Current collector including metallized multilayer film

Abstract

The current collector comprises a multilayer film and a first metal layer, the multilayer film comprises a polyester substrate layer (B) having a first surface and a second surface, a first heat-sealable layer (A1) disposed on the first surface of said polyester substrate layer, and optionally a second heat-sealable layer (A2) disposed on the second surface of said polyester substrate layer, the first metal layer is disposed on an outer surface of the first heat-sealable layer (A1), the multilayer film has a thickness of 12 μm or less, and the first metal layer has a thickness of 1000 nm or less.

Description

[Technical field]

[0001] The present invention relates to polyester films for use in current collectors, current collectors and other articles comprising same, and methods for their manufacture. In particular, the present invention relates to current collectors for use in batteries, especially lithium ion batteries. [Background technology]

[0002] Due in part to the increasing demand for consumer electronics and renewable energy storage, lithium-ion batteries are widely used in the field of rechargeable batteries, which is expected to continue to grow for the foreseeable future. During battery operation (i.e., during charging and discharging), lithium ions are transferred between an anode material and a cathode material. Commercially available lithium-ion batteries typically contain a metal foil current collector, which is placed in contact with each of the active solid electrodes. Generally, an aluminum-based foil is used as the cathode current collector and placed in contact with the cathode, while a copper-based foil is used as the anode current collector and placed in contact with the anode. In some arrangements, the cathode material may be coated on the cathode current collector and / or the anode material may be coated on the anode current collector.

[0003] However, there are problems with such existing metal foil current collectors. First, metal foil current collectors have high electrical conductivity, which may contribute excessive current throughout the battery, leading to short circuits and overheating runaway, which may result in fires. Second, metal foil current collectors are relatively thick, dense, and heavy (typically having a thickness greater than 12 μm), thus contributing significantly to the overall mass of the battery. To increase the energy density and minimize the size and mass of the battery, it is desirable to provide a current collector that is thinner and / or lighter. However, there are challenges in providing a current collector that is thinner without adversely affecting its mechanical strength.

[0004] For that purpose, metallized polymer film current collectors have been developed. Such current collectors contain an insulating or dielectric polymer substrate layer and a conductive metal layer(s) on their surface(s). As known in the art, such current collectors act as electrochemical fuses that shut off at a predetermined thermal and / or electrical load to avoid excessive current and thermal runaway. The metal layer is typically formed by a metal deposition process, which may require multiple deposition steps. During the aforementioned metal deposition process and during subsequent battery assembly, the current collector (and the polymer substrate layer within the current collector) is exposed to high temperature conditions for extended periods of time, which may lead to film overheating and permanent film damage, such as deformation and wrinkling, resulting in loss of adhesion between the metal layer and the polymer substrate layer. This is a particular problem for thin current collectors.

[0005] It is an object of the present invention to address one or more of the problems mentioned above. In particular, it is an object of the present invention to provide an improved current collector for use in batteries, preferably for use in lithium ion batteries. A particular object of the present invention is to provide a current collector that is thin and exhibits improved adhesion between the polyester layer(s) and the metal layer(s), e.g. following exposure to high temperatures during manufacture, subsequent assembly steps, and / or end use, particularly for extended periods of time. It is also a particular object of the present invention to provide a current collector that at least maintains, and preferably improves, the energy density of existing metal foil current collectors.

[0006] According to a first aspect of the present invention, there is provided a current collector comprising a multilayer film and a first metal layer, the multilayer film comprising: (i) a polyester substrate layer (B) having a first surface and a second surface; (ii) a first heat-sealable layer (A1) disposed on a first surface of the aforementioned polyester substrate layer; (iii) optionally, a second heat-sealable layer (A2) disposed on a second surface of said polyester substrate layer; The aforementioned first metal layer is disposed on the outer surface of the first heat-sealable layer (A1), the multilayer film having a thickness of 12 μm or less, and the first metal layer having a thickness of 1000 nm or less.

[0007] Preferably, the current collector further comprises a second metal layer, the first metal layer and the second metal layer being on opposite sides of the multilayer film, and the layer order is first metal layer / multilayer film / second metal layer. If present, the second metal layer has a thickness of 1000 nm or less.

[0008] The inventors have unexpectedly discovered that such current collectors are advantageously thin and exhibit excellent peel resistance between the multilayer film and the first metal layer and, if present, the second metal layer following extended exposure to high temperatures. In particular, the inventors have unexpectedly discovered that the bond formed by the thin heat-sealable layer(s) on the polyester substrate layer is strong enough to retain excellent adhesion to both the polyester substrate layer and the metal layer, even following extended exposure to high temperatures. This is particularly advantageous in the field of lithium ion batteries, which are susceptible to such conditions during manufacture and in use.

[0009] The first metal layer and, if present, the second metal layer are the outermost layers of the current collector.

[0010] Thus, the current collector comprises at least three layers. Preferably, the first heat-sealable layer (A1) is disposed directly on the first surface of the polyester substrate layer (B) and the first metal layer is disposed directly on the opposite surface of the first heat-sealable layer, so that the layer sequence is first metal layer / first heat-sealable layer (A1) / polyester substrate layer (B). Thus, in this preferred embodiment, there is no intermediate layer between the first metal layer and the first heat-sealable layer, and between the first heat-sealable layer and the polyester substrate layer, respectively, so that the current collector consists of three layers.

[0011] Preferably, the current collector comprises at least four layers. Preferably, the first heat-sealable layer (A1) is disposed directly on the first surface of the polyester substrate layer (B), the second heat-sealable layer (A2) is disposed directly on the second surface of the polyester substrate layer (B), and the first metal layer is disposed directly on the opposite surface of the first heat-sealable layer, so that the layer sequence is first metal layer / first heat-sealable layer (A1) / polyester substrate layer (B) / second heat-sealable layer (A2). In this preferred embodiment, there are no intermediate layers between the first metal layer and the first heat-sealable layer, between the first heat-sealable layer and the polyester substrate layer, and between the second heat-sealable layer and the polyester substrate layer, respectively, so that the current collector consists of four layers.

[0012] Instead, the first heat-sealable layer (A1) is disposed directly on a first surface of the polyester substrate layer (B), the first metal layer is disposed directly on the opposite surface of the first heat-sealable layer, and the second metal layer is disposed directly on the second surface of the polyester substrate layer (B), so that the layer sequence is first metal layer / first heat-sealable layer (A1) / polyester substrate layer (B) / second metal layer. In this preferred embodiment, there are no intermediate layers between the first metal layer and the first heat-sealable layer, between the first heat-sealable layer and the polyester substrate layer, and between the polyester substrate layer and the second metal layer, respectively, so that the current collector consists of four layers.

[0013] Most preferably, the current collector comprises at least five layers. Preferably, the first heat-sealable layer (A1) is disposed directly on the first surface of the polyester substrate layer (B), the second heat-sealable layer (A2) is disposed directly on the second surface of the polyester substrate layer (B), the first metal layer is disposed directly on the opposite surface of the first heat-sealable layer, and the second metal layer is disposed directly on the opposite surface of the second heat-sealable layer (A2). Thus, the layer order is first metal layer / first heat-sealable layer (A1) / polyester substrate layer (B) / second heat-sealable layer (A2) / second metal layer. In this preferred embodiment, there are no intermediate layers between the first metal layer and the first heat-sealable layer, between the first heat-sealable layer and the polyester substrate layer, between the polyester substrate layer and the second heat-sealable layer, and between the second heat-sealable layer and the second metal layer, so that the current collector consists of five layers.

[0014] Such a current collector is further illustrated in Figure 1. Figure 1 shows, in cross-section, a current collector (10) including a first metal layer (5), a first heat-sealable layer (A1) (4), a polyester substrate layer (B) (1), a second heat-sealable layer (A2) (3), and a second metal layer (2).

[0015] The substrate layer is a free-standing film, which means a film that is capable of existing independently without a supporting base.

[0016] Thermoplastic polyester materials, especially linear polyesters, are preferred.

[0017] The term polyester as used herein refers to homopolyesters or copolyesters derived from one or more diols, at least one of which is an aliphatic diol, and one or more dicarboxylic acids, at least one of which is an aromatic dicarboxylic acid. Suitable dicarboxylic acids include terephthalic acid, isophthalic acid, phthalic acid, 2,5-, 2,6- or 2,7-naphthalenedicarboxylic acid, succinic acid, sebacic acid, adipic acid, azelaic acid, 4,4'-diphenyldicarboxylic acid, hexahydroterephthalic acid or 1,2-bis-p-carboxyphenoxyethane (optionally with a monocarboxylic acid, such as pivalic acid). Suitable diols include aliphatic diols, such as ethylene glycol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol and 1,4-cyclohexanedimethanol, and cycloaliphatic diols. Preferably, the aromatic dicarboxylic acid is selected from terephthalic acid and 2,5-, 2,6- or 2,7-naphthalenedicarboxylic acid, preferably terephthalic acid and 2,6-naphthalenedicarboxylic acid. Preferably, the aliphatic diol is ethylene glycol. Preferably, the polyester is a homopolyester. Preferably, the polyester is polyethylene terephthalate (PET) or polyethylene naphthalate (PEN).

[0018] The preferred polyethylene terephthalate (PET) and polyethylene naphthalate (PEN) polyesters may optionally contain, as one or more comonomer(s), relatively small amounts (preferably less than 10% by weight or less than 5% by weight) of one or more residues derived from other dicarboxylic acids and / or diols. Other dicarboxylic acids include succinic acid, glutaric acid, sebacic acid, adipic acid, azelaic acid, suberic acid or pimelic acid, isophthalic acid, phthalic acid, 1,4-, 2,5- or 2,7-naphthalenedicarboxylic acid, 4,4'-diphenyldicarboxylic acid, hexahydroterephthalic acid, 1,10-decanedicarboxylic acid, and dicarboxylic acids of the general formula C n H 2nThe polyesters include aliphatic dicarboxylic acids of formula (COOH)2, where n is 2 to 8. Other diols include aliphatic and cycloaliphatic glycols, such as diethylene glycol, propylene glycol, dipropylene glycol, 1,3-propanediol, 1,4-butanediol, and 1,4-cyclohexanedimethanol. Preferably, the polyesters contain only one dicarboxylic acid, i.e., terephthalic acid or 2,6-naphthalenedicarboxylic acid, preferably terephthalic acid. Preferably, the polyesters contain only one diol, i.e., ethylene glycol.

[0019] Preferably, the substrate layer is a PET film or a PEN film.

[0020] The polyester is the major component of the polyester substrate layer and comprises at least 60% by weight, preferably at least 70% by weight, and preferably at least 80% by weight of the total weight of the substrate layer. For example, the polyester may comprise at least 85% by weight, at least 90% by weight, or at least 95% by weight of the total weight of the substrate layer.

[0021] The substrate layer may further comprise any other additives conventionally employed in the manufacture of polymer films. Such conventional additives may be present in a small proportion, typically 35% by weight or less, typically 20% by weight or less, typically 5% by weight or less, typically 2% by weight or less, based on the total weight of the layer. Thus, agents such as particulate fillers, hydrolysis stabilizers, antioxidants, UV stabilizers, crosslinkers, dyes, lubricants, radical scavengers, heat stabilizers, surfactants, slip aids, antiblocking agents, flame retardants, gloss enhancers, prodegradants, viscosity modifiers, dispersion stabilizers, etc. may be incorporated as required. As is well known in the art, particulate fillers are particularly useful for improving handling and winding during manufacture. Particulate fillers are typically particulate inorganic fillers (e.g., calcium carbonate, clay, silica, zeolites, silicone beads (such as functionalized polydimethylsiloxane), dicalcium phosphate, tricalcium phosphate, cenospheres, zeospheres, talc, titanium dioxide, barium sulfate, and barium titanate). The filler particle size distribution can be monomodal, bimodal, and trimodal. Preferably, the volume weighted average particle size (D (4,3) ) is in the range of 0.1 to 10 μm for monomodal, bimodal and trimodal distributions. Preferably, the filler particle size distribution is bimodal, so that there are two maxima. Preferably, the first maximum of the particles is at a volume weighted average particle size (D) of about 0.5±0.3 μm. (4,3) ) and the second maximum of the particles has a volume weighted mean diameter (D (4,3) ). The particle size of the filler particles is suitably measured by laser light diffraction. Particulate inorganic fillers are present in relatively small amounts, typically less than 5.0 wt%, typically less than 2.0 wt%, typically less than 1.0 wt%.

