KR20010020328A - Composite Material Suitable for Aircraft Interiors - Google Patents

Abstract

In the present invention there is provided a fiber reinforced prepreg comprising a thermosetting resin having a carbon paper substrate and a flame retardant component, which is particularly useful for making aircraft interior materials. The substrate may contain fan carbon fibers and an alcohol binder. The resin may comprise about 50 to 80% of the prepreg.

Description

Composite Material Suitable for Aircraft Interiors}

Electrical and office device exterior materials, such as computer cases, copier cases and telephone devices, have previously been made of thermoplastic resins such as polycarbonate, acrylonitrile butadiene styrene (ABS) and polypropylene. These materials have beneficial properties such as the ability to meet UL specifications by including toughness, flexibility and flame retardant additives. However, thermoplastic resins have the drawback that they are not rigid due to low modulus and inherent high (molecular weight) melt viscosity makes it impossible to flow into the detail mold. In addition, even when using mixed thermoplastic resins, high melt viscosities make it impossible to mix with 10 to 40% chopped reinforcing fibers, resulting in a modulus value of less than half that obtainable with thermosetting resins. In addition, due to the relatively high melt viscosity and lower modulus, thicker wall portions and in some cases, the ribs should be designed in the molded portion to provide adequate stiffness and to prevent complete combustion (melt) during flammability testing. As a practical problem, excessive difficulty is encountered in molding the wall area to less than 0.060 "due to the high melt viscosity of the thermoplastics and thus the inability to flow into narrow wall cavities using conventional injection molding apparatus. Thermoplastic resins exhibit a melting phenomenon when applied, which is a flame retardant test UL 94 5 V (complete combustion), which is modified to prevent the gas flame source from being positioned at an angle of 20 degrees below the sample, thereby preventing the molten material from falling into the flame. Test).

One way to overcome the drawbacks of melting (distortion) and thick wall design necessity due to low modulus is to use thermosetting resins. However, conventional thermosetting resins (i.e. epoxy and phenolic resins) are not strong enough for these applications and will crack due to their relatively low impact strength.

In the aircraft industry, tough lightweight composite materials that can be used for the interior walls and other nonstructural components of the aircraft, such as overhead storage boxes, doors, ceilings, and floors, are preferred. These composite materials must meet the flammability requirements within the Federal Aviation Advance (FAA) aircraft. The desired material should be inexpensive, lightweight, and have a smooth surface finish. The composite material should be able to be compression molded into a metal mold, sandwiched, and bonded to the honeycomb core.

Typical composite materials used for aircraft interiors include woven composite materials, which require additional processing time and cost because the fabric must be woven. These woven composites are not strong enough to withstand the stresses generated inside the aircraft, including the movement of baggage during takeoff and landing. In order to apply any paint or other decoration to the surface of these conventional woven materials, the surface of the finished woven material is first of all because the surface of the woven material is not smooth enough to allow paint or other decoration to adhere to the surface. It must be polished. In addition, these woven materials cannot easily flow up to micro-molded details, such as ribs or decoratively etched or molded fabrics, requiring additional finishing to the woven material to obtain micro-molded details.

There is a need for composite materials that circumvent these and other problems of known composite materials, and the present invention is for this purpose.

Summary of the Invention

The present invention provides prepregs that are particularly suitable for use in shaping nonstructural components for aircraft interiors, such as floors, ceilings, overhead bins, and doors. The present invention further provides a lightweight, tough and inexpensive composite material. In addition, the composite material may have a smooth surface finish that is allowed to be decorated without further polishing it. In addition, the composite material may flow into the mold to form a molded article with fine molding details. In addition, the composite material meets FAA aircraft internal flammability requirements for low heat release rate and low smoke density during combustion.

According to the present invention, a modified thermosetting resin having a flame retardant component; The modified thermosetting resin may comprise a predetermined weight% of 1.27 cm (0.5 inch) long polyacrylonitrile carbon fiber and a predetermined weight% of 2.54 cm (1 inch) long polyacrylonitrile carbon fiber and an alcohol binder. A composite material is provided comprising an impregnated carbon paper substrate. The thermosetting resin may be a phenolic novolac resin, and the amount of the resin may be 50 to 80% by weight based on the total weight of the prepreg. The substrate may have metal fibers to increase the electromagnetic shielding of the prepreg.

The present invention relates to prepregs and molded articles made therefrom which may contain thermosetting resins having a flame retardant material capable of meeting specific flammability requirements for aircraft interior applications and substrates impregnated with thermosetting resins.

