DE102005058910A1 - Sealable, biaxially-oriented, multilayer polyester film for use, e.g. as cover film on plastic meal trays, has a sealable, particle-free outer layer on one side and a non-sealable, micronised silica-containing layer on the other - Google Patents

Abstract

Multilayer, biaxially-oriented, transparent, sealable polyester film (I) with a base layer (B), a sealable outer layer (A) on one side and a non-sealable outer layer (C) on the other side, in which (a) layer (A) contains less than 0.01 wt% extraneous particles and (b) layer (C) contains a pigment with an average particle diameter (d50) of 2-5 microns, a SPAN98 number (scatter of particle size distribution) of 1.2-2 and a concentration of 0.12-0.4 wt% in (C). An independent claim is included for a method for the production of (I) by making a multilayer film with layers (A), (B) and (C) as above by co-extrusion, stretching the film biaxially and then heat-fixing it.

Description

The The invention relates to a transparent, sealable, biaxially oriented polyester film comprising a base layer B, a sealable cover layer A and a not sealable Topcoat C. The invention further relates to a process for the preparation the film and its use.

Sealable, biaxial Oriented polyester films of the prior art are known.

In GB-A 1 465 973 discloses a coextruded, two-layered polyester film described, whose one layer of isophthalic and terephthalic acid-containing Copolyesters and their other layer of polyethylene terephthalate consists. about the sealing behavior of the film can be found in the font no usable Information. Due to lack of pigmentation, the film is only limited can be wound and processed.

In EP-A-0 035 835 discloses a co-extruded sealable polyester film described, which improves the winding and processing behavior particles are added in the sealing layer whose average particle size is the layer thickness exceeds the sealing layer. By the particulate Additives surface protrusions are formed the unwanted Prevent blocking and sticking of the film to rollers or guides. About the other. not sealable Layer of the film, no details for incorporation made of antiblocking agents. It remains open, if this layer Antiblock contains. By choosing particles with a larger diameter as the thickness of the sealing layer and that given in the examples Concentrations worsen the sealing performance of the film. The sealed seam is produced at 140 ° C and the seal seam strength at 23 ° C determined, and it lies in a range of 63 to 120 N / m (corresponding to 0.97 to 1.8 N / 15 mm film width).

In EP-A-0 515 096 discloses a coextruded, multilayer, sealable polyester film described on the sealable Layer an additional one Having additive. The additive may e.g. contain inorganic particles and is preferably as aqueous Layer applied to the film during their production. hereby the good sealing properties are to be maintained and the Be easy to process film. The back of the slide contains only a lot few particles, mainly on the Regranulate get into this layer. Details of the sealing temperature range the film are not made in this document. The sealed seam becomes at 140 ° C and the seal seam strength is determined at 23 ° C, and it is more than 200 N / m (corresponding to 3 N / 15 mm film width). For a 3 μm thick sealing layer becomes a sealed seam strength of 275 N / m (corresponding to 4.125 N / 15 mm film width).

In the EP 0 920 381 B1 there is described a coextruded, multilayered polyester film having a sealable overcoat and a non-sealable basecoat. The base layer may be composed of one or more layers, wherein one of the layers is in contact with the sealable layer. The other (outer) layer then forms the second, non-sealable cover layer. The sealable topcoat may consist of isophthalic and terephthalic acid containing copolyesters. The film also contains a UV absorber, which is added to the base layer in an amount of 0.1 to 10 wt .-%. The base layer of this film is equipped with conventional antiblocking agents. The film is characterized by a good sealability, but does not have the desired processing behavior and has deficits in the optical properties. For example, the haze of the film is given as <75%.

In EP-A-1 138 480 discloses a biaxially oriented, sealable polyester film with a base layer B, a sealable top layer A and a other, not sealable Cover layer C described. The sealable cover layer A has a Seal initiation temperature (also called minimum seal temperature) of a maximum of 110 ° C and a seal seam strength of at least 1.3 N / 15 mm film width. The topographies of the two outer layers A and C are determined by certain Characteristics marked. The film according to the invention is particularly suitable for the Use in flexible packaging, especially for use on high-speed packaging machines. In Comparative Example 1 of the application, a film is described in which the sealing layer is pigment-free. However, the film has unacceptable handling and an unacceptable processing behavior.

