Pan-UPE composite membranes for filtration

Abstract

The disclosure relates to a composite membrane comprising: a porous carrier layer comprising polyethylene and having an upper surface and a lower surface, wherein the lower surface of the porous carrier layer defines a first outer surface of the composite membrane; and a separation layer disposed on the upper surface of the porous carrier layer, the separation layer comprising polyacrylonitrile, a copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, or a mixture thereof, and defining a second outer surface of the composite membrane; and a filter comprising said composite membrane, wherein the composite membrane has multiple pleats.

Description

[0001] PAN-UPE Composite Membranes for Filtration

[0002] Technical Field

[0003] The present disclosure relates to composite membranes and more particularly composite membranes that exhibit chemical stability in solvents and that are mechanically stable.

[0004] More particularly, the present disclosure relates to a composite membrane comprising: a porous carrier layer comprising polyethylene and having an upper surface and a lower surface, wherein the lower surface of the porous carrier layer defines a first outer surface of the composite membrane; and a separation layer disposed on the upper surface of the porous carrier layer, the separation layer comprising a phase-inverted polyacrylonitrile, a copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, or mixtures thereof, and defining a second outer surface of the composite membrane; and a filter comprising said composite membrane, wherein the composite membrane is folded such that it has multiple pleats.

[0005] Background

[0006] Composite membranes include a porous carrier membrane on which a separation layer is applied by known methods, such as spraying, printing, roller application, nozzle coating or injection- or immersion methods. This separation layer provides the selectivity needed to achieve sufficient separation of a substance. Generally, for commercial applications, this separation layer is applied as thinly and defect-free as possible and must adhere well to the carrier membrane. This separation layer can be made solventstable, in addition, by suitable methods, such as e.g., crosslinking techniques. When applying a solvent-stable separation layer on a solvent-stable carrier membrane, the obtained membranes are per se solvent-stable.

[0007] Air filtration membranes comprising electrospun PAN fibers sandwiched between polyethylene / polypropylene (PE / PP) bi-component nonwoven layers have been described for particulate matter filtration. See, e.g., Zhou et al., Sep. Purif. Tech. 289 (2022) 120726. However, such sandwich structures are designed for air filtration with pore sizes in the micrometer range (0.779-2.705 pm) and utilize electrospun PAN fibers rather than phase-inverted PAN membranes. These air filtration structures are unsuitable for liquid filtration applications requiring nanometer-scale pore sizes and are not designed for chemical stability in polar organic solvents.Membranes formed from polyacrylonitrile (PAN) (cross-linked and uncross-linked), as described in WO 2015 / 082546 A1 and WO 2015 / 071276 A1, demonstrate improved chemical stability in certain solvents when compared to other solution processable membranes. Membranes formed from cross-linked and uncross-linked PAN have an integrally asymmetrical structure. A membrane having an integrally asymmetrical structure, when viewed from the upper side (feed side) of the membrane, has an increasing porosity in a direction towards the underside (filtrate side) of the membrane. The actual separation capabilities of the membrane can be adjusted by choice of solvents in principle from pore-free to pores in the micrometer range on the upper side (feed side) of the membrane. With decreasing pore size, membranes for ultrafiltration or microfiltration can be obtained. These membranes can be used directly for substance separation and are also suitable for use as a separation layer in a composite membrane.

[0008] Summary

[0009] There is a need in the art for polymer membranes for filtration which not only show good filtration properties and chemical stability, but also high mechanical stability which allows for pleating the membrane without surface defects.

[0010] As discussed herein, membranes formed from PAN (cross-linked and uncross-linked) demonstrate improved chemical stability in certain solvents when compared to other membranes. However, because PAN membranes have an integrally asymmetric structure, they lack sufficient mechanical stability to withstand manipulation such as bending, folding, and pleating which can lead to the formation of defects and cracks which is undesirable due to potential particle shedding. Additionally, any cracks that form in the selective layer of a composite membrane when pleating the composite membrane may lead to a reduction in the separation quality of the composite membrane.

[0011] Prior art composite membranes comprising polyacrylonitrile separation layers have been described using various carrier materials. For example, WO 2016 / 104797 describes solvent-resistant separation membranes with infusible polyacrylonitrile and lists numerous potential carrier materials including polyethylene, polypropylene, and various other polymers. However, WO 2016 / 104797 teaches that, from the viewpoint of stability to acid, alkali, and organic solvents and suppressing membrane shrinkage during high-temperature processing, polytetrafluoroethylene resin, polyphenylene sulfide resin, or carbon fiber are preferred as carrier materials, with polyphenylene sulfide being particularly preferred.

[0012] The inventors have discovered that, contrary to the teachings of WO 2016 / 104797, polyethylene — and particularly ultra-high molecular weight polyethylene — provides superior mechanical stability when combined with a phase-inverted PAN separation layer, enabling the composite membrane to withstand pleating without surface defects. This specific combination addresses the problem of PAN's insufficient mechanical stability for manipulation such as bending, folding, and pleating. The use of polyethylene, rather than the preferred materials taught in WO 2016 / 104797, provides the necessary balance of mechanical support and compatibility with the PAN layer to achieve a pleated membrane suitable for semiconductor chemical filtration applications.

[0013] While prior art membranes may be described as theoretically 'suitable' for pleating or 'applicable' to pleated configurations, the present disclosure provides composite membranes that have been actually demonstrated to withstand pleating without surface defects. This distinction is an important feature for practical applications in semiconductor manufacturing, where any defects or cracks in the membrane can lead to particle shedding and contamination of high-purity chemicals. The Examples herein demonstrate that the specific combination of a polyethylene carrier layer with a phase-inverted poly(meth)acrylonitrile separation layer achieves this practical pleating capability.

