FR2640630A1 - TRANSPARENT ACRYLATE SHOCK-RESISTANT MASSES, PREPARATION AND USE THEREOF - Google Patents

Abstract

A transparent and impact-resistant molding compound which does not become cloudy or color under the action of heat and humidity or on exposure to the elements, is composed according to the invention of: A) 10 to 90% of a coherent hard phase, composed essentially of methyl methacrylate and having a glass transition temperature of more than 70 degree (s) C and B) 90 to 10% of a resilient phase distributed in the hard phase and partly united to it by covalent bonding, having a glass transition temperature less than -10 degree (s) C, an average particle size of the resilient phase less than 130 nm and a particle size heterogeneity of the phase resilient of less than 0.5, consisting of at least 50% (based on B) of a lower alkyl acrylate and 0.5 to 5% of a graft crosslinker or at least a trifunctional crosslinker ; C) not more than 0.05% of water soluble constituents.

Description

The invention relates to a molding material which is transparent and resistant to

  acrylate-based impact, thin sheets and multilayer moldings made from this molding compound, and a process for preparing the same. Already known from US Pat. Nos. 3,808,180 and 3,843,753 are acrylate-based impact-resistant molding compositions, which can be transparent if the components are suitably selected. However, transparency easily disappears under conditions frequently encountered in the use of objects made from these masses. Thus, under the action of high temperatures or high humidity, the masses become cloudy or white and when there are white or cloudy areas under the effect of shocks or

bending forces.

  The known molding compounds consist of an emulsion polymerization product consisting of several phases, one of the phases being made of a hard thermoplastic methacrylic ester polymer and the other of an acrylic elastomer distributed in this phase. polymer particles of 50 to 300 nm, preferably of & 200 nm in size. Their preparation is carried out by emulsion polymerization in two stages, a latex of the acrylic elastomer, referred to as a resilient phase, being first produced, then, in the second stage, the

  methacrylic ester hard polymer being grafted onto it.

  This polymer is called hard phase. The acrylic elastomer produced in the first step is characterized by a glass transition temperature of less than -10 ° C. It is constituted by at least 50% by weight of an alkyl or aralkyl acrylate, with a maximum of 10% by weight of a hydrophilic comonomer, as well as with 0.05 to 5% by weight or cross-linking polymerization and graft crosslinking agent. In addition, a small proportion of styrene is usually incorporated in order to harmonize the refractive index of the resilient phase with that of the hard phase and thus to avoid a disturbance of the material by dispersion of the light at the particle surfaces of the resilient phase. The graft crosslinking mentioned has the effect that at least 20% of the hard phase produced in the second stage are grafts on the resilient phase,

  that is, attached thereto by covalent bonding.

  The known process leaves, in the qualitative and quantitative choice, sufficient freedom so that it is practically impossible to prepare and test all the possible variants which are clearly distinguishable. US Patent 3,843,753 provides another possible variation. namely melt blending the two-phase polymer with another thermoplastic molding material. Those skilled in the art who would like to follow the teaching of this patent to produce molding masses having certain combinations of characteristics have no other resource than to prepare, by methodical variations, a very large number of products. experimental to the extent that it fails to achieve the specified characteristics by chance, or to acquire new knowledge on the dependence of the desired characteristics on the constitution of the two-step polymerization product. The aim of the invention was to reduce, or even to eliminate, the aforementioned tendency of the molding composition to form a cloudiness or to stain under the effect of heat and moisture or to exposure to the elements, as well as what is called a white break under the effect of shocks or bending forces. This goal was only achieved after it was discovered that the characteristics mentioned are complexly related to the particle size of the phase.

  elastomer, to the particle size heterogeneity of

  ci, the minimum content and nature of the crosslinking monomers and the content of substances soluble in water. Furthermore, it has been found that the fixed goal can not be attained in the case of simultaneous use of styrene or other vinylaromatic carbides in the elastomer phase, so that an equalization of the optical refraction indices of the two phases could not be achieved using cheap monomer components. In the molding compositions preferred according to the invention, a difference in refractive index of more than 0.02 between the two phases has been observed, which should inevitably lead to the formation of

  disorders according to the experience of those skilled in the art.

