HK1138541A - Sealable, peelable film - Google Patents

Description

Sealable and peelable film

The present invention relates to sealable and peelable films and methods for making the films.

WO-A-96/04178 discloses A peelable film comprising A core layer comprising an olefin polymer and A heat-sealable layer comprising A mixture of Low Density Polyethylene (LDPE) and A material incompatible with the LDPE, for example an olefin polymer or A copolymer or terpolymer of ethylene, propylene or butene. Such a film structure can be heat sealed to a plastic container to form the lid of the container or itself form the package.

US2001/0031371 describes a sealable film comprising an inner layer comprising an olefin-containing polymer, a sealing layer and a separable layer located between the inner layer and the sealing layer, the separable layer comprising (1) an ethylene-propylene block copolymer or (2) a mixture of polyethylene and another olefin incompatible with the polyethylene, in particular (i) a polypropylene homopolymer or (ii) an ethylene-propylene block copolymer. Methods of making the sealable film are described.

WO96/20085 relates to a multi-layer polymeric film comprising a polypropylene base layer, a non-hollow intermediate layer on the base layer and a heat-sealable polymer layer on the intermediate layer, the non-hollow intermediate layer having an internal tack lower than the bond of the intermediate layer to either the base layer or the heat-sealable layer and lower than the internal tack of either the base layer or the heat-sealable layer. Such films enable the formation of a peelable seal by rupture of the intermediate layer, since the internal tack of the intermediate layer is lower than the internal tack of the core layer or the heat-sealable layer.

US4565738 describes composite multilayer films suitable for use as packaging films having a propylene polymer base layer and at least one skin layer formed from a mixture of a propylene-ethylene block copolymer and an ethylene-higher olefin random copolymer. The composite film is preferably coextruded and is suitable as a substrate for an additional polymeric layer, such as a heat sealable coating, which may be adhered to the substrate by a polymeric primer resin.

EP- ｃA-746468 describes ｃA multilayer film which is peeled off by breaking ｃA layer, referred to in the specification as an intermediate layer, between ｃA base layer and ｃA heat-sealable layer. The intermediate layer preferably comprises a mixture of polymers that do not co-crystallize.

U.S. Pat. No. 6,451426 discloses an oriented sealant film comprising an inner layer of an olefin polymer, a sealing copolymer layer, and a separable layer containing a block copolymer between the inner layer and the sealing layer.

United states patent No. 5,443,915 discloses an oriented polyolefin film having a white opaque cold-seal receptive skin layer on one side of the core layer and a vacuum deposited metal layer on the other side of the core layer.

U.S. Pat. No. 5,358,792 discloses heat sealable compositions comprising (a) from about 30 to about 70 wt% of a low melting polymer comprising a very low density ethylene-based copolymer having a density of about 0.88g/cm³To about 0.915g/cm³Melt index of about 1.5dg/min to about 7.5dg/min, molecular weight distribution (M)_w/M_n) Not more than about 3.5, and (b) about70 wt% to about 30 wt% of a propylene-based polymer.

U.S. patent No. 5,482,780 discloses an oriented poly-alpha-olefin film having: isotactic propylene homopolymer core layer; a cold seal release (cold seal release) skin layer adhered to one side of the core layer; and a surface treated receiving cold seal layer on the other side of the core layer or such treated layer having a cold seal adhesive composition on the treated surface of the layer. The release cold seal skin layer comprises a slip agent and a blend of two polymers, an ethylene-propylene random copolymer comprising about 2% to 8% ethylene in the copolymer and an ethylene-butylene copolymer comprising about 0.5% to 6% ethylene in the copolymer. The cold seal receptive layer is an ethylene-propylene random copolymer containing about 2 to 8% ethylene.

Us patent No. 5,500,265 discloses a peelable film comprising (a) a core layer comprising an olefin polymer, (b) a skin layer on at least one surface of the core layer, the skin layer comprising: a butene polymer and another olefin polymer or a polymer of polybutene and at least one other olefin, and (c) a coating layer on the skin layer.

Us patent No. 5,716,698 relates to a peelable, oriented, opaque, multi-layer polyolefin film comprising at least one opaque layer and a peelable skin layer.

U.S. patent No. 6,248,442 relates to multilayer films that are heat sealable over a wide temperature range. The patent also relates to multilayer films that provide easy opening and sealing of the package. The film in this patent is composed of a core layer comprising linear low density polyethylene (LLPDE) and at least one skin layer having a melting point at least 10 ℃ lower than the melting point of the core layer.

5,997,968 discloses a multilayer polyolefin film comprising at least three coextruded layers comprising an opaque base layer, a middle layer and an outer strippable skin layer comprising two incompatible polyolefins wherein the middle layer comprises at least 80% by weight of a polyolefin and the polyolefin has a melting point or glass transition temperature lower than the polyolefin forming the base layer.

