Transparent PVDF with a usage temperature above its melting point

Abstract

This invention provides a composition, an article containing the composition, and a method for manufacturing the article. The composition comprises a fluorinated polymer, a quaternary ammonium salt, and a crosslinking accelerator. The article has high transparency and a maximum continuous use temperature that exceeds the melting point of the fluorinated polymer.

Description

Technical Field

[0001] Field of the Invention The present invention provides a composition, an article comprising the composition, and a method of manufacturing the article. The composition comprises a fluorinated polymer, a quaternary ammonium salt, and a crosslinking accelerator. The article has high transparency and a maximum continuous use temperature exceeding the melting point of the fluorinated polymer.

Background Art

[0002] Background Crosslinked (polyvinylidene fluoride) PVDF polymers are often used in wire and cable applications due to high temperature requirements. Good examples include using crosslinked PVDF polymers as insulation for automotive cables or as heat shrinkable tubes. Crosslinked PVDF polymers are often used under the bonnet of automobiles due to high temperature requirements, and therefore it is necessary to provide resistance to automotive liquids and resistance to melt flow at high temperatures. In some cases, there are also applications that require the ability to see through the crosslinked PVDF polymer so that marks under the PVDF jacket can be inspected or identified.

[0003] Some methods for enhancing the transparency of PVDF polymers are known in the art. A common method for improving transparency is by copolymerizing vinylidene fluoride with a comonomer. The presence of the copolymer reduces crystallinity and results in higher transparency. Transparency increases by introducing a high level of comonomer, but the resulting level of transparency is still lower than the level required for its applications. Another method for improving transparency is by introducing additives such as acrylic polymers or plasticizers.

[0004] Adding acrylic polymers to PVDF is a known method for improving transparency. Polymethyl methacrylate ("PMMA") resin is one of the few polymers that can be fully miscible with PVDF resin and blended with it in any ratio. To provide the desired level of transparency, PMMA needs to be added in relatively large quantities, usually at a minimum acrylic level of more than 10% by weight. Adding PMMA resin to PVDF is not generally done due to the significant property loss associated with its addition. For example, adding enough PMMA to PVDF resin to provide useful transparency results in a decrease in tensile strength and a significant decrease in flame and smoke, both of which are considered adverse effects and undesirable for wire and cable applications. Adding PMMA also lowers the melting point and crystallinity of PVDF resin, reducing its ability to withstand environments such as under a car hood. PVDF polymers are known to have very good chemical resistance, meaning they retain more than 80% of their unaged mechanical properties after exposure to acids, bases (pH less than 12), and organic solvents and hydrocarbon solvents. However, adding acrylic polymers results in a significant decrease in the chemical resistance of PVDF polymers (measured by the loss of mechanical properties). Most importantly, the addition of acrylic polymers leads to a loss of V0 properties (evaluated according to UL94), a property inherent to PVDF polymers, which is a measure of flame and smoke propagation in the event of a fire. V0 evaluation is extremely important in wire and cable applications. Furthermore, the addition of acrylic polymers can reduce crosslinking efficiency and decrease the creep resistance of the composite material.

[0005] Furthermore, the addition of plasticizers can be used as a means to improve the transparency of PVDF polymers and provide several advantageous properties, such as a decrease in flexural modulus and an increase in flexibility (both considered useful in many wire and cable applications). One of the main problems with plasticizers is that they are low molecular weight, mobile species, and therefore are not considered permanent in the composition. Plasticizers tend to migrate to the polymer surface, which ultimately leads to property changes, including flexibility, crack resistance, low color retention, and transparency. Most importantly, the addition of plasticizers negatively impacts the electron beam crosslinking process. In the crosslinking reaction, plasticizers compete to prevent the increase in molecular weight of the fluoropolymer while crosslinking. This competitive reaction reduces the number of effective crosslinks between fluoropolymer chains, thereby decreasing the crosslinking efficiency. To compensate for the presence of plasticizers, significantly high levels of electron beam irradiation are required to effectively crosslink PVDF polymers. Unfortunately, high electron beam irradiation results in unacceptable property changes associated with the breakdown of polymer crystallinity (low melting point) and chain severance (low mechanical properties). In summary, the presence of plasticizers negatively impacts crosslinking efficiency and does not provide long-term transparency.

