WO2018184045A1

WO2018184045A1 - A nonwoven web designed for use as a hot cooking oil filter media

Info

Publication number: WO2018184045A1
Application number: PCT/AT2017/000026
Authority: WO
Inventors: Tom Carlyle; Mirko Einzmann; Gisela Goldhalm; Malcolm John Hayhurst; Katharina Mayer; Ibrahim SAGERER-FORIC
Original assignee: Lenzing Ag
Priority date: 2017-04-03
Filing date: 2017-04-03
Publication date: 2018-10-11

Abstract

This invention relates to a nonwoven material which has excellent dimensional and thermal stability in a wide variety of hot liquids, specifically for use as hot oil filter media, containing at least a first cellulosic nonwoven web, characterized in that the cellulosic nonwoven web is made from essentially pure cellulose formed of essentially continuous filaments which are multibonded by merged filaments, hydrogen bonding and physical intermingling of the filaments. Further it relates to composite nonwoven materials, where at least one web is characterized by being essentially pure cellulose formed of essentially continuous filaments which are multibonded by merged filaments, hydrogen bonding and physical intermingling of the filaments. The individual layers may, or may not, be designed to have different pore size construction to impart specific filtration performance efficiencies. It also relates to the use of the inventive nonwoven material as a hot oil filtration media, or product as well as to using of the inventive nonwoven material for the manufacture of a hot oil filter media, or product.

Description

A nonwoven web designed for use as a hot cooking oil filter media

This invention relates to a nonwoven web suitable to be used as a hot cooking oil filter media, and, more particularly, to an essentially pure cellulose nonwoven web formed from essentially continuous filaments and multibonded by merged filaments, hydrogen bonding and the physical intermingling of filaments. This web provides the wet strength and dimensional stability in hot oil, the ability to remove fine particulates, for multiple cleaning cycles, with no hot oil extractables and is able to qualify for indirect food contact.

The term "essentially pure cellulose" shall address the fact that cellulosic moulded bodies, e.g. made according to the lyocell process, always contain a small amount of polymers other than cellulose, namely hemicellulose. This does not influence in any way the suitability for the use according to this invention.

Prior Art

The use of nonwoven webs as hot oil filter media is well known, including filtering of the hot oil used for deep frying and cooking. U.S. 4,604,203 teaches the use of nonwoven sheets for filtering hot oil. U.S. 7,566,468 discloses the need for an efficient nonwoven filter media capable of removing all of the particulates in cooking oil in a single pass, while U.S. 20130183421 discloses the use of an efficient nonwoven capable or removing particulates down to 1 micron in size. U.S. 8,066,889 teaches the use of needlepunched polyester, while U.S. 20090250414 proposes the use of a nonwoven of polyester, polypropylene or nylon which shrinks in hot oil to a desired structure. U.S. 20110126925 discloses the use of nonwovens composed of polyester or rayon or combinations of polyester and rayon. U.S. 9,498,932 discloses the use of multilayer meltblown synthetic polymers for filtering liquids.

Nonwoven substrates for hot cooking oil filter media has been the subject of much research, as the requirements are stringent and demanding. For example, the nonwoven must be able to withstand extended periods of time immersed in oil at a temperature up to 400° F (-205° C), must be approved by appropriate regulatory agencies for indirect food contact, must be able to filter particulates down to 1 micron, and must be able to remove sufficient particulates at realistic pressure drops to make the filtering process

economically feasible. It must be durable enough to withstand multiple filtration cycles. Compostability would be an advantage for such a filter media, to simplify disposal.

Many types of nonwovens can be used for hot cooking oil filter media, including spunlace nonwovens, needlepunch nonwovens, airlaid nonwovens, wetlaid nonwovens, spunlaid nonwovens and chemical bonded nonwovens. All but spunlaid nonwovens employ primarily staple or cut fibres, or wood pulp. A spunlaid nonwoven consists of continuous filaments (either remaining as continuous or cut in the manufacturing process). One issue with spunlaid nonwovens is the thermal stability of the polymers used in hot oil up to 400° F (205° C). Polypropylene melts below this temperature. Most manufacturers do not recommend using polyester or standard nylon at above 162° C, with only high temperature nylons like Nomex being useful at 204° C to 232° C. These high temperature nylons are not commonly spunlaid. Spunlace, needlepunch, wetlaid and airlaid nonwovens can rely on cellulosic fibres, but they all share low strength and dimensional stability in prolonged immersion in hot oil and are not efficient at removing particulates down to 1 micron.

