Surface finishing molding materials

Abstract

A molding material comprising: (a) a structural reinforcement layer comprising a fiber reinforcement material, optionally in combination with a second resin composition; and (b) a surface reinforcement layer for contacting a mold or tool surface, the surface reinforcement layer comprising a first nonwoven fiber carrier in combination with a first resin composition containing a rheology modifier and a curing agent, wherein the first resin composition provides the outer mold or tool contact surface of the molding material. The molding material can be cured to form a molded article having a high-quality surface finish that requires minimal preparation prior to painting and / or application in its intended use. The molded article can be provided with a sacrificial discontinuous indicator means to help uniformly remove a portion of the surface reinforcement layer of the molded article for a specific application.

Description

[0001] The present invention relates to molding materials providing an enhanced surface finish, methods for preparing the same, methods for preparing molded articles by curing such molding materials, and molded articles obtainable by such methods. The present invention particularly relates to fiber-reinforced composite molding materials that can be cured at low temperatures and comprise a surface finishing layer to provide molded articles having a high-quality surface finish that require minimal preparation after curing, particularly, but not exclusively, for use in the wind turbine and automotive industries.

[0002] Composite materials have well-documented advantages over traditional building materials, particularly in providing excellent mechanical properties at very low material density. As a result, the use of such composite materials has become widespread in many industries, including aerospace, automotive, marine, and wind turbines.

[0003] Prepregs comprising an array of fibers impregnated with a thermosetting resin such as an epoxy resin are widely used to produce such composite materials. Typically, many such prepreg plies are "laid up" as needed, and the resulting assembly or laminate is placed in a mold and cured, typically by exposure to elevated temperatures, optionally under pressure, to produce a cured composite laminate. However, without any surface treatment, such composite materials typically cure to produce a poor surface finish, which can manifest itself as a rough, wavy, or pinhole-filled surface or as narrow grooves on the surface of a molded structure where adjacent prepreg plies have overlapped to ensure a continuous layer. This tendency to form uneven surfaces appears to be closely related to the roughness of the underlying reinforcement, with the rougher the reinforcement, the more pronounced the problem. This can be a particular problem when the rough reinforcement is used for structural rigidity and a smooth surface finish is desired (such as, for example, in the production of automotive body panels, where Class A finish is required, or in the production of wind turbine blades).

[0004] There are many different methods for improving the surface finish of fiber-reinforced composite molding materials and molded articles produced from such materials. Manufacturers of large composite structures (such as wind turbine blades) typically use in-mold gel coatings or process coatings, which act as a surface finishing layer that can be finished after demolding by filling defects and sanding to remove mold release agent and minor imperfections and "keying in" the surface, followed by applying a top coat of paint to protect the structure from environmental conditions. Essentially, this type of gel coating method involves pasting a flowable composition on the inner surface of the mold, which is then partially cured to form a gel layer, and the prepreg assembly is placed on the gel layer before curing. During the curing process, the prepreg and gel coating fuse together, which generally results in a composite material with a smooth surface. However, this method requires an initial curing step, is very labor-intensive, and tends to produce a gel layer of uneven thickness. In addition, the layer needs to be relatively thick (e.g., 0.3 mm on average) to cover defects, which can lead to undesirable weight gain.

[0005] Other approaches have used surface finishing films incorporated into the mold-engaging surface of a composite molding material, which typically comprises a thermosetting resin supported on a nonwoven mat carrier. For example, WO 2008 / 007094A2 discloses a composite assembly comprising: a) a surface reinforcement layer comprising at least one fiber layer having an aspect ratio greater than 5:1, and b) a structural layer comprising at least one reinforcing fiber and at least one polymer matrix. This document discloses that the fibers used in the surface reinforcement layer can be prepared by segmenting the fibers longitudinally and then forming a film or veil from the segmented fibers, resulting in a much denser veil structure with increased fiber density for the same weight. This document discloses that the denser veil structure provides a surface finish that is improved in both appearance and smoothness.

[0006] Manufacturers of large composite parts, such as wind turbine blades, are also keen to ensure that any traces of release agent, which is used to coat the mold to facilitate demoulding of the composite part after curing and is subsequently transferred to the surface of the cured part, are removed to ensure good adhesion of the final paint topcoat to the composite surface. Such release agent traces are typically removed using sanding methods. However, one problem that has been discovered when incorporating surface finishing films into the mold-engaging surfaces of composite molding materials is that end users sand laminates containing surface finishing films to such an extent that they destroy their structure and produce the very same pinholes on the surface that the finishing films are intended to prevent. When sanding, end users typically look for changes in the surface gloss level as an indicator of sufficient sanding. It seems that surfaces produced by using finishing films as described above are more resistant to sanding than their previous surfaces, and as a result, they tend to use more aggressive sanding regimens, resulting in damage.

[0007] One approach to overcoming this problem is to improve the sandability of the surface reinforcement layer, ensuring that any traces of release agent can be easily removed under typical sanding conditions. For example, WO 2010 / 046682 A1 discloses a prepreg assembly comprising resin and fiber and comprising an uppermost curable resin surface layer, such that when the assembly is cured, the uppermost surface layer has a sandability of at least 0.30 mg / cycle over 200 cycles, as measured according to ASTM D4060 using a Taber 5151 abrasion tester equipped with H18 wheels and a 1.0 kg weight. In a preferred embodiment, the uppermost curable resin surface layer comprises at least 10.0% by weight of granular particulate material in the form of glass spheres having a particle size of from 5 to 50 μm to provide the necessary sanding properties.

[0008] Other approaches have addressed the problem of sliding of fiber reinforced composite molding materials when laid up in a mold, which can lead to irregularities in the surface of the molded article after curing. This problem can be particularly important in cases where adjacent reinforcement layers or prepreg layers overlap in the mold (which can lead to a lack of resin in the overlapping area and cause narrow indentations to form along the overlapping seams when cured). For example, WO 2017 / 021147 A1 discloses a molding material comprising a layer of fiber material in a curable resin matrix, provided with a surface finishing film comprising a tacky resin on at least one surface, wherein a veil is provided on the surface of the finishing film away from the molding material, and perforations are formed in the veil to allow the tacky resin of the surface finishing film to penetrate the veil during the molding operation. This document discloses that the presence of such perforations in the veil allows a small amount of tacky resin to provide a slight adhesion between the molding material and the mold surface, thereby holding the molding material in place.

[0009] Various methods of improving the surface finish of fiber-reinforced composite molding materials and molded articles produced therefrom have certain disadvantages, such as the need to cure an additional gel coat in the mold, or the need to use a surface finish layer containing longitudinally chopped fibers, or the need to include additional glass spheres to improve the sandability of the surface finish layer, or the need to perforate any fiber veils in the surface finish layer, which may in turn affect resin flow and surface finish.