EP-A 1 471 096, EP-A 1 471 097, EP-A 1475 228, EP-A 1 475 229, EP-A 1 471,094 and EP-A 1 471 098 describe heat-sealable and opposite APET / CPET peelable Polyester films with ABC structure, to set the desired Peel properties in the peelable and heat sealable Cover A either about 2-10 Wt .-% of inorganic or organic particles or a polyester incompatible Polymer such as e.g. a norbornene / ethylene copolymer.

• – eine verbesserte Siegelfähigkeit gegenüber sich selbst, gegenüber Substraten aus APET, A/CPET, CPET oder Metallen,
• – eine verbesserte Wickelung,
• – verbessertes Verarbeitungsverhalten und
• – durch verbesserte optische Eigenschaften (Trübung, Glanz)

auszeichnet.
(APET = amorphes Polyethylenterephthalat (PET); CPET = kristallines PET; A/CPET = zweischichtiges Laminat, innen APET, außen CPET (bei einer Schale))It is an object of the present invention to provide a sealable, biaxially oriented polyester film which does not have the disadvantages of the prior art films and which is particularly notable for use in the art

• An improved sealability to itself over substrates made of APET, A / CPET, CPET or metals,
• An improved winding,
• - improved processing behavior and
• - by improved optical properties (haze, gloss)

distinguished.
(APET = amorphous polyethylene terephthalate (PET); CPET = crystalline PET; A / CPET = two-layer laminate, inside APET, outside CPET (in one shell))

One particular concern of the present invention was the seal the film against other (not sealable) polyester films or Trays (menu trays) made of polyester, as well as to improve against metallic substrates. This means a minimum sealing temperature of the cover layer A in relation to itself itself of <110 ° C, preferably <108 ° C and especially preferably <106 ° C and a Sealing seam strength of this outer layer A to itself (at 130 ° C) of 1.5 to 10 N / 15 mm, preferably from 1.6 to 10 N / 15 mm and particularly preferred from 1.7 to 10 N / 15 mm. Against an APET substrate, the minimum sealing temperature the cover layer A <140 ° C, preferably <139 ° C and especially preferably <138 ° C and the seal seam strength of this cover layer A over one A / CPET substrate (at 140 ° C) 1.5 to 10 N / 15 mm, preferably from 1.6 to 10 N / 15 mm and especially preferably from 1.7 to 10 N / 15 mm. It should also take care be worn, that the film is well windable and on high-speed Machines can be processed. In the production of the film should also be guaranteed be that accumulating waste material as Regenerat in one Amount of preferably up to 60 wt .-%, based on the total weight the film, can be returned to the manufacturing process without that while the physical and optical properties of the film negative to be influenced.

A Topcoat is then not sealable when its seal initiation temperature, also called minimum sealing temperature, greater than 125 ° C (against himself) is.

• a) die siegelfähige Deckschicht A weniger als 0,01 Gew.-% externe Partikel enthält (bezogen auf das Gesamtgewicht der Deckschicht A) und
• b) die nicht siegelfähige Deckschicht C ein Pigment enthält, das durch die folgenden Merkmale gekennzeichnet ist: • der mittlere Durchmesser der Partikel (d₅₀-Wert) liegt im Bereich von 2 bis 5 μm; • die Streuung der Partikelgrößenverteilung, ausgedrückt durch den SPAN98, liegt im Bereich von 1,2 bis 2, und • die Konzentration der Partikel liegt im Bereich von 0,12 bis 0,40 Gew.-%, bezogen auf das Gesamtgewicht der Deckschicht C.

