Process for working up emulsion polymers

Details Process for working up emulsion polymers Process for working up emulsion polymers

2001-12-14

2004-06-08

Seidleck, James J. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Treating polymer containing material or treating a solid...

C528S487000, C528S488000, C528S934000, C528S936000, C526S219500, C526S191000

Reexamination Certificate

active

06747124

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to emulsion polymerization process and more particularly to the coagulation of latex particles.
SUMMARY OF THE INVENTION
A process for working up polymer components prepared by emulsion polymerization is disclosed. The process is characterized in that coagulation of the aqueous polymer latex present after emulsion polymerization is performed using a combination of: A) an aqueous solution of at least one salt selected from the group consisting of sodium chloride, calcium chloride, magnesium chloride, aluminum chloride, sodium sulfate, magnesium sulfate and aluminum sulfate; B) an aqueous solution of at least one salt of an acid selected from the group consisting of hypophosphorous acid (H
3
PO
2
), phosphorous acid (H
3
PO
3
or HPO
2
) and ascorbic acid; and, optionally, C) an aqueous dilute acid selected from the group consisting of sulfuric acid, phosphoric acid and acetic acid.
BACKGROUND OF THE INVENTION
The invention provides a process for working up polymeric material systems prepared by emulsion polymerization, wherein working up of the corresponding latices is performed using a special salt mixture.
The conversion of aqueous polymer latices into polymer molding compositions is usually performed in such a way that coagulation of the latex particles is triggered by the addition of aqueous salt solutions and/or dilute acids.
Examples of salts are sodium chloride, sodium sulfate, magnesium sulfate, calcium chloride, aluminium sulfate, examples of acids are sulfuric acid, phosphoric acid, acetic acid (see, e.g., U.S. Pat. Nos. 2,366,460, 3,108,983, 3,248,455, DE-A 1 958 498).
A disadvantage of these electrolytes, which are well-known for use as coagulants, is that they may lead to a deterioration in the polymer color.
DETAILED DESCRIPTION OF THE INVENTION
It has now been found that molding compositions with greatly improved inherent color (color of the material without adding colorants) are obtained when a special material system is used in the coagulation step of emulsion polymerized polymers (herein referred to as “polymer components”).
Thus, the invention provides a process for working up polymer components characterized in that the coagulation of the aqueous polymer latex resulting upon the emulsion polymerization is carried out in the presence of
A) an aqueous solution of at least one salt selected from the group consisting of sodium chloride, calcium chloride, magnesium chloride, aluminium chloride, sodium sulfate, magnesium sulfate and aluminum sulfate,
B) an aqueous solution of at least one salt of an acid selected from the group consisting of hypophosphorous acid (H
3
PO
2
), phosphorous acid (H
3
PO
3
or HPO
2
) and ascorbic acid and optionally
C) an aqueous dilute acid preferably selected from the group consisting of sulfuric acid, phosphoric acid and acetic acid.
Compared with previously known thermoplastically processable molding compositions containing polymer components prepared by emulsion polymerization, molding compositions containing the polymer components worked up by the process according to the invention differ in that they have a much improved inherent color without the other properties being adversely affected. The invention also provides these molding compositions.
According to the invention, the individual components are used in amounts of 0.1 to 5 wt. %, preferably 0.2 to 4 wt. % and particularly preferably 0.5 to 2 wt. % of A), 0.01 to 2 wt. %, preferably 0.02 to 1.5 wt. % and particularly preferably 0.05 to 1 wt. % of B) and 0 to 5 wt. %, preferably 0 to 4 wt. % and particularly preferably 0 to 2.5 wt. % of C) (each with respect to the latex solids).
Suitable components A), according to the invention, are sodium chloride, calcium chloride, magnesium chloride, aluminium chloride, sodium sulfate, magnesium sulfate, aluminium sulfate in the form of their aqueous solutions, preferably sodium chloride, calcium chloride, magnesium sulfate and aluminium sulfate in the form of their aqueous solutions.
In principle, mixtures of these salt solutions may also be used e.g., mixtures of magnesium sulfate and aluminium sulfate.
The preferred component A) is magnesium sulfate.
The concentration of salt in the aqueous solution may be varied over a wide range. According to the invention, concentrations of 0.1 to 10 wt. % are especially suitable, in particular concentrations of 0.5 to 5 wt. %.
Suitable components B) according to the invention are salts of hypophosphorous acid (H
3
PO
2
) or phosphorous acid (H
3
PO
3
or HPO
2
) or ascorbic acid in the form of their aqueous solutions.
Particularly suitable salts are sodium hypophosphite, potassium hypophosphite, magnesium hypophosphite, calcium hypophosphite, sodium phosphite, potassium phosphite, calcium phosphite, sodium ascorbate, potassium ascorbate, and calcium ascorbate.
In principle, mixtures of these salt solutions may also be used here for preparing aqueous solutions, e.g., mixtures of sodium hypophosphite and sodium phosphite or of sodium hypophosphite and sodium ascorbate.
The preferred component B) is sodium hypophosphite and/or sodium phosphite and/or sodium ascorbate, particularly preferably sodium hypophosphite.
In the case of component B) the concentration in the aqueous solution may be varied over a wide range; concentrations of 0.2 to 5 wt. % are especially suitable, in particular concentrations of 0.5 to 3 wt. %.
As optional acid components which can be used in addition to A) and B), in principle any compounds present in the form of aqueous acids may be used. In practice, aqueous sulfuric acid, aqueous phosphoric acid and aqueous acetic acid have proven useful.
Aqueous sulfuric acid and aqueous acetic acid are particularly preferred, aqueous acetic acid being very particularly preferred.
Application of the combination of A) and B) and optionally C) to prepare elastic/thermoplastic and thermoplastic molding compositions according to the invention may be performed in a number of ways.
Thus, for example, an aqueous solution, in which components A) and B) and optionally C) are present together, may be used, but separate solutions of the individual components may be also used in any sequence at all for coagulation purposes.
The procedure may be such that components A), B) and optionally C) are added to the latex to be coagulated, or else the latex may be added to components A), B) and optionally C).
The following modes of operation have proven to be particularly advantageous:
1.) Adding some of or the entire amount of the aqueous solution of component B) to the latex to be coagulated, distributing this in the latex and then placing the resulting mixture in contact with the entire amount of the aqueous solution of component A) and optionally the remainder of component B) or
2.) Adding the entire amount of the aqueous solution of component A) to the latex to be coagulated or adding the latex to be coagulated to the entire amount of the aqueous solution of component A) and then placing the resulting mixture in contact with the entire amount of the aqueous solution of component B).
The optionally used additional component C) may be added at any time at all; it is preferably used together with component A).
Coagulation of the polymer present in the emulsion form using the combination of A), B) and optionally C) according to the invention may be performed at any temperature at all.
In practice, these temperatures are generally between 40° C. and 140° C., preferably between 60° C. and 100° C.; isolation of the resulting polymer component from the aqueous slurry may be achieved by conventional separating processes such as, for example, by filtration or centrifuging.
A drying step using well-known methods normally follows this isolation process.
The ratio by weight of components A:B used is 20:1 to 1:1, preferably 10:1 to 2:1 and particularly preferably 5:1 to 3:1. In the event of the additional use of component C), this is used in amounts such that the pH of the polymer slurry after the coagulation step is 3 to 8, preferably 4 to 7 and particularly preferably 4

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