Patent Application
20080299856
The invention relates to a process and to a device for manufacturing a composite strand formed by combining a plurality of continuous glass filaments intermingled with continuous organic thermoplastic filaments.
Processes for producing a composite strand comprising such glass filaments and an organic thermoplastic are already known.
EP-A-0 367 661 describes a process employing a first installation comprising a bushing that contains molten glass, from which continuous glass filaments are attenuated, and a second installation comprising a spinning head, supplied under pressure with an organic thermoplastic that delivers continuous filaments. During assembly, the two types of filaments may be in the form of webs, or in the form of a web and a strand.
This process allows a composite strand to be obtained in which the thermoplastic filaments surround the glass filaments, which are thus protected from the effects of abrasion due to rubbing on the members for guiding, assembling and collecting said strand.
EP-A-0 505 275 proposes a process for manufacturing a composite strand similar to that described above in EP-A-0 367 661, which uses at least one spinning head normally used in the industrial field of synthetic fibers.
This document recommends drawing the organic filaments into one or more webs defining, partly or completely, a region or conical or pyramidal shape comprising an open sector via which the glass strand is introduced.
Document EP-A-0 599 695 describes the manufacture of a composite strand consisting of commingled glass filaments and thermoplastic filaments which consists in combining a bundle or web of continuous glass filaments emanating from a bushing with a web of continuous thermoplastic filaments produced from a spinning head, said thermoplastic filaments having, during their penetration into the glass web or bundle, a drawing speed greater than the speed of the glass filaments.
The improvement consists here in overdrawing the thermoplastic filaments in order to compensate for their shrinkage, thereby making it possible to obtain a composite strand exhibiting no waviness during its formation and being stable over time.
EP-A-0 616 055 also proposes a process for producing a glass/thermoplastic composite strand by commingling a web of thermoplastic filaments with a bundle or web of glass filaments, in which the thermoplastic filaments upstream of the point of convergence are heated to a temperature above their relaxation temperature drawn and then cooled.
Finally, WO-A-02/31231 describes the manufacture of a glass/thermoplastic composite strand of high linear density. According to that process, the glass filaments and the thermoplastic filaments are divided into several webs, at least one thermoplastic web is mingled with each glass web and the filaments are gathered together into at least one composite strand. This process helps to improve the commingling of the filaments.
The composite strand obtained by the processes that have just been described has the desired properties for producing composite products with a fiber-reinforced thermoplastic matrix. In particular, its mechanical properties have a satisfactory level of performance, which is assessed by the good quality of the bonding between the thermoplastic matrix and the material that reinforces it.
However, certain applications require the composite product to be provided with additional properties, for example the ability to be fire resistant and/or resistant to ultraviolet and/or heat, the possibility of being colored and the capability of conducting electrical current.
Conventionally the intended properties are obtained by treating the composite strand or assemblies of these strands (meshes, mats, wovens, knits, braids) with appropriate compounds, such as fire retardants, antioxidants and thermal stabilizers, dyes, and conductive fillers in order to fulfill the aforementioned functions. The way in which the treatment is carried out is known and this may especially be powder coating, spraying, immersion in a bath of liquid material (solution, dispersion or emulsion) or molten material, or coating. The treatments are generally carried out by the final user and require particularly expensive and bulky installations that generate problems (dust, moisture, etc.), which have, among other drawbacks, that of being able to treat only the surface of the strand.
Now, it proves to be beneficial to be able to treat the composite strand “right to the core” by incorporating compounds capable of fulfilling the aforementioned functions within the constituent filaments of the strand, more particularly on or in the thermoplastic material in the filamentary state.
This task is made difficult by the fact that said compounds are not usually “spinnable” and that, as a consequence, they cannot be introduced in the form of filaments into the composite strand.
Furthermore, usually said compounds are chemically incompatible or barely compatible with the thermoplastic of the filaments. Now, it is known that in general the deposition of such compounds on filaments in the course of formation or their introduction into the thermoplastic before spinning, for example into the extruder that feeds the spinning head, upsets the spinning operation or even makes it impossible.
Moreover, the quality of the spinning of the thermoplastic filaments must be as constant as possible, especially as regards the diameter of the filaments, given that these have to be combined with the glass filaments and that consequently this combining operation must not disturb the fiberizing of the glass either.
