FI106009B - Sealing white propylene polymer film with good technical properties - Google Patents

Description

1 106009

Sealing white propylene polymer film with good technical properties

The invention relates to a biaxially stretched, white film with a propylene polymer based titanium dioxide carrier support layer as defined in the claims, and to the manufacture and use of a surface layer on one or both sides.

A film of this kind is known, e.g., from EP-A-0 244 614.

In this film, the carrier layer consists of a polymer blend of polypropylene and polystyrene 10 and contains 5-15% by weight of fine fillers.

Mixtures of calcium carbonate, silica and titanium dioxide are also suitable as fillers. The particle size is in the range of 2 to 5 micrometers. It is also known in the art to add titanium dioxide pigments coated with silica and alumina to thermoplastic resins (DE-A-2 740 561).

EP-B-0 044 515 teaches the use of aluminum, zinc, titanium, zirconium and / or magnesium oxides and certain organic substances such as long chain fatty acids, alcohols or polydimethylsiloxane • ·: Ti02 pigments in paper-based plastic coatings made e.g.

• · Λ: Polyethylene. Finally, it is known from DE-A-2 646 965 to use 20 fatty acid ester coated TiO 2 or CaCO 3 particles as filler in ·: ·: thermoplastic plastics such as polypropylene. Further described is a polypropylene film containing TiO2 particles coated with SiO2 and Al2O3, optionally coated with an organic polymeric silicon compound or polyol (DE-A-3,817,909).

II *. The TiO2 pigment, which is capable of *: ** resisting yellowing in polymers such as polypropylene, is known from U.S. Patent No. 100,245. The TiO 2 -: V: pigment is coated with an inorganic oxide and then coated with an organic acid. However, Fl-100245 does not disclose films. # It only mentions the very general form of coated titanium dioxide! ! 30 use of pigments in the polymer but no indication is given of the amounts of titanium dioxide pigments the polymers should contain.

GB-A-A-1,047,539 discloses titanium oxide particles having improved wetting and dispersion properties in an organic medium such as polypropylene. The titanium particles are first coated with metal oxide and then with alkyl silicate. However, GB-A 1 047 539 does not disclose 2 106009 films. Nor does it disclose the particle size of titanium dioxide particles or the amount of titanium dioxide used.

It is therefore an object of the present invention to improve the whiteness and mechanical properties of such films. In addition, the film must have good aging properties. This means that polymers subjected to electromagnetic radiation such as light, and in particular UV radiation, exhibit only slight cleavage or brittleness, resulting in a deterioration and yellowing of the mechanical properties of the white film. The yellowing tendency is particularly troublesome if the white 10 film is used as an article wrapper, e.g., as a packaging film, a label, or as a coating film for cardboard, cardboard, or paper. In addition, the film must provide a good barrier to light, in particular UV radiation, so that it can be used in particular for the packaging of radiation-sensitive goods such as fatty foods. It is a further object of the invention to provide an economical method of making this film.

The film according to the invention is a film having the characteristics of the «· * ·" mentioned in claim 1, which can be produced by the process described in claim 6. Suitable modifications of the film or process are disclosed in the dependent claims.

20 The propylene polymer forming the backing layer of the film: ·: ··: is an isotactic homopolymer or copolymer of propylene and ethylene or alpha-olefins having from 4 to 8 carbon atoms or a mixture of propylene homopolymers and propylene copolymer ..... / or other polyolefins, especially those containing 2 to 6 carbon atoms. 25 polyolefins such that the mixture contains at least 50%, in particular at least 75% by weight of propylene homopolymer. Suitably, the proportion of isotactic homopolymers soluble in n-heptane is up to 15% by weight. In copolymers, the amount of comonomers formed by ethylene and alpha-olefins having from 4 to 8 carbon atoms is generally no more than 10% by weight of the copolymer. , 30 calculated. Preferred comonomers are ethylene and butene (1).