The object is achieved by providing a transparent, biaxially oriented, sealable polyester film having a base layer B, a sealable top layer A and a top layer C, wherein

• a) the sealable outer layer A contains less than 0.01% by weight of external particles (based on the total weight of the outer layer A) and
• b) the non-sealable topcoat C contains a pigment characterized by the following features: the average diameter of the particles (d ₅₀ value) is in the range of 2 to 5 μm; The scattering of the particle size distribution, expressed by the SPAN98, is in the range of 1.2 to 2, and the concentration of the particles is in the range of 0.12 to 0.40 wt.%, Based on the total weight of the cover layer C. ,

Under Pigments are also anti-blocking agents, fillers, external or inert particles, which are characterized by said parameters to understand. Typical pigments are inorganic and / or organic particles, for example, calcium carbonate, amorphous silica, talc, magnesium carbonate, Barium carbonate, calcium sulfate, barium sulfate, lithium phosphate, calcium phosphate, Magnesium phosphate, alumina, LiF, calcium, barium, zinc or manganese salts of the dicarboxylic acids used, carbon black, titanium dioxide, kaolin or particulate Polymers such as e.g. crosslinked polystyrene or acrylate particles.

According to the invention Three-layer film and includes the base layer B, the sealable topcoat A and the non-sealable Cover layer C (A-B-C).

Prefers is the cloudiness the transparent film is less than 5.0%. In the other case, the Foil e.g. For Applications in which it is printed in reverse printing (for example, outer lamination on metal sheets), less well suited.

The sealable outer layer A preferably contains less than 0.01 wt .-% (based on the mass of the outer layer A), in particular no external particles. In this case the seal is opposite yourself and the best materials listed above. Between the sealing layer A and the substrate, no bubbles form and the seal is full-surface. In the other case, cavities form, for example, through the tips of the fillers, which worsen the seal and lead to optical defects in the laminated film.

It has been found that the particle diameter d ₅₀ , the scattering SPAN98 and the concentration of the pigments used in the non-sealable cover layer C are decisive for good winding, good processability and good appearance of the film.

To obtain a good winding and a good processability of the film, the cover layer C contains a pigment in which the average diameter (d ₅₀ value) in the range of 2.0 to 5.0 .mu.m, preferably from 2.1 to 4.9 and more preferably from 2.2 to 4.8 microns and the SPAN98 in the range of 1.2 to 2.0, preferably from 1.25 and 1.9 and more preferably from 1.3 and 1.8.

Contains the topcoat C, however, a pigment in which the average diameter and / or the SPAN98 outside the range of the invention lie, so it has a negative effect on the winding, the processability and on the optical properties of the film.

Contains the topcoat C is a pigment in which the mean diameter is greater than 5 μm, so the filter behavior deteriorates; the SPAN98 is bigger than 2, so the optical properties and the winding of the film worse.

Contains the topcoat C of the film as the sole pigment one in which the average diameter is smaller than 2 μm is, so increased the cloudiness, and the shine gets worse; is the SPAN98 smaller than 1.2, so the winding of the film is worse, it tends, for example to 'blocking'.

The Covering layer C is to improve the winding behavior and the Processability high filled with inert, that is added pigments. The Concentration of the inert particles in the cover layer C is between 0.12 and 0.40 wt .-%, preferably between 0.14 and 0.35 wt .-% and in the most preferred embodiment, between 0.16 and 0.30 wt .-% (based on the mass of the cover layer) and straightened essentially according to the optical properties to be achieved the foil.

In addition, other pigments, but with a smaller d ₅₀ value than the main pigment, may additionally be incorporated into the cover layer C. If, however, the d ₅₀ values and / or SPAN98 values of the main pigment deviate from the abovementioned values or if such a pigment is not present, the disadvantages described above arise.

used Polymers for the base layer B and for the cover layer C:

Base material:

The Base layer B of the film is preferably at least 90% by weight made of a thermoplastic polyester. Suitable for this are polyester Ethylene glycol and terephthalic acid (= Polyethylene terephthalate, PET), from ethylene glycol and naphthalene-2,6-dicarboxylic acid (= polyethylene 2,6-naphthalate, PEN), 1,4-bis-hydroxymethyl-cyclohexane and terephthalic acid (= poly (1,4-cyclohexanedimethylene terephthalate, PCDT) and ethylene glycol, naphthalene-2,6-dicarboxylic acid and Biphenyl-4,4'-dicarboxylic acid (= polyethylene-2,6-naphthalate bibenzoate, PENBB). Particularly preferred are polyesters which are at least 90 Mol%, preferably at least 95 mol%, of ethylene glycol and terephthalic acid units or consist of ethylene glycol and naphthalene-2,6-dicarboxylic acid units. The remaining monomer units are derived from other aliphatic, cycloaliphatic or aromatic diols or dicarboxylic acids.

