Method and device for identifying and marking at least one defect in a glass sheet

Abstract

The invention relates to a method for identifying and marking at least one defect (10) in a glass sheet (1), in which method: at least one defect (10) is identified on the surface or in the glass sheet (1), then an ink mark is sprayed onto a face of the glass sheet and onto the defect (10), preferably completely covering the defect (10), wherein the ink is selected from the group comprising two-component inks comprising a curing agent, self-crosslinking inks and photo-crosslinking inks.

Description

DESCRIPTION TITLE: Method and device for locating and marking at least one defect in a sheet of glass

[0001] The present invention relates to the field of glass manufacturing.

[0002] More specifically, this invention relates to the identification of defects on glass ribbons, or sheets of flat glass, manufactured industrially.

[0003] As is well known, glass is usually manufactured as a continuous ribbon of float glass or cast glass.

[0004] This continuous ribbon is then cut into trays, or sheets, of glass, each of which can typically have dimensions of 3.21 m x 6 m, or 2.55 m x 3.21 m.

[0005] These glass plates are then cut according to each specific need, the optimization of this cutting being carried out using dedicated algorithms to minimize waste.

[0006] Preferably, this optimization must take into account the defects in the glass, so as to be able to place them in the offcuts: WO2015 / 121548 describes a method allowing this optimization, comprising a step of identifying the defects in the glass.

[0007] From a practical point of view, the identification of glass defects can be carried out according to two principles.

[0008] The first principle consists of identifying defects, for example by optical means, and generating a mapping file of these defects which is uniquely associated with a glass plate by tattooing this plate.

[0009] This tattoo may include, for example, the affixing of an optical code such as a QR code, as taught, for example, by WO2015 / 121548.

[0010] Subsequently, reading this tattoo allows you to instantly recall the file of the mapping of the defects of the plateau, and to carry out the optimized cutting of this plateau thanks to this mapping.

[0011] This first principle of identifying glass defects may require a fairly complex interface with existing glass ribbon production equipment.

[0012] For this reason, a second principle for detecting glass defects, which is simpler to implement, is often preferred.

[0013] According to this second principle, after having identified the defects in the glass, for example by optical means, they are marked with a spot of colored paint (often blue), the latter being projected onto the surface of the glass by a spray gun.

[0014] Although simple and robust, such a process is not entirely satisfactory, particularly due to the poor adhesion of the paint to the glass.

[0015] The present invention thus relates to a method for locating and marking at least one defect in a sheet of glass, in which: - at least one defect is identified on the surface or in said glass sheet, then - a spot of ink is projected onto one side of said glass sheet and onto said defect, preferably completely covering said defect, said ink being selected from the group comprising two-component inks comprising a hardening agent, self-crosslinking inks and photo-crosslinking inks.

[0016] In the context of the present invention, the notion of "defect" designates the presence of an inhomogeneous particle (a particle of composition different from the composition of its environment) in the thickness of the glass or on the surface of the glass or of a mechanical defect such as a hollow, a crack, a scratch, etc. on the surface of the glass. In a known manner, a defect has a critical size such that its presence in a glass product (glazing) cannot be accepted for the purchaser or the end user of this glass product.

[0017] In the context of the present invention, the notion of "stain" refers to the fact that the flat shape of the ink which is projected is not precisely controlled. It can be a generally oval shape or a generally round shape.

[0018] Said ink is preferably an ink opaque in the visible light wavelength range.

[0019] In one variant, a two-component ink is used; this two-component ink is an ink in which a hardening agent is added to the solvent in which the pigment of the ink is found, at the time when it is desired to use this ink.

[0020] In one variant, a self-crosslinking ink is used; this self-crosslinking ink is an ink whose pigment is suspended inside a resin capable of spontaneously polymerizing on contact with open air.

[0021] In the context of the present invention, a photo-crosslinkable ink is an ink whose pigment is suspended inside a resin capable of polymerizing under the effect of photo-activation produced for example by ultraviolet rays.

[0022] After numerous tests and research, it has emerged that by using paints of the above-mentioned type, a very strong adhesion of paint stains to the surface of the glass sheet is achieved.

[0023] According to other optional characteristics of the method according to the invention, taken alone or in combination:

[0024] - a two-component ink is used, this two-component ink comprising a pigment, a solvent, and a silane-based curing agent, for example based on amino-silane;

[0025] - the solvent is ethyl acetate and the pigment is, preferably, an epoxy pigment;

[0026] - a two-component ink is used, this two-component ink comprising an epoxy pigment, ethyl acetate as solvent, and amino-silane as hardening agent: it turns out that this hardening agent constitutes a particularly effective adhesion promoter of the ink to the surface of the glass sheet;

[0027] - a self-crosslinking ink is used, this self-crosslinking ink is polyurethane resin: very good adhesion characteristics on glass are obtained with such a resin;

[0028] - the ink stain is projected onto the said defect before the glass sheet is coated with a functional layer: such a layer, deposited for example by magnetron process, can fulfill different functions including protection against solar radiation;

