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Air filtration is not only a question of large ventilation and air-conditioning systems. For each of us it is a natural part of everyday life. Each time we use our vacuum cleaner, the objective is to get rid of dust and dirt in our living space. The vacuumed dirt particles have to be securely deposited in the vacuum cleaner bag else we only redistribute them to the surfaces just cleaned. This is of particular importance to people suffering from allergies. As in any other air filtration application, the utilised vacuum cleaner bag is the heart of this filtration unit: Initially utilised dust bags were mere collecting vessels for dust and dirt. Textile vacuum cleaner bags, on the other hand, are highly efficient filters, providing for clean air.
Both in household and industrial applications, vacuum cleaner bags are required to feature optimum filtration efficiency, easy handling and particular stability to prevent the bag from tearing during replacement.
This stability is by no means self-evident.
Soft synthetic vacuum cleaner bags made of Sandler sawascreen® or sawabond® nonwovens are adaptable to different types of vacuum cleaners according to customer requirements. Nevertheless, all Sandler nonwovens for vacuum cleaner bags have one characteristic in common: they feature a soft, textile touch, but securely retain dust and organic materials deposited. The synthetic materials are sturdy, unaffected by moisture and offer no breeding grounds to mould or germs.
All of these properties are achieved without chemical additives, making these filtration nonwovens particularly kind to the skin and earning them certification according to the Oeko-Tex® standard 100.
Nonwovens facilitate optimum air circulation owing to their porous structure which also makes them permeable to other substances. According to DIN EN ISO 9237, air-permeability is determined by clamping a flat sample of material into a testing device and passing an air stream through it at a defined differential pressure. The flow resistance is measured.
- Automotive: Sandler nonwovens are acclaimed as open-pore upholstery materials for seating, particularly for actively ventilated climate seats.
- Technical applications: Applied as processing aids, frequently in combination with other materials, nonwovens protect delicate surfaces. Their air-permeability can be tailored to the specific application and they remain air-permeable, even when retaining other substances.
In filtration, the relevant factor is the interaction of air-permeability and the pressure drop, induced by the filter’s flow resistance. The pressure building up in front of the filter is higher than that behind the filter. A low pressure drop in combination with a high air-permeability of the filter medium reduces the amount of energy necessary to force the required amount of air through the filter—a contribution to the filter’s energy efficiency and to long-term cost-savings in the operation of the filtration plant. The durability of Sandler nonwovens further supports these savings by prolonging the filter’s operating life and reducing replacements.
The pressure drop is tested according to WSP 70.1 by measuring the filter’s flow resistance in a defined volume flow. Multiple measurements at varying volume flows can be aggregated into a curve depicting the development of the pressure drop. Sandler nonwovens are tested for this property online during production as well as by external institutes and customers. These external partners conduct tests using flat material samples as well as ready-made filters from Sandler material.
Further relevant standards on this subject are DIN 53887 and DIN EN ISO 9237.
See also: Breathability
A filter medium’s efficiency is determined by the arrestance, namely the percentage of particles a filter retains. Apart from mechanical effects, the level of particle deposition is also based on a natural or artificially generated electrostatic charge of the medium. An ideal filter would retain all particulate matter whilst remaining permeable to air.
Development of the arrestance during use is vital in evaluating a filter. High efficiency throughout the operating life is required, even after discharge. During use, the filter medium’s electrostatic charge reduces and consequently, the arrestance decreases. This effect can be caused by an accumulation of dust particles on the surface of the fibres or by specific aerosols such as water-vapour, oil mist or soot particles. A characteristic of Sandler media is high discharged efficiency, achieving high arrestance throughout the operating life due to reliance on mechanical deposition effects: fine fibres of less than 1 µm in diameter create a large filtration surface for optimum mechanical deposition.
Filters are classified based on the average efficiency. Coarse and fine dust filters up to grade F9 are classified according to DIN EN 779 standard; particulate air filters grade E10 and higher are classed according to EN 1822 in its latest revision. The filter is loaded with a predetermined amount of artificial testing dust until the resistance limit is reached. The arrestance or efficiency is measured several times during the test period. The efficiency of Sandler nonwovens is determined by external testing institutes, where the media are tested under standard as well as real-life conditions.