  All the more surprising was the finding that not only the molding masses having a constitution

  in accordance with the claims are transparent and

  colorless after molding, but also that this characteristic persists, even when exposed to heat and moisture, weather and

shocks or bending forces.

  To ensure the optical transparency in the ground state, a particle size of the resin phase less than 130 nm, preferably below 70 nm, has proved essential, but it is not sufficient in itself. It is only by adjusting a particle size homogeneity of the resilient phase of less than 0.5, preferably less than 0.2, that the

transparency has been achieved.

  While according to US Pat. No. 3,808,180, a proportion of the resilient phase of 0.5% by weight is sufficient, it has been found, in the context of the invention, that a minimum proportion of 10% in weight

was absolutely necessary.

  Critical selection has also been essential in terms of the nature and proportion of the reticulating monomers. The cited patents distinguish cross-linking from cross-linking and grafting crosslinkers and qualify both groups as indispensable. To the troupe of the reticulants this crossing belong monomers which contain at least two acryl or methacryl remains; they are used, in the examples of the US patents, in a proportion of 0.5% by weight of the resilierate phase. Cross-linking grafting agents are monomers which contain, in addition to an acryl or methacryl residue, an ethylenically unsaturated group whose polymerization tendency is significantly lower, as a rule an allyl group. The share of these monomers in the resilient phase was chosen

between 0% and 0.4% by weight.

  In order to achieve the objects of the invention, it was necessary for the graft crosslinkers to be at least 0.5% by weight, preferably at least 1% by weight, based on the weight of the resilient phase. It can, however, be replaced with such good effect by monomers which contain three or more acryl or methacryl groups in the molecule. On the other hand, crossing crosslinking has proved to be superfluous, although useful in many cases, in a proportion of 0.05

  at 2% by weight of the resilient phase.

  It has also been found that the proportion of water-soluble constituents in the mass to be molded should be kept below 0.05% by weight in order to guarantee a lasting transparency, in particular under the action of moisture. The water-soluble constituents are introduced into the mass to be molded in the form of residues of the polymerization initiator, in particular peroxodisulphates, or emulsifiers. This is primarily the case in the usual operating mode in which the aqueous phase of the base latex is separated from the emulsion polymerization product by evaporation, for example by the spray drying process. This process is applied in some exemplary embodiments of the US patent, while in other examples a substantial portion of the aqueous phase is separated in liquid form from the melt of the emulsion polymerization product. Under these conditions, most of the water-soluble constituents of the latex

is also eliminated.

  It has been discovered that the tendency for cloud formation under the effect of moisture disappears when the latex is coagulated at the time of preparation of the mass to be molded, and the aqueous phase in liquid form is separated from the coagulate. a sufficient measure so that it remains in the mass only 0.05% by weight of water-soluble constituents. This step of the process is of considerable importance according to the invention, since a relatively large amount of water-soluble emulsifiers which, in the absence of careful separation, must be used for the necessary small particle size adjustment. 'with the mass to be molded, would give rise to the subsequent formation of an accentuated disorder under

the effect of moisture.

  It is only the described combination of steps of choice concerning the proportions of the phases, the particle size of the emulsion polymerization product, its particle size heterogeneity, the nature and the quantity of crosslinking monomers and the final content of water-soluble constituents. Thus, the operations necessary for this purpose could lead to the product according to the invention and to its excellent properties. The selected features are known per se, in

  as such, in other combinations.

  Preparation of the emulsion polyzrisation product The impact resistant and transuene molding composition of the invention is based on at least two phase emulsification polymerization material which can be processed as such or in admixture with another molded, molded ready. The incorporation of other phases into the bene fi t of additional effects is limited only to the extent that the benefits of the products according to the invention are not limited.

Reduts have this fact.

  The hard phase of the polymerization product emulsifies at a glass transition temperature of about 2 ° Celsius (7 ° C) and may be composed solely of methyl methacrylate. i may be there at a later date. enu. as comonomers, alkali metal acrylates. in particular to 4 carbon atoms in the remainder akjve. in a zroportion which can go up to 2w in zoods compared to the hard phase, provided that the glass transition temperature

  mentioned not scit ras exceeded downward.

