MOLDING MATERIAL FOR SURFACE FINISHES

Abstract

A molding material comprising: (a) a structural reinforcement layer comprising a fibrous reinforcing material optionally combined with a second resin composition; and (b) a surface enhancement layer for contacting a mold or tool surface, comprising a first nonwoven fiber carrier combined with a first resin composition containing a rheology modifier and a curing agent, wherein the first resin composition provides an external 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 requiring minimal preparation prior to painting and / or application in its intended use.The molded article may be provided with sacrificial discontinuous indicating means to aid in the uniform removal of a portion of the surface enhancement layer of the molded article for specific applications.

Description

MOLDING MATERIAL FOR SURFACE FINISHES The present invention relates to molding materials that provide an improved surface finish, a process for preparing the same, a process for preparing molded articles by curing said molding materials, and molded articles obtainable by said process. The present invention relates particularly to fiber-reinforced molding composite materials that can be cured at low temperatures and include a surface finish layer to provide a molded article having a high-quality surface finish that requires minimal preparation after curing, especially, but not exclusively, for use in the automotive and wind turbine industries. Composite materials have well-documented advantages over traditional construction materials, particularly in providing excellent mechanical properties at very low material densities. As a result, the use of such composite materials has become widespread in various industries, including aerospace, automotive, marine, and wind turbine. Prepregs, comprising an arrangement of fibers impregnated with a thermosetting resin, such as epoxy resin, are widely used in the production of such composite materials. Typically, a number of layers of these prepregs are applied as desired, and the resulting assembly, or laminate, is placed in a mold and cured, usually by exposure to elevated temperatures, optionally under pressure, to produce a cured composite laminate. However, without any surface treatment, these composites often cure to a poor surface finish, which may manifest as a rough, wavy, or pitted surface, or as narrow grooves on the surface of a molded structure where adjacent layers of prepregs have overlapped to ensure a continuous layer.This tendency to form an uneven surface appears to be closely related to the roughness of the underlying reinforcement, with the problem becoming more pronounced the rougher the reinforcement. This can be a particular issue when rough reinforcement is used for structural stiffness, yet a smooth surface finish is desirable, such as in the production of automotive body panels, where a Class A finish is required, or in the production of wind turbine blades. There have been several different methodologies 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, for example, commonly use an in-mold gelcoat or process coat that acts as a surface finish layer. This can be further finished after demolding by filling defects and sanding to remove mold release agents and minor imperfections, and to smooth the surface, before applying a topcoat of paint to protect the structure from environmental conditions.Essentially, this gel coating process involves bonding a fluid composition to the inner surface of the mold, which then partially cures to form a gel layer. The pre-impregnated assembly is placed onto the gel layer before curing. During curing, the pre-impregnation and the gel layer fuse together, typically resulting in a smooth surface of the molded compound. However, the process is labor-intensive, requiring an initial curing step, and tends to produce a gel layer of uneven thickness. Furthermore, the layer must be relatively thick (e.g., 0.3 mm on average) to cover imperfections, which can lead to an undesirable increase in weight. Other methodologies have used surface finishing films incorporated into a mold mating surface of the molding composite material, which typically comprise a thermosetting resin supported on a nonwoven backing mat. WO2008 / 007094 A2, for example, describes a composite material assembly comprising: (a) a surface enhancement layer comprising at least one layer of fibers having a length-to-width dimensional ratio of more than 5:1; and (b) a structuring agent comprising at least one reinforcing fiber and at least one polymer matrix. This document describes that the fibers used in the surface enhancement layer can be prepared by segmenting the fibers longitudinally and then forming a film or veil from the segmented fibers, such that the resulting veil structure is much denser, having an increased fiber density for the same weight.This document describes how the denser veil structure provides an improved surface finish in terms of both appearance and smoothness. Manufacturers of large composite parts, such as wind turbine blades, are also keen to ensure that any traces of mold release agent—used to coat the mold to facilitate the release of the composite part after curing, and which is subsequently transferred to the surface of the cured part—are removed to guarantee good adhesion of the final topcoat of paint to the composite surface. Such traces of mold release agent are typically removed using a sanding process.However, a problem encountered when surface finishing films are incorporated into a mold-mapping surface of a molding composite material is that end users sand laminates comprising the surface finishing film to such an extent that they damage its structure and produce the same surface holes that the finishing film was intended to prevent. When sanding, end users typically look for a change in the surface gloss level as an indication of sufficient sanding. It appears that surfaces produced using a finishing film as described above are more resistant to sanding than they are accustomed to, and as a result, they tend to use a more aggressive sanding regime, resulting in damage. One approach to overcoming this problem has been to improve the sandability of the surface enhancement layer to ensure that any traces of mold release agent can be easily removed under typical sanding conditions. WO2010 / 046682A1, for example, describes a prepreg assembly comprising resin and fibers and comprising a top curable resin surface layer, such that when the assembly is cured, the top surface layer has a sandability of at least 0.30 mg / cycle in 200 cycles, as measured in accordance with ASTM D4060 using a Taber 5151 abrasion tester equipped with H18 wheels and a 1.0 kg weight. In a preferred embodiment, the resin surface layer MA / a / zuzz / uuoui a superior curable comprises at least 10.0% by weight of a particulate granular material in the form of glass spheres having a particle size between 5 pm and 50 pm, to provide the necessary sanding properties.Other approaches have addressed the issue of slippage of fiber-reinforced molding composites when placed in a mold, which can lead to surface irregularities in the molded article after curing. This problem can be particularly relevant when adjacent layers of reinforcement or prepreg overlap in a mold, potentially causing resin exhaustion in the overlap area and resulting in the formation of a narrow indentation along the overlap junction after curing.WO2017 / 021147A1, for example, describes a molding material comprising a layer of fibrous material in a curable resin matrix provided on at least one surface with a surface finish film comprising sticky resin, wherein a veil is provided on the surface of the finish film away from the molding material and perforations are formed in the veil to allow the sticky resin of