[0022] Formation of the polyester is readily accomplished by conventional synthetic methods well known in the art. For example, the polyester may be made by a first step of direct esterification or transesterification, followed by a second step of polycondensation. Preferably, the synthetic procedure further includes a solid-state polymerization (SSP) step to increase the molecular weight of the polyester, as is known in the art. Suitable solid-state polymerization techniques are disclosed, for example, in EP-A-0419400, the disclosure of which is incorporated herein by reference. Thus, SSP typically increases the crystalline melting point (T M ) is 10 to 50°C lower than the glass transition temperature (T g ) (or above the highest glass transition temperature if the polyester exhibits multiple glass transition temperatures). An inert atmosphere of dry nitrogen or vacuum is used to prevent degradation. In a preferred embodiment, the solid state polymerization is carried out at 220° C. under vacuum for 16 hours.

[0023] The inherent viscosity of polyesters suitable for use in the present invention is at least 0.5 dL / g, preferably at least 0.55 dL / g, preferably at least 0.6 dL / g, preferably at least 0.7 dL / g, preferably at least 0.8 dL / g.

[0024] The substrate layer is a single layer film.

[0025] The thickness of the substrate layer is 12 μm or less, preferably about 11.0 μm or less, preferably about 10.0 μm or less, preferably about 7.0 μm or less, preferably about 6.0 μm or less. The thickness of the substrate layer is preferably at least about 2.0 μm, preferably at least about 3.0 μm, preferably at least about 4.0 μm. Thus, the thickness of the substrate layer is preferably about 2.0 to about 11.0 μm, preferably about 2.0 to about 10.0 μm, preferably about 3.0 to about 7.0 μm, preferably about 4.0 to about 6.0 μm.

[0026] The thickness of the substrate layer is generally greater than the thickness of each of the first (A1) and second (A2) heat-sealable layers.

[0027] The thickness of the substrate layer is preferably at least about 50%, preferably at least about 60%, preferably at least about 70%, preferably at least about 75%, preferably at least about 80%, and preferably no more than about 99%, preferably no more than about 98%, preferably no more than about 95%, preferably no more than about 90%, and preferably no more than about 85% of the total thickness of the multilayer film.

[0028] The first heat-sealable layer (A1), and if present the second heat-sealable layer (A2), comprise a heat-sealable material that should be softened sufficiently so that its viscosity is low enough to allow adequate wetting thereto to allow it to adhere to the surface(s) to which it is joined.

[0029] The heat-sealable layer(s) may be formed from any polymeric material suitable as a heat-sealable layer on a polyester substrate.

[0030] In a first embodiment, hereinafter referred to as embodiment A, the first heat-sealable layer and, if present, the second heat-sealable layer, independently, comprise at least one copolyester.

[0031] Preferably, the copolyester is derived from at least one aliphatic diol and at least two dicarboxylic acids. Preferably, the copolyester is derived from an aliphatic diol, a first dicarboxylic acid, and a second dicarboxylic acid, the second dicarboxylic acid being different from the first dicarboxylic acid. The aliphatic diol, the first dicarboxylic acid, and the second dicarboxylic acid may be selected from those described above.

[0032] In one preferred embodiment, hereinafter referred to as embodiment A1, the heat-sealable layer comprises a copolyester derived from an aliphatic diol, a first aromatic dicarboxylic acid, and a second aromatic dicarboxylic acid, the second aromatic dicarboxylic acid being different from the first aromatic dicarboxylic acid. Preferably, the dicarboxylic acid is terephthalic acid and one other aromatic dicarboxylic acid, preferably isophthalic acid. Thus, a preferred copolyester is derived from ethylene glycol, terephthalic acid, and isophthalic acid.

[0033] The concentration of the second aromatic dicarboxylic acid, preferably isophthalic acid, is preferably in the range of about 1 to about 50 mol %, preferably about 10 to about 45 mol %, of the acid fraction of the copolyester. Particularly preferred concentrations of the second aromatic dicarboxylic acid, preferably isophthalic acid, are in the range of (i) about 15 to about 20 mol %, preferably about 18 mol %, of the acid fraction of the copolyester, (ii) about 10 to about 15 mol %, preferably about 12 mol %, of the acid fraction of the copolyester, or (iii) about 30 to about 45 mol %, preferably about 40 mol %, of the acid fraction of the copolyester.

[0034] In an alternative preferred embodiment, hereinafter referred to as embodiment A2, the heat-sealable layer comprises a copolyester derived from an aliphatic diol, an aromatic dicarboxylic acid, and an aliphatic dicarboxylic acid. Preferably, the aromatic dicarboxylic acid is terephthalic acid, and the aliphatic dicarboxylic acid is selected from succinic acid, sebacic acid, adipic acid, and zelaic acid, preferably azelaic acid. Thus, a preferred copolyester is derived from ethylene glycol, terephthalic acid, and azelaic acid.

[0035] The concentration of the aliphatic dicarboxylic acid, preferably azelaic acid, is preferably in the range of about 10 to about 50 mol %, preferably about 30 to about 48 mol %, preferably about 45 mol %, of the acid fraction of the copolyester.

[0036] In an alternative preferred embodiment, hereinafter referred to as embodiment A3, the heat-sealable layer comprises a copolyester derived from an aliphatic diol, a cycloaliphatic diol, and at least one dicarboxylic acid, preferably an aromatic dicarboxylic acid. Examples include copolyesters of terephthalic acid with an aliphatic diol and a cycloaliphatic diol, particularly ethylene glycol and 1,4-cyclohexanedimethanol.

[0037] The concentration of the alicyclic diol (preferably 1,4-cyclohexanedimethanol) is preferably in the range of about 10 to about 60 mol %, preferably about 20 to about 40 mol %, preferably about 30 to about 35 mol %, preferably about 33 mol %, of the diol fraction of the copolyester.

[0038] Preferably, the copolyester is a copolyester of terephthalic acid having about 33 mol% 1,4-cyclohexanedimethanol and about 67 mol% ethylene glycol. An example of such a copolyester is PETG® 6763 (Eastman). In an alternative embodiment, the copolyester may include butanediol instead of ethylene glycol.

[0039] In an alternative preferred embodiment, hereinafter referred to as embodiment A4, the heat-sealable layer comprises a copolyester derived from one or more diols, one or more dicarboxylic acids, and one or more poly(alkylene oxide) glycols. The diols and dicarboxylic acids are selected from those described above. Preferably, the diol used is an aliphatic diol, most preferably ethylene glycol.

[0040] In one preferred embodiment, the dicarboxylic acid used is an aromatic dicarboxylic acid, most preferably terephthalic acid. In an alternative preferred embodiment, a first dicarboxylic acid and a second dicarboxylic acid are used, the second dicarboxylic acid being different from the first dicarboxylic acid. Preferably, the first dicarboxylic acid is a first aromatic dicarboxylic acid, and the second dicarboxylic acid is a second aromatic dicarboxylic acid (different from the first aromatic dicarboxylic acid). Preferably, the first dicarboxylic acid is terephthalic acid, and the second aromatic dicarboxylic acid is isophthalic acid. Thus, a preferred copolyester is derived from ethylene glycol, terephthalic acid, isophthalic acid, and one or more poly(alkylene oxide) glycols. Particularly preferred concentrations of the second aromatic dicarboxylic acid, preferably isophthalic acid, are in the ranges of (i) about 15 to about 20 mol %, preferably about 18 mol %, of the acid fraction of the copolyester, (ii) about 10 to about 15 mol %, preferably about 12 mol %, of the acid fraction of the copolyester, or about 30 to about 45 mol %, preferably about 40 mol %, of the acid fraction of the copolyester. Concentration (ii) is particularly preferred.

[0041] Suitable poly(alkylene oxide) glycols for the copolyester of embodiment A4 are preferably C2-C 15 , more preferably C2 to C 10 , and more preferably poly(alkylene oxide) glycols having C2-C6 alkylene chains. The poly(alkylene oxide) glycol is preferably selected from polyethylene glycol (PEG), polypropylene glycol (PPG), and poly(tetramethylene oxide) glycol (PTMO), and is most preferably polyethylene glycol. Ethylene oxide terminated poly(propylene oxide) segments may also be used. Although mixtures of poly(alkylene oxide) glycols may also be used, in a preferred embodiment the copolyester comprises only one type of poly(alkylene oxide) glycol.

[0042] The number average molecular weight (Mn) of the poly(alkylene oxide) glycol is preferably about 100 g / mol to about 20,000 g / mol, preferably about 200 g / mol to about 6,000 g / mol, preferably about 200 g / mol to about 5,000 g / mol, preferably about 5,000 g / mol or less, preferably about 4,000 g / mol or less, preferably about 200 g / mol to about 3,500 g / mol, preferably at least about 200 g / mol, preferably about 200 g / mol to about 3,000 g / mol, preferably about 250 g / mol to about 1,500 g / mol, preferably about 275 g / mol to about 700 g / mol, preferably about 300 g / mol to about 500 g / mol, preferably about 350 g / mol to about 450 g / mol, preferably about 400 g / mol. The number average molecular weight (Mn) of the poly(alkylene oxide) is preferably at least about 200 g / mol, preferably at least about 250 g / mol, preferably at least about 275 g / mol, preferably at least about 300 g / mol, for example at least about 350 g / mol. The number average molecular weight (Mn) of the poly(alkylene oxide) is preferably about 20,000 g / mol or less, preferably about 5,000 g / mol or less, preferably about 1,500 g / mol or less, preferably about 500 g / mol or less, for example about 450 g / mol or less.

[0043] Thus, in a preferred embodiment, the copolyester comprises, preferably consists of, repeat units derived from an aliphatic diol (preferably ethylene glycol), an aromatic dicarboxylic acid (preferably terephthalic acid), and a poly(alkylene oxide) glycol (preferably PPG and / or PEG, preferably PEG). In an alternative preferred embodiment, the copolyester comprises, preferably consists of, repeat units derived from an aliphatic diol (preferably ethylene glycol), a first aromatic dicarboxylic acid (preferably terephthalic acid), a second dicarboxylic acid (preferably a second aromatic dicarboxylic acid, preferably isophthalic acid), and a poly(alkylene oxide) glycol (preferably PPG and / or PEG, preferably PEG).

[0044] The poly(alkylene oxide) glycol preferably constitutes about 0.1 to about 70 wt%, preferably about 0.5 to about 65 wt%, preferably about 1 to about 60 wt%, preferably about 2 to about 50 wt%, preferably about 5 to about 30 wt%, preferably about 10 to about 20 wt%, preferably about 10 to about 15 wt%, preferably about 12 wt%, based on the total weight of the copolyester.

[0045] Formation of the copolyester is conveniently accomplished in known manner by condensation or transesterification, as discussed above, generally at temperatures up to 275°C.

[0046] In a second embodiment, hereinafter referred to as embodiment B, the first heat-sealable layer, and if present, the second heat-sealable layer, are independently heat-sealable polymer layers. The heat-sealable polymer layers may be formed from any polymeric material suitable as a heat-sealable layer on a polyester substrate. Suitable heat-sealable polymeric materials include polyvinylidene chloride (PVDC) and ethylene vinyl acetate (EVA). EVA is particularly preferred.

[0047] Suitable EVA polymers for the heat-sealable layer include EVA polymers commercially available as Elvax™ resins (DuPont) or Ateva® resins (Celanese). Typically, the EVA resins have a vinyl acetate content in the range of 5% to 50%, preferably 9% to 40%, typically 15% to 30%.