Suitable polyolefins in the polymer blend are HDPE, LDPE and LLDPE, in which case the proportion of these polyolefins in any case does not exceed 15% by weight based on the polymer blend. The melt index of these base layer polymers is suitably in the range 0.5 g / 10 min to 8 g / 10 min at 230 35 ° C with a load of 2.16 kp (DIN 53 735), particularly in the range 1.5 g / 10 min to 4 g / 10 min

3 106009

The carrier layer contains titanium dioxide particles. Titanium dioxide particles are mainly composed of rutile having a higher opacity than anatase. In a preferred embodiment, at least 95% by weight of the titanium dioxide particles are rutile. They can be prepared in the usual way e.g.

5 by the chloride or sulphate method. They have a proportion of 7 to 12% by weight based on the base layer and have a relatively small average particle size, preferably 0.15-0.30 micrometers.

In addition, the titanium dioxide particles have a coating consisting of inorganic oxides, which is conventional in the TiO2 white pigment of paper and paints to improve light resistance. TiO2 is known to be photoactive. Under the influence of UV radiation, free radicals are formed on the surface of the particles. These free radicals can migrate to the paint film forming components, resulting in cleavage reactions and yellowing. Oxides which are particularly suitable for coating are aluminum, silicon, zinc or magnesium oxide 15 or mixtures of two or more of these compounds. TiO 2 particles having a coating consisting of a plurality of such compounds are described, for example, in EP-A-0 044 515 and EP-A-0 078 633. The coating further contains compounds having organic, polar and non-polar groups. The organic '· [' '] compounds must be sufficiently thermally stable when the film is extruded from the polymer melt. Polar groups include, for example, -OH, -OR, -COOX (X = R, H or Na, R = 1-34 carbon atoms). Preferred organic compounds are alkanols and fatty acids having from 8 to 30 carbon atoms in the alkyl group, particularly fatty acids and primary n-alkanols having from 12 to 24 carbon atoms, as well as t ... .

* · ·; · * The coating consisting of titanium dioxide particles has: Y: usually 1 to 12, especially 2 to 6 g of inorganic oxides and 0.5 to 3, especially: ***: 0.7 to 1.5 g of organic compound per 100 g titanium oxide particles. The particles are · · · coated in an aqueous suspension. The inorganic oxides are doped in an aqueous suspension. In particular, water-soluble compounds such as alkali compounds, in particular sodium aluminum oxide, aluminum hydroxide, aluminum sulphate, aluminum nitrate, sodium silicate (water glass) or silica.

Inorganic oxides such as Al 2 O 3 and SiO 2 also refer to hydroxides or their various dewatering intermediates, such as oxide hydrates 35 (hydroxides), without specifying their composition or structure. After annealing and grinding in aqueous suspension, the hydroxides, e.g., aluminum and / or silicon hydroxide, are precipitated on the surface of the TiO 2 pigments and then the pigments are washed and dried. The precipitation can thus be carried out directly in the suspension formed during the manufacturing process after annealing and subsequent wet grinding. Ko. the oxides and / or hydroxides of the metals are precipitated from the water-soluble metal salts within a defined pH range. For aluminum, for example, aluminum sulfate in aqueous solution (pH less than 4) is used and the hydroxide is precipitated in a pH range of 5-9, preferably 7 to 8.5, by the addition of aqueous ammonia or sodium hydroxide. When starting from a water glass or alkaline aluminate solution, the pH of the TiO2 suspension to be treated must be strongly within the 10 basic range (pH above 8). It is then precipitated at pH 5-8 by addition of a mineral acid such as sulfuric acid. After precipitation of the metal oxides, the suspension is stirred for an additional 15 minutes to about 2 hours, whereupon the precipitated layers undergo maturation. The coated product is isolated from the aqueous dispersion and, after washing, dried at an elevated temperature, in particular 70-110 ° C.

15 Preferably, the absolute particle size of titanium dioxide should not exceed 10 micrometers, since larger particles impair the optical properties of the film and the uniformity of film production.

