GB2176490A - High strength flame resistant polypropylene compositions - Google Patents

Abstract

Flame retardant polypropylene products comprise 60% to 64% alumina hydrate surface coated with about 1.0 wt.% of isostearic acid, 0.25% to 1% organic titanate and the balance polypropylene resin.

Description

SPECIFICATION High strength flame resistant poly-olefins and methods of making the same This invention relates to high strength flame resistant poly-olefins and methods of making the same and particularly to polypropylene systems which have both unusually high strength and resistance to flaming.

The desirability of reducing the flamability of polypropylene and similar poly-olefins has long been recog nized. Most flame retardants which have been used with poly-olefins create masses of highly toxic black smoke and fumes. This is, of course, most undesirable. It has long been known that aluminum hydrate is a desirableflame retardantfor use in organic systems where it is compatable. On heating in such systemswhere it is compatable. On heating in such systems, it produces CO2 and H2O with no dark smoke ortoxicfumes.

Unfortunately, however, hydrated alumina has resisted incorporation into polypropylene and like systems and all attempts to use it in such systems have failed. The resultant mixtures have been of such low strength as to bye totally unacceptable for commercial purposes.

The present invention provides a polypropylene composition containing hydrated alumina which has high Izod impact strength, increased flow, increased elongation, increased deflection and increased Gardner impact values compared with the original polypropylene, without loss oftensile strength.

The practice ofthis invention will giveflame retardanceto any polypropylene system while enhancing the strength of the product. For example, the practice of this invention has produced polypropylene products that have impact strengths which are increased fourtimes and flow rates increased seven times over the starting material without loss of tensile or any other critical property.

The composition of the present invention is basically an alumina trihydrate filled polypropylene compound- ed with an organic titanate, isopropyl (tridiodylphosphato) titanate. The alumina trihydrate filler is Alcoa Hydrated Alumina (Lubral coated). "Lubral" is a registeredtrademark(No. 1,251,981) of Aluminum Company of America of Pittsburgh, Pennsylvania, U.S.A., applied to a surface modifie alumina hydrate composition described in their Bonsignore U. S. Patent No.4,283,316, dated August 11,1981, and in their Levenduskyetal.

Patent No.4,390,653 (col. 2, lines 39-48). As recited in said Levendusky patent (col. 2, lines 39-48), the composition is: "alumina hydrate surface coated with about 1.0 wt. % of isostearic acid".

The formulation of such a polypropylene composition according to this invention would be asfollows: 60-64% - Alcoa Hydrated Alumina (Lubral Coated) 0.25%-1.0% - Isopropyl (tridiodylphosphate) titanate Balance - Polypropylene polymer The polypropylene polymer is preferably a mixture of polypropylene copolymer such as Hercules Pup 7823 and polypropylene homopolymer, such as Hercules PP 6523, in equal amounts.

A particular preferred composition is: 35 Ib (18.4%) Hercules PP7823 polypropylene copolymer 35 Ib (18.4%) Hercules PP 6523 polypropylene homopolymer 120 Ib (63.7%) Alcoa hydrated alunina. Lubral coated 227 gms. (.05%) Kenrick KR 12 [Isopropyl (trididyl phosphate) titanate] The composition is formulated by ribbon blending all ofthe materials and then mixing in a Banbury mixer, and extruding through a single screw and die plate to pelletizethe material. The temperature during processing is critical, with a maximum process temperatu re of about 380"F. and a minum of F., ora rangeof about 40' F. If the temperatre is too low, the material cannot be processed.If the temperature is too high, water will be expelled from the system and causefoaming.

The product of this invention has been subjected to exhaustive tests by the Underwriters Laboratories and has received approval as an acceptable flameretardant atthe highest approval level.

The significance of this invention can perhaps be best understood by reference tothefollowing example: The preferred composition described above was prepared by ribbon mixing the components, then transferring the mixture to a Stewart-Bolling Banbury mixer, mixed thoroughly, then transferred to a single screw extruder and extruded through a die plate and pelletized. The mixing and extrusion was carried out at temperatures of between 350"F. to 380"F.The product was tested with the following results: Flexural Flexural UL94 Modulus Strength VBT (10-5 psi) (10-3 pSi) V-O 3.25 5.00 Unnotched Notched Melt Izod1 Izod2 Index3 (ft-lb/in) (ft-lb/in) (gilOmin) No break 4.14 7.2 Tensile Tensile Strength Strength @ Yield @ Break Elongation (Ib/in2) (Ib/in2) (%) 2814 2510 33 1.1/8"sample 2# hammer.

2.1/4"sample 109 hammer.

3. Condition N: 10 000g load; 1900C.

The foregoing test shows the very high burn testvalues and physical properties of the material ofthis invention. The first parameter is the Underwriters Lab. Vertical Burn Test (UL 94VBT). The material easily passed this test. The notched Izod impact value to be acceptable must be near 1.0 ft-lb/in. This was exceeded by fourtimes. The unnotched Izod test showed no break at the standard test conditions. The high melt indexand tensile are apparentfrom the test data.

The test shows a remarkable set of physical characteristics combined with flame retardance, a combination which heretofore could not be obtained with polypropylene.

The foregoing specification sets out certain preferred practices and embodiments ofthis invention; however, it will be understood thatthis invention may be otherwise embodied within the scope ofthefollowing

Claims (9)

claims. CLAIMS

1. Aflame retardant polypropylene composition comprising about 60% to 64% alumina hydrate surface coated with about 1.0 wt.% of isostearic acid, about 0.25% to 1% organictitanate and the balance polypropylene resin.

2. Aflame retardant polypropylene composition as claimed in claim 1 wherein the organictitanate is isopropyl (tridiodylphosphato) titanate.

3. Aflame retardant composition as claimed in claim 1 Or 2 wherein the polypropylene resin is a mixture of polypropylene copolymer and polypropylene homopolymer.

4. Aflame retardant composition as claimed in claim 1 having the composition of 63.7% alumina hydrate surface coated with about 1.0 wt.% of isostearic acid, 18.4% polypropylene homopolymer, 18.4% polypropy- lene copolymer and 0.5% isoprophyl (tridyl-phosphato) titanate.

5. The method of making a flame retardant polypropylene composition comprising the steps of: (a) mixing polypropylene resin, which is a mixture of polypropylene copolymers and polypropylene homopolymers, with alumina hydrate surface coated with about 1.0 wt. % of isostearic acid, and organic titanate; (b) extruding said mixture through a die plate to form pellets; (c) controlling thetemperature ofthe mixture between 350" F.to 3800 F. during said process steps; and (d) cooling said extruded pellets to room temperature to produce a final product.

6. The method as claimed in claim 5 wherein the polypropylene resin is a mixture of polypropylene copolymers and polypropylene homopolymers.

7. The method as recited in claim 5 wherein the mixture comprises about 60% to 64% alumina hydrate surface coated with about 1.0 wt. % of isostearicacid, about 0.25% to 1% organictitanate and the balance polypropylene resin.

8. Aflame retardant polypropylene composition substantially in accordance with the particular preferred composition described herein.

9. The method of making a flame retardant polypropylene composition in accordance with any of Claims 1 to 4 or 8 substantially as described herein.