Flame retardant thermoplastic polyurethane containing...

Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...

Reexamination Certificate

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C524S123000, C524S127000, C428S421000, C428S522000, C428S523000

Reexamination Certificate

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06777466

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to flame retardant thermoplastic polyurethane (TPU) compositions comprising melamine cyanurate at high levels as the only organic flame retardant additive, while maintaining high tensile strength of the TPU compositions. The TPU compositions are useful for applications where low flame properties are desirable, such as wire and cable applications, blown film, molding applications, and the like. This invention also relates to process to produce the TPU compositions in a twin screw extruder and process to produce wire and cable jacketing.
BACKGROUND OF THE INVENTION
Halogen additives, such as those based on chlorine and bromine, have been used to give flame retardant properties to TPU compositions. In recent years, certain end use applications are specifying that the TPU composition be halogen free. This has required TPU formulators to search for other flame retardants to replace the previously used halogen additives.
Japanese Patent 54-85242 issued to Ozaki discloses resin compositions, including TPU, with from 3 to 33.3 weight percent melamine cyanurate for flame retardency. The one example with TPU shows a level of 23 weight percent of melamine cyanurate.
U.S. Pat. No. 5,837,760 issued to Hackl et al. discloses the use of organic phosphates and/or organic phosphonates alone or as a mixture with melamine derivatives, such as melamine cyanurate, as flame retardants in TPU. The compositions are said to have 35-80 weight percent TPU, 3-15 weight percent organic phosphates and/or phosphonates, and if required, 0-50 weight percent melamine derivatives, with the weight percent based on a mixture of TPU and phosphate.
U.S. Pat. No. 5,110,850 issued to Farkas discloses using derivative free melamine at a level of 30-40 weight percent as a flame retardant for TPU.
U.S. Pat. No. 5,684,071 issued to Mogami et al. discloses an additive for thermoplastics for flame retardency and mechanical properties which is a heterocyclic compound, such as melamine cyanurate, that is coated with a compound having at least two functional groups, such as epoxy. The surface treated melamine cyanurate is used at a level of 2-50 weight percent of the polymer resin, which would be from 2-33.3 weight percent of the composition.
EP 0389768 A2 issued to Scarso discloses using melamine cyanurate with phosphates and magnesium hydroxide as flame retardant in TPU.
U.S. Pat. No. 5,037,869 issued to Sprenkle and U.S. Pat. No. 4,321,189 issued to Ohshita et al. discloses using melamine cyanurate in polyamide molding resins.
Melamine cyanurate is a known flame retardant for use in TPU and other thermoplastics but its use at high levels has been avoided in TPU because of its detrimental effect on the physical properties, such as tensile strength and molecular weight, of the TPU.
It would desirable to use melamine cyanurate at high levels in TPU compositions while achieving good tensile strength and molecular weight.
SUMMARY OF THE INVENTION
It is an object of the present invention to make a non-halogen flame retarded TPU composition which has high levels of melamine cyanurate while maintaining high ultimate tensile strength.
It is a further object of the present invention to make a TPU composition which can be used as a jacket in a wire and cable construction and pass both the UL-1581 section 1080 and UL-1581 section 1080, subject 758 section G tests.
It is another object of the present invention to make a TPU composition which although the composition has a low limiting oxygen index (% LOI), will also have a low peak rate of heat release (PRHR) value.
It is another object of the present invention to have a process for making a TPU composition which is suitable for flame retarded jacketing in wire and cable construction.
Another object of the invention is a one step process of compounding and extruding into a jacket to make wire and cable construction.
Yet another object of the present invention is to improve a flame retardant composition which contains a degrading flame retardant additive by adding a small amount of a cross linking agent when making the TPU polymer used in the TPU composition.
These and other objects are accomplished by using a thermoplastic polyurethane (TPU) composition comprising from about 28 to about 50 weight percent of melamine cyanurate as the sole organic flame retardant additive, wherein said TPU composition has an ultimate tensile strength greater than 1500 psi and the TPU polymer in the TPU composition has a weight average molecular weight (Mw) greater than 70,000 Daltons as measured on a finished product.
In one aspect, the level of melamine cyanurate is from about 34 to about 45 weight percent of the TPU composition. Another aspect is a level of from about 35 to about 45 weight percent of the TPU composition.
In one aspect, the preferred Mw of the TPU composition is from about 85,000 to about 180,000 Daltons. Another aspect is a Mw of from about 100,000 to about 160,000 Daltons.
The preferred ultimate tensile strength of the TPU composition is at least 2900 psi, and more preferred is an ultimate tensile strength of at least 3500 psi, when the TPU composition is used as a wire and cable jacket.
The TPU composition has a LOI less than 24 while having a PRHR less than 310 KW/m
2
.
DETAILED DESCRIPTION OF THE INVENTION
The thermoplastic polyurethanes (TPU for short) compositions of the present invention comprise at least one TPU polymer along with an additive of melamine cyanurate to achieve good flame retardency.
The TPU polymer type used in this invention can be any conventional TPU polymer that is known to the art and in the literature as long as the TPU polymer has adequate molecular weight. The TPU polymer is generally prepared by reacting a polyisocyanate with an intermediate such as a hydroxyl terminated polyester, a hydroxyl terminated polyether, a hydroxyl terminated polycarbonate or mixtures thereof, with one or more chain extenders, all of which are well known to those skilled in the art.
The hydroxyl terminated polyester intermediate is generally a linear polyester having a number average molecular weight (Mn) of from about 500 to about 10,000, desirably from about 700 to about 5,000, and preferably from about 700 to about 4,000, an acid number generally less than 1.3 and preferably less than 0.8. The molecular weight is determined by assay of the terminal functional groups and is related to the number average molecular weight. The polymers are produced by (1) an esterification reaction of one or more glycols with one or more dicarboxylic acids or anhydrides or (2) by transesterification reaction, i.e., the reaction of one or more glycols with esters of dicarboxylic acids. Mole ratios generally in excess of more than one mole of glycol to acid are preferred so as to obtain linear chains having a preponderance of terminal hydroxyl groups. Suitable polyester intermediates also include various lactones such as polycaprolactone typically made from &egr;-caprolactone and a bifunctional initiator such as diethylene glycol. The dicarboxylic acids of the desired polyester can be aliphatic, cycloaliphatic, aromatic, or combinations thereof. Suitable dicarboxylic acids which may be used alone or in mixtures generally have a total of from 4 to 15 carbon atoms and include: succinic, glutaric, adipic, pimelic, suberic, azelaic, sebacic, dodecanedioic, isophthalic, terephthalic, cyclohexane dicarboxylic, and the like. Anhydrides of the above dicarboxylic acids such as phthalic anhydride, tetrahydrophthalic anhydride, or the like, can also be used. Adipic acid is the preferred acid. The glycols which are reacted to form a desirable polyester intermediate can be aliphatic, aromatic, or combinations thereof, and have a total of from 2 to 12 carbon atoms, and include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,3-butanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 2,2-dimethyl-1,3-propanediol, 1,4-cyclohexanedimethanol, decamethylene glycol, dodecamethylene glycol, and the like, 1,4-butanediol is the preferred glycol.
Hydroxyl ter

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