MXPA96005609A - Polimeri films - Google Patents

Abstract

The present invention relates to biaxially oriented polyolefin films having a base layer of a propylene polymer with a printable outer layer thereon, the base layer containing at least 1000 ppm of a monoester of fatty acid glyceryl, based on the weight of the base layer and the outer layer includes a mixture of a crosslinked silicone antiblock agent and an inorganic antiblocking agent. Such films have good hot and cold slip characteristics for treated and untreated film surfaces

Description

POLYMERIC FILMS Description of the invention This invention is concerned with polymeric films and in particularly polypropylene films that have good characteristics of cold and hot slippage for treated film surfaces and not treated.

It is known in the art of polypropylene films modification of the slip characteristics of such films by a variety of methods. One such method is to incorporate to the movies one or more additives in a core or core layer of the films, the additives are such way that they migrate from the central layer through the layers of the film externally in such a way that they form a surface layer on the outer layers Of the movies. Common to such additives are the fatty acid amides and glyceryl esters of long chain fatty acids.

Polyolefin films containing migrating additives can generally be printed, especially if the surface of the films being printed undergoes a treatment which increases the surface energy of the films, such methods are well known in the art of films of polypropylene.

However, a main disadvantage of using migrating additives to modify the slip characteristics of the films of polypropylene is that the slip characteristics tend to change with the weather. Thus, immediately after the films have been manufactured, REF: 23467 when little or nothing of the slip additive has migrated to the surface of the film, the films have relatively poor slip properties, while after storage of the films by some time, the films can become excessively slippery with the consequent difficulties in the use of the films in the packaging machinery. In addition, the increased amounts of additives that migrated onto the surface of the film for a period of time can reduce the optical properties of the films. An alternative procedure to the problem of modifying the slip characteristics of polypropylene films has been to include non-migrating slip agents on the outer surfaces of such films. While antiblocking agents which are usually included in the outer surface layers of the polypropylene films modify the inherently poor slip properties of the polymers from which the outer surfaces are manufactured, such agents generally can not be used alone. to provide the degree of slippage which is required for such films. Hence, the use of separate migrating slip agents. Alternatively, a slip agent can be coated on the outer surface of the films, instead of being incorporated with the body of the film. Silicones, and in particular polydiorganosiloxanes, have hitherto been proposed as non-migrating slip additives, which impart slip, to be added to the outer layers of polypropylene films. They have also been used as skid-imparting coatings, which are applied to the outer surfaces of polypropylene films. The use of these materials has the advantage that the slip properties of films in general do not change with time, their slip properties are substantially constant from manufacture and throughout storage over substantial periods of time. A major disadvantage of using silicones to modify the slip characteristics of the films is that they tend to reduce the printability of the films, especially when using water-based inks. In addition, the treatment of the films to improve their surface energy and hence their printing capacity can not generally be used on the surfaces of the film which contain composite silicone or have a silicone coating, since the treatment tends to have a highly adverse effect on the silicone, for example leading to a reduction in the slip characteristics of the film surface and / or the thermal sealing capability of the film surface when such surface is otherwise thermally sealable. According to the present invention, there is provided a biaxially oriented polyolefin film comprising a base layer comprising a propylene polymer with a printable outer layer thereon, the base layer containing at least 1000 ppm of a glyceryl monoester of a fatty acid, based on the weight of the base layer and the outer layer includes a mixture of a crosslinked silicone antiblock agent and an inorganic antiblocking agent. Films according to the present invention have shown good slip properties since manufacture, such properties are obtained with much less than a change in slip properties over a period of time. In addition, a particularly good control of the slip properties can be obtained in comparison with the films which use a silicone in the outer layer instead of a migrating fatty acid amide as a slip agent. In addition to these advantages, the films according to the present invention have shown good optical properties and good machinability. These properties have also been observed in combination with a good printing capacity, especially with water-based inks. The base layer is formed from a propylene polymer which is preferably a propylene homopolymer or a propylene polymer and in a minor amount, preferably less than 2% by weight, of a comonomer, for example ethylene. The base layer of the films of the present invention contains at least 1000 ppm of a glyceryl monoester of a long chain fatty acid and preferably at least 1500 ppm, based on the weight of the base layer. By increasing the amount of the glyceryl monoester in the base layer, the slippage of the films generally increases, but it reaches a point where a further increase in slippage with the increased amounts of the glyceryl monoester is marginal and may still be accompanied by undesirable effects. It is therefore preferred not to use more than about 6000 ppm of a glyceryl monoester based on the weight of the base layer. The particularly preferred range of glyceryl monoester amounts for the base layer is from 1000 to 4500, based on the weight of the base layer. Examples of glyceryl monoesters which may be used include glyceryl monostearate, glyceryl acid monobenehate and hydroxy fatty acid glycerides, for example glyceryl tri- (i2-hydroxy) stearate. Other migratory additives may be included in the base layer, for example fatty acid amides. The amount of the fatty acid amide in the base layer is preferably not more than 5000 ppm based on the weight of the base layer, since higher amounts may adversely affect the ability of the outer layer to heat seal at low pressures. when it is a thermally sealable polymer. Advantageously, the amount of fatty acid amide in the outer layer is less than 4000 ppm and more especially from 1000 to 3750 ppm based on the weight of the base layer. If the amount of fatty acid amide is greatly reduced, the beneficial effects of its presence may not be observed. The fatty acid amides and derivatives thereof, which can be used as the slip agent in the base layer of the films according to the present invention, include fatty acid amides of 10 to 40 carbon atoms and corresponding hydroxy fatty acids and derivatives thereof, for example erucamide, oleamide, ethylene bis-steramide, stearyl erucamide and oleyl palmitamide. The basecoat also preferably contains an anti-static migrant agent, for example a bis- (hydroxyalkyl) -alkyl (of 10 to 20 carbon atoms) amine, preferably derived from an alkylamine containing from 12 to 18 carbon atoms. The hydroxyalkyl