[0006] The challenge of producing transparent PVDF resins that maintain the required physical and mechanical properties after electron beam crosslinking is solved by implementing this invention. Adding quaternary ammonium salts can improve transparency and result in a slight decrease in modulus without significantly altering the percentage of crystallinity. This invention provides a transparent crosslinked resin using quaternary ammonium salts and a crosslinking agent. Unexpectedly, unlike other methods for improving the transparency of PVDF resins, this invention can produce transparent materials that remain transparent after crosslinking and maintain other desirable properties for many applications, including wire and cable applications. Desired properties for wires and cables include low modulus, high melting temperature, V0 rating for smoke and flame, chemical resistance, crosslinkability, tensile strength, flexibility, and elongation. Chemical resistance may include resistance to liquids such as automotive fluids. Automotive fluids may include brake fluid, transmission fluid, coolant, cleaning fluid, grease, engine oil, and of course, various fuels.

[0007] Unlike other methods for improving the transparency of PVDF, such as adding plasticizers or acrylic polymers, this invention retains desirable properties, such as chemical resistance and flame resistance, even after crosslinking. The crosslinked product of this invention offers a unique combination not previously seen in PVDF polymers.

[0008] US3269862 teaches the use of TAIC crosslinking accelerators to enhance the crosslinking of PVDF polymers.

[0009] US6610766 teaches that the electrical resistivity of polymers can be increased using alkyl quaternary ammonium sulfates or sulfites with PVDF. They also describe the increase in the transparency of PVDF. Their examples, and in particular Figure 4, show that the melting temperature decreases as the amount of added ammonium salt increases.

[0010] WO2020137108A1 and WO20137116A1 further teach the use of alkyl quaternary ammonium sulfate or sulfite in combination with PVDF. The composition achieves good transparency and suppresses yellowing in thicker areas by having an alkali metal concentration of 60 ppm or less in the polyvinylidene fluoride resin composition, a hydrogen fluoride concentration of 5 ppm or less in the polyvinylidene fluoride, and / or a heterogeneity ratio of 4% or more in the polyvinylidene fluoride. It is not mentioned that the addition of quaternary ammonium salts increases the melting temperature of PVDF.

[0011] WO2007145668 teaches the use of onium salts with PVDF. The composition is annealed at high temperature, and / or the onium salt is modified with nanoclay to achieve a composition with piezoelectric properties, a high melting temperature, and a low flexural modulus. It is not mentioned that the onium salt imparts transparency to the PVDF composition.

[0012] WO15048697 teaches the use of ammonium and phosphonium salts with PVDF containing residual surfactants having acidic end groups. The salts are said to react with the acidic end groups, improving the color stability of the product after melt treatment. A preferred family of salts is quaternary ammonium halides. The effect of the salts on the transparency, melt temperature, or modulus of the polymer is not mentioned.

[0013] When transparent PVDF polymer compositions or articles are crosslinked with an electron beam to increase their maximum continuous use temperature, their properties may be adversely affected, for example, they may become less transparent or hazy. This invention solves this problem by maintaining useful properties such as transparency, flexural modulus, flame resistance and smoke resistance, chemical resistance, and crosslinking efficiency.

[0014] By using the present invention, a transparent PVDF article (measured with low haze) can be obtained that has a maximum continuous use temperature of 150°C or higher, 175°C or higher, and up to 200°C, regardless of the initial melting point of the resin, while retaining useful properties. For example, by using this invention, a PVDF copolymer (not crosslinked) with a melting point of 145°C, a use temperature of 130°C, and relatively high haze can be made transparent while retaining all of its original properties, and can have a continuous use temperature exceeding 150°C, 155°C or 165°C. The present invention solves the problem by crosslinking a PVDF composition in a molded article containing a crosslinking accelerator and a quaternary ammonium salt by irradiation. [Overview of the project]

[0015] Brief description of the invention

[0016] The present invention provides a composition comprising a PVDF polymer, a quaternary ammonium salt (TBAHS), and a crosslinking accelerator. The PVDF polymer is a homogeneous copolymer, also referred to as a homopolymer or random copolymer. The amount of the quaternary ammonium salt is at least 0.01% by weight and less than 2.5% by weight relative to the weight of the PVDF polymer, and the amount of the crosslinking accelerator is at least 0.01% by weight and less than 5% by weight relative to the weight of the PVDF polymer.

[0017] Furthermore, the present invention provides a transparent article with a maximum continuous use temperature exceeding the melting point of the PVDF polymer and a haze of less than 40% at a thickness of 1 mm, using the composition of the present invention. A higher maximum continuous use temperature is achieved by crosslinking the article by irradiation in the presence of a crosslinking accelerator and a quaternary ammonium salt. This transparent PVDF technology achieves transparency (low haze), useful physical properties, and retains the flame and smoke properties after electron beam irradiation without adversely affecting electron beam crosslinking.