Suitable other aliphatic diols are, for example, diethylene glycol, triethylene glycol, aliphatic glycols of the general formula HO- (CH ₂ ) _n -OH, where n is an integer from 3 to 6 (in particular propane-1,3-diol, butane-1,4 -diol, pentane-1,5-diol and hexane-1,6-diol) or branched aliphatic glycols having up to 6 carbon atoms. Of the cycloaliphatic diols, mention may be made of cyclohexanediols (in particular cyclohexane-1,4-diol). Suitable other aromatic diols correspond for example to the formula HO-C ₆ H ₄ -XC ₆ H ₄ -OH, where X is -CH ₂ -, -C (CH ₃ ) ₂ -, -C (CF ₃ ) ₂ -, -O -, -S- or -SO ₂ - stands. In addition, bisphenols of the formula HO-C ₆ H ₄ -C ₆ H ₄ -OH are also very suitable.

Other aromatic dicarboxylic acids are preferably benzenedicarboxylic acids, naphthalenedicarboxylic acid ren, for example naphthalene-1,4- or 1,6-dicarboxylic acid, biphenyl-x, x'-dicarboxylic acids, in particular biphenyl-4,4'-dicarboxylic acid, diphenylacetylene-x, x'-dicarboxylic acids, in particular diphenylacetylene-4,4 'dicarboxylic acid, or stilbene x, x'-dicarboxylic acids. Of the cycloaliphatic dicarboxylic acids, mention may be made of cyclohexanedicarboxylic acids, in particular cyclohexane-1,4-dicarboxylic acid. Of the aliphatic dicarboxylic acids, the (C ₃ to C ₁₉ ) alkanedioic acids are particularly suitable, it being possible for the alkane part to be straight-chain or branched.

The Preparation of the polyesters may e.g. after the transesterification process respectively. It is based on dicarboxylic acid esters and diols, the with the usual Transesterification catalysts, such as zinc, calcium, lithium, magnesium and manganese salts, to be implemented. The intermediates will be then generally more common in the presence Polycondensation catalysts, such as antimony trioxide or titanium salts, polycondensed. The production can be just as good after the direct esterification process in the presence of polycondensation catalysts. there starting directly from the dicarboxylic acids and diols. Polyester according to the invention are available as commercial products.

Sealable topcoat A:

The preferably applied by coextrusion to the base layer B. sealable Cover layer A preferably consists essentially of copolyesters, the predominantly from isophthalic and terephthalic acid units and composed of ethylene glycol units. The remaining Monomer units are derived from other aliphatic, cycloaliphatic or aromatic diols or dicarboxylic acids, as in the base layer can happen. The preferred copolyesters which provide the desired sealing properties are those made from ethylene terephthalate and ethylene isophthalate units are constructed. The proportion of ethylene terephthalate is preferred 60 to 95 mol% and the corresponding proportion of ethylene isophthalate 40 to 5 mol%. Also preferred are copolyesters in which the proportion of ethylene terephthalate 65th to 90 mol% and the corresponding amount of ethylene isophthalate 35 to 10 mol%, and most preferred are copolyesters in which the proportion of ethylene terephthalate 70 to 85 mol% and the corresponding amount of ethylene isophthalate 30 to 15 mol% is.

Non-sealable topcoat C:

For the other, in the sense of the invention non-sealable cover layer C can in principle the same polymers are used as previously for the base layer B were described.

Sealing properties of the sealable Cover layer A:

The desired Sealing properties of the outer layer A are probably from the Combination of the chemical composition of the copolyester used, the top layer thickness and topography (smooth surface).

