GB2343639A

GB2343639A - Diffuse reflection glass

Info

Publication number: GB2343639A
Application number: GB9824990A
Authority: GB
Inventors: Georges Pilloy
Original assignee: Glaverbel Belgium SA
Current assignee: AGC Glass Europe SA
Priority date: 1998-11-13
Filing date: 1998-11-13
Publication date: 2000-05-17
Also published as: GB9824990D0

Abstract

A coated glass sheet having diffuse reflection properties for use in furnishing applications carries a coating formed of a two-phase transparent polymer resin composition, characterised in that the coated sheet has a resolution in the range 1 to 6 lines/mm. The resin composition may comprise a varnish containing a dispersion of a solid particulate material of average diameter 0.1-60ž, the proportion of particulate material in the coating being 0.1-10 wt%. The resin may be heat treated to adjust the resolution and gloss.

Description

DIFFUSE REFLECTION GLASS The present invention relates to glass having diffuse reflection properties, otherwise known as matt glass, and to a method for its preparation.

There is a wide variety of applications for glass in which the surface should desirably have a matt finish. These include applications in which specular reflection is an inconvenience, for example television screens, computer displays, liquid crystal displays, photographic screens, light bulbs, display cabinets, picture frames and high quality furnishings.

The matt effect has traditionally been achieved by a roughened glass surface. This diffuses the reflected incident light and thereby reduces or eliminates specular reflection or glare.

The most important measurements in determining the optical characteristics of a matt surface are its gloss, i. e. a measure of its brilliance, and its resolution, i. e. the perception of details through the surface. Gloss is typically measured by a glossmeter in which a light beam is directed at the surface, for example at an angle of 60 ,. nd the intensity of reflection is observed by a receiver aligned with the reflected beam. A high gloss value indicates poor light diffusion properties.

The resolution of the surface can be evaluated by placing the surface parallel to a target carrying a series of bar codes. Each bar code typically comprises two sets of five regularly spaced lines at right angles to each other, each code in the series having a different spacing distance between the lines (expressed as lines/mm). The differently sized bar codes are arranged on the target in a graded sequence. Glass having a matt surface to be analysed is placed at a given distance (generally 5 mm) from the target. An observer at a fixed distance (e. g. 300 mm) from the target notes the maximum number of lines/mm, i. e. the finest bar code, which may be counted.

The typical method of producing a matt surface was to etch the glass with a fluoride material but such materi. tls are now generally unacceptable environmentally and for recycling. Attempts have therefore been made to create a matt effect by other methods.

One approach (US patent No. 5725957) relates to a coated glass substrate to serve as a faceplate for use with the screen of a cathode ray tube. The coating may be formed from a precursor solution of an organosilicon material and/or a metal oxide such as indium tin oxide and is applied as one or more layers from the precursor solution, each applied layer being densified by heating to an elevated temperature such as 500 C.

Another approach has been to use a transparent polymer varnish filled with small particles, for example of silica, as a coating on the glass surface. The filler particles have an optical effect similar to a roughened surface presenting to incident light a pattern of peaks and troughs across the glass surface, and thus creating a diffuse pattern of reflection of the light. WO 96/20418 relates to a method for manufacturing a glass substrate with reduced reflectivity, and thus reduced surface glare, by forming on the glass a film coating from a suspension of sub-micron transparent particles and a binder and then drying the film in such a manner that in situ flocculation of the said particles takes place.

The present invention relates to modifications in the composition of the coating which provide improvements in the optical properties of a coated glass sheet and control of obtaining the required properties.

According to the present invention there is provided a coated glass sheet having diffuse reflection properties for use in furnishing applications, which sheet carries a film coating formed of a two-phase transparent polymer resin composition, characterised in that the coated sheet has a resolution (as defined herein) in the range 1-6 lines/mm.

Matt glass according to the invention is especially useful in the fields of furniture glass, including glass for picture framing. The resolution for pictureframing glass is preferably not less than 4 lines/mm.

The invention provides coated glass sheets having a gloss in the range 50 to 90. For picture framing glass the gloss is preferably in the range 60 to 80; for decorative glass is preferably less than 60 and for glass having a low diffuse reflection, such as anti-Newton ring glazing, is preferably greater than 80.

The thickness of the coating depends upon the required application but should generally be in the range 5 to 500 pm. For many applications, notably for furniture glass, the coating thickness is preferably in the range 10 to 30 pm.

In general the resolution is inversely proportional to the coating thickness.