The present invention relates to the use of specially designed nonwoven substrates produced using novel variants of the spunlaid nonwoven process, comprising essentially pure cellulose polymers. There are known methods and products using spunlaid cellulose webs. U.S. 6,358,461 , U.S. 7,067,444, U.S. 8,012,565, U.S. 8,191 ,214, U.S. 8,263,506 and U.S. 8,318,318 as well as WO 98/26122, WO 99/47733, WO 98/07911 , US 6,197,230, WO 99/64649, WO 05/106085, EP 1 358 369, EP 2 013 390, WO 07/124521 A1 and WO 07/124522 A1 all teach methods for producing and using spunlaid cellulose webs. None of these teaches production methods for, or products,

addressing the specific requirements for hot cooking oil filtration media. Problem

Cooking oil is used in restaurants and in the food preparation industry for the cooking of various food items. One common use for cooking oil is in the cooking process known as deep-fat frying. Such frying is frequently carried out in containers of cooking oil, with the food to be cooked immersed in cooking oil that is heated to a temperature between about 250° F. and 400° F. (or about 121° C. and about 205° C). As food is introduced into the fryers and cooking transpires, the cooking oil becomes contaminated with suspended food particles, water, flour, breading, spices and other introduced

contaminants. These contaminants will react with themselves and/or other components of the hot cooking oil to degrade the hot oil, causing a change in colour, a change in alkalinity or acidity, a reduction in thermal efficiency and an increase in the potential for smoking or burning. In addition, dispersed and suspended particulates can consume some of the energy of the hot oil, causing increasing cooking times and heating energy needs. Over time heat will cause suspended particles to become charred or carbonized. This carbonization is frequently accompanied by chemical breakdown of the cooking oil, resulting in the production of impurities such as free fatty acids, alkalines and other polar compounds. These contaminants can degrade the oil. Additionally, these contaminants can negatively affect food during the frying process, adversely affecting the taste of the food and/or creating negative health issues.

Restaurants frequently fry food items in batches, and they generally do not discard the cooking oil after cooking a single batch. Filtration is commonly employed to reduce contaminants and to extend the useful life of the cooking oil. In typical restaurant operations, the cooking oil in a deep-fat fryer is filtered once or twice each day, most often by employing a portable batch-type filtration device. However, despite such filtration, a typical restaurant facility that utilizes a conventional filtration process generally discards its cooking oil every five to ten days due to accumulated particulate contamination and degradation.

Conventional filtration devices generally operate by draining the cooking oil from the fryer into a filtration container and then cycling the cooking oil through a filter. Generally, when the filtration operation is begun, the cooking oil is at or near cooking temperature, and batch filtration continues until a subjective determination is made that the filtering process has achieved a desired result. After filtration, usually comprising multiple passes through the filter, the filtered cooking oil is returned to the fryer. It is not unusual for cooking oil to be filtered by passing it through a conventional filter for 30 minutes or longer. Depending on the amount of time elapsed during filtration, the cooking oil may be as much as 285° F. (140° C.) or more below cooking temperature when it is returned to the fryer. Consequently, the filtered oil must be heated to increase it to cooking temperature prior to resuming cooking operations.

Particulate removal is the purpose of filtration. The efficiency of a specific filter material is measured by the size of the particulate material that it can filter, the amount of particulate that can be retained, and the volume of hot oil that can flow through the filter in a given period of time at the operating pressure of the filtration device. Conventional filters often become laden with particulate material from the frying process in high volume operations, thus making it difficult to maintain an adequate flow of cooking oil through the filter. Under such circumstances, the speed of filtration is greatly reduced. Consequently, fryer operators may attempt to scrape the filter surface to reduce the accumulated particulate to increase the filtration flow.