The sealable Covering layer A has opposite itself a sealing temperature of less than 110 ° C and a Sealing seam strength (the sealing seam is produced at 130 ° C, the seal seam strength at 23 ° C determined) of at least 1.5 N / 15 mm film width; opposite one Substrate from APET a sealing temperature of less than 140 ° C and a Sealing seam strength (the sealing seam is produced at 140 ° C, the seal seam strength at 23 ° C determined) of at least 1.5 N / 15 mm film width. The best sealing properties receives the film one, if the copolyester no further additives, in particular no inorganic or organic fillers are added. For this Case gets for a given copolyester and given layer thickness the lowest seal initiation temperature and the highest seal seam strength.

If the sealable Topcoat A least amounts of antiblocking agents are added so it has to be cheap proved to use the same anti-blocking agent as for the top layer C.

The Base layer B may additionally contain conventional additives such as UV stabilizers, hydrolysis stabilizers, antiblocking agents (e.g., via the regenerate). The other layer C may additionally contain conventional additives such as stabilizers included. These additives will be appropriate to the Polymer or the polymer mixture already added before melting. As stabilizers, for example, phosphorus compounds, like phosphoric acid ester, used.

In the case of the film, the thickness of the cover layer C is generally greater than 0.4 μm and is preferably within Range of 0.5 to 10.0 microns, in particular in the range of 0.8 to 9.0 microns and more preferably in the range of 1.0 to 8.0 microns.

at of the film, the thickness of the cover layer A is generally greater than 0.4 μm and is preferably in the range of 0.5 to 10.0 .mu.m, in particular in the range of 0.8 to 9.0 μm and more preferably in the range of 1.0 to 8.0 μm.

The Total thickness of the polyester film according to the invention can vary within wide limits. It is preferred 5 to 500 μm, in particular 7 to 300 μm, preferably 10 to 100 microns.

production method

The The invention also relates to a process for the preparation of the polyester film according to the invention according to the known from the literature coextrusion.

in the Under this procedure, the procedure is that the individual Layers A, B and C of the film corresponding melts by a flat die coextruded, the resulting film for solidification one or more rolls is withdrawn, the film then biaxially stretched, the biaxially stretched film heat-set and optionally corona treated on the surface layer intended for the treatment becomes.

The Biaxial stretching (orientation) generally becomes consecutive carried out, the successive biaxial stretching, at first along (in Machine direction) and then across (perpendicular to the machine direction) is stretched, is preferred.

First, be as usual in the coextrusion process the polymer or the polymer mixtures for the individual layers in an extruder compressed and liquefied, with the optionally as additives provided additives already in the polymer or in the polymer mixture may be included. The melts are then pressed simultaneously through a flat die (slot die), and the extruded multi-layer melt is on or withdrawn several take-off rolls, wherein the melt cools and solidifies into a prefilm.

The Biaxial stretching is generally performed sequentially. there Preferably, the prefilm is first longitudinally (i.e., in the machine direction = MD direction) and then in the transverse direction (i.e., perpendicular to the machine direction = TD direction) stretched. this leads to to a spatial Orientation (orientation) of the polymer chains. The stretching in the longitudinal direction let yourself with the help of two different according to the desired stretch ratio fast rotating rollers. Used for cross stretching you generally have a corresponding clip frame in which the film on both edges clamped and then at elevated Temperature is drawn to both sides.

The Temperature at which the stretching is carried out can be done in a relative huge Range vary and depends on the desired properties of the film. In general, the longitudinal stretching is at a temperature in the range of 80 to 130 ° C and the transverse extent in the range from 90 to 150 ° C carried out. The longitudinal stretching ratio is generally in the range of 2.5: 1 to 6: 1, preferably 3.0: 1 to 5.5: 1st The transverse stretch ratio is generally in the range of 3.0: 1 to 5.0: 1, preferably 3.5: 1 to 4.5: 1. Before the transversal stretching one or both surfaces of the Coat film according to the known methods in-line. The in-line coating For example, it may improve adhesion of a metal layer or one possibly later applied ink, but also to improve the antistatic Behavior or processing behavior.

at the subsequent heat setting is the film over a Duration of about 0.1 to 10 seconds at a temperature of about 150 up to 250 ° C held. Subsequently The film is in the usual Wrapped up way.

