FR2924718A1 - VARNISH ANTI-BUEE - Google Patents

Abstract

The invention relates to a single-component varnish composition for application to an optical substrate, said varnish giving said substrate an anti-fog, anti-scratch, UV-resistant effect, which comprises: at least one blocked isocyanate; at least one polyol: at least one polymerizable surfactant, with at least one free hydroxyl, amine or mercaptan group, optionally at least one other additive capable of reducing the surface tension of the varnish composition; at least one solvent; - At least one catalyst.This varnish is useful for glasses, visors, windows and other optical glasses.

Description

1 Anti-fogging varnish

FIELD OF THE INVENTION: The invention relates to an anti-fog, anti-scratch, UV-resistant, single-component varnish composition applicable to transparent or opaque parts, and in particular to optical glasses.

STATE OF THE ART Fog, which disturbs the optical images, comprises small drops of water which diffuse the light. Condensation of water vapor on a solid surface can lead to the formation of small drops; it forms fog. The problem of preventing by the application of a suitable surface coating the formation of drops or small droplets of water on a solid surface, which have the effect of modifying the optical characteristics of this surface, and in particular, in the In the case of 15 surfaces of transparent objects, decreasing its optical transparency and altering the quality of the images viewed in transparency through this surface, has been approached in different ways.

It has long been known that a hydrophilic coating can promote the formation of a continuous film of water from drops or droplets, which avoids or reduces light scattering phenomena by these drops or droplets. These coatings must adhere well to their support, and must have sufficient mechanical strength in the conditions of use of the object they cover. In particular, their scratch resistance must be sufficient, since the presence of scratches may also modify the optical characteristics of the surface covered by said coating. For this purpose, US Pat. No. 4,551,484 (Sant-Gobain Vitrage) proposes in a very general manner a process for treating plastic films or coatings crosslinked with the aid of a surface-active agent (surfactant) capable of diffusing at least partially inside said film or coating. More specifically, US Pat. No. 5,877,254 (Film Specialties, Inc.) discloses liquid compositions comprising an isocyanate-based prepolymer, such as a polyisocyanate, a hydrophilic polyol and a surfactant which carries hydroxyl functions, said liquid compositions being capable of forming a crosslinked polyurethane film. U.S. Patent 4,810,582 (Tyndale Plains-Hunter Ltd.) discloses improved strength polyurethane-based polymers that result from a blend of hydrophilic polyether-polyurethane polymers with hydrophobic polyurethane-polyester polymers. This mixture can be obtained in the liquid state or by coextrusion. The polyether polyurethane polymer can be obtained by the reaction of polyoxyethylene glycol with a polyisocyanate, preferably methylene di (cyclohexyl isocyanate).

The document WO 2004/013063 (Central Glass Company) describes a bi-component anti-mist varnish, which comprises (i) an isocyanate and (ii) a hydrophilic polyol, a hydrophobic polyol and a surfactant capable of reacting with the isocyanate function.

The state of the art shows the use of blocked isocyanates in the manufacture of polyurethanes, and more specifically in polyurethane-based anti-fogging compositions. Indeed, the isocyanate groups associated with urethane bonding agents are highly reactive vis-à-vis many compounds. This reactivity can thus lead to problems of stability and make it necessary to store the compositions in two-component form (coating and precursor of polymers), because of the limited shelf life of the stocks and the capacity of the groups N = C = O to react with the humidity of the atmosphere. Blocking technologies have been developed in order to overcome these disadvantages and to allow stable storage and in the form of a single component, which can be reactivated thermally or chemically. In this use, in a first step, the isocyanate function (R-N = C = O) is released (unblocked) by thermal activation, optionally in the presence of a catalyst; then, in a second step, this isocyanate reacts with hydroxyl groups available in the reaction medium. Thus blocked isocyanates are known which, in the presence of a catalyst (for example dibutyltin dilaurate), are released at a temperature of about 120 ° C to 130 ° C. However, this temperature is too high for many organic substrates, which may deform hot. US 2004/0137155 discloses an anti-fog coating which comprises an isocyanate-based prepolymer and a water-soluble polyhydroxyl polymer without surfactant. The isocyanate may be a reactive isocyanate or a blocked isocyanate. The mixture is applied to the surface to be coated, and then it is fired at a temperature typically above 80 ° C.