Us patent No. 6231975 discloses a sealable film comprising an inner layer of any olefin polymer, a sealing layer and a separable layer therebetween. The separable layer comprises an ethylene-propylene copolymer or a mixture of polyethylene and another olefin, which forms an incompatible mixture (mix) or blend.

US2003/0134159 a1 discloses a sealable film comprising a core layer of an olefin polymer and a separable layer outside the core layer, and further an optical modifying layer and a sealing layer, wherein the optical modifying layer is located between the separable layer and the sealing layer.

US2004/0115457 a1 and US2004/0115458 a1 both describe sealable and peelable films having a relatively thick peelable core layer.

WO 00/78545 discloses an openable bag.

Another type of peelable seal is described in our co-pending uk patent application No. 0514785.5.

There is a continuing need in the field of sealable and peelable film structures for improved products. There is a particular need for a film structure having a sealable outer layer that seals well to itself or to other surfaces over a wide range of temperatures and/or pressures, and is capable of being peeled away in one layer of a multilayer film while maintaining at least one of the following properties acceptable for the end use of the film: gloss, haze, opacity, printability, and COF. There is a particular need for peelable films that can be easily opened without causing "z-direction" tears. In stretched polyolefin films, especially in biaxially oriented polypropylene films, the mechanical strength of the sealing seam is generally higher than the film itself, so that not only the sealing seam breaks when opening the sealed package. Typically, upon opening the package, the tear propagates uncontrollably throughout the film. Peelable films are films that once sealed can be mechanically separated again without damaging or destroying the film itself. Peelable films are generally required to have good sealing properties and also to allow controlled opening of the bag or package. A peelable heat sealable film can be formed when a coating film is formed by coating a biaxially oriented polypropylene film, which is a multilayer film composed of a core layer of a homopolymer of polypropylene, a skin layer formed on each side or major surface of the core layer, and a heat sealable coating layer. Such skin layers may be formed from copolymers such as copolymers of propylene and ethylene, including block copolymers. When the skin layer is coated with incompatible phases in the cladding layer, the skin layer formed as the cladding layer during the film manufacturing process is considered to give a peel seal. This limits the failure to the cladding layer and away from the core layer, thereby avoiding any possibility of tearing the core seal. The result is a weaker seal than a conventional seal, but the same seal strength as a whole is achieved without tearing.

When the film is torn at the seal, the z-direction tear breaks the integrity of the multilayer film. The film with the z-direction tear has not yet completely separated at the seal line. Instead, the separation or tear has already extended to the other layers of the film. It is difficult to completely reclose a package having a z-direction tear, thereby affecting the ability of the package to maintain the freshness or integrity of its contents. If the z-direction tear can be eliminated, the package is easily refolded and sealed by simple mechanical means such as clips or adhesive labels.

It is an object of the present invention to provide a sealable polymer film having peelability. It is another object of the present invention to provide a thermoplastic film structure having a sealable outer layer that seals well over a wide temperature range. It is another object of the present invention to provide a thermoplastic film structure having a sealable outer layer that can be easily opened when sealed without creating a z-direction tear. It is another object of the present invention to provide such films having satisfactory optical and hot tack properties. It is another object of the present invention to provide such a film for packaging and peelably sealing objects or products.

The present invention provides a sealable and peelable film comprising a four layer coextruded layer comprising a core layer which contributes primarily to the thickness of the film, a first sealing layer on one side of the core layer and a second sealing layer or laminate layer on the other side of the core layer and the film comprising a peelable layer between the first sealing layer and the core layer and/or between the second sealing layer or laminate layer and the core layer and wherein the peelable layer is adjacent the first sealing layer and/or the second sealing layer and/or laminate layer and wherein the relative thickness (p: s/l ratio) of the peelable layer to its adjacent sealing layer and/or laminate layer is from 1: 10 to 5: 1.

In the case where the film of the invention is made as a single web, the four-layer structure comprises a first sealing layer on one side of the core layer and a second sealing layer on the other side of the core layer, wherein the peelable layer is located between the core layer and at least one of the sealing layers and adjacent to at least one of the sealing layers.

In the case where the film of the invention is made into a laminate, the four-layer structure comprises a first sealing layer on one side of the core layer and a laminate layer on the other side of the core layer, the two separate webs of the film being laminated to each other (laminate layer to laminate layer) to form a seven-layer laminate structure (the two laminate layers effectively forming separate layers in the laminate structure), wherein the peelable layer is located between the core layer and the first sealing layer and/or laminate layer and adjacent to the first sealing layer and/or laminate layer.