group of such compounds is preferably a 2-hydroxyethyl group. An example of a specific antistatic agent which can be used in the base coat is bis- (2-hydroxyethyl) tallow aniña The amount of the migrating antistatic agent used in the base layer is preferably 0.01 to 0.20% by weight of the base layer. The outer layer is preferably formed of a polyolefin which is or can be rendered printable, for example by a suitable surface treatment. The outer layer is also preferably thermally sealable. Examples of polyolefins which can be used to form the outer layer include copolymers of propylene with at least one of ethylene and 1-butene, for example copolymers of propylene / ethylene and terpolymers of propylene / ethylene / 1-butene. The outer layer can also be formed from a mixture of two or more olefin polymers. The outer layer of the films of the present invention contains a mixture of a cross-linked silicone antiblock agent and an inorganic antiblocking agent. The total amount of these two types of antiblocking agent present in the outer layer is preferably not more than 5000 ppm, based on the weight of the outer layer, the larger amounts tend to reduce the heat sealing capacity of the outer layer when such The layer is made of a thermally sealable polymer. The total amount of these antiblocking agents is preferably less than 4000 ppm, based on the weight of the outer layer and more preferably 1000 to 3750 ppm. If an insufficient amount of the anti-blocking agent is present, the films will exhibit blocking. It is generally preferred that the mixture of the antiblocking agents in the outer layer contain 25 to 75% by weight, preferably 40 to 60% by weight, of crosslinked silicone and 75 to 25% by weight, preferably 60% by weight. to 40% by weight, of an inorganic antiblocking agent. The cross-linked silicone antiblock agent is preferably as described in EP0242055-A. The inorganic antiblocking agent can be selected from the antiblock agents proposed hitherto in the art of polypropylene films, for example silica and silicates. The average particle size of each antiblock agent will usually be in the range of 1 to 6 microns. In general, the relative sizes of the two different types of the antiblocking agent are not significant to achieve the effect obtained by the present invention and therefore an anti-blocking agent can have a relatively small average particle size, while the other has a size of average particle relatively large. However, if the average particle sizes of the two types of antiblocking agent are significantly different, the adverse effects caused by such differences can be reduced by adjusting the amount of the fatty acid amide in the base layer, since this can reduce the effects of such differences in the average particle size. The films according to the present invention may consist only of the two specified layers. However, it is generally preferred that the base layer has an additional layer thereon, remote from the specified outer layer, whereby the three-layer films are manufactured. Additional layers may also be present, for example between the specified outer layer and the base layer or between the base layer and an additional layer or layers on the side of the far base layer of the specified outer layer. The additional outer layer is preferably of an olefin polymer, for example of the same composition as the specified outer layer. However, it is preferably of a composition different from that of the particularly specified outer layer, because this may allow differential slip properties to be obtained between the outer surfaces of the films, even if the two outer layers contain substantially identical blends. of a cross-linked silicone antiblock agent and an inorganic antiblocking agent. Particularly preferred films according to the present invention have an outer surface formed of a propylene / ethylene copolymer with the other surface formed of a mixture of a propylene / ethylene copolymer and a propylene / ethylene / 1-butene terpolymer. Such films have shown surface slippage, which makes them of particular advantage in the wrapping of articles wherein the slippage of the film to the article is desirably lower than the slippage from film to film for the wrapped articles. It is generally preferred not to add a fatty acid amide in the outer layer or layers of the films of the present invention, other than that which may by necessity be present as a dispersing agent for the antiblocking agents which are included in these layers . The outer layer or layers of the films of the present invention can include an antistatic agent, preferably an alkyl sulfonate. It is generally preferred to subject the outer layer containing the mixture of the cross-linked silicone antiblocking agent and the inorganic antiblocking agent to a treatment which increases its surface energy, for example corona discharge treatment or flame treatment. If desired, one or more layers of the films of the present invention may include organic or inorganic particles which induce the formation of microvoids when biaxially stretched. In general, the hollow layer will be the base layer, but other layers which may be present that can be recessed, these are usually those consisting of a propylene polymer with substantially all of the propylene derived units. Examples of the particulate materials which can be used to induce void formation include polyamides, for example nylons, polyesters, for example polyethylene terephthalate and polybutylene terephthalate, chalk, barium sulfate and zinc sulphide. In general, these particulate materials should have an average particle size of 1 to 10 microns, in order to effect the formation of voids. Any of the various layers of the films of the present invention can, if desired, contain a pigment, for example titanium dioxide. The films according to the present invention can be produced by known methods, for example by co-extrusion of the base layer and the specified outer layer and with any additional layer which is desired and then biaxially stretching the extrusion product. The biaxial stretching can be carried out simultaneously in the extrusion direction and in the transverse direction when using the so-called bubble process. However, it is preferred to perform the stretch sequentially by first stretching the tape in the extrusion direction and then in the transverse direction. Sequential stretching is particularly preferred when it is desired to manufacture films having one or more layers which include microvoids. The following examples are given by way of illustration only. In each case, the films were tested for their slip properties according to the following methods. The cold slip was tested by using a "Davenport" slip tester with a 700 g harrow and a crawl speed of 80 cm / min. The hot slip was tested by using a RDM CF800 slip test apparatus at 40 ° C, 60 ° C and 80 ° C with a 700 g harrow. Hot film / film slip tests were carried out by clamping the film to the hot plate of the test apparatus. The luster of the film was tested at 20 ° C and the thermal seal threshold temperature of the films was tested with the use of a gradient bar. Film / film rub tests were carried out by initially wrapping the film to be tested around a block with the surface of the treated film on the outer side. The film was thermally sealed around the block with the seal along the side of the block. Then the wrapped blocks were heated in an oven at 100 ° C until the inside of the blocks had reached 40 ° C and then the film / film hot slip was determined by rubbing two heated blocks together. The determination was made on a subjective scale of 1, which is the most slippery, upwards.