  The resilient phase is composed of lower alkyl acrylates for at least 50%. preferably greater than 80% by weight, resulting in a glass transition temperature of less than 10 ° C, generally between -20 and -80 ° C. Insofar as the specified glass transition temperature is reached, other aliphatic comonomers capable of radical polymerization, which may be copolymerized with the alkyl acrylates, may be used simultaneously, as is known in the state of the art. . On the other hand, appreciable proportions of aromatic comonomers, such as styrene, α-methylstyrene or vinyl toluene, must be excluded. because they lead - especially in case of exposure to the intemneries - to caracteristicues

undesirable mass molding.

  The part of the graft cross-linking agent or the cross-linking agent that can be used has its place. having three unsaturated residues ethv. ienicue susceptibies of polvmerisaticn

  radicaire or Dlus, is chosen within the limits of.

  at 5% in boids. in the manner in which it is produced in the Dolvm oroduct, in at least 15% by weight of the solid phase, or at least 15% by weight in the solid phase. covalent. The dere this -a bond apoarait the dissolution of a quill alicuote the product of pol-vmerisation in emulsion in a solvent for the hard phase. Under these conditions, the resilient phase and the hard-core portion of it; is united by ccvalente bond remain undisclosed. The weight of the undissolved fraction must be at least 5%. 30 to 50% of the peptide calculates the hard phase, at which time it calculates the effective strength of the alumose. However. the weight of the Ereff4-ae crosslinking agent should in no case be less than 0.5% by weight and is preferably in the range of from 1 to 4% by weight.

of the resilient phase.

  The graft crosslinker in the emulsion polymerization products according to the invention is relatively strong and gives rise, in general, to sufficient crosslinking of the resilient phase, so that an additional crosslinking crosslink is superfluous. general rule. If, however, the desired characteristics of impact resistance are not achieved, the simultaneous use of 0.05 to 2% by weight of a crosslinking crosslinker, in addition to the graft crosslinking agent in the resilient phase, may be indicated. In this case, the crossing crosslinking agent

  must contain at least two acryl or methacryl remains.

  The allyl esters of acrylic or methacrylic acid are preferred as graft crosslinking agents, but other graft crosslinkers mentioned in US Pat. Nos. 3,808,180 and 3,843,753 are also suitable. Cross-linking crosslinkers comprising at least three ethylenically unsaturated radicals capable of radical polymerization, such as allyl groups, or acryl or methacryl radicals, which can be used in their place, belong to triallyl cyanurate, triacrylate and trimethylolpropane trimethacrylate. triacrylate and pentaerythritol trimethacrylate and related compounds for which other examples

  are given in DE-A 33 00 526.

  The two or multiphase emulsion polymerization product is conventionally produced by emulsion polymerization in two or more stages in the aqueous phase. In the first step, the resilient phase is produced. We must then devote particular attention to the correct setting of the particle size and particle size heterogeneity. Although these known methods with use of a seed latex or with gradual addition of the monomers are applicable in principle, the characteristics desired according to the invention can be best achieved by a process in which the monomer mixture for the resistive phase is emulsified and polymerizes

as a whole.

  The particle size of the resilient phase depends essentially on the concentration of the emulsifier. Particles having an average (weight average) size of less than 130, preferably less than 70 nm, with a particle size heterogeneity of less than 0.5, preferably less than 0.2, are obtained with emulsifier concentrations. from 0.15 to 1.0% by weight relative to the aqueous phase. With smaller amounts of emulsifier, a higher average particle size is observed and, with larger amounts of emulsifier, heterogeneity

  bigger. Heterogeneity is even lower -

  that is to say, the particle size homogeneity is all the greater as the duration of the particle formation phase at the beginning of the emulsion polymerization is shorter. It is especially important to avoid a new formation of particles after the start of the polymerization, which can occur in case of subsequent addition of emulsifier. The rate of polymerization can also influence particle size and granulomtric heterogeneity: if the radical stream is too weak, heterogeneity is excessive; if it is too strong - especially if polymerization is triggered by peroxidisulfates - it can

  result in a sensibiiite moisture too high.