Conventional filters used in filtration devices include those comprised of paper, nonwovens including latex bonded wetlaid nonwovens and spunlaid polymers, and metal screens. Some filtration devices employ flat filters that are retained in a support frame; others employ filter envelopes that wrap around a grid or frame. Conventional filter media types vary in their

effectiveness. Paper filters are inexpensive; however, paper filters are fragile and are frequently damaged if scraped to remove accumulated particulate. Paper filters cannot generally be used for multiple filtration cycles.

Consequently, if a restaurant filters its cooking oil twice a day using paper filters, it will most likely use two filters each day. Paper filters provide limited separation efficiency, retaining particles within the range of 20-30 microns and larger. Cellulose based nonwovens also are susceptible to damage if scraped. Most are not usable for multiple filtration cycles. Cellulose based nonwovens retain particles within the range of 1-5 microns and larger. Spunlaid

nonwovens can retain fine particles in the range of 1-5 microns, and such nonwovens are most capable of reuse. But spunlaid nonwovens usually are affected by the temperatures of the oil being filtered, either damaging the filter material or requiring cooling of the oil prior to filtering. Stainless steel filter screens are durable and may be reused indefinitely, but they are considerably more expensive than paper filters and nonwovens. They provide only limited filtration efficiency, retaining particles within the range of 80-120 microns and larger.

Conventional filters generally provide passive surface filtration, in which the cooking oil is drawn through the filter surface by vacuum, retaining particles from the oil on the filter surface. To provide a measure of depth filtration, cooking oil to be filtered must be circulated through paper filters, nonwovens and metal screen filters for 3-5 minutes in order to build a filter cake of particulates to effectively enhance the filtration efficiency. The creation of such a filter cake provides pore structures for retaining particulate during

subsequent filtration. Sometimes, a powdered filter aid is used with

conventional filter materials to increase filtration efficiency, primarily by increasing depth filtration. Such filter aids are dispersed in the cooking oil and form a powder cake on the filter surface (along with accumulated particulate contaminants) to increase the filtration surface area, and thereby enhance the removal of relatively small particles. Such filter powder, when accumulated as a filter cake on the filter, provides a plurality of channels permeable to liquid, yet more effective in mechanically filtering small particulates. The addition of a powdered filter aid thus provides additional depth filtration and generally results in the removal of smaller particles than can be removed by filtering through paper, cellulose pad or metal screen filters alone. For example, a use of paper filters in conjunction with a powdered filter aid will generally result in the retention of particles within the range of 1-5 microns and larger. A use of stainless steel filter screens in conjunction with a powdered filter aid will generally result in the retention of particles within the range of 5-10 microns and larger. Nonwovens can be produced which preclude the need for such filter aids.

Generally, the quantity of contaminants removed during the filtration process depends on the type of filter material used, the presence of filter aids used and the filtration time.

Although filters of spunlaid nonwovens have been employed for solid-liquid separation in other wet and dry applications, the use of such materials for filtering cooking oils is not common because the relatively high cooking temperatures involved are generally at or above the recommended application temperatures for such nonwovens.

A filter material is needed for hot cooking oil operations that is more efficient than conventional filter materials, like paper, wetlaid nonwovens or even steel mesh. It is also required that this filter material be strong and durable and dimensionally stable enough when filtering hot oil to be usable for multiple filtering and cleaning cycles. Biodegradability and sustainability are also desired. Any material used for filtering hot cooking oil must be safe for indirect food contact.

Any filter material based on polypropylene or polyester will be durable and dimensionally stable at normal temperatures, but not at the elevated temperatures at which hot cooking oil is filtered. Any filter material based on cellulosic or other staple fibres are usually not durable to multiple cycles. Metal based filters are durable to hot oil, but cannot filter out the 1-5 micron particulates as required.

The optimal product has the filtration efficiency to remove particulates of 1-5 microns, and the durability, strength and dimensional stability in hot cooking oil to survive multiple cleaning cycles. Description

It is an object of the present invention to provide a nonwoven material which has excellent dimensional stability in hot oil at temperatures up to 400° F (~205° C) for use in hot oil filter media, containing at least a first cellulosic nonwoven web, wherein the cellulosic nonwoven web is made from

essentially pure cellulose formed of essentially continuous filaments which are multibonded by merged filaments, hydrogen bonding and physical

intermingling of the filaments. The nonwoven web is produced using a spunbond or meltblown die or head to form the continuous filaments, in principle known from the prior art cited above.

