefin matrix", and 5 to 20 wt .-% of this lin-polyolefin matrix of thermoplastic elastomers, such as TPE , of which preferably so-called TPO, which includes thermoplastic olefin copolymer elastomers such as ethylene-octene copolymers, or

A2) from a lin polyolefin matrix, which consists of mixtures of 20 to 65% by weight of PE and a proportion of PP of 35 to 80

% By weight of PP consists of the PE portion containing LLDPE as a flexibilizing agent and 5 to 20% by weight of this lin polyolefin matrix consists of thermoplastic elastomers (TPE), of which preferably so-called TPO, including thermoplastic olefin copolymer Elastomers such as ethylene

Octene copolymers are to be understood, with particular preference being given to physically branched PPPE, that is to say so-called random-heterogeneous 2-phase rubber PPPE copolymers, and that

B) finely ground, mineral pigments are kneaded into the plastic matrix in accordance with AI or A2 or main components thereof before the melt extrusion in such a way that the total filling level of the finished dead film is in a range from 2 to 10% by weight. Points, preferably 3 to 7% by weight, below which the CPVC lies.

10. A process for the production of dead-fold films according to claim 9, characterized in that the mixtures of linear propylene-homo- and / or propylene-ethylene copolymers are those based on physically branched polypropylene / polyethylene copolymers, so-called random -heterogeneous 2-phase rubber-PPPE copolymers.

11. The method according to claim 9 or 10, characterized in that The percentage of LLDPE in the total PE portion of the lin polyolefin matrix according to A2 is selected depending on the total PE portion by:

7 to 10

% LLDPE = 100 x

% By weight PE in the lin polyolefin matrix

for so-called "low PE systems" in which the PE content is 20 to 50% by weight.

12. The method according to any one of claims 9 to 11, characterized in that the percentage LLDPE share in the total PE share of the lin polyolefin matrix for "high PE systems", that is systems with a PE share of more than 50 to 70% by weight in the lin polyolefin matrix depending on the total PE content is selected by:

25 to 28% LLDPE = 100 x

Wt. PE in the lin polyolefin matrix.

13. The method according to any one of claims 9 to 12, characterized in that the fillers in the polymer matrix see mineral pigments and / or color pigments, preferably talc and / or calcium carbonate.

14. The method according to any one of claims 9 to 13, characterized in that the fillers used have an average grain size below 10 microns with a grain size distribution of not more than 5 wt .-% over 20 microns, an average grain size below 7 microns, with a Grain size distribution of not more than 2% by weight over 10 μm is preferred.

15. The method according to any one of claims 9 to 14, characterized in that before the film extrusion, the pigments used as fillers are kneaded in such a way that the granules have a degree of filling of up to 60 wt .-%, preferably up to 50 wt .-% , and that these filler concentrate granules together with the equalizing amounts of pure polymer to achieve the desired film composition with a film filling level in the formulation window below the CPVC are fed to the film extruder.

16. The method according to any one of claims 9 to 15, characterized in that in the case of Al for the construction of the polymer matrix, mixtures of linear PP, in conjunction with thermoplastic elastomers (TPE), are used.

17. The method according to any one of claims 9 to 16, characterized in that mixtures of linear homo-polypropylenes are used to build up the polymer matrix in the case of Al.

18. The method according to any one of claims 9 to 17, characterized in that to build up the polymer matrix according to AI in addition to linear polypropylene thermoplastic elastomers (TPE) based on polypropylene-polyethylene random copolymers, which 2-phase block copolymerized with ethylene -Propylene rubbers are used.

19. The method according to any one of claims 9 to 18, characterized in that in the case of A2 to build the lin polyolefin matrix in "low PE systems" mixtures of 20 to 30 wt .-% PE are used in addition to PP, the PE -Share consists of 23.3 to 50 parts by weight of LLDPE in addition to 86 to 50 parts by weight of HDPE.

20. The method according to any one of claims 9 to 19, characterized in that in the case of A2 to build the lin polyolefin matrix in "high PE systems" mixtures of 60 to 70 wt .-% PE are used in addition to PP, the PE content consists of 35.7 to 46.7 parts by weight of LLDPE in addition to 62 to 45 parts by weight of HDPE.

21. Dead-fold film produced by a process according to one of claims 9 to 20, characterized in that when using Al-polymer mixtures, the degree of film filling in a range from 25 to 36% by weight of mineral fillers including any color pigments based on the total weight of the film.

2. Dead-fold film produced by a process according to one of claims 9 to 20, characterized in that when using A2 polymer mixtures the degree of film filling in a range from 30 to 43 wt .-% of mineral fillers including any color pigments based on the total weight of the film.