[0010] It is an object of the present invention to overcome at least some of the above problems and / or to provide improvements generally.

[0011] According to the present invention, there is provided a moulding material, a method for its preparation, a method for preparing a moulded article by curing such a moulding material, and a moulded article obtainable by such a method as described hereinafter or as defined in any one of the appended claims.

[0012] Thus, in a first aspect of the present invention, there is provided a moulding material comprising: (a) a structural reinforcement layer comprising a fibre reinforcement material; and (b) a surface reinforcement layer for contacting a mould or tool surface, the surface reinforcement layer comprising a first nonwoven fibre carrier in combination with a first resin composition comprising a rheology modifier and a curing agent, wherein the first resin composition provides an outer mould or tool contacting surface of the moulding material.

[0013] The first resin composition at least partially impregnates the first nonwoven layer, and in a preferred embodiment, completely impregnates the first nonwoven layer. However, an essential feature of the present invention is that a sufficient amount of the first resin composition is present on the surface of the first nonwoven layer remote from the structural reinforcement layer to form a continuous layer on the outer mold or tool contact surface of the molding material.

[0014] In the context of this invention, the term "molding material" refers to a fiber-reinforced composite material that can be laid up with other such materials in a mold or tool and cured to form a composite part in the shape of the mold or tool. Such molding materials can be used to make many different parts, including but not limited to components of wind turbines, including nacelles, propellers, and rotor blades.

[0015] The structural reinforcement layer may take many forms. Typically, the moulding material according to the invention will contain several structural reinforcement layers, although for some applications a single layer may be sufficient.

[0016] The fiber reinforcement material can be in the form of a sheet or a continuous mat or continuous filament. In other embodiments, the fiber reinforcement material comprises short length fibers, such as chopped strand mats. The fiber reinforcement material can be in the form of multiple fiber tows, each fiber tow containing multiple fiber filaments to form each tow. The tows can be sewn or woven to form a fabric. The fiber can be composed of: natural materials, such as cotton, flax, hemp, wool or silk; or semi-synthetic materials, such as rayon, viscose, modal, etc.; or synthetic materials, such as carbon, polyester, mineral, nylon, acrylic, glass, aramid (aramid), etc. In a preferred embodiment, the fiber reinforcement comprises carbon fiber or glass fiber.

[0017] In some embodiments, the fiber reinforcement material is in the form of a woven fabric. In other embodiments, the fiber reinforcement material comprises a unidirectional (UD) fabric, in which most of the fibers, rovings or tows present in the fabric extend in only one direction, although a few fibers, rovings or tows may extend in a direction different from the majority, for example as a cross stitch, in order to maintain the unidirectional alignment of the latter. The fibers, rovings or tows in the unidirectional fabric can be kept aligned by a variety of different methods, including weaving, stitching and combining. Therefore, such unidirectional fabrics can be woven or non-woven. In further embodiments, the fiber reinforcement material comprises a combination of a unidirectional fabric and a biaxial or multiaxial fabric or mat, in which any component can be woven or non-woven.

[0018] Suitable woven and nonwoven fabrics for composite materials are commercially available from specialist manufacturers including, but not limited to, Chomarat Textiles Industries of Esher, Surrey, UK, Hexcel Reinforcements UK Limited of Narborough, Leicestershire, UK, and Zhenshi Group Hengshi Fibreglass Fabrics Co., Ltd. of Tongxiang Economic Development Zone, Jiaxing City, Zhejiang Province, China 314500. In one embodiment, the woven or nonwoven fabric is a carbon fiber or glass fiber fabric such as BB200, BB600 or BB1200, where, for example, the designation BB1200 refers to a fiber having a fiber weight of 1200 g / m 2 The area weight of biaxial glass fabric is .

[0019] Hybrid or mixed fiber systems are also conceivable.The use of broken (ie stretch-broken) or selectively discontinuous fibers may be advantageous in facilitating the layup of the molding material according to the invention and improving its formability.

[0020] The area weight of fiber reinforcement is usually from 40 to 4,000 g / m 2In a preferred embodiment, the fiber area weight is preferably in the range of 100 to 2,500 g / m 2 , more preferably 150 to 2,000 g / m 2 within the range.

[0021] The fibre reinforcement in the structural reinforcement layer or layers where more than one is present will typically be a heavyweight non-crimped fabric such as a glass fabric. For glass reinforcement, fibres of 68 to 2400 tex (g / km yarn) are particularly suitable.

[0022] The surface reinforcement layer of the molding material according to the present invention comprises a first nonwoven fiber carrier. In the context of the present invention, a nonwoven fiber carrier means any nonwoven material that is permeable to both air and resin. Suitable nonwoven fiber carriers are heavy, preferably less than 100 g / m 2 , but preferably robust enough to carry a resin layer and withstand processing in the method of the present invention. The nonwoven fibrous support may comprise continuous fibers or discontinuous fibers. In one embodiment, the first nonwoven fibrous support comprises a veil (sometimes referred to as a fleece). In the context of the present invention, the term "veil" refers to a thin, heavyweight (i.e., having an area weight of not more than 100 g / m 2 ), porous, nonwoven, fiber reinforcement. In a preferred embodiment, the first nonwoven fiber carrier is composed of thermoplastic fibers, preferably wherein an organic binder is used to bind the fibers together to give the material structural integrity. In a specific embodiment, the thermoplastic material comprises polyester or aliphatic or semi-aromatic polyamide, such as nylon and polyester fibers. In another embodiment, the nonwoven fiber carrier comprises a veil formed from a thermoplastic fiber blend (such as a blend of polyester and nylon fibers). The organic binder is typically present in an amount of 1% to 10% by weight based on the total weight of the first nonwoven fiber carrier. The purpose of the first nonwoven fiber carrier is to act as a support or carrier for the first resin composition and to control the way the first resin composition interacts with the mold or tool surface so as to provide a good surface finish. In one embodiment, the first nonwoven fiber carrier has an openness between 1% and 10%, preferably between 2% and 9%, and / or a surface roughness between 75 and 350 μm. 2 In a preferred embodiment, the first nonwoven fiber carrier has an average open area of ​​1 to 80 g / m 2 , preferably from 5 to 50 g / m 2 , more preferably from 10 to 40 g / m 2 In one embodiment, the first nonwoven fiber carrier has an area weight of about 2,300 L / m under an applied pressure of 200 Pa. 2The air permeability of the nonwoven fiber carrier can be measured by ASTM D737-18 - Standard Test Method for Air Permeability of Textile Fabrics. Suitable thermoplastic fiber veils include those available from Burnside Mills, Kendal, Cumbria, United Kingdom under the trade name T2761-00 are commercially available ones.

