GB2534080A

GB2534080A - Process

Info

Publication number: GB2534080A
Application number: GB1605436.3A
Authority: GB
Inventors: James Read Simon
Original assignee: Innovia Films Ltd
Current assignee: Innovia Films Ltd
Priority date: 2013-08-09
Filing date: 2013-08-09
Publication date: 2016-07-13
Anticipated expiration: 2033-08-09
Also published as: GB201314334D0; GB2534080B; WO2015019063A1; GB2516978A; GB2516978B; EP3030494A1

Abstract

A release liner is produced by providing a web of film 11; subjecting at least a first surface of the film web to a first plasma discharge treatment 14 in the presence of a gas (introduced at 13) which effectively functionalises the first surface of the film web to provide thereon functional groups which are capable of actively binding to a release compound and/or a precursor thereof; and subsequently depositing a coating of a release compound (introduced at16) onto the functionalized (with ketone, aldehyde, glyoxyl, amide, amine, hydroxide, nitride or vinyl groups) first surface of the film web by contacting the release compound and/or a precursor thereof with the functionalised first surface during a second plasma discharge treatment 17. The exemplified film 11 comprises a coextruded bubble film having a polypropylene core ethylene propylene copolymer skins. It is subjected to dielectric barrier discharge plasma treatments with ammonia in nitrogen and then with hexamethyl disiloxane in nitrogen, to produce a 50nm thick polydimethylsiloxane (PDMS) release coating. The release liners can be used with pressure sensitive adhesive labels and packaging films.

Description

PROCESS

The present invention relates to a process for manufacturing a release liner. More specifically, it relates to a process for manufacturing a release liner using plasma discharge treatment.

Release liners are used in a variety of applications. In particular, release liners are used with adhesive labels, for example pressure sensitive adhesive labels, and with packaging films. Release liners are generally made up of a substrate and a release coating. Typical release coatings are formed from waxes, silicones or fluoropolymers. The release coating aids the removal of the release liner from the adhesive surface to which it is attached.

It is known in the art to manufacture release liners by applying a release coating to a substrate using solvent-based wet-chemical coating. However, this process involves the use of volatile organic compounds which are expensive and harmful to the environment.

As an alternative to solvent-based wet-chemical coating, release liners have been manufactured using plasma discharge treatment to deposit a release coating onto a substrate. This avoids the use of harmful volatile organic compounds and can be run as a continuous process. Plasma discharge treatment tends to be carried out in the presence of an inert gas, for example a noble gas such as argon, or nitrogen.

EP 1 978 067 describes a release liner for use in a pressure-sensitive adhesive sheet comprising a release layer on a substrate, wherein the release liner is obtainable by a process comprising the steps of: providing a substrate; producing an atmospheric pressure plasma discharge in the presence of a gas; exposing the substrate to said atmospheric pressure plasma discharge; introducing a liquid aerosol comprising a precursor into said atmospheric pressure plasma discharge, thereby forming a release layer on the substrate; and curing the release layer on the substrate.

However, there are numerous problems associated with the prior art processes, for example, the release coating tends to be weakly bonded to the substrate. Further to this, the release coating includes low molecular weight species which migrate to the opposite surface of the substrate. This is particularly problematic when the release liner is wound into a roll since it can result in the contamination of the material attached to the release liner, for example a label facestock film, which may cause printing issues. Additionally, the release liner will tend to have a release force which is insufficient for most high speed applications.

Thus, there is a need for a process for manufacturing a release liner which does not suffer from the problems of the prior art. From the description that is to follow, it will become apparent how the present invention addresses the deficiencies associated with the prior art processes, while presenting numerous additional advantages.

According to a first aspect of the present invention, there is provided a process for manufacturing a release liner, comprising the steps of: a. providing a web of film; b. subjecting at least a first surface of the film web to a first plasma discharge treatment in the presence of a gas which effectively functionalises the first surface of the film web to provide thereon functional groups which are capable of actively binding to a release compound and/or a precursor thereof; and c. subsequently depositing a coating of a release compound onto the functionalised first surface of the film web by contacting the release compound and/or a precursor thereof with the functionalised first surface during a second plasma discharge treatment.

