EP1337487A1

EP1337487A1 - Glass enamelling

Info

Publication number: EP1337487A1
Application number: EP01988700A
Authority: EP
Inventors: Sergio Glaberbel-Centre R. & D. SPERDUTI
Original assignee: Glaverbel Belgium SA
Current assignee: AGC Glass Europe SA
Priority date: 2000-10-26
Filing date: 2001-10-22
Publication date: 2003-08-27
Also published as: BE1013813A3; WO2002034686A1; AU2002221747A1

Abstract

The invention concerns glass enamelling. The application of an enamel layer brings about a substantial modification in surface stresses of the glass sheet. Said modifications embrittle the sheet. In order to avoid such effects or at least to minimise them, the invention provides a treatment which consists in limiting the enamel composition curing. The inventive treatment is applicable to all uses wherein the enamelled part is subjected to mechanical loads, which is the case, for example, of enamelled zones whereon accessories are bonded.

Description

Glazing for glazing

The present invention relates to the glazing of glazing. Enamelling located on glazing is very widely used for different purposes. In particular, when applied to the edges of automobile glazing, this involves masking, by means of a layer of opaque enamel, the bonding elements of these glazing on the frame. In this type of application the function of the enamel is to improve the aesthetics by concealing the bonding area which, otherwise, would be visible by transparency. It is also to protect the adhesive material and the seals against too rapid aging when exposed to solar radiation, aging which compromises the effectiveness of adhesion, ei or the sealing of the seals.

Enamel layers have also been proposed, in places other than on the edges of the glazing. It is always, by means of an opaque layer, to locally mask an object located behind transparent glazing. In this sense for example, it is usual to have a layer of enamel under the locations corresponding to the bonding of accessories such as mirrors, lights fixed on the rear glasses, and in general all the elements likely to be hidden , at least in part, although located behind the glazing.

It is also known to use enamels, not in the form of a uniform layer, but in a discreet manner, to constitute various patterns. These are in particular identification markings, but it can also involve applying decorative motifs.

Enameling can also be carried out so as to limit the transparency of a glazing. In this case, locally, or over the entire surface of the glazing considered, the enamel is applied in the form of points of small dimensions, arranged in a regular pattern masking a more or less significant fraction of the glazing, and thereby limiting the surface effectively transparent to radiation. This type of product has been used, for example, for making vehicle roofs which allow only a fraction of the solar radiation to pass. The dimensions of the points constituting these patterns are small enough for the visual impression from inside the vehicle to be that of attenuated light transmission, without it being possible to distinguish the points themselves. The same type of application according to a dot pattern is also used according to a variable density so as to obtain a gradual degradation of the transmission. This is widely applied to the strips at the edge of the glazing. This mode is also found applied around certain areas of glazing carrying an accessory whose attachment is concealed by a uniform layer of enamel.

If the application of a layer of enamel to the surface of a glazing is essentially intended to modify the optical characteristics, it also causes mechanical modifications. The enamelled layers are formed on the glass by what is called "fusion" of the frit which goes into their composition. This fusion is carried out at temperatures of the order of 550 to 720 ° C. depending on the compositions used. This fusion leads to the formation of a homogeneous layer which strongly adheres to the glass sheet to which it is applied. After enamelling, which can be carried out simultaneously with a thermal and mechanical treatment of the glass sheet, for example a bending and / or tempering operation, the glass sheet brought back to room temperature is affected by the differences in characteristics. metric dilato of the glass and the enamel layer. In general, the enamel layers have a lower coefficient of thermal expansion than that of the glass on which they are applied. Consequently, upon cooling of the enameled sheet, surface stresses in extension are created on the sheet, at the locations coated with the enamel.

The local modification of the stresses in the glass sheet is a factor of embrittlement thereof. In the most common applications mentioned above, these modifications have no negative consequences. The glazing retains sufficient mechanical characteristics for the use made of it.

