WO2009002815A1

WO2009002815A1 - Process for assembly of thermoplastic pieces

Info

Publication number: WO2009002815A1
Application number: PCT/US2008/067599
Authority: WO
Inventors: Christophe Ducret; Eric Amaral
Original assignee: Ocv Intellectual Capital, Llc
Priority date: 2007-06-22
Filing date: 2008-06-20
Publication date: 2008-12-31

Abstract

The present invention relates to a process for assembly of thermoplastic pieces in which the assembly surfaces of the pieces to be assembled are covered with glue, and they are put in contact, at least one of the pieces to be assembled, based on thermoplastic material(s), integrating at least one fluffy material in such a way that this material at the same time projects in part from the assembly surface of the piece and is in part integrated in said piece. The invention also relates to the pieces that are used, to their manufacturing, and to the products obtained.

Description

PROCESS FOR ASSEMBLY OF THERMOPLASTIC PIECES

TECHNICAL FIELD AND INDUSTRIAL APPLICABILITY OF THE INVENTION

The present invention relates to the assembly (or connection or binding) of at least one piece based on thermoplastic material(s) with another piece; it relates particularly to the assembly of pieces based on thermoplastic material(s) with one another, and in particular relates to a process making it possible to effectively bind together pieces of varied shapes and sizes, particularly pieces of large size (such as boat hull elements which can amount to a few meters), in particular when the thermoplastic organic materials of the piece or pieces to be assembled are polyolefms.

BACKGROUND OF THE INVENTION

There are a number of methods for assembly of thermoplastic pieces, in particular assembly by simple glue coating, assembly by heat-melting (consisting of melting the parts to be assembled on the surface and assembling said parts by applying pressure), particularly by mirror welding or laser welding or induction welding or infrared welding or ultrasonic welding or welding by injection of current, and mechanical assembly by use of rivets, clips, screws, and/or by the presence of matching shapes (fitting together) on the pieces to be assembled. These methods are sometimes constraining and/or expensive and can be unsuitable or ineffective, particularly when the pieces to be assembled are complex and/or large and/or when the shapes of the surfaces put in contact do not fit together perfectly, and/or when the materials of the pieces and/or the glues are not perfectly compatible, and/or when the thermoplastic organic material(s) of the pieces are polyolefms, etc.

The present invention therefore aims to develop an advantageous process (particularly with respect to the processes mentioned in the preceding) making possible the effective assembly of at least one piece based on thermoplastic material(s) with another piece, making possible in particular the assembly of a wide variety of thermoplastic pieces (particularly pieces of large size and/or pieces of which the shapes of the assembling surfaces do not fit together perfectly and/or pieces based on polyolefms) with one another or with other pieces. SUMMARY OF THE INVENTION

This aim is attained by the assembly (or binding) process according to the present invention, in which the assembly surfaces of the pieces to be assembled are covered with glue (or coated with glue), and they are put in contact, at least one of the pieces to be assembled, based on thermoplastic material(s), integrating at least one fluffy material (or structure or compound or product) in such a way that this material at the same time projects in part from the assembly surface of the piece and is in part integrated in said piece. In the embodiment in which the two pieces to be assembled are thermoplastic (- based) pieces, each of the pieces to be assembled preferably integrates at least one fluffy material in such a way that this material at the same time projects in part from the assembly surface of the piece and is in part integrated in said piece, the assembly surfaces of the pieces to be assembled are covered with glue, and they are put in contact in such a way that the fluffy materials impregnated with glue at least in part coincide. If necessary, the process according to the invention includes at least one preliminary step in which at least one fluffy material is integrated in each of the pieces to be assembled under consideration (thermoplastic [piece(s)] initially devoid of the aforementioned fluffy material), in such a way that this material at the same time projects in part from the assembly surface of the piece and is in part integrated in said piece, so as to obtain the aforementioned piece or pieces integrating a fluffy material. "Fluffy" or "cottony" or "downy" or "full" is understood advantageously to mean a material, in particular based on fibers, which is capable of absorbing (or being impregnated with) glue at least in part and which is capable of absorbing at least in part the thermoplastic material(s), in the melted state, of the thermoplastic piece or pieces to be assembled, so as to obtain mechanical coupling. Generally, this material also advantageously has a softening temperature or melting temperature higher than the melting temperature of the thermoplastic (organic) material composing the piece or pieces to be assembled (this material being generally polypropylene, for example), so that it can be integrated effectively in said pieces during their manufacturing (as explained later on), and allows partial absorption (or impregnation) by said thermoplastic material (or matrix) so that it can project in part from said piece or pieces. Preferably also, this fluffy material is flexible or supple or deformable, so that in particular it can be draped correctly on the pieces to be assembled and if necessary, compensate for the surface imperfections.