[0014] In a first aspect, the present disclosure relates to a composite membrane comprising: a porous carrier layer comprising polyethylene and having an upper surface and a lower surface, wherein the lower surface of the porous carrier layer defines a first outer surface of the composite membrane; and a separation layer disposed on the upper surface of the porous carrier layer, the separation layer comprising polyacrylonitrile, a copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, or mixtures thereof defining a second outer surface of the composite membrane.

[0015] In a second aspect, the present disclosure relates to a filter comprising a composite membrane as described herein, wherein the composite membrane has multiple pleats.In a third aspect, the present disclosure relates to the use of a filter as described herein in the semiconductor manufacturing industry, particularly for filtering chemicals used for photolithography.

[0016] Brief Description of the Drawings

[0017] The disclosure may be more completely understood in consideration of the following description of various illustrative embodiments in connection with the accompanying drawings in which:

[0018] Figure 1 shows a membrane in accordion fold;

[0019] Figure 2 shows a three-dimensional coordinate diagram indicating the X-Y-Z-axes;

[0020] Figure 3 is a schematic drawing of an exemplary filter including a pleated PAN composite membrane as described herein;

[0021] Figure 4 shows a scanning electron micrograph of a cross-section of the PAN composite membrane prepared using a 6.0 wt.-% PAN lacquer as described in the Examples section;

[0022] Figure 5 shows a scanning electron micrograph of a cross-section of the PAN composite membrane prepared using a 6.5 wt.-% PAN lacquer as described in the Examples section;

[0023] Figure 6 shows a scanning electron micrograph of a cross-section of the PAN composite membrane prepared using a 7.0 wt.-% PAN lacquer as described in the Examples section; and

[0024] Figure 7 shows a scanning electron micrograph of a cross-section of the PAN-PEI composite membrane prepared using a 9.5 wt.-% PAN lacquer as described in the Examples section.While the disclosure is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit aspects of the disclosure to the particular illustrative embodiments described. On the contrary, the intention is to coverall modifications, equivalents, and alternatives falling within the spirit and scope of the disclosure.

[0025] Detailed Description

[0026] As used in this specification and the appended claims, the singular forms “a”, “an”, and “the” include plural referents unless the content clearly dictates otherwise. As used in this specification and the appended claims, the term “or” is generally employed in its sense including “and / or” unless the content clearly dictates otherwise.

[0027] The following detailed description should be read with reference to the drawings in which similar elements in different drawings are numbered the same. The detailed description and the drawings, which are not necessarily to scale, depict illustrative embodiments and are not intended to limit the scope of the invention. The illustrative embodiments depicted are intended only as exemplary. Selected features of any illustrative embodiment may be incorporated into an additional embodiment unless clearly stated to the contrary.

[0028] Composite Membrane

[0029] In a first aspect, the present invention relates to a composite membrane comprising: a porous carrier layer comprising polyethylene and having an upper surface and a lower surface, wherein the lower surface of the porous carrier layer defines a first outer surface of the composite membrane; and a separation layer disposed on the upper surface of the porous carrier layer, the separation layer comprising polyacrylonitrile, a copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, or mixtures thereof defining a second outer surface of the composite membrane. In certain aspects, the separation layer comprises polyacrylonitrile defining a second outer surface of the composite membrane.

[0030] The second outer surface of the composite membrane is preferably the upstream or feed side of the composite membrane.The first outer surface of the composite membrane is preferably the downstream or filtrate side of the composite membrane.

[0031] The carrier layer comprises polyethylene and, in certain embodiments, comprises ultra-high molecular weight polyethylene (UHMWPE). While various polymeric materials could theoretically serve as carrier layers for composite membranes, the inventors have found that polyethylene provides unique advantages for the specific application of creating mechanically robust, pleat-able membranes for semiconductor chemical filtration.

[0032] The selection of polyethylene, particularly ultra-high molecular weight polyethylene (UHMWPE), as the carrier material facilitates the mechanical robustness required for pleating without defects. Unlike other carrier materials such as polyester, polypropylene, or the polyphenylene sulfide preferred in prior art solvent-resistant membranes, polyethylene combines:

[0033] (a) Mechanical flexibility and toughness that accommodates the stress of pleating operations without cracking;

[0034] (b) Compatibility with the phase-inverted PAN layer that ensures strong interfacial adhesion during the precipitation process;

[0035] (c) Chemical stability in polar organic solvents used in semiconductor photolithography, including PGME, PGMEA, ethyl lactate, GBL, and cyclohexanone; and

[0036] (d) Thermal stability that allows the composite membrane to withstand the crosslinking temperatures (70-125°C) without deformation of the carrier layer.

[0037] The combination of these properties in polyethylene, especially UHMWPE with molecular weights of 1,000-10,000 kg / mol, enables the composite membrane to be successfully pleated as demonstrated in the Examples, whereas PAN membranes without such a carrier exhibit cracks and wrinkles when subjected to similar manipulation. Additionally, the use of polyethylene as the carrier, particularly UHMWPE,enables pleatable composite membranes with the required chemical stability and filtration performance.

[0038] In some embodiments, the carrier layer can comprise other components in addition to the polyethylene such as, for example, polymers different from polyethylene, additives or fillers. These other components are known in the art.

[0039] For example, in one embodiment, the amount of these other components can be up to 50.0 wt.-%, up to 25.0 wt.-%, or up to 15.0 wt.-%, based on the total weight of the carrier layer. In one embodiment, the polyethylene and the other components make up 100 wt.-% of the carrier layer.

[0040] In another embodiment, the carrier layer consists of only polyethylene (i.e., polyethylene alone makes up 100 wt.-% of the carrier layer).