The present invention is particularly applicable to composite materials suitable for making shaped articles that can be used for interior non-structural components of aircraft. Such matters are described in the specification of the present invention. However, it will also be appreciated that the composite material according to the invention has better utility.

Broadly, the present invention relates to prepregs comprising a thermosetting resin that can be impregnated on and within a substrate. Each of these components is described separately below. As is known to those skilled in the art, the term "prepreg" refers to a combination of a substrate, such as a mat, fabric, nonwoven material, or irradiated, and a resin, typically undergoing a B curing step. In the curing cycle of the thermosetting resin, step A means the initial stage in the reaction of the resin in which the resin is still soluble and fused. Step B is an intermediate step in the reaction where the thermosetting resin melt is heated and still dissolved in the particular solvent. In manufacture, the treated substrate is typically precured at this stage to facilitate handling and processing prior to final curing. Step C is the final step in curing the thermosetting resin, which becomes insoluble and insoluble in conventional solvents.

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In the following, preferred resin compositions of the composite material according to the present invention are described. The resin component used in the prepreg of the present invention may be a thermosetting phenol formaldehyde resin, that is, a formaldehyde condensate with malamine phenol. These resins are often referred to as "phenolic" resins. The phenolic resin may be in the form of novolac or resol. However, novolaks are preferred because of the lower amount of free phenol and / or formaldehyde in these resins. The difference between these two types of phenolic resins comes mainly from the ratio of phenol to formaldehyde used to prepare the resin. Resol resins are typically prepared using molar excess of formaldehyde relative to phenol in the range of 1: 1.5-2 under alkaline conditions. Novolak resins are typically prepared using molar excess of phenol relative to formaldehyde in the range of about 1.25: 1 under acidic conditions (oxalic acid or hydrochloric acid). In resol resins, trace amounts of nitrogen are typically added to the resin in the form of ammonia bubbled through the liquid, or the hexamethylenetetraamine powder is mixed to facilitate the reaction between phenol and formaldehyde. Resol type resins are semi-solid or liquid resins of relatively lower molecular weight (highly monomeric). It tends to be less stable than highly polymerized solid novolac resins at ambient temperatures. Phenolic formaldehyde resins are known and described in K.J.Saunders, Organic Polymer Chemistry Applications and Performance, Springer-Verlong, N.Y. 1985.

materials

The substrate of the composite material according to the present invention is described below. The substrate used in the present invention can be any discontinuous fiber, including carbon, glass, kevlar or other conventional fiber reinforcements. Desirable results can be obtained using a carbon paper substrate having a weight of approximately 3 oz / yd ² . This material allows prepreg manufacturers to obtain higher prepreg yields, and the consumer has fewer sheets to control the weight imposed. Preferred carbon paper can be made from "PAN" fibers, where "pan" means fibers or fillers made of polyacrylonitrile starting resin. To bond the carbon fibers together, an alcohol binder such as polyvinyl alcohol (PVA) can be used. The alcohol binder may comprise about 10 to about 20 weight percent of the substrate and the preferred substrate may comprise about 5 weight percent PVA.

It is also possible to use lower weight substrate materials, for example those having a weight of 2 and 2.5 oz / yd ² . The substrate may contain 0.5 inch long and / or 1.0 inch long fan carbon fibers. The substrate may contain 50 to 100 weight percent 0.5 inch long fan carbon fibers and 0 to 50 weight% 1.0 inch long fan carbon fibers. Preferred substrates may contain 50% by weight 0.5 inch long carbon fibers and 50% by weight 1.0 inch long carbon fibers. The length of the fibers can vary depending on the mechanical properties required for the molded article and / or molded article made from the prepreg.

Preparation of Prepregs

In the following, a method for producing a prepreg according to the present invention is described. The resin composition can be produced by dissolving the thermosetting resin in a suitable solvent for resin. Solvents that can be used include acetone, methyl ethyl ketone, methylene chloride, or any other low boiling point (less than 60 ° C.) solvent. Additives such as pigments, flame retardants, lubricants, or curing accelerators (eg hexamethylenetetraamine) can be added to the resulting solution. Prepregs with novolac phenolic resins can be stored at room temperature, while resol type phenolic resin carbon prepregs must be refrigerated during storage.

The prepreg may comprise 20-50% by weight of the substrate and 50-80% by weight of the resin, and the preferred prepreg may comprise about 80% by weight of the resin and about 20% by weight of the substrate.

