GB2226324A

GB2226324A - Clear viscous moulding composition

Info

Publication number: GB2226324A
Application number: GB8928658A
Authority: GB
Inventors: Ernst Heil; Uwe Numrich; Walter Schellhaas; Barbara Geppert; Thomas Rhein
Original assignee: Roehm GmbH; Roehm GmbH Darmstadt
Current assignee: Roehm GmbH; Roehm GmbH Darmstadt
Priority date: 1988-12-20
Filing date: 1989-12-19
Publication date: 1990-06-27
Anticipated expiration: 2009-12-19
Also published as: DE3842796A1; FR2640630B1; IT8967811A0; IT1233902B; DE3842796C2; FR2640630A1; GB8928658D0; NL8903093A; ES2017409A6; GB2226324B

Description

1 CLEAR VISCOUS MOULDING COMPOSITION The invention relates to a clear

viscous moulding composition based on acrylate, to films and multi-layer mouldings produced therefrom and to a process for preparing the moulding composition.

US Patent Nos. 3 808 180 and 3 843 753 disclose viscous moulding compositions based on acrylate which can be clear, if the components are suitably selected.

However, this clarity is easily lost under conditions which often arise when the objects produced therefrom are used. Thus, the compositions become cloudy or white under the effect of high temperatures or high humidity of the air or cloudy or white spots may be formed as a result of impact or bending stresses.

The known moulding compositions consist of an emulsion polymer made up of several phases, one phase consisting of a hard thermoplastic methacrylic ester polymer whilst the other phase consists of an acrylic elastomer distributed therein in particles ranging from to 300 nm, preferably 160 to 200 nm in size. The polymer is produced by two-step emulsion polymerisation in which first of all a latex of the acrylic elastomer, the so-called viscous phase, is produced and then in the second step the hard methacrylic ester polymer is grafted on. This is referred to as the hard phase.

The acrylic elastomer produced in the first step is characterised by a glass transition temperature of less than -10'C. It is made up of at least 50% by weight of an alkyl or aralkyl acrylate, up to 10% by weight of a hydrophilic comonomer and 0.05 to 5% by weight each of a polymerisation crosslinker and a graft crosslinker. In addition, at least a small amount of styrene is incorporated in order to bring the optical refractive index of the viscous phase into conformity with that of the hard phase and thereby avoid clouding of the 2 material by refraction of light from the surfaces of the viscous phase particles. The graft crosslinker mentioned has the effect of ensuring that at least 20% of the hard phase produced in the second step is grafted 5 onto the viscous phase, i.e. covalently bonded thereto.

The known process gives such a freedom of choice in the quality and quantity of the synthesis components used that it is virtually impossible to prepare and test all the possible variations.

Another possibility is presented by US Patent No. 3 843 753, in which the two-phase polymer is mixed with another thermoplastic moulding composition in a melt.

Anyone skilled in the art who wishes to produce moulding compositions with specific combinations of properties using the teaching of this patent is directed either to produce a very great number of test products by planned variation, unless he succeeds in achieving the required properties by a stroke of luck, or to arrive at new conclusions as to the dependency of the desired properties on the structure of the two-step polymer.

The objective of the invention was to avoid or prevent the abovementioned susceptibility of the moulding composition to clouding or discolouration under the effect of heat and moisture or when exposed to the weather, as well as so-called stress whitening under the effect of impact or bending stress. It was only possible to achieve this objective once it was recognised that the above-mentioned properties are connected in a complex way to the particle size of the elastomer phase, the non-uniformity of the particle size, the minimum content and nature of the crosslinking monomers and the content of water-soluble substances. It was also found that the objective could not be achieved when styrene or other vinyl aromatic compounds were used in the elastomer phase, which meant that the optical refractive indices of the two phases could not 3 be brought into line using cheap monomer components.

