Multilayered polyolefin films

Abstract

The invention relates to a polyolefin film comprising at least five layers: a core layer (a), comprising a polyolefin; an outer supporting layer (b), comprising copolymers of ethylene and propylene; an inner supporting layer (c), on the face of the core layer opposite to the outer supporting layer, comprising a polyolefin; a first coating layer (d) immediately in contact with the inner supporting layer (c), and finally a second coating layer (e) immediately in contact with the inner supporting layer (c), both comprising copolymers of ethylene with one or several polar monomers. In addition, the present invention relates to the process of manufacturing said polyolefin film and also the uses thereof for coating a substrate.

Claims

1. A polyolefin film comprising at least the following five layers: a. a core layer (a) comprising a polypropylene (PP) and a UV stabilizer; b. an outer supporting layer (b) comprising polypropylene homopolymer, random or graft copolymers of ethylene/propylene, copolymers of ethylene with vinyl acetate (VA), acrylic amide (AAm), ethyl acrylate (EA), butyl acrylate (BA), vinyl alcohol (VOH), or maleic anhydride (MAH) and/or combinations thereof and/or propylene/ethylene random copolymers and/or polyethylene of medium density or combinations thereof; c. an inner supporting layer (c) on the face of the core layer opposite to the outer supporting layer (b), comprising a polyolefin selected from copolymers or terpolymers of ethylene with higher alpha-olefins, a polyolefin plastomer, a linear low-density polyethylene (LLDPE), a metallocen LLDPE or random copolymers of ethylene with polar monomers selected from vinyl acetate (VA), acryl amide (AAm), methyl acrylate (MA), ethyl acrylate (EA), butyl acrylate (BA), vinyl alcohol (VOH), or maleic anhydride (MAH); d. a first coating layer (d) immediately in contact with the inner supporting layer (c) comprising LLDPE or copolymers of ethylene with one or several polar monomers; e. a second coating layer (e) in contact with the first coating layer (d) comprising copolymers of ethylene with one or several polar monomers; wherein layers (a), (b) and (c) are co-extruded and are biaxially oriented and wherein the first coating layer (d) and the second coating layer (e) are co-extruded by co-extrusion-coating.

2. The polyolefin film according to claim 1, wherein the first coating layer (d) comprises EVA; and/or wherein the first coating layer (d) comprises EVA with a melt index (190° C./2.16 kg) between 5 and 20 g/10 minutes; and/or wherein the first coating layer (d) further comprises other polymers like LLDPE, or copolymers of ethylene with one or several monomers selected from MA, EA, AAm, BA, VOH, or MAH; and/or the first coating layer (d) has a grammage between 5 and 50 g/m.sup.2.

3. The polyolefin film according to claim 1, wherein the second coating layer (e) comprises EVA; and/or wherein the EVA has a melt index (190° C./2.16 kg) between 20 and 400 g/10 minutes; and/or wherein the second coating layer (e) further comprises other ethylene copolymers with one or several monomers selected from MA, EA, AAm, BA, VOH or MAH; and/or wherein the second coating layer (e) has a grammage between 5 and 50 g/m.sup.2; and/or wherein the roughness of the surface of the second coating layer (e) is characterized by an R.sub.z of between 1 and 10 microns; and/or wherein the second coating layer (e) is oxidatively treated by means of a corona discharge, flame treatment or plasma treatment.

4. The polyolefin film according to claim 1, wherein the core layer (a) has a thickness between 20 and 60 microns; and/or the UV stabilizer comprises at least one hindered amine light stabilizer (HALS); and/or wherein the core layer (a) comprises an UV absorber; and/or wherein the content of HALS and UV absorbers is in the range from 0.1 to 5% by weight in respect of the total weight of layer (a); and/or wherein the core layer (a) is pigmented with inorganic pigments; and/or wherein the core layer (a) is solid or voided by means of voiding agents selected from CaCO.sub.3, polyamide (PA) or polybutylene terephthalate (PBT).

