Scratch- and abrasion-proof transparent polyurethane layer having fume resistance and energy absorbing properties, process for its preparation and laminated glass using same

The invention relates to a layer of high optical quality polyurethane having energy absorbing, scratch and abrasion resistance and anti-fogging properties, which can be used as an outer layer in safety glazing, in particular windshields.

We know from European patent publication 0 133 090, a polyurethane layer formed in a continuous process by reactive casting, on a horizontal plane support from which it is detachable, of a reaction mixture of the components of a polyurethane. By reactive casting is meant in this technical field, a casting to form a layer or a film from a liquid mixture of the components in the state of monomers or prepolymers, followed by a polymerization of this mixture by heat. .

The reaction mixture described in the cited document comprises an active hydrogen component, in particular a polyol component, and an isocyanate component comprising at least one aliphatic, cycloaliphatic diisocyanate or a diisocyanate prepolymer, this component having a viscosity of less than approximately 5 Pa.s at + 40 ° C. The polyol component comprises at least one long, difunctional polyol with a molecular mass of between 500 and 4000, at least one short diol as chain extender and, where appropriate, a small proportion of at least one polyol of superior functionality. in pairs and in particular aliphatic triols.

The proportions between the long polyol, the short diol and optionally the polyol of functionality greater than 2 are generally chosen such that for a hydroxyl equivalent, the long polyol represents approximately from 0.30 to 0.45 equivalent, the short diol approximately 0.2 to 0.7 equivalent and the polyol with a functionality greater than 2 approximately 0 to 0.35 equivalent. Under these conditions, the layer has the following mechanical characteristics, measured according to AFNOR / NFT 46 002, 51 034, 54 108 standards.<ul id="ul0001" list-style="dash"><li>a stress at the flow threshold σ_Y at -20 ° C less than or equal to 3 daN / mm²,</li><li>a breaking stress σ_R at + 40 ° C greater than or equal to 2 daN / mm²,</li><li>an elongation at break ε_R at + 20 ° C between 250 and 500%,</li><li>an initiated tear resistance Ra at + 20 ° C greater than or equal to 9 daN / mm in thickness.</li></ul>

This layer has, in addition to energy absorber properties, as indicated above, properties of resistance to scratching and abrasion making it suitable for use as an outer layer under certain conditions. Thus, it has a scratch resistance of more than 20 grams and an abrasion resistance with a blur difference of less than 4%, these values ​​being measured according to the tests described in the cited publication.

However under severe conditions of use, for example when it is used as an external layer in the glazing of motor vehicles, and when it is then subjected to all kinds of attacks and in particular to attack from certain cleaning products containing aggressive organic solvents, it is therefore not entirely satisfactory, its resistance to these products not being sufficient.

In addition, the polyurethane layers mentioned above, associated with a glass or plastic support, when placed in conditions of high humidity can, like glass panes, quickly become covered with mist which the vision through the glazing.

Patent publication FR-A-2 574 395 describes a coating layer made of a thermosetting polyurethane having surface properties and anti-fogging properties. This layer does not have the energy absorbing properties allowing it to be used as a single layer associated with a sheet of glass in safety glazing such as a windshield of a motor vehicle.

Patent publication FR-A-2 207 809 describes a thin surface layer formed from a copolymer containing alternating blocks of polyurethane and polyacrylic. This type of layer cannot have both energy absorbing, scratch resistance and anti-fog properties.

The invention provides a transparent polyurethane layer, of high optical quality, usable as an outer layer in safety glazing, having energy absorbing properties, surface properties such as resistance to scratching and to abrasion and improved resistance to fogging.