Preferred results can be obtained when the flame retardant material is added to the resin composition. Suitable flame retardant materials may include, for example, halogen / antimony compounds including tetrabrominated bis-phenol A and antimony oxide. Preferred flame retardants may be those prepared as phosphate esters, eg, product number AP422 or IFR 23 in Hoechst Celanese.

Once the resin composition is prepared, it can be impregnated into the substrate by methods conventional in the art. In general, the substrate can be passed through the resin composition. Subsequently, the substrate and the resin composition may be dried to remove the solvent, and the resin composition may be partially dried up to step B. The resulting prepregs can be sheeted, stacked or rolled, and then transported or stored.

Preparation of Molded Articles

Various molded articles can be produced from the prepregs according to the invention by methods known in the art, including compression molding and transfer molding. The prepreg can be molded into highly precise parts with wall thicknesses as thin as 1 mm. Details of the molding process, such as curing cycle, temperature and pressure, will vary depending on the configuration of the molded article to be manufactured. In general, several prepreg sheets can be cut and stacked in a mold. The arrangement of the sheets will depend on the article to be manufactured. For example, extra pieces of prepreg can be included in the final molded article where extra strength is needed. The prepregs of the present invention provide a design advantage for making molded articles with thinner wall areas because the lower melt viscosity of the resin creates a lighter weight enclosure with enhanced internal volume.

The molded article according to the invention can have a smooth, transparent and glossy surface finish since the substrate has a large amount of surface area, which means that a large amount of resin composition can be impregnated into the substrate. Thus, the prepreg according to the invention has a large resin-to-substrate ratio of 50-80% resin so that molded articles made of the prepreg have a smooth resin surface instead of a rougher substrate surface. Smooth surfaces that are different in the present invention do not require polishing of the molded article surface before further decoration. Thus, after the molded article is removed from the mold, paint or vacuum molded colored light colored polymer film can be applied onto the surface of the molded article according to the invention.

The prepreg according to the invention can be handled in a similar way as conventional woven composite materials, but the prepreg according to the invention can flow into the mold and with the ribs and decoratively etched or textured surfaces of the molded article. A molded article having the same fine molding details can be formed.

These molded articles formed from the composite material according to the present invention are less expensive than conventional woven carbon prepregs because of the discontinuous, filamentated substrates resulting in the elimination of the weaving steps required for the woven prepregs. As described in more detail below, molded articles have a low specific gravity and are capable of meeting the flammability requirements of FAA aircrafts with low heat release rate and low smoke density during combustion.

In addition, molded articles formed from the prepregs according to the present invention have novel acoustical and electrical properties that may be beneficial to the aircraft industry. In particular, the prepreg can have acoustic shielding properties as well as electromagnetic interference (EMI) shielding properties. Discontinuous, filamentated substrates can provide some EMI shielding. To further improve EMI shielding performance, stainless steel fibers or nickel coated graphite fibers may be added to the substrate. Prepregs formed from the additional fibers described above may have EMI shielding greater than 40 dB over a wide range of frequencies from 100 to 1,000 Hz. Discontinuous, filamentated substrates without additional fibers may also provide acoustic shielding because the nonwoven substrate dissipates the acoustic energy to reduce the acoustic energy delivered through the molded article.

In order to describe the present invention more clearly, the following examples are presented. This example has been presented primarily for the purpose of not allowing the specification or material proportions contained herein and any particular enumeration to be interpreted as a limitation on the concept of the invention.

In the examples, the following materials and test processes were used: HRJ 10985 refers to a phenolic novolak resin available from Schenectady International, Inc. AP422 means HOSTAFLAN AP422, a phosphate ester flame retardant marketed by Hoechst Celanese Corp. of Charlotte, North Carolina. HEXA means hexamethyleneetheramine. SOCCI wax refers to Carnauba wax emulsions containing 50% solids in water. Black Solution means a carbon black / nigrosin solution. 20301 carbon paper is available in Technical Fiber Oriducts Limited, Cambria, UK, 3 oz / yd, 7 to 10 micrometer diameter, 50% 1 "piece, 50% 1/2" piece, Fan-based carbon fiber paper with 5% PVA size. Flexural Strength and Flexural modulus were measured by ASTM D-790 process.

<Example 1>

Examples of prepregs according to the invention will have the composition and weight ranges of the components shown below.