[0041] In various embodiments, the polyethylene is an ultrahigh molecular weight polyethylene. The weight average molecular weight of the ultrahigh molecular weight polyethylene can be in the range of from 1,000 to 10,000 kg / mol, from 1,500 to 7,500 kg / mol, or from 2,500 to 6,500 kg / mol, as determined by GPC method according to ISO 16014-4 and / or ASTM D 6474.

[0042] The polyethylene can have a melt flow rate MFR2 of from 0.01 to 10.0 g / 10 min, 0.1 to 7.5 g / 10 min, or from 0.2 to 5.0 g / 10 min, determined according to ISO 1133 at 2.16 kg and 190°C.

[0043] The polyethylene can have a density of from 920 to 975 kg / m3, 930 to 970 kg / m3or from 935 to 968 kg / m3, determined according to ISO 1183.

[0044] The polyethylene can have a melting temperature of from 125 to 145°C, 127 to 142°C, or from 130 to 140°C, determined by DSC according to ISO 11357.

[0045] The polyethylene can be an ethylene homopolymer or a copolymer of ethylene with comonomer units selected from alpha-olefins having from 3 to 8 carbon atoms, such as propylene, 1 -butene, 1 -hexene and / or 1 -octene.The polyethylene can be produced in any suitable polymerization process such as a high pressure radical polymerization process or a low pressure polymerization process in the presence of a coordination catalyst. These polymerization processes are well known in the art.

[0046] Suitable polyethylenes, including suitable ultrahigh molecular weight polyethylenes are commercially available either in pelletized form or already in fiber form.

[0047] For commercial polyethylenes, the above described properties usually are given by the distributors in technical data sheets.

[0048] Polyethylene membranes, suitable as a porous carrier layer, such as described herein, can be prepared using a thermally induced phase separation (TIPS) process.

[0049] The carrier layer can have the following properties:

[0050] The carrier layer has a more porous open structure than the separation layer. Preferably the carrier layer is microporous, with an average pore size of usually less than 1 pm, not more than 0.5 pm, or not more than 0.3 pm.

[0051] The lower limit of the average pore size is usually 0.05 pm or, in some cases, 0.1 pm.

[0052] Additionally, the carrier layer preferably has a tensile strain at break in the machine direction of greater than Imm / mm; determined according to ISO 527-3. The carrier layer preferably has a tensile stress at maximum load in the machine direction of greater than 8 MPa; determined according to ISO 527-3.

[0053] Further, the carrier layer preferably has a tensile strain at break in the cross-web direction of greater than 4 mm / mm; determined according to ISO 527-3. The carrier layer preferably has a tensile stress at maximum load in the cross-web direction of greater than 4 MPa; determined according to ISO 527-3.

[0054] The separation layer can comprise polyacrylonitrile, a copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, ora mixture thereof. In certain embodiments, the separation layer comprises polyacrylonitrile.The term polyacrylonitrile, as used herein, includes polyacrylonitriles which can be substituted by a methyl group, possibly on the vinyl group, and hence also comprises poly(meth)acrylonitrile, and mixtures of polyacrylonitrile and poly(meth)acrylonitrile. Additionally, the term polyacrylonitrile, as used herein, includes copolymers based on polyacrylonitrile, such as, for example, poly(acrylonitrile-co-methyl acrylate).

[0055] Polyacrylonitrile is available in different purities or qualities and can contain up to 10% methyl acrylate. Polyacrylonitrile, as used herein, preferably contains less than 5% methyl acrylate, less than 2.5% methyl acrylate, or less than 1% methyl acrylate.

[0056] Copolymers based on acrylonitrile can be derived from monomeric acrylonitrile.

[0057] Preferably these polymers are derived from acrylonitrile to at least 80 wt% and, in some cases, to at least 90 wt%. Poly(acrylonitrile-co-methyl acrylate) is one such copolymer.

[0058] It is especially preferred that polyacrylonitrile is used as a separation layer in a composite membrane, as described herein.

[0059] The nitrile (C^N) group in polyacrylonitrile has a dipole, which lends itself to electrostatic interactions between a membrane made from polyacrylonitrile and certain contaminants desired to be removed from the feed stream, thus enhancing the retentive capabilities of a membrane made from polyacrylonitrile over membranes without such a functional group.

[0060] The separation layer can be produced by precipitation of the polyacrylonitrile, copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, or mixture thereof by a phaseinversion process. Such a phase-inversion process is described e.g., in DE 198 11 998 C1.

[0061] The polyacrylonitrile, copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, or mixture thereof is first dissolved in an organic solvent, optionally together with a crosslinker. Then the solution is coated onto the upper surface of the carrier layer. After coating, the polyacrylonitrile, copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, or mixture thereof, and the optional crosslinker are precipitated on the upper surface of the carrier layer by a phase-inversion process. After the phaseinversion step, the polyacrylonitrile, copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, or mixture thereof and the optional crosslinker are crosslinked. In a last step, the composite membrane is dried.

[0062] The polyacrylonitrile, copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, or mixture thereof, is preferably dissolved in a suitable organic solvent.

[0063] The organic solvent is preferably selected from the group consisting of dimethyl sulfoxide (DMSO), dimethylformamide (DMF), N-methylpyrrolidone (NMP), dimethylacetamide (DMAC), tetrahydrothiophene-1,1 -dioxide (sulpholane), aqueous solutions of sodium thiocyanate and / or zinc chloride and mixtures thereof. In some cases, the organic solvent is dimethyl sulfoxide (DMSO).

[0064] The content of the polyacrylonitrile, copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, or mixture thereof in the solution can range from 1 to 30 wt.-%, from 5 to 20 wt.-%, or from 7.5 to 15 wt.-%, based on the total weight of the polyacrylonitrile, copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, or mixture thereof in the organic solvent.

[0065] In one embodiment, the polyacrylonitrile, copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, or mixture thereof is crosslinked with a crosslinker.

