The conductive cores layer material
This document relates to core layer materials for closed or open mold systems, methods of making core layer materials, laminates including core layer materials, methods of making shaped articles, shaped articles, and uses of the articles
The core layer material comprises: at least one fibrous web containing a foam structure therein, the foam structure being composed of a plurality of members, wherein the members are separated from each other by channels permeable to resin; a binder; a network of conductive materials.
Background technology
The core material can be used to produce fiber-reinforced plastic materials, suitable for closed or open mold systems. Plastics reinforced with fiber webs are often used in the production of special cosmetic products, such as automotive or industrial components such as water tanks, bathtubs, road signs, siding, boats, caravans, engine rooms, motor blades, and more. In general, the addition of a fiber web to a resin material results in enhanced strength, stiffness, fatigue life, fracture toughness and environmental resistance, enhanced temperature stability, reduced weight, and reduced production cost of the resin material.
The use of core materials in fiber-reinforced plastics has been a well-known technique for decades. The purpose is to reduce the amount of resin required on the one hand to save costs and reduce weight; on the other hand, to improve some mechanical properties of the material, such as bending stiffness.
For example, manufacturers disclose the use of fiber webs, in combination with microspheres, for producing objects reinforced with such fiber webs. Although they refer to metal fibers, this refers to a mesh of fibers rather than a (separate) layer of conductive material.
In a method of producing a composite material, a web is impregnated with a curable resin and wherein a porous layer is placed on the web material. After curing the resin, bonding of the porous layer is achieved. A flexible core layer material comprising a mesh to which a conductive layer is attached is disclosed.
However, these known fiber-reinforced materials do not provide protection against electromagnetic interference, which is highly desirable in special applications.
Electromagnetic Interference (EMI) refers to the susceptibility of electronic devices to external electromagnetic fields. This affects electronic devices by causing current fluctuations, which can lead to unexpected switching eg within microprocessor units and semiconductor chips. Especially electronic equipment with high density is very susceptible to electromagnetic interference.
A well-known environmental factor for electromagnetic interference is lightning. Not only is the initial lightning strike damaging, but also the electrostatic field left behind after the strike has a damaging effect. In particular, effective electromagnetic interference shielding is highly desirable in applications that are susceptible to lightning strikes and that otherwise include a high density of advanced electronic equipment, such as aircraft and nacelles for wind turbines.
Another disadvantage of electrostatic fields is that they attract dust and other dust. Especially when some products or objects move, they can cause annoying friction. As one example, wind turbine blades, where electrostatic fields attract.
The potential damage from electromagnetic interference is mitigated by including a continuous conductive shield around sensitive electronic systems, for example by providing a Faraday cage. Within the Faraday cage, the charge within the conductive material is allowed to redistribute to eliminate the effect on the interior of the Faraday cage.
A method of providing a composite article with a continuous conductive shield involves embedding a conductive wire mesh in the composite article during the manufacturing process. Conductive layers are provided while using standard synthetic part fabrication methods. The article can be made by providing the wire mesh alone on the synthetic laminate in the mold. During the molding process, under uniform pressure, the resin flows into the voids of the wire mesh, integrating the structure.
However, this method requires precise handling of the wire mesh, which has proven to be quite difficult in practice. In many cases, the wire mesh can tear, move and/or pierce layers necessary in the production process (eg, can pierce plastic bags used in vacuum injection molding). Also, the wire mesh usually used for this synthetic material is thicker to prevent splitting. But the thick wire mesh increases the production cost of the synthetic material.
Summary of the invention
The main purpose of this paper is to provide a core material that at least partially overcomes the above-mentioned disadvantages.
We have found that this can be achieved by providing a core material with a continuous conductive shield. Accordingly, in the first aspect, the present material relates to a material suitable for a closed or open mold system, including:
at least one woven or nonwoven fibrous web comprising therein a foam structure composed of a plurality of members, wherein the members are separated from each other by resin-permeable channels;
Adhesive;
A layer of conductive material with electrical properties to achieve shielding against electromagnetic radiation.
