WO2002026463A2

WO2002026463A2 - Process of making simultaneously molded laminates

Info

Publication number: WO2002026463A2
Application number: PCT/US2001/042328
Authority: WO
Inventors: Diane M. Hulett; Ramin Dowlati
Original assignee: Decillion, Llc
Priority date: 2000-09-29
Filing date: 2001-09-27
Publication date: 2002-04-04
Also published as: AU2001296914A1; WO2002026463A3

Abstract

The present invention involves an efficient method of simultaneously molding multiple composite laminates (1a) comprising layering one or more layers of wet-laid, non-woven mats (1) comprised of particulate thermoplastic polymer and a fiber reinforcement between one or more layers of a release film material (2), and molding the combination to form multiple laminates (200).

Description

PROCESS OF MAKING SIMULTANEOUSLY MOLDED LAMINATES

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION

The present invention relates to a process of concurrently molding multiple laminates at one time, thereby providing an efficient means of mass-producing several molded sheets or parts. The laminates ofthe invention are formed from a wet-laid material comprising a fiber reinforcement and a particulate thermoplastic material that provides laminates formed therefrom with high impact resistance and rigidity.

BACKGROUND OF THE INVENTION

Composite laminates, which are used to make structural reinforcements, construction materials and formed parts may be reinforced using a mat formed from glass or other reinforcing fibers. These fibrous mats may be woven or non-woven, and may be formed by several methods. One method of forming non- woven fibrous mats involves air laying or blowing of fibers onto a collection surface followed by application of a molten or liquid binder polymer, then drying or cooling to form a fibrous mat laden with the polymer. In another method, non- woven mats are wet-laid from a slurry of fibers and a binder polymer that is prepared in a medium such as water. The use of a binder polymer has conventionally been required as a means of holding the chopped fibers together during the forming process and after the mat is dried. While the use of a polymer, such as a binder polymer, in conjunction with glass fibers should desirably contribute certain properties to the mat, the binder provides an added manufacturing expense, it may be incompatible with the impregnating polymer used in subsequent molding, and may lower the performance ofthe laminates made from the impregnating polymer and binder.

Several problems have been determined in conjunction with molding of composite laminates, generally, and, in particular, in the handling of polymer systems made with thermally sensitive polymers such as polyvinyl chloride (PNC) or PNC-blends. For example, the composite molding process typically requires prolonged exposure at the molding temperature. This may be particularly true in the manufacture of composites from one or more layers of a reinforcing material by applying heat and pressure to form a compacted layer or laminate. In these processes, sufficient heat and pressure must be applied to allow impregnation ofthe polymer between the fibers in each layer ofthe laminate. However, at high molding temperatures, degradation ofthe polymer will often result. Degradation of a polymer generally occurs upon exposure to temperature over time because each polymer system has an associated finite level of inherent stability, and, as a result, each exposure to a time-temperature combination reduces the residual stability of the system. This degradation is cumulative, and eventually will lead to decreased wet-out or contact between the fibers and the polymer, or a change in the molecular weight ofthe polymer, either of which results in a laminate that is poorly formed and lacking in strength and durability. To prevent excessive heat exposure, therefore, it has traditionally been necessary to shorten the time required for molding, or to lower the molding temperature. However, lowering the molding temperature may be ineffective if there is any appreciable amount of water in the molding composition, since at the lower temperature the water may not vaporize sufficiently. At the lower temperatures, good consolidation ofthe laminate may also not be obtained.

Moreover, the effects of time and temperature are additive, and, accordingly, each polymer system has its own intrinsic processing window within which certain time- temperature combinations can advantageously be used in handling ofthe polymer. This processing window can be maintained or extended to some degree with the use of thermal or oxidative stabilizers. It is therefore desirable to develop a process that avoids reducing the amount of inherent stability within a polymer system during the process of manufacturing a final part. Such a process should conserve the residual stability during manufacture, up to and including the formation ofthe final part.

In addition to the above-mentioned drawbacks, current molding technology often results in shearing ofthe fiber material, and, as a result, the composite that is formed includes shorter fibers. For example, the current injection molding technology for combining reinforcement and polymer results in a compound that has the length ofthe reinforcing fibers reduced by attrition, and there is an accompanying reduction in properties, such as strength, impact resistance and heat distortion temperature, in the laminates produced.

There is, additionally, a continuing need to find processes of forming and molding laminates made from wet-laid fibrous materials that can be carried out in an efficient and cost-effective manner. In this regard, it is desirable to provide for the formation of multiple laminates at the same time, while minimizing the consumption of energy and time resources. U.S. Patent No. 4,469,543 (Segal) describes a method of making composites suitable for structural or automotive parts by laminating at least one filled thermoplastic layer to at least one glass fiber mat layer, with an intermediate layer of non-filled thermoplastic polymer between the filled thermoplastic layer and the glass mat. PNC is identified as a suitable thermoplastic for use as the filled thermoplastic layer, while the non-filled intermediate layer is a polyamide, polyester, polycarbonate or polyethylene. The filler used in the filled thermoplastic layer may be metals, salts, particulates or fibers. The resulting laminate may be compression molded using closed molds or laminating belts in a continuous operation. There is no teaching of one or more removable release layers to permit the formation of multiple laminates.

