WO2013010231A1

WO2013010231A1 - Co-extruded film comprising at least three layers and use thereof

Info

Publication number: WO2013010231A1
Application number: PCT/BR2011/000232
Authority: WO
Inventors: Paulo Haipek Filho
Original assignee: Paulo Haipek Filho
Priority date: 2011-07-18
Filing date: 2011-07-18
Publication date: 2013-01-24
Also published as: BR112014000764A8; BR112014000764B1; BR112014000764A2

Abstract

The present invention solves the problems found in the prior art by means of a co-extruded film comprising at least three layers, and characterised in that the inner layer (A) made of polyethylene or polypropylene accounts for 50-80% of the thickness thereof, the outer layers (B) made of a mixture of at least two styrene-butadiene block copolymers account for 10-25% of the thickness thereof, and in that the mixture of block copolymers comprises 5-20% elastomeric thermoplastic block copolymer and 80-95% thermoplastic block copolymer. These films can be used for wrapping candy, and when they are monoaxially oriented they can be used as heat-shrinkable packaging.

Description

COEXTRUDED FILM UNDERSTANDING AT LEAST 3 LAYERS AND USE

FIELD OF INVENTION

The present invention relates to a process for producing coextruded thermoplastic films. Particularly, coextruded films with improved stiffness, torsion and shrinkage properties.

BACKGROUND OF THE INVENTION

Coextrusion is the extrusion of multilayer films simultaneously through the use of extrusion machines and special dies that combine different layered materials. This type of extrusion acts to give the final film a combination of the individual characteristics of each of the structure's component materials. It is a well known technique and has been widely used by plastic film manufacturers.

Several types of plastic films use polymers that provide stiffness properties to them and among the polymers there is the use of polylactic acid PLA, polyethylene terephthalate PET and polystyrene PS for this purpose. Among the polymers mentioned above, PS is an especially interesting polymer when thinking about coextruded balloon films, and recently several initiatives are being proposed to make the use of this polymer possible for plastic packaging. Particularly PS is known for its rigidity, clarity and ease of printing properties and the biggest disadvantages of using PS in balloon films would be its processing difficulty, especially in the case of single layer films. One of the alternatives to overcome these difficulties would be to use one or more polyolefin layers in the final film or to combine PS with certain copolymers that can reduce their undesirable properties. Particularly when thinking about the production of plastic candy wrappers, one needs packaging that can provide rigidity (due to the common sense that such wrappers should make their characteristic noise upon opening), proper twisting properties (which is a film that remains twisted once closed) and is inexpensive (both for its materials and the process used to produce it). These films are generally made of polypropylene (PP) or polyvinyl chloride (PVC) and have a preferred thickness between 30 and 50 μπι. However, these films, when made with PP, have poor torsional properties, often breaking and causing an unpleasant appearance to the end product as well as PVC meets environmental restrictions. Often, due to the low torsion capacity, it is necessary to use metal blades (eg aluminum) to ensure that the packaging is properly twisted. As for stiffness, these films are also lacking and high thicknesses are required in order to achieve the desired characteristics.

Some solutions have already been proposed in the art regarding providing coextruded films containing PS for various uses and among them:

WO1998052749 discloses a oriented coextruded film suitable for use as a mail envelope window film, which has a polyolefin layer and a non-gloss polystyrene surface layer. The document describes that there is an increase in stiffness and adhesion between film layers when oriented.

WO1998052749 discloses a core layer film comprising a polypropylene homopolymer or copolymer and an outer layer comprising a blend polystyrene and a modified modified polystyrene. The outer layer also comprises a compatibilizing compound for matching the inner polypropylene layer to the outer polystyrene layer. One of the compounds used as compatibilizers is styrene butadiene styrene (SBS) copolymer.

US2003 / 0091850 discloses a multilayer film for use as a coextrusion-produced packaging, laminating or labeling film which has two outer layers made of a polyolefin, a polyolefin blend or an olefin copolymer, and a core layer consisting of of a mixture of styrene homopolymers and styrene-butadiene-styrene block copolymers.