[0048] The heat-sealable layer preferably comprises an EVA copolymer in an amount of 20-98 wt% of the total weight of the heat-sealable layer. Preferably, the heat-sealable layer comprises a blend of two or more EVA copolymers, two or more of which have different VA contents. When the heat-sealable layer comprises a blend of two or more EVA copolymers, the preferred total amount of EVA copolymer is the same as described above. Optional components include styrenic linear block copolymer thermoplastic elastomers (e.g., those disclosed in WO-2021 / 171190-A, the disclosure of which is incorporated herein by reference), such components are typically present in an amount of about 10-50 wt%. Further optional components include tackifying resins (e.g., those disclosed in WO-2021 / 171190-A, the disclosure of which is incorporated herein by reference), such components are typically present in an amount of about 15-50 wt%. Further optional components include anti-slip agent(s) or anti-blocking agent(s) that improve the handling of the film, as is conventional in the art of sealant coatings, and such components are present in relatively small amounts, typically 5.0 wt% or less, typically 2.0 wt% or less. Suitable anti-slip agents include Carnauba wax, chemamide, talc (such as that available from Specialty Minerals under the trade name Talcron MP 15-38), and silica (such as Syloid® 620, Syloid® 244, etc.).

[0049] PVDC polymers for the heat-sealable layer of embodiment B are known in the art, and suitable PVDC materials for the heat-sealable layer are copolymers of vinylidene chloride with other monomers. Vinylidene chloride copolymers are typically obtained as latexes dispersed in a medium by polymerizing 50-99% by weight of vinylidene chloride as a starting material and 1-50% by weight of one or more other monomers copolymerizable with vinylidene chloride using conventional emulsion polymerization methods. The higher the proportion of vinylidene chloride, the higher the crystalline melting point of the vinylidene chloride copolymer. Examples of copolymerizable monomers include vinyl chloride; acrylic acid esters such as methyl acrylate, ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and 2-hydroxyethyl acrylate; methacrylic acid esters such as methyl methacrylate and glycidyl methacrylate; acrylonitrile and methacrylonitrile; and unsaturated carboxylic acids such as acrylic acid, methacrylic acid, itaconic acid, and maleic acid. One or more of such monomers may be used. The solid content concentration of the vinylidene chloride copolymer mixture latex may be appropriately modified according to the specifications of the coating device or drying-heating device, and is preferably in the range of 10-70% by weight, more preferably in the range of 30-55% by weight.

[0050] In a third embodiment, hereinafter referred to as embodiment C, the first heat-sealable layer, and, if present, the second heat-sealable layer, are independently coating layers comprising a first copolyester. Preferably, the first copolyester is derived from one or more diol(s) and two or more dicarboxylic acid(s).

[0051] Thus, in one preferred embodiment, hereinafter referred to as embodiment C1, the coating layer comprises a first copolyester. Embodiment C1 does not comprise a second copolyester.

[0052] In another preferred embodiment, hereinafter referred to as embodiment C2, the coating layer comprises a first copolyester and a second copolyester, each of which is independently derived from one or more diol(s) and two or more dicarboxylic acid(s). In embodiment C2, at least one comonomer of one of the first copolyester and the second copolyester provides heat sealability (as defined herein) to the heat-sealable coating layer (C).

[0053] Preferably, the first copolyester in embodiment C (i.e., in embodiments C1 and C2) is derived from an aliphatic glycol (preferably ethylene glycol), a first aromatic dicarboxylic acid (preferably terephthalic acid), and a second aliphatic dicarboxylic acid (preferably azelaic acid). Suitable copolyesters include those described above for embodiment A, particularly embodiment A2.

[0054] Preferably, the first copolyester in embodiment C is derived from ethylene glycol, terephthalic acid and azelaic acid. In the first copolyester, the preferred molar ratio of the first dicarboxylic acid (preferably terephthalic acid) to the second dicarboxylic acid (preferably azelaic acid) is in the range of 50:50 to 90:10, preferably in the range of 52:48 to 70:30, and preferably about 55:45.

[0055] Preferably, the second copolyester in embodiment C2 is derived from an aliphatic glycol (preferably ethylene glycol), a first aromatic dicarboxylic acid (preferably terephthalic acid), and a second aromatic dicarboxylic acid (preferably isophthalic acid). Suitable copolyesters include those described above for embodiment A, particularly embodiment A1. Preferably, the second copolyester in embodiment C2 is derived from ethylene glycol, terephthalic acid, and isophthalic acid. In the second copolyester, the preferred molar ratio of the first dicarboxylic acid (preferably terephthalic acid) to the second dicarboxylic acid (preferably isophthalic acid) is in the range of 50:50 to 90:10, preferably in the range of 55:45 to 70:30, and preferably about 60:40.

[0056] In a fourth embodiment, hereinafter referred to as embodiment D, the first heat-sealable layer and, if present, the second heat-sealable layer, are independently layers comprising crosslinked sulfopolyester.

[0057] In embodiment D, the heat-sealable layer comprises a crosslinked sulfopolyester. Thus, preferably, the heat-sealable layer is derived from a composition comprising a crosslinker and a sulfopolyester.

[0058] Suitable crosslinkers include melamine, isocyanate, oxazoline, aziridine, carbodiimide, epoxy resin, silane, and zirconium-based crosslinkers. The crosslinker is preferably a melamine crosslinker. Suitable melamine crosslinkers for use in the present invention may be selected from those available from Cytec under the trade name Cymel®, such as Cymel® XW3106 and Cymel® 350, preferably Cymel® XW350. Cymel® XW3106 is a water-insoluble, especially alkylated, high solids melamine resin. Cymel® 350 is a water-soluble, highly methylated monomeric melamine resin.

[0059] Suitable sulfopolyesters comprise, and preferably consist of, monomer units derived from one or more diol(s), one or more dicarboxylic acid(s), and one or more sulfomonomers. The descriptions and preferred examples of the one or more diol(s) and one or more dicarboxylic acid(s) described above are equally applicable to the sulfopolyesters of embodiment D.

[0060] Preferably, the sulfomonomer is selected from sulfonated aromatic dicarboxylic acids in which the sulfonic acid group is attached to an aromatic nucleus. Preferably, the sulfonic acid group of such sulfomonomer is a sulfonate salt, preferably a sulfonate salt of a Group I or II metal, preferably lithium, sodium or potassium, more preferably sodium. Ammonium salts may also be used. The sulfonated aromatic dicarboxylic acid may be selected from any suitable aromatic dicarboxylic acid, for example, terephthalic acid, isophthalic acid, phthalic acid, 2,5-, 2,6- or 2,7-naphthalenedicarboxylic acid. However, preferably, the aromatic dicarboxylic acid of the sulfomonomer is isophthalic acid. Preferred sulfomonomers are 5-sodium sulfate-isophthalic acid and 4-sodium sulfate-isophthalic acid.

[0061] Suitable sulfopolyesters for embodiment D may be selected from those available from Eastman under the trade name Eastek™ 1200. Eastek™ 1200 is an aqueous dispersion of a sulfopolyester derived from 5-sodium sulfate-isophthalic acid, supplied as an aqueous solution containing 2% n-propanol and 30 wt % solids.

[0062] The composition of embodiment D may include any of the conventionally used additives, such as catalysts, surfactants, antiblocking agents, and anti-slip agents.

[0063] The composition of embodiment D may further include small amounts of conventional acidic or basic catalysts, such as alkali metal carboxylates and quaternary ammonium halides. Examples of suitable catalysts include ammonium p-toluenesulfonate (APTSA) and ammonium nitrate.

[0064] The weight percent ratio of sulfopolyester / crosslinker in the dry heat-sealable layer of embodiment D is preferably from about 100 / 1 to about 100 / 50, preferably from about 100 / 10 to about 100 / 20. The weight percent ratio of crosslinker / catalyst in the dry heat-sealable layer is preferably from about 100 / 1 to about 5 / 1, preferably from about 30 / 1 to about 5 / 1, preferably about 10 / 1. Thus, such catalysts are typically present in the range of from about 1% to about 20%, preferably from about 3% to about 18%, preferably from about 5% to about 15%, preferably about 10%, by weight based on the weight of the crosslinker in the dry heat-sealable layer.

[0065] The composition of embodiment D may further include small amounts of a conventional surfactant, such as polysorbate 20. An example of a suitable surfactant is Tween® 20, available from Sigma Aldrich. Tween® 20 is a polyoxyethylene sorbitol ester.

[0066] Such surfactants are typically present in an amount of about 1.0% by weight or less, typically about 0.5% by weight or less, for example about 0.2% by weight, based on the total solids content of the composition of embodiment D.

[0067] The total thickness of the heat-sealable layers (i.e., the thickness of the first heat-sealable layer (A1) without the second heat-sealable layer (A2) present, or the total thickness of the first heat-sealable layer (A1) and the second heat-sealable layer (A2) with the second heat-sealable layer (A2) present) is preferably no more than about 50% of the total thickness of the multilayer film, preferably no more than about 40%, preferably no more than about 30%, preferably no more than about 25%, preferably no more than about 20%, preferably at least about 1%, preferably at least about 10%, preferably about 15%.

[0068] The thickness of the first heat-sealable layer (A1), and, if present, the second heat-sealable layer (A2), is preferably each independently about 0.1 to about 3.5 μm, preferably about 0.2 to about 3.0 μm, preferably about 0.5 to about 2.0 μm, preferably about 0.6 to about 1.5 μm, preferably about 0.7 to about 1.0 μm.

[0069] The total thickness of the multilayer film is preferably about 3.0 to 12 μm, preferably about 3.5 to about 11.0 μm, and preferably about 4.0 to about 8.0 μm.

[0070] The multilayer films are preferably uniaxially or biaxially oriented, preferably biaxially oriented.

[0071] In a preferred embodiment, the multilayer film is a coextruded film, preferably according to embodiment A described herein.

[0072] In an alternative preferred embodiment, the multilayer film is a coated film, preferably according to embodiments B, C, and D described herein.

[0073] Preferably, the multilayer film has a thickness of at least about 100 g / 25 mm. 2 , preferably at least about 200g / 25mm 2 , preferably at least about 275g / 25mm 2 , preferably at least about 500g / 25mm 2 The adhesive strength of the adhesive to itself is shown.

[0074] Advantageously, the multilayer film can be, and preferably is, produced in air, i.e., the film is not produced (including the extrusion, casting, and drawing steps) under an atmosphere of inert gas (such as nitrogen or a noble gas such as argon). Thus, the compositions and films described herein are thermally stable and do not require any special handling conditions, especially an inert atmosphere, during production or storage.

[0075] The formation of the multilayer film can be accomplished by conventional techniques known in the art. The method of forming the multilayer film depends on the identity of the heat-sealable layer(s). Conventional techniques include casting or coating the heat-sealable layer(s) on a preformed polyester substrate layer. Advantageously, the formation of the heat-sealable layer and the substrate layer is accomplished by coextrusion, which is particularly suitable for embodiment A described herein. Another method of forming the multilayer substrate includes forming a substrate layer and then coating the heat-sealable material on the substrate layer, which is particularly suitable for embodiments B, C, and D described herein.

[0076] When both the first heat-sealable layer (A1) and the second heat-sealable layer (A2) are present, a combination of techniques can be employed. For example, the first heat-sealable layer (A1) and the substrate layer can be subjected to coextrusion and the second heat-sealable layer (A2) can be coated. Alternatively, the second heat-sealable layer (A2) and the substrate layer can be subjected to coextrusion and the first heat-sealable layer (A1) can be coated. However, it is preferred that the first heat-sealable layer (A1) and the second heat-sealable layer (A2) are each subjected to the same technique, i.e., coextrusion for each or coating for each.

[0077] Thus, the formation of the substrate layer and / or the coextruded multilayer film may be accomplished by conventional extrusion techniques known in the art. In general, the process involves extruding a layer of molten polymer at a temperature within a range appropriate for the melting temperature of the polymer, for example, in the range of about 270 to about 300°C (or typically about 15°C or less, preferably about 10°C or less, above the crystalline melting point of the polymer), and then rapidly quenching the extrudate to ensure that the polymer is quenched to an amorphous state. The quenched extrudate is then biaxially oriented by stretching in two mutually perpendicular directions in the plane of the film at a temperature above the glass transition temperature(s) of the polymer to achieve a satisfactory combination of mechanical and physical properties. Biaxial orientation may be achieved by sequential biaxial orientation or simultaneous biaxial orientation. In the present invention, the film is advantageously produced by extruding a thermoplastic polymer tube, e.g., by simultaneous biaxial orientation in a tubular process, which is then quenched, reheated, expanded by internal gas pressure to induce transverse orientation, and drawn in at a speed to induce longitudinal orientation. In particular, suitable simultaneous biaxial orientation processes are disclosed in EP-2108673-A and US-2009 / 0117362-A1, the disclosures of which are incorporated herein by reference.