[0018] Crosslinking of PVDF containing a quaternary ammonium salt and a crosslinking accelerator provides articles exhibiting transparency measured at low haze and a maximum continuous use temperature exceeding the melting point of uncrosslinked PVDF. Generally, the maximum continuous use temperature of uncrosslinked PVDF is about 15°C lower than its melting point. For a PVDF homopolymer with a melting point of 165°C, the maximum continuous use temperature is about 150°C. Using the present invention, transparent PVDF articles (measured at low haze) can be obtained with a maximum continuous use temperature of 150°C or higher, or 165°C or higher, or 175°C or higher, and up to 200°C, while retaining useful properties, regardless of the initial melting point of the resin. In contrast, articles of the present invention can be used at temperatures above 150°C, preferably above 165°C, more preferably above 175°C, and in some embodiments up to 220°C. This unique combination does not adversely affect other properties that limit the use of the polymer. For example, flame and smoke properties, as well as mechanical properties, are substantially maintained.

[0019] The quaternary ammonium salts that can produce transparent Kynar® PVDF resin belong to the family of tetrabutyl quaternary ammonium salts, such as tetrabutylammonium bisulfate (TBAHS).

[0020] Transparency is sometimes described as having "see-through" capabilities, allowing for easy visual inspection of connections and reading of labels through the PVDF even at such high temperatures. The combination of higher maximum continuous operating temperature and transparency is unique for certain applications, such as wire and cable and automotive tubing.

[0021] Embodiments of the Invention

[0022] A first aspect of the present invention provides a composition comprising a PVDF polymer, a quaternary ammonium salt, and a crosslinking accelerator, wherein the PVDF polymer is either a homopolymer or a homogeneous copolymer, the amount of the quaternary ammonium salt is at least 0.1% by weight to less than 5% by weight, preferably less than 3% by weight, more preferably less than 2.5% by weight based on the weight of the PVDF polymer, and the amount of the crosslinking accelerator is from 0.01% by weight to less than 5% by weight, preferably less than 4% by weight, more preferably less than 3.5% by weight based on the weight of the PVDF polymer.

[0023] A second aspect of the present invention provides the composition of the first aspect, wherein the quaternary ammonium salt is a tetrabutyl quaternary ammonium salt.

[0024] A third aspect of the present invention provides one or more of the previous aspects, wherein the PVDF polymer comprises a homopolymer.

[0025] A fourth aspect of the present invention provides any combination of any of the previous aspects, wherein the PVDF polymer comprises a copolymer having 1 to 20% by weight of comonomer units.

[0026] A fifth aspect of the present invention provides the fourth aspect, wherein the comonomer unit is HFP.

[0027] A sixth aspect provides any combination of any of the previous aspects, wherein the aforementioned crosslinking accelerator is selected from the group consisting of cis-1,2-polybutadiene (1,2-BR), diallyl terephthalate (DATP), triallyl cyanurate (TAC), and triallyl isocyanurate (TAIC).

[0028] A seventh aspect provides any combination of any of the previous aspects, wherein the aforementioned crosslinking accelerator comprises TAIC.

[0029] The eighth aspect provides any combination of any of the previous aspects, wherein the quaternary ammonium salt contains at least one of an alkyl quaternary ammonium salt or an aryl-containing quaternary ammonium salt.

[0030] The ninth aspect provides any combination of any of the previous aspects, wherein the quaternary ammonium salt contains at least one of tetrabutylammonium bisulfate, tetrabutylammonium tetrafluoroborate or tetrabutylammonium hexafluorophosphate.

[0031] The tenth aspect provides any combination of any of the previous aspects, wherein the quaternary ammonium salt contains tetrabutylammonium hydrogen sulfate (TBAHS).

[0032] The eleventh aspect is a method for manufacturing an article, a) providing a composition in any combination of any of the previous aspects, b) melt-processing the aforementioned composition to form a shape, c) exposing the shape to electron beam irradiation sufficient to crosslink the aforementioned composition to yield an article. A method is provided that includes the above steps.

[0033] The twelfth aspect provides the eleventh aspect where the amount of irradiation is 3 to 15 rads.

[0034] The thirteenth aspect is an article comprising a crosslinked PVDF homopolymer or copolymer, a quaternary ammonium salt, and a crosslinking accelerator, wherein the aforementioned article has a maximum continuous use temperature of at least 150 °C and a transparency of less than 40% measured by haze (ASTM D1003) for an article with a thickness of 1 mm.