The inventors of the present invention have surprisingly found that the process of the present invention results in the coating of release compound being more strongly bonded to the surface of the film web.

Without wishing to be bound by any such theory, the inventors of the present invention believe that the first plasma treatment functionalises the surface of the film web to provide reactive functional groups thereon. These functional groups then covalently bond to the release compound and/or precursor thereof during the second plasma discharge treatment. Thus, producing a release liner in which the coating of release compound is strongly bonded to the surface of the film web.

Due to the strong bond between the coating of release compound and the surface of the film web, the tendency of the release compound to migrate to the opposite surface of the release liner is significantly reduced, if not eliminated. Further to this, the release force of the release liner has been found to increase.

Step b. and step c. may be carried out within the same reactor. For example, a single reactor with a first and a second plasma treatment zone which the film web sequentially passes through. Alternatively, step b. and step c may be carried out in different reactors.

The first and second plasma discharge treatments may be atmospheric pressure plasma discharge treatments. Preferably, the atmospheric pressure plasma discharge treatment is a dielectric barrier discharge (DBD) treatment.

The first and second plasma discharge treatments may be carried out in the presence of an inert carrier gas, for example a noble gas such as argon, and/or nitrogen The gas in step b. may comprise at least one functional agent. Preferably, the functional agent is selected from ammonia, 1,2-butadiene, 1,3-butadiene, 1,3-hexafluorobutadiene, 1-butene, 1-butyne, 2,2-dimethylpropane, cis-2-butene, trans-2-butene, acetylene, nitrous oxide, dimethylamine, ethylamine, methyl vinyl ether, methylamine, trimethylamine, carbon dioxide, carbon monoxide and hydrogen.

The functional agent may be present in an amount of from about 10 ppm to about 20000 ppm. Preferably, the functional agent is present in an amount of from about 200 ppm to about 5000 ppm.

The functional agent effectively functionalises the first surface of the film web to provide thereon functional groups which are capable of actively binding to a release compound and/or precursor thereof. The functional groups may include ketones, aldehydes, glyoxyls, amides, amines, hydroxides, nitrides and/or vinyls.

It has unexpectedly been found by the inventors of the present invention that the presence of a functional agent in the first plasma discharge treatment results in the grafting of functional groups on the surface of the film web which form strong covalent bonds with the release compound during the second plasma discharge treatment. Thus, forming a release compound coating which is strongly bonded to the surface of the film web.

The gas in step b. may comprise at least one oxidising agent such as oxygen, ozone, carbon dioxide, carbon monoxide, nitric and nitrous oxides or sulphur oxide, dioxide or trioxide. The oxidising agent may be present in an amount of from about 10 ppm to about 20000 ppm. Preferably, the oxidising agent is present in an amount of from about 200 ppm to about 5000 ppm.

The gas in step b. may comprise at least one cross-linker, for example, an unsaturated hydrocarbon such as ethylene or propylene. This is particularly advantageous when the release compound comprises an organosilicone since the cross-linker stabilises the organosilicone release compound. The cross-linker may be present in an amount of from about 10 ppm to about 1000 ppm. Preferably, the cross-linker is present in an amount of from about 50 ppm to 200 ppm.

The release compound precursor may comprise an organosilicone. The organosilicone may comprise at least one of a silane, a silanol, a silicide and a siloxane. Preferably, the release compound precursor comprises hexamethyl disiloxane (HMDSO), tetramethyl disiloxane (TMDSO) and/or 3-glycidyloxyethyl trimethoxysilane.

The release compound precursor may be present in an amount of from about 10 ppm to about 20000 ppm. Preferably, the release compound is present in an amount of from about 200 ppm to about 5000 ppm.

The release compound itself may comprise a polymer resulting from polymerisation of the release compound precursor. For example, the release compound may comprise poly(dimethyl siloxane), poly(dimethyl dichloro silane), poly(divinyl silane), poly(diphenyl siloxane), poly(phenylmethyl siloxane), 1,3-tetraphenyl 1,3-dimethyl disiloxane, and/or 1,3-diphenyl 1,2-tetramethyl disiloxane. Preferably, the release compound comprises poly(dimethyl siloxane).