Additionally, the film produced is suitable for a label film and a packaging film, particularly as candy film. In one embodiment of US2003 / 0091850 a 5-layer film is produced wherein the innermost layer comprises a polyolefin, polyolefin mixture or olefin copolymers; two layers adjacent to the innermost layer comprising styrene homopolymer and styrene-butadiene-styrene block copolymers; and two outer layers comprising polyolefins, blend of polyolefins and / or olefin copolymers.

Thus, the present invention aims to find alternatives to plastic films of the art and which are films that can reconcile high rigidity, good torsion characteristics and low PS consumption. Additionally, the present invention aims to find films having the above characteristics and which films are suitable for use as plastic packaging for a variety of purposes.

BRIEF DESCRIPTION OF THE INVENTION

The present invention solves the problems of the art. through a coextruded film comprising at least 3 layers, characterized in that it comprises 50 to 80% thickness in the inner layer (A) comprising Polyethylene or Polypropylene, 10 to 25% in thickness in the outer layers (B) comprising a mixture of at least two styrene-butadiene block copolymers, wherein said mixture of block copolymers comprises from 5 to 20% of a thermoplastic elastomeric block copolymer and from 80 to 95% of a thermoplastic block copolymer.

Additionally said film may preferably be mono-oriented at stretch ratios between 1: 1.2 and 1: 3.0, providing even greater rigidity to the final film, as well as providing said film with advantageous shrinkage and adhesion characteristics between the layers. .

Said film is suitable as candy wrappers and, when provided with stretch characteristics, suitable as hygienic wrappers and for certain types of heat shrinkable labels.

DESCRIPTION OF THE FIGURES

Figure 1 shows a 1.5 micron horizontal micrograph of the styrene-butadiene thermoplastic block copolymer structure obtained by Transmission Electron Microscopy (MET).

Figure 2 shows a 12 micron horizontal micrograph of a high impact polystyrene (HIPS) obtained by MET.

Figure 3 shows a linear schematic of the structural arrangement of molecules within a styrene-butadiene thermoplastic block copolymer according to the present invention.

Figure 4 shows a front view of the arrangement of molecules within a styrene-butadiene thermoplastic block copolymer according to the present invention. invention.

Figure 5 shows a superior schematic of the arrangement of molecules within a styrene-butadiene thermoplastic elastomeric block copolymer according to the present invention. (that "spheres" are styrene blocks and "spirals" styrene-butadiene blocks)

DETAILED DESCRIPTION OF THE INVENTION

In the context of the present patent application when reading "film" it is to be understood as a material comprising one or more polymer layers and having a thickness of less than approximately 250 μπι.

In the context of the present patent application when reading "thermoplastic elastomeric block copolymer" is to be understood as a copolymer capable of elastic deformation due to the distribution of chemically bonded styrene-butadiene copolymer chains to styrene molecules as shown in Figure 5. Particularly, the present invention utilizes styrene / butadiene thermoplastic elastomeric block copolymer, also known as S-TPE (Styrene thermoplastic elastomer) obtained by styrene / butadiene block copolymerization with a "rigid" and "flexible" block sequence and containing a continuous elastomer phase formed by internal random poly (styrene / co-butadiene) blocks resulting in a structure with characteristics as shown in Figure 5. In addition, such copolymer contains at least 65% styrene and a fraction of at least one elastomer the 70%. The elastomeric fraction being provided with a structure as defined in Figure 5.

In the context of the present patent application when reading "thermoplastic block copolymer" is to be understood as a copolymer that is formed by the bonding of blocks. of different and intercalated polymers on a regular basis. Particularly, the present invention utilizes thermoplastic block copolymers according to the molecular structures of Figures 3 and 4. The micrograph of the molecular structure of the thermoplastic block copolymer of the present invention is shown in Figure 1 and a well-organized structure of the present invention can be seen. same.

The present invention solves the problems of the art by a coextruded film comprising at least 3 layers, characterized in that it comprises 50 to 80% thickness in the inner layer (A) comprising Polyethylene or Polypropylene, 10 to 25% in thickness in the outer layers (B ) comprising a mixture of at least two styrene-butadiene block copolymers, wherein said mixture of block copolymers comprises from 5 to 20% of a thermoplastic elastomeric block copolymer and from 80 to 95% of a thermoplastic block copolymer .

