Matt polyolefin film having release properties

Abstract

The invention relates to transparent multilayer biaxially oriented polyolefin films comprising a base layer and at least one outer matt covering layer, which contains at least two incompatible polymers and has a surface roughness of at least 2.0 [mu]m. The covering layer contains a polydialkyl siloxane having a viscosity of 100,000 to 500,000 mm2/s. The surface of said covering layer is pre-treated by means of corona.

Claims

1. A transparent, multilayer, biaxially oriented polyolefin film comprising a base layer and at least one matt outer cover layer, wherein the outer cover layer consists essentially of two incompatible polymers and has a surface roughness of at least 2.0 m with a cut-off of 25 m, wherein the matt outer cover layer contains a polydialkyl siloxane with a viscosity from 150,000 to 400,000 mm.sup.2/s and the surface of this matt outer cover layer has undergone corona surface treatment and wherein the surface tension of the surface of the outer cover layer is 37 to 50 mN/m after corona treatment and the mixture of incompatible polymers consists essentially of a propylene polymer and polyethylene polymer which is an MDPE.

2. The film according to claim 1, wherein the polypropylene polymer is a propylene copolymer or a propylene terpolymer or a propylene homopolymer.

3. The film according to claim 1, wherein the polypropylene polymer is a propylene copolymer and/or propylene terpolymer.

4. The film according to claim 1, wherein the matt cover layer contains >0.5% by weight polydialkyl siloxane relative to the weight of the cover layer.

5. The film according to claim 1, wherein the matt cover layer further contains an antiblocking agent.

6. The film according to claim 5, wherein the antiblocking agent is a crosslinked silicone or crosslinked polymethyl methacrylate particles.

7. The film according to claim 1, wherein the matt cover layer has a thickness from 1 to 10 m.

8. The film according to claim 1, wherein the inner surface of the film is printed and furnished with a cold seal adhesive.

9. The film according to claim 1, wherein the matt outer cover layer contains a polydialkyl siloxane with a viscosity from 250,000 to 350,000 mm.sup.2/s.

10. The film according to claim 1, wherein the polydialkyl siloxane is polydimethyl siloxane.

11. The film according to claim 1, wherein the polydialkyl siloxane is present in an amount from 0.5 to 5% by weight in the cover layer.

12. The film according to claim 1, wherein the polydialkyl siloxane is present in an amount from 0.5 to 3% by weight in the cover layer.

13. The film according to claim 1, wherein the polydialkyl siloxane is present in an amount of 1.5% by weight in the cover layer.

14. A laminate of a polyolefin base film that has been laminated with a film as described in claim 1 by means of laminating adhesive or extrusion lamination, wherein the inner surface of the base film is laminated with the inner surface of the film as described in claim 1 and a cold seal adhesive is applied to the outer surface of the base film.

15. The laminate according to claim 14, wherein the inner surface of the base film is printed.

16. The laminate according to claim 14, wherein the inner surface of the film is reverse printed.

17. A process to produce a packaging product which comprises utilizing the laminate according to claim 14, wherein the outer side of the film forms the outer side of the packaging.

18. A process to produce a packaging product which comprises utilizing the film according to claim 1 to produce a packaging product, wherein the outer side of the film according to claim 1 forms the outer side of the packaging.

Description

EXAMPLE 1

(1) A transparent, triple-ply film comprising base layer B and one inner and one outer cover layer having a total thickness of 20 m was produced by coextrusion and subsequent sequential lengthwise and transverse orientation. The outer matt cover layer had a thickness of about 2 m, the inner cover layer was about 0.6 m thick.

