DE102014211021A1 - Impregnated filter materials and filter elements made therefrom - Google Patents

Abstract

The invention relates to a process for producing an impregnated filter material from a woven fabric, a drained nonwoven fabric or a wet laid nonwoven fabric and a particulate binder, and an impregnated filter material obtainable thereby. The particulate binder is distributed uniformly in at least part of the impregnated filter material.

Description

FIELD OF THE INVENTION

The invention relates to a process for the preparation of impregnated filter materials, in which particulate binders are used, as well as impregnated filter materials obtainable therefrom and filter elements produced therefrom.

STATE OF THE ART

Impregnated filter materials are used today in many areas of gas and liquid filtration. In the simplest case, such an impregnated filter material consists of a carrier made of paper, synthetic fleece, fabric or foam, which is impregnated with a polymeric binder. Impregnation is required to render the impregnated filter material resistant to adverse conditions such as heat, moisture or aggressive fluids. In addition, the impregnation gives the impregnated filter material the strength, rigidity and foldability required for its further processing and application.

The most common are impregnated filter materials which are impregnated with a liquid, polymeric binder. These binders can be divided into two groups. One group is the binders dissolved or dispersed in water, such as melamine-formaldehyde solutions or resin dispersions, also called latex. The second group is formed by the binders dissolved in an organic solvent, such as phenolic resins or epoxy resins.

The German patent DE 10 2009 006 586 A1 describes, for example, an impregnated filter material which has been impregnated with binders dissolved in water or organic solvents.

In the patent US 2,918,173 A discloses an impregnated filter material having an aqueous dispersion as a binder.

Although liquid impregnating agents are very widespread, they also have many disadvantages. First, the solvent compatibility of the binder to be used for the process of impregnation is a mandatory requirement. Furthermore, both the water and the organic solvents must be removed from the filter material after impregnation. The necessary drying process is very energy intensive. The use of organic solvents adds to the health risk to employees. In addition, organic solvents must be collected consuming and disposed of in an environmentally friendly manner. For flammable solvents, attention must also be paid to explosion protection.

Liquid impregnating agents are susceptible to migration, which means that the binder polymers can migrate to the outside during drying. This results in an enrichment of the binder on the two surfaces of the impregnated filter material, while the center is depleted of binder. As a result, the strength of the impregnated filter material suffers. Too high a binder concentration undesirably reduces the pores on the surface of the impregnated filter material. This effect is particularly pronounced in the case of the use of long-chain polymers, for example polymer dispersions in water. Long-chain polymers tend to form a film between the individual fibers during drying and thus greatly reduce the pore cross-section. The expert calls this "sail formation". The sails shorten the life of the filters, because the impregnated filter material is quickly added to the surface due to the reduced pore cross-section.

In the past, therefore, attempts have been made to overcome these disadvantages by alternative impregnation methods.

The publication DE 10 2005 032 395 A1 discloses an impregnated filter material obtained by soaking a fiber material with a radiation curing resin and then curing it by irradiation with, for example, UV light or electron beam radiation. A disadvantage of this method is that the fibers of the fiber material cast shadows and the binder is not or only insufficiently cured in these shadows. The presence of oxygen in the fiber material can also lead to an inhibition of the free-radical polymerization, as a result of which the binder is also insufficiently cured. In addition, radiation-curing resins are generally highly viscous Liquids that often form a film between the individual fibers of the material when cured. This leads to undesirable "sail formation".

Another attempt to avoid the disadvantages of impregnating a fiber material with liquid binders, is in the document WO 95/04857 A1 described. In the preparation of the impregnated filter paper, a particulate binder is added to the pulp, which melts upon drying and solidifies the paper. Particulate binders in the pulp but have the disadvantage that a large part of the binder is discharged in the dewatering of the formed paper web on the papermaking fabric with the filtered water and does not remain in the paper. In addition, the particulate binders melt on drying in the paper machine and cause sticking of the paper web to the hot surfaces of the drying cylinders. Furthermore, the dewatering of the formed paper web on the papermaker's fabric causes, above all, finer binder particles to be washed out with the excess water from the interior of the paper layer so that a relatively high concentration of fine binder particles occurs on the surface of the resulting paper material. This is especially true for the lower surface of the paper layer. The uneven distribution of the binder in the resulting filter material adversely affects its permeability and mechanical strength.

In the publication US 4,983,193 A An impregnated filter material for air filters and air conditioners is described, which is impregnated with a dry, particulate binder. By applying the binder to only one side of the fibrous material and then densifying the resulting impregnated filter material under heat, an impregnated filter material is obtained having a decreasing concentration of binder and a decreasing degree of compaction seen from one side to the other. It is expressly pointed out that only nonwovens which have a very low fiber density of about 7 × 10 ^-4 to 10 ^-2 , ie are very fluffy, are suitable for producing such an impregnated filter material. However, such nonwovens are mechanically very unstable and very difficult to handle in large-scale manufacturing processes. Thus, the corresponding filter materials are not suitable for filtration of liquids in which the filter material is exposed to much higher mechanical loads.

The object of the present invention was therefore to provide a method for producing an impregnated filter material which does not have the disadvantages listed. The impregnated filter materials obtainable by the process should have sufficiently high mechanical strength and rigidity to enable their long-term use in both gas filtration and liquid filtration.

SUMMARY OF THE INVENTION

• a) Gleichmäßige Imprägnierung eines Fasermaterials, das vorzugsweise eine mittlere Faserdichte von nicht weniger als 0,003, mehr bevorzugt von nicht weniger als 0,01 hat, und aus der Gruppe bestehend aus einem Gewebe, einem nassgelegten Vlies und einem trockengelegten Vlies ausgewählt ist, mit mindestens einem partikelförmigen Bindemittel;
• b) Wärmebehandlung des Materials aus dem Schritt a), wobei das partikelförmige Bindemittel zumindest teilweise aufgeschmolzen wird.