U.S. Patent No. 4,510,199 (Brooker) describes the preparation of release sheets for use in laminating assemblies to make decorative cellulose-based laminates, comprising a fibrous core sheet layer impregnated with a thermosetting resin and coated on at least one side with a wax-alginate salt film. According to the patent, this release paper may be used to form stacked laminates, in which the core layer ofthe release paper becomes an integral part ofthe laminate, but which may be removed by sanding. Use of such materials has however not been applied in the preparation of laminates from nonwoven wet-laid reinforcing fibers.

U.S. Patent No. 5,259,901 (Davis) discloses a method for making an inflatable elastomer mandrel for use in fabricating composite articles. The method comprises, in sequence, preparing a rigid, water-soluble mandrel; applying a mold releasing ply to the water soluble mandrel; applying a first layer of uncured elastomer to cover the water soluble mandrel; curing this layer to form a base layer as a work piece mandrel; applying a second layer of uncured elastomer; winding a first layer of fiber onto the work piece mandrel; applying a third layer of uncured elastomer; winding on a second layer of fiber; and applying a fourth layer of uncured elastomer. The multiple layers are then cured, and the water-soluble mandrel is dissolved. The resulting product is a filament-wound composite comprised of alternating layers of elastomer and fiber. Such a product is not a molded composite laminate. Accordingly, a need exists for a process of producing multiple layers of fiber- reinforced composite laminates by molding the multiple layers at the same time using a material to separate the multiple laminate layers that may be easily removed, and which does not become a part ofthe final laminate product. There also exists a need for molding laminates of high quality that show superior impact resistance and rigidity, and which may be molded under less extreme processing conditions than are typically required for fiberglass laminate products known in the art. Additionally, there is a need for a method that avoids the use of a conventional binder which degrades the interface with the reinforcing material; as well as a process that avoids a significant decrease in the inherent stability ofthe polymer system as the polymer is degraded. Moreover, a molding process that avoids degradation of fiber length is also desirable. These needs are fulfilled by the invention described below.

SUMMARY OF THE INVENTION

The present invention relates to a method of simultaneously molding a plurality of composite laminates at the same time. The laminates ofthe invention comprise at least one or more layers of a fibrous mat, preferably a fibrous, wet-laid, non- woven mat, and at least one layer of a release film. Specifically, the invention comprises a method of producing a laminate composite having a plurality of separable contiguous laminate layers. In a first step, a stack of multiple layers of laminatable materials is prepared wherein each layer independently comprises a mat having a first layer of reinforcing fiber material treated with at least one particulate thermoplastic polymer and a second contiguous layer comprising a pealably removable release film. Each ofthe laminatable material layers may be alike or different. In a second step, the stack is molded at an elevated temperature range and pressure to form the laminate composite. Once formed, individual laminate layers may be separated from the composite at the release film interface by removing the film. The separated release film may be used again in subsequent laminate production operations. In one aspect, the invention comprises a method of producing a laminate composite having a plurality of separable laminate layers comprising: preparing a stack of multiple layers of laminatable materials containing a first laminatable layer comprising a mat of reinforcing fiber material treated with at least one particulate thermoplastic polymer and a second layer comprising a removable release film, wherein each laminatable layer is alike or different; molding the stack to form the laminate composite.

In another aspect, the invention comprises a method of simultaneously molding a plurality of separable laminates, alike or different, comprising: preparing a multilayer stack of laminate components comprising a plurality of layers of laminate components, alike or different, wherein each layer is separated by a release film, including at least one layer having a component layer comprising a first wet-laid, non-woven glass fiber mat; a second contiguous component layer of at least one particulate thermoplastic polymer; and a third contiguous component layer comprising a removable release film; molding the stack to form a stack comprising a plurality of separable laminates; optionally, separating one or more laminates from the stack by removing the release film.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a representation of a continuous laminating process for concurrently forming multiple laminates according to the present invention.

Fig. 2 is a representation of a batch compression molding process according to the invention.

Fig. 3 is a cross-sectional view of a several multi-ply laminates concurrently formed according to the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The present invention provides a process for the simultaneous manufacture of multiple laminates or composite sheets from wet-laid mats comprising molding together one or more layers of a wet-laid, nonwoven mat comprised of fiber reinforcements and one or more layers of a release film. The wet-laid mats are formed from an aqueous white water system. The method of manufacture according to the present invention may be performed via a batch method, such as compression molding, or in a continuous manner, for example, using a double belt press. While the invention described herein is described in terms ofthe preferred method of molding together one or more layers wherein one layer preferably comprises a wet-laid, non-woven mat containing one or more fiberous materials for reinforcement, it is apparent to one skilled in the art that with minor modifications the method ofthe invention can be applied to the manufacture of mats of other and different materials, independent ofthe means or method by which the fibrous reinforcing material is initially deposited, for example, wet-laid or blown, woven or non-woven. As used, herein, the term "aqueous white water system" means a water-based slurry of reinforcing fibers, a particulate thermoplastic polymer and, optionally, one or more additives as may be desired to impart certain characteristics to the Whitewater. The term "wet-laid mat", as it is used herein, includes sheets, mats, webs or veils formed from deposition ofthe white water slurry onto a flat surface wherein the slurry is allowed to drain and solidify, wherein such materials are dried to a moisture content of less than about 2% by weight; as well as such materials that have been surface treated with one or more additives. The term "binder", as used herein, means a resin in liquid or molten form which is applied to, or incorporated with, a fiber reinforcement material to provide adhesion between the fibers thereof. As used herein, the term "in the absence of a binder" means that no binder is added to the slurry or the materials formed therefrom at any point during manufacture.