The film of the present invention must comprise the four-layer structure or the laminated seven-layer structure described above, but may also comprise further or additional layers by coextrusion, coating or lamination. The sealable and peelable film structure of the present invention may therefore further comprise one or more intermediate layers between the core layer and the first sealing layer, between the core layer and the second sealing layer, between the core layer and the laminate layer, between the core layer and the peel layer, as the case may be.

In the films of the present invention, the release layer is isolated from contact with the external environment at its major surface by at least the sealing and/or lamination layers adjacent thereto, and thus the effectiveness of the release layer is enhanced and/or the film can be maintained for a longer period of use in its final application.

The release layer preferably comprises at least one block copolymer component.

The block copolymer component in the release layer preferably contains at least one olefinic component, more preferably at least two olefinic components are present, the block copolymer being formed at least in part by block copolymerisation of one olefinic component or mixture of olefinic components with another olefinic component or mixture of olefinic components. For example, the block copolymer matrix may include polypropylene and polyethylene.

In one embodiment of the invention, the release layer is comprised entirely of the block copolymer component. In alternative embodiments, the block copolymer substrate may be mixed with one or more other suitable materials to form a release layer, provided that the release layer retains its releasable properties. The film release layer may thus comprise a blend of the block copolymer matrix with another polymeric material such as polyethylene, polypropylene, blends thereof, and/or other known polyolefins.

The peelable sealable film of the present invention can provide satisfactory optical properties and can be obtained in a multilayer film in which a block copolymer component is used in the release layer. The wide angle haze value of the films of the present invention is preferably less than about 5, more preferably less than about 4, and most preferably less than about 3. The gloss value (at 45 ℃) of the films of the present invention is preferably at least about 75, more preferably at least about 80, yet more preferably at least about 85 and most preferably at least about 90. Without wishing to be bound by theory, it is believed that one or more desirable optical properties of the film can be maintained by ensuring that the release layer is thin-i.e., by controlling the p: s/l ratio.

The sealing layer may be sealable itself or may be coated with a sealable coating.

"sealable" means heat sealable, cold sealable, press sealable, or any suitable combination of these forms of sealing. For most applications, heat-sealable films are used.

The matrix or core layer contributes primarily to the thickness of the film, preferably meaning that the matrix (or each bonded matrix) or core layer is the thickest monolayer in the film, more preferably the matrix (or each bonded matrix) or core layer is thicker than the other layers bonded in the film. Preferably the substrate (or each bonded substrate) or core layer contains more than 90%, more preferably more than 95%, yet more preferably more than 97.5% of the total film thickness.

The release layer is preferably adjacent to the core layer of the film. This preferably means that there is no intermediate layer between the release layer and the core layer.

The release layer is adjacent to the first sealing layer of the film, or adjacent to the second sealing layer of the film, or adjacent to the lamination layer of the film, as the case may be. This preferably means that there is no intermediate layer between the peeling layer and the first sealing layer (if adjacent thereto) or between the peeling layer and the second sealing layer (if adjacent thereto) or between the peeling layer and the lamination layer of the film (if adjacent thereto), as the case may be.

The relative thickness (p: s/l) between the release layer and the sealing and/or lamination layer adjacent thereto may be selected depending on the end use of the film. In contemplated form-fill-seal bag making applications and other applications of the film, the p: s/l ratio is from about 1: 10 to about 5: 1, preferably from about 1: 8 to about 3: 1, more preferably from about 1: 6 to about 2: 1, and more preferably from about 1: 4 to about 1: 1.

The thickness of the release layer can be selected such that the peel strength (when measured at a temperature of 110 ℃ to 140 ℃ and a heat seal threshold of 15psi/2 secs) is less than about 750g/25mm²Preferably less than about 650g/25mm²And more preferably less than about 600g/25mm²And most preferably less than about 550g/25mm²。

The thickness of the release layer can be selected such that the peel strength (when measured at a temperature of 110 ℃ to 140 ℃ and a heat seal threshold of 5psi/0.5 secs) is less than about 650g/25mm²Preferably less than about 600g/25mm²And more preferably less than about 550g/25mm²And most preferablyLess than about 500g/25mm²。

The thickness of the release layer is selected to be thick enough to provide consistent release, but thin enough to provide good optical properties to the film. The thickness of the release layer is preferably 0.3 μm to 3 μm, more preferably 0.35 μm to 2.5 μm, yet more preferably 0.4 μm to 2.0 μm, and most preferably 0.5 μm to 1.5 μm.

