Notch impact-resistant graft polymers.

0001The invention relates to graft polymers with a silicone rubber as the core, which is surrounded by at least two chemically different shells, and their use as thermoplastic molding compositions.

0002ABS (acrylonitrile-butadiene-styrene) plastics are of great technical importance; Because of the diene contained therein in polymeric form (eg butadiene), their weather resistance is unsatisfactory, so that they can only be used outdoors to a limited extent. This deficiency can only be remedied incompletely with UV-absorbing substances or light stabilizers. If you replace the oxidation-sensitive diene rubber, for example by an alkyl acrylate rubber, then the impact resistance and the appearance of the moldings are not satisfactory. For good physical properties, the acrylic ester rubbers used instead of the diene rubber must be cross-linked. In order to produce crosslinked acrylic ester rubbers, suitable monomers have been polymerized in an emulsion together with polyfunctional monomers or the initially uncrosslinked polymer has been treated with an organic peroxide, for example benzoyl peroxide.

0003The impact strength of such molding compositions based on acrylate rubber, especially at low temperatures, is still not sufficient for many applications.

0004Silicone rubbers are characterized by very good low-temperature properties; however, grafting them with resin-forming monomers to obtain thermoplastic molding compositions with high-quality properties is difficult.

0005It has been found that silicone rubbers can be encased as crosslinked, particulate particles with crosslinked acrylate rubber and that these core / shell rubbers can be grafted with resin-forming monomers; it has also been found that such graft applicators have particularly good application properties, even though the silicone rubber is virtually shielded by the acrylate rubber.

0006The invention relates to particulate graft polymers comprising a core (a) which is a crosslinked silicone rubber, a first shell (b) which is a crosslinked acrylate rubber and a second shell (c) which is a polymer or copolymer of resin-forming monomers.

0007The weight ratio of the core (a) and the first shell (b) is 0.1 to 99.9 to 90 to 10, preferably 10 to 90 to 50 to 50, and the proportion of (c) in the total graft polymer is 90 to 20, preferably 80 to 40% by weight. The graft polymers according to the invention have average particle diameters (d₅₀) of 0.05 to 10 μm, preferably 0.1 to 2 μm. Particularly preferred particle diameters are 0.1 to 1 µm.

0008The material of the core (a) is a crosslinked silicone rubber and contains units of the general formula R₂SiO, RSiO_3/2, R₃SiO_1/2 and SiO₂, where R represents a monovalent organic radical.

0009The amounts of the individual siloxane units are such that 0 to 10 mol units of the formula RSiO per 100 mol units of the formula R₂SiO_3/2, 0 to 1.5 mol units of R₃SiO_1/2 and 0 to 3 mol units of the formula SiO₂ are present.

0010R can be a monovalent saturated hydrocarbon radical having 1 to 18 carbon atoms, the phenyl radical or an alkoxy radical or a radical attackable group such as the vinyl or γ-mercaptopropyl radical. It is preferred that at least 80% of all radicals R are methyl; combinations of methyl and ethyl are particularly preferred.

0011Preferred silicone rubbers (a) contain built-in units of groups which can be attacked by free radicals, ie those which are capable of radical addition or transfer reaction, in particular vinyl, allyl, chloroalkyl, mercapto groups, preferably in amounts of 2-10 mol%, based on all radicals R. .

0012The first shell (b) is a crosslinked acrylate rubber and is in particular a crosslinked polymer made from alkyl acrylates, optionally in a mixture with up to 40% by weight of other vinyl monomers. Suitable polymerizable acrylic acid esters include C₁-C₈ alkyl esters, for example methyl, ethyl, butyl, octyl and 2-ethylhexyl esters, haloalkyl esters, preferably C₁-C₈ haloalkyl esters, such as chloroethyl acrylate, and aromatic esters such as benzyl acrylate and phenethylacrylate. They can be used individually or in a mixture, at least one alkyl ester should be present in the mixture. Polyfunctional monomers are copolymerized for crosslinking. Examples are: esters of unsaturated carboxylic acids with a polyol (preferably 2 to 20 carbon atoms in the ester group), such as ethylene glycol dimethacrylate, esters of a polybasic carboxylic acid with an unsaturated alcohol (preferably 8 to 30 carbon atoms in the ester residue), such as triallyl cyanurate, triallyll isocyanurate; Divinyl compounds such as divinylbenzene; Esters of unsaturated carboxylic acids with unsaturated alcohols (preferably 6 to 12 carbon atoms in the ester radical), such as allyl methacrylate; Phosphoric acid esters, for example triallyphosphate and 1,3,5-triacryloyl-hexahydro-s-triazine. Particularly preferred polyfunctional monomers are triallyl cyanurate, triallyl isocyanurate, triallyl phosphate, allyl methacrylate.