:: Good whiteness can be achieved with a titanium dioxide particle content of 7-12% based on the carrier layer (base layer).

| y 20 The surface layers coated on one or both sides of the carrier layer can be both cold and heat sealable. These layers may cover one or both sides of the base layer.

«

The two-sided surface layers may be of the same or different material. The conventional heat sealing layer has a softening point of at least 10 ° C

• · 25 lower than the softening point of the carrier layer. Preferably, the sealing layer is *: ** ethylene homopolymer (high density polyethylene or low density polyethylene), LLDPE, mixed polymer consisting of propylene: [[[: main component and ethylene preferably 4% ethylene] -10% by weight (based on copolymer), copolymer formed. 30 propylene as the main component and butene (1) with a butene content of ** preferably 10-15% by weight (based on the copolymer), a terpolymer consisting of propylene, ethylene and an alpha-olefin having from 4 to 10 carbon atoms, preferably is 93.2 to 99.0% by weight of propylene, 0.5 to 1.9% by weight of ethylene, and 0.5 to 4.9% by weight of 35 alpha-olefins containing 4 to 10 carbon atoms or a mixture of two or more of such polymers. The distribution of comonomers in the polymers is essentially statistical.

Suitable cold sealing layers consist of polymers based on natural or synthetic rubber. Suitable outer surface layers 5 also consist of acrylates as described in EP-A-0 214 790, EP-A-0 254 417 and CH-632 777, or vinylidene chloride copolymers as described in EP-A-0 088 535 These compounds must be bonded with an adhesive layer to the underlying polyolefin layer. Suitable primers are also disclosed in said publications.

10 When the film is used as a packaging material, a lubricant must be added to the top layer (s) to improve the sliding ability to achieve sufficient machine runnability and to avoid friction during bag filling. Suitably the lubricant is a polydialkylsiloxane, preferably one having from 1 to 4 carbon atoms in the alkyl group, wherein the amount of polydialkylsiloxane used in the surface layer or layers is from 0.2 to 2.5% by weight, preferably from 0.5 to 1.6% by weight. .

* · *: The total thickness of the film is 20-120, preferably 25-60 micrometers, wherein the surface layer (s) is in each case 0, 2-2, preferably 0-5-5 µm: 1 micrometer.

In order to further improve certain properties of the film ·: ··: according to the invention, both the base layer and the top layer (s) may contain appropriate additives in each effective amount, and in particular antistatic agents and nucleating agents (nucleating agents) may be mentioned. ..... For example, dibenzylidene sorbitol or sodium benzoate may be used as nucleating agents, and dibenzylidene sorbitol or antistatic agents, such as sodium benzoate, and ethoxylated amines or: V: fatty acid amides. In particular, the addition of machining stabilizers to the core layer has proved positive. These are compounds having mm ['. the task is to prevent the thermal degradation of the polymers in the manufacture of the film! ! 30 period. Such compounds include phosphite stabilizers and / or diphosphite stabilizers such as tris (2,4-ditert-butylphenyl) phosphite and bis (2,4-ditert-butylphenyl) pentaerythritol diphosphite in an amount of 0.05 to 0.3 % by weight based on core layer. It has also proved to be particularly advantageous to add an optical brightener having an application rate of 100 to 500, preferably 150 to 250 ppm, based on the core layer 35. Specifically, to improve workability, 0.1 to 1% by weight of an organic or inorganic antifouling agent may be added to the surface layer or layers. Suitable anti-caking agents include, for example, organic polymers such as polyamides, polyesters, polycarbonates and the like, which repel the surface layer polymer and are in particulate form. Inorganic particles, in particular silica particles, are also suitable.

The film is prepared by extruding the support layer or co-molding the individual layers to form melt-flowable polymeric materials through a flat die, hardening and bonding the melt, then stretching biaxially in the longitudinal and transverse directions and finally heat bonding. The film is biaxially stretched by heating the film and stretching it first in the longitudinal direction and then in the transverse direction. The longitudinal stretching takes place, for example, at 120-130 ° C in a ratio of 5: 1 to 7: 1 and then in the transverse direction at 160-170 ° C in a ratio of 8: 1 to 10: 1. The heat application is carried out for about 0.5 to 10 seconds at 150 to 160 ° C.

