WO2005081859A2

WO2005081859A2 - Draw resonant resistant multilayer films

Info

Publication number: WO2005081859A2
Application number: PCT/US2005/005172
Authority: WO
Inventors: Kevin G. Hetzler; Viktor Skatchkov; Xixian Zhou; JR. Gordon Vincent SHARPS
Original assignee: Saint-Gobain Performance Plastics Corporation
Priority date: 2004-02-20
Filing date: 2005-02-18
Publication date: 2005-09-09
Also published as: JP4643595B2; KR100900159B1; JP2007524532A; KR20070007109A; EP1722972A4; WO2005081859A3; EP1722972A2

Abstract

The disclosure is directed to a multilayer film (100) including a first layer (102) and a second layer (104). The first layer (102) has a fluorinated polymer. The second layer (104) has a melt strain-hardening component and forms no more than about 30% by volume of the multilayer film (100).

Description

DRAW RESONANT RESISTANT MULTILAYER FILMS

TECHNICAL FIELD This invention, in general, relates to draw resonant resistant multilayer films, methods for manufacturing same, and articles including same.

BACKGROUND ART Increasingly, manufacturers are turning to polymers to create surfaces that are resistant to chemical and environmental damage. For example, fluorinated polymers exhibit a resistance to damage caused by exposure to chemicals, such a methyl ethyl ketone (MEK), a resistance to stains, and a resistance to damage caused by exposure to environmental conditions. Such polymers have been used in applications, such as airplane and train cargo hold liners, vinyl siding surface treatments, and photovoltaic protective coverings. However, processing of such films for use in these applications is difficult. Line speed in production is often limited by the appearance of draw resonance at relatively low line speeds, such as below 50 feet per minute. These processing limitations increase costs and reduce the availability of these beneficial films. As such, robust multilayer films having preferred mechanical and processing properties are generally desirable in the art.

DISCLOSURE OF INVENTION In a particular embodiment, a multilayer film includes a first layer and a second layer. The first layer has a fluorinated polymer. The second layer comprises at least about 70% by weight of a melt strain-hardening component and forms no more than about 30% by volume of the multilayer film. In another embodiment, a multilayer film has a first layer and a second layer. The first layer includes greater than about 70% by weight of a non-polyolefin melt strain-hardening polymer. The non-polyolefin melt-strain hardening polymer has an increasing tensile force in a draw ratio domain between draw ratios of about 5:1 and about 30:1. The first layer forms no more than about 30% by volume of the multilayer film. The second layer includes a second polymer. The second polymer has a generally flat tensile force in the draw ratio domain. In a further embodiment, a method of manufacturing a multilayer film includes extruding a first layer having greater than about 70% by weight of a non-polyolefin melt strain-hardening polymer. The non-polyolefin melt-strain hardening polymer has an increasing tensile force in a draw ratio domain between draw ratios of about 5:1 and about 30:1. The first layer forms no more than about 30% by volume of the multilayer film. The method further includes extruding a second layer including a second polymer. The second polymer has a generally flat tensile force in the draw ratio domain.

In one particular embodiment, the disclosure is directed to a multilayer film comprising a first polymer layer and a second polymer layer. The first polymer layer comprises a blend of a first fluoropolymer having a first average molecular weight and a second fluoropolymer having a second average molecular weight. The first average molecular weight is greater than the second average molecular weight.

In a further embodiment, the disclosure is directed to a multilayer polymeric film comprising a first polymer layer and a second polymer layer. The first polymer layer comprises a fluoropolymer having a bimodal molecular weight distribution.

In another embodiment, the disclosure is directed to a multilayer film comprising a polymeric layer including a first fluoropolymer having a first average molecular weight and a second fluoropolymer having a second average molecular weight. The first average molecular weight is greater than the second average molecular weight. The multilayer film is adapted to be drawn at a linespeed of at least about 50 ft/min with a thickness variance no more than about 5%.

In a further embodiment, the disclosure is directed to a method of manufacturing a multilayer film. The method includes extruding a first polymer layer and extruding a second polymer layer. The first polymer layer comprises a blend of a first fluoropolymer having a first average molecular weight and a second fluoropolymer having a second average molecular weight. The first average molecular weight is greater than the second average molecular weight.

In another embodiment, a multilayer polymeric film comprises a first polymer layer and a second polymer layer. The first polymer layer comprises a fluoropolymer having a bimodal molecular weight distribution of molecules and the first polymer layer has a melt phase tensile strength at least about 50% greater than the melt phase tensile strength of the second layer.

BRIEF DESCRIPTION OF THE DRAWINGS The present disclosure may be better understood, and its numerous objects, features, and advantages made apparent to those skilled in the art by referencing the accompanying drawings.

FIGS. 1, 2 and 3 depict exemplary embodiments of multilayer films.

FIGS.4 and 5 depict extensional velocity data for exemplary film components. The use of the same reference symbols in different drawings indicates similar or identical items. MOPES FOR CARRYING OUT THE INVENTION In a particular embodiment, the disclosure is directed to a multilayer film. The multilayer film typically has a layer including a material that is resistant to damage caused by chemical and/or environmental exposure. The multilayer film also has a second layer comprising a melt strain- hardening material. The multilayer film may further include additional layers including materials having desirable mechanical properties.

In another embodiment, the disclosure is directed to a multilayer film typically including a layer having properties useful for the processing of the multilayer film and a layer having properties that provide mechanical properties in the resulting multilayer film. The multilayer film may further include a layer that provides desirable surface properties. These surface properties may include chemical resistance or adhesiveness. In one exemplary application, the multilayer film may be used in fluoropolymer processing.

FIG. 1 depicts an exemplary multilayer film. The exemplary film 100 has at least two layers, 102 and 104. Layer 102 comprises a damage resistant polymer that is resistant to damage by chemical and environmental exposure. Layer 104 includes a polymer or polymer blend that provides processing characteristics and desired processing behaviors. For example, layer 104 may comprise a melt strain- hardening component that exhibits higher tensile force than the polymer of first layer in the melt phase. In another example, layer 104 comprises a blend of fluoropolymers having different molecular weight. In a particular embodiment, layer 104 forms no more than about 30% by volume of the multilayer film 100. For example, layer 104 may form no more than about 10% by volume of the multilayer film, such as about 5% by volume of the multilayer film.