the surface finish film to pass through the veil during a molding operation. This document describes that the presence of such perforations in the veil allows small amounts of the sticky resin to provide light adhesion between the molding material and a mold surface, thereby holding the molding material in place. The various methodologies for improving the surface finish of fiber-reinforced molding composite materials and molded articles produced from such materials described above all suffer from certain disadvantages, such as the need to cure additional gel coating layers in molds, or to use surface finish layers containing longitudinally sectioned fibers, or to include additional glass spheres to improve the sandability of the surface finish layer, or to pierce any fiber veil in the surface finish layer, which in turn can have an effect on resin flow and surface finish. The present invention aims to overcome at least some of the problems mentioned above and / or provide improvements in general. According to the present invention, a molding material, a process for preparing the same, a process for preparing molded articles by curing said molding materials, and molded articles that can be obtained by a process as described below or as defined in any of the appended claims are provided. Therefore, in a first aspect of the invention, a molding material is provided comprising: (a) a structural reinforcement layer comprising a fibrous reinforcing material; and (b) a surface enhancement layer, for contacting a surface of a mold or tool, comprising a first nonwoven fiber carrier combined with a first resin composition containing a rheology modifier and a curing agent, wherein the first resin composition provides an external mold or tool contact surface of the molding material. The first resin composition at least partially impregnates the first nonwoven layer and, in preferred embodiments, completely impregnates the first nonwoven layer. However, it is an essential feature of the invention that a sufficient quantity of the first resin composition is present on the surface of the first nonwoven layer away from the structural reinforcement layer to form a continuous layer on the outer mold or tool contact surface of the molding material. In the context of the present invention, the term molding material refers to a fiber-reinforced composite material that can be placed with other materials in a mold or tool and cured to form a composite part that takes the shape of the mold or tool. Such molding materials can be used to prepare many different components, including, but not limited to, wind turbine components such as nacelles, propellers, and rotor blades. The structural reinforcement layer can take many forms. Typically, the molding material according to the present invention will contain several layers of structural reinforcement, although for some applications a single layer may suffice. The fibrous reinforcement material may be in the form of a sheet, a continuous mat, or continuous filaments. In other embodiments, the fibrous reinforcement material comprises short-length fibers, for example, a chopped-strand mat. The fibrous reinforcement material may be in the form of multiple fiber tows, each containing multiple fiber filaments. The tows may be sewn or woven together to form a fabric. The fibers may consist of natural materials, such as cotton, linen, hemp, wool, or silk; or semi-synthetic materials, such as rayon, viscose, modal, etc.; or synthetic materials, such as carbon, polyester, mineral fibers, nylon, acrylic, glass, aramid (aromatic polyamide), etc. In preferred embodiments, the fiber reinforcement comprises carbon fibers or glass fibers. In some embodiments, the fibrous reinforcement material is in the form of a woven fabric. In other embodiments, the fibrous reinforcement material comprises a unidirectional (UD) fabric in which the majority of the fibers, yarns, or strands present in the fabric extend in a single direction, although a small number of fibers, yarns, or strands may extend in a direction different from the majority, for example, as cross-stitching, in order to maintain the unidirectional alignment of the fabric. The fibers, yarns, or tows in a unidirectional fabric may be kept in alignment by a number of different methods, including weaving, sewing, and bonding. Accordingly, such unidirectional fabrics may be woven or nonwoven. In further embodiments, the fibrous reinforcement material comprises a unidirectional fabric combined with a biaxial or multiaxial fabric or mat, in which either component may be woven or nonwoven. Suitable woven and nonwoven fabrics for use in composite materials are commercially available from specialist manufacturers including, but not limited to, Chomarat Textiles Industries, Esher, Surrey, UK; Hexcel Reinforcements UK Limited, Narborough, Leicestershire, UK; and Zhenshi Group Hengshi Fibreglass Fabrics Co., Ltd., Tongxiang Economic Development Zone, Jiaxing, Zhejiang, 314500 China. In one embodiment, the woven or nonwoven fabric is a carbon fiber or fiberglass fabric, such as BB200, BB600, or BB1200, where the designation BB1200, for example, refers to a biaxial glass fabric having a surface weight of 1200 g / m². Hybrid or mixed fiber systems may also be considered. The use of cracked (i.e., broken by stretching) or selectively discontinuous fibers may be advantageous for facilitating the placement of the molding material according to the present invention and improving its formability. The weight per unit area of ​​the fibrous reinforcing material is generally between 40 g / m2 and 4000 g / m2. In preferred embodiments, the weight per area of ​​the fibers is preferably in the range between 100 g / m2 and 2500 g / m2, more preferably between 150 g / m2 and 2000 g / m2. The fibrous reinforcement material in the structural reinforcement layer, or layers where more than one layer is present, will generally be a heavy, non-crimped fabric, such as fiberglass. For glass reinforcements, fibers between 68 tex and 2400 tex (grams per kilometer of yarn) are specially suited. The surface enhancement 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 lightweight, preferably less than 100 g / m², but preferably robust enough to carry a resin layer and withstand processing in the processes of the invention. The nonwoven fiber carriers may comprise continuous or staple fibers. In one embodiment, the first nonwoven fiber carrier comprises a veil (sometimes referred to as a fleece). In the context of the present invention, the term veil refers to a thin, lightweight (i.e., area weight not exceeding 100 g / m²), porous, nonwoven fibrous reinforcement.In a preferred embodiment, the first nonwoven fiber carrier consists of fibers of a thermoplastic material, preferably bonded using an organic binder to impart structural integrity to the material. In one particular embodiment, the thermoplastic material comprises a polyester, or an aliphatic or semiaromatic polyamide, such as nylon or polyester fibers. In another embodiment, the nonwoven fiber carrier comprises a web formed from a mixture of thermoplastic fibers, such as a mixture of polyester and nylon fibers. The organic binder is generally present in an amount between 1% and 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 how the first resin composition interacts with the surface of a mold or tool 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 an average open area between 75 sq ft and 350 sq ft. In preferred embodiments, the first nonwoven fiber carrier has a weight per unit area in the range of 1 g / m² to 80 g / m², preferably between 5 g / m² to 50 g / m², and more preferably between 10 g / m² to 40 g / m². In one embodiment, the first nonwoven fiber carrier has an air permeability of approximately 2300 L / m² / s at an applied pressure of 200 Pa. The air