[0035] The fourteenth aspect provides the thirteenth aspect where the quaternary ammonium salt contains TBAHS.

[0036] The fifteenth aspect provides the thirteenth or fourteenth aspect where the crosslinking accelerator contains TAIC.

[0037] The sixteenth aspect provides any combination of the thirteenth, fourteenth, or fifteenth aspects, wherein the maximum continuous operating temperature is at least 165°C.

[0038] The 17th aspect provides any combination of the 13th, 14th, or 15th aspects, wherein the maximum continuous operating temperature is at least 175°C.

[0039] The 18th aspect provides any combination of the 13th, 14th, or 15th aspects, wherein the maximum continuous operating temperature is at least between 165°C and 220°C.

[0040] Description of the Invention The documents cited in this application are incorporated herein by reference.

[0041] The percentages used here are weight percentages unless otherwise specified, and the molecular weights are weight-average molecular weights unless otherwise specified. Melt viscosity (MV) is measured using ASTM D-3835 at 230°C for 100 seconds. -1 It is measured at [location / location].

[0042] The term "homopolymer" is used to mean a polymer having a single monomer unit. The term "copolymer" is used to mean a polymer having two or more different monomer units. The term "polymer" is used to mean both homopolymers and copolymers. For example, as used herein, "PVDF" and "polyvinylidene fluoride" are used to imply both homopolymers and copolymers unless otherwise specified. Polymers can be linear, branched, star-shaped, comb-shaped, or other structures. A polymer described as "homogeneous" is one that forms a single continuous phase in the solid state. All homopolymers are inherently homogeneous. Homogeneous copolymers of this invention are produced when comonomer units are statistically randomly distributed along the polymer chain. This may also be called a random copolymer. A polymer can be called a homogeneous copolymer if the probability of finding a particular type of monomer residue at a particular point in the chain is equal to the mole fraction of that monomer residue in the chain. A polymer described as "heterogeneous" is one that forms two or more phases in the solid state. In many cases, heterogeneous polymers are described as having a phase rich in monomers and a phase rich in another homopolymer. Heterogeneous copolymers can be formed when some polymer chains contain high levels of comonomer units, while other polymer chains do not contain comonomers, and the two types of chains do not mix with each other, resulting in phase separation. The polymers of the present invention are not heterogeneous. For example, polymers made according to US6187885 and US10570230 are considered heterogeneous.

[0043] Crosslinking is defined as a bond or short sequence that connects multiple polymer chains. Crosslinked polymers exhibit increased viscosity depending on the amount of crosslinking in the polymer.

[0044] Crosslinking accelerators are polyfunctional and highly reactive small molecules (or oligomers) containing unsaturated pendant groups (multiple vinyl groups). Adding crosslinking accelerators enables higher levels of crosslinking at lower electron beam exposure levels. Therefore, crosslinking accelerators are often added to improve crosslinking efficiency.

[0045] The operating temperature is the temperature of the intended operating environment. For example, the operating temperature described for use under a car's hood can be evaluated as 125°C, 150°C, 175°C, 200°C, and above, depending on the temperatures expected at various points under the hood. The maximum continuous operating temperature is the highest permissible temperature over the reasonable service life of the tested product at which the mechanical properties of the article (e.g., tensile strength, impact strength) deteriorate significantly. The maximum continuous operating temperature must be equal to or higher than the operating temperature.

[0046] The maximum continuous use temperature of a crosslinked article is measured using torsional dynamic mechanical analysis, as referred to in ASTM D4065. A rectangular test specimen measuring 50 mm × 12.5 mm × 1 mm is subjected to sinusoidal deformation with a small strain of 0.1% at a constant frequency of 1 Hz, and the temperature is given a stepwise gradient from 25°C to 200°C at a heating rate of 2°C / min. The change in shear storage modulus G' is observed during the temperature sweep. As long as the storage modulus G' of the crosslinked article remains at least 30% or more, preferably at least 50%, and more preferably at least 70%, of the value measured at the melting point (the melting point of uncrosslinked PVDF), it has not reached the maximum continuous use temperature. If the modulus measured at melting is below 30%, the PVDF has reached the maximum continuous use temperature. For the purposes of this invention, the maximum continuous use temperature is 220°C or less.

[0047] Cross-linked articles maintain their mechanical properties over a wide range of operating temperatures.

[0048] Generally, the maximum continuous use temperature assigned to PVDF resin (non-crosslinked) is approximately 15°C lower than its melting point. For a PVDF homopolymer with a melting point of 165°C, the maximum continuous use temperature is 150°C. For PVDF copolymers with lower melting points, a lower maximum continuous use temperature is assigned. For the purposes of this invention, the maximum continuous use temperature is 220°C or lower.

