Anti-fog coating

Abstract

The present invention relates to an optical component having a crosslinked anti-fog coating obtainable by covalent attachment of a silane derivative of the formula (2) to the surface of the optical component and crosslinking of adjacent molecules:
R.sub.oX.sub.mSiB.sub.n(2)
wherein
m=1 to 3, n=1 or 2 and o=0 or 1, with the proviso that m+n+o=4;
the radical X is selected from halogen or C.sub.1-4-alkoxy, and
for m=2 or 3 the individual radicals X may be identical or different,
the radical R is C.sub.1-4-alkyl,
the radical B has the structure -B1-B2, in which -B2 is a terminal hydrophilic group which is crosslinked to at least one hydrophilic group of an adjacent molecule of the anti-fog coat, and -B1- represents either a spacer group, which joins the hydrophilic group B2 to the Si atom, or a covalent bond,
where the terminal hydrophilic group -B2 is poly(meth)acrylate, and for n=2 the individual radicals B may be identical or different.

Claims

1. An optical component comprising a crosslinked anti-fog coating produced by covalent attachment of a silane derivative of the formula (2) to the surface of the optical component and crosslinking of adjacent molecules:
R.sub.oX.sub.mSiB.sub.n(2) wherein: m=1 to 3, n=1 or 2, and o=0 or 1, with the proviso that m+n+o=4; the radical X is selected from a halogen or C.sub.1-4 alkoxy, and for m=2 or 3 the individual radicals X are identical or different, the radical R is C.sub.1-4-alkyl, the radical B has the structure -B1-B2, in which -B2 is a terminal hydrophilic group which is crosslinked to at least one hydrophilic group of an adjacent molecule of the anti-fog coat, and -B1- represents either a spacer group, which joins the hydrophilic group B2 to the Si atom, or a covalent bond, the terminal hydrophilic group -B2 is poly(meth)acrylate, and for n=2 the individual radicals B are identical or different, and the anti-fog coating has a coat thickness of 100 nm or less.

2. The optical component according to claim 1, where the covalent attachment of the compound of the formula (2) to the surface of the optical component takes place by reacting at least one of the reactive SiX groups with a suitable reactive surface group to form SiO.

3. The optical component according to claim 1, where the optical component comprises an anti-reflection coat and the anti-fog coating is applied to the anti-reflection coat.

4. The optical component according to claim 1, wherein the poly(meth)acrylate of the terminal hydrophilic group -B2 comprises monomer units which are selected from CH.sub.2C(CH.sub.3) COOC.sub.1-4-alkyl, CH.sub.2C(H) COOC.sub.1-4-alkyl, hydroxyethylene methacrylate, 2-acrylamido-2-methylpropanesulphonic acid, trimethylolpropane triacrylate and pentaerythritol tetraacrylate or mixtures thereof.

5. A method for producing a crosslinked anti-fog coating on an optical component comprising: covalently bonding a precursor compound to the surface of the optical component, the precursor compound having the formula (3):
R.sub.oX.sub.mSiC.sub.n(3) wherein: m=1 to 3, n=1 or 2, and o=0 or 1, with the proviso that m+n+o=4, the radical X is selected from a halogen or C.sub.1-4 alkoxy, and for m=2 or 3 the individual radicals X are identical or different, the radical R is C.sub.1-4-alkyl, the radical C has the structure -C1-C2, in which -C2 is a terminal group comprising a (meth)acrylate functionality and -C1- represents either a spacer group or a covalent bond; reacting the terminal group -C2 with (meth)acrylate monomers to give a hydrophilic poly(meth)acrylate group; and, crosslinking of the hydrophilic poly(meth)acrylate groups of adjacent molecules, wherein the step of covalently bonding a precursor compound to the surface of the optical component does not include a surfactant in the step or in the precursor compound bonded to the surface of the optical component.

