GB2579362A

GB2579362A - Coating composition

Info

Publication number: GB2579362A
Application number: GB1819384.7A
Authority: GB
Inventors: Hutchinson Simon; Waddington Matthew; Wood David
Original assignee: Louver Lite Ltd
Current assignee: Louver Lite Ltd
Priority date: 2018-11-28
Filing date: 2018-11-28
Publication date: 2020-06-24
Anticipated expiration: 2038-11-28
Also published as: GB201819384D0; GB2579362B

Abstract

The coating comprises glass microspheres in an aqueous emulsion of a polymeric binder. The (optionally hollow) microspheres have average diameter = 5-100 micrometres (10-50 µm). The preferred composition comprises 20-40 (25-35) wt.% polymeric binder, 1-20 (3-10) wt.% sodium borosilicate glass, 25-50 (30-40) wt.% water, (0.95 wt.%) antimicrobial agent, (0.1 wt.%) zirconium pollen denaturing agent, (9.5 wt.%) flame retardant and (2 wt.%) thickener (rheology modifying agent). The preferred binder comprises vinyl chloride and vinyl acetate. Other exemplified additives are 14.25 wt.% white titanium dioxide pigment, 0.1 wt.% foam control agent and 1.9 wt.% humecant. The coated window blinds are also claimed. “Low e” gives the reflectance of a polyester blind fabric coated with the composition.

Description

Coating Composition The present invention relates to a coating composition, in particular to a coating composition for use with window blind fabrics.

Window blind fabrics are often coated to reduce solar gain into a building and also to reduce thermal loss from the building (i.e. improve thermal insulation). In this context, solar gain refers to an increase in the temperature within a building resulting from solar (IR light) energy passing through windows and other architectural openings. The solar energy that passes through a window glazing panel either passes through the blind fabric (transmission), is absorbed by the blind fabric (absorbance) or is reflected by the blind fabric (reflectance). It is understood by those skilled in the art of window blinds that solar gain results from the transmission of solar energy through the blind fabric and, to some extent, by absorption of the solar energy by the blind fabric.

Accordingly, in order to minimise the amount of solar gain in a building and minimise thermal loss from the building, it is desired to coat window blind fabrics such that the ability of the blind fabric to reflect solar energy, particularly infra-red light, is maximised, and the transmission of solar energy and thermal energy through the blind fabric and the absorption of solar energy by the blind fabric is minimised.

Existing blind fabric coatings typically utilise mica particles having a substantially laminar structure in order to minimise solar gain within a building. Such particles are typically able to at least partially reflect IR light radiation. However, the inventors of the subject invention have found that alternative materials can be included within coating compositions which are able to reduce the solar gain compared with coating compositions which utilise mica particles, which reduce thermal losses and/or which have a similar reduction in solar gain/thermal loss, but which provide alternative advantages to the use of mica particles.

According to a first aspect of the invention, there is provided a coating composition for use with window blind fabrics, the formulation comprising an aqueous emulsion of a polymeric binder and glass microspheres dispersed within the polymeric binder emulsion, wherein the glass microspheres have an average diameter of 5 to 100 micrometres.

It has been found that the glass microspheres provide a similar or better performance with regard to minimising solar gain and/or reducing thermal losses compared with mica particles. In addition, the glass microspheres are more environmentally friendly, as they can be recycled more easily, they tend to be cheaper to source than mica particles, and coatings which include the glass microspheres are easier to apply, as they require fewer application steps.

Furthermore, while the glass microspheres are able to reflect a relatively high proportion of infrared (IR) light energy, most of the visible light (e.g. at least 90% of the visible light) which strikes the glass microspheres is transmitted through them. The skilled person will appreciate that the transmitted light undergoes refraction as it passes through the microsphere walls.

In addition, it has been found that the glass microspheres have less of an impact on the appearance of the coated surface (mica particles cause the coated surface to look "shiny") and are less likely to give the appearance of defects in the base fabric itself. Furthermore, the glass microspheres have inherent fire-retardant properties. As such, either no additional fire retardant agents are required in the coating composition or a reduced amount of fire retardant agent is required to meet local fire safety requirements.

In the context of the present invention, the average diameter of the glass microspheres is based on a pre-determined volume of them. Thus, the average diameter is a volume average diameter. It is known that the diameter of the glass microspheres tends to follow a bell-shaped distribution curve for a given volume. The glass microspheres of the present invention suitably have a symmetrical bell-shaped distribution about the average diameter.

The glass microspheres of the present invention are suitably hollow glass microspheres, which are often referred to as glass bubbles or glass microballoons. Such glass microspheres are known to aggregate or clump in certain applications. In order to avoid this aggregation effect and to provide an even distribution of the glass microspheres in the composition, the skilled person can control the average particle size of the glass microspheres and also the percentage of the glass microspheres present in the composition.

