GB2132507A

GB2132507A - Mirrors

Info

Publication number: GB2132507A
Application number: GB08236343A
Authority: GB
Inventors: Pierre Laroche
Original assignee: Glaverbel Belgium SA
Current assignee: AGC Glass Europe SA
Priority date: 1982-12-21
Filing date: 1982-12-21
Publication date: 1984-07-11
Also published as: FR2537969B1; DE3346048C2; ES528669A0; DE3346048A1; FR2537969A1; GB2132507B; BE898481A; JPS59174546A; ES8505320A1

Abstract

A mirror comprises a reflective layer 2 on the rear surface of a transparent sheet 1, the reflective layer being covered by one or more protective layers 3,4. The or a protective layer 4 is formed by applying a coating of an electron beam curable resin composition to the coated (2,3) rear surface of the sheet and curing the resin in one or more electron beams to form an adherent protective coating. <IMAGE>

Description

SPECIFICATION Mirrors This invention relates to a method of manufacturing a mirror comprising applying a reflective layer to a rear surface of a transparent glass sheet and covering the reflective layer with one or more protective layers.

In the most common mirror production methods, a transparent glass sheet is coated on its rear surface with a reflective layer usually of silver. The silver layer is covered with a copper layer and the copper layer is then painted or varnished. The paint layer serves to protect the underlying metal layers against corrosion and abrasion.

A major disadvantage of such methods is that the protective paint layer takes some time to dry and it is accordingly necessary to store freshly manufactured mirrors in such a way that their rear surfaces are not contacted while the paint is still wet. This is inconvenient in line production and requires considerable additional storage space when mirrors are manufactured on a large scale.

In the usual production methods hitherto used, the protective coating sets by evaporation of solvent. This leads to pollution of the production plant atmosphere by solvent vapours especially in large scale production. Also drying is not sufficiently rapid unless the mirrors are heated.

It is an object of the present invention to provide a mirror manufacturing method in which this disadvantage is avoided.

According to the present invention, there is provided a method of manufacturing a mirror comprising applying a reflective layer to a rear surface of a transparent glass sheet and covering the reflective layer with one or more protective layers, characterised in that the or a said protective layer is formed by applying a coating of an electron-beam curable resin composition to the coated rear surface of the sheet and curing the resin in one or more electron beams to form an adherent protective layer.

By making use of the present invention, the resin layer can be cured in a matter of seconds so that freshly manufactured mirrors can be stacked as desired without having to take precautions against marring a still-wet protective layer and continuous line production can be facilitated. Also the problem of solvent pollution can be substantially eliminated.

Furthermore, electron-beam curing presents considerable advantages over photonic radiation curing methods. Firstly, it is not necessary to use a photo-initiator in the resin composition. Secondely, the resin layer need no longer be translucent to the photonic radiation so that the resin can incorporate any desired pigments or fillers, and the layer can be thicker so that it affords better protection to the reflective layer.

In fact there has been a prejudice against electron-beam curing of resin compositions applied for whatever reason to a glass sheet. This is because it is theoretically predictable that electron beam irradiation of a glass sheet will have a marked deleterious effect on its optical properties. In fact it has now been found that the predicted adverse effects are not so serious as was expected and that any deterioration in the properties of the mirror is well within acceptable limits. Accordingly, use can be made of electron beam curing with the benefit of the advantages specified.

Said electron beam curing should take place in an inert atmosphere, for example a nitrogen atmosphere, since the presence of oxygen at that stage adversely affects the quality of the protective coating formed. A substantially inert atmosphere can be maintained quite easily even in a continuous process, for example by effecting curing in a tunnel chamber continuously supplied with inert gas at above atmospheric pressure. The use of nitrogen as inert gas is preferred for reasons of economy and convenience.