According to one aspect of the present invention we therefore provide a clear viscous moulding composition which comprises:

A) 10 to 90% by weight of a cohesive hard phase having a glass transition temperature of above 70C and comprising a) 80 to 100% by weight (based on A) of methylmethacrylate and b) 20 to 0% by weight of lower alkyl acrylate; B) 90 to 10% by weight of a viscous phase, distributed in said hard phase, having a glass transition temperature of below -10C, the average particle size of the viscous phase being less than 130 nm and having a non-uniformity of the particle size of less than 0.5, and the viscous phase comprising C) e) at least 50% by weight (based on B) of a lower alkyl acrylate, d) 0.5 to 5% by weight of a graft crosslinker or a crosslinking monomer with three or more ethylenically unsaturated, radically polymerisable groups, and optionally, other ethylenically unsaturated, radically (co)polymerisable, aliphatic comonomers; and C) not more than 0.05% by weight of water-soluble constituents, at least 15% by weight of the hard phase being covalently bonded to the viscous phase.

4 In the preferred moulding compositions according to the invention, a difference in refractive index of more than 0.02 between the two phases was discovered, which, to judge from the experience of those skilled in the art, would inevitably lead to clouding.

It was therefore all the more surprising that the moulding compositions produced according to the present invention not only remained clear and colourless after moulding but retained this property even under the effect of heat and moisture, and when exposed to weathering and impact or bending stress.

To ensure optical clarity in the basic state, a particle size for the viscous phase of less than 130 nm, preferably less than 70 nm, proved to be essential but was not sufficient on its own. only when the nonuniformity of the viscous phase particles was adjusted to below 0.5, preferably below 0.2, was clarity achieved.

Whereas according to US Patent No. 3 808 180 a viscous phase content of 0.5% by weight is sufficient, within the scope of the invention a minimum content of 10% by weight was found to be absolutely essential.

A critical choice also proved to be essential with regard to the nature and amount of the crosslinking monomers. The patents referred to above make a distinction between crosslinkers and graft crosslinkers and refer to both categories as indispensible. The category of crosslinkers includes monomers which contain at least two acrylic or methacrylic groups; they are used in the Examples of the US patents in an amount of 0.5% by weight of the viscous phase. The term "graft crosslinkers" is used to denote monomers which contain, in addition to an acrylic or methacrylic group, an ethylenically unsaturated group of significantly reduced tendency to polymerisation, usually an allyl group. The proportion of these monomers in the viscous phase was selected between 0.2 and 0.4% by weight.

In order to achieve the objective of the invention, the proportion of graft crosslinkers had to be increased to at least 0.5%, better still to 1 to 4% by weight, based on the weight of the viscous phase. However, it may equally well be replaced by monomers which contain three or more acrylic or methacrylic groups in the molecule. By contrast, crosslinkers have proved to be inessential, even though in some cases they were found to be essential, in an amount of 0.05 to 2% by weight of the viscous phase.

It was also found that the proportion of watersoluble components in the moulding composition must be kept below 0.05% by weight in order to ensure permanent clarity, particularly under the effect of moisture.

Water-soluble components are entrained into the moulding composition in the form of residues of the polymerisation initiator, such as peroxodisulphates, or the emulsifiers. This is particularly the case in the usual procedure in which the aqueous phase of the basic latex is separated from the emulsion polymer by evaporation, particularly by spray drying. This method is used in some of the embodiments of the US patents, whereas in other examples a substantial proportion of the aqueous phase is separated off in liquid form from the melt of the emulsion polymer. The majority of water-soluble components of the latex are also removed.

It has been found that the susceptibility to clouding under the effect of moisture disappears if the latex is coagulated during the preparation of the moulding composition and the aqueous phase is separated off in liquid form from the coagulate to such an extent that not more than 0.05% by weight of water-soluble constituents remain in the composition. This step is of considerable importance according to the invention, since a relatively large amount of water-soluble emulsifiers have to be used in order to adjust the particle size to the small dimensions required, and if 6 the aqueous phase were not carefully separated from the moulding composition this would result in subsequent severe clouding in the presence of moisture.

The product according to the invention and its outstanding properties have only been achieved by means of the above-described combination of selection steps regarding the proportions of the phases, the particle si4e of the emulsion polymer, the non-uniformity of particle size, the nature and quantity of crosslinking monomers and the final content of water-soluble constituents and the procedure required for this.

