FR2704552A1 - Process for the preparation of foamed and highly charged polymeric materials based on polymethyl methacrylate. - Google Patents

Abstract

The invention relates to a process for the preparation of foamed and highly charged polymeric materials based on polymethyl methacrylate in a suitable form, in which a VL pre-solution of 5-70 parts by weight of methyl methacrylate and of 1- is prepared. 15 parts by weight of polymethyl methacrylate prepolymer PP, in which there is incorporated with rapid stirring, with the formation of a suspension, the inorganic filler in FS particles in an amount of 30 to 80% by weight relative to the suspension formed, being specified that gaseous or solid carbon dioxide is introduced regularly in fine distribution in the pre-solution or in the suspension, after which the carbon dioxide is removed by external heating or by the heat of reaction of the polymerization initiated by an initiator redox, while the polymerization is taking place, and demolding is carried out after the completion of the polymerization.

Description

The invention relates to a polymer material based on

  polymethacrylate, highly charged and foamed.

  Highly loaded cast resins, for example based on PMMA, have been successfully launched on the market for a long time (cf. EP 218 866; US 3,847,865; US

  4,221,697, US 4,251,576, US 4,826,901; US 4,786,660).

  Admittedly, such polymeric materials enriched with mineral fillers, which can be used for example for kitchen sinks, in the sanitary sector and, generally, as plate materials in the building sector, approach, in Particularly in the most modern embodiments, technical requirements regarding appearance, durability, workability, etc., but these are relatively heavy materials. For example, in the case of P [A. having a filler content of 60-70% by weight of silicon dioxide or aluminum hydroxide,

  we can base it on a density of 1.8 g / cm3.

  Quite quickly, attempts were made to obtain a foamed polymeric material. DE-P 10 17 784 describes, for the production of porous molded bodies, mainly composed of PMXA, a process in which carbon dioxide snow is incorporated into the mixture composed of polymer and monomers, at least to partially reach the prescribed low temperature and, at the same time, to obtain a porous structure of the product formed during the polymerization. In the same patent, it is mentioned that dyes, pigments, etc. or fillers can be added to the polymerizable mass. A method of general application for the manufacture of porous molded bodies consists, according to FR 1 055 058, of heating above their softening point thermoplastics which contain gases in solution, the matrix of material

  plastic being swollen by expanding gases.

  Other protection rights relate to a foamed polymeric material in which the foaming gas is produced by the action of a component of the polymer containing water on a component of the polymer which contains calcium carbide (South African patent 68.08312), or polymeric materials which are foamed by means of peroxide compounds <Japan-KCokai 78/105 565,

  Chem. Abstr. 90 39 662a; Japan-Kokai 75/151 278, Ghem.

Abstr. 84 151 530h).

  It is known from EP 0 503 156, for the preparation of cast resins, to emulsify Up to% by weight of water in a suspension of methyl methacrylate containing a filler. After hardening, the

  part of the water is removed from the poured object by heating.

  There remains a highly charged foam material.

  The production of highly charged foamed methyl polymethacryate, i.e. a material containing at least 40% and up to 80% by weight of an inorganic filler, places the technique before a task which is qualitatively different from that imposed for example by the manufacture of "porous molded bodies, mainly composed of polymethyl methacrylate" according to DE-PS 10 17 784. This is a variant of the chamber polymerization process, in which dry ice is mixed with stirring, so as to be distributed as homogeneously as possible, with the usual prepolymer containing an initiator,

  and this mixture is loaded into the molding chamber. At-

  below O'C, the mixture is pourable, it gels on heating into a solid mass. The state of the art therefore did not open a route that could be borrowed directly for the manufacture of highly charged foamed polymeric materials based on PMNA. We therefore set ourselves the goal of providing a process which makes it possible to prepare foamed, highly charged polymeric materials, based on polymethyl methacrylate, while maintaining the characteristics which must be required of resins.

  following the example of proven technologies.