The two phases of the transparent polymer composition can be provided by a transparent polymer varnish with solid particulate material dispersed therein or by a transparent polymer resin which itself is in two phases by virtue of the presence of a phase dispersant material, e. g. a polyamide dispersed in a uv-hardened acrylate system.

For coatings comprising a transparent polymer varnish with solid particulate material dispersed therein, the preferred particle size of the dispersed material is related to the thickness of the coating. The particles should be level with or protrude beyond the coating surface, either because their size is greater than the thickness of the coating or because they rise through the coating.

In general the dispersed material should have an average particle diameter in the range 0.1 to 60 pm. Particles of less than 0.1 pm diameter, especially of 10-20 nm or of colloidal material, tend to agglomerate to an unacceptable degree. The preferred average particle diameter is in the range 5 to 35 pm. These selected particle size ranges provide for good flexibility in the level of light diffusion.

In one embodiment of the invention the dispersed material is present in two distinct fractions, comprising a fraction of particles of large average particle size and a fraction of small average particle size. In this embodiment the diffuse reflection of the surface is created by the combined reflection of the large and small particles. For example, a fraction of particles with an average particle diameter of 25 pm can be used in combination with a fraction of particles with an average particle diameter of 10 pm in a coating with a dry thickness of 20 pm.

The large particles are generally spread evenly across the coating. The small particles may be dispersed close to the surface, where they increase the gloss, or may be evenly distributed through the depth of the coating, in which case they create internal diffusion of light and reduce the resolution. It is preferred that the quantity of small particles be greater than the quantity of large particles.

The proportion of dispersed particulate material in the coating should be in the range 0. 1 to 10% by weight, preferably 0.2 to 2% by weight.

The particulate material to be dispersed is preferably selected from metal oxides, such as alumina, silica, stannic oxide and titanium dioxide, glass microbeads and particulate polymers such as polyamides and polyesters.

It is desirable that the resin is of a type resistant to ultra-violet radiation.

Preferred materials include polyurethanes, modified epoxy resins, stabilised polyesters and acrylic resins including epoxy acrylates, polyester acrylates, polyether acrylates, for example amine-modified polyether acrylates, acrylic acrylates and urethane acrylates. They can be applied to the glass sheet by spraying, by roller or as a curtain. They can be applied in solution or as a powder, in all cases preferably together with the associated particles and any other components. The preferred method of application is by a curtain.

In further embodiments of the invention the coating comprises one or more additives such as anti-ultra-violet agents, anti-fading agents and anti- oxidants. The presence of such additives assists in increasing the stability of the coating.

In producing coated glass according to the invention the resin can advantageously be subjected to heat treatment. This provides a means of adjusting the resolution and gloss. Curing of the coating is preferably effected by heating in two stages, the first being at a temperature in the range 20-80 C, preferably 30-50 C, and for a period of 30 seconds to 5 minutes, preferably for not more than 2 minutes 30 seconds. The temperature for the second stage should be in the range 50-140 C, preferably 70-100 C, for a period of 30 seconds to 5 minutes, again preferably for not more than 2 minutes 30 seconds.

The heating stages can conveniently be effected by radiant heaters. The curing converts the resin from a liquid or viscous state into a hardened solid layer.

The particulate material can optionally be subjected to a surface treatment to improve its hydrophilic or hydrophobic properties as appropriate and thus to assist thorough dispersion in the respective resin medium. The surface treatment can be employed to impart to the particles a stronger or weaker surface tension than that of the resin, according to whether or not they are required to float to the surface. This permits control of their degree of flotation and/or their speed of rising to the surface of the layer during hardening, thereby providing a further means for controlling the levels of resolution and gloss.

Silica particles being naturally hydrophilic do not need hydrophilic treatment but may benefit from hydrophobic treatment.

The heating temperature and duration of the curing step also have an effect on the gloss of the coated glass. In general the use of higher temperatures or prolonged periods of heating tends to increase the resultant gloss. A possible explanation for this is that the solid particles appear to rise towards the coating surface in the course of the curing.

For certain resins it may also be beneficial to follow the steps of heating the resin by an infra-red or ultra-violet treatment to complete its curing. This further treatment increases the resistance of the coating to scratching.

The glass sheet is preferably preheated prior to the application of the resin. This is conveniently effected by passing the sheet through a glass-heating furnace. The preheating is preferably to a temperature in the range 50 to 80 C.

The so-heated sheet assists in establishing a low viscosity in the coating during its application and thereby encourages good dispersion of the solid particles.

The invention thus provides considerable flexibility in selecting the heating conditions to achieve a desired gloss level.

