WO2001049473A1

WO2001049473A1 - Process and apparatus for producing reinforced composite systems

Info

Publication number: WO2001049473A1
Application number: PCT/US2000/033618
Authority: WO
Inventors: William G. Hager; Jay J. Beckman; John D. Rinehart; James V. Gauchel
Original assignee: Owens Corning; Owens Corning Fiberglas Corp
Current assignee: Owens Corning
Priority date: 1999-12-29
Filing date: 2000-12-12
Publication date: 2001-07-12
Anticipated expiration: 2002-06-29
Also published as: AU2088401A

Abstract

A method and apparatus for producing reinforced composites is provided. The method includes impregnating a compressed reinforcement with a foamable resin under high pressure and then allowing the foam and reinforcement to expand simultaneously under controlled conditions to a lower pressure.

Description

PROCESS AND APPARATUS FOR PRODUCING REINFORCED COMPOSITE SYSTEMS

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION

The present invention relates to a method and apparatus for producing reinforced composite systems in which reinforcement material is impregnated with a foamable resin while compressed and is allowed to expand with the resin such that the resulting part is reinforced uniformly throughout its cross-section.

BACKGROUND OF THE INVENTION

It is known in the art to produce a reinforced foam structure wherein a low density, fast reacting liquid foamable resin is sprayed under pressure into a low density mat to penetrate and wet the fibers. See U.S. Patent No. 4,372,900. The foam expands within the fiberglass mat, forming a low density foam sheet. However, such a process allows the foam to freely expand, which makes it difficult to control the density of and the location of reinforcement material within the final product. It would be desirable to be able to better control the foaming operation so that the final product has a desired uniform density, is reinforced uniformly with reinforcement material, and so that a variety of composite parts may be formed. It would also be desirable to form such composite parts using a continuous pultrusion process.

Accordingly, a need still exists in the art for an improved method of forming a reinforced composite part in which a reinforcement material is impregnated with a foamable resin.

SUMMARY OF THE INVENTION

These needs are met by the present invention in which a compressed reinforcement material is impregnated under pressure with a foamable resin such that the reinforcement material is substantially completely impregnated with the resin. Foaming is initiated at substantially the same or at a slightly greater pressure as impregnation to allow the formation of a fine grain foam structure (that is, having small cells of about 30 microns in diameter). Thereafter, the foaming resin and the reinforcement material are permitted to expand to a lower pressure state. The reinforcement material expands with the foaming resin such that the resultant part is reinforced throughout substantially its entire volume.

According to one aspect of the invention, a method of producing a reinforced composite part is provided comprising the steps of providing a reinforcement material and passing the reinforcement material into a die apparatus such that the reinforcement material is compressed. A foamable resin is then injected into the die apparatus at a first pressure such that the resin substantially impregnates the reinforcement material throughout its entire cross-section. The reinforcement material and the foamable resin are then allowed to expand substantially simultaneously at a second pressure which is lower than the first pressure.

The method preferably further includes the step of curing the resin impregnated reinforcement material after expansion. The reinforcement material is preferably cured in a heated curing die or by radiation.

Preferably, the die apparatus comprises three dies including an injection die, a foaming die, and an expansion die. The foamable resin is injected into the injection die, foaming of the resin initiates in the foaming die, and the resin is allowed to expand in the expansion die.

The foamable resin is preferably selected from the group consisting of polyesters, vinyl esters, polyurethanes, phenolic resins, and epoxy resins. Preferably, a blowing agent is mixed with the foamable resin in a static mixer just prior to injection into the injection die.