0013The amount of the polyfunctional monomers used for the crosslinking is preferably 0.05 to 5.0% by weight of the mass of the first shell (b). The elastomer of the first shell (b) may additionally contain a copolymerizable monomer or several such monomers of the vinyl or vinylidene type in copolymerized form. Examples are: methyl methacrylate, butyl acrylate, acrylonitrile, styrene, α-methyl styrene, acrylamides, vinyl alkyl ethers. These comonomers can be copolymerized in amounts of up to 40% by weight of the polymer (b).

0014The second shell (c) is a graft-polymerized polymer composed of resin-forming α, β-unsaturated, free-radically polymerizable monomers, in particular from the series α-methylstyrene, styrene, p-methylstyrene, halostyrene, acrylonitrile, methacrylonitrile, and acryl methacrylates with up to 8 C- Atoms in the alcohol part, maleic acid derivatives, especially maleimides, vinyl acetate, vinyl chloride, vinylidene fluoride. Copolymers of at least two monomers from the series styrene, α-methylstyrene, acrylonitrile and methyl methacrylate are particularly preferred.

0015Another object of the invention is a process for the preparation of the graft polymers according to the invention.

0016In a first stage, an emulsion of the core material (a) is produced:

0017The preparation of an emulsion of a long-chain, OH-terminated silicone oil by emulsion polymerization is described, for example, in US Pat. No. 2,891,910 and in GB Pat. No. 1,024,024. The method disclosed in the British patent specification is particularly preferred to use an alkylbenzenesulfonic acid, since the emulsifier and polymerization catalyst are present in one. After the polymerization, the acid is neutralized.

0018Accordingly, the emulsifier concentration can be kept low, and one has little disruptive foreign molecules from the catalyst in the finished product after completion of the emulsion. Instead of the alkylbenzenesulfonic acids mentioned, n-alkylsulfonic acids can also be used. In addition to the catalytically active sulfonic acid, it is also possible to use emulsifiers other than co-emulsifiers.

0019Such co-emulsifiers can be nonionic or anionic in nature. Particularly suitable anionic co-emulsifiers are salts of the abovementioned n-alkyl or alkylbenzenesulfonic acids. Nonionic co-emulsifiers are polyoxyethylene derivatives of fatty alcohols, fatty acids and the like. Examples of such emulsifiers are POE (3) lauryl alcohol (POE = polyoxyethylene (x) with x = degree of polymerization), POE (20) oleyl alcohol, POE (7) nonylphenol or POE (10) stearate (the notation POE (3 ) -Lauryl alcohol means that 3 units of ethylene oxide have been added to one molecule of lauryl alcohol, the number 3 representing an average).

0020In general, those silicone oils which are formed by emulsion polymerization in the presence of nonionic co-emulsifiers are of lower molecular weight than those in which no co-emulsifier was used. The molecular weight of the OH-terminated silicone oil formed in the emulsion polymerization is controlled, for example further on the temperature during equilibrium formation between siloxane, water and the silane oil initially formed by ring opening of the siloxane (for details on the relationship between temperature and molecular weight, see the work of DR Weyenberg et al., J. Polymer Sci. Part C , <u style="single">27</u> pp 27-34 (1969)).

0021Radically attackable groups can be incorporated into the preferred silicone copolymer by working in the presence of suitable siloxane oligomers. Suitable starting oligomers are, for example, tetramethyltetravinylcyclotetrasiloxane or γ-mercaptopropylmethyldimethoxysilane or its hydrolyzate.

0022These functional oligomers are added to the base oligomer octamethylcyclotetrasiloxane for copolymerization in the desired amounts.

0023The incorporation of longer-chain alkyl radicals R, such as, for example, ethyl, propyl or the like, or the incorporation of phenyl groups, can also be achieved analogously.