The first aspect of the present invention relates to a method for producing an impregnated filter material, characterized in that the method comprises the following steps:

• a) uniform impregnation of a fibrous material which preferably has an average fiber density of not less than 0.003, more preferably not less than 0.01, and is selected from the group consisting of a fabric, a wet laid nonwoven and a drained nonwoven, with at least a particulate binder;
• b) heat treatment of the material from step a), wherein the particulate binder is at least partially melted.

In step a), the particles of the particulate binder in the fiber material are evenly distributed. By a subsequent heat treatment of the material in step b), the particles of the particulate binder are at least partially melted. This includes the case that only a part of the particles of the particulate binder are melted therein, while the remaining particles of the particulate binder are merely softened and are still discernible as discrete particles, and also the case that individual particles are only partially melted. In partial melting, the binder particles are firmly bonded by adhesive forces with fibers of the fiber material. Thus, the binder can not be removed from the impregnated filter material by mechanical stresses that are common in the use of impregnated filter materials. The impregnated filter material according to the invention thus has a significantly higher bursting strength and permeability to gaseous and liquid media than conventionally impregnated filter materials.

Advantageously, the proportion of molten particles of the particulate binder in the impregnated filter material according to the invention ≥ 90 wt .-%, more preferably ≥ 95 wt .-% based on the mass of the particulate binder used in total.

Preferably, the heat treatment in step b) comprises a first heat treatment step and a second heat treatment step, wherein the temperature of the impregnated filter material in the second heat treatment step is above the melting temperature of the particulate binder. The temperature in the first heat treatment step can be chosen so that it only comes to a softening of the binder particles, whereby these are firmly connected by adhesion forces with fibers of the fiber material. The binder particles are then visible in the microscope as discrete particles. The product obtained after the first heat treatment step is sometimes referred to herein as "semi-finished impregnated product". The impregnated semi-finished product is subjected to a second heat treatment step in which the binder is largely melted and optionally cured or crosslinked. Thus, the impregnated filter material of the invention obtains excellent mechanical strength. Incidentally, in the present specification, curing and crosslinking, and therefore also hardeners and crosslinkers, are understood synonymously.

In a further preferred embodiment, the impregnated semi-finished product may be subjected to mechanical processing before being subjected to the second heat treatment step. Examples of the mechanical processing are u. a. Creasing, embossing, transverse shafts, longitudinal creasing or cutting of the impregnated semi-finished product.

Another aspect of the present invention is the impregnated filter material obtainable from a fibrous material by the method of the invention.

According to one embodiment, it is an impregnated filter material based on a fiber material selected from the group consisting of a fabric, a wet-laid nonwoven and a drained nonwoven, and preferably has an average fiber density of not less than 0.003, more preferably not less than 0.01 and characterized in that at least a portion of the fiber material in the thickness direction is uniformly impregnated with a particulate binder, which is at least partially melted. In this embodiment of the impregnated filter material according to the invention, preferably at least one particle of the particulate binder is present in discrete form, and more preferably at least one particle of the particulate binder per mm ^{3 of} the binder-uniformly impregnated region of the fiber material is in discrete form.

When it is said in this specification that particles of the particulate binder are in discrete form, this means that when representative cross-sections of the impregnated filter material, preferably using an optical microscope, are still recognizable as delimited units, without being confused with the particles other particles to be connected to a uniform binder phase. Such a uniform binder phase is observed in fiber materials impregnated with conventional liquid binders.

In a preferred embodiment, the binder in the impregnated filter material according to the invention contains at least one thermoplastic polymer.

In a further preferred embodiment, the binder has a melting temperature which is at least 5 ° C below the lowest melting temperature of the fibers of the fiber material.

The fibers of the fiber material may be at least partially multicomponent fibers and the binder may have a melting temperature that is at least 5 ° C below the melting temperature of the higher melting component of multicomponent fibers of the fiber material.

The impregnated filter material according to the invention preferably has a gap strength of at least 1.5 N / 25 mm, preferably of at least 2.0 N / 25 mm.

Another aspect of the present invention is a filter element comprising the impregnated filter material of the invention.

In another aspect, the present invention relates to the use of an impregnated filter material obtainable by a process according to any one of claims 1 to 10 for the filtration of liquids, especially fuels and oils.

DETAILED DESCRIPTION OF THE INVENTION

The impregnated filter material of the present invention has excellent mechanical stability and high permeability, enabling its use for filtration of fluids such as gases and liquids. Thus, the impregnated filter material according to the invention differs fundamentally from known from the prior art and largely impermeable composite materials.

The impregnated filter material according to the invention comprises at least one fiber material selected from the group consisting of wet-laid nonwovens, drained nonwovens such. Dry laid staple fiber webs and fabrics.

Under drained nonwovens u. a. Dry laid fiber webs such as dry laid Stapelfaservliese, Meltblownvliese and spunbonded to understand.

Dry laid staple fiber webs consist of fibers of finite length. Both natural and synthetic fibers can be used to produce dry laid staple fiber webs. Examples of natural fibers are cellulose, wool, cotton, flax. Synthetic fibers are, for example, polyolefin fibers, polyester fibers, polyamide fibers, polytetrafluoroethylene fibers, polyphenylene sulfide fibers. The fibers used can either be straight or crimped. For solidification, the air-laid staple fiber fleece can contain one-component or multi-component meltbond fibers which melt completely or partially at a temperature below the melting temperature of the other fibers and solidify the fleece. The preparation of the air-laid Stapelfaservliese takes place according to the known prior art as in the book "Nonwovens, W. Albrecht, H. Fuchs, Wiley-VCH, 2012" described. The dried Stapelfaservliese can be solidified by the aforementioned one- or multi-component meltbonding fibers. Other solidification options are, for example, needling, water jet needling or soaking or spraying the fleece with liquid binders followed by drying.

