GB2277477A - Preparation of lustrous polymer articles - Google Patents

Description

2277477 11Preparation of lustrous Dolvmer articles" This invention relates

to lustrous polymer articles and their preparation. More particularly it relates to moulded polymer articles made of highly filled cast resins with metallic shining, optionally coloured surfaces, the surface effect being produced by varnishing and heat-set.

It is already known from German Patent 693 824 that colourant-containing layers may be embedded close to the surface in moulded articles produced by mould polymerisation. This can be achieved by applying such layers containing colourant and a binding agent which is virtually insoluble in the compounds to be polymerised onto the wall of the mould and then carrying out the polymerisation in a manner known Der ge after the liquid compounds to be polymerised have been introduced. The colourantcontaining layers may be distributed uniformly or in an irregular manner and may be multicoloured when various colourant-containing layers are used. The use of (organic) solvents for the binding agents employed is also intended. A subsequent treatment, for example the application of a top layer may, however, be dispensed with.

DE-A 30 23 964 discloses a process for preparing colourant-containing zones close to the surface in acrylic and methacrylic resins during the polymerisation of the monomers and prepolymers which produce the resins. This process is carried out in moulding polymerisation chambers, and is characterised in that colourants homogenously distributed in a binding agent are initially applied as a layer onto the wall of the polymerisation chamber, the binding agent being soluble 2 - or at least swellable in the liquid resin or its precursors, and that the polymerisation is carried out in a manner known per se to form resins, after the mononers and/or prepolymers to be polymerised have been introduced.

EP 061 245 discloses a process for producing a moulded article, in which the composition is hardened in a mould comprising at least two parts defining a cavity, and in which, before the composition capable of being hardened is introduced into the cavity of the mould, a part of the surface forming said cavity is provided with a deposit from a material producing a colour contrast with the hardenable composition, the deposit being applied onto surfaces of the mould which correspond to the surfaces of the hardened moulded article on which the colour contrast is intended to be produced. In this process, the deposit consists of at least a finely distributed pigment mixed with at least a finely distributed filler of an average particle size of 100 gm or less, and that the mixture is applied as a suspension in a volatile carrier material.

EP-A 0 217 544 discloses a process for preparing moulded parts from hardenable compositions with surface areas in contrasting colours, one surface of the mould, before the hardenable compositions are filled in, being coated with a colourant which consists of a) at least 25 weight-% of a liquid carrier containing 0 100 parts by weight of a polymerisable liquid and 100 0 parts by weight of a non- polymerisable organic liquid, b) 0.1 - 10 weight-% of an inorganic pigment or 0.0001 - 1 weight-% of organic dyes, c) 0 - 60 weight-% of a finely distributed filler, d) 0.1 50 weight-% of a drying alkyd resin soluble in the carrier a), and e) a polymer soluble in the liquid.

v _.... 1 EP-A 0 526 818 discloses a process for preparing moulded polymer articles made of highly filled cast resins with surface areas of contrasting colours, in which one surface of the moulding tool, before it is filled with cast resin, is coated with a hardenable covering of a colourant- containing composition so that a colour differentiation is produced, the coating being applied onto the intended surface regions of the tool in at least two varnishing steps and after the drying of the layers of varnish, the tool being filled with the cast resin and polymerised while heating and finally removed from the mould.

A special pigment coloration of e.g. printing inks or varnishes may be achieved by means of nacreous pigments, the so-called called effect pigments. The effect of the nacreous lustre, a metallic sheen, is very popular for decorative purposes.

Acrylic glass with a glossy effect may be produced by adding nacreous pigment to the acrylate or methacrylate compound to be polymerised, for example by stirring in. By this conventional method, however, we have found that hardened objects with metallic shiny surfaces caused by nacreous pigment cannot be produced from highly filled systems. By "highly filled" are intended those resins containing more than 20% by weight of filler.