Examples of preferred fluffy materials will be given subsequently. The process according to the invention, while remaining simple and fast, makes possible the effective and economical assembly of thermoplastic pieces (for example, metallic pieces, etc.), this assembly combining types of coupling (particularly mechanical, chemical) and intermediate materials for better binding at the interface between the pieces, this process in particular making possible the assembly of pieces of large sizes (for example, boat hulls on the order of 4 m in length) and/or pieces whose assembly surfaces are not planar or do not coincide exactly.

The pieces to be assembled are thermoplastic pieces generally formed by at least one thermoplastic organic material (chosen, for example, from the polyolefins, particularly polyethylene (PE), polypropylene (PP), the thermoplastic polyesters, particularly ethylene polyterephthalate, butylene polyterephthalate, the elastomers, particularly an ethylene- propylene polymer (EPDM), or polyvinyl chloride (PVC), or the polyamides, polyphenylene sulfide, etc.), and if necessary, by at least one material for reinforcement of this thermoplastic organic material (generally chosen from the known natural or synthetic, mineral or plant reinforcement materials, in particular from materials such as glass, carbon, aramid, etc.), this reinforcing material preferably being glass. Advantageously, the thermoplastic piece or pieces to be assembled are based on (have a thermoplastic matrix of) polyolefins (or are formed by at least one thermoplastic organic material chosen from the polyolefins such as polyethylene or polypropylene, in particular a polypropylene which, in connection with the fluffy material and the conditions of incorporation of the latter material (conditions of molding in particular, as will be explained later), makes possible the desired partial impregnation of the latter material.

The reinforcing material included if necessary in the piece or pieces to be assembled is generally present, at least in part, in the form of fibers (strands and/or filaments, the filaments being of very small diameter, for example, on the order of 5-24 microns in diameter in the case of glass, and the strands being generally formed by a number of filaments put together), with it possible for these fibers to be chopped or continuous, dispersed or assembled (parallel strips, networks of interlaced fibers, etc.), with it possible for the thermoplastic organic material to incorporate (and therefore serve as matrix for) said reinforcing fibers (or with it possible to incorporate reinforcements and/or loads in other forms), and/or with it also possible to be present at least initially and/or in part in the form of fibers. PREFERREED EMBODIMENTS OF THE INVENTION

In particular and preferably, the pieces to be assembled incorporate and/or are formed using mixed strands obtained by the simultaneous joining and spooling of organic fibers (the material of these organic fibers, if necessary, forming the thermoplastic organic material of the pieces) and of reinforcing fibers, and preferably incorporate and/or are formed using so-called co-mixed or composite strands composed of organic filaments and of reinforcing filaments mixed within the strands, these strands being generally obtained by assembly of the filaments directly during their manufacture (as described, for example, in the patents EP 0 599 695, EP 0 616 055, EP 0 367 661 and WO 98/01751 in which, during drawing of the glass filaments, organic filaments are simultaneously extruded and carried along the paths, followed by the filaments converging before said filaments are put together into at least one composite strand). The most common composite strands consisting of glass filaments (in proportions of 60-75 wt%) and of filaments of thermoplastic organic material intimately mixed are marketed under the trade name Twintex® by the company Saint-Gobain Vetrotex France. The melting of the organic material is facilitated because of the use of these co-mixed strands, making possible a gain in productivity, with it possible for the products obtained to be more homogeneous and to have improved mechanical properties with respect to the traditional products, with it also possible to better control the orientation of the reinforcing strands in the finished product. Preferably, the percentage of reinforcements (or of reinforcing material) in the pieces to be assembled is on the order of 20-70 wt% of the pieces, and the percentage of possible loads (such as calcium carbonate, talc, kaolin, micas, aluminum hydrate, etc., used, for example, for improving the dimensional stability) is on the order of 0-20 wt%, the total percentage of reinforcements and loads not exceeding 80 wt%. Generally, the piece or pieces to be assembled are present at the time of assembly in rigid or consolidated form, shaped in particular by rolling and/or molding (for example, using networks of the composite strands mentioned in the preceding), and incorporate, at the time of assembly, at least one fluffy material as defined according to the invention.

