FR2864072A1 - Glass fibre coated with a sizing composition containing polyvinyl acetate, ethylene-vinyl acetate copolymer and epoxy resin, used for production of resin-fibre composites by open-mould or closed-mould methods - Google Patents

Abstract

Glass fibre coated with an aqueous sizing composition (I) containing, as adhesive film-forming agents (A) polyvinyl acetate, (B) a copolymer of vinyl acetate and another unsaturated monomer and (C) epoxy resin. Independent claims are also included for (1) sizing compositions containing an aqueous mixture (I) as above (2) composites containing a thermosetting polymer and reinforcing glass fibres coated with (I).

Description

GLASS YARN ENSIMES FOR REINFORCING MATERIALS

POLYMERS, IN PARTICULAR BY MOLDING.

  The invention relates to glass threads coated with a sizing composition for reinforcing organic materials of the polymer type, the sizing composition used for coating said yarns and the composites thus obtained.

  The glass threads used for reinforcement in general are industrially produced from molten glass threads flowing from the multiple orifices of a die. These nets are drawn mechanically in the form of continuous filaments, and are then combined into base wires which are then collected, for example by winding on a rotating support. Before their assembly, the filaments are coated with a sizing composition by passing on a suitable device such as coating rolls.

  The sizing composition proves essential for several reasons.

  During the manufacture of reinforcing son, the sizing composition protects the glass filaments from the abrasion that occurs when they rub at high speed on the various organs used to guide and collect them. It also establishes bonds between the filaments which makes it possible to give cohesion to the thread. The wire being made more integrity, its handling, especially during weaving operations, is improved and unwanted breaks are avoided.

  During the manufacture of composite materials, the sizing composition promotes the wetting and impregnation of the glass son by the matrix to be reinforced, which matrix is generally implemented in the form of a more or less fluid resin. The mechanical properties of the final composite are therefore significantly improved.

  The materials to be reinforced can integrate the glass threads in different forms: continuous or cut threads, mats of continuous or cut threads, fabrics, ...

  Composites incorporating cut glass yarns can be obtained, inter alia, by the contact molding technique of coating the interior of an open mold, without counter-mold, with resin to be reinforced and threads. glass of variable length. In the particular method of simultaneous projection molding, the resin and the cut son are projected together on the inner walls of the mold by means of a gun comprising an incorporated cutter capable of cutting the son extracted from one or more windings, in general in the form of rovings, and a device for spraying the resin, fed for example by a pneumatic pump. This process, simple and flexible, is particularly suitable for the production of single or small series of parts based on thermosetting polymers belonging to the family of polyesters or epoxies.

  Another technique for manufacturing composites, also by molding, is known under the name LFI or Long Fiber Injection. It consists in projecting into a mold, simultaneously, son cut at a high speed (of the order of 300 to 1200 meters per minute) in cycles of a duration of a few tens of seconds and reactive monomers capable of giving a resin by polymerization, and then apply a counter-mold. This technique is particularly suitable for producing polyurethane parts, especially in the form of foam.

  The quality of the composites obtained by these processes largely depends on the properties provided by the glass strands, and therefore on the size which coats them.

  In particular, it is sought to obtain compositions giving a size that can be easily wetted or impregnated on the surface by the resin to ensure close contact between the son and the resin and thus obtain the expected mechanical strength properties.

  It is also desired that these compositions are compatible with rapid implementation, in particular that the son / resin or son / monomer mixture which is sprayed onto the mold in the form of overlapping strips may spread evenly. In particular, the subsequent step of rolling already mentioned to eliminate air bubbles and ensure a better distribution of son in the resin must also be short. But also, it is necessary that the sizing composition has a certain incompatibility with the resin, that is to say that it is not too soluble in the resin so as to prevent the son / resin mixture form a compact mass that collapses by simple gravity. This parameter is important when it comes to producing thick parts requiring to project a large amount of mixture into the mold. In this case, it is desired to reduce the speed of impregnation of the wire with the resin. However, the impregnation rate should not be too low because then the son / resin mixture has a poor conformability that is to say that it is not able to perfectly fit the shape of the mold. The criterion of conformability becomes all important when the mold has a large dimension, from a few meters to several tens of meters.