There remains a need, therefore, to provide a suitable process for preparing objects from hardened highly filled systems, which have lustrous surfaces because of the nacreous pigment. Such cast resin articles are of particular interest for use in the sanitary field. For this purpose they must be provided with a uniform lustrous layer of sufficient colour and pigment depth in order to counteract effectively any bleaching caused by moisture ("water- whitening").

We have now been able to produce from hardened, highly filled cast resins articles which have lustrous surfaces and are coloured with nacreous pigment. With their characteristics, these articles largely fulfil the desired requirements. Surprisingly, it has been found that the articles with their uniformly coloured surfaces may be produced according to the process, known from EP-A 0 526 818, for preparing moulded polymer articles made of cast resins and having differently coloured 10 surface regions.

According to one aspect of the invention, therefore, we provide moulded polymer articles made of highly filled cast resins with lustrous surfaces in which the lustrous is surface is a nacreous pigment-containing coating. The nacreous pigment may be coloured.

The invention also relates to a process for preparing new moulded polymer articles, made of highly filled cast resins with lustrous, optionally coloured, surfaces, in which a surface of the mould before the mould is filled with the resin to be cast resin, is coated with a hardenable nacreous pigment-containing varnish composition L and after the varnish layer has dried the mould is filled with resin which is then polymerised.

The article may then be removed from the mould.

Preferred cast resins include those from the class of acrylic, including methacrylic resins.

In addition to the nacreous pigment-containing varnish L, a further, nacreous pigment-free but fillercontaining varnish L' can also be used for the surface preparation.

In order to prepare the lustrous surfaces, the process of the invention is carried out using at least a singlestage, optionally a two-stage varnishing. A varnishing k_ - dispersion L is used, together with the nacreous pigment addition, in the main varnishing step. Binding agents B and liquid carrier components T preferably also form part of the varnish dispersions L and optionally M.

The nacreous pigments used in the process, according to the invention, for producing the lustrous surfaces of the new moulded polymer articles include white and coloured nacreous pigments based on mica or titanium dioxide or iron(III)-oxide having grain sizes within the range of 0.1 to about 50 gm. Known nacreous pigments are used industrially, for example, under the trade mark IriodinO. They are used in printing inks, plastics colorations and varnishes such as car paints. The colour effects of these pigments are produced by light absorption and interference. Nacreous pigments of a certain particle thickness meet the interference conditions and show iridescent colours.

The use of IriodinO 9111 Rutil Feinsatin WR, according to the invention, produces a moulded polymer particle which has an extremely uniform highly glossy surface with a silver-coloured metal effect. The use of red IriodinO 9514 Silkrot WR II produces a polymer article after removal from the mould which has a highly shining, dark red metallic surface.

In general, nacreous pigment G or filler F and binding agent B are used in a ratio of 1: 1 to 20: I parts by weight, preferably 2: 1 to 10: 1 parts by weight. In a first approximation, the binding agents B under consideration may be divided into polymeric binding agents (B-P) and reactive binder systems (B-R) (cf. H. Wagner & H.F. Sarx, Lackkunstharze, Carl Hanser Verlag, Mdnchen 1959), which may be dissolved in the carrier component T. The polymeric binding agents B-P may, advantageously, belong to the same polymer class as the cast resins themselves. They are chosen, for example, from the group of poly(meth)acrylates, more particularly polymethylmethacrylate and copolymers thereof.

Generally, the molecular weight Mw of the polymeric binding agent is within the range of 10,000 - 1,000,000, preferably within the range of 100,000 - 500,000 Dalton. Here, it is important that the criterion of solubility 10 in the carrier component T is met. The binding agent B-P is used, dissolved in a suitable solvent, preferably in the carrier component T.

The presence of the polymeric binding agent B-P is not an absolute necessity, but the varnish coating must be hardenable and at least one reactive binder system B-R is generally required for hardening. These systems may comprise only one reactive binder, for example an alkyd resin such as AlkydalO F26, or two or several components which harden under existing conditions (cf. H. Wagner, H.F. Sarx, Lackkunstharze loc.cit; Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd. Ed., Vol. 6, pg. 427 - 445, J. Wiley 1979).