[0049] Polymers need to provide a maximum continuous use temperature that is the same as or higher than the expected use temperature for a particular application. The maximum continuous use temperature of uncrosslinked polymers is lower than their melting point. This is because when an article reaches the melting point of the polymer, the polymer flows and deforms, and the shape of the article cannot be maintained. In the present invention, articles made from the polymer composition of the present invention can be used at temperatures above the melting point of the uncrosslinked polymer.

[0050] Electron beam irradiation is a known technique used to induce crosslinking between polymer chains by applying energy.

[0051] PVDF polymer In this invention, PVDF homopolymer or copolymer is used.

[0052] The term PVDF copolymer refers to a copolymer of vinylidene fluoride (VDF) containing one or more other fluorinated comonomers or non-fluorinated comonomers, preferably fluorinated ones. In the PVDF copolymer of the present invention, vinylidene fluoride units account for more than 80% by weight of the total weight of all monomer units in the polymer, more preferably more than 82% by weight, and most preferably more than 85% by weight. One or more fluorinated comonomers preferably account for at least 0.5% by weight, preferably 1% by weight, and more preferably 4% by weight of the PVDF copolymer. One or more fluorinated comonomers preferably account for 0.5% to 20% by weight, more preferably 1% to 18% by weight.

[0053] The fluorinated comonomer is selected from compounds containing a ring-opening vinyl group for polymerization, and which contain at least one fluorine atom, at least one fluoroalkyl group, or at least one fluoroalkoxy group directly bonded to the vinyl group, provided that VDF already present in the PVDF copolymer is excluded. Examples of fluorinated comonomers include, but are not limited to, vinyl fluoride, trifluoroethylene (VF3), chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), 2,3,3,3-tetrafluoropropylene, 1,3,3,3-tetrafluoropropylene, 3,3,3-trifluoropropylene, perfluoro(alkyl vinyl) ethers, such as perfluoro(methyl vinyl) ether (PMVE), perfluoro(ethyl vinyl) ether (PEVE), and perfluoro(propyl vinyl) ether (PPVE), as well as perfluoro(1,3-dioxole) and perfluoro(2,2-dimethyl-1,3-dioxole) (PDD). Preferred PVDF copolymers include copolymers of VDF and HFP, copolymers of VDF and 2,3,3,3-tetrafluoropropylene, copolymers of VDF and 3,3,3-trifluoropropylene, and copolymers of VDF, HFP, and TFE.

[0054] PVDF copolymers can be copolymers of VDF and HFP. In one embodiment, the copolymer has hexafluoropropene (HFP) units ranging from at least 1% by weight to a maximum of 20% by weight, preferably up to 18% by weight.

[0055] The PVDF copolymer may have at least 80% by weight, preferably at least 82% by weight, of VDF units.

[0056] The PVDF copolymer used in this invention has a high molecular weight. Here, "high molecular weight" refers to the molecular weight measured at 230°C and 100 sec according to the ASTM D-3835 method. -1This means that the melt viscosity measured is greater than 1.0 kilopoise, preferably greater than 5 kilopoise, and more preferably greater than 10 kilopoise.

[0057] The PVDF copolymer used in this invention is generally produced by aqueous free radical emulsion polymerization using means known in the art, but suspension, solution, and supercritical CO2 polymerization processes can also be used.

[0058] In a typical emulsion polymerization process, deionized water, a water-soluble surfactant capable of emulsifying the reactant mass during polymerization, and an optional paraffin wax antifouling agent are added to the reactor. In some polymerizations, the surfactant is not used. The mixture is stirred to remove oxygen. A predetermined amount of chain transfer agent CTA is then introduced into the reactor, the reactor temperature is raised to the desired level, and vinylidene fluoride and optionally one or more comonomers are supplied to the reactor. Once the initial addition of vinylidene fluoride and the optional comonomers is introduced and the pressure in the reactor reaches the desired level, the initiator emulsion or solution is introduced to start the polymerization reaction. The reaction temperature can be varied depending on the properties of the initiator used, and those skilled in the art will know how to do this. Typically, the temperature is about 30–150°C, preferably about 60–120°C. Once the desired amount of polymer is reached in the reactor, the supply of monomers is stopped, although the supply of initiators may be continued to consume any remaining monomers. The residual gas (containing unreacted monomers) is released, and the latex is recovered from the reactor.