6. The method according to claim 5, comprising: providing the optical component and the covalent attachment of the silane derivative of the formula (3) by chemical reaction with reactive groups on the surface of the optical component, followed by the crosslinking of the hydrophilic groups C2 of adjacent molecules of the anti-fog coating.

7. The method according to claim 5, wherein the (meth)acrylate monomers are selected from the group consisting of CH.sub.2C(CH.sub.3)COOC.sub.1-4-alkyl, CH.sub.2C(H)COOC.sub.1-4-alkyl, hydroxyethylene methacrylate, 2-acrylamido-2-methylpropanesulphonic acid, trimethylolpropane triacrylate and pentaerythritol tetraacrylate or mixtures thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be described with reference to the drawings wherein:

(2) FIG. 1 shows, diagrammatically, the surface of an optical component that has been modified with silane compounds of the formula (1) to form an anti-fog coating. In the upper compound of FIG. 1, the hydrophobic group -A1- is a -phenylene- and the terminal hydrophilic group is polyethoxy. In the lower compound of FIG. 1, the hydrophobic group -A1- is a -poly(propoxylene)- and the terminal hydrophilic group is again polyethoxy.

(3) FIG. 2 shows diagrammatically the surface of an optical component that has been modified with silane compounds of the formula (1) to form an anti-fog coating. In the upper compound of FIG. 2, the hydrophobic group -A1- is a perfluorinated -poly(propoxylene)- and the terminal hydrophilic group is polyethoxy. In the lower compound of FIG. 2, the hydrophobic group -A1- is a perfluorinated -alkylene- and the terminal hydrophilic group is again polyethoxy.

(4) FIG. 3 shows diagrammatically the surface of an optical component that has been modified with silane compounds of the formula (1) to form an anti-fog coating. In the compound of FIG. 3 the hydrophobic group -A1- is a -phenylene- and the terminal hydrophilic group is a sulphonic acid or a sulphonic ester.

(5) FIG. 4 shows, diagrammatically, a surface of an optical component that has been coated with a precursor compound of the formula (3).

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

(6) The optical component may comprise, for example, optical lenses made of glass or plastic, or else a beam splitter component. Mention may be made by way of example in this context of eyewear lenses, telescope lenses, cover plates or cover glasses, or else lenses such as ocular lenses, camera lenses or front lenses.

(7) In one preferred embodiment the optical component has an anti-reflection coat (AR coat). The anti-fog coating may be applied directly on the AR coat.

(8) The coat thickness of the anti-fog coating may be varied over a wide range, for example from a monomolecular (i.e. single-layer) coat through to a multi-layer coat with a coat thickness of up to 150 nm. Where the optical component has an anti-reflection coat (AR coat), the coat thickness of the anti-fog coating is preferably selected so as not to impair the function of the AR coat. Where the anti-fog coating is present on an AR coat, the coat thickness of the anti-fog coating is preferably in the range from single-layer to 100 nm, more preferably in the range from 10 nm to 20 nm.

(9) Silane derivatives of the formula (1) are available commercially or can be prepared via synthesis techniques known to the skilled person.

(10) Methods for the covalent attachment of silane derivatives to reactive surfaces are known in principle to the skilled person. According to one variant, the silane derivative in a suitable solvent is contacted with the surface under reactive conditions. Alternatively, the silane derivative can also be reacted with the surface via the gas phase.

(11) According to a further aspect, the present invention relates to a method for producing an anti-fog coating on an optical component, comprising the provision of the optical component and the covalent attachment of the silane derivative of the formula (1) by chemical reaction with reactive groups on the surface of the optical component.

(12) With regard to the properties of the silane derivative of the formula (1) and of the optical component, reference may be made to the statements above.

(13) According to a further aspect, the present invention relates to the use of the silane derivative of the formula (1) for providing an anti-fog coating on an optical component.