permeability of the nonwoven fiber carrier can be measured using ASTM D737-18 - Standard Test Method for Air Permeability of Textile Fabrics.Suitable thermoplastic fiber veils include those commercially available under the trade name Optiveil® T2761-00 from Technical Fibre Products Limited, Burnside Mills, Kendal, Cumbria, UK. The surface enhancement layer includes a first resin composition in addition to the first nonwoven fiber carrier. The first resin composition generally comprises a thermosetting resin, such as a polyester resin, polyurethane resin, polyurethane / polyurea resin, phenol-formaldehyde resin, urea-formaldehyde resin, vinyl ester resin, cyanate ester resin, polyimide resin, or epoxy resin. In one embodiment, the first resin composition is a thermosetting resin composition, preferably an epoxy resin composition, i.e., comprising an epoxy resin or a mixture of epoxy resins. Suitable epoxy resins include the M9 and M79 ranges of epoxy resins available from Hexcel Composites Limited, Duxford, Cambridgeshire, UK. In one embodiment, the first resin composition comprises an epoxy resin having an epoxy equivalent weight (EEW) in the range of 150 to 1500, preferably in the range of 150 to 1250, preferably in the range of 150 to 1000, 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. The first resin composition includes at least one curing agent to facilitate resin crosslinking and curing of the molding material, especially at temperatures of 100°C or lower. In the context of the present invention, the term "curing agent" includes any curing agent and / or accelerators capable of effecting or increasing the crosslinking rate of the first resin composition. Such curing agents and / or accelerators for use in the invention are 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 the range of materials available under the trade name Dyhard® from AlzChem Group AG, Trostberg, Germany, which includes UR200, UR300, UR400, UR500, UR600, and UR700, and the range of materials available under the trade name Omicure® from Emerald Performance Materials, Moorefield, New Jersey, USA, which includes U-24M, U-35M, U-52, U-52M, U-210, U-210M, U-405, U-405M, U-410M, and U-415M. In additional embodiments, the curing agent may comprise a curative dicyandiamide combined with the substituted urea. The curing agent may be present in any quantity suitable to cause the resin to cure under selected conditions.In some forms, the curing agent is present in an amount between 1% by weight and 25% by weight, between 1% by weight and 20% by weight, between 1% by weight and 15% by weight, between 1% by weight and 10% by weight, or between 2% by weight and 8% by weight based on the total weight of the resin composition, or any combination thereof. It is important that the first resin composition contains a rheology modifier. In the context of the present invention, the term rheology modifier refers to a compound or substance capable of imparting non-Newtonian rheological properties to materials such as the first resin composition. In the present invention, the rheology modifier must increase the minimum viscosity of the resin under shear compared to the modified resin without the modifier, and it must also increase the viscosity of the resin when not under shear by a greater amount compared to the modified resin without the modifier. This can be quantified using a shear sweep viscosity method. Suitable conditions for a shear sweep viscosity method are parallel 25 mm plates with a 1 mm gap configured to provide a shear rate between 0.1s and 100s, and a temperature of 60 °C. In the present invention, the rheology modifier is preferably selected so that when measured as set out above, the first resin composition has a viscosity at 60 °C and 0.1 s1 between 200 Pa.s and 1000 Pa.s; and a viscosity at 60 °C and 100 s1 of 25% or less of the viscosity at 0.1 s1, provided that the viscosity at 60 °C and 100 s1 is not less than 25 Pa.s. A shear sweep viscosity method can be carried out using any viscometer adapted to provide the above conditions, for example, using a TA HR-2 Discovery hybrid rheometer manufactured by TA Instruments, New Castle, Delaware, USA Suitable rheology modifiers include treated and untreated grades of fumed silica, such as hydrophobic silica. Hydrophilic silica may also be used, but preferably in combination with a thixotropic enhancer. Organophilic phyllosilicates may also be used. Suitable silicas include Aerosil® R 202, available from Evonik Resource Efficiency GmbH, Germany, and Cab-O-Sil® TS720, available from Cabot Corporation, Alpharetta, Georgia, USA. Suitable organophilic phyllosilicates include Garamite-7305, available from BYK (Altana Group). Suitable thixotropic enhancers include those available under the trade name Rheobyk® from BYK-Chemie GmbH, Wesel, Germany. In one application, the rheology modifier is a hydrophobic fumed silica, such as Aerosil® R202. The rheology modifier, optionally combined with a thixotropic enhancer, may be present in an amount between 1 wt% and 20 wt% based on the total weight of the first resin composition. In preferred embodiments, the rheology modifier is present in an amount between 1 wt% and 15 wt%, between 1 wt% and 12 wt%, between 1 wt% and 10 wt%, between 2 wt% and 10 wt%, between 3 wt% and 9 wt%, between 4 wt% and 8 wt%, or any combination thereof, based on the total weight of the first resin composition. We have discovered that the use of a lightweight, tightly closed microfiber veil combined with a rheologically modified epoxy resin composition having the viscosity characteristics described above provides a surface enhancement layer that has good gap-filling properties, resulting in greatly reduced hole formation, and also reduces or completely eliminates narrow grooves caused when layers of molding material overlap during placement. The first resin composition may also include other components, such as hardening agents, particulate fillers (such as microballoons, glass spheres, talc, etc.), colorants, air release agents or pigments, etc. The first resin composition is provided on an external mold or tool contact surface of the molding material; that is, a surface of the molding material that makes contact with the surface of a mold or tool when the molding material is disposed ready for curing. In its simplest form, for example, the molding material comprises a layer of the first resin composition on top of which lies a non-woven fiber carrier such as a lightweight surface veil, which together form the surface enhancement layer, and on top of which lies a layer of fibrous reinforcing material such as a heavy glass cloth mat, which forms the structural reinforcement layer.In this case, the first resin composition layer will generally be a thick layer that has a high weight per area because the amount of the first resin composition must be sufficient to impregnate not only the surface veil but also the fibrous reinforcement layer once the layers are consolidated. In another embodiment, the structural reinforcement layer is combined with a second resin composition. In this case, the molding material may comprise a layer of the first resin composition topped with a lightweight surface veil, which together form the surface enhancement layer. This is followed by a layer of heavy fibrous reinforcement material and, finally, a layer of a second resin composition, the last two of which form the structural reinforcement layer. In a further embodiment, the second resin composition layer may be sandwiched between the fibrous reinforcement material and the nonwoven fiber carrier layers. In either case, the second resin composition may partially or fully impregnate the structural reinforcement layer after the layers have bonded, for example, to form a semi-pre-impregnated or pre-impregnated structure. Any of the resin compositions 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 void-filling properties, it is not essential that the second resin composition comprise a rheology modifier; however, the second resin composition may include a rheology modifier if desired. In certain preferred embodiments, the second resin composition is the same as the first resin composition but does not contain a rheology modifier, and in certain other preferred embodiments, the second resin composition is the same as the first resin composition that includes the rheology modifier. 