This web will provide the ability to filter 1-5 micron particulates, as well as strength, durability and dimensional stability during filtration of hot cooking oil at temperatures as high as 400° F. (or about 205° C.) and retains these properties through multiple filtration cycles. This web is biodegradable, compostable, made from a sustainable manufacturing process, and is able to qualify for indirect food contact.

In particular the invention is directed to hot cooking oil filtration and to hot cooking oil filter media. But the specific properties of the material of the invention can be used for other filtration applications in a beneficial way, as well, in particular for the filtration of other liquid media at temperatures up to 400° F (-205° C), provided that the media are compatible with the cellulose.

Preferably the nonwoven material according to the invention is further bonded or treated by a hydroentanglement, needlepunch or chemical bonding process to modify the physical properties.

This invention can also exist in a multi-layer structure of the same essentially continuous filaments and multibonded by merged filaments, hydrogen bonding and/or the physical intermingling of filaments. In this multi-layer structure, each layer can consist of different pore size construction by controlling the filament diameter, the degree of merged filaments and the thickness of each layer. In said multi-layer structure it is possible to provide a gradient of decreasing pore size to maximize filtration efficiency and minimize the pressure drop across the filter media. These layers can be produced in a single process where multiple layers are formed on top of one another, or produced in a separate step where the layers are laminated together via bonding processes such as adhesive bonding, hydroentangling,

needlepunching and/or chemical bonding.

In particular preferred the first cellulosic nonwoven web of the nonwoven material according to the invention is made according to a lyocell process.

Cellulosic fibres can be produced by various processes. In one embodiment a lyocell fibre is spun from cellulose dissolved in N-methyl morpholine N-oxide (NMMO) by a meltblown process, in principle known from e.g. EP 1093536 B1 , EP 2013390 B1 and EP 2212456 B1. Where the term meltblown is used it will be understood that it refers to a process that is similar or analogous to the process used for the production of synthetic thermoplastic fibres (filaments are extruded under pressure through nozzles and stretched to required degree by high velocity/high temperature extension air flowing substantially parallel to the filament direction), even though the cellulose is dissolved in solution (i.e. not a molten thermoplastic) and the spinning & air temperatures are only moderately elevated. Therefore the term "solution blown" may be even more appropriate here instead of the term "meltblown" which has already become somewhat common for these kinds of technologies. For the purposes of the present invention both terms can be used synonymously. In another embodiment the web is formed by a spun bonding process, where filaments are stretched via lower temperature air. In general, spunbonded synthetic fibres are longer than meltblown synthetic fibres which usually come in discrete shorter lengths. Fibres formed by the solution blown lyocell process can be continuous or discontinuous depending on process conditions such as extension air velocity, air pressure, air temperature, viscosity of the solution, cellulose molecular weight and distribution and combinations thereof.

In one embodiment for making a nonwoven web the fibres are contacted with a non-solvent such as water (or water/NMMO mixture) by spraying, after extrusion but before web formation. The fibres are subsequently taken up on a moving foraminous support to form a nonwoven web, washed and dried.

Freshly-extruded lyocell solution ('solvent spun', which will contain only, for example, 5-15% cellulose) behaves in a similar way to 'sticky' and deformable thermoplastic filaments. Causing the freshly-spun filaments to contact each other while still swollen with solvent and with a 'sticky' surface under even low pressure will cause merged filament bonding, where molecules from one filament mix irreversibly with molecules from a different filament. Once the solvent is removed and coagulation of filaments completed, this type of bonding is impossible.

It is another object of the present invention to provide a process for the manufacture of a nonwoven material consisting of essentially continuous cellulosic filaments by:

a. Preparation of a cellulose-containing spinning solution

b. Extrusion of the spinning solution through at least one spinneret containing closely-spaced meltblown jet nozzles

c. Attenuation of the extruded spinning solution using high velocity air streams,

d. Forming of the web onto a moving surface [e.g. a perforated belt or drum], e. Washing of the formed web