  It is equally necessary that the cut threads retain their integrity and do not filamentize, that is to say do not burst while releasing the filaments that constitute them, during the projection but also during the other treatments they are such as the rolling / boiling operation already mentioned.

  It is still essential that the wire can be extracted from the roving without forming loops, without generating tension and giving the least possible wadding so as not to disturb the operation of the cutter.

  Already known glass son adapted to these molding techniques.

  In EP-A-0 869 927 there are described glass threads coated with a sizing composition comprising, as sticky film-forming agents, the combination of at least one low molecular weight polyvinyl acetate A and at least one vinyl acetate copolymer B self-crosslinkable thermally in a weight ratio A / B greater than or equal to 1. These son have a high rate of impregnation with the resin.

  In WO-A-02/059055, the glass strands are coated with a substantially aqueous size composition which comprises at least one bis-silane A and at least one unsaturated monosilane (B) selected from vinylsilanes and methyl ( acrylosilanes).

  Sizing increases the life of the cutter blades. The speed of impregnation of the threads is important.

  In FR-A-2,279,688, the glass strands are coated with a lubricant comprising an aqueous mixture based on polyvinyl acetate, a fatty acid lubricant, methacrylato chromic chloride and gamma (ethylene diamine) propyltrimethoxysilane.

  Two types of molded glass fibers marketed by Owens Corning are still known.

  The yarns belonging to the first type (reference OC 1662) are coated with a size based on polyvinyl acetate and compounds comprising chromium. If these wires are satisfactory from the point of view of their properties and their ability to mold by simultaneous projection, they have the disadvantage of containing chromium which in some respects may prove to be toxic and / or present risks of pollution. for the environment.

  The son of the second type (OC 900 reference) are coated with a size comprising a vinyl acetate polymer and methylolacrylamide and they are adapted more particularly to the LFI technique. Nevertheless, the level of performance is insufficient with regard to certain parameters: the number of loops present per unit length of wire remains high and the integrity of the wire remains low. The object of the present invention is to provide a sizing composition for reinforcement yarns, in particular intended for open-mold molding, in particular for simultaneous projection molding, or for closed-mold molding, in particular for LFI molding, which does not contain no chromium and which provides performance equivalent to those known glass son for these applications, especially in terms of speed of impregnation son by the resin, production of flock and integrity.

  The invention relates to glass yarns coated with an aqueous sizing composition which comprises, as tackifying film-forming agents, at least one polyvinyl acetate, at least one copolymer of vinyl acetate and another monomer. unsaturated and at least one epoxy.

  In the present invention, by glass threads coated with a sizing composition which comprises ..., not only are the glass threads coated with the composition in question as obtained at the immediate exit of the organ or the sizing members, but also these same threads after they have undergone one or more other treatments. By way of example, mention may be made of the drying operations aimed at eliminating the liquid phase from the composition, and the treatments leading to the polymerization and crosslinking of certain constituents of the sizing composition.

  Still in the context of the invention, yarn means the son of base from the gathering under the die of a multitude of filaments, and products derived from these son, including the assemblies of these strands of rovings. Such assemblies can be obtained by unwinding simultaneously several windings of basic son, and then gathering them in locks which are wound on a rotating support. It can also be direct rovings of titre (or linear density) equivalent to that of assembled rovings, obtained by the gathering of filaments directly under the die and the winding on a rotating support.

  According to the invention, the term "aqueous sizing composition" is intended to mean a sizing composition in the form of a solution in which the liquid phase consists of 97% by weight of water, preferably 99% and better still 100%. , the complement being constituted as the case may be of one or more essentially organic solvents which can help to solubilize certain constituents of the sizing composition.

  According to the invention, the sizing composition comprises, as sticky film-forming agents, the mixture of at least one polyvinyl acetate, at least one copolymer of vinyl acetate and of another unsaturated monomer, and at least one an epoxy.

  Polyvinyl acetate is important to quickly achieve a high level of impregnation of the son by the resin and obtain good conformability of the 10 son / resin mixture in the mold.

