EP2959044A1

EP2959044A1 - Fiber-based carrier structure for liquids and solid particles

Info

Publication number: EP2959044A1
Application number: EP14705188.2A
Authority: EP
Inventors: Gerald Ortlepp; Renate LÜTZKENDORF; Thomas Reussmann; Martin Danzer; Wolfgang Schmitz; Cornelia Finckh; Dörte Marlow
Original assignee: SGL Automotive Carbon Fibers GmbH and Co KG
Current assignee: SGL Automotive Carbon Fibers GmbH and Co KG
Priority date: 2013-02-20
Filing date: 2014-02-19
Publication date: 2015-12-30
Also published as: JP2016510091A; KR20150120445A; HK1215597A1; DE102014102079A1; US20150354111A1; WO2014128149A1; CN105339540A; CA2900996A1

Abstract

The invention relates to a fiber-based carrier structure made of fractions of industrially produced reinforcing fibrous materials, which comprises endless fibers in a tangled arrangement as a first reinforcing fiber component and which comprises endless fiber bundles as a second reinforcing fiber component, wherein the fiber-based carrier structure also has a pore system. According to the invention, endless individual fibers and endless fiber bundles are used as a mixture preferably in an isotropic tangled arrangement to produce a fiber-based carrier structure, the pore system of which is an open-cell pore system and is openly accessible from outside. Said fiber-based carrier structure enables the absorption of liquids and/or solid particles by the selection of a defined mixture ratio of endless fiber bundles and endless individual fibers, wherein the capacity to be impregnated with and the capacity to absorb liquid and/or solid powdery materials can be set by means of the mixture ratio.

Description

The present invention relates to a fiber-based carrier structure comprising proportions of industrially produced reinforcing fibrous webs comprising as a first reinforcing fiber component finite fibers in a confused array and comprising as a second reinforcing fiber component finite fiber bundles, the fiber-based carrier structure further comprising a pore system.

[State of the art]

WO 2012/072 405 A1 describes a fiber preform having a unidirectional fiber ribbons, which is constructed from two zones which differ from one another. This known fiber preform thus has an anisotropic structure. In a first zone reinforcing fiber bundles are arranged, the one

Resin composition, while the second zone comprises a unidirectionally oriented reinforcing yarn strand, as well as a resin composition. The aim of this document is to provide a fiber preform that allows adaptation to the respective local loads in the component.

WO 2010/139077 A1 describes a method for producing a composite material having the features of the aforementioned type. This comprises a core layer comprising at least 20% by volume of air pores comprising a fiber-reinforced thermoplastic and reinforcing strips of continuous, parallel, unidirectional reinforcing fibers which are embossed on one or both sides into the surface of the core layer. The reinforcing fibers of the outer layer are thermally welded to the core layer using thermoplastic binders. It remains unclear how the airborne content in the core layer is deliberately adjusted. could be or whether these pores are still accessible from the outside. Here there is a high product anisotropy between core and outer layer. The embossed in the surface of the core layer reinforcing fiber strips are aligned parallel to each other. This document is about producing a composite material with high strength and rigidity, which is a good one

Sound absorption has. The pores have no significance for the uptake of liquids or solid particles, i. it is not desired to drink. DE 10 2007 012 608 A1 relates to a method for producing a preform for a force-flow-compatible fiber composite structure in which a flat sliver obtained by spreading a fiber bundle is placed at a predefined position and then fixed by means of a binder material. Since a load-oriented arrangement of the slivers is sought here, results in a high product aisotropy. No defined mixtures of individual fibers and fiber bundles are used.

DE 10 2008 026 161 A1 describes a method for producing a fiber composite component in which continuous reinforcement fibers are used, which are combined with a matrix material to form an impregnated fiber material in the immediate vicinity of a molding die. Again, it is a load-based arrangement of reinforcing fibers, resulting in a high anisotropy in fiber orientation, with endless reinforcing fibers are used.