US 2006/0047064 A1 describes a two-component anti-icing coating. The first component comprises an agent containing an isocyanate group. The second component comprises a polyol compound comprising at least one water-absorbing polyol, a hydrophobic polyol, a surfactant containing a group reactive with the isocyanate group. In this document, the isocyanate is not blocked, which imposes an impractical choice of solvent, namely diacetone alcohol or t-butanol. As soon as the two components are mixed, the viscosity of the product begins to increase, until the formation of a gel (typically after a few days); this product is difficult to use by soaking, and impractical due to its short life. In addition, t-butanol takes a long time to dry.

The problem that the present invention seeks to solve is to propose a novel liquid composition for the manufacture of a surface coating which is suitable as an anti-fog coating for optical glasses, organic or inorganic, which has good scratch and ray resistance. UV, and which effectively prevents the formation of drops to as low a temperature as possible; the application of this coating should not involve temperatures higher than 120 ° C, and the liquid varnish should be single-component, applicable by traditional routes, and have a ready-to-use stability as long as possible. Object of the invention

The present invention relates to an anti-fog, anti-scratch, UV-resistant, single component, and applicable to any type of optical substrate, which comprises: at least one blocked isocyanate; at least one polyol, such as polycaprolactone polyol; at least one polymerizable surfactant, with at least one free hydroxyl group; Optionally at least one other additive capable of reducing the surface tension of the lacquer composition, and preferably an additive comprising at least one silicone or siloxane; at least one solvent; at least one catalyst. Description of the invention

The composition according to the invention comprises at least five mandatory ingredients. In addition, it may include optional ingredients. A) The blocked isocyanate The blocked isocyanate must be able to be released by firing at a temperature of at most 120 ° C, and preferably below 115 ° C. As long as the isocyanate has not been removed, the varnish film formed on the substrate remains opaque or tacky; when the temperature is raised to the deblocking temperature, the deblocking reaction is almost instantaneous. In the context of the present invention, it is preferred to use blocked di-isocyanates or blocked tri-isocyanates. More particularly, aliphatic isocyanates, and especially aliphatic polyisocyanates, are preferred. Indeed, the aromatic isocyanates have a very limited UV stability, especially if they lead to polyurethanes which yellow very quickly, which limits their use to substrates intended to be used indoors. It is essential that the used isocyanate be available in a solvent compatible with the substrate on which the composition is to be applied. For example, primary alcohols attack nylon, ketones attack polycarbonate. b) Polyol The polyol must have the capacity to absorb water. The preferred polyol is polyethylene glycol (PEG). PEG absorbs up to 40% moisture. The Applicant has found that the higher the molecular weight of the PEG, the more the anti-fogging effect is accentuated. But we also know that the higher the molecular weight of PEG, the more difficult it is to dissolve.

In an advantageous embodiment, a mixture of a polyether polyol such as PEG and a short polyol polyester polyol which contains 2 or 3 OH functions per molecule is used. The linear diol polyesters derived from caprolactone and ending with hydroxyl primary groups are particularly preferred. The polycaprolactone thus obtained provides the polyurethane film with flexibility as well as abrasion resistance. The presence of a short polyol chain lengthens the polyurethane chain, which reinforces its hardness without compromising its elasticity. Advantageously, the molecular weight of this short polyol chain is between 60 and 200. Below 60, the flexibility of the layer is not satisfactory, whereas above 200, the hardness is too low.

A particularly preferred polyester product is CAPA 2125, a linear polyester diol derived from the 1250 molecular weight caprolactone monomer. It has a typical OH value of 90 mg KOH / g. It has a melting point between 35 ° C and 45 ° C, and a viscosity at 60 ° C of about 175 mPa.s.