  The molecular weight of the polyvinyl acetate is generally less than 80,000 g / mol, preferably less than 70,000 g / mol and preferably is between 40,000 and 65,000 g / mol. The amount of polyacetate used is generally 20 to 50% by weight of the solids in the sizing composition, preferably 30 to 40%.

  The copolymer is obtained by co-polymerization of vinyl acetate and other unsaturated monomer, for example an olefinic type monomer. Preferably, the monomer is ethylene. The copolymer has a lower resin solubility than polyvinyl acetate; it thereby contributes to decreasing the speed of impregnation of the son by the resin. By modulating the copolymer content relative to that of polyvinyl acetate, it is possible to best adjust the properties of the final sizing.

  The amount of copolymer is generally 20 to 45% by weight of the solids of the composition, preferably 30 to 40%. When the content is greater than 45%, the conformability is insufficient. When the content is less than 20%, the thread loses its stiffness.

  Preferably, the weight ratio of polyvinyl acetate to copolymer ranges from 30:70 to 70:30, and more preferably from 40:60 to 60:40.

  More preferably, the sum of the vinyl polyacetate and copolymer content amounts to 50 to 80% by weight of the solids of the sizing composition.

  The epoxy promotes the bonding of the filaments, thus making it possible to improve the stiffness of the yarn, which contributes to a more homogeneous distribution of the cut yarns in the resin after projection into the mold. It also helps to limit the formation of fluff.

  The epoxy is generally selected from resins having a molecular weight greater than 5,000 g / mol, preferably less than 20,000 g / mol. They advantageously have an epoxide index greater than 800 g / equivalent, preferably between 1200 and 2000, and more preferably of the order of 1500 g / equivalent.

  By way of examples, mention may be made of the epoxy resins resulting from the reaction of epichlorohydrin and an alcohol, for example bisphenol A or F, polyethylene glycols, glycerol, pentaerythritol or novolak resins.

  Preferably, the epoxy results from the reaction of epichlorohydrin and bisphenol A. Advantageously, the epoxy is used in combination with another epoxy bearing one or more amine functions which has the role of providing stiffness to wire without significantly affecting conformability. The amount of epoxy is generally 10 to 20% by weight of the solids of the sizing composition, preferably 12 to 16%. In addition to the aforementioned components which essentially participate in the structure of the size, the sizing composition may advantageously comprise one or more other components (hereinafter referred to as additives).

  The sizing composition may thus comprise one or more lubricating agents in an amount representing 1 to 20% by weight of the solids of the sizing composition.

  In addition to protecting the filaments against mechanical abrasion, the lubricant (s) helps to limit the formation of flock, to increase the stiffness of the thread and to prevent the gluing of the turns on the windings of threads. basic.

  In general, these agents are chosen from polyalkylene imide type cationic compounds, and poly (oxyalkylene) type poly (alkylene glycol) fatty acid esters and ionic compounds, such as polyethylene glycol monolaurate, or amide type. fatty acids and poly (oxyalkylene) such as hydrogenated tallow amides and polyethylene.

  The sizing composition may also comprise at least one coupling agent for hanging the size on the surface of the glass filaments. The coupling agent is generally chosen from silanes such as gamma-glycidoxypropyltrimethoxysilane, gamma-acryloxypropyltrimethoxysilane, gamma-methacryloxypropyltrimethoxysilane, poly (oxyethylene / oxypropylene) trimethoxysilane, gamma-aminopropyltriethoxysilane, vinyltrimethoxysilane and phenylaminopropyltrimethoxysilane. or styrylaminoethylaminopropyltrimethoxysilane, siloxanes, titanates, zirconates and mixtures of these compounds.

  Preferably, the silanes are selected.

  The amount of coupling agent generally represents less than 5% by weight of the solids of the sizing composition, preferably is greater than 2% and most often is of the order of 3%.

  All of these additives contribute to obtaining easily-made reinforcing yarns which retain good integrity, which can be cut without any problem and thrown into a mold by being slowly impregnated with the resin or resin precursor monomers. .

  It is still possible to introduce an anti-static agent such as lithium chloride into the sizing composition. The amount of this agent generally represents less than 5% of the weight of the solids contained in the sizing composition.

  The glass strands coated with the sizing composition according to the invention have a loss on ignition of less than 2.2%, preferably greater than 1.1% and more preferably between 1.4 and 1.60%.