In the production of fiber layers in the classic textile industry in the field of nonwovens or fleece-like fillers, it is always the endeavor to completely singulate the finite fibers used as completely as possible. Remaining fiber bundles, also called cut bundles in man-made fibers, are defined as defects and should not occur as far as possible. Accordingly, according to the current state of the art, nonwovens are used, which are characterized in that they consist of fibers whose position can only be described by the methods of statistics. Nonwovens are made according to the fiber material (eg the polymer in man-made fibers), the bonding process a distinction is made between fiber type (staple or continuous fibers), fiber fineness and fiber orientation. The fibers can be deposited defined in a preferred direction or be completely stochastically oriented as the random nonwoven fabric or random web. A nonwoven fabric with defined proportions of fiber bristles and individual fibers as a support structure for substances and its use in the field of fiber composites has hitherto not been known. The support structure here can be a loose fiber bed up to the solidified 2D and SD structure, eg nonwoven fabric = 2D. Conventional nonwovens, which may be bonded mechanically, thermally or chemically, have detectable properties, depending on the pulp, fiber geometry (thickness, length), pulp mixture and production or solidification, in order to bind liquids or solid particles in the form of powders. In the case of liquids, this is referred to as a certain pumping speed, which is expressed by the fact that more or less large quantities of liquid - mostly aqueous, low-viscosity systems for applications in the area of cleaning or of absorbing in the sense of disposal, in a nonwoven fabric be absorbed into the inner layers. Tough liquids or melts can only be absorbed at the fleece surface without additional measures. As the viscosity of the liquid increases, it becomes increasingly difficult to penetrate it into the core of a nonwoven layer. Here you can help yourself with long drinking times, with an additional elaborate suction of the nonwoven fabric, for example by means of vacuum or pressure injection with only limited success.

It is similarly problematic to introduce solid particles in the form of powders or fine particles into such conventional nonwoven fabrics made of individual fibers. They usually remain on the fleece surface and penetrate only in shallow layers. The narrow-pored system of intermediate spaces when using single fibers prevents deeper penetration into the fleece core. This high particle retention capacity of conventional nonwovens is advantageously utilized, for example, in dust or aerosol filtration, but is used in other applications, for example in the production of fiber-reinforced plastics, where later curing matrix materials in the form of viscous liquids or powders must be introduced as homogeneous as possible in reinforcing fiber nonwovens, fillings or mats, extremely hindering.

In the field of fiber-reinforced plastics, it is necessary for pulverulent binders and viscous liquid binders to penetrate the thickest possible reinforcing fiber layers uniformly in order to obtain a uniform fiber content over the product cross section in the later fiber composite material. Here one helps oneself, by using sometimes mats from 100% Schnittfaserbündeln. Although such so-called Schnittrovingmatten, for example based on glass fibers, have good penetrability with highly viscous liquids and binding powders, but are not able to absorb such binding substances in the sense of depot formation in large quantities binding and to hold.

OBJECT OF THE INVENTION

The object of the present invention is to define a fiber-based support structure with the features mentioned, made for example of fiber beds of finite fibers random arrangement / orientation, the matt-like or three-dimensionally shaped as reinforcing kung semi-finished a high and controllable impregnability with viscous liquids and Having powders and at the same time deposit high amounts of these substances in the interior evenly distributed.

The solution to this problem provides a fiber-based support structure of the aforementioned type with the features of the main claim.

The invention provides a fiber-based carrier structure for the production of fiber-reinforced composite materials, which by using a defined mixture of finely randomly arranged fiber bundles and finely randomly arranged individual fibers, in particular for the absorption of liquids, melts and / or

Solid particles is suitable, wherein on the mixing ratio fiber bundle: individual fibers, the impregnability and the absorption capacity of liquid, viscous, and / or solid powdery substances is adjustable. The fiber In this case, the structure, in terms of length, width and thickness, has the same structure and is characterized by an open-cell, openly accessible pore system. The fibrous carrier structure according to the invention does not consist of at least two different product zones of different composition and orientation as described in WO2012 / 072405 A1 or, as described in WO 2010/139077, a core and a completely differently constructed top layer of continuous fibers.

Preferably, in the present invention, the finite fiber bundles result from initially endless but finely shrunk reinforcing fiber bundles or multifilament yarn pieces in which the individual fibers adhere to one another mechanically by non-natural bonding means for at least 50% of their length. However, it may also be fibrous materials from recycling processes, if they result in a bundle-like manner in the context of this invention.