f. Drying of the washed web

wherein in step c. and/or d. coagulation liquor, i.e. a liquid which is able to cause coagulation of the dissolved cellulose; in a lyocell process this preferably is water or a diluted solution of NMMO in water, is applied to control the merged filament bonding. The amount of merged filament bonding is directly dependent on the stage of coagulation of the filaments when the filaments come into contact. The earlier in the coagulation process that the filaments come into contact, the greater the degree of filament merging that is possible. Both placement of the coagulation liquor application and the speed at which the application liquor is applied can either increase, or decrease, the rate of coagulation. Which results in control of the degree (or amount) of merged filament bonding that occurs in the material. Preferably the merged filament bonding is further controlled by filament spinning nozzle design and arrangement and the configuration and temperature of filament extension air. The degree of molecular alignment that is present as the solution exits the spinning nozzle has an impact on the coagulation rate. The more aligned the molecules are, the faster the coagulation rate, and conversely, the less aligned the molecules are, the slower the coagulation rate. The spinning nozzle design and arrangement, along with the molecular weight of the cellulosic raw material used will determine the starting coagulation rate at the exit of the spinning nozzle. Additionally, the rate of cooling (temperature decrease) of the solution upon spinning nozzle exit will impact the coagulation rate as well. The slower the cooling rate, the slower the coagulation rate, and conversely, the faster the cooling rate, the faster the coagulation rate. Therefore, configuration of the filament extension air can directing impact the cooling rate and therefore, impact the coagulation rate, which impacts the achievable amount of merged filament bonding that is possible.

In a preferred embodiment of the process according to the invention at least two spinnerets (also known as jets), preferably between two and ten, and further preferred between 2 and 6, each one arranged to form a layer of nonwoven web, are used to obtain a multilayer nonwoven material. By applying different process conditions at the individual spinnerets it is even possible to obtain a multilayer nonwoven material wherein the individual layers have different properties. This may be useful to optimize the nonwoven material according to the invention for different applications. In one

embodiment this could provide a gradient of filament diameters from one side of the material to the other side by having each individual web having a standard filament diameter that is less than the web on top, it is possible to create a material suitable for use as an air filter media that will provide a gradient of pore size (particle size capture). This will provide an efficient filtration process and result in a lower pressure drop across the filter media compared to a single web with similar characteristics at the same basis weight and pore size distribution. Preferably the filaments are spun using a solution of cellulose in an aqueous amine oxide and the coagulation liquor is water, preferably with a content of amine oxide not being able to dissolve cellulose, also referred to as a lyocell process; the manufacture of such a solution is in principle known, e.g. from U.S. 6,358,461 , U.S. 7,067,444, U.S. No. 8,012,565, U.S. 8,191 ,214, U.S. 8,263,506 and U.S. 8,318,318; preferably the amine oxide is NMMO.

The present invention describes a cellulosic nonwoven web produced via a meltblown or spunbond-type process. The filaments produced are subjected to touching and/or compaction and/or intermingling at various points in the process, particularly before and during initial web formation. Contact between filaments where a high proportion of solvent is still present and the filaments are still swollen with said solvent causes merged filament bonding to occur. The amount of solvent present as well as temperature and contact pressure (for example resulting from extension air) controls the amount of this bonding.

In particular the amount of filament intermingling and hydrogen bonding can be limited by the degree of merged filament bonding. This is the result of a decrease in filament surface area and a decrease in the degree of flexibility of the filaments. For instance, as the degree of merged filament bonding increase, the amount of overall surface area is decreased, and the ability of cellulose to form hydrogen bonds is directly dependent on the amount of hydroxyl groups present on the cellulosic surface. Additionally, filament intermingling happens as the filaments contact the forming belt. The filaments are traveling at a faster rate of speed than the forming belt. Therefore, as the filament contacts the belt, it will buckle and sway side to side, and back and forth, just above the forming belt. During this buckling and swaying, the filaments will intermingle with neighboring filaments. If the filaments touch and merge prior to the forming belt, this limits the number of neighboring filaments by which it can intermingle with. Additionally, filaments that merge prior to contacting the forming belt with not have the same degree of flexibility as a single filament and this will limit the total area over which the filament will buckle and sway. Surprisingly, it has been found that high levels of control of filament merging can be achieved by modifying key process variables. In addition, physical intermingling of at least partially coagulated cellulose filaments can occur after initial contact with non-solvent, particularly at initial filament laydown to form the web. It arises from the potential of the essentially continuous filaments to move laterally during initial filament formation and initial laydown. Degree of physical intermingling is influenced by process conditions such as residual extension air velocity at the foraminous support (forming belt). It is completely different from the intermingling used in production of webs derived from cellulose staple fibers. For staple fibers, an additional process step such as calendaring is applied after the web has been formed. Filaments which still contain some residual solvent are weak, tender and prone to damage.