[0023] In addition to the first nonwoven fiber carrier, the surface reinforcement layer also includes a first resin combination. The first resin combination generally includes a thermosetting resin, such as a polyester resin, a polyurethane resin, a polyurethane / polyurea resin, a phenol-formaldehyde resin, a urea-formaldehyde resin, a vinyl ester resin, a cyanate resin, a polyimide resin or an epoxy resin. In one embodiment, the first resin combination is a thermosetting resin composition, preferably an epoxy resin composition, i.e., includes an epoxy resin or an epoxy resin blend. Suitable epoxy resins include the M9 and M79 series epoxy resins available from the Hexcel Composites Limited in Duxford, Cambridgeshire, England.

[0024] In one embodiment, the first resin composition comprises an epoxy resin having an epoxy equivalent weight (EEW) in the range of 150 to 1,500, preferably in the range of 150 to 1,250, preferably in the range of 150 to 1,000, preferably in the range of 150 to 750, preferably in the range of 150 to 500, preferably in the range of 200 to 500, preferably in the range of 200 to 450, preferably in the range of 250 to 350, or any combination thereof.

[0025] The first resin composition comprises at least one curing agent to promote crosslinking of the resin and curing of the molding material, especially at temperatures of 100°C or less. In the context of the present invention, the term "curing agent" is understood to include any curing agent and / or accelerator that is capable of influencing or increasing the crosslinking rate of the first resin composition. Such curing agents and / or accelerators for use in the present invention are well known in the art. In one embodiment, the first resin composition comprises a latent curing agent that is a substituted urea. Suitable substituted urea curing agents include those available from AlzChemGroup AG of Trostberg, Germany under the trade name A range of materials available from Emerald Performance Materials in Moorfield, New Jersey, USA, including UR200, UR300, UR400, UR500, UR600 and UR700; and A series of materials obtained include U-24M, U-35M, U-52, U-52M, U-210, U-210M, U-405, U-405M, U-410M and U-415M. In a further embodiment, the curing agent can include a combination of a dicyandiamide curing agent and a substituted urea. The curing agent can be present in any amount suitable for causing the resin to cure under selected conditions. In an embodiment, the curing agent is present in an amount of 1wt% to 25wt%, 1wt% to 20wt%, 1wt% to 15wt%, 1wt% to 10wt% or 2wt% to 8wt% or any combination thereof based on the gross weight of the resin composition.

[0026] It is important that the first resin composition contains a rheology modifier. In the context of the present invention, the term "rheology modifier" is used to refer to a compound or substance that is capable of imparting non-Newtonian rheological properties in a material such as the first resin composition. In the present invention, the rheology modifier should cause the minimum viscosity of the resin under shear to increase compared to a non-viscosity modified resin, and should also cause the viscosity of the resin under non-shear to increase by a greater amount compared to a non-rheology modified resin. This can be measured using a shear sweep viscosity method. Suitable conditions for the shear sweep viscosity method are 25 mm parallel plates with a gap set to 1 mm to provide a viscosity range from 0.1 to 100 -s In the present invention, the rheology modifier is preferably selected so that the first resin composition has a shear rate of 0.1s at 60°C and 0.1s when measured as described above. -1 Viscosity from 200 to 1000 Pa.s at 0.1s -1 25% or less of the viscosity at 60°C and 100s -1 The viscosity is at 60℃ and 100s -1 The viscosity is not less than 25Pa.s.

[0027] The shear sweep viscosity method can be performed using any viscometer suitable for providing the above conditions, such as a TA HR-2 Discovery Hybrid Rheometer manufactured by TA Instruments, New Castle, Delaware, USA.

[0028] Suitable rheology modifiers include treated and untreated grades of fumed silica, such as hydrophobic silica. Hydrophilic silicas may also be used, but are preferably used in combination with thixotropy enhancers. Organophilic layered silicates may also be used. Suitable silicas include those available from Evonik Resource Efficiency GmbH, Germany. R202 and Cab-O- available from Cabot Corporation, Alpharetta, Georgia, USA TS720. Suitable organophilic layered silicates include Garamite-7305 available from BYK (Altana Group). Suitable thixotropy enhancers include those available from BYK-Chemie GmbH of Wesel, Germany under the trade name In one embodiment, the rheology modifier is a hydrophobic fumed silica, such as R202.

[0029] The rheology modifier, optionally in combination with the thixotropy enhancer, may be present in an amount of 1% to 20% by weight, based on the total weight of the first resin composition. In a preferred embodiment, the rheology modifier is present in an amount of 1% to 15% by weight, 1% to 12% by weight, 1% to 10% by weight, 2% to 10% by weight, 3% to 9% by weight, 4% to 8% by weight, or any combination thereof, based on the total weight of the first resin composition.

[0030] We have discovered that the use of a lightweight, highly closed microfiber veil in combination with a rheology-modified epoxy resin composition having the viscosity characteristics described above provides a surface reinforcement layer having good gap-filling properties, resulting in greatly reduced pinhole formation, and also reducing or completely eliminating narrow grooves caused when plies of molding material are overlapped during the layup process.

[0031] The first resin composition may further comprise other components, such as toughening agents, particulate fillers (such as microspheres, glass spheres, talc, etc.), dyes, air release agents, pigments, and the like.

[0032] The first resin combination is provided on the external mold or the tool contact surface of molding material, i.e. the molding material surface that contacts with mold or tool surface when stacking molding material to prepare to solidify.In its simplest form, for example, molding material comprises the first resin combination layer, on the top of the first resin combination layer is a nonwoven fiber carrier, such as a lightweight surface veil, and they form a surface reinforcement layer together, on the top of the surface reinforcement layer is a fiber-reinforced material (such as a heavy glass fabric mat) layer, which forms a structural reinforcement layer. In this case, the first resin combination layer will normally be a thick layer with high area weight, because in case each layer is consolidated, the amount of the first resin combination must be enough to not only impregnate the surface veil but also impregnate the fiber-reinforced layer.

[0033] In another embodiment, structural reinforcement layer exists in combination with the second resin combination.In this case, molding material can comprise the first resin combination layer, and on the top of the first resin combination layer is a lightweight surface veil, and they form a surface reinforcement layer together, and on the top of the surface reinforcement layer is a heavy fiber-reinforced material layer, and finally the second resin combination layer, and the latter two layers form structural reinforcement layer.In a further embodiment, the second resin combination layer can be between fiber-reinforced material and non-woven fiber carrier layer.In either case, the second resin combination can be partially or completely impregnated with structural reinforcement layer after layer consolidation, for example, to form semipreg or prepreg structure.

[0034] Any resin composition discussed with respect to the first resin composition is suitable for use as the second resin composition. However, since the purpose of the second resin composition is primarily structural rather than providing gap-filling properties, it is not necessary for the second resin composition to include a rheology modifier; however, if desired, the second resin composition may include a rheology modifier. In certain preferred embodiments, the second resin composition is identical to the first resin composition but does not contain a rheology modifier, and in certain other preferred embodiments, the second resin composition is identical to the first resin composition that includes a rheology modifier.

