GB2145640A - Protecting vitreous articles with peelable polymers - Google Patents

Abstract

In order to protect the surface of a body of flat vitreous material 1 against abrasion, soiling and humidity during storage or transport of a stack of such bodies, one or more peelable bodies of polymeric material 5 is formed adherent to a face of the flat vitreous material. The or each polymeric body is formed by applying to that face an actinically curable material which is then cured actinically (6) to form an adherent, peelable, polymeric body. <IMAGE>

Description

SPECIFICATION Protecting vitreous articles with peelable polymers This invention relates to a method of forming one or more peelable bodies of polymeric material adherent to a face of a body of flat vitreous material.

The body of vitreous material may be in the form of a panel which comprises a single vitreous sheet, for example it may be a sheet of window glass or a mirror, or it may be constituted by for example a hollow glazing panel. Alternatively such body may be a continuous ribbon of glass which has yet to be cut into sheets.

Such sheets or panels are usually stacked in facing relationship for transport and storage. There is a risk of dust or grit being trapped between such panels and this can lead to marring of their surfaces.

Also, it may be difficult to separate panels which are stacked in face-to-face contact due to adhesion forces between them.

It has accordingly become common practice to apply one or more peelable bodies of polymeric material to a face of such a panel. Such a body may take the form of a continuous coating for example as described in Institute National du Verre's British patent specification No. 1,291,242 to protect the whole surface of the panel against abrasion, soiling and humidity. Alternatively, a plurality of peelable strips or spots of polymeric material may be applied in order to hold adjacent stacked panels out of face-to-face contact so that any intervening grit is not ground into the surfaces of the panels and so that they may be separated easily.

It is clearly desirable for ease of application that the material for forming the polymeric bodies should be applied in fluid form and that it should be caused to set in situ.

Various ways of achieving this end have been attempted.

For example Institute National du Verre's above specification suggests causing or allowing setting of a polymeric film by evaporation of a volatile solvent or by using a film-forming composition containing ingredients which react in situ to form the film. The application of heat is also suggested. It is also known to apply polymeric material while hot so that it can set on cooling.

It will be apparent that panels provided with peelable bodies of polymeric material cannot be stacked in face-to-face relation until those bodies are sufficiently hard. A principal disadvantage of the prior art methods of applying such bodies resides in the length of time required for setting of the polymer which in turn entails a requirement for a large storage area until the panels can be stacked. Such methods are difficult to put into operation in a continuous manner at ordinary production line speeds without high energy expenditure to effect hardening of the polymeric material.

It is an object of the present invention to provide a method of forming one or more peelable bodies of polymeric material adherent to a face of a vitreous panel in which these problems are reduced and to enable this to be done rapidly and at ambient temperature.

According to the present invention, there is provided a method of forming one or more peelable bodies of polymeric material adherent to a face of a body of flat vitreous material, characterised in that the or each polymeric body is formed by applying to said face an actinically curable material which is then cured actinically to form an adherent, peelable, polymeric body.

Operation in accordance with the invention as so defined enables much more rapid setting of the polymeric body or bodies than has hitherto been achievable, with the result that the panels can be stacked in face-to-face relation earlier than has hitherto been possible when use is made of those bodies to prevent face-to-face contact of the stacked panels. This is more convenient in practice, and reduces the storage area required for a given rate of production throughput of such panels. The invention also allows savings in time and labour by reducing the number of operations required in stacking, stocking and packing.

The face of the vitreous body on which the peel able polymeric body is formed may be coated or not.

Such a coating if present could for example take the form of a solar radiation screening or infra-red radiation screening coating.

As has been adverted to earlier in this specification, the cured polymeric body may take the form of a continuous film, but it is preferred that at least one peelable body is formed on said face to act as a spacer. Spacing of stacked sheets or panels greatly reduces adhesion forces acting between them so that they can be separated easily, and minimises the risk of abrasion due to small particles of grit which may be trapped between them.