For example, the glass microspheres may have an average diameter of 10 to 50 micrometres. The lower end of the range may be 10, 15, 20 or 25 micrometres and the upper end of the range may be 35, 40, 45 or 50 micrometres. The average diameter of the glass microspheres may be in the range 25 to 35 micrometres, for example 30 micrometres.

Additionally, the glass microspheres may be present in the composition in an amount of 1 to 20% by weight of the composition. The lower end of the range may be 1%, 2%, 2.5%, 3%, 3.5%, 4% or 4.5%. the upper end of the range may be 5%, 5.5%, 6%, 7%, 8%, 9%, 10%, 12%, 15% 17% or 20%. The amount of the glass microspheres present in the composition may be in the range 3% to 6% by weight, for example in the range 4% to 5% by weight.

By controlling the average particle size of the glass microspheres and the amount of the glass microspheres present in the composition, it is possible to maximise the reflectance of solar energy and minimise thermal losses (i.e. loss of heat energy from within a building or room), while minimising the risk of unwanted aggregation of the glass microspheres within the composition.

It is also possible to control the light diffusion properties of the coating, the fabric handle (the "feel" of the fabric to the touch), the crack resistance of the coating, the colour and/or the viscosity of the coating composition by controlling the average particle size of the glass microspheres and the amount of the glass microspheres present in the coating composition.

The glass microspheres may be formed from any glass-forming compounds or mixtures of compounds. For example, the glass microspheres may be formed from aluminosilicates, from sodium silicates or from borosilicates. Glass microspheres having an aluminosilicate structure are often produced as a waste product from coal-fired furnaces, whereas borosilicate and sodium silicate-based microspheres may be engineered, for example using an ultrasonic spray pyrolysis process. On the basis that borosilicate glasses have very low coefficients of thermal expansion, the glass microspheres are suitably formed from borosilicates, such as soda-lime borosilicate glass.

In embodiments in which hollow glass microspheres (i.e. glass bubbles) are incorporated into the composition, the hollow microspheres may contain a gas therein which has a composition that is different to the composition of air. For example, the hollow microspheres may contain a mixture of sulphur dioxide (502) and oxygen (02). These gases may be in any molar ratio, for example from 502:02=1:4 to 502:02=4:1. In addition, the gases within the hollow glass microspheres may be at a pressure which is below 100kPa (i.e. below 1 atmosphere of pressure).

The polymeric binder used in the composition may comprise vinyl chloride. Vinyl chloride binders are useful in window blind coating compositions as they are heat and UV stable. Suitably, the polymeric binder comprises a co-polymer comprising vinyl chloride and vinyl acetate. Such a polymeric binder provides desired properties for the coated blind fabric, such as handle and crack resistance.

The binder may be present in the composition in an amount of 20% to 40% by weight. Suitably, the binder is present in the composition in an amount of 25% to 35% by weight.

In the invention, the binder is present in the composition as an aqueous emulsion. As such, the composition suitably includes water. The water may be present in the composition in an amount of 25% to 50% by weight. Less than 25% by weight of water may make the coating composition difficult to handle and apply. Similarly, more than 50% water may result in insufficient amounts of the other components of the composition to achieve the desired properties.

Aqueous emulsions of the polymeric binder avoid the need for organic solvents, which are more difficult to handle and require specialist disposal.

In an embodiment of the invention, water is present in the composition in an amount of 30% to 40% by weight.

During the coating process, the water is removed from the composition to leave a layer of the polymeric binder containing within it the additional components of the composition The glass microspheres are suitably substantially uniformly distributed throughout the polymeric binder. This provides the polymeric binder with a structure that is similar to a cellular structure, wherein the glass microspheres form the "cells" within the polymeric binder. In other words, the polymeric binder and dispersed microspheres may have a foam-like structure. This is in contrast to known solar-reducing coatings in which the mica particles tend to form a substantially continuous layer at or near to a boundary surface of the coating. Without wishing to be bound by theory, it is believed that the distribution of the glass microspheres within the polymeric binder contributes to the properties of the coating composition.

It is desired to prevent or resist the growth of microbes on blind fabrics. As such, blind fabric coating compositions may further include an antimicrobial agent. The antimicrobial agent may prevent or resist the growth of bacteria and/or fungi on the surface of the blind fabric. Thus, the antimicrobial agent may comprise an antibacterial component and/or an antifungal component.

Suitably the antimicrobial agent is active against the proliferation of both bacterial and fungal cells or colonies.

In addition to preventing or resisting microbial growth on the surface of the window blind, it is also desired to reduce the amount of allergens entering a building, such as pollen. It is known from W02017/098280 that pollen denaturing agents may be included in coating compositions for window blinds. Accordingly, the coating composition may further include a pollen denaturing agent. The pollen denaturing agent suitably comprises a zirconium compound.