The fluffy material is generally a fibrous material, but it can also be a foam or any other material capable of at least partially absorbing the glue and the melted thermoplastic materials of the thermoplastic piece or pieces to be assembled. For this purpose, it preferably has a porosity between 70 and 99%, and particularly between 75 and 95%, and particularly between 85 and 92%, the porosity being defined by the following equation: M.

P = IOO x i - p ^χ ( ∑^ )

X=I P_x in which:

P is the porosity in %, n is the number of materials (thermoplastic, reinforcing, etc.) with different densities present in the fluffy material,

M_x is the weight fraction of material x with respect to the weight of the fluffy material, p_x is the density of material x (in g/cm³), p is the density of the fluffy material (in g/cm ). In the advantageous case in which the fluffy product is formed by a single material

(for example, a polymer material, in particular in the form of fibers, or even of a foam, or a reinforcing material such as glass, in particular in the form of fibers), P = 100 x [1 - p x (Mi / pi)] with Mi = 100% = 1, pi being the density of the material forming the fluffy material; more simply, P = 100 x [1 - p/pi]. In another case, for example, in which the fluffy product is formed by two materials (for example, a polymer material (material No. "1") and a reinforcing material such as glass or another polymer material (material No. "2"), in particular in the form of intermingled fibers or reinforcing fibers impregnated with polymer), P = 100 x [l - p x ((Mi/pi) + (M₂/p2))], Mi and pi being respectively the weight fraction and the density of polymer material 1 , and M₂ and p₂ being respectively the weight fraction and the density of the reinforcing material or of the other polymer material.

The fluffy material is preferably present in the form of a set (in two or three dimensions) or network (woven or nonwoven) of interlaced or intermingled fibers, for example, in the form of a web or a mat or a felt (three-dimensional set of fibers connected, for example, by needle bonding or fluid jet) of continuous or chopped strands, or else in the form of a fabric or a bundle of strands connected together by connecting strands, etc., with it possible for the fibers to be natural fibers, plant fibers (cellulosic fibers, etc.), mineral fibers (glass, basalt, etc.), synthetic fibers (polymer, for example, polyester, acrylic, polyaramid, etc.), etc. As various non-exhaustive examples, it can be a matter of a polymer web or felt, of a mat of continuous or chopped glass strands, etc., or even of a set of fibers of carpet type, cotton wool, cotton fabric, etc. In a preferred embodiment illustrated later on, it is advantageously a matter of at least one (or at least one layer of) polyester (-fiber-based) web or felt.

Preferably, when the fluffy material is a fibrous material, in particular, when it is in the form of a network of intermingled fibers, it also has a surface density (or grammage) of at least 150 g/m², and in particular between approximately 250 and 1000 g/m², in order to promote the desired partial impregnation, the surface density varying if necessary as a function of the thickness and of the material of the pieces to be assembled, and as a function of the molding conditions.

The fluffy structure (formed by one or more identical or different fluffy materials as defined in the preceding) is preferably partially integrated in the pieces to be assembled during the manufacturing process of these pieces, in particular, during the molding which generally enables one to obtain said pieces. As already mentioned and as a function of the thermoplastic material of the pieces, the fluffy material(s) is (are) advantageously chosen (choice, in particular, of the material(s) constituting them) in such a way that they do not melt during said molding, and in such a way that, in conjunction with controlled molding conditions (in particular, the duration of molding depending on the pieces to be molded), they are only partially impregnated by the thermoplastic material of the piece during plastic flow of said material during molding. The fluffy material(s), after removal of the piece from the mold, are thus in part taken into the piece and in part project from said piece.

