ULTRA-THIN PRE-PREG SHEETS AND COMPOSITE MATERIALS THEREOF

Abstract

Novel ultra-thin unidirectional pre-preg tapes are disclosed. They can be used to produce ultra-thin woven, bias, multiaxial, chopped-oriented etc. types of pre-pregs. These ultra-thin pre-pregs enable production of composite material products with well-controlled dimensional tolerances and smooth/even surfaces. Further, they render the production of composite material products relatively simpler, tidier, quicker, and economical. The obtained composite material products are relatively thinner, lighter, and mechanically higher-performing.

Claims

1. A pre-preg sheet comprising a fibre reinforcement and either a thermoset for thermoplastic matrix material, wherein the fibre reinforcement comprises unidirectional spread fibres and the pre-preg sheet has a thickness of less than 100 micrometers.

2. The pre-preg sheet of claim 1, wherein the thickness is in the range of 10-70 micrometers and preferably in the range of 15-50 micrometers, and most preferably in the range of 20-40 micrometers.

3. The pre-preg sheet of claim 1, wherein the pre-preg sheet is in the form of a tape, having a length exceeding 5 mm and a width exceeding 2 mm.

4. The pre-preg sheet of claim 1, wherein the crimp angle of its fibres is less than 3 degrees, and preferably less than 2 degrees.

5. The pre-preg sheet of claim 1, wherein a volume-fraction of fibres within the pre-preg sheet is 40% or more, and preferably 50% or more, and most preferably 60% or more.

6. The pre-preg sheet of claim 1, wherein a volume-fraction of fibres within the pre-preg sheet is equal to or less than 90%.

7. The pre-preg sheet of claim 1, wherein the weight of the matrix material is within the range of 5-50% of the total weight of the pre-preg sheet, and preferably within the range 20-50%, and most preferably within the range 20-40%.

8. The pre-preg sheet of claim 1, wherein it has a fibre areal weight in the range 5-100 g/m.sup.2, and preferably 10-80 g/m.sup.2, and most preferably 15-50 g/m.sup.2.

9. The pre-preg sheet of claim 1, wherein the fibres comprises carbon fibres, and preferably ultra high modulus carbon fibres (UHMCF).

10. The pre-preg sheet of claim 1, wherein the thermoset matrix material is in solid-state below a first temperature, and soft and tacky above said temperature, and wherein the matrix material is irreversibly cured when heated above a second temperature for a certain duration of time, wherein the first temperature is 20 degrees C. or more, and wherein the second temperature is higher than said first temperature.

11. The pre-preg sheet of claim 1, wherein the matrix material is provided in the form of continuous or discontinuous lines, extending at least partly in a direction different from the direction of the fibres.

12. The pre-preg sheet of claim 1, wherein the matrix material is provided in the form of disconnected dots or speckles.

13. The pre-preg sheet of claim 1, wherein the thermoset or thermoplastic matrix material is provided in the form of layer, attached to at least one surface of the fibre reinforcement, said layer being provided with pores or openings for exposing fibres of the reinforcement through said layer.

14. A multi-ply arrangement comprising at least two pre-preg sheets in accordance with claim 1, wherein the pre-preg sheets are arranged at least partly overlapping each other, and wherein the overlapping pre-preg sheets have their fibres oriented in mutually different directions.

15. The multi-ply arrangement of claim 14, wherein at least some of the pre-preg sheets are tapes extending over the entire width and/or length of the multi-ply arrangement.

16. The multi-ply arrangement of claim 15, wherein at least some of the pre-preg sheets are short tapes, preferably having a length of 5-80 mm and a width of 2-30 mm, and most preferably a length of 20-50 mm and a width of 5-20 mm.

17. Use of a pre-preg sheet according to claim 1 for the manufacture of a composite material.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0055] For exemplification purpose, the inventions will be described in closer detail in the following with reference to embodiments thereof illustrated in the attached drawings, wherein:

[0056] FIG. 1 exemplifies ultra-thin pre-preg sheets in the form of uni-directional spread fibre tapes bearing just-sufficient amount of resin in differently distributed patterns.

[0057] FIGS. 2a and 2b exemplify different types of woven pre-preg sheets; the former exemplifies the ultra-thin pre-preg tapes of different types occurring as warps and wefts in a woven material, and the latter exemplifies a woven material pre-preg comprising ultra-thin spread fibre tapes.