As noted above, the glass microspheres have an inherent fire retardant property and may be used without an additional fire retardant agent. Nevertheless, a further fire retardant agent may be included within the coating composition.

The coating composition may be applied to a blind fabric. In order to achieve this, the rheological properties of the composition must be appropriate for the desired application process.

Accordingly, the coating composition may further include a rheology modifying agent, such as a thickener, for example.

It may be desired to match a colour of a coated surface of a blind fabric with a reverse surface of the fabric. In such embodiments, the coating composition may further include a colouring agent, such as a pigment. For example, if it is desired to have the coated surface of the window blind fabric white, then the coating composition may include a white pigment, such as titanium dioxide.

In a second aspect of the invention, there is provided a fabric coated with a coating composition as defined anywhere herein in connection with the first aspect of the invention. The fabric may be a window blind fabric. In other words, the fabric may be a fabric which is suitable for or intended for use in a window blind.

According to a third aspect of the invention, there is provided a window blind including a blind substrate formed from a window blind fabric as defined in connection with the second aspect of the invention. The blind substrate may be in the form of a single sheet of the window blind fabric, such as for example a roller blind, a Roman blind or a pleated blind; or it may be in the form of a plurality of separate substrate elements, such as for example a vertical louver blind, a Venetian blind, or a cellular blind.

An embodiment of the invention will now be described, by way of example only, with reference to the following drawing in which: Figure 1 shows a graph of the percentage of incident IR light that is reflected by fabric samples.

Example 1

An example of the coating composition is set out below.

Component Description/function Quantity (wt%)

Polymeric binder Vinyl acetate/vinyl chloride binder 22.80 Polymeric binder Vinyl chloride/vinyl acetate binder 6.65 Glass bubbles Soda Lime borosilicate hollow glass microspheres 4.75 White pigment Titanium dioxide white pigment 14.25 Flame retardant Flame retardant agent 9.50 Thickener Rheology modifying agent 2.00 Antimicrobial Antimicrobial agent 0.95 Antipollen Zirconium-based pollen denaturing agent 0.10 De-foamer Foam control agent 0.10 Humectant Agent to control rate of drying 1.90 Water 37.00 The flame retardant agent, thickener, antimicrobial agent, de-foaming agent and humectant are all conventional components typically used in fabric coating compositions. The antipollen agent is a zirconium agent in accordance with W02017/098280.

The glass bubbles contain a mixture of sulphur dioxide (SO2) and oxygen (02) in a molar ratio of 2:1 and at a pressure of about 33kPa (1/3 atm). Such glass bubbles are commercially available.

The hollow glass microspheres are dispersed within a portion of the water and thickener to form a 25% liquid dispersion of the hollow glass microspheres (the hollow glass microspheres form 25% by weight of the dispersion). The dispersion is added to the remainder of the water in a mixing vessel and the remaining components (polymeric binders, pigment, flame retardant, antimicrobial, anti-pollen agent, defoamer and humectant) are added. The composition is then mixed at 450 rpm for 25 minutes.

The resultant coating composition is then placed in a reservoir of a coating apparatus, where the coating is applied to a base fabric (e.g. a polyester blind fabric) using a doctor blade in a conventional manner. Two layers of the coating are applied, with a drying/curing stage between applications. The total coating of the composition on the fabric is about 40gsm dry weight of the coating composition.

The coated fabrics have been found to provide superior IR light reflectance and thermal resistance properties than corresponding fabrics which have been coated with a conventional mica-based coating composition or which are coated with a coating composition that contains no light-reflecting particles (a "clearcoat").

Example 2

The thermal resistance of a coated polyester base fabric that contained no light-reflecting particles in the coating composition (Comp 1) was compared with the thermal resistance of the same polyester base fabric which had been coated with a composition according to Example 1 (Ex 1).

Comp 1 had a thermal resistance of 0.07 m2K/W Ex 1 had a thermal resistance of 0.12 m2K/W These results demonstrate that the fabric which had been coated with a composition according to the invention has a 71% improvement in thermal resistance compared to the coated fabric in which the coating included no light-reflecting particles.

The thermal resistance of the fabric samples was measured in accordance with ISO 5085-1: 1989. Three specimens of each sample were measured independently of each other and the values stated above represent the mean value of the three specimens.

Example 3

The thermal resistance of a heavier weight polyester base fabric coated with a mica-based coating composition (an SPC coating applied by Louver-Lite Limited) (Comp 2) was compared with the thermal resistance of the same polyester base fabric, but coated with a composition according to Example 1 (Ex2).

Comp 2 had a thermal resistance of 0.21 m2K/W.

Ex 2 had a thermal resistance of 0.23 m2K/W.