The fiber reinforcements useful in the invention include dispersible materials, non- dispersible materials and combinations ofthe two forms. Preferred dispersible reinforcements include materials such as wet-used-chopped strands of glass, aramids, carbon, polyvinyl alcohol (PVA), hemp, jute, organic materials, mineral fibers and rayon. Preferred non-dispersible reinforcement materials include dry-used-chopped strands and glass fibers designed for applications such as SMC (sheet molding compound) and BMC (bulk molding compound); and continuous panel fabrication; chopped and continuous reinforcements such as aramid, carbon, glass, woUastonite, jute, mica, flake glass, glass and carbon spheres, mats, organic materials, mineral fibers, and fabrics.

The preferred fiber reinforcement materials may be selected from filamentized organic and inorganic materials such as glass fibers, carbon fibers, metal fibers, cellulose fibers, polymer fibers such as polyamide and polyolefm fibers, and any combination thereof. Such fibers may be in the form of rovings, strands or individual fibers that have been chopped or otherwise segmented into lengths varying from about 0.125 to 2.0 inch (about 3.2 to about 50.8 mm), designated herein as "long fibers", and segments having a length of from about 0.031 to 0.125 inch (about 0.79 to 3.2 mm), designated herein as "short fibers", and mixtures thereof. Suitably, the fibers ofthe reinforcement material may be of a diameter of from about 3 microns (0.003 mm) to about 90 microns (0.090 mm). The fibers may be used in the form of strands comprised of from about 50 to about 4000 fibers. Preferably, the reinforcement material is a chopped long fiber glass prepared by chopping rovings comprising from about 200 to 4000 fibers, each having a diameter of from about 3 microns (0.003 mm) to about 25 microns (0.025 mm), which may be used in wet or dry form.

The fibers ofthe reinforcement material are preferably surface treated with chemical sizing or coupling agents known in the art. Preferred sizings are selected so as to aid in dispersion without negatively affecting the dispersion properties ofthe white water slurry. Preferably the sizing composition is selected so as to aid in the dispersion of the reinforcement in the white water slurry. For example, a preferred sizing for a continuous glass roving reinforcement will allow for use of a wet roving as the reinforcement, that is having about 2 to about 19% by weight water. The preferred sizing should also be compatible with the particulate thermoplastic polymer such that the properties ofthe thermoplastic polymer in the white water slurry are optimized. The sizings are preferably water-based and may comprise one or more cross-linking agents, such as silanes, film-formers, surfactants, lubricants or other conventional additives. For example, where the fiber reinforcement is wet-used-chopped strand (WUCS), it may be purchased as a pre-sized product. Examples of such materials are wet-used chopped strand products sized with proprietary sizings 786, 9501 or 9502, which are commercially available under these designations from Owens Corning Inc.

When a particulate polymer such as polyvinyl chloride (PVC) is used in the white water slurry, a compatible sizing for the glass fiber reinforcement may comprise an amino silane such as: "A-l 126", which is a modified aminoorganosilane ; "A-l 120", which is N- beta-(aminoethyl)-γ-(amino)propyltrimethoxysilane; "A- 1102", which is γ- (amino)propyltriethoxysilane; or "A-l 100", which is a γ-(amino)-propyltriethoxysilane; all of which are available from the Crompton Corporation. Preferably, the fiber reinforcement for use in the invention may be a sized glass reinforcement, which may be used wet, in continuous strand or chopped form. Typical water content for wet chopped strands ranges from about 10% to about 25% by weight. For continuous roving it ranges from about 2% to about 15% by weight. Most preferably, such a fiber reinforcement is used in wet, chopped form. An example of such a material is wet chopped strand of approximately 1.25-inch (31.75 mm) length and about 16 microns (0.016 mm) in diameter, which is commercially available from Owens Corning. The wet chopped strand may be used unsized or sized with a compatible sizing.

The fiber reinforcement generally comprises from about 0.02% by weight to about 3% by weight ofthe white water slurry. Preferably, the amount ofthe fiber reinforcement comprises from about 0.03% by weight to about 0.1% by weight ofthe slurry before it is dewatered.

The white water system ofthe present invention includes at least one particulate polymer, in the form of solid particles, granules or microspheres. As used herein the term particulate polymer refers to solid polymer particles, generally in the form of a powder. A single polymer or blend of different polymers as particles may be used. Suitable particulate polymers may be either thermoplastic or thermosetting, and are typically in solid form at the temperature at which the white water is formulated. Suitably, the particulate polymer should also be heat fusible. The term "heat fusible", as used herein, means that the polymer particles are capable of deformation under heat to conform to the surfaces ofthe filaments ofthe reinforcement material, but without melting; thereby joining the particles and the filaments to form a unitary structure. In this respect, the particulate polymer ofthe present invention functions differently from the binder resins that are conventionally used in the preparation of wet-laid materials. Such binder resins melt and flow readily to form an amorphous solid structure with the polymer having accumulated a significant heat history in the process. The heat fusible particulate polymer ofthe present invention is also desirably a hydrophobic, water insoluble polymer. The particulate polymer should also be thermally stable. The term "thermally stable", as used herein, means that the polymer has a relatively high degree of inherent stability. Thermally stable polymers according to the invention include polymers that may be processed or combined with a suitable thermal stabilizer. Examples of such stabilizers include, but are not limited to, organometallic compounds such as alkyltin derivatives or mixed metal salts such as Ba/Zn carboxylates. Preferably, the stabilizers should be organometallic materials. Most preferably, the particulate polymer is a thermoplastic polymer, which may additionally be stabilized with butyltin thermal stabilizers.

