Filter media

Abstract

The present disclosure relates to a filtration medium comprising a fibrous web impregnated with a resin composition comprising lignin. The fibrous web comprises lignin in an amount of 0.1 to 30 weight percent, by weight of the fibrous web, and the lignin has a density of less than 1.2 g / cm 3 or a weight average molecular weight of less than 20,000 g / mol. The present disclosure also relates to a method of manufacturing the filtration medium.

Description

TECHNICAL FIELD

[0001] The present invention relates to filtration media, and more particularly to resin-impregnated filtration media such as can be used to filter fluids in automotive, industrial, and domestic applications. BACKGROUND

[0002] Filtration media for automotive, industrial, and domestic applications are typically formed by impregnating a fibrous substrate (such as paper) with a chemical binder such as a phenolic resin (resole or novolac or a blend of novolac and resole) or a latex resin. The resin provides structural rigidity and resistance to tearing or breaking to the substrate, which would otherwise occur during filtration when exposed to pressurized and heated fluids. Once impregnated with resin, the substrate is heat cured to crosslink the resin and remove any excess solvent that can be present. The substrate can then be pleated, cut, and folded into the desired shape. The folded substrate can be assembled into its final form with additional support elements, which in some applications can be cylindrical (e.g., for oil and fuel filters for automotive engines) and in other applications can be in the form of a panel (e.g., for air conditioning filters). Further heat treatment can be applied to the assembled substrate to fix it in position.

[0003] Conventional resole phenolic resins used in the above-described processes are synthesized in a base-catalyzed reaction of bisphenol A with phenol and formaldehyde. Conventional novolac phenolic resins used in the above-described processes are synthesized in an acid-catalyzed reaction of cresol (methylphenol). These resins have the desirable properties of water, oil, and chemical resistance, and are stable at high temperatures, making them particularly suitable for automotive filtration applications. However, a disadvantage of these resins is that they readily release toxic phenol and formaldehyde gases, which can have a negative impact on the health of anyone exposed to them, and on the environment.

[0004] Another disadvantage of conventional phenolic resins is that their starting materials are typically obtained from non-renewable hydrocarbon sources, and they require large amounts of reagents, solvents, energy, and manufacturing inputs to produce. As a result, they are both environmentally and economically expensive.

[0005] One alternative to using pure phenolic resins is to combine them with resin binders. Lignoform® is a thermoplastic lignin-type resin material derived from pine wood. As disclosed in US 5656733A, US 5683497A, and US 5702521A, it consists of a complex mixture of high molecular weight phenolic compounds, abietic acid, neutral materials, and several minor components.

[0006] US 3294582 discloses a method of making a filter paper element for automotive applications. The filter paper is impregnated with a resin varnish consisting of a mixture of a thermosetting resol phenol-formaldehyde resin, water, resorcinol and formaldehyde. US 3294582 discloses that the resin is preferably present in an amount of about 25 parts by weight per 100 parts by weight of phenolic solids, and the resorcinol is present in an amount of about 3 parts by weight.

[0007] The use of the resin to impregnate the filter medium has the disadvantage that it has a high density (~1.33 g / ml) and viscosity (20-300 mPa.s at 25°C) making it difficult to impregnate into the filter medium substrate. This can result in the filter medium having an inconsistent or incomplete coating which can lead to structural failure during use. The high viscosity can result from the high molecular weight of the primary lignin component of ~20,000 g / mol. Another disadvantage of the resin is that it has poor solubility in most solvent systems suitable for coating filter media.

[0008] There is therefore a need for a filter medium which at least to some extent addresses the above problems. More specifically, the present invention provides a filter medium which is manufactured by a method which is more environmentally friendly and safer to operate than existing methods, as it reduces the emission of phenol and formaldehyde. The present invention achieves this advantage whilst also using a resin composition which has physical properties which enable it to be effectively and uniformly processed and impregnated. It is a further object of the present invention for the filter medium to exhibit comparable operating performance to filter media known in the art. SUMMARY

[0009] According to a first aspect of the present invention there is provided a filter medium comprising a fibrous web impregnated with a resin composition comprising lignin, wherein:

[0010] the fibrous web comprises lignin in an amount of 0.1 to 30 wt% by weight of the fibrous web; and

[0011] the lignin has a density of less than 1.2 g / cm 3 or a weight average molecular weight of less than 20,000 g / mol when measured according to ASTM D4001-13 standard.

[0012] The lignin can have a pH of less than 7, preferably 3 to 5, or most preferably 4 to 4.5.

[0013] ​The resin composition can have a dynamic viscosity of less than 15 mPa.s, preferably between 5 and 13 mPa.s, and more preferably between 7.5 and 9.5 mPa.s when measured according to the ISO 2555:2008 standard.

[0014] The resin composition can have a pH of 4 to 7, preferably 5 to 6.

[0015] The lignin can have a density of less than 1 g / cm 3 , preferably between 0.20 g / cm 3 and 0.75 g / cm 3 , and more preferably comprised between 0.25 g / cm 3 and 0.45 g / cm 3 .

[0016] The resin composition can further comprise a formaldehyde scavenger having at least one primary or secondary amine function or being a polyamine, and the formaldehyde scavenger can be selected from urea, ammonia, melamine, dicyandiamide, polyethyleneimine or polyvinylamine, and can preferably be urea.

[0017] The resin composition can comprise an epoxy-based component, also known as polyepoxide or epoxy resin. The epoxy-based component can be selected from aromatic or aliphatic polyepoxides, such as reaction products formed from bisphenol and epichlorohydrin, from novolak and epichlorohydrin or from aliphatic alcohol and epichlorohydrin, and can preferably be bishpenol A - diglycidyl ether.

[0018] The resin composition can comprise lignin and phenolic resin, which can preferably be present in a weight ratio of lignin:phenolic resin of 1 : 1 to 1 : 9, preferably 1 : 1 to 1 : 4, and more preferably 1 : 2.