This definition excludes the known fiber bundles of natural fibers such as flax, hemp, nettle and kenaf.

These long, parallel and mechanically detachable adhering fibers in the fiber bundle differ significantly from the fiber bundles mentioned in the literature, for example in the meshing or needling nonwovens, which only a short distance «50% of the fiber lengths, for example, in the local summarization of random fibers in a Vermaschungshäkchen or are formed in the barbs when needling from sporadically present individual fibers. These fiber bundles described in the literature, in contrast to the finite fiber bundles described in the present application, are held together only locally by external pressing forces or binding points. They are formed only during textile processing and are referred to in the literature as mechanical consolidation points, whereas the fiber bundles in the described invention already in the starting material, the pulp, are present and not specifically formed during the processing process. The individual fibers used in the mixture used may consist of the same or a different polymer as the fiber bundles used. This particular support structure, formed from both fiber systems, fiber bundles and single fibers in a defined uniform or different thickness and / or basis weight, is mechanically, thermally and / or chemically stabilized and fixed in such a way that at least 10, at most 90% of the resulting, consolidated fiber support Fiber bundles with a minimum of 10 parallel adhering individual fibers and an open-pore system open over the entire structure open. The pore system comprises a plurality of interconnected cavities which are interconnected by transport channels to transport externally applied powders and / or liquids in the cavities can. According to the invention, it is provided to produce the product from a defined mixture of individual finite fibers and finite fiber bundles, to form them into a surface or three-dimensionally and then to fix them. The proportion of the fiber bundles used determines to a decisive degree the impregnability or the penetration depth of highly viscous and powdery substances into the product layer. The proportion of individual fibers determines to a decisive extent the penetrability of storable liquids or powders. The higher the proportion of fiber bundles in the structure, the higher the proportion of larger cavities with macropores and partly continuous channels, the higher the proportion of individual fibers in the structure, the higher the proportion of smaller cavities. The cavities are connected to each other by transport channels to transport externally applied powder and / or liquids or melts in the cavities can. Surprisingly, it has been found that, depending on the mass fractions of individual fibers into fiber bundles, the impregnability of such a structure changes with viscous liquids and powders. The higher the proportion of single fibers, the longer it takes to soak, and the worse a powder penetrates into this structure.

According to the invention, it is provided that this effect is specifically designed and controlled via a specifically adjustable mixture of the two components. In the product according to the invention therefore finely fibrous materials of the same or different types in two forms, a bundled, undefibered form and a fiber-singled form in defined proportions processed so that in a nonwoven mat or a three-dimensional molding at least 10%, but not more than 90% of the fibers used still remain as undecorated bundles and thus significantly determine their further usability as semi-finished fiber products for reinforcing plastics. In a preferred embodiment, the fiber bundles and the individual fibers are present in a random arrangement, without defined orientation, as can be achieved, for example, by a confused filling.

Such mixtures can be generated defined on the one hand by gravimetric weighing of one or more bundled fiber components with one or more fiber-isolated fiber components and subsequent mixing, for example by means of textile mixing technology. On the other hand, it is possible, starting from a> 90% fiber-bundled starting material by subsequent processing processes such as textile fiber opening by means of opener, the treatment by a mill (DE102009023641) with ripper, carding or similar-working units an adjustable depending on Öffungsintensität mass ratio between fiber bundles and To produce single fibers. In test series, the aperture technique, number of passages and parameters to be used are adjusted to one another in conjunction with the character of the fiber-bundled starting material in such a way that the desired residual bundle fraction in the product results. The main influencing parameters in the starting material are the fiber bundle length and the adhesion intensity of the individual fibers in the fiber bundles presented. The mechanically detachable parallel sticking together of the individual fibers over a length of> 50% of the individual fiber length in the bundles is decisively determined by the type and amount of adhesive polymer-foreign substances, such as, for example, sizes and finishes, on the fiber surface. When

Binders in the bundles can also be used non-crosslinked and / or uncured polymers. An important criterion is that these bundles must be mechanically relatively easy to dissolve. In this way, it is technically possible to produce constant proportions of 10% to 90% fiber bundles and the remainder as individual fibers in a quantity of fiber which, by mechanical and / or pneumatic processing, subsequently to a constant or variable thickness and basis weight. ierenden fiber layer can be constructed. The fiber bundles are characterized in that they consist of at least 10 parallel adhering individual fibers that adhere to each other over at least 50% of their length. The fiber bundles can be mechanically resolved relatively easily and without fiber damage into smaller bundles or individual fibers.