Suitable particulate thermoplastic polymers may, for example, be selected from suspension-polymerizable polymers. The term "suspension-polymerizable", as used herein, means that such polymers are formed from monomers contained in a suspension, and the polymer so formed may then be separated from the suspension before use. Suspension polymerization typically occurs in the presence of an initiator, which may be selected from any compatible, conventionally known initiators, depending on the particular monomer or blend of monomers used. Suspension polymerizable polymers such as polyvinylchloride (PVC) and acrylonitrile-butadiene-styrene (ABS) are among the preferred. Additionally, suitable particulate polymers may be selected from addition and condensation polymers such as, for example, polyolefins, polystyrenes, phenolics, epoxies, butadienes, acrylonitriles, and acrylics. A blend of polymers may also be used. The particulate polymer or blend of polymers may also include a heat stabilizer, which retards degradation ofthe particulate polymer.

Typically, the particle size ofthe polymer may be larger than the filament diameter ofthe reinforcement material. The average polymer particle size may range from about 10 microns (0.010 mm) to about 500 microns (0.500 mm). Preferably, the average particle size may be from about 75 microns (0.075 mm) to about 200 microns (0.200 mm). The particle size may be selected to optimize the performance ofthe polymer in the product, while minimizing waste. Where the particle size is too small, a large amount ofthe particulate polymer may be filtered out with the aqueous fraction when the Whitewater slurry is dewatered. Conversely, where the particle size is too large, the particles do not become fully integrated between the filaments ofthe reinforcement material during dewatering; instead the particles accumulate on the surface ofthe product and block airflow during the consolidation step.

The particulate polymer for use in the invention should preferably be of a molecular weight that provides improved impact resistance in composites made according to the invention. Preferably, for example, the inherent viscosity, which may be correlated to molecular weight, ofthe PVC particulate polymer is from about 0.5 to about 1.2, most preferably from about 0.50 to 0.95. It has been found, for example, that a particulate polyvinyl chloride having an inherent viscosity of either about 0.52 or 0.92 produces a composite with excellent impact resistance and good heat distortion properties.

The particulate polymer used in the processes of this invention may, for example, be prepared as a dilute aqueous suspension containing monomeric molecules to be polymerized. The suspension may also contain an initiator, and, depending upon the polymer being formed, a heat stabilizer. The heat stabilizer may be added at the time of polymerization, or at any other convenient time during the process of manufacturing the polymer. A preferred particulate thermoplastic polymer is a suspension-polymerized rigid polyvinyl chloride (PVC) resin in dry, powdered form, which additionally contains a heat stabilizer. Examples of such preferred resins are those stabilized with a butyltin thermal stabilizer and having a particle size of about 125 microns (0.125 mm) and an inherent viscosity of either about 0.52 or about 0.92. Such polymers are manufactured, for example, by Oxyvinyls Inc.

The particulate polymer is generally added to the white water in an amount ranging from about 20 to about 90 percent by weight ofthe total solids (based on the combined dry weight of the weight of fibers and polymer.

Any suitable additive useful for contributing desired physical, chemical or mechanical properties to the fibrous compound or mat, or to the composites formed therefrom, may be included in the white water. Examples of additives that may be added to the white water include dispersants, surfactants such as amine oxides, polyethoxylated derivatives of amide condensation products of fatty acids and polyethylene polyamines, antioxidants, antifoaming agents, foaming agents, bactericides, radiation absorbers, thickeners, softeners, hardeners, UV stabilizers or colorants.

The process ofthe present invention may be used to prepare a wet-laid mat that may be molded directly after dewatering and drying a white water slurry comprising a reinforcement material and a particulate polymer. Such a process is described in detail in U.S. Patent No. 6,093,359, issued July 25, 2000. The dried mat typically has a moisture content of less than 2% by weight, preferably less than 1% by weight. The dried mat may be processed into intermediate products that can be subsequently molded, or it may be molded directly into the composite products desired for specific end-use applications. The process of making a wet-laid mat according to the present invention is advantageous in that it requires a reduced number of processing steps in comparison to conventional wet lay-up processes. For example, the steps of preparing a liquid binder, such as by melting or dissolution in a solvent before combining it with the reinforcement material is eliminated. Additionally, there is no need for a separate processing step in which a liquid binder is applied to a laid and dewatered mat. Because this step is eliminated, the need for additional apparatus used to apply the liquid binder, such as sprayers, pad or rollers, is also eliminated. Even more significantly, the process dramatically increases the available options in terms of molding and performance, compared to previous methods using equal reinforcement content. Properties such as impact, flexural and tensile strengths are increased dramatically compared to conventionally reinforced molded composites. The wet-laid mats ofthe invention may be used to make reinforced molding compounds. The wet-laid mat may also be used in the manufacture of a wide range of laminated composite articles such as roofing materials, automobile parts and structural materials such as fencing.

