GB2225018A - Preparation of flame retardant, fine denier, mass pigmented polypropylene fibers - Google Patents

Abstract

Fine denier mass pigmented polypropylene filaments and fiber is rendered flame retardant by mixing flame retardant compounds such as a product which contains both aliphatic and aromatic bromine with an anti-oxidant and a U.V. stabilizer with polypropylene powder resin in order to make a flame retardant concentrate prior to mixing with polypropylene resin and pigments to make a color concentrate.

Description

METHOD FOR RENDERING FINE DENIER MASS PIGMENTED POLYPROPYLENE FILAMENTS AND FIBER FLAME RETARDS BACKGROUND AND DISCUSSON OF PRIOR ART Flame retardancy has become a major consideration for many plastic articles used in industrial, commercial and household products.

Widespread use of plastics in products for industry commerce and household, has created the need to insure that such plastics are flame retardant. The polyolefins have been, and are being further considered in these areas. For example, polyolefins are highly flammable, and when used in the manufacture of fibers for clothing, upholstery, carpeting and the like, the need for flame retardancy is even more apparent. It is likewise well recognized that polyolefin fibers used in upholstery and carpets have in the past incresed the severity of fires, especially in large commercial establishments.

However, the art has not been able to develop a satisfactory fire retardant additive, or additives for extruded polyolefin fibers.

With respect to additives, Hancock Patent 4,532,278, discloses a fire retardant polypropylene fiber which results from combining the polypropylene polymer with a bromophenyl compound and which may include C12H2Br80; tetrabromobisphenol A; Bis (2-hydroxyethyl ether) of tetrabromo bisphenol A; and octabromobisphenyl oxide. The flame retarding compound according to Hancock, is simply blended into the polypropylene resin prior to or during extrusion.

However, to date, no one has been able to develop a suitable system which will impart fire retardancy to polyolefins without affecting some of the desirable resin properties.

In another aspect, the synthetic textile industry was desirous of obtaining a fire retardant polyolefin fiber or fabric, wherein the presence of the fire retardant in the fiber or frabric would in one respect, be effective as a flame retardant while in another respect, would not alter the desirable properties of the fabric, particularly, color and hand. This is particularly important in fabrics for household and personal use, such as in clothing and furniture coverings.

In Listner, U.S. Patent No. 3,650,300 granted March 21, 1972, polyolefins were rendered flame retardant by the incorporation of an anti-oxidant, a halogen phosphate, a free radical initiator and a dispersant into the thermoplastic melt.

In Versnel, U.S. Patent No. 3,893,870 granted July 8, 1975, a phosphite adjuvant is incorporated into molten polypropylene.

In Goldborn et al I. U.S. Patent No. 3,870,711, granted April 9, 1974; Goldborn et al II, U.S. Patent No. 3,870,771, granted March 11 1975; Goldborn et al III, U.S. Patent No. 3,935,162 and Goldborn et al IV, U.S. Patent No. 3,976,620, various alkyl-aryl phosphonates were proposed for incorporation into polyolefin thermoplastic melts to provide flame retardancy.

Certain other prior art references were directed to flame proofing specific polymers with a bromine compound. In Ekhhorn, U.S.

Patent No. 3,058,926, there is disclosed a method for making flame proof alkenyl aromatic resin composition by incorporating an organil bromine compound and an organic peroxide.

Fine denier polypropylene fibers are manufactured by extruding the melted polypropylene resin through very fine spinneret orifices; if the flame retardant compound is not completely mixed with the melted polypropylene resin prior to extrusion, the fire retardant compound tends to agglomerate into itself, creating lumps in the extrusion melt which will clog the spinneret filters or orifices and will result in down time on a commercial line. In addition, smaller lumps of the flame retardant compound which can pass through the filter and spinneret die orifice, will displace sufficient polymer in the resulting fine denier filament to create a weak spot in the continuous filament; which may result in breakage that shuts down the production line.Incomplete mixing of the flame retardant compound with the polypropylene resin may also have a deleterious effect on the ability of the flame retardant compound to generate cooling gases within a localized area which serve to render the material flame retardant.

DESCRIPTION OF THE INVENTION When a fiber producer tries to manufacture fine denier flame retardant polypropylene fiber, he will face two different problems, the first problem is the inability to obtain a good mix of the melted polypropylene with the flame retardant, because, if the compound is not well made, it will agglomerate on itself resulting in clogging the spinneret filters or produce a weak spot on fibers, resulting in broken filaments because of the agglomerates.