Layer 102 comprises a polymer component resistant to chemical and/or environmental exposure. In other exemplary embodiments, the material may have nonstick properties and be resistant to staining. The polymer component may be a fluorinated polymer. For example, the polymer component may be a fluorinated polymer, such as a fluorine substituted olefin polymer comprising at least one monomer selected from the group consisting of vinylidene fluoride, vinylfluoride, tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, chlorotrifluoroethylene, ethylene- chlorotrifluoroethylene, and mixtures of such fluoropolymers. The fluoropolymer polymers include polyvinylidene fluoride (PVDF) and PVDF copolymers, such as vinylidene fluoride/hexafluoropropylene copolymer. Many fluoropolymers are commercially available from suppliers in various grades. For example suppliers can supply multiple resins having nominally the same composition but different properties, such as different molecular weights to provide specific viscosity characteristics. Exemplary PVDF polymers include PVDF 1010 and PVDF 21510 by Solvay and Kynar 760, Kynar 740 and Kynar 720 by Atofina. It is contemplated that the fluoropolymer component of the layer 102 can include a melt blend of multiple fluoropolymers in place of one such polymer. Alloys of PVDF homopolymer and PVDF copolymer may provide the film with improved elastic modulus and gloss reduction. In one exemplary embodiment, the polymer may consist essentially of fluorinated polymer and substantially no melt strain-hardening components. Layer 104 may comprise a polymer component exhibiting melt strain hardening and/or higher multiphase tensile force at processing conditions. Melt strain hardening is exhibited when the melt- phase tensile force smoothed slope relative to a draw ratio domain is significantly positive for a polymeric component. In one exemplary embodiment, the melt strain hardening component is a non- polyolefin polymer that exhibits melt strain hardening at draw ratios greater than 10:1. In another exemplary embodiment, the melt strain hardening component is a non-polyolefin polymer component exhibiting a melt-phase tensile force smoothed slope in the melt phase of greater than about 0.03 cN between the draw ratios of 0 and greater than 30:1. For example, the melt-phase tensile force to draw ratio slope may be greater than about 0.04 cN, such as at least about 0.05cN or at least about 0.08 cN, in the draw ratio domain between about 10:1 to about 20:1 or about 10:1 to about 15:1. In another embodiment, the melt strain hardening component may exhibit increasing smoothed melt-phase tensile force in the draw ratio domain between about 5:1 and about 30:1, such as between about 10:1 and about 1 :1 or between about 20:1 and about 30:1. In a further exemplary embodiment, the melt strain hardening polymer exhibits melt strain hardening in which the polymer exhibits a positive ratio of change in melt-phase tensile force to change in draw ratio in the draw ratio domain between a first draw ratio and a second draw ratio, wherein the damage resistant polymer may exhibit a melt plateau in the same domain. According to a particular embodiment, the melt strain hardening polymer exhibits a melt-phase tensile force to draw ratio slope of greater than about 0.03 cN in the desired draw ratio domain. For example, the melt strain-hardening polymer may exhibit a slope of not less than about 0.03 cN over a specific draw ratio domain, such as not less than about 0.04 cN, not less than about 0.05 cN, or not less than about 0.08 cN, over a specific draw ratio domain. In contrast, a mechanical property or surface property polymer may exhibit a small slope or generally flat slope of less than about 0.03 cN, such as less than about 0.005 cN or substantially zero cN over the specific draw ratio domain. In a further exemplary embodiment, the melt strain hardening polymer exhibits a positive ratio change in melt-phase tensile force to change in draw ratio in the draw ratio domain of about 10:1 and about 15: 1 during processing at about 230°C. The damage resistant polymer exhibits a generally flat slope in the same draw ratio domain under the same processing conditions. In a further exemplary embodiment, the melt strain hardening component may exhibit a greater melt-phase tensile force to draw ratio slope than the mechanical or surface components over a draw ratio domain, such as at least about 30%, at least about 50%, at least about 80%, at least about 100%, or at least about 300%. greater slope.

The melt strain hardening polymer may, for example, be a non-polyolefin polymer, such as an acrylic polymer, and not a polyethylene or polypropylene. In another exemplary embodiment, the melt strain hardening polymer may be a high average molecular weight fluoropolymer. In one exemplary embodiment, the non-polyolefin polymer may be a branched polymer. In another exemplary embodiment, the non-polyolefin polymer may be a linear polymer. The acrylic polymer may be an alkyl group having from 1-4 carbon atoms, a glycidyl group or a hydroxyalkyl group having from 1-4 carbon atoms. Representative acrylic polymers include polymethyl methacrylate, polyethyl methacrylate, polybutyl methacrylate, polyglycidyl methacrylate, polyhydroxyethyl methacrylate, polymethyl acrylate, polyethyl acrylate, polybutyl acrylate, polyglycidyl acrylate, polyhydroxyethyl acrylate and mixtures thereof.

The acrylic polymer may, for example, be an impact grade or impact modified acrylic. Impact-modified acrylic polymers generally comprise a copolymer of monomers of acrylic monomers with an effective amount of suitable comonomer or graft moiety to produce the desired elastic modulus and impact resistance. An acrylic elastomer, sometimes referred to as acrylate rubber, polyacrylate rubber, polyacrylic elastomer or "ACM" and which is a composition based on a mixture of a polyacrylate and poly ethacrylate, a polyacrylate and ethylene methacrylate copolymer ("EMAC"), [such as Chevron Chemicals EMAC 2260] or a polyacrylate and ethylene butylacrylate ("EBAC") can be used. Alternatively, a thermoplastic impact-modified acrylic polymer can be a blend of a clear glassy acrylic polymer, such as a plastic copolymer of ethylene and a carboxylic acid compound selected from acrylic acid, methacrylic acid and mixtures thereof, with elastomeric components, for example.

