WO2009030710A1

WO2009030710A1 - Impregnation method

Info

Publication number: WO2009030710A1
Application number: PCT/EP2008/061629
Authority: WO
Inventors: Jan Vanherck; Jan Wastiels; Olivier Remy; Michel Dannau
Original assignee: Vrije Universiteit Brussel VUB; Universite Libre de Bruxelles ULB
Current assignee: Vrije Universiteit Brussel VUB; Universite Libre de Bruxelles ULB
Priority date: 2007-09-03
Filing date: 2008-09-03
Publication date: 2009-03-12
Anticipated expiration: 2010-03-03

Abstract

The invention relates to calendering devices for impregnating a flexible support structure with liquid impregnating substance characterized in that said roll assembly (2) comprises two parallel horizontally aligned rolls mounted onto a calender frame (3), the said two parallel aligned rolls are positioned at a distance relative to one another defining a slit in between said rolls, wherein each roll comprises a central rotation axis (4), wherein the surface of at least one roll is a relief surface (8) defining a notched, teethed or grooved pattern; the device further comprising two lateral retaining parts (5), said retaining parts being flexibly interconnected over a pivot axis (6) such that the retaining parts are movable relative to one another in the direction of the rotation axes (4), wherein the lateral retaining parts (5) are positioned at a distance over the two parallel horizontal rolls (2), wherein the lower parts of the retaining parts are shaped to fit between the rolls (2), and wherein the area between the retaining parts in connection with the roll surfaces defines a receptacle (7) for receiving and temporarily housing the impregnating substance. The invention further relates to methods for impregnating a flexible support structure with liquid impregnating substance and to the uses of the products obtained by these methods.

Description

IMPREGNATION METHOD

FIELD OF THE INVENTION

The present invention relates to the impregnation of flexible support structures with impregnating substance(s) for the production of end products, in particular laminated end products such as e.g. fibre reinforced laminates. In particular, the present invention relates to new and inventive calendering devices for an improved impregnation of support material with impregnating substance(s).

BACKGROUND OF THE INVENTION

When fabricating laminates reinforced with support material or support structure, the support structure must be first wetted by the impregnating substance (e.g. uncured resin), before the reinforced laminate or other composite material is produced which then will be further shaped into the final product. In the known mechanical fabrication techniques, including pultrusion, filament winding or tape winding, this is achieved by first passing the support material of choice through a bath of impregnating substance, wherein the impregnating substance is picked up by the support material in a rather uncontrolled amount. Adjustment of the amount of impregnated substance taken up is then controlled by a subsequent system which usually is a series of rollers, cylindrical or not, or a calendering system. A typical impregnation of support material with impregnating substance known in the art thus generally consists of two phases. In a first phase the support material is wetted in a rather uncontrolled way with the impregnating substance present in a bath. Since the impregnating substance is continuously picked up from the bath, the impregnating substance in this bath should have a sufficiently long pot life, to allow a continuous operation, e.g. a pot life of several hours to days. The term pot life is known in the art and refers to the length of time that a catalyzed resin system retains a viscosity low enough to be used in processing (also known as 'working life' or 'usable life').

In a second phase the ratio between support material and impregnation substance is adjusted in a controlled way by submitting the mixture of support material and impregnating substance to an impregnation system such as e.g. a calendering system. The calendering system known in the art typically comprises two vertically superimposed rolls. EP 1688231 discloses an apparatus wherein two parallel aligned rolls are fixed onto a mounting bracket.

Finally, the impregnating substance will be hardened after shaping the impregnated support material by increasing the temperature, or application of UV. The present invention aims at solving the above-mentioned drawbacks in the known impregnation methods. The present invention aims at providing superior impregnation methods for obtaining a composite comprising an impregnating substance and a support structure by using an improved calendering device.

The present invention furthermore aims at providing a superior impregnation method for obtaining a composite comprising an impregnating substance and a support structure by simultaneously wetting and impregnating the support material with the impregnating substance.

SUMMARY OF THE INVENTION In impregnated support structures, such as reinforced laminates, the ratio of support material to impregnating substance is of paramount importance for the properties of the final composite, and a precise control is essential for the quality of the manufactured composite product.

The present invention aims at providing a superior impregnation method for obtaining an impregnated support material by using an improved calendering device and combining the phases of wetting and impregnating the support material so as to simultaneously perform these actions.

In particular, the present invention provides a calendering device (1 ) comprising a roll assembly (2) for impregnating a flexible support structure with liquid impregnating substance characterized in that said roll assembly (2) comprises two parallel horizontally aligned rolls mounted onto a calender frame (3), the said two parallel aligned rolls are positioned at a distance relative to one another defining a slit in between said rolls, wherein each roll comprises a central rotation axis (4), wherein the surface of at least one roll is a relief surface (8) defining a notched, teethed or grooved pattern; the device further comprising two lateral retaining parts (5), said retaining parts being flexibly interconnected over a pivot axis (6) such that the retaining parts are movable relative to one another in the direction of the rotation axes (4), wherein the lateral retaining parts (5) are positioned at a distance over the two parallel horizontal rolls (2), wherein the lower parts of the retaining parts are shaped to fit between the rolls (2), and wherein the area between the retaining parts in connection with the roll surfaces defines a receptacle (7) for receiving and temporarily housing the impregnating substance.