The polyurethane layer according to the invention is formed by deposition on a support by reactive casting or reactive spraying of a reaction mixture of an isocyanate component comprising at least one aliphatic, cycloaliphatic diisocyanate or a diisocyanate prepolymer, this component having a viscosity of less than approximately 5 Pa.s at + 40 ° C. and of a polyol component comprising at least one long difunctional polyol of molecular mass between 500 and 10,000 and preferably between 1,000 and 3,000, comprising at least part of the ethylene oxide and if appropriate propylene oxide segments, the weight percentage of ethylene oxide segment relative to the total mass of the polyurethane being at least 20%, at least one short diol as chain extender and, where appropriate, a small proportion of at least one polyol with a functionality greater than two, the OH ratio of the free NCO groups of the isocyanate component to the free OH groups of the component polyol being between 1.5 and 2, and in that the surface intended to be oriented towards the outside of the glazing is treated by bringing it into contact with a surface treatment compound chosen from acrylic derivatives and isocyanates of functionality greater than 2.

According to an advantageous characteristic of the invention, the contacting of the face of the layer with the surface treatment compound is carried out at the same time as the manufacture of the layer from the reaction mixture. To this end, the reaction mixture is poured or sprayed onto the formation support which has previously been coated with a thin layer of an acrylic derivative or an isocyanate of functionality greater than two. After polymerization of the layer, it is removed from the support and it comprises on its face which was in contact with said support, the acrylic polymer or the isocyanate-based polymer of functionality greater than two.

A method of manufacturing the layer according to the invention therefore consists in forming on a support, in particular a horizontal plane support which is coated beforehand with a separating agent, a thin coating based on acrylic monomers or prepolymers, or acrylic polymers carrying free hydroxyl groups, or isocyanates of functionality greater than two, then depositing on said coating the reaction mixture of the components capable of forming the polyurethane layer, subjecting the assembly to a polymerization cycle during which the polymerization of the acrylics or isocyanates is carried out as well as the polymerization of the polyurethane layer, in the presence of a polymerization initiator in the case of the acrylics, and then to remove of the support, the layer of polyurethane superficially associated with the acrylic polymer or derived from isocyanates of functionality greater than two.

The acrylic monomers and / or prepolymers used to form the thin coating layer on the casting support are chosen in particular from acrylates and methacrylates, polyacrylates and polymethacrylates of low molecular weight, for example isobutyl methacrylate, dipropylene glycol diacrylate , triethylene glycol diacrylate, 1,6-hexanediol diacrylate, 1,4-butanediol diacrylate.

When the coating is formed from acrylic polymers bearing free hydroxyl groups, methacrylic resins such as methacrylate with a hydroxyl index less than 100 are chosen in particular. When methacrylic resins with a hydroxyl index greater than 100 are used, hard, chemically resistant but scratchable surfaces are obtained. The hydroxyl index is the quantity of potassium hydroxide in mg, necessary for the neutralization of the free hydroxyls of 1 g of substance.

A viscous acrylic derivative is preferably chosen which does not tend to be removed from the support during the pouring of the reaction mixture.

The initiator for acrylic polymerization thermally is, for example, benzoyl peroxide, alkyl perbenzoates, azo-bis-isobutyronitrile or other known initiators. It is used in an amount of about 0.5 to 5% by weight of the acrylic compound.

The thin layer or coating film is advantageously formed on the horizontal plane support by depositing a solution of acrylic monomers and / or prepolymers, or acrylic polymers carrying free hydroxyl groups, followed by evaporation of the solvents.

Suitable solvents are for example simple hydrocarbons, halogenated hydrocarbons, ketones.

When the surface treatment is carried out using isocyanate of functionality greater than 2, it is possible to use with advantage a triisocyanate such as an isocyanate biuret or a triisocyanurate, or an isocyanate trimer, for example a biuret, a isocyanurate or the trimer of hexamethylenediisocyanate. Also preferably chosen here is a viscous isocyanate derivative.