(14) According to a further aspect, the present invention relates to an optical component having a crosslinked anti-fog coating obtainable by covalent attachment of a silane derivative of the formula (2) to the surface of the optical component and crosslinking of adjacent molecules:
R.sub.oX.sub.mSiB.sub.n(2)

(15) where

(16) m=1-3, n=1-2 and o=0-1, with the proviso that m+n+o=4;

(17) the radical X is selected from halogen or C.sub.1-4-alkoxy, and for m=2-3 the individual radicals X may be identical or different,

(18) the radical R is C.sub.1-4alkyl,

(19) the radical B has the structure -B1-B2, in which -B2 is a terminal hydrophilic group which is crosslinked to at least one hydrophilic group of an adjacent molecule of the anti-fog coat, and -B1- represents either a spacer group, which joins the hydrophilic group B2 to the Si atom, or a covalent bond,

(20) where the terminal hydrophilic group -B2 is selected from polyethoxy, poly(meth)acrylate, sulphonic acid or a salt thereof, sulphonic ester, or a combination of these groups,

(21) and for n=2 the individual radicals B may be identical or different.

(22) The covalent attachment of the compound of the formula (2) to the surface of the optical component is accomplished by reacting at least one of the reactive, hydrolyzable SiX groups with a suitable reactive surface group (e.g. an OH group) to form SiO. This type of surface attachment of a silicon compound having a reactive, hydrolyzable group is known in principle to the skilled person.

(23) Preferably X is methoxy, ethoxy or Cl.

(24) In the context of the present invention it has been found that through the selection of suitable hydrophilic groups in the silane derivative of formula (2) and the crosslinking of adjacent molecules in the anti-fog coating, on the one hand the SiO bond, via which the molecules of the anti-fog coating are bonded to the surface of the optical component, is shielded more effectively from water, and the stability of the anti-fog coating with respect to hydrolysis can be enhanced, and, furthermore, the contact angle of the water to the anti-fog coating is kept low.

(25) In the context of the present invention it has also emerged that the crosslinked anti-fog of the invention significantly reduces the unwanted adsorption of the hydrophilic group -B2 on the surface of the optical component, leading in turn to an increased occupation density of the molecules of the anti-fog coat on the surface of the optical component.

(26) As stated above, the terminal hydrophilic group -B2 is selected from polyethoxy, poly(meth)acrylate, sulphonic acid or a salt thereof, sulphonic ester, or a combination of these groups.

(27) With regard to the properties of these hydrophilic groups, reference may be made to the above statements concerning the description of the silane derivative (1).

(28) The degree of ethoxylation of the polyethoxy group can be varied over a wide range and is situated for example in the range from 4 to 20.

(29) Where the hydrophilic group -B2 comprises a poly(meth)acrylate, the latter may be constructed exclusively from identical monomer units such as CH.sub.2C(CH.sub.3)COOC.sub.1-4-alkyl (e.g. CH.sub.2C(CH.sub.3)COOCH.sub.3), CH.sub.2C(H)COOC.sub.1-4-alkyl (e.g. CH.sub.2C(H)COOCH.sub.3), hydroxyethylene methacrylate (HEMA), 2-acrylamido-2-methylpropanesulphonic acid (AMPS), trimethylolpropane triacrylate or pentaerythritol tetraacrylate, or from a mixture of these monomer units, and may alternatively also contain further comonomer units. The poly(meth)acrylate as hydrophilic group B2 may be linked for example via an ester group with the spacer group -B1- or the Si atom.

(30) The sulphonic ester in question is preferably the methyl or ethyl ester.

(31) In the context of the present invention the spacer group where present, may be varied to a broad extent. A suitable spacer group, for example, is an alkylene group such as C.sub.1-8alkylene, more preferably C.sub.1-3alkylene.

(32) Silane derivatives of the formula (2) are available commercially or can be prepared via synthesis techniques known to the skilled person.

(33) Methods for the covalent attachment of silane derivatives to reactive surfaces are known in principle to the skilled person. According to one variant, the silane derivative in a suitable solvent is contacted with the surface under reactive conditions. Alternatively, the silane derivative can also be reacted with the surface via the gas phase.

