Polypropylene film having cling properties.

0001The invention relates to a non-sealable, multi-layer polypropylene film, its production and its use.

0002Sealable and non-sealable polypropylene films are described in numerous publications. A problem that occurs again and again with these films is the adhesion of coatings, prints or adhesives to such films, which is usually inadequate due to the highly non-polar nature of the polyolefins. Due to increasingly strict environmental protection regulations, aqueous coating systems are becoming increasingly important, but here, in particular, there are very special liability problems due to their polarity.

0003EP-A-0 234 758 describes a special polypropylene film which, in particular, is said to have good coatability with aqueous coatings. However, this film has the essential defect that it only has good coatability shortly after production, but loses with increasing storage time. In the production of laminates with this film using aqueous adhesives, it has been shown that the curing of the adhesives is delayed very much with the storage time.

0004The object of the present invention was to provide a polypropylene film which, in addition to the usually essential properties such as gloss, scratch resistance, transparency, etc., should in particular have a particularly good long-term stability of its adhesive properties with respect to coatings, in particular aqueous coating systems, printing and adhesives.

0005This object is achieved by a film of the type mentioned at the outset, the characteristic features of which can be seen in the fact that it comprises at least one cover layer on a base layer made of polypropylene, which comprises a mixture of a propylene-butylene copolymer and an ethylene-propylene-butylene Terpolymers containing from 0.1 to 7% by weight of ethylene, from 68 to 95.9% by weight of propylene and from 4 to 25% by weight of butylene, based on the total weight of the mixture, wherein the layer thickness of the cover layer is not greater than 0.3 µm.

0006The base layer of the multilayer film according to the invention consists of a propylene polymer which consists predominantly of propylene and has a melting point preferably of 162 to 168 ° C. Isotactic polypropylene with an n-heptane soluble content of 6% by weight and less is a preferred propylene polymer. The propylene polymer of the base layer generally has a melt index of 1.5 to 5 g / 10 min at 230 ° C. and 21.6 N Load (DIN 53735).

0007The top layer consists in particular of a mixture of copolymer and terpolymer in a mixing ratio of 4: 1 to 1: 4, the copolymer having a propylene content of 98 to 75% by weight and a butylene content of 2 to 25% by weight, and wherein the terpolymer has an ethylene content of 0.1 to 7% by weight, a propylene content of 95.9 to 68% by weight and a butylene content of 4 to 25% by weight. Such a mixture has a p-xylene-soluble fraction of from 25 to 70% by weight, preferably from 40 to 60% by weight, at 20 ° C. The melting point of the mixture is 130 ° C or higher, the melt flow index in the range of 0.1 to 16 g / 10 min at 230 ° C and 21.6 N load.

0008The copolymer from alfa olefins, which Mitsui Petrochemicals offers under the name TAFMER XR-107 L, has proven to be particularly suitable.

0009In order to further improve certain properties of the film according to the invention, the layers can contain suitable active ingredient components in each case in effective amounts, preferably antistatic agents and / or lubricants.

0010Preferred antistatic agents are essentially straight-chain and saturated aliphatic, tertiary amines with an aliphatic radical having 10 to 20 carbon atoms, which are substituted by 2-hydroxyalkyl (C₁-C₄) groups, including N, N-bis (2-hydroxyethyl) -alkylamines with C₁₀-C₂₀, preferably C₁₂-C₁₈, are particularly suitable as alkyl groups. The effective amount of antistatic is in the range from 0.05 to 1% by weight, based on the layer. It has proven particularly expedient to provide the base layer with 0.1 to 0.25% by weight of an N, N-bis-ethoxyalkylamine with aliphatic radicals with 10 to 22 carbon atoms.

0011Carboxylic acid amides such as erucic acid amide and stearic acid amide or polydiorganosiloxanes are suitable as lubricants.

