JP5017650B2 - Method for preparing hollow silica particles - Google Patents

Description

  The present invention relates to a method for producing silica hollow particles comprising a series of processes in which a shell is formed by hydrolysis of silicon alkoxide represented by tetraethyl silicate using calcium carbonate as a core substance, and then the core is dissolved by an acid.

  In general, hollow particles composed of an inorganic substance typified by silica are obtained by foaming, such as spray pyrolysis, and the core is formed after depositing the shell material on the core material. Manufactured by a removal method (template method).

    By the template method, hollow particles having a uniform shape can be obtained. Typical templates include latex particles and emulsions. However, when these are used, spherical hollow particles can be obtained as template particle characteristics.

    As described in Patent Document 1, when inorganic particles typified by calcium carbonate are used as templates, particles having various shapes reflecting the crystal shape can be obtained. The core is easily removed with an acid such as hydrochloric acid.

However, ammonia water is usually used as a catalyst in the hydrolysis of silicon alkoxide in the process of forming a silica shell around a calcium carbonate core as described in the above patent document.
JP-A-2005-263550

  The conventional method has problems such as toxicity and odor because ammonia water is used as a catalyst. Moreover, exhaust equipment was necessary for those problems.

  This invention is made | formed in view of the said conventional situation, Comprising: Development of the reaction process without an odor and toxicity is made into the subject.

  In order to solve the above problem, an aqueous sodium carbonate solution is used as a catalyst instead of the aqueous ammonia solution.

    A sodium carbonate aqueous solution and a silicon alkoxide are sequentially added to an alcohol solution in which calcium carbonate is dispersed. After the silicon alkoxide is hydrolyzed by stirring or shaking, unreacted silicon alkoxide and sodium carbonate are removed by filtration through a filter or centrifugation.

    Subsequently, an acid is added to dissolve the calcium carbonate in the core, and the silica particles are separated by filtration or centrifugation. At this time, in order to maintain dispersibility, addition of a surfactant or the like, adjustment of pH, etc. are performed as necessary.

    Compared with aqueous ammonia solution, aqueous sodium carbonate solution is stable at room temperature and odorless. The gas that evaporates is also carbon dioxide, and the amount generated in the synthesis is harmless to the human body than ammonia.

    The aqueous sodium carbonate solution is easily prepared from a stable powder, so that it is not necessary to pay as much attention to storage as aqueous ammonia. Sodium carbonate used in the reaction is easily removed by filtration immediately after the reaction and filtration after dissolving the core with hydrochloric acid.

  3.2 g of a substantially cubic calcium carbonate particle aqueous dispersion (8.9 wt%) having a primary particle diameter of about 80 nm was diluted with 15 ml of ethyl alcohol and well dispersed by ultrasonic irradiation.

Subsequently, 1 ml of an aqueous solution of sodium carbonate 1.0 moldm ⁻³ was added, and further 1 ml of ethyl tetrasilicate was added, followed by shaking in a constant temperature water bath at 20 ° C. for 1 hour.

  After completion of the reaction, vacuum filtration was performed using an amphiphilic filter (pore diameter: 0.1 mm). Subsequently, 1 ml of 3N hydrochloric acid was added to remove the core calcium carbonate particles.

  A transmission electron microscope image of the particles is shown in FIG. Hollow particles composed of a uniform silica shell of about 10 nm can be confirmed.

  It can be applied to heat insulating paints, low dielectric materials, lightweight fillers, antireflection films and the like.

2 is a transmission electron microscope image of the particles of Example 1. FIG.

Claims (1)

A method for preparing silica hollow particles using calcium carbonate as a template, wherein only sodium carbonate is used as a catalyst for a hydrolysis reaction of silicon alkoxide.