The subject of the present invention is a process for manufacturing a composite strand that makes it possible to incorporate nonspinable compounds in the filamentary stage and to provide the composite strand with specific properties “right to the core”.
The problem posed by introducing nonspinable compounds into the composite strand is solved by a process for manufacturing a composite strand formed by combining continuous glass filaments emanating from at least one bushing with continuous thermoplastic filaments emanating from at least one spinning head, these filaments being drawn and commingled in the form of a web into a bundle or web of glass filaments, in which the thermoplastic filaments are obtained by coextruding a main organic thermoplastic with a secondary organic thermoplastic containing at least one nonspinable compound.
The term “nonspinable compound” is understood here to mean a compound that is not capable of giving filaments under the conventional conditions of extrusion-spinning processes.
The term “main organic thermoplastic” is understood to mean the organic thermoplastic present in a major amount, which constitutes as it were the core of the thermoplastic filaments and serves as support for the nonspinable compound(s) blended with the thermoplastic present in a minor amount, as will be explained below. For the sake of simplification, the main organic thermoplastic will be called hereafter “main material”.
The term “secondary organic thermoplastic” is understood to mean the blend of the organic thermoplastic present in a minor amount with at least one nonspinable compound as such. The secondary organic thermoplastic will be denoted hereafter by “secondary material”.
The coextrusion allows the secondary material in melt form to be incorporated into the main material, also in melt form, and be transported by the core filaments when they are drawn.
According to a first preferred embodiment, the coextrusion is carried out under conditions such that the secondary material is distributed over all or part of the surface of the main material serving as core. The secondary material may be uniformly distributed or randomly distributed on the main material, and it may take the form, for example, of a continuous or discontinuous coating, or of clumps (platelets, droplets etc.). The form that the secondary material can adopt is not critical, the essential point being that it is capable of serving as a carrier for the nonspinable compound(s). The nonspinable compound(s) especially when in the form of particles, may be entirely included in the secondary material or partly therein, the other part being in the main material and/or being free on the surface.
According to another embodiment, the coextrusion is carried out under conditions such that the secondary material is included in the main material. The distribution of the secondary material within each thermoplastic filament depends on the spinning head used, as will be explained later. This procedure makes it possible to introduce the nonspinable compound(s) into the thermoplastic filament. However, the spinning under these conditions is more tricky than previously. Because of the imperfect extrusion of the secondary material, due to the presence of nonspinable compound(s), the filaments have a diameter that varies over the course of time, giving in the end a strand having a more irregular linear density.
The coextrusion makes it possible to introduce compounds that are intrinsically nonspinable onto or into the thermoplastic filaments. After the thermoplastic filaments thus produced have been combined with the glass filaments, the composite strand has “right to the core” specific functions that depend on the nature of the nonspinable compounds that it contains.
The organic thermoplastics of the main material and of the secondary material must be, at least partly, chemically compatible so as to avoid problems of delamination of these materials.
The main material is chosen from polyolefins such as polyethylene and polypropylene, polyesters such as polyethylene terephthalate and polybutylene terephthalate, polyamides such as nylon-6, nylon-6,6 and nylon-12, polyphenylene sulfide and polyurethanes. Preferably, polypropylene is used.
The organic thermoplastic of the secondary material may be chosen from the organic thermoplastics mentioned in the case of the main material in the previous paragraph. It may be of the same or different nature. Preferably, the main and secondary materials are of the same nature.
The nonspinable compounds may be:
The amount of main material represents at least 50%, preferably 70 to 95%, of the total weight of the thermoplastic filaments the balance to 100% being represented by the secondary material.
The weight content of nonspinable compound(s) in the secondary material is less than 80%, preferably varying from 1 to 50% and better still varying from 10 to 30%.
In the strand, the content of nonspinable compound(s) varies depending on the chemical nature and the properties to be conferred on the composite strand and to be given to the final composite obtained from this strand. In general, the amount of nonspinable compound(s) represents 0.1 to 30% preferably 0.5 to 15% by weight of the thermoplastic. Above 30%, the spinability is greatly reduced, with a high risk of breaking the thermoplastic filaments or breaking the glass filaments during the combining with thermoplastic filaments having substantial irregularities, for example in terms of the diameter or the distribution of the nonspinable compound(s).