The present invention further provides a method for impregnating a flexible support structure with liquid impregnating substance using the calendering device according to the present invention, comprising the steps of: a. providing impregnating substance in receptacle (7) of the device as described herein; b. providing a flexible support structure between the rolls (2) of said device as described herein; c. put into operation the device according to the present invention as described herein, wherein the rotation axes (4) rotate in opposite directions relative to one another so as to guide the flexible support structure downward through the rolls, d. simultaneously wetting and impregnating the flexible support structure with the impregnating substance by guiding the said flexible support structure through the impregnating substance in receptacle (7) between the retaining parts (5) and the rolls (2) of said device according to the present invention as described herein. The device and the method according to the present invention provides for an improved impregnation and compaction of the support material with the impregnating substance.

Furthermore, the device and the method according to the present invention allow the use of impregnating substances having a short pot life.

SHORT DESCRIPTION OF THE FIGURES

Figure 1 shows a calendering device according to the present invention comprising a roll assembly (2) in a horizontal plane with at least on roll, and preferably both rolls (2) having a surface relief, and a pair of lateral retaining parts (5) having a shape fitting the space between both cylindrical rolls (2). Figure 2 shows a (dual) feeding pump (9) for providing the receptacle (7) with impregnating substance. The feeding pump shown is a screw pump.

Figure 3 shows various surface reliefs which may be provided on at least one roll of the calendering device of the present invention. Within the present invention, the surface relief may define a pattern such as a notched, teethed or grooved pattern. In Figures 3A to 3C it is shown that these patterns may have shapes chosen from e.g. square (10), rectangular (1 1 ), rounded (13) or conical (12, 14) shapes. The relief pattern may occupy partially or completely the roll surface.

DETAILED DESCRIPTION Within the present specification, the expression "impregnating substance" refers to a matrix substance used to permeate or saturate a flexible support structure. The expression "liquid impregnating substance" refers to an impregnating substance which is substantially liquid and may optionally comprise solid particles such as, e.g., powders or short fibres, while remaining liquid as a whole. The expressions "support structure", "support material", and "support layer" are used interchangeably and refer to a flexible support used within the present invention to be impregnated with an impregnating substance to manufacture an impregnated composite comprising support material and impregnating substance that, after curing of the impregnating substance and shaping is transformed in the final end product. The support material supports the impregnating substance and becomes a reinforcement material after curing the impregnating substance. The term "composite" as used within the present specification refers to a semi-solid or solid material which is composed of a support material and an impregnating substance. The term "reinforced" refers to a strengthened state of being of a composite obtained by the methods of the present invention due to the presence of a support material. The terms "calender" and "roll" are used interchangeably and refer to a cylindrical roll structure as part of the roll assembly of the calendering device. The present invention will now be explained with reference to Figures 1 to 3.

The present invention provides devices and methods for producing a composite material composed out of a support material and an impregnating substance. In particular, the present invention provides for an improved impregnation of support material by using a calendering device (1 ) having two rolls (2) of which at least one roll is provided with a surface relief (3). Furthermore, the calendering device (1 ) according to the present invention is provided with a pair of lateral retaining parts (5) which are movable in the direction of the rotation axes (4) and fit between the rolls (2) of the roll assembly to form, in combination with the roll surfaces, a receptacle (7) for receiving and temporarily housing the impregnating substance. Impregnating substance may be provided in the receptacle (7) via a feeding pump system (9) while the support material is fed to the roll assembly (2).

As such, the present invention provides for the support material being wetted with the impregnating substance in a controlled way while simultaneously being impregnated with same.

Accordingly, the present invention provides devices and methods for producing a composite, wherein a support material is contacted with impregnating substance, such as uncured resin; while being guided between the rolls (2) of the roll assembly. The flexible support structure leaving the roll assembly (2) is transported by an element. The composite is then conditioned to cure the resin.

Each roll in the calendering device has a central rotation axis (4). The axis run parallel, thus positioning the roll axes in one plane. This plane is parallel to the plane formed by the calender frame (3) or both planes are situated at an inclination angle preferably between 0 and 90, more preferably between 0 and 20, most preferably between 0 and 10 degrees.

Both rolls are positioned at a distance relative to one another defining a slit having a maximal length being equal to the length of the rolls. This is shown in Figure 1. The distance between both rolls is such that the liquid impregnating substance is retained from leaking out while allowing support material to pass through. Accordingly, suitable liquid impregnating substances for use within the present invention have a viscosity comprised between 500 mPas and 20000 mPas. More suitable liquid impregnating substances for use within the present invention have a viscosity comprised between 2000 mPas and 10000 mPas. A particular suitable liquid impregnating substance for use within the present invention has a viscosity of about 7000 mPas. When the liquid impregnating substance presents a shear thinning behaviour, as for example obtained by addition of a thickening agent, this is favorable for retaining its leaking out between the rolls.

Accordingly, in a further embodiment of the present invention, methods are provided for impregnating a flexible support structure with liquid impregnating substance using a calendering device as described herein, wherein the said impregnating substance has a viscosity comprised between 500 mPas and 20000 mPas, preferably between 2000 mPas and 10000 mPas and more preferably of about 7000 mPas.