Usable binders may be selected from polycondensation resins, polyaddition resins and polymerisation resins. They include for example the groups of alkyd resins, more particularly oil-modified ones, for example the oxidised alkyd resins alkyd resins plus diisocyanate #v If plus chlorinated plastics 91 If 99 If 09 qv 91 If It 11 01 plus polystyrene plus nitrocellulose plus vinyl- and epoxy resin plus aminoplastics (plus epoxy resin) plus silicone 11 oil-modified epoxy resins plus amino plastics. T oil content may here be about 20 - 80 weight-%.

phenoplastics (with or without epoxy-, vinylacetal or aminoplastics component) vinylacetals with or without phenolic allylaminoplastics component polyester- and triazine resins allylpolyesters complex amino resins indene- and coumarone resins Mention is 'made, for example, of binding agents B-R produced from an aromatic polyisocyanate (e.g. commercial products of the DESMODURO type, made by Bayer AG) and polyesters or polyethers with free hydroxyl groups (e.g. commercial products of the DESMOPHENO type made by Bayer AG) or those obtained by reacting polyisocyanates with hydroxy group-containing acrylic resins (e.g. commercial product JAGOTEXO F232, made by J&ger, Fabrik chemischer Rohstoffe). In order to achieve a three- dimensional cross-linking, at least one of the reaction partners must have three or more reactive groups in the molecule.

The varnishes L and optionally L' may also contain functionalised monomers such as (meth)acrylic acid, in amounts of 0 to 50 weight-% based on the binding agents B-P + B-R, in order to improve the adhesive strength. They may also contain cross-linking monomers known per se (cf. Rauch-Puntigam, Acryl- und Methacrylverbindungen, Springer-Verlag 1967), such as (meth)acrylic acid esters of multi-valent alcohols (polyols) for example glycoldimethacrylate and the like, usually in amounts below 15 weight-%. The binding agents include, for example, combinations of binders B-P such as polymethylmethacrylate, optionally with a comonomer amount, mostly < 15 weight-%, of for example methylacrylate, 2-ethylhexyl(meth)acrylate and the like with a binder B-R, formed for example from an aromatic polyisocyanate (e.g. commercial product DESMODURO N 75) and a hydroxyl group-containing polyacrylate (commercial product JAGOTEXO F 232). A weight ratio between B-P and B-R of (3 - 1): 1 is given as a guide.

The liquid carrier component T in the varnish L ensures injectable properties and is selected in order to evaporate after a certain, suitably chosen (drying) time. Thus, as a guide, the carrier component T has a boiling point (under normal conditions) within the range of 50 - 22WC preferably within the range of 75 - 17WC. If necessary, the combination of a higher-boiling and a lower- boiling component may also lead to the required result). The carrier component T may therefore be suitably selected from the group of - monomers more particularly radically polymerisable monomers such as of the (meth)acrylic acid ester type, in particular with C 1-6 -alkyl groups, more particularly C, or C 2 -ester (= T-M) - solvents, for example from the type of (aromatic) hydrocarbons, ketones (= T-L) An evaporation number (based on ether = 1) of 2 - 100, especially 2.5 - 50, may be used as an additional selection criterion for the carrier component T-L. The evaporation number is defined as the time at which a specific amount of solvent (normally 0. 3 ml, applied onto filter paper from a 10 mm distance) evaporates within 5 sec, as compared with ethylether. (Cf. DIN 53 170; Ullmanns EncyclopAdie der Techn. Chemie, 4th Edition Vol. 16, p. 289, V.C. 1978).

fi 9 - Examples of the carrier component T-M include methylmethacrylate, methylacrylate, ethylmethacrylate, n-butylmethacrylate and the like. Examples of the carrier component T-L include butylacetate, ethoxyethylacetate and the like and hydrocarbons such as Shellsolc. A combination of T-L + T-M may be of advantage.