The reinforcement material preferably comprises a fiberglass mat. Alternatively, the reinforcement material may comprise a three-dimensional woven fabric, or bulked or blown roving. It is preferred that the reinforcement material be capable of being compressed to about 25% to about 50% of its original thickness such that it will automatically "spring back", or return to substantially its original expanded form, during the expansion step. An example reinforcement material is a continuous wet laid mat with a thermoset binder which is commercially available from Owens Corning under the product designation OC4500. The method of the present invention may be used to form a variety of reinforced composite parts including ladder rails, containers, car seats, toys, and the like. BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic illustration of an apparatus constructed in accordance with the present invention; and

Fig. 2 is a schematic illustration in cross-section of a reinforced composite part formed using the method of the present invention.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS OF THE INVENTION

In accordance with the present invention, a compressed reinforcement pack is substantially completely impregnated with a foamable resin. Foaming of the resin is permitted to occur at about the same or slightly higher pressure as impregnation so as to achieve a uniform foam density. Thereafter, the foaming resin and the reinforcement material or pack are allowed to expand to a lower pressure state. The compressed reinforcement pack expands simultaneously with the resin such that it extends continuously throughout the entire volume of the part. The degree of expansion of the resin and the reinforcement may be matched so as to achieve desired properties of the resultant part such as composite part density, or insulation value. The process is preferably a continuous pultrusion process.

The method may be performed with or without post forming. For example, reinforced thermoplastic foamed structures formed in accordance with the present invention may be used in conjunction with postforming equipment to make reformed shaped parts.

Reinforcement materials for use in the present invention include glass or polymer fibers, rovings or bundles of fibers, continuous filament or chopped strand mats, glass or polymer fiber cloths, veils, or combinations thereof. Preferred for use in the present invention is a continuous filament fiberglass mat which provides the desired compressibility and springback. Other suitable reinforcements include three-dimensional woven fabrics and bulked or blown roving. Any needlestitched reinforcement having the desired amount of compressibility and springback may also be used. However, while the invention has been described primarily with regard to the use of expandable reinforcements, it should be appreciated that combinations of expandable and non- expandable reinforcements may be used as long as the desired springback is achieved. The preferred foamable resins for use in the present invention include any polymeric materials which c an be foamed. The polymeric material may be thermoplastic or thermoset. Suitable polymers include polyolefins, polyvinylchloride, alkenyl aromatic polymers, polycarbonates, polyetherimides, polyamides, polyesters, polyvinylidene chloride, polymethylmethacrylate, polyurethanes, polyisocyanurates, phenolics, copolymers and terpolymers of the foregoing, thermoplastic polymer blends, rubber modified polymers, and the like.

The polymeric material preferably comprises phenolic resins. Preferred phenolic resins for use in the present invention include Bakelite™ available from Union Carbide Corp., Durez™ available from Hooker Chemical, Genal™ available from General Electric, Arochems™ available from Ashland Chemical Company, Plyophen™ and Beckacite™ available from Reinhold Chemicals, Inc., and Resinox™ available from Monsanto Co.

Suitable blowing agents for use in the present invention include inorganic blowing agents, organic blowing agents, and chemical blowing agents. Inorganic blowing agents which may be used include carbon dioxide, nitrogen, argon, water, air, nitrogen and helium. Suitable organic blowing agents include aliphatic hydrocarbons, aliphatic alcohols, and fully and partially halogenated aliphatic hydrocarbons such as fiuorocarbons. Suitable chemical blowing agents include azodicarbonamide, azodiisobutyro-nitrile, benzenesulfonhydrazide, 4,4-oxybenzene sulfonyl-semicarbazide, p-toluene sulfonyl semi-carbazide, barium azodicarboxylate, N,N'-dimethyl-N,N'- dinitrosoterephthalamide, and trihydrazino triazine. The blowing agents may be used either alone or in combination with other blowing agents or mixtures thereof.