The impact-modified acrylic polymer generally includes fine particles of the elastomer dispersed uniformly in the plastic copolymer. The impact grade acrylic may comprise transparent toughened thermoplastic blends prepared by blending 10 to 99 weight percent of a block copolymer; 0.1 to 1 weight percent of particulate rubber having a particle size from 0.1 to 10 microns; and the balance a clear glassy polymer. Another suitable technique for making impact-modified acrylic polymer employs the use of a so-called "core/shell" product, such as Atofina DR-101 resin. These generally are polymer particles that have a central core of one polymer surrounded by a shell of another polymer. The core can be either the plastic or elastomer component and the shell will be the opposite, i.e., elastomer or plastic component. The core/shell particles are fed to a melt mixing apparatus, such as a melt extruder in which the core and shell domains are blended in the melt phase to form a homogeneous blend on a much smaller scale and a film is formed from the extrudate of this homogeneous blend.

In one particular embodiment, the melt strain hardening material may be a linear impact modified acrylic. In a further exemplary embodiment, the melt strain hardening acrylic may be a branched impact modified acrylic. Generally, linear acrylic polymers that are not impact modified, such as those typically used in adhesive layers, are not suitable. However, an acrylic exemplifying melt strain hardening behavior in the desired draw ratio domain is suitable.

In one exemplary embodiment, the layer 104 comprises a blend of melt strain-hardening polymer and other components. For example, the layer 104 may comprise greater than about 70% of the melt strain-hardening component, such as, impact grade acrylic. In an exemplary embodiment, the layer may comprise greater than about 75% impact grade acrylic or greater than about 80% impact grade acrylic. Layer 104 may also include other components, such as the damage resistant polymer.

For example, the layer 104 may include a polymer blend having impact grade acrylic and no more than about 25% PVDF, PVDF copolymer or blends thereof by weight. In other exemplary embodiments, the blend may include no more than about 20% PVDF by weight, such as no more than about 10% PVDF by weight. In one embodiment, layer 104 consists essentially of the melt-strain hardening component.

In another exemplary embodiment, the melt strain hardening components or higher melt-phase tensile force component may include a higher average molecular weight polymer. For example, in fluoropolymer applications, layer 104 may include a blend of fluoropolymers that includes a low to medium average molecular weight fluoropolymer and a high average molecular weight fluoropolymer that exhibits melt strain hardening and higher melt-phase tensile force at a given draw ratio. In one particular embodiment, the lower average molecular weight polymer may include PVDF having a weight average molecular weight not greater than about 200 kg/mol, such as not greater than about 190 kg/mol or not greater than about 180 kg/mole. The higher average molecular weight polymer may include PVDF having a molecular weight at least about 200 kg/mole, such as at least about 250 kg/mole, at least about 285 kg/mole, or at least about 365 kg/mole. In alternative embodiments, the average molecular weight may be determined using number average molecular weight and z-average molecular weight methods. The higher average molecular weight polymer may have a molecular weight distribution that peaks at a molecular weight at least about 25% higher than the peak of the molecular weight distribution of the lower average molecular weight polymer. For example, the higher average molecular weight polymer distribution peak may be at least about 50%, at least about 60%, at least about 80% or at least about 90% higher than the peak of the lower average molecular weight polymer distribution. In an exemplary embodiment in which the fluoropolymers are derived from the same monomer, the resulting blend produces a bimodal molecular weight distribution of polymer molecules.

Exemplary fluoropolymers include fluorine substituted olefin polymers and polymers comprising at least one monomer selected from the group consisting of vinylidene fluoride, vinylfluoride, tetrafluoroethylene, hexafluoropropylene, trifluoroethylene, chlorotrifluoroethylele, ethylene-chlorotrifluoroethylene, and mixtures of such fluoropolymers. The fluoropolymer polymers include polyvinylidene fluoride (PVDF) and PVDF copolymers, such as vinylidene fluoride/hexafluoropropylene copolymer. Many fluoropolymers are commercially available from suppliers in various grades. For example, suppliers can supply multiple resins having nominally the same composition but different properties, such as different molecular weights to provide specific viscosity characteristics. Exemplary PVDF polymers include PVDF 1010 and PVDF 21510 by Solvay Solexis. Other examples include Kynar 720, Kynar 740, and Kynar 760 by Atofina. Kynar 760 has a higher average molecular weight than Kynar 720 and Kynar 740. It is contemplated that the polymer component of the layer 104 may include a melt blend of multiple fluoropolymers in place of one such polymer. Alloys of PVDF homopolymer and PVDF copolymer may provide the film with improved elastic modulus and gloss reduction. In one exemplary embodiment, the polymer may consist essentially of fluorinated polymer.

In one particular embodiment, layer 104 includes a blend of the higher average molecular weight polymer and the low or moderate average molecular weight polymer. In a particular embodiment, the blend includes at least about 60% by weight of the high average molecular weight polymer. For example, the blend may include at least about 70%, at least about 75%, at least about 80%), at least about 85%, at least about 90%, or as high as 100% by weight of the high average molecular weight polymer. In another exemplary embodiment, the polymer blend may include not more than about 40% by weight of the low or moderate average molecular weight polymers. For example, the polymer blend may include not more than about 30%, not more than about 25%, not more than about 20%, not more than about 15% or not more than about 10% of the low or moderate average molecular weight polymer. In one particular embodiment, the high average molecular weight polymer is Kynar 760, the moderate average molecular weight polymer is Kynar 740, and the low average molecular weight polymer is Kynar 720.

In addition, layers 102 and 104 may include inorganic fillers, organic fillers, antioxidants, UV additives, flame retardants, antidegradation additives, and adjuvants, among others. For example, layer 102 may include minor but significant fractions of antidegradation additives and adjuvants. The inorganic filler may, for example, include titanium dioxide, zinc oxide, iron oxide, calcium carbonate, carbon black, color pigments and clays.