[0035] In one embodiment, the molding material according to the present invention further comprises a second nonwoven fiber carrier between the structural reinforcement layer and the surface reinforcement layer. The second nonwoven fiber carrier can be the same as the first nonwoven fiber carrier, but preferably, the second nonwoven fiber carrier has a greater area weight than the first nonwoven fiber carrier.

[0036] The second nonwoven fiber carrier can comprise continuous fibers or discontinuous fibers. In one embodiment, the second nonwoven fiber carrier comprises a veil (sometimes referred to as fleece). The second nonwoven fiber carrier is typically composed of the following: nonwoven fibers of glass, carbon, polyester, polyamide, aramid (aromatic polyamide) or a combination thereof, which are combined together using an organic binder to give the material structural integrity. Preferably, the second nonwoven fiber carrier comprises glass wool. The organic binder is typically present in an amount of 1% to 10% by weight based on the gross weight of the second nonwoven fiber carrier. Typically, the area weight or surface density of the second nonwoven fiber carrier will be slightly higher than the first nonwoven fiber carrier. In a preferred embodiment, the second nonwoven fiber carrier is an area weight of 20 to 100 g / m 2 , preferably 20 to 90 g / m 2 , more preferably 30 to 80 g / m 2 , even more preferably 30 to 60 g / m 2 Suitable nonwoven glass mats or fleece are available from Johns Manville in Denver, Colorado, USA under the trade name Commercial purchases, including but not limited to ST-3022, S 4030 and S 5030, and available under the trade name of Taishan Fiberglass Inc., Taian Economic Development Zone, Shandong Province, China Commercial purchases, including but not limited to S-SM30, S-SM50, S-HM30 and S-HM50.

[0037] The presence of the second nonwoven fiber material helps prevent the fiber reinforcement in the structural reinforcement layer from "printing through" and appearing on the surface of the molded material after curing, and also ensures that sufficient second resin composition remains in the surface reinforcement layer during the curing process, thereby avoiding the formation of narrow grooves or other surface irregularities due to resin starvation. Like the first nonwoven fiber material, the second nonwoven fiber material can also be used to prevent the formation of air bubbles in the first, second, or third resin compositions or to help dissipate air bubbles.

[0038] The second nonwoven fiber carrier may be present in combination with the third resin composition. The third resin composition may be positioned on either side of the second nonwoven fiber carrier and may help adhere the second nonwoven fiber carrier to the first nonwoven fiber carrier and / or the structural reinforcement layer. After consolidation, the third resin composition may partially or completely impregnate the second nonwoven fiber carrier.

[0039] When present, the second nonwoven fibrous carrier may optionally be provided attached to the fibrous reinforcement material of the structural reinforcement layer, for example the layers may be pre-attached by a resin material or by sewing.

[0040] Any resin composition discussed with respect to the first or second resin composition is suitable for use as the third resin composition. However, it is not necessary for the third resin composition to include a rheology modifier, but if desired, it may include a rheology modifier. In certain preferred embodiments, the third resin composition is identical to the first resin composition and / or the second resin composition, but does not contain a rheology modifier, and in certain other preferred embodiments, the second resin composition is identical to the first and / or second resin composition that includes a rheology modifier. When present, using the same resin composition as the first, second, and third resin compositions is particularly advantageous because it simplifies the process and prevents any problems caused by possible incompatibilities between the different resin compositions.

[0041] In one embodiment, the molding material further comprises at least one additional structural reinforcement layer on a surface of the molding material remote from the surface reinforcement layer. The one or more additional structural reinforcement layers may be the same as or different from the first structural reinforcement layer. In one embodiment, the one or more additional structural reinforcement layers are different from the first structural reinforcement layer, and the additional reinforcement layers may be associated with the same resin composition as the first structural reinforcement layer or a different epoxy resin composition. In this embodiment, the one or more additional structural reinforcement layers may be conventional prepregs, such as those available from Hexcel Composites GmbH & Co KG of Neumarkt, Austria under the trade name Commercially available ones include but are not limited to M79 and M9 series prepregs.

[0042] The total amount of resin provided in the molding material of the present invention will depend on the material's intended use. For example, where the molding material is intended to be laid up and cured with other impregnated or partially impregnated materials, the resin content can be relatively high. Alternatively, where the molding material of the present invention is intended to be used in combination with unimpregnated (dry) fiber layers in an intermediate structure that will subsequently be impregnated with resin before curing, the resin content can be relatively low. In all cases, however, there should be sufficient resin to form a layer on the outer surface of the surface reinforcement layer, i.e., the layer that contacts the mold or tool surface during the molding material layup process. However, typically, the total amount of resin present in the molding material of the present invention is from 10 wt % to 60 wt % by weight of the molding material. More preferably, in molding materials intended for impregnation or partial impregnation, the total resin content is from 20 wt % to 60 wt %, even more preferably from 30 wt % to 50 wt % by weight of the molding material; and in molding materials intended for use in infusion systems, the total resin content is preferably from 10 wt % to 50 wt % by weight of the molding material.

[0043] Thus, the areal weight of the resin layer(s) in the molding material of the present invention can vary significantly depending on the number of resin layers(s), the presence of one or two structural reinforcement layers, and in particular the weight of the fiber reinforcement material forming the structural reinforcement layer(s) and the presence of any additional structural reinforcement layers. As provided herein, the total resin can be composed of a variety of different resin compositions, but in a preferred embodiment, the same resin composition is used throughout the molding material.

[0044] In the case where different resin compositions are associated with different layers of the molding material, when the molding material is assembled before consolidation, the various resins are initially provided in contact with the layers with which they are associated. In the case where the same resin composition is present throughout the molding material, it may initially be provided throughout the molding material as multiple layers, or it may initially be provided as a single layer; however, after consolidation, at least a portion of the resin composition should be present on the surface of the first nonwoven fibrous carrier remote from the structural reinforcement layer to provide the outer mold or tool contact surface of the molding material.

[0045] In one embodiment, the molding material according to the present invention further comprises a discontinuous indicator means attached to the mold or tool contacting surface of the molding material which does not completely penetrate the surface strengthening layer.

[0046] In the context of the present invention, the term "attached" means that the discrete indicator means is associated with the mold or tool contacting surface of the molded material and therefore cannot be accidentally or easily removed during transportation to the end user or during subsequent processing steps.

[0047] In the context of the present invention, "non-continuous" means that the indicator means provides discrete indicator areas within the surface strengthening layer and provides an indication of which areas of the surface have been treated, for example sanded, during post-curing of the moulding material.