According to another aspect of the present invention there is provided a process for preparing a clear, viscous moulding composition which comprises the aqueous emulsion polymerisation of a monomer or monomer mixture comprising a) 80 to 100% by weight (based on A) of methylmethacrylate and b) 20 to 0% by weight of a lower alkylacrylate to obtain a hard phase with a glass transition temperature of above 700C, said polymerization being conducted in the presence of a viscous phase, dispersed in water, with a glass transition temperature of below -100C, an average particle size of less than 130 nm and a non-uniformity of particle size of less than 0.5, the viscouse phase comprising c) at least 50% by weight (based on B) of a lower alkyl acrylate, d) 0.5 to 5% by weight of a graft crosslinker or a crosslinking monomer with three or more ethylenically unsaturated, radically polymerisable groups, and optionally, other ethylenically unsaturated, radically (co)polymerisable, aliphatic comonomers; 1 7 at least 15% by weight of the hard phase being grafted onto the viscous phase, coagulating the resulting dispersion, separating the liquid aqueous phase from the coagulate and melting the coagulate to obtain a moulding composition. There is also provided a product prepared by such a process.

The clear, viscous moulding composition of the invention is based on an at least two-phase emulsion polymer which can be processed as such or in admixture with another moulding composition to produce shaped objects. The incorporation of other phases to achieve additional effects is possible only if this does not cancel out the particular advantages of the products according to the invention.

The hard phase of the emulsion polymer has a glass transition temperature of at least 70C and may consist of methylmethacrylate alone. As comonomers, lower alkyl acrylates, particularly those with 1 to 4 carbon atoms in the alkyl group, may be present, up to a proportion of 20% by weight, based on the hard phase, provided that the glass transition temperature does not fall below that specified.

The viscous phase is made up of at least 50%, preferably more than 80% by weight of lower alkylacrylates, preferably (Cl-4)alkyl acrylates, resulting in a glass transition temperature of less than -10C, generally from -20 to -90C. Provided that the required glass transition temperature is achieved, other radically polymerisable aliphatic comonomers which are capable of copolymerisation with the alkyl acrylates may also be used if desired, as is known from the prior art. However, appreciable amounts of aromatic comonomers such as styrene, alpha-methylstyrene or vinyl toluene, must not be used since they will result in undesirable properties for the moulding composition, particularly on exposure to the weather.

8 The proportion of the graft crosslinker or the crosslinker which may be used in its stead with three or more ethylenically unsaturated, radically polymerisable groups is selected within the range from 0.05 to 5% by weight, so that in the finished emulsion polymer at least 15% by weight of the hard phase is covalently bonded to the viscous phase. The degree of bonding becomes apparent when an aliquot amount of the emulsion polymer is dissolved in a solvent for the hard phase.

The viscous phase and the proportion of hard phase covalently bonded thereto remain undissolved. The weight of the undissolved proportion must be greater than the calculated weight of the viscous phase of the aliquot sample by at least 15, preferably 30 to 80% by weight of the calculated weight of the hard phase. However, under no circumstances must the proportion of graft crosslinker fall below 0.5% by weight and it is preferably in the range from 1 to 4% by weight of the viscous phase. 20 The proportion of graft crosslinker in the emulsion polymers according to the invention is comparatively high and generally produces sufficient crosslinking of the viscous phase, so that there is not usually any need for an additional crosslinker. If the desired properties of impact strength are not achieved, it may be useful to add 0. 05 to 2% by weight of a crosslinker to the viscous phase together with the graft crosslinker. The crosslinker in this case must contain at least two acrylic or methacrylic groups. The preferred graft crosslinkers are the allyl esters of acrylic or methacrylic acid, but other graft, crosslinkers as specified in US-A-3 808 180 and US-A3 843 753 are also suitable. Examples of crosslinkers with three or more ethylenically unsaturated, radically polymerisable groups, such as allyl groups or acrylic or methacrylic groups, which can be used in their place include triallylcyanurate, trimethylolpropane- 9 triacrylate and trimethacrylate, pentaerythritol triacrylate and trimethacrylate and related compounds, other examples of which appear in DE-A-33 00 526.