[0066] The crosslinker is preferably added to the solution containing the polyacrylonitrile, copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, or mixture thereof in the organic solvent.

[0067] The crosslinker can be an amino group containing polymer, which is preferably selected from polyethylene imine, polyvinyl amine, polyallylamine and mixtures thereof.

[0068] In some cases, the crosslinker is polyethylene imine.

[0069] The use of polyethylene imine (PEI) as a crosslinker provides several advantages: First, PEI creates a robust three-dimensional crosslinked network within the PAN separation layer that enhances both chemical stability and mechanical strength. Second, the crosslinking reaction between PEI's amino groups and PAN's nitrile groups occurs homogeneously throughout the separation layer, providing uniform mechanicalreinforcement. Third, the PEI crosslinking complements the mechanical support provided by the polyethylene carrier layer, creating a synergistic effect that enables successful pleating without defects. As demonstrated in Table 2 and Figure 7, crosslinked (PAN-PEI)-UPE composite membranes exhibit bubble points of 19-27 nm and can be pleated without surface defects, demonstrating the effectiveness of this crosslinking approach in combination with the polyethylene carrier.

[0070] The crosslinker can have a number average molecular weight (Mn) of from 1,000 to 2,000,000 g / mol, from 2,500 to 1,000,000 g / mol, or from 5,000 to 500,000 g / mol, determined by GPC method according to ISO 16014-4 and / or ASTM D 6474.

[0071] The crosslinker can be added to the solution in the form of a precursor compound, the crosslinker being released in situ from the precursor compound. The precursor compounds are thereby for example blocked polyethylene imine, blocked polyvinyl amine, blocked polyallyl amine and / or mixtures thereof. In one embodiment, the crosslinker can be a blocked polyethylene imine (PEI).

[0072] The blocked polyethylene imine, blocked polyvinyl amine, blocked polyallyl amine and / or mixtures thereof, can have a number average molecular weight Mn of from 1,000 to 2,000,000 g / mol, from 2,500 to 1,000,000 g / mol, or from 5,000 to 500,000 g / mol, determined by GPC method according to ISO 16014-4 and / or ASTM D 6474.

[0073] “Blocked” thereby means that the respective crosslinking-active functionalities of the previously mentioned amines are inactive, i.e., are chemically masked. This can be achieved, for example, by the corresponding amines being converted with ketones to form corresponding ketimines. In one example, aliphatic ketones, in particular methyl isobutyl ketone are used. Exemplary precursor compounds include the ketimine of polyethylene imine, the ketimine of polyvinyl amine and the ketimine of polyallyl amine, wherein the keto group is preferably derived from aliphatic ketones, in particular from methyl-iso-butylketone. Release of the crosslinker could be observed under the influence of temperature and / or moisture.

[0074] The total content of the crosslinker, relative to poly(meth)acrylonitrile, the copolymer based on (meth)acrylonitrile or mixtures thereof, can range from 1 to 50 wt.-%, 3 to 20wt.-%, or from 8 to 14 wt.-%, based on the weight of the poly(meth)acrylonitrile, the copolymer based on (meth)acrylonitrile or mixtures thereof.

[0075] In some embodiments, the crosslinking reaction is induced by elevated temperature. Therefore, the solution of the (meth)acrylonitrile or mixture thereof or, in some cases, the poly(meth)acrylonitrile, and the crosslinker in the organic solvent is preferably maintained at a temperature below 40°C, such as from 10 to 35°C.

[0076] In another embodiment the polyacrylonitrile, copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, or mixture thereof, is not crosslinked with a crosslinker.

[0077] In said embodiment with no crosslinker, the polyacrylonitrile, copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, or mixture thereof is added to the solution without a crosslinker.

[0078] In this exemplary embodiment, the solution consists of polyacrylonitrile, a copolymer based on polyacrylonitrile, a poly(meth)acrylonitrile, ora mixture thereof in the organic solvent. In one case, the solution consists of polyacrylonitrile in the organic solvent.

[0079] In one embodiment, the solution comprises a non-solvent in which the polyacrylonitrile, copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, or mixture thereof does not dissolve. The non-solvent must, however, be miscible with the solvent and the precipitant (e.g., water). The choice of non-solvent affects the physical properties of the membrane formed (e.g., pore size, pore structure, flowthrough the membrane).

[0080] In certain embodiments, the non-solvent is selected from the group consisting of heterocyclic compounds such as 1,3-dioxolane, ketones such as acetone, polyalkylene glycol such as polyethylene glycol, tetraalkylene glycol such as tetraethylene glycol, alcohols such as isopropanol, and ethanol, alkyl lactates such as ethyl lactate, and mixtures thereof. In certain embodiments, the non-solvent is acetone.

[0081] The content of the non-solvent, relative to the content of the organic solvent or of the mixture of at least two organic solvents, can be 5 to 60 wt.-% or, in some cases, 25 to 55 wt.-%, based on the total weight of the mixture of organic solvent(s) and non-solvent.In the presence of a non-solvent in the solution, the content of the polyacrylonitrile, copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, or mixture thereof, in the solution can range from 1 to 30 wt.-%, 4 to 20 wt.-%, or from 5 to 15 wt.-%, based on the total weight of the solution of the polyacrylonitrile, copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, or mixture thereof in the mixture of organic solvent(s) and nonsolvent. In certain embodiments, the content of polyacrylonitrile in the solution can range from 1 to 30 wt.-%, 4 to 20 wt.-%, or from 5 to 15 wt.-%, based on the total weight of the solution of the polyacrylonitrile in the mixture of organic solvent(s) and non-solvent.

[0082] The solution can have a viscosity of 0.2 to 20 Pas or 1 to 10 Pas.

[0083] The solution is preferably disposed onto the upper surface of the carrier layer.