[0078] Stretching is typically accomplished so that the dimensions of the oriented film are 2 to 7 times, preferably 2 to 5 times, more preferably 2.5 to 4.5 times, more preferably 3.0 to 4.5 times, more preferably 3.0 to 4.0 times, their original dimensions in each direction of stretching. Preferably, the film is stretched 3.2 to 3.6 times its original dimensions in the machine direction (MD) and preferably 3.3 to 3.8 times its original dimensions in the transverse direction (TD). Stretching is performed by increasing the T of the polymer composition. g higher than T g at least about 5° C. higher, preferably at least about 15° C. higher, preferably about T g +5℃~approx.Tg +75°C, preferably around T g +5℃~approx.T g +30° C. If the polymer composition is PET, stretching is typically performed at a temperature ranging from about 85 to about 110° C., preferably from about 95 to about 100° C. If the polymer composition is PEN, stretching is typically performed at a temperature ranging from about 130 to about 155° C., preferably from about 140 to about 145° C. It is not necessary to stretch equally in the machine and transverse directions, but this is preferred if balanced properties are desired.

[0079] The stretched film can then be dimensionally stabilized. In a first step, the film is annealed under dimensional support (or constraint) to induce the desired crystallinity of the polymer. A temperature of at least about 200° C. is preferred. Preferably, the temperature used is above the glass transition temperature(s) of the polyester of the substrate layer, but below its melting temperature (T M Within those constraints, preferred annealing temperatures are typically about 40° C. below the melting temperature of the substrate layer (i.e., T M -40℃) to T M Approximately 10°C below (i.e., T M −10° C.), preferably at about T M -30°C. If the film is a multilayer film, the temperature used is also preferably below the melting temperature (T M(HS) ) or the melting temperature (T M(HS) Within those constraints, the preferred annealing temperature is typically about 25° C. above the melting temperature of the heat-sealable layer(s) (i.e., T M(HS) +15°C) to about 5°C above the melting temperature of the heat-sealable layer(s) (i.e., T M(HS) +5°C), preferably at about T M(HS)+10°C. Thus, the annealing temperature depends on the polymer composition used. For example, if the heat-sealable layer(s) comprises a copolyester derived from ethylene glycol, terephthalic acid, and isophthalic acid, where the isophthalic acid is about 18 mol% of the acid fraction of the copolyester, the annealing temperature is suitably in the range of about 200 to about 245°C, preferably about 215 to about 235°C. The time that the film is held at this temperature is preferably 0 to 60 seconds, preferably 0.1 to 10 seconds, preferably 0.5 to 5 seconds, preferably 0.7 to 3 seconds.

[0080] After annealing under dimensional constraints, the film may then be subjected to dimensional relaxation, preferably simultaneous dimensional relaxation, in both the transverse direction (TD) and the machine direction (MD). The relaxation step is suitably an in-line relaxation step, i.e. a stage in a film production line. The film is preferably relaxed by about 0.5 to about 5.0%, preferably about 1.0 to about 4.0%, preferably about 1.0 to about 3.0%, preferably about 1.0 to about 2.0% in each of the transverse direction (TD) and the machine direction (MD). In the relaxation step, the film is heated with lower MD and TD tensions, preferably at a temperature equal to or lower than the temperature of the immediately preceding annealing step. The MD relaxation is controlled by reducing the speed of the film line and the TD relaxation is controlled by reducing the distance between the film clamps on the opposing transverse edges of the film, each of which results in a reduction in the tension experienced by the film in the relevant dimension in this stage of production. Preferred is a temperature of at least about 200° C., preferably about 200° C. to about 240° C., preferably about 210° C. to about 230° C., preferably about 215° C. to about 230° C., preferably about 215° C. to 225° C. The heating duration of the relaxation step depends on the temperature used, but is typically in the range of 0 to 30 seconds, preferably 0.1 to 10 seconds, preferably 0.4 to 4 seconds, preferably 0.9 to 3.8 seconds.

[0081] Preferably, a second relaxation step is then performed (in this case the relaxation step described above is referred to as the first relaxation step). The second relaxation step is performed in the same manner as described for the first relaxation step. A temperature of at least about 195°C is preferred, and a temperature of at least about 200°C is most preferred. Preferably, the second relaxation step can be performed at a similar temperature to the first relaxation step. Alternatively, the second relaxation step can be performed at a lower temperature than the first relaxation step, typically at a temperature about 20°C lower than the first relaxation step. The heating duration of the second relaxation step depends on the temperature used, but is typically in the range of 0 to 30 seconds, preferably 0.1 to 10 seconds, preferably 0.4 to 3.5 seconds, preferably 0.7 to 3.0 seconds.

[0082] After the annealing step and relaxation step(s), the film may be rapidly cooled.

[0083] If the heat-sealable layer(s) are instead coated onto the substrate layer, coating can be accomplished using any suitable coating technique, including gravure roll coating, reverse roll coating, dip coating, bead coating, extrusion coating, melt coating, or electrostatic spray coating. Coating can be performed "off-line", i.e., after stretching and any subsequent dimensional stabilization employed during the manufacture of the polyester substrate, or "in-line", i.e., the coating step occurs before, during, or between any stretching operation(s) employed, and is preferably performed "off-line" or "in-line". When coating is performed in-line, it is preferably performed between the forward and sideways stretching of a biaxial stretching operation ("between-draw" coating).

[0084] When the first heat-sealable layer (A1) and / or the second heat-sealable layer (A2) are coated and according to embodiment C, the composition from which the heat-sealable coating layer is derived preferably comprises at least about 1 wt.-%, preferably at least about 5 wt.-%, preferably at least about 10 wt.-%, preferably at least about 12 wt.-% of the first copolyester, based on the total weight of the composition before drying. Preferably, the composition from which the heat-sealable coating layer is derived comprises no more than about 20 wt.-%, preferably no more than about 18 wt.-%, preferably no more than about 16 wt.-%, preferably no more than about 15 wt.-%, preferably no more than about 14 wt.-% of the first copolyester, based on the total weight of the composition before drying.

[0085] Thus, preferably, the composition from which the heat-sealable coating layer of embodiment C is derived contains the first copolyester in an amount ranging from about 1% to about 20% by weight, preferably from about 5% to about 18% by weight, preferably from about 10% to about 16% by weight, preferably from about 10% to about 15% by weight, preferably from about 12% to about 14% by weight, based on the total weight of the composition before drying.

[0086] When the first heat-sealable layer (A1) and / or the second heat-sealable layer (A2) are coated and according to embodiment C, the composition from which the heat-sealable coating layer is derived preferably comprises at least about 0.1% by weight, preferably at least about 0.5% by weight, preferably at least about 1% by weight, preferably at least about 2% by weight, preferably at least about 3% by weight of the second copolyester, based on the total weight of the composition before drying. Preferably, the composition from which the heat-sealable coating layer is derived comprises no more than about 10% by weight, preferably no more than about 8% by weight, preferably no more than about 6% by weight, preferably no more than about 5% by weight, preferably no more than about 4% by weight of the second copolyester, based on the total weight of the composition before drying.

[0087] Thus, preferably, the composition from which the heat-sealable coating layer of embodiment C2 is derived contains from about 0.1% to about 10% by weight of the second copolyester, preferably from about 0.5% to about 8% by weight, preferably from about 1% to about 6% by weight, preferably from about 2% to about 5% by weight, preferably from about 3% to about 4% by weight, based on the total weight of the composition before drying.

[0088] The heat-sealable coating layer of embodiment C may also include anti-slip or anti-blocking agents to improve handling of the film, as is conventional in the art of sealant coatings. Suitable anti-slip or anti-blocking agents for the heat-sealable coating layer of the present invention may be selected from fatty amide anti-slip agents available from PMC Biogenix under the trade name Kemamide EZ and / or available from Grace under the trade name Sylobloc®, such as Sylobloc 48. Such ingredients are present in relatively small amounts, typically 5.0 wt% or less, typically 2.0 wt% or less, typically 1.0 wt% or less, based on the total weight of the composition before drying.

[0089] The heat-sealable coating layer of embodiment C may also include a particulate filler material. The particulate filler is preferably a particulate inorganic filler, such as alumina, titania, talc (such as that available from Specialty Minerals under the trade name Talcron MP 15-38), as well as metal or semi-metal oxides, such as silica (especially precipitated or diatomaceous silicas and other silica gels), calcined china clay, and alkali metal salts (calcium and barium carbonates and sulfates). Any inorganic filler present should be finely divided, and its volume distribution median particle diameter (often referred to as the "D(v,0.5)" value, the diameter of the equivalent sphere corresponding to 50% of the total volume of the particles, loaded against the cumulative distribution curve related volume percentages for the diameter of the particles) is preferably in the range of 0.01 to 5 μm, more preferably 0.05 to 1.5 μm, especially 0.15 to 1.2 μm. Preferably at least 90% by volume, more preferably at least 95% by volume, of the inorganic filler particles are within ±0.8 μm, especially ±0.5 μm, of the volume distribution median particle size. The particle size of the filler particles can be measured by electron microscopy, Coulter counter, sedimentation analysis, and static or dynamic light scattering. Techniques based on laser light diffraction are preferred. The median particle size can be determined by plotting a cumulative distribution curve representing the percentage of particle volume below a selected particle size and measuring the 50th percentile. Such components are present in relatively small amounts, typically 5.0 wt% or less, typically 4.0 wt% or less, typically 3.0 wt% or less, based on the total weight of the composition before drying.

[0090] The composition from which the heat-sealable coating layer of embodiment C is derived suitably comprises a first copolyester, optionally a second copolyester (i.e., in embodiment C2), and a coating vehicle. Typically, the first copolyester and the second copolyester (if present) are dispersed or dissolved within the coating vehicle. The coating vehicle can be any suitable coating vehicle, in particular tetrahydrofuran (THF) or a combination of tetrahydrofuran (THF) and toluene. When the coating vehicle comprises THF and toluene, the weight ratio of THF to toluene is preferably in the range of 70:30 to 90:10, preferably about 80:20.

[0091] The composition from which the heat-sealable coating layer of embodiment C is derived preferably comprises the coating vehicle in an amount such that the composition has a solids content of 5 to 30% by weight, preferably 8% to 25% by weight, preferably 10 to 20% by weight, preferably 15% to 19% by weight, relative to the total weight of the composition.

[0092] It will be appreciated that the first copolyester, if present, the second copolyester, the anti-slip agent, the anti-blocking agent, and / or the specific filler material typically comprise the solids content of the composition from which the heat-sealable coating layer is derived. Preferably, the first copolyester and the second copolyester together comprise at least about 85% by weight, preferably at least about 90% by weight, preferably at least about 93% by weight, preferably at least about 95% by weight of the solids content of the composition from which the heat-sealable coating is derived.

[0093] In embodiment C1, the first copolyester preferably constitutes at least about 85% by weight, preferably at least about 90% by weight, preferably at least about 93% by weight, preferably at least about 95% by weight of the solids content of the composition from which the heat-sealable coating layer is derived.

[0094] In embodiment C2, the first copolyester preferably constitutes at least about 70% by weight, preferably at least about 73% by weight, preferably at least about 75% by weight of the solids content of the composition from which the heat-sealable coating is derived. Preferably, the second copolyester constitutes at least about 15% by weight, preferably at least about 17% by weight, preferably at least about 18% by weight of the solids content of the composition from which the heat-sealable coating is derived.

[0095] If the first heat-sealable layer (A1) and / or the second heat-sealable layer (A2) are coated and according to embodiment D, preferably the composition from which the heat-sealable layers are derived comprises at least about 0.1 wt.-%, preferably at least about 0.2 wt.-%, at least about 0.5 wt.-%, of a crosslinking agent, based on the total weight of the composition before drying. Preferably the composition from which the heat-sealable layers are derived comprises no more than about 3 wt.-%, preferably no more than about 2 wt.-%, preferably no more than about 1.5 wt.-%, of a crosslinking agent, based on the total weight of the composition before drying.

