MXPA96006163A

MXPA96006163A - Multiple layer film based on polyethylene

Info

Publication number: MXPA96006163A
Application number: MXPA/A/1996/006163A
Authority: MX
Inventors: Brambilla Giuseppe
Original assignee: Manuli Stretch Spa
Priority date: 1995-12-06
Filing date: 1996-12-05
Publication date: 1998-01-01

Abstract

The present invention relates to a process for the preparation of a multilayer film based on polyethylene starting from a linear low density polyethylene (LLDPE) by casting-structuration, characterized in that the multilayer material that comes out of a spreader head it gathers on a first roller cooled with water maintained between 10ø and 25øC and the film leaving the first cooling roller is sent to the second roller cooled with water maintained at a lower temperature than that of the first roller and the second roller has a peripheral speed or rotation speed 10-40% higher than that of the first roller. A multilayer film that has a point of deformation and a final elongation comprised within certain limits

Description

PFI TOTJT Q OF MULTIPLE LAYERS FLIGHT OF POLYETIST ENO IIEIIQRIfl OF THE INVENTION The present invention relates to a multilayer film particularly adapted for the packaging of loading units in platform and the method of preparing it. In a previous Italian patent application, multi-layer films having high tenacity and effective drawing capacity have been described, obtained from linear low density polyethylene (LLÜPE) mixed with low density polyethylene (LDPE). The preparation method described in the previous application consists of the following steps: The extrusion, with a series of extruders, of LLDPE polyethylene mixed with LDPE and at least one polyrnomeric material having adhesion properties; - The stratification of the material at the exit of the extruders as a function of the extruder from which it comes; - The exit to the atmosphere of the stratified material through the lip of a spreader head and the deposition thereof on a first cooling roller with high rotation speed, cooled with water maintained between 10 ° and 30 ° C; - The feeding of the sheet that leaves the first roller to the second roller cooled with water at a temperature lower than that of the first roller and maintained between 10% and 20%, with the peripheral speed (rotation speed) of the second roller being 10-40 % greater than the speed of the first roller. The slit of the spreading head, the distance between the lip of the head and the first roller, and the lip and the point of contact on the first roller are included within well-defined scales. The film obtained in this way has values of the deformation point of between 15 and 35 N / mma and the final elongation of between 200 and 500%. It has now been unexpectedly discovered that it is possible to obtain multilayer films having stiffness and stretchability characteristics comprised within the films described in the previous Italian application and films having also new characteristics with respect to those of the film. from the previous Italian application (more rigid but still with stretch capacity) starting with the polyethylene LLDPE without addition of the LDPE polyethylene. It has further been discovered that by properly regulating the conditions of cooling and expanding the film it is possible to obtain highly rigid but still stretchable films also from the LLDPE mixed with a huge proportion of LDPE (in an amount from? 40% by weight).

The method of preparing the film is similar to that described in the previous Italian application. However, some differences are introduced for the preparation of very rigid films. The preparation of the films is carried out by the well-known technique of casting-extrusion. This technique uses a series of extruders (two or more), generally single screw extruders, screw that is of variable extension, to obtain a convenient ovenification of the material, extruders that feed an appliance (power block that, by means of a mechanical action, which stratifies the material coming from the extruders as a function of the extruder it comes from The bar that comes from the feed block is formed of several layers of which the central layer comes from the larger diameter extruder and the lateral layers They come from the other extruders.The bar is then fed to a spreader head, from which, by effect of a mechanical reaction, it is forced out into the atmosphere through a small aperture slit forming a plastic film in which the width over the thickness prevails.The plastic film is deposited on a first cooled roller, which rotates at high speed, which is oriented to the The film that comes from this first roller feeds a second roller also cooled with water.