The process of the invention has the benefit that beyond the customary requirement that the sheet be thoroughly clean before application of the coating there is generally no need for other pretreatment prior to application of the coating. In certain instances it may however be useful to treat the sheet surlace with an adhesion primer.

The invention will now be described in more detail with reference to the following non-limiting examples.

Examples 1-30 The ingredients, proportions and treatment steps. or the examples are summarised in the accompanying table.

All the examples employed sheets of clear soda-lime float glass having a thickness of 1.9 mm. The sheets were thoroughly washed, rinsed and dried. In Examples 1 to 7,9,11 to 13 and 16 the sheets were placed in a heating furnace in which their temperature was raised to 40 C. In Examples 8 and 10 the sheets were passed through a heating furnace with a residence time of 4 minutes to raise their temperature to 80 C. They were then coated with a resin material, incorporating anti-UV or other additives.

For all examples except Example 12 the resin was an acrylic-urethane paint containing 4% by weight of a reticulating agent and 3% by weight of an adhesion promoter. Example 12 used an acrylic-based uv-hardenable resin containing benzophenone as a photoinitiator. The resins included dispersed silica particulate material which for all except examples 27 and 28 had an average particle size of 20 hum (with a size range of 10 to 30 pm). For Examples 27 and 28 the average particle diameters were respectively 60 pm and 15 pm.

The means of application of the resin for Example 1 was applied a spray method and for Example 3 was by a roller coater. For all the other Examples the resin was applied as a curtain.

The curing medium for all the Examples except Example 16 and Example 28 was heated air, in the case of Examples 9 and 10 being supplemented by infra-red heating. For Example 16 the curing medium was a gas burner and for Example 28 was ambient temperature air.

Examples 1 to 13 and 27 employed a two-stage heating for the curing.

The other examples, except Examples 16 and 28, employed a single stage heating to the temperature recorded in the table, which temperature was achieved in 4 minutes (5 minutes for Example 14c and 6 minutes for Example 15). In Exampie 16 the gas burner produced an increasing and then declining temperature, peaking at 130 C.

TABLE Ex.Silica Anti-Anti-Coating Curing Curing Curing Curing Curing Curing Gloss Resoltn Colour Anti-UV Ex.

UV fading thickness temp. 1 period 1 temp. 2 period 2 IR UV absorber (wt %) (wt %) (wt %) (m) ( C) (min.) ( C (min.) (Hunter b) (wt %) 1 0. 5 none none 20 40 1. 0 80 10 no no 80 4--1 2 0. 5 none none 20 40 2. 5 80 2 5 no no 95 5--2 3 0. 5 none none 20 40 2. 0 80 2 0 no no 85 4. 5--3 4 0. 5 none none 20 40 2. 0 50 2. 0 no no 80 4. 5--4 5 0. 5 none none 20 40 2. 0 70 2. 0 no no 78 4. 5--5 6 0. 5 none none 20 40 2. 0 90 2. 0 no no 80 4. 5--6 7 1. 25 none none 20 40 2. 0 80 2. 0 no no 75 4. 5--7 8 125 none none 20 40 2. 0 80 2. 0 no no 65 4--8 9 1. 25 none none 20 40 2. 0 80 2. 0 yes no 85 4. 5--9 10 1. 25 none none 20 40 2. 0 80 2. 0 yes no 62 4--10 11 0. 5 none none 19 40 2. 0 80 2. 0 yes no 88 4. 5--11 12 0. 5 none none 24 40 2. 0 80 2. 0 yes yes 60 4--12 13 1. 5 none none 20 40 2. 0 80 2. 0 yes no 62 4--13 14a 0. 5 none none 20 60 10. 0--no no 60 4. 5--14a 14b 0. 5 none none 20 80 10. 0--no no 68 4. 5--14b 14c 0. 5 none none 20 100 10. 0--no no 70 4--14c 15 0. 5 none none 20 120 10. 0--no no 75 4--15 16 0. 5 none none 20 130--no no 90 4--16 17 0. 5 none none 20 60 10. 0--no no 65 4. 5 0. 64-17 18 0. 5 none 0. 5 20 60 10. 0--no no 67 4. 5 0. 61-18 19 0. 5 none 1. 0 20 60 10. 0--no no 68 4. 5 0. 57-19 20 0. 5 none 2. 0 20 60 10. 0--no no 66 4. 5 0. 40-20 21 0. 5 none 3. 0 20 60 10. 0--no no 67 4 0. 03-21 22 0. 5 none none 20 60 10. 0--no no 75 4. 5-70. 0 22 23 0. 5 2. 0 none 20 60 10. 0--no no 72 4. 5-7. 0 23 24 0. 5 3. 0 none 20 60 10. 0--no no 70 4-2. 85 24 25 0. 5 4. 0 none 20 60 10. 0--no no 65 4-1. 3 25 260. 55. 0none2060100--nono653-0. 726 27 0. 5 none none 17 40 2. 0 80 2 0 no no 45 32--27 28 3. 0 none none 20 ambient 24 hrs--no no 15 1. 25--28 29 0. 5 none none 10 60 10. 0--no no 50---29 30 0. 5 none none 40 60 10. 0---no no 95---30