FIG. 2 depicts another exemplary embodiment of a multilayer film. The multilayer film 200 includes layers 202, 204, and 206. Layer 202 may, for example, include a damage resistant polymer. In an alternative embodiment, layer 202 may be an adhesive layer. Layer 204 may provide the desired processing properties and behaviors in the melt phase and may include polymers or polymer blends that exhibit the desired processing behaviors. For example, layer 204 may include melt strain hardening polymers or higher melt-phase tensile force polymers that exhibit desired processing behaviors within specified draw ratio domains or at specific draw ratios. In one exemplary embodiment, layer 204 may include acrylic or acrylic blends. In another exemplary embodiment, layer 204 may include a high average molecular weight polymer or a bimodal molecular weight distribution of molecules formed from a common monomer. Layer 206 may include a polymer component exhibiting a desirable mechanical property. In one exemplary embodiment, layer 206 includes a fluoropolymer/acrylic blend. In an alternative embodiment, layer 204 and layer 206 may be interchanged.

In one exemplary embodiment, layer 202 comprises no more than about 30% by volume of the multilayer film. For example, layer 202 may comprise no more than about 20% by volume, no more than about 10% by volume or no more than about 5% by volume of the multilayer film. Layer 204 may comprises no more than about 30% by volume of the multilayer film. For example, layer 204 may comprise no more than about 20%), no more than about 10% of the multilayer film or no more than about 5% of the multilayer film. Layer 206 may comprise greater than about 40% by volume of the multilayer film. For example, layer 206 may comprise greater than about 60% by volume, greater than about 80% by volume, or at least about 90% by volume of the multilayer film.

Layer 202 may comprise blends of damage resistant polymers, other polymers, and inorganic fillers. For example, layer 202 may include a damage resistant polymer, such as a fluorinated polymer, such as PVDF. In an alternative embodiment, layer 202 may comprise an adhesive component, other polymers, and inorganic fillers. Layer 204 may comprise a melt strain-hardening component and may be a blend including other polymers, such as the damage resistant component. Alternatively, layer 204 may include a blend of fluorinated polymers including a high average molecular weight, high tensile force fluorinated polymer.

Layer 206 may comprise a component with desirable mechanical properties, which are manifested in the resulting multilayer film. Such mechanical properties include elongation, flexibility and drape. These properties may, for example, be similar to the properties of fluoropolymer film. In one exemplary embodiment, layer 206 comprises the damage resistant component in a blend of other components. Layer 206 may comprise a fluorinated polymer. In a particular embodiment, layer 206 comprises greater than about 20% by weight of a fluorinated polymer, such as those fluorinated polymers listed above, such as PVDF. Layer 206 may also include inorganic fillers, organic fillers, antioxidants, UV additives, flame retardants, antidegradation additives, adjuvants, the melt strain- hardening component, such as impact grade acrylic, and other acrylics, among others. For example, layer 206 may include minor but significant fractions of antidegradation additives and adjuvants. The inorganic filler may, for example, be titanium dioxide, zinc oxide, iron oxide, calcium carbonate, carbon black, color pigments and clays. In one exemplary embodiment, layer 206 comprises greater than about 30% by weight PVDF, no more than about 35% impact grade acrylic, an inorganic filler, and antidegradation additive.

Layers should have adequate compatibility with the adjacent layers and the substrate compositions to adhere well to both. In alternative embodiments, layers 206 and 204 may be reversed in order. In another alternative embodiment, layer 202 may be absent or substituted with a layer identical to layer 206.

FIG. 3 depicts an exemplary embodiment of a multilayer film. The multilayer film includes five layers, 302, 304, 306, 308, and 310. Layers 302 and 310 may, for example, comprise damage resistant polymer components, such as fluorinated polymers, such as PVDF, or an adhesive polymer, such as an acrylic. Layers 304 and 308 may, for example, comprise a melt strain-hardening component, such as impact grade acrylic polymers or may, for example, comprise high molecular weight fluoropolymers. Layer 306 may, for example, comprise a polymer with desirable mechanical properties and may, for example, be a blend of the fluorinated polymer and acrylic. In an alternative embodiment, layers 304 and 308 may comprise a polymer with desirable mechanical properties and layer 306 may comprise a melt strain-hardening component.

In one embodiment, layers 302 and 310 formed of a damage resistant polymer component, together comprise no more than about 20% by volume of the multilayer film. For example, each layer 302 and 310 may comprise no more than about 10% by volume, or no more than about 5% by volume of the multilayer film. Layers 304 and 308 formed of the melt strain-hardening component or the high molecular weight, high tensile force component, together may comprise no more than about 40%) by volume of the multilayer film. For example, layers 304 and 308 may form no more than about 10% by volume each, or no more than 5% by volume each of the multilayer film. Layer 306, formed of a component having desirable mechanical properties, may comprise greater than about 40% by volume of the multilayer film. For example, layer 306 may form greater than about 60% of the multilayer film, or even greater than about 80% of the multilayer film. In an alternative example, in which layer 306 is split into multiple layers, the combined layers provide greater than about 40% by volume of the multilayer film.

In one exemplary embodiment, the film structure may be A/C/B/C/A where each letter represents a different material extruded from a unique extruder. Layer A may, for example, be a 100% Solvay PVDF 1010 and each layer A may form about 10% by volume of the multilayer film. Layer B may be a PVDF/ acrylic blend comprising greater than about 60% by weight PVDF homopolymer and/ or copolymer and not more than about 40% acrylic by weight. Layer B may form greater than about 40%) by volume of the multilayer film. Layers C may be formed of Atofina impact grade acrylic DR101 and each of the C layers may make up less than about 10% by volume of the multilayer film, such as about 5% by volume. Alternatively, the C layers may be formed of a blend of a higher average molecular weight, high melt-phase tensile force component and a lower average molecular weight component, such as a blend of PVDF polymers.

In another exemplary embodiment, the film structure may be A/C/B/C/D where each letter represents a different material extruded from a unique extruder. Layer A may, for example, be a 100%) Solvay PVDF 1010 and may form about 10%> by volume of the multilayer film. Layer B may be a PVDF/acrylic blend comprising greater than about 60% by weight PVDF and not more than about 40%) acrylic by weight. Layer B may form greater than about 40% by volume of the multilayer film. Layers C may be formed of Atofina impact grade acrylic DR101, each of the C layers making up less than about 10%, such as about 5% by volume of the multilayer film. Alternatively, the C layers may be formed of a blend of a higher average molecular weight, high melt-phase tensile force component and a lower average molecular weight component, such as a blend of PVDF polymers. Layer D may form approximately 30% by volume of the multilayer film. Layer D may comprise similar materials to

Layer B. However, Layer D may be enhanced for custom properties, such as having a lower melting temperature (e.g. more acrylic) for heat sealing. Layer B may also be used exclusively for the addition of recycle and trim.