[0019] The filtration medium can comprise 10 to 50 wt.%, preferably 10 to 40 wt.%, and more preferably 10 to 30 wt.% of the resin composition.

[0020] The fibrous web can comprise at least 80 wt.%, preferably at least 90 wt.%, or more preferably at least 95 wt.% of cellulosic fibers, based on the total weight of fibers.

[0021] The fibrous web can comprise at least 80 wt.%, preferably at least 90 wt.%, or more preferably at least 95 wt.% of synthetic fibers, based on the total weight of fibers.

[0022] The fibrous web can comprise a mixture of cellulosic fibers and synthetic fibers. Synthetic fibers can be present in the fibrous web in an amount of at most 50 wt.%, or preferably 10-30 wt.% of the total weight of fibers in the web.

[0023] The cellulose fibres can be selected from one or more of softwood fibres, hardwood fibres, plant fibres and regenerated cellulose fibres.

[0024] The filter medium can be selected from oil filter media, air filter media, fuel filter media, hydraulic filter media, industrial filter media, dielectric fluid filter media and water filter media. The air filter media can be used in heavy duty panel filters, or in duty air panel filters.

[0025] According to a second aspect of the present application, there is provided a method of manufacturing a filter medium as defined above, the method comprising impregnating a fibrous web with a resin composition comprising lignin and curing the impregnated fibrous web.

[0026] The present application will be better understood in connection with the following examples, which are given by way of illustration and should not be construed as limiting and with the attached drawings. BRIEF DESCRIPTION OF DRAWINGS

[0027] In the drawings:

[0028] Figure 1 is a graph illustrating the burst strength of cured resin compositions comprising 10%, 20%, 30%, 40% and 50% lignin;

[0029] Figure 2 is a graph illustrating the burst strength of cured resin compositions comprising 10%, 20%, 30%, 40% and 50% lignin after aging at 160°C for 24 hours;

[0030] Figure 3 is a graph illustrating the curing rate of resin compositions of Figure 1 and Figure 2 ;

[0031] Figure 4 is a graph illustrating the burst strength of resin compositions comprising hexamine and paraformaldehyde;

[0032] Figure 5 is a graph illustrating the burst strength of resin compositions of Figure 4 after aging at 160°C for 24 hours;

[0033] Figure 6 is a graph illustrating the emission levels of formaldehyde and phenol of filter media impregnated with phenol-formaldehyde resin and phenol-formaldehyde resin comprising 30% lignin according to the present application;

[0034] Figure 7is a graph illustrating the filtration performance of an oil filter medium comprising 30% of lignin measured as differential pressure (kPa) vs. flow rate (L / min) according to the present application;

[0035] Figure 8 is a graph illustrating the average filtration efficiency of an oil filter of Figure 7 vs. particle size;

[0036] Figure 9 is a graph illustrating the differential pressure vs. time measured for an oil filter of Figure 7 and Figure 8 ;

[0037] Figure 10 is a graph comparing the hot oil burst strength at 140°C of a filtration medium comprising a lignin resin composition comprising 30% of lignin and a filtration medium comprising a resin composition without lignin;

[0038] Figure 11 is a graph comparing the particle size filtration efficiency of (i) a planar filtration medium impregnated with a phenol formaldehyde resin containing 30% of lignin according to the present application and (ii) a planar filtration medium impregnated with a phenol formaldehyde resin only. DETAILED DESCRIPTION

[0039] As used herein and in the appended claims, the following terms are intended to have the following definitions, unless the context requires otherwise.

[0040] “Comprise” or variations such as “comprises” or “comprising” will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.

[0041] “Fiber” is a fibrous or filamentous structure having a high length to diameter ratio.

[0042] “Staple fibre” means a fiber that naturally has or has been cut or further processed into a defined, relatively short piece or individual length.

[0043] “Fibrous” means a material that is primarily composed of fibers and / or staple fibers.

[0044] The term “nonwoven” or “web” means a collection of fibers and / or staple fibers in the form of a web or mat that are randomly interlocked, entangled, and / or bonded to one another to form self-supporting structural elements.

[0045] “Synthetic fibres” means fibres made from fibre-forming substances, including polymers synthesised from chemical compounds, modified or transformed natural polymers and siliceous (glass) materials. Such fibres can be produced by conventional melt spinning, solution spinning, solvent spinning and similar filament production techniques.

[0046] “Formaldehyde scavenger” means a compound capable of capturing formaldehyde gas emissions.

[0047] In the following, the term “water-soluble” must be understood as a compound which is at least 10% soluble in water at room temperature (20°C) at atmospheric pressure.

[0048] The present disclosure provides filtration media suitable for various automotive, industrial, and household fluid purification applications.

[0049] The filtration media comprises a fibrous web impregnated with a resin composition comprising lignin. The lignin is present in the fibrous web in an amount of 0.1 to 30 wt.%, preferably 0.1 to 20 wt.%, or more preferably 0.1 to 15 wt.% of the weight of the fibrous web.

[0050] The lignin has one or both of (i) a density of less than 1.2 g / cm 3 and (ii) a weight average molecular weight of less than 20,000 g / mol when measured according to ASTM D4001-13 standard, which is a standard test method for determining weight average molecular weight of polymers by light scattering detection.

[0051] The lignin density can be less than 1 g / cm 3 , preferably between 0.20 g / cm 3 and 0.75 g / cm 3 , more preferably between 0.25 g / cm 3 and 0.45 g / cm 3 , and most preferably between 0.35 g / cm 3 and 0.40 g / cm 3 .

[0052] The lignin has a pH of less than 7, preferably between 3 and 5, or most preferably between 4 and 4.5. The pH can be determined in a dilute 30% lignin aqueous solution according to standard ISO 10523:2008 procedure. This standard determines the pH of lignin by measuring the potential difference of an electrochemical cell, where one of the two half-cells is a measuring electrode and the other is a reference electrode. The potential of the measuring electrode is a function of the hydrogen ion activity of the solution being measured.

