WO1996025456A1

WO1996025456A1 - Flame retardant polymer composition

Info

Publication number: WO1996025456A1
Application number: PCT/FI1996/000080
Authority: WO
Inventors: Matti Hirvensalo; Outi Wiklund; Tiina Vanne; Riitta Teimola; Veli-Matti Enkenberg
Original assignee: Borealis A/S
Priority date: 1995-02-17
Filing date: 1996-02-13
Publication date: 1996-08-22
Also published as: FI950716A; AU4624996A; FI950716A0

Abstract

The invention relates to filler-containing polymer compositions in which the filler is soap stone. The invention relates in particular to a flame retardant polymer blend which comprises (A) an organic polymer; (B) soap stone as a filler; and (C) silicone fluid or gum.

Description

Flame retardant polymer composition

The invention relates to polymer compositions which contain a filler, and in particular to a flame retardant polyolefin composition which contains a filler.

Various fillers are generally used in plastics. The aim may in such a case be to alter the properties of plastics, for example, to affect the strength and other mechanical proper¬ ties, the highest temperature for use, electrical properties, or the price. Fillers used include fiber reinforcements (e.g. carbon, glass, aramide) or inorganic fillers (e.g. aluminum hydroxide, calcium carbonate, kaolin, mica, talc).

Large amounts, typically 50-60 % by weight, of inorganic fillers may also be used for improving flame retardancy.

Commercial flame retardant polyolefin compositions typically contain large amounts, 10-50 % by weight, of halogen compounds together with, for example, antimony trioxide. In recent years, however, there has been, for environmental reasons, a clear move away from the use of halogen compounds.

Various phosphorus compounds have also been used widely to improve flame retardancy, although they are often difficult to handle and may be acidic and/or toxic, and they are needed in large quantities.

Silicone fluids have sometimes been added to flame retardant polyolefin compositions. US Patent 4.273.691 discloses a polymer composition which contains 70-98 % of polyolefin, 1-10 % of silicone, and 1-20 % of a Group HA metal -Ca, carboxylic acid salt.

Inorganic hydroxides have been used in polyolefin compositions which do not contain halogen compounds; for example, Japanese patent publication JP 01060642 discloses a composition in which the principal component is polyolefin and which additionally contains 30-100 parts by weight of aluminum hydroxide or calcium hydroxide or hydrotalcite, 10-40 parts by weight of magnesium oxide, carbonate or hydroxide, and 1-10 parts by weight of red phosphorus, barium compounds, lead compounds and sili¬ cone fluid. However, the use of hydroxides in, for example, cable applications of plastics is harmful, since they have a deleterious effect on the electrical properties of polymer compositions.

Patent application publication EP 0 393 959 describes a polyolefin composition which contains (A) at minimum 40 % by weight of an ethylene copolymer in which the comonomer is a (meth)acrylate, (meth)acrylic acid, or vinyl acetate; (B) silicone fluid or gum; and (C) an inorganic filler which is a Group HA metal compound but not hydroxide. Preferably the filler is magnesium oxide, magnesium carbonate or calcium carbonate.

The object of the present invention has been to find a new advantageous filler which could be used in many types of polymers, and preferably also in flame retardant polymer compositions, in particular polyolefin compositions.

It has been observed, surprisingly, that one such filler is soap stone powder, which is produced at soap stone quarries and factories as a byproduct of machining. The use of such powder as a filler in accordance with the invention is highly economical, since it has so far been regarded primarily as a waste. The particle size of the filler to be used is 1-100 μ , preferably 2-30 μm. A suitable amount of filler in compositions according to the invention is 10-250 parts by weight, preferably 25-100 parts by weight, to 100 parts by weight of polymer.

Soap stone powder can be used as a filler in various plastics, such as polyolefins, PVC, polyesters, polyurethanes, etc. Such plastics can be used for manufacturing many kinds of products, such as cable products (insulators and mantles), electrical engineering products, pipes, profiles, wall and floor coverings toys, household objects, automobile parts, bitumen products, etc. In other words, the uses include all the products in which filler-containing polymers are used. In addition, the known good thermal conductivity properties of soap stone can be exploited.

Filler-containing polymer compositions according to the invention may, of course, contain other additives conventionally used, such as stabilizers, colorants, etc.