Example 1 A three-layer polymeric tape is produced by coextruding a base layer of propylene homopolymer which contains 3.5% by weight of chalk (average particle size 3.5 microns), 1.6% by weight of titanium dioxide, 0.03% by weight of bix-ethoxylated amine, 0.064% by weight of erucamide and 0.128% by weight of glyceryl monostearate, with two outer layers on each surface of the base layer. The two outer layers consisted of a propylene / ethylene / 1-butene copolymer (91.4% by weight of propylene, 3.8% by weight of ethylene, 4.7% by weight of 1-butene) containing 0.2% by weight of a crosslinked silicone (Tospearl 120, former GE Silicones - average particle size 2 microns), 0.1% by weight of an additional crosslinked silicone (Tospearl 145, ex GE Silicones - average particle size 4.5 microns) and 0.125% by weight of silica with an average particle size of 4 microns. Then the coextruded three-layer tape was stretched 4.5 times in the extrusion direction by passing it over a series of 120X rolls rotating at differential peripheral speand then 10 times in the transverse direction in a 160 ° endless oven. C. Then the first outer layer of the biaxially stretched film was subjected to corona discharge treatment and the film was finally rolled up. The film had a total thickness of 40 microns, each outer layer was 1.5 microns thick. The coefficient of friction for the metal treated face, evaluated as described above at 40 ° C, was 0.19.

EXAMPLE 2 A three-layer polymeric tape is produced by co-extruding a base layer of propylene homopolymer containing 3.5% by weight of chalk (average particle size 3.5 microns), 1.6% by weight of titanium dioxide, 0.03% by weight of bix-ethoxylated amine, 0.064% by weight of erucamide and 0.328% by weight of glyceryl monostearate, with two outer layers on each surface of the base layer. The two outer layers consisted of a propylene / ethylene / 1-butene copolymer (91.4% by weight of propylene, 3.8% by weight of ethylene, 4.7% by weight of 1-butene) containing 0.1% by weight of a crosslinked silicone (Tospearl 120, former GE Silicones - average particle size of 2 microns), 0.15% by weight of an additional crosslinked silicone (Tospearl 145, former GE Silicones - average particle size 4.5 microns) and 0.165% by weight of silica with a average particle size of 4 microns. Then the coextruded three-layer tape was stretched 4.5 times in the extrusion direction by passing it over a series of rollers at 120 ° C rotating at differential peripheral speand then 10 times in the transverse direction in an endless belt oven. 160 ° C. Then the first outer layer of the biaxially stretched film was subjected to corona discharge treatment and the film was finally rolled up. The film had a total thickness of 40 microns, each outer layer was 1.5 microns thick. The coefficient of friction for the metal treated face, evaluated as described above at 40 ° C was 0.18.