For the same performance of the extruder and other conditions, the thickness of the film depends on the peripheral speed (rotation speed) of the first roller: in reality, the higher the speed of this roller, the lower the film thickness. The film coming from the group of the cooling rollers is then assembled on winding reels of adapted width and length. The movement of the film in the winding reel is made uniform by constant tensioning of the film by a series of motorized rollers each of which has positive relative rotation. In accordance with the process of the invention, the LLDPE polyethylene and at least one polymeric material compatible with the LLDPE and which gives the film adhesion properties and, optionally, other materials compatible with the LLDPE, are extruded by a series of extruders. The material coming out of the extruders is stratified according to the extruder from which it comes and the stratified bar is forced out through the lip of the spreader head to form a plastic film which is deposited on a first roller that rotates at high speed peripheral (300 to 450 in / rnin), and cooled with water that is maintained at a temperature of 10 ° to 25 ° C, and then on a second roller, cooled with water that is maintained at a temperature lower than that of the first roll and which is between 10 ° and 20 ° C.

The second roller has a peripheral speed (rotation speed) 10-40% greater than the speed of the first roller. The temperature of the material coming from the spacer head is generally between 230 ° and 260 ° C. The slit varies between 0.3 and 0.5 mm; the distance between the lip of the spreader head and the first roller is between 2 and 5 mm, preferably 3-5 rn, and the distance between the lip and the point of con + act on the first roller is between 10 and 15 cm . The slit is adjusted as a function of the final thickness of the film in the extent to which it can be subjected to the film. The distance between the lip of the spacer head and the point of contact of the material on the first roller is regulated by means of bringing the roller closer to the lip at the outlet of the spreader head and by means of a decrease in the pressure made with a device for the aspiration of air that operates near the point of contact of the film on the cooling roller. The reduction achieved in the pressure allows an effective adhesion of the film on the roller. By changing the suction, the profile is changed with which the material travels the distance from the lip of the spreader head to the cooling roller, and simultaneously, the contact point. The greater the distance between the lip and the point of contact, the greater the elastic yield of the material. The operation is such that the sliding of the film between the first and second rollers is prevented. This result is obtained, for example, by subjecting the film to back pressure. For the preparation of the film in which it has a high point of deformation (between 40 and 80 N / m? R) and a final enlargement still high (between 50 and 100%) is operated at a temperature of the cooling water of the first roller maintained on the scale between 15 ° and 18 ° C, while the temperature of the cooling water of the second roller is maintained between 12 ° and 15 ° C. The peripheral speed (rotation speed) of the second roller is 20-30% higher than that of the first roller. The aforementioned conditions are also applied to the preparation of the multilayer film having a high point of deformation (between 35 and 70 N / inpP) and final elongation of between 60 and 200%, obtained from the polyethylene LLDPE mixed with LDPE in amounts between 8 and 40% by weight. With respect to the film obtained from the LLDPE only, that obtained from the LLDPE mixed with LDPE requires, with the other conditions and the point of deformation being equal, a larger difference between the speeds of the cooling rolls.

The thickness of the multilayer film according to the invention is between 2 and 100 micrometers; The preferred thickness varies between 8 and 20 icrônetros. The LLÜPE polyethylene used for the preparation of the film is a well-known polymer. It can be prepared by using either Ziegler-Natta catalysts or rnetalocene catalysts. LLDPE polyethylene can also be mixed with other polyester materials in order to improve its processing capacity. Smaterials may include, for example, partially crystalline propylene copolymers with lower proportions of butane and / or ethylene. The density of the LLDPE is preferably comprised between 0.915 and 0.935 g / cma (OSTM D 1505). The melt index is preferably between 2 and 3 g / 10 (RSTM D 238-65T, condition E). LLDPE is also a well-known polymer. In order to confer adhesion properties to the film, the LLDPE polyethylene is constructed with a layer of polyrnomeric material compatible with the LLDPE, preferably selected from among LLDPEs with a density of between 0.895 and 0.910 g / cm3. For certain applications, sliding properties of the film are needed to avoid adhesion between the platforms when they come into contact with one another.

The sliding ability that can be imparted to the inner or outer side of the film can preferably be obtained by using LLDPE with a density of about 0.930 g / crna. The film according to the invention therefore comprises a main layer, generally a core layer, a cap of material with adhesion properties, and optionally a layer of LLDPE with higher density than that of the LLDPE used p >.; for the main layer. The polymers used for the preparation of the film may contain the additives normally used in this field sas pigments, antioxidants, nucleation agents. Polymers compatible with LLDPE can also be used in san amount that it is adapted to improve the properties of LLDPE. The film according to the invention is characterized by its high rigidity and also by its effective stretching ability. With respect to the conventional LLDPE film obtained under normal casting-extrusion conditions, the film according to the invention has values at its deformation point which can reach values three times or more higher. The values of the deformation point vary between 15 and 80 N / rnrn55. The final elongation is included in a scale of practical interest that is between 50 and 500%.