The preferred molding process for shaping the thermoplastic pieces to be assembled according to the invention is vacuum molding, but (thermo)compression molding can also be used, or even possibly another molding process or obtaining process (for example, by rolling), the manufacturing of said pieces being generally brought about with heat and under pressure.

During this molding, the constituents of the piece to be obtained, for example, in the form of one or more identical or different layers, are inserted in the mold, with it possible for the fluffy material(s) to be arranged in the mold before the layers which are to form the bare thermoplastic piece (without the fluffy material) and/or simultaneously and/or consecutively, depending on the mold and on the type of piece to be formed, the fluffy material(s) being present, for example, in the form of one or more strips or pieces, before closing of the mold and molding under the conditions of temperature, pressure, vacuum, etc., necessary for molding of the piece, these conditions being adjusted with respect to the conditions necessary for the molding of the originally desired piece (bare piece) so as to make possible the partial impregnation of the fluffy material(s) by the material capable of plastic flow of the formed piece.

The constitutive layers (or the blanks or inserts) of the originally desired piece and as inserted in the mold can, for example, be one or more of the following layers: networks of strands of the type of fabric(s) or knit(s) or non-woven(s), strips of parallel strands crossed and/or connected together by connecting strands and/or filaments (made of glass and/or polymer) based on continuous or chopped strands, with or without one or more preferential directions of orientation of the strands and/or of the reinforcing material (if necessary), continuous or solid or consolidated layers (layers in which, in general, the organic material has been melted in order to form a matrix in which the reinforcing fibers are buried, if necessary, and/or assembled layers, for example, assembled with heat and under pressure), for example, in the form of slabs or sheets; the fibers and/or strands can at least in part be reinforcing fibers, possibly impregnated, and/or composite strands, and can be continuous and/or chopped depending on the layers, layers of organic material such as layers or films of polypropylene, etc., and preferably integrate at least one layer formed by a network of intermingled composite strands (mentioned in the preceding).

If necessary, elements such as inserts (for example, metallic inserts, etc.) can also be added. If necessary, the step of packing the mold can also be preceded by a step of pre- forming and/or preliminary heating of the elements and/or layers which are to constitute the molded piece so as, for example, to give the layers a certain flexibility and to make them more capable of draping the mold, and/or so as to facilitate molding. If necessary, at least parts of the mold can be treated before packing with at least one product capable of aiding in the later removal of the molded piece from the mold. The fluffy structure (in one or more parts) is generally arranged over at least a part of the assembly surfaces (surfaces and/or groups of zones intended for being put in contact during assembling) of the pieces to be assembled, or even over the entire assembly surfaces, and when the two pieces to be assembled are provided with this (these) fluffy material(s), they are preferably arranged in such a way that, during assembly, the fluffy materials of the two pieces to be assembled at least partially and preferably mostly or entirely coincide.

The assembly of the pieces according to the invention is brought about by coating

(covering) the assembly surfaces and the part or parts of the fluffy material projecting from said surfaces with glue, and then putting said surfaces in contact, under pressure if necessary, in order to maintain the contact between the two pieces during drying and/or hardening and/or cross-linking, etc., of the glue, in such a way that, when the two pieces to be assembled are provided with this material, the fluffy materials impregnated with glue coincide (or overlap or intermingle) at least partially, and preferably mostly or even entirely.

The glue which is used is generally and preferably chosen as a function of the material of the pieces to be assembled, and can, for example, be a resin or a glue which is capable of polymerizing cold (at room temperature), which is capable of thermosetting or which is thermoplastic, a single- or two-component glue, a hot-melt, etc., for example, a glue based on at least one organic material chosen from the polyolefms (polyethylene, polypropylene, ...) or from the polyesters, or a glue based on an epoxy resin, or a glue of the acrylic, polyurethane or elastomer (neoprene, etc.) type, etc. In a preferred embodiment, the gluing takes place at room temperature (particularly between 10 and 45⁰C, 113⁰F).