  However, it has been discovered that the method according to the invention is well suited to achieving the goal thus set. The invention relates to a process for the preparation of highly charged foamed polymeric materials, based on polymethyl methacrylate, in an appropriate form, with the use of solid carbon dioxide, process which starts with a pre-solution VL, prepared from 70 to 95 parts by weight of methyl methacrylate and from 5 to 30 parts by weight of polymethyl methacrylate prepolymer PP, as well as from 0 to 5, optionally from 0.05 to 5 parts by weight of a crosslinker bifunctional and from 0 to 5, possibly from 0.5 to 5, preferably from 0.5 to 1.5 parts by weight of a silanizing agent SI-K. To this VL pre-solution, the inorganic filler in the form of FS particles is added, with rapid stirring, in proportions of 30 to 80% by weight (relative to the foamed material constituting the final product) and it is distributed uniformly therefrom. carbon dioxide in the form of carbon dioxide snow or dry ice (fragmented / crushed) in proportions of 0.5 to 30% by weight relative to the suspension formed, or in the form of carbon dioxide gas, then, while the polymerization develops, the carbon dioxide is removed by external heating or by the heat of reaction resulting from the polymerization process, preferably by means of a redox initiator system and, after the completion of the polymerization, the mold is removed . The introduction of carbon dioxide can be carried out in the VL pre-solution or in the

suspension formed.

  Consider, for example, as PM prepolymer, the PMMA polymers ordinarily used in this field, which may possibly contain minor proportions, up to approximately 15% by weight, of judiciously chosen comonomers, such as for example methyl acrylate. Prepolymers ordinarily have molecular weights in the range of 2 x 104 to 4 x 10 dalton [determined

  by size exclusion chromatography <SEC)].

  If necessary, it can also be added to the pre-

  solution a crosslinker, for example in the form of the (meth) acrylic ester of polyalcohols, in proportions of 0.1 to 1.5% by weight relative to the monomers. Finely divided inorganic or organic materials commonly used for cast resins are suitable as FS fillers. It is advisable that a grain size of 200 gm in diameter, preferably 50 μm, is not exceeded. Preferably, when cristobalite is used as a filler, at least 95% of the particles must be less than 10 μm in size. As far as possible, the particles having a size 0.1 µm should not constitute more than 10% of the total number of particles. The particle size is determined by known methods tcf. B. Scarlett in "Filtration & Separation", p. 215, 1965). For the determination of the particle size, the largest dimensions of the particles are taken into account. The

  preference is given to grain-shaped particles.

  Occasionally, it can be advantageous to rid the particles of the moisture which is fixed there by adsorption, by heating, for example at 150'G. FS fillers can be natural products or be manufactured synthetically. The mechanical properties, such as hardness, modulus of elasticity in shear, are judged by the intended application of the cast resins. Adjustment of a modulus of elasticity at

  shear of at least 5 GNm-2 may be advantageous.

  Suitable for example are minerals such as aluminum oxides, aluminum hydroxides and derivatives, for example double oxides of alkali metals and

  alkaline earth and alkali metal hydroxides

  earthy, clays, silicon dioxide in its different variants, silicates, aluminosilicates, carbonates, phosphates, sulfates, sulfides, oxides. coal, metals and metal alloys. Synthetic materials such as sprayed glass, ceramics, porcelain, slag, finely divided synthetic SiO 3 are also suitable. Mention will be made of the variants of silicic acid such as quartz (quartz powder), zridymite and cristobalite, as well as kaolin, talc, mica. feldspar, apatite, barite, gypsum, chalk, limestone, dolomite. If necessary, it is also possible to use charge mixtures. The proportion of filler in the cast resins preferably amounts to at least 40% by weight. In general, a proportion of 80% by weight is not exceeded. As an indicative value, mention will be made of a filler content of the cast resin between 50 and 80% by weight. The preparation of fillers in the appropriate grain sizes can be carried out according to known methods, for example by crushing and grinding. In addition to aluminum hydroxide, the

  cristobalite is particularly preferred.

  In a preferred embodiment, the average particle size is in the range of 60 to 0.5 µm. Preferably, the hardness (according to Mohs: cf. Rbmpp's Chemie-Lexikon, 9th edition, p. 1700, Georg Thieme Verlag, 1990) of the FS charges is> 6 in the case of cristobalite and 2.5-3 , 5 in that of

aluminum hydroxide.

  The SI-X silanizing agents serve, in a manner known per se, as adhesion agents between the filler and the organic phase. We can therefore use the compounds

  organosilicon known in the state of the art [of.

