US20160265157A1

US20160265157A1 - Structured flock fiber reinforced layer

Info

Publication number: US20160265157A1
Application number: US14/642,987
Authority: US
Inventors: John M. Rice; Armand F. Lewis; Yong K. Kim
Original assignee: UMass Dartmouth
Current assignee: UMass Dartmouth
Priority date: 2015-03-10
Filing date: 2015-03-10
Publication date: 2016-09-15
Also published as: WO2016144629A1

Abstract

Various embodiments of structured flock fiber reinforced layers include fibrous organic polymer composite reinforcing materials that have been “pre-flocked” with Z-Axis reinforcing fibers. These “pre-flocked” fibrous materials (woven, knitted, mat, nonwoven or pre-pregs) are then supplied as “off-the-shelf,” “ready-to-use,” already flock reinforced, dry to the touch, pre-manufactured, storable, inventoried organic polymer composite structured flock fiber reinforced layers that are ready as needed to be laid-up and impregnated with matrix resin and cured to form fiber based z-directional reinforced composites having enhanced inter-laminar strength, impact toughness, transmission properties (electrical and thermal conduction) and coefficient of thermal expansion are provided. Methods for forming such reinforced layers are also provided.

Description

RELATED APPLICATION(S)

This application is related to U.S. Provisional Patent Application Ser. No. 60/863,680, filed on Oct. 31, 2006, entitled “Fabric Based Laminar Composite and Method for Manufacture Thereof,” and U.S. patent application Ser. No. 11/931,416, filed on Oct. 31, 2007, entitled “Materials Methodology To Improve The Delamination Strength Of Laminar Composites,” issued as U.S. Pat. No. 7,981,495 on Jul. 19, 2011. The entire teachings and contents of these Patent Applications are hereby incorporated by reference herein in their entirety.

FIELD OF USE

The present disclosure relates to structured flock fiber reinforced layers used to manufacture fabric based laminar composites showing high inter-laminar strength, in particular to z-axis oriented, structured flock fiber reinforced layers.

BACKGROUND

Delamination of layered fabric-reinforced composites represents one of the most prevalent structural, life-limiting failure modes of such materials. As an example, Organic Polymer Laminar Composite (OPLC) materials based on layered fabrics have many advantageous property and processing features. However, one structural drawback is their generally poor interlaminar shear strength. Layered OPLCs have little or no fiber reinforcement in the thickness direction. Therefore, their inter-ply strength is less than their longitudinal strength which can result in poor impact and/or inter-laminar flexural fatigue strength.
Various techniques have been introduced to enhance the inter-laminar strength of layered composite materials. A common technique is to use a rubber-toughened matrix material resin. However, these resins are generally not thermally durable. An alternative approach is to manufacture special pre-forms using advanced textile technologies such as 3-D knitting/weaving/braiding or through-the-fabric stitching/pinning processes. However, these methods are slow, inefficient, and expensive. While fabricated pre-forms may include yarns in a z-directional orientation, these reinforcements are generally not conducive to an optimized stress distribution in the mechanically functioning structure component. Such 3-D structures are prone to stress concentrations under mechanical service leading to poor fatigue resistance. These approaches appear to work in their primary goal, but they degrade the composite's in-plane properties.
Furthermore, Kim et al., “Fracture Toughness of Flock Reinforced Layered Composites”, Proceedings of 1^stIndustrial Simulation Conference 2003, Jun. 9-11, UPV, Valencia, Spain, p. 477-482 (2003) and Kim et al., “Through-Thickness Reinforcement of Laminar Composites”, Journal of Advanced Materials”, Vol. 36, no. 3, July 2004, pp 25-31, the entirety of these references hereby incorporated herein by reference, disclose that composites reinforced with z-directional fibers appear to have the potential to exhibit improved inter-laminar strength. However, z-directional reinforcement remains highly unpredictable due to the large number of variables (e.g., fiber type, flock fiber density (the number of perpendicularly-oriented flock fibers per unit area of interface between the substrates), fiber denier (mass in grams per 9000 m), fiber length, binder resin type, bonding strength between fiber and binder resin, etc.) present in such a composite. As a result, many such composites do not show improved inter-laminar shear properties and/or suffer a decrease in toughness.
Conventional fiber reinforcement for organic polymer composites include the flocking of short Z-Axis reinforcing fibers onto individual (uncured) resin impregnated fibrous layers, for example, woven fabric, nonwoven random mat, and pre-impregnated fabrics (pre-preg). When these flock fiber z-axis containing fibrous layers are consolidated into a so-called “wet lay-up” laminar assembly, this Z-Axis reinforced organic polymer organic structure is subsequently cured in a heated laminating press (or autoclave under “vacuum bagging”) type process. The resulting Z-Axis reinforced by flock fibers composite material was found to have dramatically improved inter-laminar shear strength and impact resistance.
Reinforcing fibers are re-arranged or placed so that they can bridge across the laminar plies. This could lead to a more structurally isotropic laminate. In pursuing this approach, special pre-form fabrics were fabricated using advanced textile technologies such as multi-directional knitting, 3-D weaving or through-the-fabric stitching and pinning processes. While these methods are found to be slow, they resulted in the desired 3-D orientation of yarn fibers in the reinforcing fabric's structure. Unfortunately, these methods are very expensive as well as design restrictive; they also have scalability difficulties. Furthermore, these 3-D fiber orientations are usually not conducive to optimized strength utilization of the parent yarn due to the obliqueness at the yarn structure's interlacing points. Therefore, some of these 3-D structures are prone to stress concentrations under mechanical service leading to poor fatigue resistance. All these approaches work in their special application area but in many cases they often degrade the composite's in-plane properties. This is especially true for the through-thickness textile stitching methods. Therefore, there is a need in the art for a composite showing improved characteristics such as inter-laminar shear strength and/or fracture toughness and corresponding sub structures which facilitate the manufacture of these composites.

