FR2863621A1 - Light-diffusing acrylic material for use in lamps and signs, contains methyl methacrylate (co)polymer, halogenated polyphosphonate and-or halogenated phosphate ester fire retardant and nano-scale silica - Google Patents

Abstract

Light-diffusing methacrylic polymer material (I) based on methyl methacrylate (co)polymer and halogenated polyphosphonate and/or halogenated phosphate ester fire retardant also contains 1-5% silica with an elementary particle size of less than 500 (preferably less than 100) nm.

Description

2863621 -1-

  The present invention relates to the field of materials used for the manufacture of articles belonging to the electrical domain (such as electrical boxes) and more particularly to the field of luminaires or signage in public places, such as exit signs. help. More specifically, it relates to a methacrylic polymer material diffusing light and having improved fire resistance.

  The interest shown by methacrylic (co) polymers in the manufacture of the abovementioned articles is particularly known from the application WO 03/037975, because of their exceptional optical properties, especially of transparency.

  It is also known that these methacrylic (co) polymers pose fire resistance problems that prevent their use in the manufacture of these articles. These are in fact generally subjected to high temperatures either by the radiation of the light sources which illuminate them or, if necessary, by undesired prolonged contact with a heating element. Therefore, in order to obtain suitable materials for the manufacture of these articles, it is necessary to combine these methacrylic (co) polymers with a certain amount of flame retardants.

  The above-mentioned application WO 03/037975 thus recommends using as a methacrylic polymer material a specific combination of a methacrylic (co) polymer containing predominantly methyl methacrylate units, with, as flame retardants, at least one halogenated polyphosphonate compound and at least one a halogenated neutral ester compound of phosphoric acid.

  The materials described by this application are generally in the form of plates of variable thickness which are then shaped in particular by thermoforming, cutting, gluing to give the desired articles. However, the fireproofing efficiency of the abovementioned compounds decreases considerably with the thickness of these plates, so that it becomes insufficient for the thin plates.

  The present invention aims to remedy this drawback without altering the optical properties expected otherwise for the material. It is based on the fact that it has been found that the incorporation of a silica specific for the flame-retarding agents described by the application WO 03/037975 makes it possible, surprisingly, to improve the fire resistance of the methacrylic polymer material, particularly when the latter is in the form of thin plates, for example with a thickness of between 2.5 and 8 mm.

  The present application therefore relates to a light-diffusing methacrylic polymer material comprising: - from 80 to 90% of a methacrylic (co) polymer containing predominantly methyl methacrylate units, - from 5 to 15% of a compatible flame retardant agent with methyl methacrylate and methacrylic (co) polymer, said agent being chosen from a halogenated polyphosphonate compound, a halogenated neutral ester compound of phosphoric acid or a mixture of these two compounds, and - from 1 to 5% of a silica having an elemental grain size of less than 500 nm, preferably less than 100 nm, and even more preferably less than 10 nm.

  In the absence of any indication to the contrary, the percentages given herein are weight percentages expressed on the basis of the total weight of the polymeric material.

  The polymeric material according to the invention possesses advantageous optical properties which are in accordance with those which are expected from the materials used for the manufacture of lighting, display or signaling lighting devices (intended for example for billboards or illuminated signs). whether it is the transmission of light in the visible, or a light scattering power high enough to ensure illumination as uniform as possible.

  The polymer material according to the invention offers these properties combined with a fire resistance quite remarkable for an acrylic material. This last property is measured according to a method developed by the International Electrotechnical Commission (IEC) and listed under the number 60695-2-12.

  This method consists of applying the end of an incandescent wire previously heated to a known temperature for 30 seconds and with a determined force, and then measuring the extinction time of the flames or the disappearance of the incandescence imparted to the material, after removal of the wire.

  The material is considered to have passed the test if the flame or incandescence goes out less than 30 seconds after the removal of the wire, and in three successive tests. The method starts with the glow wire at a temperature of 960 ° C: if the test fails, the wire temperature is lowered in steps of 50 ° C until a successful test is obtained. The corresponding temperature, called glow wire resistance temperature or GWR, characterizes the fire resistance of the material, the latter being all the better than the GWR is higher. This method therefore makes it possible to obtain a relative evaluation of the fire resistance of the tested materials.

  According to a preferred variant, the material according to the invention comprises: from 82 to 86% of the methacrylic (co) polymer, from 10 to 12% of the flame retardant, and from 2 to 4% of silica.

  This material advantageously makes it possible to achieve a GWR greater than or equal to 850 ° C., and sometimes even equal to 960 ° C., even when it is in the form of thin plates, for example between 2.5 and 8 mm. .