The present invention also relates to the thermoplastic piece which is developed and used for the process according to the invention, this piece being based on thermoplastic material(s) and integrating at least one fluffy material in such a way that this material at the same time projects in part from the piece (on at least a part of its surface corresponding generally to its future surface of assembly with other pieces) and is in part integrated in said piece.

The present invention also relates to a process for obtaining the preceding piece, according to which the fluffy material is integrated in the piece during its manufacture (in particular during its molding), as already described in the preceding. The present invention also relates to the (composite) product which is obtained, in particular according to the process of the invention, by assembly of two pieces, including at least one thermoplastic piece, this product having at least one intermediate layer (that is, between two other layers) formed by at least one fluffy material impregnated with glue, and/or including at least one fluffy material of which a part is impregnated with glue and of which another part (or the other part or the remaining part) is impregnated with at least one thermoplastic material. The fluffy material is at least in part in an intermediate layer also containing the glue and at least in part in a layer (generally external) also containing at least one thermoplastic material (if necessary, at least one material for reinforcing of said material). In one embodiment (product coming particularly from the assembly of two thermoplastic pieces by the process of the invention), the intermediate layer contains at least two fluffy materials, impregnated with glue, which are in contact (superposed, mixed, intermingled, etc.), and the product also has at least two external layers based on thermoplastic materials (identical or different) enclosing (or sandwiching) the intermediate layer, one of the fluffy materials being in part buried in (impregnated with) the thermoplastic material of one of the external layers, and the other being buried in the thermoplastic material of the other layer. The product assembled according to the invention has a good cohesiveness between the different elements composing it and good mechanical strength properties. This product can constitute the finished product or only form a part of it, and can undergo other treatments for the purpose of obtaining the final product (painting, etc.).

The following examples illustrate the present invention without limiting it. In these examples, the assembly of two pieces is compared, pieces which are identical to one another and each of which is obtained by vacuum molding of a fabric based on glass/polypropylene composite strands containing 60 wt% glass and having a surface density on the order of 745 g/m², the molding temperature and pressure being the temperature and pressure necessary for the plastic flow of the organic material (polypropylene), the pieces to be assembled which are obtained being presented (cut) in the form of test pieces with the dimensions 120 x 20 x 1 mm, these pieces undergoing or having undergone the following treatments:

- Reference Example 1 : no treatment;

- Reference Example 2: pumicing the surface;

- Example 1 according to the invention: insertion in each piece, during its molding, and with care taken that the molding time allows only partial impregnation, of the fluffy material by the polypropylene (in this case, a duration of heating of 20 min), of a fluffy material in such a way that this material projects from a part (with dimensions 20 x 40 mm) of one side of the test piece in one of its ends, the fluffy material being one of the following materials: - Example Ia: a mat of chopped glass strands with a surface density on the order of

500 g/m²; - Example Ib: a needle bonded mat of chopped glass strands, obtained according to the process described in the patent FR2862987, with a surface density on the order of 500 g/m²;

- Example Ic: a stitched mat of chopped glass fibers with a surface density on the order of 800 g/m²;

- Example Id: a polyester (strand-based) web/felt with a surface density on the order of 250 g/m² and marketed under the reference T- 1700-046 by the company Freudenberg;

- Example Ie: two polyester (strand-based) webs/felts each with a surface density on the order of 150 g/m² and marketed by the company Pont Aurel.

The test pieces are then glued onto one another over an area of 40 x 20 mm (assembly surfaces where the fluffy materials project), the fluffy materials (mats or webs/felts) of the two pieces coinciding in Examples 2a to 2e [sic]. Used as glue is an inexpensive adhesive used in sailing and which polymerizes cold (at room temperature), formed from 100 g of polyester resin marketed under the reference Synolite 1717 by the company Loctite, 1.5 g of butanox peroxide, and 80 g of curing agent marketed under the reference NL 51 P by the company Akzo Nobel. The gluing time does not exceed one hour at room temperature.