The components capable of forming the polyurethane layer having anti-fogging properties according to the invention are described below:    The suitable diisocyanates used in the context of the invention are chosen in particular from the following aliphatic difunctional isocyanates: hexamethylenediisocyanate (HMDI), 2,2,4-trimethyl1,6-hexanediisocyanate (TMDI), bis 4-isocyanatocyclohexylmethane (Hylene W), bis 3-methyl-4-isocyanatocyclohexylmethane, 2.2 bis (4-isocyanatocyclohexyl) propane, 3 -isocyanatomethyl-3,5,5 trimethylcyclohexylisocyanate (IPDI), m-xylylènediisocyanate (XDI), m- and p-tetramethylxylylènediisocyanate (m- and p- TMXDI), cis and transcyclohexane-1,4 diisocyanate (CHDI), 1,3 - (diisocyanatomethyl) cyclohexane (hydrogenated XDI).

An isocyanate component containing urea functions can be used. These urea functions improve certain mechanical properties of the layer. The level of urea can represent up to approximately 10% of the total weight of the isocyanate component with urea functions. Preferably, the urea level is between 5 and 7% of the total weight of said component. For the reason mentioned above, preferably 3-isocyanatomethyl-3,5,5 trimethylcyclohexyldiisocyanate containing urea functions (IPDI and derivatives) is preferably used.

The long polyol comprising segments of ethylene oxide and optionally of propylene oxide may be a polyol of molecular mass between 500 and 10,000. The content of ethylene oxide segments is generally greater than 40% by weight to satisfy the condition set out above, namely, forming a polyurethane having an ethylene oxide segment content of at least 20% by weight. Suitable polyols are, for example, polyols sold under the name SYNPERONIC by the company ICI, polyglycols with ethylene oxide segments sold by the company HOECHST, for example the product P 41-300 with a molecular weight of approximately 5000, which contains 80% by weight of ethylene oxide segments.

The preferred polyols for obtaining the desired mechanical properties are those having a molecular weight of between 1000 and 3000. When the molecular weight is greater than 3000, it is generally necessary to use a higher NCO / OH ratio in order to maintain properties. satisfactory mechanical.

The long polyol comprising segments of ethylene oxide and optionally of propylene oxide can also be a sulfonated polyether polyol, in particular a polyoxyalkylene ether of formula:         R₁CH₂O - (C₂H₄O-)_not(C₃H₆O-)_mCH₂CHR₃-CH₂-SO₃X with<chemistry id="chem0001" num="0001"><img file="EP0344045B1_D0001.tif" /></chemistry> with<dl id="dl0001"><dt>R₂ =</dt><dd>CH₃, C₂H₅, C₃H₇</dd><dt>R₃ =</dt><dd>H, CH₃</dd><dt>X =</dt><dd>H, alkali or ammonium ion</dd><dt>n =</dt><dd>0 100</dd><dt>m =</dt><dd>0 at 30</dd><dt>n +</dt><dd>m ≧ 1</dd></dl> having a molecular weight of about 500 to 10,000.

Suitable chain extenders are short diols with a molecular weight of less than about 300 and preferably less than 150, such as: ethylene glycol, propanediol-1,2, propanediol-1,3, butanediol-1,2, -1,3, -1,4, dimethyl-2,2 propanediol-1,3 (neopentylglycol), pentanediol-1,5, hexanediol-1,6, octanediol-1,8, decanediol-1,10, dodecanediol-1,12, cyclohexanedimethanol, bisphenol A, methyl-2 pentanediol-2,4, methyl-3 pentanediol-2,4, ethyl- 2 hexanediol-1,3, trimethyl-2,2,4-pentanediol-1,3, diethylene glycol, triethylene glycol, tetraethylene glycol, butyne-2-diol-1,4, butènediol-1,4 and decynediol substituted and / or etherified, hydroquinone-bis-hydroxyethyl ether, bisphenol A etherified by two or four groups of propylene oxide, dimethylolproponic acid. In general, the shorter the diol, the harder the layer.

Preferably 1,4-butanediol is used, which is a good compromise for obtaining a layer which is neither too hard nor too flexible.