Claims

CLAIMS 1. A coated glass sheet having diffuse reflection properties for use in furnishing applications, which sheet carries a film coating formed of a two-phase transparent polymer resin composition, characterised in that the coated sheet has a resolution (as defined herein) in the range 1-6 lines/mm.
2. A coated glass sheet as claimed in claim 1, which has a gloss in the range 50 to 90.
3. A coated glass sheet as claimed in claim 1 or claim 2, in which the coating has a thickness in the range 5 to 500 pm.
4. A coated glass sheet as claimed in claim 3, in which the coating has a thickness in the range 10 to 30 pm.
5. A coated glass sheet as claimed in any preceding claim, in which the transparent polymer resin comprises a transparent polymer varnish containing a dispersion of a solid particulate material having an average particle diameter in the range 0.1 to 60 pm.
6. A coated glass sheet as claimed in claim 5, in which the dispersed particulate material has an average particle diameter in the range 5 to 35 pm.
7. A coated glass sheet as claimed in claim 5 or claim 6, in which the dispersed material is present in two distinct fractions, comprising a fraction of particles of large average particle size and a fraction of small average particle size.
8. A coated glass sheet as claimed in any of claims 5 to 7, in which the proportion of dispersed particulate material in the coating is in the range 0.1 to 10% by weight.
9. A coated glass sheet as claimed in claim 8, in which the proportion of dispersed particulate material in the coating is in the range 0.2 to 2% by weight.
10. A coated glass sheet as claimed in any of claims 5 to 9, in which the dispersed particulate material is selected from metal oxides, such as alumina, silica, stannic oxide and titanium dioxide, glass microbeads and particulate polymers such as polyamides and polyesters.
11. A coated glass sheet as claimed in any of claims 1 to 4, in which the transparent polymer resin comprises a transparent two-phase polymer.
12. A coated glass sheet as claimed in any preceding claim, in which the resin is selected from polyurethanes, modified epoxy resins, stabilised polyesters and acrylic resins including epoxy acrylates, polyester acrylates, polyether acrylates, for example amine-modified polyether acrylates, acrylic acrylates and urethane acrylates.
13. A coated glass sheet as claimed in any preceding claim, in which the coating comprises one or more additives to enhance its anti-fading, antiultra-violet and/or anti-oxidant properties.
14. A process for adjusting the resolution and gloss of a coated glass sheet as claimed in any preceding claim, in which the polymer resin is subjected to heat treatment.
15. A process for adjusting the resolution and gloss of a coated glass sheet as claimed in claim 14, in which the polymer resin is cured by heating in two stages, the first being in the range 20-80 C for a period of 30 seconds to 5 minutes and the second being in the range 50-140 C for a period of 30 seconds to 5 minutes.
16. A process as claimed in claim 15, in which the temperature in the first heating stage is in the range 30-50 C, and in the second heating stage is in the range 70-100 C.
17. A process as claimed in claim 15 or claim 16, in which the period of each of the two heating stages is not more than 2 minutes 30 seconds.
18. A process as claimed in any of claims 14 to 17, in which the heating of the resin is followed by an infra-red or ultra-violet treatment.
19. A process as claimed in any of claims 14 to 18, in which the sheet is preheated prior to the application of the resin.
20. A process as claimed in claim 19, in which the preheating is to a temperature in the range 50 to 80 C.
21. A process as claimed in any of claims 14 to 20, in which the resin is applied to the glass sheet in the form of an emulsion, in solution or as a powder.
22. A process as claimed in any of claims 14 to 21, in which the resin is applied together with any particles and any other components.
23. A process as claimed in any of claims 14 to 22, in which the resin is applied by a curtain.
24. A process as claimed in any of claims 14 to 23, in which the resin comprises dispersed particulate material and the said material is subjected to a surface treatment to improve its hydrophilic or hydrophobic properties.