The tensile stress at break is then measured according to the standard ISO 527. The values obtained are the following: Reference 1 : 0.02 MPa, Reference 2: 1.78 MPa;

Example Ia: 3.09 MPa; Example Ib: 3.87 MPa; Example Ic: 2.84 MPa; Example Id: 9.1 MPa; Example Ie: 8.97 MPa. It is observed that the assembly according to the invention has a particularly high performance in comparison in particular with the reference methods, the break occurring moreover in the jaws of the traction machine or in one of the pieces (and not at the interface) in the case of Examples 2d and 2e. Furthermore, the polyester glue is in this case particularly satisfactory in combination with the materials used and the process of the invention.

The products assembled according to the invention can be different types of products such as boat parts, (deck, hull, stiffeners), etc.

Claims

WHAT IS CLAIMED IS:

1. A process for assembly of thermoplastic pieces, in which the assembly surfaces of the pieces to be assembled are covered with glue, and they are put in contact, at least one of the pieces to be assembled, based on thermoplastic material(s), integrating at least one fluffy material in such a way that this material at the same time projects in part from the assembly surface of the piece and is in part integrated in said piece.

2. A process according to Claim 1, in which the two pieces to be assembled are thermoplastic pieces, characterized by the fact that each of the pieces to be assembled preferably integrates at least one fluffy material in such a way that this material at the same time projects in part from the assembly surface of the piece and is in part integrated in said piece, and by the fact that the assembly surfaces of the pieces to be assembled are put in contact in such a way that the fluffy materials impregnated with glue coincide at least in part.

3. A process according to Claim 1 or 2, characterized by the fact that it includes at least one preliminary step in which at least said fluffy material is integrated in each of the pieces to be assembled under consideration initially devoid of said fluffy material in such a way that this material at the same time projects in part from the assembly surface of the piece and is in part integrated in said piece, so as to obtain said piece or pieces which integrate a fluffy material.

4. A process according to one of Claims 1-3, characterized by the fact that the thermoplastic pieces to be assembled are based on polyolefms.

5. A process according to one of Claims 1-4, characterized by the fact that the thermoplastic pieces to be assembled incorporate and/or are formed using composite strands.

6. A process according to one of Claims 1-5, characterized by the fact that the fluffy material has a porosity between 70 and 99%.

7. A process according to one of Claims 1-6, characterized by the fact that the fluffy material is a fibrous material, in particular in the form of a network of intermingled fibers, for example, in the form of a web or felt or mat of continuous or chopped strands.

8. A process according to Claim 7, characterized by the fact that the fluffy material is a polyester web and/or felt.

9. A process according to either of Claims 7 and 8, characterized by the fact that the fluffy material has a surface density of at least 150 g/m², and in particular between approximately 250 and 1000 g/m².

10. A process according to one of Claims 1-9, characterized by the fact that the glue is chosen from among the resins or glues which are capable of polymerizing at room temperature, which are capable of thermosetting or which are thermoplastic, single- or two-component glues, hot-melt glues, and for example, is a glue based on at least one organic material chosen from the polyolefms or the polyesters, or based on an epoxy resin, or of acrylic or polyurethane or elastomer type.

11. A process according to one of Claims 1-10, characterized by the fact that the gluing takes place at room temperature.

12. A thermoplastic piece, suitable for implementation of the process according to one of Claims 1-11, this piece being based on thermoplastic material(s) and integrating at least one fluffy material in such a way that this material at the same time projects in part from the piece and is in part integrated in said piece.

13. A process for obtaining the piece according to Claim 12, according to which the fluffy material is integrated in the piece during its manufacturing, in particular during its molding.

14. A process according to Claim 13, characterized by the fact that the molding of the piece is a vacuum molding or (thermo)compression molding process.

15. A product obtained by assembly of two pieces including at least one thermoplastic piece, in particular by the process according to one of Claims 1-11, this product having at least one intermediate layer formed by at least one fluffy material impregnated with glue, and/or including at least one fluffy material of which a part is impregnated with glue and of which another part is impregnated with at least one thermoplastic material.