Prefers After biaxial stretching, the non-sealable surface of the Film corona- or flame-treated according to one of the known methods. The treatment intensity is generally in the range of over 50 mN / m.

Advantages of the invention

The film of the invention is characterized by an excellent sealability, a very good Winding, a very good processing behavior and a very good look. The sealable outer layer A seals against itself, against the non-sealable cover layer C and against substrates of APET, A / CPET, CPET or metal (eg aluminum, steel, painted steel, chromed or tinned steel) and the film is thus in many areas can be used, for example, as lidding foil for (menu) dishes, pouches or as cover layer on metal sheets.

Of the Gloss (especially that of the A-layer) and transparency the film could be significantly improved (lower turbidity). Besides In the production of the film, it is ensured that the waste material (Regenerated) in an amount in the range of about 20 to 60% by weight, based on the total weight of the film, be fed back to the extrusion can, without doing the physical and optical properties the film are appreciably negatively affected, especially not her visual appearance.

The The table below (Table 1) summarizes the most important film properties according to the invention once together.

to Characterization of the raw materials and the films were in the frame the present invention uses the following measurement methods:

Measurement of the mean particle diameter d ₅₀

The determination of the mean particle diameter d ₅₀ was carried out by laser on a Master Sizer (Malvern Instruments, UK) according to the standard method (other measuring devices are eg Horiba LA 500 (Horiba Ltd., Japan) or Helos (Sympatec GmbH, Germany), which use the same measuring principle). The samples were placed in a cuvette with water and then placed in the meter. The measuring process is automatic and includes the mathematical determination of the d ₅₀ value. By definition, the d ₅₀ value is determined from the (relative) cumulative particle size distribution curve: the point of intersection of the 50% by weight ordinate value with the cumulative curve gives the desired d ₅₀ value on the abscissa axis (cf. 1 ).

Measurement of SPAN98

The determination of the SPAN98 was carried out with the same measuring device as described in the determination of the mean diameter d ₅₀ . The SPAN98 is defined as follows:

For the determination of d ₉₈ and d ₁₀ again the cumulative curve of the particle size distribution is used. The point of intersection of the 98% ordinate value with the cumulative curve gives the desired d ₉₈ value on the abscissa axis, and the point of intersection of the 10% ordinate value with the cumulative curve gives the desired d ₁₀ value on the abscissa axis (cf. 2 ).

Sealing seam strength (compared to APET)

To determine the seal seam strength, a film strip (100 mm long x 15 mm wide) is placed on the APET side of a corresponding strip of a menu dish and at the set temperature of 140 ° C, a sealing time of 0.5 s and a sealing pressure of approx. 3 bar (sealing device HSG / ET from Brugger, Germany, double-sided heated sealing jaw) sealed. Corresponding 3 the sealed strips are clamped in the tensile testing machine (eg universal testing machine TC-FR1.0TH.D09 from Zwick, Germany) and the 180 ° seal strength, ie the force required to separate the test strips, with a take-off speed of 200 mm / min and a Test temperature of 23 ° C determined. The seal seam strength is given in N per 15 mm foil strip (eg 2 N / 15 mm).

Determination of minimum sealing temperature (across from APET)

With the sealing device HSG / ET from Brugger become, as before, in the measurement of the seal seam strength described, heat-sealed Samples (sealed seam 15 mm × 100 mm), the film at different temperatures with the help of two heated sealing jaws at a sealing pressure of 3 bar and a sealing time of 0.5 s is sealed. The 180 ° seal strength was measured as in the determination of the seal seam strength. The minimum sealing temperature is the temperature at which a sealed seam strength of at least 0.5 N / 15 mm is reached (= sealing temperature).