In liquid filtration, the separation efficiency takes precedence—a filter medium’s ability to separate contaminants from a fluid. Synthetic fuel filter media, for example, separate water and particulates to prevent damage to the engine and encourage efficient combustion. Small pores of a defined size range are distributed evenly in the medium, fostering deposition solely reliant on mechanical effects and upholding the high efficiency of Sandler filter media.
Especially in technical applications, nonwovens come into contact with various fluids, chemicals including organic solvents and may also be exposed to sunlight or humidity. Sandler nonwovens are predominantly made of synthetic raw materials such as polyester or polypropylene and are resistant to most inorganic and organic substances. This resistance makes them durable and their specific properties are maintained throughout their operating life. By choosing a suitable Sandler nonwoven, discolouration, softening, bulging, detachment of coatings or blistering become things of the past.
In the automotive industry, this durability is tested according to VDA 621 by dripping selected test fluids on the material or moistening it with them. The temperature at which the test is performed may vary. Sandler nonwovens are tested according to VDA 621 by external institutes.
Specific applications require resistance against specific media or exposures:
Resistance to alkali
In construction, nonwovens come into contact with materials such as concrete or cement mortar. If the level of humidity increases, these building materials are prone to emit large quantities of alkaline salts. Sandler nonwovens are resistant to these alkalis: The nonwoven is unaffected, no disintegration occurs and fabric remains stable. These nonwovens are therefore highly suited to applications in construction. Their resistance to alkali is determined by subjecting them to different test media, usually over a period of several months. A subjective examination of the nonwoven’s structure is subsequently carried out and any decrease in weight and tear-resistance are measured. Sandler nonwovens are tested for resistance to alkali in our in-house laboratory.
Hydrophobicity & hydrophilicity
Hydrophobic nonwovens are water-repellent resulting in reduced fluid absorption. This characteristic is achieved without any additional finishes, using only specific polymers and the appropriate manufacturing technology.
- Automotive: Hydrophobic nonwovens in exterior applications such as wheel house liners withstand any wind and weather.
- Construction: Hydrophobic nonwovens dry quickly and thereby prevent an accumulation of moisture.
In contrast, hydrophilic nonwovens easily attract water and transport it. Special product variants can also be applied for storing fluids. These nonwovens are highly suited to hygiene products or wipes.
Oleophobicity & oleophilicity
The term oleophobicity describes the characteristic of repelling oils and fats. These substances do not penetrate the material but simply run off its surface. Sandler nonwovens for the automotive industry are permanently resistant to engine fluids such as transmission fluid, engine oil or diesel and are in-house tested for oleophobicity according to the drop test method. Likewise, Sandler nonwovens for filtration are resistant oils and fats.
Oleophilic nonwovens, on the other hand, easily absorb oils and fats and amongst others are especially in high demand for environmental applications.
Resistance to fungi, bacteria and moisture
Sandler nonwovens made of thermoplastic polymers are bacteriostatic, i.e. they prevent the proliferation of colony-forming units by denying any breeding grounds for fungi or bacteria. In humid conditions, this characteristic is particularly enhanced by their resistance to moisture: The fibres do not absorb moisture, therefore the nonwoven dries quickly.
- Filtration: Sandler nonwovens are tested for their resistance by external institutes. Corresponding certificates attest to the nonwovens’ suitability for application in ventilation and air-conditioning systems according to VDI 6022.
- Construction: This characteristic helps to prevent the growth of mould in buildings, protecting the health of the occupants.
Bacteriostatic properties are determined according to the DIN EN ISO 846 standard by evaluating the impact of micro organisms on synthetic materials. The nonwoven is placed on a culture medium to which different fungal spores and bacteria are applied. After a period of 4 weeks under defined temperature and lighting conditions, the growth of both fungi and bacteria is visually observed.
In construction, for roofing and façades as well as in technical applications the utilised materials are frequently subjected to sunlight. Use of specifically chosen polymers result in Sandler nonwovens being UV-resistant: The material’s structure remains intact, neither discolouration nor disintegration being an issue.