The layer of conductive material is preferably a separate layer. The separate layer can be secured to the web by means of an adhesive. Alternatively, the layer of conductive material may be attached to the mesh by adhesive, eg by applying a separate mesh of low melting point material and heating the stack material so that the layer is fused into the mesh. Mechanical attachment means, such as stitching, may also be used.
This core material has been found to be well suited for applications requiring electromagnetic shielding. In addition, the core material of this material maintains good drape, compression resistance, and proper permeability. Being a flexible material, the material can be folded into any desired shape before adding resin.
The network may be a wire mesh of conductive material, achieved by providing the web with a network of conductive fibers. Further, a network of conductive material is provided by sputtering through a vacuum mold. Preferably, the network is in the form of a wire mesh.
The thickness of the wire mesh may be 500 microns or less, preferably 200 microns or less, such as 100 microns or less, or 50 microns or less. Typically, the wire mesh is 5 microns or more, such as 10 microns or more. Therefore, according to the present material, very thin wire mesh can be used, thereby reducing the cost and weight of the finished product.
The size of the mesh can vary with the specific application. Usually, the mesh size is about 10-1000 microns, such as 20-500 microns or 50-200 microns.
Typical conductive materials are metals. In principle, any type of metal can be used. Preferably, the conductive material includes copper, aluminum, and stainless steel. Different types of conductive materials can be used for different applications. For example, copper is highly conductive, while aluminum is relatively light and inexpensive. Conductive materials including carbon fibers can also be made.
The conductivity of the core material may be in the range of 35 X 106 S/m to 63 X 106 S/m at 20 °C, preferably in the range of 37 X 106 S/m to 60 X 106 S/m at 20 °C.
If the core layer material comprises a conductive wire mesh, the fiber mesh having a foamed structure can advantageously be used as an electrical insulator between the wire mesh and the conductive article to which the core layer material can be applied. It is advantageous in applications where conductive carbon is used due to its mechanical properties, but it is not desired to have an electrical current passing through the conductive carbon which affects the mechanical properties of the carbon.
A further advantage of the core material is that once prepared, the core material can be easily cut to a size suitable for the application. Also, due to the drapability, the magnetic material can be easily bent and formed. Depending on the properties of the conductive network (eg thickness and mechanical properties of the conductive material), the bending and forming of the core layer material may even be superior to that of a core layer material that does not include a conductive network.
The conductive network present in the core material can also be actively used by the intentional application of current and thus localized transfer of heat. For example, when making an article that includes a core material of conductive material within a mold, it is often advantageous to post-cure the article. This post-curing is done in a very attractive way using a conductive network. Conductive core material delivers heat precisely where it is needed. Furthermore, it can do this post-curing while the article is still in the mold.
In a similar way, the conductive core material can be applied within the walls of a mold to heat such a mold. Also, depending on the application, the mechanical properties of the core material can be tuned and optimized with the conductive network. For example, when the conductive network includes copper, the impact resistance and toughness of the final article can be improved.
The elements and channels of the core material can be distributed in an almost regular manner, for example, repeating in patterns smaller than 1 cm, more specifically smaller than 0.5 cm.
Depending on the intended use, especially the need for the resin to be able to penetrate the core material for a specific period of time, the conductive core material may be selected. Particularly good results have been obtained with core materials having a permeability in the plane of the material of at least 1 X 10-9 square meters.
We have found that the flow properties of the resin within this material are very satisfactory. For better flow properties, the permeability is preferably at least 1.5X10-9 square meters, more preferably at least greater than 5X10-9 square meters.