  The concentration of emulsifier mentioned applies above all to usual anionic emulsifiers. For example, they are part of the alkoxylated paraffins and

  sulphonated, which are particularly preferred.

  As the polymerization initiator, for example, 0.01 to 0.5% by weight of an alkali metal or ammonium peroxodisulfate is used in relation to the aqueous phase and the polymerization is initiated at temperatures of 20%. at 100'C. The process is preferably carried out with redox systems, consisting for example of 0.01 to 0.05% by weight of organic hydroperoxides and 0.05 to 0.15% by weight of Rongalite, at temperatures of 20 to 30%. C. It is essential to verify the choice of the correct polymerization conditions by measuring the average particle size and particle size heterogeneity on a test load and, if necessary,

  ie, modify in accordance with the rules set out above.

  These two quantities can be calculated according to known methods from the result of the measurement of the light diffused to the ultracentrifugation of the finished latex. Transforming the emulsion polymerization product into a molding composition The emulsion polymerization product is in the form of an aqueous dispersion having a content -r. solid material of 30 to 60% by weight which contains as a general remie. in relation to the solid matter, more than 0% by weight of water-soluble constituents. According to the invention, the emulsification product is separated from the water-soluble constituents by coagulating the d: soersicn, sequestering the liquid aqueous phase of the

  -canuiat and melting the ccagulat into a mass to be molded.

  In the case of cperazions, a scrubber is used, particularly a cupping extruder. The dispersion is in the liquid state, extruded and co-worked by the common action of shear and shear forces at a temperature above the glass transition temperature of the zone. Povmer: emulsion. As a consequence of -a: recession to: re.ne in the extruder. the aqueous phase remains icuide. even above 100'C, and is separated under pressure. through a slot or a plate merfcree in the wall of the extruder, at the same time sue the constituents dissolved therein. Suitable processes and devices are known from, for example, DE-A-27 50 682 and US-A-4 110 843. Any residual water content may be evaporated off, in known manner, in a degassing zone.

of the extruder.

  The melt is extruded from the extruder and granulated or extruded into any desired profile and cooled below the softening temperature (glass transition temperature). It is often desirable to mix the impact resistant molding material with a possibly preponderant amount of another hard molding material compatible therewith. With a solids ratio of 10: 1 to 1:10, the characteristics of the molding composition according to the invention are clearly manifested in the mixture formed, in particular in the form of an improvement in the dimensional stability when hot and stamping ability, linked to the advantageous characteristics which are characteristic of the molding compound according to the invention itself. Preferably, the mixing component is a molding compound of polymethyl methacrylate. Also suitable are hard copolymers of methyl methacrylate with acrylic esters, acrylonitrile or with maleic anhydride and styrene, and polyvinyl chloride. Such mixtures can be prepared in different ways. For example, the dispersion of the emulsion polymerization product prepared according to the invention can be mixed with an aqueous dispersion of the mixing component and the mixture is coagulated, the aqueous phase is separated off and the coagulate is melted into a mass to be molded. With this process, a particularly uniform mixture of the two masses can be obtained. As good a mixture is obtained by pumping the aqueous dispersion of the emulsion polymerization product prepared according to the invention into an extruder which contains a melt of the mixing component. The dispersion is coagulated in the melt and the aqueous phase is extracted by pressure as previously described. The components can also be prepared and isolated separately, mixed in the form of their melts or in the form of powder or granules and homogenized in an extruder.

  several screws or in a roll mill.

  Usual additives can be added in each step of the transformation that is suitable for this purpose. These include dyes, pigments, fillers, reinforcing fibers, lubricants, UV protection agents ,. etc. Polyisable UV absorbers can be introduced in polymer connection into the emulsion polymerization product together with the other monomers at the same time.

  coi-merisaticr moncmeres of the hard phase.