The position of at least one of the calenders may be adjusted accurately, so as to obtain a precise opening distance (slit) between both calenders. The second calender may be held in a fixed position by a spring of a suitable resilience (not shown), so as to retain the set opening under normal conditions, and allow for a widening in case of e.g. accidental conditions, to avoid damage of the equipment. The most suitable slit opening depends on the surface density of the support structure used. For example, when two layers of 300g/m² were fed, the maximal slit opening was 0.35 mm. The same slit opening appeared to be optimal when feeding 4 layers of 300g/m². In general, the slit typically has a width of between 0.05 (= about zero; rolls touch each other) and 1.0 mm, including the outer values. A particular suitable slit between the rolls has a width of between 0.10 and 0.75 mm, including about

0.15, 0.20, 0.25, 0.30, 0.35, 0.40, 0.45, 0.50, 0.55, 0.60, 0.65, 0.70 mm, and including the outer values. A particular suitable slit between both rolls may measure about 0.35 mm in width.

The support material that is to be impregnated is fed from above between the two calenders (2). In Figures 1 and 2, it is shown that a pair of retaining parts (5) are employed whose lower parts are shaped to fit between the rolls (2). The lateral retaining parts may be positioned at a certain required distance in accordance with the width of the support material such that the latter may be efficiently guided through the rolls while being wetted with the impregnating substance in the receptacle having also a width in accordance.

The rolls or calenders typically comprise a cylindrical structure and each has centrally positioned a horizontal rotation axis (4). The outer diameter of the rolls is typically comprised between 5 cm and 50 cm, including the outer values. A more suitable outer diameter of the rolls is between 10 cm and 40 cm. An even more suitable outer diameter of the rolls is between 12 cm and 30 cm, including 12, 13, 14, 15, 16, 17, 18, 19, 20, 21 , 22, 23, 24, 25, 26, 27, 28, 29 and 30 cm. The rolls or calenders have the same or a different diameter.

The rolls are made out of a solid material which is preferably dent and scratch resistant, chemical resistant and corrosion resistant. A suitable material is metal such as stainless steel. However, it will be appreciated that the present invention may also contemplate other solid materials for the manufacturing of the roll, such as cast iron or iron alloys. Alternatively, the rolls can be covered by hard plastics, e.g., but not limited to, high density polyethylene

(HDPE), polyurethane (PU) or teflon (PTFE). If the processing of the impregnating substance requires such, the rolls can be kept at a temperature different than the ambient temperature, e.g. by an internal heating or cooling system.

The pair of retaining parts is movably attached to an external pivot axis (6), which is typically a cylindrical rod. As such the retaining parts may be easily and accurately positioned over and between the rolls. The lower parts of the retaining parts (5) are shaped to fit between the rolls (2), and the area between these retaining parts in connection with the roll surfaces defines a receptacle (7) for receiving and temporarily housing the impregnating substance. The distance between the retaining parts may be coinciding with, or larger than the width of the support material to be impregnated. A suitable distance between the retaining parts after positioning onto the rolls is comprised between 150 cm and 30 cm, including the outer values. A more suitable distance between the retaining parts after positioning onto the rolls is comprised between 40 cm and 80 cm. A particular suitable distance between the retaining parts after positioning onto the rolls is about 60 cm. The width of the support material may be as small as a few centimeters in the case of pultrusion or tape winding.

The receptacle (7) for receiving and temporarily housing the impregnating substance is formed by the retaining parts (5), and the surface of the calenders (2) between them. An advantage is that the volume of this receptacle so formed (7) is limited. Through the functioning of the feeding pump (feature 9 in Figure 2), the liquid impregnation substance is continuously and evenly poured into the receptacle (7) so as to keep the surface level of the impregnating substance in the receptacle (7) limited and constant. A particular suitable feeding pump (9) is a screw pump providing the advantage that the constituents of particular impregnating substances may be mixed in a continuous way at the time of use. In this way, the volume of impregnating substance in the receptacle (7) remains limited since it is continuously consumed as it is produced. Relatively rapidly hardening impregnating substances may thus be used, providing the advantages that some impregnating substances which may not be sufficiently retarded for the traditional processing technique may still be used, and that the hardening after shaping may be performed quicker and with less energy. In operating mode, the calenders (2) are rotating in opposite direction relative to one another so as to guide the flexible support structure downward through the rolls. At least one of the rolls may be driven manually or mechanically. The second calender may be driven at the same or a slightly different rotational speed, but the pressure which is exerted on the composition of support structure and impregnating substance at the point of smallest distance between the calenders is usually sufficient to drag it along. In this way, the support material is transported downwards through the opening between the calenders, while it is wetted and impregnated simultaneously in a controlled way due to the pressure which is gradually build up when the support material approaches the narrowest opening (slit) between the calenders.

A particular and essential feature of the invention is that the surface of at least one calender is provided with a relief. A suitable relief is comprised of depressions such as holes, recesses, dimples, gouges, grooves, notches, impressions, teeth, wells and pores. A particular suitable relief is comprised of a notched, teethed or grooved pattern. It was observed that with such relief patterns, an increased uptake of the impregnating substance by the support material could be established (see Example 1 ).

Typically, the relief pattern is composed of a plurality of parallel circumferential notches, teeth or grooves. The term "circumferential" in this context refers to a circumferential path around the external surface of the roll(s). The notches, teeth or grooves are thus typically positioned on circumferential paths that may run in parallel or threaded. Furthermore, the plurality of parallel or threaded circumferential notches, teeth or grooves may occupy partially or completely the roll surface.

Accordingly, in one embodiment of the present invention, a calendering device is provided, wherein the relief pattern on at least one roll and preferably both rolls is composed of a plurality of parallel or threaded circumferential notches, teeth or grooves occupying partially or completely the roll surface.