[0096] Thus, preferably, the composition from which the heat-sealable layer of embodiment D is derived contains from about 0.1% to about 3% by weight of crosslinker, preferably from about 0.2% to about 2% by weight, preferably from about 0.5% to about 1.5% by weight, based on the total weight of the composition before drying. Typically, the composition from which the heat-sealable layer of embodiment D is derived contains from about 0.53% by weight of crosslinker, based on the total weight of the composition before drying.

[0097] Preferably, the composition from which the heat-sealable layer of embodiment D is derived contains at least about 0.5% by weight, preferably at least about 1% by weight, preferably at least about 2% by weight, preferably at least about 4% by weight of sulfopolyester, based on the total weight of the composition before drying. Preferably, the composition from which the heat-sealable layer of embodiment D is derived contains no more than about 20% by weight, preferably no more than about 15% by weight, preferably no more than about 10% by weight, preferably no more than about 8% by weight of sulfopolyester, based on the total weight of the composition before drying.

[0098] Thus, preferably, the composition from which the heat-sealable layer of embodiment D is derived contains in the range of about 0.5% to about 20% by weight of sulfopolyester, preferably about 1% to about 15% by weight, preferably about 2% to about 10% by weight, preferably about 4% to about 8% by weight, based on the total weight of the composition before drying. Typically, the composition from which the heat-sealable layer of embodiment D is derived contains about 6% by weight of sulfopolyester, based on the total weight of the composition before drying.

[0099] The coating composition from which the heat-sealable layer of embodiment D is derived suitably comprises a crosslinker, a sulfopolyester, and a coating vehicle. Typically, the crosslinker and the sulfopolyester are dispersed or dissolved in the coating vehicle. The coating vehicle can be any suitable coating vehicle, in particular an aqueous coating vehicle. The coating composition preferably comprises the coating vehicle in an amount such that the composition has a solids content of 1-15% by weight, preferably 3%-12% by weight, preferably 4-10% by weight, preferably 5-8% by weight, preferably 6%-7% by weight relative to the total weight of the composition.

[0100] The resulting multilayer film preferably exhibits high dimensional stability in each of the transverse direction (TD) and machine direction (MD) at high temperatures and positive thermal expansion at 200° C. Thus, the thermal response of the multilayer film in each of the machine direction and transverse direction is coordinated with that of the metal layer(s), and the current collector exhibits high dimensional stability without deformation, warping, or delamination during subsequent processing at high temperatures (e.g., during metal deposition or subsequent battery formation).

[0101] Preferably, the multilayer film exhibits a thermal expansion in air at 200° C. of from greater than 0% to less than or equal to 3.0%, preferably from greater than 0% to less than or equal to 2.0%, preferably from 0.1% to 2.0%, preferably from 0.2% to 1.5%, in each of the transverse direction (TD) and machine direction (MD). Preferably, the multilayer film exhibits isotropic thermal expansion, i.e., the layers expand by the same amount in TD and MD.

[0102] The inventors have discovered that the manufacturing steps, particularly the annealing and relaxation steps described herein, can be performed such that the multilayer film exhibits isotropic thermal expansion. In particular, the degree of dimensional relaxation in MD and TD in the relaxation steps described herein can be controlled. For example, the degree of dimensional relaxation performed in MD and TD can be different to counter the residual deformation in either MD or TD resulting from the previous manufacturing steps, so that the final resulting film exhibits balanced properties and thus isotropic thermal expansion.

[0103] Preferably, the multilayer film exhibits a positive coefficient of linear thermal expansion (CLTE) in air over the range of 32° C. to 200° C. in each of the transverse direction (TD) and machine direction (MD), preferably less than 20×10 -5 Positive CLTE less than 17 x 10 / °C, preferably -5 Positive CLTE less than 10 x 10 / °C, preferably -5 Positive CLTE less than 9 x 10 / °C, preferably -5 Positive CLTE less than 8.5 x 10 / °C, preferably -5 / °C.

[0104] The first metal layer and, if present, the second metal layer are each formed from a metallic conductive material. Preferably, the first metal layer and the second metal layer comprise the same metallic conductive material. Alternatively, the first metal layer and the second metal layer may comprise different metallic conductive materials. The metallic conductive material is preferably selected from at least one of aluminum, copper, nickel, titanium, silver, nickel-copper alloy, or aluminum-zirconium alloy. Preferably, the metallic conductive material is aluminum or copper. If the current collector is a cathode current collector, the first metal layer and, if present, the second metal layer preferably comprise aluminum. If the current collector is an anode current collector, the first metal layer and, if present, the second metal layer preferably comprise copper.

[0105] When the first metal layer and, if present, the second metal layer, comprise aluminum, the substrate layer is preferably a PET film.When the first metal layer and, if present, the second metal layer comprise copper, the substrate layer is preferably a PEN film.

[0106] The metal layer(s) preferably comprises at least 90% by weight, preferably at least 95% by weight, preferably at least 98% by weight, preferably at least 99% by weight of the metallic conductive material described above, the stated weights of the metallic conductive material being weight percentages relative to the total weight of the metallic layer. In a preferred embodiment, the metallic layer consists of the metallic conductive material.

[0107] The metal layer(s) preferably exhibit a positive coefficient of thermal expansion. Preferably, the first metal layer and, if present, the second metal layer in the current collector of the present invention independently exhibit a thermal expansion in air at 200° C. of from greater than 0% to less than or equal to 2.0%, preferably from greater than 0% to less than or equal to 1.0%, preferably from 0.25% to 0.75%, preferably from 0.3 to 0.5%. Each of the metal layers in the current collector of the present invention preferably exhibits an isotropic thermal expansion, i.e., the layers expand by the same amount in orthogonal directions, e.g., in directions corresponding to the machine direction and transverse dimensions of the multilayer film. Preferably, the first metal layer and the second metal layer exhibit the same expansion at 200° C. as each other.

[0108] Preferably, the first metal layer and, if present, the second metal layer, independently, have a molecular weight of about 10×10 -6 / ℃ to about 30×10 -6 / °C, preferably about 12 x 10 -6 / ℃ to about 18×10 -6 The positive coefficient of linear thermal expansion (CLTE) in air at 100°C up to 100°C / °C is shown.

[0109] Preferably, the thickness of each of the first metal layer and, if present, the second metal layer, independently, is in the range of about 50 nm to about 1000 nm, preferably about 100 nm to about 1000 nm, preferably about 100 nm to about 800 nm, preferably about 150 nm to about 700 nm.

[0110] Each of the first metal layer and, if present, the second metal layer is suitably deposited on the multilayer film. Any suitable deposition technique known in the art for the manufacture of metallized films may be used, including at least one of vapor deposition and electroless plating. Preferably, the first metal layer and the second metal layer are independently deposited on the multilayer film by at least one of vapor deposition and electroless plating. The vapor deposition may be at least one of physical vapor deposition (PVD), virtual cathodic deposition (VCD), or chemical vapor deposition (CVD).

[0111] Preferably, the physical vapor deposition is selected from at least one of evaporation and sputtering deposition. The evaporation is preferably at least one of vacuum evaporation, thermal evaporation, or electron beam evaporation techniques. The sputtering deposition is preferably magnetron sputtering. Suitable processes include plasma enhanced deposition techniques, such as, for example, plasma enhanced electron beam evaporation techniques and plasma enhanced sputtering techniques.

[0112] Preferably, thermal evaporation, electron beam evaporation or virtual cathode deposition is used to deposit the metal layer(s).

[0113] Typically, thermal evaporation involves placing the multilayer film and source material in a vacuum chamber. The source material is subjected to a vacuum (preferably for 10 -4 The source material is heated under a pressure of less than 100 MPa (below 100 Pa) and elevated temperatures. The evaporated source material particles disperse towards the substrate and condense on the substrate surface to form a thin film. A resistive coil, typically in the form of a powder or solid rod, is subjected to a large direct current (preferably in the range of 100-150 mA for a period of 10-15 seconds), thus generating heat that is used to evaporate the source material. Suitable apparatus include commercially available apparatus under the name "BAE 370" from Balzers AG, Liechtenstein, or commercially available equipment from Buhler and Applied Materials.

[0114] Typically, electron beam evaporation involves the evaporation of a source material using high energy electrons in the form of an intense beam. A hot filament is used to thermionically emit the electrons which, after acceleration, are used to evaporate the source material.

[0115] Typically, virtual cathode deposition is performed using a high energy density electron beam (preferably with an energy of 100 MW / cm 2 The high energy density electron beam ablates the solid target, resulting in a portion of the ablated target material (e.g., about 0.001 mm2 or less). 3 ) forms a plasma. The plasma propagates in the form of a plasma flow towards the polyester substrate. The plasma flow may have a speed of up to about 50 km / s. The target material plasma condenses on the multilayer film surface to form a thin film. For example, a thin film with a thickness of up to 0.1 nm can be formed on the multilayer film surface at a distance of 400 cm. 2 A virtual cathode may be formed pulse by pulse at 1000 Hz. Repeating high voltage pulses (e.g., at frequencies up to about 600 Hz) and / or using an apparatus including multiple virtual cathode groups allows the deposited film to grow until a desired thickness is reached. Suitable virtual cathode deposition methods and apparatus are known and include, for example, those methods and apparatus discussed in WO-2016 / 042530-A and US-2020 / 0095129-A, the disclosures of the foregoing methods and apparatus being incorporated herein by reference.

[0116] The deposition technique may require a single pass or multiple passes (such as dual passes) to deposit a metal layer of the desired thickness. Preferably, the deposition technique requires a single pass, which advantageously increases manufacturing efficiency and minimizes exposure of the multilayer film to high temperature conditions for extended periods of time.

[0117] As will be appreciated by those skilled in the art, a current collector is required to exhibit electrical conductivity when placed in a battery. Thus, electrical conductivity should be possible between the current collector outer surfaces, regardless of electrical insulation provided by the multilayer film. For example, electrical conductivity should be possible from the first metal layer to the second metal layer (if present), regardless of electrical insulation provided by the substrate layer, with the first heat-sealable layer and, if present, the second heat-sealable layer being positioned between the first and second metal layers.

[0118] In one embodiment, referred to herein as Arrangement 1, the current collector further includes at least one conductive tab connecting the first metal layer and the second metal layer, such that the current collector exhibits electrical conductivity from one surface to the other. Such conductive tabs are known in the art and are disclosed, for example, in WO-2019 / 051123-A and US-10700339-B. Preferably, the tab extends beyond the periphery of the current collector, such that the tab can connect the current collector to other components within the battery. Preferably, the tab extends from the interior to the exterior of the lithium ion battery, such that the tab can connect the battery to an external source.

[0119] In another embodiment, referred to herein as Arrangement 2, the multilayer film includes a channel extending from a first surface to an opposite second surface, (i) the sides of the channel are at least partially coated with at least one metal, and / or (ii) the channel is preferably at least partially filled with at least one metal, such as to create a conductive pathway between the first and second metal layers. Such channels are known in the art and are disclosed, for example, in US-2019 / 0305320-A. The channel may have an opening size (e.g., diameter) ranging from about 1 μm to about 5 mm. The percentage of the surface area of ​​the multilayer film consisting of channel openings is typically about 0.01 to about 10%. Such channels allow for further reduction in the weight of the battery and improve its electrochemical properties, such as charge / discharge rate and cycle life. The aforementioned metals are preferably deposited during the metal deposition step(s) used to deposit the first and second metal layers described above, preferably during a virtual cathode deposition technique. Arrangement 2 is further illustrated in FIG. 2. FIG. 2A shows the current collector arrangement in cross section. The current collector (20) has a multilayer film (6), a first metal layer (7), and a second metal layer (8) with a layer order of first metal layer / multilayer film / second metal layer. The multilayer film (6) has a number of perforations that are filled with metal (9). The metal forms a continuous connection between the first metal layer and the second metal layer. FIG. 2B shows the multilayer film in the current collector arrangement in a top view.

[0120] Arrangement 1 and arrangement 2 may reside in the same battery.

[0121] The total thickness of the current collector of the present invention is preferably about 1 μm to about 12 μm, preferably about 2 μm to about 8 μm, preferably about 4 μm to about 8 μm, preferably about 4 to about 6 μm.