(34) According to a further aspect, the present invention relates to a method for producing a crosslinked anti-fog coating on an optical component, comprising the provision of the optical component and the covalent attachment of the silane derivative of the formula (2) by chemical reaction with reactive groups on the surface of the optical component, followed by the crosslinking of the hydrophilic groups -B2 of adjacent molecules of the anti-fog coating.

(35) Suitable reaction conditions for the crosslinking of adjacent molecules having suitable reactive groups are known to the skilled person. Where the crosslinking takes place via a radical reaction, it is possible to use radical initiators such as dichlorodicyanoquinone (DDQ), for example. With certain groups, crosslinking may also be initiated by exposure to UV radiation.

(36) With regard to the properties of the silane derivative of the formula (2) and of the optical component, reference may be made to the statements above.

(37) According to a further aspect, the present invention relates to the use of the silane derivative of the formula (2) for providing an anti-fog coating on an optical component.

(38) In the context of the present invention it is also possible to produce the crosslinked anti-fog coating on the optical component by first covalently bonding a suitable precursor compound for the silane derivative of the formula (2) on the surface of the optical component, this precursor compound having a terminal group with suitable functionality and thus allowing subsequent chemical reaction with suitable reactants to give the silane derivative of the formula (2).

(39) In accordance with a further aspect, the present invention relates to a method for producing a crosslinked anti-fog coating on an optical component, where first a precursor compound of the formula (3) is bonded covalently to the surface of the optical component:
R.sub.oX.sub.mSiC.sub.n(3)

(40) where

(41) m=1-3, n=1-2 and o=0-1, with the proviso that m+n+o=4,

(42) the radical X is selected from halogen or C.sub.1-4-alkoxy, and for m=2-3 the individual radicals X may be identical or different,

(43) the radical R is C.sub.1-4alkyl,

(44) the radical C has the structure -C1-C2, in which -C2 is a terminal group having a (meth)acrylate functionality and -C1- represents either a spacer group, which corresponds to the above-described spacer group -B1-, or a covalent bond, and the terminal group C2 is reacted with (meth)acrylate monomers to give a hydrophilic poly(meth)acrylate group, followed by the crosslinking of the hydrophilic poly(meth)acrylate groups of adjacent molecules of the anti-fog coating.

(45) Examples of (meth)acrylate monomers that may be identified as suitable monomers are CH.sub.2C(CH.sub.3)COOC.sub.1-4-alkyl (e.g. CH.sub.2C(CH.sub.3)COOCH.sub.3), CH.sub.2C(H)COOC.sub.1-4alkyl (e.g. CH.sub.2C(H)COOCH.sub.3), hydroxyethylene methacrylate (HEMA), 2-acrylamido-2-methylpropanesulphonic acid (AMPS), trimethylolpropane triacrylate or pentaerythritol tetraacrylate or mixtures thereof.

(46) FIG. 4 shows, diagrammatically, a surface of an optical component that has been coated with a precursor compound (3). The terminal group of the precursor compound has a (meth)acrylate functionality, which allows the reaction with further (meth)acrylate monomers and hence the construction of a hydrophilic poly(meth)acrylate group.

(47) In the following further embodiments of the invention are described.

Embodiment 1

(48) An optical component having an anti-fog coating obtainable by covalent attachment of a silane derivative of the formula (1) to the surface of the optical component:
R.sub.oX.sub.mSiA.sub.n(1)

(49) wherein

(50) m=1 to 3, n=1 or 2 and o=0 or 1, with the proviso that m+n+o=4;

(51) the radical X is selected from halogen or C.sub.1-4-alkoxy, and for m=2 or 3 the individual radicals X may be identical or different,

(52) the radical R is C.sub.1-4alkyl,

(53) the radical A has the structure -A1-A2, in which -A1- is a hydrophobic group bonded to the Si atom, and -A2 represents a terminal hydrophilic group bonded to the hydrophobic group A1,