  The methacrylic (co) polymer containing predominantly methyl methacrylate units comprises from 51 to 100%, preferably from 80 to 99% by weight of units derived from the methyl methacrylate monomer and from 0 to 49%, preferably from 1 to 20%. % by weight of units derived from monoethylenically unsaturated comonomers copolymerizable with methyl methacrylate.

  The monoethylenically unsaturated comonomer (s) copolymerizable with the methyl methacrylate monomer is (are) in particular chosen from acrylic, methacrylic and vinylaromatic monomers.

  Acrylic monomers that may be mentioned include acrylic acid, alkyl acrylates in which the alkyl group has from 1 to 10 carbon atoms (such as methyl acrylate, ethyl acrylate, n-acrylate and the like). butyl, 2-ethylhexyl, isobutyl), hydroxyalkyl or alkoxyalkyl acrylates, in which the alkyl group has 1 to 4 carbon atoms, acrylamide, acrylonitrile.

  As methacrylic monomers, mention may be made of methacrylic acid, alkyl methacrylates in which the alkyl group has from 2 to 10 carbon atoms (such as ethyl methacrylate, isobutyl, secondary butyl, tertiary butyl). isobornyl methacrylate, methacrylonitrile, hydroxyalkyl or alkoxyalkyl methacrylates in which the alkyl group has 1 to 4 carbon atoms.

  Examples of vinyl aromatic monomers are styrene, substituted styrenes (such as α-methyl styrene, monochlorostyrene and tert-butyl styrene).

  According to a preferred variant of the invention, the methacrylic (co) polymer used in the material according to the invention is a homopolymer of methyl methacrylate.

  As indicated above, the light-diffusing methacrylic polymer material according to the invention further comprises from 5 to 15%, preferably from 10 to 12%, of a flame retardant compatible with the methyl methacrylate monomer and the (co) methacrylic polymer. By compatible, it is meant that said agents mix easily with the methyl methacrylate monomer and methacrylic (co) polymer and do not demix in time.

  The halogenated polyphosphonate compound used is described in US 3058941. It is preferred to use a chlorinated polyphosphonate, and in particular the chlorinated polyphosphonate sold by the company Clariant under the name Exolit 5087.

  Examples of the halogenated neutral ester of phosphoric acid are the tris (haloalkyl) phosphates in which the halogen is chlorine or bromine and the alkyl group has from 1 to 4 carbon atoms, such as tris (chloromethyl) phosphate, tris (chloroethyl) phosphate, tris (bromomethyl) phosphate, tris (bromoethyl) phosphate, tris (chloropropyl) phosphate, tris (chloroisopropyl) phosphate and tris (bromopropyl). Tris (2-chloroisopropyl) phosphate (hereinafter referred to as TCIP) is particularly well suited to the methacrylic polymer material according to the invention.

  Silicas having an elemental grain size of less than 500 nm, preferably less than 100 nm, and even 10 nm are commercially available. According to a preferred variant of the invention, a silica is used which is also in the form of granules having a diameter of between 50 and 500 m, preferably between 100 and 250 m. These granules make it possible to obtain a silica which is easily handled and free of dust, and therefore particularly advantageous in terms of the industrial production of the material. Such a silica can be obtained from Rhodia under the name Zeosil TS635.

  In addition to the above-mentioned components, the methacrylic polymer material according to the invention further comprises an appropriate amount of one or more light-diffusing components in the form of organic or inorganic compound particles of appropriate size. It may be pigments or dyes, such as titanium dioxide, calcium carbonate, calcium sulfate, barium sulfate or carbon black. In general, the weight content range of these compounds in the material is between 0.01 and 5%.

  The methacrylic polymer material according to the invention may furthermore optionally contain from 5 to 15% of an impact modifying compound, as described in application WO 03/037975.

  The methacrylic polymer material according to the invention is advantageously in the form of plates. These can be made by the casting method which is described in WO 03/037975.

  This process comprises the use of a polymerizable methacrylic composition comprising a polymerizable element for forming the methacrylic (co) polymer, the flame retardant (s), the silica, the light diffusing component and, optionally, the impact modifying compound. This composition is introduced into a mold consisting of two glass plates separated by a polymer seal (polyvinyl chloride, for example) which seals and whose thickness determines the thickness of the plate of the material. The mold is placed in a ventilated oven or heated pool to allow the polymerization of the monomers. The polymerization cycle comprises a polymerization step at a temperature of about 50-60 C to obtain a conversion of about 95%, then a post-polymerization step at a temperature of about 120 C. After cooling, the plate obtained is removed from the mold. The plates obtained have a thickness determined by the thickness of the joint.