SUMMARY

Various embodiments of structured flock fiber reinforced layers include fibrous organic polymer composite reinforcing materials that have been “pre-flocked” with Z-Axis reinforcing fibers. These “pre-flocked” fibrous materials (woven, knitted, mat, nonwoven or pre-pregs) are then supplied as “off-the-shelf,” “ready-to-use,” already flock reinforced, dry to the touch, pre-manufactured, storable, inventoried organic polymer composite structured flock fiber reinforced layers that are ready as needed to be laid-up and impregnated with matrix resin and cured.
In one embodiment, a structured flock fiber reinforced layer (referred to as TYPE 1) includes a fibrous laminar base-ply substrate comprising a plurality of fabric yarns forming a plurality of interstices, a thin adhesive sizing layer disposed on the fibrous laminar base-ply substrate, a plurality of reinforcing flock fibers, a majority of which are oriented substantially perpendicular to a first surface of the fibrous laminar base-ply substrate, the substantially perpendicularly oriented reinforcing flock fibers being partially embedded in the plurality of interstices, wherein the plurality of reinforcing flock fibers are bonded to surfaces of the plurality of fabric yarns by the thin adhesive sizing layer for subsequent composite ply material assembly and the sized and flocked fibrous laminar base-ply substrate remains flexible to conform to contour layups. Such reinforced layers can be combined to produce z-directional fiber reinforced composites exhibiting enhanced properties (e.g., inter-laminar strength, toughness).
In another embodiment, a structured flock fiber reinforced layer (referred to as TYPE 2) includes a pre-preg composite reinforcement ply layer structure, including a B-staged epoxy matrix outer surface; a plurality of reinforcing flock fibers, a majority of which are oriented substantially perpendicular to a first surface of the pre-preg composite reinforcement ply structure, the substantially perpendicularly oriented reinforcing flock fibers being partially embedded in the B-staged epoxy matrix outer surface of the B-staged epoxy resin pre-preg composite reinforcement ply structure, wherein the plurality of reinforcing flock fibers are secured in place within the B-staged epoxy matrix outer surface for subsequent composite ply material assembly and the pre-preg composite reinforcement ply structure remains flexible to conform contour layups.
In another embodiment, a technique for fabricating a flock fiber composite reinforcement layer includes applying a thin coating of resinous flock adhesive sizing to a dry substrate, the dry substrate comprising a plurality of fabric yarns forming a plurality of interstices and flocking a plurality of reinforcing flock fibers onto a first surface of the sized dry substrate. Flocking includes embedding the plurality of reinforcing flock fibers into the plurality of interstices while the resinous flock adhesive sizing is still fluidic and uncured and attaching the plurality of reinforcing flock fibers to surfaces of the plurality of fabric yarns by curing the adhesive sizing.
In yet another embodiment, a technique for fabricating a flock fiber composite reinforcement layer includes providing a pre-preg composite reinforcement ply structure, including B-stage epoxy matrix, softening the B-stage epoxy matrix of the pre-preg composite reinforcement ply structure to lower a B-stage epoxy matrix viscosity forming a tacky surface; and flocking a plurality of reinforcing flock fibers onto a first surface of the pre-preg composite reinforcement ply structure such that the plurality of reinforcing flock fibers penetrate an outer surface of the B-staged epoxy matrix.
Both TYPE 1 and TYPE 2 pre-flocked fibrous reinforcing layers provide the material for fabricating high laminar shear strength organic polymer composites which have many applications. Potential applications include: aerospace, aircraft, marine structures, ship hulls, military ballistic plate/panel manufacture and many other applications. Embodiments of Z-Axis pre-flocked fibrous reinforcing layers allow manufacturers to avoid getting involved with the intricacies of the flocking processes within their manufacturing plant or operation. Compared to conventional non-Z-axis reinforced composites, composites fabricated with pre-flocked fibrous reinforcing layers have an increase in inter-laminar shear strength. When manufacture design and fabricate laminar composites using pre-flocked fibrous reinforcing layers lay-up, the inter-laminar plies of the finished composite lay-up will be rendered Z-axis reinforced. A manufacturer does not have to do their own flocking capability or be concerned with flocking quality when using TYPE 1 and TYPE 2 pre-flocked fibrous reinforced/ reinforcing layers disclosed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of embodiments of the invention, as illustrated in the accompanying drawings and figures in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, with emphasis instead being placed upon illustrating the embodiments, principles and concepts of the invention. These and other features of the invention will be understood from the description and claims herein, taken together with the drawings of illustrative embodiments, wherein:

FIG. 1A schematically illustrates an exemplary embodiment of multiple structured flock fiber reinforced layers before being combined to form a z-directional fiber based reinforced composite;