[0122] Preferably, the current collector has a resistance of about 2.0 Ωsq. -1 Less than or equal to 1.5Ωsq, preferably about 1.5Ωsq -1Less than 1.0Ωsq, preferably about 1.0Ωsq -1 Preferably, the current collector exhibits a sheet resistance of at least about 0.01 Ωsq. -1 , preferably at least about 0.02 Ωsq -1 , preferably at least about 0.05 Ωsq -1 Preferably, the current collector exhibits a sheet resistance of about 0.01 Ωsq. -1 ~ approx. 2.0Ωsq -1 , preferably about 0.02Ωsq -1 ~ approx. 2.0Ωsq -1 , preferably about 0.02Ωsq -1 ~about 1.5Ωsq -1 , preferably about 0.05Ωsq -1 ~ approx. 1.0Ωsq -1 The sheet resistance of

[0123] Preferably, the current collector exhibits a breakdown current of about 35 A or less, preferably about 30 A or less, preferably about 20 A or less, preferably about 10 A or less, preferably about 5 A or less. Preferably, the current collector exhibits a breakdown temperature of about 300° C. or less, preferably about 250° C. or less, preferably about 240° C. or less, preferably about 230° C. or less, preferably about 220° C. or less. In a preferred embodiment, the breakdown temperature is less than the crystalline melting point (T M ) or less, which typically corresponds to the point at which the polyester layer begins to shrink. Thus, when the substrate layer is a PEN film, the current collector preferably exhibits a breakdown temperature of about 270° C. or less, preferably about 260° C. or less, preferably about 250° C. or less, preferably about 220° C. or less. When the substrate layer is a PET film, the current collector preferably exhibits a breakdown temperature of about 260° C. or less, preferably about 250° C. or less, preferably about 220° C. or less. The breakdown current and temperature corresponds to the point at which the current collector fails, i.e., the film acts as an electrochemical fuse that effectively prevents excessive current flow and the risk of heat propagation in the battery.

[0124] Preferably, the adhesive strength between the metal layer and the multilayer film is at least about 250 g / 25 mm, preferably at least about 280 g / 25 mm, preferably at least about 300 g / 25 mm.

[0125] Preferably, the peel resistance of the multilayer film is at least about 80%, preferably at least about 85%, preferably at least about 90%.

[0126] According to a second aspect of the present invention there is provided a method of manufacturing a current collector as described herein, the method comprising the steps of: The order of layers is first metal layer / first heat sealable layer / polyester substrate layer / optional second heat sealable layer. (i) providing a polyester substrate layer (B); (ii) disposing a first heat-sealable layer (A1) on a first surface of the polyester substrate layer (B); (iii) optionally disposing a second heat-sealable layer (A2) on a second surface of the polyester substrate layer (B); (iv) depositing a metal on the outer surface of said first heat-sealable layer (A1) to form a first metal layer; The steps include:

[0127] Preferably, the method comprises: The order of layers is first metal layer / first heat-sealable layer / polyester substrate layer / second metal layer, or first metal layer / first heat-sealable layer / polyester substrate layer / second heat-sealable layer / second metal layer. (v) further comprising the step of depositing a metal onto the second surface of the polyester substrate layer (B) or, if present, onto the outer surface of said second heat-sealable layer (A2) to form a second metal layer.

[0128] As discussed above, steps (ii) and (iii) may be carried out independently by coextrusion or coating. Steps (ii) and (iii) may be carried out separately and sequentially, or may be combined into a single technique.

[0129] Prior to application of the metal layer (steps (iv) and (v)), the exposed surfaces of the multilayer film (e.g., the exposed surfaces of the polyester substrate and / or the exposed surfaces of the first or second heat-sealable layers) may, if required, be subjected to a chemical or physical surface modification treatment to improve the bond between the multilayer film and the subsequently applied metal layer. It is particularly advantageous to subject the exposed surfaces of the multilayer film to such a treatment prior to deposition of the metal layer.

[0130] A preferred treatment is to subject the exposed surface of the multilayer film to a plasma treatment. Plasma treatment involves exposing the surface to an electrical discharge, generated and maintained by imposing a high voltage in a low pressure gas atmosphere, i.e. a so-called glow discharge. The surface is treated with electrons, ions, excited atoms, excited molecules, radicals, and activated particles of ultraviolet light that are formed during this glow discharge. One or more agents known in the art can be injected into the glow discharge and onto the substrate. One or more agents can be deposited to form a coating on the exposed surface. Known agents include organic molecules, inorganic molecules, and biomolecules. Preferred agents include a mixture of acrylic and methacrylic anhydrides, (3-glycidyloxypropyl)trimethoxysilane, N-(3-trimethoxysilylpropyl)diethylenetriamine, or (3-mercaptopropyl)trimethoxysilane. For example, suitable mixtures of acrylic acid and methacrylic anhydride include mixtures comprising 75% by weight acrylic acid and 25% by weight methacrylic anhydride, or mixtures comprising 50% by weight acrylic acid and 50% by weight methacrylic anhydride.

[0131] A preferred plasma treatment is corona treatment (sometimes referred to as air plasma) in which the exposed surfaces of the multilayer film are subjected to high voltage electrical stress associated with corona discharge. The preferred treatment with corona discharge may be accomplished in air at atmospheric pressure with conventional equipment using a high frequency, high voltage generator, preferably having a power output of 1-20 kW at a potential of 1-100 kV. Discharge is conventionally accomplished by passing the film over a dielectric support roller at a discharge station, preferably at a linear speed of 1.0-500 m per minute. The discharge electrode may be positioned 0.1-10.0 mm from the moving film surface.

[0132] Following plasma treatment, the exposed surface of the multilayer film preferably exhibits a water contact angle of about 70 degrees or less, preferably about 65 degrees or less, preferably about 60 degrees or less. Following plasma treatment, the substrate layer preferably exhibits a water contact angle of at least about 5 degrees, preferably at least about 10 degrees, preferably at least about 14 degrees. Preferably, following plasma treatment, the substrate layer exhibits a water contact angle of about 5 degrees to about 70 degrees, preferably about 10 degrees to about 65 degrees, preferably about 14 degrees to about 60 degrees.

[0133] The water contact angle between an HPLC grade water droplet and the substrate layer can be measured by a Surface Analyst 3001 (BTG Labs).

[0134] Following plasma treatment, the multilayer film preferably exhibits a surface energy of about 30 mN / m to about 100 mN / m, preferably about 30 to about 80 mN / m. The surface energy may be measured by an ink-based surface energy test, such as the Dyne Level test according to ISO 8296.

[0135] The descriptions and preferred examples of the first aspect are equally applicable to the second aspect.

[0136] According to a third aspect of the present invention there is provided the use of a multilayer film in a current collector further comprising a first metal layer, said use for providing improved adhesion strength and / or peel resistance between said multilayer film and the metal layer, said multilayer film comprising: (i) a polyester substrate layer (B) having a first surface and a second surface; (ii) a first heat-sealable layer (A1) disposed on a first surface of the aforementioned polyester substrate layer; (iii) optionally, a second heat-sealable layer (A2) disposed on a second surface of said polyester substrate layer; The aforementioned first metal layer is disposed on the outer surface of the first heat-sealable layer (A1), the multilayer film having a thickness of 12 μm or less, and the first metal layer having a thickness of 1000 nm or less.

[0137] The descriptions and preferred examples of the first and second aspects are equally applicable to the third aspect.

[0138] According to a fourth aspect of the present invention there is provided a battery comprising an anode material, an anode current collector, a cathode material, a cathode current collector, and a separator between the anode material and the cathode material, wherein at least one of the aforesaid current collectors is a current collector as described herein.

[0139] The battery may be selected from a lithium ion battery, a lithium sulfur (LiS) battery, a lithium air (LiO2) battery, or a sodium ion battery. Preferably, the battery is a lithium ion battery, a lithium sulfur (LiS) battery, or a lithium air (LiO2) battery. Preferably, the battery is a lithium ion battery. Preferably, the battery is a sodium ion battery.

[0140] Any suitable anode material, cathode material, and separator may be used as is conventional in the art.

[0141] The anode material may be selected from graphite and / or lithium titanate (LTO).

[0142] The cathode material may be selected from lithium or mixed oxides of lithium and other metal(s), in particular lithium titanate (LTO), lithium iron phosphate (LiFePO4, also known as LFP), and / or lithium nickel manganese cobalt oxide (LiNiMnCoO2, also known as NMC).

[0143] A preferred electrode is disclosed, for example, in British Patent Application No. 2115767.2, the disclosure of which is incorporated herein by reference. In particular, the aforementioned electrode may be comprised of an active material and a binder material, the binder material comprising a copolyester comprising repeating units derived from a diol, a dicarboxylic acid, and a poly(alkylene oxide). The binder material may further comprise a first metal ion-containing component selected from a conductive ceramic particulate material, and / or may further comprise additional metal ions from one or more sources other than the aforementioned conductive ceramic particulate material.

[0144] The separator may be a polymer, ceramic, nonwoven, or fabric separator. Preferred separators are disclosed, for example, in WO-2019 / 186173-A1, WO-2021 / 064359-A1, and UK Patent Application No. 2110926.9, the disclosures of which are incorporated herein by reference. In particular, the aforementioned separator may be a copolyester film comprising a copolyester comprising repeating units derived from a diol, a dicarboxylic acid, and a poly(alkylene oxide), the copolyester film may further comprise a first metal ion-containing component selected from a conductive ceramic particulate material, and the film may further comprise additional metal ions from one or more sources other than the aforementioned conductive ceramic particulate material.

[0145] Such a preferred separator may be made by a process that includes producing a copolyester film, the aforementioned process comprising: (i) reacting said dicarboxylic acid or its ester (suitably lower alkyl (C 1-4 ) ester, preferably a dimethyl ester) with said diol; (ii) polymerizing the aforementioned bis(hydroxyalkyl)-ester of the aforementioned dicarboxylic acid in the presence of a poly(alkylene oxide) in a polycondensation reaction to form a copolyester; (iii) introducing during synthesis of the copolyester in steps (i) and / or (ii) and / or during a subsequent separate combining or mixing step, said first metal ion-containing component selected from conductive ceramic particulate material, and optionally said additional metal ions from one or more sources other than said conductive ceramic particulate material, to form a copolyester composition; (iv) forming a copolyester film from the aforementioned copolyester composition, preferably by melt extruding the aforementioned composition or by solvent casting a dispersion or solution comprising the aforementioned copolyester composition; The steps include:

[0146] The separator may be synthesised in accordance with the techniques disclosed in UK Patent Application No. 2110926.9, the disclosure of which is incorporated herein by reference.

[0147] It will be appreciated that the battery includes an anode current collector and a cathode current collector, at least one of the aforementioned current collectors being a current collector as described herein. Preferably, both the anode current collector and the cathode current collector are current collectors as described herein. Alternatively, one of the anode current collector and the cathode current collector is a current collector as described herein, and the other current collector is any suitable current collector as conventional in the art. Other preferred current collectors are disclosed, for example, in UK Patent Application No. 2106834.1, the disclosure of which is incorporated herein by reference. In particular, the aforementioned other current collector may be a current collector including a biaxially oriented polymer substrate layer and a first metal layer on a side of the polymer substrate layer, the polymer substrate layer exhibiting a positive thermal expansion in air at 200° C. in each of the transverse direction (TD) and the machine direction (MD), the polymer substrate layer having a thickness of 12 μm or less, and the first metal layer having a thickness of 1000 nm or less.

[0148] The battery, preferably a lithium ion battery, may further include an electrolyte, which, if present, is preferably a conductive organic solvent that may saturate other materials present in the battery, thereby providing a mechanism for ion conduction between the anode and cathode.

[0149] Alternatively, the battery (preferably a lithium-ion battery) can be a dry cell, which contains a solid separator located between the anode and cathode materials, which acts as both the separator and the electrolyte, thus eliminating the liquid electrolyte.

[0150] In an embodiment of arrangement 1, as described above, the current collector further includes at least one conductive tab connecting the first metal layer and the second metal layer such that the current collector is conductive from one surface of the current collector to the other surface of the current collector. Preferably, the tab extends beyond the periphery of the current collector so that the tab can connect the current collector to other components within the battery. Preferably, the tab extends from the interior to the exterior of the battery so that the tab can connect the battery to an external source.

[0151] Preferably, the electrode material is coated or otherwise deposited on a current collector.

[0152] The batteries (preferably lithium ion batteries) may have any configuration known in the art, including cans, pouch cells, prismatic cells, coin cells, cylindrical cells, wound prismatic cells, and wound pouch cells.

