PL233197B1 - Multi-layer stretch film - Google Patents

Description

Description of the invention

The subject of the invention is a multilayer stretch film, especially a flat film, intended in particular for stabilization of sets of food and industrial goods formed on pallets during their storage and transport.

Stretch films are mainly made of polyethylene, the consumption of which for this type of film accounts for over 50% of polyethylene consumption for the production of polyethylene films. Due to various modifications, the stretch film is characterized by unique functional properties: it is very flexible and sticks to itself, although it does not contain an adhesive layer, it is cheaper compared to other packaging films. The foil shows good tear resistance, low temperature resistance and a water vapor barrier. Due to these properties, stretch film has been widely used, among others, in securing and connecting various types of cargo during transport, wrapping pallets with goods. It is used for wrapping light and medium heavy loads on pallets with manual or mechanical devices. Stretch films are produced by extrusion blow molding, as so-called tubular films, or by extrusion through a slotted head, so-called flat films. Due to the much greater efficiency, the method of extrusion through the slotted head ensures, despite the use of much more complicated and expensive devices constituting the processing line, the film more competitive when it is used on a large scale, for example for wrapping pallets. In recent years, multi-layer materials composed of several to several dozen layers made of various types of polyethylene copolymers, for example: linear low-density polyethylene, linear very low-density polyethylene, metallocene linear low-density polyethylene and the like, have dominated in recent years. This ensures that the product maintains better mechanical strength despite the reduction in film thickness.

Both the composition of the stretch film and the technologies of their production are the subject of many patents. Patent description PL 210951 describes a five-layer, biaxially oriented polyethylene film, which is characterized by the fact that the basic raw material of layers A, B, C, D and E is linear low-density metallocene polyethylene, with the outer layer A is an activated layer with a thickness of 2.0 μm, intermediate layers B and D are 2.5-3.5 μm thick, the middle layer C has a thickness in the range of 4.8-10.8 μm, and layer E is an unactivated layer with a thickness of 2.0 μm. Additionally, antioxidant in the amount of 0.7-1.3% by weight is introduced to all layers, the anti-blocking modifier in the form of SiO2 in the amount of 0.2-1.0% by weight is introduced into layers A and E, and layers B, % C and D with 0.5c-1.5wt% lubricants / antistatic agents. The invention application P.397124 discloses a method of producing a three-layer stretch film, in which one layer is produced from a blend of 80% octane linear ultra-low density polyethylene of 0.905 g / cm ³ , 15% low-density polyethylene of 0.920 g / cm3. cm ³ and 1% plasticizing additive and 4% anti-blocking agent based on natural silica.

Patent GB patent 182 545 discloses a method for producing a multilayer polyethylene film which is characterized in that the co-extruded through a slot die each film layer composed of a mixture of linear low density polyethylene (LLDPE) having a density in the range of 915-935 NKG / m ³ and a small polyethylene % density (LDPE) in an amount of 8-40 wt.%. in relation to the LLDPE, and then the foil web is directed to the first chill roll at a temperature of 10-25 ° C and, successively, to the second chill roll at the same temperature as the first or in the range of 10-20 ° C, the speed of rotation of the second roll is 10-40% higher than the rotation speed of the first chill roll.

In the chapter of the book Applied Plastics Engineering Handbook (Editor Kutz M.), Elsevier, Amsterdam, 2011, 401-415, edited by Zumbrunnen DA, entitled "Chaotic advection and its application to extruding micro- and nanostructured plastic materials", the author lists the advantages of foil made of polymer blends or polymer-mineral composites in which the particles of the dispersed phase are small and have a very strong orientation, obtained thanks to the phenomenon of advection.

The significant share of the films in question in the market of polyethylene films inspires producers to work on new technologies that enable them to be obtained at lower costs and at the same time with better strength parameters.

PL 233 197 B1

The aim of the present invention is to develop the composition of a multilayer stretch film with better operating parameters than known so far.