The two- or multi-phase emulsion polymer is produced in conventional manner by two-stage or multistage emulsion polymerisation in an aqueous phase. In the first step the viscous phase is produced. Particular attention has to be paid to the correct adjustment of the particle size and the non-uniformity of the particle size. Although no methods using a seed latex or the gradual addition of monomer are theoretically applicable, the properties which the invention sets out to achieve are best obtained by means of a process in which the monomer mixture for the viscous phase is emulsified and polymerised in its entirety. The particle size of the viscous phase depends essentially on the concentration of emulsifier. Particles with an average particle size (average weight) 20 of less than 130nm, preferably less than 70 nm, and with a non-uniformity of particle size of less than 0.5, preferably less than 0.2, are achieved with emulsifier concentrations of 0.15 to 1.0% by weight, based on the aqueous phase. For smaller quantities of emulsifier, a larger mean particle size is obtained, whilst with larger quantities of emulsifier greater non-uniformity is obtained. The non-uniformity is lower - in other words the uniformity of the pa-rticle size is greater the shorter the phase of particle formation at the start of the emulsion polymerisation process. Above all, a second formation of particles after the beginning of polymerisation must be avoided, which may occur when emulsifier is added subsequently. The speed of polymerisation can also influence the particle size and non-uniformity of the particle size; if the flow of radicals is too low, the non-uniformity will be too high and if it is too high, an excessive susceptibility to moisture may result, particularly if polymerisation is initiated by means of peroxodisulphates.

The emulsifier concentration referred to applies particularly to conventional anionic emulsifiers. These include, for example, alkoxylated and sulphated paraffins, which are particularly preferred.

The polymerisation initiator used may be, for excmple, 0.01 to 0.5% by weight of alkali metal or ammonium peroxodisulphate, based on the aqueous phase, and the polymerisation is initiated at temperatures of from 20 to 1OWC. Preferably, redox systems are used, 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 from 20 to WC.

It is essential to check the choice of correct polymerisation conditions by measuring the average particle size and the non-uniformity of particle size in a test batch and if necessary to adjust them following the rules explained hereinbefore. Both magnitudes can be calculated from the results of the measurement of scattered light in the ultracentrifugation of the finished latex using known methods.

The emulsion polymer occurs in the form of an aqueous dispersion with a solids content of 30 to 60% by weight which, based on the solids, generally contains more than 0.05% by weight of water-soluble components. According to the invention, the water- soluble components are separated from the emulsion polymer by coagulating the dispersion, separating the liquid aqueous phase from the coagulate and melting the coagulate to produce a moulding composition.

It is expedient to use an extruder, particularly a double screw degassing extruder, for these operations. The dispersion is pumped into the extruder in liquid form and is coagulated at a temperature above the glass transition temperature of the emulsion polymer by the combined action of heat and shear forces. Because of 1 the pressure prevailing in the extruder the aqueous phase remains liquid even above 100C and, still under pressure, is discharged through a slot or a perforated plate in the wall of the extruder together with the dissolved components. Suitable processes and apparatus are known for example from DE-A-27 50 682 and US-A4 110 843. Any residual water can be evaporated in known manner in a degassing zone of the extruder.

The molten moulding composition is removed from the extruder and granulated or shaped into a strip having any desired profile and cooled to below the softening temperature (glass transition temperature).

It is frequently desirable to mix the viscous moulding composition with another hard moulding composition compatible therewith, this second moulding composition possibly being in a larger amount than the first. Thus, according to a further aspect of the present invention there is provided a multi-layer moulding comprising a rigid, non-deformable base member and a thin surface layer of a moulding composition according to the present invention.

At a solids ratio of 10:1 to 1:10, the properties of the moulding composition according to the invention in the mixture produced become clearly apparent, particularly in terms of an improved thermal stability of shape and suitability for punching or stamping, combined with the advantageous properties which are inherent in the moulding composition according to the invention. Preferably, the mixing components consist of a polymethylmethacrylate moulding composition. Hard copolymers of methylmethacrylate with acrylic esters, acrylonitrile or maleic anhydride and styrene as well as polyvinyl chloride may also be considered.

Mixtures of this kind may be prepared in various ways. For example, the dispersion of the emulsion polymer produced according to the invention may be mixed with an aqueous dispersion of the mixing component and 12 the mixture can then be coagulated, the aqueous phase separated off and the coagulate melted to form a moulding composition. With this process, the two compositions are mixed together particularly uniformly.

An equally good mixture is obtained if the aqueous dispersion of the emulsion polymer produced according to the invention is pumped into an extruder which contains a melt of the mixing component. The dispersion is coagulated in the melt and the aqueous phase is squeezed out as described above. The components may also be prepared separately and isolated and mixed together in the form of their melts or in powder or granule form and homogenised in a multi-screw extruder or on a roller frame.