Therefore, in combination with controlling degree and type of bonding at this stage, it is essential that process conditions are not of a type which could cause filament and web damage. Initial drying of the washed but never-dried nonwoven, together with optionally compacting, will cause additional hydrogen bonding between filaments to develop. Modifying temperature, compacting pressure or moisture levels can control the degree of this hydrogen bonding. Such treatment has no effect on intermingling or the merged filament bonding.

In a preferred embodiment of the invention the nonwoven material is dried prior to subsequent bonding/treatment.

In a preferred embodiment of the invention the percentage of each type of bonding is controlled using a process with up to two compaction steps, where one of these compaction steps is done after step d. of the inventive process where the spun filaments are still swollen with a solvent, and one of these compaction steps is done before or in step e. of the inventive process where all or most of the solvent has been removed and the web has been wet with water. As previously discussed, control of the coagulation of the spun solution is a factor in controlling the degree of merged filament bonding. This preferred embodiment concerns decreasing the coagulation rate to a state where additional compaction steps can be used after filament laydown to further increase the actual amount of merged filament boding that is achievable. It might be helpful to view the maximum achievable filament bonding as the state where we have merged all filaments into an essentially film-like structure.

The present invention describes a process and product where merged filament bonding, physical intermingling and hydrogen bonding can be controlled independently. However, the degree of merged filament bonding can limit the degree of physical intermingling and hydrogen bonding that can occur. In addition, for the production of multi-layer web products, process conditions can be adjusted to optimise these bonding mechanisms between layers. This can include modifying ease of delamination of layers, if required.

In addition to merged filament, intermingling and hydrogen bonding being independently set as described above, additional bonding/treatment steps may optionally be added. These bonding/treatment steps may occur while the web is still wet with water, or dried (either fully or partially). These

bonding/treatment steps may add additional bonding and/or other web property modification. These other bonding/treatment steps include hydroentangling or spunlacing, needling or needlepunching, adhesive or chemically bonding. As will be familiar to those skilled in the art, various post- treatments to the web may also be applied to achieve specific product performance. By contrast, when post-treatments are not required, it is possible to apply finishes and other chemical treatments directly to the web of this invention during production which will not then be removed, as occurs with, for example, a post-treatment hydroentanglement step.

Varying the degree of merged filament bonding provides unique property characteristics for nonwoven cellulose webs with regards to softness, stiffness, dimensional stability and various other properties. Properties may also be modified by altering the degree of physical intermingling before and during initial web formation. It is also possible to influence hydrogen bonding, but the desired effect of this on web properties is minor. Additionally, properties can be adjusted further by including an additional

bonding/treatment step such as hydroentangling, needlepunching, adhesive bonding and/or chemical bonding. Each type of bonding/treatment provides benefits to the nonwoven web. For example, hydroentangling can add some strength and soften the web as well as potentially modifying bulk density; needling is typically employed for higher basis weights and used to provide additional strength; adhesive and chemical bonding can add both strength and surface treatments, like abrasive material, tackifiers, or even surface lubricants.

The present invention allows independent control of the key web bonding features: merged filaments, intermingling at web formation, hydrogen bonding and optional additional downstream processing. Manipulation of merged filament bonding can be varied to predominantly dictate the properties of the nonwoven web.

In a preferred embodiment of the invention the nonwoven material comprises a second cellulosic nonwoven web, which is essentially formed of continuous filaments, pulp fiber or staple fiber, is formed on top of the first cellulosic nonwoven web, and subsequently both layers are hydroentangled together.

In another preferred embodiment of the invention the nonwoven material comprises multiple layers of nonwoven webs, suitable for use as hot oil filtration media, wherein at least one layer is essentially pure cellulosic material formed of essentially continuous filaments and is bonded by merged fibers, hydrogen bonding and physical intermingling of filaments and subsequently at least two of these layers are hydroentangled together. In a specific embodiment of the invention all layers within the nonwoven material are essentially pure cellulosic material formed of essentially continuous filaments and are bonded by merged fibers, hydrogen bonding and physical intermingling of filaments and subsequently all of these layers are

hydroentangled together.