This mixture of fiber bundles and individual fibers with a defined and constant over the production time proportion of fiber bundles and individual fibers lead to a defined thickness and surface mass profile, the thickness and the basis weight in the formation of the fiber bed in time and area uniform or deliberately different can.

Conventional fiber-processing aggregates of the textile industry such as openers, mixing chambers, filling shafts, airlay and fiber blowing plants can be used for the production and processing of this fiber mixture of bundled and singulated fiber components, which, however, must be technically and technologically modified such that the desired mixing ratio of bundles and sporadic fibers is ensured. Such modifications include a reduction in the number of fiber-opening passages, the absence of carding and carding in the processing process, the reduction of opening roll speeds, the use of coarser roller fittings during mixing, homogenizing and dosing and the increase of distances between zerfasernd acting work units. All measures are used, in contrast to the prior art, to fiberize the fiber bundle components which advantageously act in the end product or only to a small degree. Therefore, in a preferred embodiment, the use of carding and carding in the processing process is dispensed with. The type of modifications depends on the plant technology used, the fiber material used and the fraction of fiber bundles desired in the end product. In tests, therefore, all influencing parameters must be coordinated with each other and the necessary plant and technology modifications must be made. In principle, mechanically and / or pneumatically operated aggregates such as filling shafts, airlay or fiber blowing plants are suitable for laying the loose fibrous layer of bundled and shredded fractions. Here, too, systems and processes must be specially designed by means of the abovementioned measures in such a way that they not only homogenize the mix but also define their fiber opening / fiberization intensity and only have a strong fiber opening in such a way that the desired target range of fiber bundle fraction and single fiber fraction is achieved. If fiber-opening aggregates are used to a certain extent, the fissuring effect of these aggregates must be taken into account by a higher fiber bundle content in the starting material provided. The mixture of fiber bundles and individual fibers is deposited confused.

During the processes of mixing and homogenizing and laying the fibrous layer, it is already possible to introduce pulverulent substances, thermally binding components or liquid binders which are not originally part of the fibers and / or fiber bundles used. These binding components are used to fix the pore system and the support structure of single fibers and fiber bundles and / or as a binding component in the formation of the fiber-reinforced composite materials. After the formation of the loose fiber layer of homogeneously distributed fiber bundles and individual fibers of defined proportions, it is necessary to fix this special structure and to make it resistant to pressure and tensile stress against handling stresses. For this purpose, mechanical methods such as needling or meshing or binder strengthening of binder-containing or thermoplastic bulk layers can be used.

Exposure to contact or radiant heat, or hot air flow, fuses or dries liquid binder fractions. The application of binders for fixing the pore system and the support structure of individual fibers and fiber bundles and / or as a binding component in the formation of fiber-reinforced composite materials after bulk layer formation in the form of a powdering or spraying is also technically possible and is determined by the intended use of the solidified layer. Again, the solidification is usually carried out by a binder drying or a melting or melting heat treatment. Through these processes, the purposefully generated Pore system fixed in the nonwoven semifinished product. The open pore system of the fleece-like semi-finished product consists of small cavities, which form insbeondere as spaces between the tangled, intersecting and diameter very thin single fibers, and larger cavities, which arise as spaces between the tangled intersecting and diameter substantially larger fiber bundles. Depending on the proportion of fiber bundles on the individual fibers, a correspondingly finer or coarser open-pored cavity system or pore system with different impregnabilities and substance storage capacity results. These pores or cavities, which can be selectively adjusted in accordance with the proportions of individual fibers and fiber bundles, perform the function of binder transport or binder infiltration of the nonwoven semifinished product as well as retention of the binder in the nonwoven semifinished product in subsequent processing. The coarser, open pore system forms transport channels for thick, viscous binder resins and powders that reach into the center of the nonwoven layer. This makes it possible to substantially support a targeted, complete impregnation with viscous liquids and powders, which simplifies the impregnation technology on the cost and technology side, shortens impregnation times and makes it possible to use thicker reinforcing semi-finished fiber products. The finer pores based on the individual fibers in the product ensure that the penetrated binding components are retained in the product like a sponge and stored.