[0058] FIGS. 3a and 3b exemplify different types of bias pre-preg sheets; the former exemplifies the ultra-thin pre-preg tapes of different types occurring in mutually angular orientations in a bias material, and the latter exemplifies a bias material pre-preg comprising ultra-thin spread fibre tapes.

[0059] FIG. 4 exemplifies an organo reinforcement material comprising differently chopped pieces of ultra-thin pre-preg tapes occurring in random orientations.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0060] In the following detailed description, preferred embodiments of the present invention will be disclosed. However, it is to be understood that features of the different embodiments are exchangeable between the embodiments and may be combined in different ways, unless anything else is specifically indicated. It may be also noted that, for the sake of clarity, the dimensions of certain components illustrated in the drawings may differ from the corresponding dimensions in real-life implementations of the invention. Even though in the following description numerous specific details are set forth to provide with a more thorough understanding of the present invention, it will be apparent to one skilled in the art that the present invention may be practiced without these specific details. In other instances, well known constructions or functions are not described in detail to not obscure the present invention.

[0061] The novel ultra-thin pre-preg tapes of this invention are produced by first spreading the carbon fibre tows, employing a modified method based on one or more suitable known methods, for example pressure contact (GB 841098, GB 1395925, GB 1476929, U.S. Pat. Nos. 4,989,799, 5,101,542, EP 1652978, U.S. Pat. No. 7,536,761), vibratory (U.S. Pat. Nos. 3,798,095, 4,959,895, JP 2036236, U.S. Pat. No. 5,042,122), lateral expansion (GB 694789, GB 1112578, U.S. Pat. Nos. 3,961,396, 4,301,579, JP 2145830, U.S. Pat. No. 6,049,956), fluid (U.S. Pat. Nos. 3,431,602, 3,698,039, GB 1312455, U.S. Pat. Nos. 3,713,590, 3,873,389, 4,421,584, 6,032,342, JP 3382603, U.S. Pat. No. 7,571,524), electrical discharge (U.S. Pat. Nos. 3,358,436, 3,657,871, DE 19650608) etc.

[0062] The obtained ultra-thin spread tows are next subjected to a novel patterned impregnation process wherein the required resin or matrix material, whether thermoset or thermoplastic, is applied in a controlled and calculated amount in a patterned form. Advantageously such patterned ultra-thin pre-preg tapes are producible using conventional equipment and methods, for example those found in the textile printing industry. Such known methods and equipment are unnecessary to describe here. If wanting to use thermoplastic films, then either its suitably perforated type or small pieces transferable from the film can be adhered to the ultra-thin spread fibres for achieving application of the calculated amount of thermoplastic resin. In any case, whether using thermoset or thermoplastic, the resin pattern is so laid out on either one or both the surfaces of the ultra-thin spread fibres that the applied just-sufficient amount of resin's distribution arrangement ensures the shortest paths for its quick spreading and coalescing to wet-out the fibres upon applying the necessary heat and pressure. The pattern of applied resin involves factoring in the resin's viscosity and composition.

[0063] Some constructs of the novel ultra-thin pre-preg tapes/sheets are exemplified in FIG. 1 showing highly magnified views of some different types of ultra-thin pre-preg tapes.

[0064] In FIG. 1a is indicated a dry ultra-thin tape which is a basis for obtaining the ultra-thin pre-preg tapes. It may be noted that the fibres therein are shown separated from each other to only represent or convey that they are substantially oriented in the longitudinal direction of the tape. Showing them occurring touchingly to each other will only create a solid figure which will not help illustrate the point clearly. The thickness of the individual tape is in the range specified earlier. Due to the ultra-thinness of the tape, substantial number of fibres of the tape occur exposed at the front and back surfaces of the tape. This is highly advantageous because the resin or matrix material does not have to flow deeply into the fibre mass to wet them. Hence, wetting of fibres will be uniquely achieved easily, quickly, uniformly and thoroughly.