Simultaneous molding ofthe multiple laminates according to the invention is achieved by molding at least one or more contiguously laid layers ofthe wet-laid mat together with one or more layers of a release film material, thereby forming multiple individual laminates separated by a release film layer. One or more layers of other materials may be included to form the individual laminates, with the outer layer of each laminate separated from the outer layer ofthe other laminates by at least one layer of release film. Such other layers may include, but are not limited to, non-fiber containing layers, functional layers, wear overlayers, decorative layers, permeation barrier layers, tie- layers that are bondable with an adhesive layer, impact-modifying layers and insulating layers. The number of layers is determined by the heat transfer of the pack , the amount of exposure relative to the stability ofthe polymer system, and the characteristics (conductivity) ofthe release paper selected. For the PVC system, 48 plys of #6 basis weight wet-laid mat separated by 2 single-sided release ply such as teflon, vegetable parchment paper, or A4000 (Airtech) is recommended as the optimum or maximum output per pack while maintaining acceptable residual stabilizer laminate. Stability is required for post processing for PVC systems. Optimums for other resin systems depend on thermo properties and stability on exposure to molding conditions. Suitably, between about 1 to about 50 layers may be molded together to form a single laminate or to form multiple laminates separated by a release film. Most preferably, between about 4 to about 16 layers, and even most preferably, 4, 6, 8, or 12 layers may be molded together to a total of 50 layers.

The release film may be any suitable film that releases cleanly from the surface of the laminate after molding is complete and has a suitable conductivity to allow the consolidation process to occur at a proper rate for the system being molded. For PVC, teflon, Airtech A4000, and vegetable parchment paper have the release characteristics and thermal characteristics necessary for this invention. The release film should not become consolidated or integrated into the laminate itself; nor should it mar the laminate surface as it is being removed. Preferably, the release film must be capable of withstanding the temperatures normally used in the molding process without degradation. In addition, preferably, the release film is impermeable to the resin such that no resin is capable of passing through but air and volatile vapors. The type of release film used in the present invention will depend on factors such as elongation and modulus properties, thickness, ability to withstand heat, porosity, and type of application ofthe molded mats. Preferably properties include heat resistance, elongation, impermeability to resin, non-marring and no transfer of chemical upon release. Suitable release films include paper sheets, such as that commercially available from F.D. Warren Co.; polytetrafluoroethylene, such as Teflon®, including glass- reinforced Teflon®; release films such as A4000 which is a halogen release film commercially available from Airtech; polyamide release films, polyolefin release films, such as polyethylene films, including low density polyethylene (LDPE) and high density polyethylene (HDPE), a laminate of HDPE/Nylon/HDPE, polyvinylidene chloride, cellophane, and blends of polyamides with release agent materials, such as those disclosed in U.S. Patent No. 5,959,031; and choices related to processing paper and parchment modes with desirable surface effects.

Preferred release films include Silicure® (Wurttembergische Kunststoffplatten- Werke GMBH &Co. KG), Release Ease 234 TFNP non-pourous teflon-coated fiberglass (Airtech International Inc.), A-4000- Clear/Red/No perforations (Airtech International Inc.), Ultracast/Universal/"pattern name" and Ultracast/PRC/"pattern name" (Sappi, a S. D. Warren Company), Sulpack Q576 and Sulfu Release s2s Boeing (Ahlstrom Dalle Industrial Products). The most preferred release medium for compression is fiberglass/teflon.

An important feature ofthe present invention is the finding that in the laminating process ofthe invention the release film may be reused in the lamination process. This feature ofthe invention has a strong favorable effect on the convenience and overall economics ofthe laminating process ofthe invention. The molding technique used may be a batch process, such as a batch compression molding process, or a continuous process, for example using a double belt laminating press. Referring to Fig. 1, in a continuous laminating process according to the invention, one or more rolls of dried, wet-laid mat 1 may be molded to form laminates using a double belt press 100. In this method, rolls of mat 1 and a roll of release film 2 are unwound and stacked together in a continuous layer as the rolls are unwound, to form a continuous charge la comprised of multiple layers of mat superimposed upon a layer of release film. Alternatively, the continuous charge la may be prepared from stacked input layers (not shown). One or more layers of other materials, selected from functional layers, wear overlayers, decorative layers, permeation barrier layers or impact-modifying layers as previously described herein, may be stacked or layered together with the mat 1 and the release film 2 to form the charge la. The continuous charge la is then passed through one or more series of entry rollers 3 to compact the layers before they are transported into the compression zone 30 of a continuous double belt press 100. The entry rollers pre-mold the charge la by applying slight pressure that is sufficient to compress the fiber pack ofthe charge la, but not sufficient to break the individual fibers. For example, a pressure of up to about 5 psi (34.47 kPa) may be used. The size ofthe gap between the entry rollers 3 may, for example, be calibrated to provide sufficient pressure on the charge la, depending on its thickness, to generate a partially consolidated material that can then be compacted to form a laminate.

Typically, the double belt press 100 is a flat bed press comprised of two endless belts 4, usually made of steel, which run one above the other around two pairs of upper and lower drums 5 to form a thermally controlled compression zone 30 between them. Within this compression zone 30, the charge la is compressed under heat and elevated temperature to form a laminate. After exiting the entry rollers 3, the charge la is then passed through the thermally controlled compression zone 30 ofthe double belt press 100. The belts 4 are maintained at a temperature sufficient to heat the layers ofthe charge to permit fusing and compaction ofthe reinforcement and particulate polymer, which, in turn eliminates air voids from between the filaments and polymer particles in the wet-laid mat. Preferably, this temperature range is from about 320°F to about 390°F (about 160°C to about 199°C).