[0029] - at least one layer, and in particular at least one thin layer having a thickness of between 1 nm and 200 nm, is deposited on said face after said ink projection, the deposition of said layer preferably being carried out under vacuum: thanks to the very strong adhesive power of the ink, the stain does not leave in a process requiring washing; said ink stain is still present after this washing; when the deposition of a layer is carried out under vacuum, the ink is applied in an ambient environment (not under vacuum), the washing is also carried out in an ambient environment (not under vacuum) and the marking process is thus simplified;

[0030] - detection means detect at least one defect on said layer and these detection means also detect said ink stain: this makes it possible to carry out with a single machine and in a single operation the inspection of the defects of the glass and of the layer, prior to the cutting of the glass sheet by means of a cutting optimization algorithm;

[0031] - said task is projected onto said defect by means of a paint marking bridge, said bridge being fixed and extending transversely relative to a direction of advance of said sheet passing underneath: simple marking equipment, not requiring no particular adaptation, can thus be used, which makes the method according to the invention particularly economical.

[0032] - said glass sheet is a ribbon of float glass obtained by floating on a bath of molten tin and said at least one defect is identified on the surface or in said ribbon of float glass;

[0033] - said glass sheet is a mineral glass sheet.

[0034] The present invention also relates to a method for obtaining a marked glass sheet comprising: - a floating step on a molten tin bath to obtain a ribbon of float glass corresponding to said glass sheet; and - the steps of the marking process as defined above, said at least one defect being identified on the surface or in said glass ribbon and the ink stain being projected onto one side of said float glass ribbon and onto said defect to obtain the marked glass sheet.

[0035] The present invention also relates to a marking device for implementing the above-mentioned method, comprising at least one reservoir containing an ink in accordance with the above, and at least one means for projecting this ink onto a sheet of glass.

[0036] Preferably, this marking device comprises a marking bridge in which said reservoir and said projection means are slidably mounted on a transverse beam.

[0037] Other characteristics and advantages of the invention will emerge from reading the description which follows, with reference to the appended figures, which illustrate: [Fig. 1]: a schematic perspective view of a marking bridge according to the invention overlapping a sheet of glass to be marked, and [Fig. 2]: A schematic perspective view showing a glass sheet coated with a functional layer passing through a defect inspection device.

[0038] Referring to Figure 1, a glass sheet 1 is shown in the form of a ribbon running transversely (arrow F) to the direction of a marking bridge 3 according to the invention.

[0039] The said ribbon is a float glass ribbon.

[0040] Said float glass ribbon is obtained by floating on a bath of molten tin.

[0041] Typically, this tape can be 3.21 m wide, and cut every 6 m.

[0042] The glass making up the glass sheet 1 is a mineral glass.

[0043] The glass constituting the glass sheet 1 preferably has a composition of the silico-soda-lime type, that is to say a composition comprising silica (SiC>2) as the forming oxide and oxides of sodium (soda Na2O) and calcium (lime CaO).

[0044] Optical detection means known per se, which may include in particular a camera, make it possible to identify defects in the glass of the ribbon.

[0045] The marking bridge 3 comprises at least one reservoir 5 of marking ink according to the invention, and a gun 7 for projecting this ink onto the surface of the glass sheet 1.

[0046] This projection gun 7 and possibly the marking ink reservoir 5, are slidably mounted on the transverse beam 9 of the marking bridge 3, under the action of a motorization interfaced on the one hand with the means for driving the glass ribbon, and on the other hand with the optical detection means.

[0047] In the case of photocurable ink, UV illumination (e.g. UV / LED) immediately follows the gun so as to cure the ink instantly.

[0048] Thus, when a defect 10 of the glass sheet 1 arrives at the right of the marking bridge 3, the projection gun 7 is placed above this defect, and the means control of this gun 7 causes a projection of a stain of ink coming from the reservoir 5 onto the defect 10 of the glass sheet 1.

[0049] In most cases, the glass sheet 1 must be coated with at least one functional layer, for example by magnetron process, such a functional layer making it possible, for example, to attenuate solar radiation through the glass sheet 1.

[0050] Processes using such a functional layer generally require preliminary washing of the glass sheet in a specific, highly abrasive washing machine. Such washing helps to brighten the surface of the glass and promote the adhesion of the functional layer to this surface.

[0051] It is therefore essential that the defect detection tasks on the glass sheet 1 have excellent adhesion characteristics, in order to limit the risk of them coming off when washed.

[0052] After extensive research and a large number of laboratory tests, specific inks have been identified which enable us to meet these very demanding specifications.

[0053] These are two-component inks containing a curing agent, self-crosslinking inks and photo-crosslinking inks.

[0054] A two-component ink is an ink in which a hardening agent is added to the solvent in which the ink pigment is found, at the time when the ink is to be used.

[0055] One such example of a two-component ink is Dubuit's 8600: this ink contains a pigment suspended in ethyl acetate as a solvent, and the hardener component to be mixed when using the ink is based on amino-silane.

[0056] Amino-silane exhibits good adhesion properties on “fresh” glass forming the float glass ribbon.

[0057] Such an ink has the advantage of being very quickly dry to the touch (less than a minute), which is compatible with rapid stacking of the glass sheets after marking.