The coating of release compound may be a nano-coating. In this context, the term 'nano-coating' may mean a coating with a thickness up to about 100nm, for example up to about 75nm, about 50nm or about 25nm, or with a thickness of from about 1nm to about 100nm, for example from about mm to about 75nm, from about ln m to about 50nm or from about lnm to about 25nm.

The film web may be formed by any process known in the art, including, but not limited to, cast sheet, cast film, or blown film.

The film web may comprise a substrate layer.

The substrate layer may comprise a polyolefin, for example polyethylene, polypropylene, polybutylene, mixtures, blends or copolymers thereof; a polyester, for example polyethylene terephthalate; a polyamide, for example nylon a polyurethane; a polyvinyl halide, for example polyvinyl chloride; an acetate and/or a biopolymer, for example cellulose and/or its derivatives, polylactic acid or polyhydroxyalkanoate.

Preferably, the substrate layer comprises polypropylene, for example biaxially oriented polypropylene (BOPP). The BOPP may be prepared as a balanced film using substantially equal machine direction and transverse direction stretch ratios, or can be unbalanced, where the film is significantly more orientated in one direction (MD or TD). Sequential stretching can be used, in which heated rollers effect stretching of the film in the machine direction and a stenter oven is thereafter used to effect stretching in the transverse direction. Alternatively, simultaneous stretching, for example, using the so-called bubble process, or simultaneous draw stenter stretching may be used.

The substrate layer may have a modulus in the range of from about 0.1 GPa to about 10 GPa. More specifically, the substrate layer may have a modulus in the range of from about 0.5 GPa to about 5 GPa. Even more specifically, the substrate layer may have a modulus in the range of from about 1 GPa to about 3 GPa.

Modulus is defined as the ratio of tensile stress to tensile strain as measured using a Tensometer. Young's modulus (E) describes tensile elasticity, or the tendency of an object to deform along an axis when opposing forces are applied along that axis. It is often referred to simply as elastic modulus.

The film web may comprise at least one skin layer. The skin layer is preferably the outermost layer of the film web.

The skin layer may be coextruded or laminated onto the substrate layer. Alternatively, the skin layer may be applied by coating techniques, including extrusion coating.

The skin layer may comprise a polyolefin for example polyethylene, polypropylene, polybutylene, mixtures, blends or copolymers thereof; a polyester, for example polyethylene terephthalate; a polyamide, for example nylon; a polyurethane; a polyvinyl halide, for example polyvinyl chloride; an acetate and/or a biopolymer, for example cellulose and/or its derivatives, polylactic acid or polyhydroxyalkanoate.

Additionally or alternatively, the skin layer may comprise an ethylene-propylene copolymer (EPM), an ethylene propylene-diene monomer copolymer (EPDM), polybutadiene, polyisoprene, a styrene-butadiene copolymer, a styrene-isoprene copolymer, a urethane, a polyester and/or mixtures or blends thereof.

Preferably, the skin layer comprises an ethylene-propylene copolymer, an ethylene propylene diene monomer copolymer or amorphous polyester.

The skin layer may have a thickness of from about 0.01 pm to about lOpm. Preferably, the skin layer has a thickness of from about 0.5pm to about 5pm, more preferably from about 0.7pm to about 2pm The skin layer may have a modulus of at least about 1% less than the modulus of the substrate layer. More preferably, the skin layer has a modulus of at least about 5% less than the modulus of the substrate layer. More preferably still, the skin layer has a modulus of at least about 10%, at least about 20%, at least about 30%, at least about 40%, at least about 50%, at least about 60%, at least about 70%, at least about 80% or at least about 90% less than the modulus of the substrate layer.

It has been found that by altering the modulus of the skin layer with respect to the modulus of the substrate layer, the release force of the release liner can be manipulated. Thus, it is possible to manufacture a release liner with a release force tailored to its application.