The operating parameters for the double belt press 100 may be modified according to the desired characteristics ofthe final laminates or composite sheets. For example, the production capacity ofthe press may be determined according to the following formula: k= (v)(b)(μ) wherein k is the production capacity, v is the production speed, b is the width ofthe product, and μ is the utilization factor. The utilization factor is the compensation for a net production time of less than 24 hours per day. The speed (x) is the distance over time (L/t), wherein L is distance and t is the dwell time. Accordingly, the length ofthe double band press may be determined according to the following formula:

L = (k)(t)/(b)(μ) Therefore, as the capacity and dwell time increases, the length ofthe press increases; as the width and utilization factor increases, the length ofthe press decreases. The dwell time should be sufficient to effectuate the consolidation ofthe mats into single individual mats. This factor will depend upon the thickness ofthe desired laminates. Returning to Fig. 1, as the incoming charge la is then drawn through the entrance ofthe thermally controlled compression zone 30, it is seized between the upper and lower belts, and is "sandwiched" between the belts as it moves through the thermally controlled compression zone 30. The charge la is drawn through the machine continuously at constant speed while it is exposed to a fixed pressure, or is drawn through a machine with a constant controlled gap between the belts 4, through which pressure is vertically applied at a 90° angle to the horizontal direction of movement ofthe charge la. The amount of pressure applied may vary from about 10 psi (68.94 kPa) to about 450 psi (3102.3 kPa), and is preferably from about 150 psi (1034.1 kPa) to about 250 psi (1723.5 kPa). The temperature in the thermally controlled compression zone is maintained at a range of from about 320°F to about 390°F (about 160°C to about 199°C), and is preferably maintained within the range of from about 340°F to about 370°F (about 171°C to about 188°C). The actual contact time between the heated surfaces in the thermally controlled compression zone is on the order of about 30 to about 300 seconds.

After exiting the thermally controlled compression zone 30, the contiguously positioned laminates 200 may be passed through a cooling zone 6, having an atmosphere at ambient or less than ambient temperature. Within the cooling zone 6, the formed laminates 200 are drawn over one or more cooling rolls 7. The temperature within the cooling zone 6 is preferably maintained by the flow of a cooling medium such as water (not shown) within the cooling rolls or through a series of cooling plates (not shown) that are in contact with the cooling rolls 7. Within or adjacent to the cooling zone 6 may be positioned separators 40 which remove, and optionally rewind the release film 2, leaving fully formed, freestanding multiple laminates 200.

After separation, the laminate 200 may be subjected to one or more downstream operations, depending on the desired end-use application. For example, each laminate 200 may optionally be embossed by contacting the laminate 200 with one or more embossing rolls 8 to form a decorative or textured pattern on the surface ofthe laminate. Alternatively, the laminate may be embossed by stamping or any other means conventionally known in the art, with or without further heating ofthe laminate surface. Additionally, the laminates 200 may optionally be sanded, trimmed or stacked before packaging and shipping. For example, according to Fig. 1, each laminate 200, may be passed through a trimmer 9, then cut using any suitable cutting means 10 and stacked into sheets 250 or otherwise packaged (not shown) according to the desired application. In an alternative embodiment ofthe invention, the laminates may be simultaneously molded in batches using a single-cavity or multi-cavity batch compression- molding machine. For example, as shown in Fig. 2, multiple laminates may be formed using a single-cavity batch compression molding process. In such a process, dewatered, dried, wet-laid mat 1 formed according to the invention is weighed and cut or otherwise divided to form one or more layers that may be superimposed one over the other to form a charge 50. The charge 50 further comprises one or more layers of a release film 2 that permits separation ofthe laminates formed by molding ofthe layers between the one or more layers of release film 2. The charge 50 may also include one or more other layers selected from other materials desired to create certain physical, chemical or aesthetic characteristics in the finished laminate product. For example, one or more layers of other materials selected from functional layers, wear overlayers, decorative layers, permeation barrier layers or impact-modifying layers as previously described herein, may be conjoined or adjacent to the one or more layers of wet-laid mat 1 and stacked onto a support plate 13. The support plate may be formed of any suitable material, such as a metal, for example aluminum foil or ferro plates, or steel plates of a desired thickness, The order ofthe layers stacked onto the support plate 13 may be modified depending on, for example, the thickness ofthe laminates, and the molding time. The sequence may be repeated as laid out previously limited by a maximum of 50 mat layers, as governed by the laminate thickness desired. Heat transfer, molding time, length of heating and cooling zone "available thermal cycle" contributes to the determination of optimum layering.

The charge 50 is then placed into the form of a tool 300, which has been preheated to a suitable molding temperature. As used herein, "suitable molding temperature" means that range of temperatures appropriate for molding a selected resin material at either ambient or elevated pressure. The range of suitable molding temperatures will vary depending on the type of resin material that forms the resinous matrix to be molded into a composite. For example, where the wet-laid compound or mat ofthe present invention includes a particulate PVC resin, these materials may be processed into composites at temperatures ranging from about 340°F to about 390°F (about 171°C to about 199 °C). The form o the tool 300 may be comprised of opposing inner surfaces 11 of opposing platen 12, each inner surface conFig.d to fit intimately with the opposing inner surface in the absence of any intervening material, such that when an intervening material such as the charge 50 is placed between these inner surfaces 11, the charge 50 may be evenly compressed and cooled during molding to consolidate it into a composite laminate ofthe desired shape, size and surface configuration. The form ofthe tool 300 may be designed to shape the layers into flat, curved or other shapes. Suitably, the charge 50 may be placed in the tool 300 while the form is cold or at ambient temperature. Alternatively, the charge 50 may be preheated to molding temperature, and placed in the tool 300 which has been maintained at temperature greater than ambient temperature, but less than or equal to the molding temperature. Alternatively, the charge 50 may be preheated to a suitable molding temperature, placed in a tool kept at an elevated temperature that is below the molding temperature appropriate to the resin material being molded, as defined above, after which molding pressure is applied. For example, where the method above uses PVC resin, the mold temperature can be kept between about 150°F to about 250°F (about 66°C to about 121°C).