5. The polyolefin film according to claim 1, wherein the outer supporting layer (b) comprises a polypropylene homopolymer, or graft or random copolymers of ethylene/propylene, or copolymers of ethylene with vinyl acetate (VA), acryl amide (AAm), ethyl acrylate (EA), butyl acrylate (BA), vinyl alcohol (VOH), or maleic anhydride (MAH) or combinations thereof and/or propylene ethylene random copolymers and/or polyethylene of medium density and/or combinations thereof; and/or has a thickness between 1 and 5 microns; and/or the outer supporting layer (b) comprises an UV stabilizer; and/or wherein the outer supporting layer (b) comprises an UV absorber; and/or the outer supporting layer (b) comprises a mineral filler; and/or the outer supporting layer (b) comprises an inorganic voiding agent.

6. The polyolefin film according to claim 1, wherein the inner supporting layer (c) comprises a polyolefin plastomer; and/or the inner supporting layer (c) has a thickness between 1 and 5 microns; and/or wherein the inner supporting layer (c) comprises antiblocking particles.

7. The polyolefin film according to claim 1, further comprising an outer coating layer (f) on top of the outer supporting layer (b), wherein the outer coating layer (f) comprises acrylates, unsaturated polyesters, urethanes, acrylic copolymer resins or combinations thereof and/or comprises pigments; and/or said outer coating layer (f) has a dry grammage of 0.05 to 5.0 g/m.sup.2.

8. The polyolefin film according to claim 1, further comprising an outer coating layer (g) on top of layer (b) or layer (f), if present, wherein said outer coating layer (g) comprises epoxy acrylates, polyester acrylates, polyether acrylate, urethane acrylates, acrylic acrylates, melamine acrylates, or blends thereof; and/or wherein said outer coating layer (g) has a dry grammage of 3 to 80 g/m.sup.2; and/or wherein said outer coating layer (g) is applied by gravure, flexo printing technology or die coating technology; and/or wherein said outer coating layer (g) is cured by UV or E-beam technology.

9. The polyolefin film according to claim 1, further comprising an outer coating layer (h) on top of the second coating layer (e) comprising acrylates, unsaturated polyesters, ionomers, urethanes, acrylic copolymer resins or blends thereof; and/or wherein said coating layer (h) has a dry grammage of 0.01 to 1.0 g/m.sup.2.

10. The polyolefin film according to claim 1, wherein layers (a), (b) and (c) are co-extruded and biaxially oriented, and wherein layers (d) and (e) are applied in a single step by co-extrusion coating; wherein layer (d) comprises EVA, with a VA content between 10 and 20% by weight in respect of the EVA weight and with a melt index (190° C./2.16 kg) between 10 and 20 g/10 minutes and has a grammage between 10 and 25 g/m.sup.2; wherein layer (e) comprises EVA, with a VA content between 20 and 35% by weight in respect of the EVA weight and with a melt index (190° C./2.16 kg) between 50 and 200 g/10 minutes and has a grammage between 10 and 25 g/m.sup.2 and has a roughness characterized by a R.sub.z of between 2 and 7 microns; wherein layer (a) comprises polypropylene, a mineral filler comprising TiO.sub.2 and at least one UV stabilizer, has a thickness between 20 and 60 microns; wherein layer (b) comprises propylene homopolymer or a propylene ethylene random copolymer, both optionally MAH grafted, and has a thickness between 1 and 5 microns, and comprises at least one HALS and at least one mineral filler selected from CaCO.sub.3, TiO.sub.2 or mixes thereof and at least one inorganic voiding agent selected from CaCO.sub.3, talc, PBT or PA; wherein layer (c) comprises an ethylene octene-1 plastomer with a melt index (190° C./2.16 kg) of 1 to 10 g/10 minutes and has a thickness between 1 and 5 microns.