The relief pattern may further be composed of grooves, teeth or notches having a particular shape. The particular pattern of grooves, teeth or notches may have an arrangement such that a transversal section through roll(s) through the pattern defines opposite series of juxtapositioned depressions, each depression represented by a two-dimensional plane composed of an upper and a lower part relative to an imaginary transversal central axis through the series of depressions, wherein said upper and lower parts are equal or not (see Figure 3). The shape of the sum of these lower and upper parts may present geometric shapes such as square, rectangular, conical and round shapes. Accordingly, in a further embodiment of the present invention, a calendering device is provided, wherein the shape of the grooves, teeth or notches is chosen from the group comprising square, rectangular, rounded and conical.

Through a suitable choice of depth, distance and shape of the notches, teeth or grooves, these will act as channels for transporting the impregnating material to the narrowest zone

(slit) between the calenders, where due to the pressure exerted by the top of the relief structure; the support material is well impregnated. Figure 3 shows a number of suitable relief shapes, including, but not limited to, square, rectangular, conical and rounded depressions. The surface relief may be present along the entire length of the cylindrical roll, or may be present in a number of regions distributed along the length of the cylinder such as shown in Figure 3B; i.e., separated by zones of smooth roll surface. Alternatively, both rolls may have a surface relief wherein both rolls may show an equal relief or not.

At least one roll is provided with a surface relief and the pattern may be composed of a grooved, teethed or notched pattern comprising equal-sized grooves, teeth or notches or may be composed of grooves, teeth or notches having mixed and/or different shapes and sizes.

The relief provides a number of additional advantages. For example, a further effect of the presence of grooves, teeth or notches is that the slit between the calenders may be made smaller than with a smooth calender surface. This leads to a higher pressure and thus as well to a better impregnation and lower air entrapment. Moreover the grooves, teeth or notches grip the support material, and guide it through the machine without slipping or need to pull it through. As such, the support material does not need to be rigid and strong, it can be discontinued locally (e.g. to change a fibre roll), and large widths may be processed. As such, widths of, e.g., 125 cm, corresponding to the standard width of e.g., rolls of glass fibre and construction panels, may be efficiently processed; but in general, there is no upper limit.

Moreover, due to the narrow slit between the calenders (typically less than 1.0 mm), an impregnating substance presenting sufficiently high viscosity or treshhold for flow will not leak through the opening, even when no support material is present, or when the calenders are not in operation. In addition, the presence of grooves, notches or teeth is particularly useful when two or more support layers are fed and processed together, while the feeding of the impregnating substance may be performed between the support materials, e.g., fibre layers, and not between the fibre and the calender surface. In this way, the exerted pressure squeezes the impregnating substance in and through the support material into the grooves, where it will be partially picked up by the support layer at its coming out of the slit between both rolls. This results in a very good, uniform and homogeneous simultaneous wetting and impregnation.

Various types of support materials may be employed with the methods according to the present invention and impregnated in a controlled way. Non-limiting examples of suitable support materials include carbon/graphite, aramid, polymer and glass fibres which are mainly used in the advanced composite industry; and stitched or braided structures, yarns, rovings, chopped strand mat (CSM), woven fabric, and continuous filament mats which are mainly used in advanced composite manufacture.

Accordingly, there is provided a method for impregnating a flexible support structure with liquid impregnating substance using a calendering device as described herein, wherein the flexible support structure is chosen from the group comprising carbon/graphite, aramid, polymer and/or glass fibres, stitched or braided structures, yarns, rovings, chopped strand mat, woven fabric, and continuous filament mats.

Each of these support structures has its own special application. When prepreg material is to be manufactured, woven fabric or mats are most preferred.

A fibrous support layer may be composed out of a grouping of bundles of several hundreds to thousands individual filaments, and several individual support layers may be impregnated together. As an example, four layers of glass CSM of 300 g/m2, or three layers of glass CSM of 450 g/m2 may be processed in one step. Support structures that are processed together may be of a different nature, for instance a low density core, a surface mat, etc.

A support structure of a certain thickness, presenting a concentration of fibres at the outer surfaces (sandwich buildup), may be impregnated symmetrically, leading to a concentration of support material at these outer surfaces, which may be a preferred situation. Normally no support material pick-up by the calenders occurs, but if this would be the case with support material composed out of very loose fibres, a traditional comb structure placed directly after the slit may avoid this. The presence of grooves, teeth or notches highly facilitates the fine placement of the comb structure, and thus its efficiency.

The presence of grooves, teeth or notches allow for an improved impregnation of support material with impregnating substance. Suitable grooves, teeth or notches for use with the present invention are at a distance of between 1 and 5 mm, including the outer values. A more suitable distance is between 1.5 mm and 3.0 mm, including the outer values. A particular suitable distance measures about 2.5 mm. Suitable grooves, teeth or notches for use with the present invention have a depth of between 0.5 and 2 mm. A more suitable depth is comprised between 0.8 mm and 1.2 mm. A particular suitable depth measures about 1 mm.

Accordingly, in a further embodiment of the present invention, a calendering device is provided, wherein the groove, teeth or notch distance is between 1.0 mm and 5.0 mm, preferably between 1.5 mm and 3.0 mm.

In a further embodiment of the present invention, a calendering device is provided, wherein the groove, teeth or notch distance is about 2.5 mm.