Recently, however, on the occasion of changes in the thicknesses of certain glazing units, it has become apparent that the presence of certain layers of enamel could annoyingly weaken the glass sheet. This is particularly the case for localized applications corresponding to the fixing of accessories when the glass sheet is very thin. Thus the tests for resistance to tearing off elements of the mirror type, fixed on windshields, have shown an insufficiency for laminated glazing whose sheet on which the enamel is applied has a thickness of the order of 1 6mm. Previously the same use on sheets of 2.1mm raised no problem.

The object of the invention is therefore to achieve applications of enamelled layers meeting the traditional requirements for this type of product, and which do not compromise the mechanical characteristics of the glass sheets to which they are applied, even when the thickness of the glass sheet is relatively thin. In other words, the object of the invention is to ensure that the application of an enamel layer on a glass sheet does not induce too great a modification of the surface constraints.

The invention proposes to replace the usual enamelled layer completely vitrified, by a layer whose "cooking" is "incomplete". The firing of enamel is a characteristic that manufacturers express on the one hand in terms of temperature, and on the other hand according to the time required during which the temperature in question must be maintained. As indicated above, optionally after drying intended to remove the medium which binds the solid components together and facilitates the application of the composition, normal cooking makes it possible to melt the constituents of the frit into a vitreous layer in which the pigments remain dispersed.

The transformation of the enamel composition at baking temperatures takes place gradually. The temperature rise conditions of the grains constituting these compositions is not uniform. The heterogeneous phase fusion explains that the fusion is not frank, and that it is necessary to maintain the temperature for a certain time.

If the temperature is kept below the indicative values provided by the manufacturers, or if the treatment time is manifestly too short for the fusion to take place completely, the layer formed is not uniform. In particular, it seems that the reaction of the enamel with the glass sheet is less. Everything happens as if the glass surface was only partially affected by the enamel, and / or that the less homogeneous enamel layer, did not oppose the same resistance to dimensional variations of the glass under the effect of the modifications imposed temperatures.

Whatever the exact origin of this result, it can be seen according to the invention, by carrying out an "incomplete baking", that the mechanical characteristics of the glasses thus treated can be maintained under acceptable conditions, where the "normal" treatment s 'would accompany excessive embrittlement.

In practice, the manufacturers of enamels give firing temperatures which extend over a range of a few tens of degrees to take account of the variable conditions of implementation (inertia temperature of the support, not perfectly homogeneous distribution of temperatures in the cooking chamber ...) and of the effective treatment time. This range is typically of the order of 30 to 80 ° C, and most often around fifty degrees. The implementation of the invention preferably results in locating the treatment temperature outside and below this range. In a particularly preferred manner, the firing temperature according to the invention will be at least 10 ° C and better still, at least 20 ° C below the range recommended by the manufacturers of enamels.

These temperature conditions are given for sufficient processing times, such as those also indicated by the manufacturers. It goes without saying that cooking can be shortened. In this case the treatment temperature can be raised accordingly.

In practice, when it is enamels whose firing is carried out during a bending / tempering operation of the glass sheet, it is the thermal cycle and time conditions imposed by this operation which lead to the choice of suitable enamel. Also in this case, the duration of the treatment generally exceeds the minimum time necessary to obtain the complete fusion of the enamel. Consequently, the choice of suitable enamel is based mainly on the treatment temperature. The more refractory enamel has a firing temperature which is higher than that of bending / quenching under the preferred conditions indicated above.

The bending temperature quenching of the traditional glasses used being around 600-650 ° C, the temperature recommended for baking the enamels used according to the invention on glasses subjected to these treatments, will advantageously be above 630 ° C and preferably above 650 ° C.

The invention will be described in more detail below with reference to the drawing board in which:

- Figure 1 shows a part of a windshield comprising a traditional enamelling for fixing the base of the interior mirror;

- Figure 2 shows the first step of an application mode of an enamel according to the invention, on an element similar to that of Figure 1; - Figure 3 shows the second step of an application mode of an enamel according to the invention.