FIG. 1B schematically illustrates the multiple structured flock fiber reinforced layers of FIG. 1 after being combined to form a z-directional fiber based reinforced composite;

FIG. 1C schematically illustrates an exemplary embodiment of a double sided structured flock fiber reinforced layer;

FIG. 1D schematically illustrates an exemplary embodiment of the double sided structured flock fiber reinforced layer of FIG. 1D, inter-layered or inter-leaved with non-structured flock reinforced fibrous layers;

FIG. 2 is a side view of an exemplary embodiment of a dry substrate structured flock fiber reinforced layer;

FIG. 3 is a cross sectional view (along section 3-3) of the dry substrate structured flock fiber reinforced layer of FIG. 2 showing a thin adhesive sizing layer disposed on the dry fibrous laminar base-ply substrate;

FIG. 4 is a side view of an exemplary embodiment of a pre-preg substrate structured flock fiber reinforced layer;

FIG. 5 is a cross sectional view (along section 5-5) of the pre-preg substrate structured flock fiber reinforced layer of FIG. 4 showing the flock fibers embedded in the B-staged epoxy matrix of the pre-preg fibrous laminar base-ply substrate; and

FIG. 6 is a top view of an exemplary embodiment of a woven dry substrate structured flock fiber reinforced layer showing a thin adhesive sizing layer disposed on the dry fibrous laminar base-ply woven substrate.

DETAILED DESCRIPTION

Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the reinforced layers and methods of fabrication disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the reinforced layers and methods specifically described herein and illustrated in the accompanying drawings are non-limiting embodiments and that the scope of the present disclosure is defined solely by the claims. The features illustrated or described in connection with one embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present disclosure.
In general, the present disclosure provides fiber based z-directional reinforced layers specifically configured and optimized to allow manufacturers to employ flocked Z-Axis reinforced layer materials without getting involved with any in the intricacies of flocking processes within their manufacturing plant or operation. Off-the-shelf availability of Z-Axis fiber modified organic polymer fibrous reinforcing materials is facilitated by embodiments disclosed herein.
The inventors have discovered that fracture toughness (inter-laminar shear strength) of organic polymer laminar composites (OPLC) can be improved by applying Z-Axis oriented flock fibers to the interfacial zones of the composites and have demonstrated several Z-Axis reinforcement application processes functionally applicable to their use in OPLC fabrication. In one embodiment, a “pre-flocking” process is an efficient technique for introducing Z-Axis flock fibers into a fabricated OPLC.
Now referring to FIG. 1A, multiple structured flock fiber reinforced layer 100 a-100 n (commonly referred to as reinforced layers 100) before being laid up to form composite 10. Here the layers 100 are shown with release sheets 104 disposed adjacent to the free ends of a plurality of reinforcing flock fibers 110. In one embodiment the release sheets include but are not limited to a thin, light-weight fabric lightly flocked with high denier packaging flock fibers and a thin, light-weight fabric lightly flocked with high denier packaging flock fibers. The high denier packaging flock fibers are longer and stiffer than the reinforcing flock fibers 110 positioned on the surface of the pre-flocked substrate layer.
The structured flock fiber reinforced layers for organic polymer laminar composites can be groups into two basic fibrous material types. TYPE-1: “Bare”, as-received from the textile mill, woven and knitted yarn fabrics, nonwoven fabrics and fibrous (open) mat products, and TYPE 2: so-called pre-preg composite reinforcing layers. The primary types of fibers that can be used to prepare TYPE 1 and TYPE 2 base “pre-flocked” reinforcing layers, include but are not limited to glass, carbon, polyaramid (Kevlar®) based textile fibers and generally yarns. In the TYPE 2 pre-flocks, the main resin composition here would be “B” staged epoxy resin—also the pre-preg's fiber yarn that is imbedded in the “B” staged epoxy resin is unidirectional yarn, woven fabric and chopped fiber mat type fiber reinforcement geometry. The methodology for fabricating TYPE 1 and TYPE 2 pre-flocked composite reinforcement entities is described below in more detail. “Pre-Flocking” of OPLC structured flock fiber reinforced layers before they are assembled into a laminar composite is an effective way of introducing flocked Z-Axis fibers into an OPLC structure.
FIG. 1B shows a finished OPLC after the release sheets have been removed, the layers 100 have been combined with a non-flocked substrate 106 and the combined laminar configuration 20 is then, in one embodiment, impregnated (throughout) with the liquid matrix resin 140 and this stack of Z-axis fiber reinforced fibrous plies are then consolidated by a vacuum bag or flat-press curing process.
FIG. 1C shows double-sided structured flock fiber reinforced layer 102 (also referred to as a double sided pre-Flocked reinforcement fabric ply DSP). In one embodiment, a double-sided flock fiber structured reinforced layer is fabricated by applying an un-cured layer of adhesive sizing resin to both opposed surfaces of the substrate, and then flocking reinforcing fibers onto both opposed coated surfaces of a fibrous laminar base-ply substrate 130.
FIG. 1D shows the double-sided structured flock fiber reinforced layer 102 inter-layered (inter-leaved) with non-structured flock reinforced fibrous layers (SNF) 106 in an SNF/DSP/SNF/DSP/SNF lay-up configuration before a matrix resin is applied. It is understood that in various embodiments DSPs can be combined with SNF layers of different compositions and in different lay-up configurations.
Now referring to FIG. 2, a structured flock fiber reinforced layer 100 includes a fibrous laminar base-ply substrate 130, a thin adhesive sizing layer 120 disposed on the fibrous laminar base-ply substrate 130, a plurality of reinforcing flock fibers 110 a-110 n (commonly referred to as reinforcing flock fibers 110), a majority of which are oriented substantially perpendicular to a first surface 128 of the fibrous laminar base-ply substrate 130. In one embodiment, the fibrous laminar base-ply substrate 130 is a fibrous mat and in another embodiment it is similar to the non-flocked substrate 106. During the manufacturing process the fibrous laminar base-ply substrate 130 is coated with a thin adhesive sizing layer 120 which in one embodiment is fluid before the flock fibers are attached and subsequently cured to attach the flock fibers in place. In one embodiment, the thin adhesive sizing layer is a resin, including but not limited to a sprayable polyurethane lacquer coating, a sprayable epoxy-based lacquer coating, a sprayable water based acrylic adhesive, a dilute water dip-able, water based acrylic adhesive and a dilute solvent based dip-able resin/lacquer coating system.
In one embodiment, the flock density of the reinforcing flock fibers is about 70 fibers/mm²to about 200 fibers/mm². In another embodiment, the reinforcing flock fibers have an average fiber length of about 0.5 mm to about 2.0 mm. In yet another embodiment, the reinforcing flock fibers have an average fiber fineness of about 1.0 denier to about 20 denier. The flock fibers include, but are not limited to synthetic fibers, glass fibers, carbon fibers, natural fibers, and metal fibers.
An exemplary manufacturing process generally includes applying a thin coating of resinous flock adhesive sizing to a dry fibrous substrate and flocking a plurality of reinforcing flock fibers onto a first surface of the sized dry substrate. The dry substrate includes a plurality of fabric yarns forming a plurality of interstices. The flocking step includes embedding the reinforcing flock fibers into the interstices and attaching the plurality of reinforcing flock fibers to surfaces of the plurality of fabric yarns while the resinous flock adhesive sizing is still fluidic and uncured. Flocking the reinforcing flock fibers can be accomplished by various techniques including, but not limited to, vacuum assisted flocking (VAF), shaking and vibration assisted flocking (SAF) and a combination of VAF and SAF. The resinous flock adhesive sizing includes, but is not limited to:

- a water based acrylic adhesive;
- a sprayable polyurethane lacquer coating;
- a sprayable epoxy-based lacquer coating;
- a sprayable water based acrylic adhesive;
- a dilute water dip-able, water based acrylic adhesive; and
- a dilute solvent based dip-able resin/lacquer coating system.
  In one embodiment, applying a thin coating of resinous flock adhesive sizing to the dry substrate includes applying uncured resinous flock adhesive sizing at a thickness of about 0.01 mm to about 0.05 mm.

FIG. 3 shows a cross sectional view (along section 3-3) of the dry substrate structured flock fiber reinforced layer 100 of FIG. 2 showing a thin adhesive sizing layer 120 disposed on the dry fibrous laminar base-ply substrate 130. In this embodiment the dry fibrous laminar base-ply substrate 130 includes multiple fabric yarns 134 which can have multiple filaments 136 and can also have individual filaments 132 forming multiple interstices 210. The substantially perpendicularly oriented reinforcing flock fibers 110 are partially embedded in the plurality of interstices 210. Some reinforcing flock fibers (e.g., reinforcing flock fiber 110 h) are attached to a top surface of the filaments 132 or yarns 134 of the dry fibrous laminar base-ply substrate 130. The reinforcing flock fibers 110 are attached to surfaces of the plurality of fabric yarns 134, and filaments 132 by the thin adhesive sizing layer 120 for subsequent composite ply material assembly. The amount of adhesive sizing and processing of the flock fiber reinforced layer 100 allows the flock fiber reinforced layer 100 (i.e., the sized and flocked fibrous laminar base-ply substrate) to remain flexible, open and porous to conform to contour-shaped layups.
Now referring to FIG. 4, a structured flock fiber reinforced layer 400 similar to the structured flock fiber reinforced layer 100 of FIG. 2 includes a pre-preg fibrous laminar base-ply substrate 430, a B-staged epoxy matrix outer surface 420 of the pre-preg fibrous laminar base-ply substrate 430, reinforcing flock fibers 110, a majority of which are oriented substantially perpendicular to a first surface 428 of the pre-preg fibrous laminar base-ply substrate 430.
During the manufacturing process the pre-preg fibrous laminar base-ply substrate 430 is processed such that the reinforcing flock fibers 110 are partially embedded in the B-staged epoxy matrix outer surface 420. In one embodiment, the matrix outer surface 420 (top layer) of the pre-preg fibrous laminar base-ply substrate 430 includes a portion of a B-staged epoxy matrix of the pre-preg fibrous laminar base-ply substrate 430 which has been processed (e.g., by careful heating) so that the reinforcing flock fibers 110 can be embedded (by flocking) into the pre-preg fibrous laminar base-ply substrate 430.
FIG. 5 shows a cross sectional view (along section 5-5) of the structured flock fiber reinforced layer 400 of FIG. 4 showing the B-staged epoxy matrix outer surface 420 on the dry fibrous laminar base-ply substrate 130. In this embodiment the pre-preg fibrous laminar base-ply substrate 430 includes multiple fabric yarns 134 which can have multiple filaments 136 and can also have individual filaments 132 embedded in B-staged epoxy matrix 432. The substantially perpendicularly oriented reinforcing flock fibers 110 are partially embedded in the B-staged epoxy matrix outer surface 420 for subsequent composite ply material assembly. The structured flock fiber reinforced layer 400 is processed to remain flexible in order to conform to contour layups.
Now referring to FIG. 6, a structured flock fiber reinforced layer 600 similar to the structured flock fiber reinforced layer 100 of FIG. 2 includes a woven fibrous laminar base-ply substrate 630 including horizontal fibers 634 a-634 l and vertical fibers 632 a-632 k forming interstices 610, a thin adhesive sizing layer 120 disposed on the woven fibrous laminar base-ply substrate 630, a plurality of reinforcing flock fibers 110 a - 110 n (commonly referred to as reinforcing flock fibers 110), a majority of which are oriented substantially perpendicular to the woven fibrous laminar base-ply substrate 630. During the manufacturing process the fibrous laminar base-ply substrate 130 is coated with a thin adhesive sizing layer 120.