[0048] The discontinuous indicator means can be applied to the first resin composition on the outer mold or tool contact surface of the molding material during assembly of the various layers and prior to consolidation, but preferably, the discontinuous indicator means is applied after consolidation of the structural reinforcement layer and the surface strengthening layer (and any additional layers) but prior to curing. At this stage, i.e., prior to curing, the indicator means is loosely attached to the mold or tool contact surface of the molding material due to the adhesion of the resin layer present on the mold or tool contact surface.

[0049] Upon curing of the molding material, the discontinuous indicator means become permanently fixed or embedded in the upper region of the surface strengthening layer and will therefore be sufficiently attached to the mold or tool contacting surface of the curing molding material that they are not removed by handling the material.

[0050] The indicator means may be attached only to the surface of the mold or tool contact surface of the molded material, or they may penetrate into the surface. In the case of discontinuous indicator means penetrating the surface finishing layer, they may penetrate to any depth as long as they do not completely penetrate the layer, i.e., such that the indicator means does not contact the structural reinforcement layer (or, when present, the second nonwoven fibrous carrier), so that if the surface reinforcement layer is removed (e.g., by sanding) to a depth where all of the discontinuous indicator means are removed, no damage will be caused to the underlying layer. Thus, the indicator means may penetrate the surface reinforcement layer to any depth from 0% of the layer depth (i.e., attached only to the surface) to nearly, but not completely, 100% of the depth. In a preferred embodiment, the indicator means penetrates the surface reinforcement layer to from 0.1% to 95%, more preferably from 1% to 50%, of its depth.

[0051] The molding material of the present invention is particularly suitable for including an indicator means on the mold or tool contacting surface of the molding material because the rheology modifier of the first resin composition provides the rheological properties of the surface reinforcement layer. In particular, the enhanced viscosity of the first resin composition means that the indicator means will attach to or embed into the surface layer and will remain in a discrete shape and will not significantly diffuse outward or inward, so that a clear pattern is maintained.

[0052] When the cured article is demoulded, the discontinuous indicator means remains on the surface of the article, allowing the article to be easily sanded without the risk of complete removal of the surface finish. In practice, the operator can determine whether the entire surface or article has been adequately sanded by assessing whether all of the discontinuous indicator means have been removed.

[0053] The discontinuous indicator means may comprise any regular or irregular shape, and the shapes may be arranged in any regular or irregular array, as long as they serve as an indicator of sufficient surface treatment. Suitable shapes include lines (straight or curved), dots (including circular, square or irregular dots), or mixtures thereof in regular or irregular arrays. Preferably, the distance between individual shapes is generally less than the distance covered in a single sanding motion during manual sanding of a surface. Preferably, the indicator means comprises a regular array of regular dots, as this makes it easier to assess which areas have been surface treated, for example, which areas have had the indicator means removed by sanding, and which areas have not been sufficiently treated.

[0054] The discontinuous indicator means may comprise any suitable material that will remain visible on the surface of the molded material after curing. In one embodiment, the indicator means comprises a refractive compound such as, for example, a refractive metal oxide such as titanium dioxide. The use of a refractive compound may be useful where the sanding of the article is automated and may facilitate the use of light scanning techniques rather than visual inspection to assess progress. In other embodiments, the indicator means may be formed from a dye or pigment such as, for example, carbon black or other similar substances. Suitable forms of carbon black for use in the present invention include, but are not limited to, those manufactured under the trade name Orion Engineered Carbons LLC of 4501 Magnolia Cove Drive, Suite 106, Houston, Texas 77345, USA. In such embodiments, it may be desirable to use a dye that is insoluble in the first resin composition to prevent "bleeding" of the dye into other areas of the second resin composition. However, it will be apparent that the discontinuous approach according to the present invention is not limited to the illustrative examples described above.

[0055] The indicator means may be applied to the mold or tool engaging surface of the molding material in any suitable manner, for example by applying a perforated stencil thereto and spraying the surface with a solution or dispersion or solid particles of a suitable metal oxide, dye or pigment, followed by light pressure, such as by using a hand roller. Alternatively, the indicator means may be applied by spraying or printing.

[0056] In a second aspect of the present invention, there is provided a method for preparing a molding material, the method comprising the steps of:

[0057] (a) providing a structural reinforcement layer comprising a fiber reinforcement material;

[0058] (b) providing a surface reinforcement layer for contacting a mold or tool surface, the surface reinforcement layer comprising a first nonwoven fibrous support in combination with a first resin composition containing a rheology modifier and a curing agent, wherein the first resin composition is provided on an outer mold or tool contacting surface of the molding material remote from the structural reinforcement layer; and

[0059] (c) consolidating the layers so that at least the first nonwoven fibrous support is impregnated with the first resin composition without curing the resin composition.

[0060] In the method of the present invention, consolidation is performed after assembling the structural reinforcement layer and the surface strengthening layer, and any other layers that may be included. Consolidation can be performed in any conventional manner for forming composite materials, preferably by heating the molded material under pressure. For example, consolidation can be performed by passing the combined layers through consolidation rollers (such as one or more S-type rolls) and heating to, for example, 80°C.

[0061] In the method of the present invention, a fiber reinforcement material may optionally be present in combination with the second resin composition.

[0062] In one embodiment, the method according to the second aspect of the present invention further comprises the step of providing a second nonwoven fibrous carrier, optionally in combination with a third resin composition, between the structural reinforcement layer and the surface reinforcement layer before the consolidation step.

[0063] In one embodiment, the method according to the second aspect of the present invention further comprises the step of providing at least one additional structural reinforcement layer on a surface of said moulding material remote from said surface strengthening layer before said consolidating step.

[0064] Where the structural reinforcement layer is provided in combination with the second resin composition and / or the second nonwoven fibrous carrier is provided in combination with the third resin composition, the material may be provided with a structural material that has been at least partially impregnated with resin. Alternatively, in a preferred embodiment, during assembly of the molding material, the structural layer and the resin layer are provided as separate layers, and during the consolidation step, the resin layer is caused to at least partially impregnate the respective layers.

[0065] In the method of the present invention, the first resin composition, the first nonwoven carrier, and, where present, the second resin composition, the second nonwoven fiber carrier, the third resin composition and / or one or more additional structural reinforcement layers can each optionally be defined as similar materials in the molding material of the present invention.

[0066] In one embodiment, the method according to the second aspect of the present invention further comprises the following steps: applying a discontinuous indicator means to the mold or tool contact surface of the molding material, and applying pressure and optionally heat so as to attach the discontinuous indicator means to the first resin composition without completely penetrating the surface strengthening layer. In the context of the present invention, the term "attached" means that the discontinuous indicator means is associated with the mold or tool contact surface of the molding material and therefore cannot be accidentally or easily removed during transportation to the end user or during subsequent processing steps. After curing, the discontinuous indicator means remains visible on the mold or tool contact surface of the cured molding and may partially penetrate into the surface strengthening layer.