During the actual compression, a pre-selected amount of pressure may be applied to the material to be molded over a period of time, thereby permitting intermingling ofthe components ofthe various layers to form a composite. Heat may also be applied, at a temperature sufficient to promote flowability ofthe resin component ofthe molding material. Preferably, the compression-molding machine is set to apply a pressure of from about 150 psi (1034.1 kPa) to about 450 psi (3102.1 kPa). For example, the pressure may be set at 200 psi (1378.8 kPa). Pressure may be applied for a desired period of time that may vary depending on the thickness or number of layers ofthe charge material and the nature ofthe components thereof. After the molding process is complete, the temperature ofthe mold may be reduced gradually, while maintaining pressure, until the inner surface temperature is about 200°F (about 93°C). The resulting finished laminate may then be removed from the tool and cooled to room temperature.

Fig. 3 depicts a cross-section of simultaneously formed, hypothetical multiple composite laminates that may be made according to the present invention. According to Fig. 3, laminates 260, formed from multiple layers of dried wet-laid mat 1 comprising a WUCS reinforcement and a particulate PVC polymer and an overlayer 14 of an impact resistant resin such as a vinyl resin may be co-molded with a laminate 270 comprised of one or more layers of layers of dried wet-laid mat 1 and one or more additional layers. For example, an insulator layer 15, such as woven glass mat sold under the tradename NYTEX, may be included to improve the molding. In addition, other layers such as an asphalt-backed nonwoven glass mat layer 16, for example G-2 glass felt, may be included. The laminates 260 and 270 are separated by at least one layer of release film 2 between each laminate, allowing them to be separated after molding is completed.

The composites formed according to the present invention may be manufactured in any form conventionally attainable by molding means known in the art for the manufacture of molded composite products from a wet-laid compound or mat. For example, the wet-laid mat ofthe invention may be molded into articles such as roofing shingles, shakes or tiles, structural panels for use in construction, cladding, artificial fencing, decking, truck and automobile parts for manufacture or repair purposes; and miscellaneous parts such as appliance lids, conveyor belts, counter tops, entry doors, garage doors, hurricane shutters, satellite dishes, concrete forms, railroad ties, seating, ready-to-assemble furniture, and laminate flooring.

The composites and, in particular, laminates formed according to the present invention provide certain improvements over laminates formed from wet-laid, binder- added mat formed according to the prior art. Such improvements include increased rigidity and impact resistance ofthe laminate product, as well as increased fiber length retention in the finished product. In particular, a continuous molding process such as the double belt laminating process, when utilized to process laminates from the fibrous, nonwoven mat ofthe present invention, results in increased retention of fiber length when the mat is subjected to a molding process. In such a process, the improvement in retained average fiber length may be about 1.5 times or higher. As a result of this improvement, mechanical properties ofthe resulting laminates, such as tensile strength, impact resistance, HDT are enhanced over equivalent reinforced laminates flexural modulus and coefficient of thermal expansion are enhanced. In addition, the proportion of reinforcing fiber material may also affect these properties.

In this regard, exemplary laminates formed according to the continuous double belt molding process described herein, wherein the reinforcing fiber material is glass present in an amount up to about 35% by weight, may demonstrate a weight average fiber length of from about 10 mm to about 32 mm. The tensile strength of such laminates may range from about 12 kpsi (82.7 MPa) to about 30 kpsi (206.8 MPa), while the flexural strength may range from about 17 kpsi (117.2 MPa) to about 40 kpsi (275.8 MPa), and the impact strength, as measured by the notched Izod test, may range from about 3 ft-lbs/in (13.3 N.m/m) to about 15 ft-lbs/in (66.7 N.m/m). These composite laminates also show heat distortion temperatures ranging from about 75°C to about 185°C (about 167°F to about 365°F).

The following examples are representative, but are in no way limiting as to the scope of this invention.

EXAMPLES Example 1

Dried 12 ft x 12 ft (3.66 m x 3.66 m) mats formed by dewatering an aqueous white water slurry containing WUCS reinforcement (Owens Corning) and heat-stabilized particulate PVC resin (Geon Inc.) were layered to form a charge for a compression molding process. Airtech A4000 red perforated release film was placed on top of a ferro support plate, followed successively by four layers ofthe dried wet-laid mat, another sheet ofthe Airtech A4000 release film, four layers of dried, wet-laid mat, another sheet of release film, four layers of dried, wet-laid mat, one sheet of release film, four layers of mat, one sheet of release film, four layers of mat, one sheet of release film, and another ferro support plate. The multi-layered charge was then placed in a preheated tool configured to the dimensions of a standard electrically-heated compression molding press (Pasadena, 30 ton (2.72 kg) and 200 ton (18.14 kg) capacity) at a temperature of 410°F (210°C). The pressure was increased to about 600 psi (4136.4 kPa) and held at that level for 1.5 minutes. While maintaining the pressure, the temperature ofthe tool was then allowed to cool to below 200°F (93°C). The tool was removed; the laminates were de- molded and the release film layers were removed. The individual laminates were then further cooled under ambient conditions. According to this process, five (5) individual laminates were formed.

Examples 2-5 Laminates were prepared according to the procedure described for Example 1.

Layers of wet-laid mat and other materials were put together in various configurations.