Such a spacer could be of any desired form, for example it could be constituted by spots of polymeric material, but for ease of peeling and to help assure reliable spacing it is preferred that at least one of said spacers be formed as a strip.

Such spacer strips can be formed by several methods but a preferred and very simple method is to cause the vitreous body to pass St least one extrusion orifice from which actinically curable material is extruded. Said material can be advantageously applied to said face as substantially parallel strips.

For greatest ease of separation of stacked sheets and panels, it is preferred that said spacers are each formed at least 1.5 mm thick. This is advantageous especially in the packaging of hollow glazing units to ensure that the corners of successive panels do not contact one another with a consequent risk of chipping.

Such curing is preferably effected by causing the vitreous body to which the actinically curable material has been applied to pass at least one ultra-violet discharge tube so that the curable material is irradiated thereby. In this way curing can be effected very rapidly and at substantially ambient temperature.

Preferably, the or each body of curable material is caused to pass along a path towards which ultraviolet radiation from a said discharge tube is focused. Alternatively, or in addition, the or each said discharge tube is preferably arranged parallel to the direction of passage of the body or bodies of curable material. These features respectively promote efficient use of energy for rapid polymerisation and thorough polymerisation of the applied curable material.

The method according to the invention enables rapid treatment of vitreous mate'rival and is especially useful when the speed of passage of the vitreous body under the ultra-violet discharge tube or tubes is from 5 to 30 m/min. Indeed production rates of between 20 m/min and 30 m/min or even more are readily attainable.

In some preferred embodiments of the invention, said body of vitreous material is a continuous ribbon of freshly formed glass. The curable material may thus be applied to a ribbon of glass as it emerges from an annealing lehr prior to being cut into sheets, so that the sheets cut from the ribbon can then be stacked without any intermediate operation. This is especially suitable when the glass is to be used or transported, or to be stored for any great length of time, as single sheets.

In other preferred embodiments of the invention, said body of vitreous material is a sheet of a multiple glazing panel.

It is desirable for the cured polymeric material to have sufficient adhesion to withstand manipulation during stacking or packing and transport while being readily peelable without leaving any trace on the face from which it has been peeled, and it is also desirable for the material applied to be readily curable.

A suitable actinically curable material to be used in the method according to the invention comprises: (1) at least one radiation reactive prepolymer, (2) at least one reactive monomer, (3) a photo-initiator system, and (4) conventional additives.

A wide variety of materials can be used as the prepolymer component of the actinically curable material.

As it is desirable that the prepolymer or prepolymers used has or have, on the one hand, a relatively high viscosity before curing and on the other hand, elastomeric properties after curing, the most preferred prepolymer will be an acrylated polyurethane, ie. a polyurethane having terminal acryloyl groups.

As an example of such an acrylated polyurethane, there can be mentioned the polymers having the structure A-[-B-C-]n-B-A wherein A is a residue of a hydroxyalkyl acrylate, B is a residue of an organic diisocyanate, C is a residue of an organic diol, such as a polyester diol, a polyether diol, a polycaprolactone diol and the like, and n is an integer from 1 to 20.

However, other radiation reactive prepolymers may be used such as polyester-acrylates or epoxy-acrylates.

Polyester-acrylates are generally produced by polyesterification of dicarboxyiic acids with a stoichiometric excess of hydroxyl groups of dior polyhydric alcohols, the hydroxyl groups in excess then being esterified with acrylic acid or one of its functional derivatives.

Epoxy-acrylates are for example the reaction products of a polyepoxide, such as bisphenol A diglycidyl ether and epoxidised soya bean oil, with acrylic acid.

Polyene-polythiol compositions such as described in U.S. patents 3,725,229; 3,708,413; 3,697,397 and 3,725,228 (W.R. GRACE & Co) may also be mentioned.

Other suitable radiation reactive prepolymers are readily apparent to the skilled polymer chemist, the above- mentioned listing being only illustrative and not all-inclusive.