This arrangement of layers and materials acts causing a significant increase in stiffness, especially when considering the small amount of styrene-butadiene copolymer (both rigid and rubbery) used in comparison to the films currently used in the art, ie with a rigid material in the outer layers and a filler material in the inner layer.

However, the use of an outer layer containing only a rigid block copolymer still has the drawbacks of containing several of the undesirable characteristics inherent in PS (easy breakage and difficult processing), as well as the need to improve interaction with the hardness layer. PE or PP present in the film core. The present invention circumvents this problem of the art by combining said rigid block copolymer mixed with a rubber block copolymer. The addition of this new thermoplastic elastomeric block copolymer decreases the characteristic stiffness that the use of polystyrene causes and improves the processability of the film during its production and increased interaction between the outer and inner layers.

Thus, the film of the present invention can provide films with high stiffness, but with a considerable decrease in processing difficulties inherent in polystyrene.

The filler material consists in principle of Polyethylene or Polypropylene and can easily be replaced by other polyolefins which may interact properly with the block copolymers used in the present invention.

The thermoplastic and thermoplastic elastomeric block copolymers of the present invention (the morphology of which is shown in the micrograph of Figure 1) have morphologies and molecular structures quite distinct from grafted styrene butadiene copolymers generally known by the acronym HIPS (High Impact Polystyrene) of figure 2). Differences in morphology and molecular structure between block copolymers and grafted copolymers are responsible for different physicochemical properties such as toughness, transparency, viscosity, gloss, etc.

The copolymers used in the outer layers of the present invention are styrene-butadiene block copolymers. These copolymers have a high polarity compared to other similar block copolymers such as SBS or SEBS and act to increase the compatibility of the PE or PP containing layer and copolymer layers by increasing the adhesion between them in a proportionate manner. participation of copolymers in the formulation. In a preferred embodiment said film may be mono-oriented at stretch ratios between 1: 1.3 and 1: 3.0. This stretch thus provides said film with advantageous stiffness characteristics that will be added to the already inherent characteristics of the multilayer film and provides greater adhesion between the copolymer layers and the PE. Additionally, since these films are in a stressed state after processing, they are considered to be excellent shrinkable films, ie films that when applying a temperature close to their thermal stabilization temperature, that is, the temperature at which submitted the film shortly after the mono-orientation process, suffer a controlled shrinkage towards its orientation. Such films are particularly useful when thinking about toilet paper packaging.

In a preferred embodiment said film is a 3 layer film comprising an inner layer of PE or PP, outer layers comprising a mixture of at least two styrene-butadiene block copolymers and wherein the mixture of block copolymers comprises 5 20% of a thermoplastic elastomeric block copolymer and 80 to 95% of a thermoplastic block copolymer.

In a preferred embodiment said mixture of block copolymers comprises from 7 to 15% of thermoplastic elastomeric block copolymer and 93 to 85% of thermoplastic block copolymer, more preferably from 7 to 10% of thermoplastic elastomeric block copolymer and 93 to 85%. 90% of thermoplastic block copolymer.

In a preferred embodiment the PE or PP-containing inner layer adjacent to the layer containing a mixture of at least two styrene-butadiene block copolymers is an inner layer with up to 10% of a thermoplastic elastomeric block copolymer. That is, for movies with 5 In layers, only the layers adjacent the outer layer as described in the present invention will contain up to 10% of a thermoplastic elastomeric block copolymer.

The films of the present invention may be added with film friction controllers, anti-blocking additives, antistatic additives, additives designed to give a specific color to the final product, among others.

The films of the present invention are extruded with thicknesses between 18 and 180 micrometers, preferably between 22 and 100 micrometers. When said films are oriented these films have thicknesses between 15 and 60 micrometres, preferably between 18 and 45 micrometres.

In a preferred embodiment the films of the present invention have a thickness arrangement between the layers according to table 1:

said thicknesses are always the same on the outer layers in order to prevent a "flickering" effect of the film.