c) The surfactant The surfactant allows the formation of a film of water on the surface of the substrate. Surfactants having a function of OH, amine or mercapto are preferred in order to readily react with the isocyanate; this makes it possible to sustainably maintain the anti-fogging effect even after saturation of the lacquer film with water. Particularly preferred are polymethylsiloxane derivatives having OH functions. Preferably, a polyoxyethylene sorbitan monolaurate, such as polyoxyethylene (20) sorbitan monolaurate, also known under the name polysorbate 20 and under the trademark TWEEN 20 is used. Polysorbates 40, 45, 60, 80 and 100 can also be used. . The Applicant has found that the higher the molecular weight, the greater the anti-fogging effect, but the more the product is difficult to disperse in the polymer, leading to a very viscous product. A content by weight percent surfactant content of between 9% and 25% is preferred. Below 9%, the anti-fog property of the varnish obtained is often unsatisfactory. Above 25%, there are problems related to insufficient mechanical strength. The use of surfactants comprising a mercapto function can cause an olfactory nuisance, in the production workshop and also in some cases when using the coated substrate. d) Catalyst The catalyst, preferably an organometallic tin or bismuth compound, can be a tin or bismuth carboxylate. Dibutyltin dilaurate (DBTL) (C 4 H 9) 2 Sn (OOC (CH 2) 10 CH 3) 2 may be suitable, but this does not always make it possible to unblock the isocyanate at a sufficiently low temperature. Thus, in a preferred embodiment, a bismuth carboxylate (for example the product sold under the name K-KAT 348 by the company King Industries) is used. In particular, it facilitates the unblocking of blocked aliphatic isocyanates. In particular, it is thus possible to obtain a release from 100 ° C. The use of this catalyst makes it possible to use single-component polyurethanes on the majority of substrates, thus making it possible to obtain coatings with excellent stability, even under the influence of UV (no yellowing problems). , and excellent gloss retention. The use of the bismuth carboxylate also allows a better curing of the varnish and a longer stability of the stored composition. E) The additive reducing the surface tension This additive aims at spreading the varnish on the surface of the substrate without sagging, as homogeneously as possible. A polymerizable additive is preferred. An additive comprising dimethyl polysiloxane can be used. As such, the product BYK TM 375 can be used, but it tends to opacify the substrate. A suitable product is the product BYK TM 340 which is known as a paint spreading agent, but this product does not prevent the ingress of moisture during drying. We must add other additives if we want to use these products. A polyether-modified dimethyl polysiloxane is preferred, which gives a slippery effect to the composition, and allows anti-scratch treatment; Furthermore, on polycarbinate substrates, it forms a hydrophobic skin (probably comprising dimethylsiloxane groups on the surface) which prevents the entrapment of water that the polycarbonate can not absorb. BYK TM SILCLEAN 3700 is a preferred product.

In general, the additive decreasing the surface tension is not essential for substrates of simple shape (especially flat), but becomes important for substrates of complex shape.

f) Solvent Any type of alcohol may be suitable, provided that its boiling point does not exceed 200 ° C. Beyond this temperature, the evaporation rate of the solvent is too slow, and the creation of a thickness gradient between the top and bottom of the part to be coated is observed. The lighter of the alcohols, namely methanol, may be suitable. The preferred solvent for the anti-fogging varnish composition according to the invention is 1-methoxy-2-propanol. This solvent has an ideal evaporation rate, and its use also makes it possible to avoid parasitic reactions. 2-Methoxy-1-propanol is usable, but leads to a fairly low stability of the composition. Iso-butanol is usable but gives off a strong odor. Isopropyl alcohol is suitable but evaporates too quickly, which causes losses of solvent in the bath. Diacetone alcohol is suitable but evaporates too slowly, leading to inconvenient drying times. Butoxyethanol evaporates too slowly. Methoxyproanol acetate is incompatible with the polycarbonate it attacks.

g) Other optional additives In a particular embodiment of the present invention, sub-micron silica particles are added to the anti-fogging varnish composition. By this we mean particles whose dimensions are less than about one meter. Products called silica nanoparticles fall into this category. Thus we obtain an even harder coating. Particles of this size do not create an undesirable optical effect (opacity, milky appearance, etc.).

h) Particularly advantageous compositions The compositions in which the isocyanate / alcohol weight ratio (excluding the alcohol of the solvent) is between 1.1 and 1.3 are preferred. Below 1.1, it is observed that the abrasion resistance of the film is too low, despite a good anti-fogging effect. Above 1.3, a hard polyurethane is obtained but little anti-fog effect.