The second problem is the lack of tenacity retention during the use of these fibers in the end use, because bromine materials used to manufacture the flame retardant fiber have a very low decomposition temperature, lower than the processing temperature, because of that, free bromine is generated which attacks chemically the polymer and the fiber decomposition starts at the beginning of the fiber manufacture; to avoid that it is necessary to use an anti-oxidant agent to provide heat stability to the polymer and bromine compound, and a hindered amine which could react chemically with the free bromine produced dt the processing step.

Achieving ccmplete dispersion of all the compounds, and avoiding the polymer degradation with the hindered amine, polypropylene fibers can be rendered flame retardant and they will be used to manufacture fabrics or carpets obtaining the desired rate in the common flame retardancy tests, exhibiting no changes in fiber properties.

The preferred method of making the flame retardant polypropylene fibers of the present invention, is carried out in the following steps: 1. The following materials are dry-mixed: a. aliphatic and aromatic bromine compound - bis (2,3 dibromopropyl ether) of tetrabromobisphenol A from 20% to 35t depending on the final application.

b. hindered amine (Cyassorb from Cyanamid or Chimassorb from Ciba Geigy 25% to 35% depending on the final application.

c. thermal anti-oxidant (phenolic plus phosphite) Irganox from Ciba Geigy or Cyanox from Cyanamid 2 to 4% depending on processing temperature.

d. MFI-12 polypropylene powder resin.

The mixture is dosified in a two screw extruder through a two mouth dosifier merging through one mouth 60% of this dry mixture, and the other mouth 40% of MFI-35 pelletized polypropylene resin, and from the exit of the extruder to a pelletizing line to form pellets.

2. The following materials are dry mixed and extruded to make a color concentrate: a. 20% of pellets formed by Step 1.

b. adequate percentaye of different pigment dispersions to provide the necessary color to the final fiber (pigments used could be organic or inorganic).

c. MFI-35 polypropylene pellets enough to make 100% of the mix.

d. 20% of pellets formed in Step 2, are dosified to an extruder with 80% of MFI-35 polypropylene pellets to obtain the final fiber (staple or continuous filament).

The standard melt spinning process of Step c, can be carried out at spinning speeds of from 600 to 1400 meters per minute.

Claims (9)

CLAIMS:

1. A method for rendering fine denier polypropylene fibers flame retardant, comprising a) dispersing fire retardant material, thermal anti-oxidant and hindered amines in a blend of polypropylene powder resin and pelletized polypropylene resin; extruding and pelletizing to form additive pellets; b) mixing the additive pellets with pigment dispersions and further pelletized polypropylene resin and extruding and pelletizing to obtain a color concentrate; and c) mixing the color concentrate with further pelletized polypropylene resin and extruding and spinning to obtain the fine polypropylene fibers.

2. The method of claim 1 where the flame retardant material is bis (2,3-dibromopropyl) ether of tetrabromobisphenol A.

3. The method of either of claims 1 and 2 where the flame retardant, the anti-oxidant and hindered amine are dispersed in said polypropylene powder resin to form a dry powder blend comprising from 20 to 35% flame retardant, from 20 to 35% hindered amine, from 2 to 4% of thermal anti-oxidant and the remaining percentages up to 100% of polypropylene powder resin blend and the remaining percentage to cover the 100% is MFI-12 polypropylene powder resin in the powder dry blend.

4. The method of claim 1 where the powder dry blend of claim 3 is blended in approximately a 60% proportion of such dry blend with approximately 40% of MFI-35 pelletized polypropylene resin.

5. The method of claim 1 where the pelletized compound of claim 4 is blended with pigment dispersion and further pelletized polypropylene resin to obtain the color concentrate containing approximately 20% of such pelletized compound.

6. The method of any one of claims 1 to 5 where approximately 20% of the color concentrate is mixed with pelletized polypropylene to complete the 100%.

7. The method of any one of claims 1 to 6 where the hindered amine is a high molecular weight hindered amine.

8. A method for rendering fine denier polypropylene fibers flameretardant substantially as hereinbefore described.

9. Polypropylene fibers made in accordance with the method according to any one of claims 1 to 8.