These results demonstrate that the polyester fabric which was coated with a composition according to Example 1 has a 9.5% improvement in thermal resistance compared to the comparative fabric, which was coated with a conventional mica-based coating.

The thermal resistance of the fabric samples was measured in accordance with ISO 5085-1: 1989.

Three specimens of each sample were measured independently of each other and the values stated above represent the mean value of the three specimens.

Example 4

The light reflectance of three different samples of window blind fabrics which had been coated with a composition according to Example 1 were compared with corresponding fabric samples which were coated with a composition that included mica particles or which had been coated with a composition that contained no reflective particles. The results are shown in Figure 1.

As shown by the graph of Figure 1, the fabric samples which were coated with the composition according to Example 1 reflected a much higher percentage of the incident IR light radiation. This means that a correspondingly smaller percentage of the light radiation is absorbed by the fabric or transmitted through it. It will be appreciated that the transmitted IR component of the light contributes to the "solar gain" on the internal side of the blind. In other words, the transmitted IR component effectively heats the room within which the blind is located.

In the Figure 1, the legends have the following meanings: "Clearcoat" represents a coated fabric in which the coating composition does not include mica or glass microbeads (a comparative fabric); "SRC" represents a coated fabric wherein the coating composition includes mica particles (also a comparative fabric); and "Low e" represents a coated fabric wherein the coating composition includes glass microspheres in accordance with the invention.

Samples 1, 2 and 3 represent different weight and differently coloured polyester base fabrics.

It will be noted that the fabric samples that were coated with the coating composition according to the invention exhibited improved reflectance properties compared with the same base fabrics that had been coated with a composition that did not include any light reflecting particles and which has been coated with a composition that included conventional mica particles.

The light reflectance was measured using a Perkin Elmer UV/VIS/NIR Lambda 900 Spectrometer. Each fabric sample was exposed to a full spectrum of electromagnetic light waves representing solar irradiation. The Spectrometer measured the percentage of the emitted light that was reflected by the surface of the sample fabric, the percentage of the emitted light that was absorbed by the sample fabric and the percentage of the emitted light that was transmitted through the sample fabric, for each of the UV, visible and IR wavelengths of the emitted light. The values used in the graph shown in Figure 1 are the percentage of IR light that was reflected by the fabric samples.

The skilled person will appreciate that different compositions within the scope of the claims appended hereto can be formulated according to the desired properties of the coating composition.

Claims

Claims 1. A coating composition for use with window blind fabrics, the formulation comprising an aqueous emulsion of a polymeric binder and glass microspheres dispersed within the polymeric binder emulsion, wherein the glass microspheres have an average diameter of 5 to 100 micrometres.
2. A coating composition according to Claim 1, wherein the glass microspheres have an average diameter of 10 to 50 micrometres.
3. A coating composition according to Claim 1 or Claim 2, wherein the glass microspheres are present in the composition in an amount of 1 to 20% by weight.
4. A coating composition according to Claim 3, wherein the glass microspheres are present in the composition in an amount of 3 to 10% by weight.
5. A coating composition according to any of Claims 1 to 4, wherein the glass microspheres are formed from a borosilicate glass material.
6. A coating composition according to Claim 5, wherein the glass microspheres are formed from a sodium borosilicate material.
7. A coating composition according to any of Claims 1 to 6, wherein the polymeric binder comprises vinyl chloride.
8. A coating composition according to Claim 7, wherein the polymeric binder comprises vinyl chloride and vinyl acetate.
9. A coating composition according to any of Claims 1 to 8, wherein the polymeric binder is present in the composition in an amount of 20 to 40% by weight
10. A coating composition according to Claim 9, wherein the polymeric binder is present in the composition in an amount of 25 to 35% by weight.
11. A coating composition according to any of Claims 1 to 10, wherein the composition contains water in an amount of 25 to 50% by weight.
12. A coating composition according to Claim 11, wherein the water is present in the composition in an amount of 30 to 40% by weight.
13. A coating composition according to any of Claims 1 to 12, wherein the composition further includes an antimicrobial agent.
14. A coating composition according to any of Claims 1 to 13, wherein the composition further includes a pollen denaturing agent.
15. A coating composition according to Claim 14, wherein the pollen denaturing agent comprises a zirconium compound.
16. A coating composition according to any of Claims 1 to 15, wherein the composition further includes a flame retarding agent.
17. A coating composition according to any of Claims 1 to 16, wherein the composition further includes a thickener.
18. A fabric coated with a coating composition as defined in any of Claims 1 to 17.
19. A window blind fabric coated with a coating composition as defined in any of Claims 1 to 17.
20. A window blind including a blind substrate formed from a window blind fabric according to Claim 19.
21. A window blind according to Claim 20, wherein the substrate is in the form of a single sheet of the window blind fabric or in the form of a plurality of separate substrate elements.