Meltblown nonwovens consist of polymeric continuous fibers. To produce the meltblown nonwoven fabric for the filter material according to the invention, the meltblown process known in the art is used, as described, for example, in US Pat. In A. van Wente, "Superfine Thermoplastic Fibers", Industrial Engineering Chemistry, Vol. 48, pp. 1342-1346 is described. Suitable polymers are, for example, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polyamide, polyphenylene sulfide, polyolefin, polycarbonate. The typical fiber diameter range between 0.5-10 μm, preferably between 0.5-3 μm. Depending on the requirements, it is also possible to add additives such as crystallization accelerators or paints to the polymers. In addition, if necessary, the meltblown webs can be densified by means of a calender.

Spunbonded nonwovens are also made of polymeric filaments whose fiber diameter is usually much larger than that of meltblown fibers. Spun nonwovens are produced by the spunbonding process known to the experts, as described, for example, in the patents US 4,340,563 A . US Pat. No. 3,802,817 . US 3,855,046 A and US 3,692,618 A is described. For the spunbonding process suitable polymers are, for. For example, polyethylene terephthalate, polybutylene terephthalate, polyethylene naphthalate, polybutylene naphthalate, polyamide, polyphenylene sulfide, polyolefin.

Wet-laid nonwovens - also sometimes referred to herein as "papers" - in the sense of this invention are all nonwovens which can be produced with the wet-laying processes known in the art for the production of filter papers. The wet-laid webs for the impregnated filter material according to the invention consist of natural, synthetic, inorganic fibers or a mixture thereof. Examples of natural fibers are cellulose, cotton, wool, hemp, wherein the cellulosic material used may be wood-free and / or wood-containing celluloses of coniferous and / or deciduous trees, regenerated celluloses and fibrillated celluloses. Inorganic fibers are, for example, glass fibers, basalt fibers, quartz fibers and metal fibers. Suitable synthetic fibers are, for example, one-component synthetic fibers such as polyester fibers, polypropylene fibers, polyamide fibers and polyacrylonitrile fibers, multicomponent synthetic fibers with different melting points of the individual components, such as core-sheath fibers, and mixtures thereof. Examples of core-shell synthetic fibers are polyester core and polyester sheath fibers, and polyester core and polyamide sheath. The denier of the synthetic fibers is typically 0.1 dtex-8.0 dtex, preferably 0.5 dtex-5 dtex, particularly preferably 1.0 dtex-3 dtex, for example 1.7 dtex. The cut length is typically 3 mm-20 mm, preferably 4 mm-12 mm, particularly preferably 5 mm-8 mm, for example 6 mm. The use of nonwovens or papers made from such fibers allows a particularly efficient impregnation with a particle-shaped binder having an average particle size of less than 50 μm. Furthermore, this will a possible migration to the surface of the filter material during the melting and possibly curing of the particulate binder avoided particularly effective.

Moreover, it is possible that the impregnated filter material according to the invention contains fibers with different cutting lengths and titers.

The wet-laid webs for the impregnated filter material can either consist of 100% natural, synthetic or inorganic fibers, but it is also any mixture of these types of fibers, such as. As a mixture of cellulose and thermoplastic polymer fibers such as polyester fibers possible.

In a preferred embodiment, the wet-laid web for the production of the impregnated filter material consists entirely of cellulose fibers.

In a further preferred embodiment, the wet laid nonwoven for the production of the impregnated filter material contains about 80 wt .-% to 90 wt .-% cellulose and 10 wt .-% to 20 wt .-% glass or plastic fibers, based on the total weight of the fleece. The plastic fibers of this embodiment are preferably thermoplastic polymer fibers such. B. polyester fibers.

In a further preferred embodiment, the wet laid nonwoven for the production of the impregnated filter material consists entirely of plastic fibers, which are preferably cut fibers. The plastic fibers of this embodiment may be at least partially made of one or more thermoplastics such as polyester. Corresponding wet-laid nonwovens can be solidified by a partial melting of the plastic fibers, which leads to an additional improvement of the mechanical properties of the impregnated filter material according to the invention. Furthermore, a partial melting of the plastic fibers has a positive effect on the mechanical stability of the nonwoven during the production of the impregnated filter material.

In a further preferred embodiment, the wet-laid nonwoven for the production of the impregnated filter material contains about 80 wt .-% to 95 wt .-% plastic fibers, which are, for. B. may be cut fibers, and 5 wt .-% to 20 wt .-% cellulose fibers, based on the total weight of the web. Similar to the embodiment described above, the nonwoven fabric can be preconsolidated by melting thermoplastic resin fibers.

On the basis of his knowledge and experience, the skilled person knows how to select the right composition according to the required paper properties and in particular the field of application of the impregnated filter material. The paper layer can consist of several layers, which are produced and brought together either in a paper machine with a suitable headbox or made up of individual paper webs which are joined together in a separate operation. The individual layers can be designed differently in their properties. By combining several individual layers, properties of the resulting impregnated filter material and filter element made therefrom can be adapted to its intended use.

Preferably, the impregnated filter material according to the invention is planar, d. H. It has two opposite sides or surfaces, which are particularly preferably arranged parallel to each other.