The film core layer may include a polyolefin film, such as polyethylene, polypropylene, blends thereof, and/or other known polyolefins. The polymer film can be made by any process known in the art including, but not limited to, cast sheet, cast film, or blown film. The film core may be a single layer or a multi-layer structure. The invention is particularly applicable to films comprising cavitated or non-cavitated polypropylene having a polypropylene core and skin layers (sealing and/or laminating layers) of substantially lower thickness than the core layer and formed, for example, from copolymers of ethylene and propylene or terpolymers of propylene, ethylene and butene. The film may comprise a biaxially oriented polypropylene (BOPP) film, which may be made into a balanced film with substantially the same machine and transverse direction stretch, or may be unbalanced, wherein the film is significantly more oriented in one direction (MD or TD). Continuous stretching can also be used, where heated rolls stretch the film in the machine direction, followed by a stenter oven to stretch the film in the cross direction. Alternatively, simultaneous stretching, for example, by a so-called foaming process, or simultaneous draw stenter stretching (simultaneous draw stentering stretching) may be used.

Alternatively, the film core layer may comprise, for example, a polyester film, a polyamide film, or an acetate film.

The core layer may be non-cavitated or it may be cavitated if an opaque film is desired.

One of the advantages of the sealable peelable film of the present invention is the peelability provided by the release layer, which allows the manufacturer to adjust the core layer and/or skin layers and/or intermediate layers and/or coatings at will to meet manufacturing requirements such as gloss, haze, opacity, printability, COF, etc.

The films of the present invention are typically used in commercial packaging such as in ream wrap (ream wrap), overwrap, and other types of packaging.

The present invention provides a sealed package formed from a sealable and peelable film, the film comprising a four-layer coextruded layer comprising a core layer which contributes mainly to the thickness of the film, a first sealing layer on one side of the core layer, and a second sealing layer or laminate layer on the other side of the core layer, and the film comprising a peel layer between the first sealing layer and the core layer and/or between the second sealing layer or laminate layer and the core layer, and wherein the peel layer is adjacent to the first sealing layer and/or the second sealing layer and/or the laminate layer, and wherein the relative thickness (p: s/l ratio) of the peel layer and the sealing layer and/or laminate layer adjacent thereto is from 1: 10 to 5: 1, the package being formed by wrapping the film around an object to be packaged in such a way that at least one film overlap region is obtained, and heat sealing the obtained overlapping film portions to each other to provide at least one sealed region of the package, the sealed region can be subsequently opened by manually separating the overlapping film portions without substantially tearing the film at or around the sealed region.

Without wishing to be bound by theory, it appears that the block copolymer release layer provides the desired release properties by allowing the heat seal film to be peeled from the adjacent film with which it overlaps, by peeling within the block copolymer release layer of the film.

Preferably, the polymeric film is a multilayer film comprising a core layer, a block copolymer release layer and two skin layers of a different material than the release layer. The skin layer (sealing layer and/or lamination layer) may comprise a polymeric material and may comprise a homopolymer and/or copolymer material and may be a mixture of two or more such materials. The skin layer may comprise a non-block copolymer structure, such as a random copolymer structure, a homopolymer structure, or a suitable mixture of materials. The skin layer is formed by co-extrusion onto the substrate.

The presence of the skin layer may help to achieve a more preferred aspect of the present invention because peeling initiated in the release layer, e.g., between two block copolymer components, may be prevented or hindered from propagating outside the release layer. Propagation of the peel through the film skin layer may produce a torn film rather than a peelable film.

The invention accordingly provides, in one of its preferred aspects, a sealed package formed from a sealable and peelable film, the film comprising four coextruded layers including a core layer which contributes primarily to the thickness of the film, a first sealing layer on one side of the core layer, and a second sealing layer or laminate layer on the other side of the core layer, and the film comprising a peeling layer between the first sealing layer and the core layer and/or between the second sealing layer or laminate layer and the core layer, and wherein the peeling layer is adjacent the first sealing layer and/or the second sealing layer and/or the laminate layer, and wherein the relative thickness (p: s/l ratio) of the peeling layer and its adjacent sealing layer and/or laminate layer is from 1: 10 to 5: 1, the package being formed by wrapping the film around an object to be packaged in such a way that at least one region of overlap of the film is obtained, and sealing the resulting overlapping film portions to one another to provide at least one sealed region of the package which can be subsequently opened by manually separating the overlapping film portions without substantially tearing the film at or around the sealed region.

Preferably, the sealable material and/or the sealable coating is a heat sealable material and the overlapping film portions are sealed to each other by heat sealing.

Preferably, the sealed package of the present invention is formed by cutting a sheet of polymeric film from a roll of polymeric film, wrapping the cut sheet of polymeric film around an object to form a film tube, with the ends of the package overlapping and sealing the overlapped ends to form a circumferential seal. Preferably, the cartridge is closed and sealed at each end to form an envelope or wrap seal.