[0067] The discontinuous indicator means can be applied to the mold or tool contact surface of the molding material at any stage during the material layup and before solidification, for example, before the consolidation step. Preferably, however, the discontinuous indicator means is added after the consolidation step but before solidification. The discontinuous indicator means can be added to the surface in any suitable manner. For example, the indicator means can be applied to the mold or tool contact surface of the molding material in the following manner: a perforated template is applied thereto and the surface is sprayed with a solution or dispersion or solid particles of a suitable metal oxide, dye or pigment, followed by light pressure, such as by using a hand roller. Alternatively, the indicator means can be applied by spraying or printing.

[0068] In a third aspect of the present invention, there is provided a moulding material obtainable by the method according to the second aspect of the present invention.

[0069] In a fourth aspect of the present invention, there is provided a method for preparing a moulded article, the method comprising curing the moulding material according to the first or third aspect of the present invention, optionally wherein before the curing step at least one additional structural reinforcement layer is laid up onto the moulding material on a surface of the moulding material remote from the surface strengthening layer.

[0070] The molding material of the present invention can be cured in any conventional manner to form a molded article, taking into account the one or more resins and one or more curing agents present in each layer. Accordingly, the appropriate conditions required to cure an article prepared from the molding material according to the present invention can be determined empirically according to standard procedures used in the prepreg industry.

[0071] In a fifth aspect of the present invention, there is provided a moulded article obtainable by the method according to the fourth aspect of the present invention.

[0072] In one embodiment, the molded article has an average pinhole area of ​​less than 1%, preferably less than 0.1% and / or an average pinhole size of less than 0.5 mm. 2 , preferably less than 0.05mm 2 and / or a molding surface having less than 10%, preferably less than 5%, overlap defects.

[0073] In a sixth aspect of the present invention, there is provided a method for preparing a finished molded article, the method comprising the steps of:

[0074] (a) preparing a molded material by the method of the present invention, comprising the steps of: applying a discontinuous indicator means to a mold or tool contact surface of the molded material, and applying pressure and optionally heat so as to attach the discontinuous indicator means to the first resin composition without completely penetrating the surface strengthening layer;

[0075] (b) curing the molding material in a mold or tool, wherein the discontinuous indicator means is in contact with the mold or tool, optionally wherein at least one additional structural reinforcement layer is laid up to the molding material on a surface of the molding material remote from the surface strengthening layer prior to the curing step;

[0076] (c) removing the molded article from the mold or tool, and conditioning the molded article of step (b) by abrading the mold or tool contacting surface of the article to a depth sufficient to remove the discontinuous indicator means without completely removing the surface strengthening layer.

[0077] In this aspect of the invention, the discontinuous indicator provides a signal to the operator that the outermost portion of the molded article's surface strengthening layer, which may be contaminated with release agent after demolding, has been uniformly removed without risking removal of the entire surface strengthening layer.

[0078] In another aspect of the present invention, there is provided a finished article obtainable by a method according to the present invention in its sixth aspect.

[0079] Figure 1 A partially sanded molding material according to a preferred embodiment of the present invention is shown. Example

[0080] Example 1

[0081] Resin composition 1 was prepared as follows:

[0082] 72.3g LY1589 (a semisolid bisphenol A diglycidyl ether epoxy resin manufactured by Huntsman Advanced Materials (Switzerland) GmbH, Basel, Switzerland);

[0083] 18.17g LY1556 (liquid bisphenol A diglycidyl ether epoxy resin manufactured by Huntsman Advanced Materials (Switzerland) GmbH, Basel, Switzerland);

[0084] 0.10g DW 0135 (blue pigment paste manufactured by Huntsman Advanced Materials (Switzerland) GmbH, Basel, Switzerland);

[0085] 0.18 g BYK-A530 (an air release agent manufactured by BYK-Chemie GmbH, Wesel, Germany);

[0086] 6.00g R202 (a hydrophobic fumed silica rheology modifier manufactured by Evonik Resource Efficiency GmbH, Hanau-Wolfgang, Germany); and

[0087] 2.82g UR500 (a difunctional latent urone accelerator in powder form manufactured by Alzchem Group AG, Trostberg, Germany).

[0088] The components were mixed thoroughly at a temperature of 50° C. to 60° C. until the mixture was uniform in color and consistency. The same resin composition 1 was used for each resin layer of the molding material.

[0089] Construct a molding material 1 having the following architecture:

[0090] (1)400g / m 2 1 layer of a resin composition;

[0091] (2) One layer of LBB1200 fabric (1250 g / m2 manufactured by Hexcel Reinforcements UK Limited, Narborough, Leicestershire, United Kingdom) 2 triaxial non-crimped glass fabric);

[0092] (3) First floor S 5030 (made by Johns Manville, Denver, Colorado, USA with a 50 g / m 2 area weight of glass fiber fleece);

[0093] (4) 200g / m 2 1 layer of a resin composition;

[0094] (5) A lightweight, fully synthetic nonwoven fiber veil layer comprising a blend of polyester and nylon fibers having a 15 g / m 2 areal weight, manufactured by Technical Fiber Products Limited, Browns Mills, Kendal, Cumbria, United Kingdom); and

[0095] (6) 200g / m 2 1 layer of the resin composition.

[0096] The assembled layers were consolidated by passing them through an S-type hugging roller system heated to 80° C. to form the molding material 1 .

[0097] After consolidation, a layer of P34 RF260 (a FEP fluoropolymer release film having a staggered 12.7 mm center perforation pattern and a nominal pore size of 1.143 mm manufactured by Tygavac Advanced Materials Limited, The Causeway, Broadway Business Park, Chaderton, Oldham OL9 9XD, UK) was positioned on top of the resin composition layer on the bottom surface of the prepreg (i.e., layer (6) - the surface adjacent to the mold surface that becomes the part surface upon demoulding). Tioxide TR-81 (titanium dioxide in powder form manufactured by Huntsman Advanced Materials (Switzerland) GmbH, Basel, Switzerland) was dusted onto the film surface and then lightly pressed with a rubber roller before removing excess titanium dioxide and release film. Moulding material 1 left an area weight of approximately 1.7 g / m2 on the resin layer at the mold or tool contact surface. 2 A regular array of titanium dioxide dots.

[0098] The composite part is produced by placing the molding material 1 on the Watershield TM The composite tool was treated with a silicone-free water-soluble release agent (manufactured by Freeman Manufacturing and Supply Company of Avon, Ohio, USA) and the assembly was cured under vacuum at 80°C and 1 bar pressure for 6 hours. Upon cooling, the cured molded part was removed from the tool, revealing a discrete array of titanium dioxide-colored dots against a blue background of cured resin. The dots were able to uniformly remove a portion of the surface reinforcement layer of the composite part by sanding (see Figure 1 ).