  Most often, the son of glass according to the invention are in the form of son son windings which is subjected to a heat treatment. This treatment is intended essentially to eliminate the water provided by the sizing composition and, where appropriate, to accelerate the crosslinking of film-forming agents. The conditions of the treatment may vary according to the mass of the winding. In general, the drying is carried out at a temperature of the order of 110 to 140 ° C. for several hours, preferably 12 to 18 hours.

  The son coated with the sizing composition according to the invention may be made of glass of any kind as long as it is capable of being fiber-reinforced, for example E, C, AR (alkali-resistant) glass, or at a low temperature. boron level (less than 5%).

  These same son consist of filaments whose diameter may vary to a large extent, for example 9 to 17 m, preferably 11 to 13 m. Advantageously, these threads have a titer of between 30 and 160 tex, preferably 40 and 60 tex. Such cut glass son are distributed evenly and homogeneously within the resin, even when the thickness projected on the mold is important, which allows to have a reinforcement of excellent quality.

  Another subject of the invention relates to the sizing composition suitable for coating said glass yarns, which composition is characterized in that it comprises an aqueous mixture of at least one polyvinyl acetate, at least one copolymer of vinyl acetate and at least one other unsaturated monomer and at least one epoxy as defined above.

  The sizing composition is an aqueous mixture comprising the constituents below, in the following weight contents expressed as percentages of the solids: at 50% of at least one polyvinyl acetate, preferably 30 to 40% at 45% at least one copolymer of vinyl acetate and at least one other unsaturated monomer, advantageously an olefinic monomer such as ethylene, preferably 30 to 40% to 20% of at least one epoxy, preferably at 16% - 1 to 20% of at least one lubricating agent, - 0 to 5% of at least one coupling agent, preferably greater than 2% to 5% of at least one anti-static agent.

  Preferably, the sizing composition comprises between 5 and 15% by weight of solids, preferably between 7 and 12%. Advantageously, the liquid phase consists of 100% water.

  Another object of the invention relates to composites comprising glass son coated with the sizing composition. Such composites comprise at least one thermosetting material, preferably a polyester, a vinylester, an acrylic, a polyurethane, a phenolic or epoxy resin, and glass threads consisting, in whole or in part, of glass yarns conforming to invention.

  The level of glass within the composite is generally between 20 and 45% by weight, and preferably between 25 and 35%.

  In addition to their advantages related to the use by molding (slow impregnation speed and good conformability), the glass son give the composites that contain them better resistance to aging, especially in a humid environment.

  The invention also relates to the use of glass son coated with the sizing composition for the production of parts by the open mold molding technique, in particular by simultaneous projection of said son and resin.

  The invention also relates to the use of said glass son for the manufacture of molded parts operating in a closed mold, in particular by the technique LFI.

  The following examples illustrate the invention without limiting it.

  In these examples, the properties relating to the glass strands coated with the sizing composition and to the composites incorporating said strands are measured as follows: the loss on ignition, as a percentage, of the sized glass strand is measured under the conditions of the standard ISO 1887, the flock is measured by simultaneously passing the strands unwound from 2 rovings on a bunch, at a speed of 200 m / min. The flock is defined by the amount of fibrils, in mg, obtained after scrolling. a mass of yarn of 3 kg. It is expressed in mg / kg of yarn.

EXAMPLE 1

  A sizing composition is prepared in the form of an aqueous solution comprising, in weight percent of solids: agents film-forming agents - polyvinyl acetate (1); molecular weight: 50,000 35.7 ethylene vinyl acetate copolymer (2) 35.7 epoxy resin (3) 12.6 (4) amino epoxy resin 3.7 γ-methacryloxypropyltriethoxysilane coupling agents (5) 2, Lubricants mineral oil (5) 0.8 silicone (7) polyethylene glycol (molecular weight: 1000) (8) 1.7 anti-static agent: LiCl 4.5 30 water: enough to give 100 ml of sizing composition The preparation of the sizing composition is carried out as follows: The methoxy groups of the silane (5) are hydrolyzed by addition of acid in an aqueous solution of this silane maintained with stirring. The other constituents are then introduced, still with stirring, and the pH is adjusted to a value of 4 0.2, if necessary.