The resin composition used preferably comprises by weight: At least one unsaturated monomeric and/or oligomeric substance as curable base material 1090% At least one monomeric and/or oligomeric and/or poiymeric substance as reactive diluent curable with the base material 0-90% Plasticiser O 40% Pigment and/or filler 0-40% Other additive(s) 0.510% The electron beam acts on the base material to effect rapid curing by chain-extending and/or cross linking reactions. Examples of suitable oligomers are of the following types: polyurethane acrylates, epoxy acrylates, polyester-polyol acrylates, polyether-polyol acrylates and polyenepolythiols.

Reactive diluents are used, for example to reduce the viscosity of the base material. Mono- or multifunctional acrylates may be used, particularly for reducing the viscosity of polyurethane and epoxy acrylate base materials. The reactive diluents combine with the base material on activation of the latter by the electron beam.

Plasticisers, pigments, fillers and other additives conventionally used in the manufacture of paints may also be used if desired.

Advantageously, said curing is effected by sweeping the resin coated face of the sheet with one or more electron beams in the form of a curtain. This is a simple and convenient method of effecting curing.

Preferably, said radiation-curable resin coating is applied by a curtain-coating technique. Such techniques are beneficial for forming thin coatings of high quality and uniform thickness.

Advantageously, said resin coating is applied and cured to leave a said adherent protective layer whose thickness is at least 20 m and preferably lies in the range 30 ym to 80 ,um.

Coatings of the specified minimum thickness give excellent protection to the reflective layer, and the adoption of the said preferred thickness range contributes to ease of curing and economy of use of resin.

Preferably, the resin composition is caused to absorb a dosage of between 3 and 10 m rad to effect said curing. Such a dosage contributes to efficient and rapid curing.

The present invention is particularly applicable to continuous line production of mirrors in which a plurality of said mirrors is conveyed successively through resin-coating and curing stations, as is preferred.

The invention includes a mirror manufactured by a method as herein defined and extends to an intermediate product for use in such method.

Accordingly the present invention also provides an intermediate product for use in the manufacture of a mirror by a method characterised in that such product comprises a transparent glass sheet whose rear surface bears a reflective layer and an overcoating of an electron beam curable resin composition which is so curable to form an adherent protective layer.

Preferred embodiments of the present invention will now be described by way of Example and with reference to the accompanying diagrammatic drawings in which: Figure 1 is a cross sectional view of a mirror formed in accordance with the present invention, and Figure 2 is a schematic view of a portion of apparatus for carrying the invention into effect.

Figure 1 shows a mirror formed by a transparent glass sheet 1 bearing on its rear (upper) face a reflective layer 2 covered by an intermediate layer 3 and a protective layer 4formed from an electronbeam cured resin coating.

The reflective layer 2 and the intermediate layer 3, for example of silver and copper respectively may be applied by any known process. The principal purpose of intermediate layer 3 is to guard against oxidation of the reflective layer 2. The present invention is characterised by the mode of applying the protective layer 4.

Apparatus for applying the adherent protective layer 4 is illustrated in Figure 2. In Figure 2, transparent glass sheets 5 bearing reflective coatings (not shown) and optional intermediate coatings (not shown) are carried by a conveyor 6 beneath a coating apparatus 7, suitably a curtain coating apparatus, where a coating 8 of electron-beam curable resin is applied. The conveyor 6 carries the thus coated sheets through a tunnel chamber 9 where the applied coating 8 is treated by an electron beam 10 generated by a curtain type electron processor 1 The tunnel chamber 9 is flushed with inert gas, such as nitrogen, from a reservoir 12.The entrance 1 3 of the tunnel is as low as possible while giving clearance to the coated sheets 5 and the tunnel exit 14 may be closed as shown by a flexible curtain 1 5 to facilitate maintenance of a substantially inert atmosphere within the tunnel chamber 9 with a low consumption of gas from reservoir 12.