[0153] The descriptions and preferred examples of the first to third aspects are equally applicable to the fourth aspect.

[0154] According to a fifth aspect of the present invention there is provided the use of a current collector as described herein in a battery as described herein, preferably a lithium-ion battery.

[0155] The descriptions and preferred examples of the first to fourth aspects are equally applicable to the fifth aspect.

[0156] According to a sixth aspect of the present invention there is provided a method of manufacturing a battery as described herein (preferably a lithium ion battery), the method comprising the steps of: (i) preparing a current collector as described herein; (ii) assembling a battery (preferably a lithium ion battery), the battery comprising an anode material, a cathode material, a separator between the anode material and the cathode material, an anode current collector, and a cathode current collector, at least one of the aforesaid current collectors being the current collector obtained from step (i).

[0157] Preferably, the anode or cathode material may be coated or otherwise deposited on the current collector described herein using any suitable coating or deposition technique conventional in the art for electrode preparation. It will be appreciated that the anode material is coated or otherwise deposited on the outer surface of the metal layer of the anode current collector, whereas the cathode material is coated or otherwise deposited on the outer surface of the metal layer of the cathode current collector. High processing temperatures (e.g., about 200° C.) are used during this coating or deposition step. In a preferred embodiment, the electrode material is coated on the current collector.

[0158] The electrode / current collector assembly is suitably dried at a temperature of about 50° C. to about 170° C., preferably about 80° C. to 160° C. It will be appreciated that the drying step may include a variety of different temperature zones with appropriate heating profiles.

[0159] The dried electrode / current collector assembly is preferably compacted, for example, by calendering between a rotating pair of rollers. During calendering, the aforementioned assembly may be exposed to electrostatic discharge and cleaned, for example, by a brush or air stream. Optionally, all or part of the compacting step may be heated, for example, by pre-heating the sections and / or rollers in the calendering, for example, to a temperature of about 50° C. to about 250° C.

[0160] The descriptions and preferred examples of the first to fifth aspects are equally applicable to the sixth aspect.

[0161] The invention will be further illustrated with reference to the figures as described below.

[0162] Figure 1 shows the assembly of the multilayer film as described above. Figure 2 shows the assembly of the current collector according to arrangement 2 as described above. Figure 2A shows the current collector in cross section. Figure 2B shows the multilayer film in the current collector arrangement in top view.

[0163] Characteristic measurements The following test methods were used to characterize the properties of the current collectors and batteries described herein.

[0164] (i) The glass transition temperature (T g ) and crystalline melting point (T m ) were measured. Unless otherwise stated, measurements were made following standard test methods and based on the methods described in ASTM E1356-98. Samples were kept under an atmosphere of dry nitrogen for the duration of the scan (approximately 1.5-3 hours). Samples (approximately 7 mg) were heated from 20° C. to 250° C. at a rate of 20° C. / min, held at 250° C. for 5 minutes, then cooled to 20° C. at a rate of 20° C. / min, and then heated from 20° C. to 250° C. at 10° C. / min. Thermal properties were recorded for the second heating scan.

[0165] As described in ASTM E1356-98, T is defined as the extrapolated onset temperature of the glass transition observed for a DSC scan (heat flow (W / g) versus temperature (°C)). g The value was taken.

[0166] T from the DSC scan as the temperature at which peak heat flow was observed at each transition. m The value was taken.

[0167] (ii) Expansion of multilayer films A sample of the multilayer film having dimensions of 5 mm x 8 mm was subjected to thermomechanical analysis using a thermomechanical analyzer (TMA Q400 by TA Instruments Inc.). The longer dimension of the sample (i.e., the 8 mm dimension) corresponds to the direction of the sample in which expansion was tested. The sample was mounted on the instrument and subjected to a strain of 1 N / mm in either the machine direction (MD) or the transverse direction (TD). 2 and a heating rate of 10°C / min from 32°C to 220°C. The thermal expansion in air at a temperature of 200°C was measured. Thermal expansion in air at 200°C is defined as the % change in the dimension of the film in a given direction (i.e., in MD or TD) and is calculated as (L1-L0) / L0 x 100, where L0 is the dimension at 32°C and L1 is the dimension at 200°C. As one skilled in the art would recognize, a negative thermal expansion indicates thermal shrinkage.

[0168] (iii) Coefficient of linear thermal expansion (CLTE) A procedure similar to that in (ii) was used. For the coefficient of linear thermal expansion measurement (b), the CLTE value was derived from the following formula: CLTE = (L1-L0) / (L0x(T2-T1)) (L1-L0) is the measured change in sample length over the temperature range (T2-T1), where L0 is the original specimen length at 32° C. Suitably, T2 was 200° C. and T1 was 32° C. The data can be plotted as a function of the % change in specimen length with temperature normalized to 32° C.

[0169] (iv) Sheet resistance The sheet resistance of the conductive layer was measured using a linear four-point probe (Jandel Model RM2) according to ASTM F390-98 (2003).

[0170] (v) Breakdown current and temperature at breakdown A current collector sample having dimensions of 50 mm x 10 mm was held at each end between a pair of conductive clamps. The sample was clamped to a 10 mm 2 The sample was clamped such that the sample was held within the clamp. Current was passed through the sample at a ramp rate of 2 A / min until failure was observed. The temperature profile of the sample was monitored using a thermal imaging camera throughout the test to determine the temperature at failure.

[0171] (vi) The adhesive strength of the multilayer film to itself The adhesion (heat seal) strength of a film to itself was measured as follows: A4 samples of multilayer films were prepared. Thus, a multilayer film of the present invention was prepared, comprising a polyester substrate layer (B) and at least one heat sealable layer (A). The multilayer film was folded in the MD direction so that the heat sealable layer was in contact with itself. The samples were heat sealed using a Sentinel Model 12 (Packaging Industries Group Inc.) machine under the following conditions: 140°C (upper jaw) and 40°C (lower jaw) for 1 second under a pressure of 40 psi. The sealed samples were cut into 25 mm wide pieces and the adhesion strength was determined using an Instron Model 4464. The jaws were set 50 mm apart. The upper jaw held one piece of the sealed sample and moved up at a speed of 250 mm / min, while the lower jaw held the other piece of the sealed sample and remained stationary. The force required to peel the two pieces of the sample apart at 90 degrees was measured and reported as the average of 13 results.

[0172] (vii) Current collector adhesive strength The adhesive strength of a metallized film (commercially available as Vistafix (TP) from UCB Sidac Division) to EAA (ethylene acrylic acid film) having a thickness of 25 μm was evaluated as follows: A sample of current collector and a sample of EAA film were positioned together such that the outer surface of the metallized multilayer film was in contact with the surface of the EAA film. The samples were heat sealed using a Sentinel Model 12 (Packaging Industries Group Inc.) machine under the following conditions: 10 seconds under 50 psi pressure at 115° C. (upper jaw) and 25° C. (lower jaw). The sealed samples were cut into 25 mm wide sections and the adhesive strength was determined using an Instron Model 4464. The jaws were set 50 mm apart. The upper jaw held the EAA piece of the sealed sample and moved up at a speed of 300 mm / min, while the lower jaw held the current collector piece of the sealed sample and remained stationary. The average peel force was measured and reported as the average of the 5 results. Planes of adhesive failure were also noted.

[0173] When the adhesive strength between the metal layer and the multilayer film is lower than that between the metal layer and the EEA film (about 800 g / 25 mm), the test sample peels along the interface of the metal layer and the multilayer film. In this case, the average peel force represents the adhesive strength between the metal layer and the multilayer film.

[0174] When the adhesive strength between the metal layer and the multilayer film is higher than the adhesive strength between the metal layer and the EEA film (800 g / 25 mm), the test sample peels off along the interface of the metal layer and the EEA film.

[0175] A further failure plane is a coherent failure within the metallization layer itself, which indicates that the adhesive strength between the metal layer and the multilayer film is greater than the force required to cause a coherent failure (thus typically the adhesive strength between the metal layer and the multilayer film is greater than about 800 g / 25 mm).

[0176] (viii) Resistance to peeling of current collectors Peel resistance was evaluated by subjecting the current collector to high temperatures, specifically by placing it in a heating oven at 200° C. for 5 minutes and then at 130° C. for the same 5 minutes. Adhesion strength was measured by the method described above before and after the aforementioned heat treatment to evaluate the peel resistance of the current collector after exposure to high temperature conditions representative of conditions used during a typical battery manufacturing process. Peel resistance is defined as follows: Peel resistance = 100*((A TT -A0) / A0) A TT = Adhesion strength of current collector after heat treatment A0 = adhesive strength of current collector before heat treatment

[0177] (ix) Multilayer film thickness The thickness of the multilayer film and the thickness of the heat-sealable layer(s) (A) of the multilayer film can be measured using the "point thickness" method. A sample of the multilayer film having a length of about 2 cm was prepared. The thickness of the multilayer film was measured using a Mercer gauge. The heat-sealable layer(s) was then dissolved and removed using a suitable solvent (e.g., chloroform). The thickness of the remaining polyester substrate layer was measured using a Mercer gauge. As one skilled in the art will recognize, the difference between those thickness measurements (i.e., the difference between the thickness before and after dissolving the heat-sealable layer(s)) will provide the thickness of the heat-sealable layer(s).

[0178] (x) Molecular weight of poly(alkylene oxide) glycol (M n and M w ) GPC measurements were performed on Malvern / Viscotek TDA 301 using a 2 x 30 cm PL HFIPgel column in addition to an Agilent PL HFIPgel guard column. -1A solution of HFIP with 25 mM NaTFAc was used as the eluent at a nominal flow rate of 1000 s. All experimental runs were performed at 40 °C using a refractive index detector. Molecular weights are referenced to polymethylmethacrylate calibrators. Data acquisition and subsequent data analysis were performed using Omnisec software. Samples were diluted to 2 mg mL, with 20 mg of sample dissolved in 10 mL of eluent. -1 The solutions were stirred at room temperature for 24 hours and then heated at 40° C. for 30 minutes to completely dissolve the polymer. Each sample was filtered through a 0.45 μm polytetrafluoroethylene membrane before injection.

[0179] M w The determination is made using GPC measurements as described herein.

[0180] experiment Polyester composition P1 contained a PET polymer with an IV=0.56.

[0181] Copolyester composition P2 included an IPA-containing PET-based copolyester (TA:IPA=82:18 mol %) with IV=0.57, Tg=74°C, and Tm=210°C.

[0182] Example 1 A multilayer film comprising a substrate layer of polyester composition P1 and a heat-sealable layer of copolyester P2 was extruded and cast using a standard melt coextrusion system. The coextrusion system was assembled using two independently operating extruders that fed separate supplies of polymer melt into a standard coextrusion block or junction where the streams met. From the coextrusion block, the melt-stream was transferred to a conventional, flat film extrusion die. The melt temperature of polyester P1 was 275°C and that of copolyester P2 was 235°C. The melt curtain was cast from the common coextrusion die and then temperature quenched on a rotating, cooled metal drum. The cast film was collected. The cast extrudate was stretched in MD and TD to approximately 3.45 times its original dimensions at a temperature of 95°C. The biaxially stretched film was annealed under dimensional constraint at a temperature of 225° C., and then subjected to a first simultaneous relaxation step in both MD and TD at −1.5% at a temperature of 225° C. for 0.9 seconds. The biaxially stretched film was then subjected to a second simultaneous relaxation step in both MD and TD at −1.5% at a temperature of 200° C. for 1.3 seconds. Thus, the total relaxation in both MD and TD was −3% at an average temperature of 215° C. The final multilayer film was 6 μm in thickness and comprised two layers with AB structure, the heat-sealable copolyester layer (A) being approximately 0.73 μm thick.

[0183] A metal layer of Al with a thickness of 68 nm was then deposited on the surface of the heat-sealable copolyester layer (A), so that the layer sequence of the current collector was: substrate layer (B) / heat-sealable copolyester layer (A) / first metal layer. The metal layer was deposited via thermal evaporation using an apparatus "BAE 370" from Balzers AG.