The polyol component can contain a small proportion of at least one polyol with a functionality greater than two and in particular aliphatic triols monomers such as glycerol, trimethylolpropane, triols with polyether chains, polycaprolactone triols, the molecular mass of these triols being generally between 90 and 1000, mixed polyether / polyester polyols with a functionality greater than 2, for example with functionality between 2 and 3. The addition of a polyol with a functionality greater than 2 causes additional bridging bonds between the polyurethane chains and can thus further improve the cohesion of the layer. Preferably, a polyol with a functionality greater than 2, having a hydrophilic character, is used.

The proportions between the long polyol, the short diol and optionally the polyol of functionality greater than 2 can vary according to the desired properties. Generally, proportions are chosen such that for a hydroxyl equivalent the long polyol represents approximately 0.30 to 0.45 equivalent, the short diol approximately 0.2 to 0.7 equivalent and the polyol with a functionality greater than 2 approximately 0 at 0.35 equivalent.

The layer can also be produced by replacing part of the polyol component with a product with different active hydrogens such as an amine.

According to an embodiment of the plastic layer, the isocyanate component may contain in limited proportions, for example less than about 15% in NCO equivalent, at least one triisocyanate such as an isocyanate biuret or a triisocyanurate.

The components are taken in an amount such that the ratio between the free NCO groups of the isocyanate component and the free OH groups of the polyol component varies between 1.5 and 2 and preferably between 1.7 and 1.9. When the NCO / OH ratio is less than 1.5, the mechanical properties of the layer formed are not satisfactory. When the NCO / OH ratio is greater than 2, the large excess of NCO can cause toxicity problems and in addition the cost price of the layer is higher. A ratio of between 1.7 and 1.9 is a good compromise for obtaining the desired layer.

In a variant of the invention, the polyurethane layer having the desired properties is obtained in two stages: a first step consisting in forming the polyurethane layer on a formation support and after formation of the layer, its separation from its support and its possible assembly with a substrate such as a sheet of glass to form the glazing, a second step consisting in " treating "the free face with the surface treatment compound, acrylic or isocyanate, by soaking in a bath a solution of said acrylic treatment compound or an isocyanate of functionality greater than two, in particular a triisocyanate, followed by draining and polymerization of the acrylic compound or the isocyanate compound.

According to a preferred characteristic of the invention, the coating film of the treatment compound has a thickness of less than 20 microns and preferably less than 10 microns.

Other advantages and characteristics of the invention will appear in the following description of examples of the manufacture of a polyurethane layer having improved energy absorber, anti-fog and surface properties.

EXAMPLE

1

On a continuously moving movable glass support, coated with a separation agent which is a modified addition product of ethylene oxide, a solution of the following composition is deposited using a roller:<ul id="ul0002" list-style="dash"><li>1000 parts of hexanediol diacrylate</li><li>1500 acetone parts</li><li>25 parts of azo-bis-isobutyronitrile as initiator for the heat polymerization of acrylic monomers.</li></ul>

It is dried at 60 ° for approximately 2 minutes and a film approximately 2 microns thick is obtained.

To manufacture the polyurethane layer, the polyol component is prepared beforehand by mixing a long polyol which is a copolymer comprising ethylene oxide segments at a rate of 57% by weight and propylene oxide segments, of molecular mass 1900 (by example the product sold under the name SYNPERONIC L35 by the company ICI), with 1,4-butanediol and a polyol with a functionality greater than 2 (for example a triol sold under the name Desmophen 1100 by the company Bayer), the proportions of the constituents being such that the polyol copolymer provides 0.35 equivalent in groups hydroxyls while 1,4-butanediol provides 0.50 and the polyol with functionality greater than 2 provides 0.15.

The polyol component incorporates a stabilizer at a rate of 0.5% by weight of the total mass of the polyol component and the isocyanate component, a coating agent at a rate of 0.05% by weight calculated in the same way and a catalyst namely dibutyltin dilaurate in an amount of 0.03% by weight calculated in the same way as above.

The isocyanate component used is 3-isocyanatomethyl-3,5,5-trimethylcyclohexylisocyanate (IPDI) having urea functions obtained by partial hydrolysis of IPDI and having a content of NCO groups of approximately 31.5% by weight.