The example of implementation of the invention which is given below, relates to automobile glazing, and more precisely a windshield on which a mirror is stuck on. The invention is nevertheless applicable to all cases in which an enamel applied to a glazing must have sufficient opacity, and therefore to be applied uniformly over the entire coated surface, while modifying the stresses induced by this enamel as little as possible. this surface.

The example shown in Figure 1 corresponds to the upper middle part of a traditional windshield. Several enameled patterns are applied to the sheet of glass facing the passenger compartment. The application of the patterns can be carried out by any known means, and in particular by screen printing, but other techniques such as that known as “ink jets”, can advantageously be used. The implementation of the invention is not dependent on a particular mode of application.

On the windshield 1, an enamel strip 2 corresponds to the upper edge of the windshield, a part which is glued to the vehicle body. This strip is generally opaque so as to mask and protect the bead of adhesive and possibly the seal.

A bonding zone 3 for the base of the mirror is also coated with an opaque enamel composition. The dimensions and shape of this area are such that it is slightly larger than the base to be bonded, so as to hide it completely, regardless of the positioning differences that may appear on the assembly lines. Optionally a zone 4 is provided to form a semi-transparent part partially concealing the mirror. This area consists of a pattern made of dots leaving a more or less significant fraction not coated with enamel. This zone 4 can be homogeneous in point density. There may also be, for example, zones whose density of enamel points varies away from the peripheral strip 2.

In the form shown in FIG. 1, the various enamelled patterns: peripheral band 2, bonding zone of the base 3, and semi-transparent zone 4, are advantageously made with the same enamel composition. In this case, for an application by screen printing, a single operation makes it possible to produce all of the patterns.

In the mode according to the invention represented in FIGS. 2 and 3, the application of the enameling compositions is carried out in two stages. The first step leads, as before, to the application of a layer of a first enamel composition forming the patterns corresponding to the peripheral strip 2, to the semi-transparent zone 4.

Zone 5, at the location of the mirror base is left without application of the first enamel composition. This same zone is then the subject of the application of a second composition of enamel, that of which the subsequent baking is "incomplete".

Given the fact that in a screen printing type application it is difficult to ensure perfect positioning of the second application 7 relative to the location left free during the first application, it is preferable that this second application 7 slightly protrudes on the first. In this way it can be guaranteed that, in the zone considered, there is no risk of there being any part free of coating, and which would appear as a "hole" in this enameled zone. This defect would be particularly visible in this case.

To further improve the aesthetics, it may be advantageous to surround the zone 5 with a frame 6 formed from the first enamel composition, and on which the second application 7 extends. This way makes it possible to conceal the differences in overlap around of zone 5, which would appear through the semi-transparent enameled part 4. By imposing an opaque frame, a limited defect in positioning of the application of the second enamel composition is not visible by transparency due to the opacity of the frame 6. FIG. 3 therefore shows that once the second application has been made, seen from the inside, part of the frame 6 is covered by the application of the second enamel composition. This results in a seemingly less wide frame.

The sequence described above is not imperative. It is possible in particular to reverse the order of application of the compositions. In addition, the sequence described is envisaged in the case of an application by screen printing. In the case of an application of another type, and in particular by ink jet, the precision of the application can be appreciably increased, and consequently, the arrangements intended to compensate for the relative positioning defects of the two applications can be significantly less restrictive.

After the application of the compositions as just described, the sheets forming the laminated windshield are matched and subjected to the bending / quenching operations. For this, whatever the technique used, the sheets are passed through an oven and subjected to a heat treatment which brings them to the softening temperature which is of the order of 600 to 650 ° C., before being quickly brought back to room temperature, to be frozen.

