FR2654673A1 - Application of anti-blocking composite polyester films as support (backing) for the formation of at least one polyurethane layer which can be used in safety glass - Google Patents

Abstract

The invention relates to the application of an anti-blocking polyester film as a support for the formation of sheets of plastic comprising at least one polyurethane layer of high optical quality by the addition of at least one liquid mass onto the said stretched movable horizontal flat support. In the application according to the invention, the anti-blocking polyester film is constituted by a support film made of semicrystalline oriented polyester (A) which includes, on at least one of its faces, a fluoropolymer coating (B).

Description

The subject of the present invention is the application of novel non-stick composite polyester films as temporary supports for the manufacture of polymer films and in particular for the manufacture of at least one layer of high optical quality polyurethane, suitable for use in glass pane. security.

It is known that plastic sheets or films meeting particular requirements as to their physical properties (scratch resistance, transparency, surface condition, self-healing ability of scratches, tear resistance in particular) are used for manufacture of so-called asymmetric laminated glazing comprising a monolithic or laminated support made of glass and / or of plastic material, and said sheet of plastic material. These glazings can be used as building glazing, as glazing for motor vehicles, as glasses for safety glasses, etc ... Thus, in French patents 2 187 719, 2 251 608 and European 0 132 198 for example, it has been proposed to place on the sheet of glass intended to be oriented towards the interior of the passenger compartment of the vehicle, a layer of an elastic crosslinked polyurethane (thermosetting) having excellent properties of. anti-laceration and self-healing, that is to say possessing an ability to remove accidental scratches. The polyurethane layer can be used alone or in combination with another layer having adhesion and / or energy absorber properties, in particular a thermoplastic polyurethane layer or a polyurethane layer obtained by reactive casting or reactive spraying. of a mixture of reaction components as described in the aforementioned European patent publication 0 132 198.

These polyurethane layers must have good optical quality and in particular must be free from surface defects. By good optical quality is meant according to the invention the optical quality necessary for the use of these layers in a transport vehicle glazing. It has already been proposed to manufacture these layers by casting the liquid mass comprising the polyurethane precursors, on a stretched flexible support, made of plastic material, delivered continuously from coils as the casting proceeds. When the thermosetting polyurethane layer is formed it can be immediately separated from the temporary plastic support or, preferably, it can be rolled up with said support which then acts as a protective film until its final use.

When the polyurethane sheet comprises a thermosetting layer and a layer having adhesion and / or energy absorber properties (hereinafter referred to in the description as layer AE), the precursors of these layers are successively cast in an order indifferent, so that the temporary support can be in contact either with the AE layer or with the thermosetting layer.

The plastic material forming the temporary support must meet various requirements relating to its surface condition, its chemical inertness with respect to the polyurethane precursors, its elasticity, its windability and its ability to easily separate from the material. polyurethane sheet under the effect of traction, while maintaining good adhesion in the absence of traction. Polyester films which meet a certain number of these requirements have been proposed as temporary supports for composite or non-composite polyurethane sheets, for example in French patent publications 2,480,669 and 2,546,810. However, polyester films do not achieve a excellent compromise between a sufficient adhesion to the polyurethane sheet and an aptitude for easy separation under the effect of a traction exerted on the support film. The applicant therefore proposed as an objective the use of a new polyester film composite as a temporary support for polyurethane sheets which can be easily separated therefrom under the effect of traction, without damage to the surface of the polyurethane film, that is to say without tearing off this surface and / or without deposit on this surface of material torn from the temporary support film.

More specifically, the present invention relates to the use, as a support for forming a layer of high optical quality polyurethane suitable for use in the manufacture of safety glazing, a non-stick composite polyester film, this film being consisting of a semi-crystalline oriented polyester support film (A) comprising on at least one of its faces a coating of fluoropolymer (B).