[0053] The low density, acidic pH, and relatively low molecular weight provide the lignin of the present disclosure with a favorable low viscosity of less than 15 mPa.s, which enables the lignin to be relatively easily dissolved in the resin composition and impregnated into the fibrous web. In addition, the low viscosity of the resin can improve the uniformity and speed of impregnation of the fibrous web. This can be in contrast to Resins form a contrast, Resins have a high density of 1.33 g / cm 3 a high viscosity of 20-300 mPa.s at 25 °C, and poor solubility in most solvent systems.

[0054] Lignin can be obtained, for example, from a Kraft process. As is well known in the art, the Kraft process (also known as kraft pulping or sulfate process) is a process for converting wood into cellulose fiber pulp. The process includes treating wood chips with a hot mixture of water, sodium hydroxide (NaOH), and sodium sulfide (Na2S) to break the bonds between lignin, hemicellulose, and cellulose. The method includes several mechanical and chemical steps that result in the formation of two product streams: a cellulose fiber stream and a lignin stream. The wood used for the Kraft process to obtain lignin therefrom can be softwood (i.e., from gymnosperm trees, such as coniferous trees, e.g., pine), hardwood (i.e., from angiosperm trees), or a combination thereof. Lignin obtained from the Kraft process represents a renewable source of resin that has a lower environmental impact than resins obtained from oil-based hydrocarbon sources. Since Kraft lignin is a byproduct of the Kraft process, minimal processing is required to obtain the Kraft lignin.

[0055] In addition to including lignin, the resin composition includes a phenolic (phenol-formaldehyde resin, such as resols or novolacs) resin. The phenolic resin can be present in the resin composition in an amount of 50 wt% to 90 wt%, preferably 60 wt% to 90 wt%, or more preferably 70 wt% to 90 wt%, based on the total weight of the resin composition. Resols can be formed by an alkali-catalyzed reaction of bisphenol A with phenol and formaldehyde. Novolac resins can be formed by an acid-catalyzed reaction of cresol (methylphenol).

[0056] The lignin and the phenolic resin can be present in the resin composition in a lignin:phenolic resin weight ratio of 1 : 1 to 1 :9, preferably 1 : 1 to 1 :4, and more preferably 1 :2. The weight ratio of lignin:phenolic resin does not change when the resin is dried and remains substantially equal after the drying step, enabling the removal of the solvent used to impregnate the fibrous web, or after the curing step, enabling the crosslinking of the resin composition.

[0057] The resin composition can also comprise a crosslinking agent, such as hexamine, paraformaldehyde or a dicyandiamide-formaldehyde condensate. The dicyandiamide-formaldehyde condensate is preferably a water-soluble thermosetting resin composition comprising s as described in US-4,383,077 A. The dicyandiamide-formaldehyde condensate can be obtained by the method claimed in US-4,383,077 and preferably those dicyandiamide-formaldehyde condensates disclosed in the examples of US-4,383,077. The crosslinking agent is capable of crosslinking the resin composition with the fibrous web during the curing step. The crosslinking agent can be present in the resin composition in an amount of up to 20 wt.%, based on the total weight of the resin composition.

[0058] The resin composition can also comprise a formaldehyde scavenger having at least one primary or secondary amine functionality or being a polyamine. The formaldehyde scavenger can be selected from urea, ammonia, melamine, dicyandiamide, polyethylene imine and polyvinyl amine. If the formaldehyde scavenger is urea, it is particularly useful. The amine group of the formaldehyde scavenger can react with residual formaldehyde in the resin, converting the formaldehyde into a Schiff base compound, which has reduced volatility and toxicity. Since these types of reactions are typically acid catalyzed, the resin composition preferably has a pH of 7 or less. The resin composition typically has a pH of 4 to 7, preferably 5 to 6. More particularly, the use of a formaldehyde scavenger enables the emission of formaldehyde to be close to zero.

[0059] According to another embodiment, the resin composition can include an epoxy-based component, also known as a polyepoxide or epoxy resin. The epoxy-based component can be selected from aromatic or aliphatic polyepoxides, such as reaction products formed from bisphenol and epichlorohydrin, or from novolac and epichlorohydrin, or from aliphatic polyols and epichlorohydrin, and can preferably be bisphenol A-diglycidyl ether. The epoxy-based component can be used to replace some or all of the phenolic resin, and also to reduce the content of such compounds in the resin composition. For example, based on the total weight of the lignin, epoxy resin, and phenolic resin in the resin composition, the lignin is preferably present in an amount of 10-80 wt% (more preferably 25-50 wt%), the epoxy resin is preferably present in an amount of 10-80 wt% (more preferably 25-50 wt%), and the phenolic resin is preferably present in an amount of 10-80 wt% (more preferably 25-50 wt%). According to another embodiment, the resin composition contains less than 5 wt% of phenolic resin (preferably 0 wt%), and the lignin:epoxy resin weight ratio in the resin composition is, for example, 1 : 1 to 1 :9. In both cases, if present, the lignin:epoxy resin and phenolic resin weight ratios do not change when the resin is dried, and remain substantially equal after the drying step, enabling the removal of the solvent used to impregnate the fibrous web, or after the curing step, enabling the cross-linking of the resin composition. The epoxy functional groups of the epoxy-based component are able to react with the lignin and the phenolic resin, acting as a cross-linking agent for the resin composition, like the formaldehyde. Thus, the addition of such an epoxy-based component enables the user to reduce the formaldehyde content in the resin composition, without adversely affecting the final performance of the filtration medium.

[0060] The resin composition has a dynamic viscosity of less than 15 mPa.s, preferably between 5 and 13 mPa.s, and more preferably between 7.5 and 9.5 mPa.s, when measured according to ISO 2555:2008 (Standard procedure for determining the apparent viscosity of resins in liquid or similar state using a rotational viscometer, also known as the Brookfield test method).