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 enhancement layer. The second nonwoven fiber carrier may be the same as the first nonwoven fiber carrier, but preferably the second nonwoven fiber carrier has a higher weight per unit area than the first nonwoven fiber carrier. The second nonwoven fiber carrier may comprise continuous or staple fibers. In one embodiment, the second nonwoven fiber carrier comprises a web (sometimes referred to as a fleece). The second nonwoven fiber carrier generally consists of nonwoven fibers of glass, carbon, polyester, polyamide, aramid (aromatic polyamide), or combinations thereof, bonded together using an organic binder to impart structural integrity to the material. Preferably, the second nonwoven fiber carrier comprises a glass fleece. The organic binder is generally present in an amount between 1% and 10% by weight based on the total weight of the second nonwoven fiber carrier. Generally, the second nonwoven fiber carrier will have a slightly higher weight per area or surface density than the first nonwoven fiber carrier.In a preferred embodiment, the second nonwoven fiber carrier is a nonwoven veil having a weight per area between 20 g / m² and 100 g / m², preferably between 20 g / m² and 90 g / m², more preferably between 30 g / m² and 80 g / m², and even more preferably between 30 g / m² and 60 g / m². Suitable nonwoven glass mats or fleeces are commercially available under the trade name Evalith® from Johns Manville, Denver, Colorado, USA, including, but not limited to, Evalith® ST-3022, S 4030, and S 5030, and under the trade name Changhai® from Taishan Fiberglass Inc., Economic Development Zone. Taian, Shandong, PR China, including, but not limited to, Changhai® S-SM30, S-SM50, S-HM30 and S-HM50. The presence of the second nonwoven fiber material helps prevent the fiber reinforcement material in the structural reinforcement layer from showing through on the surface of the molded material after curing. It also ensures that sufficient second resin composition is retained within the surface enhancement layer during curing, preventing the formation of narrow grooves or other surface irregularities due to resin exhaustion. Like the first nonwoven fiber material, the second nonwoven fiber material can also prevent air bubble formation or aid in the dissipation of air bubbles with the first, second, or third resin composition. The second nonwoven fiber carrier may be combined with a third resin composition. This third resin composition can be applied to both sides of the second nonwoven fiber carrier and can help bond it to the first nonwoven fiber carrier and / or the structural reinforcement layer. After consolidation, the third resin composition may partially or fully impregnate the second nonwoven fiber carrier. When present, the second non-woven fiber carrier can be optionally provided bonded to the fibrous reinforcement material of the structural reinforcement layer; for example, these layers can be pre-bonded using a resin material or by stitching. Any of the resin compositions discussed for the first or second resin composition are suitable for use as the third resin composition. However, it is not essential that the third resin composition include a rheology modifier, although it may include one if desired. In certain preferred embodiments, the third resin composition is the same as the first and / or second resin composition but does not contain a rheology modifier, and in certain other preferred embodiments, the second resin composition is the same as the first and / or second resin composition but includes the rheology modifier. Using the same resin composition for the first, second, and third resin compositions, when present, is particularly advantageous, as it simplifies the process and avoids any problems arising from potential incompatibilities between different resin compositions. In one embodiment, the molding material further comprises at least one additional structural reinforcement layer on a surface of the molding material away from the surface enhancement layer. The additional structural reinforcement layer(s) may be the same as the first structural reinforcement layer or may be different. In one embodiment, the additional structural reinforcement layer(s) are different from the first structural reinforcement layer, and the additional reinforcement layers may be associated with the same resin compositions as the first structural reinforcement layer or with different epoxy resin compositions. In this embodiment, the additional structural reinforcement layer(s) may be conventional prepregs, such as those commercially available under the trade name HexPly® from Hexcel Composites GmbH & Co KG, Neumarkt, Austria, which include, among others, the HexPly® M79 and M9 prepreg ranges. The total amount of resin provided in the molding materials of the present invention will depend on the intended use of the material. For example, when a molding material is intended to be The discontinuous indicator medium can be applied to the first resin composition on the external mold or tool contact surface of the molding material during the assembly of the various layers and before consolidation. However, it is preferable that the discontinuous indicator medium be applied after the consolidation of the structural reinforcement layer and the surface improvement layer (and any additional layers), but before curing. At this stage, i.e., before curing, the indicator medium adheres freely 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. When the molding material cures, the discontinuous indicating media become permanently fixed or embedded in the upper region of the surface enhancement layer and will therefore bond sufficiently to the mold or tool-contact surface of the cured molding materials so that they are not removed by handling the material. The indicator medium can bond only to the surface of the mold or the surface in contact with the molding material tool, or it can penetrate the surface. When the discontinuous indicator medium penetrates the surface finish layer, it can do so to any depth, provided it does not penetrate the layer completely, i.e., so that the indicator medium does not come into contact with the structural reinforcement layer (or the second nonwoven fiber carrier, when present). This ensures that if the surface improvement layer is removed (e.g., by sanding) to a depth that removes all the discontinuous indicator medium, no damage will be caused to the underlying layers. Therefore, the indicator medium can penetrate the surface improvement layer to any depth from 0% of the layer depth (i.e., bonded only to the surface) to almost, but not completely, 100% of the depth.In preferred modalities, the indicator medium penetrates the surface enhancement layer between 0.1% and 95%, more preferably between 1% and 50% of its depth. The molding materials of the present invention are particularly suitable for incorporating indicator media into the mold or tool-contact surface of the molding material due to the rheological properties of the surface enhancement layer provided by the rheology modifier of the first resin composition. In particular, the enhanced viscosity of the first resin composition means that the indicator medium will bind or become embedded in the surface layer