The polyesters used for obtaining the support (A) of the composite films used according to the invention are those which have usually been used for obtaining bi-oriented semi-crystalline films. These are linear film-forming polyesters, crystallizable by orientation and obtained in the usual way from one or more aromatic dicarboxylic acids or their derivatives (esters of lower aliphatic alcohols, halides for example) and from one or more aliphatic glycols. . As examples of aromatic diacids, mention may be made of phthalic, terephthalic, isophthalic and 2,5-naphthalenedicarboxylic acids; 2,6-naphthalenedicarboxylic These acids can be associated with a minor amount of one or more aliphatic dicarboxylic acids such as adipic, azelaic, hexahydroterephthalic acids. As non-limiting examples of aliphatic diols, mention may be made of ethylene glycol; propanediol-1,3; butanediol -1.4. These diols can be combined with a minor quantity of one or more aliphatic diols more condensed in carbon (neopentylglycol for example) or cycloaliphatic (cyclohexanedimathanol). Preferentially, the crystallizable film-forming polyesters are polyterephthalates or polynaphthalenedicarboxylates and alkyenediediarboxylates, in particular, polyethylene glycol terephthalate (PET) or 1,4-butanediol or copolyesters comprising at least 80% by moles of terephthalate or naphthalenedicarboxylate units of alkylene glycols. Advantageously, the polyester is a polyethylene glycol terephthalate, the intrinsic viscosity of which, measured at 250 ° C. in o-chlorophenol, is between 0.6 and 0.75 dl / g.

The polyester support films (A) can themselves be simple or composite. Thus, it is possible to use a coextruded polyester film, one layer of which is loaded to impart to said layer sufficient roughness to ensure the machinability of the assembly and the other layer of which is unloaded or comprises fillers whose particle size is chosen. so as not to cause any surface defect in the non-stick coating. It is also possible to use composite polyester films consisting of a semi-crystalline oriented polyester film of the sulfonated copolyester type comprising on at least one of its faces a primary adhesion coating deposited by coating or by coextrusion such as those described in the applications. of European Patents Nos. 267 856, 275 801, 260 203, 272 993.

The fillers present in the polyester support films (A) may have been introduced during the polycondensation or into the polymer by the usual processes or they may result from the precipitation of catalytic residues under the influence of additives introduced during the polycondensation. . The nature of these charges is not critical, they may be mineral compounds (oxides or salts of elements of groups II, III and IV of the periodic table).

By way of illustration, mention may be made of silicas, silico-aluminates, calcium carbonate, titanium oxide, magnesium oxide, alumina, barium sulfate, polystyrene preferably crosslinked with divinylbenzene, thermotropic polymers (polyester in particular).

The amount of filler and the average diameter of the particles are chosen so as to give the polyester support film surface properties (roughness and friction coefficients) sufficient to ensure good machinability, without causing the appearance of surface defects. on the non-stick coating (B) by carryover effect.

In general, the average particle diameter is less than 3 Wm; it is preferably between 0.02 and 2 Fun. The amount of filler is less than or equal to 1% of the weight of polyester and preferably lies in a range of 0.01 to 0.1%.

The support films (A) are obtained by the usual filming processes which include in particular the extrusion of a crystallizable amorphous polyester film, the quenching then the stretching, the heat-setting and the winding of the oriented semi-crystalline film.

The thickness of the polyester support films (A) can vary between 20 and 200 Wm and preferably between 30 and 150 wtt.

The non-stick layer (B) is obtained by depositing on at least one of the faces of the support film (A) an aqueous composition, emulsion or suspension of a fluoropolymer.

The molecular weight and the structure of the fluoropolymer are not critical.

The fluorinated polymers which are suitable for the implementation of the invention can be in particular the polymers and copolymers of vinylidene fluoride, of trifluorochlorethylene, of tetrafluoroethylene, of hexafluoropropylene with one another or with non-fluorinated monomers (ethylene for example). polyvinylidene fluoride (PVDF) is very particularly suitable. These fluoropolymers can be used in the form of powders or in the form of emulsions or aqueous dispersions, for example such as those obtained by polymerization in emulsion or in suspension of the monomer (s). The solids content of the fluoropolymer emulsions or dispersions is not critical. These emulsions or suspensions also contain cationic, anionic or nonionic surfactants, preferably fluorinated.

Prior to coating, the polyester support film may have been subjected to a surface treatment usually used. Thus the face intended to receive the fluoropolymer coating can be subjected to a treatment by electric discharges (corona treatment) or by ionizing radiations.

The amount of aqueous fluoropolymer coating composition deposited on the film depends on the one hand on its solids content and on the other hand on the desired thickness for the layer (B) of fluoropolymer. This amount also depends on the coating process; in the case of in-line coating, it is obviously necessary to take into account the variation in thickness of the coating before and after stretching. The thickness of the fluoropolymer layer (B) can vary within wide limits ... In general, it corresponds to the thickness of a deposit of 40 to 400 mg / m2 of dry extract.