The usual additives may be added thereto at any suitable stage of the process. Such additives include dyes, pigments, fillers, reinforcing fibres, lubricants, UV protectors and the like. Polymerisable UV absorbers may be polymerised into the emulsion polymer together with the other monomers during polymerisation of the hard phase monomers.

If the clear viscous moulding composition according to the invention has a high content of viscous phase within the range claimed, it is suitable for the production of clear flexible films by extrusion of the melt through a flat die and smoothing on a roller frame. Thus, the present invention also provides a film having a thickness of less than lmm and comprising a moulding composition according to the present invention. Films of this kind are characterised by their permanent clarity, resistance to heat and cold, resistance to weathering, low tendency to yellowing and embrittlement and low tendency to stress whitening when bent or folded and are therefore suitable for example as windows in canvas awnings, car hoods or sails. Films of this kind are less than 1 mm thick, for example 0.05 to 0.5 mm thick.

A 13 One particular type of application consists in the formation of thin surface layers of, for example, 0.05 to 0.5 mm thick on rigid, stable base members such as sheet metal, cardboard, chipboard, plastics sheets and the like. In this case the proportion of viscous phase may be considerably smaller and consequently the moulding composition will be harder. There are various methods of producing such coatings. For example, the moulding composition may be extruded to form a sheet which is then smoothed and laminated onto the substrate. Using the technique of extrusion coating, an extruded strip may be applied to the surface of the substrate and smoothed by means of a roller. If a thermoplastic plastic material is used as the substrate itself, there is the possibility of coextruding the two masses to fo=, a surface layer from the clear moulding composition according to the invention.

Mixtures of the viscous moulding composition, particularly with polymethylmethacrylate, are suitable for the production of moulded objects with a wall thickness of more than 1 mm; for example, extruded strips with a thickness from 1 to 10 mm, which are easy to punch or stamp and can be used, for example, to produce housings for electrical appliances, capable of receiving printed inscriptions, or for the production of high quality injection moulded objects, e.g. vehicle windscreens.

14 Example 1

A 60% emulsion I was prepared by emulsifying 99 parts by weight of butylacrylate 1 part by weight triallylcyanurate 0. 12 parts by weight of tertbutylhydroperoxide in 67 parts by weight of 0. 15% aqueous solution of sodium laurylsulphate.

A 50% emulsion II was prepared by emulsifying 96 parts by weight of methylmethacrylate 4 parts by weight of butylacrylate 0.4 parts by weight of dodecylmercaptan 0.1 parts by weight of tertbutylhydroperoxide in 100 parts by weight of a 0.06% aqueous solution of sodium laurylsulphate.

60 parts by weight of an aqueous phase containing 1% by weight of sodium laurylsulphate, 0.15% by weight of rongalite, 0.02 % by weight of acetic acid and 0.0008 parts by weight of iron (II) sulphate was placed in a polymerization vessel with a stirrer, external cooling and a feed vessel. Within two hours, 50 parts by weight of emulsion I were metered in with stirring, at a temperature of 55C. The viscous phase polymer formed has a glass transition temperature of -35'C. Then, over a period of a further two hours, 140 parts by weight of emulsion II were metered in, the hard phase polymer being formed with a glass transition temperature of 90C. The difference between the optical refractive indices of the two phases was 0.021. And the aqueous dispersion was produced with a solids content of 40% by weight. By measurement of solubility on a coagulated polymer sample it was established that 25% by weight of the hard phase was bonded to the viscous phase.

z is The particles of viscous phase formed from emulsion I had a weight average of particle size of 60 nm at the end of the first polymerisation step, increasing to 88 nm on polymerisation of emulsion II in the second step. The particle sizes were determined by the light scattering method; measuring instrument 1INanosizer(R)11 made by Coulter Electronics. The non-uniformity of the viscous Phase particles, determined by ultracentrifugation, was U.. = 0.12.

In order to recover the solids from the dispersion obtained, a tightly meshing contra-rotating double screw extruder with a screw diameter of D = 30 mm was used.

The lengths are given in terms of multiples of the diameter D. The screws were sealed off relative to the gear by means of a gland.