Permeability is primarily provided by channels, which are formed by regions that do not contain members. Here, the permeability (k) is defined according to Darcy’s law for steady flow as:
Among them, q is the resin flow, and its unit is m3/s; A is the total surface area of the cross-section through which the resin flows, and its unit is m2; n is the resin viscosity, and its unit is Ns/m2; /’, △p is the pressure difference, and its unit is N/m2; Ax is the distance between the pressure difference and the resin flow, and its unit is m. Permeability is defined in the plane of the material, that is, not perpendicular to the material, but parallel to its upper and lower surfaces.
In this literary composition, drapability is defined as the ability that core material meets waved surface (especially mould). Especially,, and can not cause core material to become irreversibly deformed basically, think that so this core material has drapability if the core material that defines in this literary composition can be 10mm or following angular distortion around a radius. This allows material in mold, to dangle in good mode, and can produce the product of smooth molding thus. The core material of the present invention preferably has and allows around the overhanging property of radius for 5mm only or following angular distortion.
Here, compressive performance is defined as the ability to resist forces that tend to crush or bend. The compressive properties were measured by determining the height of the material before applying pressure and when applying 1 bar of pressure perpendicular to the plane of the material. The compressive performance can be calculated as:
Compression resistance can be selected over a wide range due to the type of application and performance requirements. At 1 bar pressure, good results have been obtained with core materials having a compression resistance of at least 40%. Where the core material is suitable for use in a closed mould system, it is preferred that the compression resistance is at least 60% at 1 bar pressure and even 70% or more at 1 bar pressure. This resistance has been found to be very advantageous because the tendency of the channels to press together is low, compromising the entrance of the resin into the channels when processing in a closed mold. Correspondingly, at a pressure of 1 bar, a core layer material having a compressive resistance greater than 75%, at least 80%, at least 90%, or at least 95% is more preferred.
Nonetheless, in some cases, one chooses a core material that is less compressive, eg, about 50% or less.
If used as a core material for hand lay-up or spray systems, in principle a lower compressive resistance is sufficient, especially a 30% compressive resistance at pressures of 1 bar or more.
Surface quality is important, but also limits the use of resin and the weight of the final composition, then one may choose to use materials with lighter material components, such as microsphere foam structures; materials with larger components, such as in the range of 1 -3mm; material with narrower channels between components, eg less than 1 mm; lower free volume eg in the range of 40-60 vol.%.
If surface quality is critical, but weight or cost is less critical, one may choose a core material with smaller components, for example in the range of 0.5-2mm (assuming a core material where the pattern is not irregular: 0 .5-1.5mm), highly irregular component patterns, or resins that do not easily shrink after curing, such as epoxy resins.
If drape and surface quality are important, one may choose to use wider channels, for example, with an average diameter of 0.5-2 mm (assuming a core material where the pattern is not irregular: 0.5-0.75 mm ), in combination with smaller components such as average diameter less than 1 mm, highly irregular, or relatively flexible fibrous materials such as polyester fibers and acrylate adhesives.
The components form “islands” within or on the net, and these components are mainly surrounded by channels through which resin can pass. The channels are largely free of mesh material but may have some fibrous material to provide sufficient coherence to the core material. In general, the content of the material in the channels should be low enough to allow adequate penetration of the resin, preferably allowing a permeability of at least 1 X 10-9m2.
The members are typically made of closed-cell foam structures, and these members may also include or be formed from microspheres. These microspheres are discussed below.
These components primarily contribute to the compression resistance of the core material and are generally not inherently resin-infiltrating. In any case, the permeability of these elements is somewhat less than 1X 10-9m2.
These members can be of any shape. Good structures have been obtained using core material in which at least a majority of the members are selected from members with circular, elliptical, and polygonal cross-sections parallel to the plane of the material. Of course, combinations of the above can also be used. Preferred members with a polygonal cross-section are those with a triangular, quadrilateral, pentagonal, hexagonal, heptagonal, or octagonal cross-section.
Irregular distributions can be obtained using nearly identically shaped members with the same or different dimensions. For example, good results have been obtained using core layer materials wherein at least most or substantially all of the components have circular or elliptical cross-sections parallel to the plane of the material.