Thanks to the invention, the nonspinable compounds are included in the composite strand in the filamentary stage and are not distributed just on the surface of the strand as is known hitherto. The nonspinable compounds may be incorporated into the composite strand in a large amount without the spinning of the thermoplastic filaments being disturbed thereby.
Another advantage of the process is that it allows one or more nonspinable compounds to be deposited in a constant amount by precise control of the output, which is difficult to achieve with certain treatments such as powder coating and other coating treatments.
Yet another advantage of the process is that it can be modulated and it allows the nonspinable compound(s) to be changed in a very short time since only one feed for said compound(s) is needed per spinning head. Consequently, it is easy to purge the device and make it operate with a new blend of the same secondary material or with another one, with one or more other nonspinable compounds. In the event of an incident, the restart operation in the spinning head is also easier.
The invention also proposes a device for implementing this process.
According to the invention, to manufacture the composite strand formed from continuous glass filaments and continuous organic thermoplastic filaments, this device comprises, on the one hand, an installation comprising at least one bushing supplied with molten glass, the lower face of which has a very large number of holes, this bushing being combined with a coater, and, on the other hand, an installation comprising at least one spinning head suitable for coextrusion and supplied under pressure with the main material in melt form and with the secondary material also in melt form, this spinning head having a very large number of holes and being combined with means for drawing and spraying said filaments for the purpose of mingling them with the glass filaments, and finally means common to the two installations for assembling and optionally winding at least one composite strand.
When the strand is not collected in the form of a wound package, the device includes a moving receiving support, for example a conveyor belt, onto which the strand, following assembly of the filaments, is directly projected so as to form a continuous strand mat.
The device may further include a chopper that cuts up the strand before it is projected onto the receiving support, in order to form a chopped strand mat or granules that can be used for example to produce injection-molded or compression-molded parts.
The bushing supplied with molten glass preferably has 400 to 8000 holes from which the glass filaments are attenuated.
The spinning head may be chosen from known spinning heads, in particular those known for producing multicomponent textile strands. Preferably, the spinning head has 400 to 8000 holes from which the main and secondary materials are coextruded.
Combined with the spinning head are two extruders used for supplying molten organic thermoplastics, one for the main material and the other for the secondary material.
The spinning head includes a spinneret plate provided with a very large number of holes preferably distributed in the form of a ring or of a series of concentric rings from which the main material and the secondary material are coextruded in order to form filaments that are drawn before being commingled with the glass filaments.
Preferably, the spinning head has an internal geometry allowing the main material and the secondary material to be delivered separately right to the spinneret plate. The spinning head is thus suitable for distributing the materials in such a way that the main material flows as the predominant stream of all the extruded materials and serves as a carrier for catching and transporting the secondary material that contains the nonspinable compound(s).
The flow rates of the materials are controlled so that the stream of the main material represents at least 50%, preferably 70 to 95%, by weight of all of the materials entering the spinning head.
The spinning heads according to the invention make it possible to obtain filaments in which either the secondary material lies on the periphery and the main material occupies the center, for example of the orange segment type (
Spinning heads that allow the secondary material to be distributed around the periphery of the main material or that allow the main and secondary materials to be juxtaposed are preferred.
The means for drawing the thermoplastic filaments may for example be a drawing unit of the type comprising drums, which is described in WO-A-98/01751 or EP-A-0 599 695. The thermoplastic filaments are drawn prior to being and commingled with the glass filaments, which makes it possible to limit their shrinkage and to prevent waviness in the composite strand. Such a strand proves to be advantageous for producing cross-wound packages.
Advantageously, the drawing unit is of the type described in EP-A-0 616 055. It comprises at least three groups of drums, the first group being composed of heated drums. The second group comprises drums rotated at a speed higher than that of the preceding drums and the third group comprises cooled drums rotated at a speed identical to that of the last drum of the second group. The additional heating/cooling step improves the stability of the strand over time.
The means for projecting the thermoplastic filaments may be formed by the combination of two rolls, namely a first guide roll, which serves to direct the web of thermoplastic filaments toward a second roll, where the commingling with the glass filaments takes place (see EP-A-0 616 055), or this means may consist of a Venturi system.
These means cause intermingling of the glass filaments on the one hand and the thermoplastic filaments on the other, these filaments arriving with identical speeds. The commingled filaments are thus linear. Preferably, the speed of projection of the thermoplastic filaments into the glass filaments is of the order of 1000 meters per minute.