[0059] The surfactants used in polymerization are non-fluorinated surfactants known in this art to be useful for PVDF emulsion polymerization. The PVDF polymer emulsion of the present invention does not contain fluorosurfactants, and no fluorosurfactants are used in any part of the polymerization. The surfactants used in polymerization also do not contain acidic groups. This is because such groups have been shown to have poor interaction with the quaternary organic salts of the present invention and to hinder the desired improvement of the properties of the PVDF polymer. Non-fluorinated, acid-free surfactants useful for PVDF polymerization of this invention may have either ionic or nonionic properties and, but are not limited to, sodium alkyl sulfates, sodium aryl sulfates, sodium alkyl sulfonates, sodium aryl sulfonates, polyvinyl sulfonates, polyethylene glycol and / or polypropylene glycol, and their block copolymers, and siloxane surfactants. In some embodiments, the emulsion polymerization does not contain a surfactant.

[0060] The PVDF used in the present invention may be in the form of latex for mixing with additives and crosslinking accelerators, or it may first be dried into a powder by means known in the art, such as spray drying, freeze-drying, solidification, and drum drying, and then mixed with additives and TAIC.

[0061] In some embodiments, a copolymer of VDF and HFP is used. In some embodiments, a homopolymer of VDF is used.

[0062] Preferably, the composition does not contain any other fluorinated molecules other than the fluorinated monomers in the PVDF polymer.

[0063] Quaternary ammonium salts Quaternary ammonium salts act as nucleating additives for PVDF.

[0064] Quaternary ammonium salts can be prepared in a masterbatch at a maximum quaternary ammonium salt concentration of 15% by weight in a carrier resin. This masterbatch is added to PVDF to obtain a final quaternary ammonium salt concentration of 5% or less in the PVDF that is melt-processed into an article. In this application, the term “masterbatch” refers to a composition consisting of quaternary ammonium salts pre-dispersed in a carrier polymer. The term “carrier polymer” refers to the main component of the masterbatch used to contain the quaternary ammonium salts. The carrier polymer may be the same polymer composition that is extruded or melt-processed into an article, or may contain the same polymer composition. Alternatively, the carrier polymer may be a different polymer composition that does not adversely affect the melt-processing behavior of the PVDF formed into an article, or may contain the different polymer composition. In this application, the extruded polymer composition, i.e., the matrix polymer, includes PVDF.

[0065] Quaternary ammonium salts are used in amounts of 0.1 to 5% by weight relative to the weight of the PVDF being melted into the article. Quaternary ammonium salts contain a quaternary ammonium cation center that forms four covalent bonds, each bond being connected to an alkyl group. Examples of quaternary ammonium salts include alkylammonium salts, such as tetrabutylammonium bisulfate, tetrabutylammonium tetrafluoroborate, and tetrabutylammonium hexafluorophosphate.

[0066] PVDF may contain one or more quaternary ammonium salts. In this invention, the total amount of quaternary ammonium salts may be at least 0.1% by weight and 2.5% by weight or less, relative to the total weight of the PVDF polymer. The amount of any one of the quaternary organic salts may be 0.1 to 2%, preferably 0.02 to 1.5%. The amount of the quaternary organic salt may be 0.2 to 2% by weight relative to the weight of the PVDF.

[0067] Crosslinking accelerator Adding crosslinking accelerators provides increased crosslinking efficiency, enabling higher levels of crosslinking with lower levels of electron beam exposure. In most cases, adding crosslinking accelerators allows for a significant reduction in the effective crosslinking electron beam dose, which in turn helps improve physical properties (and reduces undesirable property changes). The ability to reduce the effective electron beam dose for effective crosslinking is considered useful in improving the overall performance of the polymer.

[0068] The composition contains one or more crosslinking accelerators.

[0069] The crosslinking accelerators used in the present invention include organic substances containing at least one group selected from maleimide groups, (methyl)acrylate groups, allyl groups, or polymers containing more than 50% vinyl. Examples of commercially available crosslinking accelerators include 1,2-polybutadiene cis-1,2-polybutadiene (1,2-BR), diallyl terephthalate (DATP), divinylbenzene (DVB), triallyl cyanurate (TAC), and / or triallyl cyanurate (TAP), triallyl isocyanurate (TAIC), or derivatives thereof. Preferably, triallyl isocyanurate, cis-1,2-polybutadiene (1,2-BR), diallyl terephthalate (DATP), and triallyl cyanurate (TAC). The preferred crosslinking accelerator used in the present invention is TAIC.