Using a variety of differently shaped members, irregular distributions can be obtained. Good results have been obtained using core layer materials where at least most or substantially all of the components have a polygonal cross-section parallel to the plane of the material. The differently shaped members of this core material are selected from the group consisting of triangles, quadrilaterals, pentagons, and hexagons.
We have found that particularly good surface quality can be achieved using a core material having an irregular pattern, where at least a majority or substantially all of the components have a diameter in the plane of the material of less than 3 mm, as defined by the enveloping circle. 5mm。 Moreover, at least most of the components or all of the components in this book have a diameter of less than 2.5mm in the plane of the material. Particularly good results have been obtained with core materials, where at least the majority of the components are less than 1.5mm in diameter.
The diameter lower limit of member is not crucial especially.For common application, the minimum diameter of most of The lower diameter limit of the member is not particularly critical. For typical applications, at least most of the components have a minimum diameter of at least about 0.2 mm. In practice, the diameter is usually at least about 0.5 mm. In addition to surface quality, a factor related to component diameter is the degree to which one wishes to limit the use of resin in a closed mold system.
For example, most of the channels between the components have an average diameter of less than 2mm (in the case of irregular patterns), some less than 1mm (in the case of irregular patterns), and even less than 0.5mm. As defined in the text, the lower limit of the channel is not particularly critical as long as the permeability is maintained high enough. It depends on the resin and molding conditions, and professional technicians can regularly determine the appropriate lower limit. Typically, most channels have a minimum average diameter of at least 0.3 mm. Using a larger diameter, such as 0.5-2mm (0.5-0.75 if the core material does not have an irregular pattern), has the advantage of rapid resin flow through the material and high drape of the material. Smaller diameters, such as 0.3-0.5mm, benefit from lower resin absorption and higher surface quality.
Although thicker or thinner core material can be made, the thickness of the core material varies over a wide range, for example between 1mm and 4mm, with a general choice between 1.5mm and 3mm.
The free volume of the fiber web containing the foam structure is less than 80 vol.%, and can also be 50-70% of the volume. In this regard, free volume means the volume of material into which the resin can be impregnated. The rest of the volume is formed by members (and some fibers).
This layer of web includes at least 20 wt.% fibers and up to 80 wt.% foamed adhesive material. The closed-cell foam structures forming the components can be made from (optionally expandable) microspheres which are introduced into the mesh using a foamed adhesive material.
Good structures have been obtained using a core layer material comprising microspheres with an activation temperature of at least 120 degrees Celsius and a free volume within the mesh of at most 80 vol.%. The mesh can be bonded mechanically, physically or chemically.
The core material, comprises at least 30 wt. % fibers, up to 70 wt. % binder material also contains expandable microspheres. In practice, the amount of expandable microspheres are typically less than 15 wt.%, preferably 1-10 wt.%, based on the overall weight of the core material.
Microspheres swell and these microspheres have an activation temperature of at least 120 °C.
Very good results have been obtained using core layer materials in which expanded thermoplastic microspheres, such as those based on alkyl methyl methacrylates, acetonitrile (polyacetonitrile (PAN)), vinyl chloride or combinations thereof Microspheres of the polymer are present within the web, and the initial expansion temperature of the microspheres is lower than the curing temperature of the adhesive. Commercially available microspheres such as Expancel TM manufactured by AKZO-NOBEL.
Core materials produced using known techniques for the production of fiber reinforced plastic materials can be used.
In the conductive core material, a wire mesh is placed on a fiber web, expandable microspheres are introduced into the fiber web through a binder material, the microspheres are expanded, and the binder is cured. The adhesive force of the adhesive attaches the wire mesh to the core material. Below the curing temperature of the binder material, the microspheres begin to expand.
The core material of the present material can be suitably prepared by a method wherein the non-woven fabric is imprinted with a foam or non-foam adhesive and also contains expanded microspheres, such as polymer, glass or ceramic microspheres, placed with a conductive wire mesh on the non-woven.