In a variant, it is possible to obtain composite strands whose glass filaments are linear and whose thermoplastic filaments are wavy. This type of relatively bulky strand is desirable in certain textile applications requiring good “covering” power. To do this, all that is required is to modify the speed of rotation of the drums of the drawing unit so as to give the thermoplastic filaments a higher speed than that of the glass filaments before they are commingled.
The devices described make it possible to produce a composite strand consisting of glass filaments and thermoplastic filaments containing nonspinable material distributed in the strand, either on the surface or within the thermoplastic filaments, unlike the strands of the prior art in which said material lies only on the surface of the strand.
Such devices also have the advantages of taking up less room in the spinning heads, of being able to be fitted onto an existing installation usually having several positions for fiberizing the glass, without requiring consequent modifications, and of allowing the spinning head maintenance and cleaning operations to be carried out without disturbing the operation of the rest of the manufacturing line.
A further subject of the invention is the composite strand obtained according to the process of the invention.
This strand preferably consists of 400 to 8000 glass filaments and 400 to 8000 thermoplastic filaments. The glass filaments may be made of any known type of glass, for example AR (alkaline-resistant) glass R-glass, S-glass or E-glass, the latter being preferred.
The linear density of the composite strand is at least equal to 100 tex and at most equal to 10 000 tex. Preferably, the linear density is at least 500 tex and advantageously at least 1500 tex.
This glass/thermoplastic composite strand may be used to produce parts made of composites consisting of a thermoplastic matrix reinforced by glass strands using the techniques of pultrusion and filament winding. The strand may also be used to produce intermediate products, such as mats, wovens, knits and braids, suitable for vacuum molding, bladder molding membrane molding and compression molding. If appropriate, these products may undergo a heat treatment for the purpose of partially melting the thermoplastic so as to consolidate their structure and allow better handling.
Further details and features of the invention will become apparent on reading the detailed description below, illustrated by the following figures:
a-2c show a longitudinal sectional view of spinning heads according to the invention at a coextrusion orifice; and
a-3e show a cross-sectional view of the thermoplastic filaments obtained according to the invention.
The invention illustrated in
The bushing 1, whatever the type of feed, is generally made of a platinum-rhodium alloy and is heated by resistance heating so as to keep the glass at a high temperature or to remelt it, depending on the case. A multitude of streams of molten glass flow from the bushing 1, these being attenuated in the form of a bundle 2 by a device (not shown), which also forms the wound package 3. Placed in the path of the bundle 2 is a coating roll 4, for example made of graphite, which deposits on the glass filaments a size composition intended to prevent or limit the rubbing of the filaments on the various members with which they come into contact. The size may be any known aqueous or anhydrous (containing less than 5% water) size and it may contain compounds which form part of the composition of the thermoplastic filaments 5 that will combine with the glass filaments to form the composite strand 6.
Thermoplastic filaments 5 are extruded from the spinning head 7, which is shown schematically. The spinning head is fed with the molten main material coming from the extruder 8 (not shown) fed with granules and with the secondary material, which is also molten, comprising the blend of a molten organic thermoplastic and a nonspinable compound, output by the extruder 9 (not shown) fed with granules of organic thermoplastic and of powder of a nonspinable compound.
The main and secondary thermoplastics flow under pressure into the spinneret and are extruded through the very many holes in a spinneret plate into filaments 5 that are immediately drawn. As soon as they are formed, the filaments 5 are cooled by a blowing device 10 supplied with a gaseous fluid. The filaments then pass over a roll 11, which makes it possible on the one hand, to gather them in the form of a web 12 and, on the other hand, to deflect their path. The web 12 is then directed toward the drum drawing unit 13 which here consists of six drums 14, 15, 16, 17, 18 and 19.
The drums 14, 15, 16, 17, 18 and 19 have different speeds so that they create an acceleration in the run direction of the web 12. Here, the drums operate in pairs—associated with the drums 14, 15 forming the first pair is a heater, for example an electrical heater (not shown), which makes it possible, by contact, to increase the temperature of the thermoplastic filaments uniformly and rapidly. The rise in temperature depends on the nature of the thermoplastics used. The drums 14, 15 are rotated at the same speed, which allows the thermoplastic filaments 5 to be drawn from the spinning head 7.
