EP-4736986-A1 - METHOD FOR PRODUCING A FILTER MEDIUM CONTAINING ABSORBENT PARTICLES AND FILTER MEDIUM CONTAINING ADSORBENT PARTICLES

EP4736986A1EP 4736986 A1EP4736986 A1EP 4736986A1EP-4736986-A1

Abstract

Inventors

PROST, Claire
Ambrosini, Cristiano

Assignees

Ahlstrom Oyj

Dates

Publication Date: 20260506
Application Date: 20241031

Claims (17)

Method for producing a filter medium containing absorbent particles, comprising the following steps: providing a first nonwoven support layer (1), applying adsorbent particles onto a first surface of the first nonwoven support layer (1), subsequently applying a second porous layer (2) with a first surface thereof onto the first surface of the first nonwoven support layer (1) to form a package of layers, and subsequently joining the first nonwoven support layer (1) and the second porous layer (2) to form a stack of joint layers, characterized in that a solid adhesive and a liquid adhesive are applied to one or more of the first surface of the first nonwoven support layer (1), the adsorbent particles and/or the first surface of the second porous layer (2).
Method according to claim 1, wherein before applying the second porous layer (2) with its first surface onto the first surface of the first nonwoven support layer (1) the adhesive application and activation steps are carried out in the following manner: i. the adsorbent particles are applied together with the solid adhesive as a mixture onto a first surface of the first nonwoven support layer (1), ii. optionally, additional solid adhesive is applied onto a first surface of the first nonwoven support layer (1), iii. the first nonwoven support layer (1) is treated with pressure and/or elevated temperatures sufficient to activate the solid adhesive, iv. the liquid adhesive is applied onto the first surface of the first nonwoven support layer (1) and/or on a first surface of a second porous layer (2).
Method according to claim 1, wherein the adhesive application and activation steps are carried out in the following manner and order: i. the adsorbent particles are applied together with the solid adhesive as a mixture onto a first surface of the first nonwoven support layer (1), ii. the liquid adhesive is sprayed onto the first surface of the first nonwoven support layer (1) prior to and/or subsequent to the application of the mixture of the solid adhesive and the adsorbent particles, iii. the second porous layer (2) with a first surface thereof onto the first surface of the first nonwoven support layer (1) to form a package of layers, iv. the package is treated with pressure and/or elevated temperatures sufficient to activate the solid adhesive to join the first nonwoven support layer (1) and the second porous layer (2) to form a stack of joint layers.
Method according to one of the preceding claims, characterized in that the solid adhesive and the liquid adhesive differ in their chemical composition.
Method according to one of the preceding claims, characterized in that the solid adhesive is in powder form, with a preferred mean particle size from 100 to 800 µm, especially preferred 250 to 700 µm, measured according to DIN ISO 4610:2002 standard.
Method according to one of the preceding claims, characterized in that the solid adhesive is selected form the group consisting of thermoplastic adhesives, which preferably are selected from the group consisting of ethylene-vinyl-acetate (EVA) adhesives, copolyester adhesives, co-polyamide adhesives, thermoplastic urethane (TPU) adhesives and mixtures and combinations of the aforementioned adhesives and/or the liquid adhesive is selected from the group consisting of PUR adhesives, polyolefin adhesives and mixtures and combinations of the aforementioned adhesives.
Method according to one of the preceding claims, characterized in that the adsorbent particles and the solid adhesive, especially in powder form, are mixed to form a mixture and said mixture being applied onto the first surface of the first nonwoven support layer (1).