The components are taken in quantities such that the NCO / OH ratio is 1.8.

After degassing the components under vacuum, the mixture brought to about 40 ° C. is poured using a casting head like that described in French patent publication 2 347 170, on the acrylic film previously formed. A layer of approximately 0.70 mm thick is thus formed which is subjected to a polymerization cycle consisting of 2 hours of heating at approximately 120 ° C.

During this cycle also occurs the polymerization of hexanediol diacrylate to form an acrylic polymer.

The polyurethane layer which carries the acrylic coating is then removed from the support.

This sheet obtained can be assembled with a sheet of annealed or toughened glass to form a safety glazing, the assembly being carried out by placing the face of the polyurethane layer coated with the acrylic coating on the outside relative to the sheet of glass.

The sheet obtained and the glazing which uses it are subjected to the tests described below.

EXAMPLE

2

The procedure is the same as in Example 1 except that the hexanediol diacrylate is replaced by the butanediol diacrylate in the acrylic composition while retaining the same proportions.

The plastic sheet obtained after polymerization is easily detached from the casting support.

EXAMPLE

3

A 10% solution in methyl ethyl ketone is deposited on a continuously moving movable glass support, coated with a separating agent which is a modified ethylene oxide adduct. a methacrylic resin (methacrylate), having a hydroxyl index I_OH of 50 and a dry extract of 60% in a mixture of 4 parts of xylene for 1 part of butyl acetate (methacrylic resin sold under the name DEGALAN VPLS 50 by the German company DEGUSSA), the deposited solution containing at a rate of 2.5% by weight of the dry extract of the resin of azo-bis-isobutynonitrile as a thermal initiator.

It is dried at 120 ° C for 20 minutes and a film approximately 1 micron thick is obtained.

The procedure is then as in Example 1 to form the polyurethane layer on the acrylic film.

EXAMPLE

4

The procedure is as in Example 3, except that the methacrylic resin with hydroxyl index I is replaced_OH 50 with a methacrylic resin with hydroxyl index I_OH 73, for example the resin sold under the name DEGALAN VPLS 73, by the company DEGUSSA).

EXAMPLES

5

AT

8

The procedure is the same as in Examples 1 to 4, except that the ratio between the polyols of the polyol component is modified by using respectively 0.35, 0.45 and 0.20 OH equivalent for the polyol comprising the oxide segments. ethylene and propylene oxide, 1,4-butanediol, the polyol with a functionality greater than 2 being a polycaprolactonetriol (for example the product sold under the name NIAX 301 by the company UNION CARBIDE).

EXAMPLE

9

AND

10

The procedure is as in Example 1, except that the NCO / OH ratio is modified by taking an NCO / OH ratio equal to 1.5 and 2.0 respectively.

EXAMPLE

11

The procedure is as in Example 1 except that on the casting support, no longer an acrylic film but a film 2 microns thick of triisocyanate (for example the product sold under the name TOLONATE HDT by the company RHONE-POULENC).

EXAMPLE

12

The procedure is the same as in Example 1 to form the polyurethane layer except that the reaction mixture of the components is poured directly onto the casting support coated with the separating agent, therefore without having previously formed a layer. acrylic coating.

After polymerization, the polyurethane layer is detached from the support and is assembled with a sheet of glass.

The glass sheet-polyurethane layer assembly is immersed in a 10% solution in methyl ethyl ketone of a methacrylic resin having a hydroxyl index IOH of 50 with a dry extract of 60% in a mixture of 4 parts of xylene for 1 part of butyl acetate, the solution also containing an initiator for the photochemical polymerization of the methacrylic resin.

The duration of the soaking is 1 minute, after which the glazing is rinsed with methyl ethyl ketone and the assembly is dried at 10 min at 60 ° C. then the face of the glazing carrying the polyurethane layer is irradiated for 90 seconds by a lamp. 400 watt UV.