[0065] In FIG. 1b. is shown an ultra-thin pre-preg tape with the resin applied partly, for example by fine spraying or printing, on both surfaces forming tiny dots/speckles/dabs/blobs/beads/flecks etc. in a suitable pattern. Preferably the dots/speckles etc. on the two surfaces occur mutually offset, but suitably closely and uniformly distributed to achieve quicker and uniform wetting of the fibres from both surface sides simultaneously when heated up under pressure. The applied dots/speckles of the resin adhere/stick to the fibres of the ultra-thin tape. Each of these dots/speckles connect a high number of fibres/filaments in the ultra-thin tape's thickness and width directions. Some of such fibres may occur commonly connected to the resin dots/speckles existing at the two surfaces of the tape as these fibres are generally extremely fine (their diameter is in micrometres). Therefore, the illustration of the ultra-thin pre-preg tape in FIG. 1b is only a coarse representation.

[0066] In FIG. 1c is shown another type of ultra-thin pre-preg tape which has the resin applied in multiple whirl/spiral/coil strand-like pattern. For processing convenience, the whirling/coiling strands of resin are preferably extending substantially along the length direction of the tape, and preferably on both the surfaces of the tape in a closely alternating and offset manner so that the whirling resin strands on the two surfaces preferably do not overlap each other. The applied whirling/coiling strands of the resin adhere/stick to the tape. Because these whirling resin strands run in curving form in a continuous manner, they connect a high number of the extremely fine fibres/filaments in the tape's thickness and width directions. Many of the fibres thus occur commonly connected, at some point or the other along their length direction, to the resin whirls/spirals existing at both the surfaces of the tape. Such strands may be also applied discontinuously. Again, FIG. 1c is only a coarse representation.

[0067] In FIG. 1d is shown yet another type of ultra-thin pre-preg tape which has the resin applied in multiple linear stripe-like pattern. For processing convenience, the linear stripe-like resin is preferably applied substantially along the length direction of the tape, and preferably on both the surfaces of the tape in a manner that the linear stripe-like resin preferably occurs on the two surfaces closely alternatingly arranged, preferably without mutually overlapping, as indicated in the figure, for uniform and quick wetting of the fibres. Alternatively, the linear stripe-like resin can be also applied in another orientation, for example, diagonally or at any angle relative to the longitudinal edge/s of the ultra-thin tape, including perpendicularly. The applied linear stripe-like resin adheres/sticks on the tape's two surfaces. Because these linear stripe-like resin run substantially straight in a continuous manner, they connect with a high number of the extremely fine fibres/filaments in the tape's thickness and width directions. When the linear stripe-like resin is applied at an angle relative to the longitudinal edge/s of the tape, some of the fibres in the tape width direction may occur commonly connected, at some point or the other, to the stripe-like resin which occurs at both the surfaces of the tape. Such stripes may be also applied discontinuously. Again, FIG. 1d is only a coarse representation.

[0068] In FIG. 1e is shown yet another type of ultra-thin pre-preg tape which has the resin applied in multiple non-linear or curvy stripe-like pattern. For processing convenience, the curvy stripe-like resin is preferably applied substantially along the length direction of the tape, and preferably on both the surfaces of the tape in a manner that the non-linear curvy stripe-like resin on the two surfaces preferably occur in a closely alternating arrangement without overlapping each other and with uniform distribution as indicated in the figure. The applied curvy stripe-like resin adheres/sticks on both the surfaces of the tape. Because these stripe-like resin runs in curving form in a continuous manner, each of them connects with a high number of the extremely fine fibres/filaments in the tape's thickness and width directions. Some of the fibres may occur commonly connected, at some point or the other, to the curvy stripe-like resin which occurs at both the surfaces of the tape. Such non-lineary stripes may be also applied discontinuously. Again, FIG. 1e is only a coarse representation.

[0069] Apart from the above disclosed different styles of resin applications, such as dots/speckles, stripe-like, strand-like etc., other types could be also considered depending on end-use and economic considerations. For example, wherein the resin does not run continually as a strand or stripe but is in a discontinuous zigzag form, or a repeating motif made of a series of dots/speckles, or it is in an individual pattern that repeats regularly and uniformly distributed, such as squares, circles, ring-like, line-like etc. forms, or gapped or perforated stripe-like form, or other parallel lines form, or combination of some of the various described types, or other different types etc. All such resin patterns may occur on either one or both the surfaces of the ultra-thin pre-preg tapes.