The fibers of the impregnated filter material according to the invention are bound, that is they are no longer freely movable. For papers which typically contain cellulosic fibers, this fiber bonding occurs through the hydrogen bonds between the individual fibers. The fibers of Synthesiebliesen that do not have these hydrogen bonds, z. B. by needling, fusing or preimpregnation with a liquid binder together. The fibers of fabrics are joined together, for example, by weaving or knitting. A measure of the interconnection of the fibers with one another is the bursting strength.

The unimpregnated fiber material for producing the impregnated filter material according to the invention preferably has a Mullen burst strength of at least 20 kPa, preferably of at least 40 kPa, more preferably of at least 50 kPa, a basis weight of 10 g / m ² -300 g / m ² from 20 g / m ^{2 to} 200 g / m ² , particularly preferably from 50 to 170 g / m ² , an air permeability of 10 l / m ² s-8000 l / m ² s, preferably of 80 l / m ² s 8000 l / m ² s, more preferably from 200 l / m ² s-2000 l / m ² s, a pore size of 10 μm-150 μm, preferably from 20 μm-120 μm, particularly preferably from 50 μm-80 μm, a thickness of 0.1 mm-3.0 mm, preferably 0.3 mm-2.0 mm, more preferably 0.5-1.5 mm, and an average fiber density of not less than 0.01, preferably 0.1-0 , 8, more preferably from 0.1-0.7, most preferably from 0.1-0.5.

In the present case, the term "pore size" is used for the largest pore of the fiber material or impregnated filter material, as described in the so-called bubble pressure test (bubble point test) according to US Pat DIN ISO 4003 can be determined, wherein in the bubble pressure test, a mixture of 96 wt .-% ethanol and 4 wt .-% water is used as the test liquid.

The mean fiber density is the quotient of material density (bulk density) and average density of the fibers used. It is calculated using the following formula:

Impregnated filter media for the filtration of fluids are usually impregnated with binder. The impregnation gives the impregnated filter material high rigidity and resistance to aggressive fluids such as hot engine oils, hydraulic oils, fuels, acids, alkalis, acidic and hot gases. Since most impregnated filter materials or impregnated semi-finished products are folded in a further processing step, a high rigidity and good processability is required. A high proportion of thermoplastic particulate binder can improve the processability of the impregnated filter material according to the invention or of the impregnated semi-finished product according to the invention. Impregnated filter materials according to the invention are stiff and the resulting wrinkles resist the filtration pressure even at high flow rates and temperatures. Thus, they are excellently suited for use in filter elements intended especially for the filtration of liquids.

Fluids in the present application are liquids, gases or mixtures thereof. Preferably, the fluids are liquids such as, for. As fuels and oils such as engine oils, hydraulic oils, etc.

Particulate binders are used in the production of the impregnated filter material according to the invention. According to a preferred embodiment of the invention, the particulate binders are dry particulate binders. These particulate binders are present as particles, preferably in the form of amorphous solids. The corresponding particulate binders can consist of natural or synthetic polymers and are preferably thermoplastic, ie they melt under the action of heat and bond the fibers of the fiber material together. One can divide these particulate binder into two large groups. The first group includes all polymers which are purely thermoplastic, that is to say they can be melted again and again by suitable introduction of energy, for example polyethylene, polypropylene, polyvinyl ether, polyvinyl chloride, polyvinylidene chloride, polyvinylidene fluoride, polyvinyl acetate, polyacrylate, polymethacrylate, polyacrylamide, polyamide, Polystyrene, polyvinyl alcohol, polyurethane, polyesters, copolymers and / or mixtures thereof.

The second group is formed by polymers, which melt in the first stage and then crosslink with further energy input. After crosslinking these polymers can not be remelted again. Examples of such polymers are phenolic resins, epoxy resins, melamine-formaldehyde resins, unsaturated polyesters, unsaturated polyurethanes, copolymers and / or mixtures thereof.

The crosslinking of the particulate binder is carried out either with itself (crosslinking particulate binder) or using a suitable crosslinking agent, which the person skilled in the art can select based on his knowledge, depending on the requirements. Examples of suitable crosslinkers are polyamines, polyamides, polycarboxylic acids, polycarboxylic anhydrides, dicyandiamide, isocyanates, imidazoles, hexamethylenetetramine, methylolurea, resol, methylolmelamine, polyol compounds or mixtures thereof.

In a particularly preferred embodiment, the particulate binder is a phenolic resin with hexamethylenetetramine as crosslinker. Such a particulate binder typically has a melting range of about 87-90 ° C. A corresponding particulate binder is commercially available under the name EXP 8E2038P from Dynea Erkner GmbH. The corresponding particulate binder is particularly suitable for the impregnation of wet-laid nonwovens, for example of cellulosic papers, so that the resulting impregnated filter material of the present invention has excellent bursting resistance and air permeability. During the melting and optionally hardening of this particulate binder no migration takes place on the surfaces of the impregnated filter material. A correspondingly impregnated filter material is therefore very well suited for the production of the filter elements.

The melting temperature of the particulate binder plays a special role in its selection. It should be at least 5 ° C, preferably 10 ° C below the lowest melting temperature of the fibers used, when using multi-component fibers below the melting point of the higher-melting component. If the fibers of the fiber material consist, for example, of a mixture of cellulose and polyester fibers, then the melting temperature of the particulate binder should be at least 5 ° C. below the melting temperature of the polyester used.

If a crosslinking particulate binder is selected, the curing temperature should be clearly, preferably not less than 10 ° C., more preferably not less than 20 ° C., above its melting point. If, for example, a phenolic resin with hexamethylenetetramine is used as the crosslinking agent as a particulate binder, it can be melted at about 115 ° C. to 125 ° C. and then cured at about 150 ° C. to 170 ° C.