and remain as discrete shapes, without significantly diffusing outward or inward, thus maintaining a clear pattern. During demolding of the cured article, the discontinuous indicator medium remains on the surface, allowing the article to be easily sanded without risk of the surface finish layer being completely removed. In practice, an operator can determine whether the entire surface or article has been sufficiently sanded by assessing whether all the discontinuous indicator medium has been removed. The discontinuous indicator medium may comprise any regular or irregular shape, and the shapes may be arranged in any regular or irregular pattern, provided they function as an indicator of sufficient surface treatment. Suitable shapes include lines (linear or curved), points (including round, square, or irregular points), or mixtures thereof, in regular or irregular arrangements. Preferably, the distances between individual shapes are generally less than the distance covered in a single sanding stroke during manual sanding of a surface. Preferably, the indicator medium comprises a regular arrangement of regular dots, as this makes it easier to assess which areas of the surface have been treated, for example, which areas have had the indicator medium removed by sanding and which have been insufficiently treated. The discontinuous indicating medium may comprise any suitable material that remains visible on the surface of the molding material after curing. In one embodiment, the indicating medium comprises a refractive compound, such as, for example, a refractive metal oxide similar to titanium dioxide. The use of a refractive compound may be useful when the sanding of the article is automated and may facilitate the use of light scanning technology to assess progress instead of visual inspection. In other embodiments, the indicating medium 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 invention include, but are not limited to, products sold under the trade name Printex®V manufactured by Orion Engineered Carbons LLC, 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 dye bleeding into other areas of the second resin composition. However, it will be readily apparent that the batch methods according to the present invention are not limited to the illustrative examples described above. The indicating medium may be applied to the mold or tool mating surface of the molding material in any suitable manner, for example, by applying a perforated template thereto and spraying the surface with a solution or dispersion or solid particles of a suitable metallic oxide, dye, or pigment, followed by light pressure, such as by using a hand roller. Alternatively, the indicating medium may be applied by spraying or printing. In a second aspect of the present invention, a process is provided for preparing a molding material, comprising the steps of: (a) provide a structural reinforcement layer comprising a fibrous reinforcing material; (b) providing a surface enhancement layer, for contacting a surface of a mold or tool, comprising a first nonwoven fiber carrier combined with a first resin composition containing a rheology modifier and a curing agent, wherein the first resin composition is provided on an external mold or tool contact surface of the molding material that is away from the structural reinforcement layer; and (c) consolidating the layers to impregnate at least the first nonwoven fiber carrier with the first resin compositions without curing the resin composition. In the process of the present invention, consolidation is carried out after the assembly of the structural reinforcement layer and the surface enhancement layers, and any other layers that may be included. Consolidation can be carried out in any conventional manner to form a composite material, preferably by heating the pressure-molded material. For example, consolidation can be carried out by passing the combined layers through consolidation rollers (such as one or more S-wrap rollers) and heating them to, for example, 80°C. In the process of the present invention, the fibrous reinforcing material may optionally be present combined with a second resin composition. In one embodiment, the process according to the second aspect of the present invention further comprises the step of providing a second non-woven fiber carrier, optionally combined with a third resin composition, between the structural reinforcement layer and the surface enhancement layer prior to the consolidation stage. In one embodiment, the process 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 the molding material away from the surface enhancement layer prior to the consolidation step. When the structural reinforcement layer is provided in combination with a second resin composition and / or the second nonwoven fiber carrier is provided in combination with a third resin composition, the materials may be supplied with the structural materials already at least partially infused with the resin. Alternatively, in preferred embodiments, the structural and resin layers are provided as separate layers during the assembly of the molding material, and the resin layers are made to at least partially impregnate the respective layers during the consolidation stage. In the process of the present invention, the first resin composition, the first non-woven carrier and, when present, the second resin composition, the second non-woven fiber carrier, the third resin composition and / or additional structural reinforcement layers may each optionally be as defined for similar materials in the molding material of the present invention. In one embodiment, the process according to the second aspect of the present invention further comprises the step of applying discontinuous indicating means to the mold or tool-contact surface of the molding material and applying pressure, and optionally heat, to bond the discontinuous indicating means to the first resin composition without fully penetrating the surface enhancement layer. In the context of the present invention, the term "bond" means that the discontinuous indicating means are associated with the mold or tool-contact surface of the molding material and, therefore, cannot be accidentally or easily removed during transport to end users or in the course of subsequent processing steps. After curing, the discontinuous indicating means remains visible on the mold or tool-contact surface of the cured molding material and may partially penetrate the surface enhancement layer. The discontinuous indicating medium can be applied to the mold or tool contact surface of the molding material at any stage during material placement and before curing, for example, before the consolidation stage. Preferably, however, the discontinuous indicating medium is added after the consolidation stage but before curing. The discontinuous indicating medium can be added to the surface in any suitable manner. For example, the indicating medium could be applied to the mold or tool contact surface of the molding material by applying a perforated template and spraying the surface with a solution, dispersion, or solid particles of a suitable metallic oxide, dye, or pigment, followed by light pressure, such as by using a hand roller. Alternatively, the indicator medium could be applied by spraying or printing. In a third aspect of the present invention, a molding material is provided that can be obtained by a process according to the second aspect of the present invention. In the fourth aspect of the present invention, a process for preparing a molded article is provided comprising curing a molding material according to the first or third aspect of the present invention, optionally wherein the molding material is placed with at least one additional structural reinforcement layer on a surface of the molding material away from the surface enhancement