[0070] It may be noted that resin formulations of either same kind or different kinds may be advantageously applied on either one or both the surfaces of the ultra-thin pre-preg tapes to engineer specific properties for certain end-uses. Different types of resin formulations may be also applied for combination effect of their different properties, on either one or both the surfaces of the ultra-thin tapes.

[0071] When relatively narrow ultra-thin pre-preg tapes are produced, for example up to 100 mm wide, they could be used directly as continuous-length tape-like warps and wefts to produce bi-directional woven fabrics. Such woven fabrics may be produced in either close or open structural configurations to meet with the end-use requirements. Production of woven materials using tape-like warps and wefts is known from e.g. U.S. Pat. No. 8,129,294 (B2).

[0072] In FIG. 2a is exemplified a woven material produced using the ultra-thin pre-preg tapes of this invention. For illustration purpose, the ultra-thin pre-preg tapes, as the warps and wefts, are shown to be of different constructs for ease of distinguishing them. In actual practice the warps and wefts could be same type of ultra-thin pre-preg tapes. In the illustrated example, the resin occurs as whirling/coiling strand in the warp tapes, and as non-linear/curving strand-like in the weft tapes. The shown woven fabric is of open structure configuration. It may be also produced in close structure configuration. Such a woven ultra-thin pre-preg tape results in a correspondingly thin woven pre-preg. It may be warmed up, either entirely or in select places, for temporarily adhering the warp-weft tapes to each other for handling convenience, if necessary. Such a woven pre-preg can be used directly, either individually or by plying/stacking two or more of them in accordance with the end-use requirements. Further, such a woven pre-preg can be cut into pieces of required shape and dimensions and draped and plied in mutually different orientations to obtain improved multiaxial load-bearing capability and capacity of the final composite material. Further, such a woven pre-preg may be combined with any other suitable kind of ultra-thin pre-pregs to achieve the required performance characteristics of the final composite material.

[0073] In FIG. 2b is exemplified conversion of a tape-woven fabric, composed of ultra-thin tapes, into a woven pre-preg by applying the resin in a patterned manner on its one or both surfaces using suitable standard equipment. In the illustration, the resin is shown to be applied in the form of well-distributed dots/speckles on both its surfaces. The produced woven ultra-thin pre-preg may be warmed up, either entirely or in select places, for temporarily adhering the warp-weft tapes to each other for handling convenience, if necessary. Such a woven pre-preg can be used directly, either individually or by plying/stacking two or more of them in accordance with the end-use requirements. Further, such woven pre-preg can be cut into pieces of required shape and dimensions, draped, and plied in mutually different orientations to obtain improved multiaxial load-bearing capability and capacity of the final composite material. Further, such a tape-woven pre-preg can be combined with any other suitable kind of pre-preg to achieve the required performance characteristics of the final composite material.

[0074] Narrow ultra-thin pre-preg tapes, for example up to 100 mm wide, could be also used directly to produce bi-directional bias orientation fabrics wherein the continuous-length tapes occur in acute/obtuse angles relative to the longitudinal direction of the fabric. Such bias fabrics can be produced in either close or open structural configurations to meet with the end-use requirements. Production of bi-directional bias fabrics using tapes is known from e.g. EP 2 479 327. It may be noted that such a bias fabric, called OFT, is technically neither woven nor braided as explained in detail therein, though generally incorrectly called by the said conventional names.

[0075] In FIG. 3a is exemplified a bi-directional bias oriented pre-preg produced using ultra-thin pre-preg tapes. For illustration purpose, different constructs of ultra-thin pre-preg tapes are shown in the two different bias orientations for ease of distinguishing them. In actual practice these bias tapes could be same type of ultra-thin pre-preg tapes. The resin occurs as whirling/coiling strand-like form on the tapes of one of the bias orientations, i.e. in the +45° orientation, and as non-linear/curving stripe-like form on the tapes of the other bias orientation, i.e. in the −45° orientation. The shown bi-directional bias fabric is of close structure configuration. It may be also produced in open structure configuration. Such a bias pre-preg is ultra-thin. It may be warmed up, either entirely or in select places, for temporarily adhering the bias-oriented tapes to each other for handling convenience, if necessary. Such bias ultra-thin pre-pregs can be used directly, either individually or by plying/stacking two or more of them in accordance with the end-use requirements. Further, such a bias ultra-thin pre-preg can be cut into pieces of required shape and dimensions and draped and plied in mutually different orientations to obtain improved multiaxial load-bearing capability and capacity of the final composite material. Further, such a bias ultra-thin pre-preg may be combined with any other suitable kind of ultra-thin pre-preg to achieve the required performance characteristics of the final composite material.