One very advantageous use for the filler according to the invention consists of flame retardant polyolefin compositions, in particular for cable applications. Such a flame retardant polymer composition for cable applications comprises (A) at minimum 40 % by weight of an organic polymer; (B) the filler according to the invention, i.e. soap stone powder; and (C) possibly silicone fluid or gum.

The organic polymer is preferably a copolymer of ethylene with one or more comonomers, which comonomers have been selected from the group C,-C_β-alkyl acrylates, Cι-C₆-alkyl methacrylates, CrCβ-hydroxyalkylacrylates, Ci- -hydroxyalkyl methacrylates, acrylic acid, methacrylic acid, and vinyl acetate. Such a preferred polymer composition contains at minimum 40 % by weight, preferably at minimum 60 % by weight, of a copolymer of ethylene with above-mentioned comonomers. The term copolymer covers in this context also grafted copolymers, in which for example acrylic acid has been grafted to polyethylene. In addition to ethylene, the polymer may contain small amounts, less than 10 % by weight, of other olefins, such as propylene. Especially preferably the ethylene copolymer according to the invention is, for example, an ethylene/methyl acrylate, ethylene/ethyl acrylate, ethylene/butyl acrylate, ethylene hydroxyethyl methacrylate, ethylene/vinyl acetate/hydroxyethyl methacrylate, or ethylene/vinyl acetate copolymer.

Silicone fluids or gums which can be used in compositions according to the invention are, for example, organopolysiloxane polymers having siloxy groups. Organopolysiloxanes have a viscosity of approx. 600 10* - 300 10* cP at a temperature of 25 °C. One example of a suitable compound is polydimethyl siloxane. The silicone fluid or gum may contain silica, which is often used for stiffening silicone gums, at maximum 50 % by weight. In compositions according to the invention the amount of silicone fluid or gum is 0.5-100 parts by weight, preferably 2-45 parts by weight, calculated from the amount of polymer. Often it is advantageous to use a ready-made silicone fluid master batch, i.e. a blend in which silicone fluid has been mixed with, for example, polyethylene. The handling and mixing of such a product is considerably easier.

When necessary, the polymer composition according to the invention can be cross- linked. The cross-linking of thermoplastic polymer compositions by using cross-linking catalysts, such as peroxides, is generally known. If the polyolefin has silane groups, a silanol condensation catalyst can be used.

The suitable amounts of polymer, silicone fluid or gum, and soap stone to be contained in a flame retardant polyolefin composition are given above. It is clear for an expert in the art that the proportions of the ingredients used vary according to the properties desired for the final product. This applies in particular when a balance between flame retardancy and strength properties is being sought. It has been observed that a good combination of properties is obtained by using 2-8 % by weight of polymethyl siloxane and 15-50 % by weight of soap stone. Soap stone itself is an excellent filler as compared with many others, since it has good mechanical properties.

Flame retardant polymer blends can be prepared by mixing an organic polymer, silicone fluid and soap stone in a conventional mixing or compounding apparatus, such as a Banbury mixer, a 1- or 2-screw extruder, or a 2-roll mill. The mixing should be carried out using an apparatus having a sufficiently high temperature in order for the polymer to soften, in general within a temperature range of 120-300 °C.

The polymer blends described above can be used for many purposes. The blends can be worked, for example, into castings, sheets or fibers. An especially important use is the insulation of cables and wires, cable mantles, and filler mantles. If the blends are used as insulation layers, they are preferably cross-linked. The invention is described in greater detail with the help of the following examples:

Example 1.

The following materials were used in the experiments:

NCPE 0467 = ethylene/vinyl acetate/hydroxyethyl methacrylate terpolymer (E/VA/HEMA), manufacturer Borealis Polymers Oy NCPE 5810 = ethylene/ethyl acrylate copolymer E/EA), Borealis NV BY 27-002 = blend of silicone gum and polyethylene (1 : 1), a so-called silicone gum master batch, Dow Chemicals

Q4-2735 = silicone gum, Dow Chemicals

I-B 215 = antioxidant, Ciba-Geigy soap stone = Nunnalahti soap stone powder, Tulikivi Oy

The polymer blends were prepared using a Brabender mixer. After grinding, sheets 3 mm thick were compressed at a temperature of 150 °C. The oxygen index (LOT) was measured by the standard method ASTM D2863-77 by using as the flame source a Roson Hi-Heat butane torch (supplier Stanton Redcroft). The torch was held against the surface of the test specimen for 20 seconds. The results and the materials used in the various experiments are shown in Table 1.