[0061] Inclusion of lignin in the resin composition has the advantageous effect of reducing the amount of phenol and formaldehyde gases emitted from the resin. The reduction in emission of these gases can be correlated to the amount of lignin in the resin composition, such that higher amounts of lignin result in greater reductions in emissions and lower amounts of lignin provide lower reductions in emissions. Thus, the presence of lignin in the resin composition results in a more environmentally friendly product. It also reduces the negative health effects on workers operating the manufacturing process for producing the conventional filter media known in the art, as compared to the manufacturing process used to produce those filter media. Without wishing to be bound by theory, it is believed that the emission of phenol and formaldehyde from the resol phenolic resin can be attributed to leaching from unreacted starting materials, or to decomposition of the phenolic resin into its constituent components. By including lignin in the resin composition, the total amount of phenolic resin and its starting materials is reduced. Alternatively or additionally, the lignin can act to protect the phenolic resin from degradation. The amount of phenol and formaldehyde emitted from the filter media can be measured in milligrams of phenol or formaldehyde emitted per kilogram of filter media. The filter media impregnated with the resin composition including lignin can emit 50%, 60%, 70%, 80%, 90%, or 99% less phenol and / or formaldehyde as compared to filter media impregnated with a phenolic resin that does not include lignin. Furthermore, it should be noted that lignin is derived from a renewable resource as compared to phenolic resins derived from fossil fuels. This further contributes to the environmentally friendly nature of the resin composition described herein.

[0062] The resin composition can include additional or alternative polymers to the phenolic resin, such as styrene acrylic, polyethylene chlorovinyl, styrene butadiene rubber, polystyrene acrylate, polyacrylate, polyvinyl chloride, polynitrile, polyvinyl acetate, polyvinyl alcohol derivatives, starch polymers, phenolics, and combinations thereof, including waterborne and solvent forms. In some cases, the additional or alternative resin can be in the form of a latex, such as a water-based emulsion.

[0063] To enhance the internal bonding between fibers, the fibrous web can include binder fibers.

[0064] These are bicomponent thermoplastic fibers that include a thermoplastic core fiber surrounded by a meltable coating of a thermoplastic polymer having a lower melting point than the core. Thus, when softened or partially melted by heat during processing of the fibrous web, the low melting point coating can act as a thermoplastic adhesive, adhering to adjacent fibers of the web. The higher melting point material forming the core can serve as a structural material.

[0065] The resin composition can also include one or more additive components. The additive components can be: a dyeing agent, which can be desired to impart a good appearance to the filter; a fiber retention agent; a separation aid (e.g., a siloxane additive and associated catalyst); a fire or flame retardant; a hydrophilic or hydrophobic agent; a wetting agent; an antistatic agent; or an antimicrobial agent. If present, these additives can be present in an amount greater than 0 wt.%, 0.01 wt.%, 0.1 wt.%, 1 wt.%, 5 wt.%, 10 wt.% and / or less than about 30 wt.%, 25 wt.%, 20 wt.%, 15 wt.%, 10 wt.%, 9 wt.%, 8 wt.%, 7 wt.%, 6 wt.%, 5 wt.%, 4 wt.%, 3 wt.%, 2 wt.%, 1 wt.% or any combination thereof, including, for example, between 0.01 wt.% and 1 wt.%, based on the total weight of the resin composition. According to particular embodiments, the resin composition can include between 10 wt.% and 20 wt.% of a flame retardant, such as phosphoric acid.

[0066] The filter medium can include 10 wt.% to 50 wt.%, preferably 10 wt.% to 40 wt.%, and more preferably 10 wt.% to 30 wt.% of the resin composition. The remainder of the filter medium is primarily composed of the fibrous web.

[0067] The fibrous web can include at least 80 wt.%, preferably at least 90 wt.%, or more preferably at least 95 wt.% of cellulosic fibers, based on the total weight of the fibers. The cellulosic fibers can be selected from one or more of softwood fibers, hardwood fibers, plant fibers, and regenerated cellulosic fibers.

[0068] Alternatively, the fibrous web can include at least 80 wt.%, preferably at least 90 wt.%, or more preferably at least 95 wt.% of synthetic fibers, based on the total weight of the fibers. The synthetic fibers can be selected from one or more of synthetic polymeric fibers, modified or converted natural polymeric fibers, or siliceous (glass) fibers. Exemplary fibers suitable for use in the fibrous web include polyesters (e.g., polyalkylene terephthalates such as polyethylene terephthalate (PET), polybutylene terephthalate (PBT), etc.), polyalkylenes (e.g., polyethylene, polypropylene, etc.), polyacrylonitrile (PAN), and polyamides (nylons, e.g., nylon-6, nylon 6,6, nylon-6, 12, etc.).

[0069] According to another alternative, the fibrous web can include a mixture of cellulosic fibers and synthetic fibers. The synthetic fibers can be present in the fibrous web in an amount of up to 50 wt.%, preferably 10 wt.% to 30 wt.%, or preferably 15 wt.% to 25 wt.% of the total weight of the fibers in the web.

[0070] The filtration medium can be selected from the group consisting of air filtration media, fuel filtration media, oil filtration media, hydraulic filtration media, industrial filtration media, dielectric fluid filtration media, and water filtration media.

[0071] The present disclosure extends to a method of manufacturing a filtration medium as defined herein. The method comprises impregnating a fibrous web with a resin composition comprising lignin, drying and curing the impregnated fibrous web.