UV-resistance is determined by means of an exposure test. Samples of the nonwoven may for example be placed behind window glass and subjected to real climate variations. Prior to and after the test, the nonwoven’s mechanical properties are determined, by checking for any detrimental effect from exposure to the UV-rays, in relation to the duration of exposure.
Mechanical stability is a vital property in nonwovens. It describes their resistance to tearing or breaking caused by mechanical influences. In many applications, nonwovens are subject to strains such as vibrations during processing and use or to compression. Mechanically stable nonwovens withstand these forces, being tear-resistant and having low elongation values in machine and cross machine directions.
- Wipes: Variants featuring reduced elongation for household and industrial cleaning support even heavy-duty applications.
- Filtration: Mechanically stable nonwovens resist the volume flow in use as well as vibration in the filtration plant.
- Technical applications: Mechanically stable nonwovens are used for sheathing and other reinforcements.
To determine a material’s mechanical stability, maximum tensile force and maximum elongation in machine and cross-machine directions are measured at varying parameters according to WSP 110.4. Mechanical stability also embraces several properties specific to the respective application:
In car seats, in furniture, in technical applications and even in cleaning wipes nonwovens are subject to abrasion, which may weaken the nonwoven’s structure. Since the nonwoven is made up of single fibres, these fibres have to be well anchored in the fibre matrix to provide appropriate cross-directional stability. In this way, abrasion resistance is achieved. In the production of nonwovens, Sandler relies on fibres with a high resistance to breakage, thereby fulfilling these requirements.
The abrasion resistance of a nonwoven can be determined using the so-called Martindale test method or according to the DIN EN 530 standard. The materials are classified in requirement categories, depending on the number of scrub cycles as determined by testing. The more cycles endured by the nonwoven, the higher its abrasion resistance. This test can be carried out by our external partners if required.
No fibre shedding and minimised fibre breaking
Sandler nonwovens are made of synthetic fibres that do not shed and due to their elasticity and resistance to breakage, result in the minimum of fibre debris. These media do not cause skin irritation and present no health risks—for example in the automotive industry or in construction. Sandler nonwovens thus meet the requirements of product class 1 of the Oeko-Tex® standard 100, bearing the “Confidence in Textiles” label.
In filtration, this characteristic is of paramount importance: If the fibres are brittle, fibre fragments may become detached and contaminate the source of the clean air stream.
Materials featuring high resistance to bending demonstrate high stability even under strain. This property is particularly relevant for use in self-supporting structures intended to be installed overhead using only few fastening points. Vibrations may develop in use, transposing the component’s weight into a strain. Stiff materials do not deform under load and do not sag. They retain their residual stiffness over the long term.
- Automotive: Nonwovens featuring high bending stiffness are in demand for moulded parts such as headliners.
- Construction industry: Stiff nonwovens are applied for acoustic ceiling panels and other ceiling structures.
At Sandler, bending stiffness is determined using the three-point-method according to DIN EN ISO 14125: A sample is deformed at a constant rate; the applied force and the deflection are measured. This test is performed in our own laboratory.
In roof construction, the raw materials are literally being walked on. Sandler nonwovens for insulation laid on the rafters or bituminous strips feature a pressure- and tread-proof upper side for safety in roof work. Even under pressure they remain firm, due to their high bending stiffness.
Flame-resistant products meet particular demands in the event of fire. Subjected to blaze, sparks or open fire, they do not catch fire immediately. When ignited, these structures do not continue to burn, but extinguish after a specific time.
Depending on the specific application and national regulations, various test standards apply:
- Automotive applications: DIN 75200, MV SS 302, PV 3357 and UL 94
- Filtration: The provisions regarding flame-resistance are laid down in DIN 53438 standard.
- Construction: Nonwovens for office fittings and mattresses used on ships and trains are evaluated according to DIN 4102 or DIN EN 13501 standards.
- Upholstered furniture: BS 5852 standard is decisive in this sector.