11. A wood board laminate which comprises the polyolefin film according to claim 1.

12. Process for the manufacture of the polyolefin film or the laminate of claim 1, comprising the following steps: a. preparing the compositions of layers (a), (b) and (c); b. co-extruding layers (a), (b) and (c); c. stretching the three-layer film obtained in step (b) biaxially; d. optionally applying a corona, flame or plasma treatment on layer (b); e. applying layers (d) and (e), by co-extrusion coating in a single step; f. optionally applying a corona, flame or plasma treatment on layer (e); g. optionally applying layers (f), (g) and/or (h) by wet coating technology selected from flexo or rotogravure or die coating; and h. optionally laminating the film obtained in steps ((e), (f) or (h) on a substrate.

13. A polyolefin film or laminate obtained by the process of claim 12.

14. The polyolefin film according to claim 1, wherein the polar monomers in the first coating layer (d) and the second coating layer (e) are selected from VA, AAm, MA, EA, BA, VOH or MAH.

15. The polyolefin film according to claim 2, wherein the first coating layer (d) comprises EVA with a VA content between 5 and 25% by weight in respect of the EVA weight; and/or wherein the first coating layer (d) comprises EVA with a melt index (190° C./2.16 kg) between 10 and 20 g/10 minutes; and/or the first coating layer (d) has a grammage between 8 and 35 g/m.sup.2.

16. The polyolefin film according to claim 3, wherein the second coating layer (e) comprises EVA with a VA content between 15 and 40% by weight in respect of the EVA weight; and/or wherein the EVA has a melt index (190° C./2.16 kg) between 50 and 200 g/10 minutes; and/or wherein the second coating layer (e) has a grammage between 8 and 35 g/m.sup.2; and/or wherein the roughness of the surface of the second coating layer (e) is characterized by an R.sub.z of between 2 and 7 microns; and/or wherein the second coating layer (e) is oxidatively treated by means of a corona discharge, flame treatment or plasma treatment, by corona discharge.

17. The polyolefin film according to claim 5, wherein the UV stabilizer is at least one HALS; and/or wherein the mineral filler of the outer supporting layer (b) is selected from CaCO.sub.3, TiO.sub.2 or mixes thereof; and/or the inorganic voiding agent of the outer supporting layer (b) is selected from CaCO.sub.3, talc, polybutylene terephthalate (PBT) or polyamide (PA).

18. The polyolefin film according to claim 6, wherein the polyolefin plastomer of the inner supporting layer (c) is an ethylene octene-1 plastomer with a melt index (190° C./2.16 kg) of 1 to 10 g/10 minutes; and/or the antiblocking particles in said inner supporting layer (c) are silica or PMMA particles.

19. The polyolefin film according to claim 7, wherein the outer coating layer (f) comprises an aliphatic urethane, acrylic copolymer resin blends or combinations thereof; and/or said outer coating layer (f) has a dry grammage of 0.1 to 4.0 g/m.sup.2; and/or said outer coating layer (f) is applied by wet coating flexo or rotogravure.

20. The polyolefin film according to claim 9, wherein said an outer coating layer (h) comprises an aliphatic urethane or acrylic copolymer resin blends; and/or wherein said coating layer (h) has a dry grammage of 0.02 to 0.5 g/m.sup.2; and/or wherein said outer coating layer (h) is applied by wet coating flexo or rotogravure.

21. A method of protecting a wood substrate from UV damage, which comprises applying the polyolefin film of claim 1 to the wood substrate.

Description

DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 illustrates the multilayer structure of the polyolefin film of the invention.

EXAMPLES

(2) In order to provide a better understanding of the invention, the following is a detailed explanation of some of the preferred embodiments of the invention, which is provided to give an illustrative example of the invention but which, by no means, should be considered to limit the same.

Example 1

(3) The manufacturing process begins with the production of a biaxially oriented polypropylene substrate, comprising layers (a), (b) and (c) and being referred herein as BOPP substrate, having a total thickness of 50 microns and a density between 0.9 to 1.0 g/cm.sup.3.