Weight% (low) Weight% (high) Furtherance 42 48.90 Phenolic novolak resin (binder matrix) -hrj10985 3.5 4.08 Ammonium Polyphosphate (Flame Retardant) -AP422 5.6 6.52 Tetra-bromobisphenol-A (flame retardant) 1.4 1.63 Antimony Trioxide (Rising Flame Retardant) 3.85 4.48 Zinc borate (smoke inhibitor) 2.1 2.45 SOCCI waxes (release agents and gloss accelerators) 1.75 2.04 Zinc stearate (release agent and gloss promoter) 0.7 0.82 Sodium hydroxide (hardening accelerator) 7 8.15 HEXA (cross-linking system) 2.1 2.45 Black solution (surface completeness enhancer) 30 18.5 20301 carbon paper Total = 100% Total = 100%

Each manufacturing step of the prepreg according to the invention is described. First, a resin solution was prepared.

Preparation of Resin Solution

A resin solution was prepared by combining phenolic novolac resin, ammonium polyphosphate, tetra-bromobisphenol-A, antimony trioxide, zinc borate, SOCCI wax, sodium hydroxide, and HEXA, each amount being based on the total amount of the solution. It is wealth.

The solution was stirred for approximately 10 minutes, to the resulting solution was added 1.75 to 2.04% by weight of zinc stearate and the resulting solution was stirred for an additional 10 minutes. After this time was over, 2.1 to 2.45 wt% black solution was added and the resulting solution was stirred for an additional 3 minutes.

Preparation of Prepregs

To prepare the prepreg, 20301 carbon paper was passed from the roll into the bath containing the resin solution prepared above at approximately 130 inches per minute. The resin-impregnated paper is passed through a pair of driven stainless steel nip rolls held at intervals of 0.018 to 0.024 inches to remove excess resin solution and achieve a desirable pick-up of 70-8% of the resin solution. It was. The impregnated paper was passed through convective heat in a forced air oven at 215E-250EF to remove the acetone solvent. The residence time in the convective heat zone was 8-12 minutes. The product was dried non-rigid prepreg comprising about 80% by weight solid resin and about 20% by weight carbon paper. Samples of prepreg were cured by heating for 180 seconds at 1500-3200 psi, 150-180EF in matched metal dies. Cured samples had the physical properties shown in the table below. The samples were also compared with the flammability requirements inside the FAA aircraft.

Property FAA Flammability Requirements Example 1 Peak heat release rate [kW.m ² ] <65 38-44 Heat release rate over 2 minutes [kW.m ² ] <65 39-46 Smoke Density [Ds @ 4m] <200 141-155 Flammable 60 seconds <15 0 Vertical combustion digestion time [sec] Flammable 60 sec Vertical Combustion Length [inches] <6 1.75 Flammability 60 sec vertical combustion drip time [sec] N / A-thermosetting resin is not dropped Average Long Beam Bending Strength [Ksi] N / A 11.2-18 Medium Long Beam Flexural Strength [Ksi] N / A 10-12 Glass Transition Temperature-Flexible TMA [° C] N / A 164

While the foregoing is directed to specific embodiments of the present invention, it will be understood by those skilled in the art that modifications may be made to this embodiment without departing from the spirit and spirit of the present invention and the scope defined by the appended claims. will be.

Claims (9)

Modified thermosetting resins having flame retardant components; A predetermined weight% of 1.27 cm (0.5 inch) long polyacrylonitrile carbon fiber and a predetermined weight% of 2.54 cm (1 inch) long polyacrylonitrile carbon fiber and an alcohol binder, impregnated with the modified thermosetting resin A prepreg comprising a carbon paper substrate. The prepreg of claim 1, wherein the resin is a phenolic novolac resin. The prepreg of claim 1, wherein the substrate comprises 50 wt% of 1.27 cm (0.5 inch) long polyacrylonitrile carbon fiber and 50 wt% of 2.54 cm (1 inch) long polyacrylonitrile carbon fiber. The prepreg of claim 1, wherein the amount of resin is from about 50 to about 80 weight percent based on the total weight of the prepreg. The prepreg of claim 1, wherein the amount of resin is about 80% by weight based on the total weight of the prepreg. The prepreg of claim 1, wherein the alcohol binder comprises polyvinyl alcohol. The prepreg of claim 1, wherein the substrate further comprises a metal fiber to enhance electromagnetic shielding of the prepreg. A molded article made from the prepreg of claim 1. The prepreg of claim 1, wherein the flame retardant component is ammonium polyphosphate.