The curing time of the particulate binder depends on the resin used and is typically between 2 minutes and 2 hours, preferably between 5 minutes and 1 hour, for example between 10 minutes and 20 minutes. For example, a phenolic resin with hexamethylenetetramine as crosslinker within 5 to 20 minutes, z. B. be cured within 10 minutes at 160 ° C.

When a mixture of a plurality of particulate binders is present, the term "melting point of the particulate binder" in the present specification means the melting point of the highest melting particulate binder in the blend.

Depending on requirements, it is also possible for the particulate binder to be admixed with various functional additives, for example hydrophilicizing agents, water repellents, flameproofing agents, paints, charge particles, biologically active substances.

In the impregnation in step a) of the process for producing the impregnated filter material according to the invention, the particles of the particulate binder are evenly distributed in the fiber material. Thus, the resulting impregnated filter material according to the invention has a uniform distribution of the particles of the particulate binder. A uniform distribution of the particles of the particulate binder in at least one part of fiber material is understood here to mean that the concentration of the particulate binder per unit representative volume unit in this part of the fiber material (eg per mm ³ , per 10 ⁶ μm ³ or per 10 ³ μm ³ ) at any point in this part of the impregnated fiber material by less than 10%, preferably less than 5%, more preferably less than 2%, most preferably less than 1% of the average concentration of the particulate binder in that part the impregnated fiber material deviates altogether.

In step a) of the process according to the invention for producing the impregnated filter material, the particles of the particulate binder are uniformly distributed in the thickness direction in at least part of the fiber material. Preferably, this uniform distribution in the thickness direction is at least half the thickness of the fiber material, more preferably at least half the thickness to at most three quarters, more preferably over the entire thickness (ie 100% of the thickness) of the fiber material. In the latter case, one speaks of a "Durchimprägnierung" of the fiber material. The impregnation of the fiber material, ie the wet or drained nonwoven or fabric, is carried out in the context of the invention preferably substantially flat, d. H. over at least 99% of the area of the fibrous material, in the thickness of the fibrous material, as stated above. According to a particularly preferred embodiment, consequently, the fiber material is impregnated over its entire surface, ie completely, with the particulate binder.

The size of the particles in the particulate binder (hereinafter for the sake of simplicity "particle size of the particulate binder") according to the invention is preferably such that 95% of the particles have a size of less than 500 microns, more preferably less than 100 microns, and most preferably from below 50 microns have. To determine the particle size of the particulate binder sieve analysis, particularly advantageous an air jet sieve after DIN EN ISO 8620 used. If 95% of the particles have a size of less than 500 microns, this means that 95% of the particles through a 500 micron sieve, so a sieve with a Mesh size of 500 microns, go through. The particle size of the particulate binder is advantageously matched to the pore size of the fiber material to allow efficient absorption and distribution of the particulate binder in the impregnated filter material.

Binders in which 95% of the particles are smaller than the pore size of the fiber material (as defined above) are preferred, and binders in which 99% of the particles are smaller than the pore size of the fiber material, ie through a sieve with a mesh size, are particularly preferred corresponding to the pore size of the fibrous material.

The impregnation is carried out by the known methods, such as scattering of the particulate binder on the fiber material or spraying by means of electrostatic spray device. Furthermore, it is possible to impregnate the starting material by sucking a gas stream containing the particulate binder through the fibrous material. The particulate binder can be applied to the fiber material on one or both sides.

The distribution of the particulate binder in the fiber material takes place in the impregnation step a) by suitable methods known to the person skilled in the art, for example mechanical shaking, ultrasound application, alternating electric field, application of a negative pressure.

In step b), the material from step a) is subjected to a heat treatment. This can be achieved for example by the entry of heat energy z. B. done by infrared emitters or by the entry of ultrasound. In step b) of the production process according to the invention, it is preferable to achieve extensive melting, in particular complete melting of the binder particles, which are preferably dry, and, if appropriate, curing. In order to achieve a substantial, in particular complete melting of the binder particles, the temperature during the heat treatment of the material is advantageously at least 5 ° C above the melting temperature of the particulate binder, preferably at least 10 ° C above the melting temperature of the particulate binder and more preferably at least 15 ° C. above the melting temperature of the particulate binder. When choosing the temperature, it must be ensured that the synthetic fibers possibly present in the fiber material do not melt.

Preferably, the material obtained in step a) is subjected to a first heat treatment step in step b), whereby the impregnated semi-finished product is obtained. The first heat treatment step causes the particles of the particulate binder to be firmly bonded by adhesive forces to the fibers of the fiber material. In the first heat treatment step, only a softening of the binder particles usually occurs, in which case binder particles may also partially melt. At the end of the first heat treatment step, discrete binder particles are usually detectable in the microscope. The heating temperature or the entry of ultrasonic energy is chosen so that the particulate binder is indeed softened or partially melted, which may not be present in the impregnated filter material synthetic fibers. Therefore, the temperature in the first heat treatment step is preferably slightly below the melting point of the particulate binder, preferably up to 5 ° C, more preferably up to 2 ° C below.

The impregnated semi-finished product is intended to be deformed for processing into an impregnated filter material or filter element by a mechanical process such as embossing, folding, shafts in the transverse direction, creasing in the longitudinal direction. However, this mechanical processing step is not absolutely necessary, so that the impregnated semi-finished product can be further processed after the first heat treatment step, depending on the intended use of the filter material, by a second heat treatment step to the filter material according to the invention.

When the heat treatment in the production process according to the invention takes place in two separate steps, the semi-finished product impregnated between the first and second heat treatment step has a relatively high flexibility and can be subjected to a particularly gentle mechanical processing. Any damage to the impregnated filter material is thus effectively avoided and the resulting impregnated filter material has excellent mechanical properties.