If using expandable microspheres, follow the steps below. First, a dispersion of expandable microspheres in a binder material is prepared, and the dispersion is foamed. The initial expansion temperature of the microspheres is preferably lower than the curing temperature of the binder material. Subsequently, a non-woven having a thickness less than the desired final thickness is screen-printed with the dispersion and a conductive wire mesh is placed on the non-woven. The material is then dried and heated to the expansion temperature of the microspheres. The material may be pre-dried (eg, at a temperature in the range of 70-100°C) prior to heating the material to the expansion temperature of the microspheres. Once expanded, the temperature increases further as the adhesive material cures and sets the microspheres within the web. At the same time, the wire mesh is connected to the core material. Making conductive core material in this way.
Alternatively, nonwoven base webs are used, which contain a network of conductive fibers within the web. However, dispersions of expandable microspheres can be screen printed directly on top of the base web. Due to the difficulty of ensuring the electrical performance of shielding electromagnetic radiation, this method is listed as the second choice.
The initial expansion temperature of the microspheres is between 120 and 190°C. The curing temperature of the adhesive is above 170°C.
The fiber webs to be used here are generally nonwovens based on common fibers, which can be reinforced. The production of suitable nonwovens has been described, for example, by Dr. H. Jorder in “Textilien auf Vlesbasis” (D. V. R. Fachbuch, P. Kepper Verlag). It is also possible to combine nonwoven webs and reinforcement fabrics, one within or on top of the other.
The fibers of the web are selected from natural fibers, glass fibers, metal fibers, ceramic fibers or synthetic fibers (for example acrylic, polyethylene, polypropylene, polyester, polyamide (aramid), carbon or polypropylene fibers) and their combination. Very good results have been obtained with polyester fibers. We have found that polyester fibers have very good adhesion to resins and have very low moisture content.
Nonwovens are based on a combination of polyester fibers and polyethylene-polyester bicomponent fibers (or other low-temperature melting fibers or powders). These types of webs have been thermally bonded by bicomponent fibers. By heating the web above the initial expansion temperature of the microspheres, the melting point of polyethylene bonding, the web relaxes and expands easily. After expansion and curing, the final material again has good adhesion, which is a favorable combination of the properties of the conductive core material. At the same time, it is very easy to handle at the beginning of the step due to thermal adhesion.
The fibrous web can provide microspheres composed of at least a thermoplastic synthetic resin material that is solid at room temperature. Including polystyrene, polyethylene copolymer, polyvinyl chloride, vinyl chloride copolymer, vinylidene chloride copolymer, etc.
In expandable microspheres, blowing agents have generally been incorporated. The presence of the blowing agent causes the microspheres to expand upon curing of the web comprising the microspheres. The microspheres are thus pressed into the fibrous web in an unexpanded form, for example by a paste (eg foam paste). The blowing agent can be a chemical or physical blowing agent, such as azodicarbonamide, isobutane, isopentane, pentane, freon, isooctane, etc.
In the unexpanded state, these microspheres are 4-20 microns in diameter, and in the expanded state, 10-100 microns in diameter. After the expansion of the microspheres, the amount of microspheres in the mesh is usually 10-60 vol.%. The amount depends on the amount of microspheres used and the degree of expansion of the microspheres.
In this regard, suitable adhesives are low alkyl acrylate polymers, styrene-butadiene rubber, acrylonitrile polymers, polyurethanes, epoxy resins, polyvinyl chloride, polyvinylidene chloride, vinylidene chloride and others Copolymers of monomers, polyvinyl acetate, partially hydrolyzed polyvinyl acetate, polyvinyl alcohol, polyvinyl pyrrolidone, polyester resins, and the like. These binders may have acid groups, for example by hardening the binder. A suitable hardening agent is butanediol anhydride. Definition of binder, a paste-like composition containing water, surfactants, foam stabilizers, fillers, and/or thickeners.