The second pair of drums 16, 17 is rotated at a higher speed than that of the first pair. The web 12 of thermoplastic filaments heated by passing over the first pair of drums 14, 15 undergoes an acceleration due to the difference in speed of the two pairs of drums, which acceleration results in an elongation of the filaments of the web 12 and modifies their structure.
The last pair of drums 18, 19 is rotated at the same speed or a higher speed than that of the previous pair and includes a cooling device (not shown), for example of the water-jacket type, which allows the structure of the filaments of the web 12 to be set.
The web 12 of thermoplastic filaments is heated and cooled rapidly and uniformly.
The drawing unit 13 may have a larger number of drums, provided that they comply with the three aforementioned zones, namely heating, drawing and cooling. Moreover, each of these zones may consist of only a single drum. The drawing unit may also consist of a succession of groups formed by the three zones that have just been mentioned.
The web 12 of thermoplastic filaments then passes over a deflecting roll 20 and through a Venturi system 21 which keeps them as individual thermoplastic filaments and projects them into the sheet of glass filaments 22 coming from the bundle 2. The device 21 operates by an injection of compressed air and it imparts no additional speed to the web 12, thereby limiting the risk of said glass filaments being disturbed.
The web 12 of thermoplastic filaments and the web 22 of glass filaments are joined between the coating roll 4 and the device 23 for assembling the composite strand. This arrangement makes it possible to correctly adapt the geometry of the glass web and to uniformly distribute the two types of filaments. A deflector 24 provided with notches keeps the filaments in place in particular along the edges, and helps to reduce any disturbance suffered by the glass web 22 at the moment when the web 12 of thermoplastic filaments is projected into it.
The web 25 of intermingled glass and thermoplastic filaments is assembled by the device 23 into a strand, which strand is immediately wound up into the package 3 thanks to the winding device (not shown) that operates at a given linear speed kept constant in order to guarantee the desired linear density.
This linear space which allows the glass filaments to be drawn, is in this case identical to that which the drums 18, 19 impart on the web 12 of thermoplastic filaments. In this way, the thermoplastic filaments have the same speed during the mingling and the composite strand, on its formation, has no waviness.
a-2c are longitudinal sectional schematic views of the spinning head illustrated schematically in
In
b illustrates a second embodiment for obtaining a filament 31 in which the main material 26 and the secondary material 28 are distributed as illustrated in
c illustrates a third embodiment for obtaining a filament 31 in which the secondary material 28 is included within the main material 26 as shown in
The main material 26 (shown in black) and the secondary material 28 (shown in white) are distributed in various ways in the filament.
In
In the filaments shown in
In the filament shown in
A composite strand was produced in the installation illustrated in
The strand consisted of 1600 E-glass filaments 18.5 μm in diameter and 1600 thermoplastic filaments obtained by coextruding polypropylene with a polypropylene/carbon black compound. The composite strand contained 75% glass, 24.4% polypropylene and 0.6% carbon black by weight. The strand had an intense black color allowing composite parts to be produced, especially by molding, which satisfied the color conditions imposed by automobile manufacturers.
For comparison, a composite strand was produced under the same conditions as above but modified in that the coextrusion spinning head was replaced with a “one-component” spinning head fed by a single extruder containing polypropylene and carbon black. The strand obtained contained 0.6% (control A) and 0.2% (control B) by weight of carbon black.
A molded part was produced under the following conditions from the composite strand obtained.
The composite strands coming from six packages were assembled, the strands then passing into an oven at 220° C. and then into a die heated to the same temperature in order to form a rod which was then cooled by spraying water at room temperature (20° C.) and cut to a length of 12 mm in order to form granules. These granules were introduced into a molding machine in order to form a molded part.
The following table gives the characteristics of the composite strands and of the molded parts obtained from these strands.
For the same amount of carbon black, the invention makes it possible to obtain a composite strand having better spinability than that of Control A, the latter giving rise to numerous breakages and an effective composite strand fiberizing time not exceeding 50%. The fiberizing conditions for Control A are not acceptable from an industrial standpoint.
The composite strand of Control B had good spinability owing to the reduced amount of carbon blacks but this was obtained to the detriment of the color of the molded part.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0452658 | Nov 2004 | FR | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/FR05/50960 | 11/17/2005 | WO | 00 | 7/30/2008 |