When the heat treatment in step b) is carried out in two stages, ie with a first and a second heat treatment step, the parameters of the first heat treatment step are preferably as follows: duration temperature 1. heat treatment step 0.5-30 s, preferably 0.5-20 s up to 2 ° C below the melting point of the particulate binder

The second heat treatment step is preferably carried out at a temperature at least 5 ° C above the melting point of the particulate binder. The duration of the second heat treatment step is preferably as follows: it is in the range of 0.5 to 30 seconds, for example when the particulate binder is to be melted and, if desired, the crosslinking is merely initiated, and is in the range of 5 to 20 minutes, For example, if the particulate binder to be melted and fully cured or cured. The aforementioned initiated crosslinking can be completed even at room temperature over days or weeks.

Furthermore, it is possible to carry out the first heat treatment and the second heat treatment in a single common process step. Thus, the heat treatment in step b) may be a one-step heat treatment. Preferred embodiments of such a single-stage heat treatment have been generally explained above in connection with the heat treatment in step b). Thus, the temperature is preferably at least 5 ° C above the melting point of the particulate binder and the duration is preferably in the range of 0.5 to 30 seconds, for example, when the particulate binder is to be melted and, if desired, the crosslinking merely initiated, the crosslinking subsequently even at room temperature over days or weeks can be completed.

Preferably, in the second heat treatment step, a substantial melting and, if appropriate, hardening of the particulate binder takes place and the impregnated filter material according to the invention is formed. The molten binder envelops the fibers of the filter material and forms bridges between the fibers.

For example, after the impregnation of the fibrous material in the first heat treatment step, the particulate binder may be softened or melted such that at least 5% of the maximum final strength is achieved in the impregnated semi-finished product. After shaping, the impregnated semi-finished product according to the invention can then be reheated in the second heat treatment step. In this case, the particulate binder is preferably completely melted and cured if necessary, so that it reaches its desired final strength and final rigidity in the resulting impregnated filter material.

In a preferred embodiment, the fiber material which is uniformly impregnated with at least one particulate binder in step a) of the production process according to the invention is a preconsolidated fiber material. A completely impregnated filter material obtainable by using such a preconsolidated fiber material with the production method according to the invention has a Mullen burst strength of at least 50 kPa, preferably of at least 100 kPa, a basis weight of 20 g / m ² -500 g / m ² , preferably of 40 g / m ² -300 g / m ² , an air permeability of 10 l / m ² s-8000 l / m ² s, preferably from 80 l / m ² s-8000 l / m ² s, a pore size of 10 μm-150 μm, preferably of 20 μm-100 μm, a thickness of 0.1 mm-3.0 mm, preferably of 0.3 mm-3.0 mm, a fiber density of 0.1-0.9, preferably of 0.1-0, 8 wherein 0.1-0.7 is particularly preferred, a resin content of 5 wt .-% - 95 wt .-%, preferably from 5 wt .-% - 50 wt .-% based on the total mass of the impregnated filter material, and a gap strength of at least 1.50 N / 25 mm, preferably of at least 2.00 N / 25 mm.

The method of preconsolidating the fiber material is not further limited. Irrespective of the type of fibers used, needling and water jet needling, as well as impregnation or spraying with liquid binders (latex) with subsequent drying, are suitable for dry and wet-laid nonwovens. When thermoplastic fibers, such as single or multi-component meltbond fibers, are included in the nonwovens, thermal calendering, both full-surface and point-wise, is another way of preconsolidation.

The nip strength is a measure of the uniform distribution of the particulate binder and indicates the force in the Z direction needed to crack the impregnated filter material.

In the production of a further embodiment of the impregnated filter material according to the invention is a pre-consolidated fiber material such. As fabric, paper or nonwoven fabric is uniformly impregnated only on one side with a particulate binder in such a way that it penetrates the thickness of the fiber material at least half but not more than three quarters. Such a fiber material has a Mullen burst strength of at least 50 kPa, preferably of at least 100 kPa, a basis weight of 20 g / m ² -500 g / m ² , preferably of 40 g / m ² -300 g / m ² , particularly preferred from 100 g / m ^{2 to} 200 g / m ² , an air permeability of 20 l / m ² s-8000 l / m ² s, preferably from 80 l / m ² s-8000 l / m ² s, particularly preferably from 200 l / m ² s-2000 l / m ² s, a pore size of 10 .mu.m-150 .mu.m, preferably of 20 .mu.m-100 .mu.m, particularly preferably of 40 .mu.m-800 .mu.m, a thickness of 0.1 mm-3.0 mm , preferably of 0.3 mm-2.0 mm, a fiber density of 0.1-0.9, preferably of 0.2-0.8, a resin content of 2 wt .-% - 95 wt .-% based on the total mass of the fiber material , preferably from 5 wt .-% - 50 wt .-%. For example, such a fiber material may have a basis weight of 168 g / m ² , a thickness of 0.90 mm, a bursting strength of 65 kPa, an air permeability of 500 l / m ² s, a pore size of 58 μm and a fiber density of 0.13 exhibit.

In the context of the invention, it is readily possible that the impregnated filter material according to the invention consists of several layers or layers. Furthermore, it is also possible that when used in the filtration, for example in the filter element, before and / or after the impregnated filter material according to the invention one or more layers of other materials, for. B. other impregnated filter materials are provided.

The individual layers of the impregnated filter material according to the invention are bonded either with an adhesive or via welded joints or a combination thereof.

Advantageous adhesives have a softening point of over 200 ° C. When used as intended, the impregnated filter material of the invention is exposed to temperatures up to 150 ° C and high hydrostatic pressures. The adhesive connection must not come loose. Suitable adhesives for this application are polyurethane adhesive, polyamide adhesive or polyester adhesive. Polyurethane adhesives are particularly preferred because they can crosslink with the humidity. The adhesives can be applied either as a powder or melted by means of anilox rolls or spray nozzles. The application weight of the adhesive is typically between 5-20 g / m ² , preferably between 5-10 g / m ² .

