MXPA97005328A - Blown poly film - Google Patents

Abstract

Film obtained by blowing, using the bubble method from aromatic polyester resins containing an aromatic tetracarboxylic acid dianhydride, having a thickness of less than 10

Description

SOPLRDO POLYESTER FILM DESCRIPTION OF THE INVENTION The present invention relates to thin films blown from aromatic polyester resins and to s? Preparation method. Thanks to their superior mechanical properties, aromatic polyester resins are suitable for use in the preparation of films which can be applied in several sectors, basically in the packaging of food, photographic films and electric insulation fields. The predominantly used films are mono-and bi-oriented. The films are prepared in general using the "casting" technique. The preparation by blowing using the bubble method faces difficulties due to the low melting strength of the polyester resin. The thickness of the cast film is generally between 10 and 100 μr. In the patent of US Pat. No. 4,145,466, it was proposed to increase the melt strength of polyester resins by incorporating therein small percentages of aromatic dicarboxylic acid dianhydrides (pyromellitic anhydride is the preferred compound). The resins thus modified are used for the preparation of bottles by blow molding and films using the bubble film forming technique. However, the thickness of the obtained film is above 10 μ. The preparation is carried out by blowing using the individual bubble method and starting with PET mixed with pyromellitic dianhydride in the extruder and then directly subjected to film formation. The preparation of films with thickness less than 10 μm from polyester resins added with pyromellitic anhydride is difficult to achieve due to the instability of the bubble and its tendency to burst. The possibility of obtaining films thicker than 10 μm, using the bubble-blowing method, is very interesting in that it would allow to obtain high quality films and, at the same time, reduce the costs with respect to the films obtained using the method of strained. It has now been unexpectedly found that it is possible to prepare films with a thickness of less than 10 μm by blowing using the single draw or double bubble method from resins with melting strength of at least 3-4 cN evenly distributed in the mass of resin from the molten bath that is going to be blown. The melting strength is generally between 3-15 cN (at 290 ° C.). Uniform values of the melt strength are obtained by mixing the molten ream bath with a dianhydride of an aromatic tetracarboxylic acid, extruding and pelletizing the resin and then extruding it again for the film forming process. It is also possible to obtain a uniform distribution of the dianhydride using sufficiently long residence times in the extruder in order to ensure the achievement of the desired melt strength. Residence times are in 10 minutes. The dianhydride or pyrite is the preferred compound and is used in amounts from 0.01 to 2% by weight. Other dianhydrides which may be used are the dianhydrides of 3,3'-4,4-diphenyl, tetracarboxylic acid, bis- (3,4-dicarboxyphenyl) ether of 3,3'4,4-benzophenoxy-tetracarboxylic acid, and bis- (3,4-dicarboxyphenyl) sulfone. The films obtained by blowing using the individual bubble method are unoriented. These films may have useful applications, for example, in the field of food packaging. The biaxially stretched films are obtained by blowing a double bubble in which the first bubble is further blown at a temperature higher than the Tg of the resin. Bi-oriented films have remarkable mechanical and barrier properties which are considerably superior to those of non-oriented films. Has been found, and this consists of a further aspect of the invention, ie films obtained from polyester resins added with a dianhydride of an aromatic tetracarboxylic acid and with liquid crystals (LCP) in amounts of less than 5% by weight and / or with a polyamide in quantity between 1 and 20% by weight, they have superior oxygen barrier properties to those of films obtained with resins added only with the dianhydride. It has also been found that thin films with superior mechanical properties can also be obtained from resins added with a dianhydride of a tetracarboxylic acid, in which the dianhydride is supplied in concentrated form with a polycarbonate resin. The concentrates generally contain an amount of dianhydride of less than 20% by weight. Particularly interesting results are also obtained with terephthalic ethylene copolymers in which up to 15% of the units derived from terephthalic acid are replaced by units derived from isophthalic acid and 2,6-naphthalene dicarboxylic acid, where the proportion of the units which are derived from isophthalic acid and naphthalenedicarboxylic acids is from 1: 3 to 3: 1. Aromatic polyester resins usable for the preparation of films of the invention are formed of polycondensation products of an aromatic dicarboxylic acid or an alkylaryl diester thereof, in particular dimethyl diester, with an aliphatic glycol with 2 to 12 atoms of carbon, in particular ethylene glycol, 1,4-butanediol and 1,4-di-ethylol-cyclohexane. The polycondensation, and the transesterification reaction when initiated from dimethyl esters, is carried out in accordance with known methods. Resins particularly suitable for the preparation of bioriented films that are used in the inner layer of beverage cans, are obtained from p &g terephthalateol ethanol with recurring units deriving from at least 85% in moles from ethylene glycol and 30 to 10% in moles from diethylene glycol and in which the total of recurring units derived from ethylene glycol and diethylene glycol is at least 90% in moles. Particularly suitable films are obtained from resins in which the recurring units deriving from diethylene glycol are between 15 and 25 mol%. The polyester resins used for the preparation of the films have an intrinsic viscosity generally between 0.5 and 0.8 dl / g. The preparation of films by means of individual bubble or double bubble blowing is carried out according to known methods. The polymer is extruded and passed to a blow head generally disposed vertically towards the direction of extrusion, from which a tubular product blown by air is obtained. Air is trapped in the bubble between the extrusion head at one end and the collection line at the other end. As the molten bath leaves the extrusion head and begins to cool, the tube expands several times in its diameter and flattens to form a flat tubular film which is then collected on tubular reels, or cut. The tubular product at the extruder outlet is cooled under a cold blown air stream. The temperature of the air and the point of contact on the outer surface of the bubble vary according to the desired properties of the p > elicula The speed of the extrusion head is kept as low as possible p > to allow the formation of the bubble (1 kg / h under the conditions illustrated in the examples), and the pressure of the blown air is regulated in order to obtain the maximum allowed expansion for the bubble (approximately 6 to 9 times the diameter of the bubble). the opening of the extrusion ring). In the case of double bubble blowing, the first bubble is also blown at a temperature higher than the Tg of the resin.