Thus, it can be seen that the films of the present invention, due to the specific arrangement of polymer composition and layer arrangement, can provide films that significantly reduce the amount of polystyrene copolymer employed to achieve adequate stiffness properties. for the above purposes.

EXAMPLES The present example is provided in order to demonstrate the production of the films of the present invention as well as some of the final properties of said film.

Film Preparation:

The outer layers were prepared from a mixture of two types of polystyrene (rigid polystyrene butadiene copolymer with density 1.01 g / cm ³ = 89.5%, rubbery polystyrene butadiene copolymer with density 0.998 g / cm ³ (7%), slip agent (1.5%), antiblocking agent (1.5%) and flow aid (0.5%) The core layer was prepared from a 30% blend of linear polyethylene low density metallocene and 70% low density polyethylene.

A 3 layer coextruder (Carnevalli brand) was used with a 400 mm diameter die with a 1.3 mm lip opening. The width of the film was 1360 mm which corresponds to an inflation ratio of 1: 2.16.

The outer layers (B) were produced to the same thickness (6 microns) and the inner layer (A) to 18 microns which in other words means that each of the outer layers (B) corresponds to 20% of the total thickness. and the inner layer (A) corresponds to 60% of the total film thickness. The total thickness of the extruded film was 30 microns.

Single orientation:

It was performed on longitudinal mono-orientation equipment using a 1: 1.363 stretch ratio. Such a stretch ratio reduced the original film thickness from 30 microns to 22 microns. The stretching process was performed at a speed of 45 m / min at the inlet of the equipment, preheating temperature of 97 ° C, stretching temperature of 100 ° C and stabilization at 70 ° C. Table 2 demonstrating some of the characteristics and properties of the film produced by the present invention:

DM = (Machine Direction)

DT = (transverse direction)

The present standards for measuring film properties obtained by the present invention are in accordance with the American Society for Testing and Materials (ASTM).

It should also be noted that while the invention has been described in relation to what is currently considered to be the most practical and preferred embodiment, it should be understood that the invention should not be limited to the presented embodiment, but rather lends itself to covering various modifications and equivalent arrangements included within the character and scope of the appended claims. Accordingly, the scope of the appended claims should be in accordance with a broader interpretation to encompass all such similar modifications and adjustments.

Claims

1. Coextruded film of at least 3 layers, comprising:

50 to 80% in thickness in the inner layer (A) comprising PE or PP;

10 to 25% in thickness in the outer layers (B) comprising a mixture of at least two styrene-butadiene block copolymers; on what

said mixture of block copolymers comprises from 5 to 20% of a thermoplastic elastomeric block copolymer and from 80 to 95% of a thermoplastic block copolymer.

Film according to claim 1, characterized in that said film is a 3-layer film comprising:

50 to 80% in thickness in the inner layer (A) comprising PE or PP;

said (SB) block copolymer mixture comprises from 5 to 20% of a thermoplastic elastomeric block copolymer and 80 to 95% of a thermoplastic block copolymer.

A film according to claim 1 or 2, wherein said mixture of SB block copolymers comprises from 7 to 15% of thermoplastic elastomeric block copolymer and 93 to 85% of thermoplastic block copolymer.

Film according to Claim 1 or 2, characterized in that said mixture of SB block copolymers comprises from 7 to 10% of thermoplastic elastomeric block copolymer and from 93 to 90% of block copolymer. thermoplastic.

Film according to claim 1, characterized in that said film is further monoriented at stretch ratios between 1: 1.3 to 1: 3.0.

Film according to claim 6, characterized in that said film is mono-oriented at stretch ratios between 1: 1.3 and 1: 2.0.

Coextruded film of at least 3 layers according to claim 1, characterized in that said inner layer containing PE or PP adjacent the layer containing a mixture of at least two styrene-butadiene block copolymers is a layer up to 10% of a thermoplastic elastomeric block copolymer.

Use of a film as defined in claim 1 or 2, characterized in that it is for candy wrappers.

Use of a film as defined in claim 6, characterized in that it is for shrink wrapping.