  The weight content of solids in the sizing composition is equal to 10.9%.

  The sizing composition is used to coat, in a known manner, glass filaments E about 12 μm in diameter drawn from glass threads flowing out of the orifices of a spinneret, the filaments then being collected in the form of of basewires of title equal to 57 tex.

  The winding is then dried at 130 ° C. for 12 hours.

  The base yarns extracted from 6 windings are brought together to form a roving.

  The wire thus obtained has a loss on ignition equal to 1.5%.

  The amount of flock is equal to 24 mg.

EXAMPLE 2

  Under the conditions of Example 1, a sizing composition consisting of an aqueous mixture comprising, in percentage by weight of the solids: adhesive film-forming agents - polyvinyl acetate (1); molecular weight: 50,000 36.1 - ethylene vinyl acetate copolymer (2) 36.1 - epoxy resin (3) 12.8 γ-methacryloxypropyltriethoxysilane coupling agent (5) 2.3 agent mineral oil lubricating agent) ( 6) 5.0 - silicone (7) 2.0 - ethylene glycol monolaurate (9) 3.0 polyethylene imide polyamide salt (10) 0.3 agent anti-static agent: LiCl 2.4 eau water: amount sufficient to give 100 ml of sizing composition.

  The weight content of solids in the sizing composition is equal to 7.5%.

  The yarn extracted from a roving obtained under the conditions of Example 1 has a loss on ignition equal to 1.55%.

  The amount of flock is 3.6 mg.

EXAMPLE 3

  Under the conditions of Example 1, a sizing composition consisting of an aqueous mixture comprising, in percentage by weight of the solids: polyvinyl acetate-sticky film-forming agents (1); molecular weight: 50,000 34.8 - ethylene vinyl acetate copolymer (2) 34.8 epoxy resin (3) 12.3 amino epoxy resin (4) 3.6 γ coupling agent - gamma-methacryloxypropyltriethoxysilane (5) 2,2 ^ lubricating agent mineral oil (6) 4,7 silicone (7) 1,9 - ethylene glycol monolaurate (9) 3,1 polyethylene imide polyamide salt (10) 0,3 ^ anti-static agent: LiCl 2, 2.3 water: enough to give 100 ml of sizing composition.

  The weight content of solids in the sizing composition is equal to 11.5%.

  The yarn extracted from a roving obtained under the conditions of Example 1 has a loss on ignition equal to 1.70%.

  The amount of flock is equal to 1.5 mg.

  EXAMPLE 4 (Comparative) A sizing composition consisting of an aqueous mixture comprising, in weight percentage of the solids: ^ film-forming adhesives vinyl acetate-N-methylolacrylamide copolymer (11) is prepared under the conditions of Example 1 (11) 42.2 vinyl acetate-ethylene copolymer (2 45.5 - amino-epoxy resin (4) 4.0 ^ coupling agent - gamma-methacryloxypropyltriethoxysilane (5) 2.4 ^ lubricating agents - mineral oil (6) 0, 9 - silisone (7) 3.2 polyethylene glycol (8), molecular weight: 1000 1.8 10 water: enough to give 100 ml of sizing composition.

  The weight content of solids in the sizing composition is equal to 9.9%.

  The yarn extracted from a roving obtained under the conditions of Example 1 has a loss on ignition equal to 1.89%.

  The amount of flock is equal to 12.7 mg.

  EXAMPLE 5 (Comparative) A sizing composition is produced under the conditions of Example 4 modified in that it additionally contains 0.45% by weight of LiCl.

  The weight content of solids in the sizing composition is equal to 9.8%.

  The yarn extracted from a roving has a loss on ignition equal to 1.52% The amount of flock is equal to 7.6 mg.

EXAMPLES 6 to 11

  The yarn obtained according to Examples 1 to 5 is used to manufacture composite parts by the simultaneous projection molding technique under the following conditions: the glass yarn extracted from the roving is introduced into a spray gun (APPLICATOR) which allows the cut and simultaneously project with an unsaturated polyester resin (Enydyne D05 4500 TY marketed by CRAY VALLEY) of medium and thixotropic reactivity.