layer prior to the curing stage. The molding materials of the present invention can be cured to form molded articles in any conventional manner, taking into account the resin(s) and curing agents present in the various layers. Therefore, the appropriate conditions required to cure an article prepared from a molding material according to the present invention can be determined empirically in accordance with standard procedures used in the prepreg industry. In a fifth aspect of the present invention, a molded article is provided that can be obtained by a process according to the fourth aspect of the present invention. In one embodiment, the molded article has a molded surface with an average hole area of ​​less than 1%, preferably less than 0.1%, and / or an average pinhole size of less than 0.5 mm2, preferably less than 0.05 mm2, and / or an overlap defect of less than 10%, preferably less than 5%. In a sixth aspect of the present invention, a process is provided for preparing a finished molded article, comprising the steps of: (a) preparing a molding material by the process of the present invention which includes the step of applying discontinuous indicating means to the mold or tool-contact surface of the molding material and applying pressure, and optionally heat, to bond the discontinuous indicating means to the first resin composition without fully penetrating the surface enhancement layer; (b) curing the molding material in a mold or tool with the discontinuous indicating medium in contact with the mold or tool, optionally wherein the molding material is placed with at least one additional structural reinforcement layer on a surface of the molding material away from the surface enhancement layer prior to the curing stage; (c) removing the molded article from the mold or tool, and finishing the molded article from step (b) by abrading the mold or tool contact surface of the article to a depth sufficient to remove the discontinuous indicator medium without completely removing the surface enhancement layer. In this aspect of the present invention, the discontinuous indicator provides an operator with a sign that the outermost part of the surface enhancement layer of the molded article, which may be contaminated with mold release agent after demolding, has been uniformly removed, without the risk of removing the entire surface enhancement layer. In another aspect of the present invention, a finished article is provided that can be obtained by a process according to the sixth aspect of the present invention. Figure 1 shows a partially sanded molding material according to a preferred embodiment of the present invention. Examples Example 1 A resin composition 1 was formulated from: 72.3 g of Araldite® LY1589 (a semi-solid bisphenol A diglycidyl ether epoxy resin manufactured by Huntsman Advanced Materials (Switzerland) GmbH, Basel, Switzerland); 18.17 g of Araldite® LY1556 (a liquid bisphenol A diglycidyl ether epoxy resin manufactured by Huntsman Advanced Materials (Switzerland) GmbH, Basel, Switzerland); 0.1 Og Araldite® DW 0135 (a blue pigment paste manufactured by Huntsman Advanced Materials (Switzerland) GmbH, Basel, Switzerland); 0.18 g of BYK-A530 (an air release agent manufactured by BYK-Chemie GmbH, Wesel, Germany); 6.00 g of Aerosil® R202 (a hydrophobic fumed silica rheology modifier manufactured by Evonik Resource Efficiency GmbH, Hanau-Wolfgang, Germany); and 2.82g Dyhard® UR500 (a dual-functional latent urone accelerator in powder form manufactured by Alzchem Group AG, Trostberg, Germany). The components were thoroughly mixed at a temperature between 50°C and 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. A molding material 1 was constructed that has the following architecture: (1) a layer of 400 g / m2 of resin composition 1; (2) a layer of LBB1200 fabric (1250 g / m2 uncrimped triaxial glass fabric manufactured by Hexcel Reinforcements UK Limited, Narborough, Leicestershire, United Kingdom); (3) a layer of Evalith ® S 5030 (a fiberglass fleece having a weight per area of ​​50 g / m2 manufactured by Johns Manville, Denver, Colorado, United States); (4) a 200 g / m2 layer of resin composition 2; (5) a layer of a fully synthetic, lightweight non-woven fiber veil comprising a blend of polyester and nylon fibers with an area weight of 15 g / m2 (manufactured by Technical Fibre Products Limited, Burnside Mills, Kendal, Cumbria, United Kingdom); and (6) a 200 g / m2 layer of resin composition 1. The assembled layers were consolidated by passing through an S-shaped wrapping roller system heated to 80°C, to form molding material 1. After consolidation, a layer of P34 Tygavac® RF260 (a fluoropolymer FEP release film having a 12.7 mm staggered center perforation style and a nominal hole diameter of 1.143 mm manufactured by Tygavac Advanced Materials Limited, The Causeway, Broadway Business Park, Chadderton, Oldham OL9 9XD, UK), was placed on top of the resin composition layer on the underside of the prepreg (i.e., layer (6) – the surface adjacent to the mold surface that becomes the component surface upon demolding). TR-81 titanium dioxide (a powdered titanium dioxide manufactured by Huntsman Advanced Materials (Switzerland) GmbH, Basel, Switzerland) was sprinkled onto the film surface, which was then lightly pressed with a rubber roller before removing the excess titanium dioxide and the release film. Molding material 1 was left with a regular arrangement of titanium dioxide dots having a weight per area of ​​approximately 1.7 g / m² on the resin layer of the mold or tool contact surface. A composite part was produced by placing molding material 1 into a composite tool treated with Zyvax® Watershield™ (a silicone-free, water-soluble mold release agent manufactured by Freeman Manufacturing and Supply Company, Avon, Ohio, USA) and curing the assembly under vacuum for 6 hours at 80°C and 100,000 Pa (1 bar) pressure. Upon cooling, the cured molded part was removed from the tool to reveal a discrete set of pigmented titanium dioxide dots against the blue background of the cured resin. The dots allowed for the uniform removal of a portion of the surface enhancement layer from the composite part by sanding (see Figure 1). Figure 1 shows the cured molding material 1 produced as described above. The left half of the material 3 has been sanded to remove any mold release agent remaining on the surface after curing, while the right side of the material 5 has not been sanded. The titanium dot matrix 7 applied to the molding material 1 before curing is still present on the right side of the material 5, while the absence of the regular dot matrix 7 on the left side 3 indicates at least partial removal of the top surface. The presence of scattered individual dots 9 on the left side 3 of the molding material 1 indicates areas where sanding has not been sufficient to completely remove the top surface layer and where further sanding is required. A sample of uncured molding material, prepared as described above, was cut and overlapped in the X and Y directions across the mold surface, with approximately 2–3 cm of overlap. Additional molding material was placed on top without any overlap, and the resulting assembly was cured as described above. Upon cooling and demolding, the overlap regions of the cured article showed very few defects compared to a standard part produced from non-overlapping molding material. Example 2 A resin composition 2 was formulated from: 72.9 g Kukdo KFR136SL, (a semi-solid bisphenol A diglycidyl ether epoxy resin manufactured by Kukdo Chemical Company Limited, Seoul, Korea); 18.2 g Epikote®828 (a bisphenol A diglycidyl ether liquid epoxy resin manufactured by Hexion Inc., Columbus, Ohio, United States); g Aerosil® R202 (a hydrophobic fumed silica rheology modifier manufactured by Evonik Resource Efficiency GmbH, Hanau-Wolfgang, Germany); and ινΐΛ / a / zuzz / uuou iy 2.9 g Dyhard® UR500 (a dual-functional latent urone accelerator in powder form manufactured by Alzchem Group AG, Trostberg, Germany). The components were thoroughly mixed at a temperature between 50°C and 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. A molding material 2 was constructed that has the following architecture: (1) a 400 g / m2 layer of resin composition 2; (2) a layer of LBB1200 fabric (1250 g / m2 uncrimped triaxial glass fabric manufactured by Hexcel Reinforcements UK Limited, Narborough, Leicestershire, United Kingdom); (3) a layer of Evalith ® S 5030 (a fiberglass fleece having a weight per area of ​​50 g / m2 manufactured by Johns Manville, Denver, Colorado, United States); (4) a layer of a fully synthetic, lightweight non-woven fiber veil comprising a blend of polyester and nylon fibers with an area weight of 15 g / m2 (manufactured by Technical Fibre Products Limited, Burnside Mills, Kendal, Cumbria, United Kingdom); and (5) a 400 g / m2 layer of resin composition 2. The assembled layers were consolidated by passing through an S-shaped wrapping roller system heated to 80°C, to form molding material 2. Molding material 2 was placed in a composite tool treated with Zyvax® Watershield™ (a silicone-free, water-soluble mold release agent manufactured by Freeman Manufacturing and Supply Company, Avon, Ohio, USA) with the resin composition layer (5) adjacent to the mold face. Two layers of HexPly® 79 (a prepreg manufactured by Hexcel GmbH, Neumarkt, Germany) were placed over the molding material in the mold, i.e., adjacent to the resin layer (1); and the assembly was vacuum-cured for 6 hours at 80°C and 100,000 Pa (1 bar) pressure. Upon cooling, the cured molded part was removed for inspection and further testing. In an alternative embodiment, a layer of discrete indicating media comprising a regular arrangement of titanium dioxide dots could be applied to the molding material 2 after consolidation and before curing. Test equipment and methods Matrix rheology Rheology quantifications in 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 1 mm gap set providing a shear rate of 0.1 to 100s, and a temperature of 60 °C. characterization of the veil Fiber diameter and veil aperture measurements were performed using a Keyence VHX-6000 series digital microscope manufactured by Keyence (UK) Limited, Milton Keynes, Buckinghamshire, UK. The veil used as the primary nonwoven fiber carrier (i.e., the surface veil used in the surface enhancement layer) was presented to the microscope by mounting it on a blue plastic card to help highlight the open areas when viewed on the computer monitor. The microscope was set to 175x magnification with the light output at maximum and the gain dial settings adjusted so that the open areas could be clearly identified. The saved computer image represents a total area of ​​2,951,002 sq ft. The air permeability of the nonwoven fiber carrier can be measured using ASTM D737-18 Standard Test Method for Air Permeability of Textile Fabrics. Next, Keyence software is used to measure the thickness (diameter) of individual fibers, the average open area (i.e., the empty space between fibers), and the percentage of openness. The image is also manipulated by adjusting sliders on a histogram to create a two-color image, where one color represents the veil fibers and the other represents the open space. The software is used to measure the areas of all individual open spaces. This data can be saved to a spreadsheet and used to calculate the total area occupied by open spaces (to calculate the percentage of openness) along with the average size of the open areas. Characterization of the cured surface The cured surface characterization was determined by cleaning the surface of a demolded composite part with an aqueous suspension of carbon black in acetone. Excess aqueous suspension was washed off before measurement using a Keyence VHX-6000 series digital microscope at 25X magnification with the gain setting adjusted to clearly identify surface defects. The observed 132.63 mm² image was manipulated using Keyence software, setting the histogram slider between 000 and 065, the brightness tolerance to 20, and the noise filter to 10. The software was used to quantify the mean area of ​​the observed holes and the percentage of the total observed area identified as holes. Overlap defects were quantified by first highlighting the defects along an overlap using an aqueous suspension of carbon black in acetone. After washing off any excess suspension, the length of any defect was measured using a ruler. The number of overlap defects was expressed as a percentage of the sum of the measured defects relative to the length of the overlap. Results The viscosities of the M79® resin (a commercially available non-rheological modified epoxy resin matrix manufactured by Hexcel Composites GmbH & Co., KG, Neumarkt, Austria) and the rheological modified resin composition 1 used in the molding material 1 in Example 1 above (which is in accordance with the present invention) were evaluated as set out above. For M79, the viscosity at 60 °C and 0.1 s was 40 Pa.s; and the viscosity at 60 °C and 100s was 29 Pa.s. For resin composition 1, the viscosity at 60° and 0.1 S'1 was 470 Pa.s; and the viscosity at 60 °C and 100s1 was 66 Pa.s. A material was prepared according to the present invention, cut, and overlapped in the X and Y directions across the surface of a mold, with approximately 2 cm to 3 cm regions MA / a / zuzz / uuoui a of overlap and the material was cured as discussed in Example 1. Three comparative laminates not within the scope of the invention were also prepared and treated as stated above. Comparative laminate 1 comprised a standard prepreg, e.g., M79 / 40% / LBB1200 with the biaxial portion adjacent to the mold surface, without a surface-enhancing nonwoven fiber carrier, without an intermediate nonwoven fiber carrier, and with non-rheological modified resin (M79). Comparative laminate 2 comprised a conventional prepreg, e.g., M79 / 40% / LBB1200 with the biaxial portion closest to the mold surface, without a nonwoven fiber carrier that enhances the surface, but with an S5030 nonwoven fiber carrier between the reinforcement layer and the mold, and with non-rheological modified resin (M79). Comparative laminate 3 comprised a conventional prepreg, e.g., M79 / 40% / LBB1200, with the biaxial portion closest to the mold surface, but with a surface-enhancing nonwoven fiber carrier in the outer layer adjacent to the mold and an S5030 nonwoven fiber carrier between the reinforcement layer and the surface-enhancing nonwoven fiber carrier. However, the resin in the comparative laminate was a modified non-rheological resin (M79). The surface characterization for holes and overlap defects in composite material parts prepared by curing control laminates 1, 2, and 3 and surface finishing molding material according to the present invention generally yielded the following results: Control laminate 1 Control laminate 2 Control laminate 3 Inventive example Matrix rheology Unmodified Unmodified Unmodified Modified rheology Mold adjacent to nonwoven carrier None None Thermoplastic veil Thermoplastic veil Intermediate nonwoven carrier None S5030 S5030 S5030 Area of ​​holes in cured laminate (%) 27.00% 11.60% 0.04% 0.09% Average hole size of cured laminate (mm2) 0.092 mm2 0.040 mm2 0.003 mm2 0.004 mm2 % of defects due to overlap 95% to 100% 95% to 100% 95% to 100% <5% The molding materials according to the present invention can be cured at low temperatures (typically 100°C) to provide molded articles with a good surface finish that exhibit fewer hole and overlap defects and require minimal surface processing. Such materials can be provided with discontinuous sacrificial indicator means on the molded surface to facilitate uniform surface processing.