[0084] In some embodiments, the solution is poured into the upper surface of the carrier layer.

[0085] Precipitation can be conducted in a precipitant liquid, in which the polyacrylonitrile, copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, or mixture thereof does not dissolve, such as water. The water can comprise additives to modulate pore formation or membrane properties.

[0086] When water is used as the medium of the precipitation bath, the temperature can range from 1 to 99 °C, from 10 to 80 °C, or from 20 to 60 °C.

[0087] After precipitation, the composite membrane is optionally washed in water preferably at temperatures ranging from 1 to 99 °C or, in some embodiments, from 10 to 80 °C.

[0088] In the case of the presence of a crosslinker, the crosslinking reaction is induced by increasing the temperature to at least 70°C but not higher than the melting temperature of the polyethylene of the carrier layer or the glass transition temperature of the polyacrylonitrile, copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, or mixture thereof or the glass transition temperature of the crosslinked polyacrylonitrile, copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, or mixture thereof, whichever is the lowest.The temperature of the crosslinking reaction is preferably in the range of from 70 to 125°C, such as from 70 to 99°C or, in some embodiments, from 70 to 90°C.

[0089] The optional crosslinking reaction can be conducted in dry air or a water bath, preferably in a water bath at temperatures of not more than 99°C or, in some embodiments, not more than 90°C.

[0090] In a last process step, the composite membrane is preferably dried, preferably in an air flow.

[0091] The temperature of the drying step can range from 10 to 125°C, from 15 to 99°C or, in some embodiments, from 20 to 95°C.

[0092] In the case where no crosslinking step takes place, the temperature of the drying step is usually in the range of from 10 to 60°C, 15 to 50°C, or from 20 to 40°C.

[0093] In the case where a crosslinking step takes place in air, the temperature of the drying step is usually in the range of from 60 to 125°C, 70 to 99°C or, in some embodiments, from 70 to 95°C.

[0094] The drying step can overlap with the optional crosslinking step, which, in that case, the crosslinking is conducted in dry air.

[0095] Drying the membrane usually changes the final morphology of the membrane. The residual water in the polymer generally acts as a plasticizer, and densification occurs when the membrane is dried.

[0096] The subsequent steps of deposition, precipitation, optional washing, optional crosslinking and drying can be conducted in a continuous process in which the carrier membrane is continuously transported from the deposition station to a precipitation bath, an optional washing bath, an optional crosslinking station, such as a crosslinking bath, and the drying station.

[0097] The steps of precipitation, crosslinking / washing, drying can be effected in a machine and a dry membrane according to the disclosure is obtained.The temperature treatment can thereby be implemented over a period of time ranging from 5 min to 24 hours, 15 min to 12 hours, or from 20 min to 60 min.

[0098] The process for producing the separation layer is disclosed in WO 2015082546 A1 for a non-crosslinked polymer membrane based on polyacrylonitrile and in WO 2015 / 071276 A1 fora crosslinked polymer membrane based on polyacrylonitrile.

[0099] According to various embodiments, the composite membrane comprises the carrier layer as described herein and the separation layer as described herein.

[0100] In certain embodiments, the composite membrane consists of only the carrier layer and the separation layer, without any additional layers. This two-layer configuration maximizes mechanical stability while minimizing thickness and complexity.

[0101] In other embodiments, the composite membrane can comprise one or more additional layers, such as from one to three additional layers, which are different from the carrier layer and the separation layer. When present, such additional layers can be disposed between the upper surface of the carrier layer and the separation layer, or on the second outer surface of the composite membrane (i.e., on top of the separation layer).

[0102] The carrier layer can have a thickness ranging from 10 to 100 microns, 20 to 80 microns, 35 to 70 microns, or from 45 to 70 microns.

[0103] The separation layer can have a thickness of 1 to 100 microns, 5 to 85 microns, or 10 to 60 microns.

[0104] In various embodiments, the ratio of the thickness of the separation layer to the thickness of the carrier layer is in the range of 1.0 : 10.0 to 10.0 : 1.0, 1.0 : 5.0 to 5.0 : 1.0, or 1.0 : 3.0 to 2.0 : 1.0.The composite membrane can have a total thickness ranging from 11 to 200 microns, 25 to 165 microns, or from 50 to 130 microns.

[0105] The flow rate of the composite membrane can vary by no more than 10%, no more than 5%, no more than 2%, or no more than 1% after the composite membrane has been soaked in a polar, organic application solvent for at least 1 day, at least 1 week, or at least 2 weeks.

[0106] The upper limit is usually not more than 6 months or, in some cases, not more than 3 months.

[0107] For purposes of this measurement, the term “flow rate” refers to the isopropyl alcohol flow rate measured under standard conditions (1 bar pressure, 25°C), and the variation is calculated as: [(flow rate after soaking - initial flow rate) I initial flow rate] x 100%.

[0108] The polar, organic application solvent can be any suitable polar, organic solvent, such as those commonly used in the semiconductor manufacturing industry and, more particularly, those used in a photolithography process. Exemplary solvents include, but are not limited to, propylene glycol methyl ether (PGME), propylene glycol monomethyl ether acetate (PGMEA), ethyl lactate, gamma-butyrolactone (GBL), cyclohexanone, isopropyl alcohol, and the combinations thereof.

[0109] Further, the composite membrane can have an isopropyl alcohol flow rate ranging from 5 to 500 L / m2barh, from 10 to 450 L / m2barh, or from 25 to 400 L / m2bar h.

[0110] Still further, the composite membrane can have an average pore size at the bubble point ranging from 10 to 50 nm, from 10 to 35 nm, or from 10 to 20 nm.

[0111] The bubble point of the membranes was measured by using capillary flow porometry instruments by Porometer (Porolux and Poroliq).