In a further embodiment of the present invention, a calendering device is provided, wherein the groove, teeth or notch depth is between 0.5 and 2.0 mm, preferably between 0.8 mm and 1.2 mm.

In a further embodiment of the present invention, a calendering device is provided, wherein the groove teeth or notch depth is about 1 mm.

A suitable surface relief for use within the present invention may further be composed of depressions such as grooves, teeth or notches which have equal depth and length Accordingly, in a further embodiment of the present invention, a calendering device is provided, wherein the grooves, teeth or notches have equal width and depth.

These dimensions may be adapted to the rheological properties of the impregnating substance, in order to obtain a maximum efficiency.

A calendering device may further comprise an element for transportation of the flexible support structure. Suitable elements may be a roll, plate, conveyer belt or a combination thereof. The element may be positioned at a distance below one of the rolls of the roll assembly (2), the distance is preferably between one and ten centimetres. Preferably, the element has a surface without grooves. The use of a combination existing of a roll and plate has the advantage that the roll can function as support for the plate. The use of a conveyer belt, may comprise the use of an additional roll to support the weight of a pivoting device. As a result, the compaction pressure is equally supported and distributed over the conveyer belt.

Accordingly, in a further embodiment of the present invention, a calendering device is provided, comprising an element for transportation of the flexible support structure leaving the roll assembly. The roll assembly (2) may further be arranged in the calender frame (3) in such a manner that it is pivotable along an axis parallel to the central rotation axes of the rolls (2).

Accordingly, in a further embodiment of the present invention, a calendering device is provided, wherein the roll assembly (2) is arranged in the calender frame (3) in such a manner that the calender frame is pivotable along an axis parallel to the central rotation axes of the rolls (2).

The devices and methods according to the present invention are most suitable when impregnating substances are to be used which present a high viscosity, eventually combined with a threshold limit for flow. This is the case for high performance thermosetting or thermoplastic polymers, or for resins which are heavily loaded by particles for instance to obtain better fire retardant properties, or for two component systems consisting of a powder and a liquid, or for cements.

It is known that these impregnating substances are difficult to process, as well in the wetting phase as during impregnation. The methods according to the present invention wherein wetting and impregnating is performed simultaneously surprisingly gave unexpected good results, far better than the traditional methods.

Accordingly, it is a further object of the present invention to provide a method for impregnating a flexible support structure with liquid impregnating substance using a calendering device as described herein, comprising the steps of (a) providing impregnating substance in receptacle (7) of the device according to the present invention; (b) providing a flexible support structure between the rolls (2) of said device; (c) put into operation the device according to the present invention, wherein the rotation axes (4) rotate in opposite directions relative to one another so as to guide the flexible support structure downward through the rolls; and, (d) simultaneously wetting and impregnating the flexible support structure with the impregnating substance by guiding the said flexible support structure through the impregnating substance in receptacle (7) between the retaining parts (5) and the rolls (2) of said device.

Because of their rheological properties, there is no leakage of impregnating substance through the slit between the retaining parts (5) and the calenders (2), as well as no leakage through the slit between the two calenders, even when they are not in operation.

Suitable impregnation substances or resins for use with the methods of the present invention may be synthetic products as well as natural resins or natural polymers. The resin systems used to manufacture advanced composites are of two basic types: thermosetting and thermoplastic. Known thermosets include epoxies, polyurethanes, phenolic and amino resins, bismaleimides (BMI, polyimides) and polyamides. Thermoset resins typically require the addition of a curing agent or hardener. Suitable curing agents in this respect are known to the skilled person and include aromatic, aliphatic and cycloaliphatic amines, polyaminoamides, amides and anhydrides. In contrast, thermoplastics require only heat and pressure to form the finished part. A particular suitable impregnating substance material for use in the methods according to the present invention is an uncured acidic inorganic resin. These resins being inorganic, are presenting very good temperature and fire resistance, comparable or superior to cements, and far superior to any polymer. On the other hand being acidic, they are, contrary to alkaline cements, compatible with traditional glass fibres. In this way, glass fibres can be used as reinforcement for obtaining top class incombustible composite materials, classified as A1 , the best class for European building materials.

More particularly suitable for use within the methods of the present invention are uncured acidic resins comprising an inorganic resin composition comprising an acidic solution of metal phosphate containing phosphoric acid, an oxy-boron compound and a wollastonite compound. A particular suitable impregnating substance for use with the methods of the present invention is a two component phosphate cement, such as Vubonite®.

Accordingly, in a further embodiment of the present invention, there is provided a method for impregnating a flexible support structure with liquid impregnating substance using a calendering device as described herein, wherein said impregnating substance is an uncured acidic resin.

In a further embodiment of the present invention, there is provided a method for impregnating a flexible support structure with liquid impregnating substance using a calendering device as described herein, wherein the said uncured acidic resin is an inorganic resin composition comprising an acidic solution of metal phosphate containing phosphoric acid, an oxy-boron compound and a wollastonite compound.

In a further embodiment of the present invention, there is provided a method for impregnating a flexible support structure with liquid impregnating substance using a calendering device as described herein, wherein said inorganic resin composition is a two-component phosphate cement, such as Vubonite®.