0012The cover layer or the cover layers preferably additionally contain conventional inorganic or organic antiblocking agents. Suitable antiblocking agents are inorganic additives, e.g. As silicon dioxide and calcium carbonate or the like, or organic additives, for. B. benzoguanine-formaldehyde copolymers. It is essential for the antiblocking agent that the average particle size is between 1 and 4 µm. The refractive index of the antiblocking agents is between 1.4 and 1.6. The amount added is 0.1 to 0.5% by weight, based on the weight of the cover layers.

0013The preferred thickness of the cover layer or layers is in the range from 0.10 to 0.3 μm.

0014The polyolefin film according to the invention, which consists of at least two layers, the cover layers having the same or different composition, is produced by the known coextrusion process. In this process, the procedure is such that the melts corresponding to the individual layers of the film are co-extruded through a flat die, the film obtained in this way is cooled for solidification, the film is biaxially stretched (oriented), the biaxially stretched film is heat-set and on the for corona treatment provided surface layer is corona treated. The biaxial stretching (orientation) can be carried out simultaneously or in succession, with the successive biaxial stretching, in which stretching first being longitudinal (in the machine direction) and then transverse (perpendicular to the machine direction) being preferred. First of all, as in the conventional coextrusion process, the polymer or the polymer mixture of the individual layers is compressed or liquefied in an extruder. The melts are then pressed simultaneously through a flat die (slot die), and the pressed multilayer film is cooled and solidified on one or more rollers, which are kept at about 30 to 50 ° C. by cooling. The film thus obtained is then stretched longitudinally and transversely to the direction of extrusion, which leads to an orientation of the molecular chains. Stretching is preferably 4 to 7: 1 in the longitudinal direction and preferably 8 to 10: 1 in the transverse direction. The longitudinal stretching is carried out at a film temperature of preferably 120 to 140 ° C. and the transverse stretching is preferably carried out at 160 to 175 ° C. The longitudinal stretching is expediently carried out with the aid of two rollers running at different speeds in accordance with the desired stretching ratio, and the transverse stretching is carried out with the aid of a corresponding tenter frame. The biaxial stretching of the film is followed by its heat setting (heat treatment). The film is held at a temperature of 150 to 160 ° C for about 0.5 to 10 s. The corona treatment is preferably carried out with an alternating voltage of approximately 10,000 V and 10,000 Hz, on one or both sides, as desired. The film thus produced is wound up in the usual way with the aid of a winding device and has a surface tension on the treated side of from 36 to 42 mN / m, preferably from 38 to 40 mN / m, immediately after the production.

0015The polyolefin multilayer film according to the invention is particularly suitable for the production of laminates. It has all the important properties that are required of polyolefin films with a view to their use as a laminatable or coatable film. In particular, it features:<ul id="ul0001" list-style="dash"><li>very good optical properties, especially gloss and haze,</li><li>high scratch resistance,</li><li>good immediate and long-term coatability properties, especially with aqueous systems,</li><li>good surface treatability and good odor properties as well</li><li>good processing properties.</li></ul>

0016The film of the invention is also particularly suitable as a carrier film for aqueous barrier coating systems, for. B. based on aqueous dispersions of polyvinylidene chloride or ethylene vinyl alcohol copolymers. You can also print excellent with aqueous printing inks, eg. B. with two-component reactive dyes.

0017The invention will now be explained in more detail using examples: The examples and comparative examples below are each a biaxially oriented (longitudinal stretching ratio 5: 1, transverse stretching ratio 10: 1) polyolefin film with a base layer and two cover layers, the base layer being made of an isotactic polypropylene with an n-heptane-soluble fraction of 4% by weight. -%, with a melting point of 165 ° C and a melt flow index of 3.5 g / 10 min at 230 ° C and 21.6 N load (DIN 53 735) as the main component. The base layer is about 12 µm thick, and the two cover layers that surround the base layer are each about 0.2 µm thick. The three-layer polyolefin films have been produced by the known coextrusion process.

0018All layers contain 0.1% by weight of pentaerythrityl tetrakis-3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate (Irganox 1010) for stabilization^(R)) and 0.05% by weight calcium stearate for neutralizing acid catalyst residues. The base layer also contains 0.2% by weight of N, N-bisethoxyalkylamine (alkyl radical C₁₀-C₂₂).