After coating, the polyester film is brought to a temperature sufficient to remove water. In the case of in-line coating, it is generally not necessary to carry out a heat treatment: the water evaporates during stretching and heat-setting.

In the following examples, the coefficients of friction of the films were determined by the method described in the standard ASTM D 1894-78 (method of DAVENPORT).

To manufacture, according to the invention, the polyurethane layer (s) on the polyester support film, the latter must be stretched longitudinally and laterally to form a horizontal plane support.

For this purpose, one can advantageously use the means of the device described in European patent publications 0 038 760 or 0 131 483 already cited.

The device used comprises a distributor of the polyester film, means exerting tensile forces on this tape longitudinally and transversely so as to stretch it and make it as perfectly flat and horizontal as possible, means for driving this tape in a movement of continuous advance, means for depositing in at least one place the liquid mass, capable of forming the polyurethane layer on the tape, heating means allowing the solidification of the liquid mass by polymerization of the components and / or evaporation of the volatile products , means horizontally supporting the tape over its useful width, at least at the location where the liquid mass is supplied.

According to one embodiment of the device, the means exerting tensile forces on the polyester support film are essentially a tractor roller located at the end of the line, associated with at least one resistant roller located in the upstream part of the line, and rollers. said edge rollers, which, on both sides of the polyester film, above and below said polyester film, exert on it lateral component forces outward. The edge rollers can have an adjustable action; their angle of inclination relative to the direction of advance of the polyester film may vary, as well as their clamping forces.

In a variant, the support polyester film can be stretched laterally by grippers which move simultaneously and parallel with the tape.

At the end of the casting line, means allow the winding of the formed sheet.

In one embodiment of the device, the means horizontally supporting the polyester film over its useful width, that is to say the width covered by the liquid mass at least at the locations where the liquid mass is supplied, may be rollers arranged at the locations indicated under the polyester film, and where appropriate, at other locations of the device forming the casting line.

In a variant, the means horizontally supporting the polyester film of the casting (s) at the locations and optionally at other locations are advantageously metal or glass plates themselves supported by suitable members, for example rollers, or directly. by a frame itself.

This variant is advantageous, because the plates can at the same time serve to distribute the heating of the support by zones, by conduction, by being themselves heated by electric resistances for example.

The casting line further comprises when the polyester support film is not used as a storage interlayer, means for separating the sheet from said support.

To avoid optical defects of the sheet due to the presence of foreign bodies, the casting line can also include means preventing grains of dust and other particles from being deposited on the manufactured sheet and possibly on the support, especially when the latter. this is used as a storage interlayer, and also cleaning means to remove these grains of dust which may have already been deposited.

The means to avoid the deposition of particles can be physical screens. Thus, the entire casting line, or parts of this line, such as casting and solidification zones, can be placed in an enclosure containing filtered and dust-free air.

The means for preventing the deposition of particles can also be electrostatic bars which ionize the atmosphere around the sheet.

The means for cleaning the sheet may be brushes, blades acting as scrapers, wiping elements, associated where appropriate with suction members.

In a variant, the means supporting the polyester support film, generally excluding the location or locations for the casting, are metal wires stretched between two horizontal bars arranged laterally on either side of the casting line. These wires can be placed at determined distances from one another, these distances being generally smaller near the downstream of the casting, where the casting material is still very fluid.

One of the advantages of using metal wires comes from the fact that the friction of the casting support sheet with these wires is practically eliminated and it follows that the static electricity created in particular by these friction is greatly reduced.

On the other hand, these conductive wires are capable of eliminating these electric charges.

Another advantage of the use of metal son resides in the fact that one thus eliminates the grains of dust which may get lodged between the rigid support sheets and the stretched flexible support, and which are liable to damage the flexible support or still cause surface defects on the cast layers.

In a variant of the device used to manufacture at least one layer of high optical quality polyurethane on a support polyester film, two supports extending over the entire useful length of the casting line, placed in the taut position, are used for the maintenance. along the side edges of the polyester support film, which associated with tension means allow the polyester support film to be stretched like a drum skin. Such means are described in the aforementioned European patent publication 0 131 483.

The preparation of examples of polyester support films used in the context of the invention for the manufacture of polyurethane layers will now be described.