If necessary, the surfaces of the surface layers can be further surface treated after heat bonding, for example by corona or flame treatment, to improve the adhesion of other coatings to the film and to improve the adhesiveness or laminability or the printability.

Preferably, the carrier layer is formed by a masterbatch technique, i.e., depending on the desired content of the titanium dioxide particles, the extruder 20 is fed with a polypropylene feedstock and a titanium dioxide masterbatch to form a:: ·· earth carrier layer. The term masterbatch is known to mean a granular, dust-free, high-filler concentrate of a plastic feedstock used as an intermediate in ..... pulp processing, eg as an aggregate-free filler prior to • · 25 extrusion to produce a certain amount of filler. : ** containing moldings. The masterbatch used to increase TiO 2: V used in accordance with the invention is known to contain more than 30% by weight, preferably 40 to 75% by weight of TiO 2 particles, based on the total weight of the polymers and fillers, and in the form of cylindrical or lenticular granules. Ti02 Mastebatch! Polyolefins, copolymers containing from 2 to 8 carbon atoms in each olefin unit, or mixtures of such compounds are used as carrier polymer.

A preferred carrier polymer is polypropylene, polyethylene or a mixture of polypropylene and polyethylene.

Both masterbatches have a bulk density of 700 to 1500 g / l, preferably 35 950 to 1250 g / l. The bulk density is determined in accordance with DIN 53 466. The bulk density ratio of the polypropylene raw material to the masterbatch bulk density is less than 0.80, preferably less than 0.65.

The film according to the invention is very white, has good technical properties and has a density of 0.9 to 1.1, in particular 0.95 to 1.05 g / cm 3.

Due to its advantageous properties, in particular its good and durable whiteness, the film according to the invention is suitable as a packaging material and also for technical purposes, for example as a laminating film, a label film or an adhesive tape carrier film.

The invention is further described in the following examples.

Example 1

A polypropylene film co-extruded with a heat-sealable topsheet was coextruded from a statistical ethylene-propylene copolymer (C2 content 4.5 wt.%) (ABA film) at about 270 ° C through a flat die. The film core layer (molten) mixture contained 91.0% by weight of polypropylene and 8.5% by weight of TiO 2 (rutile), with an average particle diameter of 0.2 micrometers, coated with an inorganic Al 2 O 3 coating (4 g / 100 g). TiO 2) and an organic stearic acid coating (1 g / 100 g · · · · · · Ti · 2), whereby the core layer blend is formed with: T: 84.5 wt% polypropylene and 15.5 wt% masterbatch with contains 55 to 20 parts by weight of coated TiO2 and 45 parts by weight of polypropylene. The bulk density is • · 530 g / l for polypropylene and 750 g / l for TiO2.

The film was then stretched lengthwise (stretch ratio 5: 1) and then transversely (stretch ratio 10: 1). The film thickness of the biaxially oriented film was 30 micrometers, with the sealing layers having a thickness of 0.8 micrometers each. The film density was 0.98 g / cm 3.

• · ··· * Example 2: Y: Example 1 was repeated with TiO 2 particles similarly: ***: coated with Al 2 O 3. Stearic acid ♦ ·· * was used as an additional coating for TiO2 particles. instead of polydimethylsiloxane (1.5 g / 100 g TiO 2).

Comparative Example 1 Example 1 was repeated so that the TiO 2 particles were similarly coated with Al 2 O 3 (4 g / 100 g TiO 2) and stearic acid (1 g / 100 g TiO 2). In addition, the core layer of the film contained 6% by weight of masterbatch containing 70 parts by weight of CaCO 3 and 30 parts by weight of polypropylene. The film density was 0.72 g / cm 3.

8 106009

Comparative Example 2

Comparative Example 1 was repeated with TiO 2 particles coated with Al 2 O 3 (4 g / 100 g TiO 2) only.