[0099] Figure 1 The figure shows a cured molded material 1 produced as described above. The left half of the material 3 has been sanded to remove any release agent remaining on the surface after curing, while the right side of the material 5 has not been sanded. The array of titanium dots 7 applied to the molded material 1 before curing is still present on the right side of the material 5, while the absence of a regular array of dots 7 on the left side 3 indicates at least partial removal of the upper surface. The presence of scattered individual dots 9 on the left side 3 of the molded material 1 indicates that sanding was not performed sufficiently to completely remove the upper surface layer and that further sanding should be completed.

[0100] Uncured molding material samples prepared in the above manner were cut and overlapped in the X and Y directions across the mold surface, with an overlap area of ​​approximately 2-3 cm. Additional molding material was placed on top without any overlap, and the resulting assembly was cured in the above manner. Upon cooling and demolding, the overlapped areas of the cured parts exhibited significantly fewer defects compared to standard parts produced from non-overlapping molding material.

[0101] Example 2

[0102] Resin composition 2 was prepared as follows:

[0103] 72.9 g Kukdo KFR136SL, a semisolid bisphenol A diglycidyl ether epoxy resin manufactured by Kukdo Chemical Company Limited, Seoul, South Korea);

[0104] 18.2g 828 (liquid bisphenol A diglycidyl ether epoxy resin manufactured by Hexion Inc., Columbus, Ohio, USA);

[0105] 6g R202 (a hydrophobic fumed silica rheology modifier manufactured by Evonik ResourceEfficiency GmbH, Hanau-Wolfgang, Germany); and

[0106] 2.9g UR500 (a difunctional latent urone accelerator in powder form manufactured by Alzchem Group AG, Trostberg, Germany).

[0107] The components were mixed thoroughly at a temperature of 50° C. to 60° C. until the mixture was uniform in color and consistency. The same resin composition 2 was used for each resin layer of the molding material.

[0108] Construct a molding material 2 with the following architecture:

[0109] (1)400g / m 2 2 layers of a resin composition;

[0110] (2) One layer of LBB1200 fabric (1250 g / m2 manufactured by Hexcel Reinforcements UK Limited, Narborough, Leicestershire, United Kingdom) 2 triaxial non-crimped glass fabric);

[0111] (3) First floor S 5030 (made by Johns Manville, Denver, Colorado, USA with a 50 g / m 2 area weight of glass fiber fleece);

[0112] (4) A lightweight, fully synthetic nonwoven fibrous veil layer comprising a blend of polyester and nylon fibers having a 15 g / m 2 areal weight, manufactured by Technical Fiber Products Limited, Browns Mills, Kendal, Cumbria, United Kingdom); and

[0113] (5)400g / m 2 2 layers of the resin composition.

[0114] The assembled layers were consolidated by passing them through an S-type hugging roller system heated to 80° C. to form the molding material 2 .

[0115] Place the molding material 2 on the Watershield TM (a silicone-free water-soluble mold release agent manufactured by Freeman Manufacturing and Supply Company of Avon, Ohio, USA) in a composite tool wherein the resin composition layer (5) is adjacent to the face of the mold. 79 (a prepreg manufactured by Hexcel GmbH, Neumarkt, Germany) was placed on top of the molding material in the mold, i.e., next to the resin layer (1); and the assembly was cured under vacuum at 80° C. and 1 bar pressure for 6 hours. After cooling, the cured molded part was removed for inspection and further testing.

[0116] In an alternative embodiment, a layer of discrete indicator means comprising a regular array of titanium dioxide dots may be applied to the moulding material 2 after consolidation and before curing.

[0117] Test equipment and methods

[0118] Matrix rheology

[0119] The rheological measurements of the resin compositions were performed using a TA HR-2 Discovery Hybrid Rheometer manufactured by TA Instruments, New Castle, Delaware, USA using 25 mm parallel plates with a gap set to 1 mm to provide a flow rate from 0.1 to 100 -s The shear rate was 200 nm and the temperature was 60°C.

[0120] Veil Features

[0121] Fiber diameter and veil openness measurements can be made using a Keyence VHX-6000 series digital microscope manufactured by Keyence (UK) Limited of Milton Keynes, Buckinghamshire, United Kingdom. The veil used as the first nonwoven fiber carrier (i.e., the surface veil for the surface reinforcement layer) can be presented to the microscope by mounting it on a blue plastic card to help highlight the open areas when viewed on a computer monitor. The microscope was set to 175x magnification, with the light output set to maximum, and the gain dial setting adjusted so that the open areas could be clearly identified. The saved computer image presented a 2951002μm 2 total area.

[0122] The air permeability of a nonwoven fibrous carrier can be measured by ASTM D737-18 - Standard Test Method for Air Permeability of Textile Fabrics.

[0123] The thickness (diameter), average "open area" (i.e., the empty space between fibers) and openness of the individual fibers are then measured using Keyence software. The image is also manipulated by adjusting the slider on the histogram to create a two-color image in which one color represents the veil fibers and the other represents the open space. The software is then used to measure the area of ​​all individual open spaces. This data can be saved in a spreadsheet and used to calculate the total area occupied by the open space (in order to calculate the openness %) and the average size of the open area.

[0124] Cured surface characterization

[0125] The cured surface characteristics were determined by wiping the surface of the demolded composite part with a slurry of carbon black in acetone. The excess slurry was washed off and then measured using a Keyence VHX-6000 series digital microscope using 25x magnification and a gain setting adjusted to allow clear identification of surface defects. The observed 132.63 mm 2 The image was acquired with the histogram slider set between 000 and 065, the brightness tolerance set to 20, and the noise filter set to 10. The average area of ​​observed pinholes and the percentage of the total observed area identified as pinholes were measured using the software.

[0126] Overlap defects are measured by first highlighting defects along the overlap using a slurry of carbon black in acetone. After washing off any excess slurry, the length of any defects is measured using a ruler. The amount of overlap defects is expressed as a percentage of the sum of the defects measured relative to the overlap length.

[0127] result

[0128] Test as described above The viscosity of the resin (commercially available non-rheology-modified epoxy resin matrix manufactured by Hexcel Composites GmbH and Co., KG, Neumarkt, Austria) and the rheology-modified resin composition 1 (according to the present invention) used in the molding material 1 in Example 1 above.

[0129] For M79, at 60°C and 0.1s -1 The viscosity is 40Pa.s at 60℃ and 100s -1 The viscosity is 29 Pa.s.

[0130] For resin composition 1, at 60°C and 0.1s -1 The viscosity is 470Pa.s at 60℃ and 100s -1 The viscosity is 66 Pa.s.

[0131] Materials according to the invention were prepared, cut and overlapped in the X and Y directions across the mold surface with an overlap area of ​​approximately 2-3 cm, and cured as discussed in Example 1. Three comparative laminates not falling within the scope of the invention were also prepared and processed as above.