[0184] The thermal expansion of the film in air at 200° C. was 0.71% in the MD and 1.08% in the TD. The sheet resistance of the current collector was measured as described herein and was 0.66 Ω sq. -1 It has been found that the current collector is therefore advantageously 1 Ωsq -1 A sheet resistance of less than 100 nm was achieved.

[0185] Furthermore, the peel resistance of the current collector was measured as described herein. No decrease in adhesive strength was observed. Thus, although the overall multilayer film, and especially the heat-sealable copolyester layer (A), was very thin, the adhesive strength of the current collector was surprisingly maintained after exposure to high temperatures.

[0186] Comparative Example 1 Comparative Example 1 was a monolayer film of PET having a thickness of 6 μm. The film was stretched and relaxed according to Example 1. First and second metal layers of Al, each having a thickness of 53 nm, were then deposited on the first and second surfaces of the monolayer film, such that the layer order of the comparative current collector was first metal layer / substrate layer / second metal layer.

[0187] The thermal expansion of the film in air at 200° C. was 0.54% in MD and 1.01% in TD. The peel resistance of the current collector was −4.7%.

[0188] The results of Example 1 and Comparative Example 1 demonstrate that the current collector of the present invention provides surprisingly improved resistance to delamination.

[0189] Example 2 A series of multilayer films were prepared to determine the effect of the thickness of the heat-sealable copolyester layer (A) on the adhesion of the multilayer film to itself.

[0190] In particular, multilayer films comprising a substrate layer of polyester composition P1 and a heat-sealable layer of copolyester P2 were extruded, cast, stretched and relaxed according to Example 1. Each of the final multilayer films with two layers had an AB structure, and the multilayer film and the heat-sealable copolyester layer (A) had thicknesses as shown in Table 1. The adhesive strength of the multilayer film to itself was measured as described herein, and the results are shown in Table 2. [Table 1]

[0191] As expected, the adhesive strength of the multilayer film to itself decreased with decreasing thickness of the heat sealable layer. However, the multilayer films of Example 1 and Example 2B showed surprisingly high adhesive strength compared to what was expected for such thin films. Nevertheless, it was also surprising that the multilayer film and each of the heat seal bonds therein were resistant to degradation during the subsequent metal deposition step. In particular, even the very thin multilayer film of Example 1 was able to withstand the high temperature conditions during metal deposition without film damage, and good adhesion was achieved between the metal layer and the multilayer film.

Claims

1. 1. A current collector comprising a multilayer film and a first metal layer, the multilayer film comprising: (i) a polyester substrate layer (B) having a first surface and a second surface; (ii) a first heat-sealable layer (A1) disposed on the first surface of the polyester substrate layer; the first heat-sealable layer (A1) comprises at least one copolyester, the first metal layer is disposed on the outer surface of the first heat-sealable layer (A1), the multilayer film has a thickness of 12 μm or less, the thickness of the substrate layer (B) is at least 70% of the total thickness of the multilayer film, the first metal layer has a thickness of 1000 nm or less, and the multilayer film exhibits an adhesion strength to itself of at least 100 g / 25 mm; the current collector.

2. (iii) A current collector as described in claim 1, further comprising a second heat-sealable layer (A2) disposed on the second surface of the polyester substrate layer, the second heat-sealable layer (A2) comprising at least one copolyester.

3. 3. The current collector of claim 1, further comprising a second metal layer, the first metal layer and the second metal layer being on opposite sides of the multilayer film, and the second metal layer independently having a thickness of 1000 nm or less.

4. 3. The current collector of claim 1, wherein the substrate layer (B) comprises polyethylene terephthalate or polyethylene naphthalate.

5. 3. The current collector according to claim 1, wherein the multilayer film has a total thickness of 3.0 to 12 μm.

6. 3. The current collector according to claim 1, wherein the thickness of said substrate layer (B) is 2.0 to 11.0 μm.

7. 3. A current collector according to claim 1 or 2, wherein the thickness of the substrate layer (B) is greater than the thickness of each of the first heat-sealable layer (A1) and, if present, the second heat-sealable layer (A2).

8. 3. The current collector of claim 1 or 2, wherein the thickness of the substrate layer (B) is at least 50% and not more than 99% of the total thickness of the multilayer film.

9. 3. The current collector according to claim 1, wherein the thickness of the first heat-sealable layer (A1) and, if present, the thickness of the second heat-sealable layer (A2) are each independently from 0.1 to 3.5 μm.

10. 3. The current collector according to claim 1 or 2, wherein the copolyester of the first heat-sealable layer (A1) and, if present, the copolyester of the second heat-sealable layer (A2) are independently selected from copolyesters derived from at least one aliphatic diol, a first dicarboxylic acid, and a second dicarboxylic acid.

11. The current collector of claim 10, wherein the aliphatic diol is an aliphatic diol containing from 2 to 8 carbon atoms.

12. The current collector of claim 10 wherein the first dicarboxylic acid is an aromatic dicarboxylic acid.

13. 13. The current collector of claim 12, wherein the second dicarboxylic acid is an aromatic dicarboxylic acid different from the first dicarboxylic acid.

14. 3. The current collector according to claim 1 or 2, wherein the copolyester of the first heat-sealable layer (A1) and, if present, the copolyester of the second heat-sealable layer (A2) are independently selected from copolyesters derived from ethylene glycol, terephthalic acid, and isophthalic acid, wherein the isophthalic acid is present in an amount of 1 to 50 mol %.

15. The current collector of claim 10 wherein the second dicarboxylic acid is an aliphatic dicarboxylic acid.

16. 3. The current collector according to claim 1, wherein the copolyester of the first heat-sealable layer (A1) and, if present, the copolyester of the second heat-sealable layer (A2) are independently selected from copolyesters derived from ethylene glycol, terephthalic acid, and azelaic acid.

17. 3. The current collector according to claim 1 or 2, wherein the copolyester of the first heat-sealable layer (A1) and, if present, the copolyester of the second heat-sealable layer (A2) are independently selected from copolyesters derived from an aliphatic diol, an alicyclic diol, and at least one dicarboxylic acid.

18. 18. The current collector of claim 17, wherein the aliphatic diol is as defined in claim 11, and / or the at least one dicarboxylic acid is as defined in claim 12, and / or the cycloaliphatic glycol is 1,4-cyclohexanedimethanol.

19. 18. The current collector of claim 17, wherein the copolyester of the first heat-sealable layer (A1) and, if present, the copolyester of the second heat-sealable layer (A2) are independently selected from copolyesters derived from ethylene glycol, 1,4-cyclohexanedimethanol, and terephthalic acid.

20. 3. The current collector according to claim 1 or 2, wherein the copolyester of the first heat-sealable layer (A1) and, if present, the copolyester of the second heat-sealable layer (A2) are independently selected from copolyesters derived from one or more diols, one or more dicarboxylic acids, and one or more poly(alkylene oxide) glycol(s).

21. The one or more diols are aliphatic diols containing 2 to 8 carbon atoms, and / or the one or more dicarboxylic acids are aromatic dicarboxylic acids, and / or the one or more poly(alkylene oxide) glycol(s) are C 2 ~C 15 21. The current collector of claim 20, wherein the alkylene chain is selected from the group consisting of:

22. 21. The current collector of claim 20, wherein the copolyester of the first heat-sealable layer (A1) and, if present, the copolyester of the second heat-sealable layer (A2) are independently selected from copolyesters derived from ethylene glycol, terephthalic acid, and polyethylene glycol.

23. 3. The current collector of claim 1, wherein the multilayer film is a coextruded film.

24. 3. The current collector of claim 1, wherein the multilayer film is a coated film.

25. 3. The current collector of claim 1 or 2, wherein the multilayer film is oriented.

26. 3. The current collector of claim 1, wherein the thickness of the first metal layer and, if present, the thickness of the second metal layer are each independently between 50 nm and 1000 nm.

27. 3. The current collector of claim 1 or 2, wherein the first metal layer and, if present, the second metal layer each independently comprise at least one of aluminum, copper, nickel, titanium, silver, a nickel-copper alloy, or an aluminum-zirconium alloy.

28. 3. The current collector of claim 1 or 2, wherein the first metal layer and the second metal layer are both either aluminum or copper.

29. 3. The current collector of claim 1 or 2, wherein the adhesive strength between the metal layer and the multilayer film is at least 100 g / 25 mm.

30. 0.01 Ω sq -1 ~2.0Ωsq -1 3. A current collector according to claim 1 or 2, exhibiting a sheet resistance of

31. 3. The current collector of claim 1 or 2, wherein the current collector exhibits a breakdown current of 30 A or less and / or a breakdown temperature of 300°C or less.

32. 4. The current collector of claim 3, further comprising at least one tab connecting said first metal layer and said second metal layer.

33. 3. The current collector of claim 1 or 2, wherein the multilayer film includes channels extending from a first surface to an opposite second surface, and (i) the sides of the channels are at least partially coated with at least one metal, and / or (ii) the channels are at least partially filled with at least one metal.

34. 10. A method of manufacturing the current collector of claim 1, comprising: the order of layers being first metal layer / first heat-sealable layer / polyester substrate layer; (i) providing a polyester substrate layer (B); (ii) disposing a first heat-sealable layer (A1) on a first surface of the polyester substrate layer (B); (iv) depositing a metal on the outer surface of said first heat-sealable layer (A1) to form a first metal layer; The method includes the steps of:

35. The order of layers is first metal layer / first heat-sealable layer / polyester substrate layer / second heat-sealable layer, (iii) disposing a second heat-sealable layer (A2) on the second surface of the polyester substrate layer (B); 35. The method of claim 34.

36. the order of layers is first metal layer / first heat-sealable layer / polyester substrate layer / second metal layer, or first metal layer / first heat-sealable layer / polyester substrate layer / second heat-sealable layer / second metal layer; (v) depositing a metal onto the second surface of the polyester substrate layer (B) or, if present, onto the outer surface of the second heat-sealable layer (A2) to form a second metal layer; 36. The method of claim 34 or 35.

37. 36. The method of claim 34 or 35, wherein steps (ii) and / or (iii) are accomplished by co-extrusion.

38. 36. The method of claim 34 or 35, wherein steps (ii) and / or (iii) are accomplished by coating, which comprises dispersing or dissolving a heat-sealable material in a coating vehicle to form a composition, coating the composition onto the surface of the polyester substrate layer, and then drying to form a heat-sealable coating layer.

39. 36. The method of claim 34 or 35, wherein step (iv) and / or, if present, step (v) comprises depositing the metal using thermal evaporation, electron beam evaporation, or virtual cathode deposition.

40. 1. Use of a multilayer film in a current collector further comprising a first metal layer, said use for providing improved adhesive strength and / or peel resistance between said multilayer film and a metal layer, said multilayer film comprising: (i) a polyester substrate layer (B) having a first surface and a second surface; (ii) a first heat-sealable layer (A1) disposed on the first surface of the polyester substrate layer; the first heat-sealable layer (A1) comprises at least one copolyester, the first metal layer is disposed on the outer surface of the first heat-sealable layer (A1), the multilayer film has a thickness of 12 μm or less, the thickness of the substrate layer (B) is at least 70% of the total thickness of the multilayer film, the first metal layer has a thickness of 1000 nm or less, and the multilayer film exhibits an adhesion strength to itself of at least 100 g / 25 mm; The above use.

41. (iii) The use described in Claim 40, wherein the multilayer film further comprises a second heat-sealable layer (A2) disposed on the second surface of the polyester substrate layer, and the second heat-sealable layer (A2) comprises at least one copolyester.

42. 10. A battery comprising an anode material, a cathode material, a separator between the anode material and the cathode material, an anode current collector, and a cathode current collector, wherein at least one of the current collectors is the current collector of claim 1.

43. 43. The battery of claim 42, wherein the battery is a lithium ion battery.

44. 43. The battery of claim 42, wherein the anode material is coated on the anode current collector, the anode current collector being the current collector of claim 1.

45. 43. The battery of claim 42, wherein the cathode material is coated on the cathode current collector, the cathode current collector being the current collector of claim 1.

46. 43. A method of manufacturing the battery of claim 42, comprising: (i) preparing or obtaining a current collector according to claim 1; (ii) assembling the battery, the battery including an anode material, a cathode material, a separator between the anode material and the cathode material, an anode current collector, and a cathode current collector, at least one of the current collectors being the current collector obtained from step (i); The method.

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