Dry Substrate and Pre-Preg Embodiments

Z-Axis “pre-flocked” structured flock fiber reinforced layers can be grouped into two base/substrate fibrous material types. The structural and composition details and the fabrication methodology for these two exemplary types of pre-flocked structured flock fiber reinforced layers are described in more detail below.

Pre-Flocked Type 1

The primary types of fibers that can be used to prepare TYPE 1 base “pre-flocked” reinforcing/flock support layers are glass, carbon, polyaramid (Kevlar®) based textile fibers and yarns. Reinforcing fibrous “geometries” that can be pre-flocked include: fibrous mats (long fiber and short fiber), woven and knitted fabrics, and loosely consolidated nonwoven fabrics. Reinforcing flock fibers that can be pre-flocked include, but are not limited to: nylon, polyester, carbon, graphite, and polyolefin.

Pre-Flocked Preparation Methodology

Exemplary TYPE 1 fibrous base reinforcement materials include reasonably-loose, consolidated, breathable, semi-open fiber structures. In one embodiment the fibrous substrate includes interstices (e.g., an open mesh texture) so that the reinforcing flock fibers 110 can penetrate into the fibrous structure. The deeper the reinforcing flock fibers 110 are embedded into the fibrous base material structure the stronger the reinforcing effect is achieved by these Z-Axis reinforcing flock fibers 110 when subsequently used in fabricating composite materials.
The following are exemplary steps for preparing pre-flocked TYPE 1 structured flock fiber reinforced layers:

- (a) Apply thin adhesive sizing layer onto the fibrous laminar base-ply substrate 130. This step sizes (e.g., lightly coats) the fibrous laminar base-ply substrate with a thin resinous (e.g., sticky) coating. One principle of fabricating pre-flocked Type 1 structured flock fiber reinforced layers is to flock these “bare” structured flock fiber reinforced layer using a thin adhesive sizing layer. The thin adhesive sizing layer attaches these Z-Axis reinforcing flock fibers 110 in an upright position. These reinforcing flock fibers 110 are attached to the substrate surface (e.g., sides and top surfaces to the filaments and yarns) such that the reinforcing flock fibers 110 will not shake or drop off the surface during normal packaging, storing, shipping, typical handling and fabrication lay-up manipulations. These reinforcing flock fibers 110 need not be attached to their substrate surface in a permanent manner. The adhesive sizing is also referred to as resinous coating materials or pre-flock fiber securing adhesives.

This use of the thin adhesive sizing coatings in the context of pre-flocked fibrous reinforcement layer are chosen to assure that the presence of the resinous coating does not adversely affect the mechanical properties of the final organic polymer engineering composite material. Therefore, the polymer chemical nature of the pre-flock fiber adhesive sizing is selected to be compatible with the chemistry of the resinous matrix material. In various embodiments, polyurethane (spray-able) lacquer coatings have been successfully used. In other embodiments, an epoxy coating system, EV-400 Epoxy Varnish from Polyfiber Aircraft Coatings is used. Additionally water based acrylic adhesives are also used as a pre-flock fiber securing adhesive.
In one embodiment, the average thicknesses of the thin adhesive sizing layer disposed on the fibrous laminar base-ply substrate fabric ranges from about 0.017 mm to about 0.038 mm with an intermediate thickness of about 0.026 mm. This corresponds to an areal mass density of about 0.00002 gm/mm²to about an areal mass density of about 0.00004 gm/mm²with an intermediate areal mass density of about 0.000029 gm/mm²; where the mass density of the epoxy varnish is about 0.00114 gm/mm³.