In another exemplary embodiment, the film structure may be A/C/B/C/B. Layer A may be a 100% Solvay PVDF 1010 and may comprise about 10% by volume of the multilayer film. Layers B may comprise a PVDF/acrylic blend comprising greater than about 60% PVDF and no more than about 40%) acrylic by weight. The B layers may, in combination, comprise about 70% by volume of the multilayer film. In one exemplary embodiment, the outside B layer may comprise between about 20 to 35% of the total film volume. The C layers may be an Atofina impact grade acrylic DR101. Alternatively, the C layers may be formed of a blend of a high average molecular weight, high melt- phase tensile force component and a lower average molecular weight component, such as a blend of PVDF polymers. Each of the C layers may comprise about 5% by volume of the total film volume. In a further exemplary embodiment, the film structure may be A/B/C wherein layer A is 100% Solvay PVDF 1010, comprising about 5-10% by volume of the film. Layer B is a PVDF and acrylic blend comprising about 30-80 wt% PVDF, such as about 60 wt% PVDF, and about 40 wt% acrylic. Layer B comprises about 80-90%) by volume of the film. Layer C is a PVDF and acrylic blend comprising about 55-100 wt% acrylic, such as about 60-90 wt% acrylic and about 30-40 wt%> PVDF. Layer C comprises about 5-10% by volume of the film. In one example, Layer C may include greater than 70 wt% melt strain hardening acrylic. In another example, an additional Layer D may be added comprising greater than 70 wt%> melt strain hardening acrylic.

Another exemplary structure may be an A/B or an A B/A structure. For example, layer A may include a melt strain hardening polymer and fluorinated polymer, such as a PVDF/acrylic blend having 70%) impact modified or melt strain hardening acrylic, and layer B may include a polymer blend of PVDF and acrylic polymers including at least about 70% PVDF. In another example, layer A includes a non-melt strain hardening fluoropolymer and layer B includes a blend of PVDF and acrylic including at least about 70% melt strain hardening polymer or bimodal molecular weight fluoropolymer. Another exemplary structure may be C/B/C in which layer C is a PVDF and acrylic blend comprising about 55-100 wt% acrylic, such as about 60-90% acrylic and about 10-40 wt% PVDF. Layer B is a PVDF and acrylic blend comprising about 30-80 wt%> PVDF, such as about 60 wt% PVDF and about 40 wt% acrylic. Layer C comprises about 5-10% by volume and layer B comprises about 80-90 % by volume of the film. In one exemplary embodiment, at least one of the layers C may include greater than 70 wt% melt strain hardening acrylic. In another example, an additional layer D may be added comprising greater than 70 wt%> melt strain hardening acrylic.

A further exemplary embodiment includes at least 3 layers extruded via 3 extruders. A first layer includes a fluoropolymer. A second layer includes a melt strain hardening component and a third layer is an adhesive layer comprising greater than about 55 wt% adhesive acrylic, such as greater than about 70 wt% acrylic.

Another exemplary embodiment includes at least 4 layers, such as 5 layers. Layer 1 includes a fluoropolymer. Layer 2 includes a melt strain hardening component. Layer 3 includes between about 20 wt% and 80 wt% acrylic and between about 20 wt% and 80 wt% fluoropolymer. An optional layer 4 includes the melt strain hardening component. Layer 5 is an adhesive layer. The 5-layer structure may be formed using 4 extruders.

An alternative exemplary embodiment includes at least 4 layers, such as 5 layers. Layer 1 is an adhesive layer. Layer 2 includes a melt strain hardening component. Layer 3 includes between about 20 wt% and 80 wt%ι acrylic and between about 20 wt% and 80 wt% fluoropolymer. An optional layer 4 includes the melt strain hardening component or higher melt-phase tensile force component. Layer 5 is an adhesive layer. The 5-layer structure may be formed using 4 extruders. In a further exemplary embodiment, a film includes a fluoropolymer blend having a bimodal molecular weight distribution of molecules derived from a common monomer. For example, the common monomer may be a fluorinated monomer, such as PVDF. The blend may be formed through mixing polymers having different average molecular weights. In another exemplary embodiment, a multilayer film may include a layer structure A/B/C/B/A.

Layer A may be a surface properties layer, such as a PVDF layer or an acrylic layer. Layer B may include a polymer or polymer blend having a bimodal molecular weight distribution of molecules formed from a common monomer or a blend of two polymers, such as fluoropolymers having differing average molecular weight. Layer C may be formed with a PVDF/acrylic blend. Layers A may comprise no more than about 10% of the multilayer film each or no more than about 20% of the multilayer film in combination. Layers B may form no more than about 10% by volume of the multilayer film individually or in combination no more than about 20%> by volume of the multilayer film. Layer C may comprise at least about 60% by volume of the multilayer film. In an alternative embodiment, layers B may be combined to form layer C and layer C may be divided to replace layers B.

In a further exemplary embodiment, a two-layer film may include a first layer having a blend of high average molecular weight polymer and a low or moderate average molecular weight polymer. The blend may include greater than 60% by weight of the high average molecular weight polymer. In one particular embodiment, a 30/70 blend by weight of Kynar 720 and Kynar 760, respectively, may be used. The first layer may comprise no more than about 20% by volume of the multilayer film. The second layer may be formed of a fluoropolymer or fluoropolymer/acrylic blend and comprise at least about 80% by volume of the multilayer film.