The coagulation zone was 25 D in length. It was operated under a pressure of 40 bar at a temperature of 220C. Coagulation was brought about by the combined action of heat and shear forces. Every hour, 4 kg of the dispersion were continuously pumped into the coagulation zone by means of a piston-type metering pump. Behind the coagulation zone, the aqueous phase separated off during coagulation was eliminated in liquid form in a 2 D long section of the extruder cylinder by means of a dewatering opening, a pressure chamber and a pressure valve adjusted to 25 bar. In an adjoining pressureless degassing zone with a length of 5 D, the remaining moisture amounting to about 10% of the weight of polymer was expelled in the form of vapour. In a subsequent pressure zone 5 D in length, the polymer was conveyed to the granulating die at a temperature of 200'C. The emerging strip was cooled and, once it had hardened, granulated.

16 The resulting noulding composition contained less than 0.05% by weight of water soluble components. It was extruded to form a film with a thickness of 0.05 mm and calendered. No white coloration occurred within 30 minutes in an atmosphere of 1000C with a relative humidity of 100%. When the film is bent or creased, no stress whiting can be detected in the bending zone. The film can be stamped without breaking. Sharp, clear stamped edges are produced, which are not frayed or white in colour. The film can be fixedly laminated onto a board of hard PVC by hot pressing.

ComiDarison Tests Some of the dispersion obtained in Example 1 was dewatered by spray drying. The dry product contained 0.4% by weight of water soluble components. A film produced therefrom became cloudy in a moist atmosphere under the conditions specified above.

If in the process according to Example 1 the proportion of triallylcyanurate is reduced from 1 to 0.3 parts by weight, the moulding composition obtained proves to be cloudy. only 22% by weight of acetoneinsoluble components were found, leading one to conclude that only some of the viscous phase is cross-linked and the hard phase is bonded virtually not at all to the viscous phase.

In a further modification of Example 1, 0.10 instead of 1.0 part by weight of sodium laurylsulphate was used in the initial aqueous phase.

As a result, the average particle size of the viscous phase particles increased to 132 nm and the nonuniformity of the viscous phase particle size rose to 0.52. The moulding composition produced was cloudy.

1 17 Example 2

2 parts by weight of the dispersion obtained in Example 1 and 1 part by weight of a 40% anionic aqueous emulsion polymer, the composition of which corresponded exactly to that of the hard phase of the dispersion according to Example 1, were intimately mixed and the mixture was dewatered using a 2-screw extruder as described in Example 1. The proportion of viscous phase in the resulting moulding composition was 20% by weight. The shape was stable at 95'C, i.e. 7 higher than for the moulding compositionaccording to Example 1. A 1 mm thick, very rigid film which was easy to punch or stamp is was extruded from the moulding composition. It is suitable for example for producing stamped instrument panels for motor vehicles, electrical appliances and thelike.

ExamiDle 3 In a repetition of the process according to Example 1, the triallycyanurate in emulsion 1 was replaced by an equal quantity of allylinethacrylate as graft crosslinker. The moulding composition obtained was identical to that of Example 1 in all its properties.

Example 4

In two mixtures produced according to Example 3, an additional 2.5 or 5 parts by weight, respectively, of an emulsion polymer of methylmethacrylate in the form of seed latex with a particle size of 40 nm (weight average) were added to the initial aqueous phase. The 35 following particle sizes were obtained:

18 Seed latex particles Viscous phase diameter Total diameter 2.5 5.0 parts by weight nm 94 nm 108 nm 137 nm ExamiDle 5 In a further modification of the process according to Example 3, the following quantities of emulsions 1 and II were used:

83 parts by weight of emulsion I and 100 parts by weight of emulsion II.

This results in the moulding compositions consisting of 50% by weight of viscous and 50% by weight of hard phase.

The following particle sizes were measured:

Viscous phase diameter Total diameter nm nm The moulding compositions are stable in shape at 55C. Themoulding composition is clear, does not become cloudy in a moist atmosphere, does not produce any stress whiting in the form of a 0.05 mm thick film and can be stamped out without any problems.

