Cleaning and liquid contact with solids – Processes – Work handled in bulk or groups
Utility Patent
1999-04-16
2001-01-02
Carrillo, Sharidan (Department: 1746)
Cleaning and liquid contact with solids
Processes
Work handled in bulk or groups
C134S016000, C134S025100, C134S026000, C134S029000, C134S034000, C134S036000, C134S042000, C510S244000, C510S434000, C510S512000, C521S058000, C524S127000, C524S190000, C524S284000, C524S310000, C524S492000
Utility Patent
active
06167892
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method for washing pre-expanded particles. More particularly, the present invention relates to a method for washing pre-expanded particles which are used for production of a thermoplastic resin internal die expansion molded article which is used as a cushioning and wrapping material, a carrying box, an adiabatic material, a bumper core of an automobile and the like.
BACKGROUND ART
It has been known that thermoplastic resin pre-expanded particles can be prepared by a method (hereinafter referred to as “pressure release expansion method”) comprising dispersing thermoplastic resin particles into water containing a dispersant in a pressure container, adding a volatile blowing agent thereto, impregnating the thermoplastic resin particles with the volatile blowing agent with keeping high temperature and high pressure, and releasing the particles into a lower pressure atmosphere.
In the above pressure release expansion method, in order to prevent fusion between resin particles at high temperature and high pressure, in general, there are used a slightly water soluble inorganic compound (hereinafter sometimes referred to as “inorganic dispersant”) as a dispersant and a surface active agent (hereinafter sometimes referred to as “auxiliary dispersant”). However, even after the resin particles at high temperature and high pressure are released into a lower pressure atmosphere to give pre-expanded particles, part of the inorganic dispersant remains on and attaches to the pre-expanded particles surface (hereinafter, the inorganic dispersant which remains on and attaches to the pre-expanded particles is sometimes referred to as “attaching dispersant”). If the amount of the attaching dispersant is large, fusion between the pre-expanded particles becomes bad when a mold is charged with the pre-expanded particles and the particles are heated with vapor to give an internal die expansion molded article.
In order to solve the above problem, in general, there are employed a method (A) comprising washing the pre-expanded particles with a large amount of water or warm water, and a method (B) comprising washing the pre-expanded particles with an acidic aqueous solution.
However, in the method (A), washing effect is poor, so that the attaching dispersant cannot be sufficiently removed. Also because a large amount of water is used, the method (A) is uneconomical.
On the other hand, in the method (B), because an equipment must be acid resistant, cost of the equipment becomes high. Also, in the case that the inorganic dispersant is insoluble in an acid, the method (B) is not effective.
Furthermore, waste water after washing is suitably treated and discharged. However, in the method (A), because a large amount of waste water must be treated, cost of the treatment becomes high. In the method (B), because the inorganic dispersant is water-solubilized, steps such as a reprecipitation step and an adsorption and removal step are needed. Accordingly, cost becomes high in addition to complication of the steps.
In order to provide a method for efficiently washing and removing the attaching dispersant without an acid resistant equipment, the inventors of the present invention have earnestly studied. As a result, it has been found that by washing pre-expanded particles prepared by the pressure release expansion method with an aqueous solution of a water soluble compound having a specific functional group in its molecule, the above problems can be solved. Then, the present invention has been accomplished.
DISCLOSURE OF THE INVENTION
The present invention relates to
{circle around (1)} a method for washing pre-expanded particles prepared by charging a pressure container with an aqueous dispersion containing thermoplastic resin particles, a slightly water soluble inorganic compound as a dispersant and a surface active agent, and a volatile blowing agent, increasing the temperature to reach the constant pressure and the constant temperature, impregnating the thermoplastic resin particles with the volatile blowing agent, and releasing the particles into a lower pressure atmosphere,
which is characterized in that
the pre-expanded particles are washed with an aqueous solution of a water soluble compound having at least one functional group capable of bonding to the surface of the slightly water soluble inorganic compound and at least one hydrophilic functional group in its molecule;
{circle around (2)} the above method wherein the slightly water soluble inorganic compound is tricalcium phosphate, and the water soluble compound is a water soluble phosphate, a water soluble condensated phosphate or a mixture thereof;
{circle around (3)} the above method wherein the water soluble condensated phosphate is sodium hexametaphosphate;
{circle around (4)} the above method wherein the slightly water soluble inorganic compound is tricalcium phosphate, and the water soluble compound is a water soluble silicate;
{circle around (5)} the above method wherein the slightly water soluble inorganic compound is tricalcium phosphate, and the water soluble compound is a water soluble ethylenediamineteraacetate;
{circle around (6)} the above method wherein the slightly water soluble inorganic compound is tricalcium phosphate, and the water soluble compound is a water soluble citrate, a water soluble tartrate or a mixture thereof;
{circle around (7)} the above method wherein the slightly water soluble inorganic compound is tricalcium phosphate, and the water soluble compound is a sodium polyacrylate; and
{circle around (8)} the above method wherein the slightly water soluble inorganic compound is kaolin, and the water soluble compound is ethylenediaminehydrochloride.
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, the pre-expanded particles are prepared by a conventionally known method, that is, the method (pressure release expansion method) comprising charging a pressure container with an aqueous dispersion containing thermoplastic resin particles, a slightly water soluble inorganic compound (inorganic dispersant) as a dispersant and a surface active agent (auxiliary dispersant), and a volatile blowing agent, increasing the temperature to reach the constant pressure and the constant temperature, impregnating the thermoplastic resin particles with the volatile blowing agent, and releasing the particles into a lower pressure atmosphere.
In the above pressure release expansion method, in order to prevent fusion between the thermoplastic resin particles in the pressure container, the inorganic dispersant and the auxiliary dispersant are used.
As the inorganic dispersant, conventionally used compounds can be used without particular limitation. Concrete examples of the inorganic dispersant are, for instance, an inorganic salt such as tricalcium phosphate, magnesium carbonate or calcium carbonate; clay such as bentonite or kaolin; and the like. Among them, from the viewpoint that dispersing power is great, tricalcium phosphate is preferable. From the viewpoint that dispersing power is great and no environment pollution occurs, kaolin is preferable. In general, the surface of the inorganic dispersant is charged with positive or negative electricity.
The above auxiliary dispersant is a component used for improving affinity between the thermoplastic resin particles and the inorganic dispersant and heightening dispersing power. As the auxiliary dispersant, conventionally used compounds can be used without particular limitation. Concrete examples of the auxiliary dispersant are, for instance, an anionic surface active agent such as sodium dodecylbenzenesulfonate, sodium n-paraffinsulfonate, sodium higher alcohol sulfate or sodium alkylnaphthalene sulfonate; a cationic surface active agent such as benzalkonium chloride, alkyltrimethylammonium chloride or dialkyldimethylammonium chloride; and the like. Among them, from the viewpoint that great dispersing power is imparted and biodegradation easily occurs, sodium n-paraffinsulfonate is preferable. From the viewpoint that great dispersing po
Iwamoto Tomonori
Yamaguchi Minori
Yamaguchi Takema
Armstrong, Westerman Hattori, McLeland & Naughton
Carrillo Sharidan
Kaneka Corporation
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