The proportion of fine and coarse pores is determined by the respective proportions of coarse fiber bundles and fine individual fibers in the nonwoven fabric. Depending on the web thickness, impregnating medium to be used for forming the solidified support structure or the fiber-reinforced molding and the infiltration technology, the proportions of fiber bundles and individual fibers are to be tested and determined in preliminary tests for the particular fiber material to be used. By means of mechanical needling or a similar process, additional vertical branch channels can be formed for the existing pore structure, which support a binder transport into the nonwoven layer and influence the function of impregnability. By compression of the poured fiber layer is in the

Usually reduces the Durchtriebbarkeit of the web and reduces the depot effect. In the interplay of pressing processes for the reduction of nonwoven thickness and applied nonwoven bonding, the resulting impregnability is again purposefully influenced and fixed in terms of final quality and quantity. The use of these semi-finished fiber products with defined fiber bundles focuses on the field of fiber composites. Accordingly, the fibers used are in the range of conventional reinforcing fiber substances settled. These may be organic fibers such as para-aramids as well as glass and carbon fibers including such fibers from various recycling processes.

[Examples]

Embodiment 1

Starting from a highly fiber-bundled starting material based on mechanically treated carbon fiber webs were by different fiber opening intensities on a roll opener (material 1) and a carding 2 (material 2) fiber beds of different fiber bundles produced and this to a uniform basis weight of 500 g / m ² at a constant bulk thickness built up. The carbon fibers used in a mechanical recycling process had an average length of the fiber bundles of 45 mm. The fiber bundle fraction was determined by mass on the two fiber materials by manual screening, the air flow resistance was measured as a measure of open porosity and accessibility for particles and liquids by means of an air flow method and the drop sinking times were determined by means of a drop test using a higher-viscosity liquid in accordance with the TEGE-WA. Drop test determined as a measure of the impregnability.

The following results occurred:

Parameter Unit Material Material 2

1

Fiber bundling ^* [%] 80.5 51, 9

Air flow resistance as measure [mm Isop 377 430 the porosity ^** ropanol]

Sinking time in the drop test ^*** [s] 120 - 150 280 - 310

^* Fiber bundling was determined by manually screening a fiber sample of 1 g, weighing the bundles of at least 10 individual fibers and calculating the percentage by mass.

* ^* The determination of the air flow resistance was based on a publication in 1964 by Geitel, K.: "Theory of air flow through Faserpfropfen", in "Faserforschung and Textiltechnik" 15 (1964) Issue 1, pp 21-29. Here the theory of air flow through fiber grafting is described. Thereafter, the pressure drop over a flow-through amount of fiber depends on

the amount of air flowing per unit time,

the dimensions of the measuring chamber (diameter, height),

the viscosity of the flowing medium,

the porosity of the amount of fiber and

- the fiber surface.

The porosity of a fiber graft was determined by means of the wool fatigue tester type 4/15/1 from Medimpex (Hungary) by means of this air flow method. The Faserpropfen in this case, the specimen, formed from the carrier structure produced according to the embodiment. All parameters except the fiber material to be tested were left constant. The air resistance generated by the fiber plug is read in the meter in [mm] of an isopropanol liquid column. The column height in [mm] is directly proportional to the established air flow resistance and thus indirectly proportional to porosity. The tests were each carried out on 1.4 g of fiber material at an air flow rate of 400 l / min.