Measures and analytical properties The intrinsic viscosity measurement is carried out by dissolving 0.5 g of resin in 100 rnl of a 60/40 by weight mixture of phenol and tetrachloroethane at 25 ° C operating in accordance with ASTM 4063-8G. The melt strength measurement is carried out at 290 ° C in a Goettfert rheometer equipped with a capillary of 2 nm diameter, extruding a filament with a piston speed of 0.2 rn / s. The filament is collected between toothed wheels to which a peripheral speed acceleration of 60 mm / s2 is applied. The applied tension is the force that the filament applies to the wheels at maximum speed (1000 rnrn / s). The measurement is carried out in accordance with ASTM D 4440. The following examples are provided to illustrate, but not to limit, the invention.

EXAMPLE 1 kg / h of a mixture of crystalline PET in granules (IV 0.6 dl / g) and pyromellitic dianhydride PMDA (0.3% by weight) are continuously fed, after drying at 140 ° C under vacuum for 10 hours, to a counter-rotating twin-screw extruder operated under the following conditions: Worm speed: 150 rprn Cylinder temperature: 170 ° C Granule feeding: 10 kg / h Mold type: circular -3 mm diameter PMDA feed: 0.03 kg / h Extruder residence time: .1 minute IV of the extruded product: 0.607 dl / g Melt strength of the extruded product: 3.5-4 cN The obtained granules or polymer were then extruded to produce blown film using a Brabender individual worm extruder operating at 280 ° C and equipped with a 3 cm diameter ring mold and Haake blow head. The speed at the blow head was 1 kg / h. The residence time in the Brabender extruder was 1.5 minutes. The tubular product at the outlet of the blow head was blown with air at room temperature. Cooling air was passed over the surface of the bubble at a temperature of 23 ° C. The air pressure of the blow was regulated in order to obtain maximum expansion of the bubble (20-25 crn in diameter). The speed of film collection was 3 μm and the IV of the film was 0.65 dl / g. The barrier properties of the blown film, such as the permeability to CO2 (ml / day / cm2), was 750.

EXAMPLE 2 The preparation of Example 1 was repeated, the only difference being that the following mixture was used: 95% by weight of PET, 4.4% by weight of liquid glass Vectra A 950 (from Hoechst Celanese) and 0.3% by weight of PMDA . The film thickness obtained was 4 μ. The permeability to CO2 was 550 ml / day / rn2.

EXAMPLE 3 The preparation of Example 1 was repeated, the only difference being that a mixture of 95% by weight of PET, 4.5% by weight of Nylon 6 and 0.3% by weight of PMDA was used. The film thickness was 2.5-3 μm. The permeability to CO2 was 450 rnl / day / rn2. The measurement of CO2 permeability was carried out using a Mocon Pertron equipment operating at? 3 ° C.

Claims (10)

NOVELTY OF THE INVENTION CLAIMS

1. - Film from aromatic polyester resins containing a dianhydride of an aromatic tetracarboxylic acid obtained by the bubble blowing method, having a thickness of less than 10 μm.

2. Film according to claim 1, wherein the ream is selected from polyethylene terephthalate, polybutylene terephthalate, ethylene terephthalate copolymers in which up to 15 mole percent of ethylene terephthalate units are substituted by units deriving from aromatic dicarboxylic acids selected from isophthalic acid and / or naphthalene dicarboxylic acids.

3. Film according to claim 1, in which the resin is a polyethylene terephthalate in which the recurring units derive from at least 85% by moles of ethylene glycol and by at least 10 to 30% by moles of diethylene glycol , and in which the total of recurring units deriving from ethylene glycol and diethylene glycol is at least 90% by moles.

4. Film according to claims 1, 2 and 3 above, wherein the dianhydride is pyromellitic dianhydride employed in an amount of 0.01 to 2% by weight.

5. - Film according to claim 4, wherein the pyro-dinamic dianhydrome is mixed in the molten bath with the polyester ream, in the form of a concentrate, with a polycarbonate resin.

6. Film in accordance with the claims 1, 2, 3, 4 or 5, wherein the resin contains up to 5% by weight of a liquid crystal.

7. Film according to claims 1 to 6 above, wherein the polyester resin is added with 1 to 20% by weight of a polyarynide.

8. Film according to claims 1 to 7 above, having a thickness of less than 5 μm.

9. Biorientated film obtained in accordance with claims 1 to 8 above.

10. Film according to the preceding claims, having values of fusion resistance of at least 3-4 cN.