[0070] One or more crosslinking accelerators may be present. In the present invention, the total amount of crosslinking accelerators is at least 0.01% by weight and 5% or less by weight relative to the weight of PVDF. The amount of crosslinking accelerators can be 0.01 to 5% by weight, preferably 0.02 to 3% by weight, and more preferably 0.02 to 2% by weight, relative to the weight of PVDF.

[0071] Method of manufacturing articles To obtain the benefits of the present invention, a composition comprising a PVDF polymer, a quaternary organic salt, and a crosslinking accelerator is melt-processed to form a desired article, and the formed article is then subjected to electron beam irradiation to bring about crosslinking of the PVDF polymer in the article. The amount of electron beam irradiation is at least 3 M rad, up to 20 M rad, preferably 15 M rad or less, and more preferably 13 rad or less.

[0072] The resulting articles are a) The maximum continuous use temperature that exceeds the melting point of the PVDF polymer (before crosslinking), When exposed to the same electron beam irradiation dose, compared to articles lacking the combination of organic salt and crosslinking accelerator, b) High transparency and This indicates.

[0073] Preferred modified resins have flame and smoke evaluations that differ by 10% or less compared to unmodified resins.

[0074] This invention works with homogeneous PVDF resins, either homopolymers or copolymers. This invention does not work well with heterogeneous PVDF resins or PVDF resins containing more than 20% by weight of HFP relative to the total monomer units. Heterogeneous polymers are described in US6187885 and US10570230. Adding a crosslinking accelerator improves crosslinking efficiency and thermal stability at temperatures above the melting point of the polymer before crosslinking, preferably above 175°C, which is above 150°C. The melting point of the polymer is defined as the endothermic peak during heating by DSC using ASTM D3418. [Examples]

[0075] Sample preparation: PVDF resin was compounded with quaternary organic salt TBAHS (powder) and crosslinking accelerator TAIC using a ZSK 30mm twin-screw extruder. The process temperature was 220°C or lower.

[0076] Compression molding: 1 mm compression molded plaques (2 x 3 inches) were prepared at 210°C for 10 minutes under a pressure of 10,000 lbf.

[0077] Electron beam irradiation: The irradiation dose was set to 2.5 M rad for each exposure, and higher levels of irradiation were achieved by exposing the sample to 2.5 M rad multiple times. For example, to achieve an exposure of 5.0 M rad, the sample was exposed to the electron beam twice (once on each side), and to achieve an exposure of 10.0 M rad, the sample was exposed to the electron beam four times (twice on each side).

[0078] Injection Molding: Since the TAIC-free resin was only available in a sufficiently large quantity and only once, it was injection molded only onto Type 1 ASTM tensile bars for testing purposes. Injection molding was performed on a Sumitomo DUZ 75-ton machine.

[0079] The haze of the samples was measured before and after irradiation using a BYK HazeGuard Plus unit on 1 mm thick compression-molded plaques. The results of this analysis were consistent with previous visual observations of these same samples. HazeGuard Plus conforms to ASTM D-1003 standard.

[0080] Crosslinking efficiency: Crosslinking efficiency was evaluated by small-amplitude vibrational shear rheology at 230°C. A circular plaque with a diameter of 1 inch and a thickness of 1 mm was loaded between two parallel plates heated to 230°C. Viscosity and modulus were recorded at different angular frequencies while small sinusoidal deformation was applied to the molten material. An increase in zero-shear viscosity and storage modulus after irradiation indicates that the polymer has been crosslinked. The sensitivity of the rheological method allows for the comparison of subtle differences between samples. Higher crosslinking efficiency was defined as a higher viscosity shift under equivalent electron beam exposure.

[0081] Example 1: A 1 mm thick plaque was used for optical measurements. The greater the haze reduction, the clearer the product.

[0082] Parallel plate rheology tests were performed on PVDF copolymer resins after exposure to zero or 10 M rad electron beams. Complex viscosity, measured at an angular frequency of 0.01 rad / second and 230°C, was used in the table to indicate the difference in crosslinking efficiency. Higher complex viscosity indicates higher crosslinking in the resin.

[0083] [Table 1]

[0084] High complex viscosity indicates high crosslinking, and significant haze reduction indicates a clear sample. As shown in the table, the control copolymer resin after irradiation shows an increase in complex viscosity and crosslinking in the sample, but the haze remains unchanged. On the other hand, adding TBAHS salt improves haze reduction but causes a decrease in crosslinking. Similarly, adding TAIC crosslinking accelerator promotes crosslinking in the resin but does little to help reduce haze. The combination of TBAHS and TAIC provides an intermediate product with improved complex viscosity (crosslinking) and improved haze reduction (clarity).