Table 1. Oxygen indices (LOI)

Exp 1 Exp 2 Exp 3 Exp 4 Exp 5 Exp 6 Exp

NCPE 5810, % 64,8 61,8 57,7 47,8 46,8 59,8 -

NCPE 0467, % -

— — - - — 63,7

soap stone, % 30,0 35,0 40,0 45,0 50,0 30,0 30,0

BY 27-002 - - - - - 10,0 6,0

04-2735, % 5,0 3,0 2,0 7,0 3,0 - -

I-B 215, % 0,2 0,2 0,2 0,2 0,2 0,2 0,25

LOI 33,8 31,8 31,5 34,4 33,4 33,6 27,2

Comparative example

Comparative experiments were performed according to Experiment 1 by changing the filler, the other materials and the test conditions remaining unchanged. In this case the oxygen indices were as follows:

Table 2

1 Filler Oxygen index, LOI

Magnesium carbonate 28,2

Barium sulfate 23,4

Talc 29,0

Wollastonite 28,2 i (calsium silicate) It can be seen from the results that by using soap stone powder with the same polymer and in even otherwise similar experiments, a clearly higher oxygen index is obtained than by using other conventional fillers.

Example 2. Strength properties

In cable applications it is a general requirement that the tensile strength of the material is at minimum 9 MPa. On the materials of Experiments 6 and 7 of Example 1, tensile strength tests were carried out in accordance with the standard IEC811-1-1 by using a drawing speed of 100 mm/min. The tensile strengths were 9.2 MPa (Experiment 6) and 12.4 MPa (Experiment 7). Thus the tensile strengths fulfilled the requirements.

Claims

Claims:

1. A filler-containing polymer composition, characterized in that the filler is soap stone powder.

2. A polymer composition according to Claim 1 , characterized in that the filler content is 10-250 parts by weight to 100 parts by weight of polymer.

3. A polymer composition according to Claim 2, characterized in that the filler content is 25-100 parts by weight to 100 parts by weight of polymer.

4. A polymer composition according to Claims 1-3, characterized in that the particle size of the soap stone powder is 1-100 μm, preferably 2-30 μm.

5. A polymer composition according to Claims 1-4, characterized in that it comprises

(A) organic polymer;

(B) soap stone powder as a filler; and

(C) possibly silicone fluid or gum.

6. A polymer composition according to Claim 5, characterized in that it comprises (A) organic polymer which contains at minimum 40 % by weight of a copolymer of ethylene with a comonomer selected from the group C,-C₆-alkyl methacrylates, C_rC₆- alkylacrylates, C,-C₆-hydroxyalkyl methacrylates, C,-C₆-hydroxyalkylacrylates, acrylic acid, methacrylic acid, and vinyl acetate; (B) soap stone powder as a filler; and (C) silicone fluid or gum.

7. A composition according to Claim 5 or 6, characterized in that the organic polymer is an ethylene/ethyl acrylate copolymer.

8. A composition according to Claim 5 or 6, characterized in that the organic polymer is an ethylene/vinyl acetate/hydroxyethyl methacrylate terpolymer.

9. A composition according to Claims 5-7, characterized in that the content of silicone fluid or gum is 0.5-100 parts by weight and the content of filler is 10-250 parts by weight to 100 parts by weight of organic polymer.

10. A composition according to Claims 5-8, characterized in that the content of silicone fluid or gum is 2-45 parts by weight and the content of filler is 25-100 parts by weight to 100 parts by weight of organic polymer.

11. A composition according to Claims 5-9, characterized in that the silicone fluid or gum is polydimethyl siloxane.

12. A flame retardant polymer composition, characterized in that it comprises

(A) ethylene/ethyl acrylate copolymer;

(B) soap stone powder as a filler;

(C) polydimethyl siloxane.

13. A composition according to Claim 11, characterized in that it comprises 2-8 % by weight of polydimethyl siloxane, 15-50 % by weight of soap stone, the balance being ethylene/ethyl acrylate copolymer.

14. The use of a composition according to any of the above claims in cable mantles or insulators.

15. A cable or wire in which one layer is made from a polymer composition according to any of the above claims.

16. Products in the use of which a polymer composition according to any of the above claims has been used.