  Shaping of the mass to be molded When the transparent and impact-resistant molding compound according to the invention contains a high proportion

  of resilient phase in the context of the claims,

  It is suitable for the manufacture of flexible sheets which are transparent by extrusion of the melt through a piate die and smoothing on a calender. Such films are characterized by their enduring transparency, their insensitivity to heat and cold, their resistance to intemzeries, their weak yellowing and their reduced frazilization. as well as by the mirrored formation of white bending or bending scrapes, and thus, for example, as windows in 2 bags. are capstes of cars or sails. Such sheets have a thickness of less than 1 mm,

from 0.05 to 0.5 minutes.

  An important field of application is that of the formation of thin surface layers, for example from 0.05 to 0.5 mm thick, on rigid and dimensionally stable substrates such as sheets, boards, particle boards , plates of plastic or the like. In this case, the proportion of the resilient phase can be much lower and, as a result, the mass to be molded can be harder. For the manufacture of such coatings, various methods are available. Thus, the mass to be molded can be extruded as a sheet, smoothed and laminated onto the substrate. By the technique of extrusion coating, an extrudate can be applied to the surface of the substrate and smoothed by means of a cylinder. When a thermoplastic synthetic material itself serves as a substrate, there is the possibility of coextrusion of the two masses with the formation of a surface layer of the transparent molding compound.

the invention.

  Mixtures of the impact-resistant molding compound, in particular with polymethyl methacrylate, are suitable for the production of moldings having a wall thickness of more than 1 mm, for example continuous webs extruded from 1 to 10 mm. which are suitable for stamping and can be used, for example, for the production of printable protection plates for electrical equipment or for the manufacture of high-pressure injection molded parts

  quality, for example of car windows.

  A 60% emulsion I was prepared by emulsification of 99 parts by weight of butyl acrylate 1 part by weight of triallyl cyanurate 0.1 part by weight of tertiary butyl hydroperoxide in 67 parts by weight of a solution 0.15 t of water

sodium lauryl sulphate.

  A 50% emulsion II was prepared by emulsification of 96 parts by weight of methyl methacrylate 4 parts by weight of butyl acrylate 0.4 part by weight of dodecyl mercaptan 0.1 part by weight of tertiary butyl hydroperoxide in 100 parts by weight of a 0.06% aqueous solution of

sodium lauryl sulphate.

  In a polymerization recipe equipped with a stirrer, an external cooling system, and a flow-in recinient, at least c0 parts by weight of an aqueous phase which contained 1% by weight of sodium lauryl sulphate, 0.15% by weight of Rongalite, 0.02% by weight of acetic acid and 0.0008 part by weight of ferrous sulphate. Within 2 hours, 50 parts by weight of the emulsion I was added with stirring at a temperature of 55 ° C. The formed phase polymer had a glass transition temperature of -35.degree. C. Further 140 parts by weight of the -I -mulsion were then added over a further 2 h, and under these conditions the polymer Hard phase, having a glass transition temperature of 90 ° C, was formed. The difference in the refractive indices of the two phases was 0.021. An aqueous dispersion having a solids content of 40% by weight was obtained. By solubility measurements on a coagulated copolymer, it was found that 25% of the hard phase was fixed on the resilient phase. The particles of the resilient phase formed from the emulsion I had, after the completion of the first stage of polymerization, a mean value in terms of particle size of 60 nm, which increased to 88 nm at the polymerization of the emulsion in the second step. Particle size was determined by the light scattering method

  (measuring device, "Nancsizer", Coulter Electronics).

  The granuloma-tricyclic heterogeneity of the resilient phase, determined by ultracentrifugation, was U80 = 0.12. For the recovery of the solid material from the dispersion obtained, a twin-screw extruder was used, rotating in opposite directions, with a screw diameter D = 30 mm. Each segment of the length is defined by a multiple of the diameter D. The screws were sealed against the transmission mechanism

through a cable gland.

  The coagulation zone had a length of 25 D. It operated at a pressure of 40 bar and a temperature of 220 ° C. Coagulation was produced by

  the simultaneous effect of heat and shear.