[0072] Once the resin composition comprising lignin has been formed, it is transferred to an impregnation device where the resin composition is applied by a metering roller to achieve a uniform degree of impregnation throughout the fibrous web. The amount of resin applied to the web depends on the end use of the filtration medium. Once the resin has been applied to the fibrous web, the impregnated web enters a drying oven where the solvent is removed in a drying step. The drying step is typically carried out at a temperature between 80°C and 150°C. The resin is then cross-linked to the fibrous web in a curing step by heating the impregnated web in a curing oven at a temperature between 120°C and 200°C, between 150°C and 180°C, or between 180°C and 200°C. Alternatively, curing can be achieved by ultraviolet or infrared radiation. Once fully cured, the impregnated fibrous web obtains its final properties. These properties include its weight, thickness, corrugation, burst strength resistance, permeability, pore size, resin content percentage, humidity, or curing level. According to a particular embodiment, the drying step and the curing step can be carried out simultaneously, i.e. in a single step, and in particular when a cross-linking agent is used.

[0073] Once the filtration medium has been formed, it can be corrugated, cut, folded, pleated, subjected to an additional curing step, and assembled into a final use filtration product.

[0074] The filtration medium can be an air filtration medium. The air filtration medium can be configured for filtering automotive cabin air. In particular, the filtration medium can be configured to filter particles (such as dust, pollen, soot, bacteria, and PM2.5), gases (such as ozone, benzene, SOx, and NOx), or odors from the cabin air. The filtration medium can include a carbon layer (which can be activated carbon) to help filter unwanted gases and particles from the cabin air.

[0075] The air filtration medium can be configured as an automotive intake filter, which can be configured to filter particles (such as dust, pollen, soot, bacteria, and PM2.5) from air entering the vehicle engine. The filtration medium can optionally be treated to include one or more of a fire-retardant layer, a water-resistant layer, or a nanofiber layer, fine fiber meltblown layer, or synthetic lamination layer to enhance strength and filtration performance.

[0076] Air filter media can be configured for use as industrial filter media, such as gas turbine inlet filters, air-oil separator filters (e.g., in compressed air applications), air pollution control and dust collection filter elements (such as those that can be used to reduce or eliminate particulate emissions from industrial sources into the atmosphere), or heating, ventilation, and air conditioning (HVAC) filter elements, etc.

[0077] The filter media can be configured as a fuel filter element, which can be configured to filter organic and inorganic impurities from fuel. The fuel filter element may include multiple layers of filter media and can be configured to separate and retain particulate and water impurities from fuel.

[0078] The filter medium can be configured as an oil filter medium. The oil filter medium can be configured to filter impurities from oil, such as soot, dust, and particles. In these embodiments, the filter medium can have high durability in hot oil, particularly high hot oil burst resistance.

[0079] The filter medium can be configured to filter dielectric fluids used in electrical discharge machining (EDM) processes.

[0080] This filter medium can be configured as a hydraulic filter medium for use in hydraulic applications.

[0081] This filter media can be configured for water filtration. It can be configured to filter submicron-sized contaminants from water, including organic acids, viruses, bacteria, cysts, cell debris, and trace amounts of drugs. To improve filtration performance, the filter media can be coated with an electrostatically charged layer or an activated carbon layer.

[0082] The invention is further illustrated by the following non-limiting embodiments.

[0083] Example

[0084] Process

[0085] Samples were prepared using a laboratory wet-laid hand sheet mold and a modified TAPPI T205 process, employing the improved method described herein. The ingredients described in the formulation were mixed with 2 liters of tap water and dissolved at 1500 rpm using a standard laboratory Noram disintegrator. The mixture was then poured into the wet-laid mold and diluted with approximately 25 liters of tap water, stirred three times with a foot-operated agitator, and drained through a standard paper machine screen.

[0086] The handsheet was then pressed dry with 3 passes of a couching roller, dried for an additional 5 minutes in a flat bed rapid oven at 350°F (177°C), and then dried for 5 minutes in an oven at 350°F (177°C). On the oven dried (OD) sheet, raw physical data such as raw basis weight, calliper, air permeability were taken immediately after oven drying.

[0087] The sample was then saturated with a standard phenolic resin at a 25 wt% loading based on total sheet weight (bath solids of the resin bath were 18% in methanol as the solvent). The sample was then air dried for 24 hours under ambient conditions and cured to reach SDC (saturated dry cured) level at 350°F (177°C) for 5 minutes. The SDC basis weight was recorded immediately after curing, followed by other SDC data such as SDC calliper and SDC air permeability.

[0088] Test Methods

[0089] The following test methods were used to obtain the data reported in the tables below.

[0090] Filtering performance: This is determined using a multi-pass test. The test requires the unfiltered fluid to be recirculated through the filter element and the filtering performance is measured according to various possible parameters. In some cases, a differential pressure multi-pass test is performed. Defined in ISO 4548-12 standard.

[0091] Differential pressure test Differential pressure: refers to the measurement of the pressure inside the test filter relative to the pressure around the filter, inside the housing in which the filter has been installed. The differential pressure determines how effectively the fluid moves through the filter. When the differential pressure is high, it indicates that the filter is approaching capacity.

[0092] Filter efficiency Efficiency: defined in ISO 4548-12. This refers to the ability of the filter to retain particles, expressed as the percentage of particles of a given size that the filter retains under the test. During the test, samples of the liquid or gas are measured using particle counters in front of and behind the filter medium. The concentration of particles is measured and the filtration efficiency is calculated based on the difference in the amount of particles on either side of the filter.

[0093] Flow restriction test Differential pressure: defined in ISO 4548-12 standard. This test procedure determines the contaminant capacity of a filter, its particle removal characteristics, and the differential pressure. The test is intended to apply to filter elements with an efficiency of less than 99% at particle sizes greater than 10 μιη. The test corresponds to a multi-pass filtration test with continuous contaminant injection and using an online particle counting method to evaluate the performance of full-flow lubricating oil filters for internal combustion engines. It is limited to steady-state conditions and does not address fluctuations in flow rate.

[0094] Air permeability Air Permeability: Air permeability of the media samples was measured according to TAPPI Standard T 251 cm-85 ("Air Permeability of Porous Paper, Fabric and Pulp Handsheets") using a Textest AG (Model FX3300) at a water differential of 0.5 inches (2.7 mm) and recorded in cubic feet of air flow per minute per square foot of sample area (cfm / sf), sometimes more simply referred to as cfm.