[0132] Comparative Laminate 1 comprises a standard prepreg, eg, M79 / 40% / LBB1200, with the biaxial portion adjacent to the mold surface, no surface reinforcing nonwoven fiber carrier, no intermediate nonwoven fiber carrier, and with a non-rheology modifying resin (M79).

[0133] Comparative laminate 2 comprises a standard prepreg, e.g. M79 / 40% / LBB1200, with the biaxial portion closest to the mould surface and no surface reinforcement nonwoven fibre carrier, but with an S5030 nonwoven fibre carrier between the reinforcement layer and the mould, and with a non-rheology modifying resin (M79).

[0134] Comparative laminate 3 comprises a standard prepreg, such as M79 / 40% / LBB1200, with the biaxial portion closest to the mold surface, but with a surface reinforcement nonwoven fiber carrier in the outer layer adjacent to the mold and an S5030 nonwoven fiber carrier between the reinforcement layer and the surface reinforcement nonwoven fiber carrier. However, the resin of the comparative laminate is a non-rheology modified resin (M79).

[0135] Surface characterization of pinholes and overlap defects in composite parts prepared by curing control laminates 1, 2 and 3 and the surface finished molding material according to the invention typically gave the following results:

[0136]

[0137] The molding materials according to the present invention can be cured at low temperatures (typically 100° C.) to provide molded articles with good surface finish, showing reduced pinholes and overlap defects and requiring minimal surface processing. Such materials can provide sacrificial discontinuous indicator means on the molding surface to promote uniform surface processing.

Claims

1. A molding material, comprising: (a) a structural reinforcement layer comprising a fiber reinforcement material, the structural reinforcement layer having an upper surface and a lower surface, the structural reinforcement layer comprising a non-crimped glass fabric; (b) a surface reinforcement layer comprising a first nonwoven fibrous support comprising a surface reinforcement layer having an area weight of 1 to 80 g / m 2 The thermoplastic fiber veil, the surface reinforcement layer having an upper surface and a lower surface, the first nonwoven fiber carrier having an openness of 1% to 10% and / or a thickness of 75 to 350 μm 2 an average open area between the first nonwoven fibrous carrier and the lower surface of the structural reinforcement layer; (c) a resin layer comprising an epoxy resin, a rheology modifier, and a curing agent, wherein the resin layer has an upper surface and a lower surface, and the resin composition of the resin layer is resistant to erosion at 60° C. and 0.1 s -1 The viscosity is 200 to 1000 Pa.s at 60 ° C and 100s -1 The viscosity is 0.1s -1 25% or less of the viscosity under but not less than 25 Pa.s, the resin layer is provided between the structural reinforcement layer and the first nonwoven fiber carrier, wherein the viscosity is measured by a shear sweep viscosity method; (d) a second nonwoven fibrous carrier comprising polyester, nylon fibers, or blends thereof, the second nonwoven fibrous carrier having an area weight greater than the area weight of the first nonwoven fibrous carrier; wherein the resin layer is bonded to a lower surface of the structural reinforcement layer, whereby the resin layer completely impregnates the structural reinforcement layer and the surface reinforcement layer, and the resin layer at least partially impregnates the second nonwoven fibrous carrier; Thus, after curing the molding material, a molded product having an average pinhole area of ​​less than 0.1% and / or an average pinhole size of less than 0.05 mm is formed. 2 and / or a cured article having less than 5% overlap defects.

2. The molding material according to claim 1, further comprising: (e) a discontinuous indicator means disposed in the lower surface of the second nonwoven fibrous carrier layer, the discontinuous indicator means comprising a refractive metal oxide, or a dye or pigment, the indicator means comprising an array of shapes, wherein the discontinuous indicator means does not completely penetrate the upper surface of the second nonwoven fibrous carrier layer.

3. The molded material according to claim 2, wherein the discontinuous indicator means is in the shape of a line, a dot, or a combination thereof. The molding material according to claim 3 , wherein the discontinuous indicator means comprises carbon black.

5. A method for preparing a molding material suitable for molding into an article having an excellent surface finish, the method comprising the steps of: (a) providing a structural reinforcement layer comprising a fiber reinforcement material, the structural reinforcement layer having an upper surface and a lower surface, the structural reinforcement layer comprising a non-crimped glass fabric; (b) providing a surface reinforcement layer comprising a first nonwoven fiber support, wherein the first nonwoven fiber support comprises an area weight of 1 to 80 g / m 2 The thermoplastic fiber veil, the surface reinforcement layer having an upper surface and a lower surface, the first nonwoven fiber carrier having an openness of 1% to 10% and / or a thickness of 75 to 350 μm 2 an average open area between the first nonwoven fibrous carrier and the lower surface of the structural reinforcement layer; and (c) providing a resin layer, the resin layer comprising an epoxy resin, a rheology modifier and a curing agent, the resin layer having an upper surface and a lower surface, the resin composition of the resin layer being resistant to erosion at 60° C. and 0.1 s -1 The viscosity is 200 to 1000 Pa.s at 60 ° C and 100s -1 The viscosity is 0.1s -1 25% or less of the viscosity under but not less than 25 Pa.s, the resin layer is provided between the structural reinforcement layer and the first nonwoven fiber carrier, wherein the viscosity is measured by a shear sweep viscosity method; (d) providing a second nonwoven fibrous carrier, the second nonwoven fibrous carrier comprising polyester, nylon fibers, or blends thereof, the second nonwoven fibrous carrier having an area weight greater than the area weight of the first nonwoven fibrous carrier; and (e) bonding the resin layer to the lower surface of the structural reinforcement layer, whereby the resin layer completely impregnates the structural reinforcement layer and the surface reinforcement layer, and the resin layer at least partially impregnates the second nonwoven fibrous carrier.

6. The method according to claim 5, further comprising: (f) providing a discontinuous indicator means disposed in the lower surface of the second nonwoven fibrous carrier layer, the discontinuous indicator means comprising a refractive metal oxide, or a dye or pigment, the indicator means comprising an array of shapes, wherein the discontinuous indicator means does not completely penetrate the upper surface of the second nonwoven fibrous carrier layer.

7. A method for preparing a cured molded article, the method comprising the steps of: (a) preparing a molding material by the method according to claim 6, and subsequently; (b) curing the molding material in a mold or tool, wherein the discontinuous indicator means is in contact with the mold or tool, wherein at least one additional structural reinforcement layer is laid up to the molding material on a surface of the molding material remote from the surface strengthening layer prior to the curing step; (c) removing the molded article from the mold or tool, and (d) finishing the molded article of step (b) by abrading the mold or tool contacting surface of the article to a depth sufficient to remove the discontinuous indicator means without completely removing the surface strengthening layer.

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