EXAMPLE

13

The procedure is as in Example 1, except that the copolymer with ethylene oxide and propylene oxide segments of molecular mass 1900 is replaced by a copolymer of the same family but of molecular mass 2200, comprising 47% by weight of ethylene oxide (for example the product sold under the name SYNPERONIC L44 by the company ICI).

EXAMPLE

14

The procedure is as in Example 1, except that the copolymer with ethylene oxide and propylene oxide segments is replaced by a difunctional sulfonated polyether polyol comprising ethylene oxide segments with a molecular weight of approximately 1000 g and at 100%. by weight of ethylene oxide segment in the chain and further containing a terminal SO₃-Na + group.

EXAMPLE

WITNESS

1

The procedure is as in Example 1, except that the reaction mixture of the components is poured directly onto the casting support coated with the separating agent, without having previously formed an acrylic film.

EXAMPLE

WITNESS

2

The procedure is as in Example 1, except that an NCO / OH ratio equal to 1 is used.

EXAMPLE

WITNESS

3

The procedure is as in Example 1, except that an acrylic coating 20 microns thick is formed on the casting support.

EXAMPLE

WITNESS

4

The procedure is as in Example 1, except that the copolymer with ethylene oxide and propylene oxide segments is replaced by another copolymer having a molecular weight of 1630 and comprising only 25% by weight of ethylene oxide segments.

The polyurethane layers obtained according to the examples are subjected to abrasion tests.

One of the abrasion tests is a usometry test generally used to measure the resistance of papers to wear.

A 12 cm diameter sample obtained according to the examples is placed on a turntable and a cloth is applied to the side to be tested of the sample, that is to say the side treated with the acrylic or isocyanate coating. cotton with a support weight of 1 kg. The sample is made 1000 turns. It is then removed from the device and its surface condition and its transparency are observed.

Another usometry test showing the resistance to abrasion of the layer by solvents consists of soaking the sample with cyclohexanone and subjecting it to 500 revolutions as in the previous test.