Claims

1. A molding material, comprising: (a) a structural reinforcement layer comprising a fibrous reinforcing material; and (b) a surface enhancement layer, for contacting a surface of a mold or tool, comprising a first nonwoven fiber carrier combined with a first resin composition containing a rheology modifier and a curing agent, wherein the first resin composition provides an external mold or tool contact surface of the molding material.

2. A molding material according to claim 1, wherein the first resin composition has a viscosity at 60 °C and 0.1 s1 of between 200 Pa.s and 1000 Pa.s; and a viscosity at 60 °C and 100 s1 of 25% or less of the viscosity at 0.1 s1, but not less than 25 Pa.s (as quantified by a shear sweep viscosity method).

3. A molding material according to claim 1 or claim 2, wherein the first resin composition is a thermosetting resin composition, preferably an epoxy resin composition.

4. A molding material according to any preceding claim, wherein the first nonwoven fiber carrier is a thermoplastic fiber veil, preferably having a weight per area in the range of 1 g / m2 to 80 g / m2.

5. A molding material according to any of the preceding claims, wherein the first nonwoven fiber carrier has an opening between 1% and 10% and / or an average open area of ​​approximately between 75 pm2 and 350 pm2.

6. A molding material according to any of the preceding claims, wherein the structural reinforcement layer is present combined with a second resin composition, optionally wherein the second resin composition is the same as the first resin composition.

7. A molding material according to any of the preceding claims, further comprising a second nonwoven fiber carrier between the structural reinforcement layer and the surface enhancement layer, preferably wherein the second nonwoven fiber carrier has a weight per area greater than the weight per area of ​​the first nonwoven carrier.

8. A molding material according to claim 7, wherein the second nonwoven fiber carrier is combined with a third resin composition, preferably wherein the third resin composition is the same as the first and / or second resin composition.

9. A molding material according to any of the preceding claims, wherein it further comprises at least one additional structural reinforcement layer on a surface of the molding material away from the surface enhancement layer.

10. A molding material according to any of the preceding claims, wherein it further comprises discontinuous indicating means attached to the mold or tool surface of the molding material that do not completely penetrate the surface enhancement layer.

11. A molding material according to claim 10, wherein the discontinuous indicating medium comprises a regular or irregular arrangement of shapes; preferably wherein the shapes are selected from lines, points or a mixture thereof.

12. A molding material according to claim 10 or claim 11, wherein the discontinuous indicating medium comprises a refractive metal oxide, or a dye or pigment, such as carbon black.

13. A process for preparing a molding material, comprising the steps of: (a) providing a structural reinforcement layer comprising a fibrous reinforcing material; (b) providing a surface enhancement layer, for contact with a mold or tooling surface, comprising a first nonwoven fiber carrier combined with a first resin composition containing a rheology modifier and a curing agent, wherein the first resin composition is provided on an external mold or tooling surface of the molding material that is in contact with the structural reinforcement layer; and (c) consolidating the layers to impregnate at least the first nonwoven fiber carrier with the first resin compositions without curing the resin composition; preferably wherein the consolidation is carried out by heating the molding material under pressure.

14. A process according to claim 13, wherein the first resin composition has a viscosity at 60 °C and 0.1 s1 between 200 Pa.s and 1000 Pa.s; and a viscosity at 60 °C and 100 s1 of less than 25% of the viscosity at 0.1 s1 but not less than 25 Pa.s (as quantified by a shear sweep viscosity method).

15. A process according to claim 13 or claim 14, wherein the first resin composition is a thermosetting resin composition, preferably an epoxy resin composition.

16. A process according to any of claims 13 to 15, wherein the first nonwoven fiber carrier is a thermoplastic fiber veil, preferably having a weight per area in the range of 1 g / m2 to 80 g / m2.

17. A process according to any of claims 13 to 16, wherein the first nonwoven fiber carrier has an opening between 1% and 10% and / or an average open area of ​​approximately between 75 pm2 and 350 pm2.

18. A process according to any of claims 13 to 17, wherein the structural reinforcement layer is provided combined with a second resin composition, optionally wherein the second resin composition is the same as the first resin composition.

19. A process according to any of claims 13 to 18, further comprising the step of providing a second nonwoven fiber carrier between the structural reinforcement layer and the surface enhancement layer prior to the consolidation step, preferably wherein the second nonwoven fiber carrier has a weight per area greater than the weight per area of ​​the first nonwoven carrier.

20. A process according to claim 19, wherein the second nonwoven fiber carrier is combined with a third resin composition, preferably wherein the third resin composition is the same as the first and / or second resin composition.

21. A process as claimed in any of claims 13 to 20, further comprising providing at least one additional structural reinforcement layer on a surface of the molding material away from the surface enhancement layer prior to the consolidation stage.

22. A process as claimed in any of claims 13 to 21, further comprising the step of applying discontinuous indicating means to the mold or tool-contact surface of the molding material and applying pressure, and optionally heat, to bond the discontinuous indicating means to the first resin composition without fully penetrating the surface enhancement layer.

23. A molding material that can be obtained by a process according to any of claims 13 to 22.

24. A process for preparing a molded article comprising curing a molding material as claimed in any of claims 1 to 12 or 23, optionally wherein the molding material is placed with at least one additional structural reinforcement layer on a surface of the molding material away from the surface enhancement layer prior to the curing stage.

25. A molded article obtainable by a process according to claim 24.

26. A molded article according to claim 25, wherein it has a molded surface having an average hole area of ​​less than 1%, preferably less than 0.1%, and / or an average hole size of less than 0.5 mm2, preferably less than 0.05 mm2, and / or an overlap defect of less than 10%, preferably less than 5%.

27. A process for preparing a finished molded article, comprising the steps of: (a) preparing a molding material by the process according to claim 22, and subsequently; (b) curing the molding material in a mold or tool with the discontinuous indicating medium in contact with the mold or tool, optionally wherein the molding material is placed with at least one additional structural reinforcement layer on a surface of the molding material away from the surface enhancement layer prior to the curing step; (c) removing the molded article from the mold or tool; and (d) finishing the molded article from step (b) by abrading the mold or tool contact surface of the article to a depth sufficient to remove the discontinuous indicating medium without completely removing the surface enhancement layer.

28. A finished article that can be obtained by a process according to claim 27.