GB2134912A

GB2134912A - Filled polypropylene compositions

Info

Publication number: GB2134912A
Application number: GB08300950A
Authority: GB
Inventors: Robert David Marshall Best
Original assignee: CARLESS CHEM Ltd
Current assignee: CARLESS CHEM Ltd
Priority date: 1983-01-14
Filing date: 1983-01-14
Publication date: 1984-08-22
Also published as: GB2134912B; GB8300950D0

Abstract

Filled polypropylene compositions comprise polypropylene, an alkaline earth metal soap of an oxidized paraffinic wax and a mineral filler. The presence of the soap enables increased amounts of filler to be incorporated in the polypropylene. The preferred soaps are calcium soaps and the composition suitably contains from 2.5 to 30 parts by weight of soap and up to 200 parts by weight of mineral filler (e.g. calcium carbonate, talc, silica, mica or titanium dioxide) per 100 parts by weight of polypropylene.

Description

SPECIFICATION Polypropylene compositions This invention is concerned with improvements in and relating to polypropylene compositions and, in particular, is concerned with polypropylene compositions which may contain relatively high amounts of mineral fillers.

It is known to provide polypropylene compositions containing mineral fillers such as calcium carbonate and talc. In general, however, it is difficult to increase the mineral filler content above about, say, 60 parts by weight of mineral filler per 100 parts by weight of polypropylene. It would be desirable, in many cases, to increase the content of filler, for example to provide a less expensive end-product; to increase the porosity of the mineral filled resin so that a formed product, e.g. flexible or rigid sheeting, is capable of accepting conventional oil, solvent or water-borne inks; to or provide a flexible and porous sheet which is capable of being drawn or stretched on conventional rollers to provide a synthetic paper.

It has now been found, in accordance with the present invention, that the amount of mineral filler which may be incorporated in a polypropylene composition may be markedly increased by the incorporation in the composition of an alkaline earth metal, especially calcium, soap of an oxidised paraffinic wax.

According to the invention therefore, there is provided a polypropylene composition comprising polypropylene; an alkaline earth metal soap of an oxidised paraffinic wax, and a mineral filler.

The term "polypropylene" as used herein is intended to refer not only to homopolymers of propylene but to copolymers of propylene with one or more other monomers copolymerizable therewith and derived from propylene as the major constituent.

The alkaline earth metal soap of the oxidised paraffinic wax (hereinafter simply referred to as "soap") is suitably present in an amount of at least 2.5 parts by weight per 100 parts by weight of the propylene. (in the following specification all amounts of ingredients other than the polypropylene will be expressed as parts by weight per 100 parts by weight of polypropylene using the abbreviation "phr"-parts per hundred of resin). Preferably the soap is present in an amount of from 2.5 to 30 phr, more preferably 5 to 25 phr and most preferably 10 to 25 phr.

In general the higher the soap content of the composition, relative to the polypropylene, the higher the amount of mineral filler which may be incorporated. The mineral filler may be present in relatively low amounts, e.g. amounts comparable with compositions containing no soap and, thus, may be present in amounts as lows as 20 phr.

Preferably, however, in order to take advantage of the presence of the soap, the mineral filler is present in an amount of at least 50 phr. The upper limit of the mineral filler content will generally be about 200 phr and preferred compositions of the invention will contain the mineral filler in an amount of from 50 to 200 phr.

The polypropylene employed in the compositions of the invention is suitably one of relatively high melt flow index (MFI), for example having an MFI of from 0.3 to 16, preferably from 8 to 12, as determined by the test method D/1 238-65T (BSI 2782).

Examples of mineral fillers which may be used in the compositions of the invention include calcium carbonate, talc, silica, mica and titanium dioxide.

Oxidised paraffinic waxes are well-known materials. They are commonly prepared by the air oxidation of a paraffinic wax. The starting paraffinic wax may be a so-called "microcrystalline" wax (in which it is believed that the long chain paraffins are largely in the iso-form) or a so-called "slack" wax (in which it is believed that the long chain paraffins are largely straight chain paraffins). The products (oxidates) themselves are complex mixtures containing unreacted starting material and oxidation products such as acids, lactones and esters.The degree of oxidation of the oxidised wax is commonly indicated by its acid number (the number of milligrams of potassium hydroxide required to neutralise a one gram sample of the oxidate) and for use in the present invention the oxidised wax suitably has an acid number of from 25-100, preferably from 30-75, most preferably from 40-60. The oxidate may be converted to an alkaline earth metal soap (especially a calcium soap) thereof by reaction with an appropriate saponifying agent such as an alkaline earth metal hydroxide or carbonate. The saponification is suitably carried out by direct reaction of the saponifying agent (i.e.

hydroxide or carbonate) with the molten oxidate, e.g. at a temperature of from 100 to 2000C.