- (b) Applying reinforcing flock fibers 110 onto the resin coated surfaces of the fibrous laminar base-ply substrate 130:
  The elapsed time between adhesive size coating the fibrous laminar base-ply substrate 130 and flocking (applying) reinforcing flock fibers 110, in one embodiment, is kept to a minimum so that the reinforcing flock fibers 110 contact the resin coated surfaces of the fibrous laminar base-ply substrate 130 before the thin adhesive sizing layer dries or cures depending on the type of adhesive sizing. This is especially true if the size-coating resin system is contains solvent or is solvent based. This applied resinous coating must be in a fluid “sticky” state when the flocking process commences. There is also the need for the reinforcing flock fibers 110 to penetrate as deeply as possible into the fibrous laminar base-ply substrate's structure. It is also desirable for the for reinforcing flock fibers to be applied at a low to moderate flock density, about 70 to about 200 fibers/mm². In addition to embedding the reinforcing flock fibers 110 it is understood that some of the reinforcing flock fibers 110 will be applied to top surfaces of the plurality of fabric yarns in the fibrous laminar base-ply substrate 130.

Several flock processing methods are used to assure the maximum penetration of the flock fibers into the fibrous laminar base-ply substrate's interstices. Exemplary processes are (1) Vacuum Assisted Flocking (VAF); (2) Shaking (or vibration) Assisted Flocking (SAF), and (3) a combination of VAF and SAF. These flocking processes take advantage of the open porosity and breathability of these thinly resin coated and sized fibrous structures. These processes provide a suction or vacuum force that (during the flocking process) which sucks the impinging flock fibers deeper into the fibrous laminar base-ply substrate's interstices and spaces; shaking or vibrating the fibrous mass also causes the interstices to oscillate/move back-and-fourth and therefore allows the impinging reinforcing flock fibers 110 to be embedded more deeply into the fibrous laminar base-ply substrate's interstices.

- (c) Attaching the reinforcing flock fibers:
  After the flocking procedure, the flocked fibrous layer is cured (i.e., curing the adhesive sizing) undisturbed on a flat surface. In one embodiment, this is done at room temperature. After a quiescent “setting” period, that could last, for example, up to 16 hours, the flocked on reinforcing flock fibers 110 should be attached to the fibrous laminar base-ply substrate 130. The flocked surface is then vacuumed to remove any loose, unattached reinforcing flock fibers. Finally, in one embodiment, these vacuumed “pre-flocked” surfaces are then transferred to an oven cure for a final cure (or solvent evaporation). This oven cure evaporates off solvent to reinforce the attachment of the Z-Axis reinforcing flock fibers 110 to the fibrous laminar base-ply substrate's structure. The pre-flocked composite flock fiber composite reinforcement layer 100 is then ready for packing and storage.
- (d) Packing and Storing “Pre-Flocked Fibrous Reinforcement Layers:
  In one embodiment, after the final curing step the material is ready to be cut into inventory-able sheets or carefully rolled up into a loose coil. In some embodiment, the pre-flocked surfaces are kept separated from each other using a release sheet 104. The release sheet 104, similar to release paper or polymer film is used to separate the “dry” stacked up pre-flocked layers. Care is taken not to stack the pre-flocked layers too high so as to “Crush” the Z-Axis oriented reinforcing flock fibers 110. These pre-flocked fibrous reinforcement sheets are treated with care and not submitted to abrasion or rough touching. The attached reinforcing flock fibers 110 are attached to the fibrous laminar base-ply substrate 130 with a minimum of adhesive sizing as to not adversely affect the chemical make-up, fibrous porosity, mesh or mat openness and mechanical integrity of the final composite's matrix resin. The thin pre-flock adhesive sizing coatings also help in assuring that the lay-up flexibility of the fibrous composite reinforcement layer material will not be adversely affected. It is desirable that the lay-up flexibility of these Pre-Flocked reinforcement layers be similar to non-pre-flocked reinforcement layer material.
- (e) Pre-Flock Storing and Shipping Separator/Release Sheet Material:

Pre-Flocked materials are stored and shipped in either flat sheet or roll form. The release sheet 104 is placed between the stacked or rolled up Pre-Flocked sheets. In one embodiment, thin, light-weight fabric or film material that is lightly flocked with longer, stiff flock fibers is used as the release sheet during the storage and shipping of the pre-flocked structured flock fiber reinforced layer. The release sheet materials include, but are not limit to, a light weight polyester or nylon nonwoven fabric base and a base nonwoven fabric will be flocked with 40 to 60 Denier Polyester or nylon flock fibers. The length of these flocked fibers on the release sheet are, in one embodiment, at least 25 percent longer than the length of the reinforcing flock fibers. The flock density of the flocked release sheet is in the range of 2 to 50 fibers per square millimeter. The flock adhesive for the release sheet can be flexible water based acrylic or polyurethane based. In another embodiment, the release sheet is coated or finished with a chemical release coat (e.g., silicone, fluorocarbon) as a final treatment. This assures that there is an easy release from the structured flock fiber reinforced layers. The release sheets described above are generally re-useable and low cost. Generally the release sheets protect the pre-flocked structured flock fiber reinforced layer from being crushed or damaged during warehouse storage and material shipping. The long-stiff and sparsely positioned release sheet flock fibers penetrate the pre-flocked structured flock fiber reinforced layers and serve as a stand-off to protect against any damaging abrasions and compressions that might occur during the handling, storage and shipping of pre-flocked structured flock fiber reinforced layers.