[0112] The bubble point is indicated in the case of the first measurable flow and corresponds to the largest pore, the pore at the bubble point. The average pore size is determined as the pore size in the case of 50% of the total flow. The bubble point represents ameasure of the retentive capability of the obtained membrane in conjunction with the average pore size. For example, a pore size at the bubble point of 30 nm at the bubble point, in the case of an average pore size of 20 nm, represents a very good membrane. A pore size at the bubble point of 150 nm, in the case of an average pore size of 20 nm, represents a rather poor membrane. Alternatively, the pore size corresponds to a pressure which is applied to the membrane for measurement. In this respect, it is likewise possible to define the pore size directly via the bubble point as a function of a pressure. A workable pore size can hence be defined via the bubble point test.

[0113] The quality of the membrane has hence two characteristic values:

[0114] a) the bubble point

[0115] b) average pore size.

[0116] The composite membranes, as described herein, can have an average pore size in the range of 5 to 40 nm, 5 to 30 nm, or 5 to 20 nm. As shown in Tables 1 and 2, the Examples demonstrate composite membranes having an average pore size ranging from less than 18 to 27 nm and bubble points ranging from 19-27 nm.

[0117] These average pore size ranges are specifically selected to provide optimal filtration performance for semiconductor photolithography chemicals. While prior art membranes, such as those described in WO 2016 / 104797, teach average pore sizes with a lower limit of 5 nm (0.005 pm), the working examples in that reference demonstrate average pore sizes of 22-121 nm, which are significantly larger than the ranges associated with the composite membranes as described herein. The tighter pore size control achieved by the present composite membranes, particularly in the 5-20 nm range, provides superior particle retention such as is desirable for semiconductor applications.

[0118] The composite membranes, as described herein, usually do not exhibit surface defects, such as cracks or wrinkles, when folded in a first direction along a Z axis.

[0119] Additionally, the composite membranes, as described herein, usually do not exhibit surface defects, such as cracks or wrinkles, when folded in a second direction along the Z axis.The Z-axis is illustrated in Figure 2 in which the composite membrane extends in the plane of the X- and Y-axes. The first direction along the Z-axis thereby is in the direction of positive values of the Z-axis and the second direction along the Z-axis is in the direction of negative values of the Z-axis.

[0120] The absence of surface defects allows minimizing any potential source of particle generation in a fluid stream, which is particularly important for some applications such as in the semiconductor manufacturing industry.

[0121] The composite membranes, as described herein, usually do not exhibit surface defects, such as cracks or wrinkles, when subjected to an accordion fold (i.e., pleated) as shown in Figure 1. The terms “pleats,” “pleating,” or “pleated,” as used herein, means that the composite membrane is able to be doubled over on itself a number of times.

[0122] Thus, the composite membranes, as described herein, not only show a high quality in regard of defects and porosity and high chemical stability especially in view of polar organic solvents, but also a high mechanical stability which allows folding of the membrane in Z-axis and in accordion fold, without exhibiting surface defects.

[0123] The composite membranes, as described herein, are therefore suitable for pleating.

[0124] Pleating Performance

[0125] An advantage of the composite membranes, as described herein, is their ability to be pleated without exhibiting surface defects. As demonstrated in the Examples and shown in Figures 4-7, the composite membranes comprising a polyethylene carrier layer and a PAN separation layer were successfully pleated in accordion fold configuration without cracks or wrinkles visible under SEM examination. The Examples demonstrate actual pleating of the composite membranes with total thicknesses of 77-125 pm and bubble points of 19-27 nm without observable defects. The pleating capability enables significant increases in filtration surface area within a given filter housing volume, which is particularly valuable for semiconductor chemical filtration applications where space is limited and high throughput is required.

[0126] FilterIn a second aspect, the present invention relates to a filter comprising a composite membrane as described herein, wherein the composite membrane has multiple pleats. In some embodiments, all aspects of the composite membrane as described herein apply to the filter of the second aspect.

[0127] Figure 3 shows an exemplary filter 20. The filter 20 includes filter medium 26 comprising the composite membrane as described herein.

[0128] The composite membrane is pleated to form the filter medium 26 having multiple pleats 24. The filter medium 26 is disposed in a filter housing 28. The pleats 24 are orientated vertically around filter core 30 and along a longitudinal axis Y-Y extending through the filter housing 28.

[0129] As shown in Figure 3, the filter medium 26 is situated in the housing 28 of the filter 20 such that the second outer surface of the composite membrane forming the filter medium 26 defines the upstream or feed side 36 of the filter medium 26 and the first outer surface of the composite membrane defines the downstream or filtrate side 38 of the filter medium 26. The downstream side 38 of the filter medium 26 surrounds and is oriented in a direction towards the filter core 30.

[0130] In use, a fluid enters the filter 20 via the inlet 32 and fills the housing 28. The fluid flows through the filter medium 26 in a direction from the upstream side 36 to the downstream side 38 and into the filter core 30. From the filter core, the filter fluid exits the filter 20 via outlet 34. Filter 20 can be used in a continuous filtration process to remove particulate matter from the fluid stream.

[0131] Brief description of the reference signs in Figure 3

[0132] Figure 3:

[0133] 20 filter

[0134] 24 pleats

[0135] 26 filter medium (pleated composite membrane having pleats oriented along a longitudinal axis Y-Y)

[0136] 28 filter housing

[0137] 30 filter core32 inlet

[0138] 34 outlet

[0139] 36 upstream side of filter media 26

[0140] 38 downstream side of filter media 26

[0141] Y indication of the longitudinal axis Y-Y of the filter

[0142] Use

[0143] A third aspect of the present disclosure relates to the use of a filter, as described herein, in the semiconductor manufacturing industry, particularly for filtering chemicals used for photolithography. In certain embodiments, all aspects of the composite membrane and the filter, as described herein, also apply to the use of the third aspect.