Such multilayer films may be manufactured by co-extruding the foregoing embodiments. In particular embodiments, the co-extruded film may be drawn at linespeeds of at least about 50 ft/min, such as at least about 60 ft/min or at least about 100 ft/min. The resulting multilayer film has a thickness variance of not more than about 5%, such as not more than about 4%, not more than about 3%, not more than about 2%, or not more than about 1%, and is substantially free of draw resonance. For example, the thickness may statistically vary from the average thickness by not more than about 5% of the average thickness. FIG. 4 characterizes the behavior of several materials, including damage resistant polymers

PVDF 1010 and PVDF 21510, and melt strain-hardening acrylic polymers, such as Atofina DR101. The tests are performed with a Goettfert Rheo-Tens device. The melt chamber has a diameter of 12 mm. The tests are performed with a piston speed of 0.060764 mm/s, a chamber pressure of 187 bars, and a temperature of 230 C. The capillary entrance angle is 70 degrees. The capillary has a diameter of 1 mm and a length to diameter ratio of 20. The take-off strand length is 115 mm. The wheels are standard with a 0.1 mm gap. The acceleration of draw down velocity is 3 mm/s². The exemplary damage resistant components and acrylic Cyro H-15 depict a melt plateau in which the slope of change in tensile force versus the change in draw ratio is small to zero, generally less than about 0.03 cN in the draw ratio domain of 10: 1 to 20: 1. In contrast, the melt strain-hardening components, such as Atofina DR101, exhibit a positive slope in the same regions at which the melt plateau occurs for the PVDF examples. In particular, the melt strain-hardening polymers exhibit a slope of greater than about 0.03 cN for draw ratios between 10:1 and 20: 1. In one exemplary component, the slope is greater than 0.04 cN, and may be greater than about 0.1 cN between draw ratios of 10: l and 20:1.

FIG. 5 depicts the melt-phase tensile force of exemplary polymers and polymer blends over a draw ratio domain. Melt-phase tensile force may be measured using a Geottfert Rheo-Tens apparatus. In one example, the parameters of the Georttfert Rheo-Tens apparatus include a wheel position approximately 110 mm below the die, piston speed of 0.06 mm/s, ambient wheel temperature, 12 mm barrel diameter, 180° die entry angle, 1 mm die inner diameter, 20 mm die length, 6 min dwell time, and a barrel temperature of 230°C. The take off unit may have a wheel gap of approximately 4 mm. An impact modified acrylic by Atofina (DR 101) exliibits melt strain hardening in a desired range between draw ratios 10:1 and 20:1. Similarly, a high molecular weight PVDF, such as Kynar 760 by Atofina, exhibits melt strain hardening in the same draw ratio domain. Both of these polymers exhibit higher melt-phase tensile force than a PVDF polymer by Solvay Solexis (PVDF 1010).

In addition, the graph shown in FIG. 5 depicts the melt-phase tensile force behavior of blends of the higher molecular weight Atofina Kynar 760 with a lower molecular weight Atofina Kynar 720. The blend results in a polymer blend having a bimodal molecular weight distribution of molecules formed from a common monomer, such as, in this case, PVDF. Blends are depicted having ratios by weight of Kynar 720 and Kynar 760. As the quantity of Kynar 760 decreases. The exhibited melt- phase tensile force in the given draw ratio domain decreases. For example, a 20/80 blend of Kynar 720 and Kynar 760, respectively, exliibits a higher melt-phase tensile force than the 30/70 blend and the

30/70 blend exhibits a higher melt-phase tensile force than a 40/60 blend. Medium average molecular weight PVDF, Kynar 740, and lower molecular weight PVDF Kynar 720, are shown on the graph for comparison.

In one embodiment, a mechanical properties layer in the resulting film may, for example, be formed using the Solvay Solexis PVDF 1010 or a blend of the Solvay Solexis PVDF 1010 with acrylics, including linear non-impact modified acrylics. A processing layer may be formed utilizing the Atofina DR101 impact modified acrylic, a blend of the Atofina impact modified acrylic DR101 and PVDF such as a PVDF 1010 or the Kynar PVDF 720, or a blend of the Kynar 720 and Kynar 760 such as, for example, a 20/80 blend or a 30/70 blend. According to embodiments of the present invention, various multi-layer films are provided that have desirable film properties, and which may be made economically. In particular, extruded multi-layer films are generally provided that can be drawn at a line speed greater than about 50 ft/min with substantially no draw resonance. Indeed, embodiments may be formed at substantially higher line speeds, such as greater than about 75 ft/min or even greater than 100 ft/min. In one example, a 10% tie layer comprising 100% melt strain hardening acrylic was shown to effectively reduce draw resonance at line speeds of about 100 ft/min. As utilized herein, the descriptive phrase "substantially no draw resonance," generally means no periodical gauge variations in the web direction of 30% or more. Fabrication at such high lines speeds is typically desirable, as maximum line speed, the line speed at which unacceptable draw resonance occurs or other undesirable processing conditions occur, generally dictates production throughput. In line with the foregoing, according to embodiments of the present invention, the multi-layer films may be successfully formed at relatively high draw ratios, such as greater than about 10: 1, or even greater than about 15:1. In addition to desirable processing characteristics, the multilayer films demonstrate desirable mechanical and/or chemical properties. For example, the multilayer film may exhibit desirable flexibility, elongation, and drape.

While various compositions and films are described as comprising a range of percentages of one or more components, it is understood that a change in the percentage of one component will result in a corresponding adjustment of the percentages of other components such that the total percentage of all components does not exceed 100 percent.

The above-disclosed subject matter is to be considered illustrative, and not restrictive, and the appended claims are intended to cover all such modifications, enhancements, and other embodiments, which fall within the true scope of the present invention. While various examples and embodiments have been described above, it is understood in the art that modifications thereto may be made by one of ordinary skill in that art without departing from the scope of the present claims. Thus, to the maximum extent allowed by law, the scope of the present invention is to be determined by the broadest permissible interpretation of the following claims and their equivalents, and shall not be restricted or limited by the foregoing detailed description.

Claims

CLAIMS:

1. A multi-layer film comprising: a first layer comprising a fluorinated polymer; and a second layer comprising at least about 70% by weight melt strain-hardening component and comprising no more than about 30%> by volume of the multi-layer film.