The compositions of the invention are suitably prepared by forming a mixture of particles of the polypropylene soap and filler and subsequently forming the mixture to a desired coherent mass by the action of pressure and heat, for example by extruding the mixture into sheet form or by injection-moulding or blow-moulding it.

It is generally desirable that the particles of polypropylene, soap and filler be of the same order of particle size and thus, for example, they may take the form of powders, e.g. having an average particle size of about 350-400 microns, or of granules, e.g. having an average particle of about 1 mm.

The mixture of polypropylene, soap and inert filler may be formulated as a masterbatch which may be subsequently be let down with additional polypropylene and/or filler to give a final mixture of the desired composition. The final composition, obtained from processing of the mixture, may, for example, be in the form of a sheet or film, rod or moulded product. In the case of compositions in sheet or film form these may be used as such, for example as packing materials compositions containing relatively low amounts of filler, e.g. 60 phr, being suitable for use as flexible packing materials and those containing higher amounts of filler, for example 80-100 phr, as more rigid packing materials.Thin sheets of the compositions of the invention containing high levels (e.g. 120200phr) of a filler such as calcium carbonate may be used as synthetic writing papers. Rods of the composition of the invention may be cut into short lengths and used as raw material in subsequent extrusion or moulding operations. Shaped moulded products formed from the compositions of the invention include, for example, flowerpots and like moulded containers.

The compositions of the invention may be pigmented by the addition of pigments, preferably having acid receptor sites, and in this regard it may be noted that the incorporation of the soap markedly facilitates pigmentation. Compositions containing light or white coloured fillers, e.g.

calcium carbonate tend to be light or white in colour, generally being lighter in colour with increased amounts of filler. The compositions generally have little or an acceptable odour and have good tear resistance and are susceptible of stretching.

In order that the invention may be well understood the following examples are given by way of illustration only.

The calcium soap of an oxidised paraffinic wax used in these examples was prepared as follows: 100 Kg of oxidate (Hypax 450L manufactured by the applicants) having a melt point of 550C, a pale lemon colour, an acid number of 48-50 mg KOH/g and a saponification number of 100--120 mg KOH/g was heated to a temperature of 900C in a vessel provided with an internal mixer.

45 Kg of freshly powdered calcium hydroxide (purity 99.5%) was added to the heated oxidate over a period of 30 minutes with stirring. The temperature of the mass was increased to 1 600C over a period of two hours while stirring and was maintained at that temperature for four hours with stirring.

The resultant calcium soap had a light tan colour, a melt point of 100 12000, an acid number of 4 mg KOH/g and a saponification number of 8 mg KOH/g. The soap was viscoelastic at temperatures in the range 1002000C.

The soap was granulated so as to pass through 100 mesh screen.

A masterbatch was prepared from particles of the calcium soap prepared as described above, polypropylene having an MFI of 10, and calcium carbonate, the masterbatch containing 95 phr of soap and 5 phr of calcium carbonate.

The master batch was let down with further appropriate amounts of polymer and/or calcium carbonate to give compositions having the following formulations.

Table 1 Calcium Calcium soap Carbonate Example (phr) (phr) 1 20 60 2 10 60 3 5 100 4 20 80 5 20 100 6 20 120 7 20 140 8 20 160 The compositions were then mixed with heating at 1700C for 30 minutes to ensure dispersion. Each of the heated compositions was then drawn through a heated two roll milli at a temperature of 1500C to produce the composition in the form of sheets about 0.075- 0.1 mm thick.

Each of the resulting sheets was a coherent sheet having good tear resistance and elongation potential. The sheet produced for example 1 was suitable for use as an industrial flexible packing sheet material, as a damp course and/or as a silage, roofing or newspaper sheet. The products of example 4, 5 and 6 were suitable as rigid packing sheets. The compositions of examples 4, 5 and 6 were also suitable for the manufacture of moulded products such as flower pots or coat hangers.

Claims

1. A polypropylene composition comprising polypropylene, an alkaline earth metal soap of an oxidised paraffinic wax, and a mineral filler.

2. A composition as claimed in claim 1 in which the soap is a calcium soap.

3. A composition as claimed in claim 1 or claim 2 containing at least 2.5 parts by weight of soap per 100 parts by weight of polypropylene.

4. A composition as claimed in claim 3 containing from 2.5 to 30 parts by weight of soap per 100 parts by weight of polypropylene.

5. A composition as claimed in any one of the preceding claims containing up to 200 parts by weight of mineral filler per 100 parts by weight of polypropylene.

6. A composition as claimed in claim 5 containing from 50 to 200 parts by weight of mineral filler per 100 parts by weight of polypropylene.

7. A composition as claimed in any one of the preceding claims in which the polypropylene has a melt flow index of 0.3 to 16.

8. A composition as claimed in claim 1 substantially as hereinbefore described with reference to the Examples.