The final product may have various textures depending on the particular support material used. In addition, supplementary materials may be used while feeding the support structure. For example, a flexible supplementary sheet, which is positioned directly against one of the calenders (having preferably a smooth surface), may be processed together with support material and impregnating substance at its other side. If this sheet is for instance of plastic, it can function as (temporary) support and/or cover of the manufactured composite. Other materials, presenting a good bond with the impregnating substance after hardening, like veneer for example, may be used likewise to obtain a laminate with specific surface properties. Furthermore, a (flexible or not) core material which is not fibrous may be processed together to obtain a sandwich structure. The appearance of the final composite product may be further influenced in respect of colour by the addition to the impregnating substance of e.g. pigments. For example, various liquid and solid colored pigments are commercially available for tinting resins. Alternatively, a photocatalyst may be mixed with the impregnating substance. In this respect, any kind of photocatalyst able to oxidize, in the presence of light, air and environmental humidity (oxygen and water), the polluting substances contacting the surface of the end-products of the present invention. A particular suitable photocatalyst fur use with the present invention is, e.g., titanium dioxide, or a precursor thereof, optionally doped with other atoms different from Ti. The quantity of photocatalyst present in the impregnating substance may be, e.g., about 1 % by weight to about 10% by weight of TiO₂, of one of its precursors or of another photocatalysts. Since the invention allows for the manufacturing of very thin (less than 1 mm) and thus flexible (glass) fibre reinforced composite sheets, an efficient use of the photocatalyst can be obtained compared to state of the art solutions when mixing with cement compositions of superior thickness. These very thin sheets can be applied as surface cover on various substrates.

Accordingly, in a further embodiment of the present invention, there is provided a method for impregnating a flexible support structure with liquid impregnating substance using a calendering device as described herein, wherein one or more colour pigments and/or photocatalysts are added to the impregnating substance. The ratio of support material to impregnating substance is of paramount importance for the properties of the composite material and is typically expressed in the support material volume fraction. This support material volume fraction is the ratio between the impregnating substance and the support material and is controlled exactly by changing the opening between the calenders and their groove structure in combination with the support surface weight.

After impregnation by the calendering device, a flexible support structure may be deposited on an element for transportation which moves below the roll assembly and is positioned at a distance below at least one of the rolls varying from a few up to ten centimetres.

It is only required that one of the rolls is in proximity of the element for transportation. This can be obtained with the use of rolls with a different diameter. Their upper sides can be positioned at the same height, meaning their axes are no longer horizontal versus the plane formed by the calendering frame. This can also be obtained by keeping the axes in a plane horizontal with the plane formed by the calendering frame, meaning their horizontal sides are no longer at equal height, but the reservoir function is still maintained. Alternatively, rolls with the same diameter can be used, which are placed under a small angle with regard to the element for transportation. This can be obtained by horizontally positioning the calender frame and the element for transportation and positioning the plane comprising the axes of the rolls under a small angle. Or this can be obtained by keeping the plane comprising the axes of the rolls and the plane formed by the calendering frame parallel and placing the element for transportation at a small angle.

As effect, the calendering device and the supporting plate are essentially in direct contact and a compacting pressure is applied to the impregnated flexible support structure.

A method using an element for transportation positioned in direct contact with one of the rolls, results in an improved compaction and alignment of the flexible support system before it is processed further, e.g. in pultrusion.

Accordingly, in a further embodiment of the present invention, the methods as described comprise the additional step of leading the impregnated flexible support structure between one of the rolls and an element for transportation. The methods as described may comprise an additional step of pivoting the calender frame, along an axis parallel to the parallel axes of the impregnating rolls, into a position with an inclination angle preferably between 0 and 90, more preferably between 0 and 20, most preferably between 0 and 10 degrees between the plane formed by the calendar frame and the plane formed by the central axes of the parallel aligned rolls. As a result, the calendering device and the element for transportation are essentially in direct contact, whilst a compacting pressure is applied to the impregnated flexible support structure. In this way, even when both rolls are of the same diameter, only the one roll at the largest distance from the pivoting axis has direct contact with the supporting plate, and applies a pressure on the impregnated flexile support structure. The movement of the element for transportation is not only unhindered by unwanted contact with the second roll, which rotates in counter direction, but it is in perfect synchronicity with the feeding speed of the flexible support structure, simply by imposing it through direct contact with the roll. Skewness and folding of the impregnated support structure is made impossible by definition. By means of the pivoting, this pressure is controllable by adjusting the weight of the device, independently of the thickness of the manufactured object, cfr. stacking of several layers. Problems with the application of an additional layer are reduced as the device is adjustable. This can be very useful for the fabrication of layered elements, in which some layers are not composed of impregnated flexible support structure. This may be the case with sandwich elements with a foamed core, which is after being deposited on an impregnated flexible support structure is covered with a second impregnated flexible support structure.

A constant but modifiable pressure can be obtained on the flexible support structure for compaction. This pressure is in first instance derivable from the weight of the device and can be modified by changing the weight of the device or leaving the weight unchanged and applying pressure.

This additional step results in a reduced number of folds and/or a better aligned deposit of flexible support structures onto an element for transportation. Such improved alignment is of importance, especially for wide flexible support structures such as those with a standard panel width of 125 centimetres. This additional step also results in a reduced number of air voids, when a supporting plate is passed several times below a calendering device in order to obtain a larger thickness of an end product through stacking of several layers of impregnated flexible support structure. It further has the effect that a subsequent compacting action after the calendering operation can be avoided. Accordingly, in a further embodiment of the present invention, the methods as described comprise the additional step of pivoting the calender frame along an axis parallel to the parallel axes of the impregnating rolls, into a position with an inclination angle between 0 and 90 degrees, more preferably between 0 and 20 degrees, most preferably between 0 and 10 degrees. In a further embodiment of the present invention, the methods as described comprise an additional step wherein the impregnated flexible support structure is further conditioned to cure the impregnating substance and shape the composition of support material and impregnating substance into the final product.