According to the essence of the invention, a multi-layer stretch film consists of interconnected layers, of which:

outer layer 1 is made of ethylene n-hexene copolymer with mass melt flow rate MFR of 4.0 g / 10 min, inner layer 2 composed of 1-24 layers is made of ethylene n-hexene copolymer blend mass flow rate a flow MFR of 4.0 g / 10 min, with a percentage share of 50% by mass, with an ethylene-n-hexene copolymer obtained with the participation of metallocene catalysts, with a mass melt flow rate MFR of 4.0 g / 10 min, with a percentage share of 50 % by mass, the inner layer 3 composed of 1-24 layers is made of an ethylene n-hexene copolymer with a mass melt flow index, MFR of 4.0 g / 10 min with 0.5-2.0 wt.%. addition of didecyldimethylammonium chloride bentonite (OMMT) filler, introduced as PE_B concentrate, outer layer 4 is made of ethylene-n-hexene copolymer with a mass melt flow rate MFR of 4.0 g / 10 min.

Preferably, PE_B bentonite concentrate is obtained by subjecting 100 g of a suspension of bentonite in water to a concentration of 4-10% by weight. in an alkaline environment - at pH = 7.5-9.0, at a temperature of 20-70 ° C, the action of 5-200 mmol of didecyldimethylammonium chloride (OMMT), and then the product is dried, ground into grains smaller than 0.05 mm , and sequentially, by mixing extrusion, a granulate with 8% OMMT content in low-density polyethylene (LLD PE) is obtained using a 0.5% addition of maleated polyethylene as a compatibilizer.

The method according to the invention produces multilayer stretch films 8-50 μm thick.

The invention will be described in more detail in the examples of its implementation.

For the production of the multilayer stretch film according to the invention, a technological line equipped with four extruders with the following operating parameters was used for all the embodiments:

for the outer layer 1 - diameter D = 80 mm, screw length 30D, temperature of individual heating zones in the cylinder 210-260 ° C.

for the inner layer 2 - diameter D = 140 mm, screw length 30D, temperature of individual heating zones in the cylinder 210-260 ° C.

for the inner layer 3 - diameter D = 140 mm, screw length 30D, temperature of individual heating zones of the cylinder 215-260 ° C.

for the outer layer 4 - parameters the same as for the first layer.

the temperature of the slot head and the distributor was 260 ° C, the speed of the pouring and winding roll was respectively: 605 m / min and 615 m / min

Example 1. In order to obtain the four-layer micro-nanostretch film for individual layers, the following components were used:

outer layer 1 and outer layer 4 - ethylene-n-hexene copolymer with mass melt flow index MFR of 4.0 g / 10 min, inner layer 2 - single, composed of ethylene-n-hexene copolymer with mass melt flow index MFR equal to 4.0 g / 10 min, with a percentage of 50% by mass with a copolymer of ethylene with n-hexene obtained with the participation of metallocene catalysts, with a mass melt flow rate MFR of 4.0 g / 10 min, with a percentage of 50% by mass, layer inner 3 - single, composed of an ethylene-n-hexene copolymer with a mass melt flow index, MFR of 4.0 g / 10 min with 0.5 wt.%. addition of the filler in the form of OMMT (calculated on the pure filler) introduced in the form of PE_B concentrate.

The obtained multilayer stretch film with a nominal thickness of 18 μm had clearly better strength properties than the standard stretch film obtained without the addition of modified bentonite (Table 2, line 2).

The obtained stretch film was subjected to accelerated aging tests in a climatic chamber for a period of 21 days, and no visible deterioration of the functional properties of the obtained film, exceeding 5%, was found.

PL233 197 Β1

Example 2. The outer layers 1 and 4 and the inner layer 2 were made as in example 1. The inner layer 3 was made with an addition of 1.5 wt.%. addition of the filler in the form of OMMT, introduced in the form of PE_B concentrate. A stretch film with 4 layers was obtained. The properties of the film are shown in (Table 2, line 3).

Example 3. The outer layers 1 and 4 and the inner layer 2 were made as in Example 1. The inner layer 3 was made with the addition of 2.0% by weight of the filler in the form of OMMT, introduced as a PE_B concentrate. A stretch film with 4 layers was obtained. The properties of the film are shown in (Table 2, line 4).

Example 4. Layers; the outer layers 1 and 4 and the inner layer 2 were made as in Example 1. The inner layer 3 was made with an addition of 3.0 wt. filler in the form of OMMT, introduced in the form of PE_B concentrate. A stretch film with 4 layers was obtained. The film properties are shown in (Table 2, line 5).