(2) B Base Layer

(3) 99.88% by wgt. Propylene homopolymer with melting point of 165 C. and melt flow index of 3.4 g/10 min, an n-heptane insoluble fraction of 94% 0.12% by wgt. N,N-bis-ethoxyalkyl amine (antistatic agent)
Outer Cover Layer: (Release Layer) 60% by wgt. Propylene homopolymer with melting point of 165 C. and melt flow index of 7.6 g/10 min and an n-heptane insoluble fraction of 94% 38.5% by wgt. MDPE with MFI of 14.4 g/10 min (21.6 kg and 190 C.); density 0.937 g/ccm3 and melting point 126 C. 1.5% by wgt. Polydimethyl siloxane having viscosity of 300,000 mm.sup.2/s. 0.33% by wgt. SiO.sub.2 as antiblocking agent, average particle size 5 m
Inner Cover Layer: 99.9% by wgt. Statistical ethylene-propylene-butylene terpolymer with ethylene content of 3% by weight and butylene content of 7% by weight (the rest propylene) and a melt flow index of 7.3 g/10 min 0.1% by wgt. SiO.sub.2 as antiblocking agent having an average particle size of 5 m

(4) All layers also received neutralising agent and stabiliser in the usual quantities.

(5) Production conditions in the individual process steps were:

(6) TABLE-US-00001 Extrusion: Temperatures Base layer: 250 C. Cover layers: 250 C. Temperature of draw-off roller: 20 C. Lengthwise Temperature: 110 C. stretching: Lengthwise stretching ratio: 5.5 Transverse Temperature: 170 C. stretching: Transverse stretching ratio: 9 Fixing: Temperature: 150 C. Convergence: 10%

(7) The surface of the outer cover layer underwent surface treatment in a corona process. After this treatment, the surface tension was 42 mN/m. Roughness Rz on the surface of the matt cover layer was 3.0 m.

EXAMPLE 2

(8) A film was produced as described in example 1. Differing from example 1, an ethylene-propylene copolymer having an ethylene fraction of 4% by weight (relative to the copolymer) and a melting point of 135 C.; and a melt flow index of 7.3 g/10 min at 230 C. and 2.16 kg load (DIN EN ISO 1133) was used in the matt cover layer instead of propylene homopolymer. The other composition and the process conditions as well as the corona treatment when manufacturing the film were unchanged. The film now had a roughness Rz of 3.3 m on the surface of the matt cover layer.

EXAMPLE 3

(9) A film was produced as described in example 1. Differing from example 1, the film was also subjected to flame treatment on the surface of the inner cover layer. The other composition and the process conditions as well as the corona treatment when manufacturing the film were unchanged.

EXAMPLE 4

(10) A film was produced as described in example 1. Differing from example 1, a symmetrical film was produced. The inner cover layer now had the same composition as the outer release layer of example 1. The other composition and the process conditions as well as the corona treatment when manufacturing the film were unchanged.

COMPARISON EXAMPLE 1

(11) A film was produced as described in example 1. Differing from example 1, the surface of the matt cover layer did not undergo any surface treatment. The other composition and the process conditions during production of the film were unchanged.

COMPARISON EXAMPLE 2

(12) A film was produced as described in example 1. Differing from example 1, the surface of the matt cover layer did not contain any polydimethyl siloxane. The other composition and the process conditions during production of the film were unchanged.

COMPARISON EXAMPLE 3

(13) A film was produced as described in example 1. Differing from example 1, the polydimethyl siloxane with a viscosity of 300,000 mm.sup.2/s was replaced with the same quantity of a polydimethyl siloxane having a viscosity of 30,000 mm.sup.2/s. The other composition and the process conditions during production of the film were unchanged.

COMPARISON EXAMPLE 4

(14) A film was produced as described in example 1. Differing from example 1, (as in comparison example 3), the polydimethyl siloxane with a viscosity of 300,000 mm.sup.2/s was replaced with the same quantity of a polydimethyl siloxane having a viscosity of 30,000 mm.sup.2/s. In addition, the surface of the matt cover layer was not subjected to a surface treatment (as in comparison example 1). The other composition and the process conditions during production of the film were unchanged.

COMPARISON EXAMPLE 5

(15) A film was produced as described in example 1. Differing from example 1, the polydimethyl siloxane with a viscosity of 300,000 mm.sup.2/s was replaced with the same quantity of a polydimethyl siloxane having a viscosity of 30,000 mm.sup.2/s. In addition, the MDPE in the outer cover layer was replaced with propylene homopolymer, so that this cover layer now contained about 98% by weight of the indicated propylene homopolymer. The other composition and the process conditions during production of the film were unchanged.