^*** In the modified drop test, the test liquid was a CMC solution having a viscosity (25 ° C) at shear rate 2 / s of 1.7 Pas. The mass of the test drop was always 0.5 g. Embodiment 2

Based on a highly fiber-bundled starting material based on mechanically treated carbon fiber fabric, this was achieved with 7% of a thermally enhanced The binder fiber GRILON MS 6.7 dtex / Vario cut is intimately mixed over a mixed bed and 1 mixing passage with a coarse opener using a mix-opening pin roll and feeding the material over a pair of rolls. One half of this constant starting fiber mixture of strongly fiber-bundled carbon recycling fibers and thermally softening binder fibers in the mixture ratio of 93/7 was then applied via a feeder FBK 536 from Trützschler at 2 m / min to a loose bed of 370 g / m ² . The other half of the starting material was processed as a comparison material by a 2-fold carding with a roll card when using 3 worker / Wenderpaaren at 10 m / min to cream pile and loosely stacked by means of Quertäfler, so that this resulted in a basis weight of 370 g / m ² ,

Subsequently, both loose fiber layers, feeder layer and carded and laid layer, with a Thermofix the Fa. Schott & Meissner at a flow rate of 2 m / min, a heating temperature of 190 ° C and a gap of 1, 5 mm, in which the two Fiber layers were successively passed between an upper and lower conveyor belt through the thermal consolidation system, semi-solidified to a mat and fixed the formed cavity and pore structures.

The water absorption according to DIN 53923 was then carried out on both nonwoven mats as a measure of the storage capacity for liquids. Before thermal consolidation, the mass fraction of the fiber bundles in both loose fiber layers was determined.

The following results occurred:

Sample fleece mat type

Food laid out

Water absorption according to DIN 53923

1202% 929%

2 1069% 930%

3 1097% 866%

4 1065% 846%

5 1097% 902% Mean 1106% 895%

fiber bundle

Share 85% 6.6%

While a high proportion of fiber bundles was used in the first fiber-based carrier structure according to the invention (ratio of fiber bundle to individual fibers about 5.66: 1), the single-fiber fraction was used for the carded nonwoven mat which served as comparison material (in the above table on the right). comparatively high (ratio of individual fibers to fiber bundles approx. 14.15: 1). The above table shows that the water absorption in the carrier material according to the invention is substantially higher than in the comparison material.

Claims

[Claims]

1 . Fiber-based carrier structure for liquids, melts and solid particles from proportions of industrially produced reinforcing fiber materials,

comprising as a first reinforcing fiber component finite fibers in a confused arrangement,

comprising, as a second reinforcing fiber component, finite fiber bundles, the fiber-based support structure further comprising a pore system, characterized in that

finite individual fibers and finite fiber bundles are present as a mixture in a defined mixing ratio of 1: 9 to 9: 1 and that the pore system is open-celled and accessible from the outside.

2. Fiber-based carrier structure according to claim 1, characterized in that the finite individual fibers and finite fiber bundles are present in an isotropic, confused arrangement.

3. Fiber-based carrier structure according to claim 1 or 2, characterized in that the pore structure formed by a fiber bed is partially compressed and mechanically, thermally and / or chemically stabilized and fixed.

4. Fiber-based carrier structure according to one of claims 1 to 3, characterized in that the individual fiber portions were obtained in the mixture of fiber bundles and individual fibers by not completely opening fiber bundles.

5. .Fiber-based support structure according to one of claims 1 to 4, characterized in that the fiber bundles have an average bundle thickness of at least 10 individual fibers which adhere parallel over at least 50% of the fiber length.

6. Fiber-based carrier structure according to one of claims 1 to 5, characterized in that the fiber bundles and / or at least a portion of the individual fibers have a fiber length distribution.

7. Fiber-based carrier structure according to one of claims 1 to 6, characterized in that the fiber bundles have a different from the individual fibers average length.

8. fiber-based carrier structure according to one of claims 1 to 7, characterized in that before the formation of the fiber layer, evenly distributed mixed softenable binding fibers and / or a powder.

9. Fiber-based carrier structure according to one of claims 1 to 8, characterized in that the fibrous materials used as starting material have a uniform material nature and geometry or are a mixture of fibers of different materials and / or geometry.

10. A process for producing a fiber-based carrier structure according to any one of claims 1 to 9, characterized in that weighing one or more bundled fiber components and one or more fiber-singulated fiber components each gravimetrically and then mixed with textile mixing technique.

1 1. Process for producing a fiber-based carrier structure according to claim 10, characterized in that the fiber mixture is volumetrically and / or pneumatically deposited in a layer having a thickness of 0.5 to 20 cm, preferably 2 to 10 cm, loosely and preferably without priority orientation.