[0085] This example demonstrates that both quaternary ammonium salts and crosslinking accelerators are necessary to obtain high complex viscosity and significant haze reduction.

[0086] Example 2: A 1 mm thick plaque was used for optical measurements. The greater the haze reduction, the clearer the product.

[0087] Parallel plate rheology tests were performed on PVDF homopolymer resins after exposure to zero or 10 M rad electron beams. Complex viscosity at an angular frequency of 0.01 rad / second was used in the table to indicate the difference in crosslinking efficiency. Higher complex viscosity indicates higher crosslinking in the resin.

[0088] [Table 2]

[0089] [Table 3]

[0090] Similar to copolymer resins, the control homopolymer PVDF resin after irradiation shows an increase in complex viscosity and crosslinking in the sample, but the haze remains unchanged. On the other hand, adding TBAHS salt improves haze reduction but causes a decrease in crosslinking. Similarly, adding TAIC crosslinking accelerator promotes crosslinking in the resin but does little to help reduce haze. The combination of TBAHS and TAIC provides a product with improved complex viscosity (crosslinking) and improved haze reduction (transparency).

[0091] Example 3: DSC was performed from -20°C to 210°C using a heating rate of 10°C / min, and the expected change in melting temperature measured during the second heating was confirmed.

[0092] [Table 4]

[0093] Adding TBAHS salt slightly increased the Tm compared to other clarifying additives. The table summarizes the Tm (melting point temperature) of various materials. Materials containing tetrabutylquaternary ammonium salt and crosslinking accelerators can be used for applications where the melting point exceeds those listed in the table after irradiation.

Claims

1. A composition comprising a PVDF polymer, a quaternary ammonium salt, and a crosslinking accelerator, The PVDF polymer is either a homopolymer or a homopolymer. A composition wherein the amount of the quaternary ammonium salt is at least 0.1% to less than 5% by weight, preferably less than 3% by weight, and more preferably less than 2.5% by weight, relative to the weight of the PVDF polymer, and the amount of the crosslinking accelerator is 0.01% to less than 5% by weight, preferably less than 4% by weight, and more preferably less than 3.5% by weight, relative to the weight of the PVDF polymer.

2. The composition according to claim 1, wherein the quaternary ammonium salt is a tetrabutylquaternary ammonium salt.

3. The composition according to claim 1, wherein the PVDF polymer comprises a homopolymer.

4. The composition according to claim 1, wherein the PVDF polymer comprises a copolymer having 1 to 20% by weight of comonomer units.

5. The composition according to claim 4, wherein the comonomer unit is HFP.

6. The composition according to claim 1, wherein the crosslinking accelerator is selected from the group consisting of cis-1,2-polybutadiene (1,2-BR), diallyl terephthalate (DATP), triallyl cyanurate (TAC), and triallyl isocyanurate (TAIC).

7. The composition according to claim 1, wherein the crosslinking accelerator comprises TAIC.

8. The composition according to claim 1, wherein the quaternary ammonium salt comprises at least one of an alkyl quaternary ammonium salt or an aryl-containing quaternary ammonium salt.

9. The composition according to claim 1, wherein the quaternary ammonium salt comprises at least one of tetrabutylammonium bicarbonate, tetrabutylammonium tetrafluoroborate, or tetrabutylammonium hexafluorophosphate.

10. The composition according to claim 1, wherein the quaternary ammonium salt comprises tetrabutylammonium hydrogen sulfate (TBAHS).

11. A method for manufacturing an article, d) To provide the composition described in claim 1, e) Forming a shape by melting the composition, f) Bringing the article to life by exposing the shape to electron beam irradiation sufficient to crosslink the composition, Methods that include...

12. The method according to claim 11, wherein the amount of irradiation is 3 to 15 rads.

13. An article comprising a crosslinked PVDF homopolymer or a crosslinked homogeneous PVDF copolymer, a quaternary ammonium salt, and a crosslinking accelerator, wherein the article has a maximum continuous use temperature of at least 150°C and a transparency of less than 40% as measured by haze (ASTM D1003) for an article with a thickness of 1 mm.

14. The article according to claim 13, wherein the quaternary ammonium salt comprises TBAHS.

15. The article according to claim 13, wherein the crosslinking accelerator comprises TAIC.

16. The article according to claim 13, wherein the maximum continuous operating temperature is at least 165°C.

17. The article according to claim 13, wherein the maximum continuous operating temperature is at least 175°C.

18. The article according to claim 13, wherein the article has a maximum continuous operating temperature between at least 165°C and 220°C.

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