In the process ofthe invention the more preferred conditions for molding laminates are a pressure range of 200 psi-600 psi (1378.8 kPa - 4136.4 kPa), a temperature range of 360°F-390°F (183°C-199°C) and a molding time of about 90 seconds. The most preferred conditions are apressure 200psi, a temperature of 390°F (199°C) and a molding time of 90 seconds.

Referring to Table 1, a comparison is presented ofthe mechanical properties ofthe laminates prepared according to the method ofthe present invention with commercially available glass reinforced and non-glass reinforced laminates commonly employed in structural applications. Compared to the fiberglass reinforced laminates of FiberLoc, Azdel C300 and Azdel C401, the laminates ofthe invention are superior in tensile strength, flexural strength and modulus, and compare favorably in other mechanical properties. The novel laminates are clearly superior to pine in all categories and offer important advantages over aluminum alloys.

TABLE 1

Comparison ofthe Mechanical Properties ofthe

Laminates ofthe Invention with Commercial Laminates

PVC and short Glass Fiber Glass Mat Thermoplastic Glass Mat Thermoplastic Soft Pine Aluminum Alloy

It is believed that applicant's invention includes many other embodiments, which are not herein specifically described, accordingly this disclosure should not be read as being limited to the foregoing examples or preferred embodiments.

Claims

WHAT IS CLAIMED IS:

1. A method of producing a laminate composite having a plurality of separable laminate layers, said method comprising: preparing a stack of multiple layers of laminatable materials containing a first laminatable layer (la) comprising a mat (1) of reinforcing fiber material treated with at least one particulate thermoplastic polymer and a second layer comprising a removable release film (2), wherein each laminatable layer is alike or different; molding the stack to form the laminate composite (200).

2. The method of claim 1 including the step of separating one or more ofthe laminate layers ofthe molded composite by removing the release film (2) to provide individual laminates.

3. The method of claim 1 wherein the reinforcing fiber material is selected from the group consisting of glass fibers, carbon fibers, metal fibers and organic polymer fibers.

4. The method of claim 1 wherein the particulate thermoplastic polymer is selected from the group consisting of polyvinylchloride, polyacryonitrile-butadiene- styrene, polyolefins, polystyrene, phenolics, polyepoxies, polybutadienes, polyacrylonitrile, polyacrylates and polymethacrylates.

5. The method of claim 1 wherein the particulate thermoplastic polymer has an inherent viscosity from about 0.50 to about 1.2 and a particle size of from about 75 microns (0.075 mm) to 2000 microns (2 mm).

6. The method of claim 1 wherein the average particle size ofthe particulate polymer is from about 10 microns (0.010 mm) to about 500 microns (0.500 mm).

7. The method of claim 1 wherein the average particle size ofthe particulate polymer is from about 75 microns (0.075 mm) to about 200 microns (0.200 mm).

8. The method of claim 1 wherein the thermoplastic polymer comprises dry, powdered polyvinylchloride having a particle size of about 125 microns (0.125 mm), an inherent viscosity of 0.52-0.92, and contains a heat stabilizer.

9. The method of claim 1 wherein the release film (9) is selected from the group consisting of films of: polytetrafluoroethylene, glass-reinforced polytetrafluoroethylene, polyamide and polyamides containing release agents, low density and high density polyethylene and laminates thereof, polyvinylchloride, cellophane, A4000 (Airtech) halogen release film and paper sheets.

10. The method of claim 1 wherein the laminatable layers (la) are selected from the group consisting of fiber and non-fiber containing layer, functional layers, wear overlays, decorative layer, permeation barrier layers, tie layers, impact-modifying layers and insulating layers.

11. The method of claim 1 wherein the mat is a wet-laid, non-woven mat (1).

12. The method of claim 1 wherein the molding is carried out using a continuous belt press (100).

13. The method of claim 1 wherein the molding is carried out using a batch compression molding machine (300).

14. A method of simultaneously molding a plurality of separable laminates, alike or different, comprising: preparing a multilayer stack of laminate components comprising a plurality of layers of laminate components, alike or different, wherein each layer is separated by a release film (2), including at least one layer having a component layer (la) comprising a first wet-laid, non-woven glass fiber mat (1); a second contiguous component layer of at least one particulate thermoplastic polymer; and a third contiguous component layer comprising a removable release film; molding the stack to form a stack comprising a plurality of separable laminates (50); and separating one or more laminates from the stack by removing the release film.

15. The method of claim 14 wherein the stack (50) is molded using a continuous double belt press (100).

16. The method of claim 14 wherein the stack (50) is molded in the tool of a batch compression molding machine (300), said tool having been heated to a temperature ranging from about 171°C (340°F) to about 199°C (390°F),at a pressure of from about 150 psi (1034.1 kPa) to about 1200 psi (7786.8 kPa).

17. The method of claim 14 wherein the wet-laid mat (1) is a dried mat comprising a particulate polyvinyl chloride polymer and a wet-use-chopped-strand glass fiber reinforcement; the molding temperature is from about 160°C (320°F) to about 199°C (390°F); the temperature ofthe tool is from about 66°C (151°F) to about 121°C (250°F); and the molding pressure is from about 150 psi (1034.1 kPa) to about 450 psi (3102 kPa).

18. The method of claim 14 wherein the particulate thermoplastic polymer is polyvinyl chloride and the reinforcing material is long glass fibers of about 0.125 inch (3.2 mm) to about 1.25 inches (31.75 mm) in length.

19. The method of claim 14 wherein the glass fibers have been surface treated with a chemical sizing agent.

20. Multiple composite laminates containing 1 to about 50 layers formed according to the method of claim 14.