Method according to one of the preceding claims, characterized in that the adsorbent particles are selected from the group consisting of activated carbon particles, impregnated activated carbon particles, activated carbon with additional catalytic treatment, ion exchange resin particles, silica particles, zeolite particles, molecular sieve particles, clay, alumina, sodium bicarbonate, catalyst particles, or a combination thereof, and/or have a particle size from 30 to 60 mesh and/or have a density in between 400 and 800 kg/m 3 , preferably 450 to 780 kg/m 3 , especially preferred 460 to 750 kg/m 3 measured according to ASTM D2854-09, and/or have a CTC value from 45 to 60%, preferably 50 to 55%, measured according to ASTM D5742-16, and/or are applied in an amount of 100 to 1100 g/m 2 , preferably 200 to 700 g/m2.
Method according to one of the preceding claims, characterized in that the solid adhesive is applied in an amount of 1 wt.-% to 50 wt.-%, preferably 2 wt.-% to 30 wt.-%, especially 5 to 15 wt.-% of an amount of the adsorbent particles and/or the liquid adhesive is applied in an amount of 1 to 50 g/m 2 , preferably 5 to 20 g/m 2 , especially preferred 8 to 15 g/m 2 .
Method according to one of the claims 2 to 9, characterized in that the elevated temperatures are chosen from a range of 150 °C or above, preferably 150 °C to 250 °C, especially preferred 170 to 230 °C.
Method according to one of the preceding claims, characterized in that that after the formation of the package of layers or the stack of joint layers additional liquid adhesive is applied onto a second surface of the second porous layer (2) being the surface of the second porous layer (2) lying opposite to the layer which is joined with the first side of the first nonwoven support layer (1) and/or onto a second surface of the first nonwoven support layer (1) lying opposite of the first surface of the first nonwoven support layer (1) and subsequently at least one nonwoven efficiency (3) layer is applied onto the surface which has been applied with liquid adhesive.
Filter medium containing adsorbent particles, comprising a first nonwoven support layer (1), a second porous layer (2) with a first surface thereof onto a first surface of the first nonwoven support layer (1), and adsorbent particles enclosed by and/or dispersed in the first nonwoven support layer (1) and the second porous layer (2), characterized in that the first nonwoven support layer (1), the second porous layer (2) and the adsorbent particles are adhered together by at least two adhesives which differ in their chemical composition.
Filter medium according to the preceding claim, characterized by a content of the adsorbent particles in between 100 to 1000 g/m 2 , preferably 200 to 700 g/m 2 and/or a thickness in between 2000 and 3000 µm, preferably in between 2300 and 2900 µm, measured according to ISO 9073-2:1997, and/or an air permeability in between 700 and 1800 l/m 2 /s, preferably in between 900 and 1600 l/(m 2 ·s), measured at 200 Pa according to the TAPPI Standard T 251 cm-85 ("Air Permeability of Porous Paper, Fabric and Pulp Handsheets") with 0.5 inch (12.7 mm) and/or a NaCl efficiency of > 60%, preferably > 80 % measured according to DIN 71460-1:2006 with 20 cm/s and at 0.3-0.5 µm particle size, and/or a n-butane initial breakthrough of < 10%, preferably < 5% measured according to ISO 10121-1:2015 with 10 cm/s face velocity and 80 ppm inlet gas concentration, and/or a web density of less than 500 kg/m 3 , preferably less than 300 kg/m 3 , more preferably less than 225 kg/m 3 .
Filter medium according to one of the claims 12 to 13, comprising at least one nonwoven efficiency layer (3) being present on a second surface of the second porous layer (2) being the surface of the second porous layer (2) lying opposite to the layer which is joined with the first side of the first nonwoven support layer (1) and/or on a second surface of the first nonwoven support layer (1) lying opposite of the first surface of the first nonwoven support layer (1).
Filter medium according to one of the claims 12 to 14, being part of a combi cabin air media, molecular heating, Ventilation and Air Conditioning (HVAC) medium or fuel cell air intake medium.
Filter medium according to one of the claims 12 to 15, producible by a method according to one of claims 1 to 11.
Use of a filter medium according to one of the claims 12 to 16 for combi cabin air media, molecular heating, a Ventilation and Air Conditioning (HVAC) medium or a fuel cell air intake medium.