One particular application of the film and sealed package of the present invention is ream wrap. Another application is overwrapping. Other packaging applications are also possible.

In the case of ream wrap, large quantities of paper used in copiers, computers, printers and other applications are most commonly wrapped with ream wrap made from a variety of wrapping materials for shipping, warehousing and retail. Traditionally these packaging materials are paper, plastic film or paper/plastic film laminates.

The packaging material protects the packaged paper product from physical damage and moisture during shipping and storage. The packaging material also protects the packaged paper product from physical damage during repeated handling and storage on retail shelves.

The distribution of large quantities of paper has been converted from a box package for large users to a wrapped ream of paper sold in individual packages containing, for example, 500 sheets of paper. This form of distribution of large quantities of paper has an increasing demand for packaging material due to the need to handle the individual packages more frequently. Frequent handling of the reams has resulted in more ream unraveling, damaging the wrapped paper product by absorbing moisture, tearing, or creating small curls-physical damage that can ultimately cause failure in the end user's printer or copier. However, improving the ability of the package to avoid damage caused by handling can make the packaged product more difficult to open.

One way to solve this problem is to provide sealing means which have sufficient mechanical resistance to keep the seal intact during storage and transport, for example until the package or packaging material is opened, and which still enable manual opening of the package at or near the seal, without damaging the packaged paper product.

The invention is particularly suitable for use in ream wrap technology. Thus, according to the present invention, there is provided a sealed ream wrap in which the object to be wrapped is a stack of sheets.

According to the present invention there is also provided a sealed package comprising a polymeric film printed on its skin layer with at least one ink as described above.

The film core or the skin layer of the film may comprise additional materials such as anti-tack additives, opacifiers, fillers, UV absorbers, cross-linking agents, colorants, waxes, and the like.

The film of the present invention may also be further treated, for example by corona discharge treatment, to better improve the ink receptivity of the film or the skin layer of the film.

The film used in the present invention can have various thicknesses according to the use requirements. For example, they can be from about 10 μm to about 240 μm thick, and preferably from about 15 μm to about 90 μm thick.

At least one of the skin layers in the multilayer film of the present invention is preferably inked.

The hot tack of the film is found to depend at least to some extent on the thickness of the skin layer, in particular the thickness of the sealant layer adjacent the release layer (typically the first sealant layer). The thickness of the skin layer is preferably from about 0.2 μm to about 3 μm, preferably from about 0.3 μm to about 2.5 μm, more preferably from about 0.5 μm to about 2.0 μm, and most preferably from about 1.0 μm to about 2.0 μm. In some cases, the sealing layer adjacent to the peeling layer is thicker than the sealing layer or the lamination layer not adjacent to the peeling layer.

In certain embodiments of the present invention, it is contemplated to provide a film having a functional and/or cosmetic coating.

In a preferred embodiment of the invention, a film is provided having a printable coating on at least one sealing layer.

The coating film of the present invention is suitably prepared by a coating dispersion method for a film substrate. Dispersants used for substrate coating should contain about 15% to 70% solids, preferably 20% to 60% solids, more preferably 25% to 50% solids, to achieve satisfactory film forming properties. The film formed should be uniform and continuous.

The dispersant may be coated on the surface of the selected web and dried using any suitable conventional technique. The coating composition of the present invention can be applied by any of various other known techniques, such as dip coating, weld coating, knife coating, air knife coating, gravure coating and twist roll coating, extrusion coating, inclined plate coating, curtain coating, and the like. After coating, the layer is typically dried by simple evaporation, and may be accelerated by known techniques such as convection heating. The dispersant is preferably applied using a gravure printing process and the drying step is carried out in an oven. Drying of the applied dispersant removes the water from the dispersant, leaving a uniform continuous film with any non-film-forming particles dispersed in the film.

The coating is preferably an acrylic coating.

One or more functional and/or cosmetic additive combinations may also be added to the films of the present invention. Suitable additives may be selected from one or more of the following, mixtures thereof and/or combinations thereof: UV absorbers, dyes, pigments, colorants, metallized and/or pseudo-metallized coatings, lubricants, antistatic agents (cationic, anionic and/or nonionic, such as poly (oxyethylene) sorbitan monooleate), antioxidants (such as phosphoric acid, tris (2, 4-di-tert-butylphenyl) ester), surfactants, stiffening aids, slip aids (such as hot or cold slip aids which improve the ability of the film to satisfactorily slip from the surface at about room temperature, e.g. microcrystalline waxes), gloss improvers, prodegradants, barrier coatings which alter the gas and/or moisture permeability of the film (such as polyvinylidene halides, e.g. PVdC), antiblocking aids (such as microcrystalline waxes, e.g. having an average particle size of from about 0.1 μm to about 0.6 μm), antiblocking additives (such as fumed silica, pseudo-metallized coatings, non-metallized coatings, Silicone rubber), particulate materials (e.g., talc), COF increasing additives (e.g., silicon carbide), additives that improve ink adhesion and/or printability, additives that increase stiffness (e.g., hydrocarbon resins), additives that increase shrinkage (e.g., hard resins).