Multilayer films based on LLDPE are known which are rigid and stretch able. These films are obtained, however, by subjecting a stretch film prepared by casting-extrusion. The process for preparing these films is quite complex because it involves the unwinding of the film produced by casting-extrusion and its subsequent re-winding after being stretched. To obtain high values of the deformation point, very high stretching ratios are used. The films thus obtained have values of the deformation point of about 50 N / mrn52 and of final elongation of about 60-70%. The following examples are provided to illustrate but not p > to limit the purpose of the invention.

EXAMPLE 1 A series of single screw 0-C extruders using variable extension screws is fed, in this order, with the Dow 2100 LLDPE (density 0.918 g / cm3) (Fl extruder), with Dow 4104 polyethylene (density 0.904 g / cma) (extruder B) and with LLDPE polyethylene Dow 22376 (density 0.928 g / cm3) (extruder C). The output mass of the various extruders is approximately 70%, 7% and 15%. The rotations of the screws of the extruders A-C are respectively 57, 63 and 85 rpm and the temperature of the melting material at the exit of the extruders is respectively 265 ° C, 180 ° C, and 265 ° C. The material exiting the extruders is fed to a feeding block device that stratifies the material to prepare it for the spreader head as a function of the extruder from which it comes. The spreader head has a slit of 0.5 mm and the distance between the lip of the head and the point of contact with the first cooling roller is adjusted to 15 rn. The temperature of the material coming out of the slit is 235 ° C. The water temperature of the first winding roller is maintained at 18 ° C. The peripheral speed is 340 rn / mm. The temperature of the material coming out of the first * roller is less than 90 ° C. The material is then directed to the second roller cooled with water maintained at 12 ° C. The speed of the second roller is 430 m / inm. The film coming out of the cooling rollers ba or constant tension is assembled on the reels of determined width and length. The film has a thickness of 12 microns and has the following mechanical characteristics.

Address of the machine irecríAr. cross Young's Module N / rnrn2 81 160 (ASTM D 882-88) Deformation point N / mm55 72 12 (ASTM D 882-88) Final strength N / mrn55 72 28 (RSTM D 882-88) Final elongation% 88 480 (ASTM D 882-88) Resistance to tearing rnN 150 300 (ASTM D 1922-67) Impact resistance g 50 50 (ASTM D 1709-75) Coefficient of friction g 330 650 (ASTM D 1784-78) EXAMPLE 2 Example 1 is repeated with the difference that the extruder A is fed with Dow LLDPE 2100 (density 0.918 g / cm3) and with LD LD polyethylene LD 150 with a yield in the hopper of 8% on p > that. The obtained particle has a deformation point of 60 N / rnm28 and a final wing of 90% (direction of the machine).

COMPARATIVE EXAMPLE 1 Example 1 is repeated with the difference that the temperature of the cooling water of the first roller is maintained at 30 ° -35 ° C; the temperature of the second roller is maintained at 28 ° ~ 30 ° C and the difference in speed between the first and second rollers is 5%. The mechanical characteristics of the film are the following. Direction of the machine Cross direction Young's Module N / m to 110 167 (A? TM D 882-88) Deformation point N / rnnv2 7.1 7.9 (ASTM D 882-88) Final elongation% 533 843 (ASTM D 882-88) Resistance to tearing rnN 229 416 (ASTM D 1922-67) Impact resistance g 180 180 (ASTM D 1709-75)

Claims

NOVELTY OF THE INVENTION CLAIMS

1. Process for preparing by casting-building a multilayer film based on polyethylene, further characterized in that the core layer consists of low density polyethylene (LLDPE), which consists of the steps of: a) extruding polyethylene LLDPE having a density of 10% by weight; re 0.915 and 0.935 g / crn3 and at least one polyrnomeric material having adhesion properties by a series of extruders, b) stratifying the extruded material as a function of the extruder from which it comes, c) ejecting the stratified material in the atmosphere by means of of forcing it through a lip of a spreader head, d) gathering the material coming out of the spreader head on a cooling roller cooled with water maintained between 10 ° and 25 ° C, and e) carrying the film coming out of the first cooling roller to the second cooling roller cooled with water maintained at a temperature lower than that of the first roller and comprised between 10 ° and 20 ° C while the speed Peripheral or rotational speed of the second roller is 10-40% higher than that of the first roller.