0024The silicone graft base must be at least partially cross-linked.

0025Adequate crosslinking can already take place, for example, when the preferred vinyl and mercaptopropyl groups used react with one another in the emulsion polymerization of the silicone components, so that the addition of an external crosslinker may not be necessary. Nevertheless, a crosslinking silane can be added to increase the degree of crosslinking of the silicone rubber.

0026Branches or crosslinks can be incorporated by adding, for example, tetraethoxysilane or a silane of the general formula RSiX₃, where X is a hydrolyzable group, in particular the alkoxy radical. R has the meaning described above. R = methyl and R = phenyl are preferred. In addition to tetraethoxysilane, methyltrimethoxysilane or phenyltrimethoxysilane are particularly preferred.

0027In the second stage of the process according to the invention, in the presence of the silicone rubber latex of the first stage, the acrylate rubber for the first shell (b) is produced by emulsion polymerization by emulsifying the monomers (main constituent at least one acrylate) in the latex and in a manner known per se Free radical initiators polymerized. The acrylic rubber polymerizes on the silicone rubber. It can be crosslinked during manufacture by using polyfunctional monomers.

0028In this graft polymerization of the first shell (b), the formation of new particles must be prevented as completely as possible. An emulsion stabilizer must be present in the amount required to cover the surface of the particles. The size of these particles can be varied within wide limits by carrying out the reaction. If an agglomerated latex is used as core (a) in order to obtain large particles, these can contain several silicone rubber particles. The polymerization of the first shell (b) can also be carried out in such a way that particles with a silicone rubber core and at the same time particles from pure crosslinked acrylate rubber are produced. Such mixtures can also be used in special circumstances to produce impact-resistant molding compositions.

0029After the graft polymerization of the acrylate rubber has ended, a vinyl monomer or a mixture of vinyl monomers in emulsion is polymerized on the latex obtained. The graft polymers according to the invention form with the formation of the second shell (c). In this graft polymerization known per se, which is usually in the presence of radical initiators, for example water-soluble initiators, emulsifiers or complexing agents / graft activators, as well as regulators, generally form free polymers or copolymers of the monomers forming the second shell (c) in addition to the graft polymer to a certain extent. The amount of this ungrafted polymer can be characterized by the degree of grafting or the grafting yield; it depends, inter alia the polymerization conditions, the composition of the first shell (b), the size of the particles to be grafted, and the amount of grafted acrylate rubber. "Graft polymer" in the sense of the invention is therefore the product obtained by polymerizing vinyl monomers in the presence of the rubber latex, that is to say strictly speaking a mixture of graft polymer and free copolymer of the graft monomers.

0030The graft polymers prepared in this way can be worked up by known processes, for example by coagulation of the latices with electrolytes (salts, acids or mixtures thereof) and subsequent cleaning and drying.

0031The graft polymers according to the invention are distinguished by a surprisingly good combination of technically relevant plastic properties as thermoplastic: Such properties are to be mentioned: aging stability, thermostability, especially when processing into molded articles, thermoplastic molded article surface properties, processability, low-temperature toughness, breaking strength and also acceptable economic viability.

0032The graft polymer according to the invention can be used directly if it consists of approximately 5 to 40% by weight of core (a) and first shell (b), based on the entire graft polymer. If the content (a) plus (b) is higher, a rigid resin can be mixed. Rigid resins are preferably styrene, methyl methacrylate, acrylonitrile terpolymers, styrene or α-methylstyrene, acrylonitrile copolymers, styrene, acrylonitrile, acrylic ester terpolymers or methyl methacrylate homo- or Copolymers.

0033The graft polymers according to the invention can also be mixed with known rubber-modified plastics, for example with ABS plastics or with acrylate-rubber-modified resins (“ASA resins”). In this way, the aging resistance and electrostatic properties of ABS can be improved without impairing the mechanical properties or the mechanical properties of ASA resins and the surface properties of molded articles made from them.

0034The molding compositions according to the invention can contain dyes and pigments, stabilizers against the effects of light and heat, plasticizers, foaming agents and organic or inorganic fillers in the form of granules, powders or fibers. They can be deformed, for example, by injection molding or by extrusion and are suitable for moldings of all types which must be weather-resistant and impact-resistant. For example, they can serve as the outer layer of a laminate made of several different polymers.