(4) The core layer (a) of the BOPP substrate comprises an extruded layer of 47 microns with the following composition:

(5) TABLE-US-00001 77.3% by weight of polypropylene homopolymer having a melting point of 165° C. and a melt flow index of 2.0 g/10 minutes. 22.0% by weight of titanium dioxide (rutile). 0.6% by weight of HALS. About 0.1% by weight of other stabilisers.

(6) This composition provides a white appearance, high opacity and protects the BOPP substrate from the UV degradation over time.

(7) The outer supporting layer (b) of the BOPP substrate has a thickness of 2 microns with the following composition:

(8) TABLE-US-00002 21.2% by weight of polypropylene homopolymer. 58.0% by weight of random copolymer of ethylene and propylene having a melt flow index of 5.5 g/10 min and an ethylene content characterized by a melting temperature of 127° C. 17.1% by weight of calcium carbonate. 3.0% by weight of titanium dioxide. 0.6% by weight of HALS. About 0.1% by weight of other stabilisers.

(9) This composition provides a white appearance with certain voiding properties and a good surface for printability.

(10) The inner supporting layer (c) of the BOPP substrate has a thickness of 1 micron with the following composition:

(11) TABLE-US-00003 98.0% by weight of plastomer based on ethylene octene-1. 1.9% by weight of random copolymer of ethylene and propylene. 0.5% by weight of UV stabilizer 0.1% by weight of silica as antiblocking agent with a particle size of 4 microns

(12) This inner supporting layer (c) provides a good compatibility between the BOPP substrate and the adhesive layer (d).

(13) The production conditions of this BOPP substrate (comprising layers (a), (b) and (c)) were as follows:

(14) TABLE-US-00004 Extrusion Temperatures Layer a 250° C. Layer b 235° C. Layer c 215° C. Cooling roll Temperature  45° C. Longitudinal Temperature 100-120° C.    stretching Stretching ratio 1:5.0 Transversal Temperature 160° C. stretching Stretching 1:9   ratio Setting 170° C. Setting ratio 12% Surface Corona Layer b >38 treatment discharge dynes/cm

(15) After the manufacturing of the BOPP substrate, the film is conveyed to the co-extrusion coating process where the adhesive layer comprised by layers (d) and (e) is applied. These layers (d) and (e) are applied in a co-extrusion coating process.

(16) Both layers (d) and (e) are comprised each one by an EVA with different characteristics and properties. These are the conditions and composition for each layer in this co-extrusion coating process:

(17) TABLE-US-00005 Vinyl MFI Co-extrusion acetate (190° C./ coating Temperature Grammage content 2.16 kg) Layer (d) 200-220° C. 12 g/m.sup.2 20% 20 Layer (e) 170-190° C. 12 g/m.sup.2 28% 150

(18) The co-extrusion-coated layers were cast on the film and immediately pressed against a chill roll cooled to a temperature of 25° C.

(19) After the co-extrusion, the adhesive layer (e) is corona treated to enhance the adhesion to the wood board (or to the subsequent adhesive layer (h), if was presented, as in Experimental example 2), resulting in a surface tension in adhesive layer (e) of at least 42 dynes/cm.

(20) Once the complete film structure is produced the film is rewound and slit to the required width in a subsequent process. This film is ready for being laminated in a later process mainly on a wood substrate.

(21) For the lamination process, the lamination temperature was 120° C. on the heated roll, and a medium bonding strength between the film and the wood substrate of 9N/25 mm was achieved. This bonding strength is achieved on top of wood boards produced from medium-density fibreboard (MDF) and particle board. For special wood panels such as MDI, the bonding strength was lower: 8.5 N/25 mm.

(22) The tear test was passed successfully with this adhesive structure comprising layers (d) and (e).

