Hydrotalcite compounds of low uranium (U) content and processes for their preparation

Abstract

Hydrotalcite compounds useful as additives to synthetic resins such as epoxy resins which are used as, in particular, sealant for semiconuctor devices such as transister, IC, LSI and the like, which are characterized by having a composition represented by the formula (1) below: M 1-X 2+ Al X 3+ (OH) 2 A X/2 2− ·m H 2 O  (1) in which M 2+ is at least one of Mg 2+ and Zn 2+ , x is a positive number in the range of 0.2≦x≦0.5, A 2− is at least one of CO 3 2− and SO 4 2− , and m is a number in the range of 0-2, and having a uranium (U) content of not more than 10 ppb, an average secondary particle size of not more than about 3 μm and a BET specific surface area of not more than 30 m 2 /g.

1 . Hydrotalcite compounds which are characterized in that they are represented by formula (1) below:  
       M 1-X   2+ Al X   3+ (OH) 2 A X/2   2−   ·m H 2 O  (1)  in which M 2+  is at least one of Mg 2+  and Zn 2+ ,    x is a positive number in the range of 0.2≦x≦0.5,    A 2−  is at least one of CO 3   2−  and SO 4   2− , and    m is a number in the range of 0-2,    and have a uranium (U) content of not more than 10 ppb, an average secondary particle size of not more than about 3 μm and a BET specific surface area of not more than 30 m/g.    
     
     
         2 . Hydrotalcite compounds according to  claim 1 , which are surface-treated with at least one surface-treating agent selected from the group consisting of higher fatty acids, anionic surfactants, silane-containing coupling agents, titanate-containing coupling agents, aluminium-containing coupling agents and phosphoric acid esters of higher alcohols.  
     
     
         3 . Hydrotalcite compounds according to  claim 1 , which are surface-treated with not more than 3% by weight thereof of silane-containing coupling agent.  
     
     
         4 . Hydrotalcite compounds according to any one of claims  1 - 3 , which are additives and fillers for synthetic resins.  
     
     
         5 . Hydrotalcite compounds according to any one of claims  1 - 4 , in which A 2−  in the above formula (1) is CO 3   2− .  
     
     
         6 . A process for producing the hydrotalcite compounds as defined in  claim 1  which is characterized by 
 (1) subjecting an aqueous solution of water-soluble aluminium compound and an aqueous solution of water-soluble magnesium compound and/or water-soluble zinc compound to a coprecipitation reaction under alkaline conditions, the composition of the starting materials satisfying the molar ratio within the range defined by the formula (2) below:  
                 0.15   ≦       at                 least                 one                 of                   CO   3     2   -                     and                   SO   4     2   -             M     2   +       +     Al     3   +           ≦   1.25     ,           (   2   )                         
 in which M 2+  stands for at least one of Mg 2+  and Zn 2+ , at temperatures of 10-50° C. under stirring, and  
 (2) subjecting the resulting coprecipitation product, without isolating it from the suspension which served as the mother liquor of the coprecipitation reaction, to a hydrothermal reaction at temperatures of 90-200° C. for at least 0.5 hour,  
 (3) so adjusting the reaction conditions in that occasion that the pH of the reaction suspension which has undergone the hydrothermal reaction should fall within the range of 7.0-13.5.  
 
     
     
         7 . A process for producing the hydrotalcite compounds according to  claim 6 , which comprises 
 (1) subjecting an aqueous solution of water-soluble aluminium compound and an aqueous solution of water-soluble magnesium compound and/or water-soluble zinc compound to a coprecipitation reaction under alkaline conditions, the composition of the starting materials satisfying the molar ratio within the range defined by the formula (2-a) below:                    0.15   ≦       CO   3     2   -           M     2   +       +     Al     3   +           ≦   1.25     ,           (2-a)                           in which M 2+  stands for at least one of Mg 2+  and Zn 2+ , at temperatures of 10-50° C. under stirring.    
     
     
         8 . A process for producing the hydrotalcite compounds according to  claim 6  or 7, which comprises, after carrying out the above (2) hydrothermal reaction, 
 (4) suspending the hydrothermal reaction product, which has been washed with water, in an aqueous solution of ammonium carbonate and/or alkali (hydrogen)carbonate, followed by 1-24 hours' stirring at temperatures of 10-100° C. (an elution treatment).  
 
     
     
         9 . Hydrotalcite compounds according to  claim 1 , which are free from water of crystallization or have lowered content of water of crystallization, as obtained by further heating the hydrotalcite compounds as described in  claim 1  at temperatures of 200-350° C. for 0.5-24 hours.  
     
     
         10 . Hydrotalcite compounds according to  claim 1  which are free from water of crystallization, whose “m” value referring to the formula (1) of  claim 1  is 0.05-0.