The chemical treatment used on the reinforcement material may be adjusted as desired to allow tailoring of the composite interface. For example, a foam accelerant such as finely divided talc may be placed in the sizing applied to the fibers of the reinforcement material such that foaming initiates at the reinforcement/resin interface. Alternatively, a foam inhibitor such as chemical defoaming silicone may be used in the sizing so that a foamed resin of higher density is formed around the fibers for better stress transfer. It is also contemplated that a defoamer may be applied to the reinforcement material just before the material enters into an injection die. A similar operation where a defoamer is applied to an inner surface of an impermeable carrier is discussed in U.S. Patent No. 5,955,013. Other foam materials and formulations are set out in the '013 patent, and U.S. Patent No. 5,807,514.

Referring now to the drawings, Fig. 1 illustrates a die apparatus 10 constructed in accordance with the present invention for forming a reinforced composite part. The apparatus includes an injection die 12 which receives reinforcement material or a reinforcement pack and is used to substantially fully impregnate the material with the foamable resin. Such an injection die is described in commonly assigned U.S. Patent No. 5,747,075. The injection die 12 is comprised in the illustrated embodiment of upper and lower die bodies 14 and 16. As shown, an entrance portion 18 of the injection die 12 is tapered inwardly such that the reinforcement material is gradually compressed as it is drawn or pulled through the die so as to permit sufficient resin pressure and flow to fully impregnate the material. At least one injection port which communicates with a weir 42 is provided in the injection die for injecting foamable resin with or without a blowing agent into the injection die 12. A foaming die 20 is sealingly coupled to the injection die 12 and is defined by upper and lower die bodies 22 and 24 which form a constant cross-section through which the resin-impregnated reinforcement material passes to allow the resin to initiate its foaming under high pressure. Preferably, the pressure applied by the foaming die 20 to the impregnated reinforcement is slightly greater than that applied to the reinforcement material by the injection die at its exit portion. This segment of the die is essentially a straight extension of the injection die and its length may vary depending on the line speed and the kinetics of the foaming reaction. As can be appreciated, the die dimensions may vary depending on the size of the desired part.

An expansion die 26 is sealingly coupled to the foaming die 20 and includes in the illustrated embodiment upper and lower die bodies 28 and 30. An exit portion 32 of the expansion die 26 is tapered outwardly to allow the reinforcement material and foamable resin to gradually expand under controlled pressure. The size of the expansion die may vary depending on the desired amount of expansion of the resin and the reinforcement material, and the line speed. A curing die 34 is preferably sealingly coupled to the expansion die 26 and in the illustrated embodiment, includes upper and lower die bodies 36 and 38 which define a curing chamber through which the impregnated reinforcement material passes under compression to allow the resin material to cure. The curing die has a constant cross- section preferably having about the same expanded dimensions as the exit portion of the expansion die.

It should be appreciated that heating and/or cooling apparatus (not shown) may be associated with each of the dies 12, 24, and 30 to prevent premature curing of the resin material and to maintain the proper curing temperature for the resin material.

While the dies 12, 20, 26 and 34 may be formed integrally, it is preferred that they comprise separate units which are sealingly coupled to one another in a conventional manner to allow the units to be removable where variations in die length are desired for particular applications. The dies are preferably formed from a metal material such as chrome-hardened steel.

In the embodiment shown in Fig. 1, spools 40 of reinforcement material are located upstream from the injection die 12. The reinforcement material is passed through a conventional shaping die (not shown) which properly aligns the reinforcement materials relative to one another and compresses the materials to form a reinforcement pack. In operation, the foamable resin material is injected via one or more injection ports into the weir 42 such that the pressure of the resin in the weir 42 is substantially equal to or slightly greater than a compression pressure applied by the die 12 to the reinforcement pack at an exit portion of the die 12. By impregnating at high pressure, substantially all air within the reinforcement material is removed, the foamable resin and reinforcement material are prevented from expanding prematurely, and the resin material substantially fully and completely penetrates the reinforcement material. While not wishing to be bound by any fixed amount of pressure, the injection pressure of the foamable resin is on the order of about 100 psi (689.4 kPa) or greater, and more preferably on the order of about 250 psi (1723.5 kPa) or greater. Thus, voids are minimized and the reinforcement pack is fully impregnated. The pressure may vary as it has been found that the amount of inlet pressure required for full impregnation is proportional to line speed.