[0076] In FIG. 3b is exemplified conversion of a bi-directional bias fabric composed of ultra-thin tapes into an ultra-thin pre-preg sheet. Such a bias fabric is ultra-thin and converted into a pre-preg sheet by partly applying the resin in a patterned manner on its one or both surfaces using conventional equipment. In the illustration, the resin is indicated to be applied in the form of well-distributed dots/speckles on both the surfaces by methods well known and practiced in the industry, for example in the textile printing industry. It may be warmed up, either entirely or in select places, for temporarily adhering the bias tapes to each other for handling convenience, if necessary. Such a bias ultra-thin pre-preg sheet can be used directly, either individually or by plying/stacking two or more of them in accordance with the end-use requirements. Further, such bias ultra-thin pre-preg sheet can be cut into pieces of required shape and dimensions and draped and plied in mutually different orientations to obtain improved multiaxial load-bearing capability and capacity of the final composite material. Further, such a bias ultra-thin pre-preg sheet can be combined with any other suitable kind of ultra-thin pre-preg to achieve the required performance characteristics of the final composite material.

[0077] In FIG. 4a is exemplified ultra-thin organo type pre-preg sheets composed of same-shaped chopped pieces of ultra-thin pre-preg tapes. The same-shaped chopped pieces of ultra-thin tapes are, for example dropped from a swinging feeder for scattering on an intermittently running and vibrating belt to achieve their random orientations. The deposited randomly oriented chopped pieces are arranged in a way that preferably most of them at least occur partly overlapped covering the area of required product's dimensions. Preferably, they occur uniformly distributed for realising substantially even thickness, i.e. not too many pieces stacking each other in one region than the other. The produced arrangement of chopped pieces is preferably warmed up under some pressure for temporarily adhering them to each other, if required, to enable the created assembly's handling. Following the said steps through aid of suitable implements known in the industry, the pre-preg sheet of this invention is obtained in either individual sheet form of suitable dimensions and shapes, or as continuous sheet in a roll form. Alternatively, different-shaped, different-dimensioned chopped pieces of ultra-thin pre-preg tapes may be used and scattered in random orientations and a pre-preg sheet obtained as just described. Alternatively, both different-shaped and same-shaped chopped pieces may be used in combination and oriented randomly for obtaining a corresponding pre-preg sheet on the lines just described. Alternatively, chopped pieces of same shapes with either different or same dimensions can be arranged in an ordered manner forming a sheet, for example in the brick lay-up arrangement shown in FIG. 4b. To produce with chopped tapes, a required number of partially overlapping pre-preg tapes are supplied in parallel and cut individually at relatively different positions and closely laid on a running belt which then continuously transfers the cut pieces on a reciprocating working bed to form one layer over the other. Plying/stacking a required number of such layers results in the desired ultra-thin pre-preg sheet. When laying such layers of chopped pieces, it is preferable that the chopped pieces in individual layers occur oriented in different directions relative to chopped pieces in the other layer/s. This is achieved, e.g. by altering the relative feeding direction between the working bed and the running belt for build of each layer.

[0078] In case an application requires that all the chopped pieces remain oriented in the same one direction, then it is preferable that the different layers are mutually offset so that the overlapping parts of chopped tapes in different layers do not lie coincident with each other. Alternatively, individual layers can be composed using chopped pieces of ultra-thin pre-preg tapes of relatively suitable different dimensions to prevent build-up of coincident overlapping parts of chopped tapes between the layers.

[0079] Yet another construct of pre-preg sheet can be produced by using different-shaped and same-shaped pieces of chopped ultra-thin pre-preg tapes. For example, in individual layers wherein both different-shaped and same-shaped chopped pieces occur in partly overlapping ordered orientation. Alternatively, same-shaped pieces occur in partly overlapping ordered orientation in one layer and different-shaped pieces occur likewise in another layer. Each of such arrangements of chopped pieces of ultra-thin pre-preg tapes is preferably warmed up for temporarily adhering them to each other forming the pre-preg layer. A number of such layers are plied/stacked to obtain the desired ultra-thin pre-preg sheet.