[0058] After mixing with the hardener, the ink remains liquid and is therefore usable for approximately four hours.

[0059] A self-crosslinking ink is an ink whose pigment is suspended inside a resin capable of polymerizing spontaneously upon contact with open air.

[0060] One such example of ink is the reference 7400 (PU) with polyurethane resin from the company Dubuit.

[0061] Once this ink has been poured into the reservoir 5 of the marking bridge 3, it can remain there practically without time limit before being projected onto the defects in the glass.

[0062] A photo-crosslinkable ink is an ink whose pigment is suspended inside a resin capable of polymerizing under the effect of photo-activation produced for example by ultraviolet rays applied immediately after deposition.

[0063] Once UV is applied, the ink is fully cured and dry to the touch.

[0064] One such example of ink is the EVOJET 3100 from Dubuit.

[0065] For example, photo-curable ink includes acrylates such as phenoxyacrylates or acrylic acid. Such photo-curable ink is polymerized when exposed to UV light.

[0066] By using inks in accordance with the above, there is an increase in the adhesion of the ink pigments to the surface of the glass sheet 1, including when the latter is washed for the purpose of depositing a functional layer.

[0067] The excellent adhesion of these ink stains was measured using the so-called "Erichsen Brushing Test" (Erichsen friction test) in accordance with DIN EN ISO 11998: these tests in fact indicated that the adhesion of these tasks was greater than 50 cycles.

[0068] The ink stains used to identify defects in the glass 1 thus remain firmly attached to it, even when the process requires washing the glass surface with highly abrasive machines.

[0069] Advantageously, the characteristics of the ink pigment (color, reflective power, etc.) will be chosen so that the same machine can be used to inspect the defects 13 of the functional layer and the defects 10 of the glass.

[0070] Such a machine, visible in figure 2, typically comprises a plurality of cameras 11 arranged on either side of the path of the glass sheet 1, capable of detecting defects in the functional layer and the glass.

[0071] This allows both detections to be carried out in a single operation, which saves substantial time and simplifies the inspection equipment.

[0072] Naturally, the invention is described in the foregoing by way of example. It is understood that those skilled in the art are able to carry out different variant embodiments of the invention without departing from the scope of the invention.

[0073] The invention also relates to a method for obtaining a marked glass sheet comprising: - a floating step on a molten tin bath to obtain a ribbon of float glass corresponding to said glass sheet; and - the steps of the marking method as defined above in relation to figures 1 and 2, said at least one defect 10 being identified on the surface or in said ribbon of glass and the ink stain being projected onto one face of said ribbon of float glass and onto said defect 10.

Claims

CLAIMS 1. Method for locating and marking at least one defect (10) of a glass sheet (1), in which: at least one defect (10) is identified on the surface or in said glass sheet (1), then a spot of ink is projected onto one side of said glass sheet and onto said defect (10), preferably completely covering said defect (10), said ink being selected from the group comprising two-component inks comprising a hardening agent, self-crosslinking inks and photo-crosslinking inks.

2. Method according to claim 1, in which a two-component ink is used, this two-component ink comprising a pigment, a solvent, and a silane-based curing agent, for example based on amino-silane.

3. The method of claim 2, wherein the solvent is ethyl acetate and the pigment is preferably an epoxy pigment.

4. The method of claim 1, wherein a self-crosslinking polyurethane resin ink is used.

5. Method according to any one of claims 1 to 4, in which at least one layer, and in particular at least one thin layer having a thickness of between 1 nm and 200 nm, is deposited on said face after said ink projection, the deposition of said layer preferably being carried out under vacuum.

6. Method according to claim 5, wherein said glass sheet is washed before the deposition of the thin layer.

7. Method according to any one of claims 5 or 6, in which detection means detect at least one defect (13) on said layer and these detection means also detect said ink stain.

8. Method according to any one of the preceding claims, in which said task is projected onto said defect (10) by means of a paint marking bridge (3), said bridge being fixed and extending transversely relative to a direction of advance of said sheet passing underneath.

9. A method according to any one of the preceding claims, wherein said glass sheet (1) is a float glass ribbon obtained by floating on a molten tin bath and said at least one defect (10) is identified on the surface or in said float glass ribbon.

10. Method according to any one of the preceding claims, wherein said glass sheet (1) is a mineral glass sheet.

11. Method for obtaining a marked glass sheet (1) comprising: - a floating step on a molten tin bath to obtain a ribbon of float glass corresponding to said glass sheet (1); and - the steps of the marking method according to any one of the preceding claims, said at least one defect (10) being identified on the surface or in said glass ribbon and the ink stain being projected onto one face of said float glass ribbon and onto said defect (10) to obtain the marked glass sheet (1).

12. Marking device for implementing the method according to any one of claims 1 to 10, comprising at least one reservoir (5) containing said ink, and at least one means (7) for projecting this ink onto a sheet of glass (1).

13. Marking device according to claim 12, comprising a marking bridge in which said reservoir (5) and said projection means (7) are slidably mounted on a transverse beam (9).

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