[0095] Mean flow pore (MFP) size Burst Strength: Measured according to standard test procedure ASTM F-316.

[0096] Burst strength Bend Resistance: Bend resistance of the media samples was measured according to TAPPI Standard T403 using a Bend Tester measured the pressure required to break the media sample. Results were recorded in pounds per square inch (psi) at which the media broke.

[0097] Caliper Caliper (Thickness): Caliper (thickness) of the SDC media was measured using a Thwing-Albert Instrument Company 89-100 Thickness Tester according to TAPPI Standard T411 "Thickness (caliper) of paper, paperboard and combined board" (incorporated by reference herein in its entirety).

[0098] Stiffness Bend Resistance: Bend resistance of the media samples was measured according to TAPPI Standard T403 using a TM Stiffness: Stiffness of the OD and SDC media was obtained using a Bend Tester Model 4171D (Gurley Precision Instruments).

[0099] Hot oil burst strength Hot Oil Burst Strength: The hot oil burst strength of a media sample is the maximum hydrostatic pressure required to cause the media sample to break when a controlled and increasing pressure is applied through a rubber septum to a 7.07 cm2area. The hot oil burst strength was determined by placing a media sample (size 14 cm x 10 cm) in an oil bath of a typical engine oil (e.g., MOBIL 1 TM Oil) maintained at 140°C ± about 0.1 °C for 144 hours. The media sample was then removed from the hot oil bath and cooled for about 5 minutes while excess oil was wicked away from the media sample. The hot oil burst strength was then measured using a A burst strength tester tests the sample without moisture and the results are reported in pounds per square inch (psi) of force per unit area at which the medium ruptures.

[0100] Example 1

[0101] To optimize the amount of lignin in the resin, phenolic (resol) resin samples containing 10%, 20%, 30%, 40%, and 50% (volume / volume) lignin were prepared as follows:

[0102]

[0103]

[0104] The resin compositions were applied to filter paper samples, which were cured and tested according to the test methods described above in triplicate. Their characteristics are summarized in Tables 1-5 below. In the tables below, "target" refers to the target technical performance for the parameter.

[0105] Table 1 - Test 1, 10 wt% lignin in resin composition

[0106]

[0107] Table 2 - Test 1, 20 wt% lignin in resin composition

[0108]

[0109] Table 3 - Test 1, 30 wt% lignin in resin composition

[0110]

[0111]

[0112] Figure 1 and 2 Relative burst strength of resin compositions containing 10 wt%, 20 wt%, 30 wt%, 40 wt%, and 50 wt% lignin after curing and after aging at 160°C for 24 hours is illustrated, respectively. Satisfactory results were obtained with lignin compositions up to 30 wt%. Lignin levels greater than this value resulted in significantly reduced burst resistance.

[0113] Figure 3 Cure time of the resin compositions at 165°C is illustrated as increasing with increasing lignin content.

[0114] Example 2

[0115] To determine the preferred additives, resin compositions were prepared with hexamine and paraformaldehyde to evaluate the effect of these additives on burst resistance and stiffness. Samples containing different amounts of lignin and hexamine or lignin and paraformaldehyde were prepared as shown in Table 6 below and tested according to the test methods described above.

[0116] Table 6

[0117] Test 1 - 10% lignin Test 2 - 20% lignin Test 3 - 30% lignin Soluble phenol formaldehyde resin 89.0％ 78.0％ 67.0％ Lignin 10.0％ 20.0％ 30.0％ Hexamine or paraformaldehyde 1.0％ 2.0％ 3.0％

[0118] Figure 4 and 5 Figure illustrates that paraformaldehyde produces greater burst resistance in the tested resin compositions than hexamine.

[0119] Example 3

[0120] To compare the solubility of vinsol and kraft pulp lignin, four mixtures were prepared and evaluated.

[0121] Table 7

[0122]

[0123]

[0124] Example 4

[0125] Tests were conducted to evaluate the ability of the solvent system disclosed in prior art document US 3294582 to dissolve compositions of vinsol and lignin resins. Solvent mixtures of ethanol, isopropyl alcohol, and water were prepared according to the amounts disclosed in US 3294582. Four different formulations containing vinsol and lignin were prepared and evaluated for their solubility.

[0126] Table 7

[0127]

[0128] Example 5

[0129] Formation of filter media:

[0130] Resin compositions were prepared according to the components and amounts listed in Table 8.

[0131] Table 8

[0132]

[0133] In a first step, lignin was dissolved in resol resin. The resin / lignin mixture was transferred to a reactor and crosslinking agent was added, methanol and dye were added. The combined components were then mixed to obtain a dark solution with a solids content of 64%, a viscosity of 830.5 mPa.s, a density of 1.107 g / cm3 3 , a pH of 5.53.

[0134] The resin composition was impregnated into a fibrous web using an applicator and a metering roll in order to obtain a uniform impregnation. The fibrous web comprised > 95 wt% of cellulose fibers. The impregnated fibrous web was analyzed and the results are summarized in Table 9 below.

[0135] Table 9

[0136]

[0137]

[0138] Example 6

[0139] The above impregnated filter media were evaluated for formaldehyde and phenol emissions. The method for determining free phenol or free formaldehyde in filter media paper employed UV-VIS spectroscopy. To determine free phenol in paper, a test was performed with 4-aminoantipyrine at a wavelength of 510 nm in the presence of iron(lll) hexacyanide. To determine free formaldehyde in paper, a reaction using 3-methyl-2-benzothiazolinone hydrazone hydrochloride hydrate (MBTH) and iron(lll) chloride hexahydrate was performed at a wavelength of 628 nm. In case the paper contains formaldehyde, the reaction will proceed to a blue derivative.