  The polymerizable element consists essentially of methyl methacrylate and, optionally, monoethylenically unsaturated comonomers copolymerizable with methyl methacrylate, such as those mentioned above. The methyl methacrylate may advantageously be replaced by a mixture of said monomer with a methyl methacrylate prepolymer having a conversion level of 6 to 15% (called syrup).

  When the silica used is in the form of granules (also called microbeads), they are easily dispersed after mixing with the methyl methacrylate (or the mixture of the latter with the syrup) under the following conditions. effect of even moderate agitation, to restore the particles corresponding to the elementary grain size defined above.

  In addition to the products defined above, the process for manufacturing the methacrylic polymer material according to the invention also comprises, as described in application WO 03/037975, the addition to the polymerizable composition of at least one radical polymerization initiator, a chain transfer agent, release agent, antioxidant or UV stabilizer

  According to a preferred variant of the invention, the plates of the methacrylic polymer material defined above have a thickness of between 2 and 8 mm, preferably between 3 and 6 mm. These plates are thin and have a GWR, and therefore improved security, can diversify the applications of acrylic materials in the areas of lighting or signage.

  The following examples are given purely by way of illustration of the invention, and can in no way be interpreted as limiting its scope.

  Example 1: Plate 3 mm thick of a material comprising 84% of polymethyl methacrylate (or PMMA), 7% of Exolit 5087, 5% of TCIP and 3.5% of silica. a polymerizable composition by adding, successively with stirring, 358.65 g of a methyl methacrylate syrup (hereinafter MMA): 31.5 g (ie 7%) of a chlorinated polyphosphonate sold under the name Exolit 5087 by Clariant Company - 22.5 g (5%) of TCIP - 15.75 g (3.5%) of silica having a grain size of about 3 nm, in the form of granules of 100 at 250 m sold under the name Zéosil TS 635 by the company Rhodia, 2.25 g (0.5%) of BaSO4 dispersed in dioctyl phthalate - 0.27 g (ie 600 ppm) of TiO 2 dispersed in dioctylphthalate 2.25 g of a 5% solution of AzobislsoButyroNitrile (or AIBN) in the MMA corresponding to 0.1125 g of AIBN (250 ppm) - 3.33 g of a 1% solution in the MA M terpinene (chain transfer agent) corresponding to 0.0333 g of terpinene (74 ppm) - 13.5 g of a 1% solution of Tinuvin P in MAM (UV stabilizer derived from benzotriazole sold by the company CIBA) corresponding to 0.135 g of Tinuvin P (300 ppm).

  The polymerizable composition thus obtained is stirred at ambient temperature until a mixture of homogeneous appearance is obtained. It is then poured into a mold formed of two glass plates separated by a PVC seal and held by clamps to obtain a 3 mm thick plate.

  The filled and closed mold is then placed horizontally in a ventilated air oven. The composition is then polymerized for 1 hour at 68 ° C. and then for 1 hour at 55 ° C. The polymerization temperature is then increased in the course of one hour until it reaches 125 ° C. and is maintained at this value for 20 minutes.

  After cooling the mold, the parallelepiped plate (dimensions: 300 x 300 x 3 mm) is demolded and then cut into square plates of 50 x 50 x 3 mm for measuring the resistance to glow wire (or GWR) according to IEC 60695- 2-12.

The GWR obtained is 960 C.

  Example A (comparative according to WO 03/037975): Example 1 is repeated without incorporating silica.

A 750 C GWR is measured.

Example B (control):

  Example 1 is repeated without incorporating silica or flame retardant. A GWR of 700 C. is measured.

  It is thus found that the material according to the invention allows a remarkable increase (about 200 C) of the GWR of a 3 mm plate relative to the material not comprising silica prepared in accordance with the teaching of WO 03/037975.

  Example 2: Plate 3 mm thick of a material comprising 84% of polymethyl methacrylate (or PMMA), 5% of Exolit 5087, 5% of TCIP and 3.5% of silica. Example 1 by modifying the Exolit 5087 content and incorporating 5,800 ppm TiO2 (instead of 600) and 0.65% BaSO4 (instead of 0.5%).

A GWR of 900 C is measured.

  Example 3: Plate with a thickness of 3 mm of a material comprising 84% of polymethyl methacrylate (or PMMA), 12% of TCIP and 3.5% of silica. Example 2 is repeated, incorporating as flame retardant 12% of TCIP. A GWR of 850 C is measured.

  Example 4: Plate 4 mm thick of a material comprising 84% of polymethyl methacrylate (or PMMA), 7% of Exolit 5087, 5% of TCIP and 3.5% of silica. Example 1 is repeated. using a PVC seal to obtain plates of thickness 4 mm and without incorporating BaSO4.

We measure a GWR of 960 C.