Support 1
A polyethylene glycol terephthalate having a viscosity index of 580 and containing 0.4% by weight of calcium carbonate, at 2750C, is extruded at a rate of 96 kg / h by a slit die 450 mm in width. The tablecloth
PET is contacted with a cooling drum, the surface of which is maintained at 350C, then stretched in the longitudinal direction at 750C (stretching speed 20 m / min, stretching rate 3.2). 2 g / m2 of an aqueous dispersion of PVDF at 35% by weight of
PVDF by means of a coating device comprising successively: a leveling roller, a stripping roller, a coating roller rotating at 13 m / min and a smoothing bar rotating at 7 m / min. is then subjected to transverse stretching at 95-110 C (rate 3.7) and then heat-set at 225-235 C. In this way, a film 36 Fun thick is obtained, one side of which has a coating of PVDF (0, 2 g of dry extract per m2).

This film was subjected to the measurement of the coefficient of friction of the coated face on the face according to the DAVENPORT method. The results were as follows
coefficient of static friction us: 0.38
dynamic friction coefficient Bd: 0.33
The same uncoated film has the following coefficients
us: 0.56
ud: 0.44
SUPPORT 2
A non-stick composite film is prepared by an in-line coating process analogous to that described in Example 1 by depositing 2 g / m2 of an aqueous dispersion of
PVDF at 35% by weight of dry extract on one side of a mono-stretched film obtained by coextrusion of a PET containing 0.03% by weight of silica and of a copolyester with 5-sulfo isophthalate unit and having undergone corona treatment.

The coating is carried out by means of a device of the gravure transfer type comprising an engraved roller having 120 cells of 40 wtt depth per cm 2.

The coated film is then subjected to transverse stretching and then heat-set as in Example 1, in this way a coated film of 50 wtt thick is obtained, comprising
- an internal layer A loaded with silica thickness: 48 wtt
- on each side of layer A a layer B of sulfonated copolyester (thickness 1 Wm)
- on one of the layers B of sulfonated copolyester, a layer C of PVDF coating of 0.2 g / m2.

This coated film has the following friction coefficients
A) Coated face on coated face
us: 0.65
Bd: 0.47
B) Coated face on uncoated face
us: 0.80
Bd: 0.45
The supports described above are used as supports for the manufacture of the polyurethane layers as illustrated in the following examples.
The polyurethane layers which can be manufactured according to the invention are those described for example in French patent publications 2 398 606, and European patent publications 0 132 198, Q 133 090, 0 190 517.

When it is desired to manufacture a two-layer sheet, which can be used in safety glazing as described in European patent publication 0 132 198, first of all a first layer is produced which can be either the adhesive layer having properties of energy absorber (AE layer), ie the thermosetting polyurethane layer. And on this first layer, we form the second layer.

It is thus possible first of all to manufacture a thermosetting polyurethane layer by casting the mixture of components on the casting support. After polymerization of the monomers and formation of a thermosetting layer with a thickness which may vary between 0.1 and 0.8 mm, for example, the reaction mixture of the components of the layer having energy absorber properties is cast.

It is also possible to proceed in a reverse manner, that is to say by first forming the layer having energy absorber properties (layer AE).

EXAMPLES 1 AND 2
On the supports 1 and 2 described above, a homogeneous mixture of
- 1000 g of a polyether with a molecular weight of approximately 450 obtained by condensation of 1,2-propylene oxide with 2,2-bis (hydroxymethyl) - 1-butanol and having a content of free hydroxyl radicals from about 10.5 to 12%, containing 1% by weight of a stabilizer, 0.05% by weight of a catalyst, namely dibutyltin dilaurate and 0.1% by weight of a coating agent, - 1020 gd of a 1,6-hexanediisocyanate biuret having a content of free isocyanate groups of about 23.2%.

A casting head such as that described in French patent publication 2 347 170 is used. A uniform layer is formed which, after polymerization under the effect of heat, for example about 15 minutes at 120 ° C., has a thickness of about 0.19 mm and self-healing properties.

To manufacture the layer having energy absorber properties, the polyol component is prepared beforehand by mixing a polytetramethylene glycol of molecular weight 1000 with 1,4-butanediol and a polycaprolactonetriol, the proportions of the three components being such as polytetramethylene glycol. provides 0.35 equivalent of hydroxyl groups while 1,4-butanediol provides 0.55 and the triol 0.10.