The amount of carrier component T contained in the varnish L is normally within the range of 40 - 90 weight-%, the amount of polymeric binder B-P is about 0 - 20, preferably 0.5 to 10, more particularly 1 - 10 weight-%. The amount of nacreous pigment in the sprayable varnish L is normally within the range of 1 - 20 weight-%, preferably 2 - 15 weight-%.

Therefore, a typical composition of the varnish L may be:

about 70 parts by weight of methylmethacrylate parts by weight of PMMA parts by weight of nacreous pigment parts by weight of alkyd resin, for example Alkydalc F26 The solvents used for formulating the sprayable varnish are those already listed under T such as butylacetate, ethylacetate and/or monomers for example MMA and/or ShellsolO A. They are prepared together with the above varnish recipe in a weight ratio of 1: 2 and whilst adding about 1 to 2 parts by weight per 100 parts by weight of sprayable varnish in order to produce the sprayable varnish.

In order to prepare varnish L, a possible method is to dissolve all the components on the blade stirrer in the carrier component T, with the exception of the binding agent B-R, then to add the nacreous pigment, e.g. IriodinO and thoroughly distribute it by means of the blade stirrer. Finally, the binding agent B-R is added 5 and dissolved.

According to the prior art, the cast resins are liquid synthetic resins which may be cast in moulds and hardened and form moulded polymer articles when cured.

Conventionally highly suitable cast resins G or corresponding prepolymers are disclosed in the European Patent 218 866 or US-A 4 786 660 or US-A 4 221 697 or US-A 4 251 576. Preferably, the cast resins G are acrylic resins. Particularly preferred are polymers based on methlmethacrylate, a mixture of a prepolymer and the monomers preferably being used. They are advantageously filler-containing "filled" cast resins, more particularly highly filled cast resins, especially those which have an amount of from 50 - 80 weight-% of fillers, based on the cast resin. Suitable fillers P are finely dispersed inorganic or organic materials normally used for cast resins. It is of advantage if an average grain size of a diameter of 100 gm is not exceeded. Grain-like particles are preferred. sometimes, it may be of advantage if the particles are freed of absorptively bound moisture, by heating to about 250C. The fillers F may be natural or synthetically prepared products. The mechanical properties such as hardness and elastic modulus of shearing are determined according to the intended application of the cast resins. Here, an elastic modulus of shearing of at least 5 GNm-2 may be of advantage. Suitable minerals include, for example, aluminium oxides, aluminium hydroxides and derivatives such as alkali- and alkaline earth double oxides and alkaline earth hydroxides, clays, silicon dioxide in its various modifications, silicates, aluminosilicates, carbonates, phosphates, sulphates, sulphides, oxides, carbon, metals and metal alloys. Synthetic materials such as glass powder, ceramics, porcelain, clinker, finely distributed synthetic SiO 2 are also suitable. Mention must be made of silicic acid modifications such as quartz (quartz powder), tridymite and cristobalite, as well as kaolin, talcum, mica, spar, apatite, baryte, gypsum, chalk, limestone and dolomite. Mixtures of fillers may optionally also be used. The amount of filler contained in the cast resins is normally at least 20 weight-%. Generally an amount of 80 weight-% is not exceeded. A filler content of the cast resins of 50 weight-% is given as a guide. The fillers may be prepared in suitable grain sizes by conventional methods, for example crushing and grinding. Cristobalite and aluminium hydroxide are particularly preferred.

In order to carry out the process, according to the invention, conventional moulding tools and injection devices are generally used. The modalities of the coating may be advantageously demonstrated using a metal plate (for example a nickel-plated, highly polished brass plate). A temperature of 850C may be selected for the coating of the intended metal surfaces. It is recommended that they be heated beforehand for about 30 minutes, for example in a drying cupboard at this temperature.

