Low naphthenic liquid crystalline polymer composition for use in molded parts with a small dimensional tolerance

Abstract

A thermoplastic composition that comprises a low-naphthenic, thermotropic liquid crystalline polymer blended with a combination of flow modifiers is provided. More particularly, one of the flow modifiers is a hydroxy-functional compound that contains or more hydroxyl functional groups. Without intending to be limited by theory, it is believed that the hydroxyl functional groups can react with the polymer chain to shorten its length and thus reduce melt viscosity. Aromatic dicarboxylic acids are also employed as a flow modifier in the thermoplastic composition. Again, without intending to be limited by theory, it is believed that such acids can combine smaller chains of the polymer together after they have been cut by hydroxy-functional compounds. This helps maintain the mechanical properties of the composition even after its melt viscosity has been reduced.

1 . A thermoplastic composition that comprises at least one thermotropic liquid crystalline polymer, wherein the total amount of repeating units in the polymer derived from naphthenic hydroxcarboxylic or naphthenic dicarboxylic acids is no more than 15 mol. %, the thermoplastic composition further comprising at least one hydroxy-functional compound and at least one aromatic dicarboxylic acid, wherein the weight ratio of hydroxy-functional compounds to aromatic dicarboxylic acids in the composition is from about 0.1 to about 30, and further wherein the thermoplastic composition has a melt viscosity of from about 0.5 to about 100 Pa-s, as determined in accordance with ISO Test No. 11443 at a shear rate of 1000 seconds −1  and temperature that is 15° C. above the melting temperature of the composition. 
     
     
         2 . The thermoplastic composition of  claim 1 , wherein the weight ratio of hydroxy-functional compounds to aromatic dicarboxylic acids in the composition is from about 1 to about 30. 
     
     
         3 . The thermoplastic composition of  claim 1 , wherein hydroxy-functional compounds constitute from about 0.05 wt. % to about 4 wt. % of the thermoplastic composition. 
     
     
         4 . The thermoplastic composition of  claim 1 , wherein the hydroxy-functional compound includes an aromatic diol, hydrate, or a combination thereof. 
     
     
         5 . The thermoplastic composition of  claim 4 , wherein the hydroxy-functional compound includes an aromatic diol selected from the group consisting of hydroquinone, resorcinol, 4,4′-biphenol, and combinations thereof. 
     
     
         6 . The thermoplastic composition of  claim 4 , wherein the hydroxy-functional compound includes alumina trihydrate. 
     
     
         7 . The thermoplastic composition of  claim 4 , wherein the thermoplastic composition contains a mixture of an aromatic diol and hydrate. 
     
     
         8 . The thermoplastic composition of  claim 7 , wherein the weight ratio of hydrates to aromatic diols in the mixture is from about 0.5 to about 8. 
     
     
         9 . The thermoplastic composition of  claim 1 , wherein the polymer contains monomer units derived from 4-hydroxybenzoic acid, terephthalic acid, hydroquinone, 4,4′-biphenol, acetaminophen, or a combination thereof. 
     
     
         10 . The thermoplastic composition of  claim 9 , wherein the polymer further contains monomer units derived from 6-hydroxy-2-naphthoic acid in an amount of no more than 15 mol. %. 
     
     
         11 . The thermoplastic composition of  claim 1 , wherein the composition has a melt viscosity of from about 1 to about 80 Pa-s, as determined in accordance with ISO Test No. 11443 at a shear rate of 1000 seconds −1  and temperature that is 15° C. above the melting temperature of the composition. 
     
     
         12 . The thermoplastic composition of  claim 1 , wherein the composition further comprises fibers having a volume average length of from about 1 to about 400 micrometers. 
     
     
         13 . The thermoplastic composition of  claim 1 , wherein thermotropic liquid crystalline polymers constitute from about 20 wt. % to about 90 wt. % of the composition, hydroxy-functional compounds constitute from about 0.05 wt. % to about 4 wt. % of the composition, and aromatic dicarboxylic acids constitute from about 0.001 wt. % to about 0.5 wt. % of the composition. 
     
     
         14 . The thermoplastic composition of  claim 1 , wherein the total amount of repeating units in the polymer derived from naphthenic hydroxcarboxylic or naphthenic dicarboxylic acids is no more than about 10 mol. %. 
     
     
         15 . A molded part comprising the thermoplastic composition of  claim 1 . 
     
     
         16 - 29 . (canceled)