0019The following measurement methods were used to characterize the raw materials and foils:

Melt flow index:

0020DIN 53 735 at 230 ° C and 21.6 N load.

Turbidity:

0021The haze of the film is measured in accordance with ASTM-D 1003-52, a 1 ° slit diaphragm being used instead of a 4 ° perforated diaphragm, and the haze being given in percent for four layers of film lying one above the other. The four positions were chosen because this enables the optimal measuring range to be used. The turbidity rating was -15% = very good, -15% to 25% = moderate and -25% = bad.

Shine:

0022The gloss is determined in accordance with DIN 67530. The reflector value is measured as an optical parameter for the surface of a film. Based on the standards ASTM D-523-78 and ISO 2813, the angle of incidence was set at 20 °. A light beam hits the flat test surface at the set angle of incidence and is reflected or scattered by it. The light rays striking the photoelectronic receiver are displayed as a proportional electrical quantity. The measured value is dimensionless and must be specified with the angle of incidence.

Scratch resistance or sensitivity:

0023The scratch resistance is determined based on DIN 53 754.

0024The Taber model 503 Abraser from Teledyne Taber is used to determine the scratch resistance, using Calibrade R H18 friction wheels that are loaded with 250 g. Scratch resistance or scratch sensitivity means the increase in haze of the scratched film compared to the original film after 50 revolutions of the sample plate. The scratch resistance is said to be very good if the increase in haze is 20%, moderate if the increase in haze is 20 to 25%, and poor if the increase in haze is greater than 25%.

Waste behavior and smell:

0025The corona treatment was carried out in such a way that the treated film surface in each case had a treatment intensity of 39 mN / m immediately after the treatment. The treatment intensity was determined using the so-called ink method (DIN 53 364).

0026The treatment intensity measurement was repeated every 14 days. The waste behavior was described as very good if the treatment intensity was still at least 37 mN / m after four months (ΔB ≦ 2 mN / m). The waste behavior was described as poor if the treatment intensity was ≦ 35 mN / m (ΔB ≧ 4 mN / m). The smell of the films was assessed by means of an odor test.

Odor:

0027An approximately 1 cm thick film stack (DIN A 4) is produced from the film to be assessed and is wrapped in Al film. To assess the smell, the film stack is opened after 2 days of storage and smelled between the film layers.

0028Odor notes: ++ low smell + - noticeable smell - distinct smell

Corona tradability

0029The films were subjected to a corona treatment under the same conditions. While treatment intensities of 39 mN / m were achieved in example 1 and the comparative examples VB 1 and VB 2, the comparative examples VB 3 and VB 4 only show an intensity of 36 mN / m.

Printability

0030The films were printed 14 days after their production (short-term assessment) or 6 months after their production (long-term assessment). The color adhesion was assessed using an adhesive tape test. If no colors could be removed using adhesive tape, the color adhesion was rated as very good. If there was little ink detachment, the ink adhesion was assessed as good and if there was significant ink detachment, it was rated as poor.

Can be bonded with aqueous adhesives / further processing

0031Laminates with glassine paper (basis weight 40 g / m²) were produced to assess the bondability with aqueous adhesives and the further processing properties. The aqueous reactive 2-component adhesive Aquabond A + C from Morton Thiokol GmbH, Wikolin Polymer Division (Germany) was used as the adhesive.

0032The laminates were made 10 days after the films were made and 6 months after the films were made. Laminates in which the bond strength reached the strength of the paper used immediately after production were rated as very good. The laminates that took a long time were rated as moderate.

0033Laminates that did not achieve the strength of the paper were described as poor.

0034The structure of the example films and the comparison films is shown in Table 1. The superior properties of the films according to the invention are shown in Table 2.<tables id="tabl0001" num="0001"><img file="EP0447953A2_D0001.tif" /></tables><tables id="tabl0002" num="0002"><img file="EP0447953A2_D0002.tif" /></tables>