Preferably, a blowing agent is combined with the foamable resin in a static mixer just prior to injection of both into the injection die. The amount of blowing agent added may vary, depending on the desired density of the resulting part. The foaming temperatures may also vary depending upon factors including the polymer material characteristics and blowing agent composition and concentration. As will be appreciated by those skilled in the art, the amount of foaming that occurs may be varied by controlling the amount of blowing agent used, the temperature of the dies, and the pressure within the dies.

The impregnated reinforcement pack then enters the foaming die section 20 where foaming initiates. This passage provides a constant cross-sectional area of incubation for the foam in which small gas bubbles form and disperse evenly throughout the compressed reinforcement.

As the reinforcement material is then pulled into the expansion die 26, the foam is allowed to expand at a lower pressure through the tapered exit portion 32. During this expansion, the reinforcement also expands because of the inherent springback of the reinforcement material. It is important during this stage of the process to keep the foam in an uncured state, that is, to avoid curing before the foam expansion is complete.

The reinforcement material then proceeds to the curing die where the resin is allowed to cure to form the final dimensions of the part. If desired, a topcoat or other treatment may be applied to the reinforcement material after it exits the curing die. The resulting parts formed from the process of the present invention have uniform areas of reinforcement. In Fig. 2, a reinforced composite part 44 is schematically illustrated in cross-section. It is believed that, a uniform, fine foam 46 will be formed throughout the reinforcement pack 48 with no major voids.

While certain representative embodiments and details have been shown for purposes of illustrating the invention, it will be apparent to those skilled in the art that various changes in the methods and apparatus disclosed herein may be made without departing from the scope of the invention, which is defined in the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A method o ^* producing a reinforced composite comprising the steps of: providing a reinforcement material; passing said reinforcement material into a die apparatus (10) such that said reinforcement material is compressed; injecting a foamable resin into said die apparatus at a first pressure such that said resin substantially impregnates said reinforcement material throughout its cross-section; and allowing said reinforcement material and said foamable resin to expand simultaneously at a second pressure which is lower than said first pressure.

2. The method of claim 1 further including the step of curing said resin impregnated reinforcement material.

3. The method of claim 2 wherein said resin inpregnated reinforcement material is cured in a heated curing die.

4. The method of claim 2 wherein said resin impregnated reinforcement material is cured by radiation.

5. The method of claim 1 wherein said die apparatus (10) comprises an injection die (12), a foaming die (20), and an expansion die (26).

6. The method of claim 5 wherein said foamable resin is injected into said injection die (12), said resin initiates foaming in said foaming die (20), and is allowed to expand in said expansion die (26).

7. The method of claim 1 wherein said foamable resin is selected from the group consisting of polyesters, vinyl esters, polyurethanes, phenolic resins, and epoxy resins.

8. The method of claim 1 including the step of mixing a blowing agent with said resin prior to said injecting step.

9. The method of claim 1 wherein said reinforcement material comprises a fiberglass mat.

10. The method of claim 1 wherein said reinforcement material comprises a three-dimensional woven fabric.

11. The method of claim 1 wherein said reinforcement material comprises bulked or blown roving.

12. The method of claim 1 wherein said reinforcement material is compressed to about 25%) to about 50% of its original thickness.

13. An apparatus (10) for producing a reinforced composite comprising: an injection die (12) for receiving a reinforcement material and including a weir (42) for injecting a foamable resin into said reinforcement material; a foaming die (20) coupled to said injection die for initiating foaming of said resin; and an expansion die (26) coupled to said foaming die for allowing said resin and said reinforcement material to expand substantially simultaneously; wherein the pressure in said foaming die is greater than the pressure in said expansion die.

14. The apparatus of claim 13 further including a curing die (34) coupled to said expansion die for curing said resin.