(54) the hydrophobic group -A1- being selected from -arylene-; C.sub.1-6-alkylene-arylene-; -arylene-C.sub.1-6-alkylene-; C.sub.1-6-alkylene-arylene-C.sub.1-6-alkylene-; -poly(C.sub.3-6-alkoxylene)-, fluorinated or perfluorinated -alkylene-, fluorinated or perfluorinated

(55) -poly(C.sub.2-6-alkoxylene)-, or a combination of these groups,

(56) and the terminal hydrophilic group -A2 is poly(meth)acrylate,

(57) and for n=2 the individual radicals A may be identical or different,

(58) and where the poly(meth)acrylate of the terminal hydrophilic group -A2 comprises monomer units which are selected from CH.sub.2C(CH.sub.3)COOC.sub.1-4-alkyl, CH.sub.2C(H)COOC.sub.1-4-alkyl, hydroxyethylene methacrylate, 2-acrylamido-2-methylpropanesulphonic acid, trimethylolpropane triacrylate and pentaerythritol tetraacrylate or mixtures thereof.

Embodiment 2

(59) The optical component according to Embodiment 1, where the anti-fog coating has no crosslinking between hydrophilic groups -A2 and/or hydrophobic groups -A1- of adjacent molecules.

Embodiment 3

(60) The optical component according to Embodiment 1, where the anti-fog coating has crosslinking between hydrophilic groups -A2 and/or hydrophobic groups -A1- of adjacent molecules.

Embodiment 4

(61) An optical component having a crosslinked anti-fog coating obtainable by covalent attachment of a silane derivative of the formula (2) to the surface of the optical component and crosslinking of adjacent molecules:
R.sub.oX.sub.mSiB.sub.n(2)

(62) wherein

(63) m=1 to 3, n=1 or 2 and o=0 or 1, with the proviso that m+n+o=4;

(64) the radical X is selected from halogen or C.sub.1-4-alkoxy, and for m=2 or 3 the individual radicals X may be identical or different,

(65) the radical R is C.sub.1-4-alkyl,

(66) the radical B has the structure -B1-B2, in which -B2 is a terminal hydrophilic group which is crosslinked to at least one hydrophilic group of an adjacent molecule of the anti-fog coat, and -B1- represents either a spacer group, which joins the hydrophilic group B2 to the Si atom, or a covalent bond,

(67) where the terminal hydrophilic group -B2 is poly(meth)acrylate,

(68) and for n=2 the individual radicals B may be identical or different,

(69) and where the poly(meth)acrylate of the terminal hydrophilic group -B2 comprises monomer units which are selected from CH.sub.2C(CH.sub.3)COOH.sub.1-4-alkyl, CH.sub.2C(H)COOCH.sub.1-4-alkyl, hydroxyethylene methacrylate, 2-acrylamido-2-methylpropanesulphonic acid, trimethylolpropane triacrylate and pentaerythritol tetraacrylate or mixtures thereof.

Embodiment 5

(70) The optical component according to Embodiment 1, where the covalent attachment of the compound of the formula (1) to the surface of the optical component takes place by reacting at least one of the reactive SiX groups with a suitable reactive surface group to form SiO.

Embodiment 6

(71) The optical component according to Embodiment 1, where the optical component comprises an anti-reflection coat and the anti-fog coating is applied to the anti-reflection coat.

Embodiment 7

(72) A method for producing a crosslinked anti-fog coating on an optical component comprising: covalently bonding a precursor compound to the surface of the optical component, the precursor compound having the formula (3):
R.sub.oX.sub.mSiC.sub.n(3)

(73) wherein

(74) m=1 to 3, n=1 or 2 and o=0 or 1, with the proviso that m+n+o=4,

(75) the radical X is selected from halogen or C.sub.1-4-alkoxy, and for m=2 or 3 the individual radicals X may be identical or different,

(76) the radical R is C.sub.1-4-alkyl,

(77) the radical C has the structure -C1-C2, in which -C2 is a teiminal group having a (meth)acrylate functionality and -C1- represents either a spacer group or a covalent bond; reacting the terminal group -C2 with (meth)acrylate monomers to give a hydrophilic poly(meth)acrylate group; and, crosslinking of the hydrophilic poly(meth)acrylate groups of adjacent molecules.

