Cationic layer compounds, production and use

Details Cationic layer compounds, production and use Cationic layer compounds, production and use

1997-09-25

2001-07-17

Hoke, Veronica P. (Department: 1714)

Chemistry of inorganic compounds

Carbon or compound thereof

Oxygen containing

C423S432000, C524S436000

Reexamination Certificate

active

06261530

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to special cationic layer compounds of the hydrotalcite type, to a process for their production and to their use as co-stabilizers for halogen-containing plastics stabilized in particular with calcium and/or zinc salts.
It is known that halogen-containing plastics or molding compounds produced from them tend to degrade or decompose on exposure to heat or ultraviolet light. To counteract this, heavy metal compounds based on lead, tin, barium and/or cadmium are normally used. For reasons of factory hygiene, however, there is a need to replace these thoroughly effective stabilizers by less health-damaging materials. Possible alternative stabilizers to the heavy metal compounds are, for example calcium and zinc soaps, but unfortunately they do not perform as well as the heavy metal compounds mentioned above so that co-stabilizers have to be used in order to enhance their stabilizing effect.
2. Discussion of Related Art
German patent DE-C-30 19 632 describes the use of hydrotalcites for inhibiting the thermal or ultraviolet degradation of halogen-containing thermoplastic resins. This patent specification discloses test results which show that, when readily commercially available hydrotalcites are incorporated, for example, in vinyl chloride resins, they accelerate the dechlorination of the resins on heating or even cause decomposition, blackening or foaming of the resins. In addition, it was found that these hydrotalcites show poor dispersibility in the resins and adversely affect the rheological properties of the resins during molding and also the appearance of the molded products obtained. These test results are attributed to the small crystal size of the usual hydrotalcites and to the large specific BET surface of at least about 50 m
2
/g and the coverage of the hydrotalcite particles with water. Accordingly, it is proposed in German patent DE-C-30 19 632 to use hydrotalcites which have a large crystal size and a specific BET surface of no larger than 30 m
2
/g and which may optionally be coated with an anionic surfactant, such as sodium stearate. European patent application EP-A-189 899 also describes resin compositions containing hydrotalcites having specific BET surfaces below 30 m
2
/g. It is known from this European patent application that the hydrotalcites can be modified with higher fatty acid esters, anionic surfactants and coupling agents of the silane or titanium type in order to improve the compatibility of the hydrotalcite with the resins. According to cited European patent application EP-A-189 899, the hydrotalcites are said to be modified by mechanical mixing with the modifying agents in pure or dissolved form.
DE-C-33 06 822 teaches that hydrotalcites with the formula [Mg
6
Al
2
(OH)
12
](CO
3
)
3
.4H
2
O are obtained by reaction of “active” aluminium hydroxide with magnesium hydroxide or magnesium oxide in the presence of basic magnesium carbonate as carbonate ion donor at a temperature of 50 to 100° C. and subsequent spray drying from the suspension. This process presupposes the availability of “active” aluminium hydroxide which can be obtained, for example, by precipitation from aluminium salt solutions and storage in gel form. Accordingly, this process involves an additional production step (precipitation and washing out of the aluminium hydroxide gel) or makes it necessary to obtain such a gel from a manufacturer and hence to transport large quantities of water which adversely affects the economy of the process.
U.S. Pat. No. 4,656,156 describes a process for producing hydrotalcite in which the aluminate liquor of the Bayer process is used as the aluminium component. The Bayer liquor is reacted with “active” magnesium oxide which can be obtained, for example, by calcining magnesium carbonate. This process can only be economically used in places where the Bayer liquor itself accumulates because otherwise relatively large quantities of water would again have to be transported.
DE-A-15 92 126 describes the production of hydrotalcites from different starting materials, for example from a suspension of solid aluminium hydroxide, solid magnesium hydroxide and sodium hydrogen carbonate. The reactions are carried out in batches and the products are separated from the water phase by filtration or centrifugation and washed before they are dried. The filtration or centrifugation of the very fine-particle reaction products and their subsequent washing are both complicated and time-consuming process steps which add significantly to the production costs.
The problem addressed by the present invention was to provide co-stabilizers for halogen-containing plastics which
would be compatible with calcium and/or zinc compounds,
would be dispersible in halogen-containing plastics without adversely affecting their rheological properties,
would be capable of effectively trapping the decomposition products of halogen-containing plastics and
would be inexpensive to produce,
and a process for the production of these co-stabilizers.
DESCRIPTION OF THE INVENTION
The present invention relates to formulations for stabilizing halogen-containing plastics against thermal or photochemical degradation which contain cationic layer compounds corresponding to general formula (I):
[M
(II)
x
Al(OH)
y
](A
n−
)
z
.mH
2
O  (I)
where M
(II)
stands for at least one divalent metal ion and A
n−
stands for an acid anion with the charge n−(n=1, 2 or 3) and the conditions 1<x<5, y>z, (y+nz) =2x+3 and 0<m<10 are fulfilled, characterized in that they are obtainable by adding alkali metal hydroxide to a water-containing mixture of at least one source of divalent metal ions M
(II)
, one source of the anions A
n−
and crystalline aluminium hydroxide in a quantity of 1 to 20 mole-%, based on aluminium hydroxide, heating the mixture for 10 to 240 minutes to a temperature of 100 to 240° C. and drying the mixture to form a powder without previous separation of the solid from the aqueous phase.
The cationic layer compounds corresponding to general formula I are compounds known per se of which the structure and preparation are described, for example, by W. T. Reichle in Chemtec (January 1986), pages 58 to 63. Cationic layer compounds corresponding to general formula I in which M
(II)
represents at least one divalent metal ion selected from the group consisting of magnesium, calcium and zinc are preferred for the purposes of the invention. In a preferred embodiment, M
(II)
represents only one divalent metal ion from the group mentioned, more particularly magnesium. Cationic layer compounds corresponding to general formula I, in which A
n−
represents an acid anion having a charge of n selected from the group of anions consisting of carbonate, hydrogen carbonate, perchlorate, acetate, nitrate, tartrate, oxalate and iodide, preferably carbonate, are most particularly preferred. Where reference is made to at least one divalent metal ion in the explanation of formula I above, it means that different divalent metal ions may also be present alongside one another in the cationic layer compound. The indices x, y and z and m may represent whole or broken numbers within the limits mentioned. Cationic layer compounds corresponding to general formula I, in which M
(II)
represents magnesium and A
n−
represents carbonate, are particularly advantageous. Examples of suitable cationic layer compounds are synthetic hydrotalcites which are also known as basic aluminium/magnesium carbonates and which are generally produced by the process described in DE-B-15 92 126 and by the processes described in DE-A-20 61 114 or DE-A 29 05 256. Hydrotalcites corresponding to the formula [Mg
6
Al
2
(OH)
16
]CO
3
.mH
2
O or to the formula [Mg
4
Al
2
(OH)
12
]CO
3
.mH
2
O, in which m is as already defined, are most particularly preferred.
Suitable sources of divalent metal ions are their carbonates, hydroxocarbonates, hydroxides, oxides or their wat

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