  D. Skudelny, Kunststoffe 77, 1153-1156 (1987); Kunststoffe 8 (1978) :; technical manual for Dynasilan, adhesion agent for La Dynamit Nobel, Chemie]. Firstly, they are functional organosilicon compounds comprising at least one ethylenically unsaturated group in the molecule. The functional residue carrying the ethylenically unsaturated group is generally linked to the central silicon atom by a carbon atom. The other silicon ligands are generally alkoxy residues with 1-6 carbon atoms (ether bridges can still be found in the alkyl residue). Examples include vinyltrialcoxysilanes. The C-C double bond can also be linked to the Si atom by one or more carbon atoms, for example in the form of

  allyltrialcoxysilanes or a-methacryloyloxypropyl-

  trialcoxysilanes. Dialcoxysilanes can also be used, in which another functional residue comprising a CC double bond, most often of the same type, or an alkyl residue preferably comprising i to G carbon atoms is linked to the Si atom. It is also possible that different types of organosilicon compounds are present in the organosilicon compound. Examples include vinyltrimethoxysilane, vinyltriethoxysilane,

  vinyltris (methoxyethoxy) silane, divinyldimethoxy-

  silane, vinylmethyldimethoxysilane, vinyltrichlorosilane, α-methacryloyloxypropyl-

  trimethoxysilane or α-methacryloyloxypropyl-

  tris (methoxyethoxy) silane. Advantageously, the organosilicon compounds are used at the same time as catalysts of the amine type, in particular of the alkylamine type, with 3-6 carbon atoms, in particular with n-butylamine. As an indicative value for the use of the catalytic amine, a proportion of 0.05 to 10% by weight can be taken, preferably of

  1 to 5% by weight of the organosilicon component.

  In general, the weight ratio of inorganic charges to the organosilicon compound is between

  500: 1 and 20: 1, preferably 50 25: 1.

  The process can be carried out according to

  the example of technical procedures known per se.

  The method according to the invention firstly comprises the preparation of the LV pre-solution in a manner known per se. The pre-solution conveniently contains the amine component and the silanizing agent SI-M. Then the filler FS is introduced into the pre-solution using a dissolving agent and the suspension obtained in this way is then dispersed in the presence of the dissolving agent. After the completion of the silanization reaction, part of the redox component of the redox initiator (cf. H. Rauch-Puntigam, Th. Vblker, Acryl- und Methacrylverbindungen, Springer-Verlag 1967) is conveniently added to the suspension and distributed using a paddle stirrer. One can also add - following the example of usual practice - a polymerization inhibitor, such as for example a sterically hindered phenol (cf. Ullmanns Encyclopedia of Technology, 5th ed., Vol. 20AQ, pp. 459-507, VCH 1992 ) and / or a lubricant, such as a phthalic acid diester or stearic acid. Carbon dioxide is then added. Carbon dioxide can be added in the form of dry ice as well as crushed dry ice or gas, ensuring a uniform distribution. When adding gas, the most favorable quantity must be determined. The quantity of gas cannot be deduced directly from solid CO2, because, when solid CO2 is used, a non-negligible part escapes

  the gaseous state of the suspension in the air volume.

  As soon as the gas escape from the suspension is no longer perceptible, the remaining redox components can be added with stirring to the suspension. During the exothermic redox polymerization which then develops or - in the case where one proceeds exclusively with peroxide initiators (cf. Rauch-Puntigam, op. Cit.) - as a result of the external heat supply, the

  foam suspension during hardening.

  Finally, we can then proceed to demolding.

  Particularly in the case of continuous production of the foamed polymeric material, carbon dioxide can

  also be added to the LV pre-solution.

  The suspension is prepared in mixing groups which are suitable for this purpose. Appropriate models are produced for example by the firms Respecta (DUsseldorf, RA) or Coudenhove & H bner (Vienna). The addition of the initiators must be carried out before the

leaving the mixing unit.

  By the method according to the invention, a PN [A closed-cell foam is generally obtained. As we can judge from the results obtained so far, the density of foamed plastic compared to that of unfoamed PARA containing the same proportion of filler is considerably

  reduced, possibly to half.

  Thanks to the process according to the invention, it is possible to obtain, in a relatively simple manner and in addition to the proven technology, a material of

Foamed and heavily loaded PMXA.