As examples of suitable reactive monomers, one can mention alkyl acrylates having up to about 12 carbon atoms in the alkyl radical, such as ethyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, amyl acrylate, n-lauryl acrylate, nonyi acrylate, n-octyl acrylate, etc.; alkoxyalkyl acrylates, such as methoxybutyl acrylate, ethoxyethyl acrylate, ethoxy- propyl acrylate, etc.; hydroxyalkyl acrylates, such as hydroxyethyl acrylate, hydroxybutyl acrylate, etc.; aralkyl acrylates, such as phenoxyethyl acrylate, benzyl acrylate, etc.; cycloalkyl acrylates, such as cyclohexyl acrylate; aminoalkyl acrylates, such as diethyl-aminoethyl acrylate, etc.; diacrylates of diols or ether-diols, such as 1,4- butanediol diacrylate, 1,6-hexanediol acrylate, neopentyl glycol diacrylate, di-, tri-, and/or tetra-ethylene glycol diacrylate; vinyl derivatives like Nvinylpyrrolidone and vinyl pyridine, etc. These monomers may be used alone or as mixtures.

These reactive monomers are intended to modify the viscosity of the formulation and to adapt it to the apparatus used. They may also modify the properties of the cured polymeric material.

The actinically curable material also contains a photo-initiator system including photo-sensitisers and/ or photo- initiators. The photo-sensitisers, through the intermediary of the unsaturated system(s) of the curable material or of a photo-initiator, produce free radicals or ions which initiate the cross-linking (curing) of the material.

With regard generally to photo-sensitisers or photo-initiators which may be used in the present invention, reference is made particularly to the following literature references: G. DELZENNE, Ind. Chim. Belge, 24 (1959), 739-764.

J. KOSAR, "Light Sensitive Systems", Publ. Wiley, New York, 1965.

N.J. TURRO, "Molecular Photochemistry", publ. Benjamin Inc., New York, 1967.

H.G. HEINE, H.J. ROSENKRANZ, H. RUDOLPH, Angew. Chem. 84, (1972), 1032.

The photo-initiators are essentially chemical substances belonging to the following major groups: compounds containing carbonyl groups, such as pentanedione, benzil, piperonal, bezoin and its halogenated derivatives, ethers of benzoin, anthraquinone and its derivatives, p,p'-bis(dimethylanino)-benzophenone, benzophenone and the like; compounds containing sulphur or selenium, such as di- and polysulphides, xanthogenates, mercaptans, dithiocarbamates, thioketones, betanaphthoselenazolines; peroxides; compounds containing nitrogen, such as azonitriles, diazo compounds, diazides, derivatives of acridine, phenazine, quinoxaline, quinazoline and oxime esters, such as 1-phenyl-1,2-propanedione 2-[0-(benzoyl)oxime]; halogenated compounds such as halogenated ketones or aldehydes, methyl aryl halides, sulphonyl halides or dihalides; photo-initiating dyes, such as diazonium salts, azoxybenzenes and derivatives, rhodamines, eosines, fluorescein, acriflavine and the like.

The photo-sensitisers belong to one of the following groups: ketones and their derivatives, carbocyanines and methines, polycyclic aromatic hydrocarbons, such as anthracene and the like, dyes, such as xanthenes, safrinines and acridines.

In addition to the foregoing components, the curable material can also contain conventional additives, such as viscosity modifiers, thixotropic agents, polymerisation inhibitors intended to ensure stability during storage, for example quinones, hydroquinones, substituted phenol derivatives, primary aromatic amines, copper compounds and the like, which are employed in the usual known effective concentrations.

The curable material as described herein can be cured by any of the known actinic radiation curing methods such as exposure to ultra-violet light. Irradiation can be performed using any of the known and commonly available types of radiation curing equipment, for example, medium-pressure mercury vapour lamps of at least 80 W/linear cm arc length, preferably fitted with a reflector. It has been found to be particularly useful to employ a semi-elliptical reflector with the above described mercury vapour lamps.