The release force required to remove the release liner from an adhesive surface to which it is attached may be from about 0.01 N to about 50 N. Preferably, the release force is from about 0.1 N to about 10 N. More preferably, the release force is from about 0.1 N to about 1 N. The release liner manufactured by the process of the present invention can be of a variety of thicknesses depending on the application requirements. The release liner may be from about 5pm, about 10pm, about 15pm, about 20pm, about 25pm, about 30pm to about 40pm, about 50pm, about 75pm, about 100pm, about 125pm, about 150pm, about 200pm or about 250pm Release liners manufactured by the process of the present invention may be particularly useful in applications such as pressure sensitive adhesive labels/tapes/packaging/vehicle decal films.

According to a second aspect of the present invention, there is provided a release liner obtained or obtainable by the process as hereinbefore described.

According to a third aspect of the present invention, there is provided a release liner comprising a film functionalised at its surface by one or more functional groups selected from ketone, aldehyde, glyoxyl, amide, amine, hydroxide, nitride and vinyl, and a release compound bonded thereto by means of a chemical bond with the functional group.

It should be noted that all features of the first aspect of the invention also relate to the second and third aspects of the invention.

The present invention is more specifically described with reference to the following figures: Figure 1: is a schematic representation of a web of film passing though two sequential plasma discharge treatments wherein the functional agent is injected prior to the electrode Figure 2: is a schematic representation of a web of film passing through two sequential plasma discharge treatments wherein the functional agent is injected through the electrode In Figure 1, a web of film 11 is fed into a plasma discharge reactor with the aid of roller 12. Fluid injector 13 injects a functional agent in liquid form. The functional agent is vaporised and carried by an inert carrier gas to the first discharge gap 15. The first discharge gap 15 is defined as the space between the electrode 14 and roller 12. The surface of the web of film 11 positioned within the first discharge gap 15 is functionalised such that functional groups are grafted thereto.

Fluid injector 16 injects a release compound precursor. The release compound precursor is vaporised and carried by the inert carrier gas to second discharge gap 18. The second discharge gap 18 is defined as the space between electrode 17 and roller 12 The web of film 11 is fed from the first discharge gap 15 into the second discharge gap 18 where the release compound precursor is covalently bonded to the functional groups on the surface of the web of film 11. Thus, a coating of release compound is deposited and securely bonded to the surface of web of film 11.

In Figure 2, a web of film 21 is fed into a plasma discharge reactor with the aid of roller 22. An inert carrier is passed between the first discharge gap 25, which is defined as the space between the electrode 24 and roller 22. Fluid injector 23 injects a release compound precursor through electrode 24 and into the plasma discharge gap 25 where it is vaporised. The surface of the web of film 21 positioned within the first discharge gap 25 is functionalised such that functional groups are grafted thereto.

Fluid injector 26 injects a release compound precursor through electrode 27 and into the second plasma discharge gap 28 where it is vaporised. The second discharge gap 28 is defined as the space between electrode 27 and roller 22. The web of film 21 is fed from the first discharge gap 25 into the second discharge gap 28 where the release compound precursor is covalently bonded to the functional groups on the surface of the web of film 21 Thus, a coating of release compound is deposited and securely bonded to the surface of the web of film 21.

Example 1

A web of film having a substrate layer of propylene homopolymer and coextruded skin layers of ethylene propylene copolymer (EPM) is manufactured by means of a bubble process. The three-layer film web has an overall thickness of 30pm.

The film web is subjected to a first dielectric barrier discharge treatment in the presence of 500 ppm ammonia in a nitrogen carrier gas. The power used is 65 w. min/m2 and the speed is 50m/min. The film web is then subjected to a second dielectric barrier discharge treatment in the presence of 500 ppm hexamethyl disiloxane in nitrogen. Again, the power used is 65 w.min/m2 and the speed is 275m/min. The first and second dielectric barrier discharge treatments are carried out in the same reactor.

A nano-coating of poly(dimethyl siloxane) is deposited on the surface of the film web, having a thickness of 50nm as measured by cross-sectioning the film and putting it under a scanning electron microscope (SEM) in EDX mode.