The results of these abrasion tests are contained in the following table. The appearance of the sample is noted:<ul id="ul0003" list-style="dash"><li>good: when the transparency of the sample was not affected by the test;</li><li>medium: when a slight clouding is observed;</li><li>bad: when the sample is scratched and it has lost its transparency.</li></ul><tables id="tabl0001" num="0001"><table frame="all"><tgroup cols="3" colsep="1" rowsep="0"><colspec colnum="1" colname="col1" colwidth="52.50mm" /><colspec colnum="2" colname="col2" colwidth="52.50mm" /><colspec colnum="3" colname="col3" colwidth="52.50mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="center"><u style="single">EXAMPLES</u></entry><entry namest="col2" nameend="col2" align="center">APPEARANCE OF THE SAMPLE AFTER 1000 DRY LAPS</entry><entry namest="col3" nameend="col3" align="center">APPEARANCE OF THE SAMPLE AFTER 500 LAPS IN THE PRESENCE OF CYCLOHEXANONE</entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="right">1</entry><entry namest="col2" nameend="col2" align="center">WELL</entry><entry namest="col3" nameend="col3" align="center">WELL</entry></row><row><entry namest="col1" nameend="col1" align="right">2</entry><entry namest="col2" nameend="col2" align="center">WELL</entry><entry namest="col3" nameend="col3" align="center">WELL</entry></row><row><entry namest="col1" nameend="col1" align="right">3</entry><entry namest="col2" nameend="col2" align="center">WELL</entry><entry namest="col3" nameend="col3" align="center">WELL</entry></row><row><entry namest="col1" nameend="col1" align="right">4</entry><entry namest="col2" nameend="col2" align="center">WELL</entry><entry namest="col3" nameend="col3" align="center">WELL</entry></row><row><entry namest="col1" nameend="col1" align="right">5</entry><entry namest="col2" nameend="col2" align="center">WELL</entry><entry namest="col3" nameend="col3" align="center">WELL</entry></row><row><entry namest="col1" nameend="col1" align="right">6</entry><entry namest="col2" nameend="col2" align="center">WELL</entry><entry namest="col3" nameend="col3" align="center">WELL</entry></row><row><entry namest="col1" nameend="col1" align="right">7</entry><entry namest="col2" nameend="col2" align="center">WELL</entry><entry namest="col3" nameend="col3" align="center">WELL</entry></row><row><entry namest="col1" nameend="col1" align="right">8</entry><entry namest="col2" nameend="col2" align="center">WELL</entry><entry namest="col3" nameend="col3" align="center">WELL</entry></row><row><entry namest="col1" nameend="col1" align="right">9</entry><entry namest="col2" nameend="col2" align="center">WELL</entry><entry namest="col3" nameend="col3" align="center">WELL</entry></row><row><entry namest="col1" nameend="col1" align="right">10</entry><entry namest="col2" nameend="col2" align="center">WELL</entry><entry namest="col3" nameend="col3" align="center">WELL</entry></row><row><entry namest="col1" nameend="col1" align="right">11</entry><entry namest="col2" nameend="col2" align="center">WELL</entry><entry namest="col3" nameend="col3" align="center">WELL</entry></row><row><entry namest="col1" nameend="col1" align="right">12</entry><entry namest="col2" nameend="col2" align="center">WAY</entry><entry namest="col3" nameend="col3" align="center">WAY</entry></row><row><entry namest="col1" nameend="col1" align="right">13</entry><entry namest="col2" nameend="col2" align="center">WELL</entry><entry namest="col3" nameend="col3" align="center">WELL</entry></row><row><entry namest="col1" nameend="col1" align="right">14</entry><entry namest="col2" nameend="col2" align="center">WELL</entry><entry namest="col3" nameend="col3" align="center">WELL</entry></row><row><entry namest="col1" nameend="col1" align="left">WITNESS 1</entry><entry namest="col2" nameend="col2" align="center">BAD</entry><entry namest="col3" nameend="col3" align="center">WAY</entry></row><row><entry namest="col1" nameend="col1" align="left">WITNESS 2</entry><entry namest="col2" nameend="col2" align="center">WELL</entry><entry namest="col3" nameend="col3" align="center">WELL</entry></row><row><entry namest="col1" nameend="col1" align="left">WITNESS 3</entry><entry namest="col2" nameend="col2" align="center">BAD</entry><entry namest="col3" nameend="col3" align="center">BAD</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="left">WITNESS 4</entry><entry namest="col2" nameend="col2" align="center">WELL</entry><entry namest="col3" nameend="col3" align="center">WELL</entry></row></tbody></tgroup></table></tables>

For the evaluation of the anti-fog effect, a method is applied as described in standard DIN 4648, part 8, except that the water temperature is regulated at 40 ° C. by thermostatic means. As a measure of the condensation behavior, the time which elapses until the onset of condensation on the test piece is perceptible to the naked eye (delay in the appearance of fogging). With the generally known polyurethane coating layers, the onset of condensation is perceptible immediately after the introduction of the test piece into the measuring device.

The appearance time of the fogging is greater than 5 minutes for all the examples according to the invention (1 to 14). The appearance of fogging is faster for control example 4.

The mechanical properties of the polyurethane layer obtained in Examples 1 to 14 are sufficient to give it energy absorbing properties.

The test results show that the polyurethane layer obtained by reactive casting on a support previously coated with an acrylic or isocyanate-based coating with a functionality greater than 2, of low thickness, exhibits very good abrasion resistance and anti-fog properties.

The mechanical properties of the layer of control example 2 are insufficient.

When the coating is too thick, the abrasion resistance is on the contrary decreased compared to the resistance presented by an untreated layer.

When the coating is carried out by dipping the layer of plastic material already polymerized in an acrylic bath, the improvement in the abrasion resistance is less, and a deterioration in the optical quality is observed.

The polyurethane layer according to the invention, which may or may not be combined with one or more layers of plastic material, is advantageously used as an external layer of a laminated glazing comprising a support of glass or plastic, the "treated" side of the layer being oriented towards the outside of the glazing.