[0080] Such an ultra-thin pre-preg sheet can be used directly, either individually or further plied/stacked in accordance with the end-use requirements. Such an ultra-thin pre-preg sheet is highly flexible and drape-able. This type of ultra-thin pre-preg sheet can be combined with any other suitable kind of pre-preg sheet, for example to achieve the required performance characteristics of the final composite material. An important advantage of such a material is that virtually no waste is generated as chopped/cut ultra-thin pre-preg tapes can be fully well utilised.

[0081] While the foregoing examples illustrate some constructs of ultra-thin unidirectional pre-preg sheets and bi-directional pre-preg sheets (i.e. woven and bias types), it is to be understood that other types, for example different types of multi-directional pre-preg sheets, can be also produced. For example, the exemplified woven and bias ultra-thin pre-preg sheets can be mutually plied/stacked in suitable orientations, as is practiced conventionally, to obtain a corresponding ultra-thin multi-directional pre-preg sheet. Alternatively, uni-directional ultra-thin pre-preg sheets can be combined with either woven ultra-thin pre-preg sheets, or bias ultra-thin pre-preg sheets, or their combinations, to obtain other types of multi-directional ultra-thin pre-preg sheets.

[0082] The obtained ultra-thin pre-preg sheet can be used directly in the manufacture of composite materials. As mentioned earlier, the novel ultra-thin pre-pregs can be cut into patterned pieces of required shapes and dimensions, draped, and plied/stacked in suitable orientations to achieve required performance and shape of the desired composite material product. Depending on the size and shape of the object required to be produced, the necessary number of cut patterned pieces of ultra-thin pre-preg sheets can be directly draped on a mould, which could be of either close or open types. The sheets of such ultra-thin pre-pregs can be locally warmed/heated, i.e. wherever needed, during plying/stacking procedure to enable them to temporarily stick/hold on to each other in the required form.

[0083] After the draping procedure is completed, the mould, if of close type, is closed and heated for required duration. As is known, the closing mould presses on the stacked sheets and applies the necessary pressure uniformly. Alternatively, if the shaped ultra-thin pre-preg is created on an open mould, it can be put in an autoclave and heated following the known procedures, whereby high air pressure and heat gets applied on the stack of sheets resting on the open mould. These and other conventional methods, for example wherein pressure is applied using a heated roller on pre-pregs draped on an open mould, are well-known in the field and require no further description. As can be noticed, existing equipment and practices of composite material manufacture can be advantageously used with ultra-thin pre-preg sheets to produce improved composite materials.

[0084] Upon cooling, the composite material product is extracted from the mould in the usual way. As can be understood, the ultra-thin pre-pregs of this invention enable quick and tidy production.

[0085] The inventions have been described in reference to specific embodiments of the ultra-thin pre-preg tapes and sheets, its manufacture, and the manufacture of composite material products reinforced by ultra-thin pre-pregs. To persons skilled in the art there will be motivation now to consider several possibilities. For example, those relating to alteration of fibre types, their constructs, compositions, dimensions, orientation arrangements etc.

[0086] Further, the resin may be applied in different styles/forms other than those illustrated/exemplified. Further, the order of manufacturing certain steps may be performed differently, for example stepwise or simultaneously, or the manufacturing steps of ultra-thin pre-pregs and its composite material may be combined in different ways etc. Further, the possibility of producing an ultra-thin pre-preg using a fine thermoplastic net or veil for matrix material will be also obvious.

[0087] The possibility of using ultra-thin pre-pregs for strengthening buildings, heritage monuments, bridges etc. by applying them on such structures and heating them under pressure, and achieving their adhesion to the structure, is technically akin to draping it on a mould and heating it under pressure to form a composite material product. Such use and application of the ultra-thin pre-pregs and bonding it by other suitable adhesives to the building structures, is not excluded from the scope of the disclosed inventions.

[0088] In the claims that follow, any reference to signs placed between parentheses shall not be construed as limiting to the claim. The word “comprising” does not exclude the presence of other elements or steps than those listed in the claim. The word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. Further, a single unit may perform the functions of several means recited in the claims.