A particularly advantageous composition according to the invention is indicated in Example 5 below. i) General characteristics, use and advantages of the invention The composition according to the invention is stable because the isocyanate can not be released at ambient temperature. The deblocking reaction can be carried out thanks to the specific choice of the catalyst. K-KAT TM 348 is a particularly effective catalyst.

The liquid composition according to the invention can be applied with all the known techniques, such as soaking, spraying, roller coating, inkjet. After at least partial evaporation of the solvent, the varnish is fired; It is during this cooking that the deblocking of the isocyanate is carried out, the polymerization and the formation of the polyurethane-based film. The composition according to the invention has many advantages.

With the varnish composition according to the invention, the water is absorbed by the film formed from the varnish until it is saturated; thanks to the presence of the surfactant in the composition of the varnish, a film, not a droplet, will form on the surface of the substrate which will keep all its transparency.

The life of the baths containing the anti-fogging varnish composition according to the invention is very long, typically greater than three months, in some cases greater than one year, and theoretically unlimited. This allows intermittent use of baths, depending on seasonal market demand. Moreover, the viscosity of the baths containing the anti-fogging varnish composition according to the invention is stable; this is very convenient because there is no need to adjust the process parameters to viscosity.

The anti-fogging varnish according to the invention is particularly suitable for substrates such as: Polycarbonate glass, Polyamide (nylon) glasses, Polyallyl-diglycolcarnonate (CR39) Polyethylene-terephthalate (PETG) and its alloys with polycarbonates, Copolymers of styrene and acrylonitrile (SAN), copolymers of α-methylstyrene and acrylonitrile (AMSAN), Polysulfones, Polypropylene (especially after appropriate surface pretreatment (activation), and preferably an oxidation treatment, such as: corona discharge, treatment with peroxides, treatment with maleic acid).

However, the anti-fogging varnish according to the invention is not suitable for non-activated polyolefin (including polycycloolefin), polystyrene and PVC substrates to which it adheres poorly. PMMA has a deformation temperature that is too low, like PVC.

The varnish according to the invention can be used for optical glasses (such as: eyeglasses, sunglasses, special glasses, binoculars, telescopes, cameras), optical lenses, optical filters, mirrors, building glass (such as: glass for windows and doors, interior or exterior walls), wet location equipment (such as: shower enclosures, bathroom mirrors), glass for point of sale (such as: display stands refrigerated), automotive glazing, aircraft glazing, ceramics (such as: wall tile, floor tile, decorative tile), visors (such as visors for motorcycle helmets, hard hats).

The following examples include embodiments of the invention which illustrate the present invention, but do not limit its scope.

Examples: Example 1: A blocked isocyanate (blocked cyclohexane diisocyanate, Vestanate TM 1299) was supplied with an amine (Di-isopropylamine) in a solvent (petroleum distillate known as SOLVESSO 100). PEG was refluxed (in three variants of this example, PEG 8000, PEG 6000 and PEG 4000) were used in a solvent (1-methoxy-2-propanol). These two solutions were mixed, and the catalyst (dibutyltin dilaurate) and the surfactant (BYKTM 375) were added, solvent was added to reduce the solids content of the varnish to 25%, and precipitation was observed in all cases. as soon as the temperature falls below 50 ° C. This varnish is applied hot (ie at a temperature above 50 ° C.) to a substrate and for each of the three variants, a transparent and homogeneous layer is formed. After baking at 120 ° C or 130 ° C for 1 hour, the varnish layer is dry but a slight opacity appears.

It is found that the anti-fogging effect increases with the molecular weight of PEG, but dissolution of the PEG becomes increasingly difficult as its molecular weight increases. This composition is impractical to use due to precipitation in the bath; it is difficult to add solvent at a temperature above its flash point (about 24 ° C). In addition, the opacity of the lacquer layer does not achieve excellent optical properties.

Example 2: This example aims to explore another isocyanate. The procedure of Example 1 was followed, but PEG 6000 was used, and in place of the isocyanate of Example 1 was used the product Baxenden 7480, which has a weight in N = C = O higher. After baking for 1 hour at 120 ° C, it is found that the layer of the varnish is not dry, and that it is opaque.