Example 3 comparison) A three-layer polymeric tape is produced by coextruding a base layer of propylene homopolymer containing 3.5% by weight of chalk (average particle size 3.5 microns), 1.6% by weight of titanium dioxide, 0.03% by weight. weight of bix-ethoxylated amine, 0.064% by weight of erucamide and 0.128% by weight of glyceryl monostearate, with two outer layers on each surface of the base layer. The two outer layers consisted of a propylene / ethylene copolymer (3.7% by weight of ethylene) containing 0.1% by weight of silica with an average particle size of 4 microns. Then the coextruded three-layer tape was stretched 4.5 times in the extrusion direction by passing it over a series of rollers at 120 ° C rotating at differential peripheral speand then 10 times in the transverse direction in an endless belt oven. 160 ° C. Then the first outer layer of the biaxially stretched film was subjected to corona discharge treatment and the film was finally rolled up. The film had a total thickness of 40 microns, each outer layer was 1.5 microns thick. The coefficient of friction for the metal treated face, evaluated as described above at 40 ° C was 0.23.

Example 4 A three-layer polymeric tape is produced by co-extruding a base layer of propylene homopolymer containing 3.5 wt.% Chalk (average particle size 3.5 microns), 1.6 wt.% Titanium dioxide, 0.03 wt.% t-ethoxylated amine, 0.06% by weight of erucamide and 0.33% by weight of glyceryl monostearate, with two outer layers on each surface of the base layer. The two outer layers that were formed consisted of a propylene / ethylene / 1-butene copolymer (90.7% by weight of propylene, 3.7% by weight of ethylene, 5.6% by weight of 1-butene) containing 0.10% by weight of a crosslinked silicone (Tospearl 120, ex GE Silicones - average particle size of 2 microns), 0.15% by weight of an additional crosslinked silicone (Tospearl 145, ex GE Silicones - average particle size 4.5 microns) and 0.165% by weight of silica with an average particle size of 4 microns. Then the coextruded three-layer tape was stretched 4.5 times in the extrusion direction by passing it over a series of rollers at 120 ° C rotating at differential peripheral speeds and then 10 times in the transverse direction in an endless belt oven. 160 ° C. Then the first outer layer of the biaxially stretched film was subjected to corona discharge treatment and the film was finally rolled up. The film had a total thickness of 40 microns, each outer layer was 1.2 microns thick. The treated face of the film had good slip properties in hot and cold, to themselves and to the metal. It is noted that in relation to this date, the best method known by the applicant to carry out the aforementioned invention, is the conventional one for the manufacture of the objects to which it relates. Having described the invention as above, property is claimed as contained in the following

Claims (9)

1. Claims 1. A biaxially oriented polyolefin film comprising a base layer consisting of a propylene polymer with a printable outer layer thereon, characterized in that the base layer contains at least 1000 ppm of a monoester of glyceryl of a fatty acid, based on the weight of the base layer and the outer layer includes a mixture of a crosslinked silicone antiblock agent and an inorganic antiblocking agent.
2. 2. A film according to claim 1, characterized in that the base layer contains no more than 6000 ppm of a glyceryl monoester of a fatty acid, based on the weight of the base layer.
3. 3. A film according to any of the preceding claims, characterized in that the base layer contains from 1000 to 4500 of a glyceryl monoester of a fatty acid, based on the weight of the base layer.
4. 4. A film according to any of the preceding claims, characterized in that the glyceryl monoester of a fatty acid comprises glyceryl monostearate, glyceryl monobehenate or glyceryl tri- (12-hydroxy) stearate.
5. 5. A film according to any of the preceding claims, characterized in that the mixture of antiblocking agents in the outer layer is present in an amount of not more than 5000 ppm, based on the weight of the outer layer.
6. 6. A film according to any of the preceding claims, characterized in that the mixture of antiblocking agents in the outer layer is present in an amount of 1000 to 3750 ppm, based on the weight of the outer layer.
7. 7. A film according to any of the preceding claims, characterized in that the mixture contains from 25 to 75% by weight of crosslinked silicone and from 75 to 25% by weight of an inorganic antiblocking agent.
8. 8. A film according to claim 7, characterized in that the mixture contains from 40 to 60% by weight of crosslinked silicone and from 60 to 40% by weight of an inorganic antiblocking agent.
9. 9. A film according to any of the preceding claims, characterized in that the average particle size of the mixture of antiblocking agents in the outer layer is 1 to 6 microns.