1 19

Claims

1. A clear viscous moulding composition which comprises:

A) 10 to 90% by weight of a cohesive hard phase having a glass transition temperature of above 70C and comprising a) 80 to 100% by weight (based on A) of methylmethacrylate and b) 20 to 0% by weight of lower alkyl acrylate; B) 90 to 10% by weight of a viscous phase, distributed in said hard phase, having a glass transition temperature of below -10C, the average particle size of the viscous phase being less than 130 nm and having a non-uniformity of the particle size of less than 0.5, and the viscous phase comprising C) e) at least 50% by weight (based on B) of a lower alkyl acrylate, d) 0.5 to 5% by weight of a graft crosslinker or a crosslinking monomer with three or more ethylenically unsaturated, radically polymerisable groupg, and optionally, other ethylenically unsaturated, radically (co)polymerisable, aliphatic comonomers; and C) not more than 0.05% by weight of water-soluble constituents, at least 15% by weight of the hard phase being covalently bonded to the viscous phase.

2. A composition as claimed in claim 1, wherein the hard phase and the viscous phase differ in their refractive indices by more than 0.02.

is

3. A composition as claimed in either of claims 1 and 2, wherein the viscous phase contains, as component c or as a part thereof, 0.05 to 2% by weight of a crosslinker.

4. A clear viscous moulding composition substantially as herein described with reference to the Examples.

5. A film having a thickness of less than 1 mm and comprising a composition as claimed in claim 1 or claim 2.

6. A film as claimed in claim 5, wherein the hard phase A contains 2 to 20% by weight of lower alkyl acrylate.

7. A film as claimed in claim 5 substantially as herein described with reference to the Examples.

8. A process for preparing a clear, viscous moulding composition which comprises the aqueous emulsion polymerisation of a monomer or monomer mixture comprising a) 80 to 100% by weight (based on A) of methylmethacrylate and b) 20 to 0% by weight of a lower alkylacrylate to obtain a hard phase with a glass transition temperature of above 700C, said polymerization being conducted in the presence of a viscous phase, dispersed in water, with a glass transition temperature of below 71 t 21 -10C, an average particle size of less than 130 nm and a non-uniformity of particle size of less than 0.5, the viscous phase comprising c) at least 50% by weight (based on B) of a lower alkyl acrylate, d) 0.5 to 5% by weight of a graft crosslinker or a crosslinking monomer with three or more ethylenically unsaturated, radically polymerisable groups, and e) optionally, other ethylenically unsaturated, radically (co)polymerisable, aliphatic comonomers; at least 15% by weight of the hard phase being grafted onto the viscous phase, coagulating the resulting dispersion, separating the liquid aqueous phase from the coagulate and melting the coagulate to obtain a moulding composition.

9. A process as claimed in claim 8, wherein the dispersed viscous phase contains 0.05 to 2% by weight of a crosslinker.

10. A process as claimed in claim 8 or claim 9, wherein the moulding composition obtained is mixed, in a melt, with a compatible moulding composition in the ratio 10:1 to 1:10.

11. A process as claimed in claim 10, wherein a moulding composition is used which has a composition coinciding with that of the hard phase.

12. A process as claimed in claim 8, wherein the aqueous dispersion obtained by emulsion polymerisation is mixed with an aqueous dispersion of an emulsion polymer having a composition coinciding with that of the hard phase, in a solids ratio of 10:1 to 1:10, and the 22 mixture is coagulated, separated from the aqueous phase and melted.

13. A process as claimed in any of claims 8 to 12, wherein coagulation is brought about by the combined action of heat and shear forces in an extruder.

14. A process as claimed in claim 8, wherein the melt is shaped into a moulding with a thickness of more than 1 mm and is cooled to below the softening temperature.

15. A process as claimed in claim 14, wherein a moulding composition is produced and shaped, containing 0.5 to 2% by weight of units of an alkylacrylate in the hard phase.

16. A moulding composition when prepared by a process as claimed in any of claims 8 to 15.

17. A multi-layer moulding comprising a rigid, nondeformable base member and a thin surface layer of a moulding composition as claimed in any of claims 1 to 5.

18. A multi-layer moulding as claimed in claim 17, wherein the surface layer is produced by coextrusion together with the preparation of the base member, by extrusion coating onto the surface of the base member or by laminating a film formed frqm the moulding composition onto the surface of the base member.

Published 1990atThe Patent Office. State House. 66 71 High Ho'bDrn_LcndonWC1R4TP Further copies maybe obtained Lrom The PaentOffice SI ales Branch. St Maly Cray. Orpington. Kent BR5 3RD. Printed by MiLt:,-'e% Lechniques ltd. St Mary Cray. Ken-_ Con 1 87