  The lower density of this material results in many interesting application possibilities. The examples which follow are intended to explain the invention. Examples A. Preparation of a heavily loaded suspension

Example A-1

  In 266.97 g of methyl methacrylate (MKA) and 0.03 g of 2,4dimethyl-6-tert.butylphenol, 60 g of a polymer are dissolved, at approximately ° C. and within 5 h. of MXA (t spec. / c = 130-140, Mw 400,000 approx., product PLEXIGUM X 920 from the company Rëhm GmbH), then cooled to room temperature. 5.0 g of stearic acid and 3.0 g of glycol dimethacrylate are dissolved in the syrup thus obtained. In the dissolver (product Dispermat from the company VKA Getzmann, RFA), 332.5 g of aluminum hydroxide are introduced into the syrup, with moderate stirring, before an average particle size of 45 gm <product ALC0A C33 from the company Alcoa, USA), then 332.5 g of aluminum hydroxide having an average particle size of 8 4m (product ALGOA C333). The suspension is then dispersed

  for approximately 10 minutes in the dissolver at 12.5 m / s.

  B. Preparation of the foamed polymeric material

Example B-1

  700 g of the heavily loaded suspension of example A-i are poured into a polyethylene cup (W = 9 cm, H = 15 cm). With stirring with a paddle stirrer, 7 g of dibenzoyl peroxide at 50% in dibutyl phthalate (INTEROX BP-50-FT product from Peroxid Chemie GmbH) are added and dissolved, at approximately 25 ° C. 3.5 g of azo-bis-isobutyronitrile (INTEROX NN IBN product). With stirring, 7.0 g of dry ice is then added to the suspension. After a stirring time of 5 min, the temperature of the suspension is measured. Then added, with stirring of the suspension, 7.0 g of N, N-dimethyl-p-toluidine in the form of a 50% solution in MXA. After stirring for 1 min, the agitator is removed. A polymer foam is obtained, which is characterized in Table 1.

Example B-2

  The procedure is analogous to B-1. Instead of 7.0 g of dry ice, add 35.0 g of snow

carbonic & suspension.

Example B-S

  The procedure is analogous to B-1. Instead of 7.0 g of dry ice, add 70.0 g of snow

carbonic suspension.

Example B-4

  The procedure is analogous to B-1. Instead of 7.0 g of dry ice, add 140 g of snow

carbonic suspension.

  Table 1, - Data concerning examples B-1 to 8-4 Ex Addition of Temp, after 5 min Density time of dry ice (%) of agitation ('C) hardening (min) foam (g / cm3 )

8-1 1.0 + 20 12 1.12

8-2 5.0 + 10 15 0.84

B-3 10.0 - S 20 0.66

  8-4 20.0 - 16 The foam collapses before hardening Properties of foamed polymeric materials: With the procedure according to the invention, foams are obtained which have mainly closed cells. As shown in fig. 1 & 3 (fig. 1: with 5% by weight of dry ice; fig. 2: with 5% by weight of dry, crushed ice; fig. 3: with 10% by weight of dry ice), the average size of pores increases with increasing COS content. The variation of the density of the foam as a function of the addition of C02

is shown in fig. 4.

Claims (4)

  1.- Process for the preparation of foamed and highly charged polymeric materials based on polymethyl methacrylate in an appropriate form, with the use of carbon dioxide, characterized in that a VL pre-solution of 5-70 parts by weight is prepared of methyl methacrylate and of 1-15 parts by weight of methyl polymethyl methacrylate prepolymer PP, in which there is incorporated, with rapid stirring, with the formation of a suspension, the inorganic filler in FS particles in an amount of 30 to 80% by weight relative to the suspension formed, being specified that gaseous or solid carbon dioxide is introduced regularly in fine distribution in the pre-solution or in the suspension1 after which the carbon dioxide is removed by external heating or by heat reaction of the polymerization triggered by a redox initiator, while the polymerization is taking place. and in that the demolding is carried out after the completion of the polymerization. 2. - Process according to Revenoication 1, characterized in that solid carbon dioxide, in the form of dry ice or in the form of crushed dry ice, is introduced in an amount of 0.5 to 30% by weight relative to to the suspension formed.   3.- Method according to claim 1 or 2, characterized in that aluminum hydroxide is used as a filler.   4.- Method according to claim 1 or 2, characterized in that cristobalite is used as a charge.