2. The multi-layer film of claim 1, wherein the second layer consists essentially of the melt strain-hardening component.

3. The multi-layer film of claim 1, further comprising a third layer comprising the fluorinated polymer and comprising greater than about 40% by volume of the multi-layer film.

4. The multi-layer film of claim 3, wherein the third layer comprises greater than about 20% by weight of the fluorinated polymer.

5. The multi-layer film of claim 4, wherein the third layer comprises less than about 80% by weight of the melt strain-hardening component.

6. The multi-layer film of claim 3, wherein the third layer comprises the melt strain-hardening component and greater than about 30%> by weight of the fluorinated polymer.

7. The multi-layer film of claim 3, further comprising: a fourth layer comprising the melt strain-hardening component and comprismg no more than about 20%) by volume of the multi-layer film; and a fifth layer comprising the fluorinated polymer.

8. The multi-layer film of claim 7, wherein the second layer and the fourth layer in combination comprises no more than about 40% by volume of the multi-layer film.

9. The multi-layer film of claim 1, wherein the second layer comprises no more than about 10%) by volume of the multi-layer film

10. The multi-layer film of claim 1, wherein the second layer comprises about 5% by volume of the multi-layer film.

11. The multi-layer film of claim 1, wherein the fluorinated polymer comprises PVDF.

12. The multi-layer film of claim 1, wherein the melt strain-hardening component comprises a non-polyolefin polymer.

13. The multi-layer film of claim 1, wherein the melt strain-hardening component comprises a linear chain polymer.

14. The multi-layer film of claim 13, wherein the linear chain non-olefin polymer is an impact grade acrylic

15. The multi-layer film of claim 1, wherein the melt strain-hardening component comprises an impact grade acrylic.

16. The multi-layer film of claim 1, wherein the melt strain-hardening component exhibits increasing tensile force between the draw ratios of about 5:1 and about 30: 1.

17. The multi-layer film of claim 1, wherein the melt strain-hardening component exhibits increasing tensile force between the draw ratios of about 10:1 and about 15: 1.

18. The multi-layer film of claim 1, wherein the melt strain-hardening component exhibits a positive smoothed slope of change in tensile force to change in draw ratio in the draw ratio domain between a first draw ratio and a second draw ratio.

19. The multi-layer film of claim 18, wherein the first draw ratio is 10:1 and the second draw ratio is 15:1.

20. The multi-layer film of claim 18, wherein the first draw ratio is 20:1 and the second draw ratio is 30:1.

21. The multi-layer film of claim 18, wherein the positive smoothed slope is not less than 0.03 cN.

23. The multi-layer film of claim 1, wherein the second layer comprises the fluorinated polymer and greater than about 70% by weight melt strain hardening component, the melt strain hardening component being impact grade acrylic.

24. The multi-layer film of clam 1, wherein the first layer defines a first surface, wherein the second layer defines a second surface that is opposite the first surface, and wherein the melt strain hardening component comprises acrylic, the multi-layer film further comprising an internal layer comprising greater than about 40% by weight fluorinated polymer.

25. The multi-layer film of clam 1, further comprising a third layer comprising greater than about 55% by weight acrylic.

26. The multi-layer film of claim 25, wherein the third layer defines a surface.

27. The multi-layer film of claim 25, further comprising a fourth layer comprising greater than about 30%> by weight of a fluorinated polymer.

28. The multi-layer film of claim 27, wherein the first layer defines a first surface, wherein the third layer defines a second surface that is opposite the first surface, and wherein the second layer and fourth layer are located between the first layer and the third layer.

29. The multi-layer film of clam 1, wherein the first layer comprises acrylic and greater than about 30% by weight fluorinated polymer and wherein the second layer defines a surface.

30. The multi-layer film of clam 1, further comprising a third layer comprising greater than about 55% by weight acrylic wherein the third layer defines a surface.

31. A multi-layer film comprising: a first layer comprising greater than about 70% by weight of a non-polyolefin melt strain- hardening polymer, the non-polyolefin melt-strain hardening polymer having an increasing tensile force in a draw ratio domain between draw ratios of about 5:1 and about 30:1, the first layer comprising no more than about 30%> by volume of the multi-layer film; and a second layer comprising a second polymer, the second polymer having a generally flat tensile force in the draw ratio domain.

32. The multi-layer film of claim 31 , wherein the non-polyolefin melt strain-hardening polymer comprises a linear chain polymer.

33. The multi-layer film of claim 31 , wherein the non-polyolefin melt strain hardening polymer comprises impact grade acrylic.

34. The multi-layer film of claim 33, wherein the impact grade acrylic comprises an acrylic matrix having a particulate phase therein.

35. The multi-layer film of claim 31, wherein the first layer further comprises a fluorinated polymer.

36. The multi-layer film of claim 35, wherein the fluorinated polymer is PVDF.

37. The multi-layer film of claim 31, wherein the second polymer is a fluorinated polymer.

38. The multi-layer film of claim 37, wherein the fluorinated polymer is PVDF.

39. The multi-layer film of claim 31 , wherein the second layer is an adhesive layer.

40. The multi-layer film of claim 31, wherein the second layer further comprises no more than about 40%> by weight of the non-polyolefin melt strain-hardening polymer.

41. The multi-layer film of claim 31, wherein the second layer comprises greater than about 20%) by volume of the multi-layer film.

42. The multi-layer film of claim 31, further comprising a third layer comprising the fluorinated polymer and substantially no non-polyolefin melt strain-hardening polymer. i

43. The multi-layer film of claim 31 , wherein the second polymer exhibits a melt plateau in the draw ratio domain.

44. The multi-layer film of claim 43, wherein the draw ratio domain is between about 10:1 and about 15:1.

45. The multi-layer film of claim 43 , wherein the draw ratio domain is between about 20:1 and about 30:1.

46. The multi-layer film of claim 43, wherein the non-polyolefin melt strain hardening polymer exhibits a positive melt strain ratio not less than 0.03 cN.