Pre-Flocked Type 2

These TYPE 2 structured flock fiber reinforced layers are fabricated using epoxy pre-preg composite reinforcement ply layer structures. The primary types of reinforcing fibers that in pre-preg composite reinforcement ply layer structures include, but are not limited to, glass, carbon and polyaramid (Kevlar®) based textile fibers and yarns impregnated with “B” staged epoxy resin. These pre-preg reinforcing fibers or yarns imbedded in the “B” staged epoxy resin can be positioned in the resin as unidirectional yarn, woven fabric or chopped fiber mat type fiber reinforcement geometry. Reinforcing flock fibers that can be used for z-axis flocking include, but are not limited to, nylon, polyester, carbon, graphite, polyolefin and metal.

Type 2 Pre-Flocked Preparation Methodology

Steps in Preparing Pre-Flocked Type 2 Composite Reinforcement Layers:

- (a) Heating the pre-preg composite reinforcement ply layer structure (also referred to as just pre-preg) to lower the epoxy viscosity:
  In one embodiment, the pre-preg is heated to temperatures limited to 55° C. and is later cooled down to its storage temperature where it retains its partially cured properties and can still be formed into a composite laminate. When uniformly heated between 45° C-55° C. the pre-preg become tacky and is an ideal substrate for flocking. In one embodiment, a layer of the pre-preg in a desiccated plastic bag was removed from a −20° C. freezer and allowed to reach room temperature. The pre-preg layer is fixed in a griddle type apparatus and heated to 50° C. to ease flock penetration into the carbon fiber/ pre-preg substrate.
- (b) Applying flock fibers to the tacky substrate:
  in one embodiment, after the carbon fiber/ pre-preg layer is heated it is almost immediately attached to the ceiling of an up-flocking apparatus (i.e., applying fibers from below) and the flock is applied at two density levels, 20 fibers/mm²and 50 fibers/mm². Any loose fibers are removed by orienting the layer, flock side down, and shaking it vigorously. The flocked layer is then fixed in a cardboard frame to isolate it from damage and almost immediately placed back in the freezer. The procedures can be repeated for additional layers.

In one embodiment, a unidirectional carbon prepreg IM7/977-3 that is infused with a B-stage epoxy resin system CYCOM 977-3 is flocked with a 3 denier, 1.22 mm long nylon fiber. The pre-preg remains “tacky” up to 270° F. (132° C.) and can be cured at 350° F. (177° C.) for six hours. The viscosity of the epoxy system is a function of temperature.

- (c) Packing and Storing “Pre-Flocked Fibrous Reinforcement Layers:
  the procedures for packing and storing are similar to the procedures described above in conjunction with the TYPE 1 structured flock fiber reinforced layers. After flocking is performed, the pre-preg material is covered with a release sheet and almost immediately cooled and frozen so as to stop any further thermal cure of the “B” staged epoxy matrix resin. These Type 2 pre-flocked materials are kept frozen (e.g., below 15° C.) after flocking and during subsequent storage and shipping. Keeping these pre-preg materials in a frozen state prevents the latent curing epoxy matrix resin of the composite from curing pre-maturely. The thermal aging history of pre-pregs is a very important issue because the more “heat history” the (latent cure) epoxy resin matrix resin is subjected to, the shorter the pre-preg's workable shelf life will be.

In one exemplary manufacturing technique, a manufacturer of Pre-Preg materials applies Z-Axis flock fibers to the surface of a pre-preg at the end of a manufacturing run. This technique introduces reinforcing flock fibers to pre-preg composite reinforcement materials. Applying reinforcing flock fibers to the surface of pre-preg at the time of initial manufacture is an effective and practical way of preparing “Pre-Flocked” pre-preg without subjection the latent curing epoxy matrix resin to the additional pre-preg heating stage to apply the flock.
One skilled in the art will appreciate further features and advantages of the present disclosure based on the above-described embodiments. Accordingly, the present disclosure is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.

Claims

1. A structured flock fiber reinforced layer comprising:

a fibrous laminar base-ply substrate comprising a plurality of fabric yarns forming a plurality of interstices;

a thin adhesive sizing layer disposed on the fibrous laminar base-ply substrate;

a plurality of reinforcing flock fibers, a majority of which are oriented substantially perpendicular to a first surface of the fibrous laminar base-ply substrate, the substantially perpendicularly oriented reinforcing flock fibers being partially embedded in the plurality of interstices, wherein the plurality of reinforcing flock fibers are bonded to surfaces of the plurality of fabric yarns by the thin adhesive sizing layer for subsequent composite ply material assembly; and

wherein the sized and flocked fibrous laminar base-ply substrate remains flexible to conform to contour layups.

2. The structured flock fiber reinforced layer of claim 1, wherein the thin adhesive sizing layer is a resin and comprises one of:

a sprayable polyurethane lacquer coating;

a sprayable epoxy-based lacquer coating;

a sprayable water based acrylic adhesive;

a dilute water dip-able, water based acrylic adhesive; and

a dilute solvent based dip-able resin/lacquer coating system.

3. The structured flock fiber reinforced layer of claim 1, wherein the plurality of a reinforcing flock fibers has a flock density of about 70 fibers/mm²to about 200 fibers/mm².

4. The structured flock fiber reinforced layer of claim 1, wherein the plurality of reinforcing flock fibers has an average fiber length of about 0.5mm to about 2.0 mm.

5. The structured flock fiber reinforced layer of claim 1, wherein the plurality of reinforcing flock fibers has an average fiber fineness of about 1.0 denier to about 20 denier.