Some or all of the additives listed above may be added together as a composition to coat the films of the present invention and/or to form a new layer, which may itself be coated and/or may form the outer or skin layer of the sheet. Alternatively, some or all of the foregoing additives may be separated and/or added directly to the core layer (e.g., as part of the initial polymeric composition) during film formation, and thus they may or may not form a layer or coating.

The present invention will now be described in more detail with reference to the following examples.

Examples 1 to 3

Preparation of the film

A tube having four layers of polymer was formed as follows: a core layer of polypropylene homopolymer was coextruded with two layers of polyethylene/polypropylene/polybutylene terpolymer (random copolymer) (first and second sealant layers) as skin layers on either side of the core layer, and with a peel layer of polypropylene-polyethylene block copolymer (available from Total Petrochemicals under the trade designation PPC 55660) located between the core layer and the first sealant layer. The tube is cooled and then reheated before being blown into a four-ply biaxially oriented film tube. The tube is then pinched and spliced into a single web.

First, three 30 μm films were produced in this way, each layer of which is characterized as shown in table 1 below:

TABLE 1

The films were sealed (first sealant layer to first sealant layer) and the peel strength of the films was measured at a range of sealing temperatures and the results are shown in table 2. The heat seal threshold (heat seal threshold) was set to 15psi/2 secs.

TABLE 2

The optical properties of these films were also measured and the results are shown in table 3:

TABLE 3

Sample (I)	WAH	Gloss 45 °
			1	3.5	87
2	2.4	91
			3	3	88

The hot tack of these films was also measured using the Spring Method (Spring Method) applied directly to the films after sealing, and the results are shown in table 4, showing the average seal area% open:

TABLE 4

Peel/seal strengths, although slightly different, were acceptable. The most noticeable difference between samples is the hot tack properties. It was shown that the lower coat weight BCP consistently performed well with the higher coat weight first sealant layer under a variety of test conditions.

In certain end uses of the invention, hot tack is particularly important, for example, in the manufacture of form-fill-seal packages. In this respect, hot tack is a measure of how strong a seal is while still hot and is intended to measure whether the seal will break at the bottom of the package when filled from the top, the filling step typically being performed while the seal is still hot.

Examples 4 to 10

Preparation of the film

In examples 4 to 8, tubes with four layers of polymer were formed as follows: a core layer of polypropylene homopolymer (formulated with a slip agent) and two layers of polyethylene/polypropylene/polybutylene terpolymer (random copolymer) as skin layers on either side of the core layer (first and second sealant layers), and a release layer of polypropylene-polyethylene block copolymer (available from Total Petrochemicals under the trade name PPC 5660) located between the core layer and the first sealant layer were coextruded. The tube was cooled and then reheated before being blown into a four-ply biaxially oriented film tube. The film tube was then pinched and spliced to form a single web film having four layers.

In this way 5 films were produced, the properties of the film layers being shown in table 5:

TABLE 5

Example 5 is a film with a white pigment, where the pigment was added to the polypropylene core prior to extrusion. The pigment is TiO provided by Dupont₂ R104。

In examples 9 to 10, four-layer polymer tubes were formed as follows: a core layer of polypropylene homopolymer (formulated with a slip agent) was coextruded with a layer of polyethylene/polypropylene/polybutylene terpolymer (random copolymer comprising polypropylene (92% w/w)/ethylene (4% w/w)/butylene-1 (4% w/w)) as a skin layer (first sealant layer) on one side of the core layer, and with a release layer of polypropylene-polyethylene block copolymer (available from TotalPetrochemicals under the trade name PPC 5660) located between the core layer and the first sealant layer. The other side of the core layer had a laminated layer of polyethylene/polypropylene/polybutylene terpolymer (random copolymer comprising polypropylene (82% w/w)/ethylene (1% w/w)/butene-1 (17% w/w)). The tube is cooled and then reheated before being blown into a four-ply biaxially oriented film tube. The tube is then pinched and laminated to itself (laminate layer to laminate layer) to form a laminate film having a seven-layer structure.

In this way 5 films were produced, the properties of the film layers being shown in table 6:

TABLE 6

S1 ═ first sealant layer (PP/PE/PB)

P1 ═ first peel ply (BCP)

C1 ═ first core layer (PP)

Laminated layer (PP/PE/PB)

C2 ═ second core layer (PP)

P2 ═ second peel ply (BCP)

S2 ═ second sealant layer (PP/PE/PB)

The peel strength of these films was then measured at a range of sealing temperatures and the results are shown in table 7. The heat seal threshold was set at 15psi/2 secs.