By a semi-elliptical reflector is meant a reflector which is about half an ellipse. The lamp is positioned at about the focus of the ellipse and the moving body of curable material is optimally passed through at about the point where the other focus of the ellipse would lie. Such an arrangement is used to minimise as much as possible loss of actinic radiation to the surrounding area, and thus tends to increase the efficiency of the system.

Preferred embodiments of the present invention will now be described by way of example with reference to the accompanying diagrammatic drawings in which: Figure 1 is a side view of apparatus suitable for performing the present invention, and Figure 2 is a sectional view along the line ll-ll of Figure 1.

In Figure 1, a sheet of glass 1 is conveyed on conveyor rolls 2 past a bank of extrusion nozzles 3 from whose orifices 4 are extruded strips of actinically curable material 5 so that this material is applied to the glass sheet 1 in substantially parallel strips (compare Figure 2) as the sheet passes the extrusion orifices 4. Located downstream of the extrusion orifices 4 is a bank of ultra-violet discharge tubes 6 each equipped with a reflector 7 arranged to focus radiation towards the path followed by a respective body of curable material.

From Figures 1 and 2, it will be inferred that each discharge tube 6 is arranged parallel to the direction of passage of th glass sheet 1 and so that the curable material passes along, one strip under each tube.

The material is thus exposed to ultra-violet radiation from the tubes for the maximum length of time so as to promote curing.

In a specific practical example, successive sheets 1 were conveyed at a speed of 20 m/min, and the curable material was extruded in strips with a diameter of 1.5 to 2.5 mm. The ultra-violet discharge tubes used were medium pressure mercury vapour lamps having an electrical power consumption of 80W/cm arc length and a useful arc length of 6cm (excluding the electrode ends). The reflectors used were semielliptical and the ultra-violet discharge tubes were each located at one focus of such ellipse while the paths of the curable strips led through the other ellipse foci.

It will readily be appreciated that instead of applying strips it would equally be possible to apply spots or a continuous coating of a film. In the case of a continuous film, it would of course be necessary to ensure that the whole coated surface was irradiated.

It will also be appreciated that cured adherent peelable bodies of polymeric material can likewise be formed on a continuous ribbon of freshly annealed glass, for example by locating apparatus as described with reference to the drawings at the exit from the annealing lehr.

There now follow specific examples of actinically curable material suitable for applying to form peelable bodies of polymeric material in accordance with the present invention: Example 1 An acrylated polyurethane having the following structure A-[-B-C-]n-B-A wherein A is a residue of 2-hydroxyethyl acrylate, B is a residue of tolylene diisocyanate C is a residue of polopropylene glycol (molecular weight = 1000), and n is X, is diluted 1, 6-hexanediol (HDDA) (ratio by weight of prepoiymer to HDDA is 75:25). This solution has a viscosity of 4,400 centipoises (cP) at 22"C.

A thickened formulation is prepared by mixing: 100 parts by weight of the acrylated polyurethane/HDDA solution, and 5 parts by weight of Aerosil 300 (Trade Mark of DEGUSSA).

The obtained formulation has a viscosity of 64,000 cP at 22"C and 5 r.p.m. (Brookfield Viscometer: Model HBT).

Adding 1 part by weight of benzophenone thereto will give the ready to use UV-curable material. A layer of 1 mm thickness is applied and cured at a speed of 20 m/min (UV arc length = 6 cm). The resulting polymer has a shore-A hardness of 95, adheres sufficiently to the glass sheet but remains easily peelable.

It has been found experimentally that on increasing the thickness of the applied layer to 3 mm, the am mount of benzophenone should be halved.

Examples 2 and 3 These Examples show that the hardness after UV-curing is modified on using other prepolymer/HDDA ratios.