Our nonwovens are tested for flame-resistance in cooperation with external testing institutes.
Dust holding capacity
The dust holding capacity describes a filter medium’s ability to deposit a specified amount of dust during its operating life. In order to determine the dust holding capacity, a filter is loaded with dust until a predefined pressure drop (final resistance) is reached. The total amount of dust deposited in the filter is then measured. The more dust a filter can deposit, the longer its operating life.
In practice, however, particularly filter media for synthetic vacuum cleaner bags do not experience continuous loading with comparatively low quantities of dust. More likely, they are required to accept relatively high amounts of dust at irregular intervals. Sandler filter media were developed specifically for this purpose. Due to their graded structure, these depth filter media feature high dust holding capacity, promoting a consistently high airflow.
Progressive or graded structure nonwovens combine different fibrous layers in one medium, building up from coarse to fine fibres. For instance in filtration, these materials offer depth filtration properties: Larger dust particles are deposited already in the coarse fibre layers; fine dust particles in the fine fibre layers. This characteristic also promotes a longer operating life of the filter and therefore fewer replacements.
Sandler's pleatable nonwovens for the filtration industry are suitable for processing on knife as well as rotation pleating lines. A homogenous, longitudinally oriented fibre structure provides for particularly accurate pleating and high pleat depths. The polymers utilised are temperature-stable, elastic and resistant to breakage, thus offering high stability: The pleats are dimensionally stable, yet are also flexible. They withstand mechanical influences during processing and temperature and humidity during use.
Cutting & die-cutting
Sandler nonwovens are easy-to-process using established cutting technologies such as band knives, CNC cutters, straight knives, water-jet cutting or laser cutting. Perforation cuts for tearoff wipes, for example, are also possible.
For hygiene products, automotive industry products, and for mat filters die-cutting is used, to which Sandler nonwovens are highly suited. Particularly in automobiles precision contouring facilitates accurate assembly onto the particular component. The material is also not distorted during die-cutting, resulting in accurate cuts with clean edges.
By selecting appropriate fibres, Sandler nonwovens are easily processable and can be sewn without difficulty—in the manufacture of fashion, mattress covers, car seats, and for pipe insulation or the production of pocket filters.
To achieve adhesion between layers, as an eye catcher or for the selective deformation of voluminous materials: Sandler nonwovens are embossed for a variety of applications. They are well suited to both calender and ultrasonic embossing, frequently used for the hygiene industry. In the automotive sector, embossed nonwovens are also used for example in engine cover parts. Again Sandler nonwovens are ideally suited to the processes employed in this industry, such as hot and ultrasonic embossing.
Due to the thermoplastic properties of the selected polymers utilised Sandler nonwovens are mouldable and are able to match the contours of the component. In addition, the material can also be hardened through moulding.
- Automotive industry: Nonwovens are for example processed into 3D moulded parts such as headliners or wheel house liners.
- Interior design: Acoustically efficient moulded parts made of nonwovens are also making advances into interior design. One recent example: a designer lamp shade.
In the filtration industry nonwovens are generally pre-heated prior to pleating. Sandler nonwovens are well suited to this process.
The polymers used make Sandler nonwovens totally compatible with ultrasonic welding, high-frequency welding or thermal welding techniques.
- Automotive industry: Ultrasonic or high-frequency welding spots are used to fasten nonwovens to die-cut or cover parts.
- Filtration & hygiene industry: Multi-layer composites can be bonded using ultrasonic or high-frequency welding.
- Technical applications: Nonwovens for pipe insulation are sealed using common welding technologies.
Depending on the specific application, Sandler nonwovens can be laminated with different materials to produce multi-layer structures with multifunctional properties: for improved acoustic efficiency, hardening, greater stability, resistance to heat or for improving mechanical properties. In fashion, the nonwoven is bonded to the outer fabric, in hygiene products multi-layer structures combine reliable protection with comfort in use—the possibilities are virtually endless.
In the hygiene industry, nonwovens are frequently transported to the laminating line on a vacuum conveyor belt. This process poses specific demands on the material’s air-permeability and Sandler nonwovens provide these characteristics.