[0144] In one exemplary use case, a fluid chemical used in photolithographic processes is flowed through the filter including the composite membrane, as described herein according to the various embodiments, to remove particulates and other contaminants from the fluid prior to the fluid being used in a photolithographic process.

[0145] Examples

[0146] The present disclosure is described in more detail with reference to the subsequent embodiments, and examples without restricting the disclosure to the illustrated special parameters.

[0147] Example 1

[0148] A homogeneous solution consisting of polyacrylonitrile (PAN) polymer, dimethyl sulfoxide (DMSO) solvent, and 1,3-dioxolane (DIOX) nonsolvent was prepared. The PAN concentration was varied between 6 wt.-% and 7 wt.-%. As solvent system a mixture of DMSO to DIOX was used. The homogeneous PAN solution was cast on top of the polyethylene carrier (thickness of 55 pm, pore size of 0.2 pm), using a doctor blade to drawdown the PAN solution. The membranes were precipitated, washed and dried at room temperature. Table 1 shows the membrane properties of the PAN composite membranes.Table 1: Membrane properties of uncross-linked PAN-UPE composite membranes: PAN Casting Total Pore size of composite membrane IPA Flow [wt%] gap height composite BP [nm] MFP [nm] SMP [nm] Time [s / [pm] thickness 500mL]

[0149] [pm]

[0150] 6.0 200 77 19 <18 <18 8,500 6.5 200 85 <18 <18 <18 10,500

[0151]

[0152] 7.0 200 80 <18 <18 <18 14,500

[0153] Figure 4 shows a cross-section SEM picture of resulting uncross-linked PAN-UPE composite membrane using 6.0 wt.-% PAN lacquer.

[0154] Figure 5 shows a cross-section SEM picture of resulting uncross-linked PAN-UPE composite membrane using 6.5 wt.-% PAN lacquer.

[0155] Figure 6 shows a cross-section SEM picture of resulting uncross-linked PAN-UPE composite membrane using 7.0 wt.-% PAN lacquer.

[0156] Example 2

[0157] A homogeneous solution consisting of polyacrylonitrile (PAN) polymer, polyethylenimine (PEI) polymer crosslinker, dimethyl sulfoxide (DMSO) solvent and acetone non-solvent was prepared. The PAN concentration was varied between 8 wt.-% and 10 wt.-%, the ratio of PAN to PEI 90 to 10 wt.-%. As solvent system a mixture of DMSO to acetone was used. The homogeneous PAN-PEI solution was cast on top of the polyethylene carrier (thickness of 55pm, pore size of 0.2pm), using a doctor blade to draw down the PAN-PEI solution. The membranes were precipitated at room temperature, washed at 70 °C and dried at room temperature. Table 2 shows the membrane properties of the PAN-PEI composite membranes.

[0158] Table 2: Membrane properties of cross-linked PAN-UPE composite membranes:

[0159] PAN Total Pore size of composite membrane IPA Flow [wt.-%] composite BP [nm] MFP [nm] SMP [nm] Time [s / thickness [pm] 500mL] 8.0 110 27 25 23 5800 8.5 110 24 22 21 7200 9.0 115 24 22 20 7200 9.5 120 21 20 19 9300

[0160]

[0161] 10.0 125 19 <19 <19 14500Figure 7 shows a cross-section SEM picture of resulting cross-linked PAN-UPE composite membrane using 9.5 wt.-% PAN lacquer.

[0162] Pleating Evaluation

[0163] The composite membranes prepared according to Examples 1 and 2 above were subjected to pleating tests. Membrane samples were folded in accordion-style pleats with pleat heights of approximately 10-15 mm. After pleating, the membranes were examined under optical microscopy and SEM for surface defects including cracks, wrinkles, or delamination.

[0164] All composite membranes listed in Tables 1 and 2 successfully withstood pleating without visible surface defects. The PAN separation layer remained intact and adhered to the polyethylene carrier layer throughout the pleating process. No cracks were observed in either the machine direction or cross-web direction folds. The pleated membranes maintained their filtration performance with bubble points and average pore sizes unchanged within measurement error (±5%).

[0165] For comparison, standalone PAN membranes (without the polyethylene carrier) prepared by the same phase inversion process exhibited multiple cracks and wrinkles when subjected to identical pleating procedures, confirming that the polyethylene carrier layer is essential for achieving pleat-able composite membranes.

[0166] Aspects

[0167] Aspect 1 is a composite membrane comprising: a porous carrier layer comprising polyethylene and having an upper surface and a lower surface, wherein the lower surface of the porous carrier layer defines a first outer surface of the composite membrane; and a separation layer disposed on the upper surface of the porous carrier layer, the separation layer comprising polyacrylonitrile, a copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, ora mixture thereof formed by phase inversion, and defining a second outer surface of the composite membrane. In some embodiments, the separation layer comprises polyacrylonitrile formed by phase inversion.Aspect 2 is the composite membrane according to Aspect 1 , wherein the polyacrylonitrile, copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, or mixture thereof is cross-linked with a crosslinker selected from polyethylene imine, polyvinyl amine, polyallylamine and mixtures thereof. In some embodiments, the crosslinker is polyethylene imine. In certain such embodiments, polyacrylonitrile is crosslinked with polyethylene imine.

[0168] Aspect 3 is the composite membrane according to Aspects 1 or 2, wherein the polyethylene is an ultra-high molecular weight polyethylene having a weight average molecular weight in the range of from 1,000 to 10,000 kg / mol as determined by GPC method according to ISO 16014-4 and / or ASTM D 6474.