Sealing seam strength against itself self (= FIN-seal)

to Determination of the seal seam strength two 15 mm wide film strips were superimposed and at 130 ° C, a sealing time of 0.5 s and a sealing pressure of 2 bar (device: Brugger Type NDS, one side heated sealing jaw) sealed. The seal seam strength was determined by the T-Peel method = 2 x 90 °.

Determination of minimum sealing temperature across from oneself

With the sealing device HSG / ET from Brugger become heat-sealed samples (sealed seam 20 mm × 100 mm), the film at different temperatures with the help of two heated sealing jaws at a sealing pressure of 2 bar and a sealing time of 0.5 s is sealed. From the sealed samples were test strips cut 15 mm wide. The T-seal strength was like measured in the determination of the seal strength. The minimum sealing temperature is the temperature at which a sealed seam strength of at least 0.5 N / 15 mm is achieved.

cloudiness

The cloudiness becomes according to ASTM D 1003 - 52 certainly.

shine

Of the Gloss is determined according to DIN 67530. The reflector value is measured as an optical parameter for the surface of a Foil. Based on standards ASTM-D 523-78 and ISO 2813 the angle of incidence is set at 20 °.

SV value (standard Viscosity)

The standard viscosity SV (DCE) is measured, based on DIN 53726, at 25 ° C. in dichloroacetic acid. The intrinsic viscosity (IV) of polyethylene terephthalate is calculated from the standard viscosity as follows IV = [η] = 6.907 x 10 -4 SV (DCE) + 0.063096 [dl / g]

processing behavior the foil

++++:

keine Klebeneigung an Walzen oder anderen mechanischen Teilen; keine Blockprobleme bei der Verarbeitung auf Verpackungsmaschinen; niedrige Herstellkosten

-:

Klebeneigung an Walzen oder anderen mechanischen Teilen; Blockprobleme bei der Verarbeitung auf Verpackungsmaschinen; hohe Herstellkosten.

The behavior of the film was visually evaluated during manufacture and processing.

++++:

no sticking on rollers or other mechanical parts; no block problems during processing on packaging machines; low production costs

-:

Adhesion to rollers or other mechanical parts; Block problems during processing on packaging machines; high production costs.

winding behavior

++++:

keine Blockprobleme beim Wickeln

-:

Blockprobleme beim Wickeln

The blocking of the film during winding was assessed:

++++:

no blocking problems during winding

-:

Blocking problems during winding

example 1

Chips of polyethylene terephthalate (prepared via the transesterification process with Mn as transesterification catalyst, Mn concentration: 100 ppm) were dried at a temperature of 150 ° C to a residual moisture of below 100 ppm and fed to the extruder for the base layer B. Also chips of polyethylene terephthalate and polyethylene terephthalate were dried with SiO ₂ as a pigment and fed to the extruder for the non-sealable top layer C.

Besides chips were made from a linear polyester, which consists of a amorphous copolyester with 78 mole% ethylene terephthalate and 22 mole% Ethylene isophthalate (prepared via the transesterification process with Mn as transesterification catalyst, Mn concentration: 100 ppm). The copolyester was at a temperature of 100 ° C to a residual moisture of below 200 ppm dried and the extruder for the sealable topcoat A supplied.

Then was by coextrusion and subsequent gradual orientation in longitudinal and transverse, a transparent, three-layer film with ABC structure and a total thickness of 12 μm produced. The thickness of the respective cover layers is the table 2 to remove.

Cover layer A: 100.0% by weight Copolyester with an SV value of 800

Base layer B: 100.0% by weight Polyethylene terephthalate with an SV value of 800

Topcoat C, mixture of: 80% by weight Polyethylene terephthalate with an SV value of 800 20% by weight Masterbatch of 99% by weight of polyethylene terephthalate (SV value of 800) and 1.0% by weight of Sylobloc 44 H (synthetic SiO ₂ from Grace, d ₅₀ : 2.5 μm, SPAN98: 1.8)

The production conditions in the individual process steps were:

The Film had the required good sealing properties, went well wrap and showed the desired Processing performance.

Example 2

in the Compared to Example 1, the top layer thickness of the sealable layer A from 1.5 to 2.0 microns at otherwise identical film structure and identical production method raised. The sealing properties have improved as a result, in particular, the seal seam strength has become significantly larger.