Comparative Example 3 Example 1 was repeated with TiO 2 particles coated with Al 2 O 3 (4 g / 100 g TiO 2).

Comparative Example 4

Example 1 was repeated with TiO 2 particles coated with stearic acid alone (1 g / 100 g TiO 2).

10 Comparative Example 5

Example 1 was repeated with the TiO 2 particles uncoated.

The whiteness values, yellowing tendency, elastic modulus, tensile strength and tensile elongation of the resulting film are summarized in the following table.

Whiteness was determined by a remission photometer "ELREPHO", manufacturer

Zeiss Oberkochem (DE), standard light C, 2 degree standard eyepiece. Whiteness is ·. * ·: Defined as WG = RY + 3RZ - 3RX, where WG = whiteness, RY, RY, RX =: corresponding reflection factors for Y, Z and X color measurement filters.

A barium sulphate pressed disc (DIN 20 5033, part 9) was used as the whiteness standard. The membrane sample (DIN A4 size) was irradiated for several days in the apparatus ·; ·: Suntest CPS, manufactured by Heraeus, Hanau (DE). The irradiation intensity was 765 W / m2 and after irradiation was visually compared with the non-irradiated sample.

The modulus of elasticity, the tensile strength and the tensile elongation were determined according to DIN 53 457 25.

• ·

It is clear from the table that either the whiteness of the film or: Y: the mechanical properties diminish as soon as the carrier film contains other inorganic particles; or. The TiO2 particles are not coated or not merely coated with an organic or inorganic coating.

• ♦ · • · · • · 9 106009

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Claims (9)

10 106009 A biaxially stretched white film having a carrier layer based on propylene polymers having a surface layer on one or both sides, characterized in that the carrier layer contains titanium dioxide particles, wherein the titanium dioxide particles are coated with at least one inorganic oxide and at least one the proportion is from 7 to 12% by weight based on the support layer and the average particle size of the titanium dioxide particles is 0.15-0.3 micrometers. Film according to Claim 1, characterized in that the titanium dioxide particles are mainly rutile. Film according to Claim 1 or 2, characterized in that the titanium dioxide particles are coated with 1 to 12, in particular 2 to 6 grams, of the inorganic oxides and 0.5 to 3, in particular 0.7 to 1.5 grams of organic v: compounds per 100 9 titanium dioxide particles. Film according to one or more of Claims 1 to 3, characterized in that the titanium dioxide particles are coated with inorganic oxides and organic compounds based on aluminum, silicon, magnesium and / or zinc from the group of fatty alcohols, fatty acids and polydiorgano .. ... siloxanes, especially polyalkyl hydrogen siloxanes and / or polydialkyl siloxanes, wherein the alkyl groups have from 1 to 6, preferably from 1 to 3 carbon atoms. Film according to one or more of Claims 1 to 4, characterized in that the film has a density of 0.9 to 1.1 g / cm 3, in particular 0.95 to 1.05 g / cm 3. A method according to one or more of claims 1 to 5. . 30 film, characterized by coextruding a mixture of a · · · '· carrier layer consisting of a non-inorganic polypropylene base stock and a masterbatch comprising coated titanium dioxide particles and a polypropylene base layer and a surface layer or polymer layer formed. 35 stretching longitudinally and transversely and finally heat-sealing. 11 106009 A process according to claim 6, characterized in that the titanium dioxide particles are present in the masterbatch in a proportion of 40 to 75% by weight based on the mixture of propylene polymer mass and titanium dioxide particles. Method according to claim 6 or 7, characterized in that the masterbatch has a bulk density of 700 to 1500, in particular 950 to 1250 9 / I (DIN 53466). Use of the film according to one or more of claims 1 to 5 as an adhesive tape film, a packaging material, a label or a laminating film. • • • • • • • • • • • 1 1 • • • • • 1 1 • • • • • • • • • • • • • • • • • • • • • • • • ••••••••••••••••••••••• 1 · · · · · · · • · · · · · · · · · · · · · · · · · · · · · · 106 106009