Description

The present invention relates to a method for producing a filter medium containing absorbent particles and a filter medium containing absorbent particles. According to the present invention the filter medium comprises at least two nonwoven layers and adhesive particles, wherein the at least two nonwoven layers and/or the adhesive particles are bonded to each other different adhesives, i.e. a liquid and a solid adhesive which chemically can be different. The present invention allows for the production of filter media Generally, methods of producing filter media containing adsorbent particles are known from the prior art. For example, glue powder can be mixed with activated carbon which mixture is scattered onto a support layer whereafter a further layer (e.g., an efficiency layer) may be placed on top to sandwich the activated carbon particles (referred to as "full glue powder configuration"). Then, heat and pressure is introduced (e.g. via a belt press) to melt the glue powder and allow the activated carbon particles to adhere to the support layer.). The produced filter media have good carbon adhesion, good gas adsorption performances and limited thickness. According to an alternative known procedure a liquid glue is sprayed onto the support layer. Adsorbent particles, for example activated carbon powder, is dry-scattered onto the support layer. Additional glue is sprayed and a further layer is placed on the top. The glue needs to cure and set in order to ensure good adhesion of the adsorbent particles, for example activated carbon powder (referred to as "full glue spray configuration"). The produced filter media exhibit the possibility to laminate on-line efficiency layer and stable charge/ efficiency. However, the filter media produced from a "full glue spray configuration process" has the following disadvantages: High product thickness and costly machine investment involving multiple scattering and multiple glue spray units to produce media with large amounts of activated carbon.Adsorbent media with high amounts of activated carbon need to be produced in multiple steps with at least 48h curing time in between to ensure good adsorbent adhesion.Limited production line layout flexibility due to very short open time of the glue (sticking time) In case of filter media produced from a "full glue powder configuration", the other following disadvantages can be listed: When additional layers are added, especially for the case of a charged efficiency layer, the layer may get discharged when passing in the belt press due to exposure to high temperatureSignificant pressure needs to be applied in the belt-press to get good adhesion of adsorbent particles with each other's and with additional structural/ efficiency layers this led to a compressed media with rather low air permeabilityLimited heat resistance due to low melting point of the glue powder WO 2024/038421 A1describes the use of a thick nonwoven support layer with a highly porous first (top) surface and a tighter (bottom) surface. The nonwoven is positioned with the open, porous surface facing up. Activated carbon powder is dry-scattered onto the support and falls into the pores of the nonwoven. The tighter pores of the bottom surface prevent the carbon powder from falling out. Little to no glue is used in this process. Additional layers are laminated with minimal glue above (and may also be added below) to prevent any carbon particles from falling out. The process also requires high pressure (via a belt press) to ensure the carbon particles are kept inside the porous substrate. The resulting media is very thick. WO 2024/038421 A1discloses the production of a filter medium containing up to 700 g/m2 thanks to the usage of fibrous container. This usage of fibrous container does introduce however some limitations in terms of maximum roll length in the final media being maximum 200 linear meters whereas standard requirements from our customers in mass production require rolls of ca. 400-500 linear meters. More precisely the limitation is due to the high thickness of the nonwoven container and to the maximum material length standing on the pallet (shipping/ handling of incoming good materials). On top of that, the described process ensures the adhesion of adsorbents inside the filter medium by applying high pressure in a belt press. It leads to final medium with limited air permeabilities that are an issue for certain targeted air filtration applications like cabin air applications and HVAC applications. Accordingly, the present invention intends to produce adsorbent containing media with advanced properties. Thanks to this invention, it is possible to produce adsorbent-containing media from 150 g/m2 up to 1000 g/m2 for a broad range of applications like Combi Cabin Air media, Molecular HVAC, Fuel Cell Air Intake media Molecular Clean Room, Airborne Molecular Contamination (AMC), kitchen hoods, Face masks or Air purifiers meeting target properties in terms of air