The impregnated support material may thus be shaped to the desired shape, or draped on a surface to bond, or different layers can be assembled to obtain a higher thickness, depending on the needs of the finished product.

When the as such fabricated composite material is kept after processing in conditions where the hardening of the impregnating substance is prohibited for a certain time, it is possible to manufacture prepreg material. Prepreg material typically takes three main forms: woven fabrics, roving, and unidirectional tape. Once the resin mixture has been impregnated onto the support material, the prepreg is stored in a refrigerator or freezer until ready for use in the manufacturing process. This cold storage prevents the chemical reaction from occurring prematurely. Prepreg materials are used widely in the advanced composite industry, e.g., in aircraft and aerospace. Accordingly, it is a further object of the invention to provide for the use of an impregnated support material obtainable by the methods as described herein as prepreg material.

Another object of the present invention constitutes the use of support material reinforced composites, as obtained by the methods according to the present invention, for various applications. The composites obtained with the present invention finds particular use as coating. For example, when heat resistant or fire retarding resins are used within the methods of the present invention, the composite material may be used as coating on fire doors and walls.

Accordingly, it is a further object of the invention to provide for the use of a cured and shaped impregnated support material obtainable by the methods as described herein for bonding to, or composing surfaces chosen from the group comprising walls, ceilings, doors, and benches.

The invention will now be illustrated by a number of examples which are offered by way of illustration, and not by way of limitation.

EXAMPLES

The impregnating substance used in the following examples was a phosphate cement commercialized under the brand name Vubonite® (see EP 0861216 B1 , and MvwΛ/ubonjtexom)- Vubonite® is a two-component phosphate cement. The powder grade used was "Powder HP A+". The components were mixed homogeneously before casting them in the reservoir or receptacle (7) formed by the retaining parts (5) and the calender surfaces. The fresh impregnating substance presented a viscosity of about 7000 mPas and had a pot life of about 30 minutes.

The operation was executed by impregnating fibre mats of a determined dimension (width between 200 and 400 mm, length between 300 and 600 mm), in order to be able to measure the weight of the support material and the weight of the impregnating substance which was taken up under certain conditions. This uptake is expressed as the ratio between impregnating substance and support material weight, and is a measure for the support material volume fraction in the finished product. All mentioned values in the examples are mean values of 3 to 10 measurements, with a coefficient of variation of around 0.05. The machine was hand operated, with a feeding speed between 50 and 100 mm/sec. The calenders were made from stainless steel. The surface reliefs were comprised of different groove structures and were made with cutter inserts and are summarized in Table 1.

Table 1

The depth of the grooves in all cases was 1 mm. The groove volume per unit length in the direction of the calender axis therefore was increasing from B over C1 and C2 to C3.

In Examples 1 and 2 a standard non woven chopped strand mat from Owens Corning, type M705, with a surface density of 300 g/m2 was used.

Example 1 : Influence of the groove structure

The opening between the calenders had been set to 0.45 mm. A single support layer was fed, and the impregnating substance was fed from both sides of the support layer. The following uptakes were measured for the different pairs of rolls representing the groove combinations as listed in Table 2.

Table 2

It appeared that the uptake was the lowest for the smooth surfaces, and that it was insufficient to obtain a compact composite without air entrainment, while the fibre mat was slipping between the calenders. The uptake for the combinations where at least one calender was grooved was sufficient in all cases to obtain a compact composite, while the fibre mat was guided by the calenders and was not slipping. The uptake capacity when one smooth surface was used was increasing with increasing groove volume (C3>C1 >B). When both calenders were grooved, the uptake was the highest.

Next, two support layers were fed at the same time, with the feeding of the impregnating substance only between the two layers; thus not in direct contact with the calenders. The results are shown in Table 3.

Table 3

The uptake was in all cases still sufficient to obtain a compact composite, although lower than with one layer. The same uptake (thus in absolute uptake the double amount) could be obtained for the same calender opening with two layers of support material as with one layer when one of the surfaces was smooth (C1 -C2 and C1 -C3 compared to A-C1 ). A narrowing of the groove distance from 2 to 1.5 mm did not lead to a higher uptake for the non woven chopped strand mat.

A further test was also performed with three support layers and grooves B-C1 , leading to an uptake of 2.81 , hardly lower than with two layers. The impregnating substance was however fed on both sides of all layers.

Example 2: Influence of the opening between the calenders

In all cases, two support layers were fed at the same time. The impregnating substance was fed either only between the two support layers (Middle, "M"), or between the support layers and the calender surface (All, "A"). The calender opening varied from about zero (calenders touching) to 0.55 mm. The uptake results obtained are shown in Table 4.

Table 4

In all cases, there was no problem for making the two support layers to pass between the calenders, but for about zero opening somewhat more effort was needed. There was nearly no influence on the uptake from the opening, except a slightly lower value for about zero opening, and a slightly higher one for 0.55 mm. On the other hand, there was a marked higher uptake when the feeding of the impregnating substance was also through filling the grooves (A against M). The difference in uptake between C1 , C2 and C3 was low, confirming the conclusion of Example 1 that there is a limit on the influence of further narrowing the groove distance.