Formulation parts by weight Example 2 Example 3 Acrylated polyurethane 80 70 HDDA 20 30 Benzophenone 1 1 Aerosil 300 (Trade Mark) 5 5 Viscosity (cP at 5 r.p.m.) 288,000 64,000 Shore-A hardness 93 98 Examples 4 to 7 These Examples show that the flexibility of the UV-cured polymer can be increased by replacing the diacrylate by a monoacrylate and/or by increasing the molecular weight of the acrylated polyurethane (n higher than 1).

Formulation parts by weight Example 4 Example 5 Example 6 Example 7 Acrylated polyurethane of Example 1 75 40 40 *Modified acrylated polyurethane - 40 40 90 HDDA 12.5 20 - 10 2-Ethylhexyl acrylate 12.5 - 20 Benzophenone 1 1 1 1 Aerosil 300 (Trade Mark) 5 5 5 5 Viscosity (cP) 3,600 9,800 5,000 18,000 Shore-A hardness 90 85 60 55 *Acrylated polyurethane of Example 1, but wherein C is the residue of polypropylene glycol of molecular weight 2000 and n is 2.

Example 8 This example shows the possibility of rendering hard and brittle prepolymers, such as epoxy-acrylates, flexible.

Formulation parts by weight Example 8 Epoxy-acrylate (EBECRYL 600) (Trade Mark) 80 2-ethylhexyl acrylate 20 Benzophenone 1 Aerosil 300 (Trade Mark) 5 Viscosity (cP) 4,000 Shore-A hardness 100

Claims (16)

1. A method of forming one or more peelable bodies of polymeric material adherent to a face of a body of flat vitreous material, characterised if that the or each polymeric body is formed by applying to said face an actinically curable material which is then cured actinically to form an adherent, peelable, polymeric body.

2. A method according to Claim 1, wherein at least one peelable body is formed on said face to act as a spacer.

3. A method according to Claim 2, wherein there is at least one of said spacers formed as a strip.

4. A method according to Claim 3, wherein the vitreous body is caused to pass at least one extrusion orifice from which actinically curable material is extruded.

5. A method according to Claim 3 or 4, wherein said actinically curable material is applied to said face as substantially parallel strips.

6. A method according to any of Claims 2 to 5, wherein said spacers are each formed at least 1.5 mm thick.

7. A method according to any of the preceding claims, wherein such curing is effected by causing the vitreous body to which the actinically curable material has been applied to pass at least one ultra-violet discharge tube so that the curable materal is irradiated thereby.

8. A method according to Claim 7, wherein the or each body of curable material is caused to pass along a path towards which ultra-violet radiation from a said discharge tube is focused.

9. A method according to Claim 7 or 8, wherein the or each said discharge tube is arranged parallel to the direction of passage of the body or bodies of curable material.

10. A method according to any of the preceding claims wherein the said body of vitreous material is a continuous ribbon of freshly formed glass.

11. A method according to any of claims 1 to 9, wherein the said body of vitreous material is a sheet of a multiple glazing panel.

12. A method according to any of the preceeding claims, wherein said actinically curable material comprises: (1) at least one radiation reactive prepolymer, (2) at least one reactive monomer, (3) a photo-initiator system, and (4) conventional additives.

13. A method according to Claim 12, wherein the said prepolymer is an acrylated polyurethane.

14. A method according to Claim 13, wherein said prepolymer is an acrylated polyurethane having the structure A-[-B-C-]n-B-A wherein A is a residue of a hydroxyalkyl acrylate, B is a residue of an orgasnic diisocyanate, C is a residue of an organic diol selected from the group consisting of polyester diols, polyether diols and polycaprolactone diols, and n is an integer from 1 to 20.

15. A method according to Claim 12, wherein said prepolymer is a polyester-acrylate or an epoxyacrylate.

16. A method according to Claim 12, wherein said reactive monomer is an alkyl acrylate, an alkoxyalkyl acrylate, a hydroxyalkyl acrylate, an aralkyl acrylate, a cycloalkyl acrylate, an aminoalkyi acrylate or a diacrylate of a diol or of an ether-diol.