6. The structured flock fiber reinforced layer of claim 1, wherein the plurality of reinforcing flock fibers are selected from a group consisting of synthetic fibers, glass fibers, carbon fibers, natural fibers, and metal fibers.

7. The structured flock fiber reinforced layer of claim 1 further comprising a release sheet disposed adjacent to free ends of the plurality of reinforcing flock fibers.

8. The structured flock fiber reinforced layer of claim 7 wherein the release sheet comprises one of a thin, light-weight fabric lightly flocked with a plurality of high denier packaging flock fibers; and

a thin, light-weight fabric lightly flocked with a plurality of high denier packaging flock fibers; and

wherein the plurality of high denier packaging flock fibers are longer and stiffer than the plurality of reinforcing flock fibers positioned on the surface of the fibrous laminar base-ply substrate.

9. The structured flock fiber reinforced layer of claim 1 wherein the majority of perpendicularly oriented reinforcing flock fibers being are embedded in the fibrous laminar base-ply substrate to a depth of approximately about 0.05 to about 0.1 mm.

10. A method for fabricating a flock fiber composite reinforcement layer comprising:

applying a thin coating of resinous flock adhesive sizing to a dry substrate, the dry substrate comprising a plurality of fabric yarns forming a plurality of interstices; and

flocking a plurality of reinforcing flock fibers onto a first surface of the sized dry substrate comprising:

embedding the plurality of reinforcing flock fibers into the plurality of interstices while the resinous flock adhesive sizing is still fluidic and uncured; and

attaching the plurality of reinforcing flock fibers to surfaces of the plurality of fabric yarns by curing the adhesive sizing.

11. The method of claim 10, wherein flocking a plurality of reinforcing flock fibers further comprises one of:

vacuum assisted flocking (VAF);

shaking and vibration assisted flocking (SAF); and

a combination of VAF and SAF.

12. The method of claim 10, wherein the resinous flock adhesive sizing comprises one of:

a water based acrylic adhesive;

a sprayable polyurethane lacquer coating;

a sprayable epoxy-based lacquer coating;

a sprayable water based acrylic adhesive;

a dilute water dip-able, water based acrylic adhesive; and

a dilute solvent based dip-able resin/lacquer coating system.

13. The method of claim 10, wherein applying a thin coating of resinous flock adhesive sizing to the dry substrate comprises applying uncured resinous flock adhesive sizing at a thickness of about 0.01 mm to about 0.05 mm.

14. The method of claim 10, further comprising applying a release sheet adjacent to free ends of the plurality of the flocked reinforcing flock fibers.

15. A structured flock fiber reinforced layer comprising:

a pre-preg composite reinforcement ply layer structure, including a B-staged epoxy matrix outer surface; a plurality of reinforcing flock fibers, a majority of which are oriented substantially perpendicular to a first surface of the pre-preg composite reinforcement ply structure, the majority of substantially perpendicularly oriented reinforcing flock fibers being partially embedded in the B-staged epoxy matrix outer surface of the B-staged epoxy resin pre-preg composite reinforcement ply structure, wherein the plurality of reinforcing flock fibers are secured in place within the B-staged epoxy matrix outer surface for subsequent composite ply material assembly; and

wherein the pre-preg composite reinforcement ply structure remains flexible to conform contour layups.

16. A method for fabricating a flock fiber composite reinforcement layer comprising:

providing a pre-preg composite reinforcement ply structure, including B-stage epoxy matrix;

softening the B-stage epoxy matrix of the pre-preg composite reinforcement ply structure to lower a B-stage epoxy matrix viscosity forming a tacky surface; and

flocking a plurality of reinforcing flock fibers onto a first surface of the pre-preg composite reinforcement ply structure such that the plurality of reinforcing flock fibers penetrate an outer surface of the B-staged epoxy matrix.

17. The method of claim 16, wherein softening the B-stage epoxy matrix comprises heating the B-stage epoxy matrix after the pre-preg composite reinforcement ply structure is initially manufactured; and

further comprising cooling down the epoxy matrix of the pre-preg composite reinforcement ply structure.

18. The method of claim 17, wherein heating the epoxy matrix of the pre-preg composite reinforcement ply structure comprises heating the B-staged epoxy matrix such that the B-staged epoxy matrix becomes tacky enough to accept impinging flock fibers while the pre-preg composite reinforcement ply structure remains partially uncured.

19. The method of claim 18, wherein heating the epoxy matrix of the pre-preg composite reinforcement ply structure comprises heating the epoxy matrix to a maximum temperatures of about 65° C.

20. The method of claim 16, wherein flocking a plurality of reinforcing flock fibers comprises up-flocking; and

wherein the method further comprises:

orienting the flocked pre-preg composite reinforcement ply structure, flock side down; and

shaking the composite reinforcement layer vigorously to remove unsecured flock fibers; and

refreezing the composite reinforcement layer to inhibit further curing of the B-staged epoxy matrix of the pre-preg composite reinforcement ply structure.

21. The method of claim 16, wherein softening the B-stage epoxy matrix comprises:

spraying the pre-preg surface with a solvent for the B-staged epoxy matrix; and

applying a thin coating of B-staged epoxy resin to the surface of the pre-preg composite reinforcement ply structure.