[0140] The results are shown in Figure 6 and show an 80.3% reduction in formaldehyde emissions and an 81.6% reduction in phenol emissions for filter media impregnated with a resin comprising 30% of lignin compared to filter media impregnated with resol resin only.

[0141] Example 7

[0142] Oil filter media were prepared and impregnated with the above disclosed resin composition comprising lignin. The oil filter media were subjected to flow restriction test, filtration efficiency test and differential pressure test as defined in the ISO 4548-12 standard, the results of which are shown in Figure 7 , 8 and 9. The standard tests used correspond to a multi-pass filtration test with continuous contaminant injection and employ an on-line particle counting method to evaluate the performance of full-flow lubricating oil filter media for internal combustion engines. In addition, it was noted that the oil filter media were easy to pleat and did not emit smoke or odors during use.

[0143] Example 8

[0144] Heat resistance was tested at 140°C. The heat resistance test was performed as follows. Once the sample was fully cured, a burst strength test was performed and the value of this test was recorded (initial resistance value). Five other paper samples were housed in an oil bath apparatus which was filled with about 12 liters of SLX OW30 or 5W-30 oil. The oil bath apparatus was adjusted to a temperature of 140°C. Paper samples were gradually removed from the oil bath apparatus. More particularly, one paper sample was removed from the oil bath apparatus after 24 hours, 48 hours, 72 hours, 168 hours and 500 hours. Once the paper sample was removed from the oil bath apparatus, excess oil was removed with absorbent paper and the sample was placed in a climate chamber adjusted to 25°C and 50% relative humidity for 2 hours. After this time in the climate chamber, the sample was subjected to a burst strength test and the value obtained was recorded.

[0145] The results are shown in Figure 10 and show that the resin composition comprising lignin showed higher burst resistance than the resin without lignin at all time intervals.

[0146] Example 9

[0147] The filtration efficiency of planar filter medium samples impregnated with (i) 30% phenolic resin comprising lignin and (ii) phenolic resin without lignin were tested according to the test protocol defined above. The results are provided in Figure 11 , Figure 11 showing that the filter medium impregnated with the resin composition comprising lignin showed comparable filtration efficiency as the filter medium impregnated with the phenolic resin without lignin.

[0148] The application can be further understood by reference to the following paragraphs:

[0149] 1. Filter medium comprising a fibrous web impregnated with a resin composition comprising lignin, wherein:

[0150] the fibrous web comprises lignin in an amount of 0.1 to 30 weight-%, based on the weight of the fibrous web; and

[0151] the lignin has a density of less than 1.2 g / cm 3 or a weight average molecular weight of less than 20,000.

[0152] 2. Filter medium described in paragraph 1, wherein the lignin has a pH of less than 7, preferably 3 to 5, most preferably 4 to 4.5.

[0153] ​​3. The filter medium as described in paragraph 1 or 2, wherein the resin composition has a dynamic viscosity of less than 15 mPa.s.

[0154] 4. The filter medium as described in paragraph 3, wherein the resin composition has a dynamic viscosity of between 7.5-9.5 mPa.s.

[0155] 5. The filter medium as described in any of paragraphs 1 to 4, wherein the lignin has a density of less than 1 g / cm 3 , preferably between 0.20 g / cm 3 and 0.75 g / cm 3 , and more preferably between 0.25 g / cm 3 and 0.45 g / cm 3 .

[0156] 6. The filter medium as described in any of paragraphs 1 to 5, wherein the resin composition further comprises a formaldehyde scavenger having at least one primary or secondary amine functional group or is a polyamine.

[0157] 7. The filter medium as described in any of paragraphs 1 to 6, wherein the resin composition further comprises an epoxy component, such as a polyepoxide or a polyepoxy resin.

[0158] 8. The filter medium as described in any of paragraphs 1 to 7, wherein the resin composition comprises lignin and a phenolic resin, preferably in a lignin:phenolic resin weight ratio of 1 : 1 to 1 :9, preferably 1 : 1 to 1 :4, more preferably 1 :2.

[0159] 9. The filter medium as described in paragraph 8, wherein the phenolic resin is a resol.

[0160] 10. The filter medium as described in paragraph 8, wherein the phenolic resin is a novolak resin.

[0161] 11. The filter medium as described in any of paragraphs 1 to 7, wherein the resin composition comprises lignin and a latex resin, preferably in a lignin:latex resin weight ratio of 1 : 1 to 1 :9, preferably 1 : 1 to 1 :4, more preferably 1 :2.

[0162] 12. The filter medium as described in any of paragraphs 1 to 11, comprising 10 to 50 wt% of the resin composition.

[0163] 13. The filter medium as described in any of paragraphs 1 to 11, comprising 10 to 40 wt% of the resin composition.

[0164] 14. The filter medium described in any of paragraphs 1 to 11, comprising 10 to 30 weight percent of the resin composition.

[0165] 15. The filter medium described in any of paragraphs 1 to 10, wherein the lignin has a pH from 4 to 4.5 and a density between 0.25 g / cm 3 and 0.45 g / cm 3 , the resin composition comprises lignin and phenolic resin in a lignin:phenolic resin weight ratio of 1 : 1 to 1 :4, and the filter medium comprises 10 to 30 weight percent of the resin composition.

[0166] 16. The filter medium described in any of paragraphs 1 to 10, wherein the lignin has a pH from 4 to 4.5 and a density between 0.25 g / cm 3 and 0.45 g / cm 3 , the resin composition comprises lignin and phenolic resin in a lignin:phenolic resin weight ratio of 1 : 1 to 1 :4, and the resin composition further comprises a formaldehyde scavenger having at least one primary amine functional group, and the filter medium comprises 10 to 30 weight percent of the resin composition.

[0167] 17. The filter medium described in any of paragraphs 1 to 10, wherein the lignin has a pH from 4 to 4.5 and a density between 0.25 g / cm 3 and 0.45 g / cm 3 , the resin composition comprises lignin and phenolic resin in a lignin:phenolic resin weight ratio of 1 : 1 to 1 :4, and the resin composition further comprises a formaldehyde scavenger having at least one secondary amine functional group, and the filter medium comprises 10 to 30 weight percent of the resin composition.