Example 3: Influence of the structure of the support material Different support material structures were used under similar calender settings, e.g. grooves C1-C2 and calender opening 0.45 mm. The various types of support material that were employed are summarized in Table 5.

Table 5

The obtained results are shown in Table 6.

Table 6

From the above results, it was concluded that not the surface density of the support material structure determines the uptake (similar results for CSM from 300, 450 and 600 g/m2), but rather the support material structure itself.

Claims

1. A calendering device (1 ) comprising a roll assembly (2) for impregnating a flexible support structure with liquid impregnating substance characterized in that said roll assembly (2) comprises two parallel horizontally aligned rolls mounted onto a calender frame (3), the said two parallel aligned rolls are positioned at a distance relative to one another defining a slit in between said rolls, wherein each roll comprises a central rotation axis (4), wherein the surface of at least one roll is a relief surface (8) defining a notched, teethed or grooved pattern; the device further comprising two lateral retaining parts (5), said retaining parts being flexibly interconnected over a pivot axis (6) such that the retaining parts are movable relative to one another in the direction of the rotation axes (4), wherein the lateral retaining parts (5) are positioned at a distance over the two parallel horizontal rolls (2), wherein the lower parts of the retaining parts are shaped to fit between the rolls (2), and wherein the area between the retaining parts in connection with the roll surfaces defines a receptacle (7) for receiving and temporarily housing the impregnating substance.

2. The device according to claim 1 , wherein the relief pattern on at least one roll and preferably both rolls is composed of a plurality of parallel circumferential notches, teeth or grooves occupying partially or completely the roll surface.

3. The device according to claim 1 or 2, wherein the groove, teeth or notch distance is between 1.0 mm and 5.0 mm, preferably between 1.5 mm and 3.0 mm.

4. The device according to any of claims 1 to 3 wherein said distance is about 2.5 mm.

5. The device according to any of claims 1 to 4, wherein the groove, teeth or notch depth is between 0.5 and 2.0 mm, preferably between 0.8 mm and 1.2 mm.

6. The device according to claim 5, wherein the groove depth is about 1 mm.

7. The device according to claims 1 to 6 wherein the grooves, teeth or notches have equal width and depth.

8. The device according to any of claims 1 to 7, wherein the shape of the grooves, teeth or notches is chosen from the group comprising square, rectangular, rounded and conical.

9. The device according to any of claims 1 to 8, comprising an element for transportation of the flexible support structure positioned at a distance below at least one of the rolls, the distance is preferably between one and ten centimetres.

10. The device according to any of claims 1 to 9, wherein the roll assembly (2) is arranged in the calender frame (3) in such a manner that it is pivotable along an axis parallel to the central rotation axes of the rolls (2).

1 1. A method for impregnating a flexible support structure with liquid impregnating substance using the device according to any of the previous claims, comprising the steps of: a. providing impregnating substance in receptacle (7) of the device according to any of claims 1 to 10; b. providing a flexible support structure between the rolls (2) of said device according to any of claims 1 to 10; c. put into operation the device according to any of claims 1 to 10, wherein the rotation axes (4) rotate in opposite directions relative to one another so as to guide the flexible support structure downward through the rolls, d. simultaneously wetting and impregnating the flexible support structure with the impregnating substance by guiding the said flexible support structure through the impregnating substance in receptacle (7) between the retaining parts (5) and the rolls (2) of said device according to any of claims 1 to 10.

12. The method according to claim 1 1 , wherein an additional step comprises leading the impregnated flexible support structure between one of the rolls and an element for transportation.

13. The method according to claim 11 or 12, wherein an additional step comprises pivoting the calender frame along an axis parallel to the parallel axes of the impregnating rolls, into a position with an inclination angle between 0 and 90 degrees, more preferably between 0 and 20 degrees, most preferably between 0 and 10 degrees.

14. The method according to any of claims 1 1 to 13, wherein the impregnated flexible support structure is further conditioned to cure the impregnating substance and shaping the composition of support structure and impregnating substance into the final product.

15. The method according to any of claims 1 1 to 14, wherein the said impregnating substance has a viscosity comprised between 500 mPas and 20000 mPas, preferably between 2000 mPas and 10000 mPas and more preferably of about 7000 mPas.

16. The method according to any of claims 11 to 15, wherein one or more colour pigments and/or photocatalysts are added to the impregnating substance.

17. The method according to any of claims 11 to 16, wherein said impregnating substance in an uncured acidic resin.

18. The method according to claim 17, wherein the said uncured acidic resin is an inorganic resin composition comprising an acidic solution of metal phosphate containing phosphoric acid, an oxy-boron compound and a wollastonite compound.

19. The method according to claim 18, wherein said inorganic resin composition is a two- component phosphate cement, such as Vubonite®.

20. The method according to any of the claims 11 to 19, wherein the flexible support structure is chosen from the group comprising carbon/graphite, aramid, polymer and glass fibres, stitched or braided structures, yarns, rovings, chopped strand mat, woven fabric, and continuous filament mats.

21. An impregnated support structure obtainable by a method according to any of the claims 1 1-20.

22. Use of an impregnated support structure obtainable by the method according to claim 1 1 or 12 as prepreg material.

23. Use of a cured and shaped impregnated support structure obtainable by the method according to claim 14 or any of claims 15 to 20 in combination with claim 14 for bonding to or composing surfaces chosen from the group comprising walls, ceilings, doors, and benches.