Example 5. Layers: outer 1 and 4 were made as in example 1. Inner layer 2, obtained as in example 1, was then separated into 24 layers on a separator. The inner layer 3 was made with the addition of 2.0% by weight of the filler in the form of OMMT, introduced in the form of the PE_B concentrate. Then it was separated into 24 layers on a separator. A stretch film with 50 layers was obtained. The film properties are shown in (Table 2, line 6).

Example 6 - comparative. Layers; the outer layers 1 and 4 and the inner layer 2 were made as in example 1. The inner layer 3 was also made as in example 1, but without the addition of an OMMT filler. A standard 4-layer stretch film was obtained. The properties of the film are shown in (Table 2, line 1).

The composition and number of film layers obtained in the embodiments of the invention are shown in Table 1.

Table 1

Number / number of layers Standard Example 1 Example 2 Example 3 Example 4 Example 5 1/1 PE LLD1 PE LLD1 PE LLD1 PE LLD1 PE LLD1 PE LLD1 2/1 - PE LLD2 PE LLD2 PE LLD2 PE LLD2 - 2/24 PE LLD2 PE LLD2 3/1 PE LLD1 + 0.5% MMT PELLDI + 1.5% OMMT PE LLDH 2.0% OMMT PE LLD1 + 3.0% OMMT 3/24 PE LLD2 PE LLD2 + 2.0% OMMT 4/1 PE LLD! PE LLD1 PE LLD1 PE LLD1 PELLD1 PE LLD1

Signs:

PE LLD1 - ethylene n-hexene copolymer with mass melt flow rate MFR = 4.0 g / 10 min

PE LLD2 - blend - 50% ethylene n-hexene copolymer with mass melt flow rate MFR - 4.0 g / 10 min and 50% ethylene n-hexene copolymer obtained with metallocene catalysts (MFR 4.0 g / 10 min )

OMMT - bentonite modified with didecyldimethylammonium chloride

The strength properties of the standard stretch film and the stretch film obtained in Examples 1-5 are shown in Table 2.

PL233 197 Β1

Table 2

Łp. A type of stretch film σ ₂ , MPa ε ₂ ,% σι, MPa E |,% T "° C 1. Standard 19.5 350 7.0 195 39.5 2. Example 1 23.9 675 13.9 480 41.0 3. Example 2 24.6 690 ) 4.2 490 43.0 4. Example 3 25.1 595 14.6 495 42.5 5. Example 4 26.3 710 15.7 520 44.0 6, Example 5 27.4 730 16.9 535 42.5

Explanations:

σ2 - stress at break in the direction parallel to extrusion

- elongation at break in the direction parallel to extrusion σι - stress at break in the direction perpendicular to extrusion ει - elongation at break in the direction perpendicular to extrusion

T _v - thermal resistance according to Vicat of the mixture used to produce the inner layers of the foil

Claims (2)

Patent claims 1. Multilayer stretch film, 8-50 μπι thick, characterized in that it consists of layers joined together, of which: outer layers 1,4 are made of ethylene n-hexene copolymer with a mass melt flow rate MFR of 4.0 g / 10 min, inner layer 2 composed of 1-24 layers is made of ethylene-n-hexene copolymer blend of melt flow rate MFR of 4.0 g / 10 min, percentage 50% by weight, with an ethylene-n-hexene copolymer obtained with the participation of metallocene catalysts, with a mass melt flow rate equal to MFR 4.0 g / 10 min, with % 50% by mass, the inner layer 3 composed of 1-24 layers is made of an ethylene n-hexene copolymer with a mass melt flow index, MFR of 4.0 g / 10 min with 0.5-2.0 wt.%. addition of a filler in the form of bentonite modified with didecyldimethylammonium chloride (OMMT), introduced in the form of a PE_B concentrate. 2. The multilayer film according to claim 1 The method of claim 1, characterized in that the PE_B bentonite concentrate is obtained by subjecting 100 g of a bentonite slurry with a concentration of 4-10 wt.%. in water, in an alkaline environment - at pH = 7.5-9.0, at a temperature of 20-70 ° C, with 5-200 mmoles of didecyldimethylammonium chloride (OMMT), and then the product is dried, ground into grains smaller than 0 0.05 mm, and, successively, by mixing extrusion, a granulate with 8% OMMT in Low Density Polyethylene (LLD PE) is obtained using 0.5% maleated polyethylene as a compatibilizer.