  The mold in which the cut wires and the resin are projected is a mold in the form of a staircase having a vertical wall 1 m high, then a step 0.20 m deep and 0.2 m high and finally a horizontal wall 1 m long. The 2864072 13 horizontal wall has two grooves of 2 cm deep to assess the conformability of the cut son / resin mixture.

  The mixture sprayed onto the mold contains about 30% by weight of glass and has an average thickness of about 5 mm.

  The performance of the chopped strand / resin mixture is evaluated for the following parameters: boiling / working time respectively corresponding to the ability of the air bubbles to be expelled from the mixture sprayed onto the mold by passing a boiling roller, and ability of the son to be impregnated with the resin, held in vertical wall, conformability, evaluated at the level of the grooves of the horizontal wall, speed of impregnation of the son cut by the resin.

  The evaluation of the parameters of ebullation / time of work, vertical wall strength and conformability is measured visually according to a scale of values as follows: 1 = very bad; 2 = bad; 3 = pretty good; 4 = good; 5 = very good.

  The evaluation of the impregnation rate is visually defined according to the following scale of values: 1 = very slow, 2 = slow, 3 = average, 4 = fast and 5 = very fast.

  Table 1 below collates the evaluation of the performances of the yarns according to the invention (examples 1 to 3) and comparatives (5 to 7).

  In this table, the performance of a wire glass marketed by the company Owens Corning under the reference OC 1662 is also indicated as being suitable for simultaneous projection molding (Reference 1). This wire is provided with a sizing containing chromium.

TABLE I,

  Example Example Example Example Example Example 6 7 8 9 10 11 Glass wire Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ref. 1 Ebulling / Time 4 4 4,5 3 4 4,5 working Wall resistance 5 5 5 5 5 5 vertical Conformability 4 4 4 1,5 3 4 Impregnation rate 2,5 2, 5 1 1 1 1 Wadding (mg) 24.0 3.6 1.5 12.7 7.6 27.0 It can be seen from Table 1 that Examples 6 to 8 according to the invention make it possible to reach an excellent compromise in terms of the properties application: a particularly high vertical wall strength associated with an impregnation rate that can be modulated according to the size, moderate (Examples 6 and 7) to slow (Example 8). The glass son of Example 3 allow in particular to achieve the same level of performance as glass son suitable for this technique (Reference 1).

  The glass threads coated with a size not comprising the mixture of film-forming film-forming agents (Examples 9 and 10) have insufficient conformability.

  Note that the son in accordance with the invention have a production of wad weaker than the son provided for the intended application (Reference 1). In Example 8, the production of flock is considerably reduced.

EXAMPLES 12 AND 13

  The performance of the yarn according to Example 3 is evaluated for the LFI application compared to the OC 900 yarn (Reference 2) adapted to this technique.

  The parameters are: the number of loops present on 500 meters of wire unwound from a winding, usually a roving, - the integrity of the wire subject to the following conditions: the wire unwound from a roving is introduced into a WOLFANGEL 500 cutter which cuts it and projects it substantially horizontally on a vertical wall (cutting speed: 1200 m / min, length: 12 mm). The integrity of the cut wire is measured visually on a scale of values ranging from 1 (bad, cottony appearance) to 5 (very good, no bursting of the wire) the impregnation rate of the wire cut by the resin, measured visually. on a scale from 1 (very slow speed) to 5 (very fast).

  Example 12 Example 13 Thread Example 3 Reference 2 Number of loops 30 Integrity 3.5 3.5 Impregnation speed 1 1 The yarn according to the invention has a reduced number of loops with respect to the reference yarn for integrity and identical impregnation speed.