  Example C (comparative according to WO 03/037975): Example 4 is repeated without incorporating silica. A 750 C GWR is measured.

  Example 5: Plate 4 mm thick of a material comprising 84% of polymethyl methacrylate (or PMMA), 7% of Exolit 5087, 5% of TCIP and 2% of silica. Example 4 is repeated modifying the silica content, and incorporating 0.5% BaSO4.

A GWR of 850 C is measured.

  Example 6: Plate with a thickness of 4 mm of a material comprising 84% of polymethyl methacrylate (or PMMA), 5% of Exolit 5087, 5% of TCIP and 3.5% of silica. 4 is repeated modifying the content of Exolit 5087 and incorporating 0.5% BaSO4. A GWR of 900C is measured.

  Example 7: Plate with a thickness of 4 mm of a material comprising 84% of polymethyl methacrylate (or PMMA), 12% of TCIP and 3.5% of silica. Example 6 is repeated using as the sole flame-retardant agent 12% TCIP.

A GWR of 850 C is measured.

  Example 8: 5 mm thick plate of a material comprising 84% of polymethyl methacrylate (or PMMA), 5% of Exolit 5087, 5% of TCIP and 3.5% of silica. Example 6 is repeated in using a PVC seal to obtain plates 5 mm thick and very slightly modifying the contents of TiO2 and BaSO4.

A GWR of 900 C is measured.

  Example 9: 6 mm thick plate of a material comprising 84% of polymethyl methacrylate (or PMMA), 7% of Exolit 5087, 5% of TCIP and 3.5% of silica Example 8 is repeated using a PVC seal to obtain 6 mm thick plates, modifying the Exolit 5087 content and adjusting the TiO2 content.

We measure a GWR of 960 C.

  Example D (comparative according to WO 03/037975): Example 9 is repeated without incorporating silica. A GWR of 900 C is measured.

  The illustrated materials and the results obtained are summarized in the following Table I:

Table I

  Examples Thickness of Content in Nature Content and Content of Agents GWR content plate TiO2 BaSO4 flame retardant silica (%) (C) (mm) (ppm) (%) 1 3 600 0.5 7% Exolit 5087 + 5% TCIP 3.5 960 A 3 600 0.5 7% Exolit 5087 + 5% TCIP 0 750 (comparative) B 3 600 0.5 none 0 700 (control) 2 3 800 0.65 5% Exolit 5087 + 5% TCIP 3 , 5,900 3 3,800 0,65 12% TCIP 3,5,850 4 4,600 0 7% Exolit 5087 + 5% TCIP 3,5,960 C 4,600 0 7% Exolit 5087 + 5% TCIP 0,750 (comparative) 4 600 0.5 7% Exolit 5087 + 5% TCIP 2 850 6 4 600 0.5 5% Exolit 5087 + 5% TCIP 3.5 900 7 4 600 0.5 12% TCIP 3.5 850 8 5 500 0, 4 5% Exolit 5087 + 5% TCIP 3.5 900 9 6 400 0.47% Exolit 5087 + 5% TCIP 3.5 960 D 6 400 0.4 7% Exolit 5087 + 5% TCIP 0.900 (comparative) 2863621 -11-

Claims (9)

  1. Light-diffusing methacrylic polymer material comprising: - from 80 to 90% of a methacrylic (co) polymer containing predominantly methyl methacrylate units, - from 5 to 15% of a flame-retardant agent compatible with the methacrylate monomer methyl and the methacrylic (co) polymer, said agent being chosen from a halogenated polyphosphonate compound, a halogenated neutral ester compound of phosphoric acid or a mixture of these two compounds, and from 1 to 5% of a silica having a elemental grain size less than 500 nm.   2. Material according to claim 1, characterized in that it comprises: from 82 to 86% of the methacrylic (co) polymer, from 10 to 12% of the flame retardant, and from 2 to 4% of silica.   3. Material according to one of claims 1 or 2, characterized in that the elemental grain size of the silica is less than 100 nm.   4. Material according to one of claims 1 to 3, characterized in that the elemental grain size of the silica is less than 10 nm.   5. Material according to one of claims 1 to 4, characterized in that the (co) methacrylic polymer used is a homopolymer of methyl methacrylate.   6. Material according to one of claims 1 to 5, characterized in that the halogenated polyphosphonate compound used is a chlorinated polyphosphonate.   7. Material according to one of claims 1 to 6, characterized in that the halogenated neutral ester of phosphoric acid is tris (2-chloroisopropyl) phosphate.   8. Material according to one of claims 1 to 7, characterized in that it is in the form of plates.   2863621 -12- 9. Material according to claim 8, characterized in that the plates have a thickness of between 2.5 and 8 mm, preferably between 3 and 6 mm.