Example 3

in the Compared to Example 1, a 20 μm thick film was now produced. The Cover layer thickness of the sealable Layer A was 2.5 μm and the one of the non-sealable Layer C was 2.0 μm. The sealing properties have thereby improved even further, in particular, the seal seam strength has become significantly larger. The winding of the film has tended to improve.

Comparative Example 1

in the Compared to Example 1, the sealable topcoat A has now become so high pigmented like the non-sealable topcoat C. The winding and the processing properties of the film have gone through this measure marginally improved, however, are the sealing properties and the Optics of the film have become significantly worse.

Comparative Example 2

in the Comparison to Example 1 now became the non-sealable overcoat C significantly less pigmented. The handling of the film and the processing behavior the film has become significantly worse.

Comparative Example 3

It Example 1 from EP-A-0 035 835 was worked up. The sealing behavior, the appearance, the handling and the processing behavior of the film are worse than in the inventive examples.

The The most important properties of the films thus produced are in the Tables 2 and 3 summarized below.

Claims (15)

Multilayer biaxially oriented, transparent, sealable polyester film having a base layer B, a sealable top layer A, which is on one surface of the base layer B and a non-sealable top layer C, which is on the other surface of the base layer B, characterized in that a) the sealable outer layer A less than 0.01 wt .-% (based on the mass of the outer layer A) of external particles and b) the outer layer C contains a pigment in which - the average particle diameter d ₅₀ 2 to 5 microns, the dispersion of the particle size distribution, expressed by the SPAN98, 1.2 to 2 and - the concentration of the pigment 0.12 to 0.4 wt .-%, based on the mass of the outer layer C is. Polyester film according to claim 1, characterized that the film is a cloudiness of less than 5%. Polyester film according to claim 1 or 2, characterized the base layer B contains a thermoplastic polyester. Polyester film according to one or more of claims 1 to 3, characterized in that the polyester of the base layer B at least 90 mole% ethylene glycol and terephthalic acid units or ethylene glycol and naphthalene-2,6-dicarboxylic acid units. Polyester film according to one or more of claims 1 to 4, characterized in that as polyester of the base layer B Polyethylene terephthalate is used. Polyester film according to one or more of claims 1 to 5, characterized in that the sealable outer layer A is a copolyester contains composed of ethylene terephthalate and ethylene isophthalate units is. Polyester film according to one or more of claims 1 to 6, characterized in that the copolyester of the sealable cover layer A 60-95 Mole% ethylene terephthalate and 40-5 mole% ethylene isophthalate units having. Polyester film according to one or more of claims 1 to 7, characterized in that the pigment of the cover layer contains C0 ₂ particles Polyester film according to one or more of claims 1 to 8, characterized in that the cover layer A no added Contains particles. Polyester film according to one or more of claims 1 to 9, characterized in that the cover layer A has a thickness of 0.5 to 10 μm having. Polyester film according to one or more of claims 1 to 10, characterized in that the minimum sealing temperature of Covering layer A against an APET substrate 140 ° C or less. Polyester film according to one or more of claims 1 to 11, characterized in that the cover layer A has a gloss of greater than 150 (at a measuring angle of 20 °) having. Process for producing a polyester film according to one or more of Claims 1 to 12, comprising the steps of a) producing a multilayer film by coextrusion, b) biaxially stretching the film and c) thermosetting the stretched film, the polymer of the top layer A being less than 0, 01 wt .-% (based on the mass of the cover layer A) contains particles and the cover layer C contains a pigment, wherein - the average particle diameter d ₅₀ 2 to 5 microns, - the scattering of the particle size distribution, expressed by the SPAN98 1.2 to 2 and - the concentration of the pigment 0.12 to 0.4 wt .-%, based on the mass of the cover layer C is. Use of a polyester film after one or several of the claims 1 to 12 as a bag, cover foil or cover foil for metal sheets. Use according to claim 14, as a cover film for trays from APET, CPET or A / CPET.