In a preferred embodiment of the invention the individual layers within the two- or multilayer nonwoven material are designed to have different pore size construction to impart specific filtration performance efficiencies. Most preferably the individual layers in the nonwoven material are assembled in a sequence suitable to provide a gradient of decreasing pore size in flow direction to maximize filtration efficiency and minimize the pressure drop across the filter media.

Another object of the present invention is the use of the nonwoven material according to the invention for hot oil filtration, in particular hot cooking oil filtration as well as the use of this nonwoven material for the manufacture of a hot oil filter media, in particular a hot cooking oil filter media.

Another object of the present invention is a hot oil filter media which contains a nonwoven material according to the invention.

The invention will now be illustrated by examples. These examples are not limiting the scope of the invention in any way. The invention includes also any other embodiments which are based on the same inventive concept

Examples

All samples for testing were conditioned at 23°C ±2°C and relative humidity 50% ±5% for 24 hours.

Example 1

Tensile properties and stiffness of a 50 gsm sample of the product of the invention (single layer) was compared to a commercial product of same basis weight comprising 100% cellulosic staple fiber (lyocell). Tensile properties were measured using standard method DIN EN 29 073 part 3/ISO 9073-3, although a clamping length of 8cm rather than 20cm was used.

The product of invention had comparable tensile strength with the commercial sample but the elongation in both MD and CD was 4 times less than the commercial sample.

Stiffness was measured using a 'Handle-o-meter', using standard method WSP 90.3, with ¼ inch slot width, stainless steel surface, 1000 g beam.

Sample size was to 10cm x 10cm. Overall stiffness of the product of the invention was double that of the commercial sample. As the product of invention shows less elongation and higher stiffness compared to the commercial sample, it is more able to retain its dimensional structure while under pressure during the hot oil filtration process.

Example 2

A product of the invention comprising multiple layers of the inventive nonwoven in which each layer consists of different filament diameters, and thereby exhibits different pore construction. Layer A is comprised of coarse filaments and coarse filter pores for coarse particle filtration followed by Layer B of fine filaments and fine filter pores for fine particle filtration. This prevents early filter blocking and increases filter lifetime.

Claims

1. A nonwoven material which has excellent dimensional stability in hot oil at temperatures up to 400° F (~205° C) for use in hot oil filter media, containing at least a first cellulosic nonwoven web, characterized in that the cellulosic nonwoven web is made from essentially pure cellulose formed of essentially continuous filaments which are multibonded by merged filaments, hydrogen bonding and physical intermingling of the filaments.

2. The nonwoven material of Claim 1 that is further bonded or treated by a hydroentanglement, needlepunch or chemical bonding process to modify the physical properties.

3. The nonwoven material of Claim 1 where the first cellulosic nonwoven web is made according to a lyocell process.

4. The nonwoven material of Claim 1 where a second cellulosic nonwoven web, which is essentially formed of continuous filaments, pulp fiber or staple fiber, is formed on top of the first cellulosic nonwoven web, and subsequently both layers are hydroentangled together.

5. The nonwoven material of claim 1 comprising multiple layers of nonwoven webs, suitable for use as hot oil filtration media, wherein at least one layer is essentially pure cellulosic material formed of essentially continuous filaments and is bonded by merged fibers, hydrogen bonding and physical intermingling of filaments and subsequently at least two of these layers are hydroentangled together.

6. The nonwoven material of claim 4 or 5, where the individual layers are designed to have different pore size construction to impart specific filtration performance efficiencies.

7. The nonwoven material of claim 6, where the individual layers are assembled in a sequence suitable to provide a gradient of decreasing pore size in flow direction to maximize filtration efficiency and minimize the pressure drop across the filter media.

8. Use of the nonwoven material of claim 1 for hot oil filtration, in particular hot cooking oil filtration.

9. Use of the nonwoven material of claim 1 for the manufacture of a hot oil filter media, in particular a hot cooking oil filter media. Hot oil filter media characterized in that it contains a nonwoven material according to claim 1.