DE3640337C2 - - Google Patents

Description

The invention relates to thermoplastic ABS graft poly merisate, a process for their manufacture and their Use as a modification for vinyl chloride polymers (PVC).

The modification of thermoplastic molding compounds such as PVC, polyamide, polycarbonate and polyesters with ABS As is well known, polymers lead to significant improvements in their technical properties; at for example, vinyl chloride polymers can be used improved abrasion resistance, toughness, solvent Establish resistance in this way (see EP-A 5 736).

Graft polymers of vinyl monomers on natural or synthetic rubbers have been used as modifiers for PVC, which are preferably obtained by radical emulsion polymerization of, for example, styrene, acrylonitrile, α- methylstyrene, methyl methacrylate or mixtures thereof in the presence of rubber latexes such as polybutadiene latexes, polyacrylate latexes, and SBR chewable rubber (see US 43 66 281; EP-A 1 22 516; US 43 85 157; US 45 20 165).

Such graft polymers are generally used in PVC incorporated by homogeneous mixing of PVC powder with the powdered ABS and, if necessary, with additives in mixing plants and downstream kneaders or Rolling mills. The ABS is often insufficient open-minded and poorly distributed and found in PVC in the form of domains or clusters in the final product again. Inhomogeneities remain in the finished molded article visible as a surface defect and impair the mechanical strength z. B. Toughness, elasticity and elongation at break of the modified PVC masses. The Surface defects can usually be observed in the form of specks; these are particularly noticeable when the PVC Extruded, rolled or blown or for the material Production of foils and flat moldings used (for example as cladding films, consoles or other non-structural components in motor vehicles).

Surface defects and specks due to poorly distributed ABS make the material unusable for many purposes. US-PS 48 51 157 teaches an ABS graft by grafting in a certain way manufactured bimodal polybutadiene latex, with initiators and regulators in almost any quantities and proportions can be present.

It now became an ABS graft polymer with such good opening Conclusion behavior in PVC found that in the usual Processing a homogeneous distribution of the ABS graft polymerisats in PVC is guaranteed and no specks are visible in films made of the modified PVC.

The invention relates to a process for the production of ABS graft polymers Emulsion polymerization of a mixture of

• a) 40 to 60 wt .-% (based on a + b + c) of at least one styrenic monomer and
• b) 10 to 30% by weight (based on a + b + c) of at least one monomer from the group of acrylonitrile, methyl methacrylate and methacrylonitrile
  in the presence of
• c) 20 to 40 wt .-% (based on a + b + c) polybutadiene latex with a gel content of 60 to 95 % as a graft base and with the addition of a mercaptan regulator,

characterized in that the graft base is a mixture of a polybutadiene latex with a average particle diameter of 80-150 nm and such a latex of 200 to 400 nm in a weight ratio of 45: 55 to 55: 45, which amount of persulfate used is 0.7 to 0.9% by weight (based on total polymer), the amount used The amount of mercaptan is 0.15 to 0.6% by weight (based on the total polymer) and the molar ratio Mercaptan to persulfate is 0.3 to 1.0.

The following can be used as styrenic monomers (a): styrene, methylstyrenes, halogen-substituted styrenes and α- methylstyrene and mixtures thereof; styrene is preferred. Suitable monomers (b) are: acrylonitrile, methacrylonitrile, methyl methacrylate or mixtures thereof; acrylonitrile is preferred.

According to the invention, at least two polybutadiene Latices with particles different from each other knives are used. All suitable latices have a gel content of 60 to 95%, preferably  65 to 90%, determined according to that in DE-OS 33 04 544 given method.

The mean particle diameter d ₅₀ from the centrifuge measurement is considered as the particle diameter (cf. W. Scholtan et. Al. Kolloidz. And Z. Polymer 250 (1972), 782-96).

The average particle diameter of the more finely divided both latices is 80 to 150 nm, especially 90 to 120 nm, and the particle diameter of the coarser 200 to 450 nm, preferably 250 to 350 nm. The weight ratio of fine-particle to coarse-particle polybutadiene in the latices is 55: 45 to 45: 55.

Used as an initiator for the graft polymerization according to the invention, an amount of persulfate of 0.7 to 0.9% by weight, based on the finished graft polymer. Higher quantities lead to latex overloading Electrolyte and thus to instability and coagulum education, lower amounts cause worse Powder properties and poorer distribution of the Graft polymer in PVC. The persulfate is used in the Graft polymerization preferred at the beginning before mono addition is metered in, preference is given to potassium peroxodisulfate.

According to the invention, 0.15 to 0.6% by weight of a regulating Mercaptans such as n- or t-dodecyl mercaptan added, with t-dodecyl mercaptan being preferred. The mercaptan is preferably supplied during the monomer addition. It can be dissolved in the monomer, added to the monomer stream or added separately to the polymerization. Lesser than the specified amounts set the elongation at break of the modified PVC, favor higher additives the sintering of the ABS powder.

According to the invention, the persulfate / mercaptan molar ratio are between 0.3 and 1.0. Only within this Area you will also find optimal conditions for the start of the polymerization, the precipitation behavior of ABS powder, its digestion behavior in PVC and the mechanical properties of the compound.

The grafting reaction is otherwise carried out according to a known method (see, for example, DE 33 04 544), a temperature range of 59 to 65 ° C, preferably 60 to 64 ° C, is cheap.

The graft polymer can be used at the latex stage as later mixed as a powder with other polymers be like this B. is described in DE 32 29 130. There are mixed partners in latex form preferably butadiene-acrylonitrile rubbers, acrylate rubbers and high molecular copolymers of methyl merhacrylat / acrylonitrile, whose purpose in the cited patent is explained.

The graft polymers according to the invention are then - Usually after the addition of stabilizers against Oxidation and discoloration - individually or in a mixture after known methods by adding acids and / or Salt precipitated as powder and dried.

Incorporation into other thermoplastics, preferably PVC, takes place in conventional mixing units, e.g. B. Lödige- Mixers, kneaders, screws, calenders, injection molding machinery; the resulting compounds also with the usual auxiliaries and additives such as Processing aids, colorants, additives be provided.

example 1

A mixture of the following is placed in an autoclave Latices before:

• - 15 parts by weight (calculated as a solid and based on finished solid graft polymer) of a polybutadiene Latex with a particle size of 100 nm,
• - 15 parts by weight (calculated as a solid and based on finished solid graft polymer) of a polybutadiene Latex with a particle size of 350 nm,

and complements this mixture with so much deionized Water that after the polymerization taking into account all other solutions to be added to the graft latex has a solids content of approx. 35%.

31.75 parts of a 2.5% strength solution are metered in over 20 minutes Potassium persulfate solution (= 0.79 parts solid) and designed the temperature control so that the reaction material 5 minutes after this addition has reached 64 ° C. Immit Afterwards you can dose 23.8 over 8 hours Parts of acrylonitrile, 46.2 parts of styrene and 1.8 parts of one alkaline resin soap emulsifier, dissolved in Water, too, and distributed over the first 6 hours 0.254 parts of t-dodecyl mercaptan. The temperature is off the first half hour of the dosing time at 60 to 62 ° C and the approach is constantly stirred.

After the end of dosing, the temperature is raised to 70 ° C stirred for 4 hours, then cooled, the Latex equipped with a phenolic stabilizer, with the addition of an alkaline earth metal salt and that Powder dried. It has a melt viscosity, measured as MFI at 220 ° C / 10 kg according to DIN 53 735 of 5.6.

The graft polymer becomes a PVC compound with mixed the following composition:

• - 40 parts by weight of a suspension PVC with a K value from 70
• - 40 parts by weight of the graft polymer prepared above
• - 20 parts by weight of diisodecyl phthalate
• - 2 parts by weight of a tin stabilizer

The mixture is homogenized in a mixer and extruded in an extruder at a die temperature of 190 ° C. and a screw speed of 10 rpm to form a strip with a cross section of 25 × 0.5 mm. The result is a smooth, speck-free surface. The strip is tested according to DIN 53 455 on standard rod 5 and the following values are obtained:
Tensile strength: 21 MPa; Elongation at break: 206 to 221%.

Example 2

Example 1 is repeated, but the amount t-Do Decyl mercaptan increased to 0.38 parts.

Example 3

Example 1 is repeated, but the use of t-Dodecyl mercaptan increased to 0.28 parts and the finished Graft polymer latex before precipitation according to DE 32 29 130 with 5 parts by weight (based on solids) of a copolymer Latex made of methyl methacrylate and acrylonitrile, the one Staudinger index of 3.5 dl / g owns, mixes and then like together.

Comparative tests

• a) Example 1 was repeated, but with 1.2 parts K-persulfate and without added mercaptan;
• b) Example 1 was repeated, but with 0.67 parts K-persulfate and 0.57 parts t-dodecyl mercaptan;
• c) Example 1 was repeated, but with 0.67 parts K-persulfate and without t-dodecyl mercaptan;
• d) Example 3 was repeated, but with 1.48 parts K-persulfate and without t-dodecyl mercaptan.

Table 1 shows the values obtained:

Claims (4)

1. Process for the preparation of ABS graft polymers by emulsion polymerization of a mixture of

• a) 40 to 60 wt .-% (based on a + b + c) of at least one styrenic monomer and
• b) 10 to 30% by weight (based on a + b + c) of at least one monomer from the group of acrylonitrile, methyl methacrylate and methacrylonitrile

in the presence of

• c) 20 to 40% by weight (based on a + b + c) polybutadiene latex with a gel content of 60-95% as a graft base and with the addition of a mercaptan regulator,

characterized in that the graft base is a mixture of a polybutadiene latex with an average particle diameter of 80 to 150 nm and such a latex with an average particle diameter of 200 to 450 nm in a weight ratio of 45: 55 to 55: 45, the amount of persulfate used 0, Is 7 to 0.9% by weight (based on total polymer), the amount of mercaptan used is 0.15 to 0.6% by weight (based on total polymer) and the molar ratio of mercaptan to persulfate is 0.3 to 1, Is 0. 2. Use of the ABS graft polymers prepared according to claim 1 as a modifier for PVC.