  4 kg per hour of dispersion were pumped continuously into the coagulation zone by means of a piston metering pump. Downstream of the coagulation zone, in a segment of length 2 D of the extruder barrel, the separated aqueous phase with the coagulation was discharged in liquid form by means of a drying orifice, a chamber of pressure and

  a pressure control valve set at 25 bar.

  In a consecutive zone of degassing without pressure of length D, the residual moisture, of about 10% of

  weight of the polymer, was flushed in the form of steam.

  In a subsequent pressure zone, 5 D in length, the polymer was sent to a granulation die at a temperature of 200 ° C. The extrudate produced was cooled and granulated after solidification. The molding composition obtained had a content of

  water-soluble components of less than 0.05% by weight.

  It was extruded into a 0.05 mm thick sheet which was calendered. In an atmosphere at 100 ° C with a relative air humidity of 100%, no white coloring occurs within 30 minutes. When bending or folding the sheet, no white break is observed in the fold zone. The sheet can be stamped without breaking. Bright, transparent stamping edges are obtained which are not frayed or dyed white. The sheet can be glued firmly by hot stamping on a

hard PCV panel.

  Comparative Tests Part of the dispersion obtained in Example 1 was dried by spray drying. The dry product contained 0.4% by weight of water-soluble constituents. A sheet made from this product became cloudy under the conditions indicated

  previously in a humid atmosphere.

  If the proportion of triallyl cyanurate in the process of the example is reduced from 1 to 0.3 parts by weight, the resulting molding composition appears cloudy. Only 22% was found. by weight of insoluble fractions in the acrone, which allows to conclude that only part of the resilient phase was reticulated and the hard phase

  was practically not fixed to the resilient phase.

  In another variant of Example I, 0.10 part by weight of sodium lauryl sulphate was used in the previously introduced aqueous phase instead of 0.10% by weight. As a result, the average particle size of the resilient phase increased to 132 nm and the granulometric heterogeneity of the resilient phase was 0.2. The molding material produced was cloudy. 2 parts by weight of the dispersion obtained in Example 1 and 1 part by weight of a 40% aqueous anionic emulsion polymerization product, the composition of which corresponded exactly to that of the hard phase of the dispersion of the Example 1 were intimately mixed and the mixture was dried as in Example 1 in a twin screw extruder. The proportion of the resilient phase in the molding composition obtained was 20% by weight. The dimensional stability when hot was at 95 ° C, that is 7 ° C higher than

  in the case of the molding compound of Example 1.

  From the mass to be molded, a very rigid 1 mm thick sheet was extruded.

2-6 40630

  good at stamping. It is suitable for example for the manufacture of protective plates for instruments for cars, electrical appliances, etc.

saele 3, -

  In a repetition of the procedure of Example 1, the triallyl cyanurate in the emulsion I was replaced by the same amount of allyl methacrylate as the graft crosslinking agent. The molding compound obtained coincided, in all its characteristics, with that of

Example 1

  EXAMPLE 4 In two tests carried out according to Example 3, 2.5 and 5 parts by weight of a methyl methacrylate emulsion polymerization product in addition to the previously introduced aqueous phase were added. a seed latex having a particle size of 40 nm (weight average). Under these conditions, the following particle sizes were obtained: Particles of seed latex 2.5 5.0 parts by weight Resilient phase diameter 57 nm 94 nm Total diameter 108 nm 137 nm In another variant of the method of In Example 3, the following amounts of emulsions I and II were used:

  83 parts by weight of emulsion 1; 100 parts by weight of emulsion II.

  This results in a composition of the molding masses of% by weight of resilient phase and 50% by weight of

hard phase.

  The following particle sizes were measured: Resilient phase diameter 110 nm Total diameter 140 nm The hot dimensional stability of the molding materials is 55 ° C. The molding compound is transparent, it does not become turbid in a humid atmosphere, it does not present white chips in the form of a 0.05 mm sheet

  thick and can be stamped impeccably.