The coating may be carried out by means of a suitable spray gun (e.g. SATA Minijet), using for example an 0.8 mm nozzle and a pressure of 2.5 bar. The individual varnish layers are preferably produced by spraying the varnishes L' and L twice over the entire surface of the metal plate. The varnishing takes generally 2 - 2.5 minutes. Immediately after the last varnishing, the article is placed again into the heating chamber (drying cupboard) at 85'C. Within a short time, for example less than 5 minutes, the cast resin G is introduced. The process is explained in greater detail below with reference to a filler-containing PMA/MRA cast resin.

Using the varnished metal plate, a suitable second unvarnished metal plate (of a size of e.g. 350 x 350 x 4 mm) and a sealing cord (e.g. a PVC cord of a diameter of 4 mm), a moulding chamber is produced, for example, within 3 minutes which is filled, within a short time, for example about 1.5 minutes, with the highly filled, optionally coloured, (degassed) cast resin containing for example PMMA/MA as hardenable synthetic resin and at least one initiator for the radical polymerisation, for example a perester such as bis-(4-tert.butylcyclohexyl)-peroxydicarbonate in the usual amounts (e.g. 0.5 - 5 weight-% based on the monomers). When the moulding chamber is closed the curing is carried out, initially at an elevated temperature for example at about 65C in the water bath, suitably in a horizontal position of the moulding chamber and preferably with the varnished side underneath, for example 20 minutes, and then at an even higher temperature, for example at 105'C, preferably in a drying cupboard, for 15 minutes. Finally the polymer article is removed from the moulding chamber at about 60 to 70C.

When using the process according to the invention, new polymer articles are obtained made from cast resins, which have lustrous, optionally coloured and highly uniform surfaces with a metallic effect. Even after long storage in water, e.g. after 24 hours in hot water at 900C, no white surface colouring, the so-called "water- whitening" effect is obtained.

The following Examples and data for preparing the moulded polymer articles serve to illustrate the invention further.

EXAMPLES

A) Preparing the spray varnish L Example 1:

5.0 parts by weight of a polymethylmethacrylate containing 10 weight-% of methylacrylate (Mw = about 350,000) are dissolved in 71 parts by weight of methylmethacrylate. To this solution, 1 part by weight of glycoldimethacrylate, 3 parts by weight of AlkydalO F26 (60% in xylene, made by BAYER AG) are added and dissolved. Whilst stirring with a blade stirrer, 20 parts by weight of Irioding 9111 Rutil Feinsatin WR (Merck) are added to this syrup. The stirring time is about 30 minutes. 12.5 parts by weight of ShellsolO A (Shell), 12.5 parts by weight of nbutylacetate and 1 part by weight of InteroxO BCHPC = bis-(4-tbutylcyclohexyl)- peroxidicarbonate made by Peroxid-Chemie GmbH, are added to 50 parts by weight of this iriodin-containing varnish and dissolved.

Example 2:

The method used is as in Example 1, but instead of IriodinO 9111 Rutil Feinsatin WR, the same amount of Iriodinc 9514 Silkrot WRII is used.

B) Preparing the spray varnish L' 5.0 parts by weight of a polymethylmethacrylate containing 10 weight-% of methylacrylate (Mw = about 350,000) are dissolved in 75 parts by weight of methylmethacrylate, and 45 parts by weight of silanised cristobalite (product SILBONDO 6000 MST of Quarzwerke Frechen) are dispersed on the dissolver for about 10.0 m/sec for 15 minutes. To this suspension, 1 part by weight of glycoldimethacrylate and 3 parts by weight of AlkydalO F26 (60% in xylene, a product of (BAYER AG) are added and dissolved.

To 50 parts by weight of this cristobalite-containing varnish, 12.5 parts by weight of Shellsolc A (Shell), 12.5 parts by weight of n-butylacetate and 1 part by weight of InteroxO BCHPC = bis-(4-tbutylcyclohexyl)peroxidicarbonate, made by PeroxidChemie GmbH, are added and dissolved.