  (1) marketed under the reference Vinamul 8852 by VINAMUL; solids content: 55% (2) marketed as Air Flex EP740 by AIR PRODUCTS; solids content: 55% 15 (3) marketed as Neoxil 8294 by DSM; solids content: 55% (4) marketed under the reference Neoxil PS5164 by DSM; solids content: 35% (5) marketed under the reference Silquest A-174 by GESM; solids content: 70% (6) marketed under the reference Lubronyl GF by RHONE POULENC; solids content: 100% (7) marketed under the reference Silicone 2418 by Dow Corning; solids content: 50% (8) marketed under the reference Prioowax 1000 by CESALPINA CHEM; solids content: 100% (9) marketed under the reference Ensital 4L by COGNIS; solids content: 100% (10) marketed under the reference Emery 6760 by COGNIS; solids content: 17% (11) marketed under the reference Vinamul 8828 by VINAMUL; solids content: 51%

Claims (21)

  A glass yarn coated with an aqueous sizing composition, characterized in that said composition comprises as tackifying film-forming agents at least one polyvinyl acetate, at least one vinyl acetate copolymer and one other unsaturated monomer and at least one epoxy.   2. Glass yarn according to claim 1, characterized in that the polyvinyl acetate has a molecular weight of less than 80 000 g / mol, preferably less than 70 000 g / mol and more preferably between 40 000 and 65 000 g / mol.   3. Glass yarn according to claim 1 or 2, characterized in that the copolymer is a copolymer of vinyl acetate and an olefinic monomer.   4. Glass yarn according to claim 3, characterized in that the olefinic monomer is ethylene.   Glass yarn according to one of claims 1 to 4, characterized in that the weight ratio of the polyvinyl acetate to the copolymer ranges from 30:70 to 70:30, and preferably from 40:60 to 60:40. .   6. Glass strand according to one of claims 1 to 5, characterized in that the epoxy is selected from resins having a molecular weight greater than 5000 g / mol, preferably 20 000 g / mol.   7. The glass yarn according to claim 6, characterized in that the epoxy has an epoxide index greater than 800 g / equivalent, preferably between 1200 and 2000 g / equivalent.   8. Glass yarn according to one of claims 1 to 7, characterized in that the composition further comprises a lubricating agent.   9. The glass yarn according to claim 8, characterized in that the lubricating agent is chosen from cationic compounds of the polyalkylene imide type and nonionic compounds of the fatty acid ester and poly (alkylene glycol) poly (oxyalkylene) type. or fatty acid amides and poly (oxyalkylene) type.   10. Glass yarn according to one of claims 1 to 9, characterized in that the composition further comprises a coupling agent selected from silanes, siloxanes, titanates and zirconates.   11. Glass strand according to one of claims 1 to 10, characterized in that it has a loss on ignition less than 2.2%, preferably greater than 1.1% and better still between 1.4 and 1.6%.   12. Glass strand according to one of claims 1 to 11, characterized in that it consists of filaments having a diameter ranging from 9 to 17 m.   13. Glass strand according to one of claims 1 to 12, characterized in that it has a titer of between 30 and 160 tex, preferably 40 to 60 tex.   14. Sizing composition for coating glass strands according to one of claims 1 to 13, characterized in that it comprises an aqueous mixture of at least one polyvinyl acetate, at least one copolymer of vinyl acetate and other unsaturated monomer and at least one epoxy.   15. Composition according to claim 14, characterized in that it comprises the constituents below, in the following weight contents expressed as percentages of solids: 20 to 50% of at least one polyvinyl acetate, preferably 30 to 40% to 45% of at least one copolymer of vinyl acetate and at least one other unsaturated monomer, advantageously an olefinic monomer such as ethylene, preferably 30 to 40% to 20% of at least one epoxy, preferably 12 to 16% 1 to 20% of at least one lubricating agent, 0 to 5% of at least one coupling agent, preferably greater than 2% to 5% of at least one agent anti-static.   16. Composition according to claim 14 or 15, characterized in that it comprises 5 to 15% by weight of solids, preferably 7 to 12%.   17. Composite comprising at least one thermosetting polymer material and reinforcing glass son, characterized in that all or part of the son consists of son according to one of claims 1 to 13.   18. Composite according to claim 17, characterized in that the thermosetting material is a polyester, a vinylester, an acrylic, a polyurethane, a phenolic resin or an epoxy resin.   19. Composite according to claim 17 or 18, characterized in that it comprises 20 to 45% by weight of glass.   20. Use of glass son according to one of claims 1 to 13 for the production of parts by the open mold molding technique, in particular by simultaneous projection of said son and resin.   21. Use of the glass son according to one of claims 1 to 13 for the production of parts by the closed mold molding technique, in particular by LFI.