[0169] Aspect 4 is the composite membrane according to any one of the preceding Aspects, wherein a flow rate of the composite membrane varies by no more than 10% after the composite membrane has been soaked in a polar, organic application solvent selected from propylene glycol methyl ether (PGME), propylene glycol monomethyl ether acetate (PGMEA), ethyl lactate, gamma-butyrolactone (GBL), cyclohexanone, and isopropyl alcohol for a time period of at least 1 week. In some embodiments, the time period is at least 2 weeks.

[0170] Aspect 5 is the composite membrane according to any one of the preceding Aspects, wherein the composite membrane has an isopropyl alcohol flow rate ranging from 5 to 500 L / rrf bar h. In some embodiments, the isopropyl alcohol flow rate ranges from 10 to 450 L / m2bar h. In further embodiments, the isopropyl alcohol flow rate ranges from 25 to 400 L / rrf bar h.

[0171] Aspect 6 is the composite membrane according to any one of the preceding Aspects, wherein the composite membrane has an average pore size at the bubble point ranging from 10 to 50 nm. In some embodiments, the average pore size at the bubble point ranges from 10 to 35 nm. In further embodiments, the average pore size at the bubble point ranges from 10 to 20 nm.

[0172] Aspect 7 is the composite membrane according to any one of the preceding Aspects, wherein the composite membrane has an average pore size ranging from 5 to 40 nm asdetermined by capillary flow porometry. In some embodiments, the average pore size ranges from 5 to 30 nm. In further embodiments, the average pore size ranges from 5 to 20 nm.

[0173] Aspect 8 is the composite membrane according to any one of the preceding Aspects, wherein the composite membrane is pleated such that it has an accordion fold configuration and does not exhibit surface defects, such as cracks or wrinkles.

[0174] Aspect 9 is the composite membrane according to any one of the preceding Aspects, wherein a thickness of the carrier layer ranges from 10 to 100 microns. In some embodiments, the thickness of the carrier layer ranges from 20 to 80 microns. In further embodiments, the thickness of the carrier layer ranges from 35 to 70 microns. In still further embodiments, the thickness of the carrier layer ranges from 45 to 70 microns.

[0175] Aspect 10 is the composite membrane according to any one of the preceding Aspects, wherein a thickness of the separation layer ranges from 1 to 100 microns. In some embodiments, the thickness of the separation layer ranges from 5 to 85 microns. In further embodiments, the thickness of the separation layer ranges from 10 to 60 microns.

[0176] Aspect 11 is a filter comprising a composite membrane according to any one of the preceding Aspects, wherein the composite membrane has been pleated to form multiple pleats and exhibits no surface defects.

[0177] Aspect 12 is the filter according to Aspect 11 , wherein the pleats are orientated along a longitudinal axis.

[0178] Aspect 13 is the filter according to Aspects 11 or 12, wherein the filter is disposed in a housing.

[0179] Aspect 14 is a method comprising flowing a chemical used for photolithographic processes through the filter according to any one of Aspects 11-13 to remove particulates and other contaminants from the chemical prior to its use in a photolithographic process.

Claims

Claims1. A composite membrane comprising:a porous carrier layer comprising polyethylene and having an upper surface and a lower surface, wherein the lower surface of the porous carrier layer defines a first outer surface of the composite membrane; anda separation layer disposed on the upper surface of the porous carrier layer, the separation layer comprising polyacrylonitrile, a copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, ora mixture thereof formed by phase inversion, and defining a second outer surface of the composite membrane.

2. The composite membrane according to claim 1 , wherein the polyacrylonitrile, copolymer based on polyacrylonitrile, poly(meth)acrylonitrile, or mixture thereof is cross-linked with a crosslinker, selected from polyethylene imine, polyvinyl amine, polyallylamine and mixtures thereof.

3. The composite membrane according to claims 1 or 2, wherein the polyethylene is an ultra-high molecular weight polyethylene having a weight average molecular weight in the range of from 1,000 to 10,000 kg / mol as determined by GPC method according to ISO 16014-4 and / or ASTM D 6474.

4. The composite membrane according to any one of claims 1 to 3, wherein a flow rate of the composite membrane varies by no more than 10% after the composite membrane has been soaked in a polar, organic application solvent selected from propylene glycol methyl ether (PGME), propylene glycol monomethyl ether acetate (PGMEA), ethyl lactate, gamma-butyrolactone (GBL), cyclohexanone, and isopropyl alcohol for a time period of at least 1 week.

5. The composite membrane according to any one of claims 1 to 4, wherein the composite membrane has an isopropyl alcohol flow rate ranging from 5 to 500 L / m2bar h.

6. The composite membrane according to any one of claims 1 to 5, wherein the composite membrane has an average pore size at the bubble point ranging from 10 to 50 nm.

7. The composite membrane according to any one of claims 1 to 6, wherein the composite membrane has an average pore size ranging from 5 to 40 nm as determined by capillary flow porometry.

8. The composite membrane according to any one of claims 1 to 7, wherein the composite membrane is pleated such that it has an accordion fold configuration and does not exhibit surface defects, such as cracks or wrinkles.

9. The composite membrane according to any one of claims 1 to 8, wherein a thickness of the carrier layer ranges from 10 to 100 microns.

10. The composite membrane according to any one of claims 1 to 9, wherein a thickness of the separation layer ranges from 1 to 100 microns.

11. A filter comprising a composite membrane according to any one of claims 1 to 10, wherein the composite membrane has been pleated to form multiple pleats and exhibits no surface defects.

12. The filter according to claim 11, wherein the pleats are orientated along a longitudinal axis.

13. The filter according to claims 11 or 12, wherein the filter is disposed in a housing.

14. A method comprising: flowing a chemical used for photolithographic processes through the filter according to any one of claims 11 to 13 to remove particulates and other contaminants from the chemical prior to its use in a photolithographic process.

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