47. A method of manufacturing a multi-layer film, the method comprising: extruding a first layer comprising greater than about 70% by weight of a non-polyolefin melt strain-hardening polymer, the non-polyolefin melt-strain hardening polymer having an increasing tensile force in a draw ratio domain between draw ratios of about 5:1 and about

30:1, the first layer comprising no more than about 30% by volume of the multi-layer film; and extruding a second layer comprising a second polymer, the second polymer having a generally flat tensile force in the draw ratio domain.

47. The method of claim 47, further comprising drawing the multi-layer film at a rate greater than about 50 feet per minute with substantially no draw resonance.

48. A multilayer film comprising: a first polymer layer comprising a blend of a first fluoropolymer having a first average molecular weight and a second fluoropolymer having a second average molecular weight, the first average molecular weight being greater than the second average molecular weight; and a second polymer layer.

49. The multilayer film of claim 48, wherein the first fluoropolymer and the second fluoropolymer are derived from a common monomer.

50. The multilayer film of claim 48, wherein the first fluoropolymer exhibits melt-phase tensile force that is at least about 50%> greater than melt-phase tensile force exhibited by the second fluoropolymer in the melt phase at a draw ratio.

51. The multilayer film of claim 50, wherein the draw ratio is between about 10:1 and about 30:1.

52. The multilayer film of claim 50, wherein the draw ratio is between about 10:1 and about 15:1.

53. The multilayer film of claim 48, wherein the first polymer layer comprises no more than about 30% by volume of the multilayer film.

54. The multilayer film of claim 48, wherein the first fluoropolymer comprises at least about 60% by weight of the first layer.

55. The multilayer film of claim 48, wherein the second fluoropolymer comprises no more than about 40% by weight of the first layer.

56. The multilayer film of claim 48, wherein the first fluoropolymer comprises PVDF.

57. The multilayer film of claim 48, wherein the second fluoropolymer comprises PVDF.

58. The multilayer film of claim 48, wherein the second polymer layer comprises fluoropolymer.

59. The multilayer film of claim 48, wherein the second polymer layer comprises PVDF.

60. The multilayer film of claim 48, wherein the second polymer layer comprises adhesive.

61. The multilayer film of claim 48, wherein the second polymer layer comprises fluoropolymer and acrylic.

62. The multilayer film of claim 61, wherein the second polymer layer comprises at least about 20%) by weight fluoropolymer.

63. The multilayer film of claim 61, wherein the fluoropolymer comprises PVDF.

64. The multilayer film of claim 48, wherein the multilayer film is adapted to be drawn at a linespeed of at least about 50 ft/min.

65. The multilayer film of claim 64, wherein the film thickness of the multilayer film varies no more than about 5%.

66. A multilayer polymeric film comprising: a first polymer layer comprising a fluoropolymer having a bimodal molecular weight distribution; and a second polymer layer.

67. The multilayer film of claim 66, wherein the first polymer layer has a melt-phase tensile strength at least about 50% greater than the melt-phase tensile strength of the second layer at the same draw ratio.

68. The multilayer film of claim 67, wherein the draw ratio is between about 10:1 and about 30:1.

69. The multilayer film of claim 67, wherein the draw ratio is between about 10:1 and about 15:1.

70. The multilayer film of claim 66, wherein the fluoropolymer comprises PVDF.

71. The multilayer film of claim 66, wherein the second polymer layer comprises at least about 40%) by volume of the multilayer film.

72. The multilayer film of claim 66, wherein a higher molecular weight peak in the bimodal molecular weight distribution is at least about 50% greater than a lower molecular weight peak of the bimodal molecular weight distribution.

73. The multilayer film of claim 66, wherein the second polymer layer comprises at least about 20% fluoropolymer.

74. The multilayer film of claim 73, wherein the second polymer layer comprises acrylic.

75. The multilayer film of claim 66, wherein the multilayer film is adapted to be drawn at a linespeed of at least about 50 ft/min.

76. The multilayer film of claim 75, wherein the film thickness of the multilayer film varies no more than about 5%.

77. A multilayer film comprising a polymeric layer comprising a first fluoropolymer having a first average molecular weight and a second fluoropolymer having a second average molecular weight, the first average molecular weight being greater than the second average molecular weight, wherein the multilayer film is drawn at a linespeed of at least about 50 ft/min and the thickness of the multilayer film has a variance of no more than about 5%.

78. The multilayer film of claim 77, wherein the variance is no more than about 3%.

79. The multilayer film of claim 77, wherein the first fluoropolymer and the second fluoropolymer are derived from a common monomer.

80. The multilayer film of claim 77, wherein the first fluoropolymer is PVDF.

81. The multilayer film of claim 77, further comprising a second polymeric layer comprising a blend of fluoropolymer and acrylic.

82. The multilayer film of claim 77, wherein the polymeric layer comprises no more than about 30% by volume of the multilayer film.

83. A method of manufacturing a multilayer film, the method comprising: extruding a first polymer layer comprising a blend of a first fluoropolymer having a first average molecular weight and a second fluoropolymer having a second average molecular weight, the first average molecular weight being greater than the second average molecular weight; and extruding a second polymer layer.

84. The method of claim 83, wherein extruding the first polymer and extruding the second polymer comprises co-extruding the first polymer and the second polymer.

85. The method of claim 83, wherein the first fluoropolymer and the second fluoropolymer are derived from common monomer.

86. The method of claim 83, wherein the first fluoropolymer exhibits melt-phase tensile force that is at least about 50%> greater than melt-phase tensile force exhibited by the second fluoropolymer at a draw ratio.

87. The method of claim 86, wherein the draw ratio is between about 10:1 and about 30:1.

88. The method of claim 83, wherein the first polymer layer comprises no more than about 30%) by volume of the multilayer film.

89. The method of claim 83, wherein the first fluoropolymer comprises at least about 60%> by weight of the first layer.

90. The method of claim 83, wherein the first fluoropolymer comprises PVDF.

91. The method of claim 83, wherein the second polymer layer comprises fluoropolymer and acrylic.

92. The method of claim 83, further comprising drawing the first layer and second layer at a linespeed of at least about 50 ft/min.

93. The method of claim 83, wherein the film thickness of the multilayer film varies no more than about 5%.