In the polyol component, there is incorporated a stabilizer in an amount of 0.5% by weight of the total mass of the polyol component and the isocyanate component, a coating agent in an amount of 0.05% by weight calculated in the same way and a catalyst at namely dibutyltin dilaurate in an amount of 0.02% by weight calculated in the same way as above.

The isocyanate component used is 3-isocyanatomethyl-3,5,5trimethylcyclohexylisocyanate (IPDI) exhibiting urea functions obtained by partial hydrolysis of IPDI and having a content of groups
NCO of about 31.5% by weight.

The components are taken in amounts such that the NCO / OH ratio is 1.

After degassing the components under vacuum, the mixture brought to approximately 400 ° C. is poured using a casting head such as that described in French patent publication 2 347 170, on the layer of self-healing polyurethane formed previously. A layer of approximately 0.60 mm thick is thus formed which is subjected to a polymerization cycle consisting of 25 minutes of heating at approximately 1200C.

The two-ply sheet is removed from the polyester backing and can be easily handled, stored, or used immediately thereafter for the manufacture of laminated glazing.

The sheet has the optical quality necessary for its use in safety glazing.

EXAMPLES 3 TO 4
The procedure is as in Examples 1 and 2, except that to form the polyurethane layer having self-healing properties, a homogeneous mixture of - 942 g of a trifunctional polycaprolactone having a
free OH radical content of 9.3% by weight, containing
0.015% by weight dibutyltin dilaurate, 0.1% by weight
weight of a fluoroalkyl ester as a spreading agent and
1% by weight of a UV protection agent

- 1000 g of a 1,6-hexamethylene-based triisocyanurate
diisocyanate, having a free NCO radical content of
21.5% by weight.

The layer is polymerized under the effect of heat, for example 15 minutes at 120 C.

The layer having energy absorber properties is then manufactured.

The two-layered sheet is removed from the backing. It has the optical quality necessary for use in safety glazing.

Claims (17)

1. Application of a non-stick polyester film as a support for the formation of plastic sheets comprising at least one layer of high optical quality polyurethane by adding at least one liquid mass to said movable horizontal plane support, stretched, characterized in that the non-stick polyester film consists of a semi-crystalline oriented polyester support film (A) comprising on at least one of its faces a fluoropolymer coating (B). 2. Use according to claim 1, characterized in that the support oriented polyester film consists of a polymer comprising at least 80% by moles of units derived from at least one aromatic dicarboxylic acid and ethylene glycol. 3. Application according to claim 2, characterized in that the support oriented polyester film consists of a polymer comprising at least 80% by moles of ethylene glycol terephthalate or ethylene glycol naphthalene-dicarboxylate units. 4. Application according to any one of claims 1 to 3, characterized in that the support oriented polyester film has a thickness between 20 and 200 Vm. 5. Application according to any one of claims 1 to 4, characterized in that the polyester support film comprises on the face receiving the fluoropolymer coating a primary adhesion coating. 6. Application according to claim 5, characterized in that the primary adhesion coating consists of a sulfonated copolyester. 7. Application according to any one of claims 1 to 6, characterized in that the face of the support film receiving the fluoropolymer coating has been subjected to a corona treatment. 8. Application according to any one of claims 1 to 7, characterized in that the quantity of fluoropolymer coating expressed in g of fluoropolymer per m2 of film is within a range of 0.1 to 0.4 g / m2. 9. Application according to one of claims 1 to 8, characterized in that the polyester support film is coated by means of an aqueous composition of fluoropolymer. 10. Application according to claim 9, characterized in that the coating is carried out online. 11. Application according to claim 10, characterized in that the coating is carried out in recovery. 12. Use according to any one of claims 9 to 11, characterized in that the solids content of the aqueous coating composition is between 5% and 35% by weight. 13. Application according to one of claims 1 to 12, characterized in that the fluoropolymer is polyvinylidene fluoride (PVDF). 14. Application according to one of claims 1 to 13, to the manufacture of a thermosetting polyurethane layer by supplying the reaction mixture of the components of the polyurethane to the support film. 15. Application according to one of claims 1 to 13, to the manufacture of a polyurethane layer having energy absorber properties by supplying a reaction mixture of the components of the polyurethane to the support film. 16. Application according to one of claims 1 to 13, to the manufacture of a sheet comprising two layers of polyurethane, a layer of thermosetting polyurethane and a layer of polyurethane having energy absorber properties. 17. Plastic sheet comprising at least one polyurethane layer obtained by the implementation of the application according to one of claims 1 to 16.