A laminate of conductive core material laminated with at least one fiber layer. The laminate may be formed in any manner by stitching or gluing at least one fleece to one or both sides of the core material.
The advantage of laminate is the ease of use. Laminates allow the combination of core material and glass layer to be easily arranged in one step. So the manufacturer does not need to go through different steps to put different layers (eg bottom fleece, core material, and top fleece respectively) into the mold.
Fiber fleece layers used to make the composite include glass fiber layers, carbon fiber layers, aramid fiber layers, and mixtures thereof (eg, glass carbon fiber layers, glass aramid fiber layers, or carbon aramid fiber layers).
We have found that the conductive core material is very suitable for making thin laminates while achieving a satisfactory smooth looking surface. For example, the total thickness of the laminates according to the present material is 2-10 mm. Good results can be obtained using laminates of core material with a thickness of 1-2 mm using a fiberglass layer with a thickness of about 0.4-0.8 mm and a fiberglass thickness of about 225-600 g/m2, Usually 450g/m2. Laminates with a thickness of about 2-3 mm can be obtained. After curing with resins, especially with epoxy resins, the laminates have a very good surface quality.
This material also includes methods for producing specialty articles, said webs impregnated with liquid resins and curing agents.
Liquid resins used for curing synthetic plastic materials are polyester resins, phenyl ester resins, polyurethane resins, phenolic resins, melamine-formaldehyde resins, and epoxy resins. Skilled technicians can select the appropriate resin considering the specificity of the product to be produced.
The hardener is any hardener used to cure the liquid resin of choice. The skilled artisan is familiar with these materials. The ability to combine resins with curing agents for optimum results is within the standard knowledge of those skilled in the art.
A profiled article obtainable according to the method of the present material, the core material is impregnated with resin, and the core material is cured.
Specialty articles of this material can be advantageously used as shielding materials for electrostatic charges, such as in the housings of electronic equipment, electric vehicles, and batteries. These specialty articles can be used to provide Faraday cages. For example, synthetic boxes with copper scrim on the surface can be produced. The case forms a Faraday cage and can be used to house a battery, which is particularly useful in the automotive industry as the case protects electronic systems, communications and or navigation equipment from the battery’s electromagnetic radiation. Among the wide range of electromagnetic compatibility applications are these examples: train construction, power plants, walls of operating rooms, and nacelles (eg in aircraft and wind turbines).
Now, illustrate the present invention with the following non-limiting instance.
Instance
Core material foil (scrim) combination, when applied in the primary laminate of a wind turbine nacelle, the core material-foil combination below, produces a Faraday cage to protect the electronics in the nacelle.
The copper foil was placed on a chemically bonded base web containing 80 wt. % polyester and 20 wt. % acrylate adhesive.The copper foil is a woven square mouth wire mesh. The wire mesh warp is 99.9% copper with a thickness of 0.050mm, and the wire mesh weft is 99.9% copper with a thickness of 0.050mm.
Hexagonal patterns with an average hexagonal diameter of 6 mm were printed using rotary screen printing with a microsphere binder mixture (90 wt.% acrylate binder + 10 wt.% expandable microspheres Expancel, AKZO-NOBEL; based on solids) % by weight) of the non-woven and foil combination, and then pre-dried the hexagonal pattern at approximately 90 degrees Celsius (below the expansion temperature of the microspheres). The microspheres were then expanded to a thickness of approximately 2 mm and the adhesive was cured at 200 degrees Celsius. The base web and foil are pre-dried and expanded/cured so that the base web and foil are fully bonded
Contact here to get the E-book of Conductive Surfacing Veil
ANY QUESTIONS OR COMMENTS, PLEASE GET A HOLD OF US IN WHICHEVER WAY IS MOST CONVENIENT. WE WILL REPLY YOU WITHIN 24 HOURS.