1.)

Production of a silicone emulsion

0035<ul id="ul0001" list-style="none"><li>1.1) 38.4 parts by weight of ectamethylcyclotetrasiloxane, 1.2 parts by weight of tetramethyltetravinylcyclotetrasiloxane and 0.2 part by weight of tetraethoxysilane are stirred together. 0.5 part by weight of dodecylbenzenesulfonic acid is added, then 70 parts by weight of water are added over the course of 1 hour. It is stirred intensively. The pre-emulsion is homogenized twice using a high-pressure emulsifying machine at 200 bar. A further 0.5 part by weight of dodecylbenzenesulfonic acid is added. The emulsion is stirred for 2 hours at 85 ° C. and then for 36 hours at room temperature. Is neutralized with the help of 5 n-NaOH. The result is a stable emulsion with a solids content of approx. 36%. The polymer has a gel content of 82% by weight, measured in toluene.</li></ul>

2.)

Production of a silicone rubber coated with acrylate rubber

0036<ul id="ul0002" list-style="none"><li>2.1) The following are placed in a reactor: 2500 parts by weight of latex 1.1) 288 parts by weight of water. A solution of 3 parts by weight of potassium peroxydisulfate in 100 parts by weight of water is introduced into the reactor at 70.degree. The following solutions are then metered into the reactor at 70 ° C. within 5 hours:<ul id="ul0003" list-style="none"><li>Solution 1: 387 parts by weight of n-butyl acrylate     1 part by weight of triallyl cyanurate</li><li>Solution 2: 500 parts by weight of water     10 parts by weight of Na salt of C₁₄-C₁₈ alkyl sulfonic acids</li></ul></li><li>The polymerization is then polymerized at 70 ° C. within 4 hours. The latex formed contains the polymer in a concentration of 35% by weight. The polymer has a gel content of 92% by weight, measured in toluene, and consists of 70% by weight of silicone rubber and 30% by weight of acrylate rubber.</li></ul>

3.)

Graft polymers according to the invention

0037The following are placed in a reactor: 3700 parts by weight latex 2.1) 770 parts by weight of water.

0038After initiation by means of a solution of 3.5 parts by weight of potassium peroxydisulfate in 150 parts by weight of water at 70 ° C., the following solutions are fed uniformly into the reactor within 5 hours:<ul id="ul0004" list-style="none"><li>Solution 1: 855 parts by weight of monomer</li><li>Solution 2: 1000 parts by weight of water     30 parts by weight of Na salt of C₁₄-C₁₈ alkyl sulfonic acids</li></ul>

0039The mixture is then polymerized at 70 ° C.-75 ° C. within 4 hours. The result is latices with solids contents of approximately 33% by weight.

0040The following products were manufactured:<tables id="tabl0001" num="0001"><img file="EP0246537A2_D0001.tif" /></tables>

4.)

Comparative examples

0041<ul id="ul0005" list-style="none"><li>4.1) An ABS graft polymer made from 60% by weight of coarse-particle, highly crosslinked polybutadiene and 40% by weight SAN polymer with a styrene / acrylonitrile mixture ratio of 72/88. Average particle size (d₅₀): 400 nm.</li><li>4.2) An ASA graft polymer made from 60% by weight of coarse-particle, highly crosslinked acrylate rubber and 40% by weight of SAN (same composition as in 4.1). Average particle size (d₅₀) 420 nm. The product was produced according to EP 34748.</li></ul>

5)

Thermoplastic properties

0042The molding compositions given in Table 1 are produced by compounding on a Banbury mixer BR (Pomini-Farrel) under the following mixing conditions: Melt temperature: 190 - 225 ° C Mixing times: 1.5 - 2 min. Cycle times: 2 - 4 min.

0043The mix falls from the Banbury mixer onto a two-roll mill (roll 1 T = 160 ° C, roll 2 T = 150 ° C), is removed in the form of a belt and, after cooling, is granulated.

0044Standard granules are produced from the granulate by injection molding at 220 ° C and examined according to DIN methods.

0045The resulting graft polymers according to the invention have the following properties:<tables id="tabl0002" num="0002"><img file="EP0246537A2_D0002.tif" /></tables><tables id="tabl0003" num="0003"><img file="EP0246537A2_D0003.tif" /></tables>