The welded connection can be made both by an ultrasonic system and by a thermal calender. The polymers of the layers to be welded are either completely or partially melted and welded together. The area-wise welded joints can have any geometric shapes, such as points, straight lines, curved lines, diamonds, triangles, etc. The area of the area-wise welded joints is advantageously at most 10% of the total area of the impregnated filter material according to the invention.

Gluing and welding can also be combined with each other.

The impregnated filter material according to the invention can be further processed into all conventional elemental forms. So it can be z. As tubes, bags or bags are made. Or it can be embossed on all common processing machines, folded, corrugated in the transverse direction, longitudinally grooved, etc.

If the impregnated filter material according to the invention is processed into hoses, bags or bags, the particle-shaped binder is advantageously completely melted or cured after the impregnation of the fiber material.

Test Methods

• Surface mass after DIN EN ISO 536
• Melting temperature after DIN EN ISO 3146
• Softening point of the glue after DIN EN 1238
• Thickness after DIN EN ISO 534
• Air permeability after DIN EN ISO 9237 at 200 Pa pressure difference
• Bursting strength according to Mullen DIN 53141
• Particle size after DIN EN ISO 8620
• Pore size by gas bubble test after DIN ISO 4003 on flat samples with a mixture of 96% wt .-% ethanol and 4 wt .-% water as Prüfflüssigkeit.

The proportion of binder in a paper (resin content) is calculated according to the following formula: Resin content in% = (FM Imp./FM paper) · 100% with FM Imp. = weight of dry binder per m ^{2 of} paper
FM paper = basis weight of the impregnated paper

Determination of the gap strength in the transverse direction:

From a previously 24 hours at 23 ° C and 50% relative humidity air-conditioned impregnated filter material 2 strips are cut with 50 mm wide and 200 mm in length. The 200 mm long side runs transversely to the direction of the impregnated filter material. On the front and back of these samples are then measured approximately 150 mm long strips of the Scotch 3M 365 test tape (thermosetting glass fabric adhesive tape, adhesion to steel: 60 oz./in. Width (54.5 N / 100 mm) measured after of the Standard ASTM D-3330 ; Elongation at break: 106 lbs./in. Width (2106 N / 100 mm), measured after the Standard ASTM D-3759 ; Thickness of substrate: 5 mils. (0.12 mm) measured after Standard ASTM D-3652 ; Total tape thickness: 7.2 mils. (0.18 mm) measured after Standard ASTM D-3652 ) glued without creases so that the impregnated filter material protrudes by approx. 50 mm at one end. This composite is then subsequently pressed with a 4.5 kg heavy and 50 mm wide steel roll. The steel roller is rolled over the composite by hand twice without additional pressure. From each strip, consisting of the impregnated filter material and the test adhesive tape on both sides of the impregnated filter material, a sample 25 mm wide and 200 mm long is cut. From the end at which the impregnated filter material protrudes, the tape is pulled by hand a short distance on one side by hand, so that the impregnated filter material is split over the entire width of the sample. Preferably, the splitting is carried out on the side of the impregnated filter material on which the test adhesive tape adheres the most. Depending on the impregnation of the impregnated filter material, splitting may be difficult. If the test adhesive tape is poorly adhered to the impregnated filter material to be tested and the gap strength is very high, the impregnated filter material to be tested must be carefully cut with a razor blade and then further split with the aid of the test adhesive tape. The measurement of the gap strength takes place in a universal testing machine from Zwick type Roell Z 0.5 with the following settings:
Measuring range 0.5 F
Program wet grinding gap strength
Speed 300 mm / min
Terminal distance 25 mm
Preliminary 20 mm
Test track 80 mm

The Scotch 3M 365 test tape removed by hand is clamped in the upper clamp of the tensile tester. The impregnated filter material to be tested with the second strip of the test adhesive tape adhering thereto is clamped in the lower clamp of the universal testing machine in such a way that the composite protrudes at 90 ° to the direction of pull. During the measurement, care must be taken that the cleavage takes place in the middle of the impregnated filter material to be tested, and not just individual fibers are torn from the surface of the impregnated filter material. Measurements in which the cleavage does not occur in the middle of the impregnated filter material are discarded and repeated. Measured is the average force needed to break the impregnated filter material. The result is the mean of two individual measurements.

EXAMPLES

Example 1 (Invention)

According to the well-known method of papermaking, a paper web of 84 cellulose and 14 polyester fibers (1.7 dtex / 6 mm) was produced in a paper machine. The paper is available under the name H11PESG from NEENAH Gessner, Bruckmühl. The paper thus prepared had a basis weight of 168 g / m ² , a thickness of 0.90 mm, a bursting strength of 65 kPa, an air permeability of 500 l / m ² s, a pore size of 58 μm and a fiber density of 0.13 ,

43 g / m ^{2 of} a particulate phenolic resin with hexamethylenetetramine as a hardener from Dynea Erkner GmbH, Erkner with the name EXP 8E2038P were sprinkled on this paper in a separate operation and by mechanical shaking movements over the entire thickness of the filter material distributed. The particle size of the phenolic resin was such that 95% of the particles had a size of <40 μm, and the phenolic resin had a melting range of 87-90 ° C.

Thereafter, the binder was melted in the impregnated filter material by means of an infrared radiator at 120 ° C and then cured at 160 ° C for 10 min. After cooling and storage for 24 hours at 23 ° C and 50% relative humidity, the parameters listed in Table 1 were measured.