After cooking for 1 hour at 130 ° C., the same thing is observed. It is concluded that the isocyanate has not been released under these conditions.

Example 3: These examples are intended to explore another catalyst. The procedure of Example 20 was followed, but another catalyst, bismuth ethyl-2-hexanoate (K-KAT 348 from King Industries) was used. The varnish was baked at 120 ° C for 1 hour. After cooking, it was dry, and showed no opacity.

EXAMPLE 4 This example aims to explore an alternative process to the process of Examples 1-3. A polyether polyurethane having a hydrophilic character and a polyester polyurethane having a hydrophobic character were manufactured. For this purpose, the product CAPA 2125 supplied by Solvay, which is a polyester polyol (PEG 1000), and a polyether polyol was used. From these two ingredients, three mixtures named A, B and C (composition in mass percent) were prepared: A: 75% polyester + 25% polyether B: 50% polyester + 50% polyether C: 25% polyester + 75% polyether The varnish was then applied to organic polycarbonate glass. The results are summarized in Table 1. Table 1 Composition Appearance Anti-fog effect Anti-fogging effect at Frost Huffiness A Tight No Yes Slight B Tight Low Slight Light C Tight Yes No Light 100% polyether polyol Tight Yes No Light 100 % polyester polyol Tights No Yes Light Product B has the best overall compromise, but its performance is not totally satisfactory. EXAMPLE 5 A particularly advantageous composition according to the invention comprises the following ingredients (the indications in percent by weight are given in approximate manner):

IPDI 1042 Vestanate (isophorone diisocyanate trimer): 76 g (36.2%); CAPA 2125 (as polyester polyol): 5.6 g (2.7%); Ethylene glycol: 5 g (2.4%); Tween 20 (as surfactant): 20 g (9.5%); 1-Methoxy-2-propanol (PMOH) (as solvent): 70 g (33.3%); Polyethylene glycol of molecular weight 1000 (PEG 1000): 20 g (9.5%); K-KATH 348 (as catalyst): 3 g (4.8%); -BYK-Silclean 3700 (as hydrophobic additive): 10.4 g (5%).

Claims (10)

claims A one-component varnish composition for application to an optical substrate, said varnish imparting to said substrate an anti-fog, anti-scratch, UV-resistant effect, said composition comprising: (a) at least one blocked isocyanate, preferably blocked aliphatic isocyanate; (b) at least one polyol, such as polycaprolactone polyol; (c) at least one polymerizable surfactant, with at least one free hydroxyl, amine or mercaptan group (the hydroxyl group being preferred); (d) optionally at least one other additive capable of reducing the surface tension of the varnish composition, and preferably an additive comprising at least one silicone or siloxane; (e) at least one solvent; (f) at least one catalyst. 2. Composition according to claim 1, characterized in that the blocked isocyanate is released at a temperature below 120 ° C, and preferably at a temperature below 115 ° C. 3. Composition according to claim 1 or 2, characterized in that the isocyanate is a di-isocyanate or a tri-isocyanate. 4. Composition according to any one of claims 1 to 3, characterized in that the polyol comprises polyethylene glycol. 5. Composition according to any one of claims 1 to 4, characterized in that the polymerizable surfactant is a polysorbate, and preferably polysorbate 20. 6. Composition according to any one of claims 1 to 5, characterized in that the catalyst is a salt of bismuth, and preferably a bismuth carboxylate. 7. Composition according to any one of claims 1 to 6, characterized in that it further comprises sub-micron sized silica particles. 8. Composition according to any one of claims 1 to 7, characterized in that the solvent is 1-methoxy-2propanol. 9. Composition according to any one of claims 1 to 8, characterized in that the isocyanate / alcohol mass ratio (excluding the alcohol of the solvent) is between 1.1 and 1.3. 10. Use of a composition according to any one of claims 1 to 9 for coating a substrate selected from the group consisting of: polycarbonate glass, polyamide glass (nylon), CR39, PETG and its alloys with polycarbonates, copolymers of styrene and acrylonitrile (SAN), polysulfones, polypropylene, mineral glass, building glazing, mirrors, automotive glazing, aircraft glazing, tiles, visors, optical lenses, optical filters.