EXAMPLE 5

Laminate Production

(16) After their production, the films as described in the examples and comparison examples were processed as release films to form a film composite with a white to opaque base film. Treofan SHD was used as the base film. This is a multilayer, white-opaque BOPP film with CaCO3 and TiO2 in the base layer and an intermediate propylene homopolymer layer shiny side. The SHD base film underwent printing pretreatment on one side and was printed over the full area of the shiny surface. Following application of a solvent-free, two-component PU adhesive to the printing ink, this base film was laminated with the release films described in examples 1 to 4 and comparison examples 1 and 5 with its printed inner side facing the inner side of the release films. Each film composite produced in this way was coated with two different cold seal adhesives over the entire surface opposite the outer matt layer of the release film (as recorded in the table below). The coated composite films were rolled up and corresponding blanks were placed in stacks for test purposes such that the cold seal adhesive was in contact with the matt surface of the release film, and stored in this way until testing was done. The results of the test are summarised in table 1.

EXAMPLE 6

Printing of Example 3

(17) The film produced as described in example 3 was printed on the surface of the inner, flame-treated cover layer by reverse printing. Then, a cold seal adhesive was applied to this printed side.

(18) TABLE-US-00002 TABLE 1 Laminates according to example 5 PDMS PDMS content Release Viscosity outer cover Matt cover layer film mm.sup.2/s layer release film Corona mN/m Gloss 60 B1 300,000 1.5% 65% PP/35% PE 42 15 B2 300,000 1.5% 65% C2C3 Copo/35% PE 42 15 B3 300,000 1.5% 65% PP/35% PE 42* 15 B4 300,000 1.5% 65% PP/35% PE (both sides) 42 15 VB1 300,000 1.5% 65% PP/35% PE No corona 15 VB2 / / 65% PP/35% PE 42 16 VB3 30,000 1.5% 65% PP/35% PE 42 14 VB4 30,000 1.5% 65% PP/35% PE No corona 14 VB5 30,000 1.5% 98% PP 42 84 *Additional flame treatment on the inner surface (44 mN/m) B = Example; VB = Comparison example

(19) TABLE-US-00003 TABLE 2 Henkel 22-861 cold seal adhesive Seal seam strength Cold seal/Release Release Cold seal/Cold seal blocking force Cold seal transfer film N/15 mm N/30 mm to release side B1 S = 2.3 B = 0.9 No transfer B2 S = 2.2 B = 0.8 No transfer B3 S = 2.2 B = 0.9 No transfer B4 S = 2.2 B = 0.7 No transfer VB1 S = 1.5 B = 2.5 Transfer in spots VB2 S = 2.4 B = 2.5 Transfer in spots VB3 S = 1.8 B = 1.4 Low transfer VB4 S = 1.6 B = 2.8 Significant transfer VB5 S = 1.6 B = 0.5 No transfer

(20) TABLE-US-00004 TABLE 3 Sun Chemicals S 8078 cold seal adhesive Seal seam strength Cold seal/Release Release Cold seal/Cold seal blocking force Cold seal transfer film N/15 mm N/30 mm to release side B1 S = 2.5 B = 1.1 No transfer B2 S = 2.5 B = 0.9 No transfer B3 S = 2.7 B = 0.9 No transfer B4 S = 2.6 B = 0.8 No transfer VB1 S = 1.7 B = 3.2 Significant transfer VB2 S = 2.4 B = 3.7 Complete transfer VB3 S = 1.9 B = 2.0 Transfer in spots VB4 S = 1.6 B = 2.6 Transfer in spots VB5 S = 1.8 B = 0.6 No transfer

(21) TABLE-US-00005 TABLE 4 Release film, each printed on the inner cover layer in the reverse printing process Ex. Colour adhesion Release Scratch resistance Wrinkle resistance Tesa adhesive strip test film I Printing ink, base immediate after 1 day immediate after 1 day immediate after 1 day B3 Siegwerk NC 57, blue 3 1 2 1 10% 0% Nitrocellulose B3 Siegwerk VL 31, red 2 1 2 1 5% 0% Polyvinyl butyral PVB B1, B2, B4, VB1-VB5 are not intended for reverse printing due to absence of print preparation treatment Evaluation key for scratch resistance, wrinkle resistance: 1 - no, no colour abrasion 2 - minor 3 - moderate 4 - significant