Example 2 (comparative example)

The paper from Example 1 was impregnated in a known manner with a phenol resin solution in methanol and dried at 110 ° C. The phenolic resin can be obtained under the name Fenoplast PF-14 from Lerg, Pustkow. Hexamethylenetetramine (1.2% by weight based on solids content of the formulation) was used as a crosslinker. The impregnated filter material produced in this way had a resin content of 20. Subsequently, this impregnated filter material was cured in the laboratory for 10 minutes at 160.degree. After storage for 24 hours at 23 ° C and 50% relative humidity, the parameters of the resulting impregnated filter material shown in Table 1 were measured. Table 1 Example 1 (Invention) Example 2 (comparative example) Basis weight (g / m ² ) 211 212 Thickness (mm) 1.02 0.99 Bursting strength (kPa) 496 437 Air permeability (l / m ² s) 504 482 Pore size (μm) 70 71 Gap strength (N / 25 mm) Not measurable 1.49

As can be seen from Table 1, the impregnated filter material according to the invention has a significantly higher bursting strength and air permeability than the conventionally impregnated filter material of Example 2. The cleavage strength of the impregnated filter material of Example 1 according to the invention is so high that they are not with the specified method is more measurable. This suggests that the binder is evenly distributed throughout the impregnated filter material of the present invention and that no migration has occurred to the surfaces of the impregnated filter material during fusing and curing of the impregnated filter material, as was done in the comparative example.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 102009006586 A1 [0004]
• US 2,918,173 A [0005]
• DE 102005032395 A1 [0009]
• WO 95/04857 A1 [0010]
• US 4983193 A [0011]
• US 4340563 A [0032]
• US 3802817 A [0032]
• US 3855046 A [0032]
• US 3692618 A [0032]

Cited non-patent literature

• "Nonwovens, W. Albrecht, H. Fuchs, Wiley-VCH, 2012" [0030]
• A. van Wente, "Superfine Thermoplastic Fibers", Industrial Engineering Chemistry, Vol. 48, pp. 1342-1346 [0031]
• DIN ISO 4003 [0044]
• DIN EN ISO 8620 [0059]
• DIN EN ISO 536 [0082]
• DIN EN ISO 3146 [0082]
• DIN EN 1238 [0082]
• DIN EN ISO 534 [0082]
• DIN EN ISO 9237 [0082]
• DIN 53141 [0082]
• DIN EN ISO 8620 [0082]
• DIN ISO 4003 [0082]
• Standard ASTM D-3330 [0084]
• Standard ASTM D-3759 [0084]
• Standard ASTM D-3652 [0084]
• Standard ASTM D-3652 [0084]

Claims (17)

A method of making an impregnated filter material, characterized in that the method comprises the steps of: a) impregnating a fibrous material having an average fiber density of not less than 0.003 and selected from the group consisting of a fabric, a wetlaid web, and a dry laid web is, with at least one particulate binder, such that the particles of the particulate binder in the thickness direction in at least a portion of the fiber material are evenly distributed; b) heat treatment of the material from step a), wherein the particulate binder is at least partially melted. A method according to claim 1, characterized in that the heat treatment in step b) comprises a first heat treatment step and a second heat treatment step, wherein the temperature of the impregnated filter material in the second heat treatment step is above the melting temperature of the particulate binder. A method according to claim 2, characterized in that the impregnated filter material is subjected to mechanical processing after the first heat treatment step and before the second heat treatment step. A method according to claim 1, characterized in that the heat treatment in step b) is carried out in a single process step. Method according to at least one of claims 1 to 4, characterized in that 95% of the particles of the particulate binder have a particle size of less than 100 microns. Method according to at least one of claims 1 to 5, characterized in that the particulate binder contains at least one thermoplastic polymer. Method according to at least one of claims 1 to 6, characterized in that the particulate binder has a melting temperature which is at least 5 ° C below the lowest melting temperature of the fibers of the fiber material. Method according to at least one of claims 1 to 7, characterized in that the proportion of at least partially melted binder in the impregnated filter material is 5 to 50 wt .-%. Method according to at least one of claims 1 to 8, characterized in that the fiber material is preconsolidated. Method according to at least one of claims 1 to 9, characterized in that the fiber material has an average fiber density of 0.1-0.7. Method according to at least one of claims 1 to 10, characterized in that after step b) at least one particle of the particulate binder is still present in discrete form. Impregnated filter material obtainable from a fiber material by a method according to at least one of claims 1 to 11, in particular according to claim 11. Impregnated filter material according to claim 12, characterized in that it has a gap strength of at least 1.5 N / 25 mm, preferably of at least 2.0 N / 25 mm. An impregnated filter material based on a fiber material having an average fiber density of not less than 0.003 and selected from the group consisting of a fabric, a wet laid nonwoven and a drained nonwoven, characterized in that at least a portion of the fiber material in the thickness direction uniformly with a particulate binder is impregnated, which is at least partially melted, wherein preferably at least one particle of the particulate binder is present in discrete form. Filter element comprising an impregnated filter material according to at least one of claims 12 to 14. Use of an impregnated filter material according to at least one of claims 12 to 14 or a filter element according to claim 15 for the filtration of liquids, in particular fuels and oils. Process for the filtration of liquids, in particular fuels and oils, in which an impregnated filter material is produced by a process comprising the following steps: a) impregnation of a fiber material having an average fiber density of not less than 0.003 and selected from the group consisting of a fabric, a wet laid nonwoven and a drained nonwoven, with at least one particulate binder, such that the particles of the particulate binder in the thickness direction are evenly distributed in at least a part of the fiber material; b) heat treatment of the material from step a), wherein the particulate binder is at least partially melted, and the impregnated filter material thus prepared is used to filter liquids, especially fuels and oils.