TABLE 7

The properties of the 30 micron white and clear films are similar in terms of peel strength, providing up to 500g/25mm²The sealing strength of (2). The best peel strength was achieved with a1 μm to 3 μm BCP peel layer.

The heat seal threshold/peelability of two of the films (examples 5 and 7) was determined at 15psi/secs (in/out) and the results are shown in table 8.

TABLE 8

Temperature of	Example 5(TB32A30)	Example 7(TG21D30)
			115	15	0
120	65	48
			125	Failure of	Failure of

130

Failure of

Failure of

It is clear that for a torn sheet, the type inside/outside the sealing layer is different, and therefore peeling that is sealed at 125 ℃ fails. However, if the intended end use of the film is in a form-fill-seal bag environment, the inside-outside peel strength is not determinative of whether sealing is appropriate, but rather the outside-outside peel strength.

The heat seal threshold/peelability (at 5psi/0.5secs (out/out)) of three of the films (examples 5,7 and 9) was determined and the results are shown in table 9:

TABLE 9

The optical properties of these films were also determined and the results are shown in table 10:

watch 10

Categories	WAH	Gloss 45 °
			Example 4(TG21A20)	2.2	94
Example 5(TB32A30)		51
			Example 6(TG21D30(0.5 micron))	2	95
Example 7(TG21D30(1 micron))	2.2	96
			Example 8(TG21D30(3 μm))	3.2	90

Example 9(TG21B50)	2.9	92
			Example 10(TG21B58)	3.2	92

Analysis of these results shows satisfactory optical properties, and a correlation between the thickness of the block copolymer release layer and those optical properties, specifically wide angle haze.

Hot tack properties (hot tack properties 15psi/2 secs/outer-outer/90 g spring) were also determined for three of these films and the results are shown in Table 11.

TABLE 11

Hot tack properties (hot tack properties 5psi/0.5 secs/outer-outer/90 g spring) were also determined for three of these films and the results are shown in Table 12:

TABLE 12

The release layer (BCP layer) thickness versus hot tack (15psi/2 secs/outer-outer/90 g spring) for examples 6-8 is shown in Table 13.

Watch 13

The release layer (BCP layer) thickness versus hot tack (5psi/0.5 secs/outer-outer/90 g spring) for examples 6-8 is shown in Table 14.

TABLE 14

And (3) testing the barrier property:

barrier tests were performed on the films of example 7(TG21D30 with 1 μm BCP), example 8(TG21D30 with 3 μm BCP) and example 9(TG21B50) with the results shown in Table 15:

watch 15

Examples	Thickness (Avg)/μm	OTR(cm3m-2d-1)	OTR Standard thickness (cm)3.mm m-2d-1)
				7	30	1830	54900
8	31	1690	52390
				9	50	1010	50500

These results show that OTR is not significantly different from standard PP films.

Examples 11 and 12(12 as control)

These examples are intended to investigate the suitability of one film in the ream wrap application described in the present invention.

Preparation of the film

In example 11, a four-layer polymer tube was formed as follows: a core layer of polypropylene homopolymer (formulated with a slip agent) was coextruded with a polyethylene/polypropylene/polybutylene terpolymer (comprising polypropylene (92% w/w)/ethylene (4% w/w)/butylene-1 (4% w/w)) as a skin layer (first sealant layer) on one side of the core layer, and with a release layer of a polypropylene-polyethylene block copolymer (available from Total Petrochemicals under the trade name PPC 5660) located between the core layer and the first sealant. The other side of the core layer had a laminated layer of polyethylene/polypropylene/polybutylene terpolymer (random copolymer comprising polypropylene (82% w/w)/ethylene (1% w/w)/butene-1 (17% w/w)). The tube is cooled and then reheated before being blown into a four-ply biaxially oriented film tube. The tube was then pinched and laminated to itself (laminate layer to laminate layer) to form a 58 μm thick laminate film having a seven-layer structure. A printable acrylic coating is then applied to the laminate film. The coating film was prepared as follows: coating the coating composition on both sides of the laminated film by gravure printing in an amount of 1g/m²And the coating is dried in an oven. The formulated acrylic coating serves as a source of product for the acrylic material present in coating WB1240 in large quantities. WB1240 is a dispersion of acrylic copolymer in water supplied by Cytec Surface Specialities of Rued' Andersect 33B-1620 Drogenbos Belgium, and is used in an amount necessary to provide a coating composition on a film in which WB1240 comprises 92.5 wt% of the total coating. The composition also contained 0.25 wt% polymethyl methacrylate particles as an antiblock agent and 7.5 wt% palm wax.