2. Method according to claim 1, further characterized in that the temperature of the cooling water of the first roller is maintained between 15 ° and 18 ° C and that of the second roller between 12 ° and 15 ° C, and the peripheral speed of the second roller. Roller is 20-30% higher than that of the first roller.

3. Method according to claims 1 and 2, further characterized in that the speed of the rollers is between 300 and 450 m / rnin.

4. Method according to claim 1, 2 or 3, further characterized in that the distance between the lip of the spreader head and the first roller is between 2 and 5 m, the distance between the lip and the point of contact of the extruded material. on the first roller is on the scale between 10 and 15 mrn.

5. Method according to claims 1, 2, 3 or 4, further characterized in that the spreader head gap is between 0.3 and 0.5 rnrn.

6. Method according to any of the preceding claims, further characterized in that the adhesive polymeric material is compatible with the polyethylene, said material being LLDPE with density between 0.895 and 0.910 g / cm3.

7. Method according to claim 6, further characterized in that the adhesion material is used in the amount of between 5 and 15 X of the weight of the LLDPE of the central layer.

8. Process for the preparation of a multilayer film based on p > olyethylene, further characterized in that the central film consists of LLDPE mixed with high density polyethylene (LDPE), and the film has a value at its point of deformation of between 35 and 70 N / mm2 and a final elongation of between 60 and 200 %, by casting-extortion in accordance with the steps of the process of claim 1, further characterized in that the temperature of the cooling water of the first cooling roller is maintained in the range of between 15 ° and 18 ° C and that of the second roller which is lower than that of the first roller, is maintained between 12 ° and 15 ° C, and the peripheral speed or rotation speed of the second roller is 20-30% higher than that of the first roller.

9. Method according to claim 8, further characterized in that the speed of the rollers is between 300 and 400 / min, the distance between the lip and the spreader head and the first roller is between 2 and 5 rnrn and the The distance between the lip and the point of contact of the extruded material on the first roller is between 10 and 15 rnrn, and the slit of the spreader head is between 0.3 and 0.5 mm.

10. Method according to claims 8 and 9, further characterized in that the adhesion material is LLDPE with a density between 0.895 and 0.910 g / cm3.

11. Multilayer film particularly adapted for the packaging of loading units in platform, also characterized because it consists of a main layer formed of polyethylene linc- >to the low density (LLDPE) with a density between 0.915 and 0.935 g / cm3, obtaining said film by casting-extruded and having a deformation point of between 15 and 80 N / mma and a final elongation of between 50 and 500 %.

12. Film according to claim 11, further characterized p > or the point of deformation is between 40 and 80 M / rnrn52 and the final elongation between 50 and 100%

13. Film according to claim 11, further characterized p > or LLDPE polyethylene is mixed with low density LOPE polyethylene in an amount of LDPE of between 8 and 40% by weight, and the film has a deformation point between 35 and 70 N / mrn2 and a final elongation of between 60 and 200 %. Film according to claims 11, 12 or 13, further characterized in that it consists of a layer of a material having adhesion properties compatible with the LLDPE. 15. Film according to claim 14, further characterized in that the layer of the adhesion material is formed of LLDPE with a density between 0.895 and 0.910 g / cm3. 16. Film according to claim 14 or 15, further characterized in that the layer of adhesion material is between 5 and 15% by weight with respect to LLDPE of the main layer. 17. Film according to claims 11 to 16, further characterized in that the thickness is between 2 and 100 micrometers. 18. Use of the film according to claims 11 to 17 for the € > mbalaje of units of loading on platform. 19. Use of the p > a particle according to claims 11 to 17 for the packaging of units to be loaded on a platform, characterized in that the elements of the loading units on the platform are containers of mineral water, rolls of paper, brick, mechanical parts, ceramic products , food, pharmaceutical, laminated and profiled.