[0168] 18. The filter medium described in any of paragraphs 1 to 10, wherein the lignin has a pH from 4 to 4.5 and a density between 0.25 g / cm 3 and 0.45 g / cm 3 , the resin composition comprises lignin and phenolic resin in a lignin:phenolic resin weight ratio of 1 : 1 to 1 :4, and the resin composition further comprises a formaldehyde scavenger that is a polyamine, and the filter medium comprises 10 to 30 weight percent of the resin composition.

[0169] 19. The filter medium described in any of paragraphs 1 to 18, wherein the fibrous web comprises at least 80 weight percent, preferably at least 90 weight percent, more preferably at least 95 weight percent of cellulosic fibers, based on the total weight of fibers.

[0170] 20. The filter medium according to any one of paragraphs 1 to 18, wherein the fibrous web comprises at least 80 wt.%, preferably at least 90 wt.%, more preferably at least 95 wt.% synthetic fibers, based on the total weight of fibers.

[0171] 21. The filter medium according to any one of paragraphs 1 to 18, wherein the fibrous web comprises a mixture of cellulosic fibers and synthetic fibers.

[0172] 22. The filter medium or method according to paragraph 21, wherein the synthetic fibers are present in the fibrous web in an amount of from 10 wt.% to 30 wt.% of the total weight of fibers.

[0173] 23. The filter medium according to paragraph 19 or 21, wherein the cellulosic fibers are selected from one or more of softwood fibers, hardwood fibers, plant fibers, and cellulose fibers.

[0174] 24. The filter medium according to paragraph 23, wherein the cellulosic fibers are regenerated cellulose fibers.

[0175] 25. The filter medium according to any one of paragraphs 1 to 24, wherein the filter medium is selected from the group consisting of oil filter media, air filter media, fuel filter media, hydraulic filter media, industrial filter media, dielectric fluid filter media, and water filter media.

[0176] 26. Use of the filter medium according to paragraph 25, wherein the air filter medium is used in a heavy duty panel filter, or in a load-type air panel filter.

[0177] 27. A method of manufacturing the filter medium according to any one of paragraphs 1 to 14, the method comprising impregnating a fibrous web with a resin composition comprising lignin and curing the impregnated fibrous web.

Claims

1. A filtration medium comprising a fibrous web impregnated with a resinous composition comprising lignin, wherein: the fibrous web comprises lignin in an amount of 0.1 to 30 weight percent, based on the weight of the fibrous web; and The lignin has a weight average molecular weight of less than 20,000 g / mol when measured according to the ASTM D4001-13 standard, the filter medium being characterized in that the lignin has a density of less than 1.2 g / cm 3 .

2. The filtration medium of claim 1, wherein the lignin has a pH of less than 7.

3. The filtration medium of claim 2, wherein the lignin has a pH of 3 to 5.

4. The filtration medium of any one of claims 1 to 3, wherein the resinous composition has a dynamic viscosity of less than 15 mPa.s.

5. The filter media of any of claims 1-3, wherein the lignin has a density of less than 1 g / cm 3 .

6. The filter media of claim 5, wherein the lignin has a density between 0.20 g / cm 3 and 0.75 g / cm 3 .

7. The filter media of claim 6, wherein the lignin has a density between 0.25 g / cm 3 and 0.45 g / cm 3 .

8. The filtration medium of any one of claims 1 to 3, wherein the resinous composition further comprises a formaldehyde scavenger that has at least one primary or secondary amine functional group or is a polyamine.

9. The filtration medium of any one of claims 1 to 3, wherein the resinous composition comprises lignin and phenolic resin in a lignin:phenolic resin weight ratio of 1:1 to 1:

9.

10. The filtration medium of claim 9, wherein the resinous composition comprises lignin and phenolic resin in a lignin:phenolic resin weight ratio of 1:1 to 1:

4.

11. The filtration medium of any one of claims 1 to 3, comprising 10 weight percent to 50 weight percent of the resinous composition.

12. The filtration medium of any one of claims 1 to 3, wherein the fibrous web comprises at least 95 weight percent cellulose fibers, based on the total weight of fibers.

13. The filtration medium of any one of claims 1 to 3, wherein the fibrous web comprises at least 95 weight percent synthetic fibers, based on the total weight of fibers.

14. The filtration medium of any one of claims 1 to 3, wherein the fibrous web comprises a mixture of cellulose fibers and synthetic fibers.

15. The filtration medium of claim 14, wherein the synthetic fibers are present in the fibrous web in an amount of up to 50 weight percent of the total weight of fibers.

16. The filtration medium of claim 15, wherein the synthetic fibers are present in the fibrous web in an amount of 10 weight percent to 30 weight percent of the total weight of fibers.

17. The filtration medium of claim 12, wherein the cellulose fibers are selected from one or more of softwood fibers, hardwood fibers, plant fibers, and regenerated cellulose fibers.

18. The filtration medium of any one of claims 1 to 3, wherein the filtration medium is selected from the group consisting of: industrial filtration media.

19. The filtration medium of any one of claims 1 to 3, wherein the filtration medium is selected from the group consisting of: oil filtration media, air filtration media, and water filtration media.

20. The filtration medium of any one of claims 1 to 3, wherein the filtration medium is selected from the group consisting of: fuel filtration media and hydraulic filtration media.

21. The filtration medium of any one of claims 1 to 3, wherein the filtration medium is selected from the group consisting of: dielectric fluid filtration media.

22. The filter media according to claim 19, wherein the filter media is an air filter media and is used in a heavy duty panel filter, or in a loaded air panel filter.

23. A method of making the filter media according to any one of claims 1 to 3, comprising impregnating a fibrous web with a resin composition comprising lignin and curing the impregnated fibrous web.

Images