Example 12 (comparative) used RC60, an oriented polypropylene film from Innovia Films Ltd of witton, Cumbria CA79B G, United Kingdom.

The peel strength of these films was then measured at a range of sealing temperatures and the results are shown in table 16. The heat seal threshold was set at 15psi/2 secs.

TABLE 16

The peel strength of these films was then measured at a range of sealing temperatures (heat seal threshold set at 5psi/0.5secs.) and the results are shown in table 17.

TABLE 17

Example 11 the film is peelable and is suitable for use in a peelable ream wrap. The example 12 film could not be peeled off.

Claims (22)

1. A sealable and peelable film comprising a four layer coextruded layer comprising a core layer which contributes primarily to the thickness of the film, a first sealing layer on one side of the core layer, and a second sealing layer or laminate layer on the other side of the core layer, and the film comprising a peeling layer between the first sealing layer and the core layer and/or between the second sealing layer or laminate layer and the core layer, and wherein the peeling layer is adjacent to the first sealing layer and/or the second sealing layer and/or the laminate layer, and wherein the relative thickness (p: s/l ratio) of the peeling layer to the sealing layer and/or laminate layer adjacent thereto is from 1: 10 to 5: 1.

2. The film of claim 1, made as a separate web, wherein the four-layer structure comprises a first sealing layer on one side of the core layer and a second sealing layer on the other side of the core layer, wherein the release layer is located between the core layer and at least one of the sealing layers and adjacent to at least one of the sealing layers.

3. The film of claim 1, formed into a laminate, wherein the four-layer structure comprises a first sealing layer on one side of the core layer and a laminate layer on the other side of the core layer, the two separate webs of the film being laminated to each other (laminate layer to laminate layer) to provide a seven-layer laminate structure (the two laminate layers effectively forming separate layers in the laminate structure), wherein the release layer is located between and adjacent to the first sealing layer and/or the laminate layer and the core layer.

4. A film according to any one of claims 1 to 3 comprising further or additional layers obtained by co-extrusion, coating or lamination.

5. The film of claim 4, comprising one or more intermediate layers between the core layer and the first sealing layer, between the core layer and the second sealing layer, between the core layer and the laminate layer and/or between the core layer and the release layer.

6. A film according to any one of claims 1 to 5 wherein the release layer is adjacent the core layer of the film.

7. The film of claim 6, wherein there is no intermediate layer between the release layer and the core layer.

8. The film of any one of claims 1 to 7, wherein the peeling layer is adjacent to the first sealing layer of the film, or adjacent to the second sealing layer of the film, or adjacent to the lamination layer of the film, and wherein the peeling layer is free of an intermediate layer between the sealing layer and/or lamination layer adjacent thereto.

9. The film of any one of claims 1 to 8, wherein the release layer contains at least one block copolymer component.

10. The film of claim 9, wherein the block copolymer component in the release layer contains at least one olefinic component.

11. The film of claim 10 wherein at least two olefinic components are present in the release layer, the block copolymer being formed at least in part by block copolymerization of one olefinic component or mixture of olefinic components with another olefinic component or mixture of olefinic components.

12. The film of claim 11, wherein the block copolymer matrix comprises polypropylene and polyethylene.

13. A film according to any one of claims 1 to 12 having a wide angle haze value of less than about 5.

14. The film of any one of claims 1 to 13 having a gloss value (at 45 °) of at least about 75.

15. A film as claimed in any one of claims 1 to 14 wherein the relative thickness (p: s/l) of the peel ply and the sealing and/or laminating layer adjacent thereto is from 1: 8 to 3: 1.

16. The film of any one of claims 1 to 15, wherein the thickness of the release layer is selected such that the peel strength (when measured at a heat seal threshold of 15psi/2secs at a temperature of 110 ℃ to 140 ℃) is less than 750g/25mm²。

17. The film of any one of claims 1 to 16, wherein the thickness of the release layer is selected such that the peel strength (when measured at a heat seal threshold of 5psi/0.5secs at a temperature of 110 ℃ to 140 ℃) is less than about 650g/25mm²。

18. A film according to any one of claims 1 to 17 wherein the release layer has a thickness of from 0.3 μm to 3 μm.

19. A sealed package formed from the sealable and peelable film of any one of claims 1 to 18.

20. The package of claim 19, formed by the method of: wrapping the film around an object to be packaged in such a way as to obtain at least one film overlap region, and heat-sealing the obtained overlapping film portions to each other to provide at least one sealed region of the package, which can be subsequently opened by manually separating the overlapping film portions without substantially tearing the film at or around the sealed region.

21. A package of the ream wrap of claim 20.

22. The overwrapped package of claim 20.