In a particular plant, the mirror-coated glass sheets 5 are given an electron-beam curable resin coating by a curtain coating technique while being conveyed at a speed of 20 m/min. Two electron beam accelerators are used end-to-end, each being arranged to sweep a sheet width of 1.7 m, to treat a sheet 3.4 m wide. The accelerators were 1 75 KeV accelerators from E.S.I. of Geneva, though 1 50 KeV accelerators could have been used. The resin coating was applied to a thickness of 60 ,um corresponding to approximately 120 g/m2 depending of course on the resin composition used. The dose absorbed by the resin coating was 6 m rad (6x 1 O-SGy).

Resin compositions used may have the following general composition (parts by weight): Electron beam curable base material containing unsaturated monomer or oligomer 1090% Monomeric, oligomeric and/or polymeric unsaturated polymerisable component as reactive diluent 90- 0% Plasticiser 0 0-0% Pigment and/or filler 0 40% Other additives 0.510% The following are specific examples of resin compositions for application and curing as described above.

Example 1 Plex 6628-0 (from Rohm) 60% by weight Plex 6670-0 (from Rohm) electron beam curable acrylic resin 14% Lead oxide 7% Titanium oxide 7% Calcium carbonate 10% VN3 (from Union Carbide) viscosity reducing agent 2% Example 2 As electron beam curable base material, the reaction product of: : Tetrachlorophthalic anhydride, polypropylene glycol and glycidyl acrylate 55% by weight Diethylene glycol diacrylate 15% Dioctylphthalate 2% Lead oxide 7% Calcium carbonate 10% Barium sulphate 10% BYK-W980 (from Mallinckrodt) dispersion agent 1% Example 3 Dow epoxy resin DER 661 reacted with acrylic acid to give an electron beam curable epoxy-acrylate base material 40% by weight Tetraethylene glycol diacrylate 15% p dimethylamino acrylate 1.6 hexane diol propionate mixed ester 13% Lead oxide 5% Calcium carbonate 7% Magnesium carbonate 15% Iron oxide 4% BYK-W900 U.P. (from Mallinckrodt) dispersion agent 1% The luminous reflection and energy reflection properties of thus protected mirrors are substantially the same as those of a similar mirror which had not had a protective layer cured by electron beam irradiation.

Claims

1. A method of manufacturing a mirror comprising applying a reflective layer to a rear surface of a transparent glass sheet and covering the reflective layer with one or more protective layers, characterised in that the or a said protective layer is formed by applying a coating of an electron beam curable resin composition to the coated rear surface of the sheet and curing the resin in one or more electron beams to form an adherent protective layer.

2. A method according to Claim 1, wherein said resin composition comprises by weight: At least one unsaturated monomeric and/or oligomeric substance as curable base material 1090% At least one monomeric and/or oligomeric andior polymeric substance as reactive diluent curable with the base material 0-90% Plasticiser 0 40% Pigment and/or filler 0 40% Other additive(s) 0.5-1 0%

3. A method according to Claim 1 or 2, wherein said curing is effected by sweeping the resin coated face of the sheet with one or more electron beams in the form of a curtain.

4. A method according to any preceding claim, wherein said radiation-curable resin coating is applied by a curtain coating technique.

5. A method according to any preceding claim, wherein said resin coating is applied and cured to leave a said adherent protective layer whose thickness is at least 20 ,um and preferably lies in the range 30 Mm to 80 ium.

6. A method according to any preceding claim, wherein the resin composition is caused to absorb a dosage of between 3 and 10 m rad to effect said curing.

7. A method according to any preceding claim, wherein a plurality of said mirrors is conveyed successively through resin-coating and curing stations.

8. A method of manufacturing a mirror according to any preceding claim and substantially as herein described.

9. A mirror manufactured by a method according to any preceding claim.

10. An intermediate product for use in the manufacture of a mirror by a method according to any of claims 1 to 8, characterised in that such product comprises a transparent glass sheet whose rear surface bears a reflective layer and an overcoating of an electron beam curable resin composition which is so curable to form an adherent protective layer.