Example 2

(23) A five-layered white, opaque, UV stabilized and with an adhesive layer formed by a co-extrusion of two different types of EVA film, as described in Example 1. In addition, an extra adhesive layer (h) is applied on top of adhesive layer (e), in order to enhance the adhesion of the film to the wood substrate; especially in cases with a more difficult substrate in terms of adhesion between the film and the wood substrate is used, as methylene diphenyl diisocyanate (MDI) boards as example.

(24) This adhesive layer (h) comprises an aliphatic urethane primer water-based applied by a wet coating process using rotogravure, and being after dried in an oven at a temperature between 70-80° C., in a dry thickness of 0.1-0.2 g/m.sup.2.

(25) For the lamination process, the lamination temperature was 120° C. on the heated roll and a medium bonding strength between the film and the wood substrate of 10 N/25 mm was achieved on top of a MDI wood board. In the same conditions, a bonding strength between the film and the wood substrate of 9.5 N/25 mm was achieved on top of a MDF board.

(26) This improvement on the adhesion to the wood substrates is more clearly observed on the tear test, where specially in case of MDI boards the film starts disintegrating by separating the outer part of the film from the inner part still glued faster than in case of Example 1. This means that the film is able to tear more easily, which is an advantage due to in case of film is locally separated from the wood substrate, this tear property allows to limit the damage due to a prompt break, as happens when paper is used on wood substrates.

Comparative Example 3

(27) A white, opaque, UV stabilized film as described in Example 1. But in this case, the adhesive layer is not formed by two layers (d) and (e) in a co-extrusion coating process. The only adhesive layer (d) is formed by an EVA with a vinyl acetate content of 20% and a melt flow index (190° C./2.16 kg) of 20 g/10 min, in a grammage of 24 g/m.sup.2.

(28) Adhesion strength is not as good as in Examples 1 and 2, where the adhesive layer comprises two (layers (d) and (e)) or three (layers (d), (e) and (h)) different layers.

(29) For the lamination process, the lamination temperature was 120° C. on the heated roll and a bonding strength between the film and the wood substrate of 4 N/25 mm was achieved on top of a MDF board. In the same conditions, a bonding strength between the film and the wood substrate of 2.5 N/25 mm was achieved on top of a MDI board. This bonding adhesion is not enough for the wood board lamination purpose.

(30) Also, the tear test did not show good results, because after performing this test, the film started peeling within more than 20 mm from the starting point.

Example 4

(31) The film described at Example 1, additionally comprising an outer coating formed by layers (f) and (g) on top of the outer supporting layer (b).

(32) Layer (f) consists of a coating that can be colored with different pigments or inks and can also act as a primer to improve the adhesion between layers (b) and (g). For this purpose, an aliphatic urethane water-based, combined with inks or pigments of several colors were used, applied by a wet coating process using rotogravure technology and after dried in an oven in a range of temperatures between 70-90° C., in a final dry grammage of 2 g/m.sup.2.

(33) A new coating (g) is applied on top of layer (f) in a grammage of 8 g/m.sup.2 to provide a good scratch resistance to the final product. Urethane acrylates combined with matting agents are used, applied by flexo coating equipment and cured by E-Beam technology using a dose of 40 kGy. This surface has a good scratch and stain resistance.

(34) The bonding strength values are the same than in Example 1, because the addition of this coating layers (f) and (g) does not affect the adhesion of the film to the wood board.

(35) Finally, the following chart summarizes the adhesion properties show in each Example:

(36) TABLE-US-00006 Example 1 Example 2 Example 3 Example 4 Bonding   9N/25 mm 9.5N/25 mm   4N/25 mm   9N/25 mm strength on top of MDF board Bonding 8.5N/25 mm  10N/25 mm 2.5N/25 mm 8.5N/25 mm strength on top of MDI board Initial tear 5 mm 7 mm 20 mm 5 mm value on top of MDF board Final tear 18 mm 17 mm 30 mm 18 mm value on top of MDF board Initial tear 6 mm 5 mm 25 mm 6 mm value on top of MDI board Final tear 20 mm 16 mm 40 mm 20 mm value on top of MDI board