Embodiment 8

(78) A method for producing a crosslinked anti-fog coating on an optical component according to Embodiment 4, comprising: providing the optical component and the covalent attachment of the silane derivative of the formula (2) by chemical reaction with reactive groups on the surface of the optical component, followed by the crosslinking of the hydrophilic groups -B2 of adjacent molecules of the anti-fog coating.

Embodiment 9

(79) A method for producing an anti-fog coating on an optical component, according to Embodiment 1, comprising: providing of the optical component and the covalent attachment of the silane derivative of the formula (1) by chemical reaction with reactive groups on the surface of the optical component.

Embodiment 10

(80) The optical component according to Embodiment 4, where the covalent attachment of the compound of the formula (2) to the surface of the optical component takes place by reacting at least one of the reactive SiX groups with a suitable reactive surface group to form SiO.

Embodiment 11

(81) The optical component according to Embodiment 6, where the anti-fog coating having a coat thickness of 100 nm or less.

(82) The invention is described in further detail by the following examples:

EXAMPLES

Example 1

(83) A polyethylene glycol (PEG) modified trichlorosilane (Mn500 g/mol) is dissolved in toluene so that a 5 mass % solution is obtained. A glass having an antireflective coating but no CleanCoat is dipped into the solution and then air-dried. Any remaining over-coating is removed by rubbing with a dry cloth.

Example 2

(84) A polyethylene glycol (PEG) modified trichlorosilane (Mn500 g/mol) is dissolved in toluene so that a 2.5 mass % solution is obtained. A glass having an antireflective coating but no CleanCoat is dipped into the solution and then air-dried. Any remaining over-coating is removed by rubbing with a dry cloth.

(85) By covalently attaching the PEG-modified silane to the substrate surface, coatings are obtained in Examples 1 and 2 which provide anti-fogging properties. Due to the higher concentration of the PEG-modified silane, the anti-fogging effect provided in Example 1 is higher than in Example 2.

Example 3

(86) 9.98 g 3-methacryloxypropyl trichlorosilane are dissolved in 490 ml toluene. A glass is stored in said solution for one hour and then air-dried. In a second step, the glass is dipped into a solution made of 5.0 g 2-hydroxyethyl methacrylate (HEMA), 1.0 g trimethylol propanetriacrylate (TMPTA) and 0.5 g diphenyl-(2,4,6-trimethylbenzoyl)phosphine oxide in 50 ml toluene, followed by curing with a Panacol UV-D-1000 lamp.

Example 4

(87) 10.01 g 3-methacryloxypropyl trichlorosilane are dissolved in 240 ml toluene. A glass having an antireflective coating is stored in said solution for one hour and then air-dried. In a second step, the glass is dipped into a solution made of 10.0 g 2-hydroxyethyl methacrylate (HEMA), 3.0 g trimethylol propanetriacrylate (TMPTA) and 0.5 g diphenyl-(2,4,6-trimethylbenzoyl)phosphine oxide in 100 ml toluene, followed by curing with a Panacol UV-D-1000 lamp.

(88) So, in Examples 3 and 4, a precursor compound having a terminal methacrylate functionality is covalently attached to the substrate surface in a first step, followed by a second step which includes a chemical reaction with further (meth)acrylate monomers so as to obtain the terminal poly(meth)acrylate group, and a crosslinking of neighbouring molecules.

(89) The coatings prepared in Examples 3 and 4 both provide an antifogging effect.

(90) A higher percentage of the monomer hydroxyethyl methacrylate increases the hydrophilic character of the coating and thereby its antifogging effect, whereas a higher percentage of the monomer trimethylolpropane triacrylate increases the crosslinking within the coating and thereby improves mechanical properties.

(91) It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.