Claims

CLAIMS1 A process for manufacturing a release liner, comprising the steps of: a. providing a web of film; b. subjecting at least a first surface of the film web to a first plasma discharge treatment in the presence of a gas which effectively functionalises the first surface of the film web to provide thereon functional groups which are capable of actively binding to a release compound and/or a precursor thereof; and c. subsequently depositing a coating of a release compound onto the functionalised first surface of the film web by contacting the release compound and/or a precursor thereof with the functionalised first surface during a second plasma discharge treatment.
2. A process according to Claim 1, wherein step b. and step c. are carried out within the same reactor.
3. A process according to Claim 1, wherein step b. and step c. are carried out in different reactors.
4 A process according to any one of claims 1 to 3 wherein the first and second plasma discharge treatments are atmospheric pressure plasma discharge treatments.
5. A process according to Claim 4, wherein the atmospheric pressure plasma discharge treatment is a dielectric barrier discharge treatment.
6 A process according to any one of claims 1 to 5, wherein the first and second plasma discharge treatments are carried out in the presence of an inert carrier gas.
7. A process according to Claim 6, wherein the inert carrier gas comprises a noble gas such as argon, and/or nitrogen.
8. A process according to any one of claims 1 to 7, wherein the gas in step b. comprises at least one functional agent.
9 A process according Claim 8, wherein the functional agent is selected from ammonia, 1,2-butadiene, 1,3-butadiene, 1,3-hexafluorobutadiene, 1-butene, 1-butyne, 2,2-dimethylpropane, cis-2-butene, trans-2-butene, acetylene, nitrous oxide, dimethylamine, ethylamine, methyl vinyl ether, methylamine, trimethylamine, carbon dioxide, carbon monoxide and hydrogen.
10.A process according to any one of claims 1 to 9, wherein the release compound precursor comprises an organosilicone.
11.A process according to Claim 10, wherein the organosilicone comprises at least one of a silane, a silanol, a silicide and a siloxane.
12.A process according to any one of claims 1 to 11, wherein the release compound precursor comprises hexamethyl disiloxane (HMDSO) and/or tetramethyl disiloxane (TMDSO).
13.A process according to any one of claims 1 to 12, wherein the release compound comprises poly(dimethyl siloxane).
14.A process according to any one of claims 1 to 13, wherein the coating of the release compound is a nano-coating.
15.A process according to any one of claims 1 to 14, wherein the film web comprises a substrate layer.
16.A process according to Claim 15, wherein the substrate layer comprises a polyolefin, for example polyethylene, polypropylene, polybutylene, mixtures, blends or copolymers thereof; a polyester, for example polyethylene terephthalate; a polyamide, for example nylon; a polyurethane; a polyvinyl halide, for example polyvinyl chloride; an acetate and/or a biopolymer, for example cellulose and/or its derivatives, polylactic acid or polyhydroxyalkanoate.
17. A process according to Claim 16, wherein the substrate layer comprises polypropylene.
18.A process according to any one of claims 1 to 17, wherein the film web comprises at least one skin layer.
19.A process according to Claim 18, wherein the skin layer comprises a polyolefin for example polyethylene, polypropylene, polybutylene, mixtures, blends or copolymers thereof; a polyester, for example polyethylene terephthalate a polyamide, for example nylon; a polyurethane; a polyvinyl halide, for example polyvinyl chloride; an acetate and/or a biopolymer, for example cellulose and/or its derivatives, polylactic acid or polyhydroxyalkanoate.
20.A process according to Claim 18, wherein the skin layer comprises ethylene-propylene copolymer, ethylene propylene-diene monomer copolymer, polybutadiene, polyisoprene, a styrene-butadiene copolymer, a styrene-isoprene copolymer, a urethane, a polyester and/or mixtures or blends thereof.
21.A release liner obtained or obtainable by the process of any one of claims 1 to 20
22.A release liner comprising a film functionalised at its surface by one or more functional groups selected from ketone, aldehyde, glyoxyl, amide, amine, hydroxide, nitride and vinyl, and a release compound bonded thereto by means of a chemical bond with the functional group.