The complete residence time in the oven is for example one twenty minutes. On this one, the time at the highest temperatures is only a few minutes (6 to 12 minutes) which are sufficient for the firing of the enamel with which the peripheral bands 2, the frame 6 and the semi zone are formed. -transparent 4. The part corresponding to the enamel composition whose baking temperature is above the highest temperatures reached in the oven, is undercooked to form a perfect vitrified layer. However, it adheres enough so that the subsequent bonding of the base is as resistant as when it is carried out in the traditional way on fully baked enamel. For the processing temperatures corresponding to the bending / quenching indicated (600-650 ° C), for the production of the layers according to the invention, enamels are advantageously chosen whose recommended firing temperature is of the order of 630 to 720 ° vs.

In practice, the masking enamels are opaque and dark in color, gray going towards black. The final color is established during cooking. Before complete cooking the shades are generally lighter. It is a possible way of checking the state of incomplete cooking according to the invention. This change in color does not normally create any difficulty in reproducibility, since the temperature and cooking time conditions are very constant.

As indicated previously, the problem which the invention has made it possible to resolve has appeared on vehicles for which the manufacturers have modified the thicknesses of the glazing. Thus laminated windshields, initially formed from two glass sheets of 2.3 and 2.0 mm respectively, assembled by means of a 0.76 mm polyvinyl butyral sheet, have been replaced by similar products in which the sheets of glass have respective thicknesses of 2.1 and 1.6mm. This reduction in the thickness of the sheets, and in particular of the internal sheet, substantially reduces the resistance to tearing at the level of the mirror. The tensile strength exerted peφendicular to the glazing, thus goes from 28daN to 21daN which does not appear sufficient.

In the example of implementation of the invention, the procedure is as indicated above by applying two separate enamel compositions. The first, which is fully cooked, is the product sold by the company Pemco Emails under the reference DV 172170. The application conditions recommended by the manufacturer are: cooking temperature: 590 to 640 ° C cooking time: 10 to 20 minutes . The second enamel composition is marketed by the same company under the provisional reference W 20 / 72-2. The recommended application conditions are: cooking temperature: 660 to 710 ° C cooking time: 10 to 20 minutes.

The application is made by screen printing on the internal sheet of a laminated windscreen. The thickness of the screen-printed sheet is 1.6mm.

The bending / tempering of the glass sheets leads the assembly to a maximum temperature of 650 ° C. for 10 minutes. Under these conditions the firing of the first enamel is complete, and that of the second enamel is incomplete.

The tensile tests carried out under the same conditions as above on the laminated glazing show a tear resistance of 32daN. This value is entirely acceptable, and is even higher than that obtained in prior practice. This shows the effectiveness of the use of the invention in reducing the modifications of the surface mechanical properties of the glass sheet in contact with the enamel. This advantage can be used as in the example to compensate for the reduction in resistance linked to the use of thinner glass sheets. On glazing whose previous characteristics were sufficient with regard to the requirements of the manufacturers, it can also further improve the characteristics of these glazing.

Claims

1. Glazing comprising at least one enameled part, the cooking of which is incomplete.

2. Glazing according to claim 1, wherein the incomplete cooking results from a cooking temperature lower than that recommended by the manufacturer of the enamel composition.

3. Glazing according to claim 2, in which the firing is carried out at a temperature at least 10 ° C lower than that recommended by the manufacturer of the enamel composition.

4. Glazing according to one of the preceding claims in which the enamel layer is not uniformly vitrified.

5. Glazing according to one of the preceding claims in which the enameled part whose cooking is incomplete is formed to receive an accessory subjected to mechanical forces. ô.Glazing according to claim 5 wherein the glazing is a windshield, and the accessory is a mirror.

7. Glazing according to one of the preceding claims further comprising at least one enameled part, the cooking is complete.

8. Glazing according to claim 7, wherein the enameled part whose cooking is incomplete is surrounded by an enameled frame whose cooking is complete.

9. Glazing according to one of the preceding claims wherein the cooking is carried out during a bending / quenching operation.

^'10. Glazing according to claim 9 wherein the treatment temperature is between 600 and 650 ° C, the firing temperature recommended by the enamel manufacturer being between 630 and 720 ° C.