Claims (12)

CLAIMS i. Transparent and impact-resistant molding material, containing: A) from 10 to 90% by weight of a coherent hard phase, having a glass transition temperature of more than 70 ° C. consisting of a) 80 to 100% by weight <with respect to A) of methyl methacrylate and b) 20 to 0% by weight of a lower alkyl acrylate, B) from 90 to 10% by weight of a resilient phase distributed in the hard phase, having a glass transition temperature below -10 ° C, an average particle size of the resilient phase of less than 130 nm and a particle size heterogeneity of the resiliency phase of less than 0.5, formed by c) at least 50% by weight% relative to B) of a lower alkyl acrylate, d) 0.5 to 5% by weight of a graft crosslinking agent or a crosslinking monomer containing at least three ethylenically unsaturated residues capable of radical polymerisation, e) optionally other aliphatic comonomers & ethylenic unsaturation, capable of radical (co) polymerization, C) not more than 0.05% by weight of water-soluble constituents, at least 15% by weight of the hard phase being united by covalent bond in the resilient phase.   2. Molding composition according to claim 1, characterized in that the hard phase and the resilient phase have a difference of refraction indices of more than 0.02.   3. Molding composition according to claim 1 or 2, characterized in that the resilient phase contains, in   components or as part of them   here, from 0.05 to 2% by weight of a crosslinking crosslinking agent.   4. A sheet with a thickness of less than 1 mm, comprising a molding compound according to claim 1 or 2. 5. A sheet according to claim 4, characterized in that the hard phase A contains from 2 to 20% by weight of lower alkyl acrylate.   6. Process for preparing a transparent and impact-resistant molding composition by emulsion polymerization. aqueous solution of a monomer or a mixture of 2C monomers composed of a) 80 to 100% by weight (relative to A) of methyl methacrylate and b) 20 to 0% by weight of a lower alkyl acrylate to obtain a hard phase (A) having a glass transition temperature of more than 70 ° C, in the presence of a resilient phase (B) dispersed in water, having a glass transition temperature of less than -10 ' C, an average particle size of less than 130 nm and a particle size heterogeneity of less than 0.5, constituted by c) at least 50% by weight <with respect to B> of a lower alkyl acrylate, d) 0 5 to 5% by weight of a graft crosslinking agent or a crosslinking monomer containing at least three ethylenically unsaturated radicals capable of radical polymerization, e) optionally other aliphatic ethylenically unsaturated comonomers capable of (co) polymerization radical, at least 15% by weight of the hard phase and covalently bonded to the resilient phase by coagulation of the resulting dispersion by separating the liquid aqueous phase from the coagulate and melting the   coagulate for obtaining a mass to be molded.   7. A process according to claim 6, characterized in that the resilient phase in dispersion contains 0.05   at 2% by weight of a crosslinking crosslinking agent.   5. Process according to claim 6 or 7, characterized in that the molding compound obtained is mixed in the molten state with a mass to be molded.   compatible, in a ratio of 10: 1 to i: 10.   9. A process according to claim 8, characterized in that a molding composition having a composition is used.   which coincides with that of the hard phase.   10. Process according to claim 6, characterized in that the aqueous dispersion obtained by emulsion polymerization is mixed, in a ratio of solids of 10: 1 to 1:10, with an aqueous dispersion of a polymerization product. emulsion having a composition which coincides with that of the hard phase, and the mixture is coagulated, separated from the aqueous phase and melted. 11.- Process according to any one of   Claims 6 to 10, characterized in that the   coagulation is performed under the simultaneous action of   heat and shear forces in an extruder.   12. A process according to claim 6, characterized in that the melt is put in the form of a body   molded more than 1 mm thick and cooled   below the softening temperature.   13. A process according to claim 12, characterized in that is prepared and transformed into a molded body molding material which contains, in the hard phase, 0.5 to   2% by weight of units of an alkyl acrylate.   14.- multilayer molded body, containing a rigid and dimensionally stable substrate and a thin superflective layer made of a molding compound according to   any of claims 1 to 5.   15. A multilayer molded body according to claim 14, characterized in that the surface layer has been formed by coextrusion at the same time as the production of the substrate, by extrusion coating on the surface of the substrate or by adhesive bonding. a sheet formed   from the mass to be molded on the surface of the substrate.