C) Highly filled cast resin is 50 - 80 parts by weight of an inorganic filler are dispersed to a prepolymeric initial solution, for example 40 parts by weight of a solution MMA/PMMA (weight ratio 35: 5) which also contains cross-linking agents and optionally a silane with a silanisation catalyst. Cristobalite or aluminium hydroxide are preferably used. Apart from the mould separating agent such as stearic acid, the cast resin also contains a polymerisation initiator such as bis-(4tert. butylcyclohexyl)peroxydicarbonate or a usual redox system.

D) Preparing the moulded polymer article The preparation of the moulded polymer article is described in detail in the section on the implementation of the process.

E) Testing the mouldings for "water-whitening" Specimens of 50 x 50 mm are cut from the cast plates.

The specimens are stored in water at a temperature of 900C for 24 hours. After a further storage of 24 hours l, - 15 at ambient temperature, in air, the specimens are compared with a supply sample.

Result:

After the water treatment, the mouldings, according to the invention, show virtually no whitening when compared with the supply samples. Hardened cast resins without nacreous pigment coating show a noticeable whitening according to the "water-whitening" test.

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Claims (19)

1. Moulded polymer articles made of highly filled cast resins with lustrous surfaces in which the lustrous 5 surface is a nacreous pigmentcontaining coating.

2. Moulded polymer articles as claimed in claim 1 in which the lustrous surface is produced by means of a coloured nacreous pigment.

3. Moulded polymer articles as claimed in claim 1 or claim 2, in which the cast resin comprises PMMA/MMA. as hardenable synthetic resin.

4. A process for preparing moulded polymer articles as claimed in claim 1 in which at least one surface of a mould is coated with a hardenable coating of a nacreous pigment-containing varnish composition L, and allowed to dry, resin to be cast is introduced into the mould and 20 polymerisation is carried out.

5. A process as claimed in claim 4 in which a varnish L' which contains a filler but no added nacreous pigment is applied to the mould in a first varnishing step and after drying the varnish L is applied.

6. A process as claimed in claim 4 or claim 5 in which, in addition to the nacreous pigment, varnish L and optionally L also contain a binding agent B and at least one liquid carrier component T.

7. A process as claimed in claim 6 in which the binding agent B comprises a hardening system B-R and a polymeric binder B-P.

8. A process as claimed in claim 7 in which the polymeric binder B-P is a homo- or copolymer of methylmethacrylate.

9. A process as claimed in any of claims 6 to 8 in which the liquid carrier component T has a boiling point within the range of 50 - 200'C under normal conditions.

10. A process as claimed in claim 9 the liquid carrier component T has a boiling point within the range of 75 - 17WC under normal conditions.

is

11. A process as claimed in any of claims 6 to 10 in which the carrier component T consists, either completely or in part, of radically polymerisable monomers.

12. A process as claimed in claim 11 in which the carrier component T consists, either completely or in part, of one of more alkylesters of (meth)acrylic acid having 1 to 6 carbon atoms in the alkyl group.

13. A process as claimed in claim 11 in which the carrier component T consists, either completely or in part, of methylmethacrylate.

14. A process as claimed in any of claims 4 to 13 in which the filler comprises 20% or more by weight of the cast resin.

15. A process as claimed in any of claims 4 to 13 in which the filler comprises from 50 to 80% by weight of the cast resin.

16. A process as claimed in any of claims 4 to 15 in which the grain size of the filler does not exceed 100 Am.

17. A process as claimed in any of claims 4 to 16 in 18 - which the nacreous pigment is based on mica or titanium dioxide or iron (III)-oxide and has a grain size of from 0.1 to 50 Am.

18. A process as claimed in claim 4 substantially as hereinbefore described.

19. A process as claimed in claim 4 substantially as hereinbefore described and with reference to the 10 Examples.